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

The Ah receptor is a soluble protein complex that mediates carcinogenesis by a wide range of environmental pollutants, including polycyclic aromatic hydrocarbons, heterocyclic amines, and polychlorinated aromatic compounds. The best understood activity of the receptor concerns its role in the induction of cytochrome P450IA1. We undertook a somatic cell genetic analysis of P450IA1 induction using the mouse hepatoma cell line, Hepa-1. Clones of Hepa-1 were isolated that are defective in induction of P450IA1. Evidence was obtained that the clones are mutational in origin. Cell fusion experiments demonstrated that a few of the mutants are dominant, while the majority are recessive. The dominant mutants were shown to synthesize a repressor of P450IA1 transcription. The recessive mutants were assigned to 4 complementation groups (probably corresponding to 4 different genes). Complementation group A corresponds to the P450IA1 structural gene. Mutations in the B, C and D genes all affect functioning of the Ah receptor. A 'reverse selection procedure', whereby cells that express P450IA1 inducibility can be selected from a majority population of cells lacking inducibility, was developed. The reverse selection procedure was used to isolate transfectants of representative recessive mutants in which the mutational defects are complemented by exogenously applied genomic DNA. A human DNA-derived transfectant of a C- mutant was used to clone the human C gene. The C gene is not the ligand-binding subunit of the Ah receptor but is a protein that is required for translocation of Ah receptor-ligand complexes from cytoplasm to nucleus. In analogous experiments the dominant gene from one of the dominant mutants was transfected into wild-type Hepa-1 cells. Success in transfecting the dominant gene should provide the means for cloning it.
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PMID:Genetic and molecular analysis of the Ah receptor and of Cyp1a1 gene expression. 185 44

The use of Aroclor 1254 to induce S9 liver fractions is a standard method for conducting short-term genotoxicity assays. An alternative induction procedure, using beta-naphthoflavone (beta-NF), as a safe (non-carcinogenic) substitute for polychlorinated biphenyls, combined with sodium phenobarbital (PB), was found to be equally effective. The aim of this work is to realize a novel schedule of induction for the preparation of metabolizing systems containing a wider spectrum of induced cytochrome P450s. Five inducers of different 'classes' such as PB (class IIB P450s), beta-NF (IA), isosafrol (IA2), ethanol (IIE1) and pregnenolone 16 alpha-carbonitrile (IIIA) were injected daily both separately (to achieve maximal monooxygenase induction) in male and female mice. Induction was monitored using specific P450-linked activities. In the optimal schedule for complete induction, the various monooxygenases were greater (2- to 4-fold) than those achieved by the classical schedule. More than a 14-fold increase of total P450 and 3.3-fold increase of NADPH-cytochrome (P450) c-reductase activity, over those uninduced, account for the above increase. For example, there was a marked increase in the deethylation of ethoxyresorufin (37-fold) compared to the uninduced mice that was considerably higher than classical induction (8-fold over uninduced). On the contrary, phase II reactions i.e. epoxide hydrolase, glutathione S-transferase, glutathione S-epoxide transferase and UDP-glucuronosyl transferase, examined to compare the phase I/phase II ratios in the traditional and proposed procedures, were increased to a lesser extent (2-fold over uninduced). No significant sex differences were seen. Five precarcinogens specifically metabolized by each of the induced P450s elicited a higher mutagenicity response in the presence of superinduced fractions with respect to the classical one, when tested on Salmonella typhimurium (cyclophosphamide, benzo[alpha]pyrene, 2-naphthylamine and dimethylnitrosamine) or Saccharomyces cerevisiae D7 strain (diethylstilbestrol). These novel metabolizing biosystems, with an enhanced spectrum of induced P450s and oxidative/post-oxidative reaction rates, are recommended for detecting unknown xenobiotics in genotoxicity studies.
Carcinogenesis 1991 May
PMID:Wide spectrum detection of precarcinogens in short-term bioassays by simultaneous superinduction of multiple forms of cytochrome P450 isoenzymes. 190 89

