| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Inhibition of cholesterol and sphingolipid synthesis causes paradoxical effects on permeability barrier homeostasis Mao-Qiang, M., K. R. Feingold, et al. (1993), J Invest Dermatol 101(2): 185-90. Abstract: Cholesterol, fatty acid, and sphingolipid synthesis are required for barrier homeostasis, as demonstrated by studies where synthesis of these species is stimulated in parallel with barrier repair. Moreover, blockade of synthesis of these lipids with inhibitors of two of the rate-limiting enzymes, HMGCoA reductase (lovastatin, fluvastatin) and serine palmitoyl transferase (beta-chloroalanine), alters the kinetics of barrier repair. Whereas these studies demonstrated a requirement for these lipids individually, we asked here whether these lipids are required in either an additive or cooperative fashion. We applied each class of inhibitor alone or the two classes of inhibitors together to acetone-treated skin, or each class separately to essential fatty acid deficient murine skin. When fluvastatin or beta-chloroalanine was applied individually to acetone-treated skin, each caused a delay in the early or late stages of barrier recovery, respectively (assessed as transepidermal water loss). However, when applied together they caused no further worsening at the early time point and a paradoxical improvement at the later time points. This improvement correlated with an accelerated return of sphingolipids, which was perhaps due to a global stimulation of lipid synthesis induced by HMGCoA reductase inhibitors. In essential fatty acid deficient animals, inhibition of HMGCoA reductase caused drastic worsening of both clinical appearance and barrier function, but beta-chloroalanine caused a paradoxical improvement, which correlated with a significant reduction in epidermal sphingolipids. These results are consistent with a requirement for both cholesterol and sphingolipids for barrier homeostasis, and also with the suggestion that both of these lipids must be present (with free fatty acids) for optimal barrier function. |
| Inhibition of cholesterol biosynthesis as a new antithrombotic strategy Tremoli, E., S. Colli, et al. (2001), Haematologica 86(11 Suppl 2): 35. |
| Inhibition of cholesterol biosynthesis by a water-soluble garlic extract in primary cultures of rat hepatocytes Gebhardt, R. (1991), Arzneimittelforschung 41(8): 800-4. Abstract: Cultured rat hepatocytes continually synthesize cholesterol form radiolabeled acetate during a 24 h incubation period and export it, presumably as VLDL (very low density lipoprotein) to the culture medium. Mevastatin inhibits cholesterol biosynthesis by 90%. Incubation of the cultures with water-soluble extracts of garlic powder (Kwai, Sapec) diminish cholesterol biosynthesis (20-25%) as well as its export into the medium (30-35%). The IC50-value is 90 micrograms/ml. Between about 0.25 and 10 mg/ml the average maximal inhibition amounts to about 23%. Cytotoxicity of the extracts is apparent at concentrations above 125 mg/ml only. Pure alliin alone, or after incubation with alliinase (conversion to allicin) in concentrations corresponding to its content in the extracts does not exert any inhibition. Replacement of 14C-acetate by 14C-mevalonate omits the inhibitory effect. The activity of HMGCoA (hydroxymethylglutaryl-CoA) reductase is significantly reduced by garlic extracts at 50 micrograms/ml. At higher concentrations fatty acid synthetase, cholesterol 7 alpha-hydroxylase and cholesterol acyltransferase are slightly inhibited. Fatty acid synthetase is the only one of these enzymes which is inhibited by alliin at very high concentrations. These results demonstrate that water-soluble garlic extracts diminish hepatic cholesterol biosynthesis, thus contributing to the reduction of blood cholesterol. The main target site seems to be HMGCoA-reductase. The actual active principle(s) is still unknown. Alliin, however, does not seem to be of major significance. |
