piperine and resiniferatoxin

Chemosensory signaling by the tongue is a primary determinant of ingestive behavior and is mediated by specific interactions between tastant molecules and G protein-coupled and ion channel receptors. The functional relationship between tastant and receptor should be amenable to pharmacologic methods and manipulation. We have performed a pharmacologic characterization of the taste-directed licking of mice presented with solutions of capsaicin and other transient receptor potential vanilloid-1 (TRPV1) agonists using a brief access taste aversion assay. Dose-response functions for lick-rate suppression were established for capsaicin (EC(50) = 0.5 microM), piperine (EC(50) = 2 muM), and resiniferatoxin (EC(50) = 0.02 microM). Little or no effect on lick rate was observed in response to the full TRPV1 agonist olvanil. Capsaicin lick rates of wild-type and transient receptor potential melastatin-5 (TRPM5) knockout mice were equivalent, indicating that TRPM5, a critical component of aversive signaling for many bitter tastants, did not contribute to the capsaicin taste response. The selective TRPV1 antagonists N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide (10 microM) and (E)-3-(4-t-butylphenyl)-N-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)acrylamide (AMG9810) (10 microM) effectively blocked capsaicin- and piperine-mediated lick suppression. However, (E)-3-(4-chlorophenyl)-N-(3-methoxyphenyl)-N-phenylprop-2-enamide (SB 366791) and capsazepine, also TRPV1 antagonists, were without effect at test concentrations of up to 30 and 100 microM, respectively. Our results demonstrate that TRPV1-mediated oral aversiveness presents a pharmacologic profile differing from what has been reported previously for TRPV1 pain signaling and, furthermore, that aversive tastes can be evaluated and controlled pharmacologically.

Topics: Acrylamides; Administration, Oral; Alkaloids; Anilides; Animals; Avoidance Learning; Benzodioxoles; Bridged Bicyclo Compounds, Heterocyclic; Capsaicin; Cinnamates; Diterpenes; Dose-Response Relationship, Drug; Female; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Piperidines; Polyunsaturated Alkamides; Pyrazines; Pyridines; Taste; TRPM Cation Channels; TRPV Cation Channels

TRPV1 (transient receptor potential vanilloid 1) is a ligand-gated ion channel expressed predominantly in nociceptive primary afferents that plays a key role in pain processing. In vivo activation of TRPV1 receptors by natural agonists like capsaicin is associated with a sharp and burning pain, frequently described as pungency. To elucidate the mechanisms underlying pungency we investigated a series of TRPV1 agonists that included both pungent and non-pungent compounds covering a large range of potencies. Pungency of capsaicin, piperine, arvanil, olvanil, RTX (resiniferatoxin) and SDZ-249665 was evaluated in vivo, by determining the increase in the number of eye wipes caused by direct instillation of agonist solutions into the eye. Agonist-induced calcium fluxes were recorded using the FLIPR technique in a recombinant, TRPV1-expressing cell line. Current-clamp recordings were performed in rat DRG (dorsal root ganglia) neurons in order to assess the consequences of TRPV1 activation on neuronal excitability. Using the eye wipe assay the following rank of pungency was obtained: capsaicin>piperine>RTX>arvanil>olvanil>SDZ-249665. We found a strong correlation between kinetics of calcium flux, pungency and lipophilicity of TRPV1 agonists. Current-clamp recordings confirmed that the rate of receptor activation translates in the ability of agonists to generate action potentials in sensory neurons. We have demonstrated that the lipophilicity of the compounds is directly related to the kinetics of TRPV1 activation and that the latter influences their ability to trigger action potentials in sensory neurons and, ultimately, pungency.

Topics: Action Potentials; Alkaloids; Animals; Benzodioxoles; Capsaicin; Diterpenes; Ganglia, Spinal; Kinetics; Lipid Metabolism; Male; Neurons, Afferent; Pain; Patch-Clamp Techniques; Piperidines; Polyunsaturated Alkamides; Rats; Rats, Sprague-Dawley; Recombinant Proteins; Sensory Receptor Cells; Solubility; TRPV Cation Channels; Urea

