Metabolic Activation Of Procarcinogens Research Articles

CYP2E1 plays a suppressive role in hepatocellular carcinoma by regulating Wnt/Dvl2/β-catenin signaling

ObjectiveKnowledge of the role of CYP2E1 in hepatocarcinogenesis is largely based on epidemiological and animal studies, with a primary focus on the role of CYP2E1 in metabolic activation of procarcinogens. Few studies have directly assessed the effects of CYP2E1 on HCC malignant phenotypes.MethodsThe expression of CYP2E1 in HCC tissues was determined by qRT-PCR, western blotting and immunohistochemistry. Overexpression of CYP2E1 in HCC cell was achieved by lentivirus transfection. The function of CYP2E1 were detected by CCK-8, wound healing, transwell assays, xenograft models and pulmonary metastasis model. TOP/FOPFlash reporter assay, western blotting, functional rescue experiments, Co-immunoprecipitation and reactive oxygen species detection were conducted to reveal the underlying mechanism of the tumor suppressive role of CYP2E1.ResultsCYP2E1 expression is down-regulated in HCC tissues, and this downregulation was associated with large tumor diameter, vascular invasion, poor differentiation, and shortened patient survival time. Ectopic expression of CYP2E1 inhibits the proliferation, invasion and migration and epithelial-to-mesenchymal transition of HCC cells in vitro, and inhibits tumor formation and lung metastasis in nude mice. Mechanistic investigations show that CYP2E1 overexpression significantly inhibited Wnt/β-catenin signaling activity and decreased Dvl2 expression in HCC cells. An increase in Dvl2 expression restored the malignant phenotype of HCC cells. Notably, CYP2E1 promoted the ubiquitin-mediated degradation of Dvl2 by strengthening the interaction between Dvl2 and the E3 ubiquitin ligase KLHL12 in CYP2E1-stable HCC cells. CYP2E1-induced ROS accumulation was a critical upstream event in the Wnt/β-Catenin pathway in CYP2E1-overexpressing HCC cells.ConclusionsThese results provide novel insight into the role of CYP2E1 in HCC and the tumor suppressor role of CYP2E1 can be attributed to its ability to manipulate Wnt/Dvl2/β-catenin pathway via inducing ROS accumulation, which provides a potential target for the prevention and treatment of HCC.Graphical

Association of CYP19A1 rs743572 Polymorphism with Breast Cancer Risk Factor in Iraqi Women- Case Control Study

Breast cancer (BC) is the most common cancer and the second cause of mortality in women all around the world. It is caused by several factors including genetic determinants, so that both genetic susceptibility factors and environmental factors are involved in the etiology. Significance of genes functioning in steroid hormone synthesis and metabolism are well established in breast cancer susceptibility. Polymorphisms of genes encoding enzymes involved in estrogen biosynthesis pathway and in the metabolic activation of pro-carcinogens to genotoxic intermediates, such as cytochrome P450C17α (CYP17) was closely examined in this women-based case control study of Iraqi women aged range (27–91). The associations between selected single nucleotide polymorphisms (SNPs) in the CYP17 gene and breast cancer for 105 women with breast cancer and 120disease- free controls were evaluated. Restriction fragment length polymorphism (RFLP) technique was used with MspA1 digested enzyme for the PCR products. There was no significant C→T (rs743572) CYP17 associated with breast cancer in the Iraqi women studied. Keywords: breast cancer, CYP17, P450, SNPs. DOI: 10.7176/JMPB/66-05 Publication date: June 30th 2020

213 DIOXIN SIGNIFICANTLY ENHANCED THE TUMOR MASS FORMATION IN A XENOGRAFTED MOUSE MODEL TRANSPLANTED WITH BG-1 OVARIAN CANCER CELLS

