Menthol and related cooling compounds

Shorter time to first cigarette of the day in menthol adolescent cigarette smokers

Menthol smoking is thought to contribute to the addictiveness of smoking. Given the high prevalence of menthol smoking among youth, the aim of the current analysis was to examine differences in consumption and tobacco dependence, including smoking urgency among menthol and non-menthol adolescent smokers. Data for the current analysis were collected from telephone interviews with adolescent smokers applying to a cessation treatment study. Of 572 adolescent smokers (mean age=15.6+/-1.6 years; 55.1% female; 46.9% African American, 48.2% European American), 531 smoked menthol cigarettes and 41 smoked non-menthol as their usual brand. Analysis using Fisher's Exact (one-tailed) Test revealed that menthol smokers had a significantly shorter time to first (TTF) cigarette of the day compared to non-menthol smokers (smoking within the first 5 min of the day, 45% vs. 29%, respectively; p<0.04). Independent t tests revealed no significant difference in number of cigarettes per day (CPD) (mean=12.2+/-8.5 vs. 11.4+/-8.8; p<0.28) or Fagerstrom Test for Nicotine Dependence (FTND) scores (3.4+/-1.4 vs. 3.2+/-1.3; p<0.23). While preliminary, our findings suggest greater smoking urgency among menthol compared to non-menthol adolescent cessation-treatment seekers. Further study in a broader sample of adolescent smokers is warranted to elucidate the mechanisms underlying the effects of menthol smoking for youths.

Supramedullary influences on cough

The evidence for supramedullary influences on cough is largely indirect. Cough can be voluntarily induced or inhibited, functions usually thought to reside in the cerebral cortex. A sensation of 'urge-to-cough' usually precedes cough due to an airway irritant stimulus, and this may well involve the cerebral cortex. In conditions with interruption of the pathways between the cortex and the brainstem, such as strokes and Parkinson's disease, voluntary cough may be inhibited without disruption of reflex cough from the larynx or lower airways. 'Habit cough', like Tourette's syndrome, is assumed to be cortically mediated. Placebos and many treatments based on complementary medicine are effective in inhibiting clinical cough, and the site of action is likely to be the cerebral cortex. In sleep and in anaesthesia cough is depressed and, again, this seems likely to be at a cortical level. However there are few or no experimental or clinical observation as to the localization and functions of supramedullary areas responsible for cough. It is a field of research wide open for exploration.

Psychophysical study of the effects of topical application of menthol in healthy volunteers

Cold hyperalgesia is a major clinical phenomenon, but validated experimental models are still lacking for humans. Topical menthol application has recently been proposed as a possible model for the study of cold pain. We characterized the psychophysical effects of 30% l-menthol in ethanol on glabrous skin in 39 healthy subjects, using a double-blind, randomized, crossover design, with ethanol as a control. Psychophysical testing included an assessment of pain thresholds and detection of mechanical, cold, and heat stimuli, and of the sensations induced by suprathreshold stimuli. Most subjects (90%) perceived a cooling sensation with menthol. Menthol decreased cold pain thresholds and enhanced pain responses to suprathreshold noxious cold stimuli, without affecting responses to other stimuli. Menthol therefore has selective effects on noxious cold processing. No subject displayed signs of skin irritation or redness. These data suggest that 30% menthol application may be a useful experimental model for studies of cold hyperalgesia in humans. The absence of local skin reactions also makes this test potentially suitable for use in patients.

Chemical and cold sensitivity of two distinct populations of TRPM8-expressing somatosensory neurons

The cold- and menthol-sensing TRPM8 receptor has been proposed to have both nonnociceptive and nociceptive functions. However, one puzzle is how this single type of receptor may be used by somatosensory neurons to code for two distinct sensory modalities. Using acutely dissociated rat dorsal root ganglion (DRG) neurons without culture, we show that TRPM8 receptors are expressed on two distinct classes of somatosensory neurons. One class is sensitive to menthol and features nonnociceptive neuron properties, including capsaicin-insensitive, ATP-insensitive, transient acid response, and expression of TTX-sensitive sodium channels only. This class is termed the menthol-sensitive/capsaicin-insensitive neuron class (MS/CIS). The other class is also sensitive to menthol but has characteristics of nociceptive neurons including capsaicin-sensitive, ATP-sensitive, prolonged acid response, and expression of both TTX-sensitive and TTX-resistant sodium channels. This class is termed the menthol-sensitive/capsaicin-sensitive neuron class (MS/CS). The presence of these two neuron classes in acutely dissociated DRG neurons support the idea that TRPM8 receptors can have both nonnociceptive and nociceptive functions. While both neuron classes respond to menthol and cold, the overall responses induced by menthol and cold are significantly larger in MS/CIS than in MS/CS neurons. Furthermore, low concentrations of menthol produce strong selection of the MS/CIS neuron population over the MS/CS neuron population. On the other hand, the population selection becomes weaker with higher concentrations of menthol. TRPM8 current density shows significant higher in MS/CIS neurons than in MS/CS neurons, suggesting different expression levels of TRPM8 receptors between the two neuron populations, and this difference may provide a mean of selective activation of MS/CIS neurons at low stimulation intensity.

