Regio- and stereoselectivity in the metabolism of benzo[c]phenanthrene mediated by genetically engineered V79 Chinese hamster cells expressing rat and human cytochromes P450

Albrecht Seidel, Volker J. Soballa, Gottfried Raab, Heinz Frank, Helmut Greim, Gernot Grimmer, Jürgen Jacob, Johannes Doehmer

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28 Scopus citations

Abstract

Regio- and stereoselective metabolism mediated by cytochrome P450 (CYP) and metabolite-dependent cytotoxicity of benzo[c]phenanthrene (B[c]Ph) and its trans-3,4-dihydrodiol, the metabolic precursor of the carcinogenic fjord- region B[c]Ph-3,4-dihydrodiol 1,2-epoxides (B[c]PhDE), were investigated with V79 Chinese hamster cells genetically engineered for three rat and six human CYP isoforms. The order of the capabilities of the CYP isoforms to metabolize B[c]Ph was as follows: h1A1 > r1A1 > r1A2 > h1B1 > h1A2 > r2B1 > > h2E1 > h2A6 > h3A4. Regardless of the species, all individual CYP isoforms preferentially catalyzed the oxidation of B[c]Ph at the 5,6-position (K- region) except human CYP1A1 and human CYP1A2, which oxidized both the 5,6- and the 3,4-position with similar efficiency. While human CYP1A1, rat CYP1A1 and rat CYP1A2 formed almost exclusively the (-)-B[c]Ph-3R,4R-dihydrodiol, human CYP1A2 produced both the (-)-3R,4R- and the (+)-3S,4S-dihydrodiol enantiomers in a ratio of 2:1. Stereoselective activation of B[c]Ph, the (±)-B[c]Ph-3,4-dihydrodiol and its (-)-3R,4R-enantiomer to the fjord-region (-)-anti-B[c]PhDE occurred upon incubation with rat CYP1A1 and rat CYP1A2 as indicated by the formation of two stereoisomeric tetraols, the hydrolysis products of the labile anti-B[c]PhDE. The formation of tetraols in the culture medium was accompanied by a concentration-dependent increase in cytotoxicity indicating that this effect was mediated by the fjord-region (- )-anti-B[c]PhDE formed as reactive intermediate. All human and rat CYP- expressing V79 cell lines investigated did not show any significant capacity to metabolize the (+)-3S,4S-dihydrodiol. The present study indicates that the human CYP isoforms 1A1 and 1B1 have complementary catalytic properties to activate B[c]Ph to its fjord-region B[c]PhDE, whereas other human isoforms play a minor role. Activation of B[c]Ph by human CYP1A1 and 1B1 is less efficient than by rat CYP1A1 or rat CYP1A2, but proceeds with similar stereoselectivity via the (-)-3R,4R-dihydrodiol to the strong carcinogen (- )-anti-B[c]PhDE with (R,S,S,R)-configuration.

Original languageEnglish
Pages (from-to)179-196
Number of pages18
JournalEnvironmental Toxicology and Pharmacology
Volume5
Issue number3
DOIs
StatePublished - May 1998
Externally publishedYes

Keywords

  • Benzo[c]phenanthrene
  • Cytochrome P450
  • Dihydrodiol epoxides
  • Fjord-region
  • Metabolism
  • Polycyclic aromatic hydrocarbons
  • Toxicity
  • V79 Chinese hamster cells

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