Lessons learned in acute respiratory distress syndrome from the animal laboratory

The Synthetic Surfactant CHF5633 Restores Lung Function and Lung Architecture in Severe Acute Respiratory Distress Syndrome in Adult Rabbits

PURPOSE

Acute respiratory distress syndrome (ARDS) is a major cause of hypoxemic respiratory failure in adults. In ARDS extensive inflammation and leakage of fluid into the alveoli lead to dysregulation of pulmonary surfactant metabolism and function. Altered surfactant synthesis, secretion, and breakdown contribute to the clinical features of decreased lung compliance and alveolar collapse. Lung function in ARDS could potentially be restored with surfactant replacement therapy, and synthetic surfactants with modified peptide analogues may better withstand inactivation in ARDS alveoli than natural surfactants.

METHODS

This study aimed to investigate the activity in vitro and the bolus effect (200 mg phospholipids/kg) of synthetic surfactant CHF5633 with analogues of SP-B and SP-C, or natural surfactant Poractant alfa (Curosurf®, both preparations Chiesi Farmaceutici S.p.A.) in a severe ARDS model (the ratio of partial pressure arterial oxygen and fraction of inspired oxygen, P/F ratio ≤ 13.3 kPa) induced by hydrochloric acid instillation followed by injurious ventilation in adult New Zealand rabbits. The animals were ventilated for 4 h after surfactant treatment and the respiratory parameters, histological appearance of lung parenchyma and levels of inflammation, oxidative stress, surfactant dysfunction, and endothelial damage were evaluated.

RESULTS

Both surfactant preparations yielded comparable improvements in lung function parameters, reductions in lung injury score, pro-inflammatory cytokines levels, and lung edema formation compared to untreated controls.

CONCLUSIONS

This study indicates that surfactant replacement therapy with CHF5633 improves lung function and lung architecture, and attenuates inflammation in severe ARDS in adult rabbits similarly to Poractant alfa. Clinical trials have so far not yielded conclusive results, but exogenous surfactant may be a valid supportive treatment for patients with ARDS given its anti-inflammatory and lung-protective effects.

A novel tree shrew model of lipopolysaccharide-induced acute respiratory distress syndrome

INTRODUCTION

Acute respiratory distress syndrome (ARDS) is a leading cause of respiratory failure, with substantial attributable morbidity and mortality. The small animal models that are currently used for ARDS do not fully manifest all of the pathological hallmarks of human patients, which hampers both the studies of disease mechanism and drug development.

OBJECTIVES

To examine whether the phenotypic changes of primate-like tree shrews in response to a one-hit lipopolysaccharides (LPS) injury resemble human ARDS features.

METHODS

LPS was administered to tree shrews through intratracheal instillation; then, the animals underwent CT or PET/CT imaging to examine the changes in the structure and function of the whole lung. The lung histology was analyzed by H&E staining and immunohistochemical staining of inflammatory cells.

RESULTS

Results demonstrated that tree shrews exhibited an average survival time of 3-5 days after LPS insult, as well as an obvious symptom of dyspnea before death. The ratios of PaO2 to FiO2 (P/F ratio) were close to those of moderate ARDS in humans. CT imaging showed that the scope of the lung injury in tree shrews after LPS treatment were extensive. PET/CT imaging with 18F-FDG displayed an obvious inflammatory infiltration. Histological analysis detected the formation of a hyaline membrane, which is usually present in human ARDS.

CONCLUSION

This study established a lung injury model with a primate-like small animal model and confirmed that they have similar features to human ARDS, which might provide a valuable tool for translational research.

