Daily Sepsis Research Analysis
Three high-impact studies reshape our understanding of sepsis. A JCI paper uncovers a cathepsin K–mediated proteolytic switch that converts angiopoietin-2 into Tie2 antagonists, improving survival in murine sepsis when inhibited. A Lancet Global Health cohort reveals high mortality and multidrug resistance in neonatal sepsis at Indian district hospitals, while an EBioMedicine genomic analysis identifies an IncFII plasmid driving global spread of carbapenem-resistant hypervirulent Klebsiella pneu
Summary
Three high-impact studies reshape our understanding of sepsis. A JCI paper uncovers a cathepsin K–mediated proteolytic switch that converts angiopoietin-2 into Tie2 antagonists, improving survival in murine sepsis when inhibited. A Lancet Global Health cohort reveals high mortality and multidrug resistance in neonatal sepsis at Indian district hospitals, while an EBioMedicine genomic analysis identifies an IncFII plasmid driving global spread of carbapenem-resistant hypervirulent Klebsiella pneumoniae.
Research Themes
- Endothelial injury and Tie2 signaling in sepsis
- Antimicrobial resistance in neonatal sepsis
- Pathogen genomics driving hypervirulent, drug-resistant spread
Selected Articles
1. Cathepsin K cleavage of angiopoietin-2 creates detrimental Tie2 antagonist fragments in sepsis.
Inflammation triggers cathepsin K–mediated cleavage of angiopoietin-2 into 25 and 50 kDa fragments that antagonize Tie2, destabilizing endothelium in sepsis. Pharmacologic inhibition of cathepsin K (odanacatib) improved survival in murine sepsis, and circulating ANGPT2 fragments in patients associated with worse outcomes.
Impact: This mechanistic discovery links a specific protease to ANGPT2 functional switching and demonstrates druggability with survival benefit in vivo, offering a tractable target and biomarker for vascular dysfunction in sepsis.
Clinical Implications: Cathepsin K inhibitors and assays for ANGPT2 fragments could enable prognostication and targeted endothelial-stabilizing therapy in sepsis. Tie2 pathway modulation may be revisited with context-specific strategies.
Key Findings
- Cathepsin K cleaves full-length 75 kDa ANGPT2 into 25 and 50 kDa C-terminal fragments that antagonize Tie2.
- Odanacatib (cathepsin K inhibitor) improved survival in distinct murine sepsis models.
- Circulating ANGPT2 fragments accumulated in septic patients and were associated with adverse outcomes.
- Full-length ANGPT2 improved survival only in the presence of cathepsin K inhibition; otherwise increased mortality.
Methodological Strengths
- Multi-system translational approach integrating macrophage-endothelium assays, proteomics, recombinant fragment biochemistry, murine sepsis models, and human biomarker analyses.
- Demonstration of necessity and sufficiency for cathepsin K in ANGPT2 cleavage, with pharmacologic reversal using a clinically advanced inhibitor.
Limitations
- Human data are observational; causality of ANGPT2 fragments for outcomes in patients is not established.
- Safety and efficacy of cathepsin K inhibition in clinical sepsis remain untested.
Future Directions: Develop clinical assays for ANGPT2 fragments, validate prognostic utility, and test cathepsin K/Tie2-targeted therapies in early-phase sepsis trials with endothelial phenotyping.
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. Global emergence of Carbapenem-resistant Hypervirulent Klebsiella pneumoniae driven by an IncFII
Across thousands of genomes and multiple clinical isolate collections, an IncFII plasmid was identified as a key vehicle enabling convergence of carbapenem resistance and hypervirulence in K. pneumoniae, facilitating global dissemination of CR-hvKp.
Impact: Pinpointing a specific plasmid backbone as the driver of resistance–virulence convergence provides a tangible surveillance and containment target for AMR programs.
Clinical Implications: Genomic surveillance should prioritize detection of IncFII plasmids in K. pneumoniae; infection control and stewardship policies can target plasmid-mediated spread and inform empiric therapy in high-risk settings.
Key Findings
- Integrated analysis of 67,631 genomes and multi-center clinical isolates implicated an IncFII plasmid in CR-hvKp emergence.
- IncFII-positive CR-hvKp genomes from 24 countries indicate global dissemination.
- Resistance (carbapenemase) acquisition on hvKp backgrounds underlies convergence of hypervirulence and carbapenem resistance.
Methodological Strengths
- Large-scale comparative genomics spanning tens of thousands of genomes plus clinical isolate validation.
- Multi-cohort integration (CRACKLE-2 China, multi-center isolates, GenBank) enabling global generalizability.
Limitations
- Abstracted data indicate observational genomic associations without direct transmission or fitness experiments.
- Sampling bias in public databases may influence geographic and lineage representation.
Future Directions: Prospective genomic surveillance tracking IncFII plasmid movement, functional studies of transfer dynamics and fitness costs, and targeted infection control interventions in hotspots.
