Metabolism of dietary soy isoflavones to equol by human intestinal microflora--implications for health

Involvement of a gut-retina axis in protection against dietary glycemia-induced age-related macular degeneration

Age-related macular degeneration (AMD) is the major cause of blindness in developed nations. AMD is characterized by retinal pigmented epithelial (RPE) cell dysfunction and loss of photoreceptor cells. Epidemiologic studies indicate important contributions of dietary patterns to the risk for AMD, but the mechanisms relating diet to disease remain unclear. Here we investigate the effect on AMD of isocaloric diets that differ only in the type of dietary carbohydrate in a wild-type aged-mouse model. The consumption of a high-glycemia (HG) diet resulted in many AMD features (AMDf), including RPE hypopigmentation and atrophy, lipofuscin accumulation, and photoreceptor degeneration, whereas consumption of the lower-glycemia (LG) diet did not. Critically, switching from the HG to the LG diet late in life arrested or reversed AMDf. LG diets limited the accumulation of advanced glycation end products, long-chain polyunsaturated lipids, and their peroxidation end-products and increased C3-carnitine in retina, plasma, or urine. Untargeted metabolomics revealed microbial cometabolites, particularly serotonin, as protective against AMDf. Gut microbiota were responsive to diet, and we identified microbiota in the Clostridiales order as being associated with AMDf and the HG diet, whereas protection from AMDf was associated with the Bacteroidales order and the LG diet. Network analysis revealed a nexus of metabolites and microbiota that appear to act within a gut-retina axis to protect against diet- and age-induced AMDf. The findings indicate a functional interaction between dietary carbohydrates, the metabolome, including microbial cometabolites, and AMDf. Our studies suggest a simple dietary intervention that may be useful in patients to arrest AMD.

Bacterial communities and metabolic activity of faecal cultures from equol producer and non-producer menopausal women under treatment with soy isoflavones

Background

Isoflavones are polyphenols with estrogenic activity found mainly in soy and soy-derived products that need to be metabolised in the intestine by the gut bacteria to be fully active. There is little knowledge about isoflavone bioconversion and equol production in the human intestine. In this work, we developed an in vitro anaerobic culture model based on faecal slurries to assess the impact of isoflavone supplementation on the overall intestinal bacterial composition changes and associated metabolic transformations.

Results

In the faecal anaerobic batch cultures of this study bioconversion of isoflavones into equol was possible, suggesting the presence of viable equol-producing bacterial taxa within the faeces of menopausal women with an equol producer phenotype. The application of high-throughput DNA sequencing of 16S rRNA gene amplicons revealed the composition of the faecal cultures to be modified by the addition of isoflavones, with enrichment of some bacterial gut members associated with the metabolism of phenolics and/or equol production, such as Collinsella, Faecalibacterium and members of the Clostridium clusters IV and XIVa. In addition, the concentration of short-chain fatty acids (SCFAs) detected in the isoflavone-containing faecal cultures was higher in those inoculated with faecal slurries from equol-producing women.

Conclusions

This study constitutes the first step in the development of a faecal culturing system with isoflavones that would further allow the selection and isolation of intestinal bacterial types able to metabolize these compounds and produce equol in vitro. Although limited by the low number of faecal cultures analysed and the inter-individual bacterial diversity, the in vitro results obtained in this work tend to indicate that soy isoflavones might provide an alternative energy source for the increase of equol-producing taxa and enhancement of SCFAs production. SCFAs and equol are both considered pivotal bacterial metabolites in the triggering of intestinal health-related beneficial effects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-1001-y) contains supplementary material, which is available to authorized users.

Metabolomics reveals differences between three daidzein metabolizing phenotypes in adults with cardiometabolic risk factors

SCOPE

The soy isoflavone, daidzein, is metabolized by gut microbiota to O-desmethylangolensin (ODMA) and/or equol. Producing equol is postulated as a contributing factor for the beneficial effects of soy.

METHODS AND RESULTS

This randomized, controlled, cross-over design used an untargeted metabolomic approach to assess the metabolic profile of different daidzein metabolizers. Adults (n = 17) with cardiometabolic risk factors received soy nuts or control food for 4 weeks, separated by a 2-week washout. No significant differences were detected pre- and postintervention and between interventions. Examination of the ability to metabolize daidzein revealed three groups: ODMA only producers (n = 4), equol + ODMA producers (n = 8), and nonproducers (n = 5). Analysis of the serum metabolome revealed nonproducers could be distinguished from ODMA-only and equol + ODMA producers. Differences between these phenotypes were related to obesity and metabolic risk (methionine, asparagine, and trimethylamine) with equol + ODMA producers having lower concentrations, yet paradoxically higher pro-inflammatory cytokines. In urine, nonproducers clustered with ODMA producers and were distinct from equol + ODMA producers. Urinary metabolite profiles revealed significantly higher excretion of fumarate and 2-oxoglutarate, as well as pyroglutamate, alanine, and the gut microbial metabolite dimethylamine in equol + ODMA producers.

CONCLUSION

These results emphasize that the serum and urine metabolomes are distinct based on the ability to metabolize isoflavones.

Equol Attenuates Atherosclerosis in Apolipoprotein E-Deficient Mice by Inhibiting Endoplasmic Reticulum Stress via Activation of Nrf2 in Endothelial Cells

