Occurrence of trans fatty acids in rats fed a trans-free diet: A free radical-mediated formation?

Trans isomers of unsaturated fatty acids are absorbed from the diet, due to their presence in diary fat and hydrogenated vegetable oils, and health concern has risen due to their effects on lipid risk factors in cardiovascular diseases. On the basis of the efficiency of the thiyl-radical-catalyzed cis/trans isomerization in vitro and the presence of many sulfur-containing compounds in the cell, the aim of this study was to demonstrate that trans geometry of lipid double bonds can be endogenously generated within membrane phospholipids. The study reports trans fatty acids occurrence in tissue and erythrocyte phospholipids of young adult rats fed a diet completely free of trans isomers. Results show that tissues are differently prone to the endogenous isomerization and that, following a free radical attack, trans fatty acids can reach very high amounts. The effectiveness of this process is considerably inhibited in the presence of all-trans retinol, confirming previous data in model membranes. Our results suggest that geometrical isomerization of unsaturated fatty acids, which causes a structural modification of membrane lipids and may influence basic membrane properties and vital biochemical functions, can occur under radical stress conditions and could be efficiently prevented by vitamin A.     

Effects of various numbers and positions of cis double bonds in the sn-2 acyl chain of phosphatidylethanolamine on the chain-melting temperature

In an attempt to investigate systematically the effects of various single and multiple cis carbon-carbon double bonds in the sn-2 acyl chains of natural phospholipids on membrane properties, we have de novo synthesized unsaturated C20 fatty acids comprised of single or multiple methylene-interrupted cis double bonds. Subsequently, 15 molecular species of phosphatidylethanolamine (PE) with sn-1 C20-saturated and sn-2 C20-unsaturated acyl chains were semi-synthesized by acylation of C20-lysophosphatidylcholine with unsaturated C20 fatty acids followed by phospholipase D-catalyzed base-exchange reaction in the presence of excess ethanolamine. The gel-to-liquid crystalline phase transitions of these 15 mixed-chain PE, in excess H2O, were investigated by high resolution differential scanning calorimetry. In addition, the energy-minimized structures of these sn-1 C20-saturated/sn-2 C20-unsaturated PE were simulated by molecular mechanics calculations. It is shown that the successive introduction of cis double bonds into the sn-2 acyl chain of C(20):C(20)PE can affect the gel-to-liquid crystalline phase transition temperature, Tm, of the lipid bilayer in some characteristic ways; moreover, the effect depends critically on the position of cis double bonds in the sn-2 acyl chain. Specifically, we have constructed a novel Tm diagram for the 15 species of unsaturated PE, from which the effects of the number and the position of cis double bonds on Tm can be examined simultaneously in a simple, direct, and unifying manner. Interestingly, the characteristic Tm profiles exhibited by different series of mixed-chain PE with increasing degree of unsaturation can be interpreted in terms of structural changes associated with acyl chain unsaturation.     

On the rate of genetic adaptation under natural selection.

Unsaturated fatty acids are constituents of nearly all biological membranes. They are always present in membranes which possess transmembrane potentials. Two completely different biosynthetic routes have evolved (aerobic and anaerobic) for placing cis double bonds in the 9 position on the fatty acids of membrane lipids. Bacterial membranes contain primarily monounsaturated fatty acids, whereas eukaryote membranes contain a significant fraction of polyunsaturated fatty acids. The polyunsaturated fatty acids are concentrated in organelles, such as chloroplasts and mitochondria that are known to manipulate transmembrane potentials. I propose that the function of the unsaturated fatty acids is to facilitate the transmission of a local compaction of the membrane (in response to a transmembrane potential) laterally through the membrane. The role of the cis double bond at position 9 is twofold: first to create a kink in the chains of a large fraction of membrane fatty acids enhancing the separation of two regions in the membrane and second to enhance the rigidity of the membrane in the region between the head group and the 9 double bond. This ordered region contains those carbons proximal to the 9 carbon and which are in a regular array of trans conformations. The presence of a reasonable proportion of cis double bonds at position 9 will tend to maintain these trans conformations utilizing pi-pi (van der Waals) interactions between adjacent hydrocarbon chains at position 9. The disordered region contains the carbons distal to the 9 carbon. These have greater degrees of freedom and considerable gauche conformations. The role of the double bonds in the polyunsaturated fatty acids distal to carbon 9 is to facilitate trans bilayer pi-pi (van der Waals) interactions enhancing compaction of the bilayer during the electrostriction. I further propose that it is the function of the ionic headgroups to form an interlocking polyionic network which constitutes an elastic sheet. These ionic interactions would serve as the restoring force converting the compaction into a wave. The facilitation of the compaction of the bilayer together with the polyionic restoring force permits the membrane to transmit conformational changes from one transmembrane protein to another. Since transmembrane potentials are created and responded to by proteins each in a single location, it is thus proposed that a potential compaction wave emanates from the first protein in all directions in the plane of the membrane. The proposed wave would have both physical and electrical components. The electrohydrodynamic wave would require that the compaction oscillations be coupled to an oscillating electrical field. These proposals are applied to mitochondrial oxidative phosphorylation, and to transport across biological membranes.     

