Surfactant function in lung transplantation after 24 hours of ischemia: advantage of retrograde flush perfusion for preservation

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.

Improvement of surgical techniques for orthotopic single lung transplantation in rats

Background

Although orthotopic single lung transplantation in rats has long been established, this model is still highly challenging. Therefore, we made several modifications in anesthesia, lung extraction, vascular clamp, and transplantation procedures for this model.

Methods

Fifty cases of rat left lung transplantation were performed using traditional procedures and modified surgical techniques, respectively. Two hundred Sprague Dawley male rats, half as donors and half as recipients, were randomized equally to the two groups. The modifications included orotracheal intubation via a video laryngoscope, retrograde perfusion following anterograde perfusion, a Rummel tourniquet for the occlusion of pulmonary vessels, flushing the vessels and cuffs before anastomosis with heparin, and a simple pleural drainage. The surgical time, warm and cold ischemia time, vascular complications, and survival rate on postoperative day seven were compared between the two groups.

Results

The modified surgical techniques significantly reduced the surgical duration (35.7 vs. 46.3 min, P<0.01), warm ischemia time (16.3 vs. 28.8 min, P<0.01), and vascular complications (2% vs. 16%, P=0.04). Moreover, the survival rate on postoperative day 7 was higher in the improved surgical techniques group (96% vs. 80%, P=0.03).

Conclusions

We described the improvement of surgical techniques for orthotopic single lung transplantation in rats, which could shorten anastomoses time, reduce vascular complications, and improve survival rate.

Delayed non-myeloablative irradiation to induce long-term allograft acceptance in a large animal lung transplantation model

We previously induced long-term allograft acceptance in an allogeneic lung transplantation (LTx) model in miniature swine using perioperative non-myeloablative irradiation (IRR) combined with infusion of donor specific alloantigen. In order to improve clinical applicability, we delayed induction with irradiation in this study. Left sided single LTx was performed in minipigs. Group 1 received non-myeloablative irradiation (7Gy thymus and 1.5Gy whole body IRR) before LTx and a perioperative donor specific splenocyte infusion (SpTx). Group 2 received perioperative SpTx but delayed IRR three days after LTx. Group 3 was exposed to delayed IRR without SpTx. Whereas 4 out of 7 animals from the non-delayed group never rejected their grafts and were electively sacrificed on postoperative day (POD) +500, all animals from group 2 rejected their grafts before POD 108. In group 3, 3 out of 8 animals developed long-term allograft acceptance. In all groups, donor leukocyte chimerism peaked up to 20% in peripheral blood one hour after reperfusion of the lung. Group 1 maintained prolonged chimerism beyond POD 7, whereas chimerism levels in groups 2 and 3 decreased continuously thereafter. Delayed irradiation has the potential to improve long-term graft survival, yet not as efficient as a perioperative conditioning protocol.

Review of donor and recipient surgical procedures in lung transplantation

Lung transplant remains the only durable treatment of end stage lung disease. Efficient surgical technique and preservation strategy are of critical importance in avoiding ischemia reperfusion injury and primary graft dysfunction (PGD), both associated with poorer outcomes. We present our surgical and preservation strategy for both donor and recipient procedures, including endobronchial and intracorporeal lung assessment, mediastinal dissection, lung preservation, donor pneumonectomy, back bench preparation, recipient approach, pneumonectomy, along with the bronchial, pulmonary artery, and pulmonary venous anastomoses.

