Synthetic and analytical strategies for the quantification of phenyl-γ-valerolactone conjugated metabolites in human urine

Using Targeted Metabolomics to Unravel Phenolic Metabolites of Plant Origin in Animal Milk

Milk holds a high nutritional value and is associated with diverse health benefits. The understanding of its composition of (poly)phenolic metabolites is limited, which necessitates a comprehensive evaluation of the subject. This study aimed at analyzing the (poly)phenolic profile of commercial milk samples from cows and goats and investigating their sterilization treatments, fat content, and lactose content. Fingerprinting of phenolic metabolites was achieved by using ultra-high-performance liquid chromatography coupled with triple-quadrupole mass spectrometry (UHPLC-QqQ-MS/MS). Two hundred and three potential microbial and phase II metabolites of the main dietary (poly)phenols were targeted. Twenty-five metabolites were identified, revealing a diverse array of phenolic metabolites in milk, including isoflavones and their microbial catabolites equol and O-desmethylangolensin, phenyl-γ-valerolactones (flavan-3-ol microbial catabolites), enterolignans, urolithins (ellagitannin microbial catabolites), benzene diols, and hippuric acid derivates. Goat's milk contained higher concentrations of these metabolites than cow's milk, while the sterilization process and milk composition (fat and lactose content) had minimal impact on the metabolite profiles. Thus, the consumption of goat's milk might serve as a potential means to supplement bioactive phenolic metabolites, especially in individuals with limited production capacity. However, further research is needed to elucidate the potential health effects of milk-derived phenolics.

Mechanism of procyanidins for health functionality by improving the intestinal environment

Procyanidins are one of the polyphenols consisting of multiple flavan-3-ols (eg epicatechin). They have a complex chemical structure, with the degree of polymerization and linked position of flavan-3-ols varying among various foods, such as apples and chocolate. Physiological functional studies of procyanidins have investigated their mechanisms in cells and animals based on their antioxidant effects. Recently, the intestinal environment, including the intestinal microflora, has played an important role in the energy metabolism and health status of the host. Regulation of the intestinal environment by dietary polyphenols is becoming a new concept in health functions, and we have begun to investigate the mechanism of apple procyanidins, focusing on the gut microbiota and metabolites in our functional research. In this minireview, we will discuss the effects of procyanidin ingestion on the gut microbiota and metabolites.

(Poly)phenol-related gut metabotypes and human health: an update

Dietary (poly)phenols have received great interest due to their potential role in the prevention and management of non-communicable diseases. In recent years, a high inter-individual variability in the biological response to (poly)phenols has been demonstrated, which could be related to the high variability in (poly)phenol gut microbial metabolism existing within individuals. An interplay between (poly)phenols and the gut microbiota exists, with (poly)phenols being metabolised by the gut microbiota and their metabolites modulating gut microbiota diversity and composition. A number of (poly)phenol metabolising phenotypes or metabotypes have been proposed, however, potential metabotypes for most (poly)phenols have not been investigated, and the relationship between metabotypes and human health remains ambiguous. This review presents updated knowledge on the reciprocal interaction between (poly)phenols and the gut microbiome, associated gut metabotypes, and subsequent impact on human health.

Unraveling the parahormetic mechanism underlying the health-protecting effects of grapeseed procyanidins

Proanthocyanidins (PACs), the predominant constituents within Grape Seed Extract (GSE), are intricate compounds composed of interconnected flavan-3-ol units. Renowned for their health-affirming properties, PACs offer a shield against a spectrum of inflammation associated diseases, such as diabetes, obesity, degenerations and possibly cancer. While monomeric and dimeric PACs undergo some absorption within the gastrointestinal tract, their larger oligomeric and polymeric counterparts are not bioavailable. However, higher molecular weight PACs engage with the colonic microbiota, fostering the production of bioavailable metabolites that undergo metabolic processes, culminating in the emergence of bioactive agents capable of modulating physiological processes. Within this investigation, a GSE enriched with polymeric PACs was employed to explore in detail their impact. Through comprehensive analysis, the present study unequivocally verified the gastrointestinal-mediated transformation of medium to high molecular weight polymeric PACs, thereby establishing the bioaccessibility of a principal catabolite termed 5-(3',4'-dihydroxyphenyl)-γ-valerolactone (VL). Notably, our findings, encompassing cell biology, chemistry and proteomics, converge to the proposal of the notion of the capacity of VL to activate, upon oxidation to the corresponding quinone, the nuclear factor E2-related factor 2 (Nrf2) pathway-an intricate process that incites cellular defenses and mitigates stress-induced responses, such as a challenge brought by TNFα. This mechanistic paradigm seamlessly aligns with the concept of para-hormesis, ultimately orchestrating the resilience to stress and the preservation of cellular redox equilibrium and homeostasis as benchmarks of health.

Nutrikinetics and urinary excretion of phenolic compounds after a 16-week supplementation with a flavanone-rich ingredient

Background: Polyphenols are a broad group of compounds with a complex metabolic fate. Flavanones and their metabolites provide cardiovascular protection and assistance in long-term body composition management. Objective: This study evaluates the nutrikinetics and the bioavailability of phenolic compounds after both acute and chronic supplementation with a flavanone-rich product, namely Sinetrol® Xpur, in healthy overweight and obese volunteers. Design: An open-label study including 20 volunteers was conducted for 16 weeks. Participants received Sinetrol® Xpur, either a low dose (900 mg per day) or a high dose (1800 mg per day), in capsules during breakfast and lunch. They were advised to follow an individualized isocaloric diet and avoid a list of polyphenol-rich foods 48 hours before and during the pharmacokinetic measurements. Results: Over 20 phase II and colonic metabolites were measured in the plasma. Two peaks were observed at 1 h and 7h-10 h after the first capsule ingestion. No significant differences in the AUC were observed in circulating metabolites between both doses. In urine excretion, 53 metabolites were monitored, including human phase II and colonic metabolites, at weeks 1 and 16. Cumulative urine excretion was higher after the high dose than after the low dose in both acute and chronic studies. Total urinary metabolites were significantly lower in week 16 compared to week 1. Conclusion: Although the urinary excreted metabolites reduced significantly over 16 weeks, the circulating metabolites did not decrease significantly. This study suggests that chronic intake might not offer the same bioavailability as in the acute study, and this effect does not seem to be dose-dependent. The clinical trial registry number is NCT03823196.

Automated High-Throughput Quantification of Phenyl-γ-valerolactones and Creatinine in Urine by Laser Diode Thermal Desorption

Quantification of nutritional biomarkers is crucial to accurately assess the dietary intake of different classes of (poly)phenols in large epidemiological studies. High-throughput analysis is mandatory to apply this methodology in large cohorts. However, the current validated methods to quantify (poly)phenols metabolites in biological fluids use ultra performance liquid chromatography (UPLC), leading to analysis time of several minutes per sample. To significantly reduce the run time, we developed and validated a method to quantify in urine the flavan-3-ols biomarkers, phenyl-γ-valerolactones (PVLs), using laser diode thermal desorption (LDTD). This mass spectrometry source allows direct introduction of sample extracts, resulting in analysis time of less than 10 s per sample. Also, to encompass the problem associated with the cost and availability of sulfated and glucuronide analytical standards, urine samples were subjected to enzymatic hydrolysis. Creatinine was also quantified to normalize the results obtained from the urinary spot. Results obtained with LDTD-MS/MS were cross-validated by UPLC-MS/MS using 155 urine samples. Coefficient of correlation was above 0.975 for PVLs and creatinine. For all analytes, the accuracy was between 90% and 113% by LDTD-MS/MS. Altogether, sample preparation was fully automated to demonstrate the application potential of this method to large cohorts.

Performance of Urinary Phenyl-γ-Valerolactones as Biomarkers of Dietary Flavan-3-ol Exposure

BACKGROUND

Phenyl-γ-valerolactones (PVLs) have been identified as biomarkers of dietary flavan-3-ol exposure, although their utility requires further characterization.