The development of atherosclerosis is closely related to excessive endoplasmic reticulum stress (ERs). Equol reportedly protects against cardiovascular disease; however, the underlying mechanism for this protection remains unknown. Herein, the mechanisms contributing to the atheroprotective effect of equol were addressed using apolipoprotein E knockout (apoE-/-) mice fed a high-fat diet (HFD) with or without equol. Equol intervention reduced atherosclerotic lesions in the aorta in HFD-fed apoE-/- mice. Plasma lipid analysis showed that equol intervention reduced triglycerides, total cholesterol and LDL-cholesterol and increased HDL-cholesterol. Additionally, equol administration decreased lipid accumulation in the liver. Simultaneously, equol treatment inhibited cell apoptosis induced by t-BHP and thapsigargin in human umbilical vein endothelial cells (HUVECs). Furthermore, equol treatment attenuated palmitate, t-BHP or thapsigargin-induced upregulation of ER stress markers, including p-PERK, p-eIF2α, GRP78, ATF6 and CHOP proteins expression. The same tendency was also observed in aortic lysates in apoE-/- mice fed with equol plus HFD compared with HFD alone. Moreover, equol treatment dose dependently activated the Nrf2 signaling pathway under oxidative stress. Additionally, elevation of Nrf2 induction was found in aortic lysates in apoE-/- mice fed with a HFD diet containing equol compared with a HFD diet without equol. Importantly, Nrf2 siRNA interference induced CHOP and attenuated the effect of equol to inhibit t-BHP mediated CHOP induction, furthermore, abrogated cell apoptosis induced by t-BHP, suggesting a role for Nrf2 in the protective effect of equol in HUVECs. Collectively, these findings implicate that the improvement of atherosclerosis by equol through attenuation of ER stress is mediated, at least in part, by activating the Nrf2 signaling pathway.

Soy isoflavone intake and prevalence of depressive symptoms during pregnancy in Japan: baseline data from the Kyushu Okinawa Maternal and Child Health Study

OBJECTIVE

Several observational studies and trials examined the relationship between isoflavones or soybeans and depressive symptoms among peri- and postmenopausal women. We cross-sectionally evaluated the associations between intake of soy products and isoflavones and depressive symptoms during pregnancy in Japan.

METHODS

Study subjects were 1745 pregnant women. Dietary intake during the preceding month was assessed using a self-administered diet history questionnaire. Depressive symptoms were defined by a score of 16 or over in the Center for Epidemiologic Studies Depression Scale.

RESULTS

Higher intake of total soy products, tofu, tofu products, fermented soybeans, boiled soybeans, miso soup, and isoflavones was independently related to a lower prevalence of depressive symptoms during pregnancy: The adjusted prevalence ratios (95 % confidence intervals, P for trend) between extreme quartiles were 0.63 (0.47-0.85, 0.002), 0.72 (0.54-0.96, 0.007), 0.74 (0.56-0.98, 0.04), 0.57 (0.42-0.76, <0.0001), 0.73 (0.55-0.98, 0.03), 0.65 (0.49-0.87, 0.003), and 0.63 (0.46-0.86, 0.002), respectively. A significant positive exposure-response relationship was found between miso intake and depressive symptoms during pregnancy. No material relationship was observed between soymilk intake and depressive symptoms during pregnancy.

CONCLUSIONS

Our study is the first to show independent inverse relationships between intake of total soy products, tofu, tofu products, fermented soybeans, boiled soybeans, miso soup, and isoflavones and depressive symptoms during pregnancy.

The combined effects of soya isoflavones and resistant starch on equol production and trabecular bone loss in ovariectomised mice

Equol is a metabolite of the soya isoflavone (ISO) daidzein that is produced by intestinal microbiota. Equol has greater oestrogenic activity compared with other ISO, and it prevents bone loss in postmenopausal women. Resistant starch (RS), which has a prebiotic activity and is a dietary fibre, was reported to promote equol production. Conversely, the intestinal microbiota is reported to directly regulate bone health by reducing inflammatory cytokine levels and T-lymphocytes in bone. The present study evaluated the combined effects of diet supplemented with ISO and RS on intestinal microbiota, equol production, bone mineral density (BMD) and inflammatory gene expression in the bone marrow of ovariectomised (OVX) mice. Female ddY strain mice, aged 8 weeks, were either sham-operated (Sham, n 7) or OVX. OVX mice were randomly divided into the following four groups (seven per group): OVX control (OVX); OVX fed 0·05 % ISO diet (OVX+ISO); OVX fed 9 % RS diet (OVX+RS); and OVX fed 0·05 % ISO- and 9 % RS diet (OVX+ISO+RS). After 6 weeks, treatment with the combination of ISO and RS increased equol production, prevented the OVX-induced decline in trabecular BMD in the distal femur by modulating the enteric environment and altered OVX-induced inflammation-related gene expression in the bone marrow. However, there were no significant differences in bone parameters between the ISO+RS and ISO-alone groups in OVX mice. Our findings suggest that the combination of ISO and RS might alter intestinal microbiota and immune status in the bone marrow, resulting in attenuated bone resorption in OVX mice.

A new biotechnological process to enhance the soymilk bioactivity

Equol, a daidzein metabolite produced exclusively by intestinal bacteria in some, but not all, humans, exhibits a wide range of beneficial health effects owing to its superior nutraceutical effect compared with isoflavones of soy. The aim of this work was to develop bioprocesses capable of increasing the bioactive properties of soymilk and, most importantly, increase the equol content by a biotechnological process in vitro. Biotransformation processes based on soymilk fermentation by probiotic lactic bacteria and application of the enzyme tannase caused an increase in the bioactive isoflavones and antioxidant capacity of soymilk. Furthermore, these processes approximately resulted in a 10-fold increase in the equol content of the soymilk. This is the first study to produce a significant equol concentration in soymilk using enzymatic processing only. The results suggest a new and effective biotechnological process, with major commercial potential, capable of producing a bioactive soy extract that intends to be "functional for everyone."

The Chemistry of Gut Microbial Metabolism of Polyphenols

Gut microbiota contribute to the metabolism of dietary polyphenols and affect the bioavailability of both the parent polyphenols and their metabolites. Although there is a large number of reports of specific polyphenol metabolites, relatively little is known regarding the chemistry and enzymology of the metabolic pathways utilized by specific microbial species and taxa, which is the focus of this review. Major classes of dietary polyphenols include monomeric and oligomeric catechins (proanthocyanidins), flavonols, flavanones, ellagitannins, and isoflavones. Gut microbial metabolism of representatives of these polyphenol classes can be classified as A- and C-ring cleavage (retro Claisen reactions), C-ring cleavage mediated by dioxygenases, dehydroxylations (decarboxylation or reduction reactions followed by release of H₂O molecules), and hydrogenations of alkene moieties in polyphenols, such as resveratrol, curcumin, and isoflavones (mediated by NADPH-dependent reductases). The qualitative and quantitative metabolic output of the gut microbiota depends to a large extent on the metabolic capacity of individual taxa, which emphasizes the need for assessment of functional analysis in conjunction with determinations of gut microbiota compositions.