Permeation and reservoir formation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and benzo[a]pyrene (B[a]P) across porcine esophageal tissue in the presence of ethanol and menthol

Environmental influences may affect carcinogen absorption and residency in the tissues of the aero-digestive tract. We quantified the effect of ethanol and menthol on the rates of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and benzo[a]pyrene (B[a]P) absorption using a fully validated in vitro diffusion system, capable of accurately and precisely quantifying tobacco carcinogen permeation and reservoir formation in porcine esophageal mucosa. Confocal microscopy was employed to visualize the location of B[a]P in the exposed membranes. Markedly different extents of permeation and reservoir formation for the tobacco carcinogens were recorded in the presence of ethanol and menthol. The water-soluble NNK permeated the membrane rapidly, while the lipophilic B[a]P did not appreciably diffuse through the tissue. Significantly different extents of reservoir formation were observed for the different carcinogens and in the presence of the different penetration-enhancer solvents. Alcohol (at 5% concentration) did not influence the permeation or reservoir formation of NNK. A mentholated donor solution (0.08%) both decreased the flux of NNK and significantly increased the tissue reservoir formation. The magnitude of the reservoir formed by B[a]P was relatively extensive (even though membrane permeation rates were negligible), being greatest in the presence of both ethanol and menthol. This suggests synergy between the two penetration-enhancer species acting on this carcinogen. Confocal microscopy studies confirmed that there was an appreciable intra-cellular, and specifically nuclear, association of the B[a]P species during the reservoir formation process. The aqueous solubility of the diffusing species and the presence of penetration enhancers appeared to be key factors in the absorption and cellular binding processes. The results presented support the hypothesis that the use of mentholated cigarettes, or the concomitant consumption of alcohol while smoking, may have marked effects on the fate of tobacco chemicals. This finding may help to explain elevated rates of esophageal squamous cell carcinoma in African Americans.

The Role of Menthol in Skin Penetration from Topical Formulations of Ibuprofen 5% in vivo

In vivo plasma profiles from formulations containing 5% ibuprofen were compared after a single topical application in a randomised, double-blind, cross-over trial. Ibuleve gel (Dermal Laboratories, UK) contained only ibuprofen whilst Deep Relief gel (Mentholatum, UK) also contained 3% menthol. In contrast to results obtained when these products were compared under in vitro conditions, there was no statistically significant difference in vivo between delivery of ibuprofen. Estimated relative bioavailability fraction (Deep Relief gel/Ibuleve gel) from log-transformed AUC((0-24h)) was 0.99 (95% CI: 0.94-1.04), estimated C(max )ratio was 0.96 (95% CI: 0.91-1.00) and estimated t(max) ratio was 1.01 (95% CI: 0.81-1.20). Menthol produces local vasodilation, which reduces skin barrier function, and these data demonstrate that it is inappropriate to extrapolate from in vitro data where formulation components produce biologically-mediated enhancement of permeation which cannot be modelled ex vivo. In clinical use, these products deliver comparable amounts of ibuprofen, but only Deep Reliefgel provides the secondary immediate benefit of the direct analgesic action of menthol.

Mechanisms of the placebo effect of sweet cough syrups

The review discusses the large placebo effect associated with cough medicines and speculates on the observation that most cough medicines are formulated as sweet syrups rather than capsules or tablets. The review proposes that the major benefit of cough medicines for treatment of cough associated with common cold is related to the placebo effect rather than the pharmacological effect of an active ingredient. The placebo effect is discussed in terms of physiological effects of cough syrups associated with the taste of the medicine and true placebo effects associated with belief in the therapy. The idea is developed that a sweet taste may modulate cough at the level of the nucleus tractus solitarius, possibly by influencing the production of endogenous opioids.

TRPA1 and TRPM8 activation in humans: effects of cinnamaldehyde and menthol

The aim of this study was to evaluate the psychophysical effects of both TRPA1 and TRPM8 activation in humans by application of either cinnamaldehyde or menthol. We applied 10% cinnamaldehyde or 40% menthol solutions on the forearm in 10 study participants. Quantitative sensory testing and laser Doppler imaging was performed before and after exposure to the compounds. Cinnamaldehyde evoked significant spontaneous pain and induced heat and mechanical hyperalgesia, cold hypoalgesia and a neurogenic axon reflex erythema. In contrast, TRPM8 activation by menthol produced no axon reflex reaction and resulted in cold hyperalgesia. We conclude that agonists of TRPA1 and TRPM8 channels produce strikingly different psychophysical patterns.

Enantiomeric analysis of (+)-menthol and (-)-menthol by fluorogenic derivatization and liquid chromatography

A simple and sensitive liquid chromatography is described for the quantitative analysis of enantiomeric (+)-menthol and (-)-menthol that are lack of chromophore. The method is based on the derivatization of (+)-menthol and (-)-menthol with a fluorescent reagent, naproxen acyl chloride, in toluene. The resulting diastereomic derivatives were separated on a C8 column with methanol-water-tetrahydrofuran (80:18:2, v/v) as a mobile phase; they were sensitively monitored with a fluorimetric detector (excitation 235 nm and emission 350 nm). The linear range for the quantitation of the enantiomers was 5.0-50 microM with a detection limit (signal to noise ratio = 3, injected volume 10 microl) of about 1 microM. Application of the method to the enantiomeric analysis of menthol in mint plants proved simple and feasible. Toluene was used for the extraction of menthol from the leaves of mint, and the resulting toluene extract was directly used for subsequent derivatization without solvent replacement.

