Respiratory defect as an early event in preservation-reoxygenation injury of endothelial cells

Assessment of Mitochondrial Respiration During Hypothermic Storage of Liver Biopsies Following Normothermic Machine Perfusion

Organ quality can be assessed prior to transplantation, during normothermic machine perfusion (NMP) of the liver. Evaluation of mitochondrial function by high-resolution respirometry (HRR) may serve as a viability assessment concept in this setting. Freshly collected tissue is considered as optimal sample for HRR, but due to technical and personnel requirements, more flexible and schedulable measurements are needed. However, the impact of cold storage following NMP before processing biopsy samples for mitochondrial analysis remains unknown. We aimed at establishing an appropriate storage protocol of liver biopsies for HRR. Wedge biopsies of 5 human livers during NMP were obtained and assessed by HRR. Analysis was performed after 0, 4, 8, and 12 h of hypothermic storage (HTS) in HTK organ preservation solution at 4°C. With HTS up to 4 h, mitochondrial performance did not decrease in HTS samples compared with 0 h (OXPHOS, 44.62 [34.75-60.15] pmol·s-1·mg wet mass-1 vs. 43.73 [40.69-57.71], median [IQR], p > 0.999). However, at HTS beyond 4 h, mitochondrial respiration decreased. We conclude that HTS can be safely applied for extending the biopsy measurement window for up to 4 h to determine organ quality, but also that human liver respiration degrades beyond 4 h HTS following NMP.

NDUFA8 is transcriptionally regulated by EP300/H3K27ac and promotes mitochondrial respiration to support proliferation and inhibit apoptosis in cervical cancer

Cervical cancer, a common malignancy in women, poses a significant health burden worldwide. In this study, we aimed to investigate the expression, function, and potential mechanisms of NADH: ubiquinone oxidoreductase subunit A8 (NDUFA8) in cervical cancer. The Gene Expression Profiling Interactive Analysis (GEPIA) database and immunohistochemical scoring were used to analyze NDUFA8 expression in cervical cancer tissues and normal tissues. Quantitative real-time PCR and Western blot analyses were performed to assess the expression level of NDUFA8 in cervical cancer cell lines. NDUFA8 knockdown or overexpression experiments were conducted to evaluate its impact on cell proliferation and apoptosis. The mitochondrial respiratory status was analyzed by measuring cellular oxygen consumption, adenosine triphosphate (ATP) levels, and the expression levels of Mitochondrial Complex I activity, and Mitochondrial Complex IV-associated proteins Cytochrome C Oxidase Subunit 5B (COX5B) and COX6C. NDUFA8 exhibited high expression levels in cervical cancer tissues, and these levels were correlated with reduced survival rates. A significant upregulation of NDUFA8 expression was observed in cervical cancer cell lines compared to normal cells. Silencing NDUFA8 hindered cell proliferation, promoted apoptosis, and concurrently suppressed cellular mitochondrial respiration, resulting in decreased levels of available ATP. Conversely, NDUFA8 overexpression induced the opposite effects. Herein, we also found that E1A Binding Protein P300 (EP300) overexpression facilitated Histone H3 Lysine 27 (H3K27) acetylation enrichment, enhancing the activity of the NDUFA8 promoter region. NDUFA8, which is highly expressed in cervical cancer, is regulated by transcriptional control via EP300/H3K27 acetylation. By promoting mitochondrial respiration, NDUFA8 contributes to cervical cancer cell proliferation and apoptosis. These findings provide novel insights into NDUFA8 as a therapeutic target in cervical cancer.

High-Resolution FluoRespirometry and OXPHOS Protocols for Human Cells, Permeabilized Fibers from Small Biopsies of Muscle, and Isolated Mitochondria

