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:2.6.1.1 (aspartate aminotransferase)
21,665 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ontogeny of the biotransformation of exogenous and endogenous compounds has been mostly studied using liver cells and microsomal fractions. We have used liver perfusion for the first time to characterize the development of the total P-450 cytochrome-dependent system in the rabbit, with theophylline (TH) as tool substance. Livers of 0- to 60-day-old rabbits were perfused with TH (10 micrograms/ml) for 3 hr. Metabolizing enzymes (cytochrome P-450), ATP, glutathione, and glycogen were measured in liver tissue after perfusion. Lactate dehydrogenase, glutamic-oxalacetic transaminase, glucose, and urea were assayed in the medium throughout perfusion. The pharmacokinetic profile of TH was determined. The activity of total cytochrome P-450, as well as the intrinsic unbound clearance and TH metabolites production, increased following a similar sigmoidal pattern and reached a plateau around 30-45 days of the postnatal development of rabbit liver. The perfused tissue showed no signs of age-related hepatic damage or toxic effects of TH. Thus, the results in perfused liver predict its metabolic capacity during ontogenesis.
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PMID:Pharmacokinetic profile of theophylline in isolated perfused liver of rabbits at different ages. Development of drug-metabolizing activity during ontogenesis. 136 34

The effects of modulators of cytochrome P450 and reduced glutathione (GSH) on the hepatotoxicity of enalapril maleate (EN) were investigated in Fischer 344 rats. Twenty-four hours following the administration of EN (1.5 to 1.8 g/kg), increased serum transaminases (ALT and AST) and hepatic necrosis were observed. Pretreatment of the animals with pregnenolone-16 alpha-carbonitrile, a selective inducer of the cytochrome P450IIIA gene subfamily, enhanced EN-induced hepatotoxicity, whereas pretreatment with the cytochrome P450 inhibitor, cobalt protoporphyrin, reduced the liver injury. Depletion of hepatic non-protein sulfhydryls (NPSHs), an indicator of GSH, by combined treatment with buthionine sulfoximine (BSO) and diethyl maleate (DEM) produced marked elevations in serum transaminases by 6 hr after EN treatment. Administered on its own, EN decreased hepatic NPSH content and when combined with the BSO/DEM pretreatment, the liver was nearly completely devoid of NPSHs. Protection from EN-induced hepatotoxicity was observed in animals administered L-2-oxothiazolidine-4-carboxylic acid, a cysteine precursor. Together, these observations suggest the involvement of cytochrome P450 in EN bioactivation and GSH in detoxification. The results corroborate previous in vitro observations pertaining to the mechanism of EN-induced cytotoxicity towards primary cultures of rat hepatocytes. Although the doses of EN used in this study were far in excess of therapeutic doses, under certain circumstances, this metabolism-mediated toxicologic mechanism could form the basis for idiosyncratic liver injury in patients receiving EN therapy.
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PMID:Enalapril hepatotoxicity in the rat. Effects of modulators of cytochrome P450 and glutathione. 144 35

A complete cDNA encoding cholesterol 7 alpha-monooxygenase (EC 1.14.13.17) which had been isolated from rat liver cDNA libraries by using specific antibodies to the enzyme (Noshiro, M., Nishimoto, M., and Okuda, K. (1989) FEBS Lett. 257, 97-100) was totally sequenced. The cDNA contained a 1,509-base pair open reading frame encoding 503 amino acid residues (Mr = 56,880) and an unusually long 3'-untranslated region rich in AT sequence in the total length of 3,545 base pairs. The predicted amino acid sequence displays less than 30% similarity to other sequenced cytochrome P-450s indicating that the 7 alpha-hydroxylase constitutes a novel family of cytochrome P-450. The AT-rich region often contained ATTTA motifs, 5'-AAT-3' or 5'-TAA-3' trinucleotides which were reported to be involved in rapidly degrading mRNA. Employing the specific antibodies and the cDNA as probes, a diurnal variation of the levels of the three factors, i.e. enzyme protein, mRNA, and enzyme activity, was studied on rat livers prepared at various times of the day. In normal animals, all three factors exhibited maximum level at 10:00 p.m. and minimum at 10:00 a.m. No significant sexual difference was observed. Cholestyramine feeding increased all three factors at 10:00 a.m. close to the maximum levels of the normal rats, but did not show a significant increase at 10:00 p.m. On the contrary, starvation markedly decreased all three factors either at 10:00 a.m. or at 10:00 p.m., while maintaining still the diurnal variation. A good correlation of the levels of mRNA to the enzyme activities and the protein levels demonstrates that pretranslational regulation is most likely a mechanism for the circadian rhythm of 7 alpha-hydroxylase. The marked diurnal fluctuation of the amount of protein and the level of mRNA also indicates their rapid turnover. The short half-life of mRNA could be correlated with the structure of the 3'-untranslated region of the mRNA characteristic of rapidly degrading mRNA, i.e. abundance of motif, AUUUA, and existence of 5'-AAU-3' or 5'-UAA-3' trinucleotides in single-stranded regions of the secondary structure.
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PMID:Rat liver cholesterol 7 alpha-hydroxylase. Pretranslational regulation for circadian rhythm. 169 13

