Involvement of ATP-sensitive K(+) channels in the peripheral antinociceptive effect induced by dipyrone

Antinociceptive and anti-inflammatory activity of extracts and α-pyrones isolated from Cantinoa stricta

This study evaluated the composition and the antinociceptive and anti-inflammatory activity of the crude extracts and two isolated compounds, anamarine (ANA) and 10-epi-olguine (eOL), obtained from the leaves of Cantinoa stricta (Lamiaceae). Crude ethanolic extract (EEt) and dichloromethane extract (DCM), selected based on NMR data, were submitted to pharmacological tests in male Swiss mice. The oral administration of EEt and DCM significantly reduced the second phase of formalin-induced nociception (60%), lipopolysaccharide (LPS)-induced mechanical hyperalgesia (90%), and carrageenan (Cg)-induced edema (25%). ANA and eOL, the major compounds in EEt and DCM extracts, administered orally or locally (in the paw), also reduced the LPS-induced mechanical hyperalgesia (Oral ID50 1.9 and 3.9 mg/kg; Local ID50 93.4 and 677.3 ng, respectively) without changing the thermal acute nociception or the motor performance of the animals. Local administration of ANA and eOL also reduced Cg-induced edema (40 and 23%, respectively). These isolated compounds did not change the mechanical hyperalgesia induced by tumor necrosis factor-α, interleukin-1β, prostaglandin E2, dibutyryl cyclic AMP, or forskolin but reversed the hyperalgesia induced by dopamine, epinephrine, and phorbol 12-myristate 13-acetate. The hyperalgesia induced by epinephrine was reversed in male but not in female mice, in which this response is not dependent on protein kinase C (PKC). These results suggest that C. stricta extracts possess antinociceptive and anti-inflammatory activity which is related to the presence of ANA and eOL. Differently from the known analgesics, these substances seem to exert their action mainly interfering with the sympathetic component of pain, possibly with PKC.

Synthesis of 2-(2-(4-thioxo-3H-1,2-dithiole-5-yl) phenoxy)ethyl)isoindole-1,3-thione, a novel hydrogen sulfide-releasing phthalimide hybrid, and evaluation of its activity in models of inflammatory pain

Hydrogen sulfide (H₂S) is a gaseous mediator that modulates several physiological and pathological processes. Phthalimide analogues, substances that have the phthalimide ring in the structure, belong to the group of thalidomide analogues. Both H₂S donors and phthalimide analogues exhibit activities in models of inflammation and pain. As molecular hybridization is an important strategy aiming to develop drugs with a better pharmacological profile, in the present study we synthesized a novel H₂S-releasing phthalimide hybrid, 2-(2-(4-thioxo-3H-1,2-dithiole-5-yl) phenoxy)ethyl)isoindole-1,3-thione (PTD-H₂S), and evaluated its activity in models of inflammatory pain in mice. Per os (p.o.) administration of PTD-H₂S (125 or 250 mg/kg) reduced mechanical allodynia induced by carrageenan and lipopolysaccharide. Intraperitoneal (i.p.) administration of PTD-H₂S (25 mg/kg), but not equimolar doses of its precursors 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione (14.2 mg/kg) and 2-phthalimidethanol (12 mg/kg), reduced mechanical allodynia induced by lipopolysaccharide. The antiallodynic effect induced by PTD-H₂S (25 mg/kg, i.p.) was more sustained than that induced by the H₂S donor NaHS (8 mg/kg, i.p.). Previous administration of hydroxocobalamin (300 mg/kg, i.p.) or glibenclamide (40 mg/kg, p.o.) attenuated PTD-H₂S antiallodynic activity. In conclusion, we synthesized a novel H₂S-releasing phthalimide hybrid and demonstrated its activity in models of inflammatory pain. PTD-H₂S activity may be due to H₂S release and activation of ATP-sensitive potassium channels. The demonstration of PTD-H₂S activity in models of pain stimulates further studies aiming to evaluate H₂S-releasing phthalimide hybrids as candidates for analgesic drugs.

Evaluation of the systemic and spinal antinociceptive effect of a new hybrid NSAID tetrahydropyran derivative

Pain is responsible for inducing physical and mental stress, interfering negatively in patients' quality of life. Classic analgesic drugs, such as opioids and non-steroidal anti-inflammatory drugs, are known for their wide range of adverse effects, making it important to develop new drugs. Thus, this study aimed to analyse the action of the hybrid compound cis- (±) -acetate of 4-chloro-6- (naphthalene-1-yl) -tetrahydro-2h-pyran -2-yl) methyl2- (2- [2,6-dichlorophenylamine] phenyl (LS19) under acute nociceptive conditions, and deepened the understanding of the responsible mechanisms. Male Swiss mice were evaluated in the acetic acid-induced abdominal writhing, formalin, tail flick, capsaicin- and glutamate-induced nociception, thermal stimulation in animals injected with capsaicin and rotarod tests besides the acute and subchronic toxicological evaluation. The compound showed effect on the acetic acid-induced abdominal writhing, formalin (both phases), tail flick, thermal stimulation in animals injected with capsaicin and capsaicin-induced nociception tests. In the study of the mechanism of action was observed reversion of the antihyperalgesic effect of the compound from the previous intraperitoneal and intrathecal administration of naloxone, nor-binaltorphimine, naltrindole, methylnaltrexone, 7-nitroindazole, L-NAME, ODQ, glibenclamide on the tail flick test. In the thermal stimulation in animals injected with capsaicin, the compound showed antinociceptive effect by oral and intraplantar routes, besides to reducing the levels of TNF-α, IL-1β and PGE2 in the paws previously administered with capsaicin. There were no signs of acute and subchronic intoxication with the compound. In summary, the compound LS19 presented spinal and local antihyperalgesic effect, demonstrating participation of the opioid/NO/cGMP/K+ ATP pathway and TRPV1 receptors and it demonstrated safety in its use in mice.

The Involvement of l-Arginine-Nitric Oxide-cGMP-ATP-Sensitive K+ Channel Pathway in Antinociception of BBHC, a Novel Diarylpentanoid Analogue, in Mice Model

The present study focuses on the possible involvement of l-arginine-nitric oxide-cGMP-ATP-sensitive K⁺ channel pathway in the antinociceptive activity of a novel diarylpentanoid analogue, 2-benzoyl-6-(3-bromo-4-hydroxybenzylidene)cyclohexen-1-ol (BBHC) via a chemical nociceptive model in mice. The antinociceptive action of BBHC (1 mg/kg, i.p.) was attenuated by the intraperitoneal pre-treatment of l-arginine (a nitric oxide synthase precursor) and glibenclamide (an ATP-sensitive K⁺ channel blocker) in acetic acid-induced abdominal constriction tests. Interestingly, BBHC’s antinociception was significantly enhanced by the i.p. pre-treatment of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a selective inhibitor of soluble guanylyl cyclase (p < 0.05). Altogether, these findings suggest that the systemic administration of BBHC is able to establish a significant antinociceptive effect in a mice model of chemically induced pain. BBHC’s antinociception is shown to be mediated by the involvement of l-arginine-nitric oxide-cGMP-ATP-sensitive K⁺ channel pathway, without any potential sedative or muscle relaxant concerns.

Cytochrome P450 1A2 is the most important enzyme for hepatic metabolism of the metamizole metabolite 4-methylaminoantipyrine

Aims

Metamizole (dipyrone) is a prodrug not detectable in serum or urine after oral ingestion. The primary metabolite, 4‐methylaminoantipyrine (4‐MAA), can be N‐demethylated to 4‐aminoantipyrine (4‐AA) or oxidized to 4‐formylaminoantipyrine (4‐FAA) by cytochrome P450 (CYP)‐dependent reactions. We aimed to identify the CYPs involved in 4‐MAA metabolism and to quantify the effect of CYP inhibition on 4‐MAA metabolism.

