The influence of ethanol pretreatment on the effects of nine hepatotoxic agents

The role of CYP2A5 in liver injury and fibrosis: chemical-specific difference

Liver injuries induced by carbon tetrachloride (CCL4) or thioacetamide (TAA) are dependent on cytochrome P450 2E1 (CYP2E1). CYP2A5 can be induced by TAA but not by CCL4. In this study, liver injury including fibrosis induced by CCL4 or TAA were investigated in wild-type (WT) mice and CYP2A5 knockout (cyp2a5 (-/-) ) mice as well as in CYP2E1 knockout (cyp2e1 (-/-) ) mice as a comparison. Acute and subchronic liver injuries including fibrosis were induced by CCL4 and TAA in WT mice but not in cyp2e1 (-/-) mice, confirming the indispensable role of CYP2E1 in CCL4 and TAA hepatotoxicity. WT mice and cyp2a5 (-/-) mice developed comparable acute liver injury induced by a single injection of CCL4 as well as subchronic liver injury including fibrosis induced by 1 month of repeated administration of CCL4, suggesting that CYP2A5 does not affect CCL4-induced liver injury and fibrosis. However, while 200 mg/kg TAA-induced acute liver injury was comparable in WT mice and cyp2a5 (-/-) mice, 75 and 100 mg/kg TAA-induced liver injury were more severe in cyp2a5 (-/-) mice than those found in WT mice. After multiple injections with 200 mg/kg TAA for 1 month, while subchronic liver injury as indicated by serum aminotransferases was comparable in WT mice and cyp2a5 (-/-) mice, liver fibrosis was more severe in cyp2a5 (-/-) mice than that found in WT mice. These results suggest that while both CCL4- and TAA-induced liver injuries and fibrosis are CYP2E1 dependent, under some conditions, CYP2A5 may protect against TAA-induced liver injury and fibrosis, but it does not affect CCL4 hepatotoxicity.

Paracetamol-induced hepatotoxicity at recommended dosage

In patients who develop liver damage following moderate paracetamol overdose in the order of 5-10 g daily, recent fasting and nutritional impairment have been identified as key precipitants. Hepatotoxicity caused by paracetamol at recommended dosage, in the absence of exposure to enzyme-inducing drugs, has recently been described as an idiosyncratic phenomenon. The possible importance of fasting and malnutrition in this setting is uncertain. We report a severely malnourished 53-year-old woman who developed severe hepatotoxicity whilst receiving paracetamol at recommended dosage (4 g daily) following a period of fasting, in the absence of enzyme-inducing agents. Subsequent paracetamol exposure up to 2.6 g daily thrice weekly, in the setting of ongoing malnutrition and fasting as before, did not lead to recurrent liver damage. These findings indicate that paracetamol-related liver damage occurring within recommended dosage guidelines can be a dose-dependent rather than necessarily idiosyncratic phenomenon, at least in the setting of recent fasting and severe malnutrition.

Oxidative damage to the hepatocellular proteins after chronic ethanol intake in the rat

BACKGROUND

Protein carbonyl content, a measure of oxidative damage to hepatocellular proteins, and the activities of some thiol-containing proteins were assayed in the liver and plasma, as thiol-containing protein, appear to be targets for free radicals. These may be important in the mechanism of ethanol-induced liver injury.

METHODS

Tap water containing ethanol at the concentration of 25% (v/v) and phenobarbital (500 mg/l) was the only source of drinking water for the experimental rats for 24 months. Another group of rats were administered 25% (v/v) ethanol alone in drinking water for 24 months. Control rats were administered either phenobarbital alone in drinking water or tap water for 24 months. At the end of 24 months, the rats were sacrificed. The protein carbonyl content, activities of glutamine synthase and biotinidase-sulfhydryl group containing enzymes were assayed in the liver along with alkaline protease, an enzyme that degrades oxidized proteins. The total thiol, albumin and the activity of biotinidase were measured in the plasma.

RESULTS

The protein carbonyl content of the liver was increased in the ethanol/phenobarbital-treated rats as well as in the ethanol-treated rats as compared with the controls. The activities of glutamine synthase and biotinidase were decreased significantly in the livers of ethanol/phenobarbital-treated rats as well as the ethanol-treated rats as compared with the controls. The activity of alkaline protease was increased significantly in both the ethanol-treated groups. In the plasma of ethanol/phenobarbital-treated rats as well as the ethanol-treated rats total thiol, albumin and the activity of biotinidase were decreased significantly as compared with the controls. The ethanol/phenobarbital-treated rats as well as the ethanol-treated rats developed fatty liver.

CONCLUSIONS

Damage to proteins occurs upon chronic ethanol intake in the rat, and it may play a role in the pathogenesis of alcohol-induced fatty liver.

