Cold preservation of isolated rabbit proximal tubules induces radical-mediated cell injury

Liproxstatin-1 Alleviates Lung Transplantation-induced Cold Ischemia-Reperfusion Injury by Inhibiting Ferroptosis

BACKGROUND

Primary graft dysfunction, which is directly related to cold ischemia-reperfusion (CI/R) injury, is a major obstacle in lung transplantation (LTx). Ferroptosis, a novel mode of cell death elicited by iron-dependent lipid peroxidation, has been implicated in ischemic events. This study aimed to investigate the role of ferroptosis in LTx-CI/R injury and the effectiveness of liproxstatin-1 (Lip-1), a ferroptosis inhibitor, in alleviating LTx-CI/R injury.

METHODS

LTx-CI/R-induced signal pathway alterations, tissue injury, cell death, inflammatory responses, and ferroptotic features were examined in human lung biopsies, the human bronchial epithelial (BEAS-2B) cells, and the mouse LTx-CI/R model (24-h CI/4-h R). The therapeutic efficacy of Lip-1 was explored and validated both in vitro and in vivo.

RESULTS

In human lung tissues, LTx-CI/R activated ferroptosis-related signaling pathway, increased the tissue iron content and lipid peroxidation accumulation, and altered key protein (GPX4, COX2, Nrf2, and SLC7A11) expression and mitochondrial morphology. In BEAS-2B cells, the hallmarks of ferroptosis were significantly evidenced at the setting of both CI and CI/R compared with the control, and the effect of adding Lip-1 only during CI was much better than that of only during reperfusion by Cell Counting Kit-8. Furthermore, Lip-1 administration during CI markedly relieved LTx-CI/R injury in mice, as indicated by significant improvement in lung pathological changes, pulmonary function, inflammation, and ferroptosis.

CONCLUSIONS

This study revealed the existence of ferroptosis in the pathophysiology of LTx-CI/R injury. Using Lip-1 to inhibit ferroptosis during CI could ameliorate LTx-CI/R injury, suggesting that Lip-1 administration might be proposed as a new strategy for organ preservation.

How to improve results after DCD (donation after circulation death)

The shortage of organs for transplantation has led health professionals to look for alternative sources of donors. One of the avenues concerns donors who have died after circulatory arrest. This is a special situation because the organs from these donors are exposed to warm ischaemia-reperfusion lesions that are unavoidable during the journey of the organs from the donor to the moment of transplantation in the recipient. We will address and discuss the key issues from the perspective of team organization, legislation and its evolution, and the ethical framework. In a second part, the avenues to improve the quality of organs will be presented following the itinerary of the organs between the donor and the recipient. The important moments from the point of view of therapeutic strategy will be put into perspective. New connections between key players involved in pathophysiological mechanisms and implications for innate immunity and injury processes are among the avenues to explore. Technological developments to improve the quality of organs from these recipients will be analyzed, such as perfusion techniques with new modalities of temperatures and oxygenation. New molecules are being investigated for their potential role in protecting these organs and an analysis of potential prospects will be proposed. Finally, the important perspectives that seem to be favored will be discussed in order to reposition the use of deceased donors after circulatory arrest. The use of these organs has become a routine procedure and improving their quality and providing the means for their evaluation is absolutely inevitable.

Preservation of Organs to Be Transplanted: An Essential Step in the Transplant Process

Organ transplantation remains the treatment of last resort in case of failure of a vital organ (lung, liver, heart, intestine) or non-vital organ (essentially the kidney and pancreas) for which supplementary treatments exist. It remains the best alternative both in terms of quality-of-life and life expectancy for patients and of public health expenditure. Unfortunately, organ shortage remains a widespread issue, as on average only about 25% of patients waiting for an organ are transplanted each year. This situation has led to the consideration of recent donor populations (deceased by brain death with extended criteria or deceased after circulatory arrest). These organs are sensitive to the conditions of conservation during the ischemia phase, which have an impact on the graft’s short- and long-term fate. This evolution necessitates a more adapted management of organ donation and the optimization of preservation conditions. In this general review, the different aspects of preservation will be considered. Initially done by hypothermia with the help of specific solutions, preservation is evolving with oxygenated perfusion, in hypothermia or normothermia, aiming at maintaining tissue metabolism. Preservation time is also becoming a unique evaluation window to predict organ quality, allowing repair and/or optimization of recipient choice.

Physiological Impact of Hypothermia: The Good, the Bad and the Ugly

Hypothermia is defined as a core body temperature of < 35°C, and as body temperature is reduced the impact on physiological processes can be beneficial or detrimental. The beneficial effect of hypothermia enables circulation of cooled experimental animals to be interrupted for 1-2 h without creating harmful effects, while tolerance of circulation arrest in normothermia is between 4 and 5 min. This striking difference has attracted so many investigators, experimental as well as clinical, to this field, and this discovery was fundamental for introducing therapeutic hypothermia in modern clinical medicine in the 1950's. Together with the introduction of cardiopulmonary bypass, therapeutic hypothermia has been the cornerstone in the development of modern cardiac surgery. Therapeutic hypothermia also has an undisputed role as a protective agent in organ transplantation and as a therapeutic adjuvant for cerebral protection in neonatal encephalopathy. However, the introduction of therapeutic hypothermia for organ protection during neurosurgical procedures or as a scavenger after brain and spinal trauma has been less successful. In general, the best neuroprotection seems to be obtained by avoiding hyperthermia in injured patients. Accidental hypothermia occurs when endogenous temperature control mechanisms are incapable of maintaining core body temperature within physiologic limits and core temperature becomes dependent on ambient temperature. During hypothermia spontaneous circulation is considerably reduced and with deep and/or prolonged cooling, circulatory failure may occur, which may limit safe survival of the cooled patient. Challenges that limit safe rewarming of accidental hypothermia patients include cardiac arrhythmias, uncontrolled bleeding, and "rewarming shock".

