Altered Amino Acid Levels Research Articles

Altered amino acid levels in young hypopituitarism: impact of NAFLD and insulin resistance

Elevated concentrations of amino acids (AAs) are commonly observed in patients with nonalcoholic fatty liver disease (NAFLD). Individuals with hypopituitarism (HP) are at a heightened risk of developing NAFLD due to factors such as visceral obesity, increased insulin resistance (IR), and disturbances in lipid metabolism. However, the changes in AAs concentrations associated with HP remain poorly understood. Therefore, our study aimed to investigate whether individuals with HP, who were not receiving growth hormone replacement therapy (GHRT), exhibited altered AAs compared to controls (CTs), and whether these AAs were associated with IR, the presence of NAFLD, and the Metabolic Syndrome (MetS) score. The AAs profiles of 133 young males with HP (age: 24.5 ± 5.9; 57 with NAFLD and 76 without NAFLD) and 90 age and BMI-matched CTs were analyzed using untargeted metabolomics. The results revealed that most AAs were found to be elevated in subjects with HPs compared to CTs. Glutamate, glutamine, norleucine, and branched-chain amino acids (BCAAs) (leucine and valine) were correlated with the homeostasis model assessment of insulin resistance (HOMA-IR), with glutamate and norleucine showing independent linkage. Glutamate and proline levels were specifically associated with MetS score, while alanine and proline linked to NAFLD. Given that elevated glutamate and BCAAs levels have higher prevalence of NAFLD, we hypothesized that the changes in AAs observed in HPs may be attributed to the impact of NAFLD and IR.

Relationship Between Altered Plasma-Free Amino Acid Levels and Hyperuricemia in Dyslipidemia Without and With Hypertension.

Background: Investigating the association between plasma-free amino acids (PFAAs) and hyperuricemia (HU) in dyslipidemia (DL) and dyslipidemia with hypertension (DH) is crucial, as it could provide valuable insights into the pathophysiology of these conditions and contribute to the development of targeted prevention and management strategies. Therefore, in this study, we aimed to elucidate the associations between PFAAs and HU in individuals with DL and DH. Methods: We quantified PFAAs and uric acid levels among Japanese healthy subjects (n = 1311; HU, n = 57), subjects with DL (n = 1483; HU, n = 219), and subjects with DH (n = 1159; HU, n = 237). Results: The concentrations of most PFAAs showed significant differences between subjects without and with HU across all groups (p < 0.05 to 0.001). Adjusted logistic regression analyses revealed that certain PFAAs were consistently positively or negatively associated with HU across all groups. Specifically, in the DL group, alanine, tryptophan, and tyrosine showed significant positive associations with HU, while in the DH group, citrulline and glutamate exhibited similar positive associations (p < 0.05 to 0.001). Conversely, threonine in the healthy group (p < 0.05) and glutamine in the DL group (p < 0.05) demonstrated significant inverse associations with HU. Conclusions: This study revealed a potential close relationship between alterations in PFAA profiles and HU in dyslipidemia, without and with hypertension. The findings warrant further research to elucidate the role of altered amino acid and uric acid levels as potential disease biomarkers and therapeutic targets.

Exploring altered free amino acids and metabolites: Insights into the metabolic landscape of preeclampsia

IntroductionPreeclampsia (PE) is a complex disease that poses a risk for maternal and perinatal morbidity and mortality. This study aimed to investigate the role of maternal serum amino acids (AAs) levels in PE. Materials and methodsA total of 56 pregnant women (26 with PE and 30 controls) were included in the study. The participants had a confirmed gestational age between 24 and 37 weeks. The mean body mass index (BMI) for the PE group was 33.1 kg/m2, while the control group had a mean BMI of 29.6 kg/m2. AAs levels were quantified, and statistical analyses were performed to identify significant differences between the two groups. Receiver Operating Characteristic (ROC) curve analysis was employed the diagnostic potential of specific AAs. ResultsWe observed significantly elevated levels of multiple AAs in the PE group, including citrulline, lysine, ethanolamine, ornithine and histidine. Citrulline exhibited exceptional predictive power for PE with 100.0% sensitivity and specificity at a cutoff of 7.79 µmol/L, reflected in an area under the curve (AUC) of 1.000. DiscussionOur study highlights the crucial involvement of altered amino acid levels, specifically in the urea cycle, disruptions in lysine and ethanolamine metabolism in PE development. Exploring these changes may reveal new therapeutic targets, providing insights into the disease's molecular mechanisms. Understanding amino acid metabolism in PE not only informs therapeutic strategies but also holds the potential to revolutionize early diagnosis and intervention.

