Genistin

Genistin: A Comprehensive Encyclopedic Reference

1. Identity, Chemical Nature, and Nomenclature

Genistin (also written genistine) is a naturally occurring isoflavone glycoside. It was first isolated in 1931 from a 90% methanol extract of soybean meal, when it was found that hydrolysis with hydrochloric acid produced one mole each of genistein and glucose. Chemically, it is the 7-O-beta-D-glucoside form of genistein and is the predominant form of the isoflavone naturally occurring in plants. Understanding genistin therefore requires examining it alongside its aglycone, genistein, the biologically active form to which genistin is converted in vivo.

1.1 Chemical Nomenclature and Structure

Chemically, genistin is the 7-O-beta-D-glucoside form of genistein and is the predominant form of the isoflavone naturally occurring in plants. The aglycone genistein is chemically designated 4′,5,7-trihydroxyisoflavone, also known by its IUPAC name 5,7-dihydroxy-3-(4-hydroxyphenyl)chromen-4-one. It has a molecular formula of C₁₅H₁₀O₅ and a molecular weight of 270.241 g/mol. Its structure is based on the 3-phenylchromen-4-one configuration, consisting of two aromatic benzene rings (A and C) and one non-aromatic heterocyclic pyran ring (B). At the 5-, 7-, and 4′-positions of the phenylchromenone, there are hydroxyl groups. In genistin, the hydroxyl group at position 7 carries a beta-D-glucopyranose sugar unit, rendering the molecule more water-soluble than the free aglycone.

The molecular formula is C₁₅H₁₀O₅, formula weight 270.24, with a melting point of 297–298 °C, and the compound is practically insoluble in water and is light sensitive. Genistin itself carries a higher molecular weight due to the attached glucose moiety.

1.2 Relationship Between Genistin and Genistein

The majority of genistein occurs in plant raw materials in the glycoside form as genistin (genistein 7-glucoside). Studies in the 1970s revealed that 99% of the isoflavonoid compounds in soy are present as their glucosides. The glucosides are converted by digestive enzymes in the digestive system to exert their biological effects. Genistin is also converted to genistein; thus, the biological activities including antiatherosclerotic, estrogenic, and anticancer effects are analogous.

Genistin is hydrolyzed by removing the covalently bound glucose to form genistein, and genistein is the form of the compound that is absorbed in the intestine and is the form responsible for the biological activities of the isoflavone. The digestive metabolism was first demonstrated in 2002 when gut microflora was shown to play a large role in the conversion of genistin to genistein. It was later found that enzymes present in the human small intestine and liver also have the ability to convert the isoflavone. Hydrolysis begins very quickly in the digestive system once genistin is ingested, starting in the mouth and continuing in the small intestine.

Genistein, one of the most investigated isoflavones, belongs to the group of aglycones. Isoflavones are present almost exclusively in glycosylated forms in natural sources and, only after food processing, become available in the biologically active aglycone forms.

2. Natural Sources and Botanical Origin

2.1 Principal Botanical Sources

Genistein is an isoflavone isolated for the first time in 1899 from Genista tinctoria L. (dyer's broom), belonging to the Fabaceae family. It was first isolated in 1899 from the dyer's broom, Genista tinctoria; hence the chemical name. The compound structure was established in 1926, when it was found to be identical with that of prunetol. It was chemically synthesized in 1928.

Genistein belongs to the flavonoid family, in the subgroup of isoflavones, and is a phytoestrogen mainly derived from legumes such as Lupinus albus L. (lupine), Vicia faba L. (fava bean), Glycine max (L.) Merr. (soybeans), Pueraria lobata (Willd.) Ohwi (kudzu), and Psoralea corylifolia L. (Psoralea). Genistein has also been reported, for the first time, in the marine alga Padina tetrastromatica Hauck.

The root-tuber peel extract of Flemingia vestita is a traditional medicine anthelmintic of the Khasi tribes of India; genistein was found to be the major isoflavone responsible for a deworming property. Another widely utilized source of genistin is Sophora japonica L.

