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Purpose The study investigated the effect of a non-thermal cooling agent, l -menthol, on exercise at a fixed subjective rating of perceived exertion (RPE) in a hot environment. Method Eight male participants completed two trials at an exercise intensity between ‘hard’ and ‘very hard’, equating to 16 on the RPE scale at ~35 °C. Participants were instructed to continually adjust their power output to maintain an RPE of 16 throughout the exercise trial, stopping once power output had fallen by 30%. In a randomized crossover design, either l -menthol or placebo mouthwash was administered prior to exercise and at 10 min intervals. Power output, V ˙ O 2 , heart rate, core and skin temperature was monitored, alongside thermal sensation and thermal comfort. Isokinetic peak power sprints were conducted prior to and immediately after the fixed RPE trial. Results Exercise time was greater (23:23 ± 3:36 vs. 21:44 ± 2:32 min; P  = 0.049) and average power output increased (173 ± 24 vs. 167 ± 24 W; P  = 0.044) in the l -menthol condition. Peak isokinetic sprint power declined from pre-post trial in the l -menthol l (9.0%; P  = 0.015) but not in the placebo condition (3.4%; P  = 0.275). Thermal sensation was lower in the l -menthol condition ( P  = 0.036), despite no changes in skin or core temperature ( P  > 0.05). Conclusion These results indicate that a non-thermal cooling mouth rinse lowered thermal sensation, resulting in an elevated work rate, which extended exercise time in the heat at a fixed RPE.

The selective conversion of natural or synthetic neral to (1 R ,6 S )- trans -isopiperitenol would enable and expedite sustainable routes to menthol 1 , 2 and cannabinoids 3 – 5 . However, this reaction has been considered impossible because its product is more reactive to the required acid catalysts than its starting material, resulting in several side products 6 – 9 . We now show that an unsymmetric, strong and confined chiral acid, a highly fluorinated imino-imidodiphosphate, catalyses this process with excellent efficiency and selectivity. Expanding the method to other α,β-unsaturated aldehydes could enable access to new cannabinoids and menthol derivatives not readily accessible previously. Mechanistic studies suggest that the confined catalyst accomplishes this reaction by binding the product in an unreactive conformation, thereby preventing its decomposition. We also show how (1 R ,6 S )- trans -isopiperitenol can be readily converted to pharmaceutically useful cannabinoids and menthol, each in the shortest and most atom-economic routes so far. An unsymmetric, strong and confined chiral acid, a highly fluorinated imino-imidodiphosphate, catalyses the selective conversion of neral to (1 R ,6 S )- trans -isopiperitenol, enabling sustainable routes to menthol and cannabinoids.

ObjectivesChemotherapy-induced peripheral neuropathy (CIPN) symptom is one of the side effects of paclitaxel in breast cancer patients. This randomised controlled study was conducted to investigate the effect of topical menthol applied on the hands and feet of breast cancer patients receiving chemotherapy on CIPN symptoms.Methods60 breast cancer patients receiving chemotherapy were randomly assigned to an intervention group (n=30), which received topical menthol treatment, or a control group (n=30), which received standard care. Both groups continued their routine pharmacological treatments throughout the study. The intervention group applied 1% menthol topically to their hands and feet two times a day. The effect of the intervention on CIPN symptoms was evaluated 3 weeks and 6 weeks after the intervention.ResultsThe intervention group showed a significantly greater improvement in CIPN symptoms over time compared with the control group, with an effect size of η2=0.214 for the group×time interaction. Additionally, the intervention group exhibited a notable positive change in the exposure subscale of the CIPN rating scale, with an effect size of η2=0.114.ConclusionsTopical application of menthol significantly mitigates the symptoms of CIPN in breast cancer patients. This study supports the use of menthol as an effective adjunctive treatment for CIPN.Trial registration number NCT05429814.

RationaleThere is limited understanding regarding how various e-cigarette flavorings may influence the behavior of non-regular e-cigarette users who are regular cigarette smokers.ObjectivesTo assess differences in nicotine delivery, puffing topography, subjective effects, and user satisfaction from different flavored e-liquids.MethodsEighteen daily smokers (average age, 44.1 ± 7.0; 9 males; average CPD, 13.0 ± 5.8) smoked their tobacco cigarettes during an initial visit and returned five times to try an e-cigarette (eGo type) refilled with a nicotine solution (24 mg/ml) of five different flavors: cherry, tobacco, espresso, menthol, and vanilla (randomized order). Assessments at each visit included puffing topography, blood samples for nicotine analysis, and subjective reports of nicotine effects and flavor satisfaction.ResultsVaping different flavors resulted in different levels of plasma nicotine. The flavor producing the highest plasma nicotine concentration (Cmax) was cherry (median 21.2 ng/ml), which was not significantly different than nicotine delivery from a combustible cigarette (29.2 ng/ml, p > .05). Vanilla e-liquid produced the lowest Cmax (9.7 ng/ml), and participants tended to puff less frequently on vanilla compared to tobacco flavor (p = .013). Flavors did not differ significantly in the speed of nicotine delivery (Tmax). During controlled use, puff duration for all flavors was significantly longer than a combustible cigarette (p < 0.05). After controlling for nicotine delivery, significant differences in flavor enjoyment were detected. Menthol flavored e-liquid was rated as more enjoyable than vanilla and tobacco flavored e-liquids (p < 0.05).ConclusionsFlavors tested in this study yielded different patterns of nicotine delivery and led to differences in reduction in smoking urges.Trial registrationClinicalTrials.gov Identifier: #NCT02575885