In Vitro/Ex Vivo Models for the Study of Ischemia Reperfusion Injury during Kidney Perfusion

Oxidative stress is a key element of ischemia–reperfusion injury, occurring during kidney preservation and transplantation. Current options for kidney graft preservation prior to transplantation are static cold storage (CS) and hypothermic machine perfusion (HMP), the latter demonstrating clear improvement of preservation quality, particularly for marginal donors, such as extended criteria donors (ECDs) and donation after circulatory death (DCDs). Nevertheless, complications still exist, fostering the need to improve kidney preservation. This review highlights the most promising avenues of in kidney perfusion improvement on two critical aspects: ex vivo and in vitro evaluation.

Individual and Combined Impact of Oxygen and Oxygen Transporter Supplementation during Kidney Machine Preservation in a Porcine Preclinical Kidney Transplantation Model

Marginal kidney graft preservation in machine perfusion (MP) is well-established. However, this method requires improvement in order to mitigate oxidative stress during ischemia-reperfusion, by using oxygenation or an O2 carrier with anti-oxidant capacities (hemoglobin of the marine worm; M101). In our preclinical porcine (pig related) model, kidneys were submitted to 1h-warm ischemia, followed by 23 h hypothermic preservation in Waves® MP before auto-transplantation. Four groups were studied: W (MP without 100%-O2), W-O2 (MP with 100%-O2; also called hyperoxia), W-M101 (MP without 100%-O2 + M101 2 g/L), W-O2 + M101 (MP with 100%-O2 + M101 2 g/L) (n = 6/group). Results: Kidneys preserved in the W-M101 group showed lower resistance, compared to our W group. During the first week post-transplantation, W-O2 and W-M101 groups showed a lower blood creatinine and better glomerular filtration rate. KIM-1 and IL-18 blood levels were lower in the W-M101 group, while blood levels of AST and NGAL were lower in groups with 100% O2. Three months after transplantation, fractional excretion of sodium and the proteinuria/creatinuria ratio remained higher in the W group, creatininemia was lower in the W-M101 group, and kidney fibrosis was lower in M101 groups. We concluded that supplementation with M101 associated with or without 100% O2 improved the Waves® MP effect upon kidney recovery and late graft outcome.

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.

Organ protection during aortic cross-clamping

Open surgical repair of an aortic aneurysm requires aortic cross-clamping, resulting in temporary ischemia of all organs and tissues supplied by the aorta distal to the clamp. Major complications of open aneurysm repair due to aortic cross-clamping include renal ischemia-reperfusion injury and postoperative colonic ischemia in case of supra- and infrarenal aortic aneurysm repair. Ischemia-reperfusion injury results in excessive production of reactive oxygen species and in oxidative stress, which can lead to multiple organ failure. Several perioperative protective strategies have been suggested to preserve renal function during aortic cross-clamping, such as pharmacotherapy and therapeutic hypothermia of the kidneys. In this chapter, we will briefly discuss the pathophysiology of ischemia-reperfusion injury and the preventative measures that can be taken to avoid abdominal organ injury. Finally, techniques to minimize the risk of complications during and after open aneurysm repair will be presented.

Evaluation of the protection exerted by Pisum sativum Ferredoxin-NADP(H) Reductase against injury induced by hypothermia on Cos-7 cells

Hypothermia is employed as a method to diminish metabolism rates and preserve tissues and cells. However, low temperatures constitute a stress that produces biochemical changes whose extension depends on the duration and degree of cold exposure and is manifested when physiological temperature is restored. For many cellular types, cold induces an oxidative stress that is dependent on the elevation of intracellular iron, damages macromolecules, and is prevented by the addition of iron chelators. Pisum sativum Ferredoxin-NADP(H) Reductase (FNR) has been implicated in protection from injury mediated by intracellular iron increase and successfully used to reduce oxidative damage on bacterial, plant and mammalian systems. In this work, FNR was expressed in Cos-7 cells; then, they were submitted to cold incubation and iron overload to ascertain whether this enzyme was capable of diminishing the harm produced by these challenges. Contrary to expected, FNR was not protective and even exacerbated the damage under certain circumstances. It was also found that the injury induced by hypothermia in Cos-7 cells presented both iron-dependent and iron-independent components of damage when cells were actively dividing but only iron-independent component when cells were in an arrested state. This is in agreement with previous findings which showed that iron-dependent damage is also an energy-dependent process.

MitoQ blunts mitochondrial and renal damage during cold preservation of porcine kidneys

Cold preservation has greatly facilitated the use of cadaveric kidneys for transplantation but damage occurs during the preservation episode. It is well established that oxidant production increases during cold renal preservation and mitochondria are a key target for injury. Our laboratory has demonstrated that cold storage of renal cells and rat kidneys leads to increased mitochondrial superoxide levels and mitochondrial electron transport chain damage, and that addition of Mitoquinone (MitoQ) to the preservation solutions blunted this injury. In order to better translate animal studies, the inclusion of large animal models is necessary to develop safe preclinical protocols. Therefore, we tested the hypothesis that addition of MitoQ to cold storage solution preserves mitochondrial function by decreasing oxidative stress, leading to less renal tubular damage during cold preservation of porcine kidneys employing a standard criteria donor model. Results showed that cold storage significantly induced oxidative stress (nitrotyrosine), renal tubular damage, and cell death. Using High Resolution Respirometry and fresh porcine kidney biopsies to assess mitochondrial function we showed that MitoQ significantly improved complex II/III respiration of the electron transport chain following 24 hours of cold storage. In addition, MitoQ blunted oxidative stress, renal tubular damage, and cell death after 48 hours. These results suggested that MitoQ decreased oxidative stress, tubular damage and cell death by improving mitochondrial function during cold storage. Therefore this compound should be considered as an integral part of organ preservation solution prior to transplantation.