2.2 Concentration in Foods

Soybean is the richest source of the isoflavone genistein. Of the total number of soy isoflavones, approximately 60% is represented by genistein. In mature soybeans, genistein has been shown to range from 5.6 to 276 mg/100 g. Traditional soy foods contain approximately 3.5 mg of isoflavones per gram of protein, whereas more refined soy products, such as soy protein isolate and soy protein concentrate, can lose as much as 90% of their isoflavone content during processing. On average, traditional soy foods contain 20–30 mg of isoflavones per serving (for example, 250 ml of soymilk made from whole soybeans or 100 g of tofu).

The average dietary isoflavone intake in Asian countries ranges between 25 and 50 mg/day, whereas in Western countries the estimated intake is as low as 2 mg/day. Asian populations, for whom fermented soy food and other isoflavone-containing plants are dietary staples, are estimated to consume 25–100 mg of isoflavone daily. In contrast, intake of isoflavones in the US is estimated at only 0.15–3 mg per day, with much of it being in glucoside forms.

Genistein can be found in many food products containing soy such as soy-based infant formulas, tofu, soymilk, soy flour, textured soy protein, soy protein isolates, tempeh, and miso, as well as over-the-counter dietary supplements. Legumes are considered the second most significant source of genistein, at 0.2–0.6 mg/100 g, present together with daidzein.

2.3 Effect of Processing on Genistin Content

The main dietary source of genistein is the biologically active glucoside genistin. Fermentation or digestion of soybeans or soy products results in the release of the sugar molecule from the isoflavone glycoside, genistin, leaving the isoflavone aglycone, genistein. Fermented soy products such as tempeh and miso therefore contain a higher proportion of free genistein aglycone, whereas unfermented products such as raw tofu and soymilk contain genistin predominantly in its glycoside form. Unfermented soybeans are a particularly rich source of genistin, the glucoside precursor of genistein, although the concentration varies with the strain, location, and environmental conditions of cultivation of the plant.

3. Traditional and Historical Use

3.1 Soy in Asian Food Traditions

Soy (genistein) is the major source of plant-derived phytoestrogen compounds, which has long been used as a traditional food. Soybean cultivation and consumption has a history of thousands of years in East Asia, particularly in China, Japan, and Korea. Nutrition based on soy, which is common mainly in Asia, is attributed to the fact that much lower rates of carcinomas (breast, prostate, skin) occur there, and that postmenopausal symptoms in women occur rarely. These epidemiological observations stimulated scientific interest in the bioactive constituents of soy, most prominently genistin and its aglycone genistein.

Genistein is a phytoestrogen that belongs to a class of compounds known as isoflavones, which structurally resemble endogenous estrogen. It is most often consumed by humans via soybeans or soya products and is, as an auxiliary medicinal, used to treat women's diseases. In traditional Asian medicine systems, soy preparations were consumed to address female reproductive complaints and age-related conditions, though the specific attribution to genistin or genistein as isolated compounds is a modern pharmacological framing.

3.2 Ethnobotanical Use of Genistin-Containing Plants

The root-tuber peel extract of Flemingia vestita is a traditional medicine anthelmintic of the Khasi tribes of India. Research identified genistein as the major isoflavone responsible for a deworming property. Genistein was subsequently demonstrated to be effective against intestinal parasites such as the poultry cestode Raillietina echinobothrida, the pork trematode Fasciolopsis buski, and the sheep liver fluke Fasciola hepatica, exerting its anthelmintic activity by inhibiting enzymes of glycolysis and glycogenolysis in the parasites.

In Western botanical traditions, Genista tinctoria (dyer's woad or dyer's broom) — the plant from which genistein (and by extension the genistin glucoside) was first isolated — was used historically as a diuretic and purgative in European herbal medicine, though these applications predate identification of its isoflavone content and are not specifically attributed to genistin in the scientific literature.

3.3 Isolation and Early Chemistry

Genistin was first isolated in 1931 from the 90% methanol extract of a soybean meal, when it was found that hydrolysis with hydrochloric acid produced one mole each of genistein and glucose. The early characterization of genistin as the predominant isoflavone glycoside in soy preceded later understanding of its conversion to the biologically active aglycone genistein during digestion. The compound structure of genistein was established in 1926, when it was found to be identical with that of prunetol.

