Isoflavone Mixture Research Articles

Increased serum and testicular androgen levels in F1 rats with lifetime exposure to soy isoflavones

The consequences of dietary soy isoflavones on serum and testicular androgen levels were examined in F1 male rats from a multigeneration study investigating the effects of diets varying in isoflavone content. Rats were fed either a soy-free casein based diet (AIN93G) or a diet in which alcohol-washed soy protein replaced casein as the protein source and to which increasing amounts of Novasoy, a commercially available isoflavone supplement were added. Analysis of these diets showed that the isoflavone content in each diet was 0 (diet 1; casein based control), 31.7 (diet 2; alcohol-washed soy-based diet control), 36.1 (diet 3), 74.5 (diet 4), 235.6 (diet 5) and 1046.6 (diet 6) mg total isoflavones/kg pelleted diet. The levels of isoflavones in diet 1 would represent a daily intake level of 0 mg isoflavones, diets 2 and 3 estimate a low soy-containing human diet (e.g. North American), diet 4 would correspond to Asian diets (e.g. Japanese) or adult humans taking isoflavone supplements, diet 5 approximates the isoflavone intake by babies fed soy based infant formula and diet 6 approximates fivefold the intake levels by babies or 10-fold the intake levels of adults consuming high isoflavone containing diets. Serum testosterone (T) from F1 male rats sacrificed on postnatal days (PND) 28, 70, 120, 240 and 360 were low at PND 28 (0.4 ng/ml), increased approximately five to sixfold at PND 70 (2.5–3.0 ng/ml) and thereafter declined to a steady state level of ∼1 ng/ml by PND 120. However, rats on diets 5 and 6 demonstrated altered serum testosterone profiles such that at days 120, testosterone levels remained significantly elevated at ∼3 ng/ml ( P<0.05). Serum dihydrotestosterone levels exhibited similar profiles and the levels in PND 120 rats on diet 5 or 6 were also significantly elevated (two to threefold, P<0.05). The intra-testicular testosterone concentration in rats on diet 5 was also elevated at PND 120 compared with diet 1 ( P<0.05). These findings show that F1 male rats continuously exposed to a mixture of dietary soy isoflavones from conception onwards exhibit altered serum and testicular androgen profiles.

Disposition of flavonoids via enteric recycling: enzyme-transporter coupling affects metabolism of biochanin A and formononetin and excretion of their phase II conjugates.

The purpose of this study was to continue our effort to determine how enzyme-transporter coupling affect disposition of flavonoids. The rat intestinal perfusion and Caco-2 cell models were used together with relevant microsomes. In perfusion model, isoflavone (i.e., formononetin and biochanin A) absorption and subsequent excretion of its metabolites were always site-dependent. Maximal amounts of intestinal and biliary conjugates excreted per 30 min were 31 and 51 nmol for formononetin, more than that for pure biochanin A (12 and 20 nmol). When a standardized red clover extract (biochanin A/formononetin = 10:7) was used, the results indicated that more metabolites of biochanin A than formononetin were found in the perfusate (36.9 versus 22.8 nmol) and bile (78 versus 51 nmol). In metabolism studies, rat intestinal and liver microsomes always glucuronidated biochanin A faster (p < 0.05) than formononetin, whereas intestinal microsomes glucuronidated both isoflavones faster (p < 0.05) than liver microsomes. However, rapid metabolism in the microsomes did not translate into more efficient excretion in either the rat perfusion model as shown previously or in the Caco-2 model. In the Caco-2 model, both isoflavones were rapidly absorbed, efficiently conjugated, and the conjugates excreted apically and basolaterally. More formononetin conjugates were excreted than biochanin A when used alone, but much more biochanin A conjugates were found when using the isoflavone mixture. In conclusion, efficiency of enzyme-transporter coupling controls the amounts of metabolites excreted by the intestine and liver and determines the relative contribution of enteric and enterohepatic recycling to the in vivo disposition of isoflavones.

