Pharmacological inhibition of acyl-coenzyme A:cholesterol acyltransferase alleviates obesity and insulin resistance in diet-induced obese mice by regulating food intake

BACKGROUND/OBJECTIVES

Acyl-coenzyme A:cholesterol acyltransferases (ACATs) catalyze the formation of cholesteryl ester (CE) from free cholesterol to regulate intracellular cholesterol homeostasis. Despite the well-documented role of ACATs in hypercholesterolemia and their emerging role in cancer and Alzheimer's disease, the role of ACATs in adipose lipid metabolism and obesity is poorly understood. Herein, we investigated the therapeutic potential of pharmacological inhibition of ACATs in obesity.

METHODS

We administrated avasimibe, an ACAT inhibitor, or vehicle to high-fat diet-induced obese (DIO) mice via intraperitoneal injection and evaluated adiposity, food intake, energy expenditure, and glucose homeostasis. Moreover, we examined the effect of avasimibe on the expressions of the genes in adipogenesis, lipogenesis, inflammation and adipose pathology in adipose tissue by real-time PCR. We also performed a pair feeding study to determine the mechanism for body weight lowering effect of avasimibe.

RESULTS

Avasimibe treatment markedly decreased body weight, body fat content and food intake with increased energy expenditure in DIO mice. Avasimibe treatment significantly lowered blood levels of glucose and insulin, and improved glucose tolerance in obese mice. The beneficial effects of avasimibe were associated with lower levels of adipocyte-specific genes in adipose tissue and the suppression of food intake. Using a pair-feeding study, we further demonstrated that avasimibe-promoted weight loss is attributed mainly to the reduction of food intake.

CONCLUSIONS

These results indicate that avasimibe ameliorates obesity and its-related insulin resistance in DIO mice through, at least in part, suppression of food intake.

Targeting human Acyl-CoA:cholesterol acyltransferase as a dual viral and T cell metabolic checkpoint

Determining divergent metabolic requirements of T cells, and the viruses and tumours they fail to combat, could provide new therapeutic checkpoints. Inhibition of acyl-CoA:cholesterol acyltransferase (ACAT) has direct anti-carcinogenic activity. Here, we show that ACAT inhibition has antiviral activity against hepatitis B (HBV), as well as boosting protective anti-HBV and anti-hepatocellular carcinoma (HCC) T cells. ACAT inhibition reduces CD8+ T cell neutral lipid droplets and promotes lipid microdomains, enhancing TCR signalling and TCR-independent bioenergetics. Dysfunctional HBV- and HCC-specific T cells are rescued by ACAT inhibitors directly ex vivo from human liver and tumour tissue respectively, including tissue-resident responses. ACAT inhibition enhances in vitro responsiveness of HBV-specific CD8+ T cells to PD-1 blockade and increases the functional avidity of TCR-gene-modified T cells. Finally, ACAT regulates HBV particle genesis in vitro, with inhibitors reducing both virions and subviral particles. Thus, ACAT inhibition provides a paradigm of a metabolic checkpoint able to constrain tumours and viruses but rescue exhausted T cells, rendering it an attractive therapeutic target for the functional cure of HBV and HBV-related HCC.

Expression of SOAT1 in Adrenocortical Carcinoma and Response to Mitotane Monotherapy: An ENSAT Multicenter Study

CONTEXT

Objective response rate to mitotane in advanced adrenocortical carcinoma (ACC) is approximately 20%, and adverse drug effects are frequent. To date, there is no marker established that predicts treatment response. Mitotane has been shown to inhibit sterol-O-acyl transferase 1 (SOAT1), which leads to endoplasmic reticulum stress and cell death in ACC cells.

OBJECTIVE

To investigate SOAT1 protein expression as a marker of treatment response to mitotane.

PATIENTS

A total of 231 ACC patients treated with single-agent mitotane as adjuvant (n = 158) or advanced disease therapy (n = 73) from 12 ENSAT centers were included. SOAT1 protein expression was determined by immunohistochemistry on formalin-fixed paraffin-embedded specimens.

SETTING

Retrospective study at 12 ACC referral centers.

MAIN OUTCOME MEASURE

Recurrence-free survival (RFS), progression-free survival (PFS), and disease-specific survival (DSS).

RESULTS

Sixty-one of 135 patients (45%) with adjuvant mitotane treatment had recurrences and 45/68 patients (66%) with mitotane treatment for advanced disease had progressive disease. After multivariate adjustment for sex, age, hormone secretion, tumor stage, and Ki67 index, RFS (hazard ratio [HR] = 1.07; 95% confidence interval [CI], 0.61-1.85; P = 0.82), and DSS (HR = 1.30; 95% CI, 0.58-2.93; P = 0.53) in adjuvantly treated ACC patients did not differ significantly between tumors with high and low SOAT1 expression. Similarly, in the advanced stage setting, PFS (HR = 1.34; 95% CI, 0.63-2.84; P = 0.45) and DSS (HR = 0.72; 95% CI, 0.31-1.70; P = 0.45) were comparable and response rates not significantly different.

CONCLUSIONS

SOAT1 expression was not correlated with clinical endpoints RFS, PFS, and DSS in ACC patients with mitotane monotherapy. Other factors appear to be relevant for mitotane treatment response and ACC patient survival.

New Terpendole Congeners, Inhibitors of Sterol O-Acyltransferase, Produced by Volutella citrinella BF-0440

New terpendoles N-P (1–3) were isolated along with 8 structurally related known compounds including terpendoles and voluhemins from a culture broth of the fungus Volutella citrinella BF-0440. The structures of 1–3 were elucidated using various spectroscopic experiments including 1D- and 2D-NMR. All compounds 1–3 contained a common indole–diterpene backbone. Compounds 2 and 3 had 7 and 6 consecutive ring systems with an indole ring, respectively, whereas 1 had a unique indolinone plus 4 consecutive ring system. Compounds 2 and 3 inhibited both sterol O-acyltransferase 1 and 2 isozymes, but 1 lost the inhibitory activity. Structure–activity relationships of fungal indole–diterpene compounds are discussed.

Structural insights into the inhibition mechanism of human sterol O-acyltransferase 1 by a competitive inhibitor

Sterol O-acyltransferase 1 (SOAT1) is an endoplasmic reticulum (ER) resident, multi-transmembrane enzyme that belongs to the membrane-bound O-acyltransferase (MBOAT) family. It catalyzes the esterification of cholesterol to generate cholesteryl esters for cholesterol storage. SOAT1 is a target to treat several human diseases. However, its structure and mechanism remain elusive since its discovery. Here, we report the structure of human SOAT1 (hSOAT1) determined by cryo-EM. hSOAT1 is a tetramer consisted of a dimer of dimer. The structure of hSOAT1 dimer at 3.5 Å resolution reveals that a small molecule inhibitor CI-976 binds inside the catalytic chamber and blocks the accessibility of the active site residues H460, N421 and W420. Our results pave the way for future mechanistic study and rational drug design targeting hSOAT1 and other mammalian MBOAT family members.

