Biomedical subjects

R S Newton

Publications and source records attributed to R S Newton.

At least 19 recordsLinked to original sources

PubMed1996

Opposite effects of bezafibrate and gemfibrozil in both normal and hypertriglyceridemic rats.

Chow and sucrose-fed rats were used as animal models to study the dose-responses of bezafibrate and gemfibrozil in normolipidemic and hypertriglyceridemic states, respectively. Although both drugs lowered plasma triglycerides (TG) to about the same extent in chow-fed rats, gemfibrozil lowered liver TG as well as plasma total and LDL-cholesterol (LDL-C), but elevated HDL-cholesterol (HDL-C) and plasma apo E concentrations. Bezafibrate produced opposite effects, namely, decreased HDL-C, apo E and liver TG, and tended to increase LDL-C. TG lowering for both drugs in chow-fed rats was not due to changes in TG secretion (production) in normal rats but was associated with enhanced LPL activity. In hypertriglyceridemic rats both drugs modestly reduced TG secretion rates about 40% at a dose producing maximal TG lowering, but again, gemfibrozil elevated and bezafibrate lowered HDL-C and apo E. Unlike gemfibrozil, bezafibrate induced the appearance of LDL-C in hypertriglyceridemic rats which was not detected in control animals, and also tended to increase rather than decrease plasma apo B levels. Finally, changes in liver TG concentration (mg/g) in hypertriglyceridemic rats were opposite for these drugs, resulting in significant drug-related differences in liver TG content (mg/organ). From these data we postulate that, although similar with regard to TG lowering activity and mechanisms thereof, gemfibrozil and bezafibrate produce fundamentally different effects on LDL, HDL and apolipoprotein metabolism (apo B and apo E) in rats which may relate to potential differential effects on reverse cholesterol transport and atherogenesis.

Animals↗

PubMed1996

Lack of correlation between ACAT mRNA expression and cholesterol esterification in primary liver cells.

A partial rabbit cDNA clone (14b) for ACAT has been characterized and used to demonstrate that hepatic and aortic ACAT mRNA14b abundance increased 2-3-fold in rabbits receiving a high fat/high cholesterol-diet compared to chow fed animals (Pape et al. (1995) J. Lipid Res. 36, 823-838). Because of those data we hypothesized that increased hepatic cholesteryl ester mass and synthesis rates in rabbit liver cells are associated with an increase in ACAT mRNA14b levels. To test this hypothesis we altered cellular cholesteryl ester mass and synthesis rates in primary parenchymal and nonparenchymal cells using various extracellular agents and measured the accumulated mass of ACAT mRNA14b. Parenchymal cells incubated with rabbit beta VLDL or mevalonolactone displayed a 6-10-fold increase in cellular cholesteryl ester mass over a three day treatment with no significant changes in cellular free cholesterol, triacylglycerols, or ACAT mRNA14b levels; HMG CoA reductase and LDL receptor mRNA mass decreased initially as a result of cholesteryl ester loading. Treatment of parenchymal cells with CI-976, an ACAT inhibitor, showed a marked reduction in cholesteryl ester synthetic rate compared to beta VLDL controls but displayed no change in ACAT mRNA14b levels. A mixed population of rabbit hepatic nonparenchymal cells was incubated with beta VLDL for 24 h in culture which resulted in a 6-fold increase in cellular cholesteryl ester mass; there was no change in ACAT mRNA14b levels. In an in vivo study, rabbits consuming a high fat/high cholesterol-diet for three weeks showed a 10-fold increase in hepatic cholesteryl ester with no significant changes in ACAT mRNA14b levels. Together these data indicate that rabbit liver cellular cholesteryl ester mass increases of up to 10-fold are not correlated with ACAT mRNA14b changes. Thus, hepatic ACAT mRNA14b expression and cellular cholesterol esterification do not appear to be coordinately regulated at this level of cholesteryl ester loading.

Animals↗

PubMed1996

Selective inhibition of tumor necrosis factor-induced vascular cell adhesion molecule-1 gene expression by a novel flavonoid. Lack of effect on transcription factor NF-kappa B.

