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    Keywords: MOUSE ; FUNCTIONAL GENOMICS ; DRUG ; genomic ; E ; BIOACTIVATION ; anticancer drug ; ellipticine ; genomics ; cytochrome P450 ; hepatic
    Type of Publication: Book chapter
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    Keywords: IN-VITRO ; INHIBITOR ; IN-VIVO ; VITRO ; DNA adducts ; liver ; ENZYMES ; METABOLISM ; ACTIVATION ; DNA ; kidney ; MECHANISM ; DNA ADDUCT FORMATION ; metabolic activation ; LIVER-MICROSOMES ; RAT ; AROMATIC-AMINES ; RATS ; METABOLITES ; IDENTIFICATION ; HUMANS ; ASSAY ; URINARY-BLADDER ; NUCLEOTIDES ; ADDUCTS ; RISK ASSESSMENT ; OXIDATION ; BINDS ; rodent ; CYTOCHROME-P-450 ; INHIBITORS ; DNA-ADDUCTS ; CAPACITY ; CARCINOGEN ; SELECTIVE INHIBITORS ; ADDUCT ; HEMOGLOBIN ADDUCTS ; DNA ADDUCT ; P-32-postlabeling ; rodents ; human cytochromes P450 ; o-anisidine ; TOBACCO-SPECIFIC NITROSAMINES
    Abstract: 2-methoxyaniline (o-anisidine) is an industrial and environmental pollutant and a bladder carcinogen for rodents. The mechanism of its carcinogenicity was investigated with 2 independent methods, P-32-postlabeling and C-14-labeled o-anisidine, to show that o-anisidine binds covalently to DNA in vitro after its activation by human hepatic microsomes. We also investigated the capacity of o-anisidine to form DNA adducts in vivo. Rats were treated i.p. with o-anisidine (0.15 mg/kg daily for 5 days) and DNA from several organs was analyzed by P-32-postlabeling. Two o-anisidine-DNA adducts, identical to those found in DNA incubated with o-anisidine and human microsomes in vitro, were detected in urinary bladder (4.1 adducts per 107 nucleotides), the target organ, and, to a lesser extent, in liver, kidney and spleen. These DNA adducts were identified as deoxyguanosine adducts derived from a metabolite of o-anisidine, N-(2-methoxyphenyl)hydroxylamine. This metabolite was identified in incubations with human microsomes. With 9 human hepatic microsomal preparations, we identified the specific CYP catalyzing the formation of the o-anisidine metabolites by correlation studies and by examining the effects of CYP inhibitors. On the basis of these analyses, oxidation of o-anisidine was attributed mainly to CYP2E1. Using recombinant human CYP (in Supersomes) and purified CYPs, the participation of CYP2E1 in o-anisidine oxidation was confirmed. In Supersomes, CYP1A2 was even more efficient in oxidizing o-anisidine than CYP2E1, followed by CYP2B6, 1A1, 2A6, 2D6 and 3A4. The results, the first report on the potential of the human microsomal CYP enzymes to activate o-anisidine, strongly suggest a carcinogenic potential of this rodent carcinogen for humans. (c) 2005 Wiley-Liss, Inc
    Type of Publication: Journal article published
    PubMed ID: 15828049
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    Keywords: CANCER ; human ; MODEL ; MODELS ; DNA adducts ; SITE ; SITES ; ENZYMES ; TISSUE ; RESOLUTION ; ACTIVATION ; LIGAND ; DNA ; REDUCTION ; DNA ADDUCT FORMATION ; TISSUES ; BINDING ; ACID ; PATTERNS ; HUMANS ; ASSAY ; ACTIVE-SITE ; DNA-BINDING ; METABOLIC-ACTIVATION ; ADDUCTS ; ORIENTATION ; BINDS ; aristolochic acid ; BALKAN ENDEMIC NEPHROPATHY ; CHINESE HERBS NEPHROPATHY ; P-32 POSTLABELING ANALYSIS ; DNA-ADDUCTS ; RECOMBINANT ; CRYSTALLOGRAPHIC STRUCTURE ; urothelial cancer ; CARCINOGEN ; REDUCTASE ; interaction ; development ; IRON ; ADDUCT ; ENZYME ; DNA ADDUCT ; P-32-postlabeling ; docking ; human cytochromes P450 ; computer modeling ; cytochromes P450 1A1 and 1A2 ; DNA binding ; NADPH ; reductive activation
    Abstract: Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, has been associated with the development of urothelial cancer in humans. Using the P-32-postlabeling assay we showed that AAI is activated by human recombinant cytochrome P450 (CYP) 1A1, CYPIA2 and NADPH:CYP reductase to species generating 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 by the enzymes. The formation of these AA-derived DNA adducts indicates that all the human enzymes reduce the nitro group of AAI to the putative reactive cyclic nitrenium ion responsible for adduct formation. The concentrations of AAI required for its half-maximum DNA binding were 38,65 and 126 mu M AAI for reductive activation