Methods

We investigated the metabolism of 4‐MAA in vitro using CYP expressing supersomes and the pharmacokinetics of metamizole in the presence of CYP inhibitors in male subjects.

Results

The experiments in supersomes revealed CYP1A2 as the major CYP for 4‐MAA N‐demethylation and 4‐FAA formation with CYP2C19 and CYP2D6 contributing to N‐demethylation. In the clinical study, we investigated the influence of ciprofloxacin (CYP1A2 inhibitor), fluconazole (CYP2C19 inhibitor) and the combination ciprofloxacin/fluconazole on the pharmacokinetics of metamizole in n = 12 male subjects in a randomized, placebo‐controlled, double‐blind study. The geometric mean ratios for the area under the concentration–time curve of 4‐MAA after/before treatment were 1.17 (90% CI 1.09–1.25) for fluconazole, 1.51 (90% CI 1.42–1.60) for ciprofloxacin and 1.92 (90% CI 1.81–2.03) for ciprofloxacin/fluconazole. Fluconazole increased the half‐life of 4‐MAA from 3.22 hours by 0.47 hours (95% CI 0.13–0.81, P < .05), ciprofloxacin by 0.69 hours (95% CI 0.44–0.94, P < .001) and fluconazole/ciprofloxacin by 2.85 hours (95% CI 2.48–3.22, P < .001).

Conclusion

CYP1A2 is the major CYP for the conversion of 4‐MAA to 4‐AA and 4‐FAA. The increase in 4‐MAA exposure by the inhibition of CYP1A2 and by the combination CYP1A2/CYP2C19 may be relevant for dose‐dependent adverse reactions of 4‐MAA.

Antinociceptive Synergy Between Metamizole and Hesperidin in a Model of Visceral Pain in Mice

BACKGROUND

Metamizole is used to relieve the visceral pain but its adverse effects limit its use. An alternative to improve its efficacy with lower doses is to combine it with a natural product as hesperidin.

AIM OF THE STUDY

The aim of this study was to evaluate the antinociceptive interaction between metamizole and hesperidin in a visceral pain model using an isobolographic analysis.

METHODS

Antinociception was evaluated in the writhing model using acetic acid (1%) to induce writhes in mice. Metamizole (1-316 mg/kg), hesperidin (3-300 mg/kg), or combinations with a fixed-dose ratio of 1:1 were administered intraperitoneally 30 min before the acetic acid and the number of writhes was counted for 30 min. Isobolographic analysis was employed to define the nature of the compound interaction.

RESULTS

Metamizole and hesperidin in individual administration induced dose-dependent antinociceptive effects, reached an efficacy of 84.2 ± 5.9% and 66.3 ± 7.4%, respectively. The ED₅₀ values calculated from their dose-response curves were 84.5 ± 22.7 and 108.9 ± 17.9 mg/kg, respectively. The analysis of DRC for the metamizole + hesperidin combination, in a ratio 1:1 showed a ED_{50 COMB} value lower than the ED_{50 ADD} estimated from the additivity line from the isobologram (46.7 ± 6.3 vs. 96.7 ± 11.9 mg/kg, respectively). In addition, the pharmacological interaction calculated was of 0.48. These results suggest a synergistic interaction for the antinociceptive activity of metamizole + hesperidin combination.

CONCLUSION

These data suggest that metamizole + hesperidin combination could be useful in treating visceral pain as it can interact synergistically using low dose of both drugs with the possibility of reducing the risk of adverse effects.

The PI3Kγ/AKT signaling pathway mediates peripheral antinociceptive action of dipyrone

Dipyrone (DIP), also known as metamizole, is an over-the-counter analgesic used in Europe and Latin America. Evidence suggesting that inflammatory pain attenuation by DIP is associated with a direct impact on peripheral primary nociceptive neurons through the stimulation of nitric oxide signaling pathway. However, the molecular mechanism by which DIP activates this pathway remains unknown. The PI3Kγ/AKT signaling cascade activation is one of the well-known molecular mechanisms that promote nitric oxide production in sensory neurons. Herein, we investigated the role of the PI3Kγ/AKT signaling cascade in the context of peripheral analgesic effect of DIP. DIP was administered into PGE2 pre-sensitized paws of rats and mechanical hyperalgesia was determined using electronic von Frey test after 1 h. Nonselective or selective pharmacological inhibitors of PI3Kγ and AKT were also administered in DIP-treated rats under paws sensitized with PGE2. Intraplantar injection of DIP attenuated PGE2-induced hyperalgesia in a dose-dependent manner. Treatment with nonselective (wortmannin or LY294002) or selective (AS605240) pharmacological inhibitors of PI3Kγ reduced the peripheral antihypernociceptive effect of DIP. Consistently, AKT selective inhibitor also reversed analgesic DIP effects. Corroborating these data, we found that DIP induced AKT phosphorylation in cultured dorsal root ganglion neurons, which was prevented in the presence of PI3Kγ selective inhibitor. Taken together, these findings provide evidence that peripheral analgesic effect of DIP is dependent on the activation of PI3Kγ/AKT signaling pathway.

Clindamycin inhibits nociceptive response by reducing tumor necrosis factor-α and CXCL-1 production and activating opioidergic mechanisms

Clindamycin, a bacteriostatic semisynthetic lincosamide, is useful in the management of infections caused by aerobic and anaerobic Gram-positive cocci, including bacteremic pneumonia, streptococcal toxic shock syndrome and sepsis. It has been recently demonstrated that clindamycin inhibits in vitro and in vivo inflammatory cytokine production. In the present study, we investigated the effects of clindamycin in acute and chronic models of pain and inflammation in mice and the underlying mechanisms. Intraperitoneal (i.p.) administration of clindamycin (400 mg/kg) increased the animal's latency to exhibit the nociceptive behavior induced by noxious heat (hot plate model). Intrathecal injection of clindamycin (2, 10 and 50 µg) also increased the animals' latency to exhibit the nociceptive behavior. Tactile hypersensitivity and paw edema induced by intraplantar (i.pl.) injection of carrageenan were attenuated by previous administration of clindamycin (200 and 400 mg/kg, i.p.). Clindamycin (100, 200 and 400 mg/kg, i.p.) also attenuated ongoing tactile hypersensitivity and paw edema induced by i.pl. injection of complete Freund's adjuvant (CFA). The antinociceptive activity of clindamycin (400 mg/kg, i.p.) in the hot plate model was attenuated by previous administration of naltrexone (5 and 10 mg/kg, i.p.), but not glibenclamide or AM251. CFA-induced production of TNF-α and CXCL-1 was reduced by clindamycin (400 mg/kg, i.p.). Concluding, clindamycin exhibits activities in acute and chronic models of pain and inflammation. These effects are associated with reduced production of TNF-α and CXCL-1 and activation of opioidergic mechanisms. Altogether, these results indicate that the clindamycin's immunomodulatory effects may contribute to a pharmacological potential beyond its antibiotic property.

Analgesic, antipyretic and anti-inflammatory efficacy of ketorolac in the chicks

Now-a-days, there is a need for newly, non-addicted and effective analgesics with less side effects. Therefore, the present study evaluated the analgesic, antipyretic and anti-inflammatory efficacy of ketorolac in 7–21 days old broiler chicks and its possible application in the related field. The analgesic median effective dose (ED50) of ketorolac that caused analgesia in 50% of the chicks was 9.1 mg/kg, intramuscular (IM). Ketorolac caused analgesic and antipyretic effects at multiple doses (5, 10 and 20 mg/kg, IM) in a dose dependent manner, whereas these percentages were significantly higher when ketorolac was injected @ 10 and 20 mg/kg, IM. All times recorded (15, 30, 60 and 120 min) for evaluating the analgesic effect of ketorolac produced analgesia while the higher and better analgesic efficacy was observed at 15 min after ketorolac injection. The injection of ketorolac @ 20 mg/kg, IM exerted anti-inflammatory activity by significantly reducing the right paw thickness of the chicks as a result of formaldehyde injection in comparison to control. There was no liver damage, impaired metabolism and function may be attributed to the ketorolac treatment in the chicks which was evaluated through estimation of serum AST and ALT concentrations. The study suggests the benefit of using ketorolac as an analgesic, antipyretic and antiinflammatory drug in the field of veterinary medicine due to its good, reliable and efficient efficacy.

