Direct effect of an acyl-CoA:cholesterol acyltransferase inhibitor, F-1394, on atherosclerosis in apolipoprotein E and low density lipoprotein receptor double knockout mice

Lipid-laden foam cells in the pathology of atherosclerosis: shedding light on new therapeutic targets

INTRODUCTION

Lipid-laden foam cells within atherosclerotic plaques are key players in all phases of lesion development including its progression, necrotic core formation, fibrous cap thinning, and eventually plaque rupture. Manipulating foam cell biology is thus an attractive therapeutic strategy at early, middle, and even late stages of atherosclerosis. Traditional therapies have focused on prevention, especially lowering plasma lipid levels. Despite these interventions, atherosclerosis remains a major cause of cardiovascular disease, responsible for the largest numbers of death worldwide.

AREAS COVERED

Foam cells within atherosclerotic plaques are comprised of macrophages, vascular smooth muscle cells, and other cell types which are exposed to high concentrations of lipoproteins accumulating within the subendothelial intimal layer. Macrophage-derived foam cells are particularly well studied and have provided important insights into lipid metabolism and atherogenesis. The contributions of foam cell-based processes are discussed with an emphasis on areas of therapeutic potential and directions for drug development.

EXERT OPINION

As key players in atherosclerosis, foam cells are attractive targets for developing more specific, targeted therapies aimed at resolving atherosclerotic plaques. Recent advances in our understanding of lipid handling within these cells provide insights into how they might be manipulated and clinically translated to better treat atherosclerosis.

Acyl-Coenzyme A: Cholesterol Acyltransferase (ACAT) in Cholesterol Metabolism: From Its Discovery to Clinical Trials and the Genomics Era

The purification and cloning of the acyl-coenzyme A: cholesterol acyltransferase (ACAT) enzymes and the sterol O-acyltransferase (SOAT) genes has opened new areas of interest in cholesterol metabolism given their profound effects on foam cell biology and intestinal lipid absorption. The generation of mouse models deficient in Soat1 or Soat2 confirmed the importance of their gene products on cholesterol esterification and lipoprotein physiology. Although these studies supported clinical trials which used non-selective ACAT inhibitors, these trials did not report benefits, and one showed an increased risk. Early genetic studies have implicated common variants in both genes with human traits, including lipoprotein levels, coronary artery disease, and Alzheimer’s disease; however, modern genome-wide association studies have not replicated these associations. In contrast, the common SOAT1 variants are most reproducibly associated with testosterone levels.

Tremorgenic Mycotoxins: Structure Diversity and Biological Activity

Indole-diterpenes are an important class of chemical compounds which can be unique to different fungal species. The highly complex lolitrem compounds are confined to Epichloë species, whilst penitrem production is confined to Penicillium spp. and Aspergillus spp. These fungal species are often present in association with pasture grasses, and the indole-diterpenes produced may cause toxicity in grazing animals. In this review, we highlight the unique structural variations of indole-diterpenes that are characterised into subgroups, including paspaline, paxilline, shearinines, paspalitrems, terpendoles, penitrems, lolitrems, janthitrems, and sulpinines. A detailed description of the unique biological activities has been documented where even structurally related compounds have displayed unique biological activities. Indole-diterpene production has been reported in two classes of ascomycete fungi, namely Eurotiomycetes (e.g., Aspergillus and Penicillium) and Sordariomycetes (e.g., Claviceps and Epichloë). These compounds all have a common structural core comprised of a cyclic diterpene skeleton derived from geranylgeranyl diphosphate (GGPP) and an indole moiety derived from tryptophan. Structure diversity is generated from the enzymatic conversion of different sites on the basic indole-diterpene structure. This review highlights the wide-ranging biological versatility presented by the indole-diterpene group of compounds and their role in an agricultural and pharmaceutical setting.

