Severe Ischemia-reperfusion Injury Research Articles

Adenosine A3 Receptor Activation Attenuates Lung Ischemia-Reperfusion Injury

Severe ischemia-reperfusion (IR) injury leads to primary graft dysfunction after lung transplantation. Adenosine receptors modulate inflammation after IR, and the adenosine A3 receptor (A3R) is expressed in lung tissue and inflammatory cells. This study tests the hypothesis that A3R agonism attenuates lung IR injury by a neutrophil-dependent mechanism. Wild-type and A3R knockout (A3R-/-) mice underwent 1-hour left lung ischemia followed by 2-hours reperfusion (IR). A selective A3R agonist, Cl-IB-MECA, was administered (100 μg/kg intravenously) 5 minutes prior to ischemia. Study groups included sham, IR, and IR+Cl-IB-MECA (n = 6/group). Lung injury was assessed by measuring lung function, pulmonary edema, histopathology, and proinflammatory cytokines, and myeloperoxidase levels in bronchoalveolar lavage fluid. Parallel in vitro experiments were performed to evaluate neutrophil chemotaxis, and neutrophil activation was measured after exposure to acute hypoxia and reoxygenation. Treatment of wild-type mice with Cl-IB-MECA significantly improved lung function and decreased edema, cytokine expression, and neutrophil infiltration after IR. The Cl-IB-MECA had no effects in A3R-/- mice; Cl-IB-MECA significantly decreased activation of wild-type, but not A3R-/-, neutrophils after acute hypoxia and reoxygenation and inhibited chemotaxis of wild-type neutrophils. Exogenous activation of A3R by Cl-IB-MECA attenuates lung dysfunction, inflammation, and neutrophil infiltration after IR in wild-type but not A3R-/- mice. Results with isolated neutrophils suggest that the protective effects of Cl-IB-MECA are due, in part, to the prevention of neutrophil activation and chemotaxis. The use of A3R agonists may be a novel therapeutic strategy to prevent lung IR injury and primary graft dysfunction after transplantation.

Early malperfusion, ischemia reperfusion injury, and respiratory failure in acute complicated type B aortic dissection after thoracic endovascular repair

BackgroundThe aim of this study was to determine the early mortality and major complications of acute complicated type B aortic dissection (ACBD) after thoracic endovascular aortic repair (TEVAR).MethodsTwenty-six consecutive patients with ACBD who underwent TEVAR were included. Clinical indications before TEVAR and in-hospital mortality and major complications after TEVAR were analyzed and compared with similar reports.ResultsTEVAR was technically successful in all cases. In-hospital mortality occurred in four patients (15%), and major complications occurred in an additional four patients (15%). Three of the four (75%) of the deaths were associated with malperfusion and ischemia reperfusion injury (IRI), and 3/4 (75%) of the major complications were caused by respiratory failure (RF).ConclusionsIn-hospital mortality associated strongly with severe end-organ malperfusion and IRI, while major complications associated with RF, during TEVAR. Our results indicate that malperfusion, IRI and respiratory failure during TEVAR should be carefully monitored and aggressively treated.

Adenosine–lidocaine–magnesium non-depolarizing cardioplegia: Moving forward from bench to bedside. Reply to Vinten-Johansen

