Angiopoietin-1 treatment reduces inflammation but does not prevent ventilator-induced lung injury

Background: Loss of integrity of the epithelial and endothelial barriers is thought to be a prominent feature of ventilatorinduced lung injury (VILI). Based on its function in vascular integrity, we hypothesize that the angiopoietin (Ang)-Tie2 system plays a role in the development of VILI. The present study was designed to examine the effects of mechanical ventilation on the Ang-Tie2 system in lung tissue. Moreover, we evaluated whether treatment with Ang-1, a Tie2 receptor agonist, protects against inflammation, vascular leakage and impaired gas exchange induced by mechanical ventilation. Methods: Mice were anesthetized, tracheotomized and mechanically ventilated for 5 hours with either an inspiratory pressure of 10 cmH₂O ('low' tidal volume ~7.5 ml/kg; LV_T) or 18 cmH₂O ('high' tidal volume ~15 ml/kg; HV_T). At initiation of HV_T-ventilation, recombinant human Ang-1 was intravenously administered (1 or 4 mg per animal). Non-ventilated mice served as controls. Results: HV_T-ventilation influenced the Ang-Tie2 system in lungs of healthy mice since Ang-1, Ang-2 and Tie2 mRNA were decreased. Treatment with Ang-1 increased Akt-phosphorylation indicating Tie2 signaling. Ang-1 treatment reduced infiltration of granulocytes and expression of keratinocyte-derived chemokine (KC), macrophage inflammatory protein (MIP)-2, monocyte chemotactic protein (MCP)-1 and interleukin (IL)-1β caused by HV_T-ventilation. Importantly, Ang-1 treatment did not prevent vascular leakage and impaired gas exchange in HV_T-ventilated mice despite inhibition of inflammation, vascular endothelial growth factor (VEGF) and Ang-2 expression. Conclusions: Ang-1 treatment downregulates pulmonary inflammation, VEGF and Ang-2 expression but does not protect against vascular leakage and impaired gas exchange induced by HV_T-ventilation.