Neurosteroids: Metabolism in human intestine microsomes

Abstract

Both dehydroepiandrosterone (DHEA) and epiandrosterone (EpiA) are substrate for cytochrome P450 species and enzymes that produce 7α- and 7β-hydroxylated metabolites in the brain and other organs. In contrast to DHEA and EpiA, the 7-hydroxylated derivatives were shown to mediate neuroprotection, and 7β-hydroxy-EpiA was the most potent. The suggested use of any of these steroids as drugs administered per os for neuroprotection requires the assessment of their metabolism in the human intestine and liver. To achieve this, we produced radio-labeled 7α-hydroxy-DHEA, 7β-hydroxy-DHEA, 7α-hydroxy-EpiA and 7β-hydroxy-EpiA that were used as substrates in incubations with human intestine microsomes supplemented with reduced or oxidized cofactors. Identity of the radio-labeled metabolites obtained was determined by gas chromatography/mass spectrometry after comparison with authentic steroid references. The proportions of metabolites produced resulted from their radioactivity contents. The only metabolite obtained with DHEA, EpiA, 7α-hydroxy-DHEA and 7β-hydroxy-DHEA substrates was its 17β-reduced derivative, thus inferring the presence of 17β-hydroxysteroid oxidoreductases in the human intestine microsomes. In addition to the 7α-hydroxy-EpiA and 7β-hydroxy-EpiA substrates, their 17β-reduced metabolites were obtained with 7β-hydroxy-EpiA and 7α-hydroxy-EpiA, respectively. The identity of the enzyme responsible for the 7α-hydroxy-EpiA/7β-hydroxy-EpiA inter-conversion is unknown. The incubation conditions used produced these metabolites in low but significant yields that suggest their presence in the portal blood before access to the liver.