Cutaneous application of menthol 10% solution as an abortive treatment of migraine without aura: a randomised, double-blind, placebo-controlled, crossed-over study

Activation of central and peripheral transient receptor potential melastatin 8 increases susceptibility to spreading depolarization and facilitates trigeminal neuroinflammation

BACKGROUND

Transient receptor potential melastatin 8 (TRPM8), a gene encoding a nonselective cation channel responsive to cold stimuli, has been implicated in migraine susceptibility. Despite this association, the role of TRPM8 to migraine pathogenesis remains elusive. This study aims to elucidate the potential role of TRPM8 in migraine pathophysiology.

METHODS

TRPM8 expression in the cortex and primary trigeminal ganglion (TG) cells was analyzed via immunostaining. The central role of TRPM8 was assessed using a spreading depolarization (SD) model, where intracerebroventricular injections or topical applications of TRPM8 agonists and antagonists were administered to rats to investigate their effects on KCl-evoked SD and SD-induced cortical inflammation. The peripheral role of TRPM8 in migraine was evaluated using primary cultures of rat TG cells by analyzing the effects of TRPM8 activation on calcitonin gene-related peptide (CGRP) expression, release, and trigeminal neuroinflammation.

RESULTS

TRPM8 was homogeneously distributed in the cerebral cortex, predominantly co-localizing with cortical neurons. Activation of cortical TRPM8 increased the frequency of KCl-evoked SD and exacerbated SD-induced cortical inflammation. Interestingly. Interestingly, inhibition of cerebral TRPM8 had negligible effects. In TG primary cultures, TRPM8 activation upregulated CGRP expression and release and induced cyclooxygenase-2 (Cox2) upregulation via a calmodulin kinase II (CaMKII)-dependent mechanism.

CONCLUSIONS

TRPM8 activation increased susceptibility to SD and facilitated the effects of CGRP and trigeminal neuroinflammation, implicating that TRPM8 may contribute to migraine pathophysiology through central and peripheral mechanisms.

The neurotrophic factor artemin and its receptor GFRα3 mediate migraine-like pain via the ion channel TRPM8

BACKGROUND

Migraine has a strong genetic foundation, including both monogenic and polygenic types. The former are rare, with most migraine considered polygenic, supported by genome-wide association studies (GWAS) identifying numerous genetic variants linked with migraine risk. Surprisingly, some of the most common mutations are associated with transient receptor potential melastatin 8 (TRPM8), a non-selective cation channel that is the primary sensor of cold temperatures in cutaneous primary afferents of the somatosensory system. However, it is unlikely that the temperature sensitivity of TRPM8 is relevant in migraine-related tissues, such as the meninges, suggesting other activation mechanisms underly its role in migraine pathogenesis. Thus, to define the basis of the channel's involvement, we reasoned that cellular processes that increase cold sensitivity in the skin, such as the neurotrophic factor artemin, via its receptor glial cell-line derived neurotrophic factor family receptor alpha-3 (GFRα3), also mediate TRPM8-associated migraine-like pain in the meninges.

METHODS

To investigate the role of artemin and GFRα3 in preclinical rodent migraine models, we infused nitroglycerin acutely and chronically, and measured changes in periorbital and hind paw mechanical sensitivity in male and female mice lacking GFRα3, after neutralization of free artemin with specific monoclonal antibodies, or by systemic treatment with a TRPM8-specific antagonist. Further, in mice lacking GFRα3 we tested the effects of supradural infusions of a mix of inflammatory mediators, as well as tested if dura stimulation with artemin or a TRPM8-specific agonist induce migraine-related pain in mice.

RESULTS

We find that mechanical allodynia induced by systemic nitroglycerin, or supradural infusion of inflammatory mediators, involves GFRα3. In addition, neutralization of circulating artemin reduces the nitroglycerin phenotype, demonstrating the importance of this neurotrophic pathway in headaches. Further, we show TRPM8 expression in the meninges, and that direct supradural infusion of either a TRPM8-specific agonist or artemin itself produces mechanical allodynia, with the latter dependent on TRPM8 and ameliorated by concurrent treatment with sumatriptan.

CONCLUSIONS

These results indicate that neuroinflammatory events in the meninges can produce migraine-like pain in mice via artemin and GFRα3, likely acting upstream of TRPM8, providing a novel pathway that may contribute to headaches or migraine pathogenesis.

The neurotrophic factor artemin and its receptor GFRα3 mediate migraine-like pain via the ion channel TRPM8

Background

Migraine has a strong genetic foundation, including both monogenic and polygenic types. The former are rare, with most migraine considered polygenic, supported by genome-wide association studies (GWAS) identifying numerous genetic variants associated with migraine risk. Surprisingly, some of the most common mutations are associated with TRPM8, a non-selective cation channel that is the primary sensor of cold temperatures in primary afferent neurons of the somatosensory system. However, it is unlikely that the temperature sensitivity of TRPM8 underlies its role in migraine pathogenesis. To define the basis of the channel's involvement, we reasoned that cellular processes that increase cold sensitivity in the skin, such as the neurotrophic factor artemin, via its receptor GFRα3, also mediate TRPM8-associated migraine-like pain in the meninges.

Methods

To investigate the role of artemin and GFRα3 in preclinical rodent migraine models, we infused nitroglycerin acutely and chronically, and measured changes in periorbital and hind paw mechanical sensitivity in male and female mice lacking GFRα3, after neutralization of free artemin with specific monoclonal antibodies, or by systemic treatment with a TRPM8-specific antagonist. Further, in wildtypes and mice lacking either GFRα3 or TRPM8, we tested the effects of supradural infusions of a mix of inflammatory mediators, artemin, and a TRPM8-specific agonist on migraine-related pain in mice.

Results

We find that mechanical allodynia induced by systemic nitroglycerin, or supradural infusion of inflammatory mediators, involves GFRα3. In addition, neutralization of circulating artemin reduces the nitroglycerin phenotype, demonstrating the importance of this neurotrophic pathway. Further, we show TRPM8 expression in the meninges and that direct supradural infusion of either a TRPM8-specific agonist or artemin itself produces mechanical allodynia, the latter dependent on TRPM8 and ameliorated by concurrent treatment with sumatriptan.

Conclusions

These results indicate that neuroinflammatory events in the meninges can produce migraine-like pain in mice via artemin and GFRα3, likely acting upstream of TRPM8, providing a novel pathway that may contribute to migraine pathogenesis.

Current Update on Categorization of Migraine Subtypes on the Basis of Genetic Variation: a Systematic Review

Migraine is a complex neurovascular disorder that is characterized by severe behavioral, sensory, visual, and/or auditory symptoms. It has been labeled as one of the ten most disabling medical illnesses in the world by the World Health Organization (Aagaard et al Sci Transl Med 6(237):237ra65, 2014). According to a recent report by the American Migraine Foundation (Shoulson et al Ann Neurol 25(3):252-9, 1989), around 148 million people in the world currently suffer from migraine. On the basis of presence of aura, migraine is classified into two major subtypes: migraine with aura (Aagaard et al Sci Transl Med 6(237):237ra65, 2014) and migraine without aura. (Aagaard K et al Sci Transl Med 6(237):237ra65, 2014) Many complex genetic mechanisms have been proposed in the pathophysiology of migraine but specific pathways associated with the different subtypes of migraine have not yet been explored. Various approaches including candidate gene association studies (CGAS) and genome-wide association studies (Fan et al Headache: J Head Face Pain 54(4):709-715, 2014). have identified the genetic markers associated with migraine and its subtypes. Several single nucleotide polymorphisms (Kaur et al Egyp J Neurol, Psychiatry Neurosurg 55(1):1-7, 2019) within genes involved in ion homeostasis, solute transport, synaptic transmission, cortical excitability, and vascular function have been associated with the disorder. Currently, the diagnosis of migraine is majorly behavioral with no focus on the genetic markers and thereby the therapeutic intervention specific to subtypes. Therefore, there is a need to explore genetic variants significantly associated with MA and MO as susceptibility markers in the diagnosis and targets for therapeutic interventions in the specific subtypes of migraine. Although the proper characterization of pathways based on different subtypes is yet to be studied, this review aims to make a first attempt to compile the information available on various genetic variants and the molecular mechanisms involved with the development of MA and MO. An attempt has also been made to suggest novel candidate genes based on their function to be explored by future research.