How cold is it? TRPM8 and TRPA1 in the molecular logic of cold sensation

Recognition of temperature is a critical element of sensory perception and allows us to evaluate both our external and internal environments. In vertebrates, the somatosensory system can discriminate discrete changes in ambient temperature, which activate nerve endings of primary afferent fibers. These thermosensitive nerves can be further segregated into those that detect either innocuous or noxious (painful) temperatures; the latter neurons being nociceptors. We now know that thermosensitive afferents express ion channels of the transient receptor potential (TRP) family that respond at distinct temperature thresholds, thus establishing the molecular basis for thermosensation. Much is known of those channels mediating the perception of noxious heat; however, those proposed to be involved in cool to noxious cold sensation, TRPM8 and TRPA1, have only recently been described. The former channel is a receptor for menthol, and links the sensations provided by this and other cooling compounds to temperature perception. While TRPM8 almost certainly performs a critical role in cold signaling, its part in nociception is still at issue. The latter channel, TRPA1, is activated by the pungent ingredients in mustard and cinnamon, but has also been postulated to mediate our perception of noxious cold temperatures. However, a number of conflicting reports have suggested that the role of this channel in cold sensation needs to be confirmed. Thus, the molecular logic for the perception of cold-evoked pain remains enigmatic. This review is intended to summarize our current understanding of these cold thermoreceptors, as well as address the current controversy regarding TRPA1 and cold signaling.

Effect of menthol on the pharmacokinetics and pharmacodynamics of felodipine in healthy subjects

OBJECTIVES

The present study was undertaken to determine whether menthol affects the metabolism of and pharmacological responses to the calcium channel antagonist felodipine in people.

METHODS

Eleven healthy subjects (ten female, one male) participated in a randomized, double-blind, two-way crossover study, comparing the kinetics and effects of a single oral dose of felodipine ER tablet (Plendil, 10 mg) with menthol (test) or placebo (reference) capsules. Ten subjects completed the study. At the beginning of the study, a 10-mg felodipine ER tablet and a 100-mg menthol or placebo capsule were given. During the 2nd, 5th and 7th hours of the study, 50, 25 and 25 mg menthol or placebo capsules were given, respectively. Blood samples and cardiovascular measurements were obtained at frequent intervals. Serum felodipine and dehydrofelodipine concentrations were determined by means of gas chromatography/mass spectrometry.

RESULTS

Pharmacokinetic parameters of felodipine and dehydrofelodipine (AUC0-24, Cmax, t(max), dehydrofelodipine/felodipine AUC0-24 ratio) were not markedly changed with menthol coadministration. Only eight female subjects' cardiovascular data were included in the analysis because of technical problems during the measurements. There were no statistically significant differences in blood pressures and heart rates between the two treatments.

CONCLUSIONS

We conclude that the pharmacokinetics and pharmacodynamics of felodipine were essentially unaltered by menthol.

Mentholated cigarette smoking inhibits nicotine metabolism

Smoking mentholated cigarettes has been suggested to convey a greater cancer risk compared with smoking nonmentholated cigarettes. Two of the possible mechanisms by which mentholated cigarette smoking could increase risk are by increasing systemic exposure to tobacco smoke toxins and by affecting the metabolism of nicotine or tobacco smoke carcinogens. To examine these possibilities, we performed a crossover study in 14 healthy smokers, one-half of whom were African-Americans and one-half whites. Subjects were randomly assigned to smoke mentholated or nonmentholated cigarettes for 1 week, then to cross over to the other type of cigarettes for another week. Subjects were confined to a Clinical Research Center for 3 days of each week, during which time blood levels of nicotine and carbon monoxide were measured throughout the day and an intravenous infusion of deuterium-labeled nicotine and cotinine was administered to determine the rate and pathways of nicotine metabolism. The systemic intake of nicotine and carbon monoxide was, on average, not affected by mentholation of cigarettes. Mentholated cigarette smoking did significantly inhibit the metabolism of nicotine (clearance: 1289 versus 1431 ml/min, two sided, p = 0.02). Inhibition of nicotine metabolism occurred both by slower oxidative metabolism to cotinine and by slower glucuronide conjugation. Our data do not support the hypothesis that mentholated cigarette smoking results in a greater absorption of tobacco smoke toxins. Our finding of impaired metabolism of nicotine while mentholated cigarette smoking suggests that mentholated cigarette smoking enhances systemic nicotine exposure.

Enhancement Effect ofp‐Menthane‐3,8‐diol on In Vitro Permeation of Antipyrine and Indomethacin Through Yucatan Micropig Skin

The enhancing effect of p-Menthane-3,8-diol (MDO) on skin permeation of antipyrine (ANP) and indomethacin (IM) through Yucatan micropig skin in vitro was compared with 1-menthol. p-Menthane-3,8-diol is a metabolite of 1-menthol and has little odor. It is easy to combine the vehicle because of lower lipophilicity than 1-menthol. All formulations contained 40% (v/v) ethanol. The permeation of ANP increased with MDO about three times that without enhancer by increasing ANP concentration in the skin. However, the MDO effect was about a quarter that of 1-menthol. The permeation of IM with MDO was about 15 times that with no enhancer and it was almost the same as that with 1-menthol. The lag time of permeation was not significantly changed by MDO, which was not so in the case of 1-menthol. Skin concentration of IM increased about 11 times and six times with MDO and 1-menthol, respectively. MDO and 1-menthol partitioned to the skin relatively high concentrations, 5.9 and 2.5 mg/ cm3, respectively. The solubility of IM in the skin was improved by MDO, and consequently, the permeation of IM was enhanced.

