Increased Dynamics of Tricarboxylic Acid Cycle and Glutamate Synthesis in Obese Adipose Tissue: IN VIVO METABOLIC TURNOVER ANALYSIS

Polyphenols reverse hyperglycemia-induced adipocyte dysfunction: A Metabolomic and Lipidomic study of efficacy

Hyperglycemia leads to metabolic dysfunction in human adipocytes, characterized by decreased AKT phosphorylation, downregulation of glycolysis, TCA cycle, and amino acid metabolism, as well as altered lipid profiles. This study aimed to elucidate these metabolic alterations and evaluate the potential therapeutic effects of selected polyphenols. Comprehensive metabolic profiling revealed profound disruptions, including impaired carbon metabolism, amino acids, and lipids associated with obesity. Importantly, treatment with polyphenols, particularly verbascoside and ferulic acid, effectively mitigated these metabolic disturbances, restoring adipocyte homeostasis. The polyphenols increased metabolites from carbon metabolism and amino acids, improving glycolysis, the TCA cycle, and related pathways. They also modulated lipid profiles that are negatively associated with obesity and related diseases. These findings provide valuable insights into the metabolic pathways underlying adipocyte dysfunction in hyperglycemia and highlight the therapeutic potential of polyphenols in ameliorating metabolic disorders.

Metabolites and lipid species mediate the associations of adiposity in childhood and early adulthood with mammographic breast density in premenopausal women

BACKGROUND

Mammographic breast density (MBD), a strong predictor of breast cancer, is highly influenced by body mass index (BMI) in childhood and early adulthood, but the mechanisms underlying these associations are not fully understood. Our goal is to identify biomarkers that mediate the associations of BMI at ages 10 and 18 with MBD in premenopausal women.

METHODS

This study consists of 705 premenopausal women who had their screening mammogram at Washington University in St. Louis, MO, and provided a fasting blood sample. Our comprehensive metabolomic and lipidomic profiling yielded complete data for 828 metabolites and 857 lipid species after imputation. We used Volpara to determine volumetric measures of MBD. We performed high dimensional mediation analysis using the HIMA R package, adjusted for confounders, to determine whether lipid species and metabolites mediate the associations of BMI at 10 and 18 with MBD. We applied a false discovery rate (FDR) p-value < 0.1.

RESULTS

Four metabolites (glutamate, β-cryptoxanthin, cortolone glucuronide (1), phytanate) significantly mediated the association of BMI at 10 with volumetric percent density (VPD), and two (glutamate, β-cryptoxanthin) mediated the association of BMI at 18 with VPD. Glutamate was the strongest mediator across time points. Glutamate mediated 6.7% (FDR p-value = 0.06) and 9.3% (FDR p-value = 0.008) of the association between BMI at age 10 and 18, respectively. Four lipid species (CER(18:0), LCER(14:0), LPC(18:1), PC(18:1/18:1)), mediated the association of BMI at 10 with VPD, while five lipid species (CER(18:0), LCER(14:0), PC(18:1/18:1), TAG56:5-FA22:5, TAG52:2-FA16:0) mediated the association of BMI at 18 with VPD. The strongest mediator was PC(18:1/18:1), which mediated 9.7%, (FDR-p = 0.009) and 7.7%, (FDR-p = 0.04) of the association of BMI at age 10 and 18 with VPD, respectively.

CONCLUSIONS

Metabolites in amino acid, lipid, cofactor/vitamin, and xenobiotic super-pathways as well as lipid species across the phospholipid, neutral complex lipid and sphingolipid super-pathways mediated the associations of BMI in early-life and MBD in premenopausal women. This study offers insight into the biological mechanisms underlying the link between early-life adiposity and MBD, which can support future research into breast cancer prevention.

Bariatric surgery and dimethyl fumarate-induced lymphopenia in patients with multiple sclerosis

INTRODUCTION

Lymphopenia is a known side effect of dimethyl fumarate (DMF), a disease-modifying therapy (DMT) for patients with multiple sclerosis (pwMS). A body mass index ≥ 30 kg/m2 has been identified as a protective factor; however, no data are available on lymphopenia in pwMS undergoing to weight loss due to bariatric surgery.

METHODS

We described two pwMS with history of bariatric surgery who started DMF as DMT.

RESULTS

The two pwMS experienced persistent lymphopenia during DMF-treatment, which was resolved after its discontinuation.

CONCLUSIONS

Several mechanisms might modify DMF pharmacokinetic profiles after bariatric surgery and its bioavailability. Absolute lymphocyte count should be monitored in pwMS treated with DMF and history of bariatric surgery and weight loss.

Impacts of glutamate, an exercise-responsive metabolite on insulin signaling

AIMS

Disruption of the insulin signaling pathway leads to insulin resistance (IR). IR is characterized by impaired glucose and lipid metabolism. Elevated levels of circulating glutamate are correlated with metabolic indicators and may potentially predict the onset of metabolic diseases. Glutamate receptor antagonists have significantly enhanced insulin sensitivity, and improved glucose and lipid metabolism. Exercise is a well-known strategy to combat IR. The aims of our narrative review are to summarize preclinical and clinical findings to show the correlations between circulating glutamate levels, IR and metabolic diseases, discuss the causal role of excessive glutamate in IR and metabolic disturbance, and present an overview of the exercise-induced alteration in circulating glutamate levels.

MATERIALS AND METHODS

A literature search was conducted to identify studies on glutamate, insulin signaling, and exercise in the PubMed database. The search covered articles published from December 1955 to January 2024, using the search terms of "glutamate", "glutamic acid", "insulin signaling", "insulin resistance", "insulin sensitivity", "exercise", and "physical activity".

KEY FINDINGS

Elevated levels of circulating glutamate are correlated with IR. Excessive glutamate can potentially hinder the insulin signaling pathway through various mechanisms, including the activation of ectopic lipid accumulation, inflammation, and endoplasmic reticulum stress. Glutamate can also modify mitochondrial function through Ca2+ and induce purine degradation mediated by AMP deaminase 2. Exercise has the potential to decrease circulating levels of glutamate, which can be attributed to accelerated glutamate catabolism and enhanced glutamate uptake.

SIGNIFICANCE

Glutamate may act as a mediator in the exercise-induced improvement of insulin sensitivity.

