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

Updated Views on Neutrophil Responses in Ischemia-Reperfusion Injury

Ischemia-reperfusion injury is an inevitable event during organ transplantation and represents a primary risk factor for the development of early graft dysfunction in lung, heart, liver, and kidney transplant recipients. Recent studies have implicated recipient neutrophils as key mediators of this process and also have found that early innate immune responses after transplantation can ultimately augment adaptive alloimmunity and affect late graft outcomes. Here, we discuss signaling pathways involved in neutrophil recruitment and activation after ischemia-mediated graft injury in solid organ transplantation with an emphasis on lung allografts, which have been the focus of recent studies. These findings suggest novel therapeutic interventions that target ischemia-reperfusion injury-mediated graft dysfunction in transplant recipients.

Primary Graft Dysfunction

Primary graft dysfunction (PGD) is a form of acute lung injury after transplantation characterized by hypoxemia and the development of alveolar infiltrates on chest radiograph that occurs within 72 hours of reperfusion. PGD is among the most common early complications following lung transplantation and significantly contributes to increased short-term morbidity and mortality. In addition, severe PGD has been associated with higher 90-day and 1-year mortality rates compared with absent or less severe PGD and is a significant risk factor for the subsequent development of chronic lung allograft dysfunction. The International Society for Heart and Lung Transplantation released updated consensus guidelines in 2017, defining grade 3 PGD, the most severe form, by the presence of alveolar infiltrates and a ratio of PaO₂:FiO₂ less than 200. Multiple donor-related, recipient-related, and perioperative risk factors for PGD have been identified, many of which are potentially modifiable. Consistently identified risk factors include donor tobacco and alcohol use; increased recipient body mass index; recipient history of pulmonary hypertension, sarcoidosis, or pulmonary fibrosis; single lung transplantation; and use of cardiopulmonary bypass, among others. Several cellular pathways have been implicated in the pathogenesis of PGD, thus presenting several possible therapeutic targets for preventing and treating PGD. Notably, use of ex vivo lung perfusion (EVLP) has become more widespread and offers a potential platform to safely investigate novel PGD treatments while expanding the lung donor pool. Even in the presence of significantly prolonged ischemic times, EVLP has not been associated with an increased risk for PGD.

Lyophilized allografts without pre-treatment with glutaraldehyde are more suitable than cryopreserved allografts for pulmonary artery reconstruction

Various methods are available for preservation of vascular grafts for pulmonary artery (PA) replacement. Lyophilization and cryopreservation reduce antigenicity and prevent thrombosis and calcification in vascular grafts, so both methods can be used to obtain vascular bioprostheses. We evaluated the hemodynamic, gasometric, imaging, and macroscopic and microscopic findings produced by PA reconstruction with lyophilized (LyoPA) grafts and cryopreserved (CryoPA) grafts in dogs. Eighteen healthy crossbred adult dogs of both sexes weighing between 18 and 20 kg were used and divided into three groups of six: group I, PA section and reanastomosis; group II, PA resection and reconstruction with LyoPA allograft; group III, PA resection and reconstruction with CryoPA allograft. Dogs were evaluated 4 weeks after surgery, and the status of the graft and vascular anastomosis were examined macroscopically and microscopically. No clinical, radiologic, or blood-gas abnormalities were observed during the study. The mean pulmonary artery pressure (MPAP) in group III increased significantly at the end of the study compared with baseline (P=0.02) and final [P=0.007, two-way repeat-measures analysis of variance (RM ANOVA)] values. Pulmonary vascular resistance of groups II and III increased immediately after reperfusion and also at the end of the study compared to baseline. The increase shown by group III vs group I was significant only if compared with after surgery and study end (P=0.016 and P=0.005, respectively, two-way RM ANOVA). Microscopically, permeability was reduced by ≤75% in group III. In conclusion, substitution of PAs with LyoPA grafts is technically feasible and clinically promising.

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.

Neutrophil extracellular traps are pathogenic in primary graft dysfunction after lung transplantation

RATIONALE

Primary graft dysfunction (PGD) causes early mortality after lung transplantation and may contribute to late graft failure. No effective treatments exist. The pathogenesis of PGD is unclear, although both neutrophils and activated platelets have been implicated. We hypothesized that neutrophil extracellular traps (NETs) contribute to lung injury in PGD in a platelet-dependent manner.

OBJECTIVES

To study NETs in experimental models of PGD and in lung transplant patients.

METHODS

Two experimental murine PGD models were studied: hilar clamp and orthotopic lung transplantation after prolonged cold ischemia (OLT-PCI). NETs were assessed by immunofluorescence microscopy and ELISA. Platelet activation was inhibited with aspirin, and NETs were disrupted with DNaseI. NETs were also measured in bronchoalveolar lavage fluid and plasma from lung transplant patients with and without PGD.

