Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0596263 (carcinogenesis)
 64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cytotoxic effect of 4-nitroquinoline-1-oxide (4NQO) on cultured Chinese hamster cells was drastically reduced by the presence of caffeine (0.2-1 mM). Caffeine, however, did not reduce the cytotoxicity of 4-hydroxyaminoquinoline-1-oxide (4HAQO), an active metabolite of 4NQO. The 105 000 g supernatant from the cell homogenate could catalyze the conversion of 4NQO to 4HAQO in the presence of NADPH or NADH as a hydrogen donor. This enzyme activity was strongly inhibited by caffeine (0.1-10 mM) or dicumarol (10(-8)-10(-6) M), an inhibitor of DT diaphorase (E.C.1.6.99.2). Dicumarol also reduced the cytotoxicity of 4NQO. These results clearly suggest that caffeine inhibits the conversion step of 4NQO to 4HAQO, resulting in a decrease in the cytotoxicity of 4NQO. Furthermore, the frequency of 6-thioguanine-resistant mutation by 4NQO was also strongly reduced by the presence of caffeine (1 mM) in cultured Chinese hamster cells, being consistent with the results of cytotoxicity.
Carcinogenesis 1984 Mar
PMID:Caffeine inhibition of the metabolic activation of a carcinogen, 4-nitroquinoline-1-oxide, in cultured Chinese hamster cells. 620 Feb 48

A benzo[a]pyrene (B[a]P) hydroxylase activity and epoxide hydrolase (EH) activity have been found in rat liver nucleoli obtained from untreated (C) and 3-methylcholanthrene (3-MC) pretreated rats. A comparison of the enzyme activities was made in rat nuclei and nucleoli. Light and electron microscopic observations of nucleolar preparations did not reveal significant contamination either by intact nuclei or by nuclear membranes, and glucose 6-phosphatase, a marker of microsomal activity, was not detected in our nucleolar preparations. NADPH cytochrome c-reductase could be measured in C and 3-MC nuclei and very low but detectable activity was found in the nucleoli. Nucleolar preparations revealed significant hydroxylating activity, which was inducible by 3-MC in nuclei but not in nucleoli. The presence of EH in nucleoli was demonstrated with phenanthrene 9,10-oxide and B[a]P 4,5-oxide, but the nucleolar activities were lower than those obtained using intact nuclei. The addition of 1,1,1-trichloropropene 2,3-oxide completely inhibited EH activity. Furthermore the presence of covalently-bound metabolites of B[a]P formed in isolated nucleoli was demonstrated by cytofluoromicroscopy.
Carcinogenesis 1981
PMID:Presence of benzo[a]pyrene metabolizing activities in isolated rat liver nucleoli. 627 39

The effects of treating lactating rats with 3-methylcholanthrene (3-MC) or beta-naphthoflavone (beta-NF) (three i.p. injections of 20 or 40 mg compound/kg of body weight) on hepatic microsomal enzymes of their suckling young were examined. This treatment had no apparent effect on the contents of cytochromes P-450 and b5 or on the activities of NADH- and NADPH-cytochrome c reductases in hepatic microsomes of the pups. However, these microsomes had 8- and 6-fold increased capacities for hydroxylations of benzo[a]pyrene (B[a]P) and N-2-fluorenylacetamide (2-FAA) respectively. These increases were about 5-fold greater in the hepatic microsomes of the dams, in which they were inhibited by 0.1 mM alpha-naphthoflavone (alpha-NF) in vitro 72-81 and 89-95% and by 0.1 mM beta-NF in vitro 12-41 and 60-76% respectively. In the pups, the induced activities were also inhibited, whereas the basal hydroxylations of B[a]P and 2-FAA were stimulated by alpha-NF 2.7- and 5.0-fold and by beta-NF 1.4- and 2.4-fold respectively. The inhibition of the induced hydroxylations by alpha-NF and beta-NF may be explained by their higher affinities (Ks, 0.14 and 0.28 microM, respectively) than those of B[a]P and 2-FAA (Ks, 4.4 to 8.8 and 2.4 to 3.1 microM, respectively) for cytochrome P-450. Whereas beta-NF gave a type I binding spectrum, alpha-NF gave a spectrum composed of type I and reverse-type I elements. Analysis of metabolites of 2-FAA showed differences in their type and amounts formed by hepatic microsomes of beta-NF-treated lactating rats and their pups. Thus, in the dams the formation of 1-, 3-, 5-, 7-, 9- and N-hydroxy-2-FAA was increased by 9-, 30-, 40-, 5-, 20- and 5-fold respectively. In the pups, the formation of 1-, 3-, 5-, 7- and N-hydroxy-2-FAA was increased by 2-, 30-, 18-, 4- and 27-fold respectively. All these increased hydroxylations were inhibited by 0.1 mM alpha-NF in vitro. In the hepatic microsomes of pups from the corn oil-treated dams, alpha-NF stimulated all ring-hydroxylations, but not N-hydroxylation of 2-FAA. The results support earlier findings that microsomal enzymes differ in immature and mature rat liver and suggest that N-hydroxylation of 2-FAA, the activation required for carcinogenesis, and specific ring-hydroxylations are catalyzed by different cytochrome P-450 isozymes.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Modifications of carcinogen metabolism in hepatic microsomes of suckling young by 3-methylcholanthrene or beta-naphthoflavone administered to lactating rats. 631 79

