EGCG prevents tryptophan oxidation of cataractous ocular lens human γ-crystallin in presence of H₂O₂

Abstract

Disruption of the short range order of proteins present in the ocular lens leads to cataract resulting in a loss of transparency. Human γ-crystallin (HGC), a water soluble protein present in the lens is known to aggregate with aging. A modified form of HGC (HGC^c) was isolated from cataractous human ocular lens extract and the number of Trp residues that undergo oxidation was determined. The extent of oxidized Trp (N-formyl kynurenine) in HGC due to cataract formation was determined, primarily using fluorescence spectroscopy. The ability of (−)-epigallocatechin gallate (EGCG) to retain its antioxidant effect even in the presence of H₂O₂ was investigated. This was monitored by its ability to prevent the modification of intact Trp residues in HGC^c isolated from cataractous human eye lens. Significant Trp fluorescence quenching occurs on interaction of the green tea component, EGCG with HGC^c accompanied by a red shift. Docking studies were employed to substantiate the experimental results. As eye lens proteins are prone to oxidative stress it is essential that a clear understanding of the effects of the components generated in vivo vis-à-vis the antioxidant effects of natural polyphenols be obtained.