Synergistic stabilization of a menthol Pickering emulsion by zein nanoparticles and starch nanocrystals: Preparation, structural characterization, and functional properties.

A Pickering emulsion was synergistically stabilised with zein nanoparticles (ZNPs) and starch nanocrystals (SNCs) to prepare it for menthol loading. After response surface optimisation of the emulsion preparation conditions, a Pickering emulsion prepared with a ZNPs:SNCs ratio of 1:1, a particle concentration of 2 wt% and a water:oil ratio of 1:1 provided the highest menthol encapsulation rate of the emulsions tested (83%) with good storage stability within 30 days. We examined the bilayer interface structure of the emulsion by optical microscopy, scanning electron microscopy, and confocal laser scanning microscopy. The results of simulated digestion experiments showed that the release rate of free fatty acid was 75.06 ± 1.23%, which ensured bioavailability. At the same time, the emulsions facilitated the slow release of menthol. Bacteriostatic studies revealed that the Pickering emulsion had a protective effect on menthol, with the most significant inhibitory effects on Escherichia coli and Staphylococcus aureus under the same conditions. Overall, this study proposes a novel approach for the application and development of l-menthol by combining it with Pickering emulsion.

KCNQ1 is an essential mediator of the sex-dependent perception of moderate cold temperatures.

Low temperatures and cooling agents like menthol induce cold sensation by activating the peripheral cold receptors TRPM8 and TRPA1, cation channels belonging to the TRP channel family, while the reduction of potassium currents provides an additional and/or synergistic mechanism of cold sensation. Despite extensive studies over the past decades to identify the molecular receptors that mediate thermosensation, cold sensation is still not fully understood and many cold-sensitive peripheral neurons do not express the well-established cold sensor TRPM8. We found that the voltage-gated potassium channel KCNQ1 (Kv7.1), which is defective in cardiac LQT1 syndrome, is, in addition to its known function in the heart, a highly relevant and sex-specific sensor of moderately cold temperatures. We found that KCNQ1 is expressed in skin and dorsal root ganglion neurons, is sensitive to menthol and cooling agents, and is highly sensitive to moderately cold temperatures, in a temperature range at which TRPM8 is not thermosensitive. C-fiber recordings from KCNQ1-/- mice displayed altered action potential firing properties. Strikingly, only male KCNQ1-/- mice showed substantial deficits in cold avoidance at moderately cold temperatures, with a strength of the phenotype similar to that observed in TRPM8-/- animals. While sex-dependent differences in thermal sensitivity have been well documented in humans and mice, KCNQ1 is the first gene reported to play a role in sex-specific temperature sensation. Moreover, we propose that KCNQ1, together with TRPM8, is a key instrumentalist that orchestrates the range and intensity of cold sensation.

Menthol-Modified Quercetin Liposomes with Brain-Targeting Function for the Treatment of Senescent Alzheimer's Disease.

Oxidative stress and neuroinflammation in the aging brain are correlated with the development of neurodegenerative diseases, such as Alzheimer's disease (AD). The blood-brain barrier (BBB) poses a significant challenge to the effective delivery of therapeutics for AD. Prior research has demonstrated that menthol (Men) can augment the permeability of the BBB. Consequently, in the current study, we modified Men on the surface of liposomes to construct menthol-modified quercetin liposomes (Men-Qu-Lips), designed to cross the BBB and enhance quercetin (Qu) concentration in the brain for improved therapeutic efficacy. The experimental findings indicate that Men-Qu-Lips exhibited good encapsulation efficiency and stability, successfully crossed the BBB, improved oxidative stress and neuroinflammation in the brains of aged mice, protected neurons, and enhanced their learning and memory abilities.

The Effect of Menthol Mouth Rinsing and Fluid Temperature on Male Cycling Performance in Thermoneutral Conditions.

