Characterization of the Human Skeletal Muscle Metabolome for Elucidating the Mechanisms of Bicarbonate Ingestion on Strenuous Interval Exercise

Acute changes in the metabolome following resistance exercise combined with intake of different protein sources (cricket, pea, whey)

INTRODUCTION

Separately, both exercise and protein ingestion have been shown to alter the blood and urine metabolome. This study goes a step further and examines changes in the metabolome derived from blood, urine and muscle tissue extracts in response to resistance exercise combined with ingestion of three different protein sources.

METHODS

In an acute parallel study, 52 young males performed one-legged resistance exercise (leg extension, 4 × 10 repetitions at 10 repetition maximum) followed by ingestion of either cricket (insect), pea or whey protein (0.25 g protein/kg fat free mass). Blood and muscle tissue were collected at baseline and three hours after protein ingestion. Urine was collected at baseline and four hours after protein ingestion. Mixed-effects analyses were applied to examine the effect of the time (baseline vs. post), protein (cricket, pea, whey), and time x protein interaction.

RESULTS

Nuclear magnetic resonance (NMR)-based metabolomics resulted in the annotation and quantification of 25 metabolites in blood, 35 in urine and 21 in muscle tissue. Changes in the muscle metabolome after combined exercise and protein intake indicated effects related to the protein source ingested. Muscle concentrations of leucine, methionine, glutamate and myo-inositol were higher after intake of whey protein compared to both cricket and pea protein. The blood metabolome revealed changes in a more ketogenic direction three hours after exercise reflecting that the trial was conducted after overnight fasting. Urinary concentration of trimethylamine N-oxide was significantly higher after ingestion of cricket than pea and whey protein.

CONCLUSION

The blood, urine and muscle metabolome showed different and supplementary responses to exercise and ingestion of the different protein sources, and in synergy the summarized results provided a more complete picture of the metabolic state of the body.

Effect of 1-year daily protein supplementation and physical exercise on muscle protein synthesis rate and muscle metabolome in healthy older Danes: a randomized controlled trial

BACKGROUND

The skeletal muscle mass decreases with age and the responsiveness of aging muscles' protein synthesis rate (MPS) to protein intake seems to deteriorate.

OBJECTIVE

This study investigated the impact of 12 months of protein supplementation with or without physical exercise training on the basal and postprandial MPS and the skeletal muscle metabolome of healthy older Danes (> 65 years, 29 females/37 males).

METHODS

Subjects were randomized to follow one of five intervention groups: (1) carbohydrate, (2) collagen protein, (3) whey protein, (4) home-based light resistance training with whey protein, and (5) center-based heavy-load resistance training with whey protein. Before and after the intervention, a tracer infusion trial was conducted to measure basal and postprandial MPS in response to intake of a cocktail consisting of 20 g whey hydrolysate + 10 g glucose. In addition, the skeletal muscle metabolome was measured using gas chromatography-mass spectrometry (GC-MS) at basal state and 4 h after the intake of the cocktail.

RESULTS

One year of daily protein or carbohydrate supplementation did not alter the basal and protein-stimulated postprandial muscle protein synthesis rate or the muscle metabolome of healthy older Danes. Basal MPS (%/h) at baseline for all subjects were 0.0034 ± 0,011 (mean ± SD). In contrast to previous studies, no difference was observed in basal MPS between males and females (p = 0.75). With the developed untargeted GC-MS methodology, it was possible to detect and tentatively annotate > 70 metabolites from the human skeletal muscle samples.

CONCLUSION

One year of protein supplementation in comparison to an isocaloric-control supplement seems to affect neither the MPS at basal or postprandial state nor the skeletal muscle metabolome.

CLINICAL TRIAL REGISTRY

Number: NCT02115698, clinicaltrials.gov/ct2/show/NCT02115698.

Potential metabolic biomarkers of critical limb ischemia in people with type 2 diabetes mellitus

INTRODUCTION

Type 2 diabetes mellitus (T2DM) is a significant risk factor for the development of critical limb ischemia (CLI), the most advanced stage of peripheral arterial disease. The concurrent existence of T2DM and CLI often leads to adverse outcomes, namely limb amputation.

OBJECTIVE

To identify biomarkers for improving the screening of CLI in high-risk people with T2DM.

METHODS

We investigated metabolome profiles in serum samples of 113 T2DM people with CLI (n = 23, G2) and without CLI (n = 45, G0: no lower limb stenosis (LLS) and n = 45, G1: LLS < 50%), using hydrogen nuclear magnetic resonance (¹H NMR) approach. Principle component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) were used to analyze ¹H NMR data.

