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PubMed2005

Determination of plasma genistein fatty acid esters following administration of genistein or genistein 4'7-O-dioleate in monkeys.

Soy-derived isoflavone phytoestrogens, such as genistein (4',5,7-trihydroxyisoflavone), have been shown to protect low-density lipoprotein from oxidation. In addition, human plasma was previously shown to be capable of converting genistein into lipophilic fatty acid esters that accumulate in lipoproteins in vitro. We developed a method for the quantitation of genistein fatty acid esters in plasma. Furthermore, the method was utilized to measure genistein ester concentrations in monkey plasma following administration of genistein or genistein 4',7-O-dioleate. After extraction from plasma, genistein fatty acid esters were separated from unesterified genistein by Sephadex LH-20 column chromatography. The genistein ester fraction was hydrolyzed by saponification and purified by a second chromatography on Sephadex LH-20. The hydrolyzed genistein esters were measured by time-resolved fluoroimmunoassay. Adult female rhesus monkeys (n=10) received a subcutaneous injection of genistein (24 mg, n=2) or genistein 4',7-O-dioleate (71 mg, n=3) or an oral dose of genistein (24 mg, n=2) or genistein 4',7-O-dioleate (71 mg, n=3). Plasma was collected at 4, 8, and 24 h post-dosing. Following subcutaneous administration of genistein 4',7-O-dioleate, the plasma concentrations of genistein esters became elevated in two out of three monkeys with 8-h values exceeding 7.5 nmol/L and 24-h values above 12 nmol/L. Other treatments resulted in lower plasma values ranging between 2.7 and 6.1 nmol/L. The lower limit of detection for the method was 1.44 nmol/L. Subcutaneously administered genistein 4',7-O-dioleate was also converted to water-soluble conjugates, but oral administration did not elevate plasma genistein fatty acid ester levels. The results suggest that it may be possible to introduce intact genistein ester molecules into plasma by parenteral but not oral administration.

Administration, Oral↗
PubMed2005

Kinetics of genistein and its conjugated metabolites in pregnant Sprague-Dawley rats following single and repeated genistein administration.

Diets high in soy-based products are well known for their estrogenic activity. Genistein, the predominant phytoestrogen present in soy, is known to interact with estrogen receptors (ER) alpha and beta and elicits reproductive effects in developing rodents. In the rat, genistein is metabolized predominantly to glucuronide and sulfate conjugates, neither of which is capable of activating ER. Therefore, it is critical to understand the delivery of free and conjugated genistein across the placenta to the fetus following maternal genistein exposure such that the potential fetal exposure to free genistein can be assessed. Genistein (4 or 40 mg/kg) was administered to pregnant Sprague-Dawley rats by oral gavage daily from gestation day (GD) 5 through 19 or on GD 19 alone. Maternal and GD 19 fetal tissues were collected 0.5, 1, 2, 4, 6, 8, 12, and 24 h following administration of the final dose on GD 19. Concentrations of genistein, genistein glucuronide, and genistein sulfate were quantitated by LC-MS/MS. In maternal plasma, genistein glucuronide was the predominant metabolite. In the fetal plasma, genistein glucuronide and genistein sulfate were the primary metabolites. Genistein levels in maternal and fetal plasma were much lower than its conjugates. The concentration of genistein in placental tissue was higher than either conjugate. Fetal concentrations of unconjugated genistein following administration of 40 mg/kg were above the EC50 for ERbeta activation. Repeated administration of 40 mg/kg genistein resulted in minor changes in genistein kinetics in the pregnant rat compared to single administration of the same dose. These data suggest that conjugated forms of genistein are not transported across the placenta. High placental concentrations of genistein indicate the placenta is a potential target organ for genistein action during gestation.

Administration, Oral↗
PubMed2004

Effect of genistein supplementation on tissue genistein and lipid peroxidation of serum, liver and low-density lipoprotein in hamsters.

