PO-84 | Inhibiting the peripheral degradation of anandamide reduces trigeminal hyperalgesia in a model of dural neurogenic inflammation via a CB1/CB2-independent mechanism

Background: The recent availability of CGRP-targeting drugs has improved migraine management, although it is now clear that a large portion of patients are CGRP-resistant. Inhibition of the degradation pathway of endocannabinoids may represent a new therapeutic target for non CGRP-responding patients. Indeed, the inhibition of fatty acid amide hydrolase (FAAH), the main catabolic enzyme of N-arachidonoylethanolamine (AEA), and of N-acylethanolamine-hydrolysing acid amidase (NAAA), which preferentially hydrolyses palmitoylethanolamide (PEA), may exert analgesic and anti-inflammatory effects. The aim of the study was to investigate and compare the effects of peripheral FAAH inhibition (URB937) and NAAA inhibition (ARN726) on trigeminal hyperalgesia induced in the animal model of migraine based on dural neurogenic inflammation. Methods: Migraine-like dural inflammation was induced in male Sprague-Dawley rats via a 5-minute infusion of inflammatory soup (IS, 10 μL) onto the dura. Animals were treated intraperitoneally with ARN726 (3 mg/kg; at the end of IS infusion) or URB937 (1 mg/kg; injected 1h after IS infusion), or vehicle. To further investigate the URB937 effects, additional groups were treated with cannabinoid (CB) 1 or CB2 receptor antagonists (AM251 or AM630, 1 mg/kg) in combination with URB937 treatment. Two hours after IS infusion, trigeminal nocifensive behavior was assessed using the orofacial formalin test (OFT) (1.5%, 50 µl, s.c.). Results: IS infusion produced a significant increase in trigeminal hyperalgesia during the second phase of the OFT compared to controls. URB937 treatment significantly reduced the IS-induced hyperalgesic behavior, while ARN726 had no effect. Antagonism of CB1 or CB2 receptors did not reverse URB937 anti-hyperalgesic effect. Conclusion: The combination of IS infusion with OFT shows that inflammatory mediators in the meninges activate and sensitize the nociceptive terminals of the trigeminal nerve. Peripheral inhibition of FAAH through URB937 significantly reduces IS-induced trigeminal hyperalgesia, whereas inhibition of NAAA does not produce similar effects. These findings suggest a prominent role for AEA in the pain modulation in this model of neurogenic inflammation. Notably, the anti-hyperalgesic effects of URB937 appear to be independent of CB1 and CB2 receptor activation, pointing toward alternative mechanisms of action for AEA. Overall, the data confirm peripheral FAAH as a promising therapeutic target for modulating migraine-related pain.