Two commercial brands of smokeless tobacco were extracted with water and these extracts were tested in human cell mutation assays. Using the human cell line TK-6 which expresses no cytochrome P450, the two extracts tested were found to be detectably mutagenic in the range 1-3 mg/ml extractable solids. In AHH-1 cells which constitutively express cytochrome P450IAI, a similar result was found for both brands tested. The two extracts were treated with neutral nitrite solutions to mimic physiologic oral conditions or acidic conditions or acidic conditions with nitrite to mimic physiologic gastric conditions. The mutagenicity of both extracts for both TK-6 and AHH-1 cells was markedly decreased by treatment at neutral pH with sodium nitrite (0.25 mM) and by acidic treatment (2 h, pH 3.0). Treatment of extracts with sodium nitrite at pH 3.0 did not have any effect on the mutagenicity of the untreated extracts for TK-6 cells. The mutagenicity of both the extracts destroyed by acidic treatment however, seemed to be restored to a level equivalent to the mutagenicity of the untreated extracts for the TK-6 cells. The same series of experiments with P450-proficient AHH-1 cells showed uniform reduction of mutagenic activity. Since the two cell lines are equally sensitive to mutation by aqueous tobacco extracts it is concluded that mutagenicity is not cytochrome P450 mediated. It would further appear that the extract mutagen(s) is acid and neutral nitrite labile.
Carcinogenesis 1991 May
PMID:Smokeless tobacco extracts mutate human cells. 190 93

The metabolic activation of the food-borne rodent carcinogens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1) was compared with that of the known human carcinogen 4-aminobiphenyl (ABP), using human liver microsomes, human and rat liver cytosols, and human colon cytosol. All of these aromatic amines were readily activated by N-hydroxylation with human liver microsomes (2.3-5.3 nmol/min/mg protein), with PhIP and ABP exhibiting the highest rates of cytochrome P450IA2-dependent N-oxidation, followed by MeIQx, IQ and Glu-P-1. In contrast, while ABP and 2-aminofluorene were readily N-acetylated (1.7-2.3 nmol/min/mg protein) by the polymorphic human liver cytosolic N-acetyltransferase, none of the heterocyclic amines were detectable as substrates (less than 0.05 nmol/min/mg protein). Likewise, only low activity was observed (0.11 nmol/min/mg protein) for the N-acetylation of p-aminobenzoic acid, a selective substrate for the human monomorphic liver N-acetyltransferase. The radiolabeled N-hydroxy (N-OH) arylamine metabolites were synthesized and their reactivity with DNA was examined. Each derivative bound covalently with DNA at neutral pH (7.0), with highest levels of binding observed for N-OH-IQ and N-OH-PhIP. Incubation at acidic pH (5.0) resulted in increased levels of DNA binding, suggesting formation of reactive arylnitrenium ion intermediates. These N-OH arylamines were further activated to DNA-bound products by human hepatic O-acetyltransferase. Acetyl coenzyme A (AcCoA)-dependent, cytosol-catalyzed DNA binding was greatest for N-OH-ABP and N-OH-Glu-P-1, followed by N-OH-PhIP, N-OH-MeIQx and N-OH-IQ; and both rapid and slow acetylator phenotypes were apparent. Rat liver cytosol also catalyzed AcCoA-dependent DNA binding of the N-OH arylamines; and substrate specificities were comparable to human liver, except that N-OH-MeIQx and N-OH-PhIP gave relatively higher and lower activities respectively. Human colon cytosols likewise displayed AcCoA-dependent DNA binding activity for the N-OH substrates. Metabolic activity was generally lower than that found with the rapid acetylator liver cytosols; however, substrate specificity was variable and phenotypic differences in colon O-acetyltransferase activity could not be readily discerned. This may be due, at least in part, to the varied contribution of the monomorphic acetyltransferase, which would be expected to participate in the enzymatic acetylation of some of these N-OH arylamines.(ABSTRACT TRUNCATED AT 400 WORDS)
Carcinogenesis 1991 Oct
PMID:Metabolic activation of carcinogenic heterocyclic aromatic amines by human liver and colon. 193 65

