High-capacity selective uptake of cholesteryl ester from native LDL during macrophage foam cell formation

Macrophage foam cells are a defining pathologic feature of atherosclerotic lesions. Recent studies have demonstrated that at high concentrations associated with hypercholesterolemia, native LDL induces macrophage lipid accumulation. LDL particles are taken up by macrophages as part of bulk fluid pinocytosis. However, the uptake and metabolism of cholesterol from native LDL during foam cell formation has not been clearly defined. Previous reports have suggested that selective cholesteryl ester (CE) uptake might contribute to cholesterol uptake from LDL independently of particle endocytosis. In this study we demonstrate that the majority of macrophage LDL-derived cholesterol is acquired by selective CE uptake in excess of LDL pinocytosis and degradation. Macrophage selective CE uptake does not saturate at high LDL concentrations and is not down-regulated during cholesterol accumulation. In contrast to CE uptake, macrophages exhibit little selective uptake of free cholesterol (FC) from LDL. Following selective uptake from LDL, CE is rapidly hydrolyzed by a novel chloroquine-sensitive pathway. FC released from LDL-derived CE hydrolysis is largely effluxed from cells but also is subject to ACAT-mediated reesterification. These results indicate that selective CE uptake plays a major role in macrophage metabolism of LDL.     

Aggregated LDL and lipid dispersions induce lysosomal cholesteryl ester accumulation in macrophage foam cells

Macrophage foam cells in atherosclerotic lesions accumulate substantial cholesterol stores within large, swollen lysosomes. Previous studies with mildly oxidized low density lipoprotein (OxLDL)-treated THP-1 macrophages suggest an initial buildup of free cholesterol (FC), followed by an inhibition of lysosomal cholesteryl ester (CE) hydrolysis and a subsequent lysosomal accumulation of unhydrolyzed lipoprotein CE. We examined whether other potential sources of cholesterol found within atherosclerotic lesions could also induce similar lysosomal accumulation. Biochemical analysis combined with microscopic analysis showed that treatment of THP-1 macrophages with aggregated low density lipoprotein (AggLDL) or CE-rich lipid dispersions (DISP) produced a similar lysosomal accumulation of both FC and CE. Co-treatment with an ACAT inhibitor, CP113,818, confirmed that the CE accumulation was primarily the result of the inhibition of lysosomal CE hydrolysis. The rate of unhydrolyzed CE buildup was more rapid with DISP than with AggLDL. However, with both treatments, FC appeared to accumulate in lysosomes before the inhibition in hydrolysis and CE accumulation, a sequence shared with mildly OxLDL. Thus, lysosomal accumulation of FC and CE can be attributable to more general mechanisms than just the inhibition of hydrolysis by oxidized lipids.     

A redox-sensitive pathway mediates oxidized LDL-induced downregulation of insulin-like growth factor-1 receptor

Oxidized low density lipoprotein (OxLDL) has multiple proatherogenic effects, including induction of apoptosis. We have recently shown that OxLDL markedly downregulates insulin-like growth factor-1 receptor (IGF-1R) in human aortic smooth muscle cells, and that IGF-1R overexpression blocks OxLDL-induced apoptosis. We hypothesized that specific OxLDL-triggered signaling events led to IGF-1R downregulation and apoptosis. We examined OxLDL signaling pathways and found that neither IGF-1R downregulation nor the proapoptotic effect was blocked by inhibition of OxLDL-triggered extracellular signal-regulated kinase, p38 mitogen-activated protein kinase (MAPK), or peroxisome proliferator-activated receptor gamma (PPARgamma) signaling pathways, as assessed using specific inhibitors. However, antioxidants, polyethylene glycol catalase, superoxide dismutase, and Trolox completely blocked OxLDL downregulation of IGF-1R and OxLDL-induced apoptosis. Nordihydroguaiaretic acid, AA-861, and baicalein, which are lipoxygenase inhibitors and also have antioxidant activity, blocked IGF-1R downregulation and apoptosis as well as reactive oxygen species (ROS) production. These results suggest that OxLDL enhances ROS production possibly through lipoxygenase activity, leading to IGF-1R downregulation and apoptosis. Furthermore, anti-CD36 scavenger receptor antibody markedly inhibited OxLDL-induced IGF-1R downregulation and apoptosis as well as ROS production. In conclusion, our data demonstrate that OxLDL downregulates IGF-1R via redox-sensitive pathways that are distinct from OxLDL signaling through MAPK- and PPARgamma-involved pathways but may involve a CD36-dependent mechanism.     