Molecular Imaging of Vulnerable Atherosclerotic Plaques in Animal Models

Atherosclerosis is characterized by intimal plaques of the arterial vessels that develop slowly and, in some cases, may undergo spontaneous rupture with subsequent heart attack or stroke. Currently, noninvasive diagnostic tools are inadequate to screen atherosclerotic lesions at high risk of acute complications. Therefore, the attention of the scientific community has been focused on the use of molecular imaging for identifying vulnerable plaques. Genetically engineered murine models such as ApoE^−/− and ApoE^−/−Fbn1C1039G^+/− mice have been shown to be useful for testing new probes targeting biomarkers of relevant molecular processes for the characterization of vulnerable plaques, such as vascular endothelial growth factor receptor (VEGFR)-1, VEGFR-2, intercellular adhesion molecule (ICAM)-1, P-selectin, and integrins, and for the potential development of translational tools to identify high-risk patients who could benefit from early therapeutic interventions. This review summarizes the main animal models of vulnerable plaques, with an emphasis on genetically altered mice, and the state-of-the-art preclinical molecular imaging strategies.

Exploring the natural history of atherosclerosis with intravascular ultrasound

Intravascular ultrasound has emerged as the preferred imaging modality for the characterization of atherosclerotic plaque within the coronary arteries. Ultrasonic imaging reveals the presence of more extensive atheroma than suggested by conventional angiography in patients with coronary artery disease. The ability to precisely quantify atheroma volume in an arterial segment at different time points provides the unique opportunity to investigate the factors that influence the natural history of atheroma progression. Accordingly, serial intravascular ultrasound has been incorporated into a number of clinical trials that have evaluated the impact of medical therapies that modify established risk factors and novel pathological targets. This article will review the increasing role of imaging modalities in the assessment of atherosclerosis and factors that influence its natural history.

Isoform-specific inhibitors of ACATs: recent advances and promising developments

Acyl-CoA:cholesterol acyltransferase (ACAT) is a promising therapeutic target for cardiovascular diseases. Although a number of synthetic ACAT inhibitors have been developed, they have failed to show efficacy in clinical trials. Now, the presence of two ACAT isoforms with distinct functions, ACAT1 and ACAT2, has been discovered. Thus, the selectivity of ACAT inhibitors toward the two isoforms is important for their development as novel anti-atherosclerotic agents. The selectivity study indicated that fungal pyripyropene A (PPPA) is only an ACAT2-specific inhibitor. Furthermore, PPPA proved orally active in atherogenic mouse models, indicating it possessed cholesterol-lowering and atheroprotective activities. Certain PPPA derivatives, semi-synthetically prepared, possessed more potent and selective in vitro activity than PPPA against ACAT2. This review covers these studies and describes the future prospects of ACAT2-specific inhibitors.

Current and future pharmacologic options for the management of patients unable to achieve low-density lipoprotein-cholesterol goals with statins

Low-density lipoprotein-cholesterol (LDL-C) lowering is the mainstay of the current treatment guidelines in the management of cardiovascular risk. HMG-CoA reductase inhibitors (statins) are currently the most effective LDL-C-lowering drugs. However, a substantial number of patients do not reach treatment targets with statins. Therefore, an unmet medical need exists for lipid-lowering drugs with novel mechanisms of action to reach the recommended cholesterol target levels, either by monotherapy or combination therapy. Upregulation of the LDL receptor with squalene synthase inhibitors has shown promising results in animal studies but the clinical development of the lead compound lapaquistat (TAK-475) has recently been discontinued. Ezetimibe combined with statins allowed significantly more patients to reach their LDL-C targets. Other inhibitors of intestinal cholesterol absorption such as disodium ascorbyl phytostanol phosphate (FM-VP4) and bile acid transport inhibitors have shown positive results in early development trials, whereas the prospect of acyl coenzyme A: cholesterol acyltransferase inhibition in cardiovascular prevention is dire. Selective inhibition of messenger RNA (mRNA) by antisense oligonucleotides is a new approach to modify cholesterol levels. The inhibition of apolipoprotein B mRNA is in advanced development and mipomersen sodium (ISIS 301012) has shown striking results in phase II studies both as monotherapy as well as in combination with statins.

Atorvastatin has hypolipidemic and anti-inflammatory effects in apoE/LDL receptor-double-knockout mice

