Biosynthesis of (-)-5-Hydroxy-equol and 5-Hydroxy-dehydroequol from Soy Isoflavone, Genistein Using Microbial Whole Cell Bioconversion

Protein Modelling Highlighted Key Catalytic Sites Involved in Position-Specific Glycosylation of Isoflavonoids

Uridine diphosphate glycosyltransferases (UGTs) are known for promiscuity towards sugar acceptors, a valuable characteristic for host plants but not desirable for heterologous biosynthesis. UGTs characterized for the O-glycosylation of isoflavonoids have shown a variable efficiency, substrate preference, and OH site specificity. Thus, 22 UGTs with reported isoflavonoid O-glycosylation activity were analyzed and ranked for OH site specificity and catalysis efficiency. Multiple-sequence alignment (MSA) showed a 33.2% pairwise identity and 4.5% identical sites among selected UGTs. MSA and phylogenetic analysis highlighted a comparatively higher amino acid substitution rate in the N-terminal domain that likely led to a higher specificity for isoflavonoids. Based on the docking score, OH site specificity, and physical and chemical features of active sites, selected UGTs were divided into three groups. A significantly high pairwise identity (67.4%) and identical sites (31.7%) were seen for group 1 UGTs. The structural and chemical composition of active sites highlighted key amino acids that likely define substrate preference, OH site specificity, and glycosylation efficiency towards selected (iso)flavonoids. In conclusion, physical and chemical parameters of active sites likely control the position-specific glycosylation of isoflavonoids. The present study will help the heterologous biosynthesis of glycosylated isoflavonoids and protein engineering efforts to improve the substrate and site specificity of UGTs.

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.

Engineering Escherichia coli for Conversion of Dietary Isoflavones in the Gut

Introducing metabolic pathways to the gut is important to tailor the biochemical components ultimately absorbed by the host. Given identical diets, hosts possessing different consortia of gut bacteria can exhibit distinct health outcomes regulated by metabolic capabilities of the gut microbiota. The disparate competency of the population to metabolize isoflavones, such as dietary daidzein, has shown health benefits for those individuals possessing gut bacteria capable of producing equol from daidzein-rich diets. To begin addressing health inequalities due to gut metabolic pathway deficiencies, we developed a probiotic that allows metabolism of isoflavones to provide a gut phenotype paralleling that of natural equol producers. Toward this goal, we engineered Escherichia coli to produce the enzymes necessary for conversion of daidzein to equol, and as demonstrated in a murine model, these bacteria enabled elevated serum equol levels to dietary daidzein, thus serving as a starting point for more sophisticated systems.

Biocatalytic synthesis and evaluation of antioxidant and antibacterial activities of hydroxyequols

Hydroxyequols are promising analogues of the biologically active flavonoid, equol. We recently found that the flavin-dependent monooxygenase HpaB_ro-3 of Rhodococcus opacus regioselectively synthesizes 3'-hydroxyequol from equol, whereas HpaB_pl-1 of Photorhabdus luminescens synthesizes 6-hydroxyequol. In this study, we investigated the cascade synthesis of a dihydroxyequol compound from equol using these two enzymes. When Escherichia coli cells expressing HpaB_ro-3 and cells expressing HpaB_pl-1 were simultaneously incubated with equol, the cells efficiently synthesized 6,3'-dihydroxyequol (8.7 mM, 2.4 g/L) via 3'- and 6-hydroxyequols in one pot. The antioxidant activity of the equol derivatives increased with an increase in the number of hydroxyl groups on the equol scaffold. 6,3'-Dihydroxyequol exhibited potent antioxidant activity. In addition, 6-hydroxyequol significantly inhibited the growth of E. coli. Cell survival studies suggested that 6-hydroxyequol is a bactericidal rather than bacteriostatic compound. To our knowledge, this is the first report describing the antibacterial activity of hydroxyequols.