Fluid shear stress induces a shift from glycolytic to amino acid pathway in human trophoblasts

BackgroundThe human placenta, a tissue with a lifespan limited to the period of pregnancy, is exposed to varying shear rates by maternal blood perfusion depending on the stage of development. In this study, we aimed to investigate the effects of fluidic shear stress on the human trophoblast transcriptome and metabolism.ResultsBased on a trophoblast cell line cultured in a fluidic flow system, changes caused by shear stress were analyzed and compared to static conditions. RNA sequencing and bioinformatics analysis revealed an altered transcriptome and enriched gene ontology terms associated with amino acid and mitochondrial metabolism. A decreased GLUT1 expression and reduced glucose uptake, together with downregulated expression of key glycolytic rate-limiting enzymes, hexokinase 2 and phosphofructokinase 1 was observed. Altered mitochondrial ATP levels and mass spectrometry data, suggested a shift in energy production from glycolysis towards mitochondrial oxidative phosphorylation. This shift in energy production could be supported by increased expression of glutamic-oxaloacetic transaminase variants in response to shear stress as well as under low glucose availability or after silencing of GLUT1. The shift towards amino acid metabolic pathways could be supported by significantly altered amino acid levels, like glutamic acid, cysteine and serine. Downregulation of GLUT1 and glycolytic rate-limiting enzymes, with concomitant upregulation of glutamic-oxaloacetic transaminase 2 was confirmed in first trimester placental explants cultured under fluidic flow. In contrast, high fluid shear stress decreased glutamic-oxaloacetic transaminase 2 expression in term placental explants when compared to low flow rates. Placental tissue from pregnancies with intrauterine growth restriction are exposed to high shear rates and showed also decreased glutamic-oxaloacetic transaminase 2, while GLUT1 was unchanged and glycolytic rate-limiting enzymes showed a trend to be upregulated. The results were generated by using qPCR, immunoblots, quantification of immunofluorescent pictures, padlock probe hybridization, mass spectrometry and FRET-based measurement.ConclusionOur study suggests that onset of uteroplacental blood flow is accompanied by a shift from a predominant glycolytic- to an alternative amino acid converting metabolism in the villous trophoblast. Rheological changes with excessive fluidic shear stress at the placental surface, may disrupt this alternative amino acid pathway in the syncytiotrophoblast and could contribute to intrauterine growth restriction.

Dysregulation of Amino Acid Transporters in a Rat Model of TLR7-Mediated Maternal Immune Activation.

Maternal immune activation (MIA) during pregnancy is linked to neurodevelopmental disorders in humans. Similarly, the TLR7 agonist imiquimod alters neurodevelopment in rodents. While the mechanisms underlying MIA-mediated neurodevelopmental changes are unknown, they could involve dysregulation of amino acid transporters essential for neurodevelopment. Therefore, we sought to determine the nature of such transporter changes in both imiquimod-treated rats and human placentas during infection. Pregnant rats received imiquimod on gestational day (GD)14. Transporter expression was measured in placentas and fetal brains via qPCR (GD14.5) and immunoblotting (GD16). To monitor function, fetal brain amino acid levels were measured by HPLC on GD16. Gene expression in the cortex of female fetal brains was further examined by RNAseq on GD19. In human placentas, suspected active infection was associated with decreased ASCT1 and SNAT2 protein expression. Similarly, in imiquimod-treated rats, ASCT1 and SNAT2 protein was also decreased in male placentas, while EAAT2 was decreased in female placentas. CAT3 was increased in female fetal brains. Consistent with this, imiquimod altered amino acid levels in fetal brains, while RNAseq demonstrated changes in expression of several genes implicated in autism. Thus, imiquimod alters amino acid transporter levels in pregnant rats, and similar changes occur in human placentas during active infection. This suggests that changes in expression of amino acid transporters may contribute to effects mediated by MIA toward altered neurodevelopment.

