ACAT inhibitors: the search for a novel and effective treatment of hypercholesterolemia and atherosclerosis

Phytochemistry and biological activity of Erigeron annuus (L.) Pers

Erigeron annuus L. is a flowering herb of North America, Europe, Asia and Russia. This plant is used as folk medicine in China for the cure of indigestion, enteritis, epidemic hepatitis, haematuria and diabetes. Phytochemical studies showed the presence of 170 bioactive compounds like coumarins, flavonoids, terpenoids, polyacetylenic compounds; γ-pyrone derivatives, sterols and various caffeoylquinic acids derived from the essential oil and organic extracts from its various parts such as aerial parts, roots, leaves, stems and flowers. The pharmacological studies demonstrated various extracts and the compounds of E. annuus to exhibit anti-fungal, anti-atherosclerosis, anti-inflammatory, antidiabetic, phytotoxic, cytoprotective, antiobesity and antioxidant activities. This article covers a critical compendious on geographical distribution, botanical description, phytochemistry, ethnomedicinal uses and pharmacological activities of E. annuus. However, further in-depth studies are needed to determine the medical uses of E. annuus and its chemical constituents, pharmacological activities and clinical applications.

Stealth Liposomes Encapsulating a Potent ACAT1/SOAT1 Inhibitor F12511: Pharmacokinetic, Biodistribution, and Toxicity Studies in Wild-Type Mice and Efficacy Studies in Triple Transgenic Alzheimer's Disease Mice

Cholesterol is essential for cellular function and is stored as cholesteryl esters (CEs). CEs biosynthesis is catalyzed by the enzymes acyl-CoA:cholesterol acyltransferase 1 and 2 (ACAT1 and ACAT2), with ACAT1 being the primary isoenzyme in most cells in humans. In Alzheimer's Disease, CEs accumulate in vulnerable brain regions. Therefore, ACATs may be promising targets for treating AD. F12511 is a high-affinity ACAT1 inhibitor that has passed phase 1 safety tests for antiatherosclerosis. Previously, we developed a nanoparticle system to encapsulate a large concentration of F12511 into a stealth liposome (DSPE-PEG2000 with phosphatidylcholine). Here, we injected the nanoparticle encapsulated F12511 (nanoparticle F) intravenously (IV) in wild-type mice and performed an HPLC/MS/MS analysis and ACAT enzyme activity measurement. The results demonstrated that F12511 was present within the mouse brain after a single IV but did not overaccumulate in the brain or other tissues after repeated IVs. A histological examination showed that F12511 did not cause overt neurological or systemic toxicity. We then showed that a 2-week IV delivery of nanoparticle F to aging 3xTg AD mice ameliorated amyloidopathy, reduced hyperphosphorylated tau and nonphosphorylated tau, and reduced neuroinflammation. This work lays the foundation for nanoparticle F to be used as a possible therapy for AD and other neurodegenerative diseases.

Association between ACAT1 rs1044925 and increased hypertension risk in Tongdao Dong

Hypertension is a multifactorial disease that partially caused by genetic factors, including variation in genes related to lipid metabolism. ACAT1 gene is implicated in lipid metabolism for its encoding product, the enzyme acetyl-CoA acetyltransferase 1, catalyzing the synthesis of cholesteryl ester from cholesterol and playing an important role in the metabolism of cholesterol. Until now, there's little study on the relationship between ACAT1 variants and hypertension. Here, we report a link between ACAT1 rs1044925 and hypertension in Tongdao Dong population. Polymerase chain reaction-restriction fragment length polymorphism was used to detect the genotypes of the ACAT1 SNP rs1044925 in a total of 637 subjects, including 406 hypertensive patients and 231 normotensive controls. The genotypic and allelic frequencies of rs1044925 were significantly different between the normotensive and hypertensive subjects (P = .001). AC/CC genotypes of rs1044925 were associated with an increased risk of hypertension (AC/CC vs AA: adjusted odds ratio = 1.723, 95% confidence interval = 1.160-2.559, P = .007). However, the AC/CC genotypes showed no relationship with serum lipid levels. The results suggest that the C carriers of ACAT1 rs1044925 might increase the risk of hypertension in Tongdao Dong population, and the underlying mechanism needs to be further studied.

