The role of ascorbic acid in senile cataract

Area of Science:

• Biochemistry
• Ophthalmology
• Aging Research

Background:

• Ascorbic acid (vitamin C) is found in high concentrations in the crystalline lens.
• It can react with lens proteins through nonenzymatic browning.
• This reaction may play a role in lens aging and cataract development.

Purpose of the Study:

• To investigate the nonenzymatic browning reaction between ascorbic acid and lens proteins.
• To determine if this reaction contributes to cataract formation and lens discoloration.

Main Methods:

• Model systems using bovine serum albumin and purified lens crystallins (alpha- and gamma-crystallin) were employed.
• Incubation with radiolabeled [14C]ascorbic acid.
• Analysis of yellow and brown condensation product formation and associated radioactivity.
• Comparison of fluorescence spectra with human cataractous lens homogenates.

Main Results:

• Formation of yellow and brown condensation products correlated with increased protein-bound radioactivity when proteins were incubated with ascorbic acid.
• The fluorescence spectrum of these products resembled that of human cataractous lenses.
• High dietary ascorbic acid intake did not alter murine lens fluorescence, suggesting other factors are involved.

Conclusions:

• The nonenzymatic reaction between lens crystallins and ascorbic acid may contribute to age-related lens color changes.
• This reaction could be a factor in the physical deterioration of the lens leading to senile cataract.
• The rate and extent of lens browning likely depend on the integrity of the eye's antioxidant system.