Vitamin B12 deficiency induces glucose intolerance, delays peak insulin levels and promotes ketogenesis in female rats.

Vitamin B12 (B12) deficiency is common among individuals with diabetes mellitus, but it is unknown if B12 deficiency contributes to impaired glucose homeostasis in this disorder. Female Sprague-Dawley rats were assigned to a control or B12-deficient diet for 4 weeks. Intraperitoneal glucose tolerance tests were performed after 25 days, and blood and liver samples were collected for metabolic profiling. B12 deficiency resulted in a prediabetic-like phenotype characterised by glucose intolerance, a delayed peak in plasma insulin levels following a glucose challenge and increased ketogenesis. We attributed increased ketogenesis to reduced liver anaplerosis, which limited the availability of the TCA cycle intermediates citrate, succinate and succinyl-CoA. This was associated with increased Mut mRNA levels and citrate synthase activity in the liver. One-carbon metabolite levels were altered in plasma and the liver, which was linked to reduced methylation capacity, altered amino acid levels and elevated Slc7a5 mRNA expression. Plasma folate and biotin levels were reduced, as were the majority of B vitamins in the liver. Changes in these B12-dependent processes and reduced B vitamin amounts likely contributed to deficits in glucose handling. Our findings highlight that B12 deficiency may promote the development of metabolic disorders like diabetes mellitus and emphasise the importance of adequate B12 intake for metabolic health.

Role of the gut-microbiota-metabolite axis in the rotenone model of early-stage Parkinson's Disease.

Gastrointestinal symptoms are common in the early-stage Parkinson's disease (PD), but its potential pathogenesis remains unclear. Therefore, in the present study, we used the 16S ribosomal RNA gene sequencing and gas chromatography coupled with mass spectrometry-based metabolomics to investigate the alterations of gut microbiome and serum amino acid levels in the early-stage PD mice model induced with rotenone. The results demonstrated that the microbial taxa at phylum, family and genus levels remarkably altered in rotenone-induced mice relative to vehicle-induced mice. The rotenone-induced mice had higher relative abundance of Flavobacteriaceae, Staphylococcaceae, and Prevotellaceae as well as lower relative abundance of Lachnospiraceae_UCG-001, Ruminiclostridium, and Prevotellaceae_NK3B31_group than vehicle-induced mice. The evaluation of serum amino acids revealed the alterations in several classes of amino acids, including L-proline, L-alanine, L-serine, L-asparagine, L-threonine, L-glutamine, L-methionine, and L-4-hydroxyproline. Notably, the altered serum amino acid levels were significantly associated with the abundance of gut microbiota, especially Ruminococcaceae and Ruminiclostridium. Our study explored the possible role of the gut-microbiota-metabolite axis in the early-stage PD and provided the possibility of prevention and treatment of PD by gut-microbiota-metabolite axis in the future.

Infection During Pregnancy Downregulates the Expression of Amino Acid Transporters in Rat and Human Placentas

Maternal immune activation (MIA) resulting from infection during pregnancy increases the chance of offspring having a neurodevelopmental disorder such as autism or schizophrenia. However, the mechanism underlying this association is unknown. Placental transport of amino acids from maternal to fetal circulation is essential for proper fetal neurodevelopment. We hypothesized that MIA could alter the expression of placental amino acid transporters, thereby altering fetal exposure to the amino acids required for proper brain development. Thus, the objective of this study was to examine whether MIA impacts the expression of amino acid transporters in the placentas of rats and humans. MIA was induced in pregnant rats through the administration of the viral mimetic poly(I:C) on gestational day 14. Placental and fetal tissues were collected 24 and 48 hours later. Human placentas isolated at term from pregnancies complicated with either chorioamnionitis (n = 17) or an unidentified active infection causing flu‐like symptoms (n = 6) were compared to healthy gestational age‐matched controls (n = 18). Protein expression of amino acid transporters in rat or human placentas, as well as fetal rat brains, was determined using immunoblotting. Levels of free amino acids in fetal rat brains were also quantified using reverse‐phase HPLC. In rats, poly(I:C) significantly downregulated the amino acid transporters ASCT1 and EAAT2 in the placenta, with a trend towards decreased SNAT2. SNAT5, EAAT1, and GLYT1 were also significantly reduced in fetal brains from poly(I:C)‐treated dams. Furthermore, the levels of multiple amino acids were significantly altered in fetal brains of poly(I:C)‐treated rats. In human placentas, ASCT1 was significantly downregulated in active infection cases, but not in chorioamnionitis cases. A pronounced trend of decreased SNAT2 expression was also seen in active infection cases, but this did not reach significance. To conclude, MIA decreases the expression of amino acid transporters in the placentas of rats and is associated with altered levels of free amino acids in fetal rat brains. Moreover, decreased expression of amino acid transporters is also seen in human placentas obtained from pregnancies with active infection. As amino acids are required for proper neurodevelopment, these changes in transport could provide a link between MIA and neurodevelopmental disorders.