Adaptation mechanisms of bacteria during the degradation of polychlorinated biphenyls in the presence of natural and synthetic terpenes as potential degradation inducers

In this study, we examined the effect of polychlorinated biphenyls (PCBs) in the presence of natural and synthetic terpenes and biphenyl on biomass production, lipid accumulation, and membrane adaptation mechanisms of two PCB-degrading bacterial strains Pseudomonas stutzeri and Burkholderia xenovorans LB400. According to the results obtained, it could be concluded that natural terpenes, mainly those contained in ivy leaves and pine needles, decreased adaptation responses induced by PCBs in these strains. The adaptation processes under investigation included growth inhibition, lipid accumulation, composition of fatty acids, cis/trans isomerization, and membrane saturation. Growth inhibition effect decreased upon addition of these natural compounds to the medium. The amount of unsaturated fatty acids that can lead to elevated membrane fluidity increased in both strains after the addition of the two natural terpene sources. The cells adaptation changes were more prominent in the presence of carvone, limonene, and biphenyl than in the presence of natural terpenes, as indicated by growth inhibition, lipid accumulation, and cis/trans isomerization. Addition of biphenyl and carvone simultaneously with PCBs increased the trans/cis ratio of fatty acids in membrane fractions probably as a result of fluidizing effects of PCBs. This stimulation is more pronounced in the presence of PCBs as a sole carbon source. This suggests that PCBs alone have a stronger effect on bacterial membrane adaptation mechanisms than when added together with biphenyl or natural or synthetic terpenes.     

The retina is more susceptible than the brain and the liver to the incorporation of trans isomers of DHA in rats consuming trans isomers of alpha-linolenic acid

Trans polyunsaturated fatty acids are formed during heat treatments of vegetable oils from polyunsaturated fatty acids containing cis double bonds. After dietary intake, they are distributed in the body and are incorporated into nervous tissues including the retina. Since nervous tissues are known to be rich in n-3 fatty acids such as docosahexaenoic acid (DHA), we studied the ability of the retina and the brain to incorporate trans isomers of DHA formed in vivo from the dietary precursor trans alpha-linolenic acid. Wistar rats were fed with trans isomers of alpha-linolenic acid for 21 months. A linear incorporation of trans DHA and a decrease in cis DHA was observed in the retina, whereas no major changes were observed in the brain. In parallel to the modifications in retinal cis and trans DHA levels, the retinal functionality evaluated by the electroretinogram showed defects in animals that consumed trans alpha-linolenic acid. These results suggest that the mechanisms leading to the incorporation of cis and trans fatty acids are quite different in the retina when compared to the brain and the liver, the retina being more susceptible to changes in the dietary lipid contribution.     

Phosphatidylcholine fluidity and structure affect lecithin:cholesterol acyltransferase activity

