Synergistic effect of roflumilast with dexamethasone in a neutrophilic asthma mouse model

Asthma is a chronic airway inflammatory disease with heterogeneous features. Most cases of asthma are steroid sensitive, but 5%‐10% are unresponsive to steroids, leading to challenges in treatment. Neutrophilic asthma is steroid‐resistant and characterized by the absence or suppression of the T‐helper type II (TH2) process and an increase in the TH1 and/or TH17 process. Roflumilast (ROF) has anti‐inflammatory effects and has been used to treat chronic inflammatory airway diseases, such as chronic pulmonary obstructive disease. It is unclear whether ROF may have a therapeutic role in neutrophilic asthma. In this study, we investigated the synergistic effect of ROF with dexamethasone (DEX) in a neutrophilic asthma mouse model. C57BL/6 female mice sensitized to ovalbumin (OVA) were exposed to five intranasal OVA treatments and three intranasal lipopolysaccharide (LPS) treatments for an additional 10 days. During the intranasal OVA challenge, ROF was administrated orally, and DEX was injected intraperitoneally. Protein, pro‐inflammatory cytokines, inflammatory cytokines and other suspected markers were identified by enzyme‐linked immunosorbent assay, real‐time polymerase chain reaction, and western blot. Following exposure to LPS in OVA‐induced asthmatic mice, neutrophil predominant airway inflammation rather than eosinophil predominant inflammation was observed, with increases in airway hyperresponsiveness (AHR). The lungs of animals treated with ROF exhibited less airway inflammation and hyperresponsiveness. To investigate the mechanism underlying this effect, we examined the expression of proinflammatory cytokines suspected to be involved in inflammatory cytokines and proteins. Roflumilast reduced total protein in bronchioalveolar lavage fluid; levels of interleukin (IL)‐17A, IL‐1β messenger RNA, interferon γ and tumour necrosis factor α; and recovered histone deacetylase‐2 (HDAC2) activity. Combination therapy with ROF and DEX further reduced the levels of IL‐17, IL‐22 and IL‐1β mRNA and proinflammatory cytokines. The combination of ROF and DEX reduced lung inflammation and AHR much more than one of them alone. Roflumilast reduces AHR and lung inflammation in the neutrophilic asthma mouse model. Furthermore, additive effects were observed when DEX was added to ROF treatment, possibly because of recovery of HDAC2/β‐actin activity. This study demonstrates the anti‐inflammatory properties of ROF in a neutrophilic asthma mouse model.