Polyunsaturation in cell membranes and lipid bilayers and its effects on membrane proteins

Dietary Patterns Emphasizing the Consumption of Plant Foods in the Management of Type 2 Diabetes: A Narrative Review

The prevalence of type 2 diabetes (T2D) is increasing worldwide. This complex and multifactorial metabolic condition affects both the quality and expectancy of life in adults. Therefore, appropriate lifestyle strategies are needed in order to reduce the burden of T2D. Dietary patterns characterized by a high consumption of fruits, vegetables, whole grains, legumes, nuts, and seeds, and a minimal consumption of animal products, have been suggested as a dietary approach to prevent and control T2D and related micro- and macrovascular complications. This narrative review summarizes epidemiologic and clinical trial evidence on the role of the most widely studied dietary patterns that emphasize the consumption of plant foods [vegetarian, vegan, Mediterranean, and DASH (Dietary Approaches to Stop Hypertension) diets] in the management of T2D and its complications. Furthermore, their potential underlying mechanisms are discussed. Dietary patterns emphasizing the consumption of plant foods appear to confer beneficial effects on glycemic control in different diabetic populations. Several components of these dietary patterns might confer benefits on glycemia and counterbalance the detrimental effects of animal-based foods. The limited evidence on T2D-related complications makes it difficult to draw solid conclusions.

Selective Modulation of Protein Kinase C α over Protein Kinase C ε by Curcumin and Its Derivatives in CHO-K1 Cells

Members of the protein kinase C (PKC) family of serine/threonine kinases regulate various cellular functions, including cell growth, differentiation, metabolism, and apoptosis. Modulation of isoform-selective activity of PKC by curcumin (1), the active constituent of Curcuma L., is poorly understood, and the literature data are inconsistent and obscure. The effect of curcumin (1) and its analogues, 4-[(2Z,6E)-3-hydroxy-7-(4-hydroxy-3-methoxyphenyl)-5-oxohepta-2,6-dien-1-yl]-2-methoxyphenyl oleate (2), (9Z,12Z)-4-[(2Z,6E)-3-hydroxy-7-(4-hydroxy-3-methoxyphenyl)-5-oxohepta-2,6-dien-1-yl]-2-methoxyphenyl octadeca-9,12-dienoate (3), (9Z,12Z,15Z)-4-[(2Z,6E)-3-hydroxy-7-(4-hydroxy-3-methoxyphenyl)-5-oxohepta-2,6-dien-1-yl]-2-methoxyphenyl octadeca-9,12,15-trienoate (4), and (1E,6E)-1-[4-(hexadecyloxy)-3-methoxyphenyl]-7-(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-dione (5), and didemethylcurcumin (6) on the membrane translocation of PKCα, a conventional PKC, and PKCε, a novel PKC, has been studied in CHO-K1 cells, in which these PKC isoforms are endogenously expressed. Translocation of PKC from the cytosol to the membrane was measured using immunoblotting and confocal microscopy. 1 and 6 inhibited the TPA-induced membrane translocation of PKCα but not of PKCε. Modification of the hydroxyl group of curcumin with a long aliphatic chain containing unsaturated double bonds in 2-4 completely abolished this inhibition property. Instead, 2-4 showed significant translocation of PKCα but not of PKCε to the membrane. No membrane translocation was observed with 1, 6, or the analogue 5 having a saturated long chain for either PKCα or PKCε. 1 and 6 inhibited TPA-induced activation of ERK1/2, and 2-4 activated it. ERK1/2 is the downstream readout of PKC. These results show that the hydroxyl group of curcumin is important for PKC activity and the curcumin template can be useful in developing isoform specific PKC modulators for regulating a particular disease state.

