Rhododendrin inhibits toll-like receptor-7-mediated psoriasis-like skin inflammation in mice

Many active compounds present in Rhododendron brachycarpum have been used in traditional Oriental medicine for the treatment of various skin diseases. However, the precise mechanism of action of the compounds isolated from R. brachycarpum and their relevance as therapeutics for the treatment of psoriasis remain elusive. In this study, we report that rhododendrin isolated from R. brachycarpum strongly inhibits imiquimod (IMQ)-induced psoriasis-like skin inflammation in mice. We showed that topical treatment with rhododendrin reduces IMQ-induced skin hyperplasia, inflammatory mononuclear cell infiltration and the expression of pro-inflammatory mediators in mouse skin. In addition, we found that rhododendrin inhibits the activation of the TLR-7/NF-κB and mitogen-activated protein kinase pathways in both IMQ-induced psoriasis-like skin inflammation in mice and in normal human epidermal keratinocytes treated with IMQ. These results suggest that rhododendrin has an anti-inflammatory effect and can be used as a therapeutic to fight against psoriasis and other inflammatory skin diseases. A compound found in the rhododendron plant inhibits a pathway involved in innate immunity to quell skin inflammation in mice and human cells. Researchers in South Korea led by Tae-Yoon Kim from the Catholic University of Korea in Seoul investigated the mechanism by which rhododendrin, an anti-inflammatory compound isolated from Rhododendron brachycarpum plants, can alleviate psoriasis-like skin disease. The researchers showed that topical treatment with rhododendrin reduced the signs and symptoms of inflammation in mice with experimentally induced psoriasis-like skin lesions. Both in these mice and in human skin cells, rhododendrin treatment led to reduced activity of several proteins in the signaling cascade set off by toll-like receptor 7, a known immune activator of psoriasis. The findings help explain why rhododendrin could be a beneficial treatment for psoriasis patients.