Selenium has been of interest primarily as a result of its cytotoxic effects. However, selenium has also been demonstrated to be an essential trace nutrient. Selenium deficiency has been shown to influence the hepatic metabolism and toxicity of a number of xenobiotics, and the inducibility of microsomal cytochromes P-450. Cytochrome P-450 refers to a family of liver microsomal hemoproteins that catalyze the oxidative metabolism of a wide array of endogenous and exogenous compounds. The goal of this proposal is to define and fully characterize the effects of selenium on the regulation of the induction of cytochromes P-450 by phenobarbital. To achieve this goal, studies with selenium deficient rats will be paralleled by studies utilizing the novel in vitro model system of primary monolayer cultures of adult rat hepatocytes. In hepatocyte culture, the time course and magnitude of selenium loss and repletion will be determined. These results will provide a foundation for the examination of the effects of selenium on the in vitro synthesis and degradation of the phenobarbital induced forms of cytochrome P-450 as determined by specific immunoprecipitation and immunoblot analyses. In hepatocyte culture, the effect of selenium on the expression of the genes for the phenobarbital forms of cytochrome P-450 will be examined by quantitating the level of mRNA directing the synthesis of the phenobarbital forms of cytochrome P-450. Selenium deficiency in vivo has also increased both heme synthesis and degradation. These effects can be reversed upon selenium repletion. This observation will be examined in hepatocyte culture by determining the effect of selenium concentration on the activities of Delta-amino-levulinic acid synthetase and microsomal heme oxygenase. Finally, the role of selenium in the regulation of the selenoenzyme glutathionine-peroxidase will be systematically examined in hepatocyte culture. It is anticipated that the proposed studies will demonstrate primary monolayer cultures of adult rat hepatocytes to be an excellent model system for determining the effect of trace element deficiencies and also provide new information on the induction of cytochromes P-450 by phenobarbital.

Agency
National Institute of Health (NIH)
Institute
National Institute of Environmental Health Sciences (NIEHS)
Type
Research Project (R01)
Project #
1R01ES003699-01
Application #
3251265
Study Section
Pharmacology A Study Section (PHRA)
Project Start
1985-02-01
Project End
1988-01-31
Budget Start
1985-02-01
Budget End
1986-01-31
Support Year
1
Fiscal Year
1985
Total Cost
Indirect Cost
Name
Virginia Commonwealth University
Department
Type
Overall Medical
DUNS #
City
Richmond
State
VA
Country
United States
Zip Code
23298
Hunt, C M; Watkins, P B; Saenger, P et al. (1992) Heterogeneity of CYP3A isoforms metabolizing erythromycin and cortisol. Clin Pharmacol Ther 51:18-23
Sinclair, P R; Schuetz, E G; Bement, W J et al. (1990) Role of heme in phenobarbital induction of cytochromes P450 and 5-aminolevulinate synthase in cultured rat hepatocytes maintained on an extracellular matrix. Arch Biochem Biophys 282:386-92
Wrighton, S A; Elswick, B (1989) Modulation of the induction of rat hepatic cytochromes P-450 by selenium deficiency. Biochem Pharmacol 38:3767-71
Schuetz, E G; Li, D; Omiecinski, C J et al. (1988) Regulation of gene expression in adult rat hepatocytes cultured on a basement membrane matrix. J Cell Physiol 134:309-23
Hostetler, K A; Wrighton, S A; Kremers, P et al. (1987) Immunochemical evidence for multiple steroid-inducible hepatic cytochromes P-450 in the rat. Biochem J 245:27-33
Wrighton, S A; Campanile, C; Thomas, P E et al. (1986) Identification of a human liver cytochrome P-450 homologous to the major isosafrole-inducible cytochrome P-450 in the rat. Mol Pharmacol 29:405-10
Schuetz, E G; Wrighton, S A; Safe, S H et al. (1986) Regulation of cytochrome P-450p by phenobarbital and phenobarbital-like inducers in adult rat hepatocytes in primary monolayer culture and in vivo. Biochemistry 25:1124-33
Wrighton, S A; Thomas, P E; Molowa, D T et al. (1986) Characterization of ethanol-inducible human liver N-nitrosodimethylamine demethylase. Biochemistry 25:6731-5
Watkins, P B; Wrighton, S A; Schuetz, E G et al. (1986) Macrolide antibiotics inhibit the degradation of the glucocorticoid-responsive cytochrome P-450p in rat hepatocytes in vivo and in primary monolayer culture. J Biol Chem 261:6264-71
Steward, A R; Wrighton, S A; Pasco, D S et al. (1985) Synthesis and degradation of 3-methylcholanthrene-inducible cytochromes P-450 and their mRNAs in primary monolayer cultures of adult rat hepatocytes. Arch Biochem Biophys 241:494-508