Environmental Effects on Cell Physiology and Metabolism: Response to Elevated pC0₂

Abstract

Carbon dioxide (CO₂) is a major by-product of mammalian cell metabolism. Approximately 1 mole of CO₂ is released for every mole of O₂ consumed (Aunins and Henzler, 1993). An early goal in optimizing bioprocesses was to deliver sufficient oxygen to support a large cell density. Due to the need to balance oxygen delivery with minimal cell damage, strategies employing enriched oxygen, microbubbles, and slower volumetric flow rates were developed. However, under these conditions, CO₂ can build up to high levels. pCO₂ values near 170 mm Hg have been reported for a 200 L culture with small amounts of pure O₂ sparged through a stainless steel frit (Aunins et al,, 1993) and a 2500 L production bioreactor (Aunins and Henzler, 1993; data from Drapeau et al., 1990). Other studies have shown that the growth of a variety of industrially relevant cell Unes, including CHO and BHK cells, is reduced under elevated CO₂ partial pressure (pCO₂; Kimura and Miller, 1996; Taticek et al., 1998). Elevated pCO₂ decreases CHO cell specific protein production (q_p; Drapeau et al., 1990; Kimura and Miller, 1996), while antibody production by hybridoma and NS/0 cells remains unaltered (deZengotita et al., 1998). The glycosylation of EPO and tPA are robust up to 250 mm Hg pCO₂ (Grampp et al, 1994; Kimura and Miller, 1997), while the polysialylation of NCAM is much more sensitive to elevated pCO₂ — decreasing to 20% of control levels at 170 mm Hg pCO₂, pH 7.5 (Zanghi et al., 1999).