REACTIVE OXYGEN SPECIES (ROS) GENERATED BY XANTHINE-OXIDASE IN THE CORNEAL EPITHELIUM AND THEIR POTENTIAL PARTICIPATION IN THE DAMAGE OF THE CORNEAL EPITHELIUM AFTER PROLONGED USE OF CONTACT-LENSES IN RABBITS

Prolonged use of contact lenses (for 14 days) evoked an imbalance betw een the activity of xanthine oxidase tan enzyme belonging to reactive oxygen species-generating oxidases) and catalase tan enzyme belonging to reactive oxygen species-scavenging oxidases) in the corneal epithel ium of rabbits. The activity of catalase decreased, while xanthine oxi dase activity was very high. Of other enzymes studied in the corneal e pithelium, the activities of xanthine oxidoreductase, glucoso-6-phosph ate dehydrogenase and succinate dehydrogenase were decreased. In contr ast, the activities of lactate dehydrogenase and lysosomal hydrolases (acid beta-galactosidase, dipeptidyl peptidase II) were increased and appeared in animals sacrificed immediately after contact lens removal. In rabbits sacrificed later (after Ih), an additional increase of lac tate dehydrogenase and lysosomal hydrolase activities developed in the superficial layers of the corneal epithelium. Catalase supplementatio n during use of contact lenses prevented both the significant decrease of catalase activity in the corneal epithelium and the development of additional epithelial damage. In contrast, topical treatment with 3-a minotriazole tan inhibitor of catalase) resulted in the nearly complet e loss of catalase activity in the corneal epithelium and the appearan ce of more serious epithelial damage. We conclude that ROS generated b y xanthine oxidase induce additional damage of the corneal epithelium related to the use of contact lenses.