Cholesterol Journal Articles

Record 7701 to 7720

Inhibition of the activities of P450 cholesterol side-chain cleavage and 3 beta-hydroxysteroid dehydrogenase and the amount of P450 cholesterol side-chain cleavage by testosterone and estradiol-17 beta in hen granulosa cells
Lee, H. T. and J. M. Bahr (1990), Endocrinology 126(2): 779-86.
Abstract: We have found that androgens and estradiol-17 beta (E2) produced by theca cells suppress progesterone (P4) secretion by granulosa cells of the domestic hen in a dose-dependent manner. Furthermore, testosterone (T) and E2 inhibited the conversion of cholesterol to pregnenolone (P5) and of P5 to P4, respectively. The aim of this study was to determine if T and E2 suppress P4 biosynthesis by changing activities of the cytochrome P450 cholesterol side chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) (Exp I) and the amount of P450scc (Exp II). Granulosa layers of the largest follicle of two to four hens were obtained 22 h before ovulation, pooled, and isolated granulosa cells were prepared. In Exp I, the specific activities of the P450scc and 3 beta-HSD were measured in mitochondrial and microsomal proteins of granulosa cells, respectively, in the presence of T or E2 (0-10 microM). Addition of T to mitochondrial proteins increased the Michaelis-Menten constant (Km) with no change in the maximum velocity (Vmax) of the P450scc, which suggests competitive inhibition (Ki = 30.9 microM), whereas E2 had no effect on Km and Vmax of the P450scc. Likewise, addition of E2 to microsomal proteins increased the Km with no change in the Vmax of the 3 beta-HSD, which suggests competitive inhibition (Ki = 15.1 microM), whereas T had no effect on Km and Vmax of the 3 beta-HSD. In Exp II, granulosa cells (3 x 10(5)/3 ml.tube) were incubated for 0-12 h in triplicate for each combined treatments of 25-OH-cholesterol (8 microM) and cyanoketone (10 microM), T, or E2 (0-10 microM) in the presence or absence of LH (25 ng). Protein content and P5 secretion were measured and the amount of P450scc was determined by Western blot analysis. Incubation of granulosa cells with T decreased the amount of the P450scc in granulosa cells cultured for 12 h and P5 secretion in granulosa cells cultured for 3 h or longer (P less than 0.05), without a change in protein content and cell viability. Our results suggest that P4 production by granulosa cells is suppressed by T and E2 acting as competitive inhibitors of the P450scc and 3 beta-HSD, respectively, and by T decreasing the amount of the P450scc. We conclude that steroidogenesis in the follicle of the chicken is regulated through the interaction of theca and granulosa layers.

Inhibition of the apical sodium-dependent bile acid transporter reduces LDL cholesterol and apoB by enhanced plasma clearance of LDL apoB
Huff, M. W., D. E. Telford, et al. (2002), Arterioscler Thromb Vasc Biol 22(11): 1884-91.
Abstract: OBJECTIVE: Cloning of the ileal apical sodium-dependent bile acid transporter (ASBT) has identified a new pharmacological target for the modulation of plasma lipoproteins. The objective of this study was to determine whether a novel, specific, minimally absorbed ASBT inhibitor (SC-435) decreases LDL cholesterol through the alteration of plasma apoB kinetics. METHODS AND RESULTS: Miniature pigs were treated for 21 days with 10 mg/kg/day of SC-435 or placebo. SC-435 decreased plasma cholesterol by 9% and LDL cholesterol by 20% with no effect on other lipids. Autologous (131)I-VLDL, (125)I-LDL, and (3)H-leucine were injected simultaneously to determine apoB kinetics. LDL apoB concentrations decreased significantly by 10% resulting entirely from an increase in LDL-apoB fractional catabolic rate. SC-435 had no effect on either total LDL apoB production or VLDL apoB converted to LDL. SC-435 increased VLDL apoB production by 22%; however, the concentration was unchanged as a result of increased VLDL apoB direct removal. SC-435 increased hepatic mRNA and enzymatic activity for both cholesterol 7alpha-hydroxylase and HMG-CoA reductase. Hepatic LDL receptor mRNA increased significantly, whereas apoB expression was unaffected. CONCLUSIONS: A low dose of the ASBT inhibitor, SC-435, significantly reduces plasma LDL cholesterol through enhanced LDL receptor-mediated LDL apoB clearance, secondary to increased expression of cholesterol 7alpha-hydroxylase.

