Ex vivo rehabilitation of non-heart-beating donor lungs in preclinical porcine model: delayed perfusion results in superior lung function

The endothelium: gatekeeper to lung ischemia-reperfusion injury

The success of lung transplantation is limited by the high rate of primary graft dysfunction due to ischemia-reperfusion injury (IRI). Lung IRI is characterized by a robust inflammatory response, lung dysfunction, endothelial barrier disruption, oxidative stress, vascular permeability, edema, and neutrophil infiltration. These events are dependent on the health of the endothelium, which is a primary target of IRI that results in pulmonary endothelial barrier dysfunction. Over the past 10 years, research has focused more on the endothelium, which is beginning to unravel the multi-factorial pathogenesis and immunologic mechanisms underlying IRI. Many important proteins, receptors, and signaling pathways that are involved in the pathogenesis of endothelial dysfunction after IR are starting to be identified and targeted as prospective therapies for lung IRI. In this review, we highlight the more significant mediators of IRI-induced endothelial dysfunction discovered over the past decade including the extracellular glycocalyx, endothelial ion channels, purinergic receptors, kinases, and integrins. While there are no definitive clinical therapies currently available to prevent lung IRI, we will discuss potential clinical strategies for targeting the endothelium for the treatment or prevention of IRI. The accruing evidence on the essential role the endothelium plays in lung IRI suggests that promising endothelial-directed treatments may be approaching the clinic soon. The application of therapies targeting the pulmonary endothelium may help to halt this rapid and potentially fatal injury.

Composition of ex vivo perfusion solutions and kinetics define differential cytokine/chemokine secretion in a porcine cardiac arrest model of lung preservation

Background

Ex vivo lung perfusion (EVLP) uses continuous normothermic perfusion to reduce ischemic damage and to improve post-transplant outcomes, specifically for marginal donor lungs after the donation after circulatory death. Despite major efforts, the optimal perfusion protocol and the composition of the perfusate in clinical lung transplantation have not been identified. Our study aims to compare the concentration levels of cytokine/chemokine in different perfusion solutions during EVLP, after 1 and 9 h of cold static preservation (CSP) in a porcine cardiac arrest model, and to correlate inflammatory parameters to oxygenation capacities.

Methods

Following cardiac arrest, the lungs were harvested and were categorized into two groups: immediate (I-EVLP) and delayed EVLP (D-EVLP), after 1 and 9 h of CSP, respectively. The D-EVLP lungs were perfused with either Steen or modified Custodiol-N solution containing only dextran (CD) or dextran and albumin (CDA). The cytokine/chemokine levels were analyzed at baseline (0 h) and after 1 and 4 h of EVLP using Luminex-based multiplex assays.

Results

Within 4 h of EVLP, the concentration levels of TNF-α, IL-6, CXCL8, IFN-γ, IL-1α, and IL-1β increased significantly (P < 0.05) in all experimental groups. The CD solution contained lower concentration levels of TNF-α, IL-6, CXCL8, IFN-γ, IL-2, IL-12, IL-10, IL-4, IL-1RA, and IL-18 (P < 0.05) compared with those of the Steen solution. The concentration levels of all experimental groups have correlated negatively with the oxygenation capacity values (P < 0.05). Protein concentration levels did not reach statistical significance for I-EVLP vs. D-EVLP and CD vs. CDA solutions.

Conclusion

In a porcine cardiac arrest model, a longer period of CSP prior to EVLP did not result in an enhanced protein secretion into perfusates. The CD solution reduced the cytokine/chemokine secretion most probably by iron chelators and/or by the protecting effects of dextran. Supplementing with albumin did not further reduce the cytokine/chemokine secretion into perfusates. These findings may help in optimizing the preservation procedure of the lungs, thereby increasing the donor pool of organs.

Maximizing organs for donation: the potential for ex situ normothermic machine perfusion

Currently, there is a shortfall in the number of suitable organs available for transplant resulting in a high number of patients on the active transplant waiting lists worldwide. To address this shortfall and increase the utilization of donor organs, the acceptance criteria for donor organs is gradually expanding including increased use of organs from donation after circulatory death. Use of such extended criteria donors and exposure of organs to more prolonged periods of warm or cold ischaemia also increases the risk of primary graft dysfunction occurring. Normothermic machine perfusion (NMP) offers a unique opportunity to objectively assess donor organ function outside the donor body and potentially recondition those deemed unsuitable on initial evaluation prior to implantation in the recipient. Furthermore, NMP provides a platform to support the use of established and novel therapeutics delivered directly to the organ, without the need to worry about potential deleterious 'off-target' side effects typically considered when treating the whole patient. This review will explore some of the novel therapeutics currently being added to perfusion platforms during NMP experimentally in an attempt to improve organ function and post-transplant outcomes.

Changes in the levels of free sialic acid during ex vivo lung perfusion do not correlate with pulmonary function. Experimental model

BACKGROUND

Ex vivo lung perfusion (EVLP) constitutes a tool with great research potential due to its advantages over in vivo and in vitro models. Despite its important contribution to lung reconditioning, this technique has the disadvantage of incurring high costs and can induce pulmonary endothelial injury through perfusion and ventilation. The pulmonary endothelium is made up of endothelial glycocalyx (EG), a coating of proteoglycans (PG) on the luminal surface. PGs are glycoproteins linked to terminal sialic acids (Sia) that can affect homeostasis with responses leading to edema formation. This study evaluated the effect of two ex vivo perfusion solutions on lung function and endothelial injury.

METHODS

We divided ten landrace swine into two groups and subjected them to EVLP for 120 min: Group I (n = 5) was perfused with Steen® solution, and Group II (n = 5) was perfused with low-potassium dextran-albumin solution. Ventilatory mechanics, histology, gravimetry, and sialic acid concentrations were evaluated.

RESULTS

Both groups showed changes in pulmonary vascular resistance and ventilatory mechanics (p < 0.05, Student's t-test). In addition, the lung injury severity score was better in Group I than in Group II (p < 0.05, Mann-Whitney U); and both groups exhibited a significant increase in Sia concentrations in the perfusate (p < 0.05 t-Student) and Sia immunohistochemical expression.

CONCLUSIONS

Sia, as a product of EG disruption during EVLP, was found in all samples obtained in the system; however, the changes in its concentration showed no apparent correlation with lung function.

Single-center experience of ex vivo lung perfusion and subsequent lung transplantation

BACKGROUND

The safety of lung transplantation using ex vivo lung perfusion (EVLP) has been confirmed in multiple clinical studies; however, limited evidence is currently available regarding the potential effects of EVLP on posttransplant graft complications and survival with mid- to long-term follow-up. In this study, we reviewed our institutional data to better understand the impact of EVLP.

METHODS

Lungs placed on EVLP from 2014 through 2020 and transplant outcomes were retrospectively analyzed. Data were compared between lungs transplanted and declined after EVLP, between patients with severe primary graft dysfunction (PGD3) and no PGD3 after EVLP, and between matched patients with lungs transplanted with and without EVLP.

RESULTS

In total, 98 EVLP cases were performed. Changes in metabolic indicators during EVLP were correlated with graft quality and transplantability, but not changes in physiological parameters. Among 58 transplanted lungs after EVLP, PGD3 at 72 h occurred in 36.9% and was associated with preservation time, mechanical support prior to transplant, and intraoperative transfusion volume. Compared with patients without EVLP, patients who received lungs screened with EVLP had a higher incidence of PGD3 and longer ICU and hospital stays. Lung grafts placed on EVLP exhibited a significantly higher chance of developing airway anastomotic ischemic injury by 30 days posttransplant. Acute and chronic graft rejection, pulmonary function, and posttransplant survival were not different between patients with lungs screened on EVLP versus lungs with no EVLP.

CONCLUSION

EVLP use is associated with an increase of early posttransplant adverse events, but graft functional outcomes and patient survival are preserved.

