CL 277,082: a novel inhibitor of ACAT-catalyzed cholesterol esterification and cholesterol absorption

Flavonoids and Their Metabolites: Prevention in Cardiovascular Diseases and Diabetes

The occurrence of atherosclerosis and diabetes is expanding rapidly worldwide. These two metabolic disorders often co-occur, and are part of what is often referred to as the metabolic syndrome. In order to determine future therapies, we propose that molecular mechanisms should be investigated. Once the aetiology of the metabolic syndrome is clear, a nutritional intervention should be assessed. Here we focus on the protective effects of some dietary flavonoids, and their metabolites. Further studies may also pave the way for development of novel drug candidates.

Vicinal diaryl azole-based urea derivatives as potential cholesterol lowering agents acting through inhibition of SOAT enzymes

A novel series of vicinal diaryl azole-urea derivatives were synthesized and evaluated for their potential to inhibit SOAT enzyme. Among the reported compounds, compound (12d) emerged as the most potent compound with an IC₅₀ value of 2.43 μM. In polaxamer-407 induced lipoprotein lipase inhibition model, compound (12d) reduced triglyceride turnover in vivo. Compound (12d) also showed dose-dependent prevention of serum total cholesterol and prevention of LDL-C elevation at a dose of 30 mg/kg. Furthermore, compound (12d) showed potential to stop falling levels of serum HDL-C dose-dependently and improved the atherogenic index. Effect of 12d on body weight, plaque formation and development of atherogenic lesions were studied. Toxicological study of compound (12d) indicated that at a dose of 2000 mg/kg, 12d was devoid of any signs of toxicity or mortality.

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.

Diastereoselective Synthesis of syn-β-Lactams Using Rh-Catalyzed Reductive Mannich-Type Reaction of α,β-Unsaturated Esters

The combination of Et2Zn and RhCl(PPh3)3 led to the facile generation of a rhodium-hydride complex (Rh-H) that catalyzed the 1,4-reduction of α,β-unsaturated esters. The resulting rhodium enolate performed as a Reformatsky-type reagent and reacted with various imines to give syn-β-lactams in good to excellent yields with high diastereoselectivity.

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.

The structure of acyl coenzyme A-cholesterol acyltransferase and its potential relevance to atherosclerosis

Acyl coenzyme A-cholesterol acyltransferase (ACAT) catalyzes the formation of intracellular cholesterol esters. It is present in a variety of tissues and is believed to play significant roles in cholesterol homeostasis. Under pathologic conditions, accumulation of the ACAT reaction product as cytoplasmic cholesterol ester lipid droplets within macrophages and smooth muscle cells is a characteristic feature of early lesions of human atherosclerotic plaques. ACAT is a membrane protein located in the endoplasmic reticulum. Its activity is susceptible to inactivation by detergents, and it has never been purified to homogeneity; no antibodies directed against it have been reported. Through a somatic cell and molecular genetic approach, we have recently succeeded in molecular cloning and functional expression of a human macrophage ACAT cDNA. This cDNA contains an open reading frame of 1650 base pairs encoding an integral membrane protein of 550 amino acids. Protein homology analysis shows that the predicted protein sequence shares short regions of homology with other enzymes involved in the catalysis of acyl adenylate formation with subsequent acyl thioester formation and acyl transfer. The ACAT cDNA will enable the investigation of ACAT biochemistry and molecular biology. It will speed up the design of specific ACAT inhibitors as drugs that may provide more effective therapeutic treatment or prevention of atherosclerosis. In addition, studies on the physiologic roles of ACAT in various tissues can now be undertaken through transgenic animal research.

Cholesterol-lowering nutraceuticals and functional foods

Epidemiological studies have demonstrated that elevated levels of plasma total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) are the major risk factors for coronary heart disease (CHD), whereas high concentrations of plasma high-density lipoprotein cholesterol (HDL-C) and a low ratio of TC to HDL-C are protective against CHD. A relationship between plasma TC and the risk of CHD is well established at concentrations above 240 mg/dL. In addition to the use of three main classes of cholesterol-lowering medications, including HMG-CoA reductase inhibitors, anion-exchange resins, and fibrates, a nutritionally balanced diet that reduces saturated fat and cholesterol intake has traditionally been the first goal of dietary therapy in lowering plasma TC. In recent years, nutraceuticals and functional foods have attracted much interest as possible alternative therapies for lowering plasma TC, especially for hypercholesterolemia patients, whose blood cholesterol level is marginally high (200-240 mg/dL) but not high enough to warrant the prescription of cholesterol-lowering medications. This review summarizes the findings of recent studies on the production, application, efficacy, and mechanisms of popular cholesterol-lowering nutraceuticals and functional foods.

Evolutionary conservation of drug action on lipoprotein metabolism-related targets

Genetic analysis has shown that the slower than normal rhythmic defecation behavior of the clk-1 mutants of Caenorhabditis elegans is the result of altered lipoprotein metabolism. We show here that this phenotype can be suppressed by drugs that affect lipoprotein metabolism, including drugs that affect HMG-CoA reductase activity, reverse cholesterol transport, or HDL levels. These pharmacological effects are highly specific, as these drugs affect defecation only in clk-1 mutants and not in the wild-type and do not affect other behaviors of the mutants. Furthermore, drugs that affect processes not directly related to lipid metabolism show no or minimal activity. Based on these findings, we carried out a compound screen that identified 190 novel molecules that are active on clk-1 mutants, 15 of which also specifically decrease the secretion of apolipoprotein B (apoB) from HepG2 hepatoma cells. The other 175 compounds are potentially active on lipid-related processes that cannot be targeted in cell culture. One compound, CHGN005, was tested and found to be active at reducing apoB secretion in intestinal Caco-2 cells as well as in HepG2 cells. This compound was also tested in a mouse model of dyslipidemia and found to decrease plasma cholesterol and triglyceride levels. Thus, target processes for pharmacological intervention on lipoprotein synthesis, transport, and metabolism are conserved between nematodes and vertebrates, which allows the use of C. elegans for drug discovery.