| Inhibition of cholesterol biosynthesis by allicin and ajoene in rat hepatocytes and HepG2 cells Gebhardt, R., H. Beck, et al. (1994), Biochim Biophys Acta 1213(1): 57-62. Abstract: Exposure of primary rat hepatocytes and human HepG2 cells to allicin and ajoene resulted in the concentration-dependent inhibition of cholesterol biosynthesis at different steps of this metabolic pathway. At low concentrations of ajoene sterol biosynthesis from 14Cacetate in rat hepatocytes was decreased by 18% with an IC50-value of 15 microM, while allicin was almost uneffective. In HepG2 cells, both compounds significantly inhibited sterol biosynthesis by 14% and 19% with IC50-values of 7 and 9 microM for allicin and ajoene, respectively. This inhibition was exerted at the level of HMG-CoA-reductase as revealed by the absence of inhibition, if 14Cacetate was replaced by 14Cmevalonate as a precursor, and by direct determination of enzyme activity. At somewhat higher concentrations inhibition of cholesterol biosynthesis by both, allicin and ajoene, was also observed at late steps resulting in the accumulation of the precursor lanosterol. Alliin instead was completely inactive. In the case of allicin, small amounts of dihydrolanosterol and 7-dehydrocholesterol were formed at intermediate concentrations of 5-10 microM. From these results it is concluded that a major point of inhibition at the late steps occurs at the level of lanosterol 14 alpha-demethylase. |
| Inhibition of cholesterol biosynthesis by Delta22-unsaturated phytosterols via competitive inhibition of sterol Delta24-reductase in mammalian cells Fernandez, C., Y. Suarez, et al. (2002), Biochem J 366(Pt 1): 109-19. Abstract: Dietary phytosterols are cholesterol-lowering agents that interfere with the intestinal absorption of cholesterol. In the present study, we have studied their effects on cholesterol biosynthesis in human cells, particularly in the sterol-conversion pathway. For this, both Caco-2 (intestinal mucosa) and HL-60 (promyelocytic) human cell lines were incubated with (14)Cacetate, and the incorporation of radioactivity into sterols was determined using HPLC and radioactivity detection online. Sterols containing a double bond at C-22 in the side chain (stigmasterol, brassicasterol and ergosterol) dramatically inhibited the activity of sterol Delta(24)-reductase, as indicated by the decrease in radioactivity incorporation into cholesterol and the accumulation of its precursors (mainly desmosterol). Phytosterols with the saturated side chain (beta-sitosterol and campesterol) were inactive in this regard. The inhibition of sterol (24)-reductase was confirmed in rat liver microsomes by using (14)C-labelled desmosterol as the substrate. The (22)-unsaturated phytosterols acted as competitive inhibitors of sterol (24)-reductase, with K(i) values (41.1, 42.7 and 36.8 microM for stigmasterol, brassicasterol and ergosterol respectively) similar to the estimated K(m) for desmosterol (26.3 microM). The sterol 5,22-cholestedien-3beta-ol, an unusual desmosterol isomer that lacks the alkyl groups characteristic of phytosterols, acted as a much stronger inhibitor of (24)-reductase (K(i)=3.34 microM). The usually low intracellular concentrations of the physiological substrates of (24)-reductase explains the strong inhibition of cholesterol biosynthesis that these compounds exert in cells. Given that inhibition of sterol (24)-reductase was achieved at physiologically relevant concentrations, it may represent an additional mechanism for the cholesterol-lowering action of phytosterols, and opens up the possibility of using certain (22)-unsaturated sterols as effective hypocholesterolaemic agents. |
| Inhibition of cholesterol biosynthesis by organosulfur compounds derived from garlic Liu, L. and Y. Y. Yeh (2000), Lipids 35(2): 197-203. Abstract: The study was undertaken to test the inhibitory potential on cholesterogenesis of organosulfur compounds derived from garlic. The primary rat hepatocytes maintained in Dulbecco's modified Eagle's medium were treated with 2-14Cacetate as substrate for cholesterol synthesis in the presence or absence of test compounds at 0.05 to 4.0 mmol/L. Eleven water-soluble and six lipid-soluble compounds of garlic were tested. Among water-soluble compounds, S-allyl cysteine (SAC), S-ethyl cysteine (SEC), and S-propyl cysteine (SPC) inhibited 2-14Cacetate incorporation into cholesterol in a concentration-dependent