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Van Beek MiP2010

From Bioblast
van Beek JHGM (2010) Computational model predictions of metabolic fluxes connecting cytosol and mitochondrial matrix under โ€˜Warburg effectโ€™ conditions.

Link: Abstracts Session 4

van Beek JHGM (2010)

Event: MiP2010

Proliferating cancer cells often show a high glycolytic rate with most of the glucose converted to lactate despite adequate oxygen availability and substantial mitochondrial consumption. This is known under the term โ€˜Warburg effectโ€™. The distribution of enzyme fluxes and transport fluxes between cytosol and mitochondria during such anaerobic glycolysis is not fully known.


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Regulation: Substrate, Amino acid 



Computational model 

Full text

Proliferating cancer cells often show a high glycolytic rate with most of the glucose converted to lactate despite adequate oxygen availability and substantial mitochondrial consumption. This is known under the term Warburg effect. The distribution of enzyme fluxes and transport fluxes between cytosol and mitochondria during such aerobic glycolysis is not fully known.

To investigate the possible metabolic flux distribution under these conditions of aerobic glycolysis, I designed a computational model for mitochondrial and cytosolic metabolism that contains the transport reactions between mitochondrial matrix and cytosol. In the model analysis the metabolic fluxes are balanced. Glycolysis, pentose phosphate pathway, TCA cycle, anaplerotic reactions and transport reactions between cytosol and mitochondrial matrix are included in the model. Among others the malate-aspartate shuttle pathway for reducing equivalent transport is incorporated. One type of constraint on the model is the inclusion of the irreversibility of reactions where appropriate. The model presently contains almost 60 biochemical reactions. The pathway model is analyzed by fitting possible solutions for the flux distribution to measurements of oxygen, glucose and glutamine uptake and lactate production typical for tumour-derived cell cultures. By applying a Monte Carlo Markov Chain analysis, using the Metropolis algorithm, the possible flux distributions compatible with the measurements are determined. The solution is in the form of an ensemble of possible flux distributions which have a high likelihood of predicting the measured rates of production and uptake.

As an example a result of the application of the analysis is shown in the Figure. The metabolic flux distribution is calculated based on measured uptake and release of metabolites in a typical HeLa cell culture. The result shows the likely range of net metabolic flux across the mitochondrial isocitrate dehydrogenase enzyme on the x-axis. The possible fluxes range from -175 to -30 nanomol/hour/million cells. The negative sign indicates that the flux in the first half of the TCA cycle is reversed, flowing from 2-oxoglutarate to citrate. On the y-axis, the citrate uptake in the mitochondria is given: possible fluxes range from -175 to -30 nanomol/hour/million cells. The negative uptake values indicate that citrate flows out of the mitochondria and is available to be used for fatty acid synthesis in the cytosol.

Figure 1. Computational model prediction of likely metabolic fluxes in a typical HeLa cell culture (see text). Note the range of uncertainty in the predictions. The predicted fluxes are strongly correlated. Net metabolic flux across the mitochondrial isocitrate dehydrogenase enzyme is from 2-oxoglutarate to isocitrate, as indicated by the negative value. Flux across the citrate transporter on the y-axis is out of the mitochondria, as indicated by the negative value.

The model analysis predicts that a substantial fraction of glutamine taken up by the cells flows via 2-oxoglutarate to the mitochondrial citrate pool and from there citrate flows to the cytosol where it can be used for fatty acid synthesis. According to the prediction, one quarter to one half of the citrate exported from the mitochondria is formed from glutamine carbon that is taken up by the mitochondria and is flowing back through the first half of the TCA cycle.