Porcine hepatocytes for biohybrid artificial liver devices: a comparison of hypothermic storage techniques

Subnormothermic Preservation Maintains Viability and Function in a Porcine Hepatocyte Culture Model Simulating Bioreactor Transport

Bioartificial liver (BAL) systems have been developed to bridge patients with acute liver failure (ALF) to liver transplantation or liver regeneration. Clinical application of BAL systems is dependent on the supportive quality of cells used and direct availability of the whole system. Reliable transport of BAL systems from the laboratory to remote treatment centers is therefore inevitable. Subsequently, preservation conditions play a crucial role during transport of a BAL, with temperature being one of the most determining factors. In this study, we assessed the effect of subnormothermic preservation on freshly isolated porcine hepatocytes cultured in monolayer under oxygenation. Additionally, the effect of the University of Wisconsin (UW) preservation solution was compared with Williams' E (WE) culture medium at 4°C. The control group was cultured for 3 days at 37°C, whereas the transport groups were cultured at 4°C, 15°C, 21°C, or 28°C for 24 h at day 2. All groups were tested each day for cell damage and hepatic functions. Subnormothermic culture (i.e., 15°C to 28°C) for a period of 24 h did not reduce any hepatic function and did not increase cellular damage. In contrast, culture of hepatocytes in WE medium and preservation in UW solution at 4°C significantly reduced hepatic function. In conclusion, freshly isolated porcine hepatocytes can be preserved for 24 h at subnormothermic temperatures as low as 15°C. Future research will focus on the implementation of the AMC-BAL in an oxygenated culture medium perfusion system for transport between the laboratory and the hospital.

Cryopreservation of viable hepatocyte monolayers in cryoprotectant media with high serum content: metabolism of testosterone and kaempherol post-cryopreservation

Little work in the literature focuses on the cryopreservation of primary hepatocytes as monolayer cultures, yet this technique offers many distinct advantages over other cryopreservation systems, including high recovery, high post-thaw nutrient penetration, and low numbers of trapped dead cells. This article investigates the cryopreservation of primary rat hepatocytes at -78 degrees C attached as monolayers to collagen coated culture dishes, and describes efforts to increase post-thaw viability and function through manipulation of the freeze/thaw protocol. Different concentrations of foetal calf serum (FCS) with 10% (v/v) dimethyl sulphoxide (ME2SO) were tested as cryopreservation media, and high cryoprotectant serum levels were found to be important in maintaining membrane integrity and function in the cryopreserved rat hepatocyte monolayer cultures. Cultures cryopreserved with 90% (v/v) FCS plus 10% (v/v) ME2SO maintain 79.7+/-6.5% of the monolayer area as viable cells with normal morphology (by image analysis), 112.7+/-14.2% protein concentration, 55.4+/-4.2% carboxyfluorescein diacetate de-acetylation, 27.2+/-7.5% kaempherol glucuronidation (a measure of UDP-glucuronosyl transferase activity), and 39.3+/-7.3% testosterone hydroxylation (a measure of cytochrome P-450 activity) compared with non-cryopreserved controls. This method of cryopreservation may provide a simple, convenient means of long-term storage of hepatocytes for in vitro metabolism studies.

Induction of necrosis and DNA fragmentation during hypothermic preservation of hepatocytes in UW, HTK, and Celsior solutions

Donor cells can be preserved in University of Wisconsin (UW), histidine-tryptophan-ketoglutarate (HTK), or Celsior solution. However, differences in efficacy and mode of action in preventing hypothermia-induced cell injury have not been unequivocally clarified. Therefore, we investigated and compared necrotic and apoptotic cell death of freshly isolated primary porcine hepatocytes after hypothermic preservation in UW, HTK, and Celsior solutions and subsequent normothermic culturing. Hepatocytes were isolated from porcine livers, divided in fractions, and hypothermically (4 degrees C) stored in phosphate-buffered saline (PBS), UW, HTK, or Celsior solution. Cell necrosis and apoptosis were assessed after 24- and 48-h hypothermic storage and after 24-h normothermic culturing following the hypothermic preservation periods. Necrosis was assessed by trypan blue exclusion, lactate dehydrogenase (LDH) release, and mitochondrial 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) reduction. Apoptosis was assessed by the induction of histone-associated DNA fragments and cellular caspase-3 activity. Trypan blue exclusion, LDH release, and MTT reduction of hypothermically preserved hepatocytes showed a decrease in cell viability of more than 50% during the first 24 h of hypothermic preservation. Cell viability was further decreased after 48-h preservation. DNA fragmentation was slightly enhanced in hepatocytes after preservation in all solutions, but caspase-3 activity was not significantly increased in these cells. Normothermic culturing of hypothermically preserved cells further decreased cell viability as assessed by LDH release and MTT reduction. Normothermic culturing of hypothermically preserved hepatocytes induced DNA fragmentation, but caspase-3 activity was not hanced in these cells. Trypan blue exclusion, LDH leakage, and MTT reduction demonstrated the highest cell viability after storage in Celsior, and DNA fragmentation was the lowest in cells that had been stored in PBS and UW solutions. None of the preservation solutions tested in this study was capable of adequately preventing cell death of isolated porcine hepatocytes after 24-h hypothermic preservation and subsequent 24-h normothermic culturing. Culturing of isolated and hypothermically preserved hepatocytes induces DNA fragmentation, but does not lead to caspase-3 activation. With respect to necrosis and DNA fragmentation of hypothermically preserved cells, UW and Celsior were superior to PBS and HTK solutions in this model of isolated porcine hepatocyte preservation.