We have greatly appreciated the interest by Dr Vinten-Johansen [1] in our paper investigating the beneficial impact of polarizing microplegia on biochemical, hemodynamic, echocardiographic and clinical outcomes of patients undergoing CABG for unstable angina [2]. We are really intrigued about his comments, related to the potential underestimation of the beneficial effects of our microplegia in terms of postoperative clinical outcome. Indeed, we were really impressed by our biochemical results, showing a significantly attenuated perioperative release of troponin I —which was our primary endpoint [2]. Accordingly, we have underscored also the significant amelioration of the entire “hemodynamic pattern” of patients treated with microplegia during the postoperative course, because of the better systo-diastolic left ventricular function at echocardiography, and the better hemodynamic indices of cardiac function,myocardial oxygenconsumption, andventricular–arterial coupling at PRAM monitoring [2]. However, when clinical outcome was considered, we were able to demonstrate only a significant reduction of blood products usage and a significantly shortened hospitalization. However, the level of statistical significance of our secondary clinical outcome “proxies” was significantly augmented by the Bonferroni correction, so that only a “trend” towards a shorter/lower needof inotropic support and a shorter ICU-length of stay could be detected.Whether these “preliminary” beneficial effects will translate in statistical significant differencesneed tobeascertainedonhighernumberof patients and future clinical studies. However, we agree with Dr Vinten-Johansen that improvements in length of hospitalization and usage of blood products are still sufficient to ameliorate patient's outcome and hospital costs [3]. When the risk for potential bias related to the complex combinations of substrates in both groups (Buckberg andMicroplegia) was considered, we completely agree that it is difficult at the moment to attribute the overall beneficial effect of microplegia to one or other substrate composing our “microplegic milieu”. However, we have tried to avoid all the potential biases by either strict enrollment criteria or standardized perioperative care. As example, tight glycemic control was always guaranteed by the application of Portland protocol either intraoperatively and postoperatively [4], so that only slight oscillations in glycemia could happen. Furthermore, the role of insulin in myocardial protection can be considered a “never-ending story” which has actually no data demonstrating its beneficial effect [5,6]. Furthermore, when microplegia is routinely used in clinical practice (as we do in our institution following that experimental study), thefirst “impressive” result– compared toother cardioplegic solutions – is the extremely rare need for internal cardioversion after aortic declamping, a well-known sign of adequacy of myocardial protection for cardiac surgeons. According to the pioneering studies by Dobson et al. proving the anti-ischemic, antiinflammatory and pre-conditioning effects of adenosine–lidocaine– magnesium (ALM) solutions [7,8], we think that our data can only be attributed to a better myocardial protection achieved with the entire “ALM”milieu. According to that, our results – although achieved with a lower concentration of ALM reported in other preliminary clinical experiences [1] and animal studies [7,8] – can only be the consequence of anattenuated ischemia–reperfusion injury (IRI) in a cohortof patients at high risk, because of unstable angina, for severe IRI following aortic declamping [2]. Similarly, we cannot exclude that our blood product saving can be related either to the lower hemodilution (all-blood cardioplegia vs 4:1 crystalloid dilution of our Buckberg solutions) and the higher anti-inflammatory/anti-fibrinolytic effect (a direct consequence of IRI-attenuation) of microplegia. Certainly future studies on the topic are needed for definitive conclusions. Finally,weperfectlyagreewithDrVinten-Johansenon theurgentneed for future clinical and laboratory investigations on the potential multiorgan effects of ALM in cardiac surgery. As examples, other intriguing issues needing future clinical investigations are the comparison between continuous and intermittent ALM administrations [9] and between “warm” and “cold” ALM administrations [10]. Certainly, the time to move from bench to bed has come!

High-Mobility Group box-1 Release Induced by Renal Warm Ischemia Mediates Progression of Ischemia-Reperfusion Injury in Miniature Swine

