Studies on the effect of dietary fish oil on the physical and chemical properties of low density lipoproteins in cynomolgus monkeys

To determine the effect of isocaloric substitution of dietary fish oil for lard on the physical and chemical properties of plasma low density lipoproteins (LDL), ten adult male cynomolgus monkeys were fed diets containing 11% (by weight) fish oil or lard in a crossover study consisting of two 15-week periods with a 6-week washout period in between. The atherogenic diets contained 40% of calories as fat with 0.26 mg cholesterol/kcal. Periodic measurements of plasma lipids were made throughout the study and a large blood sample was taken near the end of each 15-week period for LDL isolation and characterization, and for quantification of plasma apolipoproteins. Values for both studies were combined (mean +/- SE; n = 10) by diet. Significantly lower high density lipoprotein (HDL) cholesterol (28 +/- 2 vs. 57 +/- 8 mg/dl), apoA-I (53 +/- 11 vs. 88 +/- 7 mg/dl), and apoE (4.2 +/- 0.9 vs. 8.2 +/- 1.5 mg/dl) concentrations were found when the animals were consuming the fish oil versus the lard diet, respectively, but total plasma cholesterol (408 +/- 35 vs. 416 +/- 14 mg/dl), LDL cholesterol (356 +/- 34 vs. 331 +/- 17 mg/dl), and apoB (227 +/- 35 vs. 205 +/- 23 mg/dl) levels were not affected. LDL size was smaller during fish oil feeding (4.2 +/- 0.1 vs. 4.9 +/- 0.1 g/mumol) and LDL particle concentration was greater (2.3 +/- 0.2 vs. 1.8 +/- 0.1 microM). During fish oil feeding LDL cholesteryl esters (CE) and phospholipids (PL) were enriched in n-3 fatty acids and were relatively poor in 18:1 and 18:2 LDL CE transition temperature was about 11 degrees C lower during fish oil feeding (32 +/- 1 vs. 44 +/- 0.5 degrees C) and was positively correlated with the number of saturated, monoun-saturated, and n-6 polyunsaturated CE molecules per LDL. The results suggested that the range of transition temperatures among individual animal LDL was primarily determined by the number of monounsaturated CE, and the accumulation of n-3 polyunsaturated CE in LDL during fish oil feeding uniformly lowered the transition temperature of the LDL particle. There was a significant decrease in the percentage of LDL phosphatidylcholine (59 +/- 1 vs. 72 +/- 1%) and an increase in lysophosphatidylcholine (13 +/- 1 vs. 5 +/- 1%) and sphingomyelin (22 +/- 1 vs. 17 +/- 1%) during fish oil feeding relative to that of lard.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of dietary polyunsaturated fatty acids on contractile function of hearts isolated from sedentary and trained rats

Moderate physical training induced a decrease in arterial blood pressure in fish oil-fed rats as compared to sunflower seed oil-fed rats. The purpose of this study was to determine if these changes were due to modifications of the left ventricular function of the heart. Forty rats were fed a semi-purified diet containing either 10% sunflower seed oil or 10% fish oil (EPAX 3000TG, Pronova). Each dietary group was assigned to two sub-groups, one being constituted by sedentary animals and the other by trained animals. Training was achieved by daily running for 60 minutes at moderate intensity for three weeks. At the end of the training period, the animals were sacrificed and their hearts were immediately perfused according to the working mode. The phospholipid fatty acid composition and parameters of the left ventricular function were determined. Feeding fish oil markedly reduced the proportion of n-6 polyunsaturated fatty acids (PUFA, 18:2 n-6, 20:4 n-6, 22:4 n-6 and 22:5 n-6) in cardiac phospholipids. The n-6 PUFA were replaced by n-3 PUFA (mainly docosahexaenoic acid). In sedentary animals, the fluid dynamic (aortic and coronary flow, cardiac output) was not modified by the diet. The heart rate was reduced (-10%) in n-3 PUFA-rich hearts. Physical training did not markedly alter the polyunsaturated fatty acid profile of cardiac phospholipids. Conversely, it reduced the heart rate, aortic flow and cardiac output (-11, -21 and -14%, respectively) at a similar extent in the two dietary groups. In a second set of experiments, the training period was repeated in animals fed a commercially available diet (A103, UAR) which simultaneously provided n-6 and n-3 fatty acids. In these dietary conditions, neither the aortic flow nor the heart rate was decreased by physical exercise. These results suggest that both n-6 and n-3 PUFA in the diet are necessary to ensure a good cardiac adaptation to moderate physical training. Furthermore, the fish oil-induced decrease in arterial blood pressure in trained animals was not related to changes in cardiac contractility, but to a decrease in vascular resistances. Moderate physical training + dietary n-3 PUFA might be used to prevent hypertension and cardiovascular diseases.     

