The opposing effects of n-3 and n-6 fatty acids

Polyunsaturated fatty acids (PUFAs) can be classified in n-3 fatty acids and n-6 fatty acids, and in westernized diet the predominant dietary PUFAs are n-6 fatty acids. Both types of fatty acids are precursors of signaling molecules with opposing effects, that modulate membrane microdomain composition, receptor signaling and gene expression. The predominant n-6 fatty acid is arachidonic acid, which is converted to prostaglandins, leukotrienes and other lipoxygenase or cyclooxygenase products. These products are important regulators of cellular functions with inflammatory, atherogenic and prothrombotic effects. Typical n-3 fatty acids are docosahexaenoic acid and eicosapentaenoic acid, which are competitive substrates for the enzymes and products of arachidonic acid metabolism. Docosahexaenoic acid- and eicosapentaenoic acid-derived eicosanoids antagonize the pro-inflammatory effects of n-6 fatty acids. n-3 and n-6 fatty acids are ligands/modulators for the nuclear receptors NFkappaB, PPAR and SREBP-1c, which control various genes of inflammatory signaling and lipid metabolism. n-3 Fatty acids down-regulate inflammatory genes and lipid synthesis, and stimulate fatty acid degradation. In addition, the n-3/n-6 PUFA content of cell and organelle membranes, as well as membrane microdomains strongly influences membrane function and numerous cellular processes such as cell death and survival.     

Alteration of plasma phospholipid fatty acid profile in patients with septic shock

In septic shock patients, alterations of plasma phospholipid fatty acid profile have never been described. The purpose of this monocentric, non-interventional, observational prospective study was to describe this fatty acid profile in the early phase of septic shock in intensive care unit. Thirty-seven adult patients with septic shock were included after the first day of stay in intensive care unit, before any form of artificial nutritional support. Plasma phospholipid fatty acid composition was determined by gas chromatography. All biological data from patients with septic shock were compared with laboratory reference values. Patients presented hypocholesterolemia and hypertriglyceridemia. They had low concentrations of phospholipid fatty acids specifically n-6 and n-3 polyunsaturated fatty acids (PUFAs) with a high n-6/n-3 ratio. Plasma phospholipid PUFA concentrations were strongly correlated with cholesterolemia. PUFAs/SFAs (saturated fatty acids) and PUFAs/MUFAs (monounsaturated fatty acids) ratios were low because of low percentage of n-6 and n-3 PUFAs and high percentage of SFAs and MUFAs. Low levels of plasma long chain PUFAs (≥20 carbons) were significantly associated with mortality at 28th day. In conclusion, plasma phospholipid FA profile of septic patients is very characteristic, close to that of acute respiratory distress syndrome and mortality is associated with long chain PUFA decrease. This profile could be explained by numerous non-exclusive physio-pathological processes 1) an activation of hepatic de novo lipogenesis that could contribute to hepatic steatosis, 2) an elevated adipose tissue lipolysis, 3) an increased free radical attack of FA by oxidative stress, 4) an over-production of inflammatory lipid mediators.     

Gene and protein expression profiling of the fat-1 mouse brain

Polyunsaturated fatty acids (PUFAs) are essential structural components of all cell membranes and, more so, of the central nervous system. Several studies revealed that n-3 PUFAs possess anti-inflammatory actions and are useful in the treatment of dyslipidemia. These actions explain the beneficial actions of n-3 PUFAs in the management of cardiovascular diseases, inflammatory conditions, neuronal dysfunction, and cancer. But, the exact molecular targets of these beneficial actions of n-3 PUFAs are not known. Mice engineered to carry a fat-1 gene from Caenorhabditis elegans add a double bond into an unsaturated fatty acid hydrocarbon chain and convert n-6 to n-3 fatty acids. This results in an abundance of n-3 eicosapentaenoic acid and docosapentaenoic acid specifically in the brain and a reduction in n-6 fatty acids of these mice that can be used to evaluate the actions of n-3 PUFAs. Gene expression profile, RT-PCR and protein microarray studies in the hippocampus and whole brain of wild-type and fat-1 transgenic mice revealed that genes and proteins concerned with inflammation, apoptosis, neurotransmission, and neuronal growth and synapse formation are specifically modulated in fat-1 mice. These results may explain as to why n-3 PUFAs are of benefit in the prevention and treatment of diseases such as Alzheimer's disease, schizophrenia and other diseases associated with neuronal dysfunction, low-grade systemic inflammatory conditions, and bronchial asthma. Based on these data, it is evident that n-3 PUFAs act to modulate specific genes and formation of their protein products and thus, bring about their various beneficial actions.     

