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

The N-heterocyclic aromatic pollutant, 7H-dibenzo[c,g]carbazole (DBC), is a potent carcinogen having both local and systemic effects. The overall objective of this research was to investigate the nature of the covalent binding of DBC with nucleic acids in vitro. DBC was shown to bind to polynucleotides, RNA and DNA in an in vitro rat or hamster microsomal enzyme assay, exhibiting a preferential binding to polyguanylic acid (poly[G]). Benzo[a]pyrene (BaP) binding to these same nucleic acids was determined simultaneously and was approximately 10-fold higher than DBC binding under identical experimental conditions. DBC-nucleic acid binding was shown to be dependent upon the presence of a microsomal activating system, the results being similar for rat or hamster liver microsomes. This microsome-dependent binding was unaffected by the addition of epoxide hydrase activity modifiers but was almost completely inhibited by alpha-naphthoflavone. The nature of DBC-nucleic acid binding was investigated using fluorescence spectroscopy. Benzo[c]carbazole and 5,5,6,6-tetrahydrodibenzo[c,g]carbazole were synthesized as representatives of the effect of disruption of the DBC pi-electron system on fluorescence excitation and emission. DBC-poly[G] adducts were isolated from binding assay mixtures and separated by HPLC. Results indicated that there are at least three different DBC-poly[G] adducts formed in vitro. The emission spectra of isolated adducts were similar in shape to that of DBC; however, the adduct spectra were shifted 5-10 nm toward longer wavelengths. This suggests that the bound DBC species have intact pi-electron systems. Results are consistent with binding through the nitrogen position as well as binding through the 1,2,3,4-ring of the molecule.
Carcinogenesis 1989 Dec
PMID:Binding of 7H-dibenzo[c,g]carbazole to polynucleotides and DNA in vitro. 259 Oct 8

Authentic stable standards of 7H-dibenzo[c,g]carbazole (DBC), a potent environmental carcinogen, were synthesized in order to study the compound's metabolism and mutagenesis in whole cell systems. Complete characterization of 2-OH-DBC, 3-OH-DBC, 4-OH-DBC, 13c-OH-DBC and N-methyl-DBC was accomplished by UV, IR, fluorescence and high resolution NMR spectra, and by high resolution mass spectrometric procedures. Metabolites of DBC were isolated and separated by HPLC from extracts of rat liver microsomal incubations and the medium of primary cultures of rat liver cells. Identification of metabolites was accomplished by comparisons between the authentic standards and isolated metabolites by UV and fluorescence spectroscopy, mass spectral analyses, and by co-chromatographic techniques. 2-OH-DBC and 3-OH-DBC were found in all rat liver preparations as well as three other unidentified phenols. 4-OH-DBC, 13c-OH-DBC or N-methyl-DBC were not isolated under any conditions. The rates of appearance of DBC metabolites in cultures of rat liver cells were compared to those for benzo[a]pyrene (BaP) at 10, 25, 50 and 100 microM substrate. At 25 microM substrate or greater, DBC metabolites appeared in the culture medium at significantly faster rates than those of BaP. At 100 microM substrate, DBC metabolites appeared at a rate approximately 4-times the rate observed for BaP. When the mutagenic potential of DBC was compared to that of BaP under identical conditions in a co-cultivation system of rat liver cells and an epithelial cell line, DBC was found to produce significantly higher rates of mutagenesis than BaP at concentrations of 0.4, 4.0 and 40.0 microM in the culture medium. The mutagenic potential of DBC was compared to that of several derivatives of the parent compound. 3-OH-DBC, 13c-OH-DBC and N-methyl-DBC were found to be mutagenic in the co-cultivation system at 40 microM, with mutation frequencies of 4.4 +/- 0.8, 8.0 +/- 3.1 and 12.9 +/- 5.4 mutants per 10(5) survivors, respectively. The parent compound induced 8.0 +/- 2.8 mutants per 10(5) survivors at the same concentration. 2-OH-DBC and 4-OH-DBC were not mutagenic under the same conditions. The studies have shown that metabolism of 7H-DBC leads predominantly to phenols in rat liver cells. The results of the mutagenesis experiments indicate that, of the derivatives studied, those associated by induction to the nitrogen are mutagenic. The latter studies suggest that the nitrogen is involved in the activation of the parent compound through inductive mechanisms.
Carcinogenesis 1989 Mar
PMID:The chemistry and biology of 7H-dibenzo[c,g]carbazole: synthesis and characterization of selected derivatives, metabolism in rat liver preparations and mutagenesis mediated by cultured rat hepatocytes. 292 89