RESULTS

Twenty potential metabolites that could discriminate people with T2DM and CLI (G2) from non-CLI patients without LLS (G0) were determined in serum samples. The correct percent of classification for the PLS-DA model for the test set samples was 85% (n = 20) and 100% (n = 5) for G0 and G2 groups, respectively. Non-CLI patients with LLS < 50% (G1) were projected on the PCA abstract space built using 20 discriminatory metabolites. Eleven people with T2DM and LLS < 50% were prospectively followed, and their ankle-brachial index (ABI) was measured after 4 years. A promising agreement existed between the PCA model's predictions and those obtained by ABI values.

CONCLUSION

The findings suggest that confirmation of blood potential metabolic biomarkers as a complement to ABI for screening of CLI in a large group of high-risk people with T2DM is needed.

Identification of Novel Biomarkers in Late Preterm Neonates with Respiratory Distress Syndrome (RDS) Using Urinary Metabolomic Analysis

Urine metabolomics is gaining traction as a means of identifying metabolic signatures associated with health and disease states. Thirty-one (31) late preterm (LP) neonates admitted to the neonatal intensive care unit (NICU) and 23 age-matched healthy LPs admitted to the maternity ward of a tertiary hospital were included in the study. Proton nuclear magnetic resonance (¹H NMR) spectroscopy was employed for urine metabolomic analysis on the 1st and 3rd days of life of the neonates. The data were analyzed using univariate and multivariate statistical analysis. A unique metabolic pattern of enhanced metabolites was identified in the NICU-admitted LPs from the 1st day of life. Metabolic profiles were distinct in LPs presenting with respiratory distress syndrome (RDS). The discrepancies likely reflect differences in the gut microbiota, either due to variations in nutrient intake or as a result of medical interventions, such as the administration of antibiotics and other medications. Altered metabolites could potentially serve as biomarkers for identifying critically ill LP neonates or those at high risk for adverse outcomes later in life, including metabolic risks. The discovery of novel biomarkers may uncover potential targets for drug discovery and optimal periods for effective intervention, offering a personalized approach.

Cell selectivity in succinate receptor SUCNR1/GPR91 signaling in skeletal muscle

Succinate is released by skeletal muscle during exercise and activates SUCNR1/GPR91. Signaling of SUCNR1 is involved in metabolite-sensing paracrine communication in skeletal muscle during exercise. However, the specific cell types responding to succinate and the directionality of communication are unclear. We aim to characterize the expression of SUCNR1 in human skeletal muscle. De novo analysis of transcriptomic datasets demonstrated that SUCNR1 mRNA is expressed in immune, adipose, and liver tissues, but scarce in skeletal muscle. In human tissues, SUCNR1 mRNA was associated with macrophage markers. Single-cell RNA sequencing and fluorescent RNAscope demonstrated that in human skeletal muscle, SUCNR1 mRNA is not expressed in muscle fibers but coincided with macrophage populations. Human M2-polarized macrophages exhibit high levels of SUCNR1 mRNA and stimulation with selective agonists of SUCNR1 triggered Gq- and Gi-coupled signaling. Primary human skeletal muscle cells were unresponsive to SUCNR1 agonists. In conclusion, SUCNR1 is not expressed in muscle cells and its role in the adaptive response of skeletal muscle to exercise is most likely mediated via paracrine mechanisms involving M2-like macrophages within the muscle.NEW & NOTEWORTHY Macrophages but not skeletal muscle cells respond to extracellular succinate via SUCNR1/GPR91.

Rapid chloride and bicarbonate determination by capillary electrophoresis for confirmatory testing of cystic fibrosis infants with volume-limited sweat specimens

Objectives Cystic fibrosis (CF) is a debilitating genetic disorder that benefits from early detection. CF diagnosis relies on measuring elevated sweat chloride that is difficult in neonates with low sweat rates. We introduce a new method for sweat chloride determination from volume-limited specimens, and explore the potential utility of sweat bicarbonate in neonatal CF screening. Methods A rapid assay (< 5 min) was developed to analyze chloride and bicarbonate using capillary electrophoresis with indirect UV detection (CE-iUV). Pilocarpine-stimulated sweat samples from screen-positive CF infants were collected at two hospital sites, including confirmed CF (n = 12), CF screen-positive inconclusive diagnosis (n = 4), and unaffected non-CF cases (n = 37). All sweat chloride samples were analyzed by a coulometric titrator and CE-iUV, and the viability to measure acid-labile bicarbonate was also evaluated. Results Stability studies revealed that bicarbonate can be reliably assessed in sweat if acidification and heating were avoided. Method validation demonstrated that sweat chloride and bicarbonate were quantified with acceptable accuracy (recovery of 102%), precision (CV = 3.7%) and detection limits (∼ 0.1 mM). An inter-laboratory comparison confirmed a mean bias of 6.5% (n = 53) for sweat chloride determination by CE-iUV relative to a commercial chloridometer. However, sweat bicarbonate did not discriminate between CF and non-CF infants (AUC = 0.623, p = 0.215) unlike chloride (AUC = 1.00, p = 3.00 × 10^-7). Conclusions CE-iUV offers a robust method for sweat chloride testing from presumptive CF infants that may reduce testing failure rates. However, sweat bicarbonate does not have clinical value in newborn CF diagnosis.

