Measurement of hydrophobic interactions of mammalian cells grown in culture.

An assay was developed to measure the hydrophobic interactions of commonly used mammalian cell lines grown in culture. The assay depends on the loss of cells from an aqueous suspension following vortexing with a hydrophobic oil phase. This allowed the determination of a hydrophobicity index, which was significantly higher for Chinese Hamster Ovary (CHO) cells than either a murine hybridoma (CC9C10) or a myeloma (SP2/0). This suggests that CHO cells may have a higher intrinsic cell surface hydrophobicity. The assay was also used to study the effect of different additives on the hydrophobic interactions of the cells. A dose-dependent effect was shown for the non-ionic surfactant, Pluronic F68, in reducing the hydrophobic interaction of the CHO cells. However, the pattern of the decrease due to Pluronic F68 was different for each cell line. A higher concentration of Pluronic F68 (0.2%) was required to eliminate the hydrophobic interactions of CHO cells compared to either myelomas or hybridomas, where only 0.05% was required to reduce these interactions to a similar level. Several oils were found suitable for this assay although canola oil maximized the sensitivity of the measured changes. The assay may be useful in monitoring changes in the hydrophobic interactions of mammalian cells during growth in bioreactors. This may be important in optimizing the concentration of cell protectants such as Pluronic F68 in agitated cultures.