Activation and activators of TRPV1 and their pharmaceutical implication.

TRPV1 is a channel expressed highly in small sensory neurons. TRPV1 is a ligand-gated, cation channel that is activated by heat, acid and capsaicin, a principal ingredient in hot peppers. Because of its possible role as a polymodal molecular detector, TRPV1 is studied most extensively. In mice lacking TRPV1, thermal hyperalgesia induced by inflammation is reduced, suggesting a role for mediating inflammatory pain. Activity of TRPV1 is modulated by actions of various kinases such as protein kinase A and C. Furthermore, phosphorylation by Ca(2+)-calmodulin-dependent kinase II is required for its ligand binding. TRPV1 is activated by various endogenous lipids, such as anandamide, N-arachidonoyl-dopamine, and various metabolic products of lipoxygenases. 12-hydroperoxyeicosatetraenoic acid, an immediate metabolic product of 12-lipoxygenase, activates TRPV1 and shares 3-dimensional structural similarity with capsaicin. Because lipoxygenase products can activate TRPV1 in sensory neurons, upstream signals to lipoxygenase/TRPV1 pathway have been questioned. Indeed, bradykinin, a potent pain-causing substance, is now known to activate TRPV1 via lipoxygenase pathway. However, we cannot overlook the sensitizing effect of bradykinin via the phospholipase C or protein kinase C pathway. Interestingly, histamine, a pruritogenic substance, also appears to use the lipoxygenase/TRPV1 pathway in order to excite sensory neurons. Because of its role in the mediation of nociception, antagonists of TRPV1 are targeted for development of potential analgesics. In the present review, theoretical background of organic synthesis of SC0030, a potent antagonist of TRPV1 is presented.