Role of mentholated cigarettes in increased nicotine dependence and greater risk of tobacco-attributable disease

BACKGROUND

Cold air stimulates upper airway cold receptors causing a reflex depressive effect on respiratory activity. Menthol, in low concentrations can also stimulate these same cold receptors causing a depressive effect on respiratory activity. Menthol cigarettes when smoked, deliver enough menthol to stimulate cold receptors resulting in the smoker experiencing a "cool sensation." The "cool sensation" experienced by the menthol smoker can result in a reflex-depressive effect on respiratory activity.

METHOD

Literature searches were done for the NLM databases (e.g., MEDLINE from 1966, TOXLINE, OLDMEDLINE (1985-1965), CANCERLIT, plus tobacco industry documents and hardcopy indices. The evidence was evaluated with application to mentholated cigarette smoking.

RESULTS AND DISCUSSION

A logical progression is presented that develops the framework to prove that menthol found in mentholated cigarettes may cause respiratory depression resulting in greater exposure to the toxic substances found in tobacco smoke.

CONCLUSION

As a result of breath holding that results from the stimulation of cold receptors there is a greater opportunity for exposure and transfer of the contents of the lungs to the pulmonary circulation. For the menthol smoker this results in a greater exposure to nicotine and the particulate matter (tar) of the smoked cigarette. This exposure can result in increased nicotine dependence and greater chance of tobacco-attributable disease.

Chemosensory additivity in trigeminal chemoreception as reflected by detection of mixtures

A series of experiments probed into the degree of chemosensory detection additivity exhibited by mixtures of ethyl propanoate and heptanoate in terms of their trigeminal detectability via nasal pungency (i.e., irritation) and eye irritation. Nasal pungency was tested in subjects lacking a functional sense of smell (i.e., anosmics) to avoid olfactory biases. First, we built concentration-detection functions for each chemical and sensory endpoint. Second, we used the data from the functions to prepare mixtures of the two compounds in complementary proportions, and suitable single-chemical standards, all of which should be equally detectable under a rule of complete additivity, i.e., independence of detection. Third, we compared the experimentally obtained detectability with that expected under such rule. The outcome revealed that, at a low detectability level (but still above chance), the mixtures showed complete additivity for both trigeminal endpoints. At a high detectability level (but below perfect detection), the mixtures showed complete additivity for nasal pungency but less than complete additivity for eye irritation. In the context of previous studies, the results consolidate a picture of higher degree of detection additivity at perithreshold levels in trigeminal than in olfactory chemoreception. The outcome presents another line of evidence suggesting broader chemical tuning in chemesthesis compared to olfaction.

Characterization of the mouse cold-menthol receptor TRPM8 and vanilloid receptor type-1 VR1 using a fluorometric imaging plate reader (FLIPR) assay

1. TRPM8 (CMR1) is a Ca(2+)-permeable channel, which can be activated by low temperatures, menthol, eucalyptol and icilin. It belongs to the transient receptor potential (TRP) family, and therefore is related to vanilloid receptor type-1 (VR1, TRPV1). We tested whether substances which are structurally related to menthol, or which produce a cooling sensation, could activate TRPM8, and compared the responses of TRPM8 and VR1 to these ligands. 2. The effects of 70 odorants and menthol-related substances on recombinant mouse TRPM8 (mTRPM8), expressed in HEK293 cells, were examined using a FLIPR assay. In all, 10 substances (linalool, geraniol, hydroxycitronellal, WS-3, WS-23, FrescolatMGA, FrescolatML, PMD38, CoolactP and Cooling Agent 10) were found to be agonists. 3. The EC(50) values of the agonists defined their relative potencies: icilin (0.2+/-0.1 microM)>FrescolatML (3.3+/-1.5 microM) > WS-3 (3.7+/-1.7 microM) >(-)menthol (4.1+/-1.3 microM) >frescolatMAG (4.8+/-1.1 microM) > cooling agent 10 (6+/-2.2 microM) >(+)menthol (14.4+/-1.3 microM) > PMD38 (31+/-1.1 microM) > WS-23 (44+/-7.3 microM) > Coolact P (66+/-20 microM) > geraniol (5.9+/-1.6 mM) > linalool (6.7+/-2.0 mM) > eucalyptol (7.7+/-2.0 mM) > hydroxycitronellal (19.6+/-2.2 mM). 4. Known VR1 antagonists (BCTC, thio-BCTC and capsazepine) were also able to block the response of TRPM8 to menthol (IC(50): 0.8+/-1.0, 3.5+/-1.1 and 18+/-1.1 microM, respectively). 5. The Ca(2+) response of hVR1-transfected HEK293 cells to the endogenous VR1 agonist N-arachidonoyl-dopamine was potentiated by low pH. In contrast, menthol- and icilin-activated TRPM8 currents were suppressed by low pH. 6. In conclusion, in the present study, we identified 10 new agonists and three antagonists of TRPM8. We found that, in contrast to VR1, TRPM8 is inhibited rather than potentiated by protons.

