Pig lung transplant survival model

The combination of post-mortem sevoflurane ventilation and in situ topical cooling provides improved 6h lung preservation in an uncontrolled DCD porcine model

BACKGROUND

Recent clinical series on donation after uncontrolled cardiovascular death (uDCD) reported successful transplantation of lungs preserved by pulmonary inflation up to 3h post-mortem. This study aims to investigate the additive effects of in situ lowering of intrathoracic temperature and sevoflurane preconditioning on lung grafts in a porcine uDCD model.

METHODS

After uDCD induction, donor pigs were allocated to one of the following groups: Control - static lung inflation only (SLI); TC - SLI + continuous intrapleural topical cooling (TC); or TC+Sevo - SLI + TC + sevoflurane. Lungs were retrieved 6h post-asystole and evaluated via ex vivo lung perfusion (EVLP) for 6h. A left single lung transplant was performed using lungs from the best performing group, followed by 4h of graft evaluation.

RESULTS

Animals that received topical cooling achieved intrathoracic temperature < 15°C within 1 hour after chest filling of coolant. Only lungs from donors that received TC and TC+Sevo completed the planned post-preservation 6h EVLP assessment. Despite similar early performance of the two groups on EVLP, the TC+Sevo group was superior - associated with overall lower airway pressures, higher pulmonary compliances, less edema development, and less release of inflammatory cytokines. Transplantation was performed using lungs from the TC+Sevo group, and excellent graft function was observed post-reperfusion.

CONCLUSION

Preservation of uDCD lungs with a combination of static lung inflation, topical cooling and sevoflurane treatment maintains good pulmonary function up to 6h post-mortem with excellent early post-lung transplant function. These interventions may significantly expand the clinical utilization of uDCD donor lungs.

Amniotic fluid-derived mesenchymal stem cells reduce inflammation and improve lung function following transplantation in a porcine model

BACKGROUND

Lung transplantation is hindered by low donor lung utilization rates. Infectious complications are reasons to decline donor grafts due to fear of post-transplant primary graft dysfunction. Mesenchymal stem cells are a promising therapy currently investigated in treating lung injury. Full-term amniotic fluid-derived lung-specific mesenchymal stem cell treatment may regenerate damaged lungs. These cells have previously demonstrated inflammatory mediation in other respiratory diseases, and we hypothesized that treatment would improve donor lung quality and postoperative outcomes.

METHODS

In a transplantation model, donor pigs were stratified to either the treated or the nontreated group. Acute respiratory distress syndrome was induced in donor pigs and harvested lungs were placed on ex vivo lung perfusion (EVLP) before transplantation. Treatment consisted of 3 doses of 2 × 106 cells/kg: one during EVLP and 2 after transplantation. Donors and recipients were assessed on clinically relevant parameters and recipients were followed for 3 days before evaluation for primary graft dysfunction (PGD).

RESULTS

Repeated injection of the cell treatment showed reductions in inflammation seen through lowered immune cell counts, reduced histology signs of inflammation, and decreased cytokines in the plasma and bronchoalveolar lavage fluid. Treated recipients showed improved pulmonary function, including increased PaO2/FiO2 ratios and reduced incidence of PGD.

CONCLUSIONS

Repeated injection of lung-specific cell treatment during EVLP and post transplant was associated with improved function of previously damaged lungs. Cell treatment may be considered as a potential therapy to increase the number of lungs available for transplantation and the improvement of postoperative outcomes.

L-Alanyl-L-Glutamine Alleviated Ischemia-Reperfusion Injury and Primary Graft Dysfunction in Rat Lung Transplants

BACKGROUND

Concern of ischemia-reperfusion injury reduces utilization of donor lungs. We hypothesized adding L-alanyl-L-glutamine (L-AG) to preservation solution may protect donor lungs from ischemia-reperfusion injury through its multiple cytoprotective effects.

METHODS

A lung transplantation cell culture model was used on human lung epithelial cells and pulmonary microvascular endothelial cells, and the effects of adding different concentrations of L-AG on basic cellular function were tested. Rat donor lungs were preserved at 4 °C with 8 mmol/L L-AG for 12 h followed by 4 h reperfusion or monitored for 3 d. Lung function, lung histology, inflammation, and cell death biomarker were tested. Computerized tomography scan was used and metabolomic analysis was performed on lung tissues.