The biology and chemistry of hyperlipidemia

Coronary arterial diseases are responsible for more deaths than all other associated causes combined. Elevated serum cholesterol levels leading to atherosclerosis can cause coronary heart disease (CHD). Reduction in serum cholesterol levels reduces the risk for CHD, substantially. Medicinal chemists all around the world have been designing, synthesizing, and evaluating a variety of new bioactive molecules for lowering lipid levels. This review summarizes the disorders associated with elevation of lipids in blood and the current strategies to control them. The emphasis has been laid in particular on the new potential biological targets and the possible treatments as well as the current ongoing research status in the field of lipid lowering agents.

Effect of melatonin on cholesterol absorption in rats

This study evaluated the influence of melatonin on cholesterol absorption in rats fed on high cholesterol diet (HCD). HCD induced a remarkable increase in hepatic and plasma total cholesterol, plasma very low density lipoprotein (VLDL) and low density lipoprotein (LDL) cholesterol, a decrease in high density lipoprotein (HDL) cholesterol and an elevation in triacylglyceride (TG) levels in plasma and in the liver. Melatonin suspension (10 mg/kg), specially prepared for this purpose, cholestyramine (230 mg/kg) and ezetimibe (145 microg/kg) were administered orally to the rats fed HCD for 30 days. Melatonin significantly reduced cholesterol absorption in rats fed on HCD and caused significant decreases in total cholesterol, TG, VLDL- and LDL-cholesterol in the plasma and contents of cholesterol and TG in the liver. The level of HDL cholesterol was significantly increased after melatonin. These results suggested that inhibition of cholesterol absorption caused by melatonin could be a mechanism contributing to the positive changes in plasma cholesterol, lipoprotein profile and the lipid contents in the liver.

Human acyl-CoA: cholesterol acyltransferase inhibitory activities of aliphatic acid amides from Zanthoxylum piperitum DC

Acyl-CoA: cholesterol acyltransferase (ACAT) plays an important role in the esterification of cholesterol with its substrates, cholesterol and fatty acyl coenzyme A, to facilitate both intracellular storage and intercellular transport. ACAT-1 is more involved in macrophage foam cell formation and ACAT-2 plays a critical role in the cholesterol absorption process in intestinal enterocytes. Three aliphatic acid amides, beta-sanshool (1), gamma-sanshool (2), and hydroxy-beta-sanshool (3), were isolated by bioassay-guided fractionation of the ethanolic extracts of Zanthoxylum piperitum DC. Compounds 1 and 2 inhibited human ACAT-1 and -2 activities with IC50 values of 39.0 and 79.7 microM for 1 and of 12.0 and 82.6 microM for 2, respectively. However, the hACAT-1 and -2 inhibitory activities of compound 3 having hydroxyl group were relatively less than those of compounds 1 and 2. A semi-synthetic compound 4, which has acetyl residue at 2'-OH of compound 3, exhibited the increased hACAT-1 and -2 inhibitory activities with IC50 values of 28.1 and 87.5 microM, respectively.

Dietary conjugated linoleic acid mixture affects the activity of intestinal acyl coenzyme A: cholesterol acyltransferase in hamsters

The present study was designed to study the mechanisms by which dietary conjugated linoleic acids (CLA) decrease serum cholesterol. Hamsters were fed a semi-synthetic diet containing 1 g cholesterol/kg diet with or without supplementation with 20 g linoleic acid (LA) and 20 g CLA/kg diet. After 8 weeks, serum fasting total cholesterol (TC) and triacylglycerol (TG) were significantly lower in the LA-supplemented and CLA-supplemented groups compared with those of the control (CTL) hamsters. In contrast to LA, CLA significantly lowered hepatic cholesterol but it increased the level of adipose tissue cholesterol, suggesting that the hypocholesterolaemic mechanism of CLA is different from that of LA. CLA decreased the activity of intestinal acyl CoA:cholesterol acyltransferase (ACAT) whereas LA had no effect on this enzyme. Consequently, CLA supplementation increased the faecal excretion of total neutral sterols, but it had no or little effect on the faecal acidic sterols. If the ACAT is associated with cholesterol absorption, the part of mechanisms by which CLA decreases serum cholesterol may involve down-regulation of intestinal ACAT activity.

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.

Synthesis and biological evaluation of unprecedented classes of spiro-beta-lactams and azido-beta-lactams as acyl-CoA:cholesterol acyltransferase inhibitors

Unprecedented classes of four- and five-membered hydroxyl-spiro-beta-lactams and hydroxyl-azido-beta-lactams were prepared via regioselective ring opening of hydroxyl-epoxides. The potential of these particular beta-lactams as biologically active compounds has been confirmed by the results obtained in ACAT inhibition assays.

Hypocholesterolemic and antioxidative effects of naringenin and its two metabolites in high-cholesterol fed rats

This study was conducted to compare the hypocholesterolemic and antioxidant effects of naringenin (0.02%), and its metabolites, rho-hyproxyphenylpropionic acid (PHPP, 0.012%) and rho-hydroxybenzoic acid (PHB, 0.012%), in 1% cholesterol diet-fed rats. All supplements significantly lowered the plasma total-cholesterol (total-C), triglyceride (TG) and atherogenic index, and hepatic cholesterol levels compared with the control group. The plasma high-density lipoprotein-cholesterol (HDL-C) concentration was significantly higher in these supplemented groups. However, PHB group only affected the reduction of hepatic TG content. The hydroxyl-3-methylglutaryl-coenzyme A reductase (HMGR) activity was significantly lower in all supplemented groups, whereas only the naringenin group reduced the acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity compared with the control group. The fecal acidic sterol excretion and hepatic superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were significantly higher in all supplemented groups. All supplements also significantly decreased the contents of plasma and hepatic thiobarbituric acid reactive substances (TBARS). Accordingly, it was considered that naringenin and its metabolites were effective on improving the cholesterol and antioxidant metabolism.

