The search for viable biomarkers of aging is an active field of research. The ability to rapidly and cheaply assess biological age, the burden of cell and tissue damage and dysfunction that causes disease and mortality, would greatly speed the development of rejuvenation therapies. At present it is costly and slow to demonstrate that any given approach to rejuvenation actually works: one needs to run a life span study, which is prohibitively expensive in mice and simply impractical in humans. What is needed is a test that can be carried out immediately before and immediately after an intervention, and which accurately assesses the state of aging.
Numerous approaches to a biomarker of aging have been suggested, or are at various stages of development. Aging clocks based on selected epigenetic markers, protein levels, or portions of the transcriptome are all popular approaches. Weighted algorithmic combinations of simple metrics such as grip strength and walking speed have also been explored. Other approaches exist. For example, in today's research materials, scientists suggest that assessment of molecular changes in the lens of the eye is worthy of consideration.
The challenge with all of these biomarkers of biological age is that it is very unclear as to how they connect specifically to the underlying causes of aging. It isn't unreasonable to think that some biomarkers reflect only certain forms of the cell and tissue damage of aging, or certain downstream consequences rather than all of them. Which is fine if only looking and not intervening. But this means that one can't just run an assessment of a specific approach to rejuvenation coupled with a specific biomarker, and have any great confidence that the numbers will be meaningful at the end of the study. At the present time, any biomarker used must be calibrated against a specific rejuvenation therapy in order to determine how it responds. This rather defeats the point of the exercise, as that calibration is going to require numerous life span studies.
All people age, but individuals do so at different rates, some faster and others slower. While this observation is common knowledge, there is no universally accepted measure of biological aging. Numerous aging-related metrics have been proposed and tested, but no marker to date has been identified or noninvasive method developed that can accurately measure and track biological aging in individuals. In what is believed to be the first study of its kind, researchers have discovered that a specialized eye scanner that accurately measures spectroscopic signals from proteins in lens of the eye can detect and track biological aging in living humans.
"The lens contains proteins that accumulate aging-related changes throughout life. These lens proteins provide a permanent record of each person's life history of aging. Our eye scanner can decode this record of how a person is aging at the molecular level. Eye scanning technology that probes lens protein affords a rapid, noninvasive, objective technique for direct measurement of molecular aging that can be easily, quickly, and safely implemented at the point of care. Such a metric affords potential for precision medical care across the lifespan."
The absence of clinical tools to evaluate individual variation in the pace of aging represents a major impediment to understanding aging and maximizing health throughout life. The human lens is an ideal tissue for quantitative assessment of molecular aging in vivo. Long-lived proteins in lens fiber cells are expressed during fetal life, do not undergo turnover, accumulate molecular alterations throughout life, and are optically accessible in vivo.
We used quasi-elastic light scattering (QLS) to measure age-dependent signals in lenses of healthy human subjects. Age-dependent QLS signal changes detected in vivo recapitulated time-dependent changes in hydrodynamic radius, protein polydispersity, and supramolecular order of human lens proteins during long-term incubation (~1 year) and in response to sustained oxidation (~2.5 months) in vitro. Our findings demonstrate that QLS analysis of human lens proteins provides a practical technique for noninvasive assessment of molecular aging in vivo.