Improvement of pulmonary surfactant activity by introducing D-amino acids into highly hydrophobic amphiphilic α-peptide Hel 13-5

AbstractThe high costs of artificial pulmonary surfactants, ranging in hundreds per kilogram of body weight, used for treating the respiratory distress syndrome (RDS) premature babies have limited their applications. We have extensively studied soy lecithins and higher alcohols as lipid alternatives to expensive phospholipids such as DPPC and PG. As a substitute for the proteins, we have synthesized the peptide Hel 13-5D3 by introducing D-amino acids into a highly lipid-soluble, basic amphiphilic peptide, Hel 13-5, composed of 18 amino acid residues. Analysis of the surfactant activities of lipid-amphiphilic artificial peptide mixtures using lung-irrigated rat models revealed that a mixture (Murosurf SLPD3) of dehydrogenated soy lecithin, fractionated soy lecithin, palmitic acid (PA), and peptide Hel 13-5D3 (40:40:17.5:2.5, by weight) superior pulmonary surfactant activity than a commercially available pulmonary surfactant (beractant, Surfacten®). Experiments using ovalbumin-sensitized model animals revealed that the lipid-amphiphilic artificial peptide mixtures provided significant control over an increase in the pulmonary resistance induced by premature allergy reaction and reduced the number of acidocytes and neutrophils in lung-irrigated solution. The newly developed low-cost pulmonary surfactant system may be used for treatment of a wide variety of respiratory diseases

Roles of peptide–peptide charge interaction and lipid phase separation in helix–helix association in lipid bilayer

AbstractThe roles of peptide–peptide charged interaction and lipid phase separation in helix–helix association in lipid bilayers were investigated using a model peptide, P24, as a transmembrane α-helical peptide, and its four analogues. Fluorescence amino acids, tryptophan (P24W) and pyrenylalanine (P24Pya), were introduced into the sequence of P24, respectively. Association of these peptides permits the resonance excitation energy transfer between tryptophan in P24W and pyrenylalanine in P24Pya or excimer formation between P24Pya themselves. To evaluate the effect of charged interaction on the association between α-helical transmembrane segments in membrane proteins, charged amino acids, glutamic acid (P24EW) and lysine (P24KPya), were introduced into P24W and P24Pya, respectively. Energy transfer experiments indicated that the charged interaction between the positive charge of lysine residue in P24KPya and the negative charge of glutamic acid residue in P24EW did not affect the aggregation of transmembrane peptides in lipid membranes. As the content ratio of sphingomyelin (SM) and cholesterol (Ch) was increased in the egg phosphatidylcholine (PC), the stronger excimer fluorescence spectra of P24Pya were observed, indicating that the co-existence of SM and Ch in PC liposomes, that is, the raft of SM and Ch, promotes the aggregation of the α-helical transmembrane peptides in lipid bilayers. Since the increase in the contents of SM and Ch leads to the decrease in the content of liquid crystalline-order phase, the moving area of transmembrane peptides might be limited in the liposomes, resulting in easy formation of the excimer in the presence of the lipid-raft