Endocannabinoid and N-acylethanolamide levels in rat brain and spinal cord following systemic dipyrone and paracetamol administration

The cannabinoid system has been suspected to play a role in the mechanisms of action of dipyrone and paracetamol. Our purpose was to measure the local endocannabinoid and N-acylethanolamide levels in the brain and spinal cord of rats following dipyrone and paracetamol administration. Nociception was assessed 1, 5, and 12 h following drug injections in Wistar rats, using tail-flick and hot-plate tests. The antinociceptive effects of dipyrone (150, 300, and 600 mg/kg, i.p.) and paracetamol (30, 100, and 300 mg/kg, i.p.) were observed. After administration of the highest doses of dipyrone and paracetamol, endocannabinoid (N-arachidonoylethanolamide (AEA), 2-arachidonoylglycerol (2-AG)) and N-acylethanolamide (palmitoylethanolamide (PEA), oleoylethanolamide (OEA)) levels were measured in the periaqueductal gray (PAG), rostral ventromedial medulla (RVM), and spinal cords of rats using tandem mass spectrometry with liquid chromatography. Increased 2-AG levels were observed in the PAG and the RVM 12 h after paracetamol injection; dipyrone exerted no action on 2-AG levels. Analgesic administrations led to a reduction in AEA levels in the RVM and spinal cord; similar decreases in PEA and OEA levels were observed in the RVM and the spinal cord. Dipyrone and paracetamol administrations appear to exert complicated effects on endocannabinoid and N-acylethanolamide levels in rats.

[Pharmacology of non-opioid analgesics]

Due to high prescription rates as well as the frequent use as over the counter drugs, it is of interest to consider non-opioid analgesics when evaluating the quality and appropriateness of a given overall medication. This article sums up the basic pharmacology and main adverse effects of these analgesics. Non-opioids can be further classified according to their additional mechanisms of action besides analgesia. High-dose acetylsalicylic acid, traditional nonsteroidal anti-inflammatory drugs, and coxibs exhibit antipyretic and anti-inflammatory properties. Acetaminophen and metamizole (dipyrone) are analgesics and antipyretic agents, while metamizole exhibits also spasmolytic effects. Capsaicin and intrathecal ziconotide are pure analgesics.

Dose evaluation of intravenous metamizole (dipyrone) in infants and children: a prospective population pharmacokinetic study

PURPOSE

The prodrug metamizole is prescribed intravenously for postoperative pain in children, including off-label use in infants < 1 year. We aimed to assess the pharmacokinetics of the main metabolites of metamizole in children aged 3-72 months.

METHODS

A single dose of 10 mg/kg metamizole was administered intravenously for postoperative analgesia. Pharmacokinetic samples were drawn at predefined time points. Pharmacokinetics of the main active metabolite 4-methylaminoantipyrine and three other metabolites was characterized by both non-compartmental and population pharmacokinetic analysis. AUC_0-inf of 4-methylaminoantipyrine was calculated by non-compartmental analysis for two age cohorts (3-23 months, 2-6 years) and compared with the 80-125% range of adult dose-adjusted reference exposure (AUC_ref). Population pharmacokinetic analysis investigated age and weight dependency of the pharmacokinetics and optimal dosing strategies to achieve equivalent adult exposure.

RESULTS

A total of 25 children aged 5 months-5.8 years (7.8-24.8 kg) with at least one concentration sample were included; 19 children had ≥ 5 predefined samples up to 10 h after metamizole dose administration. AUC_0-inf of 4-methylaminoantipyrine in children 2-6 years was 29.9 mg/L/h (95% CI 23.4-38.2), significantly lower than AUC_ref (80-125% range 39.2-61.2 mg/L/h). AUC_0-inf of 4-methylaminoantipyrine in infants < 2 years was 43.6 mg/L/h (95% CI 15.8-119.0), comparable with AUC_ref, while infants < 12 months showed increased exposure. Observed variability could be partially explained by covariates weight and age.

CONCLUSIONS

Age-related changes in pharmacokinetics of 4-methylaminoantipyrine requires reduced weight-based IV dosing in infants < 1 year compared with infants and children up to 6 years (5 versus 10-20 mg/kg) to achieve equivalent adult exposure.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02660177 .

Antinociceptive Activity of Petroleum Ether Fraction of Clinacanthus nutans Leaves Methanolic Extract: Roles of Nonopioid Pain Modulatory Systems and Potassium Channels

Methanolic extract of Clinacanthus nutans Lindau leaves (MECN) has been reported to exert antinociceptive activity. The present study aimed to elucidate the possible antinociceptive mechanisms of a lipid-soluble fraction of MECN, which was obtained after sequential extraction in petroleum ether. The petroleum ether fraction of C. nutans (PECN), administered orally to mice, was (i) subjected to capsaicin-, glutamate-, phorbol 12-myristate 13-acetate-, bradykinin-induced nociception model; (ii) prechallenged (intraperitoneal (i.p.)) with 0.15 mg/kg yohimbine, 1 mg/kg pindolol, 3 mg/kg caffeine, 0.2 mg/kg haloperidol, or 10 mg/kg atropine, which were the respective antagonist of α 2-adrenergic, β-adrenergic, adenosinergic, dopaminergic, or muscarinic receptors; and (iii) prechallenged (i.p.) with 10 mg/kg glibenclamide, 0.04 mg/kg apamin, 0.02 mg/kg charybdotoxin, or 4 mg/kg tetraethylammonium chloride, which were the respective inhibitor of ATP sensitive-, small conductance Ca2+-activated-, large conductance Ca2+-activated-, or nonselective voltage-activated-K+ channel. Results obtained demonstrated that PECN (100, 250, and 500 mg/kg) significantly (P<0.05) inhibited all models of nociception described earlier. The antinociceptive activity of 500 mg/kg PECN was significantly (P<0.05) attenuated when prechallenged with all antagonists or K+ channel blockers. However, only pretreatment with apamin and charybdotoxin caused full inhibition of PECN-induced antinociception. The rest of the K+ channel blockers and all antagonists caused only partial inhibition of PECN antinociception, respectively. Analyses on PECN's phytoconstituents revealed the presence of antinociceptive-bearing bioactive compounds of volatile (i.e., derivatives of γ-tocopherol, α-tocopherol, and lupeol) and nonvolatile (i.e., cinnamic acid) nature. In conclusion, PECN exerts a non-opioid-mediated antinociceptive activity involving mainly activation of adenosinergic and cholinergic receptors or small- and large-conductance Ca2+-activated-K+ channels.

Hyperglycemia induces mechanical hyperalgesia and depolarization of the resting membrane potential of primary nociceptive neurons: Role of ATP-sensitive potassium channels

Cumulating data suggests that ion channel alterations in nociceptive neurons might be involved in the development of diabetic painful neuropathy. In the present study we investigated the involvement of ATP-sensitive potassium (K⁺_ATP) channels in the acute effect of high glucose solution in vitro and in vivo. High glucose concentrations depolarized cultured nociceptive neurons and depolarization was blocked by the K⁺_ATP opener, diazoxide or by insulin. Glucose injection at the rat dorsal root ganglia (L5) resulted in acute mechanical hyperalgesia that was blocked by diazoxide. Mannitol injection indicates that osmolarity changes are not responsible for glucose effect. Therefore, this study suggests that K⁺_ATP channels expressed in peripheral sensory neurons might be involved in the development of diabetic painful neuropathy. Since sulfonylureas, that act by blocking K⁺_ATP are used for diabetes treatment, it is important to evaluate the possible side effects of such drugs at primary sensory neurons.

