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, 11t CLA); 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 stel 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) contaning 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 (non HDL-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 non HDL-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.     

A high cholesterol/cholate diet induced fatty liver in spontaneously hypertensive rats

A high cholesterol diet was found to induce fatty liver in spontaneously hypertensive rats. Although cholesterol ester and triacylglycerol accumulated in large amounts in liver, the increases of these lipids in plasma were relatively small and no increase in cholesterol and cholesterol ester was observed in aorta. In rats fed normal diet, plasma cholesterol ester mainly consisted of arachidonate species; however, oleate and linoleate esters became the most prominent species in rats fed a high-cholesterol diet. The amounts of oleate and linoleat at the 2-position of phosphatidylcholine in both plasma and liver were increased slightly, but the fatty acids of aorta lipids changed little by feeding a high cholesterol diet. These results indicate that the livers of rats fed the high cholesterol diet do not secrete cholesterol ester and triacylglycerol with altered fatty acids as rapidly as they are synthesized and that the increased levels of cholesterol oleate in liver and plasma are not directly correlated with atherogenic lesions under these conditions.     

The effect of a histidine-excess diet on cholesterol synthesis and degradation in rats

Feeding a diet high in excess histidine (5% L-histidine) resulted in hypercholesterolemia and enlargement of the liver in rats. To clarify the mechanism of the hypercho-lesterolemia cholesterol synthesis and degradation were followed. We found that hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity in histidine-excess diet rats was significantly higher than in rats fed a basal diet. Incorporation of [³H]water into cholesterol of liver slices from rats fed the histidine-excess diet was higher than incorporation into liver slices from rats fed the basal diet (expressed per liver per 100 g body weight).In vivo incorporation of [³H]water into hepatic cholesterol was also higher, but the incorporation into cholesterol of the small intestine was lower in histidine-fed rats than in rats fed the basal diet (expressed per liver per 100 g body weight). Hepatic cholesterol 7α-hydroxylase activity was similar in both groups. The data suggest that the hypercholester-olemia caused by histidine-excess diet appears to be due to the stimulation of cholesterol synthesis in the liver.     

Egg ovomucin attenuates hypercholesterolemia in rats and inhibits cholesterol absorption in Caco-2 cells

This experiment was designed to evaluate the effect of casein or ovomucin (OV) on the micellar solubility of cholesterol and the taurocholate binding capacity in vitro. We also evaluated the effects of casein or OV on cholesterol metabolism in rats and Caco-2 cells. OV has a significantly greater bile acid-binding capacity than that of casein in vitro. Micellar cholesterol solubility in vitro was significantly lower in the presence of OV compared to casein. The cholesterol micelles containing OV significantly suppressed cholesterol uptake by Caco-2 cells compared to the cholesterol micelles containing casein. Consistent with these in vitro findings, OV-feeding significantly increased the fecal excretion of bile acids or cholesterol compared with casein-feeding. Serum total cholesterol was significantly lower in rats fed OV than in those fed casein. The concentrations of total lipids in liver were significantly lower in the OV-fed group compared with the casein group. These results suggest that the suppression of cholesterol absorption by direct interaction between cholesterol mixed micelles and OV in the jejunal epithelia is part of the mechanism underlying the hypocholesterolemic action of OV. OV may also inhibit the reabsorption of bile acids in the ileum, thus lowering the serum cholesterol level.     

Ethanol-extracted soy protein isolate results in elevation of serum cholesterol in exogenously hypercholesterolemic rats

Soy protein preparations were reported to have hypocholesterolemic actions in experimental animals and humans, while the active components and the mechanism by which this occurs are not clarified yet. The objective of this study is to address these issues by using exogenously hypercholesterolemic rats which are susceptible to dietary cholesterol. Two groups of five rats (male, 12-wk-old) were fed on AIN 93G-based diet with soy protein isolate (SPI) or ethanol-extracted SPI (EE-SPI) for 2 wk. EE-SPI was prepared by ethanol extraction to remove isoflavones and other components. Concentrations of serum and liver total cholesterol were lower in rats fed SPI than in those fed EE-SPI. The abundances of mRNA for 7α-hydroxylase and low density lipoprotein receptor in the liver were lower in EE-SPI group than those in SPI group. These results suggest that the ethanol extract from SPI has a factor(s) to alleviate hypercholesterolemia by increasing the removal of cholesterol from serum through the receptor pathway and then from liver through enhancement of bile acid synthesis.     