MEASUREMENTS AND MAIN RESULTS

NETs were increased after either hilar clamp or OLT-PCI compared with surgical control subjects. Activation and intrapulmonary accumulation of platelets were increased in OLT-PCI, and platelet inhibition reduced NETs and lung injury, and improved oxygenation. Disruption of NETs by intrabronchial administration of DNaseI also reduced lung injury and improved oxygenation. In bronchoalveolar lavage fluid from human lung transplant recipients, NETs were more abundant in patients with PGD.

CONCLUSIONS

NETs accumulate in the lung in both experimental and clinical PGD. In experimental PGD, NET formation is platelet-dependent, and disruption of NETs with DNaseI reduces lung injury. These data are the first description of a pathogenic role for NETs in solid organ transplantation and suggest that NETs are a promising therapeutic target in PGD.

Lung preconditioning in anesthesia: Review of the literature

Lung injury can arise during or after anesthesia and can lead to a complicated postoperative course with great implications for the patient. Unfortunately, treatment of acute lung injury is at the moment mainly supportive and rates of recovery have not really improved in the recent years. In many cases, lung injury can be anticipated and preventive measures seem possible. This represents a unique challenge to the anesthesiologist, as some new opportunities to reduce the frequency and/or severity of lung injury seem now available. These chances may arise from the potency of preconditioning the lungs before the main injury, with smaller injurious insults. Although preconditioning began to be applicated first on the myocardium, experimental studies have shown potentially beneficial results also for the lungs. This review summarizes the main methods of lung preconditioning that have been tried in experimental studies in the literature and the main mechanisms that are perhaps involved. Emphasis is given in the two main methods of preconditioning that seem readily applicable in the clinical praxis, that is ischemic preconditioning, as well as preconditioning with volatile anesthetics. The few, but interesting clinical studies are also summarized and the future research points in this evolving field of anesthesia are stressed.

Primary graft dysfunction

Primary graft dysfunction (PGD) is a syndrome encompassing a spectrum of mild to severe lung injury that occurs within the first 72 hours after lung transplantation. PGD is characterized by pulmonary edema with diffuse alveolar damage that manifests clinically as progressive hypoxemia with radiographic pulmonary infiltrates. In recent years, new knowledge has been generated on risks and mechanisms of PGD. Following ischemia and reperfusion, inflammatory and immunological injury-repair responses appear to be key controlling mechanisms. In addition, PGD has a significant impact on short- and long-term outcomes; therefore, the choice of donor organ is impacted by this potential adverse consequence. Improved methods of reducing PGD risk and efforts to safely expand the pool are being developed. Ex vivo lung perfusion is a strategy that may improve risk assessment and become a promising platform to implement treatment interventions to prevent PGD. This review details recent updates in the epidemiology, pathophysiology, molecular and genetic biomarkers, and state-of-the-art technical developments affecting PGD.

Biomarkers of lung injury in primary graft dysfunction following lung transplantation

Primary graft dysfunction, a form of reperfusion pulmonary edema that occurs early after lung transplantation, shares key clinical and pathological features with acute lung injury and its more severe form, the acute respiratory distress syndrome. However, in contrast to acute lung injury/acute respiratory distress syndrome, in which biomarkers in plasma, urine and lung edema fluid have prognostic and pathogenetic value, the role of biomarkers in primary graft dysfunction has been less thoroughly explored. This review summarizes human and animal studies on biomarkers in primary graft dysfunction, including cytokines and markers of acute inflammation, VEGF, endothelial markers and adhesion molecules, markers of coagulation and fibrinolysis and markers of lung epithelial injury. Similarities to the literature in acute lung injury/acute respiratory distress syndrome are highlighted where appropriate, and future directions for research on the role of biomarkers in primary graft dysfunction are suggested.

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.

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.

Differential effects of nitric oxide synthesis on pulmonary vascular function during lung ischemia-reperfusion injury

Lung ischemia-reperfusion (IR) injury causes alveolar, epithelial and endothelial cell dysfunction which often results in decreased alveolar perfusion, characteristic of an acute respiratory distress syndrome. Nitric oxide (NO) from endothelium-derived NO synthase (eNOS) helps maintain a low pulmonary vascular resistance. Paradoxically, during acute lung injury, overproduction of NO via inducible NO synthase (iNOS) and oxidative stress lead to reactive oxygen and nitrogen species (ROS and RNS) formation and vascular dysfunction. RNS potentiate vascular and cellular injury by oxidation, by decreasing NO bioavailability, and by regulating NOS isoforms. RNS potentiate their own production by uncoupling NO production through eNOS by oxidation and disruption of Akt-mediated phosphorylation of eNOS. This review focuses on effects of NO which cause vascular dysfunction in the unique environment of the lung and presents a hypothesis for interplay between eNOS and iNOS activation with implications for development of new strategies to treat vascular dysfunction associated with IR.