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.

Peppermint and menthol: a review on their biochemistry, pharmacological activities, clinical applications, and safety considerations

In this manuscript, we conducted a comprehensive review of the diverse effects of peppermint on human health and explored the potential underlying mechanisms. Peppermint contains three main groups of phytochemical constituents, including essential oils (mainly menthol), flavonoids (such as hesperidin, eriodictyol, naringenin, quercetin, myricetin, and kaempferol), and nonflavonoid phenolcarboxylic acids. Peppermint exhibits antimicrobial, antioxidant, anti-inflammatory, immunomodulatory, anti-cancer, anti-aging, and analgesic properties and may be effective in treating various disorders, including gastrointestinal disorders (e.g., irritable bowel syndrome, dyspepsia, constipation, functional gastrointestinal disorders, nausea/vomiting, and gallbladder stones). In addition, peppermint has therapeutic benefits for psychological and cognitive health, dental health, urinary retention, skin and wound healing, as well as anti-depressant and anti-anxiety effects, and it may improve memory. However, peppermint has paradoxical effects on sleep quality and alertness, as it has been shown to improve sleep quality in patients with fatigue and anxiety, while also increasing alertness under conditions of monotonous work and relaxation. We also discuss its protective effects against toxic agents at recommended doses, as well as its safety and potential toxicity. Overall, this review provides the latest findings and insights into the properties and clinical effects of peppermint/menthol and highlights its potential as a natural therapeutic agent for various health conditions.

A new gene for autosomal dominant facial palsy/migraine identified in a family by whole exome sequencing

BACKGROUND

Facial palsy manifests as unilateral or bilateral weakness and inability to move some of the facial muscles. The aetiology may be different including idiopathic, trauma, infections or brain tumours or it can be associated with chronic neurological diseases. For instance, in recurrent migraine, an increased risk of idiopathic facial palsy (often unilateral) has been observed. Migraine is a neurovascular disorder characterized by mild to severe intensity of headaches, often associated with neuro-ophthalmological symptoms.

METHODS

A family is reported where five members were affected by facial palsy associated with other clinical features including migraine, diplopia, facial swelling, eye conjunctivitis following a vertical transmission. Whole exome sequencing was performed in three members (two affected and one healthy) in order to identify potential variants causative of their phenotype.

RESULTS

A missense variant c.304G>A was found leading to the p.(Ala102Thr) substitution in the TRPM8 gene, previously related to migraine by genome wide association studies. This variant was classified as deleterious by several predictor tools, and the mutant residue was predicted to alter the protein structure in terms of flexibility and interactions with the surrounding residues.

CONCLUSION

These findings suggest that TRPM8 could be a new causative gene further linking migraine and recurrent facial palsy.

[Complementary and supplementary procedures in the treatment of headache]

In Germany, headache is one of the illnesses that most frequently leads to health impairments and to consultation with physicians. Even in children, headache is often associated with restricted activities of daily life. Nevertheless, the level of care for headache disorders is disproportionate to the medical needs. As a result, patients regularly use complementary and supportive therapeutic procedures. This review shows the procedures currently used for primary headache in childhood and adulthood, the methodological approaches and existing scientific evidence. The safety of the therapeutic options is also classified. These methods include physiotherapy, neural therapy, acupuncture, homeopathy, phytotherapy and the intake of dietary supplements. For children and adolescents with headaches, there are studies in the field of dietary supplements for coenzyme Q10, riboflavin, magnesium and vitamin D, which indicate specific effects in the reduction of headaches.

Rare variants with large effects provide functional insights into the pathology of migraine subtypes, with and without aura

Migraine is a complex neurovascular disease with a range of severity and symptoms, yet mostly studied as one phenotype in genome-wide association studies (GWAS). Here we combine large GWAS datasets from six European populations to study the main migraine subtypes, migraine with aura (MA) and migraine without aura (MO). We identified four new MA-associated variants (in PRRT2, PALMD, ABO and LRRK2) and classified 13 MO-associated variants. Rare variants with large effects highlight three genes. A rare frameshift variant in brain-expressed PRRT2 confers large risk of MA and epilepsy, but not MO. A burden test of rare loss-of-function variants in SCN11A, encoding a neuron-expressed sodium channel with a key role in pain sensation, shows strong protection against migraine. Finally, a rare variant with cis-regulatory effects on KCNK5 confers large protection against migraine and brain aneurysms. Our findings offer new insights with therapeutic potential into the complex biology of migraine and its subtypes.

Menthol excites dural afferent neurons by inhibiting leak K+ conductance in rats

Menthol-a natural organic compound-is widely used for relieving various pain conditions including migraine. However, a high dose of menthol reportedly decreases pain thresholds and enhances pain responses. Accordingly, in the present study, we addressed the effect of menthol on the excitability of acutely isolated dural afferent neurons, which were identified with a fluorescent dye, using the whole-cell patch-clamp technique. Under a voltage-clamped condition, menthol altered the holding current levels in a concentration-dependent manner. The menthol-induced current (IMenthol) remained unaffected by the addition of selective transient receptor potential melastatin 8 antagonists. Moreover, the reversal potential of IMenthol was similar to the equilibrium potential of K+. IMenthol was accompanied by an increase in input resistance, thereby suggesting that menthol decreases the leak K+ conductance. Under a current-clamped condition, menthol caused depolarization of the membrane potential and decreased the threshold for the generation of action potential. While the IMenthol was substantially inhibited by 10 μM XE-991, a selective KV7 blocker, the M-current mediated by KV7 was not detected in the nociceptive neurons tested in the present study. Moreover, IMenthol decreased under acidic extracellular pH conditions or in the presence of 3 μM A-1899, a selective K2P3.1 and K2P9.1 blocker. The present results suggest that menthol inhibits leak K+ channels, possibly acid-sensitive two-pore domain K+ channels, thereby increasing the excitability of nociceptive sensory neurons. The resultant increase in neuron excitability may partially be responsible for the pronociceptive effect mediated by high menthol doses.

Assessing the Effects of the Topical Application of L-Menthol on Pain-Related Somatosensory-Evoked Potentials Using Intra-Epidermal Stimulation

L-menthol is known to activate transient receptor potential melastatin 8 (TRPM8) and induce analgesia to thermal stimuli. However, since thermal stimulation leads to the interaction among the other TRP channels, it was unclear whether L-menthol causes analgesia to stimuli other than thermal stimuli. Therefore, we aimed to investigate whether activating TRPM8 via topical application of 10% menthol solution attenuates pain-related somatosensory-evoked potentials (pSEPs) and affects numerical rating scale (NRS) score using intra-epidermal electrical stimulation (IES). We applied 10% L-menthol or control solution on the dorsum of the right hand of 25 healthy participants. The pSEP and NRS, elicited by IES, and sensory threshold were measured before and after each solution was applied. The results showed that the topical application of 10% L-menthol solution significantly reduced N2-P2 amplitude in pSEPs compared with the control solution. Moreover, the N2 latency was significantly prolonged upon the topical application of L-menthol solution. NRS scores were similar under both conditions. These results suggest that topical application of L-menthol does not alter subjective sensation induced using IES, although it may attenuate afferent signals at free nerve endings even with stimuli that do not directly activate TRP channels.