Metabolomics research on the effect of dexamethasone‐induced chronic stress in serum of rabbits

Stress is a common factor that reduces production performance. However, the physiology of stress is not fully understood. In this study, 40-day-old rabbits were injected 1.0 mg/kg BW Dexamethasone to induce stress. A metabolomic study on serum of stress-induced rabbits was performed to research the metabolism mechanism of stress by using ultra-performance liquid chromatography coupled to mass spectrometry (UPLC–MS). Clear separations between stress rabbits and control rabbits were observed by principal component analysis (PCA) based on the data obtained using both analytical techniques and 90 significantly changed metabolites were identified as potential biomarkers of stress. Stress rabbits were characterised by altered levels of serum lysophosphatidylcholines, amino acids, phosphatidyl choline, and nucleosides, which were related to multiple perturbed metabolic pathways and contributed to the elucidation of the complex mechanism of stress. These were main linked to three different pathways: pyrimidine metabolism, aminoacyl-tRNA biosynthesis, and biosynthesis of amino acid. In summary, we provided a comprehensive understanding of metabolic alterations in the main stress-targeted tissues, helping to understand the potential mechanisms underlying stress. HIGHLIGHTS Stress alters the metabolic composition of serum in rabbits. In rabbits, dexamethasone‐induced chronic stress alters 90 metabolites in serum.

Phosphoproteomics of the developing heart identifies PERM1 - An outer mitochondrial membrane protein

Heart development relies on PTMs that control cardiomyocyte proliferation, differentiation and cardiac morphogenesis. We generated a map of phosphorylation sites during the early stages of cardiac postnatal development in mice; we quantified over 10,000 phosphorylation sites and 5000 proteins that were assigned to different pathways. Analysis of mitochondrial proteins led to the identification of PGC-1- and ERR-induced regulator in muscle 1 (PERM1), which is specifically expressed in skeletal muscle and heart tissue and associates with the outer mitochondrial membrane. We demonstrate PERM1 is subject to rapid changes mediated by the UPS through phosphorylation of its PEST motif by casein kinase 2. Ablation of Perm1 in mice results in reduced protein expression of lipin-1 accompanied by accumulation of specific phospholipid species. Isolation of Perm1-deficient mitochondria revealed significant downregulation of mitochondrial transport proteins for amino acids and carnitines, including SLC25A12/13/29/34 and CPT2. Consistently, we observed altered levels of various lipid species, amino acids, and acylcarnitines in Perm1−/− mitochondria. We conclude that the outer mitochondrial membrane protein PERM1 regulates homeostasis of lipid and amino acid metabolites in mitochondria.

Pollen Alters Amino Acid Levels in the Honey Bee Brain and This Relationship Changes With Age and Parasitic Stress.