Targeting the Metabolic Paradigms in Cancer and Diabetes

Dysregulated metabolic dynamics are evident in both cancer and diabetes, with metabolic alterations representing a facet of the myriad changes observed in these conditions. This review delves into the commonalities in metabolism between cancer and type 2 diabetes (T2D), focusing specifically on the contrasting roles of oxidative phosphorylation (OXPHOS) and glycolysis as primary energy-generating pathways within cells. Building on earlier research, we explore how a shift towards one pathway over the other serves as a foundational aspect in the development of cancer and T2D. Unlike previous reviews, we posit that this shift may occur in seemingly opposing yet complementary directions, akin to the Yin and Yang concept. These metabolic fluctuations reveal an intricate network of underlying defective signaling pathways, orchestrating the pathogenesis and progression of each disease. The Warburg phenomenon, characterized by the prevalence of aerobic glycolysis over minimal to no OXPHOS, emerges as the predominant metabolic phenotype in cancer. Conversely, in T2D, the prevailing metabolic paradigm has traditionally been perceived in terms of discrete irregularities rather than an OXPHOS-to-glycolysis shift. Throughout T2D pathogenesis, OXPHOS remains consistently heightened due to chronic hyperglycemia or hyperinsulinemia. In advanced insulin resistance and T2D, the metabolic landscape becomes more complex, featuring differential tissue-specific alterations that affect OXPHOS. Recent findings suggest that addressing the metabolic imbalance in both cancer and diabetes could offer an effective treatment strategy. Numerous pharmaceutical and nutritional modalities exhibiting therapeutic effects in both conditions ultimately modulate the OXPHOS-glycolysis axis. Noteworthy nutritional adjuncts, such as alpha-lipoic acid, flavonoids, and glutamine, demonstrate the ability to reprogram metabolism, exerting anti-tumor and anti-diabetic effects. Similarly, pharmacological agents like metformin exhibit therapeutic efficacy in both T2D and cancer. This review discusses the molecular mechanisms underlying these metabolic shifts and explores promising therapeutic strategies aimed at reversing the metabolic imbalance in both disease scenarios.

Roux-en-Y Gastric Bypass Improves Insulin Sensitivity in Obese Rats with Type 2 Diabetes Mellitus by Regulating the Grin3a/AMPK Signal Axis in Hypothalamic Arcuate Nucleus

Objective

The objective of this study was to explore the effects and related mechanisms of Roux-en-Y gastric bypass (RYGB) on insulin sensitivity in obese rats with type 2 diabetes mellitus (T2DM).

Methods

The obese T2DM rat model was constructed by feeding a high-fat diet and injecting streptozotocin (STZ), and treated with RYGB. Grin3a shRNA was injected into the bilateral hypothalamic arcuate nucleus (ARC) to knockdown the Grin3a expression on T2DM rats. Eight weeks after operation, the body weight, fasting blood glucose (FBG), fasting serum insulin (FSI), homeostatic model assessment of insulin resistance (HOMA-IR), and plasma triglyceride (TG) levels were assessed. Hematoxylin & eosin (H&E) staining was adopted to observe the white adipose tissue (WAT) of rats. Western blot and qRT-PCR were used to detect the expression of Grin3a, adenosine 5' monophosphate-activated protein kinase (AMPK) and p-AMPK in ARC of rats. Later, the plasmid over-expressing or knocking down Grin3a was transfected into differentiated 3T3-L1 adipocytes, and the TG level and the formation of lipid droplets in adipocyte were assessed by TG kit and oil red O staining. The expression of lipogenic transcription factors in cells was detected by qRT-PCR.

Results

RYGB reduced FBG, FSI, HOMA-IR and plasma TG levels in T2DM rats while increasing Grin3a expression and p-AMPK/AMPK ratio in ARC. Knockdown of Grin3a not only reversed the decrease of FBG, FSI, HOMA-IR and plasma TG levels in T2DM rats induced by RYGB, but also reversed the up-regulation of p-AMPK/AMPK ratio in ARC affected by RYGB. Moreover, knocking down Grin3a significantly increased the TG level, promoted the formation of lipid droplets and up-regulated the expressions of lipogenic transcription factors in adipocytes.

Conclusion

RYGB improved the insulin sensitivity, reduced the plasma TG level and lessens the fat accumulation in obese T2DM rats by regulating the Grin3a/AMPK signal in ARC.

NMR metabolomics study of chronic low-dose exposure to a cocktail of persistent organic pollutants

Nowadays, exposure to endocrine-disrupting chemicals (EDCs), including persistent organic pollutants (POPs), is one of the most critical threats to public health. EDCs are chemicals that mimic, block, or interfere with hormones in the body's endocrine system and have been associated with a wide range of health issues. This innovative, untargeted metabolomics study investigates chronic low-dose internal exposure to a cocktail of POPs on multiple tissues that are known to accumulate these lipophilic compounds. Interestingly, the metabolic response differs among selected tissues/organs in mice. In the liver, we observed a dynamic effect according to the exposure time and the doses of POPs. In the brain tissue, the situation is the opposite, leading to the conclusion that the presence of POPs immediately gives a saturated effect that is independent of the dose and the duration of exposure studied. By contrast, for the adipose tissues, nearly no effect is observed. This metabolic profiling leads to a holistic and dynamic overview of the main metabolic pathways impacted in lipophilic tissues by a cocktail of POPs.

Prenatal alcohol alters inflammatory signatures in enteric portal tissues following adult-onset cerebrovascular ischemic stroke

Prenatal alcohol exposure (PAE) impairs recovery from cerebrovascular ischemic stroke in adult rodents. Since the gut becomes dysbiotic following stroke, we assessed links between PAE and enteric portal inflammation. Adult control and PAE rat offspring received a unilateral endothelin-1-induced occlusion of the middle cerebral artery. Post-stroke behavioral disabilities and brain cytokines were assessed. Mesenteric adipose and liver transcriptomes were assessed from stroke-exposed and stroke-naive offspring. We identified, in the liver of stroke-naive animals, a moderate correlation between PAE and a gene network for inflammatory necroptosis. PAE inhibited the acute-phase brain inflammatory cytokine response to stroke. Post-stroke neurological function was correlated with an adipose gene network associated with B-lymphocyte differentiation and nuclear factor κB (NF-κB) signaling and with a liver pro-inflammatory gene network. Collectively, PAE inhibits brain inflammation but results in an inflammatory signature in enteric portal tissues after stroke, suggesting that PAE persistently and adversely impacts the gut-brain axis following adult-onset disease.

