Topical Application Of Menthol Research Articles

Topical menthol, a pharmacological cold mimic, induces cold sensitivity, adaptive thermogenesis and brown adipose tissue activation in mice.

Brown adipose tissue (BAT) thermogenesis has profound energy-expanding potential, which makes it an attractive target tissue to combat ever-increasing obesity and its other associated metabolic complications. Although it is fairly accepted that cold is a potent inducer of BAT activation and function, there are limited studies on the mechanisms of pharmacological cold-mimicking agents, such as the TRPM8 agonist, menthol, on BAT thermogenesis and activation. Herein, we sought to determine the effect of topical application of menthol (10% w/v [4 g/kg] cream formulation/day for 15 days) on temperature sensitivity behaviour (thermal gradient assay, nesting behaviour), adaptive thermogenesis (infrared thermography, core body temperature), BAT sympathetic innervation (tyrosine hydroxylase immunohistochemistry) and activation (18F-FDG PET-CT analysis, Uncoupling Protein 1 immunohistochemistry and BAT gene expression), whole-body energy expenditure (indirect calorimetry) and other metabolic variables in male C57BL/6N mice. We show that male C57BL/6N mice: (a) develop a warm-seeking and cold-avoiding thermal preference phenotype; (b) display increased locomotor activity and adaptive thermogenesis; (c) show augmented sympathetic innervation in BAT and its activation; (d) exhibit enhanced gluconeogenic capacity (increased glucose excursion in response to pyruvate) and insulin sensitivity; and (e) show enhanced whole-body energy expenditure and induced lipid-utilizing phenotype after topical menthol application. Taken together, our findings highlight that pharmacological cold mimicking using topical menthol application presents a potential therapeutic strategy to counter weight gain and related complications.

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

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. Twelve participants walked (1.6m s-1, 5% grade) for 30min 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. Skin conductivity expressed as time to 10, 20, 30, and 40 µS was delayed due to menthol (559 ± 251, 770 ± 292, 1109 ± 301, 1299 ± 335s, respectively) compared to the control (515 ± 260, 735 ± 256, 935 ± 300, 1148 ± 298s, 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 30min 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). Menthol application to the limbs impairs whole-body thermoregulation while walking in the heat despite perceiving the environment as cooler.

Skin Application of Menthol Enhances Maximal Isometric Lifting Performance.

Abstract Over, DM, Arjomandkhah, N, Beaumont, JD, Goodall, S, and Barwood, MJ. Skin application of menthol enhances maximal isometric lifting performance. J Strength Cond Res 37(3): 564–573, 2023—Topical application of menthol to the skin improves perception (i.e., makes subjects feel cooler) and changes submaximal neuromuscular recruitment facilitating force generation. We explored the effect of menthol (0.2% concentration; sprayed on the legs), on perception and maximal, dynamic (DLT) and isometric (IMLT) (weight) lifting tasks. Nine resistance-trained male subjects (mean ± SD: 24 ± 5 years; 75.7 ± 8.8 kg; 174 ± 10 cm; 5 repetition maximum deadlift [5RM] 132.3 ± 28.5 kg) were tested using a repeated measures design; we hypothesized that performance would improve. Before completing the DLT (i.e., deadlift performance 75% 1RM) and a midthigh pull dynamometer IMLT, subjects were sprayed with (∼125 ml) of menthol or control spray. Performance, electromyography (root mean squared [rmsEMG], rectus femoris [RF], biceps femoris [BF], and medial gastrocnemius [MG]), perceptions (leg thermal sensation [TSlegs] and comfort [TClegs] and perceived exertion [RPE] and readiness to train), heart rate, and skin temperature were measured. Data were compared using analysis of variance (effect size ) and t test to a 0.05 alpha level supported by Bayesian analysis. Dynamic lifting task performance was unchanged, although BF rmsEMG was higher (i.e., greater muscle activation in final [10th] repetition). Isometric lifting task force production was higher in the menthol spray (148 ± 30 kgf) condition (control spray 140 ± 30 kgf; p = 0.035, = 0.444) with corresponding higher rmsEMG (BF 3.8 ± 1.46 vs. control spray 2.9 ± 0.34 V; p = 0.049, = 0.403). TSlegs was lower after menthol spray before IMLT; subjects felt slightly cool. Menthol spray enhances isometric weightlifting performance with corresponding changes in neuromuscular activity, partially supporting our hypothesis.