Protocols for High-Resolution FluoRespirometry of intact cells, permeabilized cells, permeabilized muscle fibers, isolated mitochondria, and tissue homogenates offer sensitive diagnostic tests of integrated mitochondrial function using standard cell culture techniques, small needle biopsies of muscle, and mitochondrial preparation methods. Multiple substrate-uncoupler-inhibitor titration (SUIT) protocols for analysis of oxidative phosphorylation (OXPHOS) improve our understanding of mitochondrial respiratory control and the pathophysiology of mitochondrial diseases. Respiratory states are defined in functional terms to account for the network of metabolic interactions in complex SUIT protocols with stepwise modulation of coupling control and electron transfer pathway states. A regulated degree of intrinsic uncoupling is a hallmark of oxidative phosphorylation, whereas pathological and toxicological dyscoupling is evaluated as a mitochondrial defect. The noncoupled state of maximum respiration is experimentally induced by titration of established uncouplers (CCCP, FCCP, DNP) to collapse the protonmotive force across the mitochondrial inner membrane and measure the electron transfer (ET) capacity (open-circuit operation of respiration). Intrinsic uncoupling and dyscoupling are evaluated as the flux control ratio between non-phosphorylating LEAK respiration (electron flow coupled to proton pumping to compensate for proton leaks) and ET capacity. If OXPHOS capacity (maximally ADP-stimulated O₂ flux) is less than ET capacity, the phosphorylation pathway contributes to flux control. Physiological substrate combinations supporting the NADH and succinate pathway are required to reconstitute tricarboxylic acid cycle function. This supports maximum ET and OXPHOS capacities, due to the additive effect of multiple electron supply pathways converging at the Q-junction. ET pathways with electron entry separately through NADH (pyruvate and malate or glutamate and malate) or succinate (succinate and rotenone) restrict ET capacity and artificially enhance flux control upstream of the Q-cycle, providing diagnostic information on specific ET-pathway branches. O₂ concentration is maintained above air saturation in protocols with permeabilized muscle fibers to avoid experimental O₂ limitation of respiration. Standardized two-point calibration of the polarographic oxygen sensor (static sensor calibration), calibration of the sensor response time (dynamic sensor calibration), and evaluation of instrumental background O₂ flux (systemic flux compensation) provide the unique experimental basis for high accuracy of quantitative results and quality control in High-Resolution FluoRespirometry.

Do mitochondria limit hot fish hearts? Understanding the role of mitochondrial function with heat stress in Notolabrus celidotus

Hearts are the first organs to fail in animals exposed to heat stress. Predictions of climate change mediated increases in ocean temperatures suggest that the ectothermic heart may place tight constraints on the diversity and distribution of marine species with cardiovascular systems. For many such species, their upper temperature limits (Tmax) and respective heart failure (HF) temperature (T(HF)) are only a few degrees from current environmental temperatures. While the ectothermic cardiovascular system acts as an "ecological thermometer," the exact mechanism that mediates HF remains unresolved. We propose that heat-stressed cardiac mitochondria drive HF. Using a common New Zealand fish, Notolabrus celidotus, we determined the THF (27.5°C). Haemoglobin oxygen saturation appeared to be unaltered in the blood surrounding and within heat stressed hearts. Using high resolution respirometry coupled to fluorimeters, we explored temperature-mediated changes in respiration, ROS and ATP production, and overlaid these changes with T(HF). Even at saturating oxygen levels several mitochondrial components were compromised before T(HF). Importantly, the capacity to efficiently produce ATP in the heart is limited at 25°C, and this is prior to the acute T(HF) for N. celidotus. Membrane leakiness increased significantly at 25°C, as did cytochrome c release and permeability to NADH. Maximal flux rates and the capacity for the electron transport system to uncouple were also altered at 25°C. These data indicate that mitochondrial membrane integrity is lost, depressing ATP synthesis capacity and promoting cytochrome c release, prior to T(HF). Mitochondria can mediate HF in heat stressed hearts in fish and play a significant role in thermal stress tolerance, and perhaps limit species distributions by contributing to HF.

High-resolution respirometry: OXPHOS protocols for human cells and permeabilized fibers from small biopsies of human muscle

Protocols for high-resolution respirometry (HRR) of intact cells, permeabilized cells, and permeabilized muscle fibers offer sensitive diagnostic tests of integrated mitochondrial function using standard cell culture techniques and small needle biopsies of muscle. Multiple substrate-uncoupler-inhibitor titration (SUIT) protocols for analysis of oxidative phosphorylation improve our understanding of mitochondrial respiratory control and the pathophysiology of mitochondrial diseases. Respiratory states are defined in functional terms to account for the network of metabolic interactions in complex SUIT protocols with stepwise modulation of coupling and substrate control. A regulated degree of intrinsic uncoupling is a hallmark of oxidative phosphorylation, whereas pathological and toxicological dyscoupling is evaluated as a mitochondrial defect. The noncoupled state of maximum respiration is experimentally induced by titration of established uncouplers (FCCP, DNP) to collapse the proton gradient across the mitochondrial inner membrane and measure the capacity of the electron transfer system (ETS, open-circuit operation of respiration). Intrinsic uncoupling and dyscoupling are evaluated as the flux control ratio between nonphosphorylating LEAK respiration (electron flow coupled to proton pumping to compensate for proton leaks) and ETS capacity. If OXPHOS capacity (maximally ADP-stimulated oxygen flux) is less than ETS capacity, the phosphorylation system contributes to flux control. Physiological Complex I + II substrate combinations are required to reconstitute TCA cycle function. This supports maximum ETS and OXPHOS capacities, due to the additive effect of multiple electron supply pathways converging at the Q-junction. Substrate control with electron entry separately through Complex I (pyruvate + malate or glutamate + malate) or Complex II (succinate + rotenone) restricts ETS capacity and artificially enhances flux control upstream of the Q-cycle, providing diagnostic information on specific branches of the ETS. Oxygen levels are maintained above air saturation in protocols with permeabilized muscle fibers to avoid experimental oxygen limitation of respiration. Standardized two-point calibration of the polarographic oxygen sensor (static sensor calibration), calibration of the sensor response time (dynamic sensor calibration), and evaluation of instrumental background oxygen flux (systemic flux compensation) provide the unique experimental basis for high accuracy of quantitative results and quality control in HRR.

