High density lipoprotein (HDL) particles from end-stage renal disease patients are defective in promoting reverse cholesterol transport

Abstract

Atherosclerotic cardiovascular disease (CVD) represents the largest cause of mortality in end-stage renal disease (ESRD). CVD in ESRD is not explained by classical CVD risk factors such as HDL cholesterol mass levels making functional alterations of lipoproteins conceivable. HDL functions in atheroprotection by promoting reverse cholesterol transport (RCT), comprising cholesterol efflux from macrophage foam cells, uptake into hepatocytes and final excretion into the feces. ESRD-HDL (n = 15) were compared to healthy control HDL (n = 15) for their capacity to promote in vitro (i) cholesterol efflux from THP-1 macrophage foam cells and (ii) SR-BI-mediated selective uptake into ldla[SR-BI] cells as well as (iii) in vivo RCT. Compared with HDL from controls, ESRD-HDL displayed a significant reduction in mediating cholesterol efflux (p < 0.001) and SR-BI-mediated selective uptake (p < 0.01), two key steps in RCT. Consistently, also the in vivo capacity of ESRD-HDL to promote RCT when infused into wild-type mice was significantly impaired (p < 0.01). In vitro oxidation of HDL from healthy controls with hypochloric acid was able to fully mimic the impaired biological activities of ESRD-HDL. In conclusion, we demonstrate that HDL from ESRD patients is dysfunctional in key steps as well as overall RCT, likely due to oxidative modification.

Figure 1. ESRD-HDL displays defective cholesterol uptake as well as cholesterol delivery properties.

(a) Cholesterol efflux from primary mouse peritoneal macrophages towards HDL from ESRD-patients (n = 15) compared with healthy control subjects (n = 15). (b) Cellular SR-BI mediated selective cholesterol uptake from ESRD-HDL or control HDL (each n = 15) into ldla cells stably transfected with SR-BI. Data are presented as means ± SEM. ***p < 0.001.

Figure 2. HDL from ESRD patients are defective in medicating RCT in vivo.

Mice injected with macrophage foam cells loaded with radioactively labelled ³H-cholesterol were infused with either PBS, control HDL or ESRD-HDL as detailed in methods. (a) Mass changes in plasma total cholesterol, (b) mass changes in plasma free cholesterol, (c) appearance of the ³H-cholesterol tracer in plasma, (d) mass fecal neutral sterol excretion over 48 h, (e) mass fecal bile acid excretion over 48 h, (f) fecal ³H-cholesterol tracer excretion within neutral sterols, (g) fecal ³H-cholesterol tracer excretion within bile acids. Data are presented as means ± SEM, n = 6–8 mice/group. *p < 0.05, **p < 0.01.

Figure 3. Oxidation of HDL in vitro results in impaired cholesterol uptake as well as delivery properties.

(a) Cholesterol efflux from primary mouse peritoneal macrophages towards native, control HDL compared with control HDL following HOCl incubation (n = 10). (b) Cellular SR-BI mediated selective cholesterol uptake form control HDL or HOCl-modified HDL (n = 10) into ldla cells stably transfected with SR-BI. Data are presented as means ± SEM. **p < 0.01.

Figure 4. HDL oxidized in vitro is defective in mediating in vivo RCT.

Mice injected with macrophage foam cells loaded with ³H-cholesterol were infused with either control HDL or HOCl-modified HDL as detailed in methods. (a) HOCl-modified HDL had a significantly decreased capacity to mobilize macrophage-derived ³H-cholesterol to the plasma compartment compared with native HDL at the 4 h time point (p < 0.05). (b) Fecal ³H-cholesterol tracer recovery in the neutral sterol fraction, (c) Fecal ³H-cholesterol tracer recovery in the bile acid fraction. Data are presented as means ± SEM, n = 8 mice/group. *p < 0.05, **p < 0.01.