This paper presents data suggesting that chronic use of a NO-releasing NSAID attenuates Aβ plaque load in an animal model of Aβ neuropathology. Additionally, the data indicate that the efficacy of this NO-releasing NSAID was mediated by microglia activation. Based on this observation, the authors suggested that NO-releasing NSAIDs could be used for treatment of Alzheimer's disease.

It is extremely interesting to again see that microglia appear to be involved in amyloid plaque clearance. The observation is of high scientific interest. However, while beneficial to amyloid scavenging, NO has been universally involved in promoting neuronal death (Irvani et al. 2002). Chronic exposure to elevated NO levels may provoke unwanted effects.

Considering the fiasco associated with rushing of the vaccination clinical trial by Elan Pharmaceuticals (based on the similar mechanism of scavenging amyloid through stimulating microglia activities), it is necessary...  Read more

This paper presents data suggesting that chronic use of a NO-releasing NSAID attenuates Aβ plaque load in an animal model of Aβ neuropathology. Additionally, the data indicate that the efficacy of this NO-releasing NSAID was mediated by microglia activation. Based on this observation, the authors suggested that NO-releasing NSAIDs could be used for treatment of Alzheimer's disease.

It is extremely interesting to again see that microglia appear to be involved in amyloid plaque clearance. The observation is of high scientific interest. However, while beneficial to amyloid scavenging, NO has been universally involved in promoting neuronal death (Irvani et al. 2002). Chronic exposure to elevated NO levels may provoke unwanted effects.

Considering the fiasco associated with rushing of the vaccination clinical trial by Elan Pharmaceuticals (based on the similar mechanism of scavenging amyloid through stimulating microglia activities), it is necessary for a critical analysis of any treatment before we make the transition to human trials. The chronic use of NO-releasing drugs may pose serious hazards even among current users, especially within an aging population at high risk for multiple neurodegenerative disorders. Further, given that treatment with certain NSAIDs is currently the leading cause of iatrogenic illness, we need to proceed cautiously and diligently. We strongly urge the systematic and careful monitoring of current chronic users of NO-releasing drugs for signs of neurological and possibly gastro-intestinal problems.

View all comments by Giulio Pasinetti

Jantzen and colleagues have carried out a thorough and provocative study on the comparative effects of NSAIDs in reducing the amyloid burden in transgenic mice. The selective COX-2 inhibitor (Celecoxib) was ineffective, the mixed inhibitor (ibuprofen) was modestly effective, while the NO-NSAID NCX-2216 was highly effective. NO-NSAIDs have great clinical promise as COX-inhibiting agents because they retain the antiinflammatory properties of their parent NSAIDs while having greatly reduced gastrointestinal (GI) toxicity (Wallace et al., 1994). The GI tract is innervated by a system of cholinergic and nitric oxide neurons, which apparently govern the propulsion of food (Aimi et al. 1993). The NO-NSAIDs evidently exert their beneficial effects by stimulating nitric oxide receptors. NCX-2216 is an unusual member of the NO-NSAID family in that ferulic...  Read more

Jantzen and colleagues have carried out a thorough and provocative study on the comparative effects of NSAIDs in reducing the amyloid burden in transgenic mice. The selective COX-2 inhibitor (Celecoxib) was ineffective, the mixed inhibitor (ibuprofen) was modestly effective, while the NO-NSAID NCX-2216 was highly effective. NO-NSAIDs have great clinical promise as COX-inhibiting agents because they retain the antiinflammatory properties of their parent NSAIDs while having greatly reduced gastrointestinal (GI) toxicity (Wallace et al., 1994). The GI tract is innervated by a system of cholinergic and nitric oxide neurons, which apparently govern the propulsion of food (Aimi et al. 1993). The NO-NSAIDs evidently exert their beneficial effects by stimulating nitric oxide receptors. NCX-2216 is an unusual member of the NO-NSAID family in that ferulic acid, an antioxidant primarily employed as a food preservative, is used as the linker to flurbiprofen.

High doses of NSAIDs were administered in the Jantzen et al. study, being 4-10 times above therapeutic doses in humans. The most encouraging aspect of the study was that NCX-2216 had so little GI toxicity under these circumstances. It should therefore be an excellent candidate for a clinical trial in Alzheimer's disease.

The appearance of more MHC-2 positive microglia in NCX-2216 treated transgenic mice compared with non-treated transgenic mice was unexpected, but this may not be paradoxical. COX inhibitors are known to reduce neurotoxicity of stimulated microglia in vitro (Klegeris et al., 1999), but there are no data to indicate that such treatment reduces their phagocytic capability. This needs to be explored. The data of Jantzen et al. indicates that NCX-2216 actually enhances such phagocytic capability, an aspect that also deserves further exploration. It needs to be determined whether this is a special property of NCX-2216 or a general property of NO-NSAIDs. It needs further to be determined whether there are different effects of NO-releasing NSAIDs on human microglia, which have low iNOS activity, compared with mouse microglia, which have abundant iNOS activity (Walker et al., 1995). Finally, it needs to be determined how much of the intact molecule reaches the brain at the doses used in the Jantzen et al. study compared to the lower doses that would be used in humans. This is because esterases carry out substantial cleavage of NO-NSAIDs in peripheral organs and, under most circumstances, only the parent NSAID will reach the brain.

David Morgan is absolutely correct in his comments that microglial activation is a beneficial phenomenon up to the level where host cells are damaged. He poses the critical question: how to titrate microglial activation? The titration level appears to be very different in transgenic mouse models than in Alzheimer's disease. β transgenic mice generate huge overloads of human β, a foreign protein to mice. But in humans, β is a normal metabolite of βPP, which is produced in peripheral organs as well as brain (See ARF news item). It accumulates late in life only in those brain areas that have a poor clearance capacity. But when it consolidates, β vigorously activates complement because of its affinity for human C1q (Rogers et al., 1992). The microglial titration level is high. Rodent C1q binds poorly to human β (Webster et al., 1999). The microglial titration level is therefore low. As a result, vaccination of transgenic mice with β can be a useful strategy. Antibodies against the locally produced foreign protein can enhance complement-mediated phagocytosis. The same strategy should be counterproductive in Alzheimer's. One reason is that overactive complement activation already exists in Alzheimer's, leading to autodestruction by the membrane attack complex (Webster et al., 1999). The titration level is already too high. Another reason is that a general autoimmune disorder may be induced in humans because antibodies can attack the multiple sites in the body where β is produced.

