Effects of diets enriched in n−6 or n−3 fatty acids on cholesterol metabolism in older rats chronically fed a cholesterol-enriched diet

Hypocholesterolemic effects in older animals after long-term feeding are unknown. Therefore, aged rats (24 wk of age) fed a conventional diet were shifted to diets containing 10% perilla oil [PEO; oleic acid+linoleic acid+α-linolenic acid; n−6/n−3, 0.3; polyunsaturated fatty acid/saturated fatty acid (P/S), 9.6], borage oil [oleic acid+linoleic acid+α-linolenic acid; n−6/n−3, 15.1; P/S, 5.3], evening primrose oil (FPO; linoleic acid+γ-linolenic acid; P/S, 10.5), mixed oil (MIO; oleic acid+linoleic acid+γ-linolenic acid+α-linolenic acid; n−6/n−3, 1.7; P/S, 6.7), or palm oil (PLO; palmitic acid+oleic acid+linoleic acid; n−6/n−3, 25.3; P/S, 0.2) with 0.5% cholesterol for 15 wk in this experiment. There were no significant differences in the food intake and body weight gain among the groups. The liver weight in the PEO (n−6/n−3, 0.3) group was significantly higher than those of other groups in aged rats. The serum total cholesterol and very low density lipoprotein (VLDL) +intermediate density lipoprotein (IDL)+low density lipoprotein (LDL)-cholesterol concentrations of the PLO (25.3) group were consistently higher than those in the other groups. The serum high density lipoprotein cholesterol concentrations of the PEO (0.3) and EPO groups were significantly lower than in the other groups at the end of the 15-wk feeding period. The liver cholesterol concentration of the PLO (25.3) group was significantly higher than those of other groups. There were no significant differences in the hepatic LDL receptor mRNA level among the groups. Hepatic apolipoprotein (apo) B mRNA levels were not affected by the experimental conditions. The fecal neutral steroid excretion of the PLO (25.3) group tended to be low compared to the other groups. The results of this study demonstrate that both n\t-6 fatty acid and n\t-3 fatty acids such as \gg-linolenic acid and \ga-linolenic acid inhibit the increase of serum total cholesterol and VLDL+IDL+LDL-cholesterol concentrations of aged rats in the presence of excess cholesterol in the diet compared with dietary saturated fatty acid.     

Dietary conjugated linolenic acid in relation to CLA differently modifies body fat mass and serum and liver lipid levels in rats

The present study compared the effect of dietary conjugated linolenic acid (CLNA) on body fat and serum and liver lipid levels with that of CLA in rats. FFA rich in linoleic acid, α-linolenic acid, CLA, or CLNA were used as experimental fats. Male Sprague-Dawley rats (4 wk old) were fed purified diets containing 1% of one of these experimental fats. After 4 wk of feeding, adipose tissue weights, serum and liver lipid concentrations, serum tumor necrosis factor (TNF)-α and leptin levels, and hepatic β-oxidation activities were measured. Compared with linoleic acid, CLA and, more potently, CLNA were found to reduce perirenal adipose tissue weight. The same trend was observed in the weight of epididymal adipose tissue. CLNA, but not CLA, was found to significantly increase serum and liver IG concentrations. Serum FFA concentration was also increased in the CLNA group more than in the other groups. The activity of β-oxidation in liver mitochondria and peroxisomes was significantly higher in the CLNA group than in the other groups. Thus, the amount of liver TG exceeded the ability of hepatic β-oxidation. Significant positive correlation was found between the adipose tissue weights and serum leptin levels in all animals (vs. perirenal: r=0.557, P<0.001; vs. epididymal: r=0.405, P<0.05). A less significant correlation was found between adipose tissue weights and serum TNF-α level (vs. perirenal: r=0.069, P<0.1; vs. epididymal: r=0.382, P<0.05). Although the mechanism for the specific effect of CLNA is not clear at present, these findings indicate that in rats CLNA modulated the body fat and TG metabolism differently from CLA.     

