Effect of SMP-500, a novel acyl-coA:cholesterol acyltransferase inhibitor, on the cholesterol esterification and its hypocholesterolemic properties

Triterpenic Acids Present in Hawthorn Lower Plasma Cholesterol by Inhibiting Intestinal ACAT Activity in Hamsters

Hawthorn (Crataegus pinnatifida) is an edible fruit used in traditional Chinese medicine to lower plasma lipids. This study explored lipid-lowering compounds and underlying mechanisms of action of hawthorn. Hawthorn powder extracts inhibited acylCoA:cholesterol acyltransferase (ACAT) activity in Caco-2 cells. The inhibitory activity was positively associated with triterpenic acid (i.e., oleanolic acid (OA) and ursolic acid (UA)) contents in the extracts. Cholesterol lowering effects of hawthorn and its potential additive effect in combination with plant sterol esters (PSE) were further studied in hamsters. Animals were fed a semi-synthetic diet containing 0.08% (w/w) cholesterol (control) or the same diet supplemented with (i) 0.37% hawthorn dichloromethane extract, (ii) 0.24% PSE, (iii) hawthorn dichloromethane extract (0.37%) plus PSE (0.24%) or (iv) OA/UA mixture (0.01%) for 4 weeks. Compared to the control diet, hawthorn, PSE, hawthorn plus PSE and OA/UA significantly lowered plasma non-HDL (VLDL + LDL) cholesterol concentrations by 8%, 9%, 21% and 6% and decreased hepatic cholesterol ester content by 9%, 23%, 46% and 22%, respectively. The cholesterol lowering effects of these ingredients were conversely associated with their capacities in increasing fecal neutral sterol excretion. In conclusion, OA and UA are responsible for the cholesterol lowering effect of hawthorn by inhibiting intestinal ACAT activity. In addition, hawthorn and particularly its bioactive compounds (OA and UA) enhanced the cholesterol lowering effect of plant sterols.

A selective ACAT-1 inhibitor, K-604, suppresses fatty streak lesions in fat-fed hamsters without affecting plasma cholesterol levels

BACKGROUND

Acyl-coenzyme A:cholesterol O-acyltransferase-1 (ACAT-1), a major ACAT isozyme in macrophages, plays an essential role in foam cell formation in atherosclerotic lesions. However, whether pharmacological inhibition of macrophage ACAT-1 causes exacerbation or suppression of atherosclerosis is controversial.

METHODS AND RESULTS

We developed and characterized a novel ACAT inhibitor, K-604. The IC(50) values of K-604 for human ACAT-1 and ACAT-2 were 0.45 and 102.85 micromol/L, respectively, indicating that K-604 is 229-fold more selective for ACAT-1. Kinetic analysis indicated that the inhibition was competitive with respect to oleoyl-coenzyme A with a K(i) value of 0.378 micromol/L. Exposure of human monocyte-derived macrophages to K-604 inhibited cholesterol esterification with IC(50) of 68.0 nmol/L. Furthermore, cholesterol efflux from THP-1 macrophages to HDL(3) or apolipoprotein A-I was enhanced by K-604. Interestingly, administration of K-604 to F1B hamsters on a high-fat diet at a dose of >or=1mg/kg suppressed fatty streak lesions without affecting plasma cholesterol levels.

CONCLUSIONS

K-604, a potent and selective inhibitor of ACAT-1, suppressed the development of atherosclerosis in an animal model without affecting plasma cholesterol levels, providing direct evidence that pharmacological inhibition of ACAT-1 in the arterial walls leads to suppression of atherosclerosis.

Multiple mechanisms of hypocholesterolemic action of pactimibe, a novel acyl-coenzyme A:cholesterol acyltransferase inhibitor

Novel acyl-coenzyme A:cholesterol acyltransferase inhibitor pactimibe has been evaluated in vivo; it exhibited significant serum cholesterol lowering activities in hamsters and monkeys without affecting non-high density lipoprotein cholesterol levels. The mechanism of the hypocholesterolemic action of pactimibe was examined in normocholesterolemic hamsters in this study. Results with the dual-isotope plasma ratio method indicated that pactimibe inhibits cholesterol absorption from the intestine, reduces cholesteryl ester formation in the liver, and enhances its elimination from the body. The Triton WR-1339 experiment showed that pactimibe inhibited secretion of very low density lipoprotein cholesterol from the liver. These results suggest that pactimibe is likely to have multiple mechanisms of action responsible for its effectiveness in reducing serum cholesterol.

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.

Synthesis and biological activity of novel 4-phenyl-1,8-naphthyridin-2(1H)-on-3-yl ureas: Potent acyl-CoA:cholesterol acyltransferase inhibitor with improved aqueous solubility

4-Aryl-1,8-naphthyridin-2(1H)-on-3-yl urea derivatives with hydrophilic groups were synthesized in order to improve aqueous solubility and pharmacokinetic property. SMP-797 possessing (4-aminophenyl)ureido and 3-(hydroxypropoxyphenyl) moieties showed potent ACAT inhibitory activity and excellent oral efficacy.

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.

New targets for medical treatment of lipid disorders

Coronary heart disease (CHD) is the leading cause of death and disability in the industrialized world. Included among the risk factors for CHD are an elevated level of low-density lipoprotein (LDL) cholesterol and a low level of high-density lipoprotein (HDL) cholesterol. The discovery of drugs that inhibit 3-hydroxy-3-methylglutaryl coenzyme A reductase (statins), the rate-limiting enzyme in cholesterol biosynthesis, constituted a major advance in the treatment of patients with elevated plasma concentrations of LDL cholesterol. However, although the statins are potent LDL-lowering agents, they may not be the therapy of choice for all dyslipidemic patients. This is particularly true for subjects whose primary lipid abnormality is a low level of HDL cholesterol with or without hypertriglyceridemia, a group that includes about one half of patients with CHD. In this report, we review emerging options for the treatment of patients with lipid disorders, including inhibitors of cholesterol absorption, acyl coenzyme A-cholesterol acyltransferase, microsomal triglyceride transfer protein, and cholesteryl ester transfer protein, as well as liver X receptor agonists that up-regulate the expression of ATP-binding cassette transporter A1.

Effect of SMP-500, a novel ACAT inhibitor, on hepatic cholesterol disposition in rats

The effects of SMP-500, a novel ACAT inhibitor, on serum lipid levels, hepatic lipid secretion rate, and hepatic lipid disposition in rats were studied to clarify its lipid-lowering action. SMP-500 reduced the serum cholesterol level in a dose-dependent manner in rats fed a hypercholesterolemic diet. SMP-500 also reduced hepatic free cholesterol content in addition to hepatic total and esterified cholesterol contents. Biliary concentrations of cholesterol and bile acid were increased by SMP-500; however, the bile flow and lithogenic index were not affected. SMP-500 increased cholesterol 7a-hydroxylase mRNA level. Therefore, it is suggested that the increase in concentrations of cholesterol and bile acid in bile is due to both the increase of bile acid production through the increase of cholesterol 7alpha-hydroxylase and the decrease of hepatic free cholesterol content. An inhibitory effect of SMP-500 both on the cholesterol secretion and on the TG secretion from liver was observed. SMP-500 reduced the serum TG level in sucrose-fed rats. From these results, one may hypothesize that the suppression of hepatic VLDL secretion probably plays an important role on both cholesterol- and TG-lowering effects of SMP-500.