Benoxaprofen induced toxicity in isolated rat hepatocytes

The toxicity of benoxaprofen, a non-steroidal anti-inflammatory compound was investigated using rat hepatic microsomal and isolated hepatocyte suspensions. In microsomes, benoxaprofen produced a Type I binding spectra and competitively inhibited (ki 380 microM) the oxidative metabolism of aminopyrine. Marked toxicity was observed following incubation of benoxaprofen with isolated hepatocytes from either untreated, phenobarbitone (PB) or 3-methylcholanthrene (3-MC) pretreated male rats. In untreated hepatocytes increases in the intracellular lactate/pyruvate (L/P) ratio and alanine aminotransferase (ALT) release were related to the benoxaprofen concentration and duration of incubation. Alterations in L/P ratio preceded the release of cytosolic ALT and at 4 h a well defined dose-response relationship existed between the benoxaprofen concentration and the observed increases in the L/P ratio and ALT release. Pretreatment of animals with either PB or 3-MC did not affect the temporal nature nor the magnitude of the hepatocyte response to benoxaprofen. In addition, inhibitors of cytochrome P-450 isozymes (SKF-525A, metyrapone and alpha-napthoflavone) were ineffective with regard to modifying the observed toxicity. The results of this study suggest that hepatic cytochrome P-450 mediated metabolism may not be implicated in the toxicity of benoxaprofen in isolated hepatocytes. However, alterations in the cellular redox state and evidence of plasma membrane bleb formation suggest that benoxaprofen may uncouple oxidative phosphorylation and disturb intracellular calcium ion homeostasis.

Complementation analysis of the aliphatic amidase genes of Pseudomonas aeruginosa

A plasmid, pCL34, capable of autonomous replication in Escherichia coli and Pseudomonas aeruginosa has been constructed which carries the promoter and structural gene (amiE) for P. aeruginosa amidase, but not the regulator gene (amiR). Plasmid pCL34 has been mobilized from E. coli to P. aeruginosa using the broad host range plasmid RP4. Complementation studies were performed in P. aeruginosa strains carrying various amidase mutations. Measurements of amidase activity in the recipients under inducing, non-inducing and repressing conditions showed trans-complementation by the chromosomally located regulator gene product. These results confirmed the positive control model for amidase gene expression. Levels of amidase expression seen during these studies were approximately threefold higher than in the parental, amidase-positive strains.

Mechanism of action of paracetamol protective agents in mice in vivo

The mechanism of action of cysteine, methionine, N-acetylcysteine (NAC) and cysteamine in protecting against paracetamol (APAP) induced hepatotoxicity in male C3H mice in vivo has been investigated by, characterising the effect of the individual protective agents on the metabolism of an hepatotoxic dose of APAP, and determining the efficacy of the protective agents in animals treated with buthionine sulphoximine (BSO), a specific inhibitor of glutathione (GSH) synthesis. Co-administration of cysteine, methionine or NAC increased, while co-administration of cysteamine decreased, the proportion of GSH-derived conjugates of APAP excreted in the urine of mice administered APAP, 300 mg/kg. Pretreatment of animals with BSO abolished the protective effect of cysteine, methionine and NAC, whereas cysteamine still afforded protection against APAP after BSO treatment. In conjunction with other data, these results suggest the most likely mechanism for the protective effect of cysteine, methionine and NAC is by facilitating GSH synthesis, while the most likely mechanism for the protective effect of cysteamine is inhibition of cytochrome P-450 mediated formation of the reactive metabolite of APAP.

The effects of buthionine sulphoximine (BSO) on glutathione depletion and xenobiotic biotransformation

Buthionine sulphoximine (BSO) is an inhibitor of gamma-glutamylcysteine synthetase (gamma-GCS) and, consequently lowers tissue glutathione (GSH) concentrations. In fed male C3H mice, liver and kidney GSH levels were depleted by BSO in a dose dependent manner with maximum effect (35% of initial levels) occurring with doses between 0.8 and 1.6 g/kg, i.p. At these doses maximum effects on gamma-GCS and GSH were observed 2-4 hr after BSO administration; initial gamma-GCS activity and GSH content were restored approximately 16 hr post BSO. BSO, either in vivo or in vitro, had no effect on hepatic microsomal cytochrome P-450 levels, a range of cytochrome P-450 dependent enzyme activities or p-nitrophenol glucuronyl transferase activity. Similarly, BSO had no effect on phenol sulphotransferase and two GSH-transferase activities in the 105,000 g supernatant fraction. BSO had no effect on the duration of hexobarbitone induced narcosis in mice. Consistent with specific inhibition of GSH synthesis, BSO pretreatment of mice decreased the proportion of a 50 mg/kg dose of paracetamol excreted in the urine as GSH-derived conjugates but did not affect paracetamol clearance through the glucuronidation or sulphation pathways. Since BSO does not affect cytochrome P-450 or conjugating enzyme activity, its use as a specific depletor of tissue GSH in the investigation of mechanisms of xenobiotic-induced toxicities is preferable to the standard GSH-depleting agents as these have other enzymic effects.