Soy-based renoprotection

Chronic kidney disease (CKD) is a significant public health problem as risk factors such as advanced age, obesity, hypertension and diabetes rise in the global population. Currently there are no effective pharmacologic treatments for this disease. The role of diet is important for slowing the progression of CKD and managing symptoms in later stages of renal insufficiency. While low protein diets are generally recommended, maintaining adequate levels of intake is critical for health. There is an increasing appreciation that the source of protein may also be important. Soybean protein has been the most extensively studied plant-based protein in subjects with kidney disease and has demonstrated renal protective properties in a number of clinical studies. Soy protein consumption has been shown to slow the decline in estimated glomerular filtration rate and significantly improve proteinuria in diabetic and non-diabetic patients with nephropathy. Soy’s beneficial effects on renal function may also result from its impact on certain physiological risk factors for CKD such as dyslipidemia, hypertension and hyperglycemia. Soy intake is also associated with improvements in antioxidant status and systemic inflammation in early and late stage CKD patients. Studies conducted in animal models have helped to identify the underlying molecular mechanisms that may play a role in the positive effects of soy protein on renal parameters in polycystic kidney disease, metabolically-induced kidney dysfunction and age-associated progressive nephropathy. Despite the established relationship between soy and renoprotection, further studies are needed for a clear understanding of the role of the cellular and molecular target(s) of soy protein in maintaining renal function.

Equol increases cerebral blood flow in rats via activation of large-conductance Ca(2+)-activated K(+) channels in vascular smooth muscle cells

The present study was designed to investigate the effect of equol on cerebral blood flow and the underlying molecular mechanisms. The regional cerebral blood flow in parietal lobe of rats was measured by using a laser Doppler flowmetry. Isolated cerebral basilar artery and mesenteric artery rings from rats were used for vascular reactivity measurement with a multi wire myography system. Outward K(+) current in smooth muscle cells of cerebral basilar artery, large-conductance Ca(2+)-activated K(+) (BK) channel current in BK-HEK 293 cells stably expressing both human α (hSlo)- and β1-subunits, and hSlo channel current in hSlo-HEK 293 cells expressing only the α-subunit of BK channels were recorded with whole cell patch-clamp technique. The results showed that equol significantly increased regional cerebral blood flow in rats, and produced a concentration-dependent but endothelium-independent relaxation in rat cerebral basilar arteries. Both paxilline and iberiotoxin, two selective BK channel blockers, significantly inhibited equol-induced vasodilation in cerebral arteries. Outward K(+) currents in smooth muscle cells of cerebral basilar artery were increased by equol and fully reversed by washout or blockade of BK channels with iberiotoxin. Equol remarkably enhanced human BK current in BK-HEK 293 cells, but not hSlo current in hSlo-HEK 293 cells, and the increase was completely abolished by co-application of paxilline. Our findings provide the first information that equol selectively stimulates BK channel current by acting on its β1 subunit, which may in turn contribute to the equol-mediated vasodilation and cerebral blood flow increase.

The Reciprocal Interactions between Polyphenols and Gut Microbiota and Effects on Bioaccessibility

As of late, polyphenols have increasingly interested the scientific community due to their proposed health benefits. Much of this attention has focused on their bioavailability. Polyphenol-gut microbiota interactions should be considered to understand their biological functions. The dichotomy between the biotransformation of polyphenols into their metabolites by gut microbiota and the modulation of gut microbiota composition by polyphenols contributes to positive health outcomes. Although there are many studies on the in vivo bioavailability of polyphenols, the mutual relationship between polyphenols and gut microbiota is not fully understood. This review focuses on the biotransformation of polyphenols by gut microbiota, modulation of gut microbiota by polyphenols, and the effects of these two-way mutual interactions on polyphenol bioavailability, and ultimately, human health.

Dietary isoflavones and gastric cancer: A brief review of current studies

Background:

Although several in vitro and animal studies have suggested that isoflavones might exert inhibitory effects on gastric carcinogenesis, epidemiologic studies have reported inconclusive results in this field. The aim of this brief review was to investigate whether such an association exists among dietary isoflavones and gastric cancer incidence, prevention, and mortality in epidemiologic studies.

Materials and Methods:

We conducted a search of PubMed, Google Scholar, Cochrane, Science direct, and Iranian Scientific Databases including Scientific Information Database and IranMedex Database (up to November 2014) using common keywords for studies that focused on dietary isoflavones and gastric cancer risk.

Results:

A total of nine epidemiologic studies consisting of five case-controls, three prospective cohorts, and one ecologic study were included in this review. An inverse association between dietary isoflavones and gastric cancer was shown in only one case-control and one ecologic study.

Conclusion:

In summary, whether anticarcinogenic properties of isoflavones are established, research found no substantial correlation in this field. There are insufficient studies to draw any firm conclusions about the relationship between isoflavones intake and the risk of gastric cancer. Hence, further evidence from cohort and trial studies are needed.

Preparation and application of a monoclonal antibody against the isoflavone glycoside daidzin using a mannich reaction-derived hapten conjugate

INTRODUCTION

Daidzin and its aglycone daidzein are major pharmacologically active compounds of soybean (Glycine max), kudzu (Pueraria lobata), and kwao kruea khao (P. mirifica). Pharmacological activities of daidzin are mediated by its more potent metabolites daidzein and equol; however, daidzin is the predominant compound found in these medicinal plants, and the efficacy and safety of equol depend on the amount of daidzin consumed.

OBJECTIVE

To develop a specific monoclonal antibody (MAb)-based indirect competitive enzyme-linked immunosorbent assay (icELISA) for standardisation of daidzin content in herbal medicines or nutraceuticals.

METHODOLOGY

The Mannich reaction was used for the synthesis of a highly immunogenic conjugate between daidzin and a cationised carrier protein. Splenocytes of hyperimmunised mice were fused with myeloma cells to generate a hybridoma secreting antibody against daidzin.

