Analgesic Effects of Fatty Acid Amide Hydrolase Inhibition in a Rat Model of Neuropathic Pain
ABSTRACT Cannabinoid-based medicines have therapeutic potential for the treatment of pain. Augmentation of levels of endocannabinoids with inhibitors of fatty acid amide hydrolase (FAAH) is analgesic in models of acute and inflammatory pain states. The aim of this study was to determine whether local inhibition of FAAH alters nociceptive responses of spinal neurons in the spinal nerve ligation model of neuropathic pain. Electrophysiological studies were performed 14-18 d after spinal nerve ligation or sham surgery, and the effects of the FAAH inhibitor cyclohexylcarbamic acid 3-carbamoyl biphenyl-3-yl ester (URB597) on mechanically evoked responses of spinal neurons and levels of endocannabinoids were determined. Intraplantar URB597 (25 microg in 50 microl) significantly (p < 0.01) attenuated mechanically evoked responses of spinal neurons in sham-operated rats. Effects of URB597 were blocked by the cannabinoid 1 receptor (CB1) antagonist AM251 [N-1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide] (30 microg in 50 microl) and the opioid receptor antagonist naloxone. URB597 treatment increased levels of anandamide, 2-arachidonyl glycerol, and oleoyl ethanolamide in the ipsilateral hindpaw of sham-operated rats. Intraplantar URB597 (25 microg in 50 microl) did not, however, alter mechanically evoked responses of spinal neurons in spinal nerve ligated (SNL) rats or hindpaw levels of endocannabinoids. Intraplantar injection of a higher dose of URB597 (100 microg in 50 microl) significantly (p < 0.05) attenuated evoked responses of spinal neurons in SNL rats but did not alter hindpaw levels of endocannabinoids. Spinal administration of URB597 attenuated evoked responses of spinal neurons and elevated levels of endocannabinoids in sham-operated and SNL rats. These data suggest that peripheral FAAH activity may be altered or that alternative pathways of metabolism have greater importance in SNL rats.
- SourceAvailable from: Divya Ramesh
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- "It is well established that elevation of either AEA or 2-AG, via inhibition of their respective catabolic enzymes, fatty acid amide hydrolase (FAAH) or monoacylglycerol lipase (MAGL), produces analgesic and anti-inflammatory effects in vivo (Schlosburg et al., 2009b). For example, FAAH inhibition attenuates neuropathic pain (Jhaveri et al., 2006; Russo et al., 2007; Kinsey et al., 2009; Clapper et al., 2010), inflammatory pain (Booker et al., 2011), collagen-induced arthritis (Kinsey et al., 2011a), and gastric ulceration (Naidu et al., 2009; Sasso et al., 2012), as well as elicits anxiolytic-like behavioral effects (Patel and Hillard, 2006; Naidu et al., 2007) in rodents. "
ABSTRACT: The monoacylglycerol lipase (MAGL) inhibitor JZL184 produces antinociceptive and anti-inflammatory effects. However, repeated administration of high dose JZL184 (40 mg/kg) causes dependence, antinociceptive tolerance, cross-tolerance to the pharmacological effects of cannabinoid receptor agonists, and CB(1) receptor downregulation and desensitization. This functional CB(1) receptor tolerance poses a hurdle in the development of MAGL inhibitors for therapeutic use. Consequently, the present study tested whether repeated administration of low dose JZL184 maintains its antinociceptive actions in the chronic constrictive injury (CCI) of the sciatic nerve neuropathic pain model and protective effects in a model of NSAlD-induced gastric hemorrhages. Mice given daily injections of high dose JZL184 (≥16 mg/kg) for six days displayed decreased CB(1) receptor density and function in brain, as assessed in [(3)H]SR141716A binding and CP55,940-stimulated [(35)S]GTPγS binding assays, respectively. In contrast, normal CB(1) receptor expression and function were maintained following repeated administration of low dose JZL184 (≤8 mg/kg). Likewise, the antinociceptive and gastroprotective effects of high dose JZL184 underwent tolerance following repeated administration, but these effects were maintained following repeated low dose JZL184 treatment. Consistent with these observations, repeated high dose JZL184, but not repeated low dose JZL184, elicited cross-tolerance to the common pharmacological effects of Δ(9)-tetrahydrocannabinol (THC). This same pattern of effects was found in a rimonabant-precipitated withdrawal model of cannabinoid dependence. Taken together, these results indicate that prolonged, partial MAGL inhibition maintains potentially beneficial antinociceptive and anti-inflammatory effects, without producing functional CB(1) receptor tachyphylaxsis/tolerance or cannabinoid dependence.Journal of Pharmacology and Experimental Therapeutics 02/2013; DOI:10.1124/jpet.112.201426 · 3.97 Impact Factor