In the present studies, we examined the effect of flavonoids on the endothelial cell expression of adhesion molecules, an early step in inflammation and atherogenesis. Addition of tumor necrosis factor-alpha (TNF) to human aortic endothelial cells (HAECs) led to the induction of vascular cell adhesion molecule-1 (VCAM-1) expression and enhancement in expression of intercellular adhesion molecule-1 (ICAM-1). A flavonoid, 2-(3-amino-phenyl)-8-methoxy-chromene-4-one (PD 098063), markedly inhibited TNF-induced VCAM-1 cell-surface expression in a concentration-dependent fashion with half-maximal inhibition at 19 mumol/L but had no effect on ICAM-1 expression. Another structurally distinct flavonoid, 2-phenyl-chromene-4-one, similarly selectively decreased VCAM-1 expression. The inhibition in cell-surface expression of VCAM-1 by PD 098063 correlated with decreases in steady-state mRNA levels, but there was no effect on ICAM-1 mRNA levels. The decrease in VCAM-1 mRNA levels was not due to changes in mRNA stability but rather resulted from a reduction in the rate of transcription of the gene. However, electrophoretic mobility shift assays using nuclear extracts from TNF-induced HAECs treated with PD 098063 failed to show a decrease in the activation of NF-kappa B, indicating that inhibition of activation of this transcription factor may not be its mode of action. Similarly, PD 098063 did not affect chloramphenicol acetyltransferase reporter gene activity in TNF-inducible minimal VCAM-1 promoter constructs containing two NF-kappa B sites, suggesting that the compound does not affect the transactivation driven by these sites. We conclude that this compound selectively blocks agonist-induced VCAM-1 protein and gene expression in HAECs by NF-kappa B-independent mechanism(s).

Cells, Cultured↗

PubMed1996

Hypocholesterolemic actions of atorvastatin are associated with alterations on hepatic cholesterol metabolism and lipoprotein composition in the guinea pig.

Guinea pigs were fed 15% (w/W) fat, high in lauric and myristic acids, a diet known to produce hypercholesterolemia in these animals. The diet was given alone or in combination with four doses of atorvastatin equivalent to 1, 3, 10, and 20 mg/kg per day. Atorvastatin reduced plasma LDL cholesterol concentrations by 46, 50, 53, and 70%, respectively (P < 0.001). Plasma apoB concentrations were reduced by atorvastatin (P < 0.001) and compositional changes occurred in VLDL and LDL with reductions of the relative proportion of cholesteryl ester and increases in triacylglycerol. A reduction in hepatic cholesteryl ester (66%) was observed only with the highest atorvastatin dose (20 mg/kg per day) while microsomal cholesterol was reduced by 30% with 3-20 mg/kg per day. Hepatic ACAT activity was down-regulated and apoB/E receptor number was increased by atorvastatin. In contrast, HMG-CoA reductase activity and cholesterol 7 alpha-hydroxylase were not affected by the drug. VLDL apoB secretion rates were decreased by atorvastatin treatment 59 and 76% with 3 and 20 mg/kg per day, respectively. Nascent VLDL particles were larger after drug treatment, showing an increased number in triacylglycerol molecules. These results support the hypothesis that the plasma LDL lowering induced by atorvastatin is due to a decreased secretion of apoB in combination with an increase of hepatic apoB/E receptors.

Animals↗

PubMed1995

Regulation and immunolocalization of acyl-coenzyme A: cholesterol acyltransferase in mammalian cells as studied with specific antibodies.

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the formation of intracellular cholesterol esters in various tissues. We recently reported the cloning and expression of human macrophage ACAT cDNA. In the current study, we report the production of specific polyclonal antibodies against ACAT by immunizing rabbits with the recombinant fusion protein composed of glutathione S-transferase and the first 131 amino acids of ACAT protein. Immunoblot analysis showed that the antibodies cross-reacted with a 50-kDa protein band from a variety of human cell lines. These antibodies immunodepleted more than 90% of detergent-solubilized ACAT activities from six different human cell types, demonstrating that the 50-kDa protein is the major ACAT catalytic component in these cells. In multiple human tissues examined, the antibodies recognized protein bands with various molecular weights. These antibodies also cross-reacted with the ACAT protein in Chinese hamster ovary cells. Immunoblot analysis showed that the ACAT protein contents in human fibroblast cells, HepG2 cells, or Chinese hamster ovary cells were not affected by sterol in the medium, demonstrating that the main mechanism for sterol-dependent regulation of ACAT activity in these cells is not change in ACAT protein content. As revealed by indirect immunofluorescent microscopy, the ACAT protein in tissue culture cells was located in the endoplasmic reticulum. This finding, along with earlier studies, suggests that cholesterol concentration in the endoplasmic reticulum may be the major determinant for regulating ACAT activity in the intact cells.

