Intratracheal heparin improves plastic bronchitis due to sulfur mustard analog

Establishment of a Mouse Model of Mycoplasma pneumoniae-Induced Plastic Bronchitis

Plastic bronchitis (PB) constitutes a life-threatening pulmonary disorder, predominantly attributed to Mycoplasma pneumoniae (MP) infection. The pathogenic mechanisms involved remain largely unexplored, leading to the absence of reliable approaches for early diagnosis and clear treatment. Thus, the present investigation aimed to develop an MP-induced mouse model of PB, thereby enhancing our understanding of this complex condition. In the first stage, healthy BALB/c mice were utilized to investigate the optimal methods for establishing PB. This involved the application of nebulization (15-20 min) and intratracheal administration (6-50 μL) with 2-chloroethyl ethyl sulfide (CEES) concentrations ranging from 4.5% to 7.5%. Subsequently, the MP model was induced by administering an MP solution (2 mL/kg/day, 108 CFU/50 μL) via the intranasal route for a duration of five consecutive days. Ultimately, suitable techniques were employed to induce plastic bronchitis in the MP model. Pathological changes in lung tissue were analyzed, and immunohistochemistry was employed to ascertain the expression levels of vascular endothelial growth factor receptor 3 (VEGFR-3) and the PI3K/AKT/mTOR signaling pathway. The administration of 4.5% CEES via a 6 µL trachea was the optimal approach to establishing a PB model. This method primarily induced neutrophilic inflammation and fibrinous exudate. The MP-infected group manifested symptoms indicative of respiratory infection, including erect hair, oral and nasal secretions, and a decrease in body weight. Furthermore, the pathological score of the MP+CEES group surpassed that of the groups treated with MP or CEES independently. Notably, the MP+CEES group demonstrated significant activation of the VEGFR-3 and PI3K/AKT/mTOR signaling pathways, implying a substantial involvement of lymphatic vessel impairment in this pathology. This study successfully established a mouse model of PB induced by MP using a two-step method. Lymphatic vessel impairment is a pivotal element in the pathogenetic mechanisms underlying this disease entity. This accomplishment will aid in further research into treatment methods for patients with PB caused by MP.

Plastic bronchitis secondary to thoracotomy in an adult: A case report

This study presents a rare case of plastic bronchitis (PB) in a 57-year-old adult post-lung lobectomy, a condition predominantly found in post-Fontan children. The patient exhibited progressive dyspnea and complete atelectasis on the surgical side, revealing a gray rubbery bronchial cast obstructing the right main bronchus. Treatment involved repeated bronchoscopies, glucocorticoids, acetylcysteine, physiotherapy, and a low-fat diet, leading to gradual improvement. No similar cases have been reported, highlighting PB's diagnostic challenge. This underscores the need to consider rare conditions like PB in post-lobectomy complications. Timely examinations and bronchoscopies are essential for accurate diagnosis, ensuring prompt treatment and improving patient outcomes.

Pulmonary Complications in Patients With Fontan Circulation: JACC Review Topic of the Week

The Fontan operation has resulted in significant improvement in survival of patients with single ventricle physiology. As a result, there is a growing population of individuals with Fontan physiology reaching adolescence and adulthood. Despite the improved survival, there are long-term morbidities associated with the Fontan operation. Pulmonary complications are common and may contribute to both circulatory and pulmonary insufficiency, leading ultimately to Fontan failure. These complications include restrictive lung disease, sleep abnormalities, plastic bronchitis, and cyanosis. Cyanosis post-Fontan procedure can be attributed to multiple causes including systemic to pulmonary venous collateral channels and pulmonary arteriovenous malformations. This review presents the unique cardiopulmonary interactions in the Fontan circulation. Understanding the cardiopulmonary interactions along with improved recognition and treatment of pulmonary abnormalities may improve the long-term outcomes in this growing patient population. Interventions focused on improving pulmonary function including inspiratory muscle training and endurance training have shown a promising effect post-Fontan procedure.