We have evaluated the effect of the vanilloid receptor agonists resiniferatoxin (RTX), capsaicin and piperine and of the vanilloid receptor antagonist capsazepine on the resting tone in the isolated rat ileum. Capsazepine (10(-8)-3 x 10(-5) M) produced a concentration-related relaxation (8 +/-3%-49 +/-3%) of the rat ileum. By contrast RTX (up to 10(-8) M), capsaicin (up to 10(-6) M) and piperine (up to 10(-5) M) were without effect. Pre-treatment with capsaicin [either in vivo (50 mg/kg s.c.) or in vitro (10(-6) M)] did not modify the inhibitory effect of capsazepine. The L-type Ca2+ channel antagonist nifedipine (10(-6) M), but not the N-type Ca2+ channel antagonist omega-conotoxin GVIA (3 x 10(-8) M) nor the Na+ channel blocker tetrodotoxin (3 x 10(-7) M), counteracted the inhibitory effect of capsazepine. The NK1 receptor antagonist SR 140333 (10(-7) M), the NK2 receptor antagonist SR 48968 (10(-6) M), the NK3 receptor antagonist SR 142801 (10(-7) M), atropine (10(-6) M), hexamethonium (10(-4) M), phentolamine (10(-6) M) plus propranolol (10(-6) M), N(G)-nitro- L-arginine methyl ester ( L-NAME 3 x 10(-4) M), apamin (10(-7) M), methysergide (10(-6) M), the calcitonin gene-related peptide (CGRP) antagonist hCGRP 8-37 (1.5 x 10(-6) M), the VIP antagonist hGRF 1-29 (10(-5) M) did not modify the inhibitory effect of capsazepine. Capsazepine (2.5-40 mg/kg) also decreased upper gastrointestinal transit in vivo. It is concluded that the vanilloid antagonist capsazepine has a direct relaxing effect on rat intestinal smooth muscle which could involve L-type calcium channels. We found no evidence to suggest that capsazepine is antagonizing an endogenous vanilloid.

Topics: Alkaloids; Animals; Benzodioxoles; Calcium Channels, L-Type; Capsaicin; Diterpenes; Dose-Response Relationship, Drug; Gastrointestinal Transit; Ileum; In Vitro Techniques; Male; Muscle Relaxation; Muscle, Smooth; Piperidines; Polyunsaturated Alkamides; Rats; Rats, Sprague-Dawley; Receptors, Drug

In the present work we report the development of a new radioimmunoassay method for measuring the substance P content liberated from isolated rat tracheae in response to electrical or chemical (capsaicin, resiniferatoxin, piperine) stimulation. The amount of substance P released by electrical stimulation has been found to be dependent on the number of pulses and chemically elicited substance P release also proved to be dose-dependent. Our findings reinforce previous data that resiniferatoxin is approximately 100 times more potent than capsaicin and the potency ratio between piperine and capsaicin is 1/50.

Topics: Alkaloids; Animals; Benzodioxoles; Calibration; Capsaicin; Diterpenes; Electric Stimulation; Enzyme Inhibitors; Female; Neurons, Afferent; Piperidines; Polyunsaturated Alkamides; Radioimmunoassay; Rats; Rats, Wistar; Stimulation, Chemical; Substance P; Trachea

The naturally occurring capsaicin-like molecules, resiniferatoxin (RTX, Euphorbia spp.) and piperine (Piper nigrum), each stimulated oxygen uptake (VO2) in association with increased vascular resistance in a concentration-dependent manner when infused into the perfused rat hindlimb. 5 microM glyceryl trinitrate (GTN, a nitrovasodilator) significantly blocked the oxygen and pressure responses to both RTX and piperine, indicating a close relationship between changes in VO2 and the vasoconstriction. Concentrations greater than those required for maximal VO2 resulted in an inhibition of VO2, although perfusion pressure continued to increase. Time course studies showed that both RTX and piperine at high doses resulted in a tri-phasic response. An initial phase of transient VO2 stimulation was followed by a second phase of inhibition. A third phase involving an often larger but transient stimulation of VO2 followed removal of the agents and continued after the pressure returned to basal. The actions of RTX and piperine were similar to those of other active capsaicin-like molecules tested previously in this system, including capsaicinoids (Capsicum spp.), gingerols (Zingiber officinale), and shogoals (Zingiber officinale). RTX was the most potent, and piperine the least potent of this series. Although receptor involvement has yet to be unequivocally established, the data are consistent with the presence of a functional capsaicin-like (vanilloid) receptor in the vasculature of the rat hindlimb that mediates vasoconstriction and oxygen uptake. These findings may have implications for the future development of thermogenic agents.

Topics: Alkaloids; Animals; Benzodioxoles; Capsaicin; Diterpenes; Hindlimb; Male; Nitroglycerin; Oxygen Consumption; Perfusion; Piperidines; Polyunsaturated Alkamides; Rats; Rats, Wistar

Topics: Alkaloids; Animals; Anti-Ulcer Agents; Benzodioxoles; Capsaicin; Diterpenes; Ethanol; Female; Piperidines; Polyunsaturated Alkamides; Rats; Rats, Inbred Strains; Stomach Ulcer