The small molecule rhodomyrtone suppresses TNF-α and IL-17A-induced keratinocyte inflammatory responses: A potential new therapeutic for psoriasis

Psoriasis is a common skin disease pathogenically driven by TNF and IL-17A-induced epidermal hyperproliferation and inflammatory responses. The ongoing need for new therapeutic agents for psoriasis has highlighted medicinal plants as sources of phytochemicals useful for treating psoriatic disease. Rhodomyrtone, a bioactive phytochemical from Rhodomyrtus tomentosa, has well-established anti-proliferative activities. This study assessed the potential of rhodomyrtone for curtailing TNF/IL-17A-driven inflammation. Stimulating human skin organ cultures with TNF+IL-17A to model the skin inflammation in psoriasis, we found that rhodomyrtone significantly decreased inflammatory gene expression and the expression and secretion of inflammatory proteins, assessed by qRT-PCR, immunohistochemistry and ELISA assays respectively. RNA-seq analysis of monolayer primary keratinocytes treated with IL-17A/TNF showed that rhodomyrtone inhibited 724/1587 transcripts >2-fold altered by IL-17A/TNF (p<0.01), a number of which were confirmed at the mRNA and protein level. Suggesting that rhodomyrtone acts by modulating MAP kinase and NF-κB signaling pathways, rhodomyrtone inhibited TNF-induced ERK, JNK, p38, and NF-κBp65 phosphorylation. Finally, assessing the in vivo anti-inflammatory potential of rhodomyrtone, we examined its effects on imiquimod-induced skin inflammation in mice, finding rhodomyrtone reversed imiquimod-induced skin hyperplasia and epidermal thickening (p< 0.001). Taken together, these results suggest that rhodomyrtone may be useful in preventing or slowing the progression of inflammatory skin disease.