Mechanism of Metabolic Activation of the Potent Carcinogen 7,12-Dimethylbenz[a]anthracene

N. V S RamaKrishna, P. D. Devanesan, Eleanor G Rogan, Ercole Cavalieri, H. Jeong, R. Jankowiak, G. J. Small

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Abstract

The DNA adducts of 7,12-dimethylbenz[a]anthracene (DMBA) previously identified in vitro and in vivo are stable adducts formed by reaction of the bay-region diol epoxides of DMBA with dG and dA. In this paper we report identification of several new DMBA-DNA adducts formed by one-electron oxidation, including two adducts lost from DNA by depurination, DMBA bound at the 12-methyl to the N-7 of adenine (Ade) or guanine (Gua) [7-methylbenz[a]anthracene (MBA-12-CH2-N7Ade or 7-MBA-12-CH2-N7Gua, respectively]. The in vitro systems used to study DNA adduct formation were DMBA activated by horseradish peroxidase or 3-methylcholanthrene-induced rat liver microsomes. The biologically-formed depurination adducts were identified by high-pressure liquid chromatography and by fluorescence line narrowing spectroscopy. Stable DMBA-DNA adducts were analyzed by the 32P-postlabeling method. Quantitation of DMBA-DNA adducts formed by microsomes showed about 99% as depurination adducts: 7-MBA-12-CH2-N7Ade (82%) and 7-MBA-12-CH2-N7Gua (17%). Stable adducts (1.4% of total) included one adduct spot that may contain adduct(s) formed from the diol epoxide (0.2%) and unidentified adducts (1.2%). Activation of DMBA by horseradish peroxidase afforded 56% of stable unidentified adducts and 44% of depurination adducts, with 36% of 7-MBA-12-CH2-N7Ade and 8% of 7-MBA-12-CH2-N7Gua. Adducts containing the bond to the DNA base at the 7-CH3 group of DMBA were not detected. These results show that with activation by cytochrome P-450 the DMBA-DNA adducts are predominantly formed by one-electron oxidation and lost from DNA by depurination, and the adducts formed by the diol epoxide pathway are very minor. The 12-CH3 group is shown to be critical in metabolic activation of DMBA, a finding consistent with the results of carcinogenicity studies in rodents.

Original languageEnglish (US)
Pages (from-to)220-226
Number of pages7
JournalChemical Research in Toxicology
Volume5
Issue number2
DOIs
StatePublished - Mar 1 1992

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9,10-Dimethyl-1,2-benzanthracene
Carcinogens
Chemical activation
DNA Adducts
Epoxy Compounds
Horseradish Peroxidase
High pressure liquid chromatography
Electrons
Oxidation
Methylcholanthrene
DNA
Guanine
Liver Microsomes
Adenine
Microsomes
anthracene
Metabolic Activation
Liver
Cytochrome P-450 Enzyme System
Rats

ASJC Scopus subject areas

  • Toxicology

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Mechanism of Metabolic Activation of the Potent Carcinogen 7,12-Dimethylbenz[a]anthracene. / RamaKrishna, N. V S; Devanesan, P. D.; Rogan, Eleanor G; Cavalieri, Ercole; Jeong, H.; Jankowiak, R.; Small, G. J.

In: Chemical Research in Toxicology, Vol. 5, No. 2, 01.03.1992, p. 220-226.

