A novel dual ex vivo lung perfusion technique improves immediate outcomes in an experimental model of lung transplantation

Technical Advances Targeting Multiday Preservation of Isolated Ex Vivo Lung Perfusion

Indications for ex vivo lung perfusion (EVLP) have evolved from assessment of questionable donor lungs to treatment of some pathologies and the logistics. Yet up to 3 quarters of donor lungs remain discarded across the globe. Multiday preservation of discarded human lungs on EVLP platforms would improve donor lung utilization rates via application of sophisticated treatment modalities, which could eventually result in zero waitlist mortality. The purpose of this article is to summarize advances made on the technical aspects of the protocols in achieving a stable multiday preservation of isolated EVLP. Based on the evidence derived from large animal and/or human studies, the following advances have been considered important in achieving this goal: ability to reposition donor lungs during EVLP; perfusate adsorption/filtration modalities; perfusate enrichment with plasma and/or donor whole blood, nutrients, vitamins, and amino acids; low-flow, pulsatile, and subnormothermic perfusion; positive outflow pressure; injury specific personalized ventilation strategies; and negative pressure ventilation. Combination of some of these advances in an automatized EVLP device capable of managing perfusate biochemistry and ventilation would likely speed up the processes of achieving multiday preservation of isolated EVLP.

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.

Diagnostic and Therapeutic Implications of Ex Vivo Lung Perfusion in Lung Transplantation: Potential Benefits and Inherent Limitations

Ex vivo lung perfusion (EVLP), a technique in which isolated lungs are continually ventilated and perfused at normothermic temperature, is emerging as a promising platform to optimize donor lung quality and increase the lung graft pool. Over the past few decades, the EVLP technique has become recognized as a significant achievement and gained much attention in the field of lung transplantation. EVLP has been demonstrated to be an effective platform for various targeted therapies to optimize donor lung function before transplantation. Additionally, some physical parameters during EVLP and biological markers in the EVLP perfusate can be used to evaluate graft function before transplantation and predict posttransplant outcomes. However, despite its advantages, the clinical practice of EVLP continuously encounters multiple challenges associated with both intrinsic and extrinsic limitations. It is of utmost importance to address the advantages and disadvantages of EVLP for its broader clinical usage. Here, the pros and cons of EVLP are comprehensively discussed, with a focus on its benefits and potential approaches for overcoming the remaining limitations. Directions for future research to fully explore the clinical potential of EVLP in lung transplantation are also discussed.

Exploring predisposing factors and pathogenesis contributing to injuries of donor lungs

INTRODUCTION

Lung transplantation (LTx) remains the only therapeutic strategy for patients with incurable lung diseases. However, its use has been severely limited by the narrow donor pool and potential concerns of inferior quality of donor lungs, which are more susceptible to external influence than other transplant organs. Multiple insults, including various causes of death and a series of perimortem events, may act together on donor lungs and eventually culminate in primary graft dysfunction (PGD) after transplantation as well as other poor short-term outcomes.

AREAS COVERED

This review focuses on the predisposing factors contributing to injuries to the donor lungs, specifically focusing on the pathogenesis of these injuries and their impact on post-transplant outcomes. Additionally, various maneuvers to mitigate donor lung injuries have been proposed.

EXPERT OPINION

The selection criteria for eligible donors vary and may be poor discriminators of lung injury. Not all transplanted lungs are in ideal condition. With the rapidly increasing waiting list for LTx, the trend of using marginal donors has become more apparent, underscoring the need to gain a deeper understanding of donor lung injuries and discover more donor resources.

