Reduction of Ammonia Accumulation and Improvement of Cell Viability by Expression of Urea Cycle Enzymes in Chinese Hamster Ovary Cells

Previously, we developed a CHO cell line (CHO-OTC1-Al9) that expresses the first two enzymes in the urea cycle and exhibits a higher ammonia-removing ability and faster growth rate than a vector-controlled CHO cell line (CHO-neo-5). The current study was undertaken to develop a cell line with an ammonia-removing ability higher than the cell line developed previously. To accomplish this, CHO cell lines expressing the first three, first four, or all five enzymes of the urea cycle were constructed using a stable transfection method. Finally, the CHO-AS-16, CHO-AL-19, and CHO-Arg-11 cell lines expressing the first three, first four, and all five enzymes of the urea cycle, respectively, were selected and found to exhibit higher ammonia-removing ability than the CHO-OTC1-Al9 cell line. Among the three selected cell lines, CHO-AL-19 showed the highest ammonia-removing ability and highest cell viability at a higher cell density, with 40% and 15% lower ammonia concentration in the, culture media than that of CHO-neo-5 and CHO-OTC1-A19 cell lines, respectively. CHO-AL-19 also showed 44% and 10% higher cell viability than the CHO-neo-5 and CHO-OTC-Al9 cell lines, at a higher cell density, respectively. The ammonia concentrations in the culture media were expressed as the ammonia concentration/cell, and the CHO-AL-19 cells revealed 45-60% and 20% lower ammonia concentration/cell than the CHO-neo-5 and CHO-OTC1-Al9 cells, respectively.