Vitamin E, antioxidant and nothing more

All of the naturally occurring vitamin E forms, as well as those of synthetic all-rac-alpha-tocopherol, have relatively similar antioxidant properties, so why does the body prefer alpha-tocopherol as its unique form of vitamin E? We propose the hypothesis that all of the observations concerning the in vivo mechanism of action of alpha-tocopherol result from its role as a potent lipid-soluble antioxidant. The purpose of this review then is to describe the evidence for alpha-tocopherol's in vivo function and to make the claim that alpha-tocopherol's major vitamin function, if not only function, is that of a peroxyl radical scavenger. The importance of this function is to maintain the integrity of long-chain polyunsaturated fatty acids in the membranes of cells and thus maintain their bioactivity. That is to say that these bioactive lipids are important signaling molecules and that changes in their amounts, or in their loss due to oxidation, are the key cellular events that are responded to by cells. The various signaling pathways that have been described by others to be under alpha-tocopherol regulation appear rather to be dependent on the oxidative stress of the cell or tissue under question. Moreover, it seems unlikely that these pathways are specifically under the control of alpha-tocopherol given that various antioxidants other than alpha-tocopherol and various oxidative stressors can manipulate their responses. Thus, virtually all of the variation and scope of vitamin E's biological activity can be seen and understood in the light of protection of polyunsaturated fatty acids and the membrane qualities (fluidity, phase separation, and lipid domains) that polyunsaturated fatty acids bring about.     

The effects of alkylthioacetic acids (3-thia fatty acids) on fatty acid metabolism in isolated hepatocytes

Long-chain alkylthioacetic acids (3-thia fatty acids) inhibit fatty acid synthesis from [1-14C]acetate in isolated hepatocytes, while fatty acid oxidation is nearly unaffected or even stimulated. Desaturation of [1-14C]stearate (delta 9-desaturase) is also unaffected. [1-14C]Dodecylthioacetic acid (a 3-thia fatty acid) is incorporated in triacylglycerol and in phospholipids more efficiently than [1-14C]palmitate in isolated hepatocytes. The metabolism of [1-14C]dodecylthioacetic acid to acid-soluble products (by omega-oxidation) is slow compared to the oxidation of [1-14C]palmitate. In hepatocytes from adapted rats (rats fed tetradecylthioacetic acid for 4 days) the rate of [1-14C]palmitate oxidation is increased and its rate of esterification is decreased. Stearate desaturation is also decreased. The rate of cyanide-insensitive peroxisomal fatty acid beta-oxidation is several-fold increased. The metabolic effects of long-chain 3-thia fatty acids are discussed and it is concluded that they behave essentially like normal fatty acids except for their slow breakdown due to the sulfur atom in the 3 position, which blocks normal beta-oxidation.     

Food components and immune function

PURPOSE OF REVIEW: Enhancing immune function or alternatively dampening inflammatory processes by specific food components has received a lot of interest. The purpose of this review is to summarize recent findings with the emphasis on underlying mechanisms. RECENT FINDINGS: Dietary beta-glucans are relatively new candidates in the field of immune modulation by diet. In-vitro and animal studies suggest that beta-glucans shift inflammatory profiles to a Th1 type, which may enhance resistance against bacterial and parasitic infections. Regarding polyunsaturated fatty acids, there is evidence that n-3 fatty acids from fish oils (eicosapentaenoic acid and docosahexaenoic acid) dampen inflammatory responses. Whether eicosapentaenoic acid or docosahexaenoic acid is responsible for this phenomenon remains controversial. It is also inconclusive whether the plant-derived n-3 fatty acid alpha-linolenic acid has the same antiinflammatory effects as observed for fish oils. Saturated fatty acids may activate toll-like receptors and consequently the inflammatory pathway. The effect of total fat intake is controversial, since high-fat diets have been found to suppress immune function, while also improving intestinal barrier function. Finally, Gingko biloba was found to lower nuclear factor kappaB and activator protein 1 activation, possibly due to its high content of polyphenols. SUMMARY: In this review we discuss the nutritional components able to enhance immune function or show antiinflammatory effects. It can be concluded that diet certainly has the potential to direct immune responses. Apart from studies on fish oils, however, evidence from human studies is limited.     