Protective technologies of modern methods of respiratory support in neonatal practice

The article  presents  an analysis of literature data  on modern  protective regimens  for invasive respiratory support  in premature newborns  with respiratory distress  syndrome. We have considered positive and negative  aspects of the used methods  of invasive ventilation of the lungs, which are currently widely used as a method  of respiratory therapy  in obstetric hospitals  at any level, even in the category  of children  with extremely and very low birth weight. Modern  protective mechanical ventilation provides for 2 main directions for reducing ventilator-induced lung damage: a decrease in tidal volume (Vt) and the principle  of tolerable  (permissive) hypercapnia. The use of the technique of permissive hypercapnia and regimens with a target volume can reduce the likelihood of ventilator-induced lung injury in newborns. Despite the limited indications for mechanical ventilation in modern neonatology and the widespread use of non-invasive ventilation, for patients who really need mechanical ventilation, the use of volume-targeted regimens offers the best chance of reducing  ventilation complications.

SARS-CoV-2-Infection (COVID-19): Clinical Course, Viral Acute Respiratory Distress Syndrome (ARDS) and Cause(s) of Death

SARS-CoV-2-infected symptomatic patients often suffer from high fever and loss of appetite which are responsible for the deficit of fluids and of protein intake. Many patients admitted to the emergency room are, therefore, hypovolemic and hypoproteinemic and often suffer from respiratory distress accompanied by ground glass opacities in the CT scan of the lungs. Ischemic damage in the lung capillaries is responsible for the microscopic hallmark, diffuse alveolar damage (DAD) characterized by hyaline membrane formation, fluid invasion of the alveoli, and progressive arrest of blood flow in the pulmonary vessels. The consequences are progressive congestion, increase in lung weight, and progressive hypoxia (progressive severity of ARDS). Sequestration of blood in the lungs worsens hypovolemia and ischemia in different organs. This is most probably responsible for the recruitment of inflammatory cells into the ischemic peripheral tissues, the release of acute-phase mediators, and for the persistence of elevated serum levels of positive acute-phase markers and of hypoalbuminemia. Autopsy studies have been performed mostly in patients who died in the ICU after SARS-CoV-2 infection because of progressive acute respiratory distress syndrome (ARDS). In the death certification charts, after respiratory insufficiency, hypovolemic heart failure should be mentioned as the main cause of death.

Validation of Messenger Ribonucleic Acid Markers Differentiating Among Human Acute Respiratory Distress Syndrome Subgroups in an Ovine Model of Acute Respiratory Distress Syndrome Phenotypes

Background

The discovery of biological subphenotypes in acute respiratory distress syndrome (ARDS) might offer a new approach to ARDS in general and possibly targeted treatment, but little is known about the underlying biology yet. To validate our recently described ovine ARDS phenotypes model, we compared a subset of messenger ribonucleic acid (mRNA) markers in leukocytes as reported before to display differential expression between human ARDS subphenotypes to the expression in lung tissue in our ovine ARDS phenotypes model (phenotype 1 (Ph1): hypoinflammatory; phenotype 2 (Ph2): hyperinflammatory).

Methods

We studied 23 anesthetized sheep on mechanical ventilation with observation times between 6 and 24 h. They were randomly allocated to the two phenotypes (n = 14 to Ph1 and n = 9 to Ph2). At study end, lung tissue was harvested and preserved in RNAlater. After tissue homogenization in TRIzol, total RNA was extracted and custom capture and reporter probes designed by NanoString Technologies were used to measure the expression of 14 genes of interest and the 6 housekeeping genes on a nCounter SPRINT profiler.

Results

Among the 14 mRNA markers, in all animals over all time points, 13 markers showed the same trend in ovine Ph2/Ph1 as previously reported in the MARS cohort: matrix metalloproteinase 8, olfactomedin 4, resistin, G protein-coupled receptor 84, lipocalin 2, ankyrin repeat domain 22, CD177 molecule, and transcobalamin 1 expression was higher in Ph2 and membrane metalloendopeptidase, adhesion G protein-coupled receptor E3, transforming growth factor beta induced, histidine ammonia-lyase, and sulfatase 2 expression was higher in Ph1. These expression patterns could be found when different sources of mRNA – such as blood leukocytes and lung tissue – were compared.

