Caroline C. van der Hoogt

Cholesteryl Ester Transfer Protein Decreases High-Density Lipoprotein and Severely Aggravates Atherosclerosis in APOE*3-Leiden Mice

Objective—The role of cholesteryl ester transfer protein (CETP) in the development of atherosclerosis is still undergoing debate. Therefore, we evaluated the effect of human CETP expression on atherosclerosis in APOE*3-Leiden (E3L) mice with a humanized lipoprotein profile. Methods and Results—E3L mice were crossbred with human CETP transgenic mice. On a chow diet, CETP expression increased plasma total cholesterol (TC) (+43%; P<0.05). To evaluate the effects of CETP on the development of atherosclerosis, mice were fed a Western-type diet containing 0.25% cholesterol, leading to 4.3-fold elevated TC levels in both E3L and CETP.E3L mice (P<0.01). On both diets, CETP expression shifted the distribution of cholesterol from high-density lipoprotein (HDL) toward very-low-density lipoprotein (VLDL)/low-density lipoprotein (LDL). Moreover, plasma of CETP.E3L mice had reduced capacity (−39%; P<0.05) to induce SR-BI–mediated cholesterol efflux from Fu5AH cells than plasma of E3L mice. After 19 weeks on the Western-type diet, CETP.E3L mice showed a 7.0-fold increased atherosclerotic lesion area in the aortic root compared with E3L mice (P<0.0001). Conclusions—CETP expression in E3L mice shifts the distribution of cholesterol from HDL to VLDL/LDL, reduces plasma-mediated SR-BI–dependent cholesterol efflux, and represents a clear pro-atherogenic factor in E3L mice. We anticipate that the CETP.E3L mouse will be a valuable model for the preclinical evaluation of HDL-raising interventions on atherosclerosis development.

Torcetrapib Does Not Reduce Atherosclerosis Beyond Atorvastatin and Induces More Proinflammatory Lesions Than Atorvastatin

Background— Although cholesteryl ester transfer protein (CETP) inhibition is regarded as a promising strategy to reduce atherosclerosis by increasing high-density lipoprotein cholesterol, the CETP inhibitor torcetrapib given in addition to atorvastatin had no effect on atherosclerosis and even increased cardiovascular death in the recent Investigation of Lipid Level Management to Understand its Impact in Atherosclerotic Events trial. Therefore, we evaluated the antiatherogenic potential and adverse effects of torcetrapib in humanized APOE*3-Leiden.CETP (E3L.CETP) mice. Methods and Results— E3L.CETP mice were fed a cholesterol-rich diet without drugs or with torcetrapib (12 mg · kg−1 · d−1), atorvastatin (2.8 mg · kg−1 · d−1), or both for 14 weeks. Torcetrapib decreased CETP activity in both the absence and presence of atorvastatin (−74% and −73%, respectively; P<0.001). Torcetrapib decreased plasma cholesterol (−20%; P<0.01), albeit to a lesser extent than atorvastatin (−42%; P<0.001) or the combination of torcetrapib and atorvastatin (−40%; P<0.001). Torcetrapib increased high-density lipoprotein cholesterol in the absence (30%) and presence (34%) of atorvastatin. Torcetrapib and atorvastatin alone reduced atherosclerotic lesion size (−43% and −46%; P<0.05), but combination therapy did not reduce atherosclerosis compared with atorvastatin alone. Remarkably, compared with atorvastatin, torcetrapib enhanced monocyte recruitment and expression of monocyte chemoattractant protein-1 and resulted in lesions of a more inflammatory phenotype, as reflected by an increased macrophage content and reduced collagen content. Conclusions— CETP inhibition by torcetrapib per se reduces atherosclerotic lesion size but does not enhance the antiatherogenic potential of atorvastatin. However, compared with atorvastatin, torcetrapib introduces lesions of a less stable phenotype.

Fenofibrate increases HDL-cholesterol by reducing cholesteryl ester transfer protein expression

In addition to efficiently decreasing VLDL-triglycerides (TGs), fenofibrate increases HDL-cholesterol levels in humans. We investigated whether the fenofibrate-induced increase in HDL-cholesterol is dependent on the expression of the cholesteryl ester transfer protein (CETP). To this end, APOE*3-Leiden (E3L) transgenic mice without and with the human CETP transgene, under the control of its natural regulatory flanking regions, were fed a Western-type diet with or without fenofibrate. Fenofibrate (0.04% in the diet) decreased plasma TG in E3L and E3L.CETP mice (−59% and −60%; P < 0.001), caused by a strong reduction in VLDL. Whereas fenofibrate did not affect HDL-cholesterol in E3L mice, fenofibrate dose-dependently increased HDL-cholesterol in E3L.CETP mice (up to +91%). Fenofibrate did not affect the turnover of HDL-cholesteryl ester (CE), indicating that fenofibrate causes a higher steady-state HDL-cholesterol level without altering the HDL-cholesterol flux through plasma. Analysis of the hepatic gene expression profile showed that fenofibrate did not differentially affect the main players in HDL metabolism in E3L.CETP mice compared with E3L mice. However, in E3L.CETP mice, fenofibrate reduced hepatic CETP mRNA (−72%; P < 0.01) as well as the CE transfer activity in plasma (−73%; P < 0.01). We conclude that fenofibrate increases HDL-cholesterol by reducing the CETP-dependent transfer of cholesterol from HDL to (V)LDL, as related to lower hepatic CETP expression and a reduced plasma (V)LDL pool.

