Lipoprotein lipases, lipoproteins and tissue lipids in rats fed fish oil or coconut oil

The effect of fish oil and coconut oil on plasma lipoproteins and lipoprotein-catabolizing enzymes [lipoprotein lipase (LPL) and hepatic endothelial lipase (HL)] was studied in rats. Male rats were fed for 4 wk purified diets containing equienergetic, amounts of either coconut oil (group A), coconut oil:fish oil, 50:50 (group B) or fish oil (group C). Whole plasma triacylglycerol, cholesterol and phospholipid concentrations were appreciably lower in group C than in group A, mainly due to a fall in very low density lipoprotein (VLDL) and subgroup 2 of high density lipoprotein (HDL2), with less consistent changes in LDL and HDL3. VLDL components of group B were also considerably lower than corresponding ones in group A. LPL and HL activities were about 50% lower in groups B and C than in group A. Increased hepatic triacylglycerol and cholesterol concentrations were observed in groups B and C. It is suggested that the decrease in LPL and HL activity of fish oil-fed rats may be an adaptive response to the low concentration of the substrate (triacylglycerols) for these enzymes.     

Plasma lipids and lipoproteins in normo- and in hyperlipidemic rabbits fed plant protein diets

The effect of a diet based on a plant protein mixture, on plasma lipids and lipoproteins was evaluated in normo-and in hyperlipidemic rabbits. The proteins comprising the experimental diet consisted of equal amounts of soy protein, cottonseed protein and wheat gluten, and was supplemented with lysine, methionine and threonine to their respective levels in casein which was the control diet. Each diet was served with (0.25%) and without cholesterol. The normolipidemic rabbits were fed the various diets for 55 days. When rendered hyperlipidemic, animals were pre-fed for 20 days the cholesterol containing casen diet and subsequently given the experimental diets for an additional 35 day period. The plant protein diet had a marked hypocholesterolemic effect, and induced a reduction in the cholesterol and in the protein VLDL + LDL to HDL ratios that were used as atherogenic parameters.     

Dietary chitosan improves hypercholesterolemia in rats fed high-fat diets

The hypolipidemic mechanism of chitosan was investigated in male Sprague-Dawley rats. Animals were divided into 5 groups (n = 8): a normal fat control group, a high-fat control group (HF), a positive control group (CR), and 2 chitosan groups (CIS1 and CIS2). Chitosan was fed at the beginning (CIS1) and after 2 weeks (CIS2). A commercial diet with 5% (wt/wt) cellulose (HF), cholestyramine (CR), or chitosan (CIS1, CIS2) was fed for 6 weeks. Chitosan did not affect food intake but decreased body weight gain and significantly increased fecal fat and cholesterol excretion, reduced the lipid level in plasma and liver, increased liver hepatic and lipoprotein lipase activities compared with HF (P < .05), and tended to relieve the degenerated fatty liver tissue. No significant differences in all measurements were found between the CIS1 and CIS2 groups although the CIS1 rats exhibited lower lipid levels compared to those in the CIS2 group. The results suggest that chitosan reduced the absorption of dietary fat and cholesterol in vivo and could effectively improve hypercholesterolemia in rats.     

Plasma lipids and lipoproteins in hypercholesterolemic men fed a lipid-lowering diet containing lean beef,lean fish,or poultry

