Effects of UV Rays and Thymol/<b><i>Thymus vulgaris</i></b> L. Extract in an ex vivo Human Skin Model: Morphological and Genotoxicological Assessment

Abstract

Ultraviolet (UV) radiation is the major environmental factor affecting functions of the skin. Compounds rich in polyphenols, such as Thymus vulgaris leaf extract and thymol, have been proposed for the prevention of UV-induced skin damage. We compared the acute effects induced by UVA and UVB rays on epidermal morphology and proliferation, cytotoxicity, and genotoxicity. Normal human skin explants were obtained from young healthy women (n = 7) after informed consent and cultured at the air-liquid interface overnight. After 24 h, the samples were divided in 2 groups: the former exposed to UVA (16 or 24 J/cm²) and the latter irradiated with UVB (0.24 or 0.72 J/cm²). One hour after the end of irradiation, supernatants were collected for evaluation of the lactate dehydrogenase activity. Twenty-four hours after UVB exposure, biopsies were processed for light and transmission electron microscopy analysis, proliferation, cytotoxicity, and genotoxicity. UVB and UVA rays induced early inhibition of cell proliferation and DNA damage compared to controls. In particular, UVB rays were always more cytotoxic and genotoxic than UVA ones. For this reason, we evaluated the effect of either T. vulgaris L. extract (1.82 µg/ml) or thymol (1 µg/ml) on all samples treated for 1 h before UVB irradiation. While Thymus had a protective action for all of the endpoints evaluated, the action of the extract was less pronounced on epidermal proliferation and morphological features. The results presented in this study could be the basis for investigating the mechanism of thymol and T. vulgaris L. extract against the damage induced by UV radiation.

Polyphenols and DNA Damage: A Mixed Blessing

“…A similar protective effect was reported by Cornaghi et al [38] in a human skin model exposed to UV(B). A citrus and rosemary extract (but at high concentrations) decreased the frequency of MN induced by X-rays in human lymphocytes, and decreased UV(B)-induced SBs in keratinocytes [37].…”

Pharmacological Properties and Molecular Mechanisms of Thymol: Prospects for Its Therapeutic Potential and Pharmaceutical Development

“…Thymol (1 μg/ml) inhibited UV radiation A (UVA) and UV radiation B (UVB) induced genotoxicity via inhibiting oxidative stress in the NCTC 2544 cell line (Calo et al, 2015). Thymol (1 μg/ml) attenuated UV radiation induced genotoxic damage in ex vivo human skin models by its potent anti-cancer properties (Cornaghi et al, 2016). …”

A systematic review on ethnopharmacology, phytochemistry and pharmacological aspects of Thymus vulgaris Linn.

“… [ 74 ] UV-protective activity in vitro Human skin cells Not defined Aqueous extract, thymol 1.82 μg/ml extract and 1 μg/ml thymol Normal cells without UV treatment, but with extract treatment Reduction of ROS induced DNA damage, Possible involvement of polyphenols in protectivity Aqueous extract of thyme leaf (1.82 μg/ml) and thymol (1 μg/ml) reduced the release lactic acid dehydrogenase (LDH), in cultured skin cells treated with UV rays. Cell proliferation was observed in thyme pre-treated skin cells in accordance with control, along with the reduction in DNA damage (p < 0.01) [ 75 ] Anthelminthic activity in vitro Eimeria spp. oocysts from Turkey fowls Not defined Essential oil 0, 1, 2, 4, 8, 10, 20, 40, 80, and 800 mg/ml Ammonia and diclazuril Not defined Thyme oil showed significant anti-helminthic activity against 4 species of Eimeria spp.…”

“…Aqueous extract of T. vulgaris L. leaf (1.82 μg/ml) and thymol (1 μg/ml) reduced the release of lactic acid dehydrogenase (LDH), in cultured skin cells treated with UV rays. Significant cell proliferation was observed in T. vulgaris L. pre-treated skin cells in accordance with that of the control used, along with the reduction in DNA damage (p < 0.01) [ 75 ]. In addition, an in vitro evaluation of thyme oil showed a significant anti-helminthic activity against 4 species of Eimeria spp.…”