Bioconversion of daidzein to equol by Bifidobacterium breve 15700 and Bifidobacterium longum BB536

A Gnotobiotic Mouse Model with Divergent Equol-Producing Phenotypes: Potential for Determining Microbial-Driven Health Impacts of Soy Isoflavone Daidzein

The implications of soy consumption on human health have been a subject of debate, largely due to the mixed evidence regarding its benefits and potential risks. The variability in responses to soy has been partly attributed to differences in the metabolism of soy isoflavones, compounds with structural similarities to estrogen. Approximately one-third of humans possess gut bacteria capable of converting soy isoflavone daidzein into equol, a metabolite produced exclusively by gut microbiota with significant estrogenic potency. In contrast, lab-raised rodents are efficient equol producers, except for those raised germ-free. This discrepancy raises concerns about the applicability of traditional rodent models to humans. Herein, we designed a gnotobiotic mouse model to differentiate between equol producers and non-producers by introducing synthetic bacterial communities with and without the equol-producing capacity into female and male germ-free mice. These gnotobiotic mice display equol-producing phenotypes consistent with the capacity of the gut microbiota received. Our findings confirm the model's efficacy in mimicking human equol production capacity, offering a promising tool for future studies to explore the relationship between endogenous equol production and health outcomes like cardiometabolic health and fertility. This approach aims to refine dietary guidelines by considering individual microbiome differences.

Advances in the Metabolic Mechanism and Functional Characteristics of Equol

Equol is the most potent soy isoflavone metabolite and is produced by specific intestinal microorganisms of mammals. It has promising application possibilities for preventing chronic diseases such as cardiovascular disease, breast cancer, and prostate cancer due to its high antioxidant activity and hormone-like activity. Thus, it is of great significance to systematically study the efficient preparation method of equol and its functional activity. This paper elaborates on the metabolic mechanism of equol in humans; focuses on the biological characteristics, synthesis methods, and the currently isolated equol-producing bacteria; and looks forward to its future development and application direction, aiming to provide guidance for the application and promotion of equol in the field of food and health products.

Relationship between Dietary Polyphenols and Gut Microbiota: New Clues to Improve Cognitive Disorders, Mood Disorders and Circadian Rhythms

Cognitive, mood and sleep disorders are common and intractable disorders of the central nervous system, causing great inconvenience to the lives of those affected. The gut-brain axis plays a vital role in studying neurological disorders such as neurodegenerative diseases by acting as a channel for a bidirectional information exchange between the gut microbiota and the nervous system. Dietary polyphenols have received widespread attention because of their excellent biological activity and their wide range of sources, structural diversity and low toxicity. Dietary intervention through the increased intake of dietary polyphenols is an emerging strategy for improving circadian rhythms and treating metabolic disorders. Dietary polyphenols have been shown to play an essential role in regulating intestinal flora, mainly by maintaining the balance of the intestinal flora and enhancing host immunity, thereby suppressing neurodegenerative pathologies. This paper reviewed the bidirectional interactions between the gut microbiota and the brain and their effects on the central nervous system, focusing on dietary polyphenols that regulate circadian rhythms and maintain the health of the central nervous system through the gut-brain axis.

Soy isoflavone-specific biotransformation product S-equol in the colon: physiological functions, transformation mechanisms, and metabolic regulatory pathways

Epidemiological data suggest that regular intake of soy isoflavones may reduce the incidence of estrogen-dependent and aging-associated disorders. Equol is a metabolite of soy isoflavone (SI) produced by specific gut microbiota and has many beneficial effects on human health due to its higher biological activity compared to SI. However, only 1/3 to 1/2 of humans are able to produce equol in the body, which means that not many people can fully benefit from SI. This review summarizes the recent advances in equol research, focusing on the chemical properties, physiological functions, conversion mechanisms in vitro and vivo, and metabolic regulatory pathways affecting S-equol production. Advanced experimental designs and possible techniques in future research plan are also fully discussed. Furthermore, this review provides a fundamental basis for researchers in the field to understand individual differences in S-equol production, the efficiency of metabolic conversion of S-equol, and fermentation production of S-equol in vitro.