RESULTS

Cold preservation with L-AG improved cell viability and inhibited apoptosis in cell culture. Rat donor lungs treated with L-AG during cold storage showed decreased peak airway pressure, higher dynamic compliance and oxygenation ability, reduced lung injury, apoptosis, and oxidative stress during reperfusion. L-AG treatment significantly changed 130 metabolites during reperfusion, with enhanced amino acid biosynthesis and tricarboxylic acid cycle. Furthermore, cold storage with L-AG decreased primary graft dysfunction grade, improved oxygenation, reduced pulmonary atelectasis, sign of infection, and pneumothorax in a rat left lung transplant 3-d survival model.

CONCLUSIONS

Adding L-AG to cold preservation solution reduced lung injury and alleviated primary graft dysfunction by inhibiting inflammation, oxidative stress, and cell death with modified metabolic activities.

Surgical Protocol for Partial Heart Transplantation in Growing Piglets

Partial heart transplantation is a new approach to deliver growing heart valve implants. Partial heart transplants differ from heart transplants because only the part of the heart containing the necessary heart valve is transplanted. This allows partial heart transplants to grow, similar to the valves in heart transplants. However, the transplant biology of partial heart transplantation remains unexplored. This is a critical barrier to progress of the field. Without knowledge about the specific transplant biology of partial heart transplantation, children with partial heart transplants are empirically treated like children with heart transplants because the valves in heart transplants are known to grow. In order to progress the field, an animal model for partial heart transplantation is necessary. Here, we contribute our surgical protocol for partial heart transplantation in growing piglets. All aspects of partial heart transplantation, including the donor procedure, the recipient procedure, and recipient perioperative care are described in detail. There are important nuances in the conduct of virtually all aspects of open heart surgery that differs in piglets from humans. Our surgical protocol, which is based on our experience with 34 piglets, will allow other investigators to leverage our experience to seek fundamental knowledge about the nature of partial heart transplants. This is significant because the partial heart transplant model in piglets is complex and very resource intensive.

Lung Transplant Immunomodulation with Genetically Engineered Mesenchymal Stromal Cells-Therapeutic Window for Interleukin-10

Lung transplantation results are compromised by ischemia-reperfusion injury and alloimmune responses. Ex vivo lung perfusion (EVLP) is used to assess marginal donor lungs before transplantation but is also an excellent platform to apply novel therapeutics. We investigated donor lung immunomodulation using genetically engineered mesenchymal stromal cells with augmented production of human anti-inflammatory hIL-10 (MSCsIL-10). Pig lungs were placed on EVLP for 6 h and randomized to control (n = 7), intravascular delivery of 20 × 106 (n = 5, low dose) or 40 × 106 human MSCs IL-10 (n = 6, high dose). Subsequently, single-lung transplantation was performed, and recipient pigs were monitored for 3 days. hIL-10 secretion was measured during EVLP and after transplantation, and immunological effects were assessed by cytokine profile, T and myeloid cell characterization and mixed lymphocyte reaction. MSCIL-10 therapy rapidly increased hIL-10 during EVLP and resulted in transient hIL-10 elevation after lung transplantation. MSCIL-10 delivery did not affect lung function but was associated with dose-related immunomodulatory effects, with the low dose resulting in a beneficial decrease in apoptosis and lower macrophage activation, but the high MSCIL-10 dose resulting in inflammation and cytotoxic CD8+ T cell activation. MSCIL-10 therapy during EVLP results in a rapid and transient perioperative hIL-10 increase and has a therapeutic window for its immunomodulatory effects.

Creating superior lungs for transplantation with next-generation gene therapy during ex vivo lung perfusion

