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1. It has previously been shown that the extent of hepatic phospholipidosis induced by chronic amiodarone treatment correlates with the degree of drug accumulation in liver tissue. 2. To investigate a possible influence of pharmacogenetic factors, biochemical and morphological investigations were carried out in two rat strains differing in debrisoquine hydroxylation. 3. Plasma and liver tissue concentrations of amiodarone and its main metabolite, desethyl-amiodarone, were significantly higher in rats with deficient hydroxylation. Microsomal enzyme induction, drug cytochrome P-450 complex formation and typical ultrastructural features of phospholipidosis were only seen in rats with deficient hydroxylation and in a more sensitive species, the guinea-pig. 4. It remains to be seen whether deficient debrisoquine hydroxylation in man is associated with an increased susceptibility to amiodarone side effects.

Mitochondria are involved in fatty acid β-oxidation, the tricarboxylic acid cycle and oxidative phosphorylation, which provide most of the cell energy. Mitochondria are also the main source of reactive oxygen species in the cell and are involved in cell demise through opening of the mitochondrial per?meability transition pore. It was therefore expected that mitochondrial dys?function could be a major mechanism of drug-induced liver disease. Microvesicular steatosis (which may cause liver failure, coma and death) is the consequence of severe impairment of mitochondrial β-oxidation. Drugs (e.g. aspirin, valproic acid, ibuprofen, or zidovudine) but also toxic derivatives (e.g. ethanol) and endogenous compounds (such as cytokines or female sex hormones) can inhibit β-oxidation directly or through a primary effect on the mitochondrial genome or the respiratory chain itself. In some patients, infections and cytokines, or inborn errors of β-oxidation enzymes or the mitochondrial genome, may favor the appearance of drug-induced microvesicular steatosis. Nonalcoholic steatohepatitis may develop under conditions causing prolonged, microvesicular and/or macrovacuolar steatosis. In this condition, chronic impairment of mitochondrial s-oxidation (causing steatosis) and respiratory chain (increasing the production of reactive oxygen species; ROS) lead to lipid peroxidation which, in turn, may cause the diverse lesions of steatohepatitis, namely, necrosis, inflammation, Mallory’sbodies and fibrosis. Finally, mitochondria are involved in several forms of drug-induced cytolytic hepatitis, through inhibition or uncoupling of respiration or through drug-induced or reactive metabolite-induced mitochondrial permeability transition. The latter effect commits hepatocytes to either apoptosis or necrosis, depending on the number of organelles that have undergone permeability transition.

Mitochondria are involved in fatty acid beta-oxidation, the tricarboxylic acid cycle, and oxidative phosphorylation, which provide most of the cell energy. Mitochondria are also the main source of reactive oxygen species in the cell and are involved in cell demise through opening of the mitochondrial permeability transition pore. It was therefore to be expected that mitochondrial dysfunction could be a major mechanism of drug-induced liver disease. Microvesicular steatosis (which may cause liver failure, coma, and death) is the consequence of severe impairment of mitochondrial beta-oxidation. Endogenous compounds (such as cytokines or female sex hormones) or xenobiotics (including toxins such as ethanol and drugs such as aspirin, valproic acid, ibuprofen, or zidovudine) can inhibit beta-oxidation directly or through a primary effect on the mitochondrial genome or the respiratory chain itself. In some patients, infections and cytokines, or inborn errors of beta-oxidation enzymes or the mitochondrial genome, may favor the appearance of drug-induced microvesicular steatosis. Nonalcoholic steatohepatitis may develop under conditions causing prolonged, microvesicular, and/or macrovacuolar steatosis. In this condition, chronic impairment of mitochondrial beta-oxidation (causing steatosis) and the respiratory chain (increasing the production of ROS) lead to lipid peroxidation, which, in turn, may cause the diverse lesions of steatohepatitis, namely, necrosis, inflammation, Mallory's bodies, and fibrosis. Finally, mitochondria are involved in several forms of drug-induced cytolytic hepatitis, through inhibition or uncoupling of respiration or through a drug-induced or reactive metabolite-induced mitochondrial permeability transition. The latter effect commits hepatocytes to either apoptosis or necrosis, depending on the number of organelles that have undergone the permeability transition.

