Effects of cholestyramine on lipoprotein levels and metabolism in Syrian hamsters

Astragalus polysaccharides lowers plasma cholesterol through mechanisms distinct from statins

To determine the efficacy and underlying mechanism of Astragalus polysaccharides (APS) on plasma lipids in hypercholesterolemia hamsters. The effect of APS (0.25g/kg/d) on plasma and liver lipids, fecal bile acids and neutral sterol, cholesterol absorption and synthesis, HMG-CoA reductase activity, and gene and protein expressions in the liver and small intestine was investigated in twenty-four hypercholesterolemia hamsters. Treatment periods lasted for three months. APS significantly lowered plasma total cholesterol by 45.8%, triglycerides by 30%, and low-density lipoprotein-cholesterol by 47.4%, comparable to simvastatin. Further examinations revealed that APS reduced total cholesterol and triglycerides in the liver, increased fecal bile acid and neutral sterol excretion, inhibited cholesterol absorption, and by contrast, increased hepatic cholesterol synthesis and HMG-CoA reductase activity. Plasma total cholesterol or low-density lipoprotein-cholesterol levels were significantly correlated with cholesterol absorption rates. APS up-regulated cholesterol-7α-hydroxylase and LDL-receptor gene expressions. These new findings identify APS as a potential natural cholesterol lowering agent, working through mechanisms distinct from statins.

Individual trans octadecenoic acids and partially hydrogenated vegetable oil differentially affect hepatic lipid and lipoprotein metabolism in golden Syrian hamsters

Trans fatty acids (TFA) from industrial sources [i.e. partially hydrogenated vegetable oil (PHVO)] have been associated with several chronic human diseases, especially coronary heart disease (CHD). The possible contribution of individual TFA to overall CHD risk remains largely unknown. The objective of the present study was to investigate the effects of 2 major trans 18:1 isomers, trans-9 18:1 [elaidic acid (EA)] and trans-11 18:1 [vaccenic acid (VA)] on plasma lipid biomarkers of CHD risk. Thirty-two male Golden Syrian hamsters were randomly assigned to 1 of 4 dietary treatments: 1) control "Western" diet; 2) PHVO supplement; 3) EA supplement; and 4) VA supplement. Fat supplements were incorporated into the respective treatment diets at 2.5 g/100 g of diet. Compared with the control diet, the PHVO diet increased the plasma ratios of total:HDL-cholesterol and nonHDL:HDL-cholesterol by 17 and 23%, respectively. In contrast, these values decreased by 27 and 46% after the EA treatment and 8 and 14% after the VA treatment, respectively, indicating an improvement (reduction) in CHD risk. With regard to liver lipids, the EA diet reduced the content of (n-3) and (n-6) PUFA relative to the other treatments, suggesting an inhibition of enzymes common to the 2 biosynthesis pathways. Overall, results demonstrate that the hypercholesterolemic effects of PHVO are not dependent on the presence of EA or VA and that other bioactive components in PHVO must be responsible for its associated adverse health effects.

Effect of melatonin on cholesterol absorption in rats

This study evaluated the influence of melatonin on cholesterol absorption in rats fed on high cholesterol diet (HCD). HCD induced a remarkable increase in hepatic and plasma total cholesterol, plasma very low density lipoprotein (VLDL) and low density lipoprotein (LDL) cholesterol, a decrease in high density lipoprotein (HDL) cholesterol and an elevation in triacylglyceride (TG) levels in plasma and in the liver. Melatonin suspension (10 mg/kg), specially prepared for this purpose, cholestyramine (230 mg/kg) and ezetimibe (145 microg/kg) were administered orally to the rats fed HCD for 30 days. Melatonin significantly reduced cholesterol absorption in rats fed on HCD and caused significant decreases in total cholesterol, TG, VLDL- and LDL-cholesterol in the plasma and contents of cholesterol and TG in the liver. The level of HDL cholesterol was significantly increased after melatonin. These results suggested that inhibition of cholesterol absorption caused by melatonin could be a mechanism contributing to the positive changes in plasma cholesterol, lipoprotein profile and the lipid contents in the liver.