Heparanase inhibition preserves the endothelial glycocalyx in lung grafts and improves lung preservation and transplant outcomes

The endothelial glycocalyx (eGC) is considered a key regulator of several mechanisms that prevent vascular injury and disease. Degradation of this macromolecular layer may be associated with post-transplant graft dysfunction. In this study, we aimed to demonstrate the benefits of eGC protection via heparanase inhibition on graft quality. We established rat models of lung grafts with damaged or preserved eGC using ischemic insult and transplanted the grafts into recipients. Lung grafts were also subjected to normothermic ex vivo lung perfusion for detailed assessment under isolated conditions. Physiologic parameters and eGC-associated cellular events were assessed in grafts before and after reperfusion. Structurally degraded eGC and highly activated heparanase were confirmed in lungs with ischemic insult. After transplant, lungs with damaged eGC exhibited impaired graft function, inflammation, edema, and inflammatory cell migration. Increased eGC shedding was evident in the lungs after reperfusion both in vivo and ex vivo. These reperfusion-related deficiencies were significantly attenuated in lungs with preserved eGC following heparanase inhibition. Our studies demonstrated that eGC plays a key role in maintaining lung graft quality and function. Heparanase inhibition may serve as a potential therapeutic to preserve eGC integrity, leading to improved post-transplant outcomes.

Ex vivo lung perfusion in lung transplantation

Lung transplantation is an established life-saving intervention for patients with end-stage lung diseases. The success of lung transplantation mainly depends on the quality and function of the implanted donor lungs, which are frequently subject to brain-death-induced lung injuries and intensive care unit (ICU)-related complications before transplantation. Recent innovations, particularly the development of ex vivo lung perfusion (EVLP), in which donor lungs are ventilated and perfused under normothermic conditions outside the body, have allowed clinicians to more accurately assess the donor lung function prior to transplantation. Therefore, EVLP has been successfully translated into clinical practice with the expansion of the donor lung pool, leading to favorable post-transplant outcomes in a growing number of transplant centers worldwide. The EVLP system and techniques, following the Toronto protocol, have recently been applied for the assessment of extended criteria brain-death donors in clinical lung transplantation in Japan. The advancement of EVLP from organ assessment to organ treatment will be the next challenging stage not only to expand donor lung pool, but also to improve graft survival and long-term outcomes after transplantation.

Cyclosporin A Administration During Ex Vivo Lung Perfusion Preserves Lung Grafts in Rat Transplant Model

BACKGROUND

Despite the benefits of ex vivo lung perfusion (EVLP) such as lung reconditioning, preservation, and evaluation before transplantation, deleterious effects, including activation of proinflammatory cascades and alteration of metabolic profiles have been reported. Although patient outcomes have been favorable, further studies addressing optimal conditions are warranted. In this study, we investigated the role of the immunosuppressant drug cyclosporine A (CyA) in preserving mitochondrial function and subsequently preventing proinflammatory changes in lung grafts during EVLP.

METHODS

Using rat heart-lung blocks after 1-hour cold preservation, an acellular normothermic EVLP system was established for 4 hours. CyA was added into perfusate at a final concentration of 1 μM. The evaluation included lung graft function, lung compliance, and pulmonary vascular resistance as well as biochemical marker measurement in the perfusate at multiple time points. After EVLP, single orthotopic lung transplantation was performed, and the grafts were assessed 2 hours after reperfusion.

RESULTS

Lung grafts on EVLP with CyA exhibited significantly better functional and physiological parameters as compared with those without CyA treatment. CyA administration attenuated proinflammatory changes and prohibited glucose consumption during EVLP through mitigating mitochondrial dysfunction in lung grafts. CyA-preconditioned lungs showed better posttransplant lung early graft function and less inflammatory events compared with control.

CONCLUSIONS

During EVLP, CyA administration can have a preconditioning effect through both its anti-inflammatory and mitochondrial protective properties, leading to improved lung graft preservation, which may result in enhanced graft quality after transplantation.

