Rapid decrease in cellular sodium and chloride content during cold incubation of cultured liver endothelial cells and hepatocytes

Optimization of long-term cold storage of rat precision-cut lung slices with a tissue preservation solution

Precision-cut lung slices (PCLS) are used as ex vivo model of the lung to fill the gap between in vitro and in vivo experiments. To allow optimal utilization of PCLS, possibilities to prolong slice viability via cold storage using optimized storage solutions were evaluated. Rat PCLS were cold stored in DMEM/F-12 or two different preservation solutions for up to 28 days at 4°C. After rewarming in DMEM/F-12, metabolic activity, live/dead staining, and mitochondrial membrane potential was assessed to analyze overall tissue viability. Single-cell suspensions were prepared and proportions of CD45⁺, EpCAM⁺, CD31⁺, and CD90⁺ cells were analyzed. As functional parameters, TNF-α expression was analyzed to detect inflammatory activity and bronchoconstriction was evaluated after acetylcholine stimulus. After 14 days of cold storage, viability and mitochondrial membrane potential were significantly better preserved after storage in solution 1 (potassium chloride rich) and solution 2 (potassium- and lactobionate-rich analog) compared with DMEM/F-12. Analysis of cell populations revealed efficient preservation of EpCAM⁺, CD31⁺, and CD90⁺ cells. Proportion of CD45⁺ cells decreased during cold storage but was better preserved by both modified solutions than by DMEM/F-12. PCLS stored in solution 1 responded substantially longer to inflammatory stimulation than those stored in DMEM/F-12 or solution 2. Analysis of bronchoconstriction revealed total loss of function after 14 days of storage in DMEM/F-12 but, in contrast, a good response in PCLS stored in the optimized solutions. An improved base solution with a high potassium chloride concentration optimizes cold storage of PCLS and allows shipment between laboratories and stockpiling of tissue samples.

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.

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.

Improvement of the cold storage of isolated human hepatocytes

Increasing amounts of human hepatocytes are needed for clinical applications and different fields of research, such as cell transplantation, bioartificial liver support, and pharmacological testing. This demand calls for adequate storage options for isolated human liver cells. As cryopreservation results in severe cryoinjury, short-term storage is currently performed at 2-8°C in preservation solutions developed for the storage of solid organs. However, besides slowing down cell metabolism, cold also induces cell injury, which is, in many cell types, iron dependent and not counteracted by current storage solutions. In this study, we aimed to characterize storage injury to human hepatocytes and develop a customized solution for cold storage of these cells. Human hepatocytes were isolated from material obtained from partial liver resections, seeded in monolayer cultures, and, after a preculture period, stored in the cold in classical and new solutions followed by rewarming in cell culture medium. Human hepatocytes displayed cold-induced injury, resulting in >80% cell death (LDH release) after 1 week of cold storage in University of Wisconsin solution or cell culture medium and 3 h of rewarming. Cold-induced injury could be significantly reduced by the addition of the iron chelators deferoxamine and LK 614. Experiments with modified solutions based on the new organ preservation solution Custodiol-N showed that ion-rich variants were better than ion-poor variants, chloride-rich solutions better than chloride-poor solutions, potassium as main cation superior to sodium, and pH 7.0 superior to pH 7.4. LDH release after 2 weeks of cold storage in the thus optimized solution was below 20%, greatly improving cold storage of human hepatocytes. The results were confirmed by the assessment of hepatocellular mitochondrial membrane potential and functional parameters (resazurin reduction, glucagon-stimulated glucose liberation) and thus suggest the use of a customized hepatocyte storage solution for the cold storage of these cells.

Evaluation of functional and structural alterations in muscle tissue after short-term cold storage in a new tissue preservation solution

