tempo and dibenzoylmethane

We previously reported on the ability of dibenzoylmethane (DBM) and a relative, Parsol 1789, used as a ultraviolet A (UVA)-absorbing sunscreen, to generate free radicals upon illumination, and as a consequence, to inflict strand breaks in plasmid DNA in vitro. This study has now been extended to determine the effects of Parsol 1789 and DBM on proteins, under UVA illumination, with the sole purpose of gaining more knowledge on the photobiological effects of sunscreen chemicals. Parsol 1789 (100 microM) caused a 2-fold increase in protein carbonyl formation (an index of oxidative damage) in bovine serum albumin (BSA) when exposed to illumination, and this damage was both concentration- and time-dependent. The degree of protein damage was markedly reduced by the presence of free radical scavengers, namely piperidinic and indolinonic nitroxide radicals, in accordance with our previous study. Vitamin E had no effect under the conditions used. The results obtained corroborate the fact that Parsol 1789 generates free radicals upon illumination and that these are, most probably, responsible for the protein damage observed under the conditions used in our system. However, at present, we cannot extrapolate from these results the relevance to human use of sunscreens; therefore, further studies should be necessary to determine the efficacy at the molecular and cellular level of this UVA-absorber in order to ascertain protection against photocarcinogenic risk.

Topics: Animals; Antioxidants; Benzoates; Chalcones; Cyclic N-Oxides; Free Radicals; Kinetics; Mice; Nitrogen Oxides; Oxidation-Reduction; Propiophenones; Serum Albumin, Bovine; Spin Labels; Sunscreening Agents; Ultraviolet Rays; Vitamin E

Indolinonic nitroxide radicals efficiently scavenge oxygen- and carbon-centered radicals. They protect lipid and protein systems against oxidative stress, but little is known about their capacity to protect DNA against radical-mediated damage. We compare indolinonic nitroxides and the piperidines TEMPO and TEMPOL for their ability to inhibit strand breaks inflicted on DNA when it is illuminated in vitro in the presence of dibenzoylmethane (DBM) and a relative, Parsol 1789, used as a UVA-absorbing sunscreen. We used spin-trapping EPR to examine the formation of radicals and plasmid nicking assays to evaluate DNA strand breakage. The results have a two-fold interest. First, they show that all the nitroxides tested efficiently prevent DNA damage in a dose-dependent fashion. Vitamin E had no effect under the conditions used. Second, they show that carbon-centered radicals are produced on illumination of DBM and its relative and that their formation is probably responsible for the direct strand breaks found when naked DNA is illuminated in vitro in their presence. Additional work on the ability of sunscreens to enter human cells and their response to the light that penetrates sunscreen-protected skin would be necessary before any conclusion could be drawn as to whether the results reported here are relevant to human use of sunscreens.

Topics: Antioxidants; Benzoates; Chalcones; Cyclic N-Oxides; DNA; DNA Damage; DNA, Bacterial; Electron Spin Resonance Spectroscopy; Humans; Indoles; Kinetics; Nitrogen Oxides; Spin Labels; Sunscreening Agents; Ultraviolet Rays