N-demethylation of N-methyl-4-aminoantipyrine, the main metabolite of metamizole

Metamizole is an old analgesic used frequently in some countries. Active metabolites of metamizole are the non-enzymatically generated N-methyl-4-aminoantipyrine (4-MAA) and its demethylation product 4-aminoantipyrine (4-AA). Previous studies suggested that 4-MAA demethylation can be performed by hepatic cytochrome P450 (CYP) 3A4, but the possible contribution of other CYPs remains unclear. Using human liver microsomes (HLM), liver homogenate and HepaRG cells, we could confirm 4-MAA demethylation by CYPs. Based on CYP induction (HepaRG cells) and CYP inhibition (HLM) we could identify CYP2B6, 2C8, 2C9 and 3A4 as major contributors to 4-MAA demethylation. The 4-MAA demethylation rate by HLM was 280 pmol/mg protein/h, too low to account for in vivo 4-MAA demethylation in humans. Since peroxidases can perform N-demethylation, we investigated horseradish peroxidase and human myeloperoxidase (MPO). Horse radish peroxidase efficiently demethylated 4-MAA, depending on the hydrogen peroxide concentration. This was also true for MPO; this reaction was saturable with a K_m of 22.5 μM and a maximal velocity of 14 nmol/min/mg protein. Calculation of the entire body MPO capacity revealed that the demethylation capacity by granulocyte/granulocyte precursors was approximately 600 times higher than the liver capacity and could account for 4-MAA demethylation in humans. 4-MAA demethylation could also be demonstrated in MPO-expressing granulocyte precursor cells (HL-60). In conclusion, 4-MAA can be demethylated in the liver by several CYPs, but hepatic metabolism cannot fully explain 4-MAA demethylation in humans. The current study suggests that the major part of 4-MAA is demethylated by circulating granulocytes and granulocyte precursors in bone marrow.

Antinociceptive Activity of Methanolic Extract of Clinacanthus nutans Leaves: Possible Mechanisms of Action Involved

Methanolic extract of Clinacanthus nutans Lindau leaves (MECN) has been proven to possess antinociceptive activity that works via the opioid and NO-dependent/cGMP-independent pathways. In the present study, we aimed to further determine the possible mechanisms of antinociception of MECN using various nociceptive assays. The antinociceptive activity of MECN was (i) tested against capsaicin-, glutamate-, phorbol 12-myristate 13-acetate-, bradykinin-induced nociception model; (ii) prechallenged against selective antagonist of opioid receptor subtypes (β-funaltrexamine, naltrindole, and nor-binaltorphimine); (iii) prechallenged against antagonist of nonopioid systems, namely, α₂-noradrenergic (yohimbine), β-adrenergic (pindolol), adenosinergic (caffeine), dopaminergic (haloperidol), and cholinergic (atropine) receptors; (iv) prechallenged with inhibitors of various potassium channels (glibenclamide, apamin, charybdotoxin, and tetraethylammonium chloride). The results demonstrated that the orally administered MECN (100, 250, and 500 mg/kg) significantly (p < 0.05) reversed the nociceptive effect of all models in a dose-dependent manner. Moreover, the antinociceptive activity of 500 mg/kg MECN was significantly (p < 0.05) inhibited by (i) antagonists of μ-, δ-, and κ-opioid receptors; (ii) antagonists of α₂-noradrenergic, β-adrenergic, adenosinergic, dopaminergic, and cholinergic receptors; and (iii) blockers of different K⁺ channels (voltage-activated-, Ca²⁺-activated, and ATP-sensitive-K⁺ channels, resp.). In conclusion, MECN-induced antinociception involves modulation of protein kinase C-, bradykinin-, TRVP1 receptors-, and glutamatergic-signaling pathways; opioidergic, α₂-noradrenergic, β-adrenergic, adenosinergic, dopaminergic, and cholinergic receptors; and nonopioidergic receptors as well as the opening of various K⁺ channels. The antinociceptive activity could be associated with the presence of several flavonoid-based bioactive compounds and their synergistic action with nonvolatile bioactive compounds.

Polymethoxyflavones from Nicotiana plumbaginifolia (Solanaceae) Exert Antinociceptive and Neuropharmacological Effects in Mice

Polymethoxylavones (PMFs) are known to exhibit significant anti-inflammatory and neuroprotective properties. Nicotiana plumbaginifolia, an annual Bangladeshi herb, is rich in polymethoxyflavones that possess significant analgesic and anxiolytic activities. The present study aimed to determine the antinociceptive and neuropharmacological activities of polyoxygenated flavonoids namely- 3,3′,5,6,7,8-hexamethoxy-4′,5′-methylenedioxyflavone (1), 3,3′,4′,5′,5,6,7,8-octamethoxyflavone (exoticin) (2), 6,7,4′,5′-dimethylenedioxy-3,5,3′-trimethoxyflavone (3), and 3,3′,4′,5,5′,8-hexamethoxy-6,7-methylenedioxyflavone (4), isolated and identified from N. plumbaginifolia. Antinociceptive activity was assessed using the acetic-acid induced writhing, hot plate, tail immersion, formalin and carrageenan-induced paw edema tests, whereas neuropharmacological effects were evaluated in the hole cross, open field and elevated plus maze test. Oral treatment of compounds 1, 3, and 4 (12.5–25 mg/kg b.w.) exhibited dose-dependent and significant (p < 0.01) antinociceptive activity in the acetic-acid, formalin, carrageenan, and thermal (hot plate)-induced pain models. The association of ATP-sensitive K⁺ channel and opioid systems in their antinociceptive effect was obvious from the antagonist effect of glibenclamide and naloxone, respectively. These findings suggested central and peripheral antinociceptive activities of the compounds. Compound 1, 3, and 4 (12.5 mg/kg b.w.) demonstrated significant (p < 0.05) anxiolytic-like activity in the elevated plus-maze test, while the involvement of GABA_A receptor in the action of compound 3 and 4 was evident from the reversal effects of flumazenil. In addition, compounds 1 and 4 (12.5–25 mg/kg b.w) exhibited anxiolytic activity without altering the locomotor responses. The present study suggested that the polymethoxyflavones (1–4) from N. Plumbaginifolia could be considered as suitable candidates for the development of analgesic and anxiolytic agents.

Dipyrone is the preferred nonopioid analgesic for the treatment of acute and chronic pain. A survey of clinical practice in German-speaking countries

PURPOSE

Nonopioid analgesics are frequently used for the treatment of acute and chronic pain. Dipyrone is an alternative to NSAIDs and paracetamol, however, data on the frequency of its usage by anaesthesiologists in the perioperative and chronic pain setting are lacking and its adverse reactions are a matter of debate.

METHODS

The link to a questionnaire on the use of nonopioid analgesics (NSAIDs, COX-2 inhibitors, paracetamol, dipyrone) and the safety of dipyrone in the perioperative and chronic pain setting was mailed to anaesthesiologists and pain physicians.

RESULTS

A total of 2237 responses were analysed. About 97.4% of the respondents used nonopioid analgesics for the treatment of acute pain, with 93.8% administering dipyrone, 54.0% NSAIDs, 41.8% COX-2 inhibitors and 49.2% paracetamol. Nonopioid analgesics were administered preoperatively by 22.3%, intraoperatively by 86.1% and postoperatively by 73.0% of the respondents. For chronic pain management, 76.7% of the respondents prescribed oral dipyrone in combination with other nonopioid analgesics; 19.9% used dipyrone as sole nonopioid, whereas 2.9% denied its use. Cases of dipyrone-associated agranulocytosis were observed by 3.5% of the respondents of the acute and 1.5% of the chronic pain questionnaire, respectively. The majority of respondents (acute pain: 73.0%, chronic pain 59.3%) performed no blood cell counts to monitor dipyrone therapy. Patients were rarely informed about possible adverse drug reactions.

