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

Simvastatin, a potent HMG-CoA reductase inhibitor, inhibits the proliferation of human and bovine endothelial cells in vitro

We investigated in vitro effect of simvastatin, a potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on the proliferation of human and bovine endothelial cells (EC) compared to that of bovine smooth muscle cells (SMC). Cells were cultured in a medium supplemented with 10% normal serum (FBS). Simvastatin at concentrations ranging from 0.1 microg/ml to 10 microg/ml were used. In each kind of cells the proliferation was markedly reduced at 1 microg/ml of simvastatin (P<0.01) which was accompanied by morphological changes in the cell shape. We conclude that simvastatin inhibits the proliferation of not only the smooth muscle cells but also the endothelial cells.

Inhibition of hydroxymethylglutaryl coenzyme A reductase activity does not affect the secretion rate of apolipoproteins B and AI by CaCo-2 cells

It is believed that the major mechanisms by which hydroxymethylglutaryl coenzyme A reductase inhibitors lower plasma cholesterol levels are by inducing hepatic low-density lipoprotein (LDL) receptor activity and by decreasing apolipoprotein B (apoB) secretion by the liver. However, the intestine is also an important cholesterogenic organ and the possibility that this class of drugs may alter lipoprotein secretion by the intestine has not been fully studied. The purpose of the present study was to examine the possible role of cholesterol in regulating apoB secretion by the intestine by testing if the suppression of cholesterol synthesis by the reductase inhibitor lovastatin affected the secretion of apoB by CaCo-2 human intestinal cells. Differentiated post-confluent CaCo-2 cells were incubated for 24-72 h in serum-free medium in the presence or absence of 5 microM lovastatin, and the secretion rate of lipids, as well as apoB and apolipoprotein AI (apoAI) into the medium, was measured. Lovastatin markedly inhibited the incorporation of [1-14C]acetate into cholesterol for at least 48 h, lowered the content of esterified cholesterol in cells, and reduced their rate of cholesterol secretion. However, under basal conditions lovastatin had no effect on the secretion rate of apoB. After stimulation of apoB secretion by addition of 0.8 mM oleic acid to the medium, lovastatin did not alter apoB secretion in the first 2 days of incubation, but reduced the content of apoB in media from the 3rd day by 30%. This could not be explained by an increase in the rate of LDL degradation. Furthermore, supplementation with mevalonic acid only reversed about one-half of the effect of lovastatin, suggesting that this effect was at least parly nonspecific or unrelated to inhibition of cholesterol biosynthesis. There was also no specific effect of lovastatin on apoAI secretion. When cells were cultured with [1-14C]acetate for 24 or 72 h, the specific activity of cholesterol in medium at the end of the incubation was the same as in cells, suggesting that cholesterol used for lipoprotein secretion was in equilibrium with bulk cellular cholesterol and was not from a segregated compartment derived from newly synthesized cholesterol. This may explain why apoB secretion by CaCo-2 cells was unaffected by inhibition of cholesterol synthesis with lovastatin.

Regulation of cholesterol uptake in the rat intestinal cell line

A new model to study cholesterol absorption in the rat intestinal cells is described. Rat intestine epithelial cells IRD98 were incubated with mixed micelles containing bile acid, phospholipid, cholesterol or its nonabsorbable analogue, sitosterol, and trace amounts of [3H]cholesterol or [14C]sitosterol. Cholesterol and sitosterol uptake was then determined following lipid extraction; specific cholesterol uptake was determined as the difference between cholesterol and sitosterol uptake. Cholesterol, but not sitosterol, uptake was time- and dose-dependent and saturable. Loading of cells with non-lipoprotein cholesterol reduced cholesterol, but not sitosterol, uptake in a dose-dependent manner. In contrast, treatment of cells with an inhibitor of cholesterol synthesis, lovastatin, stimulated cholesterol, but not sitosterol, uptake in a dose-dependent manner. Treatment of cells with palmitic, caproic and oleic acids up-regulated specific cholesterol uptake, while linoleic and stearic acids had an opposite effect. None of the fatty acids affected sitosterol uptake.

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.

Increased radioresistance of EJras-transformed human osteosarcoma cells and its modulation by lovastatin, an inhibitor of p21ras isoprenylation

Alterations in ras oncogene expression have been associated with increased cellular resistance to ionizing radiation. As an extension of studies with murine cell models, we have now explored the radioresponses of human osteosarcoma (HOS) sub-clones that differ in their EJras expression. Quantitative analysis revealed a tight correlation between the amounts of ras-encoded mRNA and p21 produced, and the degree of cell radioresistance. Interestingly, treatment of the ras-transformed cells with lovastatin, an inhibitor of p21ras post-translational processing via the mevalonate pathway, markedly decreased their radioresistance. Under the experimental conditions used, lovastatin prevented the membrane association, but not the biosynthesis, of p21. The decline in radiation resistance following lovastatin treatment could not be attributed to perturbation of cholesterol metabolism or to non-specific cell-cycle effects. In agreement, lovastatin did not alter the radiation responses of control HOS cells that do not express EJras, or those with an activated met oncogene. The results indicate that elevation in ras gene expression can lead to increased radioresistance of human tumor cells. It appears, however, that p21ras membrane localization is critical for maintenance of the radioresistant phenotype, thus providing a target for pharmacological intervention.