Engineering donor organs to better tolerate the harmful non-immunological and immunological responses inherently related to solid organ transplantation would improve transplant outcomes. Our enhanced knowledge of ischemia-reperfusion injury, alloimmune responses and pathological fibroproliferation after organ transplantation, and the advanced toolkit available for gene therapies, have brought this goal closer to clinical reality. Ex vivo organ perfusion has evolved rapidly especially in the field of lung transplantation, where clinicians routinely use ex vivo lung perfusion (EVLP) to confirm the quality of marginal donor lungs before transplantation, enabling safe transplantation of organs originally considered unusable. EVLP would also be an attractive platform to deliver gene therapies, as treatments could be administered to an isolated organ before transplantation, thereby providing a window for sophisticated organ engineering while minimizing off-target effects to the recipient. Here, we review the status of lung transplant first-generation gene therapies that focus on inducing transgene expression in the target cells. We also highlight recent advances in next-generation gene therapies, that enable gene editing and epigenetic engineering, that could be used to permanently change the donor organ genome and to induce widespread transcriptional gene expression modulation in the donor lung. In a future vision, dedicated organ repair and engineering centers will use gene editing and epigenetic engineering, to not only increase the donor organ pool, but to create superior organs that will function better and longer in the recipient.

Penehyclidine hydrochloride alleviates lung ischemia-reperfusion injury by inhibiting pyroptosis

OBJECTIVE

The aim of this research was to examine how penehyclidine hydrochloride (PHC) impacts the occurrence of pyroptosis in lung tissue cells within a rat model of lung ischemia-reperfusion injury.

METHODS

Twenty-four Sprague Dawley (SD) rats, weighing 250 g to 270 g, were randomly distributed into three distinct groups as outlined below: a sham operation group (S group), a control group (C group), and a test group (PHC group). Rats in the PHC group received a preliminary intravenous injection of PHC at a dose of 3 mg/kg. At the conclusion of the experiment, lung tissue and blood samples were collected and properly stored for subsequent analysis. The levels of malondialdehyde, superoxide dismutase, and myeloperoxidase in the lung tissue, as well as IL-18 and IL-1β in the blood serum, were assessed using an Elisa kit. Pyroptosis-related proteins, including Caspase1 p20, GSDMD-N, and NLRP3, were detected through the western blot method. Additionally, the dry-to-wet ratio (D/W) of the lung tissue and the findings from the blood gas analysis were also documented.

RESULTS

In contrast to the control group, the PHC group showed enhancements in oxygenation metrics, reductions in oxidative stress and inflammatory reactions, and a decrease in lung injury. Additionally, the PHC group exhibited lowered levels of pyroptosis-associated proteins, including the N-terminal segment of gasdermin D (GSDMD-N), caspase-1p20, and nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3).

CONCLUSION

Pre-administration of PHC has the potential to mitigate lung ischemia-reperfusion injuries by suppressing the pyroptosis of lung tissue cells, diminishing inflammatory reactions, and enhancing lung function. The primary mechanism behind anti-pyroptotic effect of PHC appears to involve the inhibition of oxidative stress.

Differential early response of monocyte/macrophage subsets to intra-operative corticosteroid administration in lung transplantation

Introduction

Lung transplantation often results in primary and/or chronic dysfunctions that are related to early perioperative innate allo-responses where myeloid subsets play a major role. Corticosteroids are administered upon surgery as a standard-of-care but their action on the different myeloid cell subsets in that context is not known.

Methods

To address this issue, we used a cross-circulatory platform perfusing an extracorporeal lung coupled to cell mapping in the pig model, that enabled us to study the recruited cells in the allogeneic lung over 10 hours.

Results

Myeloid cells, i.e. granulocytes and monocytic cells including classical CD14pos and non-classical/intermediate CD16pos cells, were the dominantly recruited subsets, with the latter upregulating the membrane expression of MHC class II and CD80/86 molecules. Whereas corticosteroids did not reduce the different cell subset recruitment, they potently dampened the MHC class II and CD80/86 expression on monocytic cells and not on alveolar macrophages. Besides, corticosteroids induced a temporary and partial anti-inflammatory gene profile depending on cytokines and monocyte/macrophage subsets.

Discussion

This work documents the baseline effects of the standard-of-care corticosteroid treatment for early innate allo-responses. These insights will enable further optimization and improvement of lung transplantation outcomes.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The Importance of Animal Models in Biomedical Research: Current Insights and Applications

Animal research is considered a key element in advance of biomedical science. Although its use is controversial and raises ethical challenges, the contribution of animal models in medicine is essential for understanding the physiopathology and novel treatment alternatives for several animal and human diseases. Current pandemics’ pathology, such as the 2019 Coronavirus disease, has been studied in primate, rodent, and porcine models to recognize infection routes and develop therapeutic protocols. Worldwide issues such as diabetes, obesity, neurological disorders, pain, rehabilitation medicine, and surgical techniques require studying the process in different animal species before testing them on humans. Due to their relevance, this article aims to discuss the importance of animal models in diverse lines of biomedical research by analyzing the contributions of the various species utilized in science over the past five years about key topics concerning human and animal health.