Previous studies suggest that environmental factors, such as high levels of meat consumption, caffeine, cigarette smoking, and endocrine disrupting chemicals (EDC), may enhance a high risk of ovarian cancer. Cytochrome P450 (CYP) 1A1 may play a major role in metabolic activation of procarcinogens to carcinogens. For example, polycyclic aromatic hydrocarbons (PAHs) and halogenated aromatic hydrocarbons (HAHs) occur by pyrolysis of fossil fuels and flow into the body by organic matter, such as tobacco leaves and contaminated water by pesticides. 2,3,7,8-tetrachlorodibenzo-ρ-dioxin (TCDD) is a commonplace pollutant and promoter of carcinogenesis as the most potent substance. In this study, we examined the effects of 17β-oestradiol (E2), TCDD, and TCDD in the presence of E2 on the expressions of CYP1A1, CYP1B1, and aryl hydrocarbon receptor (AhR) by RT–PCR analysis and Western blot analysis. In addition, the cell viability by TCDD and E2 were examined in BG-1 human ovarian cancer cells by MTT assay. To evaluate the cell viability, BG-1 cells were cultured with a negative control (0.1% DMSO), E2 (1 × 10–9 M) or TCDD (10–6–10–8 M). E2 markedly increased BG-1 cell viability ~5 times, and TCDD also induced BG-1 cell viability highest at the concentration of 1 × 10–8 M compared to a control (0.1% DMSO) (P < 0.05). When respective treatment was co-treated with ICI 182 780, an ER antagonist, BG-1 cell viability was reversed to the level of a negative control. Although the mRNA expression of CYP1B1 was not altered by E2, TCDD, or TCDD plus E2, the transcriptional level of CYP1A1 appeared to be increased by E2 and TCDD in a time-dependent manner. When the cells were treated with TCDD plus E2, the mRNA level of CYP1A1 was more greatly increased than by only TCDD or E2 treatment. In xenograft mouse models transplanted with BG-1 cells, E2 treatment significantly increased the tumour mass formation ~6 times, and TCDD also induced tumour formation ~4 times compared to a vehicle (0.1% DMSO in PBS) during 8 weeks in this xenograted mouse model. In addition, TCDD plus E2 treatment also greatly induced ovarian tumour formation compared to only E2 treatment in this mouse model. Taken together, these results indicate that TCDD may induce ovarian cancer cell growth via CYP1A1 gene expression and have disruptive effect in oestrogen receptor (ER) expressing cells or tissues.

Modulation of CYP1A1 and CYP1A2 hepatic enzymes after oral administration of Chios mastic gum to male Wistar rats.

Chios mastic gum (CMG), a resin derived from Pistacia lentiscus var. chia, is known since ancient times for its pharmacological activities. CYP1A1 and CYP1A2 enzymes are among the most involved in the biotransformation of chemicals and the metabolic activation of pro-carcinogens. Previous studies referring to the modulation of these enzymes by CMG have revealed findings of unclear biological and toxicological significance. For this purpose, the modulation of CYP1A1 and CYP1A2 enzymes in the liver of male Wistar rats following oral administration of CMG extract (CMGE), at the levels of mRNA and CYP1A1 enzyme activity, was compared to respective enzyme modulation following oral administration of a well-known bioactive natural product, caffeine, as control compound known to involve hepatic enzymes in its metabolism. mRNA levels of Cyp1a1 and Cyp1a2 were measured by reverse transcription real-time polymerase chain reaction and their relative quantification was calculated. CYP1A1 enzyme induction was measured through the activity of ethoxyresorufin-O-deethylase (EROD). The results indicated that administration of CMGE at the recommended pharmaceutical dose does not induce significant transcriptional modulation of Cyp1a1/2 and subsequent enzyme activity induction of CYP1A1 while effects of the same order of magnitude were observed in the same test system following the administration of caffeine at the mean daily consumed levels. The outcome of this study further confirms the lack of any toxicological or biological significance of the specific findings on liver following the administration of CMGE.