Beyond apoptosis: the mechanism and function of phosphatidylserine asymmetry in the membrane of activating mast cells

Loss of plasma membrane asymmetry is a hallmark of apoptosis, but lipid bilayer asymmetry and loss of asymmetry can contribute to numerous cellular functions and responses that are independent of programmed cell death. Exofacial exposure of phosphatidylserine occurs in lymphocytes and mast cells after antigenic stimulation and in the absence of apoptosis, suggesting that there is a functional requirement for phosphatidylserine exposure in immunocytes. In this review we examine current ideas as to the nature of this functional role in mast cell activation. Mechanistically, there is controversy as to the candidate proteins responsible for phosphatidylserine translocation from the internal to external leaflet, and here we review the candidacies of mast cell PLSCR1 and TMEM16F. Finally we examine the potential relationship between functionally important mast cell membrane perturbations and phosphatidylserine exposure during activation.

Foods for the prevention of diabetes: how do they work?

With the diabetes epidemic reaching menacing proportions worldwide, there is an urgent need for the development of cost-efficient prevention strategies to be effective at the population level. Great potential in this direction lies in properly designed, large-scale dietary interventions. The macronutrient composition and the caloric content of our diet are major determinants of glucose homeostasis and there is a continuously growing list of foods, nutrients or individual compounds that have been associated with an increased or reduced incidence of diabetes mellitus. These include fat, carbohydrates, fibre, alcohol, polyphenols and other micronutrients or individual dietary compounds, which have been shown to either promote or prevent a progression towards a (pre-)diabetic state. This review aims to briefly summarize relevant epidemiological data linking foods to diabetes and to provide insights into the mechanisms through which these effects are mediated. These include improvement of insulin sensitivity or promotion of insulin resistance, regulation of inflammatory pathways, regulation of glucose transport and tissue glucose uptake, aggravation or attenuation of postprandial glycaemia/insulinaemia, interactions with hormonal responses and β-cell-dependent mechanisms.

Fish oil and mental health: the role of n-3 long-chain polyunsaturated fatty acids in cognitive development and neurological disorders

Epidemiological and experimental studies have indicated that consumption of more n-3 long-chain polyunsaturated fatty acids may reduce the risk for a variety of diseases, including cardiovascular, neurological and immunological disorders, diabetes and cancer. This article focuses on the role of marine n-3 long-chain polyunsaturated fatty acids in brain functions, including the development of the central nervous system and neurological disorders. An overview of the major animal studies and clinical trials is provided here, focusing on fatty acid supplementation during pregnancy and infancy, and prevention and management of Alzheimer's disease, schizophrenia, depression and attention deficit hyperactive disorder. Although an optimal balance in n-3/n-6 long-chain polyunsaturated fatty acid ratio is important for proper neurodevelopment and cognitive functions, results from randomized controlled trials are controversial and do not confirm any useful effect of supplementation on development of preterm and term infants. The relationship between fatty acid status and mental disorders is confirmed by reduced levels of n-3 long-chain polyunsaturated fatty acids in erythrocyte membranes of patients with central nervous system disorders. Nevertheless, there are very little data supporting the use of fish oil in those patients. The only way to verify whether n-3 long-chain polyunsaturated fatty acids are a potential therapeutic option in the management and prevention of mental disorders is to conduct a large definitive randomized controlled trials similar to those required for the licensing of any new pharmacological treatment.

Modulation of phosphoinositide-protein kinase C signal transduction by omega-3 fatty acids: implications for the pathophysiology and treatment of recurrent neuropsychiatric illness

The phosphoinositide (PI)-protein kinase C (PKC) signal transduction pathway is initiated by pre- and postsynaptic Galphaq-coupled receptors, and regulates several clinically relevant neurochemical events, including neurotransmitter release efficacy, monoamine receptor function and trafficking, monoamine transporter function and trafficking, axonal myelination, and gene expression. Mounting evidence for PI-PKC signaling hyperactivity in the peripheral (platelets) and central (premortem and postmortem brain) tissues of patients with schizophrenia, bipolar disorder, and major depressive disorder, coupled with evidence that PI-PKC signal transduction is down-regulated in rat brain following chronic, but not acute, treatment with antipsychotic, mood-stabilizer, and antidepressant medications, suggest that PI-PKC hyperactivity is central to an underlying pathophysiology. Evidence that membrane omega-3 fatty acids act as endogenous antagonists of the PI-PKC signal transduction pathway, coupled with evidence that omega-3 fatty acid deficiency is observed in peripheral and central tissues of patients with schizophrenia, bipolar disorder, and major depressive disorder, support the hypothesis that omega-3 fatty acid deficiency may contribute to elevated PI-PKC activity in these illnesses. The data reviewed in this paper outline a potential molecular mechanism by which omega-3 fatty acids could contribute to the pathophysiology and treatment of recurrent neuropsychiatric illness.