RESULTS

The icELISA showed high selectivity and acceptable sensitivity for daidzin determination (1.56-100 ng/mL) with high reproducibility (coefficients of variation were < 5%). The icELISA was a reliable analytical method for daidzin in Glycine max, Pueraria lobata and P. mirifica, for which daidzin recoveries from spiked samples were 98.99-104.94%. Daidzin content of these plant-derived products determined using the icELISA were in close agreement with those determined by a HPLC-UV method.

CONCLUSION

The icELISA is useful for specific daidzin determination because of its reliability, low cost, speed and high throughput.

A novel UHPLC method for the rapid and simultaneous determination of daidzein, genistein and equol in human urine

This work reports on a novel method involving reverse-phased ultra-high performance liquid chromatography (UHPLC) plus a spectrophotometric photodiode array/fluorescence (FLR) detection system for determining the concentration of equol and major soy isoflavones (daidzein and genistein) in human urine. The proposed method was validated in terms of its linearity, sensitivity, accuracy (recovery) and precision (intra- and inter-day repeatability). The isoflavone profiles of urine samples from a group of menopausal women following oral soy isoflavone supplementation were determined and compared. Screening for equol-producer status was accomplished with high sensitivity (detection limit of the FLR detector 2.93nM). The method involves a short chromatographic run time compared to conventional HPLC methods while allowing for the simultaneous and reliable quantification of daidzein, genistein and equol in human urine. It also allows for the rapid screening of multiple urine samples when testing for equol production status and checking patient adherence to isoflavone treatment regimens.

Soy isoflavone metabolism in cats compared with other species: urinary metabolite concentrations and glucuronidation by liver microsomes

1. Soybean is a common source of protein in many pet foods. Slow glucuronidation of soy-derived isoflavones in cats has been hypothesized to result in accumulation with adverse health consequences. Here, we evaluated species' differences in soy isoflavone glucuronidation using urine samples from cats and dogs fed a soy-based diet and liver microsomes from cats compared with microsomes from 12 other species. 2. Significant concentrations of conjugated (but not unconjugated) genistein, daidzein and glycitein, and the gut microbiome metabolites, dihydrogenistein and dihydrodaidzein, were found in cat and dog urine samples. Substantial amounts of conjugated equol were also found in cat urine but not in dog urine. 3. β-Glucuronidase treatment showed that all these compounds were significantly glucuronidated in dog urine while only daidzein (11%) and glycitein (37%) showed any glucuronidation in cat urine suggesting that alternate metabolic pathways including sulfation predominate in cats. 4. Glucuronidation rates of genistein, daidzein and equol by cat livers were consistently ranked within the lowest 3 out of 13 species' livers evaluated. Ferret and mongoose livers were also ranked in the lowest four species. 5. Our results demonstrate that glucuronidation is a minor pathway for soy isoflavone metabolism in cats compared with most other species.

Pharmacokinetic Comparison of Soy Isoflavone Extracts in Human Plasma

The soy isoflavones daidzein and genistein produce several biological activities related to health benefits. A number of isoflavone extracts are commercially available, but there is little information concerning the specific isoflavone content of these products or differences in their bioavailability and pharmacokinetics. This study describes the development and validation of an analytical method to detect and quantify daidzein, genistein, and equol in human plasma using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The method was applied in a crossover, randomized, bioavailability study. Twelve healthy volunteers were administered the same total isoflavones dose from two isoflavone supplement preparations (Super-Absorbable Soy Isoflavones (Life Extension, USA) and Fitoladius (Merck, Spain)). The pharmacokinetic parameters (AUC0-24/dose and Cmax/dose) of the isoflavones from the two preparations differed significantly. Such differences in bioavailability and kinetics may have relevant effects on the health benefits derived from their intake.

Equol status and changes in fecal microbiota in menopausal women receiving long-term treatment for menopause symptoms with a soy-isoflavone concentrate

The knowledge regarding the intestinal microbial types involved in isoflavone bioavailability and metabolism is still limited. The present work reports the influence of a treatment with isoflavones for 6 months on the fecal bacterial communities of 16 menopausal women, as determined by culturing and culture-independent microbial techniques. Changes in fecal communities were analyzed with respect to the women's equol-producing phenotype. Compared to baseline, at 1 and 3 months the counts for all microbial populations in the feces of equol-producing women had increased strongly. In contrast, among the non-producers, the counts for all microbial populations at 1 month were similar to those at baseline, and decreased significantly by 3 and 6 months. Following isoflavone intake, major bands in the denaturing gradient gel electrophoresis (DGGE) profiles appeared and disappeared, suggesting important changes in majority populations. In some women, increases were seen in the intensity of specific DGGE bands corresponding to microorganisms known to be involved in the metabolism of dietary phytoestrogens (Lactonifactor longoviformis, Faecalibacterium prausnitzii, Bifidobacterium sp., Ruminococcus sp.). Real-Time quantitative PCR revealed that the Clostridium leptum and C. coccoides populations increased in equol producers, while those of bifidobacteria and enterobacteria decreased, and vice versa in the non-producers. Finally, the Atopobium population increased in both groups, but especially in the non-producers at three months. As the main findings of this study, (i) variations in the microbial communities over the 6-month period of isoflavone supplementation were large; (ii) no changes in the fecal microbial populations that were convincingly treatment-specific were seen; and (iii) the production of equol did not appear to be associated with the presence of, or increase in the population of, any of the majority bacterial types analyzed.

Deglycosylation of isoflavone C-glycosides by newly isolated human intestinal bacteria

BACKGROUND

Plant isoflavones are mostly present in the glycoside form. Isoflavone aglycones produced by intestinal microflora are reported to be more bioactive than the glycoside form. However, the deglycosylation of isoflavone C-glycosides is known to be rare, and is less studied.

RESULTS

Three new bacteria were isolated from human faecal samples, two of which hydrolysed the C-glycosidic bond of puerarin, daidzein-8-C-glucoside. They were identified as two Lactococcus species, herein designated as MRG-IFC-1 and MRG-IFC-3, and an Enterococcus species, herein designated MRG-IFC-2, based on their 16S rDNA sequences. From a reactivity study, it was found that Lactococcus sp. MRG-IFC-1 and Enterococcus sp. MRG-IFC-2 hydrolysed isoflavone C- and O-glycosides, as well as the flavone O-glycoside apigetrin, but could not hydrolyse the flavone C-glycosidic bond of vitexin. The other Lactococcus sp., MRG-IF-3, could not hydrolyse the C-glycosidic linkage of puerarin, while it showed a broad substrate spectrum of O-glycosidase activity similar to the other two bacteria. Puerarin was completely converted to daidzein within 100 min by Lactococcus sp. MRG-IFC-1 and Enterococcus sp. MRG-IFC-2, which is the fastest conversion among the reported human intestinal bacteria.

