An Ester of ß-Hydroxybutyrate Regulates Cholesterol Biosynthesis in Rats and a Cholesterol Biomarker in Humans.

In response to carbohydrate deprivation or prolonged fasting the ketone bodies, ß-hydroxybutyrate (ßHB) and acetoacetate (AcAc), are produced from the incomplete ß-oxidation of fatty acids in the liver. Neither ßHB nor AcAc are well utilized for synthesis of sterols or fatty acids in human or rat liver. To study the effects of ketones on cholesterol homeostasis a novel ßHB ester (KE) ((R)-3-hydroxybutyl (R)-3-hydroxybutyrate) was synthesized and given orally to rats and humans as a partial dietary carbohydrate replacement. Rats maintained on a diet containing 30-energy % as KE with a concomitant reduction in carbohydrate had lower plasma cholesterol and mevalonate (-40 and -27 %, respectively) and in the liver had lower levels of the mevalonate precursors acetoacetyl-CoA and HMG-CoA (-33 and -54 %) compared to controls. Whole liver and membrane LDL-R as well as SREBP-2 protein levels were higher (+24, +67, and +91 %, respectively). When formulated into a beverage for human consumption subjects consuming a KE drink (30-energy %) had elevated plasma ßHB which correlated with decreased mevalonate, a liver cholesterol synthesis biomarker. Partial replacement of dietary carbohydrate with KE induced ketosis and altered cholesterol homeostasis in rats. In healthy individuals an elevated plasma ßHB correlated with lower plasma mevalonate.

[Preliminary study on efficacy and mechanism of Atractylodes Macrocephelae Rhizoma extracts in metabolic hyperlipidemia rats].

Hyperlipidemia is a major factor causing coronary heart disease and atherosclerosis. The high-density lipoprotein cholesterol (HDL-C) is a major indicator for measuring lipid levels. However, there is no an effective medicine that can obviously increase HDL-C at present. According to previous laboratory studies, atractylodes macrocephalae extracts could significantly increase HDL-C level. In this study, the metabolic hyperlipidemia rat model was established by feeding high-sugar and fat diets and alcohol-drinking to explore the effect and mechanism of atractylodes macrocephalae extracts on hyperlipidemia rats. According to the findingins, different doses of atractylodes macrocephalae extracts could reduce the levels of TC, TG, LDL-C, ACAT and increase the contents of LCAT, HDL-C. Particularly, the atractylodes macrocephalae extracts (100 mg · kg(-1) group showed increase in HDL-C by about 50% and significant declines in HMG-CoA reductase, TC, TG. In conclusion, Atractylodes Macrocephelae Rhizoma extracts could effectively regulate the dyslipidemia of hyperlipidemia rats, especially on HDL-C. Its mechanism may be related to reduction in cholesterol synthesis by inhibiting HMG-CoA reductase in livers and increase in lipid metabolism and transport by regulating LCAT and ACAT levels.

Discovery of novel acyl coenzyme a: cholesterol acyltransferase inhibitors: pharmacophore-based virtual screening, synthesis and pharmacology.

The present study describes ligand-based pharmacophore modeling of a series of structurally diverse acyl coenzyme A cholesterol acyltransferase inhibitors. Quantitative pharmacophore models were generated using HypoGen module of Discovery Studio 2.1, whereby the best pharmacophore model possessing two hydrophobic, one ring aromatic, and one hydrogen bond acceptor feature for inhibition of acyl coenzyme A cholesterol acyltransferase showed a very good correlation coefficient (r = 0.942) along with satisfactory cost analysis. Hypo1 was also validated by test set and cross-validation methods. Developed models were found to be predictive as indicated by low error values for test set molecules. Virtual screening against Maybridge database using Hypo1 was performed. The two most potent compounds (47 and 48; predicted IC50 = 1 nM) of the retrieved hits were synthesized and biologically evaluated. These compounds showed 86% and 88% inhibition of acyl coenzyme A cholesterol acyltransferase (at 10 µg/mL) with IC50 value of 3.6 and 2.5 nM, respectively. As evident from the close proximity of biological data to the predicted values, it can be concluded that the generated model (Hypo1) is a reliable and useful tool for lead optimization of novel acyl coenzyme A cholesterol acyltransferase inhibitors.

