Quantifying the effect of nutritional interventions on metabolic resilience using personalized computational models

The manifestation of metabolic deteriorations that accompany overweight and obesity can differ greatly between individuals, giving rise to a highly heterogeneous population. This inter-individual variation can impede both the provision and assessment of nutritional interventions as multiple aspects of metabolic health should be considered at once. Here, we apply the Mixed Meal Model, a physiology-based computational model, to characterize an individual's metabolic health in silico. A population of 342 personalized models were generated using data for individuals with overweight and obesity from three independent intervention studies, demonstrating a strong relationship between the model-derived metric of insulin resistance (ρ = 0.67, p < 0.05) and the gold-standard hyperinsulinemic-euglycemic clamp. The model is also shown to quantify liver fat accumulation and β-cell functionality. Moreover, we show that personalized Mixed Meal Models can be used to evaluate the impact of a dietary intervention on multiple aspects of metabolic health at the individual level.

Metabolomics and sensory evaluation of white asparagus ingredients in instant soups unveil important (off-)flavours

Split-stream processing of asparagus waste stream is a novel approach to produce spray-dried powder and fibre. Asparagus ingredients processed by this method and a commercial asparagus powder were compared by evaluating their flavour profile in a soup formulation. Professional sensory panel and untargeted metabolomics approaches using GC-MS and LC-MS were carried out. Unsupervised and supervised statistical analyses were performed to highlight discriminatory metabolites and correlate these to sensory attributes. The spray-dried powder scored higher on asparagus flavour compared to the commercial powder. The fibre negatively impacted the taste and mouthfeel of the soups. GC-O-MS confirmed the role of dimethyl sulphide, 2-methoxy-3-isopropyl pyrazine and 2-methoxy-3-isobutyl pyrazine in asparagus odour. Seven new volatile compounds are also proposed to contribute to asparagus flavour notes, most of which were more abundant in the spray-dried powder. This research demonstrates the feasibility of upcycling asparagus waste streams into flavour-rich ingredients with good sensorial properties.

Protocol for the Brain Health Support Program Study of the Canadian Therapeutic Platform Trial for Multidomain Interventions to Prevent Dementia (CAN-THUMBS UP): A Prospective 12-Month Intervention Study

BACKGROUND/OBJECTIVES

CAN-THUMBS UP is designed as a comprehensive and innovative fully remote program to 1) develop an interactive and compelling online Brain Health Support Program intervention, with potential to positively influence dementia literacy, self-efficacy and lifestyle risk factors; 2) enroll and retain a community-dwelling Platform Trial Cohort of individuals at risk of dementia who will participate in the intervention; 3) support an open platform trial to test a variety of multidomain interventions that might further benefit individuals at risk of dementia. This manuscript presents the Brain Health Support Program Study protocol.

DESIGN/SETTING

Twelve-month prospective multi-center longitudinal study to evaluate a fully remote web-based educational intervention. Participants will subsequently be part of a Platform Trial Cohort and may be eligible to participate in further dementia prevention clinical trials.

PARTICIPANTS

Three hundred fifty older adults who are cognitively unimpaired or have mild cognitive impairment, with at least 1 well established dementia risk factor.

INTERVENTION

Participants engage in the Brain Health Support Program intervention for 45-weeks and complete pre/post intervention measures. This intervention is designed to convey best available evidence for dementia prevention, consists of 181 chapters within 8 modules that are progressively delivered, and is available online in English and French. The program has been developed as a collaborative effort by investigators with recognized expertise in the program's content areas, along with input from older-adult citizen advisors.

MEASUREMENTS

This study utilizes adapted remote assessments with accessible technologies (e.g. videoconferencing, cognitive testing via computer and mobile phone, wearable devices to track physical activity and sleep, self-administered saliva sample collection). The primary outcome is change in dementia literacy, as measured by the Alzheimer's Disease Knowledge Scale. Secondary outcomes include change in self-efficacy; engagement using the online program; user satisfaction ratings; and evaluation of usability and acceptance. Exploratory outcomes include changes in attitudes toward dementia, modifiable risk factors, performance on the Neuropsychological Test Battery, performance on self-administered online cognitive assessments, and levels of physical activity and sleep; success of the national recruitment plan; and the distribution of age adjusted polygenic hazard scores.

CONCLUSIONS

This fully remote study provides an accessible approach to research with all study activities being completed in the participants' home environment. This approach may reduce barriers to participation, provide an easier and less demanding participant experience, and reach a broader geography with recruitment from all regions of Canada. CAN-THUMBS UP represents a Canadian contribution to the global World-Wide FINGERS program (alz.org/wwfingers).

Flavor Profiling Using Comprehensive Mass Spectrometry Analysis of Metabolites in Tomato Soups

Trained sensory panels are regularly used to rate food products but do not allow for data-driven approaches to steer food product development. This study evaluated the potential of a molecular-based strategy by analyzing 27 tomato soups that were enhanced with yeast-derived flavor products using a sensory panel as well as LC-MS and GC-MS profiling. These data sets were used to build prediction models for 26 different sensory attributes using partial least squares analysis. We found driving separation factors between the tomato soups and metabolites predicting different flavors. Many metabolites were putatively identified as dipeptides and sulfur-containing modified amino acids, which are scientifically described as related to umami or having "garlic-like" and "onion-like" attributes. Proposed identities of high-impact sensory markers (methionyl-proline and asparagine-leucine) were verified using MS/MS. The overall results highlighted the strength of combining sensory data and metabolomics platforms to find new information related to flavor perception in a complex food matrix.

Quantifying the contribution of triglycerides to metabolic resilience through the mixed meal model

Despite the pivotal role played by elevated circulating triglyceride levels in the pathophysiology of cardio-metabolic diseases many of the indices used to quantify metabolic health focus on deviations in glucose and insulin alone. We present the Mixed Meal Model, a computational model describing the systemic interplay between triglycerides, free fatty acids, glucose, and insulin. We show that the Mixed Meal Model can capture deviations in the post-meal excursions of plasma glucose, insulin, and triglyceride that are indicative of features of metabolic resilience; quantifying insulin resistance and liver fat; validated by comparison to gold-standard measures. We also demonstrate that the Mixed Meal Model is generalizable, applying it to meals with diverse macro-nutrient compositions. In this way, by coupling triglycerides to the glucose-insulin system the Mixed Meal Model provides a more holistic assessment of metabolic resilience from meal response data, quantifying pre-clinical metabolic deteriorations that drive disease development in overweight and obesity.

Systemic Lactate Acts as a Metabolic Buffer in Humans and Prevents Nutrient Overflow in the Postprandial Phase

On an organismal level, metabolism needs to react in a well-orchestrated manner to metabolic challenges such as nutrient uptake. Key metabolic hubs in human blood are pyruvate and lactate, both of which are constantly interconverted by very fast exchange fluxes. The quantitative contribution of different food sources to these metabolite pools remains unclear. Here, we applied in vivo stable isotope labeling to determine postprandial metabolic fluxes in response to two carbohydrate sources of different complexity. Depending on the ingested carbohydrate source, glucose or wheat flour, the net direction of the lactate dehydrogenase, and the alanine amino transferase fluxes were adjusted in a way to ensure sufficient availability, while, at the same time, preventing an overflow in the respective metabolite pools. The systemic lactate pool acts as a metabolic buffer which is fueled in the early- and depleted in the late-postprandial phase and thus plays a key role for systemic metabolic homeostasis.