Blocking cholesterol storage to treat Alzheimer's disease

Cholesterol serves as an essential lipid molecule in various membrane organelles of mammalian cells. The metabolites of cholesterol also play important functions. Acyl-coenzyme A: cholesterol acyltransferase 1 (ACAT1), also named as sterol O-acyltransferase 1, is a membrane-bound enzyme residing at the endoplasmic reticulum (ER). It converts cholesterol to cholesteryl esters (CEs) for storage, and is expressed in all cells. CEs cannot partition in membranes; they can only coalesce as cytosolic lipid droplets. Excess CEs are found in the vulnerable region of the brains of patients with late-onset Alzheimer's disease (AD), and in cell and mouse models for AD. Reducing CE contents by genetic inactivation of ACAT1, or by pharmacological inhibition of ACAT is shown to reduce amyloidopathy and other hallmarks for AD. To account for the various beneficial actions of the ACAT1 blockade (A1B), a working hypothesis is proposed here: the increase in CE contents observed in the AD brain is caused by damages of cholesterol-rich lipid rafts that are known to occur in neurons affected by AD. These damages cause cholesterol to release from lipid rafts and move to the ER where it will be converted to CEs by ACAT1. In addition, the increase in CE contents may also be caused by overloading with cholesterol-rich substances, or through activation of ACAT1 gene expression by various proinflammatory agents. Both scenarios may occur in microglia of the chronically inflamed brain. A1B ameliorates AD by diverting the cholesterol pool destined for CE biosynthesis such that it can be utilized more efficiently to repair membrane damage in various organelles, and to exert regulatory actions more effectively to defend against AD. To test the validity of the A1B hypothesis in cell culture and in vivo, the current status of various anti-ACAT1 agents that could be further developed is briefly discussed.

Applications of fluorine to the construction of bioisosteric elements for the purposes of novel drug discovery

Introduction There continues to be an exponential rise in the number of small molecule drugs that contain either a fluorine atom or a fluorinated fragment. While the unique properties of fluorine enable the precise modulation of a molecule's physicochemical properties, strategic bioisosteric replacement of fragments with fluorinated moieties represents an area of significant growth.Areas covered This review discusses the strategic employment of fluorine substitution in the design and development of bioisosteres in medicinal chemistry. In addition, the classic exploitation of trifluoroethylamine group as an amide bioisostere is discussed. In each of the case studies presented, emphasis is placed on the context-dependent influence of the fluorinated fragment on the overall properties/binding of the compound of interest.Expert opinion Whereas utilization of bioisosteric replacements to modify molecular structures is commonplace within drug discovery, the overarching lesson to be learned is that the chances of success with this strategy significantly increase as the knowledge of the structure/environment of the biological target grows. Coupled to this, breakthroughs and learnings achieved using bioisosteres within a specific program are context-based, and though may be helpful in guiding future intuition, will not necessarily be directly translated to future programs. Another important point is to bear in mind what implications a structural change based on a bioisosteric replacement will have on the candidate molecule. Finally, the development of new methods and reagents for the controlled regioselective introduction of fluorine and fluorinated moieties into biologically relevant compounds particularly in drug discovery remains a contemporary challenge in organic chemistry.

Medical Treatment of Cushing's Disease: An Overview of the Current and Recent Clinical Trials

Cushing's disease (CD) is a serious endocrine disorder characterized by chronic hypercortisolism, or Cushing's syndrome (CS), caused by a corticotroph pituitary tumor, which induces an excessive adrenocorticotropic hormone (ACTH) and consequently cortisol secretion. CD presents a severe clinical burden, with impairment of the quality of life and increase in mortality. Pituitary surgery represents the first-line therapy, but it is non-curative in one third of patients, requiring additional treatments. Among second-line treatments, medical therapy is gradually gaining importance, although the current medical treatments are unable to reach optimal efficacy and safety profile. Therefore, new drugs and new formulations of presently available drugs are currently under clinical investigation in international clinical trials, in order to assess their efficacy and safety in CD, or in the general population of CS. Among pituitary-directed agents, pasireotide, in the twice-daily subcutaneous formulation, has been demonstrated to be an effective treatment both in clinical trials and in real-world studies, and extension studies of the phase II and III clinical trials reported evidence of long-term efficacy with general good safety profile, although associated with frequent hyperglycemia, which requires monitoring of glucose metabolism. Moreover, the most recent once-monthly intramuscular formulation, pasireotide long-acting release (LAR), showed similar efficacy and safety, but associated with potential better compliance profile in CD. Roscovitine is an experimental drug currently under investigation. Among adrenal-directed agents, metyrapone is the only historical agent currently under investigation in a prospective, multicenter, international clinical trial, that would likely clarify its efficacy and safety in a large population of patients with CS. Osilodrostat, a novel agent with a mechanism of action similar to metyrapone, seems to offer a rapid, sustained, and effective disease control of CD, according to recently completed clinical trials, whereas levoketoconazole, a different chemical formulation of the historical agent ketoconazole, is still under investigation in clinical trials, with preliminary evidences showing an effective and safe control of CS. ATR-101 is an experimental drug currently under investigation. Among glucocorticoid receptor-directed drugs, mifepristone has been demonstrated to improve clinical syndrome and comorbidities, especially hypertension and impairment of glucose metabolism, but the occurrence of hypokalemia and in women uterine disorders, due to the concomitant action on progestin receptor, requires caution, whereas the preliminary evidence on relacorilant, characterized by high selectivity for glucocorticoid receptor, suggested good efficacy in the control of hypertension and impairment of glucose metabolism, as well as a good safety profile, in CS. Finally, a limited experience has demonstrated that combination therapy might be an interesting approach in the management of CD. The current review provides a summary of the available evidences from current and recent clinical trials on CD, with a specific focus on preliminary data.

