Abstract 581: The Ability Of Apolipoprotein A-I Mimetic Peptides To Improve HDL Anti-inflammatory Properties Is Due To Their Remarkable Binding Affinities For Oxidized Lipids.
D-4, an orally effective, apoA-I mimetic peptide, reduces the inflammatory properties of HDL and decreases lesions in atherosclerosis models. Yet, because its maximal plasma concentrations reach ~300 ng/mL after oral administration in mice, and plasma contains ~ 1 mg/mL of apoA-I, it has been difficult to understand how D-4F exerts these effects, given its low plasma concentrations. We propose the following mechanistic explanation. The final step in forming mildly oxidized LDL is a nonenzymatic oxidation of LDL phospholipids (PL). This occurs when seeding molecules in LDL, such as 13-hydroperoxyoctadecadienoic acid (13(S)-HPODE) and 15-hydroperoxyeicosatetraenoic acid (15(S)-HPETE), reach a critical threshold concentration that causes nonenzymatic oxidation of a major LDL PL, 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphatidylcholine (PAPC) and generates three oxidized PLs 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphatidylcholine (POVPC), 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphatidylcholine (PGPC), and 1-palmitoyl-2-(5,6-epoxyisoprostanoyl)-sn-glycero-3-phosphatidylcholine (PEIPC) that mediate inflammation. We compared the binding affinity (KD) of D-4F and purified human apoA-I to lipids by surface plasmon resonance measurements (Biacore 3000). D-4F bound PGPC with an affinity 2 orders of magnitude greater (KD, 7.3 x 10 – 8 M) than that of apoA-I (KD, 1.0 x 10 – 6 M). D-4F bound POVPC and PEIPC with affinities 4 and 6 orders of magnitude greater than those of apoA-I (1.0 x 10–9 M & 2.3 x 10 –11 M vs. 1.0 x 10 –5 M & 2.1 x 10 –5 M respectively). Moreover, the affinities of D-4F for 13(S)-HPODE and 15(S)-HPETE were 6 and 7 orders of magnitude greater than those of apoA-I (KD, 4.8 x 10 – 8 M & 9.1 x 10 –9 M vs. 1.3 x 10 –2 M & 1.7 x 10 –2 M, respectively). D-4F and its L-amino acid enantiomer, L-4F, had almost identical binding affinities for oxidized lipids. Non-oxidized fatty acids (arachidonic, linoleic, palmitic) bound with similar KDs to D-4F, L-4F and apoA-I. Accordingly, we suggest that the in vivo anti-inflammatory and anti-atherogenic properties of D-4F result from its ability to bind oxidized lipids selectively and with high affinity, thus improving the anti-inflammatory properties of HDL.