Effect of metals on polycyclic aromatic hydrocarbon induction of CYP1A1 and CYP1A2 in human hepatocyte cultures

Environmental cocontamination by polycyclic aromatic hydrocarbons (PAHs) an d metals could affect the carcinogenic consequences of PAH exposure by modi fying PAH induction of PAH-bioactivating CYP1A. The effect of As, Pb, Hg, o r Cd (ranked as the most hazardous environmental metals by EPA and ATSDR) o n CYP1A1 and 1A2 induction by benzo[a]pyrene (BaP), benzo[b]fluoranthene (B bF), dibenzo[a,h]anthracene (DBahA), benzo[a]anthracene (BaA), and benzo[k] fluoranthene (BkF) has thus been investigated in fresh human hepatocyte cul tures. Induction was probed by ethoxyresorufin-O-deethylase activity, by im munoblots, and by RT-PCR. Uptake of PAHs into the hepatocytes varied accord ing to PAH and liver donor: 84% of 5 muM BaA and 25-40% of 5 muM DBahA was taken up in 24 h. Hepatocytes retained viability up to 1 muM Cd and 5 muM P b, Hg, or As and 5 muM PAHs. PAH induction of CYP1A in hepatocytes was vari able, some cultures expressed CYP1A1 and others CYP1A1 and 1A2, and to vari able extents. Induction efficiency (relative to DMSO controls) at 2.5 muM P AH concentration was in the order BkF (7.6-fold) > DBahA (6.1 fold) > BaP(5 .7 fold) > BbF(3.9-fold) > BaA (2.5-fold). All four metals (1-5 muM) decrea sed CYP1A1/1A2 induction by some of the PAHs with dose-, metal-, and PAH-de pendency. Arsenic (5 muM) decreased induction by 47% for BaP, 68% for BaA, 45% for BbF, 79% for BkF, and 53% for DBahA. Induced CYP1A2 protein was muc h more extensively decreased than 1A1 protein, and CYP1A2 mRNA and, to vari able extents, CYP1A1 mRNA were decreased by As. Thus the metals in PAH/meta l mixtures could diminish PAH carcinogenicity by decreasing induction of th eir bioactivation by CYP1A1/1A2. (C) 2001 Academic Press.