Steen solution protects pulmonary microvascular endothelial cells and preserves endothelial barrier after lipopolysaccharide-induced injury

OBJECTIVES

Acute respiratory distress syndrome represents the devastating result of acute lung injury, with high mortality. Limited methods are available for rehabilitation of lungs affected by acute respiratory distress syndrome. Our laboratory has demonstrated rehabilitation of sepsis-injured lungs via normothermic ex vivo and in vivo perfusion with Steen solution (Steen). However, mechanisms responsible for the protective effects of Steen remain unclear. This study tests the hypothesis that Steen directly attenuates pulmonary endothelial barrier dysfunction and inflammation induced by lipopolysaccharide.

METHODS

Primary pulmonary microvascular endothelial cells were exposed to lipopolysaccharide for 4 hours and then recovered for 8 hours in complete media (Media), Steen, or Steen followed by complete media (Steen/Media). Oxidative stress, chemokines, permeability, interendothelial junction proteins, and toll-like receptor 4-mediated pathways were assessed in pulmonary microvascular endothelial cells using standard methods.

RESULTS

Lipopolysaccharide treatment of pulmonary microvascular endothelial cells and recovery in Media significantly induced reactive oxygen species, lipid peroxidation, expression of chemokines (eg, chemokine [C-X-C motif] ligand 1 and C-C motif chemokine ligand 2) and cell adhesion molecules (P-selectin, E-selectin, and vascular cell adhesion molecule 1), permeability, neutrophil transmigration, p38 mitogen-activated protein kinase and nuclear factor kappa B signaling, and decreased expression of tight and adherens junction proteins (zonula occludens-1, zonula occludens-2, and vascular endothelial-cadherin). All of these inflammatory pathways were significantly attenuated after recovery of pulmonary microvascular endothelial cells in Steen or Steen/Media.

CONCLUSIONS

Steen solution preserves pulmonary endothelial barrier function after lipopolysaccharide exposure by promoting an anti-inflammatory environment via attenuation of oxidative stress, toll-like receptor 4-mediated signaling, and conservation of interendothelial junctions. These protective mechanisms offer insight into the advancement of methods for in vivo lung perfusion with Steen for the treatment of severe acute respiratory distress syndrome.

Evaluation of 10°C as the optimal storage temperature for aspiration-injured donor lungs in a large animal transplant model

BACKGROUND

Our recent work has challenged 4°C as an optimal lung preservation temperature by showing storage at 10°C to allow for the extension of preservation periods. Despite these findings, the impact of 10°C storage has not been evaluated in the setting of injured donor lungs.

METHODS

Aspiration injury was created through bronchoscopic delivery of gastric juice (pH: 1.8). Injured donor lungs (n = 5/group) were then procured and blindly randomized to storage at 4°C (on ice) or at 10°C (in a thermoelectric cooler) for 12 hours. A third group included immediate transplantation. A left lung transplant was performed thereafter followed by 4 hours of graft evaluation.

RESULTS

After transplantation, lungs stored at 10°C showed significantly better oxygenation when compared to 4°C group (343 ± 43 mm Hg vs 128 ± 76 mm Hg, p = 0.03). Active metabolism occurred during the 12 hours storage period at 10°C, producing cytoprotective metabolites within the graft. When compared to lungs undergoing immediate transplant, lungs preserved at 10°C tended to have lower peak airway pressures (p = 0.15) and higher dynamic lung compliances (p = 0.09). Circulating cell-free mitochondrial DNA within the recipient plasma was significantly lower for lungs stored at 10°C in comparison to those underwent immediate transplant (p = 0.048), alongside a tendency of lower levels of tissue apoptotic cell death (p = 0.075).

CONCLUSIONS

We demonstrate 10°C as a potentially superior storage temperature for injured donor lungs in a pig model when compared to the current clinical standard (4°C) and immediate transplantation. Continuing protective metabolism at 10°C for donor lungs may result in better transplant outcomes.

Novel approaches for long-term lung transplant survival

Allograft failure remains a major barrier in the field of lung transplantation and results primarily from acute and chronic rejection. To date, standard-of-care immunosuppressive regimens have proven unsuccessful in achieving acceptable long-term graft and patient survival. Recent insights into the unique immunologic properties of lung allografts provide an opportunity to develop more effective immunosuppressive strategies. Here we describe advances in our understanding of the mechanisms driving lung allograft rejection and highlight recent progress in the development of novel, lung-specific strategies aimed at promoting long-term allograft survival, including tolerance.

Endothelin-Converting Enzyme 1 and Vascular Endothelial Growth Factor as Potential Biomarkers during Ex Vivo Lung Perfusion with Prolonged Hypothermic Lung-Sparing

Lung transplantation requires optimization of donor's organ use through ex vivo lung perfusion (EVLP) to avoid primary graft dysfunction. Biomarkers can aid in organ selection by providing early evidence of suboptimal lungs during EVLP and thus avoid high-risk transplantations. However, predictive biomarkers of pulmonary graft function such as endothelin-converting enzyme (ECE-1) and vascular endothelial growth factor (VEGF) have not been described under EVLP with standard prolonged hypothermic preservation, which are relevant in situations where lung procurement is difficult or far from the transplantation site. Therefore, this study is aimed at quantifying ECE-1 and VEGF, as well as determining their association with hemodynamic, gasometric, and mechanical ventilatory parameters in a swine model of EVLP with standard prolonged hypothermic preservation. Using a protocol with either immediate (I-) or delayed (D-) initiation of EVLP, ECE-1 levels over time were found to remain constant in both study groups (p > 0.05 RM-ANOVA), while the VEGF protein was higher after prolonged preservation, but it decreased throughout EVLP (p > 0.05 RM-ANOVA). Likewise, hemodynamic, gasometric, mechanical ventilatory, and histological parameters had a tendency to better results after 12 hours of hypothermic preservation in the delayed infusion group.

Custodiol-MP for ex vivo lung perfusion - A comparison in a porcine model of donation after circulatory determination of death

INTRODUCTION

Ex vivo lung perfusion (EVLP) is an established technique to evaluate and eventually recondition lungs prior to transplantation. Custodiol-MP (C-MP) solution is a new solution, designed for clinical machine perfusion, that has been used for kidneys. The aim of this study was to compare the effects of EVLP with Custodiol-MP on lung functional outcomes to the gold standard of EVLP with Steen Solution™.

MATERIAL AND METHODS

In a porcine EVLP model of DCDD (Donation after Circulatory Determination of Death), lungs were perfused with Steen Solution™ (SS, n = 7) or Custodiol-MP solution supplemented with 55 g/l albumin (C-MP, n = 8). Lungs were stored cold for 4 h in low potassium dextran solution and subsequently perfused ex vivo for 4 h. During EVLP pulmonary gas exchange, activities of lactate dehydrogenase (LDH) and alkaline phosphatase (AP) as well as levels of lactate in the perfusate were recorded hourly.

RESULTS

Oxygenation capacity differed significantly between groups (averaged over 4 h: SS 274 ± 178 mmHg; C-MP 284 ± 151 mmHg p = 0.025). Lactate dehydrogenase activities and lactate concentrations were significantly lower in Custodiol-MP perfused lungs.In a porcine model of DCDD with 4 h of EVLP the use of modified Custodiol-MP as perfusion solution was feasible. The use of C-MP showed at least comparable lung functional outcomes to the use of Steen SolutionTM. Furthermore C-MP perfusion resulted in significantly lower lactate dehydrogenase activity and lactate levels in the perfusate and higher oxygenation capacity.

The potential of ex vivo lung perfusion on improving organ quality and ameliorating ischemia reperfusion injury

Allogeneic lung transplantation (LuTx) is considered the treatment of choice for a broad range of advanced, progressive lung diseases resistant to conventional treatment regimens. Ischemia reperfusion injury (IRI) occurring upon reperfusion of the explanted, ischemic lung during implantation remains a crucial mediator of primary graft dysfunction (PGD) and early allo-immune responses. Ex vivo lung perfusion (EVLP) displays an advanced technique aiming at improving lung procurement and preservation. Indeed, previous clinical trials have demonstrated a reduced incidence of PGD following LuTx utilizing EVLP, while long-term outcomes are yet to be evaluated. Mechanistically, EVLP may alleviate donor lung inflammation through reconditioning the injured lung and diminishing IRI through storing the explanted lung in a non-ischemic, perfused, and ventilated status. In this work, we review potential mechanisms of EVLP that may attenuate IRI and improve organ quality. Moreover, we dissect experimental treatment approaches during EVLP that may further attenuate inflammatory events deriving from tissue ischemia, shear forces or allograft rejection associated with LuTx.

