We investigated the effect of the steroid hormone dehydroepiandrosterone (DHEA) on the hepatic expression and activity of carcinogen-activating enzymes, the cytochromes P450 (CYP) 1A1, 1A2 and 1B1, in Sprague-Dawley rats. In animals fed DHEA at 200 or 400 mg/kg body weight every other day for 2 weeks prior to exposure to the aryl hydrocarbon dimethylbenz[a]anthracene (DMBA, 5 mg/kg), there was a dose-dependent decrease in hepatic CYP activity, as measured by ethoxyresorufin-O (EROD) assay, from 37.1 to 22.9 and 14.7 pmoles/min/10 g microsomes, respectively. DHEA did not directly inhibit microsomal EROD activity, however, leading us to investigate its effects on enzyme expression. To test this, we examined protein and mRNA levels of the enzymes. Western blot for CYP1A1 and CYP1A2 showed that DHEA inhibited the increase in hepatic CYP1A1 and CYP1A2 enzyme levels that are normally induced by DMBA. DMBA-induced increase in expression of CYP1A1, CYP1A2 and CYP1B1 mRNA was similarly blunted in DHEAtreated animals. DHEA was also able to significantly reduce the basal expression of CYP1A1 and CYP1A2 but not of CYP1B1. These results indicate that DHEA regulates the expression and, hence, the activity of hepatic carcinogenactivating enzymes in vivo, and this may be an important mechanism of its chemopreventive activity. Dehydroepiandrosterone (DHEA) is an adrenocortical steroid of unknown physiologic function. Along with its sulfated conjugate, DHEA is the most abundant steroid in humans, with circulating levels in young adults of 5-7 M. 1 DHEA levels decline with age, and reports have suggested that there is an inverse relation between DHEA levels and the risk of cancer. 2,3 Because of this, it has been extensively investigated for possible chemopreventive activity. DHEA has been shown to inhibit dimethylbenz[a]anthracene (DMBA)-induced carcinogenesis in rats. 4,5 DMBA is a model polycyclic aromatic hydrocarbon (PAH), a class of environmental compounds that are thought to cause cancer in humans. PAHs are procarcinogens that must be activated by certain CYP enzymes. This activation generates metabolites that are highly electrophilic and carcinogenic, capable of covalently binding DNA and introducing mutations. 6 DHEA has been shown to inhibit DMBA activation 7-9 and to reduce the binding of DMBA metabolites with DNA. 10,11 The activation of DMBA is carried out by members of the cytochrome P450 (CYP) 1A and 1B subfamilies of CYP. We have therefore examined the effect of DHEA on the expression and activity of CYP1A1, CYP1A2 and CYP1B1, the major hepatic carcinogen-activating enzymes. We report that DHEA supplementation significantly reduces the expression and therefore the activity of these enzymes in rats.
MATERIAL AND METHODS
MaterialsFemale Sprague-Dawley rats were purchased from Charles River Laboratories (Wilmington, MA). Omniscript reverse transcription kit was from Qiagen (Valencia, CA). Tris/borate/EDTA gels, sodium dodecyl sulfate-polyacrylamide gels, running and sample buffers were from Novex (San Diego, CA). [ 32...
