The hypolipidemic action of the ACAT inhibitor HL-004 in hamsters fed normal chow

1. A novel ACAT (acyl-CoA: cholesterol acyltransferase) inhibitor, HL-004, exhibited a strong inhibitory effect on the hepatic and intestinal ACAT, but was less effective on the adrenal ACAT in vitro. 2. HL-004 selectively decreased serum VLDL cholesterol, and inhibited hepatic ACAT activity in hamsters fed normal chow. 3. These results suggest that the cholesterol-lowering effect of HL-004 can be attributed to a decrease in hepatic VLDL secretion via inhibition of ACAT.     

HL-004, the ACAT inhibitor, prevents the progression of atherosclerosis in cholesterol-fed rabbits

HL-004, N-(2,6-diisopropylphenyl) tetradecylthioacetamide, a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, was evaluated concerning the possible prevention of hyperlipidemia and atherosclerosis in 1% cholesterol-fed rabbits. HL-004 (0.2, 5 and 25 mg/kg) was orally administered once a day for 12 weeks. HL-004 inhibited the rise of total serum cholesterol at a dose of 5 mg/kg and over. In the thoracic aorta, HL-004 at the doses of 5 mg/kg and 25 mg/kg reduced the total cholesterol content by 56.3% and 84.2% compared with control, and decreased ACAT activity, dose-dependently. HL-004 also attenuated the development of aortic lesions. The area of atherosclerotic lesions was reduced by 30.3% with 5 mg/kg of HL-004 and 100% with 25 mg/kg. In this study, we suggest that the main reason for HL-004 preventing the progression of atherosclerosis is its hypocholesterolemic effect due to the inhibition of cholesterol absorption in the intestine.     

Disruption of the acyl-CoA:cholesterol acyltransferase gene in mice: evidence suggesting multiple cholesterol esterification enzymes in mammals

The microsomal enzyme acyl-CoA:cholesterol acyltransferase (ACAT; EC 2.3.1.26) catalyzes the esterification of cellular cholesterol with fatty acids to form cholesterol esters. ACAT activity is found in many tissues, including macrophages, the adrenal glands, and the liver. In macrophages, ACAT is thought to participate in foam cell formation and thereby to contribute to atherosclerotic lesion development. Disruption of the gene for ACAT (Acact) in mice resulted in decreased cholesterol esterification in ACAT-deficient fibroblasts and adrenal membranes, and markedly reduced cholesterol ester levels in adrenal glands and peritoneal macrophages; the latter finding will be useful in testing the role of ACAT and macrophage foam cell formation in atherosclerosis. In contrast, the livers of ACAT-deficient mice contained substantial amounts of cholesterol esters and exhibited no reduction in cholesterol esterification activity. These tissue-specific reductions in cholesterol esterification provide evidence that in mammals this process involves more than one form of esterification enzyme.     

Acetylated low density lipoprotein inhibits the incorporation of arachidonic acid in phospholipids with a concomitant increase of cholesterol arachidonate in rat peritoneal macrophages

The aim of our work was to evaluate the influence of native low density lipoproteins (LDL) and LDL chemically modified by acetylation (acLDL) on incorporation and release of arachidonic acid (AA) in rat peritoneal macrophages. Compared to a control group without treatment, 100 micrograms/ml of acLDL for 15 h considerably increased the incorporation of [3H]AA in cholesterol-ester (CE) of rat peritoneal macrophages and induced a decrease of 3H-labeled membrane phospholipids (PL). No effect was shown with LDL treatment. In the presence of acLDL, LS3251 (100 nM), an acyl-coenzyme A:cholesterol acyltransferase (ACAT) inhibitor, inhibited the [3H]AA incorporation into CE in macrophages. [3H]AA-prelabeled macrophages cultured for 15 h with acLDL (compared to macrophages untreated or treated with LDL) showed an increase of labeled CE and a decrease of labeled PL and of cyclooxygenase and lipoxygenase eicosanoid production. After zymosan stimulation of macrophages prelabeled with [3H]AA and treated with or without LDL or acLDL, AA release and eicosanoid production increased in all groups of macrophages. The inhibition of eicosanoid production in foam cells does not seem to be linked to an inhibition of phospholipase but rather paralleled to an increase of the cholesterol [3H]arachidonate. A significant portion of cellular arachidonate released from phospholipids, in particular from phosphatidylcholine, could serve as a substrate to ACAT in this foam cell.     

