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PubMed1997

Non-enzymatic peroxidation of lipids isolated from rat liver microsomes, mitochondria and nuclei.

Studies were carried out to determine the level of lipoperoxidation ascorbate-Fe2+ dependent on polar and neutral lipids isolated from rat liver microsomes, mitochondria and nuclei subjected to an incubation at 37 degrees C for 140 min. Three experimental approaches were used: recording of low-level chemiluminescence, determination of fatty acid composition and measurement of radioactivity of lipidic species of each kind of membrane during the peroxidation process. Membrane light emission decreased in the order microsomes > mitochondria > nuclei using 1.5 mg of protein of each preparation. The peroxidizability index was profoundly affected in polar lipids whereas that of neutral lipids was not. The most sensitive fatty acids for peroxidation were arachidonic acid, C20:4 n6 and docosahexanoic acid, C22:6 n3. Experiments carried out with membranes labelled in vivo indicate a selective release of radioactivity from polar rather than from neutral lipids during the peroxidation process.

Animals↗
PubMed1981

On the role of long-chain aldehydes in mammalian plasmalogen biosynthesis.

[1-3H, 1-14C]Palmitaldehyde (3H:14C = 15) was injected intracerebrally to 18-day-old rats and incorporation of radioactivity into brain lipids was followed over a 24-h period. The substrate was metabolized primarily by oxidation to palmitic acid with loss of tritium and, to a lesser extent, by reduction to hexadecanol. The alkyl moieties of the ethanolamine phospholipids showed considerably lower 3H:14C ratios than the substrate, indicating a substantial participation in either lipid synthesis by tritium-free alcohols derived from 14C-labeled fatty acids. Virtually no 3H radioactivity was found in alkenyl moieties, indicating stereospecificity of both reduction of aldehyde and dehydrogenation of alkyl to alkenyl glycerolipid. The data are consistent with the general concept that plasmalogen biosynthesis proceeds exclusively through fatty alcohols and alkyl glycerolipids and that fatty aldehydes cannot be utilized directly.

Aldehydes↗
PubMed2000

The fatty acid composition of chylomicrons influences the rate of their lipolysis in vivo.

BACKGROUND AND AIMS: Previous work in our laboratory has shown that chylomicron triacylglycerol is lipolysed in vitro by lipoprotein lipase more rapidly when the particles are enriched with n-6 polyunsaturated as compared to saturated, monounsaturated or n-3 polyunsaturated fatty acids. It is possible, however, that this does not reflect the situation in vivo, where the active enzyme is bound to the vascular endothelium. The aim of the present study is to investigate the effect of the fatty acid composition of chylomicrons on their lipolysis in the rat in vivo. METHODS AND RESULTS: [3H]Oleate-labelled chylomicrons derived from palm, olive, corn or fish oil (enriched in saturated, monounsaturated, n-6 polyunsaturated and n-3 polyunsaturated fatty acids respectively) containing > 90% of the label in triacylglycerol were injected intravenously into functionally hepatectomised rats and blood samples were taken at time intervals up to 40 min. The radioactivity in serum triacylglycerol decreased significantly more rapidly when corn oil as compared to palm, olive or fish oil chylomicrons were used. Conversely, the radioactivity in serum free fatty acid derived from corn oil chylomicrons showed a faster increase than that derived from the other three types of particles. CONCLUSIONS: These results indicate that chylomicrons enriched with n-6 polyunsaturated fatty acids are converted to chylomicron remnants in vivo more rapidly than those enriched with saturated, monounsaturated or n-3 polyunsaturated fatty acids. This provides a partial explanation for the differential rate of removal from the blood of cholesterol carried in chylomicrons of different fatty acid composition demonstrated in previous work from this laboratory.

Animals↗
PubMed1976

Environmental effects on Tetrahymena membranes. Temperature-induced changes in membrane fatty acid unsaturation are indepedent of the molecular oxygen concentration.

