Ion channel mechanisms of rat tail artery contraction-relaxation by menthol involving, respectively, TRPM8 activation and L-type Ca2+ channel inhibition

The activity of the cold- and menthol-activated transient receptor potential melastatin 8 (TRPM8) channels diminishes over time in the presence of extracellular Ca(2+), a phenomenon referred to as desensitization or adaptation. Here we show that activation of TRPM8 by cold or menthol evokes a decrease in cellular phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] levels. The decrease in PtdIns(4,5)P(2) levels was accompanied by increased inositol 1,4,5 trisphosphate (InsP(3)) production, and was inhibited by loading the cells with the Ca(2+) chelator BAPTA-AM, showing that it was the consequence of the activation of phospholipase C (PLC) by increased intracellular Ca(2+) concentrations. PtdIns(4,5)P(2) hydrolysis showed excellent temporal correlation with current desensitization in simultaneous patch clamp and fluorescence-based PtdIns(4,5)P(2) level measurements. Intracellular dialysis of PtdIns(4,5)P(2) inhibited desensitization both in native neuronal and recombinant TRPM8 channels. PtdIns(4)P, the precursor of PtdIns(4,5)P(2), did not inhibit desensitization, consistent with its minimal effect in excised patches. Omission of MgATP from the intracellular solution accelerated desensitization, and MgATP reactivated TRPM8 channels in excised patches in a phosphatidylinositol 4-kinase (PI4K)-dependent manner. PLC-independent depletion of PtdIns(4,5)P(2) using a voltage-sensitive phosphatase (ci-VSP) inhibited TRPM8 currents, and omission of ATP from the intracellular solution inhibited recovery from this inhibition. Inhibitors of PKC had no effect on the kinetics of desensitization. We conclude that Ca(2+) influx through TRPM8 activates a Ca(2+)-sensitive PLC isoform, and the resulting depletion of PtdIns(4,5)P(2) plays a major role in desensitization of both cold and menthol responses.

LETTERS TO THE EDITORReply to “Letter to the editor: ‘Is menthol- or icilin-induced vasodilation mediated by the activation of TRPM8?'”Christopher Johnson and Alexander ZholosChristopher Johnson and Alexander ZholosPublished Online:01 Aug 2009https://doi.org/10.1152/ajpheart.00506.2009MoreSectionsPDF (30 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat reply: The letter from Dr. Ma (3) highlights the problems that are inevitable in filling in the gaps of our knowledge of the properties of heterologously expressed transient receptor potential (TRP) channels, their expression profiles, and the functional roles in tissues and whole organisms. Not only are multiple TRP isoforms commonly expressed in native cells, but also they often do not fulfill our expectations from studies of exogenously expressed channels in cultured cells (7).Although TRPA1 has only a very limited sequence homology with TRP melastatin 8 (TRPM8), both channels can be activated by icilin and menthol. It is thus difficult for pharmacological approaches to be conclusive. However, we feel strongly that our combination of methods and the absence of evidence that TRPA1 channels are expressed on vascular myocytes (2) justify our conclusions that TRPM8 channels may, indeed, contribute to vascular tone in the vessels examined in our study with the use of menthol and icilin. The experimental approaches suggested by Ma (3) are all extremely valid. However, nonpharmacological approaches also have their own inherent problems. There are several notable examples within the field of TRP channel study where molecular interventions, such as the deletion of the gene for specific channels, have not had the effects predicted (6, 7). These studies should be done but may not be conclusive in isolation. Thus future and imminent work in the field of vascular TRPM8 and TRPA1 channels should use a combination of all the approaches available, including molecular approaches outlined by Ma (3), but should also have a strong element of functional physiology/pharmacology, using the best ligands available at the time, which are constantly being reviewed (1, 4). Indeed, controversy surrounding the roles of TRPM8 and TRPA1 proteins in cold sensation, and especially conflicting reports on the role of TRPA1 in sensory neurons (5), raises awareness that the answer to the above questions may not be simple.REFERENCES1 Bödding M, Wissenbach U, Flockerzi V. Characterisation of TRPM8 as a pharmacophore receptor. Cell Calcium 42: 618–628, 2007.Crossref | PubMed | ISI | Google Scholar2 Earley S, Gonzales AL, Crnich R. Endothelium-dependent cerebral artery dilation mediated by TRPA1 and Ca2+-activated K+ Channels. Circ Res 104: 987–994, 2009.Crossref | PubMed | ISI | Google Scholar3 Ma S. Letter to the editor: “Is menthol- or icilin-induced vasodilation mediated by the activation of TRPM8?” Am J Physiol Heart Circ Physiol. doi:10.1152/ajpheart.00460.2009.Link | ISI | Google Scholar4 Ma S, G G, Ak VE, Jf D, H H. Menthol derivative WS-12 selectively activates transient receptor potential melastatin-8 (TRPM8) ion channels. Pak J Pharm Sci 21: 370–378, 2008.PubMed | ISI | Google Scholar5 McKemy DD. How cold is it? TRPM8 and TRPA1 in the molecular logic of cold sensation. Mol Pain 1: 16, 2005.Crossref | PubMed | ISI | Google Scholar6 Nilius B, Owsianik G, Voets T, Peters JA. Transient receptor potential cation channels in disease. Physiol Rev 87: 165–217, 2007.Link | ISI | Google Scholar7 Venkatachalam K, Montell C. TRP Channels. Annu Rev Biochem 76: 387–417, 2007.Crossref | PubMed | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: C. Johnson, Centre for Vision and Vascular Science, School of Medicine, Medical Biology Ctr., Queen's Univ. Belfast, 97 Lisburn Rd., Belfast BT9 7BL, UK (e-mail: [email protected]) Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 297Issue 2August 2009Pages H888-H888 Copyright & PermissionsCopyright © 2009 the American Physiological Societyhttps://doi.org/10.1152/ajpheart.00506.2009History Published online 1 August 2009 Published in print 1 August 2009 Metrics

