Effect of CD derivatives on cholesterol accumulation in NPC1 −/− cells. Primary fibroblast cells from a healthy donor or NPC patient were incubated with CD derivatives (1 mM) for 72 h and the levels of free cholesterol in cells were determined by staining with Filipin. Data shown are a representative of three independent experiments. Wild-type, primary fibroblast cells from a healthy donor; NPC1 -/- cells, primary fibroblast cells from an NPC patient. Scale bar = 50 μm