Accumulation of platelets in rat syngeneic lung transplants: a potential factor responsible for preservation-reperfusion injury

The Role of Fibrinogen and Platelets in Mouse Liver Ischemia-Reperfusion Injury: Distribution and Pathophysiological Insights

Liver ischemia-reperfusion (I/R) injury is a critical issue in clinical settings, particularly in liver transplantation and resection, leading to severe hepatocellular dysfunction and organ failure. This study investigates the role of fibrinogen and platelets in liver I/R injury, focusing on their distribution and pathophysiological impact within liver lobules. Using a mouse model, we examined the expression and localization of fibrinogen and platelets at various time points postreperfusion. In normal liver, fibrinogen is predominantly expressed in hepatic sinusoids near the portal vein, with sparse platelet distribution. Following I/R injury, fibrinogen expression significantly increases in hepatic sinusoids and hepatocytes, accompanied by substantial platelet aggregation and embolization, particularly in Zone 1 of the liver lobules. These findings highlight the zonal heterogeneity of fibrinogen distribution and its regulatory function in platelet adhesion and microthrombi formation. This study provides crucial insights for developing therapeutic strategies targeting fibrinogen and platelet interactions to mitigate liver I/R injury.

Aging exacerbates murine lung ischemia-reperfusion injury by excessive inflammation and impaired tissue repair response

Donor shortage is a major problem in lung transplantation (LTx), and the use of lungs from elderly donors is one of the possible solutions in a rapidly aging population. However, the utilization of organs from donors aged >65 years has remained infrequent and may be related to a poor outcome. To investigate the molecular events in grafts from elderly donors early after LTx, the left lungs of young and old mice were subjected to 1 hour of ischemia and subsequent reperfusion. The left lungs were collected at 1 hour, 1 day, and 3 days after reperfusion and subjected to wet-to-dry weight ratio measurement, histological analysis, and molecular biological analysis, including RNA sequencing. The lungs in old mice exhibited more severe and prolonged pulmonary edema than those in young mice after ischemia reperfusion, which was accompanied by upregulation of the genes associated with inflammation and impaired expression of cell cycle-related genes. Apoptotic cells increased and proliferating type 2 alveolar epithelial cells decreased in the lungs of old mice compared with young mice. These factors could become conceptual targets for developing interventions to ameliorate lung ischemia-reperfusion injury after LTx from elderly donors, which may serve to expand the old donor pool.

PPARγ in Ischemia-Reperfusion Injury: Overview of the Biology and Therapy

Ischemia-reperfusion injury (IRI) is a complex pathophysiological process that is often characterized as a blood circulation disorder caused due to various factors (such as traumatic shock, surgery, organ transplantation, burn, and thrombus). Severe metabolic dysregulation and tissue structure destruction are observed upon restoration of blood flow to the ischemic tissue. Theoretically, IRI can occur in various tissues and organs, including the kidney, liver, myocardium, and brain, among others. The advances made in research regarding restoring tissue perfusion in ischemic areas have been inadequate with regard to decreasing the mortality and infarct size associated with IRI. Hence, the clinical treatment of patients with severe IRI remains a thorny issue. Peroxisome proliferator-activated receptor γ (PPARγ) is a member of a superfamily of nuclear transcription factors activated by agonists and is a promising therapeutic target for ameliorating IRI. Therefore, this review focuses on the role of PPARγ in IRI. The protective effects of PPARγ, such as attenuating oxidative stress, inhibiting inflammatory responses, and antagonizing apoptosis, are described, envisaging certain therapeutic perspectives.

Subnormothermic ex vivo lung perfusion attenuates graft inflammation in a rat transplant model

OBJECTIVE

Ex vivo lung perfusion has emerged as a novel technique to safely preserve lungs before transplantation. Recent studies have demonstrated an accumulation of inflammatory molecules in the perfusate during ex vivo lung perfusion. These proinflammatory molecules, including damage-associated molecular patterns and inflammatory cytokines, may contribute to acute and chronic allograft dysfunction. At present, ex vivo lung perfusion is performed clinically at normothermic temperature (37°C). The effect of lowering temperature to the subnormothermic range during ex vivo lung perfusion has not been reported. In this study, we hypothesized that lower ex vivo lung perfusion temperature will lead to a reduction in allograft inflammation and result in improved post-transplant graft function.

METHODS

Lewis rat heart-lung blocs underwent 4 hours of ex vivo lung perfusion in 3 temperature groups: 37°C (MP37), 30°C (MP30), and 25°C (MP25). In the control group, lung grafts were preserved by static cold storage before transplantation. After ex vivo lung perfusion or static cold storage, the left lung was transplanted for 2 hours before the animal was killed. Sera and tissue were collected and analyzed.

RESULTS

There were no differences in partial pressure of arterial oxygenation to fraction of inspired oxygen ratios during 4 hours of ex vivo lung perfusion between temperature groups. Tumor necrosis factor α significantly increased in the MP37 group during ex vivo lung perfusion, whereas this was not seen at lower temperatures. Extracellular DNA and high-mobility group box 1 perfusate concentrations increased significantly during ex vivo lung perfusion in all groups, but the rate of increase was diminished at lower temperature. Two hours post-transplant, there were no significant differences in partial pressure of arterial oxygenation to fraction of inspired oxygen ratios of the lung graft or serum damage-associated molecular pattern levels among groups. On histologic grading after transplantation, greater injury was observed in the MP30 and MP37 groups, but not MP25, when compared with static cold storage.

CONCLUSIONS

Subnormothermic ex vivo lung perfusion at 25°C reduces the production of inflammatory mediators during ex vivo lung perfusion and is associated with reduced histologic graft injury after transplantation.

Human Multilineage-differentiating Stress-Enduring Cells Exert Pleiotropic Effects to Ameliorate Acute Lung Ischemia-Reperfusion Injury in a Rat Model

Posttransplantation lung ischemia-reperfusion (IR) injuries affect both patient survival and graft function. In this study, we evaluated the protective effects of infused human multilineage-differentiating stress-enduring (Muse) cells, a novel, easily harvested type of nontumorigenic endogenous reparative stem cell, against acute IR lung injury in a rat model. After a 2-h warm IR injury induction in a left rat lung, human Muse cells, human mesenchymal stem cells (MSCs), and vehicle were injected via the left pulmonary artery after reperfusion. Functionality, histological findings, and protein expression were subsequently assessed in the injured lung. In vitro, we also compared human Muse cells with human MSCs in terms of migration abilities and the secretory properties of protective substances. The arterial oxygen partial pressure to fractional inspired oxygen ratio, alveolar-arterial oxygen gradient, left lung compliance, and histological injury score on hematoxylin-eosin sections were significantly better in the Muse group relative to the MSC and vehicle groups. Compared to MSCs, human Muse cells homed more efficiently to the injured lung, where they suppressed the apoptosis and stimulated proliferation of host alveolar cells. Human Muse cells also migrated to serum from lung-injured model rats and produced beneficial substances (keratinocyte growth factor [KGF], hepatocyte growth factor, angiopoietin-1, and prostaglandin E2) in vitro. Western blot of lung tissue confirmed high expression of KGF and their target molecules (interleukin-6, protein kinase B, and B-cell lymphoma-2) in the Muse group. Thus, Muse cells efficiently ameliorated lung IR injury via pleiotropic effects in a rat model. These findings support further investigation on the use of human Muse cells for lung IR injury.