The study was designed to show whether the increase in unsaturated fatty acids in Tetrahymena pyriformis membrane phospholipids with decreasing growth temperature is due to the sharp rise in the concentration of dissolved O2 found at lower temperatures. Increasing cell density in cultures growing at a constant temperature was found to have a more drastic effect upon the O2 level than shifting a culture from one temperature extreme to the other. However, the pattern of phospholipid fatty acid unsaturation did not vary over a 30-fold gradual decrease in O2 concentration measured in cultures during logarithmic growth at 39.5 degrees C, and unsaturation in 15 degrees C cells sampled over a 5-fold decrease in O2 concentration was also unchanged. Cells grown at 39.5 degrees C under a constant relatively high O2 concentration (5--6 mg O2/l) or low O2 concentration (0.3 mg O2/l) had nearly identical distributions of membrane fatty acids. Only under almost completely anaerobic conditions was it possible to measure via radioactive labeling experiments and inhibition of fatty acid desaturation. Thus the increased membrane fatty acid unsaturation induced by decreasing growth temperature is caused by some factor other than the rising levels of dissolved O2.

Acclimatization↗
PubMed1977

Utilization of long-chain free fatty acids and glucose by human leukemic blast cells.

We have studied the utilization of free fatty acid and glucose by human leukemic blast cells. Palmitate was both incorporated into complex cellular lipids, primarily phospholipids and triglycerides, and oxidized to CO2. The predominant phospholipid synthesized was phosphatidylcholine. Only a small proportion of the incoming fatty acid was modified structurally before incorporation into lipid esters. After incubation with [1-14 C]palmitate, 91% of the radioactivity recovered in cell lipids remained in fatty acids containing 16 carbon atoms. Studies with labeled glucose revealed little de novo synthesis of fatty acid, and the majority of the radioactivity from glucose was located in the water-soluble fraction after saponification of the esters. We conclude that the free fatty acids contained in the extracellular fluid provide much of the fatty acid for required cellular lipid synthesis in human leukemic blast cells. Since there is little elongation of incoming palmitate before incorporation into cellular lipids, it may be possible to alter the fatty acid composition of membrane phospholipids by changing the proportion of the various free fatty acids available to the leukemic cells.

Carbon Dioxide↗
PubMedDate not supplied

Covalent modification of hepatic microsomal lipids of rats by carbon tetrachloride.

The present study was undertaken to isolate and identify various lipids bound to 14C label during hepatic microsomal metabolism of 14CCl4 in vitro under anaerobic conditions and in vivo in rats. The two major radioactive fractions identified by thin-layer chromatography each for neutral lipids and phospholipids from in vitro and in vivo experiments corresponded to fatty acids and triglycerides and to phosphatidylcholine (PC) and phosphatidylethanolamine (PE), respectively. Approximately 89% of the radioactivity associated with phospholipids was found in PC and PE fractions. Hydrolysis of PC and PE with phospholipase A2 (EC 3.1.1.4) released about 50% of the total radioactivity as lipid moieties corresponding to fatty acids. The radioactive neutral lipids and the lipid moieties hydrolyzed from PC and PE were methylated with boron trifluoride in methanol. These methylated lipids were separated by reversed-phase high-performance liquid chromatography (HPLC), and the elution profiles of 14C label found for the lipids obtained from in vitro experiments were similar to those from in vivo. The major radioactive fractions eluted immediately after methyl oleate were identified as trichloromethyloctadecenoic and trichloromethyleicosatrienoic acid methyl esters by chemical ionization mass spectrometry. The mass spectral analysis of these fractions also indicated the formation of dichlorocarbene adduct of oleic acid. However, similar mass spectrometric detection of trichloromethylated lipids was not evident in neutral lipids and phospholipids isolated from in vivo studies. The 14C-labeled lipids eluted as a nonpolar fraction exhibited a high molecular weight containing more than three chlorines. Dimerization and cross-linking of trichloromethylated lipids based on HPLC and mass spectral analysis are also discussed in this paper.

Animals↗
PubMed1985

Measures of de novo synthesis of milk components from propionate in lactating goats.

