Method of isolated ex vivo lung perfusion in a rat model: lessons learned from developing a rat EVLP program

Polymerized Human Hemoglobin-Based Oxygen Carrier Preserves Lung Allograft Function During Normothermic Ex Vivo Lung Perfusion

Normothermic ex vivo lung perfusion (EVLP) can resuscitate marginal lung allografts to increase organs available for transplantation. During normothermic perfusion, cellular metabolism is more active compared with subnormothermic perfusion, creating a need for an oxygen (O 2 ) carrier in the perfusate. As an O 2 carrier, red blood cells (RBCs) are a scarce resource and are susceptible to hemolysis in perfusion circuits, thus releasing cell-free hemoglobin (Hb), which can extravasate into the tissue space, thus promoting scavenging of nitric oxide (NO) and oxidative tissue damage. Fortunately, polymerized human Hb (PolyhHb) represents a synthetic O 2 carrier with a larger molecular diameter compared with Hb, preventing extravasation, and limiting adverse reactions. In this study, a next-generation PolyhHb-based perfusate was compared to both RBC and asanguinous perfusates in a rat EVLP model. During EVLP, the pulmonary arterial pressure and pulmonary vascular resistance were both significantly higher in lungs perfused with RBCs, which is consistent with RBC hemolysis. Lungs perfused with PolyhHb demonstrated greater oxygenation than those perfused with RBCs. Post-EVLP analysis revealed that the PolyhHb perfusate elicited less cellular damage, extravasation, iron tissue deposition, and edema than either RBCs or colloid control. These results show promise for a next-generation PolyhHb to maintain lung function throughout EVLP.

The role of CD38 in ischemia reperfusion injury in cardiopulmonary bypass and thoracic transplantation: a narrative review

Background and Objective

Ischemia reperfusion injury (IRI) is often the underlying cause of endothelium breakdown and damage in cardiac or transplantation operations, which can lead to disastrous post-operative consequences. Recent studies of cluster of differentiation 38 (CD38) have identified its critical role in IRI. Our objective is to provide a comprehensive overview of CD38-mediated axis, pathways, and potential CD38 translational therapies for reducing inflammation associated with cardiopulmonary bypass (CPB) or thoracic transplantation and IRI.

Methods

We conducted a review of the literature by performing a search of the PubMed database on 2 April 2023. To find relevant publications on CD38, we utilized the MeSH terms: "CD38" AND "Ischemia" OR "CD38" AND "Transplant" OR "CD38" AND "Heart" from 1990-2023. Additional papers were included if they were felt to be relevant but were not captured in the MeSH terms. We found 160 papers that met this criterion, and following screening, exclusion and consensus a total of 36 papers were included.

Key Content and Findings

CD38 is most notably a nicotine adenine dinucleotide (NAD)+ glycohydrolase (NADase), and a generator of Ca2+ signaling secondary messengers. Ultimately, the release of these secondary messengers leads to the activation of important mediators of cellular death. In the heart and during thoracic transplantation, this pathway is intimately involved in a wide variety of injuries; namely the endothelium. In the heart, activation generally results in vasoconstriction, poor myocardial perfusion, and ultimately poor cardiac function. CD38 activation also prevents the accumulation of atherosclerotic disease. During transplantation, intracellular activation leads to infiltration of recipient innate immune cells, tissue edema, and ultimately primary graft dysfunction (PGD). Specifically, in heart transplantation, extracellular activation could be protective and improve allograft survival.

Conclusions

The knowledge gap in understanding the molecular basis of IRI has prevented further development of novel therapies and treatments. The possible interaction of CD38 with CD39 in the endothelium, and the modulation of the CD38 axis may be a pathway to improve cardiovascular outcomes, heart and lung donor organ quality, and overall longevity.

Cytochrome P450 2E1 predicts liver functional recovery from donation after circulatory death using air-ventilated normothermic machine perfusion

The optimal oxygen concentration is unclear for normothermic machine perfusion (NMP) of livers from donation after circulatory death (DCD). Our purposes were to investigate the effect of air-ventilated NMP on the DCD liver, analyze the underlying mechanism and select the targets to predict liver functional recovery with NMP. NMP was performed using the NMP system with either air ventilation or oxygen ventilation for 2 h in the rat liver following warm ischemia and cold-storage preservation. Proteomics and metabolomics were used to reveal the significant molecular networks. The bioinformation analysis was validated by administering peroxisome proliferator activator receptor-γ (PPARγ) antagonist and agonist via perfusion circuit in the air-ventilated NMP. Results showed that air-ventilated NMP conferred a better functional recovery and a less inflammatory response in the rat DCD liver; integrated proteomics and metabolomics analysis indicated that intrahepatic docosapentaenoic acid downregulation and upregulation of cytochrome P450 2E1 (CYP2E1) expression and activity were associated with DCD liver functional recovery with air-ventilated NMP; PPARγ antagonist worsened liver function under air-oxygenated NMP whereas PPARγ agonist played the opposite role. In conclusion, air-ventilated NMP confers a better liver function from DCD rats through the DAP-PPARγ-CYP2E1 axis; CYP2E1 activity provides a biomarker of liver functional recovery from DCD.