Mass spectrometric analysis reveals changes in phospholipid, neutral sphingolipid and sulfatide molecular species in progressive epilepsy with mental retardation, EPMR, brain: a case study

Progressive epilepsy with mental retardation, EPMR, belongs to a group of inherited neurodegenerative disorders, the neuronal ceroid lipofuscinoses. The CLN8 gene that underlies EPMR encodes a novel transmembrane protein that localizes to the endoplasmic reticulum (ER) and ER-Golgi intermediate compartment. Recently, CLN8 was linked to a large eukaryotic protein family of TLC (TRAM, Lag1, CLN8) domain homologues with postulated functions in lipid synthesis, transport or sensing. By using liquid chromatography/mass spectrometry we analysed molecular species of major phosholipid and simple sphingolipid classes from cerebral samples of two EPMR patients representing a progressive and advanced state of the disease. The progressive state brain showed reduced levels of ceramide, galactosyl- and lactosylceramide and sulfatide as well as a decrease in long fatty acyl chain containing molecular species within these classes. Among glycerophospholipid classes, an increase in species containing polyunsaturated acyl chains was detected especially in phosphatidylserines and phosphatidylethanolamines. By contrast, saturated and monounsaturated species were overrepresented among phosphatidylserine, phosphatidylethanolamine and phosphatidylinositol classes in the advanced state sample. The observed changes in brain sphingo- and phospholipid molecular profiles may result in altered membrane stability, lipid peroxidation, vesicular trafficking or neurotransmission and thus may contribute to the progression of the molecular pathogenesis of EPMR.

Membrane lipids and sodium pumps of cattle and crocodiles: an experimental test of the membrane pacemaker theory of metabolism

The influence of membrane lipid composition on the molecular activity of a major membrane protein (the sodium pump) was examined as a test of the membrane pacemaker theory of metabolism. Microsomal membranes from the kidneys of cattle (Bos taurus) and crocodiles (Crocodylus porosus) were found to possess similar sodium pump concentrations, but cattle membranes showed a four- to fivefold higher enzyme (Na(+)-K(+)-ATPase) activity when measured at 37 degrees C. The molecular activity of the sodium pumps (ATP/min) from both species was fully recoverable when delipidated pumps were reconstituted with membrane from the original source (same species). The results of experiments involving species membrane crossovers showed cattle sodium pump molecular activity to progressively decrease from 3,245 to 1,953 (P < 0.005) to 1,031 (P < 0.003) ATP/min when subjected to two cycles of delipidation and reconstitution with crocodile membrane as a lipid source. In contrast, the molecular activity of crocodile sodium pumps progressively increased from 729 to 908 (P < 0.01) to 1,476 (P = 0.01) ATP/min when subjected to two cycles of delipidation and reconstitution with cattle membrane as a lipid source. The lipid composition of the two membrane preparations showed similar levels of saturated ( approximately 31-34%) and monounsaturated ( approximately 23-25%) fatty acids. Cattle membrane had fourfold more n-3 polyunsaturated fatty acids (11.2 vs. 2.9%) but had a reduced n-6 polyunsaturate content (29 vs. 43%). The results support the membrane pacemaker theory of metabolism and suggest membrane lipids and their polyunsaturates play a significant role in determining the molecular activity of the sodium pump.

