The time-dependent increase in the binding of benzo[a]pyrene to DNA through (+)-anti-benzo[a]pyrene-7,8-diol-9,10-epoxide in primary rat hepatocyte cultures results from induction of cytochrome P450IA1 by benzo[a]pyrene treatment.
The proportion and amount of benzo[a]pyrene (B[a]P) that binds to DNA through the carcinogenic (+)-anti-benzo[a]pyrene-7,8-diol-9,10-epoxide [(+)-anti-BPDE] increases with time of exposure to B[a]P in cell cultures derived from a number of species. Pretreatment of primary rat hepatocyte cultures for 12 h with 1 microgram B[a]P/ml medium increased the subsequent metabolism of [3H]B[a]P by 47% and [3H]B[a]P-DNA binding by 53% compared with acetone-pretreated hepatocytes. The amount of (+)-anti-BPDE bound to DNA in the B[a]P-pretreated hepatocytes increased 175%. B[a]P pretreatment also increased DNA-binding 2-fold in hepatocytes treated with [3H]7,8-dihydroxy-7,8-dihydro-B[a]P but had no effect on DNA binding in cells treated with anti-B[a]P-7,8-diol-9,10-epoxide. Western blotting showed that cytochrome P450IA1, which was not detectable prior to B[a]P treatment, was selectively increased by B[a]P treatment. A monoclonal antibody that specifically inhibits cytochrome P450IA1 reduced the binding of B[a]P to DNA by greater than 90% in microsomal preparations from B[a]P-pretreated hepatocytes. These results indicate that the time-dependent increase in the formation of (+)-anti-BPDE-DNA adducts results from an increase in the amount and proportion of B[a]P metabolized to this ultimate carcinogen by P450IA1 that is induced by the B[a]P treatment. The importance of P450IA1 induction by the B[a]P for its activation to this ultimate carcinogenic metabolite suggests that long-term exposure of cells to B[a]P could result in activation of a higher proportion of the B[a]P to the carcinogenic (+)-anti-BPDE.
Eberhart
J
J
Department of Medicinal Chemistry and Pharmacognosy, Purdue University, West Lafayette, IN 47907.
Coffing
S L
SL
Anderson
J N
JN
Marcus
C
C
Kalogeris
T J
TJ
Baird
W M
WM
Park
S S
SS
Gelboin
H V
HV
D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000378:metabolism*; D000818:Animals; D000911:Antibodies, Monoclonal; D001564:Benzo(a)pyrene / Q000378:metabolism* / Q000494:pharmacology*; D015153:Blotting, Western; D002274:Carcinogens, Environmental / Q000378:metabolism; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D018736:DNA Adducts; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
D000911:Antibodies, Monoclonal; D002274:Carcinogens, Environmental; D018736:DNA Adducts; C056612:benzo(a)pyrene-DNA adduct; D001564:Benzo(a)pyrene; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D004247:DNA; D003577:Cytochrome P-450 Enzyme System