by human CYP1A2, CYP1A1 and NADPH:CYP reductase, respectively. CYP1A1 and 1A2 homology modeling followed by docking of AAI to the CYP1A1 and 1A2 active centers was utilized to explain the potential of these enzymes to reduce AAI. Models of human CYP1A1 and 1A2 were constructed on the basis of the crystallographic structure of truncated mammalian CYP enzymes, CYP2B4, 2C5, 2C8, 2C9 and 3A4. The in silico docking of AAI to the active sites of CYP1A1I and 1A2 indicates that AAI binds as an axial ligand of the heme iron and that the nitro group of AAI is in close vicinity to the heme iron of CYPIA2 in an orientation allowing the efficient reduction of this group observed experimentally. The orientation of AAI in the active centre of CYP1A1 however causes an interaction of the heme iron with both the nitro- and the carboxylic groups of AAI. This observation explains the lower reductive potential of CYP1A1 for AAI than CYP1A2, detected experimentally. (c) 2005 Elsevier Ireland Ltd. All rights reserved
    Type of Publication: Journal article published
    PubMed ID: 16125300
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    Keywords: human ; MODEL ; MODELS ; PATHWAY ; PATHWAYS ; RISK ; ENZYMES ; METABOLISM ; ACTIVATION ; RAT ; animals ; HPLC ; METABOLITES ; carcinogenicity ; HEALTH ; HUMANS ; OXIDATION ; rodent ; cytochrome P450 ; RECOMBINANT ; PRODUCTS ; CARCINOGEN ; LEVEL ; ENZYME ; methods ; SEPARATION ; carcinogenic ; EXTRAPOLATION ; PARTICIPATION ; animal
    Abstract: OBJECTIVES: The detoxifying metabolism of a potent rodent carcinogen, 2-nitroanisole (2-NA) by human, rabbit and rat cytochromes P450 (P450) was investigated. Comparison between P450s of experimental animals and humans is essential for the extrapolation of animal carcinogenicity data to the human situation and to assess health risk. METHODS: HPLC with UV detection was employed for the separation and characterization of 2-NA metabolites formed by hepatic microsomes, human recombinant P450s and purified rat and rabbit P450s. RESULTS: An O-demethylated metabolite of 2-NA, 2-nitrophenol (2-NP), and two oxidation products of this metabolite [2,5-dihydroxynitrobenzene (2,5-DNB) and 2,6-dihydroxynitrobenzene (2,6-DNB)] were generated by microsomes and P450s from the species investigated, but at different levels. All the metabolites are detoxication products. 2-NP is the major metabolite generated by rabbit and rat microsomes, but 2,5-DNB is the predominant product in human microsomes. Using human recombinant P450s and purified rodent P450s, we found that human P450 2E1, 1A1 and 2B6 as well as orthologous animal P450s were the most efficient enzymes oxidizing 2-NA to 2-NP, while P450 2E1 and 1A1 were the most effective in the formation of 2,5-DNB and 2,6-DNB. In human hepatic microsomes, 2-NA was oxidized mainly by P4502E1. 2-NA and its reductive metabolite o-anisidine induced rat hepatic and renal P450 1A1/2 and NAD(P)H:quinone oxidoreductase (NQO1), thus modifying their own detoxication and/or activation pathways. CONCLUSIONS: The data demonstrated the participation of orthologous P450s in 2-NA oxidation by all species and indicated that the rat and rabbit might serve as suitable models to mimic 2-NA oxidation in man
    Type of Publication: Journal article published
    PubMed ID: 17159769
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    Keywords: EXPRESSION ; IN-VITRO ; INHIBITOR ; AGENTS ; human ; INHIBITION ; MODEL ; MODELS ; VITRO ; SYSTEM ; SYSTEMS ; DNA adducts ; liver ; ENZYMES ; DRUG ; METABOLISM ; DNA ; RAT ; animals ; RATS ; SUSCEPTIBILITY ; METABOLITES ; HUMANS ; ADDUCTS ; OXIDATION ; cytochrome P450 ; INHIBITORS ; DNA-ADDUCTS ; ENZYME ; DNA ADDUCT ; comparative study ; pharmacology ; Male ; animal ; magnetic resonance spectroscopy ; animal model ; CYP ; anticancer drug ; ANTICANCER DRUG ELLIPTICINE ; ANTICANCER-DRUG ; ellipticine ; drug effects ; DNA intercalation ; antagonists & inhibitors ; Antineoplastic Agents ; Cytochrome P-450 Enzyme System ; Ellipticines ; enzyme inhibitors ; Hydroxylation ; Microsomes,Liver ; Oxidation-Reduction ; Rabbits ; Rats,Wistar ; Species Specificity