Conclusion

In human and ovine ARDS subgroups, similar activated pathways might be involved (e.g., oxidative phosphorylation, NF-κB pathway) that result in specific phenotypes.

A new mouse unilateral model of diffuse alveolar damage of the lung

Objective and design

The existing biological models of diffuse alveolar damage (DAD) in mice have many shortcomings. To offset these shortcomings, we have proposed a simple, nonsurgical, and reproducible method of unilateral total damage of the left lung in ICR mice. This model is based on the intrabronchial administration of a mixture of bacterial lipopolysaccharide (LPS) from the cell wall of S. enterica and α-galactosylceramide (inducing substances) to the left lung.

Methods

Using computer tomography of the lungs with endobronchial administration of contrast material, we have been able to perform an operative intravital verification of the targeted delivery of the inducer. The model presented is characterized by more serious and homogeneous damage of the affected lung compared to the existing models of focal pneumonia; at the same time, our model is characterized by longer animal survival since the right lung remains intact.

Results

The model is also characterized by diffuse alveolar damage of the left lung, animal survival of 100%, abrupt increases in plasma levels of TNFa, INFg, and IL-6, and significant myocardial overload in the right heart. It can be used to assess the efficacy of innovative drugs for the treatment of DAD and ARDS as the clinical manifestations that are developed in patients infected with SARS-CoV-2. Morphological patterns of lungs in the noninfectious (“sterile”) model of DAD induced by LPS simultaneously with α-galactosylceramide (presented here) and in the infectious model of DAD induced by SARS-CoV-2 have been compared.

Conclusion

The DAD model we have proposed can be widely used for studying the efficacy of candidate molecules for the treatment of infectious respiratory diseases, such as viral pneumonias of different etiology, including SARS-CoV-2.

Description of ovine model for testing ventilator prototypes in the COVID-19 pandemic

The COVID-19 pandemic has revealed a ventilator deficit in the global health system for this scenario. For this reason, several national and international projects have been developed to get done prototypes of ventilators which could be easy and fast to manufacture. One of the requirements of the AEMPS for conducting clinical studies with new prototypes is through the validation of these new prototypes in an animal model. Therefore, it is important to achieve an animal model which allows us to easily reproduce different clinical scenarios. In this article, we describe the use of a sheep as a research model to assess a prototype ventilator. The animal was anesthetized for 10 h in which the prototype was tested in up to 6 different scenarios. This model is effective and easy to reproduce, making it an excellent choice for this kind of research.

Characterizing preclinical sub-phenotypic models of acute respiratory distress syndrome: An experimental ovine study

The acute respiratory distress syndrome (ARDS) describes a heterogenous population of patients with acute severe respiratory failure. However, contemporary advances have begun to identify distinct sub-phenotypes that exist within its broader envelope. These sub-phenotypes have varied outcomes and respond differently to several previously studied interventions. A more precise understanding of their pathobiology and an ability to prospectively identify them, may allow for the development of precision therapies in ARDS. Historically, animal models have played a key role in translational research, although few studies have so far assessed either the ability of animal models to replicate these sub-phenotypes or investigated the presence of sub-phenotypes within animal models. Here, in three ovine models of ARDS, using combinations of oleic acid and intravenous, or intratracheal lipopolysaccharide, we investigated the presence of sub-phenotypes which qualitatively resemble those found in clinical cohorts. Principal Component Analysis and partitional clustering identified two clusters, differentiated by markers of shock, inflammation, and lung injury. This study provides a first exploration of ARDS phenotypes in preclinical models and suggests a methodology for investigating this phenomenon in future studies.

