Development and validation of an UHPLC-HRMS protocol for the analysis of flavan-3-ol metabolites and catabolites in urine, plasma and feces of rats fed a red wine proanthocyanidin extract

Flavouring Group Evaluation 413 (FGE.413): Naringenin

The EFSA Panel on Food Additives and Flavourings (FAF) was requested to evaluate the safety of naringenin [FL-no: 16.132] as a new flavouring substance, in accordance with Regulation (EC) No 1331/2008. No other substances with sufficient structural similarity have been identified in existing FGEs that could be used to support a read-across approach. The information provided on the manufacturing process, the composition and the stability of [FL-no: 16.132] was considered sufficient. From studies carried out with naringenin, the Panel concluded that there is no concern with respect to genotoxicity. The use of naringenin as a flavouring substance at added portions exposure technique (APET) exposure levels is unlikely to pose a risk for drug interaction. For the toxicological evaluation of naringenin, the Panel requested an extended one-generation toxicity study on naringenin, in line with the requirements of the Procedure and to investigate the consequence of a possible endocrine-disrupting activity. The Panel considered that changes in thymus weight, litter size, post-implantation loss and a consistent reduced pup weight in the high-dose F2 generation could not be dismissed and selected therefore, the mid-dose of 1320 mg/kg body weight (bw) per day for the parental males as the no observed adverse effect level (NOAEL) of the study. The exposure estimates for [FL-no: 16.132] (31,500 and 50,000 μg/person per day for children and adults, respectively) were above the threshold of toxicological of concern (TTC) for its structural class (III). Using the NOAEL of 1320 mg/kg bw per day at step A4 of the procedure, margins of exposure (MoE) of 1590 and 630 could be calculated for adults and children, respectively. Based on the calculated MoEs, the Panel concluded that the use of naringenin as a flavouring substance does not raise a safety concern.

Exploring and disentangling the production of potentially bioactive phenolic catabolites from dietary (poly)phenols, phenylalanine, tyrosine and catecholamines

Following ingestion of fruits, vegetables and derived products, (poly)phenols that are not absorbed in the upper gastrointestinal tract pass to the colon, where they undergo microbiota-mediated ring fission resulting in the production of a diversity of low molecular weight phenolic catabolites, which appear in the circulatory system and are excreted in urine along with their phase II metabolites. There is increasing interest in these catabolites because of their potential bioactivity and their use as biomarkers of (poly)phenol intake. Investigating the fate of dietary (poly)phenolics in the colon has become confounded as a result of the recent realisation that many of the phenolics appearing in biofluids can also be derived from the aromatic amino acids, l-phenylalanine and l-tyrosine, and to a lesser extent catecholamines, in reactions that can be catalysed by both colonic microbiota and endogenous mammalian enzymes. The available evidence, albeit currently rather limited, indicates that substantial amounts of phenolic catabolites originate from phenylalanine and tyrosine, while somewhat smaller quantities are produced from dietary (poly)phenols. This review outlines information on this topic and assesses procedures that can be used to help distinguish between phenolics originating from dietary (poly)phenols, the two aromatic amino acids and catecholamines.

Encapsulation and Characterization of Proanthocyanidin Microcapsules by Sodium Alginate and Carboxymethyl Cellulose

Proanthocyanidins are important compounds known for their antioxidant and radical scavenging properties, but they are highly sensitive to light, heat, oxygen, and pH. In our study, proanthocyanidin was encapsulated using sodium alginate and carboxymethyl cellulose to enhance controlled release, pH stability, metal ion tolerance, temperature resistance, time release, the microencapsulation of food additives stability, antioxidant capacity analysis, and the storage period tolerance of proanthocyanidin. Fourier transforms infrared (FTIR) analysis and full-wavelength UV scanning indicated the successful immobilization of proanthocyanidins into the polymeric microcapsules. The flowability and mechanical properties of the microcapsules were enhanced. Moreover, proanthocyanidin microcapsules exhibited higher thermal, pH, metal ion, time, and microencapsulation food additive stability. In addition, due to their high antioxidant properties, the proanthocyanidin microcapsules retained a greater amount of proanthocyanidin content during the gastric phase, and the proanthocyanidin was subsequently released in the intestinal phase for absorption. Thus, the study provided a systematic understanding of the antioxidant capabilities and stability of proanthocyanidin microcapsules, which is beneficial for developing preservation methods for food additives.

