Pharmacological characterization of the vanilloid receptor in the rat dorsal spinal cord

Wardle, Kay A.; Ranson, Jennie; Sanger, Gareth J.

doi:10.1038/sj.bjp.0701199

Cited by 56 publications

(35 citation statements)

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“…However, an agonist with a low intrinsic efficacy may still induce a full response if the amount of receptors is large enough. Because there are some indications in the literature that capsaicin has a larger intrinsic efficacy than olvanil and resiniferatoxin at native vanilloid receptors (Wardle et al, 1997), we performed computer simulations to explore the possibility that agonists having different intrinsic efficacies are affected to various extents by changes in the receptor content. Allowing for variation of these parameters, the computer simulations could successfully predict the intriguing experimental observation that although capsaicin was equally potent in the two tissues, the other agonists were less effective in main bronchi than in mesenteric arteries.…”

Section: Discussionmentioning

confidence: 99%

Mechanisms Underlying Tissue Selectivity of Anandamide and Other Vanilloid Receptor Agonists

et al. 2002

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Anandamide acts as a full vanilloid receptor agonist in many bioassay systems, but it is a weak activator of primary afferents in the airways. To address this discrepancy, we compared the effect of different vanilloid receptor agonists in isolated airways and mesenteric arteries of guinea pig using preparations containing different phenotypes of the capsaicin-sensitive sensory nerve. We found that anandamide is a powerful vasodilator of mesenteric arteries but a weak constrictor of main bronchi. These effects of anandamide are mediated by vanilloid receptors on primary afferents and do not involve cannabinoid receptors. Anandamide also contracts isolated lung strips, an effect caused by the hydrolysis of anandamide and subsequent formation of cyclooxygenase products. Although capsaicin is equally potent in bronchi and mesenteric arteries, anandamide, resiniferatoxin, and particularly olvanil are significantly less potent in bronchi. Competition experiments with the vanilloid receptor antagonist capsazepine did not provide evidence of vanilloid receptor heterogeneity. Arachidonoyl-5-methoxytryptamine (VDM13), an inhibitor of the anandamide membrane transporter, attenuates responses to olvanil and anandamide, but not capsaicin and resiniferatoxin, in mesenteric arteries. VDM13 did not affect responses to these agonists in bronchi, suggesting that the anandamide membrane transporter is absent in this phenotype of the sensory nerve. Computer simulations using an operational model of agonism were consistent, with differences in intrinsic efficacy and receptor content being responsible for the remaining differences in agonist potency between the tissues. This study describes differences between vanilloid receptor agonists regarding tissue selectivity and provides a conceptual framework for developing tissue-selective vanilloid receptor agonists devoid of bronchoconstrictor activity.

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Section: Discussionmentioning

confidence: 99%

Mechanisms Underlying Tissue Selectivity of Anandamide and Other Vanilloid Receptor Agonists

et al. 2002

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“…Capsazepine, the most extensively characterized, is a competitive antagonist of capsaicin with affinity similar to that of capsaicin (Bevan et al, 1992). A problem has been its limited selectivity; it also blocks nicotinic cholinergic receptors, voltage dependent calcium channels, and purinergic receptors at concentrations comparable with those at which it is active on VR1 (Docherty et al, 1997;Wardle et al, 1997). 5-Iodo-4-hydroxy-3-methoxy RTX shows markedly enhanced potency, with an IC 50 for rat VR1 expressed in Xenopus laevis oocytes of 3.9 nM (40-fold stronger than that of capsazepine in this system) (Wahl et al, 2001).…”

Section: Camentioning

confidence: 99%

High-Affinity Partial Agonists of the Vanilloid Receptor

Wang¹,

Tóth²,

Tran³

et al. 2003

Mol Pharmacol

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The vanilloid receptor VR1 is a polymodal nociceptor sensitive to capsaicin, protons, and heat. Because VR1 represents an attractive therapeutic target for conditions ranging from long-term pain to bladder hyperreflexia, we and other groups have sought to develop novel ligands with enhanced potencies and novel pharmacological properties. Here, we characterize two compounds, N-[2-(3,4-dimethylbenzyl)-3-(pivaloyloxy) Ca2ϩ uptake in response to capsaicin were 67.3 Ϯ 24.9 nM and 3.4 Ϯ 0.5 nM, respectively. Protons, temperature, and protein kinase C all function as coactivators/modulators of rVR1. All enhanced the extent of partial agonism of JYL827 and JYL1511. Thus, at pH 5.5, for example, the extents of partial agonism increased to 54.9 Ϯ 2.5% and to 90.7 Ϯ 1.7%, respectively, relative to the response elicited by 300 nM capsaicin. The extents of partial antagonism decreased correspondingly. Compounds such as JYL827 and JYL1511 now permit exploration of the potential utility of partial agonists of rVR1 in animal models. Our results emphasize, moreover, the strong dependence of such partial agonists on other modulators of rVR1 and predict that their biological behavior will depend strongly on biological context.The vanilloid receptor VR1 has attracted great attention, because of both its biological function and its therapeutic potential. VR1, also called vanilloid receptor type 1, a member of the transient receptor potential family of ion channels, is a modestly calcium-selective ion channel located in C-fiber and A␦ sensory neurons as well as in a growing number of other sites such as the central nervous system or the bladder (Szallasi, 2001). VR1 functions as an integrative transducer for a range of nociceptive signals, including heat, protons, endogenous ligands, such as lipoxygenase products or anandamide, and exogenous compounds such as capsaicin or resiniferatoxin (Julius and Basbaum, 2001). Activation of VR1 by capsaicin may be followed by subsequent loss of responsiveness, depending on dose, duration of application, and other conditions, and reflects a combination of overlapping mechanisms, such as dephosphorylation or calcium toxicity to the neurons (Szallasi and Blumberg, 1999). This desensitization/defunctionalization by capsaicin has been exploited to treat a variety of conditions in which C-fiber sensory neurons are involved, such as pain associated with arthritis, cystitis, human immunodeficiency virus, and diabetic neuropathy (Robbins, 2000). Although capsaicin has made it possible to identify an exciting series of potential therapeutic applications, its utility has been limited by its somewhat modest potency, by the initial pain occasioned upon initial application, and by its metabolic lability (Szallasi, 2001). Attention has therefore been directed at the development and characterization of novel analogs of capsaicin. Although still in the early stages, much progress has been made.Ligands have been identified with much greater potency for VR1 than that displayed by capsaicin. Resiniferatoxi...