Human Blood Lipoprotein Predictions from 1H NMR Spectra: Protocol, Model Performances, and Cage of Covariance

Lipoprotein subfractions are biomarkers for the early diagnosis of cardiovascular diseases. The reference method, ultracentrifugation, for measuring lipoproteins is time-consuming, and there is a need to develop a rapid method for cohort screenings. This study presents partial least-squares regression models developed using ¹H nuclear magnetic resonance (NMR) spectra and concentrations of lipoproteins as measured by ultracentrifugation on 316 healthy Danes. This study explores, for the first time, different regions of the ¹H NMR spectrum representing signals of molecules in lipoprotein particles and different lipid species to develop parsimonious, reliable, and optimal prediction models. A total of 65 lipoprotein main and subfractions were predictable with high accuracy, Q² of >0.6, using an optimal spectral region (1.4-0.6 ppm) containing methylene and methyl signals from lipids. The models were subsequently tested on an independent cohort of 290 healthy Swedes with predicted and reference values matching by up to 85-95%. In addition, an open software tool was developed to predict lipoproteins concentrations in human blood from standardized ¹H NMR spectral recordings.

Systematic selection of competing metabolomics methods in a metabolite-sensory relationship study

INTRODUCTION

The relationship between the chemical composition of food products and their sensory profile is a complex association confronting many challenges. However, new untargeted methodologies are helping correlate metabolites with sensory characteristics in a simpler manner. Nevertheless, in the pilot phase of a project, where only a small set of products are used to explore the relationships, choices have to be made about the most appropriate untargeted metabolomics methodology.

OBJECTIVE

To provide a framework for selecting a metabolite-sensory methodology based on: the quality of measurements, the relevance of the detected metabolites in terms of distinguishing between products or in terms of whether they can be related to the sensory attributes of the products.

METHODS

In this paper we introduce a systematic approach to explore all these different aspects driving the choice for the most appropriate metabolomics method.

RESULTS

As an example we have used a tomato soup project where the choice between two sampling methods (SPME and SBSE) had to be made. The results are not always consistently pointing to the same method as being the best. SPME was able to detect metabolites with a better precision, SBSE seemed to be able to provide a better distinction between the soups.

CONCLUSION

The three levels of comparison provide information on how the methods could perform in a follow up study and will help the researcher to make a final selection for the most appropriate method based on their strengths and weaknesses.

Stir bar sorptive extraction of aroma compounds in soy sauce: Revealing the chemical diversity

Fermented soy sauce is used worldwide to enhance the flavour of many dishes. Many types of soy sauce are on the market, and their differences are mostly related to the country of origin, the production process applied and the ratio of ingredients used. Consequently, several aromas, tastes, colours, and textures are obtained. Nowadays, soy sauce can also be produced without microorganisms making the process shorter and cheaper. However, flavour may be lost. We have carried out a comprehensive metabolomics analysis of volatile compounds using stir bar sorptive extraction (SBSE)-GC-MS to relate differences in volatile content to production history and origin. The results revealed major differences between fermented and non-fermented soy sauces, and a list of volatile compounds is reported as being characteristic of each type. This study was able to relate volatiles to the production process using SBSE-GC-MS and to aroma characteristics using GC-O-MS.

Towards superior plant-based foods using metabolomics

Metabolomics is proving a useful approach for many of the main future goals in agronomy and food production such as sustainability/crop resilience, food quality, safety, storage, and nutrition. Targeted and/or untargeted small-molecule analysis, coupled to chemometric analysis, has already unveiled a great deal of the complexity of plant-based foods, but there is still 'dark matter' to be discovered. Moreover, state-of-the-art food metabolomics offers insights into the molecular mechanisms underlying sensorial and nutritional characteristics of foods and thus enables higher precision and speed. This review describes recent applications of food metabolomics from fork to farm and focuses on the opportunities these bring to continue food innovation and support the shift to plant-based foods.

Chemical Fingerprints of Emotional Body Odor

Chemical communication is common among animals. In humans, the chemical basis of social communication has remained a black box, despite psychological and neural research showing distinctive physiological, behavioral, and neural consequences of body odors emitted during emotional states like fear and happiness. We used a multidisciplinary approach to examine whether molecular cues could be associated with an emotional state in the emitter. Our research revealed that the volatile molecules transmitting different emotions to perceivers also have objectively different chemical properties. Chemical analysis of underarm sweat collected from the same donors in fearful, happy, and emotionally neutral states was conducted using untargeted two-dimensional (GC×GC) coupled with time of flight (ToF) MS-based profiling. Based on the multivariate statistical analyses, we find that the pattern of chemical volatiles (N = 1655 peaks) associated with fearful state is clearly different from that associated with (pleasant) neutral state. Happy sweat is also significantly different from the other states, chemically, but shows a bipolar pattern of overlap with fearful as well as neutral state. Candidate chemical classes associated with emotional and neutral sweat have been identified, specifically, linear aldehydes, ketones, esters, and cyclic molecules (5 rings). This research constitutes a first step toward identifying the chemical fingerprints of emotion.

Effects of a whole diet approach on metabolic flexibility, insulin sensitivity and postprandial glucose responses in overweight and obese adults - A randomized controlled trial

BACKGROUND & AIMS

Metabolic flexibility is the ability to adapt fuel oxidation to fuel availability. Metabolic inflexibility has been associated with obesity, the metabolic syndrome and insulin resistance, and can be improved by exercise or weight loss. Dietary changes can modulate metabolic flexibility; however, the effect of a whole diet approach on metabolic flexibility has never been studied. Therefore, our objective was to assess the effect of a healthy diet (HD), as compared to a typical Western diet (WD), on several fasting and postprandial markers of metabolic flexibility and insulin sensitivity.

METHODS

In this parallel randomized trial, overweight or obese men and women (50-70 years; BMI 25-35 kg/m²) consumed a healthy diet (HD; high in fruits and vegetables, pulses, fibers, nuts, fatty fish, and low in high-glycemic carbohydrates; n = 19) or a typical Western diet (WD; n = 21) for six weeks, following a two-week run-in period. The change in respiratory quotient upon insulin stimulation (ΔRQ), and insulin sensitivity, expressed as the M-value, were both determined with a hyperinsulinemic euglycemic clamp. Additionally, other fasting and postprandial markers of metabolic flexibility were assessed during a 5-h high-fat high-glycemic mixed meal challenge.