Baf155 regulates skeletal muscle metabolism via HIF-1a signaling

During exercise, skeletal muscle is exposed to a low oxygen condition, hypoxia. Under hypoxia, the transcription factor hypoxia-inducible factor-1α (HIF-1α) is stabilized and induces expressions of its target genes regulating glycolytic metabolism. Here, using a skeletal muscle-specific gene ablation mouse model, we show that Brg1/Brm-associated factor 155 (Baf155), a core subunit of the switch/sucrose non-fermentable (SWI/SNF) complex, is essential for HIF-1α signaling in skeletal muscle. Muscle-specific ablation of Baf155 increases oxidative metabolism by reducing HIF-1α function, which accompanies the decreased lactate production during exercise. Furthermore, the augmented oxidation leads to high intramuscular adenosine triphosphate (ATP) level and results in the enhancement of endurance exercise capacity. Mechanistically, our chromatin immunoprecipitation (ChIP) analysis reveals that Baf155 modulates DNA-binding activity of HIF-1α to the promoters of its target genes. In addition, for this regulatory function, Baf155 requires a phospho-signal transducer and activator of transcription 3 (pSTAT3), which forms a coactivator complex with HIF-1α, to activate HIF-1α signaling. Our findings reveal the crucial role of Baf155 in energy metabolism of skeletal muscle and the interaction between Baf155 and hypoxia signaling.

Protocatechuic Acid Ameliorates High Fat Diet-Induced Obesity and Insulin Resistance in Mice

SCOPE

Insulin resistance is a common feature of obesity and type 2 diabetes and partly results from an imbalance between food intake and energy expenditure. Therefore, efficient and safe insulin resistance treatment therapies are warranted. This work is aim to access the impact of protocatechuic acid (PCA), a catechol-type O-diphenol phenolic acid, in high fat diet (HFD)-induced glucose, and lipid dysregulation.

METHODS AND RESULTS

Five-week-old male C57BL/6 mice are fed with HFD for 4 weeks and then are randomly divided into two cohorts: one cohort feed with HFD is free access to sterile water for 4 weeks, another cohort is free access to PCA-containing water (2.7 mM) for 4 weeks with HFD. In this study, using a hyperinsulinemic-euglycemic mouse clamp, it is showed that PCA-treated mice display improved systemic insulin resistance via enhanced fatty acid mobilization and utilization, thereby reducing ectopic lipid accumulation and promoting hepatic and peripheral insulin action.

CONCLUSIONS

This study provides insights on the potent pharmacological effects of PCA from food sources on improving high fat diet (HFD)-induced whole-body insulin resistance and type 2 diabetes.

A Metabolomics-Based Investigation of the Effects of a Short-Term Body Weight Reduction Program in a Cohort of Adolescents with Obesity: A Prospective Interventional Clinical Study

Metabolomics applied to assess the response to a body weight reduction program (BWRP) may generate valuable information concerning the biochemical mechanisms/pathways underlying the BWRP-induced cardiometabolic benefits. The aim of the present study was to establish the BWRP-induced changes in the metabolomic profile that characterizes the obese condition. In particular, a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) targeted metabolomic approach was used to determine a total of 188 endogenous metabolites in the plasma samples of a cohort of 42 adolescents with obesity (female/male = 32/10; age = 15.94 ± 1.33 year; body mass index standard deviation score (BMI SDS) = 2.96 ± 0.46) who underwent a 3-week BWRP, including hypocaloric diet, physical exercise, nutritional education, and psychological support. The BWRP was capable of significantly improving body composition (e.g., BMI SDS, p < 0.0001), glucometabolic homeostasis (e.g., glucose, p < 0.0001), and cardiovascular function (e.g., diastolic blood pressure, p = 0.016). A total of 64 metabolites were significantly reduced after the intervention (at least p < 0.05), including 53 glycerophospholipids (23 PCs ae, 21 PCs aa, and 9 lysoPCs), 7 amino acids (tyrosine, phenylalanine, arginine, citrulline, tryptophan, glutamic acid, and leucine), the biogenic amine kynurenine, 2 sphingomyelins, and (free) carnitine (C0). On the contrary, three metabolites were significantly increased after the intervention (at least p < 0.05)-in particular, glutamine, trans-4-hydroxyproline, and the octadecenoyl-carnitine (C18:1). In conclusion, when administered to adolescents with obesity, a short-term BWRP is capable of changing the metabolomic profile in the plasma.

Prenatal metabolomic profiles mediate the effect of maternal obesity on early childhood growth trajectories and obesity risk: the Conditions Affecting Neurocognitive Development and Learning in Early Childhood (CANDLE) Study

BACKGROUND

Maternal prepregnancy obesity is an important risk factor for offspring obesity, which may partially operate through prenatal programming mechanisms.

OBJECTIVES

The study aimed to systematically identify prenatal metabolomic profiles mediating the intergenerational transmission of obesity.

METHODS

We included 450 African-American mother-child pairs from the Conditions Affecting Neurocognitive Development and Learning in Early Childhood (CANDLE) Study pregnancy cohort. LC-MS was used to conduct metabolomic profiling on maternal plasma samples of the second trimester. The childhood growth outcomes of interest included BMI trajectories from birth to age 4 y (rising-high-, moderate-, and low-BMI trajectories) as well as overweight/obesity (OWO) risk at age 4 y. Mediation analysis was conducted to identify metabolite mediators linking maternal OWO and childhood growth outcomes. The potential causal effects of maternal OWO on metabolite mediators were examined using the Mendelian randomization (MR) method.

RESULTS

Among the 880 metabolites detected in the maternal plasma during pregnancy, 14 and 11 metabolites significantly mediated the effects of maternal prepregnancy OWO on childhood BMI trajectories and the OWO risk at age 4 y, respectively, and 5 mediated both outcomes. The MR analysis suggested 6 of the 20 prenatal metabolite mediators might be causally influenced by maternal prepregnancy OWO, most of which are from the pathways related to the metabolism of amino acids (hydroxyasparagine, glutamate, and homocitrulline), sterols (campesterol), and nucleotides (N2,N2-dimethylguanosine).

