Elevated pCO affects the lactate metabolic shift in CHO cell culture processes.

The shift from lactate production to consumption in CHO cell metabolism is a key event during cell culture cultivations and is connected to increased culture longevity and final product titers. However, the mechanisms controlling this metabolic shift are not yet fully understood. Variations in lactate metabolism have been mainly reported to be induced by process pH and availability of substrates like glucose and glutamine. The aim of this study was to investigate the effects of elevated pCO concentrations on the lactate metabolic shift phenomena in CHO cell culture processes. In this publication, we show that at elevated pCO in batch and fed-batch cultures, the lactate metabolic shift was absent in comparison to control cultures at lower pCO values. Furthermore, through metabolic flux analysis we found a link between the lactate metabolic shift and the ratio of NADH producing and regenerating intracellular pathways. This ratio was mainly affected by a reduced oxidative capacity of cultures at elevated pCO. The presented results are especially interesting for large-scale and perfusion processes where increased pCO concentrations are likely to occur. Our results suggest, that so far unexplained metabolic changes may be connected to increased pCO accumulation in larger scale fermentations. Finally, we propose several mechanisms through which increased pCO might affect the cell metabolism and briefly discuss methods to enable the lactate metabolic shift during cell cultivations.