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Philadelphia: Targets in a Barely Tapped Market Keep Big Pharma Focused on AD
29 November 2007. At the l7th Annual Marian S. Ware Neurodegenerative Diseases Research Retreat, held on 9 November 2007 at the University of Pennsylvania in Philadelphia, hosts Virginia Lee and John Trojanowski pulled together a formidable roster of speakers bearing news of big pharma’s efforts in the Alzheimer arena. In a rare summit of sorts, AD leaders from Merck, Pfizer, Wyeth, and Eli Lilly met to talk about the challenges and promises of developing new medicines to treat AD. About 200 researchers and clinicians from academia and industry showed up for updates on drug discovery for Alzheimer disease.
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Barry Greenberg | |
There was ample chance for discussion and commiserating about the difficulties of running AD trials, and the need for biomarkers, after Barry Greenberg of Neurochem presented data from the tramiprosate trial (see ARF related news story). Poignantly, Trojanowski asked how many failed trials before pharma loses its appetite for AD therapies? In answer, the presenters talked about strategies and targets too numerous to leave the observer with doubt about their commitment to the disease, where the need is so great and the market so large. If the day was any indication, they are all planning to keep on trying.
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Peter Reinhart | |
What are they trying? Peter Reinhart, Senior Director of Neurodegeneration Research at Wyeth Research in Princeton, New Jersey, described his company’s strategy of moving forward on multiple targets simultaneously. The Wyeth pipeline includes both passive and active immunization approaches (see ARF related news story), inhibitors of Aβ production by both β- and γ-secretase, a plasminogen activator inhibitor (PAI)-targeted compound to boost Aβ degradation, and symptomatic treatments using neurotransmitter analogs. Reinhart said that Wyeth has a dozen candidate AD programs in the clinic, plus twice as many in preclinical stages.
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Reinhart highlighted two of these preclinical programs, a β-secretase inhibitor and a plasmin activator. In the β-secretase program, Wyeth identified selective, small, and potent inhibitors that knock down Aβ production in Tg2576 mice. Besides reducing plasma Aβ levels and brain plaques, the inhibitors produce a dose-dependent reversal of hippocampal-dependent memory deficits as measured by a contextual fear-conditioning trial. At the optimal dose of one such inhibitor, the AD animals remember just as well as non-transgenic animals, Reinhart said. The company is now trying to put their preclinical data together to move the inhibitor forward into human experiments. A recurring theme at the meeting was the uneasy dependence on mouse models for evaluating targets, with the outstanding question of how well those models predict important aspects of human disease. “Our initial clinical trials will only be as good as the models they’re based on,” was how Reinhart put it.
On the other side of the Aβ equation, Wyeth is also working on enhancing Aβ degradation by the protease plasmin, which chews up both monomeric and aggregated Aβ (see ARF related news story). Previous work has shown that Aβ aggregates induce tissue plasminogen activator (tPA), which cleaves plasminogen to yield active plasmin. There is evidence that the plasmin cascade is less active in AD. An inhibitor of tPA, plasmin activator inhibitor-1 (PAI-1), is upregulated in mouse models of AD and in human AD brain. Wyeth has identified small molecule inhibitors of PAI-1 that activate cleavage of Aβ in vitro assays. In Tg2576 mice, the inhibitor causes a dose-dependent decrease in plasma Aβ and reduces brain Aβ by about one-third after a single dose. Like the β-secretase inhibitor, the PAI-1 inhibitor reverses the memory deficits in the foot shock contextual fear-conditioning test. A naturally occurring mutation among some Amish families creates essentially a human knockout of PAI-1. These people have no obvious phenotype, suggesting that blocking PAI-1 may be a safe way to reduce Aβ, Reinhart said.
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Seabrook, Lee, Hutton, Trojanowski | |
Guy Seabrook, Senior Director and Head of AD Research at Merck’s site in West Point, Pennsylvania, talked about that company’s immunotherapy programs. This program includes an active vaccine based on a multiple antigenic peptide (MAP) vaccine
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construct. For passive immunotherapy, the company has recently focused on anti-oligomer antibodies, which they produced by immunizing mice with stable preparations of oligomers, or Aβ-derived diffusible ligands (ADDLs, licensed from Acumen). After affinity maturation and humanization, the scientists end up with highly selective anti-oligomer antibodies, Seabrook said. The antibodies preferentially block binding of ADDLs to cultured neurons, compared to Aβ monomers. When infused into rhesus monkeys, the antibodies elevated plasma Aβ. The speculation is that this Aβ is coming from the brain, which is consistent with data that the antibodies lower brain Aβ in several transgenic mouse lines, Seabrook said.
Merck is also actively seeking disease state biomarkers. On that goal, Seabrook showed results using CSF from subjects in the Oxford Project to Investigate Memory and Ageing (OPTIMA), in collaboration with A. David Smith of the University of Oxford in England. By combining information on the levels of Aβ42, tau, phospho-tau, and β-secretase, he said, his company achieved 99 percent accuracy in assigning AD in a group of elderly people with AD diagnoses confirmed postmortem.
In his keynote talk, Steven Paul, President of Lilly Research Labs in Indianapolis, focused on apolipoprotein E (ApoE) in AD. Despite being a well-established risk factor for AD, little is understood about how ApoE functions in the disease. AlzGene meta-analysis calculated that two E4 alleles elevate risk 15-fold, though a recent study with pathologically verified cases put that number as high as 25-fold (see ARF related news story). How does the E4 protein, which differs by just two amino acids from the protective E2 isoform, increase risk so dramatically? Paul thinks if researchers can sort out the role of ApoE4, the pathogenesis of AD will become much clearer. Earlier work by Paul, Kelly Bales, and Ron DeMattos at Lilly and their collaborator David Holtzman at Washington University in St. Louis, Missouri, has shown that human ApoE effectively reduces Aβ deposition/amyloid plaque formation in aging PDAPP mice. The ApoE2 and ApoE3 isoforms are more effective than the ApoE4 isoform. Consequently, Paul and colleagues have postulated that drugs that increase ApoE expression or secretion in the CNS may prevent or slow the progression of AD (see ARF related news story).
What is clear is that cholesterol transport pathways are intimately involved with the production and clearance of Aβ in the brain. ApoE is the major lipoprotein in the brain, where it is made mostly by astrocytes and microglia. With recent work showing that the lipid transporter ABCA1, which is required to transfer cholesterol to ApoE, also functions in Aβ clearance, both ABCA1 and ApoE have become important drug targets. Agonists of the liver X receptor (LXR), a steroid receptor that regulates the expression of both genes (Liang et al., 2004; Lefterov et al., 2007; ARF related news story), have been proposed as therapeutics. However, Paul cautioned, the approach may require selective compounds that would stimulate expression in brain more than in peripheral organs to avoid unwanted side effects such as a fatty liver.
ApoE may also play a role in the inflammatory response to Aβ, Paul showed. When the researchers exposed PDAPP brain slices to astrocytes in a culture dish, they found that astrocytes from adult mice avidly degraded Aβ. The adult cells picked up Aβ via receptor-mediated endocytosis in a process that requires ApoE; astrocytes from ApoE knockout mice did not do it, Paul reported.
In the wake of reports that peripheral monocytes can enter the brain and phagocytose Aβ (see ARF related news story, but see also ARF news story), Paul and his coworkers tested the effect of peripheral macrophages on the brain slices. They found that the peritoneal macrophages gobbled up Aβ without harming the brain tissue. These cells took up Aβ from diffuse plaques, but also ate amyloid, whereas neither microglia nor astrocytes could destroy amyloid. Similar to what the scientists saw with astrocytes, macrophages from ApoE knockout mice were far less effective in clearing Aβ or amyloid than cells from wild-type mice. And when macrophages expressing the human ApoE isoforms were tested, E2-expressing cells proved much better at clearing amyloid than E4-expressing cells. The activity of the Aβ-degrading enzyme matrix metalloprotease 9 was higher in ApoE2-expressing macrophages than in E4 expressers. “ApoE2-expressing macrophages are plaque-eating machines,” Paul said. Paul’s results jibe with recent reports from several groups about clearance of plaque by brain-infiltrating macrophages (see ARF related news story and ARF related conference story). Now, Paul’s group is trying to replicate the results in vivo by transplanting bone marrow from E2-expressing mice into PDAPP mice, to see if those cells can clean up plaque.
Michael Hutton of Merck presented an alternative to the Aβ-centric view in his talk on tau-targeted therapies. Hutton recently left academia to take a position as Senior Director of Neuroscience Drug Discovery at Merck Research Labs in Boston, where he is in charge of non-Aβ-directed therapies for AD.
Hutton said that arguments in favor of targeting tau in AD only start with the fact that tau pathology exists side-by-side with amyloid as a hallmark of AD. Tau itself can cause neurodegeneration, as evidenced by the 20 primary tauopathies caused by familial mutations in tau. In addition, tauopathy correlates with neuronal loss and memory decline, and its proximity to neurodegeneration may mean that tau therapies offer the best chance for disease modification. Mouse models with robust neurofibrillary tangle pathology show widespread neurodegeneration, cell loss, and functional decline, which might increase the likelihood that they will be good reporters for therapeutic effects compared to amyloid-only models. In addition, multiple rare tauopathies (considered orphan diseases) present the opportunity for proof-of-concept studies, and Hutton said he feels a responsibility for including these patients in clinical studies. Finally, elevation of phospho-tau, a validated biomarker in AD CSF, could provide a simple way to monitor therapies.
The downsides of targeting tau include its key role in microtubule function and its propensity to form intracellular lesions. In AD, no tau mutations are known, and only a weak association of risk is seen with the tau H1c haplotype variant, suggesting that tauopathy may play but a peripheral role in the disease. So far, findings in tauopathies do not show a clear pathogenic mechanism, and cell models for tauopathies are poor, Hutton said. Despite the availability of transgenic mouse models, no unambiguous or consistent therapeutic prevention or disease modification studies have been reported. Hutton said that may just be because the field is still young.
Even with these drawbacks, potential tau-directed therapies abound: kinase inhibitors, aggregation inhibitors, reducers of tau expression, and microtubule stabilizers are all possibilities that are under study in various labs. Enhanced clearance of tau by HSP90 inhibitors is another angle (see ARF related news story). Hutton noted his surprise that even tau immunotherapy shows some promise (see ARF related news story).
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Christopher Austin | |
Tau aggregation inhibitors have been identified in several high throughput screens. Hutton highlighted one from the Mandelkow lab in Hamburg (Pickhardt et al., 2007), and Christopher Austin, director of the NIH Chemical Genomics Center, talked about two more at his center. As part of the Molecular Libraries Screening Initiative, Austin’s lab screens a growing library of more than 200,000 compounds, and has developed “quantitative HTS.” This method allows the government scientists to
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use multiple concentrations already in a first screen of each compound, rather than one high concentration, as is done in many screens. By going right to dose-response curves, Austin says, his group saves time, identifies many more positive hits, and can come out of a first screen with structure-activity relationships. “This method has revolutionized our ability to draw conclusions relatively rapidly after screening,” Austin said. Last year, working with Jeffrey Kuret of Ohio State University in Columbus, they identified compounds that either inhibited or enhanced tau aggregation (Honson et al., 2007). Now, Austin says they are working with Virginia Lee on another large-scale screen of tau.
