Dietary fats and membrane function: implications for metabolism and disease

Lipids play varied and critical roles in metabolism, with function dramatically modulated by the individual fatty acid moities in complex lipid entities. In particular, the fatty acid composition of membrane lipids greatly influences membrane function. Here we consider the role of dietary fatty acid profile on membrane composition and, in turn, its impact on prevalent disease clusters of the metabolic syndrome and mental illness. Applying the classical physiological conformer-regulator paradigm to quantify the influence of dietary fats on membrane lipid composition (i.e. where the membrane variable is plotted against the same variable in the environment--in this case dietary fats), membrane lipid composition appears as a predominantly regulated parameter. Membranes remain relatively constant in their saturated (SFA) and monounsaturated (MUFA) fatty acid levels over a wide range of dietary variation for these fatty acids. Membrane composition was found to be more responsive to n-6 and n-3 polyunsaturated fatty acid (PUFA) levels in the diet and most sensitive to n-3 PUFA and to the n-3/n-6 ratio. These differential responses are probably due to the fact that both n-6 and n-3 PUFA classes cannot be synthesised de novo by higher animals. Diet-induced modifications in membrane lipid composition are associated with changes in the rates of membrane-linked cellular processes that are major contributors to energy metabolism. For example, in the intrinsic activity of fundamental processes such as the Na+/K+ pump and proton pump-leak cycle. Equally, dietary lipid profile impacts substantially on diseases of the metabolic syndrome with evidence accruing for changes in metabolic rate and neuropeptide regulation (thus influencing both sides of the energy balance equation), in second messenger generation and in gene expression influencing a range of glucose and lipid handling pathways. Finally, there is a growing literature relating changes in dietary fatty acid profile to many aspects of mental health. The understanding of dietary lipid profile and its influence on membrane function in relation to metabolic dysregulation has exciting potential for the prevention and treatment of a range of prevalent disease states.     

Fatty acid and peptide profiles in plasma membrane and membrane rafts of PUFA supplemented RAW264.7 macrophages

The eukaryotic cell membrane possesses numerous complex functions, which are essential for life. At this, the composition and the structure of the lipid bilayer are of particular importance. Polyunsaturated fatty acids may modulate the physical properties of biological membranes via alteration of membrane lipid composition affecting numerous physiological processes, e.g. in the immune system. In this systematic study we present fatty acid and peptide profiles of cell membrane and membrane rafts of murine macrophages that have been supplemented with saturated fatty acids as well as PUFAs from the n-3, the n-6 and the n-9 family. Using fatty acid composition analysis and mass spectrometry-based peptidome profiling we found that PUFAs from both the n-3 and the n-6 family have an impact on lipid and protein composition of plasma membrane and membrane rafts in a similar manner. In addition, we found a relation between the number of bis-allyl-methylene positions of the PUFA added and the unsaturation index of plasma membrane as well as membrane rafts of supplemented cells. With regard to the proposed significance of lipid microdomains for disease development and treatment our study will help to achieve a targeted dietary modulation of immune cell lipid bilayers.     

Role of diet fat in subcellular structure and function

Current concepts of the biomembrane will be extrapolated to membranes of homeotherms to illustrate the influence of the nature of dietary lipid in nutritionally complete diets on membrane polar head group content and fatty acid composition. Utilizing animal models, the controlling influence of dietary long chain fatty acids on major lipid constituents of the mitochondrial membrane in cardiac tissue, the plasma membrane of liver, and the synaptosomal membrane in brain can be demonstrated. Diet-induced alterations in membrane composition are associated with demonstrable changes in the function of specific membrane proteins. To illustrate this relationship, the effect of diet on mitochondrial ATPase activity and on a hormone receptor-stimulated function in the plasma membrane of the liver will be discussed. These observations suggest that the diet fat modulates enzyme functions in vivo by changing the surrounding lipid environment in the membrane.     