The Bronchial Arterial Circulation in Lung Transplantation: Bedside to Bench to Bedside, and Beyond

Chronic allograft dysfunction (CLAD) remains a major complication, causing the poor survival after lung transplantation (Tx). Although strenuous efforts have been made at preventing CLAD, surgical approaches for lung Tx have not been updated over the last 2 decades. The bronchial artery (BA), which supplies oxygenated blood to the airways and constitutes a functional microvasculature, has occasionally been revascularized during transplants, but this technique did not gain popularity and is not standard in current lung Tx protocols, despite the fact that a small number of studies have shown beneficial effects of BA revascularization on limiting CLAD. Also, recent basic and clinical evidence has demonstrated the relationship between microvasculature damage and CLAD. Thus, the protection of the bronchial circulation and microvasculature in lung grafts may be a key factor to overcome CLAD. This review revisits the history of BA revascularization, discusses the role of the bronchial circulation in lung Tx, and advocates for novel bronchial-arterial-circulation sparing approaches as a future direction for overcoming CLAD. Although there are some already published review articles summarizing the surgical techniques and their possible contribution to outcomes in lung Tx, to the best of our knowledge, this review is the first to elaborate on bronchial circulation that will contribute to prevent CLAD from both scientific and clinical perspectives: from bedside to bench to bedside, and beyond.

National Heart, Lung, and Blood Institute and American Association for Thoracic Surgery Workshop Report: Identifying collaborative clinical research priorities in lung transplantation

This report summarizes the discussion and recommendations from the June 2017 NHLBI-AATS Workshop on Identifying Collaborative Clinical Research Priorities in Lung Transplantation.

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.

Splenocyte Infusion and Whole-Body Irradiation for Induction of Peripheral Tolerance in Porcine Lung Transplantation: Modifications of the Preconditioning Regime for Improved Clinical Feasibility

BACKGROUND

Preoperative low-dose whole-body irradiation (IRR) with 1.5 and 7 Gy thymic IRR of the recipient, combined with a perioperative donor splenocyte infusion lead to reliable donor specific peripheral tolerance in our allogeneic porcine lung transplantation model. To reduce the toxicity of this preconditioning regime, modifications of the IRR protocol and their impact on allograft survival were assessed.

METHODS

Left-sided single lung transplantation from major histocompatibility complex and sex mismatched donors was performed in 14 adult female minipigs. Recipient animals were exposed to 3 different protocols of nonmyeloablative IRR within 12 hours before transplantation. All animals were administered a donor splenocyte infusion on the day of lung transplantation. Intravenous pharmacologic immunosuppression was withdrawn after 28 postoperative days. Allograft survival was monitored by chest radiographs and bronchoscopy.

RESULTS

IRR prolonged transplant survival in a dose- and field-dependent manner. Shielding of the bone marrow from IRR (total lymphoid IRR at 1.5 and 7 Gy thymic IRR) significantly reduced protocol toxicity defined as thrombocytopenia and consecutive increased bleeding propensity, but had a less effective impact on graft survival. Whole-body IRR at 0.5 and 7 Gy thymic IRR proved to be ineffective for reliable tolerance induction. Eventually, high levels of circulating CD4⁺CD25^high regulatory T cells were present in long-term survivors.

CONCLUSIONS

These data show that the infusion of donor-specific alloantigen in combination with IRR is efficient once a threshold dose is exceeded.

Augmentation of Transient Donor Cell Chimerism and Alloantigen-Specific Regulation of Lung Transplants in Miniature Swine

Donor alloantigen infusion induces T cell regulation and transplant tolerance in small animals. Here, we study donor splenocyte infusion in a large animal model of pulmonary transplantation. Major histocompatibility complex-mismatched single lung transplantation was performed in 28 minipigs followed by a 28-day course of methylprednisolone and tacrolimus. Some animals received a perioperative donor or third party splenocyte infusion, with or without low-dose irradiation (IRR) before surgery. Graft survival was significantly prolonged in animals receiving both donor splenocytes and IRR compared with controls with either donor splenocytes or IRR only. In animals with donor splenocytes and IRR, increased donor cell chimerism and CD4(+) CD25(high+) T cell frequencies were detected in peripheral blood associated with decreased interferon-γ production of leukocytes. Secondary third-party kidney transplants more than 2 years after pulmonary transplantation were acutely rejected despite maintained tolerance of the lung allografts. As a cellular control, additional animals received third-party splenocytes or donor splenocyte protein extracts. While animals treated with third-party splenocytes showed significant graft survival prolongation, the subcellular antigen infusion showed no such effect. In conclusion, minipigs conditioned with preoperative IRR and donor, or third-party, splenocyte infusions may develop long-term donor-specific pulmonary allograft survival in the presence of high levels of circulating regulatory T cells.

