Curcumin and Selenium Prevent Lipopolysaccharide/Diclofenac-Induced Liver Injury by Suppressing Inflammation and Oxidative Stress.

Diclofenac (DCL), an anti-inflammatory drug used to reduce pain and inflammation, ranks in the top causes of drug-induced liver injury. The inflammatory stress induced by inflammagens is implicated in DCL-induced liver injury. Curcumin (CUR) and selenium (Se) possess anti-inflammatory effects; therefore, this study evaluated their protective potential against lipopolysaccharide (LPS)/DCL-induced liver injury. Rats received CUR and/or Se for 7 days followed by a single intravenous administration of LPS 2 h before a single injection of DCL and two other doses of CUR and/or Se 2 and 8 h after DCL. Administration of nontoxic doses of LPS and DCL resulted in liver damage evidenced by the significantly elevated liver function markers in serum. LPS/DCL-induced liver injury was confirmed by histological alterations, increased lipid peroxidation and nitric oxide, and diminished glutathione and superoxide dismutase. CUR and/or Se prevented liver injury, histological alterations, and oxidative stress and boosted antioxidant defenses in LPS/DCL-induced rats. In addition, CUR and/or Se reduced serum C-reactive protein, liver pro-inflammatory cytokines, and the expression of TLR4, NF-κB, JNK, and p38, and upregulated heme oxygenase-1 (HO-1). In conclusion, CUR and/or Se mitigated LPS/DCL-induced liver injury in rats by suppressing TLR4 signaling, inflammation, and oxidative stress and boosting HO-1 and other antioxidants. Therefore, CUR and Se can hinder the progression and severity of liver injury during acute inflammatory episodes.

Underlying mechanism of regulatory actions of diclofenac, a nonsteroidal anti-inflammatory agent, on neuronal potassium channels and firing: an experimental and theoretical study.

Diclofenac (DIC), a nonsteroidal anti-inflammatory drug, is known to exert anti-nociceptive and anti-convulsant actions; however, its effects on ion currents, in neurons remain debatable. We aimed to investigate (1) potential effects of diclofenac on membrane potential and potassium currents in differentiated NSC-34 neuronal cells and dorsal root ganglion (DRG) neurons with whole-cell patch-clamp technology, and (2) firing of action potentials (APs), using a simulation model from hippocampal CA1 pyramidal neurons based on diclofenac's effects on potassium currents. In the NSC-34 cells, diclofenac exerted an inhibitory effect on delayed-rectifier K⁺ current (I(KDR)) with an IC50 value of 73 µM. Diclofenac not merely inhibited the I(KDR) amplitude in response to membrane depolarization, but also accelerated the process of current inactivation. The inhibition by diclofenac of IK(DR) was not reversed by subsequent application of either naloxone. Importantly, diclofenac (300 µM) increased the amplitude of M-type K⁺ current (I)(KM)), while flupirtine (10 µM) or meclofenamic acid (10 µM) enhanced it effectively. Consistently, diclofenac (100 µM) increased the amplitude of I(KM) and diminished the I(KDR) amplitude, with a shortening of inactivation time constant in DRG neurons. Furthermore, by using the simulation modeling, we demonstrated the potential electrophysiological mechanisms underlying changes in AP firing caused by diclofenac. During the exposure to diclofenac, the actions on both I(KM) and I(KDR) could be potential mechanism through which it influences the excitability of fast-spiking neurons. Caution needs to be made in attributing the effects of diclofenac primarily to those produced by the activation of I(KM).

Metformin and phenformin block the peripheral antinociception induced by diclofenac and indomethacin on the formalin test.