Assessment of acyl-CoA cholesterol acyltransferase (ACAT-1) role in ovarian cancer progression-An in vitro study

Abnormal accumulation of acyl-CoA cholesterol acyltransferase-1 (ACAT-1) mediated cholesterol ester has been shown to contribute to cancer progression in various cancers including leukemia, glioma, breast, pancreatic and prostate cancers. However, the significance of ACAT-1 and cholesterol esters (CE) is relatively understudied in ovarian cancer. In this in vitro study, we assessed the expression and contribution of ACAT-1 in ovarian cancer progression. We observed a significant increase in the expression of ACAT-1 and CE levels in a panel of ovarian cancer cell lines (OC-314, SKOV-3 and IGROV-1) compared to primary ovarian epithelial cells (normal controls). To confirm the tumor promoting capacity of ACAT-1, we inhibited ACAT-1 expression and activity by treating our cell lines with an ACAT inhibitor, avasimibe, or by stable transfection with ACAT-1 specific short hairpin RNA (shRNA). We observed significant suppression of cell proliferation, migration and invasion in ACAT-1 knockdown ovarian cancer cell lines compared to their respective controls (cell lines transfected with scrambled shRNA). ACAT-1 inhibition enhanced apoptosis with a concurrent increase in caspases 3/7 activity and decreased mitochondrial membrane potential. Increased generation of reactive oxygen species (ROS) coupled with increased expression of p53 may be the mechanism(s) underlying pro-apoptotic action of ACAT-1 inhibition. Additionally, ACAT-1 inhibited ovarian cancer cell lines displayed enhanced chemosensitivity to cisplatin treatment. These results suggest ACAT-1 may be a potential new target for the treatment of ovarian cancer.

The Anti-atherogenic Activity of Beauveriolide Derivative BVD327, a Sterol O-Acyltransferase 2-Selective Inhibitor, in Apolipoprotein E Knockout Mice

The fungal 13-membered cyclodepsipeptides, beauveriolides I and III, were previously reported to be atheroprotective activity in mouse models via inhibiting sterol O-acyltransferase (SOAT) activity. A total of 149 beauveriolide derivatives (BVDs) synthesized combinatorially were evaluated in in silico absorption, distribution, metabolism and excretion (ADME) analysis and inhibitory activity toward the two SOAT isozymes, SOAT1 and SOAT2. Hence, only 11 BVDs exhibited SOAT2-selective inhibition. Among these, we chose BVD327, which had the highest ADME score, for further evaluation. BVD327 administration (50 mg/kg/d, per os (p.o.)) significantly decreased atherosclerotic lesions in the aorta and heart (25.4 ± 6.9 and 20.6 ± 2.9%, respectively) in apolipoprotein E knockout (Apoe-/-) mice fed a cholesterol-enriched diet (0.2% cholesterol and 21% fat) for 12 weeks. These findings indicate that beauveriolide derivatives can be used as anti-atherosclerotic agents.

Determination of Penicillium griseofulvum-oriented pyripyropene A, a selective inhibitor of acyl-coenzyme A:cholesterol acyltransferase 2, in mouse plasma using liquid chromatography-tandem mass spectrometry and its application to pharmacokinetic studies

In this study, we developed a method for the determination of Penicillium griseofulvum-oriented pyripyropene A (PPPA), a selective inhibitor of acyl-coenzyme A:cholesterol acyltransferase 2, in mouse and human plasma and validated it using liquid chromatography-tandem mass spectrometry. Pyripyropene A (PPPA) and an internal standard, carbamazepine, were separated using a Xterra MS C18 column with a mixture of acetonitrile and 0.1% formic acid as the mobile phase. The ion transitions monitored in positive-ion mode [M + H]+ of multiple-reaction monitoring (MRM) were m/z 148.0 from m/z 584.0 for PPPA and m/z 194.0 from m/z 237.0 for the internal standard. The detector response was specific and linear for PPPA at concentrations within the range from 1 to 5,000 ng/mL. The intra-/inter-day precision and accuracy of the method was acceptable by the criteria for assay validation. The matrix effects of PPPA ranged from 97.6 to 104.2% and from 93.3 to 105.3% in post-preparative mouse and human plasma samples, respectively. PPPA was also stable under various processing and/or handling conditions. Finally, PPPA concentrations in the mouse plasma samples could be measured after intravenous, intraperitoneal, or oral administration of PPPA, suggesting that the assay is useful for pharmacokinetic studies on mice and applicable to human studies.

Celludinones, new inhibitors of sterol O-acyltransferase, produced by Talaromyces cellulolyticus BF-0307

New indanones, designated celludinones A ((±)-1) and B (2), were isolated from the culture broth of the fungal strain Talaromyces cellulolyticus BF-0307. The structures of celludinones were elucidated by spectroscopic data, including 1D and 2D NMR. Celludinone A was found to be a mixture of racemic isomers ((±)-1), which were isolated by a chiral column. Compounds (+)-1 and (-)-1 inhibited the sterol O-acyltransferase (SOAT) 1 and 2 isozymes in a cell-based assay using SOAT1- and SOAT2-expressing Chinese hamster ovary (CHO) cells, while 2 selectively inhibited the SOAT2 isozyme.

Bio-activity of aminosulfonyl ureas in the light of nucleic acid bases and DNA base pair interaction

The quantum chemical descriptors based on density functional theory (DFT) are applied to predict the biological activity (log IC₅₀) of one class of acyl-CoA: cholesterol O-acyltransferase (ACAT) inhibitors, viz. aminosulfonyl ureas. ACAT are very effective agents for reduction of triglyceride and cholesterol levels in human body. Successful two parameter quantitative structure-activity relationship (QSAR) models are developed with a combination of relevant global and local DFT based descriptors for prediction of biological activity of aminosulfonyl ureas. The global descriptors, electron affinity of the ACAT inhibitors (EA) and/or charge transfer (ΔN) between inhibitors and model biosystems (NA bases and DNA base pairs) along with the local group atomic charge on sulfonyl moiety (∑Q_Sul) of the inhibitors reveals more than 90% efficacy of the selected descriptors for predicting the experimental log (IC₅₀) values.

Design and Synthesis of A-Ring Simplified Pyripyropene A Analogues as Potent and Selective Synthetic SOAT2 Inhibitors

Currently, pyripyropene A, which is isolated from the culture broth of Aspergillus fumigatus FO-1289, is the only compound known to strongly and selectively inhibit the isozyme sterol O-acyltransferase 2 (SOAT2). To aid in the development of new cholesterol-lowering or anti-atherosclerotic agents, new A-ring simplified pyripyropene A analogues have been designed and synthesized based on total synthesis, and the results of structure-activity relationship studies of pyripyropene A. Among the analogues, two A-ring simplified pyripyropene A analogues exhibited equally efficient SOAT2 inhibitory activity to that of natural pyripyropene A. These new analogues are the most potent and selective SOAT2 inhibitors to be used as synthetic compounds and attractive seed compounds for the development of drug for dyslipidemia, including atherosclerotic disease and steatosis.

Biseokeaniamides A, B, and C, Sterol O-Acyltransferase Inhibitors from an Okeania sp. Marine Cyanobacterium

Biseokeaniamides A, B, and C (1-3), structurally novel sterol O-acyltransferase (SOAT) inhibitors, were isolated from an Okeania sp. marine cyanobacterium. Their structures were elucidated by spectroscopic analyses and degradation reactions. Biseokeaniamide B (2) exhibited moderate cytotoxicity against human HeLa cancer cells, and compounds 1-3 inhibited both SOAT1 and SOAT2, not only at an enzyme level but also at a cellular level. Biseokeaniamides (1-3) are the first linear lipopeptides that have been shown to exhibit SOAT-inhibitory activity.

Discovery of SOAT2 inhibitors from synthetic small molecules

Synthesis of new functionalized molecules and identification of biofunctional molecules can lead to the development of therapeutic leads and molecular tools for biomedical research. We have recently reported oxa-hetero-Diels-Alder reactions of enones with isatins to provide functionalized spirooxindole tetrahydropyran derivatives. Twenty-one compounds from the spirooxindole tetrahydropyran derivatives and related molecules were screened for inhibition of sterol O-acyltransferase (SOAT) isozymes SOAT1 and SOAT2. Three racemic derivatives inhibited the SOAT2 isozyme with three-fold or better selectivity for SOAT2 than for SOAT1. The enantiomerically enriched forms of the most efficient racemic inhibitor of SOAT2 were further evaluated; one enantiomer inhibited SOAT2 with an IC50 of 1.5μM and was 10-fold more selective for SOAT2 than SOAT1.