manner, achieving 42 to 55% maximal inhibition. Gamma-glutamyl-S-allyl cysteine, gamma-glutamyl-S-methyl cysteine, and gamma-glutamyl-S-propyl cysteine were less potent, exerting only 16 to 29% maximal inhibitions. Alliin, S-allyl-N-acetyl cysteine, S-allylsulfonyl alanine, and S-methyl cysteine had no effect on cholesterol synthesis. Of the lipid-soluble compounds, diallyl disulfide (DADS), diallyl trisulfide (DATS), and dipropyl disulfide (DPDS) depressed cholesterol synthesis by 10 to 25% at low concentrations (< or =0.5 mmol/L), and abolished the synthesis at high concentrations (> or =1.0 mmol/L). Diallyl sulfide, dipropyl sulfide, and methyl allyl sulfide slightly inhibited 2-14Cacetate incorporation into cholesterol only at high concentrations. The complete depression of cholesterol synthesis by DADS, DATS, and DPDS was associated with cytotoxicity as indicated by marked increase in cellular LDH release. There was no apparent increase in LDH secretion by water-soluble compounds except S-allyl mercaptocysteine, which also abolished cholesterol synthesis. Judging from maximal inhibition and IC50 (concentration required for 50% of maximal inhibition), SAC, SEC, and SPC are equally potent in inhibiting cholesterol synthesis. |
| Inhibition of cholesterol biosynthesis by squalene epoxidase inhibitor avoids apoptotic cell death in L6 myoblasts Matzno, S., T. Yamauchi, et al. (1997), J Lipid Res 38(8): 1639-48. Abstract: The relationship between the inhibition of cholesterol biosynthesis and occurrence of myopathy was studied in L6 myoblasts using two lines of cholesterol biosynthesis inhibitors, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor (simvastatin) and squalene epoxidase inhibitors (TU-2078 and NB-598). All inhibitors completely inhibited the cholesterol synthesis in L6 myoblasts at doses of 1 and 3 microM. Simvastatin (3 microM) inhibited the fusion reaction of L6 myoblasts followed by the severe cellular damage. The myoblasts also had failed actin fiber formation and creatinine phosphokinase (CPK) production. Additionally, this agent also caused apoptotic cell death in differentiated L6 muscle fiber, indicating that skeletal myopathy by HMG-CoA reductase inhibitors seems to occur not only in differentiating immature myoblasts but also in matured skeletal myotubes. In contrast, TU-2078 and NB-598 had no effect on the fusion reaction of differentiating myoblasts or on the cellular viability of muscle fiber at 3 microM, enough to completely inhibit cholesterol biosynthesis. It is conceivable that the mevalonate depletion and subsequent failure of ras farnesylation induced by simvastatin might cause the defects in differentiation and maintenance of the muscle fiber. Squalene epoxidase inhibitors did not show this adverse effect presumably because of the enzyme inhibition downstream of farnesyl synthesis. The present findings suggest the safe use of squalene epoxidase inhibitors in lipid-lowering therapy. |
| Inhibition of cholesterol biosynthesis in cultured fibroblasts by D003, a mixture of very long chain saturated fatty acids Menendez, R., R. Mas, et al. (2001), Pharmacol Res 44(4): 299-304. Abstract: The present study was undertaken to investigate the effects of D003, a mixture of very long chain saturated fatty acids isolated and purified from sugar cane wax, on cholesterol biosynthesis in cultured fibroblasts. Cholesterol biosynthesis is regulated through feedback regulation of at least two sequentially acting enzymes, 3-hydroxy-3-methyl coenzyme A (HMG-CoA) synthase and reductase. They are up-regulated when sterol levels fall and down-regulated when sterol levels rise. The exposure of cultured fibroblasts to a lipid-depleted medium (LDM) and D003 (0.05-50 microg ml(-1)) for 12 h inhibited, in a dose-dependent manner, cholesterol biosynthesis from 14C-labelled acetate (33-68%). The addition of D003 at concentrations inhibiting cholesterol biosynthesis from labelled acetate significantly decreased incorporation of radioactivity from 3H2O into sterols, but not from 14C-mevalonate. These data indicate that D003 inhibits cholesterol biosynthesis by interfering with early steps of cholesterol biosynthetic pathway. We reasoned that