Inhibition of the mevalonate pathway: benefits beyond cholesterol reduction?
Massy, Z. A., W. F. Keane, et al. (1996), Lancet 347(8994): 102-3.

Inhibition of ubiquinone and cholesterol synthesis by the monoterpene perillyl alcohol
Ren, Z. and M. N. Gould (1994), Cancer Lett 76(2-3): 185-90.
Abstract: Monoterpenes such as perillyl alcohol have been shown to cause the complete regression of advanced mammary carcinomas. Given the common origin of plant monoterpenes and many important molecules in mammalian mevalonate metabolism pathway, we investigated the effects of the monoterpene perillyl alcohol on mevalonate metabolism. NIH3T3 cells were labeled with 14Cmevalonolactone and lipids were analyzed. Perillyl alcohol inhibited ubiquinone synthesis and blocked the conversion of lathosterol to cholesterol. These two cellular effects of perillyl alcohol may contribute to the antitumor activity of the monoterpenes.

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase unmask transcriptional regulation of hepatic low-density lipoprotein receptor gene expression by dietary cholesterol
Lopez, D. and G. C. Ness (1997), Arch Biochem Biophys 344(1): 215-9.
Abstract: The mechanism by which dietary cholesterol regulates expression of the hepatic low-density lipoprotein (LDL) receptor was investigated. In a previous study (Arch. Biochem. Biophys. 325, 242-248, 1996), we demonstrated that dietary cholesterol reduces the rate of LDL receptor protein degradation without affecting steady-state levels of receptor protein. In view of these findings, it was expected that dietary cholesterol would decrease the rate of transcription of the hepatic LDL receptor gene, resulting in lower mRNA levels and lower rates of synthesis of LDL receptor protein. Surprisingly, neither the rate of transcription nor the level of LDL receptor mRNA was reduced in response to dietary cholesterol, even though hepatic cholesterol levels were increased twofold. This suggests that under normal conditions, dietary cholesterol does not affect LDL receptor gene expression at the level of transcription. In contrast, feeding 2% cholesterol to rats fed a diet supplemented with 0.04% lovastatin significantly decreased hepatic LDL receptor mRNA levels and transcription rates. These results suggest that lovastatin unmasks transcriptional regulation of the hepatic LDL receptor by dietary cholesterol. The levels of the mature nuclear forms of sterol response element binding proteins-1 and -2 were unaffected despite significant changes in hepatic cholesterol levels, mRNA levels, and transcription rates caused by lovastatin treatment. This suggests that the observed changes in transcription rates may not be mediated by these proteins in rat liver.

Inhibitors of acyl-CoA: cholesterol acyltransferase. II. Preparation and hypocholesterolemic activity of optically active dibenzb,eoxepin-11-carboxanilides
Kumazawa, T., M. Yanase, et al. (1996), Chem Pharm Bull (Tokyo) 44(1): 222-5.
Abstract: In a previous paper, we reported a novel inhibitor of acyl-CoA: cholesterol acyltransferase (ACAT), 2-bromo-N-(2,6-diisopropylphenyl)-6,11- dihydrodibenzb,eoxepin-11-carboxamide (1). In this work, we prepared both enantiomers and tested them for ability to inhibit ACAT (liver microsomes from cholesterol-fed rabbits) in vitro and to decrease serum total cholesterol in cholesterol-fed golden hamsters in vivo. The precursor carboxylic acid 4 was optically resolved with cinchonidine. The obtained (-)- and (+)-4 were converted to (-)- and (+)-1 without racemization, respectively. The enantiomer (-)-1 showed potent ACAT inhibitory activity in vitro with an IC50 value of 8 nM and was approximately 10-fold more active than (+)-1. Furthermore, (-)-1 showed strong hypocholesterolemic activity in vivo, whereas (+)-1 was inactive. A molecular modeling study showed that the difference of ACAT inhibitory activity between the enantiomers was derived from the spatial alignment of the bromine. Compound (-)-1 was selected for further evaluation as KW-3033.

Inhibitors of acyl-CoA: cholesterol O-acyl transferase (ACAT) as hypocholesterolemic agents. 6. The first water-soluble ACAT inhibitor with lipid-regulating activity
Sliskovic, D. R., B. R. Krause, et al. (1994), J Med Chem 37(5): 560-2.

Inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT). 7. Development of a series of substituted N-phenyl-N'-(1-phenylcyclopentyl)methylureas with enhanced hypocholesterolemic activity
Trivedi, B. K., T. S. Purchase, et al. (1994), J Med Chem 37(11): 1652-9.
Abstract: We recently described our initial structure-activity relationship (SAR) studies on a series of N-phenyl-N'-aralkyl- and N-phenyl-N'-(1-phenylcycloalkyl)ureas as inhibitors of acyl-CoA: cholesterol acyltransferase (ACAT). From this series of analogs, compound 1 (PD 129337) was identified as a potent inhibitor of ACAT with an IC50 value of 17 nM. It was also shown to dose-dependently lower plasma cholesterol in cholesterol-fed rats. However, further investigation led to the suggestion that this compound was poorly absorbed, due to a lack of efficacy when administered by gavage in an aqueous vehicle. To overcome this deficiency, we continued our SAR study on this novel series of ACAT inhibitors using an acute in vivo screen in which the compounds are administered to rats in an aqueous, CMC/Tween suspension vehicle. Modification of the N'-phenyl moiety by incorporating functional groups which were amenable to forming salts and/or polar groups to reduce lipophilicity led to the identification of several inhibitors which displayed excellent efficacy employing this protocol. Overall, substitution on the phenyl ring in the ortho, meta, or para positions led to inhibitors with only a slight decrease in potency in vitro compared to the parent unsubstituted compound. Bulkier groups in the para position tended to lower the ACAT inhibitory activity in vitro. Polar groups, such as carboxyl (33,34), lowered in vitro activity significantly, suggesting that polar-ionic interactions are disfavored for the enzyme activity. From this series, compound 28 was evaluated further in secondary in vivo screens. In a chronic cholesterol-fed rat model of hypercholesterolemia, compound 28 dose-dependently reduced nonHDL cholesterol and significantly elevated HDL cholesterol. It showed significantly greater aqueous solubility than the parent compound 1. However, it was shown to cause adrenal toxicity in guinea pigs. This led us to design a series of homologs (44-51) with increased basicity and lower lipophilicity. Some of these compounds were more potent ACAT inhibitors in vitro and demonstrated excellent hypocholesterolemic activity in vivo. Interestingly, compound 45, unlike 28, did not produce adrenal toxicity in guinea pigs and demonstrated excellent lipid-modulating activity in the chronic model of preestablished dyslipidemia in rats.

Inhibitors of acyl-CoA:cholesterol acyltransferase. 1. Identification and structure-activity relationships of a novel series of fatty acid anilide hypocholesterolemic agents
Roth, B. D., C. J. Blankley, et al. (1992), J Med Chem 35(9): 1609-17.
Abstract: A series of fatty acid anilides was prepared, and compounds were tested for their ability to inhibit the enzyme acyl-CoA:cholesterol acyltransferase (ACAT) in vitro and to lower plasma total cholesterol and elevate high-density lipoprotein cholesterol in cholesterol-fed rats in vivo. The compounds reported were found to fall into two subclasses with different anilide SAR. For nonbranched acyl analogues, inhibitory potency was found to be optimal with bulky 2,6-dialkyl substitution. For alpha-substituted acyl analogues, there was little dependence of in vitro potency on anilide substitution and 2,4,6-trimethoxy was uniquely preferred. Most of the potent inhibitors (IC50 less than 50 nM) were found to produce significant reductions in plasma total cholesterol in cholesterol-fed rats. Additionally, in vivo activity could be improved significantly by the introduction of alpha,alpha-disubstitution into the fatty acid portion of the molecule. A narrow group of alpha,alpha-disubstituted trimethoxyanilides, exemplified by 2,2-dimethyl-N-(2,4,6-trimethoxyphenyl)dodecanamide (39), was found to not only lower plasma total cholesterol (-60%) in cholesterol-fed rats but also elevate levels of high-density lipoprotein cholesterol (+94%) in this model at the screening dose of 0.05% in the diet (ca. 50 mg/kg).