P-selectin expression in cold preserved kidneys in University of Wisconsin and histidine-tryptophan-ketoglutarate solutions

The differences and efficacy of standard preservation solutions in kidney transplantation, University of Wisconsin (UW) and histidine-tryptophan-ketoglutarate (HTK), remain a topic of debate in recent clinical studies. P-selectins represent glycoproteins expressed on endothelial cells and platelets responsible for the earliest events in ischemia/reperfusion injury in kidney transplantation. This study aimed to compare the levels of P-selectin expression between cold preserved kidney tissues in UW and HTK solutions. Thirty kidneys were procured from male Lewis rats and stored in cold (4°C) solutions for periods of 4, 12, 16, 20, and 24h. Group 1 (n=15) kidneys were stored in UW solutions, and group 2 (n=15) kidneys were submerged in HTK solutions. At the end of each time point, the kidneys underwent preparation and levels of P-selectin expression in the tissues were measured using Immunoblot analyses and adjusted volumetric quantification of Western blot signals. For all periods of cold preservation, P-selectin expression was significantly down-regulated in kidney tissues stored in UW compared with HTK solutions (P<0.001). In summary, UW demonstrated a significant benefit over HTK solution in down-regulating P-selectin expression in cold preserved kidney grafts.

Hypothermic preconditioning of endothelial cells attenuates cold-induced injury by a ferritin-dependent process

Hypothermia for myocardial protection or storage of vascular grafts may damage the endothelium and impair vascular function upon reperfusion/rewarming. Catalytic iron pools and oxidative stress are important mediators of cold-induced endothelial injury. Because endothelial cells are highly adaptive, we hypothesized that hypothermic preconditioning (HPC) protects cells at 0 degrees C by a heme oxygenase-1 (HO-1) and ferritin-dependent mechanism. Storage of human coronary artery endothelial cells at 0 degrees C caused the release of lactate dehydrogenase, increases in bleomycin-detectible iron (BDI), and increases in the ratio of oxidized/reduced glutathione, signifying oxidative stress. Hypoxia increased injury at 0 degrees C but did not increase BDI or oxidative stress further. HPC at 25 degrees C for 15-72 h attenuated these changes by an amount achievable by pretreating cells with 10-20 microM deferoxamine, an iron chelator, and protected cell viability. Treating cells with hemin chloride at 37 degrees C transiently increased intracellular heme, HO-1, BDI, and ferritin. Elevated heme/iron sensitized cells to 0 degrees C but ferritin was protective. HPC increased iron maximally after 2 h at 25 degrees C and ferritin levels peaked after 15 h. HO-1 was not induced. When HPC-mediated increases in ferritin were blocked by deferoxamine, protection at 0 degrees C was diminished. We conclude that HPC-mediated endothelial protection from hypothermic injury is an iron- and ferritin-dependent process.

Quality control for clinical islet transplantation: organ procurement and preservation, the islet processing facility, isolation, and potency tests

Pancreatic islet transplantation has become one of the ideal treatments for patients with type 1 diabetes mellitus due to improvements in isolation techniques and immunosuppression regimens. In order to ensure the safety and rights of patients, isolated islets need to meet the criteria for regulation as both a biological product and a drug product. For the constant success of transplantation, therefore, all investigators involved in clinical islet transplantation must strive to ensure the safety, purity, and potency of islets in all the phases of clinical islet isolation and transplantation. In this review, we summarize the quality control for clinical islet isolation and transplantation, and the latest topics of pre-transplant islet assessment.