Storage of muscle preparations in vitro is required for the diagnosis of neuromuscular disorders and for electrophysiological tests. The current standard protocols for muscle storage or transport, i.e. placement on 0.9% NaCl-moistened gauze, lead to impaired function and structural alterations. For other tissues, however, improved preservation methods and solutions have recently been described. In this study, functional and structural alterations in the murine diaphragm were compared after storage on 0.9% NaCl-moistened gauze and after storage in different modifications of the new vascular preservation solution TiProtec®. Muscle force generation after nerve stimulation, histological parameters and ATP levels were investigated after 2.5 h of cold storage at 4°C in the different media and 0.5 h of rewarming at 25°C in Tyrode buffer. Murine diaphragms were injured during cold storage and rewarming, with the degree of the alteration being dependent on the type of solution used. There were no histological alterations and no caspase 3 activation in all groups. In contrast, diaphragms stored in the modified TiProtec solution showed markedly better performance concerning force generation after nerve stimulation (7.1 ± 1.1 cN · s) as well as higher ATP content (2.4 ± 0.7 μmol/g) and were superior to storage on 0.9% NaCl-moistened gauze (1.4 ± 0.4 cN · s; 0.3 ± 0.1 μmol/g). In conclusion, the modified TiProtec preservation solution showed promising results for short-term cold storage of murine diaphragms. For further evaluation, the transferability of these positive findings to storage conditions for muscles of other species, especially human muscle tissue, needs to be investigated.

Fructose 1,6 biphosphate administration to rats prevents metabolic acidosis and oxidative stress induced by deep hypothermia and rewarming

Fructose 1,6 biphosphate (F1,6BP) exerts a protective effect in several in vitro models of induced injury and in isolated organs; however, few studies have been performed using in vivo hypothermia. Here we studied the effects of deep hypothermia (21ºC) and rewarming in anaesthetised rats after F1,6BP administration (2 g/kg body weight). Acid-base and oxidative stress parameters (plasma malondialdehyde and glutathione, and erythrocyte antioxidant enzymes) were evaluated. Erythrocyte and leukocyte numbers in blood and plasma nitric oxide were also measured 3 h after F1,6BP administration in normothermia animals. In the absence of F1,6BP metabolic acidosis developed after rewarming. Oxidative stress was also evident after rewarming, as shown by a decrease in thiol groups and in erythrocyte superoxide dismutase, catalase and GSH-peroxidase, which corresponded to an increase in AST in rewarmed animals. These effects were reverted in rats treated with F1,6BP. Blood samples of F1,6BP-treated animals showed a significant increase in plasma nitric oxide 3 h after administration, coinciding with a significant rise in leukocyte number. F1,6BP protection may be due to the decrease in oxidative stress and to the preservation of the antioxidant pool. In addition, we propose that the reduction in extracellular acidosis may be due to improved tissue perfusion during rewarming and that nitric oxide may play a central role.

Iron-dependent vs. iron-independent cold-induced injury to cultured rat hepatocytes: A comparative study in physiological media and organ preservation solutions

We previously described the entity of cold-induced apoptosis to rat hepatocytes and characterized its major, iron-dependent pathway. However, after cold incubation in some solutions, e.g. cell culture medium, hepatocytes show an additional, yet uncharacterized component of cold-induced injury. We here assessed the effects of organ preservation solutions on both components of cold-induced injury and tried to further characterize the iron-independent component. None of the preservation solutions (University of Wisconsin, histidine-tryptophan-ketoglutarate, Euro-Collins, histidine-lactobionate, sodium-lactobionate-sucrose and Celsior solutions) provided significant protection against cold-induced cell injury (LDH release after 24-h cold incubation/3h rewarming >65% for all solutions); three solutions even enhanced cold-induced injury. However, when the predominant iron-dependent mechanism was eliminated by the addition of iron chelators, all preservation solutions yielded hepatocyte protection that was clearly superior to the one obtainable in cell culture medium or Krebs-Henseleit buffer with iron chelators (LDH release after 24-h cold incubation/3h rewarming <or= 35% in all preservation solutions and 65+/-10% in culture medium). The iron-dependent and the weaker iron-independent component of cold-induced injury showed a different temperature dependence, and in experiments with modified Krebs-Henseleit buffer the principle of the preservation solutions that inhibits the iron-independent component was identified as the low chloride concentration of these solutions (LDH release after cold incubation/rewarming in the presence of iron chelators: 66+/-6% in regular and 22+/-8% in chloride-poor Krebs-Henseleit buffer). Taken together, these results suggest that solutions for cold storage of hepatocytes should be chloride-poor and contain an iron chelator.