Inhibitors of acyl-CoA:cholesterol acyltransferase. 5. Identification and structure-activity relationships of novel beta-ketoamides as hypocholesterolemic agents
Augelli-Szafran, C. E., C. J. Blankley, et al. (1993), J Med Chem 36(20): 2943-9.
Abstract: A study of structure-activity relationships of substituted beta-ketoamide ACAT inhibitors I and II was performed. The results of this study suggest that whereas the beta-keto group was tolerated with no loss in activity, beta-hydroxy and oxime moieties led to significantly reduced activity in vitro and in vivo. The most potent inhibitor from the acyclic series (I) (11, IC50 = 0.006 microM) contained a C-13 alkyl chain. This compound reduced plasma total cholesterol by 38% and 66% at 3 and 30 mg/kg, respectively, in cholesterol-fed rats. Dimethylation alpha to the anilide core (5) and subsequent N-methylation of the amide NH (6) decreased in vitro potency significantly. It was also found that high potency was retained with inhibitors which incorporated the carbonyl into a lactam ring (II).

Inhibitors of acyl-CoA:cholesterol acyltransferase: novel trisubstituted ureas as hypocholesterolemic agents
Purchase, T. S., A. D. Essenburg, et al. (1997), Bioorg Med Chem 5(4): 739-47.
Abstract: Our continued interest in developing novel, potent acyl-CoA:cholesterol acyltransferase (ACAT) inhibitors, and our discovery of several active series of disubstituted urea ACAT inhibitors, have led us to investigate a series of trisubstituted ureas that are structural hybrids of our disubstituted series and of a trisubstituted urea ACAT inhibitor series disclosed by scientists at Lederle. This investigation has led to the discovery of novel trisubstituted ureas, several of which inhibit ACAT in the nanomolar range and effectively lower total plasma cholesterol when administered as a diet admixture in an acute model of hypercholesterolemia in rats. One analogue (35) also lowered total cholesterol as efficaciously as CL 277,082 in our chronic hypercholesterolemic rat model. The most notable finding of this study is that the SAR of the trisubstituted ureas diverges from that seen in our previously disclosed disubstituted urea series. This series showed optimal activity with 2,4-difluoro and 2,4,6-trifluoro substitution on the urea N-phenyl, whereas the disubstituted series showed optimal activity with bulky 2,6-disubstitution on the phenyl ring.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase (ACAT). Part 1: identification and structure-activity relationships of a novel series of substituted N-alkyl-N-biphenylylmethyl-N'-arylureas
Tanaka, A., T. Terasawa, et al. (1998), Bioorg Med Chem 6(1): 15-30.
Abstract: A series of N-alkyl-N-biphenylylmethyl-N'-arylurea and related derivatives represented by 1 have been prepared and evaluated for their ability to inhibit acyl-CoA:cholesterol O-acyltransferase in vitro and to lower plasma cholesterol levels in cholesterol-fed rats in vivo. Linking of two phenyl groups via oxygen and introduction of fluorine at appropriate positions on the biphenyl moiety improved in vitro and in vivo activity. From this series of analogs, compound 40 (FR179254), which had potent in vitro potency (rabbit intestinal microsomes IC50 = 25 nM), showed excellent plasma cholesterol-lowering activity when administered via the diet (ED50 = 0.045 mg/kg). However, the hypocholesterolemic effect of this compound was moderate when dosed by oral gavage in PEG400 as a vehicle (ED50 = 5.3 mg/kg). Modification of the N'-aryl moiety led to the identification of compound 50 (FR182980) which was efficacious in both dosing models (ED50 = 0.034 mg/kg and 0.11 mg/kg, respectively).