OBJECTIVES

We investigated the performance of a range of PVLs as biomarkers indicative of flavan-3-ol intake.

METHODS

We report the results of 2 companion studies: a 5-way randomized crossover trial (RCT) and an observational cross-sectional study. In the RCT (World Health Organization, Universal Trial Number: U1111-1236-7988), 16 healthy participants consumed flavan-3-ol-rich interventions (of apple, cocoa, black tea, green tea, or water [control]) for 1 d each. First morning void samples and 24-h urine samples were collected with diet standardized throughout. For each participant, 1 intervention period was extended (to 2 d) to monitor PVL kinetics after repeat exposure. In the cross-sectional study, 86 healthy participants collected 24-h urine samples, and concurrent weighed food diaries from which flavan-3-ol consumption was estimated using Phenol-Explorer. A panel of 10 urinary PVLs was quantified using liquid chromatography tandem mass spectrometry.

RESULTS

In both studies, 2 urinary PVLs [5-(3'-hydroxyphenyl)-γ-valerolactone-4'-sulfate and putatively identified 5-(4'-hydroxyphenyl)-γ-valerolactone-3'-glucuronide] were the principal compounds excreted (>75%). In the RCT, the sum of these PVLs was significantly higher than the water (control) after each intervention; individually, there was a shift from sulfation toward glucuronidation as the total excretion of PVLs increased across the different interventions. In the extended RCT intervention period, no accumulation of these PVLs was observed after consecutive days of treatment, and after withdrawal of treatment on the third day, there was a return toward negligible PVL excretion. All results were consistent, whether compounds were measured in 24-h urine or first morning void samples. In the observational study, the sum of the principal PVLs correlated dose dependently (Rs = 0.37; P = 0.0004) with dietary flavan-3-ol intake, with similar associations for each individually.

CONCLUSIONS

Urinary 5-(3'-hydroxyphenyl)-γ-valerolactone-4'-sulfate and putatively identified 5-(4'-hydroxyphenyl)-γ-valerolactone-3'-glucuronide are recommended biomarkers for dietary flavan-3-ol exposure.

Association of dietary flavan-3-ol intakes with plasma phenyl-γ-valerolactones: analysis from the TUDA cohort of healthy older adults

BACKGROUND

Dietary polyphenols, including flavan-3-ols (F3O), are associated with better health outcomes. The relationship of plasma phenyl-γ-valerolactones (PVLs), the products of colonic bacterial metabolism of F3O, with dietary intakes is unclear.

OBJECTIVES

To investigate whether plasma PVLs are associated with self-reported intakes of total F3O and procyanidins+(epi)catechins.

DESIGN

We measured 9 PVLs by uHPLC-MS-MS in plasma from adults (>60y) in the Trinity-Ulster-Department of Agriculture (TUDA study (2008 to 2012; n=5186) and a follow-up subset (2014 to 2018) with corresponding dietary data (n=557). Dietary (poly)phenols collected by FFQ were analyzed using Phenol-Explorer.

RESULTS

Mean (95% confidence interval [CI]) intakes were estimated as 2283 (2213, 2352) mg/d for total (poly)phenols, 674 (648, 701) for total F3O, and 152 (146, 158) for procyanidins+(epi)catechins. Two PVL metabolites were detected in plasma from the majority of participants, 5-(hydroxyphenyl)-γ-VL-sulfate (PVL1) and 5-(4'-hydroxyphenyl)-γ-VL-3'-glucuronide (PVL2). The 7 other PVLs were detectable only in 1-32% of samples. Self-reported intakes (mg/d) of F3O (r = 0.113, P = 0.017) and procyanidin+(epi)catechin (r = 0.122, P = 0.010) showed statistically significant correlations with the sum of PVL1 and PVL 2 (PVL1+2). With increasing intake quartiles (Q1-Q4), mean (95% CI) PVL1+2 increased; from 28.3 (20.8, 35.9) nmol/L in Q1 to 45.2 (37.2, 53.2) nmol/L in Q4; P = 0.025, for dietary F3O, and from 27.4 (19.1, 35.8) nmol/L in Q1 to 46.5 (38.2, 54.9) nmol/L in Q4; P = 0.020, for procyanidins+(epi)catechins.

CONCLUSIONS

Of 9 PVL metabolites investigated, 2 were detected in most samples and were weakly associated with intakes of total F3O and procyanidins+(epi)catechins. Future controlled feeding studies are required to validate plasma PVLs as biomarkers of these dietary polyphenols.

Catechin Bioavailability Following Consumption of a Green Tea Extract Confection Is Reduced in Obese Persons without Affecting Gut Microbial-Derived Valerolactones

Obesity-related cardiometabolic disorders are driven by inflammation, oxidative stress, and gut dysbiosis. Green tea catechins protect against cardiometabolic disorders by anti-inflammatory, antioxidant, and prebiotic activities. However, whether obesity alters catechin bioavailability remains unknown. We hypothesized that obesity would decrease catechin bioavailability due to altered gut microbiota composition. Obese and healthy persons completed a pharmacokinetics trial in which a confection formulated with green tea extract (GTE; 58% epigallocatechin gallate, 17% epigallocatechin, 8% epicatechin, 6% epicatechin gallate) was ingested before collecting plasma and urine at timed intervals for up to 24 h. Stool samples were collected prior to confection ingestion. Catechins and γ-valerolactones were assessed by LC-MS. Obesity reduced plasma area under the curve (AUC_0-12h) by 24-27% and maximum plasma concentrations by 18-36% for all catechins. Plasma AUC_0-12h for 5'-(3',4'-dihydroxyphenyl)-γ-valerolactone and 5'-(3',4',5'-trihydroxyphenyl)-γ-valerolactone, as well as total urinary elimination of all catechins and valerolactones, were unaffected. ⍺-Diversity in obese persons was lower, while Slackia was the only catechin-metabolizing bacteria that was altered by obesity. Ascorbic acid and diversity metrics were correlated with catechin/valerolactone bioavailability. These findings indicate that obesity reduces catechin bioavailability without affecting valerolactone generation, urinary catechin elimination, or substantially altered gut microbiota populations, suggesting a gut-level mechanism that limits catechin absorption.

Exposure to (Poly)phenol Metabolites after a Fruit and Vegetable Supplement Intake: A Double-Blind, Cross-Over, Randomized Trial

Dietary (poly)phenol intake derived from the daily consumption of five portions of fruits and vegetables could protect against the development of non-communicable diseases. However, the general population does not meet the recommended intake. Supplementation with (poly)phenol-rich ingredients, within a varied and balanced diet, could help in filling this nutritional gap. This study aimed to validate the proof-of-concept of a (poly)phenolic supplementation developed to enhance the daily consumption of potentially bioactive compounds. Oxxynea^® is a (poly)phenol-rich ingredient developed to provide the quantity and the variety corresponding to five-a-day fruit and vegetable consumption. In this double-blind, randomized cross-over study, 10 participants were supplemented with 450 mg of a (poly)phenol-based supplement or a placebo. Pharmacokinetics and urinary excretion profiles were measured for 24 and 48 h, respectively, using UPHLC-MS/MS analysis. The pharmacokinetic profile displayed a triphasic absorption, indicating peaks of circulating metabolites at 1.75 ± 0.25 h, 4.50 ± 0.34 h, 9.50 ± 0.33 h and an average T_max (time of maximal plasma concentration) of 6.90 ± 0.96 h. Similarly, the urinary profile showed maximum metabolite excretion at 3-6 h, 6-10 h and 14-24 h after supplement consumption. Compared to individual metabolites belonging to different (poly)phenolic subfamilies, the total circulating and excreted metabolites showed a reduced coefficient of variation (CV 38%). The overall bioavailability estimated was 27.4 ± 3.4%. Oxxynea^® supplementation may provide a sustained exposure to several (poly)phenolic metabolites and catabolites and reduces the inter-individual variation that could arise from supplementing only one class of (poly)phenol.