Bone marrow mesenchymal stromal cells protect allograft lung transplants from acute rejection via the PD-L1/IL-17A axis

PURPOSE

Using a rat model of allograft lung transplantation, we investigated the effectiveness of mesenchymal stromal cells (MSCs) as prophylactic and therapeutic agents against the acute rejection of lung grafts.

METHODS

Lung grafts were harvested from donor rats and transplanted orthotopically into major histocompatibility complex-mismatched rats. MSCs were administered to the recipients once (on day 0) or twice (on days 0 and 3) after transplantation. The grade of acute rejection was evaluated both macroscopically and microscopically 6 days after transplantation. To elucidate the related mechanism, mRNA levels of inflammatory cytokines and immunomodulatory receptors in the transplanted grafts were measured using quantitative RT-PCR.

RESULTS

The lung graft tissue from the rats that received MSCs post-surgically was protected from acute rejection significantly better than that from the untreated controls. Notably, the rats administered MSCs twice after surgery exhibited the least signs of rejection, with a markedly upregulated mRNA level of PD-L1 and a downregulated mRNA level of IL-17A.

CONCLUSION

This study assessed MSC protection of lung allografts from acute rejection by modulating T cell activity via enforced expression of PD-L1 in transplants and downregulation of IL-17A.

The role of platelets in the recruitment of leukocytes during vascular disease

Besides their role in the formation of thrombus during haemostasis, it is becoming clear that platelets contribute to a number of other processes within the vasculature. Indeed, the integrated function of the thrombotic and inflammatory systems, which results in platelet-mediated recruitment of leukocytes, is now considered to be of great importance in the propagation, progression and pathogenesis of atherosclerotic disease of the arteries. There are three scenarios by which platelets can interact with leukocytes: (1) during haemostasis, when platelets adhere to and are activated on sub-endothelial matrix proteins exposed by vascular damage and then recruit leukocytes to a growing thrombus. (2) Platelets adhere to and are activated on stimulated endothelial cells and then bridge blood borne leukocytes to the vessel wall and. (3) Adhesion between platelets and leukocytes occurs in the blood leading to formation of heterotypic aggregates prior to contact with endothelial cells. In the following review we will not discuss leukocyte recruitment during haemostasis, as this represents a physiological response to tissue trauma that can progress, at least in its early stages, in the absence of inflammation. Rather we will deal with scenarios 2 and 3, as these pathways of platelet–leukocyte interactions are important during inflammation and in chronic inflammatory diseases such as atherosclerosis. Indeed, these interactions mean that leukocytes possess means of adhesion to the vessel wall under conditions that may not normally be permissive of leukocyte–endothelial cell adhesion, meaning that the disease process may be able to bypass the regulatory pathways which would ordinarily moderate the inflammatory response.

Development of a Hyperactive Primary Hemostatic System During Off-Pump Lung Transplantation Resulting From an Unbalance Between von Willebrand Factor and Its Cleaving Protease ADAMTS13

An unbalance between the platelet-adhesive protein von Willebrand factor (VWF) and its cleaving protease ADAMTS13 is a risk factor for thrombosis. Here, we assessed levels and functionality of VWF and ADAMTS13 in patients undergoing off-pump lung transplantation. We analyzed plasma of 10 patients and distinguished lung transplantation-specific effects from those generally accompanying open-chest surgeries by comparing results with 11 patients undergoing off-pump coronary bypass graft (CABG) surgery. Forty healthy volunteers were included for reference values. VWF antigen levels as well as the VWF ristocetin cofactor activity/VWF antigen ratio increased during lung transplantation and after CABG surgery. An increase in VWF propeptide levels was paralleled by a decrease in ADAMTS13 activity. This was more pronounced during lung transplantation. Similarly, the capacity of plasma to support platelet aggregation under shear flow conditions in vitro was more increased during lung transplantation. The proportion of high molecular weight VWF multimers was elevated in both groups without evidence for ultra-large VWF. VWF's collagen binding activity remained unchanged. In conclusion, a hyperactive primary hemostatic system develops during lung transplantation resulting both from a pronounced (functional) increase of the VWF molecule and decrease of ADAMTS13. This may increase the risk of platelet thrombosis within the allograft.

A preliminary study of platelet activation after embolization of marrow contents

OBJECTIVES

Intravasation of bone marrow contents into venous circulation and pulmonary embolization after intramedullary nailing may be coupled with the activation of coagulation and fibrinolytic cascades. The objective of this study was to assess hemostatic response to pulmonary extravasated marrow contents. We hypothesize that activation of platelet activity and the coagulation cascade may occur after embolization of marrow contents in an experimental animal model of intramedullary nailing.

METHODS

Fifteen New Zealand white male rabbits were randomly assigned to control or fat embolism (FE) groups. In the FE group (n = 8), femurs were surgically instrumented with retrograde intramedullary nails and pressurized with bone cement. In the control group (n = 7), a sham knee incision was made that was immediately closed without drilling, reaming, or pressurization. Fibrinogen, D-dimer latex screen assay, 1 stage prothrombin time, and activated partial thromboplastin time were analyzed.

RESULTS

As the main platelet activation indicators, the marker Annexin-V percent binding increased in the FE group at 2 hours (P = 0.04) and 4 hours (P = 0.04), and the marker CD62P percent expression increased in the FE group at 2 hours (P = 0.04).

CONCLUSIONS

This preliminary study showed that pressurization of marrow and intravasation of fat and marrow products cause activation of platelets and the coagulation cascade, with or without tissue trauma. This may be relevant to the treatment of multiply injured patients with prior respiratory and coagulation abnormalities. A future larger study may be needed.

Preservation solution for lung transplantation

Despite the increasing success of lung transplantation as the mainstay therapeutic modality for end-stage lung disease, the 1-year survival rate after lung transplantation remains 80% and primary graft dysfunction (PGD) accounts for 30% of mortality. Ischemia-reperfusion injury has been identified as one of the main causes of PGD, and thus significant efforts have been made to optimize the methods for lung preservation in an attempt to minimize lung injury during the period of ischemia. The composition of the lung preservation solution used in the pulmonary artery flush has been considered to be the key to successful lung preservation, and many lung transplant programs have been shifting the use of the preservation solution from the intracellular fluid type to the extracellular fluid type because of preferable posttransplant lung function with the latter. This review summarizes the experimental and clinical studies on lung preservation, particularly focusing attention on the preservation solution being employed for clinical lung transplantation.

Proteasome peptidase activities parallel histomorphological and functional consequences of ischemia-reperfusion injury in the lung

Several lines of evidence suggest that the proteasome contributes to ischemia-reperfusion injury (I-RI) of organs. Although I-RI contributes to multiple disease processes in the lung, the regulation of proteasome activities during pulmonary I-RI is unknown. Thus, the authors performed a pilot study to define time-related changes of lung proteasome peptidase activities and to evaluate if possible alterations correspond to morphological and functional consequences of I-RI using a rat model. Animals underwent 120 minutes of unilateral lung ischemia. Ischemic and contralateral lungs were harvested at multiple time points for up to 168 hours of reperfusion (I-R30 min-168 h). Chymotryptic-like (CT-L) and tryptic-like (T-L) proteasome peptidase activities were measured in lung extracts. An early I-R-associated inactivation of proteasome activities paralleled impairment of oxygenation, edema formation, and degree of histopathology, and resolved with restoration of function within 24 to 72 hours. Although functional and histomorphological baseline conditions were still not fully achieved at I-R168h, proteasome activities increased continuously 1.4-fold (CT-L) and 5.7-fold (T-L) until I-R168h. Apparent K(M) values for the CT-L/T-L substrates were not influenced by I-R. This pilot study establishes an initial link between proteasome activities and physiological relevant consequences of lung I-RI, and further points towards a possible role of the proteasome during the postischemic tissue repair process.

