HMG-CoA reductase inhibitors

Time response of cholesterol synthesis inhibition by compactin-related compounds. In vitro quantitation of the "escape phenomenon"

The time course of the inhibition of cholesterol synthesis by low and high doses of mevinolin and monacolin X were studied in normal human skin fibroblasts, fibroblasts without low density lipoprotein receptor and HepG2 hepatoma cells. Low doses of the inhibitors (0.2 ng/mL) caused a sharp decrease in the rate of cholesterol synthesis during the first 2-3 h, which gradually increased to about 40% during the next 6 h. Further incubation led to a decrease or stabilization of the cholesterol synthesis rate. High doses of the drugs (100 mg/mL) strongly inhibited cholesterol synthesis during the first 2-3 h, followed by a moderate increase during the next 20 h. No drug or tissue selectivity was observed.

Comparison of the effect of six compactin-related compounds on cholesterol synthesis in five human cell types

We have investigated the effect of six compactin-related compounds--mevinolin, compactin, ML-236A, monacolin X, monacolin L and dihydromonacolin L--on cholesterol synthesis in human umbilical vein endothelial cells, human small intestine epithelial cells, human hepatoma cell line HEP G2, normal human skin fibroblasts and in skin fibroblasts from a patient with familial homozygous hypercholesterolemia. The inhibition of cholesterol synthesis was found to depend on both the cell type and the type of compound used. The most effective compounds were mevinolin and compactin. Monacolin X, monacolin L and ML-236A were less effective, and dihydromonacolin L was the least efficacious. Endothelial and epithelial cells were sensitive to very low concentrations of inhibitors (IC50 = 1.0-30 pg/mL), HEP G2 cells required higher concentrations (IC50 = 0.01-66 ng/mL) and fibroblasts needed even higher concentrations (IC50 = 0.1-200 ng/mL). Lactone and acid forms of the inhibitors were equally active. None of the inhibitors had any effect on either protein or fatty acid synthesis in any of the cell types studied. It can be concluded that different compactin-related compounds show a range of potencies as cholesterol synthesis inhibitors and a dose-dependent tissue-selectivity.

Inhibition of cholesterol synthesis by lovastatin tested on six human cell types in vitro

Lovastatin (mevinolin) caused a strong and dose-dependent inhibition of cholesterol synthesis in six types of cultured human cells. Fifty percent inhibition of cholesterol synthesis in human enterocytes was observed at a lovastatin concentration of about 0.004 ng/ml and in other cells at a lovastatin concentration of about 0.03 ng/ml. At lovastatin concentrations between 1.0 and 100.0 ng/ml, a moderate tissue selectivity of lovastatin action was noted. At optimal concentrations, lovastatin inhibited cholesterol synthesis in hepatocytes by 98%, in normal and LDL-receptor negative fibroblasts, arterial smooth muscle cells and hepatoma G-2 cells by about 90%, and in enterocytes by 75%. In rat enterocytes lovastatin inhibited cholesterol synthesis by only 60%.

Mevinolin, an inhibitor of cholesterol synthesis, induces mRNA for low density lipoprotein receptor in livers of hamsters and rabbits

Through the use of a quantitative solution hybridization assay with 32P-labeled cDNA probes, we found that mevinolin, an inhibitor of cholesterol synthesis, elevates the level of mRNA for the low density lipoprotein receptor in livers of hamsters and rabbits. In hamsters the maximal effect (3-fold increase) occurred at 0.1% mevinolin in the diet for 10 days. The same dose produced a maximal induction (10-fold) of mRNA levels for 3-hydroxy-3-methylglutaryl CoA reductase, the rate-limiting enzyme of cholesterol synthesis, and a maximal decrease (80%) in plasma cholesterol. The drug lowered the level of all cholesterol-carrying lipoproteins in plasma. In normal rabbits, mevinolin produced a 90% reduction in plasma low density lipoprotein-cholesterol levels, which was associated with a 2.5-fold increase in low density lipoprotein receptor mRNA levels. A similar induction of receptor mRNA occurred in livers of Watanabe-heritable hyperlipidemic rabbits, although the plasma cholesterol was not reduced to normal, presumably because the receptors produced by the mutant mRNA function poorly. These data are consistent with the hypothesis that mevinolin and other inhibitors of 3-hydroxy-3-methylglutaryl CoA reductase lower plasma cholesterol levels in part by stimulating production of mRNA for the low density lipoprotein receptor in liver.