Pharmacokinetics and bioavailability of the isoflavone biochanin A in rats

Use of physiologically based pharmacokinetic models to evaluate the impact of intestinal glucuronide hydrolysis on the pharmacokinetics of aglycone

Drug elimination via glucuronidation pathway is a complex process involving glucuronide excretion. Glucuronide excreted into the gut lumen either directly from the enterocytes or from the hepatobiliary route can be recovered back to the precursor (aglycone) through bacteria-mediated hydrolysis. As a result, the pharmacokinetics [e.g., plasma terminal half-life (T(1/2))] of aglycone might be altered. Here, impact of intestinal glucuronide hydrolysis on the pharmacokinetics of aglycone is evaluated using physiologically based pharmacokinetic (PBPK) models with liver and/or intestine as eliminating organs. It is found that compared with its absence, the presence of intestinal glucuronide hydrolysis leads to increases in the oral systemic bioavailability (F(sys)) of aglycone. The magnitude of fold increase is positively correlated with the level of metabolism, as metabolic clearance mainly contributes to recycled amount of glucuronide. Although F(sys) is independent of the glucuronide efflux in a traditional model and a segregated-flow model of the intestine, dependence of F(sys) on the glucuronide efflux can be observed in a segmental segregated-flow model of the intestine and whole-body PBPK models. Interestingly, when the ratio of apical versus basolateral efflux intrinsic clearances (of glucuronide) is fixed, their effects on the intestinal bioavailability and F(sys) cease to exist. In addition, glucuronide hydrolysis can lead to a significantly delayed elimination of the aglycone as evidenced by a prolonged (e.g., a 2.1-fold increase) T(1/2). Surprisingly, when a pharmacokinetic profile for aglycone is simulated with a flat terminal portion (a reflection of the experimental observations), changes in the aglycone bioavailabilities are limited (i.e., ≤ 1.3-fold). In conclusion, this study explores the possible role of intestinal glucuronide hydrolysis in the disposition of aglycone via simulations utilizing various PBPK models. The mechanistic observations should be helpful to better understand the complex glucuronidation in vivo.

5,7-Dimethoxyflavone and multiple flavonoids in combination alter the ABCG2-mediated tissue distribution of mitoxantrone in mice

PURPOSE

The objective of our study was to investigate the effect of 5,7-DMF on the accumulation of mitoxantrone (MX) in BCRP-expressing normal cells and to investigate its impact on the PK and tissue distribution of MX in mice.

METHODS

The in vitro effect of 5,7-DMF on MX accumulation was examined in MDCK cells transfected with BCRP. The pharmacokinetic and tissue distribution of mitoxantrone, with and without co-administration of 5,7-DMF or multiple flavonoid combinations, were determined in mice.

RESULTS

In the presence of 2.5 μM or 25 μM of 5,7-DMF, the intracellular concentration of MX was significantly increased in MDCK/Bcrp1 and MDCK/BCRP cells, but not in MDCK/Mock cells. The AUC values of MX in several tissues were significantly increased when MX was co-administered with 5,7-DMF. The most substantial elevations of MX AUC in the presence of 5,7-DMF occurred in the liver (94.5%) and kidneys (61.9%), which is in apparent agreement with the relatively high levels of mouse Bcrp1 expression in these two tissues.

CONCLUSIONS

Bcrp1-mediated DMF-MX interactions occur both in vitro and in vivo. 5,7-DMF represents a novel and very promising chemosensitizing agent for the BCRP-mediated MDR due to its low toxicity and potent BCRP inhibition.