Targeting Nociceptive Neurons and Transient Receptor Potential Channels for the Treatment of Migraine

Migraine is a neurovascular disorder that affects approximately 12% of the global population. While its exact causes are still being studied, researchers believe that nociceptive neurons in the trigeminal ganglia play a key role in the pain signals of migraine. These nociceptive neurons innervate the intracranial meninges and convey pain signals from the meninges to the thalamus. Targeting nociceptive neurons is considered promising due to their accessibility and distinct molecular profile, which includes the expression of several transient receptor potential (TRP) channels. These channels have been linked to various pain conditions, including migraine. This review discusses the role and mechanisms of nociceptive neurons in migraine, the challenges of current anti-migraine drugs, and the evidence for well-studied and emerging TRP channels, particularly TRPC4, as novel targets for migraine prevention and treatment.

Exploring Novel Therapeutic Targets in the Common Pathogenic Factors in Migraine and Neuropathic Pain

Migraine and neuropathic pain (NP) are both painful, disabling, chronic conditions which exhibit some symptom similarities and are thus considered to share a common etiology. The calcitonin gene-related peptide (CGRP) has gained credit as a target for migraine management; nevertheless, the efficacy and the applicability of CGRP modifiers warrant the search for more effective therapeutic targets for pain management. This scoping review focuses on human studies of common pathogenic factors in migraine and NP, with reference to available preclinical evidence to explore potential novel therapeutic targets. CGRP inhibitors and monoclonal antibodies alleviate inflammation in the meninges; targeting transient receptor potential (TRP) ion channels may help prevent the release of nociceptive substances, and modifying the endocannabinoid system may open a path toward discovery of novel analgesics. There may exist a potential target in the tryptophan-kynurenine (KYN) metabolic system, which is closely linked to glutamate-induced hyperexcitability; alleviating neuroinflammation may complement a pain-relieving armamentarium, and modifying microglial excitation, which is observed in both conditions, may be a possible approach. Those are several potential analgesic targets which deserve to be explored in search of novel analgesics; however, much evidence remains missing. This review highlights the need for more studies on CGRP modifiers for subtypes, the discovery of TRP and endocannabinoid modulators, knowledge of the status of KYN metabolites, the consensus on cytokines and sampling, and biomarkers for microglial function, in search of innovative pain management methods for migraine and NP.

Preventive and Therapeutic Aspects of Migraine for Patient Care: An Insight

BACKGROUND

Migraine is a common neurological condition marked by frequent mild to extreme headaches that last 4 to 72 hours. A migraine headache may cause a pulsing or concentrated throbbing pain in one part of the brain. Nausea, vomiting, excessive sensitivity to light and sound, smell, feeling sick, vomiting, painful headache, and blurred vision are all symptoms of migraine disorder. Females are more affected by migraines in comparison to males.

OBJECTIVE

The present review article summarizes preventive and therapeutic measures, including allopathic and herbal remedies for the treatment of migraine.

RESULTS

This review highlights the current aspects of migraine pathophysiology and covers an understanding of the complex workings of the migraine state. Therapeutic agents that could provide an effective treatment have also been discussed.

CONCLUSION

It can be concluded that different migraines could be treated based on their type and severity.

TRP Channels: Recent Development in Translational Research and Potential Therapeutic Targets in Migraine

Migraine is a chronic neurological disorder that affects approximately 12% of the population. The cause of migraine headaches is not yet known, however, when the trigeminal system is activated, neuropeptides such as calcitonin gene-related peptide (CGRP) and substance P (SP) are released, which cause neurogenic inflammation and sensitization. Advances in the understanding of migraine pathophysiology have identified new potential pharmacological targets. In recent years, transient receptor potential (TRP) channels have been the focus of attention in the pathophysiology of various pain disorders, including primary headaches. Genetic and pharmacological data suggest the role of TRP channels in pain sensation and the activation and sensitization of dural afferents. In addition, TRP channels are widely expressed in the trigeminal system and brain regions which are associated with the pathophysiology of migraine and furthermore, co-localize several neuropeptides that are implicated in the development of migraine attacks. Moreover, there are several migraine trigger agents known to activate TRP channels. Based on these, TRP channels have an essential role in migraine pain and associated symptoms, such as hyperalgesia and allodynia. In this review, we discuss the role of the certain TRP channels in migraine pathophysiology and their therapeutic applicability.

ThermoTRP channels in pain sexual dimorphism: new insights for drug intervention

Chronic pain is a major burden for the society and remains more prevalent and severe in females. The presence of chronic pain is linked to persistent alterations in the peripheral and the central nervous system. One of the main types of peripheral pain transducers are the transient receptor potential channels (TRP), also known as thermoTRP channels, which intervene in the perception of hot and cold external stimuli. These channels, and especially TRPV1, TRPA1 and TRPM8, have been subjected to profound investigation because of their role as thermosensors and also because of their implication in acute and chronic pain. Surprisingly, their sensitivity to endogenous signaling has been far less studied. Cumulative evidence suggests that the function of these channels may be differently modulated in males and females, in part through sexual hormones, and this could constitute a significant contributor to the sex differences in chronic pain. Here, we review the exciting advances in thermoTRP pharmacology for males and females in two paradigmatic types of chronic pain with a strong peripheral component: chronic migraine and chemotherapy-induced peripheral neuropathy (CIPN). The possibilities of peripheral druggability offered by these channels and the differential exploitation for men and women represent a development opportunity that will lead to a significant increment of the armamentarium of analgesic medicines for personalized chronic pain treatment.

Natural Herbal Non-Opioid Topical Pain Relievers-Comparison with Traditional Therapy

Pain is the predominant symptom of many clinical diseases and is frequently associated with neurological and musculoskeletal problems. Chronic pain is frequent in the elderly, causing suffering, disability, social isolation, and increased healthcare expenses. Chronic pain medication is often ineffective and has many side effects. Nonsteroidal over-the-counter and prescription drugs are frequently recommended as first-line therapies for pain control; however, long-term safety issues must not be neglected. Herbs and nutritional supplements may be a safer and more effective alternative to nonsteroidal pharmaceuticals for pain management, especially when used long-term. Recently, topical analgesic therapies have gained attention as an innovative approach due to their sufficient efficacy and comparatively fewer systemic side effects and drug-drug interactions. In this paper, we overview the main natural herbal pain relievers, their efficacy and safety, and their potential use as topical agents for pain control. Although herbal-derived medications are not appropriate for providing quick relief for acute pain problems, they could be used as potent alternative remedies in managing chronic persistent pain with minimal side effects.

Natural products for migraine: Data-mining analyses of Chinese Medicine classical literature

Background: Treatment effect of current pharmacotherapies for migraine is unsatisfying. Discovering new anti-migraine natural products and nutraceuticals from large collections of Chinese medicine classical literature may assist to address this gap. Methods: We conducted a comprehensive search in the Encyclopedia of Traditional Chinese Medicine (version 5.0) to obtain migraine-related citations, then screened and scored these citations to identify clinical management of migraine using oral herbal medicine in history. Information of formulae, herbs and symptoms were further extracted. After standardisation, these data were analysed using frequency analysis and the Apriori algorithm. Anti-migraine effects and mechanisms of actions of the main herbs and formula were summarised. Results: Among 614 eligible citations, the most frequently used formula was chuan xiong cha tiao san (CXCTS), and the most frequently used herb was chuan xiong. Dietary medicinal herbs including gan cao, bai zhi, bo he, tian ma and sheng jiang were identified. Strong associations were constructed among the herb ingredients of CXCTS formula. Symptoms of chronic duration and unilateral headache were closely related with herbs of chuan xiong, gan cao, fang feng, qiang huo and cha. Symptoms of vomiting and nausea were specifically related to herbs of sheng jiang and ban xia. Conclusion: The herb ingredients of CXCTS which presented anti-migraine effects with reliable evidence of anti-migraine actions can be selected as potential drug discovery candidates, while dietary medicinal herbs including sheng jiang, bo he, cha, bai zhi, tian ma, and gan cao can be further explored as nutraceuticals for migraine.