Fast high-performance liquid chromatography method for quality control of soy extracts

Soy extracts contain a mixture of isoflavones belonging to the group of phytoestrogens. In the quality control of soy the amount of isoflavones, both aglycones and glycosides, is usually determined by means of reversed-phase HPLC–UV. On conventional C 18-material columns, long analysis times are required in order to separate this complex mixture. In order to speed up analysis, the separation was optimized using two linked monolithic silica-based reversed-phase C 18 columns. A spectacular decrease of the analysis time, i.e. almost three-fold, was achieved by applying a flow rate of 3–4 ml/min without loosing any separation efficiency. This analysis method for determination of isoflavones in soy extracts in less than 25 min was fully validated according to the ICH guidelines.

Reproductive toxicity assessment of chronic dietary exposure to soy isoflavones in male rats

Epidemiologic and experimental data suggest that consumption of diets that are rich in isoflavones may decrease cancer risk in the breast, prostate, and other tissues. Isoflavones such as genistein and daidzein are structurally similar to endogenous estrogens, and demonstrate both estrogenic and weak anti-estrogenic activities; these activities may underlie the impaired fertility and reproductive tract disorders reported in animals exposed to high doses of isoflavones. To identify possible effects of isoflavones on male fertility, we evaluated reproductive parameters in Wistar-Unilever rats receiving dietary exposure to PTI G-2535, a characterized mixture of soy-derived isoflavones containing 45% genistein, 23% daidzein, and 4% glycitein. Beginning at 10 weeks of age, rats received chronic dietary exposure to the soy isoflavone mixture (200 or 2000 mg/kg diet) for a minimum of 12 months. Controls received unsupplemented chow diet only for the same period. Dietary exposure to isoflavones induced no gross toxicity or alterations in body weight gain. Absolute and relative weights of the testis and epididymis in groups receiving high or low doses of isoflavones were comparable to those of controls, and histopathologic evaluations demonstrated that testicular morphology was similar in all study groups. Isoflavone exposure had no significant effects on spermatid count, sperm production, or sperm morphology in any group. These data suggest that the reproductive system of adult male rats is relatively insensitive to isoflavone toxicity at dose levels that demonstrate significant activity in cancer chemoprevention, and that male reproductive function is unlikely to be affected by long-term administration of isoflavones for cancer prevention or other purposes. The results of this study conducted in adult male rats differ from the significant alterations in reproductive parameters that have been reported in female rats receiving prenatal or juvenile exposure to isoflavones.

Soy Protein with or Without Isoflavones, Soy Germ and Soy Germ Extract, and Daidzein Lessen Plasma Cholesterol Levels in Golden Syrian Hamsters

Dietary isolated soy protein (ISP, containing approximately equal amounts of daidzein and genistein), ethanol-extracted ISP (ISP (-)), soygerm or soygerm extract (containing large amounts of daidzein and glycitein and little genistein) and the isoflavone, daidzein, were hypothesized to lessen plasma cholesterol in comparison with casein. Sixty male and 60 female golden Syrian hamsters (6-8 weeks of age) were randomly assigned to six treatments fed for 10 weeks. Four of the experimental diets (ISP, daidzein, soygerm, and soygerm extract) contained 1.3 mmol total isoflavones/kg. The ISP (-) diet contained 0.013 mmol isoflavone/kg, whereas the casein diet contained no isoflavones. Hamsters fed ISP, ISP (-), daidzein, soygerm, and soygerm extract had significantly less plasma total cholesterol (by 16%-28%), less non-HDL cholesterol (by 15%-50%) and less non-HDL/HDL cholesterol ratios compared with hamsters fed casein (P < 0.01). For male hamsters, there were no differences among treatments in plasma HDL concentrations. Female hamsters fed ISP (-) had significantly greater HDL levels (P < 0.01) than females fed casein or daidzein. Triglyceride concentration was significantly less in hamsters fed ISP (-) compared with the casein-fed females. Because soy protein with or without isoflavones, soygerm and soygerm extract, and daidzein lessened plasma cholesterol to an approximately equal extent, soy protein alone, varying mixtures of isoflavones, and other extractable components of soy are responsible for cholesterol-lessening effects of soy foods, mainly due to their effects to lessen LDL cholesterol.