Novel non-systemic inhibitor of ileal apical Na+-dependent bile acid transporter reduces serum cholesterol levels in hamsters and monkeys

1-{7-[(1-(3,5-Diethoxyphenyl)-3-{[(3,5-difluorophenyl)(ethyl)amino]carbonyl}-4-oxo-1,4-dihydroquinolin-7-yl)oxy]heptyl}-1-methylpiperidinium bromide, R-146224, is a potent, specific ileum apical sodium-dependent bile acid transporter (ASBT) inhibitor; concentrations required for 50% inhibition of [3H]taurocholate uptake in human ASBT-expressing HEK-293 cells and hamster ileum tissues were 0.023 and 0.73 microM, respectively. In bile-fistula rats, biliary and urinary excretion 48 h after 10 mg/kg [14C]R-146224, were 1.49+/-1.75% and 0.14+/-0.05%, respectively, demonstrating extremely low absorption. In hamsters, R-146224 dose-dependently reduced gallbladder bile [3H]taurocholate uptake (ED50: 2.8 mg/kg). In basal diet-fed hamsters, 14-day 30-100 mg/kg R-146224 dose-dependently reduced serum total cholesterol (approximately 40%), high density lipoprotein (HDL) cholesterol (approximately 37%), non-HDL cholesterols (approximately 20%), and phospholipids (approximately 20%), without affecting serum triglycerides, associated with reduced free and esterified liver cholesterol contents. In normocholesterolemic cynomolgus monkeys, R-146224 specifically reduced non-HDL cholesterol. In human ileum specimens, R-146224 dose-dependently inhibited [3H]taurocholate uptake. Potent non-systemic ASBT inhibitor R-146224 decreases bile acid reabsorption by inhibiting the ileal bile acid active transport system, resulting in hypolipidemic activity.

Effect of silymarin and its polyphenolic fraction on cholesterol absorption in rats

This study evaluated the influence of silymarin (SM) and polyphenolic fraction (PF) of silymarin on cholesterol absorption in rats fed on high cholesterol diet (HCD). HCD induced a remarkable increase in hepatic, plasma, VLDL and LDL cholesterol, a decrease in HDL cholesterol and an elevation in triacylglycerol (TAG) levels in plasma, VLDL and in the liver. SM and PF were administered as dietary supplements (1.0%) in HCD for 18 days. Intestinal cholesterol absorption was measured by dual-isotope plasma ratio method, which calculates percent of cholesterol absorption from the ratio of two labelled cholesterol doses, one given intragastrically (14C) and one intravenously (3H). Silymarin and PF significantly reduced cholesterol absorption in rats fed on HCD and caused significant decreases in plasma and VLDL cholesterol and content of cholesterol and TAG in the liver. The level of HDL cholesterol was significantly increased after silymarin, but not after administration of PF. The levels of TAG in plasma and VLDL were not affected by either silymarin or PF. These results suggest that the inhibition of cholesterol absorption caused by silymarin and its polyphenolic fraction could be a mechanism contributing to the positive changes in plasma cholesterol lipoprotein profile and in lipid content in liver.

Direct screening of lyophilised biological fluids for bile acids using an evaporative light scattering detector

The usefulness of lyophilisation for the direct screening of biological fluids for bile acids was investigated. Human serum and urine were lyophilised without losses of the target compounds and further extracted with n-hexane in acidic medium under magnetic stirring. An integrated flow injection-liquid chromatographic system coupled to an evaporative light scattering detector (ELSD) was used for automated screening/confirmation. The continuous module allows sequential filtration of the organic phase, solvent changeover and solid-phase extraction for clean-up and preconcentration purposes. Retained bile acids were eluted with an acetonitrile-methanol (65:35, v/v) stream. For screening purposes, the effluent was directly introduced in the ELSD detector and the total bile acid content of the sample determined. For confirmatory analysis, another aliquot of the sample was processed in the screening module but the effluent was directed to the chromatographic columns, which provided the free bile acid profile of the sample. Fasting serum and urine samples obtained from healthy individuals were lyophilised and processed. Good agreement was obtained in the analysis of the two matrices assayed following the screening and confirmatory methods.