CONCLUSIONS

Our study provides further evidence that prenatal metabolomic profiles might mediate the effect of maternal OWO on early childhood growth trajectories and OWO risk in offspring. The metabolic pathways, including identified metabolite mediators, might provide novel intervention targets for preventing the intrauterine development of obesity in the offspring of mothers with obesity.

AMPK signaling and its targeting in cancer progression and treatment

The intrinsic mechanisms sensing the imbalance of energy in cells are pivotal for cell survival under various environmental insults. AMP-activated protein kinase (AMPK) serves as a central guardian maintaining energy homeostasis by orchestrating diverse cellular processes, such as lipogenesis, glycolysis, TCA cycle, cell cycle progression and mitochondrial dynamics. Given that AMPK plays an essential role in the maintenance of energy balance and metabolism, managing AMPK activation is considered as a promising strategy for the treatment of metabolic disorders such as type 2 diabetes and obesity. Since AMPK has been attributed to aberrant activation of metabolic pathways, mitochondrial dynamics and functions, and epigenetic regulation, which are hallmarks of cancer, targeting AMPK may open up a new avenue for cancer therapies. Although AMPK is previously thought to be involved in tumor suppression, several recent studies have unraveled its tumor promoting activity. The double-edged sword characteristics for AMPK as a tumor suppressor or an oncogene are determined by distinct cellular contexts. In this review, we will summarize recent progress in dissecting the upstream regulators and downstream effectors for AMPK, discuss the distinct roles of AMPK in cancer regulation and finally offer potential strategies with AMPK targeting in cancer therapy.

Impact of Maternal Obesity on the Gestational Metabolome and Infant Metabolome, Brain, and Behavioral Development in Rhesus Macaques

Maternal gestational obesity is associated with elevated risks for neurodevelopmental disorder, including autism spectrum disorder. However, the mechanisms by which maternal adiposity influences fetal developmental programming remain to be elucidated. We aimed to understand the impact of maternal obesity on the metabolism of both pregnant mothers and their offspring, as well as on metabolic, brain, and behavioral development of offspring by utilizing metabolomics, protein, and behavioral assays in a non-human primate model. We found that maternal obesity was associated with elevated inflammation and significant alterations in metabolites of energy metabolism and one-carbon metabolism in maternal plasma and urine, as well as in the placenta. Infants that were born to obese mothers were significantly larger at birth compared to those that were born to lean mothers. Additionally, they exhibited significantly reduced novelty preference and significant alterations in their emotional response to stress situations. These changes coincided with differences in the phosphorylation of enzymes in the brain mTOR signaling pathway between infants that were born to obese and lean mothers and correlated with the concentration of maternal plasma betaine during pregnancy. In summary, gestational obesity significantly impacted the infant systemic and brain metabolome and adaptive behaviors.

Glutamate regulates gliosis of BMSCs to promote ENS regeneration through α-KG and H3K9/H3K27 demethylation

Background

There is a lack of effective therapies for enteric nervous system (ENS) injury. Our previous study showed that transplanted bone marrow-derived mesenchymal stem cells (BMSCs) play a “glia-like cells” role in initiating ENS regeneration in denervated mice. Cellular energy metabolism is an important factor in maintaining the biological characteristics of stem cells. However, how cellular energy metabolism regulates the fate of BMSCs in the ENS-injured microenvironment is unclear.

Methods

The biological characteristics, energy metabolism, and histone methylation levels of BMSCs following ENS injury were determined. Then, glutamate dehydrogenase 1 (Glud1) which catalyzes the oxidative deamination of glutamate to α-KG was overexpressed (OE) in BMSCs. Further, OE-Glud1 BMSCs were targeted–transplanted into the ENS injury site of denervated mice to determine their effects on ENS regeneration.

Results

In vitro, in the ENS-injured high-glutamate microenvironment, the ratio of α-ketoglutarate (α-KG) to succinate (P < 0.05), the histone demethylation level (P < 0.05), the protein expression of glial cell markers (P < 0.05), and the gene expression of Glud1 (P < 0.05) were significantly increased. And the binding of H3K9me3 to the GFAP, S100B, and GDNF promoter was enhanced (P < 0.05). Moreover, α-KG treatment increased the monomethylation and decreased the trimethylation on H3K9 (P < 0.01) and H3K27 (P < 0.05) in BMSCs and significantly upregulated the protein expression of glial cell markers (P < 0.01), which was reversed by the α-KG competitive inhibitor D-2-hydroxyglutarate (P < 0.05). Besides, overexpression of Glud1 in BMSCs exhibited increases in monomethylation and decreases in trimethylation on H3K9 (P < 0.05) and H3K27 (P < 0.05), and upregulated protein expression of glial cell markers (P < 0.01). In vivo, BMSCs overexpressing Glud1 had a strong promotion effect on ENS regeneration in denervated mice through H3K9/H3K27 demethylation (P < 0.05), and upregulating the expression of glial cell protein (P < 0.05).

Conclusions

BMSCs overexpressing Glud1 promote the expression of glial cell markers and ENS remodeling in denervated mice through regulating intracellular α-KG and H3K9/H3K27 demethylation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02936-7.

Determination of up to twenty carboxylic acid containing compounds in clinically relevant matrices by o-benzylhydroxylamine derivatization and liquid chromatography-tandem mass spectrometry

Carboxylic acid containing compounds (R-COOH) are involved in a large number of biological processes and they are relevant for several pathological processes such as neurodegeneration or cancer. Comprehensive methodologies for the quantitative determination of R-COOH in biological samples are required. In this study we have developed a LC-MS/MS method for the quantification of 20 endogenous R-COOH belonging to different pathways such as kynurenine metabolism, serotoninergic pathway, glycolysis, tricarboxylic acid cycle, dopaminergic pathway, short chain fatty acids and glycine metabolism. The approach included derivatization with o-benzylhydroxylamine (reaction time 1 h), liquid-liquid extraction with ethyl acetate and LC-MS/MS detection (run time 10 min). The method was optimized and validated in 5 different matrices (urine, plasma, saliva, brain and liver) following two different approaches: (i) using surrogate matrices and (ii) using actual human samples by standard additions. A suitable linearity was obtained in the endogenous range of the analytes. Adequate intra and inter-assay accuracies (80-120%) and intra- and inter-assay precisions (<20%) were achieved for almost all analytes in all studied matrices. The method was applied in several scenarios to confirm (i) human urinary changes produced in glycolysis after exercise, (ii) metabolic changes produced in rat brain and plasma by methamphetamine administration and (iii) metabolic alterations in human plasma caused by vitamin B6 deficiency. Additionally, the application of the method allowed for establishing previously unreported alterations in R-COOH metabolites under these conditions. Due to the comprehensive analyte and matrix coverage and the wide applicability of the developed methodology, it can be considered as a suitable tool for the study of R-COOH status in health and disease by targeted metabolomics.