Advances in lung preservation

After a brief review of conventional lung preservation, this article discusses the rationale behind ex vivo lung perfusion and how it has shifted the paradigm of organ preservation from conventional static cold ischemia to the utilization of functional normothermia, restoring the lung's own metabolism and its reparative processes. Technical aspects and previous clinical experience as well as opportunities to address specific donor organ injuries in a personalized medicine approach are also reviewed.

Optimizing post-transplant outcomes in lung transplantation

Lung transplant recipients are at risk of numerous complications, which range from early events, such as primary graft dysfunction, to late events, including opportunistic infection or graft loss caused by chronic rejection. Although lung transplantation is often the only therapeutic option that can improve quality of life and prolong survival for many forms of end-stage lung disease, survival following lung transplantation is significantly worse than survival following transplantation of other solid organs. Carefully choosing potential recipients for listing, maximizing the likelihood that donor organs will function well following implantation, appropriate use of immunosuppressive agents to prevent allograft rejection, prophylactic or pre-emptive strategies to prevent allograft infection and appropriate surveillance to detect significant complications are key to maximizing the likelihood of prolonged graft and patient survival while avoiding significant complications following lung transplantation. Post-transplant outcomes will be optimized by a team approach to comprehensive management of the lung transplantation recipient combined with vigilant surveillance to detect complications in a timely fashion.

Preservation solution for lung transplantation

Despite the increasing success of lung transplantation as the mainstay therapeutic modality for end-stage lung disease, the 1-year survival rate after lung transplantation remains 80% and primary graft dysfunction (PGD) accounts for 30% of mortality. Ischemia-reperfusion injury has been identified as one of the main causes of PGD, and thus significant efforts have been made to optimize the methods for lung preservation in an attempt to minimize lung injury during the period of ischemia. The composition of the lung preservation solution used in the pulmonary artery flush has been considered to be the key to successful lung preservation, and many lung transplant programs have been shifting the use of the preservation solution from the intracellular fluid type to the extracellular fluid type because of preferable posttransplant lung function with the latter. This review summarizes the experimental and clinical studies on lung preservation, particularly focusing attention on the preservation solution being employed for clinical lung transplantation.

Lung transplantation for cystic fibrosis

Lung transplantation is a complex, high-risk, potentially life-saving therapy for the end-stage lung disease of cystic fibrosis (CF). The decision to pursue transplantation involves comparing the likelihood of survival with and without transplantation as well as assessing the effect of wait-listing and transplantation on the patient's quality of life. Although recent population-based analyses of the US lung allocation system for the CF population have raised controversies about the survival benefits of transplantation, studies from the United Kingdom and Canada have suggested a definite survival advantage for those receiving transplants. In response to these and other controversies, leaders in transplantation and CF met together in Lansdowne, Virginia, to consider the state of the art in lung transplantation for CF in an international context, focusing on advances in surgical technique, measurement of outcomes, use of prognostic criteria, variations in local control over listing, and prioritization among the United States, Canada, the United Kingdom, and The Netherlands, patient adherence before and after transplantation and other issues in the broader context of lung transplantation. Finally, the conference members carefully considered how efforts to improve outcomes for lung transplantation for CF lung disease might best be studied. This Roundtable seeks to communicate the substance of our discussions.

Present state of nonheart-beating lung donation

PURPOSE OF REVIEW

Indications for lung transplantation have increased through the years, and currently we have to face a lack of grafts to attend this growing demand with the subsequent increase in waiting-list deaths. Several strategies have been proposed to solve this challenging problem (living-lobe donors, extended donors, size-reduced lung grafts and so on), the use of nonheart-beating donors (NHBDs) being the most promising of them.

