The hypocholesterolemic effect of dietary soybean protein vs. casein in hamsters fed cholesterol-free or cholesterol-enriched semipurified diets

Common bean protein hydrolysate modulates lipid metabolism and prevents endothelial dysfunction in BALB/c mice fed an atherogenic diet

BACKGROUND AND AIMS

Common beans (Phaseolus vulgaris L.) protein hydrolysate is a source of bioactive peptides with known health benefits. The aim of this study was to evaluate the effect of common bean protein hydrolysate on lipid metabolism and endothelial function in male adult BALB/c mice fed an atherogenic diet for nine weeks.

METHODS AND RESULTS

Male adult mice were divided into three experimental groups (n = 12) and fed with normal control diet; atherogenic diet and atherogenic diet added with bean protein hydrolysate (700 mg/kg/day) for nine weeks. Food intake, weight gain, lipid profile, Atherogenic Index of Plasma, inflammation biomarkers and endothelial function were evaluated. APH group presented reduced feed intake, weight gain, lipid profile, tumor necrosis factor-α, angiotensin II (94% and 79%, respectively) and increased endothelial nitric oxide synthase (62%).

CONCLUSIONS

Protein hydrolysate showed hypocholesterolemic activity preventing inflammation and dysfunction of vascular endothelium, in addition to decreasing oxidative stress, indicating an adjuvant effect on reducing atherogenic risk.

Multilevel systems biology modeling characterized the atheroprotective efficiencies of modified dairy fats in a hamster model

We assessed the atheroprotective efficiency of modified dairy fats in hyperlipidemic hamsters. A systems biology approach was implemented to reveal and quantify the dietary fat-related components of the disease. Three modified dairy fats (40% energy) were prepared from regular butter by mixing with a plant oil mixture, by removing cholesterol alone, or by removing cholesterol in combination with reducing saturated fatty acids. A plant oil mixture and a regular butter were used as control diets. The atherosclerosis severity (aortic cholesteryl-ester level) was higher in the regular butter-fed hamsters than in the other four groups (P < 0.05). Eighty-seven of the 1,666 variables measured from multiplatform analysis were found to be strongly associated with the disease. When aggregated into 10 biological clusters combined into a multivariate predictive equation, these 87 variables explained 81% of the disease variability. The biological cluster "regulation of lipid transport and metabolism" appeared central to atherogenic development relative to diets. The "vitamin E metabolism" cluster was the main driver of atheroprotection with the best performing transformed dairy fat. Under conditions that promote atherosclerosis, the impact of dairy fats on atherogenesis could be greatly ameliorated by technological modifications. Our modeling approach allowed for identifying and quantifying the contribution of complex factors to atherogenic development in each dietary setup.

The α' subunit of β-conglycinin and the A1-5 subunits of glycinin are not essential for many hypolipidemic actions of dietary soy proteins in rats

PURPOSE

This study examined the effects of dietary soy protein (SP) lacking different storage protein subunits and isoflavones (ISF) on the abdominal fat, blood lipids, thyroid hormones, and enzymatic activities in rats.

METHODS

Weanling Sprague-Dawley rats (8 males and 8 females/group) were fed diets containing either 20 % casein without or with supplemental isoflavones or alcohol-washed SP isolate or SP concentrates (SPC) prepared from 6 different soy bean lines for 8 weeks.

RESULTS

Feeding of diets containing SPC regardless of their subunit compositions significantly lowered relative liver weights, blood total, free, and LDL cholesterol in both genders (P < 0.05) and also reduced serum free fatty acids (FFA) and abdominal fat in females (P < 0.05) compared to the casein or casein + ISF diets. Dietary SPC significantly elevated the plasma free triiodothyronine (T3) in both genders and total T3 in females compared to the casein diet (P < 0.05). The SPC lacking β-conglycinin α' and either the glycinin A1-3 or A1-5 subunits increased total T3 in males and reduced plasma enzymatic activities of creatine kinase and lactate dehydrogenase compared to casein or casein + ISF diet (P < 0.05).

CONCLUSIONS

Soy isoflavones were mainly responsible for the hypocholesterolemic effects and increased plasma free T3, whereas reduction in FFA, abdominal fat, liver weight and increased plasma total T3 were the effects of the soy proteins. Neither the α' subunit of β-conglycinin nor the A1-5 subunits of glycinin are essential for the hypolipidemic properties of soy proteins.

Artichoke extract lowered plasma cholesterol and increased fecal bile acids in Golden Syrian hamsters

A study was conducted in hamsters to determine if artichoke leaf extract (ALE) could lower plasma total and non-HDL cholesterol by increasing fecal excretion of neutral bile acids and sterols. Sixty-four Golden Syrian hamsters (8 week old) were fed control diet or a similar diet containing ALE (4.5 g/kg diet) for 6 weeks. No significant changes for total cholesterol, HDL, non-HDL cholesterol triglycerides or fecal neutral sterols and bile acids were found after 21 days for ALE-fed animals compared with controls. But after 42 days, ALE-fed male hamsters had significantly lower total cholesterol (15%), non-HDL cholesterol (30%) and triglycerides (22%) and female hamsters fed ALE showed reductions of 15% for total cholesterol, 29% for non-HDL cholesterol and 29% for triglycerides compared with controls. Total neutral sterol and bile acids concentrations increased significantly by 50% and 53% in fecal samples of ALE fed males, and 82.4% and 25% in ALE fed females compared with controls. The ALE lowered hamster plasma cholesterol levels by a mechanism involving the greater excretion of fecal bile acids and neutral sterols after feeding for 42 days.

Use of hamster as a model to study diet-induced atherosclerosis

Golden-Syrian hamsters have been used as an animal model to assess diet-induced atherosclerosis since the early 1980s. Advantages appeared to include a low rate of endogenous cholesterol synthesis, receptor-mediated uptake of LDL cholesterol, cholesteryl ester transfer protein activity, hepatic apoB-100 and intestinal apoB-48 secretion, and uptake of the majority of LDL cholesterol via the LDL receptor pathway. Early work suggested hamsters fed high cholesterol and saturated fat diets responded similarly to humans in terms of lipoprotein metabolism and aortic lesion morphology. Recent work has not consistently replicated these findings. Reviewed was the literature related to controlled hamster feeding studies that assessed the effect of strain, background diet (non-purified, semi-purified) and dietary perturbation (cholesterol and/or fat) on plasma lipoprotein profiles and atherosclerotic lesion formation. F1B hamsters fed a non-purified cholesterol/fat-supplemented diet had more atherogenic lipoprotein profiles (nHDL-C > HDL-C) than other hamster strains or hamsters fed cholesterol/fat-supplemented semi-purified diets. However, fat type; saturated (SFA), monounsaturated or n-6 polyunsaturated (PUFA) had less of an effect on plasma lipoprotein concentrations. Cholesterol- and fish oil-supplemented semi-purified diets yielded highly variable results when compared to SFA or n-6 PUFA, which were antithetical to responses observed in humans. Dietary cholesterol and fat resulted in inconsistent effects on aortic lipid accumulation. No hamster strain was reported to consistently develop lesions regardless of background diet, dietary cholesterol or dietary fat type amount. In conclusion, at this time the Golden-Syrian hamster does not appear to be a useful model to determine the mechanism(s) of diet-induced development of atherosclerotic lesions.

