Profiling of Phenolic Metabolites in Feces from Menopausal Women after Long-Term Isoflavone Supplementation

Biosynthesis of (S)-Equol from Soy Whey by Metabolically Engineered Escherichia coli

(S)-Equol is one of the most bioactive metabolites of the isoflavones with immense nutritional and pharmaceutical value. Soy whey is the major liquid byproduct of the soy product processing industries that is rich in nutrients and (S)-equol biosynthetic precursor daidzin. However, it is usually disposed into the sewage, causing high environmental contamination. Herein, we constructed a recombinant Escherichia coli for the biosynthesis of (S)-equol from soy whey. First, we evaluated daidzin-specific transporters and optimized the anaerobically induced P_nar in the (S)-equol biosynthesis cassette to produce (S)-equol from daidzin. Then, sucrase and α-galactosidase were co-expressed to confer sucrose, stachyose, and raffinose utilization capacity on E. coli. Meanwhile, EIIBCA^glc was inactivated to eliminate the daidzin transport inhibition induced by glucose. Finally, combining these strategies and optimizing the fermentation conditions, the optimal strain produced 91.5 mg/L of (S)-equol with a yield of 0.96 mol/mol substrates in concentrated soy whey. Overall, this new strategy is an attractive route to broaden the applications of soy whey and achieve the eco-friendly production of (S)-equol.

3-Hydroxyphenylacetic Acid: A Blood Pressure-Reducing Flavonoid Metabolite

Regular intake of polyphenol-rich food has been associated with a wide variety of beneficial health effects, including the prevention of cardiovascular diseases. However, the parent flavonoids have mostly low bioavailability and, hence, their metabolites have been hypothesized to be bioactive. One of these metabolites, 3-hydroxyphenylacetic acid (3-HPAA), formed by the gut microbiota, was previously reported to exert vasorelaxant effects ex vivo. The aim of this study was to shed more light on this effect in vivo, and to elucidate the mechanism of action. 3-HPAA gave rise to a dose-dependent decrease in arterial blood pressure when administered i.v. both as a bolus and infusion to spontaneously hypertensive rats. In contrast, no significant changes in heart rate were observed. In ex vivo experiments, where porcine hearts from a slaughterhouse were used to decrease the need for laboratory animals, 3-HPAA relaxed precontracted porcine coronary artery segments via a mechanism partially dependent on endothelium integrity. This relaxation was significantly impaired after endothelial nitric oxide synthase inhibition. In contrast, the blockade of SKCa or IKCa channels, or muscarinic receptors, did not affect 3-HPAA relaxation. Similarly, no effects of 3-HPAA on cyclooxygenase nor L-type calcium channels were observed. Thus, 3-HPAA decreases blood pressure in vivo via vessel relaxation, and this mechanism might be based on the release of nitric oxide by the endothelial layer.

Could Fecal Phenylacetic and Phenylpropionic Acids Be Used as Indicators of Health Status?

Although most of the health effects attributed to polyphenols may be linked to their phenolic-derived metabolites, the role of the intestinal derived-phenolics in human health is still far from being well understood. We determined the profile of fecal phenolic-derived metabolites, microbiota, biomarkers of oxidative stress and inflammation, and daily intake of bioactive compounds in 71 elderly volunteers. Phenylacetic and phenylpropionic acids were the main phenolic metabolites present in feces. From them, phenylacetic acid was related with a more pro-oxidant and immune stimulated status, and both were negatively associated with fecal propionate, whereas phenylpropionic acid was directly related with the fecal concentration of acetate. Moreover, phenylacetic acid was negatively associated with the Bacteroides group and Clostridium cluster XIVa and positively with Lactobacillus. These results provide a rationale to explore the potential of fecal microbial phenolic-derived metabolites as possible biomarkers of health status in future studies focused on the elderly population.

Effect of Soy Isoflavones on Growth of Representative Bacterial Species from the Human Gut

The present work aimed to assess the susceptibility of dominant and representative bacterial populations from the human gut to isoflavones and their metabolites. To do so, the minimum inhibitory concentration (MIC) of isoflavone glycosides, isoflavone aglycones, and equol to 37 bacterial strains was determined by broth microdilution. Additionally, for 10 representative strains, growth curves, growth rate (μ), and optical density (OD600 nm) of the cultures at 24 h were also determined. MICs of daidzin, genistin, daidzein, and genistein were >2048 μg mL-1 for all strains assayed, while that of equol ranged from 16 μg mL-1 for Bifidobacterium animalis subsp. animalis to >2048 μg mL-1 for Enterobacteriaceae strains. Changes in growth curves, μ, and final OD were observed among the species in the presence of all tested compounds. Genistein reduced μ of Bacteroides fragilis, Lactococcus lactis subsp. lactis, and Slackia equolifaciens, while both genistein and equol increased that of Lactobacillus rhamnosus and Faecalibacterium prausnitzii. Compared to controls, lower final OD in the presence of aglycones and equol were recorded for some strains but were higher for others. Altogether, the results suggest that isoflavone-derived compounds could modify numbers of key bacterial species in the gut, which might be associated with their beneficial properties.

Adherence to a Mediterranean Diet Influences the Fecal Metabolic Profile of Microbial-Derived Phenolics in a Spanish Cohort of Middle-Age and Older People

Despite the evidence regarding the influence of certain polyphenol food sources on the metabolic profile in feces, the association between the different phenolics provided by the diet and the fecal phenolic profile has not been elucidated. In this study, the composition of phenolic metabolites in fecal solutions was analyzed by UPLC-ESI-MS/MS in 74 volunteers. This fecal phenolic profile showed a high interindividual variation of the different compounds analyzed, phenylacetic and phenylpropionic acids being the major classes of phenolic metabolites excreted in feces. Subjects with higher adherence to a Mediterranean dietary pattern presented greater fecal concentrations of benzoic and 3-hydroxyphenylacetic acids, positively correlated with the intake of the principal classes and subclasses of polyphenols and fibers, and higher levels of Clostridium cluster XVIa and Faecalibacterium prausnitzii. These results provide a link among the Mediterranean dietary pattern, the bioactive compounds of the diet, and the fecal metabolic phenolic profile.

Gene Expression Patterns Are Altered in Athymic Mice and Metabolic Syndrome Factors Are Reduced in C57BL/6J Mice Fed High-Fat Diets Supplemented with Soy Isoflavones

Soy isoflavones exert beneficial health effects; however, their potential to ameliorate conditions associated with the metabolic syndrome (MetS) has not been studied in detail. In vitro and in vivo models were used to determine the effect of isoflavones on lipid metabolism, inflammation, and oxidative stress. In nude mice, consumption of Novasoy (NS) increased cholesterol and lipid metabolism gene expression, including Scd-1 (27.7-fold), Cyp4a14 (35.2-fold), and Cyp4a10 (9.5-fold), and reduced anti-inflammatory genes, including Cebpd (16.4-fold). A high-fat (HF) diet containing 0.4% (w/w) NS for 10 weeks significantly reduced percent weight gain (74.6 ± 2.5 vs 68.6 ± 3.5%) and hepatic lipid accumulation (20 ± 1.2 vs 27 ± 1.5%), compared to HF alone (p < 0.05) in C57BL/6J mice. NS also increased lipid oxidation and antioxidant gene expression while decreasing inflammatory cytokines. In vitro analysis in HepG2 cells revealed that genistein dose-dependently decreases oleic acid-induced lipid accumulation. Soy isoflavones may ameliorate symptoms associated with MetS via anti-inflammatory, antioxidant, and hypolipidemic modulation.