Bayesian network analysis of panomic biological big data identifies the importance of triglyceride-rich LDL in atherosclerosis development

Introduction

We sought to explore biomarkers of coronary atherosclerosis in an unbiased fashion.

Methods

We analyzed 665 patients (mean ± SD age, 56 ± 11 years; 47% male) from the GLOBAL clinical study (NCT01738828). Cases were defined by the presence of any discernable atherosclerotic plaque based on comprehensive cardiac computed tomography (CT). De novo Bayesian networks built out of 37,000 molecular measurements and 99 conventional biomarkers per patient examined the potential causality of specific biomarkers.

Results

Most highly ranked biomarkers by gradient boosting were interleukin-6, symmetric dimethylarginine, LDL-triglycerides [LDL-TG], apolipoprotein B48, palmitoleic acid, small dense LDL, alkaline phosphatase, and asymmetric dimethylarginine. In Bayesian analysis, LDL-TG was directly linked to atherosclerosis in over 95% of the ensembles. Genetic variants in the genomic region encoding hepatic lipase (LIPC) were associated with LIPC gene expression, LDL-TG levels and with atherosclerosis.

Discussion

Triglyceride-rich LDL particles, which can now be routinely measured with a direct homogenous assay, may play an important role in atherosclerosis development.

Clinical trial registration

GLOBAL clinical study (Genetic Loci and the Burden of Atherosclerotic Lesions); [https://clinicaltrials.gov/ct2/show/NCT01738828?term=NCT01738828&rank=1], identifier [NCT01738828].

Discovery of analogues of non-β oxidizable long-chain dicarboxylic fatty acids as dual inhibitors of fatty acids and cholesterol synthesis: Efficacy of lead compound in hyperlipidemic hamsters reveals novel mechanism

BACKGROUND AND AIMS

Cholesterol and triglycerides are risk factors for developing cardiovascular disease. Therefore, appropriate cells and assays are required to discover and develop dual cholesterol and fatty acid inhibitors. A predictive hyperlipidemic animal model is needed to evaluate mechanism of action of lead molecule for therapeutic indications.

METHODS AND RESULTS

Primary hepatocytes from rat, hamster, rabbit, and humans were compared for suitability to screen compounds by de novo lipogenesis (DNL) using14C-acetate. Hyperlipidemic hamsters were used to evaluate efficacy and mode of action. In rat hepatocytes DNL assay, both the central moiety and carbon chain length influenced the potency of lipogenesis inhibition. In hyperlipidemic hamsters, ETC-1002 decreased plasma cholesterol and triglycerides by 41% and 49% at the 30 mg/kg dose. Concomitant decreases in non-esterified fatty acids (-34%) and increases in ketone bodies (20%) were associated with induction of hepatic CPT1-α. Reductions in proatherogenic VLDL-C and LDL-C (-71% and -64%) occurred partly through down-regulation of DGAT2 and up-regulation of LPL and PDK4. Activation of PLIN1 and PDK4 dampened adipogenesis and showed inverse correlation with adipose mass. Hepatic concentrations of cholesteryl ester and TG decreased by 67% and 64%, respectively. Body weight decreased with concomitant decreases in epididymal fat. Plasma and liver concentrations of ETC-1002 agreed with the observed dose-response efficacy.

CONCLUSIONS

Taken together, ETC-1002 reduced proatherogenic lipoproteins, hepatic lipids and adipose tissues in hyperlipidemic hamsters via induction of LPL, CPT1-α, PDK4, and PLIN1, and downregulation of DGAT2. These characteristics may be useful in the treatment of fatty livers that causes non-alcoholic steatohepatitis.

Bempedoic Acid Lowers Low-Density Lipoprotein Cholesterol and Attenuates Atherosclerosis in Low-Density Lipoprotein Receptor–Deficient ( LDLR +/− and LDLR −/− ) Yucatan Miniature Pigs

Objective—

Bempedoic acid (BemA; ETC-1002) is a novel drug that targets hepatic ATP-citrate lyase to reduce cholesterol biosynthesis. In phase 2 studies, BemA lowers elevated low-density lipoprotein cholesterol (LDL-C) in hypercholesterolemic patients. In the present study, we tested the ability of BemA to decrease plasma cholesterol and LDL-C and attenuate atherosclerosis in a large animal model of familial hypercholesterolemia.

Approach and Results—

Gene targeting has been used to generate Yucatan miniature pigs heterozygous ( LDLR +/− ) or homozygous ( LDLR −/− ) for LDL receptor deficiency (ExeGen). LDLR +/− and LDLR −/− pigs were fed a high-fat, cholesterol-containing diet (34% kcal fat; 0.2% cholesterol) and orally administered placebo or BemA for 160 days. In LDLR +/− pigs, compared with placebo, BemA decreased plasma cholesterol and LDL-C up to 40% and 61%, respectively. In LDLR −/− pigs, in which plasma cholesterol and LDL-C were 5-fold higher than in LDLR +/− pigs, BemA decreased plasma cholesterol and LDL-C up to 27% and 29%, respectively. Plasma levels of triglycerides and high-density lipoprotein cholesterol, fasting glucose and insulin, and liver lipids were unaffected by treatment in either genotype. In the aorta of LDLR +/− pigs, BemA robustly attenuated en face raised lesion area (−58%) and left anterior descending coronary artery cross-sectional lesion area (−40%). In LDLR −/− pigs, in which lesions were substantially more advanced, BemA decreased aortic lesion area (−47%) and left anterior descending coronary artery lesion area (−48%).

Conclusions—

In a large animal model of LDLR deficiency and atherosclerosis, long-term treatment with BemA reduces LDL-C and attenuates the development of aortic and coronary atherosclerosis in both LDLR +/− and LDLR −/− miniature pigs.

Abstract 394: Ldl-cholesterol, ApoB100 Kinetics and Atherosclerosis in Ldlr-deficient Yucatan Minipigs: A New Model for Familial Hypercholesterolemia

Lack of animal models with human-like lipoprotein metabolism and pathology has hampered translational research in atherosclerosis. Recently, a model of familial hypercholesterolemia was developed in Yucatan miniature pigs, in which the LDL receptor (LDLR) was deleted through gene targeting of exon 4. The objective of the present study was to determine the plasma lipoprotein response to a high fat diet and the kinetics of apolipoprotein (apo) B metabolism in LDLR-deficient miniature pigs. LDLR+/+ (n=5), LDLR+/- pigs (n=6) and LDLR-/- pigs (n=5) were fed a diet containing 34% kcal from fat and 0.2% cholesterol (C). At 6 weeks, the kinetics of plasma apoB100 (fasting) were measured using stable isotopic techniques and multi-compartmental modeling. In chow-fed pigs, LDL-C was 0.8mM, 1.3mM and 14mM in LDLR+/+, LDLR+/- and LDLR-/- pigs, respectively. On diet for 6 weeks, LDL-C increased 1.3-fold (to 1.09mM), 1.7-fold (to 2.3mM) and 1.2-fold (to 15.8mM) in LDLR+/+, LDLR+/- and LDLR-/- pigs, respectively. The effect of genotype or diet on plasma TG and HDL-C was modest. Compared to LDLR+/+ pigs, VLDL apoB100 pool sizes increased 1.4-fold in LDLR+/- and 1.7-fold in LDLR-/- pigs, due primarily to a decrease in fractional catabolic rates (FCR) of 18% and 63%, respectively. Compared to LDL+/+ pigs, LDL apoB100 pool sizes increased 2.2-fold and 14-fold in LDLR+/- and LDLR-/-, respectively, which was due to both 1.5-fold and 2-fold increases in production rates and 24% and 85% decreases in FCR, respectively. At 23 weeks, raised lesion area in the abdominal aorta was 3.3% in LDLR+/- pigs and 48.5% in LDLR-/- pigs. In the left anterior descending coronary artery, lesion area was 14.7x10 3 μm 2 in LDLR+/- pigs and 656x10 3 μm 2 in LDLR-/- pigs. This model should prove useful for translational research in lipoprotein metabolism and atherosclerosis.

Prevention of Diet-Induced Metabolic Dysregulation, Inflammation, and Atherosclerosis in Ldlr −/− Mice by Treatment With the ATP-Citrate Lyase Inhibitor Bempedoic Acid

Objective—

Bempedoic acid (ETC-1002, 8-hydroxy-2,2,14,14-tetramethylpentadecanedioic acid) is a novel low-density lipoprotein cholesterol–lowering compound. In animals, bempedoic acid targets the liver where it inhibits cholesterol and fatty acid synthesis through inhibition of ATP-citrate lyase and through activation of AMP-activated protein kinase. In this study, we tested the hypothesis that bempedoic acid would prevent diet-induced metabolic dysregulation, inflammation, and atherosclerosis.

Approach and Results—

Ldlr −/− mice were fed a high-fat, high-cholesterol diet (42% kcal fat, 0.2% cholesterol) supplemented with bempedoic acid at 0, 3, 10 and 30 mg/kg body weight/day. Treatment for 12 weeks dose-dependently attenuated diet-induced hypercholesterolemia, hypertriglyceridemia, hyperglycemia, hyperinsulinemia, fatty liver and obesity. Compared to high-fat, high-cholesterol alone, the addition of bempedoic acid decreased plasma triglyceride (up to 64%) and cholesterol (up to 50%) concentrations, and improved glucose tolerance. Adiposity was significantly reduced with treatment. In liver, bempedoic acid prevented cholesterol and triglyceride accumulation, which was associated with increased fatty acid oxidation and reduced fatty acid synthesis. Hepatic gene expression analysis revealed that treatment significantly increased expression of genes involved in fatty acid oxidation while suppressing inflammatory gene expression. In full-length aorta, bempedoic acid markedly suppressed cholesteryl ester accumulation, attenuated the expression of proinflammatory M1 genes and attenuated the iNos / Arg1 ratio. Treatment robustly attenuated atherosclerotic lesion development in the aortic sinus by 44%, with beneficial changes in morphology, characteristic of earlier-stage lesions.