PURPOSE: The purpose of this study was to determine the effect of a menthol (MEN) mouth rinse (MR) on cycling time trial (TT) performance in thermoneutral conditions and to explore the impact of fluid temperature (cold water [CW] or thermoneutral water [TNW]) on MEN's effect on performance. METHODS: Twelve trained male cyclists (VO2 peak, 61.4 ± 12.1 mL/kg/min) completed a cycling TT in thermoneutral conditions (21 ± 0.2 °C, 40 ± 0.6% relative humidity) with four different mouth rinses: (1) MEN + CW; (2) MEN + TNW; (3) CW; and (4) TNW. The time to complete the TT and the power output (W) were recorded. The ratings of perceived exertion (RPE, Borg 6-20), thermal sensation (TS), and thermal comfort (TC) were recorded prior to and throughout the TT. The core body temperature (Tc) and heart rate (HR) were recorded throughout. RESULTS: The TT duration was not significantly different between trials (MEN + TNW: 38:11 ± 12:48, MEN + CW: 37:21 ± 13:00, CW: 38:12 ± 13:54, TNW: 36:06 ± 14:12 mins:secs, p < 0.05). The mean trial power output did not significantly differ between conditions (>0.05). The Tc, HR, RPE, TS, and TC were not significantly different between trials (p > 0.05). CONCLUSION: The results suggest that a MEN MR with either CW or TNW does not significantly improve cycling TT performance in trained male cyclists compared to a CW or TNW MR in thermoneutral conditions.

[The role of ROS/JNK/caspase 3 axis in apoptosis induction by menthol-favored electronic cigarette liquid in human periodontal ligament stem cells].

PURPOSE: To explore the cytotoxic effect of a menthol-favored E-liquid on human periodontal ligament stem cells (hPDLSCs), as well as the underlying mechanism of electronic cigarette (E-cig)-induced cell apoptosis. METHODS: PDLSCs were isolated and cultured from periodontal ligament tissues of healthy premolars extracted for orthodontic reasons. Cells in passage 3 were used to detect the surface markers of stem cells by flow cytometry. Then the cells were exposed to different doses of menthol-favored E-liquid (at 59 mg/L nicotine concentration) in the culture median (the final nicotine concentrations were 0.1 µg/mL, 1.0 µg/mL, 10 µg/mL, 50 µg/mL, 0.1 mg/mL, 0.2 mg/mL and 0.5 mg/mL, respectively) for different period of times (24, 48 and 72 h). The cell viability was analyzed by CCK-8 assay. Cell apoptosis was evaluated by flow cytometry (7-AAD and Annexin V staining) and TUNEL assay. Reactive oxygen species (ROS) production was detected with fluorescence probe DCFH-DA by confocal microscopy and flow cytometry. The protein expression levels associated with ROS/JNK/caspase 3 axis(p-JNK, JNK, c-Jun, p-c-Jun, Bcl-2, Bax and cleaved-caspase 3) were analyzed by Western blot. Immunocytofluorescense staining was applied to evaluate the expression level of p-JNK. After addition of NAC, a ROS scavenger, and MAPK/JNK specific blocker SP600125, their effects on E-cig-induced cell apoptosis were evaluated. Statistical analysis was performed with Graph Pad 5.0 software package. RESULTS: Human PDLSCs were successfully isolated and cultured and flow cytometry assay showed the mesenchymal stem cell surface biomarkers (CD73, CD90 and CD105) were positively expressed. CCK8 assay indicated cell viability was significantly(P＜0.001) different among all concentration groups at various time points (24, 48 or 72 h), and the difference in apoptosis rate among all concentration groups was also statistically significant (P＜0.001). After exposure to E-liquid with nicotine concentration ≥50 µg/mL, cell viability was significantly reduced, and the proportion of apoptotic cells and the cellular ROS level was significantly increased in a dose-dependent manner as compared with the control group(0.0 mg/mL). Western blot assay showed E-cig exposure could promote MAPK/JNK phosphorylation in a dose-dependent and time-dependent manner. Either NAC or SP600125 could partially rescue the E-cig-induced cell apoptosis via reversing up-regulation of p-JNK and cleaved caspase 3. CONCLUSIONS: ROS/JNK/caspase 3 axis is involved in menthol-favored E-liquid-induced apoptosis of hPDLSCs.

Menthol Pretreatment Alleviates Campylobacter jejuni-Induced Enterocolitis in Human Gut Microbiota-Associated IL-10-/- Mice.