Immunolocalization of acyl-coenzyme A:cholesterol O-acyltransferase in macrophages

Macrophages in atherosclerotic lesions accumulate large amounts of cholesteryl-fatty acyl esters ("foam cell" formation) through the intracellular esterification of cholesterol by acyl-coenzyme A:cholesterol O-acyltransferase (ACAT). In this study, we sought to determine the subcellular localization of ACAT in macrophages. Using mouse peritoneal macrophages and immunofluorescence microscopy, we found that a major portion of ACAT was in a dense reticular cytoplasmic network and in the nuclear membrane that colocalized with the luminal endoplasmic reticulum marker protein-disulfide isomerase (PDI) and that was in a similar distribution as the membrane-bound endoplasmic reticulum marker ribophorin. Remarkably, another portion of the macrophage ACAT pattern did not overlap with PDI or ribophorin, but was found in as yet unidentified cytoplasmic structures that were juxtaposed to the nucleus. Compartments containing labeled beta-very low density lipoprotein, an atherogenic lipoprotein, did not overlap with the ACAT label, but rather were embedded in the dense reticular network of ACAT. Furthermore, cell-surface biotinylation experiments revealed that freshly harvested, non-attached macrophages, but not those attached to tissue culture dishes, contained approximately 10-15% of ACAT on the cell surface. In summary, ACAT was found in several sites in macrophages: a cytoplasmic reticular/nuclear membrane site that overlaps with PDI and ribophorin and has the characteristics of the endoplasmic reticulum, a perinuclear cytoplasmic site that does not overlap with PDI or ribophorin and may be another cytoplasmic structure or possibly a unique subcompartment of the endoplasmic reticulum, and a cell-surface site in non-attached macrophages. Understanding possible physiological differences of ACAT in these locations may reveal an important component of ACAT regulation and macrophage foam cell formation.     

The effects of political and economic transitions on health and safety in Estonia: an Estonian-Swedish comparative study

This study has investigated in detail factors regulating accumulation, esterification, and mobilization of cholesterol in human THP-1 macrophages. Human THP-1 monocytes were differentiated into macrophages and then cholesterol enriched by exposure to acetylated LDL (AcLDL), together with [3H]free cholesterol (FC). Although THP-1 macrophages accumulated FC and esterified cholesterol (EC), assessed by both mass and radioactivity, cellular EC always demonstrated a much lower specific activity (cpm/ microg) than did cellular FC, and several potential causes of this finding were investigated. Inhibition of acyl-CoA:cholesterol acyltransferase (ACAT) during loading decreased cell [3H]EC by 95+/-1.4% but decreased cell EC mass by only 66.0+/-4.0%, indicating that some intracellular undegraded AcLDL-derived EC was present in these cells. Esterification of [3H]oleate to EC in THP-1 cells loaded with AcLDL was 2.0 nmol x mg-1 x h-1, consistent with previous literature. However, EC, triglyceride, and phospholipid fractions respectively contained 1.0+/-0.07%, 80.0+/-0.5%, and 18.9+/-0.3% of cell [3H]oleate, indicating triglycerides were much more metabolically active than EC. In addition, the mass of triglyceride in THP-1 macrophages exceeded that of EC both before and after exposure to AcLDL. Esterification of nonlipoprotein-derived cholesterol was compared in THP-1 cells and nonhuman Fu5AH, CHO, and RAW macrophage cells. Whereas the nonhuman cell lines all esterified over 30% of 2-hydroxypropyl-beta-cyclodextrin (hp-ss-CD)-delivered cholesterol within 6 hours, THP-1 cells esterified <8.0% of incorporated cholesterol. Kinetics of cholesterol efflux from AcLDL-loaded THP-1 cells were first investigated after loading with only FC, and interactions between efflux and EC hydrolysis were further assessed after loading cells with both EC and FC. Over 24 hours, human apolipoprotein (apo) A-I, apoHDL reconstituted with phosphatidylcholine, and HDL3 respectively removed 46.6+/-3.7%, 61. 3+/-3.4%, and 76.4+/-10.1% of [3H]FC from FC-enriched THP-1 cells. Cholesterol efflux to apoA-I was saturated by 24 hours and was enhanced by using apoA-I-phospholipid instead of pure apoA-I. Kinetic modeling identified that 97% of effluxed FC derived from a slow pool, with a T1/2 ranging from 27.7 hours for HDL to 69.3 hours for apoA-I. Although efflux enhanced net clearance of EC, hydrolysis of EC during concurrent inhibition of ACAT was unaffected by cholesterol efflux. Supplementation of THP-1 cultures with cAMP to stimulate hormone-sensitive lipase did not significantly enhance net hydrolysis of EC or cholesterol efflux. In conclusion, human THP-1 macrophages contain a large and metabolically active pool of triglyceride and a relatively inactive pool of EC. The low specific activity of EC relative to FC is contributed to by reduced esterification of FC, slow hydrolysis of EC, and accumulated lipoprotein EC. The relative inactivity of the EC pool may further contribute to already impaired cholesterol efflux from these cells. Net cholesterol efflux from human macrophages is achieved by pure apoA-I and is substantially further enhanced by the presence of phospholipid in acceptor particles.     

