Hypoxic Gene Expression of Donor Bronchi Linked to Airway Complications after Lung Transplantation

Alterations in Pulmonary Physiology with Lung Transplantation

Lung transplant is a treatment option for patients with end-stage lung diseases; however, survival outcomes continue to be inferior when compared to other solid organs. We review the several anatomic and physiologic changes that result from lung transplantation surgery, and their role in the pathophysiology of common complications encountered by lung recipients. The loss of bronchial circulation into the allograft after transplant surgery results in ischemia-related changes in the bronchial artery territory of the allograft. We discuss the role of bronchopulmonary anastomosis in blood circulation in the allograft posttransplant. We review commonly encountered complications related to loss of bronchial circulation such as allograft airway ischemia, necrosis, anastomotic dehiscence, mucociliary dysfunction, and bronchial stenosis. Loss of dual circulation to the lung also increases the risk of pulmonary infarction with acute pulmonary embolism. The loss of lymphatic drainage during transplant surgery also impairs the management of allograft interstitial fluid, resulting in pulmonary edema and early pleural effusion. We discuss the role of lymphatic drainage in primary graft dysfunction. Besides, we review the association of late posttransplant pleural effusion with complications such as acute rejection. We then review the impact of loss of afferent and efferent innervation from the allograft on control of breathing, as well as lung protective reflexes. We conclude with discussion about pulmonary function testing, allograft monitoring with spirometry, and classification of chronic lung allograft dysfunction phenotypes based on total lung capacity measurements. We also review factors limiting physical exercise capacity after lung transplantation, especially impairment of muscle metabolism. © 2023 American Physiological Society. Compr Physiol 13:4269-4293, 2023.

Whole-Genome Analysis Deciphers Population Structure and Genetic Introgression Among Bovine Species

It is known that throughout history and presently, taurine (Bos taurus) and indicine/zebu (Bos indicus) cattle were crossed with other bovine species (e.g., gayal, gaur, banteng, yak, wisent, and bison). Information on the role of interspecific hybridization to facilitate faster adaptation of the newly arrived domestic species to new environments is poorly known. Herein, we collected 266 samples of bovine species of the taurine, zebu, yak, and gaur from West Europe, Southwest China, Indian subcontinent, and Southeast Asia to conduct the principal component analysis (PCA), admixture, gene flow, and selection signature analyses by using SNPs distributed across the bovine autosomes. The results showed that the genetic relationships between the zebu, yak, and gaur mirrored their geographical origins. Three ancestral components of the European taurine, East Asian taurine, and Indian zebu were found in domestic cattle, and the bidirectional genetic introgression between the Diqing cattle and Zhongdian yak was also detected. Simultaneously, the introgressed genes from the Zhongdian yak to the Diqing cattle were mainly enriched with immune-related pathways, and the ENPEP, FLT1, and PIK3CA genes related to the adaptation of high-altitude hypoxia were detected. Additionally, we found the genetic components of the Zhongdian yak had introgressed into Tibetan cattle. The 30 selected genes were detected in Tibetan cattle, which were significantly enriched in the chemokine signaling pathway. Interestingly, some genes (CDC42, SLC39A2, and EPAS1) associated with hypoxia response were discovered, in which CDC42 and SLC39A2 played important roles in angiogenesis and erythropoiesis, and heart function, respectively. This result showed that genetic introgression was one of the important ways for the environmental adaptation of domestic cattle.

Hyperbaric oxygen therapy to prevent central airway stenosis after lung transplantation

BACKGROUND

Central airway stenosis (CAS) is a severe airway complication after lung transplantation associated with bronchial ischemia and necrosis. We sought to determine whether hyperbaric oxygen therapy (HBOT), an established treatment for tissue ischemia, attenuates post-transplant bronchial injury.

METHODS

We performed a randomized, controlled trial comparing usual care with HBOT (2 atm absolute for 2 hours × 20 sessions) in subjects with extensive airway necrosis 4 weeks after transplantation. Endobronchial biopsies were collected at 4, 7, and 10 weeks after transplantation for a quantitative polymerase chain reaction. Coprimary outcomes were incidence of airway stenting and acute cellular rejection (ACR) at 1 year.