Human Campylobacter jejuni infections are of worldwide importance and represent the most commonly reported bacterial enteritis cases in middle- and high-income countries. Since antibiotics are usually not indicated and the severity of campylobacteriosis is directly linked to the risk of developing post-infectious complications, non-toxic antibiotic-independent treatment approaches are highly desirable. Given its health-promoting properties, including anti-microbial and anti-inflammatory activities, we tested the disease-alleviating effects of oral menthol in murine campylobacteriosis. Therefore, human gut microbiota-associated IL-10-/- mice were orally subjected to synthetic menthol starting a week before C. jejuni infection and followed up until day 6 post-infection. Whereas menthol pretreatment did not improve campylobacteriosis symptoms, it resulted in reduced colonic C. jejuni numbers and alleviated both macroscopic and microscopic aspects of C. jejuni infection in pretreated mice vs. controls. Menthol pretreatment dampened the recruitment of macrophages, monocytes, and T lymphocytes to colonic sites of infection, which was accompanied by mitigated intestinal nitric oxide secretion. Furthermore, menthol pretreatment had only marginal effects on the human fecal gut microbiota composition during the C. jejuni infection. In conclusion, the results of this preclinical placebo-controlled intervention study provide evidence that menthol application constitutes a promising way to tackle acute campylobacteriosis, thereby reducing the risk for post-infectious complications.

Investigating the role of nicotinic acetylcholine receptors in menthol's effects in mice.

The use of menthol in tobacco products has been linked to an increased likelihood of developing nicotine dependence. The widespread use of menthol can be attributed to its unique sensory characteristics; however, emerging evidence suggests that menthol also alters sensitivity to nicotine through modulation of nicotinic acetylcholine receptors (nAChRs). Nicotinic subunits, such as ß2 and α5, are of interest due to their implications in nicotine reward, reinforcement, intake regulation, and aversion. This study, therefore, examined the in vivo relevance of ß2 and α5 nicotinic subunits on the pharmacological and behavioral effects of menthol. Data suggests that the α5 nicotinic subunit modulates menthol intake in mice. Overall, deletion or a reduction in function of the α5 subunit lessened aversion to menthol. α5 KO mice and mice possessing the humanized α5 SNP, a variant that confers a nicotine dependence phenotype in humans, demonstrated increased menthol intake compared to their WT counterparts and in a sex-related fashion for α5 SNP mice. We further reported that the modulatory effects of the α5 subunit do not extend to other aversive tastants like quinine, suggesting that deficits in α5* nAChR signaling may not abolish general sensitivity to the aversive effects of other noxious chemicals. Further probing into the role of α5 in other pharmacological properties of menthol revealed that the α5 subunit does not modulate the antinociceptive properties of menthol in mice and suggests that the in vivo differences observed are likely not due to the direct effects of menthol on α5-containing nAChRs in vitro.

Efficient nanostructured materials to reduce nutrient leaching to overcome environmental contaminants.

Nutrient leaching is a major reason for fresh and ground water contamination. Menthol is the major bioactive ingredient of Mentha arvensis L. and one of the most traded products of global essential oil market. The indigenous production of menthol crystals in developing countries of the world can prove to be the backbone for local growers and poor farmers. Therefore, present research was designed to check the effects of nano-structured plant growth regulators (PGRs) (28-homobrassinolide and ethephon) with reduced leaching potentials on the essential oil and menthol (%) of Mentha arvensis L. The prepared nano-formulations were characterized by Fourier transform infrared (FTIR) spectroscopy, Laser induced breakdown spectroscopy (LIBS), Differential scanning colorimetry-thermal gravimetric analysis (DSC-TGA), Scanning electron microscopy (SEM), Atomic absorption spectrometry (AAS) and Zeta potential and Zeta size analysis. The menthol (%) was determined by modified spectrophotometric and gas chromatographic (GC) method. The highest essential oil (%) was obtained by the application of 28-homobrassinolide-Zn-NPs-L-II (0.92 ± 0.09%) and ethephon-Ca-NPs-L-III (0.91 ± 0.05%) as compared to the control (0.65 ± 0.03%) and blank (0.62 ± 0.09%). The highest menthol (%) was obtained by applying 28-homobrassinolide-Ca-NPs-L-I (80.06 ± 0.07%), 28-homobrassinolide-Ca-NPs-L-II (80.48 ± 0.09%) and 28-homobrassinolide-Ca-NPs-L-III (80.84 ± 0.11%) and ethephon-Ca-NPs-L-III (81.53 ± 0.17%) and ethephon-Zn-NPs-L-II (81.93 ± 0.26%) as compared to control (67.19 ± 0.14%) and blank (63.93 ± 0.17%).

A Capsicum annuum L. seed extract exerts anti-neuroexcitotoxicity in HT22 hippocampal neurons.