Regioselective One-Pot Synthesis of Hydroxy-(S)-Equols Using Isoflavonoid Reductases and Monooxygenases and Evaluation of the Hydroxyequol Derivatives as Selective Estrogen Receptor Modulators and Antioxidants

Several regiospecific enantiomers of hydroxy-(S)-equol (HE) were enzymatically synthesized from daidzein and genistein using consecutive reduction (four daidzein-to-equol–converting reductases) and oxidation (4-hydroxyphenylacetate 3-monooxygenase, HpaBC). Despite the natural occurrence of several HEs, most of them had not been studied owing to the lack of their preparation methods. Herein, the one-pot synthesis pathway of 6-hydroxyequol (6HE) was developed using HpaBC (EcHpaB) from Escherichia coli and (S)-equol-producing E. coli, previously developed by our group. Based on docking analysis of the substrate or products, a potential active site and several key residues for substrate binding were predicted to interpret the (S)-equol hydroxylation regioselectivity of EcHpaB. Through investigating mutations on the key residues, the T292A variant was verified to display specific mono-ortho-hydroxylation activity at C6 without further 3′-hydroxylation. In the consecutive oxidoreductive bioconversion using T292A, 0.95 mM 6HE could be synthesized from 1 mM daidzein, while 5HE and 3′HE were also prepared from genistein and 3′-hydroxydaidzein (3′HD or 3′-ODI), respectively. In the following efficacy tests, 3′HE and 6HE showed about 30∼200-fold higher EC50 than (S)-equol in both ERα and ERβ, and they did not have significant SERM efficacy except 6HE showing 10% lower β/α ratio response than that of 17β-estradiol. In DPPH radical scavenging assay, 3′HE showed the highest antioxidative activity among the examined isoflavone derivatives: more than 40% higher than the well-known 3′HD. In conclusion, we demonstrated that HEs could be produced efficiently and regioselectively through the one-pot bioconversion platform and evaluated estrogenic and antioxidative activities of each HE regio-isomer for the first time.

An improved whole‐cell biotransformation system for ( S )‐equol production

(S)‐equol, the most active metabolite of the soybean isoflavones in vivo, has exhibited various biological activities and clinical benefits. Existing studies on the heterologous biosynthesis of (S)‐equol via the engineered E. coli constructed have been significantly progressed. In the present study, the engineered E. coli was further improved to be more suitable for (S)‐equol production. The four enzymes involved in the biosynthesis of (S)‐equol and another GDH for NADPH regeneration were combined to construct the recombinant E. coli BL21(DE3). The optimal conditions for (S)‐equol production were explored, respectively. The yield of equol reached 98.05% with 1 mM substrate daidzein and 4% (wt/vol) glucose. Even when the substrate concentration increased to 1.5 mM, (S)‐equol could maintain a high yield of 90.25%. Based on the 100 ml one‐pot reaction system, (S)‐equol was produced with 223.6 mg/L in 1.5 h. The study presented a more suitable engineered E. coli for the production of (S)‐equol.

Heterologous production of equol by lactic acid bacteria strains in culture medium and food

The isoflavones daidzin and genistin, present in soybeans, can be transformed by the intestinal microbiota into equol and 5-hydroxy-equol, compounds with enhanced availability and bioactivity, although these are only produced by a fraction of the population. Hence, there is an interest in the production of these compounds, although, to date, few bacteria with biotechnological interest and applicability in food have been found able to produce equol. In order to obtain lactic acid bacteria able to produce equol, the daidzein reductase (dzr), dihydrodaidzein reductase (ddr), tetrahydrodaidzein reductase (tdr) and dihydrodaidzein racemase (ifcA) genes, from Slackia isoflavoniconvertens DSM22006, were cloned into the vector pNZ:TuR, under a strong constitutive promoter (TuR). Lactococcus lactis MG1363, Lacticaseibacillus casei BL23, Lactiplantibacillus plantarum WCFS1, Limosilactobacillus fermentum INIA 584L and L. fermentum INIA 832L, harbouring pNZ:TuR.tdr.ddr, were able to produce equol from dihydrodaidzein, while L. fermentum strains showed also production of 5-hydroxy-equol from dihydrogenistein. The metabolization of daidzein and genistein by the combination of strains harbouring pNZ:TuR.dzr and pNZ:TuR.tdr.ddr showed similar results, and the addition of the correspondent strain harbouring pNZ:TuR.ifcA resulted in an increase of equol production, but only in the L. fermentum strains. This pattern of equol and 5-hydroxy-equol production by L. fermentum strains was also confirmed in cow's milk supplemented with daidzein and genistein and incubated with the different combination of strains harbouring the constructed plasmids. Bacteria generally recognized as safe (GRAS), such as the lactic acid bacteria species used in this work, harbouring these plasmids, would be of value for the development of fermented vegetal foods enriched in equol and 5-hydroxy-equol.

