Acyl-coenzyme A:cholesterol O-acyltransferase Research Articles

Syntheses and pharmacokinetic evaluations of four metabolites of 2-(4-(2-((1H-benzo[d]imidazol-2-yl)thio)ethyl)piperazin-1-yl)-N-(6-methyl-2,4-bis-(methylthio)pyridin-3-yl)acetamide hydrochloride [K-604], an acyl-CoA:cholesterol O-acyltransferase-1 inhibitor

We synthesized and identified four metabolites of acyl-coenzyme A:cholesterol O-acyltransferase (ACAT)-1 inhibitor, K-604 (1). Two of the metabolites M1 and M2, were prepared from 1 using a combination reagent of hydrogen peroxide and sodium tungstate with either phosphoric acid or trifluoroethanol as the solvent to control the regioselectivity. Upon exposure of 4b to tert-butyl hypochlorite at −78 °C, the monosulfoxidation afforded synthetic intermediate of M3 in excellent yield. The efficient synthesis of M4 was established. The in vitro metabolic study exhibited a high clearance value (720 μL/min/mg protein) of 1 using human liver microsomes. We orally administered a single dose of 10 mg/kg of 1 to monkeys because the in vitro metabolic patterns are quite similar. Fortunately, the drug concentration of 1 was much higher than those of M1, M2, M3 and M4.

ACAT-selective and Nonselective DGAT1 Inhibition

Acyl-coenzyme A: cholesterol O-Acyltransferase (ACAT) and Acyl-coenzyme A: diacylglycerol O-acyltransferase (DGAT) enzymes play important roles in synthesizing neutral lipids, and inhibitors of these enzymes have been investigated as potential treatments for diabetes and other metabolic diseases. Administration of a Acyl-coenzyme A: diacylglycerol O-acyltransferase 1 (DGAT1) inhibitor with very limited cellular selectivity over ACAT resulted in significant adrenocortical degenerative changes in dogs. These changes included macrosteatotic vacuolation associated with adrenocyte cell death in the zonae glomerulosa and fasciculata and minimal to substantial mixed inflammatory cell infiltration and were similar to those described previously for some ACAT inhibitors in dogs. In the mouse, similar but only transient adrenocortical degenerative changes were seen as well as a distinctive nondegenerative reduction in cortical fine vacuolation. In the marmoset, only the distinctive nondegenerative reduction in cortical fine vacuolation was observed, suggesting that the dog, followed by the mouse, is the most sensitive species for cortical degeneration. Biochemical analysis of adrenal cholesterol and cholesteryl ester indicated that the distinctive reduction in cortical fine vacuolation correlated with a significant reduction in cholesteryl ester in the mouse and marmoset, whereas no significant reduction in cholestryl ester, but an increase in free cholesterol was observed in dogs. Administration of a DGAT1 inhibitor with markedly improved selectivity over ACAT to the marmoset and the mouse resulted in no adrenal pathology at exposures sufficient to cause substantial DGAT1 but not ACAT inhibition, thereby implicating ACAT rather than DGAT1 inhibition as the probable cause of the observed adrenal changes. Recognizing that the distinctive nondegenerative reduction in cortical fine vacuolation in the mouse could be used as a histopathological biomarker for an in vivo model of the more severe changes observed in dogs, the mouse has subsequently been used as a model to select DGAT1 inhibitors free of adrenocortical toxicity.

A Novel Class of Antihyperlipidemic Agents with Low Density Lipoprotein Receptor Up-Regulation via the Adaptor Protein Autosomal Recessive Hypercholesterolemia

We have previously reported compound 2 as a inhibitor of acyl-coenzyme A:cholesterol O-acyltransferase (ACAT) and up-regulator of the low density lipoprotein receptor (LDL-R) expression. In this study we focused on compound 2, a unique LDL-R up-regulator, and describe the discovery of a novel class of up-regulators of LDL-R. Replacement the methylene urea linker in compound 2 with an acylsulfonamide linker kept a potent LDL-R up-regulatory activity, and subsequent optimization work gave compound 39 as a highly potent LDL-R up-regulator (39; EC(25) = 0.047 microM). Compound 39 showed no ACAT inhibitory activity even at 1 microM. The sodium salts of compound 39 reduced plasma total and LDL cholesterol levels in a dose-dependent manner in an experimental animal model of hyperlipidemia. Moreover, we revealed in this study using RNA interference that autosomal recessive hypercholesterolemia (ARH), an adaptor protein of LDL-R, is essential for compound 39 up-regulation of LDL-R expression.

