Simultaneous determination of glucuronic acid and sulfuric acid conjugated metabolites of daidzein and genistein in human plasma by high-performance liquid chromatography

Identification of the Metabolites of Both Formononetin in Rat Hepatic S9 and Ononin in Rat Urine Samples and Preliminary Network Pharmacology Evaluation of Their Main Metabolites

Astragalus membranaceus is a traditional Chinese medicine derived from the roots of Astragalus membranaceus (Fisch.) Bge., which has the same medicinal and edible uses in China. It is also widely used in daily food, and its pharmacological effects mainly include antioxidant effects, vascular softening effects, etc. Currently, it is increasingly widely used in the prevention of hypertension, cerebral ischemia, and stroke in China. Formononetin and its glucopyranoside (ononin) are both important components of Astragalus membranaceuss and may play important roles in the treatment of cardiovascular diseases (CVDs). This study conducted metabolic studies using formononectin and its glucopyranoside (ononin), including a combination of the in vitro metabolism of Formonetin using rat liver S9 and the in vivo metabolism of ononin administered orally to rats. Five metabolites (Sm2, 7, 9, 10, and 12) were obtained from the solution incubated with formononetin and rat hepatic S9 fraction using chromatographic methods. The structures of the five metabolites were elucidated as (Sm2)6,7,4'-trihydroxy-isoflavonoid; (Sm7)7,4'-dihydroxy-isoflavonoid; (Sm9)7,8,4'-trihydroxy-isoflavonoid; (Sm10)7,8,-dihydroxy-4'-methoxy-isoflavonoid; and (Sm12)6,7-dihydroxy-4'-methoxy- isoflavonoid on the basis of UV, NMR, and MS data. Totally, 14 metabolites were identified via HPLC-DAD-ESI-IT-TOF-MSn analysis, from which the formononetin was incubated with rat hepatic S9 fraction, and the main metabolic pathways were hydroxylation, demethylation, and glycosylation. Then, 21 metabolites were identified via HPLC-DAD-ESI-IT-TOF-MSn analysis from the urine samples from SD rats to which ononin was orally administered, and the main metabolic pathways were glucuronidation, hydroxylation, demethylation, and sulfonation. The main difference between the in vitro metabolism of formononetin and the in vivo metabolism of ononin is that ononin undergoes deglycemic transformation into Formonetin in the rat intestine, while Formonetin is absorbed into the bloodstream for metabolism, and the metabolic products also produce combined metabolites during in vivo metabolism. The six metabolites obtained from the aforementioned separation indicate the primary forms of formononetin metabolism, and due to their higher contents of similar isoflavone metabolites, they are considered the main active compounds that are responsible for pharmacological effects. To investigate the metabolites of the active ingredients of formononetin in the rat liver S9 system, network pharmacology was used to evaluate the cardiovascular disease (CVD) activities of the six primary metabolites that were structurally identified. Additionally, the macromolecular docking results of six main components and two core targets (HSP90AA1 and SRC) related to CVD showed that formononetin and its main metabolites, Sm10 and Sm12, may have roles in CVD treatment due to their strong binding activities with the HSP90AA1 receptor, while the Sm7 metabolite may have a role in CVD treatment due to its strong binding activity with the SRC receptor.

Surface modified Genistein phytosome for Breast Cancer Treatment: In-vitro Appraisal, Pharmacokinetics, and In-vivo Antitumor Efficacy