Animals↗

PubMed1995

Identification of a novel 85-kDa lipoprotein lipase binding protein on human aortic endothelial cell surface.

Lipoprotein lipase (LPL), bound to the luminal surface of vascular endothelium catalyzes lipoprotein triglyceride hydrolysis. Studies were performed to identify human aortic endothelial (HAEC) cell-surface proteins having high affinity for LPL. LPL-sepharose affinity chromatography of [35S]O4 labeled HAEC proteins identified a 220-kDa proteoglycan. Ligand blotting of HAEC plasma membrane proteins with LPL revealed two specific binding proteins of MW 116 kDa and 85 kDa, respectively, which were not released from the cell-surface by heparin treatment. Since the 220-kDa and 116-kDa proteins have been reported previously in bovine endothelial cells, we focused on the 85-kDa protein. The 85-kDa protein was not labelled by incubation of the cells with [35S]O4, suggesting that it is not a sulfated proteoglycan. Treatment of HAEC with tunicamycin markedly decreased detection of the 85-kDa protein, suggesting that it is likely a glycoprotein synthesized by HAEC. We conclude that HAEC cell surface has three specific LPL binding proteins, a 220-kDa proteoglycan, a 116-kDa protein and a novel 85-kDa protein.

Aorta↗

PubMed1995

Inhibition of tumor necrosis factor induced human aortic endothelial cell adhesion molecule gene expression by an alkoxybenzo[b]thiophene-2-carboxamide.

The effects of a novel anti-inflammatory agent, 5-methoxy-3-(1-methyl-ethoxy)benzo[b]thiophene-2-carboxamide-1-oxide (PD 144795) on adhesion molecule expression in tumor necrosis factor (TNF) stimulated human aortic endothelial cells (HAEC) were examined. PD 144795 treatment markedly inhibited the TNF-induced cell expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) protein and mRNA. Gel shift assays using nuclear extracts from HAEC treated with PD 144795 failed to show a decrease in the activation of NFkB by this compound, whereas pyrrolidine dithiocarbamate (PDTC), an antioxidant, markedly inhibited the activation of this transcription factor. Thus, PD 144795 inhibits agonist-stimulated VCAM-1 and ICAM-1 expression likely via an NFkB independent mechanism, distinct from that of PDTC. Such agents may provide a novel approach for control of adhesion molecule gene expression in inflammation.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1995

Acyl-coenzyme A:cholesterol-acyltransferase (ACAT) inhibitors modulate monocyte adhesion to aortic endothelial cells.

Increased monocyte adhesion to aortic endothelium is observed in the pathogenesis of atherosclerosis. The role of endothelial acyl-coenzyme A:cholesterol-acyltransferase (ACAT) in the regulation of monocyte adhesion is not known. To examine the potential role of this enzyme in monocyte adhesion, a specific ACAT inhibitor, CI-976, was utilized. Although the basal adhesion of U937 monocytic cells to porcine aortic endothelial cells was low, treatment of the endothelial cells with lipopolysaccharide (LPS) markedly increased monocyte adhesion. Monocyte adhesion to LPS-treated endothelial cells was markedly inhibited by CI-976 treatment of the endothelial cells. Similarly, another ACAT inhibitor, PD 132301-2, whose structure is distinct from CI-976, also decreased monocyte adhesion. CI-976 treatment of endothelial cells also decreased endothelial cell ACAT activity. Since leukotriene B4 (LTB4) is known to promote leukocyte-endothelial cell adhesion, endothelial cell production of this leukotriene was examined after incubation with CI-976. CI-976 treatment markedly decreased LTB4 synthesis. Exogenous LTB4 addition to CI-976 treated cells reversed the effects of this compound on monocyte adhesion. These data demonstrate that ACAT inhibitors decrease monocyte adhesion to endothelial cells. Similar mechanisms may contribute to antiatherosclerotic effects of ACAT inhibitors in vivo.