Phenolic composition of grape pomace and its metabolism

Grape pomace is the most important residual after wine making, and it is considered to be a very abundant source for the extraction of a wide range of polyphenols. These polyphenols exhibit a variety of bioactivities, such as antioxidant, anti-inflammatory, and anti-cancer. They are also beneficial in alleviating metabolic syndrome and regulating intestinal flora, etc. These health effects are most likely contributed by polyphenol metabolite, which are formed by the grape pomace phenolics after a complex metabolic process in vivo. Therefore, understanding the phenolic composition of grape pomace and its metabolism is the basis for an in-depth study of the biological activity of grape pomace polyphenols. In this paper, we first summarize the composition of phenolics in grape pomace, then review the recent studies on the metabolism of grape pomace phenolics, including changes in phenolics in the gastrointestinal tract, their pharmacokinetics in the systemic circulation, the tissue distribution of phenolic metabolites, and the beneficial effects of metabolites on intestinal health, and finally summarize the effects of human health status and dietary fiber on the metabolism of grape polyphenols. It is expected to provide help for the in-depth research on the metabolism and biological activity of grape pomace polyphenol extracts, and to provide theoretical support for the development and utilization of grape pomace.

A Screening of Native (Poly)phenols and Gut-Related Metabolites on 3D HCT116 Spheroids Reveals Gut Health Benefits of a Flavan-3-ol Metabolite

SCOPE

Epidemiological evidence suggests that a reduced risk of colorectal cancer (CRC) is correlated with high consumption of fruits and vegetables, which are major sources of fiber and phytochemicals, such as flavan-3-ols. However, it remains unknown how these phytochemicals and their specific gut-related metabolites may alter cancer cell behavior.

METHODS AND RESULTS

A focused screening using native (poly)phenols and gut microbial metabolites (GMMs) on 3D HCT116 spheroids is carried out using a high-throughput imaging approach. Dose-responses, IC50 , and long-term exposure are calculated for the most promising native (poly)phenols and GMMs. As a result, this research shows that (poly)phenol catabolites may play a key role in preventing cancer propagation. Indeed, µM concentration levels of (4R)-5-(3',4'-dihydroxyphenyl)-γ-valerolactone significantly decrease spheroid size at early stages of spheroid aggregation and gene expression of matrix metalloproteinases.

CONCLUSION

A chronic exposure to (4R)-5-(3',4'-dihydroxyphenyl)-γ-valerolactone may lead to a reduced CRC risk. Daily intake of monomeric, oligomeric, and polymeric flavan-3-ols may increase the colonic concentrations of this metabolite, and, in turn, this compound may act locally interacting with intestinal epithelial cells, precancerous and cancer cells.

In Vitro Faecal Fermentation of Monomeric and Oligomeric Flavan-3-ols: Catabolic Pathways and Stoichiometry

SCOPE

The study evaluates the influence of flavan-3-ol structure on the production of phenolic catabolites, principally phenyl-γ-valerolactones (PVLs), and phenylvaleric acids (PVAs).

METHODS AND RESULTS

A set of 12 monomeric flavan-3-ols and proanthocyanidins (degree of polymerization (DP) of 2-5), are fermented in vitro for 24 h using human faecal microbiota, and catabolism is analyzed by UHPLC-ESI-MS/MS. Up to 32 catabolites strictly related to microbial catabolism of parent compounds are detected. (+)-Catechin and (-)-epicatechin have the highest molar mass recoveries, expressed as a percentage with respect to the incubated concentration (75 µmol L^-1 ) of the parent compound, for total PVLs and PVAs, both at 5 h (about 20%) and 24 h (about 40%) of faecal incubation. Only A-type dimer and B-type procyanidins underwent the ring fission step, and no differences are found in total PVL and PVA production (≃1.5% and 6.0% at 5 and 24 h faecal incubation, respectively) despite the different DPs.

CONCLUSION

The flavan-3-ol structure strongly affects the colonic catabolism of the native compounds, influencing the profile of PVLs and PVAs produced in vitro. This study opens new perspectives to further elucidate the colonic fate of oligomeric flavan-3-ols and their availability in producing bioactive catabolites.

LC-MS Characterization and Quantification of Known and Unknown (Poly)phenol Metabolites-Possible Pitfalls and Their Avoidance

This review focuses on the LC-MS characterization and quantification of dietary (poly)phenols and their metabolites. It draws attention to errors, omissions, and misunderstandings that appear frequently in published papers, and suggests strategies for their avoidance. Aspects covered include the use of authentic standards and surrogate reference materials, the importance of collecting and archiving Total Ion Current MS data, the limitations of using on-line compilations of accurate mass MS data to assign unknown components when multiple isomers are possible, and the often understated magnitude of person-to-person variation that may significantly impact at population level any potential health benefit.

Daily consumption of cranberry improves endothelial function in healthy adults: a double blind randomized controlled trial

Background: Previous studies indicate cardiovascular health benefits of cranberry juice consumption. However, whether daily consumption of whole cranberries will have sustained vascular benefits in healthy individuals is currently unknown. Objective: To investigate the vascular effects of acute and daily consumption of freeze dried whole cranberry in healthy men and how effects relate to circulating cranberry (poly)phenol metabolites. Methods: A double-blind, parallel-group, randomized controlled trial was conducted in 45 healthy male adults randomly allocated to 1 month daily consumption of either cranberry (9 g powder solubilized in water equivalent to 100 g of fresh cranberries, 525 mg total (poly)phenols) or control (9 g powder, no (poly)phenols). Flow-mediated dilation (FMD, primary outcome), pulse wave velocity (PWV), aortic augmentation index (AIx), blood pressure, heart rate, blood lipids, and blood glucose were assessed at baseline and at 2 h on day 1 and after 1 month. Plasma and 24 h-urine were analyzed before and after treatment using targeted quantitative LC-MS methods including 137 (poly)phenol metabolites. Results: Cranberry consumption significantly increased FMD at 2 h and 1-month (1.1% (95% CI: 1.1%, 1.8%); p_treatment ≤ 0.001; p_{treatment × time} = 0.606) but not PWV, AIx, blood pressure, heart rate, blood lipids, and glucose. Of the 56 and 74 (poly)phenol metabolites quantified in plasma and urine, 13 plasma and 13 urinary metabolites significantly increased 2 h post-consumption and on day 1, respectively, while 4 plasma and 13 urinary metabolites were significantly higher after 1-month of cranberry consumption, in comparison with control. A multi-variable stepwise linear regression analysis showed that plasma cinnamic acid-4'-glucuronide, 4-hydroxybenzoic acid-3-sulfate, 2,5-dihydroxybenzoic acid, 3'-hydroxycinnamic acid, and 5-O-caffeoylquinic acid were significant independent predictors of 2 h FMD effects (R² = 0.71), while 3'-hydroxycinnamic acid, 4-methoxycinnamic acid-3'-glucuronide, 3-(4'-methoxyphenyl)propanoic acid 3'-sulfate, and 3-(4'-methoxyphenyl)propanoic acid 3'-glucuronide predicted the 1-month FMD effects (R² = 0.52). Conclusions: Acute and daily consumption of whole cranberry powder for 1 month improves vascular function in healthy men and this is linked with specific metabolite profiles in plasma. The National Institutes of Health (NIH)-randomized trial records held on the NIH ClinicalTrials.gov website (NCT02764749). https://clinicaltrials.gov/ct2/show/NCT02764749.

