Innovative pulmonary preservation of non-heart-beating donor grafts in experimental lung transplantation1

Lung preservation: from perfusion to temperature

PURPOSE OF REVIEW

This article will review the evidence behind elements of the lung preservation process that have remained relatively stable over the past decade as well as summarize recent developments in ex-vivo lung perfusion and new research challenging the standard temperature for static cold storage.

RECENT FINDINGS

Ex-vivo lung perfusion is becoming an increasingly well established means to facilitate greater travel distance and allow for continued reassessment of marginal donor lungs. Preliminary reports of the use of normothermic regional perfusion to allow utilization of lungs after DCD recovery exist, but further research is needed to determine its ability to improve upon the current method of DCD lung recovery. Also, research from the University of Toronto is re-assessing the optimal temperature for static cold storage; pilot studies suggest it is a feasible means to allow for storage of lungs overnight to allow for daytime transplantation, but ongoing research is awaited to determine if outcomes are superior to traditional static cold storage.

SUMMARY

It is crucial to understand the fundamental principles of organ preservation to ensure optimal lung function posttransplant. Recent advances in the past several years have the potential to challenge standards of the past decade and reshape how lung transplantation is performed.

Stereological assessment of the blood-air barrier and the surfactant system after mesenchymal stem cell pretreatment in a porcine non-heart-beating donor model for lung transplantation

More frequent utilization of non-heart-beating donor (NHBD) organs for lung transplantation has the potential to relieve the shortage of donor organs. In particular with respect to uncontrolled NHBD, concerns exist regarding the risk of ischaemia/reperfusion (IR) injury-related graft damage or dysfunction. Due to their immunomodulating and tissue-remodelling properties, bone-marrow-derived mesenchymal stem cells (MSCs) have been suspected of playing a beneficial role regarding short- and long-term survival and function of the allograft. Thus, MSC administration might represent a promising pretreatment strategy for NHBD organs. To study the initial effects of warm ischaemia and MSC application, a large animal lung transplantation model was generated, and the structural organ composition of the transplanted lungs was analysed stereologically with particular respect to the blood-gas barrier and the surfactant system. In this study, porcine lungs (n = 5/group) were analysed. Group 1 was the sham-operated control group. In pigs of groups 2-4, cardiac arrest was induced, followed by a period of 3 h of ventilated ischaemia at room temperature. In groups 3 and 4, 50 × 10⁶ MSCs were administered intravascularly via the pulmonary artery and endobronchially, respectively, during the last 10 min of ischaemia. The left lungs were transplanted, followed by a reperfusion period of 4 h. Then, lungs were perfusion-fixed and processed for light and electron microscopy. Samples were analysed stereologically for IR injury-related structural parameters, including volume densities and absolute volumes of parenchyma components, alveolar septum components, intra-alveolar oedema, and the intracellular and intra-alveolar surfactant pool. Additionally, the volume-weighted mean volume of lamellar bodies (lbs) and their profile size distribution were determined. Three hours of ventilated warm ischaemia was tolerated without eliciting histological or ultrastructural signs of IR injury, as revealed by qualitative and quantitative assessment. However, warm ischaemia influenced the surfactant system. The volume-weighted mean volume of lbs was reduced significantly (P = 0.024) in groups subjected to ischaemia (group medians of groups 2-4: 0.180-0.373 μm³) compared with the sham control group (median 0.814 μm³). This was due to a lower number of large lb profiles (size classes 5-15). In contrast, the intra-alveolar surfactant system was not altered significantly. No significant differences were encountered comparing ischaemia alone (group 2) or ischaemia plus application of MSCs (groups 3 and 4) in this short-term model.

Mesenchymal stem cell pretreatment of non-heart-beating-donors in experimental lung transplantation

Background

Lung transplantation (LTx) is still limited by organ shortage. To expand the donor pool, lung retrieval from non-heart-beating donors (NHBD) was introduced into clinical practice recently. However, primary graft dysfunction with inactivation of endogenous surfactant due to ischemia/reperfusion-injury is a major cause of early mortality. Furthermore, donor-derived human mesenchymal stem cell (hMSC) expansion and fibrotic differentiation in the allograft results in bronchiolitis obliterans syndrome (BOS), a leading cause of post-LTx long-term mortality. Therefore, pretreatment of NHBD with recipient-specific bone-marrow-(BM)-derived hMSC might have the potential to both improve the postischemic allograft function and influence the long-term development of BOS by the numerous paracrine, immunomodulating and tissue-remodeling properties especially on type-II-pneumocytes of hMSC.

