Amino Acid Signatures to Evaluate the Beneficial Effects of Weight Loss

Assessment of causal associations among gut microbiota, metabolites, and celiac disease: a bidirectional Mendelian randomization study

Background

A growing number of studies have implicated that gut microbial abundance and metabolite concentration alterations are associated with celiac disease (CD). However, the causal relationship underlying these associations is unclear. Here, we used Mendelian randomization (MR) to reveal the causal effect of gut microbiota and metabolites on CD.

Methods

Genome-wide association study (GWAS) summary-level data for gut microbiota, metabolites, and CD were extracted from published GWASs. Causal bacterial taxa and metabolites for CD were determined by two-sample MR analyses. The robustness of the results was assessed with sensitivity analyses. Finally, reverse causality was investigated with a reverse MR analysis.

Results

Genetically, increased genus Bifidobacterium was potentially associated with higher CD risk (odds ratio [OR] = 1.447, 95% confidence interval [CI]: 1.054-1.988, p = 0.022) while phylum Lentisphaerae (OR = 0.798, 95% CI: 0.648-0.983, p = 0.034) and genus Coprobacter (OR = 0.683, 95% CI: 0.531-0.880, p = 0.003) were related to lower CD risk. Moreover, there were suggestive associations between CD and the following seven metabolites: 1-oleoylglycerophosphoethanolamine, 1-palmitoylglycerophosphoethanolamine, 1,6-anhydroglucose, phenylacetylglutamine, tryptophan betaine, 10-undecenoate, and tyrosine. Sensitivity analyses deemed the results reliable without pleiotropy.

Conclusion

We investigated the causal relationships between gut microbiota, metabolites, and CD with two-sample MR. Our findings suggest several novel potential therapeutic targets for CD treatment. Further understanding of the underlying mechanism may provide insights into CD pathogenesis.

Methionine and total homocysteine in hypertensive patients with renal excretory dysfunction

The role of the kidneys in the metabolism and homeostasis of sulfur-containing amino acids is great, so the levels of methionine (Met), total homocysteine (tHcy) and their ratios can be of diagnostic value in chronic kidney disease (CKD), in a course of the arterial hypertension (AH). The aim of the study was to evaluate the Met/tHcy ratio in hypertensive patients with CKD. We used blood plasma of 76 patients aged 40-75 years with AH and the excretory dysfunction of the kidneys; subgroups: 1 - with proteinuria (n=37); 2 - without proteinuria with glomerular filtration rate (GFR) < 90 ml/min/1.73 m2 (n=39) and comparison group 3 - patients with AH without renal excretory dysfunction (n=28). Significantly lower Met levels were in subgroup 1. THcy levels were higher in subgroups 1 and 2 than in group 3. The Met/tHcy ratio revealed differences in subgroups 1 and 2 vs group 3. No differences were found in Arg and Lys levels. Positive correlations of the Met/tHcy ratio with the number of erythrocytes, but not with the level of hemoglobin, were revealed. In the ROC analysis, the cut-off points for the Met/tHcy ratio compared to group 3 were 3.08 for subgroup 1 and 3.36 for subgroup 2. With the progression of CKD, there is an increase in the levels of tHcy in the blood, and a decrease in the content of Met. A decrease in GFR, especially in a case with proteinuria, is accompanied by a decrease in the level of Met. The Met/tHcy ratio above 3.36 can be considered as the minimum of the balance between these sulfur-containing amino acids contents in a blood necessary for hypertensive patients with CKD.

Benefits of weight loss of 10% or more in patients with overweight or obesity: A review

OBJECTIVE

Modest weight loss (5%-10%) is clinically meaningful in patients with overweight or obesity. However, greater weight loss may be required to achieve improvements in or remission of certain weight-related complications. Therefore, this study reviewed the effect of large weight loss (≥10%). Most studies reporting large weight loss and relevant outcomes used bariatric surgery or lifestyle modifications.