Ex vivo lung perfusion for donor lung assessment and repair: a review of translational interspecies models

For patients with end-stage lung disease, lung transplantation is a lifesaving therapy. Currently however, the number of patients who require a transplant exceeds the number of donor lungs available. One of the contributing factors to this is the conservative mindset of physicians who are concerned about transplanting marginal lungs due to the potential risk of primary graft dysfunction. Ex vivo lung perfusion (EVLP) technology has allowed for the expansion of donor pool of organs by enabling assessment and reconditioning of these marginal grafts before transplant. Ongoing efforts to optimize the therapeutic potential of EVLP are underway. Researchers have adopted the use of different large and small animal models to generate translational preclinical data. This includes the use of rejected human lungs, pig lungs, and rat lungs. In this review, we summarize some of the key current literature studies relevant to each of the major EVLP model platforms and identify the advantages and disadvantages of each platform. The review aims to guide investigators in choosing an appropriate species model to suit their specific goals of study, and ultimately aid in translation of therapy to meet the growing needs of the patient population.

Perfusate adsorption during ex vivo lung perfusion improves early post-transplant lung function

OBJECTIVE

Improvement in ex vivo lung perfusion protocols could increase the number of donors available for transplantation and protect the lungs from primary graft dysfunction. We hypothesize that perfusate adsorption during ex vivo lung perfusion reconditions the allograft to ischemia-reperfusion injury after lung transplantation.

METHODS

Donor pig lungs were preserved for 24 hours at 4°C, followed by 6 hours of ex vivo lung perfusion according to the Toronto protocol. The perfusate was additionally adsorbed through a CytoSorb adsorber (CytoSorbents, Berlin, Germany) in the treatment group, whereas control lungs were perfused according to the standard protocol (n = 5, each). Ex vivo lung perfusion physiology and biochemistry were monitored. Upon completion of ex vivo lung perfusion, a left single lung transplantation was performed. Oxygenation function and lung mechanics were assessed during a 4-hour reperfusion period. The inflammatory response was determined during ex vivo lung perfusion and reperfusion.

RESULTS

The cytokine concentrations in the perfusate were markedly lower with the adsorber, resulting in improved ex vivo lung perfusion physiology and biochemistry during the 6-hour perfusion period. Post-transplant dynamic lung compliance was markedly better during the 4-hour reperfusion period in the treatment group. Isolated allograft oxygenation function and dynamic compliance continued to be superior in the adsorber group at the end of reperfusion, accompanied by a markedly decreased local inflammatory response.

CONCLUSIONS

Implementation of an additional cytokine adsorber has refined the standard ex vivo lung perfusion protocol. Furthermore, cytokine removal during ex vivo lung perfusion improved immediate post-transplant graft function together with a less intense inflammatory response to reperfusion in pigs. Further studies are warranted to understand the beneficial effects of perfusate adsorption during ex vivo lung perfusion in the clinical setting.

Impact of triptolide during ex vivo lung perfusion on grafts after transplantation in a rat model

OBJECTIVE

Ex vivo lung perfusion creates a proinflammatory environment leading to deterioration in graft quality that may contribute to post-transplant graft dysfunction. Triptolide has been shown to have a therapeutic potential in various disease states because of its anti-inflammatory properties. On this basis, we investigated the impact of triptolide on graft preservation during ex vivo lung perfusion and associated post-transplant outcomes in a rat transplant model.

METHODS

We performed rat normothermic ex vivo lung perfusion with acellular Steen solution containing 100 nM triptolide for 4 hours and compared the data with untreated lungs. Orthotopic single lung transplantation after ex vivo lung perfusion was performed.

RESULTS

Physiologic and functional parameters of lung grafts on ex vivo lung perfusion with triptolide were better than those without treatment. Graft glucose consumption was significantly attenuated on ex vivo lung perfusion with triptolide via inhibition of hypoxia signaling resulting in improved mitochondrial function and reduced oxidative stress. Also, intragraft inflammation was markedly lower in triptolide-treated lungs because of inhibition of nuclear factor-κB signaling. Furthermore, post-transplant graft function and inflammatory events were significantly improved in the triptolide group compared with the untreated group.