Expression of CYP1A1 and GSTP1 in Human Brain Tumor Tissues in Pakistan

Most of the exogenous and endogenous chemical compounds are metabolized by enzymes of xenobiotic processing pathways, including the phase I cytochrome p450 species. Carcinogens and their metabolites are generally detoxified by phase II enzymes like glutathione-S-transferases (GST). The balance of enzymes determines whether metabolic activation of pro-carcinogens or inactivation of carcinogens occurs. Under certain conditions, deregulated expression of xenobiotic enzymes may also convert endogenous substrates to metabolites that can facilitate DNA adduct formation and ultimately lead to cancer development. In this study, we aimed to test the association between deregulation of metabolizing genes and brain tumorigenesis. The expression profile of metabolizing genes CYP1A1 and GSTP1 was therefore studied in a cohort of 36 brain tumor patients and controls using Western blotting. In a second part of the study we analyzed protein expression of GSTs in the same study cohort by ELISA. CYP1A1 expression was found to be significantly high (p<0.001) in brain tumor as compared to the normal tissues, with ~4 fold (OR=4, 95%CI=0.43-37) increase in some cases. In contrast, the expression of GSTP1 was found to be significantly low in brain tumor tissues as compared to the controls (p<0.02). This down regulation was significantly higher (OR=0.05, 95%CI=0.006-0.51; p<0.007) in certain grades of lesions. Furthermore, GSTs levels were significantly down-regulated (p<0.014) in brain tumor patients compared to controls. Statistically significant decrease in GST levels was observed in the more advanced lesions (III-IV, p<0.005) as compared to the early tissue grades (I-II). Thus, altered expression of these xenobiotic metabolizing genes may be involved in brain tumor development in Pakistani population. Investigation of expression of these genes may provide information not only for the prediction of individual cancer risk but also for the prevention of cancer.

Modulation of chemical carcinogen-induced unscheduled DNA synthesis by dehydroepiandrosterone (DHEA) in the primary rat hepatocytes.

Modulation of unscheduled DNA synthesis by dehydroepiandrosterone (DHEA) after exposure to various chemical carcinogens was investigated in the primary rat hepatocytes. Unscheduled DNA synthesis was induced by treatment of such direct acting carcinogens as methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS) or procarcinogens including benzo(a)pyrene (BaP) and 7,12-dimethylbenz(a)anthracene (DMBA). Unscheduled DNA synthesis was determined by measuring [methyl-3H]thymidine radioactivity incorporated into nuclear DNA of hepatocytes treated with carcinogens in the presence or absence of DHEA. Hydroxyurea (5x10(-3) M) was added to growth medium to selectively suppress normal replication. DHEA at concentrations ranging from 1x10(-6) M to 5x10(-4) M did not significantly inhibit unscheduled DNA synthesis induced by either MMS (1x10(-4) M) or EMS (1x10(-2) M). In contrast, DHEA significantly inhibited unscheduled DNA synthesis induced by BaP (6.5x10(-5) M) and DMBA (2x10(-5) M). DHEA-induced hepatotoxicity in rats was examined using lactate dehydrogenase (LDH) release as an indicator of cytotoxicity. DHEA exhibit no significant increase in LDH release compared with the solvent control at 18 h. These data suggest that nontoxic concentration of DHEA does not affect the DNA excision repair process, but it probably influence the enzymatic system responsible for the metabolic activation of procarcinogens and thereby decreases the amount of the effective DNA adducts formed by the ultimate reactive carcinogenic species.

Mechanisms involved in the chemoprotective effects of rosemary extract studied in human liver and bronchial cells.

Natural polyphenols found in rosemary have not only potent antioxidant activities but also anticarcinogenic properties. We have studied some of the molecular mechanisms involved in their chemopreventive action using in vitro human liver and bronchial cell models. Rosemary extract, or its active components, carnosol or carnosic acid are potent inhibitors of DNA adduct formation induced by benzo(a)pyrene or aflatoxin B1. At least two mechanisms are involved in the anticarcinogenic action of rosemary extract: (i) inhibition of the metabolic activation of procarcinogens catalysed by the phase I cytochrome P450 enzymes; (ii) induction of the detoxification pathway catalysed by the phase II enzymes such as glutathione S-transferase.

