Pharmacokinetics of soybean isoflavones in plasma, urine and feces of men after ingestion of 60 g baked soybean powder (kinako)

Genistein prevents the glucose autoxidation mediated atherogenic modification of low density lipoprotein

Hyperglycemia has been assumed to be responsible for oxidative stress in diabetes. In this respect, glucose autoxidation and advanced glycation end products (AGE) may play a causal role in the etiology of diabetic complications as e.g. atherosclerosis. There is now growing evidence that the oxidative modification of LDL plays a potential role in atherogenesis. Glucose derived oxidants have been shown to peroxidise LDL. In the present study, genistein, a compound derived from soy with a flavonoid chemical structure (4', 5, 7-trihydroxyisoflavone) has been evaluated for its ability to act as an antioxidant against the atherogenic modification of LDL by glucose autoxidation radical products. Daidzein, (4',7-dihydroxyisoflavone) an other phytoestrogen of soy, was tested in parallel. Genistein--in contrast to daidzein--effectively prevented the glucose mediated LDL oxidation as measured by thiobarbituric acid-reactive substance formation (TBARS), alteration in electrophoretic mobility, lipid hydroperoxides and fluorescence quenching of tryptophan residues of the lipoprotein. In addition the potential of glucose-oxidized LDL to increase tissue factor (TF) synthesis human endothelial cells (HUVEC) was completely inhibited when genistein was present during LDL oxidative modification by glucose. Both phytoestrogens did not influence the nonenzymatic protein glycation reaction as measured by the in vitro formation of glycated LDL. As the protective effect of genistein on LDL atherogenic modification was found at glucose/genistein molar ratios which may occur in vivo, our findings support the suggested beneficial action of a soy diet in preventing chronic vascular diseases and early atherogenic events.

Fermentation by gut microbiota cultured in a simulator of the human intestinal microbial ecosystem is improved by supplementing a soygerm powder

An in vitro model, designated the Simulator of the Human Intestinal Microbial Ecosystem (SHIME), was used to study the effect of a soygerm powder rich in beta-glycosidic phytoestrogenic isoflavones on the fermentation pattern of the colon microbiota and to determine to what extent the latter metabolize the conjugated phytoestrogens. Initially, an inoculum prepared from human feces was introduced into the reactor vessels and stabilized over 3 wk using a culture medium. This stabilization period was followed by a 2-wk control period during which the microbiota were monitored. The microbiota were then subjected to a 2-wk treatment period by adding 2.5 g/d soygerm powder to the culture medium. The addition resulted into an overall increase of bacterial marker populations (Enterobacteriaceae:, coliforms, Lactobacillus: sp., Staphylococcus: sp. and Clostridium: sp.), with a significant increase of the Lactobacillus: sp. population. The short-chain fatty acid (SCFA) concentration increased approximately 30% during the supplementation period; this was due mainly to a significant increase of acetic and propionic acids. Gas analysis revealed that the methane concentration increased significantly. Ammonium and sulfide concentrations were not influenced by soygerm supplementation. Use of an electronic nose apparatus indicated that odor concentrations decreased significantly during the treatment period. The beta-glycosidic bonds of the phytoestrogenic isoflavones were cleaved under the conditions prevailing in the large intestine. The increased bacterial fermentation after addition of the soygerm powder was paralleled by substantial metabolism of the free isoflavones (genistein, daidzein and glycitein), resulting in recovery of only 12-17% of the supplemented isoflavones.

