[2,4-13C]β-hydroxybutyrate Metabolism in Astrocytes and C6 Glioblastoma Cells

This study was undertaken to determine if the ketogenic diet could be useful for glioblastoma patients. The hypothesis tested was whether glioblastoma cells can metabolize ketone bodies. Cerebellar astrocytes and C6 glioblastoma cells were incubated in glutamine and serum free medium containing [2,4-13C]β-hydroxybutyrate (BHB) with and without glucose. Furthermore, C6 cells were incubated with [1-13C]glucose in the presence and absence of BHB. Cell extracts were analyzed by mass spectrometry and media by 1H magnetic resonance spectroscopy and HPLC. Using [2,4-13C]BHB and [1-13C]glucose it could be shown that C6 cells, in analogy to astrocytes, had efficient mitochondrial activity, evidenced by 13C labeling of glutamate, glutamine and aspartate. However, in the presence of glucose, astrocytes were able to produce and release glutamine, whereas this was not accomplished by the C6 cells, suggesting lack of anaplerosis in the latter. We hypothesize that glioblastoma cells kill neurons by not supplying the necessary glutamine, and by releasing glutamate

Evaluation and Characterization of Bacterial Metabolic Dynamics with a Novel Profiling Technique, Real-Time Metabolotyping

BACKGROUND: Environmental processes in ecosystems are dynamically altered by several metabolic responses in microorganisms, including intracellular sensing and pumping, battle for survival, and supply of or competition for nutrients. Notably, intestinal bacteria maintain homeostatic balance in mammals via multiple dynamic biochemical reactions to produce several metabolites from undigested food, and those metabolites exert various effects on mammalian cells in a time-dependent manner. We have established a method for the analysis of bacterial metabolic dynamics in real time and used it in combination with statistical NMR procedures. METHODOLOGY/PRINCIPAL FINDINGS: We developed a novel method called real-time metabolotyping (RT-MT), which performs sequential (1)H-NMR profiling and two-dimensional (2D) (1)H, (13)C-HSQC (heteronuclear single quantum coherence) profiling during bacterial growth in an NMR tube. The profiles were evaluated with such statistical methods as Z-score analysis, principal components analysis, and time series of statistical TOtal Correlation SpectroScopY (TOCSY). In addition, using 2D (1)H, (13)C-HSQC with the stable isotope labeling technique, we observed the metabolic kinetics of specific biochemical reactions based on time-dependent 2D kinetic profiles. Using these methods, we clarified the pathway for linolenic acid hydrogenation by a gastrointestinal bacterium, Butyrivibrio fibrisolvens. We identified trans11, cis13 conjugated linoleic acid as the intermediate of linolenic acid hydrogenation by B. fibrisolvens, based on the results of (13)C-labeling RT-MT experiments. In addition, we showed that the biohydrogenation of polyunsaturated fatty acids serves as a defense mechanism against their toxic effects. CONCLUSIONS: RT-MT is useful for the characterization of beneficial bacterium that shows potential for use as probiotic by producing bioactive compounds

Impact of kinetic isotope effects in isotopic studies of metabolic systems

Background: Isotope labeling experiments (ILEs) are increasingly used to investigate the functioning of metabolic systems. Some enzymes are subject to kinetic isotope effects (KIEs) which modulate reaction rates depending on the isotopic composition of their substrate(s). KIEs may therefore affect both the propagation of isotopes through metabolic networks and their operation, and ultimately jeopardize the biological value of ILEs. However, the actual impact of KIEs on metabolism has never been investigated at the system level. Results: First, we developed a framework which integrates KIEs into kinetic and isotopic models of metabolism, thereby accounting for their system-wide effects on metabolite concentrations, metabolic fluxes, and isotopic patterns. Then, we applied this framework to assess the impact of KIEs on the central carbon metabolism of Escherichia coli in the context of C-13-ILEs, under different situations commonly encountered in laboratories. Results showed that the impact of KIEs strongly depends on the label input and on the variable considered but is significantly lower than expected intuitively from measurements on isolated enzymes. The global robustness of both the metabolic operation and isotopic patterns largely emerge from intrinsic properties of metabolic networks, such as the distribution of control across the network and bidirectional isotope exchange. Conclusions: These results demonstrate the necessity of investigating the impact of KIEs at the level of the entire system, contradict previous hypotheses that KIEs would have a strong effect on isotopic distributions and on flux determination, and strengthen the biological value of C-13-ILEs. The proposed modeling framework is generic and can be used to investigate the impact of all the isotopic tracers (H-2, C-13, N-15, O-18, etc.) on different isotopic datasets and metabolic systems. By allowing the integration of isotopic and metabolomics data collected under stationary and/or non-stationary conditions, it may also assist interpretations of ILEs and facilitate the development of more accurate kinetic models with improved explicative and predictive capabilities

