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Life Sci. 1997;60(10):681-96.
Euphorbium: modern research on its active principle, resiniferatoxin, revives an ancient medicine.
Appendino G, Szallasi A.
Dipartimento di Scienza e Tecnologia del Farmaco, Universita degli Studi di Torino, Italy.
Resiniferatoxin, an ultrapotent capsaicin analog present in the latex of Euphorbia resinifera, interacts at a specific membrane recognition site (referred to as the vanilloid receptor), expressed by primary sensory neurons mediating pain perception as well as neurogenic inflammation. Desensitization to resiniferatoxin is a promising approach to mitigate neuropathic pain and other pathological conditions in which sensory neuropeptides released from capsaicin-sensitive neurons play a crucial role. Clinical trials to evaluate the potential of topical resiniferatoxin treatment to relieve pain associated with diabetic polyneuropathy and postherpetic neuralgia are in progress. Though resiniferatoxin was isolated only two decades ago, the dried latex of Euphorbia resinifera, called Euphorbium, has been in medicinal use since the time of recorded history. This review highlights the most important events in the history of this ancient medicine, from the first written record of the therapeutic potential of Euphorbium (at the time of the reign of the Roman Emperor Augustus) to the identification of its active principle as resiniferatoxin in 1975. A brief overview of the enormous contribution of resiniferatoxin to our current understanding of the anatomical localization, function, and pharmacology of vanilloid receptors is provided. Lastly, the mechanisms are summarized by which capsaicin and resiniferatoxin, despite sharing receptors, may have dissimilar biological actions.
J Cancer Res Clin Oncol. 1984;108(1):98-109.
On the active principles of the spurge family (Euphorbiaceae). V. Extremely skin-irritant and moderately tumor-promoting diterpene esters from Euphorbia resinifera Berg.
Hergenhahn M, Kusumoto S, Hecker E.
The irritant and tumor-promoting principles were isolated from the latex of Euphorbia resinifera Berg. and from the resin derived from latex (euphorbium), which is commercially available as a drug. The irritant Euphorbia factors RL 5 (mixture), RL 6, RL 7, RL 8, and RL 10 were identified as tigliane-type 12-deoxyphorbol esters each bearing, in the 13 position, either long-chain, partially methyl-substituted acyl residues (10-16 carbon atoms) or short-chain acyl residues (4 or 5 carbon atoms) or a (substituted) phenylacetyl group with a 20-acetoxy group. Euphorbia factors RL 15 (mixture), RL 16, RL 17, RL 18, and RL 21 are the corresponding 20-deacetylated derivatives thereof. The irritant Euphorbia factors RL 11, RL 12, RL 22, RL 23 were characterized as esters of the tigliane type 12-deoxy-16-hydroxyphorbol, i.e., 13-0-phenylacetyl-16-0-benzoyl-12-deoxy16-hydroxyphorbol-20- acetate (RL 11) and 13, 16-0-phenylacetyl, tigloyl-12-deoxy-16-hydroxy-phorbol-20-acetate (RL 12), RL 22 and RL 23 representing the respective 20-deacetylated derivatives. A mixture of irritant factors, RL 13, was shown to represent long-chain 3-esters of ingenane-type ingenol with similar acyl residues (10-16 carbon atoms, partially methyl-substituted) to RL 5 (RL 15) above. A further group of E. resinifera factors was of the daphnane type: RL 9 was identified as the extremely irritant 9,13,14-orthophenylacetate of resiniferonol-20-(4-hydroxy-3-methoxy)phenylacetate (Resiniferatoxin), RL 14 as the corresponding 9,13,14-orthophenylacetate of resiniferonol, and RL 20 as 14-0-phenylacetylresiniferonol-20-(4-hydroxy-3-methoxy)-phenylacet ate (Proresiniferatoxin). The irritant factors specified below were accompanied by nonirritant esters of the tigliane type 12,20-dideoxyphorbol, i.e., RL 1 and RL 2, and of the lathyrane type ingol, i.e., RL 3 and RL 4. In tumor promotion experiments the mixture of homologous irritant factors RL 13 was equipotent with the standard tumor promoter TPA, but at 10 times the dose of TPA. Several others of the irritant factors had low activity as tumor promotors, but of the few tumors obtained in these experiments a high percentage was malignant. The very high irritant activity of the latex may be ascribed to resiniferatoxin (RL 9), representing a new class of rapidly acting skin irritants. No promoting activity was detected on administration of the highly irritant resiniferatoxin.