Characterization of the mouse cold-menthol receptor TRPM8 and vanilloid receptor type-1 VR1 using a fluorometric imaging plate reader (FLIPR) assay

1. TRPM8 (CMR1) is a Ca(2+)-permeable channel, which can be activated by low temperatures, menthol, eucalyptol and icilin. It belongs to the transient receptor potential (TRP) family, and therefore is related to vanilloid receptor type-1 (VR1, TRPV1). We tested whether substances which are structurally related to menthol, or which produce a cooling sensation, could activate TRPM8, and compared the responses of TRPM8 and VR1 to these ligands. 2. The effects of 70 odorants and menthol-related substances on recombinant mouse TRPM8 (mTRPM8), expressed in HEK293 cells, were examined using a FLIPR assay. In all, 10 substances (linalool, geraniol, hydroxycitronellal, WS-3, WS-23, FrescolatMGA, FrescolatML, PMD38, CoolactP and Cooling Agent 10) were found to be agonists. 3. The EC(50) values of the agonists defined their relative potencies: icilin (0.2+/-0.1 microM)>FrescolatML (3.3+/-1.5 microM) > WS-3 (3.7+/-1.7 microM) >(-)menthol (4.1+/-1.3 microM) >frescolatMAG (4.8+/-1.1 microM) > cooling agent 10 (6+/-2.2 microM) >(+)menthol (14.4+/-1.3 microM) > PMD38 (31+/-1.1 microM) > WS-23 (44+/-7.3 microM) > Coolact P (66+/-20 microM) > geraniol (5.9+/-1.6 mM) > linalool (6.7+/-2.0 mM) > eucalyptol (7.7+/-2.0 mM) > hydroxycitronellal (19.6+/-2.2 mM). 4. Known VR1 antagonists (BCTC, thio-BCTC and capsazepine) were also able to block the response of TRPM8 to menthol (IC(50): 0.8+/-1.0, 3.5+/-1.1 and 18+/-1.1 microM, respectively). 5. The Ca(2+) response of hVR1-transfected HEK293 cells to the endogenous VR1 agonist N-arachidonoyl-dopamine was potentiated by low pH. In contrast, menthol- and icilin-activated TRPM8 currents were suppressed by low pH. 6. In conclusion, in the present study, we identified 10 new agonists and three antagonists of TRPM8. We found that, in contrast to VR1, TRPM8 is inhibited rather than potentiated by protons.

Continual smoking of mentholated cigarettes may mask the early warning symptoms of respiratory disease

BACKGROUND

Continual use of cold preparations including those containing menthol for relief from congestion, cough, or difficulty in breathing can mask the early warning symptoms of respiratory dysfunction. These products usually carry a warning label on the packaging that indicates that they are not for continuous use and may mask the early warning symptoms of a more serious condition. Menthol can be delivered in many dosage forms including the smoke of a mentholated cigarette.

METHODS

Literature searches were done for the NLM databases (e.g., MEDLINE from 1966, TOXLINE, OLDMEDLINE (1958-1965), CANCERLIT), plus tobacco industry documents and hardcopy indices. The evidence was evaluated with application to mentholated cigarette smoking.

RESULTS

A logical progression is presented to attempt to demonstrate that the continuous smoking of mentholated cigarettes may also mask the early warning symptoms of respiratory distress. The early warning symptoms caused by chronic irritation of the respiratory tract may be reduced in severity when the menthol found in a mentholated cigarette is continually delivered to the tract.

CONCLUSION

This masking of the symptoms of an underlying respiratory disease can lead to delays in seeking medical attention resulting in a poor prognosis, additional suffering, and eventual death.

TRPM8 mRNA is expressed in a subset of cold-responsive trigeminal neurons from rat

Recent electrophysiological studies of cultured dorsal root and trigeminal ganglion neurons have suggested that multiple ionic mechanisms underlie the peripheral detection of cold temperatures. Several candidate "cold receptors," all of them ion channel proteins, have been implicated in this process. One of the most promising candidates is TRPM8, a nonselective cationic channel expressed in a subpopulation of sensory neurons that is activated both by decreases in temperature and the cooling compound menthol. However, evidence for the expression of TRPM8 in functionally defined cold-sensitive neurons has been lacking. Here, we combine fluorometric calcium imaging of cultured rat trigeminal neurons with single-cell RT-PCR to demonstrate that there are distinct subpopulations of cold responsive neurons and that TRPM8 likely contributes to cold transduction in one of them. TRPM8 is preferentially expressed within a subset of rapidly responsive, low-threshold (approximately 30 degrees C), cold-sensitive neurons. A distinct class of slowly responsive cold-sensitive neurons that is activated at lower temperatures (approximately 20 degrees C) generally lacks detectable TRPM8 mRNA. Together with previous findings, our data support the notion that cold responsive neurons are functionally heterogeneous.

Transient receptor potential (TRP) channels as potential drug targets in respiratory disease

Calcium-permeable channels have traditionally been thought of as therapeutic targets in excitable cells. For instance, voltage-operated Ca2+ channels in neurones and smooth muscle cells for neurological and cardiovascular diseases although calcium-permeable channels are also functionally important in electrically non-excitable cells. In the lung, calcium channels play a pivotal role in the activation of all the cell types present, whether resident cells such as airway smooth muscle cells and macrophages or migratory cells such as neutrophils or lymphocytes.Previously, research in this area has been hindered by the lack of obvious molecular identity. More recently, the emergence of the transient receptor potential (TRP) cation family has yielded promising candidates which may underpin the different receptor-operated calcium influx pathways. The challenge now, is to ascribe function to the TRP channels expressed in each cell type as a first step in identifying which TRP channels may be potential drug targets for asthma and chronic obstructive pulmonary disease (COPD) (Fig. 1).