D003 acts directly on HMG-CoA reductase, the main regulatory enzyme of cholesterol biosynthetic pathway. However, when enzyme activity was measured in cell extracts in the presence of various concentrations of D003 (0.5-50 microg ml(-1)), reductase activity was not inhibited. Thus, there was no evidence for a competitive or non-competitive inhibition of enzyme activity by D003. Treatment with D003 significantly suppressed (68%) the enzyme up-regulation when cells were cultured in LDM, which suggests a depression of de novo synthesis of HMG-CoA reductase and/or a stimulation of its degradation. However, since the suppressive action of D003 on cholesterol biosynthesis was observed in metabolic conditions under which synthase up-regulation was also enhanced, we cannot rule out a possible effect of D003 on HMG-CoA synthase. Thus, further studies are needed to clarify the precise mechanism of the inhibitory effect of D003 on cholesterol biosynthesis. |
| Inhibition of cholesterol biosynthesis in HepG2 cells by artichoke extracts is reinforced by glucosidase pretreatment Gebhardt, R. (2002), Phytother Res 16(4): 368-72. Abstract: High-dose aqueous extracts from artichoke leaves were found to inhibit cholesterol biosynthesis from (14)C-acetate rather moderately in HepG2 cells in contrast to primary cultured rat hepatocytes in which the inhibition was stronger. Preincubation of the extracts with several glycohydrolases revealed that pretreatment with beta-glucosidase considerably reinforced the inhibition. A significant reduction of acetate incorporation was found above extract concentrations of 0.01 mg/mL and at 0.2 mg/mL almost 60% inhibition was observed. Cytotoxic effects detected by the MTT-assay were restricted to higher concentrations of the extracts with and without beta-glucosidase pretreatment. Since cynaroside represents a major glucoside in artichoke extracts, both cynaroside and its aglycone luteolin were tested. It could be demonstrated that cynaroside is indeed one of the targets of beta-glucosidase and that the liberated luteolin is responsible for the inhibitory effect. Direct measurements of beta-glucosidase activity in rat hepatocytes and HepG2 cells revealed that endogenous enzyme activity in hepatocytes may be sufficient to convert cynaroside to its aglycone, while in HepG2 cells this may not be the case. These findings emphasize the importance of beta-glucosidase-dependent liberation of luteolin for the ability of artichoke extracts to inhibit hepatic cholesterol biosynthesis. |
| Inhibition of cholesterol biosynthesis in primary cultured rat hepatocytes by artichoke (Cynara scolymus L.) extracts Gebhardt, R. (1998), J Pharmacol Exp Ther 286(3): 1122-8. Abstract: High-dose aqueous extracts from artichoke leaves were found to inhibit cholesterol biosynthesis from 14C-acetate in primary cultured rat hepatocytes in a concentration-dependent biphasic manner with moderate inhibition (approximately 20%) between 0.007 and 0.1 mg/ml and more strong inhibition at 1 mg/ml. Cytotoxic effects detected by lactate dehydrogenase leakage and the 3-4, 5-dimethylthiazol-2-yl-2,5-dephenyl tetrazolium bromide-assay were restricted to higher concentrations. Replacement of 14C-acetate by 14C-mevalonate largely omitted the inhibiting effect of artichoke extracts indicating an inhibition at the level of hydroxymethylglutaryl-CoA-reductase. However, no direct inhibition of this enzyme could be detected and no other enzymic steps later in the biosynthetic pathway for cholesterol seemed to be affected. Instead, inhibition was found to occur in a time-dependent manner, to last for several hours even after washing out the extracts by fresh medium and to be fully reversible within 20 hr after removal of the extracts. In addition, the stimulation of HMGCoA-reductase activity by insulin was efficiently blocked by the extracts, although other insulin-dependent phenomena, such as increased lactate production, were not influenced. These results suggest an indirect modulation of hydroxymethylglutaryl-CoA-reductase activity as the most likely inhibitory mechanism of the artichoke extracts. Screening of several known constituents of artichoke extracts revealed that cynaroside and particularly its aglycone luteolin were mainly responsible for inhibition, whereas chlorogenic acid was much less effective and caffeic acid, cynarin and other dicaffeoylquinic acids were without significant influence. Indeed, luteolin also efficiently blocked the insulin effect on cholesterol biosynthesis. In conclusion, these results demonstrate that artichoke extracts may inhibit hepatic cholesterol biosynthesis in an indirect but efficient manner and, thus, may contribute via this action to the recently confirmed hypolipidemic influence of this phytopharmacon in man. |
