Abstract:Pain is an unpleasant sensation associated with a wide range of injuries and diseases, and affects approximately 20% of adults in the world. The discovery of new and more effective drugs that can relieve pain is an important research goal in both the pharmaceutical industry and academia. This review describes studies involving antinociceptive activity of essential oils from 31 plant species. Botanical aspects of aromatic plants, mechanisms of action in pain models and chemical composition profiles of the essential oils are discussed. The data obtained in these studies demonstrate the analgesic potential of this group of natural products for therapeutic purposes.

Piperine, an alkaloid present in the Piper genus, was shown to have an anticonvulsant activity, evaluated by the pilocarpine-induced model, in mice. Pilocarpine (350mg/kg, i.p.) was administered 30min after piperine (2.5, 5, 10 and 20mg/kg, i.p.) which significantly increased latencies to 1st convulsion and to death, and percentage of survivals. These parameters were also increased in the pilocarpine groups pretreated with atropine plus piperine (10 and 2.5mg/kg, respectively), as related to the pilocarpine group. However, they were not altered in the pilocarpine groups pretreated with memantine (a NMDA-type glutamate receptors blocker, 2mg/kg, p.o.) or nimodipine (a calcium channel blocker, 10mg/kg, p.o.), both associated with piperine (1 or 2.5mg/kg), as compared to the piperine plus pilocarpine group. Moreover, the pilocarpine group pretreated with diazepam (which binds to the GABAA receptor, 0.2 and 0.5mg/kg, i.p.) plus piperine (1 and 2.5mg/kg) significantly increased latency to the 1st convulsion, as related to the pilocarpine group, suggesting that the GABAergic system is involved with the piperine action. Furthermore, the piperine effect was blocked by flumazenil (2mg/kg, i.p.), a benzodiazepine antagonist. Untreated P350 animals showed decreased striatal DA and increased DOPAC and HVA levels that were not affected in the piperine plus pilocarpine groups. Piperine increased striatal levels of GABA, glycine and taurine, and reversed pilocarpine-induced increases in nitrite contents in sera and brain. Hippocampi from the untreated pilocarpine group showed an increased number of TNF-α immunostained cells in all areas, as opposed to the pilocarpine group pretreated with piperine. Taken together, piperine anticonvulsant effects are the result of its anti-inflammatory and antioxidant actions, as well as TNF-α reduction. In addition, piperine effects on inhibitory amino acids and on the GABAergic system may certainly contribute to the drug anticonvulsant activity.

In the present study, we evaluated omega-3 polyunsaturated fatty acid (PUFA) (consisting of 20:5n-3 and 22:6n-3) properties on inflammation and nociception. Among the in vivo tests, writhing, formalin, and hot plate tests were conducted in mice, and carrageenan-induced paw edema, peritonitis, and Hargreaves tests were performed in rats. Following the carrageenan-induced edema, immunohistochemistry for tumor necrosis factor-α (TNF-α) was also carried out. We found that omega-3 PUFA treatment significantly decreased acetic acid-induced abdominal contortions as well as the first and second phases of the formalin test, which were reversed by naloxone. The carrageenan-induced rat paw edema was significantly reduced, along with neutrophil migration to the peritoneal cavity in the omega-3 PUFA treatment. In addition, there was a decrease in TNF-α immunostained cells in the inflamed paw with the omega-3 treatment compared with no omega-3. Withdrawal threshold in response to the thermal stimulation was significantly increased by the omega-3 treatment in the Hargreaves and hot plate tests. The in vitro studies (myeloperoxidase, lactate dehydrogenase, MTT cell viability and lipid peroxidation assays) were performed in human neutrophils. These studies showed that omega-3 treatment significantly decreased myeloperoxidase release, presented no cytotoxicity, and did not alter lipid peroxidation. Our study suggests that omega-3 PUFA anti-inflammatory and antinociceptive actions may involve inhibition of cyclooxygenases and microglial activation, leading to a reduced release of proinflammatory cytokines such as TNF-α, among other factors. The omega-3 PUFAs are potential candidates used alone or in combination with conventional nonsteroidal anti-inflammatory drugs, for the treatment of diseases where inflammation plays an important role.

The aim of this study was to investigate the possible beneficial effects of amburoside A, AMB [4-(O-beta- D-glycopyranosyl)benzyl protocatechoate], against carbon tetrachloride (CCl (4)) toxicity in rats. AMB is a phenol glucoside from the Brazilian medicinal plant Amburana cearensis, popularly used for the treatment of respiratory tract affections. Acute AMB (25 and 50 mg/kg, I. P. or P. O.) treatments of CCl (4)-intoxicated rats significantly inhibited the increase in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, as compared to the group treated with CCl (4) only. Histological studies showed less centrolobular necrosis and inflammatory cell infiltrates in the liver of animals treated with AMB plus CCl (4), when compared to the group treated with CCl (4) alone. In hepatic tissues, AMB at both doses inhibited CCl (4)-induced thiobarbituric acid-reactive substances (TBARS) formation, indicating a blockade of CCl (4)-induced lipid peroxidation. AMB also reversed the decrement in glutathione contents of hepatic tissues in CCl (4)-intoxicated rats. Furthermore, it restored catalase activity to normal values, which was significantly increased after CCl (4) treatment. Our results indicate that CCl (4)-induced oxidative damage in hepatic tissues is reversed by AMB treatment. The protective effect of AMB is probably due to the phenolic nature of this glucoside.

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