High Isoflavone Content Research Articles

Effect of intact and isoflavone-depleted soy protein on NMU-induced rat mammary tumorigenesis.

Experiments in animal models of carcinogenesis suggest that soy consumption decreases tumor number and incidence. Genistein, an isoflavone which is present in soy at high concentrations, has been considered to be the primary antitumor constituent in soy. In the present study, the N-nitroso-N-methylurea (NMU)-induced mammary tumor model was used as a means to determine whether the chemopreventive effect of soy was attributable specifically to its high content of isoflavones. Five groups of rats (30/group) were fed the following modified AIN-93G diets: group 1, 20% intact soy protein (SP); group 2, 10% SP; group 3, 20% isoflavone-depleted soy protein (IDSP); group 4, 10% IDSP; group 5, the casein-based AIN-93G diet. The SP contained 1.07 and IDSP 0.073 mg genistein/g isolate, respectively. Experimental diets were initiated 1 week prior to NMU administration (at 50 days of age) and continued for another 18 weeks. No significant differences were found among the five groups when assessed in terms of tumor incidence, latency, multiplicity or volume. A trend towards inhibition was observed in both the 20 and 10% SP and IDSP groups when assessed in terms of total tumors/group, tumor volume and latency, but this trend did not achieve statistical significance. The results of this model study do not support the hypothesis that the isoflavone components of soy protein, or soy protein itself, inhibit chemically induced mammary tumor development.

Effects of phyto-oestrogens on tissues

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

The effect of Promensil™, an isoflavone extract, on menopausal symptoms

Objectives The primary aim was to assess whether the use of an isoflavone extract containing 40 mg or 160 mg of total isoflavones affects the frequency of menopausal flushes and other symptoms. The secondary aims were assessments of possible effects on menopause symptom scores and biological measures of estrogen activity.Methods A randomized, double-blind, placebo-controlled prospective trial of 37 postmenopausal women with symptoms of estrogen deficiency was performed over a 12-week period. The women were randomized to three treatment groups: placebo, 40 mg or 160 mg, delivered in tablet form.Results There was no significant difference in the incidence of flushes between the three groups at trial conclusion. There was no difference between the groups in Greene Menopause Symptom Scores, vaginal pH, levels of follicle stimulating hormone (FSH), sex hormone binding globulin (SHBG) or total cholesterol, liver function or blood parameters. A statistically significant increase in high-density lipoprotein (HDL) cholesterol of 18.1% (p = 0.038) occurred in the 40-mg group.Conclusion A large placebo response and inadvertent use of dietary isoflavones in the placebo group may have obscured a significant change in flushing frequency. Previous uncontrolled studies claiming a beneficial effect of foods with a high isoflavone content on menopausal symptoms may have been confounded by a large placebo response.

BIOCHANIN A AND FORMONONETIN CONTENT IN RED CLOVER VARIETIES AT SEVERAL MATURITY STAGES

A method has been developed for quantitative estimation of the isoflavones — biochanin A and formononetin in red clover. This involved scanning the paper chromatograms with a densitometer for biochanin A and with a fluorimeter for formononetin. Some variation in isoflavone content was observed between varieties. Highest isoflavone content (approximately 1% of dry weight of each isoflavone) occurred in the leaves before flowering and then it fell off rapidly. Only small amounts of isoflavone were present in stems and petioles throughout the growing season.

Study of the fate of phyto-oestrogens in the sheep by determination of isoflavones and coumestrol in the plasma and adipose tissue

A method is presented for the specific determination in plasma or adipose tissue of sheep of the phyto-oestrogens genistein (G), biochanin A (BA), formononetin (F), daidzein (D), pratensein, and coumestrol. The method is based on selective extraction, paper chromatography, spectrophotometry and fluorometry, and use of radioactive recovery standards. A modification including gas chromatography is also described. Intraruminal administration to sheep of the synthetic isoflavones G, BA, or F gave rise within 2½ hr to detectable blood levels of the compound infused. In addition, intraruminal administration of BA and F was followed by the appearance of G and D, respectively, in blood and fat depots. Such O-demethylation at the C4 position was also observed after intramuscular injection of BA or F, and in sheep grazing subterranean clover (Trifolium subterraneum L.) and red clover (T. pratense). Plasma levels of free G above 5 µg/100 ml (excluding circulating isoflavone conjugated as glucuronide) were associated with maximal uterine growth response in ovariectomized ewes, while levels of 1–5 µg/100 ml appeared to elicit a graded uterine response; free plasma F and D levels above 0.5 �g/100 ml seem to be required for detectable uterotrophic action in the 5-day assay used. G, BA, F, and D were present in the plasma of sheep grazing subterranean clover var. Yarloop in concentrations adequate to explain the observed uterine growth response, but in sheep grazing red clover, the plasma levels seemed too low to account fully for the oestrogenic action of this pasture. No free isoflavones were detected in plasma from sheep grazing subterranean clover var. Marrar, despite the high isoflavone content of the pasture.