Increases in hyperlipoproteinemia,disturbances in cholesterol metabolism and atherosclerosis induced by dietary restriction in rabbits fed a cholesterol-rich diet

The influence of dietary restriction on cholesterol transport and metabolism was investigated in rabbits given standard or cholesterol-rich diets (0.2 g cholesterol/kg body weight daily) eitherad libitum or with 50% caloric ration. Dietary restriction which has only a slight influence in control rabbits markedly aggravated the disturbances induced by exogenous cholesterol. With limited feeding, control rabbits presented a moderate increase in plasma cholesterol, whereas marked aggravation of hypercholesterolemia was observed in cholesterol-fed rabbits. Analysis of the lipoprotein profile showed that the excess of plasma cholesterol with the restricted cholesterol-rich diet corresponded to an increase in the concentration of very low density lipoprotein (VLDL) and low density lipoproteins (LDL) without any additional changes in the composition of these lipoproteins. No significant change appeared in the high density lipoprotein (HDL) concentration. The parameters of cholesterol metabolism were determined, from the curves of [³H] cholesterol radioactivity decrease, using a two-pool model. The increase in cholesterol turnover rate induced by the cholesterol-rich diet was accentuated by dietary restriction, whereas rabbits on standard restricted diet showed a slight decrease. The large increase in the size of both pools A and B in cholesterol-fed rabbits was even more pronounced with limited feeding. Dietary restriction induced additional accumulation of cholesterol in the aortic wall and the grade of the lesions was also aggravated.     

Isoflavones and hypercholesterolemia in rats

Isoflavones isolated from three commonly used pulses such as Bengalgram (Cicer arietinum), greengram (Phaseolus aureus) and blackgram (Phaseolus mungo) and p-coumaric acid were supplemented to hypercholeste rolemia-inducing diet of rats. Among isoflavones, Biochanin A and Formononetin showed hypolipidemic activity but diadzein did not; p-coumaric acid also produced a significant reduction in serum cholesterol levels.     

Induction of long-lasting hypercholesterolemia in the rat fed a cystine-enriched diet

The influence of dietary excess (5%) of L-cystine on rat plasma lipoproteins was examined. After only one week of cystine feeding, an increase in the plasma cholesterol level and a decrease in triglyceride levels were observed. The increase in cholesterol level became greater when the duration of cystine-enriched diet increased until eight weeks (+131% after eight weeks), but no further increase occurred between 8 and 20 weeks. This change was essentially due to the progressive increase in cholesterol levels in high density lipoproteins (HDL) and in lipoproteins isolated between 1.040 and 1.063 g/ml, i.e., certain low density lipoproteins (HDL₂), and containing mainly apoE-rich lipoproteins (HDL₁). The decrease in plasma triglycerides resulted from that of chylomicrons and very low density lipoproteins (VLDL). The effects observed after four or eight weeks of cystine feeding were maintained for eight weeks after replacing the cystine diet by the standard diet. Ingestion of the standard diet containing either cholestyramine (2%) or probucol (0.25%) following eight weeks of cystine feeding significantly decreased plasma cholesterol levels. It is concluded that cystine-fed rats are a useful tool of investigation for understanding mechanisms leading to increased plasma cholesterol level and for hypocholesterolemic drug trials.     

High and low density lipoprotein cholesterol levels in hypercholesterolemic school children

To most fully explicate risk to coronary heart disease (CHD) in adults and children with elevated plasma total cholesterol, the levels of high and low density lipoprotein cholesterol (C-HDL, C-LDL) must be quantitated. This report focuses upon C-HDL and C-LDL levels in children identified in a lipid and lipoprotein sampling survey of 6,775 Princeton School children, by either total plasma cholesterol ≥205 mg/dl, the approximate 95th percentile for children 6–17 years of age, or age-, sex-, and race-specific 95th percentiles for cholesterol. Using the sex-, race-specific local 95th percentiles for C-HDL and C-LDL, the hypercholesterolemic children were separated into four categories according to whether they had elevations of both C-HDL and C-LDL, C-HDL only, C-LDL only, or neither. When selection for hypercholesterolemia was based on the overall 95th percentile (205 mg/dl), black children were more likely than white to have elevations of C-HDL only, which accounted for their hypercholesterolemia, p<.05, whereas white children were much more likely to have elevations of C-LDL only, than were black children, p<.005. However, when selection for hypercholesterolemia was based on age-, sex-, and race-specific 95th percentile cholesterol levels, there were no differences in the proportion of black and white children having elevations of C-HDL and C-LDL, accounting for their hypercholesterolemia. Elevated levels of C-HDL can explain apparent hypercholesterolemia in at least 16% of children, ages 6–17, who may putatively be at reduced, rather than increased CHD risk.     

Hypercholesterolemia in rats: Combined effect of high cholesterol diet and female sex steroids

The influence of estradiol and a contraceptive steroid combination on plasma cholesterol was studied in female rats on both normal and high-cholesterol diets which did not contain thiouracil. The high-cholesterol diet resulted in moderate hypercholesterolemia without weight loss, even with prolonged feeding. Hypercholesterolemia was markedly accentuated in the presence of either endogenous or exogenous sex hormones.     

