Plasma and urinary kinetics of the isoflavones daidzein and genistein after a single soy meal in humans

Effects of phyto-oestrogens on tissues

Recent investigations on the effects of phyto-oestrogens on various tissues have revealed that these diverse molecules may improve human health, particularly by protecting against certain chronic diseases. After a brief examination of the food sources, structures, and general cellular actions of the major phyto-oestrogens, current research findings on cardiovascular disease, skeletal tissues, and reproductive cancers are reviewed. Phyto-oestrogen concentrations in blood may be maintained at high levels in those consuming soyabean (Glycine max)-based food daily at several meals and exert their effects on target cells through either genomic effects via the classical oestrogen receptors or non-genomic effects mediated by membrane-bound oestrogen receptors or other cellular proteins. The expression of oestrogen receptor (OR) subtypes alpha (a) and beta (beta) varies across tissues, and cells that preferentially express OR-beta, which may include bone cells, are more likely to respond to phyto-oestrogens. Conversely, reproductive tissues contain relatively more OR-a and may, thus, be differently affected by phyto-oestrogens. Soyabean phyto-oestrogens appear to prevent the progression of atherosclerosis through multiple interactions, including lowering of plasma lipids and lipoproteins, increased vasodilatation and, possibly, decreased activation of blood platelets and vascular smooth muscle cells. However, a favourable impact on cardiovascular disease morbidity and mortality by a soyabean-enriched western-type diet remains to be shown, and unresolved questions remain regarding dose and form of the phyto-oestrogens in relation to risks and benefits. The isoflavones of soyabean have been shown consistently to have bone-retentive effects in animal studies by several investigators using rodent models, although intakes must be above a relatively high threshold level for a lengthy period of time, and little or no extra benefit is observed with intakes above this threshold level. The reports of modest or no effects on prevention of bone loss in human and non-human primate studies respectively, may be due to the limited doses tested so far. The relationship between soyabean-food intake and cancer risk has been more extensively investigated than for any other disease, but with less certainty about the benefits of long-term consumption of phyto-oestrogen-containing foods on prevention of cancer. The observations that breast and prostate cancer rates are lower in Asian countries, where soyabean foods are consumed at high levels, and the high isoflavone content of soyabeans have led to examination of the potential protective effects of phyto-oestrogens. Establishing diet-cancer relationships has proved difficult, in part because of the conflicting data from various studies of effects of soyabean-diets on cancer. Epidemiological evidence, though not impressive, does suggest that soyabean intake reduces breast cancer risk. The isoflavone genistein has a potent effect on breast cancer cells in vitro, and early exposure of animals to genistein has been effective in reducing later development of mammary cancer. Thus, continuous consumption of soyabean foods in early life and adulthood may help explain the low breast cancer mortality rates in Asian countries. Although the evidence for a protective effect against prostate cancer may be slightly more supportive, more research is needed before any firm conclusions can be made about the phyto-oestrogen-cancer linkages.

Genistein effects on Ca2+ handling in human umbilical artery: inhibition of sarcoplasmic reticulum Ca2+ release and of voltage-operated Ca2+ channels

Isoflavones are a group of natural phytoestrogens including the compound genistein. Health beneficial effects have been attributed to the consumption of this compound, but the fact that it has estrogen-like activity has raised doubts regarding its potential risk in infants, newborns, or in the fetus and placenta during pregnancy. This work is aimed at studying genistein effects on Ca2+ handling by smooth muscle cells of the human umbilical artery (HUA). Using fluorometric techniques, we found that in these cells genistein reduces the intracellular Ca2+ peak produced by serotonin. The same result could be demonstrated in absence of extracellular Ca2+, suggesting that the isoflavone reduces Ca2+ release from the sarcoplasmic reticulum. Force measurement experiments strengthen these results, since genistein reduced the peak force attained by intact HUA rings stimulated by serotonin in a Ca2+-free solution. Moreover, genistein induced the relaxation of HUA rings precontracted either with serotonin or a depolarizing high-extracellular K+ solution, hinting at a reduction of extracellular Ca2+ entry to the cell. This was confirmed by whole-cell patch-clamp experiments where it was shown that the isoflavone inhibits ionic currents through voltage-operated Ca2+ channels. In summary, we show that genistein inhibits two mechanisms that could increase intracellular Ca2+ in human umbilical smooth muscle cells, behaving in this way as a potential vasorelaxing substance of fetal vessels. Taking into account that genistein is able to cross the placental barrier, these data show that isoflavones may have important implications in the regulation of feto-maternal blood flow in pregnant women who consume soy-derived products as part of their meals.

Soy, phyto-oestrogens and male reproductive function: a review

There is growing interest in the possible health threat posed by the effects of endocrine disruptors on reproduction. Soy and soy-derived products contain isoflavones that mimic the actions of oestrogens and may exert adverse effects on male fertility. The purpose of this review was to examine the evidence regarding the potential detrimental effects of soy and phyto-oestrogens on male reproductive function and fertility in humans and animals. Overall, there are some indications that phyto-oestrogens, alone or in combination with other endocrine disruptors, may alter reproductive hormones, spermatogenesis, sperm capacitation and fertility. However, these results must be interpreted with care, as a result of the paucity of human studies and as numerous reports did not reveal any adverse effects on male reproductive physiology. Further investigation is needed before a firm conclusion can be drawn. In the meantime, caution would suggest that perinatal phyto-oestrogen exposure, such as that found in infants feeding on soy-based formula, should be avoided.

The pharmacokinetics of S-(-)equol administered as SE5-OH tablets to healthy postmenopausal women

The soy isoflavone metabolite, S-(-)equol, has selective affinity for estrogen receptor (ER)beta and also antagonizes in vivo the action of dihydrotestosterone. It is therefore of interest as a potential new therapeutic agent in hormone-dependent conditions and is under development as a nutraceutical. Our objective in this study was to define the pharmacokinetics of natural S-(-)equol after administration of SE5-OH, a newly developed S-(-)equol supplement made by incubation of the equol-producing bacterium Lactococcus garvieae with soy germ isoflavones. In a single-center, open-label, randomized, 2-period crossover design study, the pharmacokinetics of S-(-)equol administered as single-bolus oral doses of 10 and 30 mg in the form of SE5-OH tablets was determined in 12 healthy postmenopausal women. S-(-)equol was measured in plasma and urine collected at timed intervals over a 48-h period postdosing using tandem MS. Equol-producer status was also determined after a soymilk challenge conducted after the pharmacokinetic sampling was complete. S-(-)equol was rapidly absorbed after oral administration and attained high plasma concentrations, with a plasma elimination half-life of 8 h. The maximum plasma concentration/dose, area under the plasma concentration-time curve from time 0 to infinity/dose, and the fraction of dose excreted in urine (%f(e,u)) were similar for the 2 doses, indicating a dose-proportional response in total S-(-)equol pharmacokinetics. The systemic bioavailability of S-(-)equol was very high, as the %f(e,u) was 82% for both doses, which is greater than published data for the soy isoflavones daidzein and genistein. Three participants were determined to be equol-producers, representing a 25% frequency, and equol-producer status had no effect on natural S-(-)equol pharmacokinetics.