J Biol Chem. 2004 May 7;279(19):20283-95.
Molecular determinants of vanilloid sensitivity in TRPV1.
Gavva NR, Klionsky L, Qu Y, Shi L, Tamir R, Edenson S, Zhang TJ, Viswanadhan VN, Toth A, Pearce LV, Vanderah TW, Porreca F, Blumberg PM, Lile J, Sun Y, Wild K, Louis JC, Treanor JJ.
Department of Neuroscience, Amgen Inc., MS 29-2 B, One Amgen Center Drive, Thousand Oaks, CA 91320-1799, USA. email@example.com
Vanilloid receptor 1 (TRPV1), a membrane-associated cation channel, is activated by the pungent vanilloid from chili peppers, capsaicin, and the ultra potent vanilloid from Euphorbia resinifera, resiniferatoxin (RTX), as well as by physical stimuli (heat and protons) and proposed endogenous ligands (anandamide, N-arachidonyldopamine, N-oleoyldopamine, and products of lipoxygenase). Only limited information is available in TRPV1 on the residues that contribute to vanilloid activation. Interestingly, rabbits have been suggested to be insensitive to capsaicin and have been shown to lack detectable [(3)H]RTX binding in membranes prepared from their dorsal root ganglia. We have cloned rabbit TRPV1 (oTRPV1) and report that it exhibits high homology to rat and human TRPV1. Like its mammalian orthologs, oTRPV1 is selectively expressed in sensory neurons and is sensitive to protons and heat activation but is 100-fold less sensitive to vanilloid activation than either rat or human. Here we identify key residues (Met(547) and Thr(550)) in transmembrane regions 3 and 4 (TM3/4) of rat and human TRPV1 that confer vanilloid sensitivity, [(3)H]RTX binding and competitive antagonist binding to rabbit TRPV1. We also show that these residues differentially affect ligand recognition as well as the assays of functional response versus ligand binding. Furthermore, these residues account for the reported pharmacological differences of RTX, PPAHV (phorbol 12-phenyl-acetate 13-acetate 20-homovanillate) and capsazepine between human and rat TRPV1. Based on our data we propose a model of the TM3/4 region of TRPV1 bound to capsaicin or RTX that may aid in the development of potent TRPV1 antagonists with utility in the treatment of sensory disorders.
Drug News Perspect. 2005 Apr;18(3):165-71. Related Articles, Links
TRPV1 receptor: a target for the treatment of pain, cough, airway disease and urinary incontinence.
Jia Y, McLeod RL, Hey JA.
Pulmonary and Peripheral Neurobiology, Schering-Plough Research Institute, Kenilworth, New Jersey 07033, USA. yanlin.jia@spcorp. com
The TRPV1 channel is mainly expressed in sensory nerves. Activation of the channel induces neuropeptide release from central and peripheral sensory nerve terminals, resulting in the sensation of pain, neurogenic inflammation, smooth muscle contraction and cough. The TRPV1 channel can be activated by vanilloids such as capsaicin, as well as endogenous stimulators including H(+), heat, lipoxygenase products and anandamide. TRPV1 channel function is upregulated by several endogenous mediators present in inflammatory conditions, which decreases the threshold for activation of the channel. Under these conditions, TRPV1 can be activated by physiological body temperature, slight acidification or lower concentration of TRPV1 agonists. There is evidence that TRPV1 plays a role in the development of pathophysiological changes and symptoms in several diseases. In this review, we discuss TRPV1 channel activation and regulation in normal and diseased conditions, the role of TRPV1 in pain, cough, asthma and urinary incontinence, and the potential use of TRPV1 antagonists as a novel therapy for these diseases.)