RECENT FINDINGS

The last experimental works concerning NHBDs have focused on the improvement of graft preservation in order to minimize warm ischemic injury and the capacity of noninvasive parameters in bronchial lavage to predict good function after implantation. There have also been several reports on the clinical use of controlled and uncontrolled NHBDs with excellent results.

CONCLUSION

Several methods have been effective in protecting these grafts from ischemic damage. Functional predictors will be very useful in the near future allowing us to know in a simple and noninvasive way which grafts are suitable for transplantation. Definitely, NHBDs for lung transplantation are no more a promising source of grafts but a real one, with encouraging short-term and mid-term results.

Pathogenesis, management, and consequences of primary graft dysfunction

Primary graft dysfunction continues to be a major contributing factor to morbidity and mortality after lung transplantation. This condition is presumed to be the result of ischemia-reperfusion injury, which is associated with the release of endogenous substances that can activate the innate immune system. Primary graft dysfunction has been shown to be an independent risk factor for the development of bronchiolitis obliterans syndrome indicating that it can shape alloimmune responses. In this review, we focus on the classification, pathogenesis, possible prevention strategies, management and consequences of primary graft dysfunction.

Postoperative intravenous infusion of donor-derived transplant acceptance-inducing cells as an adjunct immunosuppressive therapy in a porcine pulmonary allograft model

There is very limited published information testifying to the safety and possible complications of cell-based therapies. Accurately assessing the potential risks of translating novel, cell-based immunosuppressive protocols into clinical trials is therefore extremely difficult. This report describes the use of a pulmonary allograft model in outbred miniature pigs as a preliminary step in the development of a safe, clinically feasible, cell-based immunosuppressive protocol. Single lung transplants were performed in 22 MHC Class I-mismatched donor-recipient pairs, which were randomized between four treatment groups. For the first 28 days postoperatively, all animals were immunosuppressed with methylprednisilone and tacrolimus, with or without preoperative irradiation; subsequently, pharmacological immunosuppression was stopped in all treatment groups. Animals in two groups also received a central venous infusion of donor-derived 'transplant acceptance-inducing cells' (TAICs) on the seventh and 14th days postoperatively. Allograft survival was monitored by sequential chest X-rays, bronchoscopies and transbronchial biopsy histologies. No acute adverse events were associated with the administration of TAICs and there was no evidence of accelerated graft rejection. The observations presented in this report represent an important first step towards the development of a clinically applicable protocol for the use of TAIC therapy in lung transplantation.

Effects of exogenous surfactant instillation in clinical lung transplantation: a prospective, randomized trial

OBJECTIVE

Despite the introduction of low potassium-based preservation strategies for clinical lung transplantation, relevant early graft dysfunction occurs in up to 20% of cases after lung transplantation. This was found to be frequently associated with postreperfusion surfactant dysfunction. We performed a randomized, prospective study investigating the effect of exogenous surfactant instillation into human donor lungs on posttransplant surfactant function and on clinical outcome.

METHODS

Exogenous surfactant was instilled into 15 donor lungs before retrieval via bronchoscopy. Bronchoalveolar lavage fluids were taken before instillation as well as 24 hours after transplantation. Surfactant function, phospholipids, and protein content in bronchoalveolar lavage fluids were assessed and clinical data prospectively recorded. Pulmonary function testing was performed 4 weeks after lung transplantation. Additionally, the best forced expiratory volume in 1 second was determined within the first year after lung transplantation. The control group consisted of 14 patients receiving donor lungs without surfactant instillation in randomized order. Pulmonary function test results were further compared with those of 154 consecutive recipients of bilateral lung transplants, which were not involved in the study (historical control).

RESULTS

No deaths occurred during the first year after lung transplantation. Surfactant function in donor lungs was within normal ranges before harvest. In the control group, surfactant function was markedly impaired after reperfusion. This was significantly improved by surfactant substitution. Protein content of the bronchoalveolar lavage fluid in the surfactant group was significantly lower, indicating less leakage through the alveolocapillary membrane. Forced expiratory volume in 1 second after 4 weeks was significantly higher in the surfactant group than in either control group (P = .034 and .01, respectively). Interestingly, the best forced expiratory volume in 1 second during the first year after lung transplantation was significantly higher in both control groups compared with forced expiratory volume measured in examinations 4 weeks after lung transplantation (P = .01). The best forced expiratory volumes in 1 second of control patients were comparable with those in surfactant lungs 4 weeks after transplant.

