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

The incidence of breast cancer in women has increased dramatically over the last decade. Epidemiological markers of this increased incidence include: endocrine related phenomena (early menarche, age of first parity and age of menopause); exposure of the breast to X-radiation; and a group of seemingly disparate factors--urban residence, dietary selection and alcohol consumption. Although experimental breast cancer may be induced by estrogenic hormones, X-radiation and aromatic hydrocarbons, only aromatic hydrocarbons have not been previously implicated in human mammary carcinogenesis. The seemingly unrelated human factors can best be understood by examining the role of breast tissue in aromatic hydrocarbon metabolism. Aromatic hydrocarbons are important environmental chemicals produced by the incomplete combustion of hydrocarbons for use in energy production. Benzene, benz(a)pyrene, dibenz(ah)anthracene and 1-nitropyrene, known experimental breast carcinogens, are produced in this way. Human exposure to aromatic hydrocarbon metabolites induces and promotes altered DNA by mechanisms described as increased intracellular pro-oxidant production as well as direct adduction to DNA. The breast is anatomically embedded in a major fat depot which stores and concentrates aromatic hydrocarbons and can metabolize these hydrocarbons to carcinogenic metabolites. Ductal cells concentrate these metabolites and themselves become target cells for carcinogenesis. Some lifestyle factors increase the amount of carcinogens produced or enhance their activity. A unitary model for mammary carcinogenesis in humans as well as in experimental carcinogenesis is hypothesized. If correct, the hypothesis would account for some of the increase in breast cancer incidence in industrial countries--and would suggest environmental and dietary modifications that would inhibit hydrocarbon induced mammary carcinogenesis.
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PMID:The role of aromatic hydrocarbons in the genesis of breast cancer. 151 70

Benzene is one of the best studied of the known human carcinogens. It causes leukemia in humans and a variety of solid tumors in rats and mice. Decades of research on benzene metabolism, pharmacokinetics, cytotoxicity, genotoxicity, and carcinogenicity in vivo and in vitro are starting to converge on a small set of overlapping hypotheses about the most probable biological mechanisms of benzene toxicity and carcinogenicity. Although there is still room for surprises, it seems likely that the ultimate answer to the mystery of how benzene exerts its multiple effects will consist of elaborations and extensions of one or more of the current hypotheses. This paper reviews benzene health effects and biology, showing how various aspects of metabolism and cytotoxicity fit together with genotoxic and nongenotoxic effects to help explain how benzene may cause cancer. Its goals are: (i) to introduce the qualitative biological background needed for detailed quantitative dose-response modeling of benzene cancer risks; and (ii) to survey a rapidly evolving area of research that shows promise of producing fundamental insights into the mechanisms of toxicity and carcinogenesis for several chemicals--benzene and perhaps phenols, catechols, and other hydroxylated ring hydrocarbons--in the decade ahead.
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PMID:Biological basis of chemical carcinogenesis: insights from benzene. 194 51

Benzene, an important industrial solvent and constituent of unleaded gasoline, causes leukemia and aplastic anemia in humans. Mice are more sensitive than rats to benzene toxicity, though neither species has been shown to respond consistently with benzene-induced leukemia. Benzene biotransformation in liver to phenol, hydroquinone, catechol and/or muconaldehyde is thought to be necessary for its hematotoxicity and/or genotoxicity. Our goal is to develop a mathematical simulation model capable of describing the pathways and kinetics of benzene metabolism by rat and mouse liver microsomes and to assess the role of species metabolic differences in species sensitivity. Microsomes were incubated with 4 microM [U-14C]-benzene or 4 microM [U-14C]phenol. Metabolite production was quantified by extraction into ethyl acetate, HPLC separation and liquid scintillation spectroscopy. After 45 min, mouse liver microsomes converted 20% of the benzene to phenol, 31% to hydroquinone and 2% to catechol. Rat liver microsomes converted 23% of benzene to phenol, 8% to hydroquinone and 0.5% to catechol. Production of hydroquinone and catechol continued for 90 min for mouse liver microsomes, while production by rat liver microsomes had virtually ceased by 90 min. Muconic acid production by mouse liver microsomes was < 0.2% and < 0.04% from benzene and phenol respectively after 90 min. A quantitative simulation model was constructed to describe the in vitro metabolism of benzene, incorporating the reaction sequences: benzene-->phenol-->catechol-->trihydroxybenzene and phenol-->hydroquinone-->trihydroxybenzene. In the model, all of the reaction steps are assumed to be catalyzed by the same enzyme(s), cytochrome(s) P450, and benzene, phenol, hydroquinone and catechol in solution are all assumed to compete, through reversible binding, for the same reaction site(s) on cytochrome(s) P450. The simulation model accurately described both the benzene and phenol kinetic data, supporting this proposed mechanism. In particular, this model suggests that the observed inhibition of benzene on phenol metabolism, and of phenol on benzene metabolism, occurs through competition for a common reaction site, which can also bind catechol and hydroquinone.
Carcinogenesis 1993 Dec
PMID:Benzene and phenol metabolism by mouse and rat liver microsomes. 826 15

