Serum- and albumin-free cryopreservation of endothelial monolayers with a new solution.

Cryopreservation is the only long-term storage option for the storage of vessels and vascular constructs. However, endothelial barrier function is almost completely lost after cryopreservation in most established cryopreservation solutions. We here aimed to improve endothelial function after cryopreservation using the 2D-model of porcine aortic endothelial cell monolayers. The monolayers were cryopreserved in cell culture medium or cold storage solutions based on the 4°C vascular preservation solution TiProtec®, all supplemented with 10% DMSO, using different temperature gradients. After short-term storage at -80°C, monolayers were rapidly thawed and re-cultured in cell culture medium. Thawing after cryopreservation in cell culture medium caused both immediate and delayed cell death, resulting in 11 ± 5% living cells after 24 h of re-culture. After cryopreservation in TiProtec and chloride-poor modifications thereof, the proportion of adherent viable cells was markedly increased compared to cryopreservation in cell culture medium (TiProtec: 38 ± 11%, modified TiProtec solutions ≥ 50%). Using these solutions, cells cryopreserved in a sub-confluent state were able to proliferate during re-culture. Mitochondrial fragmentation was observed in all solutions, but was partially reversible after cryopreservation in TiProtec and almost completely reversible in modified solutions within 3 h of re-culture. The superior protection of TiProtec and its modifications was apparent at all temperature gradients; however, best results were achieved with a cooling rate of -1°C/min. In conclusion, the use of TiProtec or modifications thereof as base solution for cryopreservation greatly improved cryopreservation results for endothelial monolayers in terms of survival and of monolayer and mitochondrial integrity.

Cold Storage Injury to Rat Small-bowel Transplants-Beneficial Effect of a Modified HTK Solution.

BACKGROUND: The small bowel is prone to ischemic injury during transport before transplantation, an injury that endangers the recipient patient. The small-bowel mucosal microcirculation in particular appears to be highly sensitive to injury. Current preservation solutions such as histidine-tryptophan-ketoglutarate (HTK) solution provide some protection to the graft. However, these were developed decades ago and do not address several critical processes, such as hypoxia-induced membrane pores and free radical-mediated hypothermic injury. METHODS: To protect the graft from cold ischemic injury, we implemented a modified HTK solution here, including glycine, alanine, and iron chelators in a heterotopic, syngeneic small-bowel transplantation model of the rat. The effects of the modified solution and its major components were compared against the conventional HTK solution using intravital microscopy in the early reperfusion period. RESULTS: The amino acid glycine, added to HTK solution, slightly improved mucosal perfusion. Both, the modified base solution (without iron chelators) and iron chelators increased functional capillary density of the mucosa during the early reperfusion period. The complete modified solution (with glycine, alanine, and iron chelators) significantly increased the perfusion index, functional capillary density of the mucosa, and red blood cell velocity in the grafts after reperfusion in comparison with the grafts preserved with HTK. CONCLUSIONS: The modified preservation solution improved the microcirculation of the transplants and needs detailed evaluation in further models of small-bowel transplantation.

Serum-Free Cryopreservation of Primary Rat Hepatocytes in a Modified Cold Storage Solution: Improvement of Cell Attachment and Function.