AIMS: Recent evidence has shown that systemic administration of sulfonylureas and biguanides block the diclofenac-induced antinociception, but not the effect produced by indomethacin. However, there are no reports about the peripheral interaction between analgesics and the biguanides metformin and phenformin. Therefore, this work was undertaken to determine whether glibenclamide and glipizide and the biguanides metformin and phenformin have any effect on the peripheral antinociception induced by diclofenac and indomethacin. MAIN METHODS: Diclofenac and indomethacin were administered locally in the formalin-injured rat paw, and the antinociceptive effect was evaluated using the 1% formalin test. To determine whether peripheral antinociception induced by diclofenac or indomethacin was mediated by either the ATP-sensitive K(+) channels or biguanides-induced mechanisms, the effect of pretreatment with the appropriates vehicles or glibenclamide, glipizide, metformin and phenformin on the antinociceptive effect induced by local peripheral diclofenac and indomethacin was assessed. KEY FINDINGS: Local peripheral injections of diclofenac (50-200 µg/paw) and indomethacin (200-800 µg/paw) produced a dose-dependent antinociception during the second phase of the test. Local pretreatment with glibenclamide, glipizide, metformin and phenformin blocked the diclofenac-induced antinociception. On the other hand, the pretreatment with glibenclamide and glipizide did not prevent the local antinociception produced by indomethacin. Nonetheless, metformin and phenformin reversed the local antinociception induced by indomethacin. SIGNIFICANCE: Data suggest that diclofenac could activate the K(+) channels and biguanides-dependent mechanisms to produce its peripheral antinociceptive effects in the formalin test. Likewise, a biguanides-dependent mechanism could be activated by indomethacin consecutively to generate its peripheral antinociceptive effect.

Blockade of the antinociception induced by diclofenac, but not of indomethacin, by sulfonylureas and biguanides.

There is evidence that administration of sulfonylureas, such as glibenclamide and tolbutamide, blocks diclofenac-induced antinociception, suggesting that diclofenac activates ATP-sensitive K(+) channels. However, there is no evidence for the interaction between diclofenac and other hypoglycemic drugs, such as the biguanides metformin or phenformin. Therefore, this work was undertaken to determine whether two sulfonylureas, glibenclamide and glipizide, as well as two biguanides, metformin and phenformin, have any effect on the systemic antinociception that is induced by diclofenac and indomethacin using the rat formalin test as an animal model. Systemic injections of diclofenac (10 to 30mg/kg) and indomethacin (10 to 30mg/kg) produced dose-dependent antinociception during the second phase of the test. Systemic pretreatment with glibenclamide (3 and 10mg/kg), glipizide (3 and 10mg/kg), metformin (100 and 180mg/kg) or phenformin (100 and 180mg/kg) blocked diclofenac-induced systemic antinociception in the second phase of the test (P<0.05). In contrast, pretreatment with glibenclamide, glipizide, metformin or phenformin did not block indomethacin-induced systemic antinociception (P>0.05). These data suggest that diclofenac, but not indomethacin, activated K(+) channels and metformin and phenformin-dependent mechanisms, which resulted in systemic antinociceptive effects in the rat formalin test.

Pharmacokinetic of diclofenac in the presence and absence of glibenclamide in the rat.

PURPOSE: There is evidence that the sulfonylurea antidiabetic agent glibenclamide reduces the analgesic action of non-steroidal anti-inflammatory drugs (NSAIDs), opioids and neuromodulators in animal models. Therefore, in view of the vast clinical uses and interactions of NSAIDs with commonly used therapeutic agents, the interaction of the NSAID diclofenac and glibenclamide was investigated about pharmacokinetic profile and antinociceptive effect in rats. METHODS: Antinociception was assessed using the formalin test. Fifty microliters of diluted formalin was injected s.c. into the dorsal surface of the right hind paw. Nociceptive behavior was quantified as the number of flinches of the injected paw during 60 min after injection. Rats were treated with oral administration of vehicle or increasing doses of diclofenac (3-18 mg/kg) before formalin injection. To determine the pharmacodynamic interaction between diclofenac and glibenclamide, the effect of oral administration of glibenclamide (1-30 mg/kg) on the antinociceptive effect induced by diclofenac (18 mg/kg, p.o.) was assessed. To evaluate the pharmacokinetic interaction between diclofenac and glibenclamide, the effect of glibenclamide (10 mg/kg, p.o.) on the pharmacokinetic of diclofenac (18 mg/kg, p.o.) was studied in the rat. Blood samples were taken over 8 h and analyzed using a validated high-performance liquid chromatography method to generate the pharmacokinetic profile of diclofenac. Pharmacokinetic parameters were estimated using noncompartmental analysis. RESULTS: Systemic administration of diclofenac produced a dose-dependent antinociceptive effect in the formalin test. Systemic treatment with glibenclamide prevented diclofenac-induced antinociception. In pharmacokinetic interaction study, no significant (P>0.05) change in diclofenac concentration-time profiles in the presence of glibenclamide was detected. CONCLUSION: The experimental findings suggest that systemic glibenclamide is able to block the diclofenac-induced antinociception in the rat formalin test. Besides, this antagonism was not produced by diminution in the bioavailability of diclofenac. Likewise, the validated assay had sufficient accuracy and precision for pharmacokinetic determination of diclofenac in the rat.