N-methyl-dibenzo[c,g]carbazole (MeDBC) lacks the potent hepatocarcinogenic activity in mice characteristic for 7H-dibenzo[c,g]carbazole (DBC), while both compounds are local carcinogens, leading to papilloma and carcinoma formation in skin after topical application. Because DNA binding is considered an essential step in the initiation of chemical carcinogenesis, the DNA adduction by MeDBC was compared with that by DBC in mouse liver and skin via a 32P-postlabeling technique. Both compounds elicited chromatographically similar adducts in liver; however, the extent of total DNA binding of DBC was 343- and 265-fold greater than that of MeDBC 24 h after topical and i.p. administration, respectively, of a 37 mumol/kg dose. In skin, the adduct pattern elicited by either compound after topical application was different from that seen in liver, and three of four adducts derived from MeDBC were chromatographically distinct from those produced by DBC. Quantitative analysis revealed that total adduction in skin by DBC was 2.3-fold higher than by MeDBC. When the adduct levels were compared between liver and skin, topically applied MeDBC bound preferentially to skin versus liver DNA by a factor of 10, while the opposite was true for DBC. These data are in agreement with the carcinogenicity reported for DBC and MeDBC and support the hypothesis that the extent of covalent DNA modification by these compounds is associated with their biological activity. We conclude that an unsubstituted nitrogen is essential for the genotoxic activity of DBC in liver but not skin. The results also demonstrate the potential of the 32P-postlabeling assay in predicting the organotropism of closely related carcinogens.
Carcinogenesis 1987 Oct
PMID:N-methylation reduces the DNA-binding activity of 7H-dibenzo[c,g]carbazole approximately 300-fold in mouse liver but only approximately 2-fold in skin: possible correlation with carcinogenic activity. 365 79

The DNA adduction by the environmental carcinogen 7H-dibenzo[c,g]carbazole (DBC) and chemically synthesized 2-OH, 3-OH, and 4-OH metabolites of DBC was investigated in liver and skin of female CD-1 mice. After topical application to the skin of 37 mumol/kg of DBC or the phenolic metabolites, DNA adducts were measured by a 32P-post-labeling assay employing carrier-free [gamma-32P]ATP and ATP-deficient conditions. In liver, DBC produced four major and several minor chromatographically distinct adducts of as yet undetermined chemical structure. The adduct pattern elicited by 3-OH-DBC was qualitatively similar to the DBC adduct pattern, while this was not the case for 2-OH-DBC and 4-OH-DBC. On the basis of co-chromatography experiments under various conditions, the DBC and 3-OH-DBC adducts appeared identical, and the total of adduction elicited by these compounds in liver was substantial. Similar results were observed when DBC or 3-OH-DBC were administered i.p. As a major difference between the two compounds, one 3-OH-DBC adduct (no. 3) was 4.4- and 7.0-fold lower than the corresponding DBC adduct after i.p. and topical dosing, respectively. In skin, DBC produced two major adduct fractions after topical application, one of which could be chromatographically resolved into three subcomponents. Prominent adducts produced in skin DNA by each of the three metabolites were different from those elicited by DBC, and the level of adduction by the metabolites was significantly lower than that by DBC. Comparison of the skin and liver DBC-DNA adduct patterns after topical application of DBC showed that only one of the four major chromatographically resolved skin adducts corresponded to a major liver adduct (no. 3), and that total adduction in liver was 13.5-fold higher than in skin. These results suggested that activation of DBC to DNA-binding compounds in liver occurs through at least two pathways with 3-OH-DBC being a proximate carcinogen involved in the formation of most of the adducts; 3-OH-DBC and the other two phenolic metabolites investigated play a minor role, if any, in the formation of DBC-DNA adducts in skin; metabolic activation of DBC to DNA-binding compounds in liver and skin appears to follow pathways that are different in terms of both the chemical nature and the amount of the adducts formed; and DBC and 3-OH-DBC exhibit a strong preference for liver versus skin DNA.
Carcinogenesis 1987 Apr
PMID:32P-postlabeling analysis of DNA adduction in mice by synthetic metabolites of the environmental carcinogen, 7H-dibenzo[c,g]carbazole: chromatographic evidence for 3-hydroxy-7H-dibenzo[c,g]carbazole being a proximate genotoxicant in liver but not skin. 382 21

