(71c) Micro Heat Exchanger for Quenching the Metabolism of Mammalian Cells

Intracellular metabolite analysis (Metabolomics) is a powerful tool to describe and understand the cellular behaviour in biotechnological processes. It requires rapid quenching of the cells metabolism (at least within seconds), quantitative extraction and highly sensitive analysis of the metabolites. While in microbial fermentations the positive impact of intracellular metabolite analysis has already been shown in process optimizations and strain development, the transfer to mammalian cell culture is still hampered because of the cells' mechanical sensitivity and compartimentation. Due to the much higher mechanical sensitivity of mammalian cells (lack of a cell wall) quenching methods used for microorganisms like filtration or transfer of the cells into cold methanol (-40°C) are not applicable. We have investigated the applicability of a miniaturized cross-flow heat exchanger comprising 850 channels (width 0.1 mm, height 0.2 mm, length 14 mm) to cool mammalian cell suspenions from the physiological level of 37°C to 0°C within a few seconds. The heat exchanger was connected to a stirred vessel bioreactor, samples were taken through the heat exchanger and potential cell damage induced e.g. shear-forces in the heat exchanger channels was analysed by quantification of intracellular enzyme activities in the cell free supernatant. Only minor cell damage (i.e. low enzyme activity) could be observed and the sterility of the bioreactor was maintained. After centrifugation at -8 °C the cells intracellular metabolites were extracted and analyzed by LC-MS/MS. In summary, the micro heat exchanger used in this study seems to be a suitable technology to overcome one of the major obstacles in metabolomics in mammalian cell culture and will be investigated in future works.