4. Key Constituents, Active Compounds, and Mechanisms of Action

4.1 Genistin as Precursor to Genistein

Genistin itself is a prodrug-like glycoside; upon ingestion, genistin undergoes hydrolysis to be converted to genistein, which is absorbed in the intestine and is responsible for the biological activities. Before genistein can act, it first needs to be released from genistin. This normally happens in the stomach (acid hydrolysis) and in the intestine (action of bacterial enzymes).

Genistin, like genistein, is a phytoestrogen, as it was shown to stimulate estrogen-dependent breast cancer cell growth in vivo. This indicates that at least some biological activity may occur prior to full deglycosylation, or that rapid conversion occurs in target tissues.

4.2 Estrogenic and Anti-Estrogenic Activity

At the molecular level, genistein acts as a protein tyrosine kinase (PTK) inhibitor at high concentrations. At lower, nutritionally relevant concentrations, it acts via estrogen receptor-mediated mechanisms. Genistein can bind to estrogen receptors (ER), ERα and ERβ, but has a stronger affinity for ERβ. ERα activation is mainly implicated in cellular growth and proliferation, while ERβ activation correlates with cellular differentiation and cell fate.

Acting as a natural selective ER modulator, genistein exerts its estrogen agonist or antagonist action in a tissue- and dose-dependent manner. The primary mechanism of action of genistein is on ERβ, where it acts as an agonist with 30-fold greater affinity compared to ERα. Genistein has also been shown to exhibit agonistic activity with G protein-coupled estrogen receptor 1 (GPER1), yielding a binding affinity higher than that of estradiol at ERβ.

4.3 Protein Tyrosine Kinase Inhibition

Genistein is a recognized inhibitor of protein kinases. This activity is thought to be due to the C4′ phenolic group of this phytoestrogen, which is structurally similar to the phosphoacceptor group of tyrosine. In vitro, genistein inhibited tyrosine-specific protein kinase activity of the EGF receptor, pp60v-src, and pp110gag-fes, and therefore inhibited growth and metastasis in A-431 epidermoid carcinoma cells. In vivo, genistein was also shown to inhibit serine- and threonine-specific protein kinase activity in the EGF receptor of these cells.

4.4 Antioxidant Activity

Several in vitro and in vivo studies show that genistein aglycone has antineoplastic effects that stem from multiple actions: (a) modulation of cell growth and proliferation throughout tyrosine kinases and topoisomerase II inhibition, (b) stimulation of the immune system, (c) antiangiogenic effects, and (d) potent antioxidant capacity. Genistein has a good antioxidant effect, protecting neurons from oxidative damage.

4.5 Anti-Inflammatory Mechanisms

In ovariectomized rats, genistein downregulated the expression of MAPK, Toll-like receptor 4 (TLR4), and NF-κB in microglia, offering neuroprotection against inflammation, reducing microglial activation, protecting dopaminergic neurons, and lowering the phosphorylation levels of ERK, p38, JNK, and IκB. The anti-inflammatory effects of genistein may be associated with the suppression of the TLR4-mediated NF-κB signaling pathway.

4.6 Cell Cycle and Apoptotic Pathways in Cancer Cells

Cell cycle regulation, tyrosine kinases, DNA topoisomerases, telomerase, apoptosis, and angiogenesis have all been found to be inhibited by genistein. By modifying Bcl-2 family proteins, genistein triggers apoptosis via a mitochondrial-mediated, classical caspase-dependent mechanism. Altering the cycle-regulating proteins causes cell cycle arrest. It deactivates the MAPK (ERK1/2) and PI3K/AKT signaling pathways.

4.7 Epigenetic Mechanisms

The anticancer property of genistein may also be due to DNA methylation and/or chromatin modification. The anticancer mechanism of genistein in breast cancer involves multiple molecular pathways, including regulation of the cell cycle, antioxidant and anti-inflammatory activities, binding to hormone receptors, and modulation of cytochrome P450 (CYP450) enzymes.

4.8 GAG Synthesis Inhibition (Lysosomal Storage Disease Relevance)

The mechanism of genistein-mediated inhibition of glycosaminoglycan (GAG) synthesis operates through the epidermal growth factor (EGF)-dependent pathway. Because this pathway is involved in regulation of gene expression, the therapy of mucopolysaccharidosis based on this reaction has been called 'Gene Expression-Targeted Isoflavone Therapy' (GET IT).