Statins are first-line pharmacotherapeutic agents for hypercholesterolemia treatment in humans. However the effects of statins in animal models of atherosclerosis are not very consistent. Thus we wanted to evaluate whether atorvastatin possesses hypolipidemic and anti-inflammatory effects in mice lacking apolipoprotein E/low-density lipoprotein receptor (apoE/LDLR-deficient mice). Two-month-old female apoE/LDLR-deficient mice (n=24) were randomly subdivided into 3 groups. The control group of animals (n=8) was fed with the western type diet (atherogenic diet) and in other two groups atorvastatin was added to the atherogenic diet at the dosage of either 10 mg/kg or 100 mg/kg per day for a period of 2 months. Biochemical analysis of lipids, ELISA analysis of monocyte chemotactic protein-1 (MCP-1) in blood, quantification of lesion size and expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular cell adhesion molecule-1 (ICAM-1) in the atherosclerotic lesion by means of immunohistochemistry and Western blot analysis were performed. The biochemical analysis showed that administration of atorvastatin (100 mg/kg/day) significantly decreased level of total cholesterol, lipoproteins (VLDL and LDL), triacylglycerol, and moreover significantly increased level of HDL. ELISA analysis showed that atorvastatin significantly decreased levels of MCP-1 in blood and immunohistochemical and Western blot analysis showed significant reduction of VCAM-1 and ICAM-1 expression in the vessel wall after atorvastatin treatment (100 mg/kg/day). In conclusion, we demonstrated here for the first time strong hypolipidemic and anti-inflammatory effects of atorvastatin in apoE/LDLR-deficient mice. Thus, we propose that apoE/LDLR-deficient mice might be a good animal model for the study of statin effects on potential novel markers involved in atherogenesis and for the testing of potential combination treatment of new hypolipidemic substances with statins.

Effects of an anti-oxidative ACAT inhibitor on apoptosis/necrosis and cholesterol accumulation under oxidative stress in THP-1 cell-derived foam cells

THP-1 cell-derived foam cells were exposed to oxidative stress through combined treatment with acetylated LDL (acLDL) and copper ions (Cu2+). The foam cells showed caspase-dependent apoptotic changes on exposure to oxidative stress for 6 h, and necrotic changes with the leakage of LDH after 24 h. KY-455, an anti-oxidative ACAT inhibitor, and ascorbic acid (VC) but not YM-750, an ACAT inhibitor, prevented apoptotic and necrotic changes. These preventive effects of KY-455 and VC were accompanied by the inhibition of lipid peroxidation in culture medium containing acLDL and Cu2+, suggesting the involvement of oxidized acLDL in apoptosis and necrosis. Foam cells accumulated esterified cholesterol (EC) for 24 h in the presence of acLDL without Cu2+, which was suppressed by KY-455 and YM-750. Foam cells showed necrotic changes and died in the presence of acLDL and Cu2+. KY-455 but not YM-750 prevented cell death and reduced the amount of EC accumulated. The foam cells treated with VC further accumulated EC without necrotic changes for 24 h even in the presence of acLDL and Cu2+. YM-750 as well as KY-455 inhibited lipid accumulation when co-incubated with VC in foam cells exposed to oxidative stress. It is concluded that an anti-oxidative ACAT inhibitor or the combination of an antioxidant and an ACAT inhibitor protects foam cells from oxidative stress and effectively reduces cholesterol levels, which would be a promising approach in anti-atherosclerotic therapy.

Mouse models for atherosclerosis and pharmaceutical modifiers

Atherosclerosis is a multifactorial highly-complex disease with numerous etiologies that work synergistically to promote lesion development. The ability to develop preventive and ameliorative treatments will depend on animal models that mimic the human subject metabolically and pathophysiologically and will develop lesions comparable to those in humans. The mouse is the most useful, economic, and valid model for studying atherosclerosis and exploring effective therapeutic approaches. Among the most widely used mouse models for atherosclerosis are apolipoprotein E-deficient (ApoE-/-) and LDL receptor-deficient (LDLr-/-) mice. An up-and-coming model is the ApoE*3Leiden (E3L) transgenic mouse. Here, we review studies that have explored how and to what extent these mice respond to compounds directed at treatment of the risk factors hypercholesterolemia, hypertriglyceridemia, hypertension, and inflammation. An important outcome of this survey is that the different models used may differ markedly from one another in their response to a specific experimental manipulation. The choice of a model is therefore of critical importance and should take into account the risk factor to be studied and the working spectrum of the compounds tested.

Intravascular ultrasound assessment of novel antiatherosclerotic therapies: rationale and design of the Acyl-CoA:Cholesterol Acyltransferase Intravascular Atherosclerosis Treatment Evaluation (ACTIVATE) Study

BACKGROUND

Inhibiting the enzyme acyl-CoA:cholesterol acyltransferase (ACAT) has beneficial effects on foam cell formation and therefore has the potential to favorably influence the progression of coronary atherosclerosis. The aim of this study is to determine whether ACAT inhibition, when added to usual medical care, reduces atheroma progression in subjects with coronary artery disease.