Novel l-Cysteine Incomplete Degradation Method for Preparation of Procyanidin B2-3'-O-Gallate and Exploration of its in Vitro Anti-inflammatory Activity and in Vivo Tissue Distribution

In this study, an effective method for preparation of bioactive galloylated procyanidin B2-3'-O-gallate (B2-3'-G) was first developed by incomplete depolymerization of grape seed polymeric procyanidins (PPCs) using l-cysteine (Cys) in the presence of citric acid. The structure-activity relationship of B2-3'-G was further evaluated in vitro through establishing lipopolysaccharide (LPS)-induced inflammation in RAW264.7 cells. The results suggested that the better protective effects of B2-3'-G against inflammation were attributed to its polymerization degree and the introduction of the galloyl group, compared to its four corresponding structural units. In vivo experiments demonstrated that the B2-3'-G prototype was distributed in plasma, small intestine, liver, lung, and brain. Remarkably, B2-3'-G was able to penetrate the blood-brain barrier and appeared to play an important role in improving brain health. Furthermore, a total of 18 metabolites were identified in tissues. Potential metabolic pathways, including reduction, methylation, hydration, desaturation, glucuronide conjugation, and sulfation, were suggested.

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.

Why is it important to understand the nature and chemistry of tannins to exploit their potential as nutraceuticals?

Tannins comprise a large group of polyphenols that can differ widely in chemical composition and molecular weight. The use of tannins dates back to antiquity, but it is only in recent years that their potential use as nutraceuticals associated with the human diet is beginning to be exploited. Although the biological effects of these phytocomplexes have been studied for many years, there are still several open questions regarding their chemistry and biotransformation. The vastness of the molecules that make up the class of tannins has made their characterisation, as well as their nomenclature and classification, a daunting task. This review has been written with the aim of bringing order to the chemistry of tannins by including aspects that are sometimes still overlooked or should be updated with new research in order to understand the potential of these phytocomplexes as active ingredients or technological components for nutraceutical products. Future trends in tannin research should address many questions that are still open, such as determining the exact biosynthetic pathways of all classes of tannins, the actual biological effects determined by the interaction of tannins with other molecules, their metabolization, and the best extraction methods, but with a view to market requirements.

Prebiotic proanthocyanidins inhibit bile reflux-induced esophageal adenocarcinoma through reshaping the gut microbiome and esophageal metabolome

The gut and local esophageal microbiome progressively shift from healthy commensal bacteria to inflammatory-linked pathogenic bacteria in patients with gastroesophageal reflux disease, Barrett's esophagus and esophageal adenocarcinoma (EAC). However, mechanisms by which microbial communities and metabolites contribute to reflux-driven EAC remain incompletely understood and challenging to target. Herein, we utilized a rat reflux-induced EAC model to investigate targeting the gut microbiome-esophageal metabolome axis with cranberry proanthocyanidins (C-PAC) to inhibit EAC progression. Sprague Dawley rats, with or without reflux-induction received water or C-PAC ad libitum (700 µg/rat/day) for 25 or 40 weeks. C-PAC exerted prebiotic activity abrogating reflux-induced dysbiosis, and mitigating bile acid metabolism and transport, culminating in significant inhibition of EAC through TLR/NF-κB/P53 signaling cascades. At the species level, C-PAC mitigated reflux-induced pathogenic bacteria (Clostridium perfringens, Escherichia coli, and Proteus mirabilis). C-PAC specifically reversed reflux-induced bacterial, inflammatory and immune-implicated proteins and genes including Ccl4, Cd14, Crp, Cxcl1, Il6, Il1β, Lbp, Lcn2, Myd88, Nfkb1, Tlr2 and Tlr4 aligning with changes in human EAC progression, as confirmed through public databases. C-PAC is a safe promising dietary constituent that may be utilized alone or potentially as an adjuvant to current therapies to prevent EAC progression through ameliorating reflux-induced dysbiosis, inflammation and cellular damage.

