AIM: To optimize a xeno-free cryopreservation protocol for primary human hepatocytes.
METHODS: The demand for cryopreserved hepatocytes is increasing for both clinical and research purposes. Despite several hepatocyte cryopreservation protocols being available, improvements are urgently needed. We first compared controlled rate freezing to polystyrene box freezing and did not find any significant change between the groups. Using the polystyrene box freezing, we compared two xeno-free freezing solutions for freezing of primary human hepatocytes: a new medium (STEM-CELLBANKER, CB), which contains dimethylsulphoxide (DMSO) and anhydrous dextrose, both permeating and non-permeating cryoprotectants, and the frequently used DMSO - University of Wisconsin (DMSO-UW) medium. The viability of the hepatocytes was assessed by the trypan blue exclusion method as well as a calcein-esterase based live-dead assay before and after cryopreservation. The function of the hepatocytes was evaluated before and after cryopreservation by assessing enzymatic activity of 6 major cytochrome P450 isoforms (CYPs): CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP3A4 and CYP3A7.
RESULTS: The new cryoprotectant combination preserved hepatocyte viability significantly better than the standard DMSO-UW protocol (P < 0.01). There was no significant difference in viability estimation between both the trypan blue (TB) and the Live-Dead Assay methods. There was a correlation between viability of fresh hepatocytes and the difference in cell viability between CB and DMSO protocols (r2 = 0.69) using the TB method. However, due to high within-group variability in the activities of the major CYPs, any statistical between-group differences were precluded. Cryopreservation of human hepatocytes using the cryoprotectant combination was a simple and xeno-free procedure yielding better hepatocyte viability. Thus, it may be a better alternative to the standard DMSO-UW protocol. Estimating CYP activities did not seem to be a relevant way to compare hepatocyte function between different groups due to high normal variability between different liver samples.
CONCLUSION: The cryoprotectant combination may be a better alternative to the standard DMSO-UW protocol in primary human hepatocyte cryopreservation.