Metabolite patterns associated with individual response to supervised exercise therapy in patients with intermittent claudication

Objective

Supervised exercise therapy (SET) is the first line treatment for intermittent claudication owing to peripheral arterial disease. Despite multiple randomized controlled trials proving the efficacy of SET, there are large differences in individual patient's responses. We used plasma metabolomics to identify potential metabolic influences on the individual response to SET.

Methods

Primary metabolites, complex lipids, and lipid mediators were measured on plasma samples taken at before and after Gardner graded treadmill walking tests that were administered before and after 12 weeks of SET. We used an ensemble modeling approach to identify metabolites or changes in metabolites at specific time points that associated with interindividual variability in the functional response to SET. Specific time points analyzed included baseline metabolite levels before SET, dynamic metabolomics changes before SET, the difference in pre- and post-SET baseline metabolomics, and the difference (pre- and post-SET) of the dynamic (pre- and post-treadmill).

Results

High levels of baseline anandamide levels pre- and post-SET were associated with a worse response to SET. Increased arachidonic acid (AA) and decreased levels of the AA precursor dihomo-γ-linolenic acid across SET were associated with a worse response to SET. Participants who were able to tolerate large increases in AA during acute exercise had longer, or better, walking times both before and after SET.

Conclusions

We identified two pathways of relevance to individual response to SET that warrant further study: anandamide synthesis may activate endocannabinoid receptors, resulting in worse treadmill test performance. SET may train patients to withstand higher levels of AA, and inflammatory signaling, resulting in longer walking times.

Clinical Relevance

This manuscript describes the use of metabolomic techniques to measure the interindividual effects of SET in patients with peripheral artery disease (PAD). We identified high levels of AEA are linked to CB1 signaling and activation of inflammatory pathways. This alters energy expenditure in myoblasts by decreasing glucose uptake and may induce an acquired skeletal muscle myopathy. SET may also help participants tolerate increased levels of AA and inflammation produced during exercise, resulting in longer walking times. This data will enhance understanding of the pathophysiology of PAD and the mechanism by which SET improves walking intolerance.

Nanoflow Sheath Voltage-Free Interfacing of Capillary Electrophoresis and Mass Spectrometry for the Detection of Small Molecules

Coupling capillary electrophoresis (CE) to mass spectrometry (MS) is a powerful strategy to leverage a high separation efficiency with structural identification. Traditional CE-MS interfacing relies upon voltage to drive this process. Additionally, sheathless interfacing requires that the electrophoresis generates a sufficient volumetric flow to sustain the ionization process. Vibrating sharp-edge spray ionization (VSSI) is a new method to interface capillary electrophoresis to mass analyzers. In contrast to traditional interfacing, VSSI is voltage-free, making it straightforward for CE and MS. New nanoflow sheath CE-VSSI-MS is introduced in this work to reduce the reliance on the separation flow rate to facilitate the transfer of analyte to the MS. The nanoflow sheath VSSI spray ionization functions from 400 to 900 nL/min. Using the new nanoflow sheath reported here, volumetric flow rate through the separation capillary is less critical, allowing the use of a small (i.e., 20 to 25 μm) inner diameter separation capillary and enabling the use of higher separation voltages and faster analysis. Moreover, the use of a nanoflow sheath enables greater flexibility in the separation conditions. The nanoflow sheath is operated using aqueous solutions in the background electrolyte and in the sheath, demonstrating the separation can be performed under normal and reversed polarity in the presence or absence of electroosmotic flow. This includes the use of a wider pH range as well. The versatility of nanoflow sheath CE-VSSI-MS is demonstrated by separating cationic, anionic, and zwitterionic molecules under a variety of separation conditions. The detection sensitivity observed with nanoflow sheath CE-VSSI-MS is comparable to that obtained with sheathless CE-VSSI-MS as well as CE-MS separations with electrospray ionization interfacing. A bare fused silica capillary is used to separate cationic β-blockers with a near-neutral background electrolyte at concentrations ranging from 1.0 nM to 1.0 μM. Under acidic conditions, 13 amino acids are separated with normal polarity at a concentration ranging from 0.25 to 5 μM. Finally, separations of anionic compounds are demonstrated using reversed polarity under conditions of suppressed electroosmotic flow through the use of a semipermanent surface coating. With a near-neutral separation electrolyte, anionic nonsteroidal anti-inflammatory drugs are detected over a concentration range of 0.1 to 5.0 μM.

