Plasma Concentrations Of Genistein Research Articles

Abstract 4642: Effects of soy protein diet on plasma isoflavones levels in obese DMBA-induced mammary tumor rat model

Abstract Obesity epidemic in the US and world grows as the number of overweight and obese adults continues to rise. Obese women have higher mortality rates from all cancers including breast cancer. Several studies have reported the protective effects of soy intake on breast cancer development, while other studies report the adverse effects of soy protein diet on breast cancer development. Soybeans contain isoflavones genistein, daidzein and glycitein, known as isoflavonoids, which are structurally similar to mammalian estrogens, have estrogenic properties and are potential anticarcinogens. Gut flora metabolizes daidzein into equol, a non-steroidal estrogen and has cancer chemopreventive property. The objective of this study was to determine the effects of obesity and a high isoflavones soy protein diet on plasma isoflavones; genistein, daidzein, glycitein, equol and O-Desmethylangolensin (O-MDA) levels using 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumor model. Five-week-old female Zucker rats (45 obese fa/fa and 54 lean) were used. After one week of acclimation (age 42 days), rats were randomly assigned to the following diet groups; 1) Lean, casein; 2) Obese, casein; 3) Lean, soy and 4) Obese, soy. Rats had ad lib access to water and diet with either casein or soy protein isolate as source of protein. All rats were orally gavaged at age 50 days with 65 mg/kg DMBA. Rats were weighed and palpated twice weekly and sacrificed 21 weeks post-DMBA treatment. Plasma was collected to measure genistein, daidzein, glycitein, equol and O-MDA levels using liquid chromatography−tandem mass spectrometry (LC-MS/MS). At end of the experiment, 69% of the Lean casein rats developed mammary tumors compared to 50% in lean soy group (p= 0.176). In the obese group, 76% of the soy-fed rats developed mammary tumors compared to 15% (P<0.001) of obese casein- fed rats. Plasma daidzein and genistein concentration were not significantly different in lean vs obese soy-fed rats. However, O-MDA and equol concentration were significantly lower (P<0.05) in obese soy-fed rats compared to lean soy rats. These data suggests that obese rats fed soy protein diet containing high isoflavone levels promoted DMBA-induced mammary tumor development compared to a casein-based diet. Also, obese soy-fed rats exhibited significantly lower plasma equol concentrations than those observed in lean soy-fed rats and this reduction may aid in explaining soy's impaired cancer chemopreventative effects in obese breast cancer model. Citation Format: Reza Hakkak, Soheila Korourian. Effects of soy protein diet on plasma isoflavones levels in obese DMBA-induced mammary tumor rat model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4642.

Plasma genistein and risk of prostate cancer in Chinese population.

ObjectivesGenistein is one of the main soy isoflavones in our daily diet. There were studies proving that high-dietary intake of genistein may relate to the low morbidity and mortality of prostate cancer (PCa) in the Asian population. Since there were few studies of plasma genistein level in the Chinese population, we performed this study to preliminarily evaluate the associations among plasma genistein, epidemiologic factors and PCa in a Chinese population.MethodsBetween 2012 and 2013, 100 men over the age of 40 underwent prostate biopsy for PCa at Huashan Hospital, Shanghai, China. Clinical information, epidemiologic information and blood samples were collected prior to biopsy for each patient. All patients underwent 10-core ultrasound-guided transperineal prostate biopsy, and the pathology results were collected after biopsy. We measured the plasma genistein concentration of the blood samples and analyzed the results along with the clinical and epidemiologic information.ResultsAmong the 100 patients, 46 (46.0 %) were diagnosed with PCa. The median plasma genistein concentration of non-PCa patients (728.6 ng/ml) was significantly higher than that of PCa patients (513.0 ng/ml) (P < 0.05). In the univariate analysis, we found that age and smoking history were related to PCa (P < 0.05). In the multivariate analysis, we found that age, smoking history and plasma genistein were related to PCa (P < 0.05). The age-adjusted odds ratio of PCa risk comparing plasma genistein level above median to that below median was 0.31 (95 % CI 0.13–0.71).ConclusionOur study suggested that high concentration of plasma genistein level may contribute to the low incidence of prostate cancer in Chinese population.