RESULTS

Benefits of large weight loss were observed in patients with various overweight- or obesity-related complications, including improvements in comorbidities such as type 2 diabetes and hypertension. Improvements in glucose metabolism and cardiovascular risk factors were observed in patients who achieved large weight loss through lifestyle interventions or pharmacotherapy (phentermine/topiramate 15/92 mg once daily or subcutaneous semaglutide 2.4 mg once weekly). Other benefits associated with large weight loss included reduced cancer risk and improvements in knee osteoarthritis, sleep apnea, fertility-related end points, and health-related quality of life. While costly, bariatric surgery is currently the most cost-effective intervention, although most weight-management programs are deemed cost-effective.

CONCLUSIONS

Overall, large weight loss has a major beneficial impact on overweight- and obesity-related complications. Large weight loss should be the main treatment target when modest weight loss has had insufficient effects on obesity-related complications and for patients with severe obesity.

Does a Higher Protein Diet Promote Satiety and Weight Loss Independent of Carbohydrate Content? An 8-Week Low-Energy Diet (LED) Intervention

Both higher protein (HP) and lower carbohydrate (LC) diets may promote satiety and enhance body weight (BW) loss. This study investigated whether HP can promote these outcomes independent of carbohydrate (CHO) content. 121 women with obesity (BW: 95.1 ± 13.0 kg, BMI: 35.4 ± 3.9 kg/m2) were randomised to either HP (1.2 g/kg BW) or normal protein (NP, 0.8 g/kg BW) diets, in combination with either LC (28 en%) or normal CHO (NC, 40 en%) diets. A low-energy diet partial diet replacement (LEDpdr) regime was used for 8 weeks, where participants consumed fixed-energy meal replacements plus one ad libitum meal daily. Four-day dietary records showed that daily energy intake (EI) was similar between groups (p = 0.744), but the difference in protein and CHO between groups was lower than expected. Following multiple imputation (completion rate 77%), decrease in mean BW, fat mass (FM) and fat-free mass (FFM) at Week 8 in all was 7.5 ± 0.7 kg (p < 0.001), 5.7 ± 0.5 kg (p < 0.001), and 1.4 ± 0.7 kg (p = 0.054) respectively, but with no significant difference between diet groups. LC (CHO×Week, p < 0.05), but not HP, significantly promoted postprandial satiety during a preload challenge. Improvements in blood biomarkers were unrelated to LEDpdr macronutrient composition. In conclusion, HP did not promote satiety and BW loss compared to NP LEDpdr, irrespective of CHO content.

Metabotyping for Precision Nutrition and Weight Management: Hype or Hope?

PURPOSE OF REVIEW

Precision nutrition requires a solid understanding of the factors that determine individual responses to dietary treatment. We review the current state of knowledge in identifying human metabotypes - based on circulating biomarkers - that can predict weight loss or other relevant physiological outcomes in response to diet treatment.

RECENT FINDINGS

Not many studies have been conducted in this area and the ones identified here are heterogeneous in design and methodology, and therefore difficult to synthesize and draw conclusions. The basis of the creation of metabotypes varies widely, from using thresholds for a single metabolite to using complex algorithms to generate multi-component constructs that include metabolite and genetic information. Furthermore, available studies are a mix of hypothesis-driven and hypothesis-generating studies, and most of them lack experimental testing in human trials. Although this field of research is still in its infancy, precision-based dietary intervention strategies focusing on the metabotype group level hold promise for designing more effective dietary treatments for obesity.

Precision Medicine and Obesity

Obesity is a chronic, relapsing, and multifactorial disease, with a rising prevalence and an associated high economic burden. Achieving successful and sustained weight loss outcomes with current interventions is challenging. This is due, at least in part, to the disease's heterogenous pathophysiology that is yet to be completely understood. Technological advances and greater capabilities for the extraction and storage of information have facilitated the application of precision medicine. Several precision medicine initiatives have been proposed to improve obesity outcomes. Most of these initiatives are based on -omics technologies. Although the data generated from these technologies have led to developing hypotheses that may explain the underpinnings of obesity, their applicability to the clinical practice is yet to be determined. There are other initiatives that have identified quantitative or qualitative physiologic traits that can be targeted and that could have a more immediate clinical impact. This review aims to provide a perspective of current initiatives for precision medicine for obesity.