Two Hours of In Vivo Lung Perfusion Improves Lung Function in Sepsis-Induced Acute Respiratory Distress Syndrome

Sepsis is the leading cause of acute respiratory distress syndrome (ARDS) in adults and carries a high mortality. Utilizing a previously validated porcine model of sepsis-induced ARDS, we sought to refine our novel therapeutic technique of in vivo lung perfusion (IVLP). We hypothesized that 2 hours of IVLP would provide non-inferior lung rehabilitation compared to 4 hours of treatment. Adult swine (n = 8) received lipopolysaccharide to develop ARDS and were placed on central venoarterial extracorporeal membrane oxygenation. Animals were randomized to 2 vs 4 hours of IVLP. The left pulmonary vessels were cannulated to IVLP using antegrade Steen solution. After IVLP treatment, the left lung was decannulated and reperfused for 4 hours. Total lung compliance and pulmonary venous gases from the right lung (control) and left lung (treatment) were sampled hourly. Biochemical analysis of tissue and bronchioalveolar lavage was performed along with tissue histologic assessment. Throughout IVLP and reperfusion, treated left lung PaO2/FiO2 ratio was significantly higher than the right lung control in the 2-hour group (332.2 ± 58.9 vs 264.4 ± 46.5, P = 0.01). In the 4-hour group, there was no difference between treatment and control lung PaO2/FiO2 ratio (258.5 ± 72.4 vs 253.2 ± 90.3, P = 0.58). Wet-to-dry weight ratios demonstrated reduced edema in the treated left lungs of the 2-hour group (6.23 ± 0.73 vs 7.28 ± 0.61, P = 0.03). Total lung compliance was also significantly improved in the 2-hour group. Two hours of IVLP demonstrated superior lung function in this preclinical model of sepsis-induced ARDS. Clinical translation of IVLP may shorten duration of mechanical support and improve outcomes.

Machine Perfusion of Extended Criteria Donor Organs: Immunological Aspects

Due to higher vulnerability and immunogenicity of extended criteria donor (ECD) organs used for organ transplantation (Tx), the discovery of new treatment strategies, involving tissue allorecognition pathways, is important. The implementation of machine perfusion (MP) led to improved estimation of the organ quality and introduced the possibility to achieve graft reconditioning prior to Tx. A significant number of experimental and clinical trials demonstrated increasing support for MP as a promising method of ECD organ preservation compared to classical static cold storage. MP reduced ischemia-reperfusion injury resulting in the protection from inadequate activation of innate immunity. However, there are no general agreements on MP protocols, and clinical application is limited. The objective of this comprehensive review is to summarize literature on immunological effects of MP of ECD organs based on experimental studies and clinical trials.

Adenosine A2A receptor agonist (regadenoson) in human lung transplantation

BACKGROUND

Currently, there are no clinically approved treatments for ischemia-reperfusion injury after lung transplantation. Pre-clinical animal models have demonstrated a promising efficacy of adenosine _2A receptor (A_2AR) agonists as a treatment option for reducing ischemia-reperfusion injury. The purpose of this human study, is to conduct a Phase I clinical trial for evaluating the safety of continuous infusion of an A_2AR agonist in lung transplant recipients.

METHODS

An adaptive, two-stage continual reassessment trial was designed to evaluate the safety of regadenoson (A_2AR agonist) in the setting of lung transplantation. Continuous infusion of regadenoson was administered to lung transplant recipients that was started at the time of skin incision. Adverse events and dose-limiting toxicities, as pre-determined by a study team and assessed by a clinical team and an independent safety monitor, were the primary end-points for safety in this trial.

RESULTS

Between January 2018 and March 2019, 14 recipients were enrolled in the trial. Of these, 10 received the maximum infused dose of 1.44 µg/kg/min for 12 hours. No dose-limiting toxicities were observed. The steady-state plasma regadenoson levels sampled before the reperfusion of the first lung were 0.98 ± 0.46 ng/ml. There were no mortalities within 30 days.

CONCLUSIONS

Regadenoson, an A_2AR agonist, can be safely infused in the setting of lung transplantation with no dose-limiting toxicities or drug-related mortality. Although not powered for the evaluation of secondary end-points, the results of this trial and the outcome of pre-clinical studies warrant further investigation with a Phase II randomized controlled trial.

Use of modified Custodiol-N as perfusion solution in ex vivo lung perfusion

OBJECTIVES

Ex vivo Lung Perfusion (EVLP) is a promising tool to increase the donor pool for lung transplantation. Custodiol-N solution was originally designed for organ preservation during cold static preservation (CSP) and was successfully used for machine perfusion in kidneys. It was the aim of this study to compare the lung functional outcomes after 4 hours of EVLP using modified Custodiol-N or STEEN Solution^TM as perfusion solution.

METHODS

In a porcine DCD model, lungs were perfused either with STEEN Solution^TM (Standard SS, n=8) or modified Custodiol-N with added 1.1 g/l glucose monohydrate and 50 g/l dextran 40 (CD, n=8). For a third group 7 g/l albumin was supplemented to modified Custodiol-N (CDA, n=8). During four hours of EVLP pulmonary gas exchange and activities of lactate dehydrogenase (LDH) and alkaline phosphatase (AP) in perfusate were recorded.

RESULTS

Lungs that underwent EVLP with modified Custodiol-N showed significantly higher oxygen capacity (ΔpO₂ averaged over four hours of EVLP: SS: 236.28 ± 47.26 mmHg, CD: 402.79 ± 30.33 mmHg, CDA: 414.86 ± 9.77 mmHg) than lungs perfused with STEEN Solution^TM. The addition of albumin did not have a significant effect on lung function but these lungs showed lower wet/dry ratio.

CONCLUSION

In a porcine DCD model of 9 hours CSP followed by four hours of EVLP the use of modified Custodiol-N as perfusion solution was feasible and associated with higher oxygen capacity than STEEN Solution^TM. The addition of albumin seems to further stabilize lung function.

Liang-Ge-San, a Classic Traditional Chinese Medicine Formula, Attenuates Lipopolysaccharide-Induced Acute Lung Injury Through Up-Regulating miR-21

Background: Acute lung injury (ALI) is a life-threatening disease without effective chemotherapy at present. Liang-Ge-San (LGS) is a famous traditional Chinese medicine formula, which is used to treat ALI in China. However, only a few studies have addressed the mechanisms of LGS in ALI.

Purpose: To evaluate the anti-inflammatory effects of LGS on lipopolysaccharide (LPS)-induced ALI, and to explore its underlying molecular mechanism.

Methods: Murine RAW264.7 cells were treated with LGS and LPS (1 μg/ml). The generation of IL-6, TNF-α, IL-1β was detected by ELISA. The protein expressions of STAT3 and P-STAT3 (Tyr705) were determined by Western blotting and fluorescence confocal microscopy. STAT3 transcriptional activity was investigated by luciferase reporter gene assay. qPCR was used to detect the expressions of microRNA-21 (miR-21), STAT3, and IL-6. DSS cross-linking assay was used to assess the change of STAT3 dimer. In vivo anti-inflammatory effects of LGS were evaluated in an ALI mouse model induced by tracheal instillation of LPS (3 mg/kg). The anti-ALI effects were evaluated by ELISA, qPCR, Western blotting, BCA, and H&E assays.

Results: LGS suppressed LPS-stimulated IL-6, TNF-α, and IL-1β generation in murine macrophages RAW264.7. Moreover, LGS down-regulated protein levels of P-STAT3 (Tyr705) and STAT3, inhibited STAT3 transcriptional activity, and up-regulated miR-21. Furthermore, blockage of miR-21 antagonized the inhibitory effects of LGS on the production of IL-6 and the expressions of P-STAT3 (Tyr705) and STAT3 as well as the formation of STAT3 dimer. Critically, LGS up-regulated the expression of miR-21 and inhibited the protein expressions of STAT3 and P-STAT3 (Tyr705) to reduce the release of IL-6 and inflammatory cell infiltration as well as the degree of edema in LPS-induced ALI mice.