The long-term administration of xenobiotics carcinogens o-aminoazotoluene (o-AAT) and benz(a)pyrene (BP) to rats was found to cause induction of the liver cytochrome P-450 system which gradually decreases in spite of continued administration of the agents. Induction of microsomal oxygenases under these conditions is followed by induction of the immune response to o-AAT and BP. The data obtained correspond to the conception of the immunochemical functional system of homeostasis implying that the cytochrome-450 system and the immunity system are functionally linked and are elements of the common functional adaptive system of the organism.
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PMID:[Cytochrome P-450 induction and the subsequent induction of an immune response in rats during the chronic administration of xenobiotics]. 232 3

Carbon tetrachloride (CCl4) added to isolated rat hepatocytes produces toxic effects which were assessed by monitoring the release of aspartate aminotransferase (ASAT). CBrCl3 was equitoxic with CCl4, while CHCl3 was inactive, suggesting solvent properties not to be involved. The CCl4-mediated toxicity was markedly decreased by carbon monoxide, indicating possible activation by cytochrome P 450. 55 flavonoid compounds were tested for their ability to interfere with CCl4-induced release of ASAT. The compounds are cianidanol, 3-ethers and 3-esters thereof, flavanones, flavanolols, flavones and flavanols. The more hydrophilic compounds inhibit the CCl4-induced toxicity, while the lipophilic derivatives are potentiators. No other structure-activity relationships are apparent. The results are discussed in terms of the mechanisms of action of the compounds and of the validity of the technique as a screening test for hepatotropic agents.
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PMID:Inhibiting or potentiating effects of flavonoids on carbon tetrachloride-induced toxicity in isolated rat hepatocytes. 377 62

Two new methods are developed for synthesis of conjugated antigens of o-aminoazotoluene-bovine serum albumin (o-AAT--BSA): (1) from the microsomal fraction of the guinea pig liver which contains the cytochrome-P-450-dependent monooxygenase enzymic system and (2) from the m-chloroperbenzoic acid. A possible mechanism of the covalent binding of o-AAT with albumin under the effect of monooxigenases and of their chemical model is considered. Differences of antigenic determinants in conjugated antigens of o-AAT--BSA synthetized by the chemical and enzymic methods are detected.
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PMID:[Antibody formation to o-aminoazotoluene via the administration of conjugated antigens synthesized by enzymatic and chemical methods]. 391 Apr 3

The hepatotoxic effect of carbon tetrachloride (CCl4), reflected by augmented blood aspartate aminotransferase and alanine aminotransferase activities and the extent of histological liver damage, was observed following oral administration of CCl4 to rats. A marked increase of blood transaminase activities and severe degeneration of hepatocytes in the centrilobular region were detected 1-2 days after the administration, while the cytochrome P-450 content and the drug metabolizing activity in livers were depressed immediately after the administration. Based on these results, the effect of CCl4 on hepatic cytochrome P-450 and the histological pattern of liver cells was observed using tissue samples obtained from various liver lobes of rats given CCl4 24 hr previously. Dose-dependent inactivation of cytochrome P-450 by the administration of CCl4 was observed throughout the liver, with the most extensive decrease in the cytochrome content in the median lobe. The extent of liver damage (hydropic swelling degeneration and central necrosis in lobule) was also greater in the median and right liver lobes than in the left lobe. When a small amount of CCl4 was administered, degeneration of liver cells was detected only in the median and right lobes with only slight degeneration in the left lobe. These results indicate different susceptibilities of rat liver lobes to CCl4.
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PMID:Carbon tetrachloride-induced hepatotoxicity in rats: evidence for different susceptibilities of rat liver lobes. 688 48

