Impact of Warm Ischemia on Different Leukocytes in Bronchoalveolar Lavage From Mouse Lung: Possible New Targets to Condition the Pulmonary Graft From the Non–Heart-Beating Donor

Hemopexin alleviates sterile inflammation in ischemia-reperfusion-induced lung injury

Introduction

Pulmonary ischemia-reperfusion (IR) injury (IRI) plays a significant role in various lung disorders and is a key factor in the development of primary graft dysfunction following lung transplantation. Hemopexin (Hx) is the major serum scavenger protein for heme, which is a prooxidant and pro-inflammatory compound. In the current study, we hypothesized that Hx could confer beneficial effects in sterile inflammation induced by IR-mediated lung injury.

Methods

To examine this hypothesis, we administered Hx in an experimental mouse model of unilateral lung IRI.

Results

Our results demonstrate that treatment with Hx alleviated histopathological signs of inflammation in ischemic lungs, as evidenced by a reduction in the number of infiltrating neutrophils and decreased levels of perivascular edema. In addition, thrombotic vaso-occlusion in pulmonary blood vessels of IRI lungs was reduced by Hx. Immunohistochemical analysis revealed that Hx inhibited the up-regulation of heme oxygenase-1, an enzyme highly induced by heme, in ischemic lungs. Finally, Hx administration caused a decrease in the levels of circulating B- and CD8+ T-lymphocytes in the peripheral blood of mice with pulmonary IRI.

Conclusion

These findings suggest that the serum heme scavenger protein Hx holds therapeutic promise in alleviating lung IRI-mediated sterile inflammation. Thus, Hx may represent a preemptive therapeutic approach in IR-related lung disorders such as primary graft dysfunction in lung transplantation.

B cells mediate lung ischemia/reperfusion injury by recruiting classical monocytes via synergistic B cell receptor/TLR4 signaling

Ischemia/reperfusion injury-mediated (IRI-mediated) primary graft dysfunction (PGD) adversely affects both short- and long-term outcomes after lung transplantation, a procedure that remains the only treatment option for patients suffering from end-stage respiratory failure. While B cells are known to regulate adaptive immune responses, their role in lung IRI is not well understood. Here, we demonstrated by intravital imaging that B cells are rapidly recruited to injured lungs, where they extravasate into the parenchyma. Using hilar clamping and transplant models, we observed that lung-infiltrating B cells produce the monocyte chemokine CCL7 in a TLR4-TRIF-dependent fashion, a critical step contributing to classical monocyte (CM) recruitment and subsequent neutrophil extravasation, resulting in worse lung function. We found that synergistic BCR-TLR4 activation on B cells is required for the recruitment of CMs to the injured lung. Finally, we corroborated our findings in reperfused human lungs, in which we observed a correlation between B cell infiltration and CM recruitment after transplantation. This study describes a role for B cells as critical orchestrators of lung IRI. As B cells can be depleted with currently available agents, our study provides a rationale for clinical trials investigating B cell-targeting therapies.

Necroptosis triggers spatially restricted neutrophil-mediated vascular damage during lung ischemia reperfusion injury

Intravital imaging, oxidative lipidomics, and a transplant model were used to define mechanisms that regulate neutrophil recruitment into lungs during ischemia reperfusion injury, a clinically relevant form of sterile inflammation. We found that early neutrophil-mediated damage is largely confined to the subpleural vasculature, a process that is orchestrated by a spatially restricted distribution of nonclassical monocytes that produce chemokines following necroptosis of pulmonary cells. Neutrophils disrupt the integrity of subpleural capillaries, which is associated with impaired lung function. Neutrophil-mediated vascular leakage is dependent on TLR4 expression on vascular endothelium, NOX4 signaling, and formation of neutrophil extracellular traps. Our research provides insights into mechanisms that regulate neutrophil recruitment during sterile lung inflammation and lays the foundation for developing new therapies.