Heat-treated hull flour does not affect iron bioavailability in rats

In this study the chemical composition and iron bioavailability of hull and hull-less soybean flour from the new cultivar UFVTN 105AP was evaluated. The hemoglobin depletion-repletion method was used in Wistar rats. Soybean hull flour presented 37% more total dietary fiber and higher content of iron than hull-less soybean flour. The phytate:iron molar ratio, however, was 2-fold lower in the soybean hull flour in compared to the hull-less soybean flour. Animals fed soybean hull flour presented hemoglobin gains similar to those of the control diet group (p > 0.05). The Relative Biological Values of hull and hull-less soybean flour were 68.5% and 67.1%, respectively, compared to the control group. Heat-treated soybean hull flour (150 degrees C/30 minutes) showed high content of iron and low phytate, which favors the iron bioavailability. Thus, the soybean hull flour is a better source of dietary fiber and iron than hull-less soybean flour at comparable bioavailabilities.     

Hepatic cholesterol synthesis from mevalonate and squalene in rats: Effect of feeding cholesterol supplemented diet during weaning and following starvation

The conversion of squalene to digitonin precipitable sterols by microsomes and soluble fractions from liver and the incorporation of mevalonate into nonsaponifiable lipids and digitonin precipitable sterols by 5000 g liver supernatant was studied in suckling rats and rats weaned on diet (Purina chow) supplemented with varying levels of cholesterol. The results indicate that the conversion of squalene to digitonin precipitable sterols was low in suckling rats and high in rats weaned on Purina chow diet. Weaning rats on 1% cholesterol supplemented diet effectively eliminated the post-weaning increase in mevalonate incorporation into nonsaponifiable and digitonin precipitable sterols, and in the conversion of squalene to digitonin precipitable sterols. The incorporation of mevalonate into nonsaponifiable lipids and digitonin precipitable sterols, and of squalene into digitonin precipitable sterols also was studied in liver preparations from adult rats which were starved and refed control or cholesterol supplemented diet. It was observed that the conversion of squalene to digitonin precipitable sterols by liver fractions from fasted rats was low, while that by liver fractions from rats refed control diet was higher. Furthermore, the post-fasting increase in the conversion of mevalonate to nonsaponifiable lipids and digitonin precipitable sterols and in squalene to digitonin precipitable sterols conversion essentially was eliminated by refeeding a 1% cholesterol supplemented diet. The low conversion of squalene to digitonin precipitable sterols in suckling rats, rats weaned on cholesterol supplemented diet, and adult rats that were starved, or starved and refed cholesterol supplemented diet, was due to the reduced activity of microsomal enzymes. It is concluded from this study that dietary cholesterol prevents the increase in cholesterol synthesis observed in developing and regenerating liver by suppressing the activities of one or more enzymes between mevalonate and squalene and between squalene and cholesterol.     

Improvements in vascular health by a low-fat diet,but not a high-fat diet,are mediated by changes in adipocyte biology

Background  

Low-fat (LF) and high-fat (HF) weight loss diets improve brachial artery flow-mediated dilation (FMD) in obese individuals, although results are conflicting. Moreover, the role that adipose tissue plays in mediating these diet-related effects are unknown.     

Effect of dietary fat saturation of absorption and intestinal secretion of cholesterol by the hypercholesterolemic rat

The fate of an oral dose of [4-¹⁴C] cholesterol given to rats grown on diets with 20% safflower oil or 20% hydrogenated coconut oil was determined by analysis of digestive tract, feces and tissues. The pattern of isotope distribution did not support the view that rats fed a saturated fat absorb less cholesterol than those fed an unsaturated fat. Fasted animals growth on the diet with 5% of these two fats and beef fallow showed no clear difference in the amount of digitonin-peecipitable sterol in their intestines. A shorter transit time for intestinal contents was observed with the saturated fat groups. It is concluded that neither absorption of cholesterol from the gut nor secretion of β-hydroxy sterol into the gut accounts for the hypocholesterolemic effect of polyunsaturated fat. Journal Paper No. 4951 AES, Purdue University.     

The hypercholesterolemic effect of dietary coconut fatversus corn oil in hypo- or hyperresponsive rabbits is not exerted through influencing cholesterol absorption

In two inbred strains of rabbits with high or low response of plasma cholesterol to dietary saturatedversus polyunsaturated fatty acids, the efficiency of intestinal cholesterol absorption was measured. The feeding of a cholesterol-free purified diet containing saturated fatty acids in the form of coconut fat, when compared with a diet containing corn oil as polyunsaturated fatty acids, did not influence the efficiency of cholesterol absorption in the two rabbit strains. Irrespective of the dietary fat source, the hyperresponsive rabbits absorbed cholesterol more efficiently. It is concluded that the hypercholesterolemic effect of dietary coconut fatversus corn oil is not exerted by influencing cholesterol absorption.     