BACKGROUND: Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKp) has been increasingly reported worldwide, posing a severe challenge to public health; however, the mechanisms driving its emergence and global dissemination remain unclear. METHODS: We analysed CR-hvKp strains derived from canonical hvKp backgrounds, and acquired a carbapenemase-encoding gene. These strains were identified from 485 CRKp isolates in the CRACKLE-2 China cohort, 259 CRKp isolates from a multi-centre study, and 67,631 K. pneumoniae genomes available in GenBank. Clinical isolates harbouring the IncFII FINDINGS: Analysis of clinical CR-hvKp isolates and the 414 genomes from 24 countries available in GenBank identified an IncFII INTERPRETATION: The IncFII FUNDING: National Natural Science Foundation of China and National Institutes of Health.
3. Multidrug-resistant sepsis in special newborn care units in five district hospitals in India: a prospective cohort study.
In five Indian district hospitals, culture-positive neonatal sepsis occurred in 3.2% of admissions with a 36.6% case-fatality rate. Gram-negative pathogens predominated and 75–88% of key isolates were multidrug resistant, particularly in outborn neonates, highlighting urgent needs for IPC, blood culture capacity, and stewardship.
Impact: First prospective, multi-site district-level data quantify MDR sepsis burden and mortality in neonates, informing national policy and resource allocation beyond tertiary centers.
Clinical Implications: Implement on-site blood culture and MALDI-TOF capacity, reinforce infection prevention and control, and tailor empiric regimens using local resistance profiles; prioritize outborn neonates for surveillance and early escalation.
Key Findings
- Among 6612 neonates, 3.2% had culture-positive sepsis with a 36.6% case-fatality rate.
- Outborn neonates had higher sepsis incidence (5.0%) than inborn (2.0%).
- Gram-negative bacilli comprised 70% of isolates; 75–88% of key species (K. pneumoniae, E. coli, Enterobacter spp., A. baumannii) were multidrug resistant.
Methodological Strengths
- Prospective, multi-center design with standardized microbiology and MALDI-TOF confirmation.
- Clear MDR definition spanning key antibiotic classes and site-level comparisons.
Limitations
- Cultures obtained only from neonates meeting prespecified criteria may underestimate true incidence.
- Observational design precludes causal inference about drivers of MDR or mortality.
Future Directions: Scale up district-level microbiology capacity, implement antimicrobial stewardship bundles, and evaluate targeted IPC interventions and empiric therapy optimization in pragmatic trials.
BACKGROUND: Neonatal sepsis epidemiology has been adequately reported in tertiary-care hospitals. However, such data are scarce from district hospitals in low-income and middle-income countries. This study aimed to evaluate the incidence of sepsis, pathogen profile, and antimicrobial resistance among neonates admitted to the special newborn care units in district hospitals in India. METHODS: We prospectively enrolled neonates admitted to newborn units in five district hospitals in India between October, 2019, and December, 2021. Blood cultures were obtained from neonates who met prespecified criteria and were processed at the laboratories of the tertiary-care hospitals linked to each district hospital. Identification of pathogens and antimicrobial susceptibility testing was performed using the automated system; all isolates were confirmed using matrix-assisted laser desorption-ionisation-time of flight. The primary outcome was the incidence of culture-positive sepsis. The final label of culture-positive sepsis was assigned based on culture reports and clinical course. Multidrug resistance was defined as resistance to antibiotics in at least three of the six antibiotic classes, including third generation cephalosporins, carbapenems, and aminoglycosides. FINDINGS: The study enrolled 6612 neonates (3972 inborn [born at the same hospital] and 2640 outborn [referred from other hospitals or homes]). Mean gestation was 37·1 weeks and mean birthweight was 2540 g. 3357 (50·8%) neonates met clinical sepsis criteria. The overall incidence of culture-positive sepsis was 213 (3·2%; 95% CI 0·6-14·4); ranging from 0·6% to 10·0% across the five sites. The incidence was higher in outborn neonates than inborn neonates: 132 [5·0%] versus 81 [2·0%]. The case-fatality rate of culture-positive sepsis was 36·6% (95% CI 12·1-71·0). Gram-negative bacilli accounted for 156 (70·0%) of 223 organisms isolated: Klebsiella pneumoniae (51 [22·9%]), Escherichia coli (33 [14·8%]), and Enterobacter spp (26 [11·7%]) were the most common Gram-negative organisms. 75%-88% of isolates of K pneumoniae, E coli, Enterobacter spp, and Acinetobacter baumannii were multidrug resistant. INTERPRETATION: The high incidence of culture-positive sepsis, case-fatality rates, and multidrug resistance among common pathogens underscores an urgent need to strengthen infection prevention and control practices, establish blood culture facilities, and implement antimicrobial stewardship programmes in district-level hospitals in India. FUNDING: Bill & Melinda Gates Foundation. TRANSLATION: For the Hindi translation of the abstract see Supplementary Materials section.