Pharmacological Inhibition of the Temperature-Sensitive and Ca2+-Permeable Transient Receptor Potential Vanilloid TRPV3 Channel by Natural Forsythoside B Attenuates Pruritus and Cytotoxicity of Keratinocytes

The temperature-sensitive and calcium-permeable transient receptor potential vanilloid 3 (TRPV3) channel abundantly expressed in keratinocytes plays important functions in skin physiology. Dysfunctional gain-of-function TRPV3 gene mutations cause genetic Olmsted syndrome characterized by periorificial keratoderma, palmoplantar keratoderma, inflammation, and severe itching, which suggests that pharmacological inhibition of overactive TRPV3 function may be beneficial in treating pruritus or skin disorders. To test this hypothesis, we identified natural compound forsythoside B as a TRPV3 inhibitor through screening of human embryonic kidney 293 (HEK293) cells expressing human TRPV3 channels in a calcium fluorescent assay. Whole-cell patch-clamp recordings of HEK293 cells expressing TRPV3 confirmed that forsythoside B selectively inhibited the channel current activated by agonist 2-aminoethoxydiphenyl borate (50 mu M) in a dose-dependent fashion, with an IC50 value of 6.7 +/- 0.7 mu M. In vivo evaluation of scratching behavior demonstrated that pharmacological inhibition of TRPV3 by forsythoside B significantly attenuated acute itch induced by either the TRPV3 agonist carvacrol or the pruritogen histamine, as well as chronic itch induced by acetone-ether-water in a mouse model of dry skin. Furthermore, forsythoside B was able to prevent the death of HEK293 cells or native human immortalized nontumorigenic keratinocyte cells from human keratinocytes expressing a gain-offunction TRPV3 G573S mutant or in the presence of the TRPV3 agonist carvacrol. Taken together, our findings demonstrate the crucial role of TRPV3 in pruritus and keratinocyte toxicity; thus, specific inhibition of overactive TRPV3 by natural forsythoside B may possess therapeutic potential for treatment of chronic pruritus, skin allergy, or inflammation-related skin diseases.