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Holly Soares | |
Nearly every speaker expressed a wish for better biomarkers, both to nail an early diagnosis and to quickly assess the effects of new treatments. As Trojanowski put it, “We are not going to get very far very fast without ways to monitor disease with biomarkers.” With that, he introduced Holly Soares, a Director of Translational Medicine at Pfizer Research in Groton, Connecticut, who talked about her group’s work on serum biomarkers.
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Interest is high in blood-derived markers, with their promise of easily accessible, non-invasive diagnosis or tracking of disease progression. For example, a panel of 18 proteins was recently described by Tony Wyss-Coray and coauthors (see ARF related news story) that could distinguish elderly people with AD from those without. Those markers were discovered by measuring a larger group of 120 proteins and then comparing disease and control samples to find the set that discriminated the two populations.
Soares described a similar approach, comparing blood from 20 patients with mild to moderate AD and 20 matched controls. Blood was tested at 3, 6, and 9 months, using HumanMAP from RBM in Austin, Texas, a bead-based multiplex assay for 89 different proteins that included cardiovascular risk factors, inflammatory, and cancer markers. Of the proteins assayed in the recent Wyss-Coray paper, 44 percent were also included in the Pfizer experiment. Their test found no discriminatory power for AD versus control in these overlapping analytes. Soares said they had trouble with variability in the inflammatory markers, but did see changes in lipoproteins and tumor necrosis factor α between cases and controls. She said the beads can differentiate AD versus control plasma, but not with the same set of proteins that Wyss-Coray and coworkers reported. Soares did not see changes in the profiles over time, at least up to 1 year, but wants to do longer studies.
In another study, Soares showed data on biomarker measurements in serum samples from Pfizer’s Alzheimer Disease Cholesterol-lowering Treatment trial. That trial tested the cholesterol-lowering drug atorvastatin, and in a small study the scientists looked at the effect of cholesterol-lowering on several potential biomarkers. They saw little or no changes in plasma Aβ levels or ratios. A brain-specific cholesterol marker, cerebrosterol, was decreased in patients on the drug. When Soares applied the multiplex assay, she found significant decreases in serum amyloid P, a potential seed for amyloid fibrils, in the patients on drug. That was unexpected, and may reflect different mechanisms of action of the statins, beyond their effects on cholesterol synthesis via HMG-CoA reductase. The multiplex assays are very powerful, Soares said, because they can give a fuller picture of the effects of drugs in the context of a disease. She concluded with this optimistic assessment: “Finding biomarkers in plasma is not easy, but they are there.”
At the end of the day, John Trojanowski observed that no one had addressed the issue of trying to slow aging. What did pharma think about setting aside specific AD targets and going after aging pathways, such as the resveratrol approach? This topic seemed to be on the speakers’ radars, but still just as a blip, caught at the early stage where people are thinking about how to design animal models to test anti-aging pathways.—Pat McCaffrey.
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Comments on News and Primary Papers |
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Comment by: Feng Chen
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Submitted 3 December 2007
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Posted 4 December 2007
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I have a a question regarding Dr. Soares' talk about serum amyloid P component. Unlike CRP, the blood level of SAP is rather consistent. A lower blood level of SAP is found in chronic liver diseases such as cirrhosis and chronic active hepatitis. The question is whether the lowered SAP level Dr. Soares reported to be significant in atorvastatin-treated patients might be due to compromised liver function?
 View all comments by Feng Chen
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Comment by: Holly D. Soares
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Submitted 6 December 2007
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Posted 6 December 2007
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Reply to comment by Feng Chen
I'd like to thank the author for his thoughtful question. In answer, as part of the safety monitoring in the ADCLT study, blood-borne markers of liver transaminases (LFT panel) and altered muscle physiology (CPK) were evaluated quarterly as indicators of known adverse events that accompany statin use. Of the 64 subjects who were blinded and completed the first quarterly visit, five (all female) were instructed to discontinue based upon clinical chemistry safety monitoring related to findings in the LFT panel. The remaining patients did not experience alterations in liver enzymes, suggesting that serum amyloid P levels do not necessarily correlate with liver function in this population.
For details on withdrawal adverse events in the ADCLT study that were based upon clinical chemistry, specifically in reference to liver enzymes, see Sparks et al., 2003.
View all comments by Holly D. Soares
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Related News: ABCA1 Loss Lowers ApoE, Not Amyloid; New ApoE Immunology
Comment by: Radosveta Koldamova, Iliya Lefterov
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Submitted 21 October 2005
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Posted 21 October 2005
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The newly proposed role for ApoE in lipid antigen presentation reported by van den Elzen et al. casts a new and interesting light on the results published by Hirsch-Reinshagen et al., Koldamova et al., and Wahrle et al.. Van den Elzen et al. show that ApoE binds directly to lipid antigens and delivers them into CD1-bearing dendritic cells by receptor-mediated endocytosis much more efficiently than macropinocytosis does. This process eventually leads to the production of interferon-Aγ and other cytokines. The results in the paper point to the presentation of foreign lipids (such as bacterial pathogens), whose role in the pathogenesis of AD is not well established [Editor’s note: see ARF Live Discussion ]. However, the presentation of endogenous lipid antigens such as sulfatide could be potentially very important in activating microglia and astroglia as well, especially in the execution of their Aβ-clearing capacity. The sphingolipid sulfatide is the main constituent of mammalian brain lipids. In CNS it is transported by ApoE-containing lipoprotein particles and was found to be decreased in AD patients (3). Previous data support a role for ApoE as an immunomodulatory agent affecting both the innate and adaptive immune responses. For example, ApoE modulates the CNS inflammatory response by down-regulating glial secretion of inflammatory cytokines and neurotoxic mediators such as nitric oxide, which is important in exacerbating neurodegeneration. Another study demonstrated that ApoE deficiency results in impaired clearance of apoptotic cell remnants (1). A regulatory role of ABCA1 in the engulfment of apoptotic bodies was suggested about 10 years ago, at the time its cDNA was initially cloned, and now we know that such a role is being mediated, at least in part, by ApoE (2).
Although the genetic association of ApoE and Alzheimer disease has been known for more than 10 years now, and ApoE4 is indeed the only proven independent risk factor, these recent studies, including the papers in JBC (5,12) are helping to explain why ApoE is essential and how it works to prevent or facilitate Aβ aggregation, amyloid deposition, and clearance. More importantly, the fact that ABCA1 controls ApoE lipidation status and thus its proper function in the brain opens completely new directions for drug design and therapeutic interventions in Alzheimer disease (7). In this respect, it appears that the availability of brain cholesterol and phospholipids to different carriers is critical for their function, and maintaining the appropriate distribution of brain lipids rather than inhibition of their synthesis may have a protective or even therapeutic effect in AD.
References:
1. Grainger DJ, Reckless J, McKilligin E. Apolipoprotein E modulates clearance of apoptotic bodies in vitro and in vivo, resulting in a systemic proinflammatory state in apolipoprotein E-deficient mice. J.Immunol. 2004;173:6366-75. Abstract
2. Hamon Y, Broccardo C, Chambenoit O, Luciani MF, Toti F, Chaslin S, Freyssinet JM, Devaux PF, McNeish J, Marguet D, Chimini G. ABC1 promotes engulfment of apoptotic cells and transbilayer redistribution of phosphatidylserine.
Nat Cell Biol. 2000 Jul;2(7):399-406. Abstract
3. Han X, Fagan AM, Cheng H, Morris JC, Xiong C, Holtzman DM. Cerebrospinal fluid sulfatide is decreased in subjects with incipient dementia.
Ann Neurol. 2003 Jul;54(1):115-9. Erratum in: Ann Neurol. 2003 Nov;54(5):693. Abstract
4. Hirsch-Reinshagen V, Zhou S, Burgess BL, Bernier L, McIsaac SA, Chan JY, Tansley GH, Cohn JS, Hayden MR, Wellington CL. Deficiency of ABCA1 impairs apolipoprotein E metabolism in brain.
J Biol Chem. 2004 Sep 24;279(39):41197-207. Epub 2004 Jul 21. Abstract
5. Hirsch-Reinshagen V, Maia LF, Burgess BL, Blain JF, Naus KE, McIsaac SA, Parkinson PF, Chan JY, Tansley GH, Hayden MR, Poirier J, Van Nostrand W, Wellington CL. The absence of ABCA1 decreases soluble apoE levels but does not diminish amyloid deposition in two murine models of Alzheimer's disease.
J Biol Chem. 2005 Oct 5; [Epub ahead of print] Abstract
6. Koistinaho M, Lin S, Wu X, Esterman M, Koger D, Hanson J, Higgs R, Liu F, Malkani S, Bales KR, Paul SM. Apolipoprotein E promotes astrocyte colocalization and degradation of deposited amyloid-beta peptides.
Nat Med. 2004 Jul;10(7):719-26. Epub 2004 Jun 13. Abstract
7. Koldamova RP, Lefterov IM, Staufenbiel M, Wolfe D, Huang S, Glorioso JC, Walter M, Roth MG, Lazo JS. The liver X receptor ligand T0901317 decreases amyloid beta production in vitro and in a mouse model of Alzheimer's disease.
J Biol Chem. 2005 Feb 11;280(6):4079-88. Epub 2004 Nov 22. Abstract
8. LaDu MJ, Pederson TM, Frail DE, Reardon CA, Getz GS, Falduto MT. Purification of apolipoprotein E attenuates isoform-specific binding to beta-amyloid.
J Biol Chem. 1995 Apr 21;270(16):9039-42. Abstract
9. Shibata M, Yamada S, Kumar SR, Calero M, Bading J, Frangione B, Holtzman DM, Miller CA, Strickland DK, Ghiso J, Zlokovic BV. Clearance of Alzheimer's amyloid-ss(1-40) peptide from brain by LDL receptor-related protein-1 at the blood-brain barrier.
J Clin Invest. 2000 Dec;106(12):1489-99. Abstract
10. van den Elzen P, Garg S, Leon L, Brigl M, Leadbetter EA, Gumperz JE, Dascher CC, Cheng TY, Sacks FM, Illarionov PA, Besra GS, Kent SC, Moody DB, Brenner MB. Apolipoprotein-mediated pathways of lipid antigen presentation.
Nature. 2005 Oct 6;437(7060):906-10. Abstract
11. Wahrle SE, Jiang H, Parsadanian M, Legleiter J, Han X, Fryer JD, Kowalewski T, Holtzman DM. ABCA1 is required for normal central nervous system ApoE levels and for lipidation of astrocyte-secreted apoE.
J Biol Chem. 2004 Sep 24;279(39):40987-93. Epub 2004 Jul 21. Abstract
12. Wahrle SE, Jiang H, Parsadanian M, Hartman RE, Bales KR, Paul SM, Holtzman DM. Deletion of Abca1 increases Abeta deposition in the PDAPP transgenic mouse model of Alzheimer's disease.
