Nicorandil/ morphine crosstalk accounts for antinociception and hepatoprotection in hepatic fibrosis in rats: Distinct roles of opioid/cGMP and NO/KATP pathways

Previous report indicated that nicorandil potentiated morphine antinociception and attenuated hepatic injury in liver fibrotic rats. Herein, the underlying mechanisms of nicorandil/morphine interaction were investigated using pharmacological, biochemical, histopathological, and molecular docking studies. Male Wistar rats were injected intraperitoneally (i.p.) with carbon tetrachloride (CCl4, 40%, 2 ml/kg) twice weekly for 5 weeks to induce hepatic fibrosis. Nicorandil (15 mg/kg/day) was administered per os (p.o.) for 14 days in presence of the blockers; glibenclamide (KATP channel blocker, 5 mg/kg, p.o.), L-NG-nitro-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor, 15 mg/kg, p.o.), methylene blue (MB, guanylyl cyclase inhibitor, 2 mg/kg, i.p.) and naltrexone (opioid antagonist, 20 mg/kg, i.p.). At the end of the 5th week, analgesia was evaluated using tail flick and formalin tests along with biochemical determinations of liver function tests, oxidative stress markers and histopathological examination of liver tissues. Naltrexone and MB inhibited the antinociceptive activity of the combination. Furthermore, combined nicorandil/morphine regimen attenuated the release of endogenous peptides. Docking studies revealed a possible interaction of nicorandil on µ, κ and δ opioid receptors. Nicorandil/morphine combination protected against liver damage as evident by decreased liver enzymes, liver index, hyaluronic acid, lipid peroxidation, fibrotic insults, and increased superoxide dismutase activity. Nicorandil/morphine hepatoprotection and antioxidant activity were inhibited by glibenclamide and L-NAME but not by naltrexone or MB. These findings implicate opioid activation/cGMP versus NO/KATP channels in the augmented antinociception, and hepatoprotection, respectively, of the combined therapy and implicate provoked cross talk by nicorandil and morphine on opioid receptors and cGMP signaling pathway. That said, nicorandil/morphine combination provides a potential multitargeted therapy to alleviate pain and preserve liver function.

Evaluation of antinociceptive activity of Ilex dipyrena Wall. in mice

BACKGROUND

In order to find a new natural resource for pain-relief, the analgesic effects of Ilex dipyrena crude extract, fractions, and subfractions were evaluated in in-vivo mouse models with possible mechanism of action.

METHODS

Analgesic effects of crude extract (100 and 200 mg/kg body weight), fractions and subfractions (75 mg/kg body weight) were screened using heat-induced (tail-immersion and hot plate test) and chemical-induced (formalin and acetic acid) nociception models in mice. The samples were also tested for the elucidation of a possible mechanism through opioidergic and GABAergic systems.

RESULTS

The administration of crude extract, fractions and subfractions produced analgesic responses in acetic acid, formalin, tail immersion, and hot plate model for pain similar to those obtained with the standard. Naloxone antagonized the antinociceptive effects of the tested samples, whereas bicuculline showed partial inhibition. Considering the analgesic response, crude extract, fractions, and subfractions demonstrated promising inhibitory activity against all test models for pain, which was further supported by the possible involvement of opioidergic and GABAergic systems.

CONCLUSION

The results suggest that this plant may be useful in the development of new analgesic drugs. Further research with regard to the isolation of bioactive compounds is required to verify these findings.

Anti-nociceptive, anti-inflammatory and possible mechanism of anti-nociceptive action of methanol leaf extract of Nymphaea lotus Linn (Nymphaeceae)

The leaf of Nymphaea lotus has been used traditionally for the management of pain and inflammatory diseases. The methanol leaf extract of Nymphaea lotus (NLE) was evaluated for possible anti-nociceptive and anti-inflammatory activities in rats and mice (at the doses of 250, 500 and 1,000 mg/kg) to investigate the existence of scientific basis for the folkloric use of the plant. The standard drugs used were piroxicam (10 mg/kg) and morphine (10 mg/kg). The possible pharmacological mechanism involved in the anti-nociceptive activity was also investigated. The acute toxicity was determined in mice and rats using method of Lorke. The anti-nociceptive activity was evaluated using acetic acid-induced writhing and hot plate tests in mice, while the anti-inflammatory activity was evaluated using carrageenan-induced hind paw edema model in rats. The oral median lethal dose of NLE was found to be greater than 5,000 mg/kg in rats and mice. NLE demonstrated significant and dose-dependent protection against acetic acid induced writhes and increased the reaction time of mice in hot plate test. Pretreatment of the animals with naloxone (2 mg/kg) significantly (p < 0.05) attenuated the anti-nociception elicited by both NLE and morphine. NLE at the doses of 250 and 1,000 mg/kg significantly (p < 0.05) decreased rat paw edema at the 2^nd hour in the carrageenan-induced paw edema test. The result of the study revealed that Nymphaea lotus possesses anti-nociceptive activities which may be mediated via the opioidergic system as well as mild anti-inflammatory activities thus providing scientific basis for the use of the plant in the management of pain and inflammatory diseases.