A translational rat model for ex vivo lung perfusion of pre-injured lungs after brain death

The process of brain death (BD) detrimentally affects donor lung quality. Ex vivo lung perfusion (EVLP) is a technique originally designed to evaluate marginal donor lungs. Nowadays, its potential as a treatment platform to repair damaged donor lungs is increasingly studied in experimental models. Rat models for EVLP have been described in literature before, yet the pathophysiology of BD was not included in these protocols and prolonged perfusion over 3 hours without anti-inflammatory additives was not achieved. We aimed to establish a model for prolonged EVLP of rat lungs from brain-dead donors, to provide a reliable platform for future experimental studies. Rat lungs were randomly assigned to one of four experimental groups (n = 7/group): 1) healthy, directly procured lungs, 2) lungs procured from rats subjected to 3 hours of BD and 1 hour cold storage (CS), 3) healthy, directly procured lungs subjected to 6 hours EVLP and 4), lungs procured from rats subjected to 3 hours of BD, 1 hour CS and 6 hours EVLP. Lungs from brain-dead rats showed deteriorated ventilation parameters and augmented lung damage when compared to healthy controls, in accordance with the pathophysiology of BD. Subsequent ex vivo perfusion for 6 hours was achieved, both for lungs of healthy donor rats as for pre-injured donor lungs from brain-dead rats. The worsened quality of lungs from brain-dead donors was evident during EVLP as well, as corroborated by deteriorated ventilation performance, increased lactate production and augmented inflammatory status during EVLP. In conclusion, we established a stable model for prolonged EVLP of pre-injured lungs from brain-dead donor rats. In this report we describe tips and pitfalls in the establishment of the rat EVLP model, to enhance reproducibility by other researchers.

MG53 as a Novel Therapeutic Protein to Treat Acute Lung Injury

INTRODUCTION

Lung injury has several inciting etiologies ranging from trauma (contusion and hemorrhage) to ischemia reperfusion injury. Reflective of the injury, tissue and cellular injury increases proportionally with the injury stress and is an area of potential intervention to mitigate the injury. This study aims to evaluate the therapeutic benefits of recombinant human MG53 (rhMG53) protein in porcine models of acute lung injury (ALI).

MATERIALS AND METHODS

We utilized live cell imaging to monitor the movement of MG53 in cultured human bronchial epithelial cells following mechanical injury. The in vivo efficacy of rhMG53 was evaluated in a porcine model of hemorrhagic shock/contusive lung injury. Varying doses of rhMG53 (0, 0.2, or 1 mg/kg) were administered intravenously to pigs after induction of hemorrhagic shock/contusive induced ALI. Ex vivo lung perfusion system enabled assessment of the isolated porcine lung after a warm ischemic induced injury with rhMG53 supplementation in the perfusate (1 mg/mL).

RESULTS

MG53-mediated cell membrane repair is preserved in human bronchial epithelial cells. rhMG53 mitigates lung injury in the porcine model of combined hemorrhagic shock/contusive lung injury. Ex vivo lung perfusion administration of rhMG53 reduces warm ischemia-induced injury to the isolated porcine lung.

CONCLUSIONS

MG53 is an endogenous protein that circulates in the bloodstream. Therapeutic treatment with exogenous rhMG53 may be part of a strategy to restore (partially or completely) structural morphology and/or functional lung integrity. Systemic administration of rhMG53 constitutes a potential effective therapeutic means to combat ALI.