Bax-mediated mitochondrial outer membrane permeabilization (MOMP), distinct from the mitochondrial permeability transition, is a key mechanism in diclofenac-induced hepatocyte injury: Multiple protective roles of cyclosporin A.

Diclofenac, a widely used nonsteroidal anti-inflammatory drug, has been associated with rare but severe cases of clinical hepatotoxicity. Diclofenac causes concentration-dependent cell death in human hepatocytes (after 24-48 h) by mitochondrial permeabilization via poorly defined mechanisms. To explore whether the cyclophilin D (CyD)-dependent mitochondrial permeability transition (mPT) and/or the mitochondrial outer membrane permeabilization (MOMP) was primarily involved in mediating cell death, we exposed immortalized human hepatocytes (HC-04) to apoptogenic concentrations of diclofenac (>500 microM) in the presence or absence of inhibitors of upstream mediators. The CyD inhibitor, cyclosporin A (CsA, 2 microM) fully inhibited diclofenac-induced cell injury, suggesting that mPT was involved. However, CyD gene silencing using siRNA left the cells susceptible to diclofenac toxicity, and CsA still protected the CyD-negative cells from lethal injury. Diclofenac induced early (9 h) activation of Bax and Bak and caused mitochondrial translocation of Bax, indicating that MOMP was involved in cell death. Inhibition of Bax protein expression by using siRNA significantly protected HC-04 from diclofenac-induced cell injury. Diclofenac also induced early Bid activation (tBid formation, 6 h), which is an upstream mechanism that initiates Bax activation and mitochondrial translocation. Bid activation was sensitive to the Ca2+ chelator, BAPTA. In conclusion, we found that Bax/Bak-mediated MOMP is a key mechanism of diclofenac-induced lethal cell injury in human hepatocytes, and that CsA can prevent MOMP through inhibition of Bax activation. These data support our concept that the Ca2+-Bid-Bax-MOMP axis is a critical pathway in diclofenac (metabolite)-induced hepatocyte injury.

Inhibitory effect of medroxyprogesterone acetate on human liver cytochrome P450 enzymes.

OBJECTIVE: Medroxyprogesterone acetate (MPA), frequently used in contraception and chemotherapy, was involved in a report of drug-drug interaction (DDI) when co-administrated with phenytoin, doxifluridine and cyclophosphamide. In order to clarify the mechanism of such interaction, an in vitro study was undertaken to evaluate MPA's potential to inhibit cytochrome P450 (CYP) enzymes. METHODS: Inhibitory effects of MPA on seven CYPs, including CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2D6, CYP2E1 and CYP3A4, were conducted in human liver microsomes. Time- and NADPH-dependent inhibitions were also tested. DDI potential was predicted according to the [I]/K ( i ) value. RESULTS: MPA was found to inhibit CYP2C9 and CYP3A4; half inhibition concentration (IC(50)) was 16.1 microM and 31.5 microM, respectively. Slight inhibition was observed on CYP1A2, CYP2A6, CYP2C8 and CYP2D6 with IC(50) of more than 100 microM. MPA exhibited activation rather than inhibition on CYP2E1. Further study revealed that MPA showed a noncompetitive inhibition on CYP2C9 and a competitive inhibition on CYP3A4 with K ( i ) of 9.0 microM and 36 microM, respectively. In addition, MPA was not a mechanism-based inhibitor to any of seven isoforms tested. By using predicted concentration of MPA in liver, [I]/K ( i ) was estimated to be 0.24 and 0.06 for CYP2C9 and CYP3A4, respectively. The concentration of phenytoin co-administrated with MPA was calculated to increase by 24%. CONCLUSION: Based on our results, MPA can possibly cause clinically relevant DDI via the inhibition of CYP2C9.

