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• Purified human TRPA1 activity is gated by force-from-lipids in artificial bilayers. • The TRPA1 N-terminal ankyrin repeat domain is not required for mechanosensation. • The TRPA1 mechanosensitivity is dependent on its redox state. The role of mammalian Transient Receptor Potential Ankyrin 1 (TRPA1) as a mechanosensor is controversial. Here, we report that purified human TRPA1 (hTRPA1) with and without its N-terminal ankyrin repeat domain responded with pressure-dependent single-channel current activity when reconstituted into artificial lipid bilayers. The hTRPA1 activity was abolished by the thiol reducing agent TCEP. Thus, depending on its redox state, hTRPA1 is an inherent mechanosensitive ion channel gated by force-from-lipids. [ABSTRACT FROM AUTHOR]

• Calcium causes structural changes of purified human TRPA1 as measured by FRET. • Calcium evokes electrical activity of purified human TRPA1 in artificial bilayers. • The TRPA1 N-terminal ankyrin repeat domain is not required for the effects of calcium. • Calmodulin is not required for the effects of calcium on the purified TRPA1 proteins. Extracellular influx of calcium or release of calcium from intracellular stores have been shown to activate mammalian TRPA1 as well as to sensitize and desensitize TRPA1 electrophilic activation. Calcium binding sites on both intracellular N- and C-termini have been proposed. Here, we demonstrate based on Förster resonance energy transfer (FRET) and bilayer patch-clamp studies, a direct calmodulin-independent action of calcium on the purified human TRPA1 (hTRPA1), causing structural changes and activation without immediate subsequent desensitization of hTRPA1 with and without its N-terminal ankyrin repeat domain (N-ARD). Thus, calcium alone activates hTRPA1 by a direct interaction with binding sites outside the N-ARD. [ABSTRACT FROM AUTHOR]

Comments on a study which described the endogenous ligand for the vanilloid receptor present on primary sensory nerves and presented a molecular target for anandamide. Mechanism of action of anandamide; Formation of anandamides; Vasodilator action of anandamides.

Temperature sensors are crucial for animals to optimize living conditions. The temperature response of the ion channel transient receptor potential A1 (TRPA1) is intriguing; some orthologs have been reported to be activated by cold and others by heat, but the molecular mechanisms responsible for its activation remain elusive. Single-channel electrophysiological recordings of heterologously expressed and purified Anopheles gambiae TRPA1 (AgTRPA1), with and without the N-terminal ankyrin repeat domain, demonstrate that both proteins are functional because they responded to the electrophilic compounds allyl isothiocyanate and cinnamaldehyde as well as heat. The proteins' similar intrinsic fluorescence properties and corresponding quenching when activated by allyl isothiocyanate or heat suggest lipid bilayer-independent conformational changes outside the N-terminal domain. The results show that Ag- TRPA1 is an inherent thermo- and chemoreceptor, and analogous to what has been reported for the human TRPA1 ortholog, the N-terminal domain may tune the response but is not required for the activation by these stimuli. [ABSTRACT FROM AUTHOR]

Abstract: A series of natural and synthetic piperine amides were evaluated for activity on the human TRPV1 expressed in HEK293 cells. The agonistic effect of piperine amides was mainly dependent on the length of the carbon chain. Structural changes of double bonds and stereochemistry in the aliphatic chain of these compounds did not change their potency or efficacy, indicating that increased rigidity or planarity of the piperine structure does not affect the activity. The opening of the methylenedioxy ring or changes in the heterocyclic ring of the piperine molecule reduced or abolished activity. Furthermore, inactive compounds did not display functional antagonistic activity. [Copyright &y& Elsevier]

