Inhibition of airway hyperresponsiveness and pulmonary inflammation by roflumilast and other PDE4 inhibitors

Roflumilast is an oral, once-daily phosphodiesterase 4 (PDE4) inhibitor with anti-inflammatory activity. We compared the anti-inflammatory effects of roflumilast with those of PDE4 inhibitors rolipram, piclamilast, and cilomilast in ovalbumin (OVA)-sensitized and challenged Brown-Norway rats. Animals were treated orally 1h before OVA challenge with roflumilast (0.3, 1.0, and 3.0mg/kg), rolipram (0.8, 2.8, and 8.3mg/kg), piclamilast (10.0, 20.0, and 30.0mg/kg), or cilomilast (10.3, 34.3, and 103.0mg/kg). Airway hyperresponsiveness (AHR) against adenosine was investigated by measuring airway resistance 200min after OVA challenge. Subsequently, neutrophil influx and tumor necrosis factor-alpha (TNF-alpha) release in the lungs were determined by bronchoalveolar lavage. Direct bronchodilation at the time point of AHR assessment by PDE4 inhibitors was examined in serotonin-challenged animals. Evaluation of neutropenic animals or treatment with anti-TNF-alpha antibody revealed that AHR was independent of neutrophil accumulation or TNF-alpha release. Roflumilast (50% inhibitory dose ID(50)]=1.5mg/kg) inhibited AHR 3-, 16-, and 27-fold more potently than rolipram, piclamilast, and cilomilast, respectively. Likewise, roflumilast was a more potent inhibitor of neutrophil influx (ID(50)=0.9mg/kg) than rolipram (ID(50)=6.9mg/kg), piclamilast (ID(50)=28.1mg/kg), or cilomilast (ID(50)=37.7mg/kg). Roflumilast, rolipram, and piclamilast-but not cilomilast-suppressed OVA-induced TNF-alpha release in a dose-dependent manner. Roflumilast (ID(50)=0.9mg/kg) exhibited 9- and 23-fold more potent inhibition of TNF-alpha release than rolipram and piclamilast, respectively. Roflumilast did not inhibit serotonin-induced bronchoconstriction 4.5h after administration, suggesting that inhibition of AHR by roflumilast results from anti-inflammatory, not bronchodilatory, effects. This study suggests that roflumilast has anti-inflammatory action and provides rationale for the investigation of roflumilast in asthmatic patients.