Docosahexaenoic acid in the diet: its importance in maintenance and restoration of neural membrane function

The central nervous system has the second highest concentration of lipids after adipose tissue. Long chain fatty acids, particularly arachidonic acid and docosahexaenoic acid, are integral components of neural membrane phospholipids. Alterations in neural membrane phospholipid components cannot only influence crucial intracellular and intercellular signaling but also alter many membrane physical properties such as fluidity, phase transition temperature, bilayer thickness, and lateral domains. A deficiency of docosahexaenoic acid markedly affects neurotransmission, membrane-bound enzyme and ion channel activities, gene expression, intensity of inflammation, and immunity and synaptic plasticity. Docosahexaenoic acid deficiency is associated with normal aging, Alzheimer disease, hyperactivity, schizophrenia, and peroxisomal disorders. Although the molecular mechanism of docosahexaenoic acid involvement in the disorders remains unknown, the supplementation of docosahexaenoic acid in the diet restores gene expression and modulates neurotransmission. Also, improvements are seen in signal transduction processes associated with behavioral deficits, learning activity, peroxisomal disorders, and psychotic changes in schizophrenia, depression, hyperactivity, stroke, and Alzheimer disease.

Molecular dynamics simulations of hydrated unsaturated lipid bilayers in the liquid-crystal phase and comparison to self-consistent field modeling

Molecular dynamics simulations, using the collision dynamics method, were carried out for hydrated bilayers of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (18:0/18:1 omega 9cis PC, SOPC) and 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphatidylcholine (18:0/22:6 omega 3cis PC, SDPC). The simulation cells of the two bilayers consisted of 96 SOPC (or SDPC) molecules and 2304 water molecules: 48 lipid molecules per layer and 24 H2O molecules per lipid. The water was modeled by explicit TIP3P water molecules. The C-H bond-order-parameter -S(CH) profiles of the hydrocarbon tails, the bond orientation distribution functions and the root-mean-square values of the positional fluctuations of the lipid chain carbons were calculated. Simulation results are compared to the available experimental data and to other computer investigations of these lipid molecules. Several results of molecular-level self-consistent field calculations of these bilayers are also presented. Both theoretical methods reveal the same main characteristic features of the order-parameter profiles for the given bilayers. Some aspects of the physical properties of unsaturated lipids and their biological significance are discussed.

The effect of omega-3 fatty acids on Ca-ATPase in rat cerebral cortex

Neuronal Ca-ATPase has the essential function of keeping intracellular Ca levels in the micromolar range. This is a prerequisite for normal neurotransmission. This study was designed to determine whether Ca-ATPase is a target for docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) action: results show that both these fatty acids are inhibitors of Ca-ATPase activity in synaptosomal membranes isolated from rat cerebral cortex (-65+/-5% at [DHA]=20 microg/ml, -59+/-7% at [EPA]=20 microg/ml). The inhibition caused by EPA, but not that of DHA, could be reversed completely by the addition of calphostin, a protein kinase C blocker. In contrast, DHA could stimulate Ca-ATPase activity (+132+/-5% at [DHA]=30 microg/ml) only in calmodulin-depleted membranes. In addition, Na,K-ATPase (which drives the Na-Ca exchanger) was inhibited by both DHA and EPA, both at 30 microg/ml (-15+/-0.7% and -42+/-1%, respectively). These results suggest a mechanism that explains the dampening effect of omega-3 fatty acids on neuronal activity.

Fish consumption and self-reported physical and mental health status

OBJECTIVE

The aim of this study was to assess whether self-reported mental health status, measured using the SF-36 questionnaire, was associated with fish consumption, assessed using a food-frequency questionnaire.

DESIGN

The cross-national data were collected in the 1996/97 New Zealand Health Survey and 1997 Nutrition Survey, which were conducted using the same sampling frame. Survey respondents were categorised into those who consumed no fish of any kind and those who consumed some kind of fish, at any frequency. Data were adjusted for age, household income, eating patterns, alcohol use and smoking. Other demographic variables and potential confounding nutrients were included in the preliminary analyses but were not found to have a significant relationship with fish consumption.

SUBJECTS

Data from a nationally representative sample of 4644 New Zealand adults aged 15 years and over were used in this analysis.

RESULTS

Fish consumption was significantly associated with higher self-reported mental health status, even after adjustment for possible confounders. Differences between the mean scores for fish eaters and those who never eat fish were 8.2 for the Mental Health scale and 7.5 for the Mental Component score. Conversely, the association between fish consumption and physical functioning was in the opposite direction.