An integrative multiomics approach to characterize anti-adipogenic and anti-lipogenic effects of Akkermansia muciniphila in adipocytes

The cellular components of Akkermansia muciniphila are considered potential biotherapeutics for the improvement of obesity, diabetes, and metabolic diseases. However, the molecular-based mechanism of A. muciniphila for treatment of obesity, which can provide important evidence for human research, has rarely been explored. Here, we applied integrative multiomics approaches to investigate the underlying molecular mechanism involved in obesity treatment by A. muciniphila. First, the treatment with a cell lysate of A. muciniphila reduced lipid accumulation in 3T3-L1 cells and downregulated the mRNA expression of proteins involved in adipogenesis and lipogenesis. Our proteomic results revealed that A. muciniphila decreased the expression of proteins involved in fat cell differentiation, fatty acid metabolism, and energy metabolism in adipocytes. Moreover, A. muciniphila significantly reduced the level of metabolites related to glycolysis, the TCA cycle, and ATP in adipocytes. Interestingly, serine protease inhibitor A3 (SERPINA3) homologs were overexpressed in the 3T3-L1 cells treated with A. muciniphila. Small interfering RNA (siRNA) transfection demonstrated that A. muciniphila upregulates SERPINA3G expression and inhibits lipogenesis in adipocytes. Taken together, our multiomics-based approaches enabled to uncover the molecular mechanism of A. muciniphila for treatment of obesity and provide potent anti-lipogenic agents.

Metabolomic analysis of plasma and intramuscular adipose tissue between Wagyu and Holstein cattle

In this experiment, we studied the effects of breed differences in intramuscular adipogenic capacity on the metabolomic profiles of plasma and intramuscular adipose tissue between Wagyu (high intramuscular adipogenic capacity) and Holstein (low intramuscular adipogenic capacity) using capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS). We showed that the intramuscular fat content, intramuscular adipocyte size and the expression of adipogenic transcription factors (C/EBPβ and C/EBPα) of Wagyu were significantly higher than those of Holstein. Metabolites detected at significantly higher levels in Wagyu plasma were related to the tricarboxylic acid cycle, lipid synthesis, fatty acid metabolism, diabetes, and glucose homeostasis. In contrast, metabolites detected at significantly higher levels in Holstein plasma were related to choline metabolism, the ethanolamine pathway, glutathione homeostasis, nucleic acid metabolism, and amino acid metabolism. Metabolites detected at significantly higher levels in Holstein intramuscular adipose tissue were related to nucleic acid metabolism, amino acid metabolism, amino sugar metabolism, beta oxidation, and the ethanolamine pathway. There were no metabolites significantly higher levels in Wagyu intramuscular adipose tissue. These results indicate candidate biomarkers of breed differences in intramuscular adipogenic capacity between Wagyu and Holstein.

Polysaccharides from fermented Momordica charantia L. with Lactobacillus plantarum NCU116 ameliorate metabolic disorders and gut microbiota change in obese rats

Obesity is a chronic disease characterized by overweight resulting from fat accumulation, along with disturbance of metabolism and gut microbiota. Fermentation, as a green processing method, is beneficial for improving the nutrition capacity of food components. Polysaccharides are considered as one of the important components in food and are also potential supplements for anti-obesity treatment. This study aimed to investigate the anti-obesity effects of polysaccharides from fermented and non-fermented Momordica charantia L. with Lactobacillus plantarum NCU116 (FP and NFP) on obese rats by serum metabolomics and gut microbiota analysis. Metabolomics results revealed that abnormal lipid metabolism was formed due to obesity. The supplement of FP and NFP improved the glycerophospholipids, glycosphingolipids, and amino acid metabolism of the obese rats, which alleviated the hypercholesterolemia and overweight in rats. Furthermore, the disorder of gut microbiota was ameliorated by FP and NFP. FP promoted the growth of beneficial bacteria, such as phylum Firmicutes, Actinobacteria, and genera Anaerostipes, Coprococcus, Lactobacillus, and Bifidobacterium. FP also reduced several harmful bacteria belonging to the phylum Proteobacteria and genera Helicobacter. The positive correlation of the weight loss and lowering of serum lipids with the increased beneficial bacteria further elucidated that the anti-obesity effect of FP in obese rats is associated with the regulation of gut microbiota and serum metabolites. The results of this study could provide information for developing probiotic products in the future that may have beneficial effects on the prevention or treatment of obesity.

Chronic cold exposure enhances glucose oxidation in brown adipose tissue

The cultured brown adipocytes can oxidize glucose in vitro, but it is still not fully clear whether brown adipose tissue (BAT) could completely oxidize glucose in vivo. Although positron emission tomography (PET) with ¹⁸F‐fluorodeoxyglucose (¹⁸F‐FDG) showed a high level of glucose uptake in the activated BAT, the non‐metabolizable ¹⁸F‐FDG cannot fully demonstrate intracellular glucose metabolism. Through in vivo [U‐¹³C]glucose tracing, here we show that chronic cold exposure dramatically activates glucose oxidation in BAT and the browning/beiging subcutaneous white adipose tissue (sWAT). Specifically, chronic cold exposure enhances glucose flux into the mitochondrial TCA cycle. Metabolic flux analysis models that β3‐adrenergic receptor (β3‐AR) agonist significantly enhances the flux of mitochondrial pyruvate uptake through mitochondrial pyruvate carrier (MPC) in the differentiated primary brown adipocytes. Furthermore, in vivo MPC inhibition blocks cold‐induced glucose oxidation and impairs body temperature maintenance in mice. Together, mitochondrial pyruvate uptake and oxidation serve an important energy source in the chronic cold exposure activated BAT and beige adipose tissue, which supports a role for glucose oxidation in brown fat thermogenesis.