Identification of potential ACAT-2 selective inhibitors using pharmacophore, SVM and SVR from Chinese herbs

Acyl-coenzyme A cholesterol acyltransferase (ACAT) plays an important role in maintaining cellular and organismal cholesterol homeostasis. Two types of ACAT isozymes with different functions exist in mammals, named ACAT-1 and ACAT-2. Numerous studies showed that ACAT-2 selective inhibitors are effective for the treatment of hypercholesterolemia and atherosclerosis. However, as a typical endoplasmic reticulum protein, ACAT-2 protein has not been purified and revealed, so combinatorial ligand-based methods might be the optimal strategy for discovering the ACAT-2 selective inhibitors. In this study, selective pharmacophore models of ACAT-1 inhibitors and ACAT-2 inhibitors were built, respectively. The optimal pharmacophore model for each subtype was identified and utilized as queries for the Traditional Chinese Medicine Database screening. A total of 180 potential ACAT-2 selective inhibitors were obtained, which were identified using an ACAT-2 pharmacophore and not by our ACAT-1 model. Selective SVM model and bioactive SVR model were generated for further identification of the obtained ACAT-2 inhibitors. Ten compounds were finally obtained with predicted inhibitory activities toward ACAT-2. Hydrogen bond acceptor, 2D autocorrelations, GETAWAY descriptors, and BCUT descriptors were identified as key structural features for selectivity and activity of ACAT-2 inhibitors. This study provides a reasonable ligand-based approach to discover potential ACAT-2 selective inhibitors from Chinese herbs, which could help in further screening and development of ACAT-2 selective inhibitors.

7-Chlorofolipastatin, an inhibitor of sterol O-acyltransferase, produced by marine-derived Aspergillus ungui NKH-007

A new depsidone, named 7-chlorofolipastatin, and five known structurally related depsidones were isolated from the culture broth of the marine-derived fungus Aspergillus ungui NKM-007 by solvent extraction and HPLC using an octadecylsilyl column. The structure of 7-chlorofolipastatin was elucidated by various spectroscopic data including 1D and 2D NMR spectroscopy. 7-Chlorofolipastatin inhibited sterol O-acyltransferase (SOAT) 1 and 2 isozymes in cell-based and enzyme assays using SOAT1- and SOAT2-expressing Chinese hamster ovary (CHO) cells.

ATR-101, a Selective and Potent Inhibitor of Acyl-CoA Acyltransferase 1, Induces Apoptosis in H295R Adrenocortical Cells and in the Adrenal Cortex of Dogs

ATR-101 is a novel, oral drug candidate currently in development for the treatment of adrenocortical cancer. ATR-101 is a selective and potent inhibitor of acyl-coenzyme A:cholesterol O-acyltransferase 1 (ACAT1), an enzyme located in the endoplasmic reticulum (ER) membrane that catalyzes esterification of intracellular free cholesterol (FC). We aimed to identify mechanisms by which ATR-101 induces adrenocortical cell death. In H295R human adrenocortical carcinoma cells, ATR-101 decreases the formation of cholesteryl esters and increases FC levels, demonstrating potent inhibition of ACAT1 activity. Caspase-3/7 levels and terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate nick end labeled-positive cells are increased by ATR-101 treatment, indicating activation of apoptosis. Exogenous cholesterol markedly potentiates the activity of ATR-101, suggesting that excess FC that cannot be adequately esterified increases caspase-3/7 activation and subsequent cell death. Inhibition of calcium release from the ER or the subsequent uptake of calcium by mitochondria reverses apoptosis induced by ATR-101. ATR-101 also activates multiple components of the unfolded protein response, an indicator of ER stress. Targeted knockdown of ACAT1 in an adrenocortical cell line mimicked the effects of ATR-101, suggesting that ACAT1 mediates the cytotoxic effects of ATR-101. Finally, in vivo treatment of dogs with ATR-101 decreased adrenocortical steroid production and induced cellular apoptosis that was restricted to the adrenal cortex. Together, these studies demonstrate that inhibition of ACAT1 by ATR-101 increases FC, resulting in dysregulation of ER calcium stores that result in ER stress, the unfolded protein response, and ultimately apoptosis.

Design and synthesis of simple, yet potent and selective non-ring-A pyripyropene A-based inhibitors of acyl-coenzyme A: cholesterol acyltransferase 2 (ACAT2)

A series of pyripyropene A-based compounds were designed and synthesized by opening the upper section of the A-ring, which significantly simplifies the structure and synthesis from commercially available starting materials. Representative compound (-)-3 exhibited potent activity against ACAT2 and greater selectivity for ACAT2 than for ACAT1.

PRD125, a potent and selective inhibitor of sterol O-acyltransferase 2 markedly reduces hepatic cholesteryl ester accumulation and improves liver function in lysosomal acid lipase-deficient mice

In most organs, the bulk of cholesterol is unesterified, although nearly all possess a varying capability of esterifying cholesterol through the action of either sterol O-acyltransferase (SOAT) 1 or, in the case of hepatocytes and enterocytes, SOAT2. Esterified cholesterol (EC) carried in plasma lipoproteins is hydrolyzed by lysosomal acid lipase (LAL) when they are cleared from the circulation. Loss-of-function mutations in LIPA, the gene that encodes LAL, result in Wolman disease or cholesteryl ester storage disease (CESD). Hepatomegaly and a massive increase in tissue EC levels are hallmark features of both disorders. While these conditions can be corrected with enzyme replacement therapy, the question arose as to whether pharmacological inhibition of SOAT2 might reduce tissue EC accretion in CESD. When weaned at 21 days, Lal(-/-) mice, of either gender, had a whole liver cholesterol content that was 12- to 13-fold more than that of matching Lal(+/+) littermates (23 versus 1.8 mg, respectively). In Lal(-/-) males given the selective SOAT2 inhibitor PRD125 1,11-O-o-methylbenzylidene-7-O-p-cyanobenzoyl-1,7,11-trideacetylpyripyropene A in their diet (∼10 mg/day per kg body weight) from 21 to 53 days, whole liver cholesterol content was 48.6 versus 153.7 mg in untreated 53-day-old Lal(-/-) mice. This difference reflected a 59% reduction in hepatic EC concentration (mg/g), combined with a 28% fall in liver mass. The treated mice also showed a 63% reduction in plasma alanine aminotransferase activity, in parallel with decisive falls in hepatic mRNA expression levels for multiple proteins that reflect macrophage presence and inflammation. These data implicate SOAT2 as a potential target in CESD management.

Mitotane Inhibits Sterol-O-Acyl Transferase 1 Triggering Lipid-Mediated Endoplasmic Reticulum Stress and Apoptosis in Adrenocortical Carcinoma Cells

Adrenocortical carcinoma (ACC) is a rare malignancy that harbors a dismal prognosis in advanced stages. Mitotane is approved as an orphan drug for treatment of ACC and counteracts tumor growth and steroid hormone production. Despite serious adverse effects, mitotane has been clinically used for decades. Elucidation of its unknown molecular mechanism of action seems essential to develop better ACC therapies. Here, we set out to identify the molecular target of mitotane and altered downstream mechanisms by combining expression genomics and mass spectrometry technology in the NCI-H295 ACC model cell line. Pathway analyses of expression genomics data demonstrated activation of endoplasmic reticulum (ER) stress and profound alteration of lipid-related genes caused by mitotane treatment. ER stress marker CHOP was strongly induced and the two upstream ER stress signalling events XBP1-mRNA splicing and eukaryotic initiation factor 2 A (eIF2α) phosphorylation were activated by mitotane in NCI-H295 cells but to a much lesser extent in four nonsteroidogenic cell lines. Lipid mass spectrometry revealed mitotane-induced increase of free cholesterol, oxysterols, and fatty acids specifically in NCI-H295 cells as cause of ER stress. We demonstrate that mitotane is an inhibitor of sterol-O-acyl-transferase 1 (SOAT1) leading to accumulation of these toxic lipids. In ACC tissue samples we show variable SOAT1 expression correlating with the response to mitotane treatment. In conclusion, mitotane confers adrenal-specific cytotoxicity and down-regulates steroidogenesis by inhibition of SOAT1 leading to lipid-induced ER stress. Targeting of cancer-specific lipid metabolism opens new avenues for treatment of ACC and potentially other types of cancer.

