Metabolic Perturbation Associated With COVID-19 Disease Severity and SARS-CoV-2 Replication.

Viruses hijack host metabolic pathways for their replicative advantage. In this study, using patient-derived multiomics data and in vitro infection assays, we aimed to understand the role of key metabolic pathways that can regulate severe acute respiratory syndrome coronavirus-2 reproduction and their association with disease severity. We used multiomics platforms (targeted and untargeted proteomics and untargeted metabolomics) on patient samples and cell-line models along with immune phenotyping of metabolite transporters in patient blood cells to understand viral-induced metabolic modulations. We also modulated key metabolic pathways that were identified using multiomics data to regulate the viral reproduction in vitro. Coronavirus disease 2019 disease severity was characterized by increased plasma glucose and mannose levels. Immune phenotyping identified altered expression patterns of carbohydrate transporter, glucose transporter 1, in CD8+ T cells, intermediate and nonclassical monocytes, and amino acid transporter, xCT, in classical, intermediate, and nonclassical monocytes. In in vitro lung epithelial cell (Calu-3) infection model, we found that glycolysis and glutaminolysis are essential for virus replication, and blocking these metabolic pathways caused significant reduction in virus production. Taken together, we therefore hypothesized that severe acute respiratory syndrome coronavirus-2 utilizes and rewires pathways governing central carbon metabolism leading to the efflux of toxic metabolites and associated with disease severity. Thus, the host metabolic perturbation could be an attractive strategy to limit the viral replication and disease severity.

Genetically Higher Level of Mannose Has No Impact on Cardiometabolic Risk Factors: Insight from Mendelian Randomization.

Background: There is a handful of controversial data from observational studies on the serum levels of mannose and risks of coronary artery disease (CAD) and other cardiometabolic risk factors. We applied Mendelian Randomization (MR) analysis to obtain estimates of the causal effect of serum mannose on the risk of CAD and on cardiometabolic risk factors. Methods: Two-sample MR was implemented by using summary-level data from the largest genome-wide association studies (GWAS) conducted on serum mannose and CAD and cardiometabolic risk factors. The inverse variance weighted method (IVW) was used to estimate the effects, and a sensitivity analysis including the weighted median (WM)-based method, MR-Egger, MR-Pleiotropy RESidual Sum and Outlier (PRESSO) were applied. Radial MR Methods was applied to remove outliers subject to pleiotropic bias. We further conducted a leave-one-out analysis. Results: Mannose had no significant effect on CAD (IVW: odds ratio: 0.96 (95% Confidence Interval (95%CI): 0.71-1.30)), total cholesterol (TC) (IVW: 95%CI: 0.60-1.08), low density lipoprotein (LDL) (IVW: 95%CI = 0.68-1.15), high density lipoprotein (HDL) (IVW: 95%CI = 0.85-1.20), triglycerides (TG) (IVW: 95%CI = 0.38-1.08), waist circumference (WC) (IVW: 95%CI = 0.94-1.37), body mass index (BMI) (IVW: 95%CI = 0.93-1.29) and fasting blood glucose (FBG) (IVW: 95%CI = 0.92-1.33), with no heterogeneity for CAD, HDL, WC and BMI (all p > 0.092), while a significant heterogeneity was observed for TC (IVW: Q = 44.503), LDL (IVW: Q = 33.450), TG (IVW: Q = 159.645) and FBG (IVW: Q = 0. 32.132). An analysis of MR-PRESSO and radial plots did not highlight any outliers. The results of the leave-one-out method demonstrated that the links were not driven by a single instrument. Conclusions: We did not find any effect of mannose on adiposity, glucose, TC, LDL, TG and CAD.

Associations between serum lipids and mannose levels in coronary artery disease among nondiabetic patients.

