Metabolites are the end products of cellular regulatory processes, and their levels can be regarded as the ultimate response of biological systems to genetic or environmental changes. In parallel to the terms ‘transcriptome’ and ‘proteome’, the set of metabolites synthesized by a biological system constitute its ‘metabolome’. Yet, unlike other functional genomics approaches, the unbiased simultaneous identification and quantification of plant metabolomes has been largely neglected. Until recently, most analyses were restricted to profiling selected classes of compounds, or to fingerprinting metabolic changes without sufficient analytical resolution to determine metabolite levels and identities individually. As a prerequisite for metabolomic analysis, careful consideration of the methods employed for tissue extraction, sample preparation, data acquisition, and data mining must be taken. In this review, the differences among metabolite target analysis, metabolite profiling, and metabolic fingerprinting are clarified, and terms are defined. Current approaches are examined, and potential applications are summarized with a special emphasis on data mining and mathematical modelling of metabolism.

https://link.springer.com/content/pdf/10.1023%2FA%3A1013713905833.pdf

Metabolomics - the link between genotypes and phenotypes

The biology of cancer: metabolic reprogramming fuels cell growth and proliferation

Warburg's observation that cancer cells exhibit a high rate of glycolysis even in the presence of oxygen (aerobic glycolysis) sparked debate over the role of glycolysis in normal and cancer cells. Although it has been established that defects in mitochondrial respiration are not the cause of cancer or aerobic glycolysis, the advantages of enhanced glycolysis in cancer remain controversial. Many cells ranging from microbes to lymphocytes use aerobic glycolysis during rapid proliferation, which suggests it may play a fundamental role in supporting cell growth. Here, we review how glycolysis contributes to the metabolic processes of dividing cells. We provide a detailed accounting of the biosynthetic requirements to construct a new cell and illustrate the importance of glycolysis in providing carbons to generate biomass. We argue that the major function of aerobic glycolysis is to maintain high levels of glycolytic intermediates to support anabolic reactions in cells, thus providing an explanation for why in...

/pdf/aerobic-glycolysis-meeting-the-metabolic-requirements-of-3fer2kszx4.pdf

Aerobic Glycolysis: Meeting the Metabolic Requirements of Cell Proliferation

Proton NMR chemical shift and J-coupling values are presented for 35 metabolites that can be detected by in vivo or in vitro NMR studies of mammalian brain. Measurements were obtained using high-field NMR spectra of metabolites in solution, under conditions typical for normal physiological temperature and pH. This information is presented with an accuracy that is suitable for computer simulation of metabolite spectra to be used as basis functions of a parametric spectral analysis procedure. This procedure is verified by the analysis of a rat brain extract spectrum, using the measured spectral parameters. In addition, the metabolite structures and example spectra are presented, and clinical applications and MR spectroscopic measurements of these metabolites are reviewed.

http://pfeifer.phas.ubc.ca/refbase/files/Govindaraju-NMRBiomed-2000-13-129.pdf

Proton NMR chemical shifts and coupling constants for brain metabolites.

For much of the 20th century, lactate was largely considered a dead-end waste product of glycolysis due to hypoxia, the primary cause of the O2 debt following exercise, a major cause of muscle fatigue, and a key factor in acidosis-induced tissue damage. Since the 1970s, a ‘lactate revolution’ has occurred. At present, we are in the midst of a lactate shuttle era; the lactate paradigm has shifted. It now appears that increased lactate production and concentration as a result of anoxia or dysoxia are often the exception rather than the rule. Lactic acidosis is being re-evaluated as a factor in muscle fatigue. Lactate is an important intermediate in the process of wound repair and regeneration. The origin of elevated [lactate] in injury and sepsis is being re-investigated. There is essentially unanimous experimental support for a cell-to-cell lactate shuttle, along with mounting evidence for astrocyte–neuron, lactate–alanine, peroxisomal and spermatogenic lactate shuttles. The bulk of the evidence suggests that lactate is an important intermediary in numerous metabolic processes, a particularly mobile fuel for aerobic metabolism, and perhaps a mediator of redox state among various compartments both within and between cells. Lactate can no longer be considered the usual suspect for metabolic ‘crimes’, but is instead a central player in cellular, regional and whole body metabolism. Overall, the cell-to-cell lactate shuttle has expanded far beyond its initial conception as an explanation for lactate metabolism during muscle contractions and exercise to now subsume all of the other shuttles as a grand description of the role(s) of lactate in numerous metabolic processes and pathways.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.2003.058701