UHPLC-HRMS Spectrometric Analysis: Method Validation and Plasma and Urinary Metabolite Identification after Mango Pulp Intake

After an acute intake of 300 g of mango purée by 10 subjects, 0 and 24 h urine and plasma samples were analyzed by high-performance liquid chromatography-high-resolution mass spectrometry. The method was first validated for 44 reference polyphenols in terms of linearity, specificity, limits of detection and quantification, intra-day and inter-day precision, recovery, and matrix effects in two biological matrices. After method validation, a total of 94 microbial-derived phenolic catabolites, including 15 cinnamic acids, 3 phenylhydracrylic acids, 14 phenylpropanoic acids, 12 phenylacetic acids, 28 benzoic acids, 2 mandelic acids, 15 hydroxybenzenes, and 5 hippuric acid derivatives, were identified or tentatively identified in urine and/or plasma. These results establish the value of the UHPLC-HRMS protocol and the use of authentic standards to obtain a detailed and accurate picture of mango polyphenol metabolites, together with their phase II conjugated metabolites, in human bioavailability studies.

Revisiting the bioavailability of flavan-3-ols in humans: A systematic review and comprehensive data analysis

This systematic review summarizes findings from human studies investigating the different routes of absorption, metabolism, distribution and excretion (ADME) of dietary flavan-3-ols and their circulating metabolites in healthy subjects. Literature searches were performed in PubMed, Scopus and the Web of Science. Human intervention studies using single and/or multiple intake of flavan-3-ols from food, extracts, and pure compounds were included. Forty-nine human intervention studies met inclusion criteria. Up to 180 metabolites were quantified from blood and urine samples following intake of flavan-3-ols, mainly as phase 2 conjugates of microbial catabolites (n = 97), with phenyl-γ-valerolactones being the most representative ones (n = 34). Phase 2 conjugates of monomers and phenyl-γ-valerolactones, the main compounds in both plasma and urine, reached two peak plasma concentrations (C_max) of 260 and 88 nmol/L at 1.8 and 5.3 h (T_max) after flavan-3-ol intake. They contributed to the bioavailability of flavan-3-ols for over 20%. Mean bioavailability for flavan-3-ols was moderate (31 ± 23%, n bioavailability values = 20), and it seems to be scarcely affected by the amount of ingested compounds. While intra- and inter-source differences in flavan-3-ol bioavailability emerged, mean flavan-3-ol bioavailability was 82% (n = 1) and 63% (n = 2) after (-)-epicatechin and nut (hazelnuts, almonds) intake, respectively, followed by 25% after consumption of tea (n = 7), cocoa (n = 5), apples (n = 3) and grape (n = 2). This highlights the need to better clarify the metabolic yield with which monomer flavan-3-ols and proanthocyanidins are metabolized in humans. This work clarified in a comprehensive way for the first time the ADME of a (poly)phenol family, highlighting the pool of circulating compounds that might be determinants of the putative beneficial effects linked to flavan-3-ol intake. Lastly, methodological inputs for implementing well-designed human and experimental model studies were provided.

Identification and Quantification of Urinary Microbial Phenolic Metabolites by HPLC-ESI-LTQ-Orbitrap-HRMS and Their Relationship with Dietary Polyphenols in Adolescents

This study aimed to develop and validate a liquid chromatography/electrospray ionization-linear ion trap quadrupole-Orbitrap-high-resolution mass spectrometry (HPLC/ESI-LTQ-Orbitrap-HRMS) method to identify and quantify urinary microbial phenolic metabolites (MPM), as well as to explore the relationship between MPM and dietary (poly)phenols in Spanish adolescents. A total of 601 spot urine samples of adolescents aged 12.02 ± 0.41 years were analyzed. The quantitative method was validated for linearity, limit of detection, limit of quantification, recovery, intra- and inter-day accuracy and precision, as well as postpreparative stability according to the criteria established by the Association of Official Agricultural Chemists International. A total of 17 aglycones and 37 phase II MPM were identified and quantified in 601 spot urine samples. Phenolic acids were the most abundant urinary MPM, whereas stilbenes, hydroxytyrosol, and enterodiol were the least abundant. Urinary hydroxycoumarin acids (urolithins) were positively correlated with flavonoid and total (poly)phenol intake. An HPLC-ESI-LTQ-Orbitrap-HRMS method was developed and fully validated to quantify MPM. The new method was performed accurately and is suitable for MPM quantification in large epidemiological studies. Urinary lignans and urolithins are proposed as potential biomarkers of grain and nut intake in an adolescent population.

