Repeated lipopolysaccharide stimulation causes corticosteroid insensitive inflammation in lung via phosphoinositide-3-kinase δ signaling

Respiratory bacterial infections cause exacerbation of respiratory diseases such as severe asthma and COPD, which are corticosteroid refractory, and the aim is to set up corticosteroid insensitive animal model exposed to lipopolysaccharide (LPS) and evaluate the molecular signaling. Here we show that repeated intranasal LPS challenge induced corticosteroid insensitive inflammation in mice, and a phospoinositide-3-kinase (PI3K) δ inhibitor restored the corticosteroid action in that model. LPS was administrated intranasally to A/J male mice for 1-3 days, and IC87114 and/or fluticasone propionate (FP) were treated intranasally at 2 h before each LPS administration. BALF was collected at 24 h after the last LPS administration and neutrophils were quantified by FACS analysis. The level of CXCL1 in BALF was also determined using a commercially available kit. Repeated LPS exposure in contrast to single treatment showed significant increase in neutrophils and CXCL1 in BALF, which were not inhibited by FP (0.05 – 1.0 mg/ml). Phospho-Akt, a surrogate marker of PI3K activation, also increased. Although a selective PI3K δ inhibitor, IC87114 (4.0 mg/ml) alone did not a show beneficial effects, combination of IC87114 and FP elicited stronger inhibition of neutrophilia and CXCL1 production. In addition, combination of theophylline (2.0 mg/ml) and FP also showed significant inhibition on the airway inflammation induced by LPS. This profile suggests that a PI3K δ inhibitor with corticosteroid offers potential treatment of airway inflammation in patients with respiratory disease during bacterial infection.