Phenols produced by gut bacteria affect the skin in hairless mice

Objective: Phenol and p-cresol are metabolites of aromatic amino acid produced by gut bacteria, and are assumed to cause undesirable effects in the body. We aimed to understand how phenol and p-cresol affect the skin of hairless mice. Materials and methods: First, we compared the skin condition of hairless mice fed the basal diet and the skin condition of mice fed the tyrosine-enriched diet. In the next experiment, we administered either phenol or p-cresol intraperitoneally to mice fed the basal diet. Eventually, we isolated Morganella morganii, which is able to produce phenol, from the feces of mice fed the tyrosine-enriched diet, and Escherichia coli, which is not able to produce phenol, from the feces of mice fed the basal diet, and performed a gnotobiotic experiment. Results: In mice fed the tyrosine-enriched diet, phenol and p-cresol levels increased in cecal contents, serum, and flank skin, and a yellowish dullness, reflected by the color exam meter's b* value, was exhibited by the skin. The b* value of phenol-administered mice was higher than that of saline- or p-cresol-administered mice. Furthermore, the size of the corneocytes of phenol-administered mice was significantly smaller than that of the saline- or p-cresol-administered mice. The M. morganii gnotobiotic mice exhibited a higher b* value and smaller corneocytes than the E. coli gnotobiotic mice. Conclusions: These results suggest that phenols produced by gut bacteria affect the skin in hairless mice.