Pulmonary surfactant: a unique biomaterial with life-saving therapeutic applications

Pulmonary surfactant is a complex lipoprotein mixture secreted into the alveolar lumen by type 2 pneumocytes, which is composed by tens of different lipids (approximately 90% of its entire mass) and surfactant proteins (approximately 10% of the mass). It is crucially involved in maintaining lung homeostasis by reducing the values of alveolar liquid surface tension close to zero at end-expiration, thereby avoiding the alveolar collapse, and assembling a chemical and physical barrier against inhaled pathogens. A deficient amount of surfactant or its functional inactivation is directly linked to a wide range of lung pathologies, including the neonatal respiratory distress syndrome. This paper reviews the main biophysical concepts of surfactant activity and its inactivation mechanisms, and describes the past, present and future roles of surfactant replacement therapy, focusing on the exogenous surfactant preparations marketed worldwide and new formulations under development. The closing section describes the pulmonary surfactant in the context of drug delivery. Thanks to its peculiar composition, biocompatibility, and alveolar spreading capability, the surfactant may work not only as a shuttle to the branched anatomy of the lung for other drugs but also as a modulator for their release, opening to innovative therapeutic avenues for the treatment of several respiratory diseases.

Resveratrol-Loaded Lipid-Core Nanocapsules Modulate Acute Lung Inflammation and Oxidative Imbalance Induced by LPS in Mice

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are inflammatory and oxidative imbalance lung conditions with no successful pharmacological therapy and a high mortality rate. Resveratrol (RSV) is a plant-derived stilbene that presents anti-inflammatory and antioxidant effects. However, its therapeutic application remains limited due to its poor bioavailability, which can be solved by the use of nanocarriers. Previously, we demonstrated that nanoencapsulated RSV (RSV-LNC) pre-treatment, performed 4 h before lipopolysaccharide (LPS) stimulation in mice, increased its anti-inflammatory properties. In this study, we evaluated the anti-inflammatory and antioxidant effects, and lung distribution of RSV-LNCs administered therapeutically (6 h post LPS exposure) in a lung injury mouse model. The results showed that RSV-LNCs posttreatment improved lung function and diminished pulmonary inflammation. Moreover, RSV-LNC treatment enhanced the antioxidant catalase level together with a decrease in the oxidative biomarker in mouse lungs, which was accompanied by an increase in pulmonary Nrf2 antioxidant expression. Finally, the presence of RSV in lung tissue was significantly detected when mice received RSV-LNCs but not when they received RSV in its free form. Together, our results confirm that RSV nanoencapsulation promotes an increase in RSV bioavailability, enhancing its therapeutic effects in an LPS-induced lung injury model.

Surfactant therapies for pediatric and neonatal ARDS: ESPNIC expert consensus opinion for future research steps

Pediatric (PARDS) and neonatal (NARDS) acute respiratory distress syndrome have different age-specific characteristics and definitions. Trials on surfactant for ARDS in children and neonates have been performed well before the PARDS and NARDS definitions and yielded conflicting results. This is mainly due to heterogeneity in study design reflecting historic lack of pathobiology knowledge. We reviewed the available clinical and preclinical data to create an expert consensus aiming to inform future research steps and advance the knowledge in this area. Eight trials investigated the use of surfactant for ARDS in children and ten in neonates, respectively. There were improvements in oxygenation (7/8 trials in children, 7/10 in neonates) and mortality (3/8 trials in children, 1/10 in neonates) improved. Trials were heterogeneous for patients' characteristics, surfactant type and administration strategy. Key pathobiological concepts were missed in study design. Consensus with strong agreement was reached on four statements: 1. There are sufficient preclinical and clinical data to support targeted research on surfactant therapies for PARDS and NARDS. Studies should be performed according to the currently available definitions and considering recent pathobiology knowledge. 2. PARDS and NARDS should be considered as syndromes and should be pre-clinically studied according to key characteristics, such as direct or indirect (primary or secondary) nature, clinical severity, infectious or non-infectious origin or patients' age. 3. Explanatory should be preferred over pragmatic design for future trials on PARDS and NARDS. 4. Different clinical outcomes need to be chosen for PARDS and NARDS, according to the trial phase and design, trigger type, severity class and/or surfactant treatment policy. We advocate for further well-designed preclinical and clinical studies to investigate the use of surfactant for PARDS and NARDS following these principles.