Differential effects of dietary linoleic and α-linolenic acid on lipid metabolism in rat tissues

Comparative effects of feeding dietary linoleic (safflower oil) and α-linolenic (linseed oil) acids on the cholesterol content and fatty acid composition of plasma, liver, heart and epididymal fat pads of rats were examined. Animals fed hydrogenated beef tallow were used as isocaloric controls. Plasma cholesterol concentration was lower and the cholesterol level in liver increased in animals fed the safflower oil diet. Feeding the linseed oil diet was more effective in lowering plasma cholesterol content and did not result in cholesterol accumulation in the liver. The cholesterol concentration in heart and the epididymal fat pad was not affected by the type of dietary fatty acid fed. Arachidonic acid content of plasma lipids was significantly elevated in animals fed the safflower oil diet and remained unchanged by feeding the linseed oil diet, when compared with the isocaloric control animals fed hydrogenated beef tallow. Arachidonic acid content of liver and heart lipids was lower in animals fed diets containing safflower oil or linseed oil. Replacement of 50% of the safflower oil in the diet with linseed oil increased α-linolenic, docosapentaenoic and docosahexaenoic acids in plasma, liver, heart and epididymal fat pad lipids. These results suggest that dietary 18∶2ω6 shifts cholesterol from plasma to liver pools followed by redistribution of 20∶4ω6 from tissue to plasma pools. This redistribution pattern was not apparent when 18∶3ω3 was included in the diet.     

Dietary saturated fat level alters the competition between α-linolenic and linoleic acid

Male weanling rats were fed semi-synthetic diets high in saturated fat (beef tallow) vs high in linoleic acid (safflower oil) with or without high levels of α-linolenic acid (linseed oil) for a period of 28 days. The effect of feeding these diets on cholesterol content and fatty acid composition of serum and liver lipids was examined. Feeding linseed oil with beef tallow or safflower oil had no significant effect on serum levels of cholesterol. Serum cholesterol concentration was higher in animals fed the safflower oil diet than in animals fed the beef tallow diet without linseed oil. Feeding linseed oil lowered the cholesterol content in liver tissue for all dietary treatments tested. Consumption of linseed oil reduced the arachidonic acid content with concomitant increase in linoleic acid in serum and liver lipid fractions only when fed in combination with beef tallow, but not when fed with safflower oil. Similarly, ω3 fatty acids (18∶3ω3, 20∶5ω3, 22∶5ω3, 22∶6ω3) replaced ω6 fatty acids (20∶4ω6, 22∶4ω6) in serum and liver lipid fractions to a greater extent when linseed oil was fed with beef tallow than with safflower oil. The results suggest that the dietary ratio of linoleic acid to saturated fatty acids or of 18∶3ω3 to 18∶2ω6 may be important to determine the cholesterol and arachidonic acid lowering effect of dietary α-linolenic acid.     

Effects of dietary conjugated linoleic acids on hepatic and muscle lipids in hybrid striped bass

Conjugated linoleic acids (CLA) are the focus of numerous studies, yet the effects of these isomers of octadecadienoic acids have not been evaluated in many species of fish. In this study, graded amounts of CLA-0,0.5, 0.75, or 1.0% of the diet—were fed to juvenile hybrid striped bass for 8 wk. Dietary treatments were fed to apparent satiation twice daily to triplicate groups of fish initially weighing 13.4 g/fish. Feed intake and weight gain of fish fed 1.0% CLA were significantly reduced compared to fish fed no CLA. Fish fed 0.5 and 0.75% CLA exhibited reduced feed intake similar to fish fed 1.0% CLA, but had growth rates that were not significantly different from those of fish fed no CLA. Feed efficiency improved significantly in fish as dietary CLA concentrations increased. Total liver lipid concentrations were significantly reduced in fish fed the diets containing CLA compared to those of fish fed the control diet, and intraperitoneal fat ratio was significantly lower in fish fed 1.0% CLA compared to fish fed no CLA. Fish fed dietary CLA exhibited significant increases in hepatosomatic index and moisture content of muscle and carcass. The CLA isomers were detected in liver and muscle of fish fed the diets containing CLA, while a low concentration of one isomer was detected in liver and muscle of fish fed the control diet. Dietary CLA resulted in a significant increase in 18∶2(c-9,c-12) concentration in liver and muscle, but a significant reduction in 18∶1n−7 in these tissues. Furthermore, feeding CLA resulted in a significant increase in the concentration of 20∶5n−3 and 22∶6n−3 in liver, but a reduction of these fatty acids in muscle. This study showed that feeding CLA elevated tissue concentrations of these fatty acid isomers, reduced tissue lipid contents, improved feed efficiency, and altered fatty acid concentrations in liver and muscle of fish.     

