Pharmacokinetics of the soybean isoflavone daidzein in its aglycone and glucoside form: a randomized, double-blind, crossover study.
BACKGROUND
There are conflicting results in the literature on the bioavailability of isoflavones in the aglycone and the glucoside forms.


OBJECTIVE
The objective was to investigate the pharmacokinetics of the soy isoflavone daidzein (DAI) on oral administration of both the aglycone and glucoside form in a human intervention study. In addition, the pharmacokinetics of the bacterial and oxidative metabolites of DAI was assessed.


METHODS
Seven German men aged 22-30 y participated in a randomized, double-blind study in a crossover design. After ingestion of pure DAI or pure daidzein-7-O-beta-d-glucoside (DG) (1 mg DAI aglycone equivalent/kg body weight), blood samples were drawn before isoflavone administration and 1, 2, 3, 4.5, 6, 8, 10, 12, 24, and 48 h after the dose. Urine was collected before and 0-6, 6-12, and 12-24 h after the intake of the isoflavones. The concentrations of DAI and its major bacterial and oxidative metabolites in plasma and urine were measured with isotope dilution capillary gas chromatography-mass spectrometry.


RESULTS
The systemic bioavailability (area under the curve; AUC(inf)), the maximal plasma concentration (C(max)), and the cumulative recovery of DAI in urine after administration of DG were 3-6 times greater than after the ingestion of DAI. Except for equol, which was formed by only one volunteer, all other quantified metabolites exhibited 2-12 times greater AUC(inf), C(max), and urinary recoveries after consumption of DG.


CONCLUSIONS
Our results show that DG exhibits a greater bioavailability than its aglycone when ingested in an isolated form.
Rüfer
Corinna E
CE
Department of Physiology and Biochemistry of Nutrition, Max Rubner-Institute, Karlsruhe, Germany.
Bub
Achim
A
Möseneder
Jutta
J
Winterhalter
Peter
P
Stürtz
Melanie
M
Kulling
Sabine E
SE
D000284:Administration, Oral; D000328:Adult; D019540:Area Under Curve; D001682:Biological Availability; D018592:Cross-Over Studies; D004311:Double-Blind Method; D060754:Equol; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects; D007529:Isoflavones / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics* / Q000652:urine; D008297:Male; D013025:Glycine max / Q000737:chemistry*
C007610:4',7-dihydroxy-3,4-dihydroisoflavone; D007529:Isoflavones; D060754:Equol; C004742:daidzein