Hepatic injury in alcoholics due to intake of acetaminophen (APAP or acetylparaaminophenol) with therapeutic intent has been reported, but the extent of the phenomenon is not clear, pertinent details of the association remain insufficiently clarified, and the importance of the phenomenon is not widely appreciated. The present report describes 67 patients who developed hepatic injury after ingestion of APAP with therapeutic intent. All were regular users of alcohol. Sixty-four percent of the patients were considered to be "alcoholic" or reported intakes greater than 80 g/d, 35% took 60 g/d or less, and the remainder were vague in their reporting. Doses of APAP were in the "nontoxic" range ( < 6 g/d) in 60% of the group, within the recommended range ( < 4 g/d) in 40%, and at 4.1 to 6 g/d in 20%. Characteristic feature was the towering level reached by aspartate transaminase (AST) with figures ranging from 3,000 to 48,000 IU in more than 90% of cases. Almost 20% of the patients died. The data on these patients were similar to 94 cases of injury from APAP taken with therapeutic intent reported in the literature. This study provides further evidence of hepatic injury in regular uses of alcohol, especially chronic alcoholics, who take APAP with therapeutic intent. Susceptibility is presumably caused by induction of cytochrome P-4502EI by ethanol and by depletion of glutathione (GSH) because of the effects of alcohol, the malnutrition often associated with alcoholism, and the depletion associated with chronic use of APAP and impaired glucuronidation caused by fasting perhaps as well. The syndrome of liver injury is distinctive, marked by uniquely elevated levels of AST, and poses a significant threat.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Acetaminophen (paracetamol) hepatotoxicity with regular intake of alcohol: analysis of instances of therapeutic misadventure. 765 81

Earlier studies showed that hepatotoxicant-treated experimental animals were more susceptible than controls to the lethal effects of bacterial endotoxin. The exact mechanisms of this effect were not understood. In this paper we showed that nitric oxide (.NO) was produced in whole blood and in liver tissues of rats that had been treated with a nonlethal dose of CCl4 (1.3 g/kg) followed by a low dose of lipopolysaccharide (LPS) (100 micrograms/kg). EPR spectroscopy was used in this study to detect nitrosyl-protein complexes. Hemoglobin-nitrosyl complexes were detected in both whole blood and liver. By performing analyses of EPR spectra obtained from hepatocytes exposed to .NO, we were able to identify EPR signals attributable to nitrosyl-cytochrome P420 in rat liver. We found that nitrosyl complex formation in red blood cells and liver was inhibited by treatment with NG-mono-methyl-L-arginine, suggesting enzymatic biosynthesis of .NO. A small but significant inhibition of nitrosyl complex formation by gadolinium trichloride pretreatment was found in the liver, suggesting that Kupffer cells were also involved in .NO biosynthesis, because this treatment decreased Kupffer cells. There was a synergistic effect of CCl4 and LPS on the serum levels of the hepatic enzymes aspartate aminotransferase, alanine amino-transferase, lactate dehydrogenase, and sorbitol dehydrogenase, which are indices of parenchymal cell damage. NG-Mono-methyl-L-arginine treatment increased these hepatic enzyme activities, suggesting a protective role for .NO. EPR resonances at g approximately 2.48, 2.29, and 1.91, due to low-spin cytochromes P450/P420 (FE3+), were decreased in the livers of LPS-induced rats that had been previously treated with CCl4, indicating cytochrome P450/P420 destruction or at least a change in the valence state of the cytochrome P450/P420 heme groups to Fe2+ in the presence of .NO. Because nitrosyl-cytochrome P450 is not stable, the concomitant detection of nitrosyl-cytochrome P420 (Fe2+) could account, at least in part, for the decrease of the ferric low-spin heme groups. Our novel observations of hepatic nitrosyl species suggest that .NO plays an important role during hepatic injury caused by CCl4 in hosts exposed to endotoxin.
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PMID:Nitric oxide production during endotoxic shock in carbon tetrachloride-treated rats. 807 2

The effects of anabolic-androgenic steroid administration and exercise training on various aspects of hepatic function were investigated in sedentary and trained (treadmill for 12 wk) male and female rats treated orally with fluoxymesterone or methylandrostanolone (2 mg.kg-1 body weight, 5 d.wk-1 for 8 wk). The mean values of serum alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total and direct bilirubin, and total- and high-density lipoprotein-cholesterol remained within normal range in all groups of male animals. The same is true for female rats, except for an increase in alkaline phosphatase activity in the steroid-treated groups. Hepatic microsomal aniline p-hydroxylase activity was reduced in male and increased in female rats by either steroid, whereas no significant effect was detected on 7-ethoxycoumarin deethylase activity. The levels of cytochrome P-450 and cytochrome b5 were markedly decreased by the anabolic-androgenic steroid treatment in male rat microsomes, but neither the steroid administration nor exercise training induced significant changes in the cytochrome levels of female rat livers. Taking into account the significant increase in microsomal protein yield elicited by fluoxymesterone or methylandrostanolone treatment both in males and females, it is noteworthy that the total monooxygenase activities and cytochrome P-450 content, expressed on a per gram liver basis, were significantly increased in female whereas they were apparently unchanged in male rats. In conclusion, the present data show that the prolonged ingestion of high doses of anabolic-androgenic steroids, either with or without concurrent exercise training, can modify in a sex-dependent manner the capacity of rat liver to metabolize drugs without affecting classical serum indicators of hepatic function.
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PMID:Effect of training and anabolic-androgenic steroids on drug metabolism in rat liver. 835 Jul 4


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