Heterologous expression of equol biosynthesis genes from Adlercreutzia equolifaciens

Equol is the isoflavone-derived metabolite with the greatest estrogenic and antioxidant activity. It is produced from daidzein by fastidious and oxygen-susceptible intestinal bacteria, which hinders their use at an industrial scale. Therefore, expressing the equol production machinery into easily-cultivable hosts would expedite the heterologous production of this compound. In this work, four genes (racemase, tdr, ddr and dzr) coding for key enzymes involved in equol production in Adlercreutzia equolifaciens DSM19450^T were synthesized and cloned in a pUC-derived vector (pUC57-equol) that was introduced in Escherichia coli. Recombinant clones of E. coli produced equol in cultures supplemented with daidzein (equol precursor) and dihydrodaidzein (intermediate compound). To check whether equol genes were expressed in Gram-positive bacteria, the pUC57-equol construct was cloned into the low-copy-number vector pIL252, and the new construct (pIL252-pUC57-equol) introduced into model strains of Lacticaseibacillus casei and Lactococcus lactis. L. casei clones carrying pIL252-pUC57-equol produced a small amount of equol from dihydrodaidzein but not from daidzein, while L. lactis recombinant clones produced no equol from either of the substrates. This is the first time that A. equolifaciens equol genes have been cloned and expressed in heterologous hosts. E. coli clones harboring pUC57-equol could be used for biotechnological production of equol.

Exercise and/or Genistein Treatment Impact Gut Microbiota and Inflammation after 12 Weeks on a High-Fat, High-Sugar Diet in C57BL/6 Mice

Genistein (Gen) and exercise (Exe) have been postulated as potential strategies to ameliorate obesity, inflammation, and gut microbiota (GM) with promising results. However, the impact of the combination of both Exe and Gen is yet to be investigated. We aimed to analyze the impacts of Exe, Gen, and their combined effects on GM and inflammation in mice after a 12-week high-fat, high-sugar diet (HFD). Eighty-three C57BL/6 mice were randomized to control, HFD, HFD + Exe, HFD + Gen, or HFD + Exe + Gen. The V4 region of the 16S rRNA gene was analyzed with Illumina MiSeq. Serum samples were used to analyze interleukin (Il)-6 and Tumor Necrosis Factor alpha (TNF-alpha). The HFD + Exe and HFD + Exe + Gen treatments resulted in significantly greater microbial richness compared to HFD. All the treatments had a significantly different impact on the GM community structure. Ruminococcus was significantly more abundant after the HFD + Exe + Gen treatment when compared to all the other HFD groups. Exe + Gen resulted in serum Il-6 concentrations similar to that of controls. TNF-alpha concentrations did not differ by treatment. Overall, Exe had a positive impact on microbial richness, and Ruminococcus might be the driving bacteria for the GM structure differences. Exe + Gen may be an effective treatment for preventing HFD-induced inflammation.

Metabolism of Soy Isoflavones by Intestinal Bacteria: Genome Analysis of an Adlercreutzia Equolifaciens Strain That Does Not Produce Equol

Isoflavones are transformed in the gut into more estrogen-like compounds or into inactive molecules. However, neither the intestinal microbes nor the pathways leading to the synthesis of isoflavone-derived metabolites are fully known. In the present work, 73 fecal isolates from three women with an equol-producing phenotype were considered to harbor equol-related genes by qPCR. After typing, 57 different strains of different taxa were tested for their ability to act on the isoflavones daidzein and genistein. Strains producing small to moderate amounts of dihydrodaidzein and/or O-desmethylangolensin (O-DMA) from daidzein and dihydrogenistein from genistein were recorded. However, either alone or in several strain combinations, equol producers were not found, even though one of the strains, W18.34a (also known as IPLA37004), was identified as Adlercreutzia equolifaciens, a well-described equol-producing species. Analysis and comparison of A. equolifaciens W18.34a and A. equolifaciens DSM19450^T (an equol producer bacterium) genome sequences suggested a deletion in the former involving a large part of the equol operon. Furthermore, genome comparison of A. equolifaciens and Asaccharobacter celatus (other equol-producing species) strains from databases indicated many of these also showed deletions within the equol operon. The present results contribute to our knowledge to the activity of gut bacteria on soy isoflavones.

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.