J Biol Chem. 2005 Oct 5; [Epub ahead of print] Abstract
View all comments by Radosveta Koldamova
View all comments by Iliya Lefterov
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Related News: ABCA1 Loss Lowers ApoE, Not Amyloid; New ApoE Immunology
Comment by: Radosveta Koldamova, Iliya Lefterov
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Submitted 21 October 2005
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Posted 21 October 2005
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In our study, we used APP23 transgenic mice in which human familial Swedish AD mutant is expressed only in neurons, and we demonstrate that targeted disruption of ABCA1 transporter increases amyloid deposition. The effect was manifested by an increased level of Aβ as well as thioflavin S-positive plaques in brain parenchyma. Moreover, the lack of ABCA1 considerably increased the level of cerebral amyloid angiopathy (CAA) in APP23/ABCA1-/- mice. The fact that the elevation of the fraction of insoluble Aβ in old APP23/ABCA1-/- mice was accompanied by no change in soluble Aβ in young APP23/ABCA1-/- mice, and no difference in APP processing supports a conclusion that ABCA1 has a bigger impact on amyloid deposition than on amyloid production. Our data are in agreement with studies from Holtzman’s (12) and Wellington’s (5) groups. They demonstrated that ABCA1 deficiency in transgenic mice expressing human APP, harboring different FAD mutations and under the control of different promoters, increases amyloid deposition. In PDAPP mice (12) there was a considerable increase in insoluble Aβ level and a trend toward an increase of Aβ and thioflavin S-positive deposits. In the TgSwDI/B transgenic AD model (5), a substantial increase in thioflavin S load in hippocampus and thalamus was found, although not paralleled by changes in Aβ levels as measured by ELISA. In the same study, the Wellington group used a second APP transgenic model, APP/PS, and found no change in amyloid deposition. All three studies demonstrate a considerable increase of CAA. It is remarkable that in the three studies the elevation in parenchymal amyloid and CAA was accompanied by a dramatic decrease in soluble ApoE levels in the brain. Some of the results reported in the three papers, however, do not overlap:
1. Whereas we and Wahrle et al. (12) found a considerable increase in insoluble Aβ peptides in APP23 and PDAPP mice, Hirsch-Reinshagen et al. (5) reported no change in insoluble Aβ fraction in APP/PS1 or in TgSwDI/B transgenic mice. This discrepancy could be explained by the expression of APP transgenes producing Aβ species with different ability to aggregate or propensity for clearance. In APP/PS1 and Tg-SwDI/B mice, the expression of PS1 or Swedish, Dutch, and Iowa triple-mutant APP increases the proportion of more hydrophobic Aβ peptides (5), which are known to aggregate faster and undergo inefficient clearance compared to Aβ40 peptide.
2. While ABCA1 deficiency in APP23 and Tg-SwDI/B (5) caused an increase in amyloid plaques and a trend towards increase in PDAPP mice (12), Hirsch-Reinshagen et al. did not find a difference in amyloid deposition in APP/PS1 mice (5), which were examined at the more advanced age in terms of AD pathology. One explanation could be a role for ABCA1 in the initial period of aggregation and accumulation of amyloid.
The main conclusion from these three studies (Hirsch-Reinshagen et al., Koldamova et al., and Wahrle et al.) is that there is a negative correlation between amyloid load and the level of soluble, properly lipidated ApoE in the brain.
Two contrasting roles for ApoE on amyloid deposition have been proposed: one promoting amyloid deposition and another mediating Aβ clearance. The first is supported by numerous in vivo data demonstrating that in transgenic APP mice with genetically disrupted endogenous mouse ApoE, fibrillar thioflavin S-positive Aβ deposits in brain parenchyma and vasculature are virtually missing. The second one is supported by in vitro and in vivo data demonstrating that ApoE has an important role in Aβ clearance across blood-brain barrier (BBB) and by astrocytes, a process mediated primarily via LDL receptors LRP1 and LRP2 (6,9). The three present JBC papers help to explain these seemingly contradictory effects of ApoE on amyloid aggregation and clearance by the differential roles of its lipid-rich and lipid-poor states. First, ApoE binding to various LDL receptors depends on its lipidation status: Lipid-poor ApoE is a weak ligand for LRP and LDL receptors, and this could explain the decreased Aβ clearance in ABCA1-/- mice. Insufficient and poorly lipidated ApoE in brain decreases Aβ clearance and degradation, and its retention in CNS will consequently increase amyloid deposition. Second, it was demonstrated that lipid-poor ApoE is more effective than lipid-rich ApoE in promoting Aβ aggregation (8). Previous work by Holtzman’s and Wellington’s groups demonstrated that ApoE in CSF of ABCA1-/- mice, as well as ApoE secreted in the conditioned media of ABCA1-/- astrocytes, is in a lipid-poor state (4,11). Moreover, it is obvious that, as in the periphery of ABCA1-/- mice or Tangier patients, poorly lipidated ApoA-I and ApoE proteins in the brain are unstable and are subjected to fast catabolism, explaining their decreased level.
References:
1. Grainger DJ, Reckless J, McKilligin E. Apolipoprotein E modulates clearance of apoptotic bodies in vitro and in vivo, resulting in a systemic proinflammatory state in apolipoprotein E-deficient mice. J.Immunol. 2004;173:6366-75. Abstract
2. Hamon Y, Broccardo C, Chambenoit O, Luciani MF, Toti F, Chaslin S, Freyssinet JM, Devaux PF, McNeish J, Marguet D, Chimini G. ABC1 promotes engulfment of apoptotic cells and transbilayer redistribution of phosphatidylserine.
Nat Cell Biol. 2000 Jul;2(7):399-406. Abstract
3. Han X, Fagan AM, Cheng H, Morris JC, Xiong C, Holtzman DM. Cerebrospinal fluid sulfatide is decreased in subjects with incipient dementia.
Ann Neurol. 2003 Jul;54(1):115-9. Erratum in: Ann Neurol. 2003 Nov;54(5):693. Abstract
4. Hirsch-Reinshagen V, Zhou S, Burgess BL, Bernier L, McIsaac SA, Chan JY, Tansley GH, Cohn JS, Hayden MR, Wellington CL. Deficiency of ABCA1 impairs apolipoprotein E metabolism in brain.
J Biol Chem. 2004 Sep 24;279(39):41197-207. Epub 2004 Jul 21. Abstract
5. Hirsch-Reinshagen V, Maia LF, Burgess BL, Blain JF, Naus KE, McIsaac SA, Parkinson PF, Chan JY, Tansley GH, Hayden MR, Poirier J, Van Nostrand W, Wellington CL. The absence of ABCA1 decreases soluble apoE levels but does not diminish amyloid deposition in two murine models of Alzheimer's disease.
J Biol Chem. 2005 Oct 5; [Epub ahead of print] Abstract
6. Koistinaho M, Lin S, Wu X, Esterman M, Koger D, Hanson J, Higgs R, Liu F, Malkani S, Bales KR, Paul SM. Apolipoprotein E promotes astrocyte colocalization and degradation of deposited amyloid-beta peptides.
Nat Med. 2004 Jul;10(7):719-26. Epub 2004 Jun 13. Abstract
7. Koldamova RP, Lefterov IM, Staufenbiel M, Wolfe D, Huang S, Glorioso JC, Walter M, Roth MG, Lazo JS. The liver X receptor ligand T0901317 decreases amyloid beta production in vitro and in a mouse model of Alzheimer's disease.
J Biol Chem. 2005 Feb 11;280(6):4079-88. Epub 2004 Nov 22. Abstract
8. LaDu MJ, Pederson TM, Frail DE, Reardon CA, Getz GS, Falduto MT. Purification of apolipoprotein E attenuates isoform-specific binding to beta-amyloid.
J Biol Chem. 1995 Apr 21;270(16):9039-42. Abstract
9. Shibata M, Yamada S, Kumar SR, Calero M, Bading J, Frangione B, Holtzman DM, Miller CA, Strickland DK, Ghiso J, Zlokovic BV. Clearance of Alzheimer's amyloid-ss(1-40) peptide from brain by LDL receptor-related protein-1 at the blood-brain barrier.
J Clin Invest. 2000 Dec;106(12):1489-99. Abstract
10. van den Elzen P, Garg S, Leon L, Brigl M, Leadbetter EA, Gumperz JE, Dascher CC, Cheng TY, Sacks FM, Illarionov PA, Besra GS, Kent SC, Moody DB, Brenner MB. Apolipoprotein-mediated pathways of lipid antigen presentation.
Nature. 2005 Oct 6;437(7060):906-10. Abstract
11. Wahrle SE, Jiang H, Parsadanian M, Legleiter J, Han X, Fryer JD, Kowalewski T, Holtzman DM. ABCA1 is required for normal central nervous system ApoE levels and for lipidation of astrocyte-secreted apoE.
J Biol Chem. 2004 Sep 24;279(39):40987-93. Epub 2004 Jul 21. Abstract
12. Wahrle SE, Jiang H, Parsadanian M, Hartman RE, Bales KR, Paul SM, Holtzman DM. Deletion of Abca1 increases Abeta deposition in the PDAPP transgenic mouse model of Alzheimer's disease.
J Biol Chem. 2005 Oct 5; [Epub ahead of print] Abstract
View all comments by Radosveta Koldamova
View all comments by Iliya Lefterov
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Related News: ABCA1 Loss Lowers ApoE, Not Amyloid; New ApoE Immunology
Comment by: David Holtzman, Suzanne Wahrle
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Submitted 21 October 2005
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Posted 21 October 2005
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Comment on the Wahrle et al., Koldamova et al., and Hirsh-Reinshagen et al. papers
Our laboratory and the laboratories of Iliya Lefterov and Cheryl Wellington reported on the effects of ABCA1 deletion on deposition of Aβ in four different mouse models of Alzheimer disease (AD). As shown in previous work from our lab and that of Wellington’s, deletion of ABCA1 leads to poor lipidation of ApoE and large reductions in ApoE levels in the plasma, cerebrospinal fluid, and brain parenchyma. Since mouse models of AD that have reduced or no expression of mouse ApoE develop significantly less Aβ deposition and also greatly reduced deposition of thioflavin S-positive Aβ, we expected that the decreased levels of ApoE present in ABCA1 knockout mice would lead to less Aβ-related pathology in ABCA1-/- mice bred to mouse models of AD. Contrary to this hypothesis, all three laboratories found that deletion of ABCA1 either has no effect or even increases Aβ-related pathology in four different mouse models of AD. These results indicate that the poorly lipidated ApoE produced by ABCA1-/- mice may increase Aβ fibrillogenesis The papers come to similar conclusions with different mouse models and different methods, which strengthens and supports the finding of all three papers.
The Holtzman laboratory found that PDAPP (APPV717F) mice crossed onto an ABCA1-/- background have significantly more Aβ deposited in their brains and have a higher prevalence of cerebral amyloid angiopathy (CAA). There were no differences in APP processing in young PDAPP, ABCA1-/- mice that would account for the higher level of Aβ deposition. Additionally, the PDAPP, ABCA1-/- mice accumulated insoluble ApoE in plaques at a higher rate than PDAPP, ABCA1+/+ mice, suggesting that lipid-poor ApoE is not only more amyloidogenic but also that it binds to fibrillar Aβ. Using the APP23 (APPK670N, M671L) mouse model, the Lefterov group also showed that deletion of ABCA1 resulted in increased deposition of total and fibrillar (thioflavine S-positive) Aβ, which was not a result of altered APP processing. The Lefterov laboratory found significantly higher amounts of CAA and associated microhemorrhage in APP23, ABCA1-/- mice than APP23, ABCA1+/+ mice. The Wellington laboratory bred ABCA1-/- mice to two other mouse models: Tg-SwDI/B (APPK670N, M671L, E693Q, D694N) and APP/PS1 (APPK670N, M671L, PS1 DeltaE9). They did not see significant changes in soluble or insoluble Aβ in brain. However, this lack of an effect on Aβ deposition is still interesting given that the large decreases in ApoE levels in ABCA1-/- mice were expected to lead to large decreases in Aβ deposition. The Wellington group also noted increased insoluble ApoE in the ABCA1-/-, TgSwDI/B and ABCA1-/-, APP/PS1 mice compared to their respective ABCA1+/+ controls once plaques developed, again suggesting that the lipid-poor state of ApoE in ABCA1-/- mice may increase the fibrillogenesis of Aβ. Overall, the findings these papers suggest that modifying the lipidation state of ApoE in the brain may influence AD pathogenesis and be a potential treatment target.
