Obesity and diabetes related plasma amino acid alterations

Comparing Plant and Animal Glutamate Receptors: Common Traits but Different Fates?

Animal ionotropic glutamate receptors (iGluRs) are ligand-gated channels whose evolution is intimately linked to the one of the nervous system, where the agonist glutamate and co-agonists glycine/D-serine act as neuro-transmitters or -modulators. While iGluRs are specialized in neuronal communication, plant glutamate receptor-like (GLR) homologues have evolved many plant-specific physiological functions, such as sperm signaling in moss, pollen tube growth, root meristem proliferation, innate immune and wound responses. GLRs have been associated with Ca2+ signaling by directly channeling its extracellular influx into the cytosol. Nevertheless, very limited information on functional properties of GLRs is available, and we mostly rely on structure/function data obtained for animal iGluRs to interpret experimental results obtained for plant GLRs. Yet, a deeper characterization and better understanding of plant GLRs is progressively unveiling original and different mode of functions when compared to their mammalian counterparts. Here, we review the function of plant GLRs comparing their predicted structure and physiological roles to the well-documented ones of iGluRs. We conclude that interpreting GLR function based on comparison to their animal counterparts calls for caution, especially when presuming physiological roles and mode of action for plant GLRs from comparison to iGluRs in peripheral, non-neuronal tissues.

Altered peripheral amino acid profile indicate a systemic impact of active celiac disease and a possible role of amino acids in disease pathogenesis

BACKGROUND

We have previously performed a Genome Wide Association and linkage study that indicated a new disease triggering mechanism involving amino acid metabolism and nutrient sensing signaling pathways.

OBJECTIVE

The aim of this study was to investigate if plasma amino acid levels differed among children with celiac disease compared with disease controls.

MATERIALS AND METHODS

Fasting plasma samples from 141 children with celiac disease and 129 non-celiac disease controls, were analyzed for amino acid levels by liquid chromatography-tandem mass spectrometry (LC/MS). A general linear model using age and experimental effects as covariates was used to compare amino acid levels between children with a diagnosis of celiac disease and controls.

RESULTS

Seven out of twenty-three analyzed amino acids were elevated in children with celiac disease compared with controls (tryptophan, taurine, glutamic acid, proline, ornithine, alanine and methionine). The significance of the individual amino acids do not survive multiple correction, however, multivariate analyses of the amino acid profile showed significantly altered amino acid levels in children with celiac disease overall and after correction for age, sex and experimental effects (p = 8.4 × 10-8).

CONCLUSION

These findings support the idea that amino acids could influence systemic inflammation and play a possible role in disease pathogenesis.

Serum Metabolomics of Activity Energy Expenditure and its Relation to Metabolic Syndrome and Obesity

Modifiable lifestyle factors, including exercise and activity energy expenditure (AEE), may attenuate the unfavorable health effects of obesity, such as risk factors of metabolic syndrome (MetS). However, the underlying mechanisms are not clear. In this study we sought to investigate whether the metabolite profiles of MetS and adiposity assessed by body mass index (BMI) and central obesity are inversely correlated with AEE and physical activity. We studied 35 men and 47 women, aged 30-60 years, using doubly labeled water to derive AEE and the Sedentary Time and Activity Reporting Questionnaire (STAR-Q) to determine the time spent in moderate and vigorous physical activity. Proton nuclear magnetic resonance spectroscopy was used for serum metabolomics analysis. Serine and glycine were found in lower concentrations in participants with more MetS risk factors and greater adiposity. However, serine and glycine concentrations were higher with increasing activity measures. Metabolic pathway analysis and recent literature suggests that the lower serine and glycine concentrations in the overweight/obese state could be a consequence of serine entering de novo sphingolipid synthesis. Taken together, higher levels of AEE and physical activity may play a crucial part in improving metabolic health in men and women with and without MetS risk factors.

Plasma glutamine and glutamic acid are potential biomarkers for predicting diabetic retinopathy

INTRODUCTION

Diabetic patients with a long disease duration usually accompanied complication such as diabetic retinopathy, but in some patients had no complication.

OBJECTIVES

We analyzed differences in plasma metabolites according to the presence or absence of diabetic retinopathy (DR) in type 2 diabetic (T2D) patients with disease duration ≥ 15 years.

METHODS

A cohort of 183 T2D patients was established. Their biospecimens and clinical information were collected in accordance with the guidelines of the National Biobank of Korea, and the Korean Diabetes Association. DR phenotypes of the subjects were verified by ophthalmologic specialists. Plasma metabolites were analyzed using gas chromatography time-of-flight mass spectrometry and ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. And these results were analyzed using multivariate statistics.

RESULTS

For metabolomic study, propensity score matched case and control subjects were chosen. Mean age of the subjects was 66.4 years and mean T2D duration was 22.2 years. Metabolomic identification revealed various carbohydrates, amino acids, and organic compounds that distinguished between age- and sex-matched non-diabetic controls and T2D subjects. Among these, glutamine and glutamic acid were suggested as the most distinctive metabolites for the presence of DR. Receiver operating characteristics curves showed an excellent diagnostic value of combined (AUC = 0.739) and the ratio (AUC = 0.742) of glutamine and glutamic acid for DR. And these results were consistent in validation analyses.

CONCLUSION

Our results imply that plasma glutamine, glutamic acid, and their ratio may be valuable as novel biomarkers for anticipating DR in T2D subjects.