Activation of peripheral TRPM8 mitigates ischemic stroke by topically applied menthol

BackgroundNo reports exist as to neuroprotective effects associated with topical activation of transient receptor potential melastatin 8 (TRPM8), a noted cold receptor. In the present study, we identified whether activating peripheral TRPM8 can be an adjuvant therapy for ischemic stroke.MethodsMenthol, an agonist of TRPM8, was applied orally or topically to all paws or back of the mouse after middle cerebral artery occlusion (MCAO). We used Trpm8 gene knockout (Trpm8−/−) mice or TRPM8 antagonist and lidocaine to validate the roles of TRPM8 and peripheral nerve conduction in menthol against ischemic stroke.ResultsApplication of menthol 16% to paw derma attenuated infarct volumes and ameliorated sensorimotor deficits in stroke mice induced by MCAO. The benefits of topically applied menthol were associated with reductions in oxidative stress, neuroinflammation and infiltration of monocytes and macrophages in ischemic brains. Antagonizing TRPM8 or Trpm8 knockout dulls the neuroprotective effects of topically application of menthol against MCAO. Immunohistochemistry analyses revealed significantly higher TRPM8 expression in skin tissue samples obtained from the paws compared with skin from the backs, which was reflected by significantly smaller infarct lesion volumes and better sensorimotor function in mice treated with menthol on the paws compared with the back. Blocking conduction of peripheral nerve in the four paws reversed the neuroprotective effects of topical menthol administrated to paws. On the other hand, oral menthol dosing did not assist with recovery from MCAO in our study.ConclusionOur results suggested that activation of peripheral TRPM8 expressed in the derma tissue of limbs with sufficient concentration of menthol is beneficial to stroke recovery. Topical application of menthol on hands and feet could be a novel and simple-to-use therapeutic strategy for stroke patients.

Sauna-like conditions or menthol treatment reduce tau phosphorylation through mild hyperthermia

In Alzheimer's disease (AD), hyper-phosphorylation and aggregation of tau correlate with clinical progression and represent a valid therapeutic target. A recent 20-year prospective study revealed an association between moderate to high frequency of Finnish sauna bathing and a lower incidence of dementia and AD, but the molecular mechanisms underlying these benefits remain uncertain. Here, we tested the hypothesis that sauna-like conditions could lower tau phosphorylation by increasing body temperature. We observed a decrease in tau phosphorylation in wild-type and hTau mice as well as in neuron-like cells when exposed to higher temperatures. These effects were correlated with specific changes in phosphatase and kinase activities, but not with inflammatory or heat shock responses. We also used a drug strategy to promote thermogenesis: topical application of menthol, which led to a sustained increase in body temperature in hTau mice, concomitant with a significant decrease in tau phosphorylation. Our results suggest that sauna-like conditions or menthol treatment could lower tau pathology through mild hyperthermia, and may provide promising therapeutic strategies for AD and other tauopathies.

Menthol-induced activation of TRPM8 receptors increases cutaneous blood flow across the dermatome.

