Abstract
Protein glycation may be involved in cataract development, by altering protein structure, particularly amino acid composition, and formation of fluorophores through a Maillard reaction. This study was designed to evaluate major changes in early and advanced (fluorescent) glycation products, with special emphasis on glycation-induced changes in amino acid composition of lens proteins. We analyzed 50 human cataractous lenses (25 diabetic and 25 non-diabetic). Glycated proteins were isolated by affinity chromatography. Glycated and non-glycated proteins were separated by molecular sieve chromatography and further analyzed by RP-HPLC to establish the amino acid content. Early glycation levels were determined as furosine content and advanced glycation products were quantified by the characteristic fluorescence. Specific lens fractions (HMW and LMW) present significant differences in fluorescence levels between glycated and non-glycated proteins, specially in cataractous lenses from diabetic patients in which all proteins analyzed presented higher glycation levels than in non-diabetic patients. The amino and analysis of glycated proteins also revealed some important differences in specific basic residues (namely Lys, Arg and His) compared to the non-glycated fraction. The results suggest that protein glycation may be involved in changes in amino acid composition and fluorophore formation. This process may well account for the increased risk factor that diabetes represents for cataract development.
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