Mass spectrometric determination of Genistein tissue distribution in diet-exposed Sprague-Dawley rats

Genistein, the principal soy isoflavone, was administered in the diet to male and female Sprague-Dawley rats as part of a multigeneration study of potential endocrine modulation. The rats were exposed to genistein in utero, through maternal milk, and as adults through postnatal d 140 via essentially isoflavone-free feed (approximately 0.5 microg/g) fortified at 5, 100 and 500 microg/g with genistein aglycone. Analytical methods based on liquid chromatography, mass spectrometry and the use of deuterated genistein were developed and validated for use in measuring genistein in serum and tissues. Pharmacokinetic analysis of serum genistein showed a significant difference (P < 0.001) in the elimination half-life and area under the concentration-time curve between male [2.97 +/- 0.14 h and 22.3 +/- 1.2 micromol/(L. h), respectively] and female rats [4.26 +/- 0.29 h and 45.6 +/- 3.1 micromol/(L. h), respectively, +/- SEM]. Endocrine-responsive tissues including brain, liver, mammary, ovary, prostate, testis, thyroid and uterus showed significant dose-dependent increases in total genistein concentration. Female liver contained the highest amount of genistein (7.3 pmol/mg tissue) and male whole brain contained the least (0.04 pmol/mg). The physiologically active aglycone form was present in tissues at fractions up to 100%, and the concentration was always greater than that observed in serum in which conjugated forms predominated (95-99%). These results for measured amounts of genistein, present as aglycone and conjugates, in putative target tissues provide a link with other studies in which blood concentrations and physiologic effects of genistein are measured.

Soy isoflavone aglycones are absorbed faster and in higher amounts than their glucosides in humans

Isoflavones are contained in soybean or soy foods in two chemical forms, i.e., aglycones and glucosides. We investigated the difference in the absorption of soy isoflavone aglycones and glucosides in humans. After a single, low dose intake (0.11 mmol), the highest isoflavone concentrations in plasma were reached 2 and 4 h after ingestion of aglycones and glucosides, respectively; subjects were four men (41 y old) and four women (45 y old). The highest plasma concentration after aglycone intake was more than two times greater than that after glucoside ingestion. In a similar manner, we then compared the plasma isoflavone concentration profiles after intake of a single, high dose of isoflavones (1.7 mmol) in eight subjects (four men, 40 y old; four women, 47 y old) and found the highest plasma concentration after aglycone intake was more than five times higher than that after glucoside intake. In both high and low dose intake tests, the plasma concentration of genistein was significantly higher than that of daidzein despite the similar levels of intake. After long-term (4 wk) intakes (0.30 mmol/d), we also measured the plasma concentration of isoflavones (eight men, 45 y old). After 2 and 4 wk, these concentrations remained >100% higher after ingestion of aglycones than of glucosides. The isoflavone aglycones were absorbed faster and in greater amounts than their glucosides in humans. Isoflavone aglycone-rich products may be more effective than glucoside-rich products in preventing chronic disease such as coronary heart disease.

Inhibition of mitochondrial proton F0F1-ATPase/ATP synthase by polyphenolic phytochemicals

Mitochondrial proton F0F1-ATPase/ATP synthase synthesizes ATP during oxidative phosphorylation. In this study, we examined the effects of several groups of polyphenolic phytochemicals on the activity of the enzyme. Resveratrol, a stilbene phytoalexin that is present in grapes and red wine, concentration-dependently inhibited the enzymatic activity of both rat brain and liver F0F1-ATPase/ATP synthase (IC(50) of 12 - 28 microM). Screening of other polyphenolic phytochemicals using rat brain F0F1-ATPase activity resulted in the following ranking potency (IC(50) in parenthesis): piceatannol (8 microM)>resveratrol (19 microM)=(-)epigallocatechin gallate (17 microM)>(-)epicatechin gallate, curcumin (45 microM)>genistein=biochanin A=quercetin=kaempferol=morin (55 - 65 microM)>phloretin=apigenin=daidzein (approx. 100 microM). Genistin, quercitrin, phloridzin, (+)catechin, (+)epicatechin, (-)epicatechin and (-)epigallocatechin had little effect at similar concentrations. Tannic acid, theaflavins (tea extract) and grape seed proanthocyanidin extract (GSPE) had IC(50) values of 5, 20 and 30 microg ml(-1), respectively. Several monophenolic antioxidants and non-phenolic compounds were ineffective at concentrations of 210 microM or higher. The inhibition of F0F1-ATPase by resveratrol and genistein was non-competitive in nature. The effects of polyphenolic phytochemicals were additive. Both resveratrol and genistein had little effect on the Na(+)/K(+)-ATPase activity of porcine cerebral cortex, whereas quercetin had similar inhibitory potency as for F0F1-ATPase. In conclusion, the ATP synthase is a target for dietary phytochemicals. This pharmacological property of these phytochemicals should be included in the examination of their health benefits as well as potential cytotoxicity.

