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PubMed1997

No evidence for direct incorporation of esterified palmitic acid from plasma into brain lipids of awake adult rat.

Awake adult rats were given a solution of [9,10-3H]palmitate ([3H]PAM) by gavage. The appearance of radiolabel in plasma lipid fractions was monitored by thin-layer chromatography at fixed intervals thereafter. At 2 h, the rats were killed by microwave irradiation and radioactivity in whole brain and individual brain phospholipids was determined. In plasma, esterified [3H]PAM was mainly associated with triglyceride, phospholipid, and cholesterol ester. Radioactivity appeared to a larger extent in triglyceride than in unesterified fatty acid, suggesting that unesterified [3H]PAM in plasma was largely due to release from esterified [3H]PAM by lipoprotein lipase hydrolysis. Brain radioactivity could be accounted for entirely by incorporation of unesterified plasma [3H]PAM. Esterified [3H]PAM in chylomicrons or lipoproteins was calculated to make no measurable contribution using a published value for the incorporation coefficient of [3H]PAM into brain in the evaluation. These results suggest that ingested palmitic acid (PAM) in adult rats enters blood as esterified triglyceride within chylomicrons and lipoproteins and, in part, eventually is converted to circulating unesterified PAM. It is the circulating unesterified PAM that is incorporated into brain from blood, whereas esterified PAM within plasma chlomicrons and lipoproteins makes no measurable direct contribution.

Administration, Oral↗

PubMed1965

Folic acid involvement in cyclopropane fatty acid synthesis in lactobacilli.

Henderson, Thomas O. (North Carolina State University, Raleigh), John J. McNeill, and S. B. Tove. Folic acid involvement in cyclopropane fatty acid synthesis in lactobacilli. J. Bacteriol. 90:1283-1287. 1965.-Evidence for the involvement of folic acid in the synthesis of lactobacillic acid (11,12-methyleneoctadecanoic acid) was obtained with Lactobacillus plantarum and L. casei. L. plantarum, in the presence of aminopterin, incorporated 25% less radioactivity from methionine-methyl-C(14) into long-chain fatty acids than did control cultures, whereas the incorporation of acetate-1-C(14), representing overall fatty acid synthesis, was the same in both conditions. Control cultures of L. plantarum contained 3 to 4.5 times more lactobacillic acid than did aminopterin-grown cultures. Similarly, L. casei, in the presence of folic acid, synthesized six times more lactobacillic acid than did folic-deficient cultures. The results of this study indicate that coenzymes of the folic acid group are involved in the synthesis of lactobacillic acid in these organisms.

Acetates↗

PubMed1992

De novo synthesis and desaturation of fatty acids at the mitochondrial acyl-carrier protein, a subunit of NADH:ubiquinone oxidoreductase in Neurospora crassa.

We have cultivated the cel mutant of Neurospora crassa defective in cytosolic fatty acid synthesis with [2-14C]malonate and found radioactivity covalently attached to the mitochondrial acyl-carrier protein (ACP), a subunit of the respiratory chain NADH:ubiquinone oxidoreductase. We purified the ACP by reverse-phase HPLC: the bound acyl groups were trans-esterified to methylesters and analyzed by gas chromatography. The saturated C6 to C18 fatty acids and oleic acid were detected. De novo synthesis and desaturation of fatty acids at the ACP subunit of NADH:ubiquinone oxidoreductase and use of the products of this mitochondrial synthetic pathway for cardiolipin synthesis is discussed.

Acyl Carrier Protein↗

PubMed1977

Tracer kinetic studies on in vivo fatty acid metabolism in white adipose tissue of well-fed and starving newborn rabbits during acute or prolonged exposure to cold.