Evaluation of the antioxidant activity of different flavonoids by the chemiluminescence method

The objective of the present investigation was to study the antioxidant action of different flavonoids (quercetin, glabridin, red clover, and Isoflavin Beta, an isoflavones mixture) in order to determine if they could be added to a topical formulation used to treat damage caused by free radicals. Samples of 10 μL of the test compounds at different concentrations were mixed with 0.1 M phosphate buffer, pH 7.4, and a luminol solution was added to yield a final concentration of 0.113 mM. Hydrogen peroxide was then added at a final concentration of 0.05 mM. The reaction was started by introducing the horse-radish peroxidase enzyme at a final concentration of 0.2 IU/mL, in a final volume of 1.0 mL. Chemiluminescence was measured for 10 minutes at room temperature, and dimethylsulfoxide (DMSO) was used as a control. All samples showed marked inhibition of oxidative stress, with a concentration-dependent action for quercetin and Isoflavin Beta. The highest inhibition was observed with glabridin and the dry red clover extract. All flavonoids proved to be adequate for addition to topical formulations because of their high antioxidant activity.

Lack of significant genotoxicity of purified soy isoflavones (genistein, daidzein, and glycitein) in 20 patients with prostate cancer

Genistein may be useful in the prevention or treatment of prostate cancer; however, it causes genetic damage in cultured human cells. The objective was to assess the potential genotoxicity of a purified soy unconjugated isoflavone mixture in men with prostate cancer. Twenty patients with prostate cancer were treated with 300 mg genistein/d for 28 d and then with 600 mg/d for another 56 d. In peripheral lymphocytes, DNA strand breaks were assessed as nuclear tail moment, chromosomal damage was assessed as micronucleus frequency (MF), and translocations of the MLL gene (11q23) were assessed by using fluorescence in situ hybridization. Values are also reported for 6 healthy men. The studies were performed under Investigational New Drug application no. 54 137 at a tertiary referral academic medical center. No changes in group average or individual nuclear tail moment and MF were observed. We observed a single elevated MF value in one subject that exceeded a clinical threshold set before we initiated the study. A significant decrease in average COMET tail moment was observed on day 28 relative to day 0. We detected no genistein-induced rearrangements of the MLL gene in the 3 subjects we studied with this technique. MF increased significantly in lymphocytes exposed in vitro to unconjugated genistein at concentrations > or = 100 micromol/L. Total genistein never exceeded a peak concentration of 27.1 micro mol/L, and unconjugated genistein never exceeded a peak concentration of 0.32 micromol/L. Although isoflavones are capable of inducing genetic damage in vitro, a similar effect was not observed in subjects treated with a purified soy unconjugated isoflavone mixture.

Soy Isoflavones Increase Latency of Spontaneous Mammary Tumors in Mice

Soy protein, with and without isoflavones, is being added to foods by manufacturers in response to the Food and Drug Administration (FDA)-approved health claim for cardiovascular protection. Furthermore, soy isoflavones are increasingly consumed by women in the United States as an alternative to hormone replacement therapy. The role of these phytoestrogens in breast cancer is controversial. Although exposure of rodents to soy isoflavones during the perinatal period appears to reduce mammary cancer formation, exposure in utero or during adulthood may increase tumor growth. The mouse mammary tumor virus (MMTV)-neu mouse spontaneously develops mammary tumors due to overexpression of the ErbB-2/neu/HER2 oncogene. This model is comparable with human breast cancer because overexpression of the neu oncogene occurs in 20-40% of human breast cancers. We fed MMTV-neu mice AIN-93G diets containing no isoflavones, 250 mg/kg genistein, 250 mg/kg daidzein or an isoflavone mixture (NovaSoy, equivalent to 250 mg genistein/kg) from 7 wk of age. Mammary tumor latency was significantly delayed in mice fed isoflavones compared with the control. Once tumors formed, however, the isoflavones did not reduce the number or size of tumors such that at 34 wk of age there were no differences in tumor burden among the treatment groups. Hence, in the MMTV-neu mouse, soy isoflavones delayed mammary tumorigenesis. Further studies are warranted to define the cellular mechanisms through which these compounds affect mammary tumorigenesis in this model.

