Evaluation of the Antinociceptive, Antiallodynic, Antihyperalgesic and Anti-Inflammatory Effect of Polyalthic Acid.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are very commonly used, but their adverse effects warrant investigating new therapeutic alternatives. Polyalthic acid, a labdane-type diterpenoid, is known to produce gastroprotection, tracheal smooth muscle relaxation, and antitumoral, antiparasitic and antibacterial activity. This study aimed to evaluate the antinociceptive, antiallodynic, antihyperalgesic and anti-inflammatory effect of polyalthic acid on rats. Moreover, the effectiveness of treating hyperalgesia with a combination of polyalthic acid and naproxen was analyzed, as well as the type of drug-drug interaction involved. Nociception was examined by injecting 1% formalin into the right hind paw and thermal hyperalgesia and inflammation by injecting a 1% carrageenan solution into the left hind paw of rats. Allodynia was assessed on an L5/L6 spinal nerve ligation model. Polyalthic acid generated significant antinociceptive (56-320 mg/kg), antiallodynic (100-562 mg/kg), and antihyperalgesic and anti-inflammatory (10-178 mg/kg) effects. Antinociception mechanisms were explored by pretreating the rats with naltrexone, ODQ and methiothepin, finding the effect blocked by the former two compounds, which indicates the participation of opioid receptors and guanylate cyclase. An isobolographic analysis suggests synergism between polyalthic acid and naproxen in the combined treatment of hyperalgesia.

In vitro effects of Crotalus atrox snake venom on chick and mouse neuromuscular preparations.

The neuromuscular effect of venoms is not a major clinical manifestation shared between rattlesnakes native to the Americas, which showed two different venom phenotypes. Taking into account this dichotomy, nerve muscle preparations from mice and chicks were used to investigate the ability of Crotalus atrox venom to induce in vitro neurotoxicity and myotoxicity. Unlike crotalic venoms of South America, low concentrations of C. atrox venom did not result in significant effects on mouse neuromuscular preparations. The venom was more active on avian nerve-muscle, showing reduction of twitch heights after 120 min of incubation with 10, 30 and 100 µg/mL of venom with diminished responses to agonists and KCl. Histological analysis highlighted that C. atrox was myotoxic in both species of experimental animals; as evidenced by degenerative events, including edematous cells, delta lesions, hypercontracted fibers and muscle necrosis, which can lead to neurotoxic action. These results provide key insights into the myotoxicity and low neurotoxicity of C. atrox in two animal models, corroborating with previous genomic and proteomic findings and would be useful for a deeper understanding of venom evolution in snakes belonging to the genus Crotalus.

Antihyperalgesic effects of a novel muscarinic agonist (LASSBio-873) in spinal nerve ligation in rats.

New chemicals or adjuvants with analgesic effects on chronic pain are needed and clinically relevant due to the limited number of effective compounds that possess these characteristics. LASSBio-873, a pyrazolo[3,4-b]pyrrolo[3,4-d]pyridine derivative, activates muscarinic cholinergic receptors and has potent analgesic effects on acute and inflammatory pain. The present study evaluated the therapeutic and prophylactic effects of oral administration of LASSBio-873 in a spinal nerve ligation (SNL) model of chronic peripheral nerve injury. LASSBio-873 (100 mg/kg) inhibited the development of thermal hyperalgesia and mechanical allodynia when administered once daily for 7 consecutive days after SNL surgery and reversed these symptoms. LASSBio-873 treatment did not alter rat behaviour in open field testing measured during the first 24 h after administration and again after 7 continuous days administration. The analgesic effect of LASSBio-873 was inhibited by intrathecal methoctramine, an M2 receptor antagonist, implicating the muscarininc M2 receptor signalling pathway in the drug's action. These results reinforce the potential of LASSBio-873 as a possible prototype for the development of more effective alternatives for the treatment of neuropathic pain.

The antinociceptive properties of the novel compound (±)-trans-4-hydroxy-6-propyl-1-oxocyclohexan-2-one in acute pain in mice.

The compound (±)-trans-4-hydroxy-6-propyl-1-oxocyclohexan-2-one [(±)-δ-lactone] was isolated from the plant Vitex cymosa Bertero, and determined to be the active principle. The present study aimed to evaluate the antinociceptive effect of (±)-δ-lactone and to elucidate its mechanism of action. Mice were subjected to in-vivo models of acute pain (acetic acid-induced abdominal writhing, formalin and hot-plate tests) and the open-field test. (±)-δ-Lactone, administered orally (6-900 µmol/kg), exerted a dose-dependent antinociceptive effect in the acetic acid-induced abdominal writhing, formalin and hot-plate tests. (±)-δ-Lactone administered by the intrathecal (i.t.) and subplantar (s.p.) routes (10-600 nmol) exerted concentration-dependent antinociceptive effects in the formalin test, showing its spinal and peripheral activity, respectively. In the hot-plate test, (±)-δ-lactone was also active when administered i.t., confirming its spinal effect. The previous intraperitoneal (i.p.) application of naloxone, yohimbine, mecamylamine or glibenclamide did not alter the effect produced by the i.t. administration of (±)-δ-lactone, whereas the previous application of atropine and L-arginine significantly reduced its effects in the formalin and hot-plate tests. The previous i.p. application of L-NAME enhanced the antinociceptive effect of the i.t. administration of (±)-δ-lactone in the formalin and hot-plate tests. The previous i.p. application of L-NAME and L-arginine increased and decreased, respectively, the activity of (±)-δ-lactone administered by s.p. administration. These results indicate that (±)-δ-lactone has significant spinal and peripheral antinociceptive activity, and that its effects are at least partially mediated by a reduced nitric oxide production/release, most likely through mechanisms involving the cholinergic system.