Transgenic mouse models expressing β are, at best, a partial model of Alzheimer's disease. The limitations of such models must be clearly understood for useful therapeutic strategies in Alzheimer's disease to be developed.

View all comments by P.L. McGeer

In humans, a substantial body of evidence suggests NSAIDs confer some protection from AD. Importantly, these clinical studies on NSAIDs shed no light on whether NSAIDS could have therapeutic efficacy in patients who already have AD. In addition, it is generally accepted that chronic inflammation is a feature of end-stage AD, and that this chronic inflammatory response contributes to the disease process. Recently, together with Eddie Koo and colleagues, we have shown that some NSAIDs can directly reduce production of the longer, more pathogenic Ab peptides (see ARF news item). Our findings are consistent with a previous report (Lim et al., 2000) and this current report showing that long-term treatment of animals with ibuprofen reduces Aβ load in βPP-transgenic mice. Based on this evidence, it is possible that NSAIDs could confer protection from AD by directly reducing production of Aβ42, acting as classical...  Read more

In humans, a substantial body of evidence suggests NSAIDs confer some protection from AD. Importantly, these clinical studies on NSAIDs shed no light on whether NSAIDS could have therapeutic efficacy in patients who already have AD. In addition, it is generally accepted that chronic inflammation is a feature of end-stage AD, and that this chronic inflammatory response contributes to the disease process. Recently, together with Eddie Koo and colleagues, we have shown that some NSAIDs can directly reduce production of the longer, more pathogenic Ab peptides (see ARF news item). Our findings are consistent with a previous report (Lim et al., 2000) and this current report showing that long-term treatment of animals with ibuprofen reduces Aβ load in βPP-transgenic mice. Based on this evidence, it is possible that NSAIDs could confer protection from AD by directly reducing production of Aβ42, acting as classical anti-inflammatory agents by directly inhibiting COX, influencing other potential pro-inflammatory targets (e.g NFkB), or a combination of these actions.

In light of this background, the manuscript by Jantzen et al. raises more questions than it answers. In this case, NC-2216X administration to AbPP mice reduced Aβ load and, surprisingly, activated microglial cells. NC2216X was designed as an NSAID that would reduce gastric injury by release of NO. Thus, this study postulates that release of NO by nitro-flurbiprofen leads to activation of microglia, and this increased activation somehow results in increased Ab clearance. Such a scenario is plausible, but additional studies are needed to determine how NO-flurbiprofen or any other NSAID- like agent is acting. Such mechanistic insight will be essential for future therapeutic development.

One of the major difficulties I have with the NO-releasing hypothesis in this case is that there is no evidence that intact NC2216X gets into the brain. My understanding (which may be incorrect) is that, in the acidic environment of the gut, the NO moiety is cleaved from NC2216X (hence its protection of the gut). Because of this concern, it would be useful if the authors follow this initial study up by actually determining what form of the drug gets into the brain. In this regard, we have data that shows that flurbiprofen can lower Aβ42 in AβPP mouse brain. It is therefore possible that NC2216X, or a metabolite thereof, can reduce Aβ by inhibiting Aβ42 production directly.

Of note it is worth mentioning that most NSAIDs, although relatively safe, are "dirty drugs" with many targets besides the classically recognized cyclooxygenase enzymes. Moreover, many NSAIDs are extensively metabolized in the body, and it is conceivable that these metabolites might have unexpected actions. Epidemiologic studies on NSAIDs conferring protection from colon cancer have led to a similar debate regarding how NSAIDs confer protection from cancer. As with the studies on NSAIDs and AD, it appears that NSAIDs may confer protection against cancer through multiple mechanisms.

In any case, NSAIDS and NSAID derivatives remain a very interesting class of potential therapeutic agents for AD prevention. Whether they will work in a therapeutic setting remains much less certain. Understanding the mechanism(s) by which they confer protection will be essential. This study and other recent studies on NSAIDs and other antiinflammatory compounds (see ARF news item on curcumin) serve to reinforce the notion that in order to realize the true potential of these agents, further studies dissecting contributions of potential mechanisms of action are needed.

View all comments by Todd E. Golde

Dave Holtzman nicely summarizes some of the principal findings of the presenters. In general, there was further experimental support for the conclusion that several different immunological approaches to clearing brain Aβ are effective in mouse models. Alternatives to parenteral immunization with Aβ1-42 were discussed, and some of these were felt to have the potential to circumvent the hypothetical T cell mediated immune response to Aβ1-42 that might have caused the recent adverse reactions in humans. Progress in understanding the biology of T cell and B cell responses to various Aβ peptides should help guide current intensive efforts to develop new immunotherapeutics for AD.

View all comments by Dennis Selkoe

"The findings by Dodart and colleagues are very interesting. However, as Steven Paul points out in the Q and A session on this website, it remains to be seen if a similar effect will be observed in other transgenic AβPP mouse models and eventually in AD patients. Reversal of behavioral deficits was not associated with reduction in amyloid plaque burden or alterations in levels of total brain Aβ, but was significant at doses that allowed detection of Aβ-antibody complexes in the CSF. However, levels of soluble brain Aβ or the presence of antibodies bound to plaques were not measured.

Increase or Decrease of Soluble Aβ?
The authors speculate that the behavioral improvements may be caused by efflux of soluble Aβ out of the brain. This may be true, but the reversal of memory deficits may as well be caused by a rapid increase in soluble Aβ within the CNS, derived from plaque Aβ. However, this acute increase may not be sufficient to significantly reduce plaque burden. This alternative explanation should come as no surprise as...  Read more

"The findings by Dodart and colleagues are very interesting. However, as Steven Paul points out in the Q and A session on this website, it remains to be seen if a similar effect will be observed in other transgenic AβPP mouse models and eventually in AD patients. Reversal of behavioral deficits was not associated with reduction in amyloid plaque burden or alterations in levels of total brain Aβ, but was significant at doses that allowed detection of Aβ-antibody complexes in the CSF. However, levels of soluble brain Aβ or the presence of antibodies bound to plaques were not measured.

Increase or Decrease of Soluble Aβ?
The authors speculate that the behavioral improvements may be caused by efflux of soluble Aβ out of the brain. This may be true, but the reversal of memory deficits may as well be caused by a rapid increase in soluble Aβ within the CNS, derived from plaque Aβ. However, this acute increase may not be sufficient to significantly reduce plaque burden. This alternative explanation should come as no surprise as numerous laboratories have shown low levels of Aβ to have neurotrophic effects in cell culture, which may translate into a beneficial neuromodulatory effect in vivo. Follow-up studies measuring soluble Aβ within the brain should clarify this issue.