Taxonomic distribution and evolutionary analysis of the equol biosynthesis gene cluster

Background

Equol, an isoflavonoid metabolite with possible health benefits in humans, is known to be produced by some human gut bacteria. While the genes encoding the equol production pathway have been characterized in a few bacterial strains, a systematic analysis of the equol production pathway is currently lacking.

Results

This study presents an analysis of the taxonomic distribution and evolutionary history of the gene cluster encoding the equol production pathway. A survey for equol gene clusters within the Genome Taxonomy Database bacterial genomes and human gut metagenomes resulted in the identification of a highly conserved gene cluster found in nine bacterial species from the Eggerthellaceae family. The identified gene clusters from human gut metagenomes revealed potential variations in the equol gene cluster organization and gene content within the equol-producing Eggerthellaceae clades. Subsequent analysis showed that in addition to the four genes directly involved in equol production, multiple other genes were consistently found in the equol gene clusters. These genes were predicted to encode a putative electron transport complex and hydrogenase maturase system, suggesting potential roles for them in the equol production pathway. Analysis of the gene clusters and a phylogenetic reconstruction of a putative NAD kinase gene provided evidence of the recent transfer of the equol gene cluster from a basal Eggerthellaceae species to Slackia_A equolifaciens, Enteroscipio sp000270285, and Lactococcus garvieae 20–92.

Conclusions

This analysis demonstrates that the highly conserved equol gene cluster is taxonomically restricted to the Eggerthellaceae family of bacteria and provides evidence of the role of horizontal gene transfer in the evolutionary history of these genes. These results provide a foundation for future studies of equol production in the human gut and future efforts related to bioengineering and the use of equol-producing bacteria as probiotics.

Maximizing the Estrogenic Potential of Soy Isoflavones through the Gut Microbiome: Implication for Cardiometabolic Health in Postmenopausal Women

Soy isoflavones have been suggested as an alternative treatment for managing postmenopausal symptoms and promoting long-term health due to their structural similarity to mammalian estrogen and ability to bind to estrogen receptors. Among all soy isoflavones and their metabolites, (S)-equol is known for having the strongest estrogenic activity. Equol is a metabolite of the soy isoflavone daidzein produced through intestinal bacterial metabolism. However, more than half of the human population is not able to produce equol due to the lack of equol-producing bacteria in their gastrointestinal tract. The interpersonal variations in the gut microbiome complicate the interpretation of data collected from humans. Furthermore, because rodents are efficient equol-producers, translatability between rodent models and humans is challenging. Herein, we first summarized the current knowledge of the microbial conversion of daidzein to equol, its relation to health, and proposed the need for developing model systems by which equol production can be manipulated while controlling other known confounding factors. Determining the necessity of equol-producing capacity within a gut microbial community when consuming soy as a functional ingredient, and identifying strategies to maximize equol production by modulating the gut microbiome, may provide future therapeutic approaches to improve the health of postmenopausal women.

Dietary Isoflavones Alter Gut Microbiota and Lipopolysaccharide Biosynthesis to Reduce Inflammation

The etiopathogenesis of multiple sclerosis (MS) is strongly affected by environmental factors such as diet and the gut microbiota. An isoflavone-rich (ISO) diet was previously shown to reduce the severity of MS in the animal model experimental autoimmune encephalomyelitis (EAE). Translation of this concept to clinical trial where dietary isoflavones may be recommended for MS patients will require preliminary evidence that providing the isoflavone-rich diet to people with MS (PwMS) who lack phytoestrogen-metabolizing bacteria has beneficial effects. We have previously shown that the gut microbiota of PwMS resembles the gut microbiota of mice raised under a phytoestrogen-free (phyto-free) diet in that it lacks phytoestrogen-metabolizing bacteria. To investigate the effects of phytoestrogens on the microbiota inflammatory response and EAE disease severity we switched the diet of mice raised under a phyto-free (PF) diet to an isoflavone-rich diet. Microbiota analysis showed that the change in diet from one that is ISO to one that is PF reduces beneficial bacteria such as Bifidobacterium species. In addition we observed functional differences in lipopolysaccharide (LPS) biosynthesis pathways. Moreover LPS extracted from feces of mice fed an ISO diet induced increased production of anti-inflammatory cytokines from bone marrow-derived macrophages relative to fecal-LPS isolated from mice fed a PF diet. Eventually mice whose diet was switched from a PF diet to an ISO diet trended toward reduced EAE severity and mortality. Overall we show that an isoflavone-rich diet specifically modulates LPS biosynthesis of the gut microbiota imparts an anti-inflammatory response and decreases disease severity.