The purpose of this study was to test the hypothesis that lipid fluidity regulates lecithin:cholesterol acyltransferase (LCAT) activity. Phosphatidylcholine (PC) species were synthesized that varied in fluidity by changing the number, type (cis vs. trans), or position of the double bonds in 18 or 20 carbon sn-2 fatty acyl chains and recombined with [(3)H]cholesterol and apolipoprotein A-I to form recombinant high density lipoprotein (rHDL) substrate particles. The activity of purified human plasma LCAT decreased with PC sn-2 fatty acyl chains containing trans versus cis double bonds and as double bonds were moved towards the methyl terminus of the sn-2 fatty acyl chain. The decrease in LCAT activity was significantly correlated with a decrease in rHDL fluidity (measured by diphenylhexatriene fluorescence polarization) for PC species containing 18 carbon (r(2) = 0.61, n = 18) and 20 carbon (r(2) = 0.93, n = 5) sn-2 fatty acyl chains. rHDL were also made containing 10% of the 18 carbon sn-2 fatty acyl chain PC species and 90% of an inert PC ether matrix (sn-1 18:1, sn-2 16:0 PC ether) to normalize rHDL fluidity. Even though fluidity was similar among the PC ether-containing rHDL, the order of PC reactivity with LCAT was significantly correlated (r(2) = 0.71) with that of 100% PC rHDL containing the same 18 carbon sn-2 fatty acyl chain species, suggesting that PC structure in the active site of LCAT determines reactivity in the absence of measurable differences in bilayer fluidity. We conclude that PC fluidity and structure are major regulators of LCAT activity when fatty acyl chain length is constant.     

Interaction with membrane lipids and heme ligand binding properties of Escherichia coli flavohemoglobin

Escherichia coli flavohemoglobin has been shown to be able to bind specifically unsaturated and/or cyclopropanated fatty acids with very high affinity. Unsaturated or cyclopropanated fatty acid binding results in a modification of the visible absorption spectrum of the ferric heme, corresponding to a transition from a pentacoordinated (typical of the ligand free protein) to a hexacoordinated, high spin, heme iron. In contrast, no detectable interaction has been observed with saturated fatty acid, saturated phospholipids, linear, cyclic, and aromatic hydrocarbons pointing out that the protein recognizes specifically double bonds in cis conformation within the hydrocarbon chain of the fatty acid molecule. Accordingly, as demonstrated in gel filtration experiments, flavohemoglobin is able to bind liposomes obtained from lipid extracts of E. coli membranes and eventually abstract phospholipids containing cis double bonds and/or cyclopropane rings along the acyl chains. The presence of a protein bound lipid strongly affects the thermodynamic and kinetic properties of imidazole binding to the ferric protein and brings about significant modifications in the reactivity of the ferrous protein with oxygen and carbon monoxide. The effect of the bound lipid has been accounted for by a reaction scheme that involves the presence of two sites for the lipid/ligand recognition, namely, the heme iron and a non-heme site located in a loop region above the heme pocket.     

Inhibition of nuclear T3 binding by fatty acids: dependence on chain length, unsaturated bonds, cis-trans configuration and esterification

1. Fatty acids have the capacity for inhibition of nuclear T3 binding (INB). The present studies were undertaken to describe the INB-activity of fatty acids as a function of chain length, unsaturated bonds, cis-trans configuration, and esterification. 2. Isolated rat liver nuclei were incubated with [125I]T3 in the absence or presence of fatty acids in concentrations of 0.011, 0.033, 0.1 and 0.3 mM respectively. 3. INB-activity depended on the chain length, being greatest at 14 carbon atoms. 4. INB by unsaturated fatty acids was greater than that of saturated fatty acids, and increased with increasing number of double bonds. 5. Fatty acids in the cis configuration had greater INB-activity than those in trans configuration. 6. Esterification of fatty acids decreased INB-activity: monoglycerides still had some effect, but di- and triglycerides had no effect.     

Molecular species composition of rat liver phospholipids by ESI-MS/MS: the effect of chromatography.

Using electrospray ionization tandem mass spectrometry (ESI-MS/MS) this study shows that the loss of glycerophospholipid (GPL) after chromatography was unevenly distributed across the GPL molecular species. Both TLC and HPLC caused a preferential loss of GPL with 0 to 3 double bonds: 20% and 7.2% for choline glycerophosphates (PC) and 19.7% and 7.5% for ethanolamine glycerophosphates (PE), respectively. A consequence of these losses was that GPLs containing fatty acids with four or more double bonds had a greater contribution to the total after chromatography. ESI-MS/MS analysis also showed that PC molecular species with four or more double bonds migrated at the front of the TLC band of PCs. GPLs extracted from TLC plates occasionally contained PCs that were smaller than those in the original extract. These low molecular mass PCs were easily reduced to alcohols and formed derivatives with 2,4-dinitrophenylhydrazine, suggesting that aldehydes were generated by the oxidation of unsaturated fatty acids. Directly analyzing lipid extracts by ESI-MS/MS without preliminary chromatographic separation gives an accurate distribution of GPL molecular species in lipid mixtures. However, the ionization of the phospholipids in the electrospray jet maximized at relatively low concentrations of GPL. There was a linear response between phospholipid mass and ion intensity for concentrations around 1-2 nmol/ml for both PC and PE. The total ion intensity continued to increase with concentrations above 1-2 nmol/ml, but the response was non-linear.     

