Lens proteins are damaged during aging, presumably by the light and oxygen to which they are exposed. In many cell types, damaged proteins are selectively and rapidly removed in part by cytoplasmic ATP-and ubiquitin-dependent systems. We hypothesized that the protein-editing capability exists in young lens tissue. However, upon aging, reduced proteolytic capability may be related to the accumulation of damaged proteins in cataracts.

It is observed that lens tissue displays ATP-dependent proteolytic activity and ubiquitin-conjugating capability. Of the energy-dependent proteolytic capacity, 75% is dependent upon ubiquitin conjugation. Simulation of aging by ⁶⁰Co-irradiation of the major lens proteins, α-crystallin (0,0.1, 0.6, 2.6 mol hydroxyl radical per mole α-crystallin) caused both aggregation and lysis. Both are observed in the aged lens. Rates of degradation of differentially modified crystallin by lens proteasome indicated enhanced levels of proteolysis, with increasing photooxidation of substrate.

Antioxidant nutrients, such as ascorbate, are found in eye tissues in relation to levels in diet in guinea pigs and humans. Elevated dietary ascorbate confers protection against solar-light-induced damage to lens proteins and proteases and may delay cataracts in animals subject to various stresses. Recent epidemiological evidence also indicates that persons with higher ascorbate status have diminished risk of various forms of cataract.

Restricting dietary calorie intake in rodents delays cataract progress, extends life, prolongs immune function, diminishes incidence of cancer, etc. However, these benefits are not associated with elevated plasma levels of ascorbate.