Pool size (M), and specific radioactivities (SA) of lipids of white adipose tissue (WAT), as well as the flow rates (ms) of free fatty acids (FFA) from plasma into WAT were studied by injecting 14C-1-palmitate (20.10(6) cpm/100 g body weight) into 7-day-old rabbits reared in a thermoneutral (Group I) or a cold environment (Group II) or subjected to starvation at an ambient temperature (Ta) of 35 degrees C (Group III) or at Ta 20 degrees C (Group IV). Experiments were carried out at Ta 20 degrees C in all four groups of rabbits. The pool size of esterified and non-esterified fatty acids of WAT was reduced in both the well-fed animals raised in the cold and in the starving ones. The SA of tissue FFA and phospholipid fatty acid (PL-FA) was highest in Group III and Group IV indicating an increased FFA metabolism of WAT in animals subjected to starvation prior to acute exposure to cold. The flow rate (ms) of FFA between plasma and WAT increased twofold in Group IV but remained about one fifth that of the ms between plasma and brown adipose tissue (BAT) indicating that the contribution of WAT to cold-induced calorigenesis of the whole animal must be regarded as of secondary importance.

Adipose Tissue↗

PubMed1986

Stimulation of phosphatidylcholine synthesis by fatty acids in fetal rabbit type II pneumocytes.

After 24 h exposure to 0.1 mM oleate or 0.1 mM palmitate there was a 2- and 1.7-fold increase, respectively, in the incorporation of choline into the lipids of type II pneumocytes. Palmitate increased the labeling of disaturated phosphatidylcholine (PC) from 23.0% of total labeled PC in control cultures to 56.6% and oleate decreased labeling of disaturated PC to 9.4%. The percentage of total cellular radioactivity found in the lipid fraction was also markedly higher in the fatty acid-treated cells (83.3% for oleate and 78.7% for palmitate) than in control cultures (64.0%). Radioactivity in water-soluble choline metabolites was correspondingly lower, with phosphocholine representing more than 95% of the label in both control and experimental cultures. After a 3 h pulse-chase period, oleate and palmitate significantly increased the percentage of total cellular radioactivity in PC and decreased the percentage in phosphocholine. Similar results were obtained by adding melittin (1-2 micrograms/ml) or phospholipase C (0.05 U/ml) to the culture medium. The stimulation of PC synthesis by fatty acids was demonstrated as early as 1 h after exposure to oleate or palmitate and at all concentrations from 0.025 to 0.25 mM. Cytidylyltransferase activity in total cell homogenates was also enhanced by long-term exposure to fatty acids and short-term addition of fatty acids or phospholipase C and melittin to the culture medium. A similar increase in cytidylyltransferase activity was found in the 100 000 X g particulate fraction of type II cells exposed to fatty acids, whereas no differences were found between the cytosolic fractions of control and treated cells. These results support the concept that an increase in intracellular level of fatty acids either from an exogenous source or following the activation of endogenous phospholipases regulates PC synthesis in fetal type II pneumocytes.

Animals↗

PubMed1985

Lipid biosynthesis in synchronized cultures of the photosynthetic bacterium Rhodopseudomonas sphaeroides.

Lipid biosynthesis has been studied in photosynthetic cultures of Rhodopseudomonas sphaeroides that had been synchronized by stationary-phase cycling or by a centrifugation selection procedure. Synchrony index values in the range 0.70-0.80 were obtained for the first cell cycle with both synchronization methods. The major membrane lipids phosphatidylethanolamine and phosphatidylglycerol were accumulated discontinuously during the cell cycle, their mass doubling immediately before cell division. This accumulation of lipid corresponded to peaks in incorporation of radioactivity from either [1-14C]acetate or [2-3H]glycerol into individual acyl lipids as measured in individual portions of bacteria. For phosphatidylglycerol an additional peak of incorporation of radioactivity from [2-3H]glycerol was found midway through the cell cycle. In spite of their rather similar endogenous fatty acid compositions, the individual phosphoacylglycerols showed distinctive patterns of incorporation of radioactivity from [1-14C]acetate into their acyl moieties. The discontinuous synthesis of acyl lipids observed in cultures of Rhodopseudomonas sphaeroides synchronized by either stationary-phase cycling or centrifugation selection procedures contrasted with the accumulation of chlorophyll-protein complexes whose amounts were found to increase throughout the cell cycle. The implications of these findings for the control of lipid synthesis in bacterial photosynthetic membranes are discussed.