BACKGROUND: To reach desirable lipid and lipoprotein concentrations, patients with hypercholesterolemia are often told to replace the consumption of beef with that of fish and poultry. OBJECTIVE: The objective of this study was to compare the effects on lipoprotein profiles in hypercholesterolemic men of the incorporation of lean beef, poultry (without skin), and lean fish into an American Heart Association diet with a high polyunsaturated-to-saturated fatty acid ratio and a high fiber content. DESIGN: Three groups of subjects each rotated in a crossover design through 3 experimental periods that lasted 26 d each. The diets were planned to provide 11 713 kJ/d, of which 18% came from protein, 53% from carbohydrate, and 30% from lipids (polyunsaturated-to-monounsaturated-to-saturated fatty acid ratio: 1.0:1.1:1.0); 268 mg cholesterol/d; and 29 g fiber/d. RESULTS: The lean beef, lean fish, and poultry diets reduced plasma total and LDL cholesterol by 5-9%, LDL apolipoprotein B by 16-19%, VLDL triacylglycerols by 22-31%, and the ratio of total cholesterol to HDL cholesterol by 6-11%; they also increased the ratio of LDL cholesterol to apolipoprotein B by 18-28%. No significant difference was found in these lipid variables between the 3 experimental diets. However, the lean fish diet increased HDL(2) cholesterol significantly more (P < 0.05) than did the lean beef diet and the ratio of HDL(2) to HDL(3) cholesterol significantly more (P < 0.05) than did the lean beef and poultry diets. CONCLUSION: The results indicate that an American Heart Association diet with a high polyunsaturated-to-saturated fatty acid ratio and high fiber content induced numerous favorable changes in coronary artery disease risk factors in hypercholesterolemic men, regardless of the protein source.     

Blood lipids, lipoproteins, apoproteins, and uric acid in men fed diets containing fructose or high-amylose cornstarch

Ten hyperinsulinemic and 11 nonhyperinsulinemic men consumed for 5 wk each in a cross-over design a diet, similar to one currently consumed in the United States, with 20% of the kilocalories from either fructose or high-amylose cornstarch to determine the effects of the two diets on various blood metabolites considered to be risk factors associated with heart disease. In the hyperinsulinemic men the intake of fructose as compared with cornstarch significantly increased total triglycerides and their lipoprotein distribution; total and very-low-density lipoprotein cholesterol; apoproteins B-100, C-II, C-III; and uric acid. In the nonhyperinsulinemic men total triglycerides, total and low-density lipoprotein cholesterol and uric acid were significantly greater after the consumption of fructose than after cornstarch. The results indicate that in a diet high in saturated fatty acids and cholesterol, fructose increases the levels of risk factors associated with heart disease, especially in hyperinsulinemic men.     

Beneficial effect of wheat germ on circulating lipoproteins and tissue lipids in rats fed a high fat, cholesterol-containing diet

Adult male rats were fed for 7 wk either a low fat diet (3% fat) or a high fat-cholesterol diet (20% fat, 0.5% cholesterol) containing 7% wheat germ or not. Body weights and food intakes were unchanged by adding wheat germ to the control low fat or high fat diets. Adding wheat germ to the high fat-cholesterol diet significantly increased high density lipoprotein (HDL) cholesterol and the HDL-serum cholesterol ratio and lowered the very low density lipoprotein (VLDL) triglycerides. Thus the lipoprotein pattern was comparable to that obtained with the low fat diet, but the VLDL lipid composition remained altered. At the same time, triglyceride and cholesterol accumulation in the liver and the triglyceride content in skin were significantly decreased. When wheat germ was added to the low fat diet, cholesterol and triglycerides were not significantly modified. No adaptative change in lipase and colipase contents was observed in the pancreas of rats fed the wheat germ-supplemented diets, whereas the high fat diet increased these values. The results show a beneficial effect of wheat germ added to a high fat-cholesterol diet on the lipid status of rats; the implicated mechanisms are yet to be elucidated.     

Intestinal lymph lipoproteins in rats fed diets enriched in specific fatty acids

Four groups of rats were fed test diets with fats providing 75% of fatty acids as palmitate, stearate, oleate or linoleate. Absorption of radiolabeled cholesterol and the specific triglyceride into intestinal lymph lipoproteins and the lipid and protein content and composition of intestinal lymph were compared. Cholesterol and triglyceride absorptions were correlated significantly and were less with the saturated fatty acid diets. The fatty acid patterns of triglyceride-rich lymph lipoproteins mirrored the diet. Exogenous cholesterol was recovered primarily in chylomicrons, except with linoleate. In contrast, radiolabeled saturated fatty acids were recovered primarily in very low density lipoproteins and unsaturated fatty acids were recovered in chylomicrons. Lymph chylomicron size and lipid content were greater with unsaturated fat diets. Triglyceride-rich intestinal lipoproteins of rats fed saturated fats were polygonal by electron microscopy, related to the cooling of lymph samples below body temperature. A-I apolipoproteins were increased in relation to C apoproteins as lipid absorption was greater. Plasma triglycerides in all groups increased compared to rats fed the stock diet. A diet enriched in one specific fatty acid has its unique effects on lymph lipoprotein formation presumably affecting some intestinal subcellular mechanisms. Diet-induced changes in plasma lipids and lipoproteins are not directly related to these as yet unknown mechanisms.     