Effects of Phytoestrogens on the Developing Brain, Gut Microbiota, and Risk for Neurobehavioral Disorders

Many pregnant and nursing women consume high amounts of soy and other plant products that contain phytoestrogens, such as genistein (GEN) and daidzein. Infants may also be provided soy based formulas. With their ability to bind and activate estrogen receptors (ESR) in the brain, such compounds can disrupt normal brain programming and lead to later neurobehavioral disruptions. However, other studies suggest that maternal consumption of soy and soy based formulas containing such phytoestrogens might lead to beneficial behavioral effects. Select gut microbes might also convert daidzein and to a lesser extent genistein to even more potent forms, e.g., equol derivatives. Thus, infant exposure to phytoestrogens may result in contrasting effects dependent upon the gut flora. It is also becoming apparent that consumption or exposure to these xenoestrogens may lead to gut dysbiosis. Phytoestrogen-induced changes in gut bacteria might in turn affect the brain through various mechanisms. This review will consider the evidence to date in rodent and other animal models and human epidemiological data as to whether developmental exposure to phytoestrogens, in particular genistein and daidzein, adversely or beneficially impact offspring neurobehavioral programming. Consideration will be given to potential mechanisms by which such compounds might affect neurobehavioral responses. A better understanding of effects perinatal exposure to phytoestrogen can exert on brain programming will permit pregnant women and those seeking to become pregnant to make better-educated choices. If phytoestrogen-induced gut dysbiosis contributes to neurobehavioral disruptions, remediation strategies may be designed to prevent such gut microbiota alterations and thereby improve neurobehavioral outcomes.

Transcriptional Regulation of the Equol Biosynthesis Gene Cluster in Adlercreutzia equolifaciens DSM19450T

Given the emerging evidence of equol’s benefit to human health, understanding its synthesis and regulation in equol-producing bacteria is of paramount importance. Adlercreutzia equolifaciens DSM19450^T is a human intestinal bacterium—for which the whole genome sequence is publicly available—that produces equol from the daidzein isoflavone. In the present work, daidzein (between 50 to 200 μM) was completely metabolized by cultures of A. equolifaciens DSM19450^T after 10 h of incubation. However, only about one third of the added isoflavone was transformed into dihydrodaidzein and then into equol. Transcriptional analysis of the ORFs and intergenic regions of the bacterium’s equol gene cluster was therefore undertaken using RT-PCR and RT-qPCR techniques with the aim of identifying the genetic elements of equol biosynthesis and its regulation mechanisms. Compared to controls cultured without daidzein, the expression of all 13 contiguous genes in the equol cluster was enhanced in the presence of the isoflavone. Depending on the gene and the amount of daidzein in the medium, overexpression varied from 0.5- to about 4-log₁₀ units. Four expression patterns of transcription were identified involving genes within the cluster. The genes dzr, ddr and tdr, which code for daidzein reductase, dihydrodaidzein reductase and tetrahydrodaidzein reductase respectively, and which have been shown involved in equol biosynthesis, were among the most strongly expressed genes in the cluster. These expression patterns correlated with the location of four putative ρ-independent terminator sequences in the cluster. All the intergenic regions were amplified by RT-PCR, indicating the operon to be transcribed as a single RNA molecule. These findings provide new knowledge on the metabolic transformation of daidzein into equol by A. equolifaciens DSM19450^T, which might help in efforts to increase the endogenous formation of this compound and/or its biotechnological production.

Natural Estrogen Receptor Modulators and Their Heterologous Biosynthesis

Estrogen receptors (ERs) are transcription factors highly involved in physiological development and metabolism in the human body. They also play important roles in the treatment of cancer and metabolic diseases. Chemicals that interact with ERs can be used to treat diseases and maintain health. Phytoestrogens are natural chemicals that have been documented to possess significant ER modulatory activities. However, since phytoestrogens usually exist at low quantities in nature, heterologous biosynthesis techniques have quickly developed in recent years in order meet the demands for needed therapeutic amounts. In this review, the performance of phytoestrogens as ER modulators is described along with recent advances in biosynthesis techniques.

Monooxygenase-catalyzed regioselective hydroxylation for the synthesis of hydroxyequols

A one-step product-selective approach for synthesizing hydroxyequols from equol using oxidation biocatalysts was developed.

