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Keywords:

  • cell culture;
  • CHO cells;
  • metabolic flux analysis;
  • qCO2;
  • qO2;
  • RQ

Abstract

We present robust methods for online estimation of cell specific oxygen uptake and carbon dioxide production rates (qO2 and qCO2, respectively) during perfusion cultivation of mammalian cells. Perfusion system gas and liquid phase mass balance expressions for oxygen and carbon dioxide were used to estimate qO2, qCO2 and the respiratory quotient (RQ) for Chinese hamster ovary (CHO) cells in perfusion culture over 12 steady states with varying dissolved oxygen (DO), pH, and temperature set points. Under standard conditions (DO = 50%, pH = 6.8, T = 36.5°C), qO2 and qCO2 ranges were 5.14–5.77 and 5.31–6.36 pmol/cell day, respectively, resulting in RQ values of 0.98–1.14. Changes to DO had a slight reducing effect on respiration rates with qO2 and qCO2 values of 4.64 and 5.47, respectively, at DO = 20% and 4.57 and 5.12 at DO = 100%. Respiration rates were lower at low pH with qO2 and qCO2 values of 4.07 and 4.15 pmol/cell day at pH = 6.6 and 4.98 and 5.36 pmol/cell day at pH = 7. Temperature also impacted respiration rates with respective qO2 and qCO2 values of 3.97 and 4.02 pmol/cell day at 30.5°C and 5.53 and 6.25 pmol/cell day at 37.5°C. Despite these changes in qO2 and qCO2 values, the RQ values in this study ranged from 0.98 to 1.23 suggesting that RQ was close to unity. Real-time qO2 and qCO2 estimates obtained using the approach presented in this study provide additional quantitative information on cell physiology both during bioprocess development and commercial biotherapeutic manufacturing. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011