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Alarmins as mediators of aseptic inflammatory responses and sepsis

English title Alarmins as mediators of aseptic inflammatory responses and sepsis
Applicant Pugin Jérôme
Number 141143
Funding scheme Project funding (Div. I-III)
Research institution Division des Soins Intensifs de Médecine Département de Médecine Hôpital Cantonal - HUG
Institution of higher education University of Geneva - GE
Main discipline Pathophysiology
Start/End 01.07.2012 - 30.06.2015
Approved amount 490'529.00
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All Disciplines (2)

Discipline
Pathophysiology
Immunology, Immunopathology

Keywords (8)

Chemotaxis; Neutrophils; Toll-like receptors; Sepsis; Innate Immunity; Alarmines; Inflammasome; ARDS

Lay Summary (English)

Lead
Lay summary

A VILI rabbit model will be used to test the in vivo relevance of the abovementioned in vitro findings. In particular, alarmins will be detected in lung lavage fluids from rabbit submitted to prolonged mechanical ventilation, and alarmin inhibitors will also be tested in this model with the aim of neutrophil-dependent preventing lung injury. Finally alarmins levels will be measured in human BAL fluid from patients mechanically ventilated and in the plasma from patients with sepsis and ARDS.

A series of in vitro experiments using the cyclic stretch model aim at studying the signaling of alarmins (inflammasome), and test various inhibitors of alarmin-dependent activation of cells. These experiments will focus on the activation of lung cells by mtDNA (TLR9 pathway), ATP (caspase-1 activation) and fMLP (neutrophil activation and chemotaxis). Co-cultures with neutrophils will also be performed to investigate their relative role in epithelial cell injury during cyclic stretch.

Preliminary results using an in vitro model show that human alveolar cells submitted to cyclic stretch release such alarmins. These results serve as a proof-of-concept to further investigate the role of alarmins in the generation of aseptic lung inflammation during mechanical ventilation. We hypothesize that alarmins released from cells injured during unusual mechanical strains are responsible for the alveolar production of IL-1ß creating a local inflammatory reaction (mtDNA and ATCec). Released alarmins (mitochondrial fMLP) also attract, home to the airways, and activate neutrophils that will produce additional lung injury.

Mechanical ventilation of critically ill patients, particularly when high pressures and volumes are delivered to the lung, produces plasma membrane breaks in lung cells and recruitment of activated neutrophils to the airways. This phenomenon is now called “ventilator-induced lung injury, or VILI”. Although some of the (secondary) mediators have been recognized, such as IL-1ß and IL-8, the proximal mediators responsible for generating the local inflammation are not known. It is the aim of this proposal to test the relevance of mitochondrial alarmins and extracellular ATP in the mediation of VILI.

Mediators from human tissues responsible for generating local and systemic inflammation are poorly known. Recently, the concept of alarmins (or danger signals) released from injured (necrotic) tissues was proposed to explain the situation of inflammatory responses in the absence of an infection. Experimental models have recently identified alarming of mitochondrial origin, released from necrotic tissues that signal the presence of danger and activate the inflammatory and immune systems. Among the molecules that are released from tissues that play a local (and possibly systemic) role are: mitochondrial DNA, the formyl peptide fMLP, and adenosine triphosphate, ATP. When present extracellularly, these mediators induce an inflammatory reaction via the production of the pro-inflammatory IL-1ß cytokine by neighboring cells, via the intracytoplasmic assembly of the inflammasome. fMLP plays also an important role as a chemotactic and activating factor for neutrophils. Activated neutrophils recruited to the site of tissue injury in turn participate in further injury.

This project carries the exciting potential to unravel the role of novel and proximal endogenous mediators of lung inflammation and injury, and also to identify critical pathways that could be modulated with pharmacological inhibitors. 