Conclusions—

Bempedoic acid effectively prevents plasma and tissue lipid elevations and attenuates the onset of inflammation, leading to the prevention of atherosclerotic lesion development in a mouse model of metabolic dysregulation.

Abstract 18: Bempedoic Acid Lowers Low Density Lipoprotein-Cholesterol and Attenuates Aortic Atherosclerosis in LDL Receptor-Deficient ( LDLR +/- and LDLR -/- ) Yucatan Miniature Pigs

Bempedoic acid (ETC-1002) is an oral investigational drug that targets hepatic adenosine triphosphate-citrate lyase to reduce cholesterol biosynthesis. In Phase 2 studies (up to 12 weeks in duration), bempedoic acid lowers elevated LDL-cholesterol (C) in patients with hypercholesterolemia. The objective of the present study was to test the ability of bempedoic acid to decrease plasma-C and LDL-C, and attenuate the development of atherosclerosis in a large animal model of familial hypercholesterolemia. Gene targeting has been used to generate Yucatan miniature pigs heterozygous ( LDLR +/- ) or homozygous ( LDLR -/- ) for LDL-receptor (R) deficiency (ExeGen). LDLR +/- pigs (n=12) and LDLR -/- pigs (n=12) were fed a high fat, cholesterol-containing diet (34% kcal fat; 0.2% cholesterol) and orally administered placebo or bempedoic acid at 120 mg/d and at 240 mg/d for 160 days. Bempedoic acid was well tolerated; weight gain, caloric intake, liver enzymes and clinical chemistry analyses were unaffected by treatment. In LDLR +/- pigs at 160 days, compared to placebo, bempedoic acid significantly decreased plasma-C and LDL-C up to 43% ( P <0.01) and 63% ( P <0.002), respectively. Compared to LDLR-/- placebo pigs, in which plasma-C and LDL-C were 5-fold higher than in LDLR +/- placebo pigs, bempedoic acid significantly decreased plasma-C and LDL-C up to 26% ( P <0.04) and 29% ( P <0.03), respectively. Plasma levels of triglycerides and HDL-C, fasting glucose and insulin, and liver lipids were not affected by treatment in either genotype. In the aorta of LDLR +/- pigs, bempedoic acid treatment robustly attenuated total Sudan IV-stained lesion area (-58%, P <0.02) and area of raised lesions in the abdominal aorta (-58%, P <0.03). In LDLR -/- pigs, in which total aortic lesion area (6-fold) and area of raised abdominal lesions (12-fold) were substantially larger compared to LDLR +/- pigs, bempedoic acid significantly decreased total aortic lesion area (-47%, P <0.01) and area of raised abdominal lesions (-50%, P <0.03). The present experiments demonstrate that in a large animal model of LDLR-deficiency and atherosclerosis, long term treatment with bempedoic acid reduces LDL-C and attenuates the progression of aortic atherosclerosis in both LDLR +/- and LDLR -/- miniature pigs.

Treatment with ETC-1002 alone and in combination with ezetimibe lowers LDL cholesterol in hypercholesterolemic patients with or without statin intolerance

BACKGROUND

ETC-1002 is an oral, once-daily, first-in-class medication being developed to treat hypercholesterolemia.

OBJECTIVES

To compare 2 doses of ETC-1002, alone or combined with ezetimibe 10 mg (EZE), vs EZE monotherapy for lowering low-density lipoprotein cholesterol (LDL-C).

METHODS

This phase 2b, multicenter, double-blind trial-evaluated hypercholesterolemic patients (LDL-C, 130 to 220 mg/dL) with (n = 177) or without (n = 171) muscle-related intolerance to ≥2 statins; 1 at lowest approved dose. Subjects were randomized to 12-week treatment with ETC-1002 120 mg or ETC-1002 180 mg alone, EZE alone, ETC-1002 120 mg plus EZE, or ETC-1002 180 mg plus EZE.

RESULTS

EZE alone lowered LDL-C by 21%, whereas ETC-1002 monotherapy with 120 mg or 180 mg reduced LDL-C by 27% (P = .0008 vs EZE) and 30% (P < .0001 vs EZE), respectively. The combination of ETC-1002, 120 mg or 180 mg plus EZE reduced LDL-C by 43% and 48%, respectively (both P < .0001 vs EZE). ETC-1002 alone or combined with EZE also reduced non-high-density lipoprotein cholesterol, total cholesterol, apolipoprotein B, LDL particle number, and high-sensitivity C-reactive protein compared with EZE alone. Across all treatment groups, statin-intolerant patients reported more muscle-related adverse events than did statin-tolerant patients. ETC-1002 was safe and well tolerated, and rates of muscle-related adverse events were similar in all treatment groups.

CONCLUSIONS

In patients with and without statin intolerance, daily treatment with ETC-1002 120 mg and 180 mg alone or with EZE reduced LDL-C more than EZE alone and had a similar tolerability profile (NCT01941836).

Use of ETC-1002 to treat hypercholesterolemia in patients with statin intolerance

BACKGROUND

Once-daily, oral ETC-1002 reduces low-density lipoprotein cholesterol (LDL-C) and has beneficial effects on other cardiometabolic risk factors but has not been examined in statin intolerant patients.

OBJECTIVES

To study the efficacy and safety of ETC-1002 (a novel LDL-C-lowering agent) in patients with hypercholesterolemia and a history of statin intolerance.

METHODS

Patients intolerant to at least 1 statin were entered into this multicenter, double-blind, 8-week trial. Participants were required to have a history of muscle complaints that developed during statin treatment and resolved within 4 weeks of statin discontinuation. Patients (n = 56) were randomized in a 2:1 ratio to ETC-1002 60 mg daily or placebo. The ETC-1002 dose was increased at 2-week intervals to 120 mg, 180 mg, and 240 mg. The primary end point was the percentage change from baseline to week 8 in calculated LDL-C.

RESULTS

ETC-1002 reduced LDL-C 28.7% more than placebo (95% confidence interval, -35.4 to -22.1; P < .0001). ETC-1002 significantly reduced non-high-density lipoprotein cholesterol, total cholesterol, apolipoprotein B, and high-sensitivity C-reactive protein. Triglycerides and high-density lipoprotein cholesterol did not change with ETC-1002 treatment. Sixty-two percent of patients receiving ETC-1002 and none in the placebo group achieved the 2004 National Cholesterol Education Program Adult Treatment Panel III LDL-C goal (P < .0001). Muscle-related adverse events occurred with similar frequency in the placebo and ETC-1002 treatment groups, causing no discontinuations in ETC-1002-treated patients.

CONCLUSIONS

ETC-1002 appears to be effective at reducing LDL-C and was well tolerated in patients with statin-associated muscle complaints. Longer and larger studies are required to confirm the absence of muscle side effects.

LDL-cholesterol reduction in patients with hypercholesterolemia by modulation of adenosine triphosphate-citrate lyase and adenosine monophosphate-activated protein kinase

PURPOSE OF REVIEW

To review the profile of ETC-1002, as shown in preclinical and clinical studies, including LDL-cholesterol (LDL-C)-lowering activity and beneficial effects on other cardiometabolic risk markers as they relate to the inhibition of adenosine triphosphate-citrate lyase and the activation of adenosine monophosphate-activated protein kinase.

RECENT FINDINGS

ETC-1002 is an adenosine triphosphate-citrate lyase inhibitor/adenosine monophosphate-activated protein kinase activator currently in Phase 2b clinical development. In seven Phase 1 and Phase 2a clinical studies, ETC-1002 dosed once daily for 2-12 weeks has lowered LDL-C and reduced high-sensitivity C-reactive protein by up to 40%, with neutral to positive effects on glucose levels, blood pressure, and body weight. Importantly, use of ETC-1002 in statin-intolerant patients has shown statin-like lowering of LDL-C without the muscle pain and weakness responsible for discontinuation of statin use by many patients. ETC-1002 has also been shown to produce an incremental benefit, lowering LDL-C as an add-on therapy to a low-dose statin. In over 300 individuals in studies of up to 12 weeks, ETC-1002 has been well tolerated with no serious adverse effects.

SUMMARY

Because adenosine triphosphate-citrate lyase and adenosine monophosphate-activated protein kinase play central roles in regulating lipid and glucose metabolism, pharmacological modulation of these two enzymes could provide an important therapeutic alternative for statin-intolerant patients with hypercholesterolemia.

Efficacy and safety of ETC-1002, a novel investigational low-density lipoprotein-cholesterol-lowering therapy for the treatment of patients with hypercholesterolemia and type 2 diabetes mellitus

OBJECTIVE

8-Hydroxy-2,2,14,14-tetramethylpentadecanedioic acid (ETC-1002) is a small molecule with a unique mechanism of action shown in nonclinical studies to modulate pathways of cholesterol, fatty acid, and carbohydrate metabolism. In previous phase 2 clinical trials, once daily oral treatment with ETC-1002 significantly reduced low-density lipoprotein-cholesterol in patients with hypercholesterolemia. In this trial, the lipid-lowering efficacy of ETC-1002 was evaluated in patients with type 2 diabetes mellitus and hypercholesterolemia. Additional cardiometabolic biomarkers, including glycemic measures, were also assessed.