Effects of the isoflavonoid biochanin A on the transport of mitoxantrone in vitro and in vivo

The aim of our study was to investigate the effect of biochanin A on the accumulation and transport of mitoxantrone in breast cancer resistance protein (BCRP)-expressing normal cells and its impact on the pharmacokinetics (PK) and tissue distribution of mitoxantrone. In accumulation studies, the intracellular level of mitoxantrone was significantly increased in the presence of 2.5 or 25 microM of biochanin A in both murine and human BCRP-expressing Madin-Darby canine kidney (MDCK) cells, with no effect in corresponding MDCK/Mock cells. In bi-directional transport studies, the P(app,B-A) value of mitoxantrone with biochanin A co-treatment was much lower (6.66+/-0.84x10(-7) cm/s) than that in the absence of biochanin A (21.4+/-4.14x10(-7) cm/s), indicating inhibition of Bcrp1-mediated efflux. To evaluate whether our in vitro results might translate into an in vivo interaction, mitoxantrone PK and tissue distribution, with and without co-administration of biochanin A, was investigated. In contrast to our in vitro results, biochanin A (10 mg/kg, i.v.) had no impact on the concentration of mitoxantrone in plasma and most tissues collected (brain, heart, liver and lung). Surprisingly, the concentrations of mitoxantrone in spleen and kidney were even decreased when biochanin A was co-administered. Interestingly, it was found that the intracellular fluorescence of mitoxantrone was decreased 31.9% when co-incubated with 10 microM biochanin A in P-glycoprotein (P-gp) expressing MCF-7/ADR cells, indicating potential P-gp stimulation. The species difference of the inhibitory effect of biochanin A on BCRP, the extensive metabolism of biochanin A, as well as the stimulation effect of biochanin A on P-gp, may contribute to this in vitro-in vivo disconnect.

Biochanin A, a naturally occurring inhibitor of fatty acid amide hydrolase

BACKGROUND AND PURPOSE

Inhibitors of fatty acid amide hydrolase (FAAH), the enzyme responsible for the metabolism of the endogenous cannabinoid (CB) receptor ligand anandamide (AEA), are effective in a number of animal models of pain. Here, we investigated a series of isoflavones with respect to their abilities to inhibit FAAH.

EXPERIMENTAL APPROACH

In vitro assays of FAAH activity and affinity for CB receptors were used to characterize key compounds. In vivo assays used were biochemical responses to formalin in anaesthetized mice and the 'tetrad' test for central CB receptor activation.

KEY RESULTS

Of the compounds tested, biochanin A was adjudged to be the most promising. Biochanin A inhibited the hydrolysis of 0.5 microM AEA by mouse, rat and human FAAH with IC(50) values of 1.8, 1.4 and 2.4 microM respectively. The compound did not interact to any major extent with CB(1) or CB(2) receptors, nor with FAAH-2. In anaesthetized mice, URB597 (30 microg i.pl.) and biochanin A (100 microg i.pl.) both inhibited the spinal phosphorylation of extracellular signal-regulated kinase produced by the intraplantar injection of formalin. The effects of both compounds were significantly reduced by the CB(1) receptor antagonist/inverse agonist AM251 (30 microg i.pl.). Biochanin A (15 mg.kg(-1) i.v.) did not increase brain AEA concentrations, but produced a modest potentiation of the effects of 10 mg.kg(-1) i.v. AEA in the tetrad test.

CONCLUSIONS AND IMPLICATIONS

It is concluded that biochanin A, in addition to its other biochemical properties, inhibits FAAH both in vitro and peripherally in vivo.

Biochanin A induction of sulfotransferases in rats

Biochanin A (BCA) is a dietary isoflavone present in red clover (Trifoliumn pretense) and many herbal products. BCA has been reported to have chemopreventive actions against various cancers including prostate, breast, colon cancer, and so on. Sulfotransferases are a family of phase II drug-metabolizing enzymes, which are important for xenobiotic detoxification and regulation of biological signaling molecule biological activities. Sulfotransferase gene expressions are regulated by different hormones and xenobiotics. Improper regulation of sulfotransferases leads to improper functions of biological signaling molecules, which in turn can cause cancer or other diseases. BCA inhibits the enzyme activities of the phase I drug-metabolizing enzymes CYP1A1 and CYP1B1 in Chinese hamster ovary cells and induces the phase II drug-metabolizing enzymes UDP-glucuronosyltransferases in human prostate cancer cells. BCA induction of sulfotransferases has not been studied. This investigation evaluates the in vivo regulation of sulfotransferases at protein and mRNA levels in the liver and intestine of Sprague-Dawley rats treated with BCA (0, 2, 10, and 50 mg/kg/day) for 7 days. Our experimental results demonstrate for the first time that chronic BCA treatment can significantly induce the expression of rat sulfotransferase 1A1 (rSULT1A1, AST-IV), sulfotransferase 2A1 (rSULT2A1, STa), and rat estrogen sulfotransferase (rSULT1E1, EST) in rat liver and intestine. Our Western blot results are in good agreement with real-time RT-PCR data, suggesting that BCA induction of sulfotransferases occurs at the transcriptional level.