Dietary cholesterol reduces lipoprotein lipase activity in the atherosclerosis-susceptible Bio F(1)B hamster

We have compared lipoprotein metabolism in, and susceptibility to atherosclerosis of, two strains of male Golden Syrian hamster, the Bio F(1)B hybrid and the dominant spot normal inbred (DSNI) strain. When fed a normal low-fat diet containing approximately 40 g fat and 0.3 g cholesterol/kg, triacylglycerol-rich lipoprotein (chylomicron+VLDL) and HDL-cholesterol were significantly higher (P<0.001) in Bio F(1)B hamsters than DSNI hamsters. When this diet was supplemented with 150 g coconut oil and either 0.5 or 5.0 g cholesterol/kg, significant differences were seen in response. In particular, the high-cholesterol diet produced significantly greater increases in plasma cholesterol and triacylglycerol in the Bio F(1)B compared with the DSNI animals (P=0.002 and P<0.001 for cholesterol and triacylglycerol, respectively). This was particularly dramatic in non-fasting animals, suggesting an accumulation of chylomicrons. In a second experiment, animals were fed 150 g coconut oil/kg and 5.0 g cholesterol/kg for 6 and 12 months. Again, the Bio F(1)B animals showed dramatic increases in plasma cholesterol and triacylglycerol, and this was confirmed as primarily due to a rise in chylomicron concentration. Post-heparin lipoprotein lipase activity was significantly reduced (P<0.001) in the Bio F(1)B compared with the DSNI animals at 6 months, and virtually absent at 12 months. Bio F(1)B animals were also shown to develop significantly more (P<0.001) atherosclerosis. These results indicate that, in the Bio F(1)B hybrid hamster, cholesterol feeding reduces lipoprotein lipase activity, thereby causing the accumulation of chylomicrons that may be associated with their increased susceptibility to atherosclerosis.

Inhibition of cholesterol synthesis causes both hypercholesterolemia and hypocholesterolemia in hamsters

Effects of FR194738 ((E)-N-ethyl-N-(6,6-dimethyl-2-hepten-4-ynyl)-3-[2-methyl-2-(3-thienylmethoxy)propyloxy]benzylamine hydrochloride), a squalene epoxidase inhibitor, on lipid metabolism were compared with those of pravastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, in hamsters. Drugs were given for 10 d either as a diet mixture or as a bolus oral gavage, and similar results were obtained with each type of administration. FR194738 (0.01-0.32% as a diet mixture; 10-100 mg/kg as an oral gavage) dose-dependently decreased serum total cholesterol, non high density lipoprotein (HDL) cholesterol, HDL cholesterol and triglyceride levels, and the changes in serum parameters were similar. Pravastatin (0.01-0.32% as a diet mixture; 1-100 mg/kg as an oral gavage) increased serum cholesterol levels, and dose-dependently decreased serum triglyceride levels. Although oral gavage of FR194738 at 32 mg/kg and pravastatin at 3.2 and 10 mg/kg increased hepatic HMG-CoA reductase activity, the degree of the changes was far greater with the latter than the former drug. FR194738 slightly increased hepatic cholesterol content at 32 mg/kg, whereas pravastatin dose-dependently increased hepatic cholesterol content until it leveled off at 32 and 100 mg/kg. It is concluded that inhibition of squalene epoxidase and HMG-CoA reductase triggers both hypercholesterolemic (hepatic cholesterol synthesis) and hypocholesterolemic (hepatic cholesterol uptake) mechanisms. FR194738 appears to induce a greater enhancement of the latter rather than the former, whereas pravastatin has a greater effect on the former.