Objective: The prevention of ischemia-reperfusion injury (IRI) is important for both early and long-term graft function, particularly when using extended-criteria or donation after cardiac death (DCD). High-mobility group box 1 (HMGB1) has recently been reported to mediate inflammation and cell injury after IRI; however, there is limited data to characterize the role of HMGB1 on IRI in large animals. The aim of this study was 1) to develop a large animal model of severe renal IRI that would closely mimic the warm ischemia and cold ischemia commonly experienced in human cases of DCD and 2) to determine the role of HMGB1 in IRI, and to evaluate the cytoprotective effects of anti-HMGB1 antibody (Ab) following IRI. Methods: Warm ischemia was induced for 120 minutes in 11 CLAWN miniature swine by clamping the left renal artery and vein. Then, cold ischemia was induced by flushing the left kidney with cold perfusate and topically cooling with ice-slush for 60 minutes. In Group 1 (n=8), the artery and vein were then unclamped and animals were followed without any additional treatment. In Group 2 (n=3), an injection of 1mg/kg of anti-HMGB1 Ab was administered just before unclamping and reperfusion. Renal function was monitored by serum creatinine (Cre) and histologic evaluation of sequential biopsies obtained on postoperative days (PODs) 2, 14, 28 and 56. Serum cytokine levels such as TNF-α, IL-1β, IL-6 and HMGB1 were measured in order to characterize the inflammatory response to IRI. Results: In Group 1, three of 8 animals died within 36 hours after reperfusion. In the 5 remaining animals, serum Cre levels markedly elevated after reperfusion, peaking at a median of 5 days (peak Cre levels: 12 ± 2 mg/dL) and recovered by day 14. Sequential measurements of serum cytokine levels showed that the concentrations of HMGB1 increased as early as 30 minutes after reperfusion, followed by the elevation of TNF-α and IL-6 peaking at 6 hours. In Group 2, all animals recovered and renal function returned to near-normal by day 9. Peak Cre levels (7 ± 0.2 mg/dL) were markedly lower than group 1. The Cre area-under-the-curve during days 0-14 (AUC0-14d) for animals in group 1 was 74 mg/dL·day, but significantly lower (43 mg/dL·day; reduction of 42% (p< 0.05)) in Group 2. Renal biopsies in Group 1 showed widespread severe necrosis of renal tubules at POD2. In contrast, treatment with anti-HMGB1 Ab dramatically decreased renal injury and was associated with prompt regeneration of tubular epithelium was seen in Group 2. Conclusion: In this study, we successfully developed a CLAWN miniature swine model of severe renal IRI using 120-min of warm and 60-min of cold ischemia. We observed that HMGB1 was released as an early mediator of IRI that in turn activated the later release of TNF-α or IL-6 and that anti-HMGB1 Ab reduced IRI in this model. To our knowledge, this is the first demonstration of the beneficial effects of perioperative administration of anti-HMGB1 Ab in order to reduce renal IRI in a clinically relevant, large animal model.

The impact of prolonged cold preservation on the graft function and gene expression levels in an experimental lung transplantation model

Ischemia reperfusion injury (IRI) remains a significant cause of morbidity and mortality after lung transplantation. Early growth response-1 (EGR1) drives the expression of inflammatory mediators and has an important role in IRI. We hypothesized that the severe IRI caused by a long preservation induces a specific expression pattern of EGR1 and its target genes which would correlate with the lung graft function. SD rat lungs were preserved at 4 °C for 3 or 18 h, then transplanted and reperfused. Pulmonary grafts were evaluated for the blood gas oxygenation and pathological findings. The intra-graft mRNA levels of EGR1 and its downstream target genes were measured by real-time PCR. A Western blotting analysis of the EGR1 expression was used to validate the changes in the protein level. There was upregulation of EGR1, MIP-2 and PAI-1 when there was prolonged hypothermic preservation. The expression levels of MIP-2 and PAI-1 were observed to increase for up to 4 h in the 18 h preserved lungs. There were no differences in the expression levels of IL-1β and ICAM-1 between the lungs subjected to short and long periods of ischemia. Our data showed that prolonged hypothermic graft preservation deteriorates the pulmonary graft function, which was associated with the induction of EGR1 and its downstream target genes, which may aggravate IRI following lung transplantation.

Pretransplant Screening and Evaluation of Liver Graft Viability Using Machine Perfusion Preservation in Porcine Transplantation

A novel method using machine perfusion for pretransplant screening and evaluation of the viability of liver grafts has been proposed, seeking to prevent severe ischemia-reperfusion injury and to reduce the risk of primary graft nonfunction. This study sought to evaluate the viability of critical grafts, which were obtained from expanded criteria donors or donation after cardiac death donors during preservation with a new machine preservation perfusion system (NES-01). The normalized pressure transition in the hepatic artery was employed as an evaluation index for liver viability. As a result, the normalized pressure (p/p0) in the hepatic artery showed a distinctive transition under each experimental conditions controlled by warm ischemic time (WIT). The high viability graft, obtained under the condition of WIT as 0 minutes (WIT0), showed a quick response to hepatic artery pressure after initiating perfusion, whereas the normalized pressure showed a sudden decrease. In contrast, the normalized pressure among WIT60, which may cause the graft to lose viability, showed a poor hepatic artery response. These findings corresponded to the cumulative release of enzymes. The findings of our study suggest that monitoring of the pressure drop rate in the hepatic artery during machine perfusion can be used to evaluate liver graft viability.