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.

Substrate Utilization by Brown Adipose Tissue: What's Hot and What's Not?

Our understanding of brown adipose tissue (BAT) function in humans has increased rapidly over the past 10 years. This is predominantly due to the development of powerful non-invasive imaging techniques such as positron emission tomography that can quantify BAT mass and function using metabolic tracers. Activation of BAT during cold-induced thermogenesis is an effective way to dissipate energy to generate heat and requires utilization of multiple energy substrates for optimal function. This has led to interest in the activation of BAT as a potential therapeutic target for type 2 diabetes, dyslipidaemia, and obesity. Here, we provide an overview of the current understanding of BAT substrate utilization in humans and highlight additional mechanisms found in rodents, where BAT more prominently contributes to energy expenditure. During thermogenesis, BAT demonstrates substantially increased glucose uptake which appears to be critical for BAT function. However, glucose is not fully oxidized, with a large proportion converted to lactate. The primary energy substrate for thermogenesis is fatty acids, released from brown adipocyte triglyceride stores. Active BAT also sequesters circulating lipids to sustain optimal thermogenesis. Recent evidence reveals that metabolic intermediates from the tricarboxylic acid cycle and glycolytic pathways also play a critical role in BAT function. Understanding the role of these metabolites in regulating thermogenesis and whole body substrate utilization may elucidate novel strategies for therapeutic BAT activation.

One Anastomosis Gastric Bypass Reconstitutes the Appropriate Profile of Serum Amino Acids in Patients with Morbid Obesity

Bariatric surgery leads to metabolic benefits in patients with obesity, but their mechanisms are not well understood. The appropriate composition of serum amino acids (AA) is important for sufficient supply of these components into various tissues and organs. Obesity leads to alterations in serum AA concentrations. The aim of this study was to examine the effect of one anastomosis gastric bypass (OAGB), a promising type of bariatric surgery, on serum AA concentrations, which were assayed by LC-MS in serum of 46 bariatric patients prior to and 6–9 months after OAGB, as well as in 30 lean control subjects. The results were analyzed by principle components analysis and metabolic pathway analysis. PCA analysis showed that OAGB led to normalization of serum AA concentrations of patients with obesity to a pattern similar to the control subjects, and the concentrations of essential AA remained decreased after OAGB. Changes of individual AA and their associated metabolic pathways were also presented. OAGB caused normalization of the AA profile, which may contribute to improvement of glucose homeostasis and reduction of cardiovascular risk. Considering decreased essential AA concentrations after OAGB, increased intake of high protein food should be recommended to the patients after this type of bariatric surgery.

Circulating glutamate level as a potential biomarker for abdominal obesity and metabolic risk

BACKGROUND AND AIM

Circulating level of glutamate, a by-product of the catabolism of branched-chain amino acids, has been positively correlated with visceral adipose tissue accumulation and waist circumference (WC). The aim of the present study was to assess the potential of using glutamate level to identify individuals with abdominal obesity and a high cardiometabolic risk.

METHODS AND RESULTS

The study sample included 99 men and 99 women. Fasting serum glutamate was measured using the Biocrates p180 kit. Anthropometric and metabolic variables were used to identify individuals with abdominal obesity (WC ≥ 95 cm in both sexes), the hypertriglyceridemic waist (HTW) phenotype and the metabolic syndrome (MetS). Mean (±SD) age was 34.1 ± 10.1 years, mean BMI was 29.0 ± 6.2 kg/m² and mean WC was 92.7 ± 16.5 cm. Glutamate was strongly correlated with WC (r = 0.66 for men; r = 0.76 for women, both p < 0.0001) and multiple markers of metabolic dysfunction, particularly fasting triglyceride level (r = 0.59 for men; r = 0.57 for women, both p < 0.0001), HDL-cholesterol level (r = -0.45, p < 0.0001 in both sexes) and the HOMA-IR index (r = 0.65 for men; r = 0.60 for women, both p < 0.0001). Logistic regressions showed that glutamate had an excellent accuracy to identify individuals with abdominal obesity (ROC_AUC: 0.90 for both sexes), a good accuracy to identify those with the HTW phenotype (ROC_AUC: 0.82 for men; 0.85 for women) and fair-to-good accuracy for the MetS (ROC_AUC: 0.78 for men; 0.89 for women).

CONCLUSION

Glutamate level may represent an interesting potential biomarker of abdominal obesity and metabolic risk.

Elevated Glucose Levels Preserve Glucose Uptake, Hyaluronan Production, and Low Glutamate Release Following Interleukin-1β Stimulation of Differentiated Chondrocytes

OBJECTIVE

Chondrocytes are responsible for remodeling and maintaining the structural and functional integrity of the cartilage extracellular matrix. Because of the absence of a vascular supply, chondrocytes survive in a relatively hypoxic environment and thus have limited regenerative capacity during conditions of cellular stress associated with inflammation and matrix degradation, such as osteoarthritis (OA). Glucose is essential to sustain chondrocyte metabolism and is a precursor for key matrix components. In this study, we investigated the importance of glucose as a fuel source for matrix repair during inflammation as well as the effect of glucose on inflammatory mediators associated with osteoarthritis.

DESIGN

To create an OA model, we used equine chondrocytes from 4 individual horses that were differentiated into cartilage pellets in vitro followed by interleukin-1β (IL-1β) stimulation for 72 hours. The cells were kept at either normoglycemic conditions (5 mM glucose) or supraphysiological glucose concentrations (25 mM glucose) during the stimulation with IL-1β.

RESULTS

We found that elevated glucose levels preserve glucose uptake, hyaluronan synthesis, and matrix integrity, as well as induce anti-inflammatory actions by maintaining low expression of Toll-like receptor-4 and low secretion of glutamate.

CONCLUSIONS

Adequate supply of glucose to chondrocytes during conditions of inflammation and matrix degradation interrupts the detrimental inflammatory cycle and induces synthesis of hyaluronan, thereby promoting cartilage repair.

