Ja. Zanghi et al., Bicarbonate concentration and osmolality are key determinants in the inhibition of CHO cell polysialylation under elevated pCO(2) or pH, BIOTECH BIO, 65(2), 1999, pp. 182-191
Accumulation of CO2 in ani mal cell cu Itu res can be a significant problem
during scale-up and production of recombinant glycoprotein biopharmaceutic
als. By examining the cell-surface polysialic acid (PSA) content, we show t
hat elevated CO2 partial pressure (pCO(2)) can alter protein glycosylation.
PSA is a high-moiecular-weight polymer attached to several complex N-linke
d oligosaccharides on the neural cell adhesion molecule (NCAM), so that sma
ll changes in either core glycosylation or in polysialylation are amplified
and easily measured. Flowcytometric analysis revealed that PSA levels on C
hinese hamster ovary (CHO) cells decrease with increasing pCO(2) in a dose-
dependent manner, independent of any change in NCAM content. The results ar
e highly pH-dependent, with a greater decrease in PSA at higher pH. By mani
pulating medium pH and pCO(2), we showed that decreases in PSA correlate we
ll with bicarbonate concentration ([HCO3-]). In fact, it was possible to of
fset a 60% decrease in PSA content at 120 mm Hg pCO(2) by decreasing the pH
from 7.3 to 6.9, such that [HCO3-] was lowered to that of control (38 mm H
g pCO(2)). When the increase in osmolality associated with elevated [HCO3-]
was offset by decreasing the basal medium [NaCl], elevated [HCO3-] still c
aused a decrease in PSA, although less extensive than without osmolality co
ntrol. By increasing [NaCl], we show that hyperosmolality alone decreases P
SA content, but to a lesser extent than for the same osmolality increase du
e to elevated [NaHCO3]. In conclusion, we demonstrate the importance of pH
and pCO(2) interactions, and show that [HCO3-] and osmolality can account f
or the observed changes in PSA content over a wide range of pH and pCO(2) v
alues. (C) 1999 John Wiley & Sons, Inc.