APPROACH AND RESULTS

A single-center, double-blind, placebo-controlled trial evaluated 60 patients with type 2 diabetes mellitus and elevated low-density lipoprotein-cholesterol. Patients discontinued all diabetes mellitus and lipid-regulating drugs and were randomized to receive ETC-1002 80 mg QD for 2 weeks followed by 120 mg QD for 2 weeks or placebo for 4 weeks. ETC-1002 lowered low-density lipoprotein-cholesterol levels by 43±2.6% (least squares mean±SE), compared with a reduction of 4±2.5% by placebo at day 29 (P<0.0001; primary end point). Non-high-density lipoprotein-cholesterol and total cholesterol were also significantly lowered by ETC-1002 compared with placebo (P<0.0001). High-sensitivity C-reactive protein was reduced by 41% (median) compared with a placebo reduction of 11% (P=0.0011). No clinically meaningful safety findings were observed.

CONCLUSIONS

ETC-1002 lowered low-density lipoprotein-cholesterol and other lipids and demonstrated improvement in high-sensitivity C-reactive protein in patients with type 2 diabetes mellitus and hypercholesterolemia without worsening glycemic control. ETC-1002 was well tolerated in this population.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT# 01607294.

Efficacy and safety of a novel dual modulator of adenosine triphosphate-citrate lyase and adenosine monophosphate-activated protein kinase in patients with hypercholesterolemia: results of a multicenter, randomized, double-blind, placebo-controlled, parallel-group trial

OBJECTIVES

The aim of this study was to assess the lipid-altering efficacy and safety of ETC-1002 in subjects with hypercholesterolemia.

BACKGROUND

ETC-1002 is a small molecule that modulates pathways of cholesterol, fatty acid, and carbohydrate metabolism and may have therapeutic benefits in treating hypercholesterolemia and other cardiometabolic risk factors.

METHODS

This multicenter, randomized, double-blind, placebo-controlled, parallel-group trial evaluated patients (n = 177) with elevated low-density lipoprotein cholesterol (LDL-C) (130 to 220 mg/dl), who were stratified by baseline triglycerides (not elevated [<150 mg/dl] or elevated [150-<400 mg/dl]) and randomized to receive 40, 80, or 120 mg of ETC-1002 or placebo once daily for 12 weeks. Outcomes included changes in LDL-C (primary endpoint), other lipids, and cardiometabolic risk factors; and safety.

RESULTS

ETC-1002 40, 80, and 120 mg lowered least-squares mean ± SE LDL-C levels by 17.9 ± 2.2%, 25.0 ± 2.1%, and 26.6 ± 2.2%, respectively, versus a reduction of 2.1 ± 2.2% with placebo (all, p < 0.0001); LDL-C lowering was similar between the subgroups with nonelevated and elevated triglycerides. ETC-1002 also lowered non-high-density lipoprotein cholesterol (non-HDL-C), apolipoprotein B, and LDL particle number (all, p < 0.0001) in a dose-dependent manner; HDL-C and triglyceride levels were relatively unchanged. Post-hoc analyses suggest that ETC-1002 may have favorable effects on other cardiometabolic risk factors. The ETC-1002 and placebo groups did not demonstrate clinically meaningful differences in adverse events or other safety assessments.

CONCLUSIONS

ETC-1002 significantly lowered LDL-C levels up to 27% across a broad range of baseline triglycerides and was generally safe and well tolerated. ETC-1002 has a novel mechanism of action and may be useful for reducing LDL-C. (A Study to Assess the Efficacy and Safety of ETC-1002 in Subjects With Elevated Blood Cholesterol and Either Normal or Elevated Triglycerides; NCT01262638).

ETC-1002 regulates immune response, leukocyte homing, and adipose tissue inflammation via LKB1-dependent activation of macrophage AMPK

ETC-1002 is an investigational drug currently in Phase 2 development for treatment of dyslipidemia and other cardiometabolic risk factors. In dyslipidemic subjects, ETC-1002 not only reduces plasma LDL cholesterol but also significantly attenuates levels of hsCRP, a clinical biomarker of inflammation. Anti-inflammatory properties of ETC-1002 were further investigated in primary human monocyte-derived macrophages and in in vivo models of inflammation. In cells treated with ETC-1002, increased levels of AMP-activated protein kinase (AMPK) phosphorylation coincided with reduced activity of MAP kinases and decreased production of proinflammatory cytokines and chemokines. AMPK phosphorylation and inhibitory effects of ETC-1002 on soluble mediators of inflammation were significantly abrogated by siRNA-mediated silencing of macrophage liver kinase B1 (LKB1), indicating that ETC-1002 activates AMPK and exerts its anti-inflammatory effects via an LKB1-dependent mechanism. In vivo, ETC-1002 suppressed thioglycollate-induced homing of leukocytes into mouse peritoneal cavity. Similarly, in a mouse model of diet-induced obesity, ETC-1002 restored adipose AMPK activity, reduced JNK phosphorylation, and diminished expression of macrophage-specific marker 4F/80. These data were consistent with decreased epididymal fat-pad mass and interleukin (IL)-6 release by inflamed adipose tissue. Thus, ETC-1002 may provide further clinical benefits for patients with cardiometabolic risk factors by reducing systemic inflammation linked to insulin resistance and vascular complications of metabolic syndrome.

AMP-activated protein kinase and ATP-citrate lyase are two distinct molecular targets for ETC-1002, a novel small molecule regulator of lipid and carbohydrate metabolism

ETC-1002 (8-hydroxy-2,2,14,14-tetramethylpentadecanedioic acid) is a novel investigational drug being developed for the treatment of dyslipidemia and other cardio-metabolic risk factors. The hypolipidemic, anti-atherosclerotic, anti-obesity, and glucose-lowering properties of ETC-1002, characterized in preclinical disease models, are believed to be due to dual inhibition of sterol and fatty acid synthesis and enhanced mitochondrial long-chain fatty acid β-oxidation. However, the molecular mechanism(s) mediating these activities remained undefined. Studies described here show that ETC-1002 free acid activates AMP-activated protein kinase in a Ca(2+)/calmodulin-dependent kinase β-independent and liver kinase β 1-dependent manner, without detectable changes in adenylate energy charge. Furthermore, ETC-1002 is shown to rapidly form a CoA thioester in liver, which directly inhibits ATP-citrate lyase. These distinct molecular mechanisms are complementary in their beneficial effects on lipid and carbohydrate metabolism in vitro and in vivo. Consistent with these mechanisms, ETC-1002 treatment reduced circulating proatherogenic lipoproteins, hepatic lipids, and body weight in a hamster model of hyperlipidemia, and it reduced body weight and improved glycemic control in a mouse model of diet-induced obesity. ETC-1002 offers promise as a novel therapeutic approach to improve multiple risk factors associated with metabolic syndrome and benefit patients with cardiovascular disease.

AMP-activated protein kinase: an emerging drug target to regulate imbalances in lipid and carbohydrate metabolism to treat cardio-metabolic diseases

The adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor of energy metabolism at the cellular as well as whole-body level. It is activated by low energy status that triggers a switch from ATP-consuming anabolic pathways to ATP-producing catabolic pathways. AMPK is involved in a wide range of biological activities that normalizes lipid, glucose, and energy imbalances. These pathways are dysregulated in patients with metabolic syndrome (MetS), which represents a clustering of major cardiovascular risk factors including diabetes, lipid abnormalities, and energy imbalances. Clearly, there is an unmet medical need to find a molecule to treat alarming number of patients with MetS. AMPK, with multifaceted activities in various tissues, has emerged as an attractive drug target to manage lipid and glucose abnormalities and maintain energy homeostasis. A number of AMPK activators have been tested in preclinical models, but many of them have yet to reach to the clinic. This review focuses on the structure-function and role of AMPK in lipid, carbohydrate, and energy metabolism. The mode of action of AMPK activators, mechanism of anti-inflammatory activities, and preclinical and clinical findings as well as future prospects of AMPK as a drug target in treating cardio-metabolic disease are discussed.

Abstract 465: ETC-1002, a Novel Dicarboxylic Fatty Acid Analog, Inhibits Inflammatory Response in Primary Human Monocyte-Derived Macrophages as Well as in Adipose Tissue of Insulin-Resistant Mice via AMPK-Dependent Mechanisms

ETC-1002, a small molecule regulator of imbalances in lipid and carbohydrate metabolism, is an investigational drug currently in Phase 2 development to treat dyslipidemia and other cardiometabolic risk factors. In hyperlipidemic LDL receptor-deficient mice, robust antiatherosclerotic activities of ETC-1002 coincided with reduced levels of inflammatory markers in mouse atheroma. To further investigate anti-inflammatory properties of ETC-1002, human monocyte-derived macrophages (MDMs) differentiated in autologous serum were stimulated with 100 ng/ml of LPS in the absence or presence of the 10 μM and 30 μM of ETC-1002. TLR4-mediated activation of downstream kinases as well as the production of pro-inflammatory mediators were assessed with phosphokinase and protein arrays. Lower levels of JNK, cJUN, p38 and ERK phosphorylation in cells treated with ETC-1002 were consistent with reduced production of pro-inflammatory cytokines (TNF-α, IL-6, IL-8 and MIP1α) and chemokines (CXCL10, CXCL1, CCL2 and CCL5). ETC-1002 at 30 mg/kg dose largely diminished thioglycolate-induced homing of neutrophils and macrophages into the mouse peritoneal cavity, supporting the inhibitory effect of ETC-1002 on leukocyte chemotactic and inflammatory activity. Furthermore, in a mouse model of diet-induced obesity and insulin resistance, epididymal fat pad mass and IL-6 release by inflamed adipose tissue were significantly attenuated (by 32% and 80% respectively) in animals treated with ETC-1002. Importantly, enhanced levels of AMPK phosphorylation, changes in intracellular energy charge coupled with reduced basal rates of sterol and fatty acid synthesis by human MDMs strongly supported AMPK-dependent anti-inflammatory effects of ETC-1002. Thus, our data suggest that ETC-1002, via stimulation of AMPK activity, may provide additional clinical benefits for patients with metabolic syndrome by reducing systemic inflammation and other cardiometabolic abnormalities linked to vascular disease.

