Biophysical activity of an artificial surfactant containing an analogue of surfactant protein (SP)-C and native SP-B

摘要

pNatural surfactant preparations containing phospholipids and the hydrophobic surfactant proteins B and C (SP-B and SP-C) are effective in the treatment of respiratory distress syndrome in premature infants. The limited supply, and the risk of infectious agents and immunological reactions have promoted the evaluation of synthetic peptides in surfactant preparations. However, the folding of synthetic SP-C into an α-helix is inefficient and α-helical SP-C analogues with Val → Leu substitutions form oligomers. In order to circumvent these problems we have synthesized an SP-C analogue, named SP-C(LKS), which differs from SP-C mainly by the exchange of most of the Val residues in positions 16–28 with Leu residues to promote an α-helical conformation, and by the introduction of Lys residues at positions 17, 22 and 27 in order to locate positive charges around the helical circumference and thereby avoid self polymerization. CD spectroscopy showed a spectrum typical for α-helical peptides and SDS/PAGE disclosed a single band. The biophysical activity of artificial surfactant preparations containing SP-C(LKS) and phospholipids, with and without native SP-B, was measured using a Wilhelmy balance and a pulsating bubble surfactometer. SP-C(LKS) (3%, w/w) in a mixture of 1,2-dipalmitoyl-isn/i-glycero-3-phosphocholine (DPPC)/phosphatidylglycerol/palmitic acid (68:22:9, by wt.) suspended in 150 mM NaCl, showed rapid spreading at the air-liquid interface and produced a surface tension of & 1 mN/m at minimum bubble size (γsubmin/sub) and 42 mN/m at maximum bubble size (γsubmax/sub) in the pulsating bubble surfactometer. The addition of 2% (w/w) SP-B to the preparation reduced the maximum surface tension to 33–35 mN/m, i.e. both γsubmin/sub and γsubmax/sub values were similar to those of natural surfactant preparations. Optimal iin iv/iitro/i characteristics were also obtained from a preparation containing SP-C(LKS), SP-B, DPPC and phosphatidylglycerol, i.e. when palmitic acid was omitted from the lipid mixture. SP-B containing surfactant preparations made up in Hepes buffer at pH 6.9, instead of in 150 mM NaCl, had similar biophysical activity provided that palmitic acid was omitted, but decreased activity in the presence of palmitic acid./p