Lipids, lipid rafts and caveolae: their importance for GPCR signaling and their centrality to the endocannabinoid system

Scientific views of cell membrane organization are presently changing. Rather than serving only as the medium through which membrane proteins diffuse, lipid bilayers have now been shown to form compartmentalized domains with different biophysical properties (rafts/caveolae). For membrane proteins such as the G protein coupled receptors (GPCRs), a raft domain provides a platform for the assembly of signaling complexes and prevents cross-talk between pathways. Lipid composition also has a strong influence on the conformational activity of GPCRs. For certain GPCRs, such as the cannabinoid receptors, the lipid bilayer has additional significance. Endocannabinoids such as anandamide (AEA) are created in a lipid bilayer from lipid and act at the membrane embedded CB1 receptor. Endocannabinoids exiting the CB1 receptor are transported either by a carrier-mediated or a simple diffusion process to the membrane of the postsynaptic cell. Following cellular uptake, perhaps via caveolae/lipid raft-related endocytosis, AEA is rapidly metabolized by a membrane-associated enzyme, fatty acid amide hydrolase (FAAH) located in the endoplasmic reticulum. The entry point for AEA into FAAH appears to be from the lipid bilayer. This review explores the importance of lipid composition and lipid rafts to GPCR signaling and then focuses on the intimate relationship that exists between the lipid environment and the endocannabinoid system.     

Diet fat influences liver plasma-membrane lipid composition and glucagon-stimulated adenylate cyclase activity.

Rats were fed diets that differed in fatty acid composition or in the proportion of energy derived from fat to determine if alteration of dietary fat intake influences the structural lipid composition of liver plasma membrane and the expression of an associated hormone-receptor-mediated function. Weanling rats were fed 9% (w/w) or 20% (w/w) low-erucic acid rape-seed oil or 9% (w/w) soya-bean oil for 24 days. Plasma membranes were isolated and the effect of diet fat on the fatty acid composition of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol and sphingomyelin was determined. Diet fat significantly altered total saturated and (omega-9) and (omega-6)-unsaturated fatty acid composition in addition to the (omega-6)- to (omega-3)-unsaturated fatty acid ratio in these polar lipids. Feeding the high-fat diet increased the (omega-6)- to (omega-3)-unsaturated fatty acid ratio and the (omega-9)-unsaturated fatty acid content in all lipids except sphingomyelin. Assay of glucagon-stimulated adenylate cyclase activity at both high and low glucagon concentrations indicated that high-fat intake also decreased cyclic AMP formation. In a second experiment the fat intake was held constant (40% of energy) and oleic acid was substituted for linoleic acid by blending high- and low-linoleic acid-type safflower oils. This experiment established that a dose-response relationship exists between dietary intake of fatty acid and the fatty acid composition of plasma-membrane phospholipids. Specific diet-induced transitions in membrane phospholipid fatty acid composition were paralleled by changes in glucagon-stimulated adenylate cyclase activity. This study suggests that transitions in dietary fat intake can alter a hormone-receptor-mediated enzyme function in vivo by changing the surrounding lipid environment.     

Phospholipid surface bilayers at the air-water interface. III. Relation between surface bilayer formation and lipid bilayer assembly in cell membranes.

Lipid bilayer assembly in cell membranes has been simulated with total lipid extracts from human red blood cells and from mesophilic and thermophilic bacteria grown at several temperatures. Aqueous dispersions of these natural lipid mixtures form surface bilayers, a single bimolecular lipid state, but only at the growth temperature of the source organism. Thus, a single isolated bilayer state forms spontaneously in vitro from lipids that are available in vivo at the growth temperature of the cell. Surface bilayers form at a specific temperature that is a function of hydrocarbon chain length and degree of fatty acid unsaturation of the phospholipids; this property is proposed as an essential element in the control of membrane lipid composition.     

Lipid lateral diffusion and local microviscosity in plant mitochondrial membranes with various length and unsaturation of fatty acids

Two main aspects of the lipid dynamics, local microviscosity and lateral diffusion, were investigated in intact plant mitochondria isolated from different tissues exhibiting large differences in their fatty acids in terms of unsaturation (amount of linoleic and linolenic acids) or length of the hydrocarbon chains. In addition, the same parameters were determined in the outer and inner membranes isolated from cauliflower mitochondria, which differed not only in the fatty acid composition but also by the lipid-to-protein ratio. In intact mitochondria, local microviscosity assayed with anthroyloxy-fatty acids exhibited a transverse gradient from the surface to the center of the bilayer, which was mainly affected by the unsaturation index and the content in linoleic or linolenic acids. In contrast, lipid lateral diffusion increased as the content in linolenic or palmitic acids increased, but was not directly correlated to the unsaturation index. Interestingly, local microviscosity at the membrane surface was higher in the outer membrane than in the inner membrane, whereas no significant difference was found in lipid lateral diffusion. These results indicate that the influence of the fatty acid composition of mitochondrial membranes on the dynamics of the phospholipid bilayer depends on the type of movement considered and suggest that other parameters, such as the protein content of the bilayer, also affect membrane fluidity.     

