title: Induction of Cyp1a-1 and Cyp1a-2 gene expression by a reconstituted mixture of polynuclear aromatic hydrocarbons in B6C3F1 mice.
abstract: The potential non-additive interactions of polynuclear aromatic hydrocarbon (PAH) mixtures as inducers of Cyp1a-1 and Cyp1a-2 gene expression were investigated in B6C3F1 mice using a reconstituted PAH mixture. The chemical composition (% by weight) of the reconstituted PAH mixture was: 2-ring PAHs--indan (0.22), naphthalene (23.8), 2-methylnaphthalene (23.2) and 1-methylnaphthalene (13.3); 3-ring PAHs--acenaphthylene (7.7), acenaphthene (0.6), dibenzofuran (0.7), fluorene (4.3), phenanthrene (10.5) and anthracene (3.4); > or = 4-ring PAHs--fluoranthene (2.4), pyrene (4.3), benz[a]anthracene (1.4), chrysene (1.5), benzo[b]fluoranthene (0.8), benzo[k]fluoranthene (0.9) and benzo[a]pyrene (0.9). The composition of the 2-, 3- and > or = 4-ring PAH fractions were based on the relative concentration of individual PAHs as noted above. The > or = 4-ring PAH fractions were based on the relative concentration of individual PAHs as noted above. The > or = 4-ring PAH fraction and reconstituted mixture induced hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity and Cyp1a-1 mRNA levels, whereas the 2- and 3-ring PAHs were only weakly active. Direct comparison of the potencies of the reconstituted mixture and > or = 4-ring PAHs showed that the Cyp1a-1 induction activity of the reconstituted mixture was due to the > or = 4-ring PAHs. The reconstituted PAH mixture and > or = 4-ring PAHs also induced Cyp1a-2 hepatic mRNA levels and microsomal methoxyresorufin O-deethylase (MROD) activity; however, their dose-response curves indicated that the reconstituted PAH mixture was more potent as a Cyp1a-2 inducer than the > or = 4 ring PAHs. The differences in potency were due to 3-ring PAHs which were found to be strong inducers of hepatic Cyp1a-2 mRNA levels and microsomal MROD activity at the lowest dose administered (37 mg/kg). The 3-ring mixture caused a maximal 29-fold increase in hepatic MROD activity at a dose of 292 mg/kg, but only 28% of maximal induction of EROD activity. Northern analysis of liver mRNA from mice treated with 3-ring PAHs showed that there was minimal induction of Cyp1a-1 mRNA levels. The 3-ring PAHs did not competitively bind to the mouse hepatic cytosolic aryl hydrocarbon (Ah) receptor suggesting that 3-ring PAHs are a new class of Cyp1a-2 inducers which do not act through the Ah receptor.
authors.affiliation: Texas A & M University, College Station 77843-4466, USA.
authors.forename: K
authors.initials: K
authors.lastname: Chaloupka
authors.forename: M
authors.initials: M
authors.lastname: Steinberg
authors.forename: M
authors.initials: M
authors.lastname: Santostefano
authors.forename: L V
authors.initials: LV
authors.lastname: Rodriguez
authors.forename: L
authors.initials: L
authors.lastname: Goldstein
authors.forename: S
authors.initials: S
authors.lastname: Safe
mesh_terms: D000818:Animals; D019388:Cytochrome P-450 CYP1A2; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D003600:Cytosol / Q000201:enzymology; D004790:Enzyme Induction / Q000187:drug effects; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006579:Heterozygote; D008099:Liver / Q000201:enzymology* / Q000378:metabolism; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008862:Microsomes, Liver / Q000201:enzymology; D010088:Oxidoreductases / Q000235:genetics*; D011083:Polycyclic Compounds / Q000737:chemistry / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D011083:Polycyclic Compounds; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D019388:Cytochrome P-450 CYP1A2