The transient receptor potential-melastatin 8 (TRPM8) is a non-selective Ca2+-permeable channel, activated by cold, membrane depolarization, and different cooling compounds. TRPM8 expression has been found in gut mucosal, submucosal, and muscular nerve endings. Although TRPM8 plays a role in pathological conditions, being involved in visceral pain and inflammation, the physiological functions in the digestive system remain unclear as yet. The aims of the present study were: (i) to verify the TRPM8 expression in human distal colon; (ii) to examine the effects of TRPM8 activation on colonic contractility; (iii) to characterize the mechanism of action. Reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting were used to analyze TRPM8 expression. The responses of human colon circular strips to different TRPM8 agonists [1-[Dialkyl-phosphinoyl]-alkane (DAPA) 2–5, 1-[Diisopropyl-phosphinoyl]-alkane (DIPA) 1–7, DIPA 1–8, DIPA 1–9, DIPA 1–10, and DIPA 1–12) were recorded using a vertical organ bath. The biomolecular analysis revealed gene and protein expression of TRPM8 in both mucosal and smooth muscle layers. All the agonists tested, except-DIPA 1–12, produced a concentration-dependent decrease in spontaneous contraction amplitude. The effect was significantly antagonized by 5-benzyloxytryptamine, a TRPM8 antagonist. The DIPA 1–8 agonist resulted in the most efficacious and potent activation among the tested molecules. The DIPA 1–8 effects were not affected by tetrodotoxin, a neural blocker, but they were significantly reduced by tetraethylammonium chloride, a non-selective blocker of K+ channels. Moreover, iberiotoxin, a blocker of the large-conductance Ca2+-dependent K+-channels, but not apamin, a blocker of small-conductance Ca2+-dependent K+ channels, significantly reduced the inhibitory DIPA 1–8 actions. The results of the present study demonstrated that TRPM8 receptors are also expressed in human distal colon in healthy conditions and that ligand-dependent TRPM8 activation is able to reduce the colonic spontaneous motility, probably by the opening of the large-conductance Ca2+-dependent K+-channels.