New pyripyropene A derivatives, highly SOAT2-selective inhibitors, improve hypercholesterolemia and atherosclerosis in atherogenic mouse models

Sterol O-acyltransferase 2 (SOAT2; also known as ACAT2) is considered as a new therapeutic target for the treatment or prevention of hypercholesterolemia and atherosclerosis. Fungal pyripyropene A (PPPA: 1,7,11-triacyl type), the first SOAT2-selective inhibitor, proved orally active in vivo using atherogenic mouse models. The purpose of the present study was to demonstrate that the PPPA derivatives (PRDs) prove more effective in the mouse models than PPPA. Among 196 semisynthetic PPPA derivatives, potent, SOAT2-selective, and stable PRDs were selected. In vivo antiatherosclerotic activity of selected PRDs was tested in apolipoprotein E knockout (Apoe(-/-)) mice or low-density lipoprotein receptor knockout (Ldlr(-/-)) mice fed a cholesterol-enriched diet (0.2% cholesterol and 21% fat) for 12 weeks. During the PRD treatments, no detrimental side effects were observed. Among three PRDs, Apoe(-/-) mice treated with PRD125 (1-,11-O-benzylidene type) at 1 mg/kg/day had significantly lower total plasma cholesterol concentration by 57.9 ± 9.3%; further, the ratio of cholesteryl oleate to cholesteryl linoleate in low-density lipoprotein was lower by 55.6 ± 7.5%, respectively. The hepatic cholesteryl ester levels and SOAT2 activity in the small intestines and livers of the PRD-treated mice were selectively lowered. The atherosclerotic lesion areas in the aortae of PRD125-treated mice were significantly lower at 62.2 ± 13.1%, respectively. Furthermore, both PRDs were also orally active in atherogenic Ldlr(-/-) mice. Among the PRDs tested, PRD125 was the most potent in both mouse models. These results suggest that SOAT2-selective inhibitors such as PRD125 have a high potential as poststatin agents for treatment and/or prevention in patients with atherosclerosis and hypercholesterolemia.

Avasimibe encapsulated in human serum albumin blocks cholesterol esterification for selective cancer treatment

Undesirable side effects remain a significant challenge in cancer chemotherapy. Here we report a strategy for cancer-selective chemotherapy by blocking acyl-CoA cholesterol acyltransferase-1 (ACAT-1)-mediated cholesterol esterification. To efficiently block cholesterol esterification in cancer in vivo, we developed a systemically injectable nanoformulation of avasimibe (a potent ACAT-1 inhibitor), called avasimin. In cell lines of human prostate, pancreatic, lung, and colon cancer, avasimin significantly reduced cholesteryl ester storage in lipid droplets and elevated intracellular free cholesterol levels, which led to apoptosis and suppression of proliferation. In xenograft models of prostate cancer and colon cancer, intravenous administration of avasimin caused the concentration of avasimibe in tumors to be 4-fold higher than the IC50 value. Systemic treatment of avasimin notably suppressed tumor growth in mice and extended the length of survival time. No adverse effects of avasimin to normal cells and organs were observed. Together, this study provides an effective approach for selective cancer chemotherapy by targeting altered cholesterol metabolism of cancer cells.

Extra-hepatic metabolism of 7-ketocholesterol occurs by esterification to fatty acids via cPLA2α and SOAT1 followed by selective efflux to HDL

Accumulation of 7-ketocholesterol (7KCh) in tissues has been previously associated with various chronic aging diseases. Orally ingested 7KCh is readily metabolized by the liver and does not pose a toxicity threat. However, 7KCh formed in situ, usually associated with lipoprotein deposits, can adversely affect surrounding tissues by causing inflammation and cytotoxicity. In this study we have investigated various mechanisms for extra-hepatic metabolism of 7KCh (e.g. hydroxylation, sulfation) and found only esterification to fatty acids. The esterification of 7KCh to fatty acids involves the combined action of cytosolic phospholipase A2 alpha (cPLA2α) and sterol O-acyltransferase (SOAT1). Inhibition of either one of these enzymes ablates 7KCh-fatty acid ester (7KFAE) formation. The 7KFAEs are not toxic and do not induce inflammatory responses. However, they can be unstable and re-release 7KCh. The higher the degree of unsaturation, the more unstable the 7KFAE (e.g. 18:0>18:1>18:2>18:3≫20:4). Biochemical inhibition and siRNA knockdown of SOAT1 and cPLA2α ablated the 7KFAE synthesis in cultured ARPE19 cells, but had little effect on the 7KCh-induced inflammatory response. Overexpression of SOAT1 reduced the 7KCh-induced inflammatory response and provided some protection from cell death. This effect is likely due to the increased conversion of 7KCh to 7KFAEs, which reduced the intracellular 7KCh levels. Addition of HDL selectively increased the efflux of 7KFAEs and enhanced the effect of SOAT1 overexpression. Our data suggests an additional function for HDL in aiding extra-hepatic tissues to eliminate 7KCh by returning 7KFAEs to the liver for bile acid formation.

In vitro metabolism of pyripyropene A and ACAT inhibitory activity of its metabolites

Pyripyropene A (PPPA, 1) of fungal origin, a selective inhibitor of acyl-CoA:cholesterol acyltransferase 2 (ACAT2), proved orally active in atherogenic mouse models. The in vitro metabolites of 1 in liver microsomes and plasma of human, rabbit, rat and mouse were analyzed by ultra fast liquid chromatography and liquid chromatography/tandem mass spectrometry. In the liver microsomes from all species, successive hydrolysis occurred at the 1-O-acetyl residue, then at the 11-O-acetyl residue of 1, while the 7-O-acetyl residue was resistant to hydrolysis. Furthermore, dehydrogenation of the newly generated 11-alcoholic hydroxyl residue occurred in human and mouse-liver microsomes, while oxidation of the pyridine ring occurred in human and rabbit liver microsomes. On the other hand, hydrolysis of the 7-O-acetyl residue proceeded only in the mouse plasma. These data indicated that the in vitro metabolic profiles of 1 have subtle differences among animal species. All of the PPPA metabolites observed in liver microsomes and plasma markedly decreased ACAT2 inhibitory activity. These findings will help us to synthesize new PPPA derivatives more effective in in vivo study than 1.

Berberine decreases cholesterol levels in rats through multiple mechanisms, including inhibition of cholesterol absorption

OBJECTIVE

The objective was to determine the mechanisms of action of berberine (BBR) on cholesterol homeostasis using in vivo and in vitro models.

METHODS

Male Sprague-Dawley rats were fed the AIN-93G diet (normal control) or modified AIN-93G diet containing 28% fat, 2% cholesterol and 0.5% cholic acid with treatment of 0 (atherogenic control), 50, 100, and 150 mg/kg·d of BBR, respectively by gavaging in water for 8 weeks. Cholesterol absorption rate was measured with the dual stable isotope ratio method, and plasma lipids were determined using the enzymatic methods. Gene and protein expressions of Acyl-coenzyme A:cholesterol acyltransferase-2 were analyzed in vivo and in vitro. Cholesterol micellarization, uptake and permeability were determined in vitro.

