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

The Effect of Antioxidant Added to Preservation Solution on the Protection of Kidneys before Transplantation

Ischemia–reperfusion injury is a key clinical problem of transplantology. Current achievements in optimizing organ rinse solutions and storage techniques have significantly influenced the degree of graft damage and its survival after transplantation. In recent years, intensive research has been carried out to maintain the viability of tissues and organs outside the integral environment of the body. Innovative solutions for improving the biochemical functions of the stored organ have been developed. The article discusses directions for modifying preservation solutions with antioxidants. Clinical and experimental studies aimed at optimizing these fluids, as well as perfusion and organ preservation techniques, are presented.

Targeting Mitochondria during Cold Storage to Maintain Proteasome Function and Improve Renal Outcome after Transplantation

Kidney transplantation is the preferred treatment for end-stage kidney disease (ESKD). Compared to maintenance dialysis, kidney transplantation results in improved patient survival and quality of life. Kidneys from living donors perform best; however, many patients with ESKD depend on kidneys from deceased donors. After procurement, donor kidneys are placed in a cold-storage solution until a suitable recipient is located. Sadly, prolonged cold storage times are associated with inferior transplant outcomes; therefore, in most situations when considering donor kidneys, long cold-storage times are avoided. The identification of novel mechanisms of cold-storage-related renal damage will lead to the development of new therapeutic strategies for preserving donor kidneys; to date, these mechanisms remain poorly understood. In this review, we discuss the importance of mitochondrial and proteasome function, protein homeostasis, and renal recovery during stress from cold storage plus transplantation. Additionally, we discuss novel targets for therapeutic intervention to improve renal outcomes.

Improved hypothermic short-term storage of isolated mouse islets by adding serum to preservation solutions

Preserving isolated islets at low temperature appears attractive because it can keep islet quantity comparable to freshly isolated islets. In this study, we evaluated the effect of serum as an additive to preservation solutions on islet quality after short-term hypothermic storage. Isolated mouse islets were preserved at 4°C in University of Wisconsin solution (UW) alone, UW with serum, M-Kyoto solution (MK) alone or MK with serum. We then assessed islet quantity, morphology, viability and function in vitro as well as in vivo. Islet quantity after storage in all four solutions was well maintained for up to 120 h. However, islets functioned for different duration; glucose-stimulated insulin release assay revealed that the duration was 72 h when islets were stored in UW with serum and MK with serum, but only 24 h in UW alone, and the islet function disappeared immediately in MK alone. Viability assay confirmed that more than 70% islet cells survived for up to 48 h when islets are preserved in UW with serum and MK with serum, but the viability decreased rapidly in UW alone and MK alone. In in vivo bioassays using 48-h preserved isogeneic islets, all recipient mice restored normal blood glucose concentrations by transplants preserved in UW with serum or MK with serum, whereas 33.3% recipients and no recipient restored diabetes by transplants preserved in UW alone and in MK alone respectively. Adding serum to both UW and MK improves their capability to store isolated islets by maintaining islet functional viability.

Contribution of large pig for renal ischemia-reperfusion and transplantation studies: the preclinical model

Animal experimentation is necessary to characterize human diseases and design adequate therapeutic interventions. In renal transplantation research, the limited number of in vitro models involves a crucial role for in vivo models and particularly for the porcine model. Pig and human kidneys are anatomically similar (characterized by multilobular structure in contrast to rodent and dog kidneys unilobular). The human proximity of porcine physiology and immune systems provides a basic knowledge of graft recovery and inflammatory physiopathology through in vivo studies. In addition, pig large body size allows surgical procedures similar to humans, repeated collections of peripheral blood or renal biopsies making pigs ideal for medical training and for the assessment of preclinical technologies. However, its size is also its main drawback implying expensive housing. Nevertheless, pig models are relevant alternatives to primate models, offering promising perspectives with developments of transgenic modulation and marginal donor models facilitating data extrapolation to human conditions.