Serum and plasma amino acids as markers of prediabetes, insulin resistance, and incident diabetes

Presently, routine screening misses many cases of prediabetes and early type 2 diabetes (T2D). Therefore, better biomarkers are needed for a simple and early detection of abnormalities of glucose metabolism and prediction of future T2D. Possible candidates for this include plasma or serum amino acids because glucose and amino acid metabolism are closely connected. This review presents the available evidence of this connectivity and discusses its clinical implications. First, we examine the underlying physiological, pre-analytical, and analytical issues. Then, we summarize results of human studies that evaluate amino acid levels as markers for insulin resistance, prediabetes, and future incident T2D. Finally, we illustrate the interconnection of amino acid levels and metabolic syndrome with our own data from a deeply phenotyped human cohort. We also discuss how amino acids may contribute to the pathophysiology of T2D. We conclude that elevated branched-chain amino acids and reduced glycine are currently the most robust and consistent amino acid markers for prediabetes, insulin resistance, and future T2D. Yet, we are cautious regarding the clinical potential even of these parameters because their discriminatory power is insufficient and their levels depend not only on glycemia, but also on other components of the metabolic syndrome. The identification of more precise intermediates of amino acid metabolism or combinations with other biomarkers will, therefore, be necessary to obtain in order to develop laboratory tests that can improve T2D screening.

Biomarkers of food intake and nutrient status are associated with glucose tolerance status and development of type 2 diabetes in older Swedish women

Background: Diet is frequently associated with both the development and prevention of type 2 diabetes (T2D), but there is a lack of objective tools for assessing the relation between diet and T2D. Biomarkers of dietary intake are unconfounded by recall and reporting bias, and using multiple dietary biomarkers could help strengthen the link between a healthy diet and the prevention of T2D.Objective: The objective of this study was to explore how diet is related to glucose tolerance status (GTS) and to future development of T2D irrespective of common T2D and cardiovascular disease risk factors by using multiple dietary biomarkers.Design: Dietary biomarkers were measured in plasma from 64-y-old Swedish women with different GTS [normal glucose tolerance (NGT; n = 190), impaired glucose tolerance (IGT; n = 209), and diabetes (n = 230)]. The same subjects were followed up after 5 y to determine changes in glucose tolerance (n = 167 for NGT, n = 174 for IGT, and n = 159 for diabetes). ANCOVA and logistic regression were used to explore baseline data for associations between dietary biomarkers, GTS, and new T2D cases at follow-up (n = 69).Results: Of the 10 dietary biomarkers analyzed, β-alanine (beef) (P-raw < 0.001), alkylresorcinols C17 and C19 (whole-grain wheat and rye) (P-raw = 0.003 and 0.011), eicosapentaenoic acid (fish) (P-raw = 0.041), 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) (fish) (P-raw = 0.002), linoleic acid (P-raw < 0.001), oleic acid (P-raw = 0.003), and α-tocopherol (margarine and vegetable oil) (P-raw < 0.001) were associated with GTS, and CMPF (fish) (OR: 0.72; 95% CI: 0.56, 0.93; P-raw = 0.013) and α-tocopherol (OR: 0.71; 95% CI: 0.51, 0.98; P-raw = 0.041) were inversely associated with future T2D development.Conclusions: Several circulating dietary biomarkers were strongly associated with GTS after correction for known T2D risk factors, underlining the role of diet in the development and prevention of T2D. To our knowledge, this study is the first to use multiple dietary biomarkers to investigate the link between diet and disease risk.

Abnormal circulating amino acid profiles in multiple metabolic disorders

AIM

To evaluate circulating amino acids (AA) profiles in obesity, type 2 diabetes (T2D) and metabolic syndrome (MetS).

METHODS

Serum AA were profiled among 200; healthy, obese, T2D and MetS subjects matched by sex, age and BMI using ultra-high performance liquid chromatography tandem quadruple mass spectrometry (UPLC-TQ-MS). A meta-analysis, including 47 case-control studies (including the current study) on serum AA in obesity, T2D and MetS searched through October 2016 was conducted to explore the AA differences in obesity, T2D and MetS.

RESULTS

In comparison with healthy controls, 14 AA (10 increased and 4 decreased) were significantly altered (P<0.05) in all non-healthy subjects. Also, mean differences of valine (obese: 34.13 [27.70, 40.56]µmol/L, P<0.001, T2D: 19.49 [3.31, 35.68]µmol/L, P<0.05, MetS: 29.18 [16.04, 42.33]µmol/L, P<0.001), glutamic acid (obese: 18.62 [11.64, 25.61]µmol/L, P<0.001, T2D: 19.94 [0.28, 39.61]µmol/L, P<0.05, MetS: 12.45 [3.98, 20.91]µmol/L, P<0.001), proline (obese: 16.72 [6.20, 27.24]µmol/L, P<0.001, T2D: 20.72 [15.82, 25.61]µmol/L, P<0.001, MetS: 29.95 [25.18, 34.71]µmol/L, P<0.001) and isoleucine (obese: 11.39 [8.54, 14.24]µmol/L, P<0.001, T2D: 7.37 [1.52, 13.22]µmol/L, P<0.05, MetS: 10.40 [4.90, 15.89]µmol/L, P<0.001) were significantly higher compared to healthy controls. Similarly, mean differences of glycine (obese: -30.99 [-39.69, -22.29]µmol/L, P<0.001, T2D: -30.37 [-41.80, -18.94]µmol/L, P<0.001 and MetS: -35.24 [-39.28, -31.21]µmol/L, P<0.001) were significantly lower compared to healthy controls.

CONCLUSION

In both the case-control study and meta-analysis, obesity was related to the most circulating AA changes, followed by MetS and T2D. Valine, isoleucine, glutamic acid and proline increased, while Glycine decreased in all metabolic disorders.