Effect of dietary fish oil on blood levels of free fatty acids,ketone bodies and triacylglycerol in humans

Although the reduction of serum triacylglycerol concentrations by dietary fish oil is a well-known effect, the exact mechanism of this effect has not been previously studied in human subjects. Therefore, the aim of this study was (i) to examine the effect of short-term fish oil supplementation on blood concentrations of ketone bodies, free fatty acids and triacylglycerol in healthy humans and (ii) to verify whether the observed relationships between these variables would be consistent with reduced lipolysis and/or enhanced hepatic fatty acid oxidation after fish oil supplementation. Twenty subjects (21–23 years, normal liver function tests) were randomly divided into two groups to supplement their usual diet with either 30 g/d of fish oil (n=11) or olive oil (n=9). Venous blood samples were drawn after an overnight fast, before and after 1, 3 and 7 d of fish oil/olive oil supplementation. Blood concentrations of triacylglycerol and free fatty acids decreased consistently after fish oil supplementation; the reduction was already significant after one day of fish oil (P<0.001 for triacylglycerol andP=0.01 for free fatty acids). In contrast, neither of these blood values changed after olive oil supplementation (P>0.10). No significant changes in glucose, insulin or ketone body levels were observed in either group after supplementation. After fish oil, but not after olive oil supplementation, the ratio of blood ketone body levels to free fatty acid levels increased significantly (P<0.05). Furthermore, after fish oil supplementation only, free fatty acid levels were significantly correlated with levels of ketone bodies (day 7 of supplementation: r=0.90,P<0.001) and triacylglycerol (maximum value on day 3: r=0.77,P<0.01). These findings suggest that reduced lipolysis and increased hepatic β-oxidation/ketogenesis may contribute to reduced triacylglycerol levels after ω3 fatty acid supplementation in humans. Turnover studies are needed in order to further quantitate these processes.     

Effects of dietary n−3 fatty acid-enriched chicken eggs on plasma and tissue cholesterol and fatty acid composition of rats

The purpose of this study was to examine the effects of feeding n−3 polyunsaturated fatty acid (PUFA)-enriched chicken eggs on plasma and liver cholesterol levels and fatty acid composition in rats. Eggs were collected from laying hens fed diets containing 10% flax seed (Hn−3), 12% sunflower seed (Hn−6), or wheat and soybean meal control (CON). Yolk powders were prepared and fed at the 15% level to weanling female Sprague-Dawley rats for 28 days. Consumption of n−3 PUFA-enriched yolks significantly reduced both plasma and liver total cholesterol. Liver total lipids and phospholipids of rats fed Hn−3 diet were enriched with linolenic, eicosapentaenoic, and docosahexaenoic acids with a concomitant reduction of arachidonic acid in liver phospholipids. The plasma cholesterol of rats fed yolk powders enriched with n−6 PUFA (mainly linoleic acid) was reduced to the same extent as in those fed the n−3 enriched, but the liver cholesterol was significantly increased, indicating differential effects of dietary n−3 and n−6 PUFA. The results demonstrated that the cholesterolemic and tissue lipid modulating properties of chicken eggs could be modified in a favorable way by altering the fatty acid composition of yolk lipids through manipulation of laying hen diets.     

