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Query: UMLS:C0596263 (carcinogenesis)
 64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The rates of formation of diols of dimethylbenz[a]anthracene (DMBA-3,4-diol, DMBA-5,6-diol and DMBA-8,9-diol) have been determined in hepatic microsomes prepared from untreated rats or from animals treated with phenobarbital (PB) or Sudan III. PB treatment enhanced the formation of the proximate carcinogen, DMBA-3,4-diol, and of the 5,6-diol while treatment with Sudan III suppressed the formation of DMBA-3,4-diol but greatly increased the rates of formation of the other two diols. Metyrapone, a reagent which is specific for members of the major PB-induced cytochrome P-450 subfamily (P-450-PB3), did not alter the rate of formation of the diols other than in microsomes prepared from PB-treated animals in which formation of the 5,6-diol was inhibited. Incubation of DMBA with microsomes resulted in the formation of covalent, DMBA-microsome adducts. Treatment of the animals with PB and Sudan III increased the rate of formation of DMBA-microsome adducts to a similar extent (approximately 5-fold). The formation of adducts could be inhibited by metyrapone in microsomes from untreated and PB-treated animals but the reagent had no effect on adduct formation in microsomes from Sudan III-treated animals. These observations may indicate that adduct formation in microsomes from Sudan-treated animals involves primary epoxide metabolites while in microsomes from PB-treated animals secondary metabolites are involved and these may be formed by a P-450-PB3 isoenzyme. Specific P-450 isoenzymes involved in the regioselective formation of DMBA-diols have been identified by the use of antibodies directed against specific isoenzymes. An antibody to P-450-MC1b inhibited the formation of DMBA-5,6-diol and 8,9-diol in microsomes from Sudan III-treated animals. Western blot analysis demonstrated that P-450-MC1b was induced in microsomes of animals treated with Sudan III but was not present in the other two microsomal preparations. In accord with the observations with metyrapone, anti-P-450-PB3 inhibited formation of DMBA-5,6-diol in microsomes from PB-treated animals but was without effect on the formation of other diols. Anti-P450-PB1 inhibited the formation of DMBA-3,4-diol in microsomes from PB-treated animals. Western blot analysis of microsomes from animals treated with several xenobiotics indicated a qualitative correlation between the content of P-450-PB1 and the rate at which DMBA-3,4-diol was formed.
Carcinogenesis 1988 Aug
PMID:Role of specific cytochrome P-450 isoenzymes in the regio-selective metabolism of 7,12-dimethylbenz[a]anthracene in microsomes from rats treated with phenobarbital or Sudan III. 313 57

Free radical processes and their involvement in carcinogenesis is an unresolved question but one subjected to intense investigation recently. Using in vitro systems, we demonstrated that certain heme compounds combined with hydroperoxides catalyzed the oxidation of N-hydroxy-2-fluorenylacetamide (N-OH-2-FAA) to nitroxyl free radical intermediate which dismutated to form 2-nitrosofluorene (2-NF) and N-acetoxy-2-fluorenylacetamide (N-AcO-2-FAA). Ascorbate and certain antioxidants inhibited this reaction. Lipid hydroperoxides were effective substrates for this reaction, especially in target tissue, rat mammary gland parenchymal cells. Cytochrome P420 in the high-spin state catalyzed the reaction effectively but low-spin cytochrome P420 or P450 were ineffective. Recently, we found that 2-NF added covalently to unsaturated carbon-carbon double bonds of membrane lipids to form an adduct termed 2-nitroso-fluorene lipid adduct (N-O-LAF), which, in it oxidized state, exists in the membrane as a nitroxyl free radical. This N-O-LAF undergoes reduction-oxidation changes in the natural membrane. Formation of N-O-LAF occurred in rat liver microsomal membranes by deacylation of N-OH-2-FAA, but the esterase inhibitor paraoxon, prevented its formation from N-OH-2-FAA. The mutagenicity of 2-NF was enhanced in Salmonella typhimurium TA98 if the bacteria were cultured to contain more unsaturated membrane lipids. However, synthesized adducts were only slightly mutagenic.
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PMID:Free radicals in arylamine carcinogenesis. 628 48

