Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Acetaminophen is eliminated primarily by glucuronidation, thereby avoiding cytochrome P450-catalyzed bioactivation to a toxic reactive intermediate. Previous studies have shown that UDP-glucuronosyltransferase-deficient Gunn rats are more susceptible to acetaminophen toxicity than normal Wistar controls, from which the Gunn strain was derived. However, the Gunn and Wistar strains are not congenic, and differences in toxicologic susceptibility could be due in part to genetic differences other than UDP-glucuronosyltransferase activity. Accordingly, acetaminophen (750 mg/kg, ip) was administered to congenic RHA rats with normal (homozygous, RHA/++), moderately deficient (heterozygous, RHA/j+), and severely deficient (homozygous jaundiced, RHA/jj) activities of bilirubin UDP-glucuronosyltransferase. Acetaminophen metabolites were measured by high-performance liquid chromatography and production of the acetaminophen glucuronide conjugate was quantified by the area under plasma concentration-time curve (AUC) from 0 to 2 hr, standardized by the AUC value for acetaminophen in the same animal (glucuronidation ratio = AUC acetaminophen glucuronide/AUC acetaminophen). The 0- to 2-hr time period for AUC calculations was necessitated by the accumulation at later time points of glucuronide and sulfate conjugates in the plasma of animals experiencing severe nephrotoxicity. Acetaminophen bioactivation was quantified by the 24-hr urinary recovery of glutathione-derived conjugates. Hepatotoxicity and nephrotoxicity were assessed respectively by the peak concentrations of plasma alanine aminotransferase (ALT) and blood urea nitrogen (BUN). Glucuronidation of acetaminophen in RHA/jj rats (0.065 +/- 0.005) (mean +/- SE) was reduced 63% compared to the RHA/++ controls (0.17 +/- 0.01) (p < 0.05). RHA/jj rats demonstrated respective 230- and 7-fold increases in the peak plasma concentrations of ALT (17144 +/- 1014 vs 75 +/- 10) and BUN (128 +/- 23 vs 18.4 +/- 0.2) compared to congenic normal controls (RHA/++) (p < 0.05). Heterozygous animals (RHA/j+) demonstrated intermediary toxicity for both parameters (ALT = 2029 +/- 1581, BUN = 41 +/- 16, p < 0.05). Decreased glucuronide production correlated with elevations in ALT (r = -0.86, p < 0.001), while increased acetaminophen bioactivation correlated directly with both elevated ALT (r = 0.93, p < 0.001) and BUN (r = 0.83, p = 0.001). These results using congenic controls demonstrate that the enhanced susceptibility of UDP-glucuronosyltransferase-deficient rats to acetaminophen toxicity is due to decreased glucuronidation resulting in enhanced bioactivation, rather than to other unappreciated genetic differences.
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PMID:Biotransformation and toxicity of acetaminophen in congenic RHA rats with or without a hereditary deficiency in bilirubin UDP-glucuronosyltransferase. 144 Jun 17

The mechanisms of chronic cocaine toxicity and its potentiation by ethanol were investigated. Cocaine was administered to male C57BL/6 mice (20 mg/kg by peritoneal injection twice a day) alone or in combination with ethanol-containing diets (26% of total calories) supplied with a normal (20 IU/liter) or high content (170 IU/liter) of vitamin E. Liver levels of vitamin E, reduced glutathione, ascorbic acid, and hydroxyproline were measured. Accumulation of thiobarbituric acid-reactive substances, after in vitro stimulation of lipid peroxidation by Fe3+/ADP/ascorbate system, was measured as an index of susceptibility of hepatic membranes to oxidative stress. Plasma alanine aminotransferase, lethality, liver weight, and liver/body weight ratio were determined to assess the extent of liver toxicity. Consumption of ethanol exacerbated liver toxicity induced by cocaine treatments and reduced survival, but ethanol or cocaine treatments alone caused no or only modest mortality. Ethanol potentiated cocaine-induced accumulation of collagen in the liver and depletion of ascorbic acid. Hepatotoxicity induced by the combined ethanol plus cocaine treatment was not accompanied by a decrease in intracellular vitamin E or glutathione content. There were no changes in the basic levels and in the rate of accumulation of thiobarbituric acid-reactive substances in liver homogenates under the lipid peroxidation-stimulating system in vitro. The toxic effects of ethanol and cocaine were not reduced by the ingestion of vitamin E during short-term exposure of 21 days of treatment.
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PMID:Chronic ethanol and cocaine-induced hepatotoxicity: effects of vitamin E supplementation. 144 28