Modulation of mitochondrial ATPase sensitivity to inhibitors and stimulators by diet-induced changes in membrane lipid

• 1.1. Weanling rats were fed diets differing in fatty acid composition to determine if changes induced in cardiac mitochondrial membrane structural components alter the sensitivity of mitochondrial ATPase to inhibition by oligomycin and stimulation by 2,4-dinitrophenol.
• 2.2. Mitochondrial ATPase assayed in situ within the mitochondrial membrane isolated from animals fed diets higher in fatty acids of longer chain length, exhibited greater oligomycin sensitivity and lower 2,4-dinitrophenol-induced stimulation.
• 3.3. Concomitant diet-induced changes occur in the fatty acid, composition of phosphatidylcholine, phosphatidylethanolamine and cardiolipin, increasing overall length of fatty-acyl tails in the membrane phospholipids.
• 4.4. Diet fat mediated alterations in oligomycin sensitivity of mitochondrial ATPase and membrane fatty acid chain length suggest that _vivo changes in thickness of the lipid bilayer may alter mitochindrial ATPase functions.
• 5.5. The present study extends the concept that dietary fat affects mitochondrial membrane structure and function by demonstrating that the membrane-dependent sensitivity of mitochondrial ATPase to inhibitors and stimulators may be modulated by dietary fat.

     

Response of rat heart membranes and associated ion-transporting ATPases to dietary lipid

The effects of different dietary fat intake on the lipid composition and enzyme behaviour of sarcolemmal (Na+ + K+)ATPase and sarcoplasmic reticulum Ca2+-ATPase from rat heart were investigated. Rat diets were supplemented with either sunflower seed oil (unsatd./satd. 5.6) or sheep kidney fat (unsatd./satd. 0.8). Significant changes in the phospholipid fatty acid composition were observed in both membranes after 9 weeks dietary lipid treatment. For both membranes, the total saturated/unsaturated fatty acid levels were unaffected by the dietary lipid treatment, however the proportions of the major unsaturated fatty acids were altered. Animals fed the sunflower seed oil diet exhibited an increase in n-6 fatty acids, including linoleic (18:2(n-6] and arachidonic (20:4(n-6] while the sheep kidney fat dietary rats were higher in n-3 fatty acids, principally docosahexaenoic (22:6), with the net result being a higher n-6/n-3 ratio in the sunflower seed oil group compared to sheep kidney fat dietary animals. Fluorescence polarization indicated that the fluidity of sarcoplasmic reticular membrane was greater than that of sarcolemmal membrane, with a dietary lipid-induced decrease in fluidity being observed in the sarcoplasmic reticular membrane from sheep kidney fat dietary animals. Despite these significant changes in membrane composition and physical properties, neither the specific activity nor the temperature-activity relationship (Arrhenius profile) of the associated ATPases were altered. These results suggest that with regard to the parameters measured in this study, the two ion-transporting ATPases are not modulated by changes which occur in the membrane lipid composition as a result of the diet.     