Unsaturated fatty acid isomers: effects on the circadian rhythm of a fatty-acid-deficient Neurospora crassa mutant

The fatty acids oleic, linoleic, and linolenic, each of which has a cis double bond at the delta 9 position, are known to lengthen the circadian period of conidiation (spore formation) of strains of Neurospora crassa carrying the cel mutation. cel confers a partial fatty acid requirement on the organism and has been used to promote incorporation of exogenous fatty acids. To test whether a physical effect imparted by the cis double bonds, such as increased membrane fluidity, is critical for the perturbation of the rhythm, various isomers of these fatty acids were supplemented to the bd csp cel strain. Positional isomers of oleic acid, such as petroselinic (delta 6) and vaccenic (delta 11) acids, and longer-chain isomers, such as eicosenoic (delta 11) and erucic (delta 13) acids, did not lengthen the rhythm. The shorter-chain palmitoleic (delta 9) acid did not give a consistent lengthening of the rhythm; it may be elongated to vaccenic acid. In contrast, gamma-linolenic acid (delta 6,9,12) dramatically lengthened the period. Linoelaidic acid (the trans,trans isomer of linoleic acid) lengthened the period at 22 degrees C, but elaidic acid (the trans isomer of oleic acid) did not. Elaidic acid was shown to exert a lengthening effect, but only at lower temperatures. The data do not support a direct physical action as the source of the fatty acids' "chronobiotic" ability.     

Fluorine-19 nuclear magnetic resonance studies of lipid fatty acyl chain order and dynamics in Acholeplasma laidlawii B membranes. A direct comparison of the effects of cis and trans cyclopropane ring and double-bond substituents on orientational order

The hydrocarbon chain orientational order parameters of membranes of Acholeplasma laidlawii B, enriched with large quantities of fatty acids containing either a cis or a trans cyclopropane ring or a cis or trans double bond, plus small quantities of one of an isomeric series of monofluoropalmitic acids, were determined via fluorine-19 nuclear magnetic resonance spectroscopy over a range of temperatures spanning the corresponding gel to liquid-crystalline phase transitions (determined via differential scanning calorimetry). Membrane orientational order profiles in the liquid-crystalline state were generally similar, regardless of the particular fatty acid structure present, showing a region of relatively constant order preceding a region of progressively decreasing order toward the methyl terminus of the acyl chain. In the gel state, the order profiles in the presence of either a trans cyclopropane ring or trans double-bond substituent were similar and were characterized by a pronounced head to tail gradient of order at temperatures just below the lipid phase transition, while at temperatures far below the lipid phase transition this gradient was less pronounced, all chain positions showing a more uniformly high degree of orientational ordering. In the gel state, the order profiles in the presence of either a cis cyclopropane ring or a cis double-bond substituent were also similar but were highly unusual in that order first increased and only then subsequently decreased toward the acyl chain methyl terminus. In addition, the substituents in the cis configuration, whether a cyclopropane ring or a double bond, were overall more disordered in the gel state than the corresponding substituents in the trans configuration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of long-chain cis-unsaturated fatty acids and their alcohol analogs on aggregation of bovine platelets and their relation with membrane fluidity change

The effects of long-chain cis-unsaturated fatty acids with different alkyl chain lengths and different numbers of double bonds on aggregation of bovine platelets and membrane fluidity were investigated. All the cis-unsaturated fatty acids tested inhibited aggregation and at the same time increased membrane fluidity in accordance with their inhibitory effects. The saturated fatty acids and trans-unsaturated fatty acid tested for comparison had much lower or no effects on aggregation and membrane fluidity. The inhibitory effects of mono cis-unsaturated fatty acids increased with increase of their alkyl chain length. cis-Unsaturated fatty acids with two or more double bonds had more inhibitory effects than mono-unsaturated fatty acids. The position of the double bonds had less influence than the number of double bonds. We also examined the effects of cis-unsaturated fatty acids on membrane fluidity with diphenylhexatriene and anthroyloxy derivatives of fatty acids as probes and observed increased fluidity to be considerable in the membrane. The alcohol analogs of cis-unsaturated fatty acids also inhibited aggregation and increased membrane perturbation. These results suggest that the inhibition of platelet aggregation by cis-unsaturated compounds is due to perturbation of the lipid layer.     