Two cytochromes P450 (PB1 and PB2) have been isolated from the livers of rats treated with phenobarbital. PB2 (mol. wt. 53 500) is novel and is the first example of a phenobarbital-inducible enzyme with a Soret peak at 447 nm. Using an enzyme-linked immunosorbent assay, some immunochemical and structural similarities were observed between these cytochromes. PB1 and PB2 were induced by phenobarbital, Aroclor 1254, trans-stilbene oxide and to a lesser extent by isosafrole. Immunohistochemical localization of these proteins in the liver of untreated rats showed PB1 to be localized in a large area and PB2 in a narrow range of cells around the central vein. This demonstrates the heterogeneity of hepatocytes even within the centrilobular area and indicates that the synthesis of these two proteins is regulated differently although both are induced by the same agent, phenobarbital. Two 3-methylcholanthrene inducible cytochromes MC1 (mol. wt. 54 500) and MC2 (mol. wt. 57 000) were present at very low levels, MC2 mostly in the periportal region but also diffusely distributed throughout the lobule including some centrilobular cells, MC1 concentrated in the centrilobular region. The localization of two major groups of glutathione transferases (GST's) was also different. 'C' type proteins (Yb Yb') and microsomal epoxide hydrolase (EH), were concentrated around the central vein, whereas the 'B' type proteins (Ya Yc) and cytochrome P450 reductase were distributed in a larger area of this region. Thus, the localization was different for some members of the same enzyme family, whilst similarities in the localization existed across the border of the families: (i) PB2, MC1, EH and GST 'C' type proteins were concentrated in a narrow area around the central vein; (ii) PB1 and GST 'B' type proteins occupied a large centrilobular area; (iii) MC2 levels were very low, predominantly periportal but also diffusely distributed throughout the lobule. Treatment of the animals with inducers increased the staining intensity and in several cases extended the areas of cells containing these proteins over the adjacent zone without fundamentally altering their distributions. However, treatment with beta-naphthoflavone led to a shift of MC1 to the periportal area. This suggests that the expression of these proteins in certain cells is not an irreversible quality of differentiation but depends on the degree of suppression and derepression of regulatory components.(ABSTRACT TRUNCATED AT 400 WORDS)
Carcinogenesis 1984 Aug
PMID:Characterization, localization and regulation of a novel phenobarbital-inducible form of cytochrome P450, compared with three further P450-isoenzymes, NADPH P450-reductase, glutathione transferases and microsomal epoxide hydrolase. 643 May 87

The inhibitory effects of ten monoclonal antibodies specific for methylcholanthrene (MC)-induced P450 were determined on both C- and N-hydroxylations of 2-acetylaminofluorene (AAF) by liver microsomes from rats pretreated with MC, phenobarbital as well as untreated animals. The inhibitory effects of these antibodies were also determined on AAF hydroxylations by purified rat liver MC-P450. The inhibition patterns of AAF hydroxylations with both microsomes and the purified P450 indicate that the formation of 7-OH-, 5-OH-, 3-OH-, 1-OH- and N-OH-AAF was catalyzed by the same unique isoenzyme or at least isoenzymes of common antigenic determinants.
Carcinogenesis 1983
PMID:Inhibition of 2-acetylaminofluorene oxidations by monoclonal antibodies specific to 3-methylcholanthrene-induced rat liver cytochrome P450. 685 Sep 96

Five strains of mice were examined for microsomal cytochrome P450 (Cyt P450) activity and ability of the microsomal preparation to activate 2-aminofluorene (2-AF) to its mutagenic form. Each strain was assayed under normal and induced conditions. Group A strains known to be easily induced to carcinogenesis by chemicals (C57BL/6J and BALB/cJ) showed higher levels of Cyt P450 and increased mutagenesis activity of the metabolized 2-AF than Group B strains which are known to be high spontaneous tumor producers (CE/J, A/HeJ, C3H/HeJ). Induction of the hepatic microsomes with Aroclor 1254 increased the difference between the two groups.
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PMID:Effects of genetically different strains of mice on the microsomal activation of 2-aminofluorene. 717 3

