Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.17.3.2 (xanthine oxidase)
 8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Evidence has been obtained that implicates the generation of reactive oxygen species as an early and critical event in the promotion of neoplastic transformation in mouse JB6 cells. The time courses for specific inhibition by CuZn-superoxide dismutase (CuZn-SOD) of the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced promotion of neoplastic transformation in JB6 cells and for changes in antioxidant enzyme activities associated with TPA-exposure were examined. The antipromoting effect of CuZn-SOD was found to be critically dependent on the time of addition of CuZn-SOD relative to the start of a 14-day exposure of cells to TPA. Treatment of JB6 P+ Clone 22 and Clone 41 cells with CuZn-SOD for 18 h before, simultaneously with or up to 1 h after exposure to TPA, all inhibited promotion of transformation maximally. Delay of addition of CuZn-SOD by 2 h or more after the start of TPA treatment resulted in a marked decrease in the promotion inhibitory effect. CuZn-SOD added 24 or 48 h after TPA had no effect on promotion of transformation. Exposure of JB6 cells to 0.2- (superoxide anion radical) generated exogenously by the aerobic xanthine oxidase reaction resulted in promotion of neoplastic transformation that was prevented by concurrent addition of CuZn-SOD. Taken together these studies provide evidence that increased superoxide anion generation within the first 2 h following TPA exposure is an essential event in promotion of transformation in JB6 cells. Upon TPA exposure, JB6 Clone 41 cells exhibited time-specific activity changes in the cellular SOD, glutathione peroxidase (GSH-Px), and catalase. SOD and GSH-Px activities were reduced to 54% and 26% respectively of basal levels within 2 h of TPA treatment. GSH-Px activity recovered to basal levels within 4 h and CuZn-SOD within 48 h. Catalase activity was maximally reduced to 50% of basal within 1 h after TPA treatment and rebounded to greater than basal levels within 4 h. It is postulated that a c-kinase-dependent event induces rapid elevation of superoxide anion following TPA exposure and that this leads to reduced activity of antioxidant enzymes. Since antipromotion by exogenous CuZn-SOD is effective only during the first 2 h following TPA exposure, this suggests that the promotion-relevant 0.2- elevation is transient.
Carcinogenesis 1988 Feb
PMID:Early superoxide dismutase-sensitive event promotes neoplastic transformation in mouse epidermal JB6 cells. 282 3

Aerobic oxidation of 3-hydroxyamino-1-methyl-5H-pyrido-[4,3-b]indole [Trp-P-2(NHOH)] in neutral aqueous solution was greatly accelerated by copper-zinc superoxide dismutase (SOD). The major product in this SOD-mediated reaction was identified as 3-nitroso-1-methyl-5H-pyrido[4,3-b]indole [Trp-P-2(NO)]. This conversion was accompanied by a decrease of the mutagenicity of the mixture, as monitored by the direct-acting mutagenicity on Salmonella typhimurium TA98; a rapid change to approximately 1/3 of the original mutagenicity was followed by no further decrease of the activity. In contrast, in the spontaneous aerobic oxidation of Trp-P-2-(NHOH), the mutagenicity slowly and continuously decreased, until it was finally lost almost completely. Similar acceleration by SOD of aerobic oxidation was found for 2-hydroxyamino-6-methyldipyrido[1,2-a:3',2'-d]imidazole [Glu-P-1(NHOH)]. Again, mutagenicity of approximately 1/4 that of the original was retained in the SOD-mediated decomposition, while a complete loss of the mutagenicity was observed in the spontaneous decomposition. When Trp-P-2(NO) was treated with the superoxide-generating system, xanthine oxidase plus xanthine, Trp-P-2(NHOH) was formed. Therefore, the role of SOD in the conversion of Trp-P-2(NHOH) into Trp-P-2(NO) is the removal of superoxide anions generated by reduction of aerobic oxygen, thereby inhibiting the reverse reactions, i.e. the reduction of Trp-P-2(NO) and that of the putative intermediate nitroxide radical. In support of this proposed mechanism, phenylhydroxylamine underwent a SOD-accelerated conversion to nitrosobenzene, and nitrosobenzene was reduced to phenylhydroxylamine by the action of the xanthine oxidase-xanthine system. Hence, this reversible interchange between an arylhydroxylamine and its nitroso compound, coupled with the oxygen-superoxide cycle, may be a general phenomenon. A consequence of this finding is that the xenobiotic N-hydroxylamines may be converted by the action of SOD in the biological settings into nitroso compounds, which are chemically more stable, serving as a reservoir for mutagenicity.
Carcinogenesis 1988 Nov
PMID:Superoxide dismutase-mediated reversible conversion of 3-hydroxyamino-1-methyl-5H-pyrido[4,3-b]indole, the N-hydroxy derivative of Trp-P-2, into its nitroso derivative. 284 95