Low Spontaneous Breathing Effort during Extracorporeal Membrane Oxygenation in a Porcine Model of Severe Acute Respiratory Distress Syndrome

BACKGROUND

A lung rest strategy is recommended during extracorporeal membrane oxygenation in severe acute respiratory distress syndrome (ARDS). However, spontaneous breathing modes are frequently used in this context. The impact of this approach may depend on the intensity of breathing efforts. The authors aimed to determine whether a low spontaneous breathing effort strategy increases lung injury, compared to a controlled near-apneic ventilation, in a porcine severe ARDS model assisted by extracorporeal membrane oxygenation.

METHODS

Twelve female pigs were subjected to lung injury by repeated lavages, followed by 2-h injurious ventilation. Thereafter, animals were connected to venovenous extracorporeal membrane oxygenation and during the first 3 h, ventilated with near-apneic ventilation (positive end-expiratory pressure, 10 cm H2O; driving pressure, 10 cm H2O; respiratory rate, 5/min). Then, animals were allocated into (1) near-apneic ventilation, which continued with the previous ventilatory settings; and (2) spontaneous breathing: neuromuscular blockers were stopped, sweep gas flow was decreased until regaining spontaneous efforts, and ventilation was switched to pressure support mode (pressure support, 10 cm H2O; positive end-expiratory pressure, 10 cm H2O). In both groups, sweep gas flow was adjusted to keep Paco2 between 30 and 50 mmHg. Respiratory and hemodynamic as well as electric impedance tomography data were collected. After 24 h, animals were euthanized and lungs extracted for histologic tissue analysis.

RESULTS

Compared to near-apneic group, the spontaneous breathing group exhibited a higher respiratory rate (52 ± 17 vs. 5 ± 0 breaths/min; mean difference, 47; 95% CI, 34 to 59; P < 0.001), but similar tidal volume (2.3 ± 0.8 vs. 2.8 ± 0.4 ml/kg; mean difference, 0.6; 95% CI, -0.4 to 1.4; P = 0.983). Extracorporeal membrane oxygenation settings and gas exchange were similar between groups. Dorsal ventilation was higher in the spontaneous breathing group. No differences were observed regarding histologic lung injury.

CONCLUSIONS

In an animal model of severe ARDS supported with extracorporeal membrane oxygenation, spontaneous breathing characterized by low-intensity efforts, high respiratory rates, and very low tidal volumes did not result in increased lung injury compared to controlled near-apneic ventilation.

EDITOR’S PERSPECTIVE

Description of ovine model for testing ventilator prototypes in the COVID-19 pandemic

The COVID-19 pandemic has revealed a ventilator deficit in the global health system for this scenario. For this reason, several national and international projects have been developed to get done prototypes of ventilators which could be easy and fast to manufacture. One of the requirements of the AEMPS for conducting clinical studies with new prototypes is through the validation of these new prototypes in an animal model. Therefore, it is important to achieve an animal model which allows us to easily reproduce different clinical scenarios. In this article, we describe the use of a sheep as a research model to assess a prototype ventilator. The animal was anesthetized for 10hours in which the prototype was tested in up to 6different scenarios. This model is effective and easy to reproduce, making it an excellent choice for this kind of research.

Publication trends of research on acute lung injury and acute respiration distress syndrome during 2009-2019: a 10-year bibliometric analysis

BACKGROUND

Acute lung injury (ALI) is a common disease that usually progresses to acute respiratory distress syndrome (ARDS) with high morbidity and mortality. We aim to analyze the trends in ALI/ARDS, and to compare the differences in aspects of years, countries, institutions, journals, etc. Methods: We screened all relevant literature on ALI/ARDS from Web of Science during 2009-2019, and analyzed the research trends in this field by VOSviewer.

