Combined Endocannabinoid and Cyclooxygenase Inhibition Additively Attenuates Post-Surgical Pain

<b>Introduction:</b> Post-surgical pain arises following a clinical operation, often persisting throughout recovery. While current treatments reduce pain, repeated use increases the probability of adverse events. monoacylglycerol lipase (MAGL) inhibition has previously been shown to produce analgesia, either through CB₁ or CB₂ mechanisms, dependent on the underlying pain phenotype. Thus, this study investigated the analgesic potential of inhibiting MAGL, alone and in combination with the analgesic non-steroidal anti-inflammatory drug (NSAID) diclofenac sodium in a model of post-surgical pain. <b>Methods:</b> Male and female C57BL/6J mice were subjected to hindpaw incision (HPI) surgery. Mechanical allodynia, climbing, grip strength, and thermal preference were measured 24 h following HPI. The dose-dependent anti-allodynic effects of the MAGL inhibitors (irreversible MAGL inhibitor [JZL184] and selective MAGL inhibitor [MJN110]) and the NSAID diclofenac, as well as the additive potential of combined MAGL and cyclooxygenase (COX) inhibition, were assessed. Selective antagonists of CB₁ and CB₂ receptors were used to challenge the cannabinoid-receptor mechanism of JZL184. Similarly, the anti-allodynic effects of the CB₂-selective agonist (LY2828360) were tested. JZL184 was administered repeatedly to determine tolerance. Finally, hindpaw cytokines were quantified <i>via</i> multiplex ELISA 24 h after HPI surgery. <b>Results:</b> Approximately 24 h post-surgery, the MAGL inhibitors JZL184 (≥4 mg/kg) or MJN110 (≥5 mg/kg), as well as the NSAID diclofenac sodium (≥16.67 mg/kg), attenuated HPI-induced mechanical allodynia, as assessed with von Frey filaments. The anti-allodynic effects of JZL184 (40 mg/kg) were blocked by pre-treatment of the CB₂ antagonist SR144528 (3 mg/kg) but not the CB₁-selective antagonist rimonabant (SR141716A; 3 mg/kg), suggesting a CB₂-mediated mechanism of anti-allodynia <i>via</i> MAGL inhibition. Similarly, LY2828360 (3 mg/kg) reduced HPI-induced allodynia. Moreover, when administered repeatedly, the anti-allodynic effects of JZL184 (8 mg/kg) persisted and did not undergo tolerance. A separate cohort was administered a sub-analgesic dose of JZL184 (1 mg/kg), diclofenac sodium (1.85 mg/kg), or both compounds concurrently. This subthreshold JZL184 and diclofenac sodium combination attenuated HPI-induced allodynia, suggesting an additive drug interaction. Finally, HPI <i>per se</i> increased pro-inflammatory cytokine levels, which were unaltered by MAGL inhibition despite the anti-allodynia assessed behaviorally. <b>Conclusion:</b> These data support simultaneously targeting endocannabinoids and COX enzymes as a potential post-operative pain management approach.