Resumen de Reactive oxygen species (ROS)-generating oxidases in the normal rabbit cornea and their involvement in the corneal damage evoked by UVB rays
J. Cejková, S. Stipek, J. Crkovska, T. Ardan, A. Midelfart
The corneas of albino rabbits were irradiated (5 min exposure once a day) with UVB rays (312 nm) for 4 days (shorter procedure) or 8 days (longer procedure). The eyes were examined microbiologically and only the corneas of sterile eyes or eyes with nonpathogenic microbes were employed. Histochemically, the activities of reactive oxygen spec ies (ROS)- generating oxidases (xanthine oxidase, D-amino acid oxidase and a-hydroxy acid oxidase) were examined in cryostat sections of the whole corneas. Biochemically, the activity of xanthine oxidoreductase/xanth ine oxidase was investigated in the scraped corneal epithelium. UVB rays significantly changed enzyme activities in the corneas. In comparison to the norma l cornea, where of ROS-generating oxidases only xanthine oxidase showed significant activity in the corneal epithe lium and endothelium, D-amino acid oxida e wa very low and ahydroxy acid oxidase could not be detected at all, in the cornea repeatedly irradiated with UVB rays, increased activitie of xanthine oxidase and D-amino acid oxidase were observed in all corneal layers. Only after the longer procedure the xanthine oxidase and D-amino acid oxidase activities were decreased in the thinned epithelium in parallel with its morpho logical disturbances. Further results show that the xanthine oxida e/xanthine oxidoreducta e ratio increased in the epithelium together with the repeated irradiation with UVB rays. This might suggest that xanthine dehydrogenase is converted to xanthine oxidase.
However, in comparison to the norma l cornea l epithelium, the total amount of xanthine oxidoredutase was decreased in the irradiated epithe lium. Jt is presumed that xanthine oxidoreductase might be released extracellu larly (into tears) or the enzyme molecules were denatured due to UVB rays (particulary after the longer procedure). Comparative histochemical and biochemical findings suggest that reactive oxygen species-generating oxidases (xanthine oxidase, D-amino acid oxidase) contribute to the corneal damage evoked by UVB rays.
