Inhibition of acyl-CoA: cholesterol acyltransferase decreases apolipoprotein B-100-containing lipoprotein secretion from HepG2 cells.

There is evidence that the overproduction of apoB-100-containing lipoproteins by the liver is the underlying event in some forms of dyslipoproteinemia. This metabolic status is associated to an increased risk of developing premature coronary artery disease CAD. The conclusions from previous studies suggested that the availability to the hepatocytes of cholesterol that is readily esterified is an important determinant for VLDL and LDL secretion. In the present study, we set out to investigate the effect of the specific stimulation and inhibition of the rate-limiting enzyme of the cholesterol esterification, acyl-CoA:cholesterol acyltransferase (ACAT, E.C. 2.3.1.26), on the lipid and on the apoB-100 secretion rate from a human hepatoma cell line (HepG2). When the specific ACAT inhibitor FCE 27677 (10-5 M) was added to the cultures, a decrease of the cellular cholesteryl ester content and at the same time a significant reduction of the neutral lipids and of the apoB-100 secretion rate were noticed. The stimulation of ACAT by 25-hydroxycholesterol (20 microgram/ml) caused a 4-fold increase of the cellular cholesteryl ester content and a 2-fold increase of the lipoprotein secretion rate. FCE 27677 (10-5 M to 10-7 M) prevented the effects elicited by the oxysterol. On the contrary, lovastatin (10-6 M) and gemfibrozil (10-6 M) had no effect. The analysis of the lipid and of the apolipoprotein composition of the lipoproteins secreted in the medium revealed that ACAT inhibition had the dual effect of both decreasing the number of apoB-100-containing lipoproteins secreted as well as their cholesteryl ester load. Altogether, these data support the idea of a close relationship between ACAT activation, leading to increased cholesteryl ester availability, and apoB-100-containing lipoprotein secretion. It is speculated that ACAT inhibitors may prove useful for the treatment of human dyslipoproteinemias caused by the hepatic overproduction of apoB-100-containing lipoproteins.

Synthesis of some 3-hydroxy-5-aminopentanoic acid derivatives.

The 5-amino analogues of mevalonic acid and mevalonolactone, 5-amino-3-hydroxy-3-methylpentanoic acid (VII a) and 4-hydroxy-4-methyl-2-piperidone (III a), and some related compounds were synthesized as possible inhibitors of cholesterol biosynthesis. None of them was found effective on the synthesis of cholesterol in rat liver slices and on HMG-CoA reductase activity in vitro, but 4-hydroxy-4-(4-chlorophenyl)-2-piperidone (III b) raised high density lipoproteins (HDL) in normolipaemic rats.

Ethyl 2-([5,6-dihydro-7-(1H-imidazol-1-yl)-2-naphthalenyl]oxy)- 2-methylpropanoate as a new potent oxyisobutyrate hypolipidaemic with unusual features.

Some compounds containing the N-imidazolyl and the ethyl oxy-isobutyrate groups linked to a naphthalene ring structure and some related analogues were synthesized and tested for hypolipidaemic activity. Ethyl 2-([5,6- dihydro-7-(1H-imidazol-1-yl)-2-naphthalenyl]oxy)- 2-methylpropanoate (V) proved to be a strong hypolipidaemic agent, several times more potent than clofibrate. Structural requirements for activity and differences from clofibrate analogues are discussed.

N-imidazolylchroman-4-ones, N-imidazolyl-1-tetralones, and their alcohols as hypolipemic agents raising high-density lipoproteins.

A series of 3-(1-imidazolyl)chroman-4-ones and 2-(1-imidazolyl)-1-tetralones II, some of their alcohols, and some related compounds were synthesized and tested for hypolipidemic activity. Compounds II, bearing appropriate lipophilic substituents on the phenyl ring, strongly reduced total serum cholesterol while raising high-density lipoprotein cholesterol in diet-induced hypercholesterolemic rats. 3-(1-Imidazolyl)chroman-4-ols and 2-(1-imidazolyl)-1-tetralols corresponding to II retained the hypolipidemic activity while removal of the carbonyl or hydroxy group adjacent to imidazole gave inactive compounds. Although many of the active compounds significantly increased liver weight, the one studied as a model, 6-chloro-3-(1-imidazolyl)-2,3-dihydro-4H-1-benzopyran-4-one (5), caused no peroxisome proliferation. Compound 5 and the corresponding alcohol 40, as representatives of the ketone and alcohol series, showed significant hypolipidemic activity in normolipemic rats. Some of the compounds assayed in cholesterol biosynthesis inhibited acetate incorporation but none inhibited HMG-CoA reductase. 5-Bromo-6-hydroxy-2-(1-imidazolyl)-3,4-dihydro-1(2H)-naphthalenone (38), which showed strong activity but caused little hepatomegaly in the rat, was chosen for further pharmacological evaluation.

Effect of the antilipolytic compound acipimox on peroxisome marker enzymes, lipid pattern and biotransformation related functions in rat liver.

The antilipolytic drug acipimox (5-methylpyrazine-2-carboxylic acid 4-oxide) was given to male rats for 1 week at 500, 1000 and 2000 mg/kg/day and for 2, 6 and 7 months at 20, 100 and 500 mg/kg/day. The peroxisome proliferative effect was evaluated determining the activity of catalase and carnitine acetyltransferase, the rate of cyanide-insensitive palmitoyl CoA oxidation and the electrophoretic profile of liver polypeptides. Hepatic lipid content and distribution were evaluated after 2 and 6 months' treatment. The effect on liver detoxificating function was evaluated by assaying glutathione, cytochrome P-450, glutathione-S-transferase and glutathione-reductase activities after 7 months' treatment. Sub-acute and chronic treatment with a wide range of acipimox doses did not cause hepatomegaly, liver peroxisome proliferation or liver steatosis and did not change some important biochemical variables related to detoxification and biotransformation mechanisms. Acipimox given to rats does not have the negative side-effects of other compounds and seems a safe blood lipid lowering drug.

Hypolipidemic activity of some derivatives of 6H-dibenzo[b,d]pyran.

This paper describes the synthesis of 6-carboxy derivatives of 6H-dibenzo[b,d]pyran. These compounds are among the most rigid structures related to clofibrate ever synthesized, which means they have very few possible conformations of relative stability compared with the many for clofibrate. Compound 6H-2-chloro-6-methyl-dibenzo[b,d]pyran-6-carboxylic acid 3g showed very high hypolipidemic activity being 12 times more potent than clofibrate in reducing plasma cholesterol concentration in the hypercholesterolemic rat and 11 times more potent in reducing plasma triglyceride concentration in the normolipemic rat.