Soy-Induced Fecal Metabolome Changes in Ovariectomized and Intact Female Rats: Relationship with Cardiometabolic Health

Phytoestrogens are plant-derived compounds found in a variety of foods, most notably, soy. These compounds have been shown to improve immuno-metabolic health, yet mechanisms remain uncertain. We demonstrated previously that dietary phytoestrogen-rich soy (SOY) rescued metabolic dysfunction/inflammation following ovariectomy (OVX) in female rats; we also noted remarkable shifts in gut microbiota in SOY vs control diet-fed rats. Importantly, specific bacteria that significantly increased in those fed the SOY correlated positively with several favorable host metabolic parameters. One mechanism by which gut microbes might lead to such host effects is through production of bacterial metabolites. To test this possibility, we utilized non-targeted gas chromatography-mass spectrometry (GCMS) to assess the fecal metabolome in those previously studied animals. Partial least square discriminant analysis (PLSDA) revealed clear separation of fecal metabolomes based on diet and ovarian state. In particular, SOY-fed animals had greater fecal concentrations of the beneficial bacterial metabolite, S-equol, which was positively associated with several of the bacteria upregulated in the SOY group. S-equol was inversely correlated with important indicators of metabolic dysfunction and inflammation, suggesting that this metabolite might be a key mediator between SOY and gut microbiome-positive host health outcomes.

Recent advances in the microbial hydroxylation and reduction of soy isoflavones

Soy isoflavones are naturally occurring phytochemicals, which are biotransformed into functional derivatives through oxidative and reductive metabolic pathways of diverse microorganisms. Such representative derivatives, ortho-dihydroxyisoflavones (ODIs) and equols, have attracted great attention for their versatile health benefits since they were found from soybean fermented foods and human intestinal fluids. Recently, scientists in food technology, nutrition and microbiology began to understand their correct biosynthetic pathways and nutraceutical values, and have attempted to produce the valuable bioactive compounds using microbial fermentation and whole-cell/enzyme-based biotransformation. Furthermore, artificial design of microbial catalysts and/or protein engineering of oxidoreductases were also conducted to enhance production efficiency and regioselectivity of products. This minireview summarizes and introduces the past year's studies and recent advances in notable production of ODIs and equols, and provides information on available microbial species and their catalytic performance with perspectives on industrial application.

Metabolic engineering of glycosylated polyketide biosynthesis

Microbial cell factories are extensively used for the biosynthesis of value-added chemicals, biopharmaceuticals, and biofuels. Microbial biosynthesis is also realistic for the production of heterologous molecules including complex natural products of plant and microbial origin. Glycosylation is a well-known post-modification method to engineer sugar-functionalized natural products. It is of particular interest to chemical biologists to increase chemical diversity of molecules. Employing the state-of-the-art systems and synthetic biology tools, a range of small to complex glycosylated natural products have been produced from microbes using a simple and sustainable fermentation approach. In this context, this review covers recent notable metabolic engineering approaches used for the biosynthesis of glycosylated plant and microbial polyketides in different microorganisms. This review article is broadly divided into two major parts. The first part is focused on the biosynthesis of glycosylated plant polyketides in prokaryotes and yeast cells, while the second part is focused on the generation of glycosylated microbial polyketides in actinomycetes.

Polymeric solvent engineering for gram/liter scale production of a water-insoluble isoflavone derivative, (S)-equol

A potent phytoestrogen, (S)-equol, is a promising isoflavone derivative drawing our great attention owing to its various biological and clinical benefits. Through selective activation of the estrogen receptor ERβ or androgen receptor, (S)-equol reduces menopausal symptoms, osteoporosis, skin aging, hair loss, and incidence of prostate or ovarian cancers without adverse effects. Traditional biosynthesis of (S)-equol exploited non-productive natural equol-producing anaerobic bacteria that mainly belong to Coriobacteriaceae isolated from human intestine. Recently, we developed a recombinant Escherichia coli strain which could convert daidzein into (S)-equol effectively under an aerobic condition. However, the yield was limited up to about the 200 mg/L level due to unknown reasons. In this study, we identified that the bottleneck of the limited production was the low solubility of isoflavone (i.e., 2.4 mg/L) in the reaction medium. In order to solve the solubility problem without harmful effect to the whole-cell catalyst, we applied commercial hydrophilic polymers (HPs) and a polar aprotic co-solvent in the reaction medium. Among the examined water-soluble polymers, polyvinylpyrrolidone (PVP)-40k was verified as the most promising supplement which increased daidzein solubility by 40 times and (S)-equol yield up to 1.22 g/L, the highest ever reported and the first g/L level biotransformation. Furthermore, PVP-40k was verified to significantly increase the solubilities of other water-insoluble natural polyphenols in aqueous solution. We suggest that addition of both HP and polar aprotic solvent in the reaction mixture is a powerful alternative to enhance production of polyphenolic chemicals rather than screening appropriate organic solvents for whole-cell catalysis of polyphenols.