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. 11. Structure-activity relationships of several series of compounds derived from N-(chlorocarbonyl) isocyanate
Picard, J. A., R. F. Bousley, et al. (1994), J Med Chem 37(15): 2394-400.
Abstract: Five series of compounds (4-9) derived from N-(chlorocarbonyl) isocyanate have been synthesized and evaluated for their ability to inhibit the enzyme acyl-CoA:cholesterol O-acyltransferase and lower plasma cholesterol levels in cholesterol-fed rats. Structure-activity relationships indicate that the imino dicarboxylates (6 and 7) and the oxycarbonyl thiocarbamates (8) are the most potent and efficacious series. In these series, the combination of a 2,6-diisopropylphenyl group and an aliphatic alkyl group with a chain length between 6 and 14 carbon atoms gives good activity in vitro and in vivo. In addition, a hydrogen donor is required to maintain good in vitro activity, and the acidic proton on the central nitrogen in these series appears to be important for in vivo activity.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. 2. Identification and structure-activity relationships of a novel series of N-alkyl-N-(heteroaryl-substituted benzyl)-N'-arylureas
Tanaka, A., T. Terasawa, et al. (1998), J Med Chem 41(13): 2390-410.
Abstract: A series of N-alkyl-N-(heteroaryl-substituted benzyl)-N'-arylurea and related derivatives represented by 2 and 3 have been prepared and evaluated for their ability to inhibit acyl-CoA:cholesterol O-acyltransferase in vitro and to lower plasma cholesterol levels in cholesterol-fed rats in vivo. Among these novel compounds, the type 3 series was superior. A pyrazol-3-yl group on the N-benzyl group of this trisubstituted urea (i.e. 3, Ar1 = pyrazol-3-yl) was identified as a heteroaromatic ring providing a good profile of biological activity. As a result of optimization of the combination with the N-alkyl group (R) and N-aryl group (Ar3), compound 3aq (FR186054) was identified as a new, orally efficacious ACAT inhibitor, which exhibited potent in vitro ACAT inhibitory activity (rabbit intestinal microsomes IC50 = 99 nM) and excellent hypocholesterolemic effects in cholesterol-fed rats, irrespective of administration mode (ED50 = 0.046 mg/kg dosed via the diet, ED50 = 0. 44 mg/kg administered by gavage in PEG400 vehicle). Moreover, a toxicological study revealed compound 3aq to be nontoxic to the adrenal glands of dogs when tested at a single dose of 10 mg/kg po.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. 3. Discovery of a novel series of N-alkyl-N-(fluorophenoxy)benzyl-N'-arylureas with weak toxicological effects on adrenal glands
Tanaka, A., T. Terasawa, et al. (1998), J Med Chem 41(22): 4408-20.
Abstract: A series of N-alkyl-N-(fluorophenoxy)benzyl-N'-arylureas were prepared and evaluated for their ability to inhibit intestinal acyl-CoA:cholesterol O-acyltransferase and to inhibit accumulation of cholesteryl esters in macrophages in vitro. In vivo hypocholesterolemic activity was assessed in cholesterol-fed rats by oral administration as a dietary admixture and/or by gavage in a PEG400 vehicle. Modification of the alkyl substituent on the N'-aryl moiety and on the urea nitrogen significantly influenced macrophage assay in vitro. Toxicological study revealed a distinct relationship between macrophage assay and the toxicity observed in adrenal glands of rabbits treated with representatives of this series of compounds. Investigations utilizing the macrophage assay as an indicator for adrenal toxicity led to the identification of compounds 1g (FR190809) and 1k (FR186485, or FR195249 as its hydrochloride salt) as potent, nonadrenotoxic, orally efficacious ACAT inhibitors irrespective of the administration method.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. synthesis and pharmacological activity of (+/-)-2-dodecyl-alpha-phenyl-N-(2,4,6-trimethoxyphenyl)-2H-tetrazole-5- acetamide and structurally related tetrazole amide derivatives
O'Brien, P. M., D. R. Sliskovic, et al. (1996), J Med Chem 39(12): 2354-66.
Abstract: A series of tetrazole amide derivatives of (+/-)-2-dodecyl-alpha-phenyl-N-(2,4,6-trimethoxyphenyl)-2H-tetrazole-5- acetamide (1) was prepared and evaluated for their ability to inhibit acyl-CoA: cholesterol O-acyltransferase (ACAT) in vitro and to lower plasma total cholesterol in vivo. For this series of compounds, our objective was to systematically replace substituents appended to the amide and tetrazole moieties of 1 with structurally diverse functionalities and assess the effect that these changes have on biological activity. The ensuing structure-activity relationship (SAR) studies identified aryl (7b) and heteroaryl (7f,g) replacements for 2,4,6-trimethoxyphenyl that potently inhibit liver microsomal and macrophage ACAT in vitro and exhibit good cholesterol lowering activity (56-66% decreases in plasma total cholesterol at 30 mg/kg), relative to 1, when compared in the acute rat model of hypercholesterolemia. Replacement of the alpha-phenyl moiety with electron-withdrawing substituents (13e-h), however, significantly reduced liver microsomal ACAT inhibitory activity (IC50 > 1 microM). This is in contrast to electron-donating substituents (13ij,m-q), which produce IC50 values ranging from 5 to 75 nM in the hepatic microsomal assay. For selected tetrazole amides (1, 7b, 13n,o), reversing the order of substituents appended to the 2- and 5-positions in the tetrazole ring (36a-d), in general, improved macrophage ACAT inhibitory activity and provided excellent cholesterol-lowering activity (ranging from 65% to 77% decreases in plasma total cholesterol at 30 mg/kg) in the acute rat screen. The most potent isomeric pair in this set of unsubstituted methylene derivatives (13n and 36a) caused adrenocortical cell degeneration in guinea pigs treated with these inhibitors. In contrast, adrenal glands taken from guinea pigs treated with the corresponding alpha-phenyl-substituted analogs (7b and 36c) were essentially unchanged compared to untreated controls. Subsequent evaluation of 7b and 36c in a rabbit bioassay showed that both compounds and/or their metabolities were present in plasma after oral dosing. Unlike 7b and 36c, compound 1 and related 2,4,6-trimethoxyanilides (13j, 30c,d) showed poor oral activity in the rabbit bioassay. Nevertheless, in cholesterol-fed rabbits, both systemically available (7b, 36c) and poorly absorbed inhibitors (1, 36d) were more effective in lowering plasma total cholesterol than the fatty acid amide CI-976.