Isoflavone glycitein diminished plasma cholesterol in female golden Syrian hamsters

The soybean isoflavones, daidzein, genistein, and glycitein, were hypothesized to act as cholesterol-lowering components, separate from soy protein. Pure synthetic daidzein, genistein, or glycitein (0.9 mmol/kg diet) or a casein-based control diet was fed to groups of 10 female Golden Syrian hamsters for 4 weeks. Hamsters fed glycitein had significantly lower plasma total (by 15%) and non-HDL (by 24%) cholesterol compared with those fed casein (P<0.05). Daidzein and genistein's effects on these lipids did not differ from the effects of either casein or glycitein. Plasma HDL cholesterol and triglyceride concentrations were not significantly affected by dietary treatments. The percentage of urinary recovery of the ingested dose of each isoflavone was glycitein>daidzein>genistein (33.2%, 4.6%, 2.2%, respectively), with the apparent absorption of glycitein significantly greater than that of the other isoflavones. These data suggest that glycitein's greater cholesterol-lowering effect was due to its greater bioavailability, as reflected in its urinary recovery compared with that of the other isoflavones.

Bio F1B hamster: a unique animal model with reduced lipoprotein lipase activity to investigate nutrient mediated regulation of lipoprotein metabolism

Background

Bio F₁B hamster is an inbred hybrid strain that is highly susceptible to diet-induced atherosclerosis. We previously reported that feeding a high fat fish oil diet to Bio F₁B hamster caused severe hyperlipidaemia. In this study we compared the effects of various diets in the Bio F₁B hamster and the Golden Syrian hamster, which is an outbred hamster strain to investigate whether genetic background plays an important role in dietary fat mediated regulation of lipoprotein metabolism. We further investigated the mechanisms behind diet-induced hyperlipidaemia in F₁B hamster.

Methods

The Bio F₁B and Golden Syrian hamsters, 8 weeks old, were fed high fat diets rich in either monounsaturated fatty acids, an n-6: n-3 ratio of 5 or a fish oil diet for 4 weeks. Animals were fasted overnight and blood and tissue samples were collected. Plasma was fractionated into various lipoprotein fractions and assayed for triacylglycerol and cholesterol concentrations. Plasma lipoprotein lipase activity was measured using radioisotope method. Microsomal triglyceride transfer protein activity was measured in the liver and intestine. Plasma apolipoproteinB48, -B100 and apolipoprotein E was measured using Western blots. Two-way ANOVA was used to determine the effect of diet type and animal strain.

Results

The fish oil fed F₁B hamsters showed milky plasma after a 14-hour fast. Fish oil feeding caused accumulation of apolipoproteinB48 containing lipoprotein particles suggesting hindrance of triglyceride-rich lipoprotein clearance. There was no significant effect of diet or strain on hepatic or intestinal microsomal triglyceride transfer protein activity indicating that hyperlipidaemia is not due to an increase in the assembly or secretion of lipoprotein particles. F₁B hamsters showed significantly reduced levels of lipoprotein lipase activity, which was inhibited by fish oil feeding.

Conclusion

Evidence is presented for the first time that alterations in lipoprotein lipase activity and mRNA levels contribute to varied response of these hamsters to dietary fat, highlighting the importance of genetic background in the regulation of lipid and lipoprotein metabolism by dietary fats. Bio F₁B hamster may prove to be an important animal model to investigate nutrient mediated regulation of metabolic parameters under lipoprotein lipase deficiency.

Rumenic Acid Significantly Reduces Plasma Levels of LDL and Small Dense LDL Cholesterol in Hamsters Fed a Cholesterol- and Lipid-Enriched Semi-Purified Diet

Conjugated linoleic acids (CLAs) consist of a series of positional and geometrical isomers of linoleic acid. CLA have been reported to beneficially affect cardiovascular risk factors in animal models. In order to assess the role of individual CLA isomers on lipoprotein cholesterol concentration, 30 hamsters were fed for 12 weeks an hyperlipidic diet containing pure cis-9,trans-11 CLA (c9,t11) or pure trans-10, cis-12 CLA (t10,c12) isomers given alone or as a mixture. Plasma total cholesterol, LDL and HDL cholesterol concentrations were significantly lower in the c9,t11 CLA isomer fed hamsters relative to the Control group, with the most substantially effect on LDL cholesterol (-56%; P < 0.05). Plasma triacylglycerol concentrations did not differ significantly regarding those two groups. Plasma cholesterol parameters showed a tendency to decrease in the t10,c12 CLA isomer and CLA mixture fed hamsters compared with the Control group, but differences were not significant. For the first time, the atherogenic fraction of small dense LDL was investigated. Plasma small dense LDL cholesterol concentration was lower in the c9,t11 CLA relative to Control, while the t10,c12 and CLA mixture groups showed only a non significant tendency to decrease. Taken together, these data indicate that feeding rumenic acid (c9,t11 CLA) may beneficially affect lipoprotein profile in hamster fed a cholesterol- and lipid-enriched semi-purified diet, when t10,c12 CLA isomer or CLA mixture would be less active.

Rice bran oil and oryzanol reduce plasma lipid and lipoprotein cholesterol concentrations and aortic cholesterol ester accumulation to a greater extent than ferulic acid in hypercholesterolemic hamsters

Our laboratory has reported that the hypolipidemic effect of rice bran oil (RBO) is not entirely explained by its fatty acid composition. Because RBO has a greater content of the unsaponifiables, which also lower cholesterol compared to most vegetable oils, we wanted to know whether oryzanol or ferulic acid, two major unsaponifiables in RBO, has a greater cholesterol-lowering activity. Forty-eight F(1)B Golden Syrian hamsters (Mesocricetus auratus) (BioBreeders, Watertown, MA) were group housed (three per cage) in cages with bedding in an air-conditioned facility maintained on a 12-h light/dark cycle. The hamsters were fed a chow-based hypercholesterolemic diet (HCD) containing 10% coconut oil and 0.1% cholesterol for 2 weeks, at which time they were bled after an overnight fast (16 h) and segregated into 4 groups of 12 with similar plasma cholesterol concentrations. Group 1 (control) continued on the HCD, group 2 was fed the HCD containing 10% RBO in place of coconut oil, group 3 was fed the HCD plus 0.5% ferulic acid and group 4 was fed the HCD plus 0.5% oryzanol for an additional 10 weeks. After 10 weeks on the diets, plasma total cholesterol (TC) and non-high-density lipoprotein cholesterol (HDL-C) (very low- and low-density lipoprotein) concentrations were significantly lower in the RBO (-64% and -70%, respectively), the ferulic acid (-22% and -24%, respectively) and the oryzanol (-70% and -77%, respectively) diets compared to control. Plasma TC and non-HDL-C concentrations were also significantly lower in the RBO (-53% and -61%, respectively) and oryzanol (-61% and -70%, respectively) diets compared to the ferulic acid. Compared to control and ferulic acid, plasma HDL-C concentrations were significantly higher in the RBO (10% and 20%, respectively) and oryzanol (13% and 24%, respectively) diets. The ferulic acid diet had significantly lower plasma HDL-C concentrations compared to the control (-9%). The RBO and oryzanol diets were significantly lower for plasma triglyceride concentrations compared to the control (-53% and -65%, respectively) and ferulic acid (-47% and -60%, respectively) diets. Hamsters fed the control and ferulic acid diets had significantly higher plasma vitamin E concentrations compared to the RBO (201% and 161%, respectively) and oryzanol (548% and 462%, respectively) diets; the ferulic acid and oryzanol diets had significantly lower plasma lipid hydroperoxide levels than the control (-57% and -46%, respectively) diet. The oryzanol-fed hamsters excreted significantly more coprostenol and cholesterol in their feces than the ferulic acid (127% and 120%, respectively) diet. The control diet had significantly greater aortic TC and FC accumulation compared to the RBO (115% and 89%, respectively), ferulic acid (48% and 58%, respectively) and the oryzanol (74% and 70%, respectively) diets. However, only the RBO and oryzanol diets had significantly lower aortic cholesterol ester accumulation compared to the control (-73% and -46%, respectively) diet. The present study suggests that at equal dietary levels, oryzanol has a greater effect on lowering plasma non-HDL-C levels and raising plasma HDL-C than ferulic acid, possibly through a greater extent to increase fecal excretion of cholesterol and its metabolites. However, ferulic acid may have a greater antioxidant capacity via its ability to maintain serum vitamin E levels compared to RBO and oryzanol. Thus, both oryzanol and ferulic acid may exert similar antiatherogenic properties, but through different mechanisms.