Transient Receptor Potential Melastatin-8 (TRPM8), a recently identified member of the transient receptor potential (TRP) family of ion channels, is activated by mild cooling and by chemical compounds such as the supercooling agent, icilin. Since cooling, possibly involving TRPM8 stimulation, diminishes injury-induced peripheral inflammation, we hypothesized that TRPM8 activation may also attenuate systemic inflammation. We thus studied the involvement of TRPM8 in regulating colonic inflammation using two mouse models of chemically induced colitis. TRPM8 expression, localized immunohistochemically in transgenic TRPM8(GFP) mouse colon, was up-regulated in both human- and murine-inflamed colon samples, as measured by real-time PCR. Wild-type mice (but not TRPM8-nulls) treated systemically with the TRPM8 agonist, icilin showed an attenuation of chemically induced colitis, as reflected by a decrease in macroscopic and microscopic damage scores, bowel thickness, and myeloperoxidase activity compared with untreated animals. Furthermore, icilin treatment reduced the 2,4,6-trinitrobenzenesulfonic acid-induced increase in levels of inflammatory cytokines and chemokines in the colon. In comparison with wild-type mice, Dextran Sodium Sulfate (DSS)-treated TRPM8 knockout mice showed elevated colonic levels of the inflammatory neuropeptide calcitonin-gene-related peptide, although inflammatory indices were equivalent for both groups. Further, TRPM8 activation by icilin blocked capsaicin-triggered calcitonin-gene-related peptide release from colon tissue ex vivo and blocked capsaicin-triggered calcium signaling in Transient Receptor Potential Vaniloid-1 (TRPV1) and TRPM8 transfected HEK cells. Our data document an anti-inflammatory role for TRPM8 activation, in part due to an inhibiton of neuropeptide release, pointing to a novel therapeutic target for colitis and other inflammatory diseases.

Pulmonary hypertension (PH) is characterized by profound vascular remodeling and alterations in Ca2+ homeostasis in pulmonary arterial smooth muscle cells (PASMCs). Members of multiple transient receptor potential subfamilies (TRPC, TRPV, and TRPM) have been identified in pulmonary vascular tissue. Our previous studies showed that the expression and functions of the store‐operated TRPC1, receptor‐operated TRPC6, and the mechanosensitive TRPV4 channels are augmented in PASMCs during PH, and their upregulation contribute to PH development. In contrast, TRPM8 is down‐regulated in PASMCs of rats PH models, and activation of TRPM8 with agonists causes relaxation of pulmonary arteries (PAs)(Liu et al., Cell Physiol Biochem 2013, 31:892–904). However, the mechanism of TRPM8‐induced PA relaxation has not been determined. In this study, we examined the possible interactions of TRPM8 activation and store‐operated Ca2+ entry (SOCE) in PAs and PASMCs of normoxic and chronic hypoxic pulmonary hypertensive (CHPH) rats. We found that TRPM8 expression was down‐regulated in PAs and the TRPM8‐mediated cation entry was reduced significantly in the PASMCs of rats after 3 weeks of hypoxia (10% O2) exposure. Activation of TRPM8 with icilin (0.1–100 μM) caused concentration‐dependent relaxation of cyclopiazonic acid (CPA) and ET‐1 pre‐contracted endothelium‐denuded PAs in the presence of nifedipine. The vasorelaxant effect of icilin was abolished in the presence of the SOCE antagonist Gd3+ at submicromolar concentration. Icilin suppressed the CPA‐induced cation entry in PASMCs determined by the Mn2+ quenching technique and by Ca2+ transient measurement. The inhibitory effect of icilin on SOCE‐induced PA relaxation and Ca2+ entry were abolished by the TRPM8 antagonist AMTB, indicating that the effect was mediated specifically by TRPM8 channels. Moreover, TRPM8‐mediated inhibitory effects on CPA‐induced contraction in PAs and SOCE in PASMCs were significantly augmented in CHPH rats, probably related to the enhanced SOCE caused by PH. These results demonstrate for the first time that TRPM8 activation can cause relaxation of PA through inhibition of SOCE. Since SOCE plays many important roles in pulmonary vascular functions and is crucial for the vascular remodeling and the enhanced vasoconstriction in PH, the downregulation of TRPM8 expression and activity in PASMCs during PH may minimized the TRPM8‐dependent inhibition of SOCE, and allow unimpeded SOCE activity for PH development.Support or Funding InformationSupported by grants NSFC31571179, NSFC31371165, NSF of Fujian Province 2015J01313, and Fujian Province Hundred Experts Award.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Although the transient receptor potential melastatin 8 (TRPM8) cold receptor is highly expressed in prostate cancer (PCa) and constitutes a promising diagnostic and prognostic indicator, the natural agonists of this channel in the prostate, as well as its physiological and pathological functions, remain unknown. In this study, we identified the well-known PCa marker, prostate-specific antigen (PSA), as a physiological TRPM8 agonist. Electrophysiological and Ca(2+) imaging studies demonstrated that PSA activated TRPM8-mediated current by the bradykinin 2 receptor signaling pathway. Further investigation of this mechanism by cell-surface biotinylation revealed that the increase in TRPM8 current induced by PSA was due to an increase in the number of functional TRPM8 channels on the plasma membrane. Importantly, wound-healing and migration assays revealed that TRPM8 activation by PSA reduced motility of the PC3 PCa cell line, suggesting that plasma membrane TRPM8 has a protective role in PCa progression. Consequently, PSA was identified as a natural TRPM8 agonist in the prostate and we propose a putative physiological role for both of these proteins in carcinogenesis, making this pathway a potentially important target for anticancer agent development.