5. Pharmacokinetics and Bioavailability

5.1 Absorption and Conversion

It has been established that glycoside isoflavones are poorly absorbed in the intestine and that hydrolysis of the glycosidic bond by β-glucosidases activates the aglycone for rapid absorption across the intestinal wall. The in vivo bioavailability experiment for genistein and its glycoside genistin showed that genistein is readily bioavailable, being observed in portal vein plasma at the first point of detection at 15 min after dosing. The results indicated that the bioavailability of genistein was higher for the aglycone than for its glycoside.

The C_max of genistin, the glycoside of genistein, is approximately 1.6 times that of genistein for equivalent doses, due to its higher solubility and stability compared to the aglycone. However, the half-life is not considerably different. There is considerable individual variation in the absorption and metabolism of ingested genistin and genistein.

5.2 Phase II Metabolism

Data suggested that the level of phase II genistein glucuronide was higher than that of genistein itself, suggesting the high efficacy of enzymatic glucuronidation. UDP-glucuronosyltransferases serve as versatile and important conjugation enzymes in the phase II biotransformation of xenobiotics. After transport to the liver, the glucuronide may be excreted in the bile, where it could re-enter the small intestine, allowing genistein to be deconjugated, absorbed, and metabolized for the second time (enterohepatic circulation).

5.3 Plasma Levels and Dietary Intake

Plasma concentrations of 50–800 ng/mL are achieved for daidzein, genistein, and equol in adults consuming modest quantities of soy foods containing in the region of 50 mg/day of total isoflavones. These values are similar to those of Japanese consuming their traditional diet.

6. Scientific Evidence by Area of Use

6.1 Menopausal Symptoms (Vasomotor)

According to the current literature, genistein demonstrates efficacy in mitigating menopausal signs and symptoms such as hot flashes, bone density loss and rate of osteoporosis, and skin aging. Due to genistein's high structural similarity to estradiol, the binding capacity of genistein to the estrogen receptor is notable and thus, genistein is mainly studied in postmenopausal women.

Genistein acts as a selective estrogen receptor modulator (SERM) with benefits across a spectrum of menopausal signs and symptoms, presenting a viable alternative to estrogen replacement in perimenopausal and postmenopausal women. It also displays benefits in increasing bone mineral density but has not displayed the side effects commonly associated with estrogen replacement.

Evidence strength: Moderate. Multiple randomized controlled trials have been conducted, with the most prominent in postmenopausal women, though trials vary in duration, dose formulation, and outcome measures. Systematic reviews generally support a modest benefit for vasomotor symptoms, but results across trials are heterogeneous.

6.2 Bone Health and Osteoporosis

Morabito et al. (2002) reported the results of a study in which genistein administered for one year to postmenopausal women was shown to improve bone mineral density as well as several biochemical markers of bone health. Mixed isoflavone studies demonstrate positive effects on bone markers and lipid profiles, vasomotor symptoms, and mood in humans.

The combination of genistein 27 mg, cholecalciferol 200 IU, citrated zinc bisglycinate (4 mg elemental zinc) 20 mg per capsule in Fosteum®, a prescription medical food regulated by the FDA and indicated for the dietary management of osteopenia and osteoporosis, was tested for drug interactions and to determine the pharmacokinetic profile for genistein, the principal bone-modulating ingredient in the product.

Evidence strength: Moderate for short-to-medium-term benefit on bone mineral density in postmenopausal women, based on multiple RCTs. Long-term fracture data remain limited.

6.3 Cardiovascular Health

Genistein shows a protective effect against cardiovascular diseases by improving lipid profiles, weight changes, and reducing low-density lipoprotein cholesterol. Epidemiological and clinical studies have reported health benefits of genistein in many chronic diseases such as cardiovascular disease, diabetes, and osteoporosis.

Evidence strength: Preliminary to moderate. Improvements in lipid profiles and arterial stiffness have been reported in clinical trials, but cardiovascular endpoint data (e.g., incident myocardial infarction) are lacking in the isoflavone-specific literature.