Apolipoprotein CI stimulates the response to lipopolysaccharide and reduces mortality in Gram-negative sepsis

Gram‐negative sepsis is a major death cause in intensive care units. Accumulating evidence indicates the protective role of plasma lipoproteins such as high‐density lipoprotein (HDL) in sepsis. It has recently been shown that septic HDL is almost depleted from apolipoprotein CI (apoCI), suggesting that apoCI may be a protective factor in sepsis. Sequence analysis revealed that apoCI possesses a highly conserved consensus KVKEKLK binding motif for lipopolysaccharide (LPS), an outer‐membrane component of Gram‐negative bacteria. Through avid binding to LPS involving this motif, apoCI improved the presentation of LPS to macrophages in vitro and in mice, thereby stimulating the inflammatory response to LPS. Moreover, apoCI dose‐dependently increased the early inflammatory response to Klebsiella pneumoniae‐induced pneumonia, reduced the number of circulating bacteria, and protected mice against fatal sepsis. Our data support the hypothesis that apoCI is a physiological protector against infection by enhancing the early inflammatory response to LPS and suggest that timely increase of apoCI levels could be used to efficiently prevent and treat early sepsis.—Berbée, J. F. P., van der Hoogt, C. C., Kleemann, R., Schippers, E. F., Kitchens, R. L., van Dissel, J. T., Bakker‐Woudenberg, I. A. J. M., Havekes, L. M., Rensen, P. C. N. Apolipoprotein CI stimulates the response to lipopolysaccharide and reduces mortality in Gram‐negative sepsis. FASEB J. 20, E1560 –E1569 (2006)

Apolipoprotein CI inhibits scavenger receptor BI and increases plasma HDL levels in vivo

Apolipoprotein CI (apoCI) has been suggested to influence HDL metabolism by activation of LCAT and inhibition of HL and CETP. However, the effect of apoCI on scavenger receptor BI (SR-BI)-mediated uptake of HDL-cholesteryl esters (CE), as well as the net effect of apoCI on HDL metabolism in vivo is unknown. Therefore, we evaluated the effect of apoCI on the SR-BI-mediated uptake of HDL-CE in vitro and determined the net effect of apoCI on HDL metabolism in mice. Enrichment of HDL with apoCI dose-dependently decreased the SR-BI-dependent association of [(3)H]CE-labeled HDL with primary murine hepatocytes, similar to the established SR-BI-inhibitors apoCIII and oxLDL. ApoCI deficiency in mice gene dose-dependently decreased HDL-cholesterol levels. Adenovirus-mediated expression of human apoCI in mice increased HDL levels at a low dose and increased the HDL particle size at higher doses. We conclude that apoCI is a novel inhibitor of SR-BI in vitro and increases HDL levels in vivo.

Plasma apolipoprotein CI correlates with increased survival in patients with severe sepsis

ObjectiveWe recently reported that apolipoprotein CI (apoCI) protects against the development of murine bacterial sepsis. We now examined the time course of plasma apoCI levels in survivors and non-survivors of severe sepsis.DesignProspective study in patients meeting predefined criteria for severe sepsis.SettingUniversity hospital intensive care unit.Patients and participantsSeventeen patients with severe sepsis.InterventionsIn each patient, serial blood samples for determination of total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, apoCI, apoAI, apoB, and apoCIII protein as well as clinical outcome data were collected over 30 days.Measurements and resultsUpon hospitalization, apoCI levels were approximately 5 times lower than normal values in septic patients, i.e. median 1.34 [interquartile range (IQR) 0.82–2.16]u202fmg/dl. ApoCI gradually increased to median values of 5.51 (IQR 3.64–6.97)u202fmg/dl on dayxa028. At dayxa00, apoCI levels tended to be lower in non-survivors than in survivors. Remarkably, apoCI levels remained low in non-survivors, whereas apoCI levels gradually increased to normal levels in survivors. This difference was significant and remained so after adjustment for lipoprotein core lipids. No such effect between survivors and non-survivors could be detected for lipoprotein lipids or for apoAI, apoB, and apoCIII after lipid adjustment.ConclusionsPlasma apoCI levels are markedly decreased in patients with severe sepsis. ApoCI levels were higher in survivors, even after adjustment for lipid levels, and recovered progressively to normal levels. In contrast, apoCI levels remained low in non-survivors. Therefore, axa0high plasma apoCI level predicts survival in patients with severe sepsis.

Cholesterol 7α-Hydroxylase Deficiency in Mice on an APOE*3-Leiden Background Increases Hepatic ABCA1 mRNA Expression and HDL-Cholesterol

Objective—High-density lipoprotein (HDL) plays a key role in protection against development of atherosclerosis by reducing inflammation, protecting against LDL oxidation, and promoting reverse cholesterol transport from peripheral tissues to the liver for secretion into bile. Cholesterol 7&agr;-hydroxylase (Cyp7a1) catalyzes the rate-limiting step in the intrahepatic conversion of cholesterol to bile acids that may have a role in HDL metabolism. We investigated the effect of Cyp7a1 deficiency on HDL metabolism in APOE*3-Leiden transgenic mice. Methods and Results—Reduced bile acid biosynthesis in Cyp7a1−/−.APOE*3-Leiden mice versus APOE*3-Leiden mice did not affect total plasma cholesterol levels, but the distribution of cholesterol over various lipoproteins was different. Cholesterol was decreased in apoB-containing lipoproteins (ie, VLDL and IDL/LDL), whereas cholesterol was increased in HDL. The activity of PLTP and LCAT, which play a role in HDL catabolism, were not changed, and neither was HDL clearance. However, the hepatic cholesterol content was 2-fold increased, which was accompanied by a 2-fold elevated expression of hepatic ABCA1 and increased rate of cholesterol efflux from the liver to HDL. Conclusions—Strongly reduced bile acid synthesis in Cyp7a1−/−.APOE*3-Leiden mice leads to increased plasma HDL-cholesterol levels, as related to an increased hepatic expression of ABCA1.