Emerging roles for eicosanoids in renal diseases

PURPOSE OF REVIEW

Eicosanoids are products of arachidonic acid metabolism which have important roles in renal homeostasis and disease. In recent years the development of genetically modified animals and new drugs targeting eicosanoids producing enzymes and receptors has unveiled new roles for eicosanoids in kidney function. This review provides an overview of eicosanoid biosynthesis and receptors and discusses recent findings on their role in acute and chronic renal diseases and in renal transplantation.

RECENT FINDINGS

Products of the cyclooxygenases, 5-lipoxygenase, and cytochrome P450 pathways of arachidonic acid metabolism act through distinct receptors presented at different segment of the nephron. Apart from its role in renal physiology and hemodynamic, eicosanoids actively participate in the pathogenesis of acute and chronic renal diseases and have immunoregulatory role in kidney transplantation.

SUMMARY

The new discoveries on the role of eicosanoids in kidney functions and the development of drugs targeting eicosanoids synthesis or action should help to envisage novel therapeutic approaches for patients suffering from renal diseases.

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.

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.

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.

Isoprostanes and the kidney

Isoprostanes are not mere bystanders of oxidative injury, but possess potent biological activity and may thus contribute to the pathophysiology of various disorders associated with an increase in free radical formation. 15-F2t-IsoP (8-iso-prostaglandin F2) and 15-E2t-IsoP (8-iso-prostaglandin E2), two of the most abundant isoprostanes, are potent vasoconstrictors in various vascular beds, including the kidney. Since their discovery, numerous studies have aimed to define the receptors through which isoprostanes exert their effects. Whether the thromboxane receptor and/or other prostaglandin receptors mediate the actions of isoprostanes, or whether these compounds interact with their own unique receptors, remains to be clarified. Regardless of their exact mode of action, isoprostanes are being implicated in the pathophysiology of a variety of diseases, and their discovery might give rise to novel therapies for these diseases. Here we describe early studies that defined the vasoactive properties of isoprostanes in the kidney, and subsequent discoveries relating to their renal actions and pathophysiologic significance.

Renal siderosis in donor allograft: pathologic and clinical sequelae

Transplantation of a cadaver kidney with marked siderosis and its outcome has not been reported. Increasing use of marginal kidneys has become common practice to expand the donor pool to meet the growing demand and will lead to increased recognition of kidney disease in cadaver donors with an unknown effect on graft outcome. This is a case report of a recipient of a cadaver kidney with marked siderosis monitored by surveillance biopsies and evaluated by clinico-pathological correlation. The recipient continued to have transplant kidney function, and a surveillance biopsy shows the natural course of the pathologic resolution of renal siderosis.

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.

Cyclooxygenase 1-dependent production of F2-isoprostane and changes in redox status during warm renal ischemia-reperfusion

The detrimental role of oxidative stress has been widely described in tissue damage caused by ischemia-reperfusion. A nonenzymatic, reactive oxygen species-related pathway has been suggested to produce 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)), an epimer of prostaglandin F(2alpha) (PGF(2alpha)), which has been proposed as an indicator of oxidative stress. Using an in vivo ischemia-reperfusion model in rat kidneys, we investigated intrarenal accumulation of 8-iso-PGF(2alpha) and PGF(2alpha). Both prostanoids accumulated in the ischemic kidney and disappeared upon reperfusion. In addition, a nonselective (acetylsalicylic acid) or selective cyclooxygenase (COX) 1 inhibitor (SC-560) completely abrogated the 8-iso-PGF(2alpha) and PGF(2alpha) formation in kidneys subjected to ischemia. COX2 inhibition had no effect on the production of these prostanoids. Therefore the two metabolites of arachidonic acid seemed to be produced via an enzymatic COX1-dependent pathway. Neither COX overexpression nor COX activation was detected. We also investigated renal glutathione, which is considered to be the major thiol-disulfide redox buffer of the tissue. Total and oxidized glutathione was decreased during the ischemic period, whereas no further decrease was seen for up to 60 min of reperfusion. These data demonstrate that a dramatic decrease in antioxidant defense was initiated during warm renal ischemia, whereas the 8-iso-PGF(2alpha) was related only to arachidonate conversion by COX1.