6.4 Cancer — Preclinical and Epidemiological Data

Genistein is a phytoestrogen with a wide variety of pharmacological effects in animal cells, including tyrosine kinase inhibition, and dietary genistein ingestion has been linked, through epidemiological and animal model studies, with a range of potential health-beneficial effects including chemoprevention of breast and prostate cancers, cardiovascular disease, and postmenopausal ailments. Barnes created a table detailing 29 studies characterizing the effects of genistein and genistein-containing products on carcinogenesis in rats and mice, finding a protective effect of genistein in 21 studies, and no effect in the other 8 studies.

Investigations into mechanisms of the anti-cancer activity have revealed many pathways including induction of cell proliferation, suppression of tyrosine kinases, regulation of Hedgehog-Gli1 signaling, modulation of epigenetic activities, seizing of cell cycle and Akt and MEK signaling pathways. Notwithstanding, the observed activities have been time- and dose-dependent.

The relationship with breast cancer is particularly complex: Helferich and colleagues demonstrated that genistein, at or above 250 ppm, stimulates the growth of estrogen-dependent tumors implanted into mice in proportion to the amount of genistein consumed. Studies have reported variability in the effects of genistein across different cell lines, dosages, and administration methods, suggesting that its mechanism of action may be context-dependent and complex. There is still no consensus regarding the differential effects of genistein on various breast cancer subtypes.

Evidence strength: For cancer prevention and treatment, evidence remains preliminary. Most supporting data are from in vitro and animal studies. Clinical trial data in humans are limited and conflicting. The dual stimulatory/inhibitory role on estrogen-sensitive cancers warrants caution.

6.5 Skin Health

Regarding skin health, genistein appears to enhance photoprotection, wound healing, elasticity, and hydration, inhibits skin cancer, and reduces wrinkles. Clinical studies have investigated topical and oral genistein formulations for dermatological endpoints in postmenopausal women, including collagen synthesis. Evidence strength is preliminary to moderate; most dermatological trials are small and short-term.

6.6 Mucopolysaccharidoses (Lysosomal Storage Diseases)

The isoflavone genistein has been studied as a potential therapy for the mucopolysaccharidoses because of its putative ability to inhibit GAG synthesis and subsequent accumulation. Treatment of patients with MPS IIIB with a genistein-rich isoflavone extract at a dose corresponding to the amount of genistein equal to 5 mg/kg/day resulted in statistically important improvement of all tested parameters, including cognitive functions.

A phase III double-blinded, randomized, placebo-controlled clinical trial of high-dose oral genistein aglycone in patients with Sanfilippo syndrome was designed and initiated in Manchester. However, results in MPS I mouse models have been more discouraging: heparan sulfate and dermatan sulfate levels in bone and plasma remained unchanged after genistein supplementation in MPS I mice, while 60% of genistein-fed MPS I mice developed a scrotal hernia and/or scrotal hydrocele, manifestations which were absent in untreated mice. In contrast to studies in MPS III mice, the MPS I study demonstrated no beneficial but even potential adverse effects of genistein supplementation.

Evidence strength: Preliminary. Animal and small clinical studies show variable and disease-subtype-specific outcomes. Definitive phase III clinical trial results for Sanfilippo syndrome remain to be published.

6.7 Cognitive Function

A randomized controlled trial of 59 Alzheimer's disease patients reported that soy isoflavone treatment (Novasoy brand; 100 mg/day, of which approximately 85% was daidzin and genistin as glycosides) for 6 months did not significantly improve cognitive function over placebo, despite increased plasma levels of isoflavones.

Genistein, a cell-permeable protein tyrosine kinase inhibitor, regulates various intracellular signaling pathways by the autophosphorylation of the epidermal growth factor receptor kinase. It reduced the formation of TNF-α and TLR4, which were typical pro-inflammatory molecules, improving memory and alleviating astrogliosis in SH-SY5Y cell models with Alzheimer's disease.

Evidence strength: Weak in humans. No studies have tested genistin or genistein specifically in adequately powered trials for cognitive outcomes; the available RCT found no significant benefit.