METHODS

Five hundred thirty-four subjects with established coronary artery disease on angiography were randomized to receive the experimental ACAT inhibitor, pactimibe, 100 mg daily or matching placebo for 18 months. The primary efficacy parameter will be the nominal change in percent atheroma volume determined by analysis of pullback intravascular ultrasound (IVUS) images of matched coronary artery segments acquired at baseline and 18-month follow-up. In addition, the effect of pactimibe on plasma lipids and inflammatory markers and the incidence of clinical cardiovascular events will also be assessed.

CONCLUSION

Serial IVUS has emerged as a sensitive imaging modality to assess the impact that novel antiatherosclerotic strategies have on the arterial wall. In this study, IVUS will be used to assess whether ACAT inhibition modifies progression of atherosclerotic plaque.

3D Ultrasound Measurement of Change in Carotid Plaque Volume

BACKGROUND AND PURPOSE

New therapies are being developed that are antiatherosclerotic but that lack intermediate end points, such as changes in plasma lipids, which can be measured to test efficacy. To study such treatments, it will be necessary to directly measure changes in atherosclerosis. The study was designed to determine sample sizes needed to detect effects of treatment using 3D ultrasound (US) measurement of carotid plaque.

METHODS

In 38 patients with carotid stenosis >60%, age+/-SD 69.42+/-7.87 years, 15 female, randomly assigned in a double-blind fashion to 80 mg atorvastatin daily (n=17) versus placebo (n=21), we measured 3D plaque volume at baseline and after 3 months by disc segmentation of voxels representing carotid artery plaque, after 3D reconstruction of parallel transverse duplex US scans into volumetric 3D data sets.

RESULTS

There were no significant differences in baseline risk factors. The rate of progression was 16.81+/-74.10 mm3 in patients taking placebo versus regression of -90.25+/-85.12 mm3 in patients taking atorvastatin (P<0.0001).

CONCLUSIONS

3D plaque volume measurement can show large effects of therapy on atherosclerosis in 3 months in sample sizes of approximately 20 patients per group. Sample sizes of 22 per group would be sufficient to show an effect size of 25% that of atorvastatin in 6 months. This technology promises to be very useful in evaluation of new therapies.

Confocal scanning laser microscopy measurements of atherosclerotic lesions in mice aorta. A fast evaluation method for volume determinations

Atherosclerotic lesion size in mice is routinely evaluated by morphometrical measurements on serial sections in order to obtain volume measurements. The technique of confocal scanning laser microscopy (CSLM) makes it possible to optically scan and thereby evaluate a tissue sample. We here describe a method for measuring lesion volume in ApoE/LDLr deficient mice at 20 and 30 weeks of age using the non-destructive procedure of CSLM. Whole mount preparations of opened aorta with the lumen side facing the cover slip were analysed under 10x magnification in a CSLM (Leica). The autofluorescence of the elastic fibres of the lamina interna as opposed to the non-fluorescing lesion was used to define the bottom and top of the lesion during scanning. Ten to forty images were collected 2.4 microm apart, depending on the size of the lesion, and the stack of images was then analysed using Imaris (Bitplane). After the CSLM evaluation, the aortas were de-mounted, embedded in paraffin, sectioned, stained in hematoxylin and eosin and the volume re-evaluated with conventional morphometry. Statistical evaluation showed that the results obtained with CSLM and the results of morphometry were positively correlated. Area measurements of the plaques using en face preparations of aorta showed that the plaque area was generally larger at the left side and a significant increase of plaque area along the length of the thoracic aorta. Our results showed that atherosclerotic lesions in mice can be quantitatively evaluated by CSLM.

