Rattan,
You claim that there are *no* biological markers of aging that can be used
as a general measure of age. Surely it is far more important to find the
substances that accumulate as a function of time and *cause* the symptoms
of aging, rather than simply reflect an individuals age. Those products
that you have listed may all be possible candidates for these and if so,
are much more important than a mere age marker.
There are many such substances. You have listed some. A group of such are
those formed by the reaction of a reducing sugar with any protein. The
resultant "Amadori" product may then undergo a series of rearrangements and
dehydration (and possibly oxidative) reactions and form a heterogenous
group of compounds, termed Advanced Glycation End products (AGE products).
These products have been shown to accumulate in vivo with normal aging and
at an accelerated rate with diabetes (I can't remember the references of
the top of my head, but if you're interested, I could find and email them
to you). These AGE products have been linked to the pathology of the
diabetic condition (renal failure, atherosclerosis, retinopathy). These
same disease states reflect many found in the elderly, and in many ways
those patients with diabetes seem to be suffering a form of "advanced
aging". If these AGE products are responsible for many of the symptoms of
aging (this hasn't been shown yet, only the correlation between AGE product
accumulation and pathology), then AGE products would be a perfect measure
of "biological" aging.
It is true that different individuals will have different levels of sugar
present in the circulation as evidenced by the diabetic patients, and so
AGE products will accumulate at different rates. The age of an individual
may not be accurately reflected in the amount of AGE products formed.
But it is the aging *symptoms* and the causes of these symptoms that are
important. An accurate estimation of the amount of time that an individual
has been around from a biological marker may be irrelevant.
Tell me what you (and any other members of the list) think.
Bevan McWilliam,
Wellington School of Medicine
New Zealand.