Inhibitors of angiotensin converting enzyme decrease early atherosclerosis in hyperlipidemic hamsters. Fosinopril reduces plasma cholesterol and captopril inhibits macrophage-foam cell accumulation independently of blood pressure and plasma lipids
Kowala, M. C., R. I. Grove, et al. (1994), Atherosclerosis 108(1): 61-72.
Abstract: The effect of two angiotensin converting enzyme (ACE) inhibitors on the development of atherosclerosis was determined in hyperlipidemic hamsters. Preliminary studies indicated that only fosinopril (50 mg/kg) temporarily decreased mean arterial pressure, while after chronic dosing fosinopril and captopril (50 mg/kg) were ineffective. The same dose of fosinopril and captopril inhibited the angiotensin I pressor response, indicating these agents suppressed ACE activity in vivo. In the 3 week atherosclerosis experiment, all hamsters were fed chow supplemented with 0.05% cholesterol and 10% coconut oil. Control hamsters were compared with those receiving either 50 mg/kg per day of fosinopril or 50 mg/kg per day of captopril. After 3 weeks, fosinopril reduced plasma total cholesterol, low density lipoprotein (LDL) plus very low density lipoprotein cholesterol and total triglycerides by 17%, 27% and 45%, respectively. Captopril only reduced high density lipoprotein cholesterol by 20%. Neither fosinopril or captopril altered blood pressure at 3 weeks. Atherosclerosis was quantified from en face preparations of the lesion-prone aortic arch that were stained with oil red O (for cholesteryl ester and triglycerides). In control hamsters, oil red O labeled numerous subendothelial macrophage-foam cells located along the inner curvature of the aortic arch. Compared with controls, fosinopril reduced the number of intimal macrophage-foam cells/mm2, foam cell size and the fatty streak area by 85%, 38% and 90%, respectively. Captopril decreased these parameters by 44%, 16% and 53%. Thus captopril decreased early atherosclerosis without affecting plasma LDL cholesterol or blood pressure, which suggested that inhibiting ACE (or kininase II) directly impeded the accumulation and formation of macrophage-foam cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitors of arterial relaxation among components of human oxidized low-density lipoproteins. Cholesterol derivatives oxidized in position 7 are potent inhibitors of endothelium-dependent relaxation
Deckert, V., L. Persegol, et al. (1997), Circulation 95(3): 723-31.
Abstract: BACKGROUND: Oxidized low-density lipoproteins (LDLs) are known to impair arterial relaxation. The aim of the present study was to identify the components of oxidized LDL that may account for inhibition of endothelium-dependent relaxation. METHODS AND RESULTS: LDLs from 12 healthy subjects were either maintained at 4 degrees C (native LDL) or incubated at 37 degrees C in the presence of copper sulfate (oxidized LDL). Unlike pretreatment with native LDL, pretreatment with oxidized LDL reduced significantly the acetylcholine-mediated relaxation of rabbit aortic segments compared with control segments incubated in Krebs' buffer (maximal relaxation Emax, 72.0 +/- 6.7% versus 94.1 +/- 0.8%, respectively, P <.01; negative logarithm of the concentration required to produce a half-maximal relaxing effect pD2, 6.6 +/- 0.1 versus 7.2 +/- 0.1, respectively, P <.001). The absolute difference between Emax values obtained with oxidized and native LDL (delta Emax) correlated significantly with the formation of 7 ketocholesterol, 7 alpha-hydroxycholesterol, and 7 beta-hydroxy-cholesterol. In contrast, delta Emax did not correlate with the amount of lipoperoxides or lysophosphatidylcholine formed, and the difference of pD2 values measured with oxidized and native LDL (delta pD2) did not correlate significantly with any of the oxidation-derived LDL compounds. When added individually, 7-ketocholesterol and 7 beta-hydroxycholesterol reduced Emax values but not pD2 values in a time- and concentration-dependent manner. CONCLUSIONS: Cholesterol derivatives in oxidized LDL can reduce maximal arterial relaxation through a specific effect on vascular endothelial cells.

