Inhibition of nuclear T3 binding via PLA2-induced release of fatty acids from nuclear membranes

This study was undertaken to explore putative regulatory mechanisms involved in the inhibition of nuclear T3 binding (INB) by fatty acids. Ether extracts of intact rat liver nuclei contained INB-activity. Removement of the nuclear membrane resulted in the loss of INB-activity of the nuclei. Incubation of intact nuclei with phospholipase A2 increased nuclear INB-activity in a time- and dose-dependent manner; this was correlated with a rise of free fatty acid concentration in the ether extract. We conclude that fatty acids present in the nuclear membrane can be released by phospholipase A2, and are capable of inhibiting nuclear T3 binding.     

Interaction of amphiphiles with integral membrane proteins. I. Structural destabilization of the anion transport protein of the erythrocyte membrane by fatty acids, fatty alcohols, and fatty amines

The effect of model amphiphiles on the structural stability of the anion exchange protein (band 3) of the human erythrocyte membrane was studied by differential scanning calorimetry. The concentration of membranes, as well as the concentration, head group, alkyl chain length, degree of unsaturation, and double bond configuration of a variety of alkane derivatives were all varied in a systematic way. The depression of the denaturation temperature of band 3 per unit membrane concentration of the amphiphile was then determined in order to quantitate the potency of each drug. Saturated fatty acids of chain length C8 to C24 displayed a monotonic decrease in potency up to C20, followed by a dramatic diminution in potency at C22 and C24. Unsaturation caused only minor increases in the abilities of fatty acids to perturb the anion exchanger, and surprisingly, there was neither a trend for the number of double bonds nor a significant cis-trans distinction. Arachidonic acid, as an exception, was much more effective than any other amphiphile in destabilizing band 3. Fatty acids were about three times more potent than fatty amines and fatty alcohols; however, the enhanced partitioning of the latter into the membrane compensated at certain membrane/buffer ratios for its reduced intrinsic potency. A quantitative model interpretation of the data is presented in an accompanying paper.     

Seasonal variation in triacylglyceride fatty acids of dwarf mistletoes

Fatty acids in the triacylglyceride fraction of three species of dwarf mistletoe (Arceuthobium, Viscaceae) showed considerable seasonal variation in proportions of saturated acids and some differences in chain length for those fatty acids. Early summer aerial shoot tissue contained 34–49% saturated fatty acids, while the same species in late October had only 8–15% saturated fatty acids. Fatty acids with a chain length of C₂₀ or greater comprised 18–25% of the total in late June but only 1.5–6.4% in the autumn. Three other species analysed in only one season showed similar saturated fatty acids, and chain length patterns were also parallel to the seasonally varying species analysed in the same season. The ratio of linolenic to oleic acid remained constant with season but linolenic acid increased from less than 1% in June to 7–8% in October samples.     

Inhibition of nuclear T3 binding by fatty acids liberated from nuclear membranes via phospholipase C.

1. We have investigated whether phospholipase C (PLC) might act on phospholipids in the nuclear membrane of rat liver, resulting in inhibition of nuclear T3 binding (INB activity). 2. Incubation of intact nuclei with PLC caused a time- and dose-dependent increase of INB activity; this was correlated with a rise of the free fatty acid concentration in the nuclear ether extract. 3. Removal of the nuclear membrane resulted in a loss of INB activity of the nuclei. 4. Other compounds liberated by the action of PLC (such as diacylglycerols, IP3 and phosphoalcohols), had no INB activity. 5. We conclude that PLC can liberate fatty acids from the rat liver-nuclear membrane via further degradation of the direct product diacylglycerol. 6. These fatty acids display inhibition of nuclear T3 binding in vitro.     

Effects of fatty acids on mitochondria: implications for cell death

Fatty acids have prominent effects on mitochondrial energy coupling through at least three mechanisms: (i) increase of the proton conductance of the inner mitochondrial membrane; (ii) respiratory inhibition; (iii) opening of the permeability transition pore (PTP). Furthermore, fatty acids physically interact with membranes and possess the potential to alter their permeability; and they are also excellent respiratory substrates that feed electrons into the respiratory chain. Due to the complexity of their actions, the effects of fatty acids on mitochondrial function in situ are difficult to predict. We have investigated the mitochondrial and cellular effects of fatty acids of increasing chain length and degree of unsaturation in relation to their potential to affect mitochondrial function in situ and to cause cell death. We show that saturated fatty acids have little effect on the mitochondrial membrane potential in situ, and display negligible short-term cytotoxicity for Morris Hepatoma 1C1 cells. The presence of double bonds increases both the depolarizing effects and the cytotoxicity, but these effects are offset by the hydrocarbon chain length, so that more unsaturations are required to observe an effect as the hydrocarbon chain length is increased. With few exceptions, depolarization and cell death are due to opening of the PTP rather than to the direct effects of fatty acids on energy coupling.     