Research output: Contribution to journalArticle

RamaKrishna, N. V S ; Devanesan, P. D. ; Rogan, Eleanor G ; Cavalieri, Ercole ; Jeong, H. ; Jankowiak, R. ; Small, G. J. / Mechanism of Metabolic Activation of the Potent Carcinogen 7,12-Dimethylbenz[a]anthracene. In: Chemical Research in Toxicology. 1992 ; Vol. 5, No. 2. pp. 220-226.
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abstract = "The DNA adducts of 7,12-dimethylbenz[a]anthracene (DMBA) previously identified in vitro and in vivo are stable adducts formed by reaction of the bay-region diol epoxides of DMBA with dG and dA. In this paper we report identification of several new DMBA-DNA adducts formed by one-electron oxidation, including two adducts lost from DNA by depurination, DMBA bound at the 12-methyl to the N-7 of adenine (Ade) or guanine (Gua) [7-methylbenz[a]anthracene (MBA-12-CH2-N7Ade or 7-MBA-12-CH2-N7Gua, respectively]. The in vitro systems used to study DNA adduct formation were DMBA activated by horseradish peroxidase or 3-methylcholanthrene-induced rat liver microsomes. The biologically-formed depurination adducts were identified by high-pressure liquid chromatography and by fluorescence line narrowing spectroscopy. Stable DMBA-DNA adducts were analyzed by the 32P-postlabeling method. Quantitation of DMBA-DNA adducts formed by microsomes showed about 99{\%} as depurination adducts: 7-MBA-12-CH2-N7Ade (82{\%}) and 7-MBA-12-CH2-N7Gua (17{\%}). Stable adducts (1.4{\%} of total) included one adduct spot that may contain adduct(s) formed from the diol epoxide (0.2{\%}) and unidentified adducts (1.2{\%}). Activation of DMBA by horseradish peroxidase afforded 56{\%} of stable unidentified adducts and 44{\%} of depurination adducts, with 36{\%} of 7-MBA-12-CH2-N7Ade and 8{\%} of 7-MBA-12-CH2-N7Gua. Adducts containing the bond to the DNA base at the 7-CH3 group of DMBA were not detected. These results show that with activation by cytochrome P-450 the DMBA-DNA adducts are predominantly formed by one-electron oxidation and lost from DNA by depurination, and the adducts formed by the diol epoxide pathway are very minor. The 12-CH3 group is shown to be critical in metabolic activation of DMBA, a finding consistent with the results of carcinogenicity studies in rodents.",
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AU - RamaKrishna, N. V S

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AU - Rogan, Eleanor G

AU - Cavalieri, Ercole

AU - Jeong, H.

AU - Jankowiak, R.

AU - Small, G. J.

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N2 - The DNA adducts of 7,12-dimethylbenz[a]anthracene (DMBA) previously identified in vitro and in vivo are stable adducts formed by reaction of the bay-region diol epoxides of DMBA with dG and dA. In this paper we report identification of several new DMBA-DNA adducts formed by one-electron oxidation, including two adducts lost from DNA by depurination, DMBA bound at the 12-methyl to the N-7 of adenine (Ade) or guanine (Gua) [7-methylbenz[a]anthracene (MBA-12-CH2-N7Ade or 7-MBA-12-CH2-N7Gua, respectively]. The in vitro systems used to study DNA adduct formation were DMBA activated by horseradish peroxidase or 3-methylcholanthrene-induced rat liver microsomes. The biologically-formed depurination adducts were identified by high-pressure liquid chromatography and by fluorescence line narrowing spectroscopy. Stable DMBA-DNA adducts were analyzed by the 32P-postlabeling method. Quantitation of DMBA-DNA adducts formed by microsomes showed about 99% as depurination adducts: 7-MBA-12-CH2-N7Ade (82%) and 7-MBA-12-CH2-N7Gua (17%). Stable adducts (1.4% of total) included one adduct spot that may contain adduct(s) formed from the diol epoxide (0.2%) and unidentified adducts (1.2%). Activation of DMBA by horseradish peroxidase afforded 56% of stable unidentified adducts and 44% of depurination adducts, with 36% of 7-MBA-12-CH2-N7Ade and 8% of 7-MBA-12-CH2-N7Gua. Adducts containing the bond to the DNA base at the 7-CH3 group of DMBA were not detected. These results show that with activation by cytochrome P-450 the DMBA-DNA adducts are predominantly formed by one-electron oxidation and lost from DNA by depurination, and the adducts formed by the diol epoxide pathway are very minor. The 12-CH3 group is shown to be critical in metabolic activation of DMBA, a finding consistent with the results of carcinogenicity studies in rodents.

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