Real time measurement of myocardial oxygen dynamics during cardiac ischemia–reperfusion of rats

Because oxygen plays a critical role in the pathophysiology of myocardial injury during subsequent reperfusion, as well as ischemia, the accurate measurement of myocardial oxygen tension is crucial for the assessment of myocardial viability by ischemia-reperfusion (IR) injury. Therefore, we utilized a sol-gel derived electrochemical oxygen microsensor to monitor changes in oxygen tension during myocardial ischemia-reperfusion. We also analyzed differences in oxygen tension recovery in post-ischemic myocardium depending on ischemic time to investigate the correlation between recovery parameters for oxygen tension and the severity of IR injury. An oxygen sensor was built using a xerogel-modified platinum microsensor and a coiled Ag/AgCl reference electrode. Rat hearts were randomly divided into 5 groups: control (0 min ischemia), I-10 (10 min ischemia), I-20 (20 min ischemia), I-30 (30 min ischemia), and I-40 (40 min ischemia) groups (n = 3 per group, respectively). After the induction of ischemia, reperfusion was performed for 60 min. As soon as the ischemia was initiated, oxygen tension rapidly declined to near zero levels. When reperfusion was initiated, the changes in oxygen tension depended on ischemic time. The normalized peak level of oxygen tension during the reperfusion episode was 188 ± 27 in group I-10, 120 ± 24 in group I-20, 12.5 ± 10.6 in group I-30, and 1.24 ± 1.09 in group I-40 (p < 0.001, n = 3, respectively). After 60 min of reperfusion, the normalized restoration level was 129 ± 30 in group I-10, 88 ± 4 in group I-20, 3.40 ± 4.82 in group I-30, and 0.99 ± 0.94 in group I-40 (p < 0.001, n = 3, respectively). The maximum and restoration values of oxygen tension in groups I-30 and I-40 after reperfusion were lower than pre-ischemic values. In particular, oxygen tension in the I-40 group was not recovered at all. These results were also demonstrated by TTC staining. We suggest that these recovery parameters could be utilized as an index of tissue injury and severity of ischemia. Therefore, quantitative measurements of oxygen tension dynamics in the myocardium would be helpful for evaluation of the cardioprotective effects of therapeutic treatments such as drug administration.

Sphingosine kinase 1 protects against renal ischemia–reperfusion injury in mice by sphingosine-1-phosphate1 receptor activation

The roles of sphingosine kinases SK1 and SK2 in ischemia-reperfusion injury have not been fully elucidated since studies have found beneficial effects of SK1 while others showed no role in this injury. To help resolve this, we used SK1 or SK2 knockout mice and confirmed that renal ischemia-reperfusion injury induced SK1, but not SK2, in the kidneys. Furthermore, knockout or pharmacological inhibition of SK1 increased injury after renal ischemia-reperfusion injury. In contrast, lack of SK2 conferred renal protection following injury. In addition, we used lentiviral gene delivery to selectively express enhanced green fluorescent protein (EGFP) or human SK1 coexpressed with EGFP (EGFP-huSK1) in the kidney. Mice with kidney-specific overexpression of EGFP-huSK1 had significantly improved renal function with lower plasma creatinine, renal necrosis, apoptosis, and inflammation. Moreover, EGFP-huSK1 overexpression in cultured human proximal tubule (HK-2) cells protected against peroxide-induced necrosis. Selective overexpression of EGFP-huSK1 led to increased HSP27 mRNA and protein expression in vivo and in vitro. Functional protection as well as induction of HSP27 with EGFP-huSK1 overexpression in vivo was blocked with sphingosine-1-phosphate-1 receptor(1) (S1P(1)) antagonism. Thus, our findings suggest that SK1 is renoprotective by S1P(1) activation and perhaps HSP27 induction. Kidney-specific expression of SK1 through lentiviral delivery may be a viable therapeutic option to attenuate renal ischemia-reperfusion injury.

