The small therapeutic window imposes another obstacle. The authors applied up to 100 μM concentrations (46 mg/l). This is dangerously close to the IC50 (IP) in mice, which is 100-125 mg/kg body weight (BW) for 24 h-72 h lethality. Kader Yagiz and colleagues examined this in a different line of transgenic mice: "When an amount of 150 or 250 mg/kg BW was injected intraperitoneally, EGCG was toxic to both transgenic and wild-type mice (Table 3). Mice from both groups were dead within 24 h. The EC50 for 24-h survival of wild-type mice was about 125 mg/kg BW of EGCG, but even at 100 mg/kg BW the animals died within 48 to 72 h." (From Yagiz et al., 2006.)

Despite the remarkable effects of EGCG, unfortunately it is not a lead for CNS drug development.

View all comments by Boris Schmidt

This antibody should be very useful to test many questions in the future, and it will be interesting to see what effects it has in vivo. Data in Figure 3 of the paper suggests that the antibody stains areas around plaques, but presumably not fibrillar Aβ, in human brain. It appears that it only stains areas that are in some way in the vicinity of plaques.

An important future question to address is whether oligomeric forms of Aβ only occur in association with aggregated forms such as fibrils. Some have speculated that they occur in brains well before or independently of the process of fibril formation. The reagent in this paper should allow this issue to be addressed. This study appears to suggest that the process of oligomer and fibril formation are...  Read more

This antibody should be very useful to test many questions in the future, and it will be interesting to see what effects it has in vivo. Data in Figure 3 of the paper suggests that the antibody stains areas around plaques, but presumably not fibrillar Aβ, in human brain. It appears that it only stains areas that are in some way in the vicinity of plaques.

An important future question to address is whether oligomeric forms of Aβ only occur in association with aggregated forms such as fibrils. Some have speculated that they occur in brains well before or independently of the process of fibril formation. The reagent in this paper should allow this issue to be addressed. This study appears to suggest that the process of oligomer and fibril formation are linked, as they occur in the same regions in brain.

Also, use of this antibody should be useful in the future to see if "oligomeric" forms of Aβ are present in physiological solutions (e.g., blood or CSF).

View all comments by David Holtzman

This study demonstrates once again the exquisitely...  Read more

This study demonstrates once again the exquisitely fine-tuned ability of antibodies to discriminate among determinants formed of primary, secondary, tertiary, and quaternary structural elements of proteins. The narrowness or breadth of the specificity can be adjusted with judicious screening.

This new means of scrutinizing (and impeding) pathogenic forms of protein has several potential applications. The therapeutic implications are clear. If oligomeric toxicity is central to a variety of age-associated proteopathies (and this appears to be so), the presence of the right antibodies could reduce the risk of developing these disorders and enhance the overall quality of old age.

Experimentally, the oligomer-specific antibody represents a new type of tool for illuminating the pathogenicity of disease-related proteins. For example, it is now possible to get a preliminary purchase on the comparative pathobiology of oligomerization. Both aged nonhuman primates and AβPP-transgenic mice are surprisingly refractory to Aβ-induced neuronal loss, despite the accumulation of large quantities of Aβ in brain; is this because oligomers fail to reach toxic levels in the brains of these species, and if so, why? It would also be informative to know if this antibody reacts with any normal proteins, or more intriguingly, are there formerly unrecognized, misfolded oligomeric proteins that appear with aging or insult?

Kayed et al. have taken an important step toward demystifying the link between abnormal protein assembly and Alzheimer's disease. The findings also strengthen the concept that many degenerative diseases share important pathogenic features that are not necessarily tied to amyloid itself. Finally, the data add weight to the argument that scientists and clinicians seeking new treatments for Alzheimer's disease should be conversing, in earnest, with those studying seemingly disparate disorders such as Parkinson's disease, mad cow disease and type 2 diabetes, to name only a few.—Lary Walker, Pfizer, Ann Arbor, Michigan; Harry LeVine, University of Kentucky, Lexington, Kentucky.

View all comments by Harry LeVine III
View all comments by Lary Walker

Temporal analysis of in-vitro aggregation of Aβ1-40 and 1-42 by EM and dot blot with anti-oligo revealed that the appearance of ADDLs (  Read more

Temporal analysis of in-vitro aggregation of Aβ1-40 and 1-42 by EM and dot blot with anti-oligo revealed that the appearance of ADDLs (Lambert et al., 1998) and protofibrils (Harper et al., 1997; Walsh et al., 1997) were coincident with anti-oligo immunoreactivity, and indicate that both ADDLs and protofibrils share a common structural epitope.

Amazingly, anti-oligo also specifically detects soluble oligomeric aggregates formed by α-synuclein, islet amyloid polypeptide, polyglutamine, lysozyme, insulin, and prion protein 106-126. As with Aβ, anti-oligo did not detect the monomeric or fibrillar versions of these proteins. Thus, anti-oligo recognizes a common structural epitope independent of primary sequence.