Recent trends in analytical methods for the determination of amino acids in biological samples

Amino acids are widely distributed in biological fluids and involved in many biological processes, such as the synthesis of proteins, fatty acids, and ketone bodies. The altered levels of amino acids in biological fluids have been found to be closely related to several diseases, such as type 2 diabetes, kidney disease, liver disease, and cancer. Therefore, the development of analytical methods to measure amino acid concentrations in biological samples can contribute to research on the physiological actions of amino acids and the prediction, diagnosis and understanding of diseases. This review describes the analytical methods reported in 2012-2016 that utilized liquid chromatography and capillary electrophoresis coupled with ultraviolet, fluorescence, mass spectrometry, and electrochemical detection. Additionally, the relationship between amino acid concentrations and several diseases is also summarized.

Metabolite profiling in identifying metabolic biomarkers in older people with late-onset type 2 diabetes mellitus

Regulation of blood glucose requires precise coordination between different endocrine systems and multiple organs. Type 2 diabetes mellitus (T2D) arises from a dysregulated response to elevated glucose levels in the circulation. Globally, the prevalence of T2D has increased dramatically in all age groups. T2D in older adults is associated with higher mortality and reduced functional status, leading to higher rate of institutionalization. Despite the potential healthcare challenges associated with the presence of T2D in the elderly, the pathogenesis and phenotype of late-onset T2D is not well studied. Here we applied untargeted metabolite profiling of urine samples from people with and without late-onset T2D using ultra-performance liquid-chromatography mass-spectrometry (UPLC-MS) to identify urinary biomarkers for late-onset T2D in the elderly. Statistical modeling of measurements and thorough validation of structural assignment using liquid chromatography tandem mass-spectrometry (LC-MS/MS) have led to the identification of metabolite biomarkers associated with late-onset T2D. Lower levels of phenylalanine, acetylhistidine, and cyclic adenosine monophosphate (cAMP) were found in urine samples of T2D subjects validated with commercial standards. Elevated levels of 5′-methylthioadenosine (MTA), which previously has only been implicated in animal model of diabetes, was found in urine of older people with T2D.

Metabolite profiling of obese individuals before and after a one year weight loss program

OBJECTIVE

We and others have previously characterized changes in circulating metabolite levels following diet-induced weight loss. Our aim was to investigate whether baseline metabolite levels and weight-loss-induced changes in these are predictive of or associated with changes in body mass index (BMI) and metabolic risk traits.

METHODS

Serum metabolites were analyzed with gas and liquid chromatography/mass spectrometry in 91 obese individuals at baseline and after participating in a 1 year non-surgical weight loss program.ResultsA total of 137 metabolites were identified and semi-quantified at baseline (BMI 42.7±5.8, mean±s.d.) and at follow-up (BMI 36.3±6.6). Weight-loss-induced modification was observed for levels of 57 metabolites in individuals with ⩾10% weight loss. Lower baseline levels of xylitol was predictive of a greater decrease in BMI (β=0.06, P<0.01) and ⩾10% weight loss (odds ratio (OR)=0.2, confidence interval (CI)=0.07-0.7, P=0.01). Decreases in levels of isoleucine, leucine, valine and tyrosine were associated with decrease in BMI (β>0.1, P<0.05) and ⩾10% weight loss (isoleucine: OR=0.08, CI=0.01-0.3, leucine: OR=0.1, CI=0.01-0.6, valine: OR=0.1, CI=0.02-0.5, tyrosine: OR=0.1, CI=0.03-0.6, P<0.02).

CONCLUSIONS

Diet-induced weight loss leads to mainly reduced levels of metabolites that are elevated in obese insulin resistant individuals. We identified multiple new associations with metabolic risk factors and validated several previous findings related to weight loss-mediated metabolite changes. Levels of specific metabolites, such as xylitol, may be predictive of the response to non-surgical weight loss already at baseline.

An excessive increase in glutamate contributes to glucose-toxicity in β-cells via activation of pancreatic NMDA receptors in rodent diabetes

In the nervous system, excessive activation of NMDA receptors causes neuronal injury. Although activation of NMDARs has been proposed to contribute to the progress of diabetes, little is known about the effect of excessive long-term activation of NMDARs on β-cells, especially under the challenge of hyperglycemia. Here we thoroughly investigated whether endogenous glutamate aggravated β-cell dysfunction under chronic exposure to high-glucose via activation of NMDARs. The glutamate level was increased in plasma of diabetic mice or patients and in the supernatant of β-cell lines after treatment with high-glucose for 72 h. Decomposing the released glutamate improved GSIS of β-cells under chronic high-glucose exposure. Long-term treatment of β-cells with NMDA inhibited cell viability and decreased GSIS. These effects were eliminated by GluN1 knockout. The NMDAR antagonist MK-801 or GluN1 knockout prevented high-glucose-induced dysfunction in β-cells. MK-801 also decreased the expression of pro-inflammatory cytokines, and inhibited I-κB degradation, ROS generation and NLRP3 inflammasome expression in β-cells exposed to high-glucose. Furthermore, another NMDAR antagonist, Memantine, improved β-cells function in diabetic mice. Taken together, these findings indicate that an increase of glutamate may contribute to the development of diabetes through excessive activation of NMDARs in β-cells, accelerating β-cells dysfunction and apoptosis induced by hyperglycemia.

