Soluble thrombomodulin--a marker of reperfusion injury after orthotopic liver transplantation

A Single Preservation Solution for Static Cold Storage and Hypothermic Oxygenated Perfusion of Marginal Liver Grafts: A Preclinical Study

BACKGROUND

Hypothermic oxygenated perfusion (HOPE) improves outcomes of marginal liver grafts. However, to date, no preservation solution exists for both static cold storage (SCS) and HOPE.

METHODS

After 30 min of asystolic warm ischemia, porcine livers underwent 6 h of SCS followed by 2 h of HOPE. Liver grafts were either preserved with a single preservation solution (IGL2) designed for SCS and HOPE (IGL2-Machine Perfusion Solution [MPS] group, n = 6) or with the gold-standard University of Wisconsin designed for for SCS and Belzer MPS designed for HOPE (MPS group, n = 5). All liver grafts underwent warm reperfusion with whole autologous blood for 2 h, and surrogate markers of hepatic ischemia-reperfusion injury (IRI) were assessed in the hepatocyte, cholangiocyte, vascular, and immunological compartments.

RESULTS

After 2 h of warm reperfusion, livers in the IGL2-MPS group showed no significant differences in transaminase release (aspartate aminotransferase: 65.58 versus 104.9 UI/L/100 g liver; P  = 0.178), lactate clearance, and histological IRI compared with livers in the MPS group. There were no significant differences in biliary acid composition, bile production, and histological biliary IRI. Mitochondrial and endothelial damage was also not significantly different and resulted in similar hepatic inflammasome activation.

CONCLUSIONS

This preclinical study shows that a novel IGL2 allows for the safe preservation of marginal liver grafts with SCS and HOPE. Hepatic IRI was comparable with the current gold standard of combining 2 different preservation solutions (University of Wisconsin + Belzer MPS). These data pave the way for a phase I first-in-human study and it is a first step toward tailored preservation solutions for machine perfusion of liver grafts.

Circulating Thrombomodulin: Release Mechanisms, Measurements, and Levels in Diseases and Medical Procedures

Thrombomodulin (TM) is a type-I transmembrane protein that is mainly expressed on endothelial cells and plays important roles in many biological processes. Circulating TM of different forms are also present in biofluids, such as blood and urine. Soluble TM (sTM), comprised of several domains of TM, is the major circulating TM which is generated by either enzymatic or chemical cleavage of the intact protein under different conditions. Under normal conditions, sTM is present in low concentrations (<10 ng/mL) in the blood but is elevated in several pathological conditions associated with endothelial dysfunction such as cardiovascular, inflammatory, infection, and metabolic diseases. Therefore, sTM level has been examined for monitoring disease development, such as disseminated intravascular coagulation (DIC), sepsis and multiple organ dysfunction syndrome in patients with novel coronavirus disease 2019 (COVID-19) recently. In addition, microvesicles (MVs) that contain membrane TM (MV-TM) have been found to be released from activated cells which also contribute to levels of circulating TM in certain diseases. Several release mechanisms of sTM and MV-TM have been reported, including enzymatic, chemical, and TM mutation mechanisms. Measurements of sTM and MV-TM have been developed and explored as biomarkers in many diseases. In this review, we summarize all these advances in three categories as follows: (1) release mechanisms of circulating TM, (2) methods for measuring circulating TM in biological samples, and (3) correlation of circulating TM with diseases. Altogether, it provides a whole picture of recent advances on circulating TM in health and disease.

