Soluble Adhesion Molecules During Ex Vivo Lung Perfusion Are Associated With Posttransplant Primary Graft Dysfunction

Transient receptor potential vanilloid 4 channel inhibition attenuates lung ischemia-reperfusion injury in a porcine lung transplant model

OBJECTIVE

Transient receptor potential vanilloid 4 (TRPV4) is a nonselective cation channel important in many physiological and pathophysiological processes, including pulmonary disease. Using a murine model, we previously demonstrated that TRPV4 mediates lung ischemia-reperfusion injury, the major cause of primary graft dysfunction after transplant. The current study tests the hypothesis that treatment with a TRPV4 inhibitor will attenuate lung ischemia-reperfusion injury in a clinically relevant porcine lung transplant model.

METHODS

A porcine left-lung transplant model was used. Animals were randomized to 2 treatment groups (n = 5/group): vehicle or GSK2193874 (selective TRPV4 inhibitor). Donor lungs underwent 30 minutes of warm ischemia and 24 hours of cold preservation before left lung allotransplantation and 4 hours of reperfusion. Vehicle or GSK2193874 (1 mg/kg) was administered to the recipient as a systemic infusion after recipient lung explant. Lung function, injury, and inflammatory biomarkers were compared.

RESULTS

After transplant, left lung oxygenation was significantly improved in the TRPV4 inhibitor group after 3 and 4 hours of reperfusion. Lung histology scores and edema were significantly improved, and neutrophil infiltration was significantly reduced in the TRPV4 inhibitor group. TRPV4 inhibitor-treated recipients had significantly reduced expression of interleukin-8, high mobility group box 1, P-selectin, and tight junction proteins (occludin, claudin-5, and zonula occludens-1) in bronchoalveolar lavage fluid as well as reduced angiopoietin-2 in plasma, all indicative of preservation of endothelial barrier function.

CONCLUSIONS

Treatment of lung transplant recipients with TRPV4 inhibitor significantly improves lung function and attenuates ischemia-reperfusion injury. Thus, selective TRPV4 inhibition may be a promising therapeutic strategy to prevent primary graft dysfunction after transplant.

Modeling the Effects of IL-1β-mediated Inflammation During Ex Vivo Lung Perfusion Using a Split Human Donor Model

BACKGROUND

The association between interleukin-1β (IL-1β) concentrations during ex vivo lung perfusion (EVLP) with donor organ quality and post-lung transplant outcome has been demonstrated in several studies. The mechanism underlying IL-1β-mediated donor lung injury was investigated using a paired single-lung EVLP model.

METHODS

Human lung pairs were dissected into individual lungs and perfused on identical separate EVLP circuits, with one lung from each pair receiving a bolus of IL-1β. Fluorescently labeled human neutrophils isolated from a healthy volunteer were infused into both circuits and quantified in perfusate at regular timepoints. Perfusates and tissues were subsequently analyzed, with perfusates also used in functional assays.

RESULTS

Neutrophil numbers were significantly lower in perfusate samples collected from the IL-1β-stimulated lungs consistent with increased neutrophil adhesion ( P = 0.042). Stimulated lungs gained significantly more weight than controls ( P = 0.046), which correlated with soluble intercellular adhesion molecule-1 (R 2 = 0.71, P = 0.0043) and von-Willebrand factor (R 2 = 0.39, P = 0.040) in perfusate. RNA expression patterns for inflammatory genes were differentially regulated via IL-1β. Blockade of IL-1β significantly reduced neutrophil adhesion in vitro ( P = 0.025).

CONCLUSION

These data illustrate the proinflammatory functions of IL-1β in the context of EVLP, suggesting this pathway may be susceptible to therapeutic modulation before transplantation.

A machine-learning approach to human ex vivo lung perfusion predicts transplantation outcomes and promotes organ utilization

Ex vivo lung perfusion (EVLP) is a data-intensive platform used for the assessment of isolated lungs outside the body for transplantation; however, the integration of artificial intelligence to rapidly interpret the large constellation of clinical data generated during ex vivo assessment remains an unmet need. We developed a machine-learning model, termed InsighTx, to predict post-transplant outcomes using n = 725 EVLP cases. InsighTx model AUROC (area under the receiver operating characteristic curve) was 79 ± 3%, 75 ± 4%, and 85 ± 3% in training and independent test datasets, respectively. Excellent performance was observed in predicting unsuitable lungs for transplantation (AUROC: 90 ± 4%) and transplants with good outcomes (AUROC: 80 ± 4%). In a retrospective and blinded implementation study by EVLP specialists at our institution, InsighTx increased the likelihood of transplanting suitable donor lungs [odds ratio=13; 95% CI:4-45] and decreased the likelihood of transplanting unsuitable donor lungs [odds ratio=0.4; 95%CI:0.16-0.98]. Herein, we provide strong rationale for the adoption of machine-learning algorithms to optimize EVLP assessments and show that InsighTx could potentially lead to a safe increase in transplantation rates.