Changes in lipoprotein(a), oxidized phospholipids, and LDL subclasses with a low-fat high-carbohydrate diet

Low-fat diets have been shown to increase plasma concentrations of lipoprotein(a) [Lp(a)], a preferential lipoprotein carrier of oxidized phospholipids (OxPLs) in plasma, as well as small dense LDL particles. We sought to determine whether increases in plasma Lp(a) induced by a low-fat high-carbohydrate (LFHC) diet are related to changes in OxPL and LDL subclasses. We studied 63 healthy subjects after 4 weeks of consuming, in random order, a high-fat low-carbohydrate (HFLC) diet and a LFHC diet. Plasma concentrations of Lp(a) (P < 0.01), OxPL/apolipoprotein (apo)B (P < 0.005), and OxPL-apo(a) (P < 0.05) were significantly higher on the LFHC diet compared with the HFLC diet whereas LDL peak particle size was significantly smaller (P < 0.0001). Diet-induced changes in Lp(a) were strongly correlated with changes in OxPL/apoB (P < 0.0001). The increases in plasma Lp(a) levels after the LFHC diet were also correlated with decreases in medium LDL particles (P < 0.01) and increases in very small LDL particles (P < 0.05). These results demonstrate that induction of increased levels of Lp(a) by an LFHC diet is associated with increases in OxPLs and with changes in LDL subclass distribution that may reflect altered metabolism of Lp(a) particles.     

ACAT2 contributes cholesteryl esters to newly secreted VLDL, whereas LCAT adds cholesteryl ester to LDL in mice

The relative contributions of ACAT2 and LCAT to the cholesteryl ester (CE) content of VLDL and LDL were measured. ACAT2 deficiency led to a significant decrease in the percentage of CE (37.2 +/- 2.1% vs. 3.9 +/- 0.8%) in plasma VLDL, with a concomitant increase in the percentage of triglyceride (33.0 +/- 3.2% vs. 66.7 +/- 2.5%). Interestingly, the absence of ACAT2 had no apparent effect on the percentage CE in LDL, whereas LCAT deficiency significantly decreased the CE percentage (38.6 +/- 4.0% vs. 54.6 +/- 1.9%) and significantly increased the phospholipid percentage (11.2 +/- 0.9% vs. 19.3 +/- 0.1%) of LDL. When both LCAT and ACAT2 were deficient, VLDL composition was similar to VLDL of the ACAT2-deficient mouse, whereas LDL was depleted in core lipids and enriched in surface lipids, appearing discoidal when observed by electron microscopy. We conclude that ACAT2 is important in the synthesis of VLDL CE, whereas LCAT is important in remodeling VLDL to LDL. Liver perfusions were performed, and perfusate apolipoprotein B accumulation rates in ACAT2-deficient mice were not significantly different from those of controls; perfusate VLDL CE decreased from 8.0 +/- 0.8% in controls to 0 +/- 0.7% in ACAT2-deficient mice. In conclusion, our data establish that ACAT2 provides core CE of newly secreted VLDL, whereas LCAT adds CE during LDL particle formation.     

Inability of HDL from abdominally obese subjects to counteract the inhibitory effect of oxidized LDL on vasorelaxation

Abdominal obesity is associated with a decreased plasma concentration of HDL cholesterol and with qualitative modifications of HDL, such as triglyceride enrichment. Our aim was to determine, in isolated aorta rings, whether HDL from obese subjects can counteract the inhibitory effect of oxidized low density lipoprotein (OxLDL) on endothelium-dependent vasodilation as efficiently as HDL from normolipidemic, lean subjects. Plasma triglycerides were 74% higher (P < 0.005) in obese subjects compared with controls, and apolipoprotein A-I (apoA-I) and HDL cholesterol concentrations were 12% and 17% lower (P < 0.05), respectively. HDL from control subjects significantly reduced the inhibitory effect of OxLDL on vasodilation [maximal relaxation (E(max)) = 82.1 +/- 8.6% vs. 54.1 +/- 8.1%; P < 0.0001], but HDL from obese subjects had no effect (E(max) = 47.2 +/- 12.5% vs. 54.1 +/- 8.1%; NS). In HDL from abdominally obese subjects compared with HDL from controls, the apoA-I content was 12% lower (P < 0.05) and the triglyceride-to-cholesteryl ester ratio was 36% higher (P = 0.08)). E(max)(OxLDL + HDL) was correlated with HDL apoA-I content and triglyceride-to-cholesteryl ester ratio (r = 0.36 and r = -0.38, respectively; P < 0.05). We conclude that in abdominally obese subjects, the ability of HDL to counteract the inhibitory effect of OxLDL on vascular relaxation is impaired. This could contribute to the increased cardiovascular risk observed in these subjects.     