Several herbal remedies have produced hepatitis in humans. The medicinal plant, germander, was recalled after its use as an adjuvant to slimming diets resulted in an epidemic of hepatitis in France. We studied the hepatotoxicity of germander in isolated rat hepatocytes. A crude fraction containing the diverse furano diterpenoids of germander, or the purified main constituents of this fraction, teucrin A and teuchamaedryn A, were hepatotoxic (correction for hepatototoxic), but not fractions containing more polar or lipophilic constituents. [3H]Teucrin A covalently bound to hepatocyte proteins. The furano diterpenoid fraction decreased cell glutathione and cytoskeleton-associated protein thiols, and led to formation of plasma membrane blebs and cell demise. Pretreatment of male rats with troleandomycin, an inhibitor of cytochrome P450 3A (CYP3A), slowed the depletion of glutathione and decreased toxicity, whereas dexamethasone, an inducer of CYP3A, had opposite effects. Female rat hepatocytes, which poorly express CYP3A, exhibited little toxicity, unless the animals were treated with dexamethasone. Feeding male rats with a sulfur amino acid-deficient diet decreased cell glutathione and enhanced toxicity, whereas supplementation of the standard diet with cystine had opposite effects. We conclude that the furano diterpenoids of germander are activated by CYP3A into electrophilic metabolites that deplete glutathione and cytoskeleton-associated protein thiols and form plasma membrane blebs. We suggest that studies in isolated hepatocytes be included in the preclinical assessment of herbal remedies.

Isoniazid and pyrazinamide are well-known hepatotoxic drugs, often used in combination. The aim of this study was to assess the prognostic influence of pyrazinamide on the outcome of fulminant or subfulminant liver failure caused by antituberculous therapy. Eighteen patients with fulminant or subfulminant liver failure due to antituberculous therapy were studied. Nine patients received isoniazid and rifampicin without pyrazinamide (group 1), and nine patients received isoniazid and rifampicin together with pyrazinamide (group 2). The severity of fulminant and subfulminant liver failure, as judged by the prevalence of coma and the lowest level of factor V, was similar in the two groups. Spontaneous survival was greater in group 1 (eight of nine) than in group 2 (two of nine) (P.02). The authors conclude that pyrazinamide co-administration was associated with an increased mortality in patients with fulminant or subfulminant hepatitis occurring during antituberculous therapy. In these patients, pyrazinamide administration and an interval of more than 15 days between the onset of antituberculous treatment and jaundice, combined with grade III encephalopathy and factor V below 20%, predicted death without liver transplantation.

The antihypertensive drug dihydralazine may, on rare occasions, cause immunoallergic hepatitis characterized by anti-cytochrome P450 (P450)1A2 autoantibodies. To understand the first steps leading to this immune reaction, we studied the covalent binding fo dihydralazine metabolites to microsomes from rat and human livers. Upon incubation with NADPH and microsomes, dihydralazine formed metabolites that reacted with heme (as evidenced by destruction of heme, formation of 445-nm light-absorbing complexes, and covalent binding of heme to P450 apoprotein) and covalently bound to microsomal proteins. Formation of these metabolites was shown (by NADPH dependence, induction by beta-naphthoflavone, and immunoinhibition by anti-P4501A antibodies) to be mediated by P4501A. Finally, these metabolites appeared to bind to P4501A2, which produced them. These results support the following scheme for the first steps of this autoimmune reaction: P4501A2 metabolizes dihydralazine into reactive metabolites that then bind to it, forming a neoantigen that triggers an immune response characterized by autoantibodies against P4501A2.

