A comparative study of mechanisms of surfactant inhibition

Abstract

Pulmonary surfactant spreads to the hydrated air-lung interface and reduces the surface tension to a very small value. This function fails in acute respiratory distress syndrome (ARDS) and the surface tension stays high. Dysfunction has been attributed to competition for the air-lung interface between plasma proteins and surfactant or, alternatively, to ARDS-specific alterations of the molecular profile of surfactant. Here, we compared the two mechanisms in vitro, to assess their potential role in causing respiratory distress. Albumin and fibrinogen exposure at or above blood level concentrations served as the models for testing competitive adsorption. An elevated level of cholesterol was chosen as a known adverse change in the molecular profile of surfactant in ARDS. Bovine lipid extract surfactant (BLES) was spread from a small bolus of a concentrated suspension (27 mg/ml) to the air-water interface in a captive bubble surfactometer (CBS) and the bubble volume was cyclically reduced and increased to assess surface activity of the spread material. Concentrations of inhibitors and the concentration and spreading method of pulmonary surfactant were chosen in an attempt to reproduce the exposure of surfactant to inhibitors in the lung. Under these conditions, neither serum albumin nor fibrinogen was persistently inhibitory and normal near-zero minimum surface tension values were obtained after a small number of cycles. In contrast, inhibition by an increased level of cholesterol persisted even after extensive cycling. These results suggest that in ARDS, competitive adsorption may not sufficiently explain high surface tension, and that disruption of the surfactant film needs to be given causal consideration.

High-throughput evaluation of pulmonary surfactant adsorption and surface film formation

“…The search for new drugs of potential clinical interest directed to specific pathologically relevant targets is usually conducted through the analysis of the effect of hundreds to thousands of potential compounds, under many different possible conditions, in tests carried out under automated or semi-automated regimes (43)(44)(45). Our fluorescent plate reader assay has demonstrated its utility to evaluate surfactant inhibition effects such as those produced by serum proteins like albumin (8,46). Deactivation of surfactant by serum components and by inflammatory mediators leaked into the alveolar spaces is thought to be a major determinant of the respiratory failure in acute respiratory distress associated with lung injury (16,47).…”

Properties of modified natural surfactant after exposure to fibrinogen in vitro and in an animal model of respiratory distress syndrome

“…In contrast, a recent in vitro study under conditions resembling the exposure of surfactant to inhibitors in the lungs revealed that neither serum albumin nor fibrinogen were persistently inhibitory to pulmonary surfactant and normal near-zero minimum surface tension values were obtained after a small number of cycles (5). Moreover, there is evidence of protective effects of plasma proteins on surfactant inactivation.…”

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

“…Previous studies have shown that cholesterol is an integral component of LS, found between 7-15 in various mammalian systems 9,10,39,43,44 . However, the physiological role of cholesterol is not clear to date, since the source of the material as well as its delivery route in LS has not been firmly established.…”

“…In their study, minimal delay or rapid adsorption was noticed in BLES film formation with the presence of a pre-formed protein film. They concluded that surfactant inhibition was likely caused by a dysfunctional film instead of inhibition by way of competitive adsorption of the serum proteins 39 . This contradicted the previously reported result 11,17 .…”

“…S4. These Raman peaks, for specific phospholipids and their bond vibration designations, have been determined previously by others 38,39 .…”