In order to elucidate the role of mitochondrial dysfunction in paracetamol-induced hepatotoxicity, the effects of paracetamol on the oxygen consumption and ATP content of the isolated perfused rat liver were correlated with parameters of hepatic viability and hepatotoxicity. Paracetamol at 5 g/L reduced the oxygen consumption of the livers by about 80% and hepatic ATP content by 96%. Hepatotoxicity was evident from the nearly complete interruption of bile secretion, a marked release of enzymes [glutamate-pyruvate transaminase (GPT), lactate dehydrogenase (LDH)] in the perfusate, a depletion of hepatic glutathione and an accumulation of calcium in the liver. Paracetamol-induced hepatotoxicity could be prevented completely by using livers from non-fasted rats as well as by addition of fructose to the perfusate of livers from fasted animals. Both treatments resulted in an increased energy supply from anaerobic glycolysis as evidenced by a large release of lactate and pyruvate into the perfusate, but did not inhibit paracetamol-induced decline of oxygen consumption. The decrease in hepatic oxygen consumption depended on the dose of paracetamol and occurred first at a concentration of 0.2 g/L (-10%). LDH and GPT release, on the other hand, was elevated at 2 and 5 g/L and calcium accumulation occurred at 5 g/L paracetamol only. Inhibition of mixed-function oxidases by dithiocarb did not prevent the decrease in oxygen consumption and the resulting hepatic injury induced by paracetamol. The oral administration of the high dose of 5 g/kg paracetamol in vivo to rats exerted strong hepatotoxicity but produced maximal serum levels of 800 mg/L paracetamol only and did not decrease hepatic oxygen consumption as measured in vitro. Our results show that in the isolated perfused rat liver in vitro, only high concentrations of paracetamol can produce "chemical hypoxia" by attacking mitochondria so as to cause hepatic injury. Such high concentrations of paracetamol are not attained in vivo, however. "Chemical hypoxia", thus, seems not to be relevant to the well-known hepatotoxic action of paracetamol.
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PMID:The toxicological relevance of paracetamol-induced inhibition of hepatic respiration and ATP depletion. 163 30

Calmodulin, a low molecular weight Ca2+ binding protein, regulates a large number of cell activities including cell division. Previous studies from our laboratory indicated excessive accumulation of Ca2+ in hepatocytes succeeded by rapid glycogen breakdown and suppressed cell division in rats receiving CCl4 after previous dietary exposure to 10 ppm chlordecone. Since calmodulin plays a major role in Ca2(+)-regulated events and has been reported to be localized in mitotic apparatus during cell division, we have assessed subcellular distribution of calmodulin and estimated cytosolic phosphorylase a to indicate cytosolic free Ca2+ levels in livers of rats fed 0 ppm or 10 ppm (chlordecone) in the diet for 15 days before CCl4 (100 microliters/kg) administration to understand the role of Ca2(+)-calmodulin in chlordecone + CCl4 toxicity. Hepatotoxicity was assessed by determining serum AST and ALT succeeded by histopathological observations of liver sections. Serum aminotransferases were significantly elevated 6 hr after CCl4 administration to normal rats and returned to control level by 24 hr. However, serum AST and ALT elevations were severalfold higher, and progressive increase was observed starting 4 hr after CCl4 administration to chlordecone rats. Histopathological observations of liver sections for necrotic, swollen and lipid-laden cells provided findings commensurate with the serum enzyme data. These data indicate that normal rats do recover from CCl4 hepatotoxicity. However, the CCl4 hepatotoxicity is progressive in chlordecone rats without recovery. In normal rats, CCl4 administration resulted in a slight increase in phosphorylase a starting at 6 hr.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Carbon tetrachloride-induced alterations of hepatic calmodulin and free calcium levels in rats pretreated with chlordecone. 170 67

Eugenol produces hepatic injury in mice depleted of glutathione (GSH) by pretreatment with buthionine sulfoximine (BSO). Several eugenol analogs were examined for their ability to cause hepatic injury after administration to mice in combination with BSO. Hepatotoxicity was assessed by measuring relative liver weight, liver blood volume, and serum GPT activity in mice. Comparison of the tested compounds showed that the structural requirements for toxic potency was a phenolic ring having an allyl substituent at the 4-position. These structural requirements can be explained by assuming that a vinylogous quinone methide formed by metabolic oxidation of eugenol plays a role in inducing hepatotoxicity in GSH-depleted mice.
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PMID:Hepatotoxicity of eugenol and related compounds in mice depleted of glutathione: structural requirements for toxic potency. 188 30