RESULTS

The trial was stopped after enrolling 20 subjects (n = 10 per group) after a pre-planned interim analysis showed no difference between usual care and HBOT groups in stenting (both 40%), ACR (70% and 40%, respectively), or CAS (40% and 60%, respectively). Time to first stent placement (median [interquartile range]) was significantly shorter in the HBOT group (150 [73-150] vs 186 [167-206] days, p < 0.05). HIF gene expression was significantly increased in donor tissues at 4, 7, and 10 weeks after transplantation but was not altered by HBOT. Subjects who developed CAS or required stenting had significantly higher HMOX1 and VEGFA expression at 4 weeks (both p < 0.05). Subjects who developed ACR had significant FLT1, TIE2, and KDR expression at 4 weeks (all p < 0.05).

CONCLUSIONS

Incidence of CAS is high after severe, established airway necrosis after transplantation. HBOT does not reduce CAS severity or stenting. Elevated HMOX1 and VEGFA expressions appear to associate with airway complications.

Initial Postoperative Hemoglobin Values Are Independently Associated With One-Year Mortality in Patients Undergoing Double-Lung Transplantation Requiring Intraoperative Transfusion

OBJECTIVE

To evaluate the association of postoperative hemoglobin values and mortality in patients undergoing double- lung transplantation with intraoperative transfusion.

DESIGN

Retrospective cohort study.

SETTING

University hospital.

PARTICIPANTS

Adult patients who underwent double-lung transplantation at the authors' institution, with intraoperative transfusion of packed red blood cells between 2009 and 2015.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Intraoperative transfusion requirements and general characteristics of 554 patients were collected. A generalized additive model, controlling for postoperative hemoglobin levels, number of transfused units of packed red blood cells, perioperative change in hemoglobin levels, disease leading to lung transplantation, and postoperative extracorporeal membrane oxygenation, was created to predict one-year mortality. A postoperative hemoglobin level of 11.3 g/dL was calculated as an optimal cutoff point. The patients were stratified according to this level. The end -point was all-cause one-year mortality after double-lung transplantation, assessed using the Kaplan-Meier analysis with log-rank test. All-cause mortality of the 554 patients was 17%. Postoperatively, 171 patients (31%) were categorized as being below the cutoff point. Improved survival was observed in the group with higher postoperative hemoglobin values (p = 0.002).

CONCLUSION

Lower postoperative hemoglobin levels in double-lung transplantation recipients were associated with increased mortality during the first year after surgery. Confirmation of these findings in additional investigations could alter patient blood management for double-lung transplantation.

Cyclosporin A Administration During Ex Vivo Lung Perfusion Preserves Lung Grafts in Rat Transplant Model

BACKGROUND

Despite the benefits of ex vivo lung perfusion (EVLP) such as lung reconditioning, preservation, and evaluation before transplantation, deleterious effects, including activation of proinflammatory cascades and alteration of metabolic profiles have been reported. Although patient outcomes have been favorable, further studies addressing optimal conditions are warranted. In this study, we investigated the role of the immunosuppressant drug cyclosporine A (CyA) in preserving mitochondrial function and subsequently preventing proinflammatory changes in lung grafts during EVLP.

METHODS

Using rat heart-lung blocks after 1-hour cold preservation, an acellular normothermic EVLP system was established for 4 hours. CyA was added into perfusate at a final concentration of 1 μM. The evaluation included lung graft function, lung compliance, and pulmonary vascular resistance as well as biochemical marker measurement in the perfusate at multiple time points. After EVLP, single orthotopic lung transplantation was performed, and the grafts were assessed 2 hours after reperfusion.

