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 humor of three species of mammals: New Zealand White rabbits and humans (diurnal) and Sprague-Dawley rats (nocturnal). These molecules are L-cysteine (CYS), L-ascorbic acid (AA), glutathione (GSH), uric acid (UA) and L-tyrosine (TYR); all of these molecules have known antioxidant properties. Nocturnal rat aqueous humor is concentrated in two thiols: GSH (125 microM; n = 24 pooled eyes) and CYS (63 microM), in contradistinction to diurnal species which have high concentrations of AA. No deterioration of any of these antioxidants occurs in a synthetic aqueous humor mixture irradiated with a physiologically relevant spectral UV B dose of 30 mJ/cm2/h (5.5 UV equivalent sunlight hours). The same result occurred with addition of the endogenous aqueous humor UV B photosensitizer L-tryptophan. In a second set of experiments, human synthetic aqueous 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 TYR failed to protect AA 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 thermodynamic interactions must be recognized when choosing animal models to evaluate human aqueous humor antioxidant defense.
Richer
S P
SP
Department of Veteran Affairs Medical Center, Eye Clinic, North Chicago, IL 60064-3095, USA. Richer,s@n-chicago.va.gov
Rose
R C
RC
D000368:Aged; D000704:Analysis of Variance; D000818:Animals; D000975:Antioxidants / Q000032:analysis*; D001082:Aqueous Humor / Q000737:chemistry* / Q000187:drug effects / Q000528:radiation effects; D001205:Ascorbic Acid / Q000032:analysis; D002386:Cataract / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000032:analysis; D004195:Disease Models, Animal; D005260:Female; D005978:Glutathione / Q000032:analysis; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008322:Mammals; D016877:Oxidants / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D014364:Tryptophan / Q000494:pharmacology; D014443:Tyrosine / Q000032:analysis; D014466:Ultraviolet Rays / Q000009:adverse effects*; D014527:Uric Acid / Q000032:analysis
D000975:Antioxidants; D016877:Oxidants; D014527:Uric Acid; D014443:Tyrosine; D014364:Tryptophan; D006861:Hydrogen Peroxide; D005978:Glutathione; D003545:Cysteine; D001205:Ascorbic Acid