Benzene is myelotoxic and leukemogenic in humans. The mechanisms leading to these effects, however have not been fully elucidated. One of the underlying mechanisms is believed to be the oxidative damage caused by its metabolites. A comparative study was undertaken to examine the relationships between reactive oxygen species (ROS) production, lipid peroxidation and subsequent cytotoxicity induced by five major benzene metabolites. The generation of ROS by benzene metabolites was demonstrated by the significant and dose-dependent increase of intracellular ROS formation in HL60 human promyelocytic leukemia cells in vitro. 1,4-Benzoquinone (BQ) was found to be the most potent metabolite in induction of ROS formation, followed by 1,2,4-benzenetriol (BT) and to a lesser extent, phenol (PH) and trans, trans-muconaldehyde (MD). No significant effect was observed when the cells were treated with trans, trans-muconic acid (MA). The enhancement of ROS production by BQ was effectively inhibited by the addition of catalase, deferoxamine (DFO) and dimethyl sulfoxide (DMSO), but unchanged by superoxide dismutase (SOD), suggest that hydrogen peroxide (H2O2) and hydroxyl radicals (OH) are the two major forms of ROS involved. The results also demonstrate that the ability of benzene metabolites in enhancing ROS generation is closely correlated to their capacity in causing lipid peroxidation and subsequent cytotoxicity. These findings together with earlier parallel observations on DNA damage suggest that ROS play an important role in the mechanism of carcinogenesis induced by benzene metabolites.
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PMID:Benzene metabolites enhance reactive oxygen species generation in HL60 human leukemia cells. 873 67

Benzene is a widely recognized human carcinogen. The mechanism of DNA damage induced by major benzene metabolites 1,4-benzoquinone (1,4-BQ) and hydroquinone (1,4-HQ) was investigated in relation to apoptosis and carcinogenesis. Pulsed-field gel electrophoresis showed that cellular DNA strand breakage was induced by benzene metabolites. Internucleosomal DNA fragmentation and morphological changes of apoptotic cells were observed at higher concentrations of benzene metabolites. Flow cytometry showed an increase of peroxides in cultured cells treated with benzene metabolites. 1,4-BQ induced these changes at a much lower concentration than 1,4-HQ. Damage to DNA fragments obtained from the c-Ha-ras-1 proto-oncogene was investigated by a DNA sequencing technique. 1,4-BQ + NADH and 1,4-HQ induced piperidine-labile sites frequently at thymine residues in the presence of Cu(II). Catalase and bathocuproine inhibited DNA damage, suggesting that H2O2 reacts with Cu(I) to produce active species causing DNA damage. Electron spin resonance studies showed that semiquinone radical was produced by NADH-mediated reduction of 1,4-BQ and autoxidation of 1,4-HQ, suggesting that benzene metabolites produce O2- and H2O2 via the formation of semiquinone radical. These results suggest that these benzene metabolites cause DNA damage through H2O2 generation in cells, preceding internucleosomal DNA fragmentation leading to apoptosis. The fates of the cells to apoptosis or mutation might be dependent on the intensity of DNA damage and the ability to repair DNA.
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PMID:Oxidative DNA damage and apoptosis induced by benzene metabolites. 891 53