Preclinical Large Animal In-Vivo Experiments for Surgically Implanted Atrioventricular Valve: Reappraisal and Systematic Review

BACKGROUND

The development of atrioventricular bioprosthesis has witnessed an increasing drive toward clinical translation over the last few decades. A significant challenge in the clinical translation of an atrioventricular bioprosthesis from bench to bedside is the appropriate choice of a large animal model to test the safety and effectiveness of the device.

METHODS

We conducted a systematic review of pre-clinical in vivo studies that would enable us to synthesize a recommended framework. PRISMA (Preferred Reporting Items for Systematic Reviews and MetaAnalyses) guidelines were followed to identify and extract relevant articles.

RESULTS

Sheep was the most common choice of animal, with nine out of the 12 included studies being conducted on sheep. There were acute and chronic studies based on our search criteria. An average of ~20 and 5 animals were used for chronic and acute studies. One out of three acute studies and eight out of nine chronic studies were on stented heart valve bioprosthesis. All analyses were conducted on the implantation of atrioventricular valves with trileaflet, except for one chronic study on unileaflet valves and one chronic and acute study on bileaflet valves.

CONCLUSION

Understanding the variance in past pre-clinical study designs may increase the appropriate utilization of large animal models. This synthesized evidence provides a pre-clinical in vivo studies framework for future research on an atrioventricular bioprosthesis.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Successful 3-day lung preservation using a cyclic normothermic ex vivo lung perfusion strategy

Background

Methods

Findings

Interpretation

Funding

Reduction of primary graft dysfunction using cytokine adsorption during organ preservation and after lung transplantation

Despite improvements, lung transplantation remains hampered by both a scarcity of donor organs and by mortality following primary graft dysfunction (PGD). Since acute respiratory distress syndrome (ARDS) limits donor lungs utilization, we investigated cytokine adsorption as a means of treating ARDS donor lungs. We induced mild to moderate ARDS using lipopolysaccharide in 16 donor pigs. Lungs were then treated with or without cytokine adsorption during ex vivo lung perfusion (EVLP) and/or post-transplantation using extracorporeal hemoperfusion. The treatment significantly decreased cytokine levels during EVLP and decreased levels of immune cells post-transplantation. Histology demonstrated fewer signs of lung injury across both treatment periods and the incidence of PGD was significantly reduced among treated animals. Overall, cytokine adsorption was able to restore lung function and reduce PGD in lung transplantation. We suggest this treatment will increase the availability of donor lungs and increase the tolerability of donor lungs in the recipient.

Lung transplantation is hindered by the scarcity of organs and by mortality following primary graft dysfunction. Here, the authors show that cytokine absorption can be used in donor lungs during ex vivo lung perfusion and post-transplant, and leads to restored lung function and reduced primary graft dysfunction in animal models.

Right lung transplantation with a left-to-right inverted anastomosis in a rat model

Objective

Right lung transplantation in rats has been attempted occasionally, but the technical complexity makes it challenging to apply routinely. Additionally, basic research on inverted lobar lung transplantation is scarce because of the lack of a cost-effective experimental model. We first reported right lung transplantation in a rat model using left-to-right inverted anastomosis to imitate the principle of clinically inverted lung transplantation.

Methods

Right lung transplantation was performed in 10 consecutive rats. By using a 3-cuff technique, the left lung of the donor rat was implanted into the right thoracic cavity of the recipient rat. The rat lung graft was rotated 180° along the vertical axis to achieve anatomic matching of right hilar structures. Another 10 consecutive rats had received orthotopic left lung transplantation as a control.

Results

All lung transplantation procedures were technically successful without intraoperative failure. One rat (10%) died of full pulmonary atelectasis after right lung transplantation, whereas all rats survived after left lung transplantation. No significant difference was observed in heart-lung block retrieval (8.6 ± 0.8 vs 8.4 ± 0.9 minutes), cuff preparation (8.3 ± 0.9 vs 8.7 ± 0.9 minutes), or total procedure time (58.2 ± 2.6 vs 56.6 ± 2.1 minutes) between the right lung transplantation and standard left lung transplantation groups (P > .05), although the cold ischemia time (14.2 ± 0.9 vs 25.5 ± 1.7 minutes) and warm ischemia time (19.8 ± 1.5 vs 13.7 ± 1.8 minutes) were different (P < .001).