A

Metabolic pathways implied in the synthesis of succinoglycan produced by the Su47 strain of R. meliloti were evaluated by 13C-NMR spectroscopy after incubation with [1-13C] or [2-13C] glucose. The biosynthesis of this polymer by R. meliloti from glucose occurred by a direct polymerisation of the introduced glucose and by the pentose phosphate pathway

In-cell NMR: from metabolites to macromolecules

In-cell NMR of macromolecules has gained momentum over the last ten years as an approach that might bridge the branches of cell biology and structural biology. In this review, we put it in the context of earlier efforts that aimed to characterize by NMR the cellular environment of live cells and their intracellular metabolites. Although technical aspects distinguish these earlier in vivo NMR studies and the more recent in cell NMR efforts to characterize macromolecules in a cellular environment, we believe that both share major concerns ranging from sensitivity and line broadening to cell viability. Approaches to overcome the limitations in one subfield thereby can serve the other one and vice versa. The relevance in biomedical sciences might stretch from the direct following of drug metabolism in the cell to the observation of target binding, and thereby encompasses in-cell NMR both of metabolites and macromolecules. We underline the efforts of the field to move to novel biological insights by some selected examples

Transketolase in Trypanosoma brucei

A single copy gene, encoding a protein highly similar to transketolase from other systems, was identified in the Trypanosoma brucei genome. The gene was expressed in E. coli and the purified protein demonstrated transketolase activity with Km values of 0.2 mM and 0.8 mM respectively for xylulose 5-phosphate and ribose 5-phosphate. A peroxisomal targeting signal (PTS-1) present at the C-terminus of the protein suggested a glycosomal localisation. However, subcellular localisation experiments revealed that while the protein was present in glycosomes it was found mainly within the cytosol and thus has a dual localisation. Transketolase activity was absent from the long slender bloodstream form of the parasite and the protein was not detectable in this life cycle stage, with the RNA present only at low abundance, indicating a strong differential regulation, being present predominantly in the procyclic form. The gene was knocked out from procyclic T. brucei and transketolase activity was lost but no growth phenotype was evident in the null mutants. Metabolite profiling to compare wild type and TKT null mutants revealed substantial increases in transketolase substrate metabolites coupled to loss of sedoheptulose 7-phosphate, a principal product of the transketolase reaction

Quantitative

1H NMR analysis was carried out to determine the nature and the concentration of the poly(3-hydroxyalkanoate) (PHA) accumulated by Rhizobium meliloti M5N1. The PHA was identified as being poly(3-hydroxybutyrate) (PHB). Benzene was shown to meet ah the requirements of an internal reference for PHB quantification. NMR data were in good agreement with corresponding data obtained by Gas Chromatography (GC) analysis

Functional genomics of the muscle response to restraint and transport in chickens

International audienceIn the present study, we used global approaches (proteomics, transcriptomics, and metabolomics) to assess the molecular basis of the muscle response to stress in chickens. A restraint test, combined with transport for 2 h (RT test) was chosen as the potentially stressful situation. Chickens (6 wk old) were either nontreated (control chickens) or submitted to the RT test (treated chickens). The RT test induced a 6-fold increase in corticosterone concentrations, suggesting hypothalamic-pituitary-adrenal axis activation. The RT test decreased the relative abundance of several hexose phosphates [glucose-1-P (G1P), glucose-6-P (G6P), fructose-6-P (F6P), and mannose-6-P (M6P)] in thigh muscle. In addition, 55 transcripts, among which 39 corresponded to unique annotated genes, were significantly up- (12 genes) or downregulated (27 genes) by treatment. Similarly, 45 proteic spots, among which 29 corresponded to unique annotated proteins, were overexpressed (11 proteins), underexpressed (14 proteins), or only expressed in treated chickens. Integrative analysis of differentially expressed genes and proteins showed that most transcripts and proteins belong to 2 networks whose genes were mainly related with cytoskeleton structure or carbohydrate metabolism. Whereas the decrease in energetic metabolites suggested an activation of glycogenolysis and glycolysis in response to the RT test, the reduced expression of genes and proteins involved in these pathways suggested the opposite. We hypothesized that the prolonged RT test resulted in a repression of glycogenolysis and glycolysis in thigh muscle of chickens. The down-expression of genes and proteins involved in the formation of fiber stress after the RT test suggests a reinforcement of myofibrils in response to stress