Hepatic blood flow plays an important role in ischemia-reperfusion injury

Severe ischemia/reperfusion (IR) injury is associated with poor hepatic microperfusion. The aim of this study was to investigate the role of hepatic artery flow (HAF) and portal vein flow (PVF) in IR injury. From January 2004 to June 2008, 566 patients underwent orthotopic liver transplantation (OLT). The data were retrospectively reviewed via the transplant database. Patients with hepatic artery (HA) or portal vein (PV) thrombosis and retransplant patients were excluded. Intraoperative PVF and HAF values and graft weights were measured routinely, and the central venous pressure, mean arterial pressure, cardiac output, and cardiac index were recorded with hepatic blood flow measurements. Complete data were available for 312 primary OLT recipients (215 males and 97 females; mean age = 54 ± 10 years). The patients' follow-up ranged from 215 to 1746 days (705 ± 408 days). IR injury was defined by the aspartate aminotransferase (AST) level on postoperative day (POD) 2, and the patients were divided into 3 groups: (1) mild IR injury [AST < 500 U/L; n = 160 (51%)], (2) moderate IR injury [AST = 500-1000 U/L; n = 85 (27%)], and (3) severe IR injury [AST > 1000 U/L; n = 67 (21%)]. The demographics and pre-OLT variables (the Model for End-Stage Liver Disease score (MELD), platelet counts, PV thrombosis, transjugular intrahepatic portosystemic shunts, and shunts on computed tomography scans) were similar in all groups. The graft survival rate was 99% in group 1, 95.2% in group 2 (P = 0.02), and 92.3% in group 3 (P = 0.016). The patient survival rates were similar in the 3 groups. The cold ischemia time (CIT) was significantly higher in group 3 versus group 1 (P < 0.007). In the statistical analysis, low HAF, PVF, total liver blood flow (TLBF), and augmented HAF values were associated with a greater likelihood of elevated AST levels on POD 2. The strongest univariate predictors of AST were reduced augmented HAF (mL/minute/100 g) values (P < 0.001) and reduced TLBF (mL/minute/100 g) values (P < 0.001). In a covariate analysis with adjustments for CIT and donor variables, the blood flow parameters remained important predictors of graft function. In conclusion, this report demonstrates for the first time that reduced hepatic blood flow is a significant finding in patients with severe hepatic IR injury.

Utilisation de nouvelles molécules immunosuppres-sives non néphrotoxiques en transplantation rénale, en particulier après lésions d’ischémie-reperfusion

Medium- and long-term renal graft survival depends on 4 main factors: the quality of the harvested graft, ischemia-reperfusion injury during harvesting and re-implantation, rejection, and the nephrotoxicity of certain drugs (especially immunosuppressants) used in this setting. The most nephrotoxic immunosuppressive drugs are the anticalcineurins (cyclosporine A and tacrolimus), a class discovered in the late 1970s and currently representing a basic component of all immunosuppressive protocols for solid organ graft recipients. The renal tubular and vascular toxicity of anticalcineurins is due to their immunosuppressive mechanism: they block the calcineurin pathway and thereby prevent transmission of the first signal from the T cell receptor to the nucleus, which normally triggers cytokine synthesis, New non-nephrotoxic immunosuppressants are therefore needed, especially for grafts of poor quality or subject to severe ischemia-reperfusion injury. Attention is turning to "old " molecules such as anti-thymocyte globulins, but exciting new immunosuppressants are now appearing. Alefacept is a fusion protein that binds to the immunological synapse-associated molecule CD2, which normally interacts with LFA-3. Belatacept, another fusion protein, blocks the T cell second signal CD 28-B7.1/B7.2. Finally, new chemical agents are being developed, such as sautrasporine, a tyrosine kinase inhibitor, and tofacitinib, a Jak inhibitor.

Temporary axillobifemoral bypass as an adjunct to endovascular aneurysm repair using fenestrated stent grafts

Prolonged endovascular procedures requiring a large diameter sheath in each groin can be associated with significant intraoperative lower limb ischemia, particularly in those with pre-existing peripheral vascular disease. We report the case of a patient who suffered severe ischemia-reperfusion injury following endovascular repair of a pararenal aortic aneurysm using a fenestrated stent graft and describe the use of temporary axillobifemoral bypass in a patient with similar comorbidities undergoing the same procedure. We propose this adjunctive technique as a means of maintaining antegrade limb perfusion and avoiding the peripheral and central metabolic consequences of ischemia-reperfusion injury.