Short-term resuscitation of predamaged donor livers by brief machine perfusion: the influence of temperature

Short-term machine perfusion after liver retrieval from non-heart-beating donors has been considered a beneficial means to reverse deleterious priming of the predamaged organ. In this study, the possible impact of different temperatures during aerobic perfusion was addressed, focusing on liver metabolic functions, structural integrity, and vascular activation. Livers retrieved 30 minutes after cardiac arrest of male Wistar rats (200-300 g) were preserved with histidine-tryptophan-ketoglutarate (HTK) solution for 18 hours by simple cold storage (CS) or subjected to short-term resuscitation (STR) with oxygenated (pO(2) > 500 mm Hg) machine perfusion with HTK at 4 degrees C, 12 degrees C, or 22 degrees C for 2 hours with subsequent CS for 16 hours at 4 degrees C. Upon reperfusion in a normothermic perfusion circuit, STR significantly improved enzyme leakage (alanine aminotransferase, glutamate dehydrogenase) and metabolic recovery (tissue levels of ATP) providing best values at 12 degrees C or 22 degrees C. Moreover, a hugely increased gene expression of the adhesion molecule ICAM-1 as well as major histocompatibility complex (MHC) class II antigen was seen after CS, but significantly alleviated by STR at 4 degrees C or 12 degrees C. However, mRNA for both surface proteins rose significantly after STR at 22 degrees C compared with CS. In conclusion, STR by oxygenated perfusion is beneficial to the predamaged graft, facilitating later transportation and supervision of the graft compared with continuous machine preservation. However, increased perfusion temperature should be recommended only up to the limit of 12 degrees C to prevent overactivation of surface antigen expression.

A stirred microchamber for oxygen consumption rate measurements with pancreatic islets

Improvements in pancreatic islet transplantation for treatment of diabetes are hindered by the absence of meaningful islet quality assessment methods. Oxygen consumption rate (OCR) has previously been used to assess the quality of organs and primary tissue for transplantation. In this study, we describe and characterize a stirred microchamber for measuring OCR with small quantities of islets. The device has a titanium body with a chamber volume of about 200 microL and is magnetically stirred and water jacketed for temperature control. Oxygen partial pressure (pO(2)) is measured by fluorescence quenching with a fiber optic probe, and OCR is determined from the linear decrease of pO(2) with time. We demonstrate that measurements can be made rapidly and with high precision. Measurements with betaTC3 cells and islets show that OCR is directly proportional to the number of viable cells in mixtures of live and dead cells and correlate linearly with membrane integrity measurements made with cells that have been cultured for 24 h under various stressful conditions.

Human islet oxygen consumption rate and DNA measurements predict diabetes reversal in nude mice

There is a need for simple, quantitative and prospective assays for islet quality assessment that are predictive of islet transplantation outcome. The current state-of-the-art athymic nude mouse bioassay is costly, technically challenging and retrospective. In this study, we report on the ability of 2 parameters characterizing human islet quality: (1) oxygen consumption rate (OCR), a measure of viable volume; and (2) OCR/DNA, a measure of fractional viability, to predict diabetes reversal in nude mice. Results demonstrate that the probability for diabetes reversal increases as the graft's OCR/DNA and total OCR increase. For a given transplanted OCR dose, diabetes reversal is strongly dependent on OCR/DNA. The OCR and OCR/DNA (the 'OCR test') data exhibit 89% sensitivity and 77% specificity in predicting diabetes reversal in nude mice (n = 86). We conclude that the prospective OCR test can effectively replace the retrospective athymic nude mouse bioassay in assessing human islet quality prior to islet transplantation.

Evaluation of preservation solutions by ESR-spectroscopy: superior effects of University of Wisconsin over Histidine-Tryptophan-Ketoglutarate in reducing renal reactive oxygen species

Despite the causative role of oxidative stress in renal ischemia-reperfusion (I-R) injury effects of preservation solutions on reactive oxygen species (ROS) release have not been sufficiently evaluated. We compared the effects of most common solutions in kidney transplantation, University of Wisconsin (UW) and Histidine-Tryptophan-Ketoglutarate (HTK). ROS formation in isolated perfused rat kidney was detected by electron spin resonance spectroscopy using spin label 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine. Donor kidneys from Lewis rats were pretreated with saline (controls), in therapeutic groups, kidneys underwent 18 h of cold storage (CS) preserved by HTK or UW solution. Experimental protocol included a stabilization period followed by additional I-R. Kidneys preserved by HTK produced highest ROS values in the control period after CS, whereas levels in UW and control group did not vary significantly. A peak release induced by additional I-R was also significantly highest in HTK kidneys, and UW did not differ from controls. During reperfusion, levels in HTK exceeded control and UW values. Renal vascular resistance, caspase-3-activity, and tissue hydration were enhanced in HTK compared with UW group, whereas ATP concentration was less reduced in UW-preserved tissue. These data show the greater antioxidative potential of UW solution, which also attenuated organ impairment after CS in the early reperfusion period.