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.     

Conversion of glucose, acetate and lactate to CO2 and fatty acids in liver and adipose tissue of prairie voles (Microtus ochrogaster)

Production of CO2 and fatty acids from acetate, glucose and lactate was determined in slices of liver and adipose tissue from prairie voles fed either a high-starch or a high-cellulose diet. Acetate and lactate were oxidized to CO2 and converted to fatty acids at greater rates than was glucose in both liver and adipose tissue. Fatty acid synthesis occurred at greater rates in adipose tissue than in liver. Fatty acid synthesis per adipocyte increased with increased adipocyte diameter. Fiber content of diets had only minimal effect on metabolic activities of liver and adipose tissue.     

Competitive inhibition of T3 binding to alpha 1 and beta 1 thyroid hormone receptors by fatty acids.

This study was undertaken to investigate whether fatty acids inhibit the binding of T3 to the alpha 1 and beta 1 form of the thyroid hormone receptor. Fatty acids inhibited the binding of T3 to both receptor proteins isolated from a bacterial expression system. The effectiveness of inhibition depends on the chain length and degree of saturation of the fatty acids. The inhibition of T3 binding to the alpha 1 and beta 1 receptor by oleic acid is competitive in nature; the Ki value was 5.4 10(-6) M for the c-erbA alpha 1 protein and 3.3 10(-6) M for the c-erb beta 1 protein. The findings indicate a direct interaction of fatty acids with T3 receptor proteins.     

Fatty acids of glycosphingolipids from pig blood fractions

Four glycolipids have been isolated from three fractions of pig blood. The glycolipids were presumably cerebroside, diglycosyl ceramide, triglycosyl ceramide, and globoside. The blood fractions were erythrocytes and plasma high and low density lipoproteins. Fatty acid distributions were determined for each glycolipid as a means to assist in identifying relationships among the several glycolipids. Normal fatty acids predominated in all glycolipids except the globosides from erythrocytes in which the amount of hydroxy acids was slightly greater than the amount of normal acids. Hydroxy acids appeared to be present in all the glycolipids, but the concentration was very low in cerebrosides isolated from high density lipoproteins and erythrocytes, and in diglycosyl ceramide and globoside of the low density lipoproteins. In general, the average fatty acid chain length increased from cerebroside to globoside. This was most apparent in erythrocytes and also greater for normal acids than for hydroxy acids. Fatty acid distributions of erythrocyte glycolipids had sufficient variation to make a metabolic relationship by simple addition of a hexose appear doubtful. While the fatty acid distributions found in plasma lipoproteins were more similar, some means of acyl group selection is probably present for either the synthesis or degradation of these glycolipids.     

Nonesterified fatty acids inhibit iron-dependent lipid peroxidation

The effect of various fatty acids on lipid peroxidation of liver microsomes induced by different methods in vitro was studied using oxygen uptake and malonaldehyde (MDA) production. It was observed that fatty acids with a single double bond are effective inhibitors of peroxidation. Stereo and positional isomers of oleic acid were equally effective as oleic acid. There was an absolute requirement for a free carboxyl group, since methyl esters of fatty acids and long-chain saturated and unsaturated hydrocarbons could not inhibit peroxidation. Saturated fatty acids with a chain length of 12-16 carbon atoms showed inhibition, whereas more than 18 carbon atoms reduced the inhibitory capacity. Fatty acids of lower chain length such as capric and caprylic acids did not show inhibition. Fatty acid inhibition was partially reversed by increasing the concentration of iron in the system. Peroxidation induced by methods which were independent of iron was not inhibited by fatty acids. It was observed that intestinal microsomes which were resistant to peroxidation due to the presence of nonesterified fatty acids in their membrane lipids were able to peroxidise by methods which do not require iron. These results suggest that certain fatty acids inhibit peroxidation by chelating available free iron. In addition, they may also be involved in competing with the esterified fatty acids in the membrane lipids which are the substrates for peroxidation.     

Biosynthesis of long chain fatty acids by oligodendroglia isolated from bovine white matter.

