Effects of increasing hydrophobicity on the physical-chemical and biological properties of a class A amphipathic helical peptide

We have recently shown that a class A amphipathic peptide 5F with increased amphipathicity protected mice from diet-induced atherosclerosis (Garber et al. J. Lipid Res. 2001. -12: 545-552), We have now examined the effects of increasing the hydrophobicity of a series of homologous class A amphipathi c peptides, including 5F, on physical and functional properties related to atherosclerosis inhibition by systematically replacing existing nonpolar am ino acids with phenylalanine. The peptides, based on the sequence Ac-D-W-LK -A-F-Y-D-K-V-A-E-L-K-E-A-F-NH2 (Ac-F(14)18A-NH2 or 2F) were: 3F(3)(Ac-F(3)1 8A-NH2), 3F(14)(Ac-F(14)18A-NH2), 4F(Ac-F(3,14)18A-NH2), 5F(Ac-F(11,14,17)1 8A-NH2), 6F(Ac-F(10,11,14,17)18A-NH2), and 7F(AC-F(3,10,11,14,17)18A-NH2). Measurements of aqueous solubility, HPLC retention time, exclusion pressure for penetration into an egg phosphatidyicholine (EPC) monolayer, and rates of EPC solubilization revealed an abrupt increase in the hydrophobicity be tween peptides 4F and 5F; this was accompanied by increased ability to asso ciate with phospholipids. The peptides 6F and 7F were less effective, indic ating a limit to increased hydrophobicity for promoting lipid interaction i n these peptides, Despite this marked increase in lipid affinity, these pep tides were less effective than apoA-I in activating the plasma enzyme, leci thin:cholesterol acyltransferase, with 5F activating LCAT the best (80% of apoA-I). Peptides 4F, 5F, and 6F were equally potent in inhibiting LDL-indu ced monocyte chemotactic activity.jlr These studies suggest that an appropr iate balance between peptide-peptide and peptide-lipid interactions is requ ired for optimal biological activity of amphipathic peptides, These studies provide a rationale for the design of small apoA-I-mimetics with increased potency for atherosclerosis inhibition.