Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aim of this study was to determine the cellular source of oxygen free radicals generated by isolated hepatocytes during post-anoxic reoxygenation. Superoxide anions (O2.-) were detected by lucigenin chemiluminescence. Cell damage was assessed by LDH release. During anoxia, the chemiluminescence decreased to background levels while LDH release increased 8-fold. During reoxygenation, O2.- formation increased 15-fold within 15 min then declined towards control levels. LDH release increased from 161 to 285 mU/min in the first 30 min of reoxygenation, then declined toward the control rate. Allopurinol, an inhibitor of the xanthine-xanthine oxidase system, did not inhibit O2.- formation nor LDH release. Antimycin, a mitochondrial complex III inhibitor that does not block O2.- formation, increased both O2.- generation and LDH release 82 and 133% respectively. Diphenyleneiodonium (DPI), a mitochondrial and microsomal NADPH oxidase inhibitor, reduced O2.- and LDH release 60-70%. SOD, which catalyzes the dismutation of O2.- to H2O2, was without effect on O2.- and LDH release, but TEMPO, a stable nitroxide which mimics SOD and easily penetrates the cell membrane, decreased O2.-86% without affecting LDH. These results suggest that mitochondria or microsomes are the principal sites of O2.- production during reoxygenation of isolated hepatocytes, whereas the cytosolic xanthine/xanthine oxidase system is apparently not involved.
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PMID:Source of oxygen free radicals produced by rat hepatocytes during postanoxic reoxygenation. 754 22

We have characterized a chemically reactive propranolol (PL) metabolite which binds to proteins in rat liver microsomes. During incubation with rat liver microsomes (1 mg of protein) fortified with an NADPH-generating system, 4-hydroxypropranolol (4-OH-PL) quickly disappeared from the reaction medium, but none of the possible metabolite peaks was detected under the high-performance liquid chromatographic conditions used. The consumption of 4-OH-PL depended on microsomes and NADPH. The reaction was not affected by inhibitors of cytochrome P450 or FAD monooxygenase, but was markedly diminished in the presence of cytosol and ascorbic acid. The effect of cytosol was inhibited by potassium cyanide but not by sodium benzoate or dimethyl sulfoxide, and was also not affected by heating at 60 degrees C for 30 min, suggesting that superoxide (SO) ion was involved in the reaction and that it was blocked by superoxide dismutase (SOD) present in the cytosol. Cu,Zn-SOD, purified from cytosol, effectively mimicked the suppressive effect of cytosol. Incubation of 4-OH-PL in an SO-generating system of xanthine and xanthine oxidase generated 1,4-naphthoquinone (1,4-NQ), which was identified by TLC, HPLC, and GC/MS. 1,4-NQ was also formed in microsomal incubates containing NADPH and small amounts of microsomes (below 0.1 mg of protein). These results indicate that 4-OH-PL is converted by SO, or some reactive oxygen species derived from it, to 1,4-NQ which binds to proteins and is one of the reactive metabolites of PL.
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PMID:Characterization of a chemically reactive propranolol metabolite that binds to microsomal proteins of rat liver. 754 55

The relationship between changes in seromucoid levels, xanthine oxidase activity in plasma, and drug metabolism in rats with turpentine-induced inflammation and adjuvant-induced arthritis was studied. For antipyrine, systemic clearance decreased, the volume distribution remained the same, and the half-life increased in turpentine- and adjuvant-treated rats. In both cases seromucoid level and xanthine oxidase activity in plasma increased. Treatment of rats with dexamehasone before turpentine-induced inflammation raised the level of seromucoid. However, dexamehasone treatment of rats with adjuvant disease significantly decreased the level of seromucoid. Moreover, dexamehasone administration did not significantly protect against the effects of inflammation on the hepatic microsomal drug-metabolizing enzyme system and activity of xanthine oxidase in plasma. Thus, pharmacokinetics of different drugs can significantly change in some types of inflammation in animals and humans, particularly by dexamehasone administration.
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PMID:[The relationship between antipyrine kinetics, the seromucoid content and the xanthine oxidase activity in the plasma of rats with acute and chronic inflammation]. 758 Jul 55

Interleukin-2 (15 micrograms/mouse, i.p. twice daily for 4 days and once on the 5th day) significantly lowered cytochrome P-450 and heme content and increased heme oxygenase mRNA accumulation; the activities of 7-ethoxycoumarin O-deethylase, ethoxy- and pentoxyphenoxazone O-dealkylases were decreased. The activity of the type O form of hepatic xanthine oxidase increased, but there was no increase in lipid peroxide, expressed in terms of microsomal malondialdehyde. In vivo inactivation of xanthine oxidase activity by feeding mice with tungstate did not substantially change the degree of interleukin-2-induced cytochrome P-450 depression, suggesting that the two processes are not causally linked. Induction of tolerance to endotoxin by a 4-day pretreatment with lipopolysaccharide resulted in 50% protection against this depression despite inhibition of the interleukin-2 induced formation of tumor necrosis factor. This suggests that the release of tumor necrosis factor per se does not fully account for the depression of cytochrome P-450. Dexamethasone, already used in patients to reduce the toxicity of interleukin-2 therapy, provided full protection against the cytochrome P-450 depression.
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PMID:Mechanisms of interleukin-2-induced depression of hepatic cytochrome P-450 in mice. 779 64