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.

ACAT-1 gene polymorphism is associated with increased susceptibility to coronary artery disease in Chinese Han population: a case-control study

Several studies suggest an important role of Acyl-CoA: cholesterol acyltransferase-1(ACAT-1) in the development of atherosclerosis. The aim of present study was to investigate whether there exists a possible correlation between genetic variations in ACAT-1 genes and coronary artery disease (CAD) risk. Four polymorphisms (rs1044925, rs11545566, rs12121758 and rs10913733) were finally selected and genotyped in 750 CAD patients and 580 health controls, using the improved multiplex ligation detection reaction (iMLDR) method. We found that the rs11545566 G allele was associated with a significantly elevated CAD risk [GG vs. AA: adjusted odds ratio (AOR) = 1.62, 95% confidence interval (CI) = 1.13-2.32, P = 0.008; GA/GG vs. AA: AOR = 1.67, 95% CI = 1.22-2.29, P = 0.001]. The rs10913733 G allele was also associated with a significantly elevated CAD risk (GG vs. TT: AOR = 1.57, 95% CI = 1.08-2.28, P = 0.018; GT/GG vs. TT: AOR = 1.39, 95% CI = 1.07-1.79, P = 0.013). Multivariate linear regression analysis showed that the rs11545566 polymorphism was independently associated with the Gensini scores (P = 0.005). The Gensini score of subjects in the variant GG genotype group and the GG/GA genotype group were higher than the score of subjects in the AA genotype group (32.49 ± 26.60 and 31.26 ± 26.96 vs. 23.45 ± 21.64; P = 0.001 and 0.002, respectively). Our results demonstrate that ACAT-1 rs1154556 and rs10913733 polymorphism are novel genetic factors in the development of CAD. Rs11545566 was also associated with the severity of CAD.

ATR-101 inhibits cholesterol efflux and cortisol secretion by ATP-binding cassette transporters, causing cytotoxic cholesterol accumulation in adrenocortical carcinoma cells

BACKGROUND AND PURPOSE

To further the development of new agents for the treatment of adrenocortical carcinoma (ACC), we characterized the molecular and cellular mechanisms of cytotoxicity by the adrenalytic compound ATR-101 (PD132301-02).

EXPERIMENTAL APPROACH

We compared the effects of ATR-101, PD129337, and ABC transporter inhibitors on cholesterol accumulation and efflux, on cortisol secretion, on ATP levels, and on caspase activation in ACC-derived cell lines. We examined the effects of these compounds in combination with methyl-β-cyclodextrin or exogenous cholesterol to determine the roles of altered cholesterol levels in the effects of these compounds.

KEY RESULTS

ATR-101 caused cholesterol accumulation, ATP depletion, and caspase activation within 30 minutes after addition to ACC-derived cells, whereas PD129337 did not. Suppression of cholesterol accumulation by methyl-β-cyclodextrin or exogenous cholesterol, prevented ATP depletion and caspase activation by ATR-101. ATR-101 blocked cholesterol efflux and cortisol secretion, suggesting that it inhibited ABCA1, ABCG1, and MDR1 transporters. Combinations of ABCA1, ABCG1, and MDR1 inhibitors were also cytotoxic. Combinations of ATR-101 with inhibitors of ABCG1, MDR1, or mitochondrial functions had increased cytotoxicity. Inhibitors of steroidogenesis reduced ATP depletion by ATR-101, whereas U18666A enhanced cholesterol accumulation and ATP depletion together with ATR-101. ATR-101 repressed ABCA1, ABCG1, and IDOL transcription by mechanisms that were distinct from the mechanisms that caused cholesterol accumulation.

