Survival and function of isolated hepatocytes after cryopreservation

Cryopreservation in liquid nitrogen is presently the only way for long-term storage of isolated hepatocytes. Freeze-thaw conditions are not well defined yet; the most critical parameters appear to be the choice of the cryoprotectant, composition of the freezing medium, and cooling and thawing rates. Comparable results have been obtained with hepatocytes from various species, including man. Cryopreservation usually results in low cell recovery and early alterations of functional activities. However, both phase I and phase II xenobiotic metabolism is still active after thawing, at least during a short period. Moreover, survival and function of cryopreserved hepatocytes can be improved when these cells have a high energy status, are cryopreserved after immobilization in a gel, separated from dead cells on a Percoll gradient or placed in more favorable culture conditions (e.g. in coculture with liver non parenchymal cells). Additional studies are needed to improve freeze-thaw protocols and to better characterize liver parenchymal cells after storage, including evaluation of their responsiveness to specific inducers.