Fatty acids specifically related to the anisotropic properties of plasma membrane from rat urothelium

Four different luminal surfaces of rat urothelium differing in their fatty acid composition were prepared by dietary induction. In order to induce lipid changes, each of four groups of rat received a basal diet rich in one of the unsaturated n-3, n-6 or n-9 fatty acid families and a commercial (control) diet. The effects of the dietary regime on the fatty acid composition of luminal urothelial membranes and their relation to the mobility of fluorescent probes were studied. In comparison with the control diet membrane, all three fatty acid-rich diets induced a decrease of the percentage amount of saturated fatty acid while that of the unsaturated fatty acids was increased. Accordingly, all three diets increased the unsaturation index in comparison with the control diet. The anisotropy across each membrane fraction was assessed using the n-(9-anthroyloxy) fatty acid fluorescent probes 3-AS, 7-AS and 12-AS, which locate at different depths in the membrane. Two different anisotropy profiles were observed. One profile showed the highest anisotropy at the C7 depth, whereas the other exhibited a continuous decrease of the anisotropy from the surface to the center of the bilayer. The molecular properties (isomerization) of 18:2n-9 fatty acid may account, at least in part, for the observed V-shaped profile (the ascending trend) of the membrane anisotropy values as a function of the respective 18:2n-9 fatty acid contents. Nevertheless, the minimum value of the profile did not correspond to the minimum 18:2n-9 fatty acid content, but rather to the higher amount of docosahexaenoic (22:6n-3) fatty acid. Thus, a modulating role of the 22:6n-3 fatty acid on the rigidifying effect of 18:2n-9 fatty acid is suggested, possibly mediated by relationships between fatty acid composition, saturated and unsaturated chain lengths, and freedom of motion of the phospholipid acyl chains.     

Differential modulation of rat heart mitochondrial membrane-associated enzymes by dietary lipid

Diets supplemented with high levels of saturated fatty acids derived from sheep kidney (perirenal) fat or unsaturated fatty acids derived from sunflower seed oil were fed to rats and the effect on heart mitochondrial lipid composition and membrane-associated enzyme behaviour was determined. The dietary lipid treatments did not change the overall level of membrane lipid unsaturation but did alter the proportion of various unsaturated fatty acids. This led to a change in the omega 6/omega 3 unsaturated fatty acid ratio, which was highest in the sunflower seed oil fed rats. Arrhenius plots of the mitochondrial membrane associated enzymes succinate-cytochrome c reductase and oligomycin-sensitive adenosinetriphosphatase (ATPase) after dietary lipid treatment revealed different responses in their critical temperature. For succinate-cytochrome c reductase, the critical temperature was 29 degrees C for rats fed the sheep kidney fat diet and 20 degrees C for rats fed the sunflower seed oil diet. In contrast, no shift in the critical temperature for the mitochondrial ATPase was apparent as a result of the differing dietary lipid treatments. The results suggest that the discontinuity in the Arrhenius plot of succinate-cytochrome c reductase is induced by some change in the physical properties of the membrane lipids. In contrast, mitochondrial ATPase appears insensitive, in terms of its thermal behaviour, to changes occurring in the composition of the membrane lipids. However, the specific activity of the mitochondrial ATPase was affected by the dietary lipid treatment being highest for the rats fed the sheep kidney fat diet. No dietary lipid effect was observed for the specific activity of succinate-cytochrome c reductase. This differential response of the two mitochondrial membrane enzymes to dietary-induced changes in membrane lipid composition may affect mitochondrial oxidative phosphorylation.     

The molecular organization of the influenza virus surface. Studies using photoreactive and fluorescent labeled phospholipid probes

The membrane structures of remantadin-sensitive and remantadin-resistant influenza virus strains were studied using a photoreactive fatty acid as well as analogues of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin, carrying a fluorescent or photoreactive reporter group at the end of one of the aliphatic chains. The results obtained demonstrated for the first time that the phospholipids of the viral membrane form lateral domains differing by the fluidity of their hydrocarbon chains and, probably, by the head-group composition of the lipids. The hemagglutinin small subunit (HA2) was shown to protrude into the apolar region of the phospholipid bilayer, whereas the M1 protein makes contact only with the inner surface. In the remantadin-sensitive virions the heavy hemagglutinin chain (HA1) appears not to be in contact with the lipid bilayer, whereas in the remantadin-resistant strain HA1 has a hydrophobic segment that proved to be inserted into the bilayer.     

