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.

Ultraviolet Light as a Modulator of Melanoma Development

“…Even limited sun exposure appears to increases this risk, whereas for individuals not prone to develop naevi a relatively high cumulative lifetime UVR damage may often be necessary. Nevus cells proliferate strongly, and move to a suprabasal (malignant-like) location if subjected to only a single UVB exposure in vivo (Carrera et al, 2008). Thus naevus cells, unlike normal melanocytes within the skin, are extremely sensitive to UVB-induced damage.…”

Impact of Sunscreens on Preventing UVR-Induced Effects in Nevi

“…In our experience, no patient phenotype or phototype could be associated with a predictable or specific UVR response. This is a possible bias, since the 20 patients studied herein are representative of our clinically atypical nevi syn- 19 ), we have observed more intense inflammatory changes other than darkening or other than an increase in the number and size of globules and the network. We cannot find a relationship between which lesions or patients presented a specific change.…”

“…Patient exclusion criteria were a history of skin cancer or photodermatoses, phototoxic/ allergic drug intake, active dermatoses, phototherapy or intentional photoexposure in the previous 3 months, immunosuppressive treatment, or pregnancy. According to the previously published model to induce UV-B effects on nevi by a single, double minimal erythematous dose (2 MED) detailed by Carrera et al, 19 in the present study 23 melanocytic nevi were consecutively included in 2 groups. Criteria for selecting nevi were diameter greater than 5 mm, at least 1 axis symmetry, and no suspicion of melanoma.…”

“…Several prospective interventional studies 18 on UVR in melanocytic nevi have been carried out since 1995. This issue has been reviewed in depth in a publication 19 in which the present study model was described. Among the most remarkable effects reported using different methodologies, UVR can induce clinical changes, such as increased pigmentation, scale formation, and erythema, as well as dermoscopic changes in pigmentation, such as globules and dots (size and number), regression features (bluish gray granules), blurred pigmented network, and increased vascularity.…”

“…16 The first interventional model for in vivo evaluation of the effects of UV-B irradiation on nevi and adjacent skin, depending on the use of a physical barrier or a commercial topical sunscreen, was developed in 2008. 19 With use of this model, in the present study, the main objective was to test the effectiveness of a topical sunscreen in preventing the different UVR effects on nevi. A secondary aim was to evaluate the different types of measurable UVR effects on clinical, dermoscopic, and histopathologic examinations depending on the different phenotype of the patients.…”