Reduced superoxide dismutase activity in UVB-induced hyperproliferative pig epidermis.

Decreased superoxide dismutase (SOD) activity has been reported in various hyperproliferative keratinocytes. In order to elucidate the relationship between epidermal SOD activity and keratinocyte proliferation, we employed in vivo UVB irradiation. Following UVB irradiation at twice the minimum erythema dose, pig epidermis revealed an initial decrease in thymidine incorporation and mitotic counts for at least 48 h, followed by a marked increase, the peak of which was observed at 96 h after irradiation, and a return to basal levels by 5-7 days. The SOD activity remained constant during the initial 48 h and then decreased to about 50% at 96 h, mainly due to a decreased Cu,Zn-SOD activity. Our results indicate that the increased keratinocyte proliferation induced by UVB irradiation is accompanied by a decrease in SOD activity, and that this decrease is mainly due to a decreased Cu,Zn-SOD activity. No alteration in SOD activity was noted during the initial hypoproliferative phase following irradiation.