Genistein and daidzein prevent low potassium-dependent apoptosis of cerebellar granule cells

We have investigated the ability of certain dietary flavonoids, known to exert beneficial effects on the central nervous system, to affect neuronal apoptosis. We used cerebellar granule cells undergoing apoptosis due to potassium deprivation in a serum-free medium in either the absence or presence of the flavonoids genistein and daidzein, which are present in soy, and of catechin and epicatechin, which are present in cocoa. These compounds were used in a blood dietary concentration range. We found that genistein and daidzein, but not catechin and epicatechin, prevented apoptosis, with cell survival measured 24h after the induction of apoptosis being higher than that of the same cells incubated in flavonoid free medium (80% and 40%, respectively); there was no effect in control cells. A detailed investigation of the effect of these compounds on certain mitochondrial events that occur in cells en route to apoptosis showed that genistein and daidzein prevented the impairment of glucose oxidation and mitochondrial coupling, reduced cytochrome c release, and prevented both impairment of the adenine nucleotide translocator and opening of the mitochondrial permeability transition pore. Interestingly, genistein and daidzein were found to reduce the levels of reactive oxygen species, which are elevated in cerebellar granule cell apoptosis. These findings strongly suggest that the prevention of apoptosis depends mainly on the antioxidant properties of genistein and daidzein. This could lead to the development of a flavonoid-based therapy in neuropathies.

The pharmacokinetic behavior of the soy isoflavone metabolite S-(-)equol and its diastereoisomer R-(+)equol in healthy adults determined by using stable-isotope-labeled tracers

BACKGROUND

The nonsteroidal estrogen equol occurs as diastereoisomers, S-(-)equol and R-(+)equol, both of which have significant biological actions. S-(-)equol, the naturally occurring enantiomer produced by 20-30% of adults consuming soy foods, has selective affinity for estrogen receptor-beta, whereas both enantiomers modulate androgen action. Little is known about the pharmacokinetics of the diastereoisomers, despite current interest in developing equol as a nutraceutical or pharmaceutical agent.

OBJECTIVE

The objective was to compare the pharmacokinetics of S-(-)equol and R-(+)equol by using [13C] stable-isotope-labeled tracers to facilitate the optimization of clinical studies aimed at evaluating the potential of these diastereoisomers in the prevention and treatment of estrogen- and androgen-dependent conditions.

DESIGN

A randomized, crossover, open-label study in 12 healthy adults (6 men and 6 women) compared the plasma and urinary pharmacokinetics of orally administered enantiomeric pure forms of S-(-)[2-13C]equol, R-(+)[2-13C]equol, and the racemic mixture. Plasma and urinary [13C]R-equol and [13C]S-equol concentrations were measured by tandem mass spectrometry.

RESULTS

Plasma [13C]equol concentration appearance and disappearance curves showed that both enantiomers were rapidly absorbed, attained high circulating concentrations, and had a similar terminal elimination half-life of 7-8 h. The systemic bioavailability and fractional absorption of R-(+)[2-13C]equol were higher than those of S-(-)[2-13C]equol or the racemate. The pharmacokinetics of racemic (+/-)[2-13C]equol were different from those of the individual enantiomers: slower absorption, lower peak plasma concentrations, and lower systemic bioavailability.

CONCLUSIONS

The high bioavailability of both diastereoisomers contrasts with previous findings for the soy isoflavones daidzein and genistein, both of which have relatively poor bioavailability, and suggests that low doses of equol taken twice daily may be sufficient to achieve biological effects.

Sex-based cardiac physiology

Biological sex plays an important role in normal cardiac physiology as well as in the heart's response to cardiac disease. Women generally have better cardiac function and survival than do men in the face of cardiac disease; however, this sex difference is lost when comparing postmenopausal women with age-matched men. Animal models of cardiac disease mirror what is seen in humans. Sex steroid hormones contribute significantly to sex-based differences in cardiac disease outcomes. Estrogen is generally considered to be cardioprotective, whereas testosterone is thought to be detrimental to heart function. Environmental estrogen-like molecules, such as phytoestrogens, can also affect cardiac physiology in both a positive and a negative manner.

The relationship between fasting plasma concentrations of selected flavonoids and their ordinary dietary intake

Epidemiological studies suggest that a diet high in flavonoids protects against chronic diseases such as CVD and cancer. The objective of the present study was to evaluate the relationship between the intake of quercetin, kaempferol, isorhamnetin, apigenin and luteolin and their corresponding plasma concentrations, and further to explore whether these flavonoids can serve as biomarkers of their intake. Flavonoid intake and their plasma concentrations were analysed in ninety-two subjects consuming their habitual diet. Flavonoid intake was estimated with 7-d dietary records using available data on the flavonoid content of food. Plasma flavonoid concentrations were quantified by HPLC. In addition, we undertook a dietary intervention study to investigate plasma apigenin concentration after the consumption of celery leaf. The mean intake estimates of quercetin, kaempferol, isorhamnetin, apigenin and luteolin amounted to 13·58, 14·97, 12·31, 4·23 and 8·08 mg/d, respectively. The corresponding mean plasma concentrations were 80·23, 57·86, 39·94, 10·62 and 99·90 nmol/l. The mean 7 d intake of five flavonoids was positively correlated to their corresponding plasma concentrations, with correlation coefficients ranging from 0·33 to 0·51 (P < 0·05). In the dietary intervention study, the plasma apigenin concentration rose after celery leaf ingestion, and fell within 28 h to below the limit of detection (2·32 nmol/l). The present results suggest that quercetin, kaempferol, isorhamnetin, apigenin and luteolin are bioavailable from the diet. The levels of fasting plasma flavonoids seem to be suitable biomarkers of short-term intake. The combination of plasma flavonoids with their intake may prove useful when the possible health-protective effects of flavonoids are studied.