Hypothermic renal perfusion during aortic surgery reduces the presence of lipocalin-2 and preserves renal extraction of dimethylarginines in rats

Cold perfusion through the renal arteries during renal ischemia has been suggested to diminish postoperative renal damage after juxtarenal aortic aneurysm repair. As the kidneys play a key role in dimethylarginine metabolism, which in turn is associated with renal hemodynamics, we hypothesized that the protective effect of cold perfusion is associated with a preserved renal extraction of dimethylarginines. Renal ischemia was induced in three groups of anesthetized Wistar rats ( n = 7/group), which underwent suprarenal aortic clamping (45 min) with no perfusion ( group 1), renal perfusion with 37°C saline ( group 2), or renal perfusion with 4°C saline ( group 3), respectively, followed by 90 min of renal reperfusion in all groups. The sham group had no clamping. In group 3 (renal ischemia with cold perfusion), postoperative serum creatinine levels as well as the presence of luminal lipocalin-2 and its associated brush-border damage were lower compared with groups 1 and 2 ( P < 0.05). Also, renal extraction of asymmetrical (ADMA) and symmetrical (SDMA) dimethylarginine as well as the arginine/ADMA ratio, which defines the bioavailability of nitric oxide, remained intact in group 3 only ( P < 0.04). The arginine/ADMA ratio correlated with cortical flow, lipocalin-2, and creatinine rises. Warm and cold renal perfusion ( groups 2 and 3) during ischemia were similarly effective in lowering protein nitrosylation levels, renal leukocyte accumulation, neutrophil gelatinase-associated lipocalin (NGAL) expression in distal tubules, and urine NGAL ( P < 0.05). These data support the use of cold renal perfusion during renal ischemia in situations where renal ischemia is inevitable, as it reduces tubular damage and preserves renal extraction of dimethylarginines. Renal perfusion with saline per se during renal ischemia is effective in diminishing renal leukocyte accumulation and oxidative stress.

Role of mitochondrial-derived oxidants in renal tubular cell cold-storage injury

Cold storage (CS) is regarded as a necessary procedure during donation of a deceased-donor kidney that helps to optimize organ viability. Increased oxidant generation during CS as well as during the reperfusion (or rewarming/CS.RW) phase has been suggested to be a major contributor to renal injury, although the source of and/or biochemical pathways involved in oxidant production remain unclear. The purpose of this study was to determine if renal tubular mitochondrial superoxide is capable of inducing oxidant production and mitochondrial damage in response to a CS.RW insult. To test the role of mitochondrial superoxide in CS.RW injury, we used rat renal proximal tubular (NRK) cells overexpressing manganese superoxide dismutase (MnSOD), the major mitochondrial antioxidant. Oxidant production, mitochondrial membrane potential, respiratory complex function, and cell death were all altered after exposure of NRK cells to CS.RW. MnSOD overexpression or inhibition of nitric oxide synthase provided significant protection against oxidant generation, respiratory complex inactivation, and cell death. These findings implicate mitochondrial superoxide, nitric oxide, and their reaction product, peroxynitrite, as key signaling molecules involved in CS.RW injury of renal tubular cells and suggest that therapeutic inhibition of these pathways may protect the donor kidney.

Improving the long-term storage of a mammalian biosensor cell line via genetic engineering

The unique properties of mammalian cells make them valuable for a variety of applications in medicine, industry, and diagnostics. However, the utility of such cells is restricted due to the difficulty in storing them non-frozen for an extended time and still maintaining their stability and responsiveness. In order to extend the active life span of a mammalian biosensor cell line at room and refrigerated temperatures, we have over expressed genes that are reported to provide protection from apoptosis, stress, or oxidation. We demonstrated that over expression of genes from the extremophile, Artemia franciscana, as well as GADD45beta, extends room-temperature storage of fully active cells 3.5-fold, while over production of several anti-apoptotic proteins extended 4 degrees C storage 2- to 3-fold. Methodologies like these that improve the stability of mammalian-cell-based technologies in the absence of freezers may enable widespread use of these tools in applications that have been considered impractical based solely on limited storage characteristics.

Organ preservation solutions attenuate accumulation and nuclear translocation of hypoxia-inducible factor-1alpha in the hepatoma cell line HepG2

Hypoxia-inducible factor-1alpha (HIF-1alpha) is a key transcription factor orchestrating hypoxic and inflammatory reactions. Here, we determined the impact of organ preservation solutions (Celsior; histidine-tryptophan-ketoglutarate solution, HTK; University of Wisconsin solution; UW), oxygen supply, and temperature on HIF-1alpha accumulation, recorded by Western blotting and immunocytochemistry, in the human hepatoma cell line HepG2. Generation of reactive oxygen species (ROS), NO, and cell viability were concomitantly assessed. At 4 degrees C, HIF-1alpha accumulation was not detectable. In normothermic (37 degrees C) cell culture medium (Dulbecco's Modified Eagle's Medium, DMEM), HepG2 cells accumulated HIF-1alpha even in normoxia (21% O(2)) which was not observed in either of the preservation solutions. This correlated to high generation of NO, a normoxic stabilizer of HIF-1alpha, and L-arginine content (substrate for NO synthesis) in DMEM, and low NO production and absence of L-arginine in preservation solutions. In normothermic hypoxia up to 24 h, intracellular HIF-1alpha accumulated in all conditions, but less in preservation solutions compared to DMEM. The inhibitory effect on accumulation and nuclear translocation was most prominent for HTK, the only solution containing the activator of HIF-1alpha degradation, alpha-ketoglutarate. Addition of other intermediates of the tricarbon acid cycle-succinate, fumarate, malate-did not alter HIF-1alpha accumulation, although succinate exhibited a beneficial effect on cell viability in cold storage. In conclusion, preservation solutions attenuate accumulation and nuclear translocation of the transcription factor HIF-1alpha, and this property is seemingly related to their chemical composition (L-arginine, alpha-ketoglutarate). Thus, it appears feasible to design preservation solution specifically to modify HIF-1alpha accumulation and nuclear translocation.