Clinical features and risk factors of plastic bronchitis caused by refractory Mycoplasma pneumoniae pneumonia in children: a practical nomogram prediction model

Early assessment of refractory Mycoplasma pneumoniae pneumonia (RMPP) with plastic bronchitis (PB) allows timely removal of casts using fiberoptic bronchoscopic manipulation, which relieves airway obstruction and limit sequelae development. This study aimed to analyze clinical data for risk factors and develop a nomogram for early predictive evaluation of RMPP with PB. The clinical data of 1-14 year-old patients with RMPP were retrospectively analyzed. Patients were classified into a PB or non-PB group. The general characteristics, clinical symptoms, laboratory test results, imaging findings, and microscopic changes of the two groups were compared. A statistical analysis of the risk factors for developing PB was performed, and a nomogram model of risk factors was constructed. Of 120 patients with RMPP included, 68 and 52 were in the non-PB and PB groups, respectively. Using multivariate logistic regression analysis, fever before bronchoscopy, extrapulmonary complications, pleural effusion, cough duration, and lactate dehydrogenase (LDH) levels were identified as risk factors. A nomogram was constructed based on the results of the multivariate analysis. The area under the receiver operating characteristic curve value of the nomogram was 0.944 (95% confidence interval: 0.779-0.962). The Hosmer-Lemeshow test displayed good calibration of the nomogram (p = 0.376, R2 = 0.723).

CONCLUSION

The nomogram model constructed in this study based on five risk factors (persistent fever before bronchoscopy, extrapulmonary complications, pleural effusion, cough duration, and LDH levels) prior to bronchoscopy can be used for the early identification of RMPP-induced PB.

WHAT IS KNOWN

• Refractory Mycoplasma pneumoniae pneumonia (RMPP) in children has been increasingly reported and recognized, which often leads to serious complications. • Plastic bronchitis (PB) is considered to be one of the causes of RMPP, and bronchoscopic treatment should be improved as soon as possible to remove plastic sputum thrombus in bronchus.

WHAT IS NEW

• This study determined the risk factors for RMPP-induced PB. • The nomogram model constructed in this study prior to bronchoscopy can be used for the early identification of RMPP-induced PB, which facilitate the early bronchoscopic removal of casts, thereby promoting recovery and reducing cases with poor RMPP prognosis.

Fibrin airway cast obstruction: Experience, classification, and treatment guideline from Denver

BACKGROUND AND OBJECTIVES

Plastic bronchitis (PB) is a condition characterized by the formation of thick airway casts leading to acute and often life-threatening airway obstruction. PB occurs mainly in pediatric patients with congenital heart disease (CHO) who have undergone staged surgical palliation (Glenn, Fontan), but can also occur after chemical inhalation, H1N1, severe COVID-19, sickle cell disease, severe asthma, and other diseases. Mortality risk from PB can be up to 40%-60%, and no treatment guideline exist. The objectives herein are to develop a standardized evaluation, classification, and treatment guideline for PB patients presenting with tracheobronchial casts, based on our experience with PB at the Children's Hospital of Colorado in Denver.

METHODS

We describe 11 patients with CHO-associated PB (post-Fontan [n = 9], pre-Fontan [n = 2]) who presented with their initial episodes. We utilized histopathological analysis of tracheobronchial casts to guide treatment in these patients, utilizing our hospital-wide guideline document and classification system.

RESULTS

We found that 100% of post-Fontan PB patients had fibrinous airway casts, while pre-Fontan PB casts were fibrinous only in one of two patients (50%). Utilizing histopathology as a guide to therapy, PB patients with fibrin airway casts were treated with airway-delivered fibrinolytics and anticoagulants, as well as aggressive airway clearance and other supportive care measures. These therapies resulted in successful cast resolution and improved survival in post-Fontan PB patients.

CONCLUSION

We have shown an improved outcome in PB patients whose treatment plan was based on Denver's PB classification schema and standardized treatment guideline based on tracheobronchial cast histopathology.

Acute cytotoxicity and increased vascular endothelial growth factor after in vitro nitrogen mustard vapor exposure

Nitrogen mustard (NM) is a highly toxic alkylating agent. Inhalation exposure can cause acute and chronic lung injury. This study's aims were to develop an in vitro coculture model of mustard-induced airway injury and to identify growth factors contributing to airway pathology. Primary human bronchial epithelial cells cultured with pulmonary endothelial cells were exposed to NM (25, 50, 100, 250, or 500 μM) or PBS (control) for 1 hour. Lactate dehydrogenase (LDH) and transepithelial electrical resistance (TEER) were measured before and 24 h after NM exposure. Fixed cultures were stained for hematoxylin and eosin or live/dead staining. Culture media were analyzed for 11 growth factors. A 1-h vapor exposure to greater than or equal to 50 μM NM increased supernatant LDH, decreased TEER, and caused airway epithelial cell detachment. Endothelial cell death occurred at 500 μM NM. Vascular endothelial growth factor A (VEGF-A) and placental growth factor (PlGF) expression increased in 500 μM NM-exposed cultures compared with PBS-exposed control cultures. NM vapor exposure causes differential cytotoxicity to airway epithelial and endothelial injury in culture. Increased VEGF-A and PlGF expression occurred acutely in airway cocultures. Future studies are required to validate the role of VEGF signaling in mustard-induced airway pathology.