Alcohol exposure and paracetamol-induced hepatotoxicity

Most instances of hepatotoxicity due to paracetamol in the United Kingdom and Australia are the result of large overdoses of the drug taken with suicidal or parasuicidal intent. In contrast, serious hepatotoxicity at recommended or near-recommended doses for therapeutic purposes has been reported, mainly from the United States and in association with chronic alcohol use, leading to the widely held belief that chronic alcoholics are predisposed to paracetamol-related toxicity at relatively low doses. Yet the effects of alcohol on paracetamol metabolism are complex. Studies performed in both experimental animals and humans indicate that chronic alcohol use leads to a short-term, two- to threefold increase in hepatic content of cytochrome P4502E1, the major isoform responsible for the generation of the toxic metabolite from paracetamol, although increased oxidative metabolism of paracetamol at recommended doses has not been demonstrated clinically. A reduced hepatic content of glutathione, required to detoxify the reactive metabolite, has been documented in chronic alcoholics, due probably to associated fasting and malnutrition, providing a metabolic basis for any possible predisposition of this group to hepatotoxicity at relatively low paracetamol doses. Simultaneous alcohol and paracetamol ingestion reduces oxidative metabolism of paracetamol in both rodents and humans, predominantly as a consequence of depletion in cytosol of free NADPH. The possibilities that chronic alcohol use may predispose to paracetamol-related hepatotoxicity and that alcohol taken with paracetamol may protect against it, based on these metabolic observations, are examined in this review.

Chlorinated methanes and liver injury: highlights of the past 50 years

The chlorinated methanes, particularly carbon tetrachloride and chloroform, are classic models of liver injury and have developed into important experimental hepatoxicants over the past 50 years. Hepatocellular steatosis and necrosis are features of the acute lesion. Mitochondria and the endoplasmic reticulum as target sites are discussed. The sympathetic nervous system, hepatic hemodynamic alterations, and role of free radicals and biotransformation are considered. With carbon tetrachloride, lipid peroxidation and covalent binding to hepatic constituents have been dominant themes over the years. Potentiation of chlorinated methane-induced liver injury by alcohols, aliphatic ketones, ketogenic compounds, and the pesticide chlordecone is discussed. A search for explanations for the potentiation phenomenon has led to the discovery of the role of tissue repair in the overall outcome of liver injury. Some final thoughts about future research are also presented.

Paracetamol, alcohol and the liver

It is claimed that chronic alcoholics are at increased risk of paracetamol (acetaminophen) hepatotoxicity not only following overdosage but also with its therapeutic use. Increased susceptibility is supposed to be due to induction of liver microsomal enzymes by ethanol with increased formation of the toxic metabolite of paracetamol. However, the clinical evidence in support of these claims is anecdotal and the same liver damage after overdosage occurs in patients who are not chronic alcoholics. Many alcoholic patients reported to have liver damage after taking paracetamol with 'therapeutic intent' had clearly taken substantial overdoses. No proper clinical studies have been carried out to investigate the alleged paracetamol-alcohol interaction and acute liver damage has never been produced by therapeutic doses of paracetamol given as a challenge to a chronic alcoholic. The paracetamol-alcohol interaction is complex; acute and chronic ethanol have opposite effects. In animals, chronic ethanol causes induction of hepatic microsomal enzymes and increases paracetamol hepatotoxicity as expected (ethanol primarily induces CYP2E1 and this isoform is important in the oxidative metabolism of paracetamol). However, in man, chronic alcohol ingestion causes only modest (about twofold) and short-lived induction of CYP2E1, and there is no corresponding increase (as claimed) in the toxic metabolic activation of paracetamol. The paracetamol-ethanol interaction is not specific for any one isoform of cytochrome P450, and it seems that isoenzymes other than CYP2E1 are primarily responsible for the oxidative metabolism of paracetamol in man. Acute ethanol inhibits the microsomal oxidation of paracetamol both in animals and man. This protects against liver damage in animals and there is evidence that it also does so in man. The protective effect disappears when ethanol is eliminated and the relative timing of ethanol and paracetamol intake is critical. In many of the reports where it is alleged that paracetamol hepatotoxicity was enhanced in chronic alcoholics, the reverse should have been the case because alcohol was actually taken at the same time as the paracetamol. Chronic alcoholics are likely to be most vulnerable to the toxic effects of paracetamol during the first few days of withdrawal but maximum therapeutic doses given at this time have no adverse effect on liver function tests. Although the possibility remains that chronic consumption of alcohol does increase the risk of paracetamol hepatotoxicity in man (perhaps by impairing glutathione synthesis), there is insufficient evidence to support the alleged major toxic interaction. It is astonishing that clinicians and others have unquestion-ingly accepted this supposed interaction in man for so long with such scant regard for scientific objectivity.

The hepatic interaction of aliphatic alcohols with halogenated hydrocarbons

As has been noted, advancement in understanding of chemical interactions requires an integrated approach. Given the large number of binary mixtures of aliphatic alcohols and halogenated hydrocarbons that can be formulated, and because limitations of time and resources make it impossible to test them all, careful thought should be given to selection of pairs for laboratory experimentation. For any given pair of chemicals, the type of interaction (addition, synergism, antagonism, potentiation) should be determined and described by appropriate experimental designs and statistical methodology. This has been done for various alcohol-halocarbon mixtures. Work to expand our understanding of the mechanism(s) underlying the interaction of aliphatic alcohols and halogenated hydrocarbons would be particularly useful, as an improved mechanistic understanding would improve our ability to extrapolate across dose levels (from high laboratory exposure concentrations to typical human environmental exposure concentrations) and across species (from laboratory animals to humans).