Central Nervous System Targets: Supraspinal Mechanisms of Analgesia

While the acute sensation of pain is protective, signaling the presence of actual or potential bodily harm, its persistence is unpleasant. When pain becomes chronic, it has limited evolutionarily advantage. Despite the differing nature of acute and chronic pain, a common theme is that sufferers seek pain relief. The possibility to medicate pain types as varied as a toothache or postsurgical pain reflects the diverse range of mechanism(s) by which pain-relieving "analgesic" therapies may reduce, eliminate, or prevent pain. Systemic application of an analgesic able to cross the blood-brain barrier can result in pain modulation via interaction with targets at different sites in the central nervous system. A so-called supraspinal mechanism of action indicates manipulation of a brain-defined circuitry. Pre-clinical studies demonstrate that, according to the brain circuitry targeted, varying therapeutic pain-relieving effects may be observed that relate to an impact on, for example, sensory and/or affective qualities of pain. In many cases, this translates to the clinic. Regardless of the brain circuitry manipulated, modulation of brain processing often directly impacts multiple aspects of nociceptive transmission, including spinal neuronal signaling. Consideration of supraspinal mechanisms of analgesia and ensuing pain relief must take into account nonbrain-mediated effects; therefore, in this review, the supraspinally mediated analgesic actions of opioidergic, anti-convulsant, and anti-depressant drugs are discussed. The persistence of poor treatment outcomes and/or side effect profiles of currently used analgesics highlight the need for the development of novel therapeutics or more precise use of available agents. Fully uncovering the complex biology of nociception, as well as currently used analgesic mechanism(s) and site(s) of action, will expedite this process.

Anti-nociceptive and antioxidant activity of betaine on formalin- and writhing tests induced pain in mice

Pain is a physiological response which is mediated via the central and peripheral nervous system. Betaine, is a methyl glycine derivative and a commonly used nutrient supplement. The main purpose of the current paper is to determine the possible anti-nociceptive and antioxidant activity and sedative effect of betaine in mice. Adult male albino mice were divided into two categories, formalin and writhing tests. In the formalin test, mice were injected with betaine (10, 20 and 30 mg/kg) or morphine (5 mg/kg). For co-injections mice received betaine (30 mg/kg) + naloxone (2 mg/kg) or atropine (1 mg/kg), chlorpheniramine (20 mg/kg), flumazenil (5 mg/kg), cimetidine (12.5 mg/kg) and cyproheptadine (4 mg/kg). Then the formalin test was done and paw licking time was determined. In the writhing test, injections were the same but the animals were injected with acetic acid (0.6 %) and the percentage of writhing inhibition was recorded. At the end of the study, blood antioxidant levels were determined. According to the results, betaine reduced the pain response in a dose-dependent manner. Co-administration of the naloxone + betaine or flumazenil + betaine significantly decreased the anti-nociceptive effect of betaine on the licking and biting time of the injected paw and inhibited the number of writhing movements. Betaine decreased malondialdehyde (MDA) and improved superoxide dismutase (SOD) and glutathione peroxidase (GPx) levels in formalin receiving mice. No adverse locomotion and sedation effect were observed in betaine-treated mice. These findings suggest that betaine has anti-nociceptive and antioxidant activity in mice, and its anti-nociceptive role interacts with opioidergic and GABA receptors.

Elucidation of the possible mechanism of analgesic action of methanol stem bark extract of Uapaca togoensis pax in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Uapaca togoensis is a medicinal plant used traditionally in Africa for the treatment of rheumatism, epilepsy, cough, pneumonia, vomitting and fever. Previously, the analgesic activity of its methanol stem bark extract has been scientifically demonstrated. However, the mechanism responsible for this activity remains to be investigated.

AIM OF THE STUDY

To elucidate the possible mechanism(s) through which the methanol stem bark extract of Uapaca togoensis (MEUT) exhibits analgesic activity in mice.

MATERIALS AND METHODS

Analgesic activity of MEUT was evaluated using acetic acid-induced abdominal writhing test in mice at doses of 250, 500 and 1000 mg/kg orally. For the mechanistic studies, mice were pre-treated with Naloxone (2 mg/kg), Atropine (1 mg/kg), Yohimbine (1 mg/kg), Glibenclamide (10 mg/kg), Prazosin (1 mg/kg) and Yohimbine (1 mg/kg) 15 min prior to MEUT (1000 mg/kg) administration, then assessed using AAWT 1 h later. Data was analysed using One way Anova followed by Bonferroni post hoc test.