Somatic recombination, gene amplification and cancer

The principle objective of this research programme, to analyse chemical induction of somatic recombination and related endpoints, i.e., mobilization of transposing elements and gene amplification, has been approached by means of several assay systems. These have included Drosophila, Saccharomyces and mammalian cell cultures. 6.1. Screening assays for mitotic recombination. A large number of chemicals have been investigated in the three Drosophila assay systems employed--the multiple wing hair/flare wing spot system developed by Graf et al., 1984, the white-ivory system developed by Green et al., 1986 and the white/white+ eye spot assay developed by Vogel (Vogel and Nivard, 1993). Particularly the screening of 181 chemicals, covering a wide array of chemical classes, by the last mentioned assay has shown that measurement of somatic recombination in Drosophila constitutes a sensitive and efficient short-term test which shows a remarkably good correlation with the agent score of 83 short-term tests analysed by ICPEMC (Mendelsohn et al., 1992; Table 2) as well as the assay performance in international collaborative programmes measuring carcinogen/non-carcinogens (de Serres and Ashby, 1981; Ashby et al., 1985, 1988). Also the wing spot assay has gained wide international recognition as a similarly sensitive test. These two assay systems in Drosophila measure both intrachromosomal events and interchromosomal recombination. The white-ivory system on the other hand is based on the loss of a tandem duplication in the white locus, the mechanism of which is less known, but probably involves intrachromosomal recombination. The difference in the mechanism between this assay and the former two was indicated by the lack of response to methotrexate in the white-ivory assay, while this compound was strongly recombinogenic in both the wing spot and white/white+ assays. The use of different strains of Drosophila with the white/white+ assay demonstrated the importance of the background genotype for the outcome of the test. Up to a 60-fold variation was found between the different genotypes in the response to procarcinogens, evidently dependent on differences in the metabolic activation of procarcinogens. In 1989 Schiestl presented results on intrachromosomal recombination in the strain RS112 of Saccharomyces, which indicated a capability to detect a range of chemical carcinogens, which gave negative results in Ames Salmonella assay. Such a test system, which could identify a larger range of potential carcinogens than conventional short-term tests evidently would be of great value and it therefore seemed of importance to follow up the observations by Schiestl. However, studies within this programme on the same strain of Saccharomyces, as well as the strains D7 (measuring intragenic recombination, intergenic recombination, and point mutation) and JD1 (measuring intragenic recombination at two loci) could not support the observations and interpretation by Schiestl (1989). The Drosophila white-ivory system, which presumably responds primarily by intrachromosomal recombination, did not give positive results with these Salmonella-negative agents either. One system to measure mitotic recombination in mammalian cell cultures was developed in the present programme. It was based on heterozygous mutations in both alleles of the adenosine deaminase gene (ADA). The system selects for proficient recombinants generated by the deficient cells. So far only pilot experiments, indicating that this experimental system operates as planned, have been performed. 6.2 Mechanisms of mitotic recombination The induction of mosaic spots in the wing spot and the white/white+ assays is predominantly dependent on interchromosomal recombination. This is evident from the fact that heterozygous inversions reduce the frequency of spots. A relationship between the length of inversions and the reduction of spots was demonstrated in the white/white+ assay--the long inversion ln(l)sc4L

Metabolic Activation of Procarcinogens by Human Cytochrome P450 Enzymes in Microsomes of Adult and Fetal Livers and of Adult Lungs