Effect of exercise on tissue lipids and serum lipoproteins of rats fed two levels of fat.

Adult rats were fed a low fat (4%) or a high fat (40%) diet, and groups of other rats selected for good running were fed these two diets and were treadmill exercised 5 days a week for 6 weeks. The serum triglycerides were significantly lower in exercised rats fed the low fat diet, but not in those fed the high fat diet, as compared with corresponding controls. The liver lipids were vastly elevated in sedentary rats fed the high fat diet as compared with those fed the low fat diet. An interesting effect of exercise was reflected by the near normal liver lipid levels in rats fed the high fat diet and exercised. However, in these animals, the muscle concentration of cholesterol was significantly higher than that in all other groups. The very low density lipoproteins tended to be lower while the low density lipoproteins tended to be greater in exercised as compared with sedentary rats. It was suggested that the decline in very low density lipoproteins was due to decreased synthesis resulting from adaptive changes in the exercised animal. It was further postulated that the increase in low density lipoproteins was possibly due to increased synthesis necessitated by the need to enhance the catabolism and excretion of cholesterol in exercised animals.     

Fish protein hydrolysates affect cholesterol metabolism in rats fed non-cholesterol and high-cholesterol diets

Fish consumption is well known to provide health benefits in both experimental animals and human subjects. Numerous studies have demonstrated the beneficial effects of various protein hydrolysates on lipid metabolism. In this context, this study examined the effect of fish protein hydrolysates (FPH) on cholesterol metabolism compared with the effect of casein. FPHs were prepared from Alaska pollock meat using papain as a protease. Male Wistar rats were divided into the following four dietary groups of seven rats each: either casein (20%) or FPH (10%)?+?casein (10%), with or without 0.5% cholesterol and 0.1% sodium cholate. Serum and liver lipid levels, fecal cholesterol and bile acid excretions, and the hepatic expression of genes encoding proteins involved in cholesterol homeostasis were examined. In rats fed the FPH diets compared with casein diets with or without cholesterol and sodium cholate, the indexes of cholesterol metabolism-namely, serum cholesterol, triglyceride, and low-density lipoprotein-cholesterol levels-were significantly lower, whereas fecal cholesterol and bile acid excretions were higher. Rats fed the FPH diets compared with casein with cholesterol exhibited a lower liver cholesterol level via an increased liver cholesterol 7α-hydroxylase (CYP7A1) expression level. This study demonstrates that the intake of FPH has hypocholesterolemic effects through the enhancement of fecal cholesterol and bile acid excretions and CYP7A1 expression levels. Therefore, fish peptides prepared by papain digestion might provide health benefits by decreasing the cholesterol content in the blood, which would contribute to the prevention of circulatory system diseases such as arteriosclerosis.     

Mammary tumor lipids and plasma lipoproteins in DMBA-intubated rats fed olive or safflower oils

The effects of feeding olive and safflower oils on lipid and fatty acid composition of mammary tumors, plasma lipids and lipoproteins, and the nuclear magnetic resonance (NMR) spectra of plasma were investigated in rats. 7-12-Dimethylbenz[a]anthracene (DMBA)- and placebo-intubated male Sprague-Dawley rats were fed 20% fat diets containing 18:2n-6 (wt/wt) from either high-linoleic safflower oil (SL, 14.6% 18:2n-6), high oleic safflower oil (SO, 3.4% 18:2n-6), olive oil (OO, 1.1% 18:2n-6), or olive oil supplemented with 18:2n-6 (OL, 3.4% 18:2n-6) for 16 weeks. Our result indicated that tumor composition of 18:1n-9 and 18:2n-6 reflected the diet, but tumor neutral lipid (NL) was more reflective of diet than was tumor phospholipid (PL). The 20:4n-6 content of tumor PL was constant in all of the dietary groups despite threefold higher levels of 18:2n-6 in tumor PL from animals fed SL than from those fed SO, OO, or OL diets. This suggests a possible feedback inhibition of delta 6-desaturase by the higher content of 18:2n-6 associated with SL feeding No diet effects were obtained for tumor total lipid, NL, PL, cholesterol, and triglyceride contents. Plasma lipoprotein changes were more reflective of diet than tumorigenesis except for apolipoprotein-E, which was lower, and for very low-density lipoprotein cholesterol and low-density lipo protein, which were higher in tumor-bearing rats. Plasma NMR analysis indicated no difference in the average line widths of the methyl and methylene resonances for tumor-bearing and nontumor-bearing rats fed any of the diets.     