Platelets influence vascularized organ transplants from start to finish

This review relates the basic functions of platelets to specific aspects of organ allograft rejection. Platelet activation can occur in the donor or recipient before transplantation as well as during antibody- and cell-mediated rejection. Biopsies taken during organ procurement from cadaver donors have documented that activated platelets are attached to vascular endothelial cells or leukocytes. In addition, many patients waiting for transplants have activated platelets due to the diseases that lead to organ failure or as a result of interventions used to support patients before and during transplantation. The contribution of platelets to hyperacute rejection of both allografts and xenografts is well recognized. Intravascular aggregates of platelets can also be prominent in experimental and clinical transplants that undergo acute antibody or cell-mediated rejection. In acute rejection, platelets can recruit mononuclear cells by secretion of chemokines. After contact, monocytes, macrophages and T cells interact with platelets through receptor/ligand pairs, including P-selectin/PSGL-1 and CD40/CD154. There is a potential for therapy to inhibit platelet mediated immune stimulation, but it is counterbalanced by the need to maintain coagulation in the perioperative period.

Blockade of receptor for advanced glycation end product attenuates pulmonary reperfusion injury in mice

OBJECTIVE

The receptor for advanced glycation end products (RAGE) is expressed at high levels in the lung, particularly in type 1 alveolar cells, and has been shown to amplify injury triggered by acute stress. Previous studies suggest serum concentrations of soluble RAGE increase during pulmonary reperfusion injury after transplantation. RAGE blockade has been shown to suppress hepatic and cardiac ischemia and reperfusion injury in mice. Thus we tested the hypothesis that RAGE mediates tissue-injury mechanisms in ischemia and reperfusion injury in the lung.

METHODS

C57BL/6 mice were subjected to 30 minutes of pulmonary ischemia by clamping the left hilum, followed by 60 minutes of reperfusion. Lung function was assessed by means of blood gas analysis, and capillary leak was assessed by injecting fluorescein isothiocyanate-labeled albumin and comparing fluorescence in bronchial lavage fluid with that in serum. Histologic analysis of the lung was performed by a pathologist naive to the experimental conditions.

RESULTS

In animals subjected to RAGE blockade, significant increases in Po(2) (108 vs 73 mm Hg, P = .0094) and more than 3-fold decrease in capillary leak Relative Fluorescent Units (RFU, 6.12 vs 1.75; P = .001) were observed. Histologic examination revealed significant injury reduction in soluble RAGE-treated animals versus control animals. RAGE knockout mice exhibited a protected phenotype when exposed to pulmonary ischemia and reperfusion. Additionally, interleukin 8 production and nuclear factor kappaB activation were increased in control mice.

CONCLUSION

Abrogation of RAGE signaling attenuates pulmonary ischemia and reperfusion injury. This study suggests that RAGE might play a central role in pulmonary reperfusion injury and in transplantation and that blockade of RAGE might offer a potential target to abrogate pulmonary reperfusion injury in clinical transplantation.

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.

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.

Circulating adhesion molecules during kidney allograft reperfusion

Adhesion molecule expression is an important event during early transplant failure. The aim of the present study was to examine the release of adhesion molecules during the first minutes of kidney allograft reperfusion in relation to delayed graft function and acute graft rejection. We enrolled 49 renal transplant recipients, including 13 cases of delayed graft function (DGF) and 11 cases of acute graft rejection (AR). Plasma concentrations of E-selectin, VCAM-1 and ICAM-1 after 3 min of reperfusion were significantly higher than in the iliac vein before reperfusion. There was no statistically significant difference between patients with and without DGF as regards E-selectin, VCAM-1 and ICAM-1 concentrations in the iliac vein before and in the renal vein after 3 min of reperfusion. Concentrations of adhesion molecules in the iliac vein before reperfusion and in the renal vein after 3 min of reperfusion did not differ significantly between patients with and without AR except for ICAM-1 iliac vein concentration which was significantly increased in AR patients. Plasma levels of E-selectin, ICAM-1 and VCAM-1 were increased after kidney allograft reperfusion. Moreover, elevated serum levels of ICAM-1 before transplantation correlated with subsequent acute kidney allograft rejection. The results suggest that elevated ICAM-1 levels may be implicated in acute graft rejection.