Topical menthol-based analgesics increase skin blood flow (SkBF) through transient receptor potential melastatin 8 (TRPM8) receptor-dependent activation of sensory nerves and endothelium-derived hyperpolarization factors. It is unclear if menthol-induced TRPM8 activation mediates a reflex change in SkBF across the dermatome in an area not directly treated with menthol. The purpose of this study was to determine the effects of localized topical menthol application on SkBF across a common dermatome. We hypothesized that SkBF would be increased with menthol at the site of application and across the dermatome (contralateral limb) through a spinal reflex mechanism. In a double blind, placebo controlled, cross-over design, 15 healthy participants (7 men; age=22±1yrs) were treated with direct application (3ml over 8×13cm) of 5% menthol gel (Biofreeze™) or placebo gel on the L4 dermatome, separated by 48h. Red blood cell flux was measured using laser Doppler flowmetry over the area of application, on the contralateral leg of the same dermatome, and in a separate dermatome (L5/S1) to serve as control. Cutaneous vascular conductance was calculated for each measurement site (CVC=flux/MAP). At baseline there were no differences in CVC between menthol and placebo gels, or among sites (all p>0.05). After 30±6min, CVC increased at the treated site with menthol (0.12±0.02 vs. 1.36±0.19flux/mmHg, p<0.01) but not the placebo (0.10±0.01 vs. 0.18±0.04flux/mmHg, p=0.91). There was a modest increase in CVC at the contralateral L4 dermatome with menthol gel (0.16±0.04 vs. 0.29±0.06flux/mmHg, p<0.01), but not placebo (0.11±0.02 vs. 0.15±0.03flux/mmHg, p=0.41). There was no effect on SkBF from either treatments at the L5/S1 control dermatome (both, p>0.05), suggesting the lack of a systemic response. In conclusion, menthol containing topical analgesic gels increased SkBF at the treated site, and modestly throughout the dermatome. These data suggest menthol-induced activation of the TRPM8 receptors induces an increase in SkBF across the area of common innervation through a localized spinal reflex mechanism.

The effect of body surface area exposure to menthol on temperature regulation and perception in men.

In warm conditions topical application of menthol increases cool sensations and influences deep body temperature. The purpose of this experiment was to explore whether different body surface areas (BSA) exposed to menthol influence these responses. It was hypothesized that the forcing function exerted by menthol will be proportionally related to BSA. Using a within-participant design, 13 participants underwent three BSA exposures (Small [S; finger]; Medium [M; arm]; Large [L; upper/lower body]) to 4.13% menthol, and one Placebo exposure. During each exposure participants rested supine in a tent (30°C, 50%rh) for 30-min before their intervention and 30-min thereafter. Measures included thermal sensation, thermal comfort, irritation, skin blood flow (finger SkBF; laser Doppler flowmetry), rectal temperature (Tre), and skin temperature (chest, forearm, thigh, calf). The Area Under the Curve from minute 30 to 60 was calculated and analyzed using a one-way ANOVA or Friedman's test with post-hoc testing (0.05 alpha level). There was no significant difference in any measure of thermometry (p>0.05), while SKBF was significantly lowered in L, M, and S vs. P respectively (p<0.05). Participants in L felt cooler vs. P and S (p<0.05). Losses in thermal comfort were noted in L and M vs. P and S (p<0.05), along with increased irritation in L vs. S (p<0.05). Despite similar skin temperatures, larger BSA's exposed to menthol caused cooler sensations, likely due to the activation of a larger pool of menthol-sensitive neurons. This occurred in the absence of thermal discomfort and without perceptions of irritation exceeding 'weak'. Larger BSA's also exhibited greater alterations in Tre, likely driven by a reduction in SkBF, but despite this mean body temperature was regulated suggesting the thermoregulatory system can cope with the range of BSA exposures studied herein.

Activation of skin-resident group 2 innate lymphoid cells by cold-sensing TRPM8+ neuron-derived signals in thermo-homeostatic regulation and tissue inflammation

Abstract Innate lymphoid cells (ILCs) in the skin are a heterogeneous population of innate lymphocytes that function in local homeostatic regulation but could also cause inflammation. How homeostatic versus inflammatory functions of skin ILCs are regulated is poorly understood. To explore this question, we analyzed gene expression profiles of skin ILCs of wild-type and Rag1−/− mice and discovered that the chemokine receptor CCR10+ skin ILCs dominant in the health skin were of homeostatic properties while CCR10− skin ILCs are activated effector cells with elevated expression of various stimulatory cytokine receptors and signaling molecules. In stearoyl-CoA desaturase 1-knockout (KO) mice whose skin was defective in thermohomeostatic maintenance due to impaired fatty acid synthesis and lipid barrier formation, there was predominant activation of CCR10−CD81+ST2+ group 2 ILCs (ILC2s) while raising these mice at a thermo-neutral room temperature or feeding them with high-fat diet reduced the ILC2 activation, suggesting that skin ILC2s are activated by cold-induced signals to help thermo-homeostatic maintenance. Consistent with this, topical application of menthol, an agonist ligand for the cold-sensing receptor TRPM8, led to activation of CCR10−CD81+ST2+ skin ILC2s and increased dermal adipocyte maturation and uncoupling protein 1 production. Furthermore, compared to wild-type controls, menthol-treated TRPM8-KO and IL-18-KO mice had reduced CCR10−CD81+ activated skin ILC2s, suggesting that IL-18 mediated the TRPM8 activation of skin ILC2s. Our study reveals a neuron-derived cold-sensing pathway in activation of skin ILC2s that helps thermo-regulation but could also cause tissue inflammation if chronically activated.