Biochanin A reduces drug-induced p75NTR expression and enhances cell survival: a new in vitro assay for screening inhibitors of p75NTR expression

Following spinal cord injury (SCI) or peripheral neuropathy, increased levels of the p75(NTR) death receptor initiate the signal transduction cascade leading to cell death. Investigations of compounds that may ameliorate neuronal cell death have largely used rodent models, which are time consuming, expensive, and cumbersome to perform. Previous studies had demonstrated that steroids, particularly dexamethasone and its analog methylprednisolone sodium succinate, exhibit limited neuroprotective effects against neuronal injury. Significantly, many naturally occurring nonsteroidal plant compounds exhibit structural overlap with steroids. In this report, we present an in vitro cellular screen model to practically examine the efficacy of various phytoestrogens in modulating the ibuprofen-induced expression of p75(NTR) and reduced cell survival of CCFSTTG1 and U87MG cells in a rescue (postinjury) or prevention (preinjury) regimen. We show that the phytoestrogen, biochanin A, and, to a lesser extent, genistein are more effective than dexamethasone at reducing p75(NTR) expression and improving the viability of U87MG and CCFSTTG1 before and after p75(NTR) induction. Furthermore, these studies implicate biochanin A's inactivation of p38-MAPK as a possible contributor to reducing p75(NTR) with associated increased cell survival. This new in vitro assay facilitates a more time-efficient screening of compounds to suppress p75(NTR) expression and increase neuronal cell viability prior to their evaluation in animal models of neurological diseases.

In vivo inhibition of BCRP/ABCG2 mediated transport of nitrofurantoin by the isoflavones genistein and daidzein: a comparative study in Bcrp1 (-/-) mice

PURPOSE

The aim of this study was to determine in vivo inhibition by the isoflavones genistein and daidzein of nitrofurantoin (NTF), a well-known substrate of the ABC transporter BCRP/ABCG2.

METHODS

MDCKII cells and their human BCRP- and murine Bcrp1-transduced subclones were used to establish inhibition in transepithelial transport assays. Bcrp1(-/-) and wild-type mice were coadministered with nitrofurantoin (20 mg/kg) and a mixture of genistein (100 mg/kg) and daidzein (100 mg/kg).

RESULTS

Transepithelial NFT transport was inhibited by the isoflavones. Plasma concentration of NTF at 30 min was 1.7-fold higher (p ≤ 0.05) in wild-type mice after isoflavone administration. AUC values were not significantly different. BCRP/ABCG2-mediated secretion into milk was inhibited since milk/plasma ratios were lower in wild-type mice with isoflavones (7.1 ± 4.2 vs 4.2 ± 1.6, p ≤ 0.05). NTF bile levels were significantly decreased by isoflavone administration in wild-type animals (8.8 ± 3.4 μg/ml with isoflavones vs 3.7 ± 3.3 μg/ml without isoflavones).

CONCLUSION

Our data showed that in vivo interaction of high doses of soy isoflavones with BCRP substrates may affect plasma levels but the main effect occurs in specific target organs, in our case, liver and mammary glands.