Deferoxamine reduces cold-ischemic renal injury in a syngeneic kidney transplant model

In cell-culture models, addition of deferoxamine (DFO) to University of Wisconsin Solution (UW solution) reduces cold-storage injury. The efficacy of DFO was therefore tested in a kidney transplantation model employing inbred Wistar Furth rats. Donor left kidneys, cold stored for 18 h in UW solution with or without 0.125 mM or 0.625 mM DFO were transplanted to the recipients' left renal fosse. Deferoxamine dose-dependently and significantly increased glomerular filtration rate (GFR) and renal blood flow (RBF), and suppressed renal F2-isoprostanes (vasoactive lipid peroxidation products) and apoptotic and necrotic injury 3 days post-transplantation. In a second set of similar experiments, the remaining native kidneys of the recipient rats were removed on day 7 of transplantation. Transplanted kidneys' function assessed by serum creatinine was 75% higher in the cold-stored transplanted kidneys treated with DFO compared with untreated kidneys. Moreover, the DFO treatment was attended by a significant reduction in apoptotic and necrotic tubular injury. Thus, our consistent findings from two sets of studies in a transplant model suggest that a simple strategy of including DFO in the cold-storage solution reduces cold ischemia-associated renal transplant damage and improves renal function. Our findings have potentially important ramifications for cold preservation of kidneys, and possibly other organs, in clinical transplantation.

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.

Discovery of lipid peroxidation products formed in vivo with a substituted tetrahydrofuran ring (isofurans) that are favored by increased oxygen tension

Free radicals have been implicated in the pathogenesis of an increasing number of diseases. Lipids, which undergo peroxidation, are major targets of free radical attack. We report the discovery of a pathway of lipid peroxidation that forms a series of isomers in vivo that are characterized by a substituted tetrahydrofuran ring structure, termed isofurans (IsoFs). We have proposed two distinct pathways by which IsoFs can be formed based on 18O2 and H2 18O labeling studies. Measurement of F2-isoprostanes (IsoPs), prostaglandin F2-like compounds formed nonenzymatically as products of lipid peroxidation, is considered one of the most reliable approaches for assessing oxidative stress status in vivo. However, one limitation with this approach is that the formation of IsoPs becomes limited at high oxygen tension. In contrast, the formation of IsoFs becomes increasingly favored as oxygen tension increases. IsoFs are present at readily detectable levels in normal fluids and tissues, and levels increase dramatically in CCl4-treated rats, an animal model of oxidant injury. The ratio of IsoFs to IsoPs in major organs varies according to normal steady-state tissue oxygenation. In addition, IsoFs show a marked increase early in the course of hyperoxia-induced lung injury, whereas IsoPs do not significantly increase. We propose that combined measurement of IsoFs and IsoPs should provide a more reliable index of oxidant stress severity than quantification of either alone because of the opposing modulation of the two pathways by oxygen tension, which can vary widely in different organs and disease states.

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.

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.

Overexpression of heme oxygenase protects renal tubular cells against cold storage injury: studies using hemin induction and HO-1 gene transfer

Heme oxygenase-1 (HO-1), a 32-kd microsomal enzyme, is induced as an adaptive response to a wide variety of injurious stimuli. We examined the possible role of HO-1 in cold storage of renal proximal tubular epithelial (RPTE) cells. Hemin, a potent HO-1-inducer, caused a time-dependent increase in HO-1 mRNA and protein expression. Hemin pretreatment of human RPTE cells before cold storage conferred cytoprotection. Increased HO-1 protein was associated with a brisk and early increase in catalytically active iron and a robust increase in cellular ferritin. Deferoxamine, an iron sequestrating antioxidant, prevented hemin-induced iron release and the increase in ferritin, suggesting iron release as an antecedent mechanism for ferritin induction. To verify that the proximate cause of hemin cytoprotection was due to HO-1 induction, we transiently transfected LL-CPK1 porcine kidney cells with a HO-1 expression vector before cold storage. HO-1 transfection resulted in increased expression of HO-1 protein and reduced cell injury during cold storage. The novel observation that prior induction of HO-1 prevents cold storage-induced cell injury suggests that a similar strategy may prove efficacious in preventing cold storage-induced organ damage during transplantation.