The hippocampal memory deficit stands out as a primary symptom in neurodegenerative diseases, including Alzheimer's disease. While numerous therapeutic candidates have been proposed, they primarily serve to delay disease progression. Given the irreversible brain atrophy or injury associated with these conditions, current research efforts are concentrated on preventive medicine strategies. Herein, we investigated whether the extracts of Capsicum annuum L. seeds (CSE) and Capsicum annuum L. pulp (CPE) have preventive properties against glutamate-induced neuroexcitotoxicity (one of the main causes of Alzheimer's disease) in HT22 hippocampal neuronal cells. Pretreatment with CSE demonstrated significant anti-neuroexcitotoxic activity, whereas CPE did not exhibit such effects. Specifically, CSE pretreatment dose-dependently inhibited the elevation of excitotoxic elements (intracellular calcium influx and reactive oxygen species; ROS) and apoptotic elements (p53 and cleaved caspase-3). In addition, the glutamate-induced alterations of neuronal activity indicators (brain-derived neurotrophic factor; BDNF and cAMP response element-binding protein phosphorylation; CREB) were significantly attenuated by CSE treatment. We also found that luteolin is the main bioactive compound corresponding to the anti-neuroexcitotoxic effects of CSE. Our results strongly suggest that Capsicum annuum L. seeds (but not its pulp) could be candidates for neuro-protective resources especially under conditions of neuroexcitotoxicity. Its underlying mechanisms may involve the amelioration of ROS-mediated cell death and BDNF-related neuronal inactivity and luteolin would be an active compound.

[Effect of TRPM8 on pain symptom and neuronal proliferation in mice with interstitial cystitis/bladder pain syndrome].

Objective: To explore the effects between transient receptor potential melastatin 8 (TRPM8) on pain symptom and neuronal proliferation in mice with interstitial cystitis/bladder pain syndrome (IC/BPS). Methods: Female wild-type C57BL/6 mice (8-10 weeks old) were divided into control group, IC/BPS model group, and IC/BPS model+menthol group (6 mice each) by random number table method; TRPM8 knockout mice were randomly divided into TRPM8 knockout group and TRPM8 knockout model group (6 mice each). The IC/BPS model group, the IC/BPS model+menthol group, and the TRPM8 knockout model group were injected subcutaneously with residues 65-84 of murine uroplakin 3A (UPK3A65-84). The IC/BPS model+menthol group continued to be injected with menthol. After successful modeling, the differences in pain thresholds between the groups were assessed by mechanosensitivity. The bladder wall was injected with a cell membrane red fluorescent probe (Dil), and the dorsal root ganglion (DRG) tissues were collected 10 days later. The differences in the protein and mRNA levels of TRPM8 and GAP43 in the groups were detected by Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR), respectively. Immunofluorescence was used to detect the distribution of TRPM8 expression with GAP43 or Dil in DRG tissues. The relationship between TRPM8 and pain symptom and its role in neuronal proliferation in IC/BPS mice were analyzed. Results: The models were all constructed successfully. Compared with the control group, the pain thresholds of mice in the IC/BPS model group and IC/BPS model+menthol group were reduced [(8.50±1.22), (5.50±1.05) vs (11.67±2.16), respectively, all P<0.001]. Compared with the control group, the expression of TRPM8 mRNA was elevated in the IC/BPS model group and IC/BPS model+menthol group, while TRPM8 was not expressed in the TRPM8 knockout group [(3.16±0.05), (6.46±0.21), and 0 vs (1.00±0.06), respectively, all P<0.001]. The expression of TRPM8 protein and mRNA in each group had the same trend (P<0.001). Compared with the control group, the expression of GAP43 mRNA in the DRG of the IC/BPS model group and the IC/BPS model+menthol group was increased, whereas the expression of GAP43 mRNA in the TRPM8 knockout model group was decreased (all P<0.001). The trend of GAP43 protein expression was the same as that of mRNA expression (P<0.001). Immunofluorescence results showed an increase in the number of GAP43-positive neurons in the DRG of the IC/BPS model group and the IC/BPS model+menthol group, and a decrease in the TRPM8 knockout group compared with the control group (all P<0.001). Compared with the control group, the number of Dil-positive neurons in the DRG of the IC/BPS model group and the IC/BPS model+menthol group was increased, while the TRPM8 knockout group was decreased (all P<0.001). Conclusion: TRPM8 can exacerbate pain symptom in IC/BPS mice, and the mechanism may be related to the induction of sensory nerve proliferation at the DRG level.

