DNA adduct formation by the anticancer drug ellipticine in rats determined by 32P postlabeling.

Ellipticine is a potent antineoplastic agent whose mode of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Recently, we found that ellipticine also forms covalent DNA adducts in vitro and that the formation of the major adduct is dependent on the activation of ellipticine by cytochrome P450 (CYP). Here, we investigated the capacity of ellipticine to form DNA adducts in vivo.

Human cytosolic enzymes involved in the metabolic activation of carcinogenic aristolochic acid: evidence for reductive activation by human NAD(P)H:quinone oxidoreductase.

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.

Human enzymes involved in the metabolic activation of the environmental contaminant 3-nitrobenzanthrone: evidence for reductive activation by human NADPH:cytochrome p450 reductase.

Determining the capability of humans to metabolize the suspected carcinogen 3-nitrobenzanthrone (3-NBA) and understanding which human enzymes are involved in its activation are important in the assessment of individual susceptibility to this environmental contaminant found in diesel exhaust and ambient air pollution. We compared the ability of eight human hepatic microsomal samples to catalyze DNA adduct formation by 3-NBA. Using two enrichment procedures of the (32)P-postlabeling method, nuclease P1 digestion and butanol extraction, we found that all hepatic microsomes were competent to activate 3-NBA.

Rat microsomes activating the anticancer drug ellipticine to species covalently binding to deoxyguanosine in DNA are a suitable model mimicking ellipticine bioactivation in humans.

Ellipticine is a potent antineoplastic agent, whose mode of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Recently, we found that ellipticine also forms covalent DNA adducts and that the formation of the major adduct is dependent on the activation of ellipticine by cytochrome P450 (P450). We examined rat, rabbit, and human hepatic microsomal samples for their ability to activate ellipticine.

Kinetics of phenol oxidation by Candida tropicalis: effects of oxygen supply rate and nutrients on phenol inhibition.

The kinetics of phenol degradation was estimated in a fed-batch reactor system. Effects of oxygen and nutrient excess or limitation as well as the presence of several essential ions on the phenol- and oxygen-specific uptake rates achieved simultaneously in a bioreactor were shown. Candida tropicalis was grown on phenol as the only carbon and energy source.

Sudan I is a potential carcinogen for humans: evidence for its metabolic activation and detoxication by human recombinant cytochrome P450 1A1 and liver microsomes.

1-Phenylazo-2-hydroxynaphthol (Sudan I, C.I. Solvent Yellow 14) is a liver and urinary bladder carcinogen in mammals.

DNA adduct formation from quaternary benzo[c]phenanthridine alkaloids sanguinarine and chelerythrine as revealed by the 32P-postlabeling technique.

Using the 32P-postlabeling assay, we investigated the ability of quaternary benzo[c]phenanthridine alkaloids, sanguinarine, chelerythrine and fagaronine, to form DNA adducts in vitro. Two enhanced versions of the assay (enrichment by nuclease P1 and 1-butanol extraction) were utilized in the study. Hepatic microsomes of rats pre-treated with beta-naphthoflavone or those of uninduced rats, used as metabolic activators, were incubated in the presence of calf thymus DNA and the alkaloids, with NADPH used as a cofactor.

Covalent binding of the anticancer drug ellipticine to DNA in V79 cells transfected with human cytochrome P450 enzymes.

Ellipticine is a potent antineoplastic agent whose mechanism of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Recently, we found that ellipticine also forms covalent DNA adducts and that the formation of the major adduct is dependent on the activation of ellipticine by cytochrome P450 (CYP). We examined a panel of genetically engineered V79 cell lines including the parental line V79MZ and recombinant cells expressing the human CYP enzymes CYP1A1, CYP1A2 or CYP3A4 for their ability to activate ellipticine.

Aristolochic acid as a probable human cancer hazard in herbal remedies: a review.

