The interaction between inhibitors of nitric oxide synthase and cyclooxygenase in formalin-induced pain in mice: an isobolographic study.

BACKGROUND: An interaction between nitric oxide (NO) and cyclooxygenases (COX) in the production of prostaglandins in carrageenan-induced inflammation has been established. However, limited information is available about the interaction between inducible NO synthase (iNOS) and COX inhibitors in pain perception. Therefore, in the present study we assessed the nature of the interaction between S-methylisothiourea (a moderately selective iNOS inhibitor) with rofecoxib (selective COX-2 inhibitor) and mefenamic acid (a nonselective COX inhibitor) in formalin- induced pain in mice. METHODS: The dose-response relation of S-methylisothiourea, rofecoxib, mefenamic acid, and their combination was studied in the late phase of formalin-induced pain in mice over the time spent in licking the hindpaw after formalin injection. The interaction was evaluated by simultaneous administration of fixed proportions of S-methylisothiourea with each COX inhibitor and the nature of the interaction was determined by isobolographic analysis. RESULTS: Each drug alone produced a dose-dependent suppression of the late stage of formalin-induced behaviors with rank order of potency being rofecoxib > mefenamic acid > S-methylisothiourea. Isobolographic analysis of the combination of S-methylisothiourea with rofecoxib or mefenamic acid revealed a synergistic interaction. The experimental ED50 of the combination was significantly lower than the theoretical additive ED50 of the corresponding drug combination that substantiated the synergistic interaction between iNOS or NO and COX isoforms. CONCLUSIONS: Our results explicitly indicate the synergistic nature of the interaction between NOS and COX inhibitors in formalin-induced nociceptive behavior in mice, and provide an alternative approach for controlling pain.

Interaction between inhibitors of inducible nitric oxide synthase and cyclooxygenase in adjuvant-induced arthritis in female albino rats: an isobolographic study.

We studied the interaction of S-methylisothiourea (a selective inducible nitric oxide synthase inhibitor) with rofecoxib (a selective cyclooxygenase-2 inhibitor) and mefenamic acid (a non-selective cyclooxygenase inhibitor) in adjuvant-induced arthritis in female albino Wistar rats, applying the isobolographic analysis. Each drug was effective in reducing the progressive increase in paw volume less than 50% except rofecoxib, when used alone. Log dose-response curve was obtained for each drug along with the corresponding ED(25). Following isobolographic analysis, combination of S-methylisothiourea with rofecoxib and mefenamic acid revealed supra-additive or synergistic interaction. Experimental ED(25) of the combinations was significantly lower than the theoretical ED(25) of the corresponding drug combination which substantiated the synergistic type of interaction between inducible nitric oxide synthase and cyclooxygenase in adjuvant-induced arthritis in female albino rats. Results suggest that NO regulates the cyclooxygenase enzyme activity as the activity of cyclooxygenase enzymes in the LPS-stimulated leukocyte lysates was significantly low or hardly detectable in the presence of varying concentrations of S-methylisothiourea. Simultaneous inhibition of inducible nitric oxide synthase and cyclooxygenase appears to offer an alternative approach for ameliorating the progression of arthritis.

Synergistic anti-inflammatory interaction between meloxicam and aminoguanidine hydrochloride in carrageenan-induced acute inflammation in rats.

Interaction studies with inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) inhibitor have been conducted to assess the nature of interaction and the possible therapeutic advantage. The interaction between meloxicam--a selective COX-2 inhibitor--and aminoguanidine hydrochloride--a selective iNOS inhibitor-- was examined in carrageenan-induced paw edema in rats. Appropriate statistical method was applied to detect the nature of anti-inflammatory interaction. Different doses of meloxicam (1, 3, 10 and 30 mg/kg) or aminoguanidine hydrochloride (10, 30, 100 and 300 mg/kg) were administered orally to adult male albino rats. Higher doses of meloxicam (3, 10 and 30 mg/kg) showed statistically significant anti-inflammatory effect. However, aminoguanidine hydrochloride did not show any anti-inflammatory activity. Combination of sub-threshold dose of meloxicam (1 mg/kg) with increasing doses of aminoguanidine hydrochloride (30, 100 and 300 mg/kg) resulted in synergistic anti-inflammatory effect. Combined therapy with sub-threshold dose of aminoguanidine hydrochloride (30 mg/kg) with increasing doses of meloxicam (1, 3, 10 and 30 mg/kg) also resulted in synergistic anti-inflammatory effect. The possible mechanism of interaction could be the stimulation of COX-2 activity by nitric oxide (NO) by combining with heme component. These results suggest that co-administration of meloxicam and aminoguanidine hydrochloride may be an alternative in clinical control of inflammation.

Interaction between inhibitors of inducible nitric oxide synthase and cyclooxygenase in Brewer's yeast induced pyrexia in mice: an isobolographic study.

We studied the interaction of S-methylisothiourea (a selective inducible nitric oxide synthase inhibitor) with rofecoxib (selective cyclooxygenase-2 inhibitor) and mefenamic acid (non-selective cyclooxygenase inhibitor) in Brewer's yeast-induced pyrexia in mice by isobolographic analysis. Each drug was effective in reducing pyrexia when used alone. Log-dose-response curves of all the three drugs did not show any significant departure from parallelism indicating thereby, a common mode of antipyretic action. However, rofecoxib exhibited significantly higher potency than S-methylisothiourea. Isobolographic analysis of combination of S-methylisothiourea with rofecoxib and mefenamic acid revealed additive interaction. Experimental ED(50) of the combinations was not significantly different from theoretical additive ED(50) of the corresponding drug combination, that substantiated the additive nature of interaction between inducible nitric oxide synthase and cyclooxygenase in Brewer's yeast-induced fever in mice. Results suggest involvement of a mediator that is subservient to both inducible nitric oxide synthase and cyclooxygenase-2 enzyme activities. For further investigation, peroxynitrite ion may be considered to be the putative mediator.