6.8 Diabetes and Metabolic Conditions

Genistein has been reported to exhibit several biological effects including improvement of glucose metabolism. It also has numerous clinical implications in the treatment and prevention of diseases like diabetes. Most supporting evidence for metabolic benefits comes from animal models and small-scale human studies; large RCT evidence for clinically meaningful glycaemic outcomes is lacking.

Evidence strength: Preliminary — animal and in vitro data are encouraging; human data are limited and underpowered.

7. Dosage Forms and Reported Dosages

7.1 Dietary Supplement and Medical Food Forms

Genistein is mainly present in the form of its glycoside genistin in supplements. It is found in capsules, powder, and tablets. Genistin-containing dietary supplements are available as soy isoflavone extracts, often standardized to total isoflavone content expressed as aglycone equivalents.

7.2 Dosages Reported in Clinical Studies

• Menopausal vasomotor symptoms / bone health: A prescription medical food (Fosteum®) contains genistein 27 mg, cholecalciferol 200 IU, and citrated zinc bisglycinate (4 mg elemental zinc) 20 mg per capsule, taken twice daily for the dietary management of osteopenia and osteoporosis.
• Soy isoflavone tablet studies: In a randomized crossover pharmacokinetic trial, isoflavone tablet phases included doses of 144 mg/day and 288 mg/day (doses in aglycone equivalents), spread over three meals per day.
• Thyroid safety trial: A 12-week, randomized, double-blind, placebo-controlled trial in 43 oophorectomized Indian women evaluated the effect of 75 mg/day soy isoflavones (genistein and genistin 25%; daidzein and daidzin 15%) on thyroid function markers.
• Prostate cancer safety trial: A study in men with localized prostate cancer assessed the safety of genistein administered at the dose of 30 mg/day for 3–6 weeks prior to prostatectomy.
• MPS (lysosomal storage disease): Treatment of MPS IIIB patients with a genistein-rich isoflavone extract at the dose corresponding to genistein equal to 5 mg/kg/day resulted in statistically important improvement of all tested parameters, including cognitive functions.
• High-dose MPS I animal studies: MPS I mice were fed a genistein-supplemented diet corresponding to a dose of approximately 160 mg/kg/day for 8 weeks.
• Alzheimer's disease RCT: A trial of 59 Alzheimer's disease patients used soy isoflavone treatment at 100 mg/day (approximately 85% daidzin and genistin as glycosides) for 6 months.

8. Body Systems and Health Areas of Association

Based on the published scientific literature, genistin and its aglycone genistein are associated with effects across several organ systems:

• Endocrine/Reproductive system: Acts as a phytoestrogen and selective estrogen receptor modulator; studied in menopausal hormone dynamics, female reproductive health, and male reproductive safety.
• Skeletal system: Studied for effects on bone mineral density, osteoclast inhibition, and osteoporosis prevention.
• Cardiovascular system: Associated with improvements in lipid profiles and LDL-cholesterol levels.
• Oncology: Studied across breast, prostate, and colorectal cancer cell systems; dual estrogenic and anti-estrogenic roles create complexity.
• Neurological system: Investigated in Alzheimer's disease, Parkinson's disease models, and lysosomal storage disorders involving CNS degeneration.
• Metabolic system: Associated with glucose metabolism and insulin resistance.
• Integumentary system (skin): Studied for photoprotection, collagen synthesis, and anti-aging effects.
• Thyroid: Subject of safety studies examining goitrogenic potential.
• Lysosomes/Rare metabolic diseases: Investigated as a substrate-reduction approach in mucopolysaccharidoses.

9. Safety Considerations and Interactions

9.1 Thyroid Function

The goitrogenic effects of genistein seem to derive from a direct interaction of this isoflavone with key pathways involved in thyroid hormone synthesis, metabolism, and thyroid hormone transport proteins. In vitro and in vivo studies showed that genistein is a potent inhibitor of thyroid peroxidase (TPO), a key enzyme in thyroid hormone synthesis. Inhibition of TPO leads to a reduction of thyroid hormone levels, with a subsequent increment of TSH release, which in turn provides a strong growth stimulus to the thyroid gland.