Possible direct contributions of propionate to de novo synthesis of milk components by the mammary gland of lactating goats fed a concentrate-roughage diet have been studied in vivo by primed constant infusion of [1-carbon-14]propionate into the right mammary artery. Specific radioactivities of milk galactose, fatty acids, and protein were higher in the infused than in the uninfused half of the mammary gland, suggesting de novo synthesis of these compounds in the udder. Specific radioactivities of milk glucose in both udder halves were identical, ruling out any possibility of mammary gland-derived glucose from propionate of blood plasma under the experimental conditions. Of milk galactose, .8% was derived from propionate of blood plasma, and of milk glucose, 98% was derived from glucose of blood plasma. After intraruminal infusion of unlabeled propionic acid at 11 g/h, concentration of propionate in blood plasma was doubled, its contribution to milk galactose was increased to 1.5%, and proportions of milk odd-numbered fatty acids were increased. Propionate was incorporated largely into milk odd-numbered fatty acids (9:0, 11:0, 13:0, 15:0, 17:0). We conclude that small amounts of propionate can be incorporated into principal components of milk in the mammary gland of lactating goats.

Animals↗
PubMed1991

Phospholipid molecular species from isolated bovine rod outer segments incorporate exogenous fatty acids at different rates.

The incorporation of radiolabeled palmitic (16:0), oleic (18:1), and docosahexaenoic (22:6) acids into different molecular species of membrane phospholipids was investigated in isolated bovine rod outer segments (ROS). Phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) were isolated, and their diacylglyceroacetate and diacylglycerobenzoate derivatives were prepared, separated by HPLC, quantified, and assayed for radioactivity. Maximal incorporation of fatty acids occurred within 15-30 min. The rate of incorporation of the fatty acids into PC was three to six times higher than it was into PS or PE. The rate of incorporation of 22:6 into the molecular species, 22:6-22:6, of PC was ten to 15 times higher than into that of PE or PS, and it was three to four times higher than the incorporation rates of 22:6 into the other 22:6-containing molecular species. Similarly, incorporation of 18:1 into 18:1-22:6 was ten to 30 times more rapid in PC than in PE and PS, but in both PE and PS, 18:1 was incorporated into 18:1-22:6 at a rate of 20 to 25 times higher than the incorporation into the other molecular species analysed. For PC, incorporation of 16:0 was most rapid into 16:0-16:0, but for PE and PS it was most rapid into 16:0-20:4; for all cases, incorporation of 16:0 into these molecular species was four to six times more rapid than into the other 16:0-containing molecular species. These results are further evidence for the presence within a membranous organelle, the ROS, of an active acylation-deacylation system that is selective with regard to phospholipid, molecular species of phospholipid, and fatty acid.

Animals↗
PubMed1975

Effect of phosphatidylcholine on fatty acid and cholesterol absorption from mixed micellar solutions.

Using the experimental model of the everted sac prepared from rat jejuna, kinetic studies on [14C]oleic acid uptake from bile salt micelles were conducted in the presence and absence of phosphatidylcholine. The concentration of oleic acid was varied between 0.625 and 5 mM. At every level of fatty acid concentration studied the addition of 2 mM phosphatidylcholine produced a significant inhibition of fatty acid uptake. It was further noted that the intact phospholipid molecule was required for this effect as lysophosphatidylcholine produced little, if any, inhibition of [14C]oleic acid uptake. The effect of varying the concentration of phosphatidylcholine on fatty acid uptake was also studied. The degree of inhibition was noted to be correlated grossly with media concentrations of this phospholipid although the decrease of fatty acid uptake was not strictly proportional to concentration of this material in the medium. Studies were also performed analyzing in vitro absorption of [14C]oleic acid and [3H]cholesterol simultaneously from mixed micelles composed of sodium taurocholate, oleic acid, monoolein and cholesterol. Control medium contained no phospholipid while experimental medium contained either diester or diether phosphatidylcholine, 2 mM. Both types of phosphatidylcholine caused significant inhibition of fatty acid and cholesterol uptake. In vivo absorption studies were also performed using the isolated jejunal segment technique. A mixed micellar solution containing [3H]cholesterol and [14C]oleic acid was used as the test dose. Phospholipid in the test dose for controls was supplied as lysophosphatidylcholine and for experimentals it was in the form of diether phosphatidylcholine. Significantly less radioactively labeled cholesterol and fatty acid was absorbed by experimentals as compared to controls over a 10-min period. It is concluded that the intact molecule of phosphatidylcholine inhibits intestinal uptake of cholesterol and fatty acid from mixed micellar solutions under both in vitro and in vivo conditions.