Hepatotoxicity of diethyldithiocarbamate (DDC) was investigated in rats. Plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were markedly elevated 24 hr after subcutaneous administration of DDC and histologically, the liver showed submassive necrosis. A sustained inhibition in the liver of Cu,Zn-superoxide dismutase (Cu-SOD) activity was observed following DDC treatment. DDC produced a significant loss in liver reduced glutathione (GSH) level after 1 hr, but the nadir was observed later than that of Cu-SOD. Catalase activity decreased gradually from 7 hr. Thiobarbituric acid reactive substances (TBARS) in the liver were significantly increased from 15 hr. Hepatic haemodynamics were scarcely changed up to 15 hr. Desferrioxamine (a chelator of iron) and piperonyl butoxide (an inhibitor of cytochrome P-450) prevented DDC-induced increases of both ALT and TBARS, but GSH did not, DDC hepatotoxicity was not changed by phenobarbital induction. Thus, we have shown that subcutaneous dose of DDC caused hepatotoxicity in rats. Although the exact sequence of its hepatotoxic factors is unproven, it seems likely that lipid peroxidation through the dysfunction of antioxidant defence factors and a toxic metabolite contribute to the formation of this liver injury.
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PMID:Hepatotoxicity of diethyldithiocarbamate in rats. 196 45

Male and female Sprague-Dawley rats were administered the sodium salt of monochloroacetic acid (SMCA) by oral gavage for a period of 90 consecutive days. Dosage levels of 15, 30, 60 or 120 mg/kg per day were employed. SMCA clearly induced toxicity in both females and males, with the greatest severity in the male animals. Both the liver and kidneys were identified as target organs. At 120 mg/kg per day, 30% of females and 80% of the males died, most within the first 2 days of treatment. Hemorrhagic and congested lungs (possibly a postmortem change) were seen in the early deaths (1-3 days) whereas liver lesions were observed in later deaths. In addition, there was nephrotoxicity as evidenced by elevated creatinine, blood calcium (BCAL), and blood urea nitrogen (BUN) levels. Hepatotoxicity was indicated by increases in the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Both organs showed increased organ-to-body weight ratios. Microscopic examination revealed a significant (P less than or equal to 0.001) increase in chronic renal nephropathy and increased splenic pigmentation at 60 mg/kg per day in the males. Based on the observation of toxicity at all treatment levels in males, a lowest observed adverse effect level (LOAEL) of 15 mg/kg per day is proposed for a 90-day exposure to SMCA by oral gavage to the Sprague--Dawley rat.
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PMID:Ninety-day toxicity study of sodium monochloroacetate in Sprague-Dawley rats. 203 Dec 51

The destruction of liver microsomal cytochromes P450 by a previously administered low dose of CCl4 has been widely accepted as the mechanism of CCl4 autoprotection. However, circumstantial evidence suggests that this mechanism cannot completely explain the phenomenon of autoprotection. The protective effect of a low dose of CCl4 (0.3 ml/kg, po) on the lethal effect of a subsequently administered high dose (5 ml/kg, po) was established in male Sprague Dawley rats. The protective dose permitted 100% survival, whereas only 15% survival was observed without it. Hepatotoxicity, measured by serum enzyme elevations (aspartate transaminase, alanine transaminase, and sorbitol dehydrogenase) and histopathological changes 24 hr after the treatment with high dose, was similar in both the groups, even though the protective dose had significantly decreased liver microsomal cytochromes P450 (to 62% of normal) and associated enzymes, aminopyrine demethylase and aniline hydroxylase. Rats pretreated with CoCl2 to decrease hepatic microsomal cytochrome P450 to 44% of normal levels did not show a significant protection from the hepatotoxicity of high dose of CCl4. Previous studies have established that hepatocellular regeneration is stimulated within 6 hr after the administration of a low dose of CCl4. Based on this observation, a premise that autoprotection results from augmented recovery from injury rather than decreased injury appears likely. Hence, the role of hepatocellular regeneration was evaluated by following 3H-thymidine incorporation in hepatocellular nuclear DNA, labelling index by autoradiography, and by morphometric estimation of mitotic index. After administration of the protective dose of CCl4, stimulated nuclear DNA synthesis measured by 3H-thymidine incorporation into nuclear DNA was increased and this remained high even after subsequent administration of high dose of CCl4. Forty-eight hr after the administration of a lethal dose of CCl4 alone (5 ml/kg, po), labelling index was slightly increased, but mitotic index was not increased. In the surviving rats (15%), both labelling index and mitotic index were significantly elevated after an additional 24 hr. In rats receiving the protective dose, a significantly greater elevation of labelling index as well as mitotic index occurred 48 hr after the administration of the same lethal dose of CCl4. These results suggest that hepatocellular regeneration stimulated by the protective dose, as a biological response recruited to overcome the accompanying limited injury, may augment and sustain tissue repair processes to permit tissue restoration even after the massive liver injury elicited by the subsequent large dose of CC14.
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PMID:Role of hepatocellular regeneration in CCl4 autoprotection. 204 7