Lipid transfer proteins (LTP) and atherosclerosis

This review deals with four lipid transfer proteins (LTP): three are involved in cholesteryl ester (CE) synthesis or transport, the fourth deals with plasma phospholipid (PL) transfer. Experimental models of atherosclerosis, clinical and epidemiological studies provided information as to the relationship of these LTP(s) to atherosclerosis, which is the main focus of this review. Thus, inhibition of acyl-CoA:cholesterol acyltransferase (ACAT) 1 and 2 decreases cholesterol absorption, plasma cholesterol and aortic cholesterol esterification in the aorta. The discovery that tamoxifen is a potent ACAT inhibitor explained the plasma cholesterol lowering of the drug. The use of ACAT inhibition in humans is under current investigation. As low cholesteryl ester transfer protein (CETP) activity is connected with high HDL-C, several CETP inhibitors were tried in rabbits, with variable results. A new CETP inhibitor, Torcetrapib, was tested in humans and there was a 50-100% increase in HDL-C. Lecithin cholesterol acyl-transferase (LCAT) influences oxidative stress, which can be lowered by transient LCAT gene transfer in LCAT-/- mice. Phospholipid transfer protein (PLTP) deficiency reduced apo B production in apo E-/- mice, as well as oxidative stress in four models of mouse atherosclerosis. In conclusion, the ability to increase HDL-C so markedly by inhibitors of CETP introduces us into a new era in prevention and treatment of coronary heart disease (CHD).

Spontaneous extracranial carotid atherosclerosis evolution in asymptomatic individuals: a three-year prospective study

OBJECTIVE

To evaluate the spontaneous evolution of extracranial carotid atherosclerosis in asymptomatic patients who did not present the main risk factors associated to the disease.

METHOD

A prospective study including patients of both genders, age ranging from 40 to 70 years, not presenting any signs and symptoms of cerebrovascular disease and without the main atherosclerosis risk factors were included. Patients who were using or had used medication during the follow-up period that could potentially influence in the spontaneous course of atherosclerosis were excluded. The evaluation of the plaque and degree of stenosis were acquired using mode B, 7.5 MHz Doppler ultrasonography (USG). The follow-up was carried out for 36 months, with clinical, neurological, and USG exams repeated in a period of 6 to 8 months. Ninety-six individuals (48 women) completed the study with the presence of plaque, and 52 (26 women) with a degree of stenosis.

RESULTS

As to the degree of stenosis, 25% of the patients had worsening, 69% remained stable and 6% improved. When only the presence or absence of plaque was considered, 20% showed worsening (plaque developed during follow-up), 7% improved (disappearance of plaque), and 73% remained stable. No differences were found between the male and female patients.

CONCLUSION

These results confirm the dynamic characteristics of plaque. In asymptomatic individuals without specific treatment, spontaneous improvement may occur, however, rarely. These findings may contribute as an assessment criterion when a decision is to be made in high-risk patients.

The influence of the acyl-CoA:cholesterol acyltransferase-1 gene (−77G→A) polymorphisms on plasma lipid and apolipoprotein levels in normolipidemic and hyperlipidemic subjects

BACKGROUND

Acyl-CoA:cholesterol acyltransferase (ACAT) plays important roles in cellular cholesterol homeostasis. Two isoforms of ACAT have been reported (ACAT-1 and ACAT-2). ACAT inhibitors cannot only prevent atherosclerosis formation, but may also induce its regression in animals. In humans, an ACAT inhibitor was shown to have a lipid-lowering effect. The present study was carried out to clarify the relationship between ACAT-1 gene variants and hyperlipidemia.

METHODS AND RESULTS

To identify genetic variants, we screened 30 subjects with hyperlipidemia by direct sequencing. As a result, a missense variant (R526G) and a variant in the 5' untranslated region (-77G-->A) were identified. The genotype frequencies of each variant were determined in 178 unrelated normolipidemic and 441 unrelated hyperlipidemic subjects. The alleles frequencies of the R526G variant in normolipidemic and hyperlipidemic subjects were 0.676 and 0.633, respectively. The alleles frequencies of the -77G-->A variant in normolipidemic and hyperlipidemic subjects were 0.503 and 0.515, respectively. Differences in allele frequencies between normolipidemic and hyperlipidemic subjects were not significant in both variants. R526G variant did not affect plasma concentrations of lipids or apolipoproteins in subjects studied. However, among hyperlipidemic subjects, plasma concentrations of HDL-C and apoA-I in subjects with -77G-->A variant were significantly higher than those in subjects without variant.

CONCLUSION

Two variants in ACAT-1 gene were identified in subjects with hyperlipidemia. -77G-->A variant affects plasma HDL concentrations only in hyperlipidemic subjects. These data suggest that the intracellular FC concentration might modulate plasma HDL concentrations.