Protective and antioxidant effects of Rhizophora mangle L. against NSAID-induced gastric ulcers.

The bark of Rhizophora mangle, the red mangrove, has been used traditionally in folk medicine of Caribbean countries due to its antiseptic, astringent, haemostatic and antifungal properties. Aqueous extracts are rich in tannins and have been proven experimentally to possess antibacterial, wound healing and antiulcerogenic effects. This work was designed to determine the gastroprotective effect of Rhizophora mangle in a model of diclofenac-induced ulcers in rats and to study the mechanisms involved, using the proton pump inhibitor omeprazole as a comparison. The lyophilized extract was given by oral gavage (125 and 62.5mg/kg) three times at 12h intervals before administering diclofenac 100mg/kg. Pretreatment with the extract resulted in a significant decrease of the ulcerated area (P<0.01). Rhizophora mangle induced a recovery of PGE(2) levels, which had been depleted by diclofenac. No anti-inflammatory effect was observed ex vivo or in vitro. The highest dose of the extract provoked a marked increase in glutathione peroxidase and superoxide dismutase activity, which was comparable to omeprazole. Furthermore, lipid peroxidation levels were inhibited in a dose-dependent manner. These results suggest that the gastroprotective effect of Rhizophora mangle in this experimental model appears through an antioxidant and prostaglandin-dependent way.

Enalapril interferes with the effect of diclofenac on leucocyte-endothelium interaction in hypertensive rats.

Nonsteroidal anti-inflammatory drugs are known to attenuate the effects of some antihypertensive agents. However, the effect these drugs have on leukocyte migration when combined with antihypertensive agents has not been studied. To investigate this effect, we treated spontaneously hypertensive rats with saline, diclofenac, enalapril, or diclofenac combined with enalapril and observed leukocyte-endothelium interaction. Blood pressure was increased by diclofenac, reduced by enalapril and reduced by the combination of the two. Diclofenac did not interfere with the blood pressure-lowering effect of enalapril. Internal spermatic fascia venules were observed using intravital microscopy. Diclofenac reduced rollers, whereas enalapril, alone or combined with diclofenac, had no significant effect on rollers. All treatments reduced adherent and migrated leukocytes and expression of endothelial intercellular adhesion molecule-1. Venular shear rate, venular diameters, number of circulating leukocytes, and post-leukotriene B4 expression of l-selectin and CD11/CD18 integrin in leukocytes were unaffected by any treatment. Expression of P-selectin was reduced by diclofenac and unaffected by enalapril, even when combined with diclofenac. Our data suggest that, although diclofenac does not interfere with the enalapril anti-hypertensive effect, enalapril interferes with the effect diclofenac has on leukocyte rolling and endothelial P-selectin expression. Involvement of reduced endothelial intercellular adhesion molecule-1 expression might explain the lower numbers of adherent and migrated leukocytes. The anti-inflammatory properties of a nonsteroidal anti-inflammatory drug could therefore be attenuated in hypertensive patients receiving an angiotensin-converting enzyme inhibitor.

Modulatory effect of cyclooxygenase inhibitors on sildenafil-induced antinociception.

