Carcinogenesis, Vol. 20, No. 9, 1777-1785,
September 1999
© 1999 Oxford University Press
Carcinogenesis |
Benzylic hydroxylation of 1-methylpyrene and 1-ethylpyrene by human and rat cytochromes P450 individually expressed in V79 Chinese hamster cells
Deutsches Institut für Ernährungsforschung (DIfE), Department of Toxicology, Arthur-Scheunert-Allee 114–116, D-14558 Bergholz-Rehbrücke and
1 Institut für Toxikologie und Umwelthygiene, Technische Universität München, Lazarettstraße 62, D-80636 München, Germany
Alkyl-substituted polycyclic aromatic hydrocarbons may be metabolized to highly reactive benzylic sulfuric acid esters via benzylic hydroxylation and subsequent sulfonation. We have studied the benzylic hydroxylation of 1-methylpyrene (MP), a hepatocarcinogen in rodents, and 1-ethylpyrene (EP), whose benzylic hydroxylation would produce a secondary alcohol (
-HEP), in contrast to the primary alcohol (-HMP) formed from MP. The hydrocarbons were incubated with hepatic microsomal preparations from humans and rats, as well as with V79-derived cell lines engineered for the expression of individual cytochrome P450 (CYP) forms from human (1A1, 1A2, 1B1, 2A6, 2E1, 3A4) and rat (1A1, 1A2, 2B1). All microsomal systems and CYP-expressing cell lines used, but not CYP-deficient V79 cells, showed biotransformation of both hydrocarbons. Formation of the benzylic alcohol was detected in each case. -HMP and its oxidation product, 1-pyrenylcarboxylic acid (COOH-P), accounted for a major part of the total amount of the metabolites formed from MP in the presence of human liver microsomes (38–64%) and cells expressing human 3A4, 2E1 or 1B1 (80–85%). Likewise, cells expressing human 1A1 showed a higher contribution of -HMP and COOH-P to the total metabolites (45%) than cells expressing the orthologous enzyme of the rat (3%). EP was metabolized at a higher rate and with modified regioselectivity compared with MP, although 
-hydroxylation of the side chain was not detected with the cell lines and only accounted for a small percent of the biotransformation by the microsomal preparations. The highest contributions of -HEP to the total metabolites from EP were detected with the cells expressing human 1A1, 1B1 and 3A4 (38–51%). -HEP accounted for 16% of the metabolites formed in the presence of human hepatic microsomes. Thus, benzylic hydroxylation is a major initial step in the metabolism of MP and EP. This pathway appears to be even more important in humans than in rats. Previously, we had shown that the second step of the activation, the sulfonation of -HMP and -HEP, is also efficiently catalysed by various forms of human sulfotransferases.
Abbreviations: -HEP, 1-(1-pyrenyl)ethanol; -HMP, 1-hydroxymethylpyrene; B[a]P, benzo[a]pyrene; COOH-P, 1-pyrenylcarboxylic acid; CYP, cytochrome P450; EP, 1-ethylpyrene; MC, 3-methylcholanthrene; MP, 1-methylpyrene; PAH, polycyclic aromatic hydrocarbon; -HEP, 2-(1-pyrenyl)ethanol.
2 To whom correspondence should be addressed Email: glatt{at}www.dife.de
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  N. Bakhiya, M. Batke, J. Laake, B. H. Monien, H. Frank, A. Seidel, W. Engst, and H. Glatt Directing Role of Organic Anion Transporters in the Excretion of Mercapturic Acids of Alkylated Polycyclic Aromatic Hydrocarbons Drug Metab. Dispos., October 1, 2007; 35(10): 1824 - 1831. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Geyer, B. Doring, K. Meerkamp, B. Ugele, N. Bakhiya, C. F. Fernandes, J. R. Godoy, H. Glatt, and E. Petzinger Cloning and Functional Characterization of Human Sodium-dependent Organic Anion Transporter (SLC10A6) J. Biol. Chem., July 6, 2007; 282(27): 19728 - 19741. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Chen, X.-X. Yang, M. Huang, Z.-P. Hu, M. He, W. Duan, E. Chan, F.-S. Sheu, X. Chen, and S.-F. Zhou Small Interfering RNA-Mediated Silencing of Cytochrome P450 3A4 Gene Drug Metab. Dispos., September 1, 2006; 34(9): 1650 - 1657. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Bakhiya, M. Stephani, A. Bahn, B. Ugele, A. Seidel, G. Burckhardt, and H. Glatt Uptake of Chemically Reactive, DNA-Damaging Sulfuric Acid Esters into Renal Cells by Human Organic Anion Transporters J. Am. Soc. Nephrol., May 1, 2006; 17(5): 1414 - 1421. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 W. Teubner, W. Meinl, and H. Glatt Stable expression of rat sulfotransferase 1B1 in V79 cells: activation of benzylic alcohols to mutagens Carcinogenesis, November 1, 2002; 23(11): 1877 - 1884. [Abstract] [Full Text] [PDF]
|
|