High urinary isoflavone excretion phenotype decreases plasma cholesterol in golden Syrian hamsters fed soy protein

Apparent absorption of isoflavones varies greatly among individuals but is relatively stable within an individual. We hypothesized that high urinary isoflavone excreters would show less plasma non-HDL cholesterol (non-HDL-C) than low isoflavone excreters after soy protein feeding. Fifty Golden Syrian hamsters were fed a high-fat/casein diet (n = 10) or a high-fat/soy protein diet (n = 40) for 4 wk. We identified 2 distinct urinary isoflavone excretion phenotypes based upon HPLC analysis of urinary glycitein using a pairwise correlation plots analysis, or based upon total urinary isoflavone using a hierarchical cluster test. High isoflavone excreters showed greater urinary isoflavones (P < 0.05) than did low isoflavone excreters at wk 1 and 4. The low urinary glycitein excretion phenotype was more stable than the high urinary glycitein excretion phenotype by McNemar's test. High urinary isoflavone excreters had significantly less non-HDL-C than did the low isoflavone excreters or casein-fed controls (P < 0.05). Plasma total and non-HDL-C were negatively correlated with urinary daidzein, glycitein, and total isoflavone excretion (r = -0.45 to -0.58, P < 0.05). Urinary isoflavone excretion phenotypes predicted the cholesterol-lowering efficacy of soy protein. Isoflavone absorbability, probably due to gut microbial ecology, is an important controllable variable in studies of effects of soy protein on blood lipids.

Multiple mechanisms of hypocholesterolemic action of pactimibe, a novel acyl-coenzyme A:cholesterol acyltransferase inhibitor

Novel acyl-coenzyme A:cholesterol acyltransferase inhibitor pactimibe has been evaluated in vivo; it exhibited significant serum cholesterol lowering activities in hamsters and monkeys without affecting non-high density lipoprotein cholesterol levels. The mechanism of the hypocholesterolemic action of pactimibe was examined in normocholesterolemic hamsters in this study. Results with the dual-isotope plasma ratio method indicated that pactimibe inhibits cholesterol absorption from the intestine, reduces cholesteryl ester formation in the liver, and enhances its elimination from the body. The Triton WR-1339 experiment showed that pactimibe inhibited secretion of very low density lipoprotein cholesterol from the liver. These results suggest that pactimibe is likely to have multiple mechanisms of action responsible for its effectiveness in reducing serum cholesterol.

Conjugated linoleic acid isomers reduce blood cholesterol levels but not aortic cholesterol accumulation in hypercholesterolemic hamsters

The aim of the present study was to characterize plasma lipids and lipoprotein cholesterol and glucose concentrations in hamsters fed either cis-9,trans-11 CLA (9c,11 tCLA); trans-10,cis-12 CLA (10t,12c CLA); or linoleic acid (LA) on the accumulation of aortic cholesterol in hypercholesterolemic hamsters. One hundred male F1B strain Syrian Golden Hamsters (Mesocricetus auratus) (BioBreeders Inc., Watertown, MA) approximately 9 wk of age were housed in individual stainless steel hanging cages at room temperature with a 12-h light/dark cycle. Hamsters were given food and water ad libitum. Following a 1-wk period of acclimation, the hamsters were fed a chow-based (nonpurified) hypercholesterolemic diet (HCD) containing 10% coconut oil (92% saturated fat) and 0.1% cholesterol for 2 wk. After an overnight fast, the hamsters were bled and plasma cholesterol concentrations were measured. The hamsters were then divided into 4 groups of 25 based on similar mean plasma VLDL and LDL cholesterol (nonHDL-C) concentrations. Group 1 remained on the HCD (control). Group 2 was fed the HCD plus 0.5% 9c,11t CLA isomer. Group 3 was fed the HCD plus 0.5% 10t,12c CLA isomer. Group 4 was fed the HCD plus 0.5% LA. Compared with the control, both CLA isomers and LA had significantly lower plasma total cholesterol and HDL cholesterol concentrations (P < 0.001) after 12 but not 8 wk of treatment and were not significantly different from each other. Also, both CLA isomers had significantly lower plasma nonHDL-C concentrations (P < 0.01) compared with the control after 12 but not 8 wk of treatment and were not significantly different from each other or the LA-fed hamsters. Plasma TG concentrations were significantly higher (P < 0.004) with the 10t, 12c CLA isomer compared with the other treatments at 8 but not at 12 wk of treatment. Plasma TG concentrations were also significantly lower (P < 0.03) with the 9c,11t CLA isomer compared with the control at 12 wk of treatment. Also, the 10t,12c CLA isomer and LA had significantly higher plasma glucose concentrations compared with the control and 9c,11t CLA isomer (P < 0.008) at 12 wk of treatment, whereas at 8 wk, only the LA treatment had significantly higher plasma glucose concentrations (P < 0.001) compared with the 9c,11t CLA isomer. Although liver weights were significantly higher in 10t,12c CLA isomer-fed hamsters, liver total cholesterol, free cholesterol, cholesterol ester, and TG concentrations were significantly lower in these hamsters compared with hamsters fed the control, 9c,11t CLA isomer, and LA diets (P< 0.05). The 9c,11t CLA isomer and LA diets tended to reduce cholesterol accumulation in the aortic arch, whereas the 10t,12c CLA isomer diet tended to raise cholesterol accumulation compared with the control diet; however, neither was significant. In summary, no differences were observed between the CLA isomers for changes in plasma lipids or lipoprotein cholesterol concentrations. However, the 9c,11t CLA isomer did appear to lower plasma TG and glucose concentrations compared with the 10t,12c CLA isomer. Such differences may increase the risk of insulin resistance and type 2 diabetes in humans when the 10t,12c CLA isomer is fed separately.