ROS scavenging before 27 degrees C ischemia protects hearts and reduces mitochondrial ROS, Ca2+ overload, and changes in redox state

We have shown that cold perfusion of hearts generates reactive oxygen and nitrogen species (ROS/RNS). In this study, we determined 1) whether ROS scavenging only during cold perfusion before global ischemia improves mitochondrial and myocardial function, and 2) which ROS leads to compromised cardiac function during ischemia and reperfusion (I/R) injury. Using fluorescence spectrophotometry, we monitored redox balance (NADH and FAD), O(2)(*-) levels and mitochondrial Ca(2+) (m[Ca(2+)]) at the left ventricular wall in 120 guinea pig isolated hearts divided into control (Con), MnTBAP (a superoxide dismutase 2 mimetic), MnTBAP (M) + catalase (C) + glutathione (G) (MCG), C+G (CG), and N(G)-nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthase inhibitor) groups. After an initial period of warm perfusion, hearts were treated with drugs before and after at 27 degrees C. Drugs were washed out before 2 h at 27 degrees C ischemia and 2 h at 37 degrees C reperfusion. We found that on reperfusion the MnTBAP group had the worst functional recovery and largest infarction with the highest m[Ca(2+)], most oxidized redox state and increased ROS levels. The MCG group had the best recovery, the smallest infarction, the lowest ROS level, the lowest m[Ca(2+)], and the most reduced redox state. CG and L-NAME groups gave results intermediate to those of the MnTBAP and MCG groups. Our results indicate that the scavenging of cold-induced O(2)(*-) species to less toxic downstream products additionally protects during and after cold I/R by preserving mitochondrial function. Because MnTBAP treatment showed the worst functional return along with poor preservation of mitochondrial bioenergetics, accumulation of H(2)O(2) and/or hydroxyl radicals during cold perfusion may be involved in compromised function during subsequent cold I/R injury.

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.

Hypothermic perfusion preservation: the future of organ preservation revisited?

Hypothermic perfusion preservation (HPP) was an integral step in the development of early clinical transplantation programmes, and considerable progress was made in understanding the basic principles underlying the technique. In subsequent years, the development of better preservation solutions for cold hypoxic storage, along with pragmatic choices made on grounds of costs and logistics, saw a fall in the application of HPP. More recently, the acute shortage of suitable organ donors and the inevitable pressure to use organs from sub-optimal (or expanded criteria) donors, has forced a re-evaluation of HPP, and the development of a new generation of HPP machines and associated perfusion solutions. This review sets out the historical development of HPP across the range of organs in which the method was originally investigated, describes the biological benefits and drawbacks associated with HPP, and sets out the most recent literature on the topic (including comments on the interest in use of higher temperatures in organ perfusion).

Hypothermia-Induced Loss of Endothelial Barrier Function Is Restored after Dopamine Pretreatment: Role of p42/p44 Activation

BACKGROUND

Donor dopamine usage is associated with improved immediate graft function after renal transplantation. Although prolonged cold preservation results in an increased vascular permeability, the present study was conducted to examine in vitro and in vivo if dopamine pretreatment influences endothelial barrier function under such conditions.

METHODS

To assess cold preservation injury in vitro and in vivo, cultured human umbilical vein endothelial cells (HUVEC) and Lewis donor rats were pretreated with dopamine or isotonic saline prior to cold storage. Injury was determined by lactate dehydrogenase (LDH) release, histology, and functional analysis.

RESULTS

In vitro cold storage resulted in intercellular gap formation in both untreated and dopamine pretreated HUVEC. In the latter monolayer integrity was completely restored upon rewarming and paracellular transport of fluorescein isothiocyanate-dextran was significantly reduced. In dopamine treated HUVEC, intercellular gap formation was independent of cell death and was associated with redistribution of junctional proteins and condensation of cytoskeleton proteins. In untreated HUVEC proteolysis and cell death were clearly evident after hypothermia. Closing of intercellular gaps was dependent on p42/p44 activation. Regeneration of adenosine triphosphate was only observed in dopamine pretreated cells. Only in dopamine treated Lewis renal allografts subjected to cold storage, activation of p42/p44 occurred upon rewarming. These grafts had a better renal function and displayed less inflammatory cells five days after transplantation.

CONCLUSION

Our study demonstrates beneficial effects of dopamine treatment on cold storage induced endothelial barrier disturbances. This may contribute to the positive effects of catecholamines on immediate graft function of renal allografts in men.

Protective effect of PEG 35,000 Da on renal cells: paradoxical activation of JNK signaling pathway during cold storage

Polyethylene glycol (PEG), a high-molecular weight colloid, is added to preservation solutions in order to decrease cold- and ischemia-induced injuries of the grafted organ. We evaluated on LLC-PK1, a porcine proximal tubular epithelial cell line (1) the efficiency of several commercial preservation solutions (University of Wisconsin, Euro-Collins, Celsior, SCOT, IGL-1), and (2) whether adding PEG (400-35,000 Da) in a simple extracellular-type buffer modified cell integrity and mitogen-activated protein kinase (MAPK) signaling pathways. SCOT was the most efficient commercial solution. Moreover, only PEG 35,000 Da totally preserved cell viability, induced a decrease on reactive oxygen species production and a decrease on p38-MAPK activation. Furthermore PEG 35,000 Da stimulated c-Jun N-terminal kinase (JNK). However, the inhibition of JNK pathway, with the specific SP600125 inhibitor, in the presence of PEG 35,000 Da did not affect cell survival. We also confirmed on whole pig kidney the protective effect of PEG 35,000 Da on cold-induced tubular injuries. This study confirms PEG antioxidative properties, but we demonstrate that its effect on JNK signaling pathway had also a paradoxical effect on cell death. This sheds a new light on PEG effects during cell preservation, independently from the classical immuno-camouflaging hypothesis.

Protection of mitochondria during cold storage of liver and following transplantation: comparison of the two solutions, University of Wisconsin and Eurocollins

Injury to allografts during ischaemia/reperfusion contribute to the development of graft failure following transplantation with significant morbidity and mortality to patients. The development of University of Wisconsin solution has significantly improved the quality of graft preservation and transplant outcome relative to formerly used solutions such as Eurocollins. The aim of this study was to further characterize mitochondrial structural and functional alterations occurring in rat livers following cold storage and transplantation. Mitochondrial impairment after prolonged storage in Eurocollins included decreased cyt. c+c1, cyt. b and cyt. a+a3 concentration and dramatic falls in the activities of the respiratory chain enzymes ubiquinol-cyt. c oxidoreductase and cytochrome oxidase. Under the same conditions the highest hydroperoxide but lowest vitamin E concentrations were also found. Although both the Eurocollins and University of Wisconsin preservation solutions have limitations in preventing oxidative injuries following cold storage and reperfusion, our data indicate that mitochondrial impairment was higher in Eurocollins- than in University of Wisconsin-stored livers. Further improvements are necessary in maintaining the stability of mitochondria in order to optimize preservations solutions used in transplantations.

