**6. Isoflavones: new insights regarding the therapeutic effect**

An increased consumption of soy products has been remarqued in the last decade of the twentieth century and was associated with the awareness concerning the health benefits of these products, besides their role as a source of proteins [62]. The therapeutic activities of soy isoflavones were also evaluated in numerous studies for their estrogenic [63], lipid‐lowering [64], anti‐diabetic [65], anti‐inflammatory [66], cardioprotective [67, 68] or anticancer effects [69]. *In vitro* and *in vivo* studies were performed in order to evaluate the therapeutic potential and the mechanisms of action of these compounds [70, 71].

Isoflavones are known as phytoestrogens due to their ability to bind the estrogen receptors and to exhibit estrogenic‐like properties. Dietary supplements containing soy isoflavones are used to alleviate menopause disturbances as an alternative to hormone therapy [72]. Isoflavones attracted the attention of researchers after the observation of fertility problems in sheep grazing on a clover type rich in isoflavones [62]. The decreased risk of breast, prostate and colon cancer in Asian countries was associated with a higher intake of soy products in these population compared to western countries [70].

The possible benefits of isoflavones thus generated several studies to establish their thera‐ peutic properties. Isoflavones exhibit both estrogenic and anti‐estrogenic activity, binding to both α and β subtypes of estrogen receptor (ER) [73]. It was stated that isoflavones act as estrogen antagonists or agonists depending on estrogen concentration. Therefore, they are estrogen antagonists in a high estrogen environment, but when the estrogen quantity is reduced, they act as agonists [74]. The affinity for the estrogen receptors is different; genis‐ tein presents a 20–30 times higher affinity for ERβ than for ERα, while daidzein presents a weak affinity for both receptors, still higher for ERβ [70, 75]. Administration of 80 mg/day red clover isoflavones (containing genistein, daidzein, formononetin and biochanin A) for 90 days reduced hot flushes and night sweats, important vasomotor symptoms commonly found in postmenopausal women [76]. Low doses of isoflavones (25 mg/day containing 51.8% genistein, 43.3% daidzein and 4.9% glycitein) can reduce depression and insomnia in postmenopausal women [72].

Soy isoflavones present beneficial effects on lipid metabolism. The lipid‐lowering activity of isoflavones has been observed in studies performed in animals. Soy isoflavones reduced the levels of triglycerides (TG) and low‐density lipoprotein (LDL) in obese rats, and also exhibited benefits on obesity. The mechanisms involved are the suppression of mecha‐ nistic target of rapamycin complex 1 (mTORC1) activity that determines a reduction of AKT phosphorylation [77]. A decrease of total cholesterol, LDL cholesterol levels and an improvement of ApoA1/ApoB ratio were noticed after the administration of 435 mg isofla‐ vones/day for 2 months in women with type 2 diabetes [64].

respectively. Concerning isoflavone intake among Japanese adults, it is ranged from about 30–50 mg/day but is less than 3 mg/day in the US and Europe [27]. In Asian countries, the mean isoflavone consumption is 25–50 mg/day, whereas in Western countries, 1–2 mg/day is typical [60]. However, in the last decade, in Western countries, production and intake of soy foods have increased due to its important health benefits (relief of menopausal symp‐ toms, improvement in bone health and reduced risk of certain types of cancers) [61].

An increased consumption of soy products has been remarqued in the last decade of the twentieth century and was associated with the awareness concerning the health benefits of these products, besides their role as a source of proteins [62]. The therapeutic activities of soy isoflavones were also evaluated in numerous studies for their estrogenic [63], lipid‐lowering [64], anti‐diabetic [65], anti‐inflammatory [66], cardioprotective [67, 68] or anticancer effects [69]. *In vitro* and *in vivo* studies were performed in order to evaluate the therapeutic potential and