AIMS: The use of primary hepatocytes in pharmacological and toxicological research as well as for clinical and biotechnological applications requires adequate storage options for these cells. However, hepatocytes are very susceptible to cryopreservation injury. Based on experience in hypothermic storage of hepatocytes, we, in this study, aimed to optimize hepatocyte cryopreservation. MATERIALS AND METHODS: Rat hepatocytes were cryopreserved in serum-containing cell culture medium or in serum-free solutions optimized for hypothermic storage, all with 10% dimethyl sulfoxide, using a standard protocol (-1°C/min in a controlled-rate freezer). After rapid thawing, cells were seeded in supplemented Leibovitz-15 cell culture medium without further purification steps. Cell attachment and metabolic activity were assessed. RESULTS: Cell attachment (37% ± 15% vs. 9% ± 7% of noncryopreserved control cells) and metabolic activity (resazurin reduction: 47% ± 23% vs. 25% ± 8%; glucose release: 44% ± 6% vs. 15% ± 7%; and urea production: 31% ± 16% vs. 5% ± 8%) were significantly higher after cryopreservation in the new solution compared to cryopreservation in cell culture medium. Experiments with modified solutions suggested that the protective effect of the new solution is multifactorial. CONCLUSIONS: In summary, significant improvement of cell attachment and function compared to cell culture medium was achieved after cryopreservation in serum-free hepatocyte cold storage solution.

Characterization of injury in isolated rat proximal tubules during cold incubation and rewarming.

Organ shortage leads to an increased utilization of marginal organs which are particularly sensitive to storage-associated damage. Cold incubation and rewarming-induced injury is iron-dependent in many cell types. In addition, a chloride-dependent component of injury has been described. This work examines the injury induced by cold incubation and rewarming in isolated rat renal proximal tubules. The tissue storage solution TiProtec® and a chloride-poor modification, each with and without iron chelators, were used for cold incubation. Incubation was performed 4°C for up to 168 h, followed by rewarming in an extracellular buffer (3 h at 37°C). After 48, 120 and 168 h of cold incubation LDH release was lower in solutions containing iron chelators. After rewarming, injury increased especially after cold incubation in chelator-free solutions. Without addition of iron chelators LDH release showed a tendency to be higher in chloride-poor solutions. Following rewarming after 48 h of cold incubation lipid peroxidation was significantly decreased and metabolic activity was tendentially better in tubules incubated with iron chelators. Morphological alterations included mitochondrial swelling and fragmentation being partially reversible during rewarming. ATP content was better preserved in chloride-rich solutions. During rewarming, there was a further decline of ATP content in the so far best conditions and minor alterations under the other conditions, while oxygen consumption was not significantly different compared to non-stored control tubules. Results show an iron-dependent component of preservation injury during cold incubation and rewarming in rat proximal renal tubules and reveal a benefit of chloride for the maintenance of tubular energy state during cold incubation.

Mitochondrial Impairment as a Key Factor for the Lack of Attachment after Cold Storage of Hepatocyte Suspensions.

Isolated primary hepatocytes, which are widely used for pharmacological and clinical purposes, usually undergo certain periods of cold storage in suspension during processing. While adherent hepatocytes were shown previously to suffer iron-dependent cell death during cold (4 °C) storage and early rewarming, we previously found little iron-dependent hepatocyte death in suspension but severely decreased attachment ability unless iron chelators were added. Here, we focus on the role of mitochondrial impairment in this nonattachment of hepatocyte suspensions. Rat hepatocyte suspensions were stored in a chloride-poor, glycine-containing cold storage solution with and without iron chelators at 4 °C. After 1 wk of cold storage in the basic cold storage solution, cell viability in suspension was unchanged, while cell attachment was decreased by >80%. In the stored cells, a loss of mitochondrial membrane potential (MMP), a decrease in adenosine triphosphate (ATP) content (2 ± 2 nmol/106 cells after cold storage, 5 ± 3 nmol/106 cells after rewarming vs. control 29 ± 6 nmol/106 cells), and a decrease in oxygen consumption (101 ± 59 pmol sec-1 per 106 cells after rewarming vs. control 232 ± 83 pmol sec-1 per 106 cells) were observed. Addition of iron chelators to the cold storage solution increased cell attachment to 53% ± 20% and protected against loss of MMP, and cells were able to partially regenerate ATP during rewarming (15 ± 10 nmol/106 cells). Increased attachment could also be achieved by addition of the inhibitor combination of mitochondrial permeability transition, trifluoperazine + fructose. Attached hepatocytes displayed normal MMP and mitochondrial morphology. Additional experiments with freshly isolated hepatocytes confirmed that impaired energy production-as elicited by an inhibitor of the respiratory chain, antimycin A-can decrease cell attachment without decreasing viability. Taken together, these results suggest that mitochondrial impairment with subsequent energy deficiency is a key factor for the lack of attachment of cold-stored hepatocyte suspensions.