Biometric Profiling to Quantify Lung Injury Through Ex Vivo Lung Perfusion Following Warm Ischemia

Standard physiologic assessment parameters of donor lung grafts may not accurately reflect lung injury or quality. A biometric profile of ischemic injury could be identified as a means to assess the quality of the donor allograft. We sought to identify a biometric profile of lung ischemic injury assessed during ex vivo lung perfusion (EVLP). A rat model of lung donation after circulatory death (DCD) warm ischemic injury with subsequent EVLP evaluation was utilized. We did not observe a significant correlation between the classical physiological assessment parameters and the duration of the ischemic. In the perfusate, solubilized lactate dehydrogenase (LDH) as well as hyaluronic acid (HA) significantly correlated with duration of ischemic injury and length of perfusion ( p < 0.05). Similarly, in perfusates, the endothelin-1 (ET-1) and Big ET-1 correlated ischemic injury ( p < 0.05) and demonstrated a measure of endothelial cell injury. In tissue protein expression, heme oxygenase-1 (HO-1), angiopoietin 1 (Ang-1), and angiopoietin 2 (Ang-2) levels were correlated with the duration of ischemic injury ( p < 0.05). Cleaved caspase-3 levels were significantly elevated at 90 and 120 minutes ( p < 0.05) demonstrating increased apoptosis. A biometric profile of solubilized and tissue protein markers correlated with cell injury is a critical tool to aid in the evaluation of lung transplantation, as accurate evaluation of lung quality is imperative and improved quality leads to better results. http://links.lww.com/ASAIO/B49.

Primary Graft Dysfunction in Lung Transplantation: A Review of Mechanisms and Future Applications

Lung allograft recipients have worse survival than all other solid organ transplant recipients, largely because of primary graft dysfunction (PGD), a major form of acute lung injury affecting a third of lung recipients within the first 72 h after transplant. PGD is the clinical manifestation of ischemia-reperfusion injury and represents the predominate cause of early morbidity and mortality. Despite PGD's impact on lung transplant outcomes, no targeted therapies are currently available; hence, care remains supportive and largely ineffective. This review focuses on molecular and innate immune mechanisms of ischemia-reperfusion injury leading to PGD. We also discuss novel research aimed at discovering biomarkers that could better predict PGD and potential targeted interventions that may improve outcomes in lung transplantation.

Cell type- and time-dependent biological responses in ex vivo perfused lung grafts

In response to the increasing demand for lung transplantation, ex vivo lung perfusion (EVLP) has extended the number of suitable donor lungs by rehabilitating marginal organs. However despite an expanding use in clinical practice, the responses of the different lung cell types to EVLP are not known. In order to advance our mechanistic understanding and establish a refine tool for improvement of EVLP, we conducted a pioneer study involving single cell RNA-seq on human lungs declined for transplantation. Functional enrichment analyses were performed upon integration of data sets generated at 4 h (clinical duration) and 10 h (prolonged duration) from two human lungs processed to EVLP. Pathways related to inflammation were predicted activated in epithelial and blood endothelial cells, in monocyte-derived macrophages and temporally at 4 h in alveolar macrophages. Pathways related to cytoskeleton signaling/organization were predicted reduced in most cell types mainly at 10 h. We identified a division of labor between cell types for the selected expression of cytokine and chemokine genes that varied according to time. Immune cells including CD4⁺ and CD8⁺ T cells, NK cells, mast cells and conventional dendritic cells displayed gene expression patterns indicating blunted activation, already at 4 h in several instances and further more at 10 h. Therefore despite inducing inflammatory responses, EVLP appears to dampen the activation of major lung immune cell types, what may be beneficial to the outcome of transplantation. Our results also support that therapeutics approaches aiming at reducing inflammation upon EVLP should target both the alveolar and vascular compartments.

Mitochondrial transplant after ischemia reperfusion promotes cellular salvage and improves lung function during ex-vivo lung perfusion

BACKGROUND

In lung transplantation, ischemia-reperfusion injury associated with mitochondrial damage can lead to graft rejection. Intact, exogenous mitochondria provide a unique treatment option to salvage damaged cells within lung tissue.

METHODS

We developed a novel method to freeze and store allogeneic mitochondria isolated from porcine heart tissue. Stored mitochondria were injected into a model of induced ischemia-reperfusion injury using porcine ex-vivo lung perfusion. Treatment benefits to immune modulation, antioxidant defense, and cellular salvage were evaluated. These findings were corroborated in human lungs undergoing ex-vivo lung perfusion. Lung tissue homogenate and primary lung endothelial cells were then used to address underlying mechanisms.