The absorption, distribution and biological effects of a modified fatty acid in its free form and as an ethyl ester in rats

It has been demonstrated that the absorption of EPA and DHA is significantly lower for ethyl esters than for the corresponding free fatty acids. Since these fatty acids exist in nature and are catabolized by beta-oxidation, we instead wanted to investigate the absorption, distribution and biological effects of a non-beta-oxidizable modified fatty acid. The modified fatty acid tetradecylthioacetic acid (TTA) and the ethyl ester of TTA (EtTTA) were administered to rats for 10 days, in doses corresponding to 150 mg TTA/kg BW/day. No significant differences were found between the accumulated amounts of TTA or its Delta9 desaturated metabolite in plasma, liver, heart and epididymal white adipose tissue between EtTTA and TTA treated rats. EtTTA and TTA increased the activities of carnitine palmitoyltransferase-II and fatty acyl-CoA oxidase in liver, with no differences between the two treatment groups, but did not affect these activities in heart. EtTTA and TTA treatment decreased the plasma levels of triacylglycerols, cholesterol and phospholipids to similar extents, but no significant effects were seen in hepatic and cardiac lipid levels. EtTTA and TTA had similar effects on the fatty acid composition in plasma, liver, heart and epididymal white adipose tissue. Based on changes in fatty acid indexes it seems that these drugs had comparable stimulating effects on stearoyl-CoA desaturase and Delta6 desaturase, and reduced the Delta5 desaturase activity in liver. From the presented results we conclude that the absorption and distribution of the ethyl ester and the free form of TTA are not significantly different, and that the two administered forms of TTA have similar effects on lipid metabolism in rats.     

The ability of melatonin to counteract lipid peroxidation in biological membranes

This paper reviews recent data relevant to the antioxidant effects of melatonin with special emphasis on the changes produced in polyunsaturated fatty acids located in the phospholipids of biological membranes. The onset of lipid peroxidation within cellular membranes is associated with changes in their physicochemical properties and with the impairment of protein functions located in the membrane environment. All cellular membranes are especially vulnerable to oxidation due to their high concentration of polyunsaturated fatty acids. These processes combine to produce changes in the biophysical properties of membranes that can have profound effects on the activity of membrane-bound proteins. This review deals with aspects for lipid peroxidation of biological membranes in general, but with some emphasis on changes of polyunsaturated fatty acids, which arise most prominently in membranes and have been studied extensively in our laboratory. The article provides current information on the effect of melatonin on biological membranes, changes in fluidity, fatty acid composition and lipid-protein modifications during the lipid peroxidation process of photoreceptor membranes and modulation of gene expression by the hormone and its preventive effects on adriamycin-induced lipid peroxidation in rat liver. Simple model systems have often been employed to measure the activity of antioxidants. Although such studies are important and essential to understand the mechanisms and kinetics of antioxidant action, it should be noted that the results of simple in vitro model experiments cannot be directly extrapolated to in vivo systems. For example, the antioxidant capacity of melatonin, one of the important physiological lipophilic antioxidants, in solution of pure triglycerides enriched in omega-3 polyunsaturated fatty acids is considerably different from that in subcellular membranes.     

The metabolic syndrome and the hepatic fatty acid drainage hypothesis

Much data indicates that lowering of plasma triglyceride levels by hypolipidemic agents is caused by a shift in the liver metabolism towards activation of peroxisome proliferator activated receptor (PPAR)alpha-regulated fatty acid catabolism in mitochondria. Feeding rats with lipid lowering agents leads to hypolipidemia, possibly by increased channeling of fatty acids to mitochondrial fatty acid oxidation at the expense of triglyceride synthesis. Our hypothesis is that increased hepatic fatty acid oxidation and ketogenesis drain fatty acids from blood and extrahepatic tissues and that this contributes significantly to the beneficial effects on fat mass accumulation and improved peripheral insulin sensitivity. To investigate this theory we employ modified fatty acids that change the plasma profile from atherogenic to cardioprotective. One of these novel agents, tetradecylthioacetic acid (TTA), is of particular interest due to its beneficial effects on lipid transport and utilization. These hypolipidemic effects are associated with increased fatty acid oxidation and altered energy state parameters of the liver. Experiments in PPAR alpha-null mice have demonstrated that the effects hypolipidemic of TTA cannot be explained by altered PPAR alpha regulation alone. TTA also activates the other PPARs (e.g., PPAR delta) and this might compensate for deficiency of PPAR alpha. Altogether, TTA-mediated clearance of blood triglycerides may result from a lowered level of apo C-III, with a subsequently induction of hepatic lipoprotein lipase activity and (re)uptake of fatty acids from very low density lipoprotein (VLDL). This is associated with an increased hepatic capacity for fatty acid oxidation, causing drainage of fatty acids from the blood stream. This can ultimately be linked to hypolipidemia, anti-adiposity, and improved insulin sensitivity.     