Trends in organ preservation

Organ preservation aims to provide a viable graft with primary function post-transplant. The current basis of preservation for transplantation is static cold storage using specific preservation solutions which minimise cellular swelling and membrane pump activity, thus maintaining cellular ATP levels. The current organ shortage and consequent expansion of donor criteria places even greater reliance on minimising graft injury during preservation. This review focuses on current and future advances in preservation technology. The key areas of advance are additives to preservation solutions, alternatives/adjuncts to preservation solutions including perfluorocarbons. A major area of advance is in the modulation of organs during the storage period. This may be achieved by biochemical additives or genetic manipulation. Machine perfusion technology is improving, and this is discussed together with the recent concept of warm (normothermic) perfusion as an alternative means of preservation. The authors provide an overview over the current methods of organ preservation. Cold storage, effective in the short-term is insufficient for marginal organs, does not allow assessment of viability markers, and provokes ischaemic injury. Potential strategies for minimising ischaemic injury include additives to preservation solutions; the two-layer method with perfluorcarbons and UW solution-at present limited to pancreas preservation; organ modulation; organ preconditioning and genetic modification of organs. In particular, the authors illuminate the potential in a reappraisal of the concept of normothermic perfusion.

Evaluation of mitochondrial respiratory function in small biopsies of liver

Mitochondrial respiratory function was studied in permeabilized pig liver biopsies. The cell membrane was permeabilized mechanically in tissue samples of 2-7 mg, for application of a standardized substrate/inhibitor titration protocol in high-resolution respirometry. Specific respirometric tests demonstrated complete plasma membrane permeabilization and accessibility of substrates to intact mitochondria. High respiratory adenylate control ratios and cytochrome c conservation in the tissue preparation were comparable or even better than in isolated mitochondria. Citrate synthase and cytochrome c oxidase activities remained at 85% of controls after up to 98 h storage of liver tissue at 0 degrees C in histidine-tryptophan-ketoglutarate solution. Multiple mitochondrial defects, however, were indicated after 48 h cold storage by the decline in respiratory capacity, which was lowered to a larger extent with complex I substrates compared to respiration with substrates for complex II or IV, measured in the absence of cytochrome c. After prolonged ischemia, the adenylate control ratio was significantly reduced, and cytochrome c depletion was detected by the stimulatory effect of cytochrome c. High-resolution respirometry allows the assessment of mitochondrial function in a few milligrams of permeabilized liver tissue, without isolation of mitochondria. This provides a basis for the analysis of mitochondrial function in human liver biopsies.

Endothelial damage during myocardial preservation and storage

Preservation and storage techniques represent two major issues in routine cardiac surgery and heart transplantation. Historically, these methods were conceived to prevent ischemic injury to myocardium after cardiac arrest during heart operations. Evidence shows that endothelium plays a critical role in the maintenance of normal heart function after cardiac operation, mainly by controlling the coronary circulation. Methods for preservation and storage, developed initially to protect cardiomyocyte function, may be deleterious for vascular endothelium and compromise myocardial protection. In this review article the present knowledge about endothelial injury secondary to preservation and storage techniques is discussed.

A subpopulation of mitochondria prevents cytosolic calcium overload in endothelial cells after cold ischemia/reperfusion

BACKGROUND

Calcium represents a key mediator of cold ischemia/reperfusion (CIR) injury presumably by affecting mitochondrial function. In this study, we investigated cellular and mitochondrial changes of calcium homeostasis in sublethally damaged human endothelial cells.

METHODS

Changes in cellular and mitochondrial calcium concentrations were studied after cold ischemia in University of Wisconsin solution for 12 hr and reperfusion in ringer solution. Cytosolic-free calcium concentration ([Ca2+]c) and mitochondrial-free calcium content ([Ca2+]m) were analyzed by fura-2 and rhod-2 fluorescence, respectively. Pretreatment of cells with ruthenium red (RR) or a H+-ionophore was used to inhibit mitochondrial calcium uptake. Mitochondrial membrane potential (DeltaPsim) was measured by 5,5',6,6'-tetrachloro- 1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide and 3,3'-dihexyloxacarbocyanine iodide fluorescence.

RESULTS

Twelve-hr cold ischemia did not induce apoptosis in endothelial cells. In such sublethally damaged cells, [Ca2+]c rose from approximately 20 nmol/L after cold ischemia to approximately 120 nmol/L during reperfusion. Pretreatment with RR leads to an approximately 5-fold rise in [Ca2+]c. Image analysis revealed a significant increase of [Ca2+]m in a subpopulation of mitochondria during reperfusion. This was not the case in RR-pretreated cells. DeltaPsim decreased significantly during cold ischemia and was sustained during reperfusion. The loss of DeltaPsim can be related to a reduced portion of mitochondria exhibiting high DeltaPsim.

