Antioxidant Activity, Molecular Docking, Quantum Studies and In Vivo Antinociceptive Activity of Sulfonamides Derived From Carvacrol.

The synthesis and antioxidant, antinociceptive and antiedematogenic activities of sulfonamides derived from carvacrol-a druglike natural product-are reported. The compounds showed promising antioxidant activity, and sulfonamide derived from morpholine (S1) demonstrated excellent antinociceptive and antiedematogenic activities, with no sedation or motor impairment. The mechanism that underlies the carvacrol and derived sulfonamides' relieving effects on pain has not yet been fully elucidated, however, this study shows that the antinociceptive activity can be partially mediated by the antagonism of glutamatergic signaling. Compound S1 presented promising efficacy and was predicted to have an appropriate medicinal chemistry profile. Thus, derivative S1 is an interesting starting point for the design of new leads for the treatment of pain and associated inflammation and prooxidative conditions.

Neurobiological mechanisms of antiallodynic effect of transcranial direct current stimulation (tDCS) in a mice model of neuropathic pain.

BACKGROUND: Neuropathic pain is relatively common and occurs in approximately 6-8% of the population. It is associated with allodynia and hyperalgesia. Thus, non-pharmacological treatments, such as transcranial direct current stimulation (tDCS) may be useful for relieving pain. OBJECTIVES: This study aimed to investigate the antiallodynic effect of tDCS in a mice model of neuropathic pain, and the underlying neurotransmission systems that could drive these effects. METHODS: Male, Swiss mice, weighing 25-35 g, were subjected to partial sciatic nerve ligation (PSNL). Allodynia was assessed using a Von Frey filament (0.6 g). First, the behavioral time-course of these mice was assessed after 5, 10, 15 and 20 min of tDCS (0.5 mA). Second, the mice that underwent PSNL were assigned to either the tDCS (0.5 mA, 15 min) or tDCS sham group, and further assigned to receive either saline or a drug (i.e., naloxone, yohimbine, a-methyl-p-tyrosine, q-chlorophenylalanine methyl ester, caffeine, 1,3-dipropyl-8-cyclopentylxanthine, AM281, AM630, flumazenil, MK-801, or lidocaine). RESULTS: The antiallodynic effect of tDCS lasted 2 h and 4 h, after 10 min and 15 or 20 min of treatment, respectively (P < .001, P < .01, and P < .05, respectively). The antiallodynic effect of tDCS was associated with all the systems that were analyzed, i.e., the opioidergic (P < .01), adenosinergic (P < .001), serotonergic (P < .01), noradrenergic (P < .001), cannabinoid (P < .001), GABAergic, and glutamatergic (P < .001) systems. Lidocaine did not reverse the antiallodynic effect of tDCS (P > .05). CONCLUSION: The antiallodynic effect of tDCS was associated with different neurotransmitters systems; the duration of these after-effects depended on the time exposure to tDCS.

Antinociceptive effect of hydroalcoholic extract and isoflavone isolated from Polygala molluginifolia in mice: evidence for the involvement of opioid receptors and TRPV1 and TRPA1 channels.