Activation of benzo[a]pyrene to bind to proteins by co-oxidation with prostaglandin synthesis was studied in rat liver and lung microsomes and cytosols. The kinetics of this activation showed a two-phase reaction; a rapid initial reaction for 2-4 min after addition of arachidonic acid and then a slow reaction or a plateau state. The reaction was linear only with low contents of the enzyme proteins, and was slower with more than 1 mg of enzyme per ml of incubation mixture. Other unsaturated fatty acids were also effective in activating benzo[a]pyrene with both microsomes and cytosols. With microsomal proteins linoleic acid was more effective than arachidonic acid, whereas with cytosolic proteins arachidonic acid was the best cofactor. Linolenic acid could also activate benzo[a]pyrene, though less efficiently, but oleic acid had no influence on the binding. Indomethacin did not inhibit the activation, but nordihydroguaiaretic acid and quercetin significantly reduced the binding. Addition of hematin significantly increased the binding. The NADPH-dependent bindings of benzo[a]pyrene to proteins with liver and lung microsomes were one-third and one-twelfth the values after incubation with arachidonic acid. Addition of glutathione or Ca2+ ion reduced the binding significantly. The present results suggest the importance of co-oxidation with lipoxygenase for activation of benzo[a]pyrene and the possible role of both the arachidonic acid cascade system and the NADPH-dependent cytochrome P-450 system in metabolic activation of chemical carcinogens.
Carcinogenesis 1984 Jul
PMID:Arachidonic acid-dependent activation of benzo[a]pyrene to bind to proteins with cytosolic and microsomal fractions from rat liver and lung. 632 41

Results of various studies have shown that male Swiss Webster mice are more susceptible to toxic effects of vinylidene chloride (VDC) than are females of the same mouse strain, females and males of the C57BL mouse strain, Chinese hamsters and rats. The main targets of toxicity are kidney and liver. The kidney of male Swiss Webster mice is the only organ where VDC unambiguously induces tumours. In the present study we have investigated the ability of NADPH-foritifed postmitochondrial supernatant fractions (S-9 mix) of kidney and liver from susceptible and nonsusceptible animals to activate VDC to a bacterial mutagen. The following sequence of activating potencies was observed: mouse liver (both strains and sexes) and Chinese hamster liver greater than rat liver greater than human liver greater than Chinese hamster kidney greater than kidney from male mice of both strains greater than kidney from rats and female mice. The last two preparations only occasionally showed weak activation of VDC. Addition of purified microsomal epoxide hydrolase to S-9 mix did not affect the mutagenicity of VDC; addition of glutathione reduced the mutagenicity up to 50%. Pretreatment of animals (male rats, male and female Swiss Webster mice) with VDC did not potentiate the ability of the subcellular preparations to activate this compound. In fact, in some cases, a weaker activation was observed. Following this treatment, microsomal 7-ethoxy-coumarin O-dealkylase was decreased in mouse kidney and in rat liver. The enzyme was not affected in mouse liver and was not measurable in rat kidney. Microsomal epoxide hydrolase activity (with styrene 7,8-oxide as substrate) was not affected in mouse liver and rat kidney. In the kidney of male mice treated with a high concentration of VDC, epoxide hydrolase activity was decreased initially, but after longer treatment, in some cases a weak increase above control was noticed. A stronger increase in activity of epoxide hydrolase was observed in the rat liver and the kidney of female mice. Cytosolic glutathione transferase activity (with 2,4-dinitrochlorobenzene as substrate) was not affected by the VDC treatment in the liver of male mice, but was decreased in the kidney of male mice, and was elevated in the kidney and liver of rats and of female mice. The different effects of VDC on this enzyme may be one of the reasons for the differences in susceptibility towards the toxic and carcinogenic actions of this compound in different species, strains and sexes.
Carcinogenesis 1983 Aug
PMID:Vinylidene chloride: changes in drug-metabolizing enzymes, mutagenicity and relation to its targets for carcinogenesis. 634 25