Isoflavone supplementation reduces DNA oxidative damage and increases O-β-N-acetyl-d-glucosaminidase activity in healthy women

Phenolic compounds are believed to boost the human antioxidant defense system and health; therefore, the aim of this research was to investigate the hypothesis that soy isoflavones (IFs) provide antioxidant protection in healthy women by evaluating DNA resistance to oxidative damage and O-β-N-acetyl-D-glucosaminidase (OGA) activity. An IF supplement (80 mg/d) was given to 9 postmenopausal women and 13 young women for 6 months and then stopped up to the 14th month. The women were allowed to consume their normal diet. Blood samples were collected at the beginning of the study after 2, 4, and 6 months and then at the 8th and 14th months. Plasma concentrations of genistein and daidzein, total antioxidant capacity, plasma vitamin status, markers of oxidative stress (red blood cell membrane fluidity, activity of the red blood cell cytosolic enzyme OGA and lymphocyte DNA susceptibility to oxidative stress), and serum lipid profile were analyzed. Analysis of variance for repeated measures was used for statistical analysis. Plasma concentrations of IFs rose significantly during the supplementation period, and plasma total antioxidant capacity increased in young women; membrane fluidity and OGA activity increased, and DNA oxidative damage decreased (P < .05) at 4 months, then returned to the basal level. There was a significant inverse correlation between DNA damage and plasma IF concentrations (P < .01). The results indicated a positive effect of IF supplementation on oxidative stress in women, thus suggesting that the healthful action ascribed to soy consumption may be partially related to the antioxidant potential of IFs.

Plasma Isoflavones and the Risk of Lung Cancer in Women: A Nested Case–Control Study in Japan

Although several epidemiologic studies have found that isoflavone intake assessed by questionnaire is associated with a decreased risk of lung cancer, no prospective study has investigated this association using blood concentrations of isoflavones. We conducted a nested case-control study within a population-based prospective cohort study. A total of 24,127 women aged 40 to 69 years who returned the baseline questionnaire and provided blood samples were observed from 1990 through 2006. During a median follow-up period of 13.5 years, 126 newly diagnosed lung cancer cases were identified. For each case, we selected two controls matched for age, area, smoking status, and condition of blood draw. A conditional logistic regression model was used to estimate the odds ratios (ORs) and 95% CIs of lung cancer in relation to plasma concentrations of genistein, daidzein, glycitein, equol, and total isoflavones. After exclusion of 20 lung cancer cases diagnosed in the first 3 years after blood collection, an inverse association was found between plasma genistein concentration and lung cancer risk. The multivariate-adjusted OR (95% CI) of lung cancer in the highest quintile of plasma genistein concentration as compared with that in the lowest quintile was 0.31 (0.12, 0.86; P for trend=0.085). Other isoflavones and total isoflavones were not associated with a significant decrease in the risk of lung cancer. Plasma genistein concentration was inversely associated with lung cancer risk in Japanese women. Our data support the previously observed association between isoflavone intake and lung cancer risk.

Dietary supplementation of genistein (geniVida®) ameliorates scopolamin‐induced dry eye syndrome in rats

Abstract Purpose Dry Eye Syndrome (DES) is an ocular surface disease with higher prevalence in women than in men. It is characterized by decreased tear gland secretion, altered tear composition and tear film instability. We investigated whether supplementation with the isoflavone genistein (GEN) could alleviate artificially induced DES in rats. Methods DES was induced in 24 female Sprague Dawley rats by daily trans‐dermal treatment with scopolamine (SCOP). Animals were housed on an AIN feed containing 0, 50 or 250 ppm of GEN provided as geniVida® by DSM Nutritional Products. 8 additional animals served as not‐stressed control. After 2 and 4 weeks, levels of GEN in plasma were measured by LC/MS and the status of DES was assessed using the Zone Quick Test (ZQT). After 4 weeks, animals were sacrificed and cornea and conjunctiva were examined for Goblet Cell Density (GCD) and the extent of lid keratinization (LK). Pairwise comparisons of endpoint values were done by t‐test or Mann‐Whitney test. Results Genistein feeding resulted in significant increases of plasma genistein concentrations. The achieved levels were commensurate to those reported in a human study supplementing 60 mg/day (Ullmann et al. (2005), Planta Med. 71: 891‐896), equivalent to 100g soy beans per day. In the 0 ppm GEN group, SCOP treatment increased the extent of LK and drastically reduced ZQT and GCD values, while genistein supplementation restored tear volume (p=0.0007), GCD (p=0.0028) and LK (p=0.0009) in a dose‐dependent manner. Conclusion While these results still need to be confirmed in humans, genistein supplementation may become a treatment option that fundamentally restores natural tear physiology, offering a major improvement over the currently used topical agents. Commercial interest