In an attempt to better understand the mechanisms for pseudoalcoholic liver lesions in human beings, we determined the effects of perhexiline on mitochondrial functions in mice and rats. A first series of studies suggested that protonated perhexiline entered mouse mitochondria along the mitochondrial membrane potential. Release of a proton in the mitochondrial matrix led to uncoupling of oxidative phosphorylation, and accumulation of perhexiline inhibited complexes I and II of the respiratory chain, decreased ATP formation in vitro and decreased the mitochondrial beta-oxidation of long-, medium- and short-chain fatty acids in vitro and in vivo in mice. In cultured rat hepatocytes, exposure for 24 hr to 25 mumol/L perhexiline markedly decreased hepatocellular ATP and cell viability. Exposure to 5 mumol/L perhexiline did not modify ATP and viability but decreased the beta-oxidation of palmitic acid uniformly labeled with carbon 14 by 38%, increased hepatocyte triglyceride levels by 98% and produced microvesicular steatosis after 72 hr of culture. We conclude that perhexiline is concentrated inside mitochondria, where it inhibits both oxidative phosphorylation and the mitochondrial beta-oxidation of fatty acids. These effects may contribute to the development of necrosis, steatosis and possibly certain other pseudoalcoholic liver lesions in human beings.

Possible associations between particular human leucocyte antigen molecules and immunoallergic hepatitis have been suggested previously (HLA-A11 in halothane hepatitis, HLA-DR6 and DR2 in nitrofurantoin hepatitis, HLA-B8 in clometacin hepatitis). In this study the HLA haplotype was determined in 71 patients with idiosyncratic hepatitis due to different drugs. The prevalence of HLA-A11 was twice as high in the 71 patients in the study (23%) as in controls (12%), but p-values were not significant when corrections were made for the large number of comparisons (n = 39). The prevalences of HLA-DR2, DR6, and B8 were similar in the 71 patients and in controls. When hepatitis due to particular drugs was considered, HLA-A11 was found to be present in six of 12 patients (50%) with hepatitis caused by tricyclic antidepressants, and three of four patients (75%) with diclofenac hepatitis, compared to 12% in controls. HLA-DR6 was present in four of five patients (80%) with chlorpromazine hepatitis, compared to 22% in controls. In conclusion, the HLA phenotype does not contribute significantly to idiosyncratic drug-induced hepatitis considered collectively. Possible associations between some HLA molecules and the hepatotoxicity of certain drugs require further confirmation.

Human recombinant interleukin-2 (IL-2) administration is being tested in patients with advanced cancer. Its effects on the expression of cytochromes P-450 were determined in rats. IL-2 administration (1-25 x 10(6) U/kg i.v. twice daily for 1 to 4 days) resulted in a time- and dose-dependent decrease in cytochrome P-450 measured by the absorbance of its Fe(++)-CO complex. After 25 x 10(6) U/kg twice daily for 4 days, cytochrome P-450 decreased 44%; immunoreactive cytochrome P-450 1A1 decreased nonsignificantly (22%); but cytochrome P-450 1A2 decreased 68%; 2B1/2, 50%; 2C11, 75%; 2D1, 36%; and 3A, 70%. Aminopyrine N-demethylase activity decreased 53%, ethoxycoumarin O-deethylase 64%, benzo(a)pyrene hydroxylase 71%, ethoxyresorufin O-deethylase 42%, pentoxyresorufin O-dealkylase 81% and erythromycin N-demethylase 56%. In rats treated with 3-methylcholanthrene for 4 days, IL-2 coadministration (25 x 10(6) U/kg i.v. twice daily for 4 days) did not decrease significantly immunoreactive cytochrome P-450 1A1 and 1A2, whereas cytochromes P-450 2B1/2, 2C11 and 3A decreased 39, 54 and 67%, respectively. In rats treated with phenobarbital for 4 days, IL-2 coadministration decreased immunoreactive cytochromes P-450 2B1/2 29%, whereas cytochromes P-450 1A2, 2C11 and 3A decreased 38, 63 and 67%, respectively. We conclude that administration of high doses of IL-2 decreases the expression of several cytochromes P-450 in rats. Microsomal enzyme inducers appear to limit the effects of IL-2 on the induced forms of cytochromes P-450. Because much lower doses are used in humans, their potential effects on drug metabolism cannot be assessed from present results.