It is certainly difficult to compare behavioral studies in various immunized transgenic AβPP models of different background strains. And yet, a treatment induced-increase in brain soluble Aβ may actually explain similarities within the reported behavioral studies, whereas Dodart et al. mention that their data seem to contrast with previous findings (Janus et al., 2000; Morgan et al., 2000). Janus et al. observed behavioral improvement associated with reduction in plaques but no change in total brain Aβ. Although they suggested that cognitive improvement might be due to reductions in potentially toxic protofibrils, it may also have been caused by an increase in soluble brain Aβ levels. Morgan et al. observed a partial reversal of cognitive deficits in AβPP/PS1 mice, though cerebral amyloid burden as measured by immunohistochemistry was not significantly reduced. The authors suggested that a decrease in soluble Aβ might explain the cognitive improvement in the immunized mice, but this potential connection was not measured in their study.

Our results following 7 months of treatment suggest that the reduction in soluble brain Aβ is less than that of plaque Aβ (see related ARF news items), but we did not analyze the behavior of the mice. All the behavioral studies may fit nicely together if the cognitive improvements were caused by an increase in soluble Aβ within the CNS. This view may seem to contradict findings suggesting toxicity of soluble Aβ species (see news story), but we emphasize that the in-vivo ratio of Aβ monomers/oligomers and protofibrils/fibrils in transgenic mice and AD brain has not been thoroughly established, and any future biochemical findings will likely vary depending on the methods used. Furthermore, Aβ oligomers found in these mice may be less stable than those detected in AD brains (Kalback et al., 2002), and their toxicity has not been demonstrated. It is likely that most of the soluble Aβ in mouse brain are monomers, which may be trophic instead of toxic.

Previously, these authors showed that peripheral injection of anti-Aβ antibody decreased brain amyloid burden without binding to amyloid plaques, but the presence of Aβ-antibody complexes was not measured in the CSF (see related ARF news items) While both these studies show an extensive increase in plasma Ab levels, they cannot be easily compared because of differences in parameters measured. The present results need to be replicated in other AβPP transgenic models. They also need to be correlated with levels of soluble brain Aβ, as well as amounts of various AβPP fragments that may affect behavior. In the PDAPP model, Aβ is predominantly generated within the CNS, whereas in the Tg2576 model Aβ is formed in various peripheral organs as well. It is, therefore, likely that any sequestration of Aβ from the CNS to the periphery will be greater in the PDAPP model, and a higher dose may be needed to achieve a similar effect in Tg2576 mice.

The predictive value of the transgenic AβPP mouse models are questionable also because the plaques in the AβPP23 and the Tg2576 mouse models are much more soluble than those in AD, though vascular amyloid is as insoluble in these mice as in AD (Kuo et al., 2001; Kalback et al., 2002). This finding suggests that the mouse plaques may be more easily removed than those in AD. It may be explained by transgenic mice having fewer posttranslational modifications within the Aβ peptides, as well as by differences in the composition of amyloid-associated proteins. However, a contradicting finding in the Tg2576 model has been reported (Kawarabayashi et al., 2001), in which the portion of Aβ requiring formic acid for extraction showed an age-related increase and eventually reached similar levels as seen in AD brain. This controversy regarding the ratio of soluble versus insoluble Aβ in Tg mice needs to be resolved, and a similar study should be performed in the PDAPP model. Future therapy studies should also attempt to determine the ratio of various Aβ species.

Overall, therapeutic findings in these mouse models must be interpreted cautiously, as they may not apply to the human condition. It should be noted, however, that although amyloid burden in AD patients and AβPP transgenic mice has been reported to be similar, human plasma Aβ levels are several-fold lower than those observed in the Tg2576 mice. Therefore, a smaller amount of antibodies per weight may be needed in humans than in transgenic mice to achieve similar therapeutic results, although we should not expect that antibodies will lead to clearance of existing plaques in AD brains, which postmortem require formic acid for solubilization."

View all comments by Blas Frangione
View all comments by Einar Sigurdsson

The remarkable finding described by Dodart et al. in Nature Neuroscience adds an important page to the evolving story of Aβ toxicity in Alzheimer's disease. It builds on two related discoveries. First, thanks to the pioneering work of Dale Schenk and colleagues (Schenk et al, 1999), we have known for three years that active and passive vaccination can have a major impact on brain chemistry, a terrifically surprising and important discovery. Schenk's original findings showed that vaccination with fibril-enriched preparations of Aβ could significantly lower amyloid plaques in transgenic mice models for AD. Second, since the work of Lambert et al., 1998, we've also known that small oligomers of Aβ, soluble and globular in structure, have potent CNS effects. The disruptive activity of oligomers (aka "ADDLs") is likely to account for the...  Read more

The remarkable finding described by Dodart et al. in Nature Neuroscience adds an important page to the evolving story of Aβ toxicity in Alzheimer's disease. It builds on two related discoveries. First, thanks to the pioneering work of Dale Schenk and colleagues (Schenk et al, 1999), we have known for three years that active and passive vaccination can have a major impact on brain chemistry, a terrifically surprising and important discovery. Schenk's original findings showed that vaccination with fibril-enriched preparations of Aβ could significantly lower amyloid plaques in transgenic mice models for AD. Second, since the work of Lambert et al., 1998, we've also known that small oligomers of Aβ, soluble and globular in structure, have potent CNS effects. The disruptive activity of oligomers (aka "ADDLs") is likely to account for the imperfect correlation between dementia and plaque burden in Alzheimer's disease.

Particularly relevant to the study by Dodart et al, ADDLs rapidly inhibit LTP, a major paradigm for synaptic memory formation (Lambert, ibid, see also more recent works by Wang et al., 2002, and Walsh et al, 2002, (see related ARF news items). The fast and selective nature of LTP inhibition indicates that it is not a consequence of neuronal degeneration. Because these synaptic effects appear dysfunctional rather than degenerative, we have proposed that memory loss in AD (and in mild cognitive impairment) could actually be reversed, not just slowed down (see, e.g., Klein et al., 2001). As seen in Dodart et al., the rapid cognitive reversal in antibody-treated transgenic mice provides strong support for this hypothesis.