The Impact of Dabigatran Treatment on Sinusoidal Protection Against Hepatic Ischemia/Reperfusion Injury in Mice

Thrombin is a key player in the coagulation cascade, and it is attracting much attention as a promotor of cellular injured signaling. In ischemia/reperfusion injury (IRI), which is a severe complication of liver transplantation, thrombin may also promote tissue damage. The aim of this study is to reveal whether dabigatran, a direct thrombin inhibitor, can attenuate hepatic IRI with focusing on a protection of sinusoidal endothelial cells (SECs). Both clinical patients who underwent hepatectomy and in vivo mice model of 60-minute hepatic partial-warm IRII, thrombin generation was evaluated before and after IRI. In next study, IRI mice were treated with or without dabigatran. In addition, hepatic SECs and hepatocytes pretreated with or without dabigatran were incubated in hypoxia/reoxygenation (H-R) environment in vitro. Thrombin generation evaluated by thrombin-antithrombin complex (TAT) was significantly enhanced after IRI in the clinical study and in vivo study. Thrombin exacerbated lactate dehydrogenase cytotoxicity levels in a dose-dependent manner in vitro. In an IRI model of mice, dabigatran treatment significantly improved liver histological damage, induced sinusoidal protection, and provided both antiapoptotic and anti-inflammatory effects. Furthermore, dabigatran not only enhanced endogenous thrombomodulin (TM) but also reduced excessive serum high-mobility group box-1 (HMGB-1). In H-R models of SECs, not hepatocytes, pretreatment with dabigatran markedly attenuated H-R damage, enhanced TM expression in cell lysate, and decreased extracellular HMGB-1. The supernatant of SECs pretreated with dabigatran protected hepatocytes from H-R damage and cellular death. Thrombin exacerbated hepatic IRI, and excessive extracellular HMGB-1 caused severe inflammation-induced and apoptosis-induced liver damage. In this situation, dabigatran treatment improved vascular integrity via sinusoidal protection and degraded HMGB-1 by endogenous TM enhancement on SECs, greatly ameliorating hepatic IRI.

Extended hypothermic oxygenated machine perfusion enables ex situ preservation of porcine livers for up to 24 hours

Background & Aims

End-ischemic hypothermic oxygenated machine perfusion (HOPE) of the donor liver for 1-2 h mitigates ischemia-reperfusion injury during subsequent liver transplantation. Extended preservation time may be preferred to facilitate difficult recipient hepatectomy or to optimize logistics. We therefore investigated whether end-ischemic dual HOPE (DHOPE) could extend preservation time for up to 24 h using a porcine liver reperfusion model.

Methods

Following 30 min warm ischemia, porcine livers were subjected to 2 h static cold storage (SCS), followed by 2 h, 6 h, or 24 h DHOPE (n = 6 per group). Subsequent normothermic reperfusion was performed for 4 h using autologous blood. Two livers preserved by 24 h SCS served as additional controls. A proof of principle confirmation was carried out in 2 discarded human livers subjected to extended DHOPE. Hepatocellular and cholangiocyte injury and function were assessed. Oxidative stress levels and histology were compared between groups.

Results

Perfusion flows remained stable during DHOPE, regardless of duration. After normothermic reperfusion, livers perfused for 24 h by DHOPE had similar lactate clearance, blood pH, glucose, and alanine aminotransferase levels, and biliary pH, bicarbonate, and LDH levels, as livers perfused for 2 h and 6 h. Levels of malondialdehyde and high-mobility group box 1 in serum and liver parenchyma were similar for all groups. Histological analysis of bile ducts and liver parenchyma revealed no differences between the groups. Extended DHOPE in discarded human livers preserved hepatocellular and cholangiocyte function and histology after reperfusion. In contrast, livers preserved by 24 h SCS were non-functioning.

Conclusion

Extended end-ischemic DHOPE enabled successful preservation of porcine and discarded human donor livers for up to 24 h. Extended DHOPE enables safe extension of preservation time, which may facilitate allocation and transplantation from a logistical perspective, and further expand the donor pool.

Lay summary

It has been suggested that preserving liver grafts with a technique called (dual) hypothermic oxygenated machine perfusion ([D]HOPE) leads to better outcomes after transplantation than if livers are stored on ice, especially if an organ is of lesser quality. In this study, we showed that DHOPE could be used to preserve liver grafts for up to 24 h. This extended procedure could be used globally to facilitate transplantation and expand the donor pool.