Conclusion: LGS inhibited LPS-induced ALI through up-regulating miR-21 and subsequently inhibiting the STAT3 signaling pathway, thereby decreasing the release of IL-6.

Effects of immediate versus delayed ex-vivo lung perfusion in a porcine cardiac arrest donation model

OBJECTIVE

Ex-vivo lung perfusion is a promising tool to evaluate and recondition marginal donor lungs usually after a cold static preservation. The concept of continuous organ perfusion is supposed to reduce ischemic damage; however, the optimal perfusion protocol has not been established yet. The aim of this study was to compare immediate ex-vivo lung perfusion (I-EVLP) to delayed ex-vivo lung perfusion (D-EVLP) after a certain cold static preservation period on lung function in a large animal model.

METHODS

In a porcine model, lungs were procured after circulatory death and 60 min of no-touch warm ischemia. Lungs were preserved with single-flush cold low potassium dextran solution and prepared either for I-EVLP (n = 8) or stored cold for 9 h with subsequent D-EVLP (n = 8). Functional outcomes and morphology were compared during 4 h of ex-vivo lung perfusion, using STEEN Solution^TM as perfusion solution.

RESULTS

Pulmonary functional data, perfusate activities of lactate dehydrogenase, alkaline phosphatase, and products of lipid peroxidation did not differ significantly. There was a trend toward lower wet-dry ratio (I-EVLP: 13.4 ± 2.9; D-EVLP: 9.1 ± 2.5) and higher ΔpO₂ in D-EVLP group (I-EVLP: 209 ± 51.6 mmHg; D-EVLP: 236.3 ± 47.3 mmHg).

CONCLUSION

In this donation-after-circulatory-death model, 9 h of cold static preservation followed by ex-vivo lung perfusion results in comparable pulmonary function to I-EVLP as indicated by oxygenation capacities and wet-dry ratio. Our findings indicate that prolonged cold static preservation prior to ex-vivo lung perfusion is as safe and effective as I-EVLP in the procurement of donor lungs.

Multiday maintenance of extracorporeal lungs using cross-circulation with conscious swine

Objectives

Lung remains the least-utilized solid organ for transplantation. Efforts to recover donor lungs with reversible injuries using ex vivo perfusion systems are limited to <24 hours of support. Here, we demonstrate the feasibility of extending normothermic extracorporeal lung support to 4 days using cross-circulation with conscious swine.

Methods

A swine behavioral training program and custom enclosure were developed to enable multiday cross-circulation between extracorporeal lungs and recipient swine. Lungs were ventilated and perfused in a normothermic chamber for 4 days. Longitudinal analyses of extracorporeal lungs (ie, functional assessments, multiscale imaging, cytokine quantification, and cellular assays) and recipient swine (eg, vital signs and blood and tissue analyses) were performed.

Results

Throughout 4 days of normothermic support, extracorporeal lung function was maintained (arterial oxygen tension/inspired oxygen fraction >400 mm Hg; compliance >20 mL/cm H₂O), and recipient swine were hemodynamically stable (lactate <3 mmol/L; pH, 7.42 ± 0.05). Radiography revealed well-aerated lower lobes and consolidation in upper lobes of extracorporeal lungs, and bronchoscopy showed healthy airways without edema or secretions. In bronchoalveolar lavage fluid, granulocyte-macrophage colony-stimulating factor, interleukin (IL) 4, IL-6, and IL-10 levels increased less than 6-fold, whereas interferon gamma, IL-1α, IL-1β, IL-1ra, IL-2, IL-8, IL-12, IL-18, and tumor necrosis factor alpha levels decreased from baseline to day 4. Histologic evaluations confirmed an intact blood–gas barrier and outstanding preservation of airway and alveolar architecture. Cellular viability and metabolism in extracorporeal lungs were confirmed after 4 days.

Conclusions

We demonstrate feasibility of normothermic maintenance of extracorporeal lungs for 4 days by cross-circulation with conscious swine. Cross-circulation approaches could support the recovery of damaged lungs and enable organ bioengineering to improve transplant outcomes.

Reduced-flow ex vivo lung perfusion to rehabilitate lungs donated after circulatory death

BACKGROUND

Current ex vivo lung perfusion (EVLP) protocols aim to achieve perfusion flows of 40% of cardiac output or more. We hypothesized that a lower target flow rate during EVLP would improve graft function and decrease inflammation of donation after circulatory death (DCD) lungs.

METHODS

A porcine DCD and EVLP model was utilized. Two groups (n = 4 per group) of DCD lungs were randomized to target EVLP flows of 40% (high-flow) or 20% (low-flow) predicted cardiac output based on 100 ml/min/kg. At the completion of 4 hours of normothermic EVLP using Steen solution, left lung transplantation was performed, and lungs were monitored during 4 hours of reperfusion.

RESULTS

After transplant, left lung-specific pulmonary vein partial pressure of oxygen was significantly higher in the low-flow group at 3 and 4 hours of reperfusion (3-hour: 496.0 ± 87.7 mm Hg vs. 252.7 ± 166.0 mm Hg, p = 0.017; 4-hour: 429.7 ± 93.6 mm Hg vs. 231.5 ± 178 mm Hg, p = 0.048). Compliance was significantly improved at 1 hour of reperfusion (20.8 ± 9.4 ml/cm H₂O vs. 10.2 ± 3.5 ml/cm H₂O, p = 0.022) and throughout all subsequent time points in the low-flow group. After reperfusion, lung wet-to-dry weight ratio (7.1 ± 0.7 vs. 8.8 ± 1.1, p = 0.040) and interleukin-1β expression (927 ± 300 pg/ng protein vs. 2,070 ± 874 pg/ng protein, p = 0.048) were significantly reduced in the low-flow group.

CONCLUSIONS

EVLP of DCD lungs with low-flow targets of 20% predicted cardiac output improves lung function, reduces edema, and attenuates inflammation after transplant. Therefore, EVLP for lung rehabilitation should use reduced flow rates of 20% predicted cardiac output.

Mesenchymal Stem Cell Therapy Facilitates Donor Lung Preservation by Reducing Oxidative Damage during Ischemia

Lung transplantation is a lifesaving therapy for people living with severe, life-threatening lung disease. The high mortality rate among patients awaiting transplantation is mainly due to the low percentage of lungs that are deemed acceptable for implantation. Thus, the current shortage of lung donors may be significantly reduced by implementing different therapeutic strategies which facilitate both organ preservation and recovery. Here, we studied whether the anti-inflammatory effect of human umbilical cord-derived mesenchymal stem cells (HUCPVCs) increases lung availability by improving organ preservation. We developed a lung preservation rat model that mimics the different stages by which donor organs must undergo before implantation. The therapeutic schema was as follows: cardiac arrest, warm ischemia (2 h at room temperature), cold ischemia (1.5 h at 4°C, with Perfadex), and normothermic lung perfusion with ventilation (Steen solution, 1 h). After 1 h of warm ischemia, HUCPVCs (1 × 10⁶ cells) or vehicle was infused via the pulmonary artery. Physiologic data (pressure-volume curves) were acquired right after the cardiac arrest and at the end of the perfusion. Interestingly, although lung edema did not change among groups, lung compliance dropped to 34% in the HUCPVC-treated group, while the vehicle group showed a stronger reduction (69%, p < 0.0001). Histologic assessment demonstrated less overall inflammation in the HUCPVC-treated lungs. In addition, MPO activity, a neutrophil marker, was reduced by 41% compared with vehicle (p < 0.01). MSC therapy significantly decreased tissue oxidative damage by controlling reactive oxygen species production. Accordingly, catalase and superoxide dismutase enzyme activities remained at baseline levels. In conclusion, these results demonstrate that the anti-inflammatory effect of MSCs protects donor lungs against ischemic injury and postulates MSC therapy as a novel tool for organ preservation.

Ten year follow-up of lung transplantations using initially rejected donor lungs after reconditioning using ex vivo lung perfusion

Background

In 2006 and 2007 we performed double lung transplantation with marginal donor lungs assessed and reconditioned by Ex Vivo Lung Perfusion (EVLP), using a technique developed by Professor Stig Steen. Here we present a 10-year follow-up comparing the outcomes of lung transplantations performed at our clinic using EVLP lungs vs. conventional lungs.

