Identification of hepatocytes as the major locus of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced CYP1-related P450s, TCDDAA and TCDDAHH, in chick embryo liver.

It was recently shown that the pleiotropic response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in chick embryo liver includes the induction of cytochrome P450-mediated arachidonic acid epoxygenation, as well as 7-ethoxyresorufin deethylation (EROD) and aryl hydrocarbon hydroxylation (AHH). The TCDD-induced arachidonic acid metabolism in avian liver microsomes is catalyzed by a 55 kDa P450, TCDDAA, whereas the TCDD-induced AHH and EROD are catalyzed by a different 54.5 kDa P450, TCDDAHH. In this study, we investigated the distribution and inducibility of TCDDAA and TCDDAHH in hepatocytes and nonparenchymal cells. Sonicates of freshly isolated hepatocytes from embryos treated with solvent alone (control) metabolized [14C]arachidonic acid principally to a single metabolite, omega-OH arachidonic acid. Treatment with TCDD increased total arachidonic acid metabolism 2.9-fold and epoxygenase products [epoxyeicosatrienoic acids (EETs) and EET-diols] 36-fold. After treatment, EETs and EET-diols constituted 59% of the total metabolites. EROD in hepatocyte sonicates was increased 32-fold by TCDD treatment. The same pattern of arachidonate metabolites and degree of increase in arachidonate metabolism and EROD by TCDD treatment was observed in the hepatocyte sonicates and liver microsomes. TCDD treatment increased arachidonic acid metabolism and EROD activity 3.6- and 50-fold, respectively, in the nonparenchymal cells.(ABSTRACT TRUNCATED AT 250 WORDS)