Deletion of macrophage migration inhibitory factor protects the heart from severe ischemia–reperfusion injury: A predominant role of anti-inflammation

Inflammation plays an important role in mediating and exacerbating myocardial ischemia–reperfusion (I/R) injury. Macrophage migration inhibitory factor (MIF), a pleiotropic cytokine, facilitates inflammation and modulates metabolism. However, the role of MIF in mediating local inflammation subsequent to ischemic myocardial injury has not been established. We hypothesized that genetic deletion of MIF protects the heart against severe I/R injury by suppressing inflammation and/or modulating energy metabolism. We showed in the mouse I/R model that duration of both ischemia and reperfusion is a determinant for the degree of regional inflammation and tissue damage. Following a prolonged cardiac I/R (60min/24h) MIF KO mice had a significant reduction in both infarct size (26±3% vs. 45±4%, P<0.05) and cardiomyocyte apoptosis (1.4±0.2% vs. 5.4±0.4%, P<0.05) and preserved contractile function compared with WT. MIF KO mice with I/R had reduced expression of various inflammatory cytokines and mediators (P<0.05), suppressed infiltration of neutrophils (−40%) and macrophages (−33%, both P<0.05), and increased macrophage apoptosis (14.4±1.4% vs. 5.2±0.6%, P<0.05). Expression of toll-like receptor-4 (TLR-4), phosphorylation of c-Jun N-terminal kinase (JNK), and nuclear fraction of NF-κB p65 were also significantly lower in MIF KO hearts with I/R. Further, MIF KO mice exhibited a lower glucose uptake but higher fatty acid oxidation rate than that in WT (both P<0.05). In conclusion, MIF deficiency protected the heart from prolonged/severe I/R injury by suppressing inflammatory responses. We have identified a critical role of MIF in mediating severe I/R injury. Thus, MIF inhibitory therapy may be a novel strategy to protect the heart against severe I/R injury.

Noninvasive Delayed Limb Ischemic Preconditioning in Rats Increases Antioxidant Activities in Cerebral Tissue during Severe Ischemia-Reperfusion Injury

To study the protection offered by noninvasive delayed limb ischemic preconditioning (NDLIP) against cerebral ischemia reperfusion (I/R) injury in rats. Healthy male Wistar rats were randomly divided into four groups. The delayed protection offered by NDLIP was estimated in light of changes in the neural behavior marker and cerebral tissue antioxidative ability. Neurological functions were studied by observing neural behavior. Total superoxide dismutase (T-SOD), manganese-superoxide dismutase (Mn-SOD), glutathione peroxidase (GSH-PX), and xanthine oxidase (XOD) activity in cerebral tissue and malonaldehyde (MDA) content were detected using a spectrophotometer. Mn-SOD mRNA was measured by the reverse transcription polymerase chain reaction method. Cerebral infarct size was diminished in the early cerebral ischemia preconditioning (ECIP)+I/R and NDLIP+I/R groups compared with the I/R group (P < 0.05). The cortical and hippocampal antioxidant enzyme activity and Mn-SOD expression were increased in the ECIP+I/R and NDLIP+I/R groups. In contrast, the cortical and hippocampal XOD activity and MDA content decreased in the ECIP+I/R and NDLIP+I/R groups. NDLIP decreased cerebral infarct size, increased cerebral antioxidative ability after I/R injury, and decreased peroxidative damage. The antioxidative protection offered by NDLIP was as effective as that offered by ECIP.

Hepatocellular Calcification in Severe Ischemia–Reperfusion Injury in a Liver Allograft

Ischemia–reperfusion injury (IR) of solid organ allografts is a consequence of ischemia resulting from disruption of blood flow during organ harvest and transportation. Histologically, this manifests as variable necrosis in a pattern similar to that seen in systemic hypoperfusion. Calcification of hepatocytes has been rarely observed in ischemic injury due to systemic shock and in two cases of severe IR, both of which were associated with graft loss and death. The authors present another case of dystrophic calcification within hepatocytes occurring in a liver allograft affected by severe IR. Biochemical stains revealed that the mineralized material was calcium phosphate (likely hydroxyapatite). By electron microscopy, the hepatocyte cytoplasm was filled with variably calcified vacuoles, a subset of which likely represented swollen mitochondria. When encountered in hepatic allograft biopsies, hepatocellular calcification is associated with ischemic injury and a poor prognosis.