The 32P-postlabeling technique was used to qualitatively establish the pattern of DNA adduct formation in mammary tissue and liver following administration of 1-nitropyrene to female Sprague-Dawley rats. 1-Nitropyrene (100 mg/kg b.w.) was administered by gavage in trioctanoin and the rats were sacrificed 24 h later. DNA was isolated from mammary fat pads and liver, enzymatically hydrolyzed to deoxyribonucleoside-3'-monophosphates and then converted to [5'-32P]3',5'-bisphosphates. The polyethyleneimine-cellulose (PEI-cellulose) TLC 32P-fingerprints revealed the presence of multiple putative adducts in the mammary fat pads and in the livers. To investigate the role of nitroreduction in the formation of these adducts, calf thymus DNA was incubated with [3H]1-nitropyrene in vitro in the presence of xanthine oxidase. The DNA was isolated and analyzed by the 32P-postlabeling technique. A major adduct spot was detected and confirmed as N-(deoxyguanosin-8-yl)-1-aminopyrene. This adduct cochromatographed with a minor in vivo adduct of DNA obtained from mammary fat pads and livers. However, the major adducts detected in vivo did not appear to originate from simple nitroreduction of 1-nitropyrene. The results of this study suggest that other metabolic pathways, such as ring oxidation, or ring oxidation followed by nitroreduction, may be responsible for the putative 1-nitropyrene-DNA adducts observed in mammary fat pads and livers of female Sprague-Dawley rats.
Carcinogenesis 1989 Jan
PMID:32P-postlabeling analysis of 1-nitropyrene-DNA adducts in female Sprague-Dawley rats. 291 May 23

The ionic complex between lysozyme and either Escherichia coli DNA or pBR322 DNA was not crosslinked by two systems capable of producing nanomolar amounts of hydroxyl radicals, the oxidation of xanthine by xanthine oxidase and the iron catalyzed oxidation of ascorbic acid. Nor did effective crosslinking occur with micromolar quantities of hydroxyl radicals raised by the addition of adenosine nucleotides to ferrous iron and hydrogen peroxide. In this case, radical content was estimated by colorimetric analysis of formaldehyde following hydroxyl radical oxidation of dimethyl sulfoxide. Similar amounts of radicals generated by pulse radiolysis in a nitrous oxide atmosphere failed also to induce crosslinking. These findings do not support a role for hydroxy radicals in the N-acetoxy-2-acetylaminofluorene induced crosslinking of DNA to lysozyme proposed earlier.
Carcinogenesis 1985 Dec
PMID:Hydroxyl radicals do not crosslink a DNA-lysozyme complex. 299 38

The evidence is convincing that oxidants and agents which induce a cellular pro-oxidant state can act as carcinogens, in particular as promoters and progressors. Importantly, infiltrated phagocytes represent a source of oxidants in inflamed tissues. We have studied the mechanism of the promotional action of active oxygen (AO) in mouse epidermal cells JB6 by comparing the non-promotable clone 30 to the promotable clone 41. In order to mimick AO released by phagocytes we used xanthine/xanthine oxidase as a source of extracellular superoxide and hydrogen peroxide. We found that AO stimulated the growth only of promotable clone 41 after an initial period of moderate inhibition while it was strongly cytostatic for non-promotable clone 30. Reasons for the higher cytostatic effect of AO on the non-promotable clone 30 were discovered when we measured DNA strand breakage and poly ADP-ribosylation of chromosomal proteins. At equal doses AO induced 4-5 times more DNA breaks in clone 30 in reactions which required iron--and probably also calcium--ions. The higher amount of DNA breakage in clone 30 was reflected in a higher extent of poly ADP-ribosylation. Excessive DNA breakage and poly ADP-ribosylation which causes the depletion of NAD and ATP may be responsible for the strong cytostatic effect of AO in clone 30. We conclude that differential resistance to the cytostatic/cytotoxic effect of AO in part determines the promotability of mouse epidermal cells JB6.
Carcinogenesis 1988 Feb
PMID:Active oxygen induced DNA strand breakage and poly ADP-ribosylation in promotable and non-promotable JB6 mouse epidermal cells. 333 7