Different palm oil preparations reduce plasma cholesterol concentrations and aortic cholesterol accumulation compared to coconut oil in hypercholesterolemic hamsters

Several studies have reported on the effect of refined, bleached and deodorized palm oil (RBD-PO) incorporation into the diet on blood cholesterol concentrations and on the development of atherosclerosis. However, very little work has been reported on the influence of red palm oil (RPO), which is higher in carotenoid and tocopherol content than RBD-PO. Thus, we studied the influence of RPO, RBD-PO and a RBD-PO plus red palm oil extract (reconstituted RBD-PO) on plasma cholesterol concentrations and aortic accumulation vs. hamsters fed coconut oil. Forty-eight F1B Golden Syrian hamsters (Mesocricetus auratus) (BioBreeders, Watertown, MA) were group housed (three/cage) in hanging polystyrene cages with bedding in an air-conditioned facility maintained on a 12-h light/dark cycle. The hamsters were fed a chow-based hypercholesterolemic diet (HCD) containing 10% coconut oil and 0.1% cholesterol for 2 weeks at which time they were bled after an overnight fast and segregated into four groups of 12 with similar plasma cholesterol concentrations. Group 1 continued on the HCD, Group 2 was fed the HCD containing 10% RPO in place of coconut oil, Group 3 was fed the HCD containing 10% RBD-PO in place of coconut oil and Group 4 was fed the HCD with 10% reconstituted RBD-PO for an additional 10 weeks. Plasma total cholesterol (TC) and non-high-density lipoprotein-cholesterol (HDL-C) (very low- and low-density lipoprotein) concentrations were significantly lower in the hamsters fed the RPO (-42% and -48%), RBD-PO (-32% and -36%) and the reconstituted RBD-PO (-37% and -41%) compared to the coconut oil-fed hamsters. Plasma HDL-C concentrations were significantly higher by 14% and 31% in hamsters fed the RBD-PO and RPO compared to the coconut oil-fed hamsters. Plasma triglyceride (TG) concentrations were significantly lower in hamsters fed RBD-PO (-32%) and the reconstituted RBD-PO (-31%) compared to the coconut oil-fed hamsters. The plasma gamma-tocopherol concentrations were higher in the coconut oil-fed hamsters compared to the hamsters fed the RPO (60%), RBD-PO (42%) and the reconstituted RBD-PO (49%), while for plasma alpha-tocopherol concentrations, the coconut oil-fed hamsters were significantly higher than only the RPO-fed hamsters (21%). The coconut oil-fed hamsters also had significantly higher plasma lipid hydroperoxide concentrations compared to RBD-PO (112%) and the reconstituted RBD-PO (485%). The hamsters fed the coconut oil diet excreted significantly more fecal total neutral sterols and cholesterol compared to the hamsters fed the RBD-PO (158% and 167%, respectively). The coconut oil-fed hamsters had significantly higher levels of aortic total, free and esterified cholesterol compared to the hamsters fed the RPO (74%, 50% and 225%, respectively), RBD-PO (57%, 48% and 92%, respectively) and the reconstituted RBD-PO (111%, 94% and 94%, respectively). Also, aortic free/ester cholesterol ratio in the aortas of hamsters fed RPO was significantly higher than in those fed the coconut oil (124%). In conclusion, hamsters fed the three palm oil preparations had lower plasma TC and non-HDL-C and higher HDL-C concentrations while accumulating less aortic cholesterol concentrations compared to hamsters fed coconut oil.

Hypocholesterolemic effect of physically refined rice bran oil: studies of cholesterol metabolism and early atherosclerosis in hypercholesterolemic hamsters

Physically refined rice bran oil containing 2-4% nontriglyceride components as compared to other vegetable oils appears to be associated with lipid lowering and antiinflammatory properties in several rodent, primate and human models. These experiments were designed to investigate possible mechanisms for the hypocholesterolemic effect of the physically refined rice bran oil and to examine its effect on aortic fatty streak formation. In the first experiment, 30 hamsters were fed, for 8 weeks, chow-based diets plus 0.03% added cholesterol and 5% (wt/wt) coconut, canola, or physically refined rice bran oil (COCO, CANOLA or PRBO animal groups, respectively). Both plasma total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) were significantly reduced in PRBO but not in CANOLA relative to COCO. PRBO also showed a significant 15-17% reduction in cholesterol absorption and significant 30% increase in neutral sterol (NS) excretion with no effect on bile acid (BA) excretion. Both CANOLA and PRBO showed a significant 300-500% increase in intestinal 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and significant (>25%) decrease in hepatic HMG-CoA reductase activities with respect to COCO. In a second experiment, 36 hamsters were fed chow-based diets with 0.05% added cholesterol, 10% coconut oil and 4% additional COCO, CANOLA or PRBO. Relative to COCO and CANOLA, plasma TC and LDL-C were significantly reduced in PRBO. Early atherosclerosis (fatty streak formation) was significantly reduced (48%) only in PRBO, relative to the other two. These results suggest that the lipid lowering found in PRBO is associated with decreased cholesterol absorption, but not hepatic cholesterol synthesis, and that the decrease in fatty streak formation with this oil may be associated with its nontriglyceride components not present in the other two diets.

Soyasaponins lowered plasma cholesterol and increased fecal bile acids in female golden Syrian hamsters

A study was conducted in hamsters to determine if group B soyasaponins improve plasma cholesterol status by increasing the excretion of fecal bile acids and neutral sterols, to identify group B soyasaponin metabolites, and to investigate the relationship between a fecal group B soyasaponin metabolite and plasma lipids. Twenty female golden Syrian hamsters, 11-12 weeks old and 85-125 g, were randomly assigned to a control diet or a similar diet containing group B soyasaponins (containing no isoflavones), 2.2 mmol/kg, for 4 weeks. Hamsters fed group B soyasaponins had significantly lower plasma total cholesterol (by 20%), non-high-density lipoprotein (HDL) cholesterol (by 33%), and triglycerides (by 18%) compared with those fed casein (P < 0.05). The ratio of total cholesterol to HDL cholesterol was significantly lower (by 13%) in hamsters fed group B soyasaponins than in those fed casein (P < 0.05). The excretion of fecal bile acids and neutral sterols was significantly greater (by 105% and 85%, respectively) in soyasaponin-fed hamsters compared with those fed casein (P < 0.05). Compared with casein, group B soyasaponins lowered plasma total cholesterol levels and non-HDL cholesterol levels by a mechanism involving greater excretion of fecal bile acids and neutral sterols. Hamsters fed group B soyasaponins statistically clustered into two fecal soyasaponin metabolite-excretion phenotypes: high excreters (n = 3) and low excreters (n = 7). When high and low producers of this soyasaponin metabolite were compared for plasma cholesterol status, the high producers showed a significantly lower total-cholesterol-to-HDL-cholesterol ratio compared with the low producers (1.38 +/- 0.7 vs. 1.59 +/- 0.13; P < 0.03). Greater production of group B soyasaponin metabolite in hamsters was associated with better plasma cholesterol status, suggesting that gut microbial variation in soyasaponin metabolism may influence the health effects of group B soyasaponins.

Flaxseed reduces plasma cholesterol and atherosclerotic lesion formation in ovariectomized Golden Syrian hamsters

BACKGROUND

Dietary modification contributes significantly in reducing cardiovascular disease (CVD) risk factors including lowering cholesterol and atherosclerosis. The purpose of this study was to investigate the effects of flaxseed, a rich source of lignans, alpha-linolenic acid and soluble fiber mucilage, on the prevention of ovariectomy-induced rise in total cholesterol and atherosclerotic lesions.

METHODS

Seventy-two 6-month-old female Golden Syrian hamsters were either ovariectomized (ovx) or sham-operated (sham) and randomly assigned to six groups (n = 12): sham, ovx, or ovx plus either 17beta-estradiol (E(2), 10 microg/kg body weight) or semi-purified diet adjusted for macronutrients and fiber to contain one of the three doses of flaxseed (7.5, 15, or 22.5%) for 120 days.