CONCLUSIONS AND IMPLICATIONS

Inhibition of multiple ABC transporters and the consequent accumulation of cholesterol mediated the cytotoxicity of ATR-101. Compounds that replicate these effects in tumours are likely to be useful in the treatment of ACC.

Identification and Characterization of a New Series of Ghrelin O-Acyl Transferase Inhibitors

Ghrelin O-acyl transferase (GOAT; MBOAT4) catalyzes O-acylation at serine-3 of des-acyl ghrelin. Acyl ghrelin is secreted by stomach X/A-like cells and plays a role in appetite and metabolism. Therefore, GOAT has been expected to be a novel antiobesity target because it is responsible for acyl ghrelin production. Here, we report homogeneous time-resolved fluorescence (HTRF) and enzyme-linked immunosorbent assay (ELISA) methods utilizing human GOAT-expressing microsomes as a novel high-throughput assay system for the discovery of hit compounds and optimization of lead compounds. Hit compounds exemplified by compound A (2-[(2,4-dichlorobenzyl)sulfanyl]-1,3-benzoxazole-5-carboxylic acid) were identified by high-throughput screening using the HTRF assay and confirmed to have GOAT inhibitory activity using the ELISA. Based on the hit compound information, the novel lead compound (compound B, (4-chloro-6-{[2-methyl-6-(trifluoromethyl)pyridin-3-yl]methoxy}-1-benzothiophen-3-yl)acetic acid) was synthesized and exhibited potent GOAT inhibition with oral bioavailability. Both the hit compound and lead compound showed octanoyl-CoA competitive inhibitory activity. Moreover, these two compounds decreased acyl ghrelin production in the stomach of mice after their oral administration. These novel findings demonstrate that GOAT is a druggable target, and its inhibitors are promising antiobesity drugs.

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.

The LRP6 rs2302685 polymorphism is associated with increased risk of myocardial infarction

Background

Abnormal lipids is one of the critical risk factors for myocardial infarction (MI), however the role of genetic variants in lipid metabolism-related genes on MI pathogenesis still requires further investigation. We herein genotyped three SNPs (LRP6 rs2302685, LDLRAP1 rs6687605, SOAT1 rs13306731) in lipid metabolism-related genes, aimed to shed light on the influence of these SNPs on individual susceptibility to MI.

Methods

Genotyping of the three SNPs (rs2302685, rs6687605 and rs13306731) was performed in 285 MI cases and 650 control subjects using polymerase chain reaction–ligation detection reaction (PCR–LDR) method. The association of these SNPs with MI and lipid profiles was performed with SPSS software.

Results

Multivariate logistic regression analysis showed that C allele (OR = 1.62, P = 0.039) and the combined CT/CC genotype (OR = 1.67, P = 0.035) of LRP6 rs2302685 were associated with increased MI risk, while the other two SNPs had no significant effect. Further stratified analysis uncovered a more evident association with MI risk among younger subjects (≤60 years old). Fascinatingly, CT/CC genotype of rs2302685 conferred increased LDL-C levels compared to TT genotype (3.0 mmol/L vs 2.72 mmol/L) in younger subjects.

Conclusions

Our data provides the first evidence that LRP6 rs2302685 polymorphism is associated with an increased risk of MI in Chinese subjects, and the association is more evident among younger individuals, which probably due to the elevated LDL-C levels.

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.

2,3,22,23-tetrahydroxyl-2,6,10,15,19,23-hexamethyl-6,10,14,18-tetracosatetraene, an acyclic triterpenoid isolated from the seeds of Alpinia katsumadai, Inhibits acyl-CoA : cholesterol acyltransferase activity

In order to isolate a cholesterol-lowering compound from Alpinia katsumadai, an inhibitor for acyl-CoA : cholesterol acyltransferase (ACAT), an enzyme responsible for the cholesterol ester formation in liver, was purified, its chemical structure was determined, and in vivo and in vitro inhibition activities were performed. In a high fat diet mouse model, we discovered that the ethanol extract of Alpinia katsumadai reduced plasma cholesterol, triglyceride, and low density lipoprotein (LDL) levels. An acyclic triterpenoid showing ACAT inhibitory activity was isolated from the extract of seeds of A. katsumadai. By NMR spectroscopic analysis of its (1)H-NMR, (13)C-NMR, (1)H-(1)H correlation spectroscopy, heteronuclear multiple bond connectivity (HMBC), hetero multiquantum coherence (HMQC) and nuclear Overhauser effect, chemical structure of 2,3,22,23-tetrahydroxyl-2,6,10,15,19,23-hexamethyl-6,10,14,18-tetracosatetraene (1), were elucidated. The acyclic triterpenoid was found to be responsible for the ACAT inhibition activities of rat liver microsomes with IC(50) values of 47.9 µM. It also decreased cholesteryl ester formation with IC(50) values of 26 µM in human hepatocyte HepG2 cell. The experimental study revealed that the ethanol extract of A. katsumadai has a hypolipemic effect in high fat diet mice, and the isolated acyclic triterpenoid has ACAT inhibition activity, showing a potential novel therapeutic approach for the treatment of hyperlipidemia and atherosclerosis.

