PHOTOSENSITIZED OXIDATION IN THE OCULAR LENS: EVIDENCE FOR PHOTOSENSITIZERS ENDOGENOUS TO THE HUMAN LENS

Abstract— Numerous investigators have attempted to associate near UV light exposure with various changes which occur to lens crystallins during aging and cataractogenesis. Recently we have shown in vitro that singlet oxygen mediated oxidation of lens crystallins produces effects very similar to those documented for crystallins from old or cataractous lenses and suggested that near UV photodynamic effects may play a major role in vivo in aging in the human lens. In the present work we demonstrate that certain oxidation products of tryptophan which have been identified in human lens can act as near UV photosensitizers, producing singlet oxygen. The insoluble protein fraction from human cataracts is shown to have the capacity to act as a photosensitizer. An age‐related increase in photosensitizing capacity is also demonstrated in the soluble crystallins from human lens. These findings are discussed with respect to development of pigmented nuclear cataracts.