A 7-year experience of severe acetaminophen-induced hepatotoxicity (1987-1993)

BACKGROUND & AIMS

Five hundred sixty patients admitted between January 1, 1987, and December 31, 1993, with severe acetaminophen-induced hepatotoxicity were studied. The aim of this study was to identify why severe acetaminophen-induced hepatotoxicity still occurs and to determine how known risk factors and advances in management have affected the pattern of illness and outcome.

METHODS

This was a retrospective study of the etiologic factors and the clinical course of all acetaminophen-related admissions.

RESULTS

The number of admissions increased from 58 in 1987 to 123 in 1993. During the corresponding period, overall survival improved from just < 50% to 78%. The percentage of admissions treated with N-acetylcysteine increased from 40% in 1987 to 83% in 1993. The frequency with which grade III or IV encephalopathy developed decreased from 62% in 1987 to 40% in 1993, and the percentage of these patients who developed cerebral edema decreased from 61% to 45% during the same period. There was an increase in both the number of patients transplanted and the survival of those managed medically.

CONCLUSIONS

Severe acetaminophen-induced hepatotoxicity remains a serious condition, but the increasing use of N-acetylcysteine, advances in medical management, and the increasing availability of transplantation have resulted in a significant improvement in survival rates.

Hepatotoxicity due to repeated intake of low doses of paracetamol

The cases of two patients with fulminant hepatic failure after intake of therapeutic doses (4-8 g) of paracetamol, and who were admitted to hospital for assessment for liver transplantation, are described. In both patients starvation, due to abdominal pain, nausea and vomiting or diarrhoea, was probably contributing to the toxic effect of the drug. One of the patients also had an excessive alcohol intake. Paracetamol should not be prescribed for patients with alcoholism or with low food intake.

Ethanol decreases cadmium hepatotoxicity in rats: possible role of hepatic metallothionein induction

The present investigation examines the possibility that Cd and ethanol have a significant toxicological interaction. This examination was warranted as exposure to either chemical is known to compromise human health. Inasmuch as both chemicals affect the morphology, biochemistry, and physiology of liver, it seemed reasonable to consider liver as a possible site of interaction. Specifically, the hypothesis that ethanol alters the hepatotoxic action of Cd was evaluated. Accordingly, male rats were injected iv with hepatotoxic (3.0 mg/kg) or lethal (4.5 mg/kg) dosages of Cd, 24 hr after single-dose ethanol administration (7 g/kg, po). Cd-induced hepatotoxicity was assessed by measuring the activities of alanine aminotransferase, aspartate aminotransferase, and sorbitol dehydrogenase in serum collected 10 hr after Cd injection. Lethality was assessed by recording the number of survivors over a 7-day period. Prior exposure to ethanol substantially reduced the lethal and hepatotoxic properties of Cd. Two mechanisms were evaluated in an effort to explain ethanol-induced suppression of Cd hepatotoxicity. Ethanol pretreatment was postulated to: (1) enhance Cd excretion in bile thereby decreasing hepatic Cd content and/or (2) reduce the interaction between Cd and target sites in liver such as organelles and cytosolic high-molecular-weight (HMW) proteins. The first proposed mechanism was incorrect as the biliary excretion of Cd was nearly abolished and the concentration of Cd in whole liver increased (33%) as a result of ethanol exposure. The second proposed mechanism was a plausible explanation of ethanol-induced suppression of Cd hepatotoxicity because ethanol pretreatment decreased (approximately 60%) the content of Cd in nuclei, mitochondria, and endoplasmic reticulum, and nearly eliminated the association of Cd with cytosolic HMW proteins. Reduction in the concentration of Cd in potential target sites of intoxication was caused by a metallothionein-promoted sequestration of Cd in cytosol.

The effect of cigarette smoke on the plasma piroxicam concentrations in rats

The plasma concentration of unchanged piroxicam has been determined at 15, 30, 60 and 90 min after 10 mg kg-1 oral administration of the drug to rats exposed to cigarette smoke or pretreated with phenobarbitone, 3,4-benzpyrene or ethanol. Plasma piroxicam concentrations decreased in rats pretreated with phenobarbitone, 3,4-benzpyrene and ethanol and in rats 24 h after exposure to cigarette smoke.

