Effect of roflumilast on inflammatory cell volume density in lungs of mice chronically exposed to cigarette smoke

Rationale: The phosphodiesterase 4 (PDE4) inhibitor roflumilast was previously shown to fully prevent emphysematous-like changes in lungs of mice that were chronically exposed to cigarette smoke. This study assessed the effect of roflu- milast on inflammatory cell volume density (VV) changes in lung tissue of mice chronically exposed to cigarette smoke. Methods: C57BL/6J mice were either exposed to room air (N=5) or cigarette smoke for 7 months (N = 5). Another group of animals (N = 5) exposed to cigarette smoke received roflumilast 5 mg/kg per os on 5 days/week for 7 months. VV was assessed immunohistochemically and by point counting in lung sections. Cells were labeled with specific antibodies: neutrophils with myeloperoxidase, macrophages with Mac-3, dendritic cells with fascin, B-lymphocytes with B220, CD4+ T-cells with CD4+ antibody. Results: In mice chronically exposed to cigarette smoke, VV of neutrophils, macrophages, dendritic cells, B-lymphocytes, and CD4+ T-cells increased 1.8- to more than 6-fold as compared to air exposure (all p < 0.01). Roflumilast did not affect baseline VV but prevented VV increases of neutrophils by 78% (p < 0.05), macrophages by 70%, dendritic cells by 48%, B-lymphocytes by 100%, and CD4+ T-cells by 98% (all p < 0.01). Conclusions: In this mouse model of chronic cigarette smoke exposure, increases in broad inflammatory cell populations involved in both the innate and adaptive immune responses were demonstrated. This study suggests that roflumilast may prevent cigarette smoke-induced emphysema development through inhibition of the recruitment of neutrophils, macrophages, and cells of the adaptive immune system.