Apyrase treatment prevents ischemia-reperfusion injury in rat lung isografts

OBJECTIVE

Endothelial cells express the ectoenzyme ectonucleoside adenosine triphosphate diphosphohydrolase, an apyrase that inhibits vascular inflammation by catalyzing the hydrolysis of adenosine triphosphate and adenosine diphosphate. However, ectonucleoside adenosine triphosphate diphosphohydrolase expression is rapidly lost following oxidative stress, leading to the potential for adenosine triphosphate and related purigenic nucleotides to exacerbate acute solid organ inflammation and injury. We asked if administration of a soluble recombinant apyrase APT102 attenuates lung graft injury in a cold ischemia reperfusion model of rat syngeneic orthotopic lung transplantation.

METHODS

Male Fisher 344 donor lungs were cold preserved in a low-potassium dextrose solution in the presence or absence of APT102 for 18 hours prior to transplantation into syngeneic male Fisher 344 recipients. Seven minutes after reperfusion, lung transplant recipients received either a bolus of APT102 or vehicle (saline solution). Four hours after reperfusion, APT102- and saline solution-treated groups were evaluated for lung graft function and inflammation.

RESULTS

APT102 significantly reduced lung graft extracellular pools of adenosine triphosphate and adenosine diphosphate, improved oxygenation, and protected against pulmonary edema. Apyrase treatment was associated with attenuated neutrophil graft sequestration and less evidence of tissue inflammation as assessed by myeloperoxidase activity, expression of proinflammatory mediators, and numbers of apoptotic endothelial cells.

CONCLUSIONS

Administration of a soluble recombinant apyrase promotes lung function and limits the tissue damage induced by prolonged cold storage, indicating that extracellular purigenic nucleotides play a key role in promoting ischemia-reperfusion injury following lung transplantation.

EFFECTS OF ISCHEMIC PRECONDITIONING ON RAT LUNG: ROLE OF NITRIC OXIDE

Recent studies suggest that ischemic preconditioning (IP) of the lung may have a protective effect in ischemia-reperfusion (I/R) injury. The purpose of the present study was to investigate the preconditioning hypothesis in rat pulmonary vascular bed and to examine the role of nitric oxide (NO) in IP. Isolated rat lung was perfused with Krebs-Henseleit solution containing indomethacin at a constant flow rate and perfusion pressure changes was recorded by a pressure transducer. In rat pulmonary vascular bed, 2 hours of hypothermic ischemia significantly attenuated histamine-induced vasodilator responses without affecting sodium nitroprusside (SNP) vasodilation when compared to sham values. However, 2 cycles of 5 minutes of ischemia and reperfusion that were applied prior to 2 hours of ischemia (IP protocol) prevented the attenuation of histamine-induced vasodilation. On the other hand, IP failed to prevent pulmonary edema after ischemia. Histopathological examination of rat lungs demonstrated that IP was able to protect endothelial cells and type II pneumocytes in lung. Moreover, in IP group, malondialdehyde (MDA) contents of the lung tissue were significantly lower and tissue glutathione (GSH) contents were significantly higher than those in I/R group. Administration of NO synthase inhibitor, N(G)-nitro-L-arginine-methyl ester (L-NAME) prior to the IP protocol abolished the protective effects of IP, but not affected the tissue malondialdehyde and glutathione levels. These results suggest that I/R impaired endothelium-dependent vasodilatory response, whereas endothelium-independent SNP-induced responses were preserved in rat pulmonary vascular bed. IP prevented the impairment of pulmonary vascular endothelium-dependent responses, and these effects may be partially mediated by NO.

Soluble p-selectin and the risk of primary graft dysfunction after lung transplantation

BACKGROUND

Platelet activation with subsequent neutrophilic adherence to the vasculature initiates ischemia-reperfusion injury. We hypothesized that higher plasma P-selectin levels reflecting platelet activation would therefore be associated with primary graft dysfunction (PGD) after lung transplantation.

METHODS

In a prospective, multicenter cohort study of 376 patients who had undergone lung transplantation between 2002 and 2007, we measured soluble P-selectin levels before lung transplantation and at 6 and 24 h after lung reperfusion in 20 patients with grade III PGD (Pao(2)/fraction of inspired oxygen, < 200 mm Hg [with alveolar infiltrates seen on chest radiographs]) at 72 h after transplantation and 61 control subjects without PGD.

RESULTS

Higher postoperative soluble P-selectin levels were associated with an increased risk of PGD at 72 h after transplantation (odds ratio [OR] per 1 natural log increase in soluble P-selectin at 6 h after lung allograft reperfusion, 3.5; 95% confidence interval [CI], 1.01 to 11.8; p = 0.048) and at 24 h after lung allograft reperfusion (OR, 4.8; 95% CI, 1.4 to 16.1; p = 0.01). Higher preoperative mean pulmonary artery pressure and the use of cardiopulmonary bypass were also associated with an increased risk of PGD.

CONCLUSION

Higher postoperative soluble P-selectin levels were associated with an increased risk of PGD at 72 h following lung transplantation.

Pathophysiological role of platelets and platelet system in acute pancreatitis

The most successful approach for restoring normal long-term glucose homeostasis in type I diabetes mellitus is whole-organ pancreas transplantation. Graft pancreatitis is observed in up to 20% of patients and may lead to loss of the transplanted organ. Several pathophysiological events have been implicated in this form of pancreatitis. The most important cause of early graft pancreatitis is ischemia/reperfusion (I/R)-related disturbance of microvascular perfusion with subsequent hypoxic tissue damage. Recently, considerable evidence accumulated that, among a variety of other pathophysiological events, the activation of platelets can contribute to I/R injury in the course of acute pancreatitis experimentally and clinically. This review summarizes the events affecting platelet function and, therefore, pancreatic microcirculation leading to acute pancreatitis. Therapeutic approaches and own results are presented.

Platelet activation in the postoperative period after lung transplantation

OBJECTIVE

During lung transplantation, cells in the pulmonary parenchyma are subjected to ischemia, hypothermic storage, and reperfusion injury. Platelets, whose granular contents include adhesion receptors, chemokines, and coactivating substances that activate inflammatory and coagulant cascades, likely play a critical role in the lung allograft response to ischemia and reperfusion. The platelet response to the pulmonary allograft, however, has never been studied. Here we report significant platelet activation immediately after lung transplantation.

METHODS

We performed a prospective cohort study comparing markers of platelet activation in patients undergoing lung transplantation and patients undergoing nontransplant thoracotomy. Plasma levels of soluble P-selectin, soluble CD40 ligand, and platelet-leukocyte conjugates were measured before surgery, after skin closure, and at 6 postoperative hours.

RESULTS

Both soluble P-selectin and soluble CD40 ligand levels increased significantly after lung transplantation but not after thoracotomy. Additionally, platelet-monocyte conjugate fluorescence was significantly higher after lung transplantation than after thoracotomy alone.