View all comments by David Holtzman
View all comments by Suzanne Wahrle
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Related News: ABCA1 Loss Lowers ApoE, Not Amyloid; New ApoE Immunology
Comment by: Veronica Hirsch-Reinshagen, Cheryl Wellington
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Submitted 26 October 2005
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Posted 26 October 2005
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Three papers by Hirsch-Reinshagen et al., Koldamova et al., and Wahrle et al. (1-3) have now investigated the role of ABCA1 in Alzheimer disease neuropathology in vivo. Two very important findings were common to all three groups, demonstrating that these effects are robust and hold true across specific strains and particular animal models. Firstly, all groups corroborated prior findings of significantly reduced ApoE levels in the brains of ABCA1-deficient mice. Secondly, and contrary to all expectations, the ABCA1-mediated reduction of ApoE levels did not decrease amyloid formation, as would have been expected from previous studies showing that ApoE levels determine the extent of amyloid deposition in vivo.
All three groups reported that ABCA1 deficiency led to an 80 percent reduction in soluble ApoE levels, independent of mouse strain or AD model. Impaired ApoE secretion from both primary astrocytes and microglia has been shown to occur in ABCA1-deficient cells (4) and might partially explain this phenomenon. Additionally, increased catabolism of the poorly lipidated ApoE particles present in ABCA1-deficient brains is likely to occur, as has been demonstrated for peripheral ApoA1 in Tangier disease (5). Given that ABCA1 is required to maintain normal brain ApoE levels, and because ApoE plays a key role in AD pathogenesis, further studies elucidating the exact mechanisms by which ABCA1 participates in brain ApoE metabolism are warranted.
The other common result to all papers is that despite a large decrease in soluble ApoE levels, no reduction in amyloid burden was observed in any of the four AD models tested. This suggests that ApoE lipidation status, which is reduced in ABCA1-deficient animals, is a crucial regulator of amyloid formation. In addition, different Aβ species and their specific deposition pattern did not influence the amyloidogenic effect of lipid-poor ApoE. ABCA1-deficient mice on either Tg-SwD/I, PDAPP, or APP23 background had increased amyloid burdens compared to their wild-type controls, suggesting that neither their specific Aβ species nor its deposition pattern (predominantly vascular in the Tg-SwD/I and parenchymal in the PDAPP and APP23 models) modulates amyloid formation in the presence of poorly lipidated ApoE. Together, all three papers demonstrate that low levels of poorly lipidated ApoE support at least as much amyloid deposition as wild-type levels of normally lipidated ApoE. How lipidation of ApoE contributes to the process of Aβ fibrillization, deposition, and clearance remains to be fully elucidated.
Although the most important findings were indeed corroborated by all groups, some differences were present and may be primarily related to methodological variables and time of analysis. Firstly, Koldamova et al. report an increase in amyloid and Aβ burden in APP23 mice that lacked ABCA1. Wahrle et al. reported a significant increase in guanidine-extractable Aβ load, but did not detect a significant change in amyloid burden. Hirsch-Reinshagen et al. report an increase in amyloid load in the Tg-SwD/I model but no detectable change in amyloid load in APP/PS1 mice that lacked ABCA1, and no change in guanidine-extractable Aβ levels in either model. Even though all groups saw no reduction in amyloid deposition despite a large decrease in ApoE levels, the differences in amyloid and Aβ load between wild-type and ABCA1-deficient mice may have been dependent on the stage of progression of AD. For example, in the APP/PS1 model, where severe pathology was present at the moment of analysis, no differences were observed in amyloid burden or guanidine-extractable Aβ levels between wild-type and ABCA1-deficient mice. In all other three models, analyzed at relatively earlier stages of disease progression, ABCA1-deficient animals did show an increase in amyloid burden when compared to wild-type controls. Further studies might clarify whether the role of ApoE in amyloid formation is most important during the initial stages of Aβ fibrillization, or whether other differences among the models tested may account for the differences in Aβ compared to amyloid burden.
A second important difference among the three studies relates to the report of a shift in ApoE distribution from a soluble to an insoluble pool. Wahrle et al. and Hirsch-Reisnhagen et al. showed an increase in guanidine-extractable pool of ApoE in ABCA1-deficient brains compared to controls. Koldamova et al., using formic acid extractions, did not observe such a phenomenon. Again, it is unclear whether this discrepancy is only of methodological nature or if singularities of the mouse model used by Koldamova et al. are responsible for this. The mechanisms underlying the shift of ApoE into an insoluble form are probably closely related to the increased amyloidogenicity of lipid-poor ApoE and are therefore an interesting subject for further studies.
References:
1. Hirsch-Reinshagen V, Maia LF, Burgess BL, Blain JF, Naus KE, McIsaac SA, Parkinson PF, Chan JY, Tansley GH, Hayden MR, Poirier J, Van Nostrand W, Wellington CL. The absence of ABCA1 decreases soluble apoE levels but does not diminish amyloid deposition in two murine models of Alzheimer's disease.
J Biol Chem. 2005 Oct 5; [Epub ahead of print] Abstract
2. Koldamova R, Staufenbiel M, Lefterov I. Lack of ABCA1 considerably decreases brain Apoe level and increases amyloid deposition in APP23 mice.
J Biol Chem. 2005 Oct 5; [Epub ahead of print] Abstract
3. Wahrle SE, Jiang H, Parsadanian M, Hartman RE, Bales KR, Paul SM, Holtzman DM. Deletion of Abca1 increases Aβ deposition in the PDAPP transgenic mouse model of Alzheimer's disease.
J Biol Chem. 2005 Oct 5; [Epub ahead of print] Abstract
4. Hirsch-Reinshagen V, Zhou S, Burgess BL, Bernier L, McIsaac SA, Chan JY, Tansley GH, Cohn JS, Hayden MR, Wellington CL. Deficiency of ABCA1 impairs apolipoprotein E metabolism in brain.
J Biol Chem. 2004 Sep 24;279(39):41197-207. Epub 2004 Jul 21. Abstract
5. Oram JF. Tangier disease and ABCA1.
Biochim Biophys Acta. 2000 Dec 15;1529(1-3):321-30. Review. Abstract
View all comments by Veronica Hirsch-Reinshagen
View all comments by Cheryl Wellington
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Related News: Calling for Backup: Microglia from Bone Marrow Fight Plaques in AD Mice
Comment by: Serge Rivest
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Submitted 22 February 2006
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Posted 23 February 2006
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 I recommend the Primary Papers
I would like to thank Erene Mina and Drs. Walker and Jucker. They provide insightful comments regarding specific aspects of the study. I'd like to address a few points here.
The first one regards irradiation and its effects on the blood-brain barrier (BBB). There is not very strong evidence that irradiation alters the BBB, and brain infiltration of bone marrow-derived cells has been reported with other techniques as well. Messengale and colleagues have validated this concept using both lethal irradiation and parabiosis techniques in mice (Massengale et al., 2005). Although most (if not all) GFP cells found in the brains of chimeric mice have a microglial phenotype, the overall contributions of such cells to the brain-resident microglial populations of normal mice remain quite low (e.g., 0.5-11.5 percent of resident microglia). This is what we generally observe in our mice (Simard and Rivest, 2004). In APP mice, however, there is a robust microglial recruitment toward the plaques, and those that derive from the bone marrow are attracted at a specific time of the disease. Other groups have observed a similar pattern in irradiated APP mice (Malm et al., 2005; Stalder et al., 2005), and one can appreciate the robust microglia infiltration in the plaques of non-irradiated mice (Fig. 1 and supp. movie 1). Therefore, I do not think that infiltration is caused by alteration of the BBB in irradiated mice, but is a natural process that is especially dynamic while the plaques progress. The mechanisms explaining why bone marrow-derived microglia are no longer recruited toward the plaques at a specific time point in the disease have yet to be unraveled with future experiments.
Another point raised is that we did not look at the colocalization of Aβ in the lysosomes of the resident microglia. We actually did a meticulous analysis of such processes in the chimeric APP, and while GFP cells were almost always associated with lysosomal Aβ, the resident cells were not. This is the reason that we did not show these results, but we have discussed them.
We observed phagocytosis by bone marrow-derived microglia during a very specific time. This takes place around 6 months of age in the APP/PS1 mice, and we no longer see these cells at 9 months. Therefore, cell recruitment (of bone marrow origin) and phagocytosis are dynamic and transient phenomena, which may explain why other groups have not detected it. This also explains why inhibition of cell recruitment (APP/TK mice) from 5 to 6 months has such profound consequences on plaque growth. We are now working on new genetic strategies to enhance and improve the recruitment of these cells for a longer period of time to see if we can prevent the amyloid cascade and cognitive deficit.
Finally, multiple staining and 3D reconstructions using confocal laser-scanning microscopy are powerful tools to determine cellular compartmentalization, such as Aβ within the lysosomal GFP cells.
References:
Malm TM, Koistinaho M, Parepalo M, Vatanen T, Ooka A, Karlsson S, Koistinaho J. Bone-marrow-derived cells contribute to the recruitment of microglial cells in response to β-amyloid deposition in APP/PS1 double transgenic Alzheimer mice.
Neurobiol Dis. 2005 Feb;18(1):134-42.
Abstract
Massengale M, Wagers AJ, Vogel H, Weissman IL. Hematopoietic cells maintain hematopoietic fates upon entering the brain.
J Exp Med. 2005 May 16;201(10):1579-89.
Abstract
Simard AR, Rivest S. Bone marrow stem cells have the ability to populate the entire central nervous system into fully differentiated parenchymal microglia.
FASEB J. 2004 Jun;18(9):998-1000. Epub 2004 Apr 14.
Abstract
Simard AR, Soulet D, Gowing G, Julien JP, Rivest S. Bone marrow-derived microglia play a critical role in restricting senile plaque formation in Alzheimer's disease.
Neuron. 2006 Feb 16;49(4):489-502.
Abstract
Stalder AK, Ermini F, Bondolfi L, Krenger W, Burbach GJ, Deller T, Coomaraswamy J, Staufenbiel M, Landmann R, Jucker M. Invasion of hematopoietic cells into the brain of amyloid precursor protein transgenic mice.
J Neurosci. 2005 Nov 30;25(48):11125-32.
Abstract
View all comments by Serge Rivest
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Related News: Microglia—Medics or Meddlers in Dementia
Comment by: William Van Nostrand
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Submitted 27 March 2007
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Posted 27 March 2007
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The paper from Joseph El Khoury and colleagues presents convincing evidence that the absence of activated microglia is detrimental in the Tg2576 model. On the surface, from our study in J. Neuroscience, one may conclude that microglial activation is harmful. It likely depends on the context of how you are viewing the problem. Early on, microglial activation may be helpful by facilitating clearance of Aβ from brain; in their absence more Aβ accumulates (El Khoury). On the other hand, if Aβ is not cleared and microglia remain activated, this may lead to the chronic neuroinflammation and behavioral deficits that we observed in our model.