Apoptosis versus necrosis during cold storage and rewarming of human renal proximal tubular cells

BACKGROUND

A recent clinical study demonstrated that in renal allografts preserved in the cold apoptosis occurred soon after reperfusion. The mode of cell death during cold storage is generally considered necrotic. Whether apoptosis occurs as a part of cold storage is uncertain. The objective was to determine in human renal tubular cells whether apoptosis is specific for rewarming or it also occurs during cold storage and whether it could be modified.

METHODS AND RESULTS

Cold storage (4 degrees C) of primary human renal proximal tubular epithelial (RPTE) in University of Wisconsin (UW) solution up to 48 hr caused a time-dependent increase in cell death measured by lactic dehydrogenase (LDH) release and vital dye exclusion methods. Transmission electron microscopy (TEM) demonstrated that cell death in the cold was necrotic, involving considerable mitochondrial disruption, and was not apoptotic. The TUNEL assay that provides a specific, quantitative measure for apoptosis showed no increase in TUNEL-positivity during flow cytometry of cells stored in cold: 37 degrees C, 0.23+/-0.14%; 24 hr cold, 0.23+/-0.1%; 48 hr cold, 1.79+/-0.58%. Annexin-V staining, a sensitive method for detecting early apoptosis, similarly showed no increase in positively stained cells during cold storage. Addition of antioxidants 2-methyl aminochroman and deferoxamine to UW solution inhibited necrotic cell death and preserved mitochondrial structure. In contrast to cold storage alone, rewarming (37 degrees C for 24 hr) of cold stored cells, however, resulted in significant apoptosis (TUNEL positive: 48 hr cold: 2+/-0.6%, 48 hr cold and 24 hr rewarming: 54+/-17%), which was confirmed by the TEM based on typical apoptotic features. Addition of 2-MAC and DFO significantly inhibited rewarming-induced apoptotic cell death (plus 2-MAC: 3+/-1%, plus DFO: 3+/-2%).

CONCLUSION

Our study in human tubular cells provides evidence that cold storage per se does not result in apoptosis, but is primarily necrotic. However, rewarming is associated with significant apoptosis in the presence of ongoing necrosis, speculatively due to the activation of the apoptotic enzymic process of sublethally injured cells. Inclusion of antioxidants in the storage solution confers protection against both cold storage and rewarming-induced necrosis and apoptosis.

Mechanism and prevention of cold storage-induced human renal tubular cell injury

BACKGROUND

The recent observation that cold storage of kidneys and tubular cells causes marked increase in free radical-catalyzed F2-isoprostanes suggests that radicals might be formed during cold storage. As cold temperature is associated with reduced metabolic and enzymic activity, the notion that cold temperature causes free radical production appeared less tenable. The objective was, therefore, to seek direct evidence for the free radical production during the cold storage of human renal tubular cells, and to define the roles of extrinsic and intrinsic antioxidants in cold-induced cell injury.

METHODS

Human renal tubular cells were cold-stored at 4 degrees C for varying duration in University of Wisconsin solution and subjected to mRNA analysis, biochemical measurements, and cytoprotective studies.

RESULTS

Cold storage caused a time-dependent reduction in glutathione levels, and an increase in the formation superoxide, hydrogen peroxide, and hydroxyl radicals. Cold-induced lactate dehydrogenase (LDH) release, ATP depletion, DNA damage, and membrane degradation were suppressed with the inclusion of antioxidant 2-methyl aminochroman or deferroxamine. The cells that were structurally protected with antioxidants were also intact functionally, as they had significantly improved cell proliferation. To examine the effect of cold on intrinsic antioxidant gene expression, antioxidant mRNA levels were analyzed using reverse transcription-polymerase chain reaction. The gene expression of mitochondrial Mn-superoxide dismutase (SOD), but not of cytosolic Cu,Zn-SOD or of glutathione peroxidase expression increased with cold exposure. The oxidant-sensitive gene heme oxygenase I increased slightly with 48-hr cold storage.

CONCLUSIONS

Cold storage of human tubular cells causes marked increase in free radicals. These are likely of mitochondrial origin as there is a differential inducement of Mn-SOD gene, and are causal to cold-induced cell injury as extrinsic antioxidants abrogated the injury. Our findings support the strategy of adding antioxidants to preservation solutions or the strategy of pre-conditioning the organs to oxidative stress to minimize cold storage-induced organ damage.