Levels and catalytic activities of cytochrome P450 (P450) enzymes involved in the oxidation of drugs and carcinogens were determined in human adult lungs and fetal livers and compared with those in microsomes from adult livers. P450s immunoreactive with anti-human P450 1A1 and anti-human P450 3A antibodies were detected in fetal liver microsomes by immunoblotting analysis, and P450s related to P450 1A1, 2A6, 2C9, 2E 1, and 3A4 were determined in adult lung microsomes; all of these P450 enzymes were detected in much higher amounts in adult liver microsomes except that P450 1A2 was only the 1A subfamily of P450 found in adults. Drug oxidation activities with several substrates were determined in these microsomes, and we found that none of the activities were higher in microsomes of adult lungs and fetal livers than in adult livers. Activation of procarcinogens by P450 enzymes was also examined and it was found that activities with (+)- and (-)-enantiomers of 7, 8-dihydroxy-7, 8-dihydrobenzo[a]pyrene were higher in fetal liver microsomes than adult lung or liver microsomes. Anti-human P450 1A1 and 1A2 and a-naphthoflavone, known to inhibit P450 IA-related activities, did not affect these procarcinogen activation in fetal liver microsomes. Fetal liver microsomes catalyzed activation of aflatoxin B1 and sterigmatocystin, although activation of carcinogenic arylamines was much lower in microsomes of fetal livers and adult lungs than of adult livers. These results suggest that in human fetal livers at least two P450 enzymes, namely P450 IA-related enzyme and P450 3A7, are actually expressed and these enzymes are involved in the activation of the (+)- and (-)-enantiomers of 7, 8-dihydroxy-7, 8-dihydrobenzo[a]pyrene and the carcinogenic mycotoxins, respectively. In adult human lungs, several P450 enzymes are expressed, though the precise roles of these enzymes in the oxidation of xenobiotics were not determined due to the low level of expression of these P450s.

Formation of genotoxicity by chlorine treatment of amino acids

The metabolic activation of procarcinogens and promutagens by human liver microsomal cytochrome P-450 has been investigated by means of a newly developed method measuring the induction of umu gene in Salmonella typhimurium TA1535/pSK1002 [T. Shimada and S. Nakamura, Biochem. Pharmac.36, 1979 (1987)]. The chemicals examined were aflatoxin B1 (AFB1), eight carcinogenic heterocyclic aromatic amines isolated from protein and amino acid pyrolysates, and 2-aminoanthracene. Liver microsomes from six patients catalyzed the metabolic activation of these chemicals; 2-amino-3,5-dimethylimidazo[4,5-|] quinoline (MeIQ) and AFB1 were most actively bioactivated, followed by 2-amino-3-methylimidazo [4,5-|]quinoline (IQ), 2-aminoanthracene (2-AA) and 2-amino-3,8-dimethyl-imidazo [4,5-|]quinoxaline. At least two forms of human cytochrome P-450 may be involved in the activation of these procarcinogens. This suggestion was supported by the following lines of evidence: (a) addition of non-ionic detergent Emulgen 913 to the incubation mixture caused a more profound inhibition of microsome-catalyzed activation of AFB1 than of MeIQ, IQ and 2AA, (b) 7,8-benzoflavone stimulated the activation of AFB1 by about 2.5-fold, whereas it inhibited significantly the reactions with MeIQ, IQ and 2AA, and (c) polyclonal antibodies against a 3-methylcholanthrene-inducible form of rat cytochrome P-450 (P-450d) caused a marked inhibition of the metabolic activation of MeIQ, IQ and 2-AA by human liver microsomes though they did not show any effects on the microsomal activation of AFB1. Data are also presented showing that none of the reactions catalyzed by human liver microsomes were inhibited by antibodies to a phenobarbital-inducible form of rat cytochrome P-450 (P-450b). These results suggest that the human cytochrome P-450 isozyme that is immunochemically similar and, thus, homologous to rat P-450d plays a major role in the metabolic activation of several procarcinogens examined, and that the activation of AFB1 is catalyzed by another and, possibly, not phenobarbital-inducible form(s) of human cytochrome P-450.

