REGIONAL DIFFERENCES IN THE DISTRIBUTION OF CATALASE IN THE EPITHELIUM OF THE OCULAR LENS

Oxidative stress is thought to play a major role in cataract formation . The present experiments are aimed at gaining a better understanding of the systems that protect the lens from damage by reactive oxygen sp ecies. The aqueous humor normally contains hydrogen peroxide (H2O2), a compound capable of generating reactive oxygen species. The systems p rotecting the ocular lens from oxidative damage are primarily confined to the epithelium, a single layer of cells on the anterior side of th e organ directly beneath the lens capsule. When cultured rabbit lenses were challenged with a single dose of 0.2 mM H2O2, cells in the perip heral region of the epithelium survived; those in the central region d ied. Here we investigate the histochemical and immunoperoxidase distri butions of catalase, an enzyme which detoxifies H2O2, in cells from th e peripheral and central regions of the epithelium on flat mount prepa rations of the epithelium. In a flat mount, the entire population of l ens epithelial cells can be viewed on one preparation. The reaction pr oduct for catalase activity and its immunoperoxidase localization were more intense in peripheral epithelial cells than in cells throughout the central epithelium. Treatment of cultured lens epithelial cells or rabbit lenses with 3-aminotriazole or potassium cyanide, inhibitors o f catalase, reduced or abolished the histochemical reaction product. U ltrastructural cytochemistry confirmed the presence of catalase in mic roperoxisomes of the epithelial cells from whole lenses. The decreased level of catalase throughout the central epithelium may account for t he increased susceptibility of these cells to H2O2-induced cell death.