Research in the Field of Exercise and Metabolomics: A Bibliometric and Visual Analysis

The aim of this article was to conduct a bibliometric analysis of global research trends in the field of exercise and metabolomics between 2005 and 2020. Systematic articles were obtained from the literature in the Web of Science core collection database from 2005 to 2020. The relationship between the number of publications, citations, countries, journals, authors, and the evolution of research hotspots was analyzed. A total of 807 studies were included in the analysis. From 2005 to 2020, the number of citations and the number of published articles showed an upward trend. Keyword co-occurrence indicates that research hotspots are focused on exercise, physical activity, metabolomics, obesity, insulin resistance, inflammation, and cardiovascular disease. Keyword clustering indicates that the research frontier is focused on the field of sports medicine, which includes molecular-level studies of exercise interventions in disease and studies of the physiological mechanisms by which exercise alters the body. Overall, this trinity of models, combining chronic disease with exercise interventions and molecular-level studies of metabolomics, has become the forefront of research in the field. This historical review of the field of exercise and metabolomics will further provide a useful basis for hot issues and future development trends.

New Advances in Tissue Metabolomics: A Review

Metabolomics offers a hypothesis-generating approach for biomarker discovery in clinical medicine while also providing better understanding of the underlying mechanisms of chronic diseases. Clinical metabolomic studies largely rely on human biofluids (e.g., plasma, urine) as a more convenient specimen type for investigation. However, biofluids are non-organ specific reflecting complex biochemical processes throughout the body, which may complicate biochemical interpretations. For these reasons, tissue metabolomic studies enable deeper insights into aberrant metabolism occurring at the direct site of disease pathogenesis. This review highlights new advances in metabolomics for ex vivo analysis, as well as in situ imaging of tissue specimens, including diverse tissue types from animal models and human participants. Moreover, we discuss key pre-analytical and post-analytical challenges in tissue metabolomics for robust biomarker discovery with a focus on new methodological advances introduced over the past six years, including innovative clinical applications for improved screening, diagnostic testing, and therapeutic interventions for cancer.

The maternal serum metabolome by multisegment injection-capillary electrophoresis-mass spectrometry: a high-throughput platform and standardized data workflow for large-scale epidemiological studies

A standardized data workflow is described for large-scale serum metabolomic studies using multisegment injection-capillary electrophoresis-mass spectrometry. Multiplexed separations increase throughput (<4 min/sample) for quantitative determination of 66 polar/ionic metabolites in serum filtrates consistently detected (coefficient of variance (CV) <30%) with high frequency (>75%) from a multi-ethnic cohort of pregnant women (n = 1,004). We outline a validated protocol implemented in four batches over a 7-month period that includes details on preventive maintenance, sample workup, data preprocessing and metabolite authentication. We achieve stringent quality control (QC) and robust batch correction of long-term signal drift with good mutual agreement for a wide range of metabolites, including serum glucose as compared to a clinical chemistry analyzer (mean bias = 11%, n = 668). Control charts for a recovery standard (mean CV = 12%, n = 2,412) and serum metabolites in QC samples (median CV = 13%, n = 202) demonstrate acceptable intermediate precision with a median intraclass coefficient of 0.87. We also report reference intervals for 53 serum metabolites from a diverse population of women in their second trimester of pregnancy.

CE-MS for metabolomics: Developments and applications in the period 2018-2020

Capillary electrophoresis-mass spectrometry (CE-MS) is now a mature analytical technique in metabolomics, notably for the efficient profiling of polar and charged metabolites. Over the past few years, (further) progress has been made in the design of improved interfacing techniques for coupling CE to MS; also, in the development of CE-MS approaches for profiling metabolites in volume-restricted samples, and in strategies that further enhance the metabolic coverage. In this article, which is a follow-up of a previous review article covering the years 2016-2018 (Electrophoresis 2019, 40, 165-179), the main (technological) developments in CE-MS methods and strategies for metabolomics are discussed covering the literature from July 2018 to June 2020. Representative examples highlight the utility of CE-MS in the fields of biomedical, clinical, microbial, plant and food metabolomics. A complete overview of recent CE-MS-based metabolomics studies is given in a table, which provides information on sample type and pretreatment, capillary coatings, and MS detection mode. Finally, some general conclusions and perspectives are given.