Apolipoprotein C-I reduces cholesteryl esters selective uptake from LDL and HDL by binding to HepG2 cells and lipoproteins

Plasma cholesterol from low- and high-density lipoproteins (LDL and HDL) are cleared from the circulation by specific receptors that either totally degrade lipoproteins as the LDL receptor or selectively take up their cholesteryl esters (CE) like the scavenger receptor class B type I (SR-BI). The aim of the present study was to define the effect of apoC-I on the uptake of LDL and HDL₃ by HepG2 cells. In experiments conducted with exogenously added purified apoC-I, no significant effect was observed on lipoprotein–protein association and degradation; however, LDL- and HDL₃-CE selective uptake was significantly reduced in a dose-dependent manner. This study also shows that apoC-I has the ability to associate with HepG2 cells and with LDL and HDL₃. Moreover, pre-incubation of HepG2 cells with apoC-I reduces HDL₃-CE selective uptake and pre-incubation of LDL and HDL₃ with apoC-I decreases their CE selective uptake by HepG2 cells. Thus, apoC-I can accomplish its inhibitory effect on SR-BI activity by either binding to SR-BI or lipoproteins. We conclude that by reducing hepatic lipoprotein-CE selective uptake, apoC-I has an atherogenic character.     

Cholesteryl ester acyl oxidation and remodeling in murine macrophages: formation of oxidized phosphatidylcholine

Cholesterol is an essential component of eukaryotic cell membranes, regulating fluidity and permeability of the bilayer. Outside the membrane, cholesterol is esterified to fatty acids forming cholesterol esters (CEs). Metabolism of CEs is characterized by recurrent hydrolysis and esterification as part of the CE cycle; however, since recombinant 15-lipoxygenase (15-LO) was shown to oxidize cholesteryl linoleate of LDL, there has been interest in CE oxidation, particularly in the context atherogenesis. Studies of oxidized CE (oxCE) metabolism have focused on hydrolysis and subsequent reverse cholesterol transport with little emphasis on the fate the newly released oxidized fatty acyl component. Here, using mass spectrometry to analyze lipid oxidation products, CE metabolism in murine peritoneal macrophages was investigated. Ex vivo macrophage incubations revealed that cellular 15-LO directly oxidized multiple CE substrates from intracellular stores and from extracellular sources. Freshly harvested murine macrophages also contained 15-LO-specific oxCEs, suggesting the enzyme may act as a CE-oxidase in vivo. The metabolic fate of oxCEs, particularly the hydrolysis and remodeling of oxidized fatty acyl chains, was also examined in the macrophage. Metabolism of deuterated CE resulted in the genesis of deuterated, oxidized phosphatidylcholine (oxPC). Further experiments revealed these oxPC species were formed chiefly from the hydrolysis of oxidized CE and subsequent reacylation of the oxidized acyl components into PC.     

Influence of age and sex on levels of anti-oxidized LDL antibodies and anti-LDL immune complexes in the general population

Most studies of antibodies to oxidized LDL have been undertaken in patients with different diseases and cardiovascular risk factors. However, very few studies have researched the distribution and determining factors of antibodies to oxidized LDL in the general population. A total of 1,354 persons (817 females and 537 males) aged 5-65 years were included in this study. They were selected randomly from the population census of Málaga, in southern Spain. The females had lower levels of total cholesterol and triglycerides and higher levels of HDL-cholesterol and a very significant increase (P < 0.0001) in levels of anti-oxidized LDL [low density lipoprotein modified by malondialdehyde (MDA-LDL)] antibodies but no difference in levels of immune complexes consisting of LDL and IgG antibodies (anti-LDL immune complex). Younger persons (16-35 years) had higher levels of anti-oxidized LDL (MDA-LDL) antibodies than persons older than 35 years (P = 0.05). Levels of immune complexes were significantly higher (P = 0.05) in persons aged 5-15 years than in persons older than 40 years. A very weak association was found between levels of anti-oxidized LDL (MDA-LDL) antibodies and anti-LDL immune complexes. The higher prevalence of anti-oxidized LDL (MDA-LDL) antibodies in females and young persons is in agreement with studies that found an inverse association between atherosclerosis and the level of these antibodies.     

