Nitroxide radicals protect DNA from damage when illuminated in vitro in the presence of dibenzoylmethane and a common sunscreen ingredient

Indolinonic nitroxide radicals efficiently scavenge oxygen- and carbon-cent ered radicals. They protect lipid and protein systems against oxidative str ess, but little is known about their capacity to protect DNA against radica l-mediated damage. We compare indolinonic nitroxides and the piperidines TE MPO and TEMPOL for their ability to inhibit strand breaks inflicted on DNA when it is illuminated in vitro in the presence of dibenzoylmethane (DBM) a nd a relative, Parsol 1789, used as a UVA-absorbing sunscreen. We used spin -trapping EPR to examine the formation of radicals and plasmid nicking assa ys to evaluate DNA strand breakage. The results have a two-fold interest. F irst, they show that all the nitroxides tested efficiently prevent DNA dama ge in a dose-dependent fashion. Vitamin E had no effect under the condition s used. Second, they show that carbon-centered radicals are produced on ill umination of DBM and its relative and that their formation is probably resp onsible fur the direct strand breaks found when naked DNA is illuminated in vitro in their presence. Additional work on the ability of sunscreens to e nter human cells and their response to the light that penetrates sunscreen- protected skin would be necessary before any conclusion could be drawn as t o whether the results reported here are relevant to human use of sunscreens . (C) 1999 Elsevier Science Inc.