Absolute bioavailability of isoflavones from soy protein isolate-containing food in female BALB/c mice

Soy isoflavones, genistein and daidzein, are widely consumed in soy-based foods and dietary supplements for their putative health benefits; however, evidence for potential adverse effects has been obtained from experimental animal studies. An important prerequisite for understanding the pharmacodynamics of isoflavones is better information about pharmacokinetics and bioavailability. This study determined the bioavailability of genistein and daidzein in a mouse model by comparing plasma pharmacokinetics of their aglycone and conjugated forms following administration of identical doses (1.2 mg/kg genistein and 0.55 mg/kg daidzein) by either an intravenous injection (IV) or gavage of the aglycones in 90% aqueous solution vs a bolus administration of equimolar doses delivered in a food pellet prepared using commercial soy protein isolate (SPI) as the isoflavone source. The bioavailability of genistein and daidzein was equivalent for the gavage and dietary routes of administration despite the use of isoflavone aglycones in the former and SPI-derived glucosides in the latter. While absorption of total isoflavones was nearly quantitative from both oral routes [>84% of areas under the curve (AUCs) for IV], presystemic and systemic phase II conjugation greatly attenuated internal exposures to the receptor-active aglycone isoflavones (9-14% for genistein and 29-34% for daidzein based on AUCs for IV). These results show that SPI is an efficient isoflavone delivery vehicle capable of providing significant proportions of the total dose into the circulation in the active aglycone form for distribution to receptor-bearing tissues and subsequent pharmacological effects that determine possible health benefits and/or risks.

Simultaneous determination of genistein and its four phase II metabolites in blood by a sensitive and robust UPLC-MS/MS method: Application to an oral bioavailability study of genistein in mice

The purpose of this research was to develop a sensitive and reproducible UPLC-MS/MS method to simultaneously quantify genistein, genistein-7-O-glucuronide (G-7-G), genistein-4'-O-glucuronide (G-4'-G), genistein-4'-O-sulfate (G-4'-S) and genistein-7-O-sulfate (G-7-S) in mouse blood samples. After the method was fully validated over a wide linear range, it was applied to quantify the levels of genistein and its metabolites in a mouse bioavailability study. The linear response range was 19.5-10,000 nM for genistein, 12.5-3200 nM for G-7-G, 20-1280 nM for G-4'-G, 1.95-2000 nM for G-4'-S, and 1.56-3200 nM for G-7-S, respectively. The lower limit of quantification (LLOQ) was 4.88, 6.25, 5, 0.98 and 0.78 nM for genistein, G-7-G, G-4'-G, G-4'-S and G-7-S, respectively. Only 20 microl mouse blood sample from i.v. and p.o. administration were needed for analysis because of the high sensitivity of the method. The intra- and inter-day variance is less than 15% and accuracy is within 85-115%. The analysis was finished within 4.5 min. The applicability of this assay was demonstrated and successfully applied for bioavailability study in FVB mouse after i.v. and p.o. administration of 20mg/kg of genistein, and its oral bioavailability was approximately 23.4%.

Effect of glycosidation of isoflavones on their bioavailability and pharmacokinetics in aged male rats

There are limited reports on the bioavailability and pharmacokinetics of isoflavones in elderly humans and aged animals. The present study was conducted to assess the effect of glycosidation of isoflavones on their bioavailability and pharmacokinetics in aged (20 month old) male Fischer-344 (F-344) rats. The F-344 rat, developed by the National Institute on Aging, is an inbred rat model that is commonly used for aging studies and resembles many features of aging humans. Three sources of isoflavones; Novasoy (a commercial supplement), a mixture of synthetic aglycons (daidzein, genistein and glycitein), and a mixture of synthetic glucosides (daidzin, genistin, and glycitin) were tested. Following administration, blood samples were collected at different times (0-48 h post-oral gavage and 0-8 h post-IV dosing). Plasma isoflavones and 7-hydroxy-3-(4'-hydroxyphenyl)-chroman (a metabolite of daidzein) were measured by LC/MS. The extent of absorption was determined by comparing the area under the curve (AUC) of the plasma-concentration time curve after intravenous (IV) administration with that following oral administration. The extent of bioavailability was then calculated as: %bioabailability = (AUC(or)/AUC(IV))x(Dose(IV)/Dose(or))x100. Bioavailabilities for genistein were significantly (p = 0.013) higher for the aglycon (35 +/- 9%) compared with the glucoside forms (11 +/- 3%). In contrast, the bioavailabilities for glycitein were significantly (p = 0.011) higher in Novasoy (27 +/- 13%) and the glucoside form (21 +/- 10%) compared with the aglycon (8 +/- 3%). No significant differences in the bioavailability of daidzein were observed in aged rats dosed with aglycon, glucoside or Novasoy. However, aged rats were able to produce equol as early as 8 h post-dosing. In summary, the source of isoflavones had significant effects on genistein and glycitein bioavailability in aged male rats.

