Inhibitory effects of naturally occurring coumarins on the metabolic activation of benzo[a]pyrene and 7,12-dimethylbenz[a]anthracene in cultured mouse keratinocytes.
Several naturally occurring coumarins to which humans are routinely exposed have been previously found to be potent inhibitors and inactivators of cytochrome P450 (P450) 1A1-mediated monooxygenase in both murine hepatic microsomes and in a reconstituted system using purified human P450 1A1 [Cai et al. (1993) Chem. Res. Toxicol., 6, 872-879 and Cai et al. (1996) Chem. Res. Toxicol., 9, 729-736]. In the present study, several of these coumarins were investigated for their inhibitory effects on the metabolism and metabolic activation of benzo[a]pyrene (B[a]P) and 7,12-dimethylbenz[a]anthracene (DMBA) in cultured mouse keratinocytes. Initial analysis of B[a]P metabolism in cultured keratinocytes showed that imperatorin, isoimperatorin, coriandrin, and bergamottin, at concentrations of 2 nM equal with B[a]P, reduced the formation of water-soluble metabolites of B[a]P by 33% to 57%. Bergamottin and coriandrin were the most potent inhibitors of the compounds examined. HPLC analysis of organic solvent-soluble metabolites of B[a]P indicated that all the coumarins tested significantly reduced the formation of individual B[a]P metabolites (including phenols, diols and tetraols). However, the greatest effect was on the formation of B[a]P tetraols. Additional experiments determined the ability of selected coumarins to block covalent binding of B[a]P and DMBA to DNA in keratinocytes. Bergamottin preferentially inhibited the binding of B[a]P to DNA by 56%, while coriandrin preferentially inhibited the binding of DMBA to DNA by 48%. Notably, analysis of individual DNA adducts formed from B[a]P and DMBA indicated that both bergamottin and coriandrin specifically inhibited the formation of anti diol-epoxide DNA adducts derived from both hydrocarbons. The preferential inhibitory effect of bergamottin and coriandrin on the formation of anti diol-epoxide adducts derived from DMBA was further confirmed by separation of anti- and syn-diol-epoxide-DNA adducts using immobilized boronate chromatography. The current study demonstrates that certain naturally occurring coumarins inhibited metabolic activation of B[a]P and DMBA in cultured mouse keratinocytes and specifically inhibited the formation of DNA adducts derived from the anti diol-epoxide diastereomers from either hydrocarbon. The current data also suggest that certain naturally occurring coumarins may possess anticarcinogenic activity toward polycyclic aromatic hydrocarbons.
Cai
Y
Y
University of Texas MD Anderson Cancer Center, Department of Carcinogenesis, Smithville 78957, USA.
Baer-Dubowska
W
W
Ashwood-Smith
M
M
DiGiovanni
J
J
D015127:9,10-Dimethyl-1,2-benzanthracene / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics*; D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism / Q000493:pharmacokinetics*; D001711:Biotransformation / Q000187:drug effects; D002273:Carcinogens / Q000378:metabolism / Q000493:pharmacokinetics*; D002460:Cell Line; D003374:Coumarins / Q000494:pharmacology*; D018736:DNA Adducts / Q000378:metabolism; D005260:Female; D011564:Furocoumarins / Q000494:pharmacology; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D051379:Mice
C059444:7,12-dimethylbenz(a)anthracene-DNA adduct; D002273:Carcinogens; D003374:Coumarins; D018736:DNA Adducts; D011564:Furocoumarins; C056612:benzo(a)pyrene-DNA adduct; C055542:isoimperatorin; C063218:coriandrin; D001564:Benzo(a)pyrene; D015127:9,10-Dimethyl-1,2-benzanthracene; C068337:bergamottin; C031534:imperatorin