RESULTS

Rats on the atherogenic diet showed significantly hypercholesterolemic characteristics compared to normal control rats. Treatment with BBR in rats on the atherogenic diet reduced plasma total cholesterol and nonHDL cholesterol levels by 29%-33% and 31%-41%, respectively, with no significant differences being observed among the three doses. The fractional dietary cholesterol absorption rate was decreased by 40%-51%. Rats fed the atherogenic diet showed lower plasma triacylglycerol levels, and no changes were observed after the BBR treatment. BBR interfered with cholesterol micellarization, decreased cholesterol uptake by Caco-2 cells and permeability through Caco-2 monolayer. BBR also inhibited the gene and protein expressions of acyl-coenzyme A cholesterol acyltransferease-2 in the small intestine and Caco-2 cells.

CONCLUSION

BBR lowered blood cholesterol levels at least in part through inhibiting the intestinal absorption and further by interfering with intraluminal cholesterol micellarization and decreasing enterocyte cholesterol uptake and secretion.

Hepatitis C virus infection mediates cholesteryl ester synthesis to facilitate infectious particle production

Cholesterol is a critical component of the hepatitis C virus (HCV) life cycle, as demonstrated by its accumulation within infected hepatocytes and lipoviral particles. To cope with excess cholesterol, hepatic enzymes ACAT1 and ACAT2 produce cholesteryl esters (CEs), which are destined for storage in lipid droplets or for secretion as apolipoproteins. Here we demonstrate in vitro that cholesterol accumulation following HCV infection induces upregulation of the ACAT genes and increases CE synthesis. Analysis of human liver biopsy tissue showed increased ACAT2 mRNA expression in liver infected with HCV genotype 3, compared with genotype 1. Inhibiting cholesterol esterification using the potent ACAT inhibitor TMP-153 significantly reduced production of infectious virus, but did not inhibit virus RNA replication. Density gradient analysis showed that TMP-153 treatment caused a significant increase in lipoviral particle density, suggesting reduced lipidation. These data suggest that cholesterol accumulation following HCV infection stimulates the production of CE, a major component of lipoviral particles. Inhibition of CE synthesis reduces HCV particle density and infectivity, suggesting that CEs are required for optimal infection of hepatocytes.

Acute sterol o-acyltransferase 2 (SOAT2) knockdown rapidly mobilizes hepatic cholesterol for fecal excretion

The primary risk factor for atherosclerotic cardiovascular disease is LDL cholesterol, which can be reduced by increasing cholesterol excretion from the body. Fecal cholesterol excretion can be driven by a hepatobiliary as well as a non-biliary pathway known as transintestinal cholesterol efflux (TICE). We previously showed that chronic knockdown of the hepatic cholesterol esterifying enzyme sterol O-acyltransferase 2 (SOAT2) increased fecal cholesterol loss via TICE. To elucidate the initial events that stimulate TICE, C57Bl/6 mice were fed a high cholesterol diet to induce hepatic cholesterol accumulation and were then treated for 1 or 2 weeks with an antisense oligonucleotide targeting SOAT2. Within 2 weeks of hepatic SOAT2 knockdown (SOAT2HKD), the concentration of cholesteryl ester in the liver was reduced by 70% without a reciprocal increase in hepatic free cholesterol. The rapid mobilization of hepatic cholesterol stores resulted in a ∼ 2-fold increase in fecal neutral sterol loss but no change in biliary cholesterol concentration. Acute SOAT2HKD increased plasma cholesterol carried primarily in lipoproteins enriched in apoB and apoE. Collectively, our data suggest that acutely reducing SOAT2 causes hepatic cholesterol to be swiftly mobilized and packaged onto nascent lipoproteins that feed cholesterol into the TICE pathway for fecal excretion.

Recent failures in antiatherosclerotic drug development: examples from the thyroxin receptor agonist, the secretory phospholipase A2 antagonist, and the acyl coenzyme A: cholesterol acyltransferase inhibitor programs

PURPOSE OF REVIEW

To review the published data related to the rise and fall of three different therapeutic approaches, which were investigated to lower cardiovascular disease (CVD) risk.

RECENT FINDINGS

CVD remains a major burden of morbidity and mortality, despite therapeutic interventions. Novel strategies to address this residual risk are eagerly awaited, and a number of novel targets for therapy have been identified. Lipids and lipoproteins have been shown to play an eminent role in atherosclerosis progression, and as such, interventions that influence these biomarkers are crucial in CVD risk prevention. In recent years, however, clinical studies investigating the effect of novel lipid-modifying drugs on cardiovascular risk prevention have not always resulted in the anticipated beneficial outcome. Moreover, the development of therapies directed toward bioactive proteins acting at the crossroads of lipids and inflammation has also been disappointing.

SUMMARY

In this review, we will specifically address the rationale, design, and results of the clinical trials investigating the effects of three of the failing therapies: the thyroxin receptor agonist, the secretory phospholipase A2 antagonist, and the acyl coenzyme A:cholesterol acyltransferase inhibitor.

Synthesis and structure-activity relationship of pyripyropene A derivatives as potent and selective acyl-CoA:cholesterol acyltransferase 2 (ACAT2) inhibitors: part 3

In an effort to develop potent and selective inhibitors toward ACAT2, structure-activity relationship studies were carried out using derivatives based on pyripyropene A (PPPA, 1). In particular, we investigated the possibility of introducing appropriate 1,11-O-benzylidene and 7-O-substituted benzoyl moieties into PPPA (1). The new o-substituted benzylidene derivatives showed higher selectivity for ACAT2 than PPPA (1). Among them, 1,11-O-o-methylbenzylidene-7-O-p-cyanobenzoyl PPPA derivative 7q and 1,11-O-o,o-dimethylbenzylidene-7-O-p-cyanobenzoyl PPPA derivative 7z proved to be potent ACAT2 inhibitors with unprecedented high isozyme selectivity.

Prediction of bioactivity of ACAT2 inhibitors by multilinear regression analysis and support vector machine

Two quantitative structure-activity relationships (QSAR) models for predicting 95 compounds inhibiting Acyl-coenzyme A: cholesterol acyltransferase2 (ACAT2) were developed. The whole data set was randomly split into a training set including 72 compounds and a test set including 23 compounds. The molecules were represented by 11 descriptors calculated by software ADRIANA.Code. Then the inhibitory activity of ACAT2 inhibitors was predicted using multilinear regression (MLR) analysis and support vector machine (SVM) method, respectively. The correlation coefficients of the models for the test sets were 0.90 for MLR model, and 0.91 for SVM model. Y-randomization was employed to ensure the robustness of the SVM model. The atom charge and electronegativity related descriptors were important for the interaction between the inhibitors and ACAT2.

Synthesis and structure-activity relationship of pyripyropene A derivatives as potent and selective acyl-CoA:cholesterol acyltransferase 2 (ACAT2) inhibitors: part 2

Synthesis and structure-activity relationships of 7-O-p-cyanobenzoyl pyripyropene A derivatives with modification at C1 and 11 are described. Regioselective mono-deprotection of di-tert-butylsilylene acetal was critical in their synthesis.

Blueberry anthocyanins at doses of 0.5 and 1 % lowered plasma cholesterol by increasing fecal excretion of acidic and neutral sterols in hamsters fed a cholesterol-enriched diet

PURPOSE

The present study investigated the underlying mechanism associated with the hypocholesterolemic activity of blueberry anthocyanins by examining its effect on fecal sterol excretion and gene expression of major receptors, enzymes, and transporters involved in cholesterol metabolism.

METHODS

Hamsters were divided into three groups and fed a 0.1 % cholesterol diet containing 0 % (CTL), 0.5 % (BL), and 1.0 % (BH) blueberry anthocyanins, respectively, for six weeks. Plasma total cholesterol (TC), triacylglycerols (TAG), and non-high-density lipoproteins cholesterol (non-HDL-C) were measured using the enzymatic kits, and the gene expression of transporters, enzymes, and receptors involved in cholesterol absorption and metabolism was quantified using the quantitative PCR. GC analysis was used to quantify hepatic cholesterol and fecal acidic and neutral sterols.