Comprehensive Dipeptide Analysis Revealed Cancer-Specific Profile in the Liver of Patients with Hepatocellular Carcinoma and Hepatitis

As the physical properties and functionality of dipeptides differ from those of amino acids, they have attracted attention in metabolomics; however, their functions in vivo have not been clarified in detail. Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer, and its major cause is chronic hepatitis. This study was conducted to explore tumor-specific dipeptide characteristics by performing comprehensive dipeptide analysis in the tumor and surrounding nontumor tissue of patients with HCC. Dipeptides were analyzed by liquid chromatography tandem mass spectrometry and capillary electrophoresis tandem mass spectrometry. Principal component analysis using 236 detected dipeptides showed differences in the dipeptide profiles between nontumor and tumor tissues; however, no clear difference was observed in etiological comparison. In addition, the N- and C-terminal amino acid compositions of the detected dipeptides significantly differed, suggesting the substrate specificity of enzyme proteins, such as peptidase. Furthermore, hepatitis-derived HCC may show a characteristic dipeptide profile even before tumor formation. These results provide insight into HCC pathogenesis and may help identify novel biomarkers for diagnosis.

Effects of high intensity interval exercise on cerebrovascular function: A systematic review

High intensity interval exercise (HIIE) improves aerobic fitness with decreased exercise time compared to moderate continuous exercise. A gap in knowledge exists regarding the effects of HIIE on cerebrovascular function such as cerebral blood velocity and autoregulation. The objective of this systematic review was to ascertain the effect of HIIE on cerebrovascular function in healthy individuals. We searched PubMed and the Cumulative Index to Nursing and Allied Health Literature databases with apriori key words. We followed the Preferred Reporting Items for Systematic Reviews. Twenty articles were screened and thirteen articles were excluded due to not meeting the apriori inclusion criteria. Seven articles were reviewed via the modified Sackett’s quality evaluation. Outcomes included middle cerebral artery blood velocity (MCAv) (n = 4), dynamic cerebral autoregulation (dCA) (n = 2), cerebral de/oxygenated hemoglobin (n = 2), cerebrovascular reactivity to carbon dioxide (CO₂) (n = 2) and cerebrovascular conductance/resistance index (n = 1). Quality review was moderate with 3/7 to 5/7 quality criteria met. HIIE acutely lowered exercise MCAv compared to moderate intensity. HIIE decreased dCA phase following acute and chronic exercise compared to rest. HIIE acutely increased de/oxygenated hemoglobin compared to rest. HIIE acutely decreased cerebrovascular reactivity to higher CO₂ compared to rest and moderate intensity. The acute and chronic effects of HIIE on cerebrovascular function vary depending on the outcomes measured. Therefore, future research is needed to confirm the effects of HIIE on cerebrovascular function in healthy individuals and better understand the effects in individuals with chronic conditions. In order to conduct rigorous systematic reviews in the future, we recommend assessing MCAv, dCA and CO₂ reactivity during and post HIIE.

Lyophilized fecal short-chain fatty acid and electrolyte determination by capillary electrophoresis with indirect UV detection for assessment of pediatric inflammatory bowel disease

Short-chain fatty acids (SCFAs) and electrolytes are major constituents of human feces involved in maintaining gastrointestinal homeostasis that underlie complex diet, host and microbiome interactions. Reliable quantification of SCFAs and electrolytes is challenging given the heterogeneity of stool specimens from pediatric patients with diarrhea-predominate inflammatory bowel disease (IBD). Herein, we introduce two validated methods for determination of 3 SCFAs and 5 electrolytes consistently quantified from fecal extracts when using capillary electrophoresis with indirect UV detection (CE-iUV), where concentrations are normalized to total dried weight (mmol/kg d.w.). Lyophilization facilitates sample handling and extraction of heterogeneous stool specimens (∼ 15 mg) from a cohort of children with Crohn's disease (CD, n = 12) and ulcerative colitis (UC, n = 10) treated with exclusive enteral nutrition (EEN) or corticosteroid (CS) therapy to induce remission, respectively. Good technical precision (mean CV = 13 %, n = 14) and accuracy (recovery from 84 to 116%) is demonstrated for SCFAs and electrolytes from freeze dried stool extracts using a modified Bligh-Dyer protocol with low micromolar detection limits (∼ 2-15 μM). Fecal butyrate is 2.6-fold higher in CD as compared to UC patients (effect size = 1.51; p = 0.00291), and there is a strong co-linearity between fecal butyrate and acetate (r = 0.835) unlike propionate, which is correlated with fecal calprotectin (r = 0.517), a protein biomarker of intestinal inflammation. Also, a longitudinal study of matching stool samples collected from a sub-set of IBD patients revealed about a 7-fold enrichment in magnesium and calcium following 4 weeks of EEN as compared to baseline (F > 4.1 ; p < 0.05) unlike the CS treatment arm with no changes in other fecal SCFAs and electrolytes, including sodium, potassium, and ammonium. CE-iUV enables rapid fecal SCFA and electrolyte determination as required for new insights into the role of gut dysbiosis in IBD, as well as treatment monitoring of nutritional interventions that stabilize the disease course in affected children.

