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Journal of Lipid Research, Vol. 44, 1364-1372, July 2003
Copyright © 2003 by American Society for Biochemistry and Molecular Biology

The surface cholesteryl ester content of donor and acceptor particles regulates CETP

Richard E. Morton¹ and Diane J. Greene

Department of Cell Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH

¹ To whom correspondence should be addressed. e-mail: mortonr{at}ccf.org

Cholesteryl ester transfer protein (CETP) activity is regulated, in part, by lipoprotein composition. We previously demonstrated that CETP activity follows saturation kinetics as cholesteryl ester (CE) levels in the phospholipid surface of donor particles are increased. We propose here that the plateau of CETP activity occurs because the surface concentration of CE in the acceptor becomes rate limiting. This hypothesis was tested in CETP assays between synthetic liposomes whose CE content was varied independently. As donor CE increased, CETP activity followed saturable kinetics, but the slope of the first-order portion of the curve and the maximum achievable CE transfer rate were linearly related to the acceptor's surface CE concentration. These findings, plus studies with free cholesterol-modified LDL, strongly suggest that CE-rich donor liposomes can measure the CETP-accessible CE in acceptor lipoproteins. CETP activity from CE-rich liposomes to multiple control LDLs ranged 1.8-fold despite equivalent CETP binding capacity, suggesting that LDLs vary widely in their capacity to present CE to CETP. Thus, CETP activity depends on the surface availability of substrate lipids in the donor and acceptor.

Donor liposomes with high CE content can be used to assess how subtle changes in composition alter the substrate potential of plasma lipoproteins.

Abbreviations: CE, cholesteryl ester; CETP, cholesteryl ester transfer protein; FC, free cholesterol; PC, phosphatidylcholine; PL, phospholipid; TG, triglyceride

Supplementary key words liposomes • low density lipoprotein • free cholesterol • kinetics • cholesteryl ester transfer protein binding

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