(1/1619) Daidzein and genistein glucuronides in vitro are weakly estrogenic and activate human natural killer cells at nutritionally relevant concentrations.
Daidzein and genistein glucuronides (DG and GG), major isoflavone metabolites, may be partly responsible for biological effects of isoflavones, such as estrogen receptor binding and natural killer cell (NK) activation or inhibition. DG and GG were synthesized using 3-methylcholanthrene-induced rat liver microsomes. The Km and Vmax for daidzein and genistein were 9.0 and 7.7 micromol/L, and 0.7 and 1.6 micromol/(mg protein. min), respectively. The absence of ultraviolet absorbance maxima shifts in the presence of sodium acetate confirmed that the synthesized products were 7-O-glucuronides. DG and GG were further purified by a Sephadex LH-20 column. DG and GG competed with the binding of 17beta-(3H) estradiol to estrogen receptors of B6D2F1 mouse uterine cytosol. The concentrations required for 50% displacement of 17beta-(3H) estradiol (CB50) were: 17beta-estradiol, 1.34 nmol/L; diethylstilbestrol, 1.46 nmol/L; daidzein, 1.6 micromol/L; DG, 14.7 micromol/L; genistein, 0.154 micromol/L; GG, 7.27 micromol/L. In human peripheral blood NK cells, genistein at <0.5 micromol/L and DG and GG at 0.1-10 micromol/L enhanced NK cell-mediated K562 cancer cell killing significantly (P < 0.05). At > 0.5 micromol/L, genistein inhibited NK cytotoxicity significantly (P < 0.05). The glucuronides only inhibited NK cytotoxicity at 50 micromol/L. Isoflavones, and especially the isoflavone glucuronides, enhanced activation of NK cells by interleukin-2 (IL-2), additively. At physiological concentrations, DG and GG were weakly estrogenic, and they activated human NK cells in nutritionally relevant concentrations in vitro, probably at a site different from IL-2 action. (+info)
(2/1619) Dietary isoflavones: biological effects and relevance to human health.
Substantial evidence indicates that diets high in plant-based foods may explain the epidemiologic variance of many hormone-dependent diseases that are a major cause of mortality and morbidity in Western populations. There is now an increased awareness that plants contain many phytoprotectants. Lignans and isoflavones represent two of the main classes of phytoestrogens of current interest in clinical nutrition. Although ubiquitous in their occurrence in the plant kingdom, these bioactive nonnutrients are found in particularly high concentrations in flaxseeds and soybeans and have been found to have a wide range of hormonal and nonhormonal activities that serve to provide plausible mechanisms for the potential health benefits of diets rich in phytoestrogens. Data from animal and in vitro studies provide convincing evidence for the potential of phytoestrogens in influencing hormone-dependent states; although the clinical application of diets rich in these estrogen mimics is in its infancy, data from preliminary studies suggest beneficial effects of importance to health. This review focuses on the more recent studies pertinent to this field and includes, where appropriate, the landmark and historical literature that has led to the exponential increase in interest in phytoestrogens from a clinical nutrition perspective. (+info)
(3/1619) Serum levels and metabolic clearance of the isoflavones genistein and daidzein in hemodialysis patients.
Genistein and daidzein are biologically active isoflavones that are especially abundant in soybeans. After intestinal absorption, circulating genistein and daidzein are eliminated primarily by the kidneys. This study was undertaken to assess the metabolism of genistein and daidzein in patients with end-stage renal disease (ESRD) on hemodialysis therapy, and to test whether this treatment modality can replace the lack of kidney function, with respect to the elimination of the isoflavones. Twenty-three hemodialysis patients and 10 healthy subjects were studied. While consuming a self-selected low isoflavone diet, baseline blood levels were undetectable in eight of 10 healthy subjects and in 14 of 23 dialysis patients. The remaining participants had detectable levels, with the nine dialysis patients displaying much higher blood concentrations than the two healthy control subjects. After the evening intake of one dose of an isoflavone-rich soy protein isolate drink, the early morning blood levels of genistein and daidzein were higher in seven dialysis patients than in eight healthy subjects (genistein 1271+/-321 versus 425+/-104, P<0.05; daidzein 1304+/-352 versus 292+/-78, P<0.05). The blood clearance of the isoflavones was studied in two healthy subjects and in three dialysis patients. Genistein and daidzein were eliminated within 2 d in the healthy subjects, but had not returned to baseline in two of three ESRD patients, 7 d after intake. The half-life of both compounds was estimated to be 10-fold longer in the ESRD patients than in the healthy subjects. Finally, genistein and daidzein levels were measured before and after dialysis in five patients, both while on their regular diet and after one dose of a soy protein isolate drink. In both instances, the dialysis treatment did not affect the blood isoflavone levels. In conclusion, approximately one-third of hemodialysis patients eating the standard American renal diet experience high blood levels of the isoflavones genistein and daidzein, while the remaining two-thirds have undetectable levels. After ingestion of isoflavone-rich food such as soy products, all patients have detectable levels that remain very high for several days due to lack of renal excretion. (+info)
(4/1619) Daidzein and genistein but not their glucosides are absorbed from the rat stomach.