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.

Grape seed extract supplementation modulates hepatic lipid metabolism in rats. Implication of PPARβ/δ

Grape seed extract supplementationat low doses (25 mg per kg BW per day) modulates the transcriptional programs that controls the hepatic lipid metabolism in lean normolipidemic Wistar rats through PPARβ/δ activation.

LC-MS based metabolomic approach for the efficient identification and relative quantification of bioavailable cocoa phenolics in human urine

This study was designed to investigate the rate and extent of urinary excretion of cocoa phenolic metabolites after human intake using metabolomics approach. In this context, a feeding trial was conducted where urine samples were collected at different time points over 48-h period. Several biomarkers were highlighted in LC-MS based chemometrics using principal component (PCA) and partial least squares discriminant analysis (PLS-DA), which revealed the presence of both epicatechin and gut microbial phenyl-γ-valerolactones (PVLs) conjugated analogues. The presences of these metabolites segregated and grouped the samples based on cocoa and non-cocoa ingestion. Furthermore, semi quantification of major bioavailable metabolites was performed to determine the interindividual differences and assess the relative bioavailability of cocoa compounds in the human body. Our approach presented here is unique in displaying a combination of LC-MS based chemometrics visualization strategies, which revealed and identified significant biomarkers that could reduce the problems associated with data screening complexity.

Novel insight into biological activity and phytochemical composition of Sorbus aucuparia L. fruits: Fractionated extracts as inhibitors of protein glycation and oxidative/nitrative damage of human plasma components

Sorbus aucuparia L. is a source of edible fruits appreciated for their nutritional and medicinal properties. In this work some bioactivity mechanisms were evaluated, which might be connected with the traditional application of rowanberries in cardiovascular complications of diabetes. With the use of a panel of chemical and biological in vitro models the rowanberry extracts were proved to significantly inhibit the formation of advanced glycation end products, neutralise multiple oxidants generated in vivo, increase the non-enzymatic antioxidant capacity of human plasma and protect plasma components (proteins and lipids) against oxidative/nitrative damage at in vivo-relevant levels (1-5 µg/mL). Moreover, the extracts were found safe in cytotoxicity tests on the peripheral blood mononuclear cells. The comprehensive phytochemical profiling of the extracts (RP/HILIC-UHPLC-PDA-ESI-MS³, HPLC-PDA, and UV-spectrophotometric methods) led to the identification of 51 phenolics, including caffeic and ferulic acids pseudodepsides (34 compounds, prevailing isomers of chlorogenic acid and cynarin, total content up to 269.4 mg/g), flavonols (mostly quercetin glycosides, up to 5.8 mg/g), flavan-3-ol derivatives (proanthocyanidin oligomers and polymers, up to 17.0 mg/g), and simple phenolic acids. The experiments on model constituents of the extracts and correlation studies were used to evaluate contribution of polyphenols to the observed effects. Taking into account the possible additive and synergistic effects, the co-occurrence of various compounds was indicated as partly responsible for biological activity of the fruits. Considering both the composition and activity parameters, the methanol-water (1:1, v/v) extract and its concentrated phenolic fractions appeared to be the most advantageous for biological application.

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.

Evaluation of the potential of total proanthocyanidin content in feces as an intake biomarker

Due to the health benefits associated with proanthocyanidins (PAs), it is useful to identify dietary PA biomarkers that can be determined by simple methods. Since increased levels of circulating PA metabolites are associated with increased fecal PA content, this study explores the spectrophotometric measurement of fecal PA content and its use as a biomarker of PA intake. To this end, fecal PA content was measured using an adaptation of Porter's spectrophotometric method in samples from a preclinical study and an observational study. In the former, excretion of 250-400 mg PA polymer equivalents/100 g feces was observed during supplementation and the day after, together with a significant association (p < 0.05) between PA intake and the excretion of both intact PAs and some PA metabolites, i.e., (+)-catechin, (-)-epicatechin and syringic acid. No relationship between intake and excretion was found in the observational study, either for the entire group (mean excretion of 240 ± 226 mg PA polymer equivalents/100 g feces) or after stratification into tertiles of consumption. In conclusion, the spectrophotometric determination of total PA content in feces proved to be a valid compliance marker in a preclinical study, but it was not associated with PA intake in free-living subjects. The potential of total PA excretion in observational studies, determined in fecal samples collected the day before dietary recall or in several fecal samples from the same subject, remains to be elucidated, as does a complete validation of the method proposed here.

