Hepatic zonation of the induction of cytochrome P450 IVA, peroxisomal lipid β-oxidation enzymes and peroxisome proliferation in rats treated with dehydroepiandrosterone (DHEA). Evidence of distinct zonal and sex-specific differences

3To whom correspondence should be addressed Dehydroepiandrosterone (DHEA*) is produced in the adrenal Dehydroepiandrosterone (DHEA) is an intermediate prodcortex of many mammals including humans as an intermediate uct in the synthesis of male and female sex hormones in in the pathway for synthesis of male and female sex hormones. the adrenal cortex of man. In livers of rats and mice Although it is found at high concentrations in the human DHEA increases the levels of cytochrome P450 IVA and plasma its physiological role is not yet exactly known. DHEA peroxisomal β-oxidation enzymes associated with peroxiexhibits several beneficial effects in rodents such as antisome proliferation. Prolonged treatment of rats with DHEA diabetic and anti-obesity effects (1), and, particularly it posinduces liver tumors that are more frequent in females sesses anti-tumor properties under some experimental condiarising mainly in the periportal regions of the liver lobule tions (2–6). In contrast, long-term treatment with high doses (Metzger et al., Toxicol. Pathol. 23, 591–605, 1995). Because of DHEA leads to hepatocellular carcinomas in rats and mice of paucity of information on hepatic zonation of peroxiso(7–10). mal response to DHEA and controversial reports on genderIn rat liver DHEA induces, similar to different peroxisome specific differences of its effects the present study was proliferating drugs, significant increase of cytochrome P450 undertaken using qualitative immunohistochemical and IVA (11–13) and peroxisome proliferation associated with quantitative immunoelectron microscopical techniques in marked induction of the enzymes of the peroxisomal βaddition to Western blotting. Rats were treated for 24 oxidation (11,12,14–18). For many peroxisome proliferating weeks with 0.6% DHEA supplied with diet. Immunoblot agents it has been shown that both effects are mediated by analysis revealed marked induction of peroxisomal βthe peroxisome proliferator activated receptors (PPARs) (19). oxidation enzymes, which by quantitative analysis was Although DHEA does not activate in in vitro assay the PPAR equally strong in male and female animals, whilst catalase (19–21), recent studies have revealed that the peroxisome and urate-oxidase were not increased. Cytochrome P450 induction by DHEA is completely abolished in knock-out mice IVA, in contrast, was induced significantly stronger in male with deletion of the PPAR-α gene (22), which indicates the than in female rats. Immunohistochemistry confirmed the involvement of this receptor in the induction process. induction of cytochrome P450 IVA showing a marked In the present study we have re-investigated the effects of lobular gradient in female animals with strong induction DHEA on peroxisomes and cytochrome P450 IVA in rat liver in pericentral and almost no induction in periportal regions with particular attention to two important aspects: the liver of the liver lobule. In male animals cytochrome P450 IVA architecture and the sex specificity. It is well known, that was expressed more uniformly across the liver lobule. A various exogenous and endogenous factors induce a heterosimilar sex specific zone-dependent response was observed geneous peroxisomal response in the different zones of the for peroxisomes. DHEA induced in females a significant liver acinus thus establishing zonal gradients (23–26), and zonal gradient with marked peroxisome proliferation and recently it has been shown that DHEA-induced tumor prea strong induction of peroxisomal hydratase/dehydrogenase stages are localized almost exclusively in periportal regions in pericentral hepatocytes and a much smaller response in of the liver lobule (10). In most previous investigations of periportal regions. Livers of male animals, in contrast, DHEA effects on peroxisomes and cytochrome P450 IVA, showed a uniform peroxisomal proliferation to DHEA with however, the heterogeneity of the liver architecture has received only slight zonal differences. The striking homologies of little attention. the induction patterns of cytochrome P450 IVA and the Moreover, a variety of peroxisome proliferating agents have peroxisome proliferation in both sexes support the notion been reported to act more vigorously in male than in female of a functional relationship. In view of the almost exclusive rats (27–30). Investigations of the gender-specific effects of periportal localization of DHEA-induced tumors in female DHEA on peroxisomal parameters, however, have led to rats in contrast to the pericentral localization of the controversial results ranging from stronger effects in females peroxisomal proliferation shown by this study, it seems (31), or alternatively in males (15), all the way to the statement likely that other factors in addition to peroxisome proliferathat it is equally potent in both sexes and that the peroxisome proliferative effect of DHEA is not influenced by sex hormones