CONCLUSIONS

Our results suggest that cytosolic calcium influx during CIR is buffered by a selective portion of mitochondria in human umbilical vein endothelial cells. These mitochondria protect cells against cytosolic calcium overload and probably against subsequent cell injury.

Fibrinolytic preflush upon liver retrieval from non-heart beating donors to enhance postpreservation viability and energetic recovery upon reperfusion

BACKGROUND

Our objective was to evaluate graft equilibration with high viscosity (University of Wisconsin solution [UW]) or low viscosity (Bretschneider's histidine-tryptophan-ketoglutarate [HTK]) during liver procurement from non-heart beating donors (NHBD) and the potential impact of a preceding fibrinolysis with streptokinase on postpreservation viability.

METHODS

After 60 min of cardiac arrest, rat livers were perfused by gravity (60 cm H2O) via the portal vein with either 60 ml of HTK, 20 ml of UW, or 20 ml of Ringer's solution (22 degrees C including 7500U of streptokinase) and, subsequently, 20 ml of UW. After 24 h of storage at 4 degrees C, viability of the livers was assessed upon isolated reperfusion in vitro.

RESULTS

Magnetic resonance imaging revealed severe perfusion deficits, which were mildly attenuated with HTK, upon flush-out with UW. After preflush with streptokinase, a mostly homogenous distribution of the preservation solution was observed throughout the liver tissue. The choice of the flush-out solution (UW or HTK) had no influence on parenchymal enzyme leakage, hepatic bile production, or tissue levels of ATP after reperfusion of the livers. Fibrinolytic preflush, however, resulted in a relevant and significant improvement of structural integrity as well as functional and metabolic recovery.

CONCLUSIONS

Compromised vascular tissue perfusion upon organ harvest in NHBD triggers graft dysfunction after cold storage and can easily be circumvented by temporary fibrinolysis before graft retrieval.

Role of hepatocytes and bile duct cells in preservation-reperfusion injury of liver grafts

In liver transplantation, it is currently hypothesized that nonparenchymal cell damage and/or activation is the major cause of preservation-related graft injury. Because parenchymal cells (hepatocytes) appear morphologically well preserved even after extended cold preservation, their injury after warm reperfusion is ascribed to the consequences of nonparenchymal cell damage and/or activation. However, accumulating evidence over the past decade indicated that the current hypothesis cannot fully explain preservation-related liver graft injury. We review data obtained in animal and human liver transplantation and isolated perfused animal livers, as well as isolated cell models to highlight growing evidence of the importance of hepatocyte disturbances in the pathogenesis of normal and fatty graft injury. Particular attention is given to preservation time-dependent decreases in high-energy adenine nucleotide levels in liver cells, a circumstance that (1) sensitizes hepatocytes to various stimuli and insults, (2) correlates well with graft function after liver transplantation, and (3) may also underlie the preservation time-dependent increase in endothelial cell damage. We also review damage to bile duct cells, which is increasingly being recognized as important in the long-lasting phase of reperfusion injury. The role of hydrophobic bile salts in that context is particularly assessed. Finally, a number of avenues aimed at preserving hepatocyte and bile duct cell integrity are discussed in the context of liver transplantation therapy as a complement to reducing nonparenchymal cell damage and/or activation.

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.

High phosphorylation efficiency and depression of uncoupled respiration in mitochondria under hypoxia

Mitochondria are confronted with low oxygen levels in the microenvironment within tissues; yet, isolated mitochondria are routinely studied under air-saturated conditions that are effectively hyperoxic, increase oxidative stress, and may impair mitochondrial function. Under hypoxia, on the other hand, respiration and ATP supply are restricted. Under these conditions of oxygen limitation, any compromise in the coupling of oxidative phosphorylation to oxygen consumption could accentuate ATP depletion, leading to metabolic failure. To address this issue, we have developed the approach of oxygen-injection microcalorimetry and ADP-injection respirometry for evaluating mitochondrial function at limiting oxygen supply. Whereas phosphorylation efficiency drops during ADP limitation at high oxygen levels, we show here that oxidative phosphorylation is more efficient at low oxygen than at air saturation, as indicated by higher ratios of ADP flux to total oxygen flux at identical submaximal rates of ATP synthesis. At low oxygen, the proton leak and uncoupled respiration are depressed, thus reducing maintenance energy expenditure. This indicates the importance of low intracellular oxygen levels in avoiding oxidative stress and protecting bioenergetic efficiency.