LDL-C-Lowering therapy: Current and future therapeutic targets

Recent trials have emphasized that more intensive low-density lipoprotein cholesterol (LDL-C) lowering results in a further reduction in cardiovascular disease risk. Uptitration of statins has limited incremental LDL-C-lowering effects and leads to an increased incidence of side effects. Therefore, attention has shifted toward alternative LDL-C-lowering modalities. Several promising compounds have entered the clinical trial arena, although with mixed results. Acyl-coenzyme A: cholesterol O-acyltransferase (ACAT) inhibitors failed to show benefit. Microsomal triglyceride transfer protein and squalene synthase inhibitors, in spite of beneficial lipid profile changes, have shown adverse event profiles. In contrast, inhibitors of intestinal cholesterol absorption have shown LDL-C-lowering efficacy associated with few side effects. The inhibition of apolipoprotein B100 synthesis by antisense oligonucleotides has now been tested in phase 2 clinical trials, with promising results. Finally, compounds modifying protein convertase subtilisin/kexin type 9 levels are currently in the preclinical phase. In the present article, we discuss these LDL-C-lowering strategies.

Development of a method for simultaneous determination of eflucimibe and its three major metabolites in rat plasma by liquid chromatography/electrospray tandem mass spectrometry: a preliminary study

A high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry (HPLC/ESI-MS/MS) method has been developed for the simultaneous determination of eflucimibe, a powerful acyl-coenzyme A cholesterol O-acyltransferase (ACAT) inhibitor, and its main metabolites, in plasma. The ESI and MS/MS parameters were investigated and optimised for each of the four compounds in the positive ion mode. Plasma samples were deproteinised by precipitation with acetonitrile and directly analysed by HPLC/ESI-MS/MS in less than 4 min. Quantitation was performed in the multiple reaction monitoring (MRM) mode for highest sensitivity, selecting the protonated molecules [M+H](+) as precursor ions. The method was demonstrated to be specific and sensitive, and a linear response was observed within a 1-25 ng/mL concentration range. Correlation coefficients (r(2)) greater than 0.9960 were obtained by least-squares regression, and limits of detection down to 0.2 ng/mL were calculated. Therefore, this HPLC/ESI-MS/MS method appears to be an efficient tool, able to provide valuable information for a pharmacological purpose.

Spectrofluorimetric study of eflucimibe-γ-cyclodextrin inclusion complex

Eflucimibe, a novel and highly potent acyl-coenzyme A cholesterol O-acyl-transferase (ACAT) inhibitor, is sparingly soluble in aqueous media and exhibits a very weak natural fluorescence. However, when increasing concentrations of γ-cyclodextrin (γ-CD) are added, an increase in the fluorescence signal is observed, attesting the formation of a non-covalent inclusion complex between eflucimibe and the γ-CD. In this work, the stoichiometry of the complex and the corresponding association constant have been determined from fluorescence data by Benesi–Hildebrand's method (double reciprocal plots). As a result, a 1:1 stoichiometric ratio and a 20 M −1 formation constant were obtained. This apparent formation constant was determined in water containing 10% methanol, which was needed to improve ‘aqueous’ solubility of the drug in a CD-free medium. Owing to the extreme hydrophobicity of eflucimibe, these results provide valuable information for pharmaceutical formulation studies.

