The exact pathogenesis of acne-related post-inflammatory hyperpigmentation (PIH) is unknown. It is thought that epidermal inflammation induces the release of arachidonic acid and its oxidation products, leading to melanocyte activation and pigment production. Cutibacterium acnes (C. acnes) contributes to keratinocyte inflammation in acne pathogenesis. In severe cases inflamed sebaceous follicles may be ruptured, thereby bacteria and their metabolites can reach the melanocytes in the basal epidermal layer. We aimed to investigate whether, in addition to inducing epidermal immune activation, C. acnes may also directly affects melanocytes, thus contributing to PIH development. In our study we established C. acnes-treated normal human melanocyte and melanocyte-keratinocyte co-cultures and analyzed the properties of melanocyte immune activation and melanogenesis. We observed that direct C. acnes treatment increased the mRNA expression level of tumor necrosis factor alpha and the secreted protein levels of interleukin 6 and 8, together with the mRNA levels of tyrosinase and dopachrome tautomerase, playing roles in melanin biosynthesis. Tyrosinase enzyme activities and the intracellular melanin levels were also elevated, which we confirmed using real-time RT-PCR, L-DOPA staining, direct melanin measurement, and silver-nitrate staining. Based on our results, we propose that C. acnes or bacterial components may directly interact with melanocytes during the formation of severe acne lesions due to the disruption of intact follicles. They may induce melanocyte immune activation and increased melanogenesis, contributing to PIH symptoms.

ESDR406 - Investigating the role of Cutibacterium acnes in the development of postinflammatory hyperpigmentation (PIH)

The scientific meeting of the European Society for Dermatological Research (ESDR) is held yearly, usually in September. With an international attendance of more than 1000 skin scientists from around the globe, the four-day event includes short oral presentations from peer-reviewed abstracts, keynote lectures from international experts, sponsored symposia, satellite programs, educational events as well as an important focus on posters, networking and building collaborations amongst scientists. For more information about this year’s meeting visit our website.