Method

Between 2006 and 2007, 21 patients (6 EVLP, 15 conventional) underwent double lung transplantation (LTx) with follow-up on May 2017 at Lund University Hospital, Sweden. Pulmonary function was measured at 3/6/12 months, and annually thereafter for a period of 10 years in addition to survival and freedom from chronic lung allograft dysfunction (CLAD) being analyzed.

Results

Regarding Forced Expiratory Volume in 1 s (FEV1) and 6MWT at 3, 6, and 12 months and annually thereafter, no difference in median FEV1 nor 6MWT was found for EVLP-LTx vs. conventional-LTx (p > 0.05). No difference was shown in post-operative survival between EVLP-LTx vs. conventional LTx for patients with an overall survival up to 10-years (p > 0.05). The same pattern was shown in sub analyses for patients with a limited survival up to 1 and 5 years (p > 0.05).

Conclusion

No superiority was found in conventional-LTx over EVLP-LTx, neither in long-term survival nor pulmonary function. No difference in CLAD-free survival was seen between the two groups. We believe that EVLP is a safe and effective method to use in LTx, greatly increasing the donor pool by improving marginal lungs and providing an objective assessment of the viability of marginal donor lungs.

Regeneration of severely damaged lungs using an interventional cross-circulation platform

The number of available donor organs limits lung transplantation, the only lifesaving therapy for the increasing population of patients with end-stage lung disease. A prevalent etiology of injury that renders lungs unacceptable for transplantation is gastric aspiration, a deleterious insult to the pulmonary epithelium. Currently, severely damaged donor lungs cannot be salvaged with existing devices or methods. Here we report the regeneration of severely damaged lungs repaired to meet transplantation criteria by utilizing an interventional cross-circulation platform in a clinically relevant swine model of gastric aspiration injury. Enabled by cross-circulation with a living swine, prolonged extracorporeal support of damaged lungs results in significant improvements in lung function, cellular regeneration, and the development of diagnostic tools for non-invasive organ evaluation and repair. We therefore propose that the use of an interventional cross-circulation platform could enable recovery of otherwise unsalvageable lungs and thus expand the donor organ pool.

Ex Vivo Assessment of Porcine Donation After Circulatory Death Lungs That Undergo Increasing Warm Ischemia Times

Background

Increased utilization of donation after circulatory death (DCD) lungs may help alleviate the supply/demand mismatch between available donor organs and lung transplant candidates. Using an established porcine DCD model, we sought to determine the effect of increasing warm ischemia time (WIT) after circulatory arrest on lung function during ex vivo lung perfusion (EVLP).

Methods

Porcine donors (n = 15) underwent hypoxic cardiac arrest, followed by 60, 90, or 120 minutes of WIT before procurement and 4 hours of normothermic EVLP. Oxygenation, pulmonary artery pressure, airway pressure, and compliance were measured hourly. Lung injury scores were assessed histologically after 4 hours of EVLP.

Results

After EVLP, all 3 groups met all the criteria for transplantation, except for 90-minute WIT lungs, which had a mean pulmonary artery pressure increase greater than 15%. There were no significant differences between groups as assessed by final oxygenation capacity, as well as changes in pulmonary artery pressure, airway pressure, or lung compliance. Histologic lung injury scores as well as lung wet-to-dry weight ratios did not significantly differ between groups.

Conclusions

These results suggest that longer WIT alone (up to 120 minutes) does not predict worse lung function at the conclusion of EVLP. Expanding acceptable WIT after circulatory death may eventually allow for increased utilization of DCD lungs in procurement protocols.

Increasing circulating sphingosine-1-phosphate attenuates lung injury during ex vivo lung perfusion

BACKGROUND

Sphingosine-1-phosphate regulates endothelial barrier integrity and promotes cell survival and proliferation. We hypothesized that upregulation of sphingosine-1-phosphate during ex vivo lung perfusion would attenuate acute lung injury and improve graft function.

METHODS

C57BL/6 mice (n = 4-8/group) were euthanized, followed by 1 hour of warm ischemia and 1 hour of cold preservation in a model of donation after cardiac death. Subsequently, mice underwent 1 hour of ex vivo lung perfusion with 1 of 4 different perfusion solutions: Steen solution (Steen, control arm), Steen with added sphingosine-1-phosphate (Steen + sphingosine-1-phosphate), Steen plus a selective sphingosine kinase 2 inhibitor (Steen + sphingosine kinase inhibitor), or Steen plus both additives (Steen + sphingosine-1-phosphate + sphingosine kinase inhibitor). During ex vivo lung perfusion, lung compliance and pulmonary artery pressure were continuously measured. Pulmonary vascular permeability was assessed with injection of Evans Blue dye.

RESULTS

The combination of 1 hour of warm ischemia, followed by 1 hour of cold ischemia created significant lung injury compared with lungs that were immediately harvested after circulatory death and put on ex vivo lung perfusion. Addition of sphingosine-1-phosphate or sphingosine kinase inhibitor alone did not significantly improve lung function during ex vivo lung perfusion compared with Steen without additives. However, group Steen + sphingosine-1-phosphate + sphingosine kinase inhibitor resulted in significantly increased compliance (110% ± 13.9% vs 57.7% ± 6.6%, P < .0001) and decreased pulmonary vascular permeability (33.1 ± 11.9 μg/g vs 75.8 ± 11.4 μg/g tissue, P = .04) compared with Steen alone.

CONCLUSIONS

Targeted drug therapy with a combination of sphingosine-1-phosphate + sphingosine kinase inhibitor during ex vivo lung perfusion improves lung function in a murine donation after cardiac death model. Elevation of circulating sphingosine-1-phosphate via specific pharmacologic modalities during ex vivo lung perfusion may provide endothelial protection in marginal donor lungs leading to successful lung rehabilitation for transplantation.

One-year experience with ex vivo lung perfusion: Preliminary results from a single center

Objective:

To enlarge the donor pool for lung transplantation, an increasing number of extended criteria donor lungs are used. However, in more than 50% of multi-organ donors the lungs are not used. Ex vivo lung perfusion offers a unique possibility to evaluate and eventually recondition the injured donor lungs. The aim of our study was to assess the enlargement of the donor pool and the outcome with extended criteria donor lungs after ex vivo lung perfusion.

Patients and Methods:

Data were prospectively collected in our lung transplant database. We compared the results of lung transplants after ex vivo lung perfusion with those after conventional cold static preservation. In total, 11 extended criteria donor lungs processed with ex vivo lung perfusion and 41 cold static preservation lungs transplanted consecutively between May 2016 and May 2017 were evaluated. Normothermic ex vivo lung perfusion was performed according to the Toronto protocol for 4 h. Cold static preservation lungs were stored in low-potassium dextran solution.

Results:

Ex vivo lung perfusion lungs before procurement had significantly lower PaO2/FiO2 (P/F) ratios and more X-ray abnormalities. There were no statistically significant differences for pre-donation ventilation time, smoking history, or sex. After reconditioning with ex vivo lung perfusion, 9 out of 11 processed lungs were considered suitable and successfully transplanted. The mean postoperative ventilation time and in-hospital stay were not significantly different in ex vivo lung perfusion and cold static preservation recipients.

Conclusion:

Ex vivo lung perfusion can safely be used in the evaluation of lungs initially considered not suitable for transplantation. The primary outcome was not negatively affected and normothermic ex vivo lung perfusion is a useful tool to increase the usage of potentially transplantable lungs.

Lung transplantation, ex-vivo reconditioning and regeneration: state of the art and perspectives

Lung transplantation is the only therapeutic option for end-stage pulmonary failure. Nevertheless, the shortage of donor pool available for transplantation does not allow to satisfy the requests, thus the mortality on the waiting list remains high. One of the tools to overcome the donor pool shortage is the use of ex-vivo lung perfusion (EVLP) to preserve, evaluate and recondition selected lung grafts not otherwise suitable for transplantation. EVLP is nowadays a clinical reality and have several destinations of use. After a narrative review of the literature and looking at our experience we can assume that one of the chances to improve the outcome of lung transplantation and to overcome the donor pool shortage could be the tissue regeneration of the graft during EVLP and the immunomodulation of the recipient. Both these strategies are performed using mesenchymal stem cells (MSC). The results of the models of lung perfusion with MSC-based cell therapy open the way to a new innovative approach that further increases the potential for using of the lung perfusion platform.

