Comparative analysis of solar radiation‐induced cellular damage between ex vivo porcine skin organ culture and in vitro reconstructed human epidermis

Synopsis Reconstructed human epidermis models (RHE) constitute an innovative alternative to study phototoxicity and photoprotection in the cosmetic industry. However, little information is currently available concerning the harmful effects of solar-simulated radiation (SSR) in these in vitro skin models. In this study, the phototoxic effects of a single acute SSR dose of 275 kJ m−2 were evaluated in a validated RHE model (from SkinEthic), and were compared with those obtained from an ex vivo skin organ culture recently developed from domestic pig ears. The RHE model was well differentiated in vitro and released a significant level of the cytosolic enzymes lactate dehydrogenase (LDH) and extracellular signal-related kinase 2 (ERK2) protein in the culture medium 24 h after SSR exposure. The SSR-induced cytotoxicity was related to the formation of sunburn cells and the appearance of DNA damage (thymine dimer and DNA fragmentation) in keratinocytes. Interestingly, these DNA alterations were associated with the activation of the caspase-3 protease, mainly in the basal layers of the epidermis. In addition, the RHE model responses were comparable with porcine skin following solar irradiation, and none of the above cellular responses was observed in non-irradiated skin models. Finally, topical application of a broad-spectrum UVB + A sunscreen formulation efficiently protected both the RHE and pig skin against the deleterious effects of SSR. Thus, both RHE and ex vivo pig skin organ culture models are complementary tools in the assessment of SSR-induced DNA damage and apoptosis, and they may be used to evaluate the photoprotective capacity of cosmetic formulations. Resume Les epidermes humains reconstruits (EHR) constituent des modeles alternatifs innovants pour etudier la phototoxicite et la photoprotection dans l’industrie cosmetique. Toutefois, peu d’informations sont actuellement disponibles sur les effets nocifs des radiations solaires dans ces modeles in vitro de peau. Dans cette etude, les effets phototoxiques d’une dose unique aigue de radiation solaire de 275 kJ m−2 ont eteevalues dans un modele valide de EHR (provenant de SkinEthic). Ils ont aussi ete compares a ceux obtenus sur une culture organotypique de peau recemment developpee ex vivoa partir d’oreilles de porc domestique. Le modele EHR est bien differenciein vitro, et il libere un taux significatif d’enzymes cytosoliques, la lactate deshydrogenase (LDH) et la proteine ERK2 (extracellular signal-related kinase 2), dans le milieu de culture 24 h apres exposition solaire. La phototoxicite a ete correlee a la formation de cellules “coup de soleil” et a l’apparition de dommages a l’ADN (dimere de thymine et fragmentation de l’ADN) dans les keratinocytes du modele EHR. Il est interessant de noter que les alterations de l’ADN ont ete associees a l’activation de la protease caspase-3 majoritairement dans les couches basales de l’epiderme. De plus, le modele EHR a repondu de facon comparable a la peau de porc suite a l’irradiation solaire, et chaque reponse cellulaire observee est specifique aux modeles de peaux irradiees. Finalement, l’application topique d’un ecran solaire a large spectre UVB + A protege efficacement a la fois les peaux humaine et porcine contre les effets deleteres du rayonnement solaire. Ainsi, le modele EHR et la culture organotypique ex vivo de peau d’oreille de porc sont des outils complementaires pour etudier les dommages a l’ADN et l’apoptose induits par les radiations solaires. Ils pourraient etre utilises en complementarite pour evaluer les capacites photoprotectrices d’une formulation cosmetique.