Differential effects of cimetidine on theophylline metabolic pathways

The effects of cimetidine (1 g/day) on theophylline disposition and metabolism were examined in smokers and non-smokers for single dose intravenous and chronic oral administration of theophylline. In the intravenous study the effect of cimetidine on plasma theophylline clearance was more marked in smokers (22.7% reduction) than in non-smokers (12.2% reduction). Similarly, in the multiple dose study the effect of cimetidine on theophylline clearance was greater in smokers (28.3% decrease) than in non-smokers (11.3% decrease). The reduction in clearance was largely due to a reduction in metabolic clearances by 3-demethylation ( Cl3DM ) and 1-demethylation ( Cl1DM ) with no significant effect on clearance by 8-oxidation ( Cl80X ). There was a strong correlation between Cl3DM and Cl1DM (r = 0.98, p less than 0.001) in both control and cimetidine study phases, whereas other correlations between partial clearances were less marked and were not apparent during the cimetidine phase. The results are consistent with the view that 1- and 3-demethylation of theophylline are carried out by a common form of cytochrome P-450 which is selectively induced by cigarette smoking and preferentially inhibited by cimetidine.

Asthma associated with a circulating IgG antibody to Calliphora maggots

The case report of an angler with delayed onset asthma, following fishing with Calliphora (Blue Bottle) maggots, is presented. The investigations showed that the symptoms were associated with the presence of a circulating IgG antibody to a crude water soluble maggot extract. The patient progressed to develop symptoms suggestive of immune complex disease.

Species and dose differences in the accumulation of imipramine by mammalian lungs

Adult male mice, guinea pigs, rabbits, and rats were injected ip with 14C-imipramine (IP) at doses of either 10 or 50 mg/kg and killed 15 min or 12 hr later. Plasma, lung, liver, and kidney were analyzed for total radioactivity and for IP and desmethylimipramine (DMI). Neither mouse nor guinea pig lungs accumulated IP-derived 14C relative to the other tissues at either dose or time. Indeed, tissue/plasma (T/P) ratios for liver in these species exceeded those for lung. Rabbit and rat lung did not selectively accumulate radioactivity at either time point after 10 mg/kg or at 15 min after 50 mg/kg. However, 12 hr after 50 mg/kg, rabbit and rat lungs contained significantly more radioactivity than other tissues, lung T/P ratios being 3-4 times those of liver and kidney. Most of the radioactivity retained in rat lung was present as DMI (approximately 70%), whereas the three other species retained predominantly unchanged IP (60-80%). In rats, increasing the IP dose from 10 to 100 mg/kg resulted in a 10-fold increase in radioactivity in plasma, 3-fold increases in liver and kidney, and a 20-fold increase in lung. Studies with lung slices revealed that although all species avidly accumulated IP from the medium, all species but rabbit rapidly released the drug by efflux into drugfree medium. The data suggest that only rat and rabbit lung retain significant amounts of IP after administration of large doses to intact animals, and probably by different mechanisms. Rabbit lung retains mainly unchanged IP due to slow efflux of the drug from the lung whereas the rat rapidly demethylates IP to DMI and this metabolite is then retained by the lung.

Cimetidine: a specific inhibitor of hepatic aryl hydrocarbon hydroxylase (AHH) in the rat

Aryl hydrocarbon hydroxylase was selectively inhibited in hepatic microsomes prepared 2 hours after administration of cimetidine (150 mg/kg, i.p.) to male Wistar rats. Cytochrome P-450 content and other mixed function oxidase activities were not affected. In rats pretreated with phenobarbital or 3-methylcholanthrene, cimetidine caused a 50% and 90% reduction or aryl hydrocarbon hydroxylase activity respectively, compared to 70% inhibition in uninduced animals. Chronic administration of cimetidine (150 mg/kg, b.i.d. for 5 days) to uninduced rats resulted in 70% inhibition of aryl hydrocarbon hydroxylase but no change in other microsomal enzyme activities. Hexobarbital sleeping time was markedly prolonged 30 min after a single dose of cimetidine but had returned to control values after 24 hrs. Similar effects were observed with chronic dosing of cimetidine. It is concluded that in vivo administration of cimetidine is a relatively specific inhibitor of hepatic aryl hydrocarbon hydroxylase in the rat, and that cimetidine does not induce the microsomal mixed function oxidase system when administered chronically.