Recent Analytical Approaches for the Study of Bioavailability and Metabolism of Bioactive Phenolic Compounds

The study of the bioavailability of bioactive compounds is a fundamental step for the development of applications based on them, such as nutraceuticals, functional foods or cosmeceuticals. It is well-known that these compounds can undergo metabolic reactions before reaching therapeutic targets, which may also affect their bioactivity and possible applications. All recent studies that have focused on bioavailability and metabolism of phenolic and terpenoid compounds have been developed because of the advances in analytical chemistry and metabolomics approaches. The purpose of this review is to show the role of analytical chemistry and metabolomics in this field of knowledge. In this context, the different steps of the analytical chemistry workflow (design study, sample treatment, analytical techniques and data processing) applied in bioavailability and metabolism in vivo studies are detailed, as well as the most relevant results obtained from them.

Purified recombinant enzymes efficiently hydrolyze conjugated urinary (poly)phenol metabolites

Purified recombinant enzymes are efficient at hydrolyzing microbial (poly)phenol metabolite phase II conjugates, and hence, can be used to accurately quantify them using unconjugated analytical standards.

Effect of different patterns of consumption of coffee and a cocoa-based product containing coffee on the nutrikinetics and urinary excretion of phenolic compounds

BACKGROUND

Coffee consumption is associated with a reduced risk of several chronic diseases in a dose-dependent manner. Chronic intake results in the transient appearance of bioactive phenolic metabolites in the circulatory system. However, there is a lack of information on the impact of different patterns of coffee consumption on plasma and urinary profiles of phenolic metabolites.

OBJECTIVES

Plasma and urinary phenolic metabolites were investigated following regular consumption of different daily dosages of coffee or cocoa-based products containing coffee (CBPCC) under a real-life setting.

METHODS

A repeated-dose, randomized, crossover human intervention was conducted with 21 healthy volunteers. For 1 mo, participants consumed 1) 1 cup of coffee (1C), 2) 3 cups of coffee (3C), or 3) 1 cup of coffee + 2 CBPCC twice daily (PC). Plasma and urine samples were collected over a 24-h period after each treatment. The nutrikinetics and urinary excretion of native, human phase II, and colonic metabolites were assessed.

RESULTS

A total of 51 (poly)phenolic metabolites were quantified, with 41 metabolites being strictly related to coffee consumption. Significant differences were observed among treatments for most of the metabolites. The metabolites present in the highest amounts were the hydroxycinnamate, phenylpropanoic acid, benzaldehyde, and benzene classes, along with (-)-epicatechin and phenyl-γ-valerolactone derivatives after PC treatment. Daily average concentrations did not exceed 200 nmol/L and were <100 nmol/L for most of the metabolites. The excretion of coffee phenolics ranged from 40% to 70% of intake, indicating that coffee hydroxycinnamates are notably more bioavailable than previously thought. Interindividual variability was also investigated.

CONCLUSIONS

The absorption, metabolism, nutrikinetic profile, and bioavailability of coffee phenolics were established for different patterns of coffee consumption under real-life conditions. This work provides the basis for further nutritional epidemiology research and mode-of-action cell-based studies. This study was registered at clinicaltrials.gov as NCT03166540.

Metabotypes of flavan-3-ol colonic metabolites after cranberry intake: elucidation and statistical approaches

Purpose

Extensive inter-individual variability exists in the production of flavan-3-ol metabolites. Preliminary metabolic phenotypes (metabotypes) have been defined, but there is no consensus on the existence of metabotypes associated with the catabolism of catechins and proanthocyanidins. This study aims at elucidating the presence of different metabotypes in the urinary excretion of main flavan-3-ol colonic metabolites after consumption of cranberry products and at assessing the impact of the statistical technique used for metabotyping.

Methods

Data on urinary concentrations of phenyl-γ-valerolactones and 3-(hydroxyphenyl)propanoic acid derivatives from two human interventions has been used. Different multivariate statistics, principal component analysis (PCA), cluster analysis, and partial least square-discriminant analysis (PLS-DA), have been considered.

Results

Data pre-treatment plays a major role on resulting PCA models. Cluster analysis based on k-means and a final consensus algorithm lead to quantitative-based models, while the expectation–maximization algorithm and clustering according to principal component scores yield metabotypes characterized by quali-quantitative differences in the excretion of colonic metabolites. PLS-DA, together with univariate analyses, has served to validate the urinary metabotypes in the production of flavan-3-ol metabolites and to confirm the robustness of the methodological approach.

Conclusions

This work proposes a methodological workflow for metabotype definition and highlights the importance of data pre-treatment and clustering methods on the final outcomes for a given dataset. It represents an additional step toward the understanding of the inter-individual variability in flavan-3-ol metabolism.

Trial registration

The acute study was registered at clinicaltrials.gov as NCT02517775, August 7, 2015; the chronic study was registered at clinicaltrials.gov as NCT02764749, May 6, 2016.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00394-021-02692-z.

Metabolomics Technologies for the Identification and Quantification of Dietary Phenolic Compound Metabolites: An Overview

In the search for natural products with properties that may protect against or slow down chronic and degenerative diseases (e.g., cancer, and cardiovascular and neurodegenerative conditions), phenolic compounds (PC) with benefits for human health have been identified. The biological effects of PC in vivo depend on their bioavailability, intestinal absorption, metabolism, and interaction with target tissues. The identification of phenolic compounds metabolites (PCM), in biological samples, after food ingestion rich in PC is a first step to understand the overall effect on human health. However, their wide range of physicochemical properties, levels of abundance, and lack of reference standards, renders its identification and quantification a challenging task for existing analytical platforms. The most frequent approaches to metabolomics analysis combine mass spectrometry and NMR, parallel technologies that provide an overview of the metabolome and high-power compound elucidation. In this scenario, the aim of this review is to summarize the pre-analytical separation processes for plasma and urine samples and the technologies applied in quantitative and qualitative analysis of PCM. Additionally, a comparison of targeted and non-targeted approaches is presented, not available in previous reviews, which may be useful for future metabolomics studies of PCM.

In vitro (poly)phenol catabolism of unformulated- and phytosome-formulated cranberry (Vaccinium macrocarpon) extracts

Cranberries (Vaccinium macrocarpon) represent an important source of anthocyanins, flavan-3-ols and flavonols. This study aimed at investigating in vitro the human microbial metabolism of (poly)phenols, principally flavan-3-ols, of unformulated- and phytosome-formulated cranberry extracts. After powder characterization, a 24-h fermentation with human faecal slurries was performed, standardizing the concentration of incubated proanthocyanidins. Cranberry (poly)phenol metabolites were quantified by uHPLC-MS² analyses. The native compounds of both unformulated- and phytosome-formulated cranberry extracts were metabolized under faecal microbiota activity, resulting in twenty-four microbial metabolites. Although some differences appeared when considering different classes of colonic metabolites, no significant differences in the total amount of metabolites were established after 24 h of incubation period. These results suggested that a different formulation had no effect on flavan-3-ol colonic metabolism of cranberry and both unformulated- and phytosome-formulated extract. Both formulations displayed the capability to be a potential source of compounds which could lead to a wide array of gut microbiota metabolites in vitro.

Influence of linseed and antioxidant-rich diets in pig nutrition on lipid oxidation during cooking and in vitro digestion of pork

Enrichment of pig diets with polyunsaturated fatty acids (PUFA) is considered an emerging strategy to increase their intake in the human diet. However, PUFA are particularly vulnerable to oxidative reactions leading to the generation of toxic compounds. The aim of this study was to evaluate the effect of supplementation of pig diets with extruded linseed (L), either or not in combination with synthetic antioxidants (E, tocopheryl-acetate and selenium) or natural extracts (P, grape-skin and oregano), and basal diet (C, without linseed) on the oxidative stability in raw, grilled and in vitro digested pork. The diet supplementation with antioxidant-rich ingredients resulted in the accumulation of specific metabolites in meat. Actually, 11 different phenolic- and 6 tocopherol-derived metabolites were identified by UHPLC/HR-MS. These metabolites were potentially correlated with the reduction in the oxidative phenomena occurring during meat cooking and digestion. Specifically, 16% and 35% reduction in the amounts of lipid hydroperoxides and TBA-RS were assessed after cooking of meat from P diet, respect to the L diet. Diet supplementations with α-tocopheryl acetate and selenium reduced the oxidative reactions only during meat cooking. A significant reduction was attended at the end of in vitro digestion, showing about 24% and 34% hydroperoxides and TBA-RS concentration reductions, respectively, in P diet samples respect to the L ones. Thus, our study suggests that the appearance of phenolic metabolites in meat could be associated to a reduction in the oxidative phenomena during meat cooking and digestion.