Effect of 2-butanol and 2-butanone on rat hepatic ultrastructure and drug metabolizing enzyme activity

The effect of a single oral dose of 2-butanol (2.2 ml/kg) or 2-butanone (1.87 ml/kg) on hepatic ultrastructure and drug-metabolizing enzyme activity was studied in the rat. A 135-197% increase in acetanilide hydroxylase activity was found in rats sacrificed 12-40 h after dosing with 2-butanol or 2-butanone. A 40-h pretreatment with 2-butanone produced a 155% increase in aminopyrine N-demethylase activity. NADPH-cytochrome c reductase activity and the concentrations of cytochromes P-450 and b5 were largely unaltered 2-40 h after dosing with either agent. Electron microscopic examination of hepatocytes from rats sacrificed 16 h after 2-butanol or 2-butanone revealed a marginal increase in the prevalence of smooth endoplasmic reticulum. However, by 40 h, there was a marked proliferation of the smooth endoplasmic reticulum and reduction in rough endoplasmic reticulum in response to both agents. The most marked potentiation of CCl4 hepatotoxicity occurred when rats were pretreated with 2-butanol or 2-butanone 16 h before CCl4 administration. The coincidental finding of maximal CCl4-induced hepatic injury and elevation of microsomal xenobiotic activity within the same time frame following 2-butanol or 2-butanone supports the hypothesis that aliphatic alcohols and ketones potentiate CCl4 hepatotoxicity by enhancing biotransformation of the halocarbon to cytotoxic metabolites.

[Carbon tetrachloride poisoning in a swine model]

It was intended to establish a model for acute hepatic failure in order to test the function of isolated and auxiliary transplanted hepatocytes. 6 pigs (19.75-27.0 kg) were intoxicated with different dosages of CCl4 and ethanol. According to publications on acute hepatic failure induced in rats by CCl4, adequate dosages were applied in pigs. Three different regimens of CCl4 and C2H5OH applications were used: CCl4 was administered intragastrically alone (group 1) or combined with ethanol (group 2), and CCl4 was given intragastrically and ethanol intravenously (group 3). Animals of group 1 and 2 survived intoxication for the period of observation. Histological examination of the livers revealed central necrosis, ghost cells and swollen hepatocytes. The animals of group 3 died shortly after intoxication. Histological examination did not show any evidence for acute hepatic failure. CCl4 and C2H5OH intoxication in pigs causes effects that are different from those described in humans or laboratory rats. Therefore it should be necessary to use a large number of animals to establish a standardized model for acute hepatic failure in pigs that reflects the observations in humans.

The effect of diurnal rhythms on the hepatotoxicity of thioacetamide in male and female rats

Single 200 mg/Kg body weight i.p. injections of thioacetamide administered to litter mate male and female rats at 09.00, 13.00, 17.00 and 21.00 h caused body weight losses, elevated plasma glutamate pyruvate transaminase (GPT) levels, decreases in hepatic glycogen, zone 3-specific necrosis and leucocyte infiltration. All of these changes were more marked in males. The effects of thioacetamide on females were more severe at later injection times while no diurnal variations were apparent in males. Decreases in hepatic glycogen were most obvious in necrotic perivenous hepatocytes and correlated with increases in active glycogen phosphorylase which were probably caused by raised cytosolic calcium concentrations resulting from thioacetamide induced damage to cell membranes.

Effects of ethanol feeding and withdrawal on plasma glutathione elimination in the rat

Chronic ethanol feeding increases hepatic turnover and sinusoidal efflux of glutathione in rats. The present study was performed to determine whether the observed increase in glutathione efflux was due to increased extrahepatic requirements for glutathione. The concentration and disposition of plasma glutathione were determined in rats fed liquid diets containing 36% of calories as ethanol or pair-fed an isocaloric mixture with carbohydrate replacing ethanol calories for 5 to 8 weeks. The half-life and plasma clearance of [35S]glutathione were found to be similar in ethanol-fed and control rats and in rats withdrawn 24 hr from ethanol. Uptakes of the sulfur moiety of [35S]glutathione by kidney, jejunal mucosa, liver, lung, spleen, muscle and heart were also unchanged by ethanol feeding. The plasma glutathione concentration was significantly higher in ethanol-withdrawn rats 22.30 +/- 3.06 nmoles per ml (p less than 0.05) compared to pair-fed controls (13.51 +/- 2.04), while rats continuing to drink ethanol had intermediate levels (16.96 +/- 2.22). Plasma cysteine levels were slightly, but not significantly, higher in ethanol-fed rats. These findings suggest that increased sinusoidal efflux of glutathione in ethanol-fed rats is due to a direct effect of ethanol on hepatic glutathione transport and not due to an alteration in extrahepatic disposition of glutathione. In order to characterize further the effects of ethanol feeding on glutathione-dependent detoxification, activities of glutathione S-transferase, glutathione reductase and gamma-glutamyltransferase were determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced acetaminophen toxicity associated with prior alcohol consumption in mice: prevention by N-acetylcysteine

It is well established that hepatotoxicity is associated with an overdose of acetaminophen and that this hepatotoxicity can be increased by prior alcohol exposure in either humans or animal models. N-Acetylcysteine (NAC) has been developed as a tool to prevent the hepatotoxicity associated with acetaminophen overdosing. The present investigation observed that prior acute and chronic ingestion of alcohol to mice resulted in enhanced toxicity following acetaminophen injection. This increased toxicity was prevented by treatment with NAC. These results suggest that NAC may be a useful tool for combatting the enhanced acetaminophen toxicity associated with alcohol ingestion.