RESULTS

Dietary supplementation of 0.5 and 1.0 % blueberry anthocyanins for 6 weeks decreased plasma TC concentration by 6-12 % in a dose-dependent manner. This was accompanied by increasing the excretion of fecal neutral and acidic sterols by 22-29 % and 41-74 %, respectively. Real-time PCR analyses demonstrated that incorporation of blueberry anthocyanins into diet down-regulated the genes of NPC1L1, ACAT-2, MTP, and ABCG 8. In addition, blueberry anthocyanins were also able to down-regulate the gene expression of hepatic HMG-CoA reductase.

CONCLUSION

The cholesterol-lowering activity of blueberry anthocyanins was most likely mediated by enhancing the excretion of sterols accompanied with down-regulation on gene expression of intestinal NPC1L1, ACAT-2, MTP, and ABCG 8.

Synthesis and structure-activity relationship of pyripyropene A derivatives as potent and selective acyl-CoA:cholesterol acyltransferase 2 (ACAT2) inhibitors: part 1

In an effort to develop potent and selective inhibitors toward ACAT2, structure-activity relationship studies were carried out using derivatives based on pyripyropene A (PPPA, 1). We have successfully developed novel PPPA derivatives with a 7-O-substituted benzoyl substituent that significantly exhibit more potent ACAT2 inhibitory activity and higher ACAT2 isozyme selectivity than 1.

Using self-organizing map (SOM) and support vector machine (SVM) for classification of selectivity of ACAT inhibitors

Using a self-organizing map (SOM) and support vector machine, two classification models were built to predict whether a compound is a selective inhibitor toward the two Acyl-coenzyme A: cholesterol acyltransferase (ACAT) isozymes, ACAT-1 and ACAT-2. A dataset of 97 ACAT inhibitors was collected. For each molecule, the global descriptors, 2D and 3D property autocorrelation descriptors and autocorrelation of surface properties were calculated from the program ADRIANA.Code. The prediction accuracies of the models (based on the training/ test set splitting by SOM method) for the test sets are 88.9 % for SOM1, 92.6 % for SVM1 model. In addition, the extended connectivity fingerprints (ECFP_4) for all the molecules were calculated and the structure-activity relationship of selective ACAT inhibitors was summarized, which may help find important structural features of inhibitors relating to the selectivity of ACAT isozymes.

ACAT inhibitory activity of exudates from Calocedrus macrolepis var. formosana

Cholesterol acyltransferase (ACAT) is an enzyme controlling cholesterol esterification in cells. Large amounts of cholesterol esters accumulate in macrophages and smooth muscle cells of blood vessel walls resulting in the initial stages of atherosclerosis. Thus, atherosclerosis might be inhibited through inhibition of the activity of ACAT. In the present study, we identified by spectral analysis and chromatographic quantification that ferruginol was the most abundant component of exudates secreted from the wounding site of Calocedrus macrolepis Kurz var. formosana. Results obtained from the cholesterol absorption assay revealed that ferruginol exhibited a significant inhibitory activity on cholesterol absorption in mice macrophages (RAW 264.7 cell). Based on the results from analyzing the ratio of cholesterol esterification, ferruginol dose-dependently suppressed cholesterol esterification and the IC50 value was 2.0 microg/mL. In conclusion, ferruginol revealed strong inhibitory activities that retarded the absorption and esterification of cholesterol in cells. Our finding indicates that ferruginol might possess a potential for development as a pharmaceutical product for preventing arteriosclerosis.

Fatty acyl esterification and deesterification of 17β-estradiol in human breast subcutaneous adipose tissue

CONTEXT

Adipose tissue has an important role in peripheral estrogen synthesis. One of the metabolic pathways of estradiol (E(2)) is its conversion to lipophilic fatty acyl esters.

OBJECTIVE

The aim was to study the metabolism of E(2) fatty acyl esters in adipose tissue and, specifically, the role of hormone-sensitive lipase (HSL) in steroid ester hydrolysis.

DESIGN AND SETTING

Tissue samples were obtained during elective surgery in University Central Hospital in the years 2008-2011.

PATIENTS

Women undergoing reduction mammoplasty (n = 27) or surgery for breast cancer (n = 16) participated in the study.

INTERVENTIONS

Two sc adipose tissue samples were taken from different quadrants of the breast. Radiolabeled steroids were incubated with tissue homogenate (esterase assay) or microsomal fraction (acyl transferase assay). E(2) and E(2) fatty acyl ester concentrations were determined by fluoroimmunoassay or liquid chromatography-tandem mass spectrometry.

MAIN OUTCOME MEASURES

We evaluated the hydrolysis rate of E(2) fatty acyl esters as well as the esterification rate of E(2); we also related tissue concentrations of E(2) and E(2) esters to serum estrogen concentrations.

RESULTS

Compared to esters of dehydroepiandrosterone and cholesterol, the hydrolysis of E(2) esters was much slower, whereas the esterification rate of E(2) was higher. The hydrolysis of E(2) esters in adipose tissue was reduced by 33-51% by inhibition of HSL. Estrogen concentration in sc adipose tissue was higher than in serum in both pre- and postmenopausal women.

CONCLUSIONS

E(2) fatty acyl esters in adipose tissue surrounding the mammary gland may act as a reservoir for conversion back to biologically active E(2). This is partly dependent on HSL activity.

New verticilides, inhibitors of acyl-CoA:cholesterol acyltransferase, produced by Verticillium sp. FKI-2679

Verticillium sp. FKI-2679, a soil isolate, was found to produce inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT) in a cell-based assay using ACAT1- and ACAT2-expressing CHO cells. Three new compounds, verticilides A2, A3 and B1, were isolated along with a known compound, verticilide A1, from the fermentation broth of the fungus by solvent extraction, ODS column chromatography, silica gel column chromatography and preparative HPLC. Structure elucidation showed that these compounds were new cyclic depsipeptide. Verticilides A1, A2, A3 and B1 showed a degree of selectivity towards ACAT2, with IC(50)s 8.5-11-fold more potent than observed against ACAT1.

Tomatidine, a tomato sapogenol, ameliorates hyperlipidemia and atherosclerosis in apoE-deficient mice by inhibiting acyl-CoA:cholesterol acyl-transferase (ACAT)

It was previously revealed that esculeoside A, a new glycoalkaloid, and esculeogenin A, a new aglycon of esculeoside A, contained in ripe tomato ameliorate atherosclerosis in apoE-deficent mice. This study examined whether tomatidine, the aglycone of tomatine, which is a major tomato glycoalkaloid, also shows similar inhibitory effects on cholesterol ester (CE) accumulation in human monocyte-derived macrophages (HMDM) and atherogenesis in apoE-deficient mice. Tomatidine significantly inhibited the CE accumulation induced by acetylated LDL in HMDM in a dose-dependent manner. Tomatidine also inhibited CE formation in Chinese hamster ovary cells overexpressing acyl-CoA:cholesterol acyl-transferase (ACAT)-1 or ACAT-2, suggesting that tomatidine suppresses both ACAT-1 and ACAT-2 activities. Furthermore, the oral administration of tomatidine to apoE-deficient mice significantly reduced levels of serum cholesterol, LDL-cholesterol, and areas of atherosclerotic lesions. The study provides the first evidence that tomatidine significantly suppresses the activity of ACAT and leads to reduction of atherogenesis.