Use of an unsaturated fatty acid auxotroph of Saccharomyces cerevisiae to modify the lipid composition and function of mitochondrial membranes

KD115 (ol1), an unsaturated fatty acid auxotroph of S. cerevisiae, was grown in a semi-synthetic medium supplemented with 3.3 x 10(-4) M palmitoleic (cis 16:1) or palmitelaidic (trans 16:1) acids. The parent strain S288C was studied as a control. The lipid composition (fatty acids, neutral lipids, and phospholipids), respiratory activity (O2 consumption), and ultrastructure were compared in mutant yeast grown with each unsaturated fatty acid supplement. The fatty acid supplement represented 70-80% of the yeast fatty acids. Yeast grown in trans 16:1 contained more squalene, a higher ratio of phosphatidylethanolamine (PE) to phosphatidylcholine (PC), and had 10-20% of the respiratory activity compared to the same yeast grown in cis 16:1. The mitochondrial morphology of yeast in each growth supplement was notably different. The use of mixtures of cis and trans 16:1 in different proportions revealed that the PE/PC ratio, the squalene content, the respiratory defect, and the mitochondrial morphology were all similarly dependent on the fraction of trans 16:1 in the mixtures. As little as 10-20% of cis 16:1 in the mixture was sufficient to abrogate the physiological effects of trans 16:1 on each of the parameters noted above. The combined effects of high content of trans unsaturated fatty acid and the altered phospholipid composition seem to account for the decrease in lipid fluidity, the defective structure and function of the mitochondrial membrane.     

Domain formation in model membranes studied by pulsed-field gradient-NMR: the role of lipid polyunsaturation

The effects of increased unsaturation in the sn-2 fatty acyl chain of phosphatidylcholines (PCs) on the lipid lateral diffusion have been investigated by pulsed-field gradient NMR. Macroscopically oriented bilayers containing a monosaturated PC, egg sphingomyelin, and cholesterol (CHOL) have been studied at temperatures between 0 degrees C and 60 degrees C, and the number of double bonds in the PC was one, two, four, or six. For PC bilayers, with and without the incorporation of egg sphingomyelin and CHOL, the lateral diffusion increased with increasing number of double bonds, as a consequence of the increased headgroup area caused by the unsaturation. Addition of CHOL caused a decrease in lipid diffusion due to the condensing effect of CHOL on the headgroup area. Phase separation into large domains of liquid-disordered and liquid-ordered phases were observed in the ternary systems with PCs containing four and six double bonds, as evidenced by the occurrence of two lipid diffusion coefficients. PC bilayers with one or two double bonds appear homogeneous on the length scales probed by the experiment, but the temperature dependence of the diffusion suggests that small domains may be present also in these ternary systems.     

Pseudomonas putida NCTC 10936 balances membrane fluidity in response to physical and chemical stress by changing the saturation degree and the trans/cis ratio of fatty acids

This study explored the capability of Pseudomonas putida NCTC 10936 to maintain homeoviscosity after changing the growth temperature, incubating resting cells at different temperatures or at a constant temperature in the presence of 4-chlorophenol (4-CP). After raising the growth temperature from 20 to either 30 or 35 degrees C, the degree of saturation of the organism's fatty acids increased and the ratio of trans to cis unsaturated fatty acids decreased somewhat. In contrast, after the incubation temperature of resting cells was raised (grown at 30 degrees C) from 20 to 30 or 35 degrees C the degree of saturation of the fatty acids remained nearly constant, while the ratio of trans to cis unsaturated fatty acids increased. Incubating resting cells (grown at 30 degrees C) at 20 degrees C in the presence of 4-CP again caused no major changes in the degree of saturation, but cis to trans conversion of unsaturated fatty acids was induced, with a corresponding increase in the trans/cis ratios. Increases in both the saturation degree of the fatty acids and the trans/cis ratio of the unsaturated fatty acids correlated with increases in the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene intercalated in the bilayers of liposomes prepared from the cells of P. putida NCTC 10936. Electron transport phosphorylation (ETP) could be stabilized by adaptive adjustments in the fluidity of the cytoplasmic membrane mediated by changes in fatty acid composition such as those observed. Whether changes in the degree of saturation or in the trans/cis ratio are more effective can be decided by studying P. putida NCTC 10936.     

