TRP-channel-specific cutaneous eicosanoid release patterns

Abstract

Analyzing mechanisms and key players in peripheral nociception nonneuronal skin cells are getting more and more into focus. Herein we investigated the functional expression of TRPV1 and TRPA1 in human keratinocytes and fibroblasts and assessed proinflammatory lipid mediator release upon their stimulation as well as sensory effects after topical application, combining in vitro and in vivo approaches. In vitro, the expression of functional TRPV1 and TRPA1 channels on fibroblasts and keratinocytes was confirmed via immunofluorescence, qualitative real time (RT) polymerase chain reaction, and cellular Ca 2+ influx measurements. Additionally, the agonists allyl isothiocyanate (TRPA1) and capsaicin (TRPV1) induce a differential secretion pattern of the eicosanoids PGE 2 and LTB 4 in human dermal fibroblasts and keratinocytes, which was also detectable in vivo, analyzing suction blister fluid at various times after short-term topical application. Capsaicin provoked the release of LTB 4 at 2 and 24 hours. In contrast, PGE 2 levels were reduced upon stimulation. Allyl isothiocyanate, however, increased PGE 2 levels only at 24 hours, but did not alter LTB 4 levels. In parallel, heat pain thresholds were reduced by both agents after short-term topical application, but only AITC provoked a long-lasting local erythema. In conclusion, the agonist-induced activation of nociceptors by TRPA1 and TRPV1 elicits painful sensations, whereas nonneuronal tissue cells respond with differential release of inflammatory mediators, thus influencing local vasodilatation and neuronal sensitization. These results have implications for the application of transient receptor potential antagonists to improve inflammatory skin conditions and pain management.