Abstract 292: ETC-1002 Reduces Body Weight Gain and Hepatic Triglyceride Content and Improves Glycemic Control in a Mouse Model of Diet-Induced Obesity

ETC-1002 is an investigational drug currently in Phase 2 clinical development to treat dyslipidemia and other cardiometabolic risk factors. Previously, ETC-1002 prevented hyperlipidemia and atherosclerosis in rodent models; and improved hepatic triglycerides (TG) as well as fasting blood glucose and insulin in the KKA y insulin resistant mouse model via putative mechanisms including activation of AMP-activated protein kinase. In the present study we investigated the effect of ETC-1002 on body weight, hepatic TG and insulin sensitivity in a diet-induced obese (DIO) mouse model. C57BL/6 mice were fed a 60% high-fat diet beginning at 11 weeks of age. At 12 weeks of age mice were assigned to treatment groups and administered vehicle or ETC-1002 at 3, 10, or 30 mg/kg/day for 9 weeks. A separate cohort of mice was maintained on standard rodent chow diet throughout the study as a comparator. Food consumption, body weight, hepatic TG content, fasting blood glucose, fasting plasma insulin, insulin tolerance tests, and glucose tolerance tests were measured. Mice developed obesity, hyperinsulinemia, mild hyperglycemia and elevated hepatic triglycerides in response to the high-fat diet. ETC-1002 results were dose-dependent and statistically significant at doses of 10 and 30 mg/kg/day. ETC-1002 attenuated body weight gain 8% and 15% with no effect on food consumption. Body weight changes were associated with 12% and 32% decreases in epididymal fat pad mass. Hepatic TG content was also reduced with ETC-1002 by 34% and 46%; respectively. ETC-1002 treatment reduced fasting blood glucose 11% and 16%; plasma insulin 80% and 95%; and resulted in significant improvements in insulin tolerance tests (19% and 22% reduction in AUC) with modestly improved glucose tolerance (not significant). In an intervention study with a 12 week lead-in on high-fat diet, comparable effects on body weight, hepatic TG, and insulin sensitivity were observed. In summary, ETC-1002 reduced obesity and hepatic TG and improved glycemic parameters in a high-fat fed diet-induced mouse model of disease. The present data in the DIO mouse, combined with previously reported efficacy in rodent models supports ETC-1002 as a regulator of imbalances in lipid and carbohydrate metabolism.

HDL therapy for the acute treatment of atherosclerosis

Although pharmacologic intervention to treat atherosclerosis originally focused on lowering LDL-cholesterol levels as a therapeutic target, a number of intervention trials have also highlighted the powerful effect of elevating HDL-cholesterol levels to reduce cardiovascular morbidity and mortality. Although the mechanism(s) by which HDL beneficially alters the atherosclerotic disease process is (are) still unknown, it is presumed that high levels of HDL facilitate the efflux of cholesterol from the arterial wall, thereby enhancing the transport of cholesterol and other lipids from arteries back to the liver for biliary excretion as fecal sterols and bile acids. It has therefore been hypothesized that through a rapid facilitation of HDL mediated cholesterol efflux from arteries by infusion of synthetic apolipoprotein A-I (apoA-I)/phospholipid (A-I/PL) complexes, HDL therapy could have an acute therapeutic application to treat cardiovascular disease at the site of action, namely the vulnerable, unstable atherosclerotic plaque. Single high dose infusions and repeated injections of lower doses of apoA-I variants or mimetics complexed to phospholipids have produced remarkable effects on the progression and regression of atherosclerosis in animal models. The positive results of these preclinical experiments have compelled researchers to perform exploratory studies in human subjects in which reconstituted HDL and synthetic A-I/PL complexes are infused through a peripheral vein. These clinical studies are testing the hypothesis and the potential use of synthetic HDL as a new treatment modality for acute coronary syndromes. Given that there is an unmet medical need for new and more effective therapies to elevate HDL-cholesterol levels and improve HDL function, a historical review, update and discussion of the preclinical and clinical studies which support the use of HDL therapy for reducing cardiovascular morbidity and mortality is warranted.

Recombinant apolipoprotein A-I(Milano) infusion into rabbit carotid artery rapidly removes lipid from fatty streaks

Apolipoprotein A-I(Milano) (AIM), a natural variant of human apolipoprotein A-I, confers to carriers a significant protection against vascular disease. In previous studies, administration of recombinant AIM-phospholipid (AIM-PL) complexes to hypercholesterolemic rabbits markedly inhibited neointimal formation after arterial injury; moreover, repeated injections of AIM-PL in apoE-deficient mice significantly reduced atherosclerosis progression. The objective of the present study was to determine if a single localized infusion of AIM-PL complexes administered directly to atheromatous lesions could promote plaque regression. Lipid-rich, atheromatous plaques were generated at both common carotid arteries of 25 rabbits by applying a perivascular electric injury, followed by 1.5% cholesterol diet for 90 days. Rabbits were infused with either saline, phospholipid vesicles, or 3 different AIM-PL doses (250, 500, or 1000 mg of protein) delivered through an intravascular ultrasound (IVUS) catheter positioned at the origin of the right carotid. The lesions at the left carotid artery were therefore exposed to the agents systemically. Infusion of AIM-PL at the 2 highest doses caused reduction of right carotid artery plaque area by the end a 90-minute infusion as assessed by IVUS analysis. Plaque area regression was confirmed by histology in carotid arteries receiving direct (500 and 1000 mg doses) and systemic (500 mg dose) delivery, 72 hours after the start of the treatment. Plaque lipid content was associated with significant and similar decreases in Oil Red O staining in both arteries. These results suggest AIM-PL complexes enhanced lipid removal from arteries is the mechanism responsible for the observed plaque changes.

Atorvastatin and simvastatin have distinct effects on hydroxy methylglutaryl-CoA reductase activity and mRNA abundance in the guinea pig

The effects of atorvastatin and simvastatin on hydroxy methylglutaryl (HMG)-CoA reductase activity and mRNA abundance were studied in guinea pigs randomized to three groups: untreated animals and those treated with 20 mg/kg of atorvastatin or simvastatin. Guinea pigs were fasted for 0, 6, 12, or 18 h in an attempt to remove the drug from their systems. Reductase activity and mRNA levels were analyzed after each time point. Reductase inhibitor treatment resulted in 50-62% lower cholesterol concentrations compared to untreated guinea pigs (P < 0.0001), while plasma triacylglycerol (TAG) concentrations did not differ among groups. Plasma cholesterol and TAG were 50-70% lower after 18 h fasting in the three groups (P < 0.001). In the nonfasting state, simvastatin and atorvastatin treatment did not affect HMG-CoA reductase activity compared with untreated animals. However, after 6 h of fasting, simvastatin-treated guinea pigs had higher HMG-CoA reductase activity than untreated animals (P < 0.01), suggesting that the drug had been removed from the enzyme. In contrast, atorvastatin-treated guinea pigs maintained low enzyme activity even after 18 h of fasting. Further, HMG-CoA reductase mRNA abundance was increased by sevenfold after atorvastatin treatment and by twofold after simvastatin treatment (P < 0.01). These results suggest that simvastatin and atorvastatin have different half-lives, which may affect HMG-CoA reductase mRNA levels. The increase in reductase activity by simvastatin during fasting could be related to an effect of this statin in stabilizing the enzyme. In contrast, atorvastatin, possibly due to its longer half-life, prolonged inhibition of HMG-CoA reductase activity and resulted in a greater increase in mRNA synthesis.

The magnitude of decrease in hepatic very low density lipoprotein apolipoprotein B secretion is determined by the extent of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibition in miniature pigs

It has been postulated that the rate of hepatic very low density lipoprotein (VLDL) apolipoprotein (apo) B secretion is dependent upon the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. To test this hypothesis in vivo, apoB kinetic studies were carried out in miniature pigs before and after 21 days treatment with high-dose (10 mg/kg/day), atorvastatin (A) or simvastatin (S) (n = 5). Pigs were fed a diet containing fat (34% of calories) and cholesterol (400 mg/day; 0.1%). Statin treatment decreased plasma total cholesterol [31 (A) vs. 20% (S)] and low density lipoprotein (LDL) cholesterol concentrations [42 (A) vs. 24% (S)]. Significant reductions in plasma total triglyceride (46%) and VLDL triglyceride (50%) concentrations were only observed with (A). Autologous [131I]VLDL, [125I]LDL, and [3H]leucine were injected simultaneously, and apoB kinetic parameters were determined by triple-isotope multicompartmental analysis using SAAM II. Statin treatment decreased the VLDL apoB pool size [49 (A) vs. 24% (S)] and the hepatic VLDL apoB secretion rate [50 (A) vs. 33% (S)], with no change in the fractional catabolic rate (FCR). LDL apoB pool size decreased [39 (A) vs. 26% (S)], due to reductions in both the total LDL apoB production rate [30 (A) vs. 21% (S)] and LDL direct synthesis [32 (A) vs. 23% (S)]. A significant increase in the LDL apoB FCR (15%) was only seen with (A). Neither plasma VLDL nor LDL lipoprotein compositions were significantly altered. Hepatic HMG-CoA reductase was inhibited to a greater extent with (A), when compared with (S), as evidenced by 1) a greater induction in hepatic mRNA abundances for HMG-CoA reductase (105%) and the LDL receptor (40%) (both P < 0.05); and 2) a greater decrease in hepatic free (9%) and esterified cholesterol (25%) (both P < 0.05). We conclude that both (A) and (S) decrease hepatic VLDL apoB secretion, in vivo, but that the magnitude is determined by the extent of HMG-CoA reductase inhibition.