Importantly, anti-oligo prevented oligomer-mediated toxicity of all the proteins tested, whereas antibodies not specific for oligomers had no effect. However, the finding that the monoclonal antibody 6E10 can bind oligomers (although not specifically, Fig. 1A), but cannot attenuate oligomer-mediated toxicity (Fig. 2D) is unexpected, particularly since monoclonal antibodies generated using conventional means can rapidly reverse memory deficits in AβPP-transgenic mice by the presumed targeting of nonfibrillar soluble Aβ oligomers, e.g., Dodart et al., 2002 (see ARF related news story). This also raises a question about the role of low n-oligomers. Apparently anti-oligo apparently does not detect oligomers smaller than octamers (Fig. 1D). Are these the Aβ species that underlie reversible effects on memory and learning (Dodart et al., 2002, Walsh et al., 2002, see ARF related news story), whereas larger oligomers may be responsible for the irreversible loss of cells?

Whatever the effects of low n-oligomers, the observation that toxicity mediated by ADDLs and/or protofibrils can be ameliorated by anti-oligo suggests that their common structure may mediate toxicity by a common mechanism, and it offers a unique target for therapeutic intervention. This may enable further optimization of vaccination strategies, but in addition it suggests the possibility of designing small molecules that specifically bind to and disrupt the oligomer-specific conformation. Development of small-molecule disrupters would be particularly pertinent for use in diseases involving intracellular aggregates that are inaccessible to antibodies.

As with many significant advances, the work reported by Charlie Glabe’s group raises as many questions as it answers. For example, will the anti-oligo ELISA prove a useful diagnostic tool? The anti-oligo ELISA could lend itself to the inexpensive screening of thousands of samples and, in addition, might prove useful for the detection of other amyloid-related diseases. In this regard, the detection of oligomers in brain homogenates from patients with AD and mild Braak changes, but not in nondemented controls, is encouraging (see supporting online material), and provides the first evidence for the in-vivo relevance of protofibrils. Clearly, the availability of this unique antibody will facilitate a fuller understanding of the role of soluble oligomers in AD and other protein aggregation diseases. Exciting times!

References:
Harper et al., 1997

Walsh et al., 1997

Dodart et al., 2002: see ARF related news story

Walsh et al. (2002) Nature

View all comments by Dominic Walsh

ALZHEIMER'S AMYLOID BETA OLIGOMERS VERSUS LIPOPROTEIN ABETA

Please see my commentary on this article at Science SAGE KE (1 May 2003) [ Full Text ].

View all comments by Alexei R. Koudinov

It seems highly likely that Alzheimer’s, like most other late-onset diseases of aging, has multiple and usually weak genetic and environmental influences that modulate susceptibility. In contrast, diseases with strong single genetic or environmental risk factors will typically be more clearly causal, with earlier onset due to the potent genetic risk factors (e.g., autosomal dominant) or gross deficiencies of essential nutrients (scurvy, rickets, etc.). In this situation, common sense suggests a multifactorial approach to address these multiple risk factors for the prevention of late-onset AD. And common sense suggests that this is what...  Read more

It seems highly likely that Alzheimer’s, like most other late-onset diseases of aging, has multiple and usually weak genetic and environmental influences that modulate susceptibility. In contrast, diseases with strong single genetic or environmental risk factors will typically be more clearly causal, with earlier onset due to the potent genetic risk factors (e.g., autosomal dominant) or gross deficiencies of essential nutrients (scurvy, rickets, etc.). In this situation, common sense suggests a multifactorial approach to address these multiple risk factors for the prevention of late-onset AD. And common sense suggests that this is what current research is setting the stage for.

This is not a new lesson. With intense cancer research over the last 50 years, we have fairly good epidemiology and preclinical data to support a spectrum of risk and protective factors. We have a well-developed list of oncogenes, and multiple carcinogens and anticarcinogens present in the environment and diet. We also have some idea about initiation and promotion phases and very good animal models. We can make sensible recommendations about diet, smoking, and pollutants to minimize mutagen and carcinogen exposure.

Unfortunately, though, apart from a few successes like sunscreens, cancer chemoprevention lags behind. We can only hope that with AD, researchers will fare better, as indeed they have with atherosclerosis. There, some 50 years of concerted research has also led to a well-established list of risk and protective factors that allows the formulation of “heart healthy” recommendations with some strong clinical trial support for efficacy. With the great overlap between risk factors for AD and heart disease, we can only hope that controlling the common risk factors will limit our risk for both diseases. With this in mind, the knowledge that ACE inhibitors may increase AD risk is certainly significant, but somewhat disconcerting news.

With Alzheimer’s and other neurodegenerative diseases of aging, 20 years of intense effort have brought us less far along, but, unsurprisingly, put us on a similar track. AD researchers at the bench have only recently developed suitable (albeit still imperfect) animal models. AD clinicians were at a comparative disadvantage in establishing biomarkers. They lacked large populations of clearly high-risk patients in “remission” or at high risk of second cardiovascular events to conduct prospective clinical trials. Now that AD researchers have the animal models and the MCI patient pools, we will begin to see what translates.