Covalent adduction of DNA by chemical agents is commonly thought to be an essential part of the initiation of chemical carcinogenesis. Until recently, assays of DNA damage by covalent binding of chemicals have been restricted mostly to substances that are available in radiolabeled form, which excludes many environmental compounds with carcinogenic potential. In this paper, the binding of non-radioactive 7H-dibenzo[c,g]carbazole (DBC), a known environmental carcinogen, to DNA in female CD-1 mice after s.c. injection of 44 mumol/kg of the compound has been investigated using a 32P-postlabeling assay. DBC showed strong hepatic specificity with a mean total level of 107 adducts per 10(7) nucleotides at 24 h, while much lower levels of binding were seen in kidney, lung, spleen, skin and brain with 4.3, 2.1, 1.3, 0.4 and 0.04 adducts, respectively, per 10(7) nucleotides. Proportions of individual DBC adducts also varied considerably between tissues. The degree of hepatic preference displayed by DBC is not seen with other polycyclic aromatic carcinogens such as benzo[a]pyrene and 2-acetylaminofluorene. The DNA-binding data, together with other hepatotoxic effects of the compound, may be causally related to the known hepatocarcinogenicity of DBC.
Carcinogenesis 1985 Sep
PMID:Tissue-specific DNA adduct formation in mice treated with the environmental carcinogen, 7H-dibenzo[c,g]carbazole. 402 23

The recent observation of a high level of adducts in mitochondrial DNA (mtDNA) of cells exposed to chemical carcinogens aroused new interest in the hypothesis that carcinogen-induced damage in mitochondria plays a role in one or more stages of carcinogenesis. In order to investigate whether differences in the metabolic activation of carcinogens have qualitative and quantitative effects on ml- and nuclear DNA (nuDNA) adduct formation, mice were exposed to the potent hepatocarcinogenic and sarcomagenic polycyclic hydrocarbon 7H-dibenzo[c,g]carbazole (DBC) and to three of its derivatives that show large differences in enzymatic activation: N-acetyl-DBC (N-AcDBC), which is carcinogenic for several tissues; 5,9-dimethyl-DBC (DiMeDBC), which is exclusively hepatocarcinogenic; and N-methyl-DBC (N-MeDBC), which is exclusively sarcomagenic. Adduct formation and toxic effects were measured over 48 hr. With a moderate 5 mumol/kg dose of DBC, the adduct level in liver 24 hr after treatment was always higher in nuDNA than in mtDNA; after 48 hr a substantial increase in the level of adducts in mtDNA was observed, with a parallel decrease in the level in nuDNA. With DiMeDBC, a 4.9-fold increase in mtDNA was seen at 48 hr, whereas, at the same dose, the non-hepatocarcinogenic N-MeDBC induced a very small number of adducts. In order to obtain a nearly identical level of adducts in nu- and mtDNA at 24 hr, the dose of DBC must be three times higher (15 mumol/kg); this and higher dose levels had a strong cytotoxic effect in liver cells. Qualitative differences in adduct distribution were observed on chromatograms of mtDNA and nuDNA, showing that the access to mtDNA is a complex process. Our results confirm that mouse liver mtDNA is a major target for DBC and its hepatocarcinogenic derivatives. The possible interference of genotoxic alterations in mtDNA with carcinogenic mechanisms is discussed.
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PMID:Interaction of 7H-dibenzo[c,g]carbazole and its organspecific derivatives with hepatic mitochondrial and nuclear DNA in the mouse. 773 38