RESULTS

Following cold ischemia, mitochondrial transplant reduced lung pulmonary vascular resistance and tissue pro-inflammatory signaling and cytokine secretion. Further, exogenous mitochondria reduced reactive oxygen species by-products and promoted glutathione synthesis, thereby salvaging cell viability. These results were confirmed in a human model of ex-vivo lung perfusion wherein transplanted mitochondria decreased tissue oxidative and inflammatory signaling, improving lung function. We demonstrate that transplanted mitochondria induce autophagy and suggest that bolstered autophagy may act upstream of the anti-inflammatory and antioxidant benefits. Importantly, chemical inhibitors of the MEK autophagy pathway blunted the favorable effects of mitochondrial transplant.

CONCLUSIONS

These data provide direct evidence that mitochondrial transplant improves cellular health and lung function when administered during ex-vivo lung perfusion and suggest the mechanism of action may be through promotion of cellular autophagy. Data herein contribute new insights into the therapeutic potential of mitochondrial transplant to abate ischemia-reperfusion injury during lung transplant, and thus reduce graft rejection.

An enhanced level of VCAM in transplant preservation fluid is an independent predictor of early kidney allograft dysfunction

Background

We aimed to evaluate whether donor-related inflammatory markers found in kidney transplant preservation fluid can associate with early development of kidney allograft dysfunction.

Methods

Our prospective study enrolled 74 consecutive donated organs who underwent kidney transplantation in our center between September 2020 and June 2021. Kidneys from 27 standard criteria donors were allocated to static cold storage and kidneys from 47 extended criteria donors to hypothermic machine perfusion. ELISA assessment of inflammatory biomarkers (IL-6, IL6-R, ICAM, VCAM, TNFα, IFN-g, CXCL1 and Fractalkine) was analyzed in view of a primary endpoint defined as the occurrence of delayed graft function or slow graft function during the first week following transplantation.

Results

Soluble VCAM levels measured in transplant conservation fluid were significantly associated with recipient serum creatinine on day 7. Multivariate stepwise logistic regression analysis identified VCAM as an independent non-invasive predictor of early graft dysfunction, both at 1 week (OR: 3.57, p = .04, 95% CI: 1.06-12.03) and 3 Months (OR: 4.039, p = .034, 95% CI: 1.11-14.73) after transplant surgery.

Conclusions

This prospective pilot study suggests that pre-transplant evaluation of VCAM levels could constitute a valuable indicator of transplant health and identify the VCAM-CD49d pathway as a target to limit donor-related vascular injury of marginal transplants.

Lung Biomolecular Profile and Function of Grafts from Donors after Cardiocirculatory Death with Prolonged Donor Warm Ischemia Time

The acceptable duration of donor warm ischemia time (DWIT) after cardiocirculatory death (DCD) is still debated. We analyzed the biomolecular profile and function during ex vivo lung perfusion (EVLP) of DCD lungs and their correlation with lung transplantation (LuTx) outcomes. Donor data, procurement times, recipient outcomes, and graft function up to 1 year after LuTx were collected. During EVLP, the parameters of graft function and metabolism, perfusate samples to quantify inflammation, glycocalyx breakdown products, coagulation, and endothelial activation markers were obtained. Data were compared to a cohort of extended-criteria donors after brain death (EC-DBD). Eight DBD and seven DCD grafts transplanted after EVLP were analyzed. DCD’s DWIT was 201 [188;247] minutes. Donors differed only regarding the duration of mechanical ventilation that was longer in the EC-DBD group. No difference was observed in lung graft function during EVLP. At reperfusion, “wash-out” of inflammatory cells and microthrombi was predominant in DCD grafts. Perfusate biomolecular profile demonstrated marked endothelial activation, characterized by the presence of inflammatory mediators and glycocalyx breakdown products both in DCD and EC-DBD grafts. Early graft function after LuTx was similar between DCD and EC-DBD. DCD lungs exposed to prolonged DWIT represent a potential resource for donation if properly preserved and evaluated.