The distal pathway of lipoprotein-induced cholesterol esterification, but not sphingomyelinase-induced cholesterol esterification, is energy-dependent

The stimulation of the intracellular cholesterol esterification pathway by atherogenic lipoproteins in macrophages is a key step in the development of atheroma foam cells. The esterification pathway can also be stimulated by hydrolysis of cell-surface sphingomyelin by the enzyme sphingomyelinase (SMase). In both cases, intracellular cholesterol transport to the cholesterol esterifying enzyme, acyl-CoA:cholesterol O-acyltransferase (ACAT), is thought to be critical, although the mechanism of cholesterol transport is not known. In this report, we explore two fundamental properties of the cholesterol esterification pathway, namely its dependence on energy and the effect of other treatments that block membrane vesicle trafficking. After the atherogenic lipoprotein, beta-very low density lipoprotein (beta-VLDL), was internalized by macrophages and hydrolyzed in lysosomes, the cells were depleted of energy by treatment with sodium azide and 2-deoxyglucose or by permeabilization. Under these conditions, which allowed equal beta-VLDL-cholesteryl ester hydrolysis, cholesterol esterification was markedly decreased in the energy-depleted cells. This effect was not due to blockage of lysosomal cholesterol export. In the permeabilized cell system, energy repletion restored beta-VLDL-induced cholesterol esterification. Remarkably, stimulation of cholesterol esterification by SMase was not inhibited by energy depletion. Energy depletion also inhibited beta-VLDL-induced, but not SMase-induced, cholesterol esterification in Chinese hamster ovary cells. Similar experiments were carried out using N-ethylmaleimide, low potassium medium, or inhibitors of phosphatidylinositol 3-kinase, each of which blocks intracellular membrane vesicle trafficking. These treatments also inhibited beta-VLDL-induced, but not SMase-induced, cholesterol esterification. Finally, we show here that SMase treatment of cells leads to an increase in plasma membrane vesiculation that is relatively resistant to energy depletion. In summary, the stimulation of cholesterol esterification by lipoproteins, but not by SMase, is energy-dependent, N-ethylmaleimide-sensitive, and blocked by both low potassium and phosphatidylinositol 3-kinase inhibitors. The affected step or steps are distal to cholesterol export from lysosomes and not due to direct inhibition of the ACAT enzyme. Thus, the mechanisms involved in lipoprotein-induced versus SMase-induced cholesterol esterification are different, perhaps due to the involvement of energy-dependent vesicular cholesterol transport in the lipoprotein pathway and a novel, energy-independent vesicular transport mechanism in the SMase pathway.     

Lysosomal sequestration of free and esterified cholesterol from oxidized low density lipoprotein in macrophages of different species

Macrophage foam cells of atherosclerotic lesions store lipid in lysosomes and cytoplasmic inclusions. Oxidized low density lipoprotein (oxLDL) has been proposed to be the atherogenic particle responsible for the free and esterified cholesterol stores in macrophages. Currently, however, there is a paucity of data showing that oxLDL can induce much cholesterol accumulation in cells. The present studies compare the ability of mildly oxLDL (TBARS = 5 to 10 nmols/mg LDL protein) with acetylated LDL to induce free cholesterol (FC) and esterified cholesterol (EC) accumulation in pigeon, THP-1, and mouse macrophages. Mildly oxLDL stimulated high levels of loading comparable to acLDL where the cellular cholesterol concentrations ranged from 160 to 420 microg/mg cell protein with EC accounting for 52-80% of the cholesterol. Pigeon and THP-1 macrophages stored most (60-90%) of oxLDL cholesterol (both FC and EC) in lysosomes, and the bulk (64-88%) of acLDL cholesterol in cytoplasmic inclusions. Consistent with lysosomal accumulation, cholesterol esterification was 75% less in THP-1 macrophages enriched with oxLDL cholesterol compared with acLDL. Furthermore, addition of an acyl-CoA:cholesterol acyltransferase inhibitor did not significantly affect either cholesterol loading or the percent distribution of FC and EC in THP-1 and pigeon cells incubated with oxLDL. Surprisingly, mouse macrophages stored most of oxLDL (71%) and acLDL (83%) cholesterol within cytoplasmic inclusions. Also, in mouse macrophages, esterification paralleled cholesterol loading, and was 3-fold more in oxLDL treated cells compared with acLDL treated cells. Inhibition of ACAT led to a 62% and 90% reduction in the %EC in oxLDL and acLDL treated mouse macrophages, respectively. The results demonstrate that mildly oxidized low density lipoprotein (oxLDL) stimulates macrophage foam cell formation and lipid engorgement of lysosomes. However, the fate of oxLDL cholesterol markedly differs in macrophages of different species.     