Metabolomic analysis of primary human skeletal muscle cells during myogenic progression

Skeletal muscle constitutes more than 30% of total body mass using substrates such as glycogen, glucose, free fatty acids, and creatinine phosphate to generate energy. Consequently, multinucleated myofibers and resident mononucleated stem cells (satellite cells) generate several metabolites, which enter into circulation affecting the function of other organs, especially during exercise and atrophy. The present study was aimed at building a comprehensive profile of metabolites in primary human skeletal muscle cells during myogenic progression in an untargeted metabolomics approach using a high resolution Orbitrap Fusion Tribrid Mass Spectrometer. Identification of metabolites with multivariate statistical analyses showed a global shift in metabolomic profiles between myoblasts undergoing proliferation and differentiation along with distinctly separable profiles between early and late differentiating cultures. Pathway analyses of 71 unique metabolites revealed that Pantothenate metabolism and Coenzyme A biosynthesis and Arginine Proline metabolism play dominant roles in proliferating myoblasts, while metabolites involved in vitamin B6, Glyoxylate and Dicarboxylate, Nitrogen, Glutathione, and Tryptophan metabolism were upregulated during differentiation. We found that early and late differentiating cultures displayed differences in Phenylalanine, Tyrosine, Glycine, Serine and Threonine metabolism. Our results identify metabolites during maturation of muscle from progenitor myoblasts that have implications in muscle regeneration and pathophysiology.

Serum Metabolic Signatures of Chronic Limb-Threatening Ischemia in Patients with Peripheral Artery Disease

Peripheral artery disease (PAD) is characterized by the atherosclerotic narrowing of lower limb vessels, leading to ischemic muscle pain in older persons. Some patients experience progression to advanced chronic limb-threatening ischemia (CLTI) with poor long-term survivorship. Herein, we performed serum metabolomics to reveal the mechanisms of PAD pathophysiology that may improve its diagnosis and prognosis to CLTI complementary to the ankle-brachial index (ABI) and clinical presentations. Non-targeted metabolite profiling of serum was performed by multisegment injection-capillary electrophoresis-mass spectrometry (MSI-CE-MS) from age and sex-matched, non-diabetic, PAD participants who were recruited and clinically stratified based on the Rutherford classification into CLTI (n = 18) and intermittent claudication (IC, n = 20). Compared to the non-PAD controls (n = 20), PAD patients had lower serum concentrations of creatine, histidine, lysine, oxoproline, monomethylarginine, as well as higher circulating phenylacetylglutamine (p < 0.05). Importantly, CLTI cases exhibited higher serum concentrations of carnitine, creatinine, cystine and trimethylamine-N-oxide along with lower circulating fatty acids relative to well matched IC patients. Most serum metabolites associated with PAD progression were also correlated with ABI (r = ±0.24-0.59, p < 0.05), whereas the ratio of stearic acid to carnitine, and arginine to propionylcarnitine differentiated CLTI from IC with good accuracy (AUC = 0.87, p = 4.0 × 10^-5). This work provides new biochemical insights into PAD progression for the early detection and surveillance of high-risk patients who may require peripheral vascular intervention to prevent amputation and premature death.