Circulating amino acids as fingerprints of visceral adipose tissue independent of insulin resistance: a targeted metabolomic research in women

Introduction: Although obesity and its biomarkers have been intensively studied, little is known about the metabolomic signature of visceral adiposity independent of insulin resistance that frequently accompanies increased levels of visceral fat. Our study aimed to investigate specific changes in amino acid (AA) levels as biomarkers of increased visceral adiposity independent of insulin resistance, in healthy subjects.

Methods: Forty-two adult women were included in this cross-sectional study. Serum samples were analyzed by AAs targeted metabolomics according to their visceral fat area (<100 cm2 and ≥100 cm2).

Results: By corrected t-test and supervised partial least-squares discriminant analysis (PLS-DA) we identified 4 AAs that were significantly higher in the group with higher visceral fat: proline (variable importance in the projection [VIP] predicted value: 1.97), tyrosine (VIP: 2.21), cysteine (VIP: 1.19), isoleucine (VIP: 1.04; p-values <0.05). Also, glycine was significantly lower in the group with higher visceral fat (VIP: 1.65; p-value <0.05). All AAs identified were associated with visceral fat independent of homeo-static model assessment for insulin resistance (p-value for regression coefficients <0.05).

Conclusion: Metabolic pathways that might be disrupted in persons with increased visceral fat are phenylalanine, tyrosine, and tryptophan biosynthesis; tyrosine metabolism; glycine, serine, and threonine metabolism; glyoxylate and dicarboxylate metabolism, and cysteine and methionine metabolism.

Plasma Amino Acids and Residual Hypertriglyceridemia in Diabetic Patients Under Statins: Two Independent Cross-Sectional Hospital-Based Cohorts

Objective: The objective of the study was to investigate the relationship of amino acid metabolism with hypertriglyceridemia in diabetic patients under statins free of prior cardiovascular diseases.

Methods: Two independent cross-sectional hospital based cohorts, i.e., Liaoning Medical University First Affiliated Hospital (LMUFAH, n = 146) and the Second Affiliated Hospital of Dalian Medical University (SAHDMU, n = 294) were included in the current analysis. Hypertriglyceridemia was defined as triglyceride ≥1.7 mmol/L, and well-controlled LDL-C was defined as <2.6 mmol/L. The adjusted ORs (95% CI) of circulating metabolic measures for hypertriglyceridemia were assessed using logistic regression. Pooled results of metabolites with the same direction of association in both cohorts were combined using inverse variance-weighted fixed-effect meta-analysis. Difference of identified metabolites in patients with and without hypertriglyceridemia were also obtained in the context of LDL-C.

Results: Patients, 86 and 106, were with hypertriglyceridemia in LMUFAH and SAHDMU, respectively. We observed that elevated alanine, asparagine, leucine, and valine were consistently associated with increased hypertriglyceridemia in both cohorts. In fixed-effect pooled analysis, the OR (95% CI) per SD increase was 1.71 (1.32–2.20) for alanine, 1.62 (1.20–2.19) for asparagine, 1.64 (1.22–2.20) for leucine, and 1.62 (1.22–2.13) for valine (all P values ranged from 0.0018 to <0.0001); adjusting for C-peptide attenuated effect sizes of Ala, Leu, and Val for hypertriglyceridemia. The difference were robust in groups with well- or bad-controlled LDL-C.

Conclusion: Among 23 amino acids, alanine, asparagine, leucine, and valine were positively associated with increased residual risk of hypertriglyceridemia in diabetic patients with statin treatment.

Precision Medicine and Obesity

The highly variable response to obesity therapies justifies the search for treatment strategies that are best suited to individual patients to enhance their effectiveness and tolerability via precision medicine. Precision medicine development in recent years has been driven by the emergence of powerful methods to characterize patients ("omic" assays). Current available information has revealed that there are numerous intermediary processes that contribute to obesity and have provided a framework for partially comprehending the mechanisms behind the heterogeneity of obesity and its clinical consequences. Some of these processes have or are currently being targeted to individualize obesity therapy with some success.