    Abstract: Ellipticine is an antineoplastic agent, whose mode of action is based mainly on DNA intercalation, inhibition of topoisomerase II and formation of DNA adducts mediated by cytochrome P450 (CYP). We investigated the ability of CYP enzymes in rat, rabbit and human hepatic microsomes to oxidize ellipticine and evaluated suitable animal models mimicking its oxidation in humans. Ellipticine is oxidized by microsomes of all species to 7-hydroxy-, 9-hydroxy-, 12-hydroxy-, 13-hydroxyellipticine and ellipticine N(2)-oxide. However, only rat microsomes generated the pattern of ellipticine metabolites reproducing that formed by human microsomes. While rabbit microsomes favored the production of ellipticine N(2)-oxide, human and rat microsomes predominantly formed 13-hydroxyellipticine. The species difference in expression and catalytic activities of individual CYPs in livers are the cause of these metabolic differences. Formation of 7-hydroxy- and 9-hydroxyellipticine was attributable to CYP1A in microsomes of all species. However, production of 13-hydroxy-, 12-hydroxyellipticine and ellipticine N(2)-oxide, the metabolites generating DNA adducts, was attributable to the orthologous CYPs only in rats and humans. CYP3A predominantly generates these metabolites in rat and human microsomes, while CYP2C3 activity prevails in microsomes of rabbits. The results underline the suitability of rat species as a model to evaluate human susceptibility to ellipticine
    Type of Publication: Journal article published
    PubMed ID: 17197724
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    Keywords: IN-VITRO ; human ; IN-VIVO ; VITRO ; VIVO ; liver ; ENZYMES ; PROTEIN ; PROTEINS ; ACTIVATION ; DNA ; MECHANISM ; RAT ; SUDAN-I ; HPLC ; RATS ; BINDING ; METABOLITES ; RAT-LIVER ; carcinogenicity ; MODULATION ; CYTOCHROME-C ; ADDUCTS ; OXIDATION ; DYE ; cytochrome P450 ; RECOMBINANT ; INCREASE ; ENZYME ; methods ; SEPARATION ; technique ; in vivo ; LIQUID ; carcinogenic ; genotoxic ; CYP ; CYP1B1 ; HEME
    Abstract: OBJECTIVES: Modulation of the cytochrome P450 (CYP) 1A1-mediated oxidative activation and detoxication of carcinogenic Sudan I by the heme-protein cytochrome b(5) (b(5)) was investigated. Another aim of the study was to examine the formation of Sudan I-DNA adducts in vivo. METHODS: High performance liquid chromatography (HPLC) with ultraviolet (UV) detection was employed for the separation of Sudan I metabolites formed by human recombinant CYPs and rat CYP1A1. The (32)P-postlabeling technique was utilized to determine Sudan I-DNA adducts. RESULTS: The capabilities of the most efficient CYP enzymes oxidizing Sudan I, human and rat recombinant CYP1A1, as well as of human recombinant CYP1A2, 2A6 and 3A4 were significantly increased by b(5), while reactions catalyzed by human CYP1B1, 2C8, 2C9 and 2E1 were insensitive to this heme protein. Sudan I oxidation catalyzed by CYP2B6, 2C19 and 2D6 was even decreased by b(5). The stimulation of the CYP1A1-mediated Sudan I oxidation was dependent on concentration of b(5). Likewise, the increase in CYP1A1-mediated formation of Sudan I-DNA adducts by b(5) was concentration dependent. Other proteins containing heme such as cytochrome c or myoglobin were without this effect. The major Sudan I-DNA adducts formed in vitro are also generated in vivo, in livers of rats treated with Sudan I. CONCLUSIONS: The data are the first report on the stimulation of CYP1A1-mediated oxidative reactions by b(5). In addition, the results demonstrating covalent binding of Sudan I to rat liver DNA in vivo indicate a genotoxic mechanism of Sudan I carcinogenicity in rats
    Type of Publication: Journal article published
    PubMed ID: 17159775
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    Keywords: SPECTRA ; CANCER ; CELLS ; CELL ; human ; DNA adducts ; EXPOSURE ; RISK ; GENE ; TISSUE ; PATIENT ; DNA ; MECHANISM ; CARCINOGENESIS ; DNA ADDUCT FORMATION ; RATS ; tumour ; ASSOCIATION ; ACID ; NUMBER ; MUTATION ; p53 ; MUTATIONS ; ADDUCTS ; INDIVIDUALS ; NEPHROPATHY ; mutagenesis ; CONSUMPTION ; aristolochic acid ; CHINESE HERBS NEPHROPATHY ; DNA-ADDUCTS ; RENAL-FAILURE ; molecular ; FEATURES ; ONCOLOGY ; MOLECULAR-MECHANISM ; RE ; PATTERN ; P53 GENE ; RAS GENE ; ADDUCT FORMATION ; development ; analysis ; DNA ADDUCT ; p53 mutation ; RISK-FACTOR ; SPECTRUM ; PREDICT ; aetiology ; COVALENT DNA ADDUCTION ; HUMAN P53 GENE ; OCHRATOXIN-A