CLA prevents alterations in glycolytic metabolites induced by a high fat diet

CLA has been reported to have beneficial and controversial effects on glucose and lipid metabolism. Besides, high fat (HF) diets induce alterations in liver and muscle lipid deposition, which could be associated with anomalous glucose utilization. Therefore, our aim was to evaluate whether the intake of CLA could prevent alterations in glycolytic intermediate metabolites and glycogen deposition induced by a HF diet. For this purpose, growing mice were fed a control diet (7% corn oil), a HF diet (20% corn oil), or a HF diet containing 17% corn oil + 3% CLA for 30 days. Liver and muscle glucose intermediate metabolites and glycogen were assessed. Liver glycolysis was inhibited by HF, reflected by a decreased flow of substrates through phosphofructokinase‐1α linked to elevated citrate. CLA at HF diet prevented these alterations while increasing the lactate and glycogen synthesis. In the muscle, the HF diet emphasized the reduction of the flux through phosphofructokinase‐1α, without additional changes in total glycogen levels. In conclusion, dietary CLA partially prevented glycolytic pathway alterations in the liver but not in the muscle of mice fed a HF diet, associated with adverse effects as sustained hyperglycemia and hepatic lactate accumulation. Practical applications: The present study evaluates the potential use of CLA and its consequences on several aspects of glucose metabolism. Considering that the FDA has recently approved CLA as a Generally Recognized as Safe (GRAS) category, a measure that will foster the commercial production of food and beverages with CLA supplementation, we believe it is relevant to study its potential functional properties on glucose metabolism in an experimental animal model characterized by alterations in liver and muscle lipid deposition.     

Deuterium uptake and plasma cholesterol precursor levels correspond as methods for measurement of endogenous cholesterol synthesis in hypercholesterolemic women

To assess the validity of two techniques used to measure human cholesterol synthesis, the rate of uptake of deuterium (D) into plasma free cholesterol (FC), and plasma cholesterol precursor (squalene, lanosterol, desmosterol and lathosterol) levels were compared in 14 women [65–71 yr with low density lipoprotein-cholesterol (LDL-C)≥3.36 mmol·l ⁻¹]. Subjects consumed each of six diets for 5-wk periods according to a randomized crossover design. The experimental diets included a baseline diet (39% energy as fat, 164 mg chol·4.2 MJ⁻¹) and five reduced-fat diets (30% of energy as fat), where two-thirds of the fat was either soybean oil; squeeze, tub or stick margarines; or butter. Fractional and absolute synthesis rates (FSR and ASR) of FC were determined using the deuterium incorporation (DI) method, while cholesterol precursor levels were measured using gas-liquid chromatography. Data were pooled across diets for each variable and correlation coefficients were calculated to determine if associations were present. There was good agreement among levels of the various cholesterol precursors. In addition, FSR in pools/d (p·d⁻¹) and ASR in grams/d (g·d⁻¹) were strongly associated with lathosterol (r=0.72 and 0.71, P=0.0001), desmosterol (r=0.75 and 0.75, P=0.0001), lanosterol (r=0.67 and 0.67), and squalene (r=0.69 and 0.68) when levels of the precursors were expressed as μmol·mmol⁻¹C. Significant but lower correlations were observed between the D uptake and plasma cholesterol precursor levels when the latter were expressed in absolute amounts (μmol·L⁻¹). The wide range of fatty acid profiles of the experimental diets did not influence the degree of association between methods. In conclusion, the DI method and levels of some cholesterol precursors correspond as methods for shortterm measurement of cholesterol synthesis.     

Genetic variations in serum lipid levels of inbred mice and response to hypercholesterolemic diet

The serum lipid contents of a number of inbred and congenic strains of mice were measured. There were interstrain variations in each of the lipid fractions in mice fed a normal diet. Male and female C3H mice had the highest total cholesterol level; AKR mice showed the lowest values. Serum phospholipids were correlated well with cholesterolemia. The greatest variations between strains were in the triglyceride levels. There also was significant variation in the high density lipoprotein cholesterol serum levels (from 73–88% of the total cholesterol). The response to a hypercholesterolemic diet (1% cholesterol) was tested in seven inbred strains. All strains showed changes in serum cholesterol and in the proportions of the lipoproteins fractions. There was a large increase in the low density lipoprotein+very low density lipoprotein fractions. Feeding the diet revealed marked interstrain differences in the responses of the serum cholesterol and electrophoretic lipoprotein profiles. The C57BL/6 and B10.D2 strains were hyperresponders to the hypercholesterolemic diet with 71% and 63% of their serum cholesterol in the low density lipoprotein plus very low density lipoprotein fractions, respectively.