Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.6.1.2 (alanine aminotransferase)
 26,722 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We studied the interaction between paracetamol (acetaminophen U.S.P.) and enflurane. Sixteen rats were assigned to four groups (n = 4) to receive: paracetamol 7.5 mg/100 g body weight; paracetamol plus 1% enflurane; 1% enflurane alone, or no treatment (controls). Animals were killed 6 h later. A second series of 16 were treated identically, but were killed after 24 h. Measurements were made of fluoride concentrations in serum, liver and urine (indicators of biotransformation of enflurane), paracetamol concentrations in urine, pathological changes in liver samples, and concentrations of the enzymes aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in serum. Pretreatment with paracetamol significantly decreased urinary fluoride at 6 and 24 h after exposure to enflurane, but decreased fluoride concentrations in serum and liver only at 6 h after exposure to enflurane. Paracetamol concentrations in urine did not change after exposure to enflurane. Exposure to paracetamol alone increased AST and ALT. At 24 h after exposure to enflurane, serum concentrations of enzymes in rats pretreated with paracetamol were similar to those of control rats. Pretreatment with paracetamol may therefore inhibit metabolism of enflurane. Although no hepatic damage was observed, the increased in AST and ALT suggested subclinical liver damage in rats given only paracetamol.
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PMID:Pretreatment with paracetamol inhibits metabolism of enflurane in rats. 270 80

Mice poisoned with acetaminophen were treated with esterase inhibitors, buthionine sulfoximine, and N-acetyl-L-lysine in experiments designed to explore the mechanism of N-acetylcysteine protection in vivo. Three esterase inhibitors, phenylmethylsulfonyl fluoride, bis-(p-nitrophenyl)-phosphate, and diisopropylfluorophosphate, had no effect on the antidote effectiveness of N-acetylcysteine, although each provided partial protection against acetaminophen poisoning. Buthionine sulfoximine, a specific inhibitor of gamma-glutamyl cysteine synthetase, antagonized the antidote effect of N-acetylcysteine. Acetaminophen-induced hepatotoxicity, as measured by plasma alanine aminotransferase activity, and mortality failed to decline, consistent with stimulation of glutathione synthesis as the primary mechanism of antidote protection. N-Acetyl-L-lysine was given at doses up to ten-fold higher than N-acetylcysteine yet had no effect on acetaminophen hepatotoxicity or its prevention by N-acetylcysteine. These results advance the view that N-acetylcysteine acts primarily as a glutathione precursor. They further suggest the esterase inhibitors limit poisoning by acetaminophen and may be useful agents in antagonizing the toxicity of other metabolically activated drugs.
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PMID:Effects of esterase inhibitors and buthionine sulfoximine on the prevention of acetaminophen hepatotoxicity by N-acetylcysteine. 310 95

Over 60% of the analgesic/antipyretic drug acetaminophen is eliminated by glucuronidation, which competes with a toxifying pathway involving cytochromes P-450-catalyzed bioactivation to a hepatotoxic reactive intermediate. A genetic deficiency of bilirubin UDP-glucuronyl transferase (GT) occurs in 5 to 7% of the population (Gilbert's disease, Crigler-Najjar syndrome) and this could predispose such people to acetaminophen hepatotoxicity. This hypothesis was evaluated in the homozygous Gunn rat, which is similarly deficient in GT, and the heterozygous Gunn rat, which has intermediary GT activity. Acetaminophen, 1 g/kg, was administered by gavage to animals 6 and 11 weeks of age, and age-matched Wistar rats as controls. Hepatic and renal cellular damage were assessed by respective increases in the peak plasma concentration of alanine aminotransferase and the blood urea nitrogen concentration, and confirmed by histological examination. Acetaminophen and metabolites were measured by high-performance liquid chromatography. Compared to Wistar controls, Gunn rats demonstrated up to a 110-fold greater hepatotoxic response to acetaminophen, with significantly lower production of the glucuronide conjugate and higher plasma concentrations of acetaminophen. Elevated acetaminophen concentrations correlated positively with both increased production of the acetaminophen-cysteine conjugate, reflecting bioactivation and hepatotoxicity. Older Gunn but not Wistar rats showed up to 26-fold more hepatotoxicity compared to their younger counterparts. In younger animals, heterozygotes demonstrated intermediary hepatotoxicity between homozygotes and Wistar controls. Hepatotoxicity was similar in the older heterozygotic and homozygotic Gunn rats, as was renal toxicity, which was enhanced 2- to 3-fold over controls. These results indicate that a genetic deficiency in bilirubin GT can be an important determinant of acetaminophen bioactivation and toxicity.
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PMID:Deficiency in bilirubin UDP-glucuronyl transferase as a genetic determinant of acetaminophen toxicity. 313 68

