Anti-inflammatory and antinociceptive activities of azadirachtin in mice.

Azadirachta indica (Meliaceae) extracts have been reported to exhibit anti-inflammatory and antinociceptive properties. However, the activities of azadirachtin, a limonoid and the major bioactive compound found in the extracts, have been poorly investigated in animal models. In the present study, we investigated the effects induced by azadirachtin in experimental models of pain and inflammation in mice. Carrageenan-induced paw edema and fibrovascular tissue growth induced by subcutaneous cotton pellet implantation were used to investigate the anti-inflammatory activity of azadirachtin in mice. Zymosan-induced writhing and hot plate tests were employed to evaluate the antinociceptive activity. To explore putative mechanisms of action, the level of tumor necrosis factor-α in inflammatory tissue was measured and the effect induced by opioidergic and serotonergic antagonists was evaluated. Previous per os (p. o.) administration of azadirachtin (120 mg/kg) significantly reduced the acute paw edema induced by carrageenan. However, the concomitant increase of the paw concentration of tumor necrosis factor-α induced by this inflammatory stimulus was not reduced by azadirachtin. In addition to inhibiting the acute paw edema induced by carrageenan, azadirachtin (6, 60, and 120 mg/kg) inhibited the proliferative phase of the inflammatory response, as demonstrated by the reduced formation of fibrovascular tissue growth. Azadirachtin (120 mg/kg) also inhibited the nociceptive response in models of nociceptive (hot plate) and inflammatory (writhing induced by zymosan) pain. The activity of azadirachtin (120 mg/kg) in the model of nociceptive pain was attenuated by a nonselective opioid antagonist, naltrexone (10 mg/kg, i. p.), but not by a nonselective serotonergic antagonist, cyproheptadine. In conclusion, this study demonstrates the activity of azadirachtin in experimental models of nociceptive and inflammatory pain, and also in models of acute and chronic inflammation. Finally, multiple mechanisms, including the inhibition of the production of inflammatory mediators and activation of endogenous opioid pathways, may mediate azadirachtin activities in experimental models of inflammation and pain.

The phthalimide analogues N-3-hydroxypropylphthalimide and N-carboxymethyl-3-nitrophthalimide exhibit activity in experimental models of inflammatory and neuropathic pain.

BACKGROUND: Phthalimide analogues devoid of the glutarimide moiety exhibit multiple biological activities, thus making them candidates for the treatment of patients with different diseases, including those with inflammatory and painful disorders. In the present study, the activities of five phthalimide analogues devoid of the glutarimide moiety (N-hydroxyphthalimide, N-hydroxymethylphthalimide, N-3-hydroxypropylphthalimide, N-carboxy-3-methylphthalimide, N-carboxymethyl-3-nitrophthalimide) were evaluated in experimental models of acute and chronic inflammatory and neuropathic pain. METHODS: The phthalimide analogues were administered per os (po) in Swiss mice or Wistar rats. Nociceptive response induced by formaldehyde and mechanical allodynia induced by chronic constriction injury (CCI) of the sciatic nerve or intraplantar (ipl) injection of complete Freund's adjuvant (CFA) were used as experimental models of pain. RESULTS: N-carboxymethyl-3-nitrophthalimide (700 mg/kg, -1 h) inhibited the second phase of the nociceptive response induced by the intraplantar injection of formaldehyde in mice. N-3-hidroxypropylphthalimide (546 mg/kg, -1 h) inhibited both phases of the nociceptive response induced by formaldehyde. Treatment of rats with N-carboxymethyl-3-nitrophthalimide (700 mg/kg) or N-3-hydroxypropylphthalimide (546 mg/kg) inhibited the mechanical allodynia induced by CCI of the sciatic nerve or ipl injection of CFA in rats. Intraperitoneal administration of the opioid antagonist naltrexone (10 mg/kg, -1.5 h) attenuated the antinociceptive activity of N-carboxymethyl-3-nitrophthalimide (700 mg/kg) in the model of nociceptive response induced by formaldehyde. CONCLUSIONS: N-3-hydroxypropylphthalimide and N-carboxymethyl-3-nitrophthalimide, two phthalimide analogues devoid of the glutarimide moiety, exhibited activities in different experimental models of pain, including models of chronic inflammatory and neuropathic pain.

Antiallodynic activity of leflunomide is partially inhibited by naltrexone and glibenclamide and associated with reduced production of TNF-α and CXCL-1.