Inhibition of NMDA receptor function with an anti-GluN1-S2 antibody impairs human platelet function and thrombosis

GluN1 is a mandatory component of N-methyl-D-aspartate receptors (NMDARs) best known for their roles in the brain, but with increasing evidence for relevance in peripheral tissues, including platelets. Certain anti-GluN1 antibodies reduce brain infarcts in rodent models of ischaemic stroke. There is also evidence that human anti-GluN1 autoantibodies reduce neuronal damage in stroke patients, but the underlying mechanism is unclear. This study investigated whether anti-GluN1-mediated neuroprotection involves inhibition of platelet function. Four commercial anti-GluN1 antibodies were screened for their abilities to inhibit human platelet aggregation. Haematological parameters were examined in rats vaccinated with GluN1. Platelet effects of a mouse monoclonal antibody targeting the glycine-binding region of GluN1 (GluN1-S2) were tested in assays of platelet activation, aggregation and thrombus formation. The epitope of anti-GluN1-S2 was mapped and the mechanism of antibody action modelled using crystal structures of GluN1. Our work found that rats vaccinated with GluN1 had a mildly prolonged bleeding time and carried antibodies targeting mostly GluN1-S2. The monoclonal anti-GluN1-S2 antibody (from BD Biosciences) inhibited activation and aggregation of human platelets in the presence of adrenaline, adenosine diphosphate, collagen, thrombin and a protease-activated receptor 1-activating peptide. When human blood was flowed over collagen-coated surfaces, anti-GluN1-S2 impaired thrombus growth and stability. The epitope of anti-GluN1-S2 was mapped to α-helix H located within the glycine-binding clamshell of GluN1, where the antibody binding was computationally predicted to impair opening of the NMDAR channel. Our results indicate that anti-GluN1-S2 inhibits function of human platelets, including dense granule release and thrombus growth. Findings add to the evidence that platelet NMDARs regulate thrombus formation and suggest a novel mechanism by which anti-GluN1 autoantibodies limit stroke-induced neuronal damage.

Amino Acid Signatures to Evaluate the Beneficial Effects of Weight Loss

Aims. We investigated the relationship between circulating amino acid levels and obesity; to what extent weight loss followed by weight maintenance can correct amino acid abnormalities; and whether amino acids are related to weight loss. Methods. Amino acids associated with waist circumference (WC) and BMI were studied in 804 participants from the Malmö Diet and Cancer Cardiovascular Cohort (MDC-CC). Changes in amino acid levels were analyzed after weight loss and weight maintenance in 12 obese subjects and evaluated in a replication cohort (n = 83). Results. Out of the eight identified BMI-associated amino acids from the MDC-CC, alanine, isoleucine, tyrosine, phenylalanine, and glutamate decreased after weight loss, while asparagine increased after weight maintenance. These changes were validated in the replication cohort. Scores that were constructed based on obesity-associated amino acids and known risk factors decreased in the ≥10% weight loss group with an associated change in BMI (R² = 0.16-0.22, p < 0.002), whereas the scores increased in the <10% weight loss group (p < 0.0004). Conclusions. Weight loss followed by weight maintenance leads to differential changes in amino acid levels associated with obesity. Treatment modifiable scores based on epidemiological and interventional data may be used to evaluate the potential metabolic benefit of weight loss.

Plasma metabolomics identified novel metabolites associated with risk of type 2 diabetes in two prospective cohorts of Chinese adults

BACKGROUND

Metabolomics studies in Caucasians have identified a number of novel metabolites in association with the risk of type 2 diabetes (T2D). However, few prospective metabolomic studies are available in Chinese populations. In the present study, we sought to identify novel metabolites consistently associated with incident T2D in two independent cohorts of Chinese adults.

METHODS

We performed targeted metabolomics (52 metabolites) of fasting plasma samples by liquid chromatography-mass spectrometry in two prospective case-control studies nested within the Dongfeng-Tongji (DFTJ) cohort and Jiangsu Non-communicable Disease (JSNCD) cohort. After following for 4.61 ± 0.15 and 7.57 ± 1.13 years, respectively, 1039 and 520 eligible participants developed incident T2D in these two cohorts, and controls were 1:1 matched with cases by age (± 5 years) and sex. Multivariate conditional logistic regression models were constructed to identify metabolites associated with future T2D risk in both cohorts.

RESULTS

We identified four metabolites consistently associated with an increased risk of developing T2D in the two cohorts, including alanine, phenylalanine, tyrosine and palmitoylcarnitine. In the meta-analysis of two cohorts, the odds ratios (95% confidence intervals, CIs) comparing extreme quartiles were 1.79 (1.32-2.42) for alanine, 1.91 (1.41-2.60) for phenylalanine, 1.85 (1.37-2.48) for tyrosine and 1.63 (1.21-2.20) for palmitoylcarnitine (all P_trend ≤ 0.01).

CONCLUSIONS

We confirmed the association of alanine, phenylalanine and tyrosine with future T2D risk and further identified palmitoylcarnitine as a novel metabolic marker of incident T2D in two prospective cohorts of Chinese adults. Our findings might provide new aetiological insight into the development of T2D.

Selected GRIN2A mutations in melanoma cause oncogenic effects that can be modulated by extracellular glutamate

GRIN2A mutations are frequent in melanoma tumours but their role in disease is not well understood. GRIN2A encodes a modulatory subunit of the N-methyl-d-aspartate receptor (NMDAR). We hypothesized that certain GRIN2A mutations increase NMDAR function and support melanoma growth through oncogenic effects. This hypothesis was tested using 19 low-passage melanoma cell lines, four of which carried novel missense mutations in GRIN2A that we previously reported. We examined NMDAR expression, function of a calcium ion (Ca²⁺) channel and its contribution to cell growth using pharmacological modulators; findings were correlated with the presence or absence of GRIN2A mutations. We found that NMDAR expression was low in all melanoma cell lines, independent of GRIN2A mutations. In keeping with this, NMDAR-mediated Ca²⁺ influx and its contribution to cell proliferation were weak in most cell lines. However, certain GRIN2A mutations and culture media with lower glutamate levels enhanced NMDAR effects on cell growth and invasion. The main finding was that G762E was associated with higher glutamate-mediated Ca²⁺ influx and stronger NMDAR contribution to cell proliferation, compared with wild-type GRIN2A and other GRIN2A mutations. The pro-invasive phenotype of mutated cell lines was increased in culture medium containing less glutamate, implying environmental modulation of mutation effects. In conclusion, NMDAR ion channel function is low in cultured melanoma cells but supports cell proliferation and invasion. Selected GRIN2A mutations, such as G762E, are associated with oncogenic consequences that can be modulated by extracellular glutamate. Primary cultures may be better suited to determine the role of the NMDAR in melanoma in vivo.