Acetaminophen (ACAP) was fed to adult Swiss-Webster mice for 4 weeks to examine the effect of prolonged ACAP ingestion on hepatic reduced glutathione (GSH) concentrations. In the first experiment, male and female mice were pair-fed diets containing ACAP at levels of 0.0 (control), 0.3, 0.6, and 1.0% of diet on a dry weight basis with the total sulfur-amino acids provided at 0.5% of the diet. Hepatic GSH was depleted, and the percentage of dose excreted as the urinary ACAP-GSH-derived conjugate increased in a dose-dependent manner with increasing ACAP. Serum glutamic-pyruvic transaminase activity, relative liver weight, and hepatic microsomal protein content increased in the group given 1.0% ACAP, but microsomal aniline hydroxylation decreased. In the second experiment, adult male mice were fed ad libitum diets containing 0.0 or 0.6% ACAP with total L-methionine provided at 0.25, 0.5 (requirement level), or 1.0%. Hepatic GSH was markedly depleted 1 week after initiation of ACAP treatment in all groups except those receiving 1.0% methionine. This reduction persisted throughout the 4-week treatment period. After 4 weeks, liver cysteine was also reduced as a result of ACAP ingestion and methionine deficiency, whereas serum inorganic sulfate concentration was not changed. Reduction in hepatic cysteine levels was also prevented by 1.0% dietary methionine. The dose-dependent depletion of GSH, the trend toward an increase in ACAP-GSH-derived conjugate excretion, and the prevention of GSH depletion by providing dietary methionine in excess of requirement indicate that prolonged ingestion of ACAP may increase the requirement for sulfur-containing amino acids and limit the availability of methionine and cysteine for protein synthesis, methylation reactions, and drug detoxification.
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PMID:Effects of prolonged acetaminophen ingestion and dietary methionine on mouse liver glutathione. 324 Jul 15

The effect of prostacyclin on acetaminophen-induced liver injury has been investigated in the mouse. Two structurally unrelated thromboxane synthetase inhibitors, OKY 1581 and benzyl imidazole, were also examined in order to investigate the role of the prostacyclin-thromboxane balance in the development of hepatic lesions. Whereas prostacyclin or OKY 1581 given shortly after acetaminophen prevented mortality and reduced liver necrosis, as assessed by serum ALT activity and histology, benzyl imidazole was only effective if given prior to acetaminophen. Acetaminophen overdose resulted in an enhanced prostaglandin and thromboxane generation by liver homogenates. While OKY 1581 inhibited thromboxane production by the liver homogenates, prostacyclin synthesis was increased. Pretreatment with the cyclooxygenase inhibitor indomethacin blocked both the increase in prostacyclin generation and the protective effect of OKY 1581. Benzyl imidazole inhibited the synthesis of thromboxane but did not enhance prostacyclin production. In addition, the protective effect of benzyl imidazole was unaltered by indomethacin pretreatment. Furthermore, whereas benzyl imidazole interfered with hepatic drug metabolism, as assessed by prolongation of the pentobarbitone sleeping time, prostacyclin and OKY 1581 were without activity. Prostacyclin treatment can prevent acetaminophen-induced liver necrosis in mice. Enhanced prostacyclin synthesis by the selective thromboxane synthetase inhibitor OKY 1581 also exerts a protective role in this model.
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PMID:Reduction by prostacyclin of acetaminophen-induced liver toxicity in the mouse. 328 85