Conclusions

Right lung transplantation with a left-to-right inverted anastomosis in a rat model is technically easy to master, expeditious, and reproducible. It can potentially imitate the principle of clinically inverted lung transplantation and become an alternative to standard left lung transplantation.

The de novo assembly of a European wild boar genome revealed unique patterns of chromosomal structural variations and segmental duplications

The rapid progress of sequencing technology has greatly facilitated the de novo genome assembly of pig breeds. However, the assembly of the wild boar genome is still lacking, hampering our understanding of chromosomal and genomic evolution during domestication from wild boars into domestic pigs. Here, we sequenced and de novo assembled a European wild boar genome (ASM2165605v1) using the long‐range information provided by 10× Linked‐Reads sequencing. We achieved a high‐quality assembly with contig N50 of 26.09 Mb. Additionally, 1.64% of the contigs (222) with lengths from 107.65 kb to 75.36 Mb covered 90.3% of the total genome size of ASM2165605v1 (~2.5 Gb). Mapping analysis revealed that the contigs can fill 24.73% (93/376) of the gaps present in the orthologous regions of the updated pig reference genome (Sscrofa11.1). We further improved the contigs into chromosome level with a reference‐assistant scaffolding method. Using the ‘assembly‐to‐assembly’ approach, we identified intra‐chromosomal large structural variations (SVs, length >1 kb) between ASM2165605v1 and Sscrofa11.1 assemblies. Interestingly, we found that the number of SV events on the X chromosome deviated significantly from the linear models fitting autosomes (R² > 0.64, p < 0.001). Specifically, deletions and insertions were deficient on the X chromosome by 66.14 and 58.41% respectively, whereas duplications and inversions were excessive on the X chromosome by 71.96 and 107.61% respectively. We further used the large segmental duplications (SDs, >1 kb) events as a proxy to understand the large‐scale inter‐chromosomal evolution, by resolving parental‐derived relationships for SD pairs. We revealed a significant excess of SD movements from the X chromosome to autosomes (p < 0.001), consistent with the expectation of meiotic sex chromosome inactivation. Enrichment analyses indicated that the genes within derived SD copies on autosomes were significantly related to biological processes involving nervous system, lipid biosynthesis and sperm motility (p < 0.01). Together, our analyses of the de novo assembly of ASM2165605v1 provides insight into the SVs between European wild boar and domestic pig, in addition to the ongoing process of meiotic sex chromosome inactivation in driving inter‐chromosomal interaction between the sex chromosome and autosomes.

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

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

Animal Models in Allogenic Solid Organ Transplantation

Animal models provide the link between in vitro research and the first in-man application during clinical trials. They provide substantial information in preclinical studies for the assessment of new therapeutic interventions in advance of human clinical trials. However, each model has its advantages and limitations in the ability to imitate specific pathomechanisms. Therefore, the selection of an animal model for the evaluation of a specific research question or evaluation of a novel therapeutic strategy requires a precise analysis. Transplantation research is a discipline that largely benefits from the use of animal models with mouse and pig models being the most frequently used models in organ transplantation research. A suitable animal model should reflect best the situation in humans, and the researcher should be aware of the similarities as well as the limitations of the chosen model. Small animal models with rats and mice are contributing to the majority of animal experiments with the obvious advantages of these models being easy handling, low costs, and high reproductive rates. However, unfortunately, they often do not translate to clinical use. Large animal models, especially in transplantation medicine, are an important element for establishing preclinical models that do often translate to the clinic. Nevertheless, they can be costly, present increased regulatory requirements, and often are of high ethical concern. Therefore, it is crucial to select the right animal model from which extrapolations and valid conclusions can be obtained and translated into the human situation. This review provides an overview in the models frequently used in organ transplantation research.