Suppression of Colonic Aberrant Crypt Foci by Soy Isoflavones Is Dose-Independent in Dimethylhydrazine-Treated Rats

The potential of soy isoflavones (SIs) to reduce colon cancer has been investigated in animal models. These studies have found that outcomes are variable and depend on SI dose. The present study investigated dose-response effects of SIs on colon carcinogenesis in a chemically induced rat cancer model. Sprague-Dawley male rats were injected with 1,2-dimethylhydrazine (DMH) and were provided experimental diets that contained 0, 10, 50, 150, or 500 mg of SI aglycones/kg of diet for 12 weeks. Plasma concentrations of genistein, daidzein, and equol were determined using time-resolved fluoroimmunoassay. Plasma concentrations of these SIs tended to increase in a dose-dependent manner in DMH-treated rats. The numbers of aberrant crypt foci (ACF) and the expression of cyclooxygenase-2 (COX-2) proteins of colons were significantly decreased in the SI-fed groups compared with the control group; however, suppression was not dose-dependent. Furthermore, there were no significant correlations between plasma SI concentrations and ACF or COX-2 expression. Increased SI intake and increased plasma levels of SIs and metabolites were not associated with tissue levels of lipid peroxidation. We conclude that dietary supplementation of SIs suppresses DMH-induced ACF formation and COX-2 expression in a dose-independent manner.

Increased plasma concentrations of soy isoflavones by increased doses of soy isoflavones are irrelevant to lipid peroxidation and aberrant crypt foci formation in colonic cancer model rats

We have investigated whether soy isoflavones supplemented to diets increase plasma concentrations of soy isoflavones and equol, and whether increased plasma concentration of soy isoflavones suppresses tissue levels of lipid peroxides and aberrant crypt foci (ACF) formation in colon cancer model rats. Sprague Dawley male rats were injected with 1,2‐dimethylthydrazine (DMH) and given one of AIN93‐based experimental diets (0, 10, 50, 150, or 500 mg isoflavones per kg diet) for 12 weeks. Thiobarbituric acid reactive substances (TBARS) of plasma and homogenates of liver and kidneys were determined using TBARS assay kit. Plasma concentrations of genistein, daidzein and equol were determined using kits by competitive time‐resolved fluoroimmunoassay technique. Plasma concentrations of genistein (R2=0.521 by genistein intake, p&lt;0.001), daidzein (R2=0.623 by daidzein intake, p&lt;0.001) and equol (R2=0.528 by daidzein intake, p&lt;0.001) were increased dose‐dependently. However, the numbers of ACF decreased significantly (p&lt;0.01) in 10 or 50 mg isoflavones‐fed groups as compared with the control group, and there was no significant correlation between the number of ACF and plasma concentration of genistein, daidzein or equol. Plasma TBARS level was not influenced by either dose or plasma level of soy isoflavones. Hepatic levels of TBARS were significantly lower in 10 and 50 mg isoflavones‐fed groups as compared with the control group. The level of kidney TBARS was significantly lower in only 50 mg isoflavones‐fed group as compared with the control group. Therefore, the results indicate that optimal level of soy isoflavones seemed to be most effective in suppressing ACF formation and lipid peroxidation in DMH‐induced colon cancer model rats.