Long-term exposure to genistein improves insulin secretory function of pancreatic beta-cells

We recently found that genistein, a plant-derived natural compound, is a novel cAMP signaling agonist in pancreatic beta-cells. In the present study, we further show that exposure of clonal insulin secreting (INS-1E) cells to genistein for 48 h enhanced glucose-stimulated insulin secretion (GSIS), whereas insulin content was not altered, suggesting that genistein-enhanced GSIS is not due to a modulation of insulin synthesis. This genistein effect is protein tyrosine kinase- and K(ATP) channel-independent. In addition, genistein had no effect on glucose transporter-2 expression or cellular ATP production, but similarly augmented pyruvate-stimulated insulin secretion in INS-1E cells, indicating that the improvement of insulin secretory function by long-term genistein exposure is not related to an alternation in glucose uptake or the glycolytic pathway. The enhanced insulin secretion by genistein was associated with elevated intracellular Ca(2+) concentration and dependent on protein kinase A and new protein synthesis as this effect was completely blocked by N-[2-(p-Bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide or cycloheximide. Similarly, 48 h of genistein exposure also enhanced GSIS in freshly isolated mouse and human pancreatic islets, suggesting a non-species-specific and biologically relevant effect. These findings provide evidence that genistein may be a novel bioactive compound that has an anti-diabetic effect by improving insulin secretion from pancreatic beta-cells.

Gastrointestinal absorption and metabolism of soy isoflavonoids in ileal-canulated swine

The relative contribution of the small intestine to absorption and microbial metabolism of ingested isoflavonoids (IFN) was investigated in swine with canulae in distal ilea to facilitate collection of chyme (canula open). Weaned swine were fed a single meal containing ground roasted soybean and corn with canulae open followed by a second test soy diet at 48 h with canulae closed to allow passage of chyme into the large intestine. All remaining feedings were soy-free (corn-casein diet). Ileal effluent and urine were collected for 16 and 48 h, respectively, and analyzed for IFN and microbial metabolites of IFN. IFN in ileal effluent were present entirely as aglycones. IFN equivalents excreted for 24 h after ingesting the soy diet were not significantly different when canulae were open or closed. Urinary IFN aglycone equivalents on day 2 were similar to those on day 1 when canulae remained closed, but less than 10% of that on day 1 when canulae were open for 16 h postfeeding. Urinary concentrations of dihydrodaidzein, dihydrogenistein, O-desmethylangolensin, and equol exceeded IFN aglycone equivalents. These findings suggest extensive preabsorptive conversion of IFN glucosides to aglycones in the small intestine and relatively efficient microbial metabolism of IFN in weaned swine.

Phytoestrogenic isoflavonoids in epidemiologic and clinical research

Isoflavones (IFLs) are natural products to which humans have been traditionally exposed predominantly through soy foods; more recently humans are also exposed to them through soy protein addition to processed foods or through supplements. They are structurally similar to steroidal estrogens and can exert estrogenic or antiestrogenic effects depending on their concentrations and on the tissue considered. These properties qualify IFLs to be classified as phytoestrogens and are believed to account for many of the biological effects observed for soy and/or IFL exposure including benefits for bone and heart health or prevention of menopausal symptoms and certain types of cancer. In order to evaluate the function of IFLs, alone or when exposure happens through soy intake, pharmacokinetics and bioavailability are critical issues to be considered in epidemiologic and clinical research. For this purpose precise, accurate, robust, fast, and affordable techniques for IFL analyses are required.

Daidzein administration in vivo reduces myocardial injury in a rat ischemia/reperfusion model by inhibiting NF-kappaB activation

AIMS

We tested the hypothesis that daidzein may reduce myocardial damage by both inhibiting the release of cytokines and limiting the nuclear translocation of NF-kappaB.

MAIN METHODS

Male Sprague-Dawley rats were anesthetized, and the left anterior descending coronary artery (LAD) was ligated for 25 min. Twenty-four hours after reperfusion was established, the hemodynamics and infarct size were examined.

KEY FINDINGS

Treatment with daidzein (10 mg/kg, i.p.) 1 h prior to the ischemia/reperfusion procedure (I/R) reduced the infarct size by 52.8% (P<0.05). Daidzein also significantly improved I/R-induced myocardial contractile dysfunction by improving the left ventricular diastolic pressure and the positive and negative maximal values of the first derivative of the left ventricular pressure. In addition, daidzein reduced the plasma levels of TNF-alpha and IL-6 in I/R rats and decreased malondialdehyde levels, myeloperoxidase activity, catalase activity and neutrophil infiltration in I/R rat myocardium. Interestingly, daidzein inhibited I/R-induced myocardial apoptosis by decreasing DNA strand breaks and cleaved caspase-3 activity. Furthermore, daidzein inhibited both the nuclear translocation of NF-kappaB in I/R rat hearts and the H(2)O(2)-induced activation of NF-kappaB-luciferase activity in human umbilical vein endothelial cells.

SIGNIFICANCE

This study reveals that the administration of daidzein in vivo attenuates I/R-induced myocardial damage via inhibition of NF-kappaB activation, which in turn may suppress inflammatory cytokine expression.

Intermolecular interactions identify ligand-selective activity of estrogen receptor alpha/beta dimers

Estrogen receptor (ER) dimerization is prerequisite for its activation of target gene transcription. Because the two forms of ER, ERalpha and ERbeta, exhibit opposing functions in cell proliferation, the ability of ligands to induce ERalpha/beta heterodimers vs. their respective homodimers is expected to have profound impacts on transcriptional outcomes and cellular growth. However, there is a lack of direct methods to monitor the formation of ERalpha/beta heterodimers in vivo and to distinguish the ability of estrogenic ligands to promote ER homo- vs. heterodimerization. Here, we describe bioluminescence resonance energy transfer (BRET) assays for monitoring the formation of ERalpha/beta heterodimers and their respective homodimers in live cells. We demonstrate that although both partners contribute to heterodimerization, ligand-bound ERalpha plays a dominant role. Furthermore, a bioactive component was found to induce ERbeta/beta homodimers, and ERalpha/beta heterodimers but had minimal activity on ERalpha/alpha homodimers, posing a model that compounds promoting ERalpha/beta heterodimer formation might have therapeutic value. Thus, ER homodimer and heterodimer BRET assays are applicable to drug screening for dimer-selective selective ER modulators. Furthermore, this strategy can be used to study other nuclear receptor dimers.