Antiarrhythmic effects of n-3 fatty acids: evidence from human studies

PURPOSE OF REVIEW: N-3 fatty acids from fish reduce cardiovascular mortality including sudden cardiac death. In this paper, the authors discuss the results of human studies with regard to the hypothesis that n-3 fatty acids reduce the risk of fatal coronary heart disease through antiarrhythmic effects. RECENT FINDINGS: Results from two recent clinical trials do not support a protective effect of n-3 fatty acids. In light of the earlier published bulk of evidence that n-3 fatty acids reduce cardiovascular mortality and sudden cardiac death, it is hard to explain these findings. Two recent observational studies confirmed that intake of n-3 fatty acids from fish is associated with less cardiovascular disease in the general population. They indicated that the protective effect of a fish meal may depend on the n-3 fatty acid content or preparation method and suggested a protective effect on arrhythmia rather than on atherosclerosis. Intervention studies on electrophysiological predictors of arrhythmia do not clearly confirm a beneficial effect of n-3 fatty acids. However, most of these studies were small or performed in healthy populations. SUMMARY: The available evidence still suggests that n-3 fatty acids may prevent fatal cardiac arrhythmia, but more conclusive studies are urgently needed.     

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.     

Dietary fatty acids and arthritis

Musculoskeletal complaints are the second most frequent reason for medical treatments. Within these diseases rheumatoid arthritis (RA) and, especially, osteoarthritis (OA) are common. Although the causes of arthritis are multifactorial and not fully understood, clinical trials have generally shown benefit from dietary n-3 polyunsaturated fatty acids. This has usually been attributed to their anti-inflammatory properties. Recently we have used in vitro model systems to study the molecular mechanism(s) by which n-3 PUFAs may act to alleviate the symptoms of arthritis. These experiments showed that n-3 PUFAs reduce expression of cartilage-degrading proteinases, cyclooxygenase-2 and inflammatory cytokines. Eicosapentaenoic acid (EPA) was more effective than docosahexaenoic acid (DHA) or alpha-linolenic acid. The data provide a scientific rationale for the consumption of n-3 fatty acids as part of a healthy diet and perhaps in treating arthritis.     

Omega-3 polyunsaturated fatty acids and skeletal health

This minireview on skeletal biology describes the actions of prostaglandins and cytokines involved in the local regulation of bone metabolism, it documents the role of lipids in bone biology, and it presents relationships between fatty acids and other factors that impact skeletal metabolism. The data presented herein show consistent and reproducible beneficial effects of omega-3 (n-3) fatty acids on bone metabolism and bone/joint diseases. Polyunsaturated fatty acids modulate eicosanoid biosynthesis in numerous tissues and cell types, alter signal transduction, and influence gene expression. These effects have not been explored in the skeletal system. Future research on n-3 fatty acids in bone biology should focus on the following two aspects. First, the further elucidation of how n-3 fatty acids alter biochemical and molecular processes involved in bone modeling and bone cell differentiation, and second, the evaluation of the potential pharmaceutical applications of these nutraceutical fatty acids in maintaining bone mineral status and controlling inflammatory bone/joint diseases.     

Fat-1 transgenic mice: a new model for omega-3 research

An appropriate animal model that can eliminate confounding factors of diet would be very helpful for evaluation of the health effects of nutrients such as n-3 fatty acids. We recently generated a fat-1 transgenic mouse expressing the Caenorhabditis elegans fat-1 gene encoding an n-3 fatty acid desaturase that converts n-6 to n-3 fatty acids (which is absent in mammals). The fat-1 transgenic mice are capable of producing n-3 fatty acids from the n-6 type, leading to abundant n-3 fatty acids with reduced levels of n-6 fatty acids in their organs and tissues, without the need of a dietary n-3 supply. Feeding an identical diet (high in n-6) to the transgenic and wild-type littermates can produce different fatty acid profiles in these animals. Thus, this model allows well-controlled studies to be performed, without the interference of the potential confounding factors of diet. The transgenic mice are now being used widely and are emerging as a new tool for studying the benefits of n-3 fatty acids and the molecular mechanisms of their action.     