Synthesis of a novel series of 2-alkylthio substituted naphthoquinones as potent acyl-CoA: cholesterol acyltransferase (ACAT) inhibitors

We report a new series of naphthoquinone derivatives as potent ACAT inhibitors, which were obtained through structural variations of previously disclosed lead 1. Several analogs represented by 3i-l, 4k-m, 6a-n, 7a, and 7i demonstrated potent human macrophage ACAT inhibitory activity by a cell-based reporter assay with human HepG2 cell lines. In particular, compounds 4l and 6j emerged as highly potent inhibitors, exhibiting significantly high inhibitory potencies with IC50 values of 0.44 μM and 0.6 μM, respectively. Moreover, compound 4l significantly reduced the accumulation of cellular cholesterol in HepG2 cell lines.

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.

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.

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.

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.

Triterpenoids isolated from Zizyphus jujuba inhibit foam cell formation in macrophages

Because foam cell formation in macrophages is believed to play an essential role in the progression of early atherosclerotic lesions in vivo, prevention of foam cell formation is considered to be one of the major targets for the treatment of atherosclerosis. The present study examined the inhibitory effect of 50 crude plant extracts on foam cell formation. Among those crude extracts, Zizyphi Fructus (ZF) and Zizyphi Semen (ZS) extracts significantly inhibited the foam cell formation induced by acetylated LDL. Furthermore, triterpenoids such as oleanonic acid, pomolic acid, and pomonic acid were the major active compounds, and triterpenoids containing a carboxylic acid at C-28 play an important role in the inhibitory effect on foam cell formation in human macrophages. These data suggest that triterpenoids in Zizyphus jujuba , the plant source of ZF and ZS, may therefore be useful for the prevention of atherosclerosis.

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.

Acyl-coenzyme A:cholesterol acyltransferases

The enzymes acyl-coenzyme A (CoA):cholesterol acyltransferases (ACATs) are membrane-bound proteins that utilize long-chain fatty acyl-CoA and cholesterol as substrates to form cholesteryl esters. In mammals, two isoenzymes, ACAT1 and ACAT2, encoded by two different genes, exist. ACATs play important roles in cellular cholesterol homeostasis in various tissues. This chapter summarizes the current knowledge on ACAT-related research in two areas: 1) ACAT genes and proteins and 2) ACAT enzymes as drug targets for atherosclerosis and for Alzheimer's disease.

Novel indoline-based acyl-CoA: cholesterol acyltransferase inhibitor: Effects of introducing a methanesulfonamide group on physicochemical properties and biological activities

A novel series of indoline-based acyl-CoA: cholesterol acyltransferase (ACAT) inhibitors with a methanesulfonamide group at the 5-position were synthesized and their lipophilicity and biological activities were evaluated. Hepatic ACAT inhibitory and anti-foam cell formation activity increased dependent on lipophilicity of derivatives with various alkyl chains at the 1-position. The logD(7.0)-biological activity curve of the derivatives with a methanesulfonamide group shifted leftward compared to that of Pactimibe derivatives with a carboxymethyl group, and derivatives with no substituent, suggesting that a methanesulfonamide group plays an important role in the interaction with ACAT protein. Among derivatives, N-(1-ethyl-5-methanesulfonylamino-4,6-dimethylindolin-7-yl)-2,2-dimethylpropanamide (1b) had about twofold lower logD(7.0) than Pactimibe, while it showed twofold higher hepatic ACAT inhibition than and the same anti-foam cell formation as Pactimibe, respectively. The C(max) of 1b (10mg/kg, po) was higher than that of Pactimibe in rats. The plasma protein binding ratio of 1b was lower than that of Pactimibe: 64.8% and 97.9%, respectively. Compound 1b showed greater inhibitory effects on hepatic cholesterol secretion in mice than Pactimibe. In conclusion, the introduction of a methanesulfonamide group is effective to design less lipophilic, more efficacious and more bioavailable indoline-based ACAT inhibitors than previous indoline-based inhibitors.

