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

Comparison of Ex Vivo Lung Perfusion, With or Without Albumin, With Static Cold Storage in a Rat Ex Vivo Lung Perfusion Model

Ex vivo lung perfusion is an alternative to static cold storage for lung preservation in clinical lung transplantation. This study aimed to compare ex vivo lung perfusion with an acellular solution versus static cold storage and to assess the role of albumin as an additive to the acellular perfusion solution. Rat heart-lung blocks from Sprague-Dawley rats, after 1 hour of warm ischemia, were immersed in a low-potassium dextran solution for another hour. Blocks were then placed on ex vivo lung perfusion for 3 hours, with or without the addition of 70 g/L of albumin. Parameters such as gas exchange, dynamic lung compliance, and pulmonary vascular resistance were evaluated every 30 minutes. Control lungs were preserved in low-potassium dextran solution at 4 °C for 4 hours (static cold storage group). Lung injury was assessed using wet-to-dry ratio, histology, immunohistochemistry, and TUNEL assay. Pulmonary vascular resistance significantly decreased between 30 and 60 minutes of ex vivo lung perfusion, whereas other lung function parameters remained stable throughout the 3 hours. No significant differences were observed between the ex vivo lung perfusion and ex vivo lung perfusion + albumin groups in terms of lung function or pathology assessment. Pathological findings indicated that ex vivo lung perfusion, with or without albumin, resulted in increased edema and apoptotic activity compared with lungs preserved by static cold storage. The addition of albumin to the ex vivo lung perfusion solution did not result in significant improvements in functional parameters or pathological findings.

Prolonged dialysis during ex vivo lung perfusion promotes inflammatory responses

Ex-vivo lung perfusion (EVLP) has extended the number of transplantable lungs by reconditioning marginal organs. However, EVLP is performed at 37°C without homeostatic regulation leading to metabolic wastes' accumulation in the perfusate and, as a corrective measure, the costly perfusate is repeatedly replaced during the standard of care procedure. As an interesting alternative, a hemodialyzer could be placed on the EVLP circuit, which was previously shown to rebalance the perfusate composition and to maintain lung function and viability without appearing to impact the global gene expression in the lung. Here, we assessed the biological effects of a hemodialyzer during EVLP by performing biochemical and refined functional genomic analyses over a 12h procedure in a pig model. We found that dialysis stabilized electrolytic and metabolic parameters of the perfusate but enhanced the gene expression and protein accumulation of several inflammatory cytokines and promoted a genomic profile predicting higher endothelial activation already at 6h and higher immune cytokine signaling at 12h. Therefore, epuration of EVLP with a dialyzer, while correcting features of the perfusate composition and maintaining the respiratory function, promotes inflammatory responses in the tissue. This finding suggests that modifying the metabolite composition of the perfusate by dialysis during EVLP can have detrimental effects on the tissue response and that this strategy should not be transferred as such to the clinic.

Therapeutic reconditioning of damaged lungs by transient heat stress during ex vivo lung perfusion

Ex vivo lung perfusion (EVLP) may serve as a platform for the pharmacologic repair of lung grafts before transplantation (LTx). We hypothesized that EVLP could also permit nonpharmacologic repair through the induction of a heat shock response, which confers stress adaptation via the expression of heat shock proteins (HSPs). Therefore, we evaluated whether transient heat application during EVLP (thermal preconditioning [TP]) might recondition damaged lungs before LTx. TP was performed during EVLP (3 hours) of rat lungs damaged by warm ischemia by transiently heating (30 minutes, 41.5 °C) the EVLP perfusate, followed by LTx (2 hours) reperfusion. We also assessed the TP (30 minutes, 42 °C) during EVLP (4 hours) of swine lungs damaged by prolonged cold ischemia. In rat lungs, TP induced HSP expression, reduced nuclear factor κB and inflammasome activity, oxidative stress, epithelial injury, inflammatory cytokines, necroptotic death signaling, and the expression of genes involved in innate immune and cell death pathways. After LTx, heated lungs displayed reduced inflammation, edema, histologic damage, improved compliance, and unchanged oxygenation. In pig lungs, TP induced HSP expression, reduced oxidative stress, inflammation, epithelial damage, vascular resistance, and ameliorated compliance. Collectively, these data indicate that transient heat application during EVLP promotes significant reconditioning of damaged lungs and improves their outcomes after 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.

