Induction of cytochrome P450-dependent monooxygenase activities in rat hepatoma H-4-IIE cells in culture by 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds: mechanistic studies using radiolabeled congeners.

Abstract

Treatment of rat hepatoma H-4-IIE cells in culture with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 1,2,3,7,8-pentachlorodibenzofuran (PeCDF), 1,2,7,8-TCDF, and 2,3,7-trichlorodibenzo-p-dioxin (TrCDD) resulted in the structure-dependent induction of aryl hydrocarbon hydroxylase and ethoxyresorufin O-deethylase activities. The induction potencies followed the order 2,3,7,8-TCDD greater than 2,3,7,8-TCDF greater than 1,2,3,7,8-PeCDD approximately 1,2,3,7,8-PeCDF greater than 1,2,7,8-TCDF greater than 2,3,7-TrCDD and were comparable to structure-toxicity relationships which have previously been reported. In contrast, many of the properties of these compounds were structure-independent. For example, using tritiated congeners of high specific activity (greater than 30 Ci/mmol) the sedimentation coefficients (S) for the nuclear and cytosolic aryl hydrocarbon (Ah) receptor complexes were 5-6 and 9-10 S, respectively, for all the radioligands. Moreover, examination of the processing of nuclear Ah receptor complexes for the radiolabeled congeners showed that after 6 h, the rates of nuclear processing were very low and varied between 0.006 and 0.0385 fmol degraded/mg protein/mg total DNA. These results were consistent with the reported stability and persistence of the nuclear Ah receptor complexes and in addition, there were no apparent structure-dependent differences in the processing rates. Inspection of the nuclear receptor levels and the corresponding induced enzyme activities for the congeners showed that there was a linear correlation between average nuclear receptor complex levels (18-42 h) and induced enzyme activities (32-42 h) for all six radioligands; these data indicated that the rates of cytochrome P450-dependent gene expression correlated with the levels of nuclear Ah receptor complex. In contrast, the accumulation of occupied nuclear receptor complexes in rat hepatoma H-4-IIE cells was structure-dependent and appeared to be one of the factors which governed the observed structure-induction and the previously reported structure-toxicity relationships for 2,3,7,8-TCDD and related halogenated aryl hydrocarbons.

• Authors: T Zacharewski, M Harris, S Safe
• Journal: Archives of biochemistry and biophysics (Arch Biochem Biophys) Vol. 272 Issue 2 Pg. 344-55 (Aug 01 1989) ISSN: 0003-9861 [Print] United States
• PMID: 2546497 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Dioxins
• Polychlorinated Dibenzodioxins
• Receptors, Aryl Hydrocarbon
• Receptors, Drug
• Cytochrome P-450 Enzyme System
• Mixed Function Oxygenases
• Oxidoreductases
• Aryl Hydrocarbon Hydroxylases
• Cytochrome P-450 CYP1A1

Topics

• Animals
• Aryl Hydrocarbon Hydroxylases (biosynthesis)
• Cell Nucleus (metabolism)
• Cytochrome P-450 CYP1A1
• Cytochrome P-450 Enzyme System (biosynthesis)
• Cytosol (metabolism)
• Dioxins (pharmacology)
• Dose-Response Relationship, Drug
• Enzyme Induction (drug effects)
• Gene Expression Regulation (drug effects)
• Liver Neoplasms, Experimental (enzymology)
• Mixed Function Oxygenases (biosynthesis)
• Oxidoreductases (biosynthesis)
• Polychlorinated Dibenzodioxins (analogs & derivatives, pharmacology)
• Rats
• Receptors, Aryl Hydrocarbon
• Receptors, Drug (metabolism)
• Structure-Activity Relationship