Atherosclerosis in the apolipoprotein-E-deficient mouse: a decade of progress

Arguably the most critical advancement in the elucidation of factors affecting atherogenesis has been the development of mouse models of atherosclerosis. Among available models, the apolipoprotein E-deficient (apoE-/-) mouse is particularly popular because of its propensity to spontaneously develop atherosclerotic lesions on a standard chow diet. A Medline search reveals over 645 articles dedicated to studies using this reliable and convenient "super" animal model since its inception (Piedrahita JA et al, Proc Natl Acad Sci U S A 1992;89:4471-4475; Plump AS et al, Cell 1992;71:343-353) with a more or less steady increase from year to year. This review will examine our present understanding of the pathology and progression of plaques in this animal and highlight some of the nutritional, pharmacological, and genetic studies that have enhanced this understanding.

Measurement of Carotid Plaque and Effect of Vitamin Therapy for Total Homocysteine

BACKGROUND

Many new therapies are being developed that are anti-atherosclerotic, but which do not change clinical parameters such as blood pressure or cholesterol. In order to measure the effects of these therapies it will be necessary to measure atherosclerosis. Elevated levels of plasma total homocysteine (tHcy) are associated with increased risk of stroke and myocardial infarction. Measurement of the effect of vitamin therapy on atherosclerosis has therefore been used as an example of this approach.

METHODS

2-Dimensional measurement of carotid plaque cross-sectional area has been used to measure effects of vitamin therapy in patients whose plaque is progressing despite intensive treatment of traditional risk factors. In clinic patients, addition of vitamin therapy halted progression of atherosclerosis, in samples of 50 patients over 2.5 years. However, in patients randomized to high-dose vs. low-dose vitamins in the Vitamin Intervention for Stroke Prevention trial, no difference in plaque progression was seen between high-dose and low-dose vitamin therapy. New methods have been developed for the measurement of 3-dimensional plaque volume, and for the measurement of plaque surface roughness.

RESULTS

The accuracy and reliability of the measurement of plaque volume is 95%. This will permit measurement of effects of new anti-atherosclerotic therapies with much smaller sample sizes, in a much shorter time, than previously available methods such as intima-media thickness.

CONCLUSION

Measurement of atherosclerotic plaque volume and roughness will greatly enhance the study of new anti-atherosclerotic therapies.

Inhibitory effect of acyl-CoA:cholesterol acyltransferase inhibitor-low density lipoprotein complex on experimental atherosclerosis

KV-2920 is a novel acyl-CoA: cholesterol acyltransferase (ACAT) inhibitor. To confirm the efficacy of KV-2920-low density lipoprotein (LDL) complex (KV-LDL complex) as a drug-carrier complex on experimental atherosclerosis, we examined its inhibitory effects in vitro and in vivo. LDL was isolated from human plasma and the KV-LDL complex was prepared by incubation in the presence of Celite 545. The complex contained about 800 mol KV-2920 in 1 mol LDL. The cholesterol levels in the serum and aorta of atherogenic mice after 14 weeks of feeding were significantly higher than those of nonatherogenic mice. With the intravenous injection of KV-LDL complex, although the cholesterol levels in the serum were not influenced, the level of cholesterol ester in the aorta of atherogenic mice was significantly reduced. The concentration of cholesterol ester in the macrophages derived from ICR mice was predominantly increased by incubation with LDL for 48 h, this increase was significantly inhibited by incubation with KV-LDL complex. Moreover, the complex also inhibited the increase of cholesterol ester in macrophages following incubation with oxidized LDL. These findings suggest that KV-LDL complex inhibits the foam cell formation of macrophages though action of KV-2920 as an ACAT inhibitor, and prevents the accumulation of cholesterol ester in the aorta of atherogenic mice. Therefore, KV-LDL complex may be useful as a drug-carrier complex in antiatherosclerotic therapy.

Carotid plaque area: a tool for targeting and evaluating vascular preventive therapy

BACKGROUND AND PURPOSE

Carotid plaque area measured by ultrasound (cross-sectional area of longitudinal views of all plaques seen) was studied as a way of identifying patients at increased risk of stroke, myocardial infarction, and vascular death.

METHODS

Patients from an atherosclerosis prevention clinic were followed up annually for up to 5 years (mean, 2.5+/-1.3 years) with baseline and follow-up measurements recorded. Plaque area progression (or regression) was defined as an increase (or decrease) of >/=0.05 cm(2) from baseline.