Absorption, metabolism, and excretion of orange juice (poly)phenols in humans: The effect of a controlled alcoholic fermentation

The consumption of orange juice provides high concentrations of health-promoting bioactive compounds, the amount of which may increase upon alcoholic fermentation. Although fermentation may offer new prospects for the industry of orange-related products, there is a lack of studies reporting the influence of controlled alcoholic fermentation on the bioavailability of orange juice (poly)phenols in humans. The aim of this study was to evaluate the absorption profile, pharmacokinetic parameters, and urinary excretion of orange juice (poly)phenols in nine volunteers after acute administration of an orange juice and a beverage prepared after controlled alcoholic fermentation of the juice. Plasma and urine samples were analysed through a UHPLC-ESI-MS/MS targeted approach. A total of 24 (poly)phenol metabolites including both flavanone and phenolic acid derivatives were quantified, most of them being recorded only in urine. Phase II conjugates of hesperetin and naringenin were the main metabolites in plasma, while phenolic acids, in particular hydroxybenzoic acids, were the main compounds in urine. (Poly)phenols in both beverages were highly bioavailable (between 46 and 59%) and a notable inter-individual variability was seen. Significant treatment × time interactions were recorded for the sum of flavanones and phenolic acids in plasma, the (poly)phenols in the fermented juice being absorbed faster than after orange juice intake. Nevertheless, despite the food matrix having an impact on the absorption profile of orange juice (poly)phenols, this did not influence the pharmacokinetic parameters and urinary excretion of the (poly)phenol metabolites.

Kinetic profile and urinary excretion of phenyl-γ-valerolactones upon consumption of cranberry: a dose-response relationship

Cranberries are a rich source of poly(phenols), mainly monomeric and oligomeric flavan-3-ols. However, information on the appearance of their main circulating microbial metabolites, namely phenyl-γ-valerolactones and phenylvaleric acid, is lacking despite its relevance to understanding the health effects attributed to cranberries. The aim of this study was to evaluate the absorption, metabolism and urinary excretion of cranberry flavan-3-ols through the targeted analysis of phenyl-γ-valerolactones and their related phenylvaleric acids, considering also their potential as biomarkers of flavan-3-ol intake and inter-individual variability in their appearance in plasma and urine. A six-arm acute crossover, randomized, double-blinded, controlled intervention trial was performed in ten healthy males who consumed a cranberry juice drink (375, 716, 1131, 1396, 1741 mg of total flavan-3-ols) or an isocaloric control drink with one-week washout. Plasma and urine were analyzed by UHPLC-ESI-QqQ-MS/MS and 22 compounds were identified. Glucuronide and sulfate conjugates of 5-(3',4'-dihydroxyphenyl)-γ-valerolactone were the main circulating and excreted metabolites after cranberry juice intake, with glucuronidation appearing to be the most favorable conjugation route. These compounds reached maximum plasma concentration at about 4-6 h. Plasma and urinary concentrations of the sum of the metabolites increased in relation to the amounts of cranberry flavan-3-ols provided by the drink, showing a clear and linear dose-dependent relationship and underscoring their potential as biomarkers of flavan-3-ol intake. A high inter-individual variability in circulating and urinary metabolite levels was observed and, interestingly, some subjects seemed to display a greater efficiency in metabolizing flavan-3-ols and producing phenyl-γ-valerolactones.

Monomeric Flavanols Are More Efficient Substrates for Gut Microbiota Conversion to Hydroxyphenyl-γ-Valerolactone Metabolites Than Oligomeric Procyanidins: A Randomized, Placebo-Controlled Human Intervention Trial

SCOPE

The majority of ingested flavanols reach the colon where they are catabolized by the microbiota to form hydroxyphenyl-γ-valerolactones (HGVLs). It is not known if the HGVLs are catabolic products of monomeric (epi)catechins (EPC), oligomeric procyanidins (OPCs), or both. Using data from a randomized, double-blind, placebo-controlled crossover trial the relative contributions of catechins and OPC to the bioavailable pool of HGVLs are estimated.

METHODS AND RESULTS

Participants ingested an apple extract once daily for 28 days that delivered the following: i) 70 mg EPC and 65 mg OPC (low dose EPC), ii) 140 mg EPC and 130 mg OPC (high dose EPC), iii) 6 mg EPC and 130 mg OPC (OPC), and iv) a placebo control. Urine is collected over a 24-h period before and after treatments. The median urinary excretion of HGVLs after ingestion of the high dose EPC is tenfold higher than that excreted after ingestion of the OPC that provided an equivalent dose of PC. Approximately 22% of catechins are converted to HGVLs in contrast to PC, for which there is limited conversion.

CONCLUSION

Monomeric catechins are efficiently converted to derived HGVLs that are absorbed and excreted in human urine, whereas oligomeric PCs are much less efficiently converted.

Bioavailability of red wine and grape seed proanthocyanidins in rats

This study explored plasma levels and urinary and fecal excretion of metabolites and microbial-derived catabolites over a 24 h period following the ingestion of red wine (RWP) or grape seed (GSP) proanthocyanidin-rich extracts by rats. In total, 35 structurally-related (epi)catechin metabolites (SREMs) and 5-carbon side chain ring fission metabolites (5C-RFMs) (phenyl-γ-valerolactones and phenylvaleric acids), and 50 phenolic acid and aromatic catabolites were detected after intakes of both extracts. The consumption of the RWP extract, but not the GSP extract, led to the appearance of a ∼200 nmol L^-1 peak plasma concentration of SREMs formed from flavan-3-ol monomers. In contrast, ingestion of the GSPs, but not the RWPs, resulted in a substantial increase in microbiota-derived 5-carbon side chain ring fission metabolites (5C-RFMs) in plasma. 5C-RFMs, along with low molecular weight phenolic catabolites were detected in urine after ingestion of both extracts. The GSP and RWP extracts had respective mean degrees of polymerisation 5.9 and 6.5 subunits, and the RWP extract had an upper polymer size of 21 subunits compared to 44 subunits for the GSP extract. The differences in plasma metabolite profiles might, therefore, be a consequence of this polydispersity impacting on the microbiota-mediated rates of cleavage of the proanthocyanidin subunits and their subsequent metabolism and absorption. Urinary excretion of phenolic catabolites indicated that 11% of RWPs and 7% for GSPs were subjected to microbial degradation. In all probability these figures, rather than representing the percentage of proanthocyanidins that are completely degraded, indicate partial cleavage of monomer subunits producing a much higher percentage of shortened proanthocyanidin chains. Obtaining more detailed information on the in vivo fate of proanthocyanidins is challenging because of the difficulties in analysing unabsorbed parent proanthocyanidins and their partially degraded flavan-3-ol subunit chains in feces. Further progress awaits the development of improved purification and analytical techniques for proanthocyanidins and their use in feeding studies, and in vitro fecal and bacterial incubations, with radio and/or stable isotope-labelled substrates.