Abstract— Radioactively labelled fatty acids were incubated with interfascicular oligodendroglial preparations isolated from 9 month fetal and adult bovine CNS white matter to study their metabolism by these cells. Of the various acids studied, the uptake was greatest for palmitic acid and decreased with decreasing chain length. Laurie acid was converted to the greatest extent to other fatty acids. The incorporation of oleic and linoleic acids in the oligodendroglia from both the fetal and adult brains was higher than that of linolenic acid. Fatty acids underwent chain elongation, desaturation and oxidation. Oleic acid was elongated to nervonic acid. Fatty acids were incorporated into both cerebrosides and phospholipids, with preferential incorporation into ethanolamine phosphoglyceride.     

Essential fatty acid status of neonates born to Inuit mothers: comparison with Caucasian neonates and effect of diet.

Fatty acid compositions were determined of phospholipids isolated from venous cord plasma and from the walls of umbilical arteries and veins, collected from healthy, a terme, Inuit and Caucasian (Dutch) neonates. The Inuit fatty acid profiles were characterized by a lower essential fatty acid (EFA) status, with higher levels of monounsaturated fatty acids, of Mead acid [20:3(n-9)] and its direct elongation product, and with lower amounts of the longer chain (greater than or equal to 20 carbon atoms), highly unsaturated (greater than or equal to 4 double bonds) fatty acids of both the (n-3) and (n-6) families. Levels of linoleic- and dihomo-gamma-linolenic acids were higher in Inuit as compared to Caucasian neonates, which suggests a low activity of the delta-5-desaturase in the Inuit. Within the Inuit group, a higher intake of marine food was associated with a better neonatal (n-3) status. Although the differences between Inuit and Caucasian neonates may be of genetic rather than of dietary origin, the results imply that dietary long-chain (n-3) or (n-6) fatty acids may be particularly important during pregnancy in Inuit mothers. Further studies are indicated with respect to the EFA content of the habitual Inuit diet and levels of delta-5-desaturase activity in the Inuit.     

Structure-activity relationships influencing lipid-induced changes in eIF2α phosphorylation and cell viability in BRIN-BD11 cells

Fatty acids influence the viability of eukaryotic cells differentially such that long chain saturated molecules are poorly tolerated, whereas unsaturated species are less detrimental and can be cytoprotective. The basis for these effects is unclear but studies in yeast imply that they reflect the spatial configuration of the molecules when incorporated into the ER membrane. Using BRIN-BD11 β-cells, we show that a wide range of unsaturated free fatty acids and their methyl-esters (having differing chain length and disposition of the double bonds) elicit cytoprotection and relief of protein kinase RNA-like endoplasmic reticulum kinase-dependent ER stress. Thus, both physical properties and specific signalling events may regulate fatty acid responses in β-cells.     

Fatty acid metabolism in sn-glycerol-3-phosphate acyltransferase (plsB) mutants.

Fatty acid metabolism was examined in Escherichia coli plsB mutants that were conditionally defective in sn-glycerol-3-phosphate acyltransferase activity. The fatty acids synthesized when acyl transfer to glycerol-3-phosphate was inhibited were preferentially transferred to phosphatidylglycerol. A comparison of the ratio of phospholipid species labeled with 32Pi and [3H]acetate in the presence and absence of glycerol-3-phosphate indicated that [3H]acetate incorporation into phosphatidylglycerol was due to fatty acid turnover. A significant contraction of the acetyl coenzyme A pool after glycerol-3-phosphate starvation of the plsB mutant precluded the quantitative assessment of the rate of phosphatidylglycerol fatty acid labeling. Fatty acid chain length in membrane phospholipids increased as the concentration of the glycerol-3-phosphate growth supplement decreased, and after the abrupt cessation of phospholipid biosynthesis abnormally long chain fatty acids were excreted into the growth medium. These data suggest that the acyl moieties of phosphatidylglycerol are metabolically active, and that competition between fatty acid elongation and acyl transfer is an important determinant of the acyl chain length in membrane phospholipids.     

Fatty acid induced hemolysis. Protective action of ceruloplasmin, albumins, thiols and vitamin C

The hemolytic effect of saturated fatty acids increased rapidly, when the number of carbon atoms in the chain exceeded 12. At low fatty acid concentrations (less than 60 microM) the hemolytic effect decreased with increasing number of double bonds in the carbon chain (cis-form fatty acids). A more complex pattern was observed at higher fatty acid concentrations. Trans-unsaturated fatty acids were more hemolytic than cis-analogs. Ceruloplasmin, a serum protein with no fatty acid binding capacity, reduced the hemolytic effect of fatty acids; possibly by interacting with the cell membrane. Reducing compounds (thiols, vitamin C) also protected against fatty acid induced hemolysis.     

