Abstract Body: Background: Acute lung injury (ALI) is characterized by excessive inflammation and dysfunction of the alveolar-capillary barrier, which consists of lung vascular endothelial and alveolar epithelial cells. Therapeutic interventions that protect this barrier are promising strategies for ALI treatment. Phosphodiesterase (PDE) inhibitors are potent modulators of inflammation. These include cilostazol, a PDE3 inhibitor, and ensifentrine, a dual PED3/4 inhibitor, which are both clinically available compounds that exhibit cytoprotective and anti-inflammatory properties. However, their roles in regulating alveolar-capillary function in ALI are unknown. The aim of this study is to investigate the effects of cilostazol and ensifentrine on lung endothelial and epithelial dysfunction caused by methicillin-resistant Staphylococcus aureus (MRSA), a common bacterial pathogen involved in ALI pathogenesis.
Methods: Human primary lung endothelial cells (EC) and A549 (alveolar epithelial cell line) were pre-treated with cilostazol (CZ; 15 μM) or ensifentrine (Ens; 10 μΜ) for 1 hour and then challenged with heat-killed MRSA (2.5 x10⁸/ml). The Electrical Cell Impedance Sensing (ECIS) assay was used to assess EC barrier integrity. Pro-inflammatory signaling markers were measured by western blotting (WB) and qPCR. Cell conditioned media was analyzed for extracellular vesicle release by flow cytometry and WB.
Results: MRSA-induced EC barrier disruption was attenuated by both CZ and Ens, although Ens exhibited superior barrier protective properties. CZ and Ens suppressed MRSA-induced upregulation of the inflammatory adhesion molecules, VCAM-1 and ICAM-1, in EC. Ens, but not CZ, reduced MRSA-induced ICAM-1 upregulation in A549. MRSA caused a significant increase in the release of EC-derived extracellular vesicles, which was partially inhibited by CZ or Ens pretreatment.
Conclusions: Both cilostazol and ensifentrine exert anti-inflammatory properties in MRSA-treated lung EC. Compared to cilostazol, ensifentrine exhibits enhanced endothelial barrier protection and inhibits inflammation in both lung endothelial and epithelial cells. Future in vivo studies will evaluate the therapeutic efficacy of these inhibitors in bacterial-induced ALI.