Characterizations of mouse hepatic microsomal monooxygenase catalyzing 11beta-hydroxylation of osaterone acetate

CHARACTERIZATION OF TESTOSTERONE 11β-HYDROXYLATION CATALYZED BY HUMAN LIVER MICROSOMAL CYTOCHROMES P450

A combination of accelerator mass spectrometry (AMS) and liquid chromatography-tandem mass spectrometry has been used to clarify some new aspects of testosterone metabolism. The main pathway of testosterone oxidative metabolism by human liver microsomes is the formation of 1beta-, 2alpha-/beta-, 6beta-, 15beta-, and 16beta-hydroxytestosterones, mainly catalyzed by cytochromes P450 2C9, 2C19, and 3A4. We now report the first determination that 11beta-hydroxytestosterone (11beta-OHT) can also be formed by human liver microsomal fractions. The structures of five hydroxylated metabolites of testosterone (2beta-, 6beta-, 11beta-, 15beta-, and 16beta-OHT) and the C-17 oxidative metabolite androstenedione were determined by liquid chromatography with UV detection at 240 nm and liquid chromatography-tandem mass spectrometry. Corresponding results were obtained by high-performance liquid chromatography-AMS analysis of incubations of [4-14C]testosterone with human liver microsomes. 6beta-Hydroxylation was always the dominant metabolic pathway, but 2beta-, 15beta-, and 16beta-OHT, and androstenedione were also formed. The previously undetected hydroxytestosterone, 11beta-OHT, was found to be a minor metabolite formed by human liver microsomal enzymes. It was formed more readily by CYP3A4 than by either CYP2C9 or CYP2C19. 11beta-Hydroxylation was inhibited by ketoconazole (IC50 = 30 nM) at concentrations similar to the IC50 (36 nM) for 6beta-hydroxylation Therefore, CYP3A4 could be mainly responsible for testosterone 11beta-hydroxylation in the human liver. These findings identify human hepatic biotransformation of testosterone to 11beta-OHT as a previously unrecognized extra-adrenal metabolic pathway.

Oxidative one-carbon cleavage of the octyl side chain of olanexidine, a novel antimicrobial agent, in dog liver microsomes

1. The oxidative one-carbon cleavage reaction in the octyl side chain of olanexidine [1-(3,4-dichlorobenzyl)-5-octylbiguanide], a new potent biguanide antiseptic, was characterized in dog liver microsomes. 2. Olanexidine was initially biotransformed to a monohydroxylated metabolite, 8-[5-(3,4-dichlorobenzyl)-1-biguanidino]-2-octanol (DM-215), and DM-215 was subsequently oxidized to the diol derivative, 8-[5-(3,4-dichlorobenzyl)-1-biguanidino]-1,2-octandiol (DM-220). DM-220 was further biotransformed to 2-hydroxy aldehyde derivative, 2-hydroxy carboxylic acid derivative, and an oxidative C-1-C-2 bond cleavage metabolite, 7-[5-(3,4-dichlorobenzyl)-1-biguanidino] heptanoic acid [DM-223 (C7), a seven-carbon chain derivative], after incubation with dog liver microsomes. 3. DM-223 formation required NADPH as a cofactor and was inhibited by quinidine and quinine, relatively selective inhibitors of CYP2D subfamilies in dogs. 4. The results suggest that the one-carbon fragment of the octyl side chain of olanexidine could be removed by the oxidative C-C bond cleavage with the possible involvement of cytochrome P450 systems such as CYP2D subfamily. This oxidative C-C bond cleavage reaction by cytochrome P450s could play an important role in the removal of one-carbon fragment of other drugs or endogenous compounds containing aliphatic chains.