Evaluation of the Biological Effect of a Nicotinamide-Containing Broad-Spectrum Sunscreen on Photodamaged Skin.

Introduction: UVA-UVB increases skin matrix metalloproteinases and breaks down extracellular proteins and fibrillar type 1 collagen, leading to photodamage. Topical application of nicotinamide prevents UV-induced immunosuppression. Several studies have demonstrated the importance of protection against UV. This study aims to determine the biological effect of a high broad-spectrum UVB-UVA sunscreen containing nicotinamide and panthenol (SSNP) on photodamaged skin using linear confocal optical coherence tomography (LC-OCT), immunohistochemistry, and RNA profiling.

Methods: Two areas of severely photodamaged forearm skin (L01 and L02) and one less sun-damaged (naturally protected) area on the inner part of the forearm (L03) were identified in 14 subjects. These areas were imaged using LC-OCT and L01 and L03 were biopsied at baseline. After 4 weeks of treatment with SSNP, L02 was reimaged using LC-OCT, and biopsied. Histology, immunostaining with p21, p53, PCNA, and CPD, and RNA sequencing were performed in all samples.

Results: LC-OCT analysis showed that epidermis thickness and the number of keratinocytes is higher in the sun-exposed areas than in the non-exposed areas. Comparing before and after treatment, even though there is a trend towards normalization, the differences were not statistically significant. The expression of p21, PCNA, p53, and CPD increased in severely photodamaged skin compared to less-damaged skin. When comparing before and after treatment, only p21 showed a trend to decrease expression. RNA sequencing analysis identified 1552 significant genes correlating with the progression from non-visibly photodamaged skin to post-treatment and pre-treatment samples; in the analysis comparing pre- and post-treatment samples, 5429 genes were found to be significantly associated. A total of 1115 genes are common in these two analyses. Additionally, nine significant genes from the first analysis and eight from the second are related to collagen. Six of these collagen genes are common in the two analyses. MAPK and cGMP-PKG signalling pathways are upregulated in the progression to photodamage analysis. In the pre- and post-treatment analysis, 32 pathways are downregulated after treatment, the most statistically significant being the ErbB, Hippo, NOD-like receptor, TNF, and NF-kB signalling pathways.

Conclusion: This study demonstrates the role of SSNP in collagen generation, highlights the relevance of the cGMP-PKG and MAPK signalling pathways in photodamage, and shows the ability of SSNP to downregulate pathways activated by UV exposure. Additionally, it deepens our understanding of the effect of SSNP on immune-related pathways.