RESULTS

ΔRQ (p = 0.730) and insulin sensitivity (p = 0.802) were not significantly affected by diet. Postprandial RQ did also not show significant differences (p = 0.610), whereas postprandial glucose excursions were significantly higher in the HD group at T30 (p = 0.014) and T45 (p = 0.026) after mixed meal ingestion (p = 0.037). Fasting glucose (p = 0.530) and HbA1c (p = 0.124) remained unchanged, whereas decreases in fasting insulin (p = 0.038) and the HOMA-IR (p = 0.050) were significantly more pronounced with the HD.

CONCLUSION

A healthy diet for six weeks, without further life-style changes, did not improve metabolic flexibility and whole-body insulin sensitivity, when compared to a Western-style diet. It remains to be determined whether the short time increase in postprandial glucose is physiologically relevant or detrimental to metabolic health. This trial was registered at clinicaltrials.gov as NCT02519127.

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.

Oxylipin profiling in endothelial cells in vitro - Effects of DHA and hydrocortisone upon an inflammatory challenge

Omega-3 poly-unsaturated fatty acids have been shown to have beneficial effects on several inflammatory-driven endpoints such as cardiovascular diseases. The anti-inflammatory effects of docosahexaenoic acid (DHA) are largely mediated through various oxylipins. Yet, mechanistic insights are limited. Here, we measured 53 oxylipins using LC-MS/MS in an in vitro model of endothelial cell inflammation, and compared the changes induced by DHA to hydrocortisone, a well-established anti-inflammatory drug. DHA modified several oxylipins derived from different precursors such as DHA, AA, LA and EPA. In response to a TNFα and IL-1-β challenge, DHA clearly reduced many COX-derived pro-inflammatory oxylipins, yet to a minor extent when compared to hydrocortisone. DHA also upregulated metabolites from the CYP and LOX pathways as opposed to hydrocortisone. Thus, DHA reduced pro-inflammation and enhanced pro-resolution, while hydrocortisone blunted both the pro- and anti-inflammatory pathways. Our results may fuel further research on the mitigation of corticosteroids adverse side-effects.

Postprandial Metabolic Effects of Fiber Mixes Revealed by in vivo Stable Isotope Labeling in Humans

Food supplementation with a fiber mix of guar gum and chickpea flour represents a promising approach to reduce the risk of type 2 diabetes mellitus (T2DM) by attenuating postprandial glycemia. To investigate the effects on postprandial metabolic fluxes of glucose-derived metabolites in response to this fiber mix, a randomized, cross-over study was designed. Twelve healthy, male subjects consumed three different flatbreads either supplemented with 2% guar gum or 4% guar gum and 15% chickpea flour or without supplementation (control). The flatbreads were enriched with ~2% of ¹³C-labeled wheat flour. Blood was collected at 16 intervals over a period of 360 min after bread intake and plasma samples were analyzed by GC-MS based metabolite profiling combined with stable isotope-assisted metabolomics. Although metabolite levels of the downstream metabolites of glucose, specifically lactate and alanine, were not altered in response to the fiber mix, supplementation of 4% guar gum was shown to significantly delay and reduce the exogenous formation of these metabolites. Metabolic modeling and computation of appearance rates revealed that the effects induced by the fiber mix were strongest for glucose and attenuated downstream of glucose. Further investigations to explore the potential of fiber mix supplementation to counteract the development of metabolic diseases are warranted.

Quantification of Stable Isotope Traces Close to Natural Enrichment in Human Plasma Metabolites Using Gas Chromatography-Mass Spectrometry

Currently, changes in metabolic fluxes following consumption of stable isotope-enriched foods are usually limited to the analysis of postprandial kinetics of glucose. Kinetic information on a larger diversity of metabolites is often lacking, mainly due to the marginal percentage of fully isotopically enriched plant material in the administered food product, and hence, an even weaker ¹³C enrichment in downstream plasma metabolites. Therefore, we developed an analytical workflow to determine weak ¹³C enrichments of diverse plasma metabolites with conventional gas chromatography-mass spectrometry (GC-MS). The limit of quantification was increased by optimizing (1) the metabolite extraction from plasma, (2) the GC-MS measurement, and (3) most importantly, the computational data processing. We applied our workflow to study the catabolic dynamics of ¹³C-enriched wheat bread in three human subjects. For that purpose, we collected time-resolved human plasma samples at 16 timepoints after the consumption of ¹³C-labeled bread and quantified ¹³C enrichment of 12 metabolites (glucose, lactate, alanine, glycine, serine, citrate, glutamate, glutamine, valine, isoleucine, tyrosine, and threonine). Based on isotopomer specific analysis, we were able to distinguish catabolic profiles of starch and protein hydrolysis. More generally, our study highlights that conventional GC-MS equipment is sufficient to detect isotope traces below 1% if an appropriate data processing is integrated.

Weight loss moderately affects the mixed meal challenge response of the plasma metabolome and transcriptome of peripheral blood mononuclear cells in abdominally obese subjects

INTRODUCTION

The response to dietary challenges has been proposed as a more accurate measure of metabolic health than static measurements performed in the fasted state. This has prompted many groups to explore the potential of dietary challenge tests for assessment of diet and lifestyle induced shifts in metabolic phenotype.

OBJECTIVES

We examined whether the response to a mixed-meal challenge could provide a readout for a weight loss (WL)-induced phenotype shift in abdominally obese male subjects. The underlying assumption of a mixed meal challenge is that it triggers all aspects of phenotypic flexibility and provokes a more prolonged insulin response, possibly allowing for better differentiation between individuals.

METHODS

Abdominally obese men (n = 29, BMI = 30.3 ± 2.4 kg/m²) received a mixed-meal challenge prior to and after an 8-week WL or no-WL control intervention. Lean subjects (n = 15, BMI = 23.0 ± 2.0 kg/m²) only received the mixed meal challenge at baseline to have a benchmark for WL-induced phenotype shifts.

RESULTS

Levels of several plasma metabolites were significantly different between lean and abdominally obese at baseline as well as during postprandial metabolic responses. Genes related to oxidative phosphorylation in peripheral blood mononuclear cells (PBMCs) were expressed at higher levels in abdominally obese subjects as compared to lean subjects at fasting, which was partially reverted after WL. The impact of WL on the postprandial response was modest, both at the metabolic and gene expression level in PBMCs.

CONCLUSION

We conclude that mixed-meal challenges are not necessarily superior to measurements in the fasted state to assess metabolic health. Furthermore, the mechanisms accounting for the observed differences between lean and abdominally obese in the fasted state are different from those underlying the dissimilarity observed during the postprandial response.

Effect of Theobromine Consumption on Serum Lipoprotein Profiles in Apparently Healthy Humans with Low HDL-Cholesterol Concentrations

Scope: Theobromine is a major active compound in cocoa with allegedly beneficial effect on high-density-lipoprotein-cholesterol (HDL-CH). We have investigated the effect of theobromine (TB) consumption on the concentrations of triglyceride (TG) and cholesterol (CH) in various lipoprotein (LP) subclasses.