Plasma Isoflavones and Fibrocystic Breast Conditions and Breast Cancer Among Women in Shanghai, China

Proliferative benign breast conditions are associated with elevated risk of breast cancer, whereas nonproliferative conditions are not strongly associated with risk. Factors acting before onset of hyperplasia might be associated with both benign conditions and breast cancer, whereas those on the proliferative disease-to-cancer pathway would be associated only with cancer. Soy isoflavone exposure may influence breast cancer risk, but little is known of its association with benign conditions. We examined possible relationships between plasma genistein and daidzein concentrations and risk of breast disease in women, in a breast self-examination trial in Shanghai, China, diagnosed with breast cancer (n = 196) or a benign breast condition (n = 304), and 1,002 age-matched controls with no known breast disease. Benign conditions were classified as nonproliferative (n = 131) or proliferative with or without atypia (n = 173). Isoflavone concentrations were inversely associated with risk of nonproliferative and proliferative benign fibrocystic conditions, as well as with breast cancer, both with and without concomitant proliferative changes in ipsilateral noncancerous mammary epithelium (P(trend) < 0.01 for all comparisons with controls). Women in the highest quartile of plasma genistein (>76.95 ng/mL) were less likely to have breast cancer (odds ratio, 0.26; 95% confidence interval, 0.13-0.50) or benign conditions (odds ratio, 0.40; 95% confidence interval, 0.23-0.70) compared with women in the lowest quartile (<9.42 ng/mL). Observed risks for breast cancer with and without surrounding proliferative changes were not different, respectively, from observed risks for benign proliferative and nonproliferative conditions alone. Isoflavone exposure was inversely associated with fibrocystic breast conditions and breast cancer, and the results suggest that effects on cancer risk occur early in carcinogenesis.

Comparison of oral bioavailability of genistein and genistin in rats

Genistein (GT) is an isoflavone from Leguminosae and has received much attention as a phytoestrogen. Genistin is a glycoside form of GT (genistein-7- O-β- d-glucopyranoside, GT-glu) is mainly found in soy-derived foods. In this study, we examined the pharmacokinetic properties and bioavailability of GT in rats and compared with those of GT-glu. In order to characterize and compare the pharmacokinetics of GT and GT-glu, these compounds were administered intravenously and orally. The plasma concentration of GT was determined by HPLC after enzymatic hydrolysis. After oral administration of GT with various doses (4, 20, 40 mg/kg), the bioavailability of GT was 38.58, 24.34 and 30.75%, respectively. The T max, C max and AUC (0–∞) of GT after oral administration of GT (40 mg/kg), were 2 h, 4876.19 ng/ml, 31,269.66 ng h/ml, respectively. When smaller amount of GT was administered, the faster T max was observed. Oral administration of GT-glu resulted in longer T max, lower C max, and greater bioavailability than that of GT. The pharmacokinetic parameters of GT following oral administration of GT-glu (64 mg/kg as GT-glu, 40 mg/kg as GT) were obtained as follows: 8 h ( T max), 3763.96 ng/ml ( C max), 51,221.08 ng h/ml (AUC (0–∞)) and 48.66% (absolute bioavailability), respectively. These results indicate that the oral bioavailability of GT-glu is greater than that of GT.

Plasma enterolactone and genistein and the risk of premenopausal breast cancer

The scientific debate on the role of dietary phytoestrogens for prevention of breast cancer is still ongoing. We previously reported an inverse association between dietary phytoestrogen intake and premenopausal breast cancer risk and now examine the relationship with plasma phytoestrogen concentrations. We measured enterolactone (mammalian lignan) and genistein (isoflavone) concentrations in plasma samples of 220 premenopausal cases and 237 age-matched controls from a population-based case-control study in Germany. Median plasma enterolactone concentrations in cases and controls were 6.3 and 9.7 nmol/l, respectively, and median genistein concentrations were 4.5 and 3.7 nmol/l, respectively. Premenopausal breast cancer risk decreased with increasing plasma enterolactone concentrations. Adjusted odds ratios (95% confidence intervals) were 0.42 (0.20-0.90) and 0.38 (0.17-0.85) (P for trend 0.007) for women in the third and fourth quartile of plasma enterolactone compared to those in the lowest quartile. There was no significant association between plasma genistein concentration and premenopausal breast cancer risk. Using biomarkers of phytoestrogen intake, we confirmed the strong inverse association between enterolactone and premenopausal breast cancer risk as found with dietary intake estimates. This result gives support to the potential role of mammalian lignans for breast cancer prevention among premenopausal women in Western populations.