Dietary polyunsaturated fatty acids alter myocardial protein kinase C expression and affect cardioprotection induced by chronic hypoxia

We examined the influence of dietary fatty acid (FA) classes on the expression of protein kinase C (PKC) delta and epsilon in relation to the cardioprotective effects of chronic intermittent hypoxia (CIH). Adult male Wistar rats were fed a nonfat diet enriched with 10% lard (saturated FA [SFA]), fish oil (n-3 polyunsaturated FA [n-3 PUFA]), or corn oil (n-6 PUFA) for 10 weeks. After 4 weeks on the diet, each group was divided into two subgroups that were either exposed to CIH in a barochamber (7000 m, 8 hrs/ day) or kept at normoxia for an additional 5-6 weeks. A FA phospholipid profile and Western blot analysis of PKC were performed in left ventricles. Infarct size was assessed in anesthetized animals subjected to 20-min coronary artery occlusion and 3-hr reperfusion. CIH decreased the n-6/n-3 PUFA ratio in all groups by 23% independently of the initial value set by various diets. The combination of n-3 diet and CIH had a stronger antiarrhythmic effect during reperfusion than the n-3 diet alone; this effect was less pronounced in rats fed the n-6 diet. The normoxic n-6 group exhibited smaller infarctions (by 22%) than the n-3 group. CIH decreased the infarct size in n-3 and SFA groups (by 20% and 23%, respectively) but not in the n-6 group. Unlike PKC epsilon, the abundance of PKC delta in the myocardial particulate fraction was increased by CIH except for the n-6 group. Myocardial infarct size was negatively correlated (r=- 0.79) with the abundance of PKC delta in the particulate fraction. We conclude that lipid diets modify the infarct size-limiting effect of CIH by a mechanism that involves the PKC delta-dependent pathway.     

Different edible oil beneficial effects (canola oil, fish oil, palm oil, olive oil, and soybean oil) on spontaneously hypertensive rat glomerular enlargement and glomeruli number

We have tested the different edible oil effects on the blood pressure (BP) control and the following glomerular protection. Six groups of 12-week-old male spontaneously hypertensive rats (SHR) (n = 5), have received different edible oils (fish, canola, palm, olive, and soybean) or a placebo by gavage for 13 weeks. Renal cortex was analyzed through light microscopy and stereology. Usual BP increase, glomerulosclerosis, glomerular enlargement, and glomeruli loss in SHR has been prevented (fish, canola and palm oils) or attenuated (olive and soybean oils) by these oil long-term administration. The most favorable effect has been seen in the fish oil administration (source of n-3 polyunsaturated fatty acids, PUFA, eicosapentaenoic and docosahexaenoic acids), followed by both canola and palm oils (source of n-3 PUFA plus n-9 monounsaturated, MUFA, and saturated fatty acid, respectively), and finally both olive and soybean oils (source of n-9 MUFA and n-6 PUFA, respectively).     

Dietary fish oil prevents asynchronous contractility and alters Ca(2+) handling in adult rat cardiomyocytes

This study examined the effects of dietary incorporation of n-3 polyunsaturated fatty acids (PUFAs) into cardiac membrane phospholipids on Ca(2+) handling (using Fura-2) and arrhythmic contractility in electrically-stimulated, adult rat ventricular cardiomyocytes. Dietary lipid supplementation with fish oil (FO) for 3 weeks significantly increased the proportion of total n-3 polyunsaturated fatty acids (in particular, docosahexaenoic acid) in ventricular membrane phospholipids compared with a saturated fat (SF) supplemented diet (26.2 +/- 0.9% vs 6.9 +/- 0.9%, respectively, P < 0.001). Cardiomyocytes isolated from the FO group were significantly (P < 0.001) less susceptible to isoproterenol-induced arrhythmic contractile activity compared with the SF group over a range of isoproterenol concentrations. Isoproterenol (0.5 &mgr;M) stimulation increased end-diastolic and systolic [Ca(2+)](i) to a similar extent in both groups. The time constant of Ca(2+) transient decay was significantly increased in the FO group compared with the SF group (98.4 +/- 2.8 ms, n = 8 and 86.9 +/- 2.1 ms, n = 8, P < 0.01, respectively). The effect of dietary n-3 PUFA incorporation into membrane phospholipids was not associated with changes in sarcoplasmic reticulum Ca(2+) content (measured by rapid application of caffeine) or membrane fluidity. The increase in the time constant of decay of Ca(2+) transients following dietary supplementation with FO may indicate altered functioning of the sarcolemmal Na(+)-Ca(2+) exchanger by n-3 PUFA incorporation into membrane phospholipids.     