Incorporation of dietary linoleic and conjugated linoleic acids and related effects on eggs of laying hens

In the present study, laying hens received 29 g per kg diet of a preparation containing either 70% linoleic acid (LA) or approximately the same amount of conjugated linoleic acid (CLA) in the control and experimental treatments, respectively. The CLA preparation consisted predominantly of cis-9,trans-11 and trans-10,cis-12 fatty acid isomers as free fatty acids in a ratio of 1∶1. The diets were fed for 8 wk to determine the effect of dietary CLA on quality characteristics of eggs. In addition, the fatty acid composition of liver and heart was analyzed. Performance parameters (egg weight, feed efficiency) were not significantly affected by feeding the diets supplemented with CLA. The overall amount of CLA that was incorporated into yolk was 7.95 g CLA/100 g total fatty acids, or approximately 400 mg CLA/egg. The transfer efficiency of the cis-9,trans-11 isomer was higher than that of the trans-10,cis-12 isomer; however, the transfer rate of CLA isomers into yolk and tissues was significantly lower than that of linoleic acid. Dietary CLA increased the concentration of saturated fatty acids in yolk and tissues at the expense of monounsaturated fatty acids. The proportions of myristic, palmitic, and stearic acids in yolk lipids were also changed by dietary CLA. Additionally, long-chain polyunsaturated fatty acids (arachidonic acid and docosahexaenoic acid) were decreased without changing the balance of the n−6/n−3 ratio in egg yolk. The inclusion of CLA in layer diets altered the shape of the yolk and various egg parameters (albumen height, foam index, and yolk index). The results of this study indicate that CLA induces various changes in lipid and fatty acid metabolism of laying hens and affects quality characteristics of eggs.     

Dietary linoleic acid and the fatty acid profiles in rats fed partially hydrogenated marine oils

The influence of the linoleic acid levels of diets containing partially hydrogenated marine, oils (HMO) rich in isomeric 16∶1, 18∶1, 20∶1 and 22∶1 fatty acids on the fatty acid profiles of lipids from rat liver, heart and adipose tissue was examined. Five groups of rats were fed diets containing 20 wt% fat−16% HMO+4% vegetable oils. In these diets, the linoleic acid contents varied between 1.9% and 14.5% of the dietary fatty acids, whereas the contents oftrans fatty acids were 33% in all groups. A sixth group was fed a partially hydrogenated soybean oil (HSOY) diet containing 8% linoleic acid plus 32%trans fatty acids, mainly 18∶1, and a seventh group, 20% palm oil (PALM), with 10% linoleic acid and notrans fatty acids. As the level of linoleic acid in the HMO diets increased from 1.9% to 8.2%, the contents of (n−6) polyunsaturated fatty acids (PUFA) in the phospholipids increased correspondingly. At this dietary level of linoleic acid, a plateau in (n−6) PUFA was reached that was not affected by further increase in dietary 18∶2(n−6) up to 14.5%. Compared with the HSOY- or PALM-fed rats, the plateau value of 20∶4(n−6) were considerably lower and the contents of 18∶2(n−6) higher in liver phosphatidylcholines (PC) and heart PC. Heart phosphatidylethanolamines (PE) on the contrary, had elevated contents of 20∶4(n−6), but decreased 22∶5(n−6) compared with the PALM group. All groups fed HMO had similar contents oftrans fatty acids, mainly 16∶1 and 18∶1, in their phospholipids, irrespective of the dietary 18∶2 levels, and these contents were lower than in the HSOY group. High levels of linoleic acid consistently found in triglycerides of liver, heart and adipose tissue of rats fed HMO indicated that feeding HMO resulted in a reduction of the conversion of linoleic acid into long chain PUFA that could not be overcome by increasing the dietary level of linoleic acid.     

