Identification of Protocatechuic acid as an anti-acne component in extracts of black rice bran

Acne vulgaris is the most common dermatological problem among adolescents and young adults. Acne-associated pathogens, including Cutibacterium acnes and Staphylococcus epidermidis, and inflammation are among predominant etiologies of acne. Drugs targeting pathogens and inflammation response are an effective avenue to treat acne vulgaris. Rice bran has high pharmacological value, but its therapeutic potential for the treatment of acne remains unexplored. This study, therefore, aimed to purify and identify an anti-acne component from the ethanolic extract of Thai black rice (Oryza sativa cv. Neow Dam 3) bran and to investigate its underlying mechanisms of action. Protocatechuic acid (PA) was purified by bio-guided extraction and identified by a nuclear magnetic resonance. The antibacterial action was elucidated by minimum inhibitory concentration (MIC) determination and electron microscopy. PA cytotoxicity in HaCaT keratinocytes was assessed by an MTT assay, expression of inflammatory-associated genes and proteins by RT-qPCR, western blotting, and ELISA, and the nuclear translocation of NF-κB by immunofluorescence. The MIC of PA against C. acnes DMST 14,916 and S. epidermidis ATCC 12,228 and DMST 14,932 was 2048 µg/mL, which was similar to ferulic acid. Scanning and transmission electron microscopy demonstrated C. acnes and S. epidermidis treated with PA had unambiguous membrane damage and abnormal morphology. C. acnes lysate induced the expression of IL-6, IL-8, IL-1β, iNOS, TNF-α, and COX-2 genes, increased phosphorylated NF-κB, IL-6, and TNF-α protein levels, and caused translocation of NF-κB into the nucleus, while noncytotoxic levels of PA suppressed these effects. In summary, PA had anti-acne activity by inhibiting acne-associated pathogens, possibly through cell membrane damage, and suppressed inflammation induced by C. acnes via the NF-κB pathway suggesting that it may have therapeutic use for treating acne in the future.