Furazolidone (FZ) was administered to 42-day-old female Japanese quails as a feed additive at doses of 0, 200, 400, 600 and 800 ppm for a period of 28 days. Dose-dependent effects were observed. High levels of FZ (600 and 800 ppm) significantly altered growth, decreased feed consumption, caused marked atrophy of the ovaries and oviducts leading to cessation of egg laying, and resulted in higher mortality. Hepatotoxicity was evidenced by an increase in serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase and a decrease in serum total protein, in addition to degenerative changes of the hepatocytes in FZ-treated birds. A rise in serum urea was also observed. Symptoms leading to death included a loss of appetite causing emaciation followed by nervous disturbances (compulsive movements and circling). No signs of cardiomyopathy were observed. Japanese quails did not tolerate FZ at a concentration (400 ppm) recommended for the prevention of salmonellosis in poultry.
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PMID:Toxicological and biological studies on Japanese quails fed graded levels of furazolidone. 209 13

Interferons and interferon induction can inhibit cytochromes P-450 and reduce the bioactivation and hepatotoxicity of acetaminophen. However, since P-450 inhibition often is followed by P-450 induction, which would enhance acetaminophen hepatotoxicity, the possibility of a biphasic modulation of acetaminophen hepatotoxicity by interferons was investigated. Outbred male CD-1 mice of various ages, and young inbred male C57BL/6 mice were given the interferon inducer, polyinosinic-polycytidylic acid (Poly I-C), 10 mg/kg intraperitoneally, followed 1 to 48 days later by a single dose of acetaminophen, 300 to 450 mg/kg intraperitoneally. Hepatotoxicity was assessed by the peak plasma concentration of alanine aminotransferase (ALT) occurring between 0 and 48 hr after acetaminophen treatment. Poly I-C inhibited the hepatotoxicity of acetaminophen given within 8 days, with maximal inhibition between 1 and 4 days. Conversely, a maximal 7-fold enhancement of ALT concentration was observed in CD-1 mice when 300 mg/kg of acetaminophen was given 32 days after Poly I-C (P less than 0.05). In the C57BL/6 strain, Poly I-C inhibited the hepatotoxicity of acetaminophen when given within 16 days, whereas a maximal 20-fold enhancement of ALT concentration was observed when 300 mg/kg of acetaminophen was given 24 days after Poly I-C (P less than 0.05). The mechanism of toxicologic enhancement was examined in male C57BL/6 mice using the same treatment regimen. Biochemical assessment of hepatotoxicity was confirmed by detailed histologic evaluation. Plasma concentrations of acetaminophen and metabolites were determined by high-performance liquid chromatography. Acetaminophen bioactivation was quantified by production of the glutathione-derived cysteine and mercapturic acid conjugates of acetaminophen. Poly I-C pretreatment produced a 5-fold increase in acetaminophen-induced ALT release (P less than 0.05), which correlated with histologic evidence of centrilobular necrosis. Poly I-C pretreatment produced respective 3-fold and 1.3-fold increases in the production of cysteine and mercapturic acid conjugates (P less than 0.05), which correlated with peak ALT concentrations (cysteine, r = 0.92, P less than 0.001; mercapturic acid, r = 0.75, P = 0.006). Thus, the hepatotoxicity of acetaminophen can be inhibited when given within days after interferon induction, and conversely enhanced when given after several weeks. The toxicologic enhancement appears to be due to increased P-450-catalyzed bioactivation of acetaminophen.
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PMID:Biphasic modulation of acetaminophen bioactivation and hepatotoxicity by pretreatment with the interferon inducer polyinosinic-polycytidylic acid. 226 10


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