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.     

Polyunsaturated fatty acids,neuroinflammation and well being

The innate immune system of the brain is principally composed of microglial cells and astrocytes, which, once activated, protect neurons against insults (infectious agents, lesions, etc.). Activated glial cells produce inflammatory cytokines that act specifically through receptors expressed by the brain. The functional consequences of brain cytokine action (also called neuroinflammation) are alterations in cognition, mood and behaviour, a hallmark of altered well-being. In addition, proinflammatory cytokines play a key role in depression and neurodegenerative diseases linked to aging. Polyunsaturated fatty acids (PUFA) are essential nutrients and essential components of neuronal and glial cell membranes. PUFA from the diet regulate both prostaglandin and proinflammatory cytokine production. n-3 fatty acids are anti-inflammatory while n-6 fatty acids are precursors of prostaglandins. Inappropriate amounts of dietary n-6 and n-3 fatty acids could lead to neuroinflammation because of their abundance in the brain and reduced well-being. Depending on which PUFA are present in the diet, neuroinflammation will, therefore, be kept at a minimum or exacerbated. This could explain the protective role of n-3 fatty acids in neurodegenerative diseases linked to aging.     

Beneficial effect(s) of n-3 fatty acids in cardiovascular diseases: but, why and how?

Low rates of coronary heart disease was found in Greenland Eskimos and Japanese who are exposed to a diet rich in fish oil. Suggested mechanisms for this cardio-protective effect focused on the effects of n-3 fatty acids on eicosanoid metabolism, inflammation, beta oxidation, endothelial dysfunction, cytokine growth factors, and gene expression of adhesion molecules; But, none of these mechanisms could adequately explain the beneficial actions of n-3 fatty acids. One attractive suggestion is a direct cardiac effect of n-3 fatty acids on arrhythmogenesis. N-3 fatty acids can modify Na+ channels by directly binding to the channel proteins and thus, prevent ischemia-induced ventricular fibrillation and sudden cardiac death. Though this is an attractive explanation, there could be other actions as well. N-3 fatty acids can inhibit the synthesis and release of pro-inflammatory cytokines such as tumor necrosis factoralpha (TNFalpha) and interleukin-1 (IL-1) and IL-2 that are released during the early course of ischemic heart disease. These cytokines decrease myocardial contractility and induce myocardial damage, enhance the production of free radicals, which can also suppress myocardial function. Further, n-3 fatty acids can increase parasympathetic tone leading to an increase in heart rate variability and thus, protect the myocardium against ventricular arrhythmias. Increased parasympathetic tone and acetylcholine, the principle vagal neurotransmitter, significantly attenuate the release of TNF, IL-1beta, IL-6 and IL-18. Exercise enhances parasympathetic tone, and the production of anti-inflammatory cytokine IL-10 which may explain the beneficial action of exercise in the prevention of cardiovascular diseases and diabetes mellitus. TNFalpha has neurotoxic actions, where as n-3 fatty acids are potent neuroprotectors and brain is rich in these fatty acids. Based on this, it is suggested that the principle mechanism of cardioprotective and neuroprotective action(s) of n-3 fatty acids can be due to the suppression of TNFalpha and IL synthesis and release, modulation of hypothalamic-pituitary-adrenal anti-inflammatory responses, and an increase in acetylcholine release, the vagal neurotransmitter. Thus, there appears to be a close interaction between the central nervous system, endocrine organs, cytokines, exercise, and dietary n-3 fatty acids. This may explain why these fatty acids could be of benefit in the management of conditions such as septicemia and septic shock, Alzheimer's disease, Parkinson's disease, inflammatory bowel diseases, diabetes mellitus, essential hypertension and atherosclerosis.     