During the millennia of evolution, animals have been subjected to a relentless biological warfare mounted by the plants that they ingested. By duplication of an ancestral gene, divergent evolution of these 2 genes, and so forth, surviving animals have been endowed with multiple cytochromes P450s which can metabolize (and thus eliminate) a multitude of environmental liposoluble xenobiotics. A disadvantage of this system (fortunately limited by the concomitant installation of several protective systems) is that cytochrome P450 transforms some of these xenobiotics into chemically reactive metabolites. These free radicals or electrophilic metabolites attack tissue constituents, and may lead to mutation, cancer or tissue necrosis. Tissue necrosis affect mainly the liver, whose content in cytochrome P450 is particularly high. Indeed, reactive metabolites are usually extremely unstable, and react mainly in situ, in the same organ that forms them. When the formation of reactive metabolites is extensive, protective mechanisms are overwhelmed, extensive alterations of diverse hepatic constituents occur, and toxic hepatitis ensues. When the formation of reactive metabolites is moderate, severe toxic lesions do not occur. However, the covalent binding of reactive metabolites to hepatic proteins modifies the self of the subject. In some subjects, the presence of this modified self triggers immunization, and leads to immunoallergic hepatitis. The immune response may be directed either against protein (or peptide) epitopes modified by the presence of a reactive metabolite (reaction against modified self) and/or against normal, unmodified, epitopes of proteins (autoimmune reaction against the self, triggered by the modified self). Both metabolic factors, and the HLA phenotype, appear to modulate the likelihood of immunization.

Human lymphocytes were assessed as a cellular model for determining the effects of drugs on human mitochondria. Formation of total oxidized 14C-products was maximal with 1 mM [U-14C]palmitic acid, was linear for 90 min, linear with the number of lymphocytes, and decreased by 95% and 77% in the presence of 30 microM rotenone and 2 mM KCN. Seven drugs were tested which had previously been shown to inhibit beta-oxidation in animals; all decreased formation of total oxidized 14C-products by human lymphocytes, but with different IC50 values: 35 microM with amiodarone, 2.75 mM with tetracycline and amineptine, 3.75 mM with tianeptine, and more than 10 mM for valproic acid and the ibuprofen enantiomers. Formation of [14C]CO2 either increased or decreased, in relation to the various effects of these drugs on coupling, beta-oxidation, and the tricarboxylic acid cycle. There was a general trend for some relationship between inhibition of fatty acid oxidation and loss of cellular ATP. Those compounds, however, which uncoupled oxidative phosphorylation (2,4-dinitrophenol, amiodarone, ibuprofen) and/or inhibited the mitochondrial respiratory chain (amiodarone, rotenone, KCN) resulted in comparatively higher ATP depletion. Amiodarone, a drug which produces several effects (uncoupling, inhibition of beta-oxidation, of the tricarboxylic acid cycle and of the respiratory chain), caused a dramatic decrease in cellular ATP and cell viability at low concentrations (20-100 microM). Both these effects were prevented by the addition of 5 mM glucose, a substrate for anaerobic glycolysis. We conclude that human lymphocytes may be a useful model for assessing the effects of drugs on human mitochondrial function. IC50 values determined with this model may not necessarily apply, however, to other cells.

The liver is the first organ encountered by drugs after their absorption from the gut. It is also richly endowed in enzymatic systems that metabolize foreign compounds. In the process, highly toxic intermediates may be formed. It is not surprising, therefore, that the liver should be a principal site for adverse drug reactions. Indeed, iatrogenic liver injury is a frequent cause of liver disease in elderly individuals, who are less likely than younger ones to have been exposed recently to hepatitis viruses and are more likely to take many medications simultaneously. Whereas discontinuation of the treatment usually leads to prompt recovery, pursuing it may lead to fulminant hepatitis or chronic liver lesions. Prompt recognition of an iatrogenic cause, and immediate withdrawal of the offending drug, should therefore be a major concern for physicians.

Four patients developed acute hepatitis after receiving Atrium, an association of phenobarbital, febarbamate and difebarbomate, for the treatment of tremor or for the prevention of alcohol withdrawal symptoms. Hepatitis occurred 1 to 3 months after treatment. Asthenia was the unique clinical manifestation. Marked increase in serum aminotransferases and gamma-glutamyltranspeptidase levels were the main biological features. Histological examination showed liver cell necrosis in two cases, prominent in the centrolobular area in one case. There was no case of hepatic failure. Atrium withdrawal was followed by complete recovery within 6 to 12 weeks. The mechanism of Atrium hepatotoxicity remains unknown.