Pollen nutrition is necessary for proper growth and development of adult honey bees. Yet, it is unclear how pollen affects the honey bee brain and behavior. We investigated whether pollen affects amino acids in the brains of caged, nurse-aged bees, and what the behavioral consequences might be. We also tested whether parasitic stress altered this relationship by analyzing bees infected with prevalent stressor, Nosema ceranae. Levels of 18 amino acids in individual honey bee brains were measured using Gas Chromatography – Mass Spectrometry at two different ages (Day 7 and Day 11). We then employed the proboscis extension reflex to test odor learning and memory. We found that the honey bee brain was highly responsive to pollen. Many amino acids in the brain were elevated and were present at higher concentration with age. The majority of these amino acids were non-essential. Without pollen, levels of amino acids remained consistent, or declined. Nosema-infected bees showed a different profile. Infection altered amino acid levels in a pollen-dependent manner. The majority of amino acids were lower when pollen was given, but higher when pollen was deprived. Odor learning and memory was not affected by feeding pollen to uninfected bees; but pollen did improve performance in Nosema-infected bees. These results suggest that pollen in early adulthood continues to shape amino acid levels in the brain with age, which may affect neural circuitry and behavior over time. Parasitic stress by N. ceranae modifies this relationship revealing an interaction between infection, pollen nutrition, and behavior.

Relationship of reduced glomerular filtration rate with alterations in plasma free amino acids and uric acid evaluated in healthy control and hypertensive subjects

The potential association between altered levels of plasma free amino acids (PFAAs) and uric acid (UA) with estimated glomerular filtration rate (eGFR) remains unknown among patients with hypertension. A total of 2804 healthy controls and 2455 hypertensive patients were included in the current analysis. eGFR was defined as reduced when it was <60 ml/min/1.73 m2. The associations between reduced eGFR and individual PFAAs and UA in the healthy control and hypertension groups were explored by logistic regression analyses adjusted for potential confounding variables. Results show that UA had a significant positive association with reduced eGFR in both healthy control and hypertension groups (P < 0.001). Among the PFAAs, citrulline, glycine and phenylalanine showed significant positive associations with reduced eGFR in both healthy control (P < 0.01 to 0.001) and hypertension (P < 0.001) groups. Moreover, alanine, asparagine and methionine achieved significant positive associations with reduced eGFR only in the hypertension group (P < 0.01 to 0.001). Conversely, serine showed significant inverse associations with reduced eGFR in the hypertension group only (P < 0.001). Our findings provide first evidence for a strong relationship between distinct patterns of PFAAs and elevated UA with reduced eGFR in hypertension. The findings may appear useful in developing effective strategies for the prevention or early detection and treatment of declined kidney function in hypertension.

Plant Primary Metabolism Regulated by Nitrogen Contributes to Plant-Pathogen Interactions.

Nitrogen contributes to plant defense responses by the regulation of plant primary metabolism during plant-pathogen interactions. Based on biochemical, physiological, bioinformatic and transcriptome approaches, we investigated how different nitrogen forms (ammonium vs. nitrate) regulate the physiological response of cucumber (Cucumis sativus) to Fusarium oxysporum f. sp. cucumerinum (FOC) infection. The metabolic profile revealed that nitrate-grown plants accumulated more organic acids, while ammonium-grown plants accumulated more amino acids; FOC infection significantly increased levels of both amino acids and organic acids in the roots of ammonium-grown plants. Transcriptome analysis showed that genes related to carbon metabolism were mostly up-regulated in plants grown with nitrate, whereas in ammonium-grown plants the up-regulated genes were mostly those that were related to primary nitrogen metabolism. Root FOC colonization and disease incidence were positively correlated with levels of root amino acids and negatively correlated with levels of root organic acids. In conclusion, organic acid metabolism and expression of related genes increased under nitrate, whereas ammonium increased the level of amino acids and expression of related genes; these altered levels of organic acids and amino acids resulted in different tolerances to FOC infection depending on the nitrogen forms supplied.

Celastrol Suppresses Tryptophan Catabolism in Human Colon Cancer Cells as Revealed by Metabolic Profiling and Targeted Metabolite Analysis.

Celastrol is well known for its anti-cancer effects, yet its specific mechanisms against colon cancer are still not fully elucidated. In this study, cytotoxic effect of celastrol against HCT116 colon cancer cells was investigated based on cell viability assay and flow cytometry assay, and the possible mechanism was explored using a strategy combining metabolic profiling and targeted metabolite analysis based on ultra performance liquid chromatography (UPLC)/MS. Celastrol was found to inhibit the growth of colon cancer cells and induce apoptosis. Metabolomics analysis revealed characteristic changes in metabolic profiles of the colon cancer cells, revealing altered levels of amino acids, carnitine, and lipid markers. Most interestingly, with the assistance of targeted metabolite analysis, tryptophan (Trp) level was significantly increased whereas kynurenine (Kyn) level was decreased in colon cancer cells after celastrol treatment, together with markedly declined Kyn/Trp ratios. Western blot analysis revealed that expression of indoleamine 2,3-dioxygenase (IDO), the enzyme catalyzing Trp to generate Kyn, was dramatically inhibited in colon cancer cells after celastrol treatment, with a dose-dependent manner. These results suggest that suppression of IDO expression and tryptophan catabolism may be part of the mechanisms of celastrol in its cytotoxic effect against HCT116 colon cancer cells. This study provided scientific basis for further development of celastrol on treating colon cancer.

