Inhibitory Effect of Quercetin on Propionibacterium acnes-induced Skin Inflammation

Quercetin is a well-known antioxidant and a plant polyphenolic of flavonoid group found in many fruits, leaves, and vegetables. Propionibacterium acnes is a key skin pathogen involved in the progression of acne inflammation. Although quercetin has been applied to treat various inflammatory diseases, the effects of quercetin on P. acnes-induced skin inflammation have not been explored. This study investigated the effects of quercetin on P. acnes-induced inflammatory skin disease in vitro and in vivo. The results showed that quercetin suppressed the production of pro-inflammatory cytokines in P. acnes-stimulated HaCaT, THP-1 and RAW 264.7 cells. Additionally, quercetin reduced the production of TLR-2 and the phosphorylation of p38, ERK and JNK MAPKs in P. acnes-stimulated HaCaT and THP-1 cells. It also suppressed MMP-9 mRNA levels in two cell lines exposed to P. acnes in vitro. In the case of in vivo, P. acnes was intradermally injected into the ears of mice and it resulted in cutaneous erythema, swelling, and a granulomatous response. Treatment with quercetin markedly reduced ear thickness and swelling. These results suggested that quercetin can be a potential therapeutic agent against P. acnes-induced skin inflammation and may have diverse pharmaceutical and cosmetics applications.