Hypolipidemic and Antioxidant Activity of the Novel Acyl-CoA:Cholesterol Acyltransferase (ACAT) Inhibitor KY-455 in Rabbits and Hamsters

The hypolipidemic and antioxidant effects of N-(4,6-dimethyl-1-pentylindolin-7-yl)-2,2-dimethylpropanamide (CAS 178469-71-1, KY-455), a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, were examined in hyperlipidemic rabbits and normolipidemic hamsters. KY-455 inhibited rabbit intestinal, hepatic, macrophage and adrenal ACAT with IC50 values of 0.4, 0.9, 2.9 and 4.1 micromol/l, respectively. KY-455 also inhibited rabbit plasma and LDL-peroxidation (IC50: 0.4 and 1.7 micromol/l, respectively). In rabbits fed a high-cholesterol diet, treatment with KY-455 (30 mg/kg/day) for 8 days markedly lowered serum esterified, free, low-density lipoprotein (LDL)-cholesterol, and hepatic esterified cholesterol levels. KY-455 tended to inhibit ex vivo hepatic ACAT activity 5 h after the final administration. KY-455 also inhibited ex vivo peroxidation of plasma lipids 1 and 5 h after the final administration in rabbits. In normolipidemic hamsters fed a regular diet, treatment with KY-455 (30 mg/kg, twice a day) for 4 days significantly reduced serum esterified, free and LDL-cholesterol, and hepatic esterified and free cholesterol levels. A single administration of KY-455 (30 mg/kg) significantly inhibited ex vivo hepatic ACAT activity in hamsters. In conclusion, KY-455 showed in vitro inhibitory effects on LDL-peroxidation and macrophage ACAT activity at similar concentrations, and in vivo hypolipidemic and ex vivo antioxidative effects at the same dose. Long-term administration of KY-455 is expected to prevent the progress of atherosclerosis by lowering plasma lipid levels, inhibiting both LDL-oxidation and accumulation of cholesterol in macrophages.

Intestinal sterol transporters and cholesterol absorption inhibition

PURPOSE OF REVIEW

Statin therapy is the mainstay of lipid-lowering therapy; however, many patients, particularly those at high risk, do not achieve sufficient LDL-cholesterol (LDL-C) lowering. Thus, there remains an unmet medical need for more effective and well tolerated lipid-lowering agents. Guidelines recommend combining additional lipid-lowering agents with a complementary mode of action for these patients. One approach to complementing statin therapy is combination with inhibitors that block the intestinal absorption of dietary and biliary cholesterol. This review summarizes what is currently known about intestinal sterol transporters and cholesterol absorption inhibitors (CAIs).

RECENT FINDINGS

The only lipid-lowering agent currently available that specifically targets an intestinal sterol transporter (Niemann-Pick C1-like 1) is the CAI, ezetimibe. It is effective in lowering LDL-C, both when given alone and when combined with a statin. Clinical outcome data with ezetimibe combined with simvastatin have recently become available, and definitive evidence that the incremental LDL-C lowering attributable to the ezetimibe component reduces cardiovascular events beyond simvastatin alone is currently under study. Other novel CAIs have been evaluated based upon the structure and properties of ezetimibe, but none remain in development.

SUMMARY

Additional lipid-lowering agents are needed to fulfill an unmet medical need for those patients who do not achieve optimal LDL-C goals on statin monotherapy. The inhibition of cholesterol absorption is an important therapeutic strategy to reduce cholesterol levels. Based upon the demonstrated lipid-altering efficacy and safety of ezetimibe, several CAIs have been identified; all to date have been discontinued due to limited efficacy.

Pyripyropene A, an acyl-coenzyme A:cholesterol acyltransferase 2-selective inhibitor, attenuates hypercholesterolemia and atherosclerosis in murine models of hyperlipidemia

OBJECTIVE

Pyripyropene A (PPPA) of fungal origin is the first compound that has been found to strongly and selectively inhibit acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) isozyme activity in vitro. The purpose of the present study was to investigate in vivo efficacy of the ACAT2-selective inhibitor in atherosclerosis.

METHODS AND RESULTS

PPPA treatment (10 to 100 mg/kg) caused 30.5±4.7% to 55.8±3.3% inhibition of the cholesterol absorption from the mouse intestine. When PPPA (10 to 50 mg/kg per day) was orally administered to apolipoprotein E-knockout mice for 12 weeks, the levels of plasma cholesterol, very-low-density lipoprotein (VLDL), and low-density lipoprotein (LDL) and hepatic cholesterol content were lowered. Furthermore, the ratio of cholesteryl oleate (exclusively synthesized in hepatic ACAT2) to cholesteryl linoleate in VLDL- and LDL-derived cholesteryl ester decreased, indicating that hepatic ACAT2 activity was inhibited by PPPA. PPPA-treated mice had reduced atherogenic lesion areas that were lowered by 26.2±3.7% to 46±3.8% in the aortae and by 18.9±3.6% to 37.6±6.0% in the hearts.

CONCLUSIONS

Our findings indicate that ACAT2-selective inhibition in the intestine and the liver can be effective against atherosclerosis and that PPPA appears to be a potential antiatherogenic lead compound. This study is the first demonstration of the in vivo efficacy of PPPA, an ACAT2-selective inhibitor, in atherosclerosis. PPPA-treated atherogenic mice showed a decrease in intestinal cholesterol absorption and cholesterol and cholesteryl oleate levels in both LDL and VLDL, resulting in protection of atherosclerosis development.

Rimonabant is a dual inhibitor of acyl CoA:cholesterol acyltransferases 1 and 2

Acyl coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the intracellular synthesis of cholesteryl esters (CE). Both ACAT isoforms, ACAT1 and ACAT2, play key roles in the pathophysiology of atherosclerosis and ACAT inhibition retards atherosclerosis in animal models. Rimonabant, a type 1 cannabinoid receptor (CB1) antagonist, produces anti-atherosclerotic effects in humans and animals by mechanisms which are not completely understood. Rimonabant is structurally similar to two other cannabinoid receptor antagonists, AM251 and SR144528, recently identified as potent inhibitors of ACAT. Therefore, we examined the effects of Rimonabant on ACAT using both in vivo cell-based assays and in vitro cell-free assays. Rimonabant dose-dependently reduced ACAT activity in Raw 264.7 macrophages (IC(50)=2.9+/-0.38 microM) and isolated peritoneal macrophages. Rimonabant inhibited ACAT activity in intact CHO-ACAT1 and CHO-ACAT2 cells and in cell-free assays with approximately equal efficiency (IC(50)=1.5+/-1.2 microM and 2.2+/-1.1 microM for CHO-ACAT1 and CHO-ACAT2, respectively). Consistent with ACAT inhibition, Rimonabant treatment blocked ACAT-dependent processes in macrophages, oxysterol-induced apoptosis and acetylated-LDL induced foam cell formation. From these results we conclude that Rimonabant is an ACAT1/2 dual inhibitor and suggest that some of the atherosclerotic beneficial effects of Rimonabant are, at least partly, due to inhibition of ACAT.

The acyl-coenzyme A: cholesterol acyltransferase inhibitor CI-1011 reverses diffuse brain amyloid pathology in aged amyloid precursor protein transgenic mice

Cerebral accumulation of amyloid-beta (Abeta) is characteristic of Alzheimer disease and of amyloid precursor protein (APP) transgenic mice. Here, we assessed the efficacy of CI-1011, an inhibitor of acyl-coenzyme A:cholesterol acyltransferase, which is suitable for clinical use, in reducing amyloid pathology in both young (6.5 months old) and aged (16 months old) human APP transgenic mice. Treatment of young animals with CI-1011 decreased amyloid plaque load in the cortex and hippocampus and reduced the levels of insoluble Abeta40 and Abeta42 and C-terminal fragments of APP in brain extracts. In aged mice, CI-1011 specifically reduced diffuse amyloid plaques with a minor effect on thioflavin S-positive dense-core plaques. Reduced diffusible amyloid was accompanied by suppression of astrogliosis and enhanced microglial activation. Collectively, these data suggest that CI-1011 treatment reduces amyloid burden in human APP mice by limiting generation and increasing clearance of diffusible Abeta.