Leflunomide, an immunosuppressive drug approved for the treatment of patients with rheumatoid arthritis, exhibits many mechanisms which may affect the nociceptive processing. Therefore, the present study aimed to evaluate the effect induced by leflunomide on the mechanical allodynia in models of inflammatory and neuropathic pain in mice and investigate mechanisms mediating such effects. Per os (p.o.) administration of leflunomide (25, 50 or 100mg/kg) inhibited the inflammatory edema and mechanical allodynia induced by intraplantar carrageenan. Even ongoing inflammatory edema and mechanical allodynia were reduced by leflunomide. Previous administration of naltrexone (10mg/kg, intraperitoneal) or glibenclamide (40mg/kg, p.o.) partially attenuated leflunomide antiallodynic activity. A single administration of leflunomide (50 or 100mg/kg, p.o.) also partially inhibited ongoing mechanical allodynia induced by chronic constriction injury (CCI) or repeated administrations of paclitaxel. The antiallodynic effect induced by leflunomide (50 or 100mg/kg, p.o.) in the model of neuropathic pain induced by CCI was associated with reduced production of tumor necrosis factor-α both at the injury site and ipsilateral paw. Leflunomide also reduced production of the chemokine CXCL-1 at the paw ipsilateral to the injury site. Concluding, leflunomide partially inhibited ongoing mechanical allodynia in models of inflammatory and neuropathic pain. The antiallodynic effect was associated with activation of opioidergic receptors and ATP-sensitive potassium channels and reduced production of inflammatory mediators. These data indicate leflunomide as a drug that should be further investigated aiming to identify a new analgesic pharmacotherapy and reinforces repositioning as an important strategy to identify new uses for approved drugs.

Thiamine and riboflavin inhibit production of cytokines and increase the anti-inflammatory activity of a corticosteroid in a chronic model of inflammation induced by complete Freund's adjuvant.

BACKGROUND: The effects induced by thiamine and riboflavin, isolated or in association with corticosteroids, in models of chronic inflammation are not known. Thus, we evaluated the effect induced by these B vitamins, isolated or in association with dexamethasone, on the mechanical allodynia, paw edema and cytokine production induced by complete Freund's adjuvant (CFA) in rats. METHODS: Chronic inflammation was induced by two injections of CFA. Nociceptive threshold, paw volume and body temperature were evaluated for 21days. Tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) contents were determined in paw tissue. Riboflavin (125, 250 or 500mg/kg) or thiamine (150, 300 or 600mg/kg) were administered per os (po), twice daily. Dexamethasone (0.5mg/kgday, po) was administered every three days. RESULTS: CFA induced long lasting mechanical allodynia and paw edema. Elevation of body temperature was observed for a short period. Riboflavin reduced neither paw edema nor mechanical allodynia. Thiamine did not change paw edema, but partially inhibited mechanical allodynia. Riboflavin (500mg/kg) and thiamine (600mg/kg) exacerbated the anti-inflammatory activity of dexamethasone. Riboflavin, thiamine and dexamethasone reduced TNF-α and IL-6 production. The association of dexamethasone with thiamine induced greater inhibition of IL-6 production when compared with that induced by dexamethasone. CONCLUSIONS: Riboflavin and thiamine exacerbate the anti-inflammatory activity of dexamethasone and reduce production of TNF-α and IL-6.

Opioid pathways activation mediates the activity of nicorandil in experimental models of nociceptive and inflammatory pain.

We have previously demonstrated that nicorandil inhibits the second phase of the nociceptive response induced by formaldehyde. In the present study, we evaluated the effects induced by nicorandil in other models of nociceptive and inflammatory pain in mice and also whether opioid pathways activation mediates its activity. As we have previously demonstrated, per os (p.o.) administration of nicorandil (50, 100 or 150mg/kg; -1h) inhibited the second phase of the nociceptive response induced by intraplantar (i.pl.) injection of formaldehyde. Nicorandil (50, 100 or 150mg/kg; p.o., -1h) also exhibited activity in models of inflammatory pain induced by i.pl. injection of carrageenan (300µg) and nociceptive pain induced by exposure to noxious heat (50°C). Intraperitoneal (i.p.) administration of the opioid antagonist naltrexone (1, 5 or 10mg/kg, -30min) attenuated or abolished the antinociceptive activity of nicorandil (100mg/kg, p.o.) in the three experimental pain models. In conclusion, we demonstrate that nicorandil exhibits activity in different models of nociceptive and inflammatory pain. The demonstration that the antinociceptive effect induced by nicorandil is markedly attenuated by an opioid antagonist provides solid information about an important mechanism mediating the activity of this antianginal drug. Altogether, our data suggest that the clinical pain relief induced by nicorandil in heart ischemic conditions may result from both vasodilation and intrinsic analgesic activity.