Methods: In a randomized, double-blind, placebo-controlled, cross-over study, 44 apparently healthy women and men (age: 60 ± 6 years, BMI: 29 ± 3 kg/m²) with low baseline HDL-CH concentrations consumed a drink supplemented with 500 mg/d theobromine for 4 weeks. TG and CH concentrations in 15 LP subclasses were predicted from diffusion-edited ¹H NMR spectra of fasting serum.

Results: The LP phenotype of the subjects was characterized by low CH concentrations in the large HDL particles and high TG concentrations in large VLDL and chylomicron (CM) particles, which clearly differed from a LP phenotype of subjects with normal HDL-CH. TB only reduced CH concentrations in the LDL particles by 3.64 and 6.79%, but had no effect on TG and CH in any of the HDL, VLDL and CM subclasses.

Conclusion: TB was not effective on HDL-CH in subjects with a LP phenotype characterized by low HDL-CH and high TG in VLDL.

Toward Reliable Lipoprotein Particle Predictions from NMR Spectra of Human Blood: An Interlaboratory Ring Test

Lipoprotein profiling of human blood by ¹H nuclear magnetic resonance (NMR) spectroscopy is a rapid and promising approach to monitor health and disease states in medicine and nutrition. However, lack of standardization of measurement protocols has prevented the use of NMR-based lipoprotein profiling in metastudies. In this study, a standardized NMR measurement protocol was applied in a ring test performed across three different laboratories in Europe on plasma and serum samples from 28 individuals. Data was evaluated in terms of (i) spectral differences, (ii) differences in LPD predictions obtained using an existing prediction model, and (iii) agreement of predictions with cholesterol concentrations in high- and low-density lipoproteins (HDL and LDL) particles measured by standardized clinical assays. ANOVA-simultaneous component analysis (ASCA) of the ring test spectral ensemble that contains methylene and methyl peaks (1.4–0.6 ppm) showed that 97.99% of the variance in the data is related to subject, 1.62% to sample type (serum or plasma), and 0.39% to laboratory. This interlaboratory variation is in fact smaller than the maximum acceptable intralaboratory variation on quality control samples. It is also shown that the reproducibility between laboratories is good enough for the LPD predictions to be exchangeable when the standardized NMR measurement protocol is followed. With the successful implementation of this protocol, which results in reproducible prediction of lipoprotein distributions across laboratories, a step is taken toward bringing NMR more into scope of prognostic and diagnostic biomarkers, reducing the need for less efficient methods such as ultracentrifugation or high-performance liquid chromatography (HPLC).

Assessment of dietary exposure and effect in humans: The role of NMR

In human nutritional science progress has always depended strongly on analytical measurements for establishing relationships between diet and health. This field has undergone significant changes as a result of the development of NMR and mass spectrometry methods for large scale detection, identification and quantification of metabolites in body fluids. This has allowed systematic studies of the metabolic fingerprints that biological processes leave behind, and has become the research field of metabolomics. As a metabolic profiling technique, NMR is at its best when its unbiased nature, linearity and reproducibility are exploited in well-controlled nutritional intervention and cross-sectional population screening studies. Although its sensitivity is less good than that of mass spectrometry, NMR has maintained a strong position in metabolomics through implementation of standardisation protocols, hyphenation with mass spectrometry and chromatographic techniques, accurate quantification and spectral deconvolution approaches, and high-throughput automation. Thus, NMR-based metabolomics has contributed uniquely to new insights into dietary exposure, in particular by unravelling the metabolic fates of phytochemicals and the discovery of dietary intake markers. NMR profiling has also contributed to the understanding of the subtle effects of diet on central metabolism and lipoprotein metabolism. In order to hold its ground in nutritional metabolomics, NMR will need to step up its performance in sensitivity and resolution; the most promising routes forward are the analytical use of dynamic nuclear polarisation and developments in microcoil construction and automated fractionation.

The effect of plant sterols and different low doses of omega-3 fatty acids from fish oil on lipoprotein subclasses

SCOPE

Consumption of a low-fat spread enriched with plant sterols (PS) and different low doses (<2 g/day) of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish oil reduces serum triglycerides (TGs) and low-density lipoprotein-cholesterol (LDL-Chol) and thus beneficially affects two blood lipid risk factors. Yet, their combined effects on TG and Chol in various lipoprotein subclasses have been investigated to a limited extent.

METHODS AND RESULTS

In a randomized, double-blind, placebo-controlled, parallel study, we determined TG and Chol in 13 LP subclasses in fasting serum of 282 hypercholesterolemic subjects, who consumed either a placebo spread or one of the four spreads containing PS (2.5 g/day) and EPA+DHA (0.0, 0.9, 1.3, and 1.8 g/day) for 4 weeks. After PS treatment, total LDL-Chol was reduced, which was not further changed by EPA+DHA. No shift in the LDL-Chol particle distribution was observed. The addition of EPA+DHA to PS dose-dependently reduced VLDL-Chol and VLDL-TG mainly in larger particles. Furthermore, the two highest doses of EPA+DHA increased Chol and TG in the larger HDL particles, while these concentrations were decreased in the smallest HDL particles.

CONCLUSION

The consumption of a low-fat spread enriched with both PS and EPA+DHA induced shifts in the lipoprotein distribution that may provide additional cardiovascular benefits over PS consumption alone.

Strategies for individual phenotyping of linoleic and arachidonic acid metabolism using an oral glucose tolerance test

The ability to restore homeostasis upon environmental challenges has been proposed as a measure for health. Metabolic profiling of plasma samples during the challenge response phase should offer a profound view on the flexibility of a phenotype to cope with daily stressors. Current data modeling approaches, however, struggle to extract biological descriptors from time-resolved metabolite profiles that are able to discriminate between different phenotypes. Thus, for the case of oxylipin responses in plasma upon an oral glucose tolerance test we developed a modeling approach that incorporates a priori biological pathway knowledge. The degradation pathways of arachidonic and linoleic acids were modeled using a regression model based on a pseudo-steady-state approximated model, resulting in a parameter A that summarizes the relative enzymatic activity in these pathways. Analysis of the phenotypic parameters As suggests that different phenotypes can be discriminated according to preferred relative activity of the arachidonic and linoleic pathway. Correlation analysis shows that there is little or no competition between the arachidonic and linoleic acid pathways, although they share the same enzymes.

Variable duration of decaffeinated green tea extract ingestion on exercise metabolism

PURPOSE

The aim of this study was to investigate if the duration of decaffeinated green tea extract (dGTE) ingestion plays a role in augmenting fat oxidation rates during moderate-intensity exercise.

METHODS

In a crossover, placebo-controlled design, 19 healthy males (mean ± SD; age = 21 ± 2 yr, weight = 75.0 ± 7.0 kg, body mass index = 23.2 ± 2.2 kg·m, maximal oxygen consumption [V˙O2max] = 55.4 ± 4.6 mL·kg·min) ingested dGTE and placebo (PLA) for 28 d, separated by a 28-d washout period. On the first day (dGTE 1 or PLA 1) and after 7 d (dGTE 7 or PLA 7) and 28 d (dGTE 28 or PLA 28), participants completed a 30-min cycle exercise bout (50% Wmax), 2 h after ingestion. Indirect calorimetry was used to calculate rates of whole-body fat and carbohydrate oxidation during exercise. Blood samples were collected at rest and during exercise for analysis of plasma fatty acids, glycerol, and epigallocatechin gallate.

