Use of NaCl prevents aggregation of recombinant COMP–Angiopoietin-1 in Chinese hamster ovary cells

To investigate the effect of hyperosmotic medium on production and aggregation of the variant of Angiopoietin-1 (Ang1), cartilage oligomeric matrix protein (COMP)–Ang1, in recombinant Chinese hamster ovary (CHO) cells, CHO cells were cultivated in shaking flasks. NaCl and/or sorbitol were used to raise medium osmolality in the range of 300–450 mOsm/kg. The specific productivity of COMP–Ang1, qCOMP–Ang1, increased as medium osmolality increased. At NaCl-450 mOsm/kg, the qCOMP–Ang1 was 7.7-fold higher than that at NaCl-300 mOsm/kg, while, at sorbitol-450 mOsm/kg, it was 2.9-fold higher than that at sorbitol-300 mOsm/kg. This can be attributed to the increased relative mRNA level of COMP–Ang1 at NaCl-450 mOsm/kg which was approximately 2.4-fold higher than that at sorbitol-450 mOsm/kg. Western blot analysis showed that COMP–Ang1 aggregates started to occur in the late-exponential phase of cell growth. When sorbitol was used to raise the medium osmolality, a severe aggregation of COMP–Ang1 was observed. On the other hand, when NaCl was used, the aggregation of COMP–Ang1 was drastically reduced at NaCl-400 mOsm/kg. At NaCl-450 mOsm/kg, the aggregation of COMP–Ang1 was hardly observed. This suggests that environmental conditions are critical for the aggregation of COMP–Ang1. Taken together, the use of NaCl-induced hyperosmotic medium to cell culture process turns out to be an efficient strategy for enhancing COMP–Ang1 production and reducing COMP–Ang1 aggregation.