Dietary CLA Combined with Palm Oil or Ovine Fat Differentially Influences Fatty Acid Deposition in Tissues of Obese Zucker Rats

The effect of dietary conjugated linoleic acid (CLA) supplementation in combination with fat from vegetable versus animal origin on the fatty acid deposition, including that of individual 18:1 and 18:2 (conjugated and non-conjugated) isomers, in the liver and muscle of obese rats was investigated. For this purpose, 32 male Zucker rats were randomly assigned to one of four diets containing palm oil or ovine fat, supplemented or not with 1% of 1:1 cis(c)9,trans(t)11 and t10,c12 CLA isomers mixture. Total fatty acid content decreased in the liver and muscle of CLA-fed rats. In the liver, CLA increased saturated fatty acids (SFA) in 11.9% and decreased monounsaturated fatty acids (MUFA) in 6.5%. n-3 Polyunsaturated fatty acids (PUFA) relative proportions were increased in 30.6% by CLA when supplemented to the ovine fat diet. In the muscle, CLA did not affect SFA but decreased MUFA and PUFA percentages. The estimation of Δ9-indices 16 and 18 suggested that CLA inhibited the stearoyl-CoA desaturase activity in the liver (a decrease of 13–38%), in particular when supplemented to the ovine fat diet. Concerning CLA supplementation, the t10,c12 isomer percentage was 60–80% higher in the muscle than in the liver. It is of relevance that rats fed ovine fat, containing bio-formed CLA, had more c9,t11 CLA isomer deposited in both tissues than rats fed palm oil plus synthetic CLA. These results highlight the importance to further clarify the biological effects of consuming foods naturally enriched in CLA, alternatively to CLA dietary supplementation.     

Comparison of the effects of dietary fish oils with different n−3 polyunsaturated fatty acid compositions on plasma and liver lipids in rats

The effects of dietary fish oils with different n−3 polyunsaturated fatty acid compositions on plasma lipid profiles in rats have been studied. Forty-eight male rats, previously maintained on a cholesterol-free diet for 15 days, were fed for 60 days with diets supplemented with 10% fat of either marine hilsa fish (Hilsa ilisa, family clupeidae) or fresh-water chital fish (Notopterus chitala, family notopteridae). The diets had similar levels of total saturated (35–41%), monounsaturated (43–47%) and n−3 polyunsaturated (9–10%) fatty acids. Cholesterol contents of the diets were adjusted to 0.85%; γ-linolenic acid (3.3%) in chital oil and eicosapentaenoic acid (4.9%) in hilsa oil diets were the major n−3 contributors. The percentage of eicosapentaenoic acid in the chital oil diet was 0.57 times that of the hilsa oil diet, but the eicosapentaenoic (EPA) to arachidonic acid (AA) ratio in the latter (4.08) was 3.2 times that of the former (1.27). Sixty days of hilsa oil diet feeding decreased the levels of cholesterol (53.3±2.9 to 50.0±1.1 mg/dL), triacylglycerol (75.7±3.8 to 64.3±2.6 mg/dL) and phospholipid (55.8±1.5 to 51.7±3.1 mg/dL) in rat plasma. Similar treatment with chital oil diet elevated the plasma cholesterol level (53.3±2.9 to 62.3±7.6 mg/dL) while triacylglycerol and phospholipid contents remained unaltered. Both the dietary treatments decreased the levels of linoleic and arachidonic acids in liver but only under the hilsa oil diet did the eicosapentaenoic acid percentage increase markedly (0.8±0.06% to 5.5±0.06%) at the expense of arachidonic acid. This study strongly suggests that the hypolipidemic effect depends on the composition of the n−3 polyunsaturated fatty acids rather than on the total n−3 polyunsaturated fatty acid content of the dietary fish oil.     

Effects of dietary protein and cholesterol on phosphatidylcholine and phosphatidylethanolamine molecular species in mouse liver

