The reaction of malondialdehyde with lens proteins and the protective effect of aspirin.

Malondialdehyde, a product of lipid peroxidation and a by-product of thromboxane synthesis increases in human cataract. Malondialdehyde bound to soluble lens proteins over 4 h of incubation. Pre-incubation of lens proteins with aspirin offered protection against reaction with MDA. Gel chromatography was used to monitor aggregation of the modified protein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the reaction with malondialdehyde led to non-disulphide covalent cross-linking of gamma-crystallin, which was decreased by incubation with aspirin. Malondialdehyde has two carbonyl groups which could react with primary amino groups, forming Schiff-base conjugates and covalently cross-link proteins. The modification and cross-linking could initiate the cataractogenic process.