Biomarkers to assess graft quality during conventional and machine preservation in liver transplantation

A global rising organ shortage necessitates the use of extended criteria donors (ECD) for liver transplantation (LT). However, poor preservation and extensive ischemic injury of ECD grafts have been recognized as important factors associated with primary non-function, early allograft dysfunction, and biliary complications after LT. In order to prevent for these ischemia-related complications, machine perfusion (MP) has gained interest as a technique to optimize preservation of grafts and to provide the opportunity to assess graft quality by screening for extensive ischemic injury. For this purpose, however, objective surrogate biomarkers are required which can be easily determined at time of graft preservation and the various techniques of MP. This review provides an overview and evaluation of biomarkers that have been investigated for the assessment of graft quality and viability testing during different types of MP. Moreover, studies regarding conventional graft preservation by static cold storage (SCS) were screened to identify biomarkers that correlated with either allograft dysfunction or biliary complications after LT and which could potentially be applied as predictive markers during MP. The pros and cons of the different biomaterials that are available for biomarker research during graft preservation are discussed, accompanied with suggestions for future research. Though many studies are currently still in the experimental setting or of low evidence level due to small cohort sizes, the biomarkers presented in this review provide a useful handle to monitor recovery of ECD grafts during clinical MP in the near future.

Vascular immunotargeting to endothelial determinant ICAM-1 enables optimal partnering of recombinant scFv-thrombomodulin fusion with endogenous cofactor

The use of targeted therapeutics to replenish pathologically deficient proteins on the luminal endothelial membrane has the potential to revolutionize emergency and cardiovascular medicine. Untargeted recombinant proteins, like activated protein C (APC) and thrombomodulin (TM), have demonstrated beneficial effects in acute vascular disorders, but have failed to have a major impact on clinical care. We recently reported that TM fused with an scFv antibody fragment to platelet endothelial cell adhesion molecule-1 (PECAM-1) exerts therapeutic effects superior to untargeted TM. PECAM-1 is localized to cell-cell junctions, however, whereas the endothelial protein C receptor (EPCR), the key co-factor of TM/APC, is exposed in the apical membrane. Here we tested whether anchoring TM to the intercellular adhesion molecule (ICAM-1) favors scFv/TM collaboration with EPCR. Indeed: i) endothelial targeting scFv/TM to ICAM-1 provides ~15-fold greater activation of protein C than its PECAM-targeted counterpart; ii) blocking EPCR reduces protein C activation by scFv/TM anchored to endothelial ICAM-1, but not PECAM-1; and iii) anti-ICAM scFv/TM fusion provides more profound anti-inflammatory effects than anti-PECAM scFv/TM in a mouse model of acute lung injury. These findings, obtained using new translational constructs, emphasize the importance of targeting protein therapeutics to the proper surface determinant, in order to optimize their microenvironment and beneficial effects.

Tissue factor expression demonstrates severe sinusoidal endothelial cell damage during rejection after living-donor liver transplantation

BACKGROUND/PURPOSE

Since it is well known that endothelial cells may be important targets during rejection after living-donor liver transplantation, in this study we investigated liver sinusoidal endothelial cell (SEC) damage during rejection by focusing on thrombomodulin (TM) and hyaluronic acid (HA) as plasma markers of SEC damage. We also examined tissue factor (TF) expression in SECs, because damage to endothelial cells leads to immediate activation of the coagulation system, with the damage being triggered mainly by TF.

METHODS

Living-donor liver transplantation was performed at Mie University Hospital between March 2002 and December 2007; there were 8 patients with rejection (4 with acute cellular rejection and 4 with chronic rejection) and 32 patients without rejection. Liver biopsy tissue was immunostained with an anti-TF antibody, and assessed for SEC damage. In addition, total RNA was extracted from liver biopsy tissue and tested for TF mRNA expression by reverse-transcription polymerase chain reaction (RT-PCR).