CONCLUSIONS

This study indicates a protective effect of exogenous surfactant instillation to donor lungs before retrieval on post-lung transplantation surfactant function and on early clinical outcome. This approach may help to improve the outcome after lung transplantation in the future.

Preoperative Low-Dose Irradiation Promotes Long-Term Allograft Acceptance and Induces Regulatory T Cells in a Porcine Model of Pulmonary Transplantation

BACKGROUND

A simplified conditioning protocol including single-dose preoperative thymic and low-dose whole body irradiation with or without subsequent donor bone marrow transplantation (BMTx) can be applied in porcine lung transplantation. We hypothesized that this protocol would prolong allograft survival.

METHODS

Left-sided single lung transplantation from major histocompatibility complex (MHC)-mismatched donors was performed in 27 minipigs. Recipients received whole body (1.5 Gy) and thymic irradiation (7 Gy) before transplantation (IRR group, n=6), intravenous immunosuppression with methylprednisolone, cyclosporine, and azathioprine for 27 postoperative days (IS group, n=5) or both (IRR+IS group, n=10). BMTx group recipients were treated with irradiation, immunosuppression and a donor bone marrow infusion on postoperative day 1. Peripheral blood leukocyte phenotype and donor cell chimerism were monitored by flow cytometry. Purified CD25+ T cells from long-term survivors or rejecting animals were used for in vitro MLR suppression assays.

RESULTS

Median graft survival was: IRR 12 days, IS 55 days, IRR+IS 239 days, and BMTx 80 days (P<0.0001). Early peripheral blood macrochimerism was substantial in both the IRR+IS and the BMTX group but was lost in all groups after day 80. The frequency and suppressive function of CD4+CD25+ T cells were enhanced in IRR+IS group long-term survivors.

CONCLUSION

Although donor bone marrow infusion was not beneficial in our model, a substantial proportion of the animals treated with irradiation and a 28-day course of immunosuppression accepted their lung allografts long term. The mechanism involved in maintaining allograft tolerance may be based on peripheral T-cell regulation.

Influence of Inflated Lung Pressure on Lung Mechanical Properties during Cold Storage in Rats

The degree of lung inflation pressure during cold storage has a deep connection with lung functions after reperfusion. However, the change of the lung mechanical properties during cold storage at the different lung inflation pressure is unknown. We investigated the change of the mechanical properties both at the organ and the tissue level under different inflated lung pressure soon after the cold storage. In group I, the lungs were not preserved. In group II, the lungs were preserved in deflated condition. In groups III and IV, the lungs were inflated with room air at pressures of 14 and 25 cm H2O. After 24-hour storage, the input impedance (Z) was measured by a computer-controlled small animal ventilator (n = 8 each group). All data were analyzed using a homogeneous linear model, which includes airway resistance (R(aw)), tissue elastance (H), and tissue damping (G). Hysteresivity (eta) was calculated as G/H. After Z measurement, the tissue elasticity (Eqs) obtained from the quasi-static stress-strain curve was compared. We also analyzed the biochemical changes of surfactant in bronchoalveolar lavage (BAL) fluid. R(aw )was significantly lower in groups III and IV than in group I (p < 0.01). Hysteresivity (eta) was significantly lower in group IV than in groups I and III (p < 0.05). Eqs was significantly higher in groups III and IV than in groups I and II (p < 0.01). The total protein level in the BAL fluid of the preserved groups was significantly higher compared with group I (p < 0.01). We conclude that hyperinflated storage would deteriorate lung tissue mechanical properties.