Hypocholesterolemic effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors in the guinea pig: atorvastatin versus simvastatin

Male Hartley guinea pigs were fed a hypercholesterolemic diet rich in lauric and myristic acids with 0, 10, or 20 mg/kg of simvastatin or atorvastatin for 21 days. Atorvastatin and simvastatin resulted in a lowering of plasma low-density lipoprotein (LDL) cholesterol in a dose-dependent manner by an average of 48 and 61% with 10 and 20 mg/kg, respectively. Both statins were equally effective in lowering plasma LDL cholesterol and apolipoprotein B (apo-B) levels. Atorvastatin and simvastatin treatments yielded LDL particles that differed in composition from the control. Due to the relevance of LDL oxidation and cholesteryl ester transfer in plasma to the progression of atherosclerosis, these parameters were analyzed after statin treatment. Atorvastatin and simvastatin treatment decreased the susceptibility of LDL particles to oxidation by 95% as determined by the formation of thiobarbituric acid reactive substances. An 80% decrease in the transfer of cholesteryl ester between high-density lipoprotein (HDL) and the apo-B-containing lipoproteins was observed after simvastatin and atorvastatin treatment. In addition, statin effects on plasma LDL transport were studied. Simvastatin- and atorvastatin-treated guinea pigs exhibited 125 and 175% faster LDL fractional catabolic rates, respectively, compared with control animals. No change in LDL apo-B flux was induced by either treatment; however, LDL apo-B pool size was reduced after statin treatment. Hepatic microsomal free cholesterol was lower in the atorvastatin and simvastatin groups. However, only atorvastatin treatment resulted in an 80% decrease of acyl-CoA:cholesterol acyltransferase activity (P < 0.001). In summary, atorvastatin and simvastatin had similar LDL cholesterol lowering properties, but these drugs modified LDL transport and hepatic cholesterol metabolism differently.

9-cis retinoic acid induces monocyte chemoattractant protein-1 secretion in human monocytic THP-1 cells

Monocyte migration and activation are regulated by monocyte chemoattractant protein-1 (MCP-1). Prior studies have shown MCP-1 expression is modulated by a variety of ligands that act through extracellular receptors. In the current study, we show 9-cis retinoic acid (RA), a ligand for the nuclear hormone receptor retinoid X receptor (RXR) and retinoic acid receptor (RAR), markedly induces the expression of MCP-1. In human THP-1 monocytic leukemia cells cultured with RA (0.05 to 500 nmol/L), MCP-1 expression was induced rapidly, significantly, and dose-dependently by as much as 165-fold. MCP-1 RNA level was also increased in RA-treated cells. Expression of PPARgamma, a heterodimer partner of RXR, is also markedly induced by RA in THP-1 cells. However, BRL49653, a PPARgamma ligand, failed to induce MCP-1 secretion either alone or to modify the expression level induced by RA. In contrast, BRL49653 significantly increased MCP-1 (biotinylated MCP-1) binding to THP-1 cells, whereas RA had no effect. Other peroxisome proliferator activated receptor (PPAR) ligands, 15d-PGJ(2) and troglitazone (PPARgamma), Wy14,643 (PPARalpha), and PD195599 (PPARbeta) inhibited the induction of MCP-1 by RA. RA's effect on MCP-1 expression in human elutriated monocytes were similar to that observed in the THP-1 cells. These studies identify RA as a nuclear signal for MCP-1 induction in undifferentiated human monocytic cells. These studies also suggest monocyte MCP-1 expression induced through RA may modulate cell migration.

Inhibition of ACAT by avasimibe decreases both VLDL and LDL apolipoprotein B production in miniature pigs

An orally bioavailable acyl coenzyme A:cholesterol acyltransferase (ACAT) inhibitor, avasimibe (CI-1011), was used to test the hypothesis that inhibition of cholesterol esterification, in vivo, would reduce hepatic very low density (VLDL) apolipoprotein (apo) B secretion into plasma. ApoB kinetic studies were carried out in 10 control miniature pigs, and in 10 animals treated with avasimibe (10 mg/kg/d, n = 6; 25 mg/kg/d, n = 4). Pigs were fed a diet containing fat (34% of calories) and cholesterol (400 mg/d; 0.1%). Avasimibe decreased the plasma concentrations of total triglyceride, VLDL triglyceride, and VLDL cholesterol by 31;-40% 39-48%, and 31;-35%, respectively. Significant reductions in plasma total cholesterol (35%) and low density lipoprotein (LDL) cholesterol (51%) concentrations were observed only with high dose avasimibe. Autologous 131I-labeled VLDL, 125I-labeled LDL, and [3H]leucine were injected simultaneously into each pig and apoB kinetic data were analyzed using multicompartmental analysis (SAAM II). Avasimibe decreased the VLDL apoB pool size by 40;-43% and the hepatic secretion rate of VLDL apoB by 38;-41%, but did not alter its fractional catabolism. Avasimibe decreased the LDL apoB pool size by 13;-57%, largely due to a dose-dependent 25;-63% in the LDL apoB production rate. Hepatic LDL receptor mRNA abundances were unchanged, consistent with a marginal decrease in LDL apoB FCRs. Hepatic ACAT activity was decreased by 51% (P = 0.050) and 68% (P = 0.087) by low and high dose avasimibe, respectively. The decrease in total apoB secretion correlated with the decrease in hepatic ACAT activity (r = 0.495; P = 0.026). We conclude that inhibition of hepatic ACAT by avasimibe reduces both plasma VLDL and LDL apoB concentrations, primarily by decreasing apoB secretion.

Select 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors vary in their ability to reduce egg yolk cholesterol levels in laying hens through alteration of hepatic cholesterol biosynthesis and plasma VLDL composition

The inability to markedly attenuate cholesterol levels in chicken eggs has led to speculation that cholesterol is essential for yolk formation and that egg production would cease when yolk cholesterol deposition was inadequate for embryonic survival. However, this critical level hypothesis remains unproven. Here, we determine the relative responsiveness of laying hens to three select inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), the rate-limiting enzyme of cholesterol biosynthesis. A control diet, either alone or supplemented with one of two dietary levels (0.03 or 0.06%) of atorvastatin, lovastatin, or simvastatin, was fed to White Leghorn hens for 5 wk. Liver cholesterol concentrations (mg/g tissue) were decreased (P </= 0.05) by each HMGR inhibitor; however, total liver cholesterol (mg) did not differ among treatments. Microsomal hepatic HMGR activities were increased one- to twofold in all HMGR inhibitor-treated groups, while HMGR mRNA levels were unaffected. Diameters of plasma VLDL particles, the main cholesterol-carrying yolk precursor macromolecules, were reduced (P </= 0.05) only in hens fed 0.06% atorvastatin, and the particles contained 38% less total cholesterol (P </= 0.05) than controls. Plasma total cholesterol concentrations were lowered (P </= 0.05) by both doses of atorvastatin (-56, -63%) and simvastatin (-36,-45%). Egg cholesterol contents were maximally reduced by 46% (P </= 0.05), 7% (P > 0.05), and 22% (P </= 0.05) in hens fed the 0.06% level of atorvastatin, lovastatin, and simvastatin, respectively, while overall egg production [-19% (P </= 0.05), +4% (P > 0.05), and -3% (P > 0.05)], was much less affected. We concluded that cholesterol per se may not be an obligatory component for yolk formation in chickens and, as such, may be amenable to further pharmacological manipulation

ApoB100 secretion from HepG2 cells is decreased by the ACAT inhibitor CI-1011: an effect associated with enhanced intracellular degradation of ApoB

The concept that hepatic cholesteryl ester (CE) mass and the rate of cholesterol esterification regulate hepatocyte assembly and secretion of apoB-containing lipoproteins remains controversial. The present study was carried out in HepG2 cells to correlate the rate of cholesterol esterification and CE mass with apoB secretion by CI-1011, an acyl CoA:cholesterol acyltransferase (ACAT) inhibitor that is known to decrease apoB secretion, in vivo, in miniature pigs. HepG2 cells were incubated with CI-1011 (10 nmol/L, 1 micromol/L, and 10 micromol/L) for 24 hours. ApoB secretion into media was decreased by 25%, 27%, and 43%, respectively (P<0.0012). CI-1011 (10 micromol/L) inhibited HepG2 cell ACAT activity by 79% (P<0.002) and cellular CE mass by 32% (P<0.05). In contrast, another ACAT inhibitor, DuP 128 (10 micromol/L), decreased cellular ACAT activity and CE mass by 85% (P<0.002) and 42% (P=0.01), respectively, but had no effect on apoB secretion into media. To characterize the reduction in apoB secretion by CI-1011, pulse-chase experiments were performed and analyzed by multicompartmental modelling using SAAM II. CI-1011 did not affect the synthesis of apoB or albumin. However, apoB secretion into the media was decreased by 42% (P=0.019). Intracellular apoB degradation increased proportionately (P=0.019). The secretion of albumin and cellular reuptake of labeled lipoproteins were unchanged. CI-1011 and DuP 128 did not affect apoB mRNA concentrations. These results show that CI-1011 decreases apoB secretion by a mechanism that involves an enhanced intracellular degradation of apoB. This study demonstrates that ACAT inhibitors can exert differential effects on apoB secretion from HepG2 cells that do not reflect their efficacy in inhibiting cholesterol esterification.