Protective effect of vascular endothelial growth factor (VEGF) in frozen-thawed granulosa cells is mediated by inhibition of apoptosis

OBJECTIVES

This study was conducted to evaluate the involvement of apoptosis in the freeze-thaw process and to investigate the anti-apoptotic effect of vascular endothelial growth factor (VEGF) in the frozen-thawed granulosa cells.

STUDY DESIGN

Isolated rat granulosa cells were cultured, frozen-thawed, and were cultured for 24h. Cell viabilities (by Trypan blue exclusion test) and apoptotic patterns (by Annexin-V/propidium iodide (PI) Double-Staining) were determined at each step. Apoptotic cell death was confirmed by following DNA degradation and caspase-3 activity.

RESULTS

After freeze-thaw process and 24h of culture, reductions in the cellular viabilities and increases in the number of cells containing degraded DNA were lower in the VEGF pretreated group than in the control group (p<0.05). In the VEGF pretreated group, increases in the proportions of late apoptotic cells [Annexin-V (+)/PI (+)] were significantly lower and caspase-3 expression was prevented immediate after thawing (p<0.05). Furthermore, increases in the proportions of early apoptotic cells [Annexin-V (+)/PI (-)] and reductions in the proportions of viable cells [Annexin-V (-)/PI (-)] were significantly lower in the VEGF pretreated group after culture for 24h (p<0.05). Of the different doses of VEGF pretreated, 50ng/ml was found to be most effective with respect to protecting frozen-thawed granulosa cells from cryoinjury.

CONCLUSION

Granulosa cell damage induced by cryopreservation is mediated, at least in part, by an apoptotic process. Our preliminary results suggest that VEGF treatment before freeze-thaw process reduces rat ovarian granulosa cell damage by inhibiting apoptosis.

Improved Cold Preservation of Kidney Tubular Cells by Means of Adding Bioflavonoids to Organ Preservation Solutions

BACKGROUND

Cold ischemia and reperfusion during renal transplantation result in release of reactive oxygen species. The aim of this study is to examine whether cold storage induced cell injury can be ameliorated by adding flavonoids directly to preservation solutions.

METHODS

Cultured renal tubular epithelial cells (LLC-PK1) were stored in University of Wisconsin (UW) or Euro-Collins (EC) solution at 4 degrees C for 20 hours. Preservation solutions were supplemented with various flavonoids. After rewarming, structural and metabolic cell integrity was measured by lactate dehydrogenase (LDH) release and MTT-test, and lipid peroxidation was assessed from generation of thiobarbituric acid-reactive substances (TBARS).

RESULTS

Twenty hours of cold storage resulted in a substantial loss of cell viability in both preservation solutions (in EC: LDH release 92.4+/-2.7%; MTT-test 0.5+/-0.7%). Addition of luteolin, quercetin, kempferol, fisetin, myricetin, morin, catechin, and silibinin significantly reduced cell injury (for luteolin in EC: LDH release 2.4+/-1.6%; MTT-test 110.3+/-10.4%, P<0.01; TBARS-production (related to cold stored control cells) 8.9+/-2.6%). No cytoprotection was found for apigenin, naringenin, and rutin. Protective potency of flavonoids depends on number of hydroxyl-substituents and lipophilicity of the diphenylpyran compounds.

CONCLUSION

Cold storage induced injury of renal tubular cells was substantially ameliorated by adding selected flavonoids directly to preservation solutions.

Role of Peroxynitrite Anion in Renal Hypothermic Preservation Injury

BACKGROUND

Peroxynitrite anions may play a role in normothermic renal ischemia and reperfusion. The purpose of this study was to determine if endogenous peroxynitrite anion is involved in renal preservation injury.

METHODS

Experiments were conducted in isolated canine renal tubules and in a canine autotransplant model of hypothermic preservation injury.

RESULTS

Isolated renal tubules demonstrated progressive loss of membrane transport function after reperfusion with increasing cold storage times in UW solution as assessed by tetraethylammonium cation transport (TEA). This transport defect was not altered by reperfusion in the presence of WW85, a peroxynitrite decomposition catalyst. Likewise, tubule LDH release was not altered by WW85. Renal tubules did not demonstrate any evidence of peroxynitrite formation after cold storage (0-120 h) or after subsequent reperfusion in vitro as measured by nitrotyrosine adduct formation. Addition of exogenous peroxynitrite (1 mM) directly to freshly isolated renal tubules produced strong nitrotyrosine signals but failed to alter membrane function (TEA uptake). Conversely, SIN-1, a peroxynitrite generator molecule, failed to produce a nitrotyrosine signal in extracted renal tubule proteins but significantly impaired transport function. Finally, function of cold stored canine autografts was not affected by the scavenging of peroxynitrite anions (WW85) before kidney harvest and immediately at reperfusion. Tissue biopsies from cold stored kidney autografts also failed to show evidence of peroxynitrite synthesis either after cold storage (72 h) or after kidney transplantation (60 min reperfusion).

CONCLUSIONS

This study concludes that peroxynitrite anions are not formed and are not involved in renal preservation injury.

Oxygenation during hypothermic rat liver preservation: an in vitro slice study to demonstrate beneficial or toxic oxygenation effects

Hypothermic machine perfusion (HMP) of abdominal organs is shown to be superior compared to cold storage. However, the question remains if oxygenation is required during preservation as oxygen is essential for energy resynthesis but also generates toxic reactive oxygen species (ROS). To determine if oxygenation should be used during HMP, urea-synthesis rate, adenosine triphosphate (ATP), and generation of ROS were studied in an in vitro model, modeling ischemia-reperfusion injury. Furthermore, expression of uncoupling protein-2 (UCP-2) mRNA was assessed since UCP-2 is a potentially protective protein against ROS. Rat liver slices were preserved for 0, 24, and 48 hr in University of Wisconsin machine perfusion solution (UW-MP) with 0%, 21%, or 95% oxygen at 0-4 degrees C and reperfused for 24 hours. In the 0% and 95% groups, an increase of ROS was found after cold storage in UW-MP. After slice reperfusion, only the 0% oxygen group showed higher levels. The 0% group showed a lower urea-synthesis rate as well as lower ATP levels. mRNA upregulation of UCP-2 was, in contrast to kidney mRNA studies, not observed. In conclusion, oxygenation of UW-MP gave better results. This study also shows that ROS formation occurs during hypothermic preservation and the liver is not protected by UCP-2. We conclude that saturation of UW-MP with 21% oxygen allows optimal preservation results.