Animals↗
PubMed1987

Lipid metabolism in various regions of squid giant nerve fiber.

The purpose of this investigation was to compare the incorporation of radioactivity from various precursors into lipids of different regions of squid giant nerve fiber systems including axoplasm, axon sheath, giant fiber lobes which contain stellate ganglion cell bodies, and the remaining ganglion including giant synapses. To identify the labeled lipids, stellate ganglia including giant fiber lobes and the remaining tissue were first incubated separately with [14C]glucose, [32P]phosphate, [14C]serine, [14C]acetate and [3H]myristate. The radioactivity from glucose, after conversion to glycerol and fatty acids, was incorporated into most lipids, including triacylglycerol, free fatty acids, cardiolipin, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, phosphatidylinositol, phosphatidylserine, sphingomyelin and ceramide 2-aminoethylphosphanate [corrected]. The radioactivity from serine was largely incorporated into phosphatidylserine and, to a lesser extent, into other phospholipids, mainly as the base component. The sphingoid bases of ceramide and sphingomyelin were also significantly labeled. Saturated and monounsaturated and, to a lesser extent, polyunsaturated fatty acids of these lipids were synthesized from acetate, glucose and myristate. Among the major lipids, cholesterol was not labeled by any of the radioactive compounds used. Ganglion residues incorporated the most radioactivity in total lipids from either [14C]glucose or [14C]serine, followed by giant fiber lobes and then sheath. Axoplasm incorporated the least. Among various lipids, phosphatidylethanolamine with shorter saturated fatty acids and phosphatidylglycerol contained the most radioactivity from glucose in all regions. Axoplasm was characterized by a higher proportion of glucose radioactivity in ceramide, sphingomyelin and phosphatidylglycerol. Axoplasm and sheath contained a higher proportion of serine radioactivity than did the other two regions in ceramide. Essentially no radioactivity from [14C]galactose was incorporated in any region.

Acetates↗
PubMed1985

Metabolic products of arachidonic acid in rats.

The pattern of eicosanoid metabolites appearing in urine and feces following oral administration of radioactive arachidonic acid was investigated using rats deficient in essential fatty acids. About 70-80% of the radioactivity in the urine during the first day after feeding was adsorbed to XAD-2 resin and represented eicosanoid metabolites, whereas the rest of the radioactivity was mainly 3H2O. The eicosanoid metabolites were fractionated into different polarity classes using reverse phase Sep-Pak C18 cartridges. Gas chromatographic analysis of the urinary metabolites following their derivatization into methyl ester-methoxime-tert-butyl-dimethylsilyl ethers revealed that nearly one-half of the metabolites had ECL values less than 22 and represented metabolites more oxidized than commonly described. Only 30% of the metabolites had ECL values between 26 to 32, corresponding to the values for the metabolites that originate from exogenously infused prostaglandins. A large portion of the eicosanoid metabolites was also excreted with the feces. The isotopic patterns from the reverse phase chromatography indicated that many of the fecal metabolites may be similar to those in urine although some metabolites in feces were not present in urine. Based on the specific radioactivity of the administered arachidonic acid, it appeared that at least 6 to 8 mg of eicosanoid metabolites were excreted through urine and feces within 24 hrs following an oral bolus of 60 mg arachidonic acid. The rapid increase and subsequent decrease in eicosanoid metabolite excretion after oral administration of arachidonate indicates that the dietary intake of polyunsaturated fatty acids may have a more rapid effect upon the endogenous production of eicosanoids than is generally recognized.

Administration, Oral↗
PubMed1985

The biosynthesis and turnover of lipid during the differentiation of Dictyostelium discoideum.

