Participation of the cannabinoid system and the NO/cGMP/KATP pathway in serotonin-induced peripheral antinociception

It has already been shown that serotonin can release endocannabinoids at the spinal cord level, culminating in inhibition of the dorsal horn. At the peripheral level, cannabinoid receptors modulate primary afferent neurons by inhibiting calcium conductance and increasing potassium conductance. Studies have shown that after the activation of opioid receptors and cannabinoids, there is also the activation of the NO/cGMP/KATP pathway, inducing cellular hyperpolarization. In this study, we evaluated the participation of the cannabinoid system with subsequent activation of the NO/cGMP/KATP pathway in the peripheral antinociceptive effect of serotonin. The paw pressure test of mice was used in animals that had their sensitivity to pain increased due to an intraplantar injection of PGE2 (2 μg). Serotonin (250 ng/paw), administered locally in the right hind paw, induced antinociceptive effect. CB1 and CB2 cannabinoid receptors antagonists, AM251 (20, 40 and 80 μg) and AM630 (25, 50 and 100 μg), respectively, reversed the serotonin-induced antinociceptive effect. MAFP (0.5 μg), an inhibitor of the FAAH enzyme that degrades anandamide, and JZL184 (3.75 μg), an inhibitor of the enzyme MAGL that degrades 2-AG, as well as the VDM11 (2.5 μg) inhibitor of anandamide reuptake, potentiated the antinociceptive effect induced by a low dose (62. 5 ng) of serotonin. In the evaluation of the participation of the NO/cGMP/KATP pathway, the antinociceptive effect of serotonin was reversed by the administration of the non-selective inhibitor of NOS isoforms L-NOarg (12.5, 25 and 50 μg) and by the selective inhibitor for the neuronal isoform LNPA (24 μg), as well as by the soluble guanylate cyclase inhibitor ODQ (25, 50 and 100 μg). Among potassium channel blockers, only Glibenclamide (20, 40 and 80 μg), an ATP-sensitive potassium channel blocker, reversed the effect of serotonin. In addition, intraplantar administration of serotonin (250 ng) was shown to induce a significant increase in nitrite levels in the homogenate of the plantar surface of the paw of mice. Taken together, these data suggest that the antinociceptive effect of serotonin occurs by activation of the cannabinoid system with subsequent activation of the NO/cGMP/KATP pathway.

Evidence for the involvement of opioid and cannabinoid systems in the peripheral antinociception mediated by resveratrol

Despite all the development of modern medicine, around 100 compounds derived from natural products were undergoing clinical trials only at the end of 2013. Among these natural substances in clinical trials, we found the resveratrol (RES), a pharmacological multi-target drug. RES analgesic properties have been demonstrated, although the bases of these mechanisms have not been fully elucidated. The aim of this study was to evaluate the involvement of opioid and cannabinoid systems in RES-induced peripheral antinociception. Paw withdrawal method was used and hyperalgesia was induced by carrageenan (200 μg/paw). All drugs were given by intraplantar injection in male Swiss mice (n = 5). RES (100 μg/paw) administered in the right hind paw induced local antinociception that was antagonized by naloxone, non-selective opioid receptor antagonist, and clocinnamox, μOR selective antagonist. Naltrindole and nor-binaltorfimine, selective antagonists for δOR and kOR, respectively, did not reverse RES-induced peripheral antinociception. CB₁R antagonist AM251, but not CB₂R antagonist AM630, antagonized RES-induced peripheral antinociception. Peripheral antinociception of RES intermediate-dose (50 μg/paw) was increased by: (i) bestatin, inhibitor of endogenous opioid degradation involved-enzymes; (ii) MAFP, inhibitor of anandamide amidase; (iii) JZL184, inhibitor of 2-arachidonoylglycerol degradation involved-enzyme; (iv) VDM11, endocannabinoid reuptake inhibitor. Acute and peripheral administration of RES failed to affect the amount of μOR, CB₁R and CB₂R. Experimental data suggest that RES induces peripheral antinociception through μOR and CB₁R activation by endogenous opioid and endocannabinoid releasing.

Peltatoside Isolated from Annona crassiflora Induces Peripheral Antinociception by Activation of the Cannabinoid System

Peltatoside is a natural compound isolated from leaves of Annona crassiflora Mart., a plant widely used in folk medicine. This substance is an analogue of quercetin, a flavonoid extensively studied because of its diverse biological activities, including analgesic effects. Besides, a previous study suggested, by computer structure analyses, a possible quercetin-CB₁ cannabinoid receptor interaction. Thus, the aim of this work was to assess the antinociceptive effect of peltatoside and analyze the cannabinoid system involvement in this action. The mouse paw pressure test was used and hyperalgesia was induced by intraplantar injection of carrageenan (200 µg/paw). All used drugs were administered by intraplantar administration in Swiss male mice (n = 6). Peltatoside (100 µg/paw) elicited a local inhibition of hyperalgesia. The peripheral antinociceptive action of peltatoside was antagonized by the CB₁ cannabinoid antagonist AM251 (160 µg/paw), but not by CB₂ cannabinoid antagonist AM630 (100 µg/paw). In order to assess the role of endocannabinoids in this peripheral antinociceptive effect, we used (i) [5Z,8Z,11Z,14Z]-5,8,11,14-eicosatetraenyl-methyl ester phosphonofluoridic acid, an inhibitor of anandamide amidase; (ii) JZL184, an inhibitor for monoacylglycerol lipase, the primary enzyme responsible for degrading the endocannabinoid 2-arachidonoylglycerol; and (iii) VDM11, an endocannabinoid reuptake inhibitor. MAFP, JZL184, and VDM11 did not induce antinociception, respectively, at the doses 0.5, 3.8, and 2.5 µg/paw, however, these three drugs were able to potentiate the peripheral antinociceptive effect of peltatoside at an intermediary dose (50 µg/paw). Our results suggest that this natural substance is capable of inducing analgesia through the activation of peripheral CB₁ receptors, involving endocannabinoids in this process.