An investigation of fibroblast mitochondria enzyme activity and respiration in response to metallic ions released from dental alloys

Most cellular functions evaluated for biocompatibility are high-energy processes such as proliferation and therefore are not usually affected before a decrease in energy production is observed. Several studies have shown that metabolic functions are altered at much lower concentrations than several normally used biocompatibility tests such as viability. Therefore, the purpose of this study was to provide an in-depth evaluation of metallic ion effects on mitochondria function and thereby biocompatibility. These studies evaluated the mitochondrial function of human gingival fibroblasts exposed to the salt solutions of ions released from nickel-based dental alloys, particularly beryllium (Be(2+)), chromium (Cr(6+) and Cr(3+)), nickel (Ni(2+)), and molybdenum (Mo(6+)). Mitochondrial function was examined by NADH:CoQ reductase activity, succinate dehydrogenase activity, and oxygen consumption.

Role of the Na/H antiport in pH-dependent cell death in pulmonary artery endothelial cells

We investigated the role of intracellular pH (pH(i)) and Na/H exchange in cell death in human pulmonary artery endothelial cells (HPAEC) following a metabolic insult (inhibition-oxidative phosphorylation, glycolysis). Metabolic inhibition in medium at pH 7. 4 decreased viability (0-15% live cells) over 6 h. Cell death was attenuated by maneuvers that decreased pH(i) and inhibited Na/H exchange (acidosis, Na/H antiport inhibitors). In contrast, cell death was potentiated by maneuvers that elevated pH(i) or increased Na/H exchange (monensin, phorbol ester treatment) before the insult. HPAEC demonstrated a biphasic pH(i) response following a metabolic insult. An initial decrease in pH(i) was followed by a return to baseline over 60 min. Maneuvers that protected HPAEC and inhibited Na/H exchange (acidosis, Na(+)-free medium, antiport inhibitors) altered this pattern. pH(i) decreased, but no recovery was observed, suggesting that the return of pH(i) to normal was mediated by antiport activation. Although Na/H antiport activity was reduced (55-60% of control) following a metabolic insult, the cells still demonstrated active Na/H exchange despite significant ATP depletion. Phorbol ester pretreatment, which potentiated cell death, increased Na/H antiport activity above the level observed in monolayers subjected to a metabolic insult alone. These results demonstrate that HPAEC undergo a pH-dependent loss of viability linked to active Na/H exchange following a metabolic insult. Potentiation of cell death with phorbol ester treatment suggests that this cell death pathway involves protein kinase C-mediated phosphorylation events.

Pretransplantation assessment of renal viability with NADH fluorimetry

BACKGROUND

A pathophysiologic feature possibly involved in ischemic injury in transplant kidneys is mitochondrial dysfunction caused by disintegration of oxidative metabolic pathways. Because the ability to synthesize ATP by respiratory activity determines the organ's capacity to recover from ischemic injury, an assessment of respiratory activity may provide information related to graft viability.

METHODS

NADH fluorimetry can be used to monitor kidney cortex metabolism noninvasively. During perfusion with (an)-aerobic perfusate, NADH fluorescence images were recorded. We evaluated the NADH oxidation kinetics of 20 rat kidneys, which were divided over four experimental groups. For six minimally damaged kidneys and six kidneys that had been stored for one hour at 37 degrees C, perfusion was followed by transplantation. We related the kinetic parameters of these kidneys with their post-transplantation function and histology. The transplant function was monitored by serum creatinine and urea levels.

RESULTS

Storage of transplant kidneys for one hour at 37 degrees C significantly reduced the post-transplantation function. Isolated perfusion of grafts, however, was not detrimental for renal function. The rate of NADH oxidation decreased with decreasing graft quality, and a good correlation between NADH oxidation kinetics and post-transplantation function was found.

CONCLUSIONS

A reduction of NADH oxidation rates as a consequence of warm ischemia supports the view that mitochondrial respiratory activity is impaired by ischemic injury. The correlation between NADH oxidation kinetics in perfused grafts and their post-transplantation function indicates that NADH fluorimetry may be useful in predicting the viability of preserved grafts prior to transplantation.

Ultrastructural analysis of human endothelial cells after hypothermic storage in organ preservation solutions

BACKGROUND

Protection of vascular endothelium is a critical factor in organ preservation for transplantation. This study aims at a morphological assessment of endothelial cell injury in a comparison of storage solutions, using a cell culture model of cold preservation and rewarming.

MATERIALS AND METHODS

Human umbilical vein endothelial cells (HUVEC) were cultured in monolayer and exposed to hypothermic storage in University of Wisconsin (UW), histidine-tryptophane-ketoglutarate (HTK), and EuroCollins solutions for 6 h and subsequent rewarming for 30 min or 6 h. Alterations of subcellular structures and cell-cell contacts were analyzed by transmission electron microscopy (TEM) and light microscopic assessment after actin and nuclear staining.