Subnormothermic Ex Vivo Lung Perfusion Temperature Improves Graft Preservation in Lung Transplantation

Normothermic machine perfusion is clinically used to assess the quality of marginal donor lungs. Although subnormothermic temperatures have proven beneficial for other solid organ transplants, subnormothermia-related benefits of ex vivo lung perfusion (EVLP) still need to be investigated. Material and Methods: In a rat model, we evaluated the effects of 28 °C temperature on 4-h EVLPs with subsequent left lung transplantation. The recipients were observed for 2 h postoperatively. Lung physiology data were recorded and metabolic parameters were assessed. Results: During the 4-h subnormothermic EVLP, the lung oxygenation was significantly higher (p < 0.001), pulmonary vascular resistance (PVR) lower and dynamic compliance (Cdyn) higher when compared to the 37 °C EVLP. During an end-of-EVLP stress test, we recorded significantly higher flow (p < 0.05), lower PVR (p < 0.05) and higher Cdyn (p < 0.01) in the 28 °C group when compared to the 37 °C group. After the left lung transplantation, Cdyn and oxygenation improved in the 28 °C group, which were comparable to the 37 °C group. Chemokines RANTES, MIP-3α, MIP-1α MCP-1 GRO/KC and pro-inflammatory mediators GM-CSF, G-CSF and TNFα were significantly lower after the 28 °C EVLP and remained low in the plasma of the recipient rats after transplantation. The lungs of the 28 °C group showed significantly lowered myeloperoxidase activity and lowered levels of TNFα and IL-1β. Conclusions: Compared to the normothermic perfusion, the 28 °C EVLP improved Cdyn and PVR and reduced both the release of pro-inflammatory cytokines and myeloperoxidase activity in lung tissue. These observations were also observed after the left lung transplantation in the subnormothermic group. The 28 °C EVLP significantly improved biochemical, physiological and inflammatory parameters in lung donors.

A Novel Negative Pressure-Flow Waveform to Ventilate Lungs for Normothermic Ex Vivo Lung Perfusion

Ex vivo lung perfusion (EVLP) is increasingly used to treat and assess lungs before transplant. Minimizing ventilator induced lung injury (VILI) during EVLP is an important clinical need, and negative pressure ventilation (NPV) may reduce VILI compared with conventional positive pressure ventilation (PPV). However, it is not clear if NPV is intrinsically lung protective or if differences in respiratory pressure-flow waveforms are responsible for reduced VILI during NPV. In this study, we quantified lung injury using novel pressure-flow waveforms during normothermic EVLP. Rat lungs were ventilated-perfused ex vivo for 2 hours using tidal volume, positive end-expiratory pressure (PEEP), and respiratory rate matched PPV or NPV protocols. Airway pressures and flow rates were measured in real time and lungs were assessed for changes in compliance, pulmonary vascular resistance, oxygenation, edema, and cytokine secretion. Negative pressure ventilation lungs demonstrated reduced proinflammatory cytokine secretion, reduced weight gain, and reduced pulmonary vascular resistance (p < 0.05). Compliance was higher in NPV lungs (p < 0.05), and there was no difference in oxygenation between the two groups. Respiratory pressure-flow waveforms during NPV and PPV were significantly different (p < 0.05), especially during the inspiratory phase, where the NPV group exhibited rapid time-dependent changes in pressure and airflow whereas the PPV group exhibited slower changes in airflow/pressures. Lungs ventilated with PPV also had a greater transpulmonary pressure (p < 0.05). Greater improvement in lung function during NPV EVLP may be caused by favorable airflow patterns and/or pressure dynamics, which may better mimic human respiratory patterns.

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.

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.

Ex Vivo Modeling of Perioperative Air Leaks in Porcine Lungs

OBJECTIVE

A novel ex vivo model is described to advance the understanding of prolonged air leaks, one of the most common postoperative complications following thoracic resection procedures.

METHODS

As an alternative to in vivo testing, an ex vivo model simulating the various physiologic environments experienced by an isolated lung during the perioperative period was designed and built. Isolated porcine lungs were perfused and ventilated during open chest and closed chest simulations, mimicking intra and postoperative ventilation conditions. To assess and validate system capabilities, nine porcine lungs were tested by creating a standardized injury to create an approximately 250 cc/min air leak. Air leak rates, physiologic ventilation, and perfusion parameters were continuously monitored, while gas transfer analysis was performed on selected lungs. Segmental ventilation was monitored using electrical impedance tomography.

RESULTS

The evaluated lungs produced flow-volume and pressure-volume loops that approximated standard clinical representations under positive (mechanical) and negative (physiological) pressure ventilation modalities. Leak rate was averaged across the ventilation phases, and sharp increases in leak rate were observed between positive and negative pressure phases, suggesting that differences or changes in ventilation mechanics may strongly influence leak development.

CONCLUSION

The successful design and validation of a novel ex vivo lung model was achieved. Model output paralleled clinical observations. Pressure modality may also play a significant role in air leak severity.

SIGNIFICANCE

This work provides a foundation for future studies aimed at increasing the understanding of air leaks to better inform means of mitigating the risk of air leaks under clinically relevant conditions.