The aim of this study was to investigate the effects of genistein supplementation in a vitamin E-deficient diet on the genistein concentrations and the lipid oxidation of serum, liver and low-density lipoprotein (LDL) of hamsters. Thirty-six male hamsters were randomly divided into three groups and fed a vitamin E-deficient semisynthetic diet (AIN-76) containing different levels of genistein, i.e., G0 (control group, genistein-free diet), G50 (50 mg genistein/kg diet) and G200 (200 mg genistein/kg diet) for 5 weeks. The concentrations of genistein in serum and liver significantly increased with the increase of genistein supplementation. The vitamin E contents in LDL were higher in hamsters fed G50 or G200 diets than in hamsters fed genistein-free diet. Genistein supplementation to hamsters significantly reduced the propagation rate during conjugated diene formation of LDL oxidation, and the lag time of LDL oxidation in hamsters fed G200 diets was significantly lower than that of G0 diets. In addition, genistein supplementation significantly raised serum total antioxidant capacity and decreased the thiobarbituric acid-reactive substances (TBARS) of LDL and liver in hamsters. However, no significant differences in TBARS were found in serum, irrespective of genistein addition. On the other hand, the relative contents of polyunsaturated fatty acids in LDL were decreased after genistein supplementation. There was a negative correlation between lag time and P/S ratio, and a positive correlation between lag time and vitamin E contents. These data demonstrate that genistein supplementation markedly increased its concentrations in body tissues and reduced oxidative stress of lipid oxidation of serum, liver and LDL.

Animals↗
PubMed2005

Genistein inhibits insulin-like growth factor-I receptor signaling in HT-29 human colon cancer cells: a possible mechanism of the growth inhibitory effect of Genistein.

Genistein, a soy isoflavone, has attracted much attention for its chemopreventive properties. Overexpression and constitutive activation of receptor tyrosine kinases are frequent events in human cancer. Because genistein has previously been reported to decrease HT-29 cell growth, the present study compared the effects of genistein with daidzein on the protein levels of the members of the ErbB receptor family and insulin-like growth factor-I (IGF-I) receptor (IGF-IR). HT-29 cells were cultured in serum-free medium, with 0, 25, 50, or 100 micromol/L genistein, daidzein, and/or 10 nmol/L IGF-I. DNA synthesis was estimated by 5-bromo-2'-deoxyuridine incorporation. Apoptotic cells were analyzed by annexin-V staining followed by flow cytometry. Genistein inhibited viable HT-29 cell numbers, in a dose-dependent manner, whereas daidzein had no effect on cell growth. The decrease in cell growth caused by genistein was due to decreased DNA synthesis and apoptosis induction. Immunoblot analysis showed that neither genistein nor daidzein decreased the protein levels of either of the epidermal growth factor receptors, ErbB2 or ErbB3. Genistein did, however, decrease the IGF-IR protein levels, whereas daidzein had no effect. Genistein did not change the protein levels of insulin-receptor substrate-1 (IRS-1), the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3K), or Akt. Immunoprecipitation/western blot analyses revealed that genistein decreased IGF-I-stimulated phosphorylation of IGF-IR and IRS-1, recruitment of p85 to IGF-IR, and phosphorylation of Akt. These results suggest that inhibition of cell proliferation and induction of apoptosis by genistein are mediated, at least in part, by its ability to inhibit IGF-IR signaling and the PI3K/Akt pathway.

Annexin A5↗
PubMed1993

Effects of genistein, a tyrosine kinase inhibitor, on platelet functions. Genistein attenuates thrombin-induced Ca2+ mobilization in human platelets by affecting polyphosphoinositide turnover.

Genistein, a tyrosine kinase inhibitor, had no or only slight inhibitory effects on platelet aggregation or serotonin release induced by thrombin, while intracellular Ca2+ concentration ([Ca2+]i) elevation was substantially attenuated. It also inhibited the cyclooxygenase pathway, but this effect was not directly related to the suppressive effect of genistein on [Ca2+]i elevation. In order to clarify the mechanism by which genistein suppresses Ca2+ mobilization, its effect was examined on inositol phospholipid metabolism. The production of inositol-1,4,5-trisphosphate was inhibited by genistein in a dose-dependent manner, while 47 kDa protein phosphorylation or phosphatidic acid formation was not affected, suggesting that genistein does not inhibit phospholipase C activity. Pretreatment of unstimulated platelets with genistein increased the amount of phosphatidylinositol-4-monophosphate [PI(4)P], while that of phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2] was reduced. Thrombin stimulation of genistein-pretreated cells intensified this tendency, i.e. a further increase in the amount of PI(4)P and a decrease in the amount of PI(4,5)P2 in an inversely proportional manner. Taken together, these findings imply that genistein acted at the step of PI(4)P 5-kinase which produces PI(4,5)P2 from PI(4)P. Protein tyrosine phosphorylation induced by thrombin was not affected by genistein, suggesting that the inhibitory effect of genistein on polyphosphoinositides was unrelated to tyrosine kinase inhibition.

