The problem with curing Alzheimer’s is, as with so much of our understanding of aging and age-related diseases, that we make unexamined assumptions. Let me admit that many of our unexamined assumptions are either useful or reasonable. I assume that the sun will come up again tomorrow morning and that’s a useful and reasonable assumption. […]
The problem with curing Alzheimer’s is, as with so much of our understanding of aging and age-related diseases, that we make unexamined assumptions. Let me admit that many of our unexamined assumptions are either useful or reasonable. I assume that the sun will come up again tomorrow morning and that’s a useful and reasonable assumption. Useful, in that it allows me to plan my future, reasonable in that the sun has been coming up every morning for quite a while and is therefore likely to do so tomorrow as well. Certain unexamined assumptions are equally justifiable in dealing with Alzheimer’s disease. In the strictly poetic sense, Alzheimer’s certainly is the disease that “steals our souls”, yet no physician or researcher would actually make the assumption that the mind is some vague ethereal quantity that can be stolen by demons, let alone go on to promulgate a theory of Alzheimer’s pathology based on this assumption.
Yet we make exactly that same error, using an unexamined assumption, when we blithely assume that aging is simply the accumulation of damage and, pari passu, that Alzheimer’s disease is simply the accumulation of damaged molecules, be they amyloid, tau tangles, or altered mitochondrial enzymes. This unexamined assumption lies behind almost innumerable multi-million dollar FDA trials, academic papers, and clinical interventions. We assume, without even realizing we have made the assumption, that Alzheimer’s is merely the accumulation of damaged molecules.
We make the same unexamined assumption in looking at other age-related diseases and in the broader field of aging itself. We delve into the details of advanced glycation end-products (AGE), lipofuscin, cross-linking, and other molecular pools showing “accumulative damage”, all the time never realizing that we are making the same fallacy. We are working with completely unexamined (and erroneous) assumptions about how aging works. We naively assume that aging occurs – and age-related diseases follow – merely because things “rust” over time. We age because “molecules fall apart.”
Yet the data and logic both say differently. Let me give you a useful analogy: the cell phone. Consider a large pool (several thousand) of people who own cell phones. We know that if we examine any SINGLE cell phone, the best predictor of failure is how long it has been since production. If, however, we want to predict the percentage of failures in any large pool of owners, the best predictor is not time-since-production, but length-of-contract, that is, how often does it get turned over and replaced? Imagine two large pools of cell phone owners. In group A, the cell phones are replaced annually, with a failure rate (at equilibrium) of approximately 1%. In group B, the cell phones are replaced every ten years, with a failure rate (at equilibrium) of approximately 80%. In both groups, the rate of failure of any individual phone is the same. Furthermore, the rate of failure is only marginally related to the “genes”, i.e., whether the phone is an Apple iPhone, an Android, or some other type (a different “allele”). As the turnover rate (contract length to replacement) lengthens, the percent of failed cell phones climbs dramatically, regardless of the failure rate of any individual cell phone. In a pool of cell phones, “aging” is not a matter of passively accumulated damage, but of how actively we replace them.
The same is occurring in molecular pools in biological systems. The key predictor of “denatured” or dysfunctional molecules (e.g., AGE, beta amyloid microaggregates, cross-linking, elastin failure, collagen stiffening, etc.) is not the rate of damage but the rate of turnover. In the case of cell aging, when we reset gene expression (reset telomere length) we reset the turnover rates (anabolism and catabolism rates) of all molecular pools to those typical of “young” cells. The outcome is that molecule pool turnover is more than sufficient to deal with typical rates of damage.
Without realizing it, most of us make the mistake of thinking of molecular pools as static and damage as purely accumulative. The reality is that such pools are dynamic and the key dependent variable (as with cell phones) is not the passive rate of damage, but the active rate of turnover.
Unless we understand – and examine – our assumptions, we can never expect to cure age-related diseases. Once we start down the wrong path, all the logic and data in the world can’t make up for the fact that we are looking in the wrong place. It’s time we stopped blaming “demons” and starting thinking carefully.