Effect of dietary lipids on plasma lipoproteins and fluidity of lymphoid cell membranes in normal and leukemic mice

Mice of the GR/A strain were fed four different isocaloric semipurified diets, enriched in either (1) saturated fatty acids (palm oil), or (2) polyunsaturated fatty acids (corn oil), or (3) palm oil plus cholesterol, or (4) a fat-poor diet containing only a minimal amount of essential fatty acids. We have studied the effects of these dietary lipids on the density profile and composition of the plasma lipoproteins and on the lipid composition and fluidity of (purified) lymphoid cell membranes in healthy mice and in mice bearing a transplanted lymphoid leukemia (GRSL). Tumor development in these mice occurred in the spleen and in ascites. While the fatty acid composition of the VLDL-triacylglycerols still strongly resembled the dietary lipids, the effects of the diets decreased in the order VLDL-triacylglycerols greater than HDL-phospholipids greater than plasma membrane phospholipids. Diet-induced differences in the latter fraction were virtually confined to the content of oleic acid and linoleic acid, and they were too small to affect the membrane fluidity, as measured by fluorescence polarization using the probe 1,6-diphenyl-1,3,5-hexatriene. Healthy mice were almost irresponsive to dietary cholesterol, but in the tumor bearers, where lipoprotein metabolism has been shown to be disturbed, the cholesterol diet caused a substantial increase in the low- and very-low density regions of both blood and ascites plasma lipoproteins. The cholesterol-rich diet also increased the cholesterol/phospholipid molar ratio and lipid structural order (decreased fluidity) in GRSL ascites cell membranes, but not in the splenic GRSL cell membranes. We conclude that the composition of plasma lipoproteins and cell membrane lipids in GR/A mice is subject to exquisite homeostatic control. However, in these low-responders to dietary lipids the development of an ascites tumor may lead to increased responsiveness to dietary cholesterol. The elevated level of membrane cholesterol thus obtained in GRSL ascites cells did not affect the expression of various cell surface antigens or tumor cell growth.     

The effect of variations in growth temperature, fatty acid composition and cholesterol content on the lipid polar head-group composition of Acholeplasma laidlawii B membranes

We have systematically investigated the effect of variations in growth temperature, fatty acid composition and cholesterol content on the membrane lipid polar headgroup composition of Acholeplasma laidlawii B. Two important lipid compositional parameters have been determined from such an analysis. The first parameter studied was the ratio of the two major neutral glycolipids of this organism, monoglucosyldiacylglycerol (MGDG) and diglucosyldiacylglycerol (DGDG). As the former lipid prefers to exist in a reversed hexagonal phase at higher temperatures, with unsaturated fatty acyl chains or in the presence of cholesterol, the ratio of these two lipids reflects the phase state preference of the total A. laidlawii membrane lipids. Although we find that the MGDG/DGDG ratio is reduced in response to an increase in fatty acid unsaturation, increases in growth temperature or cholesterol content reduce this ratio only in cells enriched in a saturated but not an unsaturated fatty acid. The second parameter studied was the ratio of these neutral glycolipids to the only phosphatide in the A. laidlawii membrane, phosphatidylglycerol (PG); this parameter reflects the relative balance of uncharged and charged lipids in the membrane of this organism. We find that the MGDG + DGDG/PG ratio is lowest in cells enriched in the saturated fatty acid even though these cells already have the highest lipid bilayer surface charge density. Moreover, this ratio is not consistently related to growth temperature or changes in cholesterol levels, as expected. We therefore conclude that A. laidlawii strain B, apparently unlike strain A, does not possess coherent regulatory mechanisms for maintaining either the phase preference or the surface charge density of its membrane lipid constant in response to variations in growth temperature, fatty acid composition or cholesterol content.     

Lipid shape as a determinant of lipid composition in Clostridium butyricum. The effects of incorporation of various fatty acids on the ratios of the major ether lipids

The lipid composition of Clostridium butyricum is strongly influenced by the aliphatic chain compositions of the membrane lipids. Growth on cis-monounsaturated fatty acids in the absence of biotin was shown to affect the relative proportions of phosphatidylethanolamine, plasmenylethanolamine, and the glycerol acetal of plasmenylethanolamine most strongly, with smaller effects on the acidic lipids, phosphatidylglycerol and cardiolipin. The ratio of the glycerol acetal of plasmenylethanolamine to total phosphatidylethanolamine in cells grown on a series of fatty acids is shown to decrease in the following order; cis-vaccenic acid greater than or equal to oleic acid = C19-cyclopropane fatty acid greater than linoleic acid greater than petroselinic acid greater than elaidic acid greater than 14-methylhexadecanoic acid (anteiso-C17) greater than 12-methyltridecanoic acid (iso-C14). All fatty acids were extensively incorporated into the lipid acyl, alkenyl, and alkyl chains. There was considerable chain-elongation of the iso-C14 to iso-C16. The results are consistent with the hypothesis that the membrane lipid composition is strongly influenced by lipid shape and that the observed changes in lipid composition serve to stabilize the bilayer arrangement of the cell membrane.     