Serum and liver lipids in rats and chicks fed with diets containing different oils

OBJECTIVES: Because dietary fat composition is determinant for serum cholesterol level, which is related to cardiovascular disease, we evaluated the effects of diets containing saturated (coconut oil) or polyunsaturated fatty acids (soybean oil) supplemented or not with dietary cholesterol on serum and liver lipid composition in two animal species. METHODS: Male Wistar rats (21 d old) were assigned to one of seven groups and fed with commercial diet or diets containing 5% or 20% soybean oil or 20% coconut oil with or without 1% cholesterol. Chicks were assigned to one of four groups and fed with diets containing 15% soybean oil or 15% coconut oil with or without 1% cholesterol. RESULTS: In rats, the accumulations of hepatic cholesterol and triacylglycerols were higher in the group fed 20% soybean oil and 1% cholesterol than in the group fed 20% coconut fat and 1% cholesterol. The highest serum levels of cholesterol and triacylglycerols were observed in the group fed coconut oil and cholesterol, compared with the group fed soybean oil and cholesterol. Triacylglycerol, high-density lipoprotein, and total cholesterol serum levels increased with diet containing coconut oil and cholesterol. In chicks, the highest hepatic cholesterol accumulation occurred in the group fed 15% coconut fat and 1% cholesterol. Total and high-density lipoprotein cholesterol levels increased with diet containing coconut oil and cholesterol, although none of these diets modified serum triacylglycerol levels. CONCLUSIONS: The type of experimental animal model and the diet composition influence lipid metabolism.     

Chronic alpha 1-adrenergic blockade, serum triacylglycerols, and tissue lipoprotein lipase activity in rats fed diets high in starch or sucrose.

This study was designed to assess the individual and interactive effects of types of dietary carbohydrate and of chronic alpha 1-adrenergic blockade on some of the determinants of triacylglycerol metabolism in the rat. Specifically, dietary starch and sucrose were given chronically, with or without prazosin mixed with the diet. Serum lipid concentrations and the activity of lipoprotein lipase in several tissues were evaluated 3 h after a voluntary meal consisting of a diet that has been consumed chronically. Postprandial serum triacylglycerol levels were significantly higher (88%, P less than 0.05) after the ingestion of a meal high in sucrose than after a meal high in starch. Prazosin interacted significantly with dietary carbohydrates (P less than 0.03), in that the blocker did not affect triacylglycerol levels in starch-fed rats but greatly diminished their concentration in sucrose-fed animals. Postprandial measurement of lipoprotein lipase in epididymal white adipose tissue, brown adipose tissue, and vastus lateralis muscle showed that enzyme activity in these specific tissues was not affected by the type of dietary carbohydrate. Prazosin significantly decreased lipoprotein lipase activity in brown adipose tissue regardless of the diet, but it did not affect enzyme activity in the other tissues evaluated. These findings demonstrate that the influence of alpha 1-adrenergic blockade on triacylglycerol metabolism can be modulated by dietary components. They further suggest that, in the postprandial state, prazosin did not affect triacylglycerol concentrations by modulating total tissue activity of lipoprotein lipase, at least in the organs that were probed in this study.     

