Oxidation and cataract.

Previous work has established that oxidation of the constituents of the human lens is an early event in the development of cataract. In old pre-cataractous lenses, oxidation of the fibre membrane polypeptides is observed. Non-disulphide-linked aggregates possibly generated by photo-oxidation are also found. With the development of cataract the oxidation becomes more extensive, affecting many of the proteins of the tissue. High molecular weight, disulphide-linked aggregates are formed, involving cytosol and membrane components. Membrane rupture accompanies the process. Hydrogen peroxide has been found in elevated levels in the aqueous fluid of some cataract patients. H2O2 will cause cataract and has been shown to affect Na+,K+-ATPase. Analyses of available data suggest that (1) oxidation of membrane components may be an initiating event in cataract, and (2) the oxidizing agent may come from the exterior environment of the tissue. The problems involved in proving this hypothesis are discussed and an approach to testing the hypothesis is suggested.