Benzene is a well-characterized human carcinogen and clastogen still present in both the occupational and general environment. However, the levels of benzene encountered today are, in most cases, relatively low and new methods, more specific and sensitive than classical cytogenetics, are probably needed to assess if current benzene exposures pose a genotoxic risk to human health. Bearing in mind the leukaemogenic action of benzene, blood lymphocytes appear to be a suitable cell system for biomonitoring studies. Buccal epithelium is an alternative source of tissue for monitoring human exposure to inhaled occupational and environmental genotoxicants. New molecular cytogenetic techniques allowing us to specifically study clastogenic or aneugenic events in human cells may provide the additional sensitivity required. In the present study, fluorescence in situ hybridization was used to examine the content of micronuclei (MN) (using the pan-centromeric DNA probe SO-alphaAllCen) in lymphocytes and buccal cells and to detect numerical abnormalities of chromosome 9 (using a chromosome 9 centromere-specific alphoid DNA probe) in buccal cells from a population occupationally exposed to benzene in an Estonian petrochemical plant. Age-matched Estonian volunteers were used as a control group. Individual benzene exposure levels were estimated to be around 1 p.p.m. (8 h time-weighted average). No increases in the frequency of total MN, MN harbouring whole chromosomes or acentric chromosomal fragments or chromosome 9 numerical abnormalities were detected in relation to benzene exposure in the present study. The lack of positive results was consistent in both buccal cells and lymphocytes, indicating that the benzene exposure levels encountered did not induce detectable clastogenic or aneugenic effects in the exposed workers. Other variables and confounding factors, such as age, smoking or alcohol consumption, did not influence any of the multiple cytogenetic biomarkers analysed.
Carcinogenesis 1997 Apr
PMID:Molecular cytogenetic analysis of buccal cells and lymphocytes from benzene-exposed workers. 911 Dec 20

Benzene is a ubiquitous environmental pollutant that is known to cause hematotoxicity and leukemia in humans. The initial oxidative metabolite of benzene has long been suspected to be benzene oxide (3,5-cyclohexadiene-1,2-oxide). During in vitro experiments designed to characterize the oxidative metabolism of [14C]benzene, a metabolite was detected by HPLC-radioactivity analysis that did not elute with other known oxidative metabolites. The purpose of our investigation was to prove the hypothesis that this metabolite was benzene oxide. Benzene (1 mM) was incubated with liver microsomes from human donors, male B6C3F1 mice, or male Fischer-344 rats, NADH (1 mM), and NADPH (1 mM) in 0.1 M sodium phosphate buffer (pH 7.4) and then extracted with methylene chloride. Gas chromatography-mass spectrometry analysis of incubation extracts for mice, rats, and humans detected a metabolite whose elution time and mass spectrum matched that of synthetic benzene oxide. The elution time of the benzene oxide peak was approximately 4.1 min, while phenol eluted at approximately 8 min. Benzene oxide also coeluted with the HPLC peak of the previously unidentified metabolite. Based on the 14C activity of this peak, the concentration of benzene oxide was determined to be approximately 18 microM, or 7% of total benzene metabolites, after 18 min of incubation of mouse microsomes with 1 mM benzene. The metabolite was not observed in incubations using heat-inactivated microsomes. This is the first demonstration that benzene oxide is a product of hepatic benzene metabolism in vitro. The level of benzene oxide detected suggests that benzene oxide is sufficiently stable to reach significant levels in the blood of mice, rats, and humans and may be translocated to the bone marrow. Therefore benzene oxide should not be excluded as a possible metabolite involved in benzene-induced leukemogenesis.
Carcinogenesis 1997 Sep
PMID:Identification of benzene oxide as a product of benzene metabolism by mouse, rat, and human liver microsomes. 932 63

The tissue distribution and macromolecular binding of benzene was studied over a dose range spanning nine-orders of magnitude to determine the nature of the dose-response and to establish benzene's internal dosimetry at doses encompassing human environmental exposures. [14C]-Benzene was administered to B6C3F1 male mice at doses ranging between 700 pg/kg and 500 mg/kg body wt. Tissues, DNA and protein were analyzed for [14C]-benzene content between 0 and 48 h post-exposure (625 Ng/kg and 5 microg/kg dose) by accelerator mass spectrometry (AMS). [14C]-Benzene levels were highest in the liver and peaked within 0.5 h of exposure. Liver DNA adduct levels peaked at 0.5 h, in contrast to bone marrow DNA adduct levels, which peaked at 12-24 h. Dose-response assessments at 1 h showed that adducts and tissue available doses increased linearly with administered dose up to doses of 16 mg/kg body wt. Tissue available doses and liver protein adducts plateau above the 16 mg/kg dose. Furthermore, a larger percentage of the available dose in bone marrow bound to DNA relative to liver. Protein adduct levels were 9- to 43-fold greater than DNA adduct levels. These data show that benzene is bioavailable at human-relevant doses and that DNA and protein adduct formation is linear with dose over a dose range spanning eight orders of magnitude. Finally, these data show that the dose of bioactive metabolites is greater to the bone marrow than the liver and suggests that protein adducts may contribute to benzene's hematoxicity.
Carcinogenesis 1997 Dec
PMID:Tissue distribution and macromolecular binding of extremely low doses of [14C]-benzene in B6C3F1 mice. 945 Apr 90