Acetates↗

PubMed1997

Mobilization of arachidonate and docosahexaenoate by stimulation of the 5-HT2A receptor in rat C6 glioma cells.

In this study, we demonstrate that astroglial 5-HT2A receptors are linked to the mobilization of polyunsaturated fatty acids (PUFA). Stimulation of C6 glioma cells, prelabeled with [3H]arachidonate (AA, 20:4n6) and [14C]docosahexaenoate (DHA, 22:6n3), with serotonin and the 5-HT(2A/2C) receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) resulted in the mobilization of both [3H] and [14C] into the supernatant of the cell monolayers. The increased radioactivity in the supernatant was mainly associated with free fatty acids. Experiments using inhibitors of phosphoinositide-specific phospholipase C and PLA2, inhibited the DOI-stimulated mobilization of AA and DHA, suggesting the involvement of both phospholipases. Ketanserin (1 microM), a 5-HT(2A/2C) receptor antagonist, and MDL 100,907 (R(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-pi peridine-methanol) (1 microM), a highly selective antagonist for 5-HT2A receptors, significantly decreased the DOI-stimulated release of AA and DHA. These results indicate that the 5-HT2A receptor is coupled to the mobilization of PUFA. The release of AA and DHA in response to serotonin may represent a mechanism through which astroglia provide these polyunsaturated fatty acids to neurons.

Amphetamines↗

PubMed1988

The time course of lipid biosynthesis in pig epidermis.

In order to examine the time course of lipid metabolism in the epidermis, pairs of sites on each of two pigs were given seven intradermal injections of 10 microCi of [1-14C]-acetate at 1, 3, 6, 12, 24, 36, and 48 h before the animals were killed. A second time course was obtained with two other pigs at 1 h and 3.5, 7, 10.5, 14, 17.5, and 21 d after labeling. The epidermis over each injection site was recovered, and the lipids were extracted and analyzed by thin-layer chromatography and by autoradiography. Virtually all of the radioactivity in aliphatic chains was found first in phospholipids and was then transferred to glucosylceramides, and then into ceramides, between 1 and 7 d after labeling. Labeling of free fatty acids showed a similar time course. Most of the radioactivity acquired by acylglucosylceramide was transferred to hydroxyceramide, bound to the corneocyte envelope, between 2 and 10 d after labeling. The hydroxyacid and sphingosine moieties of the hydroxy-ceramide had equal specific activity. The results indicate that the aliphatic lipids of the stratum corneum are synthesized de novo in the epidermis via phospholipids. Cholesterol, however, was synthesized directly from acetate within hours of labeling, and its esters acquired label 3 to 7 d later.

Acetates↗

PubMed2004

Biosynthesis of oleic, arachidonic and docosahexaenoic acids from their C18 precursors in the yolk sac membrane of the avian embryo.

The yolk sac membrane (YSM) of the chicken embryo is known to express delta-9 and delta-6 desaturase activities, suggesting that biosynthesis of the unsaturated fatty acids 18:1n-9, 20:4n-6 and 22:6n-3 might occur during the transfer of yolk lipids across the YSM. If so, this biosynthesis could help to satisfy the demands of the embryonic tissues for these unsaturates. To assess the ability of the YSM to perform these conversions, pieces of the tissue were incubated in vitro with the precursor fatty acids, 14C-18:0, 14C-18:2n-6 or 14C-18:3n-3, and the recovery of radioactivity in the respective products, 18:1n-9, 20:4n-6 and 22:6n-3, was determined. After 4 h of continuous incubation, radioactivity from these precursors was incorporated primarily into triacylglycerol and phospholipid of the tissue pieces. Only small proportions (0.3-4.7%) of this incorporated radioactivity were, however, recovered as 18:1n-9, 20:4n-6 or 22:6n-3. The majority of the incorporated label was retained in the form of the precursor fatty acids. After a 1-h pulse incubation with the 14C precursors, followed by a 3-h chase incubation in the absence of exogenous label, the conversion of incorporated radioactivity to the end product unsaturates was again relatively low (0.5-8.1%). Thus, although conversions of the precursors to the end product fatty acids were detectable in this system, the biosynthesis of these unsaturates is apparently a quantitatively minor pathway in the YSM. Nevertheless, since the amount of 18:2n-6 in the yolk lipids far exceeds that of 20:4n-6, the conversion of even a small proportion of the former to the latter fatty acid could significantly increase the supply of 20:4n-6 to the embryonic tissues.

