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. 42: 545-552). We have now examined the effects of increasing the hydrophobicity of a series of homologous class A amphipathic
peptides, including 5F, on physical and functional properties related to
atherosclerosis inhibition by systematically replacing existing nonpolar
amino acids with
phenylalanine. The
peptides, based on the sequence Ac-D-W-L-K-A-F-Y-D-K-V-A-E-K-L-K-E-A-F-NH(2) (Ac-18A-NH(2) or 2F) were: 3F(3)(Ac-F(3)18A-NH(2)), 3F(14)(Ac-F(14)18A-NH(2)), 4F(Ac-F(3,14)18A-NH(2)), 5F(Ac-F(11,14,17) 18A-NH(2)), 6F(Ac-F(10,11,14,17)18A-NH(2)), and 7F(Ac-F(3,10,11,14,17) 18A-NH(2)). Measurements of aqueous solubility, HPLC retention time, exclusion pressure for penetration into an egg
phosphatidylcholine (
EPC) monolayer, and rates of
EPC solubilization revealed an abrupt increase in the hydrophobicity between
peptides 4F and 5F; this was accompanied by increased ability to associate with
phospholipids. The
peptides 6F and 7F were less effective, indicating a limit to increased hydrophobicity for promoting
lipid interaction in these
peptides. Despite this marked increase in
lipid affinity, these
peptides were less effective than
apoA-I in activating the plasma
enzyme,
lecithin:cholesterol acyltransferase, with 5F activating LCAT the best (80% of
apoA-I).
Peptides 4F, 5F, and 6F were equally potent in inhibiting
LDL-induced monocyte chemotactic activity. These studies suggest that an appropriate balance between
peptide-
peptide and
peptide-
lipid interactions is required 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.