Crystallization of Eflucimibe Drug in a Solvent Mixture: Effects of Process Conditions on Polymorphism

Nucleation and metastability of the eflucimibe (S)-2‘,3‘,5‘-trimethyl-4‘-hydroxy-dodecylthiophenyl-acetanilide, a new acyl-coenzyme A:cholesterol O-acyltransferase (ACAT) inhibitor, have been investigated according to a polythermal method. Eflucimibe exhibits two polymorphs, A and B, which crystallize simultaneously (concomitant polymorphs). The focus of this study was on the effect of the cooling rate, the initial concentration, and the seeds on metastability and polymorphism of eflucimibe. For nonseeded crystallization, it was found that the metastable zone width is large (primary nucleation) and fulfills well the linear relation between log ΔTmax and log(dT/dt). In addition, the X-ray powder diffraction and differential scanning calorimetry analyses of the powder obtained show that the desired polymorph (pure A form) is difficult to obtain. On the contrary, for seeded experiments, the metastable zone width is significantly reduced (secondary nucleation) and the occurrence of polymorphism is controlled by seeding with the desired polymorph.

Analysis of eflucimibe and related impurities by highly sensitive liquid chromatography‐electrospray‐tandem mass spectrometry

AbstractEflucimibe (F 12511) is a new and promising acyl‐coenzyme A cholesterol O‐acyl‐transferase (ACAT) inhibitor, developed at the Pierre Fabre Research Center for the treatment of atherosclerosis. Owing to the synthetic pathway, residual impurities may be present (at very low levels) in the final product, which is currently analysed by high‐performance liquid chromatography (HPLC) with UV detection. In this work, a faster, specific, and sensitive analytical method has been developed for the determination of eflucimibe and its four related impurities. Electrospray‐tandem mass spectrometry (ESI‐MS/MS) coupled with HPLC is demonstrated to efficiently enhance the detection limits (at least 1200‐fold), within a 4‐minute run time. After optimisation of the ESI and MS/MS parameters for each of the five compounds, quantitative analysis was performed in the multiple reaction monitoring (MRM) mode and the calibration curves yielded correlation coefficients (r ) greater than 0.9996. Finally, this method was successfully applied to the assay of a real batch sample.

Predicting Acyl-Coenzyme A: Cholesterol O-Acyltransferase Inhibitory Activity: Computational Approach Using Topological Descriptors

Relationship between the topological indices and acyl-coenzyme A:cholesterol O-acyltransferase (ACAT) inhibitory activity of (aminosulfonyl)ureas has been investigated. Three topological indices, Wiener's index--a distance-based topological descriptor, molecular connectivity index--an adjacency-based topological index, and eccentric connectivity index--an adjacency-cum-distance-based topological descriptor, were used for the present investigations. A data set comprising 41 analogues of substituted (aminosulfonyl)ureas was selected for the present studies. The values of wiener's index, eccentric connectivity index, and molecular connectivity index for each of the 41 compounds comprising the data set were computed using an in-house computer program. Resultant data were analyzed and suitable models were developed after identification of active ranges. Subsequently, a biological activity was assigned to each compound using these models, which was then compared with the reported in vitro ACAT inhibitory activity. Accuracy of prediction using these models was found to vary from a minimum of approximately 83% to a maximum of approximately 91%.

Predicting Acyl-Coenzyme A: Cholesterol O-Acyltransferase Inhibitory Activity: Computational Approach Using Topological Descriptors

Relationship between the topological indices and acyl-coenzyme A:cholesterol O-acyltransferase (ACAT) inhibitory activity of (aminosulfonyl)ureas has been investigated. Three topological indices, Wiener's index—a distance-based topological descriptor, molecular connectivity index—an adjacency-based topological index, and eccentric connectivity index—an adjacency-cum-distance–based topological descriptor, were used for the present investigations. A data set comprising 41 analogues of substituted (aminosulfonyl) ureas was selected for the present studies. The values of wiener's index, eccentric connectivity index, and molecular connectivity index for each of the 41 compounds comprising the data set were computed using an in-house computer program. Resultant data were analyzed and suitable models were developed after identification of active ranges. Subsequently, a biological activity was assigned to each compound using these models, which was then compared with the reported in vitro ACAT inhibitory activity. Accuracy of prediction using these models was found to vary from a minimum of ∼83% to a maximum of ∼91%.

