Changes of superoxide dismutase, catalase and glutathione peroxidase in the corneal epithelium after UVB rays. Histochemical and biochemical study

In this study, the effects of UVA and UVB rays on antioxidant enzymes (supe roxide dismutase, glutathione peroxidase, catalase) were examined in the co rneal epithelium. The corneas of albino rabbits were irradiated with a UV l amp generating UVA (365 nm wavelength) or UVB rays (312 nm wavelength), 1 x daily for 5 min, from a distance of 0.03 m, over 4 days (shorter procedure ) or 8 days (longer procedure). In contrast to UVA rays, which did not evok e significant disturbances, UVB rays changed the activities of antioxidant enzymes. The longer repeated irradiation with UVB rays was performed, the d eeper the observed decrease in antioxidant enzymes. The shorter procedure e voked a more profound decrease of glutathione peroxidase and catalase (the enzymes cleaving hydrogen peroxide) than of superoxide dismutase, an enzyme scavenging superoxide radical and producing hydrogen peroxide during the d ismutation reaction of a superoxide free radical. This may contribute to an insufficient hydrogen peroxide cleavage at the corneal surface and danger to the cornea from oxidative damage. After the longer procedure (UVB rays), the activities of all antioxidant enzymes were very low or completely abse nt. In conclusion, repeated irradiation of the cornea with UVB rays evokes a deficiency in antioxidant enzymes in the corneal epithelium, which very p robably contributes to the damage of the cornea (and possibly also deeper p arts of the eye) from UVB rays and the reactive oxygen products generated b y them.