A Combination of Short and Simple Surfactant Protein B and C Analogues as a New Synthetic Surfactant: In Vitro and Animal Experiments

Purpose: Pulmonary surfactants for preterm infants contain mostly animal-derived surfactant proteins (SPs), which are essential for lowering surface tension. We prepared artificial pulmonary surfactants using synthetic human SP analogs and performed in vitro and in vivo experiments. Materials and Methods: We synthesized peptide analogues that resemble human SP-B (RMLPQLVCRLVLRCSMD) and SP-C (CPVHLKRLLLLLLLLLLLLLLLL). Dipalmitoylphosphatidylcholine (DPPC), phosphatidylglycerol (PG), and palmitic acid (PA) were added and mixed in lyophilized to render powdered surfactant. Synsurf-1 was composed of DPPC: PG: PA: SP-B (75: 25: 10: 3, w/w); Synsurf-2 was composed of DPPC: PG: PA: SP-C (75: 25: 10: 3, w/w); and Synsurf-3 was composed of DPPC: PG: PA: SP-B: SP-C (75: 25: 10: 3: 3, w/w). We performed in vitro study to compare the physical characteristics using pulsating bubble surfactometer and modified Wilhelmy balance test. Surface spreading and adsorption test of the surfactant preparations were measured. In vivo test was performed using term and preterm rabbit pups. Pressure-volume curves were generated during the deflation phase. Histologic findings were examined. Results: Pulsating bubble surfactometer readings revealed following minimum and maximum surface tension (mN/m) at 5 minutes: Surfacten r (5.5 +/- 0.4, 32.8 +/- 1.6), Synsurf-1 (16.7 +/- 0.6, 28.7 +/- 1.5), Synsurf-2 (7.9 +/- 1.0, 33.1 +/- 1.6), and Synsurf-3 (7.1 +/- 0.8, 34.5 +/- 1.0). Surface spreading rates were as follows: Surfacten r (27 mN/m), Synsurf-1 (43 mN/m), Synsurf-2 (27 mN/m), and Synsurf-3 (27 mN/m). Surface adsorption rate results were as follows: Surfacten r (28 mN/m), Synsurf-1 (35 mN/m), Synsurf-2 (29 mN/m), and Synsurf-3 (27 mN/m). The deflation curves were best for Synsurf-3; those for Synsurf-2 were better than those for Surfacten r. Synsurf- 1 was the worst surfactant preparation. Microscopic examination showed the largest aerated area of the alveoli in the Synsurf-3 group, followed by Synsurf-1 and Surfacten r; Synsurf-2 was the smallest. Conclusion: Synsurf-3 containing both SP-B and SP-C synthetic analogs showed comparable and better efficacy than commercially used Surfacten r in lowering surface tension, pressure-volume curves, and tissue aerated area of the alveoli.