Based on phytosomes advantages over liposomes, hyaluronic acid (HA) with/out pegylated phospholipid was used to develop surface-modified genistein (Gen) phytosome as Gen pegylated hyaluophytosomes (G-PHA) and Gen hyaluophytosomes (G-HA) as novel delivery systems for breast cancer treatment. In this study, in-vitro characterization of G-HA and G-PHA shows PS 144.2 ±1.266 nm and 220.3 ±2.51 nm, ZP -30.9 ±0.75 and -32.06 ±0.305 respectively. Morphological elucidation shows HA covers the surface of G-HA and the presence of a transparent layer of PEG surrounding G-PHA. In-vitro release shows a significant slow Gen release from G-HA, and G-PHA compared to Gen solution and Gen phytosomes. In-vivo bioavailability data shows improvement in bioavailability for G-HA and G-PHA compared to Gen suspension (AUC_0- T: :3.563 ±0.067, 2.092 ±0.058, 0.374 ±0.085 µg/ml*h respectively). Therapeutic evaluation of the prepared targeted formulations was carried out by subcutaneous injection in an EAC-induced breast cancer model in mice. G-HA and G-PHA show a promising chemotherapeutic effect in terms of lowering the tumor size and tumor biomarkers (CEA: -34.6, -44.7 & CA15.3: -77.8, -81.6 respectively). This reduction in their values compared to Gen phytosomes, Gen suspension, and the control group is attributed to high Gen accumulation at the target organ owing to targeting properties of HA that are used in phytosomal surface modification in G-HA. Additionally, the presence of MPEG₂₀₀₀-DSPE in G-PHA tends to improve interstitium lymphatic drainage following SC administration, resulting in maximizing the therapeutic benefits of breast cancer despite the difference in pharmacokinetics behavior compared to G-HA. These formulations can be further studied for metastatic breast cancer.

Simultaneous determination of daidzein, its prodrug and major conjugative metabolites in rat plasma and application in a pharmacokinetic study

The developed method successfully validated that the synthesized prodrug improved the bioavailability of DAN by reducing its phase II metabolites.

A rapid ultra high performance liquid chromatography-tandem mass spectrometry method for the quantification of daidzein, its valine carbamate prodrug, and glucuronide in rat plasma samples: Comparison of the pharmacokinetic behavior of daidzine valine carbamate prodrugs

Two valine carbamate prodrugs of daidzein were designed to improve its bioavailability. To compare the pharmacokinetic behavior of these prodrugs with different protected phenolic hydroxyl groups of daidzein, a rapid and sensitive method for simultaneous quantification of daidzein, its valine carbamate prodrug, and daidzein-7-O-glucuronide in rat plasma was developed and validated in this study. The samples were processed using a fast one-step protein precipitation method with methanol added to 50 μL of plasma and were analyzed by ultra-high performance liquid chromatography with tandem mass spectrometry. To improve the selectivity, peak shape, and peak elution, several key factors, especially stationary phase and the composition of the mobile phase, were tested, and the analysis was performed using the Kinetex^® C18 column (100 × 2.1 mm, 2.6 μm) within only 2.6 min under optimal conditions. The established method exhibited good linearity over the concentration range of 2.0-1000 ng/mL for daidzein, and 8.0-4000 ng/mL for the prodrug and daidzein-7-O-glucuronide. The accuracy of the quality control samples was between 95.5 and 110.2% with satisfactory intra- and interday precision (relative standard deviation values < 10.85%), respectively. This sensitive, rapid, low-cost, and high-throughput method was successfully applied to compare the pharmacokinetic behavior of different daidzein carbamate prodrugs.

Oral genistein-loaded phytosomes with enhanced hepatic uptake, residence and improved therapeutic efficacy against hepatocellular carcinoma

Genistein (Gen) is one of the most potent soy isoflavones used for hepatocellular carcinoma (HCC) treatment. Low aqueous solubility and first-pass metabolism are the main obstacles resulting in low Gen oral bioavailability. The current study aims to introduce phytosomes as an approach to improve Gen solubility, protect it from metabolism by complexation with phospholipids (PL), and get used to PL in Gen lymphatic delivery. Different forms of PL namely: Lipiod® S100, Phosal® 53 MCT, and Phosal®75 SA were used in phytosomes preparation GP, GPM, and GPL respectively. The effect of formulation components on Gen absorption, metabolism, and liver accumulation was evaluated following oral administration to rats. Cytotoxicity and cellular uptake studies were applied on HepG2 cells and in-vivo anti-tumor studies were applied to the DEN-mice model. Results revealed that GP and GPL remarkably accumulated Gen aglycone in hepatic cells and minimized the metabolic effect on Gen. They significantly increased the intracellular accumulation of Gen in its complex form in HepG2 cells. Their cytotoxicity is time-dependent according to the complex stability. The enhanced in-vivo anti-tumor effect was observed for GP and GPL compared to Gen suspension on DEN-induced HCC in mice. In conclusion, Gen-phytosomes can represent a promising approach for liver cancer treatment.