Deep eutectic solvents have been recently reported as an interesting alternative to improve the therapeutic efficacy of conventional drugs, hence called therapeutic deep eutectic solvents (THEDES). The main objective of this work was to evaluate the potential of limonene (LIM) based THEDES as new possible systems for cancer treatment. LIM is known to have antitumor activity, however it is highly toxic and cell viability is often compromised, thus this compound is not selective towards cancer cells. Different THEDES based on LIM were developed to unravel the anticancer potential of such systems. THEDES were prepared by gently mixing saturated fatty acids menthol or ibuprofen (IBU) with LIM. Successful THEDES were obtained for Menthol:LIM (1:1), CA:LIM (1:1), IBU:LIM (1:4) and IBU:LIM(1:8). The results indicate that all the THEDES present antiproliferative properties, but IBU:LIM (1:4) was the only formulation able to inhibit HT29 proliferation without comprising cell viability. Therefore, IBU:LIM (1:4) was the formulation selected for further assessment of anticancer properties. The results suggest that the mechanism of action of LIM:IBU (1:4) is different from isolated IBU and LIM, which suggest the synergetic effect of DES. In this work, we unravel a methodology to tune the selectivity of LIM towards HT29 cell line without compromising cell viability of healthy cells. We demonstrate furthermore that coupling LIM with IBU leads also to an enhancement of the anti-inflammatory activity of IBU, which may be important in anti-cancer therapies.

PurposeWe evaluated (1) whether participating in middle- and long-distance running races augments muscle soreness, oxygen cost, respiration, and exercise exertion during subsequent running, and (2) if post-race menthol application alleviates these responses in long-distance runners.MethodsEleven long-distance runners completed a 1500-m race on day 1 and a 3000-m race on day 2. On day 3 (post-race day), either a 4% menthol solution (Post-race menthol) or a placebo solution (Post-race placebo) serving as a vehicle control, was applied to their lower leg skin, and their perceptual and physiological responses were evaluated. The identical assessment with the placebo solution was also conducted without race participation (No-race placebo).ResultsThe integrated muscle soreness index increased in the Post-race placebo compared to the No-race placebo (P < 0.001), but this response was absent in the Post-race menthol (P = 0.058). Oxygen uptake during treadmill running tended to be higher (4.3%) in the Post-race placebo vs. No-race placebo (P = 0.074). Oxygen uptake was 5.4% lower in the Post-race menthol compared to the Post-race placebo (P = 0.018). Minute ventilation during treadmill running was 6.7–7.6% higher in the Post-race placebo compared to No-race placebo, whereas it was 6.6–9.0% lower in the Post-race menthol vs. Post-race placebo (all P ≤ 0.001). The rate of perceived exertion was 7.0% lower in the Post-race menthol vs. Post-race placebo (P = 0.007).ConclusionsMiddle- and long-distance races can subsequently elevate muscle soreness and induce respiratory and metabolic stress, but post-race menthol application to the lower legs can mitigate these responses and reduce exercise exertion in long-distance runners.

In humans, cold is primarily sensed by transient receptor potential melastatin member 8 (TRPM8), a calcium channel. Yin et al. present cryo–electron microscopy structures of TRPM8 with cooling agents, membrane lipid phosphatidylinositol-4,5-bisphosphate (PIP2), and calcium. Structural and functional analyses showed that the PIP2 binding site in TRPM8 is completely different from PIP2 sites in other TRP channels. The binding of PIP2 and cooling agents allosterically enhance each other and activate the channel opening. Thus, the activation mechanism of TRPM8 is distinct from that used by other TRP channels. Science , this issue p. eaav9334 Cryo-EM structures elucidate the molecular basis for cold and menthol sensing and reveal the distinctive PIP2 dependence in the TRPM8 calcium channel. Transient receptor potential melastatin member 8 (TRPM8) is a calcium ion (Ca 2+ )–permeable cation channel that serves as the primary cold and menthol sensor in humans. Activation of TRPM8 by cooling compounds relies on allosteric actions of agonist and membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP 2 ), but lack of structural information has thus far precluded a mechanistic understanding of ligand and lipid sensing by TRPM8. Using cryo–electron microscopy, we determined the structures of TRPM8 in complex with the synthetic cooling compound icilin, PIP 2 , and Ca 2+ , as well as in complex with the menthol analog WS-12 and PIP 2 . Our structures reveal the binding sites for cooling agonists and PIP 2 in TRPM8. Notably, PIP 2 binds to TRPM8 in two different modes, which illustrate the mechanism of allosteric coupling between PIP 2 and agonists. This study provides a platform for understanding the molecular mechanism of TRPM8 activation by cooling agents.