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.

Experimental Models of Ischemic Lung Damage for the Study of Therapeutic Reconditioning During Ex Vivo Lung Perfusion

Background.

Ex vivo lung perfusion (EVLP) may allow therapeutic reconditioning of damaged lung grafts before transplantation. This study aimed to develop relevant rat models of lung damage to study EVLP therapeutic reconditioning for possible translational applications.

Methods.

Lungs from 31 rats were exposed to cold ischemia (CI) or warm ischemia (WI), inflated at various oxygen fractions (FiO₂), followed by 3 h EVLP. Five groups were studied as follow: (1) C21 (control): 3 h CI (FiO₂ 0.21); (2) C50: 3 h CI (FiO₂ 0.5); (3) W21: 1 h WI, followed by 2 h CI (FiO₂ 0.21); (4) W50: 1 h WI, followed by 2 h CI (FiO₂ 0.5); and (5) W2h: 2 h WI, followed by 1 h CI (FiO₂ 0.21). Following 3 h EVLP, we measured static pulmonary compliance (SPC), pulmonary vascular resistance, lung weight gain (edema), oxygenation capacity (differential partial pressure of oxygen), and protein carbonyls in lung tissue (oxidative stress), as well as lactate dehydrogenase (LDH, lung injury), nitrotyrosine (nitro-oxidative stress), interleukin-6 (IL-6, inflammation), and proteins (permeability edema) in bronchoalveolar lavage (BAL). Perivascular edema was quantified by histology.

Results.

No significant alterations were noted in C21 and C50 groups. W21 and W50 groups had reduced SPC and disclosed increased weight gain, BAL proteins, nitrotyrosine, and LDH. These changes were more severe in the W50 group, which also displayed greater oxidative stress. In contrast, both W21 and W50 showed comparable perivascular edema and BAL IL-6. In comparison with the other WI groups, W2h showed major weight gain, perivascular edema, SPC reduction, drop of differential partial pressure of oxygen, and massive increases of BAL LDH and proteins but comparable increase of IL-6 and biomarkers of oxidative stress.

Conclusions.

These models of lung damage of increasing severity might be helpful to evaluate new strategies for EVLP therapeutic reconditioning. A model combining 1 h WI and inflation at FiO₂ of 0.5 seems best suited for this purpose by reproducing major alterations of clinical lung ischemia-reperfusion injury.

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.

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.

Challenging the Ex Vivo Lung Perfusion Procedure With Continuous Dialysis in a Pig Model

BACKGROUND

Normothermic ex vivo lung perfusion (EVLP) increases the pool of donor lungs by requalifying marginal lungs refused for transplantation through the recovery of macroscopic and functional properties. However the cell response and metabolism occurring during EVLP generate a nonphysiological accumulation of electrolytes, metabolites, cytokines and other cellular byproducts which may have deleterious effects both at the organ and cell levels, with impact on transplantation outcomes.

METHODS

We analyzed the physiological, metabolic and genome-wide response of lungs undergoing a 6-hour EVLP procedure in a pig model in 4 experimental conditions: without perfusate modification, with partial replacement of fluid, and with adult or pediatric dialysis filters.

RESULTS

Adult and pediatric dialysis stabilized the electrolytic and metabolic profiles while maintaining acid-base and gas exchanges. Pediatric dialysis increased the level of IL-10 and IL-6 in the perfusate. Despite leading to modification of the perfusate composition, the 4 EVLP conditions did not affect the gene expression profiles which were associated in all cases with increased cell survival, cell proliferation, inflammatory response and cell movement, and with inhibition of bleeding.

CONCLUSIONS

Management of EVLP perfusate by periodic replacement and continuous dialysis has no significant effect on the lung function nor on the gene expression profiles ex vivo. These results suggest that the accumulation of dialysable cell products does not significantly alter the lung cell response during EVLP, a finding that may have impact on EVLP management in the clinic.

