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)

Aristolochic acid II (AAII), one of the major components of the carcinogenic plant extract aristolochic acid, is known to be mutagenic and to form DNA adducts in vitro and in vivo. The major fluorescent DNA adduct formed upon xanthine oxidase mediated reduction in the presence of calf thymus (CT-) DNA or deoxyadenosine was isolated by means of preparative HPLC and identified by fluorescence, UV/vis absorbance, and 1H NMR spectroscopy as 7-(deoxy-adenosin-N6-yl)aristolactam II. As a model proximate carcinogen, N-chloroaristolactam II was prepared chemically from aristolactam II, the reduction product of AAII. This model compound was spectroscopically characterized and found to react directly with CT-DNA without any activation, forming the same deoxyadenosine adduct. HPLC analysis with fluorescence monitoring detected this adduct in vivo in the liver DNA of Wistar rats treated orally with AAII. These results confirm the anticipated metabolic activation mechanism of AAII as occurring via a cyclic nitrenium ion.
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PMID:N6-adenyl arylation of DNA by aristolochic acid II and a synthetic model for the putative proximate carcinogen. 166 54

Aristolochic acid I (AA I) and aristolochic acid II (AA II), the two main ingredients of the carcinogenic plant extract aristolochic acid (AA), are metabolized to reactive intermediates which bind covalently to DNA in vitro and in vivo. DNA adduct formation was analysed by the 32P-postlabelling assay. In in vitro incubations with rat liver 9000 g supernatant (S9) and calf thymus DNA (CT-DNA), AA I showed an identical pattern of DNA adducts on thin-layer chromatograms under aerobic and anaerobic conditions, whereas AA II gave rise to DNA adduct formation only anaerobically. The anaerobically obtained DNA adduct pattern by AA II in vitro was similar to the AA I adduct patterns. Aristolactams I and II, the metabolites of AA I and AA II formed under anaerobic conditions, did not form DNA adducts in the presence of S9 mix and CT-DNA. Incubations with xanthine oxidase, known to enzymatically reduce aromatic nitro groups, also activated AA I and AA II to reactive intermediates, producing almost identical adduct patterns as obtained by S9 mix-mediated metabolism. Activation of AA I by S9 mix in the presence of poly(dG) resulted in the formation of two adducts, one of which was shown to be chromatographically indistinguishable from an adduct obtained by reaction with CT-DNA. For the in vivo studies AA I and AA II were administered orally to male Wistar rats, and DNA from liver, brain, oesophagus, stomach lining, forestomach lining, kidney and bladder was analysed for DNA adducts by 32P-postlabelling. The adduct patterns in DNA from forestomach and kidney--target tissues of AA--and DNA from non-target tissues like stomach lining and liver were similar to the patterns obtained from the in vitro incubations. In the bladder (also a target tissue) only AA II gave rise to DNA adduct formation. These findings suggest that DNA adduct formation by AA I and AA II does not directly correlate with the initiation of the carcinogenic process and subsequent tumour formation in target tissues in the rat.
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PMID:DNA adduct formation of aristolochic acid I and II in vitro and in vivo. 333 14

Aristolochic acid I (AAI) and aristolochic acid II (AAII), the two major components of the carcinogenic plant extract aristolochic acid (AA), are known to be mutagenic and to form DNA adducts in vivo. According to the structures of the major DNA adducts identified in animals and humans, nitroreduction is the crucial pathway in the metabolic activation of these naturally occurring nitroarenes to their ultimate carcinogenic species. Using the nuclease P1-enhanced version of the 32P-post-labelling assay we investigated the formation of DNA adducts by AAI and AAII in different in vitro activation systems in order to determine the most suitable in vitro system mimicking target tissue activation. Although DNA adducts resulting from oxidative activation of AAs have not yet been identified both reductive and oxidative in vitro systems were employed. In vitro incubations were conducted under standardized conditions (0.3 mM AAs; 4 mM dNp as calf thymus DNA) using rat liver microsomes, xanthine oxidase (a mammalian nitroreductase), horseradish peroxidase, lactoperoxidase and chemical reduction by zinc. Enzymatic incubations were performed under aerobic and anaerobic conditions. A combination of two independent chromatographic systems (ion-exchange chromatography and reversed-phase HPLC) with reference compounds was used for the identification of DNA adducts detected by the 32P-post-labelling assay. The two known major adducts of AAI or AAII found in vivo were generated by all in vitro systems except for incubations with AAII and horseradish peroxidase where two unknown adducts predominated. Irrespective of the in vitro activation system used, the majority of adduct spots obtained were identified as the previously characterized four AA-DNA adducts: dA-AAI, dA-AAII, dG-AAI and dG-AAII. This indicates that both reductive and peroxidative activation of AAI or AAII resulted in chromatographically indistinguishable DNA adducts. Thus, peroxidase mediated activation of AAs led to the formation of the same adducts that had been observed in vivo and upon reductive activation in several in vitro systems. Quantitative analyses of individual adducts formed in the various in vitro systems revealed relative adduct labelling (RAL) values over a 100,000-fold range from 4 in 10(3) for activation of AAII to deoxyadenosine adducts by zinc to only 3 in 10(8) for activation of AAII by lactoperoxidase. The extent of DNA modification by AAI was higher than by AAII in all enzymatic in vitro systems. Only activation by zinc resulted in higher total binding to exogenous DNA by AAII than by AAI. Aerobic incubations with rat liver microsomes generated AAI- and AAII-DNA adduct profiles reproducing profiles in target tissue (forestomach) of rats, thus providing the most appropriate activation among the in vitro systems tested.
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PMID:Comparison of DNA adduct formation by aristolochic acids in various in vitro activation systems by 32P-post-labelling: evidence for reductive activation by peroxidases. 916 96