The distinctive role of menthol in pain and analgesia: Mechanisms, practices, and advances

Menthol is an important flavoring additive that triggers a cooling sensation. Under physiological condition, low to moderate concentrations of menthol activate transient receptor potential cation channel subfamily M member 8 (TRPM8) in the primary nociceptors, such as dorsal root ganglion (DRG) and trigeminal ganglion, generating a cooling sensation, whereas menthol at higher concentration could induce cold allodynia, and cold hyperalgesia mediated by TRPM8 sensitization. In addition, the paradoxical irritating properties of high concentrations of menthol is associated with its activation of transient receptor potential cation channel subfamily A member 1 (TRPA1). Under pathological situation, menthol activates TRPM8 to attenuate mechanical allodynia and thermal hyperalgesia following nerve injury or chemical stimuli. Recent reports have recapitulated the requirement of central group II/III metabotropic glutamate receptors (mGluR) with endogenous κ-opioid signaling pathways for menthol analgesia. Additionally, blockage of sodium channels and calcium influx is a determinant step after menthol exposure, suggesting the possibility of menthol for pain management. In this review, we will also discuss and summarize the advances in menthol-related drugs for pathological pain treatment in clinical trials, especially in neuropathic pain, musculoskeletal pain, cancer pain and postoperative pain, with the aim to find the promising therapeutic candidates for the resolution of pain to better manage patients with pain in clinics.

The Effect of Ginger (Zingiber officinale Rosc.) Consumption in Headache Prophylaxis in Patients with Migraine: A Randomized Placebo-Controlled Clinical Trial

Background: Migraine sufferers seek a range of treatments according to the frequency and severity of their symptoms. Just a few research studies have shown the effectiveness of ginger derivatives for migraine treatment. Ginger has analgesic properties and is effective for the acute treatment of migraines, and there is anecdotal evidence of its effectiveness in migraine prevention. Objectives: The goal of this research was to see whether ginger may help prophylaxis of migraine episodes. Methods: This randomized, double-blind, placebo-controlled clinical study was done in the Neurology Clinic of Golestan Hospital (Ahvaz, Iran). This research enrolled 103 individuals with episodic migraine aged 18 to 50 years. Randomization was used to divide the participants into two groups: control and intervention. For three months, patients were given 500 mg dry extract of ginger (5% active component) or placebo (starch) tablets twice a day. At the baseline and end of the study, MIDAS score, the number and duration of migraine attacks, headache severity, demographic data, dietary intakes, and anthropometric indices were collected. The data were statistically analyzed using the SPSS (version 26). In all tests, a P < 0.05 was deemed statistically significant. Results: At the end of the study, MIDAS score, duration of migraine attacks, and headache severity decreased significantly in the ginger group compared to the placebo group (P < 0.05). Furthermore, there was no statistically significant difference in the number of migraine episodes between the two groups. Conclusions: Compared to the placebo, ginger has a stronger efficacy in the prevention of migraine.

β-Lactam TRPM8 Antagonist RGM8-51 Displays Antinociceptive Activity in Different Animal Models

Transient receptor potential melastatin subtype 8 (TRPM8) is a cation channel extensively expressed in sensory neurons and implicated in different painful states. However, the effectiveness of TRPM8 modulators for pain relief is still a matter of discussion, since structurally diverse modulators lead to different results, depending on the animal pain model. In this work, we described the antinociceptive activity of a β–lactam derivative, RGM8-51, showing good TRPM8 antagonist activity, and selectivity against related thermoTRP channels and other pain-mediating receptors. In primary cultures of rat dorsal root ganglion (DRG) neurons, RGM8-51 potently reduced menthol-evoked neuronal firing without affecting the major ion conductances responsible for action potential generation. This compound has in vivo antinociceptive activity in response to cold, in a mouse model of oxaliplatin-induced peripheral neuropathy. In addition, it reduces cold, mechanical and heat hypersensitivity in a rat model of neuropathic pain arising after chronic constriction of the sciatic nerve. Furthermore, RGM8-51 exhibits mechanical hypersensitivity-relieving activity, in a mouse model of NTG-induced hyperesthesia. Taken together, these preclinical results substantiate that this TRPM8 antagonist is a promising pharmacological tool to study TRPM8-related diseases.

PACAP-38 Induces Transcriptomic Changes in Rat Trigeminal Ganglion Cells Related to Neuroinflammation and Altered Mitochondrial Function Presumably via PAC1/VPAC2 Receptor-Independent Mechanism

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a broadly expressed neuropeptide which has diverse effects in both the peripheral and central nervous systems. While its neuroprotective effects have been shown in a variety of disease models, both animal and human data support the role of PACAP in migraine generation. Both PACAP and its truncated derivative PACAP(6-38) increased calcium influx in rat trigeminal ganglia (TG) primary sensory neurons in most experimental settings. PACAP(6-38), however, has been described as an antagonist for PACAP type I (known as PAC1), and Vasoactive Intestinal Polypeptide Receptor 2 (also known as VPAC2) receptors. Here, we aimed to compare the signaling pathways induced by the two peptides using transcriptomic analysis. Rat trigeminal ganglion cell cultures were incubated with 1 µM PACAP-38 or PACAP(6-38). Six hours later RNA was isolated, next-generation RNA sequencing was performed and transcriptomic changes were analyzed to identify differentially expressed genes. Functional analysis was performed for gene annotation using the Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Reactome databases. We found 200 common differentially expressed (DE) genes for these two neuropeptides. Both PACAP-38 and PACAP(6-38) treatments caused significant downregulation of NADH: ubiquinone oxidoreductase subunit B6 and upregulation of transient receptor potential cation channel, subfamily M, member 8. The common signaling pathways induced by both peptides indicate that they act on the same target, suggesting that PACAP activates trigeminal primary sensory neurons via a mechanism independent of the identified and cloned PAC1/VPAC2 receptor, either via another target structure or a different splice variant of PAC1/VPAC2 receptors. Identification of the target could help to understand key mechanisms of migraine.

Ethnomedicine and neuropsychopharmacology in Mesoamerica

ETHNOPHARMACOLOGICAL RELEVANCE

The burden of disease caused by mental and neurological disorders is increasing globally, to a disproportionate degree in Latin America. In contrast to the many psychoactive plants with a use history in Mesoamerican cultures, the translation to the wider population of knowledge around numerous botanicals used contemporarily by indigenous Mesoamerican societies to treat psychological and neurological disorders did not receive the same attention.

MATERIAL AND METHODS

We used the previously published Mesoamerican Medicinal Plant Database to extract species and associated botanical drugs used as treatments for illnesses associated with the nervous system by Mesoamerican cultures in Belize, Guatemala, and Mexico. With the critical use of published pharmacological literature, the cross-culturally most salient genera are systematically reviewed.

RESULTS

From 2188 plant taxa contained in the database 1324 are used as treatments for illnesses associated with the nervous system. The ethnomedical data was critically confronted with the available biomedical literature for the 58 cross-culturally most salient genera. For a considerable proportion of the frequently used taxa, preclinical data are available, mostly validating ethnomedicinal uses.

