Ornithine decarboxylase induction in psoralen-treated mouse epidermis used as a test of UV-A sunscreen potency

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Abstract
Inhibition by sunscreens of UV-A-induced epidermal ornithine decarboxylase (ODC) activity in 8-methoxypsoralen-treated mice was used to examine the UV-A sunscreen activity of 2 commercial preparations, Uval (p-aminobenzoic acid) and PreSun (a benzophenone derivative). Both gave significant protection against UV-A doses of up to 3 J/cm2 and Uval was more effective than PreSun in the UV-A range. At intermediate doses (5-15 J/cm2) neither Uval nor PreSun significantly altered the ODC response to UV-A. At doses of 20-40 J/cm2 UV-A, control and PreSun-treated animals showed a decline in ODC activity which histological studies suggested was due to severe epidermal damage. This decline in ODC activity and severe epidermal damage was not seen in Uval-treated animals. Topical zinc oxide was highly effective in preventing induction of ODC by UV-A irradiation at doses up to 40 J/cm2, and was significantly more effective than either PreSun or Uval.