Dietary taurine alters ascorbic acid metabolism in rats fed diets containing polychlorinated biphenyls

The effect of dietary taurine on ascorbic acid metabolism and hepatic drug-metabolizing enzymes was investigated in rats fed diets containing polychlorinated biphenyls (PCB) to determine whether taurine has an adaptive and protective function in xenobiotic-treated animals. Young male Wistar rats (60 g) were fed diets containing 0 or 0.2 g/kg diet PCB with or without 30 g/kg diet of taurine for 14 d. The rats fed the PCB-containing diets had greater liver weight, higher ascorbic acid concentrations in the liver and spleen and greater hepatic cytochrome P-450 contents than control rats that were not treated with PCB (P < 0.01). In PCB-fed rats, urinary ascorbic acid excretion was enhanced, and serum cholesterol concentration (especially HDL-cholesterol) was significantly elevated compared with those in control rats. Dietary taurine significantly potentiated the increases in the urinary excretion of ascorbic acid and the rise in the levels of cytochrome P-450 which were caused by PCB treatment. On the other hand, the supplementation of taurine to control diet did not alter these variables. Taurine may enhance the hepatic drug-metabolizing systems, leading to the stimulation of the ascorbic acid metabolism in rats fed diets containing PCB.     

Plasma and lipoprotein cholesterol in weanling and post-weaning rats fed casein and soya protein diets

Plasma and lipoprotein cholesterol levels were measured in groups of Sprague-Dawley weanlings nursed by dams fed either casein (CS) or soya protein (SP). The 6 protein diets were as follows: 8% CS, 8% SP, 8% CS-SP (1:1 mixture), 25% CS, 25% SP and 25% CS:SP (1:1 mixture). A 7th group of dams was fed Purina chow diet. Feeding was from day 15 of pregnancy through 21 days past parturition. Plasma samples taken from other litter sets of young rats fed the above diets from weaning to 6 weeks of age were also analyzed. Plasma total cholesterol was higher at weaning than at 6 weeks of age. The increased level at weaning was due mainly to a rise in LDL-cholesterol, accompanied by a corresponding decrease in HDL-cholesterol. No hypocholesterolemic effect of dietary SP, compared to CS, was evident at this age. However, the effect became manifest at 6 weeks of age (P<0.05), as shown by decreased levels of LDL-cholesterol.     

Effect of dietary safflower phospholipid on plasma and liver lipids in rats fed a hypercholesterolemic diet.

The effect of safflower phospholipid (SP) on plasma and liver lipids in rats fed a hypercholesterolemic diet was examined. Triglyceride mixture (SPO) of safflower oil and palm oil (8:2) containing almost comparable amounts of linoleic acid to safflower phospholipid was used as a control diet. Similarly, the effect of paste safflower phospholipid (PSP) which contains approximately 45% of neutral lipid was also compared to safflower oil (SO). Concentrations of total cholesterol in plasma and liver of rats fed the SP diet were markedly decreased in comparison with those of the other diets, but a slight reduction of total cholesterol in plasma and liver was observed in rats fed PSP diet. SP and PSP induced a reduction in the plasma level of low density lipoprotein (LDL) cholesterol as well as an increase in the level of high density lipoprotein (HDL) cholesterol. The activity of plasma lecithin-cholesterol acyltransferase (LCAT) was greatly increased in rats fed SP diet. These results suggest that the safflower phospholipids suppress the elevation of plasma and liver cholesterol and that this effect may depend on the phospholipid content in dietary lipid.     

Plasma lipids, lipoproteins, and fecal excretion of neutral sterols and bile acids in rats fed various high fat diets or a low fat/high sucrose diet

The effect of feeding various diets on plasma lipids and lipoproteins and on fecal excretion of neutral sterols and bile acids was studied in rats fed for 7 wk diets containing 42% of energy as either coconut oil (CO), sunflower seed oil (SO), fish body oil (FBO), cod liver oil (CLO), or a low fat/high sucrose diet (SU). Triacylglycerols (TG) in whole plasma and VLDL + LDL were lower in rats fed high amounts of polyunsaturated fatty acids (PUFA) than in those fed the CO diet. Plasma HDL2 components in FBO and CLO groups were generally lower than in the other groups. Percentages of liver and heart linoleic and arachidonic acid were higher in the SO group, but lower in groups fed marine oils, than in the CO group. There was a high relative amount of eicosapentaenoic and docosahexaenoic acid in liver and heart of rats fed marine oils. Fecal excretion of bile acids was lower in the PUFA groups than in the CO group, whereas the sum of neutral sterols was similar in all groups. Plasma HDL2 (and VLDL + LDL) correlated positively, but HDL3 negatively, with fecal bile acid excretion. Accordingly, increased bile acid excretion does not seem to account for hypolipemia following intake of PUFA diets.     