Isoflavones are known as phytoestrogens due to their ability to bind the estrogen receptors and to exhibit estrogenic‐like properties. Dietary supplements containing soy isoflavones are used to alleviate menopause disturbances as an alternative to hormone therapy [72]. Isoflavones attracted the attention of researchers after the observation of fertility problems in sheep grazing on a clover type rich in isoflavones [62]. The decreased risk of breast, prostate and colon cancer in Asian countries was associated with a higher intake of soy products in

The possible benefits of isoflavones thus generated several studies to establish their thera‐ peutic properties. Isoflavones exhibit both estrogenic and anti‐estrogenic activity, binding to both α and β subtypes of estrogen receptor (ER) [73]. It was stated that isoflavones act as estrogen antagonists or agonists depending on estrogen concentration. Therefore, they are estrogen antagonists in a high estrogen environment, but when the estrogen quantity is reduced, they act as agonists [74]. The affinity for the estrogen receptors is different; genis‐ tein presents a 20–30 times higher affinity for ERβ than for ERα, while daidzein presents a weak affinity for both receptors, still higher for ERβ [70, 75]. Administration of 80 mg/day red clover isoflavones (containing genistein, daidzein, formononetin and biochanin A) for 90 days reduced hot flushes and night sweats, important vasomotor symptoms commonly found in postmenopausal women [76]. Low doses of isoflavones (25 mg/day containing 51.8% genistein, 43.3% daidzein and 4.9% glycitein) can reduce depression and insomnia in

Soy isoflavones present beneficial effects on lipid metabolism. The lipid‐lowering activity of isoflavones has been observed in studies performed in animals. Soy isoflavones reduced the levels of triglycerides (TG) and low‐density lipoprotein (LDL) in obese rats, and also exhibited benefits on obesity. The mechanisms involved are the suppression of mecha‐ nistic target of rapamycin complex 1 (mTORC1) activity that determines a reduction of

**6. Isoflavones: new insights regarding the therapeutic effect**

the mechanisms of action of these compounds [70, 71].

266 Flavonoids - From Biosynthesis to Human Health

these population compared to western countries [70].

postmenopausal women [72].

The benefits of isoflavones in glucose and lipid metabolism have been previously reported, but the mechanisms of action are not yet fully understood [78]. Potential benefits in obesity were also observed after intake of isoflavones. Dietary modifications in early stages of this condition are important to prevent cardiovascular and metabolic disorders [79]. Some of the mechanisms involved in the anti‐diabetic properties of isoflavone genistein are the enhancing of β‐cell proliferation and the regulation of insulin secretion [65]. Isoflavones intake might reduce the risk of type 2 diabetes [53]. However, the beneficial role of isoflavones in this disease was not supported by other studies [78, 80]. A decreased risk of type 2 diabetes was noticed for women with high concentrations of genistein in plasma, but this correlation was not observed in men [81]. After the administration of a diet supplemented with 0.02% (w/w) genistein for 8 weeks (10–12 mg genistein/day) in Zucker diabetic fatty (ZDF) rats, there were no benefi‐ cial effects on glucose homeostasis or on skeletal muscle oxidative stress [78]. The conflicting results regarding the benefits of isoflavones in diabetes led to the assumption that other soy compounds might be responsible for this activity [65].

Genistein not only reduces weight gain in female obese *ob/ob* mice after the administration of 600 mg/kg diet for 4 weeks, but also promotes oxidative stress in the vasculature and inflammation in the perivascular adipose tissue [82]. Daidzin and glycitin (0.06% in diet) decrease blood glucose, insulin and HbA1c levels in mice with obesity and diabetes induced by a high‐fat diet [79].

The effects of isoflavones on components of the metabolic syndrome were also evaluated. An extract from the roots of *Pueraria lobata*, administered 0.2% in the diet of female stroke‐prone spontaneously hypertensive rats (SP‐SHR) improved blood glucose levels, decreased plasma total cholesterol levels and reduced blood pressure, thus indicating beneficial effects on risk factors that led to the development of metabolic syndrome. The major isoflavones in the extract were puerarin (25.3%), daidzin (7.1%) and daidzein (0.8%) [83].