Peripheral activation of the NO-cGMP pathway has been implicated in various nociceptive conditions. The antinociceptive effect of the PDE-5 inhibitor, sildenafil, alone or in combination with cyclooxygenase inhibitor diclofenac and nimesulide, was assessed in the different animal models of peripheral nociception. In the present study we investigated the possible interaction between cyclooxygenase and NO-cGMP pathway in writhing assay and carrageenan-induced hyperalgesia in mice and rats, respectively. Sildenafil [1-2 mg/kg, i.p. or 50-100 microg/paw, intraplantar (i.pl.)], nimesulide (1-2 mg/kg, i.p. or 25-50 microg/paw, i.pl.) and diclofenac (1-2 mg/kg, i.p. or 25-50 microg/paw, i.pl.) exhibited an antinociceptive effect in both the models. When ineffective doses of sildenafil (0.5 mg/kg, i.p and 25 microg/paw, i.pl.) were co-administered with ineffective doses of nimesulide (0.5 mg/kg, i.p. and 10 microg/paw, i.pl.) and diclofenac (0.5 mg/kg, i.p. and 10 microg/paw, i.pl.), there was a significant increase in the antinociceptive effect in both the models of peripheral nociception. Further, the potentiation of the effect was blocked by L-NAME (20 mg/kg, i.p., 100 microg/paw, i.pl.), a non-selective NOS inhibitor and methylene blue (1 mg/kg, i.p.), a guanylate cyclase inhibitor. L-NAME or methylene blue itself had little or no effect on both the models of hyperalgesia. These results suggest that cyclooxygenase, NO and cGMP are relevant in the combination-induced antinociception. In conclusion, sildenafil induced antinociception, and its potentiation of the effect of the cyclooxygenase inhibitors nimesulide and diclofenac was probably mediated through the activation of the NO-cGMP pathway and inhibition of cyclic GMP degradation.

A novel mechanism of cyclooxygenase-2 inhibition involving interactions with Ser-530 and Tyr-385.

A variety of drugs inhibit the conversion of arachidonic acid to prostaglandin G2 by the cyclooxygenase (COX) activity of prostaglandin endoperoxide synthases. Several modes of inhibitor binding in the COX active site have been described including ion pairing of carboxylic acid containing inhibitors with Arg-120 of COX-1 and COX-2 and insertion of arylsulfonamides and sulfones into the COX-2 side pocket. Recent crystallographic evidence suggests that Tyr-385 and Ser-530 chelate polar or negatively charged groups in arachidonic acid and aspirin. We tested the generality of this binding mode by analyzing the action of a series of COX inhibitors against site-directed mutants of COX-2 bearing changes in Arg-120, Tyr-355, Tyr-348, and Ser-530. Interestingly, diclofenac inhibition was unaffected by the mutation of Arg-120 to alanine but was dramatically attenuated by the S530A mutation. Determination of the crystal structure of a complex of diclofenac with murine COX-2 demonstrates that diclofenac binds to COX-2 in an inverted conformation with its carboxylate group hydrogen-bonded to Tyr-385 and Ser-530. This finding represents the first experimental demonstration that the carboxylate group of an acidic non-steroidal anti-inflammatory drug can bind to a COX enzyme in an orientation that precludes the formation of a salt bridge with Arg-120. Mutagenesis experiments suggest Ser-530 is also important in time-dependent inhibition by nimesulide and piroxicam.

Histamine H2-receptor antagonist action of ebrotidine. Effects on gastric acid secretion, gastrin levels and NSAID-induced gastrotoxicity in the rat.

The antagonism of histamine H2-receptors by ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]ethyl ] amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) was assessed on isolated guinea-pig right atrium. The dose-response curves obtained by histamine on the positive chronotropic effect in guinea-pig atrium were displaced to the right in parallel depending on the concentration of ebrotidine and ranitidine without change in the maximum response with pA2 values of 7.12 and 7.26, respectively. The slope of the regression line of log (DR-1) against log ebrotidine concentration was not significantly different from unity: 0.96 (95% confidence limits: 0.89-1.03). These results indicate that ebrotidine is a competitive H2-receptor antagonist. Following intravenous administration to rats, ebrotidine inhibited histamine- and pentagastrin-stimulated acid secretion in a dose-dependent manner, ED50 being 0.21 and 0.44 mg/kg, respectively. After oral administration to fasting rats 3 h before their sacrifice, ebrotidine decreased the total acid contents of the stomach in a dose-dependent manner, ED50 being 7.5 mg/kg. After a single dose of 100 mg/kg in fasting rats, ebrotidine increased significantly serum gastrin levels within 2 and 5 h after administration, but 8 h after administration serum gastrin levels returned to normal values. In contrast, ranitidine at a single oral dose of 100 mg/kg increased serum gastrin levels more markedly within 2 and 5 h after administration, while after 8 h, this increase still persisted although without significant differences with respect to control, and after 24 h levels returned to normal values. Both ebrotidine and ranitidine were administered orally at a dose of 100 mg/kg for 26 days showing significant increments in plasma gastrin levels 5 h after administration. Such increments were not so marked after ebrotidine and normal values were attained at 24 h after administration. The results obtained after repeated oral administration for 15 days of ebrotidine and ranitidine at the doses of 15 and 50 mg/kg demonstrated that ebrotidine did not increase significantly serum gastrin levels with respect to control 2 h after administration, and no dose-related effect was observed. In contrast, ranitidine increased serum gastrin levels significantly and in a dose-dependent manner with respect to control group. ED50 values of ebrotidine obtained in the experiments on the prevention of NSAID-induced gastrotoxicity in the rat were 12.2, 12.5, 11.5 and 9.8 mg/kg against diclofenac, ketoprofen, indometacin and naproxen, respectively. ED50 values of ranitidine were of the same order: 20.6, 13.9, > 50 and 15.1 mg/kg.