Absorption of isoflavone aglycones and glucosides was compared in rats. Daidzein, genistein, daidzin and genistin were orally administered at a dose of 7.9 micromol/kg in 25 mM Na2CO3 and next their metabolite concentration in blood plasma was monitored for 30 min. After isoflavone glucosides administration, their metabolites appeared in plasma with a few minutes delay as compared to aglycones, which suggested that aglycones, but not glucosides, were absorbed already in the rat stomach. This observation was confirmed when absorption site was restricted solely to the stomach and absorption was shown to be independent of the vehicle pH used for administration. (+info)
(5/1619) 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. (+info)
(6/1619) Soybean isoflavones reduce experimental metastasis in mice.
We investigated the effect of dietary supplementation with isoflavones on pulmonary metastasis of B16BL6 murine melanoma cells in C57BL/6 mice. Mice were fed a basal AIN-93G diet or the basal diet supplemented with the isoflavones genistein and daidzein at 113 micromol/kg, 225 micromol/kg, 450 micromol/kg, or 900 micromol/kg for 2 wk before and after the intravenous injection of 0.5 x 10(5) melanoma cells. At necropsy, the number and size of tumors that formed in the lungs were determined. The number of mice that had >15 lung tumors was 17 in the control group, and 16, 15, 13, and 10 in the groups fed isoflavones at 113 micromol/kg, 225 micromol/kg, 450 micromol/kg and 900 micromol/kg, respectively. The latter two were significantly different from the control (P = 0.05). The median number of tumors in the control group was 67, and those in the isoflavone-supplemented groups were 57, 33, 32, and 17, respectively. The last was significantly different from the control (P = 0.05). Dietary supplementation with isoflavones at 225 micromol/kg, 450 micromol/kg, and 900 micromol/kg also significantly decreased tumor size (median cross-sectional area and volume) compared to the control values. We conclude that dietary supplementation with isoflavones reduces experimental metastasis of melanoma cells in mice. (+info)
(7/1619) Inhibition of ATPase, GTPase and adenylate kinase activities of the second nucleotide-binding fold of the cystic fibrosis transmembrane conductance regulator by genistein.
In the presence of ATP, genistein, like the ATP analogue adenosine 5'-[beta,gamma-imido]triphosphate (pp[NH]pA), increases cystic fibrosis transmembrane conductance regulator (CFTR) chloride currents by prolonging open times. As pp[NH]pA is thought to increase CFTR currents by interfering with ATP hydrolysis at the second nucleotide-binding fold (NBF-2), the present study was undertaken to investigate the effects of genistein on a fusion protein comprising maltose-binding protein (MBP) and NBF-2 (MBP-NBF-2). MBP-NBF-2 exhibited ATPase, GTPase and adenylate kinase activities that were inhibited by genistein in a partial non-competitive manner with respect to ATP or GTP. Ki values for competitive and uncompetitive inhibition were respectively 20 microM and 63 microM for ATPase, 15 microM and 54 microM for GTPase, and 46 microM and 142 microM for adenylate kinase. For ATPase activity, genistein reduced Vmax by 29% and Vmax/Km by 77%. Additional evidence for complex-formation between genistein and MBP-NBF-2 was obtained by the detection of genistein-dependent alterations in the CD spectrum of MBP-NBF-2 that were consistent with the formation of a higher-ordered state. Addition of MBP-NBF-2 increased the fluorescence intensity of genistein, consistent with a change to a less polar environment. pp[NH]pA partially eliminated this enhanced fluorescence of genistein. These observations provide the first direct biochemical evidence that genistein interacts with CFTR, thus inhibiting NBF-2 activity, and suggest a similar mechanism for genistein-dependent stimulation of CFTR chloride currents. (+info)
(8/1619) Macrophage enrichment with the isoflavan glabridin inhibits NADPH oxidase-induced cell-mediated oxidation of low density lipoprotein. A possible role for protein kinase C.
Macrophage-mediated oxidation of low density lipoprotein (LDL) is considered to be of major importance in early atherogenesis; therefore, intervention means to inhibit this process are being extensively studied. In the present study, we questioned the ability of the isoflavan glabridin (from licorice) to accumulate in macrophages and to affect cell-mediated oxidation of LDL. We first performed in vitro studies, using mouse peritoneal macrophages (MPMs) and the J-774 A.1 macrophage-like cell line. Both cells accumulated up to 1.5 micrograms of glabridin/mg of cell protein after 2 h of incubation, and this process was time- and glabridin dose-dependent. In parallel, in glabridin-enriched cells, macrophage-mediated oxidation of LDL was inhibited by up to 80% in comparison with control cells. Glabridin inhibited superoxide release from MPMs in response to phorbol 12-myristate 13-acetate, or to LDL when added together with copper ions, by up to 60%. Translocation of P-47, a cytosolic component of NADPH oxidase to the plasma membrane was substantially inhibited. In glabridin-enriched macrophages, protein kinase C activity reduced by approximately 70%. All of the above effects of glabridin required the presence of the two hydroxyl groups on the flavonoid's B phenol ring. In order to assess the physiological significance of these results, we next performed in vivo studies, using the atherosclerotic apolipoprotein E-deficient (E0) mice. MPMs harvested from glabridin-treated E0 mice (20 micrograms/mouse/day for a period of 6 weeks) demonstrated reduced capability to oxidize LDL by 80% in comparison with placebo-treated mice. This latter phenomenon was associated with a reduction in the lesion oxysterols and a 50% reduction in the aortic lesion size. We thus conclude that glabridin accumulation in macrophages is associated with reduced cell-mediated oxidation of LDL and decreased activation of the NADPH oxidase system. These phenomena could be responsible for the attenuation of atherosclerosis in E0 mice, induced by glabridin. (+info)