CONCLUSION

This quantitative approach facilitates the prioritization of taxa for future pre-clinical, clinical and treatment outcome studies and gives patients, practitioners, and legislators a fundamental framework of evidence, on which to base decisions regarding phytomedicines.

Acute Treatments for Episodic Migraine in Adults: A Systematic Review and Meta-analysis

IMPORTANCE

Migraine is common and can be associated with significant morbidity, and several treatment options exist for acute therapy.

OBJECTIVE

To evaluate the benefits and harms associated with acute treatments for episodic migraine in adults.

DATA SOURCES

Multiple databases from database inception to February 24, 2021.

STUDY SELECTION

Randomized clinical trials and systematic reviews that assessed effectiveness or harms of acute therapy for migraine attacks.

DATA EXTRACTION AND SYNTHESIS

Independent reviewers selected studies and extracted data. Meta-analysis was performed with the DerSimonian-Laird random-effects model with Hartung-Knapp-Sidik-Jonkman variance correction or by using a fixed-effect model based on the Mantel-Haenszel method if the number of studies was small.

MAIN OUTCOMES AND MEASURES

The main outcomes included pain freedom, pain relief, sustained pain freedom, sustained pain relief, and adverse events. The strength of evidence (SOE) was graded with the Agency for Healthcare Research and Quality Methods Guide for Effectiveness and Comparative Effectiveness Reviews.

FINDINGS

Evidence on triptans and nonsteroidal anti-inflammatory drugs was summarized from 15 systematic reviews. For other interventions, 115 randomized clinical trials with 28 803 patients were included. Compared with placebo, triptans and nonsteroidal anti-inflammatory drugs used individually were significantly associated with reduced pain at 2 hours and 1 day (moderate to high SOE) and increased risk of mild and transient adverse events. Compared with placebo, calcitonin gene-related peptide receptor antagonists (low to high SOE), lasmiditan (5-HT1F receptor agonist; high SOE), dihydroergotamine (moderate to high SOE), ergotamine plus caffeine (moderate SOE), acetaminophen (moderate SOE), antiemetics (low SOE), butorphanol (low SOE), and tramadol in combination with acetaminophen (low SOE) were significantly associated with pain reduction and increase in mild adverse events. The findings for opioids were based on low or insufficient SOE. Several nonpharmacologic treatments were significantly associated with improved pain, including remote electrical neuromodulation (moderate SOE), transcranial magnetic stimulation (low SOE), external trigeminal nerve stimulation (low SOE), and noninvasive vagus nerve stimulation (moderate SOE). No significant difference in adverse events was found between nonpharmacologic treatments and sham.

CONCLUSIONS AND RELEVANCE

There are several acute treatments for migraine, with varying strength of supporting evidence. Use of triptans, nonsteroidal anti-inflammatory drugs, acetaminophen, dihydroergotamine, calcitonin gene-related peptide antagonists, lasmiditan, and some nonpharmacologic treatments was associated with improved pain and function. The evidence for many other interventions, including opioids, was limited.

Review of aromatherapy essential oils and their mechanism of action against migraines

ETHNOPHARMACOLOGICAL RELEVANCE

Migraines have become a major threat to human health, as they significantly affect human health and quality of life due to a high prevalence rate, attack rate and pain intensity. Aromatherapy, with its comfortable and pleasant natural characteristics and rapid and efficient characteristics, is widely favored by patients in the folk. Chinese folk also have the application history and related records of aromatic plants in the treatment of migraine.

AIM OF THE STUDY

This study was conducted to review the pathogenesis of migraine, the application of plant essential oils in the treatment of migraine, and further explore the material basis and mechanism of action of plant essential oils against migraine.

MATERIALS AND METHODS

Search the electronic literature of essential oils with anti-migraine effect in Google Scholar, PubMed and China National Knowledge Infrastructure, and further search the research situation of the monomer components of essential oils in migraine, inflammation, pain and other aspects.

RESULTS

studies show that there are 10 types of plant essential oils that could relieve migraine symptoms, and that 16 monomers may play a role in migraine treatment by effectively inhibiting neurogenic inflammation, hyperalgesia and balancing vasorelaxation.

CONCLUSION

Aromatic plant essential oils can relieve migraine effectively, these findings can be used as an important part of the development of anti-migraine drugs.

Implications of Transient Receptor Potential Cation Channels in Migraine Pathophysiology

Migraine is a common and debilitating headache disorder. Although its pathogenesis remains elusive, abnormal trigeminal and central nervous system activity is likely to play an important role. Transient receptor potential (TRP) channels, which transduce noxious stimuli into pain signals, are expressed in trigeminal ganglion neurons and brain regions closely associated with the pathophysiology of migraine. In the trigeminal ganglion, TRP channels co-localize with calcitonin gene-related peptide, a neuropeptide crucially implicated in migraine pathophysiology. Many preclinical and clinical data support the roles of TRP channels in migraine. In particular, activation of TRP cation channel V1 has been shown to regulate calcitonin gene-related peptide release from trigeminal nerves. Intriguingly, several effective anti-migraine therapies, including botulinum neurotoxin type A, affect the functions of TRP cation channels. Here, we discuss currently available data regarding the roles of major TRP cation channels in the pathophysiology of migraine and the therapeutic applicability thereof.

TRPM8 channels: A review of distribution and clinical role

Ion channels are important therapeutic targets due to their plethoric involvement in physiological and pathological consequences. The transient receptor potential cation channel subfamily M member 8 (TRPM8) is a nonselective cation channel that controls Ca²⁺ homeostasis. It has been proposed to be the predominant thermoreceptor for cellular and behavioral responses to cold stimuli in the transient receptor potential (TRP) channel subfamilies and exploited so far to reach the clinical-stage of drug development. TRPM8 channels can be found in multiple organs and tissues, regulating several important processes such as cell proliferation, migration and apoptosis, inflammatory reactions, immunomodulatory effects, pain, and vascular muscle tension. The related disorders have been expanded to new fields ranging from cancer and migraine to dry eye disease, pruritus, irritable bowel syndrome (IBS), and chronic cough. This review is aimed to summarize the distribution of TRPM8 and disorders related to it from a clinical perspective, so as to broaden the scope of knowledge of researchers to conduct more studies on this subject.

Therapeutic potential of pharmacological agents targeting TRP channels in CNS disorders

Central nervous system (CNS) disorders like Alzheimer's disease (AD), Parkinson disease (PD), stroke, epilepsy, depression, and bipolar disorder have a high impact on both medical and social problems due to the surge in their prevalence. All of these neuronal disorders share some common etiologies including disruption of Ca²⁺ homeostasis and accumulation of misfolded proteins. These misfolded proteins further disrupt the intracellular Ca²⁺ homeostasis by disrupting the activity of several ion channels including transient receptor potential (TRP) channels. TRP channel families include non-selective Ca²⁺ permeable channels, which act as cellular sensors activated by various physio-chemical stimuli, exogenous, and endogenous ligands responsible for maintaining the intracellular Ca²⁺ homeostasis. TRP channels are abundantly expressed in the neuronal cells and disturbance in their activity leads to various neuronal diseases. Under the pathological conditions when the activity of TRP channels is perturbed, there is a disruption of the neuronal homeostasis through increased inflammatory response, generation of reactive oxygen species, and mitochondrial dysfunction. Therefore, there is a potential of pharmacological interventions targeting TRP channels in CNS disorders. This review focuses on the role of TRP channels in neurological diseases; also, we have highlighted the current insights into the pharmacological modulators targeting TRP channels.