| Inhibition of cholesterol biosynthesis in rabbit hepatocytes by 3-beta-(omega-hydroxyalkoxy)cholest-5-enes Maliugin, A. V., D. K. Novikov, et al. (1996), Bioorg Khim 22(7): 541-7. Abstract: 3 beta-(2-Hydroxyethoxy)-, 3 beta-(4'-hydroxybutoxy)-, 3 beta-(6-hydroxyhexyloxy)-, 3 beta-(9-hydroxynonyloxy)-, and 3 beta-(2-hydroxy-2-3Hethoxy)cholest-5-enes were synthesized. By means of a spin probe, the influence of the synthesized compounds on the phase transition of dimyristoylphosphatidylcholine were estimated. Time and dose dependences of the incorporation of 3 beta-(2-hydroxy-2-3Hethoxy)cholest-5-ene into rabbit hepatocytes (the primary culture) were studied. 3 beta-(2-Hydroxyethoxy)- and 3 beta-(4-hydroxybutoxy)cholest-5-enes were shown to inhibit cholesterol biosynthesis from 14Cacetate in rabbit hepatocyte cultures upon a 24-hour preincubation. |
| Inhibition of cholesterol crystallization under bilirubin deconjugation: partial characterization of mechanisms whereby infected bile accelerates pigment stone formation Nakai, K., S. Tazuma, et al. (2003), Biochim Biophys Acta 1632(1-3): 48-54. Abstract: Pigment gallstones have been reported to be closely associated with biliary tract infection. We previously reported that addition of unconjugated bilirubin (UCB), which is deconjugated by beta-glucuronidase in infected bile, could enhance cholesterol crystal formation in supersaturated model bile (MB). The present study evaluated the effect of beta-glucuronidase on the processes of pigment gallstone formation and cholesterol crystallization. Supersaturated MB (taurocholate/lecithin/cholesterol at 71:18:11, a total lipid concentration of 10.0 g/dl and a cholesterol saturation index (CSI) of 2.0) and native rat bile were mixed at a ratio of 3:1. Then, mixed bile was incubated with or without beta-glucuronidase and changes of the following parameters were investigated over time: (1) the UCB/total bilirubin ratio; (2) cholesterol crystal formation; (3) the precipitate weight and the cholesterol concentration in the precipitate and supernatant; and (4) the lipid distribution of vesicles in the supernatant. Compared with beta-glucuronidase-free bile, (1) beta-glucuronidase-containing bile showed a significant increase of the UCB/total bilirubin ratio, (2) as well as a significantly longer nucleation time (96+/-17.0 vs. 114+/-20.0) and fewer cholesterol crystals. (3) The precipitate weight and the cholesterol concentration in the precipitate were significantly increased, while the cholesterol concentration in supernatant was decreased. (4) When mixed bile was incubated with beta-glucuronidase, the cholesterol concentration in the vesicles was lower than in bile without beta-glucuronidase. The precipitate weight and the cholesterol concentration in the precipitate was increased by incubation with beta-glucuronidase, while cholesterol concentration was decreased in the supernatant (especially in the vesicles). This means that bile vesicles were more stable and it was more difficult for cholesterol crystals to form. Thus, the presence of beta-glucuronidase may inhibit the formation of pure cholesterol stones even in the presence of cholesterol supersaturation. |
