Recent advances in mass spectrometry-based methodologies for static and kinetic study of lipid and lipoprotein metabolism

Les lipides s’associent aux apolipoprotéines pour former les lipoprotéines, nécessaires à leur transport au sein de l’organisme. Nombre de leurs perturbations métaboliques exposent à un risque élevé de maladies cardiovasculaires, et l’évolution de la spectrométrie de masse contribue au développement d’outils diagnostiques précoces de ces dérèglements. La découverte de marqueurs prédictifs des pathologies requiert néanmoins la compréhension fine des mécanismes physiologiques sous-jacents. L’analyse des flux métaboliques par l’utilisation de traceurs isotopiques permet l’accès à ces informations. Ces études demeurent cependant complexes et nécessitent le recours à plusieurs techniques d’analyses longues et coûteuses. L’objectif de ce travail a été de développer des approches originales basées sur la spectrométrie de masse afin d’élargir le champ de ces analyses, statiques comme dynamiques, au métabolisme lipidique. En combinant la protéolyse enzymatique et l’analyse ciblée de peptides signatures, nous avons considérablement simplifié et étendu l’étude des apolipoprotéines jusqu’à accéder simultanément à de nombreuses informations physiologiques telles que leurs concentrations, leurs taux de renouvellement et leurs éventuelles modifications polymorphiques. D’autres outils complémentaires, permettant l’étude ciblée ou non des lipides ainsi que la mesure de leurs enrichissements, ont également été développés afin d’accéder de façon efficace et sensible à leur caractérisation. Les limites de ces méthodes ont été explorées avant d’être appliquées à des études de cas concrets, portant sur des dyslipidémies ou l’efficacité de traitements hypolipémiants.Lipids bind to apolipoproteins to form lipoproteins, having in charge their transport into the circulation. Numerous metabolic disturbances of lipids expose to an increased risk of cardiovascular diseases. The last advances in mass spectrometry have recently helped to develop usefull tools for early diagnosis of these disorders. Nevertheless, the accurate characterization of predictive markers requires to decipher the physiological mechanisms involved in threir metabolism. Metabolic flux analyses with stable isotope labeled tracers can give such information. However, these studies remain complex, time-consuming and require the use of several technical processes. Therefore, we aimed to develop original mass spectrometry-based approaches to improve this kind of analyses. We have used enzymatic proteolysis and targeted analysis of specific peptides for the study of a large range of apolipoproteins. We were able to get simultaneaoulsy several physiological information such as their concentrations, kinetics and putative polymorphisms. Additional reliable tools, including both targeted and non-targeted lipid analyses as well as their enrichment measurements, have also been developed to improve our level of knowledge. The limitations of these methods were explored before to be applied to specific case studies, such as dyslipidemias (diabetes, hypertriglyceridemia, obesity) or efficacy of lipid-lowering treatments

Loss of phosphoethanolamine n-methyltransferases abolishes phosphatidylcholine synthesis and is lethal

Plants use several pathways to synthesize phosphatidylcholine (PC), the major phospholipid of eukaryotic cells. PC has important structural and signaling roles. One pathway plants use for synthesis is the phospho-base methylation pathway, which forms the head-group phosphocholine through the triple methylation of phosphoethanolamine (PEA) catalyzed by phosphoethanolamine N-methyltransferases (PEAMTs). Our understanding of that pathway and its physiological importance remains limited. We recently reported that disruption of Arabidopsis thaliana PEAMT1/NMT1 and PEAMT3/NMT3 induces severe PC deficiency leading to dwarfism and impaired development. However, the double nmt1 nmt3 knock-out mutant is viable. Here, we show that this is enabled by residual PEAMT activity through a third family member, NMT2. The triple nmt1 nmt2 nmt3 knock-out mutant cannot synthesize PC from PEA and is lethal. This shows that, unlike mammals and yeast, Arabidopsis cannot form PC from phosphatidyl ethanolamine (PE), and demonstrates that methylation of PEA is the sole, and vital, entry point to PC synthesis. We further show that Arabidopsis has evolved an expanded family of four nonredundant PEAMTs through gene duplication and alternate use of the NMT2 promoter. NMT2 encodes two PEAMT variants, which greatly differ in their ability to perform the initial phospho-base methylation of PEA. Five amino acids at the N terminus of PEAMTs are shown to each be critical for the catalysis of that step committing to PC synthesis. As a whole, these findings open new avenues for enzymatic engineering and the exploration of ways to better tune phosphocholine and PC synthesis to environmental conditions for improved plant performance