5,9-Dimethyldibenzo[c,g]carbazole (DMDBC) is a synthetic derivative of the environmental pollutant 7H-dibenzo[c,g]carbazole. DMDBC is a potent genotoxic carcinogen specific for mouse liver. Using the MutaMouse lacZ transgenic mouse model and a positive selection assay, we measured lacZ mutant frequency (MF) in the liver 28 days after a single s.c. administration of DMDBC at 3, 10, 30, 90 or 180 mg/kg. MF remained low at 3 and 10 mg/kg, but increased markedly from 30 mg/kg onwards. To investigate the reason for this non-linear response, we examined mechanisms potentially involved in mutation induction in the liver. Genotoxic effects such as DNA adduct formation were detected in 32P-post-labelling studies. Liver sections were examined for microscopic changes and cell proliferation. These parameters, and MF, were studied 2, 4, 7, 14, 21 and 28 days after a single s.c. administration of 10 or 90 mg/kg DMDBC. At 10 mg/kg, a dose found to double the MF on day 28, DNA adducts reached a level of 200-600 adducts per 10(8) nucleotides from day 4 to day 28. No changes in histology or cell proliferation were detected at this low dose. At 90 mg/kg, MF increased gradually from day 7 to day 28 (maximum 44-fold). The DNA adduct level ranged from 400 to 4500 adducts per 10(8) nucleotides on day 2, then stabilized at approximately 400 adducts per 10(8) nucleotides on day 4. An early cytotoxic effect was detected microscopically in centrilobular hepatocytes, and was followed by liver cell proliferation. These data suggest that the marked increase in MF in MutaMouse liver after treatment in vivo with DMDBC at 90 mg/kg may be explained by the induction of replicative DNA synthesis due to a cytotoxic effect, allowing the fixation of persistent DNA adducts into mutations.
Carcinogenesis 1999 Jan
PMID:Kinetics of induction of DNA adducts, cell proliferation and gene mutations in the liver of MutaMice treated with 5,9-dimethyldibenzo[c,g]carbazole. 993 59

The potent multitissue carcinogen 7H-dibenzo[c,g]carbazole and nine methylated derivatives, synthesized on the basis of the positions in the parent compound that are involved in metabolism, were tested for their ability to induce sarcomas and hepatic tumors in XVIInc/Z mice. In addition, the capacity of these compounds to induce DNA adducts in skin and liver was investigated by (32)P-postlabeling analysis after their topical administration. Induction by these compounds of cytochromes P450 of the 1A family in liver and skin was investigated and correlated to their carcinogenic potential. A clear correlation was found between the tissue specificity of DNA binding and the capacity of each compound to induce skin or liver tumors. In contrast, no direct relationship was observed between the capacity of the compounds to induce cytochromes 1A1/1A2 and the tissue specificity of carcinogenesis or DNA binding in liver or skin. The results are discussed with respect to the positions of methyl groups in the 7H-dibenzo[c,g]carbazole molecule.
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PMID:Tissue-specific activities of methylated dibenzo[c,g]carbazoles in mice: carcinogenicity, DNA adduct formation, and CYP1A induction in liver and skin. 1071 48