CONCLUSION

Two new puerarin-metabolising human intestinal bacteria were isolated and identified, and the deglycosylation activity for various flavonoid glycosides was investigated. The results could facilitate the study of C-glycosidase reaction mechanisms, as well as the pharmacokinetics of bioactive C-glycoside natural products.

Plasma isoflavone concentration is associated with decreased risk of type 2 diabetes in Korean women but not men: results from the Korean Genome and Epidemiology Study

AIMS/HYPOTHESIS

To examine the association between soybean products and risk of type 2 diabetes, we measured four isoflavone biological markers--genistein, daidzein, glycitein and equol--in a nested case-control study.

METHODS

The study population was composed of 693 cases (316 women and 377 men) and 698 matched controls (317 women and 381 men) within the Korean Genome and Epidemiology Study. The concentrations of isoflavone biomarkers were measured using HPLC-MS/MS on plasma samples that were collected at baseline. A stratified analysis was undertaken to examine the association between plasma isoflavone concentrations and risk of type 2 diabetes according to sex and equol production. Logistic regression models were used to compute ORs and 95% CIs adjusted for confounders.

RESULTS

In women, compared with the lowest quartile of plasma concentration of genistein, the highest quartile exhibited a significantly decreased risk of diabetes (OR 0.58, 95% CI 0.35, 0.95). When stratified by equol-producing status in women, the OR for diabetes in the highest vs the lowest quartile of genistein concentration was 0.31 (95% CI 0.16, 0.60) in equol producers, but genistein concentration was not associated with risk of diabetes in equol non-producers (p for interaction = 0.013). In men, isoflavone concentrations were not associated with risk of diabetes, regardless of equol-producing status.

CONCLUSIONS/INTERPRETATION

High plasma concentrations of genistein were associated with a decreased risk of type 2 diabetes in women. This inverse association was prominent in equol-producing participants. These results suggest a beneficial effect of a high intake of soybean products on risk of type 2 diabetes in women.

Dietary soy isoflavones increase metastasis to lungs in an experimental model of breast cancer with bone micro-tumors

Bone is one of the most common sites for metastasis in breast cancer (BC). Micro-metastasis in bone marrow was detected in 30% of patients with stage I, II, or III BC at primary surgery and is a strong indicator of poor prognosis. The role dietary soy isoflavones play in BC with bone micro-metastasis is unclear. In this study, we examined the effects of genistein, daidzein, (-)-equol or a mixture of soy isoflavones on BC with bone micro-metastasis using an experimental model of murine mammary cancer 4T1 cells engineered with luciferase. A small number (1000) of 4T1 cells were injected into the tibia of female Balb/c mice to establish micro-tumors in bone. Soy isoflavones were supplemented in the AIN-93G diet at 750 mg/kg and were provided to mice from 3 weeks before to 3 weeks after cell injection. Bioluminescent imaging was conducted on day 2 (D2), D6, D8, D16 and D20 post cell injection and the results indicated dietary soy isoflavones enhanced the growth of bone micro-tumors on D8. Furthermore, dietary soy isoflavones stimulated metastatic tumor formation in lungs and increased Ki-67 protein expression in these metastasized tumors. In vitro, soy isoflavones (<10 µM) had limited effects on the growth, motility or invasion of 4T1 cells. Thus, the in vivo stimulatory effect could be likely due to systemic effects between the host, 4T1 tumors and soy isoflavones. In conclusion, soy isoflavones stimulate BC with bone micro-metastasis in mice and further investigations are needed regarding their consumption by BC survivors.

Bioavailability of dietary polyphenols and gut microbiota metabolism: antimicrobial properties

Polyphenolic compounds are plant nutraceuticals showing a huge structural diversity, including chlorogenic acids, hydrolyzable tannins, and flavonoids (flavonols, flavanones, flavan-3-ols, anthocyanidins, isoflavones, and flavones). Most of them occur as glycosylated derivatives in plants and foods. In order to become bioactive at human body, these polyphenols must undergo diverse intestinal transformations, due to the action of digestive enzymes, but also by the action of microbiota metabolism. After elimination of sugar tailoring (generating the corresponding aglycons) and diverse hydroxyl moieties, as well as further backbone reorganizations, the final absorbed compounds enter the portal vein circulation towards liver (where other enzymatic transformations take place) and from there to other organs, including behind the digestive tract or via blood towards urine excretion. During this transit along diverse tissues and organs, they are able to carry out strong antiviral, antibacterial, and antiparasitic activities. This paper revises and discusses these antimicrobial activities of dietary polyphenols and their relevance for human health, shedding light on the importance of polyphenols structure recognition by specific enzymes produced by intestinal microbial taxa.

Interaction of dietary compounds, especially polyphenols, with the intestinal microbiota: a review

The intestinal microbiome plays an important role in the metabolism of chemical compounds found within food. Bacterial metabolites are different from those that can be generated by human enzymes because bacterial processes occur under anaerobic conditions and are based mainly on reactions of reduction and/or hydrolysis. In most cases, bacterial metabolism reduces the activity of dietary compounds; however, sometimes a specific product of bacterial transformation exhibits enhanced properties. Studies on the metabolism of polyphenols by the intestinal microbiota are crucial for understanding the role of these compounds and their impact on our health. This review article presents possible pathways of polyphenol metabolism by intestinal bacteria and describes the diet-derived bioactive metabolites produced by gut microbiota, with a particular emphasis on polyphenols and their potential impact on human health. Because the etiology of many diseases is largely correlated with the intestinal microbiome, a balance between the host immune system and the commensal gut microbiota is crucial for maintaining health. Diet-related and age-related changes in the human intestinal microbiome and their consequences are summarized in the paper.