In Vitro Evaluation of the Transportability of Viable Primary Human Liver Cells Originating From Discarded Donor Organs in Bioreactors

BACKGROUND

The use of primary human liver cells obtained from discarded donor organs is increasingly favored for cell-based extracorporeal liver support systems. However, as cryopreservation of primary human hepatocytes causes a significant loss of metabolic activity, the transport of bioreactors with viable liver cells is required. The aim of this study was to evaluate the impact of two major potential threats to viable cells during transport: temperature changes and mechanical stress.

METHODS

In each experiment three hollow fiber-based bioreactors were charged with primary human liver cells originating from the same discarded donor organ and were simultaneously kept under culture conditions for 8 days. In total, 18 bioreactors were evaluated. On the fifth day the bioreactors were exposed to hypothermia (4 degrees C, n = 3), to hyperthermia (42 degrees C, n = 3), or served as normothermic controls (37 degrees C, n = 3). In a second test series bioreactors were exposed to vibration (21 Hz for 20 min, thereafter 7 Hz for 160 min, n = 3), or were operated as control cultures (n = 6). The release of hepatocyte-specific enzymes was determined as an indicator for cell damage.

RESULTS

Hypothermic stress resulted in a significant release of transaminases and led to disturbances of the histological integrity, all indicating a high degree of cell damage. When compared with the control cultures, hyperthermia and mechanical stress in terms of vibration had no significant effect on the cells.

CONCLUSION

The transport of hollow fiber bioreactors charged with viable primary human liver cells appears to be feasible in transport monitors for perfusion and temperature control.

Cold ischemic injury of transplanted kidneys: new insights from experimental studies

Kidney transplantation is the preferred and definitive treatment for end-stage renal disease (ESRD), and kidneys from deceased donors are a major source for it. These kidneys are routinely cold stored to prolong viability, which, however, when prolonged can cause injury, resulting in reduced graft function and survival. Recent experimental studies have identified the release of iron and free radicals, activation of calpain, and formation of F2-isoprostanes as important components of cold ischemic injury, as are the swelling of mitochondria and activation of mitochondrial apoptotic pathways. Moreover, studies have also suggested that fortifying the storage solution with deferoxamine or preconditioning the donor kidneys with hemeoxygenase-1 may prove viable clinical strategies to limit cold ischemic injury. This review will summarize these and other new experimental data that have implications for reducing cold ischemic transplant injury, a step necessary to improve deceased-donor allograft survival.

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.

Preserved vascular reactivity of rat renal arteries after cold storage

In cultured renal tubular cells hypothermia results in cell damage caused by iron-dependent formation of reactive oxygen species. It is unknown whether cold preservation affects function of renal vessels. Rat renal arcuate arteries were stored in a physiological salt solution at 4 degrees C for 24h and compared to control arteries (not stored). To some of the stored arteries the iron chelator 2,2'-dipyridyl was added. Endothelium-independent vasoconstriction was assessed by cumulative concentration-response curves for potassium and phenylephrine in a small vessel myograph. Endothelium-independent vasodilation was assessed with sodium nitroprusside and endothelium-dependent vasodilation with histamine. Cold storage for 24h did not affect vascular reactivity of renal small arteries and no influence of the iron chelator was seen. Since 24h of cold storage considerable damages renal tubular cells both in vitro and after kidney transplantation, these results suggest that renal arteries are less sensitive to cold-induced damage than tubular cells.

Bioflavonoids attenuate renal proximal tubular cell injury during cold preservation in Euro-Collins and University of Wisconsin solutions

BACKGROUND

Cold ischemia and reperfusion during kidney transplantation are associated with release of free oxygen radicals and damage of renal tubular cells. Bioflavonoids may diminish cold storage-induced injury due to antioxidant and iron chelating activities. This study was designed to delineate the renoprotective mechanisms of bioflavonoids and to define the structural features conferring cytoprotection from cold injury.

METHODS

LLC-PK1 cells were preincubated for three hours with bioflavonoids and cold stored in University of Wisconsin (UW)- or Euro-Collins (EC)-solution for 20 hours. After rewarming, cell viability was assessed by the lactate dehydrogenase (LDH) release, MTT-test, and amino acid transport activity. Lipid peroxidation was assessed from the generation of thiobarbituric acid-reactive substances.

RESULTS

Twenty-hours of cold storage of LLC-PK1 cells resulted in a substantial loss of cell integrity that was more pronounced in the EC (LDH release, 93.6 +/- 1.6%) than the UW solution (67.2 +/- 6.9%; P < 0.0001). Pretreatment with quercetin significantly enhanced cell survival (LDH release, 5.4 +/- 2.7% for UW and 8.4 +/- 4.2% for EC) in a concentration dependent manner. Structure-activity studies revealed similar renoprotection for kaempferol, luteolin and fisetin, unlike myricetin, morin, apigenin, naringenin, catechin, silibinin and rutin. Lipid peroxidation was reduced (UW alone, 2.7 +/- 1.2 vs. UW+quercetin 0.5 +/- 0.2 nmol/mg protein, P < 0.01), and l-threonine uptake completely sustained by pretreatment with quercetin, kaempferol, luteolin, and fisetin. However, renoprotection by fisetin was rapidly lost during rewarming. Protective properties of bioflavonoids were governed by the number and arrangement of hydroxyl substitutes, electron-delocalization, sterical planarity, and lipophilicity of the basic diphenylpyran skeleton.

CONCLUSION

Cold storage-induced renal tubular cell injury is ameliorated by bioflavonoids. Renoprotective effects of bioflavonoids are defined by structure, suggesting that flavonoids are incorporated into membrane lipid bilayers and interfere with membrane lipid peroxidation.