RESULTS

The plasma TM level was significantly higher in the rejection group than in the non-rejection group. TF expression was observed in SECs, in infiltrating inflammatory cells, and in the vascular endothelium in the rejection group. TF mRNA expression was significantly higher in the rejection group than in the non-rejection group.

CONCLUSIONS

We demonstrated that TF expression revealed severe SEC damage in grafted liver during both acute cellular rejection and chronic rejection.

Anchoring fusion thrombomodulin to the endothelial lumen protects against injury-induced lung thrombosis and inflammation

RATIONALE

Endothelial thrombomodulin (TM) regulates thrombosis and inflammation. Diverse forms of pulmonary and vascular injury are accompanied by down-regulation of TM, which aggravates tissue injury. We postulated that anchoring TM to the endothelial surface would restore its protective functions.

OBJECTIVES

To design an effective and safe strategy to treat pulmonary thrombotic and inflammatory injury.

METHODS

We synthesized a fusion protein, designated scFv/TM, by linking the extracellular domain of mouse TM to a single-chain variable fragment of an antibody to platelet endothelial cell adhesion molecule-1 (PECAM-1). The targeting and protective functions of scFv/TM were tested in mouse models of lung ischemia-reperfusion and acute lung injury (ALI) caused by intratracheal endotoxin and hyperoxia, both of which caused approximately 50% reduction in the endogenous expression of TM.

MEASUREMENTS AND MAIN RESULTS

Biochemical assays showed that scFv/TM accelerated protein C activation by thrombin and bound mouse PECAM-1 and cytokine high mobility group-B1. After intravenous injection, scFv/TM preferentially accumulated in the mouse pulmonary vasculature. In a lung model of ischemia-reperfusion injury, scFv/TM attenuated elevation of early growth response-1, inhibited pulmonary deposition of fibrin and leukocyte infiltration, and preserved blood oxygenation more effectively than soluble TM. In an ALI model, scFv/TM, but not soluble TM, suppressed activation of nuclear factor-kappaB, inflammation and edema in the lung and reduced mortality without causing hemorrhage.

CONCLUSIONS

Targeting TM to the endothelium using an scFv anchor enhances its antithrombotic and antiinflammatory effectiveness in models of ALI.

Antithrombin effect on coagulation and fibrinolytic profiles after living donor liver transplantation: a pilot study

Early after liver transplantation, patients are in a hypercoagulable state because of an imbalance between coagulation and fibrinolysis because of the slow recovery of depleted anticoagulant proteins. Antithrombin (AT) is used in anticoagulant protocols to prevent thrombosis. The subjects of the present study were 17 men and eight women that underwent living donor liver transplantation. The initial 15 cases were administered AT concentrate (1500 U/day) on postoperative days (POD) 1 through 3 (AT group) and the following 10 consecutive cases were not administered AT (control). AT, thrombin-AT complex, plasmin-alpha2 plasmin inhibitor complex, thrombomodulin, fibrin degradation product D-dimer (FDP-DD) level, prothrombin time international normalized ratio, activated partial thromboplastin time, and platelet counts were measured. In the AT group, AT activity was maintained at levels >80% for 5 days after transplantation. In the control group, AT activity did not return to normal during the first 2 weeks after the operation. FDP-DD levels were significantly higher in the control group than in the AT group (P < 0.05). Six patients in the control group and three patients in the AT group required transfusions with platelet concentrate (P < 0.05). AT supplementation might reduce FDP-DD levels and prevent decreased platelet counts in the early stages after liver transplantation.