Differential Catabolism of an Anthocyanin-Rich Elderberry Extract by Three Gut Microbiota Bacterial Species

Elderberries are good sources of anthocyanins, which are poorly absorbed in the upper gastrointestinal tract but extensively transformed into phenolic metabolites at the colonic level. Because different gut microbiota strains have different metabolism, the catabolism of anthocyanins may lead to interindividual differences in metabolite production. In this work, an anthocyanin-rich elderberry extract was incubated with three single gut microbial strains (Enterobacter cancerogenous, Bifidobacterium dentium, and Dorea longicatena) up to 4 days, to assess differences in their phenolic metabolism. All of the strains degraded the elderberry anthocyanins, but the metabolic pathways followed were different. Although some metabolites were common for all of the strains, a wide disparity was observed in the kind and amount of several phenolic metabolites produced by each species. These in vitro preliminary results may be of help in the interpretation of the bioavailability of anthocyanins and give a clue to understand interindividual variability in metabolite production.

Flavonoid-Derived Human Phenyl-γ-Valerolactone Metabolites Selectively Detoxify Amyloid-β Oligomers and Prevent Memory Impairment in a Mouse Model of Alzheimer's Disease

SCOPE

Amyloid-β oligomers (AβO) are causally related to Alzheimer's disease (AD). Dietary natural compounds, especially flavonoids and flavan-3-ols, hold great promise as potential AD-preventive agents but their host and gut microbiota metabolism complicates identification of the most relevant bioactive species. This study aims to investigate the ability of a comprehensive set of phenyl-γ-valerolactones (PVL), the main circulating metabolites of flavan-3-ols and related dietary compounds in humans, to prevent AβO-mediated toxicity.

METHODS AND RESULTS

The anti-AβO activity of PVLs is examined in different cell model systems using a highly toxic β-oligomer-forming polypeptide (β23) as target toxicant. Multiple PVLs, and particularly the monohydroxylated 5-(4'-hydroxyphenyl)-γ-valerolactone metabolite [(4'-OH)-PVL], relieve β-oligomer-induced cytotoxicity in yeast and mammalian cells. As revealed by atomic force microscopy (AFM) and other in vitro assays, (4'-OH)-PVL interferes with AβO (but not fibril) assembly and actively remodels preformed AβOs into nontoxic amorphous aggregates. In keeping with the latter mode of action, treatment of AβOs with (4'-OH)-PVL prior to brain injection strongly reduces memory deterioration as well as neuroinflammation in a mouse model of AβO-induced memory impairment.

CONCLUSION

PVLs, which have been validated as biomarkers of the dietary intake of flavan-3-ols, lend themselves as novel AβO-selective, candidate AD-preventing compounds.

Acute Intake of a Grape and Blueberry Polyphenol-Rich Extract Ameliorates Cognitive Performance in Healthy Young Adults During a Sustained Cognitive Effort

Despite an increasing level of evidence supporting the individual beneficial effect of polyphenols on cognitive performance, information related to the potential synergistic action of these phytonutrients on cognitive performance during a prolonged cognitive effort is currently lacking. This study investigated the acute and sustained action of a polyphenols-rich extract from grape and blueberry (PEGB), on working memory and attention in healthy students during a prolonged and intensive cognitive effort. In this randomised, cross-over, double blind study, 30 healthy students consumed 600 mg of PEGB or a placebo. Ninety minutes after product intake, cognitive functions were assessed for one hour using a cognitive demand battery including serial subtraction tasks, a rapid visual information processing (RVIP) task and a visual analogical scale. Flow-mediated dilation (FMD) and plasma flavan-3-ols metabolites quantification were also performed. A 2.5-fold increase in serial three subtraction variation net scores was observed following PEGB consumption versus placebo (p < 0.001). A trend towards significance was also observed with RVIP percentage of correct answers (p = 0.058). No treatment effect was observed on FMD. Our findings suggest that consumption of PEGB coupled with a healthy lifestyle may be a safe alternative to acutely improve working memory and attention during a sustained cognitive effort.

Phenyl-γ-valerolactones and phenylvaleric acids, the main colonic metabolites of flavan-3-ols: synthesis, analysis, bioavailability, and bioactivity

Covering: 1958 to June 2018 Phenyl-γ-valerolactones (PVLs) and their related phenylvaleric acids (PVAs) are the main metabolites of flavan-3-ols, the major class of flavonoids in the human diet. Despite their presumed importance, these gut microbiota-derived compounds have, to date, in terms of biological activity, been considered subordinate to their parent dietary compounds, the flavan-3-ol monomers and proanthocyanidins. In this review, the role and prospects of PVLs and PVAs as key metabolites in the understanding of the health features of flavan-3-ols have been critically assessed. Among the topics covered, are proposals for a standardised nomenclature for PVLs and PVAs. The formation, bioavailability and pharmacokinetics of PVLs and PVAs from different types of flavan-3-ols are discussed, taking into account in vitro and animal studies, as well as inter-individual differences and the existence of putative flavan-3-ol metabotypes. Synthetic strategies used for the preparation of PVLs are considered and the methodologies for their identification and quantification assessed. Metabolomic approaches unravelling the role of PVLs and PVAs as biomarkers of intake are also described. Finally, the biological activity of these microbial catabolites in different experimental models is summarised. Knowledge gaps and future research are considered in this key area of dietary (poly)phenol research.

5-(Hydroxyphenyl)-γ-Valerolactone-Sulfate, a Key Microbial Metabolite of Flavan-3-ols, Is Able to Reach the Brain: Evidence from Different in Silico, In Vitro and In Vivo Experimental Models

Phenolic compounds have been recognized as promising compounds for the prevention of chronic diseases, including neurodegenerative ones. However, phenolics like flavan-3-ols (F3O) are poorly absorbed along the gastrointestinal tract and structurally rearranged by gut microbiota, yielding smaller and more polar metabolites like phenyl-γ-valerolactones, phenylvaleric acids and their conjugates. The present work investigated the ability of F3O-derived metabolites to cross the blood-brain barrier (BBB), by linking five experimental models with increasing realism. First, an in silico study examined the physical-chemical characteristics of F3O metabolites to predict those most likely to cross the BBB. Some of these metabolites were then tested at physiological concentrations to cross the luminal and abluminal membranes of brain microvascular endothelial cells, cultured in vitro. Finally, three different in vivo studies in rats injected with pure 5-(3',4'-dihydroxyphenyl)-γ-valerolactone, and rats and pigs fed grapes or a F3O-rich cocoa extract, respectively, confirmed the presence of 5-(hydroxyphenyl)-γ-valerolactone-sulfate (3',4' isomer) in the brain. This work highlighted, with different experimental models, the BBB permeability of one of the main F3O-derived metabolites. It may support the neuroprotective effects of phenolic-rich foods in the frame of the "gut-brain axis".

Improving the reporting quality of intervention trials addressing the inter-individual variability in response to the consumption of plant bioactives: quality index and recommendations

PURPOSE

The quality of the study design and data reporting in human trials dealing with the inter-individual variability in response to the consumption of plant bioactives is, in general, low. There is a lack of recommendations supporting the scientific community on this topic. This study aimed at developing a quality index to assist the assessment of the reporting quality of intervention trials addressing the inter-individual variability in response to plant bioactive consumption. Recommendations for better designing and reporting studies were discussed.

METHODS

The selection of the parameters used for the development of the quality index was carried out in agreement with the scientific community through a survey. Parameters were defined, grouped into categories, and scored for different quality levels. The applicability of the scoring system was tested in terms of consistency and effort, and its validity was assessed by comparison with a simultaneous evaluation by experts' criteria.

RESULTS

The "POSITIVe quality index" included 11 reporting criteria grouped into four categories (Statistics, Reporting, Data presentation, and Individual data availability). It was supported by detailed definitions and guidance for their scoring. The quality index score was tested, and the index demonstrated to be valid, reliable, and responsive.

CONCLUSIONS

The evaluation of the reporting quality of studies addressing inter-individual variability in response to plant bioactives highlighted the aspects requiring major improvements. Specific tools and recommendations favoring a complete and transparent reporting on inter-individual variability have been provided to support the scientific community on this field.