New Insights into the Cellular and Molecular Mechanisms of Cold Storage Injury

Solid organ grafts, but also other biologic materials requiring storage for a few hours to a few days, are usually stored under hypothermic conditions. To decrease graft injury during cold storage, organ preservation solutions were developed many years ago. However, since then, modern biochemical and cell biologic methods have allowed further insights into the molecular and cellular mechanisms of cold storage injury, including further insights into alterations of the cellular ion homeostasis, the occurrence of a mitochondrial permeability transition, and the occurrence of free–radical-mediated hypothermic injury and cold-induced apoptosis. These new aspects of cold storage injury, which are not covered by preservation solutions in current clinical use and offer the potential for improvement of organ and tissue preservation, are presented here.

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.

The RUNX1 Runt domain at 1.25A resolution: a structural switch and specifically bound chloride ions modulate DNA binding

The evolutionarily conserved Runt homology domain is characteristic of the RUNX family of heterodimeric eukaryotic transcription factors, including RUNX1, RUNX2 and RUNX3. The genes for RUNX1, also termed acute myeloid leukemia protein 1, AML1, and its dimerization partner core-binding factor beta, CBFbeta, are essential for hematopoietic development and are together the most common targets for gene rearrangements in acute human leukemias. Here, we describe the crystal structure of the uncomplexed RUNX1 Runt domain at 1.25A resolution and compare its conformation to previously published structures in complex with DNA, CBFbeta or both. We find that complex formation induces significant structural rearrangements in this immunoglobulin (Ig)-like DNA-binding domain. Most pronounced is the movement of loop L11, which changes from a closed conformation in the free Runt structure to an open conformation in the CBFbeta-bound and DNA-bound forms. This transition, which we refer to as the S-switch, and accompanying structural movements that affect other parts of the Runt domain are crucial for sustained DNA binding. The closed to open transition can be induced by CBFbeta alone; suggesting that one role of CBFbeta is to trigger the S-switch and to stabilize the Runt domain in a conformation enhanced for DNA binding.A feature of the Runt domain hitherto unobserved in any Ig-like DNA-binding domain is the presence of two specifically bound chloride ions. One chloride ion is coordinated by amino acid residues that make direct DNA contact. In a series of electrophoretic mobility-shift analyses, we demonstrate a chloride ion concentration-dependent stimulation of the DNA-binding activity of Runt in the physiological range. A comparable DNA-binding stimulation was observed for negatively charged amino acid residues. This suggests a regulatory mechanism of RUNX proteins through acidic amino acid residues provided by activation domains during cooperative interaction with other transcription factors.

Mammalian cell injury induced by hypothermia- the emerging role for reactive oxygen species

Hypothermia is a well-known strategem to protect biological material against injurious or degradative processes and is widely used in experimental and especially in clinical applications. However, hypothermia has also proved to be strongly injurious to a variety of cell types. Hypothermic injury to mammalian cells has long been attributed predominantly to disturbances of cellular ion homeostasis, especially of sodium homeostasis. For many years, reactive oxygen species have hardly been considered in the pathogenesis of hypothermic injury to mammalian cells. In recent years, however, increasing evidence for a role of reactive oxygen species in hypothermic injury to these cells has accumulated. Today there seems to be little doubt that reactive oxygen species decisively contribute to hypothermic injury in diverse mammalian cells. In some cell types, such as liver and kidney cells, they even appear to play the central role in hypothermic injury, outruling by far a contribution of the cellular ion homeostasis. In these cells, the cellular chelatable, redox-active iron pool appears to be decisively involved in the pathogenesis of hypothermic injury and of cold-induced apoptosis that occurs upon rewarming of the cells after a (sublethal) period of cold incubation.

Cell volume and ionic transport systems after cold preservation of coronary endothelial cells

BACKGROUND

Hypothermia-induced changes in cell volume and ionic transport systems of coronary endothelial cells may play a role in the development of coronary artery disease in cardiac transplant recipients.

METHODS

Coronary endothelial cells were incubated in University of Wisconsin solution or culture control medium for up to 48 hours at 4 degrees C. Parallel control cultures were incubated at 37 degrees C. Na/K-ATPase and Na/K/Cl cotransport activities were determined as ouabain- and furosemide-sensitive 86Rb+ uptake, respectively. Cell volume changes and cell death were analyzed by a FACScan flow cytometer and the release of lactate dehydrogenase, respectively.