RESULTS

Carotid plaque areas from 1686 patients were categorized into 4 quartile ranges: 0.00 to 0.11 cm(2) (n=422), 0.12 to 0.45 cm(2) (n=424), 0.46 to 1.18 cm(2) (n=421), and 1.19 to 6.73 cm(2) (n=419). The combined 5-year risk of stroke, myocardial infarction, and vascular death increased by quartile of plaque area: 5.6%, 10.7%, 13.9%, and 19.5%, respectively (P<0.001) after adjustment for all baseline patient characteristics. A total of 1085 patients had >/=1 annual carotid plaque area measurements: 685 (63.1%) had carotid plaque progression, 306 (28.2%) had plaque regression, and 176 (16.2%) had no change in carotid plaque area over the period of follow-up. The 5-year adjusted risk of combined outcome was 9.4%, 7.6%, and 15.7% for patients with carotid plaque area regression, no change, and progression, respectively (P=0.003).

CONCLUSIONS

Carotid plaque area and progression of plaque identified high-risk patients. Plaque measurement may be useful for targeting preventive therapy and evaluating new treatments and response to therapy and may improve cost-effectiveness of secondary preventive treatment.

Acyl coenzyme A:cholesterol acyltransferase inhibition: potential atherosclerosis therapy or springboard for other discoveries?

Cholesterol is an essential building block without which humans and other animals could not exist. As with most necessities, under certain conditions, excess can sharply tip the scale and lead to an unfavourable outcome. Excess cholesterol is stored as cholesteryl ester through an esterification process regulated in part by acyl coenzyme A:cholesterol acyltransferase (ACAT). ACAT is found in many tissue types which require the storage of cholesterol. Most notably, for cardiovascular disease ACAT activity is significant in intestinal and hepatic tissue and arterial macrophages. Several ACAT inhibitors have been investigated for their potential to favourably alter serum lipoprotein levels by blocking intestinal absorption, hepatic inhibition and/or slowing the progression of atherosclerosis through a non-lipid arterial inhibition. Recent evaluations of ACAT and ACAT inhibitors have provided some insight into the therapeutic potential and risks of ACAT inhibition as a means of treating atherosclerosis.

HOE 402 lowers serum cholesterol levels by reducing VLDL-lipid production, and not by induction of the LDL receptor, and reduces atherosclerosis in wild-type and LDL receptor-deficient mice

Previous rodent studies suggested that the potent hypolipidemic agent 4-amino-2-(4,4-dimethyl-2-oxo-1-imidazolidinyl)pyrimidine-5-N-(trifluoromethyl-phenyl) carboxamide monohydrochloride (HOE 402) is an inducer of the LDL receptor (LDLR). Using wild-type and heterozygous and homozygous LDLR-deficient (LDLR+/0 and LDLR0/0) mice, fed a low or high cholesterol diet, we investigated whether HOE 402 specifically induces the LDLR and whether other pathways are affected. Upon treatment with 0.05% (w/w) HOE 402, the serum cholesterol levels of wild-type, LDLR+/0 and LDLR0/0 mice, were maximally reduced by 53, 56, and 73%, respectively (P<0.05), by reducing levels in very low density-lipoprotein (VLDL), intermediate density-lipoprotein (IDL), and low density-lipoprotein (LDL) cholesterol, whereas high density-lipoprotein (HDL) cholesterol levels were increased. The observations that HOE 402 exhibited no effect on in vivo clearance of 125I-labeled LDL in wild-type mice, and clearly reduced serum cholesterol levels in LDLR0/0 mice, indicate that the LDLR is not the main target for the compound. In wild-type mice, production of VLDL-TG, and cholesterol were reduced by more than 50% by HOE 402 (P<0.05), whereas VLDL apolipoprotein B (ApoB) secretion was unaffected, indicating that HOE 402 treatment changes the size, rather than the number of the secreted VLDL particles. The reduced VLDL production was accompanied by a 22% decreased hepatic cholesterol ester concentration (P<0.05). Additionally, HOE 402 treatment strongly reduced the aortic content of atherosclerotic lesions by 90 and 72% in LDLR+/0 and LDLR0/0 mice, respectively (P<0.01). In conclusion, HOE 402 is a potent cholesterol-lowering compound, which inhibits VLDL production, and consequently attenuates atherosclerosis development.