Quantification of Urinary Phenyl-γ-Valerolactones and Related Valeric Acids in Human Urine on Consumption of Apples

Flavan-3-ols are dietary bioactive molecules that have beneficial effects on human health and reduce the risk of various diseases. Monomeric flavan-3-ols are rapidly absorbed in the small intestine and released in the blood stream as phase II conjugates. Polymeric flavan-3-ols are extensively metabolized by colonic gut microbiota into phenyl-γ-valerolactones and their related phenylvaleric acids. These molecules are the main circulating metabolites in humans after the ingestion of flavan-3-ol rich-products; nevertheless, they have received less attention and their role is not understood yet. Here, we describe the quantification of 8 phenyl-γ-valerolactones and 3 phenylvaleric acids in the urine of 11 subjects on consumption of apples by using UHPLC-ESI-Triple Quad-MS with pure reference compounds. Phenyl-γ-valerolactones, mainly as sulfate and glucuronic acid conjugates, reached maximum excretion between 6 and 12 after apple consumption, with a decline thereafter. Significant differences were detected in the cumulative excretion rates within subjects and in the ratio of dihydroxyphenyl-γ-valerolactone sulfate to glucuronide conjugates. This work observed for the first time the presence of two distinct metabotypes with regards to the excretion of phenyl-γ-valerolactone phase II conjugates.

Full 1 H and 13 C NMR spectral assignment of conjugated valerolactone metabolites isolated from urine of black tea consumers by means of SPE-prepLC-MS-LC-MS-NMR

The health benefits of black tea have been linked to polyphenol metabolites that target specific modes of action in the human body. A major bottleneck in unravelling the underlying mechanisms is the preparative isolation of these metabolites, which hampers their structural elucidation and assessment of in vitro bioactivity. A solid phase extraction (SPE)-preparative liquid chromatography (prepLC)-MS-LC-MS-NMR workflow was implemented for preparative isolation of conjugated valerolactone metabolites of catechin-based polyphenols from urine of black tea consumers. First, the urine was cleaned and preconcentrated using an SPE method. Subsequently, the clean urine concentrate was injected on a preparative LC column, and conjugated valerolactones were obtained by MS-guided collection. Reconstituted fractions were further separated on an analytical LC column, and valerolactone fractions were collected in an MS-guided manner. These were reconstituted in methanol-d₄ and identified and quantified using 1D and 2D homo- and hetereonuclear NMR experiments (at a field strength of 14.1 T), in combination with mass spectrometry. This resulted in the full spectral ¹ H and ¹³ C NMR assignments of five conjugated valerolactones. These metabolites were collected in quantities of 8-160 μg and purities of 70-91%. The SPE-prepLC-MS-LC-MS-NMR workflow is suitable for isolating metabolites that occur at sub-μM concentrations in a complex biofluid such as urine. The workflow also provides an alternative for cumbersome and expensive de novo synthesis of tea metabolites for testing in bioactivity assays or for use as authentic analytical standards for quantification by mass spectrometry.

Inter-individual variability in the production of flavan-3-ol colonic metabolites: preliminary elucidation of urinary metabotypes

PURPOSE

There is much information on the bioavailability of (poly)phenolic compounds following acute intake of various foods. However, there are only limited data on the effects of repeated and combined exposure to specific (poly)phenol food sources and the inter-individual variability in their bioavailability. This study evaluated the combined urinary excretion of (poly)phenols from green tea and coffee following daily consumption by healthy subjects in free-living conditions. The inter-individual variability in the production of phenolic metabolites was also investigated.

METHODS

Eleven participants consumed both tablets of green tea and green coffee bean extracts daily for 8 weeks and 24-h urine was collected on five different occasions. The urinary profile of phenolic metabolites and a set of multivariate statistical tests were used to investigate the putative existence of characteristic metabotypes in the production of flavan-3-ol microbial metabolites.

RESULTS

(Poly)phenolic compounds in the green tea and green coffee bean extracts were absorbed and excreted after simultaneous consumption, with green tea resulting in more inter-individual variability in urinary excretion of phenolic metabolites. Three metabotypes in the production of flavan-3-ol microbial metabolites were tentatively defined, characterized by the excretion of different amounts of trihydroxyphenyl-γ-valerolactones, dihydroxyphenyl-γ-valerolactones, and hydroxyphenylpropionic acids.

CONCLUSIONS

The selective production of microbiota-derived metabolites from flavan-3-ols and the putative existence of characteristic metabotypes in their production represent an important development in the study of the bioavailability of plant bioactives. These observations will contribute to better understand the health effects and individual differences associated with consumption of flavan-3-ols, arguably the main class of flavonoids in the human diet.

Inhibitory Effects of Green Tea Polyphenols on Microbial Metabolism of Aromatic Amino Acids in Humans Revealed by Metabolomic Analysis

The bioactivities and potential health benefits of green tea polyphenols (GTP) have been extensively investigated, but the metabolic impact of chronic GTP intake on humans is not well defined. In this study, fecal and urine samples from postmenopausal female subjects taking a GTP supplement or placebo for 12 months were compared by liquid chromatography-mass spectrometry-based metabolomic analysis. The GTP-derived and GTP-responsive metabolites were identified and characterized by structural elucidation and quantitative analysis of the metabolites contributing to the separation of control and treatment samples in the multivariate models. Major GTP and their direct sulfate and glucuronide metabolites were absent in feces and urine. In contrast, GTP-derived phenyl-γ-valerlactone and phenylvaleric acid metabolites were identified as the most abundant GTP-derived metabolites in feces and urine, suggesting extensive microbial biotransformation of GTP in humans. Interestingly, GTP decreased the levels of microbial metabolites of aromatic amino acids (AAA), including indoxyl sulfate, phenylacetylglutamine, and hippuric acid, in urine. However, it did not affect the levels of AAA, as well as other microbial metabolites, including short-chain fatty acids and secondary bile acids, in feces. 16S rRNA gene sequencing indicated that the fecal microbiome was not significantly affected by chronic consumption of GTP. Overall, microbial metabolism is responsible for the formation of GTP metabolites while GTP metabolism may inhibit the formation of AAA metabolites from microbial metabolism. Because these GTP-derived and GTP-responsive metabolites have diverse bioactivities, microbial metabolism of GTP and AAA may play important roles in the beneficial health effects of green tea consumption in humans.

Comparative analysis of fecal phenolic content between normal and obese rats after oral administration of tea polyphenols

Tea polyphenols (TP) have many health benefits, but most are metabolized into low molecular-weight phenolic acids after oral administration. In the present study, the absorption, metabolism, and excretion of catechins in rats fed a normal chow diet and in obese rats fed a high-fat and high-sugar (HFHS) diet were compared. After a ten-day oral administration of TP (500 mg per kg bw), the plasma levels of (-)-epigallocatechin gallate (EGCG) and (-)-gallocatechin gallate (GCG) in obese rats were significantly lower than those in the normal group. In obese rats, the fecal levels of EGCG, (-)-epicatechin gallate (ECG) and GCG were significantly enhanced. Ten phenolic metabolites of TP were quantitatively analyzed, and the results showed that 4-hydroxyphenylacetic acid was the primary metabolite in feces and plasma. The plasma and fecal concentrations of 4-hydroxyphenylacetic acid in the obese group were significantly lower than those in normal rats, but the levels of 4-hydroxyphenylpropionic acid in plasma and feces were increased. The content of other phenolic acids was also dramatically changed. These results suggested that a HFHS diet might influence the excretion of tea catechins, leading to insufficient metabolism of catechins by the gut microflora.