Hypothermic preservation of hepatocytes

This paper presents a review of recent research on the hypothermic storage of hepatocytes. The first focus is on the diversity of methodologies currently employed in this area. The cell damage caused by hypothermic preservation and its possible mechanism are then investigated on both morphological and molecular biology. Later, the gene expressions on a mRNA level or enzyme level after hypothermic preservation are further discussed. Finally, the improvement of hypothermic storage by preconditioning, such as by increasing temperature, is explored.

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

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 degrees C and then reperfused at 37 degrees C. RFBs were loaded with 8 x 10(9), > or = 90% viable hepatocytes at 37 degrees C for 3 h. RFBs were then flushed with 4 degrees 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 degrees 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; beta-actin primers were used as control. Total RNA was extracted by northern blotting analysis and for Bcl-2, Bax and beta-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 degrees 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.

Extracorporeal tissue engineered liver-assist devices

The treatment of acute liver failure has evolved to the current concept of hybrid bioartificial liver (BAL) support, because wholly artificial systems have not proved efficacious. BAL devices are still in their infancy. The properties that these devices must possess are unclear because of our lack of understanding of the pathophysiology of liver failure. The considerations that attend the development of BAL devices are herein reviewed. These considerations include choice of cellular component, choice of membrane component, and choice of BAL system configuration. Mass transfer efficiency plays a role in the design of BAL devices, but the complexity of the systems renders detailed mass transfer analysis difficult. BAL devices based on hollow-fiber bioreactors currently show the most promise, and available results are reviewed herein. BAL treatment is designed to support patients with acute liver failure until an organ becomes available for transplantation. The results obtained to date, in this relatively young field, point to a bright future. The risks of using xenogeneic treatments have yet to be defined. Finally, the experience gained from the past and current BAL systems can be used as a basis for improvement of future BAL technology.

Postthaw viability of precultured hepatocytes

Hepatocytes are being studied for a wide variety of applications, including drug metabolism studies, gene therapy, and use in liver-assist devices for temporary liver support. The ability to cryopreserve isolated hepatocytes would permit the pooling of cells to reach the required therapeutic coordination of the cell supply with patient care regimes and the completion of safety and quality-control testing. The objective of this investigation was to develop a method of cryopreserving isolated hepatocytes that will retain high levels of function and facilitate the use of the cells in different applications. Freshly isolated hepatocytes were cultured in a spinner flask for different periods of time, up to 48 h. The cells were cryopreserved by use of a range of solution concentrations and cooling rates. For fresh, nonfrozen hepatocytes precultured for 24 h prior to being plated on collagen, the albumin secretion rate was 0.88 +/- 0.62 mg/ml/h. When the cells were precultured for 24 h, frozen in a solution containing 10% Me2SO with a cooling rate of 1 degrees C/min, thawed, plated on collagen, and cultured, the albumin secretion rate was 0.21 +/- 0.24 microg/ml/h. In contrast, freshly isolated hepatocytes cryopreserved without preculture and cultured on collagen had an albumin secretion rate of 0.07 +/- 0.08 mg/ml/h. The influences of different solution compositions and cooling rates on postthaw function of precultured hepatocytes were also determined. These results indicate that the use of a preliminary culture step prior to cryopreservation can enhance the postthaw function of hepatocytes.

Cryopreserved porcine hepatocyte cultures

Cryopreservation of freshly isolated hepatocytes is regarded the standard technique for long term storage of liver cells. Frankly, we were not successful in reproducing viability rates of about 70% of that which have been reported by most authors as results of various freezing protocols for hepatocyte suspensions. In fact, we saw mostly devastating results. We assume that intracellular ice crystal formation as well as osmotic changes during freezing and thawing of liver cells cause hazardous effects, especially on membranes of cells after enzymatic isolation, and, thus, generally result in a severe loss in number and impaired specific hepatocyte functions in subsequent culture. We tried to improve results by freezing cell cultures instead. We allowed hepatocytes to regain a more stable condition prior to storage and placed them in tissue flasks in a uniform configuration, rather than to pack cell suspensions in vials or bags under rather indefinable conditions. Porcine hepatocytes (viability 92+/-2%) were isolated from slaughterhouse organs and cultured in a double gel (sandwich) configuration. At day 3, cultures were rate controlled frozen (RCF) and stored in a cell bank for three hours (Group A) or 14 days at -80 degrees C (Group B), respectively. Non-frozen cells (NF) and cultures subjected to a linear freezing rate of -10 degrees C/min (LFR, Group C) with 3 h of storage served as controls from identical cell batches. Upon thawing, at day 2 of subsequent culture, fluorescence microscopy studies revealed a survival rate of 75+/-10% (mean+/-S.D.) in the RCF groups. Time of storage (3 h, 14 d) did not influence results. Survival in Group C was 10+/-5%. Cell integrity was measured by LDH-release, which indicated a larger damage of cells in the LFR group, and thereby resembled the morphological findings. Functional parameters, such as albumin synthesis and CYT P 450-activity were comparable to non-frozen liver cells at 48 h after thawing in the RCF groups (A + B), and showed significantly higher levels in these groups as compared to the LFR Group (C). We recommend to freeze hepatocytes in culture in a rate controlled fashion rather than cell suspensions. This way a cell bank of cryopreserved hepatocyte cultures for batch controlled investigations can be easily obtained. This could ameliorate the availability of rare (human) cell material and might also improve the quality of data generated from in vitro experiments in hepatology or pharmacology/toxicology with liver cells from identical sources. It remains to be seen whether this technique might also be of value in hybrid bioartificial liver devices to make these systems become readily available upon clinical demand.