Application of ex vivo lung perfusion (EVLP) in lung transplantation

Lung transplantation was the ultimate method to treat the end-stage benign lung diseases. Although the lung transplantation has been increasing quickly in the past 30 years, the shortage of donor lung still limited its development. Ex vivo lung perfusion (EVLP) was a promising technique that could provide the platform to preserve, evaluate and repair the donor lung graft. In this article, we give a general review of the development of EVLP, its clinical application and the animal model. With the increasing experience of clinical EVLP, some pre-identified unsuitable donor lungs have been re-evaluated and accepted for transplantation. EVLP have now been considered to be an effective way to expand the donor pool.

Biliverdin Protects the Isolated Rat Lungs from Ischemia-reperfusion Injury via Antioxidative, Anti-inflammatory and Anti-apoptotic Effects

Background:

Biliverdin (BV) has a protective role against ischemia-reperfusion injury (IRI). However, the protective role and potential mechanisms of BV on lung IRI (LIRI) remain to be elucidated. Thus, we aimed to investigate the protective role and potential mechanisms of BV on LIRI.

Methods:

Lungs were isolated from Sprague-Dawley rats to establish an ex vivo LIRI model. After an initial 15 min stabilization period, the isolated lungs were subjected to ischemia for 60 min, followed by 90 min of reperfusion with or without BV treatment.

Results:

Lungs in the I/R group exhibited significant decrease in tidal volume (1.44 ± 0.23 ml/min in I/R group vs. 2.41 ± 0.31 ml/min in sham group; P < 0.001), lung compliance (0.27 ± 0.06 ml/cmH₂O in I/R group vs. 0.44 ± 0.09 ml/cmH₂O in sham group; P < 0.001; 1 cmH₂O=0.098 kPa), and oxygen partial pressure (PaO₂) levels (64.12 ± 12 mmHg in I/R group vs. 114 ± 8.0 mmHg in sham group; P < 0.001; 1 mmHg = 0.133 kPa). In contrast, these parameters in the BV group (2.27 ± 0.37 ml/min of tidal volume, 0.41 ± 0.10 ml/cmH₂O of compliance, and 98.7 ± 9.7 mmHg of PaO₂) were significantly higher compared with the I/R group (P = 0.004, P < 0.001, and P < 0.001, respectively). Compared to the I/R group, the contents of superoxide dismutase were significantly higher (47.07 ± 7.91 U/mg protein vs. 33.84 ± 10.15 U/mg protein; P = 0.005) while the wet/dry weight ratio (P < 0.01), methane dicarboxylic aldehyde (1.92 ± 0.25 nmol/mg protein vs. 2.67 ± 0.46 nmol/mg protein; P < 0.001), and adenosine triphosphate contents (297.05 ± 47.45 nmol/mg protein vs. 208.09 ± 29.11 nmol/mg protein; P = 0.005) were markedly lower in BV-treated lungs. Histological analysis revealed that BV alleviated LIRI. Furthermore, the expression of inflammatory cytokines (interleukin-1β, interleukin-6, and tumor necrosis factor-β) was downregulated and the expression of cyclooxygenase-2, inducible nitric oxide synthase, and Jun N-terminal kinase was significantly reduced in BV group (all P < 0.01 compared to I/R group). Finally, the apoptosis index in the BV group was significantly decreased (P < 0.01 compared to I/R group).

Conclusion:

BV protects lung IRI through its antioxidative, anti-inflammatory, and anti-apoptotic effects.

Ex Vivo Lung Perfusion in the Rat: Detailed Procedure and Videos

Ex vivo lung perfusion (EVLP) is a promising procedure for evaluation, reconditioning, and treatment of marginal lungs before transplantation. Small animal models can contribute to improve clinical development of this technique and represent a substantial platform for bio-molecular investigations. However, to accomplish this purpose, EVLP models must sustain a prolonged reperfusion without pharmacological interventions. Currently available protocols only partly satisfy this need. The aim of the present research was accomplishment and optimization of a reproducible model for a protracted rat EVLP in the absence of anti-inflammatory treatment. A 180 min, uninjured and untreated perfusion was achieved through a stepwise implementation of the protocol. Flow rate, temperature, and tidal volume were gradually increased during the initial reperfusion phase to reduce hemodynamic and oxidative stress. Low flow rate combined with open atrium and protective ventilation strategy were applied to prevent lung damage. The videos enclosed show management of the most critical technical steps. The stability and reproducibility of the present procedure were confirmed by lung function evaluation and edema assessment. The meticulous description of the protocol provided in this paper can enable other laboratories to reproduce it effortlessly, supporting research in the EVLP field.