Inhibitory effects of palmitoyl ceramide (ceramide 16:0 [Cer16]) on the metabolic/proliferative activity of human lung microvascular endothelial cells. Metabolic activity measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay in cells from nonsmoker (gray bars) and smoker (black bars) in the following conditions: (a) untreated, 16 hours, mean + SEM (n = 3; *P < 0.05); (b) following vehicle (veh; polyethylene glycol 2,000) or Cer16 treatment at the indicated concentrations (6 h), fold change versus veh, mean + SEM (n = 3; *P < 0.05, #P < 0.005 vs. veh); or (c) following veh, or Cer16 treatment for the indicated time in hours (10 μM), mean + SEM (n = 3; *P < 0.0001 and #P < 0.01 vs. vehicle control; ##P < 0.05).