CONCLUSIONS

Dipyrone is the preferred nonopioid analgesic in the perioperative and chronic pain setting. Although cases of agranulocytosis occur, benefits apparently outweigh the risks according to anaesthesiologists. Measures like patient information may improve safety.

SIGNIFICANCE

A survey of anaesthesiologist in German-speaking countries revealed dipyrone as preferred nonopioid analgesic for the treatment of acute and chronic pain. Benefits seem to outweigh the risks, specifically the risk of agranulocytosis. Information of medical staff and patients on adverse drug reactions and symptoms of agranulocytosis should be implemented.

Antihyperalgesic effect of [(±)-(2,4,6-cis)-4-chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl]methanol: participation of the NO/cGMP/KATP pathway and κ-opioid receptor

The present study used behavioral analyses to investigate the involvement of the NO/cGMP/KATP pathway, serotoninergic, and opioid systems in the antinociceptive action of [(±)-(2,4,6-cis)-4-chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl]methanol (CTHP) in mice. Oral administration of CTHP (1, 5, 10, and 30 mg/kg) exerted effects at higher doses in chemical models of nociception (the acetic acid writhing and formalin tests) as well as a thermal model (the tail-flick test). It was also found that pretreatment with L-N-nitroarginine methyl ester (nonselective nitric oxide synthase inhibitor), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (selective inhibitor of nitric oxide-sensitive guanosyl cyclase), glibenclamide (selective ATP-sensitive K channel blocker), naloxone (nonselective opioid receptor blocker), and nor-binaltorphimine (selective κ-opioid receptor blocker), but not methylnaltrexone (peripheral μ-opioid receptor blocker) or naltrindole (selective δ-opioid receptor blocker), reversed the antinociceptive effect of CTHP. In addition, CTHP induced the development of tolerance in the tail-flick test: the tolerance appeared later compared with morphine, and was only observed with a higher dose. Taken together, the present study showed that the systemic administration of CTHP reduced pain induced by chemical and thermal stimuli. We also suggest that the possible mechanisms include the involvement of the NO/cGMP/KATP pathway and the κ-opioid receptor.

Angiotensin-(1-7)/Mas receptor as an antinociceptive agent in cancer-induced bone pain

Many cancerous solid tumors metastasize to the bone and induce pain (cancer-induced bone pain [CIBP]). Cancer-induced bone pain is often severe because of enhanced inflammation, rapid bone degradation, and disease progression. Opioids are prescribed to manage this pain, but they may enhance bone loss and increase tumor proliferation, further compromising patient quality of life. Angiotensin-(1-7) (Ang-(1-7)) binds and activates the Mas receptor (MasR). Angiotensin-(1-7)/MasR activation modulates inflammatory signaling after acute tissue insult, yet no studies have investigated whether Ang-(1-7)/MasR play a role in CIBP. We hypothesized that Ang-(1-7) inhibits CIBP by targeting MasR in a murine model of breast CIBP. 66.1 breast cancer cells were implanted into the femur of BALB/cAnNHsd mice as a model of CIBP. Spontaneous and evoked pain behaviors were assessed before and after acute and chronic administration of Ang-(1-7). Tissues were collected from animals for ex vivo analyses of MasR expression, tumor burden, and bone integrity. Cancer inoculation increased spontaneous pain behaviors by day 7 that were significantly reduced after a single injection of Ang-(1-7) and after sustained administration. Preadministration of A-779 a selective MasR antagonist prevented this reduction, whereas pretreatment with the AT2 antagonist had no effect; an AT1 antagonist enhanced the antinociceptive activity of Ang-(1-7) in CIBP. Repeated Ang-(1-7) administration did not significantly change tumor burden or bone remodeling. Data here suggest that Ang-(1-7)/MasR activation significantly attenuates CIBP, while lacking many side effects seen with opioids. Thus, Ang-(1-7) may be an alternative therapeutic strategy for the nearly 90% of patients with advanced-stage cancer who experience excruciating pain.

Antihyperalgesic Effects of Indomethacin, Ketorolac, and Metamizole in Rats: Effects of Metformin

Preclinical Research Metformin-dependent mechanisms have been implicated in the antinociceptive effect of some non-steroidal anti-inflammatory drugs (NSAIDs). In this study, the effect of local peripheral or systemic administration of metformin on the local peripheral or systemic antinociception induced by indomethacin, ketorolac and metamizole was assessed in the rat carrageenan-induced thermal hyperalgesia model. Rats were injected with carrageenan (1%, 50 µl) into the right hindpaw which reduced paw withdrawal latency, a measure of thermal hyperalgesia. Local peripheral or systemic administration of indomethacin, ketorolac or metamizole dose-dependently reduced carrageenan-induced thermal hyperalgesia. Local peripheral pre-treatment with metformin (800 µg/paw) partially inhibited the anti-hyperalgesic effect of indomethacin (200 µg/paw) and metamizole (200 µg/paw), but not that of ketorolac (200 µg/paw). In contrast, systemic pre-treatment with metformin (200 mg/kg) attenuated the antihyperalgesic effect of metamizole (10 mg/kg), but not that observed with either indomethacin (10 mg/kg) or ketorolac (10 mg/kg). These findings suggest that some but not all NSAIDs have effects mediated by metformin-dependent mechanisms. Drug Dev Res 78 : 98-104, 2017. ©2017 Wiley Periodicals, Inc.

Antinociceptive effect of methanol extract of Dalbergia sissoo leaves in mice

BACKGROUND

Dalbergia sissoo DC. (Family: Fabaceae) is a medium to large deciduous tree, is locally called "shishu" in Bangladesh. It is used to treat sore throats, dysentery, syphilis, bronchitis, inflammations, infections, hernia, skin diseases, and gonorrhea. This study evaluated the antinociceptive effect of the methanol extract of D. sissoo leaves (MEDS) in mice.

METHODS

The extract was assessed for antinociceptive activity using chemical and heat induced pain models such as hot plate, tail immersion, acetic acid-induced writhing, formalin, glutamate, and cinnamaldehyde test models in mice at the doses of 100, 200, and 400 mg/kg (p.o.) respectively. Morphine sulphate (5 mg/kg, i.p.) and diclofenac sodium (10 mg/kg, i.p.) were used as reference analgesic drugs. To confirm the possible involvement of opioid receptor in the central antinociceptive effect of MEDS, naloxone was used to antagonize the effect.

RESULTS

MEDS demonstrated potent and dose-dependent antinociceptive activity in all the chemical and heat induced mice models (p < 0.001). The findings of this study indicate that the involvement of both peripheral and central antinociceptive mechanisms. The use of naloxone verified the association of opioid receptors in the central antinociceptive effect.

CONCLUSIONS

This study indicated the peripheral and central antinociceptive activity of the leaves of D. sissoo. These results support the traditional use of this plant in different painful conditions.

Mechanisms involved in antinociception induced by a polysulfated fraction from seaweed Gracilaria cornea in the temporomandibular joint of rats

Temporomandibular disorder is a common clinical condition involving pain in the temporomandibular joint (TMJ) region. This study assessed the antinociceptive effects of a polysulfated fraction from the red seaweed Gracilaria cornea (Gc-FI) on the formalin-induced TMJ hypernociception in rats and investigated the involvement of different mechanisms. Male Wistar rats were pretreated with injection (sc) of saline or Gc-FI 1h before intra- TMJ injection of formalin to evaluate the nociception. The results showed that pretreatment with Gc-FI significantly reduced formalin-induced nociceptive behavior. Moreover, the antinociceptive effect of the Gc-FI was blocked by naloxone (a non-selective opioid antagonist), suggesting the involvement of opioids selective receptors. Thus, the pretreatment with selective opioids receptors antagonists, reversed the antinociceptive effect of the Gc-FI in the TMJ. The Gc-FI antinociceptive effect depends on the nitric oxide/cyclic GMP/protein kinase G/ATP-sensitive potassium channel (NO/cGMP/PKG/K⁺_ATP) pathway because it was prevented by pretreatment with inhibitors of nitric oxide synthase, guanylate cyclase enzyme, PKG and a K⁺_ATP blocker. In addition, after inhibition with a specific heme oxygenase-1 (HO-1) inhibitor, the antinociceptive effect of the Gc-FI was not observed. Collectively, these data suggest that the antinociceptive effect induced by Gc-FI is mediated by μ/δ/κ-opioid receptors and by activation NO/cGMP/PKG/K⁺_ATP channel pathway, besides of HO-1.