Aim: Nondiabetic patients have been studied to determine whether modest elevations in plasma mannose levels may be associated with a greater incidence of coronary artery disease (CAD). Materials & methods: The plasma mannose, lipids (triglyceride, low-density lipoprotein, high-density lipoprotein, very low-density lipoprotein) and lactate dehydrogenase levels were successfully evaluated with respect to subsequent CAD using records of 120 nondiabetic patients and 120 healthy volunteers. CAD was identified from myocardial infarction and new diagnoses of angina. Results: Of 120 patients studied, the plasma mannose, triglyceride, lactate dehydrogenase and very low-density lipoprotein levels of patients were significantly higher than control groups. Conclusion: Our findings showed that elevated baseline mannose in plasma was associated with a progressive risk of CAD with time.

Triangulating evidence from longitudinal and Mendelian randomization studies of metabolomic biomarkers for type 2 diabetes.

The number of people affected by Type 2 diabetes mellitus (T2DM) is close to half a billion and is on a sharp rise, representing a major and growing public health burden. Given its mild initial symptoms, T2DM is often diagnosed several years after its onset, leaving half of diabetic individuals undiagnosed. While several classical clinical and genetic biomarkers have been identified, improving early diagnosis by exploring other kinds of omics data remains crucial. In this study, we have combined longitudinal data from two population-based cohorts CoLaus and DESIR (comprising in total 493 incident cases vs. 1360 controls) to identify new or confirm previously implicated metabolomic biomarkers predicting T2DM incidence more than 5 years ahead of clinical diagnosis. Our longitudinal data have shown robust evidence for valine, leucine, carnitine and glutamic acid being predictive of future conversion to T2DM. We confirmed the causality of such association for leucine by 2-sample Mendelian randomisation (MR) based on independent data. Our MR approach further identified new metabolites potentially playing a causal role on T2D, including betaine, lysine and mannose. Interestingly, for valine and leucine a strong reverse causal effect was detected, indicating that the genetic predisposition to T2DM may trigger early changes of these metabolites, which appear well-before any clinical symptoms. In addition, our study revealed a reverse causal effect of metabolites such as glutamic acid and alanine. Collectively, these findings indicate that molecular traits linked to the genetic basis of T2DM may be particularly promising early biomarkers.

Association of Serum Mannose With Acute Respiratory Distress Syndrome Risk and Survival.

Importance: Acute respiratory distress syndrome (ARDS) confers high mortality risk among critically ill patients. Identification of biomarkers associated with ARDS risk may guide clinical diagnosis and prognosis. Objective: To systematically evaluate the association of blood metabolites with ARDS risk and survival. Design, Setting, and Participants: In this cohort study, data from the Molecular Epidemiology of ARDS (MEARDS) study, a prospective cohort of 403 patients with ARDS and 1227 non-ARDS controls, were analyzed. Patients were recruited in intensive care units (ICUs) at Massachusetts General Hospital and Beth Israel Deaconess Medical Center, both in Boston, Massachusetts, from January 1, 1998, to December 31, 2014. Data analysis was performed from December 9, 2018, to January 4, 2019. Main Outcomes and Measures: Participants were followed up daily for ARDS development defined by Berlin criteria, requiring fulfillment of chest radiograph and oxygenation criteria on the same calendar day during invasive ventilatory assistance. A 2-stage study design was used to explore novel metabolites associated with ARDS risk and survival. Results: Of the 1630 participants from MEARDS who were admitted to the ICU , 403 (24.7%) were diagnosed with ARDS (mean [SD] age, 63.0 [17.0] years; 251 [62.3%] male) and 1227 (75.3%) were at-risk but did not have ARDS (mean [SD] age, 62.3 [16.9] years; 753 [61.4%] male). Mendelian randomization suggested that genetically regulated serum mannose was associated with ARDS risk (odds ratio [OR], 0.64; 95% CI, 0.53-0.78; P = 7.46 × 10-6) in the discovery stage. In the functional validation stage incorporating 83 participants with ARDS and matched at-risk participants in the control group from the ICU, the protective association of mannose with ARDS risk was validated (OR, 0.67; 95% CI, 0.46-0.97; P = .03). Furthermore, serum mannose was associated with 28-day (OR, 0.25; 95% CI, 0.11-0.56; P = 6.95 × 10-4) and 60-day (OR, 0.36; 95% CI, 0.19-0.71; P = 3.12 × 10-3) mortality and 28-day (hazard ratio, 0.49; 95% CI, 0.32-0.74; P = 6.41 × 10-4) and 60-day (hazard ratio, 0.55; 95% CI, 0.37-0.80; P = 2.11 × 10-3) survival. Conclusions and Relevance: In this study, genetically regulated serum mannose appeared to be associated with ARDS risk and outcome, and increased serum mannose at admission was associated with reduced ARDS risk and better survival. These findings could inform prevention and clinical intervention in ARDS cases, which have increased with the expansion of the coronavirus disease 2019 pandemic.