Despite the fact that there are only relatively slight changes in lipid composition during the differentiation of Dictyostelium discoideum, the rates of lipid synthesis were found to vary considerably. Polar lipid synthesis declined markedly during aggregation and pseudoplasmodium formation and then increased during the terminal stages of differentiation. Several neutral lipid classes (sterol, the diacylglycerols and triacylglycerol) exhibited similar changes in synthetic rates, although the effects were somewhat less pronounced. In contrast, the rates of synthesis of steryl ester and free fatty acid increased slightly throughout the differentiation period, so that, by the end of the later stages of fruiting body culmination, the rates were essentially doubled. Finally, the synthesis of an unknown component increases at least 10-fold during differentiation. Of the newly synthesized lipid, only triacylglycerol and polar lipid exhibited marked turnover. Accumulation of radioactivity in steryl ester and free fatty acid continued after the removal of radioactive acetate, presumably due to the incorporation of fatty acid produced by polar lipid degradation.

Acetates↗
PubMed1990

AT32P-dependent estimation of nanomoles of fatty acids: its use in the assay of phospholipase A2 activity.

A procedure for the assay of free fatty acids which has been adapted for the assay of phospholipase A2 is described. This consists of the conversion of long chain fatty acids to fatty acyl-CoA using the Mg2(+)-dependent fatty acyl-CoA synthetase, [alpha-32P]ATP and coenzyme A. In order to ensure the complete conversion of the acid to its CoA ester pyrophosphatase is also added to the incubation mixture. AM32P formed in stoichiometric amounts is separated from the remaining AT32P by polyethyleneimine-cellulose thin-layer chromatography and the fatty acid content is calculated from the specific radioactivity of AT32P. As little as 1 to 3 nmol of fatty acids hydrolyzed from any phospholipid using nanogram amounts of phospholipase A2 can be estimated with reliability. The real advantage of the method is that it combines the sensitivity of a radiochemical procedure without having to use radiolabeled substrates for the assay of phospholipases.

Adenosine Triphosphate↗
PubMed1978

Comparison of C18-, C20- and C22-unsaturated fatty acids in reducing fatty acid synthesis in isolated rat hepatocytes.

C18-, C20- and C22-unsaturated acids were tested for inhibition of fatty acid synthesis in hepatocytes isolated from essential fatty acid-deficient rats. Fatty acid synthesis was measured by incorporation of radioactivity from [1-14C-A1-acetate or 3H2O into fatty acids. C20-polyunsaturated fatty acids included arachidonic acid (20 : 4 (n-6)) and 4 other fatty acids formed from linoleic acid (18 : 2 (n-6)) or linolenic acid (18 : 3 (n-3)). These were (11,14)-icosadienoic acid (20 : 2 (n-6)), (8,11,14)-icosatrienoic acid (20 : 3 (n-6)), (11,14,17)-icosatrienoic acid (20 : 3 (n-3)) and (5,8,11,14,17)-icosapentaenoic acid (20 : 5 (n-3). All of these have essential fatty acid activity. The fatty acid (5,8,11)-icosatrienoic acid (20 : 3 (n-9)) was also tested. This fatty acid is formed from oleic acid (18 : 1 (n-9)) and is not an essential fatty acid or a prostaglandin precursor. C20-unsaturated fatty acids and (22 : 6 (n-3)) were as effective as stearic acid in inhibiting fatty acid synthesis and were more inhibitory than their precursor C18-unsaturated fatty acids. These results are evidence that C20-unsaturated fatty acids of the linoleic and linolenic acid series can act in short-term inhibition as well as in adaptive inhibition of fatty acid synthesis (Bloch, K. and Vance, D. (1977) Annu. Rev. Biochem. 46, 263--298). The effectiveness of (5,8,11)-icosatrienoic acid indicates that short-term inhibition by C20-unsaturated fatty acids is not limited to those fatty acids which have essential fatty acid activity.

Animals↗
PubMed1986

Properties of acid phospholipases in lysosome and extracellular medium of Tetrahymena pyriformis.