The effect of intrathecal gabapentin on neuropathic pain is independent of the integrity of the dorsolateral funiculus in rats.

AIM: This study evaluates the contribution of inhibitory pain pathways that descend to the spinal cord through the dorsolateral funiculus (DLF) on the effect of intrathecal gabapentin against spinal nerve ligation (SNL)-induced behavioral hypersensitivity to mechanical stimulation in rats. MAIN METHOD: Rats were submitted to a sham or complete ligation of the right L5 and L6 spinal nerves and a sham or complete DLF lesion. Next, the changes induced by intrathecal administration of gabapentin on the paw withdrawal threshold of rats to mechanical stimulation were evaluated electronically. KEY FINDINGS: Intrathecal gabapentin (200µg/5µl) that was injected 2 or 7days after surgery fully inhibited the SNL-induced behavioral hypersensitivity to mechanical stimulation in sham DLF-lesioned rats; gabapentin was effective against the SNL-induced behavioral hypersensitivity to mechanical stimulation also in DLF-lesioned rats. SIGNIFICANCE: The effect of intrathecally administered gabapentin against SNL-induced behavioral hypersensitivity to mechanical stimulation in rats does not depend on the activation of nerve fibers that descend to the spinal cord via the DLF.

Contribution of peripheral endothelin ETA and ETB receptors in neuropathic pain induced by spinal nerve ligation in rats.

Endothelins (ETs) contribute to the sensory changes seen in animals models of inflammatory, cancer and diabetic neuropathic pain, but little is known about their nociceptive role following peripheral nerve injury. The current study evaluated mechanisms by which ETs can drive changes in nociceptive responses to thermal stimulation of the hind paw of rats induced by unilateral lumbar L5/L6 spinal nerve ligation (SNL) injury. SNL sensitizes rats to acetone-evoked cooling of and radiant heat application (Hargreaves test) to the ipsilateral hind paw (throughout 3-40 and 9-40 days after surgery, respectively). At 12 days after SNL, intraplantar (i.pl.) injection of endothelin-1 (ET-1, 10 pmol) induces greater overt nociception that was reduced only by treatment with the selective ET(A) peptidic antagonist (BQ-123, 10 nmol, i.pl), but unchanged by the selective ET(B) peptidic antagonist (BQ-788). Cold allodynia evoked by cooling the ipsilateral hind paw with acetone was reduced by i.pl. injection of both antagonists BQ-123 or BQ-788 (3 or 10 nmol). In contrast, heat hyperalgesia evaluated by Hargreaves method was reduced only by BQ-123. SNL enhanced the [Ca(+2)](i) increases induced by ET-1 (100 nM) in neurons from L5/L6 (injured) and L4 (intact) cultured dorsal root ganglion, but did not change the responses of non-neuronal cells. Furthermore, Western blot analysis revealed that SNL increased ET(A) and ET(B) receptor protein expression in spinal nerves. Thus, SNL induces marked hind paw hypersensitivity to thermal stimulation in part via up-regulation of peripheral sensory nerve pronociceptive ET(A) and ET(B) receptor-operated mechanisms.

Peripheral kinin B(1) and B(2) receptor-operated mechanisms are implicated in neuropathic nociception induced by spinal nerve ligation in rats.

The kinin system can contribute distinctly to the sensory changes associated with different models of nerve injury-induced neuropathic pain. This study examines the roles of kinin B(1) and B(2) receptor-operated mechanisms in alterations in nociceptive responses of rats submitted to unilateral L5/L6 spinal nerve ligation (SNL) injury. Behavioural responses to ipsilateral hind paw stimulation with acetone (evaporation-evoked cooling), radiant heat (Hargreaves method) or von Frey hairs revealed that SNL rats developed long-lasting cold allodynia (from Days 3 to 40 post-surgery, peak on Day 6), heat hyperalgesia (stable peak from Days 9 to 36) and tactile allodynia (stable peak from Days 3 to 51). SNL rats manifested nocifensive responses to intraplantar injections on Day 12 of the selective B(1) receptor agonist des-Arg(9)-bradykinin (DABK) and augmented responses to the selective B(2) receptor agonist bradykinin (BK; each at 0.01-1nmol/paw). Systemic treatment of SNL rats with des-Arg(9)-Leu(8)-BK or HOE 140 (peptidic B(1) and B(2) receptor antagonists, respectively; 0.1-1mumol/kg, i.p.) selectively blocked responses triggered by DABK and BK (1nmol/paw) and alleviated partially and transiently established cold allodynia, heat hyperalgesia and (to a lesser extent) tactile allodynia. Western blot analysis revealed enhanced expression of kinin B(1) and B(2) receptor protein in ipsilateral L4-L6 spinal nerve and hind paw skin samples collected on Day 12 after SNL surgery. These results indicate that peripheral pronociceptive kinin B(1) and B(2) receptor-operated mechanisms contribute significantly to the maintenance of hind paw cold and mechanical allodynia and heat hyperalgesia induced by L5/L6 SNL in rats.