N-6 fatty acids and cardiovascular health: dietary intake recommendations

Omega-6 polyunsaturated fatty acids (n-6 PUFA) are well known for their critical role in many physiological functions and reduce risks of cardiovascular disease (CVD). However, some argue that excessive consumption of n-6 PUFA may lead to adverse effects on health and therefore recommend reducing dietary n-6 PUFA intake or fixing an upper limit. Epidemiological studies show that n-6 PUFA dietary intake significantly lowers blood LDL-cholesterol levels. In addition, n-6 PUFA intake lower several cardiovascular risk factors such as blood pressure, inflammatory markers, haemostatic parameters and obesity. Data from prospective cohort and interventional studies converge towards a specific protective role of dietary n-6 PUFA intake, in particular linoleic acid, against CVD. In regards to studies examined in this narrative review, recommendation for n-6 PUFA intake above 5%, and ideally about 10% of total energy appears justified for the prevention of ischemic heart disease.     

Protection against in vivo liver ischemia-reperfusion injury by n-3 long-chain polyunsaturated fatty acids in the rat

Abstract

N-3 polyunsaturated fatty acids (n-3 PUFA) affect inflammatory processes. This study evaluated the effects of dietary supplementation with fish oil on hepatic ischemia-reperfusion (IR) injury in the rat. Parameters of liver injury (serum transaminases and histology) and oxidative stress (serum 8-isoprostanes and hepatic GSH and GSSG), were correlated with NF-κB DNA binding and FA composition and inflammatory cytokine release. N-3 PUFA supplementation significantly increased liver n-3 PUFA content and decreased n-6/n-3 PUFA ratios. IR significantly modified liver histology and enhanced serum transaminases, 8-isoprotanes and inflammatory cytokines, with net reduction in liver GSH levels and net increment in those of GSSG. Early increase (3 h) and late reduction (20 h) in NF-κB activity was induced. All IR-induced changes were normalized by n-3 PUFA supplementation. In conclusion, prevention of liver IR-injury was achieved by n-3 PUFA supplementation, with suppression of oxidative stress and recovery of pro-inflammatory cytokine homeostasis and NF-κB functionality lost during IR.     

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.     

The effect of dietary fish oils on eicosanoid biosynthesis in peritoneal macrophages is influenced by both dietary N-6 polyunsaturated fats and total dietary fat

Recent research has implicated dietary fish oils in the reduction of eicosanoids formed from arachidonic acid and amelioration of chronic diseases such as coronary heart disease, atherosclerosis and inflammation. Feeding studies were conducted to determine if the efficacy of dietary n-3 polyunsaturated fatty acids (PUFA) from fish oils was influenced by the quantity of n-6 polyunsaturated fatty acids and the total level of fat in the diet. Groups of mice were fed diets composed of 5 and 20% total fat with varying proportions of linoleic acid as a source of n-6 PUFA. Menhaden oil as a source of n-3 PUFA was fed at two levels of n-6 at each level of total fat. Eicosanoid biosynthesis was stimulated and assayed in the mouse peritoneum using zymosan as an inflammatory stimulus. Production of LTE4 and PGE2 was enhanced by increasing n-6 PUFA in the diet at both levels of total fat. High dietary fat significantly suppressed leukotriene (LT) synthesis. Dietary menhaden oil reduced LTE4 and PGE2 synthesis at both levels of dietary n-6 in the low fat study. In animals on 20% dietary fat menhaden oil significantly reduced LT synthesis only at a relatively low dietary n-6 PUFA. On a high n-6 PUFA high fat diets, menhaden oil did not significant affect LTE4 synthesis in response to zymosan stimulation. The results suggest that the effectiveness of fish oils in reducing eicosanoids in response to specific stimulation is influenced by the level of n-6 and the total quantity of fat in the diet.     