RESULTS

Lung grafts on EVLP with CyA exhibited significantly better functional and physiological parameters as compared with those without CyA treatment. CyA administration attenuated proinflammatory changes and prohibited glucose consumption during EVLP through mitigating mitochondrial dysfunction in lung grafts. CyA-preconditioned lungs showed better posttransplant lung early graft function and less inflammatory events compared with control.

CONCLUSIONS

During EVLP, CyA administration can have a preconditioning effect through both its anti-inflammatory and mitochondrial protective properties, leading to improved lung graft preservation, which may result in enhanced graft quality after transplantation.

Management of Lung Transplant Bronchial Stenosis With Mitomycin C

BACKGROUND

Bronchial stenosis is a significant source of morbidity among lung transplant recipients, with etiologies including infection and ischemia of the airways. Current management with balloon bronchoplasty and stents is imperfect and a subset of patients requires multiple procedures to maintain airway patency. Mitomycin C (MMC) has been utilized for its antifibrotic properties in nonmalignant tracheobronchial stenosis but its application is not well studied in post-lung transplant stenosis. We performed this study to assess if MMC application decreases the need for repeated balloon bronchoplasty in lung transplant-related airway stenosis.

METHODS

This is a retrospective cohort study of all lung transplant recipients who developed airway stenosis and who were treated with MMC over 4 years. MMC was injected submucosally into the stenotic airway. We compared the rate of bronchoscopic dilation at intervals of 3 and 6 months before and after MMC therapy.

RESULTS

Eleven lung transplant recipients, with airway stenosis were included in our study, who required recurrent balloon dilation, despite airway stents in place in 73% of these patients. At 3 months after MMC treatment the median number of dilations decreased from 3 to 1 (P=0.023), and at 6 months from 3 to 2 dilations (P=0.004). There was a trend toward improvement in forced expiratory volume in one second and forced vital capacity, although it was not statistically significant. No adverse events related to MMC therapy was observed CONCLUSION:: Application of MMC is safe and is associated with a reduction in frequency of bronchoscopic balloon dilation in patients with post-lung transplant airway stenosis.

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.

Airway hypoxia in lung transplantation

Lung transplantation is a life-saving operation for patients with advanced lung disease. Pulmonary allografts eventually fail because of infection, thromboembolism, malignancy, airway complications, and chronic rejection, otherwise known as chronic lung allograft dysfunction (CLAD). Emerging evidence suggests that a highly-compromised airway circulation contributes to the evolution of airway complications and CLAD. There are two significant causes of poor perfusion and airway hypoxia in lung transplantation: an abnormal bronchial circulation which causes airway complications and microvascular rejection which induces CLAD. At the time of transplantation, the bronchial artery circulation, a natural component of the airway circulatory anatomy, is not surgically connected, and bronchi distal to the anastomosis become hypoxic. Subsequently, the bronchial anastomosis is left to heal under ischemic conditions. Still later, the extant microvessels in transplant bronchi are subjected to alloimmune insults that can further negatively impact pulmonary function. This review describes how airway tissue hypoxia evolves in lung transplantation, why depriving oxygenation in the bronchi and more distal bronchioles contributes to disease pathology and what therapeutic interventions are currently emerging to address these vascular injuries. Improving anastomotic vascular healing at the time of transplantation and preventing microvascular loss during acute rejection episodes are two steps that could limit airway hypoxia and improve patient outcomes.

Pathophysiology and Predictors of Bronchial Complications After Lung Transplantation

Bronchial anastomotic breakdown was a major complication in the early days of lung transplantation. Their solution, achieved through an understanding of airway ischemia from the laboratory, was key to the initial clinical success. Subsequently, risk factors, such as prolonged ventilation in both donor and recipient, primary graft dysfunction, and recipient age, have emerged. Innovations, such as local tissue wrapping, telescoping the anastomosis, and bronchial artery revascularization, have not stood the test of time. The short donor bronchus, with a suture line at the level of the lobar bronchus carina, is a proven technique that should be adopted by surgeons.