Objective To observe the expression of transient receptor potential melastatin 8 (TRPM8) in prostate cancer DU145 cells and the effect of TRPM8 agonist on cell proliferation and migration. Methods The expression levels of TRPM8 and transient receptor potential ankyrin 1 (TRPA1) in prostate cancer tissue, adjacent prostate tissues and DU145 cells were detected by reverse transcriptase-polymerase chain reaction (RT-PCR), immunohistochemistry and Western blotting. The effect of TRPM8 agonists menthol on proliferation and motility of DU145 cells were examined by MTT assay and scratch motility assay, and the effect of TRPM8 on cell cycle and apoptosis of DU145 cells was tested by flow cytometry detection. Results TRPM8 was significantly up-regulated, and no TRPA1 expression was detectable in prostate cancer DU145 cell. After treatment with 25, 50, 75 and 100 μmol/L menthol, DU145 relative cell number was significantly less than in the blank group [(90.01±8.52)% vs. (83.24±7.21)% vs. (71.23±6.45)% vs. (53.12±5.22)% vs. (100.00±3.26)%] (P<0.05). After treatment with 100 μmol/L menthol for 24, 48 and 72 h, the proportion of G0/G1 phase DU145 cells was significantly higher than the untreated [(60.98±7.21)% vs. (76.49±8.12)% vs. (72.03±7.65)% vs. (50.26±6.41)%] (P<0.05). After treatment with 100 μmol/L TRPM8 agonist for 24 h and 48 h, motility rate of DU145 cells was significantly lower than in the blank control group [(58.59±5.24)% vs. (48.09±4.23)% vs. (100.00±3.54)%](P<0.05). Conclusion The TRPM8 was over-expressed in prostate cancer DU145 cells. TRPM8 agonist can arrest cell cycle in G0/G1 phase, and inhibit proliferation and motility of tumor cells. Key words: Transient receptor potential melastatin 8; Prostate cancer; Proliferation; Motility

Epilepsy is a relatively common condition, but more than 30% of patients have refractory epilepsy that is inadequately controlled by or is resistant to multiple drug treatments. Thus, new antiepileptic drugs based on newly identified mechanisms are required. A previous report revealed the suppressive effects of transient receptor potential melastatin 8 (TRPM8) activation on penicillin G-induced epileptiform discharges (EDs). However, it is unclear whether TRPM8 agonists suppress epileptic seizures or affect EDs or epileptic seizures in TRPM8 knockout (TRPM8KO) mice. We investigated the effects of TRPM8 agonist and lack of TRPM8 channels on EDs and epileptic seizures. Mice were injected with TRPM8 agonist 90 min after or 30 min before epilepsy-inducer injection, and electrocorticograms (ECoGs) were recorded under anesthesia, while behavior was monitored when awake. TRPM8 agonist suppressed EDs and epileptic seizures in wildtype (WT) mice, but not in TRPM8KO mice. In addition, TRPM8KO mice had a shorter firing latency of EDs, and EDs and epileptic seizures were deteriorated by the epilepsy inducer compared with those in WT mice, with the EDs being more easily propagated to the contralateral side. These findings suggest that TRPM8 activation in epileptic regions has anti-epileptic effects.

