Roflumilast N-oxide reversed the CSE-induced persistent loss of CBF in differentiated human bronchial epithelial cells (A-C), role of cAMP (D), PKA (E). Differentiated human bronchial epithelial cells (D-BECs) were exposed to CSE at 0–20% for 24 h (A), or pre-incubated for 30 min with roflumilast N-oxide at 2 nM or 1 µM (B) or with apocynin (ACY) at 100 µM or with at NAC at 1 mM (C) or vehicle (B, C) and then exposed to CSE at 10% for 24 h. Then CBF was measured by DHSV and quantified by Fourier transformation as detailed in Methods. Results are shown as the means ± SEM of cultures from two to four donors and three experiments per donor. In (D) and (E), D-BECs were pre-incubated for 30 min with roflumilast N-oxide at 2 nM or 1 µM or with dbcAMP (1 mM) before exposure to 10% CSE. Cellular cAMP content (D) and PKA (E) were assessed after 24 h as described in Methods. Results are depicted as means ± SEM of cultures from three donors and three experiments per donor. *P < 0.05 versus control, #P < 0.05 versus CSE.