Investigation on NAAA inhibitors, a novel class of medications that reduces nicotine reward and delays opioid tolerance

N-palmitoylethanolamine (PEA) and N-oleoylethanolamine (OEA) are bioactive lipids involved in many physiological processes including pain, inflammationand food intake (Alhouayek & Muccioli, 2014; Fu et al., 2003; Guzman et al., 2004; Orefice et al., 2016)and primarily exert their action by activating peroxisome proliferator-activated receptor alpha (PPAR-alpha) (Berger & Moller, 2002). PPAR-alphaactivationnegatively modulatesnicotinic receptors expressed bydopamine (DA) neurons in the ventral tegmental area (VTA)(Melis et al., 2013)and reducesneurochemical and behavioral effect of nicotinein rodents and mammals(Mascia et al. 2011; Panlilio et al. 2012).Moreover, one of its major endogenous ligands(i.e. PEA)potentiatesmorphine analgesic effect and delaysthe development of morphine antinociceptive tolerance (Di Cesare Mannelli, Corti, Micheli, Zanardelli, & Ghelardini, 2015; Di Cesare Mannelli, Micheli, Lucarini, & Ghelardini, 2018; Di Cesare Mannelli et al., 2015).Astrategy to augment the levels of endogenousPPAR-alpha ligands (PEA and OEA) is theinhibition ofone of the enzymesresponsible for their degradation: N-Acylethanolamine-hydrolyzing acid amidase (NAAA). NAAA shows selectivity onto degrading PEA and OEA, with more reactivity for PEA,andit is not involved in endogenous cannabinoid (i.e. anandamide)degradation (Bonezzi et al., 2016; Petrosino et al., 2015; Sasso et al., 2018). A new brain permeable NAAA-inhibitor (AM11095)was synthetizedand allowsus to employ a finerstrategy to augment PEA levels. We administered AM11095 to rats andcarried out brain lipid analysis, a functionalobservational battery (FOB) to assess toxicity, in vivo electrophysiological recording from DAcells in theVTA, brain microdialysis in the nucleus accumbens shell(NAcSh)and behavioral experiments to assessits effect on nicotine-induced conditioned place preference (CPP).We also performed in vivo electrophysiological recording from noradrenergic neurons in the locus coeruleus(LC) while delivering a noxious stimulus (i.e. foot-shock)andthe paw pressure test to assess AM11095 effectson morphine antinociceptive properties and the development of opioid tolerance.AM11095 (5 and 25 mg/kg, i.p.) was devoid of neurotoxic and behavioral effects and did not affect motorbehavior and coordination. This NAAA inhibitor (5 mg/kg i.p.) increased OEA and PEA levels in the hippocampusand cortex, prevented nicotine-induced activation of mesolimbic DAneurons in the VTA,nicotine-induced elevation of DAlevels in the NAcShand decreased theexpression of nicotine CPP.Moreover, AM11095 (15 mg/kg, per o.s.) potentiate morphine antinociceptive effects and delays the development of morphine tolerancein behaving rats.Our results indicate that NAAA inhibitors represent a new class of pharmacological toolsto modulate brainPEA signaling and show potential in the treatment of nicotine dependenceand as anadditional strategy to amelioratetherapeutic useof opioids.