Disposition of flavonoids via enteric recycling: UDP-glucuronosyltransferase (UGT) 1As deficiency in Gunn rats is compensated by increases in UGT2Bs activities

Flavonoids have poor bioavailabilities largely because of metabolism via UDP-glucuronosyltransferases (UGTs). This study aims to further understand the functions of UGT in metabolizing genistein and apigenin, two compounds metabolized more extensively in the gut than in the liver. Because Gunn rats are deficient in UGT1As, we determined whether this deficiency would result in less flavonoid glucuronidation, using rat intestinal perfusion model and microsomes prepared from rat liver and intestine. In yeast-expressed rat UGT isoforms, rat UGT1A isoforms (especially UGT1A7) were mainly responsible for flavonoid metabolism. In perfusion studies, the two flavonoids were rapidly absorbed at comparable rates, but the intestinal excretions of glucuronides in Gunn rats compared with Wistar rats were not only comparable for genistein but also were higher (p < 0.05) for apigenin, suggesting up-regulation of UGT isoforms in Gunn rats. To determine the possible compensatory UGT isoforms, we first verified that UGT1A activities were significantly lower (p < 0.05) in Gunn rats by using UGT1A-specific probes 7-ethyl-10-hydroxycamptothecin (SN-38) and prunetin. We then demonstrated using UGT2B probes testosterone, ezetimibe, and indomethacin that UGT2B activities were usually significantly higher in Gunn rats. In addition, testosterone was metabolized much faster in liver microsomes than in intestinal microsomes, and in microsomes prepared from Gunn rats compared with Wistar rats. In conclusion, flavonoids are efficiently metabolized by UGT1A-deficient Gunn rats because of compensatory up-regulation of intestinal UGT2Bs and hepatic anion efflux transporters, which increases their disposition and limits their oral bioavailabilities.

Genistein induction of human sulfotransferases in HepG2 and Caco-2 cells

Sulfotransferases are phase II drug-metabolizing enzymes. While the induction of sulfotransferases by hormones and endogenous molecules is relatively well known, induction by xenobiotics is not well studied. Isoflavones are naturally occurring phyto-oestrogens, mainly existing in soy food products. They have been described as health-promoting, disease-preventing dietary supplements and as agents with cancer-preventive activities. Recently, isoflavones have been reported to interact with nuclear receptors, including those that are known to mediate the induction of drug-metabolizing enzymes. In the present investigation, the isoflavone genistein was shown to be a xenobiotic inducer of human sulfotransferases in transformed human liver cells (HepG2) and colon carcinoma cells (Caco-2). Enzymatic activity assay, Western blot, and real-time reverse transcription-polymerase chain reaction (RT-PCR) results demonstrated that genistein significantly induced protein and mRNA expression of human simple phenol sulfotransferase (hSULT1A1) and human dehydroepiandrosterone sulfotransferase (hSULT2A1) in HepG2 and Caco-2 cells. The induction was time-dependent and dose-dependent. Western blot results agreed well with real-time RT-PCR results, suggesting that induction occurred at the gene transcription level. This isoflavone is the first nutritionally related phyto-oestrogen shown to induce human sulfotransferases in HepG2 and Caco-2 cells.