Novel plasma biomarker of atenolol-induced hyperglycemia identified through a metabolomics-genomics integrative approach

INTRODUCTION

While atenolol is an effective antihypertensive agent, its use is also associated with adverse events including hyperglycemia and incident diabetes that may offset the benefits of blood pressure lowering. By combining metabolomic and genomic data acquired from hypertensive individuals treated with atenolol, it may be possible to better understand the pathways that most impact the development of an adverse glycemic state.

OBJECTIVE

To identify biomarkers that can help predict susceptibility to blood glucose excursions during exposure to atenolol.

METHODS

Plasma samples acquired from 234 Caucasian participants treated with atenolol in the Pharmacogenomic Evaluation of Antihypertensive Responses trial were analyzed by gas chromatography Time-Of-Flight Mass Spectroscopy. Metabolomics and genomics data were integrated by first correlating participant's metabolomic profiles to change in glucose after treatment with atenolol, and then incorporating genotype information from genes involved in metabolite pathways associated with glucose response.

RESULTS

Our findings indicate that the baseline level of β-alanine was associated with glucose change after treatment with atenolol (Q = 0.007, β = 2.97 mg/dL). Analysis of genomic data revealed that carriers of the G allele for SNP rs2669429 in gene DPYS, which codes for dihydropyrimidinase, an enzyme involved in β-alanine formation, had significantly higher glucose levels after treatment with atenolol when compared with non-carriers (Q = 0.05, β = 2.76 mg/dL). This finding was replicated in participants who received atenolol as an add-on therapy (P = 0.04, β = 1.86 mg/dL).

CONCLUSION

These results suggest that β-alanine and rs2669429 may be predictors of atenolol-induced hyperglycemia in Caucasian individuals and further investigation is warranted.

Amino acids in a targeted versus a non-targeted metabolomics LC-MS/MS assay. Are the results consistent?

BACKGROUND

The results of plasma amino acid patterns in samples from kidney transplant patients with good and impaired renal function using a targeted LC-MS/MS amino acid assay and a non-targeted metabolomics assay were compared.

METHODS

EDTA plasma samples were prospectively collected at baseline, 1, 2, 4 and 6months post-transplant (n=116 patients, n=398 samples). Each sample was analyzed using both a commercial amino acid LC-MS/MS assay and a non-targeted metabolomics assay also based on MS/MS ion transitions. The results of both assays were independently statistically analyzed to identify amino acids associated with estimated glomerular filtration rates using correlation and partial least squares-discriminant analysis.

RESULTS

Although there was overlap between the results of the targeted and non-targeted metabolomics assays (tryptophan, 1-methyl histidine), there were also substantial inconsistencies, with the non-targeted assay resulting in more "hits" than the targeted assay. Without further verification of the hits detected by the non-targeted discovery assay, this would have led to different interpretation of the results. There were also false negative results when the non-targeted assay was used (hydroxy proline). Several of said discrepancies could be explained by loss of sensitivity during analytical runs for selected amino acids (serine and threonine), retention time shifts, signals above the range of linear detector response and integration of peaks not separated from background and interferences (aspartate) when the non-targeted metabolomics assay was used.

CONCLUSIONS

Whenever assessment of a specific pathway such as amino acids is the focus of interest, a targeted seems preferable to a non-targeted metabolomics assay.

Specific Metabolic Profiles and Their Relationship to Insulin Resistance in Recent-Onset Type 1 and Type 2 Diabetes

CONTEXT

Insulin resistance reflects the inadequate insulin-mediated use of metabolites and predicts type 2 diabetes (T2D) but is also frequently seen in long-standing type 1 diabetes (T1D) and represents a major cardiovascular risk factor.

OBJECTIVE

We hypothesized that plasma metabolome profiles allow the identification of unique and common early biomarkers of insulin resistance in both diabetes types.

DESIGN, SETTING, AND PATIENTS

Two hundred ninety-five plasma metabolites were analyzed by mass spectrometry from patients of the prospective observational German Diabetes Study with T2D (n = 244) or T1D (n = 127) and known diabetes duration of less than 1 year and glucose-tolerant persons (CON; n = 129). Abundance of metabolites was tested for association with insulin sensitivity as assessed by hyperinsulinemic-euglycemic clamps and related metabolic phenotypes.

MAIN OUTCOMES MEASURES

Sixty-two metabolites with phenotype-specific patterns were identified using age, sex, and body mass index as covariates.

RESULTS

Compared with CON, the metabolome of T2D and T1D showed similar alterations in various phosphatidylcholine species and amino acids. Only T2D exhibited differences in free fatty acids compared with CON. Pairwise comparison of metabolites revealed alterations of 28 and 49 metabolites in T1D and T2D, respectively, when compared with CON. Eleven metabolites allowed differentiation between both diabetes types and alanine, α-amino-adipic acid, isoleucin, and stearic acid showed an inverse association with insulin sensitivity in both T2D and T1D combined.

CONCLUSION

Metabolome analyses from recent-onset T2D and T1D patients enables identification of defined diabetes type-specific differences and detection of biomarkers of insulin sensitivity. These analyses may help to identify novel clinical subphenotypes diabetes.

Metabolomics in Prediabetes and Diabetes: A Systematic Review and Meta-analysis

OBJECTIVE

To conduct a systematic review of cross-sectional and prospective human studies evaluating metabolite markers identified using high-throughput metabolomics techniques on prediabetes and type 2 diabetes.