Ischemia reperfusion injury represents a common pathological condition that is triggered by the release of endogenous ligands. While neutrophils are known to play a critical role in its pathogenesis, the tissue-specific spatiotemporal regulation of ischemia-reperfusion injury is not understood. Here, using oxidative lipidomics and intravital imaging of transplanted mouse lungs that are subjected to severe ischemia reperfusion injury, we discovered that necroptosis, a nonapoptotic form of cell death, triggers the recruitment of neutrophils. During the initial stages of inflammation, neutrophils traffic predominantly to subpleural vessels, where their aggregation is directed by chemoattractants produced by nonclassical monocytes that are spatially restricted in this vascular compartment. Subsequent neutrophilic disruption of capillaries resulting in vascular leakage is associated with impaired graft function. We found that TLR4 signaling in vascular endothelial cells and downstream NADPH oxidase 4 expression mediate the arrest of neutrophils, a step upstream of their extravasation. Neutrophil extracellular traps formed in injured lungs and their disruption with DNase prevented vascular leakage and ameliorated primary graft dysfunction. Thus, we have uncovered mechanisms that regulate the initial recruitment of neutrophils to injured lungs, which result in selective damage to subpleural pulmonary vessels and primary graft dysfunction. Our findings could lead to the development of new therapeutics that protect lungs from ischemia reperfusion injury.

Portable normothermic ex-vivo lung perfusion, ventilation, and functional assessment with the Organ Care System on donor lung use for transplantation from extended-criteria donors (EXPAND): a single-arm, pivotal trial

BACKGROUND

Donor lung use for transplantation is the lowest among solid organ tranplants because of several complex and multifactorial reasons; one area that could have a substantial role is the limited capabilities of cold ischaemic storage. The aim of the EXPAND trial was to evaluate the efficacy of normothermic portable Organ Care System (OCS) Lung perfusion and ventilation on donor lung use from extended-criteria donors and donors after circulatory death, which are rarely used.

METHODS

In this single-arm, pivotal trial done in eight institutions across the USA, Germany, and Belgium, lungs from extended-criteria donors were included if fulfilling one or more of the following criteria: a ratio of partial pressure of arterial oxygen (PaO₂) to fractional concentration of oxygen inspired air (FiO₂) in the donor lung of 300 mm Hg or less; expected ischaemic time longer than 6 h; donor age 55 years or older; or lungs from donors after circulatory death that were recruited and assessed using OCS Lung. Lungs were transplanted if they showed stability of OCS Lung variables, PaO₂:FiO₂ was more than 300 mm Hg, and they were accepted by the transplanting surgeon. Patients were adult bilateral lung transplant recipients. The primary efficacy endpoint was a composite of patient survival at day 30 post-transplant and absence of The International Society for Heart & Lung Tranplantation primary-graft dysfunction grade 3 (PGD3) within 72 h post-transplantation, with a prespecified objective performance goal of 65%. The primary analysis population was all transplanted recipients. This trial is registered with ClinicalTrials.gov, number NCT01963780, and is now complete.

FINDINGS

Between Jan 23, 2014, and Oct 23, 2016, 93 lung pairs were perfused, ventilated, and assessed on the OCS Lung. 12 lungs did not meet OCS transplantation criteria so 81 lungs were suitable for transplantation. Two lungs were excluded for logistical reasons, hence 79 (87%) of eligible lungs were transplanted. The primary endpoint was achieved in 43 (54%) of 79 patients and did not meet the objective performance goal. 35 (44%) of 79 patients had PGD3 within the initial 72 h. 78 (99%) of 79 patients had survived at 30 days post-transplant. The mean number of lung graft-related serious adverse events (respiratory failure and major pulmonary-related infection) was 0·3 events per patient (SD 0·5).

INTERPRETATION

Despite missing the objective primary endpoint, the portable OCS Lung resulted in 87% donor lung use for transplantation with excellent clinical outcomes. Many lungs declined by other transplant centres were successfully transplanted using this new technology, which implies its use has the potential to increase the number of lung transplants performed worldwide. Whether similar outcomes could be obtained if these lungs were preserved on ice is unknown and remains an area for future research.

FUNDING

TransMedics Inc.

Role of innate immunity in primary graft dysfunction after lung transplantation

PURPOSE OF REVIEW

Primary graft dysfunction (PGD), a form of acute lung injury after lung transplantation, has a significant impact on clinical outcomes after lung transplantation. This potentially reversible graft impairment occurs after ischemia-reperfusion injury. This review describes the expanding body of literature evaluating the central role of innate immune activation, nonadaptive responses and dysregulation in the development of PGD after lung transplant.