P450 and Human Cancer

Most of the chemical carcinogens in our environment are activated mainly by a restricted number of cytochrome P450 species, P450 1A1,1A2, 2E1, and 3A. This metabolic activation of procarcinogens is a crucial part of the initial host response to the environmental exposure, since most chemical carcinogens do not show any carcinogenicity by themselves. Inter‐individual variability in the metabolic activity may thus be a key host factor to explain the differences in susceptibility to chemical carcinogenesis among individuals. Recent studies on P450s in cancer etiology have provided some valuable insights into this problem.

Further validation of the E. coli multitest: in vitro and in vivo metabolic activation of procarcinogens

Further validation of the E. coli multitest: in vitro and in vivo metabolic activation of procarcinogens

Metabolic activation of environmental carcinogens and mutagens by human liver microsomes: Role of cytochrome P-450 homologous to a 3-methylcholanthrene-inducible isozyme in rat liver

The metabolic activation of procarcinogens and promutagens by human liver microsomal cytochrome P-450 has been investigated by means of a newly developed method measuring the induction of umu gene in Salmonella typhimurium TA1535/pSK1002 [T. Shimada and S. Nakamura, Biochem. Pharmac. 36, 1979 (1987)]. The chemicals examined were aflatoxin B 1 (AFB 1), eight carcinogenic heterocyclic aromatic amines isolated from protein and amino acid pyrolysates, and 2-aminoanthracene. Liver microsomes from six patients catalyzed the metabolic activation of these chemicals; 2-amino-3,5-dimethylimidazo[4,5-|] quinoline (MeIQ) and AFB 1 were most actively bioactivated, followed by 2-amino-3-methylimidazo [4,5-|]quinoline (IQ), 2-aminoanthracene (2-AA) and 2-amino-3,8-dimethyl-imidazo [4,5-|]quinoxaline. At least two forms of human cytochrome P-450 may be involved in the activation of these procarcinogens. This suggestion was supported by the following lines of evidence: (a) addition of non-ionic detergent Emulgen 913 to the incubation mixture caused a more profound inhibition of microsome-catalyzed activation of AFB 1 than of MeIQ, IQ and 2AA, (b) 7,8-benzoflavone stimulated the activation of AFB 1 by about 2.5-fold, whereas it inhibited significantly the reactions with MeIQ, IQ and 2AA, and (c) polyclonal antibodies against a 3-methylcholanthrene-inducible form of rat cytochrome P-450 (P-450d) caused a marked inhibition of the metabolic activation of MeIQ, IQ and 2-AA by human liver microsomes though they did not show any effects on the microsomal activation of AFB 1. Data are also presented showing that none of the reactions catalyzed by human liver microsomes were inhibited by antibodies to a phenobarbital-inducible form of rat cytochrome P-450 (P-450b). These results suggest that the human cytochrome P-450 isozyme that is immunochemically similar and, thus, homologous to rat P-450d plays a major role in the metabolic activation of several procarcinogens examined, and that the activation of AFB 1 is catalyzed by another and, possibly, not phenobarbital-inducible form(s) of human cytochrome P-450.

Metabolic activation of procarcinogens to genotoxic products in cultured rat liver cells.

A recently established rat liver cell line, RL-12, exhibits an unusually high sensitivity to the genotoxic effects of a number of selected procarcinogens. Significant reductions in cell survival (D37%) and induction of sister chromatid exchanges were obtained with 1 X 10(-9) M benzo[a]pyrene and 2 X 10(-8) M 7,12-dimethylbenz[a]anthracene. This rat liver epithelial cell line may serve as a useful model system to study the metabolic activation of procarcinogens to their ultimate genotoxic form.