Dodart's findings underscore the potential value in developing vaccines that target soluble toxins. The usefulness of such vaccines was suggested by earlier work from Morgan et al., 2000, who found that vaccination improved memory performance in transgenic mice whether or not plaques were eliminated. We might expect that ideal therapeutic antibodies would be able to discriminate between toxic oligomers and physiological monomers. Toxicity-neutralizing antibodies with such specificity recently have been generated by vaccination of rabbits with ADDLs (Lambert et al., 2001). Even greater specificity ultimately may be crucial. For example, vaccines that target soluble toxins but avoid insoluble amyloid deposits may circumvent the CNS inflammation recently uncovered in human clinical trials (see vaccination live chat).

In a wider venue, recent evidence by Bucciantini et al. indicates that other protein misfolding diseases, previously associated with amyloid deposition, also may have pathogenic sub-fibrillar species (see related ARF news items). It is possible, therefore, that approaches developed for targeting such species in AD ultimately may have broad application.

View all comments by William Klein

The article by Pfeifer et al. describes the exacerbation of cerebral hemorrhages seen in an aged APP-transgenic model following passive administration of anti-Aβ antibodies directed to amino acids 3-6. This particular transgenic mouse, called APP23, is described by the authors in a previous paper as a "spontaneous hemorrhagic stroke mouse model" (Winkler et al., 2001). At approximately 19 months of age onward, the mouse exhibits severe cerebral amyloid angiopathy (CAA), which is associated with recurrent hemorrhages as the mice age. Moderate to severe cerebral vascular amyloid also exists in approximately 26 percent of Alzheimer’s disease patients, as well, though the rate of hemorrhages is less than that seen in the APP23 mouse (approximately five percent of AD cases; see Greenberg et al., 1998).

When the authors gave 21-month-old APP23 mice a monoclonal antibody directed to Aβ3-6 once a week for five months, they saw that the...  Read more

The article by Pfeifer et al. describes the exacerbation of cerebral hemorrhages seen in an aged APP-transgenic model following passive administration of anti-Aβ antibodies directed to amino acids 3-6. This particular transgenic mouse, called APP23, is described by the authors in a previous paper as a "spontaneous hemorrhagic stroke mouse model" (Winkler et al., 2001). At approximately 19 months of age onward, the mouse exhibits severe cerebral amyloid angiopathy (CAA), which is associated with recurrent hemorrhages as the mice age. Moderate to severe cerebral vascular amyloid also exists in approximately 26 percent of Alzheimer’s disease patients, as well, though the rate of hemorrhages is less than that seen in the APP23 mouse (approximately five percent of AD cases; see Greenberg et al., 1998).

When the authors gave 21-month-old APP23 mice a monoclonal antibody directed to Aβ3-6 once a week for five months, they saw that the rate of hemorrhages increased about twofold above baseline. The severity of the hemorrhages also increased approximately 30 percent above levels seen in the untreated group. No control antibody group was tested, and thus, we cannot be sure that the effect was specific for the particular anti-Aβ antibody monoclonal used.

As the authors correctly point out, these types of findings have not been seen in other APP-transgenic mouse models that have been actively or passively immunized with Aβ. Though other APP transgenes, such as the PDAPP mouse that we routinely have used in our studies, do show CAA, as well (Kimchi, 2001), the amount of this type of pathology is significantly less than that seen in the APP23 mice, and this might be the reason for the novelty of the new report.

Aβ immunotherapy for Alzheimer’s disease remains an important new approach for potential treatment of this devastating disease. Clinical progress with immunization of Aβ42 (AN 1792) recently suffered a setback when a subset of treated patients developed meningoencephalitis—a condition distinct from the hemorrhagic stroke described in the APP23 mouse. This recent finding, nevertheless, adds to a growing body of literature on the subject. As with all new preclinical observations, additional experiments will be required to understand whether these new findings, in this particular animal model, will have a clinical correlate in humans or not.

See response by Alexei Koudinov: Amyloid was never clearly implicated in Alzheimer's disease, so look at Aβ from a different angle. Koudinov AR. British Medical Journal (30 November 2002).

View all comments by Dale Schenk

This an extremely interesting preliminary report. The editorial by Winblad and Blum is very careful in conveying both the excitement this data causes, and also the caution that needs to be exercised in its interpretation. Hock and his colleagues are to be congratulated for their astuteness in taking part in the Elan trial, but negotiating themselves some freedom in using their own data from their trial subjects. Let's hope that when Elan releases the data on the whole trial, the overall results confirm these preliminary data. Even if immunization turns out not to be the way forward for safety reasons, such an outcome would imply that other Aβ-reducing strategies have every chance of clinical success.

View all comments by John Hardy

It is encouraging that in a subset (n=30) of the more than 300 subjects enrolled in the Elan study who were analyzed, there is preliminary evidence that there may be a positive response. This preliminary analysis suggests that further, more conclusive studies of the immunization approach (active and passive) should continue. Though the analysis argues for more studies, the title and some of the conclusions of this study are not yet justified. As pointed out in the accompanying commentary by Winblad and Blum, the control group, which is really N=6 who received placebo or N=10 total who did not generate "antibodies," is very small. More importantly, not only is the control group small, that group deteriorated at a much faster rate than subjects with mild to moderate Alzheimer's disease normally worsen. The amount of MMSE decline in the group treated with immunization is actually what is described in patients with Alzheimer's who are on cholinesterase inhibitors, (which many of these patients were on), namely about one to three points in the first year of follow-up. It would have...  Read more

It is encouraging that in a subset (n=30) of the more than 300 subjects enrolled in the Elan study who were analyzed, there is preliminary evidence that there may be a positive response. This preliminary analysis suggests that further, more conclusive studies of the immunization approach (active and passive) should continue. Though the analysis argues for more studies, the title and some of the conclusions of this study are not yet justified. As pointed out in the accompanying commentary by Winblad and Blum, the control group, which is really N=6 who received placebo or N=10 total who did not generate "antibodies," is very small. More importantly, not only is the control group small, that group deteriorated at a much faster rate than subjects with mild to moderate Alzheimer's disease normally worsen. The amount of MMSE decline in the group treated with immunization is actually what is described in patients with Alzheimer's who are on cholinesterase inhibitors, (which many of these patients were on), namely about one to three points in the first year of follow-up. It would have been very useful if this study included all of the subjects in the Elan trial over the first year. One comment about the measurement of Aβ levels in plasma and CSF is warranted. The study measured Aβ by ELISA. If these subjects generated antibodies, they were polyclonal antibodies. These antibodies can bind to Aβ in the plasma (or CSF) and, if they are present, can potentially block binding of other antibodies used in the ELISA. No methods were used to account for this. Thus, the plasma and CSF Aβ levels are not interpretable with the technique used here. Also, there appears to be an error in Fig. 4B for CSF Aβ42. It is listed as ng/ml, but presumably is pg/ml. In the legend for Fig. 4, it appears A and B are reversed. In summary, while this clinical report is encouraging, it is preliminary.