Pharmacokinetics and bioavailability of the flavonoid 7,8-benzoflavone in rats

The flavonoid 7,8-benzoflavone was recently identified as one of the most potent inhibitors of breast cancer resistance protein (BCRP); however, little is known of the in vivo disposition of 7,8-benzoflavone. The objective of this study was to investigate the pharmacokinetics and bioavailability of 7,8-benzoflavone in rats. Three intravenous (5, 10, and 25 mg/kg) and three oral (12.5, 25, and 50 mg/kg) doses were administered to female Sprague-Dawley rats. Plasma samples were analyzed by high-performance liquid chromatography. Pharmacokinetic analysis was conducted by WinNonlin and ADAPT II. The dose-normalized plasma concentration versus time curves did not superimpose with each other, indicating the nonlinear pharmacokinetics of 7,8-benzoflavone. 7,8-benzoflavone exhibited a large volume of distribution (V(ss) approximately 1.5 L/kg) and rapid oral absorption (t(max) < 30 min). The bioavailability of 7,8-benzoflavone was low (0.61-13.2%) and dose-dependent. A pharmacokinetic model with dose-dependent bioavailability, linear absorption and nonlinear elimination best described the pharmacokinetic profiles of 7,8-benzoflavone. Using a 50 mg/kg oral dose of 7,8-benzoflavone, we could significantly increase the AUC for the BCRP substrate nitrofurantoin, demonstrating the potential for BCRP-mediated drug interactions.

Quercetin pharmacokinetics in humans

The purpose of this study was to examine the pharmacokinetics of quercetin aglycone as well as its conjugated metabolites and to develop a population pharmacokinetic model for quercetin that incorporates enterohepatic recirculation. The stability of quercetin in different matrices at various temperatures and pH, and the quercetin content of six capsules of the herbal preparation Quercetin-500 Plus were determined by HPLC. Subjects received quercetin 500 mg three times daily and blood and urine samples were obtained. The concentration of quercetin aglycone and conjugated metabolites were assayed using a liquid chromatography-tandem mass spectrometry assay. Pharmacokinetic parameters were determined using noncompartmental analysis with WinNonlin. A population compartment model incorporating input from the gallbladder was developed to account for the enterohepatic recirculation observed with quercetin. The oral clearance (CL/F) was high (3.5 x 10(4)l/h) with an average terminal half-life of 3.5 h for quercetin. The plasma concentration versus time curves exhibited re-entry peaks. A one-compartment model that included enterohepatic recirculation best described the plasma data. This represents the first comprehensive evaluation of the pharmacokinetics and enterohepatic recirculation of quercetin in humans. Population pharmacokinetic models adapted for enterohepatic recirculation allowed an assessment of the magnitude and frequency of the enterohepatic recirculation process.

Enterohepatic recirculation model of irinotecan (CPT-11) and metabolite pharmacokinetics in patients with glioma

BACKGROUND

Enterohepatic recirculation of irinotecan and one of its metabolites, SN-38, has been observed in pharmacokinetic data sets from previous studies. A mathematical model that can incorporate this phenomenon was developed to describe the pharmacokinetics of irinotecan and its metabolites.

PATIENTS AND METHODS

A total of 32 patients with recurrent malignant glioma were treated with weekly intravenous administration of irinotecan at a dose of 125 mg/m(2). Plasma concentrations of irinotecan and its three major metabolites were determined. Pharmacokinetic models were developed and tested for simultaneous fit of parent drug and metabolites, including a recirculation component.

RESULTS

Rebound in the plasma concentration suggestive of enterohepatic recirculation at approximately 0.5-1 h post-infusion was observed in most irinotecan plasma concentration profiles, and in some plasma profiles of the SN-38 metabolite. A multi-compartment model containing a recirculation chain was developed to describe this process. The recirculation model was optimal in 22 of the 32 patients compared to the traditional model without the recirculation component.