Soy food consumption does not lower LDL cholesterol in either equol or nonequol producers

BACKGROUND

Health claims link soy protein (SP) consumption, through plasma cholesterol reduction, to a decreased risk of heart disease. Soy isoflavones (ISOs), particularly in individuals who produce equol, might also contribute to lipid lowering and thus reduce SP requirements.

OBJECTIVE

The objective was to examine the contributions of SP, ISOs, and equol to the hypocholesterolemic effects of soy foods.

DESIGN

Nonsoy consumers (33 men, 58 women) with a plasma total cholesterol (TChol) concentration >5.5 mmol/L participated in a double-blind, placebo-controlled, crossover intervention trial. The subjects consumed 3 diets for 6 wk each in random order, which consisted of foods providing a daily dose of 1) 24 g SP and 70-80 mg ISOs (diet S); 2) 12 g SP, 12 g dairy protein (DP), and 70-80 mg ISOs (diet SD); and 3) 24 g DP without ISOs (diet D). Fasting plasma TChol, LDL cholesterol, HDL cholesterol, and triglycerides (TGs) were measured after each diet.

RESULTS

TChol was 3% lower with the S diet (-0.17 +/- 0.06 mmol/L; P < 0.05) than with the D diet, and TGs were 4% lower with both the S (-0.14 +/- 0.05 mmol/L; P < 0.05) and SD (-0.12 +/- 0.05 mmol/L; P < 0.05) diets. There were no significant effects on LDL cholesterol, HDL cholesterol, or the TChol:HDL cholesterol ratio. On the basis of urinary ISOs, 30 subjects were equol producers. Lipids were not affected significantly by equol production.

CONCLUSIONS

Regular consumption of foods providing 24 g SP/d from ISOs had no significant effect on plasma LDL cholesterol in mildly hypercholesterolemic subjects, regardless of equol-producing status.

Effects of isoflavone supplements vs. soy foods on blood concentrations of genistein and daidzein in adults

The objective of this investigation was to examine the pharmacokinetics of isoflavone concentrations over a 24-h period among healthy adults consuming either soy foods or soy isoflavone tablets at different doses. This randomized, cross-over trial was conducted with 12 generally healthy adults. The three phases of the intervention included isoflavone tablets at (1) 144 mg/day or (2) 288 mg/day and (3) soy foods designed to provide a calculated 96 mg isoflavones/day (doses in aglycone equivalents). Doses were spread out over three meals per day. After 6 days on each study phase, plasma isoflavone concentrations were determined on the seventh day at 0, 4, 8, 10, 12 and 24 h. Average levels of total isoflavone concentrations at 8, 10 and 12 h were >4 micromol/L for the soy food phase and for the higher dose tablet phase. Genistein concentrations were higher overall in the soy food vs. both the lower and the higher dose supplement phases of the study (P<.05). When comparing plasma concentrations for the two doses of tablets, saturation appeared more evident for genistein than for daidzein at the higher dose level. In conclusion, we observed important differences in the pharmacokinetics of genistein and daidzein contrasting the sources and doses of isoflavones when administered three times daily, including a possible advantage for increasing serum concentrations of isoflavones from consuming soy foods relative to isoflavone supplements.

The key importance of soy isoflavone bioavailability to understanding health benefits

Research over the past two decades has provided significant epidemiological and other evidence for the health benefits of the consumption of soy-based foods. A large number of dietary intervention studies have examined the effects of soy isoflavones on risk factors for cardiovascular disease and hormone-dependent cancers. However, these report large variability in outcome measures, very limited reproducibility between studies, and in some cases, controversy between the results of clinical trials using dietary soy or soy protein and isoflavone supplementation. This highlights a major gap in our understanding of soy isoflavone uptake, metabolism, distribution, and overall bioavailability. There are many potential factors that may influence bioavailability and a better knowledge is necessary to rationalize the inconsistencies in the intervention and clinical studies. This review focuses attention on our current state of knowledge in this area and highlights the importance of metabolism of the parent soy isoflavones and the critical role of gut microbiota on the bioavailability of these compounds and their metabolites.

Dietary phytoestrogens activate AMP-activated protein kinase with improvement in lipid and glucose metabolism

OBJECTIVE

Emerging evidence suggests that dietary phytoestrogens can have beneficial effects on obesity and diabetes, although their mode of action is not known. Here, we investigate the mechanisms mediating the action of dietary phytoestrogens on lipid and glucose metabolism in rodents.

RESEARCH DESIGN AND METHODS

Male CD-1 mice were fed from conception to adulthood with either a high soy-containing diet or a soy-free diet. Serum levels of circulating isoflavones, ghrelin, leptin, free fatty acids, triglycerides, and cholesterol were quantified. Tissue samples were analyzed by quantitative RT-PCR and Western blotting to investigate changes of gene expression and phosphorylation state of key metabolic proteins. Glucose and insulin tolerance tests and euglycemic-hyperinsulinemic clamp were used to assess changes in insulin sensitivity and glucose uptake. In addition, insulin secretion was determined by in situ pancreas perfusion.

RESULTS

In peripheral tissues of soy-fed mice, especially in white adipose tissue, phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase was increased, and expression of genes implicated in peroxisomal fatty acid oxidation and mitochondrial biogenesis was upregulated. Soy-fed mice also showed reduced serum insulin levels and pancreatic insulin content and improved insulin sensitivity due to increased glucose uptake into skeletal muscle. Thus, mice fed with a soy-rich diet have improved adipose and glucose metabolism.

CONCLUSIONS

Dietary soy could prove useful to prevent obesity and associated disorders. Activation of the AMPK pathway by dietary soy is likely involved and may mediate the beneficial effects of dietary soy in peripheral tissues.

Genistein potentiates protein kinase A activity in porcine coronary artery

Soy consumption is associated with a lower risk of atherosclerotic disease in the oriental population. Genistein is a soy isoflavone bearing estrogenic properties. Previous experiments in our laboratory demonstrated the potentiation of endothelium-independent relaxation of coronary artery by both estrogen and genistein. The potentiating effects of both estrogen and genistein were mediated through the cAMP-signaling pathway. We hypothesize that genistein could enhance protein kinase A (PKA) activity in porcine coronary artery smooth muscle, thereby offering a mechanism for the potentiation of vascular relaxation by genistein. In our study, a high concentration of genistein (10(-4.5) M) significantly increased PKA activity in porcine coronary artery rings. While genistein at 10(-5.5) M and forskolin at 10(-7) M had no effect on PKA activity, the combination of the two compounds at the prescribed concentrations caused a significant increase in PKA activity. The increase in PKA activity by genistein was abolished by SQ 22536 (adenylate cyclase blocker), but not by NF 449 (Gs protein blocker) or ICI 182780 (estrogen receptor antagonist). Our results suggest that the action of genistein is mediated via adenylate cyclase, but does not appear to involve Gs protein or ICI 182780-sensitive estrogen receptor.