Aggravation of cold-induced injury in Vero-B4 cells by RPMI 1640 medium - identification of the responsible medium components.

BACKGROUND: In modern biotechnology, there is a need for pausing cell lines by cold storage to adapt large-scale cell cultures to the variable demand for their products. We compared various cell culture media/solutions for cold storage of Vero-B4 kidney cells, a cell line widely used in biotechnology. RESULTS: Cold storage in RPMI 1640 medium, a recommended cell culture medium for Vero-B4 cells, surprisingly, strongly enhanced cold-induced cell injury in these cells in comparison to cold storage in Krebs-Henseleit buffer or other cell culture media (DMEM, L-15 and M199). Manufacturer, batch, medium supplements and the most likely components with concentrations outside the range of the other media/solutions (vitamin B12, inositol, biotin, p-aminobenzoic acid) did not cause this aggravation of cold-induced injury in RPMI 1640. However, a modified Krebs-Henseleit buffer with a low calcium concentration (0.42 mM), a high concentration of inorganic phosphate (5.6 mM), and glucose (11.1 mM; i.e. concentrations as in RPMI 1640) evoked a cell injury and loss of metabolic function corresponding to that observed in RPMI 1640. Deferoxamine improved cell survival and preserved metabolic function in modified Krebs-Henseleit buffer as well as in RPMI 1640. Similar Ca2+ and phosphate concentrations did not increase cold-induced cell injury in the kidney cell line LLC-PK1, porcine aortic endothelial cells or rat hepatocytes. However, more extreme conditions (Ca2+ was nominally absent and phosphate concentration raised to 25 mM as in the organ preservation solution University of Wisconsin solution) also increased cold-induced injury in rat hepatocytes and porcine aortic endothelial cells. CONCLUSION: These data suggest that the combination of low calcium and high phosphate concentrations in the presence of glucose enhances cold-induced, iron-dependent injury drastically in Vero-B4 cells, and that a tendency for this pathomechanism also exists in other cell types.

Cold storage of rat hepatocyte suspensions for one week in a customized cold storage solution--preservation of cell attachment and metabolism.

BACKGROUND & AIMS: Primary hepatocytes are of great importance for basic research as well as cell transplantation. However, their stability, especially in suspension, is very low. This feature severely compromises storage and shipment. Based on previous studies with adherent cells, we here assessed cold storage injury in rat hepatocyte suspensions and aimed to find a cold storage solution that preserves viability, attachment ability and functionality of these cells. METHODS: Rat hepatocyte suspensions were stored in cell culture medium, organ preservation solutions and modified TiProtec solutions at 4°C for one week. Viability and cell volume were determined by flow cytometry. Thereafter, cells were seeded and density and metabolic capacity (reductive metabolism, forskolin-induced glucose release, urea production) of adherent cells were assessed. RESULTS: Cold storage injury in hepatocyte suspensions became evident as cell death occurring during cold storage or rewarming or as loss of attachment ability. Cell death during cold storage was not dependent on cell swelling and was almost completely inhibited in the presence of glycine and L-alanine. Cell attachment could be greatly improved by use of chloride-poor solutions and addition of iron chelators. Using a chloride-poor, potassium-rich storage solution containing glycine, alanine and iron chelators, cultures with 75% of the density of control cultures and with practically normal cell metabolism could be obtained after one week of cold storage. CONCLUSION: In the solution presented here, cold storage injury of hepatocyte suspensions, differing from that of adherent hepatocytes, was effectively inhibited. The components which acted on the different injurious processes were identified.