Found in tobacco smoke, fossil fuel and other organic combustion products, 7H-dibenzo[c,g]carbazole (DBC) is a potent mouse lung carcinogen and potential human carcinogen. Although the first hydroxylation is critical for determining activation versus detoxication, the enzymes responsible for site-specific hydroxylation of DBC are not known. We found that DBC-DNA adduct levels are significantly higher in aromatic hydrocarbon receptor null Ahr(-/-) mice, suggesting that the induction of Aromatic hydrocarbon receptor (AHR)-regulated genes, such as those in the CYP1 family, decrease DBC genotoxicity. Using knockout mice for Cyp1a1, Cyp1a2 and Cyp1b1, we showed that the major CYP1 enzymes that metabolize DBC are CYP1A1 in beta-naphthoflavone (BNF)-induced liver, CYP1A2 in non-induced liver, CYP1B1 and CYP1A1 in induced lung and none in non-induced lung. DBC metabolism by the human CYP1 enzymes was examined in vitro using Supersomestrade mark. Each mouse CYP1, as well as each human CYP1, has a unique DBC metabolite profile. Comparison of the metabolite profile in BNF-induced mice suggested that CYP1A1 primarily generates 1-OH, 2-OH and (5 + 6)-OH-DBC, whereas CYP1A2 generates primarily (5 + 6)-OH-DBC and CYP1B1 primarily generates 4-OH-DBC. This was similar to that observed in the human CYP1 enzymes. Most importantly, lung CYP1B1 is associated with forming 4-OH-DBC, the most potent metabolite leading to DBC-DNA adducts. These studies suggest that for non-pulmonary routes of exposure (i.e. skin, gastric, i.p.), low hepatic expression of CYP1A2 and CYP1A1, together with high expression levels of lung CYP1B1 and CYP1A1, may define a phenotype for high susceptibility to carcinogens such as DBC.
Carcinogenesis 2007 Jun
PMID:7H-dibenzo[c,g]carbazole metabolism by the mouse and human CYP1 family of enzymes. 1716 82

To gain a deeper insight into the potential interactions between individual aromatic hydrocarbons in a mixture, several benzo[a]pyrene (B[a]P) and 7H-dibenzo[c,g]carbazole (DBC) binary mixtures were studied. The biological activity of the binary mixtures was investigated in the HepG2 and WB-F344 liver cell lines and the Chinese hamster V79 cell line that stably expresses the human cytochrome P4501A1 (hCYP1A1). In the V79 cells, binary mixtures, in contrast to individual carcinogens, caused a significant decrease in the levels of micronuclei, DNA adducts and gene mutations, but not in cell survival. Similarly, a lower frequency of micronuclei and levels of DNA adducts were found in rat liver WB-F344 cells treated with a binary mixture, regardless of the exposure time. The observed antagonism between B[a]P and DBC may be due to an inhibition of Cyp1a1 expression because cells exposed to B[a]P:DBC showed a decrease in Cyp1a1 mRNA levels. In human liver HepG2 cells exposed to binary mixtures for 2h, a reduction in micronuclei frequency was also found. However, after a 24h treatment, synergism between B[a]P and DBC was determined based on DNA adduct formation. Accordingly, the up-regulation of CYP1A1 expression was detected in HepG2 cells exposed to B[a]P:DBC. Our results show significant differences in the response of human and rat cells to B[a]P:DBC mixtures and stress the need to use multiple experimental systems when evaluating the potential risk of environmental pollutants. Our data also indicate that an increased expression of CYP1A1 results in a synergistic effect of B[a]P and DBC in human cells. As humans are exposed to a plethora of noxious chemicals, our results have important implications for human carcinogenesis.
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PMID:Sustained induction of cytochrome P4501A1 in human hepatoma cells by co-exposure to benzo[a]pyrene and 7H-dibenzo[c,g]carbazole underlies the synergistic effects on DNA adduct formation. 2363 21


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