Research Communication: Absorption in Humans of Isoflavones from Soy and Red Clover Is Similar

The absorption of isoflavones varies substantially among individuals. It is unknown whether isoflavone absorption differs between those originating from soy and those from red clover, which contain different mixtures of isoflavones. Because both soy and red clover are increasingly used in foods and supplements, these issues were studied in 14 subjects in a single-blind, randomized, placebo-controlled, crossover trial. Soybean isoflavone glycosides and red clover isoflavone aglycones were incorporated into a breakfast cereal and eaten daily for 2 wk each, separated by a 2-wk control or washout period. The 24-h excretions of isoflavones in urine were measured; approximately 25% of each isoflavone was recovered in urine, suggesting that similar amounts were absorbed irrespective of their glycoside/aglycone nature or the differing compositions of their sources (daidzein and genistein in soy and formononetin and biochanin in red clover). Although interindividual variability was high, there was less intraindividual variability; the amounts excreted when subjects consumed the two sources of isoflavone were correlated (r = 0.69; P = 0.007).

Overexpression of HER-2/neu enhances the sensitivity of human bladder cancer cells to urinary isoflavones

Soybean foods have been suggested to be practical chemopreventives for human urinary tract cancers. Recently, we demonstrated that the co-operative action of isoflavones results in an increased dose-dependent growth inhibition and apoptosis than any single isoflavone compound. This study aimed to examine the potential of HER-2/neu as a biological target for soy isoflavones. The sensitivity of the bladder cancer cell lines (n=7) to the isoflavones was inversely related to the amount of HER-2/neu expressed. By using HER-2/neu transfection experiments, all three stable transfectants showed a significant growth inhibition by the isoflavone mixture at concentrations attainable in normal adult urine. An increased inhibition of tyrosine phosphorylation of proteins immunoprecipitated by HER-2/Neu was observed in the neu-transfectants compared with controls. The results of this study suggest that HER-2/neu may be a practical biochemical target for urinary isoflavones in vivo.

Soy isoflavone supplementation in healthy men prevents NF-κB activation by TNF-α in blood lymphocytes

Dietary intake of soy has been associated with a decreased risk of cancer. Soy isoflavones have been postulated to be the protective compounds in soybeans; however, the precise mechanism by which soy isoflavones prevent human cancer is not known. The major soy isoflavones, genistein and daidzein, are antioxidant compounds, therefore one possible mechanism of action is through their antioxidant effect. We have previously demonstrated that the soy isoflavone, genistein, inhibits the activation of the redox-sensitive transcription factor, NF-κB, in prostate cancer cells in vitro. In this study, we have demonstrated that genistein, but not daidzein, inhibits TNF-α-induced NF-κB activation in cultured human lymphocytes. Additionally, we investigated the in vivo effect of soy isoflavone supplementation on NF-κB activation induced by TNF-α in vitro in peripheral blood lymphocytes of six healthy men. We show that healthy male subjects receiving 50 mg isoflavone mixture (Novasoy) twice daily for 3 weeks are protected from TNF-α induced NF-κB activation. Additionally, we observed a reduction of 5-hydroxymethyl-2′-deoxyuridine (5-OHmdU), a marker for oxidative DNA damage, following isoflavone supplementation. The inhibitory effect of soy isoflavones was no longer present 3 months after the supplementation. This preliminary study demonstrates that soy isoflavone supplementation may protect cells from oxidative stress-inducing agents by inhibiting NF-κB activation and decreasing DNA adduct levels.

Lack of effect of soy isoflavone on thyroid hyperplasia in rats receiving an iodine-deficient diet.

We have reported a dramatic synergism between soy intake and iodine deficiency regarding induction of thyroid hyperplasia in rats. Because isoflavones are active constituents of soybeans, in the present study, their possible contribution was examined. Female F344 rats were divided into 8 groups, exposed to diet containing a 0.2% soy isoflavone mixture (SI), 0.2% SI+iodine deficiency (ID), 0.04% SI, 0.04% SI+ID, 20% defatted soybean (DS) alone, 20% DS+ID, ID alone or basal diet alone for 5 weeks. Thyroid weight was not influenced by SI, but was increased by the ID and DS diets with a further significant increment in the DS+ID group (P<0.01). Compared to the control value, serum T4 was significantly (P<0.01) increased by 20% DS alone and decreased in all groups given the ID treatment (P<0.001). Serum thyroid stimulating hormone (TSH) level was increased by ID, and further enhanced by DS (P<0.01) but not SI. Histopathologically, diffuse hypertrophy and/or hyperplasia of thyroid follicles were observed in the ID‐treated groups, the severity being enhanced by DS but not SI. Proliferating cell nuclear antigen labeling indices (%) were elevated in the ID diet groups and again enhanced by DS, but not SI. These results thus suggest that isoflavones may not be involved in the mechanisms underlying the synergistic goitrogenic effect of soybean with iodine deficiency.