CONCLUSIONS

This is the first cross-sectional survey to demonstrate a significant relationship between fish intake and higher self-reported mental health status, therefore offering indirect support for the hypothesis that omega-3 polyunsaturated fatty acids may act as mood stabilisers.

Chronic hypoxia alters fatty acid composition of phospholipids in right and left ventricular myocardium

Adult male Wistar rats were exposed to intermittent high altitude hypoxia of 7000 m simulated in a hypobaric chamber for 8 h/day, 5 days a week; the total number of exposures was 25. The concentration of individual phospholipids and their fatty acid (FA) profile was determined in right (RV) and left (LV) ventricles. Adaptation to hypoxia decreased the concentration of diphosphatidytglycerol (DPG) in hypertrophied RV by 19% and in non-hypertrophied LV by 12% in comparison with normoxic controls. Chronically hypoxic hearts exhibited lower phospholipid n-6 polyunsaturated FA(PUFA) content mainly due to decreased linoleic acid (18:2n-6), which was opposed by increased n-3 PUFA mainly due to docosahexaenoic acid (22:6n-3) in phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI). The content of arachidonic acid (20:4n-6) was unchanged in total phospholipids, but in PC it was increased in both ventricles (by 22%) and in PE decreased in LV only (by 20%). Chronic hypoxia increased the un-saturation index of PC and PE in both ventricles. The content of monounsaturated FA (MUFA) was increased and 18:2n-6 decreased in DPG. The proportion of saturated FA was increased in PC and PI of hypoxic RV but not LV. The FA composition of phosphatidylserine was not altered in hypoxic ventricles. It is concluded that chronic hypoxia led to only minor changes in individual phospholipid concentration in rat ventricular myocardium, but markedly altered their FA profile. These changes, in particular the greater incorporation of n-3 PUFA into phospholipids and increased un-saturation index, may lead to a better preservation of membrane integrity and thereby contribute to improved ischemic tolerance of chronically hypoxic hearts.

Effects of long-chain polyunsaturated fatty acid supplementation on fatty acid status and visual function in treated children with hyperphenylalaninemia

BACKGROUND

Children with phenylalanine-hydroxylase deficiency (type-I hyperphenylalaninemia, HPA) follow a low-phenylalanine diet, severely restricted in animal foods and long-chain polyunsaturated fatty acids (LCPUFA). Consequently, they have a poor LCPUFA status, particularly for docosahexaenoic acid (DHA). DHA is relevant to visual and neural development.

OBJECTIVE

To investigate the effects of a 12-month supplementation with LCPUFA in a double-blind, placebo-controlled trial in treated children with HPA.

STUDY DESIGN

Twenty children with well-controlled HPA were randomly allocated to receive either a fat supplement (supplying 26% as fatty acids including DHA, 8%) or a placebo. The fatty acid composition of erythrocyte lipids and the visual evoked potentials were measured at baseline and after 12 months of supplementation. Reference data were obtained from healthy children of comparable age.

RESULTS

At baseline children with HPA had a poorer DHA status and prolonged P100 wave latencies than the reference group. At the end of the trial the LCPUFA group showed a significant increase in DHA levels of erythrocyte lipids. In the LCPUFA group P100 wave latency decreased and was negatively associated with the DHA changes.

CONCLUSIONS

A balanced dietary supplementation with LCPUFA in children with HPA is associated with an increase of the DHA pool and improved visual function.

Mechanisms underlying the cost of living in animals

The cost of living can be measured as an animal's metabolic rate. Basal metabolic rate (BMR) is factorially related to other metabolic rates. Analysis of BMR variation suggests that metabolism is a series of linked processes varying in unison. Membrane processes, such as maintenance of ion gradients, are important costs and components of BMR. Membrane bilayers in metabolically active systems are more polyunsaturated and less monounsaturated than metabolically less-active systems. Such polyunsaturated membranes have been proposed to result in an increased molecular activity of membrane proteins, and in this manner the amount of membrane and its composition can act as a pacemaker for metabolism. The potential importance of membrane acyl composition in metabolic depression, hormonal control of metabolism, the evolution of endothermy, as well as its implications for lifespan and human health, are briefly discussed.

