A murine two-hit model to investigate the early time-course of inflammation in acute respiratory distress syndrome

• Ein Mausmodell zur Untersuchung des frühen Zeitverlaufes der Entzündung im akuten Lungenversagen

Kanzler, Stephanie Sarah; Uhlig, Stefan (Thesis advisor); Pradel, Gabriele (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

The acute respiratory distress syndrome (ARDS) was first described in 1967 and is a clinical syndrome that is characterised by an acute onset of hypoxemia and bilateral pulmonary opacities, which cannot be explained by cardiac failure or volume overload. Inspite of more than 50 years of research, therapies are still limited and the mortality remains high with about 40%. Although promising results were achieved in preclinical studies, no clinical trial was able to show benefit of pharmacotherapies for human ARDS patients. Consequently, recent discussions focus on the existence of different subphenotypes within ARDS patients with the aim to develop clinical studies as well as pharmacotherapies based on the clinical and biologic profile of each patient. Therefore, the first aim of the present study was to develop a murine two-hit model with special regard to the establishment of a hypo- and hyperinflammatory subphenotype of experimental ARDS. Secondly, the present study aimed at characterising the hyperinflammatory response in detail to identify key inflammatory mediators using the established model. The two-hit model of experimental ARDS, consisting of an intratracheal instillation of lipopolysaccha-rides (LPS) followed by injurious mechanical ventilation, was established successfully. Mild and moderate experimental ARDS was induced by different doses of LPS and physiological parameter as well as the inflammatory response were characterised in detail and identified as hypo- and hyperinflammatory like subphenotypes of experimental ARDS. To further optimise the experimental ARDS model, the management of carbon dioxide (CO2) in mice was optimised by the development of a ventilation adapter (VA) and flow cytometry was established to characterise the inflammatory response in detail. The nicely established murine model of ARDS was then used to characterise the hyperinflammatory response in an early phase of the syndrome in detail. The analysis of 21 different inflammatory media-tors in bronchoalveolar lavage fluid showed significantly elevated levels of Interleukin-6 (IL-6), chemokine (C-X-C motif) ligand (CXCL) 1 and 2 (CXCL1 and CXCL2 represent the mice homologues of human Interleukin 8 (IL-8)). As these mediators are used as biomarkers for ARDS in clinical practice, these data suggest a high degree of transferability into the human situation. In addition, two mediators, namely CC-chemokine ligand 2 (CCL2) and granulocyte-colony stimulating factor (G-CSF) were identified as key inflammatory mediators of the hyperinflammatory response, indicating that the recruitment of neutrophils as well as their life span within the lungs are the most critical features in the fatal progression of the syndrome in the hyperinflammatory subphenotype of experimental ARDS. In conclusion, a valid murine model of experimental ARDS was established and especially the hyperinflammatory subphenotype of experimental ARDS was modelled. The mediators CCL2 and G-CSF were found to be specific for the hyperinflammatory response and their potential as biomarkers for the identification of the hyperinflammatory subphenotype of ARDS and as target for pharmacological interventions in a very early phase of the syndrome should be evaluated in detail in future studies.