Neuroimaging Of Cold Allodynia Reveals A Central Disinhibition Mechanism Of Pain.

PurposeAllodynia refers to pain evoked by physiologically innocuous stimuli. It is a disabling symptom of neuropathic pain following a lesion within the peripheral or central nervous system. In fact, two different pathophysiological mechanisms of cold allodynia (ie, hypersensitivity to innocuous cold) have been proposed. The peripheral sensitization of nociceptive neurons can produce cold allodynia, which can be induced experimentally by a topical application of menthol. An alternative mechanism involves reduced inhibition of central pain processing by innocuous cold stimuli. A model to induce the latter type of allodynia is the conduction block of peripheral A-fiber input.Patients and methodsIn the presented study, functional MRI was used to analyze these two different experimental models of cold allodynia. In order to identify the underlying cerebral activation patterns of both mechanisms, the application of menthol and the induction of a mechanical A-fiber blockade were studied in healthy volunteers.ResultsThe block-induced cold allodynia caused significantly stronger activation of the medial polymodal pain processing pathway, including left medial thalamus, anterior cingulate cortex, and medial prefrontal cortex. In contrast, menthol-induced cold allodynia caused significantly stronger activity of the left lateral thalamus as well as the primary and secondary somatosensory cortices, key structures of the lateral discriminative pathway of pain processing. Mean pain intensity did not differ between both forms of cold allodynia.ConclusionExperimental cold allodynia is mediated in different cerebral areas depending on the underlying pathophysiology. The activity pattern associated with block-induced allodynia confirms a fundamental integration between painful and non-painful temperature sensation, ie, the cold-induced inhibition of cold pain.

Drosophila menthol sensitivity and the Precambrian origins of transient receptor potential-dependent chemosensation.

Transient receptor potential (TRP) cation channels are highly conserved, polymodal sensors which respond to a wide variety of stimuli. Perhaps most notably, TRP channels serve critical functions in nociception and pain. A growing body of evidence suggests that transient receptor potential melastatin (TRPM) and transient receptor potential ankyrin (TRPA) thermal and electrophile sensitivities predate the protostome-deuterostome split (greater than 550 Ma). However, TRPM and TRPA channels are also thought to detect modified terpenes (e.g. menthol). Although terpenoids like menthol are thought to be aversive and/or harmful to insects, mechanistic sensitivity studies have been largely restricted to chordates. Furthermore, it is unknown if TRP-menthol sensing is as ancient as thermal and/or electrophile sensitivity. Combining genetic, optical, electrophysiological, behavioural and phylogenetic approaches, we tested the hypothesis that insect TRP channels play a conserved role in menthol sensing. We found that topical application of menthol to Drosophila melanogaster larvae elicits a Trpm- and TrpA1-dependent nocifensive rolling behaviour, which requires activation of Class IV nociceptor neurons. Further, in characterizing the evolution of TRP channels, we put forth the hypotheses that three previously undescribed TRPM channel clades (basal, αTRPM and βTRPM), as well as TRPs with residues critical for menthol sensing, were present in ancestral bilaterians. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

Menthol‐induced hyperthermia and its implication for a pharmacological approach to obesity prevention and treatment