Inverse modifications of heart and liver alpha-tocopherol status by various dietary n-6/n-3 polyunsaturated fatty acid ratios

The effect of dietary n-6/n-3 fatty acid ratio on alpha-tocopherol homeostasis was investigated in rats. Animals were fed diets containing fat (17% w/w) in which the n-6/n-3 ratio varied from 50 to 0.8. This was achieved by combining corn oil, fish oil, and lard. The polyunsaturated to saturated ratio and total alpha-tocopherol remained constant in all diets. Results showed that enrichment of n-3 polyunsaturated fatty acids in the diet, even at a low amount (3.9% w/w), resulted in a dramatic reduction of blood alpha-tocopherol concentration, which, in fact, is the result of a decrease in plasma lipids, since the alpha-tocopherol to total lipids ratio was not significantly altered. The most striking effect observed was a considerable alpha-tocopherol enrichment (x 4) of the heart as its membranes became enriched with n-3 polyunsaturated fatty acids. This process appeared even with a low amount of fish oil (3.9% w/w) added to the diet. Accordingly, a strong positive correlation was found between heart alpha-tocopherol and docosahexaenoic acid (r = 0.86) or docosahexaenoic acid plus eicosapentaenoic acid levels (r = 0.84). Conversely, the liver alpha-tocopherol level dropped dramatically when n-3 polyunsaturated fatty acids were gradually added to the diet. It is concluded that fish oil intake dramatically alters the alpha-tocopherol homeostasis in rats.     

Reduction of cholesterol absorption by dietary oleinate and fish oil in African green monkeys.

To determine whether diets enriched in monounsaturated or n-3 fatty acids cause a reduction in cholesterol absorption relative to those more enriched in saturated fatty acids, we measured cholesterol absorption in 18 African green monkeys fed diets enriched in lard, oleinate (oleic acid-rich safflower oil), or fish oil at two levels of dietary cholesterol (0.05 vs. 0.77 mg/kcal). All animals were initially challenged with the lard, high cholesterol diet to ascertain their responsiveness to dietary cholesterol. Based on the results of this challenge, low versus high responders were equally distributed in assignation to the low (n = 6) and high (n = 12) cholesterol regimens. Within each level of dietary cholesterol animals consumed all three dietary fats in random sequences during three experimental phases each lasting 9-12 months with a monkey chow washout period between each phase, so that each animal served as its own control. During each dietary phase measurements of plasma lipids and cholesterol absorption were performed. The animals fed the higher versus lower level of dietary cholesterol had significantly higher plasma total cholesterol and low density lipoprotein (LDL) cholesterol concentrations and lower percentage cholesterol absorption; high density lipoprotein (HDL) cholesterol levels were not affected by the level of dietary cholesterol. Dietary fish oil resulted in a 20-30% reduction (P less than 0.01) in total plasma and LDL cholesterol and a 30-40% reduction (P less than 0.01) in HDL cholesterol concentrations compared to lard and oleinate regardless of the level of dietary cholesterol. At the high level of cholesterol intake, the oleinate and fish oil diets resulted in significantly lower percentage cholesterol absorption compared to the lard fat diet (35 +/- 2%, 34 +/- 3%, 41 +/- 4%, respectively). At the lower level of dietary cholesterol, percentage cholesterol absorption values were higher than those at the high cholesterol intake (45-52% vs. 34-41%) but were not affected by the type of dietary fat. There was a significant positive correlation between plasma LDL cholesterol concentrations and percentage cholesterol absorption for the oleinate and lard diets at the high level of dietary cholesterol and a significant inverse association between plasma HDL cholesterol and percentage cholesterol absorption. We conclude that the type of dietary fat can influence cholesterol absorption in African green monkeys and that oleinate and fish oil reduce cholesterol absorption relative to lard when a high amount of cholesterol (0.77 mg/kcal) is present in the diet.     