CONCLUSION

These findings suggest that platelet activation is significantly increased after lung transplantation beyond that expected from the postoperative state. The increase in circulating platelet-monocyte conjugates suggests an important interaction between platelets and inflammatory cells. Further research should examine whether platelet activation affects early graft function after lung transplantation.

HYDROXYETHYL STARCH NORMALIZES PLATELET AND LEUKOCYTE ADHESION WITHIN PULMONARY MICROCIRCULATION DURING LPS-INDUCED ENDOTOXEMIA

Growing evidence supports substantial pathophysiological impact of platelets and their interactions on the development of septic lung failure. We developed a rat model of endotoxemia for direct in situ visualization of pulmonary microcirculation by in vivo fluorescence videomicroscopy. Male Sprague-Dawley rats were assigned to control, endotoxemia (Escherichia coli LPS, 15 mg/kg, i.v.), and fluid management for treatment of LPS-induced hypovolemia (Ringer lactate, hydroxyethyl starch [HES] 6%) groups (n = 7 each). Leukocytes were labeled in vivo by rhodamine, and 5 x 10(6) Calcein-AM-labeled nonactivated platelets were injected. Microcirculatory parameters (vessel diameter, ventilation-perfusion ratio) and adhesive characteristics of platelets and leukocytes (velocity, rolling, sticking) within the pulmonary microcirculation were quantified after endotoxin application under various regimens of fluid substitution for 60 min. A reduction of cell velocity and enhanced cell adhesion was seen in leukocytes and platelets (P < 0.05) after LPS injection. Fluid treatment with HES 6% resulted in a significant increase of platelet's velocity compared with the LPS group (442.86 +/- 20.60 vs. 343.93 +/- 11.17; P < 0.05), whereas Ringer lactate showed no beneficial effects. Similarly, HES 6% normalized LPS-induced platelet rolling and sticking as well as alterations in ventilation-perfusion ratio. Using direct visualization of the pulmonary microcirculation, we observed that platelet and leukocyte interactions are enhanced in the lung during LPS endotoxemia. Fluid therapy with HES 6% seems to have restorative effects on these cellular functions within the pulmonary microcirculation.

Efeito protetor de antagonista das gliproteínas IIb/IIa nas alterações hepáticas e pulmonares secundárias à isquemia e reperfusão do fígado em ratos

RACIONAL: A lesão de isquemia e reperfusão hepática é um evento comum e responsável por considerável morbidade e mortalidade. OBJETIVO: Avaliar efeitos de inibidor da glicoproteína IIb/IIIa, cloridrato de tirofiban, nas alterações hepáticas e pulmonares da lesão de isquemia e reperfusão de fígado de ratos. MÉTODO: Vinte e três ratos Wistar divididos em três grupos: laparotomia (n = 6), isquemia e reperfusão que receberam solução fisiológica (n = 8), e submetidos a isquemia e reperfusão e tratados com o cloridrato de tirofiban (n = 9). Foram realizadas dosagens das aminotransferases e análise histológica hepática. Avaliação pulmonar foi realizada pelo teste do azul de Evans e pela dosagem tecidual da mieloperoxidase no parênquima pulmonar. A oxidação e fosforilação mitocondrial das células hepáticas também foram avaliadas. RESULTADOS: O grupo tratado com cloridrato de tirofiban apresentou menores níveis de aminotransferases, assim como alterações histológicas menos intensas. Avaliação pulmonar demonstrou diminuição no teste de azul de Evans no grupo tratado com cloridrato de tirofiban. Grupo tratado com cloridrato de tirofiban apresentou aumento significativo do estado 3 da respiração mitocondrial e das relações adenosina difosfato utilizado para fosforilação sobre o oxigênio consumido na reação e de coeficiente respiratório. CONCLUSÕES: O uso do cloridrato de tirofiban exerceu papel protetor da lesão hepática de isquemia e reperfusão e impediu o aumento da permeabilidade vascular secundária à lesão de reperfusão hepática.

Platelets and platelet-derived serotonin promote tissue repair after normothermic hepatic ischemia in mice

Hepatic ischemia and reperfusion (I/R) leads to the formation of leukocyte-platelet aggregates. Upon activation, platelets generate reactive oxygen species and release proapoptotic and proinflammatory mediators as well as growth factors. In cold hepatic ischemia, adhesion of platelets to endothelial cells mediates sinusoidal endothelial cell apoptosis. Furthermore, platelet-derived serotonin mediates liver regeneration. We hypothesized that platelets may contribute to reperfusion injury and repair after normothermic hepatic ischemia. The aim of this study was to assess the impact of platelets in normothermic hepatic I/R injury using models of impaired platelet function and immune thrombocytopenia. Inhibition of platelet function in mice was achieved via clopidogrel feeding. Immune thrombocytopenia was induced via intraperitoneal injection of anti-CD41 antibody. Platelet-derived serotonin was investigated using mice lacking tryptophan hydroxylase 1. Mice were subjected to 60 minutes of partial hepatic ischemia and various time points of reperfusion. Hepatic injury was determined via AST and histological analysis of the necrotic area as well as leukocyte infiltration. Liver regeneration was determined via proliferating cell nuclear antigen and Ki67 immunohistochemistry. Neither inhibition of platelet function nor platelet depletion led to a reduction of I/R injury. Liver regeneration and repair were significantly impaired in platelet-depleted animals. Mice lacking peripheral serotonin were deficient in hepatocyte proliferation, but otherwise displayed normal tissue remodeling.

CONCLUSION

Platelets have no direct impact on the pathogenesis of normothermic I/R injury. However, they mediate tissue repair and liver regeneration. Furthermore, platelet-derived serotonin is a mediator of hepatocyte proliferation in the postischemic liver, but has no impact on tissue remodeling.

Lung ischemia-reperfusion injury: implications of oxidative stress and platelet-arteriolar wall interactions

Pulmonary ischemia-reperfusion (IR) injury may result from trauma, atherosclerosis, pulmonary embolism, pulmonary thrombosis and surgical procedures such as cardiopulmonary bypass and lung transplantation. IR injury induces oxidative stress characterized by formation of reactive oxygen (ROS) and reactive nitrogen species (RNS). Nitric oxide (NO) overproduction via inducible nitric oxide synthase (iNOS) is an important component in the pathogenesis of IR. Reaction of NO with ROS forms RNS as secondary reactive products, which cause platelet activation and upregulation of adhesion molecules. This mechanism of injury is particularly important during pulmonary IR with increased iNOS activity in the presence of oxidative stress. Platelet-endothelial interactions may play an important role in causing pulmonary arteriolar vasoconstriction and post-ischemic alveolar hypoperfusion. This review discusses the relationship between ROS, RNS, P-selectin, and platelet-arteriolar wall interactions and proposes a hypothesis for their role in microvascular responses during pulmonary IR.

Lipid-Mediated Transbronchial Human Interleukin-10 Gene Transfer Decreases Acute Inflammation Associated With Allograft Rejection in a Rat Model of Lung Transplantation

BACKGROUND

Transferring genes with immunoregulatory capacity to transplanted organs has the potential to modify allograft rejection (AR). We examined the effect of ex vivo lipid-mediated transbronchial human interleukin-10 (hIL-10) gene transfer on acute AR in a rat model of lung transplantation.

