The early and late effect of ultraviolet light exposure on the induction and repair of electron-induced DNA damage in rat epidermis

Abstract

Experiments were performed to determine the early and late effects of ultraviolet light (UVL) on induction and repair of DNA damage in rat epidermis by electron radiation. The dorsal skin of 28-day-old rats was irradiated with 8.0 × 10 5 or 13.6 × 10 5 ergs/mm 2 UVL or weekly exposures of 0.4 × 10 5 ergs/mm 2 UVL for 23 or 48 weeks. At 1, 48, 100, 200, or 400 days after single UVL doses or 28 days after last weekly UVL dose, the animals were irradiated with 1200 rads of electrons and the resultant alkaline labile DNA damage and repair quantitated by the S 1 nuclease assay. The cytotoxic effect of UVL on basal epidermal cells was assessed by the labeled doublets technique. Single UV doses were capable of inhibiting repair of electron induced DNA damage for up to 5 h, but did not have any measurable late effect (>20 days) on the rate or extent of DNA repair. The rate of DNA repair in epidermal cells from animals exposed to weekly doses of UVL was more rapid than in age-matched controls. The UV doses used on these experiments were shown to be cytotoxic to a large proportion of the basal epidermal cells. The results indicate that exposure of the rat skin to single cytotoxic or multiple exposures of UVL did not accelerate the age related loss of DNA repair capacity.