Effects of dietary n-3 fatty acids on contractility, Na+ and K+ currents in a rat cardiomyocyte model of arrhythmia

The n-3 polyunsaturated fatty acids (PUFAs) have been reported to prevent ventricular fibrillation in human clinical studies and in studies involving experimental animals and isolated cardiomyocytes. This study aimed to determine whether dietary n-3 PUFAs could prevent isoproterenol and free radical-induced arrhythmic (asynchronous) contractile activity in adult rat cardiomyocytes and whether whole-cell Na(+) and K(+) currents measured by patch-clamp techniques were affected. Dietary supplementation with fish oil for 3 weeks significantly increased the proportion of total n-3 PUFAs in ventricular membrane phospholipids compared with saturated fat supplementation (18.8 +/- 0.6% vs. 8.1 +/- 1.0%, respectively). Cardiomyocytes from the fish oil group were less susceptible to isoproterenol-induced asynchronous contractile activity than were those from the saturated fat group [EC(50) values: 892 +/- 130 nM, n = 6 and 347 +/- 91 nM, n = 6 (P < 0.05), respectively]. Fish oil supplementation also prolonged the time taken to develop asynchronous contractile activity induced by superoxide and hydrogen peroxide. The voltage dependence of inactivation of Na(+) currents were significantly altered (-73.5 +/- 1.2 mV, n = 5 vs. -76.7 +/- 0.7 mV, n = 5, P < 0.05, for saturated fat and fish oil treated groups, respectively). The voltage dependence of activation of Na(+) and K(+) currents was not significantly affected by the dietary fish oil treatment. These results demonstrate the antiarrhythmic effects of dietary fish oil in a cardiomyocyte model of arrhythmia.     

Effect of fish oil diet on hepatic lipid metabolism in nonhuman primates: lowering of secretion of hepatic triglyceride but not apoB

African green monkeys were fed diets containing either 11% (by weight) fish oil or lard for 2.5 yr. To test the hypothesis that fish oil decreases hepatic secretion of triglyceride (TG) and apoB, livers from these animals were perfused with a fatty acid mixture [85% (w/w) oleate containing [14C]oleate and 15% n-3 containing [3H]eicosapentaenoic acid (EPA)] at a rate of 0.1 mumol fatty acid/min per g liver. Liver perfusate was sampled every 30 min during 4 h of recirculating perfusion. The concentration of triglyceride was similar for livers of animals of both groups and there was no difference between groups in the extent of incorporation of [3H]EPA or [14C]oleate into hepatic TG. While the secretion rate for the mass of TG was less in the fish oil-fed group (8.3 +/- 2.5 vs 18.3 +/- 4.4 mg/h per 100 g liver, P less than 0.05), the apoB secretion rate was similar (0.92 +/- 0.15 vs 1.01 +/- 0.13 mg/h per 100 g liver). Significantly less [3H]EPA was incorporated into secreted TG in the fish oil group (0.4 +/- 0.1 vs 1.0 +/- 0.1% infused dose/h; P less than 0.01). The rate of secretion of [14C]TG was similar for both groups (1.3 +/- 0.3 vs 1.4 +/- 0.1% infused dose/h for fish oil and lard groups, respectively). No significant diet-related differences in [3H]TG or [14C]TG fatty acid specific activity were observed for perfusate TG or hepatic TG. After perfusion, livers from fish oil-fed monkeys contained significantly more [3H]EPA in hepatic phospholipid than livers from lard-fed monkeys (19.5 +/- 1.8 vs 11.4 +/- 1.7% infused dose; P less than 0.01) although hepatic phospholipid mass concentrations were similar. The liver phospholipids of the fish oil group were enriched in n-3 fatty acid mass and were relatively depleted of oleate and linoleate. We conclude that although apoB secretion was unaffected, dietary fish oil significantly decreased hepatic TG secretion through relatively poor utilization of EPA for the synthesis of TG destined for secretion in VLDL; at the same time, increased incorporation of [3H]EPA into hepatic phospholipid accompanied the decreased incorporation into secreted TG and these events may be coupled.(ABSTRACT TRUNCATED AT 400 WORDS)     

The interaction of dietary fatty acid and cholesterol on catecholamine-stimulated adenylate cyclase activity in the rat heart