Essential fatty acids and the brain: possible health implications

Linoleic and alpha-linolenic acid are essential for normal cellular function, and act as precursors for the synthesis of longer chained polyunsaturated fatty acids (PUFAs) such as arachidonic (AA), eicosapentaenoic (EPA) and docosahexaenoic acids (DHA), which have been shown to partake in numerous cellular functions affecting membrane fluidity, membrane enzyme activities and eicosanoid synthesis. The brain is particularly rich in PUFAs such as DHA, and changes in tissue membrane composition of these PUFAs reflect that of the dietary source. The decline in structural and functional integrity of this tissue appears to correlate with loss in membrane DHA concentrations. Arachidonic acid, also predominant in this tissue, is a major precursor for the synthesis of eicosanoids, that serve as intracellular or extracellular signals. With aging comes a likely increase in reactive oxygen species and hence a concomitant decline in membrane PUFA concentrations, and with it, cognitive impairment. Neurodegenerative disorders such as Parkinson's and Alzheimer's disease also appear to exhibit membrane loss of PUFAs. Thus it may be that an optimal diet with a balance of n-6 and n-3 fatty acids may help to delay their onset or reduce the insult to brain functions which these diseases elicit.

Membranes as possible pacemakers of metabolism

Basal metabolic rate (BMR) varies dramatically among vertebrate species, both (i) being several fold higher in the endothermic mammals and birds compared to the ectothermic reptiles, amphibians and fish, and (ii) being much greater, on a body mass basis, in small vertebrates compared to large vertebrates. These differences in whole animal BMR are also manifest at the cellular level with substantial contributions to basal metabolic activity from the maintenance of various trans-membrane gradients. The percentage contribution of various processes to basal metabolism is remarkably consistent between different vertebrates and when BMR varies, the components of metabolic activity vary in relative unison. Membrane composition also varies between vertebrates and the degree of polyunsaturation of membrane phospholipids is correlated with cellular metabolic activity. In general, the tissue phospholipids and thus membrane bilayers of endotherms are more polyunsaturated than those from similar-sized ectotherms. In mammals membrane polyunsaturation is allometrically related to body mass. We suggest that membranes can act as pacemakers for overall metabolic activity. We propose that such membrane polyunsaturation increases the molecular activity of many membrane-bound proteins and consequently some specific membrane leak-pump cycles and cellular metabolic activity. We hypothesize a possible mechanistic basis for this effect that is based on a greater transfer of energy during intermolecular collisions of membrane proteins with the unsaturated two carbon units (C=C) of polyunsaturates compared to the single carbon units of saturated acyl chains, as well as the more even distribution of such units throughout the depth of the bilayer when membranes contain polyunsaturated acyl chains compared to monounsaturated ones. The proposed pacemaker role of differences in membrane bilayer composition is briefly discussed with respect to the brain (and sensory cells), evolution of mammalian endothermic metabolism, and its clinical implications for humans.

Low C18 to C20 fatty acid elongase activity and limited conversion of stearidonic acid, 18:4(n-3), to eicosapentaenoic acid, 20:5(n-3), in a cell line from the turbot, Scophthalmus maximus