Synthesis and Biological Evaluation of Azido- and Aziridino-hydroxyl-β-lactams through Stereo- and Regioselective Epoxide Ring Opening

Two new classes of azido- and aziridino-hydroxyl-beta-lactam containing structures have been prepared by means of a stereo- and regioselective epoxide ring opening. The straightforwardness of the procedure makes this strategy useful for the synthesis of potentially bioactive compounds. Some selected examples showed promising activity in acyl CoA-cholesterol acyltransferase inhibition assays.

New ganoderic acids, bioactive triterpenoid metabolites from the mushroomGanoderma lucidum

Two new lanostanoids, 7-oxo-ganoderic acid Z (1) and 15-hydroxy-ganoderic acid S (2), were isolated from a lipophilic extract of the fruiting body of Ganoderma lucidum. The structures of both compounds were established by interpretation of their spectroscopic data. Compounds 1 and 2 both exhibited inhibitory activities against the HMG-CoA reductase and acyl CoA acyltransferase.

Pharmacological profile of SMP-797, a novel acyl-coenzyme a: cholesterol acyltransferase inhibitor with inducible effect on the expression of low-density lipoprotein receptor

We investigated the pharmacological profile of SMP-797, a novel hypocholesterolemic agent. SMP-797 showed inhibitory effects on acyl-coenzyme A: cholesterol acyltransferase (ACAT) activities in various microsomes and in human cell lines, and hypocholesterolemic effects in rabbits fed a cholesterol-rich diet and hamsters fed a normal diet. In hamsters, the reduction of total cholesterol level by SMP-797 was mainly due to the decrease of low-density lipoprotein (LDL) cholesterol level rather than that of very low-density lipoprotein (VLDL) cholesterol level. Interestingly, SMP-797 increased the hepatic low-density lipoprotein receptor expression in vivo when it decreased the low-density lipoprotein cholesterol level. SMP-797 also increased low-density lipoprotein receptor expression in HepG2 cells like atorvastatin, an HMG-CoA reductase inhibitor, although other acyl-coenzyme A: cholesterol acyltransferase inhibitor had no effect. In addition, SMP-797 had no effect on cholesterol synthesis in HepG2 cells. These results suggested that the increase of low-density lipoprotein receptor expression by SMP-797 was independent of its acyl-coenzyme A: cholesterol acyltransferase inhibitory action and did not result from the inhibition of hepatic cholesterol synthesis. In conclusion, these results suggest that SMP-797 is a novel hypocholesterolemic agent showing a cholesterol-lowering effect in which the increase of hepatic low-density lipoprotein receptor expression as well as the inhibition of acyl-coenzyme A: cholesterol acyltransferase is involved.

Isolation and identification of three new 5-alkenyl-3,3(2H)-furanones from two streptomyces species using a genomic screening approach

Analyses of biosynthetic gene clusters derived from Streptomyces aculeolatus NRRL 18422 and Streptomyces sp. Eco86 indicated that both microorganisms have similar type I polyketide synthase (PKS) gene clusters with relatively few genes encoding post-PKS elaborative enzymes. However both gene clusters included a sequence coding for a relatively uncommon oxidative enzyme related to Baeyer-Villiger, flavin-type monooxygenases. Screening of culture extracts for compounds with the predicted physicochemical properties of the end products from these loci, led to the isolation of three 5-alkenyl-3,3(2H)-furanones, one (E-837, 1) from the former and two (E-492, 2, E-975, 3) from the latter strain. The structures, confirmed by spectral analyses including MS, and ID and 2D NMR experiments, were in accord with those predicted by genomic analyses. Baeyer-Villiger type oxidation is postulated to be involved in the formation of the furanone moieties in these molecules. All three new compounds were tested for their electron transport inhibitory activities. They had IC50 values of 1-4 microg/ml against Ascaris suum NADH-fumarate reductase and 1-12 microg/ml against bovine heart NADH oxidase.

ACAT inhibitor pactimibe sulfate (CS-505) reduces and stabilizes atherosclerotic lesions by cholesterol-lowering and direct effects in apolipoprotein E-deficient mice

The objective of the present study was to determine whether a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, pactimibe sulfate (CS-505), could reduce atherosclerotic lesions beyond and independent of the reduction achieved by cholesterol lowering alone from two different types of lesions. (1) Early lesion model. Twelve-week-old apolipoprotein E (apoE)(-/-) mice were treated with 0.03 or 0.1% (w/w) CS-505, 0.1 or 0.3% avasimibe (CI-1011), or 3% cholestyramine for 12 weeks. Each treatment significantly reduced plasma cholesterol by a similar degree (43-48%). The antiatherosclerotic activity of 0.1% CS-505, however, was more efficacious than the effects of the other treatments (90% versus 40-50%). (2) Advanced lesion model. Twenty-four-week-old apoE(-/-) mice were treated with 0.03 or 0.1% CS-505 or 0.1% CI-1011 for 12 weeks. CS-505 at 0.1% revealed enhanced lesion reduction compared with 0.1% CI-1011 (77% versus 54%), whereas the plasma cholesterol-lowering effect of 0.1% CS-505 was almost the same as that of 0.1% CI-1011. Furthermore, immunohistochemical analysis demonstrated that CS-505 significantly reduced the number of macrophages and expression of matrix metalloproteinase (MMP)-2, MMP-9, and MMP-13. These data indicate that CS-505 can reduce and stabilize atherosclerotic lesions. This antiatherosclerotic activity is exerted via both cholesterol lowering and direct ACAT inhibition in plaque macrophages.