Activities of 2-phthalimidethyl nitrate and 2-phthalimidethanol in the models of nociceptive response and edema induced by formaldehyde in mice and preliminary investigation of the underlying mechanisms.

The activities of 2-phthalimidethyl nitrate (PTD-NO) and 2-phthalimidethanol (PTD-OH) were recently demonstrated in models of pain and inflammation. We expanded our investigation by evaluating their activities in models of nociceptive and inflammatory pain and inflammatory edema, the preliminary pharmacokinetic parameter for PTD-NO and the role of opioid and cannabinoid pathways in the activity of analogs. Per os (p.o.) administration of PTD-NO or PTD-OH, 1h before intraplantar injection of formaldehyde, inhibited both phases of the nociceptive response (500 and 750 mg/kg) and paw edema (125, 250, 500 and 750 mg/kg). After p.o. administration of PTD-NO, peak plasma concentrations of PTD-NO and PTD-OH were found 0.92 and 1.13 h, respectively. The plasma concentrations of PTD-NO were higher than those of PTD-OH. Intraperitoneal (i.p.) administration of CB1 (AM251) or CB2 (AM630) cannabinoid receptor antagonists (4 or 8 mg/kg, -30 min) or opioid antagonist naltrexone (5 or 10mg/kg, -30 min) did not affect the antinociceptive activities of the analogs. AM251 (8 mg/kg, i.p., -30 min) attenuated the antiedematogenic activity of both analogs, while naltrexone (10mg/kg, i.p., -30 min) only attenuated the antiedematogenic activity of PTD-NO. The antiedematogenic activities of both analogs were not affected by the CB2 cannabinoid antagonist AM630 (4 or 8 mg/kg, i.p., -30 min). Concluding, we expanded the knowledge on the activities of PTD-NO and PTD-OH by showing that these phthalimide analogs also exhibit marked activity in models of nociceptive and inflammatory pain and inflammatory edema. Opioid and cannabinoid mechanisms partially mediate the anti-inflammatory, but not the antinociceptive activity.

Activities of 2-phthalimidethanol and 2-phthalimidethyl nitrate, phthalimide analogs devoid of the glutarimide moiety, in experimental models of inflammatory pain and edema.

The reintroduction of thalidomide in the pharmacotherapy greatly stimulated the interest in the synthesis and pharmacological evaluation of phthalimide analogs with new and improved activities and also greater safety. In the present study, we evaluated the activities of two phthalimide analogs devoid of the glutarimide ring, namely 2-phthalimidethanol (PTD-OH) and 2-phthalimidethyl nitrate (PTD-NO), in experimental models of inflammatory pain and edema in male C57BL/6J mice. Intraplantar (i.pl.) injection of carrageenan (300 µg) induced mechanical allodynia and this response was inhibited by previous per os (p.o.) administration of PTD-OH and PTD-NO (750 mg/kg) and also by thalidomide (500 or 750 mg/kg). The edema induced by carrageenan was also inhibited by previous p.o. administration of PTD-OH (500 and 750 mg/kg) and PTD-NO (125, 250, 500 or 750 mg/kg), but not by thalidomide. Carrageenan increased tumor necrosis factor (TNF)-α and CXCL1 concentrations and also the number of neutrophils in the paw tissue. Previous p.o. administration of PTD-NO (500 mg/kg) reduced all the parameters, while PTD-OH (500 mg/kg) reduced only the accumulation of neutrophils. Thalidomide, on the other hand, was devoid of effect on these biochemical parameters. Plasma concentrations of nitrite were increased after p.o. administration of the phthalimide analog coupled to a NO donor, PTD-NO (500 mg/kg), but not after administration of PTD-OH or thalidomide. In conclusion, our results show that small molecules, structurally much simpler than thalidomide or many of its analogs under investigation, exhibit similar activities in experimental models of pain and inflammation. Finally, as there is evidence that the glutarimide moiety contributes to the teratogenic effect of many thalidomide analogs, our results indicate that phthalimide analogs devoid of this functional group could represent a new class of analgesic and anti-inflammatory candidates with potential greater safety.