Isoflavones restore altered redox homeostasis of antioxidant enzymes in healthy young men undergoing 80% peak oxygen consumption (VO 2pk) exercise

Isoflavones have potential health effects attributed to their antioxidant activity. The objective of this study was to test whether isoflavones affected the enzymatic antioxidant defense system in young men undergoing 80% peak oxygen consumption (VO 2pk) exercise on cycle ergometer for 30 minutes. Fifteen pairs of subjects were randomly assigned to receive either high-genistein isoflavone extract (HGI, 150 mg/day) or placebo. Subjects engaged in two 30-minute sessions of exercise before and after 4 weeks of supplementation. There was a significant increase in plasma genistein and daidzein concentrations (499 and 415 ng/mL, P < 0.0001) after the supplementation, demonstrating isoflavone bioavailability. Isoflavones significantly increased pre-exercise erythrocyte superoxide dismutase (SOD) activity ( P < 0.001). Furthermore, isoflavones prevented the exercise-induced decrease in activities of glutathione peroxidase (GPx) and catalase (CAT) and the increase in antioxidant enzyme (AE) ratio, maintaining all at pre-exercise levels. Our results suggest that isoflavones can restore the altered redox homeostasis of antioxidant enzymes due to exercise.

Dietary genistein results in larger MNU-induced, estrogen-dependent mammary tumors following ovariectomy of Sprague-Dawley rats.

Due to the estrogenic properties of soy-derived isoflavones, many postmenopausal women are using these compounds as a natural alternative to hormone replacement therapy (HRT). How isoflavones impact breast cancer in postmenopausal women is important, because a majority of breast cancer cases occur in this age group. Chemical induction of mammary tumors in female rats has been used to determine that exposure of the mammary gland to soy isoflavones prior to tumor induction is protective against tumor formation. Here we investigate the effect of dietary genistein on mammary tumors that have already formed. The study was designed to determine the action of dietary genistein in a low endogenous estrogen environment as is observed in postmenopausal women. Animals were ovariectomized (OVX) after mammary tumor development and were then placed into one of three treatment groups: positive-control (OVX+ estradiol implant), genistein (OVX+ 750 p.p.m. genistein) and negative-control (OVX alone). Tumors were distinguished as malignant or benign by histopathological examination and were further characterized as either estrogen-dependent or estrogen-independent using immunohistochemistry to identify the presence of both estrogen receptor (ER) alpha and the progesterone receptor (PR). Genistein at 750 p.p.m. increased the weight of estrogen-dependent adenocarcinomas in ovariectomized rats compared with the negative-control animals. Genistein treatment also resulted in a higher percentage of proliferative cells in tumors and increased uterine weights when compared with negative-control animals. Collectively, these effects are probably due to the estrogenic activity of genistein. Plasma genistein concentrations in animals fed the isoflavone-containing diet were at physiological levels relevant to human exposure. Estradiol concentrations in ovariectomized animals not receiving an estradiol supplement were similar to those observed in postmenopausal women. The data suggest that in an endogenous estrogen environment similar to that of a postmenopausal woman, dietary genistein can stimulate the growth of a mammary carcinogen MNU-induced estrogen-dependent mammary tumors.

Effects of soy oligosaccharides on plasma and cecal isoflavones, and cecal enzyme activities in mice.

This paper studies the effects of soy oligosaccharides on plasma and cecal isoflavones and floral enzyme activities in adult mice. The isoflavones used in this experiment were daidzein and genistein. Male 6-wk-old mice were fed a soy oligosaccharide-isoflavone (SOI) diet or cellulose-isoflavone (CEI) diet for 10 d. Plasma and cecal isoflavones were analyzed by HPLC, and cecal bacterial beta-glucosidase and beta-glucuronidase activities were also measured. The plasma genistein concentration was significantly higher in the SOI diet group than in the CEI diet group, but no significant difference was observed in plasma daidzein concentration between the two dietary groups. The total amount of cecal isoflavones existing as aglycone were significantly greater in the SOI diet group than in the CEI diet group, and both cecal beta-glucosidase and beta-glucuronidase activities were significantly higher in the SOI diet group than in the CEI diet group. These results indicate that soy oligosaccharides have an impact on the metabolic activity of intestinal microflora, plasma concentrations of isoflavones, and amount of isoflavones in the intestine. The present study suggests that ingestion of soy oligosaccharides may influence the effect of dietary isoflavones on the host.