Differential effects of soybean and fenugreek extracts on the growth of MCF-7 cells

The effect of aqueous and ethanol extracts of soybean and fenugreek on the growth of MCF-7 cells, an estrogen receptor positive breast cancer cell line, has been examined in this study. Soybean is well known for the presence of phytoestrogens and fenugreek is reported to have medicinal use including anticancer properties. In a dose dependent manner soybean aqueous and ethanol extract promoted the growth and DNA synthesis in MCF-7 cells. On the contrary ethanol extract of fenugreek decreased the cell viability and induced early apoptotic changes such as flipping of phosphatidylserine and decrease of mitochondrial membrane potential. Degradation of cellular DNA into fragments comprising multiples of approximately 180-200 base pair was also observed. Cell cycle analysis by flow cytometry showed the presence of a subG1 apoptotic population which was more prominent at higher concentrations along with cell cycle arrest at G2/M phase. Our experiments show that while the soybean extract acts as a promoter of MCF-7 cell growth, the fenugreek extract induces apoptosis.

Dual effects of daidzein, a soy isoflavone, on catecholamine synthesis and secretion in cultured bovine adrenal medullary cells

We recently demonstrated the occurrence and functional roles of plasma membrane estrogen receptors in cultured bovine adrenal medullary cells. Here we report the effects of daidzein, a phytoestrogen of soybeans, on catecholamine synthesis and secretion in the cells. Incubation of cells with daidzein for 20 min increased the synthesis of (14)C-catecholamines from [(14)C]tyrosine but not [(14)C]dihydroxyphenylalanine, in a concentration-dependent manner (10-1000 nm). The stimulatory effect of daidzein on (14)C-catecholamine synthesis was not inhibited by ICI182,780, a classical estrogen receptor inhibitor. Acetylcholine, a physiological secretagogue, stimulated the synthesis of (14)C-catecholamines, which was suppressed by daidzein at 1 mum. Daidzein at high concentrations (1-100 microm) suppressed catecholamine secretion induced by acetylcholine. Furthermore, daidzein (10-1000 nm) inhibited the specific binding of [(3)H]17beta-estradiol to plasma membranes isolated from bovine adrenal medulla. The present findings suggest that daidzein at low concentrations stimulates catecholamine synthesis through plasma membrane estrogen receptors but at high concentrations inhibits catecholamine synthesis and secretion induced by acetylcholine in bovine adrenal medulla. The latter effect of daidzein may be a beneficial action on the cardiovascular system.

Disposition of flavonoids via enteric recycling: determination of the UDP-glucuronosyltransferase isoforms responsible for the metabolism of flavonoids in intact Caco-2 TC7 cells using siRNA

Our recent study indicates that microsomal glucuronidation rates are not predictive of the cellular glucuronide excretion rates and whole cell systems are needed to accurately determine the metabolic rates. This study aims to determine the contribution of UGT isoforms responsible for the metabolism of flavonoids in intact Caco-2 cells and cell lysates using siRNA. The results showed that UGT1A6 activities (as measured by p-nitrophenol glucuronidation) and expression were typically decreased 60-80% by siRNA treatment. Using siRNA-mediated silencing, we also showed that in intact cells, siRNA treatment substantially decreased the rate of excretion of apigenin glucuronide at low and high concentrations (>35%, p < 0.05), although it only moderately decreased the rate of excretion of genistein glucuronide at a high concentration (29%). The results also indicated that well-expressed UGT isoforms in the Caco-2 cells, UGT1A1, UGT1A3, UGT1A6, and UGT2B7, were capable of metabolizing apigenin faster than genistein and that UGT1A6 silencing did not substantially increase the level of expression of genistein-metabolizing UGT isoforms. We also determined the contribution of UGT1A6 to the apigenin and genistein metabolisms as a function of concentration, and the results indicated that metabolism of apigenin and genistein was saturable and siRNA treatment greatly reduced the rate of metabolism of apigenin but not that of genistein. In conclusion, we show for the first time that siRNA can be used effectively to determine which UGT isoform contributes to the metabolism of its substrate in intact cells. The results also indicate that UGT1A6 is a major contributor to glucuronidation of apigenin but not genistein in intact Caco-2 cells and in cell lysates.

A phytoestrogen-rich diet increases energy expenditure and decreases adiposity in mice

BACKGROUND

Obesity is an increasingly prevalent health problem, and natural effective therapeutic approaches are required to prevent its occurrence. Phytoestrogens are plant-derived compounds with estrogenic activities; they can bind to both estrogen receptors alpha and beta and mimic the action of estrogens on target organs.

OBJECTIVES

The purpose of this study was to examine the influence of soy-derived phytoestrogens on energy balance and metabolism.

METHODS

Male outbred mice (CD-1) were allowed ad libitum access to either a high soy-containing diet or a soy-free diet from conception to adulthood. We measured circulating serum isoflavone levels using reverse-phase solid-phase extraction for subsequent liquid chromatography electrospray tandem mass spectrometry analysis. Adult animals were analyzed for body composition by dual-energy X-ray absorptiometry, locomotor activity by running-wheel experiments, respiratory exchange rate by indirect calorimetry, and food intake using metabolic cages. Quantitative reverse transcriptase-polymerase chain reaction was performed to determine the expression of hypothalamic neuropeptide genes.

RESULTS

We found that adult mice fed a soy-rich diet had reduced body weight, adiposity, and resistance to cold. This lean phenotype was associated with an increase in lipid oxidation due to a preferential use of lipids as fuel source and an increase in locomotor activity. The modulation of energy balance was associated with a central effect of phytoestrogens on the expression of hypothalamic neuropeptides, including agouti-related protein.

CONCLUSION

The data suggest that dietary soy could have beneficial effects on obesity, but they also emphasize the importance of monitoring the phytoestrogen content of diets as a parameter of variability in animal experiments.

Influence of inulin on plasma isoflavone concentrations in healthy postmenopausal women

BACKGROUND

Bacterial intestinal glucosidases exert an important role in isoflavone absorption. Insoluble dietary fibers such as inulin may stimulate the growth of these bacteria in the colon and, hence, stimulate the absorption of these substances in subjects who may need isoflavone supplementation.