Inflammation and Oxidative Stress in the Context of Extracorporeal Cardiac and Pulmonary Support

Extracorporeal circulation (ECC) systems, including cardiopulmonary bypass, and extracorporeal membrane oxygenation have been an irreplaceable part of the cardiothoracic surgeries, and treatment of critically ill patients with respiratory and/or cardiac failure for more than half a century. During the recent decades, the concept of extracorporeal circulation has been extended to isolated machine perfusion of the donor organ including thoracic organs (ex-situ organ perfusion, ESOP) as a method for dynamic, semi-physiologic preservation, and potential improvement of the donor organs. The extracorporeal life support systems (ECLS) have been lifesaving and facilitating complex cardiothoracic surgeries, and the ESOP technology has the potential to increase the number of the transplantable donor organs, and to improve the outcomes of transplantation. However, these artificial circulation systems in general have been associated with activation of the inflammatory and oxidative stress responses in patients and/or in the exposed tissues and organs. The activation of these responses can negatively affect patient outcomes in ECLS, and may as well jeopardize the reliability of the organ viability assessment, and the outcomes of thoracic organ preservation and transplantation in ESOP. Both ECLS and ESOP consist of artificial circuit materials and components, which play a key role in the induction of these responses. However, while ECLS can lead to systemic inflammatory and oxidative stress responses negatively affecting various organs/systems of the body, in ESOP, the absence of the organs that play an important role in oxidant scavenging/antioxidative replenishment of the body, such as liver, may make the perfused organ more susceptible to inflammation and oxidative stress during extracorporeal circulation. In the present manuscript, we will review the activation of the inflammatory and oxidative stress responses during ECLP and ESOP, mechanisms involved, clinical implications, and the interventions for attenuating these responses in ECC.

Ex Vivo Lung Perfusion: A Platform for Donor Lung Assessment, Treatment and Recovery

Lung transplantation offers a lifesaving therapy for patients with end-stage lung disease but its availability is presently limited by low organ utilization rates with donor lungs frequently excluded due to unsuitability at assessment. When transplantation does occur, recipients are then vulnerable to primary graft dysfunction (PGD), multitudinous short-term complications, and chronic lung allograft dysfunction. The decision whether to use donor lungs is made rapidly and subjectively with limited information and means many lungs that might have been suitable are lost to the transplant pathway. Compared to static cold storage (SCS), ex vivo lung perfusion (EVLP) offers clinicians unrivalled opportunity for rigorous objective assessment of donor lungs in conditions replicating normal physiology, thus allowing for better informed decision-making in suitability assessments. EVLP additionally offers a platform for the delivery of intravascular or intrabronchial therapies to metabolically active tissue aiming to treat existing lung injuries. In the future, EVLP may be employed to provide a pre-transplant environment optimized to prevent negative outcomes such as primary graft dysfunction (PGD) or rejection post-transplant.

Inflammatory responses in lungs from donation after brain death: Mechanisms and potential therapeutic targets

The vast majority of lungs used in clinical transplantation are donated after brain death (DBD). The utilization of DBD lungs is low due to brain death-induced lung injury. Moreover, inflammatory responses in DBD lungs used for transplantation contribute to ischemia-reperfusion injury and primary graft dysfunction. Work from human observational studies has demonstrated overexpression of cytokines, activation of endothelial cells, and cell death in DBD lungs, are associated with the activation of signaling pathways. Animal models have characterized the pulmonary injury induced by brain death and identified potential strategies to improve donor management. Interestingly, transcriptomic studies comparing DBD and donated after circulatory death (DCD) lungs have found that inflammatory responses are elevated in DBD lungs, while cell death pathways are elevated in DCD lungs. Development of the ex vivo lung perfusion technique, has made it possible to assess donor lungs using inflammation and cell death biomarkers. In the future, identification of potential therapeutic targets and development of novel treatments strategies may allow for lung repair during EVLP prior to transplantation.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Hypothermic Oxygenated Liver Perfusion (HOPE) Prevents Tumor Recurrence in Liver Transplantation From Donation After Circulatory Death

OBJECTIVE

The aim of this study was to investigate tumor recurrence after liver transplantation for hepatocellular carcinoma (HCC), with and without hypothermic oxygenated liver perfusion (HOPE) before transplantation.

PATIENTS AND METHODS

We analyzed all liver recipients with HCC, transplanted between January 2012 and September 2019 with donation after circulatory death (DCD) livers after previous end-ischemic HOPE-treatment (n = 70, Center A). Tumor parameters and key confounders were compared to consecutive recipients with HCC, transplanted during the same observation period with an unperfused DBD liver (n = 70). In a next step, we analyzed unperfused DCD (n = 70) and DBD liver recipients (n = 70), transplanted for HCC at an external center (Center B).

RESULTS

Tumor parameters were not significantly different between HOPE-treated DCD and unperfused DBD liver recipients at Center A. One-third of patients were outside established tumor thresholds, for example, Milan criteria, in both groups. Despite no difference in tumor load, we found a 4-fold higher tumor recurrence rate in unperfused DBD livers (25.7%, 18/70), compared to only 5.7% (n = 4/70) recipients with tumor recurrence in the HOPE-treated DCD cohort (P = 0.002) in Center A. The tumor recurrence rate was also twice higher in unperfused DCD and DBD recipients at the external Center B, despite significant less cases outside Milan. HOPE-treatment of DCD livers resulted therefore in a 5-year tumor-free survival of 92% in HCC recipients, compared to 73%, 82.7%, and 81.2% in patients receiving unperfused DBD or DCD livers, from both centers.