Omega-3 fatty acids enhance ligament fibroblast collagen formation in association with changes in interleukin-6 production

Altering dietary ratios of n-3 and n-6 polyunsaturated fatty acids (PUFA) represents an effective nonpharmaceutical means to improve systemic inflammatory conditions. An effect of PUFA on cartilage and bone formation has been demonstrated, and the purpose of this study was to determine the potential of PUFA modulation to improve ligament healing. The effects of n-3 and n-6 PUFA on the in vitro healing response of medial collateral ligament (MCL) fibroblasts were investigated by studying the cellular coverage of an in vitro wound and the production of collagen, PGE2, IL-1, IL-6, and TNF. Cells were exposed to a bovine serum albumin (BSA) control or either eicosapentaenoic acid (EPA, 20:5n-3) or arachidonic acid (AA, 20:4n-6) in the form of soaps loaded onto BSA for 4 days and wounded on Day 5. AA and EPA improved the healing of an in vitro wound over 72 hr. EPA increased collagen synthesis and the overall percentage of collagen produced, but AA reduced collagen production and total protein. PGE2 production was increased in the AA-treated group and decreased in the EPA-treated group, but was not affected by wounding. IL-1 was not produced at the time point evaluated, but TNF and IL-6 were both produced, and their levels varied relative to the PUFA or wounding treatment. There was a significant linear correlation (r2 = 0.57, P = 0.0045) between IL-6 level and collagen production. These results demonstrate that n-3 PUFA (represented by EPA in this study) positively affect the healing characteristics of MCL cells and therefore may represent a possible noninvasive treatment to improve ligament healing. Additionally, these results show that MCL fibroblasts produce PGE2, IL-6, and TNF and that IL-6 production is related to MCL collagen synthesis.     

Dietary n-3 polyunsaturated fatty acids promote activation-induced cell death in Th1-polarized murine CD4+ T-cells

Dietary n-3 PUFAs have been shown to attenuate T-cell-mediated inflammation. To investigate whether dietary n-3 PUFAs promote activation-induced cell death (AICD) in CD4+ T-cells induced in vitro to a polarized T-helper1 (Th1) phenotype, C57BL/6 mice were fed diets containing either 5% corn oil (CO; n-6 PUFA control) or 4% fish oil (FO) plus 1% CO (n-3 PUFA) for 2 weeks. Splenic CD4+ T-cells were cultured with alpha-interleukin-4 (alphaIL-4), IL-12, and IL-2 for 2 days and then with recombinant (r) IL-12 and rIL-2 for 3 days in the presence of diet-matched homologous mouse serum (HMS) to prevent loss of cell membrane fatty acids, or with fetal bovine serum. After polarization, Th1 cells were reactivated and analyzed for interferon-gamma and IL-4 by intracellular cytokine staining and for apoptosis by Annexin V/propidium iodide. Dietary FO enhanced Th1 polarization by 49% (P = 0.0001) and AICD by 24% (P = 0.0001) only in cells cultured in the presence of HMS. FO enhancement of Th1 polarization and AICD after culture was associated with the maintenance of eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) in plasma membrane lipid rafts. In conclusion, n-3 PUFAs enhance the polarization and deletion of proinflammatory Th1 cells, possibly as a result of alterations in membrane microdomain fatty acid composition.     

Enrichment of RAW264.7 macrophages with essential 18-carbon fatty acids affects both respiratory burst and production of immune modulating cytokines

Macrophages play a vital role in the innate immune system. Thereby, production of both reactive oxygen intermediates and immune modulating cytokines is crucial for successful pathogen defense. Fatty acids may interfere with immune response in several ways. In this study, we investigated the influence of essential polyunsaturated fatty acids (PUFA) on key macrophage functions. RAW264.7 macrophages were cultured in a medium supplemented with 2 or 15 μmol/L of the n-6 PUFA linoleic acid (LA) or of the n-3 PUFA α-linolenic acid (LNA), respectively. Cells were tested for incorporation of fatty acids as well as NADPH oxidase activity. Furthermore, supernatants were collected for detection of NO and cytokine release (TNF-α, IL-6, IL-10). Exposure of RAW264.7 macrophages to LA or LNA resulted in incorporation of these fatty acids and their derivatives. Thereby, supplementation with both LA and LNA caused a significant increase in NADPH oxidase activity. In contrast, synthesis of NO was not affected by PUFA supplementation. Moreover, distinct effects could be seen in the release of immune modulating cytokines. Due to enhancement of NADPH oxidase activity, PUFA presumably promote the killing of pathogens crucial in host defense. In addition, the unsaturated fatty acids tested in our study were shown to modulate cytokine release by the macrophages, thus driving immune response into an anti-inflammatory direction. Of note, distinct differences between the n-6 PUFA LA and the n-3 PUFA LNA underline the impact of PUFA family on immune response.     