PURPOSE: The plants of the genus Polygala (Polygalaceae) have been used for a long time in folk medicine to treat pain and inflammation. The species Polygala molluginifolia is native to southern Brazil and is popularly known as "cânfora". The presented study analyzes the antinociceptive effect of hydroalcoholic extract from Polygala molluginifolia (HEPm) and an isoflavone (ISO) isolated from the extract, in behavioral models of pain in mice, as well as the mechanism underlying this effect. MATERIALS AND METHODS: The phytochemical analysis of HEPm was performed through a capillary electrophoresis analysis and colorimetric test. The antinociceptive effects of HEPm and ISO (10-1000 mg/kg, i.g.) were evaluated by applying the formalin test; mechanical and thermal hyperalgesia to postoperative pain in mice. The possible involvement of opioid receptors, TRPV1 and TRPA1 channels in the antinociceptive effect of HEPm and ISO were also evaluated. Finally, the nonspecific effects of HEPm and ISO were evaluated by measuring locomotor activity (Open-field Test) and corporal temperature. RESULTS: The 5,3',4'-trihydroxy-6″,6″-dimethylpyrano[2″,3″:7,6] isoflavone (ISO) was identified in HEPm by capillary electrophoresis analysis and selected for the experimental tests. The oral administration of HEPm or of ISO significantly inhibited the neurogenic and inflammatory phases of formalin-induced pain, edema formation and local hyperemia, without causing any change to locomotor activity. Acute and repeated treatment of animals with HEPm reduced mechanical and thermal (heat and cold) hyperalgesia in the postoperative pain. In addition, administering HEPm or ISO markedly reduced nociceptive behavior induced by the peripheral and central injection of TRPV1 and TRPA1 channels activators. Finally, the antinociception provided by the administration of HEPm or ISO was reversed by the preadministration of naloxone. CONCLUSIONS: Taken together, these results provide the first experimental evidence of the significant antinociceptive effect of HEPm and ISO in animal models of acute pain without causing sedation or locomotor dysfunction. This effect appears to be mediated, at least in part, by the activation of opioid receptors and/or by the inhibition of TRPV1 and TRPA1 channels. Moreover, this study adds new scientific evidence and highlights the therapeutic potential of the medicinal plant Polygala molluginifolia in the development of phytomedicines with analgesic properties.

Ameliorative potential of standardized fruit extract of Pterodon pubescens Benth on neuropathic pain in mice: Evidence for the mechanisms of action.

ETHNOPHARMACOLOGICAL RELEVANCE: The medicinal plant Pterodon pubescens Benth has been traditionally used for a long time to treat rheumatic diseases due to its anti-inflammatory and analgesic activities. The present study aims to evaluate the antinociceptive effect of ethanolic extract from P. pubescens fruits (EEPp) in a model of neuropathic pain in mice. MATERIALS AND METHODS: The phytochemical analysis of EEPp was performed through GC-MS, HPLC and colorimetric analysis. The antinociceptive effects of EEPp (30-300 mg/kg, i.g.) were evaluated on mechanical and thermal (cold or heat) hyperalgesia in neuropathic pain induced by partial sciatic nerve ligation (PSNL) in mice. We also investigated the effects of EEPp on the nociceptive response induced by intrathecal injection (i.t.) of ionotropic (AMPA, NMDA and kainate) and metabotropic (trans-ACPD) glutamate receptor agonists, proinflammatory cytokines such as IL-1ß and TNF-α, as well as TRPV1 and TRPA1 agonists. In addition, we also investigated the safety profile of prolonged treatment with EEPp in mice. RESULTS: The phytochemical analysis showed a higher amount terpenes, being nine sesquiterpenes and seven diterpenes with vouacapan skeletons, as well as a small amount of phenols and flavonoids. The exact mechanism by which EEPp promotes its antinociceptive effect is not yet fully understood, but its oral administration causes significant inhibition of glutamate-, kainate-, NMDA-, trans-ACPD-induced biting responses, as well as of proinflammatory cytokines (TNF-α and IL-1ß) and TRPV1 and TRPA1 channels activators (capsaicin and cinnamaldehyde, respectively). These results may indicate, at least in part, some of the mechanisms that are involved in this effect. In particular, EEPp decreases neuropathic pain and clearly shows, for the first time, a thermal and mechanical hyperalgesia reduction in the model of partial sciatic nerve ligation (PSNL), without inducing tolerance. Furthermore, the prolonged treatment with EEPp (300 mg/kg, i.g.) showed a cumulative effect over 24h, in the 15th day, after last treatment. In addition, the open-field test showed that doses up to 300 mg/kg in both treatments, acute and/or prolonged, did not affect the motor activity of mice. Also, EEPp showed no toxicity according to the serum levels of the renal and hepatic injury indicators or observed macroscopic organs, after PSNL. CONCLUSIONS: Taken together, these results provide the first experimental evidence of the significant antinociceptive effect of EEPp on neuropathic pain without causing side effects, such as sedation or locomotor dysfunction. Moreover, these results appear to be mediated, at least in part, by the inhibition of glutamatergic receptors, TRPV1 and TRPA1 channels and proinflammatory cytokines. Thus, this study adds new scientific evidence and highlights the therapeutic potential of the medicinal plant P. pubescens in the development of phytomedicines for the management of neuropathic pain.