Another caveat that we must all recognize is what are the specific features of the models we work with. Each has its own strengths and weaknesses for studying specific aspects of Aβ pathology. For example, the widely used Tg2576 mouse expresses high amounts of Swedish mutant human APP in many cell types, producing high amounts of wild-type Aβ peptides and parenchymal amyloid plaques. The Tg-SwDI mouse expresses low levels of Swedish/Dutch/Iowa mutant human APP only in neurons producing low levels of vasculotropic Dutch/Iowa mutant Aβ peptides and microvascular amyloid deposits. In light of these differences in the models, some variations in results may be attributed to the sites of amyloid deposition and possibly due to differences in microglial responses to wild-type and vasculotropic mutant Aβ peptides and amyloid deposits.
View all comments by William Van Nostrand
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Related News: Microglia—Medics or Meddlers in Dementia
Comment by: Steve Barger
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Submitted 29 March 2007
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Posted 29 March 2007
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El Khoury et al. have produced a dataset that adds to those indicating a beneficial role for monocytic phagocytes (either activated microglia or hematogenous macrophages) with respect to the development of Alzheimer-related pathology. Some data have indicated that inflammation-related events elaborated by microglia contribute to AD pathology. This includes the overexpression of interleukin-1-β in APP-transgenic mouse models of AD, as well as attenuation of Aβ accumulation in these mice by anti-inflammatory agents such as ibuprofen and, more recently, minocycline (see Fan et al., 2007). But beginning with paradigms in which such mice are immunized against Aβ, increasing evidence has suggested that monocyte-derived cells can help to clear Aβ from the brain through phagocytosis and/or expression of Aβ-degrading proteases. For instance, Morgan and colleagues have shown that injection of the powerful inflammatory agent lipopolysaccharide into APP-transgenic mice results in Aβ clearance (DiCarlo et al., 2006), and the clearance or prevention of Aβ deposits in immunized mice is associated with some signs that microglia are more active.
An important question has been whether these beneficial roles of monocytic phagocytes are operative in the basal condition (and eventually overwhelmed in the development of disease) or are instead induced only by extraordinary manipulation, such as immunization or injections of lipopolysaccharide. El Khoury’s approach was to remove or reduce a chemokine receptor (CCR2) responsible for trafficking microglia and/or peripheral macrophages to sites of inflammation, which would include amyloid plaques in the APP transgenic mice. The resulting increase in Aβ accumulation (both soluble and deposits), coupled with an absence of the accumulation of monocytic phagocytes that normally arises in APP transgenics, suggests that monocyte-derived cells tonically participate in the removal of Aβ; microglia from the CCR2-knockout mice still reacted to Aβ in culture. This specific requirement for chemotaxis, then, is consistent with recent studies showing the homing of bone marrow-derived monocytic cells to plaques in APP transgenics (Simard et al., 2006). Microglia are so extensively distributed throughout the cortex that one should imagine they scarcely need to migrate if they were the primary mediators of Aβ clearance.
Of course, the caveat that an APP transgenic mouse is not a human with AD goes without saying. And that may be most relevant to the interpretation of what happens downstream of Aβ clearance. El Khoury et al. reported a decrease in lifespan in the CCR2-knockout animals, but this may have been due to cerebrovascular hemorrhage. It is possible that well-intentioned clearance of Aβ, regardless of how successful, may produce byproducts that interfere with neurophysiology. To wit, the application of the anti-inflammatory antibiotic minocycline by Fan et al. protected against behavioral deficits in APP transgenic mice without altering Aβ levels or deposition, and ibuprofen treatment is associated with a decrease in a marker of apoptosis per plaque rather than a reduction in plaques themselves (Lim et al., 2001). Thus, strategies aimed at optimizing the impact of inflammatory processes or monocytic phagocytes on AD pathogenesis should take into account the potential requirement of a balance between the benefits of Aβ clearance and the maladaptive consequences of inflammatory sequelae on neuronal function and viability.
It is somewhat unfortunate that El Khoury et al. utilized an APP-transgenic strain that has a mixed genetic background (SJL x C57BL/6). Aβ deposition is notoriously strain-dependent, with the relevant alleles remaining unknown. Any cross of a mixed background creates the opportunity for genetic variability in the progeny, even in littermates. This concern can be mitigated by analyzing sufficient numbers. El Khoury et al. used as few as three or four animals per group, which seems low except for the fact that techniques were applied which precluded the use of the same animals for some of the techniques (e.g., immunohistochemistry vs. FACS); thus, the true numbers of animals over which dramatic differences were seen was actually six or seven per genotype.
References:
Fan R, Xu F, Previti ML, Davis J, Grande AM, Robinson JK, Van Nostrand WE. Minocycline reduces microglial activation and improves behavioral deficits in a transgenic model of cerebral microvascular amyloid. J Neurosci. 2007 Mar 21;27(12):3057-63. Abstract
DiCarlo G, Wilcock D, Henderson D, Gordon M, Morgan D. Intrahippocampal LPS injections reduce Aβ load in APP+PS1 transgenic mice. Neurobiol Aging. 2001 Nov-Dec;22(6):1007-12. Abstract
Simard AR, Soulet D, Gowing G, Julien JP, Rivest S. Bone marrow-derived microglia play a critical role in restricting senile plaque formation in Alzheimer's disease. Neuron. 2006 Feb 16;49(4):489-502. Abstract
Lim GP, Yang F, Chu T, Gahtan E, Ubeda O, Beech W, Overmier JB, Hsiao-Ashe K, Frautschy SA, Cole GM. Ibuprofen effects on Alzheimer pathology and open field activity in APPsw transgenic mice. Neurobiol Aging. 2001 Nov-Dec;22(6):983-91. Abstract
View all comments by Steve Barger
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Related News: Microglia—Medics or Meddlers in Dementia
Comment by: Bo Hu
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Submitted 5 April 2007
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Posted 9 April 2007
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It is odd that an effect was noted by El Khoury et al. in a Ccr2 knockout. Cedric Raines showed in a landmark paper that Ccr2 was so redundant that it made no impact on trafficking of monocyte-related cells in EAE (experimental autoimmune encephalomyelitis).
References:
Gaupp S, Pitt D, Kuziel WA, Cannella B, Raine CS. Experimental autoimmune encephalomyelitis (EAE) in CCR2(-/-) mice: susceptibility in multiple strains. Am J Pathol. 2003;162:139-50. Abstract
View all comments by Bo Hu
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Related News: Microglia—Medics or Meddlers in Dementia
Comment by: Terrence Town
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Submitted 7 April 2007
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Posted 9 April 2007
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The report by El Khoury and colleagues shows that recruitment of macrophage-like cells to the brains of Tg2576 mice via Ccr2 plays an important role in limiting AD-like pathology. This is a very interesting finding and extends the work of Stalder et al. (2005), who noted the presence of round, non-process-bearing, macrophage-like cells in APP23 mice with appreciable amyloid deposits.
El Khoury et al. have gone further by establishing that Ccr2-dependent recruitment of microglia/macrophage-like cells is important in limiting progression of cerebral amyloidosis. If taken to the logical endpoint, this would mean that microglia and/or macrophages serve to limit amyloidosis by phagocytosing/clearing amyloid deposits in AD mice in the absence of genetic manipulation (and perhaps something similar may occur in AD patients). However, careful 3D reconstruction of microglia and amyloid in APP23 or Tg2576 mice fails to show this (Stalder et al., 2001; Wegiel et al., 2004).
An alternate explanation is that microglia/macrophages secrete a soluble factor (e.g., a cytokine or protease) that limits cerebral amyloidosis. Yet, the converse—that reactive glia produce acute phase reactants/cytokines such as ApoE, ACT and IL-1 that promote amyloidosis—has been shown (Potter et al., 2001; Nilsson et al., 2001). In light of these reports, what is the authors’ take on the mechanism responsible for their finding?
El Khoury et al. also report that Ccr2 deletion limits the lifespan of Tg2576 animals, and suggest that there is a connection between increased AD-like pathology in Ccr2-deficient Tg2576 mice and their premature death. This conclusion should be taken with caution. Although not often pointed out, Tg2576 mice actually overexpress the mutant human APP transgene in regions other than the brain (for example, peripheral vascular smooth muscle cells and endothelial cells), and it is well-established that transgene-derived Aβ is easily detected systemically in these mice, so early death of Ccr2-deficient Tg2576 mice may be CNS-independent.
The paper by Fan and colleagues presents an interesting set of results that suggest dampening microglial activation via minocycline treatment is beneficial in their mouse model of vascular amyloidosis. Interestingly, they found reduction in “activated” microglia that corresponded with mitigation of behavioral impairment. Their results fit well with the work of Greg Cole’s group, who showed that treatment of Tg2576 mice with the non-steroidal anti-inflammatory drug (NSAID) ibuprofen or the naturally occurring NSAID curcumin reduces microglial activation concomitant with reduced cerebral amyloidosis and behavioral impairment (Lim et al., 2000; Lim et al, 2001a; Lim et al., 2001b). Fan and colleagues’ data also fit well with our previous results showing that genetic or pharmacologic interruption of CD40-CD40 ligand interaction mitigates microglial activation in response to Aβ peptides, and reduces microgliosis, cerebral amyloidosis, and behavioral impairment in AD mouse models (Tan, Town et al., 1999; Tan, Town et al., 2002; Town et al., 2001; Todd Roach et al., 2004).
When taken together, the studies suggest that “activation” of microglia/macrophages is not simply one phenotype. We have suggested that these innate immune cells may respond with a range of responses from pro-phagocytic/anti-inflammatory to anti-phagocytic/proinflammatory (Town et al., 2005). Understanding the molecular underpinnings of these various responses of microglia/macrophages will likely be key in targeting these cells for therapeutic intervention in neurodegenerative diseases (particularly AD).