Discovery of a potent and orally available acyl-CoA: cholesterol acyltransferase inhibitor as an anti-atherosclerotic agent: (4-phenylcoumarin)acetanilide derivatives.

Acyl-CoA: cholesterol acyltransferase (ACAT) is an intracellular enzyme that catalyzes cholesterol esterification. ACAT inhibitors are expected to be potent therapeutic agents for the treatment of atherosclerosis. A series of potent ACAT inhibitors based on an (4-phenylcoumarin)acetanilide scaffold was identified. Evaluation of the structure-activity relationships of a substituent on this scaffold, with an emphasis on improving the pharmacokinetic profile led to the discovery of 2-[7-chloro-4-(3-chlorophenyl)-6-methyl-2-oxo-2H-chromen-3-yl]-N-[4-chloro-2-(trifluoromethyl)phenyl]acetamide (23), which exhibited potent ACAT inhibitory activity (IC50=12 nM) and good pharmacokinetic profile in mice. Compound 23 also showed regressive effects on atherosclerotic plaques in apolipoprotein (apo)E knock out (KO) mice at a dose of 0.3 mg/kg per os (p.o.).

Flavonoids from the buds of Rosa damascena inhibit the activity of 3-hydroxy-3-methylglutaryl-coenzyme a reductase and angiotensin I-converting enzyme.

Rosa damascena has been manufactured as various food products, including tea, in Korea. A new flavonoid glycoside, kaempferol-3-O-beta-D-glucopyranosyl(1-->4)-beta-D-xylopyranoside, named roxyloside A was isolated from the buds of this plant, along with four known compounds, isoquercitrin, afzelin, cyanidin-3-O-beta-glucoside, and quercetin gentiobioside. The chemical structures of these compounds were determined by spectroscopic analyses, including FAB-MS, UV, IR, (1)H and (13)C NMR, DEPT, and 2D NMR (COSY, HSQC, and HMBC). All the isolated compounds except cyanidin-3-O-beta-glucoside exhibited high levels of inhibitory activity against 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase with IC(50) values ranging from 47.1 to 80.6 microM. Cyanidin-3-O-beta-glucoside significantly suppressed angiotensin I-converting enzyme (ACE) activity, with an IC(50) value of 138.8 microM, while the other four compounds were ineffective. These results indicate that R. damascena and its flavonoids may be effective to improve the cardiovascular system.

Prevention challenges: the era of atherosclerosis regression.

Statins slow atherosclerosis progression and can even induce atherosclerosis regression. The reduction of cardiovascular events with statins by approximately one-third demonstrates not only their clinical efficacy but also the unmet clinical need. The aging of the population and the epidemics of the metabolic syndrome and diabetes contribute to the increasing burden of atherosclerosis in society, and fuel the need for novel complementary therapies to further improve clinical outcomes. Some targets, such as acyl-coenzyme A:cholesterol acyltransferase inhibition, have yielded disappointing clinical results. In contrast, there is strong evidence linking lower high density lipoprotein (HDL) cholesterol levels and greater cardiovascular risk, thus providing the rationale for targeting HDL in the prevention and treatment of cardiovascular diseases. Therapeutic approaches include direct infusions of HDL cholesterol or HDL-mimetic agents, as well as the inhibition of cholesteryl ester transfer protein (CETP). CETP inhibition appears to be one particularly promising strategy. The CETP inhibitor torcetrapib increases plasma HDL cholesterol levels by 40% to 60%, while modestly decreasing low density lipoprotein (LDL) cholesterol. Combining the HDL cholesterol-elevating properties of a CETP inhibitor with the LDL cholesterol-lowering properties of a statin may offer improved outcomes over targeting LDL cholesterol alone. This hypothesis is being extensively evaluated in a comprehensive program that involves several imaging studies and a large-scale clinical end point trial. The additional cardiovascular protection required for patients with atherosclerosis or risk equivalents will likely be provided by therapies that go beyond LDL reduction.

Effect of either gamma-tocotrienol or a tocotrienol mixture on the plasma lipid profile in hamsters.