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- "In a separate group of rats, the CB1 receptor antagonist AM251 (1 mg in 50 mL, 3.6 mM) was given 30 min prior to spinal administration of either JZL184 (100 mg in 50 mL, n = 7) or vehicle (50 mL, n = 6). The dose of AM251 employed was based on earlier reports (Ibrahim et al., 2005; Jhaveri et al., 2006). "
ABSTRACT: BACKGROUND AND PURPOSE: The cannabinoid receptor-mediated analgesic effects of 2-arachidonoylglycerol (2-AG) are limited by monoacylglycerol lipase (MAGL). JZL184 is a potent inhibitor of MAGL in the mouse, though potency is reportedly reduced in the rat. Here, we investigate for the first time the effects of spinal inhibition of MAGL via JZL184 on nociceptive processing in the rat. EXPERIMENTAL APPROACH: In vivo spinal electrophysiological experiments in the anaesthetised rat determined the effects of spinal administration of JZL184 on spinal nociceptive processing in the presence and absence of hindpaw inflammation. The contribution of the CB (1) receptor to these effects was assessed with AM251. The ability of spinal JZL184 to inhibit 2-oleoylglycerol hydrolytic activity and alter levels of 2-AG in the spinal cord was also investigated. KEY RESULTS: Spinal JZL184 dose-dependently inhibited mechanically-evoked responses of WDR neurones in naïve anaesthetised rats, in part via the CB (1) receptor. A single spinal administration of JZL184 ablated inflammation-induced expansion of the receptive fields of spinal WDR neurones. However, neither spinal nor systemic JZL184 altered levels of 2-AG, or 2-oleoylglycerol hydrolytic activity in the spinal cord, although JZL184 displayed robust inhibition of MAGL when incubated with spinal cord tissue in vitro. CONCLUSIONS AND IMPLICATIONS: We report robust anti-nociceptive effects of JZL184 at the level of the spinal cord in vivo, and that JZL184 inhibits rat spinal cord MAGL activity in vitro. The discordance between the in vivo and in vitro assays suggests that localized sites of action of JZL184 produce these profound functional inhibitory effects.British Journal of Pharmacology 08/2012; 167(8). DOI:10.1111/j.1476-5381.2012.02179.x · 4.84 Impact Factor
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- "While we are not aware that a causative relationship between endocannabinoid levels and FAAH expression has been demonstrated, it is consistent with the common theme of increased levels of a substrate leading to increased synthesis of enzymes required for its degradation. In addition to anandamide, FAAH metabolizes other proanalgesic endocannabinoids including 2-arachidonoylglycerol and oleoyl ethanolamide (Jhaveri et al., 2006; Maione et al., 2006), so the present data do not implicate a particular endocannabinoid. We speculate that altered endocannabinoid function in the BLA, as a consequence of the absence of TIP39 signaling, could be the functional basis for the nociceptive phenotype of TIP39-KO and PTH2R-KO mice. "
ABSTRACT: Tuberoinfundibular peptide of 39 residues (TIP39) synthesizing neurons at the caudal border of the thalamus and in the lateral pons project to areas rich in its receptor, the parathyroid hormone 2 receptor (PTH2R). These areas include many involved in processing nociceptive information. Here we examined the potential role of TIP39 signaling in nociception using a PTH2R antagonist (HYWH) and mice with deletion of TIP39's coding sequence or PTH2R null mutation. Intracerebroventricular (icv) infusion of HYWH significantly inhibited nociceptive responses in tail-flick and hot-plate tests and attenuated the nociceptive response to hindpaw formalin injection. TIP39-KO and PTH2R-KO had increased response latency in the 55°C hot-plate test and reduced responses in the hindpaw formalin test. The tail-flick test was not affected in either KO line. Thermal hypoalgesia in KO mice was dose-dependently reversed by systemic administration of the cannabinoid receptor 1 (CB1) antagonist rimonabant, which did not affect nociception in wild-type (WT). Systemic administration of the cannabinoid agonist CP 55,940 did not affect nociception in KO mice at a dose effective in WT. WT mice administered HYWH icv, and both KOs, had significantly increased stress-induced analgesia (SIA). Rimonabant blocked the increased SIA in TIP39-KO, PTH2R-KO or after HYWH infusion. CB1 and FAAH mRNA were decreased and increased, respectively, in the basolateral amygdala of TIP39-KO mice. These data suggest that TIP39 signaling modulates nociception, very likely by inhibiting endocannabinoid circuitry at a supraspinal level. We infer a new central mechanism for endocannabinoid regulation, via TIP39 acting on the PTH2R in discrete brain regions.Experimental Neurology 11/2010; 226(1):68-83. DOI:10.1016/j.expneurol.2010.08.004 · 4.70 Impact Factor