The role of colonic bacteria in the metabolism of the natural isoflavone daidzin to equol

Isoflavones are found in leguminous plants, especially soybeans. They have a structural similarity to natural estrogens, which enables them to bind to estrogen receptors and elicit biological activities similar to natural estrogens. They have been suggested to be beneficial for the prevention and therapy of hormone-dependent diseases. After soy products are consumed, the bacteria of the intestinal microflora metabolize isoflavones to metabolites with altered absorption, bioavailability, and estrogenic characteristics. Variations in the effect of soy products have been correlated with the isoflavone metabolites found in plasma and urine samples of the individuals consuming soy products. The beneficial effects of the soy isoflavone daidzin, the glycoside of daidzein, have been reported in individuals producing equol, a reduction product of daidzein produced by specific colonic bacteria in individuals called equol producers. These individuals comprise 30% and 60% of populations consuming Western and soy-rich Asian diets, respectively. Since the higher percentage of equol producers in populations consuming soy-rich diets is correlated with a lower incidence of hormone-dependent diseases, considerable efforts have been made to detect the specific colonic bacteria involved in the metabolism of daidzein to the more estrogenic compound, equol, which should facilitate the investigation of the metabolic activities related to this compound.

The flavan–isoflavan rearrangement: bioinspired synthetic access to isoflavonoids via 1,2-shift–alkylation sequence

An approach to 2-substituted isoflavonoids is reported based on the 1,2-shift of the aryl group in the catechin skeleton followed by the in situ alkylation. Synthesis of (−)-equol, a natural isoflavan with estrogenic activities, was achieved.

Metabolism of Kaempferia parviflora polymethoxyflavones by human intestinal bacterium Bautia sp. MRG-PMF1

Poylmethoxyflavones (PMFs) are major bioactive flavonoids, which exhibit various biological activities, such as anticancer effects. The biotransformation of PMFs and characterization of a PMF-metabolizing human intestinal bacterium were studied herein for the first time. Hydrolysis of aryl methyl ether functional groups by human fecal samples was observed from the bioconversion of various PMFs. Activity-guided screening for PMF-metabolizing intestinal bacteria under anaerobic conditions resulted in the isolation of a strict anaerobic bacterium, which was identified as Blautia sp. MRG-PMF1. The isolated MRG-PMF1 was able to metabolize various PMFs to the corresponding demethylated flavones. The microbial conversion of bioactive 5,7-dimethoxyflavone (5,7-DMF) and 5,7,4'-trimethoxyflavone (5,7,4'-TMF) was studied in detail. 5,7-DMF and 5,7,4'-TMF were completely metabolized to 5,7-dihydroxyflavone (chrysin) and 5,7,4'-trihydroxyflavone (apigenin), respectively. From a kinetics study, the methoxy group on the flavone C-7 position was found to be preferentially hydrolyzed. 5-Methoxychrysin, the intermediate of 5,7-DMF metabolism by Blautia sp. MRG-PMF1, was isolated and characterized by nuclear magnetic resonance spectroscopy. Apigenin was produced from the sequential demethylation of 5,7,4'-TMF, via 5,4'-dimethoxy-7-hydroxyflavone and 7,4'-dihydroxy-5-methoxyflavone (thevetiaflavone). Not only demethylation activity but also deglycosylation activity was exhibited by Blautia sp. MRG-PMF1, and various flavonoids, including isoflavones, flavones, and flavanones, were found to be metabolized to the corresponding aglycones. The unprecedented PMF demethylation activity of Blautia sp. MRG-PMF1 will expand our understanding of flavonoid metabolism in the human intestine and lead to novel bioactive compounds.

Role of bifidobacteria in the hydrolysis of chlorogenic acid

This study aimed to explore the capability of potentially probiotic bifidobacteria to hydrolyze chlorogenic acid into caffeic acid (CA), and to recognize the enzymes involved in this reaction. Bifidobacterium strains belonging to eight species occurring in the human gut were screened. The hydrolysis seemed peculiar of Bifidobacterium animalis, whereas the other species failed to release CA. Intracellular feruloyl esterase activity capable of hydrolyzing chlorogenic acid was detected only in B. animalis. In silico research among bifidobacteria esterases identified Balat_0669 as the cytosolic enzyme likely responsible of CA release in B. animalis. Comparative modeling of Balat_0669 and molecular docking studies support its role in chlorogenic acid hydrolysis. Expression, purification, and functional characterization of Balat_0669 in Escherichia coli were obtained as further validation. A possible role of B. animalis in the activation of hydroxycinnamic acids was demonstrated and new perspectives were opened in the development of new probiotics, specifically selected for the enhanced bioconversion of phytochemicals into bioactive compounds.

Study of conformational stability, structural, electronic and charge transfer properties of cladrin using vibrational spectroscopy and DFT calculations

In the present work, a detailed conformational study of cladrin (3-(3,4-dimethoxy phenyl)-7-hydroxychromen-4-one) has been done by using spectroscopic techniques (FT-IR/FT-Raman/UV-Vis/NMR) and quantum chemical calculations. The optimized geometry, wavenumber and intensity of the vibrational bands of the cladrin in ground state were calculated by density functional theory (DFT) employing 6-311++G(d,p) basis sets. The study has been focused on the two most stable conformers that are selected after the full geometry optimization of the molecule. A detailed assignment of the FT-IR and FT-Raman spectra has been done for both the conformers along with potential energy distribution for each vibrational mode. The observed and scaled wavenumber of most of the bands has been found to be in good agreement. The UV-Vis spectrum has been recorded and compared with calculated spectrum. In addition, 1H and 13C nuclear magnetic resonance spectra have been also recorded and compared with the calculated data that shows the inter or intramolecular hydrogen bonding. The electronic properties such as HOMO-LUMO energies were calculated by using time-dependent density functional theory. Molecular electrostatic potential has been plotted to elucidate the reactive part of the molecule. Natural bond orbital analysis was performed to investigate the molecular stability. Non linear optical property of the molecule have been studied by calculating the electric dipole moment (μ) and the first hyperpolarizability (β) that results in the nonlinearity of the molecule.