Placental Metabolomics for Assessment of Sex-specific Differences in Fetal Development During Normal Gestation

The placenta is a metabolically active interfacial organ that plays crucial roles in fetal nutrient delivery, gas exchange and waste removal reflecting dynamic maternal and fetal interactions during gestation. There is growing evidence that the sex of the placenta influences fetal responses to external stimuli in utero, such as changes in maternal nutrition and exposure to environmental stressors. However, the exact biochemical mechanisms associated with sex-specific metabolic adaptations during pregnancy and its link to placental function and fetal development remain poorly understood. Herein, multisegment injection-capillary electrophoresis-mass spectrometry is used as a high throughput metabolomics platform to characterize lyophilized placental tissue (~2 mg dried weight) from C57BL/6J mice fed a standardized diet. Over 130 authentic metabolites were consistently measured from placental extracts when using a nontargeted metabolomics workflow with stringent quality control and robust batch correction. Our work revealed distinct metabolic phenotype differences that exist between male (n = 14) and female (n = 14) placentae collected at embryonic day E18.5. Intracellular metabolites associated with fatty acid oxidation and purine degradation were found to be elevated in females as compared to male placentae (p < 0.05, effect size >0.40), including uric acid, valerylcarnitine, hexanoylcarnitine, and 3-hydroxyhexanolycarnitine. This murine model sheds new insights into sex-specific differences in placental mitochondrial function and protective mechanisms against deleterious oxidative stress that may impact fetal growth and birth outcomes later in life.

Metabolic Trajectories Following Contrasting Prudent and Western Diets from Food Provisions: Identifying Robust Biomarkers of Short-Term Changes in Habitual Diet

A large body of evidence has linked unhealthy eating patterns with an alarming increase in obesity and chronic disease worldwide. However, existing methods of assessing dietary intake in nutritional epidemiology rely on food frequency questionnaires or dietary records that are prone to bias and selective reporting. Herein, metabolic phenotyping was performed on 42 healthy participants from the Diet and Gene Intervention (DIGEST) pilot study, a parallel two-arm randomized clinical trial that provided complete diets to all participants. Matching single-spot urine and fasting plasma specimens were collected at baseline, and then following two weeks of either a Prudent or Western diet with a weight-maintaining menu plan designed by a dietician. Targeted and nontargeted metabolite profiling was conducted using three complementary analytical platforms, where 80 plasma metabolites and 84 creatinine-normalized urinary metabolites were reliably measured (CV < 30%) in the majority of participants (>75%) after implementing a rigorous data workflow for metabolite authentication with stringent quality control. We classified a panel of metabolites with distinctive trajectories following two weeks of food provisions when using complementary univariate and multivariate statistical models. Unknown metabolites associated with contrasting dietary patterns were identified with high-resolution MS/MS, as well as co-elution after spiking with authentic standards if available. Overall, 3-methylhistidine and proline betaine concentrations increased in both plasma and urine samples after participants were assigned a Prudent diet (q < 0.05) with a corresponding decrease in the Western diet group. Similarly, creatinine-normalized urinary imidazole propionate, hydroxypipecolic acid, dihydroxybenzoic acid, and enterolactone glucuronide, as well as plasma ketoleucine and ketovaline increased with a Prudent diet (p < 0.05) after adjustments for age, sex, and BMI. In contrast, plasma myristic acid, linoelaidic acid, linoleic acid, α-linoleic acid, pentadecanoic acid, alanine, proline, carnitine, and deoxycarnitine, as well as urinary acesulfame K increased among participants following a Western diet. Most metabolites were also correlated (r > ± 0.30, p < 0.05) to changes in the average intake of specific nutrients from self-reported diet records reflecting good adherence to assigned food provisions. Our study revealed robust biomarkers sensitive to short-term changes in habitual diet, which is needed for accurate monitoring of healthy eating patterns in free-living populations, and evidence-based public health policies for chronic disease prevention.

Glutathione and Nitric Oxide: Key Team Players in Use and Disuse of Skeletal Muscle

Glutathione (GSH) is the main non-enzymatic antioxidant playing an important role in detoxification, signal transduction by modulation of protein thiols redox status and direct scavenging of radicals. The latter function is not only performed against reactive oxygen species (ROS) but GSH also has a fundamental role in buffering nitric oxide (NO), a physiologically-produced molecule having-multifaceted functions. The efficient rate of GSH synthesis and high levels of GSH-dependent enzymes are characteristic features of healthy skeletal muscle where, besides the canonical functions, it is also involved in muscle contraction regulation. Moreover, NO production in skeletal muscle is a direct consequence of contractile activity and influences several metabolic myocyte pathways under both physiological and pathological conditions. In this review, we will consider the homeostasis and intersection of GSH with NO and then we will restrict the discussion on their role in processes related to skeletal muscle function and degeneration.

