This article is available online at http://dmd.aspetjournals.org ABSTRACT:This study uses stable isotope methodology to evaluate the validity of 6␤-hydroxylation clearance of endogenous cortisol as a new index for in vivo CYP3A phenotyping in humans. Important factors contradictory to the use of a conventional index of urinary ratio of 6␤-hydroxycortisol to cortisol (6␤-OHF/F) to evaluate in vivo CYP3A activity are also discussed. Stable isotopically labeled cortisol (3-5 mg) was orally administered to three healthy adult subjects to accurately determine the fractional metabolic clearance specific for the 6␤-hydroxylation of cortisol. Plasma concentrations of labeled cortisol and urinary excreted amounts of labeled cortisol and 6␤-OHF were analyzed by gas chromatography-mass spectrometry simultaneously with their endogenous counterparts. There was a good correlation between endogenous and exogenous 6␤-hydroxylation clearances in the three subjects tested (r ‫؍‬

ABSTRACT:The roles of isoflavones in the prevention of several hormonedependent cancers and osteoporosis are of great interest. Despite many pharmacokinetics studies of the isoflavones, the actual types of conjugates circulating in the body and the position(s) of conjugation sites on the flavone skeleton are still uncertain because, in general, conjugated compounds in biological fluids have been evaluated by measuring the free aglycones obtained after selective enzymatic hydrolysis. Using an high-performance (HPLC)-UV-diode-array detector (DAD) method combined with solid-phase extraction, we have obtained HPLC profiles of isoflavone glycosides [daidzin (Din) and genistin (Gin)] and of intact isoflavone metabolites in human plasma: daidzein, genistein, daizein-7-glucuronide, daidzein-4-glucuronide, genistein-7-glucuronide, genistein-4-glucuronide, daidzein-7-sulfate, daidzein-4-sulfate, genistein-7-sulfate, and genistein-4-sulfate. We investigated the plasma profile of intact isoflavone metabolites in plasma obtained 1 to-7 h after orally administration of 50 g of kinako (baked soybean powder) to two healthy volunteers. The results of DAD analysis indicated that the main isoflavone metabolite peaks were identified on the HPLC chromatogram. Furthermore, the intact glycosides Din and Gin were detected in 1-h plasma samples by their positive electrospray ionization mass spectra, demonstrating that the glycosides Din and Gin can be absorbed from the gut.

Much attention has been paid to the metabolism and disposition of isoflavones daidzein (Dein) and genistein (Gein) with regard to the prevention of several hormone-dependent diseases. Recent studies have reported that several conjugates as well as aglycones may be biologically active or may be activated within target cells. However, the disposition of Dein and Gein in plasma is still uncertain. This paper describes the identification and quantification of the highly polar metabolites, daidzein-7-glucuronide-4'-sulfate (D-7G-4'S), genistein-7-glucuronide-4'-sulfate (G-7G-4'S), daidzein-4',7-diglucuronide (D-4',7-diG), and genistein-4',7-diglucuronide (G-4',7-diG) in human plasma after dietary administration of kinako (baked soybean powder) to two healthy volunteers. The structure identification of these conjugated metabolites in plasma was performed in comparison to the LC-ESI-MS and 600 MHz (1)H-NMR spectral data of the chemically synthesized compounds. Furthermore, 16 isoflavone metabolites including D-7G-4'S, G-7G-4'S, D-4',7-diG, and G-4',7-diG in plasma were simultaneously measured by a high-performance liquid chromatography-UV-diode-array detector method combined with solid-phase extraction using an Oasis HLB cartridge. D-7G-4'S, G-7G-4'S and G-4',7-diG were found to be major metabolites of Dein and Gein in plasma, while intact aglycones were detected to be only ca. 2% in both subjects. The findings suggest that the conjugated metabolites could be the key compounds responsible for pharmacological and medicinal properties of isoflavones.

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This study was designed to evaluate the in vivo activity of cytochrome P450 3A (CYP3A) in 49 healthy Japanese subjects aged 22-58 years using endogenous cortisol 6b-hydroxylation clearance [CLm(6b)], a novel biomarker for CYP3A phenotyping. CLm(6b) in the 49 healthy subjects was 2.40 6 0.79 ml/min with an approximately 4-fold interindividual variability of CYP3A activity. The mean clearance in the 24 women was 2.50 6 0.89 ml/min; the value in the women was higher than in the 25 men (2.30 6 0.69 ml/min) by approximately 9%. We also measured the change of CLm(6b) in 14 healthy subjects in the morning at 10:00-12:00 every 2 or 3 days over a period of 36-53 days and observed a 1.5-fold to 3.4-fold dayto-day intraindividual variability in the CYP3A activity. The mean value for CLm(6b) in each subject for 36-53 days was 2.54 6 0.76 ml/min (n = 14). We also evaluated the CLm(6b) every 2 hours from 8:00-20:00 in 26 healthy subjects. The within-day intraindividual clearance variability was 1.1-fold to 2.5-fold (2.45 6 0.91 ml/min, n = 26). No characteristic diurnal rhythms were observed in the in vivo activity of CYP3A.

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