Acetaminophen can be enzymatically bioactivated, which may play a role in cataractogenesis. This study evaluated the relation of dose, sex, plasma drug concentration, cytochromes P-450 (P-450 and P-448) induction, and hepatocellular toxicity to cataractogenic susceptibility in inbred mice and rabbits. C57BL/6 or DBA/2 mice, which respectively are genetically responsive and nonresponsive to P-448 induction, were treated with acetaminophen, 300 to 1000 mg/kg intraperitoneally (ip), following pretreatment with the P-448 inducer 3-methylcholanthrene (3-MC). Bilateral cataracts developed, independent of sex, in 83% of C57BL/6 mice within 4 hr of acetaminophen administration, compared with 7% of DBA/2 mice. A dose-response relation for cataractogenesis was evident in C57BL/6 mice using doses of 300 and 400 mg/kg, with the higher dose producing similar plasma acetaminophen concentrations but twofold higher glucuronide concentrations. Both strains had increased plasma concentrations of glutamic-pyruvic transaminase (GPT). New Zealand white or Chinchilla pigmented rabbits were treated with single or multiple doses of acetaminophen, 500 to 1500 mg/kg/day ip, following pretreatment with a cytochromes P-450 inducer: phenobarbital, 3-MC, or beta-naphthoflavone. Acetaminophen given chronically caused lenticular opacities within 1 week in 19 of 20 rabbits pretreated with P-450 inducers, regardless of pigmentation, but not in animals without prior P-450 induction. No opacities were observed after a single dose of acetaminophen, even with P-450 induction. There was no increase in plasma GPT in rabbits with any treatment. Over 85% of acetaminophen was recovered in urine as a glucuronide conjugate, and the rest as acetaminophen or conjugates with sulfate, cysteine, or N-acetylcysteine. Susceptibility to acetaminophen cataractogenesis can be genetically predetermined and may involve enzymatic bioactivation. possibly independent of hepatic biotransformation and toxicity.
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PMID:Pharmacological studies on the in vivo cataractogenicity of acetaminophen in mice and rabbits. 339 87

Acetaminophen has been shown to be cataractogenic in mice and rabbits. C57BL/6 and DBA/2 mice respectively are genetically susceptible and resistant to the induction of cytochrome P-448 by 3-methylcholanthrene (3-MC). This isoenzyme is thought to bioactivate acetaminophen to a toxic reactive intermediate. These two murine strains also are correspondingly susceptible and resistant to acetaminophen cataractogenesis. To evaluate the potential role of enzymatic bioactivation as a determinant of acetaminophen cataractogenesis, C57BL/6 and DBA/2 mice were treated with acetaminophen, 300 or 400 mg/kg intraperitoneally (ip), with or without pretreatment 48 hr earlier using 3-MC, 200 mg/kg ip. Lenticular cataracts were evaluated using the unaided eye and a slit lamp, and hepatotoxicity was evaluated by determination of peak plasma concentration of alanine aminotransferase (ALT). Plasma concentrations of acetaminophen and metabolites, particularly the glutathione (GSH)-derived conjugates (cysteine and mercapturic acid) reflecting enzymatic bioactivation, were measured by high-performance liquid chromatography. Cataracts developed only in C57BL/6 mice pretreated with 3-MC, occurring in 1 of 5 and 5 of 5 animals treated respectively with 300 and 400 mg/kg of acetaminophen. Comparing these two groups of induced C57BL/6 mice, production of the cysteine conjugate of acetaminophen was 2.5-fold higher with the 400 mg/kg dose of acetaminophen (p less than 0.05). Compared to their respective dose-matched, noninduced controls, cysteine conjugate production in the 300 and 400 mg/kg dose groups of induced C57BL/6 mice respectively was 3-fold and 4-fold higher (p less than 0.05). No DBA/2 mice developed cataracts. No mercapturic acid conjugate was detectable in the plasma of DBA/2 mice, and production of the cysteine conjugate was not altered in this strain by increasing the dose of acetaminophen or by pretreatment with 3-MC. The mean peak plasma concentration of the cysteine conjugate, reflecting acetaminophen bioactivation, was 5-fold higher in animals developing cataracts compared with those without cataracts (p less than 0.001). Plasma concentrations of unmetabolized acetaminophen were similar in all groups and unrelated to the development of cataracts. All mice of both strains pretreated with 3-MC showed evidence of hepatotoxicity, indicating a dissociation between hepatotoxic and cataractogenic susceptibility.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Metabolic evidence for the involvement of enzymatic bioactivation in the cataractogenicity of acetaminophen in genetically susceptible (C57BL/6) and resistant (DBA/2) murine strains. 340 97