Vitamin E supplementation alters HDL-cholesterol concentration and paraoxonase activity in rabbits fed high-cholesterol diet: comparison with probucol

Vitamin E and probucol are well-known antioxidants that prevent cells from the oxidative stress, which is a risk factor of atherosclerosis. Male rabbits were fed either 0.03% vitamin E or 0.05% probucol in a 0.5% high-cholesterol (HC) diet for 8 weeks. Vitamin E and probucol significantly suppressed an increase in plasma total-cholesterol (total-C) and low-density lipoprotein cholesterol compared to HC-control group. However, plasma high-density lipoprotein-cholesterol (HDL-C) and HDL-C/total-C ratio levels and plasma paraoxonase activity were only significantly higher in vitamin E group after 8 weeks. Hepatic ACAT activity was significantly lower in both vitamin E and probucol groups than in HC-control group, while HMG-CoA reductase activity was the highest only in the probucol group. Total fecal sterol content was significantly higher in probucol and vitamin E groups than in the two control groups. Some atherogenic signs were discovered in the aortic fatty streak of HC-control group, yet not in other groups. Hepatic mRNA expressions of apo B-100 and apo C-III were significantly lower in probucol group than in other groups. Vitamin E supplementation was found to alter the plasma HDL-C-related factors; meanwhile, probucol supplementation was very effective in enhancing cholesterol metabolism, except for a negative effect that reduced plasma HDL-C concentration.

Effect of silymarin and its polyphenolic fraction on cholesterol absorption in rats

This study evaluated the influence of silymarin (SM) and polyphenolic fraction (PF) of silymarin on cholesterol absorption in rats fed on high cholesterol diet (HCD). HCD induced a remarkable increase in hepatic, plasma, VLDL and LDL cholesterol, a decrease in HDL cholesterol and an elevation in triacylglycerol (TAG) levels in plasma, VLDL and in the liver. SM and PF were administered as dietary supplements (1.0%) in HCD for 18 days. Intestinal cholesterol absorption was measured by dual-isotope plasma ratio method, which calculates percent of cholesterol absorption from the ratio of two labelled cholesterol doses, one given intragastrically (14C) and one intravenously (3H). Silymarin and PF significantly reduced cholesterol absorption in rats fed on HCD and caused significant decreases in plasma and VLDL cholesterol and content of cholesterol and TAG in the liver. The level of HDL cholesterol was significantly increased after silymarin, but not after administration of PF. The levels of TAG in plasma and VLDL were not affected by either silymarin or PF. These results suggest that the inhibition of cholesterol absorption caused by silymarin and its polyphenolic fraction could be a mechanism contributing to the positive changes in plasma cholesterol lipoprotein profile and in lipid content in liver.

Anticholesterolemic effect of 3,4-di(OH)-phenylpropionic amides in high-cholesterol fed rats

Two amide synthetic derivatives of 3,4-di(OH)-hydrocinnamate (HC), 3,4-dihydroxyphenylpropionic (l-serine methyl ester) amide (E030) and 3,4-dihydroxyphenylpropionic (l-aspartic acid) amide (E076), were investigated to compare their lipid-lowering efficacy with HC. Male rats were fed a 1 g/100 g high-cholesterol diet for 6 weeks with supplements of either clofibrate (0.02%, w/w), HC (0.025%, w/w), E030 (0.039%, w/w) or E076 (0.041%, w/w). The clofibrate supplement was used as a positive control for the lipid-lowering efficacy. The food intakes and body weight gains were not significantly different among the groups. The plasma and hepatic cholesterol and triglyceride levels were lower in clofibrate, HC, E030, and E076-supplemented groups compared to the control group. The supplementation of HC and its amide derivatives was as effective as clofibrate in increasing the ratio of HDL-cholesterol to total plasma cholesterol and reducing the atherogenic index (AI). The hepatic cholesterol level in the HC and E076 groups was significantly lower than that in the clofibrate group. The hepatic 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA reductase) and acyl-CoA:cholesterol acyltransferase (ACAT) activities were significantly lower in the all test groups than in the control group. The excretion of neutral sterol was significantly higher in the HC, E030, and E076-supplemented groups compared to the control group. The plasma AST and ALT activities, indirect indexes of hepatic toxicity, were significantly lower in the HC, E030, and E076-supplemented groups than in the control group. Accordingly, the current results suggest that E030 and E076, two amide synthetic derivatives of HC, are effective in lowering lipid activity.

Effect of 3,4-di(OH)-cinnamate synthetic derivative on plasma and hepatic cholesterol level and antioxidant enzyme activities in high cholesterol-fed rats