[Metamizole (dipyrone): mode of action, drug-drug interactions, and risk of agranulocytosis]

Metamizole (dipyrone) is a nonsteroidal compound with strong analgesic as well as antipyretic and spasmolytic properties. Based on a small number of cases of agranulocytosis, metamizole was withdrawn from the market in some countries. Other countries restricted its use. This paper discusses the safety aspects of metamizole and compares it with other compounds used for similar indications.

Antinociceptive effect of methanol extract of Celosia cristata Linn. in mice

BACKGROUND

Celosia cristata Linn. (Amaranthaceae) is used in traditional medicine for the treatment of headache, sores, ulcers, eye inflammations, skin eruption, painful menstruation and carpal tunnel syndrome. This study was performed to evaluate the antinociceptive activity of methanol extract of the whole plant of C. cristata (MECC).

METHODS

The evaluation of the antinociceptive effect of MECC was performed using thermal (hot plate, tail immersion test) and chemical (acetic acid, formalin, and glutamate-induced nociception test) pain models in mice at four different doses (50, 100, 200, 400 mg/kg; p.o.). Involvement of opioid receptors mediated central antinociceptive mechanism of MECC was evaluated using naloxone. Furthermore, the association of ATP-sensitive K+ channel and cGMP pathway were evaluated using glibenclamide and methylene blue respectively.

RESULTS

Oral treatment of MECC produced significant, strong and dose-dependent central and peripheral antinociceptive effect in experimental pain models. MECC significantly increased the latency time of thermal threshold in both hot plate and tail immersion test. The inhibition of writhing syndrome by the extract in the acetic acid-induced writhing test was remarkable. MECC significantly reduced the formalin-induced neurogenic and inflammatory pain. In addition, the inhibition of glutamate-induced paw licking and edema by MECC was significant. The antinociceptive effect was significantly reversed by naloxone and glibenclamide, suggesting the association of opioid and ATP-sensitive K+ channel system respectively. In addition, MECC also demonstrated the involvement of cGMP pathway in the antinociceptive action.

CONCLUSION

The study suggests that C. cristata possess significant antinociceptive effect which is associated with both central and peripheral mechanisms and provides a rationale for its extensive use at different painful conditions in traditional medicine.

[Perioperative pain therapy in dogs and cats - an overview]

Undermanaged pain leads to negative systemic effects that may greatly disturb our patients' welfare. Therefore, a pain assessment tool should be routinely implemented into clinical practice. Validated pain assessment tools are available for dogs and cats. Advanced analgesic therapy follows the principle of a multimodal approach. This means that different analgesic drugs, which act on different targets within the nociceptive pathway, are combined to achieve the desired analgesic effects. In addition to opioids, nonsteroidal anti-inflammatory drugs and local anaesthetics, α2-receptor-agonists, ketamine and gabapentin as well as different nonpharmacologic analgesic techniques are used within the framework of a multimodal analgesic plan.

Naringenin reduces inflammatory pain in mice

Naringenin is a flavonoid widely consumed by humans that present anti-inflammatory activity and low toxicity. Recently, the analgesic effect of naringenin has been demonstrated in neuropathic pain models. Herein, we tested the analgesic effects of naringenin in several models of inflammatory pain. Mice received treatment with naringenin (16.7-150 mg/kg, per oral), or with the controls anti-inflammatory drugs indomethacin (5 mg/kg, intraperitoneal) or dipyrone (80 mg/kg, intraperitoneal) prior the inflammatory stimuli injection. For acute pain, we used acetic acid- and PBQ-induced visceral pain (abdominal writhings), and formalin-, capsaicin-, and CFA-induced paw flinching and licking. By using an electronic version of von Frey filaments, we also investigated the effects of naringenin in pain intensity to a mechanical stimulus (mechanical hyperalgesia) after carrageenan, capsaicin, CFA, or PGE2 intraplantar injection. Naringenin (50 mg/kg) reduced acute pain behaviors induced by all tested stimuli, including both phases of formalin test, suggesting a direct nociceptor modulatory effect of this compound besides its anti-inflammatory activity. Accordingly, naringenin also inhibited the increased sensitivity to mechanical stimulus induced by carrageenan, capsaicin, and PGE2. Daily treatment with naringenin during 7 days also reduced CFA-induced mechanical hyperalgesia without gastric or hepatic toxicity. The mechanisms of naringenin involve the inhibition of carrageenan-induced oxidative stress, hyperalgesic cytokines (IL-33, TNF-α, and IL-1β) production and NF-κB activation in the paw skin. Naringenin also activated the analgesic NO-cyclic GMP-PKG-ATP sensitive K(+) channel signaling pathway to inhibit carrageenan-induced mechanical hyperalgesia and neutrophil recruitment. These results suggest that naringenin inhibits both inflammatory pain and neurogenic inflammation.

TRPV1 channel inhibition contributes to the antinociceptive effects of Croton macrostachyus extract in mice

Background

Previous study showed that extracts from Croton macrostachyus (Euphorbiaceae) exhibit analgesic effects in acute pain models. The present study evaluates the antinociceptive properties of the methanol/methylene chloride extract (MECM) of the stem bark of this plant using mice models of persistent inflammatory and neuropathic pain, and assesses its mechanism of action.

Methods

MECM was tested on Complete Freund adjuvant (CFA)-induced persistent thermal and mechanical pain, neuropathic pain induced by partial sciatic nerve ligation (PSNL), prostaglandin E₂ (PGE₂)-induced acute mechanical hyperalgesia, as well as on nociception induced by capsaicin in mice. Mechanical hyperalgesia was assessed using von Frey hair in awake mice. The mechanism of action of MECM was evaluated by using glibenclamide on PGE₂-induced hyperalgesia or rimonabant on capsaicin-induced pain.

Results

MECM administered orally at the doses of 250 and 500 mg/kg, induced long lasting and significant antihyperalgesic effects on CFA-inflammatory and PSNL-induced neuropathic pain. MECM significantly reduced the mechanical hyperalgesia induced by PGE₂ either when administered preventively or therapeutically. MECM also significantly and time dependently inhibited the capsaicin-induced nociception. These effects were not affected by glibenclamide or by rimonabant.

Conclusions

The present results demonstrate that the oral administration of MECM to mice resulted in long lasting antihyperalgesic activity in inflammatory and neuropathic pain as well as in acute and persistent pain. The mechanism underlying the long lasting MECM antihyperalgesic effect is currently unknown, but might be mediated, at least partially, through the modulation of TRPV1 receptors.

Effect of tramadol on metamizol pharmacokinetics and pharmacodynamics after single and repeated administrations in arthritic rats

Combined administration of certain doses of opioid compounds with a non-steroidal anti-inflammatory drug can produce additive or supra-additive effects while reducing unwanted effects. We have recently reported that co-administration of metamizol with tramadol produces antinociceptive effect potentiation, after acute treatment. However, none information about the effect produced by the combination after chronic or repeated dose administration exists. The aims of this study were to investigate whether the antinociceptive synergism produced by the combination of metamizol and tramadol (177.8 + 17.8 mg/kg, s.c. respectively) is maintained after repeated treatment and whether the effects observed are primarily due to pharmacodynamic interactions or may be related to pharmacokinetics changes. Administration of metamizol plus tramadol acute treatment significantly enhanced the antinociceptive effect of the drugs given alone (P < 0.05). Nevertheless, this effect decreased about 53% after the chronic treatment (3 doses per day, for 4 days). No pharmacokinetic interaction between metamizol and tramadol was found under acute treatment (P > 0.05). The mechanism involved in the synergism of the antinociceptive effect observed with the combination of metamizol and tramadol in single dose cannot be attributed to a pharmacokinetic interaction, and other pharmacodynamic interactions have to be considered. On the other hand, when metamizol and tramadol were co-administered under repeated administrations, a pharmacokinetic interaction and tolerance development occurred. Differences found in metamizol active metabolites’ pharmacokinetics (P < 0.05) were related to the development of tolerance produced by the combination after repeated doses. This work shows an additional preclinical support for the combination therapy. The clinical utility of this combination in a suitable dose range should be evaluated in future studies.