Identification of equol-7-glucuronide-4'-sulfate, monoglucuronides and monosulfates in human plasma of 2 equol producers after administration of kinako by LC-ESI-MS

Equol is a product formed during the biotransformation of the naturally occurring isoflavone daidzein by intestinal bacteria. The role of equol in the prevention of several hormone-dependent diseases such as prostate cancer and osteoporosis as well as vasomotor symptoms has been extensively investigated. Equol primarily occurs in the form of major metabolites such as glucuronides and sulfates, while intact equol has been detected at only ca. 1% in human plasma. However, to date, conjugated metabolites have been evaluated by measuring the free equol obtained after selective enzymatic hydrolysis. Thus, the precise types of conjugates circulating in vivo and the position(s) of the conjugation sites on the equol skeleton have yet to be clarified. Our study describes the identification of polar equol metabolites in the plasma of 2 equol-producers obtained at 8 hours after consuming 50 g of kinako (approximately 37 mg of daidzein). The structural identification of these conjugated metabolites in plasma was performed by comparison to the LC-ESI-MS n and 1H-NMR spectral data of the corresponding chemically synthesized compounds. The results of the LC-ESI-MS/MS analysis indicated that the main conjugated metabolite in plasma was (S)-equol-7-glucuronide-4'-sulfate along with lower amounts of 7- and 4'-monoglucuronides as well as 7- and 4'-monosulfates.

A Comprehensive Screening and Identification of Genistin Metabolites in Rats Based on Multiple Metabolite Templates Combined with UHPLC-HRMS Analysis

Genistin, an isoflavone belonging to the phytoestrogen family, has been reported to possess various therapeutic effects. In the present study, the genistin metabolites in rats were investigated by UHPLC-LTQ-Orbitrap mass spectrometer in both positive and negative ion modes. Firstly, the data sets were obtained based on data-dependent acquisition method and then 10 metabolite templates were established based on the previous reports. Then diagnostic product ions (DPIs) and neutral loss fragments (NLFs) were proposed to efficiently screen and ascertain the major-to-trace genistin metabolites. Meanwhile, the calculated Clog P values were used to identify the positional isomers with different retention times. Consequently, a total of 64 metabolites, including prototype drug, were positively or putatively characterized. Among them, 40 metabolites were found according to the templates of genistin and genistein, which was the same as the previous research method. After using other metabolite templates, 24 metabolites were added. The results demonstrated that genistin mainly underwent methylation, hydrogenation, hydroxylation, glucosylation, glucuronidation, sulfonation, acetylation, ring-cleavage and their composite reactions in vivo biotransformation. In conclusion, the research not only revealed the genistein metabolites and metabolic pathways in vivo comprehensively, but also proposed a method based on multiple metabolite templates to screen and identify metabolites of other natural compounds.

Cytoprotective effects of dietary flavonoids against cadmium-induced toxicity

Cadmium (Cd) damages the liver, kidney, bones, reproductive system, and other organs. Flavonoids, such as anthocyanins and flavonols, which are commonly found in plant foods, have shown protective effects against Cd-induced damage. The cytoprotective effects of flavonoids against Cd-induced diseases are mainly attributable to three mechanisms. First, flavonoids clear reactive oxygen species, thereby reducing lipid peroxide production and improving the activity of antioxidation enzymes. Second, flavonoids chelate Cd, thus reducing the accumulation of Cd and altering the levels of other essential metal ions in vivo. Third, flavonoids reduce DNA damage and inhibit apoptosis. In addition, flavonoids were found to inhibit inflammation and fibrosis and improve glycometabolism and the secretion of reproductive hormones. We introduce the daily dosage and absorption rate of flavonoids and then focus on their bioactive effects against Cd-induced toxicity and reveal the underlying metabolic pathway, which provides a basis for further study of the nutritional prevention of Cd-induced injury. In particular, a better understanding is needed of the structure-activity relationship of flavonoids against Cd toxicity, which has not yet been reported.