The present study examined the effects of two atherogenic factors, animal protein and cholesterol, on the distribution of fatty acids and the molecular species of major liver phospholipids in mice. Weanling mice were fed a semisynthetic diet supplemented with either casein or soy protein (20%, w/w) in the presence or absence of 0.5% cholesterol for 4 wk. Results from mouse liver showed that animal protein and, more so, dietary cholesterol modified the fatty acid profiles of the phospholipids. Animal protein had no significant effect on the concentration of lipids, but it altered the relative distribution and fatty acid profiles of the phospholipids, phosphatidylcholine and phosphatidylethanolamine. Dietary cholesterol, on the other hand, significantly increased the concentration of liver lipids, but it did not alter the relative distribution of phosphatidylcholine and phosphatidylethanolamine. In cholesterol-fed mice, the proportions of molecular species containing 18∶2n−6 were increased, whereas those containing 20∶4n−6 were decreased, indicating that dietary cholesterol suppressed linoleic acid metabolism. Since cholesterol feeding selectively decreased the ratio of 18∶0/20∶4n−6 in phosphatidylcholine, whereas it increased the 18∶0/18∶2n−6 ratio in phosphatidylethanolamine, this finding suggests that dietary cholesterol may affect the incorporation of fatty acids but not the rate of synthesis of phosphatidylcholine and phosphatidylethanolamine.     

The effect of dietary partially hydrogenated marine oils on desaturation of fatty acids in rat liver microsomes

The influence of dietary partially hydrogenated marine oils on distribution of phospholipid fatty acids in rat liver microsomes was studied with particular reference to the metabolism of linoleic acid. Five groups of weanling rats were fed diets containing 20% (w/w) peanut oil (PO), partially hydrogenated peanut oil (HPO), partially hydrogenated Norwegian capelin oil (HCO), partially hydrogenated herring oil (HHO), and rapeseed oil (RSO) for 10 weeks. The partially hydrogenated oils were supplemented with linoleic acid corresponding to 4.6 cal % in the diets. Accumulation of linoleic acid and reduced amount of total linoleic acid metabolites were observed in liver microsomal phospholipids from rats fed partially hydrogenated oils as compared to PO feeding. The most striking effects on the distribution of ω6-polyunsaturated fatty acids was obtained after feeding HHO, a marine oil with a moderate content oftrans fatty acids in comparison with HPO but rich in isomers of eicosenoic and docosenoic acids. Liver microsomal Δ⁶-as well as Δ⁶-desaturase activities as measured in vitro were reduced in rats kept on HHO as compared to PO dietary treatment. The results obtained suggest that the dietary influence of partially hydrogenated marine oils on the metabolism of linoleic acid might be better related to the intake of isomeric eicosenoic and docosenoic acids than to the total intake oftrans fatty acids.     

<Emphasis Type="Italic">Trans</Emphasis>–<Emphasis Type="Italic">trans</Emphasis> Conjugated Linoleic Acid Enriched Soybean Oil Reduces Fatty Liver and Lowers Serum Cholesterol in Obese Zucker Rats

Conjugated linoleic acid (CLA) is a collection of octadecadienoic fatty acids that have been shown to possess numerous health benefits. The CLA used in our study was produced by the photoisomerization of soybean oil and consists of about 20% CLA; this CLA consists of 75% trans–trans (a mixture of t8,t10; t9,t11; t10,t12) isomers. This method could be readily used to increase the CLA content of all soybean oil used as a food ingredient. The objective of this study was to determine the effects of trans–trans CLA-rich soy oil, fed as a dietary supplement, on body composition, dyslipidemia, hepatic steatosis, and markers of glucose control and liver function of obese fa/fa Zucker rats. The trans–trans CLA-rich soy oil lowered the serum cholesterol and low density lipoprotein–cholesterol levels by 41 and 50%, respectively, when compared to obese controls. Trans–trans CLA-rich soy oil supplementation also lowered the liver lipid content significantly (P < 0.05) with a concomitant decrease in the liver weight in the obese rats. In addition, glycated hemoglobin values were improved in the group receiving CLA-enriched soybean oil in comparison to the obese control. PPAR-γ expression in white adipose tissue was unchanged. In conclusion, trans–trans CLA-rich soy oil was effective in lowering total liver lipids and serum cholesterol.     