Inhibition of acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) prevents dietary cholesterol-associated steatosis by enhancing hepatic triglyceride mobilization

Acyl-CoA:cholesterol O-acyl transferase 2 (ACAT2) promotes cholesterol absorption by the intestine and the secretion of cholesteryl ester-enriched very low density lipoproteins by the liver. Paradoxically, mice lacking ACAT2 also exhibit mild hypertriglyceridemia. The present study addresses the unexpected role of ACAT2 in regulation of hepatic triglyceride (TG) metabolism. Mouse models of either complete genetic deficiency or pharmacological inhibition of ACAT2 were fed low fat diets containing various amounts of cholesterol to induce hepatic steatosis. Mice genetically lacking ACAT2 in both the intestine and the liver were dramatically protected against hepatic neutral lipid (TG and cholesteryl ester) accumulation, with the greatest differences occurring in situations where dietary cholesterol was elevated. Further studies demonstrated that liver-specific depletion of ACAT2 with antisense oligonucleotides prevents dietary cholesterol-associated hepatic steatosis both in an inbred mouse model of non-alcoholic fatty liver disease (SJL/J) and in a humanized hyperlipidemic mouse model (LDLr(-/-), apoB(100/100)). All mouse models of diminished ACAT2 function showed lowered hepatic triglyceride concentrations and higher plasma triglycerides secondary to increased hepatic secretion of TG into nascent very low density lipoproteins. This work demonstrates that inhibition of hepatic ACAT2 can prevent dietary cholesterol-driven hepatic steatosis in mice. These data provide the first evidence to suggest that ACAT2-specific inhibitors may hold unexpected therapeutic potential to treat both atherosclerosis and non-alcoholic fatty liver disease.

Estrogen decreases atherosclerosis in part by reducing hepatic acyl-CoA:cholesterol acyltransferase 2 (ACAT2) in monkeys

OBJECTIVE

Estrogens decrease atherosclerosis progression, mediated in part through changes in plasma lipids and lipoproteins. This study aimed to determine estrogen-induced changes in hepatic cholesterol metabolism, plasma lipoproteins, and the relationship of these changes to atherosclerosis extent.

METHODS AND RESULTS

Ovariectomized monkeys (n=34) consumed atherogenic diets for 30 months which contained either no hormones (control, n=17) or conjugated equine estrogens (CEE, n=17) at a human dose equivalent of 0.625 mg/d. Hepatic cholesterol content, low-density lipoprotein (LDL) receptor expression, cholesterol 7 alpha-hydroxylase and acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity, and expression levels were determined. CEE treatment resulted in lower plasma concentrations of very-low- and intermediate- density lipoprotein cholesterol (V+IDLC; P=0.01), smaller LDL particles (P=0.002), and 50% lower hepatic cholesterol content (total, free, and esterified; P<0.05 for all). Total ACAT activity was significantly lower (P=0.01), explained primarily by reductions in the activity of ACAT2. Estrogen regulation of enzymatic activity was at the protein level as both ACAT1 and 2 protein, but not mRNA levels, were lower (P=0.02 and <0.0001, respectively). ACAT2 activity was significantly associated with hepatic total cholesterol, plasma V+IDLC cholesterol, and atherosclerosis.

CONCLUSIONS

Atheroprotective effects of estrogen therapy may be related to reduced hepatic secretion of ACAT2-derived cholesteryl esters in plasma lipoproteins.

The molecular target of rubimaillin in the inhibition of lipid droplet accumulation in macrophages

The naphthohydroquinone rubimaillin, which has an angular-type three cyclic skeleton and was isolated from the Chinese medical plant Rubia cordifola, was found to inhibit lipid droplet accumulation in mouse macrophages and to selectively inhibit cholesteryl ester synthesis (IC(50): 18 microM). The metabolism of cholesterol from lysosomes to lipid droplets was inhibited by the compound with a similar IC(50) (45 microM). Moreover, rubimaillin inhibited acyl-CoA:cholesterol acyltransferase (ACAT1) activity in ACAT1-expressing cells (IC(50): 80 microM). Thus, these data strongly suggest that rubimaillin inhibits macrophage ACAT activity in order to decrease cholesteryl ester (CE) synthesis, leading to a reduction in the number of lipid droplets. Furthermore, rubimaillin was found to inhibit the ACAT2 isozyme in ACAT2-expressing cells (IC(50): 22 microM). We concluded that rubimaillin is a dual inhibitor of ACAT1 and ACAT2, but is more selective for the ACAT2 isozyme.

The selectivity of beauveriolide derivatives in inhibition toward the two isozymes of acyl-CoA: cholesterol acyltransferase

The selectivity of synthetic beauveriolide derivatives in inhibition toward the two isozymes of acyl-CoA : cholesterol acyltrasferase (ACAT), ACAT1 and ACAT2, was studied in cell-based assays using ACAT1- or ACAT2-expressing Chinese hamster ovary (CHO) cells. NBV274, 285 and 300 showed ACAT1 selective inhibition similar to that of natural beauveriolides I and III, NBV345 inhibited both isozymes with similar potency, but NBV281, 331 and 249 were found to selectively inhibit the ACAT2 isozyme. The structure-activity relationships indicated that a subtle structural difference in beauveriolide derivatives can affect the selectivity of inhibition of the ACAT isozymes.

ACAT inhibition and progression of carotid atherosclerosis in patients with familial hypercholesterolemia: the CAPTIVATE randomized trial

CONTEXT

Inhibition of acyl coenzyme A:cholesterol acyltransferase (ACAT), an intracellular enzyme involved in cholesterol accumulation, with pactimibe was developed to assist in the prevention of cardiovascular disease.

OBJECTIVE

To evaluate the efficacy and safety of pactimibe in inhibition of atherosclerosis.

DESIGN, SETTING, AND PATIENTS

A prospective, randomized, stratified, double-blind, placebo-controlled study (Carotid Atherosclerosis Progression Trial Investigating Vascular ACAT Inhibition Treatment Effects [CAPTIVATE]) of 892 patients heterozygous for familial hypercholesterolemia conducted at 40 lipid clinics in the United States, Canada, Europe, South Africa, and Israel between February 1, 2004, and December 31, 2005. Study was terminated on October 26, 2005.

INTERVENTION

Participants received either 100 mg/d of pactimibe (n = 443) or matching placebo (n = 438), in addition to standard lipid-lowering therapy.

MAIN OUTCOME MEASURES

Carotid atherosclerosis, assessed by ultrasound carotid intima-media thickness (CIMT), at baseline, 12, 18, and 24 months. Maximum CIMT was the primary end point and mean CIMT the secondary end point.

RESULTS

Because pactimibe failed to show efficacy in the intravascular coronary ultrasound ACTIVATE study, the CAPTIVATE study was terminated prematurely after a follow-up of 15 months. After 6 months of treatment with pactimibe, low-density lipoprotein cholesterol increased by 7.3% (SD, 23%) compared with 1.4% (SD, 28%) in the placebo group (P = .001). The carotid ultrasonographic scans of the 716 patients with at least 2 scans and obtained at least 40 weeks apart were analyzed. Maximum CIMT measurements did not show a pactimibe treatment effect (difference, 0.004 mm; 95% confidence interval [CI], -0.023 to 0.015 mm; P = .64); however, the less variable mean CIMT measurement revealed an increase of 0.014 mm (95% CI, -0.027 to 0.000 mm; P = .04) in patients administered pactimibe vs placebo. Major cardiovascular events (cardiovascular death, myocardial infarction, and stroke) occurred more often in patients administered pactimibe vs placebo (10/443 [2.3%] vs 1/438 [0.2%]; P = .01).

CONCLUSIONS

In patients with familial hypercholesterolemia, pactimibe had no effect on atherosclerosis as assessed by changes in maximum CIMT compared with placebo but was associated with an increase in mean CIMT as well as increased incidence of major cardiovascular events.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00151788.