Lactate metabolism: a new paradigm for the third millennium

The authors investigated concomitant lactate and glucose metabolism in primary neuronal cultures using 13C- and 1H-NMR spectroscopy. Neurons were incubated in a medium containing either [1-13C]glucose and different unlabeled lactate concentrations, or unlabeled glucose and different [3-13C]lactate concentrations. Overall, 13C-NMR spectra of cellular extracts showed that more 13C was incorporated into glutamate when lactate was the enriched substrate. Glutamate 13C-enrichment was also found to be much higher in lactate-labeled than in glucose-labeled conditions. When glucose and lactate concentrations were identical (5.5 mmol/L), relative contributions of glucose and lactate to neuronal oxidative metabolism amounted to 21% and 79%, respectively. Results clearly indicate that when neurons are in the presence of both glucose and lactate, they preferentially use lactate as their main oxidative substrate.

Lactate is a preferential oxidative energy substrate over glucose for neurons in culture.

Quantification of compartmented metabolic fluxes in maize root tips using isotope distribution from 13C- or 14C-labeled glucose.

A mathematical model of mammalian cell intermediary metabolism is presented It describes the distribution of the carbon-13 isotope (13C) at the different carbon positions of metabolites in cells fed with 13C-enriched substrates The model allows the determination of fluxes through different metabolic pathways from 13C- and 1H-NMR spectroscopy and mass spectrometry data The considered metabolic network includes glycolysis, gluconeogenesis, the citric acid cycle and a number of reactions corresponding to protein or fatty acid metabolism The model was used for calculating metabolic fluxes in a rat tumor cell line, the C6 glioma, incubated with [1-13C]glucose After evolution to metabolic and isotopic steady states, the intracellular metabolites were extracted with perchloric acid The specific enrichments of glutamate, aspartate and alanine carbons were determined from 13C-, 1H-NMR spectroscopy, or mass spectrometry data Taking into account the rate of glucose consumption and of lactate formation, determined from the evolution of glucose and lactate contents in the cell medium, and knowing the activity of the hexose monophosphate shunt, it was possible to estimate the absolute values of all the considered fluxes From the analysis the following results were obtained (a) Glucose accounts for about 78% of the pyruvate and 57% of the CoASAc (b) A metabolic channelling occurs at the citric acid cycle level; it favours the conversion of carbons 2, 3, 4, and 5 of 2-oxoglutarate into carbons 1, 2, 3, and 4 of oxaloacetate, respectively The percentage of channelled metabolites amounts to 39% (c) The pyruvate carboxylase activity and the efflux from the citric acid cycle are estimated to be very low, suggesting a lack of glutamine production in C6 cells The results emphasize different metabolic characteristics of C6 cells when compared to astrocytes, their normal counterpart

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1993.tb18265.x

Metabolic flux determination in C6 glioma cells using carbon-13 distribution upon [1-13C]glucose incubation.

Glucose and glutamine metabolism in C6 glioma cells studied by carbon 13 NMR

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2889%2980882-8

Paul Canioni

Papers

Lactate is a preferential oxidative energy substrate over glucose for neurons in culture.

Quantification of compartmented metabolic fluxes in maize root tips using isotope distribution from 13C- or 14C-labeled glucose.

Metabolic flux determination in C6 glioma cells using carbon-13 distribution upon [1-13C]glucose incubation.

Glucose and glutamine metabolism in C6 glioma cells studied by carbon 13 NMR

Polyphosphates as a source of high energy phosphates in yeast mitochondria: A 31P NMR study