The Efficacy of Topical Basil Essential Oil on Relieving Migraine Headaches: A Randomized Triple-Blind Study

OBJECTIVE

Complementary therapies have been increasingly used for the prevention and treatment of migraine so that there is a need for studies in this setting. This study sought to determine the effects of basil essential oil on the severity and frequency of migraine attack headaches.

METHODS

A triple-blind clinical trial study was performed on 144 patients diagnosed with migraine. Patients were randomly allocated by a stratified method to four groups of 36 titled basil essential oil 2, 4, 6%, and placebo groups. Medications were used topically every 8 h for 3 successive months. In addition, each individual received 325 mg of acetaminophen every 12 h. The severity and frequency of migraine attacks were measured prior to the study, at weeks 2, 4, 8, and 12. The visual analog scale was used to measure pain intensity. The marginal model and generalized estimation equations were used to compare changes in the intensity and frequency of pain over time.

RESULTS

The interaction of the dose and time factors was significant on both pain intensity (p < 0.001) and frequency of attack (p < 0.001). The odds ratio of higher pain intensity and rate ratio of higher frequency of attack in the intervention groups compared to the placebo group were decreased over the study time.

CONCLUSION

Time lapse and higher doses of basil essential oil would reduce both the intensity and frequency of migraine attacks.

Evaluation of the effect of cooling strategies on recovery after surgical intervention

Introduction

Different cooling strategies exist for emergency treatments immediately after sports trauma or after surgery. The aim of this study was to investigate the effects of three cooling regimen during the immediate postoperative phase as well as in the rehabilitation phase.

Methods

36 patients undergoing anterior cruciate ligament reconstruction received either no cooling (control-group, Con, N=12), were cooled with a menthol-containing cooling bandage (Mtl, N=12) or cooled with an ice containing cold pack (CP, N=12). During a 12-week physiotherapy treatment the cross section of the vastus medialis muscle was examined (day—1; 30; 60; 90) and painkiller consumption was documented.

Results

A significant reduction in the cross section area 30 days after surgery was observed in CP and Con (Mtl: −3.2±1.7%, p=0.14, CP: −8.8±4.3%, p<0.01, Con: −7.2±8.1%, p<0.05). After 90 days of therapy, a significant increase in muscle cross section area was observed in Mtl (Mtl: 4.6%±6.1%, p<0.05, CP: 1.9%± 8.1%, p=0.29, Con: 3.3%±9.4%, p=0.31). The absolute painkiller consumption was lower for Mtl (25.5±3.7 tablets) than for CP (39.5±6.9 tablets) or Con (34.8±4.2 tablets).

Conclusion

We observed a beneficial effect of cooling by a menthol-containing bandage during the rehabilitation phase. Reduction of muscle cross section within 30 days after surgery was prevented which highly contributed to rehabilitation success after 90 days of therapy. Painkiller consumption was reduced with Mtl.

Phytomedicines in the Treatment of Migraine

Migraine is a disabling neurovascular disorder with few targeted, tolerable and effective treatments. Phytomedicines, or plant-based medicinal formulations, hold great promise in the identification of novel therapeutic targets in migraine. Many patients also turn toward herbal and plant-based therapies for the treatment of their migraines as clinical and preclinical evidence of efficacy increases. Patients seek effective and tolerable treatments instead of or in addition to current conventional pharmacologic therapies. We review some phytomedicines potentially useful for migraine treatment-feverfew (Tanacetum parthenium), butterbur (Petasites hybridus), marijuana (Cannabis spp.), Saint John's Wort (Hypericum perforatum) and the Damask rose (Rosa × damascena)-with respect to their mechanisms of action and evidence for treatment of migraine. The evidence for feverfew is mixed; butterbur is effective with potential risks of hepatotoxicity related to preparation; marijuana has not been shown to be effective in migraine treatment, and data are scant; Saint John's Wort shows relevant physiological activity but is a hepatic enzyme inducer and lacks clinical studies for this purpose; the Damask rose when used in topical preparations did not show efficacy in one clinical trial. Other plant preparations have been considered for migraine treatment but most without blinded randomized, placebo-controlled trial evidence.

Evaluation of the effect of topical chamomile (Matricaria chamomilla L.) oleogel as pain relief in migraine without aura: a randomized, double-blind, placebo-controlled, crossover study

Phytotherapy is a source of finding new remedies for migraine. Traditional chamomile oil (chamomile extraction in sesame oil) is a formulation in Persian medicine (PM) for pain relief in migraine. An oleogel preparation of reformulated traditional chamomile oil was prepared and then standardized based on chamazulene (as a marker in essential oil) and apigenin via gas chromatography (GC) and high-performance liquid chromatography (HPLC) methods, respectively. A crossover double-blind clinical trial was performed with 100 patients. Each patient took two tubes of drug and two tubes of placebo during the study. Visual analog scale (VAS) questionnaires were filled in by the patients and scores were given, ranging from 0 to 10 (based on the severity of pain) during 24 h. Other complications like nausea, vomiting, photophobia, and phonophobia were also monitored. There was 4.48 ± 0.01 μl/ml of chamazulene and 0.233 mg/g of apigenin in the preparation (by correcting the amount with extraction ratio). Thirty-eight patients in the drug-placebo and 34 patients in the placebo-drug groups (a total number of 72 patients as per protocol) completed the process in the randomized controlled trial (RCT). Adapted results from the questionnaires showed that pain, nausea, vomiting, photophobia, and phonophobia significantly (p < 0.001) decreased by using chamomile oleogel on the patients after 30 min. Results supported the efficacy of chamomile oleogel as a pain relief in migraine without aura.

Analgesic-Like Activity of Essential Oil Constituents: An Update

The constituents of essential oils are widely found in foods and aromatic plants giving characteristic odor and flavor. However, pharmacological studies evidence its therapeutic potential for the treatment of several diseases and promising use as compounds with analgesic-like action. Considering that pain affects a significant part of the world population and the need for the development of new analgesics, this review reports on the current studies of essential oils’ chemical constituents with analgesic-like activity, including a description of their mechanisms of action and chemical aspects.

Functional interactions between transient receptor potential M8 and transient receptor potential V1 in the trigeminal system: Relevance to migraine pathophysiology

Background

Recent genome-wide association studies have identified transient receptor potential M8 (TRPM8) as a migraine susceptibility gene. TRPM8 is a nonselective cation channel that mediates cool perception. However, its precise role in migraine pathophysiology is elusive. Transient receptor potential V1 (TRPV1) is a nonselective cation channel activated by noxious heat. Both TRPM8 and TRPV1 are expressed in trigeminal ganglion (TG) neurons.

Methods

We investigated the functional roles of TRPM8 and TRPV1 in a meningeal inflammation-based migraine model by measuring the effects of facial TRPM8 activation on thermal allodynia and assessing receptor coexpression changes in TG neurons. We performed retrograde tracer labeling to identify TG neurons innervating the face and dura.

Results

We found that pharmacological TRPM8 activation reversed the meningeal inflammation-induced lowering of the facial heat pain threshold, an effect abolished by genetic ablation of TRPM8. No significant changes in the heat pain threshold were seen in sham-operated animals. Meningeal inflammation caused dynamic alterations in TRPM8/TRPV1 coexpression patterns in TG neurons, and colocalization was most pronounced when the ameliorating effect of TRPM8 activation on thermal allodynia was maximal. Our tracer assay disclosed the presence of dura-innervating TG neurons sending collaterals to the face. Approximately half of them were TRPV1-positive. We also demonstrated functional inhibition of TRPV1 by TRPM8 in a cell-based assay using c-Jun N-terminal kinase phosphorylation as a surrogate marker.

Conclusions

Our findings provide a plausible mechanism to explain how facial TRPM8 activation can relieve migraine by suppressing TRPV1 activity. Facial TRPM8 appears to be a promising therapeutic target for migraine.