Inhibitory effect of TS-962 on the formation of early atherosclerotic lesions in high fat-fed hyperlipidemic hamsters

The hypocholesterolemic and anti-atherosclerotic effect of TS-962, a specific ACAT inhibitor, was investigated in a hamster model fed a high fat diet containing 10% coconut oil and 0.05% cholesterol. Lipid accumulated atherosclerotic lesions were detected by using oil red O staining in the lesion-prone aortic arch. A high dose, estimated to be 15 mg/kg, of TS-962 decreased serum cholesterol to normal levels with reduction of liver cholesterol contents below normal levels, and as a consequence, entirely inhibited the lipid accumulation in the aortic arch. Furthermore, a low dose, estimated to be 1.5 mg/kg, of TS-962 remarkably inhibited aortic lipid accumulation by 73% compared with the control group, without changing either serum cholesterol level or liver cholesterol content. These findings suggest that TS-962 is effective in the primary prevention of atherosclerosis by directly suppressing the formation of foam cells in arteries.

Studies of cholesterol and bile acid metabolism, and early atherogenesis in hamsters fed GT16-239, a novel bile acid sequestrant (BAS)

The purpose of this study was to compare the efficacy of GT16-239, an alkylated, cross-linked poly(allylamine) bile acid sequestrant with cholestyramine on cholesterol and bile acid metabolism, and early aortic atherosclerosis in hypercholesterolemic male F1B Golden Syrian hamsters. In this controlled study, 42 hamsters were divided into six groups and were fed a chow-based hypercholesterolemic diet supplemented with a 10% oil blend (55% coconut/45% corn), 0.1% cholesterol (w/w) (control) and either 0.9 or 1.2% cholestyramine or 0.2, 0.4 or 0.6% GT16-239 for 13 weeks. Laboratory analyses included evaluating plasma lipoprotein cholesterol and triglyceride concentrations, hepatic HMG-CoA reductase and 7 alpha-hydroxylase activities, fecal excretion of bile acids and neutral sterols, hepatic cholesterol concentrations, and early atherosclerosis (aortic fatty streak area). Relative to the control diet, the 0.6% GT16-239 versus the 1.2% cholestyramine significantly inhibited the elevation of plasma lipoprotein total cholesterol (TC) (-69% vs -40%), high density lipoprotein-cholesterol (HDL-C) (-49% vs -30%), and non-HDL-C (-81 vs -48%) concentrations; increased the activities of both HMG-CoA reductase (1492% vs 62%) and 7 alpha-hydroxylase (175% vs 86%); lowered the concentration of hepatic cholesteryl ester (-94% vs -59%); increased fecal cholesterol concentration (+28% vs -10%); and decreased aortic fatty streak area (-100% vs -86%). Unexpected findings of this comparison were increased fecal concentrations of cholic acid (533%) and chenodeoxycholic acid (400%) and the reduction in lithocholic acid (-50%) in the 0.6% GT16-239 compared to the 1.2% cholestyramine group. In summary, GT16-239 had a greater impact on cholesterol metabolism and early atherosclerosis in hypercholesterolemic hamsters than cholestyramine.

Lack of predictability of classical animal models for hypolipidemic activity: a good time for mice?

Hypolipidemic drugs that are efficacious in man are not always active in classical animal models of dyslipidemia. Inhibitors of HMG-CoA reductase (statins) do not lower plasma cholesterol in rats, but yet this species was alone in providing activity for fibrate-type drugs. Nicotinic acid possesses many desirable features with regard to clinical use, but most of these actions are lacking in rats and monkeys. The metabolism of low density lipoproteins in hamsters is widely thought to be similar to that in humans, yet neither statins or fibrates lower plasma lipids in these species. With the advent of mouse models expressing specific human genes (or disruption of genes) it is now possible to re-examine the effect of established drugs and to characterize new hypolipidemic compounds with respect to site and mechanism of action. Drug responses observed in humans are now being seen in such mouse models (e.g. HDL elevation with fenofibrate in mice with the human apo A-I gene). Moreover, mice are now being screened for compounds that lower plasma (human) Lp(a), or lower plasma cholesterol in the absence of LDL receptors. It is proposed that these new genetic mouse models may afford a more focused examination of drug action and provide, for new compounds, better prediction of the human response.