Administration of troleandomycin (0.5 mmol.kg-1 p.o. daily for 5 days) decreased by 61% and 36%, respectively, the estradiol and ethinylestradiol 2/4-hydroxylase activities of hepatic microsomes from male Sprague-Dawley rats killed 2 hr after the last dose. This decrease did not appear to be due to the in vivo formation of the inactive cytochrome P-450 p Fe(II)-metabolite complex, since disruption of this complex with potassium ferricyanide did not increase estrogen hydroxylase activities. Troleandomycin administration, however, essentially suppressed cytochrome P-450 UT-A (one of the P-450 forms involved in the hydroxylation of estrogens) and resulted in the appearance of cytochrome P-450 forms whose estradiol hydroxylase activity was inhibitable by troleandomycin in vitro. Similarly, troleandomycin (2 mM) inhibited by 60% estradiol and ethinylestradiol 2/4-hydroxylase activities in microsomes from dexamethasone-treated rats, although it had no inhibitory effect in microsomes from control rats. In contrast, erythromycin and roxithromycin (2 mM) exerted no inhibitory effect, even in microsomes from dexamethasone-treated rats. In vivo, these macrolides (0.5 mmol.kg-1 p.o. daily for 5 days) decreased moderately cytochrome P-450 UT-A levels and estradiol 2/4-hydroxylase activity, and did not modify ethinylestradiol 2/4-hydroxylase activity. We conclude that the administration of troleandomycin, but not that of erythromycin or roxithromycin, decreases ethinylestradiol 2/4-hydroxylase activity in male rat liver microsomes, as a possible consequence of decreased cytochrome P-450 UT-A levels and of the induction of glucocorticoid-responsive P-450 forms whose ethinylestradiol hydroxylase activity is inhibitable by troleandomycin.

Administration of silymarin (800 mg/kg i.p.) 30 min before carbon tetrachloride (18 microL/kg i.p.) did not modify total hepatic levels of CCl4 and metabolites in mice, but decreased by 40% the in vivo covalent binding of CCl4 metabolites to hepatic lipids at 2 hr. This pretreatment decreased by 60% the exhalation of ethane during the first hour after CCl4, and decreased by 50% the incidence of liver cell necrosis. In vitro, silymarin (800 micrograms/mL) decreased by 50 to 70% various monooxygenase activities, and decreased by 20% the covalent binding of CCl4 metabolites to microsomal proteins. Silymarin (800 micrograms/mL) decreased by 70% in vitro lipid peroxidation mediated by CCl4 metabolites, and decreased by 90% peroxidation mediated by NADPH alone. Silibinin, one of the three isomers composing silymarin, also decreased carbon tetrachloride-induced lipid peroxidation; this effect, however, was less than that of silymarin in vitro, and was more transient in vivo. Pretreatment with silibinin (800 mg/kg i.p.) 30 min before CCl4 (18 microL/kg i.p.) did not improve SGPT activity or liver histology at 24 hr. We conclude that silymarin prevents carbon tetrachloride-induced lipid peroxidation and hepatotoxicity in mice, firstly, by decreasing the metabolic activation of CCl4, and, secondly, by acting as a chain-breaking antioxidant.