Modulation of Opioid Receptor Binding by Cis and Trans Fatty Acids

In synaptosomal brain membranes, the addition of oleic acid (cis), elaidic acid (trans), and the cis and trans isomers of vaccenic acid, at a concentration of 0.87 mumol of lipid/mg of protein, strongly reduced the Bmax and, to a lesser degree, the binding affinity of the mu-selective opioid [3H]Tyr-D-Ala-Gly-(Me)Phe-Gly-ol ([3H]DAMGO). At comparable membrane content, the cis isomers of the fatty acids were more potent than their trans counterparts in inhibiting ligand binding and in decreasing membrane microviscosity, both at the membrane surface and in the core. However, trans-vacenic acid affected opioid receptor binding in spite of just marginally altering membrane microviscosity. If the receptors were uncoupled from guanine nucleotide regulatory protein, an altered inhibition profile was obtained: the impairment of KD by the fatty acids was enhanced and that of Bmax reduced. Receptor interaction of the delta-opioid [3H](D-Pen2,D-Pen5)enkephalin was modulated by lipids to a greater extent than that of [3H]DAMGO: saturable binding was abolished by both oleic and elaidic acids. The binding of [3H]naltrexone was less susceptible to inhibition by the fatty acids, particularly in the presence of sodium. In the absence of this cation, however, cis-vaccenic acid abolished the low-affinity binding component of [3H]naltrexone. These findings support the membrane model of opioid receptor sequestration depicting different ionic environments for the mu- and delta-binding sites. The results of this work show distinct modulation of different types and molecular states of opioid receptor by fatty acids through mechanisms involving membrane fluidity and specific interactions with membrane constituents.     

Phospholipid ester-linked fatty acid profile changes during nutrient deprivation of Vibrio cholerae: increases in the trans/cis ratio and proportions of cyclopropyl fatty acids.

The phospholipid ester-linked fatty acids of 0-day-, 7-day-, and 30-day-starved cultures of Vibrio cholerae were compared. Statistically significant trends were noted in the fatty acid profiles as the cells starved. The amount of the cis-monoenoic fatty acids declined (e.g., 16:1 omega 7c: 0 day, 39%; 7 day, 18%; 30 day, 11%). In contrast, the saturated fatty acids, the cyclopropyl derivatives of the cis-monoenoic fatty acids, and trans-monoenoic fatty acids increased during starvation. For instance, the amounts of 16:1 omega 7t were: 0 day, 1%; 7 day, 13%; 30 day, 17%; which increased the trans/cis ratio for 16:1 omega 7 from 0.02 (0 day) to 0.70 (7 day) to 1.56 (30 day). This may be due to the reported high turnover rates of cis-monoenoic fatty acids of membrane phospholipids and the availability of enzymes for the metabolism of these isomers. During starvation-induced phospholipid loss, the cis-monoenoic fatty acids would, therefore, be preferentially utilized. The ability to either synthesize trans-monoenoic acids (which are not easily metabolized by bacteria) or modify the more volatile cis-monoenoic acids to their cyclopropyl derivatives may be a survival mechanism which helps maintain a functional (although structurally altered) membrane during starvation-induced lipid utilization. In addition, a trans/cis fatty acid ratio significantly greater than that reported for most bacterial cultures and environmental samples (less than 0.1) may be used as a starvation or stress lipid index. Such a ratio could help determine the nutritional status of ultramicrobacteria and other reported dormant cells in natural aquatic environments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phospholipid ester-linked fatty acid profile changes during nutrient deprivation of Vibrio cholerae: increases in the trans/cis ratio and proportions of cyclopropyl fatty acids