The effect of circuit resistance training on plasma levels of amino acids, alpha-hydroxybutyrate, mannose, and urinary levels of glycine conjugated adducts in obese adolescent boys.

Few studies have examined the improving effects of exercise on the association between metabolites of impaired protein metabolism and insulin resistance in obese children. Therefore, this study aims to investigate the effect of circuit resistance training (CRT) on plasma levels of amino acids, alpha-hydroxybutyrate (α-HB), mannose, and urinary levels of glycine conjugated adducts in obese adolescent boys. Forty obese adolescent boys (body mass index above the 95th percentile) with an age range of 14-17 years were randomly divided into the CRT group (n = 20) and control group (n = 20). The CRT program (3 times/week, 70%-80% of 1-repetition maximum) was performed for 8 weeks. The results indicated that the body composition and plasma levels of glucose, insulin resistance, valine, mannose, lysine, and the sum of branched-chain amino acids (BCAA) were decreased because of CRT. The plasma levels of asparagine, glycine, serine, and urinary levels of glycine conjugated adduct also increased in the CRT group. Although α-HB level decreased during CRT, it had no significant difference from that of the control group. It can be concluded that the improvement in obesity complications including insulin resistance in obese adolescent boys after CRT may be due to decrease in plasma levels of mannose and BCAA and increase urinary metabolites. Novelty: CRT improves glucose metabolism and insulin resistance in obese adolescent boys. CRT decreases plasma levels of mannose and BCAA and normalizes other amino acids. CRT increases urinary levels of glycine conjugated adducts.

Molecular and Biochemical Parameters Related to Plasma Mannose Levels in Coronary Artery Disease Among Nondiabetic Patients.

Aims: Nondiabetic patients were studied to determine whether modest elevations in plasma mannose may be associated with a greater incidence of coronary artery disease (CAD). Materials and Methods: Plasma insulin, mannose, glucose, hexokinase 1-2, GLUT1-GLUT4 levels, and serum mannose phosphate isomerase enzyme levels were evaluated with respect to subsequent CAD using records from 120 nondiabetic CAD patients and 120 healthy volunteers. CAD was identified from myocardial infarction and new diagnoses of angina. Results: Of 120 nondiabetic CAD patients studied, their plasma GLUT4 and HK1 levels were significantly lower than those of the control group. In addition, a significant increase in plasma mannose levels was found in the patient group compared to the control group. Conclusion: Our findings showed that elevated baseline mannose levels in plasma are associated with an increased risk of CAD over time.

Predictive Modeling of Type 1 Diabetes Stages Using Disparate Data Sources.

This study aims to model genetic, immunologic, metabolomics, and proteomic biomarkers for development of islet autoimmunity (IA) and progression to type 1 diabetes in a prospective high-risk cohort. We studied 67 children: 42 who developed IA (20 of 42 progressed to diabetes) and 25 control subjects matched for sex and age. Biomarkers were assessed at four time points: earliest available sample, just prior to IA, just after IA, and just prior to diabetes onset. Predictors of IA and progression to diabetes were identified across disparate sources using an integrative machine learning algorithm and optimization-based feature selection. Our integrative approach was predictive of IA (area under the receiver operating characteristic curve [AUC] 0.91) and progression to diabetes (AUC 0.92) based on standard cross-validation (CV). Among the strongest predictors of IA were change in serum ascorbate, 3-methyl-oxobutyrate, and the PTPN22 (rs2476601) polymorphism. Serum glucose, ADP fibrinogen, and mannose were among the strongest predictors of progression to diabetes. This proof-of-principle analysis is the first study to integrate large, diverse biomarker data sets into a limited number of features, highlighting differences in pathways leading to IA from those predicting progression to diabetes. Integrated models, if validated in independent populations, could provide novel clues concerning the pathways leading to IA and type 1 diabetes.