Apolipoprotein-mediated removal of cellular cholesterol and phospholipids

It is widely believed that high density lipoprotein (HDL) protects against cardiovascular disease by removing excess cholesterol from cells of the artery wall. Recent cell culture studies have provided evidence that a major pathway for removing cholesterol and phospholipids from cells is mediated by the direct interactions of HDL apolipoproteins (apo) with plasma membrane domains. These interactions efficiently clear cells of excess sterol by targeting for removal pools of cholesterol that feed into the cholesteryl ester cycle. The precursors for this pathway in vivo are likely to be lipid-free or lipid-poor apolipoproteins generated either by dissociation from the surface of HDL particles or by de novo synthesis. Fibroblasts from subjects with a severe HDL deficiency syndrome called Tangier disease have a cellular defect that prevents apolipoproteins from removing both cholesterol and phospholipids from cells. This defect is associated with a near absence of plasma HDL, markedly below normal low density lipoprotein (LDL) levels, and the appearance of macrophage foam cells in tissues. Thus, an inability of nascent apoA-I to acquire cellular lipids results in a rapid clearance of apoA-I from the plasma, decreased production and increased clearance of LDL, and sterol deposition in tissue macrophages. Although the molecular properties of this pathway are still poorly understood, these studies imply that the apolipoprotein-mediated pathway for removal of cellular lipids is a major source of plasma cholesterol and phospholipids and plays an important role in clearing excess cholesterol from macrophages in vivo.     

Immunodepletion experiments suggest that acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT-1) protein plays a major catalytic role in adult human liver, adrenal gland, macrophages, and kidney, but not in intestines

The first acyl-coenzyme A:cholesterol acyltransferase (ACAT) cDNA cloned and expressed in 1993 is designated as ACAT-1. In various human tissue homogenates, ACAT-1 protein is effectively solubilized with retention of enzymatic activity by the detergent CHAPS along with high salt. After using anti-ACAT-1 antibodies to quantitatively remove ACAT-1 protein from the solubilized enzyme, measuring the residual ACAT activity remaining in the immunodepleted supernatants allows us to assess the functional significance of ACAT-1 protein in various human tissues. The results showed that ACAT activity was immunodepleted 90% in liver (83% in hepatocytes), 98% in adrenal gland, 91% in macrophages, 80% in kidney, and 19% in intestines, suggesting that ACAT-1 protein plays a major catalytic role in all of the human tissue/cell homogenates examined except intestines. Intestinal ACAT activity is largely resistant to immunodepletion and is much more sensitive to inhibition by the ACAT inhibitor Dup 128 than liver ACAT activity.     

Age-related changes in the metabolism of acetylated low-density lipoproteins by peritoneal macrophages from C57BL/6CrScl mice

Macrophages are major precursors of foam cells in atherosclerotic lesions. Acetylated low-density lipoproteins (acetyl LDL) taken up by macrophages through scavenger receptors are degraded by lysosomes and the released cholesterol is re-esterified, leading to foam cell formation. The ability of resident peritoneal macrophages from C57BL/6CrScl mice to form foam cells in relation to the donor age was assessed by the cholesterol esterification and the metabolism of acetyl LDL. The incorporation of 14C-oleate (complexed to albumin) into cellular cholesteryl esters in the presence of acetyl LDL (100 micrograms/ml) was significantly greater in macrophages from senescent mice (24-25 months) than in cells from young (3-4 months) mice (p < .001). The degradation and cellular association of acetyl LDL by macrophages from senescent mice were significantly greater than macrophages from mature mice, (p < .001 and p < .01, respectively), whereas the binding of acetyl LDL was similar in peritoneal macrophages from mature and senescent mice. These results suggest that the uptake and degradation of acetyl LDL, and the re-esterification by macrophages increase with advancing age and that the ability of macrophages to form foam cells increases with aging. The enhanced ability of senescent macrophages to form foam cells might contribute to the development and progression of atherosclerosis related to the aging process.     