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

BackgroundWe 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.ObjectiveThe aim of this study was to investigate if plasma amino acid levels differed among children with celiac disease compared with disease controls.Materials and methodsFasting 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.ResultsSeven 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).ConclusionThese findings support the idea that amino acids could influence systemic inflammation and play a possible role in disease pathogenesis.

Long-Term Stability of Human Plasma Metabolites during Storage at −80 °C

Prolonged storage of biospecimen can lead to artificially altered metabolite concentrations and thus bias data analysis in metabolomics experiments. To elucidate the potential impact of long-term storage on the metabolite profile, a pooled human plasma sample was aliquoted and stored at -80 °C. During a time period of five years, 1012 of the aliquots were measured with the Biocrates AbsoluteIDQ p180 targeted-metabolomics assay at 193 time points. Modeling the concentration courses over time revealed that 55 out of 111 metabolites remained stable. The statistically significantly changed metabolites showed on average an increase or decrease of +13.7% or -14.5%, respectively. In detail, increased concentration levels were observed for amino acids (mean: + 15.4%), the sum of hexoses (+7.9%), butyrylcarnitine (+9.4%), and some phospholipids mostly with chain lengths exceeding 40 carbon atoms (mean: +18.0%). Lipids tended to exhibit decreased concentration levels with the following mean concentration changes: acylcarnitines, -12.1%; lysophosphatidylcholines, -15.1%; diacyl-phosphatidylcholines, -17.0%; acyl-alkyl-phosphatidylcholines, -13.3%; sphingomyelins, -14.8%. We conclude that storage of plasma samples at -80 °C for up to five years can lead to altered concentration levels of amino acids, acylcarnitines, glycerophospholipids, sphingomyelins, and the sum of hexoses. These alterations must be considered when analyzing metabolomics data from long-term epidemiological studies.

Loss of function mutation of the Slc38a3 glutamine transporter reveals its critical role for amino acid metabolism in the liver, brain, and kidney.

Glutamine, the most abundant amino acid in mammals, is critical for cell and organ functions. Its metabolism depends on the ability of cells to take up or release glutamine by transporters located in the plasma membrane. Several solute carrier (SLC) families transport glutamine, but the SLC38 family has been thought to be mostly responsible for glutamine transport. We demonstrate that despite the large number of glutamine transporters, the loss of Snat3/Slc38a3 glutamine transporter has a major impact on the function of organs expressing it. Snat3 mutant mice were generated by N-ethyl-N-nitrosurea (ENU) mutagenesis and showed stunted growth, altered amino acid levels, hypoglycemia, and died around 20 days after birth. Hepatic concentrations of glutamine, glutamate, leucine, phenylalanine, and tryptophan were highly reduced paralleled by downregulation of the mTOR pathway possibly linking reduced amino acid availability to impaired growth and glucose homeostasis. Snat3-deficient mice had altered urea levels paralleled by dysregulation of the urea cycle, gluconeogenesis, and glutamine synthesis. Mice were ataxic with higher glutamine but reduced glutamate and gamma-aminobutyric acid (GABA) levels in brain consistent with a major role of Snat3 in the glutamine-glutamate cycle. Renal ammonium excretion was lower, and the expression of enzymes and amino acid transporters involved in ammoniagenesis were altered. Thus, SNAT3 is a glutamine transporter required for amino acid homeostasis and determines critical functions in various organs. Despite the large number of glutamine transporters, loss of Snat3 cannot be compensated, suggesting that this transporter is a major route of glutamine transport in the liver, brain, and kidney.