Anilides↗

PubMed1995

Comparative effects of HMG-CoA reductase inhibitors on apo B production in the casein-fed rabbit: atorvastatin versus lovastatin.

Rabbits fed a diet enriched in casein develop an endogenous hypercholesterolemia (EH) due both to an increased low density lipoprotein (LDL) synthetic rate and decreased LDL receptor activity. Pre-established EH in this model was used to assess the ability and mechanism by which atorvastatin lowers total plasma cholesterol (TPC) compared to the reference agent lovastatin. Rabbits were fed a casein diet for 6 weeks, obtaining average TPC levels above 200 mg/dl. To ensure equivalent mean cholesterol concentrations, animals were randomized into treatment groups based on the 6-week TPC levels, and fed the casein diet alone or in combination with either atorvastatin or lovastatin for an additional 6 weeks. Under these conditions, new steady-state cholesterol values were established. Lipoprotein concentrations and distributions were determined at this point. Compared to pretreatment values, TPC were similar in untreated animals. Atorvastatin, however, significantly reduced TPC by 38%, 45%, and 54% at the 1, 3, and 10 mg/kg doses, respectively. Statistically significant lowering of TPC (35%) by lovastatin was only achieved at the 10 mg/kg dose. To determine the mechanism by which atorvastatin lowered TPC in the EH rabbits, kinetic studies using human [125I]-LDL were performed in a subset of animals maintained on the casein diet alone (n = 5), or those treated with 3 mg/kg of atorvastatin (n = 5) or lovastatin (n = 7). In this set of studies, atorvastatin significantly lowered TPC compared to control and lovastatin-treated rabbits by 57% and 46%, respectively. Lovastatin treatment resulted in a 20% decrease in TPC as compared to untreated controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1995

Lipid-lowering activity of atorvastatin and lovastatin in rodent species: triglyceride-lowering in rats correlates with efficacy in LDL animal models.

Since inhibitors of HMG-CoA reductase lower plasma triglycerides rather than cholesterol in rats, we compared the triglyceride-lowering activity of lovastatin in rats to that of atorvastatin, a more potent synthetic inhibitor, prior to evaluating these drugs in established animal models in which low density lipoproteins (LDL) rather than high density lipoproteins (HDL) are the major transporters of plasma cholesterol. Atorvastatin was more efficacious than lovastatin in normal, chow-fed rats, and more potent in rats with endogenous hypertriglyceridemia (sucrose-fed). In hypertriglyceridemic rats plasma apoB concentrations decreased only with atorvastatin (30 mg/kg), and VLDL-triglyceride secretion (Triton method) was also decreased more by atorvastatin. The inactive enantiomer of atorvastatin did not lower plasma triglycerides. Thus, triglyceride-lowering was dependent upon inhibition of HMG-CoA reductase. Liver unesterified cholesterol and cholesteryl esters (mg/g) were increased by both drugs in normal rats but remained unchanged in hypertriglyceridemic rats. In normal, chow-fed guinea pigs atorvastatin was a more potent cholesterol-lowering drug, and unlike lovastatin, lowered plasma triglycerides and VLDL-cholesterol. In casein-fed rabbits with endogenous hypercholesterolemia and in chow-fed rabbits atorvastatin lowered LDL-cholesterol more potently than lovastatin, but in chow-fed rabbits neither drug had an effect on the in vivo rate of VLDL-lipid secretion, suggesting that efficacy was due to inhibition of direct LDL production and/or enhanced LDL clearance. We conclude that normal rats can be used as a preclinical tool to assess the efficacy of HMG-CoA reductase inhibitors since triglyceride-lowering correlates with cholesterol-lowering in LDL animal models. In this regard atorvastatin is a more potent hypolipidemic agent than lovastatin in animals. A common but not sole mechanism for these drugs may be direct inhibition of the hepatic production of the major apoB-containing lipoprotein in a given species, e.g. VLDL in rats and LDL in guinea pigs and rabbits.

Animals↗

PubMed1995

Tissue specific changes in acyl-CoA: cholesterol acyltransferase (ACAT) mRNA levels in rabbits.