Menthol: effects on nasal sensation of airflow and the drive to breathe

Menthol, in lozenges, nasal sprays, vapo-rubs, inhalers, and cough syrups, is widely used as a treatment for rhinitis that is associated with acute upper respiratory tract infection and allergy. Menthol as a plant extract has been used in traditional medicine in Asia for the treatment of respiratory diseases for hundreds of years, but it was only introduced to the West as a medicine at the end of the 19th century. With the recent discovery of a menthol receptor on the sensory nerves that modulate the cool sensation, menthol has graduated from the realms of herbal medicine into the field of molecular pharmacology. This review concerns the physiologic and pharmacologic mechanisms that underlie the widespread use of menthol as a treatment for the relief of nasal congestion associated with rhinitis and its effects on the drive to breathe and symptomatic relief of dyspnea.

The powerful placebo in cough studies?

Placebo treatment has been reported to improve subjective and objective measures of disease in up to 30-40% of patients with a wide range of clinical conditions. A review of 8 clinical trials on the effects of antitussive medicines on cough associated with acute upper respiratory tract infection shows that 85% of the reduction in cough is related to treatment with placebo, and only 15% attributable to the active ingredient Treatment with a cough medicine can be viewed as consisting of three components: pharmacological, physiological (demulcent) and placebo. The placebo effect is related to belief in the effectiveness of the treatment and this idea must in some way influence the central control of cough. Studies on the placebo effect of analgesics indicate that the placebo effect may be mediated by endogenous opioid neurotransmitters and this may explain the analgesic potency of opioid medicines such as morphine. In the present paper a model is proposed to explain the antitussive effects of placebo treatment on the basis of endogenous opioid neurotransmitters. With active pharmacological ingredients contributing only 15% to the effects of cough treatment it seems reasonable to conduct more research on the other components of treatment such as placebo.

Mentholated cigarettes and smoking cessation: findings from COMMIT. Community Intervention Trial for Smoking Cessation

OBJECTIVE

To examine the association between the use of menthol cigarettes and smoking cessation, amount smoked, and time to first cigarette in the morning.

BACKGROUND

The majority of African American smokers smoke mentholated cigarettes. Some evidence suggests that African Americans may be more nicotine dependent than whites. One theory is that menthol in cigarettes is responsible for enhancing the dependence producing capacity of cigarettes; however, few studies have prospectively examined the association between menthol use and indicators of nicotine dependence.

METHODS

Baseline smokers from the Community Intervention Trial for Smoking Cessation (COMMIT) completed a telephone tobacco use survey in 1988 and were re-interviewed in 1993. Use of mentholated cigarettes was assessed by self report at baseline. Indicators of dependence examined were six month cessation in 1993, amount smoked among continuing smokers in 1993, and time to first cigarette in the morning in 1988. Multivariate regression techniques were used to assess the association of baseline menthol use with these outcomes while controlling for other factors related to dependence.

RESULTS

Overall, 24% of the sample smoked a mentholated brand in 1988. No consistent associations were observed for menthol use and indicators of dependence in both overall and race specific analyses. Factors significantly associated with increased menthol use were female sex, age 25-34 years, African American and Asian race/ethnicity, greater education, greater than 60 minutes to the first cigarette in the morning, two or more past quit attempts, and use of premium brand cigarettes. Canadian respondents and those who smoked 15-24 cigarettes per day had lower rates of menthol use. Use of mentholated cigarettes was not associated with quitting, amount smoked, or time to first cigarette in the morning.

CONCLUSION

Future work is needed to clarify the physiological and sociocultural mechanisms involved in mentholated cigarette smoking.

A novel treatment of postherpetic neuralgia using peppermint oil

BACKGROUND

Postherpetic neuralgia remains a difficult problem to treat. A number of therapies have been shown to be effective, but some patients have intractable pain.

PATIENT

The case of a 76-year-old woman whose pain had been resistant to standard therapies is described. The pattern of quantitative sensory testing results for this patient led the authors to believe that she had an "irritable nociceptor" type of pathophysiology.

INTERVENTION

The patient was instructed to apply neat peppermint oil (containing 10% menthol) to her skin, resulting in an almost immediate improvement in her pain. This pain relief persisted for 4-6 hours after application of the oil.

RESULTS

The patient was successfully treated with topical peppermint oil. During 2 months of follow-up she has had only a minor side effect, with continuing analgesia. The authors believe this is the first evidence of peppermint oil (or menthol) having a strong analgesic effect on neuropathic pain. The possible mechanisms of action of peppermint oil are discussed.

Menthol: a natural analgesic compound

Menthol, after topical application, causes a feeling of coolness due to stimulation of 'cold' receptors by inhibiting Ca++ currents of neuronal membranes. Since Ca++ channel blockers are endowed with analgesic properties, the aim of the present study was to investigate the potential antinociceptive effect of menthol. (-)-Menthol produced a dose-dependent increase in the pain threshold in the mouse hot-plate (3-10 mg kg(-1) p.o.) and abdominal constriction (3-10 mg kg(-1) p.o.; 10 microg per mouse intracerebroventricularly (i.c.v.)) tests. The antinociceptive effect of (-)-menthol was antagonised by the unselective opioid antagonist naloxone and by the selective kappa-antagonist nor-NBI. Conversely, CTOP (mu-antagonist), 7-benzylidenenal-trexone (delta(1) antagonist) and naltriben (delta(2) antagonist) did not prevent (-)-menthol antinociception. In both tests, (+)-menthol (10-50 mg kg(-1) p.o.; 10-30 microg per mouse i.c.v.) was unable to modify the pain threshold. These results indicate that (-)-menthol is endowed with analgesic properties mediated through a selective activation of kappa-opioid receptors.