Absorption and metabolism of genistin in the isolated rat small intestine

Uptake and intestinal metabolism of physiologically active genistin were studied in an ex vivo intestinal perfusion model; luminally applied concentrations were 5.9, 12.0, and 23.8 micromol/l. The intestinal absorption of genistin was 14.9% (+/-2.3, n=9), irrespective of the amounts applied. The majority of the absorbed genistin appeared as genistein glucuronide (11.6%), also recovered as the main metabolite on the luminal side (19.5%). Minor amounts of genistin (1.3%) and genistein (1.9%) were found on the vascular side, whereas 15.4% of applied genistin was luminally cleaved to yield genistein. Sulfate derivatives of genistein or genistin were not observed.

Antioxidant activity of soya hypocotyl tea in humans

Antioxidative activity of isoflavones has not been shown in humans. Newly-developed isoflavone-rich soya hypocotyl tea contains about 12 mg isoflavones per liter. 15 tea drinkers and 23 control young female students were randomly selected from volunteers, and underwent physical examination, blood chemistry and urinary analysis before and after one month of tea drinking. A three-day dietary record was taken before each physical examination. The tea drinkers showed a lower level of phosphatidylcholine hydroperoxide (PCOOH) and phosphatidyl-ethanolamine hydroperoxide (PEOOH) in the red blood cells and a significant reduction of 8-hydroxydeoxyguanine (8ohdG) in the urine compared to the controls.

Effects of isoflavone supplement on healthy women

Effects of the isoflavone supplement on hormonal states in young premenopausal women were studied by cross-over study design. Administration of 20 mg or 40 mg isoflavones (IF) by tablets, of which 1 g contained 43.5 mg daidzein, 6.0 mg genistein, 24.0 mg glycitein, to 40 young female students for one month caused a prolonged menstruation in 60% of young women, shortened menstruation in 20% of young women, 17% remained unchanged and 3% became irregular. Larger dose tended to elongate more, but 17beta-estradiol levels in both follicular and luteal phages were not different between 20 mg and 40 mg isoflavone intake. Equor excreters tended to show low plasma progesteron level in the luteal phase. Detailed hormonal analysis on 3 of students by a cross over study design showed decreased level of 17beta-estradiol throughout the menstruation cycle. SHBG significantly increased about 10% in all three. DEAS, androstendione, and testosterone showed different responses according to the follicular or luteal phase. T3 and T4 increased as a result of isoflavone tablet administration in the follicular phase, but it decreased in the luteal phase. These changes suggest that isoflavones influence not only estrogen receptor-related functions but the hypothalamo-hypophysis-gonadal axis.

Soy protein, isoflavonoids, and risk of developing coronary heart disease

The effects of soy protein and isoflavones on blood cholesterol in humans has been variable. Maximal low- density lipoprotein cholesterol lowering appears to be modest and consistently ranges from 5% to 7%. Preliminary evidence suggests a potentially beneficial effect of the isoflavone fraction of soybeans on arterial compliance. The isoflavone fraction has been demonstrated to decrease the in vitro susceptibility of low-density lipoprotein to oxidation; the significance of this finding in vivo is unknown. It is difficult to definitively say at this time whether increased consumption of soy based products will result in a decreased risk of CHD beyond their ability to displace foods high in saturated fat and cholesterol from the diet.