Diets supplemented with high levels of saturated or unsaturated fatty acids supplied by addition of sheep kidney fat or sunflower seed oil, respectively, were fed to rats with or without dietary cholesterol. The effects of these diets on cardiac membrane lipid composition, catecholamine-stimulated adenylate cyclase and beta-adrenergic receptor activity associated with cardiac membranes, were determined. The fatty acid-supplemented diets, either with or without cholesterol, resulted in alterations in the proportion of the (n-6) to (n-3) series of unsaturated fatty acids, with the sunflower seed oil increasing and the sheep kidney fat decreasing this ratio, but did not by themselves significantly alter the ratio of saturated to unsaturated fatty acids. However, cholesterol supplementation resulted in a decrease in the proportion of saturated and polyunsaturated fatty acids and a dramatic increase in oleic acid in cardiac membrane phospholipids irrespective of the nature of the dietary fatty acid supplement. The cholesterol/phospholipid ratio of cardiac membrane lipids was also markedly increased with dietary cholesterol supplementation. Although relatively unaffected by the nature of the dietary fatty acid supplement, catecholamine-stimulated adenylate cyclase activity was significantly increased with dietary cholesterol supplementation and was positively correlated with the value of the membrane cholesterol/phospholipid ratio. Although the dissociation constant for the beta-adrenergic receptor, determined by [125I](-)-iodocyanopindolol binding, was unaffected by the nature of the dietary lipid supplement, the number of beta-adrenergic receptors was dramatically reduced by dietary cholesterol and negatively correlated with the value of the membrane cholesterol/phospholipid ratio. These results indicate that the activity of the membrane-associated beta-adrenergic/adenylate cyclase system of the heart can be influenced by dietary lipids particularly those altering the membrane cholesterol/phospholipid ratio and presumably membrane physico-chemical properties. In the face of these dietary-induced changes, a degree of homeostasis was apparent both with regard to membrane fatty acid composition in response to an altered membrane cholesterol/phospholipid ratio, and to down regulation of the beta-adrenergic receptor in response to enhanced catecholamine-stimulated adenylate cyclase activity.     

Dietary n-3 polyunsaturated fatty acids modify fatty acid composition in hepatic and abdominal adipose tissue of sucrose-induced obese rats

The fatty acid profile of hepatocytes and adipocytes is determined by the composition of the dietary lipids. It remains unclear which fatty acid components contribute to the development or reduction of insulin resistance. The present work examined the fatty acid composition of both tissues in sucrose-induced obese rats receiving fish oil to determine whether the effect of dietary (n-3) polyunsaturated fatty acids (PUFAs) on the reversion of metabolic syndrome in these rats is associated to changes in the fatty acid composition of hepatocyte and adipocyte membrane lipids. Animals with metabolic syndrome were divided into a corn–canola oil diet group and a fish oil diet group, and tissues fatty acids composition were analyzed after 6 weeks of dietary treatment. Fatty acid profiles of the total membrane lipids were modified by the fatty acid composition of the diets fed to rats. N-3 PUFAs levels in animals receiving the fish oil diet plus sucrose in drinking water were significantly higher than in animals under corn–canola oil diets. It is concluded that in sucrose-induced obese rats, consumption of dietary fish oil had beneficial effects on the metabolic syndrome and that such effects would be conditioned by the changes in the n-3 PUFAs composition in hepatic and adipose tissues because they alter membrane properties and modify the type of substrates available for the production of active lipid metabolites acting on insulin resistance and obesity.     

Dietary polyunsaturated fatty acids (C18:2 omega6 and C18:3 omega3) do not suppress hepatic lipogenesis

Omega 3 polyunsaturated fatty acids are promoted as beneficial in the prevention of metabolic and cardiovascular diseases. In general, dietary omega 3 fatty acids are derived from plant sources as linolenic acid (LNA, C18:3 omega3) the precursor to eicosapentaenoic acid (EPA, C20:5 omega3) and docosahexaenoic acid (DHA, C22:6 omega3). However, it remains unclear if the polyunsaturated fatty acid (PUFA) LNA can provide the same health benefits as the very long chain highly unsaturated fatty acids (HUFA) EPA and DHA generally derived from oily fish. In this study, mice were fed synthetic diets containing lard (low in PUFA and HUFA), canola oil (to supply PUFA), or a mixture of menhaden and arasco (fish and fungal) oils (to supply HUFA) for 8 weeks. The diets were neither high in calories nor fat, which was supplied at 6%. The lard and canola oil diets resulted in high levels of hepatic triglycerides and cholesterol and elevation of lipogenic gene expression. By comparison livers from mice fed the fish/fungal oil diet had low levels of lipid accumulation and more closely resembled livers from mice fed standard laboratory chow. SREBP1c and PPARgamma gene and protein expression were high in livers of animals fed diets containing lard or canola oil compared with fish/fungal oil. Hepatic fatty acid analyses indicated that dietary PUFA were efficiently converted to HUFA regardless of source. Therefore, differences in hepatic lipid levels and gene expression between dietary groups were due to exogenous fatty acid supplied rather than endogenous pools. These results have important implications for understanding the regulation of hepatic lipogenesis by dietary fatty acids.     