Non-narcotic analgesics. Problems of overdosage

The first cases of fulminant hepatic failure due to paracetamol poisoning were reported in 1966, and in the United Kingdom this condition is now responsible for more cases of acute hepatic failure than any other cause. Adults account for the majority of serious and fatal cases of paracetamol poisoning and it is extremely rare for young children to ingest sufficient paracetamol to cause more than minimal liver damage. A single measurement of the plasma paracetamol concentration is an accurate predictor of liver damage provided that it is taken not earlier than 4 hours after ingestion of the overdose. Peak disturbance of liver function occurs 2 to 4 days after the overdose, often accompanied by mild jaundice, after which recovery is usually rapid and complete. In a few patients, fulminant hepatic failure, manifested by increasing jaundice and encephalopathy, may develop by the third to fifth day. Acute renal failure may complicate paracetamol poisoning, often in the context of severe liver damage. Renal failure, which is often non-oliguric, typically becomes apparent 24 to 72 hours after overdosage. The treatment of paracetamol intoxication should include gastric lavage, which has been shown to be of value for up to 6 hours after ingestion of a paracetamol overdose. Further general treatment may include parenteral fluid replacement and a prophylactic infusion of dextrose (5-10%) in patients at risk of hepatic failure. Specific protective agents in those patients at risk of paracetamol-induced liver damage include N-acetylcysteine and methionine which are most effective if given within 8 to 10 hours of ingestion of the overdose. Hepatic and renal failure should be managed conventionally. In recent years in the United Kingdom there has been a gradual decline in the number of hospital admissions and the number of deaths from aspirin poisoning. Salicylates in overdose directly stimulate the respiratory centre and so cause a respiratory alkalosis. Metabolic acidosis occurs in severe poisoning because of impairment of the oxidative metabolism of energy substrates. At very high salicylate concentrations respiratory depression may occur, possibly associated with neuroglycopenia, adding respiratory acidosis to the worsening metabolic acidosis. In addition to a mixed acid-base disturbance, hypokalaemia and hypoglycaemia may be present. Nausea and vomiting increase the fluid deficit. If dehydration is sufficiently severe, decreasing cardiac output may hasten development of lactic acidosis and acute renal failure.(ABSTRACT TRUNCATED AT 400 WORDS)

Alteration of hepatic glutathione S-transferases and release into serum after treatment with bromobenzene, carbon tetrachloride, or N-nitrosodimethylamine

The effects of bromobenzene, carbon tetrachloride, and N-nitrosodimethylamine (DMN) on hepatic glutathione S-transferase activity were studied in untreated and in phenobarbital- or ethanol-treated rats. In phenobarbital-treated rats, the isozymic composition of the hepatic cytosolic glutathione S-transferases was changed after giving hepatotoxic chemicals; glutathione S-transferases 2-2(AA), 3-3(A), 1-2(B), 3-4(C), and 4-4 + 5-5(D + E) were present in cytosol from control rats, but only glutathione S-transferases cochromatographing with transferases 4-4 + 5-5(D + E) were detected in rats given carbon tetrachloride or bromobenzene. A marked decrease in hepatic and an increase in serum glutathione S-transferase activity were also observed after carbon tetrachloride or bromobenzene treatment, but little change was seen after giving DMN. On the contrary, in untreated or ethanol-treated rats, DMN administration decreased hepatic glutathione S-transferase activity and caused an elevation in serum glutathione S-transferase activity. The isozymic composition of the hepatic cytosolic glutathione S-transferases after giving DMN to untreated rats was also altered, but the alteration was much less than that observed after giving carbon tetrachloride or bromobenzene to phenobarbital-treated rats. The elevation in serum glutathione S-transferase activity was accompanied by an increase in both serum glutamate-pyruvate transaminase activity and serum bilirubin concentrations. Thus, hepatic glutathione S-transferase activity was altered and released into serum after giving hepatotoxic chemicals, and the alteration in glutathione S-transferase activity was dependent on treatment with phenobarbital or ethanol.

Influence of ethanol induction on the metabolic activation of genotoxic agents by isolated rat hepatocytes

The effects of ethanol-feeding to rats, over a 6-week period, on the activation of genotoxic compounds of different chemical classes, requiring metabolic conversion to exert their mutagenic activity, were studied in isolated rat hepatocytes. The influence of such treatment on cytochrome P-450 content and N-acetylation in isolated hepatocytes was also investigated. Benzidine (BZ), dimethylnitrosamine (DMN), diethylnitrosamine (DEN), isoniazid (INH) and cyclophosphamide (CP) were more effectively activated to products mutagenic towards Salmonella typhimurium by hepatocytes from ethanol-pretreated rats than by hepatocytes from controls. The mutagenic potency of 2-aminofluorene (2-AF) and 2-acetylaminofluorene (2-AAF) was not influenced by ethanol pretreatment. Ethanol consumption was found to be associated with increased cytochrome P-450 content and enhanced N-acetylation in the isolated hepatocytes. Our results support the hypothesis that an alteration of the hepatic drug-metabolizing system may be responsible for the ethanol-induced increase in susceptibility to certain genotoxic compounds.