Transient receptor potential melastatin-8 (TRPM8) is an ion channel expressed extensively in sensory nerves, human prostate and overexpressed in a variety of cancers including prostate, breast, lung, colon and skin melanomas. It is activated by innoxious cooling and chemical stimuli. TRPM8 activation by cooling or chemical agonists is reported to induce profound analgesia in neuropathic pain conditions. Known TRPM8 agonists like menthol and icilin cross-activate other thermo-TRP channels like TRPV3 and TRPA1 and mutually inhibit TRPM8. This limits the usefulness of menthol and icilin as TRPM8 ligands. Consequently, the identification of selective and potent ligands for TRPM8 is of high relevance both in basic research and for therapeutic applications. In the present investigation, a group of menthol derivates was characterized. These ligands are selective and potent agonists of TRPM8. Interestingly they do not activate other thermo-TRPs like TRPA1, TRPV1, TRPV2, TRPV3 and TRPV4. These ion channels are also nociceptors and target of many inflammatory mediators. Investigations were performed in a recombinant system: Xenopus oocytes microinjected with cRNA of gene of interest were superfused with the test substances after initial responses of known standard agonists. Evoked currents were measured by two-electrode voltage clamp technique. The newly characterized ligands possess an up to six-fold higher potency (EC50 in low microM) and an up to two-fold increase in efficacy compared to the parent compound menthol. In addition, it is found that chemical derivatives of menthol like CPS-368, CPS-369, CPS-125, WS-5 and WS-12 are the most selective ligands for TRPM8. The enhanced activity and selectivity seems to be conferred by hexacyclic ring structure present in all ligands as substances like WS-23 which lack this functional group activate TRPM8 with much lower potency (EC50 in mM) and those with pentacyclcic ring structure (furanone compounds) are totally inactive. The new substances activate TRPM8 with a higher potency, efficacy and specificity than menthol and will thus be of importance for the development of pharmacological agents suitable for treatment and diagnosis of certain cancers and as analgesics. STATEMENT OF NOVELTY: The new compounds have an unmatched specificity for TRPM8 ion channels with additional display of high potency and efficacy. Thus these substances are better pharmacological tools for TRPM8 characterization then known compounds and it is suggested that these menthol-derivates may serve as model substances for the development of TRPM8 ligands.

Prospects for prostate cancer imaging and therapy using high-affinity TRPM8 activators

Background: Cold air is a major environmental factor that exacerbates bronchial asthma. Transient receptor potential melastatin family member 8 (TRPM8) receptor is a cold- and menthol-sensing cation channel expressed in sensory neurons as well as bronchial epithelial cells. Objectives: We sought to explore the role of TRPM8 receptor expressed in bronchial epithelial cells in airway inflammation. Methods: Human airway epithelial cell line, BEAS-2B, was treated with menthol, TRPM8 antagonist (BCTC, N-(4-tert-butylphenyl)-4-(3-chloropyridin-2-yl) piperazine-1-carboxamide) and dexamethasone in dose- and time- dependent manner. The mRNA of TRPM8 and proinflammatory cytokines such as IL-4, 6, 8, 13, 25, 33 was determined by real-time quantitative PCR. The expression of TRPM8 in bronchial epithelial cells was determined by western blotting and immunofluorescence. ELISA of TRPM8 performed using the induced sputum of asthmatics and normal controls. Results: TRPM8 protein expression was significantly increased in patients with asthma compared with healthy controls using ELISA of sputum supernatants. TRPM8 receptor was expressed primarily in bronchial epithelial cells at both mRNA and protein levels with statistical significances. Activating TRPM8 receptors by menthol was coupled with enhanced expression of the inflammatory cytokines of some IL and treatment with BCTC and dexamethasone attenuated the expression of the inflammatory cytokines. Conclusions: Activation of TRPM8 receptor of bronchial epithelial cells induces airway inflammatory cytokines, suggesting the TRPM8 receptor may involve in cold induced asthma exacerbations.

The development of novel anti-seizure drugs targeting novel mechanisms is crucial, especially for patients with intractable epilepsy. Previous studies using focal onset seizure rodent models have demonstrated that Icilin and WS-3, agonists of the transient receptor potential melastatin 8 (TRPM8) channel, suppress drug-induce epileptiform discharges (EDs) and seizures (ESs). In contrast, TRPM8 deficiency exacerbates EDs and ESs. This study investigated the mechanism underlying the anti-seizure effects of the TRPM8 agonist, WS-3, using a focal onset seizure mouse model. Mice were injected with WS-3 either before or after administering the seizure inducer, penicillin G potassium. EDs, ESs, and glutamate levels were subsequently evaluated. In wild-type (WT) mice, WS-3 injected after the seizure inducer reduced glutamate levels and ED power by 44% and 60%, respectively, with a positive correlation between WS-3 efficacy and these parameters. WS-3 injection before seizure induction suppressed the increase in glutamate levels and the development of ED and ES, with positive correlations observed among the three parameters. Conversely, TRPM8-knockout mice showed no anti-seizure effects from WS-3. TRPM8 deficiency led to a further increase in the glutamate levels, ED power, and ES severity after the seizure inducer injection. Additionally, TRPM8-deficient mice experienced EDs with fewer glutamate exposures and shortened latency to ED development following seizure induction. These findings suggest that TRPM8 agonists suppress the development of EDs and ESs by reduction of extracellular glutamate levels, indicating that TRPM8 channels may represent a promising treatment option for epilepsy.