Animals↗

PubMed1984

Studies on the assay, activity and sedimentation behaviour of acetyl-CoA carboxylase from isolated hepatocytes incubated with insulin or glucagon.

The activity of acetyl-CoA carboxylase, measured in various ways, was studied in 15000g extracts of rat liver hepatocytes and compared with the rate of fatty acid synthesis in intact hepatocytes incubated with insulin or glucagon. Hepatocyte extracts were prepared by disruption of cells with a Dounce homogenizer or by solubilization with 1.5% (v/v) Triton X-100. Sucrose-density-gradient centrifugation demonstrated that the sedimentation coefficient of acetyl-CoA carboxylase from cell extracts was 30-35S, regardless of the conditions of incubation or disruption of hepatocytes. Solubilization of cells with 1.5% Triton X-100 yielded twice as much enzyme activity (measured by [14C]bicarbonate fixation) in the sucrose-gradient fractions as did cell disruption by the Dounce homogenizer. Analysis by high-performance liquid chromatography of acetyl-CoA carboxylase reaction mixtures showed that [14C]malonyl-CoA accounted for 10-60% of the total acid-stable radioactivity, depending on the method for disrupting hepatocytes and on the preincubation of the 15000g extract, with or without citrate, before assay. Under conditions in which incubation of cells with insulin or glucagon caused an activation or inhibition, respectively, of acetyl-CoA carboxylase, only 25% of the acid-stable radioactivity was [14C]malonyl-CoA and enzyme activity was only 13% (control), 16% (insulin), and 57% (glucagon) of the rate of fatty acid synthesis. Under conditions when up to 60% of the acid-stable radioactivity was [14C]malonyl-CoA and acetyl-CoA carboxylase activity was comparable with the rate of fatty acid synthesis, there was no effect of insulin or glucagon on enzyme activity.

Acetyl-CoA Carboxylase↗

PubMed1987

A new experimental model for studies of drug actions on myocardial metabolism. Application to a study of the influence of POCA.

In order to study myocardial metabolism by external detection, quantitative information on the metabolism of a gamma-emitting iodinated fatty acid (IHA) was obtained from time-activity curves of radioactivity in different compartments. A 4-compartment mathematical model was then developed; compartments 0, 1, 2, and 3 correspond respectively to vascular IHA, intracellular IHA, esterified forms, and iodide resulting from mitochondrial oxidation of IHA. We applied this model to a study of the influence of an inhibitor of fatty acid oxidation, POCA (2-[5(4 chlorophenyl) pentyl]-oxirane-2-carboxylate). Isolated rat hearts were perfused for 20 min with Krebs liquid containing increasing concentrations of POCA. IHA was then injected as a bolus at the entrance of the coronary network. The level of cardiac radioactivity was recorded for 30 min and the division into the 4 compartments was simulated at different concentrations of POCA. The drug appeared to increase the myocardial retention of IHA and slow down the speed of degradation and storage; the variations were dose-dependent. These results correspond to those obtained by intracellular analysis. The proposed method, which is reliable and sensitive, is an interesting experiment for pharmacological studies of cardiac metabolism.