Integration of Genome-Wide SNP Data and Gene-Expression Profiles Reveals Six Novel Loci and Regulatory Mechanisms for Amino Acids and Acylcarnitines in Whole Blood.

Profiling amino acids and acylcarnitines in whole blood spots is a powerful tool in the laboratory diagnosis of several inborn errors of metabolism. Emerging data suggests that altered blood levels of amino acids and acylcarnitines are also associated with common metabolic diseases in adults. Thus, the identification of common genetic determinants for blood metabolites might shed light on pathways contributing to human physiology and common diseases. We applied a targeted mass-spectrometry-based method to analyze whole blood concentrations of 96 amino acids, acylcarnitines and pathway associated metabolite ratios in a Central European cohort of 2,107 adults and performed genome-wide association (GWA) to identify genetic modifiers of metabolite concentrations. We discovered and replicated six novel loci associated with blood levels of total acylcarnitine, arginine (both on chromosome 6; rs12210538, rs17657775), propionylcarnitine (chromosome 10; rs12779637), 2-hydroxyisovalerylcarnitine (chromosome 21; rs1571700), stearoylcarnitine (chromosome 1; rs3811444), and aspartic acid traits (chromosome 8; rs750472). Based on an integrative analysis of expression quantitative trait loci in blood mononuclear cells and correlations between gene expressions and metabolite levels, we provide evidence for putative causative genes: SLC22A16 for total acylcarnitines, ARG1 for arginine, HLCS for 2-hydroxyisovalerylcarnitine, JAM3 for stearoylcarnitine via a trans-effect at chromosome 1, and PPP1R16A for aspartic acid traits. Further, we report replication and provide additional functional evidence for ten loci that have previously been published for metabolites measured in plasma, serum or urine.In conclusion, our integrative analysis of SNP, gene-expression and metabolite data points to novel genetic factors that may be involved in the regulation of human metabolism. At several loci, we provide evidence for metabolite regulation via gene-expression and observed overlaps with GWAS loci for common diseases. These results form a strong rationale for subsequent functional and disease-related studies.

Quantifying Diet-Induced Metabolic Changes of the Human Gut Microbiome

The human gut microbiome is known to be associated with various human disorders, but a major challenge is to go beyond association studies and elucidate causalities. Mathematical modeling of the human gut microbiome at a genome scale is a useful tool to decipher microbe-microbe, diet-microbe and microbe-host interactions. Here, we describe the CASINO (Community And Systems-level INteractive Optimization) toolbox, a comprehensive computational platform for analysis of microbial communities through metabolic modeling. We first validated the toolbox by simulating and testing the performance of single bacteria and whole communities in vitro. Focusing on metabolic interactions between the diet, gut microbiota, and host metabolism, we demonstrated the predictive power of the toolbox in a diet-intervention study of 45 obese and overweight individuals and validated our predictions by fecal and blood metabolomics data. Thus, modeling could quantitatively describe altered fecal and serum amino acid levels in response to diet intervention.

An Assay of Selected Serum Amino Acids in Patients with Type 2 Diabetes Mellitus.

Amino acids are the building blocks of proteins. In case of insulin resistance, which is typical for type 2 diabetes mellitus (T2DM), proteolysis is increased and protein synthesis is decreased; therefore, we can observe changes in the levels of amino acids in diabetics vs. non-diabetics. The aim of this study was to find differences in the levels of selected amino acids between patients with diabetes (type 2) and a control group. Amino acids were derivatized with naphthalene-2,3-dicarboxaldehyde in the presence of potassium cyanide to form fluorescent 1-cyanobenz(f)isoindole product. Amino acids derivatives were measured using a high-performance liquid chromatography with fluorescence detection. The serum levels of glucose were determined using an automatic biochemistry analyzer, glycated hemoglobin HbA1c was measured by cation exchange chromatography. A total of 19 serum amino acids in T2DM patients and non-diabetics were measured. There were 9 amino acids, which were significantly different in these groups (p<0.05). Significantly decreased levels of arginine, asparagine, glycine, serine, threonine and significantly increased levels of alanine, isoleucine, leucine, valine in diabetics were found. Significant difference in metabolism of amino acids between diabetics and non-diabetics were observed. The altered levels of amino acids in diabetic patients could be a suitable predictor of diabetes.