Can n-3 PUFA reduce cardiac arrhythmias? Results of a clinical trial

Dietary n-3 polyunsaturated fatty acids (PUFA) derived from fatty fish or fish oil may reduce the incidence of lethal myocardial infarction and sudden cardiac death. This might be due to a prevention of fatal cardiac arrhythmias. So far, however, only few clinical data are available being adequate to define indications for an antiarrhythmic treatment with n-3 PUFA. In a randomized, double-blind, placebo-controlled study 65 patients with cardiac arrhythmias without coronary heart disease or heart failure were subdivided into 2 groups. One group (n = 33) was supplemented with encapsulated fish oil (3g/day, equivalent to 1g/day of n-3 PUFA) over 6 months. The other group (n = 32) was given 3g/day of olive oil as placebo. In the fish oil group a decrease of serum triglycerides, total cholesterol, LDL cholesterol, plasma free fatty acids and thromboxane B2 as well as an increase of HDL cholesterol were observed. Moreover, a reduced incidence of atrial and ventricular premature complexes, couplets and triplets were documented. Accordingly, higher grades of Lown's classification switched to lower grades at the end of the dietary period. No changes were seen in the placebo group. The data indicate an antiarrhythmic action of n-3 PUFA under conditions of clinical practice which might help to explain the reduced incidence of fatal myocardial infarction and sudden cardiac death in cohorts on a fish-rich diet or supplemented with n-3 PUFA. Further studies elucidating the possible link between the reduced incidence of cardiac arrhythmias and sudden cardiac death by dietary intake of n-3 PUFA are warranted.     

Effect of fish oil versus lard diets on the chemical and physical properties of low density lipoproteins of nonhuman primates

Twenty-four adult male African green grivet monkeys were fed diets containing 42% of calories as lard or menhaden oil and 0.76 mg of cholesterol/kcal for a period of 8 months. Plasma samples from fasting animals were then taken and low density lipoproteins (LDL) were isolated by ultracentrifugation and agarose column chromatography. The LDL were analyzed chemically, and physical properties of the particles were studied by differential scanning calorimetry. The fish oil group had significantly smaller LDL (2.91 vs. 3.43 g/mumol), which contained fewer molecules per particle of all lipid constituents, except triglyceride, compared to the lard-fed animals. The fish oil-fed group had 15% of the total cholesteryl esters as n-3 fatty acyl species and the number of n-3, but not n-6, cholesteryl esters per LDL particle was proportional to LDL size. The numbers of saturated and monounsaturated cholesteryl ester species per LDL particle were highly correlated with LDL size for both diet groups. The LDL of the fish oil group had broad reversible thermotropic transitions that were 12-13 degrees C lower than those of the lard group. These transitions were indicative of order-disorder transitions of the LDL core cholesteryl esters. The peak transition temperature of LDL of the lard group was proportional to the ratio of saturated and monounsaturated to polyunsaturated cholesteryl ester species (CEFA ratio). However, the much lower peak transition temperature of the LDL of the fish oil group was not related to the CEFA ratio nor to the triglyceride content of the particles, but rather, to the n-3 cholesteryl ester content of the particles. Studies of cholesteryl ester model systems demonstrated that relatively small amounts of n-3 cholesteryl esters (less than 15% of total cholesteryl ester) could result in a lowering of the peak transition temperature of cholesteryl linoleate similar to that seen for intact LDL. We conclude that n-3 cholesteryl esters in small quantities have a marked disordering effect on the core cholesteryl esters of LDL, resulting in a striking depression of LDL transition temperature. In addition, we conclude that n-3 cholesteryl esters are preferentially utilized relative to n-6 cholesteryl esters to increase the number of cholesteryl esters per LDL particle with LDL enlargement in fish oil-fed animals.     

Influence of dietary n-3 fatty acids on macrophage glycerophospholipid molecular species and peptidoleukotriene synthesis

