Effect of photoreactivating fight on UV radiation-induced alterations in human skin

Background/Aims: Photoreactivating light (PRL) after ultraviolet radiation (UVR) exposure causes photoreversal of cyclobutane pyrimidine dimers throug h the activation of photolyase. Although photoreversal has been demonstrate d in the 'three kingdoms of life.' its existence in man remains controversi al. We sought evidence for photoreversal in man. Methods and Results: Seven subjects were spot-irradiated at two sites with 4 minimal erythema doses (MED) of solar-simulating UVR. Of the two sites, o ne was then immediately exposed to a PRL source. Epidermal biopsies were ta ken immediately after exposure. No significant difference in the quantity o f pyrimidine dimers was detected comparing the 'UVR only' site to the 'UVR, PRL-exposed' site. Biopsies were repeated 24 h later and no significant di fference in p53 protein expression or dendritic cell number was detected. H owever, the 'UVR, PRL-exposed' site showed a greater reduction in pyrimidin e dimer quantity. Conclusions: We found no evidence for a direct effect of PRL causing photor eversal of UVR-induced pyrimidine dimers in man. Our results do, however, s uggest that some indirect effect of PRL may enhance pyrimidine dimer repair in the 24-h period following UVR exposure.