RESULTS

Ovariectomy significantly elevated plasma total-, HDL-, and free-cholesterol concentrations. Similar to estrogen, all doses of flaxseed were effective in preventing the ovx-induced rise in plasma total cholesterol. Triglyceride concentrations were significantly higher in the flax-fed hamsters. There were no significant differences in plasma non-HDL- and esterified-cholesterol among the treatment groups. Ovariectomy also increased the number of hamsters with lesions and the aortic fatty streak area. All three doses of flaxseed reduced the fatty streak area and the incidence of lesions to levels similar to the sham group.

CONCLUSION

The findings of this study show that flaxseed is beneficial in reducing plasma cholesterol and plaque formation induced by ovarian hormone deficiency.

Decreased aortic early atherosclerosis and associated risk factors in hypercholesterolemic hamsters fed a high- or mid-oleic acid oil compared to a high-linoleic acid oil

Currently, diets higher in polyunsaturated fat are believed to lower blood cholesterol concentrations, and thus reduce atherosclerosis, greater than diets containing high amounts of saturated or possibly even monounsaturated fat. The present study was designed to investigate the effect of diets containing mid- or high-linoleic oil versus the typical high-linoleic sunflower oil on LDL oxidation and the development of early atherosclerosis in a hypercholesterolemic hamster model. Animals were fed a hypercholesterolemic diet containing 10% mid-oleic sunflower oil, high-oleic olive oil, or high-linoleic sunflower oil (wt/wt) plus 0.4% cholesterol (wt/wt) for 10 weeks. After 10 weeks of dietary treatment, only the animals fed the mid-oleic sunflower oil had significant reductions in plasma LDL-C levels (-17%) compared to the high-linoleic sunflower oil group. The high-oleic olive oil-fed hamsters had significantly higher plasma triglyceride levels (+41%) compared to the high-linoleic sunflower oil-fed hamsters. The tocopherol levels in plasma LDL were significantly higher in hamsters fed the mid-oleic sunflower oil (+77%) compared to hamsters fed either the high-linoleic sunflower or high-oleic olive oil. Measurements of LDL oxidation parameters, indicated that hamsters fed the mid-oleic sunflower oil and high-oleic olive oil diets had significantly longer lag phase (+66% and +145%, respectively) and significantly lower propagation rates (-26% and -44%, respectively) and conjugated dienes formed (-17% and -25%, respectively) compared to the hamsters fed the high-linoleic sunflower oil. Relative to the high-linoleic sunflower oil, aortic cholesterol ester was reduced by -14% and -34% in the mid-oleic sunflower oil and high-oleic olive oil groups, respectively, with the latter reaching statistical significance. Although there were no significant associations between plasma lipids and lipoprotein cholesterol with aortic total cholesterol and cholesterol esters for any of the groups, the lag phase of conjugated diene formation was inversely associated with both aortic total and esterified cholesterol in the high-oleic olive oil-fed hamsters (r = -0.69, P < 0.05). The present study suggests that mid-oleic sunflower oil reduces risk factors such as lipoprotein cholesterol and oxidative stress associated with early atherosclerosis greater than the typical high-linoleic sunflower oil in hypercholesterolemic hamsters. The high-oleic olive oil not only significantly reduced oxidative stress but also reduced aortic cholesterol ester, a hallmark of early aortic atherosclerosis greater than the typical high-linoleic sunflower oil.

Effects of ileo-rectal anastomosis on cholesterol metabolism in pigs fed either casein or extruded soya beans

The importance of legume proteins in cholesterol metabolism has been recognised, but the hindgut contribution is still unclear. The present work was undertaken to address the role of the caecum-colon in cholesterol metabolism in intact (I) and ileo-rectal anastomosed (IRA) pigs fed with casein or extruded soyabean (ES) diets. Four groups of six growing pigs were assigned to the treatments (casein-I, casein-IRA, ES-I, ES-IRA) for 3 weeks. Plasma total cholesterol, LDL- and HDL-cholesterol were not modified by surgery or diet. In the liver, the ES diet significantly depressed non-esterified, esterified and total cholesterol. The treatments did not affect hepatic 3-hydroxy-3-methylglutaryl CoA reductase, cholesterol 7alpha-hydroxylase or sterol 27-hydroxylase activities. In the gallbladder bile of ES-fed pigs, total cholesterol was depressed while total bile acid concentration was increased. IRA and the ES diet markedly decreased the biliary bile acid microbial metabolites (namely hyodeoxycholic acid) and increased the primary bile acids (mainly hyocholic acid). The concentration of bile hydrophobic acids was decreased only by the ES diet. Faecal neutral sterol output was increased in ES-fed pigs, but the bile acid and the sum of neutral and acidic steroid outputs were not. Microbial transformation of neutral and acidic steroids was markedly reduced by IRA, especially in the ES-fed pigs. Thus, surgery and ES modulated the steroid profile but the caecum-colon did not seem to play a crucial role in determining cholesterolaemia in pigs.

Study of diet-induced changes in lipoprotein metabolism in two strains of Golden-Syrian hamsters

The objective of this study was to characterize two strains of Golden-Syrian hamsters for use in the study of diet-induced changes in lipoprotein metabolism. In Experiment 1, the time course and response to dietary saturated fat was investigated for serum lipoprotein profiles and aortic lesion formation in Golden-Syrian hamsters from Charles River Laboratories, Wilmington, MA (CR) and Bio Breeders, Watertown, MA (F(1)B). Hamsters were fed a nonpurified diet containing 10 g/100 g saturated fat and 0.1 g/100 g dietary cholesterol. After 12 wk, CR hamsters had significantly lower serum total and non-HDL cholesterol (TC and nHDL-C) levels, but higher aortic cholesteryl ester (CE) than the F(1)B hamsters (P < 0.05). In Experiment 2, CR hamsters were fed a nonpurified diet containing 10 g/100 g saturated fat and 0.1, 0.5 or 1 g/100 g dietary cholesterol. After 10 wk of dietary intervention, TC and nHDL-C levels were significantly higher in the 0.5 and 1.0 g/100 g cholesterol groups than in the 0.1 g/100 g cholesterol group. These levels declined after 20 wk of dietary intervention in all groups, potentially reflecting the toxic effect of high cholesterol intakes. CR hamsters fed a 10 g/100 g saturated fat containing 0.1 g/100 g dietary cholesterol for 10 wk appear to be a good model for investigating diet-induced change in plasma lipids.

Doxazosin, an alpha-1 antagonist, prevents further progression of the advanced atherosclerotic lesion in hypercholesterolemic hamsters

The aim of this study was to examine the effect of doxazosin (DOX) on the further progression and regression of the advanced atherosclerotic lesion in the hypercholesterolemic hamster. Thirty-six, male F(1)B Golden Syrian hamsters, 10 weeks of age, were divided into 3 groups of 12 and fed a nonpurified hypercholesterolemic diet (HCD) containing 10% coconut oil and 0.1% cholesterol (wt/wt) for 9 months (HCD 9). One group of hamsters was euthanized at 9 months and their aortas were collected, fixed, and stored until analysis. The remaining hamsters were either maintained on the HCD for an additional 6 months (HCD 15) or fed the HCD plus 20 mg/kg/d DOX for the 6 months. At the end of the study (15 months), the DOX-treated hamsters had significantly lower plasma total cholesterol (TC) (-68%), low-density lipoprotein-cholesterol (LDL-C) (-73%), and triglycerides (TG) (-74%) compared with the HCD 15. The lumenal narrowing and intimal thickening atherosclerotic lesions were significantly less in the DOX-treated hamsters compared with the HCD 15 (-66% and -70%, respectively). These data suggest that DOX treatment prevents further progression of the advanced atherosclerotic lesion possibly by lowering plasma TC, LDL-C, and TG in hypercholesterolemic hamsters.

