Water soluble antioxidants in mammalian aqueous humor: interaction with UV B and hydrogen peroxide

Vision Res. 1998 Oct;38(19):2881-8. doi: 10.1016/s0042-6989(98)00069-8.

Abstract

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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aged
  • Analysis of Variance
  • Animals
  • Antioxidants / analysis*
  • Aqueous Humor / chemistry*
  • Aqueous Humor / drug effects
  • Aqueous Humor / radiation effects
  • Ascorbic Acid / analysis
  • Cataract / metabolism
  • Chromatography, High Pressure Liquid
  • Cysteine / analysis
  • Disease Models, Animal
  • Female
  • Glutathione / analysis
  • Humans
  • Hydrogen Peroxide / pharmacology
  • Mammals
  • Oxidants / pharmacology
  • Rabbits
  • Rats
  • Rats, Sprague-Dawley
  • Tryptophan / pharmacology
  • Tyrosine / analysis
  • Ultraviolet Rays / adverse effects*
  • Uric Acid / analysis

Substances

  • Antioxidants
  • Oxidants
  • Uric Acid
  • Tyrosine
  • Tryptophan
  • Hydrogen Peroxide
  • Glutathione
  • Cysteine
  • Ascorbic Acid