Effects of cold or warm ischemia and ex-vivo lung perfusion on the release of damage associated molecular patterns and inflammatory cytokines in experimental lung transplantation

BACKGROUND

Lung transplantation (LTx) is associated with sterile inflammation, possibly related to the release of damage associated molecular patterns (DAMPs) by injured allograft cells. We have measured cellular damage and the release of DAMPs and cytokines in an experimental model of LTx after cold or warm ischemia and examined the effect of pretreatment with ex-vivo lung perfusion (EVLP).

METHODS

Rat lungs were exposed to cold ischemia alone (CI group) or with 3h EVLP (CI-E group), warm ischemia alone (WI group) or with 3 hour EVLP (WI-E group), followed by LTx (2 hour). Bronchoalveolar lavage (BAL) was performed before (right lung) or after (left lung) LTx to measure LDH (marker of cellular injury), the DAMPs HMGB1, IL-33, HSP-70 and S100A8, and the cytokines IL-1β, IL-6, TNFα, and CXCL-1. Graft oxygenation capacity and static compliance after LTx were also determined.

RESULTS

Compared to CI, WI displayed cellular damage and inflammation without any increase of DAMPs after ischemia alone, but with a significant increase of HMGB1 and functional impairment after LTx. EVLP promoted significant inflammation in both cold (CI-E) and warm (WI-E) groups, which was not associated with cell death or DAMP release at the end of EVLP, but with the release of S100A8 after LTx. EVLP reduced graft damage and dysfunction in warm ischemic, but not cold ischemic, lungs.

CONCLUSIONS

The pathomechanisms of sterile lung inflammation during LTx are significantly dependent on the conditions. The release of HMGB1 (in the absence of EVLP) and S100A8 (following EVLP) may be important factors in the pathogenesis of LTx.

Poly(ADP-Ribose) Polymerase Inhibition in Acute Lung Injury. A Reemerging Concept

PARP1, the major isoform of a family of ADP-ribosylating enzymes, has been implicated in the regulation of various biological processes including DNA repair, gene transcription, and cell death. The concept that PARP1 becomes activated in acute lung injury (ALI) and that pharmacological inhibition or genetic deletion of this enzyme can provide therapeutic benefits emerged over 20 years ago. The current article provides an overview of the cellular mechanisms involved in the pathogenetic roles of PARP1 in ALI and provides an overview of the preclinical data supporting the efficacy of PARP (poly[ADP-ribose] polymerase) inhibitors. In recent years, several ultrapotent PARP inhibitors have been approved for clinical use (for the therapy of various oncological diseases): these newly-approved PARP inhibitors were recently reported to show efficacy in animal models of ALI. These observations offer the possibility of therapeutic repurposing of these inhibitors for patients with ALI. The current article lays out a potential roadmap for such repurposing efforts. In addition, the article also overviews the scientific basis of potentially applying PARP inhibitors for the experimental therapy of viral ALI, such as coronavirus disease (COVID-19)-associated ALI.

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.

A method for translational rat ex vivo lung perfusion experimentation

The application of ex vivo lung perfusion (EVLP) has significantly increased the successful clinical use of marginal donor lungs. While large animal EVLP models exist to test new strategies to improve organ repair, there is currently no rat EVLP model capable of maintaining long-term lung viability. Here, we describe a new rat EVLP model that addresses this need, while enabling the study of lung injury due to cold ischemic time (CIT). The technique involves perfusing and ventilating male Lewis rat donor lungs for 4 h before transplanting the left lung into a recipient rat and then evaluating lung function 2 h after reperfusion. To test injury within this model, lungs were divided into groups and exposed to different CITs (i.e., 20 min, 6 h, 12 h, 18 h and 24 h). Experiments involving the 24-h-CIT group were prematurely terminated due to the development of severe edema. For the other groups, no differences in the ratio of arterial oxygen partial pressure to fractional inspired oxygen ([Formula: see text]/[Formula: see text]) were observed during EVLP; however, lung compliance decreased over time in the 18-h group (P = 0.012) and the [Formula: see text]/[Formula: see text] of the blood from the left pulmonary vein 2 h after transplantation was lower compared with 20-min-CIT group (P = 0.0062). This new model maintained stable lung function during 4-h EVLP and after transplantation when exposed to up to 12 h of CIT.

