Insights into pH‐induced metabolic switch by flux balance analysis

Abstract

Lactate accumulation in mammalian cell culture is known to impede cellular growth and productivity. The control of lactate formation and consumption in a hybridoma cell line was achieved by pH alteration during the early exponential growth phase. In particular, lactate consumption was induced even at high glucose concentrations at pH 6.8, whereas highly increased production of lactate was obtained at pH 7.8. Consequently, constraint-based metabolic flux analysis was used to examine pH-induced metabolic states in the same growth state. We demonstrated that lactate influx at pH 6.8 led cells to maintain high fluxes in the TCA cycle and malate-aspartate shuttle resulting in a high ATP production rate. In contrast, under increased pH conditions, less ATP was generated and different ATP sources were utilized. Gene expression analysis led to the conclusion that lactate formation at high pH was enabled by gluconeogenic pathways in addition to facilitated glucose uptake. The obtained results provide new insights into the influence of pH on cellular metabolism, and are of importance when considering pH heterogeneities typically present in large scale industrial bioreactors.

Elevated pCO2 affects the lactate metabolic shift in CHO cell culture processes

“… can induce lactate consumption as shown in their study. Furthermore, pH‐shifts to lower values can strongly reduce glucose consumption rates and have been shown before to induce lactate consumption . (ii) Increasing the mitochondrial NAD⁺ regeneration would be the second approach to reduce R and initiate lactate consumption. At first the selection of a cell line with a generally high oxidative capacity seems to be beneficial .…”

Lactate and glucose concomitant consumption as a self-regulated pH detoxification mechanism in HEK293 cell cultures

“…Nevertheless, this shift occurred at late stages of cell culture, when cell growth was halted or only residual growth was observed. Recently, extracellular lactate uptake in the presence of glucose by means of media acidification has been reported in NS0 cell cultures (Ivarsson et al 2015). Nevertheless, the lactate consumption was quite low and was accompanied with a dramatic reduction on glucose uptake and cell growth, resulting in a drop of about 30 % of the cell growth rate after the pH shift in comparison to the control cell cultures.…”

Closed loop control of lactate concentration in mammalian cell culture by Raman spectroscopy leads to improved cell density, viability, and biopharmaceutical protein production

“…Mammalian cell culture is a key technique for the manufacturing of therapeutic proteins which depend on post‐translational modifications for efficacy (Ivarsson et al, ; Ozturk and Hu, ). Culture productivity remains a bottleneck in the production of many therapeutic proteins, and increasing productivity has been the subject of numerous efforts (Dietmair et al, ; Farrell et al, ; Huang et al, ; Lu et al, ; Zalai et al, ).…”

“…Pyruvate can then be shuttled to the tricarboxylic acid (TCA) cycle for further metabolism, or be converted to lactate during regeneration of the cofactor NAD + . Many mammalian cell lines have an inefficient metabolism and will consume more glucose through the glycolytic pathway than can be further metabolized through the TCA cycle (Ivarsson et al, ). Excess glucose can lead to increased lactate production through increased glycolytic activity (Ahn and Antoniewicz, ).…”