We have previously shown that short‐term repeated treatment with topical menthol results in less body mass gain in lean Wistar rats compared to controls due to a persistent increase in energy expenditure, with limited compensatory thermoregulatory adaptations and, most unexpectedly, without affecting food intake (Vizin et al, J Appl Physiol. 2018 124(3):672–683). Menthol seems thus to be a promising drug for the prevention of obesity. Whether repeated topical application of menthol affects body weight gain in obese animals is not known. We tested the effects of topical menthol (5%) treatment on body weight gain and body temperature on both genetic obese ob/ob mice and in high‐fat diet (HFD)‐induced obesity in Wistar rats. In control mice (WT) repeated application of menthol (9 days) resulted in a reduction of body mass gain, as a consequence of increased energy expenditure, as measured by the persistent hyperthermic response after menthol. However, in obese ob/ob mice repeated application of menthol for 9 days was not sufficient to cause a significant reduction in body mass gain. The hyperthermic response of ob/ob mice to menthol was reduced as compared to WT thermoregulatory response. In HFD‐obese rats, topical menthol treatment for 9 days resulted in a decrease in ~20g in mean body weight, which is correspondent to a 5% reduction in body mass. Menthol treatment was accompanied by a hyperthermic response in obese rats, which most probably accounted for the increased energy expenditure that allowed body mass reduction. Our data support the suggestion that menthol is a promising drug not only for obesity prevention (as it reduces body mass gain in lean animals) but also for the treatment of HFD‐induced obesity as well.Support or Funding InformationFapesp (grants 2017/13062‐5 and 2015/02991‐0)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Involvement of Glucagon in Preventive Effect of Menthol Against High Fat Diet Induced Obesity in Mice.

Glucagon mediated mechanisms have been shown to play clinically significant role in energy expenditure. The present study was designed to understand whether pharmacological mimicking of cold using menthol (TRPM8 modulator) can induce glucagon-mediated energy expenditure to prevent weight gain and related complications. Acute oral and topical administration of TRPM8 agonists (menthol and icilin) increased serum glucagon concentration which was prevented by pre-treatment with AMTB, a TRPM8 blocker. Chronic administration of menthol (50 and 100 mg/kg/day for 12 weeks) to HFD fed animals prevented weight gain, insulin resistance, adipose tissue hypertrophy and triacylglycerol deposition in liver. These effects were not restricted to oral administration, but also observed upon the topical application of menthol (10% w/v). The metabolic alterations caused by menthol in liver and adipose tissue mirrored the known effects of glucagon, such as increased glycogenolysis and gluconeogenesis in the liver, and enhanced thermogenic activity of white and brown adipose tissue. Correlation analysis suggests a strong correlation between glucagon dependent changes and energy expenditure markers. Interestingly, in-vitro treatment of the serum of menthol treated mice increased energy expenditure markers in mature 3T3L1 adipocytes, which was prevented in the presence of non-competitive glucagon receptor antagonist, L-168,049, indicating that menthol-induced increase in serum glucagon is responsible for increase in energy expenditure phenotype. In conclusion, the present work provides evidence that glucagon plays an important role in the preventive effect of menthol against HFD-induced weight gain and related complications.

Impact of suggestion on the human experimental model of cold hyperalgesia after topical application of high-concentration menthol [40%

Human experimental pain models in healthy subjects offer unique possibilities to study mechanisms of pain within a defined setting of expected pain symptoms, signs and mechanisms. Previous trials in healthy subjects demonstrated that topical application of 40% menthol is suitable to induce cold hyperalgesia. The objective of this study was to evaluate the impact of suggestion on this experimental human pain model. The study was performed within a single-centre, randomized, placebo-controlled, double-blind, two-period crossover trial in a cohort of 16 healthy subjects. Subjects were tested twice after topical menthol application (40% dissolved in ethanol) and twice after ethanol (as placebo) application. In the style of a balanced placebo trial design, the subjects received during half of the testing the correct information about the applied substance (topical menthol or ethanol) and during half of the testing the incorrect information, leading to four tested conditions (treatment conditions: menthol-told-menthol and menthol-told-ethanol; placebo conditions: ethanol-told-menthol and ethanol-told-ethanol). Cold but not mechanical hyperalgesia was reliably induced by the model. The cold pain threshold decreased in both treatment conditions regardless whether true or false information was given. Minor suggestion effects were found in subjects with prior ethanol application. The menthol model is a reliable, nonsuggestible model to induce cold hyperalgesia. Mechanical hyperalgesia is not as reliable to induce. Cold hyperalgesia may be investigated under unbiased and suggestion-free conditions using the menthol model of pain.