Treatment with 3-aminobenzamide during ex vivo lung perfusion of damaged rat lungs reduces graft injury and dysfunction after transplantation

Ex vivo lung perfusion (EVLP) with pharmacological reconditioning may increase donor lung utilization for transplantation (LTx). 3-Aminobenzamide (3-AB), an inhibitor of poly(ADP-ribose) polymerase (PARP), reduces ex vivo lung injury in rat lungs damaged by warm ischemia (WI). Here we determined the effects of 3-AB reconditioning on graft outcome after LTx. Three groups of donor lungs were studied: Control (Ctrl): 1 hour WI + 3 hours cold ischemia (CI) + LTx; EVLP: 1 hour WI + 3 hours EVLP + LTx; EVLP + 3-AB: 1 hour WI + 3 hours EVLP + 3-AB (1 mg^. mL^-1 ) + LTx. Two hours after LTx, we determined lung graft compliance, edema, histology, neutrophil counts in bronchoalveolar lavage (BAL), mRNA levels of adhesion molecules within the graft, as well as concentrations of interleukin-6 and 10 (IL-6, IL-10) in BAL and plasma. 3-AB reconditioning during EVLP improved compliance and reduced lung edema, neutrophil infiltration, and the expression of adhesion molecules within the transplanted lungs. 3-AB also attenuated the IL-6/IL-10 ratio in BAL and plasma, supporting an improved balance between pro- and anti-inflammatory mediators. Thus, 3-AB reconditioning during EVLP of rat lung grafts damaged by WI markedly reduces inflammation, edema, and physiological deterioration after LTx, supporting the use of PARP inhibitors for the rehabilitation of damaged lungs during EVLP.

Donor Leukocyte Trafficking and Damage-associated Molecular Pattern Expression During Ex Vivo Lung Perfusion

Background.

While ex vivo lung perfusion (EVLP) has become established in lung transplantation, the cellular processes occurring during this period are not yet fully understood. Prior studies demonstrated that donor leukocytes (DLs) migrate from the graft into the perfusate during EVLP, but the distribution of DLs in graft and perfusate compartments has not been characterized. Moreover, cell death of DLs has been implicated in mediating graft injury during EVLP, but the underlying mechanisms have not been elucidated. We hypothesized the following: (1) there is a nonspecific migration of DLs from the graft into perfusate and (2) cell death of DLs releases damage-associated molecular patterns (DAMPs) that contribute to the inflammatory milieu during EVLP.

Methods.

EVLP was performed on rat lungs for 3 hours (N = 6). At the end of EVLP, flow cytometry was used to quantify the distribution of different DL cell types in both the graft and perfusate compartments. During EVLP, the perfusate was also sampled hourly to measure levels of DAMPs and downstream inflammatory cytokines generated during EVLP.

Results.

At the conclusion of EVLP, there was a significantly higher proportion of T and B cells present in the perfusate compartment compared with the graft compartment. There was a time-dependent increase in extracellular DNA and tumor necrosis factor α in the perfusate during EVLP.

Conclusions.

T cells and B cells are enriched in the perfusate compartment during EVLP. Cell death of DLs contributes to an accumulation of DAMPs during EVLP.

Inhibition of regulated necrosis attenuates receptor-interacting protein kinase 1-mediated ischemia-reperfusion injury after lung transplantation

BACKGROUND

Increasing evidence indicates that regulated necrosis plays a critical role during cell death caused by ischemia-reperfusion (IR) injury. Necroptosis is one form of regulated necrosis. Necrostatin-1 (Nec-1), an inhibitor of receptor-interacting protein kinase 1 (RIPK1), is known to reduce necroptosis. We investigated the effect of Nec-1 treatment on IR-induced lung injury in a rat lung transplant model.

METHODS

Lewis rats were divided into 4 groups (n = 6 each): (1) Control (no treatment), (2) Donor treatment (D), (3) Recipient treatment (R), and (4) Donor plus Recipient treatment (D+R) groups. Donor lungs were flushed and preserved for 18 hours at 4ºC before transplantation. Recipient animals underwent a left single lung transplant. After 2 hours of reperfusion, we assessed the physiologic function, cytokine expression, pathway activation, and the extent of necrosis.