The TF cell line, derived from a top predatory, carnivorous marine teleost, the turbot (Scophthalmus maximus), is known to have a limited conversion of C18 to C20 polyunsaturated fatty acids (PUFA). To illuminate the underlying processes, we studied the conversions of stearidonic acid, 18:4(n-3), and its elongation product, 20:4(n-3), in TF cells and also in a cell line, AS, derived from Atlantic salmon (Salmo salar), by adding unlabelled (25 microM), U-14C (1 microM) or deuterated (d5; 25 microM) fatty acids. Stearidonic acid, 18:4(n-3), was metabolised to 20:5(n-3) in both cells lines, but more so in AS than in TF cells. Delta5 desaturation was more active in TF cells than in AS cells, whereas C18 to C20 elongation was much reduced in TF as compared to AS cells. Only small amounts of docosahexaenoic acid (22:6(n-3)) were produced by both cell lines, although there was significant production of 22:5(n-3) in both cultures, especially when 20:4(n-3) was supplemented. We conclude that limited elongation of C18 to C20 fatty acids rather than limited fatty acyl Delta5 desaturation accounts for the limited rate of conversion of 18:3(n-3) to 20:5(n-3) in the turbot cell line, as compared to the Atlantic salmon cell line. The results can account for the known differences in conversions of C18 to C20 PUFA by the turbot and the Atlantic salmon in vivo.

Polyunsaturated fatty acids, membrane function and metabolic diseases such as diabetes and obesity

Lipids play an extraordinary range of roles in normal and deranged metabolism. In diabetes and obesity, lipids have often been seen just as impacting on the energy balance equation. New data are extending our understanding of how lipid subclasses influence carbohydrate and lipid metabolism at multiple control points: from the modulation of membrane proteins to the regulation of gene transcription.

Clinical use of lipids to control inflammatory disease

Selective dietary supplementation with lipids has long been used to influence the course of chronic inflammatory diseases. This review describes new aspects of the molecular mechanism of lipids to modulate leukocyte activity and highlights some recent clinical studies on therapeutic lipid administration. New promising advances in parenteral application of lipids as well as the impact on acute inflammatory disorders are discussed.

Omega-3 and omega-6 fatty acids in the insulin resistance syndrome. Lipid and lipoprotein metabolism and atherosclerosis

Dietary fatty acids appear to be of significant importance for several of the most-common diseases in modern societies. To obtain more knowledge about the health consequences of dietary fatty acids, we depend upon a better understanding of the mechanisms of action of these fatty acids in vivo. With regard to the IRS, omega-3 PUFA may exert beneficial effects upon many of the associated pathophysiological metabolic changes. Omega-3 PUFA reduce fasting and postprandial TG, may improve insulin sensitivity (as shown in animal experiments), decrease platelet and leukocyte reactivity, alter immunological functions, and may slightly decrease blood pressure. Omega-3 PUFA may also beneficially influence vessel wall characteristics and blood rheology. Furthermore, both types of PUFA (omega-3 and omega-6) have been shown to inhibit cardiac arrhythmias in animals. The role of omega-3 PUFA in blood clotting and fibrinolysis still remains controversial, whereas omega-6 fatty acids may lead to increased oxidation of lipoproteins. Regardless of the effects on LDL oxidizability, both types of PUFA have shown beneficial effects on the development of atherosclerosis. As yet, little is known about the effect of specific omega-6 fatty acids with respect to the IRS. Potential adverse effects of dietary PUFA must not be neglected, but should be viewed in light of the beneficial effects of these agents.

The effects of non-lamellar forming lipids on membrane protein-lipid interactions

The role of lipid polymorphism in the regulation of membrane-associated protein function is examined, based on recent studies which showed that changes in the levels of phosphatidylethanolamine (PE), cholesterol and phospholipid unsaturation, modulate the activity of the key signal transduction enzyme, protein kinase C (PKC). It is shown that effects of membrane compositional changes on PKC activity involve a perturbation of protein-lipid interactions with the head group region rather than with the hydrophobic interior of the bilayer. A key determinant in the perturbation of these interactions is suggested to be an elastic curvature energy, termed curvature stress, which results from the unfavorable packing of non-lamellar forming lipids in a planar bilayer. PKC activity is shown to be a biphasic function of curvature stress, with an optimum value of this parameter corresponding to an optimally active PKC conformation. Thus, it is shown that the maximal activity of conformationally distinct PKC isoforms may require a different optimum value of curvature stress. Furthermore, it is hypothesized that curvature stress may have differing effects on the conformation of membrane-associated PKC activity induced by diacylglycerols, phorbol esters or other activators, based on recent studies showing that these agents induce the formation of disparate active conformers of the enzyme.