Pharmacokinetic Comparison of Soy Isoflavone Extracts in Human Plasma

The soy isoflavones daidzein and genistein produce several biological activities related to health benefits. A number of isoflavone extracts are commercially available, but there is little information concerning the specific isoflavone content of these products or differences in their bioavailability and pharmacokinetics. This study describes the development and validation of an analytical method to detect and quantify daidzein, genistein, and equol in human plasma using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The method was applied in a crossover, randomized, bioavailability study. Twelve healthy volunteers were administered the same total isoflavones dose from two isoflavone supplement preparations (Super-Absorbable Soy Isoflavones (Life Extension, USA) and Fitoladius (Merck, Spain)). The pharmacokinetic parameters (AUC0-24/dose and Cmax/dose) of the isoflavones from the two preparations differed significantly. Such differences in bioavailability and kinetics may have relevant effects on the health benefits derived from their intake.

Hepatic metabolism: a key component of herbal drugs research

Liver is the largest metabolic organ for a wide range of endogenous and exogenous compounds and plays a crucial part in the pharmacokinetics and pharmacodynamics through various metabolic reactions. This review provides a progressive description of hepatic metabolism of herbal drugs with respect to metabolic types and investigational methods. In addition, the problems encountered during the research process are discussed.

Conversion of major soy isoflavone glucosides and aglycones in in vitro intestinal models

SCOPE

This study compares conversion of three major soy isoflavone glucosides and their aglycones in a series of in vitro intestinal models.

METHODS AND RESULTS

In an in vitro human digestion model isoflavone glucosides were not deconjugated, whereas studies in a Caco-2 transwell model confirmed that deconjugation is essential to facilitate transport across the intestinal barrier. Deconjugation was shown upon incubation of the isoflavone glucosides with rat as well as human intestinal S9. In incubations with rat intestinal S9 lactase phlorizin hydrolase, glucocerebrosidase, and cytosolic broad-specific β-glucosidase all contribute significantly to deconjugation, whereas in incubations with human intestinal S9 deconjugation appeared to occur mainly through the activity of broad-specific β-glucosidase. Species differences in glucuronidation and sulfation were limited and generally within an order of magnitude with 7-O-glucuronides being the major metabolites for all three isoflavone aglycones and the glucuronidation during first pass metabolism being more efficient in rats than in humans. Comparison of the catalytic efficiencies reveals that deconjugation is less efficient than conjugation confirming that aglycones are unlikely to enter the systemic circulation.

CONCLUSION

Altogether, the data point at possible differences in the characteristics for intestinal conversion of the major soy isoflavones between rat and human, especially with respect to their deconjugation.

Bioavailability and pharmacokinetics of genistein: mechanistic studies on its ADME

Genistein, one of the most active natural flavonoids, exerts various biological effects including chemoprevention, antioxidation, antiproliferation and anticancer. More than 30 clinical trials of genistein with various disease indications have been conducted to evaluate its clinical efficacy. Based on many animals and human pharmacokinetic studies, it is well known that the most challenge issue for developing genistein as a chemoprevention agent is the low oral bioavailability, which may be the major reason relating to its ambiguous therapeutic effects and large interindividual variations in clinical trials. In order to better correlate pharmacokinetic to pharmacodynamics results in animals and clinical studies, an in-depth understanding of pharmacokinetic behavior of genistein and its ADME properties are needed. Numerous in vitro/in vivo ADME studies had been conducted to reveal the main factors contributing to the low oral bioavailability of genistein. Therefore, this review focuses on summarizing the most recent progress on mechanistic studies of genistein ADME and provides a systemic view of these processes to explain genistein pharmacokinetic behaviors in vivo. The better understanding of genistein ADME property may lead to development of proper strategy to improve genistein oral bioavailability via mechanism-based approaches.