Pancreatic lipase and α-amylase inhibitory activity of extracts from selected plant materials after gastrointestinal digestion in vitro

A screening of inhibitory activity of α-amylase, as well as pancreatic lipase (PL), under the influence of aqueous and ethanolic preparations from 12 plant materials was performed. The most active aqueous extracts from the fruits of Chaenomeles japonica (CJ) and Hippophaë rhamnoides (HR) were selected for artificial gastrointestinal digestion (GID). The aim of this study was to evaluate the inhibitory effect of the fractions obtained after GID on PL and α-amylase activities using a fluorescence assay. The changes in the composition of crude extracts in GID aliquots were followed by analysis with HPLC-DAD-MSⁿ method in order to indicate active constituents. The main constituents of CJ and HR extracts were procyanidins and isorhamnetin derivatives, respectively. The most abundant compounds of extracts were found in all compartments of the digestion model correlated with relevant lipase/α-amylase inhibitory activity. What is more, the gastric and intestinal fractions inhibited enzymatic activity by at least 40%.

Bioavailability and nutrikinetics of rosemary tea phenolic compounds in humans

Rosmarinus officinalis L. is a widespread aromatic plant commonly consumed as a tea in traditional cuisine and in folk medicine to treat various illnesses due to its therapeutic properties. To the best of our knowledge, there are no reports on the bioavailability and metabolism of R. officinalis tea polyphenols in humans. This study was aimed at assessing the bioavailability and nutrikinetics of R. officinalis phenolic compounds in healthy humans for the first time. Forty-eight compounds were identified in plasma and urine. Few un-metabolized compounds were detected since rosemary polyphenols were extensively metabolized into phase II conjugates, with rapid appearance and clearance in plasma, pointing to small intestinal absorption. Phase II derivatives of caffeic acid showed kinetics compatible with both intestinal and colonic hydrolysis of rosmarinic acid yielding free caffeic and 3,4-dihydroxyphenyl-lactic acids, which were absorbed and metabolized into phase II derivatives. These metabolites, along with reduced forms of caffeic acid and their phase II metabolites, and those of hydroxyphenylpropionic, hydroxylphenylacetic, benzoic and hippuric acids, highlight the importance of colonic absorption. Total urinary excretion of the phenols added up to 235 µmol, corresponding to 22.3% of the ingested amount (1055 µM). In conclusion, rosemary tea polyphenols are partially bioavailable and extensively metabolized, mainly by the colonic microbiota.

Quantifying the human diet in the crosstalk between nutrition and health by multi-targeted metabolomics of food and microbiota-derived metabolites

BACKGROUND

Metabolomics is a powerful tool for investigating the association between nutrition and health status. Although urine is commonly employed for studying the metabolism and transformation of food components, the use of blood samples could be preferable to gain new insights into the bioavailability of diet-derived compounds and their involvement in health. However, the chemical complexity of blood samples hinders the analysis of this biological fluid considerably, which makes the development of novel and comprehensive analytical methods mandatory.

METHODS

In this work, we optimized a multi-targeted metabolomics platform for the quantitative and simultaneous analysis of 450 food-derived metabolites by ultra-high performance liquid chromatography coupled to tandem mass spectrometry. To handle the chemical complexity of blood samples, three complementary extraction methods were assayed and compared in terms of recovery, sensitivity, precision and matrix effects with the aim of maximizing metabolomics coverage: protein precipitation, reversed solid-phase extraction, and hybrid protein precipitation with solid-phase extraction-mediated phospholipid removal.