The effect of 3,4-di(OH)-phenylpropionic acid (L-phenylalanine methyl ester) amide (SL-1063), a synthetic derivative of 3,4-di(OH)-cinnamate, on the cholesterol metabolism and antioxidant enzyme system was examined in rats. Diets that included either SL-1063 (0.046%, w/w) or lovastatin (0.02%, w/w) as a supplement, plus 1 g cholesterol/100 g diet were fed to rats ad libitum for 5 weeks. The total plasma cholesterol and triglyceride levels were significantly lowered by the SL-1063 supplement compared to the control group. Meanwhile, the levels of plasma HDL-cholesterol and ratio of HDL-cholesterol/total cholesterol (%) were significantly higher in the SL-1063 group than in the control group. However, the lovastatin supplement did not affect the plasma lipid level. The hepatic cholesterol level and 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity were significantly lowered in the lovastatin group compared to the SL-1063 group; however, the hepatic triglyceride level did not differ among the groups. The activity of hepatic acyl CoA: cholesterol acyltransferase (ACAT), the enzyme that catalyzes hepatic cholesterol esterification, was significantly lower in the lovastatin and SL-1063 groups than in the control group. Furthermore, the SL-1063 supplement elevated the excretion of fecal sterols. As regards the hepatic antioxidant enzyme system, the superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and glutathione reductase (GR) activities were all significantly higher in the SL-1063 group compared to the control group, whereas only the GR activity was significantly increased by the lovastatin supplement. No marked difference in the GSH levels and glucose-6-phosphate dehydrogenase (G6PD) activities was observed among the groups. The levels of plasma and hepatic thiobarbituric acid reactive substances (TBARS) were lowered by the SL-1063 supplement compared to the control group. Accordingly, the current results suggest that SL-1063, a synthetic derivative of 3,4-di(OH)-cinnamate, is effective in lowering the plasma lipids and improving the antioxidant enzyme system.

Evaluation of hesperetin 7-O-lauryl ether as lipid-lowering agent in high-cholesterol-fed rats

The lipid-lowering efficacy of hesperetin was revealed in preliminary studies on experimental animals. As such, the current study compared the effect of hesperetin 7-O-lauryl ether, with that of hesperetin and lovastatin on the lipid profile and cholesterol-regulating mechanism in high-cholesterol-fed rats. Male rats were fed a high-cholesterol diet (1%, wt/wt) or high-cholesterol diet supplemented with lovastatin (1, 0.02%, wt/wt), hesperetin (2, 0.02%, wt/wt), or hesperetin 7-O-lauryl ether (3, 0.031%, wt/wt) for six weeks. The supplemental amount of 3 was 0.066mmol/100g diet as an equivalent to the supplemental amount of 2. The plasma total cholesterol and triglyceride levels were significantly lowered by the 2 and 3 supplements compared with the control or 1-supplemented group. The hepatic HMG-CoA reductase activities were also significantly lower in all the supplemented groups compared with the control group, and the hepatic ACAT activity was significantly lower in the 2- and 3-supplemented groups. The supplementation of 3 resulted in a higher excretion of total neutral sterol and total fecal sterol compared with the control or 1-supplemented group. Accordingly, overall, compound 3, exhibited a more potent plasma lipid-lowering effect than compound 1 based on inhibiting cholesterol biosynthesis and esterification, while also increasing the fecal sterol excretion.

Synthesis and structure–activity relationship studies on a novel series of naphthylidinoylureas as inhibitors of acyl-CoA:cholesterol O -acyltransferase (ACAT)

The synthesis and structure-activity relationships of N-phenyl-N'-[3-(4-phenylnaphthylidinoyl)]urea derivatives 3 as a novel structural class of potent ACAT inhibitors is described. A 3-methoxy group substituted on the naphthylidinone 4-phenyl ring, together with a 1-N-(n)butyl substitution, SM-32504 (3m), gave a potent ACAT inhibitor, in vitro, respectively. The most potent compound, SM-32504 (3m), decreased the serum cholesterol level significantly in a high fat and high cholesterol-fed mouse model.

The metabolic stability of acyl-CoA: cholesterol O-acyltransferase (ACAT) inhibitors, N-(4-benzyloxy-3, 5-dimethoxycinnamoyl)-N'-(2, 4-dimethylphenyl)piperazine (YIC-708-424) and its derivatives in rat liver and intestinal epithelium

The metabolic stability of the acyl-CoA: cholesterol O-acyltransferase (ACAT) inhibitor N-(4-benzyloxy-3, 5-dimethoxycinnamoyl)-N'-(2, 4-dimethylphenyl)piperazine (YIC-708-424) and its n-alkoxy derivatives containing an alkyl chain of 3 or 7 to 10 carbons, which exhibited different hypocholesterolemic activities, was investigated in vivo and in vitro in rats. After the oral administration of YIC-708-424 to rats at a dose of 5 mg/kg/d for 7 d, the parent compound was not detected in the blood. On the other hand, when the n-alkoxy derivatives were administered to rats, an increase in the alkyl chain length produced a progressive increase in the blood concentration of the parent compound. Both in the blood of rats administered YIC-708-424 and in the reaction mixture after the incubation of YIC-708-424 with rat hepatic 9000 x g supernatants, an inactive major metabolite, N-(4-benzyloxy-3, 5-dimethoxycinnamoyl)-N'-(4-carboxyl-2-methylphenyl)piperazine, was observed. The ratio of the maximum velocity to the apparent Michaelis-Menten constant (V(max)/K(m)) for the degradation of the n-propyloxy derivative in rat hepatic and intestinal microsomes was almost equivalent to that of YIC-708-424. On the other hand, an increase in the alkyl chain length of n-alkoxy derivatives produced a progressive decrease in V(max)/K(m) for the degradation of these compounds. Additionally, the in vivo hypocholesterolemic activities of YIC-708-424 and its n-alkoxy derivatives were positively correlated with the blood concentration of the parent compound and were negatively correlated with their V(max)/K(m). These results suggest that the metabolic stability of ACAT inhibitors in the liver and intestinal epithelium, which are the major target organs of these compounds, has a strong influence on their pharmacological activities in vivo.