Human serum paraoxonase (PON 1) is inactivated by oxidized low density lipoprotein and preserved by antioxidants

Human serum paraoxonase (PON1) can protect low density lipoprotein (LDL) from oxidation induced by either copper ion or by the free radical generator azo bis amidinopropane hydrochloride (AAPH). During LDL oxidation in both of these systems, a time-dependent inactivation of PON arylesterase activity was observed. Oxidized LDL (Ox-LDL) produced by lipoprotein incubation with either copper ion or with AAPH, indeed inactivated PON arylesterase activity by up to 47% or 58%, respectively. Three possible mechanisms for PON inactivation during LDL oxidation were considered and investigated: copper ion binding to PON, free radical attack on PON, and/or the effect of lipoprotein-associated peroxides on the enzyme. As both residual copper ion and AAPH are present in the Ox-LDL preparations and could independently inactivate the enzyme, the effect of minimally oxidized (Ox-LDL produced by LDL storage in the air) on PON activity was also examined. Oxidized LDL, as well as oxidized palmitoyl arachidonoyl phosphatidylcholine (PAPC), lysophosphatidylcholine (LPC, which is produced during LDL oxidation by phospholipase A2-like activity), and oxidized cholesteryl arachidonate (Ox-CA), were all potent inactivators of PON arylesterase activity (PON activity was inhibited by 35%-61%). PON treatment with Ox-LDL (but not with native LDL), or with oxidized lipids, inhibited its arylesterase activity and also reduced the ability of the enzyme to protect LDL against oxidation. PON Arylesterase activity however was not inhibited when PON was pretreated with the sulfhydryl blocking agent, p-hydroxymercurybenzoate (PHMB). Similarly, on using recombinant PON in which the enzyme's only free sulfhydryl group at the position of cysteine-284 was mutated, no inactivation of the enzyme arylesterase activity by Ox-LDL could be shown. These results suggest that Ox-LDL inactivation of PON involves the interaction of oxidized lipids in Ox-LDL with the PON's free sulfhydryl group. Antioxidants such as the flavonoids glabridin or quercetin, when present during LDL oxidation in the presence of PON, reduced the amount of lipoprotein-associated lipid peroxides and preserved PON activities, including its ability to hydrolyze Ox-LDL cholesteryl linoleate hydroperoxides. We conclude that PON's ability to protect LDL against oxidation is accompanied by inactivation of the enzyme. PON inactivation results from an interaction between the enzyme free sulfhydryl group and oxidized lipids such as oxidized phospholipids, oxidized cholesteryl ester or lysophosphatidylcholine, which are formed during LDL oxidation. The action of antioxidants and PON on LDL during its oxidation can be of special benefit against atherosclerosis since these agents reduce the accumulation of Ox-LDL by a dual effect: i.e. prevention of its formation, and removal of Ox-LDL associated oxidized lipids which are generated during LDL oxidation.

Lipoprotein lipase greatly enhances the retention of lipoprotein(a) to endothelial cell-matrix

The trapping of apolipoprotein (apo)B containing lipoproteins within the arterial subendothelial matrix (ECM) is an early event in atherosclerosis. When lipoprotein lipase, a constituent of the ECM, is prebound to ECM both LDL and oxidized LDL binding is greatly enhanced. In this study we compared the binding of lipoprotein(a) (Lp(a)), a lipoprotein correlated with atherosclerosis and restenosis, to ECM in the presence of varying concentrations of LPL. Without LPL, Lp(a) binding was low and non-saturable. In the presence of LPL, Lp(a) retention increased from 2.7 x 10(-7) to 1.13 x 10(-4) nmoles. Scatchard analysis demonstrated that the affinities of both Lp(a) and LDL to lipase were similar. In competition experiments, LDL, apoE, polymers of lysine and arginine were all capable of preventing the lipase specific [125I]Lp(a) retention. However, neither collagen nor fibronectin were capable of blocking or displacing [125I]Lp(a) from the lipase bound to ECM. In a separate set of experiments, when ECM was not saturated with lipase, both fibronectin and collagen (at 10-fold protein excess) prevented approximately 40% of total [125I]Lp(a) retention to ECM. These data suggest, in the absence of lipase, apo(a) may regulate the binding of Lp(a) to ECM. Whereas, lipase enhanced the binding of Lp(a) to ECM, most probably through the apoB moiety of the Lp(a) particle.

Induction of PPARgamma1 expression in human THP-1 monocytic leukemia cells by 9-cis-retinoic acid is associated with cellular growth suppression

9-cis-Retinoic acid (RA) and peroxisome proliferator activated receptor gamma (PPARgamma) regulates cellular growth and differentiation. In THP-1 cells, a human monocytic leukemia cell line, RA markedly induced PPARgamma1 RNA, nuclear PPARgamma1 protein and suppressed cell growth. The PPARgamma ligand, BRL49653 enhanced RA's growth suppression ability. With BRL49653 alone, THP-1 cell growth was only marginally suppressed. Cell cycle analysis revealed the G1 phase cell population was significantly increased when cells were treated with both ligands. RA induced growth suppression did not differentiate the THP-1 cells to macrophages. Phorbol ester (PMA) induced differentiation of cells to macrophage also induced PPARgamma1 expression, however when RA is given either simultaneously or sequentially to these cells, no further increase in expression of the nuclear receptor was observed. Overall, these data suggest RA induction of PPARgamma1 may block cell growth and may have application for the treatment of proliferative diseases.

Atorvastatin and gemfibrozil metabolites, but not the parent drugs, are potent antioxidants against lipoprotein oxidation

Increased atherosclerosis risk in hyperlipidemic patients may be a result of the enhanced oxidizability of their plasma lipoproteins. We have previously shown that hypocholesterolemic drug therapy, including the 3-hydroxy-3-methyl-glutaryl CoenzymeA (HMG-CoA) reductase inhibitors, and the hypotriglyceridemic drug bezafibrate, significantly reduced the enhanced susceptibility to oxidation of low density lipoprotein (LDL) isolated from hyperlipidemic patients. Although this antioxidative effect could not be obtained in vitro with all of these drugs, the active drug metabolites, which are formed in vivo, could affect lipoprotein oxidizability. We thus sought to analyze the effect of atorvastatin and gemfibrozil, as well as specific hydroxylated metabolites, on the susceptibility of LDL, very low density lipoprotein (VLDL), and high density lipoprotein (HDL) to oxidation. LDL oxidation induced by either copper ions (10 microM CuSO4), by the free radical generator system 2'-2'-azobis 2-amidino propane hydrochloride (5 mM AAPH), or by the J-774A.1 macrophage-like cell line, was not inhibited by the parent forms of atorvastatin or gemfibrozil, but was substantially inhibited (57-97%), in a concentration-dependent manner, by pharmacological concentrations of the o-hydroxy and the p-hydroxy metabolites of atorvastatin, as well as by the p-hydroxy metabolite (metabolite I) of gemfibrozil. On using the atorvastatin o-hydroxy metabolite and gemfibrozil metabolite I in combination an additive inhibitory effect on LDL oxidizability was found. Similar inhibitory effects (37-96%) of the above metabolites were obtained for the susceptibility of VLDL and HDL to oxidation in the oxidation systems outlined above. The inhibitory effects of these metabolites on LDL, VLDL, and HDL oxidation could be related to their free radical scavenging activity, as well as (mainly for the gemfibrozil metabolite I) to their metal ion chelation capacities. In addition, inhibition of HDL oxidation was associated with the preservation of HDL-associated paraoxonase activity. We conclude that atorvastatin hydroxy metabolites, and gemfibrozil metabolite I possess potent antioxidative potential, and as a result protect LDL, VLDL, and HDL from oxidation. We hypothesize that in addition to their beneficial lipid regulating activity, specific metabolites of both drugs may also reduce the atherogenic potential of lipoproteins through their antioxidant properties.

Paraoxonase inhibits high-density lipoprotein oxidation and preserves its functions. A possible peroxidative role for paraoxonase

HDL levels are inversely related to the risk of developing atherosclerosis. In serum, paraoxonase (PON) is associated with HDL, and was shown to inhibit LDL oxidation. Whether PON also protects HDL from oxidation is unknown, and was determined in the present study. In humans, we found serum HDL PON activity and HDL susceptibility to oxidation to be inversely correlated (r2 = 0.77, n = 15). Supplementing human HDL with purified PON inhibited copper-induced HDL oxidation in a concentration-dependent manner. Adding PON to HDL prolonged the oxidation lag phase and reduced HDL peroxide and aldehyde formation by up to 95%. This inhibitory effect was most pronounced when PON was added before oxidation initiation. When purified PON was added to whole serum, essentially all of it became HDL-associated. The PON-enriched HDL was more resistant to copper ion-induced oxidation than was control HDL. Compared with control HDL, HDL from PON-treated serum showed a 66% prolongation in the lag phase of its oxidation, and up to a 40% reduction in peroxide and aldehyde content. In contrast, in the presence of various PON inhibitors, HDL oxidation induced by either copper ions or by a free radical generating system was markedly enhanced. As PON inhibited HDL oxidation, two major functions of HDL were assessed: macrophage cholesterol efflux, and LDL protection from oxidation. Compared with oxidized untreated HDL, oxidized PON-treated HDL caused a 45% increase in cellular cholesterol efflux from J-774 A.1 macrophages. Both HDL-associated PON and purified PON were potent inhibitors of LDL oxidation. Searching for a possible mechanism for PON-induced inhibition of HDL oxidation revealed PON (2 paraoxonase U/ml)-mediated hydrolysis of lipid peroxides (by 19%) and of cholesteryl linoleate hydroperoxides (by 90%) in oxidized HDL. HDL-associated PON, as well as purified PON, were also able to substantially hydrolyze (up to 25%) hydrogen peroxide (H2O2), a major reactive oxygen species produced under oxidative stress during atherogenesis. Finally, we analyzed serum PON activity in the atherosclerotic apolipoprotein E-deficient mice during aging and development of atherosclerotic lesions. With age, serum lipid peroxidation and lesion size increased, whereas serum PON activity decreased. We thus conclude that HDL-associated PON possesses peroxidase-like activity that can contribute to the protective effect of PON against lipoprotein oxidation. The presence of PON in HDL may thus be a major contributor to the antiatherogenicity of this lipoprotein.