INFLUENCE OF TOPICALLY APPLIED MENTHOL COOLING GEL ON SOFT TISSUE THERMODYNAMICS AND ARTERIAL AND CUTANEOUS BLOOD FLOW AT REST

Topical application of menthol is a popular form of cold therapy and chemically triggers cold receptors and increases cutaneous blood flow. However, although cutaneous blood flow increases, it remains unknown where this increase arises from. Intramuscular temperature assessment may indirectly indicate a change in muscular blood flow. To establish intramuscular temperature, blood flow responses and subjective temperature sensation following application of menthol-based cooling gel to the anterior thigh. Controlled, randomized cross over interventional study. Twenty (age: 21.4 + 1.7) healthy males were treated on three separate days in random order with ice, a menthol-based gel or placebo gel (participant single blinded) on one anterior thigh. All measurements were taken at baseline and for 80 mins following treatment: 1) Skin, core, and intramuscular temperatures (1 & 3 cm deep); 2) femoral arterial blood flow (duplex ultrasound); 3) cutaneous blood flow (laser Doppler) and 4) subjective cold sensation. Ice and both gels decreased (p<0.0001, CI (Ice): -5.2 to -6.2 and CI (gels) -1.4 to -2.5) intramuscular temperature by 5.7 and 1.9 °C respectively, but by 80 mins were similar to each other (1.5-2 °C less than pre-treatment). Skin temperature mirrored muscle temperature with 8.8 and 4.2 °C respective decline for ice and gels. Menthol gel increased (p<0.0001) cutaneous blood flow by 0.3 ml/min compared to unaltered flow associated with the placebo gel and a decline of 0.3 ml/min for the ice. Menthol gel cold sensation was subjectively reported to be cooler (p<0.0001) than the other two treatments. Core temperature and arterial flow were unaffected. This is the first study to demonstrate the intramuscular cooling effect of menthol-based gel. However, the likely cause was from evaporative cooling despite menthol-derived increases in cutaneous blood flow and cooling sensation. Treatment, level 2.

Topical Menthol Gel Versus a Placebo Gel on Postmanipulation Pain and Range of Motion in Patients With Mechanical Neck Pain

**Purpose**: The purpose of this study is to determine whether patients with mechanical neck pain who received topical menthol gel application to their neck before cervical manipulation experienced a reduction in pain and an increase in neck range of motion following cervical manipulation. **Methods**: Patients (mean age, 35 years) with nonradicular mechanical neck pain were randomly assigned to a control (n = 31) or a treatment (n = 29) group. Five minutes before cervical manipulation, controls received topical placebo gel application to their neck, whereas the treatment received topical application of a menthol-containing gel (Biofreeze®). Participants rated their neck pain on a 10-point scale before application of the get (Pre) and at 1 min (T1), 10 min (T2), 20 min (T3), and 30 min (T4) after cervical manipulation. Six measures of neck range of motion were assessed before the topical applications of gel and at T1 and T4. Repeated-measures ANCOVA was performed to compare the pain and neck range of motion following manipulation while controlling for premeasures. **Results**: There were no significant differences between the groups’ pain or range of motion assessed at Pre. The treatment group reported significantly (P < .05) reduced pain at T2, T3, T4 compared to T1, while the control group did not experience significant change in their pain compared to T1. Neither study group rated a change in neck range of motion during the study. **Conclusion**: Topical menthol application before manipulation may reduce neck pain, but it has no measurable effect on neck range of motion following cervical manipulation among patients with mechanical neck pain.

Comparison of the Effect of Topical Application of Rosemary and Menthol for Musculoskeletal Pain in Hemodialysis Patients.