Effects of chronic ethanol feeding on glutathione turnover in the rat

Glutathione (GSH) is important in protection of cells against electrophilic drug injury and against reactive oxygen species. Both steady-state concentrations and turnover of GSH are important determinants of susceptibility of the hepatocyte to injury. Chronic ethanol administration is known to enhance susceptibility to electrophilic drug injury. We have examined the effects of chronic ethanol feeding on GSH turnover and the hepatic activities of GSH peroxidase and enzymes of the gamma-glutamyl cycle in the rat. Turnover of GSH was measured in individual animals by measuring the decrease in specific activity of GSH in bile over time after i.v. administration of [35S]cysteine. Rats fed ethanol had significantly increased rates of GSH turnover, 0.287 +/- 0.050 hr-1 vs 0.131 +/- 0.041 hr-1 (P less than 0.001), as well as steady-state GSH levels, 6.59 +/- 1.55 vs 4.30 +/- 1.28 mumoles/g liver (P less than 0.01). The activities of gamma-glutamyltransferase (GGT) and GSH-synthesizing enzymes were correspondingly increased significantly. By contrast, GSH peroxidase activity was decreased in ethanol-fed rats, 194 +/- 20.8 vs 311 +/- 89.9 nmoles NADPH oxidized/min/mg protein (P less than 0.001). Biliary output and concentrations of GSH and GSSG were similar in both groups. The increase in turnover of GSH was not due to an increase in oxidation of GSH. There was, however, an association between GSH turnover and the activity of hepatic GGT in ethanol-fed but not in control rats.

Effect of ethanol on carbon tetrachloride levels and hepatotoxicity after acute carbon tetrachloride poisoning

To study the effect of an acute dose of ethanol on carbon tetrachloride (CCl4) concentration and hepatotoxicity, female rats received ethanol (2.5 ml/kg body wt.) either intragastrically or intraperitoneally following intragastric administration of CCl4 (1.5 ml/kg body wt.). Three hours after acute CCl4 intoxication there was a striking increase in CCl4 concentration in animals treated simultaneously with ethanol intragastrically compared to those receiving ethanol intraperitoneally. This increase was significant (P less than 0.05) and amounted to 211% for blood, 236% for liver and 405% for fat tissue, whereas animals treated with CCl4 alone showed CCl4 concentrations in the range between the two other experimental groups. Serum activities of glutamate oxalacetate transaminase, glutamate pyruvate transaminase and glutamate dehydrogenase were found to be considerably higher in animals treated with the combination of CCl4 and ethanol when compared to those receiving CCl4 alone, showing that ethanol given intraperitoneally or intragastrically enhances CCl4 hepatotoxicity. Since the intraperitoneal administration of ethanol led to a reduction rather than an increase in CCl4 concentration in the early phase of intoxication, additional mechanisms independent of actual levels of CCl4, such as direct effects of ethanol on the CCl4 metabolizing enzyme of the membrane of the endoplasmic reticulum, have to be implicated in the pathogenesis of the potentiation of CCl4 hepatotoxicity by ethanol.

Ethanol diminishes the toxicity of the mushroom Amanita phalloides

Survival of mice after lethal doses of a lyophilizate from Amanita phalloides ('death cap') was markedly increased by single doses of ethanol applied 30 min before or 5 min after the mushroom. Hepatic histopathological damage (confluent necrosis) was largely prevented. Acute, but not chronic, consumption of ethanol may thus influence favorably the outcome of death cap poisoning and should be taken into consideration in the evaluation of therapeutic measures.

Drug interactions affecting analgesic toxicity

Most reports of interactions involving analgesics deal with their effects on the actions of other drugs rather than vice versa. Aspirin and ethanol have synergistic effects on the development of gastritis, gastrointestinal bleeding, and chronic gastric ulcer. This must be the most common and most important interaction affecting analgesic toxicity. Combined overdosage of aspirin with central nervous system depressants may be particularly hazardous because suppression of the salicylate-induced respiratory stimulation further shifts the disordered acid-base balance towards acidosis. The toxicity of acetaminophen (paracetamol) depends primarily on the balance between the rate of formation of the hepatotoxic metabolite and the rate of glutathione synthesis in the liver. In animals, prolonged pretreatment with ethanol increases the metabolic activation and acute toxicity of acetaminophen, and there is some evidence that chronic alcoholics are more susceptible to hepatotoxicity following acute overdosage. It has been assumed that this sensitivity in chronic alcoholics is due to microsomal enzyme induction with enhanced metabolic activation of acetaminophen. However, the metabolic activation of acetaminophen, as judged by the urinary excretion of its cysteine and mercapturic acid conjugates, is not increased in heavy drinkers or in patients induced by long-term treatment with anticonvulsants or rifampicin. Microsomal enzyme induction is complex. There are important species differences and different agents may selectively induce different variants of the multiple forms of cytochrome P-450. The acute administration of ethanol greatly reduces the metabolic activation of acetaminophen in heavy drinkers with more than a 50 percent decrease in cysteine and mercapturic acid conjugate production. Thus ingestion of ethanol should reduce the risk of liver damage following acetaminophen overdosage. Cimetidine, which inhibits the oxidative metabolism of some drugs, reduces the hepatotoxicity and increases the dose of acetaminophen in mice required to kill 50 percent of the animals. However, contrary to expectations, cimetidine does not inhibit the oxidative metabolism of acetaminophen in man. Salicylamide competes with acetaminophen for sulphate conjugation but is unlikely to potentiate toxicity following overdosage since sulphate conjugation is rapidly saturated anyway. Animal studies suggest that the hepatotoxicity of acetaminophen after overdosage may be increased by other agents which deplete glutathione, but there is no information on this point in man.