A novel compound that elevates high density lipoprotein and activates the peroxisome proliferator activated receptor

In the current studies we describe the effects of PD 72953 and related compounds on lipoprotein levels in chow-fed male rats. After 2 weeks, 10 mg/kg of PD 72953 daily was as effective as 100 mg/kg gemfibrozil for elevating HDL-cholesterol. At 100 mg/kg, PD 72953 further elevated HDL-cholesterol to 232% of control levels, and was associated with increased HDL size and plasma apoE (169% of control), despite no change in hepatic apoE mRNA. ApoA-I rose transiently (at 1 week), but by 2 weeks only apoE remained elevated. PD 72953 dose-dependently reduced plasma apoB, VLDL-cholesterol, LDL-cholesterol, and triglyceride. Hepatic apoC-III mRNA reduction parallelled triglyceride lowering. After 1 week, 30 and 100 mg/kg per day PD 72953 reduced plasma apo-CIII levels by 30 and 34%, and triglycerides by 60 and 83%, respectively. PD 72953 treatment had no effect on triglyceride production rates; however, 125I-labeled VLDL apoB disappearance was enhanced. We compared PD 72953 to a structurally similar diacid, PD 69405, that also reduced VLDL and LDL, but had no effect on HDL elevation. Compared to PD 72953, PD 69405 further accelerated 125I-labeled VLDL apoB disappearance, decreased triglyceride production, and elevated the ratio of post-heparin hepatic to lipoprotein lipase activity. Whole animal studies, transient transfection studies in HepG2 cells, and chimeric receptor studies in kidney 293 cells suggest that PD 72953 is a ligand for the peroxisomal proliferation activated receptor alpha (PPARalpha), and PPARgamma. Overall, PD 72953 may act through a peroxisomal proliferation activated receptor and result in plasma triglycerides and apoB-containing lipoprotein reduction, while also raising HDL cholesterol. Reduced apoC-III may allow triglyceride-rich remnants to more efficiently bind and present substrate to peripheral tissue lipoprotein lipase, and therefore allow enhanced shedding of remnant phospholipid surface for HDL production.

Attenuation of plasma low density lipoprotein cholesterol by select 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors in mice devoid of low density lipoprotein receptors

Low density lipoprotein (LDL) reduction independent of LDL receptor regulation was investigated using HMG-CoA reductase inhibitors in LDL receptor-deficient mice. In males, LDL cholesterol dose-dependently decreased with atorvastatin treatment after 1 week. As untreated mice grew older, their LDL cholesterol progressively rose above basal levels, but was quelled with atorvastatin treatment. In females, atorvastatin treatment time-dependently decreased LDL cholesterol levels and induced hepatic HMG-CoA reductase activity. Unlike males, cholesterol-lowering effects of the drug were sustained in females. Lovastatin, simvastatin, and pravastatin also reduced total and LDL cholesterol; however, additional studies in females demonstrated that atorvastatin caused the greatest dose-dependent and sustained effect after 2 weeks. In females, hepatic HMG-CoA reductase mRNA inversely correlated with LDL cholesterol lowering, with atorvastatin showing the greatest increase in mRNA levels (17.2-fold), followed by lovastatin (10.7-fold), simvastatin (4.1-fold), and pravastatin (2.5-fold). Atorvastatin effects on lipoprotein production were determined after acute (1 day) or chronic (2 week) treatment prior to intraperitoneal injection of Triton WR1339. Acute treatment reduced cholesterol (-29%) and apoB (-16%) secretion, with no change in triglyceride secretion. In contrast, chronic treatment elevated cholesterol (+20%), apoB (+31%), and triglyceride (+57%) secretion. Despite increased cholesterol and apoB secretion, plasma levels were reduced by 51% and 46%, respectively. Overall, under acute or chronic conditions, apoB paralleled cholesterol secretion rates, and triglyceride to cholesterol secretion ratios were elevated by 38% and 32%, respectively. We propose that atorvastatin limits cholesterol for lipoprotein assembly, which is compensated for by triglyceride enrichment. In addition, with either acute or chronic atorvastatin treatment, apoB-100 secretion was blocked, and compensated for by an increased secretion of apoB-48. The apoB-48 particles produced are cleared by LDL receptor-independent mechanisms, with an overall effect of reducing LDL production in these mice. These studies support the idea that HMG-CoA reductase inhibitors modulate lipoprotein levels independent of LDL receptors, and suggest they may have utility in hyperlipidemias caused by LDLreceptor disorders.

Inhibition of HMG-CoA reductase by atorvastatin decreases both VLDL and LDL apolipoprotein B production in miniature pigs

In the present studies, the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor atorvastatin was used to test the hypothesis that inhibition of cholesterol biosynthesis in vivo with a consequent reduction in the availability of hepatic cholesterol for lipoprotein synthesis, would (1) reduce very low density lipoprotein (VLDL) apolipoprotein B (apoB) secretion into the plasma, (2) reduce the conversion of VLDL apoB to LDL apoB, and (3) reduce LDL apoB direct synthesis. ApoB kinetic studies were carried out in six control miniature pigs and in six animals after 21 days of administration of atorvastatin (3 mg/kg per day). Pigs were fed a fat- (34% of calories; polyunsaturated to monounsaturated to saturated ratio, 1:1:1) and cholesterol- (400 mg/d cholesterol; 0.1%; 0.2 mg/kcal) containing pig chow-based diet. Atorvastatin treatment significantly reduced plasma total cholesterol, LDL cholesterol, total triglyceride, and VLDL triglyceride concentrations by 16%, 31%, 19%, and 28%, respectively (P < .01). Autologous 131I-VLDL, 125I-LDL, and [3H]leucine were injected simultaneously into each pig, and apoB kinetic data were analyzed using multicompartmental analysis (SAAM II). The VLDL apoB pool size decreased by 29% (0.46 versus 0.65 mg/kg; P = .002), which was entirely due to a 34% reduction in the VLDL apoB production rate (PR) (1.43 versus 2.19 mg/kg per hour; P = .027). The fractional catabolic rate (FCR) was unchanged. The LDL apoB pool size decreased by 30% (4.74 versus 6.75 mg/kg; P = .0004), which was due to a 22% reduction in the LDL apoB PR (0.236 versus 0.301 mg/kg per hour; P = .004), since the FCR was unchanged. The reduction in LDL apoB PR was primarily due to a 34% decrease in conversion of VLDL apoB to LDL apoB; however, this reduction was not statistically significant (P = .114). Hepatic apoB mRNA abundance quantitated by RNase protection assay was decreased by 13% in the atorvastatin-treated animals (P = .003). Hepatic and intestinal LDL receptor mRNA abundances were not affected. We conclude that inhibition of hepatic HMG-CoA reductase by atorvastatin reduces both VLDL and LDL apoB concentrations, primarily by decreasing apoB secretion into the plasma and not by an increase in hepatic LDL receptor expression. This decrease in apoB secretion may, in part, be due to a reduction in apoB mRNA abundance.

Selective inhibition of tumor necrosis factor-induced vascular cell adhesion molecule-1 gene expression by a novel flavonoid. Lack of effect on transcription factor NF-kappa B

In the present studies, we examined the effect of flavonoids on the endothelial cell expression of adhesion molecules, an early step in inflammation and atherogenesis. Addition of tumor necrosis factor-alpha (TNF) to human aortic endothelial cells (HAECs) led to the induction of vascular cell adhesion molecule-1 (VCAM-1) expression and enhancement in expression of intercellular adhesion molecule-1 (ICAM-1). A flavonoid, 2-(3-amino-phenyl)-8-methoxy-chromene-4-one (PD 098063), markedly inhibited TNF-induced VCAM-1 cell-surface expression in a concentration-dependent fashion with half-maximal inhibition at 19 mumol/L but had no effect on ICAM-1 expression. Another structurally distinct flavonoid, 2-phenyl-chromene-4-one, similarly selectively decreased VCAM-1 expression. The inhibition in cell-surface expression of VCAM-1 by PD 098063 correlated with decreases in steady-state mRNA levels, but there was no effect on ICAM-1 mRNA levels. The decrease in VCAM-1 mRNA levels was not due to changes in mRNA stability but rather resulted from a reduction in the rate of transcription of the gene. However, electrophoretic mobility shift assays using nuclear extracts from TNF-induced HAECs treated with PD 098063 failed to show a decrease in the activation of NF-kappa B, indicating that inhibition of activation of this transcription factor may not be its mode of action. Similarly, PD 098063 did not affect chloramphenicol acetyltransferase reporter gene activity in TNF-inducible minimal VCAM-1 promoter constructs containing two NF-kappa B sites, suggesting that the compound does not affect the transactivation driven by these sites. We conclude that this compound selectively blocks agonist-induced VCAM-1 protein and gene expression in HAECs by NF-kappa B-independent mechanism(s).

