The profile of FR140423, a novel anti-inflammatory compound, in yeast-induced rat hyperalgesia

Effect of systemic FR140423, a new analgesic compound, in a rat model of postoperative pain: contribution of delta-opioid receptors

We investigated the anti-hyperalgesic effect of FR140423, 3-(difluoromethyl)-1-(4-methoxyphenyl-5-[4-(methylsulfinyl)phenyl]pyrazole, in a rat model of postoperative pain. Oral administration of FR140423 at doses between 1 and 100 mg/kg after surgery dose dependently attenuated the punctate mechanical hyperalgesia caused by an incision of the plantar surface of the hind paw with an ED50 value of 59 mg/kg. The anti-hyperalgesic effect of systematically administered FR140423 was blocked by naloxone, a non-selective opioid receptor antagonist. Furthermore, the delta-opioid receptor antagonist naltrindole (0.2 mg/kg) reversed anti-hyperalgesia induced by FR140423. Naloxonazine and nor-binaltorphimine failed to antagonize the anti-hyperalgesic effect of FR140423. The action of FR140423 differs from the naloxonazine-reversible anti-hyperalgesia induced by morphine. The present findings suggest that delta-opioid systems play a role in the rat anti-hyperalgesia produced by FR140423 for postoperative pain characterized by mechanical hyperalgesia.

FR143166 attenuates spinal pain transmission through activation of the serotonergic system

We investigated the antinociceptive effect of 1-(4-fluorophenyl)-3-methyl-5-[4-(methylsulfinyl)phenyl]pyrazole (FR143166) in the tail-pinch test in mice. The p.o. and i.t. injection of FR143166 exerted dose-dependent antinociceptive actions with ED(50) values of 24 mg/kg and 15 micro g/mouse, respectively. However, i.c.v. injection of FR143166 at a maximum dose of 128 micro g/mouse did not show any antinociceptive effect. The antinociceptive effect of FR143166 injected i.t. was abolished by co-administration of the nonselective serotonin (5-hydroxytryptamine, 5-HT) receptor antagonist, methysergide, but not by the adrenoceptor antagonists, phentolamine and propranolol. Moreover, the effect of FR143166 was also reversed by the 5-HT(2A) receptor antagonist, ketanserin, and the 5-HT(3) receptor antagonist, MDL-72222 (3-tropanyl-3,5-dichlorobenzoate). The effect of FR143166 was attenuated by p-chlorophenylalanine, but not by 6-hydroxydopamine plus nomifensine pretreatment. These results suggest that the descending serotonergic system, especially spinal 5-HT(2A) and 5-HT(3) receptors, is involved in the antinociceptive activity of spinally administered FR143166 on noxious mechanical stimuli.

The spinal antinociceptive effect of FR140423 is mediated through kyotorphin receptors

We investigated the antinociceptive effect of a novel anti-inflammatory and analgesic drug, 3-(difluoromethyl)-1-(4-methoxyphenyl)-5-[4-(methylsulfinyl)phenyl]pyraz ole (FR140423), in the tail-pinch test in mice, and evaluated the mechanism of action of FR140423 using L-leucyl-L-arginine (Leu-Arg), a kyotorphin (endogenous Met-enkephalin releaser) receptor antagonist, L-NG-nitroarginine methylester (L-NAME), an inhibitor of nitric oxide (NO) synthase, and methylene blue (MB), an inhibitor of activation of guanylate cyclase. Oral administration of FR140423, at doses of 5-80 mg/kg, produced a dose-dependent antinociceptive effect with an ED50 value of 18 mg/kg. This antinociception was reversed by intrathecal (i.t.) (10 microg/mouse), but not by intracerebroventricular (i.c.v.) (100 microg/mouse), injection of Leu-Arg. Moreover, the antinociceptive effect of i.t. injection of FR140423 with an ED50 value of 3.7 microg/mouse was completely antagonized by co-administered Leu-Arg 10 microg/mouse. However, L-NAME (2000 mg/kg s.c.) and MB (200 mg/kg s.c.) did not antagonize the antinociception of FR140423. These findings suggest that FR140423 plays a role in nociceptive modulation in the spinal cord, being antinociceptive via the kyotorphin-Met-enkephalin pathway but not via the peripheral NO-cyclic GMP pathway.

Antinociceptive properties of FR140423 mediated through spinal delta-, but not mu- and kappa-, opioid receptors

We investigated the antinociceptive effect of FR140423, 3-(difluoromethyl)-1-(4-methoxyphenyl)-5-[4-(methylsulfinyl)phenyl] pyrazole, in the tail-pinch test in mice, and evaluated the mechanism of action using various opioid receptor antagonists. P.o. and i.t. injection of FR140423 exerted dose-dependent antinociceptive activities with ED50 values of 21 mg/kg and 3.1 microg/mouse, respectively. However, i.c.v. injection of FR140423 did not show an antinociceptive effect. The antinociceptive effects of FR140423 were completely abolished by naloxone and naltrindole but not by naloxonazine, beta-funaltrexamine and nor-binaltorphimine. FR140423 did not affect any opioid receptor binding in mouse spinal membranes at concentrations up to 100 microM in vitro. Naloxone-induced jumping and diarrhea tests for morphine-like physical dependence of FR140423 gave negative results. These results suggest that FR140423 can induce antinociception by acting on the spinal but not the supraspinal site, and that spinal delta-opioid systems indirectly play a role in the antinociception produced by FR140423 in mice.