Cardiac proinflammatory pathways are altered with different dietary n-6 linoleic to n-3 alpha-linolenic acid ratios in normal, fat-fed pigs

Although dietary fat has been associated with inflammation and cardiovascular diseases (CVD), most studies have focused on individuals with preexisting diseases. However, the role of dietary fatty acids on inflammatory pathways before the onset of any abnormality may be more relevant for identifying initiating factors and interventions for CVD prevention. We fed young male pigs one of three diets differing in n-6 and n-3 polyunsaturated fatty acids (PUFA) linoleic acid (LA, 18:2n-6) and alpha-linolenic acid (ALA, 18:3n-3) for 30 days. Cardiac membrane phospholipid fatty acids, phospholipase A(2) (PLA(2)) isoform activities, and cyclooxygenase (COX)-1 and -2 and 5-lipoxygenase (5-LO) expression were measured. The low PUFA diet (% energy, 1.2% LA+0.06% ALA) increased arachidonic acid (AA) and decreased eicosapentaenoic acid (EPA) in heart membranes and increased Ca(2+)-independent iPLA(2) activity, COX-2 expression, and activation of 5-LO. Increasing dietary ALA while keeping LA constant (1.4% LA+1.2% ALA) decreased the heart membrane AA, increased EPA, and prevented proinflammatory enzyme activation. However, regardless of high ALA, high dietary LA (11.6% LA and 1.2% ALA) decreased EPA and led to a high heart membrane AA, and Ca(2+)-dependent cPLA(2) with a marked increase in nitrosative stress. Our results suggest that the potential cardiovascular benefit of ALA is achieved only when dietary LA is reduced concomitantly rather than fed with high LA diet. The increased nitrosative stress in the unstressed heart with high dietary LA suggests that biomarkers of nitrosative stress may offer a useful early marker of the effects of dietary fat on oxidative tissue stress.     

Effects of polyunsaturated fatty acids on hibernation and torpor: a review and hypothesis

Polyunsaturated fatty acids (PUFAs) can have strong effects on hibernation and daily torpor in mammals. High dietary PUFA contents were found to increase proneness for torpor, decrease body temperatures, prolong torpor bout duration, and attenuate hibernation mass loss. The mechanism by which PUFAs enhance torpor and hibernation is unknown, however. On the basis of a review of the literature, and on reexamining our own data on alpine marmots, we propose that effects on hibernation are not due to PUFAs in general, but to shifts in the ratio of n-6 PUFAs to n-3 PUFAs in membrane phospholipids. Specifically, high ratios of n-6 to n-3 PUFAs increase the activity of the Ca2+-Mg2+ pump in the sarcoplasmic reticulum of the heart (SERCA) and counteract Q10 effects on SERCA activity at low tissue temperatures. Therefore, high n-6 to n-3 PUFA ratios in cardiac myocyte membranes appear to protect the hibernating heart from arrhythmia, which in hypothermic nonhibernators is caused by massive increases in cytosolic Ca2+. The resulting reduced risk of cardiac arrest during hypothermia may explain why increased dietary uptake of n-6 PUFAs, but not of n-3 PUFAs, can strongly enhance the propensity for hibernation, and allows heterotherms to reach lower body temperatures, with associated increased energy savings. Therefore, at least for herbivorous hibernators, such as marmots, linoleic acid (C18:2 n-6)--the dietary source of all n-6 PUFAs--appears to represent a crucial and limited resource in natural environments.     