RESULTS

After careful optimization of the extraction conditions, protein precipitation enabled the most efficient and high-throughput extraction of the food metabolome in plasma, although solid-phase extraction-based protocols provided complementary performance for the analysis of specific polyphenol classes. The developed method yielded accurate recovery rates with negligible matrix effects, and good linearity, as well as high sensitivity and precision for most of the analyzed metabolites.

CONCLUSIONS

The multi-targeted metabolomics platform optimized in this work enables the simultaneous detection and quantitation of 450 dietary metabolites in short-run times using small volumes of biological sample, which facilitates its application to epidemiological studies.

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.

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.

Rethinking the Mechanism of the Health Benefits of Proanthocyanidins: Absorption, Metabolism, and Interaction with Gut Microbiota

Proanthocyanidins, as the oligomers or polymers of flavan-3-ol, are widely discovered in plants such as fruits, vegetables, cereals, nuts, and leaves, presenting a major part of dietary polyphenols. Although proanthocyanidins exert several types of bioactivities, such as antioxidant, antimicrobial, cardioprotective, and neuroprotective activity, their exact mechanisms remain unclear. Due to the complexity of the structure of proanthocyanidins, such as their various monomers, different linkages and isomers, investigation of their bioavailability and metabolism is limited, which further hinders the explanation of their bioactivities. Since the large molecular weight and degree of polymerization limit the bioavailability of proanthocyanidins, the major effective site of proanthocyanidins is proposed to be in the gut. Many studies have revealed the effects of proanthocyanidins from different sources on changing the composition of gut microbiota based on in vitro and in vivo models and the bioactivities of their metabolites. However, the metabolic routes of proanthocyanidins by gut microbiota and their mutual interactions are still sparse. Thus, this review summarizes the chemistry, absorption, and metabolic pathways of proanthocyanidins ranging from monomers to polymers, as well as the mutual interactions between proanthocyanidins and gut microbiota, in order to better understand how proanthocyanidins exert their health-promoting functions.

Phenolic Metabolites in Plasma and Thigh Meat of Chickens Supplemented with Grape Byproducts

Grape byproducts are rich sources of polyphenols with powerful antioxidant and health-promoting effects. The impact of supplementing chicken diets with grape byproducts on plasma and thigh meat concentrations of phenolic metabolites was evaluated by analyzing samples by high-performance liquid chromatography quadrupole time of flight mass spectrometry. Chickens were fed three experimental diets: Control diet, Control+8% grape pomace, and Control+0.1% grape seed extract. In plasma, 32 phenolic metabolites were identified, some of which were conjugated catechin/epicatechin metabolites exclusively identified in chickens fed diets enriched in grape byproducts. Also, these chickens showed significantly higher plasmatic concentrations of 21 phenolic metabolites. In thigh meat, 14 phenolic metabolites were identified, but no differences were found between diets. Higher plasmatic tocopherol was found when supplementing diets with grape byproducts, while no changes were observed in meat. Thus, supplementing chicken diets with grape byproducts leads to a significant increase in the circulation of phenolic metabolites and tocopherol.

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.

Targeted Screening Approach to Systematically Identify the Absorbed Effect Substances of Poria cocos in Vivo Using Ultrahigh Performance Liquid Chromatography Tandem Mass Spectrometry

Poria cocos are extensively used as nutritious food, dietary supplements, and oriental medicine in Asia. However, the effect substances are still not very clear. In this study, a targeted screening approach was developed to systematically identify absorbed constituents of Poria cocos in vivo using ultrahigh performance liquid chromatography tandem mass spectrometry combined with UNIFI software. First, incubation reactions in vitro with rat intestinal microflora and rat liver microsomes were conducted to sum up metabolic rules of main constituents. Second, the absorbed constituents in vivo were picked out and identified based on the results of metabolic study in vitro. Finally, the absorbed active constituents in the treatment of Alzheimer's disease were screened by targeted network pharmacology analysis. A total of 62 absorbed prototypes and 59 metabolites were identified and characterized in dosed plasma. Thirty potential active constituents were screened, and 86 drug-targets shared by absorbed constituents and Alzheimer's disease were discovered by targeted network pharmacology analysis. In general, this proposed targeted strategy comprehensively provides new insight for active ingredients of Poria cocos.