Peroxisome Proliferator-activated Receptor γ (PPARγ) as a Molecular Target for the Soy Phytoestrogen Genistein

The principal soy phytoestrogen genistein has an array of biological actions. It binds to estrogen receptor (ER) alpha and beta and has ER-mediated estrogenic effects. In addition, it has antiestrogenic effects as well as non-ER-mediated effects such as inhibition of tyrosine kinase. Because of its complex biological actions, the molecular mechanisms of action of genistein are poorly understood. Here we show that genistein dose-dependently increases estrogenic transcriptional activity in mesenchymal progenitor cells, but its biological effects on osteogenesis and adipogenesis are different. At low concentrations (< or =1 microm), genistein acts as estrogen, stimulating osteogenesis and inhibiting adipogenesis. At high concentrations (>1 microm), however, genistein acts as a ligand of PPARgamma, leading to up-regulation of adipogenesis and down-regulation of osteogenesis. Transfection experiments show that activation of PPARgamma by genistein at the micromolar concentrations down-regulates its estrogenic transcriptional activity, while activation of ERalpha or ERbeta by genistein down-regulates PPARgamma transcriptional activity. Genistein concurrently activates two different transcriptional factors, ERs and PPARgamma, which have opposite effects on osteogenesis or adipogenesis. As a result, the balance between activated ERs and PPARgamma determines the biological effects of genistein on osteogenesis and adipogenesis. Our findings may explain distinct effects of genistein in different tissues.

Absolute bioavailability of [14C] genistein in the rat; plasma pharmacokinetics of parent compound, genistein glucuronide and total radioactivity.

The systemic plasma pharmacokinetics of genistein were determined in rats to evaluate the absolute oral bioavailability and make comparison with similar data in the literature derived from humans subjects. The plasma concentrations of genistein, genistein glucuronide and carbon-14 were determined by LC-MS/MS and liquid scintillation counting following oral and intravenous dosing with [14C]genistein (4 mg kg(-1) body weight). The absorption of total radioactivity from the gut, (parent compound and metabolites), was 56 and 111% in male and female rats, respectively. In contrast, the absolute oral bioavailability of genistein in male and female rats was 7 and 15%. There was a significant (P<0.001) difference between Cmax of genistein after intravenous (6921 and 4392 ng/ml) and oral (21 and 22 ng/ml) dosing in male and female rats, respectively. After oral administration, the concentration profile of genistein glucuronide in plasma greatly exceeded that of parent compound during the absorption/distribution phase suggesting extensive first pass metabolism, and provided evidence of entero-hepatic circulation. Selective plasma analysis by LC-MS/MS, without prior enzymatic hydrolysis, enabled ready discrimination between parent and conjugated metabolites and prevented gross overestimation of genistein bioavailability. Pharmacokinetic parameters Cmax, Tmax and AUC were similar to those reported in humans, which supports the use of the rat model for genistein toxicity studies.

Physiological Concentrations of Dietary Genistein Dose-Dependently Stimulate Growth of Estrogen-Dependent Human Breast Cancer (MCF-7) Tumors Implanted in Athymic Nude Mice

