CUTANEOUS OXIDATIVE STRESS INDUCED BY POLLUTION (PARTICULATE MATTER) AND ITS AGGRAVATION BY ENVIRONMENTAL ULTRAVIOLET RADIATION (UV)

Atmospheric pollution is a serious health concern and particulate matter (PM) from combustion is considered as particularly deleterious. In fact, ultrafine particles smaller than 100 nM in size contain toxic compounds such as poly aromatic hydrocarbons (PAH) adsorbed at their surface. Moreover, they can translocate from lung capillaries to blood circulation and be distributed in the whole body. Up to now, no precise estimation of pollutants in living skin is available, but plasma concentration can reach nanomolar range. Contamination of dermis and epidermis, either by penetration from skin surface or by systemic exposure, is highly probable since PAH can be found in cortex of human hair follicle. Some PAH are photo- reactive and phototoxic: sunlight and pollution might thus synergistically compromise skin health. After summing up current knowledge about dermatological damage induced by pollution, experimental data obtained in vitro using normal human keratinocytes or reconstructed epidermis will be presented. At very low concentrations (in the nanomolar range), some PAH such as benzopyrene or indenopyrene displayed a strong phototoxicity under exposure to daily UV (300-400 nm) and also to UVA1 (340-400 nm). Even when cytotoxicity was low, PAH- induced photo-oxidative stress could impair mitochondrial function (membrane polarization and ATP production) and impacted endogenous glutathione (GSH) homeostasis. Interestingly, among genes controlling GSH metabolism, SLC7A11 was particularly overexpressed (at gene and protein levels). This protein is an antiporter in charge of cystine supply. SLC7A11 upregulation suggests that regeneration of GSH might be of huge importance to ensure protection against “photo-pollution” stress. As proof, pretreatment of cells by buthionine sulfoximine BSO, an inhibitor of GSH biosynthesis, significantly increased PAH-induced phototoxicity. Our results highlight that pollutants could aggravate skin photodamage: specific photoprotection strategies for skin care in polluted area will be discussed.