Development of rat prostatitis model by oral administration of isoflavone and its characteristics.

Inflammation of the prostate can be induced experimentally in rats by the subcutaneous administration of estrogen. However, it is usually achieved at the price of some alteration in the sex steroid hormone balance and morphological changes in the prostate. In this study, a soy-extracted isoflavone mixture with weak estrogenic activity was administered orally in an attempt to induce prostatitis in a more physiologic way and to characterize the inflammation induced. A total of 36 male Sprague-Dawley rats, 8 weeks old, were divided into 2 groups. The control group was fed with only an AIN-76A diet containing no detectable phytoestrogen and the experimental group was fed with AIN-76A and a soy- extracted isoflavone mixture (genistein 60.0% and daidzein 19.6%), 300 mg/kg body weight for 9 weeks. The sequential body weight and prostate weight at necropsy were measured. A histologic examination and histomorphometry assessed the changes in the prostate. The serum concentrations of testosterone and dihydrotestosterone were measured to estimate the effects on the androgen level. Intraprostatic concentrations of genistein and daidzein were measured by gas chromatography/ mass spectroscopy (GC/MS). While no sign of prostate inflammation was apparent in the control group, severe inflammatory changes in the stroma, increased epithelial detachment and inflammatory exudates within the glandular lumen of the dorsolateral prostate were observed in more than 80%(15/18) of the experimental group. However, there was no significant difference in the ventral prostate between the two groups. The daidzein and genistein concentrations in both the lateral and ventral prostates were significantly higher in the experimental group than in the control group where no isoflavone was detectable. In addition, the concentrations were much higher in the dorsolateral than in the ventral prostate. Although the body weight gain was not consistent in the experimental group, there were no significant differences in the prostate weight and serum androgen level between groups. In summary, when a soy-extracted genistein and daidzein-rich isoflavone mixture was administered orally into rats, prostatic inflammation with characteristic lobe specificity developed. The present method of inducing prostatitis seems to be a more physiologic than an estrogen-induced experimental model, and sequential pharmacokinetic studies might help in establishing this model as a more valuable tool in assisting future research in this field.

Lack of modifying effects of environmental estrogenic compounds on the development of thyroid proliferative lesions in male rats pretreated with N-bis(2-hydroxypropyl)nitrosamine (DHPN).

The modifying effects of various environmental estrogenic compounds on thyroid carcinogenesis were investigated in a rodent two‐stage carcinogenesis model. The compounds examined were a soy isoflavone mixture (SI) and genistein (GEN) as phytoestrogens, nonylphenol (NP) as a xenoestrogen, 3‐chloro‐4‐(dichloromethyl)‐5‐hydroxy‐2(5H)‐furanone (MX) as a thyroid carcinogen and sulfadimethoxine (SDM) as a known thyroid tumor promoter. Five‐week‐old male F344 rats were given a single subcutaneous injection of N‐bis(2‐hydroxypropyl)nitrosamine (DHPN; 2800 mg/kg, body weight) or the vehicle alone. Starting one week thereafter, GEN (250 or 25 ppm in diet), SI (400 ppm in diet), NP (250 or 25 ppm in diet), MX (30 ppm, in drinking water) or SDM (1000 ppm in drinking water) was administered for 12 weeks. Major organs including the thyroid, pituitary, liver, kidney, testis, brain and pancreas were weighed and histopathological observation was performed. Thyroid weights were significantly increased (P < 0.001) only in the SDM treatment groups, especially with DHPN pretreatment. Kidney weights were slightly increased in the NP or MX treatment groups, albeit without statistical significance. Histopathologically, thyroid proliferative lesions were only observed in the SDM alone or DHPN+SDM group with significant focal hyperplasias, adenomas and adenocarcinomas limited to the combined treatment case. There were no organ weight changes or histopathological lesions in the major organs including the thyroid in the GEN, SI, NP, and MX treatment groups regardless of DHPN pretreatment. Our results thus indicate that the weakly estrogenic compounds GEN, SI and NP and the environmental rat thyroid carcinogen MX do not exert any modifying effects on thyroid carcinogenesis in rats under the present experimental conditions.