RESULTS

Structural alterations of mitochondria, endoplasmic reticulum, nuclei, and cytoskeletal fibers as well as disruption of intercellular contacts were found after cold storage in HTK and EuroCollins solutions. In contrast, storage in UW solution resulted in minimum changes of stress fibers only. A rapid rearrangement of structural alterations was achieved during rewarming in cell culture medium in all experimental groups.

CONCLUSIONS

Preservation of endothelial cell structure is best achieved by UW solution. Ultrastructural cell damage is a direct consequence of hypothermic storage and is fully reversible during rewarming after short storage times.

Expression of stress proteins, adhesion molecules, and interleukin-8 in endothelial cells after preservation and reoxygenation

Endothelial activation is a central feature of preservation-induced allograft injury. The present study aims at a quantitative assessment of stress proteins, adhesion molecules, and interleukin-8 in a cell culture-based model of organ preservation. Human umbilical vein endothelial cells were exposed to cold, hypoxic storage in University of Wisconsin (UW), histidine-tryptophane-ketoglutarate (HTK), and EuroCollins solutions for 8 h with subsequent rewarming/reoxygenation (rew/reox) for 1 and 4 h. A cell-based ELISA was designed for detection of heat shock proteins (HSP) 60 and 70, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and endothelial leukocyte adhesion molecule-1 (ELAM-1). Immunohistochemical staining was performed for comparison. Interleukin-8 was quantified by ELISA. HSP 70 was expressed after cold storage in HTK and EuroCollins solution and after rew/reox in all groups. A constitutive expression of HSP 60 was observed with further upregulation after rew/reox following cold storage in all experimental groups. ICAM-1 was clearly upregulated, but VCAM-1 showed only weak expression after cold storage and rew/reox. ELAM-1 was detectable in minimal amounts after cold storage but was considerably upregulated after 4 h of rew/reox. A significant increase of interleukin-8 release could be found after 4 h of rew/reox following storage in EuroCollins solution. Expression of stress proteins can be considered as a new parameter of preservation-associated endothelial activation. Apart from possible protective effects, allograft vasculopathy could be in part a consequence of the antigeneic potential of heat shock proteins connected with effects caused by adhesion molecules and inflammatory cytokines.

Inferior outcome of cadaveric kidneys preserved for more than 24 hr in histidine-tryptophan-ketoglutarate solution. Leuven Collaborative Group for Transplantation

BACKGROUND

During recent years, an increasing number of transplant centers within the Eurotransplant organization have used histidine-tryptophan-ketoglutarate (HTK) solution instead of University of Wisconsin (UW) solution as their preferred cold storage solution for abdominal organ preservation. We report on our single-center experience on the outcome of imported kidneys preserved with either HTK or UW solution in relation to the duration of cold ischemia time (CIT).

METHODS

Between July 1989 and July 1997, 323 cadaveric kidneys preserved with UW or HTK and imported as a result of an exchange within the Eurotransplant organization were transplanted at our institution. CIT was <24 hr in 216 kidneys (UW: n=174, HTK: n=42) and > or =24 hr in 107 kidneys (UW: n=67, HTK: n=40). Renal functional outcome was evaluated by comparing delayed graft function and initial non-function rates, daily urinary output, the evolution of serum creatinine, and creatinine clearance at 1, 3, 5, 7, and 14 days and at 1, 3, 6 and 12 months, and graft survival at 1 year after transplantation in relation to the type of cold storage solution and CIT < or > or =24 hr.

RESULTS

Whereas the incidence of delayed graft function did not differ significantly between kidneys preserved for less than 24 hr in UW (18.6%) or HTK (26.2%), this rate increased to 50% in HTK kidneys compared to 23.9% in UW kidneys when CIT exceeded 24 hr (P=0.006). Mean serum creatinine and creatinine clearance values were better at 1 and 5 days postoperatively in kidneys preserved <24 hr with UW as compared to HTK (P<0.05). After 24 hr of CIT, HTK-preserved kidneys showed an impaired renal function, not only in the immediate postoperative phase but also at 1, 3, 6, and 12 months after transplantation (P<0.05). Graft survival at 1 year was 92.9% in UW vs. 87.5% in HTK kidneys preserved for <24 hr (NS), and 91% vs. 77.4% when CIT exceeded 24 hr (P=0.059).

CONCLUSIONS

From these single-center findings, it can be concluded that UW is superior to HTK in kidney preservation, particularly when CIT exceeds 24 hr.