Daily Respiratory Research Analysis
Three impactful studies advance respiratory care across mechanisms, systems, and ventilation. A JCI paper reveals cathepsin K–mediated cleavage of angiopoietin-2 converts it into Tie2 antagonists, worsening sepsis, while pharmacologic inhibition improves survival. A Lancet Global Health analysis across 39 LMICs shows unreliable oxygen availability and major system gaps. A PNAS porcine ARDS study quantifies energy dissipation and pinpoints rapid recruitment/derecruitment as a focal driver of vent
Summary
Three impactful studies advance respiratory care across mechanisms, systems, and ventilation. A JCI paper reveals cathepsin K–mediated cleavage of angiopoietin-2 converts it into Tie2 antagonists, worsening sepsis, while pharmacologic inhibition improves survival. A Lancet Global Health analysis across 39 LMICs shows unreliable oxygen availability and major system gaps. A PNAS porcine ARDS study quantifies energy dissipation and pinpoints rapid recruitment/derecruitment as a focal driver of ventilator-induced lung injury.
Research Themes
- Sepsis endothelial mechanisms and therapeutic targeting (Tie2/Angiopoietin-2, cathepsin K)
- Global oxygen systems and access for respiratory care
- Ventilator-induced lung injury mechanics and energy dissipation
Selected Articles
1. Cathepsin K cleavage of angiopoietin-2 creates detrimental Tie2 antagonist fragments in sepsis.
Inflammation-driven cathepsin K cleaves angiopoietin-2 into 25/50 kDa fragments that antagonize Tie2, destabilizing the endothelium in sepsis. Pharmacologic inhibition with odanacatib improved survival in murine models, and ANGPT2 fragments accumulated in septic patients and associated with worse outcomes.
Impact: This study uncovers a proteolytic switch that converts ANGPT2 from a Tie2 agonist to antagonist and demonstrates therapeutic rescue via cathepsin K inhibition. It also proposes clinically measurable ANGPT2 fragments as biomarkers.
Clinical Implications: Cathepsin K inhibition (e.g., odanacatib) may stabilize endothelial Tie2 signaling in sepsis; circulating ANGPT2 fragments could stratify risk and guide therapy. This informs trials targeting the ANGPT2–Tie2 axis in inflammatory shock.
Key Findings
- Macrophage-stimulated endothelial cells released ANGPT2 with loss of full-length 75 kDa form and emergence of 25/50 kDa C-terminal fragments.
- Cathepsin K was necessary and sufficient to generate ANGPT2 fragments that bound and antagonized Tie2.
- Odanacatib improved survival in murine sepsis; benefit depended on full-length ANGPT2 and was reversed by cANGPT225.
- Septic patients had circulating ANGPT2 fragments associated with adverse outcomes.
Methodological Strengths
- Mechanistic dissection across in vitro, multiple murine sepsis models, and human observational validation
- Use of recombinant fragments, peptide sequencing, and pharmacologic inhibition to establish causality
Limitations
- Human data are observational and cannot establish clinical efficacy of cathepsin K inhibition
- Safety and dosing of odanacatib in sepsis require dedicated trials
Future Directions: Prospective trials of cathepsin K inhibitors in septic shock with ANGPT2 fragment monitoring; development of clinical assays to quantify ANGPT2 fragments and patient stratification strategies.
Elevated angiopoietin-2 is associated with diverse inflammatory conditions, including sepsis, a leading global cause of mortality. During inflammation, angiopoietin-2 antagonizes the endothelium-enriched receptor Tie2 to destabilize the vasculature. In other contexts, angiopoietin-2 stimulates Tie2. The basis for context-dependent antagonism remains incompletely understood. Here, we show that inflammation-induced proteolytic cleavage of angiopoietin-2 converts this ligand from Tie2 agonist to antagonist. Conditioned media from stimulated macrophages induced endothelial angiopoietin-2 secretion. Unexpectedly, this was associated with reduction of the 75 kDa full-length protein and appearance of new 25 and 50 kDa C-terminal fragments. Peptide sequencing proposed cathepsin K as a candidate protease. Cathepsin K was necessary and sufficient to cleave angiopoietin-2. Recombinant 25 and 50 kDa angiopoietin-2 fragments (cANGPT225 and cANGPT250) bound and antagonized Tie2. Cathepsin K inhibition with the phase 3 small-molecule inhibitor odanacatib improved survival in distinct murine sepsis models. Full-length angiopoietin-2 enhanced survival in endotoxemic mice administered odanacatib and, conversely, increased mortality in the drug's absence. Odanacatib's benefit was reversed by heterologous cANGPT225. Septic humans accumulated circulating angiopoietin-2 fragments, which were associated with adverse outcomes. These results identify cathepsin K as a candidate marker of sepsis and a proteolytic mechanism for the conversion of angiopoietin-2 from Tie2 agonist to antagonist, with therapeutic implications for inflammatory conditions associated with angiopoietin-2 induction.
2. A rapid facility-level assessment of oxygen systems in 39 low-income and middle-income countries: a cross-sectional study.
