Stabilization of lung surfactant particles against conversion by a cycling interface.

The large active particles of pulmonary surfactant are depleted in patients with acute respiratory distress syndrome and in animal models of this disorder. We studied in vitro conversion of large to small particles, separated by differential sedimentation, to determine how factors lavaged from rabbits injured by intravenous oleic acid would affect conversion. In half-filled test tubes rotated end over end, samples from injured animals increased the recovery of large particles from 40 +/- 6% of uncycled samples for controls to 62 +/- 21%. We hypothesized that proteins in the injured samples, and perhaps also the proteinase inhibitors used previously to block conversion (N. J. Gross and R. M. Schultz. Biochim. Biophys. Acta 1044: 222-230, 1990), stabilized surfactant particles by limiting access to the cycling interface. Hemoglobin, neutrophil elastase, and alpha1-antiproteinase (alpha1-PI) oxidized to eliminate its antiproteinase activity all stabilized large particles against conversion. Hemoglobin was most effective, increasing recovery from 18 +/- 5% for controls to 86 +/- 5% with 0.4 mg/ml hemoglobin. Native alpha1-PI had no effect on conversion. Our results suggest that acceleration of normal conversion is unlikely to explain the depletion of large particles in injured lungs. They also suggest that conversion of surfactant particles separated by differential sedimentation requires no proteinase susceptible to inhibition by alpha1-PI. They provide an alternate hypothesis related to interfacial effects rather than proteinase inhibition for the previously reported effect of alpha1-PI on conversion of particles separated according to density.

Phosphatidylcholine molecular species of calf lung surfactant.

This paper reports the detailed composition of molecular species of the phosphatidylcholines (PCs) in pulmonary surfactant from calves. PC isolated by thin-layer chromatography (TLC) was converted to benzoylated diradyl glyceride derivatives, which were separated by TLC according to linkage group. Quantification of linkage groups by analysis of total fatty acid content demonstrated that surfactant PC contained 97.2% diacyl, 2.4% alkyl-acyl, and 0.4% alkenyl-acyl compounds. The diacyl and alkyl-acyl diglyceride derivatives were separated into individual molecular species by high-performance liquid chromatography. Four major species constituted 87% of the diacyl compounds. Dipalmitoyl phosphatidylcholine (DPPC) was the most abundant constituent, contributing 41% of the total PC. A second disaturated species, palmitoyl-myristoyl phosphatidylcholine (PMPC), also contributed an additional 12% of total PC. At least 65% of PMPC occurred as the 1-palmitoyl-2-myristoyl/isomer, which has a lower melting point than the 1-myristoyl-2-palmitoyl compound. These results show that most of pulmonary surfactant PC is a relatively simple mixture, that numerous minor compounds are present in small but possibly important amounts, and that in surfactant from calves, the widely reported estimate that DPPC constitutes 60% of surfactant PC is too large by 50%.