Fats, lipids and blood coagulation

Saturated and n-3 fatty acids, postprandial lipaemia, and the combined effects of fatty acids and lipid-lowering drugs have been of principal interest in recent studies in the field of dietary fats, lipids and haemostasis. The sex-specific effect of individual saturated fatty acids on coagulation factor VII activity has been discovered, and the significant effect of factor VII R353Q polymorphism on the postprandial response has also been found. An increased intake of n-3 fatty acids or fat reduction when combined with intensive lifestyle interventions may lead to reduced thrombotic potential in type 2 diabetic patients and obese individuals. Furthermore, positive effects on haemostasis by combined treatment with long-chain n-3 fatty acids and simvastatin indicate that n-3 fatty acids may be of some relevance with lipid-lowering drugs. The possible unfavourable effect of n-3 fatty acids on plasminogen activator inhibitor-1 activity is still a matter of dispute, but recent studies suggest that n-3 fatty acids, including alpha-linolenic acid, may have antithrombotic effects by enhancing protein C activity.     

Age-related changes of n-3 and n-6 polyunsaturated fatty acids in the anterior cingulate cortex of individuals with major depressive disorder

Accumulating evidence finds a relative deficiency of peripheral membrane fatty acids in persons with affective disorders such as unipolar and bipolar depression. Here we sought to investigate whether postmortem brain fatty acids within the anterior cingulate cortex (BA-24) varied according to the presence of major depression at the time of death. Using capillary gas chromatography we measured fatty acids in a depressed group (n=12), and in a control group without lifetime history of psychiatric diagnosis (n=14). Compared to the control group, the depressed group showed significantly lower concentrations of numerous saturated and polyunsaturated fatty acids including both the n-3 and n-6 fatty acids. Additionally, significant correlations between age at death and precursor (or metabolites) in the n-3 fatty acid pathway were demonstrated in the depressed group but not in control subjects. In the n-6 fatty acid family, the ratio of 20:3(n-6)/18:2(n-6) was higher in patients than in control groups, whereas the ratio of 20:4(n-6)/20:3(n-6) was relatively decreased in patients. Lastly, a significant negative correlation between age and the ratio of 20:4(n-6) to 22:6(n-3) was found in patients, but not in controls. Taken together, decreases in 22:6(n-3) may be caused, at least in part, by the diminished formation of 20:5(n-3), which is derived from 20:4(n-3) through a Δ5 desaturase reaction. The present findings from postmortem brain tissue raise the possibility that an increased ratio of 20:4(n-6) to 22:6(n-3) may provide us with a biomarker for depression. Future research should further investigate these relationships.     

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.     

A microsomal fatty acid synthetase from the integument of Blattella germanica synthesizes methyl-branched fatty acids, precursors to hydrocarbon and contact sex pheromone.

Methyl-branched fatty acids present in the integument of the German cockroach, Blattella germanica, were identified by gas chromatography-mass spectrometry of their methyl esters and reduction products (alkanes) as n-3-, n-4-, n-5-, n-7-, n-8-, and n-9-monomethyl fatty acids and as n-5,9-, n-3,9-, and n-3,11-dimethyl fatty acids with 16 to 20 total carbons. These fatty acids have the same branching patterns as do the major hydrocarbons of this insect, including 3,11-dimethylnonacosane, the precursor to the major contact sex pheromone, and are presumed to be intermediates in hydrocarbon formation. A novel microsomal fatty acid synthetase (FAS) located in the integument of this insect incorporated [methyl-14C]methylmalonyl-CoA into methyl-branched fatty acids as demonstrated by radio-high-performance liquid chromatography. A cytosolic FAS is also present in the integument. Both the microsomal and the soluble FAS incorporated [methyl-14C]methylmalonyl-CoA into fatty acids, but only the microsomal FAS was able to efficiently use methylmalonyl-CoA as the sole elongating agent. This is the first report of the characterization of methyl-branched fatty acids from the integument of an insect and of an integumental microsomal FAS that incorporates methylmalonyl-CoA into branched fatty acids.     