A human cDNA clone (K1) was recently isolated that encodes functional acyl-CoA:cholesterol acyltransferase (ACAT) protein (Chang et al. J. Biol. Chem. 1993. 268: 20747-20755). We used the K1 clone to screen a rabbit liver cDNA library and isolated a 919 base pair partial rabbit cDNA (ACAT14b) that was greater than 90% homologous with the human nucleotide sequence. Northern blotting using the rabbit ACAT cDNA14b revealed the existence of at least six related mRNA species (ranging from 6.2 to 1.7 kb) in various rabbit tissues. Using an RNAse protection assay, ACAT mRNA14b was detected in twelve separate rabbit organs. Adrenal gland contained the highest concentrations of ACAT mRNA14b (per microgram of total RNA) being 20-, 30-, and 50-fold higher than small intestine, aorta, and liver, respectively. Additional studies with isolated liver cell populations revealed that rabbit hepatic nonparenchymal cells contained 30-fold more ACAT mRNA14b (per microgram of total RNA) than parenchymal cells. To determine whether ACAT mRNA14b levels are regulated in vivo, rabbits were fed for 4 weeks a high fat/high cholesterol diet (HFHC; 0.5% cholesterol, 3% coconut oil, 3% peanut oil) at which point they were either kept for an additional 4 weeks on the HFHC-diet or switched to the HFHC-diet plus CI-976 (50 mg/kg), a potent and specific ACAT inhibitor; another group of rabbits was fed a chow diet for the entire 8 weeks. The HFHC-diet caused a 2- and 3-fold increase in hepatic and aortic ACAT mRNA14b levels, respectively, in comparison to chow-fed animals; there was no change in adrenal or small intestine levels. CI-976 treatment lowered ACAT mRNA14b levels by 60% and 40% in liver and aorta, respectively, in comparison to the HFHC controls; again there was no change in adrenal or small intestine levels. These data indicate that ACAT mRNA14b levels increase in a tissue specific manner in response to dietary fat and cholesterol.

Animals↗

PubMed1995

Gemfibrozil significantly lowers cynomolgus monkey plasma lipoprotein[a]-protein and liver apolipoprotein[a] mRNA levels.

Eight male cynomolgus monkeys (Macaca fascicularis) on a normal chow diet were orally administered gemfibrozil daily using a weekly rising dose protocol for 3 weeks (50, 125, and 200 mg/kg per day). At these drug doses, Lp[a] levels were reduced: 83.7% +/- 3.2 (SEM), (P < 0.024); 63.7% +/- 4.1 (P < 0.013); and 36.2% +/- 1.1 (P < 0.002), respectively, of pretreatment values. Lp[a] reduction was directly related to blood gemfibrozil concentration (range 36-428 microM, r = 0.969) and occurred without concomitant changes in apolipoprotein B. Three weeks posttreatment Lp[a] levels returned to pretreatment values. A specific ribonuclease protection assay demonstrated that liver apolipoprotein[a] (apo[a]) mRNA expression was decreased in all animals to an average of 19.1% +/- 3.0 (P < 0.0026), of pretreatment values after the 200 mg/kg treatment, whereas, albumin, apolipoprotein A-I, apolipoprotein E, and glyceraldehyde-3-phosphate dehydrogenase mRNAs were unchanged. Lp[a] levels were unaffected by gemfibrozil in HepG2 cells permanently transfected with an apo[a] 10-kringle cDNA construct containing partial 5'- and 3'-untranslated sequences and under control of a constitutive CMV promoter. However, both Lp[a] and apo[a] mRNA in primary cynomolgus monkey hepatocytes were coordinately lowered in a dose-dependent fashion by gemfibrozil. Thus, Lp[a] can be regulated by gemfibrozil at the level of apo[a] mRNA expression.

Animals↗

PubMed1995

Hypolipidemic activity of select fibrates correlates to changes in hepatic apolipoprotein C-III expression: a potential physiologic basis for their mode of action.