View all comments by David Holtzman

Since this is a clinical study involving human subjects, one cannot expect it to be without unavoidable limitations. The numbers of patients are small, the follow-up is of relatively short duration, and these are both problems, as Winblad and Blum point out. The mental state of AD patients can fluctuate widely, so I think more specific functional tests will have to be done to strengthen the case for a positive effect.

Let's assume that some of the patients show improvement and this is correlated with antibody levels. Can we rule out some nonspecific immunological reactions that cause improvement independent of the ability of the antibodies to bind to Aβ? If these were experimental animals, one would be able to test the effects of immunizing with different forms of synthetic peptides. This is clearly not possible with human subjects. I am also concerned about the different results that are reported for the ELISA tests and the authors' tissue amyloid plaque assay. It is possible that they are looking at different conformational epitopes, as the authors suggest, but one...  Read more

Since this is a clinical study involving human subjects, one cannot expect it to be without unavoidable limitations. The numbers of patients are small, the follow-up is of relatively short duration, and these are both problems, as Winblad and Blum point out. The mental state of AD patients can fluctuate widely, so I think more specific functional tests will have to be done to strengthen the case for a positive effect.

Let's assume that some of the patients show improvement and this is correlated with antibody levels. Can we rule out some nonspecific immunological reactions that cause improvement independent of the ability of the antibodies to bind to Aβ? If these were experimental animals, one would be able to test the effects of immunizing with different forms of synthetic peptides. This is clearly not possible with human subjects. I am also concerned about the different results that are reported for the ELISA tests and the authors' tissue amyloid plaque assay. It is possible that they are looking at different conformational epitopes, as the authors suggest, but one should not overlook the fact that the tissue assay involves "fixed" tissue (they don't specify how) that is embedded in paraffin. It is not stated whether the Aβ peptides were similarly treated. If they were not, I would look first at the differences in antigenicity related to antigen preparation before concluding that conformational differences explain differences in immunoreactivity.

I find it puzzling that serum antibodies against Aβ remain high in the patients, without changes in circulating Aβ levels.

View all comments by Vincent Marchesi

This paper continues the rollercoaster of emotion regarding the use of amyloid vaccines to treat Alzheimer's disease. The identification that Aβ vaccination could dramatically reduce amyloid deposition in the PDAPP mouse (Schenk et al., 1999), followed by demonstration that the vaccine also protected mice from learning and memory deficits (Janus et al., 2000; Morgan et al., 2000), led to early trials of the vaccine in humans. Although Phase I trials found no adverse consequences, six percent of the Phase II trial patients developed aseptic meningoencephalitis (Schenk, 2002), which in some cases was severe (Nicoll et al., 2003). This led to premature termination of the trial, with cessation of any further inoculations with the Aβ...  Read more

This paper continues the rollercoaster of emotion regarding the use of amyloid vaccines to treat Alzheimer's disease. The identification that Aβ vaccination could dramatically reduce amyloid deposition in the PDAPP mouse (Schenk et al., 1999), followed by demonstration that the vaccine also protected mice from learning and memory deficits (Janus et al., 2000; Morgan et al., 2000), led to early trials of the vaccine in humans. Although Phase I trials found no adverse consequences, six percent of the Phase II trial patients developed aseptic meningoencephalitis (Schenk, 2002), which in some cases was severe (Nicoll et al., 2003). This led to premature termination of the trial, with cessation of any further inoculations with the Aβ peptide. Thus, as rapidly as hope was raised by the early successes in animal models, all the enthusiasm for the vaccine as a potential therapy crashed, leading some to accuse Elan of proceeding too rapidly into human trials in spite of the safety testing performed in Phase I. For the last year, very few grants were supported that proposed to investigate the amyloid vaccine, even if it was only used as a tool to reduce Aβ deposits. Several other reports appeared suggesting that Aβ vaccination would have adverse consequences, such as hemorrhage (Pfeifer et al., 2002) or invasion of T cells into the CNS (Furlan et al., 2003). It seemed increasingly unlikely that the scientific community could be convinced that anti-Aβ immunotherapy should continue to be investigated. Now, this manuscript by Hock et al., reporting on their subset of patients from the Elan clinical trial, shows (by some measures) a significant slowing of cognitive deterioration in those patients with plaque-reactive antibodies. Moreover, the patients with the highest antibody titers have remained stable or even improved their cognitive functions over a year's time. Thus, the immunotherapy rollercoaster begins another climb up the track. It has risen, phoenix-like, to again generate hope among the millions with relatives suffering from end-of-life dementias. It will be important in this swing of the pendulum to avoid hype and promotion, and to maintain a sober outlook while investigating the advantages and disadvantages of this approach to dementia therapy. At the AD-PD meeting in Seville in early May 2003, where the Hock et al. data were presented, the representatives from Elan were quick to point out that this is a subset of patients from their trial. They also indicated that, at least based upon intention to treat (i.e., comparing the group receiving the vaccine vs. placebo), there was no benefit in the ADAS-COG scores in the complete dataset. It remains to be determined if, overall, the subset of patients with plaque-reactive anti-Aβ antibodies do still show benefit from the vaccination. The 12-month decline in cognitive function in the group lacking anti-Aβ antibodies in the Hock et al. study is greater than is typically observed over this period (see commentary by Winblad). However, this report will once again encourage the investigation of anti-Aβ immunotherapy as a treatment for dementias, and will permit neuroscientists and immunologists to develop alternative methods of increasing anti-Aβ titers while avoiding meningoencephalitis and other potential problems associated with this once-again promising avenue of therapy.