The susceptibility of the aortic root: porcine aortic rupture testing under cardiopulmonary bypass

Background

In our earlier study on the functional limits of the aneurysmal aortic root we determined the pig root is susceptible to failure at high aortic pressures levels. We established a pig rupture model using cardiopulmonary bypass to determine the most susceptible region of the aortic root under the highest pressures achievable using continuous flow, and what changes occur in these regions on a macroscopic and histological level. This information may help guide clinical management of aortic root and ascending aorta pathology.

Methods

Five pigs underwent 4D flow MRI imaging pre surgery to determine vasopressor induced wall sheer stress and flow parameters. All pigs were then placed on cardiopulmonary bypass (CPB) via median sternotomy, and maximal aortic root and ascending aorta flows were initiated until rupture or failure, to determine the most susceptible region of the aorta. The heart was explanted and analysed histologically to determine if histological changes mirror the macroscopic observations.

Results

The magnetic resonance imaging (MRI) aortic flow and wall sheer stress (WSS) increased significantly in all regions of the aorta, and the median maximal pressures obtained during cardiopulmonary bypass was 497 mmHg and median maximal flows was 3.96 L/m. The area of failure in all experiments was the non-coronary cusp of the aortic valve. Collagen and elastin composition (%) was greatest in the proximal regions of the aorta. Collagen I and III showed greatest content in the inner aortic root and ascending aorta regions.

Conclusions

This unique porcine model shows that the aortic root is most susceptible to failure at high continuous aortic pressures, supported histologically by different changes in collagen content and subtypes in the aortic root. With further analysis, this information could guide management of the aortic root in disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13019-021-01667-9.

Static lung storage at 10°C maintains mitochondrial health and preserves donor organ function

[Figure: see text].

Pilot Trial of Extended Hypothermic Lung Preservation to Analyze Ischemia-reperfusion Injury in Pigs

BACKGROUND

In lung transplantation (LT), the length of ischemia time is controversial as it was arbitrarily stablished. We ought to explore the impact of extended cold-ischemia time (CIT) on ischemia-reperfusion injury in an experimental model.

METHODS

Experimental, randomized pilot trial of parallel groups and final blind analysis using a swine model of LT. Donor animals (n=8) were submitted to organ procurement. Lungs were subjected to 6h (n=4) or 12h (n=4) aerobic hypothermic preservation. The left lung was transplanted and re-perfused for 4h. Lung biopsies were obtained at (i) the beginning of CIT, (ii) the end of CIT, (iii) 30min after reperfusion, and (iv) 4h after reperfusion. Lung-grafts were histologically assessed by microscopic lung injury score and wet-to-dry ratio. Inflammatory response was measured by determination of inflammatory cytokines. Caspase-3 activity was determined as apoptosis marker.

RESULTS

We observed no differences on lung injury score or wet-to-dry ratio any given time between lungs subjected to 6h-CIT or 12h-CIT. IL-1β and IL6 showed an upward trend during reperfusion in both groups. TNF-α was peaked within 30min of reperfusion. IFN-γ was hardly detected. Caspase-3 immunoexpression was graded semiquantitatively by the percentage of stained cells. Twenty percent of apoptotic cells were observed 30min after reperfusion.

CONCLUSIONS

We observed that 6 and 12h of CIT were equivalent in terms of microscopic lung injury, inflammatory profile and apoptosis in a LT swine model. The extent of lung injury measured by microscopic lung injury score, proinflammatory cytokines and caspase-3 determination was mild.

The pig as a medical model for acquired respiratory diseases and dysfunctions: An immunological perspective

By definition no model is perfect, and this also holds for biology and health sciences. In medicine, murine models are, and will be indispensable for long, thanks to their reasonable cost and huge choice of transgenic strains and molecular tools. On the other side, non-human primates remain the best animal models although their use is limited because of financial and obvious ethical reasons. In the field of respiratory diseases, specific clinical models such as sheep and cotton rat for bronchiolitis, or ferret and Syrian hamster for influenza and Covid-19, have been successfully developed, however, in these species, the toolbox for biological analysis remains scarce. In this view the porcine medical model is appearing as the third, intermediate, choice, between murine and primate. Herein we would like to present the pros and cons of pig as a model for acquired respiratory conditions, through an immunological point of view. Indeed, important progresses have been made in pig immunology during the last decade that allowed the precise description of immune molecules and cell phenotypes and functions. These progresses might allow the use of pig as clinical model of human respiratory diseases but also as a species of interest to perform basic research explorations.