RESULTS

Coronary endothelial cells stored in University of Wisconsin solution up to 6 hours showed an increased Na/K-ATPase activity compared to control cells, whereas no changes were observed in Na/K/Cl cotransport activity or cell volume. Long-term preservation (24 and 48 hours) was associated with a partial loss of cell viability, as demonstrated by lactate dehydrogenase release, and dramatic alterations in ionic transport system activities.

CONCLUSIONS

University of Wisconsin solution seems to prevent coronary endothelial cells Na/K/Cl cotransport activity changes during cold preservation, which could alter cell volume regulation and cause cell injury.

Chloride binding by the AML1/Runx1 transcription factor studied by NMR

It is known that the DNA binding Runt domain of the AML1/Runx1 transcription factor coordinates Cl(-) ions. In this paper we have determined Cl(-) binding affinities of AML1 by (35)Cl nuclear magnetic resonance (NMR) linewidth analysis. The Runt domain binds Cl(-) with a dissociation constant (K(d,Cl)) of 34 mM. If CBFbeta is added to form a 1:1 complex, the K(d,Cl) value increases to 56 mM. Homology modeling suggests that a high occupancy Cl(-) binding site overlaps with the DNA binding surface. NMR data show that DNA displaces this Cl(-) ion. Possible biological roles of Cl(-) binding are discussed based on these findings.

A role for sodium in hypoxic but not in hypothermic injury to hepatocytes and LLC-PK1 cells

BACKGROUND

Hypothermia is considered to be responsible for sodium influx during cold hypoxic incubation. However, we have previously shown that hypothermia alone leads to a pronounced decrease in cellular sodium content when liver endothelial cells or hepatocytes are incubated under such conditions. In the research described here, we therefore studied the effects of hypothermia and hypoxia, alone or combined, on cellular sodium homeostasis and assessed the role sodium plays in the pathogenesis of hypoxic and hypothermic injury to cultured liver and kidney cells.

METHODS

Isolated hepatocytes and LLC-PK1 cells were incubated in Krebs-Henseleit buffer or a sodium-free modification thereof under normoxic and hypoxic conditions at 4 degrees C as well as at 37 degrees C. Cytosolic sodium concentration was determined in isolated hepatocytes under both warm and cold conditions using digital fluorescence microscopy and the Na+-sensitive dye sodium-binding benzofuran isophthalate.

RESULTS

When hepatocytes were incubated under cold normoxic conditions the cellular sodium concentration decreased. However, it increased strongly under hypoxic conditions at 4 degrees C and at 37 degrees C. When either hepatocytes or LLC-PK1 cells were incubated under hypoxic conditions at 4 degrees C or 37 degrees C, sodium-free medium provided protection. In contrast, sodium-free medium did not alleviate the hypothermic injury observed when cells were incubated under cold normoxia.

CONCLUSIONS

The sodium influx observed during cold hypoxia is triggered by hypoxia and not by hypothermia. Sodium plays a prominent role in hypoxic injury to cultured liver and kidney cells, although hypothermic injury of these cells is independent of sodium homeostasis.

Experimental studies on the endothelium ultrastructure of heart capillaries under moderate (28-30 degrees) and deep (22-24 degrees) hypothermia without perfusion

Ultrastructural changes in endothelial cells (EC) of myocardial capillaries were studied in 24 dogs which underwent hypothermia without perfusion. Biopsy specimens for electron microscopy were taken from the left ventricle of each dog in the control group, during anesthesia (prior to active cooling), and at the end of moderate (28-30 degrees ) and deep (22-24 degrees ) artificial body cooling. The following morphological types of the EC were identified both in the control group and in all test groups: those with moderately dense cytoplasm, light, dark, and irreversibly damaged cells. Dark cells showed increased numbers of plasmalemmal vesicles and appeared to be more transport-specialized as opposed to other types. In all stages of the experiment the amount of dark cells continuously increased (to 23.80, 34.62, and 47.17%, respectively). On cooling to 28-30 degrees, subcellular manifestation of reduced synthetic activity of organelles (nucleus, Golgi complex, and rough endoplasmic reticulum) was observed in all types of the EC. These changes persisted, or even increased, at the end of deep hypothermia. The transport activity of the EC changed differently in three experimental groups in all cell types. Micropinocytotic activity increased under spontaneous mild hypothermia (34-35 degrees ) during anesthesia and tended to decrease with subsequent artificial lowering of the temperature to 22-24 degrees. These ultrastructural changes seem to make up an integral part of the process of capillary endothelium adaptation to body surface cooling, and they might contribute to the development of tolerance to subsequent ischemic exposure during cardiac arrest.