Glutathione improves the function of porcine pulmonary grafts stored for twenty-four hours in low-potassium dextran solution

BACKGROUND

Flush perfusion with low-potassium dextran is the standard strategy in clinical lung preservation. Despite improved outcome, endothelial cell injury and surfactant dysfunction remain a significant problem after lung transplantation. The radical scavenger glutathione has been shown to be responsible for the efficacy of Celsior solution in lung preservation. We tested the hypothesis that the addition of glutathione to low-potassium dextran might further improve graft function by ameliorating ischemia-reperfusion injury.

METHODS

In 12 domestic pigs, lungs were flush preserved with either low-potassium dextran (n = 6) or low-potassium dextran supplemented by 5 mmol glutathione (n = 6). Left single lung transplantation was performed after 24-hour storage in low-potassium dextran at 8 degrees C. After 15 minutes of reperfusion the right main bronchus and pulmonary artery were crossclamped. Hemodynamic and respiratory measures were recorded in 30-minute intervals for a total observation period of 7 hours. Bronchoalveolar lavage fluid was obtained from the native lung and 2 hours after reperfusion from the graft. Bronchoalveolar lavage fluid and surfactant composition, and surfactant function analyses were performed. Neutrophil sequestration was assessed by myeloperoxidase activity assay. Tissue water content was calculated from wet/dry weight ratios at the end of the experiment.

RESULTS

In the low-potassium dextran group, 2 animals died during reperfusion. After reperfusion, pulmonary vascular resistance (P = .01) and pulmonary artery pressure remained lower in the glutathione/low-potassium dextran group, which was associated with a higher cardiac output (P = .05) in this group. Also, the oxygenation index at the end of the observation period was higher in the glutathione/low-potassium dextran group compared with the low-potassium dextran group (430 +/- 130 vs 338 +/- 184, respectively; P < .05). The graft water content representing postreperfusion lung edema was not different between the 2 study groups. Alteration of surfactant was less in the glutathione/low-potassium dextran group with a significantly decreased small to large aggregate ratio (P = .03) versus low-potassium dextran group. Myeloperoxidase activity was twice as high in the low-potassium dextran group when compared with the glutathione/low-potassium dextran group (glutathione/low-potassium dextran: 134 +/- 110 mU/g vs low-potassium dextran: 274 +/- 168 mU/g, P = .07).

CONCLUSION

The addition of glutathione to low-potassium dextran preservation solution reveals beneficial effects on vascular function and surfactant composition in transplanted lungs. Therefore, glutathione ameliorates ischemia-reperfusion injury in a preclinical model of lung transplantation. Future studies are needed to evaluate this promising modification in clinical lung transplantation.

Effects of Cold Preservation on the Lung Mechanical Properties in Rats

In lung transplantation, cold preservation is an important process. However, the mechanical changes in the airway and tissue during cold preservation, especially before reperfusion, are unknown. To test the hypothesis that the mechanical changes in the airway and lung parenchyma start during cold preservation, we investigated the mechanical properties of the rat lung as a whole organ and in excised lung strips. In the 0 h group, the lungs were not preserved. In the 9 and 24 h group, the lungs were preserved for 9 and 24 h at 4 degrees C. After preservation, we evaluated the static compliance (Csta) of the whole lung as obtained from the pressure volume curves (n=5 in each group). Also, we measured the input impedance taken by a computer-controlled small-animal ventilator (n=9 in each group). All data were analyzed using a homogeneous linear model, which includes airway resistance (Raw), tissue elastance (H), and tissue resistance (G). Hysteresivity (eta) was calculated as G/H. Moreover, the tissue elasticity (Eqs) obtained from the quasi-static stress-strain curves was compared. There was no significant difference in Csta among the three groups. Raw was significantly lower in the 24 h group than in the 0 h group (p<0.01). Eqs was significantly higher in the preserved groups than in the 0 h group (p<0.01). These results demonstrated that the changes in the three mechanical properties of the airway and the tissue started within 9 h of preservation.