Strategies to achieve significant physiological concentrations of bioactive phytoestrogens in plasma

The benefits to health attributed to the intake of phytoestrogens (PEs) have been demonstrated in previous studies with significant physiological concentrations of bioactive PEs, such as genistein, equol, enterolignans and urolithins in plasma. However, the achievement of high bioactive PE levels in plasma is restricted to a select population group, mainly due to the low intake of plant PEs and/or the absence, or inhibition, of the microbiota capable of producing these bioactive forms. In this study, the intake of plant PEs, the concentration of bioactive PEs in plasma, the ability of the intestinal microbiota to produce bioactive PEs, as well as the different mechanisms used by GRAS bacteria to increase the level of bioactive PEs were evaluated concluding that the use of GRAS bacteria bioactive PE producers and the development of fermented foods enriched in bioactive PEs in addition to a high intake of plant PEs and taking care of the intestinal microbiota, are some of the different strategies to achieve significant physiological concentrations of bioactive PEs in the intestine and, subsequently, in plasma and targets organs which are essential to improve menopausal symptoms or reduce the risk of some pathologies such as breast and colon cancer, or cardiovascular disease.

Modulation of the Gut Microbiota Structure with Probiotics and Isoflavone Alleviates Metabolic Disorder in Ovariectomized Mice

The decrease in ovarian hormone secretion that occurs during menopause results in an increase in body weight and adipose tissue mass. Probiotics and soy isoflavones (SIFs) could affect the gut microbiota and exert anti-obesity effects. The objective of this study was to investigate the effects of probiotics and a diet containing SIF (SIF diet) on ovariectomized mice with menopausal obesity, including the gut microbiome. The results demonstrate that Bifidobacterium longum 15M1 can reverse menopausal obesity, whilst the combination of Lactobacillus plantarum 30M5 and a SIF diet was more effective in alleviating menopausal lipid metabolism disorder than either components alone. Probiotics and SIFs play different anti-obesity roles in menopausal mice. Furthermore, 30M5 alters the metabolites of the gut microbiota that increase the circulating estrogen level, upregulates the expression of estrogen receptor α in abdominal adipose tissue and improves the production of short-chain fatty acids (SCFAs). A SIF diet can significantly alter the structure of the fecal bacterial community and enrich the pathways related to SCFAs production. Moreover, 30M5 and a SIF diet acted synergistically to effectively resolve abnormal serum lipid levels in ovariectomized mice, and these effects appear to be associated with regulation of the diversity and structure of the intestinal microbiota to enhance SCFAs production and promote estrogen circulation.

Impact of prebiotics on equol production from soymilk isoflavones by two Bifidobacterium species