Arachidonic Acid↗
PubMed1997

Modulation of liver canalicular transport processes by the tyrosine-kinase inhibitor genistein: implications of genistein metabolism in the rat.

Rat liver cells express the multispecific organic anion transporter (cmoat, cmrp, mrp2) and P-glycoprotein (Pgp) in their canalicular membranes, proteins that are homologous to the multidrug-resistance related protein (MRP) and multidrug resistance (MDR) gene products in multidrug resistant tumor cells. We tested whether genistein, a modulator of drug resistance in tumor cells, affects biliary secretion of substrates of canalicular multispecific organic anion transporter (cmoat) (glucuronides of bilirubin and rhodamine, glutathione conjugate of bromsulphthalein) and of P-glycoprotein (Pgp) (rhodamine), respectively. Using the isolated perfused rat liver of control Wistar rats (TR+) and of a mutant strain (TR-) that expresses Pgp but not cmoat, we show that genistein effectively inhibits the secretion of anionic substrates of cmoat in Wistar rats but stimulates secretion of cationic rhodamine in TR- rats. Genistein is subject to glucuronidation and sulfatation and secretion of genistein and its metabolites stimulates bile flow in Wistar rats, but secretion is nearly absent in TR- rats. Because genistein and its metabolites are substrates for cmoat, inhibition of anion secretion by genistein is partially explained by competition for this transporter. Genistein is also a substrate of uridindiphosphate (UDP)-glucuronyltransferase isoenzyme(s). Inhibition of glucuronidation reduces the availability of bilirubin and rhodamine glucuronates for transport via cmoat, but unconjugated cationic rhodamine becomes available for transport via Pgp at an increased cellular concentration. Daidzein, a genistein analogue with no effect on protein tyrosine kinase (PTK) shows Similar effects on secretion of organic anions and cations supporting the conclusion that genistein affects transport in liver mainly through competition with other substrates at the sites of glucuronidation and transport via cmoat.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMedDate not supplied

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.

Animal Feed↗
PubMed2005

Lactational transfer of the soy isoflavone, genistein, in Sprague-Dawley rats consuming dietary genistein.

Exposures of Sprague-Dawley rats to the soy isoflavone, genistein, throughout the entire lifespan have produced a number of effects on reproductive tissues, immune function, neuroendocrine function and behavior. Our previous studies investigated pharmacokinetics and disposition of genistein during adult and fetal periods and this study describes the internal exposures of post-natal day 10 (PND10) rat pups due to lactational transfer of genistein. Conjugated and aglycone forms of genistein were measured by using LC/MS/MS in serum (PND10) and milk (PND7) from lactating dams consuming a genistein-fortified soy-free diet, and in serum from their pups at a time when milk was the only food source (PND10). This study shows that limited lactational transfer of genistein to rat pups occurs and that internal exposures to the active aglycone form of genistein are generally lower than those measured previously in the fetal period. These results suggest that developmental effects attributable to genistein exposure in our chronic and multi-generation studies are more likely to result from fetal exposures because of the higher levels of the active estrogenic aglycone form of genistein in utero, although the possibility of neonatal responses cannot be excluded.

Animals↗
PubMed1998

Anabolic effect of genistein and genistin on bone metabolism in the femoral-metaphyseal tissues of elderly rats: the genistein effect is enhanced by zinc.