[Peppermint oil in the acute treatment of tension-type headache]

Tension-type headache is the most frequent form of headache. The local topical treatment with peppermint oil (oleum menthae piperitae) has proven to be significantly more effective than placebo in controlled studies. Peppermint oil targets headache pathophysiology in multiple ways. The efficacy is comparable to that of acetylsalicylic acid or paracetamol. Solutions of 10 % peppermint oil in ethanol are licensed for the treatment of tension-type headache in adults and children above 6 years. It is included in treatment recommendations and guidelines by the respective professional societies and is regarded as a standard treatment for the acute therapy of tension-type headaches.

TRPM8 and Migraine

Migraine is among the most common diseases on earth and one of the most disabling, the latter due in large part to poor treatment efficacy. Development of new therapeutics is dependent on the identification of mechanisms contributing to migraine and discovery of targets for new drugs. Numerous genome-wide association studies (GWAS) have implicated the transient receptor-potential M8 (TRPM8) channel in migraine. This channel is predominantly expressed on peripheral sensory neurons and is known as the sensor for cold temperature in cutaneous tissue but is also expressed on deep visceral afferents where cold is not likely a stimulus. Consequently, a number of alternative endogenous agonists have been proposed. Apart from its role in cold sensation, TRPM8 also contributes to cold allodynia after nerve injury or inflammation, and it is necessary for cooling/menthol-based analgesia. How it might contribute to migraine is less clear. The purpose of this review is to discuss the anatomical and physiological mechanisms by which meningeal TRPM8 may play a role in migraine as well as the potential of TRPM8 as a therapeutic target. TRPM8 is expressed on sensory afferents innervating the meninges, and these neurons are subject to developmental changes that may influence their contribution to migraine. As in viscera, meningeal TRPM8 channels are unlikely to be activated by temperature fluctuations and their endogenous ligands remain unknown. Preclinical migraine studies show that activation of meningeal TRPM8 by exogenous agonists can both cause and alleviate headache behaviors, depending on whether other meningeal afferents concurrently receive noxious stimuli. This is reminiscent of the fact that cold can trigger migraine in humans but menthol can also alleviate headache. We propose that both TRPM8 agonists and antagonists may be potential therapeutics, depending on how migraine is triggered in individual patients. In this regard, TRPM8 may be a novel target for personalized medicine in migraine treatment.

Why We Must Continue to Investigate Menthol's Role in the African American Smoking Paradox

BACKGROUND

The disproportionate burden of tobacco use among African Americans is largely unexplained. The unexplained disparities, referred to as the African American smoking paradox, includes several phenomena. Despite their social disadvantage, African American youth have lower smoking prevalence rates, initiate smoking at older ages, and during adulthood, smoking rates are comparable to whites. Smoking frequency and intensity among African American youth and adults are lower compared to whites and American Indian and Alaska Natives, but tobacco-caused morbidity and mortality rates are disproportionately higher. Disease prediction models have not explained disease causal pathways in African Americans. It has been hypothesized that menthol cigarette smoking, which is disproportionately high among African Americans, may help to explain several components of the African American smoking paradox.

PURPOSE

This article provides an overview of the potential role that menthol plays in the African American smoking paradox. We also discuss the research needed to better understand this unresolved puzzle.

METHODS

We examined prior synthesis reports and reviewed the literature in PubMed on the menthol compound and menthol cigarette smoking in African Americans.

RESULTS

The pharmacological and physiological effects of menthol and their interaction with biological and genetic factors may indirectly contribute to the disproportionate burden of cigarette use and diseases among African Americans.

CONCLUSIONS

Future studies that examine taste sensitivity, the menthol compound, and their effects on smoking and chronic disease would provide valuable information on how to reduce the tobacco burden among African Americans.

IMPLICATIONS

Our study highlights four counterintuitive observations related to the smoking risk profiles and chronic disease outcomes among African Americans. The extant literature provides strong evidence of their existence and shows that long-standing paradoxes have been largely unaffected by changes in the social environment. African Americans smoke menthols disproportionately, and menthol's role in the African American smoking paradox has not been thoroughly explored. We propose discrete hypotheses that will help to explain the phenomena and encourage researchers to empirically test menthol's role in smoking initiation, transitions to regular smoking and chronic disease outcomes in African Americans.

A review on the management of migraine in the Avicenna's Canon of Medicine

Migraine is a common type of headache which has a deep history dating back thousands of years. Avicenna (980-1032), a Persian scholar, made a great contribution to neurology including headache and migraine. The aim of this study is to consider Avicenna's description about migraine (Shaghighe in Persian language) including definition, etiology and intervention. Also, his definition and treatment approaches were considered based on current concepts and findings. Although Avicenna believed in humoral theory and divided migraine into two categories, hot and cold, and suggested special treatments for them as well as general considerations, most of his definitions and explained pathologies are supported by current concepts of medicine. He believed that the migraine can result from bone of skull and also intra-parenchymal; or from skull underneath membrane (dura-mater); or reaching substances from the painful side or from outer vein and arteries (extra cranial); or from brain and meninges (pia-mater). Furthermore, current findings show most medicinal plants mentioned by Avicenna for the treatment of migraine can have potentially significant effects such as remedies which stop central and peripheral sensitization [anti-neuroinflammatory agents, decreasing nitric oxide level, cyclooxygenase (COX)-2 inhibitors], as well as serotonergics, neuroprotective agents and analgesics.

Function and postnatal changes of dural afferent fibers expressing TRPM8 channels

BACKGROUND

Genome-wide association studies have identified TRPM8 (transient receptor potential melastatin 8) as one of the susceptibility genes for common migraine. Here, we investigated the postnatal changes of TRPM8-expressing dural afferent fibers as well as the function of dural TRPM8 channels in mice.

RESULTS

First, we quantified the density and the number of axonal branches of TRPM8-expressing fibers in the dura of mice expressing farnesylated enhanced green fluorescent protein (EGFPf) from one TRPM8 allele between postnatal day 2 (P2) to adulthood. The number of axonal branches on individual dural EGFP-positive fibers was decreased by 30% between P2 and P11. The density of dural EGFP-positive fibers was subsequently reduced by 50% between P16 and P21. Conversely, the density and the number of branches of axons expressing calcitonin gene-related peptide remained stable in postnatal mouse dura. The density of TRPM8-expressing fibers innervating the mouse cornea epithelium was significantly increased from P2 to adulthood. Next, we tested the function of dural TRPM8 channels in adult mice and found that TRPM8 agonist menthol effectively inhibited the nocifensive behavior evoked by dural application of inflammatory mediators.

CONCLUSIONS

Our results indicate that the TRPM8-expressing dural afferent fibers undergo cell- and target tissue-specific axonal pruning during postnatal development. Activation of dural TRPM8 channels decreases meningeal irritation-evoked nocifensive behavior in adult mice. This provides a framework to further explore the role of postnatal changes of TRPM8-expressing dural afferents in the pathophysiology of pediatric and adult migraine.

Menthol concentration in topical cold gel does not have significant effect on skin cooling

BACKGROUND

Topical menthol gels are used in the treatment of various pain conditions. However, the effect of the menthol concentration to skin cooling or cooling sensation is not clear. We hypothesized that increasing menthol concentration enhances skin cooling and causes elevated cooling sensation.

METHODS

Ten healthy male volunteers (age range 25-30 years) were recruited for this study. Application of three gels with different menthol concentrations (0.5%, 4.6% and 10.0%) was tested in random sequence on the left thigh of the subjects. Skin cooling was recorded with a digital infrared camera (FLIR Systems Inc., USA), and cooling sensation was measured with the visual analogue scale rating.