The phospholipid ester-linked fatty acids of 0-day-, 7-day-, and 30-day-starved cultures of Vibrio cholerae were compared. Statistically significant trends were noted in the fatty acid profiles as the cells starved. The amount of the cis-monoenoic fatty acids declined (e.g., 16:1 omega 7c: 0 day, 39%; 7 day, 18%; 30 day, 11%). In contrast, the saturated fatty acids, the cyclopropyl derivatives of the cis-monoenoic fatty acids, and trans-monoenoic fatty acids increased during starvation. For instance, the amounts of 16:1 omega 7t were: 0 day, 1%; 7 day, 13%; 30 day, 17%; which increased the trans/cis ratio for 16:1 omega 7 from 0.02 (0 day) to 0.70 (7 day) to 1.56 (30 day). This may be due to the reported high turnover rates of cis-monoenoic fatty acids of membrane phospholipids and the availability of enzymes for the metabolism of these isomers. During starvation-induced phospholipid loss, the cis-monoenoic fatty acids would, therefore, be preferentially utilized. The ability to either synthesize trans-monoenoic acids (which are not easily metabolized by bacteria) or modify the more volatile cis-monoenoic acids to their cyclopropyl derivatives may be a survival mechanism which helps maintain a functional (although structurally altered) membrane during starvation-induced lipid utilization. In addition, a trans/cis fatty acid ratio significantly greater than that reported for most bacterial cultures and environmental samples (less than 0.1) may be used as a starvation or stress lipid index. Such a ratio could help determine the nutritional status of ultramicrobacteria and other reported dormant cells in natural aquatic environments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of structural changes of fatty acids on lipid accumulation in adipocytes and primary hepatocytes

Conjugated linoleic acids (CLAs), tetradecylthioacetic acid (TTA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are all shown to differently affect lipid homeostasis. Additionally, previous studies have shown that introducing a methyl group in the molecule potentiates the hypolipidemic effect of EPA. The objective of this study was to determine how cis9,trans11 CLA, trans10,cis12 CLA, TTA, EPA and DHA affect lipid accumulation in 3T3-L1 adipocytes and in cultured primary rat hepatocytes, and to what extent changes in cis/trans configuration or introducing a methyl group in the molecules influence their way of affecting lipid accumulation in these cells. Our results show that trans10,cis12 CLA is highly specific in preventing lipid accumulation in adipocytes, and that small structural changes in the molecule (changing to trans/trans or introducing an alpha-methyl group) totally abolish this effect and up-regulate the expression levels of adipogenic marker genes towards control levels. Furthermore, all the fatty acids increased hepatic lipid accumulation, whereas the lipid content was normalized after adding an alpha-methyl group into the molecules. Taken together, our data demonstrate that the various fatty acids are highly specialized molecules, and that small structural changes markedly alter their way of affecting lipid accumulation in adipocytes and hepatocytes.     

Homogeneous catalytic hydrogenation of lipids in the photosynthetic membrane: Effects on membrane structure and photosynthetic activity

We have carried out a series of experiments in which the lipid composition of the photosynthetic membrane has been altered by the homogeneous catalytic hydrogenation of the unsaturated fatty acid residues of membrane lipids. The modified membrane was investigated by electron microscopy, electron-spin resonance and fluorescence polarization methods. Alteration in the functional characteristics of the hydrogenated membrane was monitored by the measurement of photophosphorylation and electron-transport activities. The following results were found. (a) Saturation of 10% of the fatty acyl double bonds induced a definite decrease in the dimension of both thylakoids and loculi. Microdensitometry showed that these structural changes arose from a thickening of the single membranes with a simultaneous decrease in the spacing between membranes. These changes might be accounted for by the alignment of the hydrocarbon chains of saturated lipids and the increased hydrophobicity of the membranes. (b) The orientational pattern of chlorophyll-a molecules was not altered by saturating up to 50% of fatty acyl double bonds in membrane lipids, indicating that the energy-transfer processes amongst the chlorophyll molecules remained functional after hydrogenation. (c) Saturation of double bonds of lipids inhibited whole electron transport prior to the inhibition of Photosystem II and Photosystem I activity, which may suggest that the unsaturation level of fatty acids plays a crucial role by ensuring the lateral mobility of plastoquinone between Photosystem II and Photosystem I.