Background:Pain is the most common problem experienced by hemodialysis patients, especially musculoskeletal pain in lower extremities, which is usually not completely treated and adversely affects their quality of life. The present study was conducted with the aim to determine and compare the effects of topical application of menthol and rosemary for musculoskeletal pain in hemodialysis patients.Materials and Methods:The present single-blind clinical trial recruited 105 eligible patients undergoing hemodialysis in selected hospitals affiliated to Isfahan University of Medical Sciences; patients were selected by convenient sampling. Participants’ severity of pain was determined prior to intervention. They were then randomly divided into rosemary, menthol, and placebo groups. All three groups applied medication on the site of pain on their legs three times a day for three days and recorded the severity of pain four hours after morning and afternoon applications. The statistical analysis of data was performed using SPSS 18.Results:The mean score of severity of pain before the intervention was not significantly different among the three groups (p = 0.83), but it became significantly different after intervention (p = 0.001). Significant differences were observed in mean severity of pain before and after intervention in rosemary and menthol groups (p < 0.001), but not in the placebo group (p = 0.21).Conclusions:Topical application of menthol and rosemary can alleviate severity and frequency of recurrence of musculoskeletal pain in hemodialysis patients; however, according to the results of the study, none had precedence over the other.

Topical Menthol Application Augments Cutaneous Microvascular Blood Flow

Menthol, the active ingredient in several topical analgesic gels, activates transient receptor potential melastatin 8 (TRPM8) receptors on sensory nerves, eliciting a cold sensation and potentially vasoconstriction. Menthol can also act on vascular TRPM8 receptors inducing vasodilation. PURPOSE: We sought to characterize the cutaneous vascular effects of topical menthol application and to determine the mechanism(s) through which menthol may alter skin blood flow (SkBF). METHODS: Three distinct protocols were conducted in three groups of 10 young (24±1 years), healthy subjects in a double blind placebo control design. Red cell flux was measured via laser speckle contrast imaging (Moor FLPI) in all protocols and normalized to cutaneous vascular conductance (CVC=flux*mmHg-1). Protocol 1: Placebo and 4% menthol gels were applied separately to 60cm2 of skin without local thermal control and SkBF was continuously measured. Protocol 2: Seven concentrations of menthol gel (0.04%, 0.4%, 1%, 2%, 4%, 7%, 8%) were applied to the skin to model the dose-response relation. Protocol 3: Both with and without pretreatment with topical lidocaine, placebo and 4% menthol gels were applied to skin under local thermal control (33°C). Post-occlusive reactive hyperemia (PORH) and local heating (42°C) protocols were conducted to determine the contribution of endothelium derived hyperpolarizing factors (EDHFs) and nitric oxide, respectively. Data were expressed as CVC for all protocols. RESULTS: Topical menthol application increased SkBF compared to placebo (3.4±0.3 v 1.1±0.2 CVC: p<0.001). During the dose response, SkBF increased with increasing doses of menthol (main effect, p<0.05) with an ED50 of 1%. Similarly, SkBF was augmented with menthol application during PORH (3.6±0.3 v 2.5±0.2 CVC; p<0.001), but not local heating (3.0±0.2 v 2.9±0.3 CVC; p=0.44). Concurrent sensory nerve inhibition attenuated menthol-mediated dilation at thermoneutral baseline (1.3±0.2 CVC; p<0.001) and during PORH (2.8±0.3 CVC; p<0.001), but not during local heating (3.4±0.2 CVC; p=0.1). CONCLUSION: Topically applied menthol dose-dependently increases blood flow in the cutaneous microvasculature. This increase in blood flow is mediated, in-part by EDHFs and sensory nerves.