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.
Carcinogenesis 1988 Feb
PMID:DNA adduct formation of aristolochic acid I and II in vitro and in vivo. 333 14

Xanthine oxidase catalyzed mutagenicity of 4-nitrobiphenyl (NBP), a dog-bladder carcinogen, was tested in Ames assay using Salmonella typhimurium TA98 strains. NBP was active as a mutagen in the parent strain TA98 which is proficient in nitroreductase, while it was inactive in the strain TA98NR which is deficient in nitroreductase. However, preincubation of NBP at 37 degrees C with NADH and commercial preparations of xanthine oxidase for 30 min resulted in a dose-dependent increase in the mutagenic activity in TA98NR. Allopurinol blocked the xanthine oxidase catalyzed mutagenicity of NBP in TA98NR and the extent of inhibition was dependent upon the concentration of the inhibitor. Rat-liver and dog-bladder cytosol preparations also enhanced the mutagenic activity of NBP in TA98NR in a dose-dependent manner. In addition, the cytosol-mediated activity was also inhibited by allopurinol, implying that the cytosolic enzyme activity might be due to xanthine oxidase. In vitro enzymatic reduction of NBP using bacterial cell lysates of TA98 and TA98NR revealed the major product of reduction to be 4-aminobiphenyl. The transient intermediates of reduction were not detected during the in vitro incubation. The reduction intermediate N-hydroxylaminobiphenyl showed direct and equal mutagenic activity in both TA98 and TA98NR, in contrast to NBP. These results suggest that N-hydroxylaminobiphenyl is generated during the preincubation of NBP with xanthine oxidase or cytosolic preparations and the former might account for the mutagenicity of NBP. Furthermore, the occurrence of such enzyme(s) in the target tissue for NBP carcinogenesis, support the hypothesis that metabolic activation of the bladder carcinogen NBP could occur within the target organ by virtue of its intrinsic metabolic potential.
 ...
PMID:Xanthine oxidase-mediated mutagenicity of the bladder carcinogen 4-nitrobiphenyl. 353 36

Treatment of normal human diploid fibroblasts with 0.3-22 microM 1-nitrosopyrene resulted in a dose-dependent decrease in relative cloning efficiency and an increase in anchorage-independent growth in soft agar. When compared to previous experiments, 1-nitrosopyrene was 10- to 20-fold more cytotoxic and 5- to 10-fold more potent at inducing morphological transformation than 1-nitropyrene. Incubation of the fibroblasts with 8 microM 1-nitropyrene in the presence of xanthine oxidase, a mammalian nitroreductase, resulted in the formation of one major DNA adduct, N-(deoxyguanosin-8-yl)-1-aminopyrene, at a level of 1.1 adducts per 10(6) nucleotides. Fibroblasts treated with 1-nitrosopyrene formed the same DNA adduct; however, only a 0.3 microM concentration was required to give 0.7 adducts per 10(6) nucleotides in the fibroblast DNA. These data indicate that a limiting step in the cellular toxicity and transformation of normal human diploid fibroblasts by 1-nitropyrene is the initial reduction to 1-nitrosopyrene.
Carcinogenesis 1986 Aug
PMID:Cytotoxicity, cellular transformation and DNA adducts in normal human diploid fibroblasts exposed to 1-nitrosopyrene, a reduced derivative of the environmental contaminant, 1-nitropyrene. 373 81