Alteration of polyunsaturated fatty acid status and metabolism in health and disease

Essential polyunsaturated fatty acids (PUFA) cannot be synthesised in the body and must be ingested by food. A balanced intake of both n-6 and n-3 PUFA is essential for good health. PUFA are the basic constituents of phospholipid membranes and determine cellular membrane fluidity and modulate enzyme activities, carriers and membrane receptors. They are also precursors of active metabolites known collectively as eicosanoids (prostaglandins, prostacyclins, thromboxanes and leukotrienes) which regulate our cellular functions. Studies indicate that n-3 PUFA have anti-inflammatory, antithrombotic, antiarrhythmic actions and immuno-modulating properties. Erythrocyte fatty acid status is a reflection of dietary fat intake. It also explores PUFA metabolism and gives information about the integration of these fatty acids into cellular membranes. Thus, erythrocyte fatty acid analysis can detect PUFA insufficiencies and imbalances from the diet, but also metabolic abnormalities and lipid peroxidation. It can be helpful in the prevention and the control of chronic diseases in which PUFA alterations have been observed as coronary heart diseases, hypertension, cancer, diabetes, inflammatory and auto-immune disorders, atopic eczema, Alzheimer dementia, major depression, schizophrenia, multiple sclerosis, etc.     

Dietary n-3 fats as adjunctive therapy in a prototypic inflammatory disease: issues and obstacles for use in rheumatoid arthritis

Eicosanoids derived from the n-6 fatty acid, arachidonic acid, and the cytokines interleukin-1beta and tumour necrosis factor-alpha are involved in the signs and symptoms of inflammatory joint disease, as well as the cartilage degradation seen in established rheumatoid arthritis (RA). Then n-3 fatty acids in fish and fish oil can inhibit production of both eicosanoid and cytokine inflammatory mediators and therefore, have the potential to modify RA pathology. Epidemiological studies suggest that fish intake may be preventive for RA and double-blind placebo-controlled studies demonstrate that dietary fish oil can alleviate the signs and symptoms of RA. The implementation of these findings will require among other things, a range of n-3 fat enriched foods, as well as physician awareness of the possibilities for dietary n-3 fat increases to be used as adjunctive therapy in RA.     

Feeding into old age: long-term effects of dietary fatty acid supplementation on tissue composition and life span in mice

Smaller mammals, such as mice, possess tissues containing more polyunsaturated fatty acids (PUFAs) than larger mammals, while at the same time live shorter lives. These relationships have been combined in the ‘membrane pacemaker hypothesis of aging’. It suggests that membrane PUFA content might determine an animal’s life span. PUFAs in general and certain long-chain PUFAs in particular, are highly prone to lipid peroxidation which brings about a high rate of reactive oxygen species (ROS) production. We hypothesized that dietary supplementation of either n-3 or n-6 PUFAs might affect (1) membrane phospholipid composition of heart and liver tissues and (2) life span of the animals due to the altered membrane composition, and subsequent effects on lipid peroxidation. Therefore, we kept female laboratory mice from the C57BL/6 strain on three diets (n-3 PUFA rich, n-6 PUFA rich, control) and assessed body weights, life span, heart, and liver phospholipid composition after the animals had died. We found that while membrane phospholipid composition clearly differed between feeding groups, life span was not directly affected. However, we were able to observe a positive correlation between monounsaturated fatty acids in cardiac muscle and life span.     