In human clinical studies, however, recent studies suggest that genistein shows a good profile of safety on the thyroid, although definitive conclusions have not been reached. The only variation found in the 75 mg/day soy isoflavone trial was a modest decrease in serum FT3. In the prostate cancer trial (30 mg/day, 3–6 weeks), serum levels of thyroid hormones remained statistically unchanged. Overall, there is a scarcity of information about the effect of pure isoflavones such as genistein on thyroid safety in humans.

9.2 Estrogenic Risk in Hormone-Sensitive Conditions

Genistin, like genistein, is a phytoestrogen, as it was shown to stimulate estrogen-dependent breast cancer cell growth in vivo. Genistein has the highest content of all isoflavones in soybeans and soy products. As a type of phytoestrogen, genistein is classed as an endocrine-disrupting chemical due to its estrogenic activity in vitro and in vivo. Consequently, excessive consumption of soy products has been linked to disruption of the reproductive organs, such as the uterus, breast, and testis.

Achievable concentrations of genistein in humans are low, and the use of soybean as a functional food is not devoid of concerns, which are related to genistein's potential side effects resulting from its estrogenic and goitrogenic effects.

9.3 Endocrine Effects in Children

An ultra-high dose of genistein aglycone (160 mg/kg/day; BONISTEIN) for 12 months was generally well-tolerated, but several children experienced changes in hormone levels and progression into puberty. Development of Tanner stage II breast tissue was observed in 3 male participants (ages 4.3, 7.9, and 7.6 years), which was not present at baseline. Two male participants showed elevated testosterone levels during the study, one of whom had elevated gonadotropin levels and evidence of progression into puberty at 9.5 years old. One female participant developed biochemical and clinical evidence of progression into puberty at 9.1 years old.

9.4 Drug Interactions via CYP450 Enzymes

The possibility of interaction of isoflavonoids with concomitantly taken drugs was studied. Inhibition of nine forms of cytochrome P450, including CYP3A4, CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C19, CYP2C9, CYP2D6, and CYP2E1, by 12 isoflavonoids including genistein, daidzein, genistin, and other glucosides was studied systematically. The most potent inhibitors were genistein and daidzein, inhibiting noncompetitively CYP2C9 with Ki of 35.95 ± 6.96 and 60.56 ± 3.53 μmol/l, and CYP3A4 inhibited by genistein with Ki of 23.25 ± 5.85 μmol/l, also by a noncompetitive mechanism.

In vitro human liver microsome CYP450 assays were used to test a medical food containing genistein for potential drug interactions with the isoforms 1A2, 2C8, 2C9, 2C19, 2D6, and 3A4. Due to specific 2C8 and 2C9 inhibition, a steady-state pharmacokinetic study was performed to assess serum genistein concentrations in healthy fasting and fed postmenopausal women. Because the serum genistein levels were below those required to cause inhibition in the in vitro liver microsome assays, these results indicate a low potential for drug interactions at doses used in that specific medical food formulation.

9.5 Adverse Effects at High Doses in MPS Models

In MPS I mice, 60% of genistein-fed animals developed a scrotal hernia and/or scrotal hydrocele, manifestations which were absent in wild-type or untreated MPS I mice. In contrast to studies in MPS III mice, the study in MPS I mice demonstrated no beneficial but even potential adverse effects of genistein supplementation. The results urge for a cautious approach on the use of genistein, at least in patients with MPS I.

9.6 Supplement Standardization Concerns

Soy isoflavone supplement products are not standardized, and the amounts of soy isoflavones they provide may vary considerably. For example, in an analysis of a soy supplement purchased at a local health food store containing genistein, the genistein content measured was 1.4 mg/tablet; the value represented 48% of the genistein level listed on the product label.

9.7 Overall Evidence Limitations

Although the potential for genistein to have diverse biological activity in humans has been extensively studied, there is only limited evidence of its specific effects. Certain limitations, such as low bioavailability, biological estrogenic activity, and effects on target organs, have limited the clinical applications of genistein to some extent. Despite gradual elucidation of genistein's mechanism of action, several unresolved questions remain. Studies have reported variability in the effects of genistein across different cell lines, dosages, and administration methods, suggesting that its mechanism of action may be context-dependent and complex.

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