RESULTS

The ingestion of dGTE did not significantly change whole-body fat oxidation rates during exercise on day 1, 7, or 28 compared with PLA. There were also no changes in plasma concentrations of fatty acids and glycerol at rest and during exercise as a result of dGTE ingestion at any time point compared with PLA. Plasma epigallocatechin gallate concentrations, immediately before the exercise bout, in the three dGTE trials were elevated compared with PLA but not different between 1, 7, and 28 d.

CONCLUSION

In contrast to previous reports, we found that the duration of dGTE ingestion had no effect on whole-body fat oxidation rates or fat metabolism-related blood metabolites during exercise in physically active healthy males.

Metabolic response to decaffeinated green tea extract during rest and moderate-intensity exercise

We previously reported that a 7 day ingestion of caffeinated green tea extract (cGTE) induced marked metabolic differences during rest and exercise. Here, we report the metabolic effects of 1, 7, and 28 day ingestions of decaffeinated GTE (dGTE). In this crossover placebo-controlled study, 19 healthy males ingested dGTE or placebo (PLA) for 28 days, separated by a 28 day wash-out period. On days 1, 7, and 28, participants completed a 30 min cycling exercise 2 h after the ingestion of dGTE or PLA. Blood samples were collected at rest (t = 0 and 120 min) and during exercise (t = 150 min). Plasma was analyzed using untargeted four-phase metabolite profiling and targeted profiling of catecholamines and catechins. dGTE abolished several metabolic effects when compared to our previous study with cGTE. However, following 7 and 28 day dGTE ingestions, increases in 3-hydroxybutyrate, a metabolic marker of fat oxidation, were observed at t = 0 min. dGTE ingestion did not induce significant acute or acute-on-chronic effects on endogenous metabolites just prior to and during exercise.

Acute effects of green tea extract intake on exogenous and endogenous metabolites in human plasma

The acute effects of green tea extract (GTE) on plasma metabolites in vivo are largely unknown. In this parallel, double-blind study, the transient changes in total and free concentrations of catechins were measured in plasma from healthy males following the consumption of a single GTE dose (559.2 mg total catechins, 120.4 mg caffeine). Furthermore, the acute effects on endogenous metabolites were assessed 2 h after GTE intake using four-phase metabolite profiling. The ratios of the catechin concentrations in plasma to those in the GTE followed the order ECG/CG > EC > GCG > EGCG > EGC > C > GC. The gallated catechins EGCG, CG/ECG, GC, and GCG were also present in their free form. Sixteen out of 163 mostly endogenous metabolites were affected by acute GTE ingestion, when compared to placebo. These included caffeine, salicylate, hippurate, taurine, 3,4-dihydroxyphenylethylene-glycol, serotonin, some cholesterylesters, fatty acids, triglycerides, and sphingosines. Our results on the exogenous metabolites largely confirm previous studies, while our findings on the endogenous metabolites are novel and may suggest specific biological targets.

No effect of 1 or 7 d of green tea extract ingestion on fat oxidation during exercise

PURPOSE

The aim of this study was to investigate the effects of 1 and 7 d of green tea extract (GTE) ingestion on whole body fat oxidation during moderate-intensity exercise.

METHODS

Thirty-one men completed two exercise trials (60-min cycle, 50% Wmax). After the baseline trial (day 0), subjects were randomly assigned to one of three conditions involving a week supplementation of the following: 1) 7 d of placebo, 2) 6 d of placebo followed by 1 d of GTE (GTE1), and 3) 7 d of GTE ingestion (GTE7). The morning after the supplementation week, subjects consumed an additional supplement and completed a second exercise trial (day 8). V˙O2 and V˙CO2 measurements were taken during exercise to calculate whole body fat oxidation rates. Blood samples, for analysis of plasma fatty acids (FA), glycerol, and epigallocatechin gallate, were collected at rest and during exercise.

RESULTS

On day 8, the plasma kinetics and maximal plasma concentrations of epigallocatechin gallate were similar in the GTE1 and GTE7 group (206 ± 28 and 216 ± 25 ng·mL, respectively). One day of GTE ingestion did not affect markers of lipolysis during the exercise bout. Seven days of GTE ingestion significantly increased plasma glycerol during exercise (P = 0.045) and plasma FA during exercise (P = 0.020) as well as at rest (P = 0.046). However, fat oxidation did not change in any of the groups.

CONCLUSIONS

There was no effect of 1 d of GTE ingestion on markers of lipolysis or fat oxidation during exercise. Seven days of GTE ingestion increased lipolysis, indicated by increased plasma FA and glycerol concentrations, but did not result in significant changes in fat oxidation.

Interactions of black tea polyphenols with human gut microbiota: implications for gut and cardiovascular health

Epidemiologic studies have convincingly associated consumption of black tea with reduced cardiovascular risk. Research on the bioactive molecules has traditionally been focused on polyphenols, such as catechins. Black tea polyphenols (BTPs), however, mainly consist of high-molecular-weight species that predominantly persist in the colon. There, they can undergo a wide range of bioconversions by the resident colonic microbiota but can in turn also modulate gut microbial diversity. The impact of BTPs on colon microbial composition can now be assessed by microbiomics technologies. Novel metabolomics platforms coupled to de novo identification are currently available to cover the large diversity of BTP bioconversions by the gut microbiota. Nutrikinetic modeling has been proven to be critical for defining nutritional phenotypes related to gut microbial bioconversion capacity. The bioactivity of circulating metabolites has been studied only to a certain extent. Bioassays dedicated to specific aspects of gut and cardiovascular health have been used, although often at physiologically irrelevant concentrations and with limited coverage of relevant metabolite classes and their conjugated forms. Evidence for cardiovascular benefits of BTPs points toward antiinflammatory and blood pressure-lowering properties and improvement in platelet and endothelial function for specific microbial bioconversion products. Clearly, more work is needed to fill in existing knowledge gaps and to assess the in vitro and in vivo bioactivity of known and newly identified BTP metabolites. It is also of interest to assess how phenotypic variation in gut microbial BTP bioconversion capacity relates to gut and cardiovascular health predisposition.

Assessment of inflammatory resilience in healthy subjects using dietary lipid and glucose challenges

BACKGROUND

Resilience or the ability of our body to cope with daily-life challenges has been proposed as a new definition of health, with restoration of homeostasis as target resultant of various physiological stress responses. Challenge models may thus be a sensitive measure to study the body's health. The objective of this study was to select a dietary challenge model for the assessment of inflammatory resilience. Meals are a challenge to metabolic homeostasis and are suggested to affect inflammatory pathways, yet data in literature are limited and inconsistent.