To demonstrate whether there are any pathways of nitrite formation from N-nitrosamines other than reductive denitrosation by cytochrome P-450 we performed the following experiments. An esterified alpha-hydroxylated nitrosamine was incubated in a microsomal system to test if nitrite generation is coupled with or linked to the oxidative bioactivation pathway. Simultaneously, inhibitors of microsomal esterases were added to test if the intact molecule or a metabolite from the oxidative metabolism was responsible for nitrite formation. To check if the superoxide radical anion could be related to the mechanism of nitrite generation, nitrosamines were incubated with a xanthine oxidase/hypoxanthine system. To test if the OH radical was involved in nitrite formation, nitrosamines were incubated with an artificial hydroxy-radical generating system (xanthine oxidase/hypoxanthine system supplemented with Fe2+/EDTA). Measurable amounts of nitrite were detected after incubation of the esterified-hydroxylated N-nitrosamine when the hydrolysis by microsomal esterases was inhibited by diisopropylfluorophosphate or paraoxon and when the N-nitrosamines were incubated with the artificial hydroxy-radical generating system. Nitrite formation could not be detected in the O2(-)-generating system (xanthine oxidase/hypoxanthine) or when the esterified alpha-hydroxylated N-nitrosamine was incubated without inhibition of the microsomal esterases. These results demonstrate that besides reductive denitrosation by cytochrome P-450, nitrite generation from N-nitrosamines can also be caused by hydroxy-radicals. The importance of this possible pathway for the in vivo situation of nitrosamine metabolism is discussed.
Carcinogenesis 1986 Apr
PMID:Metabolic nitrite formation from N-nitrosamines: are there other pathways than reductive denitrosation by cytochrome P-450? 375 94

1-Nitropyrene is an environmental mutagen and carcinogen which undergoes both oxidative and reductive metabolism. We have previously shown that nitroreduction to N-hydroxy-1-aminopyrene leads to the formation of arylamine--DNA adducts. In the present study, we have investigated the oxidative metabolism of 1-nitropyrene and the subsequent binding of ring-oxidized metabolites to DNA. In vitro incubations were conducted using hepatic microsomes from uninduced rats or from rats pretreated with phenobarbital, Aroclor 1254, 3-methylcholanthrene, or 3-methylcholanthrene and trans-stilbene oxide. H.p.l.c. analysis of the incubation mixtures indicated the presence of the previously reported metabolites, 1-aminopyrene, 3-, 6-, and 8-hydroxy-1-nitropyrene, and 1-nitropyrene trans-4,5-dihydrodiol. In addition, 1-nitropyrene 4,5-oxide, 1-nitropyrene 9,10-oxide, 1-nitropyrene trans-9,10-dihydrodiol and 1-pyrenol were identified. The formation of both K-region dihydrodiols could be increased by trans-stilbene oxide induction of microsomal epoxide hydrase. Formation of the K-region epoxides was greatest using phenobarbital- and Aroclor-induced microsomes and increased with increasing oxygen tension, while 1-pyrenol formation was highest in 3-methylcholanthrene-induced microsomal incubations and was not affected by the oxygen tension. When calf thymus DNA was added to the microsomal incubations, similar levels of DNA-binding occurred in incubations conducted under oxygen, air, argon or anaerobic conditions. H.p.l.c. analysis of the enzymatically hydrolyzed DNA indicated the presence of multiple DNA adducts with the major product coeluting with N-(deoxyguanosin-8-yl)-1-aminopyrene. The K-region oxides bound directly to DNA to give adducts similar to the minor products detected in the microsomal incubations. Incubation of the K-region oxides with the nitroreductase, xanthine oxidase, increased the DNA-binding and resulted in an additional adduct which coeluted with N-(deoxyguanosin-8-yl)-1-amino pyrene. 3-Hydroxy-1-nitropyrene bound extensively to DNA upon nitroreduction by rat liver cytosol or xanthine oxidase, while 6- and 8-hydroxy-1-nitropyrene bound only slightly. None of these oxidized metabolites was activated to DNA-binding species by cytosolic nitroreduction followed by AcCoA-dependent acetylation. The fact that oxidized metabolites of 1-nitropyrene are reduced to DNA-binding derivatives more easily than 1-nitropyrene itself may be important in vivo where 1-nitropyrene has been shown to be readily oxidized.
Carcinogenesis 1986 Jul
PMID:Oxidative microsomal metabolism of 1-nitropyrene and DNA-binding of oxidized metabolites following nitroreduction. 375 82


<< Previous 1 2 3 4 5 6 7 8 Next >>