For the last 30 years fibrates have been widely prescribed to treat human dyslipidemia. However, the primary mechanism by which they lower plasma lipid levels is still unknown. Studies with transgenic mice have suggested that changes in apoC-III expression levels have a dramatic influence on plasma triglyceride levels. These results suggested that fibrates could reduce lipid levels by lowering apoC-III gene expression. In the current studies, we sought to determine whether the selected fibrates, bezafibrate, clofibrate, fenofibrate, and gemfibrozil, could reduce hepatic apoC-III mRNA and plasma apoC-III levels. Chow-fed rats were orally gavaged daily with a dosing vehicle alone or with 100 mg/kg of each of the fibrates for 1 week and in addition with gemfibrozil for 2 weeks. Bezafibrate and fenofibrate lowered plasma triglyceride by approximately half and dramatically reduced hepatic apoC-III mRNA and plasma apoC-III levels. In contrast, clofibrate did not reduce plasma triglyceride levels and only partially reduced apoC-III mRNA and plasma protein levels. Gemfibrozil strongly reduced plasma triglyceride levels and had an intermediate but significant effect on apoC-III mRNA and plasma apoC-III levels. Some of the fibrates, especially gemfibrozil also reduced plasma apoC-II levels, an effect that could contribute to the observed triglyceride-lowering effect. In addition, the ratio of plasma apoE to plasma apoC-II plus apoC-III was strongly and inversely correlated with plasma triglyceride levels. As plasma apoE levels were not reduced in gemfibrozil-treated animals, this could also have contributed to the triglyceride-lowering effect of this fibrate. Fibrate-mediated triglyceride lowering was not the result of a decreased apoB or VLDL production and, therefore, suggested an enhanced VLDL remnant catabolism. Our results suggest that the mechanism by which fibrates lower plasma triglycerides is by reducing the level of hepatic apoC-III expression.

Animals↗

PubMed1994

ACAT inhibition decreases LDL cholesterol in rabbits fed a cholesterol-free diet. Marked changes in LDL cholesterol without changes in LDL receptor mRNA abundance.

Rabbits fed low-fat, cholesterol-free diets containing casein as the sole protein source develop endogenous hypercholesterolemia (EH). To test the hypothesis that lipoprotein cholesteryl esters in EH rabbits are acyl coenzyme A:cholesterol acyltransferase (ACAT) derived, we treated EH rabbits with CI-976, a potent and selective ACAT inhibitor. In addition, since cholesterol and bile acid synthesis as well as low-density lipoprotein (LDL) receptor activity are reduced in EH rabbits, we determined whether changes in gene expression for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, 7 alpha-hydroxylase, and the LDL receptor might be associated with the efficacy due to ACAT inhibition. Compared with EH controls, CI-976-treated rabbits (50 mg/kg per day for 5 weeks) had decreased plasma total cholesterol (-43%), very-low-density lipoprotein (VLDL) cholesterol (-62%), LDL cholesterol (-43%), plasma apolipoprotein B (-23%), liver cholesteryl esters (-39%), LDL size, VLDL and LDL cholesteryl ester content (percent of total lipids), cholesteryl oleate/cholesteryl linoleate ratios in VLDL and LDL (25% to 30%), and ex vivo liver ACAT activity. The triglyceride/cholesteryl ester ratio increased twofold to fourfold in these apolipoprotein B-containing lipoproteins. Endogenous cholesterol absorption appeared to be unaffected by drug treatment. CI-976 failed to alter specific hepatic mRNAs involved in cholesterol metabolism, but comparisons among dietary control groups revealed a marked reduction in 7 alpha-hydroxylase mRNA, no change in LDL receptor mRNA, and an increase in HMG-CoA reductase mRNA in EH rabbits compared with normal chow-fed controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Anilides↗

PubMed1993

Evaluation of two novel biochemicals on plasma and egg yolk lipid composition and laying hen performance.

PD132301-2, an inhibitor of acyl-coenzyme A:cholesterol O-acyltransferase (ACAT; EC 2.3.1.26), and 1-stearylboronic acid (SBA), a fatty acid analogue, were orally administered to White Leghorn hens in separate experiments to evaluate their effects on layer performance and plasma and egg yolk lipids. Five 60-wk-old hens each were fed either a corn-soybean meal basal layer ration, or the basal diet supplemented with .0121, .0363, or .1089% PD132301-2. In a second experiment, 12 37-wk-old hens each were fed either a basal layer ration, or the basal diet supplemented with .20 or .40% SBA. The duration of the experiments were 21 and 16 days, respectively. Neither compound significantly affected hen-day production, egg weight, yolk weight, BW gain, feed consumption, feed efficiency, plasma total cholesterol and triglyceride concentrations, or egg yolk cholesterol content. PD132301-2 had no effect on yolk fatty acid profiles, and C22:6n3 was the only fatty acid altered by SBA. Although 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors have been successful in reducing egg cholesterol, ACAT inhibitors and fatty acid analogues apparently hold little promise in this regard. The results of the present work also support the concept that, in order to pharmacologically alter the cholesterol content of eggs, direct inhibition of key enzymes in the cholesterol biosynthetic pathway is necessary.