Intravenous lipid emulsions to deliver omega 3 fatty acids

A rapid supply of n-3 polyunsaturated fatty acids (PUFA) may be indicated in some acute conditions because of the ability of n-3 PUFA to decrease inflammatory responses and cell sensitivity to various stimuli, and to improve endothelial dysfunction. To achieve these objectives, n-3 PUFA content needs to be quickly raised in cell membranes of key organs. Intravenous fish oil (FO) emulsions are available but their slow hydrolysis limits their infusion rate. Mixtures containing both FO triglycerides and medium chain triglycerides may overcome this problem. These new preparations are rapidly cleared from plasma and efficiently deliver n-3 PUFA to several tissues, largely via direct particle uptake. Recent data suggest that n-3 PUFA incorporation in phospholipids promptly modulates important cell functions. This review also focuses on a novel approach to rapidly supply n-3 PUFA to targeted organs which may offer interesting perspectives in the management of acute illnesses.     

Unique fatty acid composition of normal cartilage: discovery of high levels of n-9 eicosatrienoic acid and low levels of n-6 polyunsaturated fatty acids

We report here the finding that normal, young cartilages, in distinction from all other tissues examined, have unusually high levels of n-9 eicosatrienoic (20:3 cis-delta 5,8,11) acid and low levels of n-6 polyunsaturated fatty acids (n-6 PUFA). This pattern is identical to that found in tissues of animals subjected to prolonged depletion of nutritionally essential n-6 polyunsaturated fatty acids (EFA). This apparent deficiency is consistently observed in cartilage of all species so far studied (young chicken, fetal calf, newborn pig, rabbit, and human), even though levels of n-6 PUFA in blood and all other tissues is normal. The n-9 20:3 acid is particularly abundant in phosphatidylethanolamine, phosphatidylinositol, and the free fatty acid fractions from the young cartilage. Several factors appear to contribute to the reduction in n-6 PUFA and the appearance of high levels of the n-9 20:3 acid in cartilage: 1) limited access to nutritional sources of EFA due to the impermeability and avascularity of cartilage, 2) rapid metabolism of n-6 PUFA to prostanoids by chondrocytes, and 3) a unique fatty acid metabolism by cartilage. Evidence is presented that each of these factors contributes. Previously, EFA deficiency has been shown to greatly suppress the inflammatory response of leukocytes and rejection of tissues transplanted into allogeneic recipients. Because eicosanoids, which are derived from EFA, have been implicated in the inflammatory responses associated with arthritic disease, reduction of n-6 PUFA and accumulation of the n-9 20:3 acid in cartilage may be important for maintaining normal cartilage structure.     

Diets enriched in menhaden fish oil, seal oil, or shark liver oil have distinct effects on the lipid and fatty-acid composition of guinea pig heart