Failure of calcium antagonistic agents to prevent hepatotoxicity induced by diclofenac.

Diclofenac (0.5-2 mM) dose- and time-dependently reduces the viability of isolated hepatocytes. This effect cannot be counteracted by the calcium channel blockers diltiazem (0.05-0.1 mM) and verapamil (0.05-0.5 mM), the calmodulin antagonist calmidazolium (0.01 mM) or Quin 2-AM (0.1 mM), an intracellular calcium chelating agent. On the contrary, verapamil even accentuates the toxic effects of diclofenac. It is concluded from these results, that diclofenac causes cell damage by other mechanisms than calcium overload.

Central antinociceptive effects of non-steroidal anti-inflammatory drugs and paracetamol. Experimental studies in the rat.

BACKGROUND: These studies were undertaken to investigate the site and nature of the antinociceptive effect of NSAIDs (Non-Steroidal Anti-Inflammatory Drugs) and paracetamol in the central nervous system (CNS). METHODS: Different nociceptive test models were employed: the tail-flick and hot-plate tests (thermoreceptors), the writhing test (visceral chemoreceptors) the "scratching, biting, licking" (SBL) behaviour and the colorectal distension test (mechanoreceptors). Drugs were given intraperitoneally (i.p.), intracerebroventricularly (i.c.v.), intrathecally (i.t.) or as local injection via cannulae implanted stereotactically. Nerve destruction was made by local injection of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT). Whole brain and spinal cord contents of serotonin and 5-hydroxyindole acetic acid (5-HIAA) were analysed by high pressure liquid chromatography (HPLC). RESULTS: Injections of diclofenac induced antinociception in visceral pain models (writhing test, colorectal distension test), but not in two models of somatosensory pain (tail-flick and hot-plate test). The antinociceptive effect of diclofenac (i.p., i.c.v., or i.t.) was reversed by i.p. naloxone. Naloxone also reversed the effect of diclofenac injected locally into thalamic and hypothalamic areas involved in pain transmission as well as in n. paragigantocellularis or n. raphe magnus. In addition, chemical destruction of the n. raphe region attenuated the antinociceptive effect of diclofenac. Inhibition of serotonergic transmission by pretreatment with methiothepin, ritanserin, parachlorophenylalanine (PCPA) or 5,7-DHT also reduced the antinociceptive effect of diclofenac in a visceral pain model. Pretreatment with diclofenac or ibuprofen blocked pain behaviour (SBL) after activation of excitatory amino acid receptors of the NMDA type, but not pain behaviour after activation of AMPA or substance P (SP) receptors. Paracetamol inhibited hyperalgesia after both NMDA and SP. The antinociceptive effects of diclofenac, ibuprofen and paracetamol were reversed by L-arginine, but not by D-arginine. CONCLUSIONS: The antinociceptive effect of diclofenac involves a central nervous component which may be elicited from several defined areas in the CNS. Part of the antinociceptive effect seems to be mediated by descending inhibitory opioid, serotonin and/or other neurotransmitter systems interfering with visceral pain impulse traffic at the spinal level. NSAIDs and paracetamol interfere with nociception associated with spinal NMDA receptor activation. This effect involves an inhibitory action on spinal nitric oxide (NO) mechanisms. Possibly, the supraspinal antinociceptive effect of NSAIDs may be explained by an analogous action.

