Impact of LDL apheresis on atheroprotective reverse cholesterol transport pathway in familial hypercholesterolemia

Abstract

In familial hypercholesterolemia (FH), low HDL cholesterol (HDL-C) levels are associated with functional alterations of HDL particles that reduce their capacity to mediate the reverse cholesterol transport (RCT) pathway. The objective of this study was to evaluate the consequences of LDL apheresis on the efficacy of the RCT pathway in FH patients. LDL apheresis markedly reduced abnormal accelerated cholesteryl ester transfer protein (CETP)-mediated cholesteryl ester (CE) transfer from HDL to LDL, thus reducing their CE content. Equally, we observed a major decrease (-53%; P < 0.0001) in pre-β1-HDL levels. The capacity of whole plasma to mediate free cholesterol efflux from human macrophages was reduced (-15%; P < 0.02) following LDL apheresis. Such reduction resulted from a marked decrease in the ABCA1-dependent efflux (-71%; P < 0.0001) in the scavenger receptor class B type I-dependent efflux (-21%; P < 0.0001) and in the ABCG1-dependent pathway (-15%; P < 0.04). However, HDL particles isolated from FH patients before and after LDL apheresis displayed a similar capacity to mediate cellular free cholesterol efflux or to deliver CE to hepatic cells. We demonstrate that rapid removal of circulating lipoprotein particles by LDL apheresis transitorily reduces RCT. However, LDL apheresis is without impact on the intrinsic ability of HDL particles to promote either cellular free cholesterol efflux from macrophages or to deliver CE to hepatic cells.

Fig. 1.

Individual plasma levels of pre-β1-HDL (A), plasma endogenous CETP-dependent CE transfer from HDL to apoB-containing lipoproteins (B), and plasma CETP concentration (C) determined in 18 FH patients before (open circles) and after (closed circles) LDL apheresis.

Fig. 2.

Bar graph showing plasma efflux capacities determined in 18 FH patients before (open bar) and after (closed bar) LDL apheresis. Fractional cholesterol efflux was determined following 4 h of incubation in the presence of 40-fold-diluted plasma using various cell lines. A: Rat hepatoma Fu5AH cells expressing high levels of SR-BI or cholesterol-loaded human THP-1 macrophages. B: CHO-K1 and CHO-K1 overexpressing the human ABCG1 gene. The ABCG1-dependent efflux corresponded to the difference between efflux to hABCG1-transfected CHO-K1 cells and efflux to wild-type CHO-K1 cells. C: Mouse macrophage Raw264.7 cells incubated in the absence or presence of 8Br-cAMP to induce ABCA1 gene expression. The ABCA1-dependent efflux was calculated as the difference between fractional cholesterol efflux to cells in the presence or absence of 8Br-cAMP. Values are mean ± SE. **P < 0.0001 and *P < 0.05 versus before LDL apheresis.

Fig. 3.

Bar graph showing the capacity of HDL2 or HDL3 subfractions isolated from 18 FH patients before (open bar) and after (closed bar) LDL apheresis to mediate free cholesterol efflux through the SR-BI (A) and ABCG1 (B) pathways or from cholesterol-loaded THP-1 macrophages (C). Fractional free cholesterol efflux from cells was determined after 4 h incubation in the presence of isolated HDL particles: 10 µg phospholipid/ml for Fu5AH (SR-BI-dependent efflux); 5 µg phospholipid/ml for CHO-K1 and CHO-K1 overexpressing the human ABCG1 gene (ABCG1-dependent efflux); 15 µg phospholipid/ml for cholesterol-loaded THP-1 macrophages. Values are mean ± SE.

Fig. 4.

Schematic representation of the impact of LDL apheresis on the RCT pathway in FH patients. Dashed arrows indicate steps of the RCT pathway that are known from the literature to be reduced but that have not been directly assessed in the present study.