Isobolographic analysis of interaction between cyclooxygenase inhibitors and tramadol in acetic acid-induced writhing in mice.

Non-steroidal anti-inflammatory drugs (NSAIDs) and opioids are the most commonly used analgesics in the management of acute and chronic pain. Combined use of NSAIDs and opioids has been indicated for achieving better analgesia with reduced side effects. The present study was aimed at evaluating the combination of different NSAIDs, which inhibit cyclooxygenase (COX) enzymes and tramadol against acetic acid-induced writhing in mice. The expected beneficial effect of combination regimen was analyzed by isobolographic analysis. The oral and intrathecally administered tramadol, a mu-opioid and naproxen, a nonselective COX inhibitor produced dose-dependent antinociception, however, rofecoxib, a selective COX-2 inhibitor lacked analgesic efficacy in writhing test. Isobolographic analysis showed synergistic or supra-additive interactions for the combinations of naproxen and tramadol after oral and intrathecal administration. However, similar interaction was not observed when tramadol was combined with rofecoxib. Pretreatment with naloxone partially reversed the antinociceptive effect of tramadol per se and its combination with naproxen without modifying the per se effect of NSAID. The results demonstrated marked synergistic interaction between naproxen and tramadol and such interaction involved opioid as well as non-opioid mechanisms of tramadol and inhibition of COX-1 but not COX-2 by naproxen.

Effect of selective inhibition of cyclooxygenase-2 on lipopolysaccharide-induced hyperalgesia.

Lipopolysaccharide (LPS) is known to increase the expression and release of various pro-inflammatory mediators, including cyclooxygenase-2 (COX-2) and produce hyperalgesia. It is also well known that prostaglandins (PGs), synthesised both in the periphery and centrally by COX isoforms, play a key role in sensitisation of nociceptors and nociceptive processing. To investigate the role of COX-2 in LPS-induced hyperalgesia, parecoxib, a selective COX-2-inhibiting pro-drug, was injected intravenously 30 min before assessing hyperalgesia induced by intraperitoneal or subcutaneous administration of LPS (50 microg/mouse or 25 microg/paw of rat, respectively). Acetic acid-induced writhing and tail immersion assay in mice and paw withdrawal response to thermal and mechanical stimuli in rats were used to assess the effect of inhibition of COX-2 on LPSinduced hyperalgesia. Animals showed significant hyperalgesic behavior 8 h after LPS injection. Parecoxib (up to 20 mg/kg, i.v.) had no effect in the two acute nociceptive assays but showed marked antinociceptive activity in writhing and tail immersion assay in LPS-pretreated mice. Similarly, parecoxib reversed the hyperalgesia in the LPS-injected paw but not in the contralateral paw of rats. Pre-treatment with dexamethasone, an inhibitor of COX-2 expression before LPS injection significantly affected the development of hyperalgesia in both mice and rats. These findings suggest that inducible COX-2 derived PGs are involved in central nociceptive processing, which resulted in hyperalgesic behavior following LPS administration and inhibition of COX-2 or its expression attenuated LPS-induced hyperalgesia.

Effect of U-74500A, a 21-aminosteroid on renal ischemia-reperfusion injury in rats.

Renal ischemia-reperfusion injury constitutes the most common pathogenic factor for acute renal failure and is the main contributor to renal dysfunction in allograft recipients and revascularization surgeries. Many studies have demonstrated that reactive oxygen species play an important role in ischemic acute renal failure. The aim of the present study was to investigate the effects of the synthetic antioxidant U-74500A, a 21-aminosteroid in a rat model of renal ischemia-reperfusion injury. Renal ischemia-reperfusion was induced by clamping unilateral renal artery for 45 min followed by 24 h of reperfusion. Two doses of U-74500A (4.0 mg/kg, i.v.) were administered 45 min prior to renal artery occlusion and then 15 min prior to reperfusion. Tissue lipid peroxidation was measured as thiobarbituric acid reacting substances (TBARS) in kidney homogenates. Renal function was assessed by estimating serum creatinine, blood urea nitrogen (BUN), creatinine and urea clearance. Renal morphological alterations were assessed by histopathological examination of hematoxylin-eosin stained sections of the kidneys. Ischemia-reperfusion produced elevated levels of TBARS and deteriorated the renal function as assessed by increased serum creatinine, BUN and decreased creatinine and urea clearance as compared to sham operated rats. The ischemic kidneys of rats showed severe hyaline casts, epithelial swelling, proteinaceous debris, tubular necrosis, medullary congestion and hemorrhage. U-74500A markedly attenuated elevated levels of TBARS as well as morphological changes, but did not improve renal dysfunction in rats subjected to renal ischemia-reperfusion. These results clearly demonstrate the in vivo antioxidant effect of U-74500A, a 21-aminosteroid in attenuating renal ischemia-reperfusion injury.

Oxidative stress-mediated renal dysfunction by cyclosporine A in rats: attenuation by trimetazidine.

Cyclosporine A (CsA) is one of the first line immunosuppressants employed in the management of solid organ transplantation and autoimmune diseases. The clinical utility of CsA is limited by the frequent occurrence of chronic nephrotoxicity, characterized by tubular atrophy, interstitial fibrosis and progressive renal impairment. The pathogenesis of CsA nephrotoxicity is still not well delineated. Recent evidences suggest that reactive oxygen species (ROS) play an important role in CsA nephrotoxicity. The present study was designed to demonstrate the role of oxidative stress, its relation to renal dysfunction and to investigate the effect of trimetazidine (TMZ), an anti-ischemic agent with free radical scavenging property, in CsA-induced nephrotoxicity. TMZ (2.5 mg/kg, p.o., twice a day) was administered 24 h before and 21 days concurrently with CsA (20 mg/kg, s.c.). Tissue lipid peroxidation was measured as thiobarbituric acid reacting substances (TBARS). Renal function was assessed by measuring the plasma and urine creatinine concentrations, blood and urine urea nitrogen levels and the creatinine and urea clearances. Renal morphological alterations were assessed by histopathological examination of Hematoxylin-Eosin, PAS and Masson's trichome stained sections of the kidneys. CsA (20 mg/kg, s.c) administration for 21 days produced elevated levels of TBARS and decreased renal function as assessed by increased plasma creatinine, BUN and decreased creatinine and urea clearances as compared to vehicle treated rats. The kidneys of CsA treated rats showed severe striped interstitial fibrosis, arteriolopathy, glomerular basement thickening, tubular vacuolization and hyaline casts. TMZ (2.5 mg/kg) markedly reduced elevated levels of TBARS, significantly attenuated renal dysfunction and the morphological changes in CsA treated rats. These results clearly demonstrate the pivotal role of reactive oxygen species and their relation to renal dysfunction and point to the therapeutic potential of an anti-ischemic agent, trimetazidine, in CsA-induced nephrotoxicity.