Microbiome-Derived Indole-3-lactic Acid Attenuates Cutibacterium acnes–Induced Inflammation via the Aryl Hydrocarbon Receptor Pathway

Acne vulgaris is a chronic inflammatory dermatosis where conventional therapies of-ten face limitations in efficacy and safety, necessitating the development of microbi-ome-targeted interventions. This study investigated the immunomodulatory potential of microbiome-derived tryptophan metabolites as a novel therapeutic strategy for Cutibacterium acnes-induced inflammation, focusing on the aryl hydrocarbon receptor (AHR) pathway. We evaluated indole-3-lactic acid (ILA), indole-3-acrylic acid (IAA), and indole-3-propionic acid (IPA) in comparison to tapinarof, utilizing C. ac-nes-stimulated human epidermal keratinocytes and a C. acnes-induced acne mouse model. In vitro, ILA and IPA significantly suppressed C. acnes-driven inflammatory mediators, including TNF-a, IL-1ß, and COX2, whereas IAA demonstrated limited ef-ficacy. In vivo, ILA treatment exhibited superior therapeutic activity, markedly reduc-ing inflammatory cell infiltration, epidermal hyperplasia, and IL-1ß expression. Tran-scriptomic analysis confirmed that ILA attenuates inflammatory signaling (e.g., IL-17 and TNF pathways) while upregulating AHR-responsive genes such as CYP1A1 and CYP1B1. Collectively, these findings establish ILA as a potent postbiotic that mitigates cutaneous inflammation through selective activation of the AHR. Future studies should prioritize the clinical translation of ILA-based topical fomulations, with rigorous evaluation of their efficacy and safety in well-designed human trials, to support their development as a non-antibiotic therapeutic alternative for acne management. Overall design: RNA-seq profiling of primary human epidermal keratinocytes in untreated control, Cutibacterium acnes-stimulated, and four different treatment groups (indole-3-lactic acid (ILA), indole-3-acrylic acid (IAA), indole-3-propionic acid (IPA) and tapinarof(TAPI))