METHOD

The kinetic responses of three different dietary challenges and a water control challenge were assessed on various metabolic and inflammatory markers in 14 healthy males and females using a full cross-over study design. The dietary challenges included glucose (75 g glucose in 300 ml water), lipids (200 ml whipping cream) and a mix of glucose and lipids (same amounts as above), respectively. Blood samples were collected at baseline and at 0.5, 1, 2, 4, 6, 8 and 10 h after consumption of the treatment products. Inflammation (IFNγ, IL-1β, IL-6, IL-8, IL-10, IL-12p70, TNF-α CRP, ICAM-1, VCAM-1, SAA, E-selectin, P-selectin, thrombomodulin, leukocytes, neutrophils, lymphocytes) and clinical (e.g. glucose, insulin, triglycerides) markers as well as gene expression in blood cells and plasma oxylipin profiles were measured.

RESULTS

All three dietary challenges induced changes related to metabolic control such as increases in glucose and insulin after the glucose challenge and increases in triglycerides after the lipid challenge. In addition, differences between the challenges were observed for precursor oxylipins and some downstream metabolites including DiHETrE's and HODE's. However, none of the dietary challenges induced an acute inflammatory response, except for a modest increase in circulating leukocyte numbers after the glucose and mix challenges. Furthermore, subtle, yet statistically significant increases in vascular inflammatory markers (sICAM-1 and sVCAM-1) were found after the mix challenge, when compared to the water control challenge.

CONCLUSIONS

This study shows that dietary glucose and lipid challenges did not induce a strong acute inflammatory response in healthy subjects, as quantified by an accurate and broad panel of parameters.

Postprandial fatty acid specific changes in circulating oxylipins in lean and obese men after high-fat challenge tests

SCOPE

Circulating oxylipins may affect peripheral tissues and are assumed to play an important role in endothelial function. They are esterified in triglyceride-rich lipoproteins that are increased after a high-fat (HF) meal, depending on BMI and fatty acid (FA) type. Yet, it is unclear which oxylipins appear in circulation after HF meals differing in FA composition.

METHODS AND RESULTS

In a double-blind randomized crossover challenge study, we characterized the postprandial oxylipin response after different HF challenges in lean and obese men receiving HF milkshakes, either high in saturated FAs (SFA), monounsaturated FAs (MUFA), or omega 3 (n-3) polyunsaturated FAs (PUFA). Plasma oxylipin profiles were significantly altered at 2 and 4 h after shake consumption when compared to baseline. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) derived oxylipins increased after n-3 PUFA shake consumption. MUFA shake consumption increased levels of cytochrome P450 mediated oxylipins. SFA shake consumption led to strong increases in linoleic acid (LA) derived HODEs. No differences were observed between lean and obese individuals at baseline and after any shake consumption.

CONCLUSION

We are the first demonstrating acute effects on circulating oxylipins after HF meal challenges. These changes were strongly influenced by different dietary FAs and may affect endothelial function.

Gender-dependent associations of metabolite profiles and body fat distribution in a healthy population with central obesity: towards metabolomics diagnostics

Obesity is a risk factor for cardiovascular diseases and type 2 diabetes especially when the fat is accumulated to central depots. Novel biomarkers are crucial to develop diagnostics for obesity and related metabolic disorders. We evaluated the associations between metabolite profiles (136 lipid components, 12 lipoprotein subclasses, 17 low-molecular-weight metabolites, 12 clinical markers) and 28 phenotype parameters (including different body fat distribution parameters such as android (A), gynoid (G), abdominal visceral (VAT), subcutaneous (SAT) fat) in 215 plasma/serum samples from healthy overweight men (n=32) and women (n=83) with central obesity. (Partial) correlation analysis and partial least squares (PLS) regression analysis showed that only specific metabolites were associated to A:G ratio, VAT, and SAT, respectively. These association patterns were gender dependent. For example, insulin, cholesterol, VLDL, and certain triacylglycerols (TG 54:1-3) correlated to VAT in women, while in men VAT was associated with TG 50:1-5, TG 55:1, phosphatidylcholine (PC 32:0), and VLDL ((X)L). Moreover, multiple regression analysis revealed that waist circumference and total fat were sufficient to predict VAT and SAT in women. In contrast, only VAT but not SAT could be predicted in men and only when plasma metabolites were included, with PC 32:0 being most strongly associated with VAT. These findings collectively highlight the potential of metabolomics in obesity and that gender differences need to be taken into account for novel biomarker and diagnostic discovery for obesity and metabolic disorders.

Gut microbial metabolism of polyphenols from black tea and red wine/grape juice is source-specific and colon-region dependent

The colonic microbial degradation of a polyphenol-rich black tea extract (BTE) and red wine/grape juice extract (RWGE) was compared in a five-stage in vitro gastrointestinal model (TWINSHIME). Microbial metabolism of BTE and RWGE polyphenols in the TWINSHIME was studied subsequently in single- and continuous-dose experiments. A combination of liquid or gas chromatography with mass spectrometry (LC-MS or GC-MS) and NMR-based metabolic profiling was used to measure selected parent polyphenols, their microbial degradation into phenolic acids, and the production of short-chain fatty acids (SCFAs) in different colon compartments. Acetate production was increased by continuous feeding of BTE but not RWGE. During RWGE feeding, gallic acid and 4-hydroxyphenylpropionic acid remained elevated throughout the colon, while during BTE feeding, they were consumed in the distal colon, while 3-phenylpropionic acid was strongly produced. Gut microbial production of phenolics and SCFAs is dependent on colon location and polyphenol source, which may influence potential health benefits.

Metabolic response to green tea extract during rest and moderate-intensity exercise

BACKGROUND

Green tea catechins have been hypothesized to increase energy expenditure and fat oxidation by inhibiting catechol-O-methyltransferase (COMT) and thus promoting more sustained adrenergic stimulation. Metabolomics may help to clarify the mechanisms underlying their putative physiological effects.

OBJECTIVE

The study investigated the effects of 7-day ingestion of green tea extract (GTE) on the plasma metabolite profile at rest and during exercise.

METHODS

In a placebo-controlled, double-blind, randomized, parallel study, 27 healthy physically active males consumed either GTE (n=13, 1200 mg catechins, 240 mg caffeine/day) or placebo (n=14, PLA) drinks for 7 days. After consuming a final drink (day 8), they rested for 2 h and then completed 60 min of moderate-intensity cycling exercise (56% ± 4% VO(2)max). Blood samples were collected before and during exercise. Plasma was analyzed using untargeted four-phase metabolite profiling and targeted profiling of catecholamines.

RESULTS

Using the metabolomic approach, we observed that GTE did not enhance adrenergic stimulation (adrenaline and noradrenaline) during rest or exercise. At rest, GTE led to changes in metabolite concentrations related to fat metabolism (3-β-hydroxybutyrate), lipolysis (glycerol) and tricarboxylic acid cycle (TCA) cycle intermediates (citrate) when compared to PLA. GTE during exercise caused reductions in 3-β-hydroxybutyrate concentrations as well as increases in pyruvate, lactate and alanine concentrations when compared to PLA.

