ABSTRACT
Mammalian cell lines are used extensively for the production of therapeutic proteins in a variety of in vitro culture systems, and the characterization, understanding, and ultimately the redistribution of their basic metabolic behavior are needed to improve their performance and to design optimized production systems. The metabolic patterns of mammalian cells are altered substantially when the original homeostatic environment in a tissue of stressful pluricellular organisms is changed by the stressful in vitro culture system environment and the genetic alterations occurring during the immortalization process, leading to the establishment of a production cell line. Consequently, mammalian cell lines exhibit a highly deregulated metabolism when cultured in vitro. This is characterized by a very high and inefficient consumption of the main carbon, nitrogen, and energy sources, glucose and glutamine, and leads to the generation of waste metabolic end products, mainly lactate, ammonium, and some amino acids, such as alanine or proline. To understands this altered metabolism, one should consider the interaction of the different metabolic pathways in the cells. The main pathways reviewed in this chapter cannot be considered individually but as part of a more complex and flexible structure. In addition, the cellular compartmentalization of mammalian cells must also be considered in this analysis, particularly those processes occurring in the mitochondrion or in the cytosol. The central metabolic pathways considered comprise glycolysis, pentose phosphate pathway, tricarboxylic acid (TCA) cycle, oxidative phosphorylation, glutaminolysis, and the metabolism of other amino acids. They will be discussed in combination with the different transport mechanisms both from the external medium into the cells and from the cytosolic medium into the mitochondria, and, taking into account the interaction between them, by the malate shunt or the transamination (TA) pathways. A number of authors have reviewed different aspects of animal cell metabolism prior to this study, some very extensively (1-3).