Catechin is present as metabolites in human plasma after consumption of red wine

Flavonoids are components of fruits, vegetables and wines. An abundance of flavonoids in the diet is correlated with reduced heart disease mortality, suggesting that they act as protective nutrients. However, little is known about the absorption and metabolism of flavonoids after normal foods are consumed. This study measured the levels of one abundant flavonoid, (+)-catechin, and its metabolites in plasma after five male and four female volunteers consumed 120 mL of red wine (RW) one day and de-alcoholized red wine (DRW) on a separate day. Each wine sample contained 35 +/- 1 mg catechin (mean +/- SEM). Plasma levels of catechin and its metabolite 3'-O-methylcatechin (3'MC) were determined by gas chromatography-mass spectrometry (GC-MS) of the trimethylsilylated (TMS) derivatives. Glucuronide and sulfate conjugates were determined after enzymatic hydrolysis. Before RW or DRW consumption, plasma levels of catechin, 3'MC and all conjugates were <2 nmol/L. After 1 h, average levels of catechin, 3'MC and all conjugates increased to 91 +/- 14 nmol/L (RW) and 81 +/- 11 nmol/L (DRW). At 1 h, 21 +/- 1% of the metabolites were methylated and <2% of catechin and 3'MC were unconjugated. Catechin was present as both a sulfate conjugate and a conjugate containing both glucuronide and sulfate residues. 3'MC was present primarily as a glucuronide conjugate. At every time point, catechin was present almost exclusively as metabolites, and these levels were independent of ethanol. Therefore, if flavonoids are protective nutrients, the active forms are likely to be metabolites, which are far more abundant in plasma than the forms that exist in foods.

Urinary disposition of the soybean isoflavones daidzein, genistein and glycitein differs among humans with moderate fecal isoflavone degradation activity

Glycitein metabolism was compared with other isoflavones to begin to understand the effect of this compound. Total isoflavones of 4.5 micromol/kg body weight from soymilk (high in genistein and daidzein) and soygerm (high in daidzein and glycitein) was fed to seven women and seven men. To minimize interindividual variation, only subjects with moderate fecal isoflavone degradation rates (half-lives of daidzein and genistein were 15.7 and 8.9 h, respectively) were included. The average 48-h urinary excretion of glycitein, daidzein and genistein was approximately 55, 46 and 29% of the dose ingested, respectively, which was significantly different from each other in men and women (P < 0.001). Plasma isoflavone concentrations at 6 and 24 h after soymilk feeding paralleled relative amounts of isoflavones in soymilk (genistein > daidzein > glycitein) (P < 0.05) in men and women, but plasma isoflavone concentrations after soygerm feeding did not parallel soygerm isoflavone concentrations in women because genistein and glycitein did not differ from each other at 6 h after feeding. Six hours after soygerm dosing, plasma isoflavone concentrations paralleled soygerm isoflavone levels in men. Based on plasma isoflavone concentrations at 6 h after dosing, the bioavailabilities of daidzein and genistein were similar in men and women. At the high glycitein dose (soygerm), plasma concentration at 24 h after dosing suggested a modest gender difference in glycitein bioavailability.

Maternal and neonatal phytoestrogens in Japanese women during birth

OBJECTIVE

High levels of soy isoflavonoids among adult Japanese persons are associated with a low incidence of hormone-dependent cancers, but nothing is known about isoflavonoids in pregnancy.

STUDY DESIGN

We studied 7 young healthy Japanese women at delivery by measuring 6 phytoestrogen metabolites in maternal and cord plasma and in amniotic fluid.

RESULTS

Total maternal plasma isoflavonoid concentrations ranged from 19 to 744 nmol/L (mean 232 nmol/L), cord plasma values ranged from 58 to 831 nmol/L (mean 299 nmol/L), and amniotic fluid values ranged from 52 to 779 nmol/L (mean 223 nmol/L). Maternal and cord plasma and amniotic fluid lignan values were low.

CONCLUSIONS

The high levels of isoflavonoid phytoestrogens found in healthy neonatal Japanese infants indicate transfer of isoflavonoids from the maternal to the fetal compartment. These compounds may modify estrogen metabolism and action during fetal life and perhaps affect cancer risk.