ToxSci Advance Access originally published online on July 11, 2003
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Toxicological Sciences 75, 271-278 (2003)
Copyright © 2003 by the Society of Toxicology
CARCINOGENICITY |
Enhanced Mitochondrial Gene Transcript, ATP, Bcl-2 Protein Levels, and Altered Glutathione Distribution in Ethinyl Estradiol-Treated Cultured Female Rat Hepatocytes
* Department of Environmental Health Sciences, Division of Toxicological Sciences, The Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205–2179; and
Electron and Confocal Microscopy Laboratory, Department of Physiology, The Johns Hopkins School of Medicine, 625 North Wolfe Street, Baltimore, Maryland 21205
Ethinyl estradiol (EE) is a strong promoter and weak hepatocarcinogen in rats. Previously, we demonstrated that EE enhanced the transcript levels of nuclear genome- and mitochondrial genome-encoded genes and respiratory chain activity in female rat liver, and also inhibited transforming growth factor beta (TGFß)-induced apoptosis in cultured liver slices and hepatocytes from female rats. In this study, using cultured female rat hepatocytes, we observed that EE, within 24 h, increased the transcript levels of the mitochondrial genome-encoded genes cytochrome oxidase subunits I, II, and III. This effect was accompanied by increased mitochondrial respiratory chain activity, as reflected by increased mitochondrial superoxide generation, and detected by lucigenin-derived chemiluminescence and cellular ATP levels. EE also enhanced the levels of Bcl-2 protein. Biochemical analyses indicated that EE significantly increased both the levels of glutathione (reduced [GSH] and oxidized [GSSG] forms) per mg protein in mitochondria and nuclei, while the percentage of total glutathione in the oxidized form was not affected. This finding was supported by confocal microscopy. These effects caused by EE may contribute, at least in part, to the EE-mediated inhibition of hepatic apoptosis.
Key Words: ethinyl estradiol; rat hepatocytes; glutathione; mitochondria; apoptosis.
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