The hypocholesterolemic and antiatherogenic effects of Cholazol H, a chemically functionalized insoluble fiber with bile acid sequestrant properties in hamsters

Cholazol H (Alpha-Beta Technology, Worcester, MA), a chemically functionalized, insoluble dietary fiber with bile acid sequestrant properties, was studied in 30 male F1 B Golden Syrian hamsters for its effect on plasma lipid concentrations and early atherogenesis in experiment 1. In experiment 2, 30 male Golden Syrian hamsters were studied for the effects on plasma lipids and fecal excretion of bile acids. In experiment 1, three groups of 10 hamsters each were fed a chow-based hypercholesterolemic diet supplemented with 5% coconut oil and 0.1% cholesterol for 6 weeks. After 6 weeks, hamsters were continued on the diet with either 0% drug (hypercholesterolemic diet [HCD]), 0.5% cholestyramine (CSTY), or 0.5% Cholazol H for 8 weeks. Fasting plasma lipids were measured at weeks 6, 10, and 14, and early atherosclerosis (fatty streak formation) was measured at week 14. Relative to HCD, CSTY and Cholazol H significantly lowered plasma total cholesterol (TC) (-37%, P < .03, and -30%, P < .04, respectively) and plasma very-low and low-density lipoprotein-cholesterol (nonHDL-C) (-45%, P < .02, and -36%, P < .03, respectively) with no significant effects on plasma HDL-C or triglycerides (TG). Despite similar reductions in nonHDL-C, only Cholazol H significantly prevented early atherosclerosis (-38%, P < .02) relative to HCD. In experiment 2, three groups of 10 hamsters each were fed a chow-based hypercholesterolemic diet supplemented with 10% coconut oil and 0.05% cholesterol and either 0% drug HCD, 0.5% CSTY, or 0.5% Cholazol H for 4 weeks. Fasting plasma lipids were measured at weeks 2 and 4, and fecal bile acids were measured at week 4. Both Cholazol H and CSTY were equally effective in significantly lowering plasma TC (-16%, P < .003, and -13%, P < .01, respectively) and nonHDL-C (-22%, P < .004, and -18%, P < .02, respectively), with no significant effect on HDL-C and TG relative to HCD. Cholazol H and CSTY produced a significantly greater concentration of fecal total bile acids (39%, P < .001, and 28%, P < .002, respectively) relative to HCD. Also, there was a 48% (P < .002) and 65% (P < .001) greater fecal concentration of cholic acid (CA) for Cholazol H-treated hamsters compared with HCD- and CSTY-treated hamsters, respectively. Cholazol H also significantly increased fecal concentration of deoxycholic acid (DCA; 56%, P < .02) compared with HCD. In summary, Cholazol H is as effective as CSTY for prevention of diet-induced hypercholesterolemia and early atherosclerosis in hamsters.

The ACAT inhibitor, CI-1011 is effective in the prevention and regression of aortic fatty streak area in hamsters