CONCLUSION

We suggest that a simple machine liver perfusion approach appears advantageous to protect from HCC recurrence after liver transplantation, despite extended tumor criteria.

Endothelin receptor antagonist improves donor lung function in an ex vivo perfusion system

BACKGROUND

A lung transplant is the last resort treatment for many patients with advanced lung disease. The majority of donated lungs come from donors following brain death (BD). The endothelin axis is upregulated in the blood and lung of the donor after BD resulting in systemic inflammation, lung damage and poor lung graft outcomes in the recipient. Tezosentan (endothelin receptor blocker) improves the pulmonary haemodynamic profile; however, it induces adverse effects on other organs at high doses. Application of ex vivo lung perfusion (EVLP) allows the development of organ-specific hormone resuscitation, to maximise and optimise the donor pool. Therefore, we investigate whether the combination of EVLP and tezosentan administration could improve the quality of donor lungs in a clinically relevant 6-h ovine model of brain stem death (BSD).

METHODS

After 6 h of BSD, lungs obtained from 12 sheep were divided into two groups, control and tezosentan-treated group, and cannulated for EVLP. The lungs were monitored for 6 h and lung perfusate and tissue samples were processed and analysed. Blood gas variables were measured in perfusate samples as well as total proteins and pro-inflammatory biomarkers, IL-6 and IL-8. Lung tissues were collected at the end of EVLP experiments for histology analysis and wet-dry weight ratio (a measure of oedema).

RESULTS

Our results showed a significant improvement in gas exchange [elevated partial pressure of oxygen (P = 0.02) and reduced partial pressure of carbon dioxide (P = 0.03)] in tezosentan-treated lungs compared to controls. However, the lungs hematoxylin-eosin staining histology results showed minimum lung injuries and there was no difference between both control and tezosentan-treated lungs. Similarly, IL-6 and IL-8 levels in lung perfusate showed no difference between control and tezosentan-treated lungs throughout the EVLP. Histological and tissue analysis showed a non-significant reduction in wet/dry weight ratio in tezosentan-treated lung tissues (P = 0.09) when compared to control.

CONCLUSIONS

These data indicate that administration of tezosentan could improve pulmonary gas exchange during EVLP.

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.

Cell-free DNA in human ex vivo lung perfusate as a potential biomarker to predict the risk of primary graft dysfunction in lung transplantation

BACKGROUND

Cell-free DNA (cfDNA), such as mitochondrial DNA (mtDNA) and nuclear DNA (nuDNA), are known to be released from injured cells and as such have been explored as biomarkers for tissue injury in different clinical settings. Ex vivo lung perfusion (EVLP) has been developed as an effective technique for marginal donor lung functional assessment. We hypothesized that the level of cfDNA in EVLP perfusate may reflect tissue injury and thus can be developed as a biomarker to quantify the degree of donor lung injury or predict the development of primary graft dysfunction (PGD) after lung transplantation (LTx).

METHODS

The perfusate from 62 donor lungs transplanted at our institution between May 2010 and December 2015 was sampled for cfDNA at 1 and 4 hours of perfusion. Sequences of genes encoding nicotinamide adenine dinucleotide dehydrogenase 1 (NADH-1) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were used to represent mtDNA and nuDNA, respectively. Levels were quantified by real-time polymerase chain reaction and correlated with clinical outcome after LTx.

RESULTS

In our entire cohort, 14 patients developed PGD grade 3 (PGD3) within 72 hours after LTx. The non-PGD group included 48 patients (PGD0-1). Concentrations of mtDNA in the perfusate of the PGD3 group were significantly higher than those in non-PGD group at 1 hour of EVLP (1874 ± 844 vs 1259 ± 885 copies/μL; P = .011). The perfusate of the PGD3 group had significantly higher levels of nuDNA compared with the non-PGD group at both 1 hour (1498 ± 1895 vs 675 ± 391 copies/μL; P = .008) and 4 hours (4521 ± 5810 vs 1764 ± 1494 copies/μL; P = .001). In donation after cardiac death (DCD) cases, mtDNA levels were significantly higher in the PGD3 group compared with the non-PGD group at 1 hour of EVLP (2060 ± 997 vs 1184 ± 782 copies/μL; P = .040), and the levels of nuDNA were significantly higher in the PGD3 group compared with the non-PGD group at both 1 hour (1021 ± 495 vs 606 ± 305 copies/μL; P = .041) and 4 hours (2358 ± 1028 vs 1185 ± 967 copies/μL; P = .006). In donation after brain death (DBD) cases, cfDNA scores did not show a significant difference.