Even though the effects on obesity and diabetes were not sustained by other studies, an increase in bone mass was noticed in obese mice treated with 600 mg genistein/kg for 4 weeks [84]. The bone protective properties were also observed for other compounds. Formononetin, an isoflavone found mainly in the roots of *Astragalus membranaceus* and *Astragalus mongholicus*, improved the mechanical properties of the bones and exerted beneficial effects in rats with osteoporosis induced by ovariectomy after the administration of 10 mg/kg formononetin for 4 weeks [85]. The results of a meta‐analysis investigating trials that evaluated the effects of isofla‐ vone in osteoporosis, revealed that the effects of these compounds depend on dose and dura‐ tion of administration. An increase in mineral density of the bone by 54% and a reduction in the fracture risk were noticed in women included in these studies [86]. A clinical trial regarding the effects of soy isoflavones on bone loss and menopausal symptoms did not reveal benefits in this condition. Women included in the study received tablets containing 200 mg soy isoflavones (genistein and daidzein)/day for 2 years [87].

The cardiovascular diseases are more frequent in women after menopause, due to the modifications in the production of estrogen [88]. Compounds with estrogenic properties, such as the isofla‐ vones found in soy, were evaluated for their potentially cardioprotective activity [89, 90]. The administration of 80 mg/day isoflavones extracted from soybeans for 12 weeks in patients with primary or recurrent ischemic stroke determined a decrease in high sensitivity, C‐reac‐ tive protein and improved vascular endothelial function [68]. A meta‐analysis evaluating the results of nine trials concluded that isoflavone supplementation improves endothelial func‐ tion in postmenopausal women that presents low flow‐mediated dilatation (FMD) levels, but not in ones with high baseline FMD levels [89]. Nevertheless, the benefits of isoflavones regarding the protective effects in ischemic stroke are questionable. Yu et al. associated the high intake of soy isoflavones (53.6 mg isoflavones/day) with an increase in the risk of ischemic stroke in women [91].

The protective effect against the inflammatory vascular disease of isoflavones is due to their anti‐inflammatory activity. The inhibition of monocyte adhesion to endothelial cells that involves the activation of PPARγ is related to this effect [66]. The anti‐inflammatory properties are due to inhibition of interleukin‐6 (IL‐6), interleukin‐12 (IL‐12), interleukin‐1β (IL‐1β), and tumor necrosis factor‐α (TNF‐α) production, NF‐κB regulation and their antioxidant activity [92]. Pro‐oxidant effects at high doses were also noticed for these compounds. The supple‐ mentation with 640 mg/kg daidzein in pigs revealed antioxidant properties in muscle, but were accompanied by pro‐oxidant effects in fat and liver tissues [93].

Administration of soy isoflavones (daidzein, genistein and glycetin) in capsules, 20 mg twice daily in female patients improved irritable bowel disease and association with vitamin D can determine a synergistic effect [94]. The estrogen‐like effects of isoflavones genistein and daidzein seem to be involved in their beneficial effects on sleep status. A high intake of isoflavones was related to an optimal sleep duration and an increased quality of sleep in Japanese adults [95].

Age‐related skin modifications in women emerging with a decline in estrogen production can be reduced by isoflavones. Genistein improves skin appearance and is used to reduce wrinkles and skin dryness in cosmetic preparations. It increases the skin resistance and contributes to skin reparation [96].

Anti‐bacterial effects were also reported for isoflavones. For instance, biochanin A, a methylated isoflavone from red clover, inhibits the growth of *Chlamydia trachomatis* and *Chlamydia pneumoniae* [97]. Isoflavones act as anti‐viral agents against several types of viruses including herpes simplex virus and human immunodeficiency virus (HIV). Genistein, a tyrosine kinase inhibi‐ tor, is one of the compounds most studied for these properties and revealed positive effects in inhibiting HIV‐1 infection, especially when applied in entry and early post‐entry stages [98].