Inhibitors of cholesterol biosynthesis increase hepatic low-density lipoprotein receptor protein degradation
Ness, G. C., Z. Zhao, et al. (1996), Arch Biochem Biophys 325(2): 242-8.
Abstract: Inhibitors of cholesterol biosynthesis are believed to lower serum cholesterol levels by enhancing the removal of serum low-density lipoprotein (LDL) by increasing hepatic LDL receptor function. Thus, the effects of several different inhibitors of cholesterol biosynthesis were examined for their effects on the expression of the hepatic LDL receptor in rats. We found that administration of inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase such as lovastatin, pravastatin, fluvastatin, and rivastatin resulted in increased hepatic LDL receptor mRNA levels. Surprisingly, these agents failed to increase levels of immunoreactive LDL receptor protein in rat liver even when the dose and length of treatment were increased. Treatment of rats with zaragozic acid A, an inhibitor of squalene synthase, caused even greater increases in hepatic LDL receptor mRNA levels, but did not increase levels of immunoreactive protein. Further investigation revealed that the rate of degradation of the hepatic LDL receptor was increased in rats given inhibitors of cholesterol biosynthesis. The greatest increase in the rate of degradation was seen in animals treated with zaragozic acid A which caused the largest increase in hepatic LDL receptor mRNA levels. In contrast, hepatic LDL receptor protein was stabilized in cholesterol-fed rats. It appears that increased potential for LDL receptor protein synthesis, reflected in increased mRNA levels, is offset by a corresponding increase in the rate of receptor protein degradation resulting in constant steady-state levels of hepatic LDL receptor protein. These findings are suggestive of increased cycling of the hepatic LDL receptor. This postulated mechanism can provide for enhanced hepatic uptake of lipoproteins without increasing steady-state levels of LDL receptor protein.

Inhibitors of cholesterol biosynthesis. 1. 3,5-Dihydroxy-7-(N-imidazolyl)-6-heptenoates and -heptanoates, a novel series of HMG-CoA reductase inhibitors
Chan, C., E. J. Bailey, et al. (1993), J Med Chem 36(23): 3646-57.
Abstract: 3,5-Dihydroxy-7-(N-imidazolyl)heptanoates 4 and the corresponding heptenoates 5 were synthesized as novel classes of potent HMG-CoA reductase (HMGR) inhibitors in which members of the latter series possess enzyme inhibitory activity greater than that of lovastatin 1 and pravastatin 2. Structure-activity studies show that the 7-(N-imidazolyl)heptenoates 5 are more active than the corresponding heptanoates 4. For both imidazolyl series, the 4-fluorophenyl group is preferred at C-5, and a broad range of aryl substituents which promote widely different lipophilicities is tolerated at C-4. While the CF3 group is preferred at C-2 in the heptanoate series, the 2-(1-methylethyl) substituent is optimal in the heptenoate series. The 2-(1-methylethyl) and 5-(4-fluorophenyl) groups can be interchanged in the latter series as exemplified by 5ab. Enzyme inhibitory activity resides principally in the 3R,5S series. These potent HMGR inhibitory activities by members of the heptenoate series translated well into whole cell activities in HepG2 cells. X-ray crystallographic studies on the active enantiomer 28 reveal noncoplanarity of the heptenoate C-C double bond with the imidazole ring; this finding provides an explanation for the high acid stability of the heptenoate series.

Cholesterol Articles and Abstracts

Cholesterol Journal Articles