The effect of genistein and genistin on bone components in the femoral-metaphyseal tissues obtained from elderly female rats was investigated in vitro. The metaphyseal tissues were cultured for 24 h in a medium containing either vehicle, genistein (10(-8)-10(-5) M) or genistin (10(-7)-10(-5) M). The presence of genistein or genistin caused a significant increase in alkaline phosphatase activity, deoxyribonucleic acid (DNA) and calcium contents in the metaphyseal tissues. The effect of genistein was greater than that of genistin. The bone components increased by genistein (10(-5) M) or genistin (10(-5) M) were completely blocked by the presence of cycloheximide (10(-6) M). The presence of zinc sulfate (10(-5) M) caused a significant increase in the genistein (10(-5) M)-elevated alkaline phosphatase activity, DNA and calcium contents. The enhancement with zinc was not seen by genistin (10(-5) M). The stimulatory effect of zinc on the genistein-induced increase in bone components of the metaphyseal tissues was completely blocked by the presence of cycloheximide (10(-6) M). The present results suggest that genistein and genistin have an anabolic effect on bone metabolism in the femoral-metaphyseal tissues of elderly rats, and that the genistein effect is enhanced by zinc, an essential trace element.

Aging↗
PubMed2004

Genistein-induced changes in gene expression in Panc 1 cells at physiological concentrations of genistein.

OBJECTIVES: To investigate the effect of genistein on gene expression in Panc 1 cells using microarray technology. METHODS: Panc 1 cells were treated with 10 micromol/L genistein or DMSO (vehicle control) for 0, 1, 3, 6, or 12 hours. Total RNA from each sample was isolated, and biotin-labeled probes were hybridized to the human genome U133A chip, after which the chip was washed and scanned. Data were analyzed using DMT software (Affymetrix). For genes that showed large changes in expression due to genistein, these changes were confirmed using real-time PCR assays. RESULTS: Two independent microarray experiments showed that genistein significantly changed the expression of 47 genes: up-regulating of egr-1 and IL-8 and down-regulating of EGF-R AKT2, CYP1B1, NELL2, SCD, DNA ligase III, Rad as well as 18s and 28s rRNA and others. These alterations in expression were confirmed using real-time PCR, although the increase in change was not exactly the same in the 2 assays. CONCLUSIONS: Our data suggest the reported apparent ability of genistein to inhibit carcinogenesis may involve a number of pathways. The most obvious target is the EGF-R signaling pathway since the expression of 5 genes related to this pathway was reduced (EGFR, egr-1, AKT2, CYP1B1, and NELL2). Genistein may also act by disabling cancer cell self-protection by inhibiting expression of AKT2, CYP1B1, and DNA ligase III. Furthermore, genistein may inhibit car-cinogenesis by inhibiting expression of SCD. Finally, our data support findings indicating that genistein inhibits rRNA formation, which is an important mechanism by which genistein regulates tumor cell growth.

Adenocarcinoma↗
PubMedDate not supplied

Inhibition of human breast cancer growth by GCP (genistein combined polysaccharide) in xenogeneic athymic mice: involvement of genistein biotransformation by beta-glucuronidase from tumor tissues.

The role of beta-glucuronidase in genistein biotransformation was investigated in a human breast cancer MDA-MB-231 xenogeneic athymic mouse model. Genistein combined polysaccharide (GCP), a genistein aglycone rich functional food supplement was used in these experiments. Tumor-bearing mice were subjected to oral administration of GCP for 28 days. GCP treatment significantly inhibited tumor growth. Induction of apoptosis by GCP treatment was related to activation of cleavage of poly(ADP-ribose)polymerase, induction of the p21 protein expression and reduction of cyclin B1 expression in the tumor tissues. Genistein exists as a glucuronide conjugate in normal organ tissues, and the conjugated genistein lacks the physiological activity of the aglycone. Tumor tissues contain large amounts of beta-glucuronidase, the enzyme that converts the genistein beta-glucuronide conjugate into genistein aglycone. The resulting genistein aglycone exerts its chemopreventive activities, including the induction of apoptosis in tumor tissues, and, finally, leads to tumor growth inhibition.

Animals↗
PubMed2003

Accumulation of genistein and lipophilic genistein derivatives in lipoproteins during incubation with human plasma in vitro.