Hydrogen gas inhalation during ex vivo lung perfusion of donor lungs recovered after cardiac death

BACKGROUND

Ex vivo lung perfusion (EVLP) is a system that circulates normothermic perfusate into procured lungs, allowing for improved lung function and lung assessment. We investigated whether ventilation with hydrogen gas during EVLP improves the donation after cardiac death lung function and whether this effect persists after actual transplantation.

METHODS

Ten pigs were randomly divided into a control group (n = 5) and a hydrogen group (n = 5). No treatment was administered to induce warm ischemic injury for 1 hour after cardiac arrest, and EVLP was applied in procured lungs for 4 hours. During EVLP, the control group was given room air for respiration, and the hydrogen group was given 2% hydrogen gas. After EVLP, the left lung graft was orthotopically transplanted into the recipient and reperfused for 3 hours. During EVLP and reperfusion, the functional parameters and arterial blood gas analysis (ABGA) were measured every hour. Superoxide dismutase, heme oxygenase, interleukin (IL)-6, IL-10, tumor necrosis factor-α, and nucleotide-binding oligomerization domain-like receptor protein 3 were evaluated in lung tissue after reperfusion. Pathologic evaluations were performed, and the degree of apoptosis was evaluated. The wet/dry ratio was measured.

RESULTS

During EVLP and reperfusion, functional parameters and ABGA results were better in the hydrogen group. The expressions of superoxide dismutase (p = 0.022) and heme oxygenase-1 (p = 0.047) were significantly higher in the hydrogen group. The expressions of IL-6 (p = 0.024) and nucleotide-binding oligomerization domain-like receptor protein 3 (p = 0.042) were higher in the control group, but IL-10 (p = 0.037) was higher in the hydrogen group. The lung injury severity score and the number of apoptotic cells were higher and the degree of pulmonary edema was more severe in the control group than in the hydrogen group.

CONCLUSIONS

Hydrogen gas inhalation during EVLP improved donation after cardiac death lung function via reduction of inflammation and apoptosis, and this effect persisted after LTx.

Mesenchymal stromal cell-derived extracellular vesicles attenuate lung ischemia-reperfusion injury and enhance reconditioning of donor lungs after circulatory death

Background

Lung ischemia-reperfusion (IR) injury after transplantation as well as acute shortage of suitable donor lungs are two critical issues impacting lung transplant patients. This study investigates the anti-inflammatory and immunomodulatory role of human mesenchymal stromal cells (MSCs) and MSC-derived extracellular vesicles (EVs) to attenuate lung IR injury and improve of ex-vivo lung perfusion (EVLP)-mediated rehabilitation in donation after circulatory death (DCD) lungs.

Methods

C57BL/6 wild-type (WT) mice underwent sham surgery or lung IR using an in vivo hilar-ligation model with or without MSCs or EVs. In vitro studies used primary iNKT cells and macrophages (MH-S cells) were exposed to hypoxia/reoxygenation with/without co-cultures with MSCs or EVs. Also, separate groups of WT mice underwent euthanasia and 1 h of warm ischemia and stored at 4 °C for 1 h followed by 1 h of normothermic EVLP using Steen solution or Steen solution containing MSCs or EVs.

Results

Lungs from MSCs or EV-treated mice had significant attenuation of lung dysfunction and injury (decreased edema, neutrophil infiltration and myeloperoxidase levels) compared to IR alone. A significant decrease in proinflammatory cytokines (IL-17, TNF-α, CXCL1 and HMGB1) and upregulation of keratinocyte growth factor, prostaglandin E2 and IL-10 occurred in the BAL fluid from MSC or EV-treated mice after IR compared to IR alone. Furthermore, MSCs or EVs significantly downregulated iNKT cell-produced IL-17 and macrophage-produced HMGB1 and TNF-α after hypoxia/reoxygenation. Finally, EVLP of DCD lungs with Steen solution including MSCs or EVs provided significantly enhanced protection versus Steen solution alone. Co-cultures of MSCs or EVs with lung endothelial cells prevents neutrophil transendothelial migration after exposure to hypoxia/reoxygenation and TNF-α/HMGB1 cytomix.

Conclusions

These results suggest that MSC-derived EVs can attenuate lung inflammation and injury after IR as well as enhance EVLP-mediated reconditioning of donor lungs. The therapeutic benefits of EVs are in part mediated through anti-inflammatory promoting mechanisms via attenuation of immune cell activation as well as prevention of endothelial barrier integrity to prevent lung edema. Therefore, MSC-derived EVs offer a potential therapeutic strategy to treat post-transplant IR injury as well as rehabilitation of DCD lungs.

Users' guide to the surgical literature: how to assess a noninferiority trial

SUMMARY

A well-planned randomized controlled trial (RCT) is the most optimal study design to determine if a novel surgical intervention is any different than a prevailing one. Traditionally, when we want to show that a new surgical intervention is superior to a standard one, we analyze data from an RCT to see if the null hypothesis of "no difference" can be rejected (i.e., the 2 surgical interventions have the same effect). A noninferiority RCT design seeks to determine whether a new intervention is not worse than a prevailing (standard) one within an acceptable margin of risk or benefit, referred to as the "noninferiority margin." In the last decade, we have observed an increase in the publication of noninferiority RCTs. This article explores this type of study design and discusses the tools that can be used to appraise such a study.

In vivo lung perfusion rehabilitates sepsis-induced lung injury

BACKGROUND

Sepsis is the leading cause of lung injury in adults and can lead to acute respiratory distress syndrome (ARDS). Using a novel technique of isolated in vivo lung perfusion (IVLP), we hypothesized that normothermic IVLP will improve oxygenation and compliance in a porcine model of sepsis-induced lung injury.

METHODS

Mature adult swine (n = 8) were administered lipopolysaccharide (LPS; 50 μg/kg over 2 hours) via the external jugular vein, followed by sternotomy and central extracorporeal membrane oxygenation (ECMO) cannulation (right atrium to ascending aorta). The left pulmonary artery (inflow) and left superior and inferior pulmonary veins (outflow) were dissected out and cannulated to deliver isolated perfusion to the left lung. After 4 hours of normothermic IVLP with Steen solution, the left lung then underwent 4 hours of reperfusion after IVLP decannulation. Airway pressures and lung-specific pulmonary vein blood gases from the right lung (LPS control) and left lung (LPS + IVLP) of the same animal were compared.

RESULTS

All animals demonstrated a significant reduction in the ratio of partial pressure of oxygen in arterial blood (PaO₂)/fraction of inspired oxygen (FiO₂) (P/F ratio) and total lung compliance at 2 hours after the start of LPS infusion (mean, 469 ± 19.7 mm Hg vs 222.2 ± 21.4 mm Hg; P < .0001). After reperfusion, 6 animals (75%) exhibited improved lung function, allowing for ECMO decannulation. Lung-specific oxygenation was superior in the left lung after 4 hours of reperfusion (mean, 310.5 ± 54.7 mm Hg vs 201.1 ± 21.7 mm Hg; P = .01). Similarly, total lung compliance improved after IVLP of the left lung. The lung wet weight to dry weight ratio demonstrated reduced edema in rehabilitated left lungs (mean, 6.5 ± 0.3 vs 7.5 ± 0.4; P = .04).

CONCLUSIONS

IVLP successfully rehabilitated LPS-injured lungs compared to ECMO support alone in this preclinical porcine model.

Pharmacological Reconditioning of Marginal Donor Rat Lungs Using Inhibitors of Peroxynitrite and Poly (ADP-ribose) Polymerase During Ex Vivo Lung Perfusion

BACKGROUND

Donor lungs obtained after prolonged warm ischemia (WI) may be unsuitable for transplantation due to the risk of reperfusion injury, but could be reconditioned using ex-vivo lung perfusion (EVLP). Key processes of reperfusion injury include the formation of reactive oxygen species (ROS)/nitrogen species (RNS) and the activation of poly(adenosine diphosphate-ribose) polymerase (PARP). We explored whether rat lungs obtained after WI could be reconditioned during EVLP using the ROS/RNS scavenger Mn(III)-tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) or the PARP inhibitor 3-aminobenzamide (3-AB).