| Inhibition of cholesterol efflux by 7-ketocholesterol: comparison between cells, plasma membrane vesicles, and liposomes as cholesterol donors Gaus, K., R. T. Dean, et al. (2001), Biochemistry 40(43): 13002-14. Abstract: Cholesterol removal from lipid-loaded macrophages is an important, potentially antiatherogenic process, and we have previously shown that an oxysterol, 7-ketocholesterol (7K), can impair efflux to lipid-free apoprotein A-1 (apoA-1). This publication investigates whether incorporation of 7K into membranes could account for this impairment of cholesterol efflux. Cholesterol efflux was studied from lipoprotein-loaded THP-1 cells, from plasma membrane vesicles obtained from these cells, and from artificial, protein-free liposomes. Impairment of cholesterol efflux by 7K was observed for all cholesterol donor systems whether measured as decline in cholesterol removal rates or as the percentage mass of total cellular cholesterol exported. 7-Ketocholesterol itself was not removed by apoA-1 from any of the cholesterol donor systems. Increasing membrane cholesterol content increased the rate of cholesterol removal by apoA-1 (as seen with plasma membrane vesicles), the quantity of cholesterol removed at equilibrium (liposomes), or both (whole cells). Although the minimum inhibitory 7K concentrations varied between the cholesterol donor systems, 7K inhibited cholesterol efflux in all systems. It was concluded that 7K induces alteration in membranes which decreased the efficiency of cholesterol efflux and the quantity of removed cholesterol induced by apoA-1. As cell membrane proteins are not essential for cholesterol efflux in these systems, the impairment of such by 7K suggests that its effect on membrane lipid composition and its structure are key regulatory elements in this efflux process. |
| Inhibition of cholesterol ester transfer protein CGS 25159 and changes in lipoproteins in hamsters Kothari, H. V., K. J. Poirier, et al. (1997), Atherosclerosis 128(1): 59-66. Abstract: As a result of screening, several isoflavans were identified to be antagonists of cholesterol ester transfer protein (CETP) activity. The present study evaluates CGS 25159, a synthetic isoflavan, as a putative inhibitor of CETP activity of human and hamster plasma. Determined by 3CE transfer from HDL to VLDL + LDL fraction or by fluorescent-CE transfer assay, CGS 25159 inhibited CETP in both human plasma bottom fraction (d = 1.21 g/ml) and in plasma from Golden Syrian Hamsters with an IC50 < 10 microM. The compound also inhibited (IC 50 approximately equal to 15 microM) the reciprocal transfer of triglycerides in the incubated whole plasma from normal and hyperlipidemic hamsters. When orally administered to normolipidemic hamsters, CGS 25159 (10 mg/kg, 4 days) reduced plasma transfer activity by 35-60%. Treatment with CGS 25159 (10 and 30 mg/kg, p.o.) resulted in dose dependent and time dependent changes in CETP activity. After two weeks of treatment at 10 mg/kg, the changes in VLDL + LDL cholesterol, total triglycerides and HDL cholesterol were -22 +/- 4.6*, -23 +/- 7.5 and +10 +/- 2.8%, respectively. The corresponding changes at 30 mg/kg were -28 +/- 5.5*, -38 +/- 6.8* and +29 +/-4.4.*%, (*, P, 0.05; mean +/- S.E.M., n = 6). A single spin gradient density ultracentrifugation of plasma lipoproteins and treated animals showed an increase in HDL cholesterol and a redistribution to larger HDL particles. These data support the contention that pharmacological down regulation of CETP activity could result in favorable changes in lipoprotein profile. |
| Inhibition of cholesterol esterification by DuP 128 decreases hepatic apolipoprotein B secretion in vivo: effect of dietary fat and cholesterol Burnett, J. R., L. J. Wilcox, et al. (1998), Biochim Biophys Acta 1393(1): 63-79. Abstract: To further test the hypothesis that newly synthesized cholesteryl esters regulate hepatic apolipoprotein B (apoB) secretion into plasma, apoB kinetic studies were carried out in seven control miniature pigs and in seven animals after 21 days intravenous administration of the acyl coenzyme A:cholesterol acyltransferase (ACAT) inhibitor DuP 128 (2.2 mg/kg/day). Pigs were fed a fat (34% of calories; polyunsaturated/monounsaturated/saturated ratio, 1:1:1) and cholesterol (400 mg/day; 0.1%; 0.2 mg/kcal) containing pig chow based diet. DuP 128 significantly reduced total plasma triglyceride and very low density lipoprotein (VLDL) triglyceride concentrations by 36 and 31%, respectively (P<0.05). Autologous 131I-VLDL and 125I-LDL were injected simultaneously into each pig and apoB kinetic data was analyzed using multicompartmental analysis (SAAM II). The VLDL apoB pool size decreased by 26% (0.443 vs. 0.599 mg/kg; P<0. 