OBJECTIVE

The objective was to assess the influence of inulin on plasma isoflavone concentrations after intake of soybean isoflavones in healthy postmenopausal women.

DESIGN

Twelve healthy postmenopausal women participated in a randomized, double-blind, crossover study. They consumed 40 mg of a conjugated form of soybean isoflavones (6 mg daidzein and 18 mg genistein as free form) with or without 3.66 g inulin twice daily in two 21-d experimental phases. Blood samples were collected 0, 1, 2, 3, 4, 6, 10, 12, and 24 h after intake of isoflavones with breakfast and dinner at the end of each 21-d experimental phase. Plasma concentrations of isoflavones were assessed by HPLC with an electrochemical detector.

RESULTS

Plasma 24-h areas under the curve indicated that the intake of soybean isoflavones with inulin for 21 d was followed by higher plasma concentrations of daidzein and genistein (38% and 91%, respectively) compared with the formulation without inulin. Furthermore, the time for the maximum concentration of daidzein and genistein appeared to be lower after the 21-d intake of soybean isoflavones, with or without inulin. However, the time for the maximum concentration of daidzein and genistein after supplementation with the inulin-containing formulation on day 21 was not significantly different from that after supplementation with the formulation without inulin.

CONCLUSIONS

Inulin may increase the apparent plasma concentrations of the soybean isoflavones daidzein and genistein in postmenopausal women. The higher plasma concentrations of the 2 isoflavones suggests that the absorption of each was facilitated by the presence of inulin.

The bioavailability and disposition kinetics of genistein in cats

The absorption and disposition kinetics of the soy isoflavone genistein were determined in cats (n = 6). An oral dose of 100 mg/kg was administered, which has previously been demonstrated to be the minimum oral estrogenic dose, and was administered intravenously at a dose of 20 mg/kg, being the largest practical dose that could be safely administered. Plasma free, and total (conjugated + free) genistein concentrations were determined by HPLC following organic extraction. Noncompartmental analysis revealed a half-life of 21.67 +/- 7.9 h (free) and 9.95 +/- 2.7 h (conjugated), volume of distribution 31.94 +/- 10.38 L/kg (free) and 11.82 +/- 3.96 L/kg (conjugated) following intravenous administration. Following oral administration the half-lives were determined to be 17 +/- 4.8 h (free) and 8.56 +/- 4.65 h (conjugated), with tmax = 4.4 +/- 0.6 h (free) and 4.42 +/- 0.99 h (conjugated), and Cmax = 0.276 +/- 0.1 microg/mL (free) and 6.24 +/- 6.58 microg/mL (conjugated). Oral bioavailabilities were 1.379 +/- 0.9% (free) and 29.85 +/- 22.61% (conjugated). The ratio of total:free genistein ranged from 25.9 to 5.5. Poor oral absorption and efficient conjugation explain the low bioavailability of free genistein. Accumulation of genistein in peripheral lipophilic compartments may occur.

Can the combination of flaxseed and its lignans with soy and its isoflavones reduce the growth stimulatory effect of soy and its isoflavones on established breast cancer?

Consumption of phytoestrogen (PE)-rich foods (i. e., soy and flaxseed (FS)) is increasing because of their suggested health benefits. However, recent studies raise concern over the safety of soy and its isoflavones, particularly genistein (GEN), for postmenopausal breast cancer (BC), due to their potential stimulatory effects on human breast tissue and on the growth of existing tumors in rodents. FS, rich in PE lignans, which is metabolized to the mammalian lignans enterolactone (ENL) and enterodiol (END), has consistently been shown to have tumor inhibitory effects in a human clinical trial as well as rodent BC models. Using the preclinical athymic mouse postmenopausal BC model, combining FS with soy protein or GEN with END and ENL, was found to negate the tumor stimulatory effects of soy protein or GEN alone. The mechanism may be related to the modulation of estrogen receptor and MAPK signaling pathways. If these studies can be confirmed in clinical trials, then consumption of combined soy and FS, or their PEs, may reduce the tumor growth stimulatory effect of soy or GEN. This may indicate that if soy is consumed with lignan-rich foods, it may continue to induce its other beneficial health effects, without inducing adverse effect on postmenopausal BC.

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.

Natural polyphenol disposition via coupled metabolic pathways

A major challenge associated with the development of chemopreventive polyphenols is the lack of bioavailability in vivo, which are primarily the result of coupled metabolic activities of conjugating enzymes and efflux transporters. These coupling processes are present in disposition tissues and organs in mammals and are efficient for the purposes of drug metabolism, elimination and detoxification. Therefore, it was expected that these coupling processes represent a significant barrier to the oral bioavailabilities of polyphenols. In various studies of this coupling process, it was identified that various conjugating enzymes such as uridine 5'-diphosphate-glucuronosyltransferase and sulfotransferase are capable of producing very hydrophilic metabolites of polyphenols, which cannot diffuse out of the cells and needs the action of efflux transporters to pump them out of the cells. Additional studies have shown that efflux transporters, such as multi-drug resistance-associated protein 2, breast cancer-resistant protein and the organic anion transporters, appear to serve as the gate keeper when there is an excess capacity to metabolise the compounds. These efflux transporters may also act as the facilitator of metabolism when there is a product/metabolite inhibition. For polyphenols, these coupled processes enable a duo recycling scheme of enteric and enterohepatic recycling, which allows the polyphenols to be reabsorbed and results in longer than expected apparent plasma half-lifes for these compounds and their conjugates. Because the vast majority of polyphenols in plasma are hydrophilic conjugates, more research is needed to determine if the metabolites are active or reactive, which will help explain their mechanism of actions.

Effect of soy isoflavones on endometriosis: interaction with estrogen receptor 2 gene polymorphism

BACKGROUND

Progression of endometriosis is considered estrogen-dependent. Dietary soy isoflavones may affect the risk of endometriosis, and polymorphisms in estrogen receptor genes may modify this association. We examined associations among soy isoflavone intake, estrogen receptor 2 (ESR2) gene polymorphisms and risk of endometriosis.

METHODS

We recruited women age 20-45 years old who had consulted a university hospital for infertility in Tokyo, Japan in 1999 or 2000. A total of 138 eligible women were diagnosed laparoscopically and classified into 3 subgroups: control (no endometriosis), early endometriosis (stage I-II) and advanced endometriosis (stage III-IV). We measured urinary levels of genistein and daidzein as markers for dietary intake of soy isoflavones, and genotyped ESR2 gene RsaI polymorphisms.