Previously our laboratory has shown that the soy isoflavone, genistein, stimulates growth of human breast cancer (MCF-7) cells in vivo and in vitro. In this study, the dose-response analysis of genistein at the physiologically achievable concentration range between 125 and 1,000 microg/g in the diet was conducted in ovariectomized athymic nude mice implanted with MCF-7 cells. We hypothesized that genistein at this concentration range can stimulate dose-dependently the breast tumor growth, cell proliferation and an estrogen-responsive pS2 gene induction. Tumor size and body weight were monitored weekly. At completion of the study, we analyzed cellular proliferation of tumors using incorporation of BrdU, pS2 expression of tumors using a Northern blot analysis and total genistein level in plasma using liquid chromatography-isotope dilution mass spectrometry (LC-ES/MS). Dietary genistein (> or = 250 microg/g) increased tumor size in a dose-dependent manner [8.4x the negative control (NC) group in the 250 microg/g group, 12.0x in the 500 microg/g group, 20.2x in the 1,000 microg/g group and 23.2x in the positive control (PC) group]. The percentage of proliferating cells was significantly increased by genistein at and above 250 microg/g (5.3x the NC group in the 250 microg/g, 5.6x in the 500 microg/g, 5.0x in the 1,000 microg/g and 4.8x in the PC group). Expression of pS2 mRNA was also significantly increased with increasing dietary genistein levels (11.25x the NC group in the 500 microg/g group and 15.84x in the 1,000 microg/g group). Total plasma genistein concentrations were between 0.39 and 3.36 micromol/L in mice fed between 125 and 1,000 microg/g genistein. In conclusion, dietary treatment with genistein at physiological concentrations produces blood levels of genistein sufficient to stimulate estrogenic effects, such as breast tumor growth, cellular proliferation and pS2 expression in athymic mice in a dose-responsive manner similar to that seen in vitro.

Dietary soy exerts an antihypertensive effect in spontaneously hypertensive female rats.

This study tested the hypothesis that dietary soy would attenuate the development of hypertension in female spontaneously hypertensive rats (SHR). Female SHR and control Wistar-Kyoto rats were obtained at 4 wk of age, randomly assigned to either an ovariectomized (OVX) group or a sham-operated group, and placed on a soy diet or control casein diet. After a minimum of 8 wk on their respective diets, mean arterial pressure (MAP) and heart rate (HR) were recorded before and after inhibition of nitric oxide synthase, air-jet stress, or ganglionic blockade. The major finding of this study is that MAP was reduced in the OVX SHR consuming soy diet compared with the casein-fed controls (150 +/- 4 vs. 164 +/- 3 mmHg). Plasma genistein concentrations were increased in the soy-fed OVX SHR (1.23 +/- 0.31 microM) compared with the casein-fed OVX SHR (nondetectable). However, there was no difference in plasma genistein concentrations between sham-operated and OVX SHR (1.37 +/- 0.42 vs. 1.23 +/- 0.31 microM). Inhibition of nitric oxide synthase increased MAP and decreased HR in all groups; diet did not affect this response. Air-jet stress increased MAP and HR in all groups. However, these responses were exaggerated in the soy-fed SHR. Finally, ganglionic blockade abolished the antihypertensive effect of soy diet in the OVX SHR. These findings indicate that dietary soy exerts an antihypertensive effect in OVX SHR. This effect does not involve the nitric oxide system but may be related to an as yet undefined interaction with the autonomic nervous system.

Effect of a phytoestrogen food supplement on reproductive health in normal males

Animal studies and human intervention trials have demonstrated the cancer chemopreventive properties of plant phytoestrogens, and phytoestrogen supplements are now widely available 'over-the-counter'. However, consumption of phytoestrogen-rich diets can cause impaired fertility and reproductive tract disorders in some animals and the apparent decline in human sperm quality over recent decades may be related to increased exposure to environmental endocrine disruptors. The present study determines the effects of a short-term phytoestrogen supplement on semen quality and serum sex steroid and gonadotrophin levels in human males. Healthy volunteers took a supplement containing 40 mg of isoflavones daily for 2 months and donated blood and semen samples monthly for 2 months before and 4 months after supplementation. Semen samples were analysed for ejaculate volume, sperm concentration, total sperm count, motility and morphology. Blood samples were analysed for sex hormone and gonadotrophin levels and phytoestrogen concentrations, and testicular volume was measured using an orchidometer. The phytoestrogen supplement increased plasma genistein and daidzein concentrations to approx. 1 microM and 0.5 microM respectively; yet, there was no observable effect on endocrine measurements, testicular volume or semen parameters over the study period. This is the first study to examine the effects of a phytoestrogen supplement on reproductive health in males. We conclude that the phytoestrogen dose consumed had no effect on semen quality.