Population epidemiology and concordance for plasma amino acids and precursors in 11-12-year-old children and their parents

Amino acid (AA) concentrations are influenced by both exogenous (e.g. diet, lifestyle) and endogenous factors (e.g. genetic, transcriptomic, epigenetic, and metabolomic). Fasting plasma AA profiles in adulthood are predictive of diabetes risk over periods of up to 12 years. Data on AA profiles in cross-generational cohorts, including individuals from shared gene-environment settings are scarce, but would allow the identification of the contribution of heritable and environmental factors characterising the levels of circulating AAs. This study aimed to investigate parent–child (familial dyad) concordance, absolute differences between generations- (children versus adults), age- (in adults: 28–71 years), and sex-dependent differences in plasma AA concentrations. Plasma AA concentrations were measured by UHPLC/MS–MS in 1166 children [mean (SD) age 11 (0.5) years, 51% female] and 1324 of their parents [44 (5.1) years, 87% female]. AA concentrations were variably concordant between parents and their children (5–41% of variability explained). Most AA concentrations were higher in adults than children, except for the non-essential AAs arginine, aspartic acid, glutamine, hydroxy-proline, proline, and serine. Male adults and children typically had higher AA concentrations than females. The exceptions were alanine, glutamine, glycine, hydroxy-proline, serine, and threonine in girls; and glycine and serine in women. Age, sex, and shared familial factors are important determinants of plasma AA concentrations.

Integrated omics analysis reveals the alteration of gut microbe-metabolites in obese adults

Obesity, a risk to health, is a global problem in modern society. The prevalence of obesity was approximately 13% among world's adult population. Recently, several reports suggested that the interference of gut microbiota composition and function is associated with metabolic disorders, including obesity. Gut microbiota produce a board range of metabolites involved in energy and glucose homeostasis, leading to the alteration in host metabolism. However, systematic evaluation of the relationship between gut microbiota, gut metabolite and host metabolite profiles in obese adults is still lacking. In this study, we used comparative metagenomics and metabolomics analysis to determine the gut microbiota and gut-host metabolite profiles in six normal and obese adults of Chinese origin, respectively. Following the functional and pathway analysis, we aimed to understand the possible impact of gut microbiota on the host metabolites via the change in gut metabolites. The result showed that the change in gut microbiota may result in the modulation of gut metabolites contributing to glycolysis, tricarboxylic acid cycle and homolactic fermentation. Furthermore, integrated metabolomic analysis demonstrated a possible positive correlation of dysregulated metabolites in the gut and host, including l-phenylalanine, l-tyrosine, uric acid, kynurenic acid, cholesterol sulfate and glucosamine, which were reported to contribute to metabolic disorders such as obesity and diabetes. The findings of this study provide the possible association between gut microbiota-metabolites and host metabolism in obese adults. The identified metabolite changes could serve as biomarkers for the evaluation of obesity and metabolic disorders.

Association of Circulating Metabolites With Risk of Coronary Heart Disease in a European Population: Results From the Biomarkers for Cardiovascular Risk Assessment in Europe (BiomarCaRE) Consortium

Importance

Risk stratification for coronary heart disease (CHD) remains challenging because of the complex causative mechanism of the disease. Metabolomic profiling offers the potential to detect new biomarkers and improve CHD risk assessment.

Objective

To evaluate the association between circulating metabolites and incident CHD in a large European cohort.

Design, Setting, and Participants

This population-based study used the Biomarkers for Cardiovascular Risk Assessment in Europe (BiomarCaRE) case-cohort to measure circulating metabolites using a targeted approach in serum samples from 10 741 individuals without prevalent CHD. The cohort consisted of a weighted, random subcohort of the original cohort of more than 70 000 individuals. The case-cohort design was applied to 6 European cohorts: FINRISK97 (Finland), Monitoring of Trends and Determinants in Cardiovascular Diseases/Cooperative Health Research in the Region of Augsburg (MONICA/KORA; Germany), MONICA-Brianza and Moli-sani (Italy), DanMONICA (Denmark), and the Scottish Heart Health Extended Cohort (United Kingdom).

