Avaliação do efeito e mecanismo antinociceptivo periférico do 2-araquidonoilglicerol (2-ag) na dor neuropática por constrição do nervo isquiático em camundongos

Abstract

INTRODUCTION: Neuropathic pain is a chronic condition that impairs quality of life and presents challenging pharmacological treatment. The endocannabinoid 2arachidonoylglycerol (2AG) demonstrates antinociceptive effects in animal models; however, its mechanisms of action are not fully elucidated. Thus, this study aimed to evaluate the antinociceptive effect of 2AG in an experimental model of neuropathic pain induced by sciatic nerve injury in mice and to investigate the endogenous analgesic systems involved in this process. METHODS: Male Swiss mice were used (CEUA 241/2024). Neuropathy was induced by the chronic constriction injury model of the sciatic nerve. The nociceptive threshold was assessed by the paw withdrawal test on day 12. To investigate the cannabinoid system, antagonists of CB1 (AM251) and CB2 (AM630) receptors were used, as well as inhibitors of anandamide reuptake (VDM11) and degradation (MAFP). To evaluate the opioidergic system, the nonselective opioid receptor antagonist naloxone and the selective antagonists of μ (clocinnamox), δ (naltrindole), and κ (norbinaltorphimine) receptors were used, along with the enkephalinase inhibitor bestatin. The involvement of PI3Kγ was assessed using the inhibitor AS605240. The nitrergic pathway was evaluated using the nitric oxide synthase inhibitor (LNOArg), the soluble guanylate cyclase inhibitor (ODQ), and the selective inhibitors of inducible and neuronal NOS isoforms (LNIL and LNPA), in addition to the selective inhibitor of cyclic GMPspecific phosphodiesterase (zaprinast). To assess potassium channels, inhibitors of voltagedependent K⁺ channels (Kv) (tetraethylammonium), ATPsensitive K⁺ channels (KATP) (glibenclamide), and Ca²⁺activated K⁺ channels of high and low conductance (BKCa and SKCa) (paxilline and dequalinium) were used. RESULTS AND DISCUSSION: 2AG promoted analgesia on day 12, when neuropathy was fully established. Cannabinoid receptor antagonists (AM251 and AM630) reversed the peripheral antinociception induced by the highest analgesic dose of 2AG. MAFP and VDM11 potentiated the peripheral antinociception induced by the intermediate analgesic dose of 2AG. Regarding the opioidergic system, naloxone reversed the antinociception induced by the highest analgesic dose of 2AG, as did the selective antagonists clocinnamox, norbinaltorphimine, and naltrindole. Bestatin potentiated the effect of the intermediate analgesic dose of 2AG. Inhibition of PI3Kγ reversed the antinociception. Similar effects were observed for the nitrergic pathway, in which antinociception was reversed by LNOArg, the selective inhibitors LNIL and LNPA, and ODQ. Zaprinast potentiated the peripheral antinociception induced by the intermediate analgesic dose of 2AG. Regarding potassium channels, reversal of peripheral antinociception induced by 2AG was observed only with tetraethylammonium and dequalinium. Glibenclamide and paxilline did not reverse the peripheral antinociception under the same conditions. CONCLUSIONS: Peripherally administered 2AG exerts antinociceptive effects in neuropathy induced by sciatic nerve constriction through a complex mechanism involving multiple endogenous analgesic systems that may be activated simultaneously or sequentially. We propose that 2AG directly or indirectly activates the cannabinoid and opioid systems, leading to activation of the PI3Kγ/AKT/NOS pathway and modulation of Kv and SKCa channels.