References:
Furlan R, Brambilla E, Sanvito F, Roccatagliata L, Olivieri S, Bergami A, Pluchino S, Uccelli A, Comi G, Martino G. Vaccination with amyloid-beta peptide induces autoimmune encephalomyelitis in C57/BL6 mice. Brain. 2003 Feb;126(Pt 2):285-91. Abstract

Janus C, Pearson J, McLaurin J, Mathews PM, Jiang Y, Schmidt SD, Chishti MA, Horne P, Heslin D, French J, Mount HT, Nixon RA, Mercken M, Bergeron C, Fraser PE, St George-Hyslop P, Westaway D. A beta peptide immunization reduces behavioural impairment and plaques in a model of Alzheimer's disease. Nature. 2000 Dec 21-28;408(6815):979-82. Abstract

Morgan D, Diamond DM, Gottschall PE, Ugen KE, Dickey C, Hardy J, Duff K, Jantzen P, DiCarlo G, Wilcock D, Connor K, Hatcher J, Hope C, Gordon M, Arendash GW. A beta peptide vaccination prevents memory loss in an animal model of Alzheimer's disease. Nature. 2000 Dec 21-28;408(6815):982-5. Abstract

Nicoll JA, Wilkinson D, Holmes C, Steart P, Markham H, Weller RO. Neuropathology of human Alzheimer disease after immunization with amyloid-beta peptide: a case report. Nat Med. 2003 Apr;9(4):448-52. Abstract

Pfeifer M, Boncristiano S, Bondolfi L, Stalder A, Deller T, Staufenbiel M, Mathews PM, Jucker M. Cerebral hemorrhage after passive anti-Abeta immunotherapy. Science. 2002 Nov 15;298(5597):1379. Abstract

Schenk D. Opinion: Amyloid-beta immunotherapy for Alzheimer's disease: the end of the beginning. Nat Rev Neurosci. 2002 Oct;3(10):824-8. Abstract

Schenk D, Barbour R, Dunn W, Gordon G, Grajeda H, Guido T, Hu K, Huang J, Johnson-Wood K, Khan K, Kholodenko D, Lee M, Liao Z, Lieberburg I, Motter R, Mutter L, Soriano F, Shopp G, Vasquez N, Vandevert C, Walker S, Wogulis M, Yednock T, Games D, Seubert P. Immunization with amyloid-beta attenuates Alzheimer-disease-like pathology in the PDAPP mouse. Nature. 1999 Jul 8;400(6740):173-7. Abstract

View all comments by Dave Morgan

During the last 10 years, much evidence has been reported in support of the amyloid hypothesis for the progression of AD. However, the key finding of whether inhibitors of Aβ amyloidogenesis would lead to a cognitive improvement was missing. In this very interesting article, Hock et al. report for the first time preliminary results indicating that this may be the case. In addition to the practical implications for treatment, in my opinion the great importance of this study, as well as the previous publication by Nicoll et al., is that it provides crucial data to understand the molecular mechanism of AD pathogenesis in humans. It should also boost the race to develop safer immunization strategies and other anti-Aβ production, misfolding, and aggregation approaches for AD treatment. I concur with Winblad and Blum's caution on the interpretation of results with very small number of patients, but Hock, Nitsch, and colleagues should be congratulated for making these results public and imitated by the rest of the...  Read more

During the last 10 years, much evidence has been reported in support of the amyloid hypothesis for the progression of AD. However, the key finding of whether inhibitors of Aβ amyloidogenesis would lead to a cognitive improvement was missing. In this very interesting article, Hock et al. report for the first time preliminary results indicating that this may be the case. In addition to the practical implications for treatment, in my opinion the great importance of this study, as well as the previous publication by Nicoll et al., is that it provides crucial data to understand the molecular mechanism of AD pathogenesis in humans. It should also boost the race to develop safer immunization strategies and other anti-Aβ production, misfolding, and aggregation approaches for AD treatment. I concur with Winblad and Blum's caution on the interpretation of results with very small number of patients, but Hock, Nitsch, and colleagues should be congratulated for making these results public and imitated by the rest of the centers involved in the Elan Phase II trial.

View all comments by Claudio Soto

This paper shows that immunization with Aβ may slow the progression of Alzheimer’s disease, but does not restore cognitive function. These results contrast with studies of immunoneutralization of Aβ in AβPP-transgenic mice, which demonstrate reversal of memory loss and restoration of cognitive function (Kotilinek et al., 2002; Dodart et al., 2002). The most likely explanation for this discrepancy is that important differences in pathology exist between AβPP-transgenic mice and Alzheimer’s disease.

During the first year following the appearance of memory deficits in Tg(APPNL)2576 mice, neurons and synapses are largely intact (Irizarry et al., 1997). During the second year, postsynaptic markers decline, while presynaptic markers and neurons remain unchanged (G. Cole and B. Hyman, personal communication). We have proposed that soluble Aβ assemblies...  Read more

This paper shows that immunization with Aβ may slow the progression of Alzheimer’s disease, but does not restore cognitive function. These results contrast with studies of immunoneutralization of Aβ in AβPP-transgenic mice, which demonstrate reversal of memory loss and restoration of cognitive function (Kotilinek et al., 2002; Dodart et al., 2002). The most likely explanation for this discrepancy is that important differences in pathology exist between AβPP-transgenic mice and Alzheimer’s disease.

During the first year following the appearance of memory deficits in Tg(APPNL)2576 mice, neurons and synapses are largely intact (Irizarry et al., 1997). During the second year, postsynaptic markers decline, while presynaptic markers and neurons remain unchanged (G. Cole and B. Hyman, personal communication). We have proposed that soluble Aβ assemblies impair memory in Tg(APPNL)2576 mice (Ashe, 2001; Westerman, 2002), and have suggested that the rapid restoration of memory by passive immunization against Aβ indicates that Aβ assemblies disrupt memory by altering neuronal function, but not neuronal structure.

Patients with Alzheimer’s disease differ from Tg(APPNL)2576 mice because they have substantial plaque and tangle deposition as well as significant cell loss in vulnerable brain regions important for memory. The relative benefit conferred by Aβ immunization in the Hock et al. paper may reflect the inhibition of the disruptive effects of Aβ assemblies on cognitive function or the improvement of certain aspects of amyloid pathology taking place in the setting of ongoing neurodegeneration. Achieving in humans the dramatic results observed in mice is more likely to occur if interventions are administered in earlier stages of disease. Understanding how to improve cognitive function in later stages of Alzheimer’s disease will require a new generation of mouse models to study.