Soy protein with or without isoflavones, soy germ and soy germ extract, and daidzein lessen plasma cholesterol levels in golden Syrian hamsters

Dietary isolated soy protein (ISP, containing approximately equal amounts of daidzein and genistein), ethanol-extracted ISP (ISP (-)), soygerm or soygerm extract (containing large amounts of daidzein and glycitein and little genistein) and the isoflavone, daidzein, were hypothesized to lessen plasma cholesterol in comparison with casein. Sixty male and 60 female golden Syrian hamsters (6-8 weeks of age) were randomly assigned to six treatments fed for 10 weeks. Four of the experimental diets (ISP, daidzein, soygerm, and soygerm extract) contained 1.3 mmol total isoflavones/kg. The ISP (-) diet contained 0.013 mmol isoflavone/kg, whereas the casein diet contained no isoflavones. Hamsters fed ISP, ISP (-), daidzein, soygerm, and soygerm extract had significantly less plasma total cholesterol (by 16%-28%), less non-HDL cholesterol (by 15%-50%) and less non-HDL/HDL cholesterol ratios compared with hamsters fed casein (P < 0.01). For male hamsters, there were no differences among treatments in plasma HDL concentrations. Female hamsters fed ISP (-) had significantly greater HDL levels (P < 0.01) than females fed casein or daidzein. Triglyceride concentration was significantly less in hamsters fed ISP (-) compared with the casein-fed females. Because soy protein with or without isoflavones, soygerm and soygerm extract, and daidzein lessened plasma cholesterol to an approximately equal extent, soy protein alone, varying mixtures of isoflavones, and other extractable components of soy are responsible for cholesterol-lessening effects of soy foods, mainly due to their effects to lessen LDL cholesterol.

Interaction between dietary protein and fat in triglyceride metabolism in the rat: effects of soy protein and menhaden oil

The objective of the present study was to determine the mechanisms by which dietary proteins interact with dietary lipids in the regulation of triglyceridemia in rats. Male Sprague-Dawley rats (n = 56) were subjected to 28-d experimental diets containing different combinations of proteins (20% w/w) and lipid sources (14% w/w): (i) casein-menhaden oil, (ii) casein-beef tallow, (iii) soy protein-menhaden oil, and (iv) soy protein-beef tallow. Significant protein-lipid interactions were observed on triglyceridemia and hepatic cholesterol in fasted rats. The combination of casein and beef tallow was associated with high plasma TG and hepatic cholesterol concentrations, which were reduced by substitution either of soy for casein or of menhaden oil for beef tallow. Therefore, triglyceridemia and liver cholesterol remained low with soy protein feeding, independently of the lipid source, as well as with menhaden oil feeding, regardless of the protein source. The menhaden oil diets reduced plasma cholesterol, hepatic TG, and TG secretion compared with beef tallow diets independently of the dietary protein source. Modifying the source of dietary proteins and lipids had no effect on post-heparin plasma lipoprotein lipase activity. These results demonstrate that soy protein can lower rat triglyceridemia relative to casein when associated with beef tallow consumption, whereas menhaden oil can attenuate hypertriglyceridemia when rats are fed casein. The data further suggest that part of the hypotriglyceridemic effect of soy protein in the rat may be mediated by reduced hepatic lipid synthesis, as is the case for menhaden oil.

Decreased aortic early atherosclerosis in hypercholesterolemic hamsters fed oleic acid-rich TriSun oil compared to linoleic acid-rich sunflower oil

Previous studies have demonstrated that low density lipoprotein (LDL) enriched in polyunsaturated fatty acids (PUFA) are more susceptible to oxidation (ex vivo) than those containing monounsaturated fatty acids (MUFA). To test whether this observation was associated with various parameters considered to be related with the development of early aortic atherosclerosis, hamsters were fed commercial hypercholesterolemic diets (HCD) containing either the PUFA, sunflower oil (SF) or the MUFA, TriSun oil (TS) at 10% with 0.4% cholesterol (wt/wt). LDL isolated from hamsters fed TS had significantly longer lag phase (30%, P < 0.05), a decreased propagation phase (-62%, P < 0.005), and fewer conjugated dienes formed (-37%, P < 0.007) compared to hamsters fed SF. Aortic vasomotor function, measured as degree of aortic relaxation, was significantly greater in the TS vs SF-fed hamsters whether acetylcholine or the calcium ionophore A23187 was used as the endothelium-dependent agonist. As a group, the SF-fed hamsters had significantly more early atherosclerosis than hamsters fed TS (46%, P < 0.006). When animals across the two diets were pair-matched by plasma LDL-C levels, there was an 82% greater mean difference (P < 0.002) in early atherosclerosis in the SF versus the TS-fed hamsters. While there were no significant associations with plasma lipids and lipoprotein cholesterol, early atherosclerosis was significantly correlated with lag phase (r = -0.67, p < 0.02), rate of LDL conjugated diene formation (r = 0.74, p < 0.006) and maximum dienes formed (r = 0.67, p < 0.02). Compared to TS-fed animals, aortic sections from hamsters fed the SF-containing diet revealed that the cytoplasm of numerous foam cells in the subendothelial space reacted positively with the monoclonal anti-bodies MDA-2 and NA59 antibody, epitopes found on oxidized forms of LDL. The present study suggests that compared to TS, hamsters fed the SF-diet demonstrated enhanced LDL oxidative susceptibility, reduced aortic relaxation, greater early aortic atherosclerosis and accumulation of epitopes found on oxidized forms of LDL.

Influence of photoperiod, laboratory caging and aging on plasma lipid response to an atherogenic diet among F1B hamsters

The effects and interactions of photoperiod, animal caging, aging and diet on plasma lipid levels in male F1B hamsters were examined in the current study. Sixteen young and sixteen old animals were housed one or four per cage. Eight young animals from each housing group were placed in an animal room with either 12/12 h (PT-12) or 10/14 h (PT-10) light/dark cycle while the sixteen old animals were maintained under a PT-12 light cycle. Plasma cholesterol and triglyceride concentrations were determined in all animals after a 2-week period of acclimation on chow diet and following 4-week intervention on atherogenic diet. Baseline total cholesterol (TC) levels were 131+/-25 mg/dl and 142+/-39 mg/dl for young and old animals, respectively, while baseline triglyceride (Tg) levels were 202+/-48 mg/dl and 160+/-37 mg/dl respectively for the same animals. Following 4-weeks on an atherogenic diet, single-caged PT 12 animals had elevated but significantly lower TC levels than group-caged animals (161+/-30 mg/dl and 240 +/-58 mg/dl, respectively) while single and group housed PT10 animals had TC levels of 296+/-75 mg/dl and 351+/-124 mg/dl, respectively. Similarly, plasma Tg levels rose to 330+/-100 mg/dl and 486+/-200 mg/dl in single and group housed PT12 animals (respectively) and to 668+/-270 mg/dl and 545+/-199 mg/dl in single and group housed PT10 animals (respectively). No significant changes related to atherogenic diet were observed in plasma TC or Tg levels in the older animals. Although caging conditions influence the cholesterol and triglyceride response to the atherogenic diet (p<.05), light cycle photoperiod seems to exert a greater effect (p<.005). In conclusion, photoperiod length dramatically affects diet-induced plasma lipid concentrations in young male F1B hamsters, and thus needs be considered in experimental designs of animal-housed lipid research.