Reduction of inflammation and chronic tissue damage by omega-3 fatty acids in fat-1 transgenic mice with pancreatitis

Pancreatitis is a severe debilitating disease with high morbidity and mortality. Treatment is mostly supportive, and until now there are no clinically useful strategies for anti-inflammatory therapy. Although omega-3 polyunsaturated fatty acids (n-3 PUFA) are known to have anti-inflammatory effects, the utility of these fatty acids in the alleviation of pancreatitis remained to be investigated. The aim of this study was to examine the effect of n-3 PUFA on both acute and chronic pancreatitis in a well-controlled experimental system. We used the fat-1 transgenic mouse model, characterized by endogenously increased tissue levels of n-3 PUFA, and their wild-type littermates to examine the effect of n-3 PUFA on both acute and chronic cerulein-induced pancreatitis. Disease activity and inflammatory status were assessed by both histology and molecular methods. In acute pancreatitis, fat-1 mice showed a trend towards decreased necrosis and significantly reduced levels of plasma IL-6 levels as well as reduced neutrophil infiltration in the lung. In chronic pancreatitis there was less pancreatic fibrosis and collagen content accompanied by decreased pancreatic stellate cell activation in the fat-1 animals with increased n-3 PUFA tissue levels as compared to wild-type littermates with high levels of omega-6 (n-6) PUFA in their tissues. Our data provide evidence for a reduction of systemic inflammation in acute pancreatitis and of tissue fibrosis in chronic pancreatitis by increasing the tissue content of omega-3 polyunsaturated fatty acids. These results suggest a beneficial potential for n-3 PUFA supplementation in acute and particularly chronic pancreatitis.     

Tumor necrosis factor production by murine resident peritoneal macrophages is enhanced by dietary n-3 polyunsaturated fatty acids

Tumor necrosis factor (TNF) is a macrophage derived peptide that has an antitumor action and modulates immune and inflammatory reactions. Dietary fatty acids may modulate TNF production as dietary n-3 polyunsaturated fatty acids suppress human monocyte TNF production, but enhance its secretion by murine peritoneal macrophages. Mice were maintained for 5 weeks on diets containing different amounts of n-3 and n-6 fatty acids. TNF, PGE2 and 6-keto PGF1 alpha production was monitored following in vitro stimulation of resident peritoneal macrophages with lipopolysaccharide. Macrophages from mice fed the high n-3 diet produced 8-fold more TNF and half the PGE2 produced by macrophages from mice on the other diets. Indomethacin caused an increase in the TNF production by macrophages from mice on all diets but macrophages from mice on the high n-3 diet produced more TNF than macrophages from mice on the other diets. Exogenous PGE2 (100 nM) greatly decreased TNF production by macrophages from mice on all diets, but macrophages from mice on the high n-3 diet secreted 70% more TNF than macrophages from mice fed the other diets, indicating that PGE2 is only partly responsible for the effects observed. The results show that feeding n-3 polyunsaturated fatty acids may cause enhanced TNF production by resident peritoneal macrophages and that PGE2 is partly responsible for the effect.     

Could n-3 polyunsaturated fatty acids reduce pathological pain by direct actions on the nervous system?

The intake of n-3 polyunsaturated fatty acids (PUFAs) in many industrialized countries is relatively low and its increased consumption has protective and modifying effects on such diverse conditions as atherosclerosis, ventricular arrhythmias, multiple sclerosis, major depression and inflammatory and autoimmune diseases. In addition, n-3 PUFAs have been shown to alleviate pain in patients with rheumatoid arthritis, inflammatory bowel disease and in a number of other painful conditions. This has been attributed to the inhibition of pro-inflammatory eicosanoid and cytokine production by peripheral tissues. n-3 PUFAs have also been shown to inhibit eicosanoid production in glial cells, block voltage-gated sodium channels (VGSCs), inhibit neuronal protein kinases and modulate gene expression. They also appear to have mood-stabilizing and sympatholytic effects. The present article explores the possibility that, based on what is known about their neural and non-neural effects, n-3 PUFAs directly attenuate the neuronal and glial processes that underlie neuropathic and inflammatory pain.