Benzene oxide (BO) reacts with cysteinyl residues in hemoglobin (Hb) and albumin (Alb) to form protein adducts (BO-Hb and BO-Alb), which are presumed to be specific biomarkers of exposure to benzene. We analyzed BO-Hb in 43 exposed workers and 42 unexposed controls, and BO-Alb in a subsample consisting of 19 workers and 19 controls from Shanghai, China, as part of a larger cross-sectional study of benzene biomarkers. The adducts were analyzed by gas chromatography-mass spectrometry following reaction of the protein with trifluoroacetic anhydride and methanesulfonic acid. When subjects were divided into controls (n = 42) and workers exposed to < or =31 (n = 21) and >31 p.p.m. (n = 22) benzene, median BO-Hb levels were 32.0, 46.7 and 129 pmol/g globin, respectively (correlation with exposure: Spearman r = 0.67, P < 0.0001). To our knowledge, these results represent the first observation in humans that BO-Hb levels are significantly correlated with benzene exposure. Median BO-Alb levels in these 3 groups were 103 (n = 19), 351 (n = 7) and 2010 (n = 12) pmol/g Alb, respectively, also reflecting a significant correlation with exposure (Spearman r = 0.90, P < 0.0001). The blood dose of BO predicted from both Hb and Alb adducts was very similar. These results clearly affirm the use of both Hb and Alb adducts of BO as biomarkers of exposure to high levels of benzene. As part of our investigation of the background levels of BO-Hb and BO-Alb found in unexposed persons, we analyzed recombinant human Hb and Alb for BO adducts. Significant levels of both BO-Hb (19.7 pmol/g) and BO-Alb (41.9 pmol/g) were detected, suggesting that portions of the observed background adducts reflect an artifact of the assay, while other portions are indicative of either unknown exposures or endogenous production of adducts.
Carcinogenesis 1998 Sep
PMID:Hemoglobin and albumin adducts of benzene oxide among workers exposed to high levels of benzene. 977 26

Two of the most common cytogenetic changes in therapy- and chemical-related leukemia are the loss and long (q) arm deletion of chromosomes 5 and 7. The detection of these aberrations in lymphocytes of individuals exposed to potential leukemogens may serve as useful biomarkers of increased leukemia risk. We have used a novel fluorescence in situ hybridization (FISH) procedure to determine if specific aberrations in chromosomes 1, 5 and 7 occur at an elevated rate in the blood cells of workers exposed to benzene. Forty-three healthy workers exposed to a wide range of benzene concentrations (median 31 p.p.m., 8 h time-weighted average) and 44 unexposed controls from Shanghai were studied. Whole blood was cultured and metaphase spreads were harvested at 72 h. Benzene exposure was associated with increases in the rates of monosomy 5 and 7 but not monosomy 1 (P < 0.001, P < 0.0001 and P = 0.94, respectively) and with increases in trisomy and tetrasomy frequencies of all three chromosomes. Long arm deletion of chromosomes 5 and 7 was increased in a dose-dependent fashion (P = 0.014 and P < 0.0001) up to 3.5-fold in the exposed workers. These results demonstrate that leukemia-specific changes in chromosomes 5 and 7 can be detected by FISH in the peripheral blood of otherwise healthy benzene-exposed workers. We suggest that aberrations in chromosomes 5 and 7 may be useful biomarkers of early biological effect for benzene exposure.
Carcinogenesis 1998 Nov
PMID:Increased aneusomy and long arm deletion of chromosomes 5 and 7 in the lymphocytes of Chinese workers exposed to benzene. 985 9


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