Aerobic glycolysis in cancer cells supplies ATP while preventing excess metabolic thermogenesis

A general feature of cancer metabolism is ATP regeneration via substrate-level phosphorylation even under normoxic conditions (aerobic glycolysis). However, it is unclear why cancer cells prefer the inefficient aerobic glycolysis over the highly efficient process of oxidative phosphorylation for ATP regeneration. Here, we show that a beneficial aspect of aerobic glycolysis is that it reduces metabolic heat generation during ATP regeneration. 13C-metabolic flux analysis of 12 cultured cancer cell lines and in silico metabolic simulation revealed that metabolic heat production during ATP regeneration via aerobic glycolysis was considerably lesser than that produced via oxidative phosphorylation. The dependency on aerobic glycolysis was partly alleviated upon culturing under low temperatures. In conclusion, thermogenesis is required for maintaining thermal homeostasis and can govern aerobic glycolysis in cancer cells.

METAMDB: METABOLIC ATOM MAPPING DATABASE

MetAMDB (https://metamdb.tu-bs.de/) is an open source metabolic atom mapping database, providing atom mappings for around 75000 metabolic reactions. Each atom mapping can be inspected and downloaded either as a RXN file or as a graphic in SVG format. In addition, MetAMDB offers the possibility of automatically creating atom mapping models based on user-specified metabolic networks. These models can be of any size (small to genome scale) and can subsequently be used in standard 13C metabolic flux analysis software.

13C Metabolic Flux Analysis Indicates Endothelial Cells Attenuate Metabolic Perturbations by Modulating TCA Activity

Disrupted endothelial metabolism is linked to endothelial dysfunction and cardiovascular disease. Targeted metabolic inhibitors are potential therapeutics; however, their systemic impact on endothelial metabolism remains unknown. In this study, we combined stable isotope labeling with 13C metabolic flux analysis (13C MFA) to determine how targeted inhibition of the polyol (fidarestat), pentose phosphate (DHEA), and hexosamine biosynthetic (azaserine) pathways alters endothelial metabolism. Glucose, glutamine, and a four-carbon input to the malate shuttle were important carbon sources in the baseline human umbilical vein endothelial cell (HUVEC) 13C MFA model. We observed two to three times higher glutamine uptake in fidarestat and azaserine-treated cells. Fidarestat and DHEA-treated HUVEC showed decreased 13C enrichment of glycolytic and TCA metabolites and amino acids. Azaserine-treated HUVEC primarily showed 13C enrichment differences in UDP-GlcNAc. 13C MFA estimated decreased pentose phosphate pathway flux and increased TCA activity with reversed malate shuttle direction in fidarestat and DHEA-treated HUVEC. In contrast, 13C MFA estimated increases in both pentose phosphate pathway and TCA activity in azaserine-treated cells. These data show the potential importance of endothelial malate shuttle activity and suggest that inhibiting glycolytic side branch pathways can change the metabolic network, highlighting the need to study systemic metabolic therapeutic effects.

Metabolic mechanism of Saccharomyces cerevisiae under different physiological conditions based on non-stationary 13C metabolic flux analysis

Crabtree effect is well known for Saccharomyces cerevisiae, and is defined as glucose-induced repression of respiratory flux. Even though a number of hypotheses have been formulated, its triggering mechanisms are still unknown. At present, the information about intracellular metabolic flux can be obtained by the 13C isotope labeling experiments. 13C metabolic flux analysis(13C-MFA) is a traditional method for calculating metabolic flux based on isotopic steady state. Another new method (INST-13C-MFA: Isotopically nonstationary metabolic flux analysis) based on isotope non-steady state is being used by researchers. In this review, we have chemostatized S. cerevisiae at three different dilution rates (D=0.12, 0.22, 0.32 h-1) and obtained the metabolic flux distribution of the intracellular central carbon metabolic of S. cerevisiae using INST-13C-MFA. Combined with the metabolome and metabolic fluxome data, we found obvious metabolic flux shift under the three different physiological states. In this process, pyruvate decarboxylase, ethanol dehydrogenase and acetyl-CoA synthase(AcCoA) catalyzed reactions were key points. Negative correlation between relative flux of embden meyerh of pathway(EMP) and tricarboxylic acid cycle(TCA) and biomass yield, while positive correlation for pentose phosphate pathway(PPP) were observed. Yield of acetate and glycerol did not change significantly, while that of ethanol increased sharply. In the central carbon metabolism (CCM), most of the carbon flux (70%) was directed to the EMP. At the same time, the energy charge increased with dilution rate, and the cell's energy supply mode gradually shifted from oxidative respiration to substrate level phosphorylation mode.