The colon carcinogen 1,2-dimethylhydrazine (SMDH), a non-mutagen in the standard Ames assay, has been shown in previous experiments to become weakly mutagenic in Salmonella TA 1535 in vitro, when specific test conditions were used. The present studies were performed to determine more precisely the nature of metabolic factors and experimental conditions for optimal mutagenesis of SDMH in the same strain of Salmonella. First, it was confirmed that both the presence of rat liver S9 fractions (25 microliters/ml incubation mixture) and prolonged pre-incubation periods in liquid medium of at least 120 min were necessary to elicit SDMH mutagenesis. In contrast to results obtained with dimethylnitrosamine, which served as a model compound for the activation through oxidative, cytochrome P-450- and NADPH-dependent enzymatic processes, the activation of SDMH to mutagenic factors was not dependent on the presence of NADPH: in fact, NADPH strongly reduced the SDMH-induced mutation yields. It was also observed that growth of the indicator bacteria is an important prerequisite for mutation induction by SDMH. Aminoacetonitrile and disulfiram, two inhibitors of SDMH metabolism and carcinogenicity in mammals, also strongly inhibited SDMH mutagenesis in the present in vitro assay. It can, therefore, be concluded that (i) the right test protocol is of crucial importance for the detection of SDMH as a bacterial mutagen, and (ii) that activation pathways in vitro are (partially) different from presumed in vivo metabolism and activation.
Carcinogenesis 1984 Apr
PMID:Factors influencing the mutagenic activity of the colon carcinogen 1,2-dimethylhydrazine in Salmonella typhimurium strain TA 1535 in vitro. 636 35

N-Acetylcysteine (NAC), reduced (GSH) and oxidized (GSSG) glutathione were negative in the Ames test with 7 Salmonella strains, while L-cysteine was activated by rat liver S-9 fractions to metabolites mutagenic to strains TA102, TA97 and TA100. The mutagenic response in S. typhimurium strains (TA1535, TA98, TA100, TA102) and the levels of enzyme activities, responsible for NADP+ or GSSG reduction and for the utilization of NADPH or GSH in rat liver S-9 fractions, were investigated following in vitro preincubation of NAC with four direct-acting mutagens and six procarcinogens. Treatment with this nucleophilic and reducing compound resulted in a dose-related decrease of the direct mutagenicity of epichlorohydrin, hydrogen peroxide and, sharply, of 4-nitroquinolino-N-oxide and sodium dichromate. The mutagenicity of these compounds, both in the absence and in the presence of NAC, was decreased by rat liver S-9 fractions and to some extent by lung S-9 fractions. A diphasic effect was observed in the case of procarcinogens (cyclophosphamide, 2-aminofluorene, cigarette smoke condensate, Trp-P-2, aflatoxin B1 and benzo[a]pyrene), i.e., an enhancement of S-9 requiring mutagenicity at intermediate NAC doses, which could be ascribed to metabolic factors acting in vitro, and a loss of mutagenicity at high NAC doses, which could be ascribed to trapping of electrophilic metabolites. Out of the five S-9 enzyme activities under study, i.e., glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, malic enzyme, GSH peroxidase and GSSG reductase, only the last one showed significant changes following mutagen and/or NAC treatment.
Carcinogenesis 1984 Apr
PMID:In vitro effects of N-acetylcysteine on the mutagenicity of direct-acting compounds and procarcinogens. 636 36