Central, naloxone-reversible antinociception by diclofenac in the rat.

The antinociceptive effect of subcutaneously (s.c.), intracerebroventricularly (i.c.v.) or intrathecally (i.t.) administered diclofenac was studied in a series of experiments employing the tail-flick (0.01-10.0 mg/kg body weight i.p., 1-50 micrograms i.c.v., 1-10 micrograms i.t.) and hot-plate (0.01-50 mg/kg body weight i.p., 1-50 micrograms i.c.v., 1-10 micrograms i.t.) models representing somatosensory stimuli and the writhing test (0.001 mg-10 mg s.c., 0.1-200 micrograms i.c.v., 0.1-100 micrograms i.t.) and colorectal distension (1-200 micrograms i.c.v.) models representing noxious visceral stimuli. Diclofenac did not exert any antinociceptive effects in the tail-flick or hot-plate models. In the writhing test, diclofenac dose-dependently inhibited the number of writhings after s.c. administration (0.001-10.0 mg/kg body weight) with an ED50 of 1 mg/kg. A similar dose-dependent action of diclofenac was seen after i.c.v. (0.1-200 micrograms) and i.t. (0.1-100 micrograms) administration with an ED50 of 3 micrograms in both cases. The antinociceptive effect of diclofenac administered s.c., i.c.v. or i.t. was almost completely reversed by pretreatment with naloxone, (1 mg/kg body weight s.c.). In the colorectal distension model, the i.c.v. administration of diclofenac (1-200 micrograms), which attenuated the cardiovascular response to colorectal distension, was reversed by naloxone. The pressor and tachycardia response to a 20 s, 80 mmHg colorectal distension was inhibited by diclofenac 100 micrograms i.c.v. (16.1 +/- 1.7 mmHg or 58% and 39.4 +/- 0.4 bpm or 70% versus control, respectively). It is concluded that diclofenac exerts a central, naloxone-reversible antinociceptive action in experimental animals after noxious visceral stimuli but not after somatosensory stimuli.

Acute antiinflammatory and gastric effects of the seleno-organic compound ebselen.

Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one), a seleno-organic compound with glutathione peroxidase-like activity in vitro, was compared with indomethacin, BW 755C, and levamisole as an inhibitor of carrageenan- and CVF (cobra venom factor)-induced paw oedema in the rat. The antiinflammatory potency of ebselen against CVF-induced oedema (ED50 = 56 mg/kg p.o.) was similar to that of BW 755C, while indomethacin was weakly active in this model, and levamisole exerted stronger activity. In the carrageenan model, ebselen exhibited weak inhibitory potency, like BW 755C, while indomethacin markedly inhibited this inflammatory response, and levamisole was inactive. Unlike cyclooxygenase inhibitors, ebselen produced almost no gastric irritation in rats up to 316 mg/kg p.o. Moreover, ebselen inhibited significantly diclofenac-induced gastric intolerance at 31.6 and 316 mg/kg p.o. Thus, ebselen represents a new tool for antiinflammatory therapy.

Cytoprotective effect of free radical scavengers against mucosal damage produced by different antirheumatic drugs.

Following 200 mg aspirin, 20 mg indomethacin or 100 mg diclofenac, gastric mucosal damage was evoked after five hours in rats. By administering vitamin A, vitamin E, MTDQ (6,6-methylenebis-2,2,4-trimethyl-1,2-dihydroquinoline), vitamin C, lipoic acid and penicillamine intragastrically at the time of the application of the damaging agent, the authors studied the beneficial effect of these free-radical scavengers upon the mucosal lesions. Vitamin C and penicillamine exerted no significant protective effect. Among the other drugs, the most effective were the lipid-soluble ones: vitamin A, vitamin E and MTDQ. The authors hypothesized that the gastric damage may be connected with the degradation of the polyunsaturated fatty acid components of the cellular membranes and thus the lipid-soluble free radical scavengers were able to offer protection.