Ethanol potentiates the inhibitory effect of D-galactosamine on protein synthesis in isolated hepatocytes

The effect of the combined addition of D-galactosamine and ethanol on hepatic protein synthesis was studied in isolated mouse hepatocytes. 2.5 mM D-galactosamine or 40 mM ethanol alone caused slight or no inhibition of amino acid incorporation into proteins. However, a profound inhibition (about 80%) was observed if D-galactosamine of the same dose was added after a preincubation of the cells with 40 mM ethanol and vice versa. It shows that there is a strong mutual potentiation between D-galactosamine and ethanol in the inhibition of protein synthesis.

Effect of an acute dose of ethanol on the hepatotoxicity due to carbon tetrachloride

To study the effect of an acute dose of alcohol on the hepatotoxicity due to CCl4, rats received alcohol (4 g/kg BW) and/or CCl4 (1.5 ml/kg BW) by concomitant intragastric intubation. Compared to animals receiving CCl4 alone, the simultaneous application of CCl4 and alcohol resulted 12 h after administration in significantly lower serum activities of glutamate oxalacetate transaminase (1005 +/- 70 vs 739 +/- 47; p less than 0.01) and glutamate pyruvate transaminase (746 +/- 10 vs 330 +/- 41; p less than 0.01), whereas 36 h after administration, an increase of serum enzyme activities was observed. No significant differences could be demonstrated 24 h after application. By histological assessment, liver damage was also much less pronounced 12 h after combined administration of CCl4 and ethanol, compared to CCl4 alone, whereas the reversed constellation could be demonstrated 36 h after administration. These results therefore show that in the early phase of CCl4 intoxication an acute dose of alcohol may partially protect from CCl4 hepatotoxicity, whereas potentiation was observed under these experimental conditions in the late phase of CCl4 intoxication.

Potentiation of hepatotoxicity by ethanol in galactosamine-induced hepatitis in rats: role of propylthiouracil protection

Chronic ingestion of ethanol (5 g/kg/day) for 6 weeks increased the hepatotoxicity of a single injection of D-galactosamine (330 mg/kg) in rats. Plasma transaminases, alkaline phosphatase, gamma glutamyl transpeptidase and sulphobromophthalein retention were consistently high in alcohol-fed rats compared to sucrose-fed controls, 25 hours after galactosamine administration. Liver histology in sucrose-fed rats revealed typical inflammatory changes and cytoplasmic vacuolation without cell necrosis was seen. Propylthiouracil treatment had no beneficial or protective effect in alcohol-fed rats in this animal model of hepatitis.

Effects of dithiocarb and (+)-catechin against carbon tetrachloride-alcohol-induced liver fibrosis

Treatment of male rats with carbon tetrachloride (CCl4, 2 x weekly 0.2 ml/kg p.o.) and a 5% alcohol solution, instead of drinking water, for 4 weeks led to marked increases in serum enzyme activities (GOT, GPT, SDH), hepatic triglyceride and hydroxyproline content. Diethyl dithiocarbamate (dithiocarb, 200 mg/kg p.o.) simultaneously applied with CCl4 totally suppressed the elevation in serum enzyme activities and hepatic hydroxyproline concentration, and partially suppressed that of the triglyceride content. (+)-Catechin (50-300 mg/kg p.o.) simultaneously applied with CCl4 had no influence on the enhanced serum enzymes, but depressed the augmented content of both hepatic triglyceride and hydroxyproline in a dose-dependent way. The most effective dose with respect to the reduction of the hydroxyproline concentration was 100 mg/kg (+)-catechin; the highest dose (300 mg/kg), however, enhanced the CCl4-alcohol-induced hydroxyproline augmentation.

Alcohol ingestion, liver glutathione and lipoperoxidation: metabolic interrelations and pathological implications

Data reviewed here indicate that acute and chronic ethanol ingestion induce a decrease in the concentration of GSH and an increase in lipoperoxidation in the liver both in experimental animals and in man, changes that are closely interrelated GSH depletion is suggested to be due to an oxidation in the liver tissue and to a translocation into the extrahepatic medium as free glutathione and/or as conjugates with ethanol-derived acetaldehyde. As a result, the hepatic GSH/GSSG ratio is drastically reduced. Lipoperoxidation seems to be related to the metabolism of ethanol and acetaldehyde by secondary pathways that are known to generate oxygen-related free radicals. Being lipoperoxidation a process associated with cell damage and death, its stimulation by ethanol ingestion could play a role in the production of alcoholic liver damage in man. The involvement of several contributory factors in the development of a high lipoperoxidative index in the liver in this situation is discussed.