Electronegative LDL circulating in smokers impairs endothelial progenitor cell differentiation by inhibiting Akt phosphorylation via LOX-1

Endothelial progenitor cells (EPCs), important for endothelial regeneration and vasculogenesis, are reduced by cigarette smoking. To elucidate the mechanisms, we examined the effects of electronegative LDL, circulating in chronic smokers, on EPC differentiation. Using ion-exchange chromatography, we purified smoker LDL into five subfractions, L1-L5. In matched, nonsmoking healthy subjects, L5, the most electronegative subfraction, was either absent or scanty. Sustained L5 treatment inhibited CD31 and KDR expression and EPC differentiation, whereas L1-L4 had no effect. L5 also inhibited telomerase activity to accelerate EPC senescence in correlation with reduced Akt phosphorylation. Transfection of day 3 EPCs with dominant negative Akt constructs inhibited CD31 and KDR expression, stalled EPC differentiation, and promoted early senescence. In contrast, transfection with constitutively active Akt rendered the EPCs resistant to L5, allowing normal maturation. L5 upregulated the lectin-like oxidized low density lipoprotein receptor 1 (LOX-1), and pretreatment of EPCs with TS20, a LOX-1-neutralizing antibody, blocked internalization of L5 by EPCs and prevented L5-mediated inhibition of EPC differentiation. Mixing L5 with L1 to physiological L5/L1 ratios did not attenuate L5's effects. These findings suggest that cigarette smoking is associated with the formation of L5, which inhibits EPC differentiation by impairing Akt phosphorylation via the LOX-1 receptor.     

Oxidized LDL-induced endolysosomal phospholipidosis and enzymatically modified LDL-induced foam cell formation determine specific lipid species modulation in human macrophages

Recruitment of circulating monocytes and formation of macrophage foam cells in the arterial intima are characteristic features of atherogenesis. Foam cells are formed by cellular uptake and storage of atherogenic lipoproteins, including oxidized LDL (oxLDL) and enzymatically modified LDL (eLDL). Dissection of oxLDL- and eLDL-induced cellular phenotypes indicates that these two LDL-modifications are coupled with two fundamentally different cellular responses in macrophages. Oxidized LDL preferentially up-regulates scavenger receptors required for its internalization, induces preferential lipid storage in the acidic compartment resembling drug-induced endolysosomal phospholipidosis, parallel with increased cellular content of the endolysosomal signature lipid bis(monoacylglycero)phosphate, pro-apoptotic signalling and appearance of ceramide-enriched surface membrane microdomains. By contrast, challenge of macrophages by eLDL leads to expanded cholesterol- and sphingomyelin-enriched surface membrane microdomains, up-regulation of diverse pattern recognition receptors required for phagocytosis of eLDL, parallel with extensive lipid droplet formation, increased endoplasmic reticulum (ER)-stress and membrane contact site formation for interorganelle trafficking and signalling, and enhanced cellular content of the mitochondrial lipid cardiolipin.This review focuses on biological activities of oxLDL and eLDL in human macrophages, and discusses some lipidomic considerations related to foam cell formation and phospholipidosis.     

Low density lipoprotein (LDL), atherosclerosis and antioxidants

A crucial and causative role in the pathogenesis of atherosclerosis is believed to be the oxidative modification of low density lipoprotein (LDL). The oxidation of LDL involves released free radical driven lipid peroxidation. Several lines of evidence support the role of oxidized LDL in atherogenesis. Epidemiologic studies have demonstrated an association between an increased intake of dietary antioxidant vitamins, such as vitamin E and vitamin C and reduced morbidity and mortality from coronary artery diseases. It is thus hypothesized that dietary antioxidants may help prevent the development and progression of atherosclerosis. The oxidation of LDL has been shown to be reduced by antioxidants, and, in animal models, improved antioxidants may offer possibilities for the prevention of atherosclerosis. The results of several on going long randomized intervention trials will provide valuahle information on the efficacy and safety of improved antioxidants in the prevention of atherosclerosis. This review a evaluates current literature involving antioxidants and vascular disease, with a particular focus on the potential mechanisms.     