Prediction of Graft Dysfunction Based on Extended Criteria Donors in the Model for End-Stage Liver Disease Score Era

To explain the influence of recipient status combined with the accumulation of extended criteria donor (ECD) variables on the appearance of severe ischemia-reperfusion injury and graft survival in a model for end-stage liver disease (MELD)-based system, we analyzed our most recent consecutive liver transplantations (LTs), dividing them into two periods: 400 LTs (1992-2002; pre-MELD era) and 275 LTs (2002-2007; post-MELD era). Primary dysfunction (PD) was defined as primary graft failure that required emergency retransplantation or as initial poor function. Donor variables were included in a regression model to assess the probability of PD. Donor age, macrovesicular steatosis more than 30%, and cold ischemia time were associated with allograft dysfunction. Mean probability of PD was 14.8%, 19.2%, 27.5%, and 37.4% for ECD 0, 1, 2, and more than or equal to 3, respectively (P=0.003). Distribution of no-mild, moderate, and severe ischemia-reperfusion injuries among MELD categories was 72.53%, 24.17%, and 3.30% (MELD group=12-19); 56.52%, 36.96%, and 6.5% (MELD group=20-28); and 23.91%, 54.35%, and 21.74% (MELD group >or=29), respectively (P=0.043). The development of PD according to ECD variables was 18.8%, 18.1%, 28.0%, and 35.3% for ECD 0, 1, 2, and more than or equal to 3, respectively (P=0.047). These variables were independent predictors of PD (Cox proportional regression model): ECD 2 (relative risk [RR]=1.59; 95% confidence interval [CI]=1.25-1.62), ECD 3 (RR=2.74; 95% CI=2.38-3.13), MELD 21 to 30 (RR=1.89; 95% CI=1.32-2.06), and MELD more than or equal to 30 (RR=3.38; 95% CI=2.43-3.86). Graft survival decreased, whereas MELD and the number of ECD variables increased. The combination of three or more ECD variables and an MELD more than or equal to 29 is the worst scenario for graft success after LT.

Hypoxemic Versus Normoxemic Reperfusion in a Large Animal Model of Severe Ischemia-Reperfusion Injury

Prior studies have suggested a significant benefit of using deliberate hypoxemia to reperfuse ischemic tissue beds, primarily by reducing free radical injury. We sought to examine the effects of a hypoxemic reperfusion strategy in a large animal model of severe truncal ischemia. Adult swine were subjected to 30 min of supraceliac aortic occlusion and randomized to two groups: normoxemia group (n = 9), with resuscitation at a pO2 >100 mmHg or hypoxemia group (n = 10), with initial resuscitation at a pO2 of 30-50. The two groups were compared using physiologic parameters, fluid and pressor requirements, inflammatory and oxidative markers, and histologic analysis of end-organ injury. All animals developed significant hemodynamic instability immediately upon reperfusion. Average mean arterial pressure at baseline rose significantly after 30 min of cross-clamp (76.8 versus 166.3 mmHg, P < 0.001). Upon reperfusion, all animals required epinephrine and fluids to maintain mean arterial pressure (MAP) greater than 60 mmHg. After stabilization, the two groups were similar in terms of central and pulmonary hemodynamics. The hypoxemic group required more mean total epinephrine (18.35 mg versus 5.28 mg, P < 0.01) with no significant difference in total fluid volume (hypoxemic 9111 ml versus 8420 mL, P = 0.730). The hypoxemic group demonstrated a more severe metabolic acidosis at all time intervals after reperfusion (pH 7.02 versus 7.16 and lactate 17 versus 13, both P < 0.01). There was no difference in malondialdehyde concentration between the two groups, but the hypoxemic group had a higher antioxidant reductive capacity at all intervals after 30 min of reperfusion (0.23 versus 0.27 uM, P = 0.03). While there was significant end-organ damage on pathologic examination of all liver and kidney specimens (mean severity of injury 1.59 and 1.76, respectively, on a scale of 1-3), there was no significant difference between the two groups. A hypoxemic reperfusion strategy in this large animal model failed to demonstrate any significant clinical benefit. Although there was chemical evidence of improved antioxidant capacity with hypoxemia, it was associated with more instability, metabolic and physiologic derangements, and no evidence of end-organ protection.