Identification of the interaction site within acyl-CoA:cholesterol acyltransferase 2 for the isoform-specific inhibitor pyripyropene A

Targeted deletion of acyl-CoA:cholesterol acyltransferase 2 (ACAT2) (A2), especially in the liver, protects hyperlipidemic mice from diet-induced hypercholesterolemia and atherosclerosis, whereas the deletion of ACAT1 (A1) is not as effective, suggesting ACAT2 may be the more appropriate target for treatment of atherosclerosis. Among the numerous ACAT inhibitors known, pyripyropene A (PPPA) is the only compound that has high selectivity (>2000-fold) for inhibition of ACAT2 compared with ACAT1. In the present study we sought to determine the PPPA interaction site of ACAT2. To achieve this goal we made several chimeric proteins where parts of ACAT2 were replaced by the analogous region of ACAT1. Differences in the amino acid sequence and the membrane topology were utilized to design the chimeras. Among chimeras, A2:1-428/A1:444-550 had 50% reduced PPPA selectivity, whereas C-terminal-truncated ACAT2 mutant A2:1-504 (C-terminal last 22 amino acids were deleted) remained selectively inhibited, indicating the PPPA-sensitive site is located within a region between amino acids 440 and 504. Three additional chimeras within this region helped narrow down the PPPA-sensitive site to a region containing amino acids 480-504, representing the fifth putative transmembrane domain of ACAT2. Subsequently, for this region we made single amino acid mutants where each amino acid in ACAT2 was individually changed to its ACAT1 counterpart. Mutation of Q492L, V493L, S494A resulted in only 30, 50, and 70% inhibition of the activity by PPPA, respectively (as opposed to greater than 95% with the wild type enzyme), suggesting these three residues are responsible for the selective inhibition by PPPA of ACAT2. Additionally, we found that PPPA non-covalently interacts with ACAT2 apparently without altering the oligomeric structure of the protein. The present study provides the first evidence for a unique motif in ACAT2 that can be utilized for making an ACAT2-specific drug.

Human ACAT inhibitory effects of shikonin derivatives from Lithospermum erythrorhizon

Three naphthoquinones were isolated by bioassay-guided fractionation from the CHCl(3) extracts of roots of Lithospermum erythrorhizon. They were identified as acetylshikonin (1), isobutyrylshikonin (2), and beta-hydroxyisovalerylshikonin (3) on the basis of their spectroscopic analyses. The compounds 1-3 were tested for their inhibitory activities against human ACAT-1 (hACAT-1) or human ACAT-2 (hACAT-2). Compound 2 preferentially inhibited hACAT-2 (IC(50)=57.5microM) than hACAT-1 (32% at 120microM), whereas compounds 1 and 3 showed weak inhibitory activities in both hACAT-1 and -2. To develop more potent hACAT inhibitor, shikonin derivatives (5-11) were synthesized by semi-synthesis of shikonin (4), which was prepared by hydrolysis of 1-3. Among them, compounds 5 and 7 exhibited the strong inhibitory activities against hACAT-1 and -2. Furthermore, we demonstrated that compound 7 behaved as a potent ACAT inhibitor in not only in vitro assay system but also cell-based assay system.

Anti-atherosclerotic and anti-inflammatory activities of catecholic xanthones and flavonoids isolated from Cudrania tricuspidata

The catecholic xanthones and flavonoids 1-13 were isolated from the root bark of Cudrania tricuspidata. Compounds 1 and 3-8 exhibited significant antioxidant activity against low-density lipoprotein (LDL) oxidation in the thiobarbituric acid-reactive substance (TBARS) assay. Among them, prenylated flavonoids 10-12 showed an inhibitory effect on the NO production and iNOS expression in RAW264.7 cells. Also, compounds 1, 2, 5, 7, 9, and 11 preferentially inhibited hACAT-2 than hACAT-1, whereas compounds 3, 4, 6, and 8 showed a similar specificity against hACAT-1 and -2. However, flavonoids 10, 12, and 13 dominantly inhibited hACAT-2, not hACAT-1.

Liver-specific inhibition of acyl-coenzyme a:cholesterol acyltransferase 2 with antisense oligonucleotides limits atherosclerosis development in apolipoprotein B100-only low-density lipoprotein receptor-/- mice

OBJECTIVE

The purpose of this study was to determine the effects of liver-specific inhibition of acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) on the development of hypercholesterolemia and atherosclerosis in mice.