Rapid metabolic shifts occur during the transition between hunger and satiety in Drosophila melanogaster

Metabolites are active controllers of cellular physiology, but their role in complex behaviors is less clear. Here we report metabolic changes that occur during the transition between hunger and satiety in Drosophila melanogaster. To analyze these data in the context of fruit fly metabolic networks, we developed Flyscape, an open-access tool. We show that in response to eating, metabolic profiles change in quick, but distinct ways in the heads and bodies. Consumption of a high sugar diet dulls the metabolic and behavioral differences between the fasted and fed state, and reshapes the way nutrients are utilized upon eating. Specifically, we found that high dietary sugar increases TCA cycle activity, alters neurochemicals, and depletes 1-carbon metabolism and brain health metabolites N-acetyl-aspartate and kynurenine. Together, our work identifies the metabolic transitions that occur during hunger and satiation, and provides a platform to study the role of metabolites and diet in complex behavior.

The relationship between metabolomic and behavioral changes is not well understood. Here, the authors analyze metabolome changes in D. melanogaster heads and bodies during hunger and satiety, and develop the Flyscape tool to visualize the resulting metabolic networks and integrate them with other omics data.

Metabolic control of gene transcription in non-alcoholic fatty liver disease: the role of the epigenome

Non-alcoholic fatty liver disease (NAFLD) is estimated to affect 24% of the global adult population. NAFLD is a major risk factor for the development of cirrhosis and hepatocellular carcinoma, as well as being strongly associated with type 2 diabetes and cardiovascular disease. It has been proposed that up to 88% of obese adults have NAFLD, and with global obesity rates increasing, this disease is set to become even more prevalent. Despite intense research in this field, the molecular processes underlying the pathology of NAFLD remain poorly understood. Hepatic intracellular lipid accumulation may lead to dysregulated tricarboxylic acid (TCA) cycle activity and associated alterations in metabolite levels. The TCA cycle metabolites alpha-ketoglutarate, succinate and fumarate are allosteric regulators of the alpha-ketoglutarate-dependent dioxygenase family of enzymes. The enzymes within this family have multiple targets, including DNA and chromatin, and thus may be capable of modulating gene transcription in response to intracellular lipid accumulation through alteration of the epigenome. In this review, we discuss what is currently understood in the field and suggest areas for future research which may lead to the development of novel preventative or therapeutic interventions for NAFLD.

The brominated flame retardant BDE 47 upregulates purine metabolism and mitochondrial respiration to promote adipocyte differentiation

Adipocyte differentiation is closely associated with obesity and obesity-induced metabolic disorders. Epidemiological studies have demonstrated the association of obesity with environmental pollutants, such as polybrominated diphenyl ethers (PBDEs), common flame retardants in various consumer products. However, their obesogenic effects and mechanism are underexplored. We employed non-targeted metabolomics studies based on liquid chromatography-high resolution mass spectrometry to determine how 2,2',4,4'-tetra-brominated biphenyl ether (BDE 47), one of the main congeners of PBDEs detected in human tissue, promotes adipocyte differentiation of mouse preadipocyte 3 T3-L1 cells. The promoting effects of BDE 47 exposure (5 or 10 μM) on adipocyte differentiation were confirmed by enhancing lipid accumulation and expression levels of biomarkers of adipogenesis. For the first time, we demonstrated that BDE 47 upregulated purine metabolism and altered glutathione metabolism to promote oxidative stress and uric acid production in adipocytes. BDE 47 also elevated mitochondrial respiration and glycolysis in adipocytes to induce more ATP to combat oxidative stress. Antioxidant treatments, including the suppression of xanthine oxidase, inhibited the effects of BDE 47 on inducing oxidative stress and lipid accumulation. BDE 47 may be a potential environmental obesogen by providing a permissive oxidative environment to induce adipocyte differentiation.

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.

Mammary cell proliferation and catabolism of adipose tissues in nutrition-restricted lactating sows were associated with extracellular high glutamate levels

Background

Persistent lactation, as the result of mammary cellular anabolism and secreting function, is dependent on substantial mobilization or catabolism of body reserves under nutritional deficiency. However, little is known about the biochemical mechanisms for nutrition-restricted lactating animals to simultaneously maintain the anabolism of mammary cells while catabolism of body reserves. In present study, lactating sows with restricted feed allowance (RFA) (n = 6), 24% feed restriction compared with the control (CON) group (n = 6), were used as the nutrition-restricted model. Microdialysis and mammary venous cannulas methods were used to monitor postprandial dynamic changes of metabolites in adipose and mammary tissues.

Results

At lactation d 28, the RFA group showed higher (P < 0.05) loss of body weight and backfat than the CON group. Compared with the CON group, the adipose tissue of the RFA group had higher (P < 0.05) extracellular glutamate and insulin levels, increased (P < 0.05) lipolysis related genes (HSL and ATGL) expression, and decreased (P < 0.05) glucose transport and metabolism related genes (VAMP8, PKLR and LDHB) expression. These results indicated that under nutritional restriction, reduced insulin-mediated glucose uptake and metabolism and increased lipolysis in adipose tissues was related to extracellular high glutamate concentration. As for mammary glands, compared with the CON group, the RFA group had up-regulated (P < 0.05) expression of Notch signaling ligand (DLL3) and receptors (NOTCH2 and NOTCH4), higher (P < 0.05) extracellular glutamate concentration, while expression of cell proliferation related genes and concentrations of most metabolites in mammary veins were not different (P > 0.05) between groups. Accordingly, piglet performance and milk yield did not differ (P > 0.05) between groups. It would appear that activation of Notch signaling and adequate supply of glutamate might assist mammogenesis.

Conclusions

Mammary cell proliferation and catabolism of adipose tissues in nutrition-restricted lactating sows were associated with extracellular high glutamate levels.

Electronic supplementary material

The online version of this article (10.1186/s40104-018-0293-6) contains supplementary material, which is available to authorized users.

Hypoxanthine Secretion from Human Adipose Tissue and its Increase in Hypoxia

OBJECTIVE

The production of uric acid in murine white adipose tissue (mWAT), and that such production was augmented in obese mice, was recently reported. However, little is known about the secretion of metabolites associated with purine catabolism in human WAT (hWAT). The present study analyzed this in hWAT.

METHODS

Freshly isolated hWAT and mWAT were cultured. The secretion of metabolites associated with purine catabolism was measured. Tissue distribution profiles of genes associated with purine metabolism and metabolite profiling of adipocytes in hypoxia were analyzed.