The hypocholesterolemic and anti-atherogenic properties of sulfamic acid ((2,4,6-tris (1-methylethyl) phenyl) acetyl) 2,6-bis(1-methylethyl) phenyl ester, the ACAT inhibitor, CI-1011, was tested in 120 male F1B hamsters fed a hypercholesterolemic chow-based diet containing 10%, coconut oil and 0.05% cholesterol plus: (i) no drug treatment (HCD); (ii) 3 mg/kg per day (HCD+3): (iii)10 mg/kg per day (HCD+10); (iv) 30 mg/kg per day (HCD+30) of CI-1011; or (v) 500 mg/kg per day of cholestyramine (CSTY). Plasma samples were collected at 8 and 10 weeks for measurement of total cholesterol (TC), very low-density lipoprotein cholesterol (VLDL-C), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and triglycerides (TG). For the progression studies, animals were euthanized after 10 weeks for aortic fatty streak area and hepatic cholesterol analysis. For the regression study, a cohort of the HCD was treated with 30 mg/kg per day of CI-1011 (regression) for an additional 8 weeks. The HCD+3, HCD+10, HCD+30 and CSTY lowered plasma TC (25, 32, 34 and 32%, respectively), VLDL-C (62, 74, 71 and 75%, respectively), LDL-C (25, 38, 47 and 46%, respectively) and TG (48, 47, 42 and 45%, respectively). All treatments resulted in a significant lowering of aortic fatty streak area (68, 86, 93 and 94%, respectively) and reduction in hepatic cholesteryl esters (57, 65, 67 and 70%, respectively). Regression of aortic fatty streak area was 90% after 8 weeks of HCD+30 treatment. Also during the regression phase, plasma TC, LDL-C and TG were lowered 23, 33 and 47%, respectively, as well as, hepatic cholesteryl esters (76%). Significant correlations between plasma LDL-C concentration and aortic fatty streak area (r=0.62, P < 0.004) in the HCD+10 group, suggest that CI-1101 altered aortic lipid infiltration primarily by its effect on plasma lipids. However the 30 mg/kg per day dose of CI-1011 which additionally reduced aortic fatty streak area by 51% relative to the 10 mg/kg per day dose was only associated with a 14% further decrease in plasma LDL-C. Finally the 10-fold regression of aortic fatty streak area was associated with only a 35% reduction in plasma LDL-C. These exceptions to the lipid-lesion relationship raise the possibility of additional effects of CI-1011, which may occur independent of or in concert with lipoprotein cholesterol lowering. It is concluded that in hypercholesterolemic hamsters, CI-1011 is approximately 50 times more potent than cholestyramine in cholesterol-lowering, reduction and regression of aortic fatty streak area.

Reduced cholesterol absorption in hamsters by crilvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor

Crilvastatin, a new drug from the pyrrolidone family, has been previously shown to inhibit the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, in vitro and in vivo, to reduce the absorption of dietary cholesterol and to stimulate the activity of cholesterol 7 alpha-hydroxylase in the rat. The aim of this study was to evaluate the effects of crilvastatin on cholesterol and bile acid metabolism in the hamster. In hamsters fed on a lithogenic diet for 8 weeks, crilvastatin treatment (200 mg/day per kg body weight) did not change plasma lipid levels, failed to improve bile parameters and did not prevent gallstone formation. In hamsters fed on a basal cholesterol-rich (0.2%) diet for 8 weeks, crilvastatin at the same dose reduced the cholesterol level in the plasma by 20%, with a decrease of both low-density and high-density lipoprotein cholesterol. The drug did not significantly stimulate the biliary secretion of bile acids but significantly decreased the activity of acyl coenzyme A:cholesterol acyltransferase in the small intestine by 64%. This effect was enhanced when cholestyramine, a bile acid-sequestering resin, was given in combination with crilvastatin. Crilvastatin alone did not change the activity of cholesterol 7 alpha-hydroxylase in the liver, despite the marked reduction in both hepatic cholesterogenesis and intestinal absorption of dietary cholesterol (the absorption coefficient was 44 +/- 2% in treated hamsters vs. 61 +/- 7% in controls).