Hypoxia-reoxygenation contributes to increased frequency of venous thromboembolism in air travellers

Commercial air travel is widespread, with close to 2 billion people traveling each year. The association between venous thromboembolism (VTE) and confined sitting has been established and a correlation between the distance traveled and its incidence had been documented. Most studies underscore stasis caused by immobility as the cause of VTE and ignore the possible contribution of additional factors including coagulation and the blood vessel wall. Recent studies indicate that hypobaric hypoxia may contribute to blood vessel wall alteration and activation of coagulation. We suggest that air travel associated hypobaric hypoxia may lead to endothelial injury and initiation of a pro-coagulatory response, effects which are augmented by the reoxygenation upon landing, thus culminating in thrombosis. Prevention of air travel associated hypoxia and reoxygenation injury may decrease the incidence of flight associated VTE.

Thrombomodulin: tumour biology and prognostic implications

BACKGROUND

Thrombomodulin (TM) is an endothelial receptor that exerts anti-coagulant, anti-fibrinolytic, and anti-inflammatory activity by inhibiting thrombin and cellular adhesion. There is growing evidence that TM plays a role in tumour behaviour.

METHODS

The electronic literature (1966-2004) was reviewed with a specific focus on tumour biology.

RESULTS

TM is expressed on both the endothelium and tumour cells in several cancers. Loss of expression denotes a more malignant profile with poorer prognosis. Loss of TM is mediated by hypoxia, endotoxin, and various cytokines, while up-regulation can be achieved by pharmacological manipulation (e.g. pentoxyfylline and statins).

CONCLUSION

Originally described as an endothelial anticoagulant, TM plays a key role in tumour biology and prognostics, and provides a potential therapeutic target in impeding cancer spread.

Liver and kidney preservation by perfusion

The clinical boundaries of transplantation have been set in an era of simple cold storage. Research in organ preservation has led to the development of flush solutions that buffer the harsh molecular conditions which develop during ischaemia, and provide stored organs that are fit to sustain life after transplantation. Although simple and efficient, this method might be reaching its limit with respect to the duration, preservation, and the quality of organs that can be preserved. In addition, flush preservation does not allow for adequate viability assessment. There is good evidence that preservation times will be extended by the provision of continuous cellular substrate. Stimulation of in-vivo conditions by ex-vivo perfusion could also mean that marginal organs will be salvaged for transplantation. Perfusion will also allow for assessing the viability of organs before transplantation in a continuous fashion. The cumulative effect of these benefits would include expansion of the donor pool, less risk of primary non-function, and extension of the safe preservation period. Use of non-heart-beating donors, international organ sharing, and precise calculation of the risk of primary organ failure could become standard.

Beta-galactosidase as a marker of ischemic injury and a mechanism for viability assessment in porcine liver transplantation

Glycohydrolases are a group of enzymes contained predominantly within lysosomes, which are released during Kupffer cell activation or death. One of these, beta-galactosidase, has been proposed as a marker of ischemia-reperfusion injury in the liver because Kupffer cell activation represents a primary event in the injurious reperfusion cascade. In this study, we compared B-galactosidase with more traditional indicators of liver injury and function in a porcine model of liver preservation. Porcine livers were allocated into two groups: group C (n = 5), preserved in University of Wisconsin solution by standard cold storage for 24 hours, and group W (n = 5), perfused with oxygenated autologous blood on an extracorporeal circuit for 24 hours. Both groups were subsequently tested on the circuit during a 24-hour reperfusion phase. The perfusate was sampled for levels of beta-galactosidase, as well as traditional markers of liver injury and function. A sharp increase in beta-galactosidase levels was seen on reperfusion of cold preserved livers to a level of 1,900 IU/mL. This contrasted dramatically with normothermically preserved livers, in which the level never exceeded 208 IU/mL (P =.002). beta-Galactosidase levels showed much earlier and greater increases compared with transaminase levels in livers injured by ischemia. A rapid elevation in beta-galactosidase levels corresponded well with poor liver function and more liver injury. Measurement of beta-galactosidase is a simple test that quantifies ischemia-reperfusion injury of preserved livers. It is more sensitive than transaminases, with faster and larger increases in levels after ischemic injury. It can be useful in assessing the viability of a liver during machine preservation.