Methods

Asystolic pigs (n = 5/group) were ventilated for 3 h of warm ischemia (groups 2–4). 50x106 mesenchymal-stem-cells (MSC) were administered in the pulmonary artery (group 3) or nebulized endobronchially (group 4) before lung preservation. Following left-lung-transplantation, grafts were reperfused, pulmonary-vascular-resistance (PVR), oxygenation and dynamic-lung-compliance (DLC) were monitored and compared to control-lungs (group 2) and sham-controls (group 1). To prove and localize hMSC in the lung, cryosections were counter-stained. Intra-alveolar edema was determined stereologically. Statistics comprised ANOVA with repeated measurements.

Results

Oxygenation (p = 0.001) and PVR (p = 0.009) following endovascular application of hMSC were significantly inferior compared to Sham controls, whereas DLC was significantly higher in endobronchially pretreated lungs (p = 0.045) with overall sham-comparable outcome regarding oxygenation and PVR. Stereology revealed low intrapulmonary edema in all groups (p > 0.05). In cryosections of both unreperfused and reperfused grafts, hMSC were localized in vessels of alveolar septa (endovascular application) and alveolar lumen (endobronchial application), respectively.

Conclusions

Preischemic deposition of hMSC in donor lungs is feasible and effective, and endobronchial application is associated with significantly better DLC as compared to sham controls. In contrast, transvascular hMSC delivery results in inferior oxygenation and PVR. In the long term perspective, due to immunomodulatory, paracrine and tissue-remodeling effects on epithelial and endothelial restitution, an endobronchial NHBD allograft-pretreatment with autologous mesenchymal-stem-cells to attenuate limiting bronchiolitis-obliterans-syndrome in the long-term perspective might be promising in clinical lung transplantation. Subsequent work with chronic experiments is initiated to further elucidate this important field.

Electronic supplementary material

The online version of this article (doi:10.1186/s13019-014-0151-3) contains supplementary material, which is available to authorized users.

Effects of exogenous surfactant on the non-heart-beating donor lung graft in experimental lung transplantation - a stereological study

The use of non-heart-beating donor (NHBD) lungs may help to overcome the shortage of lung grafts in clinical lung transplantation, but warm ischaemia and ischaemia/reperfusion injury (I/R injury) resulting in primary graft dysfunction represent a considerable threat. Thus, better strategies for optimized preservation of lung grafts are urgently needed. Surfactant dysfunction has been shown to contribute to I/R injury, and surfactant replacement therapy is effective in enhancing lung function and structural integrity in related rat models. In the present study we hypothesize that surfactant replacement therapy reduces oedema formation in a pig model of NHBD lung transplantation. Oedema formation was quantified with (SF) and without (non-SF) surfactant replacement therapy in interstitial and alveolar compartments by means of design-based stereology in NHBD lungs 7 h after cardiac arrest, reperfusion and transplantation. A sham-operated group served as control. In both NHBD groups, nearly all animals died within the first hours after transplantation due to right heart failure. Both SF and non-SF developed an interstitial oedema of similar degree, as shown by an increase in septal wall volume and arithmetic mean thickness as well as an increase in the volume of peribron-chovascular connective tissue. Regarding intra-alveolar oedema, no statistically significant difference could be found between SF and non-SF. In conclusion, surfactant replacement therapy cannot prevent poor outcome after prolonged warm ischaemia of 7 h in this model. While the beneficial effects of surfactant replacement therapy have been observed in several experimental and clinical studies related to heart-beating donor lungs and cold ischaemia, it is unlikely that surfactant replacement therapy will overcome the shortage of organs in the context of prolonged warm ischaemia, for example, 7 h. Moreover, our data demonstrate that right heart function and dysfunctions of the pulmonary vascular bed are limiting factors that need to be addressed in NHBD.

Retrograde flush is more protective than heparin in the uncontrolled donation after circulatory death lung donor

BACKGROUND

Formation of microthrombi after circulatory arrest is a concern for the development of reperfusion injury in lung recipients from donation after circulatory death (DCD) donors. In this isolated lung reperfusion study, we compared the effect of postmortem heparinization with preharvest retrograde pulmonary flush or both.

