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Validation of precision-cut liver slices in dynamic organ culture as an in vitro model for studying CYP1A1 and CYP1A2 induction.

The utilization of precision-cut liver slices in dynamic organ culture as an in vitro model was validated by comparing the induction of the biomarker responses following in vitro (rat liver slice) and in vivo exposure of rats to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The biomarker responses investigated were cytochrome P450s 1A1 and 1A2 (CYP1A1 and CYP1A2) mRNA, protein, and activities. Precision-cut rat liver slices were incubated in dynamic organ culture for 24 hr with medium containing 0.001-10 nM TCDD or medium without TCDD (control). The resultant mean TCDD concentration in the slices ranged from 19 to 80,925 ppt (wet wt), respectively. A concentration-dependent induction of CYP1A1 mRNA, protein, and activities and a more modest induction of CYP1A2 mRNA was observed in liver slices at all medium concentrations of TCDD. The O-demethylation of 7-methoxyresorufin, a marker for CYP1A2 activity, was induced at TCDD medium levels of 0.01 nM and greater, whereas a detectable increase in CYP1A2 protein occurred only at the higher concentrations. Comparable liver concentrations of TCDD (8-64,698 ppt wet wt) were achieved at 24 hr following a single in vivo exposure of rats to TCDD at doses ranging from 0.002 to 5 microg/kg po. Concentration-effect and dose-response relationships for induction of CYP1A1 and CYP1A2 were similar following in vitro and in vivo exposure to TCDD, although the magnitude of induction was greater for in vivo exposure. The data support the use of liver slices in dynamic organ culture for assessing the relative in vivo potency of a compound to induce CYP1A1 and CYP1A2. Human tissue can also be readily utilized in this in vitro model to predict the biological and toxicological effects of a given in vivo exposure to TCDD.