WATER-SOLUBLE ANTIOXIDANTS IN MAMMALIAN AQUEOUS-HUMOR - INTERACTION WITH UV-B AND HYDROGEN-PEROXIDE

HPLC/electrochemical detection was used to identify five major low MW water soluble electrochemically active molecules from the aqueous humo r of three species of mammals: New Zealand White rabbits and humans (d iurnal) and Sprague-Dawley rats (nocturnal). These molecules are L-cys teine (CYS), L-ascorbic acid (AA), glutathione (GSH), uric acid (UA) a nd L-tyrosine (TYR); all of these molecules have known antioxidant pro perties. Nocturnal rat aqueous humor is concentrated in two thiols: GS H (125 mu M; n = 24 pooled eyes) and CYS (63 mu M), in contradistincti on to diurnal species which have high concentrations of AA. No deterio ration of any of these antioxidants occurs in a synthetic aqueous humo r mixture irradiated with a physiologically relevant spectral UV B dos e of 30 mJ/cm(2)/h (5.5 UV equivalent sunlight hours). The same result occurred with addition of the endogenous aqueous humor UV B photosens itizer L-tryptophan. In a second set of experiments, human synthetic a queous humor was subjected to hydrogen peroxide induced oxidant stress . The decay of antioxidants was CYS > GSH > AA > UA > TYR. The second highest concentrated antioxidant in human aqueous humor is TYR. Yet TY R failed to protect PLA against H2O2-induced free radical damage in a synthetic aqueous humor model system (P = 0.10; ANOVA). The existence of multiple electrochemically active constituents and their thermodyna mic interactions must be recognized when choosing animal models to eva luate human aqueous humor antioxidant defense. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.