Pilot Trial of Extended Hypothermic Lung Preservation to Analyze Ischemia-reperfusion Injury in Pigs

BACKGROUND

In lung transplantation (LT), the length of ischemia time is controversial as it was arbitrarily stablished. We ought to explore the impact of extended cold-ischemia time (CIT) on ischemia-reperfusion injury in an experimental model.

METHODS

Experimental, randomized pilot trial of parallel groups and final blind analysis using a swine model of LT. Donor animals (n=8) were submitted to organ procurement. Lungs were subjected to 6h (n=4) or 12h (n=4) aerobic hypothermic preservation. The left lung was transplanted and re-perfused for 4h. Lung biopsies were obtained at (i) the beginning of CIT, (ii) the end of CIT, (iii) 30min after reperfusion, and (iv) 4h after reperfusion. Lung-grafts were histologically assessed by microscopic lung injury score and wet-to-dry ratio. Inflammatory response was measured by determination of inflammatory cytokines. Caspase-3 activity was determined as apoptosis marker.

RESULTS

We observed no differences on lung injury score or wet-to-dry ratio any given time between lungs subjected to 6h-CIT or 12h-CIT. IL-1β and IL6 showed an upward trend during reperfusion in both groups. TNF-α was peaked within 30min of reperfusion. IFN-γ was hardly detected. Caspase-3 immunoexpression was graded semiquantitatively by the percentage of stained cells. Twenty percent of apoptotic cells were observed 30min after reperfusion.

CONCLUSIONS

We observed that 6 and 12h of CIT were equivalent in terms of microscopic lung injury, inflammatory profile and apoptosis in a LT swine model. The extent of lung injury measured by microscopic lung injury score, proinflammatory cytokines and caspase-3 determination was mild.

A novel experimental porcine model to assess the impact of differential pulmonary blood flow on ischemia-reperfusion injury after unilateral lung transplantation

BACKGROUND

Primary graft dysfunction (PGD) remains a major obstacle after lung transplantation. Ischemia-reperfusion injury is a known contributor to the development of PGD following lung transplantation. We developed a novel approach to assess the impact of increased pulmonary blood flow in a large porcine single-left lung transplantation model.

MATERIALS

Twelve porcine left lung transplants were divided in two groups (n = 6, in low- (LF) and high-flow (HF) group). Donor lungs were stored for 24 h on ice, followed by left lung transplantation. In the HF group, recipient animals were observed for 6 h after reperfusion with partially clamping right pulmonary artery to achieve a higher flow (target flow 40-60% of total cardiac output) to the transplanted lung compared to the LF group, where the right pulmonary artery was not clamped.

RESULTS

Survival at 6 h was 100% in both groups. Histological, functional and biological assessment did not significantly differ between both groups during the first 6 h of reperfusion. injury was also present in the right native lung and showed signs compatible with the pathophysiological hallmarks of ischemia-reperfusion injury.

CONCLUSIONS

Partial clamping native pulmonary artery in large animal lung transplantation setting to study the impact of low versus high pulmonary flow on the development of ischemia reperfusion is feasible. In our study, differential blood flow had no effect on IRI. However, our findings might impact future studies with extracorporeal devices and represent a specific intra-operative problem during bilateral sequential single-lung transplantation.

Expression of Claudin-4 in Lung Ischemia-Reperfusion Injury in Experimental Lung Transplantation

OBJECTIVE

To assess the presence of CLDN4 in bronchoalveolar lavage fluid (BALF) and pulmonary tissue as an early indicator of LIRI and its relationship with changes in pulmonary physiology, edema formation and histology in an experimental porcine model of LTx with CIT of 50 min or 6 h.

METHODS

In 12 pigs, LIRI was produced by: group I (n = 6) LTx with 50 min of CIT (LTx-50 min-CIT); and group II (n = 6) LTx with 6 h of CIT (LTx-6h-CIT). The lung function, edema formation, macroscopic and microscopic changes were assessed. CLDN4 expression in BALF and pulmonary tissue were determined.

RESULTS

Both groups presented similar clinical, edema, and histological damage, as well as similar expression of CLDN4 in BALF and tissue (p > 0.05, RM-ANOVA).