Sources of superoxide anion (O2-.) production in calf pulmonary artery smooth muscle homogenate and subcellular fractions were examined in this study by measurement of the chemiluminescence produced by the reaction of O2-. with 50 microM lucigenin, because recent evidence suggests that endogenously produced reactive O2 species appear to mediate certain vascular responses. In the homogenate fraction, an NADH (0.1 mM)-dependent oxidoreductase activity was the major detected source of chemiluminescence. NADPH (0.1 mM) produced only 3% of the O2-. observed with NADH. Quantitation of certain other potential sources of O2-. (under optimized conditions), including xanthine oxidase (0.1 mM hypoxanthine), mitochondria (5 mM succinate + 30 microM antimycin), cyclooxygenase/lipoxygenase (1 microM arachidonic acid + 0.1 mM NADPH), or autooxidation (0.1 mg/ml superoxide dismutase), resulted in the detection of minimal amounts (< 3% of NADH) of chemiluminescence. Estimation of mitochondrial O2-. production from tissue respiration rates suggests that lucigenin is a poor detector of intramitochondrial O2-.. These observations were confirmed by examination of chemiluminescence produced by subcellular fractions, where the major activity detected was an NADH oxidoreductase, which fractionated in a manner closely matching the activity of the microsomal marker enzyme rotenone-insensitive NADH-cytochrome c reductase. Because this NADH oxidoreductase appears to be a major vascular smooth muscle-derived source of O2-. production, this system has the potential to be an important endogenous source for the generation of vasoactive reactive O2 species.
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PMID:Sites of superoxide anion production detected by lucigenin in calf pulmonary artery smooth muscle. 781 Jun 85

1. A series of flavonoids isolated from Indian medicinal plants: kaempferol-3-O-galactoside, hispidulin, nepetin, scutellarein, scutellarein-7-O-glucuronide, hibifolin and morelloflavone were studied for their activity as inhibitors of microsomal lipid peroxidation and scavengers of oxygen free radicals in vitro as well as in a model of xenobiotic toxicity in mouse. 2. All compounds inhibited lipid peroxidation in vitro. The most potent compounds were nepetin (non-enzymic lipid peroxidation) and morelloflavone (enzymic lipid peroxidation) with IC50's in the micromolar range. Some of the compounds behaved as scavengers of hydroxyl radical in the deoxyribose degradation assay, with a calculated rate constant for kaempferol-3-O-galactoside of 1.55 x 10(10) M-1 s-1. 3. Scutellarein and nepetin were found to be inhibitors of xanthine oxidase activity, whereas morelloflavone acted as a scavenger of superoxide generated by hypoxanthine/xanthine oxidase. 4. Treatment of mice with scutellarein, hispidulin, nepetin and kaempferol-3-O-galactoside after bromobenzene intoxication decreased serum glumate-pyruvate transaminase activity, although only the last flavonoid was able to significantly reduce hepatic lipid peroxidation products and to increase the reduced glutathione level. In contrast, morelloflavone increased bromobenzene toxicity.
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PMID:Influence of a series of natural flavonoids on free radical generating systems and oxidative stress. 797 32

Microsomes and reconstituted systems containing cytochrome P450 can oxidize glycerol to formaldehyde in a reaction catalyzed by an oxidant produced from the interaction of nonheme iron with H2O2. To evaluate the mechanism for this oxidation, the generation of glycerol radicals by various systems was compared to rates of formaldehyde production from glycerol. Photolysis of H2O2, oxidation of xanthine by xanthine oxidase in the presence of iron catalysts, or NADPH-dependent microsomal electron transfer in the presence of ferric-EDTA produced hydroxyl radicals. In the presence of glycerol these reaction systems produced DMPO-glycerol radical adducts which were detected by ESR spectroscopy. Despite the production of .OH and glycerol spin-trapped adducts by these reaction systems, very low amounts or nondetectable amounts of formaldehyde were produced from the glycerol. However, significant amounts of formaldehyde were observed when microsomes were incubated in the presence of ferric ammonium sulfate or ferric-ATP, although .OH production was lower with these iron catalysts than with ferric-EDTA. These results fail to support correlation between .OH production and oxidation of glycerol to formaldehyde. Under conditions in which glycerol was oxidized to formaldehyde, no glycerol radical species could be observed with DMPO as the spin-trapping agent. These results suggest the oxidant (not .OH) derived from the interaction of H2O2 with iron apparently cleaves glycerol to formaldehyde without the formation of a radical intermediate. Alternatively, the radical intermediate may be produced at a too low concentration to be detected or the radical intermediate may not be formed as a free species and therefore cannot be spin-trapped.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Oxidation of glycerol to formaldehyde by microsomes: are glycerol radicals produced in the reaction pathway? 806 25