Naringenin 7-O-cetyl ether as inhibitor of HMG-CoA reductase and modulator of plasma and hepatic lipids in high cholesterol-fed rats

Numerous studies in vitro have shown a close relationship between the chemical structure and biologic activity of flavonoids, whereby their basic structure is modified to increase or decrease their biologic activity. The effects of naringenin (1) and its synthetic derivative, naringenin 7-O-cetyl ether (2), on the lipid profile, the cholesterol-regulating enzyme activity and the excretion of sterol were compared in rats fed a high-cholesterol (1% wt/wt) diet. Either 1 or 2 was supplemented with a high-cholesterol diet for 6 weeks at a dose of 0.073 mmol/100g diet. The supplementation of 1 or 2 significantly lowered the levels (mean+/-SE) of the plasma total cholesterol (4.93+/-0.19 and 4.75+/-0.16 mmol/L vs 5.87+/-0.36 mmol/L, p<0.05) and hepatic triglyceride (0.12+/-0.01 and 0.11+/-0.01 mmol/g vs 0.18+/-0.01 mmol/g, p<0.05) and cholesterol (0.23+/-0.01 and 0.21+/-0.01 mmol/g vs 0.31+/-0.01 mmol/g, p<0.05) compared to those of the control. The compound 1 or 2 supplementation appeared to decrease the excretion of neutral sterols. The plasma HDL-cholesterol concentration and ratio of HDL to total cholesterol were significantly higher in 1 and 2 groups than in control group. Although the biological effect of 2 on inhibiting hepatic HMG-CoA reductase and ACAT activities was only significant compared to the control group, both compounds exhibited a significant hypocholesterolemic effect in rats fed a high-cholesterol diet. The results suggest that cholesterol biosynthesis and esterification were concomitantly reduced by 2, as indicated by the decreased HMG-CoA reductase and ACAT activities.

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

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

Taurine suppresses development of atherosclerosis in Watanabe heritable hyperlipidemic (WHHL) rabbits

While the hypocholesterolemic effects of taurine have extensively been studied using experimental animals, the anti-atherosclerotic effects of taurine have been given less attention. We examined the effect of taurine on atherosclerotic lesions in Watanabe heritable hyperlipidemic (WHHL) rabbits. Treatment of WHHL rabbits with taurine (0.3% in drinking tap water) for 24 weeks decreased aortic lesions by 31%, estimated as intimal thickening. Taurine significantly decreased cholesteryl ester content of aortic arch, thoracic aorta, and abdominal aorta by 35, 43, and 54%, respectively. Concomitantly, activity of acyl-CoA:cholesterol acyltransferase (ACAT), an enzyme responsible for cholesterol esterification, was also significantly decreased. Immunohistochemical analysis revealed decreased macrophages in the intima of taurine-treated rabbits. Taurine had no apparent effect on blood pressure and serum cholesterol levels. Contents of thiobarbituric acid reactive substances (TBARS), a marker of lipid peroxidation, was reduced in serum and aorta by 29 and 50%, respectively, when taurine was ingested. In addition, LDL from taurine-treated rabbits was resistant to copper-induced oxidative modification. These results revealed that taurine prevents development of atherosclerosis and that the anti-atherosclerotic effects of taurine are independent of serum cholesterol levels. The anti-oxidant action of taurine may be involved in inhibiting atherosclerosis in these rabbits.

Cholesterol esters regulate apoB48 secretion in CaCo2 cells

In this study, we investigated the effect of atorvastatin, an HMG-CoA reductase inhibitor and CL277082, an ACAT inhibitor, on apolipoprotein B48 synthesis, degradation and secretion in transformed human intestinal enterocytes (CaCo2 cells). Cells were incubated with atorvastatin or CL277082 in the absence or presence of sterol containing media and pulsed with [S35]-methionine and chased with unlabelled methionine. Concomitantly, the effect of atorvastatin and CL277082 on the relative amount of apoB48 protein in cells and media was also quantified by western blotting using an apoB antibody and enhanced chemiluminescence. Suppression of cholesterol synthesis with atorvastatin did not attenuate the production or secretion of apoB48 from CaCo2 cells under basal conditions. On the other hand, suppression of cholesterol biosynthesis with atorvastatin under stimulatory conditions accelerated the degradation of apoB48 in cells without affecting its synthesis or secretion. There was no effect of exogenous sterols on apoB48 secretion. Taken together, neither endogenous nor exogenous cholesterol appears to acutely modulate apoB48 secretion from intestinal cells. In contrast, inhibition of cholesterol esterification with ACAT inhibitor significantly attenuated apoB48 secretion under basal and stimulatory conditions by a mechanism which enhanced apoB48 degradation. Collectively, our results suggest that in CaCo2 cells, newly synthesized cholesterol ester may be an immediate regulator apoB48 secretion.

Inhibition of acyl coenzyme A-cholesterol acyltransferase: a possible treatment of atherosclerosis?

Our full understanding of atherosclerosis and our ability to prevent its sequellae are incomplete. As a result, further investigation of novel antiatherosclerotic mechanisms and agents continues. Acyl coenzyme A-cholesterol acyltransferase (ACAT) inhibition has been evaluated as a potential mechanism by which the current treatment arsenal may be expanded. ACAT is present in a variety of tissues and is responsible for catalyzing the conversion of free cholesterol to the more readily stored cholesteryl esters. Impressive lipid effects demonstrated in animals have not generally been demonstrated in human clinical trials. Partial ACAT inhibition with specific agents has resulted in lesion regression and decreased progression, whereas complete ACAT inhibition via genetic alterations has led to an exacerbation of cholesterol deposition in tissues in animal models. No ACAT inhibitor has yet been fully evaluated in human clinical trials for its impact on atherosclerotic disease progression. Several hurdles, such as sample size requirements needed to detect effect over background therapy and lack of sensitive surrogate efficacy markers, have served as a deterrent to the development of this class of investigational drug. However, with recent technologic advancements, more sensitive methods of measuring disease progression may be available. Human clinical trials are currently underway, with several agents reported in Phase II clinical trials. Within the next few years, results from these trials may determine whether or not ACAT inhibitors will be added to the list of treatment options for the prevention of atherosclerotic disease progression.