References:
El Khoury J, Toft M, Hickman SE, Means TK, Terada K, Geula C, Luster AD. Ccr2 deficiency impairs microglial accumulation and accelerates progression of Alzheimer-like disease. Nature Medicine. 2007, March 11. Advanced online publication. Abstract
Fan R, Xu F, Previti ML, Davis J, Grande AM, Robinson JK, Van Nostrand WE. Minocycline reduces microglial activation and improves behavioral deficits in a transgenic model of cerebral microvascular amyloid. J Neurosci. 2007;27(12):3057-63. Abstract
Lim GP, Yang F, Chu T, Chen P, Beech W, Teter B, Tran T, Ubeda O, Ashe KH, Frautschy SA, Cole GM. Ibuprofen suppresses plaque pathology and inflammation in a mouse model for Alzheimer's disease. Journal of Neuroscience. 2000 Aug 1;20(15):5709-14. Abstract
Lim GP, Yang F, Chu T, Gahtan E, Ubeda O, Beech W, Overmier JB, Hsiao-Ashec K, Frautschy SA, Cole GM. Ibuprofen effects on Alzheimer pathology and open field activity in APPsw transgenic mice. Neurobiology of Aging. 2001;22(6):983-91. Abstract
Lim GP, Chu T, Yang F, Beech W, Frautschy SA, Cole GM. The curry spice curcumin reduces oxidative damage and amyloid pathology in an Alzheimer transgenic mouse. Journal of Neuroscience. 2001;21(21):8370-7. Abstract
Nilsson LN, Bales KR, DiCarlo G, Gordon MN, Morgan D, Paul SM, Potter H. Alpha-1-antichymotrypsin promotes beta-sheet amyloid plaque deposition in a transgenic mouse model of Alzheimer's disease. Journal of Neuroscience. 2001;21(5):1444-51. Abstract
Potter H, Wefes IM, Nilsson LN. The inflammation-induced pathological chaperones ACT and apo-E are necessary catalysts of Alzheimer amyloid formation. Neurobiology of Aging. 2001;22(6):923-30. Abstract
Stalder M, Deller T, Staufenbiel M, Jucker M. 3D-Reconstruction of microglia and amyloid in APP23 transgenic mice: no evidence of intracellular amyloid. Neurobiology of Aging. 2001;22(3):427-34. Abstract
Stalder AK, Ermini F, Bondolfi L, Krenger W, Burbach GJ, Deller T, Coomaraswamy J, Staufenbiel M, Landmann R, Jucker M. Invasion of hematopoietic cells into the brain of amyloid precursor protein transgenic mice. Journal of Neuroscience. 2005;25(48):11125-32. Abstract
Tan J, Town T, Paris D, Mori T, Suo Z, Crawford F, Mattson MP, Flavell RA, Mullan M. Microglial activation resulting from CD40-CD40L interaction after beta-amyloid stimulation. Science. 1999;286(5448):2352-5. Abstract
Tan J, Town T, Crawford F, Mori T, DelleDonne A, Crescentini R, Obregon D, Flavell RA, Mullan MJ. Role of CD40 ligand in amyloidosis in transgenic Alzheimer's mice. Nature Neuroscience. 2002;5(12):1288-93. Abstract
Todd Roach J, Volmar CH, Dwivedi S, Town T, Crescentini R, Crawford F, Tan J, Mullan M. Behavioral effects of CD40-CD40L pathway disruption in aged PSAPP mice. Brain Research. 2004;1015(1-2):161-8. Abstract
Town T, Tan J, Mullan M. CD40 signaling and Alzheimer's disease pathogenesis. Neurochemistry International. 2001;39(5-6):371-80. Abstract
Town T, Nikolic V, Tan J. The microglial "activation" continuum: from innate to adaptive responses. Journal of Neuroinflammation. 2005;2:24. Abstract
Wegiel J, Imaki H, Wang KC, Wegiel J, Rubenstein R. Cells of monocyte/microglial lineage are involved in both microvessel amyloidosis and fibrillar plaque formation in APPsw tg mice. Brain Research. 2004;1022(1-2):19-29. Abstract
View all comments by Terrence Town
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Related News: A Blood Test for AD?
Comment by: Anne Fagan, ARF Advisor
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Submitted 15 October 2007
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Posted 15 October 2007
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The recent Nature Medicine paper by Ray, Britschgi, Wyss-Coray, and colleagues is the culmination of a series of elegant and rigorous proteomics experiments designed to identify possible biomarkers of AD in blood. As those who follow the AD biomarkers literature know all too well, the search for plasma/blood markers has yielded few, if any, viable candidates. Whether the paucity of promising candidates reflects true disease biology or methodological challenges and limitations remains to be determined. However, the present study provides compelling evidence for changes in a variety of interesting signaling molecules in blood that correlates with the clinical disease phenotype (i.e., probable AD dementia). Although the percent agreement with clinical diagnosis does not reach 100 percent with the panel of 18 markers, one would not expect it to perfectly discriminate the groups due to the known presence of preclinical AD pathology in non-demented elderly individuals (Morris and Price, 2001) and the difficulties in providing an accurate clinical diagnosis, especially at the early stages of the disease. In fact, the authors rightly avoid the terms “sensitivity,” “specificity,” or “accuracy” (which imply autopsy-confirmed disease diagnosis) when describing the performance of the biomarker panel, and instead use the terms “percent agreement with clinical diagnosis.” Potential comorbidities, medication use, condition of plasma samples (e.g., degree of hemolysis), etc., may also contribute to less than 100 percent agreement with clinical diagnosis. It would be interesting to know whether the samples that fall outside the appropriate clinical clusters are different from other samples in such respects. The inclusion of a clinical group with rheumatoid arthritis is an excellent control given the number of immune- and hematopoiesis-related proteins in their panel.
The plasma panel of biomarkers also appears to perform well in predicting which subjects with MCI will go on to develop probable AD dementia, an issue that has clear therapeutic implications. Since substantial AD pathology, including plaques, tangles, and neuron/synapse loss, as well as cognitive impairment, is already apparent in the MCI stage in individuals who go on to develop AD dementia (Morris et al., 2001; Markesbery et al., 2006), an even more pressing issue is to identify markers that predict which individuals will go on to develop AD dementia but do so while they are still cognitively normal, i.e., prior to substantial neuron/synapse loss. The ratio of CSF tau/Aβ42 has been shown to be promising in this regard (Fagan et al., 2007; Li et al., 2007). It will be interesting to know how the current plasma panel performs in such cohorts of non-demented individuals who are clinically followed over years, or in individuals (especially those who are cognitively normal) with known amyloid pathology (Klunk et al., 2004; Fagan et al., 2006; Mintun et al., 2006).
Although the accuracy of the plasma panel for discriminating clinical groups may not be greater than some of the more “tried and true” CSF biomarkers (including Aβ42, tau and ptau, and their ratios) (Galasko et al., 1998; Kanai et al., 1998; Andreasen et al., 1999; Sunderland et al., 2003; Fagan et al., 2007), the fact that a set of proteins in blood could yield such good discrimination of clinical groups is remarkable and incredibly promising in terms of possible future clinical application. I eagerly await the results of the next generation of experiments by Wyss-Coray and colleagues.
References:
Andreasen N, Hess C, Davidsson P, Minthon L, Wallin A, Winblad B, Vanderstichele H, Vanmechelen E, Blennow K (1999) Cerebrospinal fluid b-amyloid(1-42) in Alzheimer's disease: Differences between early- and late-onset Alzheimer's disease and stability during the course of disease. Arch Neurol 56:673-680. Abstract
Fagan A, Roe C, Xiong C, Mintun M, Morris J, Holtzman D (2007) Cerebrospinal fluid tau/Ab42 ratio as a prediction of cognitive decline in nondemented older adults. Arch Neurol 64:343-349. Abstract
Fagan A, Mintun M, Mach R, Lee S-Y, Dence C, Shah A, LaRossa G, Spinner M, Klunk W, Mathis C, DeKosky S, Morris J, Holtzman D (2006) Inverse relation between in vivo amyloid imaging load and CSF Ab42 in humans. Ann Neurol 59:512-519. Abstract
Galasko D, Chang L, Motter R, Clark CM, Kaye J, Knopman D, Thomas R, Kholodenko D, Schenk D, Lieberburg I, Miller B, Green R, Basherad R, Kertiles L, Boss MA, Seubert P (1998) High cerebrospinal fluid tau and low amyloid b42 levels in the clinical diagnosis of Alzheimer's disease and relation to apolipoprotein E genotype. Arch Neurol 55:937-945. Abstract
Kanai M, Matsubara E, Isoe K, Urakami K, Nakashima K, Arai H, Sasaki H, Abe K, Iwatsubo T, Kosaka T, Watanabe M, Tomidokoro Y, Shizuka M, Mizushima K, Nakamura T, Igeta Y, Ikeda Y, Amari M, Kawarabayashi T, Ishiguro K, Harigaya Y, Wakabayashi K, Okamoto K, Hirai S, Shoji M (1998) Longitudinal study of cerebrospinal fluid levels of tau, Ab1-40, and Ab1-42(43) in Alzheimer's disease: A study in Japan. Ann Neurol. 1998 Jul;44(1):17-26.
Abstract
Klunk W, Engler H, Nordberg A, Wang Y, Blomqvist G, Holt D, Bergström M, Savitcheva I, Huang G-F, Estrada S, Ausén B, Debnath M, Barletta J, Price J, Sandell J, Lopresti B, Wall A, Koivisto P, Antoni G, Mathis C, Långström B (2004) Imaging brain amyloid in Alzheimer's disease with Pittsburgh Compound-B. Ann Neurol 55:306-319. Abstract
Li G, Sokal I, Quinn J, Leverenz J, Brodey M, Schellenberg G, Kaye J, Raskind M, Zhang J, Peskind E, Montine T (2007) CSF tau/Ab42 ratio for increased risk of mild cognitive impairment: A follow-up study. Neurology 69:631-639. Abstract
Markesbery W, Schmitt F, Kryscio R, Davis D, Smith C, Wekstein D (2006) Neuropathologic substrate of Mild Cognitive Impairment. Arch Neurol 63:38-46. Abstract
Mintun M, LaRossa G, Sheline Y, Dence C, Lee S-Y, Mach R, Klunk W, Mathis C, DeKosky S, Morris J (2006) [11C]PIB in a nondemented population: Potential antecedent marker of Alzheimer disease. Neurology 67:446-452. Abstract
Morris J, Price J (2001) Pathologic correlates of nondemented aging, mild cognitive impairment, and early stage Alzheimer's disease. J Mol Neurosci 17:101-118. Abstract
Morris J, Storandt M, Miller J, McKeel D, Price J, Rubin E, Berg L (2001) Mild cognitive impairment represents early-stage Alzheimer's disease. Arch Neurol 58:397-405. Abstract
Sunderland T, Linker G, Mirza N, Putnam K, Friedman D, Kimmel L, Bergeson J, Manetti G, Zimmermann M, Tang B, Bartko J, Cohen R (2003) Decreased b-amyloid1-42 and increased tau levels in cerebrospinal fluid of patients with Alzheimer's disease. JAMA 289:2094-2103. Abstract
View all comments by Anne Fagan
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Related News: A Blood Test for AD?
Comment by: John Trojanowski, ARF Advisor
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Submitted 16 October 2007
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Posted 16 October 2007
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This study is impressive. It was conducted by a sophisticated group familiar with the Alzheimer disease (AD) biomarker field, who report on a panel of blood chemicals that may be able to distinguish those with AD from normal individuals. These analytes may also identify those persons at increased risk of developing AD. As such, this is a very important study. What’s needed now is confirmation of the present findings in a larger sample of patients and controls, including comparisons of people who have dementia due to AD with people whose dementia is caused by other mechanisms.
It also is important to follow as many living subjects as possible to autopsy to confirm the clinical diagnoses, as has been done for CSF tau and Aβ, two of the AD biomarkers most extensively studied to date. This is no small task. It has taken more than a decade, and studies of thousands of living AD patients, controls, and other dementia subjects, as well as autopsy studies on more than a hundred patients and controls to confirm and validate the potential utility of CSF tau and Aβ as AD biomarkers (1,2,6,7). This is critical for the candidate biomarkers reported by Ray et al., since the analytes they identified were not among those that were selected as being the most promising AD biomarkers by an AD Biological Markers Working Group in 2003 (2). Most are also not among those that have been reported in more recent proteomic studies of plasma from AD patients (3,4). It is well known that many initially promising biomarkers of AD have not stood up to further testing along the lines suggested above (2), so additional follow-up studies are needed before one can judge the utility of the plasma analytes reported by Ray et al. for the diagnosis of AD. However, the rigor of the studies reported here offers promise that the analytes the investigators identified may have staying power.