Ethanol-extracted soy protein isolate does not modulate serum cholesterol in golden Syrian hamsters: a model of postmenopausal hypercholesterolemia

Soy protein consumption has been linked to reduction in hypercholesterolemia, a risk for coronary heart disease. However, to what extent soy protein itself or its non-nutritive components, e.g., isoflavones and saponins, exert this cholesterol-lowering effect requires further investigation. To evaluate the effect of the protein component alone on lipid variables, ethanol-extracted, isoflavone-depleted soy protein isolate (SPe) was studied in ovarian hormone-deficient hamsters. Forty-eight 6-month-old female Golden Syrian hamsters were either sham-operated or ovariectomized and fed casein-based or SPe-based diets for 70 d. Ovariectomy, but not protein source, significantly (P < 0.05) increased serum phospholipids and total, non-high density lipoprotein, free and esterified cholesterol concentrations. Serum HDL cholesterol concentrations were not altered with either treatment. No significant differences were observed in liver total lipids or liver total cholesterol among the groups. Soy protein isolate, however, lowered serum triglyceride concentrations in both sham-operated and ovariectomized hamsters. These findings confirm the ovariectomized hamster as a model of postmenopausal hypercholesterolemia. The results are consistent with earlier observations that isoflavones or other nonprotein components, perhaps in combination with soy protein, play an important role in exerting this hypocholesterolemic effect. Further studies are needed to investigate whether isolated nonprotein components of soy would be able to prevent the ovarian hormone deficiency-associated rise in serum cholesterol regardless of dietary protein source.

A buckwheat protein product suppresses gallstone formation and plasma cholesterol more strongly than soy protein isolate in hamsters

This study was conducted to investigate the effects of a buckwheat protein product (BWP) on plasma cholesterol, gallbladder bile composition and fecal steroid excretion in hamsters fed diets with 5 g/kg cholesterol. Diets also contained 200 g/kg of casein, soy protein isolate (SPI) or BWP as protein sources. After 2 wk, plasma and liver concentrations of cholesterol in the hamsters fed BWP were significantly lower than those in the hamsters fed casein and SPI. The molar proportion of cholesterol in gallbladder bile was significantly lower in the BWP group than in the other groups, whereas that of bile acids was slightly higher in the BWP group (P Collapse

Key Words Collapse

MESH Headings

• Animals
• Bile/chemistry
• Cholelithiasis/pathology
• Cholesterol/blood
• Cholesterol, Dietary/pharmacology
• Cricetinae
• Energy Intake/drug effects
• Fagopyrum
• Feces/chemistry
• Lipid Metabolism
• Lipids/blood
• Liver/metabolism
• Male
• Mesocricetus
• Plant Proteins/pharmacology
• Glycine max
• Weight Gain/drug effects

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Grants Collapse

Affiliation(s)

H Tomotake Development, Health Care, Kissei Pharmaceutical Company, Ltd., Matsumoto 399-8710, Japan
I Shimaoka
J Kayashita
F Yokoyama
M Nakajoh
N Kato

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Cholesteryl ester enrichment of plasma low-density lipoproteins in hamsters fed cereal-based diets containing cholesterol

Male Syrian hamsters were fed 0.02, 0.03, or 0.05% cholesterol to test the hypothesis that moderate cholesterol intake increases the cholesteryl ester content of the plasma low-density lipoproteins (LDL). Dietary cholesterol levels of 0.02%-0.05% were chosen to reflect typical human intakes of cholesterol. Hamsters were fed ad libitum a cereal-based diet (modified NIH-07 open formula) for 15 weeks. Increasing dietary cholesterol from 0.02% to 0.05% resulted in significantly increased plasma LDL and high-density lipoprotein cholesterol concentration, increased liver cholesterol concentration, and increased total aorta cholesterol content. The cholesteryl ester content of plasma LDL was determined as the molar ratio of cholesteryl ester to apolipoprotein B and to surface lipid (i.e., phospholipid + free cholesterol). Increasing dietary cholesterol from 0.02% to 0.05% resulted in significantly increased cholesteryl ester content of LDL particles. Furthermore, cholesteryl ester content of LDL was directly associated with increased total aorta cholesterol, whereas a linear relationship between plasma LDL cholesterol concentration and aorta cholesterol was not observed. Thus, the data suggest that LDL cholesteryl ester content may be an important atherogenic feature of plasma LDL.

Gender differences in response to a hypercholesterolemic diet in hamsters: effects on plasma lipoprotein cholesterol concentrations and early aortic atherosclerosis

Gender is a strong predictor of coronary heart disease (CHD) susceptibility and reports indicate that males are more likely to develop CHD compared to age-matched premenopausal females. To test whether similar gender differences exist in hamsters, 16 male and 16 female F1B Golden Syrian hamsters, aged 10 weeks, were fed a hypercholesterolemic nonpurified diet (HCD) containing 10% coconut oil and 0.05% cholesterol for 12 weeks. Plasma lipid and lipoprotein cholesterol concentrations, LDL oxidative susceptibility, LDL tocopherol concentrations, LDL fatty acid composition, LDL particle size, plasma estradiol and testosterone concentrations, and early aortic atherosclerosis were analyzed. Female hamsters had significantly lower plasma total cholesterol and nonhigh-density lipoprotein cholesterol (nonHDL-C) and greater high-density lipoprotein cholesterol (HDL-C) concentrations compared to male hamsters (-15, -33, and 33%; respectively). Female hamsters had significantly greater LDL particle size (4%), LDL 22:6 (21%) fatty acid, and rate of LDL oxidation (34%) compared to male hamsters. Female hamsters had a significantly higher concentration of plasma estradiol (49%) compared to male hamsters. Female hamsters also had significantly less early aortic atherosclerosis compared to male hamsters (-77%). In female hamsters, aortic fatty streak formation was significantly associated with plasma nonHDL-C (r = 0.76, P<0.0007), LDL particle size (r = -0.66, P<0.005), plasma TC (r = 0.68. P<0.004), and lag phase of LDL oxidation (r = 0.84. P<0.02). In male hamsters, aortic fatty streak formation was significantly associated with plasma nonHDL-C (r = 0.52, P<0.04), plasma TC (r = 0.55, P<0.03), plasma TG (r = 0.79, P<0.0003), and LDL 22:6 (r = -0.78, P<0.03) with no association with any measures of LDL oxidation susceptibility. This study demonstrates that female hamsters have an improved plasma lipoprotein cholesterol profile, larger LDL particle size, and less early aortic atherosclerosis compared to male hamsters fed the same HCD.