CONCLUSIONS

We found that the amount of cfDNA, especially nuDNA, in EVLP perfusate was higher in the severe PGD group (PGD3) compared with the non-PGD group. This proof-of-concept study supports the concept that the analysis of cfDNA levels in EVLP perfusate can help estimate the damage to donor lungs before implantation. Larger studies are needed to validate this concept.

Assessment of Organ Quality in Kidney Transplantation by Molecular Analysis and Why It May Not Have Been Achieved, Yet

Donor organ shortage, growing waiting lists and substantial organ discard rates are key problems in transplantation. The critical importance of organ quality in determining long-term function is becoming increasingly clear. However, organ quality is difficult to predict. The lack of good measures of organ quality is a serious challenge in terms of acceptance and allocation of an organ. The underlying review summarizes currently available methods used to assess donor organ quality such as histopathology, clinical scores and machine perfusion characteristics with special focus on molecular analyses of kidney quality. The majority of studies testing molecular markers of organ quality focused on identifying organs at risk for delayed graft function, yet without prediction of long-term graft outcome. Recently, interest has emerged in looking for molecular markers associated with biological age to predict organ quality. However, molecular gene sets have not entered the clinical routine or impacted discard rates so far. The current review critically discusses the potential reasons why clinically applicable molecular quality assessment using early kidney biopsies might not have been achieved yet. Besides a critical analysis of the inherent limitations of surrogate markers used for organ quality, i.e., delayed graft function, the intrinsic methodological limitations of studies assessing organ quality will be discussed. These comprise the multitude of unpredictable hits as well as lack of markers of nephron mass, functional reserve and regenerative capacity.

Hypothermic machine perfusion in liver transplantation

Dynamic preservation strategies are a promising option to improve graft quality before transplantation, and to extend preservation time for either logistic or treatment reasons. In contrast to normothermic oxygenated perfusion, which intends to mimic physiological conditions in the human body, with subsequent clinical application for up to 24 hrs, hypothermic perfusion is mainly used for a relatively short period with protection of mitochondria and subsequent reduction of oxidative injury upon implantation. The results from two randomized controlled trials, where recruitment has finished are expected this year. Both ex situ perfusion techniques are increasingly applied in clinical transplantation including recent reports on viability assessment, which could open the door for an increased liver utilization in the future.

Normothermic machine perfusion of donor-lungs ex-vivo: promoting clinical adoption

PURPOSE OF REVIEW

Lung transplantation offers the only realistic therapeutic option for patients with end-stage lung disease. However, this is impacted by a shortfall in availability of suitable donor-lungs. Normothermic machine perfusion of donor-lungs outside the donor body also known as ex-vivo lung perfusion (EVLP) offers a potential solution through objective assessment, reconditioning and treatment of donor-lungs initially deemed unsuitable for use. This review discusses key advances and challenges in the wider clinical adoption of this technology.

RECENT FINDINGS

This review will summarize key research within the following areas: recent clinical trials utilizing EVLP, logistical challenges, EVLP protocol innovations, novel assessment methods and current research into therapeutic modulation of lung function during EVLP.

SUMMARY

Normothermic machine perfusion of donor-lungs ex-vivo offers a promising platform to assess and modulate donor-lung quality prior to transplantation. Consensus on how and when to best utilize EVLP is yet to be reached, meaning that widespread clinical adoption of the technology has not yet become a reality. Further work is needed on agreed indications, perfusion protocols and organization of services before becoming a regularly used procedure prior to lung transplantation.

Ex Vivo Lung Perfusion: A Review of Research and Clinical Practices

End-stage lung disease is ultimately treated with lung transplantation. However, there is a paucity of organs with an increasing number of patients being diagnosed with end-stage lung disease. Ex vivo lung perfusion has emerged as a potential tool to assess the quality and to recondition marginal donor lungs prior to transplantation with the goal of increasing the donor pool. This technology has shown promise with similar results compared with the conventional technique of cold static preservation in terms of primary graft dysfunction and overall outcomes. This review provides an update on the results and uses of this technology. The review will also summarize clinical studies and techniques in reconditioning and assessing lungs on ex vivo lung perfusion. Last, we discuss how this technology can be applied to fields outside of transplantation such as thoracic oncology and bioengineering.

