PROBING LACTATE METABOLISM VARIATIONS IN LARGE-SCALE BIOREACTORS

摘要

Lactate metabolism variations are frequently encountered in mammalian cell culture processes, especially during process scale-up. In this work, we took a multipronged approach to investigate the impact of pH, pCO_2, osmolality, base addition, and mixing conditions on the observed lactate variations in a Chinese Hamster Ovary (CHO) fed-batch process at 2,000 L scale. Two cultivating methods, CO_2-controlled and pH-controlled, were used to decouple the individual and synergistic effects from those factors. The individual effects from pH, pCO_2, and osmolality on lactate consumption/reproduction in the stationary phase were insignificant in the ranges studied though the initial lactate production rates varied. In contrast, lactate metabolism was found to be impacted by an interaction between mixing conditions and CO_2 accumulation. High CO_2 accumulation and poor mixing led to lactate reproduction, whereas either low CO_2 or improved mixing were sufficient to result in lactate consumption. Base addition was not required for pH control in the low CO_2 conditions, and therefore lactate reproduction was correlated with base addition under poor mixing conditions and high CO_2. Under good mixing conditions, CO_2-triggered base addition did not pose significant impact on lactate reproduction. It is reasonable to postulate that increased mixing times promoted lactate production during base addition. As lactate reproduction results in more base addition to maintain pH, a cycle could be formed between lactate production and base addition. As a remediation, we showed that lactate reproduction could be eliminated by improving CO_2 removal at 2,000 L scale.