BACKGROUND/AIMS: Tocotrienols has been shown to inhibit the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity; however, the published animal and human studies yield conflicting results. We investigated the effects of a 4-week dietary supplement of either gamma-tocotrienol (86% gamma-T3) or a mixture of tocotrienols (29.5% alpha-T3, 3.3% beta-T3, 41.4% gamma-T3, 0.1% delta-T3: mix-T3) on the plasma lipid profile in hamsters receiving a high fat diet. METHODS: The hamsters were randomized into 7 groups: no treatment, 16 mg/day/kg BW simvastatin, 23, 58, 263 mg/day/kg BW gamma-tocotrienol, and 39 or 263 mg/day/kg BW for the mixture of tocotrienols. Plasma lipid levels were measured after 2 and 4 weeks of treatment. RESULTS: In all groups treated with tocotrienol total cholesterol levels were decreased, ranging from 7 to 23% after 2 weeks of treatment and from 7 to 15% after 4 weeks. Low-density lipoprotein plasma levels changed accordingly: a decline of 6-37% after 2 weeks and of 12-32% at the end of the study was observed. After 4 weeks of treatment, total cholesterol and low-density lipoprotein plasma levels were significantly reduced in the 263 mg/day/kg BW mixed tocotrienols and the 58 mg/day/kg BW and 263 mg/day/kg BW gamma-tocotrienol groups when compared to the no treatment group. Plasma triglycerides and high-density lipoprotein levels did not change significantly. CONCLUSION: This study provides further evidence that tocotrienols lower total cholesterol and low density lipoprotein plasma levels in hamsters and that gamma-tocotrienol is a more potent agent than a mixture of tocotrienols.

Inhibition of cholesterol biosynthesis by allicin and ajoene in rat hepatocytes and HepG2 cells.

Exposure of primary rat hepatocytes and human HepG2 cells to allicin and ajoene resulted in the concentration-dependent inhibition of cholesterol biosynthesis at different steps of this metabolic pathway. At low concentrations of ajoene sterol biosynthesis from [14C]acetate in rat hepatocytes was decreased by 18% with an IC50-value of 15 microM, while allicin was almost uneffective. In HepG2 cells, both compounds significantly inhibited sterol biosynthesis by 14% and 19% with IC50-values of 7 and 9 microM for allicin and ajoene, respectively. This inhibition was exerted at the level of HMG-CoA-reductase as revealed by the absence of inhibition, if [14C]acetate was replaced by [14C]mevalonate as a precursor, and by direct determination of enzyme activity. At somewhat higher concentrations inhibition of cholesterol biosynthesis by both, allicin and ajoene, was also observed at late steps resulting in the accumulation of the precursor lanosterol. Alliin instead was completely inactive. In the case of allicin, small amounts of dihydrolanosterol and 7-dehydrocholesterol were formed at intermediate concentrations of 5-10 microM. From these results it is concluded that a major point of inhibition at the late steps occurs at the level of lanosterol 14 alpha-demethylase.

The use of amphotericin B to detect inhibitors of cellular cholesterol biosynthesis.

Pores formed in the membranes of animal cells by complexes of sterols and the polyene antibiotic amphotericin B can efficiently kill the cells. Thus, in the absence of exogenous sources of cholesterol, inhibitors of enzymes in the cholesterol biosynthetic pathway render cells resistant to amphotericin B. Preincubation of Chinese hamster ovary cells with compactin or 25-hydroxycholesterol, inhibitors of the synthesis of the key intermediate mevalonate, protected cells from amphotericin B killing and this protection was reversed by the addition of exogenous mevalonate. The ability of compactin to confer amphotericin B resistance on normal cells was abolished when cells were provided exogenous cholesterol by the receptor-mediated endocytosis of low density lipoprotein. Low density lipoprotein receptor-defective Chinese hamster ovary cells were not subject to this low density lipoprotein-dependent amphotericin B killing. Exogenous mevalonate did not prevent 4,4,10 beta-trimethyl-trans-decal-3 beta-ol, an inhibitor of mevalonate conversion to sterols, from protecting cells from amphotericin B. A simple two-step protocol in which cells are preincubated (15-24 h) with potential inhibitors and then treated (3-6 h) with amphotericin B was devised to provide a sensitive method for detecting direct (e.g., competitive) and regulatory inhibitors of cholesterol biosynthesis. This protocol may prove useful in detecting potential antihypercholesterolemia drugs and is currently being used to isolate mutants in receptor-mediated endocytosis.