TRPM8 inhibits substance P release from primary sensory neurons via PKA/GSK-3beta to protect colonic epithelium in colitis.

Transient receptor potential melastatin 8 (TRPM8) is a cold sensory receptor in primary sensory neurons that regulates various neuronal functions. Substance P (SP) is a pro-inflammatory neuropeptide secreted by the neurons, and it aggravates colitis. However, the regulatory role of TRPM8 in SP release is still unclear. Our study aimed to investigate TRPM8's role in SP release from primary sensory neurons during colitis and clarify the effect of SP on colonic epithelium. We analyzed inflammatory bowel disease patients' data from the Gene Expression Omnibus dataset. Dextran sulfate sodium (DSS, 2.5%)-induced colitis in mice, mouse dorsal root ganglion (DRG) neurons, ND7/23 cell line, and mouse or human colonic organoids were used for this experiment. Our study found that TRPM8, TAC1 and WNT3A expression were significantly correlated with the severity of ulcerative colitis in patients and DSS-induced colitis in mice. The TRPM8 agonist (menthol) and the SP receptor antagonist (Aprepitant) can attenuate colitis in mice, but the effects were not additive. Menthol promoted calcium ion influx in mouse DRG neurons and inhibited the combination and phosphorylation of PKAca from the cAMP signaling pathway and GSK-3ß from the Wnt/ß-catenin signaling pathway, thereby inhibiting the effect of Wnt3a-driven ß-catenin on promoting SP release in ND7/23 cells. Long-term stimulation with SP inhibited proliferation and enhanced apoptosis in both mouse and human colonic organoids. Conclusively, TRPM8 inhibits SP release from primary sensory neurons by inhibiting the interaction between PKAca and GSK-3ß, thereby inhibiting the role of SP in promoting colonic epithelial apoptosis and relieving colitis.

Neuronal Excitability in the Medial Habenula and Ventral Tegmental Area Is Differentially Modulated by Nicotine Dosage and Menthol in a Sex-Specific Manner.

The medial habenula (MHb) has been identified as the limiting factor for nicotine intake and facilitating nicotine withdrawal. However, few studies have assessed MHb neuronal excitability in response to nicotine, and, currently, a gap in knowledge is present for finding behavioral correlates to neuronal excitability in the region. Moreover, no study to date has evaluated sex or nicotine dosage as factors of excitability in the MHb. Here, we utilized an e-vape self-administration (EVSA) model to determine differences between sexes with different nicotine dosages ± menthol. Following this paradigm, we employed patch-clamp electrophysiology to assess key metrics of MHb neuronal excitability in relation to behavioral endpoints. We observed female mice self-administered significantly more than males, regardless of dosage. We also observed a direct correlation between self-administration behavior and MHb excitability with low-dose nicotine + menthol in males. Conversely, a high dose of nicotine ± menthol yields an inverse correlation between excitability and self-administration behavior in males only. In addition, intrinsic excitability in the ventral tegmental area (VTA) does not track with the amount of nicotine self-administered. Rather, they correlate to the active/inactive discrimination of mice. Using fast-scan cyclic voltammetry, we also observed that dopamine release dynamics are linked to reinforcement-related behavior in males and motivation-related behaviors in females. These results point to a sex-specific difference in the activity of the MHb and VTA leading to distinct differences in self-administration behavior. His could lend evidence to clinical observations of smoking and nicotine-use behavior differing between males and females.

Topical application of L-Menthol - Physiological and genetic considerations to assist in developing female athlete research: A narrative review.

L-menthol is a cyclic monoterpene derived from aromatic plants, which gives a cooling sensation upon application. With this in mind, L-menthol is beginning to be considered as a potential ergogenic aid for exercise and sporting competitions, particularly in hot environments, however female-specific research is lacking. The aim of this narrative review is to summarize available literature relating to topical application of L-menthol and provide commentary on avenues of consideration relating to future research developments of topical L-menthol in female athletes. From available studies in male participants, L-menthol topical application results in no endurance exercise performance improvements, however decreases in thermal sensation are observed. Mixed results are observed within strength performance parameters. Several genetic variations and single nucleotide polymorphisms have been identified in relation to sweat production, fluid loss and body mass changes - factors which may influence topical application of L-menthol. More specifically to female athletes, genetic variations relating to sweat responses and skin thickness, phases of the menstrual cycle, and body composition indices may affect the ergogenic effects of L-menthol topical application, via alterations in thermogenic responses, along with differing tissue distribution compared to their male counterparts. This narrative review concludes that further development of female athlete research and protocols for topical application of L-menthol is warranted due to physiological and genetic variations. Such developments would benefit research and practitioners alike with further personalized sport science strategies around phases of the menstrual cycle and body composition indices, with a view to optimize ergogenic effects of L-menthol.