METHODS AND RESULTS

Apolipoprotein B100-only low-density lipoprotein (LDL) receptor-/- mice were given saline, a nontargeting control antisense oligonucleotide (ASO), or ASOs targeting ACAT2 biweekly for a period spanning 16 weeks. Mice treated with ACAT2 targeting ASOs had liver-specific reduction in ACAT2 mRNA, yet intestinal ACAT2 and cholesterol absorption was left undisturbed. ASO-mediated knockdown of ACAT2 resulted in reduction of total plasma cholesterol, increased levels of plasma triglyceride, and a shift in LDL cholesteryl ester (CE) fatty acid composition from mainly saturated and monounsaturated to polyunsaturated fatty acid enrichment. Furthermore, the liver-specific depletion of ACAT2 resulted in protection against diet-induced hypercholesterolemia and aortic CE deposition. This is the first demonstration that specific pharmacological inhibition of ACAT2, without affecting ACAT1, is atheroprotective.

CONCLUSIONS

Hepatic ACAT2 plays a critical role in driving the production of atherogenic lipoproteins, and therapeutic interventions, such as the ACAT2-specific ASOs used here, which reduce acyltransferase 2 (ACAT2) function in the liver without affecting ACAT1, may provide clinical benefit for cardiovascular disease prevention.

The prototypical inhibitor of cholesterol esterification, Sah 58-035 [3-[decyldimethylsilyl]-n-[2-(4-methylphenyl)-1-phenylethyl]propanamide], is an agonist of estrogen receptors

We have shown recently that estrogen receptor (ER) ligands share a diphenyl ethane pharmacophore with Sah 58-035 [3-[decyldimethylsilyl]-N-[2-(4-methylphenyl)-1-phenylethyl]-propanamide], a prototypical inhibitor of the acyl-cholesterolacyl-transferase (ACAT), which enabled us to establish that ER ligands were potent inhibitors of ACAT and blocked the formation of foam cells. In the present study, we have tested whether this structural similarity means that Sah 58-035 is an ER modulator. We report that Sah 58-035 bound to ERalpha and ERbeta with an IC(50) of 2.9 and 3.1 microM, respectively. Docking studies using molecular modeling of Sah 58-035 with the X-ray structure of the ER showed that Sah 58-035 fits well into the ligand binding site known for 4-hydroxy-tamoxifen. Despite having high three-dimensional structural similarities with the pure antiestrogen ICI 164,384 [(N-n-butyl-N-methyl-11-[3,17beta-di-hydroxyestra-1,3, 5(10)-trien-7alpha-yl]-undecanamide], we showed that Sah 58-035 is an agonist of ER for transcription and cellular proliferation. These data showed that Sah 58-035 was an estrogen receptor agonist and that the size and the chemical nature of the side chain were critical for agonist versus antagonist activity on ER. This new molecular mechanism of action for Sah 58-035 has to be taken into account in understanding better its pharmacological activities. Moreover, these data give new structural insights into the understanding of agonist versus antagonist activities of ER ligands and also for the conception of new drugs with a dual ACAT inhibition and ER modulation potential and their evaluation in different pathologies where both targets are involved, such as atherosclerosis, Alzheimer's disease, and cancer.

Saucerneol B derivatives as human acyl-CoA: cholesterol acyltransferase inhibitors

A series of 2a-i were prepared from a lead compound, saucerneol B (1) for evaluating their acyl-CoA: cholesterol acyltransferase inhibitory activities. Compounds 2a-g exhibited the high specificity of hACAT-1 than hACAT-2, whereas 2h and 2i showed very weak inhibitory activities in both hACAT-1 and hACAT-2. Saucerneol B (1) exhibited strong cholesterol-lowering effect in high cholesterol-fed mice.

Triterpenoids from the Flower of Campsis grandiflora K. Schum. as Human Acyl-CoA: Cholesterol Acyltransferase Inhibitors

The flower of Campsis grandiflora K. Schum. was extracted with 80% aqueous MeOH, and the concentrated extract was partitioned with EtOAc, n-BuOH and H2O. From the EtOAc fraction, seven triterpenoids were isolated through the repeated silica gel, ODS column chromatographies and preparative HPLC. From the result of physico-chemical data including NMR, MS and IR, the chemical structures of the compounds were determined as 3beta-hydroxyolean-12-en-28-oic acid (oleanolic acid, 1), 3beta-hydroxyurs-12-en-28-oic acid (ursolic acid, 2), 3beta-hydroxyurs-12-en-28-al (ursolic aldehyde, 3), 2alpha,3beta-dihydroxyolean-12-en-28-oic acid (maslinic acid, 4), 2alpha,3beta-dihydroxyurs-12-en-28-oic acid (corosolic acid, 5), 3beta,23-dihydroxyurs-12-en-28-oic acid (23-hydroxyursolic acid, 6) and 2alpha,3beta,23-trihydroxyolean-12-en-28-oic acid (arjunolic acid, 7). These teriterpenoids were isolated for the first time from this plant. Also, compounds 4, 5, 6, and 7 revealed relatively high hACAT-1 inhibitory activity with the value of 46.2+/-1.1, 46.7+/-0.9, 41.5+/-1.3 and 60.8+/-1.1% at the concentration of 100 microg/mL, respectively.