Inhibition of angiotensin-converting enzyme by captopril: a novel approach to reduce ischemia-reperfusion injury after lung transplantation

OBJECTIVES

Ischemia-reperfusion injury after lung transplantation involves the generation of free radicals. Captopril has been shown to be protective in models of ischemia-reperfusion injury in other organs by acting as a free radical scavenger. The purpose of this study was to assess the protective effects of captopril against ischemia-reperfusion injury and to evaluate the ability of captopril to scavenge free radicals and inhibit neutrophil activation in an experimental model of lung transplantation.

METHODS

A rat single-lung transplant model was used. Donor lungs were flushed and preserved in low-potassium dextran-glucose solution with (n = 5) and without captopril (500 micromol/L; n = 5) for 18 hours at 4 degrees C and then transplanted and reperfused for 2 hours. At the conclusion of the 2-hour reperfusion period, arterial blood gases, blood pressure, and peak airway pressure were measured. Lung tissue biopsy specimens were obtained for assessment of wet/dry weight ratios, histology, and neutrophil sequestration (myeloperoxidase activity). Lipid peroxidation (F(2)-isoprostane assay) was analyzed from plasma samples and tissue lysates.

RESULTS

The addition of captopril to the lung preservation solution significantly improved postreperfusion PO (2) (312 +/- 63.3 mm Hg vs 202 +/- 21.1 mm Hg; P =.006), peak airway pressure (11.4 +/- 1.1 cm H(2)O vs 15.6 +/- 1.5 cm H(2)O; P =.001), and wet/dry weight ratio (4.9 +/- 0.4 vs 15.8 +/- 10.9; P =.008). Blood pressures did not differ significantly between groups. No significant differences were seen in myeloperoxidase activity or F(2)-isoprostane levels.

CONCLUSIONS

The use of captopril in the preservation solution ameliorates ischemia-reperfusion injury in transplanted lungs after an extended cold preservation period. The mechanisms by which captopril is protective remain elusive but do not appear to include inhibition of neutrophil sequestration or lipid peroxidation. This novel approach to ischemia-reperfusion injury may lead to improved lung function after transplantation and provide further insight into the pathogenesis of acute lung injury.

Cell biology and molecular mechanisms of injury in ischemic acute renal failure

The pathogenesis of acute renal failure has been attributed to persistent vasoconstriction and leukocyte-endothelial interactions, resulting in inflammation and compromise of local blood flow to the outer medulla, the loss of tubular epithelial cell polarity with multiple functional sequelae, necrosis or apoptosis of epithelial cells, and the de-differentiation, migration and proliferation of surviving cells. In this paper, the authors present their views of pathophysiology of ischemic acute renal failure.

Measurement of F(2)-isoprostanes as an index of oxidative stress in vivo

In 1990 we discovered the formation of prostaglandin F(2)-like compounds, F(2)-isoprostanes (F(2)-IsoPs), in vivo by nonenzymatic free radical-induced peroxidation of arachidonic acid. F(2)-IsoPs are initially formed esterified to phospholipids and then released in free form. There are several favorable attributes that make measurement of F(2)-IsoPs attractive as a reliable indicator of oxidative stress in vivo: (i) F(2)-IsoPs are specific products of lipid peroxidation; (ii) they are stable compounds; (iii) levels are present in detectable quantities in all normal biological fluids and tissues, allowing the definition of a normal range; (iv) their formation increases dramatically in vivo in a number of animal models of oxidant injury; (v) their formation is modulated by antioxidant status; and (vi) their levels are not effected by lipid content of the diet. Measurement of F(2)-IsoPs in plasma can be utilized to assess total endogenous production of F(2)-IsoPs whereas measurement of levels esterified in phospholipids can be used to determine the extent of lipid peroxidation in target sites of interest. Recently, we developed an assay for a urinary metabolite of F(2)-IsoPs, which should provide a valuable noninvasive integrated approach to assess total endogenous production of F(2)-IsoPs in large clinical studies.