Immunolocalization of Acyl-Coenzyme A:CholesterolO-Acyltransferase in Macrophages

Macrophages in atherosclerotic lesions accumulate large amounts of cholesteryl-fatty acyl esters ("foam cell" formation) through the intracellular esterification of cholesterol by acyl-coenzyme A:cholesterol O-acyltransferase (ACAT). In this study, we sought to determine the subcellular localization of ACAT in macrophages. Using mouse peritoneal macrophages and immunofluorescence microscopy, we found that a major portion of ACAT was in a dense reticular cytoplasmic network and in the nuclear membrane that colocalized with the luminal endoplasmic reticulum marker protein-disulfide isomerase (PDI) and that was in a similar distribution as the membrane-bound endoplasmic reticulum marker ribophorin. Remarkably, another portion of the macrophage ACAT pattern did not overlap with PDI or ribophorin, but was found in as yet unidentified cytoplasmic structures that were juxtaposed to the nucleus. Compartments containing labeled beta-very low density lipoprotein, an atherogenic lipoprotein, did not overlap with the ACAT label, but rather were embedded in the dense reticular network of ACAT. Furthermore, cell-surface biotinylation experiments revealed that freshly harvested, non-attached macrophages, but not those attached to tissue culture dishes, contained approximately 10-15% of ACAT on the cell surface. In summary, ACAT was found in several sites in macrophages: a cytoplasmic reticular/nuclear membrane site that overlaps with PDI and ribophorin and has the characteristics of the endoplasmic reticulum, a perinuclear cytoplasmic site that does not overlap with PDI or ribophorin and may be another cytoplasmic structure or possibly a unique subcompartment of the endoplasmic reticulum, and a cell-surface site in non-attached macrophages. Understanding possible physiological differences of ACAT in these locations may reveal an important component of ACAT regulation and macrophage foam cell formation.

The actin cytoskeleton is important for the stimulation of cholesterol esterification by atherogenic lipoproteins in macrophages.

Stimulation of intracellular cholesterol esterification, which is catalyzed by the enzyme acyl-coenzyme A: cholesterol O-acyltransferase (ACAT), by atherogenic lipoproteins in macrophages is a key step in the ability of these cells to store lipoprotein-cholesterol and in the eventual development of atheroma foam cells. Herein, we provide evidence that the actin cytoskeleton plays an important role in the stimulation of cholesterol esterification by atherogenic lipoproteins in macrophages. When the actin cytoskeleton of cultured mouse peritoneal macrophages was disrupted by treatment with cytochalasin D or Clostridial C2 toxin, the ability of beta very low density lipoprotein (beta-VLDL) to stimulate cholesterol esterification was decreased 3-6-fold, even under conditions in which beta-VLDL protein degradation, cholesteryl ester hydrolysis, or net cholesterol delivery to the cells was matched. Esterification of cellular phospholipids and triglycerides was not affected by this treatment. Cytochalasin D treatment of macrophages also inhibited the ability of acetyl-low density lipoprotein, another foam cell-forming lipoprotein, to stimulate cholesterol esterification, but stimulation of cholesterol esterification by 25-hydroxycholesterol was not inhibited by cytochalasin D. Cytochalasin D was found to inhibit neither the exit of beta-VLDL-derived cholesterol from lysosomes nor the ability of beta-VLDL to down-regulate endogenous cholesterol synthesis. From these data we conclude that an intact actin cytoskeleton is necessary for efficient stimulation of cholesterol esterification by atherogenic lipoproteins in macrophages. Although the exact function of actin in the cholesterol esterification pathway remains to be determined, our data rule out a general role for actin in intracellular cholesterol trafficking or maintenance of ACAT enzyme activity. Rather, we speculate that actin filaments play a role in specific cellular entry processes of atherogenic lipoproteins and/or in establishing transport or contact between the plasma membrane cholesterol substrate pool and the ACAT enzyme in macrophages.

Comparison of CI-976, an ACAT inhibitor, and selected lipid-lowering agents for antiatherosclerotic activity in iliac-femoral and thoracic aortic lesions. A biochemical, morphological, and morphometric evaluation.