The intestinal microflora and its colon cancer connection

Epidemiologic studies suggest that the incidence of colon cancer is influenced by environmental factors, especially diet. The high beef-high fat-low fiber diet of Western societies is associated with a high risk of colon cancer. The intestinal microflora may play a role in colon cancer by metabolic activation of procarcinogens in the lumen of the large bowel. The link between diet and colon cancer can be explained, in part, by the alterations in fecal bacterial enzyme activity induced by a Western-style diet. For example, fecal bacterial beta-glucuronidase, nitroreductase, azoreductase and steroid 7-alpha-dehydroxylase activities are increased in animals or humans consuming a high beef diet. These enzyme activities can be reduced by eating a grain diet, by the addition of Lactobacillus acidophilus to the diet, or by administration of low dose antibiotics. In experimental animals these three measures to reduce the activity of the microflora also produce few colon tumors in animals given the chemical carcinogen dimethylhydrazine. Further studies are needed to establish whether alterations in the metabolism of the colonic microflora can reduce the risk of large bowel cancer in humans.

Retinol (vitamin A) as a modifier of 2-aminofluorene and 2-acetyl-aminofluorene mutagenesis in the Salmonella/microsome assay.

Vitamin A (retinol)has been demonstrated to modify the mutagenic activity of the aromatic amines, 2-aminofluorene (2AF) and 2-acetylaminofluorene (2AAF) when added to the Ames Salmonella/mammalian microsome assay. Low amounts of retinol(2-20 micrograms/plate) increased the mutagenicity of both 2AF and 2AAF. At higher doses (50-150 micrograms/plates) the mutagenicity of 2AAF remained unchanged while the mutagenicity of 2AF gradually decreased. The present data do not support the hypothesis that retinol generally acts as an inhibitor of in vitro metabolic activation of procarcinogens.

Enhanced pulmonary and intestinal activation of procarcinogens and mutagens after chronic ethanol consumption in the rat.

Recent epidemiological surveys have indicated that alcoholics exhibit increased incidences of a variety of cancers. We have investigated, as a possible contributing factor to carcinogenesis in this population, the effect of chronic ethanol consumption on metabolic activation of procarcinogens by microsomes isolated from lungs and small intestine. These tissues are major sites through which procarcinogens enter the body and are also potential sites of procarcinogen metabolism. Rat litter-mates were pair-fed nutritionally adequate liquid diets which contained either ethanol as 36% of total energy or an equivalent energy content of carbohydrates in place of ethanol. Chronic ethanol consumption produced significant increases in pulmonary microsomal cytochrome P-450 and microsomal ethanol oxidation. The ethanol diet also enhanced the capacity of pulmonary microsomes to activate compounds present in tobacco pyrolyzates to mutagens detectable in the Ames Salmonella auxotroph reversion assay. The ethanol diet did not alter the capacity of pulmonary microsomes to hydroxylate benzo(a)pyrene (BaP) or to activate BaP to a mutagen. In contrast, microsomes from the upper small intestine of ethanol-fed rats did exhibit both higher levels of BaP hydroxylase activity and enhanced activation of BaP to a mutagen. The ethanol feeding also enhanced the capacity of the intestinal microsomes to activate to mutagens both tryptophan pyrolyzate and 2-aminofluorene but did not influence the metabolic activation of these promutagens by pulmonary microsomes. Chronic ethanol consumption thus influences carcinogen metabolism in the intestine and lung in a manner which varies with respect to both carcinogen and tissue.

Carcinogen-induced dna repair in primary rat liver cell cultures; a possible screen for chemical carcinogens

Primary rat liver cell cultures were exposed to a direct acting carcinogen, methyl methanesulfonate, and procarcinogens requiring metabolic activation, aflatoxin B1 and B2. DNA damage by these agents was evidenced by the induction of DNA repair, measured as unscheduled DNA synthesis. The sensitivity of these cultures to the potent porcarcinogen aflatoxin B1 indicates that this system may be adapted for screening suspected chemical procarcinogens, and for investigating the relationship between metabolic activation of procarcinogens, DNA damage, DNA repair, and carcinogenicity.