Human peripheral blood T lymphocyte proliferation after activation of the T cell receptor: effects of unsaturated fatty acids

Oils enriched in certain polyunsaturated fatty acids suppress joint pain and swelling in rheumatoid arthritis patients with active synovitis. Because T lymphocyte activation is important for propagation of joint tissue injury in patients with rheumatoid arthritis, we examined the effects of fatty acids added in vitro on proliferation of human T lymphocytes stimulated with monoclonal antibodies to CD3 and CD4. Unsaturated fatty acids reduced T cell proliferation in a dose dependent manner (dihomogammalinolenic acid > gammalinolenic acid > eicosapentaenoic acid > arachidonic acid). Removal of fatty acids from cultures before cell stimulation did not change the effects, but addition of fatty acids after cell stimulation failed to reduce T cell responses. The saturated palmitic acid did not influence T cell growth. These studies indicate that small changes in cellular fatty acids can have profound effects on early events in T cell signaling and on T cell function.     

Oleic acid and adipokines synergize in inducing proliferation and inflammatory signalling in human vascular smooth muscle cells

In the context of obesity, perivascular fat produces various adipokines and releases free fatty acids, which may induce inflammation and proliferation in the vascular wall. In this study we investigated how adipokines, oleic acid (OA) and the combined treatment regulate human vascular smooth muscle cell (hVSMC) proliferation and migration and the underlying signalling pathways. Adipocyte‐conditioned media (CM) generated from human adipocytes induces a prominent proliferation and migration of hVSMC. Autocrine action of adiponectin totally abolishes CM‐induced proliferation. Furthermore, OA but not palmitic acid induces proliferation of hVSMC. CM itself does not contain fatty acids, but CM in combination with OA markedly enhances proliferation of hVSMC in a synergistic way. Both the nuclear factor (NF)‐κB and the mammalian target of rapamycin (mTOR) pathway were synergistically activated under these conditions and found to be essential for hVSMC proliferation. Expression of iNOS and production of nitric oxide was only enhanced by combined treatment inducing a marked release of VEGF. Combination of OA and VEGF induces an additive increase of hVSMC proliferation. We could show that the combination of CM and OA led to a synergistic proliferation of hVSMC. Expression of iNOS and production of nitric oxide were only enhanced under these conditions and were paralleled by a marked release of VEGF. These results suggest that the combined elevated release of fatty acids and adipokines by adipose tissue in obesity might be critically related to hVSMC dysfunction, vascular inflammation and the development of atherosclerosis.     

Arachidonic acid as a second messenger. Interactions with a GTP-binding protein of human neutrophils.

Arachidonic acid (20:4) and other cis-unsaturated fatty acids exert direct effects on a variety of cells, effects that do not depend on the metabolism of fatty acids via cyclooxygenase or lipoxygenase pathways. In these studies arachidonic acid and other cis-unsaturated fatty acids (but not trans-unsaturated or saturated fatty acids) increased the specific binding of the nonhydrolyzable analog of GTP, [35S]GTP gamma S, to purified neutrophil membrane preparations and elicited superoxide anion generation from intact neutrophils. There was a positive correlation (r = 0.70) between the capacity of fatty acids to increase nucleotide binding and to elicit the respiratory burst. Scatchard plot analysis of binding at equilibrium demonstrated an increase in the number of available GTP binding sites in the presence of 50 microM arachidonic acid. Nonsteroidal antiinflammatory agents interfered with the arachidonic acid effect on [35S]GTP gamma S binding. ADP-ribosylation of the pertussis toxin substrate Gi alpha within the plasmalemma-reduced specific [35S]GTP gamma S binding and blocked arachidonate-dependent enhancement of binding. Moreover, pertussis toxin treatment of intact neutrophils inhibited arachidonic acid-induced superoxide anion generation. The data indicate that arachidonic acid directly activates a GTP binding protein in the neutrophil plasma membrane and may thereby act as a second messenger in signal transduction.     