METHODS

Left single lung transplantations were performed between a highly histoincompatible rat combination: Brown Norway to Lewis. The extracted donor left lung was intrabronchially instilled with a plasmid encoding hIL-10 or Escherichia coli beta-galactosidase (control), mixed with a cationic lipid. On day 6 posttransplantation, the degree of AR was graded histologically (stages 1-4) based upon pathological categories of inflammation: perivascular, peribronchial, and peribronchiolar lymphocytic infiltrates, edema, intraalveolar hemorrhage, and necrosis.

RESULTS

The stage of AR in the IL-10 group (3.1 +/- 0.4) was significantly lower than the control group (3.8 +/- 0.4). Pathological scores for edema, intraalveolar hemorrhage, and necrosis in the IL-10 group (2.3 +/- 0.8, 0.3 +/- 0.5, and 0.3 +/- 0.5, respectively) were also significantly decreased compared with those in the control group (3.2 +/- 0.4, 2.2 +/- 0.8, and 1.2 +/- 0.4, respectively).

CONCLUSION

Ex vivo lipid-mediated transbronchial hIL-10 gene transfer attenuated acute inflammation associated with AR in a rat model of lung transplantation.

Pathophysiological role of platelets in acute experimental pancreatitis: influence of endothelin A receptor blockade

The potential pathophysiological role of platelet-endothelium interactions was investigated during ischemia/reperfusion (I/R), and the effect of a selective endothelin(A) receptor antagonist (ET(A)-RA) was evaluated in an acute pancreatitis model. Acute pancreatitis was induced by warm ischemia (60 min) in Wistar rats, and its effects with and without antagonist treatment were investigated. Equivalent sham-operated animals were also studied. Microcirculatory changes were assessed by in vivo microscopy, and serum levels for lipase/amylase and histological specimens were investigated. Capillary constriction to 83.7 +/- 6.7% of sham-operated diameters was observed after 60 min of ischemia. A capillary density of 56.8 +/- 9.3% of the sham-operated group (396.3 +/- 15.8 mm(-1)) was measured after reperfusion. Stagnant leukocytes (329.5 +/- 30.4%) and platelets (337.5 +/- 32.3%) increased in postcapillary venules (P < 0.05). Administration of the ET(A)-RA significantly reduced I/R injury. Capillary diameters were maintained (101.4 +/- 4.5%), and capillary density was improved to 73.3 +/- 7.6% of sham-operated animals (P < 0.05). Stagnant leukocytes (152.3 +/- 10.6%) and platelets (207.1 +/- 19.8%) in sinusoids and postcapillary venules were reduced (P < 0.05). The extent of acute pancreatitis was reduced in the therapy group as indicated by serum lipase/amylase values and histological tissue damage (P < 0.05). Thus, ET(A)-RA therapy was effective in reducing I/R-induced pancreatitis in this experimental model.

Role of P-Selectin in Platelet Sequestration in Pulmonary Capillaries during Endotoxemia

BACKGROUND

There is growing evidence that platelets accumulate in the lung and contribute to the pathogenesis of acute lung injury during endotoxemia. The aims of the present study were to localize platelet sequestration in the pulmonary microcirculation and to investigate the role of P-selectin as a molecular mechanism of platelet endothelial cell interaction.

METHODS

We used in vivo fluorescence microscopy to quantify the kinetics of fluorescently labeled erythrocytes and platelets in alveolar capillary networks in rabbit lungs.

RESULTS

Six hours after onset of endotoxin infusion we observed a massive rolling along and firm adherence of platelets to lung capillary endothelial cells whereas under control conditions no platelet sequestration was detected. P-selectin was expressed on the surface of separated platelets which were incubated with endotoxin and in lung tissue. Pretreatment of platelets with fucoidin, a P-selectin antagonist, significantly attenuated the endotoxin-induced platelet rolling and adherence. In contrast, intravenous infusion of fucoidin in endotoxin-treated rabbits did not inhibit platelet sequestration in pulmonary capillaries.

CONCLUSION

We conclude that platelets accumulate in alveolar capillaries following endotoxemia. P-selectin expressed on the surface of platelets seems to play an important role in mediating this platelet-endothelial cell interaction.

Adenovirus mediated IL-10 gene transfer to the airway of the rat lung for prevention of lung allograft rejection

BACKGROUND

The ability to express genes with potential immunoregulatory capacity could reduce allograft rejection (AR). We examined the feasibility of transferring the viral interleukin-10 (vIL-10) gene into rat lungs by intra-bronchial instillation and the subsequent effects of delivered vIL-10 on acute lung AR.

METHODS

First, the adenoviral beta-galactosidase vector (adv-beta-gal) particles were instilled into the airway of the rat lung and protein synthesis of beta-gal was examined by histochemical staining. Next, the ability of the adenoviral vIL-10 vector (adv-vIL-10) transfection to modify AR was examined in a highly histoincompatible rat lung transplant model (BN-->Lew). Donor left lungs were transfected with 3 x 10(8) pfu/0.3 mL of adv-vIL-10 (vIL-10 group) or adv-beta-gal (control group) 3 days before transplantation. On day 6 post-transplant, lung allografts were harvested and AR was graded histologically (stage 0-4). Several pathological categories of inflammation (perivascular, peribronchial, or peribronchiolar mononuclear infiltrates, edema, vasculitis, intraalveolar hemorrhage, and necrosis) were also examined and scored on a scale of 0-4 as previously described.

RESULTS

A successful transgene protein synthesis by adv-beta-gal in alveolar epithelial cells and alveolar macrophages was confirmed by histochemical staining with X-gal. The vIL-10 group showed a trend toward an improved stage of AR (3.75 +/- 0.5 vs. 4.0 +/- 0), and also a decreased pathological scores for edema (3.5 +/- 0.6 vs. 4.0 +/- 0), intraalveolar hemorrhage (2.3 +/- 1.0 vs. 2.5 +/- 0.6) and necrosis (1.5 +/- 0.5 vs. 1.75 +/- 1.3) compared with the control group, however, the differences in any pathological scores between the two groups did not reach a statistical significance.

CONCLUSIONS

1. A successful transgene protein synthesis in alveolar epithelial cells was ensured by intra-bronchial instillation of an adenoviral vector encoding beta-galactosidase gene. 2. Transferring the vIL-10 gene into rat lungs by intra-bronchial instillation did not seem to reduce lung AR significantly, as opposed to the results of our previous experiments in a rat cardiac allograft model. This discrepancy may be explained by several potential factors including the immunogenecity of adenoviral vectors in conjunction with the nature of the lung more susceptible to immune response and inflammation.

Protective effect of carbon monoxide in transplantation

During the last decades due to the development of new immunosuppressive agents and improvements in organ preservation methods, surgical techniques, and postoperative care, organ transplantation has become an ultimate therapeutic option for irreversible organ failure. Early graft survival has significantly improved; however, the long-term outcome remains unsatisfactory. Multiple factors, both immunogenic and non-immunogenic etiologies, are involved in the deterioration of the allografts, and the recent use of expanded criteria donors to overcome the organ shortage may also contribute to the graft losses. Carbon monoxide (CO) is commonly viewed as a poison in high concentrations due to its ability to interfere with oxygen delivery. However, CO is endogenously produced in the body as a byproduct of heme degradation by the heme oxygenase (HO) and has recently received notable attention as a gaseous regulatory molecule. In fact, an augmentation of endogenous CO by induction of HO-1 or exogenously added CO is known to have potent cytoprotective effects in various disease models. Several recent reports have demonstrated that CO provides potent cytoprotective effects in the field of organ and cell transplantation. CO is able to prevent ischemia/reperfusion injury, allograft rejection, and xenograft rejection via its anti-inflammatory, anti-apoptotic and anti-proliferation effects, suggesting that CO might be a valuable therapeutic option in the field of transplantation. Based on the recent advancement of our understanding of CO as a new therapeutic molecule, this review attempts to summarize the functional roles as well as biological and molecular mechanisms of CO in transplantation and discusses potential CO application to the clinical transplant setting.

