Pharmacological Blockade of TRPM8 Ion Channels Fails to Reduce Behavioral and Biological Markers of Acute Oral Pain in Irradiated C57BL/6J Mice

Radiation-associated pain (RAP) after head and neck cancer treatment often results in significant discomfort, yet the mechanisms underlying this pain remain poorly understood. Transient receptor potential cation channel subfamily M (melastatin) member 8 (TRPM8) channels, known to mediate cold sensation, have been implicated in RAP. Previous studies suggested that inhibition of TRPM8 might offer a therapeutic approach for alleviating radiation-induced pain. We tested the effects of PBMC, a small molecule inhibitor of TRPM8, on radiation-induced glossitis and associated pain behaviors in C57BL/6J mice following tongue irradiation. We evaluated the impact of phenylethyl(2-aminoethyl)(4-(benzyloxy)-3-methoxybenzyl)carbamate (PBMC) on weight loss, burrowing, grooming behavior, and nest building. Additionally, mRNA expression of TRPM8 and other relevant ion channels was assessed in the trigeminal ganglion (TG) using qRT-PCR and in situ hybridization (ISH). Irradiated mice exhibited significant glossitis, weight loss, and altered behaviors, including impaired burrowing and grooming. PBMC treatment provided no measurable protection against glossitis and only weakly mitigated weight loss and abnormal burrowing behavior. Exposure to radiation led to downregulation of TRPM8 expression in the TG, contrasting with previous findings of upregulation. Interestingly, female mice showed greater susceptibility to RAP than males, highlighting a sex-dependent response. Our findings suggest that TRPM8 inhibition with PBMC does not alleviate radiation-induced pain or glossitis in the C57BL/6J murine model. The observed downregulation of TRPM8 expression challenges prior assumptions, and our results suggest that compensatory mechanisms or model-specific factors may contribute to the failure of PBMC to impact pain outcomes. Future studies incorporating genetic models and evaluating protein expression are necessary to better understand the role of TRPM8 in radiation-induced pain and to explore more effective therapeutic strategies.