The transient receptor potential melastatin 8 (TRPM8) is well-known for its role in cold sensation in somatosensory neurons. TRPM8 was first identified as a prostate epithelial cell-specific gene, however, its role was unclear due to the absence of its endogenous agonist. We are the first to discover the novel role of TRPM8 as a rapid testosterone receptor. The TRPM8 mRNA is highly expressed in prostate cancer (PC) and is lost during the transition to androgen-independent prostate cancer (AIPC). Although emerging studies have shed light regarding androgen regulation of TRPM8 mRNA expression, we found that the addition of androgen receptor (AR) on the lipid bilayers inhibited testosterone-TRPM8 induced Ca2+ uptake. Additionally, our IHC revealed increased internalization of the TRPM8 protein in high-grade PC and that TRPM8 protein was targeted for proteasomal degradation in PC. We observed that inhibition of AR and UBA1 promoted the stabilization of TRPM8 on the plasma membrane, triggering Ca2+-induced cytotoxicity and apoptosis in both androgen dependent and androgen independent PC cells. Furthermore, in line with previous studies, we showed that testosterone-induced TRPM8 activation on the planar lipid bilayers also required phosphatidylinositol 4,5-bisphosphate (PIP2). Loss of PTEN is associated with tumor recurrence and the transition to AIPC. Thus, PTEN loss mediated PIP2 deficiency may be an important mechanism of TRPM8 desensitization in PC. Therefore, we propose that the rescue of TRPM8 activity on the plasma membrane combined with AR targeting may be an effective therapy for PC. Citation Format: Kiran Velpula, Katherine Shishido, Susovon Bayen, Swapna Asuthkar. TRPM8 ion channel role in prostate cancer: Actions as a rapid testosterone signaling receptor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5670.

Increasing basal energy expenditure via uncoupling protein 1 (UCP1)-dependent non-shivering thermogenesis is an attractive therapeutic strategy for treatment of obesity. Transient receptor potential melastatin 8 (TRPM8) channel activation by cold and cold mimetics induces UCP1 transcription and prevents obesity in animals, but the clinical relevance of this relationship remains incompletely understood. A review of TRPM8 channel agonism for treatment of obesity focusing on menthol was undertaken. Adipocyte TRPM8 activation results in Ca2+ influx and protein kinase A (PKA) activation, which induces mitochondrial elongation, mitochondrial localization to lipid droplets, lipolysis, β-oxidation, and UCP1 expression. Ca2+-induced mitochondrial reactive oxygen species activate UCP1. In animals, TRPM8 agonism increases basal metabolic rate, non-shivering thermogenesis, oxygen consumption, exercise endurance, and fatty acid oxidation and decreases abdominal fat percentage. Menthol prevents high-fat diet-induced obesity, glucose intolerance, insulin resistance, and liver triacylglycerol accumulation. Hypothalamic TRPM8 activation releases glucagon, which activates PKA and promotes catabolism. TRPM8 polymorphisms are associated with obesity. In humans, oral menthol and other TRPM8 agonists have little effect. However, topical menthol appears to increase core body temperature and metabolic rate. A randomized clinical control trial of topical menthol in obese patients is warranted.

Transient receptor potential melastatin 8 (TRPM8) is a member of the TRP family, and is activated at temperatures below 22°C, or by cooling compounds such as menthol. In this study, it was found that a new role of TRPM8 activation on prostaglandin E2 (PGE2), an inflammatory cytokine and dendritogenesis stimulator of normal human melanocytes. Normal human keratinocytes were pretreated with menthol or incubated at 22°C for TRPM8 activation before ultraviolet (UV)-B irradiation. To examine the specificity between TRPM8 activation and PGE2 release, we inhibited TRPM8 with the antagonist (capsazepine), or introduced TRPM8 siRNA for a gene silencing experiment. UV-B irradiation significantly induced PGE2 release in normal human keratinocytes. Interestingly, activation of TRPM8 at 22°C or with menthol inhibited UV-B-induced PGE2 release. The effect of the TRPM8 agonist was completely blocked by pretreatment with the TRPM8 antagonist, capsazepine. When TRPM8 expression was suppressed by siRNA, UV-B irradiation still upregulated PGE2 in keratinocytes, but pretreatment of menthol or low temperature did not inhibit UV-B-induced PGE2. In conclusion, the activation of TRPM8 inhibits UV-B-induced PGE2 production in keratinocytes, and the activation of TRPM8 may reduce inflammatory responses in skin.