Platelet dysfunction in asphyxiated newborn piglets resuscitated with 21% and 100% oxygen

Hemostatic disturbances are common in asphyxiated newborns after resuscitation. We compared platelet function in hypoxic newborn piglets reoxygenated with 21% or 100% oxygen. Piglets (1-3 d, 1.5-2.1 kg) were anesthetized and acutely instrumented for hemodynamic monitoring. After stabilization, normocapnic hypoxia was induced with an inspired oxygen concentration of 10-15% for 2 h. Piglets were then resuscitated for 1 h with 21% or 100% oxygen, followed by 3 h with 21% oxygen. Platelet counts and collagen (2, 5, and 10 microg/mL)-stimulated whole blood aggregation were studied before hypoxia and at 4 h of post-hypoxia/reoxygenation. Platelet function was studied using transmission electron microscopy and by measuring plasma thromboxane B2 (TxB2) and matrix metalloproteinase (MMP)-2 and -9 levels. Control piglets were sham-operated without hypoxia/reoxygenation. The hypoxemic (PaO2 33 mm Hg) piglets developed hypotension with metabolic acidosis (pH 7.02-7.05). Upon reoxygenation, piglets recovered and blood gases gradually normalized. At 4 h reoxygenation, platelet aggregation ex vivo was impaired as evidenced by a rightward-downward shifting of the concentration-response curves. Electron microscopy showed features of platelet activation. Plasma MMP-9 but not MMP-2 activity significantly increased. Resuscitation with 100% but not 21% oxygen increased plasma TxB2 levels. Platelet counts decreased after hypoxia/reoxygenation but were not different between groups during the experiment. Resuscitation of hypoxic newborn piglets caused platelet activation with significant deterioration of platelet aggregation ex vivo and increased plasma MMP-9 levels. High oxygen concentrations may aggravate the activation of prostaglandin-thromboxane mechanistic pathway.

Platelet-derived serotonin mediates liver regeneration

The liver can regenerate its volume after major tissue loss. In a mouse model of liver regeneration, thrombocytopenia, or impaired platelet activity resulted in the failure to initiate cellular proliferation in the liver. Platelets are major carriers of serotonin in the blood. In thrombocytopenic mice, a serotonin agonist reconstituted liver proliferation. The expression of 5-HT2A and 2B subtype serotonin receptors in the liver increased after hepatectomy. Antagonists of 5-HT2A and 2B receptors inhibited liver regeneration. Liver regeneration was also blunted in mice lacking tryptophan hydroxylase 1, which is the rate-limiting enzyme for the synthesis of peripheral serotonin. This failure of regeneration was rescued by reloading serotonin-free platelets with a serotonin precursor molecule. These results suggest that platelet-derived serotonin is involved in the initiation of liver regeneration.

Inhibition of inducible nitric oxide synthase attenuates platelet adhesion in subpleural arterioles caused by lung ischemia-reperfusion in rabbits

Oxidative stress, induced by lung ischemia-reperfusion, leads to platelet and leukocyte activation and may contribute to decreased alveolar perfusion by platelet adhesion to the arteriolar wall. We investigated the hypothesis that ischemia-reperfusion injury increases inducible nitric oxide synthase (iNOS) activity and subsequent generation of reactive nitrogen species with P-selectin-dependent platelet-endothelial interactions and vasoconstriction during lung reperfusion. Subpleural arterioles, labeled platelets, and leukocytes were examined in anesthetized, open-chest rabbits by intravital fluorescence microscopy. Ischemia was caused by reversible occlusion of the right pulmonary artery for 1 or 2 h (1IR and 2IR groups). During 2 h of reperfusion, postischemic platelet rolling and adhesion were independent from leukocyte-arteriolar wall interactions and correlated with pulmonary arteriolar constriction in proportion to the length of ischemia. In rabbits treated with an iNOS inhibitor (1400W) before occlusion (2IR + 1400W group), platelet-arteriolar wall interactions and vasoconstriction were prevented. iNOS expression and activity in ischemic lung tissue were markedly greater than control and also were proportional to ischemia duration. NOS activity, immunochemically detected P-selectin, and nitrotyrosine expression in ischemic lung tissue from animals subjected to ischemia-reperfusion, as well as the plasma level of soluble P-selectin, were significantly higher than in nonischemic lungs and were inhibited by pretreatment with 1400W. These results show that platelet adhesion and arteriolar constriction during early reperfusion in the ventilated lung can result from increased iNOS activity and is highly correlated with reactive nitrogen species and P-selectin expression.

Improvement of postischemic hepatic microcirculation after endothelinA receptor blockade--endothelin antagonism influences platelet-endothelium interactions

Endothelin (ET) contributes to disturbances of hepatic microcirculation after ischemia/reperfusion (I/R) by causing vasoconstriction and enhancing leukocyte- and platelet-endothelium interactions. The aim of this study was to investigate a possible protective role of a selective endothelin(A) receptor antagonist (ET(A)-RA) in this setting. In a rat model, warm ischemia of the left lateral liver lobe was induced for 90 minutes under intraperitoneal anesthesia with xylazine and ketamine. Groups of rats consisted of sham-operated (SO, n=14), untreated ischemia (n=14), and treatment with BSF208075 (5 mg/kg body weight IV, n=14). The effect of the ET(A)-RA on I/R was assessed by in vivo microscopy 20 to 90 minutes after reperfusion; by measurement of local tissue Po(2), serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and glutathione S-transferase alpha levels, and by histologic investigation. In the untreated group, sinusoidal constriction to 69.4+/-6.7% of diameters of SO rats was observed, leading to a significant decrease in perfusion rate (74.3+/-2.1% of SO) and liver tissue Po(2) (43.5+/-3.2% of SO) (P < 0.05). In addition, we found an increased percentage of stagnant leukocytes (142.9+/-11.9%) and platelets (450.1+/-62.3%) in sinusoids and in postsinusoidal venules (P < 0.05). Hepatocellular damage (AST and ALT increase to 1330+/-157 U/L and 750+/-125 U/L respectively; previously, 27.1+/-3.5 U/L and 28.5+/-3.6 U/L) was detected 6 hours after reperfusion (P < 0.05). Administration of the ET(A)-RA before reperfusion significantly reduced I/R injury. Sinusoidal diameters were maintained (108.5+/-6.6%), and perfusion rate (93.1+/-1.8%) and tissue Po(2) (95.3+/-5.7%) were significantly increased (P < 0.05). According to reduced leukocyte-endothelium interactions after therapy, both platelet rolling and adhesion were significantly reduced (P < 0.05). The number of stagnant platelets in sinusoids was 199.5+/-12.3% of 50 (P < 0.05). After treatment, hepatocellular damage was decreased (AST and ALT levels after 6 hours of reperfusion: 513+/-106 U/L and 309+/-84 U/L, respectively; P < 0.05), and histologic changes were reduced in the long term. Our results provide evidence that the new therapeutic approach with an ET(A)-RA is effective in reducing hepatic I/R injury. In addition to reduced leukocyte-endothelium interactions, the number of stagnant and rolling platelets in sinusoids and venules was significantly reduced. The reduction in microcirculatory damages is responsible for better organ outcome.