RESULTS

The extract (at the doses of 250, 500 and 1000 mg/kg) and morphine (10 mg/kg) significantly (p < 0.05) decreased the number of abdominal writhes. Naloxone (opioid receptor antagonist), Atropine (muscarinic receptor antagonist) and Glibenclamide (ATP-sensitive K+ channel blocker) significantly (p < 0.05) reversed the analgesic effect of MEUT. On the other hand, Prazosin and Yohimbine (α₁ and α₂ receptor antagonists respectively) had no effect on the analgesic action of MEUT.

CONCLUSION

The results obtained from this study suggests the possible involvement of opioidergic, cholinergic and sensitive potassium ATP channel pathways in the analgesic activity of the methanol stem bark extract of Uapaca togoensis.

Chemical Composition and Role of Opioidergic System in Antinociceptive Effect of Ziziphora Clinopodioides Essential Oil

Introduction:

Ziziphora Clinopodioides has been used widely for various therapeutic purposes in Iranian folk medicine. The current study aimed to determine interaction of antinociceptive effect of the Essential Oil of Ziziphora Clinopodioides (EOZC) and opioidergic system in male rats using formalin test.

Methods:

Sixty-four male Wistar rats were divided into eight groups. The groups 1 to 7 were injected with normal saline, vehicle (Tween-80, 0.5%), 10, 20, 40 mg/kg of the EOZC, morphine (5 mg/kg) and naloxone (2 mg/kg), respectively. Thirty minutes later, the formalin test was performed by intraplantar injection of formalin (50 μL, 2%). In group 8, naloxone (2 mg/kg) was injected 15 min before injection of EOZC (20 mg/kg), followed by formalin at 15 min later. The formalin test was done as time spent for licking and biting of the injected paw. Formalin induced a biphasic pain reaction. The chemical composition of EOZC was identified using Gas Chromatography-Mass Spectrometry (GC-MS).

Results:

EOZC (10, 20, and 40 mg/kg) dose dependently and morphine (5 mg/kg) reduced pain responses in the both phases of pain (P<0.05). Naloxone (2 mg/kg) alone had no effect on the severity of pain (P>0.05) but pretreatment with naloxone inhibited EOZC-induced antinociception activity (P<0.05). Based on the GC-MS results, EOZC comprised 65.22% carvacrol, 19.51% thymol, 4.86% p-cymene and 4.63% γ-terpinene.

Conclusion:

These results demonstrate that EOZC has antinociceptive effect and this effect might mediate via opioidergic pathways.

Albizia zygia (DC.) J.F. Macbr. (Leguminosae-Mimosoideae) root extract exhibits anti-nociceptive and antipyretic activities in murine models

ETHNOPHARMACOLOGICAL RELEVANCE

The root extract of Albizia zygia (DC.) J.F. Macbr. (Leguminosae-Mimosoideae) is traditionally used in the management of pain and fever. However, little scientific data exists in literature to support its use.

AIM OF STUDY

The present study evaluated the anti-nociceptive and antipyretic properties of the hydroethanolic extract of the roots of Albizia zygia in animal models.

MATERIALS AND METHODS

The analgesic effects were investigated in chemical (acetic acid-induced abdominal writhing and formalin tests), thermal (tail-immersion test) and mechanical (carrageenan-induced hyperalgesia) pain models. Possible mechanisms of anti-nociception were also assessed with antagonists in the formalin test. The anti-pyretic effect was evaluated using the baker yeast-induced pyrexia model in young rats.

RESULTS

The extract (30-300mg/kg, p.o.) and positive controls, diclofenac (3-30mg/kg, i.p.) and morphine (1-10mg/kg, i.p.), significantly (at least P<0.01) attenuated acetic acid-induced visceral pain, formalin- induced paw pain (both neurogenic and inflammatory), thermal pain as well as carrageenan-induced mechanical hyperalgesia in animals. The anti-nociceptive effect of the extract was reversed (at least P<0.05) by the pre-emptive administration of naloxone and atropine; the administration of theophylline, however, exhibited no significant (P>0.05) inhibition of anti-nociception. The extract (30-300mg/kg, p.o) and paracetamol (15-150mg/kg, p.o.) both reversed yeast-induced pyrexia in rats with ED₅₀ values of 48.59±2.59 and 26.19±1.33mg/kg respectively.

CONCLUSION

The findings indicate that the extract possesses significant anti-nociceptive and antipyretic effects which justify its traditional use in the management of pain and fever. Also, anti-nociceptive effect of the extract involves opioidergic and muscarinic cholinergic mechanisms.