Among 2,884 facilities in 39 LMICs, reliable oxygen availability was low: 24.5% of primary, 52.4% of secondary, and 66.8% of tertiary facilities. Functional gaps spanned sources, distribution, delivery, monitoring, and QA, with significant disparities across regions.
Impact: Defines a global oxygen systems baseline and reveals critical bottlenecks for respiratory care scale-up, guiding investments and policy.
Clinical Implications: Programs should prioritize reliable oxygen sources, bedside pulse oximetry, distribution infrastructure, and QA/maintenance, especially in primary care. Results support oxygen-specific financing and implementation frameworks.
Key Findings
- Reliable oxygen availability: 24.5% (primary), 52.4% (secondary), 66.8% (tertiary) across 2,884 facilities.
- Functional availability of key components (sources, piping, delivery devices, oximetry, QA) varied widely with significant regional disparities.
- Findings indicate urgent need for targeted investments to close system gaps.
Methodological Strengths
- Large multi-country, multi-level facility assessment with standardized instrumentation
- Component-level evaluation (sources, distribution, delivery, monitoring, QA)
Limitations
- Cross-sectional design with purposive sampling may limit generalizability
- Self-reported elements and no direct patient outcome linkage
Future Directions: Link facility oxygen readiness to patient-level outcomes; evaluate cost-effective packages (source+oximetry+maintenance) and region-tailored implementation strategies.
BACKGROUND: Unequal access to medical oxygen is a key driver of global inequities in morbidity and mortality. We aimed to describe reliable oxygen availability (ie, whether availability is uninterrupted) and functional availability (ie, whether oxygen system components are in working order) in 39 low-income and middle-income countries and to compare across WHO subregions. METHODS: We report cross-sectional survey data from primary, secondary, and tertiary level health facilities across six WHO subregions. Facilities were selected via purposive and stratified random sampling. Data collectors visited facilities from September 2022, to February 2023, to administer a standardised questionnaire to facility leadership. All approached facilities responded. Questions assessed reliable oxygen availability over the preceding 3 months and the functional availability of system components: oxygen sources (ie, cylinders, concentrators, plants, and liquid oxygen), distribution systems (ie, piping, cylinder transport, and respiratory tubing), delivery devices (ie, nasal interfaces, face masks, and advanced modalities), monitoring devices (ie, pulse oximeters and multiparameter monitors), and quality assurance (ie, oxygen concentration control and maintenance schedule). We report descriptive statistics and compare across subregions using χ
3. Mechanical ventilation energy analysis: Recruitment focuses injurious power in the ventilated lung.
A new energy accounting framework in porcine ARDS shows that rapid, localized recruitment/derecruitment dissipates a small fraction of total energy but at damaging intensity, correlating with injury and recovery. Overdistension and viscoelastic losses were less predictive, reframing ventilator power targets.
Impact: Introduces a quantifiable partition of ventilatory energy and identifies recruitment/derecruitment as the focal injurious component, guiding ventilator strategies beyond global power metrics.
Clinical Implications: Supports strategies minimizing cyclic recruitment (adequate PEEP, open-lung approaches, avoiding derecruitment) and suggests monitoring energy components could reduce VILI risk.
Key Findings
- Developed a method to quantify ventilatory energy transport/dissipation and partition into airflow, tissue viscoelasticity, and recruitment/derecruitment (RD).
- Only RD energy tracked with physiologic recovery/injury despite constituting ~2–5% of total dissipation.
- RD is injurious due to high power intensity over small areas; estimated intensity on the order of ~100 W/m (incomplete unit in abstract).
Methodological Strengths
- Controlled porcine ARDS model with independent manipulation of overdistension and RD
- Multimodal measurements (flows, tracheal/esophageal pressures, impedance, oxygen transport) with histologic validation
Limitations
- Animal model and 6-hour observation limit direct clinical generalizability
- Specialized instrumentation/analysis may be challenging for bedside translation
Future Directions: Translate energy partitioning to bedside surrogates; test ventilation strategies specifically minimizing RD intensity and validate against VILI outcomes in clinical trials.
The progression of acute respiratory distress syndrome (ARDS) from its onset due to disease or trauma to either recovery or death is poorly understood. Currently, there are no generally accepted treatments aside from supportive care using mechanical ventilation. However, this can lead to ventilator-induced lung injury (VILI), which contributes to a 30 to 40% mortality rate. In this study, we develop and demonstrate a technique to quantify forms of energy transport and dissipation during mechanical ventilation to directly evaluate their relationship to VILI. A porcine ARDS model was used, with ventilation parameters independently controlling lung overdistension and alveolar/airway recruitment/derecruitment (RD). Hourly measurements of airflow, tracheal and esophageal pressures, respiratory system impedance, and oxygen transport were taken for six hours following lung injury to track energy transfer and lung function. The final degree of injury was assessed histologically. Total and dissipated energies were quantified from lung pressure-volume relationships and subdivided into contributions from airflow, tissue viscoelasticity, and RD. Only RD correlated with physiologic recovery. Despite accounting for a very small fraction (2 to 5%) of the total energy dissipation, RD is damaging because it occurs quickly over a very small area. We estimate power intensity of RD energy dissipation to be 100 W/m