CONCLUSIONS

GTE supplementation resulted in marked metabolic differences during rest and exercise. Yet these metabolic differences were not related to the adrenergic system, which questions the in vivo relevance of the COMT inhibition mechanism of action for GTE.

Structural elucidation and quantification of phenolic conjugates present in human urine after tea intake

In dietary polyphenol exposure studies, annotation and identification of urinary metabolites present at low (micromolar) concentrations are major obstacles. To determine the biological activity of specific components, it is necessary to have the correct structures and the quantification of the polyphenol-derived conjugates present in the human body. We present a procedure for identification and quantification of metabolites and conjugates excreted in human urine after single bolus intake of black or green tea. A combination of a solid-phase extraction (SPE) preparation step and two high pressure liquid chromatography (HPLC)-based analytical platforms was used, namely, accurate mass fragmentation (HPLC-FTMS(n)) and mass-guided SPE-trapping of selected compounds for nuclear magnetic resonance spectroscopy (NMR) measurements (HPLC-TOFMS-SPE-NMR). HPLC-FTMS(n) analysis led to the annotation of 138 urinary metabolites, including 48 valerolactone and valeric acid conjugates. By combining the results from MS(n) fragmentation with the one-dimensional (1D)-(1)H NMR spectra of HPLC-TOFMS-SPE-trapped compounds, we elucidated the structures of 36 phenolic conjugates, including the glucuronides of 3',4'-di- and 3',4',5'-trihydroxyphenyl-γ-valerolactone, three urolithin glucuronides, and indole-3-acetic acid glucuronide. We also obtained 26 h-quantitative excretion profiles for specific valerolactone conjugates. The combination of the HPLC-FTMS(n) and HPLC-TOFMS-SPE-NMR platforms results in the efficient identification and quantification of less abundant phenolic conjugates down to nanomoles of trapped amounts of metabolite corresponding to micromolar metabolite concentrations in urine.

Structural elucidation and quantification of phenolic conjugates present in human urine after tea intake

In dietary polyphenol exposure studies, annotation and identification of urinary metabolites present at low (micromolar) concentrations are major obstacles. To determine the biological activity of specific components, it is necessary to have the correct structures and the quantification of the polyphenol-derived conjugates present in the human body. We present a procedure for identification and quantification of metabolites and conjugates excreted in human urine after single bolus intake of black or green tea. A combination of a solid-phase extraction (SPE) preparation step and two high pressure liquid chromatography (HPLC)-based analytical platforms was used, namely, accurate mass fragmentation (HPLC-FTMS(n)) and mass-guided SPE-trapping of selected compounds for nuclear magnetic resonance spectroscopy (NMR) measurements (HPLC-TOFMS-SPE-NMR). HPLC-FTMS(n) analysis led to the annotation of 138 urinary metabolites, including 48 valerolactone and valeric acid conjugates. By combining the results from MS(n) fragmentation with the one-dimensional (1D)-(1)H NMR spectra of HPLC-TOFMS-SPE-trapped compounds, we elucidated the structures of 36 phenolic conjugates, including the glucuronides of 3',4'-di- and 3',4',5'-trihydroxyphenyl-γ-valerolactone, three urolithin glucuronides, and indole-3-acetic acid glucuronide. We also obtained 26 h-quantitative excretion profiles for specific valerolactone conjugates. The combination of the HPLC-FTMS(n) and HPLC-TOFMS-SPE-NMR platforms results in the efficient identification and quantification of less abundant phenolic conjugates down to nanomoles of trapped amounts of metabolite corresponding to micromolar metabolite concentrations in urine.

Between Metabolite Relationships: an essential aspect of metabolic change

Not only the levels of individual metabolites, but also the relations between the levels of different metabolites may indicate (experimentally induced) changes in a biological system. Component analysis methods in current 'standard' use for metabolomics, such as Principal Component Analysis (PCA), do not focus on changes in these relations. We therefore propose the concept of 'Between Metabolite Relationships' (BMRs): common changes in the covariance (or correlation) between all metabolites in an organism. Such structural changes may indicate metabolic change brought about by experimental manipulation but which are lost with standard data analysis methods. These BMRs can be analysed by the INdividual Differences SCALing (INDSCAL) method. First the BMR quantification is described and subsequently the INDSCAL method. Finally, two studies illustrate the power and the applicability of BMRs in metabolomics. The first study is about the induced plant response of cabbage to herbivory, of which BMRs are a considerable part. In the second study-a human nutritional intervention study of green tea extract-standard data analysis tools did not reveal any metabolic change, although the BMRs were considerably affected. The presented results show that BMRs can be easily implemented in a wide variety of metabolomic studies. They provide a new source of information to describe biological systems in a way that fits flawlessly into the next generation of systems biology questions, dealing with personalized responses. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11306-011-0316-1) contains supplementary material, which is available to authorized users.

Impact of short-term intake of red wine and grape polyphenol extract on the human metabolome

Red wine and grape polyphenols are considered to promote cardiovascular health and are involved in multiple biological functions. Their overall impact on the human metabolome is not known. Therefore, exogenous and endogenous metabolic effects were determined in fasting plasma and 24 h urine from healthy male adults consuming a mix of red wine and grape juice extracts (WGM) for 4 days in a placebo-controlled, crossover study. Syringic acid, 3-hydroxyhippuric acid, pyrogallol, 3-hydroxyphenylacetic acid, and 3-hydroxyphenylpropionic acid were confirmed as the strongest urinary markers of WGM intake. Overall, WGM had a mild impact on the endogenous metabolism. Most noticeable were changes in several amino acids deriving from tyrosine and tryptophan. Reductions in the microbial metabolites p-cresol sulfate and 3-indoxylsulfuric acid and increases in indole-3-lactic acid and nicotinic acid were observed in urine. In plasma, tyrosine was reduced. The results suggest that short-term intake of WGM altered microbial protein fermentation and/or amino acid metabolism.

In vitro bioconversion of polyphenols from black tea and red wine/grape juice by human intestinal microbiota displays strong interindividual variability

Dietary polyphenols in tea and wine have been associated with beneficial health effects. After ingestion, most polyphenols are metabolized by the colonic microbiota. The current study aimed at exploring the interindividual variation of gut microbial polyphenol bioconversion from 10 healthy human subjects. In vitro fecal batch fermentations simulating conditions in the distal colon were performed using polyphenols from black tea and a mixture of red wine and grape juice. Microbial bioconversion was monitored by NMR- and GC-MS-based profiling of diverse metabolites and phenolics. The complex polyphenol mixtures were degraded to a limited number of key metabolites. Each subject displayed a specific metabolite profile differing in composition and time courses as well as levels of these metabolites. Moreover, clear differences depending on the polyphenol sources were observed. In conclusion, varying metabolite pathways among individuals result in different metabolome profiles and therefore related health effects are hypothesized to differ between subjects.

