Over the last decades, a great array of molecular mediators have been identified as potential targets for the treatment of chronic pain. Among these mediators, transient receptor potential (TRP) channel superfamily members have been thoroughly studied. Namely, the nonselective cationic channel, transient receptor potential ankyrin subtype 1 (TRPA1), has been described as a chemical nocisensor involved in noxious cold and mechanical sensation and as rivalling TRPV1, which traditionally has been considered as the most important TRP channel involved in nociceptive transduction. However, few TRPA1-related drugs have succeeded in clinical trials. In the present review, we attempt to discuss the latest data on the topic and future directions for pharmacological intervention.

TRPA1 and TRPM8 are transient receptor potential channels expressed in trigeminal neurons that are related to pathophysiology in migraine models. Here we use a mouse model of nitroglycerine-induced chronic migraine that displays a sexually dimorphic phenotype, characterized by mechanical hypersensitivity that develops in males and females, and is persistent up to day 20 in female mice, but disappears by day 18 in male mice. TRPA1 is required for development of hypersensitivity in males and females, whereas TRPM8 contributes to the faster recovery from hypersensitivity in males. TRPM8-mediated antinociception effects required the presence of endogenous testosterone in males. Administration of exogenous testosterone to females and orchidectomized males led to recovery from hypersensitivity. Calcium imaging and electrophysiological recordings in in vitro systems confirmed testosterone activity on murine and human TRPM8, independent of androgen receptor expression. Our findings suggest a protective function of TRPM8 in shortening the time frame of hypersensitivity in a mouse model of migraine.

TRPM8 antagonists derived from its cognate ligand, (−)-menthol, are underrepresented. We determine the absolute stereochemistry of a well-known TRPM8 antagonist, (−)-menthyl 1, using VCD and 2D NMR. We explore 1 for its antagonist effects of the human TRPM8 (hTRPM8) orthologue to uncover species-dependent inhibition versus rat channels. (−)-Menthyl 1 inhibits menthol-and icilin-evoked Ca 2+ responses at hTRPM8 with IC 50 values of 805 ± 200 nM and 1.8 ± 0.6 μM, respectively, while more potently inhibiting agonist responses at the rat orthologue (rTRPM8 IC 50 (menthol) = 117 ± 18 nM, IC 50 (icilin) = 521 ± 20 nM). Whole-cell patch-clamp recordings of hTRPM8 confirm the 1 inhibition of menthol-stimulated currents, with an IC 50 of 700 ± 200 nM. We demonstrate that 1 possesses ≥400-fold selectivity for hTRPM8 versus hTRPA1/hTRPV1. (−)-menthyl 1 can be used as a novel chemical tool to study hTRPM8 pharmacology and differences in species commonly used in drug discovery.

The mechanisms contributing to the high prevalence of chronic migraine in females are yet elusive. Here, we used a mouse model of nitroglycerin-induced chronic migraine that displays a sexual dimorphic phenotype and unveiled a role of TRPM8 as a testosterone receptor that provides antinociceptive resilience exclusively in males. Nitroglycerin induced similar mechanosensitivity to both sexes trough activation of TRPA1 channels, but triggered persistent hypersensitivity solely in females, as males readily recovered from the migraine crisis. Notably, we found that testosterone exerted an antinociceptive activity through its interaction with the TRPM8 channel. Downregulation of this protective mechanism in males led to persistent mechanical hypersensitivity, whereas administration of testosterone to females favoured their recovery. Thus, our findings reveal a novel protective function of TRPM8 through pre-clinical models of acute and chronic pain and highlights the interest of molecular solutions mimicking the pain-relieving activity of testosterone on TRPM8.

Neurosensory disorders such as pain and pruritus remain a major health problem greatly impacting the quality of life, and often increasing the risk of mortality. Current pre-clinical models to investigate dysfunction of sensory neurons have shown a limited clinical translation, in part, by failing to mimic the compartmentalized nociceptor anatomy that exhibit a central compartment containing the soma and a peripheral one harboring the axon endings with distinct molecular and cellular environmental composition. Thus, there is a need to validate compartmentalized preclinical neurosensory models for investigating the pathophysiology of peripheral sensory disorders and to test drug candidates. Here, we have addressed this issue and developed a microfluidic-based preclinical nociceptor model and validated it for investigating inflammatory and neuropathic peripheral disorders. We show that this model reproduces the peripheral sensitization and resolution produced by an inflammatory soup and by the chemotherapeutic drug paclitaxel. Furthermore, compartmentalized nociceptor primary cultures were amenable to co-culture with keratinocytes in the axonal compartment. Interaction of axonal endings with keratinocytes modulated neuronal responses, consistent with a crosstalk between both cell types. These findings pave the way towards translational pre-clinical sensory models for skin pathophysiological research and drug development.