Topical menthol increases cutaneous blood flow

Menthol, the active ingredient in several topically applied analgesics, activates transient receptor potential melastatin 8 (TRPM8) receptors on sensory nerves and on the vasculature inducing a cooling sensation on the skin. Ilex paraguariensis is also a common ingredient in topical analgesics that has potential vasoactive properties and may alter the mechanisms of action of menthol. We sought to characterize the microvascular effects of topical menthol and ilex application and to determine the mechanism(s) through which these compounds may independently and combined alter cutaneous blood flow. We hypothesized that menthol would induce vasoconstriction and that ilex would not alter skin blood flow (SkBF). Three separate protocols were conducted to examine menthol and ilex-mediated changes in SkBF. In protocol 1, placebo, 4% menthol, 0.7% ilex, and combination menthol+ilex gels were applied separately to the skin and red cell flux was continuously measured utilizing laser speckle contrast imaging (LSCI). In protocol 2, seven concentrations of menthol gel (0.04%, 0.4%, 1%, 2%, 4%, 7%, 8%) were applied to the skin to model the dose–response curve. In protocol 3, placebo, menthol, ilex, and menthol+ilex gels were applied to skin under local thermal control (34°C) both with and without sensory nerve blockage (topical lidocaine 4%). Post-occlusive reactive hyperemia (PORH) and local heating (42°C) protocols were conducted to determine the relative contribution of endothelium derived hyperpolarizing factors (EDHFs)/sensory nerves and nitric oxide (NO), respectively. Red cell flux was normalized to mean arterial pressure expressed as cutaneous vascular conductance (CVC: flux·mmHg−1) in all protocols. Topical menthol application increased SkBF compared to placebo (3.41±0.33 vs 1.1±0.19CVC: p<0.001). During the dose–response, SkBF increased with increasing doses of menthol (main effect, p<0.05) with an ED50 of 1.0%. Similarly, SkBF was increased after menthol application during PORH (3.62±0.29 vs. 2.50±0.21flux·mmHg−1; p<0.001), but not local heating (2.98±0.24 vs 2.86±0.32flux·mmHg−1; p=0.44). Concurrent sensory nerve inhibition attenuated menthol-mediated vasodilation at thermoneutral baseline (1.29±0.19flux·mmHg−1; p<0.001) and during PORH (2.79±0.28flux·mmHg−1; p<0.001), but not during local heating (3.45±0.21flux·mmHg−1; p=0.1). Topically applied menthol, but not ilex, dose-dependently increases blood flow in the cutaneous microvasculature. This increase in blood flow is mediated, in-part by sensory nerves and EDHFs.

Effects of menthol on thermoregulatory responses after exercise-induced hyperthermia

Menthol is a chemical compound stimulating TRPM8 which is activated in relatively cool environment below 28 °C [1] and induces cooling sensation on human skin [2]. Many researchers have explored menthol's thermo-physiological influences on humans. Lee and colleagues [3] found that rectal temperature increased faster and total sweat rate was lower than control when a 0.8 % menthol solution was applied on the upper body. Most researches have focused on menthol application during or before heat exposure, but in the practical situation menthol products are used for relieving thermal discomfort or muscular fatigue after intensive exercise. Therefore, the effects of topical menthol application on physiological responses, including sweat secretion after exercise-induced hyperthermia were investigated in the present study. We hypothesized that menthol application during recovery after exercise would relieve thermal sensation without increasing deep body temperature.

Effects of Topical Menthol on Skin Blood Flow and Active Sweat Gland Density during Hyperthermia

Topical application of menthol evokes cold sensation and cutaneous vasoconstriction without actual reduction in tissue temperature via the stimulation of a specific cold receptor family known as TRPM8. While being widely used to reduce joint pain, muscle inflammation, and soft tissue injuries in athletes and individuals with musculoskeletal disease, topical menthol may adversely affect body’s heat loss mechanisms. PURPOSE: To investigate if topical application of menthol reduces skin blood flow (SkBF) and active sweat gland density (ASGD) to the extent to which body heat loss is significantly reduced during recovery from exercise-induced hyperthermia. METHODS: Ten healthy male subjects (22±1 yrs) underwent two trials of cycle exercise at 50% VO2max in the heat (45°C, 50%) until their rectal temperatures (Tre) elevate 1.5°C above the baseline. Following the cessation of exercise, either 10g of 3.1% menthol gel (MEN) or placebo Lanolin cream (PBO) was applied on the limbs except hands and feet after which subjects recovered on a chair for 30min in thermoneutral condition (23°C, 50%). SkBF and ASGD were measured using a laser Doppler flowmetery and an iodine-impregnated cotton paper on ventral forearm and anterior thigh. Thermal measurements included Tre, 4-sites mean skin temperature (Tsk), and thermal sensation (TS: −4 very cold ~ 4 very hot). RESULTS: Cold TS in MEN was significantly greater than in PBO (F=29.22, P<.01) while reduction in SkBF and ASGD in MEN did not show significant difference compared to PBO. These slight alterations in vasomotor/sudomotor responses to topical menthol did not significantly impair Tre or Tsk recovery from hyperthermia.Table: No title available.CONCLUSION: Topical application of menthol does not adversely affect body heat loss during recovery from exercise-induced hyperthermia while significantly inducing cold TS.