Induction of peroxisomal enzymes by dehydroepiandrosterone: metabolic activation by sulfate conjugation

Effects of Dehydroepiandrosterone (DHEA) on Hepatic Lipid Metabolism Parameters and Lipogenic Gene mRNA Expression in Broiler Chickens

The aim of the present study was to identify the effects of dehydroepiandrosterone (DHEA) on hepatic lipid metabolism parameters and lipogenic gene mRNA expression in broiler chickens. A total of 72 1-day-old broiler chicks received a common basal diet with DHEA added at either 0 (control), 5 or 20 mg/kg feed. In the present study, the hepatic triglyceride (TG) concentration was significantly lower in male and female broilers that had bed administered DHEA than in control birds. In contrast, DHEA administration caused a marked rise in the hepatic non-esterified fatty acid (NEFA) concentration in both male and female broilers and also increased lipase (HL) activity in male broilers, while in female birds, no significant differences were observed in HL activity. The expression of peroxisome proliferators-activated receptor alpha (PPARalpha) and carnitine palmitoyl transferase I (CPTI) mRNA was decidedly enhanced following treatment with DHEA, and a similar tendency was also observed in the expression of acyl-Coenzyme A oxidase 1 (ACOX1). However, no significant differences were observed in the expression of either sterol regulatory element binding protein-1c (SREBP-1c) or acetyl CoA carboxylase (ACC) mRNA, except for a decline in the expression of ACC in females treated with 5 mg DHEA/kg. Numerous peroxisomes without a core and an increased number of peroxisomes were evident during morphological observations of broiler livers, in animals that had been treated with DHEA. Overall, the results of the present study indicated that DHEA accelerated lipid catabolism by direct regulation of hepatic lipid metabolism and by induction of relevant gene expression.

HEPATOCARCINOGENESIS BY PEROXISOME PROLIFERATORS

It is well known that various kinds of hypolipidemic drugs induce marked changes in the livers of rats and mice. The initial hepatic responses in rodents are marked hepatomegaly, proliferation of peroxisomes in association with changes in peroxisome structure and enzyme composition. Furthermore, since many of hypolipidemic peroxisome proliferators induce hepatocellular carcinomas in both rats and mice, the relationship between peroxisome proliferation and hepatocarcinogenicity of these drugs has become extremely important. However, it has not yet been established whether there are any direct relationships among pharmacological action, peroxisome proliferation and carcinogenicity of these drugs. In order to clarify this task, we have studied the involvement of HGF in hepatocarcinogenesis caused by peroxisome proliferators. After male F-344 rats were orally given Wy-14,643, hepatocarcinomas and (pre) neoplastic nodules were observed in the livers. At that time, the content of HGF and the expression of HGF mRNA were significantly decreased in the liver tumors. These findings may indicate that decreases in hepatic HGF levels are specific events induced by peroxisome proliferators but not by genotoxic carcinogenesis, and that those changes play an important role in the promotion of neoplastic or preneoplastic cell growth induced by peroxisome proliferators. Decrease in HGF induced by peroxisome proliferators such as Wy-14,643 would inhibit the growth of normal hepatocytes and then lend an advantageous circumstance for the selective growth of neoplastic or preneoplastic cells, resulting in the development of growth of tumors.