Early expression of adhesion molecules after lung transplantation: evidence for a role of aggregated P-selectin-positive platelets in human primary graft failure

BACKGROUND

Primary graft failure (PGF) secondary to ischemia-reperfusion injury is the main cause of death in the first month after lung transplantation. The aim of this study was to identify early cellular and immunologic events associated with PGF in human lung transplants.

METHODS

Induction of P-selectin, E-selectin and intercellular adhesion molecule-1 (ICAM-1) and evaluation of leukocytes and platelets accumulation were investigated in 18 post-reperfusion surgical specimens of lung allografts by an immunohistochemical technique.

RESULTS

Selectins were restricted to the venular plexus after reperfusion as in the normal lung, whereas ICAM-1 was induced in all cases on alveolar capillaries. Numerous polymorphonuclear cells (18 of 18 cases) and aggregated platelets (7 of 18 cases) were identified along the venular plexus after reperfusion. Compared with the other patients, those with aggregated P-selectin-positive platelets were characterized by a longer duration of mechanical ventilation (p < 0.01), a lower PaO2/FiO2 ratio (p < 0.01) and the presence of radiologic edema (p < 0.05) within the first 3 post-operative days.

CONCLUSIONS

We showed in the reperfused lung a distinct expression of adhesion molecules on venous and capillary pulmonary endothelia that may influence the role of leukocytes and platelets during the early course of transplantation. Furthermore, the knowledge of an association between the presence of P-selectin-positive platelet aggregates and PGF criteria might have implications for graft management and therapeutic strategies.

Effects of pulmonary ischemia-reperfusion on platelet adhesion in subpleural arterioles in rabbits

Reperfusion of the ischemic lung is associated with increased pulmonary vascular resistance and reduced alveolar perfusion in conjunction with an inflammatory response. To determine the contribution of platelet-endothelial interactions, we examined effects of pulmonary ischemia-reperfusion (IR) on platelet adhesion and diameter of arterioles and investigated the hypothesis that this process is P-selectin mediated. In anesthetized rabbits with open-chest and ventilated lungs, we examined subpleural arterioles by fluorescence microscopy. Ischemia was caused by reversibly occluding the right pulmonary artery for 2 h. Fluorescently labeled platelets were injected into the right atrium and the right lung was observed after 0.5, 1.0, and 2.0 h of reperfusion. Platelets rolling and adherence along arterioles occurred with a decrease in diameter that was significant during IR, but not after 3- to 5-min occlusion (control). Systemic pretreatment with Fucoidan (a ligand to P- and L-selectin) inhibited platelet rolling, adherence, and the decrease in diameter. Pretreatment of only exogenously labeled platelets with monoclonal antibody (MoAb) to P-selectin prevented platelet rolling and adherence, but not the decrease in diameter. These results indicate that in the intact lung, pulmonary IR causes platelet rolling and adhesion along arteriolar walls, and suggest that this process, which is mediated by P-selectin, contributes to vasoconstriction and hypoperfusion. Thus, it appears that platelet-endothelial interactions may contribute to the development of pulmonary IR injury.

Platelet-endothelial cell interactions during hepatic ischemia-reperfusion in vivo: a systematic analysis

Platelets have been implicated in the pathophysiology of ischemia-reperfusion (I/R) injury. This study was designed to analyze platelet-endothelial cell interactions after I/R of the liver in vivo in dependence of the duration of ischemia and reperfusion. In C57BL/6 mice, a warm (37 degrees C) lobar hepatic ischemia was induced for 30, 60, or 90 min. Platelets were isolated from syngeneic donors, labeled ex vivo by rhodamine-6G, and infused intraarterially. Platelet-endothelial cell interactions and sinusoidal perfusion were analyzed using intravital fluorescence microscopy after 20-240 min of reperfusion. Hepatic I/R induced platelet rolling and adhesion in terminal arterioles and postsinusoidal venules as well as platelet accumulation in sinusoids already after 20 min of reperfusion. The number of platelets interacting with the endothelium was significantly increased as ischemia time was prolonged from 30 min up to 60 and 90 min. Postischemic platelet adhesion was associated with an increase in thrombin activity and a loss of platelets from the systemic circulation. Moreover, I/R-induced platelet adhesion was linearly correlated with an impairment of sinusoidal perfusion. The prolongation of reperfusion time up to 4 h did not further enhance platelet-endothelial cell interactions. These in vivo results indicate that hepatic I/R induces platelet-endothelial cell interactions in arterioles, sinusoids, and venules already during early reperfusion. The extent of these interactions is dependent on the duration of ischemia, but not on reperfusion time. Adherent platelets seem to participate in the development of sinusoidal perfusion failure in the postischemic liver.

P-selectin mediates platelet-endothelial cell interactions and reperfusion injury in the mouse liver in vivo

Platelets are suggested to participate in the pathogenesis of hepatic ischemia-reperfusion (I/R) injury. This study was designed to analyze platelet-endothelial cell interactions in the postischemic mouse liver in vivo and to define the role of endothelial versus platelet P-selectin for these interactions. Platelet-endothelial cell interactions were quantitatively analyzed using intravital fluorescence microscopy after lobar hepatic I/R in C57BL/6 wild-type and P-selectin-deficient mice after infusion of ex vivo rhodamine-6G-labeled wild-type and P-selectin-deficient platelets. Reperfusion injury and apoptosis were assessed by established methods. In wild-type animals, hepatic I/R caused significantly enhanced platelet-endothelial cell interactions in terminal arterioles and postsinusoidal venules as well as platelet stagnation in sinusoids. Concomitantly, transaminase and caspase-3 activities were elevated and sinusoidal perfusion was impaired. In contrast, platelet-endothelial cell interactions were nearly absent in arterioles and venules of mice lacking endothelial P-selectin, irrespective of the presence of P-selectin on infused platelets, but still significantly elevated in sinusoids. Simultaneously, sinusoidal perfusion failure was ameliorated, and transaminase- and caspase-3 activities were significantly reduced in P-selectin-deficient mice as compared with wild-type animals. The present intravital microscopic study provides, for the first time, quantitative analyses of platelet-endothelial cell interactions in the postischemic hepatic microcirculation. Our in vivo data show that endothelial P-selectin is critical for postischemic platelet-endothelial cell interactions within hepatic presinusoidal arterioles and postsinusoidal venules. P-selectin deficiency prevents microvascular injury and apoptosis after warm hepatic I/R.

Platelet adhesion mediated by fibrinogen-intercelllular adhesion molecule-1 binding induces tissue injury in the postischemic liver in vivo

BACKGROUND

Platelets are thought to be involved in the induction of hepatic ischemia-reperfusion (I/R) injury. The mechanisms of platelet adhesion in the hepatic microvasculature and the role of platelets in the pathogenesis of I/R-induced liver damage in vivo remain unclear.