Animals↗

PubMed1978

Esterification of palmitic acid in swine aortic homogenates.

The incorporation of [1-14C] palmitic acid into tissue lipids of the medial and intimal layers of swine aortic homogenates was investigated. The homogenates obtained were metabolically active as indicated by their ready incorporation of labeled palmitic acid into phospholipids, diglycerides and triglycerides in the presence of alpha-glycerophosphate in the incubation medium. Predominantly, labeling of phospholipids and especially of phosphatidylcholine was found when alpha-glycerophosphate or lysolecithin served as the fatty acid acceptor. Glycerol and monoolein did not serve as fatty acid acceptors. More than 98% of the radioactivity was recovered as the rephosphatidylcholine fraction at the level of 0.64 micromoles/ml of lysolecithin in the incubation medium.

Animals↗

PubMed1992

Effect of dietary fat on the in vitro hepatotoxicity of paracetamol.

In the present study, we have examined the effect of dietary fat on paracetamol-induced liver injury in an in vitro rat liver slice model. Rats were fed, for 7-10 days, diets containing either butter or polyunsaturated vegetable margarine, two fat sources commonly consumed in the human diet. Liver slices were then exposed to paracetamol for 2 hr and further incubated for 4 hr without paracetamol. Cell damage in the slices was quantified at 6 hr by measuring leakage of lactate dehydrogenase, increase in water content and potassium loss. Covalent binding of radioactive paracetamol to liver and the membrane fatty acid composition of the liver were also measured. Liver slices from rats fed butter diets were significantly more sensitive to the toxic effects of paracetamol than those from margarine fed rats. The membrane lipid composition of the livers also reflected the differing fatty acid content of the two diets.

Acetaminophen↗

PubMed1982

Metabolism of palmitaldehyde in human cardiac muscle-II. Fatty chain elongation and shortening.

1. The metabolism of [1-14C[ palmitaldehyde has been studied in human heart homogenates. 2. Incorporation of the radioactivity into the individual acyl chains of nonpolar (NPL) and polar (PL) lipid fractions was assessed as well as changes in the weight percentage distribution of these chains. 3. Incorporation of the radioactivity into specific lipid fractions of free fatty acids (FFAcd), free fatty aldehydes (FFAld) and cholesterol esters were also studied. 4. A significant amount of incorporation into fatty chains of both fewer and more than 16 carbons was observed. 5. Chain shortening was found to be favored by NAD while the chain elongation required NADPH.

Aldehydes↗

PubMed1983

Platelet-activating factor stimulates metabolism of phosphoinositides in horse platelets: possible relationship to Ca2+ mobilization during stimulation.

Stimulation of horse platelets with platelet-activating factor (PAF) induces a rapid degradation of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. Addition of 0.1 microM PAF for 5 sec to platelets prelabeled with 32P induces a 50% loss of [32P]PtdIns(4,5)P2. 32P-Labeled phosphatidylinositol 4-monophosphate (PtdIns4P) and [32P]phosphatidylinositol (PtdIns) also are decreased, albeit at a slower rate. Loss of 32P radioactivity correlates with a net loss of fatty acids from both polyphosphoinositides. Stimulation of platelets with PAF also produces formation of [32P]phosphatidic acid and [32P]lysophosphatidylinositol. The initial disappearance of inositol lipids is subsequently followed by resynthesis, as evidenced by increased incorporation of 32P into PtdIns(4,5)P2, PtdIns4P, and PtdIns. The resynthesis of the inositides increases with time and is proportional to the concentration of PAF. Prostacyclin (1 microM) inhibits (i) the formation of phosphatidic acid and lysophosphatidylinositol and (ii) the resynthesis of polyphosphoinositides induced by 0.03 microM PAF without affecting the initial loss of PtdIns(4,5)P2. The loss of inositol lipids appears to be a primary event of platelet activation. The initial loss of polyphosphoinositides might be linked to the initiation of cellular activation by mobilizing membrane-bound Ca2+, whereas the subsequent formation of these lipids might be involved in mechanisms to prevent overstimulation of the cell.

