Effect of Cholesterol on the Biophysical and Physiological Properties of a Clinical Pulmonary Surfactant

Abstract

Pulmonary surfactant is a complex mixture of lipids and proteins that forms a surface-active film at the air-water interface of alveoli capable of reducing surface tension to near 0 mN/m. The role of cholesterol, the major neutral lipid component of pulmonary surfactant, remains uncertain. We studied the physiological effect of cholesterol by monitoring blood oxygenation levels of surfactant-deficient rats treated or not treated with bovine lipid extract surfactant (BLES) containing zero or physiological amounts of cholesterol. Our results indicate no significant difference between BLES and BLES containing cholesterol immediately after treatment; however, during ventilation, BLES-treated animals maintained higher PaO2 values compared to BLES+cholesterol-treated animals. We used a captive bubble tensiometer to show that physiological amounts of cholesterol do not have a detrimental effect on the surface activity of BLES at 37 degrees C. The effect of cholesterol on topography and lateral organization of BLES Langmuir-Blodgett films was also investigated using atomic force microscopy. Our data indicate that cholesterol induces the formation of domains within liquid-ordered domains (Lo). We used time-of-flight-secondary ion mass spectrometry and principal component analysis to show that cholesterol is concentrated in the Lo phase, where it induces structural changes.

Effect of cholesterol on the molecular structure and transitions in a clinical-grade lung surfactant extract

“…Reasonably, the addition of cholesterol to clinical formulations will have an impact on the treatments of LS deficiency-related syndromes (e.g., neonatal respiratory distress syndrome). Several studies have reported negative effects of cholesterol on the performance of LSE (14,58), even though cholesterol is naturally present in the in vivo LS system. The rationale behind the reported negative effects of cholesterol remains unclear and the discrepancy may be related to differences other than the cholesterol content between the extracts and the in vivo system.…”

“…The multilayer structure has been proposed to have arrangements similar to the bulk phases formed in LS extracts (LSEs) (6,(12)(13)(14) and in clinical multivesicular dispersions (15,16). Two types of multilayer structures have been observed: lamellar bodies with spherically concentric bilayers and a tetragonal structure called tubular myelin (6,17).…”

“…We use a porcine LSE developed for use in clinical treatments and we add or remove cholesterol to this system. Most extracts that are available for clinical use today have reduced cholesterol content [0 to 1 wt % with the exception of Infasurf, which contains 5 wt % cholesterol (14,22)] compared with the natural LS that contains ca. 10 wt % cholesterol (2).…”

Effect of Serum, Cholesterol and Low Density Lipoprotein on the Functionality and Structure of Lung Surfactant Films

“…These LS are also found to have reduced surface activity, although the cause for this is not clear 11 . An early study by Haas and Longmore showed that although the lung can produce cholesterol much larger in amount than its own requirement, the main mechanism used in the production of surfactant cholesterol is the use of lipoprotein cholesterol supplied form the blood, since about 2 wt of the cholesterol is from endogenous synthesis 12 .…”

“…However previous studies also suggest that excess cholesterol also has deleterious effects, e.g., it retards the achievement of minimum surface tension to near zero value during complete film compression and decrease of post collapse re-spreading 11 .…”