Atherosclerosis is initiated by the uptake and retention of oxidized low-density lipoprotein (LDL) into the arterial intima. We have previously shown that dietary isoflavone phytoestrogens inhibit LDL oxidation in vitro. The inhibition could have been caused by undetected isoflavone metabolites associated with lipoproteins. In the present study, we incubated human plasma with [3H]genistein, both with and without the lecithin:cholesterol acyltransferase (LCAT) inhibitor dithionitrobenzoic acid (DTNB). Our results indicated that the 3H-label was attached to both high-density lipoprotein (HDL) and LDL, and that it represented both underivatized genistein and lipophilic derivatives of genistein, part of which were identified as fatty acid monoesters. The latter was demonstrated by the findings that DTNB decreased the HDL and LDL associated radioactivity in the lipophilic fraction isolated by hydrophobic chromatography and that saponification hydrolysis liberated a corresponding part of the 3H-label. Two-dimensional reversed-phase thin-layer chromatography (TLC) demonstrated that a corresponding part of the radioactivity comigrated with genistein monoester standards in the absence of DTNB but was abolished if DTNB had been present in the incubation. In summary, incubation of plasma with [3H]genistein resulted in accumulation of underivatized genistein as well as lipophilic genistein derivatives in lipoproteins. A smaller part of the latter were genistein monoesters, while part remained unidentified. Our results suggest an explanation for the increased oxidation resistance of isolated LDL during intake of soybean isoflavones.

Dithionitrobenzoic Acid↗
PubMed2005

Influence of dietary genistein levels on tissue genistein deposition and on the physical, chemical, and sensory quality of rainbow trout, Oncorhynchus mykiss.

Genistein, the primary isoflavone in soybean, is one of the chemical components responsible for some of the off-flavors associated with soy-based foods. The potential effects of genistein on the sensory and chemical quality of fish muscle may affect the full utilization of soybean meal as an alternative protein in aquaculture diets. Fingerling trout fed commercial diets containing 0, 500, 1000, or 3000 ppm pure genistein were analyzed after 6 and 12 months of feeding. Genistein was extracted by enzymatic digestions in Tris buffer and quantified by high-performance liquid chromatography. Moisture, fat, protein, ash, and tristimulus color of the fillets were determined. The extent of lipid oxidation occurring in fillets harvested after 12 months of feeding was studied by measurements of thiobarbituric acid reactive substances (TBARS) after 4 and 8 days of refrigerated storage at 4 degrees C. Triangle tests were performed to determine if there were any detectable sensory differences. A dietary genistein content of 3000 ppm led to the deposition of approximately 5.4 pmol of genistein/mg of fillet. Triangle test panelists were unable to detect any significant (p < or = 0.05) differences between the fillets from trout fed the 0 and 3000 ppm genistein concentrations. Moisture, ash, and protein content were influenced by time of harvest, while color was unaffected. TBARS levels on days 4 and 8 were significantly (p < 0.05) higher in the fillets from the 0 ppm genistein level than in fillets from fish fed dietary genistein.

Animals↗
PubMed2000

Increased induction of aberrant crypt foci by 1,2-dimethylhydrazine in rats fed diets containing purified genistein or genistein-rich soya protein.

The isoflavonoid genistein inhibits mitosis and increases apoptosis in a variety of tumour cell lines in vitro, and may exert anticarcinogenic effects in vivo. To assess its effects on the colon, rats were fed a semi-synthetic control diet, or similar diets enriched with genistein (0.25 g/kg), either as the pure isoflavone or as part of a soya protein isolate, for 7 days before receiving subcutaneous injections of saline or 1,2-dimethylhydrazine (DMH). After 48 h, rats given saline were killed and samples of their small and large intestinal mucosa were obtained for assessment of crypt cell mitosis and apoptosis by visual analysis of isolated intact crypts. Rats given DMH were fed control diet and killed after 48 h for assessment of crypt cytokinetics or maintained for 42 days then killed and their colonic mucosa analysed for aberrant crypt foci (ACF). Two further groups were given control diet before DMH, followed by the genistein or soya-based diet for 42 days before assessment of ACF. Neither genistein nor soya protein isolate had a significant effect on crypt cell mitosis or apoptosis in untreated rats, or on the proliferative response to treatment with DMH. However, consumption of pure genistein or the soya protein isolate before treatment with DMH was associated with a 3-fold (P < 0.001) or 2-fold (P < 0.05) increase, respectively, in ACF in the distal colon. There was no significant effect of genistein or soya protein isolate given after DMH treatment. We conclude that genistein has no detectable effect on colonic crypt mitosis or apoptosis in the rat in vivo, but that it promotes induction of ACF by an as yet undefined mechanism when fed immediately before treatment with DMH.