Influence of topical menthol gel on thermoregulation and perception while walking in the heat.

PURPOSE: Menthol is known to elicit opposing thermoregulatory and perceptual alterations during intense exercise. The current purpose was to determine the thermoregulatory and perceptual effects of topical menthol application prior to walking in the heat. METHODS: Twelve participants walked (1.6 m s-1, 5% grade) for 30 min in the heat (38 °C, 60% relative humidity) with either a 4% menthol or control gel on the upper (shoulder to wrist) and lower (mid-thigh to ankle) limbs. Skin blood flow (SkBF), sweat (rate, composition), skin conductivity, heart rate, temperature (skin, core), and thermal perception were measured prior to and during exercise. RESULTS: Skin conductivity expressed as time to 10, 20, 30, and 40 µS was delayed due to menthol (559 ± 251, 770 ± 292, 1109 ± 301, 1299 ± 335 s, respectively) compared to the control (515 ± 260, 735 ± 256, 935 ± 300, 1148 ± 298 s, respectively, p = 0.048). Sweat rate relative to body surface area was lower due to menthol (0.55 ± 0.16 L h-1 m(2)-1) than the control (0.64 ± 0.16 L h-1 m(2)-1, p = 0.049). Core temperature did not differ at baseline between the menthol (37.4 ± 0.3 °C) and control (37.3 ± 0.4 °C, p = 0.298) but was higher at 10, 20, and 30 min due to menthol (37.5 ± 0.3, 37.7 ± 0.2, 38.1 ± 0.3 °C, respectively) compared to the control (37.3 ± 0.4, 37.4 ± 0.3, 37.7 ± 0.3 °C, respectively, p < 0.05). The largest rise in core temperature from baseline was at 30 min during menthol (0.7 ± 0.3 °C) compared to the control (0.4 ± 0.2 °C, p = 0.004). Overall, the menthol treatment was perceived cooler, reaching "slightly warm" whereas the control treatment reached "warm" (p < 0.001). CONCLUSION: Menthol application to the limbs impairs whole-body thermoregulation while walking in the heat despite perceiving the environment as cooler.

Inhibition of TRPM8 function by prostacyclin receptor agonists requires coupling to Gq/11 proteins.

BACKGROUND AND PURPOSE: The TRPM8 ion channel is involved in innocuous cold sensing and has a potent anti-inflammatory action. Its activation by lower temperature or chemical agonists such as menthol and icilin induces analgesic effects, reversing hypersensitivity and reducing chronic pain. On the other hand, prostacyclin (PGI2) enhances pain and inflammation by activating the IP receptors. Due to the critical roles of TRPM8 and IP receptors in the regulation of inflammatory pain, and considering their overlapping expression pattern, we analysed the functional interaction between human TRPM8 and IP receptors. EXPERIMENTAL APPROACH: We transiently expressed human TRPM8 channels and IP receptors in HEK293T cells and carried out intracellular calcium and cAMP measurements. Additionally, we cultured neurons from the dorsal root ganglia (DRGs) of mice and determined the increase in intracellular calcium triggered by the TRPM8 agonist, icilin, in the presence of the IP receptor agonist cicaprost, the IP receptor antagonist Cay10441, and the Gq/11 inhibitor YM254890. KEY RESULTS: Activation of IP receptors by selective agonists (cicaprost, beraprost, and iloprost) inhibited TRPM8 channel function, independently of the Gs-cAMP pathway. The potent inhibition of TRPM8 channels by IP receptor agonists involved Gq/11 coupling. These effects were also observed in neurons isolated from murine DRGs. CONCLUSIONS AND IMPLICATIONS: Our results demonstrate an unusual signalling pathway of IP receptors by coupling to Gq/11 proteins to inhibit TRPM8 channel function. This pathway may contribute to a better understanding of the role of TRPM8 channels and IP receptors in regulating pain and inflammation.

Inducible desensitization to capsaicin with repeated low-dose exposure in human volunteers.