Mannose is an insulin-regulated metabolite reflecting whole-body insulin sensitivity in man.

Mannose is a glucose-associated serum metabolite mainly released by the liver. Recent studies have shown several unexpected pleiotropic effects of mannose including increased regulatory T cells (Tregs), prevention of auto-immune disease and ability to reduce growth of human cancer cells. We have previously shown in large cohorts that elevated serum mannose levels are associated with future development of type 2 diabetes (T2D) and cardiovascular disease. However, potential direct effects of mannose on insulin sensitivity in vivo or in vitro are unknown. We here show that administration of mannose (0.1 g/kg BW twice daily) for one week in man did not elicit negative effects on meal-modified glucose tolerance, markers of inflammation or insulin levels. Tregs number and insulin signaling in human liver cells were unchanged. These data suggest that mannose is a marker, and not a mediator, of insulin resistance. To verify this, we examined serum mannose levels during long-term euglycemic hyperinsulinemic clamps in non-diabetic and T2D individuals. Mannose was reduced by insulin infusion in proportion to whole-body insulin sensitivity. Thus, mannose is a biomarker of insulin resistance which may be useful for the early identification of diabetic individuals with insulin resistance and increased risk of its complications.

Distinct Gut Microbiota and Serum Metabolites in Response to Weight Loss Induced by Either Dairy or Exercise in a Rodent Model of Obesity.

Energy imbalance is a primary cause of obesity. While the classical approach to attenuate weight gain includes an increase in energy expenditure through exercise, dietary manipulation such as the inclusion of dairy products has also been proven effective. In the present study, we explored the potential mechanisms by which dairy and exercise attenuate weight gain in diet-induced obese rats. Male Sprague-Dawley rats were fed a high fat, high-sugar (HFHS) diet to induce obesity for 8 weeks. Rats were then further grouped into either control (HFHS + casein) or dairy diet (HFHS + nonfat skim milk) with and without treadmill exercise for 6 weeks. Serum and fresh fecal samples were collected for gut microbiota, serum metabolomics, and metallomics analysis. Diet and exercise resulted in distinct separation in both gut microbiota and serum metabolite profiles. Most intriguingly, obesogenic bacteria including Desulfovibrio and Oribacterium were reduced, and bioactive molecules such as mannose and arginine were significantly increased in the dairy group. Correlations of at least six bacterial genera with serum metal ions and metabolites were also found. Results reveal distinct impacts of dairy and exercise on the gut microbiota and in the modulation of circulating metabolites with the former primarily responsible for driving microbial alterations known to attenuate weight gain.

Quantification of d-mannose in plasma: Development and validation of a reliable and accurate HPLC-MS-MS method.

The present paper describes the development and the validation process - in compliance with the EMA guidelines - of a method based on tandem mass spectrometry coupled to liquid chromatography for the accurate quantification of mannose in human plasma samples. The quick sample preparation procedure, simplified by the absence of any derivatization step, makes the assay suitable for routine use in a clinical chemistry laboratory. The method validation yielded satisfactory selectivity, with a good separation of mannose from its epimers (glucose and galactose), linearity over the whole concentration range of interest (0.31-40 µg/mL), reproducibility with RSD <10%, and accuracy in the range 96-104%. Instrumental LLOD (0.31 µg/mL) and LLOQ (1.25 µg/mL) were good enough to detect endogenous plasma mannose levels and in agreement with recent data from the literature. Sensitivity was affected by a 5-fold dilution factor, which, if necessary, can be reduced. The method robustness was proven in >600 injections, most of them being of plasma samples, used also to assess the reference ranges in healthy subjects (9.93 ±â€¯3.37 µg/mL) and type 2 diabetic patients (23.47 ±â€¯6.19 µg/mL).