Dietary oxidized cholesterol modulates cholesterol metabolism and linoleic acid desaturation in rats fed high-cholesterol diets

The interactive effect of high dietary levels of oxidized cholesterol on exogenous cholerterol and linoleic acid metabolism was examined in male 4-wk-old Sprague-Dawley rats given high-cholesterol diets. The rats were pair-fed purified diets free of or containing either 0.5% cholesterol alone or both 0.5% cholesterol and 0.5% oxidized cholesterol mixture (containing 93% oxidized cholesterol) for 3 wk. Hepatic 3-hydroxy-3-methylglutaryl CoA reductase activity was reduced in rats given cholesterol alone or both cholesterol and oxidized cholesterol. However, hepatic cholesterol 7α-hydroxylase activity was lowered only when rats were given both cholesterol and oxidized cholesterol, although dietary cholesterol increased this activity. Reflecting this effect, acidic steroid excretion was lowest among the groups of rats given cholesterol and oxidized cholesterol. On the other hand, the activity of hepatic Δ6 desaturase, a key enzyme in the metabolism of linoleic acid to arachidonic acid, was increased in rats given both cholesterol and oxidized cholesterol, although dietary cholesterol alone lowered its activity. As a result, the Δ6 desaturation index, 20∶3n-6+20∶4n-6/18∶2n-6, in liver and serum phosphlipids tended to be higher in the group fed both cholesterol and oxidized cholesterol than in the one fed cholesterol alone. Thus, dietary oxidized cholesterol significantly modulated exogenous cholesterol metabolism and promoted linoleic acid desaturation even when it was given at high levels together with a high cholesterol diet.     

Dietary sunflower oil reduces plasma and liver triacylglycerols in fasting rats and is associated with decreased liver microsomal phosphatidate phosphohydrolase activity

Plasma and liver lipids were studied in male weanling rats fed diets containing moderate levels of fat (6% by weight) as sunflower oil (SF diet, rich in linoleic acid), salmon oil (SM diet, rich in long-chain n-3 fatty acids), or a blend of peanut and rapeseed oil (PR diet, rich in oleic acid). After nine weeks of feeding, the fasting plasma cholesterol concentrations were 49 and 24% lower in groups SM and SF, respectively, as compared to group PR. Both dietary salmon oil and sunflower oil lowered the tricylglycerol concentration of plasma and liver but, unexpectedly, the response was higher with sunflower oil. Indeed, in group SM the values were 15 and 30% lower in plasma and liver, whereas in group SF, they were 24 and 53% lower, respectively. As compared to group PR, liver triacylglycerols and microsomes contained 2.5- and 2.3-fold less oleic acid, respectively, in group SF, and they were 9.2- and 3.2-fold enriched in n-3 fatty acids, respectively, in group SM. The liver triacylglycerol concentrations were correlated with changes in the microsomal Mg²⁺-dependent phosphatidate phosphohydrolase activity (r=0.47,P<0.01). As oleic acid, unlike long-chain n-3 fatty acids, is considered to promote the triacylglycerol synthesis and secretion, our findings suggest that changes in the membrane fatty acid composition could affect the triacylglycerol content of liver and plasma. Moreover, the availability within the liver, of oleic acid, predominantly incorporated into triacylglycerols, might limit the triacylglycerol production in SF-fed rats.     

Conjugated linoleic acid modulates hepatic lipid composition in mice

Conjugated linoleic acid (CLA) is a chemoprotective fatty acid that inhibits mammary, colon, forestomach, and skin carcinogenesis in experimental animals. We hypothesize that the ubiquitous chemoprotective actions of dietary CLA in extrahepatic tissues are dependent upon its role in modulating fatty acid composition and metabolism in liver, the major organ for lipid metabolism. This study begins to evaluate the role of CLA in lipid metabolism by determining the modulation of fatty acid composition by CLA. Female SENCAR mice were fed semipurified diets containing 0.0% (Diet A), 0.5% (Diet B), 1.0% (Diet C), or 1.5% (Diet D) CLA (by weight) for six weeks. Mice fed Diets B, C, and D exhibited lower body weights and elevated amounts of extractable total lipid in livers compared with mice fed diets without CLA (Diet A). Analyses of the fatty acid composition of liver by gas chromatography revealed that dietary CLA was incorporated into neutral and phospholipids at the expense of linoleate in Diets B, C, and D; oleate increased and arachidonate decreased in neutral lipids of CLA diet groups. In addition, increasing dietary CLA was associated with reduced linoleate in hepatic phospholipids. In an in vitro assay, CLA was desaturated to an unidentified 18:3 product to a similar extent as linoleate conversion to γ-linolenate (9.88, and 13.63%, respectively). These data suggest that CLA may affect metabolic interconversion of fatty acids in liver that may ultimately result in modified fatty acid composition and arachidonate-derived eicosanoid production in extrahepatic tissues. In addition to determining how dietary CLA modulates eicosanoid synthesis, further work is needed to identify enzymatic products that may result from desaturation of CLA.     