ACAT2 stimulates cholesteryl ester secretion in apoB-containing lipoproteins

Previous studies in nonhuman primates revealed a striking positive correlation between liver cholesteryl ester (CE) secretion rate and the development of coronary artery atherosclerosis. CE incorporated into hepatic VLDL is necessarily synthesized by ACAT2, the cholesterol-esterifying enzyme in hepatocytes. We tested the hypothesis that the level of ACAT2 expression, in concert with cellular cholesterol availability, affects the CE content of apolipoprotein B (apoB)-containing lipoproteins. In a model system of lipoprotein secretion using COS cells cotransfected with microsomal triglyceride transfer protein and truncated forms of apoB, ACAT2 expression resulted in a 3-fold increase in microsomal ACAT activity and a 4-fold increase in the radiolabeled CE content of apoB-lipoproteins. After cholesterol-cyclodextrin (Chol-CD) treatment, CE secretion was increased by 27-fold in ACAT2-transfected cells but by only 7-fold in control cells. Chol-CD treatment also caused the percentage of CE in the apoB-lipoproteins to increase from 3% to 33% in control cells and from 16% to 54% in ACAT2-transfected cells. In addition, ACAT2-transfected cells secreted 3-fold more apoB than control cells. These results indicate that under all conditions of cellular cholesterol availability tested, the relative level of ACAT2 expression affects the CE content and, hence, the potential atherogenicity, of nascent apoB-containing lipoproteins.     

Relationship of IgG and IgM autoantibodies and immune complexes to oxidized LDL with markers of oxidation and inflammation and cardiovascular events: results from the EPIC-Norfolk Study

Levels of IgG and IgM autoantibodies (AA) to malondialdehyde (MDA)-LDL and apoB-immune complexes (ICs) were measured in 748 cases and 1,723 controls in the EPIC-Norfolk cohort and their association to coronary artery disease (CAD) events determined. We evaluated whether AA and IC modify CAD risk associated with secretory phospholipase A(2) (sPLA(2)) type IIA mass and activity, lipoprotein-associated PLA(2) activity, lipoprotein (a) [Lp(a)], oxidized phospholipids on apoB-100 (OxPL/apoB), myeloperoxidase, and high sensitivity C-reactive protein. IgG ICs were higher in cases versus controls (P = 0.02). Elevated levels of IgM AA and IC were inversely associated with Framingham Risk Score and number of metabolic syndrome criteria (p range 0.02-0.001). In regression analyses adjusted for age, smoking, diabetes, LDL-cholesterol, HDL-cholesterol, and systolic blood pressure, the highest tertiles of IgG and IgM AA and IC were not associated with higher risk of CAD events compared with the lowest tertiles. However, elevated levels of IgM IC reduced the risk of Lp(a) (P = 0.006) and elevated IgG MDA-LDL potentiated the risk of sPLA(2) mass (P = 0.018). This epidemiological cohort of initially healthy subjects shows that IgG and IgM AA and IC are not independent predictors of CAD events but may modify CAD risk associated with elevated levels of oxidative biomarkers.     

Cellular localization of the receptor-dependent and receptor-independent uptake of human LDL in the liver of normal and 17 alpha-ethinyl estradiol-treated rats

The cellular localization in the liver of the receptor-dependent and -independent uptake of human low density lipoprotein (LDL) in normal and 17 alpha-ethinyl estradiol-treated rats was investigated by the simultaneous in vivo injection of human 131I-LDL and human reductive methylated 125I-LDL. The cells were subsequently isolated by a low temperature method. In untreated rats, after 30 min of in vivo circulation of human LDL, 57% of the receptor-dependent liver-association of human LDL occurs in non-parenchymal cells and 43% in parenchymal cells. Estradiol treatment of rats for 3 days selectively increases the receptor-dependent cell-association of human LDL with hepatocytes (17-fold), while the receptor-dependent cell-association with non-parenchymal cells is not affected.     