RESULTS

Higher levels of urinary genistein and daidzein were associated with decreased risk of advanced endometriosis (P for trend = 0.01 and 0.06, respectively) but not early endometriosis. For advanced endometriosis, the adjusted odds ratio for the highest quartile group was 0.21 (95% confidence interval = 0.06-0.76) for genistein and 0.29 (0.08-1.03) for daidzein, when compared with the lowest group. Inverse associations were also noted between urinary isoflavones and the severity of endometriosis (P for trend = 0.01 for genistein and 0.07 for daidzein). For advanced endometriosis, ESR2 gene RsaI polymorphism appeared to modify the effects of genistein (P for interaction = 0.03).

CONCLUSIONS

Dietary isoflavones may reduce the risk of endometriosis among Japanese women.

Isoflavonoid glucosides are deconjugated and absorbed in the small intestine of human subjects with ileostomies

BACKGROUND

Although soy isoflavonoids have a number of health-promoting benefits, information concerning the sites of their absorption and metabolism in humans remains limited. Isoflavonoid absorption from the gut requires deconjugation of glucosides to aglycones.

OBJECTIVE

The objective was to investigate the role of the small intestine in isoflavonoid absorption and metabolism in humans.

DESIGN

Human subjects with fully functional gastrointestinal tracts (n = 6) and ileostomy subjects (n = 6) were fed a single soy meal containing 64.8 mg isoflavonoid aglycone equivalents (95% as glucosides). Metabolism of isoflavonoids in the upper gastrointestinal tract was examined by analyzing ileal effluent from ileostomy subjects, and absorption was assessed indirectly by quantifying isoflavonoids and several metabolites in 24-h urine pools.

RESULTS

Chyme contained 36.7% of ingested isoflavonoid aglycone equivalents, primarily (95.8%) as aglycones. Qualitative profiles (x +/- SEM) of isoflavonoid excretion in urine (daidzein > glycitein > genistein) and the quantity of isoflavonoid equivalents were not significantly different between the control (18.4 +/- 2.2 mg) and ileostomy (13.5 +/- 3.2 mg) subjects. Dihydrodaidzein was present in the urine of all subjects, although the amount excreted by ileostomy subjects was less than that excreted by the control subjects. The percentage of producers and mean quantities of dihydrogenistein, equol, and O-desmethylangolensin in the urine of ileostomy subjects also were lower than those of control subjects.

CONCLUSIONS

Ileostomy subjects efficiently deglycosylate isoflavonoid glucosides in the small intestine and appear to absorb aglycones with an efficiency comparable with that of control subjects. However, the production of microbial metabolites of isoflavonoids is limited in ileostomy subjects.

Urinary isoflavone kinetics: the effect of age, gender, food matrix and chemical composition

Urinary isoflavone excretion is used to monitor compliance and examine biological effects. The present study determined if there were alterations in urinary isoflavone excretion following the ingestion of different soya foods and if age and gender potentially modified profiles. Twenty premenopausal women, seventeen post-menopausal women and twenty men received a defined single oral bolus dose (0·44mg isoflavones/kg body weight) of soya milk, textured vegetable protein (TVP) or tempeh on three separate occasions. Baseline and four consecutive complete 24h pooled urines were collected during each period. Urinary genistein recovery was influenced by gender and food matrix. For women the urinary genistein recovery was higher following soya-milk consumption compared with TVP (P<0·05). Tempeh consumption also resulted in an increased urinary genistein recovery relative to soya milk in premenopausal women (P<0·052). No differences in urinary genistein recoveries between soya foods were observed in the men. Although urinary daidzein excretion was similar across the foods studied and was not affected by age or gender, conversion to its intestinal metabolite, equol, resulted in potential matrix and chemical composition effects; urinary equol excretion was higher (P<0·01) following tempeh ingestion among equol producers. Together these data suggest that the fractional absorption of genistein is potentially different in men and women and is influenced by the food matrix and chemical composition. Furthermore, the data suggest that the metabolism of daidzein may be altered by the chemical composition of the isoflavones ingested. Further studies are required to examine the effect of higher intake and define the relative influence of these factors in elderly population groups.

Genistein modulates the effects of parathyroid hormone in human osteoblastic SaOS-2 cells

Genistein and parathyroid hormone (PTH) are anabolic agents that stimulate bone formation through their direct actions in osteoblastic cells. In the present study, we aimed to determinewhether genistein modulates the actions of PTH in human osteoblastic SaOS-2 cells in an oestrogen-depleted condition. The present results showed that genistein (10−8to 10−6m) induced alkaline phosphatase (ALP) activity and osteoprotegrin (OPG) expression in SaOS-2 cells in a dose-dependent manner. These effects could be completely abolished by co-treatment with oestrogen antagonist ICI 182780 (7α-[9-[(4,4,5,5,5-pentafluoropentyl)sulfonyl]nonyl]-estra-1,3,5(10)-triene-3,17β-diol). Genistein (at 1μm) could stimulate the mRNA expression of receptor activator of NF-κB ligand (RANKL). As OPG and RANKL are known to modulate osteoclastogenesis, the ability of genistein to modulate OPG and RANKL expression in SaOS-2 cells suggested that it might modulate osteoclastogenesis through its direct actions on osteoblastic cells. PTH (at 10nm) stimulated ALP activity, induced RANKL mRNA expression and suppressed OPG mRNA expression in SaOS-2 cells, confirming its bi-directional effects on osteoblastic cells. Pre-treatment of SaOS-2 cells with genistein andoestrogen not only enhanced PTH-induced ALP activity, but also attenuated PTH up regulation ofRANKL mRNA expression and PTH down regulation of OPG mRNA expression. Taken together, the present study provides the first evidence that genistein could modulate the actions of PTH in human osteoblastic SaOS-2 cells in an oestrogen-depleted condition.

