Dehydroepiandrosterone (DHEA) is a naturally occurring C19-steroid that is found in the peripheral circulation of mammals, including humans. The feeding of DHEA to rodents has been shown to inhibit chemical carcinogenesis in colon, liver, and lung. Therefore, the effect of DHEA on hepatic enzyme activities that are associated with carcinogen metabolism was assessed. Microsomal NADPH-cytochrome P-450 reductase activity and the content of cytochrome b5 were induced 1.8- and 1.4-fold, respectively, upon feeding male Sprague-Dawley rats a synthetic diet containing 0.45% DHEA (w/w). No significant changes in total content of microsomal cytochrome P-450 or the activities of microsomal NADH-cytochrome b5 reductase and cytosolic or microsomal NAD(P)H-quinone oxidoreductase were noted at day 7 of feeding. Cytosolic glutathione S-transferase activity was decreased to 68% of control activity. Administration of DHEA p.o. or by i.p. injection for 5 days led to the same extent of induction of NADPH-cytochrome P-450 reductase activity. Maximal induction of this flavoprotein reductase was noted between days 3 and 4 of feeding or at a dose of 80–120 mg/kg i.p. A small but statistically significant increase in total microsomal cytochrome P-450 was observed after DHEA administration i.p.

Rats fed DHEA had a slower growth rate compared with rats fed control diet, whereas rats treated with DHEA i.p. had growth rates identical to those of controls. The liver weights of rats given DHEA by p.o. or i.p. routes were increased significantly compared to those of control rats. Pair feeding of rats with DHA-containing or control diets served to demonstrate that the levels of induction of hepatic microsomal NADPH-cytochrome P-450 reductase and at least one form of cytochrome P450 (P-450IVA1) were the same as those seen in livers of rats fed DHEA ad libitum. This finding suggested that the induction of the flavoprotein and at least one form of the cytochrome was not due to caloric restriction.

The increase in NADPH-cytochrome P-450 reductase content of liver microsomes prepared from rats either fed or treated i.p. with DHEA was also observed by Western blotting techniques. DHEA did not appear to induce any of the major forms of rat liver microsomal cytochrome P-450 that are normally increased by either phenobarbital, β-naphthoflavone, or dexamethasone pretreatment of rats in vivo. However, the measurement of androstenedione and testosterone metabolism in vitro showed pronounced decreases in the 16α-hydroxylase activities of liver microsomes following DHEA feeding. In contrast, the 16β-hydroxylase activities increased approximately 6-fold. A significant 17-fold increase in laurate 12-hydroxylase activity was observed with a concomitant increase in the level of cytochrome P-450IVA1 as determined by Western immunoblotting techniques. Maximal induction of cytochrome P450IVA1 by DHEA feeding was observed at 3–4 days or at a dose of 160 mg/kg DHEA i.p. The activities of catalase and KCN_insensitive palmitoyl-CoA oxidase in homogenates of rat liver were also increased 1.9- and 9.3-fold, respectively, by p.o. DHEA administration. These findings suggest that treatment of rats with DHEA by p.o. or i.p. administration causes an increase in specific enzymes that are characteristically associated with peroxisome proliferation.

1

Supported in part by USPHS Grants CA43311 (L. M., R. A. P.) and GM16488 (R. W. E.) and by Robert A. Welch Foundation Grant I-959 (R. W. E.).

This content is only available via PDF.