Identification of a cold receptor reveals a general role for TRP channels in thermosensation

The cellular and molecular mechanisms that enable us to sense cold are not well understood. Insights into this process have come from the use of pharmacological agents, such as menthol, that elicit a cooling sensation. Here we have characterized and cloned a menthol receptor from trigeminal sensory neurons that is also activated by thermal stimuli in the cool to cold range. This cold- and menthol-sensitive receptor, CMR1, is a member of the TRP family of excitatory ion channels, and we propose that it functions as a transducer of cold stimuli in the somatosensory system. These findings, together with our previous identification of the heat-sensitive channels VR1 and VRL-1, demonstrate that TRP channels detect temperatures over a wide range and are the principal sensors of thermal stimuli in the mammalian peripheral nervous system.

Specificity of cold thermotransduction is determined by differential ionic channel expression

Sensations of cold are mediated by specific thermoreceptor nerve endings excited by low temperature and menthol. Here we identify a population of cold-sensitive cultured mouse trigeminal ganglion neurons with a unique set of biophysical properties. Their impulse activity during cooling and menthol application was similar to that of cold thermoreceptor fibers in vivo. We show that cooling closes a background K+ channel, causing depolarization and firing that is limited by the slower reduction of a cationic inward current (Ih). In cold-insensitive neurons, firing is prevented by a slow, transient, 4-AP-sensitive K+ current (IKD) that acts as an excitability brake. In addition, pharmacological blockade of IKD induced thermosensitivity in cold-insensitive neurons, a finding that may explain cold allodynia in neuropathic pain. These results suggest that cold sensitivity is not associated to a specific transduction molecule but instead results from a favorable blend of ionic channels expressed in a small subset of sensory neurons.

Effect of pH on skin permeation enhancement of acidic drugs by l-menthol-ethanol system

The effect of pH on the skin permeation enhancement of three acidic drugs by the l-menthol-ethanol system was investigated. The total flux of acidic drugs from the system remarkably varied over the pH range 3.0-8.0, and the permeation enhancement factor depended on the system pH and drug. A skin permeation model, which consists of two permeant (unionized and ionized) species, two system (oily and aqueous) phases, and two permeation (lipid and pore) pathways, was developed. The assumptions were made that only the unionized species can distribute to the oily phase and transport via the lipid pathway. The model explained the relationship between the concentration of drug in the aqueous phase and system pH. The skin permeability data were also described by the model and permeability coefficients corresponding to the physicochemical properties of permeant were calculated for the lipid and pore pathways. The model simulation showed that the permeation of acidic drugs occurred from the aqueous phase and the oily phase acted as a reservoir. Whether the total flux increased with increase of pH was dependent on the lipophilicity of drug. These results suggest that the pH of l-menthol-ethanol system should be given attention to elicit the maximum permeation enhancement.

Herbal Therapy

Herbal medicine (phytomedicine) uses remedies possessing significant pharmacological activity and, consequently, potential adverse effects and drug interactions. The explosion in sales of herbal therapies has brought many products to the marketplace that do not conform to the standards of safety and efficacy that physicians and patients expect. Unfortunately, few surgeons question patients regarding their use of herbal medicines, and 70% of patients do not reveal their use of herbal medicines to their physicians and pharmacists. All surgeons should question patients about the use of the following common herbal remedies, which may increase the risk of bleeding during surgical procedures: feverfew, garlic, ginger, ginkgo, and Asian ginseng. Physicians should exercise caution in prescribing retinoids or advising skin resurfacing in patients using St John's wort, which poses a risk of photosensitivity reaction. Several herbal medicines, such as aloe vera gel, contain pharmacologically active ingredients that may aid in wound healing. Practitioners who wish to recommend herbal medicines to patients should counsel them that products labeled as supplements have not been evaluated by the US Food and Drug Administration and that no guarantee of product quality can be made.

Nasal airflow in health and disease

This review examines our present understanding of the physiology, pathophysiology and pharmacology of nasal airflow. The main aim of the review is to discuss the basic scientific and clinical knowledge that is essential for a proper understanding of the usefulness of measurements of nasal airflow in the clinical practice of rhinology. The review concludes with a discussion of the measurement of nasal airflow to assess the efficacy of surgery in the treatment of nasal obstruction. Areas covered by the review include: influence of nasal blood vessels on nasal airflow; nasal valve and control of nasal airflow; autonomic control of nasal airflow; normal nasal airflow; nasal cycle; central control of nasal airflow; effect of changes in posture on nasal airflow; effect of exercise on nasal airflow; effect of hyperventilation and rebreathing on nasal airflow; nasal airflow in animals; cerebral effects of nasal airflow; sensation of nasal airflow; sympathomimetics and sympatholytics; histamine and antihistamines; bradykinin; and corticosteroids.

Role of cold receptors and menthol in thirst, the drive to breathe and arousal

Menthol is widely used in candy, chewing gum, toothpastes, cigarettes and common cold medications. Menthol has been shown to stimulate cold receptors in the mouth and nose. The present paper puts forward the hypothesis that menthol, by its effects on oral and nasal cold receptors, may influence thirst, the drive to breathe, and arousal. The satisfying effects of menthol on thirst and breathing, together with an effect on arousal, may explain the popularity of menthol and account for the very large amount of menthol-containing products that are consumed each day.