Microvascular injury after lung transplantation

PURPOSE OF REVIEW

Airway microvessel injury following transplantation has been implicated in the development of chronic rejection. This review focuses on the most recent developments in the field describing preclinical and clinical findings that further implicate the loss of microvascular integrity as an important pathological event in the evolution of irreversible fibrotic remodeling.

RECENT FINDINGS

When lungs are transplanted, the airways appear vulnerable from the perspective of perfusion. Two vascular systems are lost, the bronchial artery and the lymphatic circulations, and the remaining vasculature in the airways expresses donor antigens susceptible to alloimmune-mediated injury via innate and adaptive immune mechanisms. Preclinical studies indicate the importance of hypoxia-inducible factor-1α in mediating microvascular repair and that hypoxia-inducible factor-1α can be upregulated to bolster endogenous repair.

SUMMARY

Airway microvascular injury is a feature of lung transplantation that limits short-term and long-term organ health. Although some problems are attributable to a missing bronchial artery circulation, another significant issue involves alloimmune-mediated injury to transplant airway microvessels. For a variety of reasons, bronchial artery revascularization surgery at the time of transplantation has not been widely adopted, and the current best hope for this era may be new medical approaches that offer protection against immune-mediated vascular injury or that promote microvascular repair.

Novel Magnetic Resonance Imaging for Assessment of Bronchial Stenosis in Lung Transplant Recipients

Bronchial stenosis in lung transplant recipients is a common disorder that adversely affects clinical outcomes. It is evaluated by spirometry, CT scanning, and bronchoscopy with significant limitations. We hypothesize that MRI using both ultrashort echo time (UTE) scans and hyperpolarized (HP) ¹²⁹ Xe gas can offer structural and functional assessment of bronchial stenosis seen after lung transplantation. Six patients with lung transplantation-related bronchial stenosis underwent HP ¹²⁹ Xe MRI and UTE MRI in the same session. Three patients subsequently underwent airway stent placement and had repeated MRI at 4-week follow-up. HP ¹²⁹ Xe MRI depicted decreased ventilation distal to the stenotic airway. After airway stent placement, MRI showed that low-ventilation regions had decreased (35% vs. 27.6%, p = 0.006) and normal-ventilation regions had increased (17.9% vs. 27.6%, p = 0.04) in the stented lung. Improved gas transfer was also seen on ¹²⁹ Xe MRI. There was a good correlation between UTE MRI and independent bronchoscopic airway diameter assessment (Pearson correlation coefficient = 0.92). This pilot study shows that UTE and HP ¹²⁹ Xe MRI are feasible in patients with bronchial stenosis related to lung transplantation and may provide structural and functional airway assessment to guide treatment. These conclusions need to be confirmed with larger studies.

Safety of hyperbaric oxygen therapy for management of central airway stenosis after lung transplant

BACKGROUND

Central airway stenosis (CAS) is common after lung transplantation and causes significant post-transplant morbidity. It is often preceded by extensive airway necrosis, related to airway ischemia. Hyperbaric oxygen therapy (HBOT) is useful for ischemic grafts and may reduce the development of CAS.

METHODS

The purpose of this study was to determine whether HBOT could be safely administered to lung transplant patients with extensive necrotic airway plaques. Secondarily, we assessed any effects of HBOT on the incidence and severity of CAS. Patients with extensive necrotic airway plaques within 1-2 months after lung transplantation were treated with HBOT along with standard care. These patients were compared with a contemporaneous reference group with similar plaques who did not receive HBOT.

RESULTS

Ten patients received HBOT for 18.5 (interquartile range, IQR 11-20) sessions, starting at 40.5 (IQR 34-54) days after transplantation. HBOT was well tolerated. Incidence of CAS was similar between HBOT-treated patients and reference patients (70% vs 87%, respectively; P=.34), but fewer stents were required in HBOT patients (10% vs 56%, respectively; P=.03).

CONCLUSIONS

This pilot study is the first to demonstrate HBOT safety in patients who develop necrotic airway plaques after lung transplantation. HBOT may reduce the need for airway stent placement in patients with CAS.