The effects of paracetamol overdose on glycogen metabolism in rat liver have been investigated and related to its cytotoxicity. Paracetamol was administered to male rats by gavaging after a 24-h fast and refeeding was not permitted. An early (9-12-h) increase in histochemically demonstrable glycogen phosphorylase alpha activity in perivenous hepatocytes preceded major loss of membrane integrity as assessed by serum glutamate-pyruvate transaminase (SGPT) activity and uptake of trypan blue during perfusion. These changes occurred only after a decrease in the concentration of reduced glutathione, which is generally observed about 4 h after paracetamol treatment. The activation of glycogen phosphorylase in perivenous hepatocytes occurred concurrently with an increase in glycogen content of periportal hepatocytes, indicating a clear heterogeneity in the response of the two-cell populations to the hepatotoxin. The use of trypan blue perfusion together with histochemical techniques allowed changes in glycogen content and phosphorylase alpha activity of individual hepatocytes to be assessed with reference to the extent of membrane damage evident. The relevance of the results to possible mechanisms of hepatotoxicity is discussed.
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PMID:Histochemical and biochemical observations on the cytotoxicity of paracetamol and its effects on glycogen metabolism in rat liver. 342 88

The purpose of this investigation was to correlate the in vitro and in vivo toxicity of the hepatotoxicant, acetaminophen. Hamsters were pretreated with either phenobarbital (70 mg/kg) or 3-methylcholanthrene (20 mg/kg) or an appropriate vehicle for 3 days. In non-pretreated hamsters, single doses of acetaminophen (200-400 mg/kg i.p.) caused elevations in serum alanine aminotransferase and sorbitol dehydrogenase activities in a dose-related manner. 3-Methylcholanthrene significantly potentiated, while phenobarbital significantly reduced acetaminophen-induced elevations in serum liver enzyme activities. Both phenobarbital and 3-methylcholanthrene significantly reduced acetaminophen plasma T1/2 while only 3-methylcholanthrene increased APAP clearance. Phenobarbital pretreatment increased the urinary excretion of APAP-glucuronide. Exposure of isolated hepatocytes to acetaminophen (0.01-2.0 mM) resulted in concentration-related decreases in hepatocyte viability. Cells from 3-methylcholanthrene-pretreated hamsters were more markedly susceptible to acetaminophen toxicity than cells isolated from non-induced animals. Hepatocytes isolated from phenobarbitol pretreated animals were slightly but significantly more susceptible to acetaminophen toxicity than cells from control animals. Hepatocytes isolated from 3-methylcholanthrene pretreated animals had increased formation of an acetaminophen-glutathione conjugate compared to control. Pre-treatment with either phenobarbital or 3-methylcholanthrene enhanced glucuronidation of acetaminophen in vitro. These data demonstrate a lack of correlation between in vivo hepatotoxicity and in vitro cytotoxicity in that phenobarbital pre-treatment protected hamsters from acetaminophen-induced liver toxicity, but failed to protect hepatocytes exposed to acetaminophen in vitro.
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PMID:In vivo and in vitro hepatotoxicity and metabolism of acetaminophen in Syrian hamsters. 356 56

Acetaminophen (Tylenol) is a widely used analgesic/antipyretic drug which is enzymatically bioactivated, or toxified, by the cytochromes P-450 to a hepatotoxic reactive intermediary metabolite. Brief general anesthesia with diethyl ether has been shown to inhibit both the toxifying cytochromes P-450 and enzymatic glucuronidation, the latter constituting up to 60% of acetaminophen elimination via a nontoxifying pathway. Thus ether potentially could produce a temporally differentiated inhibition of bioactivating and "detoxifying" pathways, resulting in an enhancement of acetaminophen hepatotoxicity if the balance favored bioactivation. To evaluate this possibility, separate groups of male NIH strain mice were treated with acetaminophen at different times after 5 min of anesthesia with ether. Ether produced a 40-fold enhancement in acetaminophen hepatotoxicity as determined by plasma glutamic-pyruvic transaminase (GPT) concentrations. This toxicologic enhancement was observed only if acetaminophen administration was delayed, with a maximal enhancement when acetaminophen was given 6 hr after ether, and no effect with a delay of 16 hr. Similar studies in male CD-1 mice were carried out using halothane (Fluothane) as the general anesthetic given either over 5 min or over 1 hr. While halothane given over 5 min had no effect, a 1 hr anesthetic duration produced a 10-fold increase in acetaminophen hepatotoxicity as determined by peak GPT concentration, with no observed hepatotoxicity in the halothane controls. Toxicologic enhancement occurred only with delayed administration of acetaminophen; however, the maximal enhancement observed with a 6-hr delay was still evident with a 12-hr delay. Conversely, inhibition of acetaminophen hepatotoxicity was observed if acetaminophen was given either 2 hr or 18 hr after halothane.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Delayed enhancement of acetaminophen hepatotoxicity by general anesthesia using diethyl ether or halothane. 369 20


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