Induction of peroxisomal beta-oxidation in 7800 C1 Morris hepatoma cells in steady state by fatty acids and fatty acid analogues

(1) The activities of peroxisomal beta-oxidation and palmitoyl-CoA hydrolase in Morris hepatoma 7800 C1 cells were studied. The cells were grown until they reached steady state (constant DNA content per dish) and then were cultured in the presence of fatty acids or alkylthioacetic acids, i.e., S-substituted fatty acid analogues. (2) The fatty acid analogues increased the activity of the cyanide-insensitive palmitoyl-CoA oxidase several-fold. The effect was dose-dependent; 5 microM tetradecylthioacetic acid (TTA) was sufficient to give a significant induction. With 20 microM TTA, the increase in enzyme activity was discernable after 3 h and reached a maximum after 3 days. The inducing effect of the alkylthioacetic acids increased with the length of the hydrophobic alkyl end of the analogue. The inducing ability disappeared when the fatty acid analogue was omega-oxidized to the corresponding dicarboxylic acid. Oxidation of the sulfur atom resulted in inhibited cellular uptake and abolished enzyme induction. (3) At higher concentrations (0.5-1 mM), normal fatty acids also induced cyanide-insensitive palmitoyl-CoA oxidation. Myristic acid was the most potent inducer, whereas fatty acids with shorter as well as longer carbon chains were less efficient. The inducing effect increased with the number of double bounds in the fatty acid. (4) The normal fatty acids as well as the fatty acid analogues also induced palmitoyl-CoA hydrolase, but the relative changes were much less pronounced than with the palmitoyl-CoA oxidase.     

Cancer cells incorporate and remodel exogenous palmitate into structural and oncogenic signaling lipids

De novo lipogenesis is considered the primary source of fatty acids for lipid synthesis in cancer cells, even in the presence of exogenous fatty acids. Here, we have used an isotopic fatty acid labeling strategy coupled with metabolomic profiling platforms to comprehensively map palmitic acid incorporation into complex lipids in cancer cells. We show that cancer cells and tumors robustly incorporate and remodel exogenous palmitate into structural and oncogenic glycerophospholipids, sphingolipids, and ether lipids. We also find that fatty acid incorporation into oxidative pathways is reduced in aggressive human cancer cells, and instead shunted into pathways for generating structural and signaling lipids. Our results demonstrate that cancer cells do not solely rely on de novo lipogenesis, but also utilize exogenous fatty acids for generating lipids required for proliferation and protumorigenic lipid signaling. This article is part of a special issue entitled Lipid Metabolism in Cancer.     

Mass Spectrometry in Carbohydrate Chemistry

In this study, the physiological effects of fatty acids with conjugated double bonds were widely examined in vitro and in vivo. Initially, a method for determination of conjugated fatty acids in food and biological samples was established. I then clarified that the oxidative stability of conjugated fatty acids was improved by the form of triacylglycerol and addition of an antioxidant, and the influence of this effect on the metabolism and pharmacokinetics of conjugated fatty acids was clarified in vivo. In addition, antitumor, anti-angiogenesis, and antiobesity effects of conjugated fatty acids were found for the first time, thus demonstrating the usefulness of conjugated fatty acids. This communication mainly outlines the data obtained for conjugated linolenic acid. In addition, this review summarizes my research on conjugated fatty acid.     

Effects of fatty acid chain length and saturation on gastric inhibitory polypeptide release in obese hyperglycaemic (ob/ob) mice

Plasma gastric inhibitory polypeptide (GIP) responses to equimolar intragastrically administered emulsions of fatty acids (2.62 mmol/7.5 ml/kg) were examined in 18 h fasted obese hyperglycaemic (ob/ob) mice. Propionic acid (C3:0), a saturated short-chain fatty acid, and capric acid (C10:0), a saturated medium chain fatty acid, did not signilicantly stimulate GIP release. However, the saturated long-chain fatty acid stearic acid (C18:0), and especially the unsaturated long-chain fatty acids oleic (C18:1), linoleic (C18:2) and linolenic (C18:3) acids produced a marked GIP response. The results show that chain length and to a lesser extent the degree of saturation are important determinants of fatty acid-stimulated GIP release. The GIP-release action of long-chain, but not short-chain, fatty acids may be r e l a t e d to differences in their intracellular handling.     

