Characterization of Surfactant Subtypes of Beractant and a Synthetic Peptide Containing Surfactant KL4 following Surface Area Cycling and Addition of Fibrinogen

Surfactant is not a homogeneous material and can be separated into subtypes. Subtype conversion is clinically important because it is thought to occur naturally and because surface activity varies depending on the subtype. Fibrinogen, a naturally occurring serum protein, is known to affect this conversion. In this study we studied two surfactants, beractant and KL₄, to examine their subtype characteristics. Surface area cycling, an in vitro method, was used in conjunction with sucrose gradient ultracentrifugation to separate subtypes in both surfactants. Activity, expressed as minimum surface tension of these subtypes, was measured using a pulsating bubble surfactometer. The effect of fibrinogen on subtype conversion and subsequent change in activity was elucidated. Our results indicate that following surface area cycling, beractant and KL₄ have different subtypes and different responses to fibrinogen. Cycling of beractant resulted in two bands, representing a heavy and a light subtype. In the presence of fibrinogen, cycling resulted in two separate heavy subtypes. Cycling of KL₄ surfactant also yielded light and heavy subtypes. However, in the presence of fibrinogen, cycling of KL₄ resulted in ultraheavy subtypes. These ultraheavy subtypes retained minimum surface tension comparable to that of native KL₄ surfactant. We conclude that these two surfactant preparations have different subtype conversions when subjected to surface area cycling and in the presence of fibrinogen. These conversions result in different activities toward lowering surface tension. We speculate that endogenous fibrinogen will also affect these two surfactants differently in vivo and thus affect their clinical effectiveness. Accepted for publication: 14 November 1996