Inhibitory effects of Bifidobacterium-fermented soy milk on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced rat mammary carcinogenesis, with a partial contribution of its component isoflavones

High consumption of soybean and soybean-related products is hypothesized to contribute to protection against breast cancer. Soybean is a rich source of genistein, a putative cancer chemopreventive agent. Fermented soy milk (FSM), which is made of soy milk fermented with the Bifidobacterium breve strain Yakult, contains larger amounts of the isoflavone aglycones genistein and daidzein than unfermented soy milk. In the present study, we examined the effects of FSM and its component isoflavone mixture (genistein:daidzein 4:1) on 2-amino-1-methyl-6-phenylimidazo[4, 5-b]pyridine (PhIP)-induced mammary carcinogenesis in rats. Starting at 7 weeks of age, female Sprague-Dawley rats were given PhIP at a dose of 85 mg/kg body wt by intragastric administration four times a week for 2 weeks. They were fed control high fat basal diet or experimental high fat diet containing 10% FSM or 0.02 or 0.04% isoflavone mixture during and after carcinogen exposure. The incidences (percentage of rats with tumors) of mammary gland tumors were 71% in the control diet group, 51% in the FSM group and 68 and 61% in the groups treated with isoflavone mixture at 0.02 and 0.04%, respectively. Mammary tumor multiplicities (number of tumors per rat) were 1.2 +/- 0.2 for 10% FSM, 2.2 +/- 0.4 for 0.02% isoflavone mixture and 1.5 +/- 0.3 for 0.04% isoflavone mixture, being clearly smaller than the control diet value (2.6 +/- 0.5). Furthermore, feeding of FSM and the isoflavone mixture at both doses reduced the sizes of mammary tumors. Since the amounts of isoflavones in 10% FSM are approximately equivalent to those in the 0.02% isoflavone mixture, the chemopreventive activity of FSM could be partly attributable to the presence of isoflavones such as genistein and daidzein.

All We Are Saying Is Give Plants a Chance!

This article has no abstract.

Supplemental Intake of Isoflavones and Zinc-Containing Mineral Mixture Enhances Bone Components in the Femoral Tissue of Rats with Increasing Age.

The effect of the supplemental intake of isoflavone and a zinc-containing mineral mixture on bone components in the femoral tissue of rats was investigated. Rats (5 weeks old) were orally administered either vehicle, isoflavone glycoside (5mg/100g body weight), aglycone isofavone (5mg/100g, including 3.772mg daidzein, 0.395mg genistein, and 0.833mg glycitein), zinc-containing mineral mixture (0.833mg zinc, 50mg calcium, 25mg magnesium, and 0.208μg vitamin D3 per 100g body weight, respectively), or both aglycone isoflavone (5mg/100g) and zinc-containing mineral mixture for 7d. Administrations resulted in a significant increase in femoral dry weight, calcium content, alkaline phosphatase activity, and DNA content in the femoral-diaphyseal and metaphyseal tissues. Femoral zinc content was significantly increased by the administration of zinc-containing mineral mixtures with or without aglycone isoflavone. The effect of aglycone isoflavone in elevating bone components was significantly enhanced in combination with the zinc-containing mineral mixture. Moreover, the oral administration of both aglycone isoflavones and zinc-containing mineral mixture to aged rats (50 weeks old) for 21d resulted in a significant increase in femoral dry weight, zinc content, and bone components. This study demonstrates that supplemental intake of both aglycone isoflavone and a zinc-containing mineral mixture has an anabolic effect on bone components in aged rats, suggesting the role of nutrients in the prevention of osteoporosis with increasing age.