RESULTS

Secretion of hypoxanthine from hWAT was higher than those of xanthine and uric acid. On the other hand, secretion of uric acid was relatively higher than xanthine and hypoxanthine in mWAT. Xanthine oxidoreductase (XOR) mRNA expression levels in hWAT were markedly lower than that in the human liver. In murine tissues, XOR mRNA expression levels in mWAT were comparable with those in the liver. Cultured human adipocytes secreted hypoxanthine, and its secretion was increased under hypoxia. The metabolic analysis of human adipocytes showed that hypoxia increased metabolites associated with de novo biosynthesis of purine nucleotides.

CONCLUSIONS

The present study revealed that hypoxanthine was secreted from human adipose tissue, and the secretion might be increased in local hypoxia.

Metabolomic and microarray analyses of adipose tissue of dapagliflozin-treated mice, and effects of 3-hydroxybutyrate on induction of adiponectin in adipocytes

Sodium/glucose cotransporter 2 (SGLT2) inhibitor improves systemic glucose metabolism. To clarify the effect of dapagliflozin, we performed gene expression microarray and metabolomic analyses of murine adipose tissue. Three groups of mice were used; non-diabetic control KK mice (KK), diabetic KKAy mice (KKAy), and KKAy mice treated with dapagliflozin (KKAy + Dapa). Plasma glucose levels were significantly reduced in KKAy + Dapa compared with KKAy. Food consumption was larger in KKAy + Dapa than KKAy, and there were no significant differences in body and adipose tissue weight among the groups. Metabolomic analysis showed higher levels of many intermediate metabolites of the glycolytic pathway and TCA cycle in KKAy than KK, albeit insignificantly. Dapagliflozin partially improved accumulation of glycolytic intermediate metabolites, but not intermediate metabolites of the TCA cycle, compared with KKAy. Interestingly, dapagliflozin increased plasma and adipose 3-hydroxybutyric acid (3-HBA) levels. Microarray analysis showed that adipocytokines were downregulated in KKAy compared with KK mice, and upregulated by dapagliflozin. In vitro, 3-HBA induced β-hydroxybutyrylation of histone H3 at lysine 9 and upregulation of adiponectin in 3T3-L1 adipocytes independent of their acetylation or methylation. Our results suggest that 3-HBA seems to provide protection through epigenetic modifications of adiponectin gene in adipocytes.

Regulatory Roles of Invariant Natural Killer T Cells in Adipose Tissue Inflammation: Defenders Against Obesity-Induced Metabolic Complications

Adipose tissue is a metabolic organ that plays a central role in controlling systemic energy homeostasis. Compelling evidence indicates that immune system is closely linked to healthy physiologic functions and pathologic dysfunction of adipose tissue. In obesity, the accumulation of pro-inflammatory responses in adipose tissue subsequently leads to dysfunction of adipose tissue as well as whole body energy homeostasis. Simultaneously, adipose tissue also activates anti-inflammatory responses in an effort to reduce the unfavorable effects of pro-inflammation. Notably, the interplay between adipocytes and resident invariant natural killer T (iNKT) cells is a major component of defensive mechanisms of adipose tissue. iNKT cells are leukocytes that recognize lipids loaded on CD1d as antigens, whereas most other immune cells are activated by peptide antigens. In adipose tissue, adipocytes directly interact with iNKT cells by presenting lipid antigens and stimulate iNKT cell activation to alleviate pro-inflammation. In this review, we provide an overview of the molecular and cellular determinants of obesity-induced adipose tissue inflammation. Specifically, we focus on the roles of iNKT cell-adipocyte interaction in maintaining adipose tissue homeostasis as well as the consequent modulation in systemic energy metabolism. We also briefly discuss future research directions regarding the interplay between adipocytes and adipose iNKT cells in adipose tissue inflammation.

Substantial Metabolic Activity of Human Brown Adipose Tissue during Warm Conditions and Cold-Induced Lipolysis of Local Triglycerides

Current understanding of in vivo human brown adipose tissue (BAT) physiology is limited by a reliance on positron emission tomography (PET)/computed tomography (CT) scanning, which has measured exogenous glucose and fatty acid uptake but not quantified endogenous substrate utilization by BAT. Six lean, healthy men underwent ¹⁸fluorodeoxyglucose-PET/CT scanning to localize BAT so microdialysis catheters could be inserted in supraclavicular BAT under CT guidance and in abdominal subcutaneous white adipose tissue (WAT). Arterial and dialysate samples were collected during warm (∼25°C) and cold exposure (∼17°C), and blood flow was measured by ¹³³xenon washout. During warm conditions, there was increased glucose uptake and lactate release and decreased glycerol release by BAT compared with WAT. Cold exposure increased blood flow, glycerol release, and glucose and glutamate uptake only by BAT. This novel use of microdialysis reveals that human BAT is metabolically active during warm conditions. BAT activation substantially increases local lipolysis but also utilization of other substrates such as glutamate.

Robust Regression Analysis of GCMS Data Reveals Differential Rewiring of Metabolic Networks in Hepatitis B and C Patients

About one in 15 of the world’s population is chronically infected with either hepatitis virus B (HBV) or C (HCV), with enormous public health consequences. The metabolic alterations caused by these infections have never been directly compared and contrasted. We investigated groups of HBV-positive, HCV-positive, and uninfected healthy controls using gas chromatography-mass spectrometry analyses of their plasma and urine. A robust regression analysis of the metabolite data was conducted to reveal correlations between metabolite pairs. Ten metabolite correlations appeared for HBV plasma and urine, with 18 for HCV plasma and urine, none of which were present in the controls. Metabolic perturbation networks were constructed, which permitted a differential view of the HBV- and HCV-infected liver. HBV hepatitis was consistent with enhanced glucose uptake, glycolysis, and pentose phosphate pathway metabolism, the latter using xylitol and producing threonic acid, which may also be imported by glucose transporters. HCV hepatitis was consistent with impaired glucose uptake, glycolysis, and pentose phosphate pathway metabolism, with the tricarboxylic acid pathway fueled by branched-chain amino acids feeding gluconeogenesis and the hepatocellular loss of glucose, which most probably contributed to hyperglycemia. It is concluded that robust regression analyses can uncover metabolic rewiring in disease states.