Cremophore E1 (CR), a frequently used solubilizer and emulsifier in the pharmaceutical, cosmetic and animal-raising industries, is made up of ethylene oxide and castor oil. Since ethylene oxide has been shown to be a potent genotoxic agent, we have studied the clastogenic activity of CR and its co-clastogenic activity with benzene (BZ) in mice. Male CD1 mice were divided into untreated, vehicle control and experimental groups. Mice in the experimental groups were treated orally with 0.03, 0.3 or 3% CR in water, 440 mg/kg BZ in olive oil, BZ plus the three different doses of CR (1 h apart) or BZ plus 3% CR separated by 1, 3 and 5 h intervals. Mice were killed at 30 h after the treatment for the single-treatment groups and after the first treatment for the combined treatment groups. Bone marrow cells were harvested for determination of micronuclei (MN) frequencies in polychromatic erythrocytes (PCE). The presence of known genotoxic metabolites of benzene (phenol and trans,trans muconic acid) was quantitated in collected urine. The effect on hepatic cytochrome P450 isoenzyme expression in livers of treated mice were also analyzed. We found that CR did not induce any significant or dose-dependent increase in MN. However, CR enhanced the clastogenic activity of BZ in a dose-dependent manner (from 41.6 to 47.3, 60.5 and 67.1 MN/1000 PCE respectively; P less than 0.05). The combined treatment showed an inverse time-dependent change in MN frequencies when CR was administered at 1, 3 and 5 h after BZ (41.6 to 67.1, 43.4 and 42.0 MN/1000 PCE respectively). The enhancement effect of CR is apparently due to its ability to induce significantly the cytochrome P450I family when CR was administered 1 h after treatment with BZ. However, no positive synergistic effect was observed when the combined treatment intervals were extended to 3 and 5 h. Enhanced induction of these isoenzymes is correlated with increased metabolic activation of BZ to excrete increased amounts of trans,trans muconic acid, the putative active metabolite of BZ, in urine. Our integrated study demonstrates that an apparently innocuous agent that is consumed by the general population can enhance the genotoxic activity of a ubiquitous environmental carcinogen. The potential existence of this type of interaction in our daily lives is frequently overlooked and should be investigated.
Carcinogenesis 1991 Jan
PMID:Mechanism of clastogenic and co-clastogenic activity of cremophore with benzene in mice. 198 82

Studies were carried out to investigate the metabolism of senecionine by human liver microsomes and the role of human cytochrome P450IIIA4 in this process. Human liver microsomes metabolized senecionine to two major products, (+/-)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP) and senecionine N-oxide. The rates of product formation (DHP and senecionine N-oxide) varied widely with the microsomal samples tested. There was a 30-fold difference in DHP formation and a 25-fold difference in N-oxidation between the poorest metabolizer and the highest metabolizer of senecionine. The conversion of senecionine to DHP and senecionine N-oxide in human liver microsomes was markedly inhibited by the mechanism-based inactivators of P450IIIA4, gestodene and triacetyloleandomycin. Anti-P450IIIA4 IgG, at a concentration of 1 mg/nmol of P450, was found to inhibit completely the formation of DHP and senecionine N-oxide in human liver microsomes (HL101) having low activity toward senecionine. At 5 mg IgG/nmol P450, anti-P450IIIA4 inhibited 90 and 84% respectively of the formation of DHP and senecionine N-oxide in liver microsomes (HL110) with the highest activity toward senecionine. The formation of DHP or senecionine N-oxide was highly correlated with the amount of P450IIIA4 measured in the microsomes using polyclonal anti-P450IIIA4 IgG. The rate of DHP production also had a strong correlation with the rate of senecionine N-oxide formation (r = 0.999) and with the rate of nifedipine oxidation (r = 0.998). Our present studies provide evidence that P450IIIA4 is the major enzyme catalyzing the bioactivation (DHP formation) and detoxication (senecionine N-oxide formation) of senecionine in human liver.
Carcinogenesis 1991 Mar
PMID:Role of cytochrome P450IIIA4 in the metabolism of the pyrrolizidine alkaloid senecionine in human liver. 200 96

Several species of fish from the genus Poeciliopsis differ dramatically in their response to the carcinogen N-nitrosodiethylamine (NDEA). The differential induction of tumors among genotypes exposed to NDEA may, in part, result from differences in liver cytochrome P450pj activity (the piscine equivalent of mammalian P450j). Evidence for the existence of cytochrome P450pj activity and mRNA expression has been found in several Poeciliopsis genotypes (species and strains). Biochemical evidence suggests that a microsomal cytochrome P450 enzyme catalyzes the metabolism of NDEA to acetaldehyde and other intermediates in Poeciliopsis. This reaction was inhibited by carbon monoxide, and required molecular oxygen and reducing equivalents (NADPH). Differences were found in maximal activity as well as temperature optima among genotypes. Poeciliopsis, a livebearing fish from desert streams of northwestern Mexico, appears to have thermal optima for cytochrome P450pj activity between 25 and 30 degrees C depending on the genotype. Western blot analysis (using anti-rat P450IIE1 antibodies) detected a 55-60 kd band in microsomes isolated from rat and Poeciliopsis. Using a 49mer probe specific for rat cytochrome P450j, Northern blots revealed a 3.3 kb mRNA from livers of a Poeciliopsis genotype and rat, but none in muscle mRNA from either organism. S1 nuclease protection assays, using the same probe, revealed that a mRNA fragment protected by the probe against digestion was induced on exposure of the whole organism to ethanol (via uptake from the aquatic environment). The assays also demonstrated that ethanol treatments both induced and suppressed this mRNA, depending on concentration and exposure time.
Carcinogenesis 1991 Apr
PMID:Nitrosodiethylamine metabolism in the viviparous fish Poeciliopsis: evidence for the existence of liver P450pj activity and expression. 201 28