The influence of commercial prebiotics (fructo-oligosaccharides and inulin) and sugars (glucose and sucrose) on enhancing equol production from soymilk isoflavones by Bifidobacterium longum BB536 and Bifidobacterium breve ATCC 15700 was evaluated in vitro. Sterilized soymilk was inoculated with each bacterial species at 37 °C for 48 h. The growth and β-glucosidase enzyme activity for the two Bifidobacterium species in soymilk throughout fermentation were assessed. The highest viable count for B. breve (8.75 log CFU/ml) was reached at 36 h and for B. longum (8.55 log CFU/ml) at 24 h. Both bacterial species displayed β-glucosidase activity. B. breve showed increased enzyme activity (4.126 U) at 36 h, while B. longum exhibited maximum activity (3.935 U) at 24 h of fermentation. Among the prebiotics screened for their effect in isoflavones transformation to equol, inulin delivered the highest effect on equol production. The co-culture of B. longum BB536 and B. breve ATCC15700 in soymilk supplemented with inulin produced the highest level (11.49 mmol/l) of equol at 48 h of fermentation process. Level of daidzin declined whereas that of daidzein increased, and then gradually decreased due to formation of equol when soymilk was fermented using bifidobacterial. This suggests that the nutritional value of soymilk may be increased by increasing bioavailability of the bioactive ingredients. Collectively these data identify probiotics and prebiotic combinations suitable for inclusion in soymilk to enhance equol production.

Equol: A Bacterial Metabolite from The Daidzein Isoflavone and Its Presumed Beneficial Health Effects

Epidemiological data suggest that regular intake of isoflavones from soy reduces the incidence of estrogen-dependent and aging-associated disorders, such as menopause symptoms in women, osteoporosis, cardiovascular diseases and cancer. Equol, produced from daidzein, is the isoflavone-derived metabolite with the greatest estrogenic and antioxidant activity. Consequently, equol has been endorsed as having many beneficial effects on human health. The conversion of daidzein into equol takes place in the intestine via the action of reductase enzymes belonging to incompletely characterized members of the gut microbiota. While all animal species analyzed so far produce equol, only between one third and one half of human subjects (depending on the community) are able to do so, ostensibly those that harbor equol-producing microbes. Conceivably, these subjects might be the only ones who can fully benefit from soy or isoflavone consumption. This review summarizes current knowledge on the microorganisms involved in, the genetic background to, and the biochemical pathways of, equol biosynthesis. It also outlines the results of recent clinical trials and meta-analyses on the effects of equol on different areas of human health and discusses briefly its presumptive mode of action.

Bacterial metabolism as responsible of beneficial effects of phytoestrogens on human health

Phytoestrogens (PE) are compounds found in plants such as soy (isoflavones), flax seeds and cereals (lignans) and pomegranates (ellagitannins). PE have shown estrogenic/antiestrogenic, antioxidant, anti-inflammatory, antineoplastic and apoptotic activities. The human studies are showing promising although inconsistent results about the beneficial effects of PE on ameliorating the menopausal symptoms or reducing the risk of certain cancers, cardiovascular disease or diabetes. The effects of PE on the organism are mediated by the intestinal microbiota, which transforms them into bioactive PE such as genistein, equol, enterolignans and certain urolithins. In this work, we review the most recent findings about the bacteria able to metabolize PE, together with the latest studies on the effects of PE on health. In addition, we describe the possible factors hindering the demonstration of the beneficial effect of PE on health, evincing the importance of measuring the actual circulating PE in order to encompass the variability of PE metabolism due to the intestinal microbiota. With this in mind, we also explore an approach to ensure the access to bioactive PE.

Bifidobacterium breve MCC1274 with glycosidic activity enhances in vivo isoflavone bioavailability

Polyphenols are plant derived compounds that exert many beneficial health effects to the human host. However, associated health benefits of dietary polyphenol are highly dependent on their intestinal metabolism, bioavailability, and absorption. Bifidobacteria, which represent the key members of gut microbiota, have been suggested to promote gut microbial homeostasis and may be involved in the metabolism of polyphenols. In this study, the capabilities of thirteen Bifidobacterium strains in hydrolysing polyphenol glycosides were evaluated. Among the tested strains, Bifidobacterium breve MCC1274 was found to possess the highest β-glucosidase activity and strong capability to convert daidzin and trans-polydatin to their aglycones; while kinetic analysis revealed that B. breve MCC1274 hydrolysed more than 50% of daidzin and trans-polydatin at less than 3 h of incubation. Further investigation using rats with an antibiotics-disturbed microbiome revealed that following the ingestion of daidzin glycoside, oral administration of B. breve MCC1274 significantly enhanced the plasma concentration of daidzein in rats pre-treated with antibiotics as compared to antibiotics-pre-treated control and non-treated control groups. The relative abundance of Actinobacteria and the total numbers of B. breve were also significantly higher in antibiotics-pre-treated rats administered with B. breve MCC1274 than that of the control groups. These findings suggest that B. breve MCC1274 is effective in enhancing the bioavailability of daidzein in the gut under dysbiosis conditions and may potentially improve intestinal absorption of isoflavones and promote human health.