Administration, Oral↗

PubMed1992

Lipoprotein lipase-mediated lipolysis of very low density lipoproteins increases monocyte adhesion to aortic endothelial cells.

Lipoprotein lipase (LPL) bound to vascular endothelial cells hydrolyses triglycerides in plasma lipoproteins. To explore the role of LPL in atherogenesis, the effect of LPL-mediated lipolysis of very low density lipoproteins (VLDL) on monocyte adhesion to endothelial cells was examined. Adhesion of U937 monocytes to porcine aortic endothelial cells that were incubated with VLDL and purified bovine milk LPL was markedly higher than endothelial cells that were incubated with VLDL alone. The increase in monocyte adhesion obtained with VLDL was dependent on the concentration of the lipoprotein, monocyte dose and time of incubation. The increase in adhesion correlated with generation of free fatty acids from the hydrolysis of triglycerides in VLDL by LPL. Furthermore, direct addition of oleic acid to endothelial cells also increased adhesion of monocytes. We postulate that LPL-derived lipolytic products increase monocyte adhesion to vascular endothelium and thereby promote atherogenesis.

Animals↗

PubMed1992

Inhibitors of cholesterol biosynthesis. 6. trans-6-[2-(2-N-heteroaryl-3,5-disubstituted- pyrazol-4-yl)ethyl/ethenyl]tetrahydro-4-hydroxy-2H-pyran-2-ones.

A series of N-heteroaryl-substituted mevalonolactones were prepared and evaluated for their ability to inhibit the enzyme HMG-CoA reductase both in vitro and in vivo, and to lower plasma cholesterol in a hypercholesterolemic dog model. The goal of the strategy employed was to design an inhibitor which possessed the pharmacological properties of lovastatin (1), and the physicochemical properties (increased hydrophilicity) of pravastatin (2). Two compounds 20a and 20b, were more potent than lovastatin at inhibiting cholesterol biosynthesis both in vitro and in vivo. In terms of plasma cholesterol lowering, 20a was much more efficacious than lovastatin. In addition to possessing increased biological activity, these compounds are significantly less lipophilic than lovastatin, in fact, 20b has a CLOGP value comparable to pravastatin.

Animals↗

PubMed1992

Hepatic and nonhepatic sterol synthesis and tissue distribution following administration of a liver selective HMG-CoA reductase inhibitor, CI-981: comparison with selected HMG-CoA reductase inhibitors.

Since cholesterol biosynthesis is an integral part of cellular metabolism, several HMG-CoA reductase inhibitors were systematically analyzed in in vitro, ex vivo and in vivo sterol synthesis assays using [14C]acetate incorporation into digitonin precipitable sterols as a marker of cholesterol synthesis. Tissue distribution of radiolabeled CI-981 and lovastatin was also performed. In vitro, CI-981 and PD134967-15 were equipotent in liver, spleen, testis and adrenal, lovastatin was more potent in extrahepatic tissues than liver and BMY21950, pravastatin and PD135023-15 were more potent in liver than peripheral tissues. In ex vivo assays, all inhibitors except lovastatin preferentially inhibited liver sterol synthesis; however, pravastatin and BMY22089 were strikingly less potent in the liver. CI-981 inhibited sterol synthesis in vivo in the liver, spleen and adrenal while not affecting the testis, kidney, muscle and brain. Lovastatin inhibited sterol synthesis to a greater extent than CI-981 in the spleen, adrenal and kidney while pravastatin and BMY22089 primarily affected liver and kidney. The tissue distribution of radiolabeled CI-981 and lovastatin support the changes observed in tissue sterol synthesis. Thus, we conclude that a spectrum of liver selective HMG-CoA reductase inhibitors exist and that categorizing agents as liver selective is highly dependent upon method of analysis.

Animals↗