Impaired cellular cholesterol efflux by oxysterol-enriched high density lipoproteins

One of the proposed antiatherogenicity role of high-density lipoproteins (HDL) is believed to stimulate removal of cholesterol from the peripheral cells back to the liver for excretion. We have investigated the effects of oxidation-related modifications of HDL on their ability to stimulate cholesterol efflux from cultured cells. Human HDL (HDL3, 1.13 < d < 1.21 g/ml) have been modified either by malondialdehyde or by copper-mediated oxidation (Ox-HDL3). Compared with native HDL3, the modified HDL3 resulted in a significantly reduced efflux of labeled cholesterol from preloaded macrophages (P388D1 cell line). Analysis of lipid composition of Ox-HDL3 by gas chromatography revealed the presence of oxysterols (OS). Enrichment of native HDL3 with oxysterols resulted in a reduced capacity to stimulate cholesterol efflux. The reduced ability of OS-enriched HDL3 to elicit cholesterol efflux may contribute to cellular cholesterol accumulation and subsequently to atherosclerosis.     

High density lipoprotein receptors, binding proteins, and ligands

Several HDL binding proteins, quite disparate in structure, have recently been cloned and their role in HDL metabolism is currently being assessed. High density lipoprotein binding protein, HBP (vigilin), which lacks a transmembrane domain is responsive to cell cholesterol levels, but its physiological significance remains unknown. On the other hand much is known about SR-B1, a member of the class B scavenger receptors. The level of SR-B1 expression correlates with both the selective transfer of cholesteryl ester into cells and cholesterol efflux from cells, the transfers probably mediated after docking of HDL at the cell surface. SR-B1 exhibits broad ligand specificity and, in animal models, appears to be regulated by the action of pituitary hormones that stimulate steroidogenesis, suggesting an important role for steroid hormone production in supplying precursor cholesterol. Another candidate HDL receptor, HB2, one of a pair of liver HDL binding proteins, shows high sequence homology with adhesion molecules, particularly activated leukocyte-cell adhesion molecule (ALCAM). When HB2 is overexpressed in cells, HDL binding increases. After PMA-induced differentiation of monocytes into macrophages, HB2 mRNA is strikingly elevated, which correlates with increased binding of HDL, but is down-regulated by cholesterol loading of macrophages. The ligand specificity of the HDL receptors, confounded by nonspecific lipid interactions, remains controversial. Their affinity for apoA-I versus apoA-I/A-II-rich HDL particles has clinical implications; both specific sequences in apoA-I and amphipathic alpha-helices may determine binding events. Post-receptor-mediated signalling events may regulate cell functions which, although not primarily related to lipid transport, nevertheless protect against coronary artery disease. Growing evidence for the involvement of lipid-poor apoA-I as a mediator of such pathways is also discussed.     

Relationship between ATP synthesis and 201Tl uptake in transformed and non-transformed cell lines

The effects of vitamin E on cholesteryl ester (CE) metabolism in J774 cells were examined. Pretreatment of J774 cells with vitamin E at concentrations above 50 microM significantly decreased acetylated low density lipoprotein (LDL)-induced incorporation of [14C]oleate into CE in cells in a dose-dependent manner. This was partly due to vitamin E also significantly inhibiting the uptake of [3H]CE-labeled acetylated LDL by J774 cells. A trend existed toward suppression of acyl-CoA:cholesterol acyltransferase (ACAT) activity in the cell lysate at high vitamin E concentration, but there was no effect on hydrolysis of CE. These data indicate that vitamin E reduces the uptake of modified LDL and suppresses ACAT activity, resulting in less cholesterol esterification in macrophages: a novel mechanism underlying the antiatherogenic properties of vitamin E.     