The first 1000 cultured species of the human gastrointestinal microbiota

The microorganisms that inhabit the human gastrointestinal tract comprise a complex ecosystem with functions that significantly contribute to our systemic metabolism and have an impact on health and disease. In line with its importance, the human gastrointestinal microbiota has been extensively studied. Despite the fact that a significant part of the intestinal microorganisms has not yet been cultured, presently over 1000 different microbial species that can reside in the human gastrointestinal tract have been identified. This review provides a systematic overview and detailed references of the total of 1057 intestinal species of Eukarya (92), Archaea (8) and Bacteria (957), based on the phylogenetic framework of their small subunit ribosomal RNA gene sequences. Moreover, it unifies knowledge about the prevalence, abundance, stability, physiology, genetics and the association with human health of these gastrointestinal microorganisms, which is currently scattered over a vast amount of literature published in the last 150 years. This detailed physiological and genetic information is expected to be instrumental in advancing our knowledge of the gastrointestinal microbiota. Moreover, it opens avenues for future comparative and functional metagenomic and other high-throughput approaches that need a systematic and physiological basis to have an impact.

Genistein supplementation increases bone turnover but does not prevent alcohol-induced bone loss in male mice

Chronic alcohol consumption results in bone loss through increased bone resorption and decreased bone formation. These effects can be reversed by estradiol (E2) supplementation. Soy diets are suggested to have protective effects on bone loss in men and women, as a result of the presence of soy protein-associated phytoestrogens such as genistein (GEN). In this study, male mice were pair-fed (PF), a control diet, an ethanol (EtOH) diet, or EtOH diet supplemented with 250 mg/kg of GEN for 8 weeks to test if GEN protects against bone loss associated with chronic drinking. Interestingly, alcohol consumption reduced cortical area and thickness and trabecular bone volume in both EtOH and EtOH/GEN groups when compared to the corresponding PF and PF/GEN controls, P < 0.05. However, in the trabecular bone compartment, we observed a significant increase in overall trabecular bone density in the PF/GEN group compared to the PF controls. Bone loss in the EtOH-treated mice was associated with the inhibition of osteoblastogenesis as indicated by decreased alkaline phosphatase staining in ex vivo bone marrow cultures, P < 0.05. GEN supplementation improved osteoblastogenesis in the EtOH/GEN cultures compared to the EtOH group, P < 0.05. Vertebral expression of bone-formation markers, osteocalcin, and runt-related transcription factor 2 (Runx2) was also significantly up-regulated in the PF/GEN and EtOH/GEN groups compared to the PF and EtOH-treated groups. GEN supplementation also increased the expression of receptor activator of nuclear factor κ-B ligand (RANKL) in the PF/GEN, an increase that persisted in the EtOH/GEN-treated animals (P < 0.05), and increased basal hydrogen peroxide production and RANKL mRNA expression in primary bone marrow cultures in vitro, P < 0.05. These findings suggest that GEN supplementation increases the overall bone remodeling and, in the context of chronic alcohol consumption, does not protect against the oxidative stress-associated EtOH-mediated bone resorption.

Obesity prevalence in relation to gut microbial environments capable of producing equol or O-desmethylangolensin from the isoflavone daidzein

BACKGROUND/OBJECTIVES

Studies have observed associations between the gut microbiome and obesity. O-desmethylangolensin (ODMA) and equol are gut bacterial metabolites of daidzein, a compound found in high amounts in soy foods. Approximately 80-95% and 25-60% of individuals harbor gut microbial communities capable of producing ODMA or equol, respectively. Given that other phenotypes of gut bacterial metabolism of dietary compounds have been associated with obesity, we hypothesized that daidzein-metabolizing phenotypes would be associated with obesity. The objective of this study was to compare the prevalence of ODMA-producer and equol-producer phenotypes in obese, overweight and normal-weight individuals.

SUBJECTS/METHODS

Adults aged 18-95 years (n=297) provided a first-void urine sample after a 3-day soy challenge, and urinary ODMA and equol concentrations were used to classify individuals as producers or non-producers. Body mass index was calculated from self-reported weight and height.

RESULTS

There were 60 ODMA non-producers and 173 equol non-producers. Obese individuals were 2.8 times more likely to be ODMA non-producers (odds ratio (OR)=2.8, 95% confidence interval (CI): 1.2, 6.2) compared with normal-weight individuals, when adjusted for age, race (white vs non-white), and gender and menopausal status (male, premenopausal female and postmenopausal female). Obesity was not associated with equol-producer phenotype (OR=1.1, 95% CI: 0.5, 2.2). Stronger associations with obesity were observed in the ODMA non-producers who were also equol producers than in the equol non-producers.

CONCLUSIONS

Results from this analysis suggest that the ODMA-producer phenotype, but not equol-producer phenotype, is associated with obesity in adults. These results support further work to replicate these findings and evaluate the mechanisms of the observed associations.

Daidzein, R-(+)equol and S-(-)equol inhibit the invasion of MDA-MB-231 breast cancer cells potentially via the down-regulation of matrix metalloproteinase-2

PURPOSE

Soy isoflavones may inhibit tumor cell invasion and metastasis via their effects on matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs). The current study investigates the effects of daidzein, R- and S-equol on the invasion of MDA-MB-231 human breast cancer cells and the effects of these compounds on MMP/TIMP expression at the mRNA level.

METHODS

The anti-invasive effects of daidzein, R- and S-equol (0, 2.5, 10, 50 μM) on MDA-MB-231 cells were determined using the Matrigel invasion assay following 48-h exposure. Effects on MMP-2, MMP-9, TIMP-1 and TIMP-2 expression were assessed using real-time PCR. Chiral HPLC analysis was used to determine intracellular concentrations of R- and S-equol.

RESULTS

The invasive capacity of MDA-MB-231 cells was significantly reduced (by approximately 50-60 %) following treatment with 50 μM daidzein, R- or S-equol. Anti-invasive effects were also observed with R-equol at 2.5 and 10 μM though overall equipotent effects were induced by all compounds. Inhibition of invasion induced by all three compounds at 50 μM was associated with the down-regulation of MMP-2, while none of the compounds tested significantly affected the expression levels of MMP-9, TIMP-1 or TIMP-2 at this concentration. Following exposure to media containing 50 μM R- or S-equol for 48-h intracellular concentrations of R- and S-equol were 4.38 ± 1.17 and 3.22 ± 0.47 nM, respectively.