RESEARCH DESIGN AND METHODS

We searched MEDLINE and EMBASE databases through August 2015. We conducted a qualitative review of cross-sectional and prospective studies. Additionally, meta-analyses of metabolite markers, with data estimates from at least three prospective studies, and type 2 diabetes risk were conducted, and multivariable-adjusted relative risks of type 2 diabetes were calculated per study-specific SD difference in a given metabolite.

RESULTS

We identified 27 cross-sectional and 19 prospective publications reporting associations of metabolites and prediabetes and/or type 2 diabetes. Carbohydrate (glucose and fructose), lipid (phospholipids, sphingomyelins, and triglycerides), and amino acid (branched-chain amino acids, aromatic amino acids, glycine, and glutamine) metabolites were higher in individuals with type 2 diabetes compared with control subjects. Prospective studies provided evidence that blood concentrations of several metabolites, including hexoses, branched-chain amino acids, aromatic amino acids, phospholipids, and triglycerides, were associated with the incidence of prediabetes and type 2 diabetes. We meta-analyzed results from eight prospective studies that reported risk estimates for metabolites and type 2 diabetes, including 8,000 individuals of whom 1,940 had type 2 diabetes. We found 36% higher risk of type 2 diabetes per study-specific SD difference for isoleucine (pooled relative risk 1.36 [1.24-1.48]; I(2) = 9.5%), 36% for leucine (1.36 [1.17-1.58]; I(2) = 37.4%), 35% for valine (1.35 [1.19-1.53]; I(2) = 45.8%), 36% for tyrosine (1.36 [1.19-1.55]; I(2) = 51.6%), and 26% for phenylalanine (1.26 [1.10-1.44]; I(2) = 56%). Glycine and glutamine were inversely associated with type 2 diabetes risk (0.89 [0.81-0.96] and 0.85 [0.82-0.89], respectively; both I(2) = 0.0%).

CONCLUSIONS

In studies using high-throughput metabolomics, several blood amino acids appear to be consistently associated with the risk of developing type 2 diabetes.

Changes in glucose-elicited blood metabolite responses following weight loss and long term weight maintenance in obese individuals with impaired glucose tolerance

AIMS

Weight loss improves insulin sensitivity and glucose tolerance in obese subjects with impaired glucose tolerance (IGT), but the long term dynamic effects on blood metabolites other than glucose during an oral glucose tolerance test (OGTT), are largely unknown. Here, we studied changes in OGTT-elicited metabolite patterns in obese subjects during a diet-induced weight loss study.

METHODS

Blood samples from 14 obese individuals with IGT were collected at 0, 30 and 120 min during a standard 75 g OGTT at baseline (BMI 44 ± 2 kg/m(2)), after weight loss (BMI 36 ± 2 kg/m(2)) and after weight maintenance (BMI 35 ± 2 kg/m(2)). Serum metabolite levels were analyzed by gas chromatography/mass spectrometry and compared to a lean glucose tolerant group.

RESULTS

Changes in the OGTT-elicited metabolite patterns occurred differentially during weight loss and weight maintenance. Enhanced suppression of aromatic amino acids were associated with decreased insulinogenic index observed after weight loss (tyrosine: r=0.72, p=0.013; phenylalanine: r=0.63, p=0.039). The OGTT-elicited suppression and/or lack of increase in levels of glutamate, glutamine, isoleucine, leucine, and the fatty acids laurate, oleate and palmitate, improved towards the lean profile after weight maintenance, paralleling an improvement in glucose tolerance. The greater heterogeneity in the response before and after weight loss in the obese, compared to lean subjects, was markedly reduced after weight maintenance.

CONCLUSIONS

Diet-induced weight loss followed by weight maintenance results in changes in metabolite profiles associated with either hepatic insulin sensitivity or peripheral glucose tolerance. Our results highlight the importance of evaluating the effects of weight loss and weight maintenance separately.

Dietary fibers influence the intestinal SCFAs and plasma metabolites profiling in growing pigs

Dietary fibers (DFs), widely used as food additives to replace fat, can benefit metabolic disorders.

Plasma Glycine and Risk of Acute Myocardial Infarction in Patients With Suspected Stable Angina Pectoris

Background

Glycine is an amino acid involved in antioxidative reactions, purine synthesis, and collagen formation. Several studies demonstrate inverse associations of glycine with obesity, hypertension, and diabetes mellitus. Recently, glycine‐dependent reactions have also been linked to lipid metabolism and cholesterol transport. However, little evidence is available on the association between glycine and coronary heart disease. Therefore, we assessed the association between plasma glycine and acute myocardial infarction (AMI).

Methods and Results

A total of 4109 participants undergoing coronary angiography for suspected stable angina pectoris were studied. Cox regression was used to estimate the association between plasma glycine and AMI, obtained via linkage to the CVDNOR project. During a median follow‐up of 7.4 years, 616 patients (15.0%) experienced an AMI. Plasma glycine was higher in women than in men and was associated with a more favorable baseline lipid profile and lower prevalence of obesity, hypertension, and diabetes mellitus (all P<0.001). After multivariate adjustment for traditional coronary heart disease risk factors, plasma glycine was inversely associated with risk of AMI (hazard ratio per SD: 0.89; 95% CI, 0.82–0.98; P=0.017). The inverse association was generally stronger in those with apolipoprotein B, low‐density lipoprotein cholesterol, or apolipoprotein A‐1 above the median (all P_interaction≤0.037).

Conclusions

Plasma glycine was inversely associated with risk of AMI in patients with suspected stable angina pectoris. The associations were stronger in patients with apolipoprotein B, low‐density lipoprotein cholesterol, or apolipoprotein A‐1 levels above the median. These results motivate further studies to elucidate the relationship between glycine and lipid metabolism, in particular in relation to cholesterol transport and atherosclerosis.

