Avaliação do efeito antinociceptivo do canabidiol no tratamento agudo da dor neuropática e mecanismos antinociceptivos endógenos envolvidos nesse evento

Abstract

More than 100 phytocannabinoids are known and cannabidiol (CBD) is the most abundant non-psychoactive component in plants of the genus Cannabis. It can be used for the treatment of various diseases such as Alzheimer's, Parkinson's, epilepsy, depression, multiple sclerosis, diabetes, various types of pain, including neuropathic pain. Its analgesic effect for the treatment of neuropathy is widely studied, however, little is known about its effects on acute treatment when administered peripherally. Our proposal is to evaluate the antinociceptive effects of CBD when administered peripherally for acute treatment of neuropathic pain and which endogenous analgesic systems may be involved. Neuropathic pain was induced by constriction of the sciatic nerve and the nociceptive threshold was measured by the mouse paw pressure test. Endocannabinoids were taken by LC-MS and nitrite was taken using Griess Reaction. For pharmacological tests, the statistical analyses were performed through the One-way ANOVA followed by the Bonferroni post-test. For the dosages, two-way ANOVA was used, followed by Newman-Keuls post-tests. All drugs were administered intraplantarly, except for the drugs used in the motor coordination assessment test. The technique used was efficient to induce neuropathy, and CBD (5, 10 and 30 μg/paw) induced antinociception in a dose-dependent manner. The dose used that induced a more potent effect (30 μg/paw) did not induce systemic response, demonstrated by both the Motor Coordination Assessment Test (RotaRod) and by the antinocicceptive effect restricted to the paw treated with CBD. AM251 (80 μg/paw) and AM630 (100 μg/paw), CB1 and CB2 antagonist cannabinoids receptors, respectively, reversed the antinociceptive effect induced by CBD, demonstrating the participation of these receptors. MAFP (0.5 μg/paw), FAAH enzyme inhibitor, JZL184 (3.75 μg/paw), inibidor of the MAGL enzyme and VDM11 (2.5 μg/paw),inibidor of anandamide reuptake, potentiated the antinociceptive effect of CBD administered at its lowest dose (5 μg/paw) suggesting the participation of endocannabinoids in this event, although the CBD administration has not been shown to increase the level of these substances in neuropathic animals, as demonstrated by the biomolecular technique of endocannabinoid dosage. The technique also demonstrated that CBD reduced anandamide levels in neuropathic animals, suggesting that CBD negatively controls the levels of this endocannabinoid. The non-selective antagonist opioid receptor, naloxone (50 μg/paw), as well as clocinnamox (40 μg/paw), μ selective antagonist receptor reversed CBD-induced antinociception. Naltrindole (60 μg/paw) δ selective antagonist receptor, and nor-binaltorfimin (200 μg/paw), κ selective antagonist receptors, partially reversed CBD-induced antinociception. In line with these results, a bestatin enhanced the antinociceptive effect of the lowest administered dose of CBD (5 μg/paw), suggesting the participation of opioid receptors and endogenous opioid peptides in the event studied. The antinociceptive effect of CBD was also reversed by the administration of AS605240 (90 μg/paw), inhibitor of the PI3Kγ enzyme, rapamycin (30 μg/paw), selective mTOR protein inhibitor, L-NOArg (24 μg/paw), non-selective NOS isoform inhibitor, ODQ (100 μg/paw), soluble guanilate cyclase inhibitor, glibenclamide (80 μg/paw) KATP channel blocker, suggesting the participation of the PI3K/AKT/mTOR/NO/GMPc/KATP pathway.. The administration of cannabidiol increased the production of NO in CBD-naive, control-Operated and CBD-Operated groups when compared to the control group (naive) did not increase the production of NO when compared to the operated group. On the other hand, the administration of NAN 190 (10 μg/paw), selective antagonist of 5-HT1A receptors, and SB-366791 (16 μg/paw), selective antagonist of TRPV1, partially reversed the antinociception induced by CBD. Our results provide evidence that the mechanism of action by which cannabidiol induces antinociception in neuropathic animals is complex and involves the participation of various analgesic systems. Our hypothesis is that cannabidiol can bind to the present cannabinoid receptors in nociceptors, inhibiting neuronal excitation, or induce increased production of endocannabinoids and these bind to cannabinoid receptors in nociceptors and/or in immune cells and resident cells, releasing opioid peptides, which induce antinociception by direct activation of these receptors in nociceptors and also by activation of the PI3K/AKT/mTOR/NOS/NOS/GMPc/KATP pathway. Additionally, CBD activates 5HT1A receptors present in nociceptors, causing inhibition of nociceptors; CBD also activates TRPV1, with subsequent desensitization, inducing analgesia.