RESULTS

We had screened 7,890 publications with a total cited frequency of 164,713. The United States contributed the largest number of publications (2,612, 33.11%), cited frequency (81,376, 48.61%), and the highest H-index (107). Journal of Critical Care Medicine published the largest number of literatures on ALI/ARDS, MATTHAY MA published the majority of articles in this field (147), while SLUTSKY AS received the most cited frequency (10015). University of California San Francisco had the largest number of publications (243, 3.08%) among all full-time institutions. In the aspect of clinical research in ALI/ARDS, the keyword "Berlin definition" emerged in recent years, with an average year of 2016.3; in the basic research, the key word "protects" appeared latest, and the average years were 2016.5. The current research trend indicates that basic research is gradually transforming into clinical research.

CONCLUSIONS

The United States have made the most significant contribution to the ALI/ARDS field in the last decade. The current research 'hotspot' mainly appeared in clinical research, such as "Berlin definition". In regards to basic research, studies tend to explore the protective mechanisms against ALI/ARDS.

Smouldering ashes: burning questions after the outbreak of electronic cigarette or vaping-associated lung injury (EVALI)

In the summer of 2019, the Center for Disease Control and Prevention (CDC) declared an emergency of electronic cigarettes and/or vaping (vaping)-associated lung injury (EVALI) in the USA. The outbreak abated by January 2020, which the CDC attributed to heightened public awareness, 'user actions to reduce risk' and potentially the removal of vitamin E acetate (VEA) from vaping products (VEA is an oily chemical cutting agent, strongly associated with the disease). Even though the EVALI outbreak appears to be over, numerous epidemiological and medical questions are left still open. First, why were there practically no cases outside the USA, which represents nearly a quarter of the global vaping market? Comparative studies to map the differences in device/fluids/user habits between countries might be needed urgently. Second, what is the pathomechanism that sickens vapers irrespective of VEA exposure? VEA was only confirmed in about half of the cases and the presumed toxicity is yet to be determined. Aetiology/epidemiology focused research is needed to investigate/interpret the broader context to explain the outbreak. Third, could any socioeconomic/environmental factors have influenced the course of the outbreak? Finally, what should we expect in the years to come? Was EVALI a serious but reversible emergency medicine condition or is vaping as detrimental to long-term health as smoking? Besides the complex legislative, regulatory, ethical aspects of EVALI, biomedical research is also difficult: in-vitro experiments have limited inferential value to real real-life vaping due to its complexity; user habits are self-reported and under-researched; there is an active black market pouring unknown quality counterfeit products and, in the USA, federal restrictions limit cannabis research. Vaping is a toxicological, multidimensional conundrum; therefore, stringent quality control, transparent legal/ethical boundaries, meticulous international research and user education are paramount to prevent potential future outbreaks and determine the parameters safe vaping (if these exist).

Systems Biology ARDS Research with a Focus on Metabolomics

Acute respiratory distress syndrome (ARDS) is a clinical syndrome that inflicts a considerably heavy toll in terms of morbidity and mortality. While there are multitudes of conditions that can lead to ARDS, the vast majority of ARDS cases are caused by a relatively small number of diseases, especially sepsis and pneumonia. Currently, there is no clinically agreed upon reliable diagnostic test for ARDS, and the detection or diagnosis of ARDS is based on a constellation of laboratory and radiological tests in the absence of evidence of left ventricular dysfunction, as specified by the Berlin definition of ARDS. Virtually all the ARDS biomarkers to date have been proven to be of very limited clinical utility. Given the heterogeneity of ARDS due to the wide variation in etiology, clinical and molecular manifestations, there is a current scientific consensus agreement that ARDS is not just a single entity but rather a spectrum of conditions that need further study for proper classification, the identification of reliable biomarkers and the adequate institution of therapeutic targets. This scoping review aims to elucidate ARDS omics research, focusing on metabolomics and how metabolomics can boost the study of ARDS biomarkers and help to facilitate the identification of ARDS subpopulations.