Clinical Trial Registration

URL: https://www.clinicaltrials.gov. Unique identifier: NCT00354081.

Hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry method for the simultaneous determination of l-valine, l-leucine, l-isoleucine, l-phenylalanine, and l-tyrosine in human serum

l-Valine, l-leucine, l-isoleucine, l-phenylalanine, and l-tyrosine are important proposed biomarkers for the early detection and diagnosis of type 2 diabetes. A simple and selective hydrophilic interaction chromatography with tandem mass spectrometry method was developed for the simultaneous determination of these amino acids in human serum, using stable isotope-labeled amino acids as internal standards. Chromatographic separation was carried out on a Syncronis HILIC column (150 mm × 2.1 mm, 5 μm) with the column temperature of 35°C and a mobile phase consisted of acetonitrile/120 mM ammonium acetate (89:11, v/v), and the run time was 11.0 min. The mass spectrometric analysis was performed using a QTRAP 5500 mass spectrometer coupled with an electrospray ionization source in positive ion mode. As these five amino acids are endogenous compounds in serum, we used the corresponding stable isotope-labeled amino acids to evaluate the matrix effect and recovery in serum. The matrix effect was 98.7-107.3%, and the recovery was 92.7-102.3%. Calibration curves spiked unlabeled amino acids in water were linear over the range of 0.200-100 μg/mL. The accuracy, inter-, and intraday precision were below 10.2%. Analytes were stable during the study. This assay method has been validated and applied to the early diagnosis research of type 2 diabetes.

Combining citrulline with atorvastatin preserves glucose homeostasis in a murine model of diet-induced obesity

BACKGROUND AND PURPOSE

NO is a crucial regulator of energy and lipid metabolism, whose homeostasis is compromised during obesity. Combination of citrulline and atorvastatin potentiated NO production in vitro. Here we have assessed the effects of this combination in mice with diet-induced obesity (DIO).

EXPERIMENTAL APPROACH

C57BL/6J male mice were given a standard diet (control) or a high fat-high sucrose diet (DIO) for 8 weeks. DIO mice were then treated with DIO alone, DIO with citrulline, DIO with atorvastatin or DIO with citrulline and atorvastatin (DIOcit-stat) for 3 weeks. Thereafter, body composition, glucose tolerance, insulin sensitivity and liver fat metabolism were measured.

KEY RESULTS

DIOcit-stat mice showed lower body weight, fat mass and epididymal fat depots compared with other DIO groups. Unlike other DIO groups, glucose tolerance and insulin sensitivity of DIOcit-stat, along with blood glucose and insulin concentrations in response to feeding, were restored to control values. Refeeding-induced changes in liver lipogenic activity were also reduced in DIOcit-stat mice compared with those of DIO animals. This was associated with decreased gene expression of the transcription factor SREBP-1, liver X receptor α, ChREBP and of target lipogenic enzymes in the liver of DIOcit-stat mice compared with those of other DIO groups.

CONCLUSIONS AND IMPLICATIONS

The citrulline-atorvastatin combination prevented fat mass accumulation and maintained glucose homeostasis in DIO mice. Furthermore, it potentiated inhibition of hepatic de novo lipogenesis activity. This combination has potential for preservation of glucose homeostasis in patients receiving statin therapy.

A systems view of type 2 diabetes-associated metabolic perturbations in saliva, blood and urine at different timescales of glycaemic control

AIMS/HYPOTHESIS

Metabolomics has opened new avenues for studying metabolic alterations in type 2 diabetes. While many urine and blood metabolites have been associated individually with diabetes, a complete systems view analysis of metabolic dysregulations across multiple biofluids and over varying timescales of glycaemic control is still lacking.

METHODS

Here we report a broad metabolomics study in a clinical setting, covering 2,178 metabolite measures in saliva, blood plasma and urine from 188 individuals with diabetes and 181 controls of Arab and Asian descent. Using multivariate linear regression we identified metabolites associated with diabetes and markers of acute, short-term and long-term glycaemic control.

RESULTS

Ninety-four metabolite associations with diabetes were identified at a Bonferroni level of significance (p < 2.3 × 10(-5)), 16 of which have never been reported. Sixty-five of these diabetes-associated metabolites were associated with at least one marker of glycaemic control in the diabetes group. Using Gaussian graphical modelling, we constructed a metabolic network that links diabetes-associated metabolites from three biofluids across three different timescales of glycaemic control.

CONCLUSIONS/INTERPRETATION

Our study reveals a complex network of biochemical dysregulation involving metabolites from different pathways of diabetes pathology, and provides a reference framework for future diabetes studies with metabolic endpoints.

Asparaginase treatment side-effects may be due to genes with homopolymeric Asn codons (Review-Hypothesis)

The present treatment of childhood T-cell leukemias involves the systemic administration of prokary-otic L-asparaginase (ASNase), which depletes plasma Asparagine (Asn) and inhibits protein synthesis. The mechanism of therapeutic action of ASNase is poorly understood, as are the etiologies of the side-effects incurred by treatment. Protein expression from genes bearing Asn homopolymeric coding regions (N-hCR) may be particularly susceptible to Asn level fluctuation. In mammals, N-hCR are rare, short and conserved. In humans, misfunctions of genes encoding N-hCR are associated with a cluster of disorders that mimic ASNase therapy side-effects which include impaired glycemic control, dislipidemia, pancreatitis, compromised vascular integrity, and neurological dysfunction. This paper proposes that dysregulation of Asn homeostasis, potentially even by ASNase produced by the microbiome, may contribute to several clinically important syndromes by altering expression of N-hCR bearing genes. By altering amino acid abundance and modulating ribosome translocation rates at codon repeats, the microbiomic environment may contribute to genome decoding and to shaping the proteome. We suggest that impaired translation at poly Asn codons elevates diabetes risk and severity.