Non-digestible food ingredients, colonic microbiota and the impact on gut health and immunity: a role for metabolomics

Increasing health issues related to immune and gut function such as inflammatory disorders, resistance to infections and metabolic syndrome demand modern analytical approaches to accelerate nutritional research aimed at health promotion and disease prevention. Gut microbial-human mutualism endows the host 'superorganism' with a fitness advantage including nutritional, immune and intestinal health aspects. The gut microbiome enlarges our genome and enhances our metabolic potential. Dietary modulation can significantly alter the microbiota community and metabolic activity, and consequently impacts on nutrient bioavailability and host metabolism. Although in an early stage, microbial metabolites generated during colonic fermentation of food stuffs may have beneficial or deleterious effects on intestinal health and immunity, as summarized in this review. However, current evidence is largely based on in vitro and animal studies while substantiation in humans is lacking. The challenge to establish coherent links between the bioconversion of non-digestible food ingredients, their bioavailability and their downstream effects on the host metabolism may be achieved by metabolomics. In this review, metabolomics studies focusing on microbe-host mutualism have demonstrated that metabolomics is capable of detecting and tracking diverse microbial metabolites from different non-digestible food ingredients, of discriminating between phenotypes with different inherent microbiota and of potentially diagnosing infection and gastrointestinal diseases. Integrative approaches such as the combined analysis of the metabolome in different biofluids together with other -omics technologies will cover exogenous and endogenous effects and hence show promise to generate novel hypotheses for innovative functional foods impacting gut health and immunity.

Multilevel data analysis of a crossover designed human nutritional intervention study

A new method is introduced for the analysis of 'omics' data derived from crossover designed drug or nutritional intervention studies. The method aims at finding systematic variations in metabolic profiles after a drug or nutritional challenge and takes advantage of the crossover design in the data. The method, which can be considered as a multivariate extension of a paired t test, generates different multivariate submodels for the between- and the within-subject variation in the data. A major advantage of this variation splitting is that each submodel can be analyzed separately without being confounded with the other variation sources. The power of the multilevel approach is demonstrated in a human nutritional intervention study which used NMR-based metabolomics to assess the metabolic impact of grape/wine extract consumption. The variations in the urine metabolic profiles are studied between and within the human subjects using the multilevel analysis. After variation splitting, multilevel PCA is used to investigate the experimental and biological differences between the subjects, whereas a multilevel PLS-DA model is used to reveal the net treatment effect within the subjects. The observed treatment effect is validated with cross model validation and permutations. It is shown that the statistical significance of the multilevel classification model ( p << 0.0002) is a major improvement compared to a ordinary PLS-DA model ( p = 0.058) without variation splitting. Finally, rank products are used to determine which NMR signals are most important in the multilevel classification model.

(1)H NMR metabolite profiling of feces as a tool to assess the impact of nutrition on the human microbiome

Current research increasingly recognizes the human gut microbiome as a metabolically versatile biological 'digester' that plays an essential role in regulating the host metabolome. Gut microbiota recover energy and biologically active molecules from food that would otherwise be washed out of the intestinal tract without benefit. In this study, a protocol for NMR-based metabolite profiling has been developed to access the activity of the microbiome. The physicochemical properties of fecal metabolites have been found to strongly affect the reproducibility and coverage of the profiles obtained. Metabolite profiles generated by water and methanol extraction of lyophilized feces are reproducible and comprise a variety of different compounds including, among others, short-chain fatty acids (e.g. acetate, propionate, butyrate, isobutyrate, isovalerate, malate), organic acids (e.g. succinate, pyruvate, fumarate, lactate), amino acids, uracil, trimethylamine, ethanol, glycerol, glucose, phenolic acids, cholate, and lipid components. The NMR profiling approach was validated on fecal samples from a double-blinded, placebo-controlled, randomized cross-over study, in which healthy human subjects consumed a placebo and either a grape juice extract or a mix of grape juice and wine extract over a period of 4 weeks, each. The considerable inter- and intra-individual variability observed originates in the first instance from variable metabolite concentrations rather than from variable metabolite compositions, suggesting that different colonic flora share general biochemical characteristics metabolizing different substrates to specific metabolic patterns. Whereas the grape juice extract did not induce changes in the metabolite profiles as compared with the placebo, the mixture of grape juice and wine extract induced a reduction in isobutyrate, which may indicate that polyphenols are able to modulate the microbial ecology of the gut.

GC-MS methods for metabolic profiling of microbial fermentation products of dietary polyphenols in human and in vitro intervention studies

Flavonoids, a subclass of polyphenols, are major constituents of many plant-based foods and beverages, including tea, wine and chocolate. Epidemiological studies have shown that a flavonoid-rich diet is associated with reduced risk of cardiovascular diseases. The majority of the flavonoids survive intact until they reach the colon where they are then extensively metabolized into smaller fragments. Here, we describe the development of GC-MS-based methods for the profiling of phenolic microbial fermentation products in urine, plasma, and fecal water. Furthermore, the methods are applicable for profiling products obtained from in vitro batch culture fermentation models. The methods incorporate enzymatic deconjugation, liquid-liquid extraction, derivatization, and subsequent analysis by GC-MS. At the level of individual compounds, the methods gave recoveries better than 80% with inter-day precision being better than 20%, depending on the matrix. Limits of detection were below 0.1 microg/ml for most phenolic acids. The newly developed methods were successfully applied to samples from human and in-vitro intervention trials, studying the metabolic impact of flavonoid intake. In conclusion, the methods presented are robust and generally applicable to diverse biological fluids. Its profiling character is useful to investigate on a large scale the gut microbiome-mediated bioavailability of flavonoids.

Probing gender-specific metabolism differences in humans by nuclear magnetic resonance-based metabonomics

The measurement of metabolite profiles that are interpreted to yield biomarkers using multivariate data analysis is now a well-established approach for gaining an improved understanding of the impact of genetic modifications, toxicological and therapeutic interventions, and exposure to stimuli (e.g., noxious agents, stressors, nutrients) on the network of transcripts, proteins, and metabolites present in cells, tissues, or whole organisms. This has been termed metabonomics. In this study, multivariate analysis of (1)H nuclear magnetic resonance (NMR) spectra of metabolite profiles of urine and plasma from 150 healthy humans revealed that in young people and/or individuals with low body mass indexes, females had higher rates of lipid biosynthesis than did males, whereas males had higher rates of protein turnover than did females. With increasing age, overall lipid biosynthesis decreased in females, whereas metabolism increasingly favored lipid synthesis over protein turnover in males. By relating the derived metabonomic data to known metabolic pathways and published biochemical data, it appears that females synthesize relatively more lipoproteins and unsaturated lipids than do males. Furthermore, the changes in lipid biosynthesis and urinary citrate excretion in females showed a positive correlation. Estrogen most likely plays an essential role in the regulation of, and communication between, protein and lipid biosynthesis by controlling pH in mitochondria and the cytoplasm and hence the observed altered citrate levels.