Machine perfusion strategies in liver transplantation

Machine perfusion is a hot topic in liver transplantation and several new perfusion concepts are currently developed. Prior to introduction into routine clinical practice, however, such perfusion approaches need to demonstrate their impact on liver function, post-transplant complications, utilization rates of high-risk organs, and cost benefits. Therefore, based on results of experimental and clinical studies, the community has to recognize the limitations of this technology. In this review, we summarize current perfusion concepts and differences between protective mechanisms of ex- and in-situ perfusion techniques. Next, we discuss which graft types may benefit most from perfusion techniques, and highlight the current understanding of liver viability testing. Finally, we present results from recent clinical trials involving machine liver perfusion, and analyze the value of different outcome parameters, currently used as endpoints for randomized controlled trials in the field.

Endothelial Glycocalyx Shedding Occurs during Ex Vivo Lung Perfusion: A Pilot Study

Background

Damage to the endothelium has been established as a key pathological process in lung transplantation and ex vivo lung perfusion (EVLP), a new technology that provides a platform for the assessment of injured donor lungs. Damage to the lung endothelial glycocalyx, a structure that lines the endothelium and is integral to vascular barrier function, has been associated with lung dysfunction. We hypothesised that endothelial glycocalyx shedding occurs during EVLP and aimed to establish a porcine model to investigate the mechanism underlying glycocalyx breakdown during EVLP.

Methods

Concentrations of endothelial glycocalyx breakdown products, syndecan-1, hyaluronan, heparan sulphate, and CD44, were measured using the ELISA and matrix metalloproteinase (MMP) activity by zymography in the perfusate of both human (n = 9) and porcine (n = 4) lungs undergoing EVLP. Porcine lungs underwent prolonged EVLP (up to 12 hours) with perfusion and ventilation parameters recorded hourly.

Results

During human EVLP, endothelial glycocalyx breakdown products in the perfusate increased over time. Increasing MMP-2 activity over time was positively correlated with levels of syndecan-1 (r = 0.886; p=0.03) and hyaluronan (r = 0.943; p=0.02). In the porcine EVLP model, hyaluronan was the only glycocalyx product detectable during EVLP (1 hr: 19 (13–84) vs 12 hr: 143 (109–264) ng/ml; p=0.13). Porcine hyaluronan was associated with MMP-9 activity (r = 0.83; p=0.02) and also with dynamic compliance (r = 0.57; p=0.03).

Conclusion

Endothelial glycocalyx products accumulate during both porcine and human EVLP, and this accumulation parallels an accumulation of matrix-degrading enzyme activity. Preliminary evidence in our porcine EVLP model suggests that shedding may be related to organ function, thus warranting additional study.

17β-Estradiol protects against lung injuries after brain death in male rats

BACKGROUND

Brain death elicits microvascular dysfunction and inflammation, and thereby compromises lung viability for transplantation. As 17β-estradiol was shown to be anti-inflammatory and vascular protective, we investigated its effects on lung injury after brain death in male rats.

METHODS

Wistar rats were assigned to: sham-operation by trepanation only (SH, n = 7); brain death (BD, n = 7); administration of 17β-estradiol (280 μg/kg, iv) at 60 minutes after brain death (BD-E2, n = 7). Experiments were performed 180 minutes thereafter. Histopathological changes in the lung were evaluated by histomorphometry. Gene expression of inducible nitric oxide synthase (iNOS), endothelial nitric oxide synthase (eNOS), and endothelin-1 was measured by real-time polymerase chain reaction. Protein expression of NO synthases, endothelin-1, platelet endothelial cell adhesion molecule-1 (PECAM-1), vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), BCL-2, and caspase 3 was assessed by immunohistochemistry. Cytokines were quantified by enzyme-linked immunosorbent assay.

RESULTS

Treatment with 17β-estradiol after brain death decreased lung edema and hemorrhage (p < 0.0001), and serum levels of cytokine-induced neutrophil chemoattractant-1 (CINC-1; p = 0.0020). iNOS (p < 0.0001) and VCAM-1 (p < 0.0001) also diminished at protein levels, while eNOS accumulated (p = 0.0002). However, gene expression of iNOS, eNOS, and endothelin-1 was comparable among groups, as was protein expression of endothelin-1, ICAM-1, BCL-2, and caspase 3.

CONCLUSIONS

17β-Estradiol effectively reduces lung injury in brain-dead rats mainly due to its ability to regulate NO synthases. Thus, the drug may improve lung viability for transplantation.

Feasibility of Lung Transplantation From Donation After Circulatory Death Donors Following Portable Ex Vivo Lung Perfusion: A Pilot Study

BACKGROUND

Donation after circulatory death (DCD) has the potential to significantly alleviate the shortage of transplantable lungs. We report our initial experience with the use of portable ex vivo lung perfusion (EVLP) with the Organ Care System Lung device for evaluation of DCD lungs.