Identification of multiple constituents in the traditional Chinese medicine formula Zhi-zi-chi decoction and rat plasma after oral administration by liquid chromatography coupled to quadrupole time-of-flight tandem mass spectrometry

RATIONALE

Liquid chromatography (LC) coupled to positive electrospray ionization (ESI) tandem mass spectrometry (MS/MS) employing a time-of-flight tandem mass spectrometer was established to identify multi-components of Zhi-zi-chi decoction, a traditional Chinese medicine formula, and the constituents in rat plasma after oral administration of Zhi-zi-chi decoction.

METHODS

The LC separation was achieved on a C(18) column. The mobile phase consisted of acetonitrile/0.2% formic acid with gradient program. The quadrupole time-of-flight (Q-TOF) mass spectrometer was operated in the positive ion mode with an electrospray ionization source (ESI+). The capillary voltage of the ion source was set at 4500 V and the capillary exit was 90 V. The nebulizer pressure was maintained at 1.2 bar. Hexapole radio frequencies 1 and 2 were set to 200 Vpp and 250 Vpp, respectively.

RESULTS

A total 47 compounds in the Zhi-zi-chi decoction and 24 constituents in rat plasma after oral administration of Zhi-zi-chi decoction were identified. Of the 47 detected compounds in the Zhi-zi-chi decoction, 15 were identified by comparing the retention time and MS data with that of reference compounds and the rest were identified by MS analysis and retrieving the reference literature. Of the identified 24 compounds in rat plasma, 19 were the original form of the compounds absorbed from the 47 detected compounds, and the other five were the metabolites of the compounds existing in the Zhi-zi-chi decoction.

CONCLUSIONS

A fast and sensitive LC/Q-TOF MS method has been developed and successfully utilized to screen the active ingredients of a Chinese medical formula, Zhi-zi-chi decoction, for the first time. The results indicated that the 24 compounds identified in rat plasma were the potential active ingredients of Zhi-zi-chi decoction, which provided helpful chemical information for further pharmacology and active mechanism research on Zhi-zi-chi decoction and other traditional Chinese medicines.

Evaluation of different extraction approaches for the determination of phenolic compounds and their metabolites in plasma by nanoLC-ESI-TOF-MS

Sample preparation is an important step for the determination of phenolic compounds in biological samples. Different extraction methods have been tested to determine phenolic compounds and their metabolites in plasma by nano-liquid chromatography coupled to electrospray ionisation-time-of-flight mass spectrometry (nanoLC-ESI-TOF-MS). The sample treatment optimisation was performed using commercial foetal bovine serum spiked with representative phenolic standards, namely naringenin, luteolin, verbascoside, apigenin, rutin, syringic acid and catechin. Different protein-precipitation conditions were evaluated as well as enzymatic digestion with trypsin and solid-phase extraction using different phases such as C-18, ABN and ENV+, working at different pH values. The optimum extraction procedure consisted of a previous protein-precipitation step using HCl 200 mmol/L in methanol for 2.5 h at 50 °C followed by a solid-phase extraction using C-18 cartridges at pH 2.5. This procedure was finally applied to the plasma of rats overfed with a phenolic-rich Lippia citriodora extract. These samples were analysed by nanoLC-ESI-TOF-MS, enabling the identification of five compounds previously found in the administered L. citriodora extract and one metabolite.

Absorption and plasma disposition of genistin differ from those of genistein in healthy women

The chemical forms in which isoflavones appear in food or supplements seem to play an important role in their absorption efficiency. However, the influence of the chemical form of isoflavones on their plasma disposition has never been reported, although the metabolites of isoflavones circulating in the blood may have biological activity themselves. The purpose of the study was to investigate the pharmacokinetic profiles of genistein (GEN) and its phase II metabolites in the plasma and urine of healthy young women after multiple doses of pure aglycone and glucoside forms of GEN. Genistein-7-glucuronide (G-7-G), 4'-glucuronide (G-4'-G), 7-sulfate (G-7-S), 4'-sulfate (G-4'-S), 4',7-diglucuronide (G-4',7-diG), and 7-glucuronide-4'-sulfate (G-7-G-4'-S) besides unconjugated GEN were observed in human plasma after ingestion of GEN and its glucoside. Among these metabolites, G-4',7-diG and G-7-G-4'-S were the major ones, comprising both about 30% of the total amount of GEN in plasma. Compared with the aglycone, the amount of total GEN in vivo and those of G-4',7-diG and G-7-G-4'-S were increased after the glucoside intake. No difference was observed in urinary excretion between the aglycone and the glucoside. Overall, the absorption and plasma disposition of GEN were affected by the glucoside form.