5,6-Diphenylpyridazine derivatives as acyl-CoA:cholesterol acyltransferase inhibitors

Alkyl-5,6-diphenylpyridazine derivatives combining several main features of ACAT inhibitors, such as a long alkyl side chain linked to a heterocycle and the o-diphenyl system, were synthesized and tested. Moreover, modeling studies on representative terms were performed. Some compounds displayed ACAT inhibition in the micromolar range, both on the enzyme isolated from rat liver microsomes and in cell-free homogenate of murine macrophages.

Structure-activity relationships of N-(3,5-dimethoxy-4-n-octyloxycinnamoyl)-N'-(3,4-dimethylphenyl)piperazine and analogues as inhibitors of acyl-CoA: cholesterol O-acyltransferase

A novel series of acyl-CoA: cholesterol O-acyltransferase (ACAT) inhibitors were synthesized from a lead compound, 1-(4-hydroxy-3-methoxyphenyl)-7-phenylhept-1-en-3-one (1, Yakuchinone B) through a modification of three regions (A, B, C) in the molecule. In this study, the compounds prepared were tested for in vitro inhibitory activity on microsomal ACAT from the liver of rats and for in vivo hypocholesterolemic activity in rats given a high cholesterol diet. N-(3,5-Dimethoxy-4-n-octyloxycinnamoyl)-N'-(3,4-dimethylphenyl)piperazine (45), which belongs to the amide compounds, has finally been discovered. Compound 45 inhibited rat hepatic ACAT in a more striking manner than CI-976, an amide compound ACAT inhibitor, and it exhibited a high level of hypocholesterolemic activity in vivo. Since 45 strongly inhibited both microsomal ACAT prepared from HepG2 (a cell line derived from human hepatocarcinoma) and Caco2 (a cell line derived from human colon adenocarcinoma), there is speculation that 45 might have the ability to inhibit ACAT in both the human intestine and liver independent of the difference in the distribution of ACAT isozymes. On the other hand, 45 did not induce adrenotoxicity in subacute toxicity studies in rats. These results suggest that it has promise for development as a new therapeutic agent for hypercholesterolemia and atherosclerosis.

Acyl-CoA:cholesterol acyltransferase inhibitor avasimibe reduces atherosclerosis in addition to its cholesterol-lowering effect in ApoE*3-Leiden mice

BACKGROUND

The present study investigated whether the ACAT inhibitor avasimibe can reduce atherogenesis independently of its cholesterol-lowering effect in ApoE*3-Leiden mice.

METHODS AND RESULTS

Two groups of 15 female ApoE*3-Leiden mice were put on a high-cholesterol (HC) diet; 1 group received 0.01% (wt/wt) avasimibe mixed into the diet. The HC diet resulted in a plasma cholesterol concentration of 18.7+/-2.6 mmol/L. Addition of avasimibe lowered plasma cholesterol by 56% to 8.1+/-1.2 mmol/L, caused mainly by a reduction of and composition change in VLDL and LDL. In a separate low-cholesterol (LC) control group, plasma cholesterol was titrated to a level comparable to that of the avasimibe group (10.3+/-1.4 mmol/L) by lowering the amount of dietary cholesterol. After 22 weeks of intervention, atherosclerosis in the aortic root area was quantified. Treatment with avasimibe resulted in a 92% reduction of lesion area compared with the HC control group. Compared with the LC control, avasimibe reduced lesion area by 78%. After correction for the slight difference in cholesterol exposure between the LC control and avasimibe groups, the effect of avasimibe on lesion area (73% reduction) remained highly significant. In addition, monocyte adherence to the endothelium, free cholesterol accumulation, and lesion severity were reduced by avasimibe treatment.

CONCLUSIONS

Treatment with avasimibe potently lowered plasma cholesterol levels in ApoE*3-Leiden mice and considerably reduced atherosclerotic lesion area in addition to its cholesterol-lowering effect. Because monocyte adherence to the endothelium and lesion severity were also reduced by avasimibe, treatment with avasimibe may result in higher plaque stability and therefore a reduced risk of plaque rupture.

Acyl coenzyme A: cholesterol acyltransferase inhibition and hepatic apolipoprotein B secretion

Acyl coenzyme A: cholesterol acyltransferase (ACAT) is postulated to play a role in hepatic and intestinal lipoprotein secretion. There is accumulating evidence, both in vitro and in vivo, that cholesterol and/or cholesteryl ester availability can regulate hepatic VLDL secretion. How ACAT inhibition regulates the assembly and secretion of apolipoprotein (apo) B containing lipoproteins within the hepatocyte has not been clearly established. ApoB kinetic studies performed in animals indicate that reduction in VLDL apoB secretion is an important mechanism whereby ACAT inhibitors decrease the plasma concentrations of these lipoproteins. However, in cultured hepatocytes, the effect of ACAT inhibition on apoB secretion has been inconsistent. Recent evidence has suggested the existence of more than one ACAT enzyme in mammals, which has culminated in the recent cloning of ACAT2. ACAT1 and ACAT2 respond differently to ACAT inhibitors of differing structures and classes. ACAT2 is present in the liver and intestine, the sites of apoB containing lipoprotein secretion and may represent the enzyme responsible for generating cholesteryl esters destined for lipoprotein assembly and secretion.