CONCLUSION

CLDN4 expressed in BALF and the pulmonary tissue during the first 5 h within 72 h of the PGD window are not associated by the deterioration of lung function, edema and lung histological injury, in LTx with CIT 50 min or 6 h, CLDN4 does not seem to be a valuable indicator of LIRI.

Large Animal Models in Regenerative Medicine and Tissue Engineering: To Do or Not to Do

Rapid developments in Regenerative Medicine and Tissue Engineering has witnessed an increasing drive toward clinical translation of breakthrough technologies. However, the progression of promising preclinical data to achieve successful clinical market authorisation remains a bottleneck. One hurdle for progress to the clinic is the transition from small animal research to advanced preclinical studies in large animals to test safety and efficacy of products. Notwithstanding this, to draw meaningful and reliable conclusions from animal experiments it is critical that the species and disease model of choice is relevant to answer the research question as well as the clinical problem. Selecting the most appropriate animal model requires in-depth knowledge of specific species and breeds to ascertain the adequacy of the model and outcome measures that closely mirror the clinical situation. Traditional reductionist approaches in animal experiments, which often do not sufficiently reflect the studied disease, are still the norm and can result in a disconnect in outcomes observed between animal studies and clinical trials. To address these concerns a reconsideration in approach will be required. This should include a stepwise approach using in vitro and ex vivo experiments as well as in silico modeling to minimize the need for in vivo studies for screening and early development studies, followed by large animal models which more closely resemble human disease. Naturally occurring, or spontaneous diseases in large animals remain a largely untapped resource, and given the similarities in pathophysiology to humans they not only allow for studying new treatment strategies but also disease etiology and prevention. Naturally occurring disease models, particularly for longer lived large animal species, allow for studying disorders at an age when the disease is most prevalent. As these diseases are usually also a concern in the chosen veterinary species they would be beneficiaries of newly developed therapies. Improved awareness of the progress in animal models is mutually beneficial for animals, researchers, human and veterinary patients. In this overview we describe advantages and disadvantages of various animal models including domesticated and companion animals used in regenerative medicine and tissue engineering to provide an informed choice of disease-relevant animal models.

Donor prone positioning protects lungs from injury during warm ischemia

A large proportion of controlled donation after circulatory death (cDCD) donor lungs are declined because cardiac arrest does not occur within a suitable time after the withdrawal of life-sustaining therapy. Improved strategies to preserve lungs after asystole may allow the recovery team to arrive after death actually occurs and enable the recovery of lungs from more cDCD donors. The aim of this study was to determine the effect of donor positioning on the quality of lung preservation after cardiac arrest in a cDCD model. Cardiac arrest was induced by withdrawal of ventilation under anesthesia in pigs. After asystole, animals were divided into 2 groups based on body positioning (supine or prone). All animals were subjected to 3 hours of warm ischemia. After the observation period, donor lungs were explanted and preserved at 4°C for 6 hours, followed by 6 hours of physiologic and biological lung assessment under normothermic ex vivo lung perfusion. Donor lungs from the prone group displayed significantly greater quality as reflected by better function during ex vivo lung perfusion, less edema formation, less cell death, and decreased inflammation compared with the supine group. A simple maneuver of donor prone positioning after cardiac arrest significantly improves lung graft preservation and function.

Inactivating hepatitis C virus in donor lungs using light therapies during normothermic ex vivo lung perfusion

Availability of organs is a limiting factor for lung transplantation, leading to substantial mortality rates on the wait list. Use of organs from donors with transmissible viral infections, such as hepatitis C virus (HCV), would increase organ donation, but these organs are generally not offered for transplantation due to a high risk of transmission. Here, we develop a method for treatment of HCV-infected human donor lungs that prevents HCV transmission. Physical viral clearance in combination with germicidal light-based therapies during normothermic ex-vivo Lung Perfusion (EVLP), a method for assessment and treatment of injured donor lungs, inactivates HCV virus in a short period of time. Such treatment is shown to be safe using a large animal EVLP-to-lung transplantation model. This strategy of treating viral infection in a donor organ during preservation could significantly increase the availability of organs for transplantation and encourages further clinical development.

Organs from donors with transmissible viral infections, such as hepatitis C virus (HCV), are not offered for transplantation due to a high risk of transmission. Here, Galasso et al. develop a method for treatment of HCV-infected human donor lungs that is safe and prevents HCV transmission in the pig model.