Main Outcomes and Measures

Associations with time to CHD onset were assessed individually by applying weighted and adjusted Cox proportional hazard models. The association of metabolites with CHD onset was examined by C indices.

Results

In 10 741 individuals (4157 women [38.7%]; median [interquartile range] age, 56.5 [49.2-62.2] years), 2166 incident CHD events (20.2%) occurred over a median (interquartile range) follow-up time of 9.2 (4.5-15.0) years. Among the 141 metabolites analyzed, 24 were significantly associated with incident CHD at a nominal P value of .05, including phosphatidylcholines (PCs), lysoPCs, amino acids, and sphingolipids. Five PCs remained significant after correction for multiple testing: acyl-alkyl-PC C40:6 (hazard ratio [HR], 1.13 [95% CI, 1.07-1.18]), diacyl-PC C40:6 (HR, 1.10 [95% CI, 1.04-1.15]), acyl-alkyl-PC C38:6 (HR, 1.11 [95% CI, 1.05-1.16]), diacyl-PC C38:6 (HR, 1.09 [95% CI, 1.04-1.14]) and diacyl-PC C38:5 (HR, 1.10 [95% CI, 1.05-1.16]). Lower levels of these metabolites were associated with increased risk of incident CHD. The strength of the associations competes with those of classic risk factors (C statistics: acyl-alkyl-PC C40:6, 0.756 [95% CI, 0.738-0.774], diacyl-PC C40:6, 0.754 [95% CI, 0.736-0.772], acyl-alkyl-PC C38:6, 0.755 [95% CI, 0.736-0.773], diacyl-PC C38:6, 0.754 [95% CI, 0.736-0.772]), diacyl-PC C38:5, 0.754 [95% CI, 0.736-0.772]). Adding metabolites to a base risk model including classic risk factors high-sensitivity C-reactive protein and high-sensitivity troponin I did not improve discrimination by C statistics.

Conclusions and Relevance

Five PCs were significantly associated with increased risk of incident CHD and showed comparable discrimination with individual classic risk factors. Although these metabolites do not improve CHD risk assessment beyond that of classic risk factors, these findings hold promise for an improved understanding of the pathophysiology of CHD.

Maternal plasma metabolic markers of neonatal adiposity and associated maternal characteristics: The GUSTO study

Infant adiposity may be related to later metabolic health. Maternal metabolite profiling reflects both genetic and environmental influences and allows elucidation of metabolic pathways associated with infant adiposity. In this multi-ethnic Asian cohort, we aimed to (i) identify maternal plasma metabolites associated with infant adiposity and other birth outcomes and (ii) investigate the maternal characteristics associated with those metabolites. In 940 mother-offspring pairs, we performed gas chromatography-mass spectrometry and identified 134 metabolites in maternal fasting plasma at 26–28 weeks of gestation. At birth, neonatal triceps and subscapular skinfold thicknesses were measured by trained research personnel, while weight and length measures were abstracted from delivery records. Gestational age was estimated from first-trimester dating ultrasound. Associations were assessed by multivariable linear regression, with p-values corrected using the Benjamini-Hochberg approach. At a false discovery rate of 5%, we observed associations between 28 metabolites and neonatal sum of skinfold thicknesses (13 amino acid-related, 4 non-esterified fatty acids, 6 xenobiotics, and 5 unknown compounds). Few associations were observed with gestational duration, birth weight, or birth length. Maternal ethnicity, pre-pregnancy BMI, and diet quality during pregnancy had the strongest associations with the specific metabolome related to infant adiposity. Further studies are warranted to replicate our findings and to understand the underlying mechanisms.

[Homoarginine level and methionine-homocysteine balance in patients with ischemic heart disease.]