Natural Diterpenes from Coffee, Cafestol, and Kahweol Induce Peripheral Antinoceception by Adrenergic System Interaction

Cafestol and kahweol are diterpenes found only in the non-saponified lipid fraction of coffee. They are released during boiling and retained in the filtration process. Previous studies have shown peripheral antinociception induced by endogenous opioid peptides released by these diterpenes. Considering that the activation of the opioid system leads to a noradrenaline release, the aim of this study was to verify the participation of the noradrenergic system in the peripheral antinociception induced by cafestol and kahweol. Hyperalgesia was induced by an intraplantar injection of prostaglandin E2 (2 µg). Cafestol or kahweol (80 µg/paw) were administered locally into the right hindpaw alone, and after the agents α 2-adrenoceptor antagonist yohimbine (5, 10 and 20 µg/paw), α 2 A-adrenoceptor antagonist BRL 44 408 (40 µg/paw), α 2B-adrenoceptor antagonist imiloxan (40 µg/paw), α 2 C-adrenoceptor antagonist rauwolscine (10, 15 and 20 µg/paw), α 2D-adrenoceptor antagonist RX 821 002 (40 µg/paw), α 1-adrenoceptor antagonist prazosin (0.5, 1 and 2 µg/paw), or β-adrenoceptor antagonist propranolol (150, 300 and 600 ng/paw), respectively. Noradrenaline reuptake inhibitor reboxetine (30 µg/paw) was administered prior to cafestol or kahweol low dose (40 µg/paw) and guanetidine 3 days prior to the experiment (30 mg/kg, once a day), depleting the noradrenaline storage. Intraplantar injection of cafestol or kahweol (80 µg/paw) induced a peripheral antinociception against hyperalgesia induced by PGE2. This effect was reversed by intraplantar injections of yohimbine, rauwolscine, prazosin and propranolol. Reboxetine injection intensified the antinociceptive effect of cafestol or kahweol low-dose, and guanethidine reversed almost 70 % of the cafestol or kahweol-induced peripheral antinociception. This study gives evidence that the noradrenergic system participates in cafestol and kahweol-induced peripheral antinociception with the release of endogenous noradrenaline.

Tingenone, a pentacyclic triterpene, induces peripheral antinociception due to opioidergic activation

Plants belonging to the genus Maytenus are routinely used in folk medicine for the treatment of pain diseases. Our previous phytochemical study of the roots of Maytenus imbricata resulted in the isolation and characterization of tingenone, a pentacyclic triterpene. Natural triterpenoids are of growing interest because they have several biological activities, including analgesic properties. The present study assessed the involvement of the opiodergic pathway in the tingenone-induced antinociceptive effect against hyperalgesia induced by prostaglandin E2 (2 µg) in the peripheral pathway. We evaluated the effect of several antagonists to opioid receptors using the mouse paw pressure test. Tingenone administered into the right hind paw induced a local antinociceptive effect that was antagonized by naloxone, a nonselective antagonist to opioid receptors. Clocinnamox, naltrindole, and nor-binaltorphimine are selective antagonists to µ, δ, and κ receptors, respectively, which reverted the peripheral antinociception induced by tingenone. Bestatine acts as an inhibitor of aminopeptidase, an enzyme that degrades endogenous opioid peptides, and was shown to intensify the antinociceptive effect of tingenone. The results suggest that the opioidergic system participates in the peripheral antinociception induced by tingenone.

Hydroethanolic extract of Pyrostegia venusta (Ker Gawl.) Miers flowers improves inflammatory and metabolic dysfunction induced by high-refined carbohydrate diet

ETHNOPHARMACOLOGICAL RELEVANCE

Pyrostegia venusta is used in traditional Brazilian medicine as a general tonic to treat any inflammatory disease. Several studies have demonstrated that medicinal plants constitute a therapeutic approach for the treatment of obesity-related metabolic and inflammatory disarrangement. Accordingly, we investigated the effects of hydroethanolic extract of Pyrostegia venusta flowers (PvHE) supplementation for the treatment of inflammatory and metabolic dysfunction induced by high-refined-carbohydrate (HC) diet.

MATERIAL AND METHODS

The BALB/c mice were fed chow or HC diet for 8 weeks. Part of these animals was fed with HC diet supplemented with PvHE on the 9th week until the 12th week. At the end of the dietary intervention, animals were sacrificed.

RESULTS

We observed that PvHE decreased adiposity and adipocyte area; improved glucose intolerance; reduced serum triacylglycerol levels and systemic inflammatory cells; and also reduced some inflammatory mediators levels in adipose tissue and liver.

CONCLUSION

The results showed that PvHE has beneficial effects and may treat inflammatory and metabolic dysfunction induced by HC diet, that are associated to a negative modulation of the inflammatory process at systemic and local levels.