METHODS

Rat lungs obtained after 3 hours cold ischemia (CI group, control), or 1 hour WI plus 2 hours CI (WI group) were placed in an EVLP circuit for normothermic perfusion for 3 hours. Lungs retrieved after WI were treated or not with 3-AB (1 mg/mL) or MnTBAP (0.3 mg/mL), added to the perfusate. Measurements included physiological variables (lung compliance, vascular resistance, oxygenation capacity), lung weight gain, levels of proteins, lactate dehydrogenase, protein carbonyl (marker of ROS), 3-nitrotyrosine (marker of RNS), poly(adenosine diphosphate-ribose) (PAR, marker of PARP activation) and IL-6, in the bronchoalveolar lavage or the lung tissue, and histology.

RESULTS

In comparison to the CI group, the lungs from the WI group displayed higher protein carbonyls, 3-nitrotyrosine, PAR, lactate dehydrogenase and proteins in bronchoalveolar lavage, lung weight gain, perivascular edema, as well as reduced static compliance, but similar oxygenation. All these alterations were markedly attenuated by 3-AB and MnTBAP.

CONCLUSIONS

After EVLP, lungs obtained after WI exhibit oxidative stress, PARP activation, and tissue injury, which are suppressed by pharmacological inhibitors of ROS/RNS and PARP.

Models of Lung Transplant Research: a consensus statement from the National Heart, Lung, and Blood Institute workshop

Lung transplantation, a cure for a number of end-stage lung diseases, continues to have the worst long-term outcomes when compared with other solid organ transplants. Preclinical modeling of the most common and serious lung transplantation complications are essential to better understand and mitigate the pathophysiological processes that lead to these complications. Various animal and in vitro models of lung transplant complications now exist and each of these models has unique strengths. However, significant issues, such as the required technical expertise as well as the robustness and clinical usefulness of these models, remain to be overcome or clarified. The National Heart, Lung, and Blood Institute (NHLBI) convened a workshop in March 2016 to review the state of preclinical science addressing the three most important complications of lung transplantation: primary graft dysfunction (PGD), acute rejection (AR), and chronic lung allograft dysfunction (CLAD). In addition, the participants of the workshop were tasked to make consensus recommendations on the best use of these complimentary models to close our knowledge gaps in PGD, AR, and CLAD. Their reviews and recommendations are summarized in this report. Furthermore, the participants outlined opportunities to collaborate and directions to accelerate research using these preclinical models.

Ex Vivo Lung Perfusion Rehabilitates Sepsis-Induced Lung Injury

BACKGROUND

Sepsis is the number one cause of lung injury in adults. Ex vivo lung perfusion (EVLP) is gaining clinical acceptance for donor lung evaluation and rehabilitation and may expand the use of marginal organs for transplantation. We hypothesized that 4 hours of normothermic EVLP would improve compliance and oxygenation in a porcine model of sepsis-induced lung injury.

METHODS

We used intravenous lipopolysaccharide (LPS) to induce a systemic inflammatory response in a porcine model of lung injury. Two groups of 4 animals each received a 2-hour infusion of LPS through the external jugular vein. Serial measurements of blood gases were performed every 30 minutes until the partial pressure of oxygen/fraction of inspired oxygen ratio dropped below 150 on two consecutive readings. Lungs were then randomized to treatment with 4 hours of normothermic EVLP with STEEN Solution (XVIVO Perfusion Inc, Englewood, CO) or 4 additional hours of in vivo perfusion (control). Airway pressures and blood gases were recorded for calculation of dynamic lung compliance and partial pressure of oxygen/fraction of inspired oxygen ratios. EVLP was performed with hourly recruitment maneuvers and oxygen challenge.

RESULTS

All animals reached a partial pressure of oxygen/fraction of inspired oxygen ratio of less than 150 mm Hg within 3 hours after start of the LPS infusion. Oxygenation and compliance in the control animals continued to decline during the 4-hour in vivo perfusion period, and 3 of the 4 animals died of severe hypoxia within 4 hours. The EVLP group demonstrated significant improvements hour 1 to hour 4 in oxygenation (365.8 ± 53.0 vs 584.4 ± 21.0 mm Hg, p = 0.02) and dynamic compliance (9.0 ± 2.8 vs 15.0 ± 3.6, p = 0.02 mL/cm H₂O).

CONCLUSIONS

EVLP successfully rehabilitated LPS-induced lung injury in this preclinical porcine model and may thus provide a means to rehabilitate many types of acute lung injury.

Lungs donated after circulatory death and prolonged warm ischemia are transplanted successfully after enhanced ex vivo lung perfusion using adenosine A2B receptor antagonism

OBJECTIVE

The current supply of acceptable donor lungs is not sufficient for the number of patients awaiting transplantation. We hypothesized that ex vivo lung perfusion (EVLP) with targeted drug therapy would allow successful rehabilitation and transplantation of donation after circulatory death lungs exposed to 2 hours of warm ischemia.

METHODS

Donor porcine lungs were procured after 2 hours of warm ischemia postcardiac arrest and subjected to 4 hours of cold preservation or EVLP. ATL802, an adenosine A_2B receptor antagonist, was administered to select groups. Four groups (n = 4/group) were randomized: cold preservation (Cold), cold preservation with ATL802 during reperfusion (Cold + ATL802), EVLP (EVLP), and EVLP with ATL802 during ex vivo perfusion (EVLP + ATL802). Lungs subsequently were transplanted, reperfused, and assessed by measuring dynamic lung compliance and oxygenation capacity.

RESULTS

EVLP + ATL802 significantly improved dynamic lung compliance compared with EVLP (25.0 ± 1.8 vs 17.0 ± 2.4 mL/cmH₂O, P = .04), and compared with cold preservation (Cold: 12.2 ± 1.3, P = .004; Cold + ATL802: 10.6 ± 2.0 mL/cmH₂O, P = .002). Oxygenation capacity was highest in EVLP (440.4 ± 37.0 vs Cold: 174.0 ± 61.3 mm Hg, P = .037). No differences in oxygenation or pulmonary edema were observed between EVLP and EVLP + ATL802. A significant decrease in interleukin-12 expression in tissue and bronchoalveolar lavage was identified between groups EVLP and EVLP + ATL802, along with less neutrophil infiltration.

CONCLUSIONS

Severely injured donation after circulatory death lungs subjected to 2 hours of warm ischemia are transplanted successfully after enhanced EVLP with targeted drug therapy. Increased use of lungs after uncontrolled donor cardiac death and prolonged warm ischemia may be possible and may improve transplant wait list times and mortality.

Ex Vivo Porcine Organ Perfusion Models as a Suitable Platform for Translational Transplant Research

In transplantation surgery, extending the criteria for organ donation to include organs that may have otherwise been previously discarded has provided the impetus to improve organ preservation. The traditional method of cold static storage (CS) has been tried and tested and is suitable for organs meeting standard criteria donation. Ex vivo machine perfusion is, however, associated with evidence suggesting that it may be better than CS alone and may allow for organ donation criteria to be extended. Much of our knowledge of organ preservation is derived from animal studies. We review ex vivo porcine organ perfusion models and discuss the relevance to the field of transplantation surgery. Following a systematic literature search, only articles that reported on experimental studies with focus on any aspect(s) of ex vivo and porcine perfusion of organs yet limited to the context of organ transplantation surgery were included. The database search and inclusion/exclusion criteria identified 22 journal articles. All 22 articles discussed ex vivo porcine organ perfusion within the context of transplant preservation surgery: 8 liver, 3 kidney, 3 lung, 2 pancreas/islet, 4 discussed a combined liver-kidney multiorgan model, 1 small bowel, and 1 cardiac perfusion model systems. The ex vivo porcine perfusion model is a suitable, reliable, and safe translational research model. It has advantages to investigate organ preservation techniques in a reproducible fashion in order to improve our understanding and has implications to extend the criteria for organ donation.

