LARGE AND CHOLESTERYL ESTER-RICH HIGH-DENSITY-LIPOPROTEINS IN CHOLESTERYL ESTER TRANSFER PROTEIN (CETP) DEFICIENCY CAN NOT PROTECT MACROPHAGES FROM CHOLESTEROL ACCUMULATION INDUCED BY ACETYLATED LOW-DENSITY LIPOPROTEINS

High-density lipoprotein (HDL) has been speculated to have an anti-ath erogenic function. Many in vitro studies have demonstrated that HDL ha s the ability to remove cholesteryl ester (CE) from lipid-laden macrop hages. However, the effect of alteration in chemical composition and p article diameter on the in vivo function of HDL is unknown. In the stu dy described here, we have isolated the HDL from patients homozygous f or cholesteryl ester transfer protein (CETP) deficiency and examined i ts function in vitro, in order to clarify the anti-atherogenic propert y of HDL in CETP-deficient subjects. Apolipoprotein (apo) E-free HDL(2 ) from the patients, separated by heparin-Sepharose column chromatogra phy, was rich in CE, poor in triglycerides (TG), and enlarged in size on 4-30% nondenaturing polyacrylamide gradient gel electrophoresis. In contrast, HDL(3) from the patients was normal in size and in its chem ical composition. First, we examined the effect of HDL on CE accumulat ion in macrophages. After mouse peritoneal macrophages had been incuba ted with both acetylated low-density lipoproteins (Ac-LDL) and HDL, ce llular CE content was determined by an enzymatic, fluorometric method. Ac-LDL alone induced a 9-fold accumulation of CE. The addition of apo E-free HDL(2) and HDL(3) from controls and patients' HDL(3) prevented CE accumulation in macrophages, while patients' HDL(2) had no prevent ive effect. We next investigated the in vitro ability of HDL to remove cellular CE from lipid-laden macrophages after incubation with Ac-LDL . After loading of macrophages with cholesterol by Ac-LDL, HDL was add ed to the culture medium and the cellular CE content was measured. The apo E-free HDL(2) and HDL(3) from controls and patients' HDL(3) reduc ed the CE content in macrophages, while the patients' HDL(2) had no si gnificant effect. These results suggest that the large and CE-rich HDL (2) from CETP-deficient patients is functionally abnormal in vitro and that particle diameter and chemical composition of HDL may be importa nt for its anti-atherogenic function in vivo. CETP may play a crucial role in preventing CE accumulation in HDL, thereby making HDL more act ive in its antiatherogenic function.