Extracellular nucleic acid scavenging rescues rats from sulfur mustard analog-induced lung injury and mortality

Sulfur mustard (SM) is a highly toxic war chemical that causes significant morbidity and mortality and lacks any effective therapy. Rats exposed to aerosolized CEES (2-chloroethyl ethyl sulfide; 10% in ethanol), an analog of SM, developed acute respiratory distress syndrome (ARDS), which is characterized by increased inflammation, hypoxemia and impaired gas exchange. We observed elevated levels of extracellular nucleic acids (eNA) in the bronchoalveolar lavage fluid (BALF) of CEES-exposed animals. eNA can induce inflammation, coagulation and barrier dysfunction. Treatment with hexadimethrine bromide (HDMBr; 10 mg/kg), an eNA neutralizing agent, 2 h post-exposure, reduced lung injury, inhibited disruption of alveolar-capillary barrier, improved blood oxygenation (PaO₂/FiO₂ ratio), thus reversing ARDS symptoms. HDMBr treatment also reduced lung inflammation in the CEES-exposed animals by decreasing IL-6, IL-1A, CXCL-1 and CCL-2 mRNA levels in lung tissues and HMGB1 protein in BALF. Furthermore, HDMBr treatment also reduced levels of lung tissue factor and plasminogen activator inhibitor-1 indicating reduction in clot formation and increased fibrinolysis. Fibrin was reduced in BALF of the HDMBr-treated animals. This was further confirmed by histology that revealed diminished airway fibrin, epithelial sloughing and hyaline membrane in the lungs of HDMBr-treated animals. HDMBr completely rescued the CEES-associated mortality 12 h post-exposure when the survival rate in CEES-only group was just 50%. Experimental eNA treatment of cells caused increased inflammation that was reversed by HDMBr. These results demonstrate a role of eNA in the pathogenesis of CEES/SM-induced injury and that its neutralization can serve as a potential therapeutic approach in treating SM toxicity.

Bronchiolitis Obliterans and Pulmonary Fibrosis after Sulfur Mustard Inhalation in Rats

Inhalation of powerful chemical agents, such as sulfur mustard (SM), can have debilitating pulmonary consequences, such as bronchiolitis obliterans (BO) and parenchymal fibrosis (PF). The underlying pathogenesis of disorders after SM inhalation is not clearly understood, resulting in a paucity of effective therapies. In this study, we evaluated the role of profibrotic pathways involving transforming growth factor-β (TGF-β) and platelet-derived growth factor (PDGF) in the development of BO and PF after SM inhalation injury using a rat model. Adult Sprague-Dawley rats were intubated and exposed to SM (1.0 mg/kg), then monitored daily for respiratory distress, oxygen saturation changes, and weight loss. Rats were killed at 7, 14, 21, or 28 days, and markers of injury were determined by histopathology; pulmonary function testing; and assessment of TGF-β, PDGF, and PAI-1 concentrations. Respiratory distress developed over time after SM inhalation, with progressive hypoxemia, respiratory distress, and weight loss. Histopathology confirmed the presence of both BO and PF, and both gradually worsened with time. Pulmonary function testing demonstrated a time-dependent increase in lung resistance, as well as a decrease in lung compliance. Concentrations of TGF-β, PDGF, and PAI-1 were elevated at 28 days in lung, BAL fluid, and/or plasma. Time-dependent development of BO and PF occurs in lungs of rats exposed to SM inhalation, and the elevated concentrations of TGF-β, PDGF, and PAI-1 suggest involvement of these profibrotic pathways in the aberrant remodeling after injury.