Cellular distribution of thrombomodulin as an early marker for warm ischemic liver injury in porcine liver transplantation: protective effect of prostaglandin I2 analogue and tauroursodeoxycholic acid

BACKGROUND

Warm ischemia of the graft from non-heart-beating donors is considered a risk factor for posttransplant graft dysfunction. The early administration of cytoprotective agents may help improve graft dysfunction.

METHODS

Four groups of 10 pigs each underwent orthotopic liver transplantation. Prostaglandin I2 analogue, OP-41483, was administered intraportally 30 min before warm ischemic insult in donors and after reperfusion in recipients in one group. In the other study group, additional intravenous tauroursodeoxycholic acid (TUDC) was given before the warm ischemic insult in donors and after reperfusion, then maintained continuously until postoperative day (POD) 7.

RESULTS

Exposure of liver grafts to warm ischemia resulted in severe congestion with the disappearance of thrombomodulin (Tm) from the sinusoidal endothelial cells (SECs) and smooth muscle cells (SMCs) around biliary epithelial cells (BEpCs) 2 hr after reperfusion, followed by positive immunoreactivity of Tm in BEpCs with hyperbilirubinemia, which was related to high mortality. Combined administration of OP-41483 and TUDC had a protective effect, demonstrated by sustained immunoreactivity of Tm from SECs and SMCs until POD 7, without that reactivity in BEpCs. This was associated with reduced congestion and hyperbilirubinemia, similar to the control group not subjected to warm ischemia.

CONCLUSIONS

These findings suggest that negative immunoreactivity of Tm in SECs and SMCs surrounding BEpCs and positive in BEpCs may be an early marker for ischemic liver injury, and that OP-41483 and TUDC may protect against the microcirculatory and biliary derangement.

Neutrophil elastase and oxygen radicals enhance monocyte chemoattractant protein- expression after ischemia/reperfusion in rat liver

BACKGROUND

The monocyte chemoattractant protein-1 (MCP-1) is produced during reperfusion injury and induces tissue factor that is the initiator of the clotting cascade. Neutrophil elastase is a crucial mediator of inflammatory tissue damage. Activation of the coagulation system stimulates cytokine production by activated leukocytes. We investigated the effects of neutrophil elastase and oxygen radicals generated by hypoxia associated with microthrombus formation on MCP-1 expression after ischemia/reperfusion in rat liver.

METHODS

In vitro MCP-1 production by macrophages after stimulation with human neutrophil elastase (HNE) or oxygen radicals generated by hypoxanthine and xanthine oxidase was examined. Liver ischemia was induced in rats by occluding the portal vein for 30 min. An inhibitor of human neutrophil elastase (ONO-5046*Na, 10 mg/kg) and antithrombin III (AT-III, 250 U/kg) were injected i.v. 5 min before vascular clamping. Serum concentrations of MCP-1 were measured by enzyme-linked immunosorbent assay.

RESULTS

Human neutrophil elastase or oxygen radicals significantly enhanced in vitro MCP-1 production by macrophage. Serum MCP-1 concentrations reached a peak at 6 hr after reperfusion and then gradually decreased. However, pretreatment of animals with AT-III or ONO-5046*Na alone resulted in significantly smaller increases in serum concentrations of MCP-1 after reperfusion. Pretreatment with both ONO-5046*Na and AT-III produced additive effects. The combined treatment with ONO-5046*Na and AT-III significantly reduced MCP-1 mRNA in liver after ischemia/reperfusion.

CONCLUSIONS

MCP-1 production by macrophages is stimulated by neutrophil elastase and oxygen radicals generated by hypoxia, probably due to microthrombus formation after ischemia/reperfusion of the rat liver.

