Menthol Attenuates Respiratory Irritation and Elevates Blood Cotinine in Cigarette Smoke Exposed Mice

Abstract

Addition of menthol to cigarettes may be associated with increased initiation of smoking. The potential mechanisms underlying this association are not known. Menthol, likely due to its effects on cold-sensing peripheral sensory neurons, is known to inhibit the sensation of irritation elicited by respiratory irritants. However, it remains unclear whether menthol modulates cigarette smoke irritancy and nicotine absorption during initial exposures to cigarettes, thereby facilitating smoking initiation. Using plethysmography in a C57Bl/6J mouse model, we examined the effects of L-menthol, the menthol isomer added to cigarettes, on the respiratory sensory irritation response to primary smoke irritants (acrolein and cyclohexanone) and smoke of Kentucky reference 2R4 cigarettes. We also studied L-menthol’s effect on blood levels of the nicotine metabolite, cotinine, immediately after exposure to cigarette smoke. L-menthol suppressed the irritation response to acrolein with an apparent IC₅₀ of 4 ppm. Suppression was observed even at acrolein levels well above those necessary to produce a maximal response. Cigarette smoke, at exposure levels of 10 mg/m³ or higher, caused an immediate and marked sensory irritation response in mice. This response was significantly suppressed by L-menthol even at smoke concentrations as high as 300 mg/m³. Counterirritation by L-menthol was abolished by treatment with a selective inhibitor of Transient Receptor Potential Melastatin 8 (TRPM8), the neuronal cold/menthol receptor. Inclusion of menthol in the cigarette smoke resulted in roughly a 1.5-fold increase in plasma cotinine levels over those observed in mice exposed to smoke without added menthol. These findings document that, L-menthol, through TRPM8, is a strong suppressor of respiratory irritation responses, even during highly noxious exposures to cigarette smoke or smoke irritants, and increases blood cotinine. Therefore, L-menthol, as a cigarette additive, may promote smoking initiation and nicotine addiction.

Sensory Effects of Menthol and Nicotine in an E-Cigarette

“…21,22 Evidence from the studies in mice also indicate that menthol's inhibitory effects depend upon TRPM8, which has been shown to underlie the analgesic effects of cold on acute and inflammatory pain via an opioid-dependent central neural pathway. 49 An analgesic action of menthol via a central neural mechanism raises the possibility that menthol stimulation in both the upper and lower airways may contribute to reducing the sensory irritation of nicotine that is sensed most acutely in the throat and lungs.…”

“…The authors of a recent study of menthol cigarettes concluded there was no consistent effect of menthol on perceived harshness and overall impact, 20 whereas a previous study indicated that menthol could either increase or decrease the perceived harshness of a cigarette depending on nicotine concentration. 8 Studies in mice 21,22 indicate that menthol can reduce the sensory irritation from constituents of cigarette smoke, including nicotine, that stimulate the pain receptor TRPA1, 23,24 which has been shown to play a role in cough. 25 However, the numerous other chemical and particulate irritants in tobacco smoke 5,26 have precluded direct measurement of the effect of menthol on the perception of nicotine irritation alone.…”

Menthol decreases oral nicotine aversion in C57BL/6 mice through a TRPM8-dependent mechanism

“…7 Together these data suggested that menthol may facilitate smoking initiation by reducing aversion to noxious smoke. [6][7][8] It is currently controversial whether menthol's counterirritant activity extends to oral nicotine and its aversive effects. Most studies examining the effects of menthol in the context of tobacco use were performed in chronic smokers and provide no information about menthol's behavioural effects during initiation of tobacco use.…”

“…Higher levels of cotinine were detected in the mice inhaling mentholated cigarette smoke than in the mice inhaling non-mentholated smoke, implying that menthol increases nicotine uptake. 7 These effects were observed at menthol levels present in smoke of commercial menthol cigarettes. 7 Together these data suggested that menthol may facilitate smoking initiation by reducing aversion to noxious smoke.…”

“…7 These effects were observed at menthol levels present in smoke of commercial menthol cigarettes. 7 Together these data suggested that menthol may facilitate smoking initiation by reducing aversion to noxious smoke. [6][7][8] It is currently controversial whether menthol's counterirritant activity extends to oral nicotine and its aversive effects.…”