Intracellular Na+ accumulation and hepatocyte injury during cold storage

BACKGROUND

The mechanisms responsible for liver damage during cold storage are still not completely understood. We have investigated the role played by alterations of Na+ homeostasis in cell injury during cold hypoxia.

METHODS

The changes in Na+ distribution were investigated in isolated rat hepatocytes stored at 4 degrees C under hypoxic conditions.

RESULTS

Hepatocyte cold stored up to 72 hr in Krebs-Henseleit-Hepes buffer showed a progressive increase in intracellular Na+ content that preceded the loss of cell viability. Na+ accumulation and cell death were prevented using Na+-free, acidic (pH 6.5) or glycine-supplemented storage media. The Na+ ionophore monensin reverted the cytoprotection exerted by glycine and by the acidic medium, but not that given by Na+-free Krebs-Henseleit-Hepes. A low Na+ content was also important for the cytoprotection observed using University of Wisconsin solution.

CONCLUSIONS

Na+ overload might contribute to liver graft injury occurring during cold storage.

Cold-induced apoptosis in cultured hepatocytes and liver endothelial cells: mediation by reactive oxygen species

When cultured hepatocytes were incubated in cell culture medium at 4 degreesC for up to 30 h and then returned to 37 degreesC, blebbing of the plasma membrane, cell detachment, chromatin condensation and margination, enhanced nuclear stainability with Hoechst 33342, ruffling of the nuclear membrane, and DNA fragmentation occurred. Similar to hepatocytes, cultured liver endothelial cells exhibited blebbing, chromatin condensation and margination, marked nuclear condensation, and increased stainability with Hoechst 33342 when exposed to hypothermia/rewarming. In both cell types, the occurrence and extent of these alterations were dependent on the duration of the cold incubation period. This cold-induced apoptosis was inhibited by hypoxia, by an array of free radical scavengers/antioxidants, and by iron chelators. However, the extent of the protection by the different antioxidants was different in the two cell types: iron chelators provided complete protection in liver endothelial cells but only partial protection in hepatocytes, whereas lipophilic antioxidants such as alpha-tocopherol provided complete protection in both cell types. During cold incubation, and especially during rewarming, lipid peroxidation occurred. These results suggest that the formation of reactive oxygen species (ROS) is a key mediator of cold-induced apoptosis, with ROS formation being completely iron-mediated in liver endothelial cells and partially iron-mediated in hepatocytes.

Cold-induced release of reactive oxygen species as a decisive mediator of hypothermia injury to cultured liver cells

The mechanisms of hypothermia-induced cell injury are still unclear. The present study provides experimental evidence for the involvement of reactive oxygen species in hypothermia injury: cultured rat hepatocytes incubated in cold (4 degrees C) Krebs-Henseleit buffer or cell culture medium were injured under normoxic conditions and even more so under hyperoxic conditions, whereas the hepatocytes were protected under hypoxic conditions. During warm (37 degrees C) incubation in cell culture medium, on the other hand, cell injury was minimal under normoxic conditions, only slightly increased under hyperoxic conditions, but substantially increased under hypoxic conditions. The injury occurring during cold normoxic incubation was also largely decreased by the addition of the spin-trap 5,5-dimethyl-1-pyrroline N-oxide, the hydroxyl radical scavenger dimethyl sulfoxide, the flavonoid silibinin, or the transition metal chelator 2,2'-dipyridyl to the medium, or by preincubating the cells with the iron chelator deferoxamine or the lipophilic antioxidant alpha-tocopherol before the hypothermic incubation. In addition, marked lipid peroxidation was observed during cold incubations without inhibitors, but not during warm incubations. Similar results were obtained with cultured rat liver endothelial cells. These results suggest that in hepatocytes and in liver endothelial cells, cold-induced release of reactive oxygen species, most likely of hydroxyl radicals, is the main injurious factor under hypothermic conditions.