Iloprost to improve surfactant function in porcine pulmonary grafts stored for twenty-four hours in low-potassium dextran solution

OBJECTIVES

The optimal strategy for pulmonary graft preservation remains elusive. Experimental work and initial clinical experience support low-potassium dextran solutions as lung perfusates. We have previously shown a protective effect of prostaglandin E 1 on ischemia-reperfusion injury in lung transplantation by a shift from proinflammatory to anti-inflammatory cytokines in a rat lung transplantation model. In this study, we tested the hypothesis that the addition of a prostacyclin analog (iloprost) to low-potassium dextran might lead to improved surfactant and ultimately graft function.

METHODS

In a randomized, blinded study with a porcine left single-lung transplantation model, donor lungs were flushed with 1 L of either low-potassium dextran solution or low-potassium dextran solution modified by the addition of 250 microg iloprost (n = 6 in each group). Grafts were stored at 4 degrees C for 24 hours. After transplantation, the right bronchus and pulmonary artery were clamped, and the animals remained dependent on the graft. Posttransplantation graft function was assessed throughout a 7-hour observation period by measuring oxygenation (30-minute intervals), different pulmonary and systemic hemodynamic parameters, and wet/dry lung weight ratios. Bronchoalveolar lavage fluid was obtained before and 2 hours after reperfusion. Surfactant function was measured from bronchoalveolar lavage fluid with a pulsating bubble surfactometer. Neutrophil sequestration was assessed by a myeloperoxidase assay performed on lung tissue specimens taken at the end of the observation period.

RESULTS

Pulmonary vascular resistance remained lower in the iloprost group than in the control group (P < .05). Tissue water content after 7 hours of reperfusion remained lower in the iloprost group (P < .05). In addition, significantly reduced myeloperoxidase tissue activity was observed in the iloprost group (P < .05). Although there was no difference in degradation of surface active surfactant large aggregates to small aggregates, the surface tension measured at minimal bubble diameter was lower in the iloprost group (P < .05).

CONCLUSIONS

Modification of low-potassium dextran solution with the prostacyclin analog iloprost resulted in a significant amelioration of ischemia-reperfusion injury and improved preservation of surfactant function in transplanted lungs. This intriguing approach merits further evaluation with respect to the mechanisms involved and, ultimately, potential introduction into clinical lung transplantation.

Lung preservation

Better understanding of the mechanisms of ischemia-reperfusion injury, improvement in the technique of lung preservation, and the recent introduction of a new preservation solution specifically developed for the lungs have helped to reduce the incidence of primary graft dysfunction after lung transplantation. Currently, the limitation in extending the ischemic time is more often related to the increasing use of non-ideal lung donors rather than to poor lung preservation. In this review, we have focused our attention on the experimental and clinical work performed to optimize the methods of lung preservation from the time of retrieval to the period of reperfusion after graft implantation.

Histopathological and immunohistochemical detection of protective effects of University of Wisconsin solution supplemented with iloprost on donor lung damage

OBJECTIVE

Histopathological evaluation and immunohistochemical markers of surfactant B and CD34 were used to detect alveolar type II cell and pulmonary endothelial cell damage in order to assess the efficacy on donor lung protection of University of Wisconsin (UW) solution supplementation with iloprost.

METHODS

Twelve rats were divided into two groups: UW solution was used alone in group I, and UW iloprost solution in group II. Lung samples were taken at regular intervals for pathological examination to evaluate alveolar cell integrity with hematoxylin and eosin staining. Preservation, of alveolar type II cell and pulmonary endothelial cells was assessed using surfactant B and CD34 immunomarkers, respectively.

RESULTS

In both groups, alveolar integrity, surfactant, and CD34 revealed time-dependent, progressive damage, although this deterioration was less apparent among the iloprost-supplemented group. Alveolar integrity was better preserved at 4, 6, 8, 12, and 48 hours among group II rate. Surfactant staining showed significantly more deterioration at 12 and 24 hours in group I. Similarly, CD34 demonstrated significantly more injury at 6, 12, 24, and 48 hours in group I.