Isoflavones

Phytoestrogens are naturally occurring nonsteroidal phenolic plant compounds that, due to their molecular structure and size, resemble vertebrate steroids estrogens. This review is focused on plant flavonoids isoflavones, which are ranked among the most estrogenic compounds. The main dietary sources of isoflavones for humans are soybean and soybean products, which contain mainly daidzein and genistein. When they are consumed, they exert estrogenic and/or antiestrogenic effects. Isoflavones are considered chemoprotective and can be used as an alternative therapy for a wide range of hormonal disorders, including several cancer types, namely breast cancer and prostate cancer, cardiovascular diseases, osteoporosis, or menopausal symptoms. On the other hand, isoflavones may also be considered endocrine disruptors with possible negative influences on the state of health in a certain part of the population or on the environment. This review deals with isoflavone classification, structure, and occurrence, with their metabolism, biological, and health effects in humans and animals, and with their utilization and potential risks.

Bioactivity of dietary polyphenols: The role of metabolites

A polyphenol-rich diet protects against chronic pathologies by modulating numerous physiological processes, such as cellular redox potential, enzymatic activity, cell proliferation and signaling transduction pathways. However, polyphenols have a low oral bioavailability mainly due to an extensive biotransformation mediated by phase I and phase II reactions in enterocytes and liver but also by gut microbiota. Despite low oral bioavailability, most polyphenols proved significant biological effects which brought into attention the low bioavailability/high bioactivity paradox. In recent years, polyphenol metabolites have attracted great interest as many of them showed similar or higher intrinsic biological effects in comparison to the parent compounds. There is a huge body of literature reporting on the biological functions of polyphenol metabolites generated by phase I and phase II metabolic reactions and gut microbiota-mediated biotransformation. In this respect, the review highlights the pharmacokinetic fate of the major dietary polyphenols (resveratrol, curcumin, quercetin, rutin, genistein, daidzein, ellagitannins, proanthocyanidins) in order to further address the efficacy of biometabolites as compared to parent molecules. The present work strongly supports the contribution of metabolites to the health benefits of polyphenols, thus offering a better perspective in understanding the role played by dietary polyphenols in human health.

Determination of in vitro isoflavone degradation in rumen fluid

The aim of this study was to determine the degradation of dietary isoflavones in rumen fluid under 2 feeding regimens. The experiments were performed in vitro using a rumen fluid buffer system. The rumen fluid was taken from cows fed either a hay diet or a concentrate-rich diet (the diet consisted of 34.6% maize silage, 17.6% haylage, 12.8% alfalfa hay, and 35.0% supplemental mixture on a dry matter basis). As a source of isoflavones, 40% soybean extract (Biomedica, Prague, Czech Republic) at levels of 5, 25, 50, and 75 mg per 40 mL of rumen fluid was used. Samples of soybean extract were incubated in triplicate at 39°C for 0, 3.0, 6.0, 12.0, and 24.0 h in incubation solution. The metabolism of daidzein and genistein was faster under concentrate-rich diet conditions. In general, production of equol started after 3 to 6 h of incubation and reached the highest rate after approximately 12 h of incubation regardless of the type of diet or concentration of extract. In most of the experiments, production of equol continued after 24 h of incubation. Generally, equol production was greater under the hay diet conditions. Furthermore, experiments with higher amounts of added soybean extract revealed possible inhibitory effects of high levels of isoflavones on the rumen microflora.