Recent studies indicate that cytochrome P450 (P450) 3A4 plays important roles in the activation of procarcinogens such as aflatoxin B1 and sterigmatocystin, as well as in the oxidation of a number of structurally diverse chemicals and endogenous compounds. Since P450 3A5 has been reported to be present at significant levels in liver microsomes in approximately 25% of human adults, we examined and compared the role of P450 3A4 and 3A5 in procarcinogen activation in humans. Immunoblot experiments with liver microsomes from 60 human samples suggested that 4/30 Japanese and 4/30 Caucasians contained considerable levels of P450 3A5, although P450 3A4 could be determined at relatively high levels in all of the human samples examined. Good correlation was observed between P450 3A4, but not P450 3A5, levels versus activation of aflatoxin B1 and stergmatocystin in these human samples. Comparisons of the activation of procarcinogens in reconstituted monooxygenase systems containing modified P450 3A4 and 3A5 enzymes expressed in Escherichia coli were carried out in Salmonella typhimurium TA1535/pSK1002 or NM2009 tester strain for genotoxicity assay, and it was found that P450 3A4 had similar activities to or higher rates than P450 3A5 for the 24 procarcinogens tested.
Carcinogenesis 1995 Sep
PMID:Procarcinogen activation by cytochrome P450 3A4 and 3A5 expressed in Escherichia coli and by human liver microsomes. 755 70

Treatment of cultures of spontaneously immortalized human epidermal cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) sensitized them to carcinogen toxicity. While the tryptophan pyrolysis product 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and the mycotoxin sterigmatocystin were highly toxic to the cultures at moderate concentration (1 microgram/ml), the potency of each agent was increased > or = 10-fold in the presence of TCDD. A toxicity increase was also evident in the several-fold stimulation by TCDD of protein and DNA adducts formed by Trp-P-1. In contrast, the cells were insensitive to toxicity from 3-amino-1-methyl-5H-pyrido[4,3-b]indole. DNA damage mediated by Trp-P-1 was capable of producing inheritable effects, as judged by the induction of hprt mutants in a TCDD-stimulated fashion. Northern blotting showed that TCDD strongly stimulated expression of P4501A1 and 1B1 in the cells, enzymes important for xenobiotic metabolism. These findings demonstrate the potential usefulness of SIK cultures as a model for studying keratinocyte responses to carcinogens activated by TCDD-induced cytochromes P450.
Carcinogenesis 1995 Sep
PMID:2,3,7,8-Tetrachlorodibenzo-p-dioxin sensitization of cultured human epidermal cells to carcinogenic heterocyclic amine toxicity. 755 73

Liarozole has been reported to inhibit P450 enzymes responsible for the catabolism of retinoic acid. This suggests that it may increase the effectiveness of cancer chemopreventive agents, such as retinoic acid, and pro-vitamin A carotenoids, such as beta-carotene, which may yield retinoids. To test this we have utilized the 10T1/2 cell assay system of neoplastic transformation. Simultaneous treatment with Liarozole (10(-5) M) potentiated by a factor of 1000 the ability of low concentrations of retinoic acid (10(-10) M) to inhibit carcinogen-induced neoplastic transformation, to up-regulate gap junctional communication and to increase connexin43 expression. When tested under conventional culture conditions, Liarozole itself partially suppressed neoplastic transformation and up-regulated gap junctional communication; this ability appears due to the presence of retinol in the serum component of cell culture medium. When assays for junctional communication and of connexin43 expression were performed under defined conditions, in the absence of serum, Liarozole was ineffective alone, yet still augmented the effects of retinoic acid. HPLC analysis of cell culture medium demonstrated that Liarozole (10(-5) M) completely protected retinoic acid (10(-6) M) from catabolism over a 48 h period. Potential effects of Liarozole on the activities of carotenoids were also examined. Inhibition of neoplastic transformation by the pro-vitamin A carotenoid beta-carotene, but not by the non-pro-vitamin A carotenoid canthaxanthin, was moderately potentiated by Liarozole. The augmentation of response to beta-carotene was more apparent when tested under defined conditions; here Liarozole strongly increased junctional communication and Cx43 expression. In contrast, Liarozole did not potentiate the activity of canthaxanthin under defined conditions, while increasing the activity of 4-keto retinoic acid, a likely metabolite. Liarozole also elevated connexin43 expression in early passage human fibroblasts. These data indicate that rapid catabolism of retinoic acid limits its in vitro activities, that a portion of the action of beta-carotene as a cancer preventive agent is due to its conversion to retinoic acid and that canthaxathin exerts its chemopreventive action largely independent of conversion to 4-keto retinoic acid.
Carcinogenesis 1995 Sep
PMID:Liarozole potentiates the cancer chemopreventive activity of and the up-regulation of gap junctional communication and connexin43 expression by retinoic acid and beta-carotene in 10T1/2 cells. 755 78