Airway pressure release ventilation during ex vivo lung perfusion attenuates injury

OBJECTIVE

Critical organ shortages have resulted in ex vivo lung perfusion gaining clinical acceptance for lung evaluation and rehabilitation to expand the use of donation after circulatory death organs for lung transplantation. We hypothesized that an innovative use of airway pressure release ventilation during ex vivo lung perfusion improves lung function after transplantation.

METHODS

Two groups (n = 4 animals/group) of porcine donation after circulatory death donor lungs were procured after hypoxic cardiac arrest and a 2-hour period of warm ischemia, followed by a 4-hour period of ex vivo lung perfusion rehabilitation with standard conventional volume-based ventilation or pressure-based airway pressure release ventilation. Left lungs were subsequently transplanted into recipient animals and reperfused for 4 hours. Blood gases for partial pressure of oxygen/inspired oxygen fraction ratios, airway pressures for calculation of compliance, and percent wet weight gain during ex vivo lung perfusion and reperfusion were measured.

RESULTS

Airway pressure release ventilation during ex vivo lung perfusion significantly improved left lung oxygenation at 2 hours (561.5 ± 83.9 mm Hg vs 341.1 ± 136.1 mm Hg) and 4 hours (569.1 ± 18.3 mm Hg vs 463.5 ± 78.4 mm Hg). Likewise, compliance was significantly higher at 2 hours (26.0 ± 5.2 mL/cm H₂O vs 15.0 ± 4.6 mL/cm H₂O) and 4 hours (30.6 ± 1.3 mL/cm H₂O vs 17.7 ± 5.9 mL/cm H₂O) after transplantation. Finally, airway pressure release ventilation significantly reduced lung edema development on ex vivo lung perfusion on the basis of percentage of weight gain (36.9% ± 14.6% vs 73.9% ± 4.9%). There was no difference in additional edema accumulation 4 hours after reperfusion.

CONCLUSIONS

Pressure-directed airway pressure release ventilation strategy during ex vivo lung perfusion improves the rehabilitation of severely injured donation after circulatory death lungs. After transplant, these lungs demonstrate superior lung-specific oxygenation and dynamic compliance compared with lungs ventilated with standard conventional ventilation. This strategy, if implemented into clinical ex vivo lung perfusion protocols, could advance the field of donation after circulatory death lung rehabilitation to expand the lung donor pool.

Donation After Circulatory Death Lungs Transplantable Up to Six Hours After Ex Vivo Lung Perfusion

BACKGROUND

Despite the critical need for donor lungs, logistic and geographic barriers hinder lung utilization. We hypothesized that lungs donated after circulatory death subjected to 6 hours of cold preservation after ex vivo lung perfusion (EVLP) would have similar outcomes after transplantation as lungs transplanted immediately after EVLP, and that both would perform superiorly compared with lungs transplanted immediately after procurement.

METHODS

Donor porcine lungs were procured after circulatory death and 15 minutes of warm ischemia. Three groups (n = 5 per group) were randomized: immediate left lung transplantation (Immediate group), EVLP for 4 hours followed by transplantation (EVLP group), or EVLP for 4 hours followed by 6 hours of cold preservation followed by transplantation (EVLP+Cold group). Lungs were reperfused for 2 hours before obtaining pulmonary vein samples for partial pressure of oxygen/fraction of inspired oxygen ratio calculations, airway pressures for compliance measurements, and wet/dry weight ratios.

RESULTS

The partial pressure of oxygen/fraction of inspired oxygen ratios in the EVLP and EVLP+Cold groups were significantly improved compared with those in the Immediate group (429.7 ± 51.8 and 436.7 ± 48.2 versus 117.4 ± 22.9 mm Hg, respectively). In addition, dynamic compliance was significantly improved in the EVLP and EVLP+Cold groups compared with immediate group (26.2 ± 4.2 and 27.9 ± 3.5 versus 11.1 ± 2.4 mL/cmH₂O, respectively). There were no differences in oxygenation capacity or dynamic compliance between the EVLP and EVLP+Cold groups. Inflammatory cytokine levels were significantly lower in the EVLP and EVLP+Cold groups.

CONCLUSIONS

Lungs donated after circulatory death can be successfully transplanted as much as 6 hours after EVLP. Cold preservation of lungs after ex vivo assessment and rehabilitation may improve organ allocation, even to distant recipients, without compromising allograft function.

Ex Vivo Perfusion With Adenosine A2A Receptor Agonist Enhances Rehabilitation of Murine Donor Lungs After Circulatory Death

BACKGROUND

Ex vivo lung perfusion (EVLP) enables assessment and rehabilitation of marginal donor lungs before transplantation. We previously demonstrated that adenosine A2A receptor (A2AR) agonism attenuates lung ischemia-reperfusion injury. The current study utilizes a novel murine EVLP model to test the hypothesis that A2AR agonist enhances EVLP-mediated rehabilitation of donation after circulatory death (DCD) lungs.

METHODS

Mice underwent euthanasia and 60 minutes warm ischemia, and lungs were flushed with Perfadex and underwent cold static preservation (CSP, 60 minutes). Three groups were studied: no EVLP (CSP), EVLP with Steen solution for 60 minutes (EVLP), and EVLP with Steen solution supplemented with ATL1223, a selective A2AR agonist (EVLP + ATL1223). Lung function, wet/dry weight, cytokines and neutrophil numbers were measured. Microarrays were performed using the Affymetrix GeneChip Mouse Genome 430A 2.0 Array.

RESULTS

Ex vivo lung perfusion significantly improved lung function versus CSP, which was further, significantly improved by EVLP + ATL1223. Lung edema, cytokines, and neutrophil counts were reduced after EVLP and further, significantly reduced after EVLP + ATL1223. Gene array analysis revealed differential expression of 1594 genes after EVLP, which comprise canonical pathways involved in inflammation and innate immunity including IL-1, IL-8, IL-6, and IL-17 signaling. Several pathways were uniquely regulated by EVLP + ATL1223 including the downregulation of genes involved in IL-1 signaling, such as ADCY9, ECSIT, IRAK1, MAPK12, and TOLLIP.

CONCLUSIONS

Ex vivo lung perfusion modulates proinflammatory genes and reduces pulmonary dysfunction, edema, and inflammation in DCD lungs, which are further reduced by A2AR agonism. This murine EVLP model provides a novel platform to study rehabilitative mechanisms of DCD lungs.

Expanding the lung donor pool: advancements and emerging pathways

PURPOSE OF REVIEW

The number of patients listed for lung transplantation largely exceeds the number of available transplantable organs because of a shortage of organ donors and a low utilization rate of lungs from those donors who are available. In recent years, novel strategies have been developed to increase the donor lung pool: improved donor management, the use of lungs from donations after cardiac death (DCD), the use of lobar lung living-donors (LLLD) and the use of ex-vivo lung perfusion (EVLP) to assess and repair injured donor lungs.

RECENT FINDINGS

An adapted donor management strategy could expand the donor pool up to 20%. DCD lung transplant is an increasing part of the donor pool expansion. Outcomes after controlled DCD seem to be similar to donation after brain death. LLLD transplantation has excellent results for small and critically ill patients. EVLP treatment allows for a significant increase in the rate of suitable lungs and represents an optimal platform for lung reconditioning and specific lung therapies.

SUMMARY

A significant increase in the number of available lungs for transplantation is expected in the future because of the wider use of lungs from controlled or uncontrolled DCD and LLLD lungs, and with organ-specific EVLP treatment strategies.

Ex vivo lung perfusion

Lung transplantation is an established life-saving therapy for patients with end-stage lung disease. Unfortunately, greater success in lung transplantation is hindered by a shortage of lung donors and the relatively poor early-, mid-, and long-term outcomes associated with severe primary graft dysfunction. Ex vivo lung perfusion has emerged as a modern preservation technique that allows for a more accurate lung assessment and improvement in lung quality. This review outlines the: (i) rationale behind the method; (ii) techniques and protocols; (iii) Toronto ex vivo lung perfusion method; (iv) devices available; and (v) clinical experience worldwide. We also highlight the potential of ex vivo lung perfusion in leading a new era of lung preservation.