Responses to capsaicin are reduced following repeated exposure, a phenomenon known as capsaicin desensitization. Heavy consumers of chilies consistently report reduced oral burn relative to infrequent consumers, presumably due to chronic desensitization. However, the mechanism(s) underlying capsaicin desensitization remain poorly understood. We hypothesized that reduced response to capsaicin due to repeated oral exposure may result from a change in the expression of the capsaicin receptor (TRPV1) gene. To test this, we conducted two longitudinal desensitization studies in healthy human volunteers. In Study 1, 51 adults completed a 17-day capsaicin desensitization protocol. The study consisted of three in-person visits where they were asked to sample stimuli, including 3, 6, and 9 ppm capsaicin, and rate intensity on a general labeled magnitude scale (gLMS). Between days 3 & 17, participants rinsed at home with 6 ppm capsaicin (n = 31) or a control (n = 20) solution (20 uM sucrose octaccetate; SOA) twice a day. Before and after the oral exposure protocol, a clinician collected fungiform papillae. Participants randomized to the capsaicin rinse showed a statistically significant reduction in oral burn ratings that was not observed in controls, indicating repeated low-dose exposure can systematically induce desensitization. TRPV1 expression was not associated with reported capsaicin burn, and there was no evidence of a decrease in TRPV1 expression following capsaicin exposure. In Study 2, participants (n = 45) rinsed with 6 ppm capsaicin in a similar protocol, rating capsaicin, vanillyl butyl ether (VBE), cinnamaldehyde, ethanol, menthol, and sucrose on days 1, 3, & 17. Burn from capsaicin, VBE, cinnamaldehyde, and ethanol all showed a statistically significant change - capsaicin, VBE and cinnamaldehyde burn all dropped ∼20 %, and a larger reduction was seen for ethanol - while menthol cooling and sucrose sweetness did not change. Collectively, this suggests reductions in oral burn following chronic capsaicin exposure generalizes to other stimuli (i.e., cross desensitization) and this cannot be explained by a change in TRPV1 mRNA expression. More work is needed to elucidate the underlying mechanism for capsaicin desensitization in the oral cavity.

Menthol dural application alters meningeal arteries tone and enhances excitability of trigeminocervical neurons in rats.

Headaches, including migraines, can have a causal relationship to exposure to cold, and this relationship may be both positive and negative, as cold can both provoke and alleviate cephalgia. The role of thermoreceptors responsible for transduction of low temperatures belongs to the transient receptor potential cation channel subfamily melastatin member 8 (TRPM8). These channels mediate normal cooling sensation and have a role in both cold pain and cooling-mediated analgesia; they are seen as a potential target for principally new anti-migraine pharmaceuticals. Using a validated animal migraine models, we evaluated effects of menthol, the TRPM8-agonist, on trigeminovascular nociception. In acute experiments on male rats, effects of applied durally menthol solution in various concentrations on the neurogenic dural vasodilatation (NDV) and firing rate of dura-sensitive neurons of the trigeminocervical complex (TCC) were assessed. Application of menthol solution in concentrations of 5 % and 10 % was associated with NDV suppression, however amplitude reduction of the dilatation response caused not by the vascular dilatation degree decrease, but rather due to the significant increase of the meningeal arterioles' basal tone. In electrophysiological experiments the 1 % and 30 % menthol solutions intensified TCC neuron responses to the dural electrical stimulation while not changing their background activity. Revealed in our study excitatory effects of menthol related to the vascular as well as neuronal branches of the trigeminovascular system indicate pro-cephalalgic effects of TRPM8-activation and suggest feasibility of further search for new anti-migraine substances among TRPM8-antagonists.

Ten weeks of Capsicum annuum L. extract supplementation did not change adipose tissue-derived hormones, appetite, body composition, and muscle strength when combined with resistance training in healthy untrained men: A clinical trial study.