Animals↗

PubMed1993

Biphasic effects of low-molecular-weight and conventional heparins on chylomicron clearance in rats.

Chylomicrons labeled in vivo with [14C]triglycerides and [3H]retinyl esters were injected in rats at a series of times after administration of conventional unfractionated heparin (UFH), low-molecular-weight heparin (LMWH), or saline. In saline controls the clearance of both chylomicron triglycerides and retinyl esters seemed to follow exponential courses, with half-lives of about 5 and 10 minutes, respectively. Five minutes after administration of LMWH or UFH, the triglyceride clearance rates were dramatically increased and were associated with an increased appearance of the radiolabel in circulating free fatty acids (FFAs). The clearance of [3H]retinol radioactivity, ie, chylomicron particles, was also enhanced 5 minutes after heparin injection. From 75% to 90% disappeared from the circulation within the first 5 minutes. Their continued disappearance was much slower, with a slope similar to that of the saline-treated rats. Hence, it was as if a new, rapid exponent had been added to the disappearance curve that accounted for most of the particle clearance. Injection of chylomicrons 1 hour after the heparins resulted in substantially slower clearance compared with saline-treated controls of both triglyceride and retinol radioactivity in rats given a high dose of LMWH or a low dose of either heparin. Appearance of label in plasma FFAs was also decreased, suggesting that impeded lipolysis was responsible, at least in part, for the impeded chylomicron clearance. Four and 24 hours after heparin injection all studied parameters of chylomicron clearance had returned to normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Uptake and hormonally induced hydrolysis of [3H]phosphatidyl choline in the isolated rabbit heart.

Tritiated phosphatidyl choline (1-palmitoyl,2-[3H]palmitoyl or 1-stearoyl,2-[3H]arachidonyl) is taken up unchanged by the isolated perfused rabbit heart. Isoproterenol, vasopressin or A23187 enhanced the output of tritium in these hearts, whereas bradykinin, angiotensin II or acetylcholine had no effect. These data demonstrate that [3H]phosphatidyl choline is incorporated directly into a phospholipid pool that is accessible to some, but not all, hormonally stimulated lipases. In hearts labeled with 1-stearoyl,2-[3H]arachidonyl phosphatidyl choline, the radioactivity released by isoproterenol consisted of free fatty acid and lysophosphatidyl choline, indicating that isoproterenol stimulates both phospholipase(s) A1 and A2. Vasopressin and A23187 increased the release of free fatty acid, but not lysophosphatidyl choline, suggesting that these agents stimulate only phospholipase A2.

Acetylcholine↗

PubMed1977

Fatty acid and glucose metabolism in selenium deficient rats and lambs.

Fatty acid analyses were done on tissues of lambs from ewes fed purified diets, and injected with selenium and/or vitamin E in a 2 X 2 factorial treatment. The concentrations of arachidonic acid averaged 9.3% of the total fatty acid content in semitendinosus muscle from lambs given vitamin E and selenium, but averaged 19.4% in this muscle from lambs given vitamin E without selenium. Arachidonic acid comprised 28.3% and 33.7%, respectively, of the total fatty acids in livers from selenium supplemented and deficient rats. Twice as much radioactivity from [1-(14)C]acetate was recovered in rat liver phospholipid arachidonate in selenium deficient rats as in selenium supplemented ones, indicating a greater turnover rate of this fatty acid in deficient rats. Fifty-five percent of dosed 14C-glucose (either [1-(14)C] or [6-(14)C]glucose) was recovered within 3 hours as 14CO2 from selenium deficient rats. This recovery dropped to one-half this value when these rats were fed a diet containing 0.1 ppm selenium for only 7 days. This increased glucose metabolism is suggestive of a greater metabolic rate in selenium deficient animals, which may be responsible for the differences observed in tissue fatty acid composition.

Animals↗