Due to the potential importance of acyl-coenzyme A:cholesterol O-acyltransferase (ACAT) in the generation of lipid-filled monocytes-macrophages, the ACAT inhibitor CI-976 (2,2-dimethyl-N-(2,4,6-trimethoxyphenyl)dodecanamide) was evaluated relative to selected lipid-lowering agents for their effect on atherosclerotic lesion regression and progression. Atherosclerotic lesions comparable in composition to human fatty streaks were induced by chronic endothelial denudation in the iliac-femoral artery of hypercholesterolemic New Zealand White rabbits before intervention, while naturally occurring fatty streaks developed in the thoracic aorta. CI-976 administered in a hypercholesterolemic diet at a dose that did not lower plasma cholesterol prevented the accumulation of monocytes-macrophages within the preestablished iliac-femoral lesion and reduced the foam cell area by 27-29% relative to the initiation of intervention. CI-976 also blunted the development of thoracic aortic fatty streak-like lesions and decreased the cholesteryl ester enrichment by 46%. CI-976 had no effect on plasma triglycerides and, more importantly, had no effect or decreased liver, iliac-femoral, and thoracic aortic free cholesterol content. Dietary intervention alone increased monocyte-macrophage involvement in the iliac-femoral lesion despite reductions in plasma, liver, and thoracic aortic cholesterol content. Conventional lipid-lowering therapy such as cholestyramine or cholestyramine/niacin required substantial decreases in plasma cholesterol levels to achieve comparable vascular changes. We conclude that inhibition of ACAT within the arterial wall by the potent and specific ACAT inhibitor CI-976, even in the absence of plasma cholesterol lowering, can result in the inhibition of atherosclerotic lesion progression and can enhance regression.

The antihypertensive drug propranolol enhances LDL catabolism and alters cholesterol metabolism in human cultured fibroblasts

The effects of 3 β-blockers with different pharmacological properties (non-selective: propranolol; β 1-selective: metoprolol; and with intrinsic sympathomimetic activity: pindolol) were comparatively studied on LDL and lipid metabolism in human fibroblasts. At 10 −4 M, propranolol increased low density lipoprotein binding, uptake and degradation by 1.5-, 2.2- and 1.8-fold, respectively, whereas metoprolol and pindolol had no effect. This effect of propranolol is mainly due to an increase in LDL receptor number. Propranolol also enhanced sterol, triacylglycerol, fatty acid and phospholipid synthesis by 2–3-fold from sodium acetate. Cholesterol esterification by oleic acid was significantly and specifically decreased 4-fold by propranolol. Metoprolol and pindolol affect neither sterol synthesis nor cholesterol esterification. Pretreatment of cultured fibroblasts with propranolol induced an increase in hydroxymethylglutaryl-coenzyme A reductase activity and a decrease in acyl-coenzyme A: cholesterol- O-acyltransferase (ACAT) activity. Propranolol inhibited the induction of ACAT activity by exogenous cholesterol. Preincubation of a cell-free extract with propranolol also induced inhibition of ACAT activity. Propranolol decreased the cholesteryl ester content of cultured cells. These effects of propranolol on LDL and cholesterol metabolism might be related to the amphiphilic properties of the drug and suggest an effect on the cholesterol intracellular traffic. The decrease in cholesterol esterification and in the cholesteryl ester cellular level induced by propranolol may be involved in its antagonizing effect on experimental atherogenesis.

The effects of perhexiline maleate on low density lipoprotein processing and cholesterol metabolism in cultured human fibroblasts.

The effects of perhexiline maleate (PM, Pexid) on low density lipoprotein (LDL) processing and cholesterol metabolism were investigated after a 24 h pretreatment with the drug. Perhexiline maleate increased LDL uptake in the range 10(-6) to 10(-5) M (180% of control for 10(-5) M), whereas LDL binding and degradation were not affected. Sterol synthesis from sodium acetate was enhanced by perhexiline maleate (X 2.2 for 10(-5) M), while cholesterol esterification with oleic acid was decreased (40% of control for 10(-5) M). These effects of perhexiline on cholesterol metabolism are specific, since the synthesis of triacylglycerols from sodium acetate is not affected and since the incorporation of oleic acid into triacylglycerols is much less impaired. The decreased cholesterol esterification is accompanied by a reduction of acylcoenzyme A-cholesterol-O-acyltransferase (ACAT) activity measured in vitro on cell extracts.