Evaluation of protective effect of thymol and thymus vulgaris leaf extract on UVB-induced damage in an ex-vivo human skin tissue model

The ultraviolet radiation (UV) is the major environmental factor that affects the functions and survival of many skin cell types. For this reason, the use of human skin tissue obtained from plastic aesthetic surgery represents a simple but efficient experimental approach to reproduce a physiological condition to test the early effects of an exogenous stimulus as UV radiation. Normal human skin explants were obtained from healthy young non smoking women 20-40 years old (n=4) after informed consent. Explants were cultured with epidermal side up at the air-liquid interface overnight in a Transwell system. Each of the experiments consisted of an internal control sample (not exposed) and three treatment groups: 1) UVB irradiation doses ranging from 0.048 J/cm2 to 0.72 J/cm2, 2) pretreatment for 1 h with thymole (1μg/ml) before the UVB irradiation and 3) pretreatment for 1 h with thymus vulgaris aqueous extract (1.82 μg/ml) before the UVB irradiation. Samples were harvested 24 hours after the end of UV exposure and were processed by light microscopy and by indirect immunofluorescence in order to investigate epidermal proliferation; Lactate Dehydrogenase (LDH) assay and alkaline comet and micronucleus tests were used to assess cytotoxicity and genotoxicity, respectively. Pretreatment, with Thymol and vegetable extract in comparable dosage, showed a reduction of the damage following UV exposure regarding morphological and genotoxic aspects. Altogether these results strongly support the use of ex vivo human skin as a relevant method for safety evaluation of UV skin exposure.