The level of homoarginine (hArg) in terms of prognostic significance may exceed the natriuretic peptides and other well-known markers according to the latest data about the progression of cardiovascular diseases. The lack of data on the association of hArg levels with levels of other metabolites makes it difficult to understand its role in the pathogenesis of cardiovascular diseases. Relationships of hArg and other amino acids, including methionine (Met) and total homocysteine (tHcy), and their ratio in patients with ischemic heart disease were evaluated. The study included 74 patients with coronary heart disease (57 men and 17 women) aged 62 (57 - 67) years before coronary artery bypass surgery and 27 healthy people of similar age. In patients, the level of hArg was almost 2 times lower (p < 0.05) than in healthy individuals and rates lower than 1.4 μM were in half of them. The statistically significant decrease (p = 0.0025) of the Met/tHcy ratio corresponded to a decrease in the level of hArg. This ratio did not correlate with glucose level or body mass index. Less statistical significance of hArg correlation with levels of Met or tHcy separately was observed. In the subgroup of patients with hAarg level above 2.1 μM, a lower incidence of myocardial infarction was noted. Thus, a low hArg level is associated with impaired metabolism of sulfur-containing amino acids involved in transmethylation reactions, in patients with ischemic heart disease. The Met/tHcy ratio, closely correlating with the level of hArg, apparently reveals a link between the reactions of creatine formation and transmethylation, highlighting a cohort of patients with the most profound and dangerous changes in tissue metabolism.

Are we close to defining a metabolomic signature of human obesity? A systematic review of metabolomics studies

INTRODUCTION

Obesity is a disorder characterized by a disproportionate increase in body weight in relation to height, mainly due to the accumulation of fat, and is considered a pandemic of the present century by many international health institutions. It is associated with several non-communicable chronic diseases, namely, metabolic syndrome, type 2 diabetes mellitus (T2DM), cardiovascular diseases (CVD), and cancer. Metabolomics is a useful tool to evaluate changes in metabolites due to being overweight and obesity at the body fluid and cellular levels and to ascertain metabolic changes in metabolically unhealthy overweight and obese individuals (MUHO) compared to metabolically healthy individuals (MHO).

OBJECTIVES

We aimed to conduct a systematic review (SR) of human studies focused on identifying metabolomic signatures in obese individuals and obesity-related metabolic alterations, such as inflammation or oxidative stress.

METHODS

We reviewed the literature to identify studies investigating the metabolomics profile of human obesity and that were published up to May 7th, 2019 in SCOPUS and PubMed through an SR. The quality of reporting was evaluated using an adapted of QUADOMICS.

RESULTS

Thirty-three articles were included and classified according to four types of approaches. (i) studying the metabolic signature of obesity, (ii) studying the differential responses of obese and non-obese subjects to dietary challenges (iii) studies that used metabolomics to predict weight loss and aimed to assess the effects of weight loss interventions on the metabolomics profiles of overweight or obese human subjects (iv) articles that studied the effects of specific dietary patterns or dietary compounds on obesity-related metabolic alterations in humans.

CONCLUSION

The present SR provides state-of-the-art information about the use of metabolomics as an approach to understanding the dynamics of metabolic processes involved in human obesity and emphasizes metabolic signatures related to obesity phenotypes.

Integrated analysis of genomics, longitudinal metabolomics, and Alzheimer's risk factors among 1,111 cohort participants