CONCLUSION

A recirculation chain incorporated in a multi-compartment pharmacokinetic model of irinotecan and its metabolites appears to improve characterization of this drug's disposition in patients with glioma.

The red clover (Trifolium pratense) isoflavone biochanin A inhibits aromatase activity and expression

Biochanin A is an isoflavone isolated from red clover (Trifolium pratense), and is a commercially available nutraceutical for women suffering from postmenopausal symptoms. Isoflavones resemble the structure of oestrogen, and display agonistic and antagonistic interactions with the oestrogen receptor. Overexposure of oestrogen is a major contributing factor in the development of breast cancer, and cytochrome P450 (CYP) 19 enzyme, or aromatase, catalyses the reaction converting androgen to oestrogen. In the present study the effect of biochanin A on the gene regulation and enzyme activity of aromatase was investigated. By assaying MCF-7 cells stably transfected with CYP19, biochanin A inhibited aromatase activity and hampered cell growth attributing to the enzyme activity. In addition, 25 microm-biochanin A significantly reduced CYP19 mRNA abundance in the oestrogen receptor-negative breast cancer cells SK-BR-3. The transcriptional control of the CYP19 gene is exon-specific, and promoter regions I.3 and II have been shown to be responsible for CYP19 expression in SK-BR-3 cells. Luciferase reporter gene assays also revealed that biochanin A could repress the transcriptional control dictated by the promoter regulation. Interestingly, genistein did not inhibit aromatase but it might down regulate promoter I.3 and II transactivation. Since genistein is a major metabolite of biochanin A, it might contribute to biochanin A's suppressive effect on CYP19 expression. The present study illustrated that biochanin A inhibited CYP19 activity and gene expression.

Bioavailability of soy isoflavones in rats Part I: application of accurate methodology for studying the effects of gender and source of isoflavones

There are limited and controversial reports about the effects of gender and source of isoflavones on their bioavailability. Moreover, several previous studies have not used appropriate methodology to determine the bioavailability of soy isoflavones, which requires comparing the area under the plasma concentration-time curve after both oral and intravenous injection (IV) administration. Therefore, the present study was conducted to determine the bioavailability of isoflavones from different sources following both oral and IV administration in male and female rats. Three sources of isoflavones; Novasoy (a commercial supplement), a mixture of synthetic aglycones (daidzein, genistein and glycitein) and a mixture of synthetic glucosides (daidzin, genistin and glycitin) were tested. Following administration, blood samples were collected at several time points (0, 10, 30 min and 1, 2, 8, 24, 48 h post oral gavage and 0, 10, 30, 45 min and 1, 2, 3, 4, 8 h post-IV dosing) and plasma isoflavones were measured by LC/MS. Bioavailability values for daidzein, genistein and glycitein were significantly (p <0.05) higher (up to sevenfold) in Novasoy and the glucoside forms of isoflavones compared with those of the aglycone forms. Moreover, significant (p <0.05) gender differences in the bioavailability of 7-hydroxyl-3-(4'-hydroxyphenyl)-chroman (a metabolite of daidzein), glycitein and daidzein were observed for Novasoy, with higher values in male rats. In summary, the source of isoflavones and the sex of rats had significant effects on isoflavone bioavailability.

Improving metabolic stability of cancer chemoprotective polyphenols

Dietary flavonoids and other polyphenols have the potential to be developed as effective food supplements as well as drugs for the prevention, as well as treatment of, cancer and other disease conditions. However, their very poor oral bioavailability, mainly due to extensive conjugation by glucuronidation and sulfation, is a severe limiting factor. First, this review shows the use of a simple, commercially available model system, the human hepatic S9 fraction, by which metabolic stability can be assessed effectively and accurately. Second, permethylation of the polyphenols effectively blocks the metabolic conjugation reactions, thereby dramatically increasing both metabolic stability and intestinal absorption, while maintaining or even increasing the biologic activities. Thus, permethylated polyphenols may have a future as chemoprotective agents.