CONCLUSIONS

Treatment of lung grafts with triptolide during ex vivo lung perfusion may serve to enhance graft preservation and improve graft protection resulting in better post-transplant outcomes.

Comparative Study of Capillary Filtration Coefficient (Kfc) Determination by a Manual and Automatic Perfusion System. Step by Step Technique Review

The purpose of calculating the capillary filtration coefficient is to experimentally evaluate edema formation in models of pulmonary ischemia-reperfusion injury. For many years, the obtaining of this coefficient implies a series of manual maneuvers during ex-vivo reperfusion of pulmonary arterial pressure, venous pressure and weight, as well as the calculation of the Kfc formula. Through automation, the calculation of capillary filtration coefficient could be easier and more efficient. To describe an automatic method designed in our laboratory to calculating the capillary filtration coefficient and compare with traditional determination of capillary filtration coefficient as gold standard method. An automatic three valve perfusion system was constructed, commanded by a mastery module connected to a graphical user interface. To test its accuracy, cardiopulmonary blocks of Wistar rats were harvested and distributed in manual (n=8) and automated (n=8) capillary filtration coefficient determination groups. Physiological parameters as pulmonary arterial pressure, pulmonary venous pressure, weight and capillary filtration coefficient were obtained. Results: Capillary filtration coefficient, pulmonary arterial pressure, venous arterial pressure shown no statistical significance difference between the groups. The automated perfusion system for obtaining Kfc was standardized and validated, giving reliable results without biases and making the process more efficient in terms of time and personal staff.

The Bronchial Arterial Circulation in Lung Transplantation: Bedside to Bench to Bedside, and Beyond

Chronic allograft dysfunction (CLAD) remains a major complication, causing the poor survival after lung transplantation (Tx). Although strenuous efforts have been made at preventing CLAD, surgical approaches for lung Tx have not been updated over the last 2 decades. The bronchial artery (BA), which supplies oxygenated blood to the airways and constitutes a functional microvasculature, has occasionally been revascularized during transplants, but this technique did not gain popularity and is not standard in current lung Tx protocols, despite the fact that a small number of studies have shown beneficial effects of BA revascularization on limiting CLAD. Also, recent basic and clinical evidence has demonstrated the relationship between microvasculature damage and CLAD. Thus, the protection of the bronchial circulation and microvasculature in lung grafts may be a key factor to overcome CLAD. This review revisits the history of BA revascularization, discusses the role of the bronchial circulation in lung Tx, and advocates for novel bronchial-arterial-circulation sparing approaches as a future direction for overcoming CLAD. Although there are some already published review articles summarizing the surgical techniques and their possible contribution to outcomes in lung Tx, to the best of our knowledge, this review is the first to elaborate on bronchial circulation that will contribute to prevent CLAD from both scientific and clinical perspectives: from bedside to bench to bedside, and beyond.

A Decrease in Hypoxic Pulmonary Vasoconstriction Correlates With Increased Inflammation During Extended Normothermic Ex Vivo Lung Perfusion

Normothermic ex vivo lung perfusion (EVLP) is an evolving technology to evaluate function of donor lungs to determine suitability for transplantation. We hypothesize that hypoxic pulmonary vasoconstriction (HPV) during EVLP will provide a more sensitive parameter of lung function to determine donor lung quality for lung transplantation. Eight porcine lungs were procured, and subsequently underwent EVLP with autologous blood and STEEN solution for 10 h. Standard physiologic parameters including dynamic compliance, peak airway pressure, and pulmonary vascular resistance (PVR) remained stable (P = 0.055), mean oxygenation (PO₂ /FiO₂ ) was 400 ± 18 mm Hg on average throughout perfusion. Response to hypoxia resulted in a robust increase in PVR (ΔPVR) up to 4 h of perfusion, however the HPV response then blunted beyond T6 (P < 0.01). The decrease in HPV response inversely correlated to cytokine concentrations of Interleukin-6 and tumor necrosis factor-α (P < 0.01). Despite acceptable lung oxygenation and standard physiologic parameters during 10 h of EVLP, there is a subclinical deterioration of lung function. HPV challenges can be performed during EVLP as a simple and more sensitive index of pulmonary vascular reactivity.