The effects of short-chain fatty acids on the neuronal membrane functions ofHelix pomatia. III.22Na efflux from the cells

The effect of short-chain fatty acids on both ouabain-sensitive and ouabain-insensitive fractions of 22Na efflux from the neurons of Helix pomatia was studied. Fatty acids, having fewer than 10 carbon atoms in the hydrocarbon chain, increased the ouabain-sensitive 22Na efflux from the neurons, while fatty acids, having more than 9 carbon atoms, inhibited the 22Na efflux in comparison with that in normal physiological solution. All the fatty acids used had an inhibiting effect on the ouabain-insensitive 22Na efflux from the cells independent on the number of carbon atoms in the hydrocarbon chain. These studies indicate that these short-chain fatty acids can be effective modulators of both ouabain-sensitive and ouabain-insensitive fractions of Na efflux from the cells.     

Effects of various non-esterified fatty acids on the particle size redistribution of high density lipoproteins induced by the human cholesteryl ester transfer protein

The effects of various non-esterified fatty acids on the CETP-mediated particle size redistribution of HDL were studied by incubating HDL3 and CETP for 24 h at 37 degrees C in the absence or in the presence of either saturated, monounsaturated or polyunsaturated non-esterified fatty acids. In the absence of non-esterified fatty acids, CETP induced a redistribution of the initial population of HDL3 (Stokes' radius 4.3 nm) by promoting the appearance of one larger (Stokes' radius 4.8 nm) and two smaller (Stokes' radii 3.9 and 3.7 nm) HDL subpopulations. Whereas the non-esterified fatty acids alone did not modify the HDL3 distribution profile, they were able to alter markedly the capacity of CETP to induce the particle size redistribution of HDL. All the saturated fatty acids with at least 10 carbons were able to increase the formation of the very small sized particles (Stokes' radius 3.7 nm) in a concentration dependent manner, the medium chain fatty acids (12 and 14 carbons) being the best activators. The potential effect of non-esterified fatty acids was also influenced by the presence of double bonds in their monomeric carbon chain. While at low concentrations of non-esterified fatty acids (0.1 mmol/l) the enhancement of the formation of very small HDL particles appeared to be greater with oleic and linoleic acids than with stearic acid, at higher concentrations (0.4 mmol/l), oleic, linoleic and arachidonic acids decreased the formation of the 3.7 nm radius particles. The inhibition of the process at high concentrations of unsaturated fatty acids was linked to the degree of unsaturation of their carbon chain, arachidonic acid being the strongest inhibitor. The present study has demonstrated that non-esterified fatty acids can modulate the particle size redistribution of HDL3 mediated by the cholesteryl ester transfer protein even in the absence of any other lipoprotein classes. The effect of non-esterified fatty acid is dependent on both the length and the degree of unsaturation of their monomeric carbon chain.     

Uptake and utilization of lipids by Paramecium tetraurelia

Uptake rates of a variety of 14C-labeled fatty acids and complex lipids by Paramecium tetraurelia during 48 h of log-phase growth varied. Fatty acid uptake was maximal during lag phase of growth when phagosome (food vacuole) formation was minimal. Food vacuole formation was shown to be suppressed by the presence of exogenous lipids and by starvation. The rates of uptake of lipids were significantly greater than those of small organic compounds such as amino acids, cyclitols, fatty acid precursors and metabolic intermediates. Significant amounts of radioactivity from 14C-labeled fatty acids were metabolized to 14CO2. The uptake rates of different saturated, straight-chain fatty acids of even carbon numbers were different and were not correlated with chain length, results suggesting that the primary mechanism for uptake of these compounds was neither by bulk transport nor simple diffusion and that carrier-mediated processes could possibly be involved.     

Use of long-chain fatty acid-CoA ligase (AMP-forming) from Pseudomonas fragi for the ''in vitro'' synthesis of natural penicillins

Five different naturally occurring penicillins containing as side chains hexanoic, trans-3-hexenoic, heptanoic, octanoic or trans-3-octenoic acids have been synthesized 'in vitro' by coupling long-chain fatty acid-CoA ligase (AMP-forming) (EC 6.2.1.3) from Pseudomonas fragi (LFCoA-L) with acyl-CoA: 6-aminopenicillanic acid acyltransferase (AT) from Penicillium chrysogenum. The quantity of penicillin produced was directly related with the carbon length of the side chain precursor tested, being maximal with octanoic acid. Fatty acids with a lower length than C5 were not recognized as substrates and nor were certain aromatic molecules.