Opposite effects of bezafibrate and gemfibrozil in both normal and hypertriglyceridemic rats

Chow and sucrose-fed rats were used as animal models to study the dose-responses of bezafibrate and gemfibrozil in normolipidemic and hypertriglyceridemic states, respectively. Although both drugs lowered plasma triglycerides (TG) to about the same extent in chow-fed rats, gemfibrozil lowered liver TG as well as plasma total and LDL-cholesterol (LDL-C), but elevated HDL-cholesterol (HDL-C) and plasma apo E concentrations. Bezafibrate produced opposite effects, namely, decreased HDL-C, apo E and liver TG, and tended to increase LDL-C. TG lowering for both drugs in chow-fed rats was not due to changes in TG secretion (production) in normal rats but was associated with enhanced LPL activity. In hypertriglyceridemic rats both drugs modestly reduced TG secretion rates about 40% at a dose producing maximal TG lowering, but again, gemfibrozil elevated and bezafibrate lowered HDL-C and apo E. Unlike gemfibrozil, bezafibrate induced the appearance of LDL-C in hypertriglyceridemic rats which was not detected in control animals, and also tended to increase rather than decrease plasma apo B levels. Finally, changes in liver TG concentration (mg/g) in hypertriglyceridemic rats were opposite for these drugs, resulting in significant drug-related differences in liver TG content (mg/organ). From these data we postulate that, although similar with regard to TG lowering activity and mechanisms thereof, gemfibrozil and bezafibrate produce fundamentally different effects on LDL, HDL and apolipoprotein metabolism (apo B and apo E) in rats which may relate to potential differential effects on reverse cholesterol transport and atherogenesis.

Hypocholesterolemic actions of atorvastatin are associated with alterations on hepatic cholesterol metabolism and lipoprotein composition in the guinea pig

Guinea pigs were fed 15% (w/W) fat, high in lauric and myristic acids, a diet known to produce hypercholesterolemia in these animals. The diet was given alone or in combination with four doses of atorvastatin equivalent to 1, 3, 10, and 20 mg/kg per day. Atorvastatin reduced plasma LDL cholesterol concentrations by 46, 50, 53, and 70%, respectively (P < 0.001). Plasma apoB concentrations were reduced by atorvastatin (P < 0.001) and compositional changes occurred in VLDL and LDL with reductions of the relative proportion of cholesteryl ester and increases in triacylglycerol. A reduction in hepatic cholesteryl ester (66%) was observed only with the highest atorvastatin dose (20 mg/kg per day) while microsomal cholesterol was reduced by 30% with 3-20 mg/kg per day. Hepatic ACAT activity was down-regulated and apoB/E receptor number was increased by atorvastatin. In contrast, HMG-CoA reductase activity and cholesterol 7 alpha-hydroxylase were not affected by the drug. VLDL apoB secretion rates were decreased by atorvastatin treatment 59 and 76% with 3 and 20 mg/kg per day, respectively. Nascent VLDL particles were larger after drug treatment, showing an increased number in triacylglycerol molecules. These results support the hypothesis that the plasma LDL lowering induced by atorvastatin is due to a decreased secretion of apoB in combination with an increase of hepatic apoB/E receptors.

Lack of correlation between ACAT mRNA expression and cholesterol esterification in primary liver cells

A partial rabbit cDNA clone (14b) for ACAT has been characterized and used to demonstrate that hepatic and aortic ACAT mRNA14b abundance increased 2-3-fold in rabbits receiving a high fat/high cholesterol-diet compared to chow fed animals (Pape et al. (1995) J. Lipid Res. 36, 823-838). Because of those data we hypothesized that increased hepatic cholesteryl ester mass and synthesis rates in rabbit liver cells are associated with an increase in ACAT mRNA14b levels. To test this hypothesis we altered cellular cholesteryl ester mass and synthesis rates in primary parenchymal and nonparenchymal cells using various extracellular agents and measured the accumulated mass of ACAT mRNA14b. Parenchymal cells incubated with rabbit beta VLDL or mevalonolactone displayed a 6-10-fold increase in cellular cholesteryl ester mass over a three day treatment with no significant changes in cellular free cholesterol, triacylglycerols, or ACAT mRNA14b levels; HMG CoA reductase and LDL receptor mRNA mass decreased initially as a result of cholesteryl ester loading. Treatment of parenchymal cells with CI-976, an ACAT inhibitor, showed a marked reduction in cholesteryl ester synthetic rate compared to beta VLDL controls but displayed no change in ACAT mRNA14b levels. A mixed population of rabbit hepatic nonparenchymal cells was incubated with beta VLDL for 24 h in culture which resulted in a 6-fold increase in cellular cholesteryl ester mass; there was no change in ACAT mRNA14b levels. In an in vivo study, rabbits consuming a high fat/high cholesterol-diet for three weeks showed a 10-fold increase in hepatic cholesteryl ester with no significant changes in ACAT mRNA14b levels. Together these data indicate that rabbit liver cellular cholesteryl ester mass increases of up to 10-fold are not correlated with ACAT mRNA14b changes. Thus, hepatic ACAT mRNA14b expression and cellular cholesterol esterification do not appear to be coordinately regulated at this level of cholesteryl ester loading.

Regulation and immunolocalization of acyl-coenzyme A: cholesterol acyltransferase in mammalian cells as studied with specific antibodies

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the formation of intracellular cholesterol esters in various tissues. We recently reported the cloning and expression of human macrophage ACAT cDNA. In the current study, we report the production of specific polyclonal antibodies against ACAT by immunizing rabbits with the recombinant fusion protein composed of glutathione S-transferase and the first 131 amino acids of ACAT protein. Immunoblot analysis showed that the antibodies cross-reacted with a 50-kDa protein band from a variety of human cell lines. These antibodies immunodepleted more than 90% of detergent-solubilized ACAT activities from six different human cell types, demonstrating that the 50-kDa protein is the major ACAT catalytic component in these cells. In multiple human tissues examined, the antibodies recognized protein bands with various molecular weights. These antibodies also cross-reacted with the ACAT protein in Chinese hamster ovary cells. Immunoblot analysis showed that the ACAT protein contents in human fibroblast cells, HepG2 cells, or Chinese hamster ovary cells were not affected by sterol in the medium, demonstrating that the main mechanism for sterol-dependent regulation of ACAT activity in these cells is not change in ACAT protein content. As revealed by indirect immunofluorescent microscopy, the ACAT protein in tissue culture cells was located in the endoplasmic reticulum. This finding, along with earlier studies, suggests that cholesterol concentration in the endoplasmic reticulum may be the major determinant for regulating ACAT activity in the intact cells.

Hypolipidemic activity of select fibrates correlates to changes in hepatic apolipoprotein C-III expression: a potential physiologic basis for their mode of action

For the last 30 years fibrates have been widely prescribed to treat human dyslipidemia. However, the primary mechanism by which they lower plasma lipid levels is still unknown. Studies with transgenic mice have suggested that changes in apoC-III expression levels have a dramatic influence on plasma triglyceride levels. These results suggested that fibrates could reduce lipid levels by lowering apoC-III gene expression. In the current studies, we sought to determine whether the selected fibrates, bezafibrate, clofibrate, fenofibrate, and gemfibrozil, could reduce hepatic apoC-III mRNA and plasma apoC-III levels. Chow-fed rats were orally gavaged daily with a dosing vehicle alone or with 100 mg/kg of each of the fibrates for 1 week and in addition with gemfibrozil for 2 weeks. Bezafibrate and fenofibrate lowered plasma triglyceride by approximately half and dramatically reduced hepatic apoC-III mRNA and plasma apoC-III levels. In contrast, clofibrate did not reduce plasma triglyceride levels and only partially reduced apoC-III mRNA and plasma protein levels. Gemfibrozil strongly reduced plasma triglyceride levels and had an intermediate but significant effect on apoC-III mRNA and plasma apoC-III levels. Some of the fibrates, especially gemfibrozil also reduced plasma apoC-II levels, an effect that could contribute to the observed triglyceride-lowering effect. In addition, the ratio of plasma apoE to plasma apoC-II plus apoC-III was strongly and inversely correlated with plasma triglyceride levels. As plasma apoE levels were not reduced in gemfibrozil-treated animals, this could also have contributed to the triglyceride-lowering effect of this fibrate. Fibrate-mediated triglyceride lowering was not the result of a decreased apoB or VLDL production and, therefore, suggested an enhanced VLDL remnant catabolism. Our results suggest that the mechanism by which fibrates lower plasma triglycerides is by reducing the level of hepatic apoC-III expression.

Identification of a novel 85-kDa lipoprotein lipase binding protein on human aortic endothelial cell surface

Lipoprotein lipase (LPL), bound to the luminal surface of vascular endothelium catalyzes lipoprotein triglyceride hydrolysis. Studies were performed to identify human aortic endothelial (HAEC) cell-surface proteins having high affinity for LPL. LPL-sepharose affinity chromatography of [35S]O4 labeled HAEC proteins identified a 220-kDa proteoglycan. Ligand blotting of HAEC plasma membrane proteins with LPL revealed two specific binding proteins of MW 116 kDa and 85 kDa, respectively, which were not released from the cell-surface by heparin treatment. Since the 220-kDa and 116-kDa proteins have been reported previously in bovine endothelial cells, we focused on the 85-kDa protein. The 85-kDa protein was not labelled by incubation of the cells with [35S]O4, suggesting that it is not a sulfated proteoglycan. Treatment of HAEC with tunicamycin markedly decreased detection of the 85-kDa protein, suggesting that it is likely a glycoprotein synthesized by HAEC. We conclude that HAEC cell surface has three specific LPL binding proteins, a 220-kDa proteoglycan, a 116-kDa protein and a novel 85-kDa protein.