CHO Metabolic Network Reconstruction
The metabolic network of the CHO cell was reconstructed using information from public databases and primary literature. Stoichiometry, reversibility, and the elemental composition of metabolites was modeled for every reaction. Enzymatic reactions were mapped to corresponding genes based on a genome annotation for mouse.
The model comprises different cellular compartments (cytosol, mitochondria, ER, Golgi) and the fermenter. It accounts for the glycoform structure and amino acid composition of the product molecule as well as for known cell line specific genetic modifications of metabolic enzymes.
First, we applied the model to characterize the reference process based on time series of extracellular metabolite concentrations from a fed-batch fermentation. For each physiologically distinct process phase, cell-specific rates of nutrient uptake, growth, and product formation were calculated from mass balances (Figure 1), employing Monte Carlo simulation to calculate error propagation.
From these extracellular rates, we computed intracellular flux distributions using metabolic flux analysis and the CHO network model. By comparing the flux distributions in different process phases, it is possible to identify (i) pathways with significant flux changes during the fermentation and (ii) process phases with favorable flux distribution.
Such information cannot be inferred from measured concentration time series alone, but requires the use of an appropriate model. Moreover, the results obtained provide a first assessment of cellular energy status and of nutrient fractions supplied by cellular uptake and/or synthesis, respectively.