Objective To determine whether 3% w/w levomenthol added to ibuprofen gel (5% w/w) improves its efficacy compared with ibuprofen gel alone or diclofenac gel (1.16%) for the treatment of soft-tissue injuries. Methods A total of 182 patients with acute soft-tissue injuries participated in a randomised, single-blind, single-dose study to assess the efficacy and safety of three topical analgesic gels. Efficacy was assessed as the score change in a numeric rating scale for pain. Results The median time to significant pain relief was 20 minutes for the ibuprofen/levomenthol and diclofenac gels but 25 minutes for ibuprofen gel. At 2 hours, significantly more patients treated with ibuprofen/levomenthol gel reported a cooling sensation (45.8%) compared with diclofenac (16.4%) or ibuprofen (14.7%) gels, and both ibuprofen/levomenthol and diclofenac gels provided significantly more effective global pain relief compared with ibuprofen gel. Few adverse events and no serious adverse events related to study medication were recorded. Conclusions Although all gels effectively relieved pain, both ibuprofen/levomenthol and diclofenac gels provided superior global pain relief compared with ibuprofen gel, with a shorter median time to significant pain relief. Only ibuprofen/levomenthol gel provided cooling for up to 2 hours. None of the gels were associated with serious safety concerns. EudraCT No 2015-005240-33 EU Clinical Trials Register URL: https://www.clinicaltrialsregister.eu/ctr-search/search

PurposeCognition can be impaired during exercise in the heat, potentially contributing to military casualties. To our knowledge, the independent role of elevated core temperature during exercise has not been determined. The aim of the current study was to evaluate effects of elevated core temperature on cognition during physically encumbering, heated exercise, and to determine whether the perceptual cooling effects of menthol preserves cognition.MethodsEight participants complete three trials in randomised order: one normothermic (CON) and two with elevated (38.5°C) core temperature, induced by prior immersion in neutral versus hot water The CON trial and one hot trial (HOT) used a water mouth-rinse following each cognitive task of the trial, (HOT) while the other used a menthol mouth-rinse (MENT). Participants walked in humid heat (33°C, 75% relative humidity) in military clothing, completing a cognitive battery of reaction time, perceptual processing, working memory, executive function, cognitive flexibility, vigilance, and declarative memory.ResultsNo differences in cognitive performance were observed between any conditions. Near-infrared spectroscopy showed greater oxygenated haemoglobin tissue content in HOT and MENT compared to CON (ΔO2Hb-deO2Hb: 2.3 ± 4.5 µM, p < .024), and lower deoxygenated haemoglobin in MENT than in CON or HOT (p = .017), suggesting higher brain metabolism during the more stressful conditions.ConclusionModerately elevated core (38.5°C) and skin temperature does not appear to impair cognitive performance during exercise despite mildly elevated cerebral metabolism. The effects of menthol remain undetermined due to the lack of heat-mediated cognitive impairment.

The hallmark of enzymes from secondary metabolic pathways is the pairing of powerful reactivity with exquisite site selectivity. The application of these biocatalytic tools in organic synthesis, however, remains under-utilized due to limitations in substrate scope and scalability. Here, we report how the reactivity of a monooxygenase (PikC) from the pikromycin pathway is modified through computationally guided protein and substrate engineering, and applied to the oxidation of unactivated methylene C–H bonds. Molecular dynamics and quantum mechanical calculations were used to develop a predictive model for substrate scope, site selectivity and stereoselectivity of PikC-mediated C–H oxidation. A suite of menthol derivatives was screened computationally and evaluated through in vitro reactions, where each substrate adhered to the predicted models for selectivity and conversion to product. This platform was also expanded beyond menthol-based substrates to the selective hydroxylation of a variety of substrate cores ranging from cyclic to fused bicyclic and bridged bicyclic compounds. The reactivity of a monooxygenase (P450 PikC) has been modified through protein and substrate engineering, and applied to the oxidation of unactivated methylene C–H bonds. The protein engineering was guided by using molecular dynamics and quantum mechanical calculations to develop a predictive model for substrate scope, site selectivity and stereoselectivity of the C–H hydroxylation.