CONCLUSION

Daidzein, R- and S-equol inhibit the invasion of MDA-MB-231 human breast cancer cells in part via the down-regulation of MMP-2 expression, with equipotent effects observed for the parent isoflavone daidzein and the equol enantiomers.

Phytoestrogens in postmenopause: the state of the art from a chemical, pharmacological and regulatory perspective

Phytoestrogens represent a diverse group of non-steroidal natural products, which seem to have some oestrogenic effects and are often marketed as food supplements. Population exposed to phytoestrogens is potentially increasing, in part because an unfavourable risk-benefit profile of Hormone Replacement Therapy (HRT) for prolonged treatments (e.g., osteoporosis prevention) highlighted by the publication of the Women Health Initiative (WHI) trial in 2002, but also because many post-menopausal women often perceived phytoestrogens in food supplements as a safer alternative than HRT. Despite of increasing preclinical and clinical studies in the past decade, appealing evidence is still lacking to support the overall positive risk-benefit profile of phytoestrogens. Their status as food supplements seems to discourage studies to obtain new evidence, and the chance to buy them by user's initiative make it difficult to survey their prevalence and pattern of use. The aim of the present review is to: (a) outline the clinical scenario underlying the increased interest on phytoestrogens, by overviewing the evolution of the evidence on HRT and its main therapeutic goals (e.g., menopausal symptoms relief, chemoprevention, osteoporosis prevention); (b) address the chemical and pharmacological features (e.g. chemical structure, botanical sources, mechanism of action) of the main compounds (e.g., isoflavones, lignans, coumestans); (c) describe the clinical evidence on potential therapeutic applications; (d) put available evidence on their riskbenefit profile in a regulatory perspective, in light of the recent regulation on health claims of food supplements.

Dietary intake of natural antioxidants: vitamins and polyphenols

Oxidative stress is a condition in which oxidant metabolites exert their toxic effect because of an increased production or an altered cellular mechanism of protection; oxidative stress is rapidly gaining recognition as a key phenomenon in chronic diseases. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions by being oxidized themselves. Endogenous defence mechanisms are inadequate for the complete prevention of oxidative damage, and different sources of dietary antioxidants may be especially important. This article calls attention to the dietary antioxidants, such as vitamins A, C, and E and polyphenols. Compelling evidence has led to the conclusion that diet is a key environmental factor and a potential tool for the control of chronic diseases. More specifically, fruits and vegetables have been shown to exert a protective effect. The high content of minerals and natural antioxidant as vitamins A, C, and E and polyphenols in fruits and vegetables may be a main factor responsible for these effects.

Effect of soybean processing on content and bioaccessibility of folate, vitamin B12 and isoflavones in tofu and tempe

PURPOSE

To compare the content of bioaccessible folate, vitamin B12, and isoflavones in tofu and tempe, as influenced by soybean variety and food processing, particularly fermentation.

PRINCIPAL RESULTS

Raw soybeans contained 2207-2671 μg/kg (dry matter) folate, cooked tempe 1493-4143, and cooked tofu 968-1273 μg/kg, the difference was attributed to the fermentation in tempe. Vitamin B12 was detected only in tempe (0.16-0.72 μg/kg). Isoflavone aglycones were formed during soaking of soybeans, with only minor differences between the contents in cooked tempe (average 1922-2968 μg/kg) or tofu (1667-2782 μg/kg) but strongly depending on bean variety.

CONCLUSIONS

Folate and vitamin B12 contents were mainly influenced by microbial activity during fermentation, whereas isoflavone aglycone content was determined by bean variety. Tofu had lower folate and vitamin B12, but equal isoflavone contents as tempe. Bioaccessibility of folate (80-100%) and isoflavone aglycones (100%) were high.

Estrogen receptor and PI3K/Akt signaling pathway involvement in S-(-)equol-induced activation of Nrf2/ARE in endothelial cells

S-(-)equol, a natural product of the isoflavone daidzein, has been reported to offer cytoprotective effects with respect to the cardiovascular system, but how this occurs is unclear. Interestingly, S-(-)equol is produced by the human gut, suggesting a role in physiological processes. We report that treatment of human umbilical vein endothelial cells and EA.hy926 cells with S-(-)equol induces ARE-luciferase reporter gene activity that is dose and time dependent. S-(-)equol (10-250 nM) increases nuclear factor-erythroid 2-related factor 2 (Nrf2) as well as gene products of Nrf2 target genes heme oxygenase-1 (HO-1) and NAD(P)H (nicotinamide-adenine-dinucleotide-phosphate) quinone oxidoreductase 1 (NQO1). Endothelial cells transfected with an HA-Nrf2 expression plasmid had elevated HA-Nrf2, HO-1, and NQO1 in response to S-(-)equol exposure. S-(-)equol treatment affected Nrf2 mRNA only slightly but significantly increased HO-1 and NQO1 mRNA. The pretreatment of cells with specific ER inhibitors or PI3K/Akt (ICI182,780 and LY294002) increased Nrf2, HO-1, and NQO1 protein, impaired nuclear translocation of HA-Nrf2, and decreased ARE-luciferase activity. Identical experiments were conducted with daidzein, which had effects similar to S-(-)equol. In addition, DPN treatment (an ERβ agonist) induced the ARE-luciferase reporter gene, promoting Nrf2 nuclear translocation. Cell pretreatment with an ERβ antagonist (PHTPP) impaired S-(-)equol-induced Nrf2 activation. Pre-incubation of cells followed by co-treatment with S-(-)equol significantly improved cell survival in response to H2O2 or tBHP and reduced apoptotic and TUNEL-positively-stained cells. Notably, the ability of S-(-)equol to protect against H2O2-induced cell apoptosis was attenuated in cells transfected with an siRNA against Nrf2. Thus, beneficial effects of S-(-)equol with respect to cytoprotective antioxidant gene activation may represent a novel strategy to prevent and treat cardiovascular diseases.