The purpose of this investigation was to determine whether diets supplemented with oils from three different marine sources, all of which contain high proportions of long-chain n-3 polyunsaturated fatty acids (PUFA), result in qualitatively distinct lipid and fatty acid profiles in guinea pig heart. Albino guinea pigs (14 days old) were fed standard, nonpurified guinea pig diets (NP) or NP supplemented with menhaden fish oil (MO), harp seal oil (SLO) or porbeagle shark liver oil (PLO) (10%, w/w) for 4-5 weeks. An n-6 PUFA control group was fed NP supplemented with corn oil (CO). All animals appeared healthy, with weight gains marginally lower in animals fed the marine oils. Comparison of relative organ weights indicated that only the livers responded to the diets, and that they were heavier only in the marine-oil fed guinea pigs. Heart total cholesterol levels were unaffected by supplementing NP with any of the oils, whereas all increased the triacylglycerol (TAG) content. The fatty-acid profiles of totalphospholipid (TPL), TAG and free fatty acid (FFA) fractions of heart lipids showed that feeding n-3 PUFA significantly altered the proportions of specific fatty-acid classes. For example, all marine-oil-rich diets were associated with increases in total monounsaturated fatty acids in TPL (p < 0.05), and with decreases in total saturates in TAG (p < 0.05). Predictably, the n-3 PUFA enriched regimens significantly increased the cardiac content of n-3 PUFA and decreased that of n-6 PUFA, although the extent varied among the diets. As a result, n-6/n-3 ratios were significantly lower in all myocardial lipid classes of marine-oil-fed guinea pigs. Analyses of the profiles of individual PUFA indicated that quantitatively, the fatty acids of the three marine oils were metabolized and/or incorporated into TPL, TAG and FFA in a diet-specific manner. In animals fed MO-enriched diets in which eicosapentaenoic acid (EPA) > docosahexacnoic acid (DHA), ratios of DHA /EPA in the hearts were 1.2, 2.2 and 1.5 in TPL, TAG and FFA, respectively. In SLO-fed guinea pigs in which dietary EPA DHA, ratios of DHA/EPA were 0.9, 3.4 and 2.1 in TPL, TAG and FFA, respectively. Feeding NP + PLO (DHA/EPA = 4.8), resulted in values for DHA/EPA in cardiac tissue of 2.1, 10.6 and 2.9 in TPL, TAG and FFA, respectively. In the TAG and FFA, proportions of n-3 docosapentaenoic acid (n-3 DPA) were equal to or higher than EPA in the SLO- and PLO-fed animals. The latter group exhibited the greatest difference between the DHA/n-3 DPA ratio in the diet and in cardiac TAG and FFA fractions (7, 3.4 and 3.1, respectively). Quantitative analysis indicated that 85% of the n-3 PUFA were in TPL, 7-11% were in TAG, and 2-6% were FFA. Specific patterns of distribution of EPA, DPA and DHA depended on the dietary oil. Both the qualitative and quantitative results of this study demonstrated that in guinea pigs, n-3 PUFA in different marine oils are metabolized and/or incorporated into cardiac lipids in distinct manners. In support of the concept that the diet-induced alterations reflect changes specifically in cardiomyocytes, we observed that direct supplementation of cultured guinea pig myocytes for 2-3 weeks with EPA or DHA produced changes in the PUFA profiles of their TPL that were qualitatively similar to those observed in tissue from the dietary study. The factors that regulate specific deposition of n-3 PUFA from either dietary oils or individual PUFA are not yet known, however the differences that we observed could in some manner be related to cardiac function and thus their relative potentials as health-promoting dietary fats.     

The effect of fish oil supplementation on cytokine production in children

The ex vivo production of inflammatory cytokines during fish oil supplementation (n-3 polyunsaturated fatty acids, n-3 PUFA) is a matter of considerable controversy. Studies on human subjects have generally reported decreased lymphocyte proliferation and decreased production of IL-2, interferon-gamma, IL-1beta, IL-6 and TNF-alpha, but other studies showed no effect or even increased production. There are no published reports on ex vivo cytokine production in children on long-term, n-3 PUFA supplementation. The current double-blind study explored cytokine production by peripheral blood mononuclear cells (PBMCs), with and without lipopolysaccharide (LPS) stimulation in children on 12 weeks' supplementation with 300 mg/day of n-3 PUFA. Twenty-one children (aged 8-12 years) were randomized to receive 1 g canola oil (control) or 300 mg n-3 PUFA + 700 mg canola oil in a chocolate spread. Blood was then drawn and PBMCs were separated and cultured for 24 h in a culture medium with or without 10 microg/mL LPS for 5 x 10(6) PBMCs. The pro-inflammatory cytokines, IL-1beta, TNF-alpha and IL-6, and the anti-inflammatory cytokines, IL-10 and IL-1RA, were evaluated by ELISA. The levels of all the cytokines were higher in non-stimulated and LPS-stimulated cultures, from n-3 PUFA-treated subjects as compared to controls. There was no difference in the IL-1beta/IL-1RA ratio between the two groups, with and without LPS stimulation. Nevertheless, the ratio tended to be lower in the treated subjects on both occasions. In conclusion, our results indicate an increased production of both pro-inflammatory and anti-inflammatory cytokines, with and without LPS stimulation, in children on 12 weeks' n-3 PUFA supplementation.