Peripheral cannabinoid receptor activation attenuates frostbite-induced chronic pain via modulation of TRP channels, neuroinflammation, and autophagy.

Frostbite injury is a debilitating cold injury encountered in extreme high-altitude and subzero environments, frequently resulting in persistent chronic pain even after tissue healing. Using our previously validated frostbite-induced chronic pain model, we further investigated the contribution of neuroimmune, excitatory mechanisms and evaluated the therapeutic efficacy of peripheral cannabinoid receptor activation. Frostbite produced significant mechanical allodynia, mechanical hyperalgesia, and cold hypersensitivity, along with increased spontaneous ongoing pain behaviors. Local peripheral administration of CB13, a peripherally acting CB1/CB2 receptor dual agonist, dose-dependently attenuated both mechanical and cold allodynia without impairing locomotor activity, indicating a lack of central nervous system side effects. At the molecular level, frostbite induced marked peripheral and spinal sensitization, demonstrated by elevated expression of TRPV1, TRPA1, TRPV4, and TRPM8 channels, increased levels of pro-inflammatory cytokines, and enhanced c-Fos expression as an indicator of heightened neuronal activation in DRG and spinal cord of rats. These alterations were accompanied by microglial activation and upregulation of the NLRP3 inflammasome. CB13 treatment significantly reversed these pathological changes and concurrently restored Beclin-1-associated autophagy signaling, suggesting engagement of both neuroimmune and intracellular homeostasis pathways. Notably, frostbite injury was associated with marked oxidative and nitrosative stress in the sciatic nerve, as evidenced by reduced glutathione depletion and elevated lipid peroxidation and nitrite levels, which were significantly normalized by CB13 treatment. Collectively, these findings demonstrate that peripheral cannabinoid receptor activation effectively inhibit frostbite induced chronic pain through modulation of nociceptive, neuroinflammatory, redox, and cellular stress pathways. This work highlights peripherally selective cannabinoid receptor agonists as promising, safer therapeutic strategies for chronic pain associated with cold injuries.