Phospholipase activity in the lysosomes of the protozoan Tetrahymena pyriformis strain NT-1 was studied using phospholipids radioactively labeled in the fatty acid moieties. Lysosomal homogenates showed high phospholipase activity with an acidic pH optimum. Unlike the phospholipases in rat liver lysosomes, almost all activity was recovered from the membranous fraction of the lysosomes. The activity was partially solubilized by treatment of the membranes with a detergent or trypsin. Using specifically labeled phospholipids revealed that phospholipase. A1 and C are predominant in Tetrahymena lysosomes, no appreciable phospholipase A2 or lysophospholipase activity was detected in the fraction. There are two catabolic pathways of the hydrolysis of phospholipid: Hydrolysis is initiated by deacylation at the 1-position by phospholipase A1 and the 2-acyllysophospholipid thus formed is successively attacked by (lyso)phospholipase C; hydrolysis is initiated by cleavage of phosphodiester by phospholipase C and the diacylglycerol thus formed is attacked by lipase. Both pathways give the same end products, free fatty acid and 2-monoacylglycerol. The former pathway might be predominant in Tetrahymena lysosomes under physiological conditions since the pathway is independent of detergent. Phospholipases A1 and C activities were partially released into the medium. At least two different phospholipases C are present in the medium as judged by chromatographic behavior and their substrate specificities.

Animals↗
PubMed1992

An in vitro model for essential fatty acid deficiency: HepG2 cells permanently maintained in lipid-free medium.

A stable essential fatty acid-deficient cell type, known as HepG2-EFD, was derived from the lipoprotein-producing human hepatoma cell line HepG2. These cells are particularly useful for quantitative studies involving essential fatty acids (n-6 and n-3 fatty acids) in secreted lipoproteins. Radiolabeled essential fatty acids can be delivered to these cells without altering the specific activity of the fatty acids, since the deficient cells contain no endogenous essential fatty acids. Using these cells, radioactivity data (dpm) from metabolic studies can be converted directly to mass, and masses as low as a few pmoles can be accurately measured. HepG2-EFD cell cultures were established by growing HepG2 cells in medium containing delipidated serum. After 10 days of growth in delipidated medium, HepG2 cells were completely depleted of all essential fatty acids. Compensatory increases in nonessential fatty acids (n-9 and n-7 fatty acids) including 20:3n-9 (the Mead acid), which is the hallmark fatty acid of essential fatty acid deficiency, were also observed in HepG2-EFD cells. Despite the lack of exogenous fatty acids in the medium and the lack of essential fatty acids in the cells, export of very low density lipoprotein (VLDL)-associated apolipoprotein B by HepG2-EFD was the same as observed for parent HepG2 cells. However, the activity of beta-oxidation of fatty acids in HepG2-EFD cells was much lower than in the parent cell line.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoproteins B↗
PubMed1986

Effect of catecholamines on the metabolic fate of nonesterified fatty acids in isolated hepatocytes from newborn rats.

Isolated hepatocytes from newborn rats are able to produce ketone bodies from added medium-chain and long-chain fatty acids. Carnitine enhances the rate of ketone body synthesis from palmitate as well as from caprinoate. The 3-OHB/AcAc ratios indicate a highly reduced state of the mitochondrial redox carriers in the presence of both fatty acids and carnitine. Ketogenesis from palmitate accounts for about 90% of the total beta-oxidation. At recovery of 95% of the radioactivity two thirds of totally fatty acid uptake are channeled into esterification, whereas the remainder is oxidized. alpha- and beta-agonists stimulate glycogen degradation and glucose release and reduce net lactate production in hepatocytes from newborn rats. The (1-14C)-palmitate uptake is not altered by alpha- and beta-agonists. Phenylephrine significantly enhances 14CO2 production from (1-14C)-palmitate. Neither of the agonists affects the rate of esterification or of ketone body production with palmitate as substrate. Isoproterenol, however, stimulates ketogenesis from caprinoate even in the presence of optimal carnitine concentrations.

Animals↗