Dietary CLA affects lipid metabolism in broiler chicks

A total of 120 three-wk-old broiler chicks were randomly assigned to three diets containing 0, 2, or 3% CLA and fed for 5 wk. Fat content and FA composition of liver, plasma, and feces were analyzed. Key enzymes involved in FA synthesis and catabolism in liver, TG, cholesterol, and FFA content of plasma were also determined. Dietary CLA increased TG, total cholesterol, and HDL cholesterol levels in plasma. The increased plasma TG level could be caused by increased FA synthesis in the liver after CLA feeding, because the activity of FA synthase in the liver increased after dietary CLA treatment. Dietary CLA changed the FA composition of feces but had no effect on fat content. Compared to the amounts of linoleic and linolenic acids present in the control diet, the amounts excreted into the feces of CLA-treated birds were significantly higher. Liver weights of broilers significantly increased after CLA feeding, but there was no difference in liver fat content among the different CLA treatments. CLA treatment did not influence total FFA content in plasma; however, there was a significant difference in the composition of FFA. Dietary CLA reduced the content of linoleic and arachidonic acids in both plasma and liver.     

Linoleoyl-enriched triacylglycerol species increase in maternal liver during late pregnancy in the rat

In view of the previously reported changes in the fatty acid composition of maternal liver triacylglycerols in late pregnancy, changes in the composition of maternal liver triacylglycerol species were assessed in rats fed a semipurified diet during pregnancy. Between day 18 and day 21 of pregnancy, total maternal liver triacylglycerols increased by 50%. Triacylglycerol species with a total acyl carbon number (C) of 50 or 60 (C50, C60) remained unchanged while C48 and C52–C58 were relatively increased. The individual triacylglycerol species containing one, two or three linoleoyl moieties were incompletely recovered using a polar high temperature gas-liquid chromatography (GLC) column. Nevertheless, at day 21 compared to day 18, the linoleoyl-containing species were relatively increased by 62–463%, while tripalmitin was decreased by 38%. Our data suggest that despite an adequate intake of linoleic acid (25 g/kg in the diet), maternal hepatic triacylglycerol content of linoleic acid decreased during mid-pregnancy but increased significantly toward term possibly in preparation for the transfer of linoleic acid to the neonate during lactation.     

Comparative hypocholesterolemic effects of six vegetable oils in cholesterol-fed rat

The hypocholesterolemic efficacies of various polyunsaturated fatty acids were compared in rats given cholesterol-enriched diets.Oenothera biennis Linn oil (OBLO, linoleic +γ-linolenic), sunflower oil (linoleic), palm oil (PLO, oleic+linoleic), soybean oil (linoleic+α-linolenic), high-oleic safflower oil (oleic+linoleic), or mixed oil (linoleic+α-linolenic) was added to the diet at 200 g/kg (20% groups). OBLO was also added at 100 g/kg diet (10% group). The serum total and very low density lipoprotein+intermediate lipoprotein+low density lipoprotein cholesterol concentrations of the 10 and 20% OBLO groups were consistently lower than those in the other groups. The liver cholesterol concentration in the PLO group was lower in all groups. The liver cholesterol concentrations in the 10 and 20% OBLO groups were also lower than in the other groups. There were no significant differences in the fecal neutral sterol and bile acid extraction among groups.