View all comments by Karen Hsiao Ashe

One of the critical questions in β-amyloid immunotherapy is whether depletion of the amyloid plaques is accompanied by improvement in behavioral/neurophysiological impairments and in a reduction in the nerve cell death of Alzheimer’s disease. In other words, does immunization with Aβ simply clear a neuropathological byproduct, or can it cure the disease? Anti-β-amyloid immunization of the AD mouse model showed remarkable efficacy in reducing amyloid and restoring cognitive function. The present data is the first attempt to compare cognitive test results in human AD patients—a small number so far—before and one year after vaccination. Indeed, patients with serum antibodies against β-amyloid plaques showed diminished cognitive decline and slowed disease progression, and the "dose-response" relationship between antibody levels and clinical effects constitutes evidence that amyloid proteins are indeed a primary cause of Alzheimer’s symptoms. The treated patients, suffering mild or moderate dementia, received only two injections and throughout the year...  Read more

One of the critical questions in β-amyloid immunotherapy is whether depletion of the amyloid plaques is accompanied by improvement in behavioral/neurophysiological impairments and in a reduction in the nerve cell death of Alzheimer’s disease. In other words, does immunization with Aβ simply clear a neuropathological byproduct, or can it cure the disease? Anti-β-amyloid immunization of the AD mouse model showed remarkable efficacy in reducing amyloid and restoring cognitive function. The present data is the first attempt to compare cognitive test results in human AD patients—a small number so far—before and one year after vaccination. Indeed, patients with serum antibodies against β-amyloid plaques showed diminished cognitive decline and slowed disease progression, and the "dose-response" relationship between antibody levels and clinical effects constitutes evidence that amyloid proteins are indeed a primary cause of Alzheimer’s symptoms. The treated patients, suffering mild or moderate dementia, received only two injections and throughout the year were dosed with antiinflammatory and antioxidant protection drugs. Finding the antibodies 12 months after the last administration suggests an impressive long-lasting immunization effect induced by a relatively small amount of antigen. Moreover, data suggest that a low titer of antibodies is enough to affect plaque development.

Site-directed antibodies induced by various immunological approaches are aimed at treatment of a disease that is caused by abnormal conformational changes or folding of a peptide or protein, as presented in Alzheimer’s disease and other amyloidosis disorders (Solomon, 2002). However, any effective immunization strategy must identify not only the specific nature of the antigen or the epitope, but also address the formulation and method of delivery of the antigen or antibodies as a major and critical parameter.

Unfortunately, humans may develop self-antibodies when immunized with whole or fragments of AβPP. These antibodies are capable of binding to a variety of Aβ species in the brain; thus, immunization could have beneficial effects, such as inhibition of amyloid fibril formation, while microglial overactivation may lead to neuroinflammation. The consequence of this on inflammatory pathology in AD brains needs to be considered before immunization is used as a strategy for treating AD. As recently reported, interactions of human microglia with antibody-opsonized amyloid showed increased inflammation (Lue et al., 2002).

Several strategies directed towards prevention of neuroinflammation are under investigation. Active immunization with synthetic Aβ1-42 peptide reduces β-amyloid plaques in AβPP-transgenic mice without detectable toxicity, but the extension of this approach to AD patients induced a neuroinflammatory reaction in some of the study subjects, precluding further testing of the preparation. Vaccination with nontoxic, small antiaggregating epitopes of AβPP may partially avoid the undesirable effects of neuroinflammation, e.g., by preventing T cell activation (Frenkel et al., 2003).

Administration of intravenous immunoglobulin (IVIG), which has well-recognized antiinflammatory activities independent of the antigen-specific effect, may modulate the inhibitory FcR pathway, thus controlling autoantibody-mediated inflammation induced by self-antigens or antibodies in immunotherapeutic strategies for treatment of AD. Another approach may be passive immunization with antibodies devoid of Fc, which may prevent overactivation of microglia and, thus, attenuation of autoantibody-triggered neuroinflammation. Progress in vector development for brain delivery of such antibodies, as well as clearance of immunocomplex devoid of Fc region, was recently reported (Frenkel and Solomon, 2002).

Many important questions remain open. Is the reported improvement in the behavior of AD patients caused by dissolving existing plaques or preventing formation of new plaques, or is it caused by sequestration of soluble AβPP? How many antibodies are required? How can inflammation and/or overactivation of microglia be prevented? In spite of these questions, the immunotherapeutic approach towards amyloid peptide remains the most fascinating therapeutic target for generating agents potentially able to modify the natural history of AD.

References:
Solomon B. Immunological approaches as therapy for Alzheimer's disease. Expert Opin Biol Ther. 2002 Dec;2(8):907-17. Abstract

Lue LF, Walker DG. Modeling Alzheimer's disease immune therapy mechanisms: interactions of human postmortem microglia with antibody-opsonized amyloid beta peptide. J Neurosci Res. 2002 Nov 15;70(4):599-610. Abstract

Frenkel D, Dewachter I, Van Leuven F, Solomon B. Reduction of beta-amyloid plaques in brain of transgenic mouse model of Alzheimer's disease by EFRH-phage immunization. Vaccine. 2003 Mar 7;21(11-12):1060-5. Abstract

Frenkel D, Solomon B. Filamentous phage as vector-mediated antibody delivery to the brain. Proc Natl Acad Sci U S A. 2002 Apr 16;99(8):5675-9. Abstract

View all comments by Beka Solomon

I believe the bystander effect is heavily implicated here and anyone familiar with comments on alzforum know that although autoimmunity and BBB leakage are important aspects in AD I still hold firmly to the belief that amyloid beta is an important catalyst (or cocatalyst) for immune response gone awry and for BBB leakage and TAU, CDK5 (amongst others) involved in intracellular hyperphosporylation.

View all comments by Jacob Mack

Two independent studies provided morphological evidence suggesting that accumulations of amyloid in mouse cerebral blood vessels are associated with amyloid plaques, which are typically detected in the CNS of AD patients. There is a wealth of evidence confirming vascular pathology in AD, and it was suggested years ago that amyloid plaques might originate from vessels.

The characterization of the different morphological types of amyloid plaques has been an important research focus in our laboratory. It is becoming increasingly clear that each distinct type of plaque may arise from separate mechanisms and that the concept that diffuse plaques gradually evolve into dense-core plaques or vice versa, may not be valid.

The Kumar paper suggested that all plaques are of vascular origin in the transgenic mouse brains; hence, in these models, there is no randomness to the distribution of the amyloid plaques. The Miao paper implied that diffuse and nonfibrillar amyloid in the cortex of the Tg-SwD1 mice remained diffuse and nonfibrillar, and that fibrillar amyloid in the thalamus...  Read more

Two independent studies provided morphological evidence suggesting that accumulations of amyloid in mouse cerebral blood vessels are associated with amyloid plaques, which are typically detected in the CNS of AD patients. There is a wealth of evidence confirming vascular pathology in AD, and it was suggested years ago that amyloid plaques might originate from vessels.

The characterization of the different morphological types of amyloid plaques has been an important research focus in our laboratory. It is becoming increasingly clear that each distinct type of plaque may arise from separate mechanisms and that the concept that diffuse plaques gradually evolve into dense-core plaques or vice versa, may not be valid.