[Pediatric perioperative systemic pain therapy: Austrian interdisciplinary recommendations on pediatric perioperative pain management]

BACKGROUND

Many analgesics used in adult medicine are not licensed for pediatric use. Licensing limitations do not, however, justify that children are deprived of a sufficient pain therapy particularly in perioperative pain therapy. The treatment is principally oriented to the strength of the pain. Due to the degree of pain caused, intramuscular and subcutaneous injections should be avoided generally.

NON-OPIOIDS

The basis of systemic pain therapy for children are non-opioids and primarily non-steroidal anti-inflammatory drugs (NSAIDs). They should be used prophylactically. The NSAIDs are clearly more effective than paracetamol for acute posttraumatic and postoperative pain and additionally allow economization of opioids. Severe side effects are rare in children but administration should be carefully considered especially in cases of hepatic and renal dysfunction or coagulation disorders. Paracetamol should only be taken in pregnancy and by children when there are appropriate indications because a possible causal connection with bronchial asthma exists. To ensure a safe dosing the age, body weight, duration of therapy, maximum daily dose and dosing intervals must be taken into account. Dipyrone is used in children for treatment of visceral pain and cholic. According to the current state of knowledge the rare but severe side effect of agranulocytosis does not justify a general rejection for short-term perioperative administration.

OPIOIDS

In cases of insufficient analgesia with non-opioid analgesics, the complementary use of opioids is also appropriate for children of all age groups. They are the medication of choice for episodes of medium to strong pain and are administered in a titrated form oriented to effectiveness. If severe pain is expected to last for more than 24 h, patient-controlled anesthesia should be implemented but requires a comprehensive surveillance by nursing personnel.

KETAMINE

Ketamine is used as an adjuvant in postoperative pain therapy and is recommended for use in pediatric sedation and analgosedation.

The antinociceptive effects of magnesium sulfate and MK-801 in visceral inflammatory pain model: The role of NO/cGMP/K(+)ATP pathway

CONTEXT

Magnesium and MK-801 (dizocilpine), antagonists of N-methyl-d-aspartate receptors, are involved in the processing of pain.

OBJECTIVE

This study determines whether magnesium sulfate (MS) and MK-801 affects visceral inflammatory pain and determines a possible mechanism of action.

MATERIALS AND METHODS

Analgesic activity was assessed using the acetic acid-induced writhing test in rats. MS (1-45 mg/kg) or MK-801 (0.005-0.03 mg/kg) was administrated subcutaneously (s.c.). To assess possible mechanisms of action, we examined the effects of l-NAME (10 mg/kg, intraperitoneal), methylene blue (0.5 mg/kg, s.c.), and glibenclamide (3 mg/kg, s.c.) on the effect of MS or MK-801.

RESULTS

MS and MK-801 showed biphasic and linear dose-response pattern, respectively. MS reduces the number of writhing on the dose of 1, 5, and 15 mg/kg by 60, 50, and 78%, respectively, while it has no effects on the doses of 30 and 45 mg/kg. MK-801 (0.005-0.03 mg/kg) showed decrease in the number of writhing by 33-79%. The mean effective doses of MS and MK-801 were 6.6 (first phase) and 0.009 mg/kg, respectively. Both drugs did not impair the rotarod performance. l-NAME, methylene blue, and glybenclamide reduced the effect of MK-801 by 100, 43, and 64%, respectively, but not the effect of MS.

CONCLUSIONS

The results suggest that MS and MK-801 may be useful analgesics in the management of visceral inflammatory pain, at doses that do not induce motor impairment. The modulation of NO/cGMP/K+ATP pathway plays an important role in the antinociceptive mechanism of MK-801, but does not contribute to the antinociceptive effect of MS.

Involvement of the NO/cGMP/KATP pathway in the antinociceptive effect of the new pyrazole 5-(1-(3-fluorophenyl)-1H-pyrazol-4-yl)-2H-tetrazole (LQFM-021)

The pyrazol compounds are known to possess antipyretic, analgesic and anti-inflammatory activities. This study was conducted to investigate the peripheral antinociceptive effect of the pyrazole compound 5-(1-(3-Fluorophenyl)-1H-pyrazol-4-yl)-2H-tetrazole (LQFM-021) and involvement of opioid receptors and of the NO/cGMP/K(ATP) pathway. The oral treatments in mice with LQFM-021 (17, 75 or 300 mg/kg) decreased the number of writhing. In the formalin test, the treatments with LQFM-021 at doses of 15, 30 and 60 mg/kg reduced the licking time at both neurogenic and inflammatory phases of this test. The treatment of the animals with LQFM-021 (30 mg/kg) did not have antinociceptive effects in the tail-flick and hot plate tests. Furthermore, pre-treatment with naloxone (3 mg/kg i.p.), L-name (10 mg/kg i.p.), ODQ (10 mg/kg i.p.) or glibenclamide (3 mg/kg i.p.) antagonized the antinociceptive effect of LQFM-021 in both phases of the formalin test. In addition, it was also demonstrated that the treatments of mice with LQFM-021(15, 30 and 60 mg/kg) did not compromise the motor activity of the animals in the chimney test. Only the highest dose used in the antinociceptive study promoted changes in the open field test and pentobarbital-induced sleep test, thus ruling out possible false positive effects on nociception tests. Our data suggest that the peripheral antinociception effects of the LQFM-021 were mediated through the peripheral opioid receptors with activation of the NO/cGMP/KATP pathway.

Tingenone, a pentacyclic triterpene, induces peripheral antinociception due to NO/cGMP and ATP-sensitive K(+) channels pathway activation in mice

Substances derived from plants play an important role in the development of new analgesic drugs, among them, triterpenoids. The connection between the participation of L-arginine/NO/cGMP pathway and the activation of ATP-sensitive K(+) channels (KATP) has been established on the peripheral antinociception induced by various drugs. The study assessed the involvement of L-arginine/NO/cGMP/KATP pathway in the antinociceptive effect induced by tingenone, from Maytenus imbricata, against the hyperalgesia evoked by prostaglandin E2 (PGE2) in peripheral pathway. The paw pressure test was used, with hyperalgesia induced by intraplantar injection of PGE2 (2 μg). Tingenone (200 µg/paw) administered into the right hind paw induced a local antinociceptive effect, that was antagonized by l-NOArg, nonselective nitric oxide synthase (NOS) inhibitor and by L-NPA, selective neuronal NOS (nNOS) inhibitor. The L-NIO, selective inhibitor of endothelial (eNOS), and the L-NIL, selective inhibitor of inducible (iNOS), did not alter the peripheral antinociceptive effect of the tingenone. The ODQ, selective soluble guanylyl cyclase inhibitor, prevented the antinociceptive effect of tingenone, and zaprinast, inhibitor of the phosphodiesterase that is cyclic guanosine monophosphate (cGMP) specific, intensified the peripheral antinociceptive effect of the smaller dose of tingenone. Glibenclamide, ATP-sensitive K(+) channels (KATP) blocker, but not tetraethylammonium chloride, voltage-dependent K(+) channel blocker; dequalinium dichloride, blocker of the small conductance Ca(2+)-activated K(+) channel, and paxilline, a potent blocker of high-conductance Ca(2+)-activated K(+) channels, respectively, prevented the peripheral antinociceptive effect of tingenone. The results demonstrate that tingenone induced a peripheral antinociceptive effect by L-arginine/NO/cGMP/KATP pathway activation, with potential for a new analgesic drug.

