Abstract 1949: Mechanism for Atheroprotection in Mice by 5A, a bi-helical ApoA-I Mimetic Peptide
5A, a peptide specific for promoting lipid efflux by the ABCA1 transporter, has been shown to significantly reduce atherosclerosis in apoE-K/O mice. We investigate the mechanism in this study. Incubation of 5A-POPC (1:9 molar ratio; 4mg/mL) with human-normolipedemic whole blood for 45 min resulted in an 11% increase in total plasma cholesterol and a corresponding decrease in red blood cell cholesterol content. HDL-C increased by 173% (p<0.01) and was larger in size and enriched in phospholipids, whereas LDL-C was reduced by 30% (p<0.05) and larger in size. IV infusion of 5A-POPC in C57BL6 mice resulted in a dose dependent increase in HDL-C that peaked at 1–3h and decayed to baseline by 6–24h. The HDL-C response saturated at 120 mg/kg of 5A-POPC, which resulted in a 2.4-fold increase. In ABCA1-K/O mice, a similar HDL-C dose response curve was observed for 5A-POPC but a marked >90% reduction in the rise of HDL-C was observed in SR-BI-K/O mice. Hepatic cholesterol content was decreased by 17% (p<0.05) in C57BL6 mice, 45 min after treatment (120 mg/kg), but no significant changes were observed in most other tissues. 24h after the last dose, hepatic cholesterol levels were increased by 21% (p<0.01) after chronic administration of 5A-POPC. Global cholesterol efflux from peripheral tissues into plasma, as determined by steady state isotope dilution, was found to increase by 78% to 30±1 mg/kg/h in rats after 5A-POPC treatment. 5A-POPC also increased the transfer of 3H-cholesterol from peritoneal ex vivo labeled macrophages to the stool, and ten 5A-POPC treatments over 14 days lowered the cholesteryl ester content of peritoneal macrophages by 64% (p<0.02) in cholesterol-fed apoE-K/O mice. 5A-POPC or serum from 5A-POPC treated mice removed cholesterol from peritoneal macrophages from wild type, ABCG1-K/O and SR-BI-K/O mice to a similar degree but was approximately 35% less effective from ABCA1-K/O macrophages.
In summary, 5A-POPC markedly increases HDL-C, but the majority of the initial increase appears to be from the liver and red blood cells and occurs mainly by a SR-BI-dependent pathway. 5A-POPC also increases overall cholesterol efflux from peripheral tissues, and in particular from macrophages but is independent of SR-BI.