Nonmalignant Adult Thoracic Lymphatic Disorders

The thoracic lymphatic disorders are a heterogeneous group of uncommon conditions that are associated with thoracic masses, interstitial pulmonary infiltrates, and chylous complications. Accurate diagnosis of the thoracic lymphatic disorders has important implications for the newest approaches to management, including embolization and treatment with antilymphangiogenic drugs. New imaging techniques to characterize lymphatic flow, such as dynamic contrast-enhanced magnetic resonance lymphangiogram, are redefining approaches to disease classification and therapy.

Sulfur mustard inhalation: mechanisms of injury, alteration of coagulation, and fibrinolytic therapy

Acute lung injury due to sulfur mustard (SM) inhalation causes the formation of airway fibrin casts that obstruct airways at multiple levels, leading to acute respiratory failure and death. These pathophysiological effects are seen in rodent models of acute SM vapor inhalation, as well as in human victims of acute SM inhalation. In rat models, the initial steps in activation of the coagulation system at extravascular sites depend on tissue factor (TF) expression by airway cells, especially in the microparticle fraction, and these effects can be inhibited by TF pathway inhibitor protein. Not only does the procoagulant environment of the acutely injured lung contribute to airway cast formation, but these lesions persist in airways because of the activation of multiple antifibrinolytic pathways, including plasminogen activator inhibitor-1, thrombin-activatable fibrinolysis inhibitor, and α2-antiplasmin. Airway administration of tissue plasminogen activator can overwhelm these effects and save lives by preventing fibrin-dependent airway obstruction, gas-exchange abnormalities, and respiratory failure. In human survivors of SM inhalation, fibrotic processes, including bronchiolitis obliterans and interstitial fibrosis of the lung, are among the most disabling chronic lesions. Antifibrotic therapies may prove useful in preventing either or both of these forms of chronic lung damage.

Emerging targets for treating sulfur mustard-induced injuries

Sulfur mustard (SM; bis-(2-chlororethyl) sulfide) is a highly reactive, potent warfare agent that has recently reemerged as a major threat to military and civilians. Exposure to SM is often fatal, primarily due to pulmonary injuries and complications caused by its inhalation. Profound inflammation, hypercoagulation, and oxidative stress are the hallmarks that define SM-induced pulmonary toxicities. Despite advances, effective therapies are still limited. This current review focuses on inflammatory and coagulation pathways that influence the airway pathophysiology of SM poisoning and highlights the complexity of developing an effective therapeutic target.

Airway tissue plasminogen activator prevents acute mortality due to lethal sulfur mustard inhalation

RATIONALE

Sulfur mustard (SM) is a chemical weapon stockpiled today in volatile regions of the world. SM inhalation causes a life-threatening airway injury characterized by airway obstruction from fibrin casts, which can lead to respiratory failure and death. Mortality in those requiring intubation is more than 80%. No therapy exists to prevent mortality after SM exposure. Our previous work using the less toxic analog of SM, 2-chloroethyl ethyl sulfide, identified tissue plasminogen activator (tPA) an effective rescue therapy for airway cast obstruction (Veress, L. A., Hendry-Hofer, T. B., Loader, J. E., Rioux, J. S., Garlick, R. B., and White, C. W. (2013). Tissue plasminogen activator prevents mortality from sulfur mustard analog-induced airway obstruction. Am. J. Respir. Cell Mol. Biol. 48, 439-447). It is not known if exposure to neat SM vapor, the primary agent used in chemical warfare, will also cause death due to airway casts, and if tPA could be used to improve outcome.

METHODS

Adult rats were exposed to SM, and when oxygen saturation reached less than 85% (median: 6.5 h), intratracheal tPA or placebo was given under isoflurane anesthesia every 4 h for 48 h. Oxygen saturation, clinical distress, and arterial blood gases were assessed. Microdissection was done to assess airway obstruction by casts.

RESULTS

Intratracheal tPA treatment eliminated mortality (0% at 48 h) and greatly improved morbidity after lethal SM inhalation (100% death in controls). tPA normalized SM-associated hypoxemia, hypercarbia, and lactic acidosis, and improved respiratory distress. Moreover, tPA treatment resulted in greatly diminished airway casts, preventing respiratory failure from airway obstruction.

CONCLUSIONS

tPA given via airway more than 6 h after exposure prevented death from lethal SM inhalation, and normalized oxygenation and ventilation defects, thereby rescuing from respiratory distress and failure. Intra-airway tPA should be considered as a life-saving rescue therapy after a significant SM inhalation exposure incident.