Jasmine green tea epicatechins are hypolipidemic in hamsters (Mesocricetus auratus) fed a high fat diet

These studies were designed to test the hypolipidemic activity of green tea epicatechins (GTE) isolated from jasmine green tea. In Experiment 1, three groups of hamsters were given a semisynthetic diet containing 200 g lard/kg and 1 g cholesterol/kg for 4 wk. The control group received distilled water, and the other two groups received either 15 g/L green tea water extract (GTWE) or 5.0 g/L GTE solution. Both the GTWE and GTE groups had lower concentrations of serum total cholesterol (TC) and triacylglycerols (TG) than the controls (P < 0.05). In Experiment 2, four groups of hamsters received tap water as the drinking fluid, but they were given the same high fat and cholesterol diet supplemented with 0 (control), 1.1, 3.4 or 5.7 g GTE/kg diet. The hypolipidemic effect of jasmine GTE was dose dependent. In Experiment 3, the time-course of changes in serum TC and TG was monitored in hamsters given the high fat diet supplemented with 5.7 g GTE/kg in comparison with that of controls. The hypolipidemic effects of dietary GTE were evident after feeding for 2 wk. Dietary supplementation of GTE did not affect liver fatty acid synthase. However, GTE-supplemented hamsters had higher fecal excretions of total fatty acids, neutral sterols and acidic sterols compared with the control group. In Experiment 4, hamsters were fed nonpurified diet; the control group drank distilled water, and the GTE group drank distilled water containing 5.0 g GTE/L. No differences in activities of 3-hydroxy-3-methyl glutaryl coenzyme A reductase and intestinal acyl CoA:cholesterol acyltransferase were observed. This study suggests that the hypolipidemic activity of GTE is not due to inhibition of synthesis of cholesterol or fatty acid but is most likely mediated by its influence on absorption of dietary fat and cholesterol.

Cholesterol-lowering effects of NTE-122, a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, on cholesterol diet-fed rats and rabbits

Pharmacological characterization of NTE-122 (trans-1,4-bis[[1-cyclohexyl-3-(4-dimethylamino phenyl)ureido]methyl]cyclohexane), a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, was performed with both in vitro and in vivo assay systems. NTE-122 inhibited microsomal ACAT activities of various tissues (liver of rabbit and rat, small intestine of rabbit and rat, and aorta of rabbit) and cultured cells (HepG2 and CaCo-2), with IC50 values from 1.2 to 9.6 nM. The inhibition mode of NTE-122 was competitive for HepG2 ACAT. NTE-122 had no effect on other lipid metabolizing enzymes, such as 3-hydroxy-3-methylglutaryl-CoA reductase, acyl-CoA synthetase, cholesterol esterase, lecithin:cholesterol acyltransferase, acyl-CoA:sn-glycerol-3-phosphate acyltransferase and cholesterol 7alpha-hydroxylase up to 10 microM. When NTE-122 was administered to the cholesterol diet-fed rats, serum and liver cholesterol levels were markedly reduced with an ED50 of 0.12 and 0.44 mg/kg/day, respectively. In the cholesterol diet-fed rabbits, NTE-122 significantly lowered plasma and liver cholesterol levels at more than 2 mg/kg/day. These results indicate that NTE-122 is a potent, selective and competitive inhibitor of ACAT, making it a worth while therapeutic agent for hypercholesterolemia and atherosclerosis.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. 3. Discovery of a novel series of N-alkyl-N-[(fluorophenoxy)benzyl]-N'-arylureas with weak toxicological effects on adrenal glands

A series of N-alkyl-N-[(fluorophenoxy)benzyl]-N'-arylureas were prepared and evaluated for their ability to inhibit intestinal acyl-CoA:cholesterol O-acyltransferase and to inhibit accumulation of cholesteryl esters in macrophages in vitro. In vivo hypocholesterolemic activity was assessed in cholesterol-fed rats by oral administration as a dietary admixture and/or by gavage in a PEG400 vehicle. Modification of the alkyl substituent on the N'-aryl moiety and on the urea nitrogen significantly influenced macrophage assay in vitro. Toxicological study revealed a distinct relationship between macrophage assay and the toxicity observed in adrenal glands of rabbits treated with representatives of this series of compounds. Investigations utilizing the macrophage assay as an indicator for adrenal toxicity led to the identification of compounds 1g (FR190809) and 1k (FR186485, or FR195249 as its hydrochloride salt) as potent, nonadrenotoxic, orally efficacious ACAT inhibitors irrespective of the administration method.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. 2. Identification and structure-activity relationships of a novel series of N-alkyl-N-(heteroaryl-substituted benzyl)-N'-arylureas

A series of N-alkyl-N-(heteroaryl-substituted benzyl)-N'-arylurea and related derivatives represented by 2 and 3 have been prepared and evaluated for their ability to inhibit acyl-CoA:cholesterol O-acyltransferase in vitro and to lower plasma cholesterol levels in cholesterol-fed rats in vivo. Among these novel compounds, the type 3 series was superior. A pyrazol-3-yl group on the N-benzyl group of this trisubstituted urea (i.e. 3, Ar1 = pyrazol-3-yl) was identified as a heteroaromatic ring providing a good profile of biological activity. As a result of optimization of the combination with the N-alkyl group (R) and N-aryl group (Ar3), compound 3aq (FR186054) was identified as a new, orally efficacious ACAT inhibitor, which exhibited potent in vitro ACAT inhibitory activity (rabbit intestinal microsomes IC50 = 99 nM) and excellent hypocholesterolemic effects in cholesterol-fed rats, irrespective of administration mode (ED50 = 0.046 mg/kg dosed via the diet, ED50 = 0. 44 mg/kg administered by gavage in PEG400 vehicle). Moreover, a toxicological study revealed compound 3aq to be nontoxic to the adrenal glands of dogs when tested at a single dose of 10 mg/kg po.