High Throughput Screening of Serum γ-Glutamyl Dipeptides for Risk Assessment of Nonalcoholic Steatohepatitis with Impaired Glutathione Salvage Pathway

Nonalcoholic fatty liver disease (NAFLD) is the most common preventable chronic liver disorder in developed countries, the prevalence of which is increasing worldwide due to its association with obesity and type 2 diabetes. However, the exact mechanisms of NAFLD pathophysiology remain poorly understood including its progression to the more severe nonalcoholic steatohepatitis (NASH). New advances for early detection and monitoring of NASH progression are limited due to the lack of specific blood biomarkers, thus requiring invasive liver biopsies for histopathology. Herein, multisegment injection-capillary electrophoresis-tandem mass spectrometry (MSI-CE-MS/MS) is validated as a high throughput, robust, and quantitative platform for targeted analysis of a panel of 16 serum γ-glutamyl dipeptides from a cohort of NASH adult patients from Japan (median age = 53 years, median BMI = 27 kg/m², n = 116). Multiplexed separations based on MSI-CE-MS/MS enable the design of unique data workflows that rely on customizable serial sample injection formats for accurate determination of γ-glutamyl dipeptides with quality control. Also, the introduction of a liquid coolant device to the capillary outlet improves long-term migration time stability in CE. Unsupervised pattern recognition methods revealed two distinctive NASH subgroups based on their contrasting γ-glutamyl dipeptide status despite patients having similar clinical phenotypes and NASH activity scores (median NAS ≈ 6.0). There was an inverse correlation between serum γ-glutamyl dipeptide concentrations and γ-glutamyltransferease (GGT) enzyme activity (r = -0.46; p = 2.5 × 10^-7), which was indicative of a low-risk (n = 64) as compared to a high-risk (n = 52) patient subgroup with impaired glutathione salvage pathway and likely poor clinical prognosis. Our findings highlight the key role of defects in the γ-glutamyl cycle for differentiation of NASH patients, which may enable better risk assessment of long-term survivorship as a complement to standard liver enzyme screens and histopathology.

High-Intensity Interval Training Decreases Resting Urinary Hypoxanthine Concentration in Young Active Men-A Metabolomic Approach

High-intensity interval training (HIIT) is known to improve performance and skeletal muscle energy metabolism. However, whether the body’s adaptation to an exhausting short-term HIIT is reflected in the resting human metabolome has not been examined so far. Therefore, a randomized controlled intervention study was performed to investigate the effect of a ten-day HIIT on the resting urinary metabolome of young active men. Fasting spot urine was collected before (−1 day) and after (+1 day; +4 days) the training intervention and 65 urinary metabolites were identified by liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy. Metabolite concentrations were normalized to urinary creatinine and subjected to univariate statistical analysis. One day after HIIT, no overall change in resting urinary metabolome, except a significant difference with decreasing means in urinary hypoxanthine concentration, was documented in the experimental group. As hypoxanthine is related to purine degradation, lower resting urinary hypoxanthine levels may indicate a training-induced adaptation in purine nucleotide metabolism.

Metabolic Perturbations from Step Reduction in Older Persons at Risk for Sarcopenia: Plasma Biomarkers of Abrupt Changes in Physical Activity

Sarcopenia is the age-related loss of skeletal muscle mass, strength and function, which may be accelerated during periods of physical inactivity. Declines in skeletal muscle and functionality not only impacts mobility but also increases chronic disease risk, such as type 2 diabetes. The aim of this study was to measure adaptive metabolic responses to acute changes in habitual activity in a cohort of overweight, pre-diabetic older adults (age = 69 ± 4 years; BMI = 27 ± 4 kg/m², n = 17) when using non-targeted metabolite profiling by multisegment injection-capillary electrophoresis-mass spectrometry. Participants completed two weeks of step reduction (<1000 steps/day) followed by a two week recovery period, where fasting plasma samples were collected at three time intervals at baseline, after step reduction and following recovery. Two weeks of step reduction elicited increases in circulatory metabolites associated with a decline in muscle energy metabolism and protein degradation, including glutamine, carnitine and creatine (q < 0.05; effect size > 0.30), as well as methionine and deoxycarnitine (p < 0.05; effect size ≈ 0.20) as compared to baseline. Similarly, decreases in uremic toxins in plasma that promote muscle inflammation, indoxyl sulfate and hippuric acid, as well as oxoproline, a precursor used for intramuscular glutathione recycling, were also associated with physical inactivity (p < 0.05; effect size > 0.20). Our results indicate that older persons are susceptible to metabolic perturbations due to short-term step reduction that were not fully reversible with resumption of normal ambulatory activity over the same time period. These plasma biomarkers may enable early detection of inactivity-induced metabolic dysregulation in older persons at risk for sarcopenia not readily measured by current imaging techniques or muscle function tests, which is required for the design of therapeutic interventions to counter these deleterious changes in support of healthy ageing.