Antinociceptive activity of the ethanolic extract, fractions, and aggregatin D isolated from Sinningia aggregata tubers

The present study investigated the effects of the ethanolic extract (ESa), fractions, and compounds isolated from Sinningia aggregata in male Swiss mice on carrageenan-induced paw edema, neutrophil migration, mechanical hyperalgesia, formalin-induced nociception, and lipopolysaccharide-induced fever. The ESa did not alter edema, neutrophil migration, or fever at any of the doses tested. However, the ESa reduced phase II of formalin-induced nociception and carrageenan-induced mechanical hyperalgesia. The petroleum ether (PE) and ethyl acetate (EA) fractions and aggregatin D (AgD; isolated from the EA fraction) reduced formalin-induced nociception. Anthraquinones from the PE fraction were ineffective. AgD also inhibited carrageenan-induced mechanical hyperalgesia. Neither the ESa nor AgD altered thermal nociception or motor performance. Local administration of AgD also reduced hyperalgesia induced by carrageenan, bradykinin, tumor necrosis factor-α, interleukin-1β, cytokine-induced neutrophil chemoattractant, prostaglandin E2, and dopamine but not hyperalgesia induced by forskolin or dibutyryl cyclic adenosine monophosphate. The positive control dipyrone reduced the response induced by all of the stimuli. Additionally, glibenclamide abolished the analgesic effect of dipyrone but not the one induced by AgD. AgD did not change lipopolysaccharide-induced nitric oxide production by macrophages or the nociception induced by capsaicin, cinnamaldehyde, acidified saline, or menthol. These results suggest that the ESa has important antinociceptive activity, and this activity results at least partially from the presence of AgD. AgD reduced mechanical hyperalgesia induced by several inflammatory mediators through mechanisms that are different from classic analgesic drugs.

Involvement of L-arginine/NO/cGMP/K(ATP) channel pathway in the peripheral antinociceptive actions of ellagic acid in the rat formalin test

The present study was conducted to evaluate the local antinociceptive actions of EA and the possible involvement of l-arginine/NO/cGMP/KATP channel pathway in this effect using formalin test in rats. To evaluate the involvement of l-arginine/NO/cGMP/KATP channel pathway in the antinociceptive action of EA, rats were pre-treated intraplantarlly with l-NAME (NOS inhibitor, 25-100μg/paw), methylene blue (guanylyl cyclase inhibitor, 100-400μg/paw), glibenclamide (ATP-sensitive K(+) channel blocker, 25-100μg/paw), l-arginine (a nitric oxide precursor, 25-100μg/paw) and sodium nitroprusside (125-500μg/paw). The local peripheral ipsilateral, but not contralateral, administration of EA into the right paw (30-300μg/paw) produced a dose-related antinociception during both early and late phases of formalin test which is comparable with morphine (25μg/paw). Moreover, local pre-treatment with l-NAME, methylene blue and glibenclamide dose-dependently prevented EA (100μg/paw)-induced antinociception in late phase. Additionally, administration of l-arginine and sodium nitroprusside significantly potentiated the antinociception induced by EA in the late phase. However, these treatments had no significant effect on antinociceptive response of EA in the early phase of the formalin test. The results of the present study showed that EA-induced local peripheral antinociception during the both phases of formalin test. Also, our data suggested the activation of the l-arginine/NO/cGMP/KATP channels pathway in EA-induced antinociception in late phase of formalin test. Topical application of EA by ointment or jelly might be a useful method to relieving the inflammatory pain states.

Antinociceptive effect of ethanol extract of leaves of Lannea coromandelica

ETHNOPHARMACOLOGICAL RELEVANCE

Lannea coromandelica (Houtt.) Merr. is a plant locally called "Jiga", found all over Bangladesh. Leaf of the plant is traditionally used in the treatment of local swellings, pains of body, toothache etc. This study evaluated the antinociceptive effect of the ethanol extract of L. coromandelica leaves (EELC).

MATERIALS AND METHODS

The antinociceptive activity of the extract (at the doses of 50, 100, and 200 mg/kg) was evaluated by using chemical- and heat-induced pain models such as acetic acid-induced writhing, hot plate, tail immersion, formalin, and glutamate test. To verify the possible involvement of opioid receptor in the central antinociceptive effect of EELC, naloxone was used to antagonize the effect. Besides, the involvements of ATP-sensitive K(+) channel and cGMP pathway were also justified by using glibenclemide and methylene blue.

RESULTS

EELC demonstrated significant dose-dependent antinociceptive activity in the chemical- and heat-induced nociception in mice models (p<0.05). These findings imply the involvement of both peripheral and central antinociceptive mechanisms. The use of naloxone confirmed the association of opioid receptors in the central antinociceptive effect. EELC also showed the involvements of ATP-sensitive K(+) channel and cGMP pathway for antinociceptive activity.

CONCLUSIONS

This study reported the antinociceptive activity of the leaf of L. coromandelica and rationalized the traditional use of the leaf in the treatment of different painful conditions.

Antinociceptive activity of methanolic extract of Muntingia calabura leaves: further elucidation of the possible mechanisms

Background

Muntingia calabura (Elaecoparceae) is a medicinal plant traditionally used, particularly, by the Peruvian people to alleviate headache and cold, pain associated with gastric ulcers or to reduce the prostate gland swelling. Following the recent establishment of antinociceptive activity of M. calabura leaf, the present study was performed to further elucidate on the possible mechanisms of antinociception involved.

Methods

The methanol extract of M. calabura (MEMC) was prepared in the doses of 100, 250 and 500 mg/kg. The role of bradykinin, protein kinase C, pottasium channels, and various opioid and non-opioid receptors in modulating the extract’s antinociceptive activity was determined using several antinociceptive assays. Results are presented as Mean ± standard error of mean (SEM). The one-way ANOVA test with Dunnett's multiple comparison was used to analyze and compare the data, with P < 0.05 as the limit of significance.

Results

The MEMC, at all doses, demonstrated a significant (p < 0.05) dose-dependent antinociceptive activity in both the bradykinin- and phorbol 12-myristate 13-acetate (PMA)-induced nociception. Pretreatment of the 500 mg/kg MEMC with 10 mg/kg glibenclamide (an ATP-sensitive K⁺ channel inhibitor), the antagonist of μ-, δ- and κ-opioid receptors (namely 10 mg/kg β-funaltrexamine, 1 mg/kg naltrindole and 1 mg/kg nor-binaltorphimine), and the non-opioid receptor antagonists (namely 3 mg/kg caffeine (a non-selective adenosinergic receptor antagonist), 0.15 mg/kg yohimbine (an α₂-noradrenergic antagonist), and 1 mg/kg pindolol (a β-adrenoceptor antagonist)) significantly (p < 0.05) reversed the MEMC antinociception. However, 10 mg/kg atropine (a non-selective cholinergic receptor antagonist), 0.15 mg/kg prazosin (an α₁-noradrenergic antagonist) and 20 mg/kg haloperidol (a non-selective dopaminergic antagonist) did not affect the extract's antinociception. The phytochemicals screening revealed the presence of saponins, flavonoids, tannins and triterpenes while the HPLC analysis showed the presence of flavonoid-based compounds.

Conclusions

The antinociceptive activity of MEMC involved activation of the non-selective opioid (particularly the μ-, δ- and κ-opioid) and non-opioid (particularly adenosinergic, α₂-noradrenergic, and β-adrenergic) receptors, modulation of the ATP-sensitive K⁺ channel, and inhibition of bradikinin and protein kinase C actions. The discrepancies in MEMC antinociception could be due to the presence of various phytochemicals.