The Kumar paper suggested that all plaques are of vascular origin in the transgenic mouse brains; hence, in these models, there is no randomness to the distribution of the amyloid plaques. The Miao paper implied that diffuse and nonfibrillar amyloid in the cortex of the Tg-SwD1 mice remained diffuse and nonfibrillar, and that fibrillar amyloid in the thalamus was tightly associated with vessels, suggesting a vasculature origin.

Although the primary focus of these papers was on "extracellular" amyloid (plaques), I found it surprising that there was little mention of intracellular amyloid in nearby neurons, or in smooth muscle cells as observed in AD. Perhaps the intent was to keep the paper focused on plaques, or maybe there were technical issues that did not show intracellular amyloid, or were not observed in the mouse model.

For example, there was a loss of smooth muscle cells in the amyloid-laden vessels (Miao paper), but no discussion of the presence of amyloid in smooth muscle cells, which is frequently observed. If one was to extrapolate observations that the intracellular accumulation of amyloid in neurons is linked directly to plaque formation, it is not unreasonable to suspect a similar scenario here. Hence, amyloid could accumulate in vascular smooth muscle cells over time before they die, leaving amyloid casts (= vascular plaques). Furthermore, any cell damage, especially smooth muscle cell death, would evoke the observed inflammatory response (gliosis).

Apparently, only diffuse, thioflavin S-negative plaques were detected in the frontotemporal cortex. Were microglia associated with these diffuse plaques detected in the prefrontal cortex, or were they only associated with "affected" vessels of the Tg-SwD1 mice? I would speculate that neither microglia nor activated astrocytes were associated with these diffuse plaques of the frontocortex, akin to the diffuse plaques observed in the human AD cerebellum and cerebrum. Therefore, if our earlier hypothesis is true—that dense-core (classical, thioflavin S-positive, etc.) plaques, but not diffuse plaques, originate from amyloid-laden neurons—then the lack of those plaques in regions of the CNS could account for the lack of consistent AD-like behaviors in such “AD” models.

On another aspect, it was noted that “Ig occasionally stained neuronal surfaces,” but no follow-up or comment was printed. One of our recent studies reported neurodegenerative characteristics on these Ig-positive neurons.

I still have trouble with the concept that AD is well-characterized by the steady deposition of amyloid from neurons in the brain and entering into the vasculature (Kumar, Fig. 10). Why couldn’t it be the other way around—that the brain is slowly and steadily accumulating vascular-derived amyloid, perhaps via BBB dysfunction? This issue needs to be resolved.

View all comments by Michael D'Andrea

Regarding Dr. D’Andrea’s remarks, we studied only ThS-positive “dense” plaques and not diffuse plaques, as also suggested by the title “Dense-core plaques in Tg2576 and PSAPP mouse models of Alzheimer disease are centered on vessel walls.” Within the text, however, we mostly refrained from using the term dense-core plaques (calling them dense-plaques instead). That's because the plaques observed in the studied mouse models differ from the classical dense-core plaques observed in AD, especially those observed in the Flemish APP pathology where we had earlier shown their proximity to vessels (Kumar-Singh et al. Am J Pathol, 2002).

Secondly, as Dr. D’Andrea suggested, we indeed came across intracellular amyloid in nearby neurons and sometimes amyloid related to smooth muscle cells. However, the primary focus of our paper were dense, extracellular amyloid deposits. Similarly, our observation that “Ig occasionally stained neuronal surfaces” was there to support our observation that there are at least subtle BBB disturbances in these mouse models, as has also been observed in...  Read more

Regarding Dr. D’Andrea’s remarks, we studied only ThS-positive “dense” plaques and not diffuse plaques, as also suggested by the title “Dense-core plaques in Tg2576 and PSAPP mouse models of Alzheimer disease are centered on vessel walls.” Within the text, however, we mostly refrained from using the term dense-core plaques (calling them dense-plaques instead). That's because the plaques observed in the studied mouse models differ from the classical dense-core plaques observed in AD, especially those observed in the Flemish APP pathology where we had earlier shown their proximity to vessels (Kumar-Singh et al. Am J Pathol, 2002).

Secondly, as Dr. D’Andrea suggested, we indeed came across intracellular amyloid in nearby neurons and sometimes amyloid related to smooth muscle cells. However, the primary focus of our paper were dense, extracellular amyloid deposits. Similarly, our observation that “Ig occasionally stained neuronal surfaces” was there to support our observation that there are at least subtle BBB disturbances in these mouse models, as has also been observed in humans, and that clearly has other important implications, especially towards therapeutics.

Lastly, despite a strong neuronal promoter used in these mouse models, there are some reports showing Aβ secretion from non-neuronal cells (i.e., ref. 57). Nevertheless, we have to agree that the majority of Aβ still comes from the neurons. With saturating parenchymal Aβ-degrading pathways, Aβ (especially Aβ40) is trafficked towards vessels for clearance. Although the model sums up more probable theories and published work for mouse AD models, we kept open the possibility that Aβ might also come back from vessels into brain either by receptor-mediated influx or by free diffusion taken that BBB is dysfunctional at these sites. While more studies have to be performed (especially with models that have predominantly Aβ42), one of the strongest evidence for a neurovascular Aβ flow for PSAPP and Tg2576 was that the earliest vascular deposits observed ultrastructurally occurred on the abluminal surface of capillaries and small parenchymal vessels.

References:
Kumar-Singh S, Pirici D, McGowan E, Serneels S, Ceuterick C, Hardy J, Duff K, Dickson D, Van Broeckhoven C. Dense-core plaques in Tg2576 and PSAPP mouse models of Alzheimer’s disease are centered on vessel walls. Am. J. Pathol. 2005;167:527-543. Abstract

Miao J, Xu F, Davis J, Otte-Holler, Verbeek MM, Van Nostrand WE. Cerebral Microvascular Amyloid {beta} Protein Deposition Induces Vascular Degeneration and Neuroinflammation in Transgenic Mice Expressing Human Vasculotropic Mutant Amyloid {beta} Precursor Protein. Am. J. Pathol. 2005;167:505-515. Abstract

Kumar-Singh S, Cras P, Wang R, Kros JM, van Swieten J, Lubke U, Ceuterick C, Serneels S, Vennekens K, Timmermans J-P, Van Marck E, Martin J-J, van Duijn C, Van Broeckhoven C: Dense-core senile plaques in the Flemish variant of Alzheimer’s disease are vasocentric. Am J Pathol 2002, 161:507-520. Abstract

View all comments by Samir Kumar-Singh