Effects of cholesterol on surface activity and surface topography of spread surfactant films.
Pulmonary surfactant forms a monolayer of lipids and proteins at the alveolar air/liquid interface. Although cholesterol is a natural component of surfactant, its function in surface dynamics is unclear. To further elucidate the role of cholesterol in surfactant, we used a captive bubble surfactometer (CBS) to measure surface activity of spread films containing dipalmitoylphosphatidylcholine/1-palmitoyl-2-oleoylphosphatidylcholine/1-palmitoyl-2-oleoylphosphatidylglycerol (DPPC/POPC/POPG, 50/30/20 molar percentages), surfactant protein B (SP-B, 0.75 mol %), and/or surfactant protein C (SP-C, 3 mol %) with up to 20 mol % cholesterol. A cholesterol concentration of 10 mol % was optimal for reaching and maintaining low surface tensions in SP-B-containing films but led to an increase in maximum surface tension in films containing SP-C. No effect of cholesterol on surface activity was found in films containing both SP-B and SP-C. Atomic force microscopy (AFM) was used, for the first time, to visualize the effect of cholesterol on topography of SP-B- and/or SP-C-containing films compressed to a surface tension of 22 mN/m. The protrusions found in the presence of cholesterol were homogeneously dispersed over the film, whereas in the absence of cholesterol the protrusions tended to be more clustered into network structures. A more homogeneous dispersion of surfactant lipid components may facilitate lipid insertion into the surfactant monolayer. Our data provide additional evidence that natural surfactant, containing SP-B and SP-C, is superior to surfactants lacking one of the components, and furthermore, this raises the possibility that the cholesterol found in surfactant of warm-blooded mammals does not have a function in surface activity.
Diemel
Robert V
RV
Departments of Biochemistry and Cell Biology and of Science of Food of Animal Origin, Graduate School of Animal Health, Faculty of Veterinary Medicine, Utrecht University, P.O. Box 80176, The Netherlands.
Snel
Margot M E
MM
Van Golde
Lambert M G
LM
Putz
Günther
G
Haagsman
Henk P
HP
Batenburg
Joseph J
JJ
D000327:Adsorption / Q000187:drug effects; D000818:Animals; D002417:Cattle; D002784:Cholesterol / Q000737:chemistry* / Q000494:pharmacology; D004338:Drug Combinations; D008051:Lipid Bilayers / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D010713:Phosphatidylcholines / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D037701:Pulmonary Surfactant-Associated Protein B / Q000737:chemistry* / Q000648:ultrastructure; D037721:Pulmonary Surfactant-Associated Protein C / Q000737:chemistry* / Q000648:ultrastructure; D013499:Surface Properties; D013500:Surface Tension / Q000187:drug effects; D013552:Swine
D004338:Drug Combinations; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D037701:Pulmonary Surfactant-Associated Protein B; D037721:Pulmonary Surfactant-Associated Protein C; C060037:1-palmitoyl-2-oleoylglycero-3-phosphoglycerol; D002784:Cholesterol; C017251:1,2-oleoylphosphatidylcholine; C028694:1-palmitoyl-2-oleoylphosphatidylcholine