The old herbal drug aristolochic acid (AA), derived from Aristolochia spp., has been associated with the development of a novel nephropathy, designated aristolochic acid nephropathy (AAN), and urothelial cancer in AAN patients. There is clear evidence that the major components of the plant extract AA, aristolochic acid I (AAI) and aristolochic acid II (AAII), both nitrophenanthrene carboxylic acids, are genotoxic mutagens forming DNA adducts after metabolic activation through simple reduction of the nitro group.

New selective inhibitors of cytochromes P450 2B and their application to antimutagenesis of tamoxifen.

2-Isopropenyl-2-methyladamantane (2-PMADA) and 3-isopropenyl-3-methyldiamantane (3-PMDIA) showed potent and selective inhibition of cytochrome P450 (CYP) 2B6-mediated reactions with K(i) values of 5.27 and 2.17 microM, respectively.

Carcinogenic and nephrotoxic alkaloids aristolochic acids upon activation by NADPH : cytochrome P450 reductase form adducts found in DNA of patients with Chinese herbs nephropathy.

Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, has been found to be implicated in an unique type of renal fibrosis, designated Chinese herbs nephropathy (CHN), and associated with the development of urothelial cancer in CHN patients. Understanding, which enzymes are involved in AA activation and/or detoxication is important in the assessment of individual susceptibility of humans to this natural carcinogen. Using the nuclease P1 version of the 32P-postlabeling assay we examined the ability of microsomal NADPH: CYP reductase to activate AA to metabolites forming DNA adducts.

Carcinogenic aristolochic acids upon activation by DT-diaphorase form adducts found in DNA of patients with Chinese herbs nephropathy.

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.

Mechanism of peroxidase-mediated oxidation of carcinogenic o-anisidine and its binding to DNA.

2-Methoxyaniline (o-anisidine) is a urinary bladder carcinogen in both mice and rats. Since the urinary bladder contains substantial peroxidase activity, we investigated the metabolism of this carcinogen by prostaglandin H synthase (PHS), a prominent enzyme in the urinary bladder, and lactoperoxidase as model mammalian peroxidases. Horseradish peroxidase (HRP)-mediated oxidation of o-anisidine was also determined and compared with the reactions catalyzed by mammalian peroxidases.

Flavonoids-potent and versatile biologically active compounds interacting with cytochromes P450.

Flavonoids represent a group of phytochemicals exhibiting a wide range of biological activities arising mainly from their antioxidant properties and ability to modulate several enzymes or cell receptors. Flavonoids have been recognized to exert anti-bacterial and anti-viral activity, anti-inflammatory, anti-angionic, analgesic, anti-allergic effects, hepatoprotective, cytostatic, apoptotic, estrogenic and anti-estrogenic properties. However, not all flavonoids and their actions are necessarily beneficial.

Evidence for activation of carcinogenic o-anisidine by prostaglandin H synthase: 32P-postlabelling analysis of DNA adduct formation.

2-Methoxyaniline (o-anisidine) is a urinary bladder carcinogen in both mice and rats. Since the urinary bladder contains substantial peroxidase activity, we examined the ability of prostaglandin H synthase (PHS), a prominent enzyme in the urinary bladder, to activate this carcinogen to metabolites binding to macromolecules. Using [14C]-labeled o-anisidine, we observed substantial PHS-dependent binding of o-anisidine to protein, DNA and polydeoxyribonucleotides [poly(dX)].

The anticancer agent ellipticine on activation by cytochrome P450 forms covalent DNA adducts.

Ellipticine is a potent antitumor agent whose mechanism of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Using [3H]-labeled ellipticine, we observed substantial microsome (cytochrome P450)-dependent binding of ellipticine to DNA. In rat, rabbit, minipig, and human microsomes, in reconstituted systems with isolated cytochromes P450 and in Supersomes containing recombinantly expressed human cytochromes P450, we could show that ellipticine forms a covalent DNA adduct detected by [32P]-postlabeling.

alpha-Naphthoflavone acts as activator and reversible or irreversible inhibitor of rabbit microsomal CYP3A6.