Fat and protein from olive oil-fried sardines interact to normalize serum lipoproteins and reduce liver lipids in hypercholesterolemic rats

Fatty fish consumption has been recommended due to its high (n-3) PUFA content. However, an effect of its protein on serum lipids and lipoproteins has also been suggested. The present study was designed to determine the acceptability of diets containing sardines fried in olive oil or the fat extracted from those sardines and the normalization of serum lipids and lipoproteins, the hepatic lipid profile, and the fatty acid composition of the liver of growing Wistar rats fed these diets after dietary loading of cholesterol. Hypercholesterolemia was induced for 3 wk by feeding rats a casein/olive oil/cholesterol diet. Rats were then switched for 2 wk to cholesterol-free purified diets containing casein plus olive oil (CO), sardines fried in olive oil (S) and casein plus the fat extracted from sardines fried in olive oil (CSF). The S and CSF diets were well accepted by the rats. Withdrawal of dietary cholesterol markedly reduced (P < 0.05) serum cholesterol level in all of the groups, but the S group had the greatest decrease and the CO group the smallest decrease. The S group had a more normal lipoprotein profile, in which HDL was the major lipid carrier, whereas rats of the CO group still had beta-VLDL particles. CSF-fed rats had an intermediate profile. Liver fat and total, free and esterified cholesterol levels were lower (P < 0,05) in the S group than in the other two groups. The S and CSF diets increased (P < 0.05) the (n-3) PUFA content in hepatic triacylglyceride, cholesterol ester and phospholipid fractions. The liver fatty acid profile of the S group was more normalized than those of the other two groups. These findings suggest that the inclusion in the diet of whole sardines fried in olive oil normalizes cholesterol metabolism in hypercholesterolemic rats more quickly than consumption of their extracted fat.     

Dietary fibre-rich oat-based products affect serum lipids, microbiota, formation of short-chain fatty acids and steroids in rats

Wistar rats (ten per group) were fed either an oat-free control diet or a dietary fibre-rich test diet containing 500 g oat-based products/kg for 6 weeks. The oat-based products, containing 4-128 g/kg resistant starch, 30-92 g/kg beta-glucan and 122-304 g/kg total dietary fibre, were oat flour extrudate, flour/Novelose (commercial resistant starch) extrudate (80:20 w/w), oat bran, bran/Novelose extrudate (80:20 w/w) and autoclaved oat flour. Serum total cholesterol decreased in the groups fed flour, flour/Novelose and bran/Novelose (P<0.05). In most of the test groups, count numbers of bifidobacteria were higher (P<0.001) and of coliforms were lower (P<0.05). The mass of the caecum walls and contents was greater in groups fed Novelose- and bran-containing diets (P<0.005). In all the test groups, pH values were lower in the intestinal contents (P<0.001), and caecal concentrations of acetate (P<0.001), propionate (P<0.05), butyrate (P<0.005) and total SCFA (P<0.001) were higher. The lowest concentrations of steroids were found in rats fed the autoclaved flour. In the other test groups, more bile acids appeared in the caecal (P<0.001) and colonic contents (P<0.005), as well as in the faeces, at week 6 (P<0.001). The highest bile acid excretion was found after feeding bran-containing diets. In the intestinal contents of all the test groups, more primary bile acids (P<0.001) appeared than in the control group. The excretion of steroids increased within the experimental period. Using extrusion technology, dietary fibre-rich oat-based products, which have beneficial physiological effects in rats, can be produced. Oat flour and bran are excellent sources for the preparation of directly edible oat products. Their nutritional properties can be further improved by the addition of resistant starch.