RESULTS

All gels decreased skin temperature significantly (P < 0.05) at least for one hour. However, the variation in menthol concentration seemed not to have a significant effect on skin cooling. Subjects experienced that gel with 4.6% menthol concentration caused significantly stronger cooling effect than 0.5% and 10.0% gels. Gel application had no significant effect on skin temperature in surrounding skin areas.

CONCLUSION

In contrast to our hypothesis, menthol concentration was not connected to skin cooling, while moderate menthol concentration of 4.6% may induce stronger cooling sensation compared to low (0.5%) or high (10.0%) concentration gels.

Cancer treatment-related neuropathic pain: proof of concept study with menthol--a TRPM8 agonist

PURPOSE

Effective treatment of neuropathic pain without unacceptable side effects is challenging. Cancer sufferers increasingly live with long-term treatment-related neuropathic pain, resulting from chemotherapy-induced peripheral neuropathy (CIPN) or surgical scars. This proof-of-concept study aimed to determine whether preclinical evidence for TRPM8 ion channels in sensory neurons as a novel analgesic target could be translated to clinical benefit in patients with neuropathic pain, using the TRPM8 activator menthol.

PATIENTS AND METHODS

Patients with problematic treatment-related neuropathic pain underwent a baseline assessment using validated questionnaires, psychophysical testing, and objective functional measures. The painful area was treated with topical 1 % menthol cream twice daily. Assessments were repeated at 4-6 weeks. The primary outcome was the change in Brief Pain Inventory total scores at 4-6 weeks. Secondary outcomes included changes in function, mood and skin sensation.

RESULTS

Fifty-one patients (female/male, 32/19) were recruited with a median age of 61 (ranging from 20 to 89). The commonest aetiology was CIPN (35/51), followed by scar pain (10/51). Thirty-eight were evaluable on the primary outcome. Eighty-two per cent (31/38) had an improvement in total Brief Pain Inventory scores (median, 47 (interquartile range, 30 to 64) to 34 (6 to 59), P < 0.001). Improvements in mood (P = 0.0004), catastrophising (P = 0.001), walking ability (P = 0.008) and sensation (P < 0.01) were also observed.

CONCLUSION

This proof-of-concept study indicates that topical menthol has potential as a novel analgesic therapy for cancer treatment-related neuropathic pain. Improvements in patient-rated measures are supported by changes in objective measures of physical function and sensation. Further systematic evaluation of efficacy is required.

Efficacy and Tolerability of STOPAIN for a Migraine Attack

Objective: To determine whether topical menthol 6% gel will relieve a migraine attack.

Materials and Methods: A single-center, open-label pilot trial of 25 patients with at least 1 year of diagnosed episodic migraine and <15 headache days per month. Patients treated one migraine attack with STOPAIN topical menthol 6% gel to skull base within 2 h of headache onset. Headache pain severity was assessed prior to and after gel application.

Results: Thirty-two patients enrolled and 25 completed the study. Prior to treatment, 7 patients had mild pain, 13 moderate pain, and 5 severe pain. Two hours following gel application, 7 (28%) patients had no pain, 7 (28%) mild pain, 6 (25%) moderate pain, and 5 (20%) severe pain. The majority of patients had similar pain intensity (8; 32%) or improvement (13; 52%). At 24-h, only two non-rescued patients still had mild headache. Of the 25 completers, 2 patients took rescue medication prior to the 2-h period, and an additional 10 patients rescued between 2 and 24 h.

Conclusion: Study results showed a significant improvement in headache intensity by 2 h after gel application. This pilot study shows STOPAIN gel may be effective in treating an acute migraine attack.

The TRPM8 channel forms a complex with the 5-HT(1B) receptor and phospholipase D that amplifies its reversal of pain hypersensitivity

Effective relief from chronic hypersensitive pain states remains an unmet need. Here we report the discovery that the TRPM8 ion channel, co-operating with the 5-HT(1B) receptor (5-HT(1B)R) in a subset of sensory afferents, exerts an influence at the spinal cord level to suppress central hypersensitivity in pain processing throughout the central nervous system. Using cell line models, ex vivo rat neural tissue and in vivo pain models, we assessed functional Ca(2+) fluorometric responses, protein:protein interactions, immuno-localisation and reflex pain behaviours, with pharmacological and molecular interventions. We report 5-HT(1B)R expression in many TRPM8-containing afferents and direct interaction of these proteins in a novel multi-protein signalling complex, which includes phospholipase D1 (PLD1). We provide evidence that the 5-HT(1B)R activates PLD1 to subsequently activate PIP 5-kinase and generate PIP2, an allosteric enhancer of TRPM8, achieving a several-fold increase in potency of TRPM8 activation. The enhanced activation responses of synaptoneurosomes prepared from spinal cord and cortical regions of animals with a chronic inflammatory pain state are inhibited by TRPM8 activators that were applied in vivo topically to the skin, an effect potentiated by co-administered 5-HT(1B)R agonists and attenuated by 5-HT(1B)R antagonists, while 5-HT(1B)R agents alone had no detectable effect. Corresponding results are seen when assessing reflex behaviours in inflammatory and neuropathic pain models. Control experiments with alternative receptor/TRP channel combinations reveal no such synergy. Identification of this novel receptor/effector/channel complex and its impact on nociceptive processing give new insights into possible strategies for enhanced analgesia in chronic pain.

Genes, molecules and patients--emerging topics to guide clinical pain research

This review selectively explores some areas of pain research that, until recently, have been poorly understood. We have chosen four topics that relate to clinical pain and we discuss the underlying mechanisms and related pathophysiologies contributing to these pain states. A key issue in pain medicine involves crucial events and mediators that contribute to normal and abnormal pain signaling, but remain unseen without genetic, biomarker or imaging analysis. Here we consider how the altered genetic make-up of familial pains reveals the human importance of channels discovered by preclinical research, followed by the contribution of receptors as stimulus transducers in cold sensing and cold pain. Finally we review recent data on the neuro-immune interactions in chronic pain and the potential targets for treatment in cancer-induced bone pain.

Central mechanisms of menthol-induced analgesia

Menthol is one of the most commonly used chemicals in our daily life, not only because of its fresh flavor and cooling feeling but also because of its medical benefit. Previous studies have suggested that menthol produces analgesic action in acute and neuropathic pain through peripheral mechanisms. However, the central actions and mechanisms of menthol remain unclear. Here, we report that menthol has direct effects on the spinal cord. Menthol decreased both ipsilateral and contralateral pain hypersensitivity induced by complete Freund's adjuvant in a dose-dependent manner. Menthol also reduced both first and second phases of formalin-induced spontaneous nocifensive behavior. We then identified the potential central mechanisms underlying the analgesic effect of menthol. In cultured dorsal horn neurons, menthol induced inward and outward currents in a dose-dependent manner. The menthol-activated current was mediated by Cl(-) and blocked by bicuculline, suggesting that menthol activates γ-aminobutyric acid type A receptors. In addition, menthol blocked voltage-gated sodium channels and voltage-gated calcium channels in a voltage-, state-, and use-dependent manner. Furthermore, menthol reduced repetitive firing and action potential amplitude, decreased neuronal excitability, and blocked spontaneous synaptic transmission of cultured superficial dorsal horn neurons. Liquid chromatography/tandem mass spectrometry analysis of brain menthol levels indicated that menthol was rapidly concentrated in the brain when administered systemically. Our results indicate that menthol produces its central analgesic action on inflammatory pain probably via the blockage of voltage-gated Na(+) and Ca(2+) channels. These data provide molecular and cellular mechanisms by which menthol decreases neuronal excitability, therefore contributing to menthol-induced central analgesia.