Circulating HDL and Non-HDL Associated Apolipoproteins and Breast Cancer Severity

Plasma lipids are carried within lipoproteins with various apolipoprotein content. This study evaluates the interest of measuring the apolipoproteins of circulating lipoproteins in breast cancer. Patients with early-stage breast cancer (n = 140) were included. Tumors differed by the expression of estrogen and progesterone receptor (HR− and HR+ for negative and positive expression) and the proliferation marker Ki-67 (≤20% or ≥30%). Apolipoprotein concentrations were determined in plasma, HDL and non-HDL fractions, and results are given in mg/dL, median (25th–75th). Patients did not differ in their plasma and lipoprotein lipid concentrations. HDL apoC-I and non-HDL apoC-II were reduced (1.34 (1.02–1.80) vs. 1.61 (1.32–2.04), p = 0.04; 0.31 (0.18–0.65) vs. 0.63 (0.39–1.02), p = 0.01; respectively), in RH-/high Ki-67 patients in comparison to RH-/low Ki-67 patients, while plasma apoD and HDL apoD were higher (3.24 (2.99–4.16) vs. 3.07 (2.39–3.51), p = 0.04; 2.74 (2.36–3.35) vs. 2.45 (2.01–2.99), p = 0.04; respectively). When RH+/high Ki-67 patients were compared with RH+/low Ki-67 patients, HDL apoC-I and HDL apoC-III were higher (1.56 (1.20–1.95) vs. 1.35 (1.10–1.62), p = 0.02; 2.80 (2.42–3.64) vs. 2.38 (1.69–2.96), p = 0.02; respectively). The distribution of exchangeable apolipoproteins, such as apoC-I, apoC-II, apoC-III, apoD, between lipoproteins is linked to the severity of breast cancer.Medicine, Faculty ofNon UBCMedicine, Department ofReviewedFacultyResearche

Spirulina Liquid Extract Protects against Fibrosis Related to Non-Alcoholic Steatohepatitis and Increases Ursodeoxycholic Acid

Non-alcoholic steatohepatitis (NASH) is characterized by an excess of lipids and oxidative stress in the liver. Spirulina was reported to possess hypolipemic and antioxidative effects and might counteract NASH development. C57Bl/6J mice were fed a western diet (WD) during 25 weeks with or without spirulina liquid extract (SLE) at 2 different doses (WDS1 and WDS2 groups) in drinking water. Liver histology, inflammation, and oxidative stress were assessed as well as glucose tolerance status, lipid metabolism, and gallbladder bile acid profile. WDS2 gained significantly less weight than WD. Liver weight-to-body weight ratio and plasma alanine aminotransferase were significantly lower in WDS2 mice. A reduced liver fibrosis and NFκBp65 protein expression were measured in the supplemented group as a lower accumulation of superoxide anion, nitric oxide, and thiobarbituric reactive substances. WDS2 mice showed also a preserved glucose tolerance, a strong decrease of plasma cholesterol, and a significant increase of gallbladder ursodeoxycholic acid and β-muricholic acid. Our findings demonstrate a protective effect of SLE against WD induced NASH that is related to less inflammation and oxidative stress, a preserved glucose tolerance, and less hepatotoxic bile acid profile

Late-Stage Glioma Is Associated with Deleterious Alteration of Gut Bacterial Metabolites in Mice

Brain-gut axis refers to the bidirectional functional connection between the brain and the gut, which sustains vital functions for vertebrates. This connection also underlies the gastrointestinal (GI) comorbidities associated with brain disorders. Using a mouse model of glioma, based on the orthotopic injection of GL261 cell line in syngeneic C57BL6 mice, we show that late-stage glioma is associated with GI functional alteration and with a shift in the level of some bacterial metabolites in the cecum. By performing cecal content transfer experiments, we further show that cancer-associated alteration in cecal metabolites is involved in end-stage disease progression. Antibiotic treatment results in a slight but significant delay in mice death and a shift in the proportion of myeloid cells in the brain tumor environment. This work rationally considers microbiota modulating strategies in the clinical management of patients with late-stage glioma

Bariatric Surgery Improves the Atherogenic Profile of Circulating Methylarginines in Obese Patients: Results from a Pilot Study

