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-atherogenic function. Many in vitro studies have demonstrated that HDL has the ability to remove cholesteryl ester (CE) from lipid-laden macrophages. However, the effect of alteration in chemical composition and particle diameter on the in vivo function of HDL is unknown. In the study described here, we have isolated the HDL from patients homozygous for cholesteryl ester transfer protein (CETP) deficiency and examined its function in vitro, in order to clarify the anti-atherogenic property of HDL in CETP-deficient subjects. Apolipoprotein (apo) E-free HDL(2) from the patients, separated by heparin-Sepharose column chromatography, 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 chemical composition. First, we examined the effect of HDL on CE accumulation in macrophages. After mouse peritoneal macrophages had been incubated with both acetylated low-density lipoproteins (Ac-LDL) and HDL, cellular 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 preventive 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 added 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) reduced the CE content in macrophages, while the patients' HDL(2) had no significant 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 important for its anti-atherogenic function in vivo. CETP may play a crucial role in preventing CE accumulation in HDL, thereby making HDL more active in its antiatherogenic function.