This report describes the effect of alpha-naphthoflavone (alpha-NF), a known substrate, inhibitor and activator of several cytochromes P450 (CYP), on rabbit CYP3A6. Hepatic microsomes of rabbit pretreated with rifampicine (RIF), enriched with CYP3A6, as well as purified CYP3A6 reconstituted with isolated NADPH:CYP reductase were used as enzymatic systems in this study. The data from difference spectroscopy experiments showed that alpha-NF does yield a type I binding spectrum.

Evidence for reductive activation of carcinogenic aristolochic acids by prostaglandin H synthase -- (32)P-postlabeling analysis of DNA adduct formation.

Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, is implicated in an unique type of renal fibrosis, designated Chinese herbs nephropathy (CHN), which can develop to urothelial cancer. 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 prostaglandin H synthase (PHS) to activate AA to metabolites forming DNA adducts with the nuclease P1 and 1-butanol extraction enrichment procedure of the (32)P-postlabeling assay.

Human enzymes involved in the metabolic activation of carcinogenic aristolochic acids: evidence for reductive activation by cytochromes P450 1A1 and 1A2.

Aristolochic acid (AA), a naturally occurring nephrotoxin and rodent carcinogen, has recently been associated with the development of urothelial cancer in humans. Determining the capability of humans to metabolize AA and understanding, which human enzymes are involved in AA activation is important in the assessment of individual susceptibility. Using the nuclease P1-enhanced version of the (32)P-postlabeling assay, we compared the ability of human, minipig and rat hepatic microsomal samples to activate AA to metabolites forming DNA adducts.

Oxidation of xenobiotics by plant microsomes, a reconstituted cytochrome P450 system and peroxidase: a comparative study.

The microsomal fraction from tulip bulbs (Tulipa fosteriana, L.) contains cytochrome P450 (CYP3, EC 1.14.

Prostaglandin H synthase-medicated oxidation and binding to DNA of a detoxication metabolite of carcinogenic Sudan I, 1-(phenylazo)-2,6-dihydroxynaphthalene.

The metabolite of the carcinogenic azo dye Sudan I, 1-(phenylazo)-2,6-dihydroxynaphthalene (6-OH-Sudan I), which is considered to be the detoxification product of this dye is metabolized by prostaglandin H synthase (PHS) in the presence of arachidonic acid or H2O2 in vitro. The apparent Michaelis constant value for 6-OH-Sudan I as a substrate is 98.9 microM.

Aristolactam I a metabolite of aristolochic acid I upon activation forms an adduct found in DNA of patients with Chinese herbs nephropathy.

Aristolochic acid (AA) a naturally occuring nephrotoxin and carcinogen is implicated in a unique type of renal fibrosis, designated Chinese herbs nephropathy (CHN). We identified AA-specific DNA adducts in kidneys and in a ureter obtained from CHN patients after renal transplantation. AA is a plant extract of aristolochia species containing AA I as the major component.

Direct evidence for the formation of deoxyribonucleotide adducts from carcinogenic N-nitroso-N-methylaniline revealed by the 32P-postlabeling technique.

N-Nitroso-N-methylaniline (NMA) is an esophageal carcinogen in the rat. NMA forms a benzenediazonium ion (BDI) during microsomal cytochrome P-450 2B1 (CYP2B1) catalyzed metabolism. Using the nuclease P1-enhanced version of the 32P-postlabeling assay we investigated the formation of adducts by NMA with deoxyadenosine 3'-monophosphate (dAp) and deoxyguanosine 3'-monophosphate (dGp).

An investigation of the metabolism of N-nitrosodimethylamine and N-nitrosomethylaniline by horseradish peroxidase in vitro.

The demethylation of carcinogenic N-nitrosodimethylamine (NDMA) and N-nitrosomethylaniline (NMA) is catalyzed by horseradish peroxidase in the presence of hydrogen peroxide. NMA is a better substrate for peroxidase than NDMA. The Km values are 0.