A prospective comparison of simultaneous and sequential live-donor renal transplantation

BACKGROUND

Traditionally, we have performed live- donor renal transplantations sequentially with a cold ischemic time (preservation time) of approximately 3 hr. By performing live-donor renal transplantations simultaneously, cold ischemic times can be reduced to 30 min or less. The purpose of this prospective study was to compare clinical outcomes and biologic markers of kidney function between live-donor renal transplantations performed either simultaneously or sequentially.

METHODS

Nine consecutive live-donor renal transplantations were performed in a simultaneous manner by two transplant surgeons. For comparison, 18 consecutive live-donor transplantations were performed sequentially by a single surgeon. Donor and recipient demographic factors, before transplantation, were compared. Posttransplantation comparisons included daily serum creatinine measurements for 5 days, urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) for 72 hr postoperatively, nuclear glomerular filtration rate (GFR) at 18 hr postoperatively, creatinine clearance at 96 hr postoperatively, and creatinine clearance at 3 and 6 months posttransplantation.

RESULTS

There were no differences in donor and recipient demographic factors preoperatively between the two groups. With simultaneous and sequential recipients, only the cold ischemic times were significantly different (simultaneous: mean=23.6 min; sequential: mean=191.7 min; P<0.01). After transplantation, no differences were detected in the daily fall of serum creatinine, nuclear GFR at 18 hr, or creatinine clearance at 96 hr, 3 months, or 6 months. In both groups, urinary NAG excretion reached a peak at 1 hr postoperatively and then slowly returned to baseline by 72 hr. There was no difference in the amount of NAG excretion between the two groups.

CONCLUSIONS

Our study found that there is no difference in tubular injury or postoperative GFR in live-donor kidney transplantations performed simultaneously or sequentially. Our findings indicate that a modest prolongation of the cold ischemic time has no detectable influence on posttransplantation renal function for live-donor transplantations.

The role of caspases in cryoinjury: caspase inhibition strongly improves the recovery of cryopreserved hematopoietic and other cells

Cryopreserved cells and tissues are increasingly used for stem cell transplantation and tissue engineering. However, their freezing, storage, and thawing is associated with severe damage, suggesting the need for better cryopreservation methods. Here, we show that activation of caspase-3 is induced during the freeze-thaw process. Moreover, we demonstrate that prevention of caspase activation by the caspase inhibitor zVAD-fmk strongly improves the recovery and survival of several cryopreserved cell types and hematopoietic progenitor cells. A short preincubation with the caspase inhibitor after thawing also enhances the colony-forming activity of hematopoietic progenitor cells up to threefold. Furthermore, overexpression of Bcl-2, but not the blockade of the death receptor signaling, confers protection, indicating that cryoinjury-associated cell death is mediated by a Bcl-2-controlled mitochondrial pathway. Thus, our data suggest the use of zVAD-fmk as an efficient cryoprotective agent. The addition of caspase inhibitors may be an important tool for the cryopreservation of living cells and advantageous in cell transplantation, tissue engineering, and other genetic technologies.

Cold induces catalytic iron release of cytochrome P-450 origin: a critical step in cold storage-induced renal injury

Earlier experimental studies have suggested a role for iron in cold-storage-induced organ injury. Whether the cytochrome P-450 enzymes, shown to be a source for iron in several injury models, contribute to cold-induced iron release is not known. Storage of human proximal tubular epithelial (RPTE) cells at 4 degrees C in the University of Wisconsin (UW) solution caused a significant and time-dependent increase in bleomycin-detectable iron (BDI). To identify the cellular source of BDI, RPTE cells were subfractionated and stored at 4 degrees C for 4 h. Bleomycin-detectable iron release was highest in the microsomes, next in the cytosol and none in the mitochondria. As microsomes are rich in iron-containing cytochrome P-450 enzymes, microsomes were cold stored with P-450 inhibitors, cimetidine and piperonyl butoxide. P-450 inhibitors significantly reduced cold-induced BDI release. Furthermore, cimetidine and iron chelator deferoxamine (DFO) significantly reduced cold-induced cell injury, suggesting a role for P-450-derived iron in cold-induced cell injury. In rat kidney experiments, BDI and LDH release were significantly higher in cold-stored kidneys than in control kidneys. Inclusion of cimetidine and DFO in the cold-storage solution significantly suppressed the BDI and LDH release, and reduced the ultrastructural changes. Our data demonstrate for the first time that cold-induced catalytic iron release may be at least in part of microsomal cytochrome P-450 origin, and that it participates in cold-storage-induced renal injury. In the clinical setting, sequestering free iron released during cold storage is possible and may prove to be useful in limiting organ injury.

The translation state of differentially expressed mRNAs in the hibernating 13-lined ground squirrel (Spermophilus tridecemlineatus)

The translation state of differentially expressed mRNAs were compared in kidney and brown adipose tissue of the hibernating ground squirrel, Spermophilus tridecemlineatus. Polysome analysis revealed a striking disaggregation of polyribosomes during hibernation and the redistribution of Cox4 (cytochrome c oxidase subunit 4) and Oct2 (organic cation transporter type 2) transcripts into monosome and mRNP fractions of kidney cytoplasmic extracts. Additionally, OCT2 protein levels decreased in kidney of hibernating animals in line with a strong decrease (85%) in translation rate compared with euthermic kidney. There was no translational depression in brown adipose tissue during hibernation and the H isoform of fatty-acid-binding protein (H-FABP), that is up-regulated during hibernation, was increasingly abundant in the heavy polyribosome fraction isolated from the brown adipose of hibernators. This may indicate the existence of a tissue-specific mechanism for the translational control of a subset of genes that are physiologically relevant to the survival of hibernation.

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.

Effects of adenosine on ischaemia-reperfusion injury associated with rat pancreas transplantation

BACKGROUND

During cold preservation, cellular consumption of adenosine triphosphate leads to the accumulation of nucleotides and nucleosides. The precise role of adenosine in modulating the inflammatory response of cold-preserved pancreas after reperfusion remains to be elucidated. The aim of this study was to assess the influence of adenosine on the inflammatory response associated with the process of ischaemia-reperfusion in rat pancreas transplantation.

METHODS

The effect of adenosine from preservation solution on the levels of high-energy nucleotides and their breakdown products after cold ischaemic preservation was determined. In addition, the inflammatory response associated with the process of ischaemia-reperfusion in pancreas transplantation was quantified with and without pretreatment with the adenosine antagonist theophylline, and during preservation of the organ in University of Wisconsin solution with and without adenosine.

