SYNTHETIC AMPHIPATHIC HELICAL PEPTIDES THAT MIMIC APOLIPOPROTEIN-A-I IN CLEARING CELLULAR CHOLESTEROL

Clearance of excess cholesterol from cells by HDL is facilitated by th e interaction of HDL apolipoproteins with cell-surface binding sites o r receptors, a process that may be important in preventing atheroscler osis. In this study, synthetic peptides containing 18-mer amphipathic helices of the class found in HDL apolipoproteins (class A) were teste d for their abilities to remove cholesterol and phospholipid from cult ured sterol-laden fibroblasts and macrophages and to interact with cel l-surface HDL binding sites. Lipid-fret peptides containing two identi cal tandem repeats of class A amphipathic helices promoted cholesterol and phospholipid efflux from cells and depleted cellular cholesterol accessible for esterification by acyl CoA/cholesterol acyltransferase, similar to what was observed for purified apolipoprotein A-I. Peptide -mediated removal of plasma membrane cholesterol and depletion of acyl CoA/cholesterol acyltransferase-accessible cholesterol appeared to oc cur by separate mechanisms, as the latter process was less dependent o n extracellular phospholipid. The dimeric amphipathic helical peptides also competed for high-affinity HDL binding sites on cholesterol-load ed fibroblasts and displayed saturable high-affinity binding to the ce ll surface. In contrast, peptides with a single helix had little or no ability to remove cellular cholesterol and phospholipid, or to intera ct with HDL binding sites, suggesting that cooperativity between two o r more helical repeats is required for these activities. Thus, synthet ic peptides comprising dimers of a structural moth common to exchangea ble apolipoproteins can mimic apolipoprotein A-I in both binding to pu tative cell-surface receptors and clearing cholesterol from cells.