Effects of a soybean isoflavone mixture on carcinogenesis in prostate and seminal vesicles of F344 rats.

Several epidemiological studies have suggested an inverse association between the risk of prostate cancer and intake of soybeans and their products. In vitro data pointing to possible anti‐carcinogenic properties of the soybean isoflavone, genistein, led us to investigate the chemopreventive potential of soybean isoflavones in a rat carcinogenesis model induced by 3,2′‐dimethyl‐4‐aminobi‐phenyl (DMAB) and testosterone propionate (TP). Animals received DMAB s.c. injections at 2‐week intervals for the first 20 weeks and implanted silicon tubes containing 40 mg of TP, replaced at 6‐week intervals throughout the experiment. The soybean isoflavone mixture consisting of 74% genistein and 21% daidzein was mixed in basal diet (AIN‐76A) at concentrations of 100 and 400 ppm and fed to F344 male rats throughout the experiment. Rats treated with carcinogens and administered isoflavone mixture at 100 and 400 ppm developed adenocarcinomas at incidences of 35% and 29%, respectively, in the prostate and seminal vesicles, whereas the figure was 60% for those maintained on control diet. Feeding of the isoflavone mixture at 100 and 400 ppm significantly inhibited the number of argyrophilic nucleolar organizer regions (AgNORs) in adenocarcinomas of the accessory sex glands as compared to those of rats fed control diet. No influence on the development of neoplastic lesions originating in other organs was noted. The results of this study provide evidence that soybean isoflavones may have potential as chemopreventive agents against carcinogenesis in the prostate.

Phytoestrogens Reduce Bone Loss and Bone Resorption in Oophorectomized Rats

To examine a potential role for phytoestrogens in postmenopausal bone loss, the oophorectomized (OOX) rat model has been used in three studies to investigate the effects of the phytoestrogens coumestrol, zearalanol and a mixture of isoflavones on estrogen-dependent bone loss. In the studies of coumestrol and zearalanol, the rats were allocated to a control group, a phytoestrogen-treated group (1.5 μmol coumestrol or 3.1 mmol zearalanol twice per week, intramuscular) or, in the coumestrol study, an estrogen-treated group (28.1 nmol, intramuscular). In the isoflavone study, the rats were allocated to a control group, an estrogen treated group or a treatment group that received 131.25 mg of phytoestrogens per week incorporated into the nonpurified rat diet. Bone mineral density was measured globally and at the spine and femur at base line and 6 wk post-oophorectomy. In the coumestrol study, blood and urine samples were collected. Compared with the control group, rats receiving coumestrol and zearalanol had significantly reduced bone loss at all sites measured. The estrogen-treated group had significantly greater bone density than the control and the coumestrol-treated groups in the spine and global measurements. Coumestrol reduced urine calcium excretion and the bone resorption markers pyridinoline and deoxypyridinoline after 1 wk of treatment. Oral isoflavone phytoestrogens had no effect on oophorectomized rats including bone loss at the dose used. Thus, for the first time, the bioactivity of coumestrol and zearalanol in preventing bone loss has been demonstrated in a well-recognized model of postmenopausal bone loss.

Constitutive isoflavones as modulators of indole-3-acetic acid oxidase activity of acidic cell wall isoperoxidases from lupin hypocotyls

The effect of isoflavones on the indole-3-acetic acid (IAA) oxidase activity of acidic cell wall isoperoxidases from lupin hypocotyls was tested using as isoflavone source a mixture of isoflavones obtained from the whole hypocotyl, isoflavones isolated from five different growth zones, and individual isoflavones purified by thin-layer chromatography. The results showed that 2′-hydroxygenistein was the most potent inhibitor of the enzymatic activity, genistein and wighteone having similar, but lower, inhibitory effects. Since 2′-hydroxygenistein is accumulated in the cell walls of young tissues, it can be expected that the strong inhibitory effect shown by isoflavones isolated from the most apical zones is due mainly to 2′-hydroxygenistein. These results are discussed on the basis of the compartimentalization of auxin catabolism in both young epidermal cells and differentiating vascular tissues of lupin seedlings.