Adverse drug reactions may mimic almost any kind of liver disease. Acute hepatitis is often due to the formation of reactive metabolites in the liver. Despite several protective mechanisms (epoxide hydrolases, conjugation with glutathione), this formation may lead to predictable toxic hepatitis after huge overdoses (e.g. paracetamol), or to idiosyncratic toxic hepatitis after therapeutic doses (e.g. isoniazid). Both genetic factors (e.g. constitutive levels of cytochrome P-450 isoenzymes, or defects in protective mechanisms) and acquired factors (e.g. malnutrition, or chronic intake of alcohol or other microsomal enzyme inducers) may explain the unique susceptibility of some patients. Formation of chemically reactive metabolites may also lead to allergic hepatitis, probably through immunization against plasma membrane protein epitopes modified by the covalent binding of the reactive metabolites. This may be the mechanism for acute hepatitis produced by many drugs (e.g. amineptine, erythromycin derivatives, halothane, imipramine, isaxonine, α-methyldopa, tienilic acid, etc.). Genetic defects in several protective mechanisms (e.g. epoxide hydrolase, acetylation) may explain the unique susceptibility of some patients, possibly by increasing exposure to allergenic, metabolite-altered plasma membrane protein epitopes. Like toxic idiosyncratic hepatitis, allergic hepatitis occurs in a few patients only. Unlike toxic hepatitis, allergic hepatitis is frequently associated with fever, rash or other hypersensitivity manifestations; it may be hepatocellular, mixed or cholestatic; it promptly recurs after inadvertent drug rechallenge. Lysosomal phospholipidosis occurs frequently with three antianginal drugs (diethylaminoethoxyhexestrol, amiodarone and perhexiline). These cationic, amphiphilic drugs may form phospholipid-drug complexes within lysosomes. Such complexes resist phospholipases and accumulate within enlarged lysosomes, forming myeloid figures. This phospholipidosis has little clinical importance. In a few patients, however, it is associated with alcoholic-like liver lesions leading to overt liver disease and, at times, cirrhosis. Subjects with a deficiency in a particular isoenzyme of cytochrome P-450 poorly metabolize perhexiline and are at higher risk of developing liver lesions. Prolonged, drug-induced liver-cell necrosis may also lead to subacute hepatitis, chronic hepatitis or even cirrhosis. This usually occurs when the drug administration is continued, either because the liver disease remains undetected or because its drug aetiology is overlooked. Several autoantibodies may be present. Physicians should consider the possibility of a drug-related aetiology in any patient with hepatobiliary disease. Prompt withdrawal of suspected drugs will usually avoid extension or prolongation of the liver disease. There are exceptions, however, either when the drug slowly leaves the liver (e.g. amiodarone or perhexiline), or perhaps when autoimmunity is present. Determination of the mechanisms of hepatitis may permit the safer use of present drugs and the rational development of safer analogues. Increased efforts to characterize the various genetic defects responsible for the unique susceptibility of some individuals to certain drugs may make it possible to detect subjects at risk.

We report the cases of 2 female patients aged 69 and 61 yr, suffering from fulminant hepatitis induced by pirprofen, a new nonsteroidal antiinflammatory drug. The duration of pirprofen administration before the onset of hepatitis was long, 7 and 9 mo, respectively. Hepatitis was not preceded or accompanied by hypersensitivity manifestations. The liver lesion consisted of massive, predominantly centrilobular hepatic cell necrosis and microvesicular steatosis. One patient died of liver failure. Although the risk of fulminant hepatitis is very low, we recommend that, in patients taking pirprofen for more than 2 mo and complaining of asthenia, nausea, or vomiting, serum aminotransferase levels should be measured and administration of the drug should be interrupted as soon as an increased level is noted.

1. The effects of arachidonic acid on hepatic drug-metabolizing enzymes was investigated in male ICR-Swiss mice. 2. A single administration of arachidonic acid, 100 mg/kg i.p., doubled the hexobarbital sleeping time. Arachidonic acid in vitro gave a type I binding spectrum with hepatic microsomes; it inhibited the metabolism of hexobarbital and of ethylmorphine, two type I binding drugs, but not that of aniline, a type II binding drug; the inhibition of hexobarbital metabolism by arachidonic acid was competitive. 3. Repeated administration of arachidonic acid up to a total dose of 1000 mg/kg i.p., either in the course of 5 hours, or in the course of 5 days, decreased microsomal cytochrome P-450 levels and NADPH-cytochrome c reductase activity. 4. It is concluded that the administration of arachidonic acid may impair drug metabolism in two ways, mainly, by competitively inhibiting the activity of drug-metabolizing enzymes, and secondarily, by decreasing the hepatic concentration of these enzymes.