Correlation between von Willebrand factor levels and early graft function in clinical liver transplantation

Cold preservation/reperfusion leads to sinusoidal endothelial cell (SEC) activation and damage in nearly every liver transplantation; the extent of these changes influences early graft function. Upon reperfusion, activated SEC show increased expression of adhesion molecules, including von Willebrand factor (vWF) which is released into the circulation. This study was designed to evaluate the levels of vWF measured in the caval effluent and correlate these findings with known markers of SEC damage and early graft function. Data were obtained from 35 patients undergoing orthotopic liver transplantation (LTx). Two samples were taken from each patient for measurement of vWF: a) from the portal vein immediately prior to reperfusion; and b) from the first 50 ml of the caval effluent. Commercial assays were used to measure vWF, as well as hyaluronic acid (HA), thrombomodulin (TM), IL-1 beta, IL-6, IL-8 and TNF-alpha. Patients were divided into two groups based on early graft function. Poor early graft function (PEGF) was defined as a peak aspartate transaminase (AST) or alanine transaminase (ALT) level > 2500 U/L during the first three postoperative days (POD) and a prothrombin time (PT) > 16 s on POD 2 (n = 8). The remaining 27 patients had good early graft function (GEGF). In patients with GEGF, vWF levels dropped significantly between the two time points. This change was not observed in those with PEGF. A positive linear correlation was observed in the PEGF group between vWF and HA and IL-6. The different pattern of change in vWF between the two groups, as well as the positive correlation between HA, IL-6 and vWF in PEGF, suggest that vWF may be a useful marker of early graft function.

A stable prostacyclin analog, beraprost sodium, attenuates platelet accumulation and preservation-reperfusion injury of isografts in a rat model of lung transplantation

BACKGROUND

Recent studies have shown that the extent of platelet accumulation in the vasculature of transplanted organs correlates with the degree of preservation-reperfusion injury. In this study, we examined the effect of a stable prostacyclin analog, beraprost sodium, which possesses potent antiplatelet activity, on parameters of platelet accumulation and preservation-reperfusion injury of isografts in a rat model of lung transplantation.

METHODS

The heart-lung blocks of donor rats were flushed with and preserved in modified Euro-Collins solution at 4 degrees C for 6 hr or 24 hr. The left lung was transplanted into recipient rats and reperfused for 1 hr. Lung injury was evaluated by the pulmonary blood flow ratios to the lung isografts, the weight gain of the isografts, and histological examination. Small portions of the lung isografts were excised and stained with an antibody specific for rat platelets. A scoring system was developed to semiquantitate the intensity of antibody staining (score 0-4). The recipient rats received oral administration of beraprost sodium (0.3 mg/kg) before lung transplantation. Control animals received no beraprost sodium.

RESULTS

In the 6-hr preservation study, administration of beraprost sodium significantly reduced the score for platelet accumulation (1.8+/-0.4 vs. 3.3+/-0.5, P<0.01). This observation was accompanied by a significantly decreased degree of preservation-reperfusion injury as evidenced by an increased blood flow ratio (13.7+/-2.6% vs. 4.5+/-3.6%, P<0.01) and a reduced weight gain (0.7+/-0.2 g vs. 1.1+/-0.2 g, P<0.01). Histological examination revealed severe capillary congestion in three of six cases in the control group, while no capillary congestion was observed in the beraprost group. In the 24-hr preservation study, no differences were seen in platelet accumulation scores or parameters of lung injury.

CONCLUSION

Beraprost sodium, an antiplatelet agent, reduces platelet accumulation and preservation-reperfusion injury of lung transplants at 6 hr in this rat isograft model.

Reperfusion induces sublethal endothelial injury

BACKGROUND

Endothelial cells are pivotal in regulating thrombosis and hemostasis. In this study, we sought to characterize endothelial dysfunction and endothelial cell injury in vitro after hypoxia/reoxygenation.

MATERIALS AND METHODS

Cultured human umbilical vein endothelial cells (ECs) were exposed to 120 min of hypoxia followed by reoxygenation. The release of thrombomodulin (TM) and the production of prostaglandin I2 (PGI2) were measured. Endothelial cell injury in hypoxia/reoxygenation was measured by two assays, the Fura-2 release assay and the 51chromium (51Cr) release assay.