Ergosterol Peroxide from Flowers of Erigeron annuus L. as an Anti-Atherosclerosis Agent

Flowers of Erigeron annuus L. were extracted with 80% aqueous MeOH, and the concentrated extract was partitioned with EtOAc, n-BuOH, and H2O. Repeated silica gel and ODS column chromatography of the EtOAc fraction led to the isolation of a sterol, through activity-guided fractionation, using ACAT inhibitory activity measurements. From the physico-chemical data, including NMR, MS, and IR, the chemical structure of the compound was determined to be an ergosterol peroxide (1), which has been isolated for the first time from this plant. This compound exhibited hACAT-1 and Lp-PLA2 inhibitory effects, with inhibitory values of 51.6 +/- 0.9 and 51.7 +/- 1.2%, at a treatment concentration of 0.23 mM.

Acyl-CoA: cholesterol acyltransferase inhibitory activities of fatty acid amides isolated from Mylabris phalerate Pallas

Unsaturated fatty acid amides, 9(Z)-octadecenamide (2) and 9(Z),12(Z)-octadecadienamide (4) as inhibitors of acyl-CoA: cholesterol acyltransferase (ACAT) were isolated from the ethyl acetate extracts of the insect, Mylabris phalerate Pallas, and elucidated by their spectroscopic data analysis. Compounds 2 and 4 inhibited rat liver microsomal ACAT, hACAT-1, and hACAT-2 with IC(50) values of 170, 85, and 63 microM for 2 and of 151, 53, and 45 microM for 4, respectively.

ACAT2 is localized to hepatocytes and is the major cholesterol-esterifying enzyme in human liver

BACKGROUND

Two acyl-coenzyme A:cholesterol acyltransferase (ACAT) genes, ACAT1 and ACAT2, have been identified that encode 2 proteins responsible for intracellular cholesterol esterification.

METHODS AND RESULTS

In this study, immunohistology was used to establish their cellular localization in human liver biopsies. ACAT2 protein expression was confined to hepatocytes, whereas ACAT1 protein was found in Kupffer cells only. Studies with a highly specific ACAT2 inhibitor, pyripyropene A, in microsomal activity assays demonstrated that ACAT2 activity was highly variable among individual human liver samples, whereas ACAT1 activity was more similar in all specimens. ACAT2 provided the major cholesterol-esterifying activity in 3 of 4 human liver samples examined.

CONCLUSIONS

The data suggest that in diseases in which dysregulation of cholesterol metabolism occurs, such as hypercholesterolemia and atherosclerosis, ACAT2 should be considered a target for prevention and treatment.

Tamoxifen Is a Potent Inhibitor of Cholesterol Esterification and Prevents the Formation of Foam Cells

Tamoxifen is a selective estrogen receptor modulator (SERM) used for the treatment and prevention of breast cancer. Tamoxifen has been reported to protect against the progression of coronary artery diseases in human and different atherosclerosis animal models by blocking the appearance of the atheromatous plaque. However, the molecular mechanism of this effect remains unknown. Acyl-CoA:cholesterol acyl transferase (ACAT) catalyzes the biosynthesis of cholesteryl esters, which are the major lipids found in the atheromatous plaque. In this paper we have tested whether ACAT might be inhibited by tamoxifen. We show, using molecular modeling, that tamoxifen displays three-dimensional structural homology with Sah 58-035 (3-[decyldimethylsilyl]-N-[2-(4-methylphenyl)-1-phenylethyl]-propanamide), a prototypical inhibitor of ACAT. We report that tamoxifen inhibits ACAT in a concentration-dependent manner on rat liver microsomal extract. We show that the presence on estrogen receptor ligands of a backbone isosteric to the diphenyl ethane backbone of Sah 58-035 constitutes a pharmacophore for ACAT inhibition. More importantly, tamoxifen was able to inhibit ACAT on intact macrophages stimulated with acetylated low-density lipoproteins and blocked the formation of foam cells, a step that precedes the formation of the atheromatous plaque. This work constitutes the first evidence that tamoxifen is an inhibitor of ACAT and foam cell formation at therapeutic doses and that this may account for its atheroprotective action.