001) which was due entirely to a 28% reduction in VLDL apoB production or secretion rate (1.831 vs. 2.548 mg/kg/h; P=0.006). The fractional catabolic rate (FCR) for VLDL apoB was unchanged. The LDL apoB pool size and production rate were unaffected by DuP 128 treatment. Hepatic microsomal ACAT activity decreased by 51% (0.44 vs. 0.90 nmol/min/mg; P<0.001). Although an increase in hepatic free cholesterol and subsequent decrease in both LDL receptor expression and LDL apoB FCR might be expected, this did not occur. The concentration of hepatic free cholesterol decreased 12% (P=0.008) and the LDL apoB FCR were unaffected by DuP 128 treatment. In addition, DuP 128 treatment did not alter the concentration of hepatic triglyceride or the activity of diacylglycerol acyltransferase, indicating a lack of effect of DuP 128 on hepatic triglyceride metabolism. In our previous studies, DuP 128 treatment of miniature pigs fed a low fat, cholesterol free diet, decreased VLDL apoB secretion by 65% resulting in a reduction in plasma apoB of 60%. We conclude that in miniature pigs fed a high fat, cholesterol containing diet, the inhibition of hepatic cholesteryl ester synthesis by DuP 128 decreases apoB secretion into plasma, but the effect is attenuated relative to a low fat, cholesterol free diet. |
| Inhibition of cholesterol esterification in macrophages and vascular smooth muscle foam cells: evaluation of E5324, an acyl-CoA cholesterol acyltransferase inhibitor Nicholson, A. C., K. B. Pomerantz, et al. (1995), Lipids 30(8): 771-4. Abstract: Cholesteryl esters (CE) comprise the principal lipid class that accumulates within macrophages and smooth muscle cells of the atherosclerotic lesion. Acyl-CoA cholesterol acyl-transferase (ACAT) is the major enzyme responsible for esterification of intracellular cholesterol. We evaluated the ability of E5324 (n-butyl-N'--2-3-(5-ethyl-4-phenyl-1H-imidazol-1-yl)propoxy-6- methyl-phenylurea), a novel, orally absorbable ACAT inhibitor, to inhibit esterification of fatty acids to cholesterol and CE accumulation in macrophages and in smooth muscle cells. E5324 significantly inhibited cholesterol esterification in rat aortic smooth muscle cells and in macrophages. In addition, E5324 reduced the cellular mass of CE, the significant measure of the efficacy of drugs designed to modulate cholesterol metabolism. E5324 treatment of macrophages exposed to acetylated low-density lipoprotein reduced CE mass by 97%, and treatment of lipid-loaded smooth muscle cells reduced CE mass by 29%. Although free cholesterol increased approximately twofold, this free cholesterol would presumably be accessible to the membrane for efflux in vivo (reverse cholesterol transport). These results demonstrate that E5324 can inhibit cholesterol esterification and CE mass in atherosclerotic foam cells, derived from either macrophages or arterial smooth muscle cells. |
| Inhibition of cholesterol production but not of nonsterol isoprenoid products induces neuronal cell death Michikawa, M. and K. Yanagisawa (1999), J Neurochem 72(6): 2278-85. Abstract: Deficiency of nonsterol isoprenoids, intermediate metabolites of the cholesterol biosynthetic pathway, has been known to cause an inhibition of DNA synthesis and cell growth, and to induce apoptosis in nonneuronal cells. To investigate whether this is also the case in neurons, we examined the effect of a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor on the viability of neuronal cultures prepared from fetal rat brains. Treatment with compactin, a competitive inhibitor of HMG-CoA reductase, induced neuronal death in a dose-dependent manner. Concurrent treatment with cholesterol, beta-migrating very low density lipoprotein, mevalonate, or squalene substantially inhibited the induction of neuronal death by compactin. Cell death was also induced by treatment with squalestatin, which specifically inhibits cholesterol biosynthesis at a site downstream from the generation of nonsterol metabolites. Furthermore, squalestatin-induced neuronal death was inhibited by concurrent incubation with squalene but not mevalonate. In contrast, cell growth of proliferating cells such as NIH 3T3 and PC12 cells was exclusively dependent on the level of nonsterol isoprenoid products and not that of cholesterol. The results of this study clearly indicate that the viability of neurons, different from that of nonneuronal cells, depends on the intracellular cholesterol content and not on the intermediate nonsterol isoprenoid products. |