Free fatty acids and skeletal muscle insulin resistance

PURPOSE OF REVIEW: Acute exposure to fatty acids causes insulin resistance in muscle, and excess dietary lipid and obesity are also strongly associated with muscle insulin resistance. Relevant mechanisms, however, are still not fully elucidated. Here we examine the latest evidence as to why lipids might accumulate in muscle and the possible mechanisms for lipid-induced insulin resistance. RECENT FINDINGS: Muscle lipid metabolites such as long chain fatty acid coenzyme As, diacylglycerol and ceramides may impair insulin signalling directly. Crosstalk between inflammatory signalling pathways and insulin signalling pathways, mitochondrial dysfunction and oxidative stress have also been put forward as major contributors to the development or maintenance of lipid-induced insulin resistance in muscle. Several animal models with gene deletions in pathways of fatty acid synthesis and storage also show increased metabolic rate, reduced intramuscular lipid storage and improved insulin action when challenged with a high lipid load. SUMMARY: Studies in genetic and dietary obese animal models, genetically modified animals and humans with obesity or type 2 diabetes suggest plausible mechanisms for effects of fatty acids, lipid metabolites, inflammatory pathways and mitochondrial dysfunction on insulin action in muscle. Many of these mechanisms, however, have been demonstrated in situations in which lipid accumulation (obesity) already exists. Whether the initial events leading to muscle insulin resistance are direct effects of fatty acids in muscle or are secondary to lipid accumulation in adipose tissue or liver remains to be clarified.     

Determination of natural resistance of mice fed dietary lipids to experimental infection induced by Listeria monocytogenes

Current understanding based on the effect of dietary lipid manipulation upon immune system function indicates that fatty acids are involved in the modulation of the immune response through different and complex pathways. Reduction of several immune parameters by fatty acid action may be applied in the treatment of diseases characterised by an overactivation of the immune system. As a consequence, a reduction of host resistance against infectious agents has been reported in animals fed dietary lipids. The present study confirms the action of dietary lipids on the survival of mice infected with the pathogenic bacterium Listeria monocytogenes. A significant increase in peritoneal cells from mice fed a hydrogenated coconut oil diet was found, while a significant reduction of bacterial recovery from spleens of these mice was observed in this group. In addition, both eicosanoid and phospholipase inhibitors did not promote any modification of lymphocyte proliferation from mice fed olive oil or fish oil.     

Fish oil and 3-thia fatty acid have additive effects on lipid metabolism but antagonistic effects on oxidative damage when fed to rats for 50 weeks

The 3-thia fatty acid tetradecylthioacetic acid (TTA) is a synthetic modified fatty acid, which, similar with dietary fish oil (FO), influences the regulation of lipid metabolism, the inflammatory response and redox status. This study was aimed to penetrate the difference in TTA's mode of action compared to FO in a long-term experiment (50 weeks of feeding). Male Wistar rats were fed a control, high-fat (25% w/v) diet or a high-fat diet supplemented with either TTA (0.375% w/v) or FO (10% w/v) or their combination. Plasma fatty acid composition, hepatic lipids and expression of relevant genes in the liver and biomarkers of oxidative damage to protein were assessed at the end point of the experiment. Both supplements given in combination demonstrated an additive effect on the decrease in plasma cholesterol levels. The FO diet alone led to removal of plasma cholesterol and a concurrent cholesterol accumulation in liver; however, with TTA cotreatment, the hepatic cholesterol level was significantly reduced. Dietary FO supplementation led to an increased oxidative damage, as seen by biomarkers of protein oxidation and lipoxidation. Tetradecylthioacetic acid administration reduced the levels of these biomarkers confirming its protective role against lipoxidation and protein oxidative damage. Our findings explore the lipid reducing effects of TTA and FO and demonstrate that these bioactive dietary compounds might act in a different manner. The experiment confirms the antioxidant capacity of TTA, showing an improvement in FO-induced oxidative stress.