In the present study, we investigated Phase I (cytochrome P450; DT-diaphorase, DTD) and Phase II (epoxide hydrolase, EH; glutathione-S-transferases, GSTs) enzymes in normal colon from patients without colorectal adenocarcinoma and in peritumoral and tumoral tissues from patients with colorectal adenocarcinoma. No significant changes in levels of cytochrome P450IIIA4 (the only P450 detectable in this tissue), EH, GSTs and DTD activity were found between normal and peritumoral tissues. In tumoral tissue, compared with peritumoral tissues, we observed significant decreases in cytochrome P450IIIA4 (-50%, P less than 0.002) and EH (-60%, P less than 0.03), no change in DTD activity and significant increases in GST pi (+40%, P less than 0.03) and total GST activity (+30%, P less than 0.01). The numerous changes observed in tumoral tissues suggest that variations in drug-metabolizing enzyme expression in colorectal adenomatous polyps could represent pretumoral markers. Moreover, a better understanding of the expression of these enzymes in tumoral tissues would help us to choose the most appropriate colon tumor cell lines for the testing of new anti-cancer drugs.
Carcinogenesis 1991 May
PMID:Drug-metabolizing enzyme expression in human normal, peritumoral and tumoral colorectal tissue samples. 202 56

Administration of a single oral dose (20 mg/kg) of [U-14C]3,3'-dichlorobenzidine to rats resulted in the in vivo covalent binding of the compound to hepatic lipids. More than 70% of the lipid-3,3'-dichlorobenzidine adducts were accounted for in microsomes. Loss of the lipid-bound 3,3'-dichlorobenzidine residues from either total liver or endoplasmic reticulum occurred in at least two phases--an initial fast phase and a terminal slow phase. In vitro studies with hepatic microsomes in the presence of antibodies to specific P450 isozymes and chemical inhibitors to determine the enzymes that activate 3,3'-dichlorobenzidine to the lipid-binding derivative(s) implicated cytochrome P450d. The 3,3'-dichlorobenzidine-bound microsomal lipids were not mutagenic to Salmonella TA98 in the Ames test. The results suggest that adduct formation between 3,3'-dichlorobenzidine and membrane lipids may provide a measure of 3,3'-dichlorobenzidine activation. It is speculated that covalent interaction of the compound with membrane lipids may modify cellular processes, leading to either enhancement or attenuation of carcinogenesis by the chemical.
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PMID:Covalent interaction of 3,3'-dichlorobenzidine with hepatic lipids. Enzymic basis and stability of the adducts. 211 1

We report that, in a human cell line, human cytochrome P450IIA3 is capable of metabolizing aflatoxin B1, benzo[a]-pyrene, N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) to cytotoxic and mutagenic species. Cytochrome P450IIA3-mediated activation of NDMA and NDEA was compared with human cytochrome P450IIE1-mediated activation in the same cell system. P450IIE1 was more effective at activating NDMA than P450IIA3, while P450IIA3 was more effective at activating NDEA than P450IIE1. Whole cells and microsomal fractions obtained from control cells and from cells expressing the P450IIA3 cDNA were characterized for expression of P450IIA3. Microsomal coumarin 7-hydroxylase activity was some 40 times greater in the transfected cells than in the control cells and was catalyzed by a protein that was immunochemically related to the rat liver cytochrome P450IIA gene family. Immunoblot analysis demonstrated that this protein was readily detectable in transfected cells but barely detectable in control cells. We also report the DNA and deduced amino acid sequence of the P450IIA3 cDNA isolate used in this study. Our isolate encodes a protein 489 amino acids that is five amino acids shorter at the N terminus but otherwise identical to a previously reported human P450IIA3 cDNA sequence.
Carcinogenesis 1990 Aug
PMID:Human cytochrome P450IIA3: cDNA sequence, role of the enzyme in the metabolic activation of promutagens, comparison to nitrosamine activation by human cytochrome P450IIE1. 211 2


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