| Inhibition of cholesterol side-chain cleavage. Part 5. Synthesis of 22-(p-chlorophenyl) cholesterol analogues Bergstrom, C. P., R. Clarke, et al. (1991), Drug Des Deliv 7(4): 259-68. Abstract: Three 22-(p-chloroaryl) analogues of cholesterol (6a-c) were synthesized and evaluated as potential inhibitors of the adrenal cholesterol side-chain cleavage enzyme, in comparison with the known 20-aryl analogue, 20-(p-chlorophenyl)-5-prenen-3 beta,20-diol (2b). All were potent inhibitors. An oxygen at C-22 (analogues 6a and 6b) enhanced the strong binding to the enzyme. Two compounds (6b and 6c) are potential substrates of the enzyme. Possible pharmaceutical uses for these compounds and their derivatives are discussed. |
| Inhibition of cholesterol synthesis and cataract Hockwin, O., M. Kojima, et al. (1991), Fortschr Ophthalmol 88(4): 393-5. Abstract: The cholesterol requirements of the lens for the formation of plasma membranes are met by self-synthesis only until early postnatal life. This ability subsequently decreases with increasing age and probably ceases altogether. The cholesterol supply then has to come from exogenous sources. These findings are of great importance for the qualitative assessment of extrahepatic side effects of HMG-CoA-reductase inhibitors given for disturbances of lens transparency. The observation of cataracts in chronic toxicity tests with high doses in beagle dogs suggested that the lens enzyme was also affected by the inhibitor, thus causing cataracts. In contrast to other workers' results, we did not find any activity of HMG-CoA-reductase in our experiments with calf, bovine, dog and rat lenses. Preliminary studies with bovine eyes demonstrate a direct correlation between the cholesterol serum level and the content of the aqueous humor. This shows the importance of the exogenous supply for the lens requirements. A further strong argument is that the use of HMG-CoA-reductase inhibitors in patients with pathologically increased cholesterol level is safe as far as the lens transparency is concerned, as demonstrated in clinical trials. |
| Inhibition of cholesterol synthesis and esterification regulates high density lipoprotein interaction with isolated epithelial cells of human small intestine Sviridov, D. D., M. Y. Pavlov, et al. (1990), J Lipid Res 31(10): 1821-30. Abstract: The effect of two inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, lovastatin and monacolin L, and an inhibitor of acyl coenzyme A:cholesterol acyltransferase (ACAT), Sandoz compound 58-035, on the interaction of 125I-labeled high density lipoprotein-3 (HDL3) with isolated human enterocytes was studied. Both HMG-CoA reductase inhibitors inhibited cholesterol synthesis and 125I-labeled HDL3 binding and degradation by enterocytes; a strong correlation between changes in cholesterol synthesis and interaction of 125I-labeled HDL3 with cells was observed. Lovastatin caused reduction of the apparent number of 125I-labeled HDL3 binding sites without affecting the binding affinity. No changes of cell cholesterol content were observed after incubation of cells with lovastatin. Mevalonic acid reversed the effect of lovastatin on 125I-labeled HDL3 binding. Lovastatin blocked up-regulation of the HDL receptor in response to loading of cells with nonlipoprotein cholesterol and modified cholesterol-induced changes of 125I-labeled HDL3 degradation. Lovastatin also reduced HDL-mediated efflux of endogenously synthesized cholesterol from enterocytes. The ACAT inhibitor caused a modest increase of 125I-labeled HDL3 binding to enterocytes and significantly decreased its degradation; both effects correlated with inhibition of cholesteryl ester synthesis. The results allow us to assume that the intracellular free cholesterol pool may play a key role in regulation of the HDL receptor. |