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 sub types. Subtype conversion is clinically important because it is though t 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 a rea 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 fibrin ogen on subtype conversion and subsequent change in activity was eluci dated, Our results indicate that following surface area cycling, berac tant and KL4 have different subtypes and different responses to fibrin ogen. 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, cyc ling of KL4 resulted in ultraheavy subtypes. These ultraheavy subtypes retained minimum surface tension comparable to that of native KL4 sur factant. We conclude that these two surfactant preparations have diffe rent subtype conversions when subjected to surface area cycling and in the presence of fibrinogen. These conversions result in different act ivities toward lowering surface tension. we speculate that endogenous fibrinogen will also affect these two surfactants differently in vivo and thus affect their clinical effectiveness.