Hamsters and guinea pigs differ in their plasma lipoprotein cholesterol distribution when fed diets varying in animal protein, soluble fiber, or cholesterol content

There were two objectives to these studies: 1) to compare the lipoprotein cholesterol distribution in two animal models in response to different dietary treatments and 2) to assess whether the hypercholesterolemia induced by high cholesterol intake could be reversed by consumption of vegetable-protein and/or dietary fiber. Guinea pigs, which carry the majority of plasma cholesterol in LDL, and hamsters, with a higher distribution of cholesterol in HDL, were evaluated in three different studies. In Study 1, animals were fed semi-purified diets for 4 wk with proportions of 60:40, 20:80 or 0:100 (w/w) of casein/ soybean protein. Hamsters and guinea pigs that consumed 100% soybean protein had lower plasma total cholesterol (TC) than those fed diets containing casein (P < 0.01). In Study 2, three doses of dietary pectin (2.7, 5.4, or 10.7 g/100g) added in place of cellulose were tested. Intake of 10.7 g/100 g pectin resulted in the lowest plasma TC concentrations for both species (P < 0.01). Although the TC lowering was similar in studies 1 and 2, the lipoprotein cholesterol distribution differed. Whereas the differences in plasma cholesterol were in LDL in guinea pigs, hamsters exhibited differences in both non-HDL and HDL cholesterol. In study 3, animals were fed 100% soybean protein, 10.7 g/100 g pectin, and three doses of dietary cholesterol: 0.04, 0.08, or 0.16 g/100 g, which is equivalent to 300, 600, or 1,200 mg/d in humans. Guinea pigs and hamsters had the highest plasma LDL and hepatic cholesterol concentrations when they consumed 0.16 g/100 g of cholesterol (P < 0.01). However, intake of 0.08 g/100 g of cholesterol resulted in lower plasma LDL cholesterol concentrations than did consuming high animal protein (60:40 casein/ soy) or low soluble fiber (2.7 g/100 g). Relatively high levels of dietary cholesterol combined with vegetable protein and soluble fiber resulted in desirable lipoprotein profiles in animal models that significantly differ in their lipoprotein cholesterol distribution.

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.

Soy lecithin reduces plasma lipoprotein cholesterol and early atherogenesis in hypercholesterolemic monkeys and hamsters: beyond linoleate

The current study was designed to investigate the hypocholesterolemic and anti-atherogenic properties of soy lecithin beyond its fatty acid content. In experiment 1, 18 cynomolgus monkeys were divided into three groups of six and fed diets which approximated either the average American diet (AAD), the American Heart Association (AHA) Step I diet, or a modified AHA (mAHA) Step I diet containing 3.4% soy lecithin for 8 weeks. Plasma samples were collected from food-deprived monkeys and analyzed for total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), very low- and low-density lipoprotein cholesterol (non-HDL-C), and triglyceride (TG) concentrations. Group comparisons revealed that monkeys fed the mAHA Step 1 diet had significantly lower plasma TC (-46%) and non-HDL-C (-55%) levels compared to the AAD diet, whereas monkeys fed the AHA Step 1 diet had lesser reductions in plasma TC (-21%) and non-HDL-C (-18%) levels. The monkeys fed the mAHA Step I diet had significantly lower plasma TC (-32%) and non-HDL-C (-45%) compared to the monkeys fed the AHA step diet. Also, only the mAHA Step I diet significantly reduced pre-treatment plasma TC and non-HDL-C levels by - 39 and -51% respectively with no significant effect on plasma HDL-C or TG levels. In experiment 2, 45 hamsters were divided into three groups of 15 and fed the following three modified non-purified diets for 8 weeks: a hypercholesterolemic diet (HCD) containing 10%, coconut oil and 0.05%, cholesterol, HCD plus 3.4%, soy lecithin (+SL), or the HCD with added levels of linoleate and choline equivalent to the +SL diet but no lecithin (-SL). Plasma lipids were determined as in experiment 1 and aortas were perfusion-fixed and Oil Red O stained for morphometric analyses of fatty streak area. Relative to the HCD group, the +SL-treated hamsters had significantly lower plasma TC (-58%), non-HDL-C (-73%) and aortic fatty streak area (-90%). Relative to the -SL group, hamsters fed the +SL diet had significantly lower plasma TC (-33%), non-HDL-C (-50%) and significantly reduced aortic fatty streak area (-79%). In conclusion, the first experiment suggests that the cholesterol-lowering efficacy of the AHA Step I diet can be enhanced with the addition of soy lecithin without reducing plasma HDL-C levels. whereas the second experiment suggest that the hypocholesterolemic, and in particular, the anti-atherogenic properties of soy lecithin cannot be attributed solely to its linoleate content.

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.

Effects of soy protein on plasma cholesterol and bile acid excretion in hamsters

The effect of dietary casein and soy protein on lipoprotein metabolism was compared in the Golden Syrian hamster (Mesocricetus auratus). Total plasma cholesterol was similar in animals fed either protein, but significant differences were seen in lipoprotein profile. In animals fed soy protein, cholesterol concentrations were lower in very-low-density lipoproteins (VLDL) but higher in low-density and high-density lipoproteins, compared with those fed casein. Significant differences were also seen depending on the nutritional state of the animals. In casein-fed hamsters, total plasma triacylglycerol and chylomicron + VLDL cholesterol and triacylglycerol were significantly higher when blood was collected during feeding, compared with animals that had been fasted overnight. By contrast, no significant change was seen in animals on the soy protein diet. This suggests that either intestinally derived lipoproteins are more rapidly cleared on the soy protein diet or that soy inhibits feeding-induced VLDL secretion. Fecal bile acid excretion was higher in the soy protein group, and there was a significant correlation between soy intake and bile acid excretion. Hepatic cholesterol decreased as the amount of soy protein consumed increased, suggesting that it is this pool of cholesterol that is used to replace the excreted bile acids. No significant difference was seen in plasma insulin or glucagon between hamsters fed the two proteins. Plasma triiodothyronine concentrations were, however, significantly higher and thyroxine concentrations lower in the soy protein-fed animals. This study shows specific effects of dietary proteins on plasma lipoprotein concentrations dependent on nutritional status of the animal.

Effects of soya milk and Bifidobacterium-fermented soya milk on plasma and liver lipids, and faecal steroids in hamsters fed on a cholesterol-free or cholesterol-enriched diet

The effects of freeze-dried soya milk (SM) and Bifidobacterium-fermented soya milk (FSM) on plasma and liver lipids, and faecal steroid excretion were estimated in hamsters fed on a cholesterol-free or cholesterol-enriched diet. Hamsters fed on the cholesterol-free diet containing 300 g FSM/kg had lower levels of plasma VLDL + LDL cholesterol than the animals fed on the control diet. SM in the diet produced a similar pattern without significant differences. In the cholesterol-enriched diet group, SM and FSM decreased the levels of plasma total cholesterol and VLDL + LDL-cholesterol. SM and FSM decreased the plasma triacylglycerol level in both the cholesterol-free and -enriched diet groups. The liver total cholesterol contents in the SM and FSM groups were lower than that in the control group, for hamsters fed on the cholesterol-free diet. The liver triacylglycerol content was not modified by SM or FSM in hamsters fed on either the cholesterol-free or -enriched diet. SM and FSM increased the total bile acid excretion and the proportion of cholesterol entering the cholic acid biosynthesis pathway in both the cholesterol-free and -enriched diet groups. SM and FSM did not affect neutral steroid excretion in the cholesterol-free or -enriched diet group. There was an inverse relationship between VLDL + LDL-cholesterol and faecal bile acid excretion in hamsters fed on the cholesterol-free (r -0.670, P < 0.01) and cholesterol-enriched (r -0.761, P < 0.001) diets respectively. These results indicated that SM had an anti-atherogenic effect, and that this effect was not diminished by prior fermentation.