Fig. 4

Effect of roflumilast on Airway Surface Liquid (ASL). a Calibration of ASL measurements shows a good correlation between added and measured Δ volumes in 12 mm Corning Transwell filters measured 30 min after addition (n = 7). Similar results were found when measuring after 3 h (not shown). b Following ASL volumes over time after exposure to air shows an initial increase in ASL volume that returns to baseline after 24 h. Roflumilast enhances the response and keeps ASL above baseline at the 24 h time point (six different lungs, n = 6, # p < 0.05 for comparison between control and roflumilast treated cells at different time points). c Following ASL volumes over time after exposure to cigarette smoke shows a blunted initial increase. Roflumilast on the other hand, increases initial volume and restores the ASL volume response after smoke exposure, comparable to air exposure, keeping the ASL volume close to baseline at 24 h (six different lungs, n = 6, # p < 0.05 for comparison between control and roflumilast treated cells at different time points). Black and red dotted line in B/C for comparison of baseline of control (black) and roflumilast treated (red) cultures. d Control experiments with DMSO as vehicle do not show any difference in Δ ASL measurements between 1 and 4 h in air versus cigarette smoke exposed cultures (two lungs; n = 4). * p < 0.05