The endogenous C18 N-acylethanolamines (NAEs) N-linolenoylethanolamine (18:3 NAE), N-linoleoylethanolamine (18:2 NAE), N-oleoylethanolamine (18:1 NAE), and N-stearoylethanolamine (18:0 NAE) are structurally related to the endocannabinoid anandamide (20:4 NAE), but these lipids are poor ligands at cannabinoid CB1 receptors. Anandamide is also an activator of the transient receptor potential (TRP) vanilloid 1 (TRPV1) on primary sensory neurons. Here we show that C18 NAEs are present in rat sensory ganglia and vascular tissue. With the exception of 18:3 NAE in rat sensory ganglia, the levels of C18 NAEs are equal to or substantially exceed those of anandamide. At submicromolar concentrations, 18:3 NAE, 18:2 NAE, and 18:1 NAE, but not 18:0 NAE and oleic acid, activate native rTRPV1 on perivascular sensory nerves. 18:1 NAE does not activate these nerves in TRPV1 gene knock-out mice. Only the unsaturated C18 NAEs elicit whole cell currents and fluorometric calcium responses in HEK293 cells expressing hTRPV1. Molecular modeling revealed a low energy cluster of U-shaped unsaturated NAE conformers, sharing several pharmacophoric elements with capsaicin. Furthermore, one of the two major low energy conformational families of anandamide also overlaps with the cannabinoid CB1 receptor ligand HU210, which is in line with anandamide being a dual activator of TRPV1 and the cannabinoid CB1 receptor. This study shows that several endogenous non-cannabinoid NAEs, many of which are more abundant than anandamide in rat tissues, activate TRPV1 and thus may play a role as endogenous TRPV1 modulators. [ABSTRACT FROM AUTHOR]

Acetaminophen (paracetamol) is a popular domestic analgesic and antipyretic agent with a weak anti-inflammatory action and a low incidence of adverse effects as compared with aspirin and other non-steroidal anti-inflammatory drugs. Here we show that acetaminophen, following deacetylation to its primary amine, is conjugated with arachidonic acid in the brain and the spinal cord to form the potent TRPV1 agonist N-arachidonoylphenolamine (AM404). This conjugation is absent in mice lacking the enzyme fatty acid amide hydrolase. AM404 also inhibits purified cyclooxygenase (COX)-1 and COX-2 and prostaglandin synthesis in lipopolysaccharide-stimulated RAW264.7 macrophages. This novel metabolite of acetaminophen also acts on the endogenous cannabinoid system, which, together with TRPV1 and COX, is present in the pain and thermoregulatory pathways. These findings identify fatty acid conjugation as a novel pathway for drug metabolism and provide a molecular mechanism for the occurrence of the analgesic N-acylphenolamine AM404 in the nervous system following treatment with acetaminophen. [ABSTRACT FROM AUTHOR]

Paracetamol, one of the most widely used pain-relieving drugs, is deacetylated to 4-aminophenol (4-AP) that undergoes fatty acid amide hydrolase (FAAH)-dependent biotransformation into N -arachidonoylphenolamine (AM404), which mediates TRPV1-dependent antinociception in the brain of rodents. However, paracetamol is also converted to the liver-toxic metabolite N -acetyl- p -benzoquinone imine already at therapeutic doses, urging for safer paracetamol analogues. Primary amine analogues with chemical structures similar to paracetamol were evaluated for their propensity to undergo FAAH-dependent N -arachidonoyl conjugation into TRPV1 activators both in vitro and in vivo in rodents. The antinociceptive and antipyretic activity of paracetamol and primary amine analogues was examined with regard to FAAH and TRPV1 as well as if these analogues produced acute liver toxicity. 5-Amino-2-methoxyphenol (2) and 5-aminoindazole (3) displayed efficient target protein interactions with a dose-dependent antinociceptive effect in the mice formalin test, which in the second phase was dependent on FAAH and TRPV1. No hepatotoxicity of the FAAH substrates transformed into TRPV1 activators was observed. While paracetamol attenuates pyrexia via inhibition of brain cyclooxygenase, its antinociceptive FAAH substrate 4-AP was not antipyretic, suggesting separate mechanisms for the antipyretic and antinociceptive effect of paracetamol. Furthermore, compound 3 reduced fever without a brain cyclooxygenase inhibitory action. The data support our view that analgesics and antipyretics without liver toxicity can be derived from paracetamol. Thus, research into the molecular actions of paracetamol could pave the way for the discovery of analgesics and antipyretics with a better benefit-to-risk ratio. Image 1 • Paracetamol is a painkiller acting in the central nervous system via FAAH and TRPV1. • Analogues of paracetamol were evaluated for interaction with FAAH and TRPV1. • Analogues of paracetamol induced FAAH- and TRPV1-dependent antinociception in mice. • Antinociceptive paracetamol analogues without liver toxicity can be designed. • Antinociceptive paracetamol analogues without antipyretic properties can be designed. [ABSTRACT FROM AUTHOR]