Dark chocolate modulates platelet function with a mechanism mediated by flavan-3-ol metabolites

Cocoa is a rich source bioactive compounds, i.e., flavan-3-ols, and its consumption has been associated with several beneficial effects, such as the positive modulation of the hemostasis targeted by the platelet function. However, these phenolic compounds have a very low bioavailability and extensively undergo phase I and II metabolism, with the appearing into the bloodstream of (epi)catechin conjugates and phenyl-γ-valerolactones and their conjugates, at different times.The aims of this study were to explore the effect of dark chocolate on platelet function and to investigate the relationship between this interplay and flavan-3-ol derived metabolites.Eighteen healthy male volunteers ingested 50 g of 90% cocoa chocolate within 5 minutes. Blood samples were collected immediately before chocolate ingestion (T0) and 4 hours afterwards (T1). Platelet function analyzer (PFA)-100 closure time was assessed using collagen/adenosine-5'-diphosphate (COL/ADP) and collagen/epinephrine (COL/EPI) cartridges. Plasma flavan-3-ol metabolites were identified and quantified by means of liquid chromatography coupled to a triple quadrupole mass spectrometer (UHPLC-ESI-MS/MS).Results evidenced a significant increase of COL/ADP-induced PFA-100 closure time, but not COL/EPI, 4 hours after ingestion of dark chocolate. Total plasma structurally-related (epi)catechin metabolite (SREM) concentration significantly increased at T1, together with 4 out of the 6 detected metabolites. Total phenyl-γ-valerolactone concentrations remained unchanged. Spearman correlations evidenced a strong correlation between COL/ADP closure time and SREMs, mainly led by (epi)catechin-sulfate isomers.These data confirm that the potential beneficial effect of dark chocolate on primary hemostasis may be mediated by flavan-3-ol circulating metabolites.

A critical evaluation of the use of gas chromatography- and high performance liquid chromatography-mass spectrometry techniques for the analysis of microbial metabolites in human urine after consumption of orange juice

The present study compared and validated two analytical methods, HPLC-HRMS, and GC-MS using MSTFA as derivatization agent, for the analysis of microbiota-derived phenolic acids and aromatic compounds accumulating in urine, collected over a 24 h period after the consumption of 500 mL of orange juice. In addition, purification procedures using SDB-L and HLB solid phase cartridges were compared when HPLC-HRMS technique was used. Both HPLC-HRMS and GC-MS methodologies were successfully validated in terms of specificity, sensitivity, limit of detection and quantification, recovery and matrix effects. HPLC-HRMS, unlike GC-MS, does not require sample derivatization prior to analysis. GC-MS was not suitable for the analysis of phenolic sulfate and glucuronide metabolites because of their lack of volatility. These phase II metabolites could, however, be analysed by HPLC-HRMS which, as a consequence, provided more detailed and complete information on the phenolic compounds derived from microbiota-mediated degradation of orange juice (poly)phenols. Furthermore, the use of SDB-L and HLB cartridges for sample purification prior to HPLC-HRMS analysis is suitable for free phenolics and glucuronide metabolites but not sulfate derivatives. These findings highlight that the use of an inappropriate analytical protocol can adversely affect studies on the bioavailability of dietary (poly)phenols in which microbiota-derived phenolic catabolites play an important role.

An exploratory study of red raspberry (Rubus idaeus L.) (poly)phenols/metabolites in human biological samples

Red raspberry (Rubus idaeus L.) contains a variety of polyphenols including anthocyanins and ellagitannins. Red raspberry polyphenols absorbed in different forms (parent compounds, degradants or microbial metabolites) are subject to xenobiotic metabolism in the intestine, liver, and/or kidney, forming methylate, glucuronide, and sulfate conjugated metabolites. Upon acute exposure, (poly)phenol/metabolite presence in the blood depends mainly on intestinal absorption, enterohepatic circulation, and metabolism by resident microbiota. However, chronic exposure to red raspberry polyphenols may alter metabolite patterns depending on adaptions in the xenobiotic machinery and/or microbiota composition. Understanding the metabolic fate of these compounds and their composition in different biological specimens relative to the exposure time/dose will aid in designing future health benefit studies, including the mechanism of action studies. The present exploratory study applied ultra-high performance liquid chromatography (UHPLC) coupled with quadrupole time-of-flight (QTOF) and triple quadrupole (QQQ) mass spectrometries to characterize red raspberry polyphenols in fruit and then their appearance, including metabolites in human biological samples (plasma, urine and breast milk) after the chronic intake of red raspberries. The results suggested that the most abundant polyphenols in red raspberries included cyanidin 3-O-sophoroside, cyanidin 3-O-glucoside, sanguiin H6 and lambertianin C. Sixty-two (poly)phenolic compounds were tentatively identified in the plasma, urine and breast milk samples after the intake of red raspberries. In general, urine contained the highest content of phenolic metabolites; phase II metabolites, particularly sulfated conjugates, were mainly present in urine and breast milk, and breast milk contained fewer parent anthocyanins compared to urine and plasma.

Use of LC-MS for the quantitative analysis of (poly)phenol metabolites does not necessarily yield accurate results: Implications for assessing existing data and conducting future research

Plant-derived, dietary (poly)phenols have potential effects on disease-risk reduction and primary disease prevention. The characterization of (poly)phenol absorption, distribution, metabolism and excretion (ADME) is recognized as crucial step to further advance nutritional and biomedical research of these compounds; and given that (poly)phenols are extensively metabolized after ingestion, accurate assessments of their in vivo metabolites is required. It has become common practice to use unmetabolized parent compounds as reference standards when quantifying (poly)phenol metabolites by LC-MS, although little is known about the accuracy of this approach. To investigate this situation with routinely used LC-MS conditions, the signal yielded by the flavan-3-ol (-)-epicatechin was compared to those of authentic standards of its phase II and microbiota-derived metabolites. The results obtained revealed underestimations up to 94% and overestimations up to 113% of individual epicatechin metabolites. Inaccurate quantitative estimates were also obtained when phase II metabolites of other (poly)phenols were quantified by reference to their unmetabolized parent compounds. This demonstrates the importance of using structurally-identical authentic metabolites as reference compounds when quantifying (poly)phenol metabolites by LC-MS. This is of importance, not just to the accuracy of ADME studies, but for the identification and validation of (poly)phenol metabolites as biomarkers of intake in epidemiological studies.

Host: Microbiome co-metabolic processing of dietary polyphenols - An acute, single blinded, cross-over study with different doses of apple polyphenols in healthy subjects

Apples are one of the most commonly consumed fruits and their high polyphenol content is considered one of the most important determinants of their health-promoting activities. Here we studied the nutrikinetics of apple polyphenols by UHPLC-HRMS metabolite fingerprinting, comparing bioavailability when consumed in a natural or a polyphenol-enriched cloudy apple juice. Twelve men and women participated in an acute single blind controlled crossover study in which they consumed 250 mL of cloudy apple juice (CAJ), Crispy Pink apple variety, or 250 mL of the same juice enriched with 750 mg of an apple polyphenol extract (PAJ). Plasma and whole blood were collected at time 0, 1, 2, 3 and 5 h. Urine was collected at time 0 and 0-2, 2-5, 5-8, and 8-24 h after juice consumption. Faecal samples were collected from each individual during the study for 16S rRNA gene profiling. As many as 110 metabolites were significantly elevated following intake of polyphenol enriched cloudy apple juice, with large inter-individual variations. The comparison of the average area under the curve of circulating metabolites in plasma and in urine of volunteers consuming either the CAJ or the PAJ demonstrated a stable metabotype, suggesting that an increase in polyphenol concentration in fruit does not limit their bioavailability upon ingestion. Faecal bacteria were correlated with specific microbial catabolites derived from apple polyphenols. Human metabolism of apple polyphenols is a co-metabolic process between human encoded activities and those of our resident microbiota. Here we have identified specific blood and urine metabolic biomarkers of apple polyphenol intake and identified putative associations with specific genera of faecal bacteria, associations which now need confirmation in specifically designed mechanistic studies.