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“…So far, only a single antagonist of VR1, capsazepine, has been studied extensively (Bevan et al, 1992). Unfortunately, capsazepine has only modest potency and is somewhat nonspecific, also antagonizing voltage sensitive calcium channels and the nicotinic cholinergic receptor (Docherty et al, 1997;Liu and Simon, 1997;Wardle et al, 1997).…”

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confidence: 99%

High Affinity Antagonists of the Vanilloid Receptor

et al. 2002

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The vanilloid receptor VR1 has attracted great interest as a sensory transducer for capsaicin, protons, and heat, and as a therapeutic target. Here we characterize two novel VR1 antagonists, KJM429 [N-(4-tert-butylbenzyl)-NЈ-[4-(methylsulfonylamino)benzyl]thiourea] and JYL1421 [N-(4-tertbutylbenzyl)-NЈ-[3-fluoro-4-(methylsulfonylamino)benzyl]-thiourea], with enhanced activity compared with capsazepine on rat VR1 expressed in Chinese hamster ovary (CHO) cells. JYL1421, the more potent of the two novel antagonists, inhibited [ 3 H]resiniferatoxin binding to rVR1 with an affinity of 53.5 Ϯ 6.5 nM and antagonized capsaicininduced calcium uptake with an EC 50 of 9.2 Ϯ 1.6 nM, reflecting 25-and 60-fold greater potencies than capsazepine. Both JYL1421 and KJM429 antagonized RTX as well as capsaicin and their mechanism was competitive. The responses to JYL1421 and KJM429 differed for calcium uptake by rVR1 induced by heat or pH. JYL1421 antagonized the response to both pH 6.0 and 5.5, whereas KJM429 antagonized at pH 6.0 but was an agonist at lower pH (Ͻ5.5). For heat, JYL1421 fully antagonized and KJM429 partially antagonized. Capsazepine showed only weak antagonism for both pH and heat. Responses of rVR1 to different activators could thus be differentially affected by different ligands. In cultured dorsal root ganglion neurons, JYL1421 and KJM429 likewise behaved as antagonists for capsaicin, confirming that the antagonism is not limited to heterologous expression systems. Finally, JYL1421 and KJM429 had little or no effect on ATP-induced calcium uptake in CHO cells lacking rVR1, unlike capsazepine. We conclude that JYL1421 is a competitive antagonist of rVR1, blocking response to all three of the agonists (capsaicin, heat, and protons) with enhanced potency relative to capsazepine.A vanilloid receptor (VR1) that is activated by capsaicin, low pH, and temperatures higher than 42°C has been cloned from rat dorsal root ganglia (Caterina et al., 1997;Tominaga et al., 1998). It is a nonselective cation channel, with high permeability for divalent cations, expressed on unmyelinated pain-sensing nerve fibers (C-fibers) and small A␦ fibers in the dorsal root, trigeminal, and nodose ganglia. Initially, activation of VR1 by pungent agonists such as capsaicin leads to excitation of primary sensory neurons gating nociceptive inputs to the central nervous system. Subsequently, these fibers may become desensitized/defunctionalized, and this desensitization forms a basis for the therapeutic use of VR1 agonists . Potential therapeutic applications include detrusor hyperreflexia, postherpetic neuralgia, diabetic neuropathy, cluster headache, osteoarthritis, and pruritus (Rains and Bryson, 1995;Kim and Chancellor, 2000).The exciting potential therapeutic applications for vanilloids have motivated efforts to identify or design novel derivatives with improved properties (Walpole et al., 1993a,b,c;Wrigglesworth et al., 1996). An important advance was the identification of resiniferatoxin (RTX), a diterpene related to the phorbol...

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Pharmacological characterization of the vanilloid receptor in the rat dorsal spinal cord

Cited by 56 publications

References 18 publications

Mechanisms Underlying Tissue Selectivity of Anandamide and Other Vanilloid Receptor Agonists

Mechanisms Underlying Tissue Selectivity of Anandamide and Other Vanilloid Receptor Agonists

High-Affinity Partial Agonists of the Vanilloid Receptor

High Affinity Antagonists of the Vanilloid Receptor

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