METHODS

We performed a retrospective review of the DCD lung transplantation (LTx) experience at a single institution through the use of a prospective database.

RESULTS

From 2011 to 2015, 208 LTx were performed at the University of Alberta, of which 11 were DCD LTx with 7 (64%) that underwent portable EVLP. DCD lungs preserved with portable EVLP had a significantly shorter cold ischemic time (161 ± 44 vs 234 ± 60 minutes, P = .045), lower grade of primary graft dysfunction at 72 hours after LTx (0.4 ± 0.5 vs 2.1 ± 0.7, P = .003), similar mechanical ventilation time (55 ± 44 vs 103 ± 97 hours, P = .281), and hospital length of stay (29 ± 11 vs 33 ± 10 days, P = .610). All patients were alive at 1-year follow-up after LTx with improved functional outcomes and acceptable quality of life compared with before LTx, although there were no intergroup differences.

CONCLUSIONS

In our pilot cohort, portable EVLP was a feasible modality to increase confidence in the use of DCD lungs with validated objective evidence of lung function during EVLP that translates to acceptable clinical outcomes and quality of life after LTx. Further studies are needed to validate these initial findings in a larger cohort.

A single-center experience of 1500 lung transplant patients

OBJECTIVE

Over the past 30 years, lung transplantation has emerged as the definitive treatment for end-stage lung disease. In 2005, the lung allocation score (LAS) was introduced to allocate organs according to disease severity. The number of transplants performed annually in the United States continues to increase as centers have become more comfortable expanding donor and recipient criteria and have become more facile with the perioperative and long-term management of these patients. We report a single-center experience with lung transplants, looking at patients before and after the introduction of LAS.

METHODS

We retrospectively reviewed 1500 adult lung transplants at a single center performed between 1988 and 2016. Patients were separated into 2 groups, before and after the introduction of LAS: group 1 (April 1988 to April 2005; 792 patients) and group 2 (May 2005 to September 2016; 708 patients).

RESULTS

Differences in demographic data were noted over these periods, reflecting changes in allocation of organs. Group 1 patient average age was 48 ± 13 years, and 404 subjects (51%) were male. Disease processes included emphysema (52%; 412), cystic fibrosis (18.2%; 144), pulmonary fibrosis (16.1%; 128) and pulmonary vascular disease (7.2%; 57). Double lung transplant (77.7%; 615) was performed more frequently than single lung transplant (22.3%; 177). Group 2 average age was 50 ± 14 years, and 430 subjects (59%) were male. Disease processes included pulmonary fibrosis (46%; 335), emphysema (25.8%; 188), cystic fibrosis (17.7%; 127) and pulmonary vascular disease (1.6%; 11). Double lung transplant (96.2%; 681) was performed more frequently than single lung transplant (3.8%; 27). Overall incidence of grade 3 primary graft dysfunction (PGD) in group 1 was significantly lower at 22.1% (175) than in group 2 at 31.6% (230) (P < .001). Nonetheless, overall hospital mortality was not statistically different between the 2 groups (4.4% vs 3.5%; P < .4). Most notably, survival at 1 year was statistically different at 646 (81.6%) for group 1 and 665 (91.4%) for group 2 (P < .02).

CONCLUSIONS

Patient demographics over the study period have changed with an increased number of fibrotic patients transplanted. In addition, more aggressive strategies with donor/recipient selection appear to have resulted in a higher incidence of primary graft dysfunction. This does not, however, appear to affect patient survival on index hospitalization or at 1 year. In fact, we have observed a significant improvement in survival at 1 year in the more recent era. This observation suggests that continued expansion of possible donors and recipients, coupled with a more sophisticated understanding of primary graft dysfunction and long-term chronic rejection, can lead to increased transplant volume and prolonged survival.

Machine perfusion of thoracic organs

This article summarizes recent knowledge and clinical advances in machine perfusion (MP) of thoracic organs. MP of thoracic organs has gained much attention during the last decade. Clinical studies are investigating the role of MP to preserve, resuscitate, and assess heart and lungs prior to transplantation. Currently, MP of the cardiac allograft is essential in all type DCD heart transplantation while MP of the pulmonary allograft is mandatory in uncontrolled DCD lung transplantation. MP of thoracic organs also offers an exciting platform to further investigate downregulation of the innate and adaptive immunity prior to reperfusion of the allograft in recipients. MP provides a promising technology that allows pre-transplant preservation, resuscitation, assessment, repair, and conditioning of cardiac and pulmonary allografts outside the body in a near physiologic state prior to planned transplantation. Results of ongoing clinical trials are awaited to estimate the true clinical value of this new technology in advancing the field of heart and lung transplantation by increasing the total number and the quality of available organs and by further improving recipient early and long-term outcome.