Late presentation of acetaminophen hepatotoxicity

A 37-year-old alcoholic presented to hospital with metabolic acidosis, hypoglycemia, hypoprothrombinemia, and markedly elevated SGOT level. Despite the absence of volunteered information, acetaminophen hepatotoxicity was considered the probable cause, and this diagnosis was eventually supported. This combination of findings appears to be highly suggestive of well-established acetaminophen hepatotoxicity and implies that the drug-induced lesion selectively impairs certain hepatocellular functions early in the progression of the injury.

Clinical pharmacokinetics of paracetamol

In therapeutic doses paracetamol is a safe analgesic, but in overdosage it can cause severe hepatic necrosis. Following oral administration it is rapidly absorbed from the gastrointestinal tract, its systemic bioavailability being dose-dependent and ranging from 70 to 90%. Its rate of oral absorption is predominantly dependent on the rate of gastric emptying, being delayed by food, propantheline, pethidine and diamorphine and enhanced by metoclopramide. Paracetamol is also well absorbed from the rectum. It distributes rapidly and evenly throughout most tissues and fluids and has a volume of distribution of approximately 0.9L/kg. 10 to 20% of the drug is bound to red blood cells. Paracetamol is extensively metabolised (predominantly in the liver), the major metabolites being the sulphate and glucuronide conjugates. A minor fraction of drug is converted to a highly reactive alkylating metabolite which is inactivated with reduced glutathione and excreted in the urine as cysteine and mercapturic acid conjugates. Large doses of paracetamol (overdoses) cause acute hepatic necrosis as a result of depletion of glutathione and of binding of the excess reactive metabolite to vital cell constituents. This damage can be prevented by the early administration of sulfhydryl compounds such as methionine and N-acetylcysteine. In healthy subjects 85 to 95% of a therapeutic dose is excreted in the urine within 24 hours with about 4, 55, 30, 4 and 4% appearing as unchanged paracetamol and its glucuronide, sulphate, mercapturic acid and cysteine conjugates, respectively. The plasma half-life in such subjects ranges from 1.9 to 2.5 hours and the total body clearance from 4.5 to 5.5 ml/kg/min. Age has little effect on the plasma half-life, which is shortened in patients taking anticonvulsants. The plasma half-life is usually normal in patients with mild chronic liver disease, but its prolonged in those with decompensated liver disease.

Effects of microsomal enzyme induction on paracetamol metabolism in man

1 The metabolism of paracetamol after a single oral dose of 20 mg/kg was compared in fifteen patients with microsomal enzyme induction taking anticonvulsants or rifampicin and twelve healthy volunteers. 2 Induction was confirmed by measurement of the plasma antipyrine half-life (mean 6.4 h in the patients compared with 12.8 h in the volunteers). 3 The glucuronide conjugation of paracetamol was enhanced in the induced patients as shown by lower plasma paracetamol concentrations, a shorter paracetamol half-life, higher paracetamol glucuronide concentrations and an increased ratio of the area under the plasma concentration time curves of the glucuronide to the unchanged drug. There were no significant differences in sulphate conjugation. 4 There was a corresponding change in the pattern of urinary metabolite excretion. The induced patients excreted significantly less unchanged drug and sulphate conjugate and more glucuronide conjugate than the healthy volunteers. 5 The urinary excretion of the mercapturic acid and cysteine conjugated of paracetamol was the same in both groups. 6 Conversion of paracetamol to its potentially hepatotoxic metabolite does not seem to be increased in patients induced with anticonvulsants or rifampicin. There would seem to be no contraindication to the use of these drugs in combination.

Influence of hypoxia on the hepatotoxic effects of carbon tetrachloride, paracetamol, allyl alcohol, bromobenzene and thioacetamide

Exposure of rats to a reduced oxygen tension (6% O2, 94% N2) for 6 h increased the serum enzyme and the histological lesions induced by carbon tetrachloride (CCl4). Hypoxia did not enhance the hepatotoxic response to paracetamol, allyl alcohol, bromobenzene or thioacetamide. No correlation was found between the changes in hepatotoxicity induced by hypoxia and those after treatment with ethanol. Hepatic hypoxia therefore was not the pathogenetic mechanism responsible for ethanol-induced enhancement of hepatotoxicity.

Effect of a concomitant single dose of ethanol on the hepatotoxicity and metabolism of acetaminophen in mice

A concomitant single dose of ethanol (1 g/kg) protected mice from hepatic injury induced by acetaminophen (250 mg/kg) as evidenced by the lowering of plasma transaminases. Pharmacokinetic studies with [14C]acetaminophen indicated that ethanol enhanced the initial blood concentrations of radiolabel and its rate of elimination. A tissue distribution study suggested that these effects were probably due to an ethanol-induced inhibition of the biliary clearance of acetaminophen from the blood. Examination of the urinary and biliary metabolites indicated that ethanol inhibited the excretion of the degradation products derived from the glutathione-deactivated hepatotoxic acetaminophen intermediate. The decrease in acetaminophen induced hepatotoxicity was therefore attributed to an inhibitory effect of ethanol on the biotransformation of acetaminophen to the toxic intermediate.