RESULTS

Adenosine from preservation solution is able to modify the nucleotide and nucleoside content of preserved pancreas, indicating that adenosine is incorporated and metabolized in tissue. Administration of the adenosine antagonist to transplanted rats moderated the increases in nitrite and nitrate, myeloperoxidase activity and lipoperoxidation levels in the pancreas.

CONCLUSION

Adenosine in the preservation solution may enhance the inflammatory response in rat pancreas transplantation.

Hypothermia injury/cold-induced apoptosis--evidence of an increase in chelatable iron causing oxidative injury in spite of low O2-/H2O2 formation

When incubated at 4 degrees C, cultured rat hepatocytes or liver endothelial cells exhibit pronounced injury and, during earlier rewarming, marked apoptosis. Both processes are mediated by reactive oxygen species, and marked protective effects of iron chelators as well as the protection provided by various other antioxidants suggest that hydroxyl radicals, formed by classical Fenton chemistry, are involved. However, when we measured the Fenton chemistry educt hydrogen peroxide and its precursor, the superoxide anion radical, formation of both had markedly decreased and steady-state levels of hydrogen peroxide did not alter during cold incubation of either liver endothelial cells or hepatocytes. Similarly, there was no evidence of an increase in O2-/H2O2 release contributing to cold-induced apoptosis occurring on rewarming. In contrast to the release/level of O2- and H2O2, cellular homeostasis of the transition metal iron is likely to play a key role during cold incubation of cultured hepatocytes: the hepatocellular pool of chelatable iron, measured on a single-cell level using laser scanning microscopy and the fluorescent indicator phen green, increased from 3.1 +/- 2.3 microM (before cold incubation) to 7.7 +/- 2.4 microM within 90 min after initiation of cold incubation. This increase in the cellular chelatable iron pool was reversible on rewarming after short periods of cold incubation. The cold-induced increase in the hepatocellular chelatable iron pool was confirmed using the calcein method. These data suggest that free radical-mediated hypothermia injury/cold-induced apoptosis is primarily evoked by alterations in the cellular iron homeostasis/a rapid increase in the cellular chelatable iron pool and not by increased formation of O2-/H2O2.

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.

Time-dependent impairment of mitochondrial function after storage and transplantation of rabbit kidneys

BACKGROUND

The mitochondrial respiratory chain is implicated as a major target of kidney damage after ischemia-reperfusion. This study measures changes in integrated mitochondrial function and in the activity of enzymes of the respiratory chain after cold storage and transplantation-reperfusion in vivo.

METHODS

Mitochondrial oxygen consumption and activities of respiratory chain enzymes and citrate synthase were measured in cortical mitochondria isolated from rabbit kidneys after 1-48 hr of cold ischemia with or without transplantation-reperfusion.

RESULTS

State 4 mitochondrial oxygen consumption was significantly increased after 48 hr of ischemia or 24-48 hr of ischemia with transplantation. Prolonged (24 or 48 hr) ischemic storage with and without transplantation caused a significant decrease in state 3 oxygen consumption, as did transplantation after 1, 24, and 48 hr of cold storage. Complex I and complex II-III activity decreased after 24 or 48 hr of ischemia, with transplantation having little additional effect. Complex IV activity was significantly decreased after 48 hr of ischemia, this decrease being exacerbated by transplantation-reperfusion. Complex V activity decreased significantly after 1 hr of ischemia and continued to decrease after 24-48 hr of ischemia. Transplantation after 1-24 hr (but not 48 hr) of ischemia resulted in partial recovery of complex V activity. Citrate synthase activity was decreased significantly only after 48 hr of ischemia and reperfusion, consistent with the loss of mitochondrial membrane integrity seen in electron micrographs of the transplanted 48-hr group.

CONCLUSIONS

These data suggest that individual rabbit kidney mitochondrial complexes have different susceptibilities to cold ischemic and reperfusion damage.

Cold storage induces time-dependent F2-isoprostane formation in renal tubular cells and rat kidneys

BACKGROUND

Previous findings suggest a possible role for free radicals in cold-storage-associated tissue injury. Because free radical-induced lipid peroxidation catalyzes the cyclooxygenase-independent formation of vasoconstrictive F2-isoprostanes, the hypothesis that isoprostanes are produced during cold storage was tested in this study.

METHODS

Total isoprostanes (free and esterified) in renal tubular epithelial (LLC-PK1) cells or whole kidneys, subjected to cold storage, were quantitated employing the gas chromatographic-mass spectroscopic method. LLC-PK1 cells were stored at 4 degrees C in a University of Wisconsin (UW) solution for 0, 24, 48, and 72 hours or 48 hours with desferrioxamine (DFO) or the lazaroid compound 2-methyl aminochroman (2-MAC). In the rat model, kidneys were perfused and stored for 48 hours in the UW solution with or without added DFO or 2-MAC.

RESULTS

Isoprostanes in LLC-PK1 cells increased by fivefold following 24 hours of cold storage (36 +/- 2 pg/well to 185 +/- 6, mean +/- SE, following 24 hours of cold storage, P < 0.0001), and the levels continued to increase significantly at 48 and 72 hours. DFO and 2-MAC caused significant suppression of isoprostane formation. Cold storage of the kidneys in UW solution for 48 hours was accompanied by an eightfold increase in isoprostanes compared with control kidneys not subjected to cold storage (25.0 +/- 3.0 vs. 2.9 +/- 0.1 ng/g, P < 0.0001). The addition of 2-MAC or DFO to the UW solution was associated with a near complete suppression of 48-hour cold-induced isoprostane formation.

CONCLUSION

Our findings provide evidence for the formation of large quantities of antioxidant-suppressible isoprostanes in kidney cells and whole kidney during cold-preservation. Based on this, it is hypothesized that (a) isoprostanes, which are potent renal vasoconstrictors, may contribute to immediate post-transplant vasoconstriction and dysfunction in kidneys subjected to extended cold storage, and that (b) the addition of 2-MAC or DFO to a UW solution in such circumstances may attenuate these alterations partly by suppressing isoprostane formation.

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.