Prevention of lens protein glycation by taurine.

Abstract

Modifications in lens protein structure and function due to nonenzymic glycosylation and oxidation have been suggested to play a significant role in the pathogenesis of sugar and senile cataracts. The glycation reaction involves an initial Schiff base formation between the protein NH2 groups and the carbonyl group of a reducing sugar. The Schiff base then undergoes several structural modifications, via some oxidative reactions involving oxygen free radicals. Hence certain endogenous tissue components that may inhibit the formation of protein-sugar adduct formation may have a sparing effect against the cataractogenic effects of sugars and reactive oxygen. The eye lens is endowed with significant concentration of taurine, a sulfonated amino acid, and its precursor hypotaurine. It is hypothesized that taurine and hypotaurine may have this purported function of protecting the lens proteins against glycation and subsequent denaturation, in addition to their other functions. The results presented herein suggest that these compounds are indeed capable of protecting glycation competitively by forming Schiff bases with sugar carbonyls, and thereby preventing the glycation of lens proteins per se. In addition, they appear to prevent oxidative damage by scavenging hydroxyl radicals. This was apparent by their preventive effect against the formation of the thiobarbituric acid reactive material generated from deoxy-ribose, when the later was exposed to hydroxyl radicals generated by the action of xanthine oxidase on hypoxanthine in presence of iron.