Protein-associated pigments that accumulate in the brunescent eye lens. Identification of a quinoline derivative

Brunescent (dark brown) cataract is particularly prevalent in the tropics. Enzymatic digestion of the insoluble protein fraction of brunescent cataractous eye lenses from India, followed by high performance liquid chromatographic separation of the pigments and spectroscopic investigations, have led to the identification of one of the pigments as 4-hydroxyquinoline-3-[alpha-aminoacetic acid] (compound A). The 4-hydroxyquinoline moiety is shown to be a photodynamic agent that generates O2.- and leads to protein crosslinking. This suggests that the compound A may play a long-term deleterious role in situ in the lens.