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

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

Effect of diets containing different oils on brain fatty acid composition in sea bass (Dicentrarchus labrax L.)

Four groups of adult sea bass were given diets containing about 8% of one of four different oils having a different fatty acid composition: linseed oil, grape-seed oil, containing high amounts of linolenic and linoleic acids respectively, hydrogenated coconut oil, mainly containing saturated fatty acids, and cod liver oil which was considered as reference. Total lipid, phospholipid and polar lipid contents of the brain of the different groups of sea bass were unaffected. The fatty acid composition of the brain agreed with the dietary history of sea bass: thus adult sea bass brain is capable of incorporating dietary fatty acids. Sea bass brain and structural lipids of the liver appeared to be similarly sensitive to the dietary input in contrast with mammalian brain which was reported to be more resistant than other tissues. The more striking dietary effect on liver total lipid fatty acid composition is ascribed to the incorporation of dietary fatty acids in depot fats.     

Fluid phase lipid areas and bilayer thicknesses of commonly used phosphatidylcholines as a function of temperature

The structural parameters of fluid phase bilayers composed of phosphatidylcholines with fully saturated, mixed, and branched fatty acid chains, at several temperatures, have been determined by simultaneously analyzing small-angle neutron and X-ray scattering data. Bilayer parameters, such as area per lipid and overall bilayer thickness have been obtained in conjunction with intrabilayer structural parameters (e.g. hydrocarbon region thickness). The results have allowed us to assess the effect of temperature and hydrocarbon chain composition on bilayer structure. For example, we found that for all lipids there is, not surprisingly, an increase in fatty acid chain trans-gauche isomerization with increasing temperature. Moreover, this increase in trans-gauche isomerization scales with fatty acid chain length in mixed chain lipids. However, in the case of lipids with saturated fatty acid chains, trans-gauche isomerization is increasingly tempered by attractive chain-chain van der Waals interactions with increasing chain length. Finally, our results confirm a strong dependence of lipid chain dynamics as a function of double bond position along fatty acid chains.     

Comparative study of the lateral motion of extrinsic probes and anthracene-labelled constitutive phospholipids in the plasma membrane of Chinese hamster ovary cells

9-(2-Anthryl)-nonanoic acid is a new photoactivatable fluorescent probe which has been designed for the study of the lateral diffusion and distribution of lipids in biological membranes by means of the anthracene photodimerization reaction. This anthracene fatty acid can be incorporated metabolically into the glycerophospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol) of Chinese hamster ovary (CHO) cells in culture. The diffusion coefficient of intrinsic lipids in the plasma membrane of these eukaryotic cells can thus be measured using the fluorescence recovery after a photobleaching technique, since illumination of the fluorescent anthracene groups yields non-fluorescent photodimers. For the sake of comparison, the extrinsic lipophilic probes 5-(N-hexadecanoyl)-aminofluorescein, 12-(9-anthroyloxy)-stearic acid, 9-(2-anthryl)-nonanoic acid and a synthetic anthracene-phosphatidylcholine were also used to label the plasma membrane of CHO cells. The diffusion coefficients for the extrinsic and intrinsic probes ranged over 1 - 2 x 10(-9) cm2/s. Small but significant differences were observed between the various probes reflecting differences they exhibit in size and polarity. All the extrinsic probes were free to diffuse, with a mobile fraction close to 100%. In contrast, a fractional recovery of only 75% was observed for the intrinsic anthracene-labelled phospholipids, suggesting that the anthracene fatty acid was metabolically incorporated into membrane lipid regions which were inaccessible to the extrinsic probes.     

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

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