Influence of insulin on cholesterol removal from macrophages and cholesterol ester uptake by HepG2 cells

The fact that an increased blood insulin level is observed in patients with coronary artery disease (CAD) confirms the hypothesis that insulin promotes the development of atherosclerosis. The low high-density lipoprotein (HDL) concentration observed in such patients may contribute to alteration in reverse cholesterol transport and promote the accumulation of sterols in vascular tissue. We examined the effect of insulin (20-1000 microU mL-1) on cholesterol efflux into HDL3 particles from human blood monocyte/macrophages and rat peritoneal macrophages preloaded with labelled cholesterol esters, and the influence of insulin on the accumulation of sterols by rat liver cells and HepG2 cell line in vitro models. Insulin at concentrations up to 250 microU mL-1 inhibited the efflux of cholesterol from rat macrophages and promoted high uptake of sterols by both types of hepatic cells. Pharmacological concentrations higher than 250 microU mL-1 exerted the opposite effect. In the case of human macrophages, an insulin concentration of 20 microU mL-1 increased cholesterol removal, whereas 100-200 microU mL-1 insulin inhibited cholesterol removal from cells, and very high concentrations (> 350 microU mL-1) again increased cholesterol removal. We have shown that insulin excess counteracts the beneficial effects of HDL in removing cellular cholesterol and, therefore, may promote development of atherogenesis.     

Induction of apoptosis in p53-null HL-60 cells by inhibition of lanosterol 14-alpha demethylase

To determine the role of cholesterol deprivation in cell proliferation and, eventually, in apoptosis, HL-60 promyelocytic cells were incubated in a cholesterol-depleted medium in the presence of SKF 104976, a specific inhibitor of lanosterol 14-alpha demethylase. As expected, SKF 104976 efficiently blocked the [14C]-acetate incorporation into cholesterol, whereas it induced the accumulation of both lanosterol and, especially, dihydrolanosterol. As a consequence, cell proliferation was greatly depressed at 24 h of treatment with the drug, and clear signs of apoptosis--annexin V binding, condensed and fragmented nuclei and DNA ladder--were observed thereafter. Provided that the HL-60 cell line does not express p53, it may be concluded that apoptosis induced by cholesterol deprivation is not dependent on this tumor suppressor protein. Supplementing the incubation medium with LDL-cholesterol or pure free cholesterol, fully prevented cell growth inhibition and apoptosis induction, whereas mevalonate was ineffective. These results indicate that cholesterol plays a specific role in cell proliferation, a function that is not shared by its precursors lanosterol and dihydrolanosterol.     

Cholesterol biosynthesis, peroxisomes and peroxisomal disorders: mevalonate kinase is not only deficient in Zellweger syndrome but also in rhizomelic chondrodysplasia punctata

We examined the inhibitory potency of F-1394 ((1S,2S)-2-[3-(2,2-dimethylpropyl)-3-nonylureido]cyclohexane -1-yl 3-[(4R)-N-(2,2,5,5-tetramethyl-1,3-dioxane-4-carbonyl)amino]propionate), an acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, on ACAT activity and its hypolipidemic effect. F-1394 inhibited whole-cell ACAT activity in HepG2 cells with an IC50 value of 42 nM. The potency of F-1394 was greater than that of the five other ACAT inhibitors tested (YM-17E, CI-976, 57-118, CL-277,082 and DL-melinamide). In rats made hyperlipidemic by Triton WR-1339, F-1394 caused a reduction in the hepatic secretion rate of cholesterol. These data suggest that inhibition of hepatic ACAT activity helps to reduce very low density lipoprotein secretion from the liver into the circulation.     

Simvastatin inhibits myointimal hyperplasia following carotid artery injury in cholesterol-fed rabbits

The effect of simvastatin, a potent inhibitor of 3-hydroxy 3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) was evaluated in an experimental model of myointimal hyperplasia in cholesterol-fed rabbits. Myointimal hyperplasia was induced by an air-drying injury of the left carotid artery followed by a 2%-cholesterol diet for 14 days. A 2-week oral treatment with simvastatin (6 mg/kg/day, p.o.) significantly lowered the circulating levels of cholesterol and triglycerides (41% and 49% inhibition respectively) as well as the low density lipoprotein (LDL)-cholesterol and high density lipoprotein (HDL)-cholesterol levels. Simvastatin also strongly affected the uptake of cholesterol in the arteries occurring as a consequence of vascular injury (44% inhibition, P < 0.001). Morphometric analysis revealed that both the intima and the media areas increased substantially 2 weeks after the lesion and showed a considerable smooth muscle cell accumulation in the neointima together with the presence of numerous foam cells. A 16-day oral treatment with simvastatin strongly reduced smooth muscle cells hyperplasia occurring in both the media and the intima following deendothelialization (19% and 60% inhibition respectively) suggesting that simvastatin may be a useful inhibitor of restenosis which occurs following vascular injury.