Potential interactions among phenolic compounds and probiotics for mutual boosting of their health-promoting properties and food functionalities - A review

Several foods are rich sources of phenolic compounds (PC) and their beneficial effects on human health may be increased through the action of probiotics. Additionally, probiotics may use PC as substrates, increasing their survival and functionality. This review presents available studies on the effects of PC on probiotics, including their physiological functionalities, interactions and capability of surviving during exposure to gastrointestinal conditions and when incorporated into food matrices. Studies have shown that PC can improve the adhesion capacity and survival of probiotics during exposure to conditions that mimic the gastrointestinal tract. There is strong evidence that PC can modulate the composition of the gut microbiota in hosts, improving a variety of biochemical markers and risk factors for chronic diseases. Available literature also indicates that metabolites of PC formed by intestinal microorganisms, including probiotics, exert a variety of benefits on host health. These metabolites are typically more active than parental dietary PC. The presence of PC commonly enhances probiotic survival in different foods. Finally, further clinical studies need to be developed to confirm in vitro and experimental findings concerning the beneficial interactions among different PC and probiotics.

Probiotic Bacteria for Healthier Aging: Immunomodulation and Metabolism of Phytoestrogens

Age-related degeneration gives rise to a number of pathologies, many of them associated with imbalances of the microbiota and the gut-associated immune system. Thus, the intestine is considered a key target organ to improve the quality of life in senescence. Gut microbiota can have a powerful impact in the deterioration linked to aging by its nutritional and immunomodulatory activity. Reduced numbers of beneficial species and low microbial biodiversity in the elderly have been linked with pathogenesis of many diseases. A healthy lifestyle with an elderly customized diet including probiotics can contribute to reducing the chronic proinflammatory status and other age-related pathologies. Beneficial effects of probiotic lactic acid bacteria and bifidobacteria to alleviate some of these disorders based on their immunomodulatory properties as well as their capacity to produce bioactive metabolites from dietary phytoestrogens are summarized. On one hand, the preservation of gut barrier integrity and an increased ability to fight infections are the main reported immune benefits of probiotics. On the other hand, the intake of a diet rich in phytoestrogens along with the presence of selected probiotic bacteria may lead to the production of equol, enterolignans, and urolithins, which are considered protective against chronic diseases related to aging.

Bioactivation of Phytoestrogens: Intestinal Bacteria and Health

Phytoestrogens are polyphenols similar to human estrogens found in plants or derived from plant precursors. Phytoestrogens are found in high concentration in soya, flaxseed and other seeds, fruits, vegetables, cereals, tea, chocolate, etc. They comprise several classes of chemical compounds (stilbenes, coumestans, isoflavones, ellagitannins, and lignans) which are structurally similar to endogenous estrogens but which can have both estrogenic and antiestrogenic effects. Although epidemiological and experimental evidence indicates that intake of phytoestrogens in foods may be protective against certain chronic diseases, discrepancies have been observed between in vivo and in vitro experiments. The microbial transformations have not been reported so far in stilbenes and coumestans. However, isoflavones, ellagitanins, and lignans are metabolized by intestinal bacteria to produce equol, urolithins, and enterolignans, respectively. Equol, urolithin, and enterolignans are more bioavailable, and have more estrogenic/antiestrogenic and antioxidant activity than their precursors. Moreover, equol, urolithins and enterolignans have anti-inflammatory effects and induce antiproliferative and apoptosis-inducing activities. The transformation of isoflavones, ellagitanins, and lignans by intestinal microbiota is essential to be protective against certain chronic diseases, as cancer, cardiovascular disease, osteoporosis, and menopausal symptoms. Bioavailability, bioactivity, and health effects of dietary phytoestrogens are strongly determined by the intestinal bacteria of each individual.