The authors report the cases of 3 patients who died from fulminant hepatitis after receiving iproclozide, a hydrazine-containing monoamine oxidase inhibitor. Fulminant hepatitis in these patients resembled that reported in patients receiving other hydrazine-containing monoamine oxidase inhibitors: (1) the 3 patients were women; (2) the monoamine oxidase inhibitor has been ingested for 1 month or more; (3) the main clinical manifestations were jaundice and disorders of consciousness; (4) hypersensitivity manifestations were absent; (5) the predominant liver lesion was necrosis; (6) all 3 patients died. In our 3 patients, jaundice occurred 7 to 10 days after the adjunction to iproclozide of a microsomal enzyme inducer. These observations suggest that concomitant administration of iproclozide and of microsomal enzyme inducers may produce fulminant hepatitis in man. It is speculated that iproclozide could be, like iproniazid, transformed into a hepatotoxic metabolite, the production of which would be increased by microsomal enzyme induction.

The authors report 6 cases of fulminant hepatitis in patients treated with isoniazid and rifampin. In 4 of these patients, the treatment had been started within 3 days after a general anesthesia. The course of the disease was remarkably similar in all 6 patients: (1) the time interval from the beginning of the isoniazid-rifampin administration to the onset of jaundice was 6 to 10 days; (2) disorders of consciousness appeared less than 3 days after the onset of jaundice; (3) serum transaminases were 26 to 80 times the upper limit of normal; (4) the main liver lesion was centrilobular necrosis; (5) hypersensitivity manifestations were absent; (6) all 6 patients recovered. Fulminant hepatitis might be attributable to a hepatotoxic metabolite of isoniazid, the production of which would be attributable to a hepatotoxic metabolite of isoniazid, the production of which would be increased as a consequence of the enzyme-inducing effect of rifampin and, possibly, other drugs administered for general anesthesia.

Administration of [14C]tianeptine (0.5 mmol/kg i.p.) to non-pretreated hamsters resulted in the in vivo covalent binding of [14C]tianeptine metabolites to liver, lung and kidney proteins; this very high dose (360-fold the human therapeutic dose) depleted hepatic glutathione by 60%, and increased SGPT activity 5-fold. Lower doses (0.25 and 0.125 mmol/kg) depleted hepatic glutathione to a lesser extent and did not increase SGPT activity. Pretreatment of hamsters with piperonyl butoxide decreased in vivo covalent binding to liver proteins, and prevented the increase in SGPT activity after administration of tianeptine (0.5 mmol/kg i.p.). In contrast, pretreatment of hamsters with dexamethasone increased in vivo covalent binding to liver proteins, and increased SGPT activity after administration of tianeptine (0.5 mmol/kg i.p.). Nevertheless, liver cell necrosis was histologically absent 24 hr after the administration of tianeptine (0.5 mmol/kg i.p.) to non-pretreated or dexamethasone-pretreated hamsters. In vivo covalent binding to liver proteins also occurred in mice and rats, being increased by 100% in dexamethasone-pretreated animals. In vivo covalent binding to liver proteins was similar in untreated female Dark Agouti rats and in female Sprague-Dawley rats. These results show that tianeptine is transformed in vivo by cytochrome P-450, including glucocorticoid-inducible isoenzymes, into chemically reactive metabolites that covalently bind to tissue proteins. The metabolites, however, exhibit no direct hepatotoxic potential in hamsters below the sublethal dose of 0.5 mmol/kg i.p. The predictive value of this study regarding possible idiosyncratic and immunoallergic reactions in humans remains unknown.

Seven patients developed acute hepatitis after receiving Plethoryl for obesity for 4 to 16 weeks. Jaundice was generally associated with or preceded by asthenia, nausea and pruritus. Serum aminotransferase activities were markedly increased whereas alkaline phosphatase and gamma-glutamyltransferase activities were moderately elevated. There was no hepatic failure. In all cases, Plethoryl administration was promptly discontinued. In 6 cases, jaundice disappeared within 2 to 4 weeks, and recovery occurred within 2 to 5 months. In one case, however, jaundice disappeared within 12 weeks and recovery took 10 months.

