Carcinogenesis, Vol 18, 1491-1498, Copyright © 1997 by Oxford University Press
K Beier, A Volkl, C Metzger, D Mayer, P Bannasch and HD Fahimi
Dehydroepiandrosterone (DHEA) is an intermediate product in the synthesis
of male and female sex hormones in the adrenal cortex of man. In livers of
rats and mice DHEA increases the levels of cytochrome P450 IVA and
peroxisomal beta-oxidation enzymes associated with peroxisome
proliferation. Prolonged treatment of rats with DHEA induces liver tumors
that are more frequent in females arising mainly in the periportal regions
of the liver lobule (Metzger et al., Toxicol. Pathol. 23, 591-605, 1995).
Because of paucity of information on hepatic zonation of peroxisomal
response to DHEA and controversial reports on gender-specific differences
of its effects the present study was undertaken using qualitative
immunohistochemical and quantitative immunoelectron microscopical
techniques in addition to Western blotting. Rats were treated for 24 weeks
with 0.6% DHEA supplied with diet. Immunoblot analysis revealed marked
induction of peroxisomal beta- oxidation enzymes, which by quantitative
analysis was equally strong in male and female animals, whilst catalase and
urate-oxidase were not increased. Cytochrome P450 IVA, in contrast, was
induced significantly stronger in male than in female rats.
Immunohistochemistry confirmed the induction of cytochrome P450 IVA showing
a marked lobular gradient in female animals with strong induction in
pericentral and almost no induction in periportal regions of the liver
lobule. In male animals cytochrome P450 IVA was expressed more uniformly
across the liver lobule. A similar sex specific zone-dependent response was
observed for peroxisomes. DHEA induced in females a significant zonal
gradient with marked peroxisome proliferation and a strong induction of
peroxisomal hydratase/dehydrogenase in pericentral hepatocytes and a much
smaller response in periportal regions. Livers of male animals, in
contrast, showed a uniform peroxisomal proliferation to DHEA with only
slight zonal differences. The striking homologies of the induction patterns
of cytochrome P450 IVA and the peroxisome proliferation in both sexes
support the notion of a functional relationship. In view of the almost
exclusive periportal localization of DHEA-induced tumors in female rats in
contrast to the pericentral localization of the peroxisomal proliferation
shown by this study, it seems likely that other factors in addition to
peroxisome proliferation may contribute to the hepatocarcinogenic effect of
DHEA.
ARTICLES
Hepatic zonation of the induction of cytochrome P450 IVA, peroxisomal lipid beta-oxidation enzymes and peroxisome proliferation in rats treated with dehydroepiandrosterone (DHEA). Evidence of distinct zonal and sex-specific differences
Institut fur Anatomie und Zellbiologie II, Heidelberg, Germany.
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