Targeted metabolomic analysis reveals the association between the postprandial change in palmitic acid, branched-chain amino acids and insulin resistance in young obese subjects

Obesity is the result of a positive energy balance and often leads to difficulties in maintaining normal postprandial metabolism. The changes in postprandial metabolites after an oral glucose tolerance test (OGTT) in young obese Chinese men are unclear. In this work, the aim is to investigate the complex metabolic alterations in obesity provoked by an OGTT using targeted metabolomics. We used gas chromatography-mass spectrometry and ultra high performance liquid chromatography-triple quadrupole mass spectrometry to analyze serum fatty acids, amino acids and biogenic amines profiles from 15 control and 15 obese subjects at 0, 30, 60, 90 and 120 min during an OGTT. Metabolite profiles from 30 obese subjects as independent samples were detected in order to validate the change of metabolites. There were the decreased levels of fatty acid, amino acids and biogenic amines after OGTT in obesity. At 120 min, percent change of 20 metabolites in obesity has statistical significance when comparing with the controls. The obese parameters was positively associated with changes in arginine and histidine (P<0.05) and the postprandial change in palmitic acid (PA), branched-chain amino acids (BCAAs) and phenylalanine between 1 and 120 min were positively associated with fasting insulin and HOMA-IR (all P<0.05) in the obese group. The postprandial metabolite of PA and BCAAs may play important role in the development and onset of insulin resistance in obesity. Our findings offer new insights in the complex physiological regulation of the metabolism during an OGTT in obesity.

Glutamate receptors in the kidney

l-Glutamate (l-Glu) plays an essential role in the central nervous system (CNS) as an excitatory neurotransmitter, and exerts its effects by acting on a large number of ionotropic and metabotropic receptors. These receptors are also expressed in several peripheral tissues, including the kidney. This review summarizes the general properties of ionotropic and metabotropic l-Glu receptors, focusing on N-methyl-d-aspartate (NMDA) and Group 1 metabotropic glutamate receptors (mGluRs). NMDA receptors are expressed in the renal cortex and medulla, and appear to play a role in the regulation of renal blood flow, glomerular filtration, proximal tubule reabsorption and urine concentration within medullary collecting ducts. Sustained activation of NMDA receptors induces Ca(2+) influx and oxidative stress, which can lead to glomerulosclerosis, for example in hyperhomocysteinemia. Group 1 mGluRs are expressed in podocytes and probably in other cell types. Mice in which these receptors are knocked out gradually develop albuminuria and glomerulosclerosis. Several endogenous agonists of l-Glu receptors, which include sulfur-containing amino acids derived from l-homocysteine, and quinolinic acid (QA), as well as the co-agonists glycine and d-serine, are present in the circulation at concentrations capable of robustly activating ionotropic and metabotropic l-Glu receptors. These endogenous agonists may also be secreted from renal parenchymal cells, or from cells that have migrated into the kidney, by exocytosis or by transporters such as system x(-)(c), or by transporters involved in ammonia secretion. l-Glu receptors may be useful targets for drug therapy, and many selective orally-active compounds exist for investigation of these receptors as potential drug targets for various kidney diseases.

Plasma amino acid profiles at various reproductive stages in female rats

We measured the plasma levels of amino acids at various reproductive stages in female rats, including the estrous cycle, pregnancy and lactation, and compared the resulting amino acid profiles using two- or three-dimensional figures. These figures revealed that the amino acid profiles of pregnant and lactating dams differed considerably from those during the estrous cycle or in male rats. The plasma levels of individual amino acids were almost the same between proestrus, estrus, metestrus and diestrus, and their profiles did not differ significantly. However, the amino acid profiles changed during pregnancy and lactation in dams. The plasma Ser level decreased significantly in mid and late pregnancy, whereas Tyr, Gly and His decreased significantly in the late and end stages of pregnancy, and Trp and Lys significantly decreased and increased at the end of pregnancy, respectively. Much larger changes in amino acid profiles were observed during lactation, when the levels of many amino acids increased significantly, and none showed a significant decrease. Plasma Pro, Ser and Gly levels increased continuously from day 1 until day 15 of lactation, whereas Asn and Met increased significantly from days 1 and 5 respectively until the end of lactation. These results suggest that the profiles of plasma amino acids show characteristic changes according to reproductive stage and that it may be necessary to consider such differences when performing amino acid-based diagnosis.

Metabolite profile deviations in an oral glucose tolerance test-a comparison between lean and obese individuals

OBJECTIVE

While impaired glucose tolerance diagnosed by the oral glucose tolerance test (OGTT) is a common trait in obese individuals, less is known about changes in levels of other metabolites. The aim was to reveal the complex alterations in metabolite levels provoked by an OGTT and its perturbation in obese individuals.

METHODS

Gas chromatography/mass spectrometry was used to profile metabolite levels in serum from 14 obese participants (body mass index [BMI] of 43.6 ± 1.5 kg m(-2) [mean ± SEM]) at 0, 30, and 120 min during a standard 2-h 75 g OGTT. Metabolite profiles from six lean individuals (BMI of 22.4 ± 2.4 kg m(-2) ), collected from a previous study, were included for comparison.

RESULTS

In the obese group, 59 metabolite profiles were determined. Among these, 16 deviated from profiles in the lean group. Deviating metabolites were categorized into three groups. Delayed reduction in levels of five fatty acids. Increased levels at 30 min of five amino acids, including isoleucine and leucine. A blunted increase at 30 min of six metabolites.

CONCLUSIONS

Metabolomics analysis revealed distinct differences in alterations of metabolite levels during an OGTT in obese and lean subjects. To this end, our data suggests a disrupted regulation of ketogenesis, lipolysis and proteolysis in obese individuals.