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Augmented renal clearance, low β-lactam concentrations and clinical outcomes in the critically ill: an observational prospective cohort study.
Huttner A (2015), Augmented renal clearance, low β-lactam concentrations and clinical outcomes in the critically ill: an observational prospective cohort study., in Int J Antimicrob Agents, 45(4), 385-392.
Clinical features and viral kinetics in a rapidly cured patient with Ebola virus disease
Schibler M (2015), Clinical features and viral kinetics in a rapidly cured patient with Ebola virus disease, in Lancet Infect Dis, 15(9), 1034-1040.
Efficacy and safety of citrate-based anticoagulation compared to heparin in patients with acute kidney injury requiring continuous renal replacement therapy: a randomized controlled trial.
Stucker F (2015), Efficacy and safety of citrate-based anticoagulation compared to heparin in patients with acute kidney injury requiring continuous renal replacement therapy: a randomized controlled trial., in Critical Care, 19, 91.
Adrenomedullin: a vasodilator to treat sepsis?
Pugin J (2014), Adrenomedullin: a vasodilator to treat sepsis?, in Crit Care, 18(3), 152.
Challenges in the culture-independent analysis of oral and respiratory samples from intubated patients
Lazarevic V (2014), Challenges in the culture-independent analysis of oral and respiratory samples from intubated patients, in Front Cell Infect Microbiol, 4, 65.
Selective antibody intervention of Toll-like receptor 4 activation through Fc γ receptor tethering
Shang L (2014), Selective antibody intervention of Toll-like receptor 4 activation through Fc γ receptor tethering, in J Biol Chem, 289(22), 15309-15318.
Increased FGF21 plasma levels in humans with sepsis and SIRS.
Gariani K (2013), Increased FGF21 plasma levels in humans with sepsis and SIRS., in Endocr Connect, 2(3), 146-153.

Collaboration

Group / person Country
Types of collaboration
Réanimation Médicale, CHU Dijon France (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel

Associated projects

Number Title Start Funding scheme
122034 Role of alarmins and opsonophagocytosis in innate immunity in critically ill patients 01.04.2009 Project funding (Div. I-III)
122034 Role of alarmins and opsonophagocytosis in innate immunity in critically ill patients 01.04.2009 Project funding (Div. I-III)
122034 Role of alarmins and opsonophagocytosis in innate immunity in critically ill patients 01.04.2009 Project funding (Div. I-III)

Abstract

Endogenous mediators responsible for generating local and systemic inflammation are poorly known. Recently, the concept of alarmins (or danger signals) released from injured (necrotic) tissues was proposed to explain the situation of aseptic inflammatory responses. Experimental models have recently identified mitochondrial alarmins released from necrotic tissues that signal the presence of danger and activate the inflammatory and immune systems. Among the molecules that are released from tissues that play a local (and possibly systemic) role are: mitochondrial DNA, the formyl peptide fMLP, and adenosine triphosphate, ATP. When present extracellularly, these mediators induce an inflammatory reaction via the production of IL-1ß by neighboring cells, via the assembly of the inflammasome. fMLP plays also an important role as a chemotactic and activating factor for neutrophils. Activated neutrophils recruited to the site of tissue injury in turn participate in further injury. Mechanical ventilation of critically ill patients, particularly when high pressures and volumes are delivered to the lung, produces plasma membrane breaks in lung cells and recruitment of activated neutrophils to the airways. This phenomenon is now called “ventilator-induced lung injury, or VILI”. Although some of the (secondary) mediators have been recognized, such as IL-1ß and IL-8, the proximal mediators responsible for generating the local inflammation are not known. It is the aim of this proposal to test the relevance of mitochondrial alarmins and extracellular ATP in the mediation of VILI. Preliminary results using an in vitro model show that human alveolar cells submitted to cyclic stretch release such alarmins. These results serve as a proof-of-concept to further investigate the role of alarmins in the generation of aseptic lung inflammation during mechanical ventilation. We hypothesize that alarmins released from cells injured during unusual mechanical strains are responsible for the alveolar production of IL-1ß creating a local inflammatory reaction (mtDNA and ATCec). Released alarmins (mitochondrial fMLP) also attract, home to the airways, and activate neutrophils that will produce additional lung injury. A series of in vitro experiments using the cyclic stretch model aim at studying the signaling of alarmins (inflammasome), and test various inhibitors of alarmin-dependent activation of cells. These experiments will focus on the activation of lung cells by mtDNA (TLR9 pathway), ATP (caspase-1 activation) and fMLP (neutrophil activation and chemotaxis). Co-cultures with neutrophils will also be performed to investigate their relative role in epithelial cell injury during cyclic stretch.A VILI rabbit model will be used to test the in vivo relevance of the abovementioned in vitro findings. In particular, alarmins will be detected in lung lavage fluids from rabbit submitted to prolonged mechanical ventilation, and alarmin inhibitors will also be tested in this model with the aim of neutrophil-dependent preventing lung injury. Finally alarmins levels will be measured in human BAL fluid from patients mechanically ventilated and in the plasma from patients with sepsis and ARDS.This project carries the exciting potential to unravel the role of novel and proximal endogenous mediators of lung inflammation and injury, and also to identify critical pathways that could be modulated with pharmacological inhibitors. These findings will potentially be translated to patients suffering from aseptic neutrophil-induced tissue injury such as ARDS, but also other diseases such as alcoholic hepatitis, paniculitis, ANCA vasculitis, etc.
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