Further, it is important to emphasize that AD biomarkers can have different uses. These include identifying those at greatest risk to develop AD, confirming the diagnosis of AD, epidemiological screening, predictive testing, monitoring progression and response to treatment, enriching clinical trials with specific subsets of patients or at-risk individuals, studying brain-behavior relations. Not all AD biomarkers are likely to be informative for each of these clinical and research applications, and some that are suitable to aid in clinical diagnosis may not be useful for monitoring responses of AD patients to therapeutic interventions (7). As initially proposed by the NIA/Reagan Working Group on Biological Markers of Alzheimer’s Disease (6), ideal AD biomarkers should be 1) linked to fundamental features of AD neuropathology; 2) validated in neuropathologically confirmed AD cases; 3) able to detect AD early in its course and distinguish it from other dementias; 4) reliable, non-invasive, simple to perform, and inexpensive. That working group also recommended that AD biomarkers should be evaluated for their sensitivity, specificity, prior probability, positive predictive value, and negative predictive value (6).
The findings reported here are very exciting, and meet some of the criteria mentioned above, but it may take several years to do the studies needed before we could take these analytes to the stage where CSF tau and Aβ measures currently are for use as AD biomarkers. Indeed, CSF tau and Aβ are the standards for the AD biomarker field against which any new biomarkers should be compared. That said, this report certainly will stimulate interest in confirming and extending these studies. There are many opportunities for doing this in a timely and effective manner, including partnering with the Alzheimer’s Disease Neuroimaging Initiative, which is an innovative study supported by a public/private partnership to identify, standardize, and validate neuroimaging and chemical biomarkers for the diagnosis of AD and assessing the risk of developing AD (5).
References:
1. Clark CM, Xie S, Chittams J, Ewbank D, Peskind E, Galasko D, Morris JC, McKeel, DW Jr, Farlow M, Weitlauf SL, Quinn J, Kaye J, Knopman D, Arai H, Doody RS, DeCarli C, Leight S, LeeVM-Y, and Trojanowski JQ. Cerebrospinal fluid tau and beta-Amyloid: How well do these biomarkers reflect autopsy-confirmed dementia diagnoses. Arch Neurol. 2003;60:1696-1702. Abstract
2. Frank RA, Galasko D, Hampel H, Hardy J, de Leon M, Mehta PD, Rogers J, Siemers E, Trojanowski JQ. Biological markers for therapeutic trials in Alzheimer’s disease - Proceedings of The Biological Measures Working Group: NIA initiative on neuroimaging in Alzheimer’s Disease. Neurobiol. Aging. 2003;24:521-536. Abstract
3. Hye A, Lynham S, Thambisetty M, Causevic M, Campbell J, Byers HL, Hooper C, Rijsdijk F, Tabrizi SJ, Banner S, Shaw CE, Foy C, Poppe M, Archer N, Hamilton G, Powell J, Brown RG, Sham P, Ward M, Lovestone S. Proteome-based plasma biomarkers for Alzheimer's disease. Brain. 2006;129:3042-3050. Abstract
4. Irizarry MC. Biomarkers of Alzheimer disease in plasma.
NeuroRx. 2004;(2):226-234. Abstract
5. Mueller SG, Weiner MW, Thal LJ, Petersen RC, Jack CR, Jagust W, Trojanowski JQ, Toga AW, Beckett L. The Alzheimer's Disease Neuroimaging Initiative. Neuroimaging Clin. N. Amer. 2005;15:869-877. Abstract
6. Ronald and Nancy Reagan Institute of the Alzheimer’s Association and National Institute on Aging Working Group on Biological Markers of Alzheimer’s Disease (Growdon, J.H., Selkoe, D.J., Roses, A., Trojanowski, J.Q., Davies, P., Appel, S., Gilman, S., Radebaugh, T.S., Khachaturian, Z., Working Group Advisory Committee). Consensus report of the Working Group on Biological Markers of Alzheimer’s Disease. Neurobiol. Aging. 1998;19:109-116. Abstract
7. Shaw LM, Korecka M, Clark CM, Lee VM-Y, Trojanowski JQ. Biomarkers of neurodegeneration for diagnosis and monitoring therapeutics. Nat. Rev. Drug Discovery. 2007;6:295-303. Abstract
View all comments by John Trojanowski
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Related News: A Blood Test for AD?
Comment by: Eric Blalock
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Submitted 16 October 2007
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Posted 16 October 2007
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Dr. Wyss-Coray and colleagues investigated cytokine protein expression profiles from clinical blood samples of control, MCI, and AD subjects. Of the 120 protein species that were detectable, 18 were selected based on bioinformatic classification analyses as being highly discriminant for AD versus control subjects. There are three critical findings here:
1. the assumption that cytokine-inflammation perturbations reported by others in AD brain tissue are reflected (albeit in a seemingly distorted manner) in blood appears to be supported;
2. the MCI group can be subdivided by the same 18-protein panel into subjects that do or do not convert to AD; and
3. this panel also discriminated AD from other degenerative diseases.
Of course, there are caveats to be considered. Although these results are encouraging, before this panel can be anointed a diagnostic test, it will need testing across a much larger sample of the population. Mechanistically, it is intriguing to note that many of the inflammatory signatures reported to be upregulated in neural tissue with AD in prior studies are shown to be downregulated in blood by the present work, and this deserves further investigation. Taken together, these findings suggest that this panel may become a blood-based diagnostic test that will allow clinicians to initiate treatment in early MCI converters. In conjunction with newer treatments that appear to reduce the rate of decline in AD, this panel may become a vital component of early detection and treatment in AD.
View all comments by Eric Blalock
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Related News: A Blood Test for AD?
Comment by: Eric Siemers
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Submitted 23 October 2007
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Posted 23 October 2007
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Wyss-Coray et al. report an investigational diagnostic test for AD that could represent a major advance for the field if their results can be replicated. A method of improving the diagnostic accuracy of AD would be valuable immediately to ensure that patients enrolled in clinical trials indeed have AD pathology. Therapeutics now in development that target Aβ are likely to be effective only in those patients with amyloid pathology (1). Additionally, while a clinical diagnosis of MCI does have predictive value for later progression to AD, a more accurate method to determine the presence or absence of amyloid pathology would facilitate the development of disease-modifying drugs for this group of patients. Diagnosis of AD versus other dementias and the identification of MCI patients who progress to manifest AD are addressed in this paper.
The 18 signaling proteins found in this study are of interest not only as a collective diagnostic marker, but also as clues to understanding the pathophysiology of the disease. A point to consider is that the 120 known signaling proteins initially screened were chosen based in part on the availability of an assay to quantify each of them simultaneously. Genetic studies can be based on evaluations of candidate genes or based on an agnostic genome-wide screen using SNPs; similarly, proteomic studies may examine candidate proteins or use a more agnostic approach using mass spectroscopy. The proteomics approach used in this study is broader than an analysis of specific candidate proteins, but is somewhat limited in that it focuses only on the signaling proteins that were available for the described filter-based arrayed sandwich ELISA. Most of the 18 signaling proteins identified in this study have not been discussed previously as potential biochemical biomarkers for AD (2-4); while this does not necessarily detract from their utility as diagnostic markers, they are likely to reflect only a portion of the pathophysiology of AD.
This study very nicely demonstrates the accuracy of this diagnostic method when comparing AD patients to control subjects and to patients with other neurological conditions. A limitation in the vast majority of studies of diagnostic tests is that the “gold standard” is based on a clinical rather than autopsy diagnosis. The use of a training set of samples followed by a test set to some degree addresses this limitation, since identical confounding variables in two disparate cohorts would be relatively unlikely. Additionally, the authors report results for a small number of patients for whom the diagnosis was confirmed at autopsy; the plasma markers correctly classified eight of nine individuals with AD pathology and 10 of 11 subjects with other causes of dementia. For patients with MCI, even with a relatively short follow-up period of 2-6 years, the results from this study appear promising.
The utility of this technique will also need to be compared with other imaging and CSF diagnostic techniques now in development (4-8). The relative ease of using a blood sample makes this technique attractive—if this method were used to screen large numbers of people, either with clinical symptoms or at-risk, a staged approach with imaging or CSF analysis following a positive plasma test could be considered. Relative costs of these diagnostic modalities will also be an important consideration.
The ultimate utility of this technique will be determined by replication in other cohorts. The Alzheimer’s Disease Neuro Imaging (ADNI) study is a large longitudinal observational study of research subjects with AD, MCI, or normal aging (9,10). A number of biochemical and imaging biomarkers are incorporated in the study such that cross-sectional and longitudinal data are obtained for subjects in each of the three diagnostic cohorts. Imaging techniques employed in ADNI include volumetric MRI, FDG-PET, and PIB; biochemical biomarkers evaluated in plasma and CSF include Aβ, tau, and isoprostanes; clinical data include ADAS-cog scores and a neuropsychological battery. Data from ADNI are available to any qualified investigator via the ADNI website. Additionally, physiologic fluid specimens (plasma, CSF, and urine) can be obtained with appropriate approval. The plasma samples obtained from ADNI could provide one source of replication for the diagnostic test described by Wyss-Coray et al.
References:
1. Siemers ER, Dean RA, Demattos R, May PC. New Pathways in Drug Discovery for Alzheimer’s disease. Curr Neurol Neurosci Rep 2006;6:372-378. Abstract
2. Frank RA, Galasko D, Hampel H, Hardy J, de Leon MJ, Mehta PD, Rogers J, Siemers E, Trojanowski JQ. Biological markers for therapeutic trials in Alzheimer’s disease; Proceedings of a biological markers working group; NIA initiative on neuroimaging in Alzheimer disease. Neurobiol Aging 2003;24:521-536. Abstract
3. Thal LJ, Kantarci K, Reiman EM, Klunk WE, Weiner MW, Zetterberg H, Galasko D, Praticò D, Griffin S, Schenk D, Siemers E. The Role of Biomarkers in Clinical Trials for Alzheimer’s Disease. Alzheimer’s Dis Assoc Disord 2006;20:6-15. Abstract
4. Morris JC, Quaid KA, Holtzman DM, Kantarci K, Kaye J, Reiman EM, Klunk WE, Siemers ER. Role of biomarkers in studies of presymptomatic Alzheimer’s disease. Alzheimer’s and Dementia 2005;1:145-151.
5. Fagan AM. Mintun MA. Mach RH. Lee SY. Dence CS. Shah AR. LaRossa GN. Spinner ML. Klunk WE. Mathis CA. DeKosky ST. Morris JC. Holtzman DM. Inverse relation between in vivo amyloid imaging load and cerebrospinal fluid Abeta(42) in humans. Ann Neurol 2006;59:512-519. Abstract
6. Fagan AM, Roe CM, Xiong C, Mintun MA, Morris JC, Holtzman D. Cerebrospinal fluid tau/β-Amyloid42 ratio as a prediction of cognitive decline in nondemented older adults. Arch Neurol 2007; 64:343-349. Abstract
7. Hansson O, Zetterberg H, Buchhave P, Londos E, Blennow K, Minthon L. Association between CSF biomarkers and incipient Alzheimer's disease in patients with mild cognitive impairment: a follow-up study. Lancet Neurol 2006;5:228-234. Abstract
8. Blennow K. Hampel H. CSF markers for incipient Alzheimer's disease. Lancet Neurology. 2003; 2: 605-13. Abstract
9. Fletcher PT, Wang AY, Tasdizen T, Chen K, Jagust W, Koeppe R, Reiman E, Weiner MW, Minoshima S, Foster NL. Variability of normal cerebral glucose metabolism from the Alzheimer’s Disease Neuroimaging Initiative (ADNI): Implications for clinical trials. Ann Neurol (in press).