Sensitive and selective gas chromatographic methods for the quantitation of camphor, menthol and methyl salicylate from human plasma

Analytical methods using gas chromatography-flame ionization detection (GC-FID) for the quantitation of camphor and menthol and GC-MS for the quantitation of methyl salicylate have been developed for measurement of low concentrations from human plasma. Anethole serves as the internal standard for camphor and menthol and ethyl salicylate serves as the internal standard for methyl salicylate. Plasma samples undergo multiple, sequential extractions with hexane in order to provide optimal recovery. For menthol and camphor, the extracting solvent is reduced in volume and directly injected onto a capillary column (Simplicity-WAX). Extracted methyl salicylate is derivatized with BSTFA prior to injection onto a capillary column (Simplicity-5). Between-day variation (% RSD) at 5 ng/ml varies from 6.2% for methyl salicylate to 13.5% for camphor. The limit of detection for each analyte is 1 ng/ml and the limit of quantitation is 5 ng/ml. These analytical methods have been used in a clinical study to assess exposure from dermally applied patches containing the three compounds.

Smoke constituent exposure and stage of change in black and white women cigarette smokers

Differences in smoke constituent exposure by ethnicity and menthol preference and differences in decisional balance and habit strength by stage of change, ethnicity, and menthol preference were examined in this 2-factor study design. Ninety-five women, half of whom were Black and half of who smoked menthol cigarettes, participated in a cigarette smoking bout in the Clinical Research Center. Measures of smoking topography, plasma cotinine and nicotine, and expired carbon monoxide were obtained in addition to self-report of the pros and cons of smoking, time to first cigarette, and smoking history. Black women smoked significantly fewer cigarettes per day, but had higher cotinine levels compared to White women. Menthol smokers (n = 49) had significantly larger puff volumes, higher cotinine levels, and shorter time to first cigarette compared to nonmenthol smokers (n = 46). Precontemplators (n = 44) were significantly lower on beliefs about the negative aspects of smoking compared to contemplators and those in preparation stage. Black women, all stages combined, had higher negative beliefs about smoking than did White women. Implications for assessment of smoking patterns and intervention are discussed.

Effect of menthol cigarettes on biochemical markers of smoke exposure among black and white smokers

STUDY OBJECTIVES

Black smokers have been reported to have higher serum cotinine levels than do white smokers, and have higher rates of most smoking-related diseases, despite smoking fewer cigarettes per day. Another striking racial difference is the preference for mentholated cigarettes among black smokers. The contribution of menthol to variability in biochemical markers of cigarette smoke exposure (end-expiratory carbon monoxide and serum cotinine) was evaluated in a biracial sample.

DESIGN

Descriptive cross-sectional.

SETTING

A university smoking research laboratory.

PARTICIPANTS

Sixty-five black and 96 white adult established smokers who were paid for their participation.

MEASUREMENTS

Information was obtained through direct observation, self-report (interview and self-administered questionnaires), measurement of butts collected for a week, and laboratory analyses of the biochemical markers of exposure.

RESULTS

Compared with the white smokers, the black smokers had significantly higher cotinine and carbon monoxide levels per cigarette smoked and per millimeter of smoked tobacco rod (both p < 0.001). After adjusting for race, cigarettes per day, and mean amount of each cigarette smoked, menthol was associated with higher cotinine levels (p = 0.03) and carbon monoxide concentrations (p = 0.02).

CONCLUSIONS

The use of menthol may be associated with increased health risks of smoking. Menthol use should be considered when biochemical markers of smoke exposure are used as quantitative measures of smoking intensity or as indicators of compliance with smoking reduction programs. In addition, the effect of menthol on total "dose" should be considered in any efforts to regulate the amount of nicotine in cigarettes.

Effect of topically applied menthol on thermal, pain and itch sensations and biophysical properties of the skin

The effect of menthol and alcohol as its vehicle on thermal sensations, pain, experimental itch and irritation were studied in 18 subjects, using a computerized thermal sensory analyzer, laser Doppler flowmetry and an evaporimeter for transepidermal water loss (TEWL). Menthol had a subjective cooling effect lasting up to 70 min in 12/18 subjects; however, it did not affect cold and heat threshold, nor did it affect cold and heat pain threshold. Alcohol produced an immediate cold sensation lasting up to 5 min in 4/18 subjects and lowered the sensitivity of cold sensation threshold (P < 0.05). Histamine injection did not change thermal and pain thresholds. Menthol did not alleviate histamine-induced itch magnitude, nor its duration. Following histamine injection, cold sensation median threshold decreased by 1.2 degrees C from (29.9 degrees C to 28.7 degrees C) on the site treated with menthol (P < 0.01) with similar changes in thresholds at the alcohol-treated site (P < 0.05). Warm sensation and pain threshold in subjects receiving histamine injections, measured after menthol and alcohol application, did not differ from their baseline values with histamine alone. TEWL at the site treated with menthol was significantly higher (P < 0.05) than at the alcohol-treated and the control site (P < 0.01), suggesting that menthol has a higher skin irritating effect, or at least alters the stratum corneum water permeability. Our results suggest that menthol fulfills the definition of a counterirritant, but does not affect histamine-induced itch, nor does it affect pain sensation.