CONCLUSION

Although progressive lung tissue damage assessed by histopathological and immunohistochemical methods was observed in both groups, our findings suggest less deterioration in the iloprost-supplemented group.

Lung transplantation. Lung preservation

Over the past decade, improvements in the technique of lung preservation have led to significant reduction in the incidence of ischemia-reperfusion-induced lung injury after lung transplantation. The challenge remains to improve the number of donor lungs available for transplantation. While the number of patients on the waiting list is constantly increasing, only 10% to 30% of donor lungs are currently being used for transplantation. Hence, the development of new strategies to assess, repair, and improve the quality of the lungs could have a tremendous impact on the number of transplants performed. In addition, an improved understanding of the mechanisms involved in lung preservation might help elucidate the potential link between acute lung injury and chronic graft dysfunction. In the future, genetic analysis using novel technologies such as microarray analysis will help researchers determine which genes control the injury seen in the transplantation process. Hopefully, this information will provide new insights into the mechanisms of injury and reveal potential new strategies and targets for therapies to improve lung preservation.

Improved lung function by means of retrograde flush in canine lung transplantation with non-heart-beating donors

OBJECTIVE

Use of lungs from non-heart-beating donors would increase the pulmonary donor pool. The aim of this study was to evaluate the effects of retrograde flush in canine lung transplantation from non-heart-beating donors.

METHODS

Left lung transplantation was performed in 12 weight-matched pairs of dogs. Donors were killed without heparinization, left at room temperature for 2 hours, and then randomized into 2 groups. In group AF (n = 6) lung retrieval was performed after flushing the lung block with low potassium dextran glucose (50 mL/kg) solution through the pulmonary artery. In group AF+RF (n = 6) additional retrograde flushing (low potassium dextran glucose, 25 mL/kg) was performed through the left atrium before retrieval. Flushed solution was sampled at intervals to measure hemoglobin concentrations. The lungs were preserved at 4 degrees C for 2 hours, and the left lung was implanted to the recipient being subjected to a total ischemic time of 5 hours. After left lung transplantation, the right pulmonary artery and main bronchus were ligated. Lung function, including arterial blood gas and pulmonary hemodynamics, was measured for 3 hours. For lung function study, statistical analyses were performed by using 1-way analysis of variance with repeated measures.

RESULTS

Group AF+RF had significantly better gas exchange and lower wet/dry weight ratio of the transplanted lung than group AF. Changes of hemoglobin concentration in the flushed solution indicated that additional retrograde flush could remove residual microthrombi after antegrade flush.

CONCLUSIONS

This study supports the theory that additional retrograde flush improves lung function after lung transplantation by removing residual pulmonary microthrombi in the lungs of non-heart-beating donors.

Ischemia-reperfusion-induced lung injury

Ischemia-reperfusion-induced lung injury is characterized by nonspecific alveolar damage, lung edema, and hypoxemia occurring within 72 hours after lung transplantation. The most severe form may lead to primary graft failure and remains a significant cause of morbidity and mortality after lung transplantation. Over the past decade, better understanding of the mechanisms of ischemia-reperfusion injury, improvements in the technique of lung preservation, and the development of a new preservation solution specifically for the lung have been associated with a reduction in the incidence of primary graft failure from approximately 30 to 15% or less. Several strategies have also been introduced into clinical practice for the prevention and treatment of ischemia-reperfusion-induced lung injury with various degrees of success. However, only three randomized, double-blinded, placebo-controlled trials on ischemia-reperfusion-induced lung injury have been reported in the literature. In the future, the development of new agents and their application in prospective clinical trials are to be expected to prevent the occurrence of this potentially devastating complication and to further improve the success of lung transplantation.

What is the role of surfactant and inhaled nitric oxide in lung transplantation?

Although numerous studies over the past 40 years have addressed this problem, initial graft failure is still a key question in clinical lung transplantation. As a possible tool to avoid and treat initial graft failure after lung transplantation, laboratory evidence and clinical reports currently emphasize the role of substitution therapy of surfactant combined with inhaled nitric oxide.