RECENT FINDINGS

The innate immune system, highlighted by Toll-like receptor pathways and neutrophil migration and influx, plays an important role in the initiation and propagation of ischemia-reperfusion injury. Recent plasma biomarker and gene association studies have identified several genes and proteins composing innate immune pathways to be associated with PGDs. Long pentraxin-3 and Toll-like receptors, as well as inflammasomes and Toll-interacting protein, are associated with the development of PGD after lung transplantation.

SUMMARY

Innate immune pathways are involved in the development of PGD and may provide attractive targets for therapies. It may be possible to prevent or treat PGD, as well as to allow pre-transplant PGD risk stratification. To improve understanding of the mechanisms behind clinical risk factors for PGD will require further in-depth correlation of donor-specific and recipient-related triggers of nonadaptive immune responses.

Assessing lung transplantation ischemia-reperfusion injury by microcomputed tomography and ultrashort echo-time magnetic resonance imaging in a mouse model

PURPOSE

Ischemia-reperfusion injury (I/R) is a common early complication after lung transplantation. The purpose of this study was to compare ultrashort echo-time (UTE) sequences in magnetic resonance imaging (MRI) with a microcomputed tomography (micro-CT) reference standard for detection of I/R injury in a lung transplantation mouse model.

MATERIALS AND METHODS

Six mice (C57BL/6) underwent orthotopic lung transplantation using donor grafts that were exposed to 6-hour cold ischemia. Imaging was performed within 24 hours after the transplantation with high-resolution micro-CT (tube voltage, 50 kV; current, 500 mA; aluminum filter, 0.5 mm; voxel size, 35 × 35 × 35 μm³) and small-animal MRI at 4.7 T with a linearly polarized whole-body mouse coil. The imaging protocol comprised radial 3-dimensional UTE sequences with different echo times (repetition time, 8 milliseconds; echo time, 50/75/100/500/1500/3000/4000/5000 μs; voxel size, 350 × 350 × 350 μm³). Images were assessed visually and through calculation of contrast-to-noise ratio (CNR) values. Calculated S0 values and T2* transverse relaxation times (MRI) of lung parenchyma were compared with Hounsfield unit (HU) density in micro-CT images. Receiver operating characteristic curves and area under the curve values were calculated for comparison of diagnostic power. All samples underwent a histologic examination.

RESULTS

The results of both UTE MRI and micro-CT showed an excellent depiction of pulmonary infiltration due to I/R injury, with MRI exhibiting a significantly higher CNR (mean [SD] CNR MRI, 19.7 [8.0]; mean [SD] CNR micro-CT, 10.3 [2.5]; P < 0.001). Measured parametrical values were as follows: mean (SD) HU, -416 (120); mean (SD) S0 value, 1655 (440); mean (SD) T2*, 895 (870) μs for the non-transplanted right lung and mean (SD) HU, 29 (35); mean (SD) S0 value, 2310 (300); and mean (SD) T2*, 4550 (3230) μs for the transplanted left lung. Slight infiltration could be better discriminated with micro-CT, whereas, in strong infiltration, a better contrast was provided by UTE MRI. The area under the curve values resulting from the receiver operating characteristic curve analysis were 0.99 for HU density, 0.89 for S₀, 0.96 for T2*, and 0.98 for the combination of S₀ and T2*.

CONCLUSIONS

Results show that MRI of the lung has a similar diagnostic power compared with that of micro-CT regarding the detection of I/R injury after experimental lung transplantation. Both modalities provide complementary information in the assessment of dense and slight infiltration in the early phase after lung transplantation. Therefore, UTE MRI seems to be a promising addition to computed tomographic imaging in the assessment of I/R injury after lung transplantation.

N-Acetyl Cysteine Attenuates the Inflammatory Response in Warm Ischemic Pig Lungs

BACKGROUND

Lungs donated after cardiac death (DCD) may significantly reduce current organ shortage. However, the warm ischemic period following circulatory arrest may enhance ischemia-reperfusion injury (IRI). We investigated the possible therapeutic effect of N-acetyl cysteine (NAC), a potent anti-oxidative agent on IRI in a porcine ex vivo lung reperfusion model.