Although Alzheimer's disease (AD) is highly heritable, genetic variants are known to be associated with AD only explain a small proportion of its heritability. Genetic factors may only convey disease risk in individuals with certain environmental exposures, suggesting that a multiomics approach could reveal underlying mechanisms contributing to complex traits, such as AD. We developed an integrated network to investigate relationships between metabolomics, genomics, and AD risk factors using Wisconsin Registry for Alzheimer's Prevention participants. Analyses included 1,111 non-Hispanic Caucasian participants with whole blood expression for 11,376 genes (imputed from dense genome-wide genotyping), 1,097 fasting plasma metabolites, and 17 AD risk factors. A subset of 155 individuals also had 364 fastings cerebral spinal fluid (CSF) metabolites. After adjusting each of these 12,854 variables for potential confounders, we developed an undirected graphical network, representing all significant pairwise correlations upon adjusting for multiple testing. There were many instances of genes being indirectly linked to AD risk factors through metabolites, suggesting that genes may influence AD risk through particular metabolites. Follow-up analyses suggested that glycine mediates the relationship between carbamoyl-phosphate synthase 1 and measures of cardiovascular and diabetes risk, including body mass index, waist-hip ratio, inflammation, and insulin resistance. Further, 38 CSF metabolites explained more than 60% of the variance of CSF levels of tau, a detrimental protein that accumulates in the brain of AD patients and is necessary for its diagnosis. These results further our understanding of underlying mechanisms contributing to AD risk while demonstrating the utility of generating and integrating multiple omics data types.

Circulating glutamate concentration as a biomarker of visceral obesity and associated metabolic alterations

Background

Visceral adipose tissue (VAT) area is a strong predictor of obesity-related cardiometabolic alterations, but its measurement is costly, time consuming and, in some cases, involves radiation exposure. Glutamate, a by-product of branched-chain-amino-acid (BCAA) catabolism, has been shown to be increased in visceral obese individuals. In this follow-up data analysis, we aimed to investigate the ability of plasma glutamate to identify individuals with visceral obesity and concomitant metabolic alterations.

Methods

Measurements of adiposity, targeted blood metabolomics and cardiometabolic risk factors were performed in 59 healthy middle-aged women. Visceral and subcutaneous adipose tissue areas were measured by computed tomography (CT) whereas body fat and lean mass were assessed by dual-energy x-ray absorptiometry (DEXA).

Results

The univariate Pearson correlation coefficient between glutamate and VAT area was r = 0.46 (p < 0.001) and it was r = 0.36 (p = 0.006) when adjusted for total body fat mass. Glutamate allowed to identify individuals with VAT areas ≥100 cm² (ROC_AUC: 0.78, 95% CI: 0.66–0.91) and VAT ≥130 cm² (ROC_AUC: 0.71, 95% CI: 0.56–0.87). The optimal glutamate concentration threshold determined from the ROC curve (glutamate ≥34.6 μmol/L) had a greater sensitivity than the metabolic syndrome (MetS) and the hypertriglyceridemic waist (HTW) phenotype to identify individuals with VAT ≥100 cm² (83% for glutamate vs 52% for the MetS and 35% for the HTW). Variance analysis showed that women with a high circulating glutamate level (≥34.6 μmol/L) had an altered metabolic profile, particularly regarding total triglyceride levels and the amount of triglycerides and cholesterol in very-low-density lipoproteins (all p < 0.01).

Conclusion

Circulating glutamate is strongly associated with VAT area and may represent a potential screening tool for visceral obesity and alterations of the metabolic profile.

FTO associations with obesity and telomere length

This review examines the biology of the Fat mass- and obesity-associated gene (FTO), and the implications of genetic association of FTO SNPs with obesity and genetic aging. Notably, we focus on the role of FTO in the regulation of methylation status as possible regulators of weight gain and genetic aging. We present a theoretical review of the FTO gene with a particular emphasis on associations with UCP2, AMPK, RBL2, IRX3, CUX1, mTORC1 and hormones involved in hunger regulation. These associations are important for dietary behavior regulation and cellular nutrient sensing via amino acids. We suggest that these pathways may also influence telomere regulation. Telomere length (TL) attrition may be influenced by obesity-related inflammation and oxidative stress, and FTO gene-involved pathways. There is additional emerging evidence to suggest that telomere length and obesity are bi-directionally associated. However, the role of obesity risk-related genotypes and associations with TL are not well understood. The FTO gene may influence pathways implicated in regulation of TL, which could help to explain some of the non-consistent relationship between weight phenotype and telomere length that is observed in population studies investigating obesity.

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.