Activity of synthetic lung surfactants containing phospholipase-resistant phosphonolipids plus purified surfactant proteins or synthetic peptides

This thesis investigates the surface activity and inhibition resistance of novel synthetic lung surfactants containing C16:0 phospholipase-resistant ether-linked (DEPN-8) or sulfur-linked (SO2-lipid, S-lipid) phosphonolipids with structural analogy to dipalmitoyl phosphatidylcholine (DPPC) plus purified bovine surfactant proteins (SP)-B/SP-C or synthetic amphipathic peptides. A fourth unsaturated phosphonolipid (C16:1; UnDEPN-8) is also examined as a secondary component in selected mixtures. Experimental assessments include surface pressure-area behavior in spread monolayers and surface-excess films, stirred-subphase adsorption studies, dynamic surface activity on a pulsating bubble apparatus, and physiological activity in improving pressure-volume (P-V) mechanics in excised, lavaged rat lungs (an FDA-approved assay used in the manufacture of two current bovine-derived clinical surfactant drugs). All phosphonolipids had better adsorption and film respreading than DPPC, and were chemically resistant to phospholipase A2 (PLA2). All C16:0 phosphonolipids also had much greater surface activity than DPPC on the bubble apparatus. Synthetic lung surfactants containing DEPN-8 or SO 2-lipid plus bovine surfactant proteins (0.75% SP-13 + 0.75% SP-C or 1.5% mixed SP-B/C) had overall dynamic surface activity similar to calf lung surfactant extract (CLSE). DEPN-8 + 1.5% bovine SP exceeded CLSE in resisting biophysical inhibition by lysophosphatidylcholine (LPC) and was similar to CLSE in resisting inhibition by serum albumin. Surfactants containing DEPN-8 plus a synthetic amphipathic peptide (Mini-B, Poly (K, F), FK20, or F 4K) also had high surface activity, but less than mixtures containing purified bovine SP. DEPN-8 + 1.5% SP-B/C had equal activity to CLSE in improving P-V mechanics when instilled into surfactant-deficient rat lungs with and without serum albumin present, and greater efficacy than CLSE in improving lung mechanics in the presence of PLA2 or LPC. DEPN-8 + 1.5% Poly (K, F) was less effective in improving mechanics, at least in part because of problems related to alveolar delivery in the rat lung model used. Phospholipase-resistant synthetic lung surfactants containing DEPN-8 or sulfur-linked phosphonolipids plus bovine SP or synthetic amphipathic peptides are highly surface active, and have potential utility for future therapeutic applications in lung diseases where endogenous surfactant is deficient or dysfunctional. However, future work optimizing formulation and synthetic peptide constituents is also needed.