10. Jack Jr CR, Berstein MA, Fox NC, Thompson P, Alexander GE, Harvey D, Borowski B, Britson PJ, Whitwell J, Ward C, Dale AM, Felmlee JP, Gunter JL, Hill DLG, Killiany R, Schuff N, Fox-Bosetti S, Lin C, Studholme C, DeCarli CS, Krueger G, Ward HA, Metzger GJ, Scott KT, Mallozzi R, Blezek D, Levy J, Debbins JP, Fleisher AS, Albert M, Green R, Bartzokis G, Glover G, Mugler J, Weiner MW. The Alzheimer’s Disease Neuroimaging Initiative (ADNI): MRI methods. JMRI (in press).
View all comments by Eric Siemers
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Related News: Philadelphia: European Trial of Alzhemed Ends, Marketing Morphs to Supplement
Comment by: Samuel Gandy
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Submitted 20 November 2007
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Posted 21 November 2007
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Unacknowledged in the public dialog surrounding Alzhemed's failure is the virtual certainty that trials of other anti-amyloid strategies that remain hopeful will exclude Alzhemed users.
The desperation of the disease can drive families and carers to make irrational choices. But, Alzhemed "nutraceutical" users, Caveat Emptor: You may unintentionally deny yourselves access to trials of immunotherapies and/or secretase modulators that, unlike Alzhemed/tramiprosate, continue to hold promise for slowing cognitive decline.
View all comments by Samuel Gandy
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Related News: Philadelphia: European Trial of Alzhemed Ends, Marketing Morphs to Supplement
Comment by: Gregory Cole, ARF Advisor
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Submitted 21 November 2007
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Posted 21 November 2007
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The decision to market tramiprosate as a supplement is surprising news. It does not speak well of nutraceuticals as a refuge for drugs that fail in clinical trials. From my perspective, it would be okay to fail in a clinical trial if they had compelling biomarker data from humans showing that the drug can really move a target, and established the dosing required to do it. The hippocampal volume data looks promising, but needs its own supplement, perhaps with a CSF biomarker cocktail that includes tau given the report from Avila (see ARF related news story) that the compound can promote tau aggregation. One problem with people self-dosing a nutraceutical is the typical lack of information about the dose required to move an endpoint. And at least they have a dose response on the hippocampal volume, and apparently at least some patients clamoring for more because they thought that it helped them.
The great value with nutraceuticals would be for prevention. There, the clinical endpoint is hard to come by, especially in diseases with long and very expensive trials. Also, insurance may not pay without a diagnosis. So I think you could argue that tramiprosate might work for prevention but not with established AD. In the absence of a convincing clinical trial, tramiprosate needs solid data to show that it moves a panel of biomarkers relevant to pathogenesis. I have been unable to understand how tramiprosate could get into the brain as a charged compound, and not understanding makes me suspicious.
My Alzheimer Center colleagues pointed out that tramiprosate is a modification of taurine. Taurine is a major component of the "energy drink" Red Bull, which is also loaded with caffeine. At SfN, Gary Arendash talked at a news conference about how caffeine is treating his transgenics and is blocking both β- and γ-secretase. So it is beginning to sound like we'll be seeing something like a cross between Red Bull and Rock Star (another energy drink containing ginkgo extract and caffeine) for seniors, Perhaps we should have a naming contest? Combining the last too initials in the cross would tempting, but so far I like Senior Bull.
View all comments by Gregory Cole
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Related News: Philadelphia: European Trial of Alzhemed Ends, Marketing Morphs to Supplement
Comment by: Lon Schneider, ARF Advisor
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Submitted 23 November 2007
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Posted 27 November 2007
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Reader advisory: These comments may appeal only to readers of a certain age, who remember black-and-white TV and Richard Nixon.
Sean Silcoff, a reporter for Neurochem’s hometown paper, The Toronto Financial Post, describes the Alzhemed story as playing out like the Monty Python dead parrot sketch, a discussion between a pet store owner and a customer over whether a dead parrot is dead or just resting or stunned.
Neurochem had been going around and around about the vital status of its North American trial, and landed its most recent stunner on November 8, 2007, the essence of which is that since there is no evidence for tramiprosate’s efficacy by any conventional scientific standard, Neurochem will market homotaurine—the amino acid formerly known as the drug tramiprosate—as a food supplement or nutraceutical so that people with Alzheimer disease can buy it over-the-counter and not be deprived of the drug’s perceived potential benefits that the company touted in prior news releases and presentations.
This may be great news to some, “but wait, there’s more!” as Ron Popeil, the consummate TV purveyor of Veg-O-Matics, might say. According to the Financial Post, Neurochem expects to “scare up US $1 billion-plus sales” selling this nutraceutical and will use the proceeds to develop an effective AD drug, presumably one minimally effective enough that the FDA could actually approve it. In the meantime, people with or without AD can soon take tramiprosate thinking that it will both help them directly and also help fund Neurochem to develop effective future drugs.
One such Neurochem gleam-in-the-eye is the previously unheard-of NRM-8499, said to be a pro-drug of the very “food supplement” they will be selling—inevitably—on their TV infomercials. Neurochem states that NRM-8499 is five times more potent than their “Alzhemed” brand of homotaurine. (This of course begs the question why consumers shouldn’t just buy five times more of the nutraceutical than they would have bought of the prescription drug had it been demonstrated effective). The sales message—to be voiced probably by Hollywood and medical celebrities—could be, “Help Neurochem fight AD as you help yourself.” A Beverly Hills celebrity statistician could make an appearance here, too, because statistical modeling is so much a part of the Alzhemed story.
While they are at it, Neurochem could go further and tithe a portion of their proceeds to the Alzheimer’s Association, gaining a hefty tax credit and stating on each bottle of the Alzhemed brand of homotaurine, “all proceeds to Alzheimer’s charity.”
Even as the company announces that tramiprosate is not worth pursuing as an ethical pharmaceutical product, it continues to imply that there is efficacy to be found somewhere deep within the North American trial data. Seven months after they knew their results, they still speak of “promising results from preliminary post-hoc analysis,” “descriptive data” showing “numerical differences in favor of tramiprosate on the primary clinical endpoints,” “descriptive data also shows…differences between groups on the primary disease modification endpoint of change in the volume of the hippocampus,” or, to further obfuscate, “preliminary post-hoc analysis…that allowed adjustment for potential confounding factors showed a dose-dependent reduction in hippocampal atrophy in patients treated with tramiprosate.” Never mind inferential statistics; facts about efficacy matter less now than they had before for the marketers of a food supplement.
And now for something completely different…(as I am trying to “always look on the bright side....”):
Having acknowledged—not by its press spin but by its business actions—that the North American trial did not show efficacy and that the company could not withstand the risks of its European trial, Neurochem might now just put their bird to rest. It should post the North American trials database, statistical analyses, data files, and clinical study report on their website for others to review and analyze. They cannot get FDA approval and by law cannot make specific AD health claims for a food supplement. Any manufacturer can make homotaurine or conceivably extract it from one or another species of algae, so they no longer have a proprietary need to hide the data. Posting the data would provide the best and most transparent support for their press releases. Consumers will be able to examine directly the efficacy evidence and judge for themselves.
Open access to the database and statistical models would allow clarification of the alleged methodological problems that Neurochem enumerates but doesn’t document (e.g., site variability, diagnostic uncertainty, confounding, and metrical issues). It may even allow other methodologists—using other Veg-O-Matics—to find things that may have eluded the Neurochem experts. Academics and advisors to companies and the NIH would learn more about AD clinical trials methods, avoid the repetition of mistakes that might be dooming otherwise effective drugs, and improve future trials methods. This, in turn, might help us to find effective drugs for AD sooner by improving the designs of trials and serve the common good. Of course, other companies and the NIA ADCS should post their clinical trials data, as well, and may do so if Neurochem sets the example. Finally, posting these data and reports would not undermine the publication of a primary paper in any major journal.
I leave it to others to explain why such a modest proposal for companies to share their data from negative trials so that others can benefit would be dead on arrival.
Disclosure: See 14 September 2007 comment.
View all comments by Lon Schneider
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Related News: The Brain and Microglial Recruitment—Think Local, Not Global
Comment by: Lary Walker, ARF Advisor
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Submitted 29 November 2007
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Posted 29 November 2007
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The protean and itinerant nature of phagocytes has compelled researchers to devise increasingly ingenious experiments to establish their role in brain disorders, as exemplified nicely by the studies of Mildner et al. and Ajami et al. These researchers make a reasonably compelling case that significant infiltration of the brain by peripheral, bone marrow-derived macrophages requires a weakening of normal host barriers. Since phagocytes exist on both sides of the cerebrovascular wall, does it matter to the brain where the cells come from? I think it does; there is growing evidence for functional specialization in otherwise similar-appearing macrophages, and (from an evolutionary perspective) why would the brain be endowed with such an effective—and selective—obstacle to circulating phagocytes if their pedigree was unimportant?
Regarding the enduring discussion of the role of phagocytes in Alzheimer disease, one additional issue—cerebral β amyloid angiopathy (CAA)—is worth a comment. The degree of CAA in Alzheimer disease is highly variable, but affected vessels can be appreciably impaired, as evidenced by an elevated risk of hemorrhagic stroke. It is therefore conceivable that CAA might augment the infiltration of circulating monocytes into the brain, thereby modifying the pathologic signature and course of disease. On the flip side, the presence of CAA could reflect subtle functional differences in brain phagocytes. El Khoury et al., 2007 found that the disruption of microglial accumulation via Ccr2 deficiency causes the early appearance of CAA and microhemorrhage in APP-transgenic mice. Phagocytes thus may help to regulate the compartmentalization of Aβ aggregates in brain, suggesting that the presence and phenotype of these cells can influence the risk of CAA in older humans.
View all comments by Lary Walker
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Related News: Paper Alert: Plasminogen Activator Inhibitor-1 Is Anti-Amyloid Target
Comment by: Chris Exley
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Submitted 23 June 2008
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Posted 1 July 2008
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I have not yet read the full paper in PNAS (awaiting requested PDF), but it is extremely pleasing to find that plasmin is still very much on the AD agenda. We were the first to demonstrate that plasmin cleaves Aβ42 (1) and subsequently to show that its activity was inhibited by aluminum (2). While it would appear that the focus of the current study is on AD therapy, one might assume that it will also inform the discussion concerning AD etiology.
I congratulate this group on their research and await in anticipation the opportunity to read the full paper.
References:
1. Exley C, Korchazhkina OV. Plasmin cleaves Abeta42 in vitro and prevents its aggregation into beta-pleated sheet structures. Neuroreport. 2001 Sep 17;12(13):2967-70. Abstract
2. Korchazhkina OV, Ashcroft AE, Kiss T, Exley C. The degradation of Abeta(25-35) by the serine protease plasmin is inhibited by aluminium. J Alzheimers Dis. 2002 Oct;4(5):357-67. Abstract
View all comments by Chris Exley
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