Effects of hyodeoxycholic acid and alpha-hyocholic acid, two 6 alpha-hydroxylated bile acids, on cholesterol and bile acid metabolism in the hamster

The effects of hyodeoxycholic (HDCA) and alpha-hyocholic acids (alpha-HCA), on cholesterol, bile acid and lipoprotein metabolism, were studied in hamsters. The animals were fed a low cholesterol control diet supplemented with 0.1% HDCA or alpha-HCA for 3 weeks. In both treated groups, the LDL-cholesterol concentration was significantly lowered and was associated with a global hypocholesterolemic effect. Moreover, hepatic cholesterol ester storage was reduced and HMGCoA reductase activity was respectively enhanced 13.5-times and 7.7-times in HDCA and alpha-HCA groups compared to controls. In contrast, cholesterol 7 alpha-hydroxylase activity and LDL-receptor activity and mass were not modified. In bile, the cholesterol saturation index was increased 5-fold (HDCA group) and 2-fold (alpha-HCA group) as a consequence of an enlarged proportion of biliary cholesterol. The two 6-hydroxylated bile acids induced an enhanced fecal excretion of neutral sterols (HDCA group: 11.6-times, alpha-HCA group: 3.2-times versus controls) which was consistent with a 59% decrease in intestinal cholesterol absorption in the HDCA group. The major effects due to bile acid treatments were a decrease in LDL-cholesterol concentration, a strong stimulation of hepatic cholesterol biosynthesis and an excessive loss of cholesterol in feces. These perturbations might be the result of the enrichment of bile with hydrophilic bile acids, leading to a limited return of endogenous cholesterol from the intestine to the liver.

Lovastatin inhibits diet induced atherosclerosis in F1B golden Syrian hamsters

3-Hydroxy-3-methylglutaryl-CoA (HMG CoA) reductase inhibitors are the drugs most commonly prescribed in the US to lower blood cholesterol. Previous studies have shown their efficacy in reducing plasma low density lipoprotein (LDL) cholesterol. However, little is known about their effects on preventing diet induced atherosclerosis. We have investigated the changes in lipoprotein profiles and extent of atherogenesis in hamsters (F1B strain) consuming an atherogenic diet with and without lovastatin. Thirty-six animals were randomized into 3 groups of 12 animals each, with similar plasma cholesterol levels. One group of animals received a basal chow diet, and the other two groups a basal diet plus 10% (w/w) coconut oil and 0.05% cholesterol. After 2.5 weeks, one of the groups received the latter diet supplemented with lovastatin (25 mg/kg/day). A second study was carried out in which animals received the same diets, but lovastatin was given during the 10 week period at a dose of 12.5 mg/kg/day. At the end of the experimental period, animals were sacrificed and lipoprotein cholesterol, liver enzymes, and aortic foam cell development were determined. Animals fed the high fat diet plus lovastatin had significantly lower levels of non-high density lipoprotein (HDL) cholesterol than those fed the unsupplemented high fat diet. No differences were observed in mean levels of this parameter between animals fed the low fat diet and those receiving lovastatin. The amount of aortic lipid staining was significantly less in the lovastatin and low fat groups when compared to the unsupplemented high fat groups. These results indicate that lovastatin can prevent diet induced aortic lipid deposition in this animal model.

Evaluation of cultured hamster hepatocytes as an experimental model for the study of very low density lipoprotein secretion

The secretion of triacylglycerol, cholesterol and cholesteryl ester in very low density lipoprotein (VLDL) by cultured hamster hepatocytes was studied, and the results compared with those obtained previously using cultured rat hepatocytes and the human hepatoma cell line HepG2. The hamster cells secreted apolipoprotein B and VLDL triacylglycerol, cholesterol and cholesteryl ester linearly during 24 h in culture, and this time period was used in all experiments. Addition of oleate (1 mM) to the culture medium resulted in increased secretion of triacylglycerol, but cholesterol ester output were unchanged. Triacylglycerol secretion was also increased in the presence of lipogenic substrates (10 mM lactate + 1 mM pyruvate) plus dexamethasone (1 microM), but not with either of these agents alone. Inhibition of cholesterol synthesis in the hamster cells by incubation with mevinolin (2 micrograms/ml) did not change VLDL lipid secretion, but stimulation using mevalonate lactone resulted in decreased triacylglycerol output. Manipulation of the rate of cholesterol esterification in the hepatocytes by inhibiting or stimulating the activity of acyl coenzyme A cholesterol:acyl transferase using the inhibitor Dup128 (25 microM) and 25-hydroxycholesterol (50 microM), respectively, had no effect on the secretion of VLDL lipid. In the presence of 1 mM oleate plus 25-hydroxycholesterol, however, a rise in the output of triacylglycerol and cholesteryl ester was observed. Hepatocytes prepared from hamsters fed 2% cholestyramine secreted significantly less triacylglycerol than those from animals given the control diet, but cholesterol and cholesteryl ester output were unchanged, despite a decrease of about 40% in the total cholesterol content of the cells. These results show that the secretion of lipid in VLDL in hamster hepatocytes differs from that in rat and human liver in its response to dietary cholestyramine, and from rat hepatocytes and HepG2 cells in its response to changes in the rate of lipogenesis and cholesterol synthesis and esterification. Overall, hamster hepatocytes appear to be less susceptible to modification the rate of hepatic VLDL secretion, and should provide a useful additional tool for the investigation of this process.

