Date on Master's Thesis/Doctoral Dissertation

5-2004

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biochemistry and Molecular Biology

Committee Chair

Prough, Russell A.

Author's Keywords

Pure sciences; Dehydroepiandrosterone; Adrenal steroid; Cytochrome P450; PPAR

Subject

Dehydroepiandrosterone--Physiological effect

Abstract

Dehydroepiandrosterone (DHEA) is a C-19 adrenal steroid and the most abundant circulating hormone in humans. Since circulating levels decline in late adulthood, treatment of humans with DHEA has been suggested to have beneficial health effects. Although the mechanism of action is unknown, DHEA may be metabolized to active metabolites that exert their physiological effects by receptor-mediated processes and cell signaling pathways. The purpose of this study was to investigate the mechanistic processes of DHEA action. Since DHEA may exert its pleotropic effects by being metabolized to biologically active species, a GC/MS method was developed to quantify the liver microsomal metabolism of DHEA of various species and identify the P450 enzymes responsible for metabolism. 16alpha-hydroxy-DHEA and 7alpha-hydroxy-DHEA were formed in rat, hamster, pig and human. CYP3A4 and CYP3A5 formed 7alpha-hydroxy-DHEA, 16alpha-hydroxy-DHEA, and the unique human metabolite, 7beta-hydroxy-DHEA, while the fetal enzyme CYP3A7 formed only 16alpha-hydroxy and 7beta-hydroxy-DHEA. By using this method to examine the metabolite profiles of various P450s, the developmental expression patterns of the human cytochrome P4503A forms could be classified and therefore have significant clinical relevance. Nuclear receptors transduce the effects of hormones into transcriptional responses. DHEA and metabolites were screened in a cell-based assay to determine the interaction with estrogen receptors alpha and beta (ERalpha and ERbeta). DHEA, DHEA-S, and androstendiol activated ERalpha, while DHEA, 7-oxo-DHEA, androstenedione and androstenediol activated ERbeta demonstrating ER is activated directly by DHEA and some metabolites. These and other studies from our laboratory demonstrate that DHEA is metabolized into various monohydroxylated metabolites. DHEA and metabolites directly activate ER as well as the pregnane X receptor (PXR). Additionally, DHEA has been shown to activate another nuclear receptor, peroxisome proliferator activated receptor alpha (PPARalpha) "in vivo." This research suggests that DHEA action is mediated by multiple receptors and metabolites with various biological activities, comprising of a complex mode of action of DHEA.

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