MATERIALS AND METHODS

NAC (50 mg/kg) was nebulized to pigs (n = 6/group) prior to sacrifice (NAC-DCD). In DCD-NAC, animals received NAC 15 min after death. Control animals did not receive an aerosol (DCD). Interleukin (IL)-1beta, tumor necrosis factor-alpha, IL-8, lactate dehydrogenase activity and thiobarbituric acid reactive substances were measured and cells were counted in broncho-alveolar lavage from the right lung after a 3-h warm plus 1-h cold ischemic interval.

RESULTS

There were no differences in cells between groups, however cell death was lower in NAC-DCD (10.3 +/- 1.5%) and DCD-NAC (7.83 +/- 1.8%) compared to DCD (18.0 +/- 3.8%). IL-1beta levels (111.5 +/- 28.8 pg/mL and 92.2 +/- 51.0 pg/mL versus 250.3 +/- 56.6 pg/mL) and lactate dehydrogenase activity (1258.0 +/- 440.9 U/L and 1606.0 +/- 289.0 U/L versus 2848.0 +/- 760.9 U/L) were significantly lower in NAC-DCD and DCD-NAC compared with DCD, respectively. These postischemic inflammatory markers correlated with functional parameters upon reperfusion of the left lung, reported in a previous study.

CONCLUSIONS

Administration of NAC prior to or shortly after circulatory arrest results in a marked reduction of inflammation during the warm ischemic phase.

Azithromycin reduces airway inflammation in a murine model of lung ischaemia reperfusion injury

Clinical studies revealed that azithromycin reduces airway neutrophilia during chronic rejection after lung transplantation. Our aim was to investigate the possible effect of azithromycin on ischaemia-reperfusion injury. Azithromycin or water was administered to mice every other day during 2 weeks (n = 6/group). On the 14th day, the left lung was clamped to induce ischaemia (90 min). In two additional groups, animals underwent the same protocol, followed by 4 h of reperfusion. Two control groups were included with thoracotomy only. Inflammatory parameters and oxidative stress were measured in broncho-alveolar lavage of the left lung. Leukocytes, lymphocytes, neutrophils, 8-isoprostane and IL-1beta levels after ischaemia and reperfusion were significantly reduced in mice treated with azithromycin. There was a trend towards lower IL-6 and KC levels. A significant correlation was seen between 8-isoprostanes and neutrophils (Pearson r = 0.72; P = 0.0086), IL-6 (Pearson r = 0.84; P = 0.0006), KC (Pearson r = 0.88; P = 0.0002) and IL-1beta (Pearson r = 0.62; P = 0.0326). We conclude (i) that azithromycin reduces inflammation and oxidative stress in our IRI model, and (ii) that oxidative stress is correlated with the number of neutrophils and IL-6, KC and IL-1beta levels after ischaemia and reperfusion. Azithromycin should be further investigated as a novel drug to prevent lung ischaemia-reperfusion injury.

The importance of lymphocytes in lung ischemia-reperfusion injury

In a murine model of lung ischemia-reperfusion injury (IRI), we previously demonstrated that lymphocytes increase in the alveolar space during the ischemic period. We hypothesized that these lymphocytes play an important role during ischemia in the development of lung IRI. In the present study, severe combined immunodeficiency (SCID) mice, lacking T cells, were used to further investigate our hypothesis. SCID and control mice underwent 90 minutes of left lung ischemia followed by 4 hours of reperfusion. A significant decrease in neutrophils, together with lower levels of interleukin-1beta, was found in SCID mice after reperfusion. We concluded that lymphocytes invading the lung during ischemia trigger an inflammatory response upon reperfusion. Antilymphocyte therapies in the donor should be further investigated as treatment strategies against IRI.

A mouse model of orthotopic vascularized aerated lung transplantation

Outcomes after lung transplantation are markedly inferior to those after other solid organ transplants. A better understanding of cellular and molecular mechanisms contributing to lung graft injury will be critical to improve outcomes. Advances in this field have been hampered by the lack of a mouse model of lung transplantation. Here, we report a mouse model of vascularized aerated single lung transplantation utilizing cuff techniques. We show that syngeneic grafts have normal histological appearance with minimal infiltration of T lymphocytes. Allogeneic grafts show acute cellular rejection with infiltration of T lymphocytes and recipient-type antigen presenting cells. Our data show that we have developed a physiological model of lung transplantation in the mouse, which provides ample opportunity for the study of nonimmune and immune mechanisms that contribute to lung allograft injury.