Capsiate (CAP) is a nonpungent capsaicin analog (Capsicum annuum L. extract) that has been studied as a potential antiobesity agent. However, the interaction between chronic CAP supplementation and resistance training is not clear. The purpose of this study was to examine the changes in adipose tissue-derived hormones, body composition, appetite, and muscle strength after 10 weeks of resistance training, combined with chronic CAP supplementation in healthy untrained men. We hypothesized that CAP could induce higher benefits when combined with resistance training after 10 weeks of intervention compared to resistance training alone. Twenty-four young men (age, 22.0 ± 2.9) were randomized to either capsiate supplementation (CAP = 12 mg/day) or placebo (PL), and both groups were assigned to resistance training. Body composition, leptin and adiponectin concentrations, subjective ratings of appetite, energy intake, and exercise performance were assessed at before and after 10 weeks of progressive resistance training. There was a significant increase in body mass (P < .001), fat-free mass (CAP: 58.0 ± 7.1 vs. post, 59.7 ± 7.1 kg; PL: pre, 58.4 ± 7.3 vs. post, 59.8 ± 7.1 kg; P < .001), resting metabolic rate (CAP: pre, 1782.9 ± 160.6 vs. post, 1796.3 ± 162.0 kcal; PL: pre, 1733.0 ± 148.9 vs. post, 1750.5 ± 149.8 kcal; P < .001), maximal strength at 45 leg press (P < .001) and bench press (P < .001) in both groups, but no significant (P > .05) supplementation by training period interaction nor fat mass was observed. For subjective ratings of appetite, energy intake, leptin, and adiponectin, no significant effect of supplementation by training period interaction was observed (P > .05). In conclusion, 10 weeks of resistance training increased total body weight, muscle mass, and maximum strength in healthy untrained men; however, CAP supplementation (12 mg, 7 days per week) failed to change adipose tissue-derived hormones, appetite, body composition and muscle strength in this population. Registered under Brazilian Registry of Clinical Trials (RBR-8cz9kfq).

A contrast of emerging contaminants rac- and l-menthol toxicities to Microcystis aeruginosa through biochemical, physiological, and morphological investigations.

Fragrances rac- and l-menthol extracted from peppermint are widely used and considered as emerging contaminants recently, which are persistent in the environment. Menthol has always been considered as a safe chemical for humans, but its potential adverse ecological effects on aquatic organisms and the toxic mechanisms have not yet been fully understood. The present study aims to investigate the physiological response of Microcystis aeruginosa after exposure to the two menthol isomers, and to explore the toxic mechanisms and ecological risks of these two chemicals. Results showed that rac-menthol exhibited a hormesis effect on the cell growth, chlorophyll a and protein contents; while l-menthol showed an inhibition effect. Adenosine triphosphate (ATP) content increased significantly at day 3 and then decreased markedly at day 6 after exposure to the two chemicals. Compared with rac-menthol, l-menthol can cause damage to the antioxidant system and plasmalemma more severely, promote the production and release of microcystins-LR (MC-LR) more dramatically, upregulate the expression of MC-transportation-related gene mcyH, and induce higher apoptosis rates. Overall results revealed that the toxic effects of l-menthol on cyanobacteria were significantly greater than those of rac-menthol. The significant increase in the malondialdehyde (MDA) content and the ultrastructural characteristics of the cells indicated that the plasma membranes were damaged. Thus, further attention should be paid to the scientific use, ecological and environmental risk assessment of chiral menthol. This study will also provide a scientific basis for future water quality criteria establishment on emerging contaminants such as fragrances.

Efficacy of levocetirizine in isolated rat tracheal smooth muscle.

Histamine receptor-1 (H1) antagonists like levocetirizine are frequently used nowadays to treat rhinitis patients who experience rhinorrhea and sneezing. The trachea may be affected by the H1 antagonist when it is used to treat nasal symptoms, either orally or through inhalation. The purpose of this study was to ascertain in vitro effects of levocetirizine on isolated tracheal smooth muscle. As a parasympathetic mimetic, methacholine (10-6 M) causes contractions in tracheal smooth muscle, which is how we tested effectiveness of levocetirizine on isolated rat tracheal smooth muscle. We also tested the drug's impact on electrically induced tracheal smooth muscle contractions. The impact of menthol (either before or after) on the contraction brought on by 10-6 M methacholine was also investigated. According to the results, the addition of levocetirizine at concentrations of 10-5 M or more caused a slight relaxation in response to methacholine's 10-6 M contraction. Levocetirizine could prevent spike contraction brought on by electrical field stimulation (EFS). As the concentration rose, it alone had a neglect effect on the trachea's basal tension. Before menthol was applied, levocetirizine might have also inhibited the function of the cold receptor. According to this study, levocetirizine might potentially impede the parasympathetic function of the trachea. If levocetirizine was used prior to menthol addition, it also reduced the function of cold receptors.