Effects of equol on deoxycorticosterone acetate salt-induced hypertension and associated vascular dementia in rats

Oxidative stress is the major cause of neuronal cell degeneration observed in neurodegenerative diseases including vascular dementia (VaD), and hypertension has been found to increase the probability of VaD. Here, we investigated the effects of equol in deoxycorticosterone acetate (DOCA)-salt-induced hypertensive rats (DHRs) and the associated VaD. The systolic blood pressure of rats treated with low- (10 mg per kg body weight) and high-dose (20 mg per kg body weight) equol for 4 weeks was lower than that of the control group by 12.18 and 17.48% in a dose-dependent manner, respectively (p < 0.05), which was regulated by inhibiting angiotensin-converting enzyme (ACE) activity and increasing the nitric oxide (NO) production. Equol-treated DHRs showed a significant decrease in both the swimming distance and time required to reach the escape platform (78.20 to 82.56%, p < 0.05). In addition, the probe trial session and working memory test indicated that equol improved the long- and short-term memory of the rats. Moreover, the brain antioxidant activity was increased by elevating the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) levels, and the malondialdehyde (MDA) content and acetylcholinesterase (AChE) activity were decreased, indicating that equol suppressed oxidative stress. In conclusion, we demonstrated that equol exhibited comparable blood pressure (BP)-lowering and VaD-improving effects with the clinically used drug, lisinopril in DHRs while there was a positive correlation between the doses. Therefore, this bioactive compound may be useful for developing functional foods, thereby extending the application of equol-containing crops.

Isoflavone metabolism by a collection of lactic acid bacteria and bifidobacteria with biotechnological interest

Almost all soy isoflavones exist as glycosides, daidzin, genistin, and glycitin. We analyzed the capacity of 92 strains of lactic acid bacteria (LAB) and bifidobacteria with biotechnological interest to process the glycosylated isoflavones daidzin, genistin, and glycitin in their more bioavailable aglycones and their metabolites as dihydrodaidzein (DHD), O-desmethylangolensin, and equol. Representative strains of the four genera studied Lactobacillus, Enterococcus, Lactococcus, and Bifidobacterium were able to produce daidzein, genistein, and glycitein, with the exception of the lactobacilli, which did not produced glycitein in soy extracts. The production of the aglycone isoflavones could be correlated with the β-glucosidase activity of the strains. The isoflavone metabolism is limited to the glycoside hydrolysis in the most of these strains. Moreover, Enterococcus faecalis INIA P333 and Lactobacillus rhamnosus INIA P540 were able to transform daidzein in DHD. LAB and bifidobacteria studied in the present work have a great potential in the metabolism of isoflavones and could be selected for the development of functional fermented soy foods.

P212A Mutant of Dihydrodaidzein Reductase Enhances (S)-Equol Production and Enantioselectivity in a Recombinant Escherichia coli Whole-Cell Reaction System

(S)-Equol, a gut bacterial isoflavone derivative, has drawn great attention because of its potent use for relieving female postmenopausal symptoms and preventing prostate cancer. Previous studies have reported on the dietary isoflavone metabolism of several human gut bacteria and the involved enzymes for conversion of daidzein to (S)-equol. However, the anaerobic growth conditions required by the gut bacteria and the low productivity and yield of (S)-equol limit its efficient production using only natural gut bacteria. In this study, the low (S)-equol biosynthesis of gut microorganisms was overcome by cloning the four enzymes involved in the biosynthesis from Slackia isoflavoniconvertens into Escherichia coli BL21(DE3). The reaction conditions were optimized for (S)-equol production from the recombinant strain, and this recombinant system enabled the efficient conversion of 200 μM and 1 mM daidzein to (S)-equol under aerobic conditions, achieving yields of 95% and 85%, respectively. Since the biosynthesis of trans-tetrahydrodaidzein was found to be a rate-determining step for (S)-equol production, dihydrodaidzein reductase (DHDR) was subjected to rational site-directed mutagenesis. The introduction of the DHDR P212A mutation increased the (S)-equol productivity from 59.0 mg/liter/h to 69.8 mg/liter/h in the whole-cell reaction. The P212A mutation caused an increase in the (S)-dihydrodaidzein enantioselectivity by decreasing the overall activity of DHDR, resulting in undetectable activity for (R)-dihydrodaidzein, such that a combination of the DHDR P212A mutant with dihydrodaidzein racemase enabled the production of (3S,4R)-tetrahydrodaidzein with an enantioselectivity of >99%.

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.