In the Tsukamoto-French model, ethanol causes an important 10-20-fold induction of ethanol-inducible cytochrome P4502E1 (CYP2E1), mediated through enzyme stabilization and increased rate of gene transcription. The CYP2E1 induction results in a pronounced increase in the rate of NADPH-dependent microsomal lipid peroxidation, an elevation which is not seen after simultaneous administration of the CYP2E1 inhibitor diallylsulfide. Increased amounts of lipid peroxides are seen in plasma and red blood cells of both rats and humans during high ethanol intake. A mechanism for ethanol-dependent liver damage is proposed which involves the CYP2E1-dependent lipid peroxide formation, either directly by its capability to induce NADPH-dependent peroxidation in the microsomal membranes or indirectly by a hypoxia-mediated transformation of xanthine dehydrogenase to xanthine oxidase, in activation of Ito cells and Kupffer cells to yield cytokine and collagen production. The CYP2E1 gene is polymorphic among Caucasians. Four different unrelated or partially linked polymorphisms have been observed. One polymorphism in the 5'-flanking region has been described to be associated with altered enzyme expression in vitro, and the rare allele was found to be less frequent among Swedish patients having lung cancer when compared to two different control groups. Another polymorphism, detectable with Dra I restriction endonuclease fragment length polymorphism (RFLP), was localized to intron 6, and the rare allele was less common among Italian alcoholics with clinical signs of liver cirrhosis, as compared to controls. Several other mutations in the CYP2E1 gene were found to be associated with this allele. However, further research is needed to relate the CYP2E1 gene polymorphism with incidence of liver cirrhosis.
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PMID:Ethanol-inducible cytochrome P4502E1: genetic polymorphism, regulation, and possible role in the etiology of alcohol-induced liver disease. 812 98

Aldehyde oxidase was purified about 120-fold from rat liver cytosol by sequential column chromatography using diethylaminoethyl (DEAE) cellulose, Benzamidine-Sepharose 6B and gel filtration. The purified enzyme was shown as a single band with M(r) of 2.7 x 10(5) on polyacrylamide gel electrophoresis (PAGE) and M(r) of 1.35 x 10(5) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Using this purified enzyme, in vitro conversion of allopurinol, pyrazinamide and pyrazinoic acid was investigated. Allopurinol and pyrazinamide were oxidized to oxypurinol and 5-hydroxy-pyrazinamide, respectively, while pyrazinoic acid, the microsomal deamidation product of pyrazinamide, was not oxidized to 5-hydroxypyrazinoic acid. The apparent Km value of the enzyme for pyrazinamide was 160 microM and that for allopurinol was 1.1 mM. On PAGE, allopurinol- or pyrazinamide-stained band was coincident with Coomassie Brilliant Blue R 250-stained band, respectively. These results suggest that aldehyde oxidase may play a role in the oxidation of allopurinol to oxypurinol and that of pyrazinamide to 5-hydroxypyrazinamide with xanthine dehydrogenase which can oxidize both allopurinol and pyrazinamide in vivo. The aldehyde oxidase may also play a major role in the oxidation of allopurinol and pyrazinamide in the subgroup of xanthinuria patients (xanthine oxidase deficiency) who can oxidize both allopurinol and pyrazinamide.
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PMID:In vitro oxidation of pyrazinamide and allopurinol by rat liver aldehyde oxidase. 821 57

In an attempt to clarify the possible mechanism of the interaction between theophylline (TP) and mexiletine (ME), the elimination kinetics and in vitro metabolism of TP and its metabolites were investigated in rats. The plasma elimination of TP, 1,3-dimethyluric acid (1,3-DMU) and 1-methyluric acid (1-MU) was significantly delayed by the intravenous (i.v.) administration of ME. The oral administration of ME also decreased the elimination rate of TP to the same extent as the i.v. dosing. The in vitro metabolic experiment showed that ME significantly inhibited the metabolic conversion of TP to 1,3-DMU and, 1,3-DMU to 1-MU, and slightly inhibited the conversion of TP to 3-methylxanthine, these processes being mediated by microsomal enzymes, with no inhibition of xanthine oxidase. Our results indicated that ME could inhibit the metabolic conversion of TP and its metabolite in rat, as reported in man.
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PMID:Effect of mexiletine on elimination and metabolic conversion of theophylline and its major metabolites in rats. 836 52


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