Modulation of Pro-apoptotic (Bax) and Anti-apoptotic (Bcl-2) Gene Expression in Isolated Porcine Hepatocytes Perfused within a Radial-flow Bioreactor after Low-temperature Storing

Abstract

Due to the scarcity of available human livers, porcine hepatocytes are currently being evaluated as a xenogeneic cell source for extracorporeal bioartificial liver (BAL). Hypothermic storage of isolated porcine hepatocytes could support stocking of cell-loaded bioreactors for BAL use and may provide bioreactors ready to be used at the patient's bedside. For the development of this technology, it is of utmost importance to ensure cell viability and differentiated functions after low-temperature storage and following warm reperfusion. We compared cell viability, functional activity and apoptosis in isolated porcine hepatocytes which were perfused within a radial-flow bioreactor (RFB), stored at 4°C and then reperfused at 37°C. RFBs were loaded with 8 × 10⁹ ≥ 90% viable hepatocytes at 37°C for 3 h. RFBs were then flushed with 4° C University of Wisconsin solution (UW) and subsequently stored for 24 h or 48 h. RFBs were then reperfused for 8 h with recirculating medium plus serum at 37°C. Cytochrome P450 (CYP) activity was studied before and after cold storage by means of monoethylglycinexylide (MEGX) detection in the effluent medium, after repeated lidocaine injections. After reperfusion experiments, hepatocytes were harvested for total RNA isolation. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used in order to amplify specific mRNAs for Bcl-2 and Bax genes, by using appropriate primers; ß-actin primers were used as control. Total RNA was extracted by northern blotting analysis and for Bcl-2, Bax and ß-actin RNA messenger detection, RT-PCR amplification was used. Freshly isolated hepatocytes perfused into the RFB showed a progressive increase of MEGX while a loss in Bax expression was paralleled by an increase in Bcl-2 expression, in comparison to starting hepatocytes. After 4° C storage and warm reperfusion, MEGX production was preserved in 24 h- and 48 h-stored bioreactors as well as a sharp increase of Bcl-2 and a decrease of Bax mRNAs. Our study suggests that refrigeration of hepatocyte-bioreactors is a suitable strategy to maintain both viability and function of isolated hepatocytes, for up to 48 h a time-length that is compatible with long-distance delivery of ready-to-use bioreactors.