Incubation of [14C]amineptine (1 mM) with hamster liver microsomes resulted in the irreversible binding of an amineptine metabolite to microsomal proteins. Covalent binding measured in the presence of various concentrations of amineptine (0.0625-1 mM) followed Michaelis-Menten kinetics. Pretreatment with phenobarbital increased not only the Vmax, but also the Km, for this binding. Covalent binding required NADPH and molecular oxygen and was decreased when the incubation was made in the presence of inhibitors of cytochrome P-450 such as piperonyl butoxide (4 mM), SKF 525-A (4 mM) or carbon monoxide (80:20 CO-O2 atmosphere). In contrast, binding was increased when microsomes from untreated hamsters were incubated in the presence of 0.5 mM 1,1,1-trichloropropene 2,3-oxide, an inhibitor of epoxide hydrolase. Metabolic activation also occurred in kidney microsomes. In vitro covalent binding to kidney microsomal proteins required NADPH and was decreased by piperonyl butoxide (4 mM) but was not increased by pretreatment with phenobarbital. We conclude that amineptine is activated by hamster liver and kidney microsomes into a chemically reactive metabolite that covalently binds to microsomal proteins.

Certain drugs are transformed into reactive metabolites by cytochrome P-450, a hepatic microsomal enzyme. The reactive metabolites covalently bind to hepatocyte macromolecules, thus determining liver lesions. Induction of microsomial enzymes increases the formation of reactive metabolites and exaggerates hepatotoxicity of these drugs.

The possibility of a relationship between hepatic and renal cytochrome P-450 contents was assessed in rats with liver disease. In rats killed 3 days after two-thirds hepatectomy (a model for hepatocellular insufficiency), the total microsomal cytochrome P-450 content of the whole liver was decreased by 60% as compared to that in control rats; renal cytochrome P-450 was increased by 30% while the 7-ethoxycoumarin deethylase activity of kidney microsomes was increased by 80%. In rats killed 7 days after bile duct ligation (a model for cholestasis) or 35 days after bile duct ligation (a model for biliary cirrhosis), hepatic cytochrome P-450 was decreased by 60% and 45%, respectively, while renal cytochrome P-450 content was increased by 50% and 150%, respectively. In contrast, in rats killed 15 days after the last dose of carbon tetrachloride, 1.3 ml/kg twice weekly for 3 months (a model for post-necrotic cirrhosis), both hepatic and renal cytochrome P-450 contents remained unchanged. Phenobarbital (80 mg/kg daily for 3 days) was a poor inducer of renal cytochrome P-450 in sham-operated rats but became a potent inducer of renal cytochrome P-450 in rats with two-thirds hepatectomy. We conclude that renal cytochrome P-450 is increased in three models in which hepatic cytochrome P-450 contents are decreased (two-thirds hepatectomy, cholestasis and biliary cirrhosis), but remains unchanged in a model of severe liver pathology, in which hepatic cytochrome P-450 content is not modified (late, post-necrotic cirrhosis). The hypothetical role of endogenous inducer(s) is discussed.

The mechanism for trichloroethylene hepatotoxicity was investigated in male Sprague-Dawley rats. Phenobarbital pretreatment increased and CoCl2 pretreatment decreased trichloroethylene hepatotoxicity. After administration of 1(14)C]trichloroethylene, a radioactive material became irreversibly bound to hepatic proteins, while negligible amounts were bound to muscle proteins. When 1(14)C]trichloroethylene was incubated under air with hepatic microsomes and a NADPH-generating system, a radioactive material became irreversibly bound to microsomal proteins; binding was negligible when the NADPH-generating system was omitted; binding was inhibited by carbon monoxide and by piperonyl butoxide; the amount of bound material was greater with microsomes from phenobarbital-pretreated rats and lower with microsomes from CoCl2-pretreated rats than with microsomes from nonpretreated rats. Trichloroethylene administration decreased hepatic glutathione in normal rats but not in piperonyl butoxide-pretreated rats; in vitro, glutathione decreased the amount of trichloroethylene material that bound to microsomal proteins. The reported results are consistent with the view that 1) trichloroethylene is metabolized by cytochrome P-450 into a chemically reactive metabolite which reacts with, and binds to, either proteins or glutathione, 2) binding to proteins produces liver lesions and 3) binding to glutathione decreases the amount of reactive metabolite available for binding to proteins.