Superoxide Dismutase in Epidermis: Its Relation to Keratinocyte Proliferation

Abstract

AbstractDecreased superoxide dismutase (SOD) activity has been reported in various hyperproliferative tissues. In order to elucidate the significance of SOD activity in keratinocyte proliferation, we measured the SOD activity in several pathologic epidermal conditions. The SOD activity was significantly decreased in psoriatic hyperproliferative epidermis as well as in basal cell epithelioma, squamous cell carcinoma and seborrheic keratosis.Following tape stripping in vivo, pig epidermis revealed a marked increase in thymidine uptake and mitotic counts. The peak of the thymidine uptake was observed at 24 h, which was followed by the increased mitotic counts (peak at 48 h). The pig skin revealed a decreased epidermal SOD activity following the tape stripping. A decline of SOD activity was observed within 7 days after the tape stripping and about a 50% decrease was observed at 48 h. Epidermis is known to contain both Cu, Zn‐SOD and Mn‐SOD activities; the decreased SOD activity after tape stripping was mainly due to decreased Cu, Zn‐SOD activity without any significant alteration of Mn‐SOD activity.Following UVB irradiation (2MED) in vivo, pig epidermis revealed decreased thymidine incorporation as well as decreased mitotic counts. Epidermal SOD activity, however, was not altered by the UVBirradiation. Pig epidermis is also known to indicate decreased cell proliferative activity in the presence of various chemicals in vitro. These modalities, which include retinoid (Ro 10‐1670), colchicine and protein synthesis inhibitors (puromycin, actinomycin D, cycloheximide), had no effect on the epidermal SOD activity.Our results indicate that, although the decreased SOD activity appears to be comcomitant with keratinocyte hyperproliferation, no alteration of SOD activity is observed in hypoproliferative epidermis. The significance of the altered SOD activity in the regulatory mechanism of keratinocyte proliferation remains unknown at present.