Aristolochic acid (AA), a naturally occurring nephrotoxin and rodent carcinogen, has recently been associated with the development of urothelial cancer in humans. Understanding which enzymes are involved in AA activation and/or detoxication is important in the assessment of an individual susceptibility to this natural carcinogen. We examined the ability of enzymes of rat renal and hepatic cytosolic fractions to activate AA to metabolites forming DNA adducts by the nuclease P1-enhanced version of the (32)P-postlabeling assay. Cytosolic fractions of both these organs generated AA-DNA adduct patterns reproducing those found in renal tissues from humans exposed to AA. 7-(Deoxyadenosin-N(6)-yl)aristolactam I, 7-(deoxyguanosin-N(2)-yl)aristolactam I and 7-(deoxyadenosin-N(6)-yl)aristolactam II were identified as AA-DNA adducts formed from AAI and 7-(deoxyguanosin-N(2)-yl)aristolactam II and 7-(deoxyadenosin-N(6)-yl)aristolactam II were generated from AAII by hepatic cytosol. Qualitatively the same AA-DNA adduct patterns were observed, although at lower levels, upon incubation of AAs with renal cytosol. To define the role of cytosolic reductases in the reductive activation of AA, we investigated the modulation of AA-DNA adduct formation by cofactors, specific inducers or selective inhibitors of the cytosolic reductases, DT-diaphorase, xanthine oxidase (XO) and aldehyde oxidase. The role of the enzymes in AA activation was also investigated by correlating the DT-diaphorase- and XO-dependent catalytic activities in cytosolic sample with the levels of AA-DNA adducts formed by the same cytosolic sample. On the basis of these studies, we attribute most of the cytosolic activation of AA to DT-diaphorase, although a role of cytosolic XO cannot be ruled out. With purified DT-diaphorase, the participation of this enzyme in the formation of AA-DNA adducts was confirmed. The binding orientation of AAI in the active site of DT-diaphorase was predicted by computer modeling based on published X-ray structures. The results presented here are the first report demonstrating a reductive activation of carcinogenic AAs by DT-diaphorase.
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PMID:Carcinogenic aristolochic acids upon activation by DT-diaphorase form adducts found in DNA of patients with Chinese herbs nephropathy. 1196 Sep 15

Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, has been associated with the development of urothelial cancer in humans. Understanding which human enzymes are involved in AA metabolism is important in the assessment of an individual's susceptibility to this carcinogen. Using the 32P-postlabeling assay we examined the ability of enzymes of cytosolic samples from 10 different human livers and from one human kidney to activate the major component of the plant extract AA, 8-methoxy- 6-nitro-phenanthro-(3,4-d)-1,3-dioxolo-5-carboxylic acid (AAI), to metabolites forming adducts in DNA. Cytosolic fractions of both organs generated AAI-DNA adduct patterns reproducing those found in renal tissues from humans exposed to AA. 7-(Deoxyadenosin-N6-yl)aristolactam I, 7-(deoxyguanosin-N2-yl)aristolactam I and 7-(deoxyadenosin-N6-yl)aristolactam II, indicating a possible demethoxylation reaction of AAI, were identified as AA-DNA adducts formed from AAI by all human hepatic and renal cytosols. To define the role of human cytosolic reductases in the activation of AAI, we investigated the modulation of AAI-DNA adduct formation by cofactors or selective inhibitors of the NAD(P)H:quinone oxidoreductase (NQO1), xanthine oxidase (XO) and aldehyde oxidase. We also determined whether the activities of NQO1 and XO in different human hepatic cytosolic samples correlated with the levels of AAI-DNA adducts formed by the same cytosolic samples. Based on these studies, we attribute most of the activation of AA in human cytosols to NQO1, although a role of cytosolic XO cannot be ruled out. With purified NQO1 from rat liver and kidney and XO from buttermilk, the major role of NQO1 in the formation of AAI-DNA adducts was confirmed. The orientation of AAI in the active site of human NQO1 was predicted from molecular modeling based on published X-ray structures. The results demonstrate for the first time the potential of human NQO1 to activate AAI by nitroreduction.
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PMID:Human cytosolic enzymes involved in the metabolic activation of carcinogenic aristolochic acid: evidence for reductive activation by human NAD(P)H:quinone oxidoreductase. 1286 22