Bioavailability of Pure Isoflavones in Healthy Humans and Analysis of Commercial Soy Isoflavone Supplements

The pharmacokinetic behavior of naturally occurring isoflavones has been determined for the first time in healthy adults. We compared plasma kinetics of pure daidzein, genistein and their beta-glycosides administered as a single-bolus dose to 19 healthy women. This study demonstrates differences in the pharmacokinetics of isoflavone glycosides compared with their respective beta-glycosides. Although all isoflavones are efficiently absorbed from the intestinal tract, there are striking differences in the fate of aglycones and beta-glycosides. Mean time to attain peak plasma concentrations (t(max)) for the aglycones genistein and daidzein was 5.2 and 6.6 h, respectively, whereas for the corresponding beta-glycosides, the t(max) was delayed to 9.3 and 9.0 h, respectively, consistent with the residence time needed for hydrolytic cleavage of the glycoside moiety for bioavailability. The apparent volume of distribution of isoflavones confirms extensive tissue distribution after absorption. Plasma genistein concentrations are consistently higher than daidzein when equal amounts of the two isoflavones are administered, and this is accounted for by the more extensive distribution of daidzein (236 L) compared with genistein (161 L). The systemic bioavailability of genistein [mean AUC = 4.54 microg/(mL x h)] is much greater than that of daidzein [mean AUC = 2.94 microg/(mL x h)], and bioavailability of these isoflavones is greater when ingested as beta-glycosides rather than aglycones as measured from the area under the curve of the plasma appearance and disappearance concentrations. The pharmacokinetics of methoxylated isoflavones show distinct differences depending on the position of the methoxyl group in the molecule. Glycitin, found in two phytoestrogen supplements, underwent hydrolysis of the beta-glycoside moiety and little further biotransformation, leading to high plasma glycitein concentrations. Biochanin A and formononetin, two isoflavones found in one phytoestrogen supplement, were rapidly and efficiently demethylated, resulting in high plasma genistein and daidzein concentrations typically observed after the ingestion of soy-containing foods. These differences in pharmacokinetics and metabolism have implications for clinical studies because it cannot be assumed that all isoflavones are comparable in their pharmacokinetics and bioavailability. An analysis of 33 phytoestrogen supplements and extracts revealed considerable differences in the isoflavone content from that claimed by the manufacturers. Plasma concentrations of isoflavones show marked qualitative and quantitative differences depending on the type of supplement ingested. These studies indicate a need for improvement in quality assurance and standardization of such products.

Genistein Inhibits Growth of Estrogen-Independent Human Breast Cancer Cells in Culture but Not in Athymic Mice

The studies presented were conducted to assess the effect of the soy isoflavone genistein on proliferation of estrogen-independent human breast cancer cells (MDA-MB-231) in vitro and in vivo. Genistein (20 mcmol/L) inhibited cell proliferation in vitro by approximately 50%. Cell cycle progression was blocked in G(2)/M with 40 and 80 mcmol/L genistein. To evaluate the effect of dietary genistein on tumor growth in vivo, genistein was fed to female athymic mice inoculated with MDA-MB-231 cells. After solid tumor masses had formed, mice were fed genistein at a dose (750 mcg/g AIN-93G diet), shown to produce a total plasma genistein concentration of approximately 1 mcmol/L. This dose of genistein did not significantly (P > 0.05) alter tumor growth. Studies were then conducted to assess the effect of dietary genistein on initial tumor development and growth. Genistein (750 mcg/g AIN-93G diet), fed 3 d before cells were inoculated into mice, did not significantly (P > 0.05) inhibit tumor formation or growth. The plasma concentration of genistein in mice fed this dose of dietary genistein (750 mcg/g AIN-93G diet) does not appear sufficient to inhibit tumor formation or growth. Dietary genistein at 750 mcg/g AIN-93G diet does not inhibit tumor formation or growth. Additional studies were conducted to determine the effect of dietary dosages ranging from 0 to 6000 mcg/g AIN-93G diet on plasma genistein concentration. Plasma genistein concentration increased in a dose-dependent manner up to 7 mcmol/L at 6000 mcg/g AIN-93G diet. These data suggest that although genistein inhibits cancer cell growth in vitro, it is unlikely that the plasma concentration required to inhibit cancer cell growth in vivo can be achieved from a dietary dosage of genistein.