Phytoestrogen biomonitoring: an extractionless LC-MS/MS method for measuring urinary isoflavones and lignans by use of atmospheric pressure photoionization (APPI)

We present here a high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying phytoestrogenic isoflavones (daidzein, equol, genistein, and O-desmethylangolensin) and lignans (enterodiol and enterolactone) in urine without the use of extraction or the preconcentration techniques inherent in existing methods. The development of this concept was made possible by use of atmospheric pressure photoionization (APPI); an ionization technique that we found to improve analyte sensitivity relative to electrospray ionization and atmospheric pressure chemical ionization for this particular group of compounds. The analytical performance of this method was equal to or exceeded that of comparable methods. Between-run coefficients of variation (CVs) across three quality control (QC) pool levels analyzed in duplicate over 20 days were 3.1-5.8% CV; within-run CVs were 2.3-6.0%. Accuracy, as determined by average spike recovery in QC pools, was generally within ±10% of being quantitative (100%). Relative limits of detection were 0.04-0.4 ng/mL urine, with absolute detection limits as low as 0.1 pg. This method was applied to the analysis of >2,500 urine specimens for the 2005-2006 Centers for Disease Control and Prevention's National Health and Nutrition Examination Survey (NHANES). The method was capable of quantifying these compounds in 95-100% of study samples. This work is the first ever report of using APPI for the LC-MS/MS determination of these compounds in urine. It is also the first method of its kind to do so without any need for analyte extraction or preconcentration prior to analysis.

Metabolism and disposition of isoflavone conjugated metabolites in humans after ingestion of kinako

Isoflavone aglycones daidzein (Dein) and genistein (Gein) are present primarily as glucuronides and sulfates in human plasma; however, very little is known about the plasma pharmacokinetics of isoflavone conjugates after soy ingestion. The aim of this study was to investigate metabolism and disposition of the isoflavone conjugated metabolites glucuronide or sulfate or both after ingestion of kinako (baked soybean flour) by 10 volunteers. The quantifications of 16 metabolites in plasma and urine were performed by our previously reported high-performance liquid chromatography-UV-diode-array detector method. Plasma concentrations of total Dein and Gein metabolites reached maximal values of 0.64 ± 0.18 μM at 4.7 ± 2.5 h and 1.58 ± 0.55 μM at 5.4 ± 2.1 h, respectively. The area under the curve from 0 to 48 h demonstrated that daidzein-7-glucuronide-4'-sulfate (D-7G-4'S) (53.3%) was a major metabolite of Dein and that genistein-7-glucuronide-4'-sulfate (G-7G-4'S) (54.0%) and genistein-4',7-diglucuronide (G-4',7-diG) (26.6%) were major metabolites of Gein in plasma. The compositions of isoflavone metabolites in urine and plasma were greatly different. Approximately half of the 48-h urinary excretion of total Dein metabolites consisted of daidzein-7-glucuronide. The total amounts of genistein-7-glucuronide and genistein-4'-glucuronide were half the total amount of the urinary Gein metabolites. Excretion into urine of D-7G-4'S and G-7G-4'S accounted for only 16% each of the total Dein and Gein metabolites, respectively. The plasma and urine profiles of 16 metabolites of Dein and Gein demonstrate the involvement of desulfation and deglucuronidation of the conjugated metabolites D-7G-4'S, G-7G-4'S, and G-4',7-diG in the process of renal excretion.

Identification and quantification of daidzein-7-glucuronide-4'-sulfate, genistein-7-glucuronide-4'-sulfate and genistein-4',7-diglucuronide as major metabolites in human plasma after administration of kinako

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.