Amino acid feeding reduces ammonia production through rearrangement of
metabolic fluxes in central carbon metabolism of CHO cells
Ammonia is a toxic byproduct of CHO cell metabolism, which inhibits cell
growth, reduces cell viability, alters glycosylation, and decreases
recombinant protein productivity. In an attempt to minimize the ammonium
accumulation in cell culture media, different amino acids were added
individually to the culture medium before the production phase to
alleviate the negative effects of ammonium on cell culture performance.
Among all the amino acids examined in this study, valine showed the most
positive impact on CHO cell culture performance. When the cultured CHO
cells were fed with 5 mM valine, EPO titer was increased by 25%
compared to the control medium, and ammonium and lactate production were
decreased by 23 and 26%, respectively, relative to the control culture.
Moreover, the sialic acid content of the EPO protein in valine-fed
culture was higher than in the control culture, most likely because of
the lower ammonium concentration. Flux balance analysis (FBA) results
demonstrated that the citric acid cycle was enriched by valine feeding.
The analysis revealed that there might be a link between promoting
tricarboxylic acid (TCA) cycle metabolism in valine-fed culture and
reduction in lactate and ammonia accumulation. Furthermore, in
valine-fed culture, FBA outcomes showed that alanine was excreted into
the medium as the primary mechanism for reducing ammonium concentration.
It was predicted that the elevated TCA cycle metabolism was concurrent
with an increment in recombinant protein production. Taken together, our
data demonstrate that valine addition could be an effective strategy for
mitigating the negative impacts of ammonium and enhancing glycoprotein
production in both quality and quantity.