Properties of monoclonal antibodies to human immunoglobulin kappa and lambda chains

Hybridomas have been produced from mice immunized with human IgG. Culture supernates were assayed for the presence of antibody-producing cells by passive haemagglutination. Hybridomas producing antibodies to human kappa (kappa) and lambda (lambda) light chains have been cloned and grown as ascitic tumours in BALB/c mice. The antigen-binding characteristics of the monoclonal antibodies, contained in the ascitic fluid, were assessed by haemagglutination inhibition, ELISA and radioimmunoassay systems and by the binding of radiolabelled antigen in analytical flat-bed iso-electric focussing gels. One monoclonal anti-kappa reacted better with free than with combined kappa chains; for another the reverse was true. Antibody fractions separated by DEAE chromatography of ascitic fluids were coupled to ox red cells with chromic chloride and compared with polyclonal antibodies for the detection of cell-surface immunoglobulins.

Effect of a specific 5HT uptake inhibitor (citalopram) on drug accumulation by rat lung slices

Rat lung slices were used to examine the effects of citalopram, a compound reported to be a specific inhibitor of neuronal uptake of 5-hydroxytryptamine (5HT), on the pulmonary accumulation of 5HT, noradrenaline (NA), imipramine (IP) and paraquat (PQ). 5 X 10(-9) mol/l citalopram inhibited 5HT uptake by 30-40% but NA uptake was not affected at any of the concentrations of citalopram studied. At the highest concentrations of citalopram (10(-5) to 10(-4) mol/l) the accumulation of IP and PQ was reduced by25-30%. It is concluded that at low concentrations, citalopram is a specific and potent inhibitor of 5HT uptake by rat lung slices.

Hepatic cytochrome P-450-dependent metabolism and enzymatic conjugation of foreign compounds in vitamin A-deficient rats

The temporal effects of vitamin A deficiency on hepatic cytochrome P-450-dependent and conjugation reactions were studied in the rat. Cytochrome P-450 levels and N-methyl-p-chloroaniline N-demethylase activity were significantly reduced in the deficient animals. No other changes in parameters dependent on cytochrome P-450 were observed in vitro. Decreases in hepatic cytochrome P-450 were accompanied by a prolongation in hexobarbital sleeping times in deficient animals. The p-aminobenzoic acid N-acetyltransferase activity was higher in the deficient animals at 8 weeks, but by 10 weeks the activity in fact was significantly lower as compared to controls. Activities of 'native' and UDP N-acetylglucosamine 'activated' UDP-glucuronyltransferase were reduced in vitamin A deficiency. In contrast to this general pattern of impaired drug metabolism in vitamin A deficiency, glutathione S-aryltransferase activity was markedly enhanced at all time points from 4 to 10 weeks. Activities of this enzyme were twice controls at 6 weeks, a time at which no other enzyme changes were observed.

The effect of unilateral pneumonectomy on in vitro drug metabolism by the contralateral lung of rabbits

The effect of unilateral pneumonectomy on the drug-metabolizing capability of the remaining lung of male rabbits was studied 3, 10, and 28 days after surgery. During the period of compensatory lung growth which follows pneumonectomy, the contralateral lung had a reduced ability to metabolize some model drug substrates. The activities of 4-chloro-N-methylaniline demethylase, glutathione transferase, and 4-aminobenzoate N-acetyltransferase were significantly decreased in pneumonectomizd animals relative to shamoperated controls at 10 days. By 28 days most of these parameters of drug metabolism had returned to control levels. Lung hydroxyproline concentration, an index of collagen, did not differ in pneumonectomized and control animals at any of the time points. 3-Methylcholanthrene failed to induce the pulmonary mono-oxygenase system in pneumonectomized animals. The response of pulmonary drug-metabolizing enzymes to unilateral pneumonectomy in rabbits was temporally and qualitatively similar to the response in rat liver following partial hepatectomy.

Choleretic and cholestatic effects of infused bile salts in the rat

In rats, at low infusion rates taurocholate (TC), taurochenodeoxycholate (TCDC) and taurodeoxycholate (TCD) each produced an increase in bile flow of 20-50%. However, at high infusion rates (5-20 mumoles min-1kg-1) the cholestatic effects of the bile salts were revealed and the relative toxicity of the bile salts was seen to be TDC greater than TCDC greater than TC.

Effect of chlorpromazine and erythromycin on bile salt-induced cholestasis in the rat

The effects of subacute administration of chlorpromazine HCI (CPZ), erythromycine base and erythromycin estolate on the cholestatic response to intravenous taurolithocholate (TLC) and taurochenodeoxycholate (TCDC) in the rat were investigated. All three enhanced the recovery of bile flow after TCDC but not after TLC. Erythromycin base and estolate enhanced bile flow recovery after TCDC and potentiated the increase of plasma 5'-nucleotidase, as did CPZ. Neither erythromycin estolate nor CPZ precipitated a cholestatic response in rat maintained for 9-13 days on a diet supplemented with 0.05% lithocholic acid. It is concluded that the interaction of CPZ and erythromycins with bile salts is not based on the cholestatic properties of the drugs, and hence is not a practical way of distinguishing cholestatic from non-cholestatic drugs.