RESULTS

Pulmonary gas exchange in D+R group was significantly better than in the other 3 groups (p = 0.003). Lung edema was significantly lower in the D+R group compared with the Control group (p = 0.006). The expression of interleukin-6 in lung tissue and plasma was significantly reduced in the D+R group compared with the Control group (p = 0.036). The percentage of necrotic cells in D+R group was significantly lower than in the Control and D groups (p = 0.01), indicating Nec-1inhibited regulated necrosis.

CONCLUSIONS

The administration of Nec-1 to both donor and recipient improved graft function after lung transplantation through the reduction of necroptosis. The inhibition of regulated necrosis appears to be a promising strategy to attenuate IR lung injury after lung transplantation.

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.

CD47 blockade reduces ischemia/reperfusion injury in donation after cardiac death rat kidney transplantation

Modulation of nitric oxide activity through blockade of CD47 signaling has been shown to reduce ischemia-reperfusion injury (IRI) in various models of tissue ischemia. Here, we evaluate the potential effect of an antibody-mediated CD47 blockade in a syngeneic and an allogeneic DCD rat kidney transplant model. The donor organ was subjected to 1 hour of warm ischemia time after circulatory cessation, then flushed with a CD47 monoclonal antibody (CD47mAb) in the treatment group, or an isotype-matched immunoglobulin in the control group. We found that CD47mAb treatment improved survival rates in both models. Serum markers of renal injury were significantly decreased in the CD47mAb-treated group compared with the control group. Histologically the CD47mAb-treated group had significantly reduced scores of acute tubular injury and acute tubular necrosis. The expression of biomarkers related to mitochondrial stress and apoptosis also were significantly lower in the CD47mAb-treated groups. Overall, the protective effects of CD47 blockade were greater in the syngeneic model. Our data show that CD47mAb blockade decreased the IRI of DCD kidneys in rat transplant models. This therapy has the potential to improve DCD kidney transplant outcomes in the human setting.

Epigallocatechin Gallate Reduces Ischemia/Reperfusion Injury in Isolated Perfused Rabbit Hearts

Cardioplegic arrest during heart operations is often used in cardiac surgery. During cardioplegia, the heart is subjected to a global ischemia/reperfusion-injury. (−)-epigallocatechin gallate (EGCG), one of the main ingredients of green tea, seems to be beneficial in various cardiac diseases. Therefore, the aim of our study was to evaluate EGCG in a rabbit model of cardioplegic arrest. Twenty four mature Chinchilla rabbits were examined. Rabbit hearts were isolated and perfused according to Langendorff. After induction of cardioplegia (without and with 20 µmol/L EGCG, n = 6 each) the hearts maintained arrested for 90-min. Thereafter, the hearts were re-perfused for 60 min. During the entire experiment hemodynamic and functional data were assessed. At the end of each experiment, left ventricular samples were processed for ATP measurements and for histological analysis. Directly after cessation of cardioplegia, all hearts showed the same decline in systolic and diastolic function. However, hearts of the EGCG-group showed a significantly faster and better hemodynamic recovery during reperfusion. In addition, tissue ATP-levels were significantly higher in the EGCG-treated hearts. Histological analysis revealed that markers of nitrosative and oxidative stress were significantly lower in the EGCG group. Thus, addition of EGCG significantly protected the cardiac muscle from ischemia/reperfusion injury.

Olesoxime Inhibits Cardioplegia-Induced Ischemia/Reperfusion Injury. A Study in Langendorff-Perfused Rabbit Hearts

Objective: During cardioplegia, which is often used in cardiac surgery, the heart is subjected to global ischemia/reperfusion injury, which can result in a post-operative impairment of cardiac function. Mitochondria permeability transition pores (MPTP) play a key role in cardiomyocyte survival after ischemia/reperfusion injury. It was shown in clinical settings that blockers of MPTP like cyclosporine might have a positive influence on cardiac function after cardioplegic arrest. Olesoxime, which is a new drug with MPTP blocking activity, has been introduced as a neuroprotective therapeutic agent. This drug has not been investigated on a possible positive effect in ischemia/reperfusion injury in hearts. Therefore, the aim of our study was to investigate possible effects of olesoxime on cardiac recovery after cardioplegic arrest.