RESULTS

TM release from ECs during normoxic incubation was undetectable, while it was slightly increased during hypoxic incubation. After reoxygenation, the release of TM increased, and it became significantly higher at 120 min after reoxygenation compared with hypoxic incubation. The production of PGI2 significantly decreased during hypoxic incubation and further decreased within 30 min after reoxygenation, but returned to normoxic levels at 120 min after reoxygenation. In the Fura-2 release assay, a rapid and significantly greater release of Fura-2 was observed in hypoxia/reoxygenation compared with hypoxic incubation. In the 51Cr release assay which demonstrates cell death, 51Cr release did not increase in hypoxia/reoxygenation.

CONCLUSIONS

The present study suggests that 120 min of hypoxia/reoxygenation induces endothelial dysfunction of ECs but does not cause cell death.

Effluent levels of thrombomodulin predict early graft function in clinical liver transplantation

Thrombomodulin is a surface protein on vascular endothelial cells that serves as a binding site for thrombin and plays an important role as an anticoagulant factor. We correlated plasma thrombomodulin levels with early graft function after liver transplant in 58 recipients. Blood samples were collected at the following time points: before surgery, just before reperfusion, 30, 60, 120 min after reperfusion, and post-operative day 1. The first and last 20 cc of caval effluent were also collected. Plasma thrombomodulin levels were measured by a sandwich enzyme-binding assay in the blood samples; tissue expression was determined by immunohistochemistry. Poor early graft function was defined as peak aspartate aminotransferase (AST) or alanine aminotransferase (ALT) >2500 U/l during the first 3 post-operative days and prothrombin time >16 s on post-operative day 2. Thrombomodulin levels in the first 20 cc of caval effluent ranged from 1.33 to 91 FU/ml and showed a significant positive correlation with ischemic time, intra-operative blood transfusion requirement, and early graft function. In grafts with high effluent thrombomodulin (>20 FU/ml, n=12), the incidence of poor early graft function and primary nonfunction was 66.7% and 25.0%, respectively; in grafts with low effluent thrombomodulin (<20 FU/ml, n=46), graft function was not impaired. By immunohistochemistry, thrombomodulin was detected in large vessels of every donor liver. Sinusoidal cells, however, showed positive staining only in livers with poor early graft function. Effluent thrombomodulin levels reflect the extent of preservation injury and might be a useful marker for predicting graft function after liver transplantation.

Neutrophil elastase: a determinant of endothelial damage and reperfusion injury after liver transplantation?

Reperfusion injury has been implicated in the development of primary graft dysfunction (PGD) after liver transplantation. Neutrophil migration and activation may be involved in the pathogenesis of this injury. We studied neutrophil activation and its role in the etiology of PGD by measuring neutrophil elastase by radioimmunoassay, in serial blood samples of 19 patients before, during, and for 24 hr after transplantation. In a subgroup of patients, we also measured soluble thrombomodulin at the same time points as a marker of endothelial damage. The pretransplant elastase level was significantly raised (40.13+/-4.84 ng/ml, mean+/-SEM) compared with levels of healthy controls (18.7+/-5.6 ng/ml, P<0.05). A marked increase in elastase activity followed reperfusion, with a peak at 2 hr (370+/-50.5 ng/ml, P<0.01). Thereafter, there was a decline, but elastase remained elevated at 24 hr (186+/-60.94 ng/ml). The mean increase in neutrophil elastase after reperfusion correlated significantly with markers of graft function (P<0.05) and with the mean rise in soluble thrombomodulin (P=0.042), which increased from a pretransplant level of 81.2+/-11.32 to 186+/-50.4 ng/ml, 6 hr after reperfusion (P<0.05). The results of this study indicate that marked neutrophil activation and endothelial cell damage occurs after graft reperfusion during orthotopic liver transplantation, and the degree of activation correlates with markers of graft function, which may suggest a role in the etiology of PGD.