METHODS

In C57BL/6 mice, platelet- and leukocyte-endothelial cell interactions were quantitatively analyzed using intravital fluorescence microscopy in sham-operated animals, after warm lobar hepatic I/R (90/20 min) in wild-type and intercellular adhesion molecule (ICAM)-1-deficient mice, and after I/R in wild-type mice treated with an antifibrinogen antibody. Fibrinogen deposition on the endothelium was detected by intravital microscopy and by immunostaining. Reperfusion injury was assessed by measurement of liver enzyme and caspase-3 activities and of lipid peroxidation.

RESULTS

Hepatic I/R induced fibrinogen deposition on hepatic endothelium, followed by a dramatic increase in the number of firmly adherent platelets in the liver microvasculature. Simultaneously, the number of adherent leukocytes in postsinusoidal venules and the aspartate aminotransferase/alanine aminotransferase and caspase-3 activities were elevated. Although ICAM-1 deficiency attenuated postischemic adherence of both platelets and leukocytes, the application of an antifibrinogen antibody selectively reduced the number of adherent platelets but did not influence leukocyte adhesion. The selective blockade of platelet adherence significantly prevented the postischemic increase in liver enzyme and caspase-3 activities. Furthermore, sinusoidal perfusion failure and lipid peroxidation were attenuated in the treated group.

CONCLUSIONS

These in vivo data show that platelet adhesion mediated through fibrinogen deposition on ICAM-1 expressed on the endothelium of postischemic hepatic microvessels induces microvascular injury and hepatocellular apoptosis after I/R of the liver during early reperfusion.

Efeito da N-acetilcisteína no pulmão após isquemia hepática em ratos

Na síndrome de isquemia e reperfusão os pulmões podem ser alvo de lesão a distância como nos casos de choque, trauma ou ainda nos casos de transplante hepático. Objetivo: Avaliar o efeito protetor da N-acetilcisteína (NAC) sobre os pulmões após isquemia hepática. Métodos: Foram utilizados 12 ratos, machos, linhagem EPM-1 Wistar, separados aleatoriamente em dois grupos com seis animais (controle e experimento). Os animais de ambos os grupos foram submetidos à anestesia com cloridrato de quetamina e cloridrato de xilazina. Realizou-se a incisão mediana longitudinal, identificação do hilo hepático e da veia cava caudal. Quinze minutos antes do clampeamento injetou-se solução glicosada a 5% no grupo controle e NAC diluída em solução glicosada a 5% no grupo experimento. Os animais foram mantidos em isquemia hepática durante 30 minutos, sendo em seguida realizada toracotomia e remoção cirúrgica dos pulmões para avaliação histológica com coloração pela hematoxilina-eosina. Resultados: A análise dos cortes do parênquima pulmonar mostrou semelhança nos dois grupos estudados, ocorrendo colapso alveolar, infiltrado neutrofílico, congestão vascular e áreas hemorrágicas, compatíveis com a repercussão sistêmica da isquemia hepática. Conclusão: A NAC não modifica a lesão pulmonar decorrente da isquemia, à microscopia óptica.

Platelet-mediated activation of endothelial cells: implications for the pathogenesis of transplant rejection

BACKGROUND

Platelets exert their normal functions at sites of endothelial disruption by plugging discontinuities in blood vessels and secreting products that promote thrombosis, inflammation, and the healing of wounds. Whether platelets might induce these changes in xenograft blood vessels, leading to development of acute vascular rejection, has been uncertain.

METHODS

To examine the role of human platelets in modulation of xenograft endothelium, pig endothelial cells were treated with human platelets.

RESULTS

Treatment of quiescent porcine endothelial cells with human platelets modulated the endothelial cells. Whereas resting human platelets caused little change in normal porcine endothelial cells, platelets activated with small amounts of thrombin induced striking changes in the endothelial cells, including the induction of tissue factor activity, the expression of E-selectin, and the secretion of endothelin-1. These changes were induced, at least in part, by interleukin-1 (IL-1) associated with the platelet surface and were modified by the secretion of transforming growth factor-beta (TGF-beta).

CONCLUSION

These findings may explain how the activation of platelets at an early point in the rejection of vascularized organ xenografts or in chronic diseases might contribute to thrombotic, ischemic, and inflammatory changes characteristic of an organ xenograft undergoing rejection.

Platelets induce sinusoidal endothelial cell apoptosis upon reperfusion of the cold ischemic rat liver

BACKGROUND & AIMS

Sinusoidal endothelial cell (SEC) apoptosis is a central feature of reperfusion injury in liver transplantation. Platelet sequestration occurs after transplantation with possible deleterious effects. We tested the hypothesis that platelets mediate SEC apoptosis.

METHODS

Livers were perfused after 24 hours of cold preservation in University of Wisconsin solution in an isolated perfused rat liver model. The perfusate contained isolated syngeneic red blood cells and purified platelets. Effects of inhibiting platelet adhesion on SEC apoptosis was tested using sialyl Lewis-X oligosaccharide (sLe(x)), a natural ligand of selectin adhesion molecules. Reperfusion injury was assessed by established markers of injury. Apoptosis was determined by TUNEL and electron microscopy.

RESULTS

A third of the circulating platelets was rapidly sequestered in the liver after reperfusion. This was associated with increased graft injury. Single platelets were adherent to sinusoidal lining without morphological or dynamic evidence of impairment of microcirculation. TUNEL staining revealed a 6-fold increase in the number of apoptotic SECs at 1 hour of reperfusion. No hepatocyte death or evidence of necrosis was detected up to 3 hours of reperfusion. Addition of sLe(x) inhibited adhesion and significantly reduced SEC apoptosis.

CONCLUSIONS

Platelets cause SEC apoptosis upon reperfusion of liver grafts. Prevention of adhesion is protective.

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.

Ischemia/reperfusion injury in human kidney transplantation: an immunohistochemical analysis of changes after reperfusion

Organs used for transplantation undergo varying degrees of cold ischemia and reperfusion injury after transplantation. In renal transplantation, prolonged cold ischemia is strongly associated with delayed graft function, an event that contributes to inferior graft survival. At present, the pathophysiological changes associated with ischemia/reperfusion injury in clinical renal transplantation are poorly understood. We have performed an immunohistochemical analysis of pre- and postreperfusion biopsies obtained from cadaver (n = 55) and living/related donor (LRD) (n = 11) renal allografts using antibodies to adhesion molecules and leukocyte markers to investigate the intragraft changes after cold preservation and reperfusion. Neutrophil infiltration and P-selectin expression were detected after reperfusion in 29 of 55 (53%) and 24 of 55 (44%) cadaver renal allografts, respectively. In marked contrast, neutrophil infiltration was not observed in LRD allografts, and only 1 of 11 (9%) had an increased level of P-selectin after reperfusion. Immunofluorescent double-staining demonstrated that P-selectin expression resulted from platelet deposition and not from endothelial activation. No statistically significant association was observed between neutrophil infiltration and P-selectin expression in the glomeruli or intertubular capillaries despite the large number of cadaver renal allografts with postreperfusion changes. Neutrophil infiltration into the glomeruli was significantly associated with long cold ischemia times and delayed graft function. Elevated serum creatinine levels at 3 and 6 months after transplantation were also associated with the presence of neutrophils and platelets after reperfusion. Our results suggest that graft function may be influenced by early inflammatory events after reperfusion, which can be targeted for future therapeutic intervention.