Lack of effect on the low density lipoprotein receptor in hamsters treated with 17 alpha-ethinyl estradiol

High pharmacological doses of 17 alpha-ethinyl estradiol are known to increase the number of low density lipoproteins (LDL)-receptors in rats and rabbits, leading to a profound decrease in plasma cholesterol levels. Here, using rats as a positive control, we demonstrate that in hamsters ethinyl estradiol does not upregulate liver LDL-receptors, nor change plasma LDL turnover or plasma LDL-cholesterol. The lack of effect in estradiol-treated hamsters suggests that the hormonal control is different from that in rats.

SK&F 97426-A a more potent bile acid sequestrant and hypocholesterolaemic agent than cholestyramine in the hamster

SK&F 97426-A is a novel bile acid sequestrant which was selected for comparison with cholestyramine in vivo because of its superior in vitro bile acid binding properties. The effects of the two sequestrants on faecal bile acid excretion, plasma total cholesterol, VLDL + LDL and HDL cholesterol and triglyceride concentrations and on liver enzymes involved in the synthesis and metabolism of cholesterol were investigated in normocholesterolaemic hamsters. Four studies were conducted to determine the relative potencies of the two resins using a range of doses of the sequestrants over treatment periods of up to 2 weeks. Curves fitted to the resulting data allowed common maximum responses and separate ED50s to be calculated for each sequestrant. The maximum response of both sequestrants was to increase bile acid excretion by 352% and lower plasma total cholesterol by 37-58%. LDL + VLDL and HDL cholesterol were reduced by 56-75% and 25-41%, respectively. SK&F 97426-A was 3 times more potent than cholestyramine at increasing the excretion of bile acids in the faeces and 2.1-3.4-fold and 2.3-3.2-fold more potent at lowering total plasma cholesterol and LDL plus VLDL cholesterol, respectively. In some of the experiments SK&F 97426-A was also more potent than cholestyramine at lowering HDL cholesterol. Plasma triglycerides were also lowered by both sequestrants by up to 31% after 1 week but the relative potency could not be determined. These HDL cholesterol and total triglyceride lowering effects of bile acid sequestrants in the hamster are known not to occur in people treated with cholestyramine. There were minimal differences between hamsters treated for 1 or 2 weeks in the relative potencies or ED50s calculated for the total plasma cholesterol, LDL + VLDL and HDL cholesterol. Both sequestrants may have been slightly more efficacious on these parameters after 2 weeks of treatment. Liver weights were reduced by about 15% by both sequestrants at 2% (w/w) in the diet for 1 week. The activities of the liver HMG-CoA reductase and cholesterol 7 alpha-hydroxylase were increased as expected, whilst the activity of the acyl-CoA:cholesterol acyltransferase was reduced by both sequestrants at this dose. SK&F 97426-A was, therefore, 2-3-fold more potent as a bile acid sequestrant and hypocholesterolaemic agent than cholestyramine when tested in the hamster.