A mineral sunscreen affords genomic protection against ultraviolet (UV) B and UVA radiation: in vitro and in situ assays.

Abstract

Ultraviolet (UV) radiation has been shown to be responsible for different biological effects on human skin, including the initiation of photocarcinogenesis. Both UVB and UVA have been described as mutagenic, but the processes by which they alter the DNA are different. Although cells can repair DNA damage, some deleterious mutations nevertheless appear and can promote cancer. The risk of photocarcinogenesis is acknowledged and the frequency of photogenodermatosis is increasing. In order to evaluate the protection efficacy of a high sun protection factor (SPF) mineral sunscreen against UVB- and UVA-induced genomic alterations, we have followed two approaches. First, we have tested the sunscreen for its ability to decrease the unscheduled DNA synthesis response in vitro in human fibroblasts, as an indirect measure of UVB-induced lesions (0.005 and 0.01 J/cm2), and second, we have verified its ability to reduce the in situ end-labelling intensity in human skin as a direct measure of UVA-induced single-strand breaks (10 J/cm2). Microscopic analysis clearly demonstrated the protective effect of the sunscreen against UVB and UVA. A dose-dependent effect of mineral sunscreens was observed. There was also a relationship between the SPF and genomic protection. By limiting the accumulation of UV-induced lesions on DNA, this mineral sunscreen could limit the mutation frequency.