International audienceBariatric surgery improves obesity-related comorbidities. Methylarginines are biomarkers of cardiometabolic risk, liver steatosis, and insulin resistance. Here, we aimed to investigate methylarginines in obese patients undergoing bariatric surgery and compared them to age- and sex-matched healthy subjects. Thirty-one obese patients who underwent bariatric surgery and 31 healthy individuals were used for this retrospective study. The basal serum methylarginine levels were determined in the healthy individuals and the obese patients, before surgery and 6 and 12 months after surgery, by mass spectrometry. Compared with the healthy individuals, the obese patients displayed elevated monomethylarginine (mean change: +95%, p < 0.001), asymmetric-dimethylarginine (+105%, p < 0.001), symmetric-dimethylarginine (+25%, p = 0.003), and dimethylguanidino valerate (+32%, p = 0.008) concentrations. Bariatric surgery durably reduced the body mass index by 28% (12 months, 95%CI: 24–33, p = 0.002) and improved plasma lipids, insulin resistance, and liver function. Bariatric surgery reduced the serum levels of monomethylarginine and asymmetric-dimethylarginine by 12% (95%CI: 6–17) and 36% (95%CI: 27–45) (12 months, p = 0.003), respectively, but not symmetric-dimethylarginine or dimethylguanidino valerate. The monomethylarginine and asymmetric-dimethylarginine concentrations were strongly correlated with markers of dyslipidemia, insulin resistance, and a fatty liver. Serum dimethylguanidino valerate was primarily correlated with glycemia and renal function, whereas serum symmetric-dimethylarginine was almost exclusively associated with renal function. In conclusion, the monomethylarginine and asymmetric-dimethylarginine levels are efficiently decreased by bariatric surgery, leading to a reduced atherogenic profile in obese patients. Methylarginines follow different metabolic patterns, which could help for the stratification of cardiometabolic disorders in obese patients

A reference measurement of circulating ATPase inhibitory factor 1 (IF1) in humans by LC-MS/MS: Comparison with conventional ELISA

International audienceATPase inhibitory factor 1 (IF1) is a 9.5 kDa protein that binds to mitochondrial and plasma membrane ATP synthase and selectively inhibits ATP hydrolysis. Recently, IF1 was identified in systemic circulation in humans. IF1 appeared as an independent determinant of HDL-cholesterol with lower levels in coronary heart disease (CHD) patients. Moreover, IF1 was also found to negatively associate with mortality in these patients, supporting the notion that circulating IF1 could be a promising biomarker of cardiovascular disease. However, in previous studies, IF1 was quantified by a non-standardized competitive enzyme-linked immunosorbent assay (ELISA). Herein, we have validated a liquid chromatography-tandem mass spectrometry method (LC-MS/MS) enabling the accurate quantification of IF1 in human plasma. Plasma IF1 was trypsin-digested through an optimized procedure before LC-MS/MS analysis. The method was successfully validated over 4 independent experiments into the range of 100-1500 ng/mL. Intraand inter-assay variation coefficients had never exceeded 14.2% and accuracy ranged between 95% and 102% for the selected EAGGAFGK peptide marker. Subsequently, the results of the LC-MS/MS method were compared with those obtained using ELISA in 204 individuals from the GENES study. We found that IF1 plasma levels obtained using both techniques were strongly correlated (r = 0.89, p < 0.0001), while the Bland-Altman plot did not indicate any major statistically significant differences. To clinically validate LC-MS/MS, we confirmed the positive correlation between IF1 plasma levels and HDL-cholesterol (r = 0.38, p < 0.0001). Besides, we found lower IF1 plasma levels in CHD patients compared to controls (431 +/- 132 ng/mL and 555 +/- 173 ng/mL, respectively; p < 0.0001). Hence, it can be concluded that the presented LC-MS/MS analytical method provides a highly specific strategy for IF1 quantification in human plasma and could be proposed as a reference method

Late-Stage Glioma Is Associated with Deleterious Alteration of Gut Bacterial Metabolites in Mice

Brain-gut axis refers to the bidirectional functional connection between the brain and the gut, which sustains vital functions for vertebrates. This connection also underlies the gastrointestinal (GI) comorbidities associated with brain disorders. Using a mouse model of glioma, based on the orthotopic injection of GL261 cell line in syngeneic C57BL6 mice, we show that late-stage glioma is associated with GI functional alteration and with a shift in the level of some bacterial metabolites in the cecum. By performing cecal content transfer experiments, we further show that cancer-associated alteration in cecal metabolites is involved in end-stage disease progression. Antibiotic treatment results in a slight but significant delay in mice death and a shift in the proportion of myeloid cells in the brain tumor environment. This work rationally considers microbiota modulating strategies in the clinical management of patients with late-stage glioma