Increased oxidative modification of albumin when illuminated in vitro in the presence of a common sunscreen ingredient: Protection by nitroxide radicals

We previously reported on the ability of dibenzoylmethane (DBM) and a relat ive, Parsol 1789, used as a ultraviolet A (UVA)-absorbing sunscreen, to gen erate free radicals upon illumination, and as a consequence, to inflict str and breaks in plasmid DNA in vitro. This study has now been extended to det ermine the effects of Parsol 1789 and DBM on proteins, under UVA illuminati on, with the sole purpose of gaining more knowledge on the photobiological effects of sunscreen chemicals. Parsol 1789 (100 mu M) caused a 2-fold incr ease 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 marked ly reduced by the presence of free radical scavengers, namely piperidinic a nd indolinonic nitroxide radicals, in accordance with our previous study. V itamin E had no effect under the conditions used. The results obtained corr oborate the fact that Parsol 1789 generates free radicals upon illumination and that these are, most probably, responsible for the protein damage obse rved under the conditions used in our system. However, at present. we canno t 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 ascertai n protection against photocarcinogenic risk. (C) 2000 Elsevier Science Inc.