Invited Commentary

The Registry of the International Society for Heart and Lung Transplantation reports that 29,732 lung transplants have been performed worldwide through June of 2008, and the 2,708 procedures reported in 2007 were the highest of any year to date [1]. Survival rates have been consistently improving with current survival rates of 89% at 3 months, 79% at 1 year, 52% at 5 years, and 29% at 10 years [1]. Primary graft failure due to severe ischemia-reperfusion injury (IRI) remains the major cause of death within 30 days, whereas bronchiolitis obliterans syndrome (BOS) becomes the predominant cause of death after the first year.

Hypoxemic versus Normoxemic Reperfusion in a Large Animal Model of Severe Ischemia-Reperfusion Injury

Hypoxemic versus Normoxemic Reperfusion in a Large Animal Model of Severe Ischemia-Reperfusion Injury

Aero-medical Considerations in Casualty Air Evacuation (CASAEVAC)

One of the advantages of partial Resuscitative Endovascular Balloon Occlusion of the Aorta (pREBOA) compared to the original model is the mitigation of reperfusion injury. The safety and efficacy of pREBOA have not been demonstrated in the setting of aeromedical evacuation. We hypothesized that the pREBOA would result in less ischemia-reperfusion injury after altitude exposure.Twenty-four swine underwent femur fracture with hemorrhage for 20 min, followed by resuscitative endovascular balloon occlusion of the aorta (REBOA) deployment to Zone 1 and were randomized to pREBOA-PRO (Prytime Medical Devices Inc) full inflation, partial inflation, or sham inflation and then an altitude exposure of ground level or 8000 ft for 15 min. The primary endpoint was to examine if the balloon functioned at altitude. Our secondary endpoint was investigating evidence of ischemia-reperfusion by hemodynamic instability, electrolyte derangements, and acidosis. Comparisons were made by ANOVA.After deflation, the partially inflated group maintained a higher mean arterial pressure (MAP) compared to fully inflated group (P = 0.026). Full REBOA pigs were more tachycardic compared to sham pREBOA at ground (P < 0.001) and this was exacerbated at altitude (P < 0.001). Full REBOA pigs were more acidotic than sham and pREBOA at ground pigs (P = 0.0006 and P = 0.0002, respectively). Altitude increased the acidosis in full REBOA pigs, resulting in a greater base deficit (P < 0.0001), lactate (P < 0.0001), and IL-6 (P = 0.006).PREBOA resulted in less severe ischemia-reperfusion injury at both altitude and ground, while full balloon inflation at altitude exacerbated acidosis and ischemia-reperfusion injury. Efforts should therefore be made to utilize partial balloon occlusion when employing the REBOA catheter.

Blockade of KATP Channels Reduces Endothelial Hyperpolarization and Leukocyte Recruitment upon Reperfusion After Hypoxia

Ischemia/reperfusion injury in renal transplantation leads to slow or initial nonfunction, and predisposes to acute and chronic rejection. In fact, severe ischemia reperfusion injury can significantly reduce graft survival, even with modern immunosuppressive agents. One of the mechanisms by which ischemia/reperfusion causes injury is activation of endothelial cells resulting in inflammation. Although several therapies can be used to prevent leukocyte recruitment to ischemic vessels (e.g. antiadhesion molecule antibodies), there have been no clinical treatments reported that can prevent initial immediate neutrophil recruitment upon reperfusion. Using intravital microscopy, we describe abrogation of immediate neutrophil recruitment to ischemic microvessels by the K(ATP) antagonist glibenclamide (Glyburide). Further, we show that glibenclamide can reduce leukocyte recruitment in vitro under physiologic flow conditions. ATP-regulated potassium channels (K(ATP)) are important in the control of cell membrane polarization. Here we describe profound hyperpolarization of endothelial cells during hypoxia, and the reduction of this hyperpolarization using glibenclamide. These findings suggest that control of endothelial membrane potential during ischemia may be an important therapeutic tool in avoiding ischemia/reperfusion injury, and therefore, enhancing transplant long-term function.