The study examined the ability of dietary n-3 fatty acids to modify mouse peritoneal macrophage glycerophospholipid molecular species and peptidoleukotriene synthesis. After a 2-week feeding period, fish versus corn oil feeding significantly (P less than 0.01) lowered n-6 polyunsaturated fatty acid (PUFA) mol % levels, i.e., arachidonic acid (20:4n-6) in diacylphosphatidylserine (PtdSer), diacylphosphatidylinositol (PtdIns), diacylglycerophosphoethanolamine (PtdEtn), alkenylacylglycerophosphoethanolamine (PlsEtn), and diacylglycerophosphocholine (PtdCho). A notable exception was alkylacylglycerophosphocholine (PakCho), where only moderate decreases in 16:0-20:4n-6 and 18:0-20:4n-6 species were observed after fish oil supplementation. The predominant n-3 PUFA in macrophage phospholipid subclasses was docosapentaenoic acid (22:5n-3). The major n-3 species were 18:0-22:5n-3 in PtdIns, PtdSer, glycerophosphoethanolamines (EtnGpl) and 16:0-22:5n-3 in PtdCho and PlsEtn. The major n-3-containing species in PakCho were 16:0-20:5n-3 and 18:1-22:6n-3. These findings indicate that n-3 PUFA are differentially incorporated into macrophage phospholipid subclasses after dietary fish oil supplementation, and suggest that phospholipid remodeling enzymes selectively discriminate between substrates based on compatibility of sn-1 covalent linkage and the composition of the sn-1 and sn-2 aliphatic chains. Macrophage peptidoleukotriene synthesis was also strongly influenced after fish oil feeding; the LTC5/LTC4 ratio was significantly higher (P less than 0.01) in fish oil-fed animals than in corn oil-fed animals, 0.85 versus 0.01, respectively. These ratios were subsequently compared to phospholipid molecular species 20:5n-3/20:4n-6 ratios in order to determine potential sources of eicosanoid precursors.     

Dietary fish oil replacement with canola oil up-regulates glutathione peroxidase 1 gene expression in yellowtail kingfish (Seriola lalandi)

The marine carnivore yellowtail kingfish (YTK, Seriola lalandi) was fed diets containing 5% residual fish oil (from the dietary fish meal) plus either 20% fish oil (FO), 20% canola oil (CO), 20% poultry oil (PO), 10% fish oil plus 10% canola oil (FO/CO) or 10% fish oil plus 10% poultry oil (FO/PO) and the effects on fish growth and hepatic expression of two glutathione peroxidase (GPx 1 and GPx 4) and two peroxiredoxin (Prx 1 and Prx 4) antioxidant genes were investigated. Partial (50%) replacement of the added dietary fish oil with poultry oil significantly improved fish growth whereas 100% replacement with canola oil significantly depressed fish growth. The fatty acid profiles of the fish fillets generally reflected those of the dietary oils except that there was apparent selective utilization of palmitic acid (16:0) and oleic acid (18:1n-9) and apparent selective retention of eicospentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). The Prx 1 and 4 genes were expressed at 10- and 100-fold the level of the GPx 4 and 1 genes, respectively, and at one-tenth the level of the highly expressed β-actin reference gene. Dietary fish oil replacement with canola oil significantly up-regulated GPx 1 gene expression and there was a non-significant tendency towards down-regulation of Prx 1 and Prx 4. The results are discussed in terms of the effects of fish oil replacement on the peroxidation index of the diets and the resulting effects on the target antioxidant enzymes.     

Dietary n-3 PUFAs affect the blood pressure rise and cardiac impairments in a hyperinsulinemia rat model in vivo

The cardiovascular consequences of eicosapentaenoic acid (EPA)- and docosahexaenoic acid (DHA)-specific intake were evaluated in vivo in a hyperinsulinemia (HI) model induced by dietary fructose intake. Wistar rats were fed a diet containing (or not for control) either EPA or DHA. The rise in blood pressure (BP), heart rate, and ECG were continuously monitored using an intra-abdominal telemetry system. The myocardial phospholipid fatty acid profile was significantly affected by DHA intake but less by EPA intake. The data indicated a reduced rise in BP in both DHA and EPA HI groups compared with controls. This result was confirmed by tail-cuff measurement after 5 wk [133.3 +/- 1.67 and 142.5 +/- 1.12 mmHg in n-3 polyunsaturated fatty acid (PUFA) and control groups, respectively], whereas n-3 PUFA did not affect BP in non-HI rats (116.3 +/- 3.33 mmHg). The heart rate was lower in the HI DHA group than in the other two dietary HI groups. Moreover, DHA induced a significantly shorter QT interval. It is concluded that the cardioactive component of fish oils is DHA through a mechanism that may involve the cardiac adrenergic system.     