Detection of the tuberculosis biomarker mannose-capped lipoarabinomannan in human serum: Impact of sample pretreatment with perchloric acid.

The development of an accurate and rapid diagnostic test for tuberculosis (TB) to use at point of need is vital to efforts aimed at reducing the global burden from this disease. This paper builds on our previous studies of mannose-capped lipoarabinomannan (ManLAM) as a serum biomarker for active TB infection by means of a heterogeneous immunoassay. That work found that complexation with components in serum (e.g., proteins) sterically hindered the capture and/or labeling of ManLAM in an immunoassay at levels <10 ng mL-1, compromising the clinical utility of this biomarker for detection of active TB infection. We also showed that the acidification of ManLAM-containing serum samples with perchloric acid improved the detectability of ManLAM by 250× by complex disruption when compared to measurements of untreated serum. The present study examined what effects the PCA treatment of serum samples may have on the recovery and structural integrity of ManLAM, owing to its potential susceptibility to acid hydrolysis. Recovery was assessed with an enzyme-linked immunosorbent assay (ELISA). The possible impact of acid hydrolysis on the ManLAM structure was investigated by gas chromatography-mass spectrometry and carbohydrate chemical degradation methods. The ELISA study indicated that while the signal strength for ManLAM in the serum spike-in experiments was significantly stronger after PCA pretreatment when compared to untreated human serum, it was only ∼20% of the ManLAM measured in physiological buffer. This loss in detectability was shown by structural analysis to arise mainly from the acid-induced degradation of the arabinan domains of ManLAM that are targeted by antibodies used for antigen capture and/or tagging. The implications of these findings in terms of the detection of this important biomarker for TB are also discussed.

Plasma Mannose Levels Are Associated with Incident Type 2 Diabetes and Cardiovascular Disease.

Plasma mannose levels are elevated in subjects with insulin resistance independently of obesity. Here, we found that elevated plasma mannose levels are strong markers of future risk of several chronic diseases including T2D, CVD, and albuminuria, and that it may contribute to their development rather than just being a novel biomarker.

Global and targeted serum metabolic profiling of colorectal cancer progression.

BACKGROUND: Patients with colorectal adenoma polyps (PLPs) are at higher risk for developing colorectal cancer (CRC). However, the development of improved and robust biomarkers to enable the screening, surveillance, and early detection of PLPs and CRC continues to be a challenge. The aim of this study was to identify biomarkers of progression to CRC through metabolomic profiling of human serum samples with a multistage approach. METHODS: Metabolomic profiling was conducted with the Metabolon platform for 30 CRC patients, 30 PLP patients, and 30 control subjects, and this was followed by the targeted validation of the top metabolites in an additional set of 50 CRC patients, 50 PLP patients, and 50 controls with liquid chromatography-tandem mass spectrometry. Unconditional multivariate logistic regression models, adjusted for covariates, were used to evaluate associations with PLP and CRC risk. RESULTS: For the discovery phase, 404 serum metabolites were detected, with 50 metabolites showing differential levels between CRC patients, PLP patients, and controls (P for trend < .05). After validation, the 3 top metabolites (xanthine, hypoxanthine, and d-mannose) were validated: lower levels of xanthine and hypoxanthine and higher levels of d-mannose were found in PLP and CRC cases versus controls. A further exploratory analysis of metabolic pathways revealed key roles for the urea cycle and caffeine metabolism associated with PLP and CRC risk. In addition, a joint effect of the top metabolites with smoking and a significant interaction with the body mass index were observed. An analysis of the ratio of hypoxanthine levels to xanthine levels indicated an association with CRC progression. CONCLUSIONS: These results suggest the potential utility of circulating metabolites as novel biomarkers for the early detection of CRC. Cancer 2017;123:4066-74. © 2017 American Cancer Society.

Effect of alprazolam on rat serum metabolic profiles.