Hepatocarcinogenic aromatic amines such as 4-aminoazobenzene derivatives and heterocyclic aromatic amines of cooked food origin were found to be liver-selective cytochrome P450IAZ (CYP1A2) inducers. Each aromatic amine showed different species-specificity among rodent experimental animals in terms of the extent of P450 induction. Carcinogenic susceptibility of an animal to the amine was well correlated with the activity and/or inducibility of CYP1A2 in the animals in the early initiation phase of the carcinogenesis. In hyperplastic nodules of rat liver, expression and induction of CYP1A2 as suppressed, especially in the placental form of glutathione S-transferase-positive foci. Despite the decrease of P450s including CYP1A2 in the rat liver bearing hyperplastic nodules. DNA adducts formed by a carcinogenic aromatic amine increased, as compared to the controls, suggesting that the activity of DNA repair enzyme(s) for the amine-derived DNA adducts might decrease in the hyperplastic nodules of rat liver. Treatment of rats with lead nitrate revealed a pattern of P450 expression in the liver similar to that observed with rats bearing hyperplastic nodules. These findings may provide valuable information on the roles of P450s in carcinogenic susceptibility of animals to aromatic amines and in the carcinogenic process.
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PMID:Induction of cytochrome P450 isoforms by carcinogenic aromatic amines and carcinogenic susceptibility of rodent animals. 758 95

Cigarette smoking has been established as a risk factor for the development of cervical cancer. Polycyclic aromatic hydrocarbons such as benzo[a]pyrene (B[a]P), which are present in cigarette smoke, might account for this increased risk. The effects of B[a]P on cell growth, aryl hydrocarbon hydroxylase, DNA adducts and p53 levels was measured in cervical cells. Since 90% of cervical preneoplastic lesions are positive for the human papillomavirus (HPV) we compared the effects of these chemicals in normal ectocervical epithelial cells (ECE) and human papillomavirus 16 (HPV16) immortalized ectocervical epithelial cells (ECE16-1). Exposure of normal ECE and HPV immortalized ECE16-1 cells to B[a]P inhibited cell proliferation. Inhibition occurred at 20-fold lower concentrations in the normal ECE cells compared to ECE16-1 cells. The proliferation of cervical cells which express mutated p53 was unaffected by B[a]P. Neither cervical stromal cells nor endometrial stromal cells were affected by these compounds. The effects of B[a]P on normal ECE cell proliferation correlated with increased terminal differentiation as measured by increased envelope formation. In contrast, B[a]P exposure did not induce envelope formation in immortalized ECE16-1 cells or in cervical tumor cells. Pretreatment of both ECE and ECE16-1 cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin, which induces P450 expression and activity, did not alter B[a]P metabolism in either normal or immortalized cells. Furthermore, equivalent levels of DNA adducts were formed by B[a]P in ECE and ECE16-1 cells. Neither the extent of adduct formation nor the rate of their removal differed in normal and immortalized cervical cells. Therefore, the diminished growth inhibition of the ECE16-1 cells as compared to normal ECE cells by B[a]P is not due to changes in cytochrome P450 of the 1A family metabolism or DNA adduct number. Furthermore, analysis of the p53 levels in both normal and ECE16-1 cells revealed that p53 levels are higher in normal versus immortalized ectocervical cells, and p53 is induced in both cell types following B[a]P treatment. Thus reduced p53 levels in ECE16-1 cells may contribute to a lack of growth suppression following B[a]P treatment. These results demonstrate that HPV16 immortalization diminishes ectocervical epithelial cell responsiveness to toxicant damage (i.e. decreased cell proliferation and increased terminal differentiation). As a result, ECE16-1 cells that sustain genotoxic damage which leads to DNA adduct formation continue to proliferate and may be at increased risk for mutations and further progression towards a fully transformed phenotype.
Carcinogenesis 1995 Oct
PMID:Differential response of normal and HPV immortalized ectocervical epithelial cells to B[a]P. 758 44


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