    Abstract: Balkan endemic nephropathy (BEN) is found in certain rural areas of the Balkans and affects at least 25 000 inhabitants. Of the many hypotheses on BEN, the Aristolochia hypothesis has recently gained ground substantiated by the investigations on aristolochic acid nephropathy (AAN). On both clinical and morphological grounds, AAN is very similar to BEN. That exposure to aristolochic acid (AA) of individuals living in endemic areas through consumption of bread made with flour contaminated with seeds of Aristolochia clematitis is responsible for BEN is an old hypothesis, but one which is fully consistent with the unique epidemiologic features of BEN. Here, we propose an approach to investigate AA-induced mutagenesis in BEN that can provide molecular clues to the aetiology of its associated urothelial cancer. The molecular mechanism of AA-induced carcinogenesis demonstrates a strong association between DNA adduct formation, mutation pattern and tumour development. A clear link between urothelial tumours, p53 mutations and AA exposure should emerge as more tumour DNA from BEN patients from different endemic areas becomes available for mutation analysis. We predict that the observed p53 mutation spectrum will be dominated by AT -〉 TA transversion mutations as has already been demonstrated in the human p53 gene of immortalized cells after exposure to AAI and urothelial tumours from BEN patients in Croatia. Moreover, the detection of AA-specific DNA adducts in renal tissue of a number of BEN patients and individuals living in areas endemic for BEN in Croatia provides new evidence that chronic exposure to AA is a risk factor for BEN and its associated cancer
    Type of Publication: Journal article published
    PubMed ID: 17434925
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    Keywords: EXPRESSION ; human ; liver ; ENZYMES ; PROTEIN ; TIME ; ACTIVATION ; DNA ; 3-aminobenzanthrone ; 3-nitrobenzanthrone ; DIESEL EXHAUST ; DNA ADDUCT FORMATION ; AIR-POLLUTION ; INDUCTION ; LIVER-MICROSOMES ; RAT ; SUDAN-I ; CONTAMINANT 3-NITROBENZANTHRONE ; RATS ; RAT-LIVER ; HUMAN ACETYLTRANSFERASES ; BODY ; air pollution ; INCREASE ; WEIGHT ; LEVEL ; ENZYME ; P-32-postlabeling ; reductive activation ; P-32-POSTLABELING ANALYSIS ; BIOTRANSFORMATION ENZYMES ; NAD(P)H-QUINONE OXIDOREDUCTASE ; NITROPOLYCYCLIC AROMATIC-HYDROCARBONS
    Abstract: 3-Nitrobenzanthrone (3-NBA), a suspected human carcinogen occurring in diesel exhaust and air pollution, and its human metabolite 3-aminobenzanthrone (3-ABA) were investigated for their ability to induce biotransformation enzymes in rat liver and the influence of such induction on DNA adduct formation by the compounds. Rats were treated (i.p.) with 0.4, 4, or 40 mg/kg body weight 3-NBA or 3-ABA. When hepatic cytosolic fractions from rats treated with 40 mg/kg body weight 3-NBA or 3-ABA were incubated with 3-NBA, DNA adduct formation, measured by P-32-postlabeling analysis, was 10-fold higher in incubations with cytosols from pretreated rats than with controls. The increase in 3-NBAderived DNA adduct formation corresponded to a dose-dependent increase in protein levels and enzymatic activity of NAD(P) H: quinone oxidoreductase (NQO1). NQO1 is the major enzyme reducing 3-NBA in human and rat livers. Incubations of 3-ABA with hepatic microsomes of rats treated with 3-NBA or 3-ABA (40 mg/ kg body weight) led to as much as a 12-fold increase in 3-ABA-derived DNA adduct formation compared with controls. The observed stimulation of DNA adduct formation by both compounds was attributed to their potential to induce protein expression and enzymatic activity of cytochromes P450 1A1 and/ or -1A2 (CYP1A1/2), the major enzymes responsible for 3-ABA activation in human and rat livers. Collectively, these results demonstrate for the first time, to our knowledge, that by inducing hepatic NQO1 and CYP1A1/2, both 3-NBA and 3-ABA increase the enzymatic activation of these two compounds to reactive DNA adduct-forming species, thereby enhancing their own genotoxic potential
    Type of Publication: Journal article published
    PubMed ID: 16714372
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