We developed a serum metabolomic method by gas chromatography-mass spectrometry (GC-MS) to evaluate the effect of alprazolam in rats. The GC-MS with HP-5MS (0.25 µm × 30 m × 0.25 mm) mass was conducted in electron impact ionization (EI) mode with electron energy of 70 eV, and full-scan mode with m/z 50-550. The rats were randomly divided to four groups, three alprazolam-treated groups and a control group. The alprazolam-treated rats were given 5, 10 or 20 mg/kg (low, medium, high) of alprazolam by intragastric administration each day for 14 days. The serum samples were corrected on the seventh and fourteenth days for metabolomic study. The blood was collected for biochemical tests. Then liver and brain were rapidly isolated and immersed for pathological study. Compared with the control group, on the seventh and fourteen days, the levels of d-glucose, 9,12-octadecadienoic acid, butanoic acid, l-proline, d-mannose and malic acid had changed, indicating that alprazolam induced energy metabolism, fatty acid metabolism and amino acid metabolism perturbations in rats. There was no significant difference for alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, urea and uric acid between controls and alprazolam groups. According to the pathological results, alprazolam is not hepatotoxic. Metabolomics could distinguish different alprazolam doses in rats.

Plasma mannose level, a putative indicator of glycogenolysis, and glucose tolerance in Japanese individuals.

AIMS/INTRODUCTION: Mannose is a monosaccharide constituent of glycoproteins and glycolipids. Experiments in rats have shown previously that the plasma mannose level decreases after glucose load, but does not decrease in diabetic rats, and that hepatic glycogenolysis is a source of this plasma mannose; however, these results are not fully elucidated in humans. Plasma mannose levels before/after glucose loading in humans with various degrees of glucose intolerance were examined to analyze their association with clinical factors. MATERIALS AND METHODS: The 75-g oral glucose tolerance test was carried out in Japanese individuals not taking diabetes medications. Participants were classified into normal glucose tolerance, impaired glucose metabolism and diabetes mellitus groups. Insulinogenic index as an index of insulin secretion, and Matsuda Index as an index of insulin sensitivity were calculated. Mannose was assayed by the established method using high-performance liquid chromatography after labeling. RESULTS: After glucose load, the plasma mannose level decreased gradually in the normal glucose tolerance group, but did not decrease in the diabetes mellitus group. Plasma mannose changes during 120 min from baseline (M120 -M0 ) were significantly different among the three groups (normal glucose tolerance: -16.7 ± 1.7; impaired glucose metabolism: -9.0 ± 1.9; diabetes mellitus: -1.4 ± 1.8 µmol/L [n = 25 in each group], P < 0.0001). Plasma glucose 120 min after glucose loading (R2  = 0.412) or loge -insulinogenic index, loge -Matsuda Index and age (R2  = 0.230) were determinants of M120 -M0 in multiple regression analyses. CONCLUSIONS: We clarified the relationship between plasma mannose level and glucose tolerance in humans. The present results are compatible with those using rats, in which mannose derived from glycogenolysis plays an important role in the alteration of mannose levels after glucose loading.

D-mannose: a novel prognostic biomarker for patients with esophageal adenocarcinoma.

Metabolomic profiling is a promising approach to identify new biomarkers for cancer prognosis. However, the role of circulating metabolites as prognostic indicators in esophageal adenocarcinoma (EAC) has not been well explored. In this study, we aimed to evaluate the prognostic value of three serum metabolites, d-mannose, l-proline (LP), and 3-hydroxybutyrate (BHBA), which were significantly different between EAC patients and controls, identified through a global and targeted metabolite profiling. We measured the levels of d-mannose, LP, and BHBA in pretreatment serum from 159 EAC patients, using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) methods. A multivariable Cox model was used to estimate the hazard ratios (HRs) and 95% confidence intervals (95% CIs) for the association of these metabolites with recurrence and overall survival. We found that serum levels of d-mannose were significantly associated with recurrence and overall survival in EAC patients, whereas levels of LP and BHBA were not. Compared with patients with a low (first tertile) level of d-mannose, those with a high (second plus third tertiles) level had 49% reduced risk of recurrence (HR = 0.51; 95% CI: 0.29-0.91; P = 0.02), and 56% reduced risk of death (HR = 0.44; 95% CI: 0.25-0.77, P < 0.01). The significant association of high d-mannose levels with better prognosis was consistent among patients with early-stage and advanced-stage EAC. Our results suggest that serum level of d-mannose may be used as a novel prognostic biomarker for patients with EAC. Further studies in independent populations are warranted to confirm our findings.