We will likely end up with a set of “alzogens” to limit our exposure and “anti-alzogens” whose intake we want to optimize, albeit being mindful of potential side effect profiles. The polyphenolic antioxidants including green tea catechins, resveratrol, and curcumin (and doubtlessly others as yet unexplored) have real potential as protective factors for several diseases of aging, including AD. While these polyphenols have several overlapping antioxidant and anti-inflammatory properties, each of them also has its own unique targets, issues, and merits that add up to a reasonable case for further investigation. The catechins seem to reduce Aβ production, while curcumin limits Aβ aggregation and resveratrol may be particularly useful in protecting DNA via sirtuin.

I am personally convinced that cocktails of protective agents, notably including the polyphenols, would be a logical way to go, but optimizing and clinically testing more than one drug is a formidable task. Our choice to pursue curcumin for AD came after an initial in-vivo Aβ infusion model drug screen made some 10 years ago, together with a broad consideration of multiple factors, including the advanced stage of preclinical and clinical drug development for other diseases, costs of production, remarkably benign toxicity profile, and long history of use. Another factor was curcumin’s “cocktail” of active products tetrahydrocurcumin, vanillin, and ferulic acid. Today we can point to multiple mechanisms of action and an ever-increasing list of diseases where curcumin and its natural products look useful in animal models. There is even data on lifespan extension.

View all comments by Gregory Cole

I refer to the recent ARF news article (1), which reports that Wolozin and colleagues find that the relative risk for AD in the CABG group was 1.7-fold that of the PTCA group.

It's interesting that Pell et al. (2) report that 22 percent of CABG patients were on angiotensin-converting enzyme inhibitors, compared with 15 percent of PTCA patients.

References:
1. ARF related news story.

2. Pell JP, Walsh D, Norrie J, Berg G, Colquhoun AD, Davidson K, Eteiba H, Faichney A, Flapan A, Hogg KJ, Jeffrey RR, Jennings K, McArthur J, Mankad P, Oldroyd K, Pell AC, Starkey IR. Outcomes following coronary artery bypass grafting and percutaneous transluminal coronary angioplasty in the stent era: a prospective study of all 9890 consecutive patients operated on in Scotland over a two year period. Heart. 2001 Jun;85(6):662-6. Abstract

View all comments by Mary Reid

The oral bioavailability of resveratrol is almost null due to efficient metabolism by the kidney system (see Wenzel and Somoza, 2005). Therefore we do not believe that resveratrol could be used per se as an anti-amyloidogenic drug in vivo. Its potential biological activity in the brain after peripheral administration is, therefore, very questionable. However,...  Read more

The oral bioavailability of resveratrol is almost null due to efficient metabolism by the kidney system (see Wenzel and Somoza, 2005). Therefore we do not believe that resveratrol could be used per se as an anti-amyloidogenic drug in vivo. Its potential biological activity in the brain after peripheral administration is, therefore, very questionable. However, this observation is a powerful starting point for screening analogues of resveratrol for more active and more stable compounds, a task in which our laboratory is actively involved.

View all comments by Philippe Marambaud

We need to try to think in terms of risk/benefit ratios. I take vitamin C and vitamin E every day, and have done so for years, as it seems reasonably clear that the risk/benefit ratio is in favor of these compounds. They may lower my risk of AD more than they raise my risk of cardiovascular disease. It's hard to come up with real numbers, or any degree of certainty, with the...  Read more

We need to try to think in terms of risk/benefit ratios. I take vitamin C and vitamin E every day, and have done so for years, as it seems reasonably clear that the risk/benefit ratio is in favor of these compounds. They may lower my risk of AD more than they raise my risk of cardiovascular disease. It's hard to come up with real numbers, or any degree of certainty, with the compounds Gabrielle Strobel discusses.

I've been thinking about our approach in this area. We test everything in short-term studies to see if it makes a difference to the cognitive performance of AD patients, but this is a high hurdle to climb, and most of the compounds discussed in this article are unlikely to succeed in these studies. Does this mean that they are useless? Probably not. A diet rich in fruit and veggies, moderate or no alcohol consumption, no smoking, lots of exercise, physical and mental—all this probably lowers your risk of AD.

Would switching patients who already have the disease to a healthy lifestyle improve cognitive function? Unlikely, and so we dismiss these factors in favor of the next "wonder drug." But I suspect that if we all adopted this kind of lifestyle, the incidence of AD would decline significantly. If you believe the epidemiology, adding vitamins C and E would cut the incidence of AD by about 50 percent. Add the other goodies, and perhaps we could do even better.

But we don't think this way because we don't care about populations; we care about individuals, especially ourselves. I want a drug that will stop me from getting AD, or treat AD if I do get it. I don't want my relative risk decreased—I want it eliminated! It isn't likely that any of the lifestyle factors will do this, and they will probably end up being largely ignored. We want cures that can be taken "just in time," not major, lasting changes to our lifestyles that may or may not work for us.

View all comments by Peter Davies