1,2-Dimethylhydrazine↗
PubMed2002

Effect of a single treatment (imprinting) with genistein or combined treatment with genistein+benzpyrene on the binding capacity of glucocorticoid and estrogen receptors of adult rats.

Hormonal imprinting takes place perinatally at the first encounter between the hormone and its target receptor. This is needed for the normal finishment of the maturation of the receptor-signal transduction system. In excess of foreign molecules, which can also bind to the receptor, faulty imprinting develops with life-long consequences. Genistein, a soybean phytosteroid (isoflavone), has estrogen-like effects and can be bound by steroid receptors. In the present experiments, single neonatal treatment (imprinting) with 20 microg of genistein, or combined treatment with 20 microg of genistein+20 microg of benzpyrene was done and liver and thymus glucocorticoid receptors of adult male and female rats and uterine estrogen receptors were studied. There was no difference in the binding capacity of uterine estrogen receptors. Genistein treatment alone caused a significant reduction of liver glucocorticoid receptor density in males; however, there were no other significant alterations. After combined genistein+benzpyrene treatment, more.than half of the thymus and liver glucocorticoid receptor values significantly changed. The results call attention to the imprinting-modifying effect of a second (environmental) imprinter.

Animals↗
PubMed2006

Genetic analysis of the anti-mutagenic effect of genistein in Escherichia coli.

Genistein, the main isoflavone in soy, has received considerable attention for its potential anti-carcinogenic properties. In a previous report, we investigated the possible role of genistein in anti-mutagenesis, using an Escherichia coli reversion assay system. Genistein reduced ENU-induced mutagenesis in a dose-dependent manner and the reduction of mutation frequency was differential among several categories of mutation. Most notable was a loss of transversion mutations, which require SOS functions. In this report, we further investigated the anti-mutagenic effect of genistein using a genetic approach. E. coli strains having alterations in genes involved in SOS-mutagenesis were examined, as were strains having defects in proteins that might serve as potential targets for genistein. The results showed that ENU-induced mutations produced in recA730 and lexA(Def) strains, both expressing a constitutive SOS response, were reduced by genistein to a lesser extent than in the wild-type strain. The effect of genistein was not entirely abolished, however. ENU mutagenesis in a umuC derivative, which reflects predominantly transition mutations, was unaffected by genistein. ENU-induced mutations in strains having defects in topA, gyrA, typA or uspA were not different than the wild-type, suggesting that these gene products were not involved in genistein's anti-mutagenic effect. In addition, we determined the distribution of genistein in various cellular fractions using HPLC. These studies revealed that genistein could be recovered from E. coli cells grown on agar media containing genistein; the intracellular concentration was similar to that in the agar plates. Further, most of the genistein recovered was associated with proteins in the cytosolic fraction and little partitioned in the membrane fraction. In vitro studies showed that genistein could be precipitated from a protein (BSA) containing solution. Finally, we examined the effect of genistein on formation of the RecA filament on ssDNA in vitro and observed an inhibition at high concentrations of genistein. In total, these results suggested that genistein may reduce SOS-dependent mutagenesis by reducing the interaction of RecA protein with ssDNA. As a consequence, genistein could cause a reduction in (1) the overall SOS response (confirmed using beta-galactosidase assays) and (2) trans-lesion DNA synthesis by DNA polymerase V.

Anticarcinogenic Agents↗
PubMed2004

Anticancer therapeutic potential of soy isoflavone, genistein.