Carbohydrate composition of circulating multiple-modified low-density lipoprotein.

Atherogenic modification of low-density lipoprotein (LDL) plays a crucial role in the pathogenesis of atherosclerosis, as modified LDL, but not native LDL, induces pronounced accumulation of cholesterol and lipids in the arterial wall. It is likely that LDL particles undergo multiple modifications in human plasma: desialylation, changes in size and density, acquisition of negative electric charge, oxidation, and complex formation. In a total LDL preparation isolated from pooled plasma of patients with coronary atherosclerosis and from healthy subjects, two subfractions of LDL could be identified: desialylated LDL bound by a lectin affinity column and normally sialylated (native) LDL that passed through the column. The desialylated LDL subfraction therefore represents circulating modified LDL. In this work, we performed a careful analysis of LDL particles to reveal changes in the composition of glycoconjugates associated with proteins and lipids. Protein fraction of LDL from atherosclerotic patients contained similar amounts of glucosamine, galactose, and mannose, but a 1.6-fold lower level of sialic acid as compared to healthy donors. Lipid-bound glycoconjugates of total LDL from patients with coronary atherosclerosis contained 1.5-2-fold less neutral monosaccharides than total LDL from healthy donors. Patient-derived LDL also contained significantly less sialic acid. Our results demonstrate that carbohydrate composition of LDL from atherosclerotic patients was altered in comparison to healthy controls. In particular, prominent decrease in the sialic acid content was observed. This strengthens the hypothesis of multiple modification of LDL particles in the bloodstream and underscores the clinical importance of desialylated LDL as a possible marker of atherosclerosis progression.

Integrated Network Analysis Reveals an Association between Plasma Mannose Levels and Insulin Resistance.

To investigate the biological processes that are altered in obese subjects, we generated cell-specific integrated networks (INs) by merging genome-scale metabolic, transcriptional regulatory and protein-protein interaction networks. We performed genome-wide transcriptomics analysis to determine the global gene expression changes in the liver and three adipose tissues from obese subjects undergoing bariatric surgery and integrated these data into the cell-specific INs. We found dysregulations in mannose metabolism in obese subjects and validated our predictions by detecting mannose levels in the plasma of the lean and obese subjects. We observed significant correlations between plasma mannose levels, BMI, and insulin resistance (IR). We also measured plasma mannose levels of the subjects in two additional different cohorts and observed that an increased plasma mannose level was associated with IR and insulin secretion. We finally identified mannose as one of the best plasma metabolites in explaining the variance in obesity-independent IR.

Plasma High-Mannose and Complex/Hybrid N-Glycans Are Associated with Hypercholesterolemia in Humans and Rabbits.

N-glycans play important roles in various pathophysiological processes and can be used as clinical diagnosis markers. However, plasma N-glycans change and their pathophysiological significance in the setting of hypercholesterolemia, a major risk factor for atherosclerosis, is unknown. Here, we collected plasma from both hypercholesterolemic patients and cholesterol-fed hypercholesterolemic rabbits, and determined the changes in the whole-plasma N-glycan profile by electrospray ionization mass spectrometry. We found that both the hypercholesterolemic patients and rabbits showed a dramatic change in their plasma glycan profile. Compared with healthy subjects, the hypercholesterolemic patients exhibited higher plasma levels of a cluster of high-mannose and complex/hybrid N-glycans (mainly including undecorated or sialylated glycans), whereas only a few fucosylated or fucosylated and sialylated N-glycans were increased. Additionally, cholesterol-fed hypercholesterolemic rabbits also displayed increased plasma levels of high-mannose in addition to high complex/hybrid N-glycan levels. The whole-plasma glycan profiles revealed that the plasma N-glycan levels were correlated with the plasma cholesterol levels, implying that N-glycans may be a target for treatment of hypercholesterolemia.