Methods: We evaluated 14 mature Chinchilla bastard rabbits of 1,500–2,000 g. Rabbit hearts were isolated and perfused with constant pressure according to Langendorff. After induction of cardioplegic arrest (30 ml 4°C cold Custodiol cardioplegia without and with 5 μmol/L olesoxime, n = 7 each) the hearts maintained arrested for 90-min. Thereafter, the hearts were re-perfused for 60 min. At the end of each experiment left ventricular samples were frozen in liquid nitrogen for ATP measurements. Furthermore, heart slices were embedded in paraffin for histological analysis. During the entire experiment hemodynamic and functional data such as left ventricular pressure (LVP), dp/dt(max) and (min), pressure rate product (PRP), coronary flow, pO₂, and pCO₂ were also assessed.

Results: Histological analysis revealed that despite the same ischemic burden for both groups markers of nitrosative and oxidative stress were significantly lower in the olesoxime group. Moreover, hearts of the olesoxime-group showed a significantly faster and better hemodynamic recovery during reperfusion. In addition, tissue ATP-levels were significantly higher in the olesoxime treated hearts.

Conclusions: Olesoxime significantly protected the cardiac muscle from ischemia/reperfusion injury.

Opportunities for the repurposing of PARP inhibitors for the therapy of non-oncological diseases

The recent clinical availability of the PARP inhibitor olaparib (Lynparza) opens the door for potential therapeutic repurposing for non-oncological indications. Considering (a) the preclinical efficacy data with PARP inhibitors in non-oncological diseases and (b) the risk-benefit ratio of treating patients with a compound that inhibits an enzyme that has physiological roles in the regulation of DNA repair, we have selected indications, where (a) the severity of the disease is high, (b) the available therapeutic options are limited, and (c) the duration of PARP inhibitor administration could be short, to provide first-line options for therapeutic repurposing. These indications are as follows: acute ischaemic stroke; traumatic brain injury; septic shock; acute pancreatitis; and severe asthma and severe acute lung injury. In addition, chronic, devastating diseases, where alternative therapeutic options cannot halt disease development (e.g. Parkinson's disease, progressive multiple sclerosis or severe fibrotic diseases), should also be considered. We present a preclinical and clinical action plan for the repurposing of PARP inhibitors.

LINKED ARTICLES

This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Pyrrolidine dithiocarbamate administered during ex-vivo lung perfusion promotes rehabilitation of injured donor rat lungs obtained after prolonged warm ischemia

Damaged lung grafts obtained after circulatory death (DCD lungs) and warm ischemia may be at high risk of reperfusion injury after transplantation. Such lungs could be pharmacologically reconditioned using ex-vivo lung perfusion (EVLP). Since acute inflammation related to the activation of nuclear factor kappaB (NF-κB) is instrumental in lung reperfusion injury, we hypothesized that DCD lungs might be treated during EVLP by pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-κB. Rat lungs exposed to 1h warm ischemia and 2 h cold ischemia were subjected to EVLP during 4h, in absence (CTRL group, N = 6) or in presence of PDTC (2.5g/L, PDTC group, N = 6). Static pulmonary compliance (SPC), peak airway pressure (PAWP), pulmonary vascular resistance (PVR), and oxygenation capacity were determined during EVLP. After EVLP, we measured the weight gain of the heart-lung block (edema), and the concentration of LDH (cell damage), proteins (permeability edema) and of the cytokines IL-6, TNF-α and CINC-1 in bronchoalveolar lavage (BAL), and we evaluated NF-κB activation by the degree of phosphorylation and degradation of its inhibitor IκBα in lung tissue. In CTRL, we found significant NF-κB activation, lung edema, and a massive release of LDH, proteins and cytokines. SPC significantly decreased, PAWP and PVR increased, while oxygenation tended to decrease. Treatment with PDTC during EVLP inhibited NF-κB activation, did not influence LDH release, but markedly reduced lung edema and protein concentration in BAL, suppressed TNFα and IL-6 release, and abrogated the changes in SPC, PAWP and PVR, with unchanged oxygenation. In conclusion, suppression of innate immune activation during EVLP using the NF-κB inhibitor PDTC promotes significant improvement of damaged rat DCD lungs. Future studies will determine if such rehabilitated lungs are suitable for in vivo transplantation.