Comparison of two strategies for ex vivo lung perfusion

BACKGROUND

Two clinically used strategies for ex vivo lung perfusion (EVLP) were compared in a porcine model with respect to lung function, metabolism, inflammatory response, oxidative stress, and cell viability.

METHODS

Porcine lungs (n = 20) were preserved, harvested, and kept cooled for 2 hours. After randomization, EVLP was performed using a cellular perfusate and open left atrium (COA group) or an acellular perfusate and a closed left atrium (ACA group). Oxygenation (partial pressure of arterial oxygen/fraction of inspired oxygen), compliance, dead space, weight, and perfusate oncotic pressure were registered before and after a 4-hour period of reconditioning. Lung tissue samples were collected before and after EVLP for quantitative polymerase chain reaction analysis of gene expression for inflammatory markers, measurement of tissue hypoxia (hypoxia inducible factor-1α) and oxidative stress (ascorbyl radical), and viability (trypan blue staining) and lung histopathology.

RESULTS

In 3 of 10 lungs undergoing EVLP in the ACA group, EVLP was terminated prematurely because of severe lung edema and inability to perfuse the lungs. There were no significant differences in changes of lung oxygenation or pulmonary vascular resistance between groups. Compliance decreased and lung weights increased in both groups, but more in the ACA group (p = 0.083 and p = 0.065, respectively). There was no obvious difference in gene expression for hypoxia inducible factor-1α, inflammatory markers, free radicals, or lung injury between groups.

CONCLUSIONS

Lung edema formation and decreased lung compliance occurs with both EVLP techniques but were more pronounced in the ACA group. Otherwise, there were no differences in lung function, inflammatory response, ischemia/reperfusion injury, or histopathologic changes between the EVLP techniques.

How to minimise ventilator-induced lung injury in transplanted lungs: The role of protective ventilation and other strategies

Lung transplantation is the treatment of choice for end-stage pulmonary diseases. In order to avoid or reduce pulmonary and systemic complications, mechanical ventilator settings have an important role in each stage of lung transplantation. In this respect, the use of mechanical ventilation with a tidal volume of 6 to 8 ml  kg(-1) predicted body weight, positive end-expiratory pressure of 6 to 8 cmH2O and a plateau pressure lower than 30 cmH2O has been suggested for the donor during surgery, and for the recipient both during and after surgery. For the present review, we systematically searched the PubMed database for articles published from 2000 to 2014 using the following keywords: lung transplantation, protective mechanical ventilation, lung donor, extracorporeal membrane oxygenation, recruitment manoeuvres, extracorporeal CO2 removal and noninvasive ventilation.

Tissue Engineering and Regenerative Medicine 2015: A Year in Review

This may be the most exciting time ever for the field of tissue engineering and regenerative medicine (TERM). After decades of progress, it has matured, integrated, and diversified into entirely new areas, and it is starting to make the pivotal shift toward translation. The most exciting science and applications continue to emerge at the boundaries of disciplines, through increasingly effective interactions between stem cell biologists, bioengineers, clinicians, and the commercial sector. In this "Year in Review," we highlight some of the major advances reported over the last year (Summer 2014-Fall 2015). Using a methodology similar to that established in previous years, we identified four areas that generated major progress in the field: (i) pluripotent stem cells, (ii) microtissue platforms for drug testing and disease modeling, (iii) tissue models of cancer, and (iv) whole organ engineering. For each area, we used some of the most impactful articles to illustrate the important concepts and results that advanced the state of the art of TERM. We conclude with reflections on emerging areas and perspectives for future development in the field.