1,2-Dibromo-[1,2-14C]ethane was bound irreversibly to DNA when glutathione S-transferase or rat liver cytosolic components were added to incubations of calf thymus DNA and glutathione at 37 degrees C. There was no DNA binding of 1,2-dibromoethane when glutathione was absent or in incubations of DNA with microsomal proteins with or without NADPH, thus supporting the proposal that the major route of DNA binding by 1,2-dibromoethane occurs via conjugation to glutathione. In vitro binding of 1,2-dibromoethane occurred most effectively when the YaYc (or 'B') isozyme of glutathione S-transferase was included in incubations of DNA with 1,2-dibromoethane and glutathione. Other dihaloalkanes were incubated with DNA in the presence of glutathione S-transferase and [35S]glutathione. Of these, only 1,2-dibromo-3-chloropropane and tris-(2,3-dibromopropyl)-phosphate led to significant DNA binding of [35S]glutathione. 1,2-Dibromo-3-chloro-[1,3-14C]propane was bound to DNA when glutathione and glutathione S-transferase were present. However, even higher 1,2-dibromo-3-chloropropane binding to DNA occurred when cytosol or microsomes were included in incubations without glutathione. When glutathione was added to incubations containing cytosol and 1,2-dibromo-3-chloropropane, total DNA binding was decreased. Thus, the actual amount of DNA binding by dihaloethanes in vivo may be the result of a complicated balance among the opposing roles of glutathione conjugation in detoxicating and activating processes.
Carcinogenesis 1984 Jun
PMID:Glutathione-mediated binding of dibromoalkanes to DNA: specificity of rat glutathione-S-transferases and dibromoalkane structure. 637 44

N-Nitramines are biologically active compounds of environmental significance. In this study the suggested bioactivation of N- nitrodimethylamine via oxidation at the methyl-group was confirmed, as was indicated by formaldehyde liberation. N- Nitrodimethylamine and formaldehyde as well as the suggested metabolites, N- nitrohydroxymethylmethylamine and N- nitromethylamine were tested for mutagenicity in histidine auxotrophic Salmonella typhimurium strains in a variety of conditions. N- Nitrodimethylamine was mutagenic only in S. typhimurium TA 100 after pre-incubation with bacteria and a complete metabolizing mixture containing 9000 g liver supernatant and NADPH-regenerating cofactors. N- Nitrohydroxymethylmethylamine and formaldehyde were approximately equally mutagenic without the metabolizing mixture in TA 100 and TA 98, but not in TA 1535. The addition of the 9000 g supernatant of homogenized liver increased the yield of his+ revertants induced by the two compounds. N- Nitromethylamine was not mutagenic with or without the metabolic activation system. The results suggest that formaldehyde is possibly the mutagenically active intermediate formed during in vitro metabolism of N- nitrodimethylamine . Furthermore the participation of formaldehyde as the mutagenic intermediate of other non-alkylating N-nitro and N-nitroso compounds is demonstrated.
Carcinogenesis 1984 Jun
PMID:Formaldehyde as a possible mutagenic metabolite of N-nitrodimethylamine and of other agents which are suggested to yield non-alkylating species in vitro. 637 45

Trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) and the anti-isomer of trans-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) were found to be activated by microsomes isolated from 3-methylcholanthrene (MC)-treated rats to reactive intermediates that bound covalently to microsomal proteins. The extent of binding was markedly reduced by the presence of reduced glutathione (GSH) or cysteine. Fluorescence spectroscopic studies on the products derived from BP-7,8-diol and BPDE after microsomal activation in presence of GSH or cysteine revealed the formation of a common reactive intermediate with unique fluorescence properties. The involvement of cytochrome P-448 in the activation of BP-7,8-diol and BPDE to protein-binding products was inferred by the requirement for NADPH and almost complete inhibition by alpha-naphthoflavone. Furthermore, microsomes from MC-treated rats could be replaced by a reconstituted system containing purified cytochrome P-448, NADPH-cytochrome reductase and co-factors. The conjugation of the reactive intermediates from BP-7,8-diol and BPDE with GSH or cysteine did not require the presence of either microsomes or cytosol, thus indicating a non-catalytic reaction. These results emphasize the importance of cellular nucleophiles such as GSH and cysteine in the deactivation of reactive benzo[a]pyrene (BP) intermediates and also provides evidence for the further activation of the ultimate carcinogen BPDE to more reactive electrophiles and may thus have relevance concerning the regulation of BP-induced carcinogenesis.
Carcinogenesis 1984 Feb
PMID:Metabolic activation of benzo[a]pyrene-7,8-dihydrodiol and benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide to protein-binding products and the inhibitory effect of glutathione and cysteine. 642 2


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