Dietary Fat Influences the Expression of Contractile and Metabolic Genes in Rat Skeletal Muscle

Dietary fat plays a major role in obesity, lipid metabolism, and cardiovascular diseases. To determine whether the intake of different types of dietary fats affect the muscle fiber types that govern the metabolic and contractile properties of the skeletal muscle, we fed male Wistar rats with a 15% fat diet derived from different fat sources. Diets composed of soybean oil (n-6 polyunsaturated fatty acids (PUFA)-rich), fish oil (n-3 PUFA-rich), or lard (low in PUFAs) were administered to the rats for 4 weeks. Myosin heavy chain (MyHC) isoforms were used as biomarkers to delineate the skeletal muscle fiber types. Compared with soybean oil intake, fish oil intake showed significantly lower levels of the fast-type MyHC2B and higher levels of the intermediate-type MyHC2X composition in the extensor digitorum longus (EDL) muscle, which is a fast-type dominant muscle. Concomitantly, MyHC2X mRNA levels in fish oil-fed rats were significantly higher than those observed in the soybean oil-fed rats. The MyHC isoform composition in the lard-fed rats was an intermediate between that of the fish oil and soybean oil-fed rats. Mitochondrial uncoupling protein 3, pyruvate dehydrogenase kinase 4, and porin mRNA showed significantly upregulated levels in the EDL of fish oil-fed rats compared to those observed in soybean oil-fed and lard-fed rats, implying an activation of oxidative metabolism. In contrast, no changes in the composition of MyHC isoforms was observed in the soleus muscle, which is a slow-type dominant muscle. Fatty acid composition in the serum and the muscle was significantly influenced by the type of dietary fat consumed. In conclusion, dietary fat affects the expression of genes related to the contractile and metabolic properties in the fast-type dominant skeletal muscle, where the activation of oxidative metabolism is more pronounced after fish oil intake than that after soybean oil intake.     

Whole body and hepatic cholesterol synthesis rates in the guinea-pig: effect of dietary fat quality

The effects of polyunsaturated, monounsaturated and saturated dietary fat on total and hepatic cholesterol synthesis were studied in the guinea-pig. Male Hartley guinea-pigs were fed semi-synthetic diets containing 7.5% (w/w) of either corn oil (CO), olive oil (OL) or lard for a period of 5 weeks and rates of endogenous cholesterol synthesis were determined from the incorporation of [3H]water into digitonin-precipitable sterols (DPS) and by measurement of sterol balance. In addition, total and expressed 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activities were determined in hepatic microsomes. Rates of whole body cholesterol synthesis determined by incorporation of [3H]water into DPS were significantly lower for guinea-pigs on the CO diet with values of 18.7 +/- 1.8 mumol/h (n = 4) vs. 26.7 +/- 4.8 and 24.6 +/- 1.8 mumol/h for animals on the OL (n = 4) and lard (n = 3) diets (P less than 0.001), respectively. Hepatic cholesterol synthesis rates were significantly decreased in animals on the OL diet, whether determined from incorporation of [3H]water into DPS or by analysis of HMG-CoA reductase activity. Hepatic total and free cholesterol levels were not different for animals on the three dietary fats; however, cholesteryl ester levels were 35% lower in guinea-pigs fed the lard diet (P less than 0.02). Sterol balance measurements indicated that whole body cholesterol synthesis rates were not affected by dietary fat quality (51.9 +/- 12.2, 42.8 +/- 7.6 and 51.2 +/- 20.2 mg/kg per day for animals on the CO, OL and lard diets, respectively). This is in striking contrast to the observed reduction in cholesterol synthesis rates for animals on the polyunsaturated CO diet as determined by incorporation of [3H]water into DPS. One possible explanation for the discrepancy between the sterol balance and [3H]water incorporation data is a polyunsaturated fat-mediated effect on energy utilization, which affects the equilibration of NADPH with the body water pool such that the [3H]NADPH has a lower specific activity than body [3H]water.     

Effects of dietary polyunsaturated fatty acid on platelet aggregation in rats

In the present study, we changed the fatty acid profile in blood and platelet membranes by dietary manipulation, and examined the effect on platelet aggregation in rats. Fifty-five rats were divided into five groups and fed for 56 days with 1% cholesterol and different types of fatty acid-rich diets: basal, lard, lard + fish oil, soybean oil, and soybean oil + fish oil. a decrease in serum arachidonic acid (20:4, omega-6, AA) and an increase in serum eicosapentaenoic acid (20:5, omega-3, EPA) were found in all experimental dietary groups fed with refined fish oil. Similar changes in the polyunsaturated fatty acids were also found in the platelet membrane phospholipids. Platelet aggregation, quantitated by the slope and height of the aggregation curve induced by different concentrations of ADP in a platelet aggregometer, was inhibited in all groups fed with refined fish oil. This inhibition of platelet aggregation may be related to an increase in the ratio of EPA and AA in the platelet membrane phospholipids after dietary manipulation. The differences in the platelet aggregation and thromboxane B2 (TXB2) concentration between the lard and the lard + fish oil groups were more profound than that between the soybean oil and the soybean oil + fish oil group. However, the malondialdehyde (MDA) concentration revealed no significant differences between the five groups.