Bioavailability of isoflavone phytoestrogens in postmenopausal women consuming soya milk fermented with probiotic bifidobacteria

We investigated the effects of consuming an isoflavone aglycone-enriched soya milk containing viable bifidobacteria on urinary isoflavone excretion and percentage recovery. Sixteen postmenopausal women were randomly divided into two groups to consume either fermented or non-fermented soya milk. Each group participated in a double-blind, crossover study with three 14 d supplementation periods, separated by a 14 d washout. Subjects ingested three daily dosages of isoflavone via the soya milk and collected four 24 h pooled urine specimens per supplementation period. Soya milks were prepared with soya protein isolate and soya germ, followed by fermentation with bifidobacteria. Isoflavone levels were quantified using HPLC. Non-fermented soya milks at 20, 40 and 80 mg isoflavone/200 ml contained 10 %, 9 % and 7 % aglycone, respectively, with their fermented counterparts containing 69 %, 57 % and 36 % aglycone (P<0·001). A trend to a greater percentage urinary recovery of daidzein and glycitein was observed among women consuming fermented soya milk at a dosage of 40 mg isoflavone (P=0·13). A distinct linear dose response for the fermented soya milk group (R2=0·9993) compared with the non-fermented group (R2=0·8865) suggested less interindividual variation in isoflavone absorption. However, total urinary isoflavone excretion was similar for both groups (P>0·05), with urinary isoflavone recovery at approximately 31 %. Increasing the isoflavone dosage correlated positively with its urinary excretion, but urinary percentage recovery of isoflavone was inversely related to dosage level. Hence, a modest dosage ranging from 20 to 30 mg/d may provide the most bioavailable source of isoflavone, regardless of whether it is via an aglycone-rich fermented soya milk or a glucoside-rich soya milk.

Frequency of soy food consumption and serum isoflavone concentrations among Chinese women in Shanghai

Objective:

The food-frequency questionnaire (FFQ) can be an efficient tool to evaluate dietary intake in large, population-based studies, especially for specific foods. The objective of this study was to validate the assessment of soy and isoflavone (daidzein and genistein) intakes, measured by an FFQ, by comparing intakes with serum isoflavone concentrations.

Design and setting:

Soy and isoflavone intakes and serum isoflavone concentrations were determined as part of a case–control study of dietary factors and risks of benign breast disease and breast cancer. The FFQ, administered during an in-person interview, included six soy-specific line items. Blood was drawn within one week of FFQ completion.

Subjects:

In total, 1823 women living in Shanghai, People's Republic of China.

Results:

In this population, soybean milk, fresh bean curd and other bean foods were eaten once per week, and fermented bean curd, fried bean curd puff and soybeans were eaten less than once per week. A significant linear trend (P > 0.01) in serum isoflavone concentrations across increasing categories of soy and isoflavone intakes was observed, indicating that soy and isoflavone intakes, measured by the FFQ, well distinguished serum isoflavone concentrations. Linear trends were also observed in both case and control groups in stratified analyses, suggesting little differential bias by case–control status.

Conclusions:

The results suggest that the FFQ provides a useful marker of soy food consumption and isoflavone exposure in this population.

Pharmacokinetic study of puerarin in rat serum by liquid chromatography tandem mass spectrometry

A highly sensitive and specific atmospheric pressure chemical ionization liquid chromatography-tandem mass spectrometry method was developed for serum pharmacokinetic studies of puerarin in rats. Chromatography was carried out on a reversed-phase Phenomenex Synergi 4 microm Fusion-RP80 column (150 x 2.0 mm i.d.) using a mobile phase consisting of acetonitrile-water (10:90, v/v) in 10 mm NH(4)OAc with a flow rate of 0.2 mL/min. Puerarin was analyzed in the multiple reaction monitoring mode with a precursor/product ion transition of m/z 415/267. The method was demonstrated to be specific and sensitive, and a linear response was observed over a range of 2-5000 ng/mL in rat serum. The validated method was successfully applied to the characterization of the pharmacokinetics of puerarin in rat serum after oral administration to spontaneously hypertensive rats. The blood concentration-time profile of puerarin showed a rapid initial increase, reaching a maximum and then declining within 1 h. Puerarin could not be detected after 24 h. The main pharmacokinetic parameters for puerarin after oral administration were as follows: C(max) (3.54 +/- 2.03 mg/L), T(max) (0.68 +/- 0.37 h), AUC(0-t) (7.29 +/- 3.79 mg h/L), AUC(0-infinity) (9.17 +/- 4.87 mg h/L), T(1/2) (1.7 +/- 0.6 h), CL/F (7.24 +/- 4.27 L/h/kg) and V/F (17.88 +/- 13.55 L/h/kg).

Review of the factors affecting bioavailability of soy isoflavones in humans

Soy isoflavones have anticarcinogenic, antioxidant, and antiatherosclerotic activities. They also interact with the estrogen receptor, which makes them weak or moderate phytoestrogens. Because of their bioactivity, isoflavone bioavailability has been extensively studied in humans. This review summarizes data from intervention studies in humans, focusing on the factors that affect bioavailability. Summarizing data from 16 studies shows that the maximum concentration in plasma normalized to a constant dose of genistin is approximately 1.6 times that of genistein, and daidzin is approximately 1.8-fold higher than daidzein, whereas the half-life is not significantly different for aglycone and glucoside. There is a wide variation in the reported percentage urinary excretion that is not dependent on dose. Bioavailability is increased by a rapid gut transit time and by low fecal digestion rates and is decreased by a fiber-rich diet. There is no difference in bioavailability between pre- and postmenopausal women. The daily ingestion of soymilk for 1 wk does not affect bioavailability, but daily ingestion for a month increases excretion of equol in women. The factors or habitual diet characteristics that influence equol production are not clear, but equol production is limited with an immature flora. There is no consensus on which source of isoflavones results in the highest isoflavone bioavailability, and published studies present different results, although bioavailability is affected by whether the dose is given as food or drink. In conclusion, it is important to consider the factors affecting bioavailability of isoflavones when designing intervention studies.

Anti-obesity activities of fermented soygerm isoflavones by Bifidobacterium breve

Soygerm isoflavones were subjected to fermentation by Bifidobacterium breve. Most of isoflavone glycosides (daidzin, glycitin and genistin) in soygerms were deglycosylated to their corresponding isoflavone aglycones (daidzein, glycitein and genistein) within 24 h fermentation. Fermented isoflavones significantly inhibited pancreatic lipase activity in fermentation-time and dosage dependant manner. When fermented isoflavones were orally administered with olive oil to SD rats, the triglyceride (TG) level in plasma after 2 h of ingestion was significantly lower than the control of only olive oil administered group whereas no such significant decrease in plasma TG was observed in unfermented isoflavone administered group. This result indicates that oral administration of fermented isoflavones effectively suppressed absorption of excessive lipid into a body. Addition of either unfermented or fermented soygerm isoflavones effectively inhibited adipocyte differentiation from 3T3-L1 in a dose dependent manner. In conclusion, B. breve successfully converted soygerm isoflavones into their aglycones, and these aglycones were more effective in suppressing lipid absorption as well as adipocytes differentiation than their glycosides.