METHODS

Domestic pigs (n = 6/group) were sacrificed by ventricular fibrillation and left at room temperature for 1 h. This was followed by 2.5 h of topical cooling. In control group [C], no heparin and no pulmonary flush were administered. In group [R], lungs were flushed with Perfadex in a retrograde way before explantation. In group [H], heparin (300 IU/kg) was administered 10 min after cardiac arrest followed by closed chest massage for 2 min. In the combined group, animals were heparinized and the lungs were explanted after retrograde flush [HR]. The left lung was assessed for 60 min in an ex vivo reperfusion model.

RESULTS

Pulmonary vascular resistance at 50 and 55 min was significantly lower in [R] and [HR] groups compared with [C] and [H] groups (P < 0.01 and P < 0.001) and at 60 min in [R], [H], and [HR] groups compared with [C] group (P < 0.001). Oxygenation, compliance, and plateau airway pressure were more stable in [R] and [HR] groups. Plateau airway pressure was significantly lower in [R] group compared with the [H] group at 60 min (P < 0.05). No significant differences in wet-dry weight ratio were observed between the groups.

CONCLUSIONS

This study suggests that preharvest retrograde flush is more protective than postmortem heparinization to prevent reperfusion injury in lungs recovered from donation after circulatory death donors.

Effect of preprocurement ventilation on lungs donated after cardiac death in a canine lung transplantation model

BACKGROUND

One method of countering chronic lung donor shortages is the practice of donation after cardiac death (DCD). However, this technique inevitably leads to pulmonary dysfunction related to warm ischemia. One promising method of alleviating this problem is ventilation. However, it can rarely be initiated from the onset of cardiac arrest, particularly in uncontrolled DCD donors. We investigated the protective effect of the last 60 min of ventilation during a 240-min warm ischemic time.

METHODS

We rendered donor dogs cardiac dead and left them at room temperature. Six dogs received ventilation with 100% oxygen for 60 min starting at 180 min after cardiac arrest (ventilation group). Eight dogs received no ventilation. Lungs were harvested 240 min after cardiac arrest, then transplanted into recipient dogs. At 60 min after reperfusion, the right pulmonary artery was ligated, and the function of the left transplanted lung was evaluated.

RESULTS

In the ventilation group, all six animals survived for 240 min after reperfusion, whereas in the nonventilation group, only four of eight survived. The ventilation group demonstrated significantly better pulmonary oxygenation, shunt fraction, and wet-to-dry weight ratio. Furthermore, the ventilation group revealed significantly higher levels of high-energy phosphates in the lung tissues, fewer apoptotic cells, lower levels of tumor necrosis factor-α and interleukin-8 messenger RNA in the lung tissues, and lower levels of interleukin-6 messenger RNA in the serum.

CONCLUSION

Our results suggest that ventilation during the late phase of the preprocurement period may ameliorate ischemia-reperfusion injury in DCD donors.

A practical approach to clinical lung transplantation from a Maastricht Category III donor with cardiac death

Although donation after cardiac death (DCD) has the potential to provide a novel source of organs for lung transplantation, even in a controlled DCD situation such as a Maastricht Category III donor (withdrawal of treatment), the limited time frame available after the declaration of death to initiate procurement and preservation remains challenging. Indeed, no publication has detailed the exact time frames and technique applicable for successful Maastricht Category III DCD lung procurement. In this patient report, withdrawal of life-support treatment and death certification was performed in the intensive care unit and the lungs were procured in an operating room 49 minutes after cardiac arrest and successfully transplanted (cold ischemia time <6 hours) into a severely ill recipient with primary pulmonary hypertension.

Non-heart-beating donors

The widespread application of lung transplantation is limited by the shortage of suitable donor organs resulting in longer waiting times for listed patients with a substantial risk of dying before transplantation. To overcome this critical organ shortage, some transplant programs have now begun to explore the use of lungs from circulation-arrested donors, so called non-heart-beating donors (NHBDs). This review outlines the different categories of NHBDs, the relevant published experimental data that support the use of lungs coming from these donors and the clinical experience worldwide so far. Techniques for NHBD lung preservation and pretransplant functional assessment are reviewed. Ethical issues involved in transplanting lungs from asystolic donors are discussed.