Toxicological Sciences, Vol 51, 224-235, Copyright © 1999 by Society of Toxicology
J Chen, Y Li, JA Lavigne, MA Trush and JD Yager
Ethinyl estradiol (EE) is a strong promoter of hepatocarcinogenesis.
Treatment of rats with EE and other hepatic promoters induces a
mitosuppressed state characterized by decreased hepatocyte turnover and
reduced growth responsiveness. Previously, we identified several nuclear
and mitochondrial genome-encoded mitochondrial genes whose transcripts were
increased during EE-induced hepatic mitosuppression in rats and in
EE-treated HepG2 cells (Chen et al. Carcinogenesis, 17, 2783-2786, 1996 and
Carcinogenesis, 19, 101-107, 1998). In both cultured rat hepatocytes and
HepG2 cells, EE increased respiratory chain activity (reflected by
increased mitochondrial superoxide production detected as increased
lucigenin-derived chemiluminescence (LDCL). In this paper, we provide
additional characterizations of these effects. Increased LDCL was detected
in mitochondria isolated from EE- treated rats, documenting that these
estrogen effects on mitochondrial function are not confined to cells in
culture. EE and estradiol (E2) increased LDCL in cultured rat hepatocytes
and HepG2 cells in a dose- (beginning at 0.25 microM levels) and
time-dependent response. Inhibition of P450-mediated estrogen metabolism
inhibited, while direct exposure to E2 catechol metabolites enhanced LDCL.
Co-treatment with glutathione ester or with the specific antiestrogen, ICI
182708 inhibited LDCL. In contrast, estrogen-induced LDCL was enhanced by
glutathione depletion, and by inhibition of catechol-o- methyltransferase.
These results support a working hypothesis that in liver cells, increased
respiratory chain activity induced by estrogen treatment requires both
metabolism to catechols and an estrogen receptor-mediated signal
transduction pathway.
ARTICLES
Increased mitochondrial superoxide production in rat liver mitochondria, rat hepatocytes, and HepG2 cells following ethinyl estradiol treatment
Department of Environmental Health Sciences, Johns Hopkins School of Hygiene and Public Health, Baltimore, Maryland 21205-2179, USA.
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