The nitrite/alpha crystallin reaction: A possible mechanism in lens matrixdamage

Recent work has explored the potential deleterious role that nitric oxide ( NO) and its derivatives may have in human disease. The many by-products of NO include nitrite ion, which accumulates in the anterior chamber during oc ular inflammation and can be derived from cigarette smoking. Cigarette smok ing has been strongly linked to nuclear cataract formation, although the me chanism remains unknown. We have previously observed that nitrite reactions with the matrix proteins elastin and collagen produce damaging effects tha t mimic those observed in age- and smoking-related illnesses. In the presen t study we report on the reaction of nitrite with alpha crystallin, the maj or lens matrix protein. Incubations at neutral pH and body temperature of n itrite with alpha crystallin resulted in protein modifications indicative o f oxidative damage and similar to changes seen in the aging lens as well as cataracts. These include increased fluorescence, yellowing and protein cro ss-linking. L-kynurenine, a tryptophan derivative, was identified as a reac tion product. L-kynurenine was also formed from the reaction of nitrite wit h free tryptophan. Thus, this non-enzymatic nitration of alpha crystallin p rovides a novel mechanism by which lens proteins may be damaged in vivo. Si nce human exposure to nitrite is increased by cigarette smelting, this reac tion could provide an explanation for the association between nuclear catar acts and smoking. (C) 2000 Academic Press.