Expression of caveolin‐1 in hepatic cells increases oxidized LDL uptake and preserves the expression of lipoprotein receptors

Oxidized LDL (OxLDL) that are positively associated with the risk of developing cardiovascular diseases are ligands of scavenger receptor‐class B type I (SR‐BI) and cluster of differentiation‐36 (CD36) which can be found in caveolae. The contribution of these receptors in human hepatic cell is however unknown. The HepG2 cell, a human hepatic parenchymal cell model, expresses these receptors and is characterized by a very low level of caveolin‐1. Our aim was to define the contribution of human CD36, SR‐BI, and caveolin‐1 in the metabolism of OxLDL in HepG2 cells and conversely the effects of OxLDL on the levels/localization of these receptors. By comparing mildly (M)‐ and heavily (H)‐OxLDL metabolism between control HepG2 cells and HepG2 cells overexpressing CD36, SR‐BI, or caveolin‐1, we found that (1) CD36 increases M‐ and H‐OxLDL‐protein uptake; (2) SR‐BI drives M‐OxLDL through a degradation pathway at the expense of the cholesterol ester (CE) selective uptake pathway; (3) caveolin‐1 increases M‐ and H‐OxLDL‐protein uptake and decreases CE selective uptake from M‐OxLDL. Also, incubation with M‐ or H‐OxLDL decreases the levels of SR‐BI and LDL‐receptor in control HepG2 cells which can be overcome by caveolin‐1 expression. In addition, OxLDL move CD36 from low to high buoyant density membrane fractions, as well as caveolin‐1 in cells overexpressing this protein. Thus, hepatic caveolin‐1 expression has significant effects on OxLDL metabolism and on lipoprotein receptor levels. J. Cell. Biochem. 108: 906–915, 2009. © 2009 Wiley‐Liss, Inc.     

Phenolic antioxidants attenuate neuronal cell death following uptake of oxidized low-density lipoprotein

Oxidative stress is implicated in neuronal loss associated with neurodegeneration such as in Parkinson’s disease, Alzheimer’s disease and age-related cognitive decline. Recent reports indicate that the consumption of flavonoid-rich fruits partly reverses the age-related neuronal and cognitive decline. In this study, cultured striatal neurons were exposed to oxidized lipids in the form of low-density lipoprotein (oxLDL) as a model for the induction of oxidative injury, and the abilities of phenolic antioxidants, flavonoids and hydroxycinnamic acid derivatives, to attenuate this neuronal damage were examined. OxLDL was demonstrated to enter neuronal cells and to be capable of eliciting neurotoxicity in a dose- and time-dependent manner, inducing DNA fragmentation and cell lysis. Flavonoids exert protective effects, which appear to be related to specific structural characteristics, particularly relevant being those defining their reduction potentials and partition coefficients. In summary, these data suggest a possible role for flavonoids in reducing neurodegeneration associated with chronic disorders in which oxidative stress is implicated.     

In vivo cholesteryl ester selective uptake of mildly and standardly oxidized LDL occurs by both parenchymal and nonparenchymal mouse hepatic cells but SR-BI is only responsible for standardly oxidized LDL selective uptake by nonparenchymal cells

In blood circulation, low density lipoproteins (LDL) can undergo modification, such as oxidation, and become key factors in the development of atherosclerosis. Although the liver is the major organ involved in the elimination of oxidized LDL (oxLDL), the identity of the receptor(s) involved remains to be defined. Our work aims to clarify the role of the scavenger receptor class B type I (SR-BI) in the hepatic metabolism of mildly and standardly oxLDL as well as the relative contribution of parenchymal (hepatocytes) and nonparenchymal liver cells with a special emphasis on CE-selective uptake. The association of native LDL and mildly or standardly oxLDL labeled either in proteins or in cholesteryl esters (CE) was measured on primary cultures of mouse hepatocytes from normal and SR-BI knock-out (KO) mice. These in vitro assays demonstrated that hepatocytes are able to mediate CE-selective uptake from both LDL and oxLDL and that SR-BI KO hepatocytes have a 60% reduced ability to selectively take CE from LDL but not towards mildly or standardly oxLDL. When lipoproteins were injected in the mouse inferior vena cava, parenchymal and nonparenchymal liver cells accumulated more CE than proteins from native, mildly and standardly oxLDL, indicating that selective uptake of CE from these lipoproteins occurs in vivo in these two cell types. The parenchymal cells contribute near 90% of the LDL-CE selective uptake and SR-BI for 60% of this pathway. Nonparenchymal cells capture mainly standardly oxLDL while parenchymal and nonparenchymal cells equally take up mildly oxLDL. An 82% reduction of standardly oxLDL-CE selective uptake by the nonparenchymal cells of SR-BI KO mice allowed emphasizing the contribution of SR-BI in hepatic metabolism of standardly oxLDL. However, SR-BI is not responsible for mildly oxLDL metabolism. Thus, SR-BI is involved in LDL- and standardly oxLDL-CE selective uptake in parenchymal and nonparenchymal cells, respectively.