Genistein (4'5, 7-trihydroxyisoflavone) occurs as a glycoside (genistin) in the plant family Leguminosae, which includes the soybean (Glycine max). A significant correlation between the serum/plasma level of genistein and the incidence of gender-based cancers in Asian, European and American populations suggests that genistein may reduce the risk of tumor formation. Other evidence includes the mechanism of action of genistein in normal and cancer cells. Genistein inhibits protein tyrosine kinase (PTK), which is involved in phosphorylation of tyrosyl residues of membrane-bound receptors leading to signal transduction, and it inhibits topoisomerase II, which participates in DNA replication, transcription and repair. By blocking the activities of PTK, topoisomerase II and matrix metalloprotein (MMP9) and by down-regulating the expression of about 11 genes, including that of vascular endothelial growth factor (VEGF), genistein can arrest cell growth and proliferation, cell cycle at G2/M, invasion and angiogenesis. Furthermore, genistein can alter the expression of gangliosides and other carbohydrate antigens to facilitate their immune recognition. Genistein acts synergistically with drugs such as tamoxifen, cisplatin, 1,3-bis 2-chloroethyl-1-nitrosourea (BCNU), dexamethasone, daunorubicin and tiazofurin, and with bioflavonoid food supplements such as quercetin, green-tea catechins and black-tea thearubigins. Genistein can augment the efficacy of radiation for breast and prostate carcinomas. Because it increases melanin production and tyrosinase activity, genistein can protect melanocytes of the skin of Caucasians from UV-B radiation-induced melanoma. Genistein-induced antigenic alteration has the potential for improving active specific immunotherapy of melanoma and carcinomas. When conjugated to B43 monoclonal antibody, genistein becomes a tool for passive immunotherapy to target B-lineage leukemias that overexpress the target antigen CD19. Genistein is also conjugated to recombinant EGF to target cancers overexpressing the EGF receptor. Although genistein has many potentially therapeutic actions against cancer, its biphasic bioactivity (inhibitory at high concentrations and activating at low concentrations) requires caution in determining therapeutic doses of genistein alone or in combination with chemotherapy, radiation therapy, and/or immunotherapies. Of the more than 4500 genistein studies in peer-reviewed primary publications, almost one fifth pertain to its antitumor capabilities and more than 400 describe its mechanism of action in normal and malignant human and animal cells, animal models, in vitro experiments, or phase I/II clinical trials. Several biotechnological firms in Japan, Australia and in the United States (e.g., Nutrilite) manufacture genistein as a natural supplement under quality controlled and assured conditions.

Animals↗
PubMed1998

Actions of genistein on cystic fibrosis transmembrane conductance regulator channel gating. Evidence for two binding sites with opposite effects.

Previous studies have shown that genistein increased cystic fibrosis transmembrane conductance regulator (CFTR) channel activity in the presence of saturating concentrations of forskolin and calyculin A in intact cells. Possible molecular mechanisms for genistein's action include inhibition of tyrosine kinases, inhibition of serine/threonine protein phosphatases, or direct binding of genistein to CFTR. Since genistein inhibits several enzymes that hydrolyze ATP, and ATP hydrolysis is an intrinsic property of CFTR, we examined the effect of genistein on CFTR gating in excised inside-out patches from Hi-5 insect cells and NIH3T3 cells expressing recombinant CFTR. Genistein (50 microM) did not open phosphorylated CFTR channels by itself, but increased the ATP- induced CFTR channel current by approximately twofold. A similar magnitude of enhancement was observed when genistein was applied with PKI, a specific inhibitor of protein kinase A, or vanadate, a tyrosine phosphatase inhibitor, suggesting that inhibition of protein phosphatases or tyrosine kinases does not account for genistein's effects. The enhancement of channel current increased with increasing concentrations of genistein and reached a maximum at 35 microM genistein. At higher concentrations of genistein concentration, CFTR channel current decreased, resulting in a bell-shaped dose-response relationship. In the absence of genistein, both open- and closed-time histograms could be fitted with a single exponential function, yielding a mean open time (tauO) of 0.302 +/- 0.002 s, and a mean closed time (tauC) of 0.406 +/- 0.003 s. In the presence of 50 microM genistein, the open time histogram could be fitted with a double exponential function with tauO1 = 0.429 +/- 0. 003 s and tauO2 = 2.033 +/- 0.173 s. Thus, genistein induced a prolonged open state, an effect that mimics that of nonhydrolyzable ATP analogs. Closed time analysis showed that 50 microM genistein caused a prolonged closed state with a time constant of 2.410 +/- 0.035 s. We thus conclude that (a) the effects of genistein are likely caused by a direct binding of the drug to the CFTR protein, and (b) at least two binding sites are required to explain the effects of genistein: a high affinity site that decreases the closing rate and a low affinity site that reduces the opening rate.

Adenosine Triphosphate↗