Development of a Human in vivo Method to Study the Effect of Ultraviolet Radiation and Sunscreens in Melanocytic Nevi

Abstract

Background: Ultraviolet radiation (UVR) plays an important role in the development of melanocytic lesions. Sunscreens have shown an impact in the prevention of UVR damage; however, their role in melanocytes has not been well established. The aim was to design and validate an in vivo human model to study the influence of UVR and sunscreen protection on nevi. Methods: A model describing clinical, dermoscopic, histopathological and molecular changes after UVR with or without protection was elaborated. Two UVB minimal erythema doses were irradiated on 4 nonsuspicious nevi from 4 patients; previously one half of each lesion was protected, in 2 cases with a physical opaque material and in the other 2 lesions by applying a high physical and chemical protection sunscreen (containing octocrylene, Parsol 1789, titanium dioxide, Mexoryl SX™, Mexoryl XL™). Lesions were excised 7 days afterwards. Results: After 7 days, clinical and dermoscopic changes (more pigmentation, erythema, dotted vessels, blurred network) were noted comparing the lesions before and after irradiation, especially when comparing both sides of each nevus (protected and nonprotected). Histopathological and immunohistochemical studies demonstrated marked melanocytic activation on nonprotected areas and a high proliferation index of keratinocytes. Both physical and sunscreen protections seem to avoid these changes. Conclusion: A useful and secure human model to study the UVR influence, and efficacy of sunscreens, on melanocytic lesions was developed. In vivo and ex vivo differences between irradiated nevus versus irradiated nevus plus sunscreen or physical protection were found.