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Measles-virus-persistent infection in BGM cells. Modification of the incorporation of [3H]arachidonic acid and [14C]stearic acid into lipids.

In BGM cells chronically infected with measles virus, although the composition of the phospholipids is unaltered, the fatty acid composition is modified. Uninfected, lytic and persistently infected cells were labelled with [3H]arachidonic acid and [14C]stearic acid and their metabolic fate analysed. No difference in the total incorporation was observed in the different systems. However, the [14C]stearic acid and [3H]arachidonic acid were incorporated up to 2-fold and 13-fold respectively greater into the neutral lipid of persistently infected compared with that of uninfected cells. Both radioactive fatty acids were specifically accumulated in the triacylglycerol and non-esterified fatty acids fractions. Lytically infected cells were similar to uninfected cells. Although there was no significant difference in the incorporation of radioactivity into the total phospholipid in either system, there was a large decrease in [3H]arachidonic acid incorporated into phosphatidylethanolamine and to a lesser extent phosphatidylcholine and phosphatidylinositol in persistently infected cells. [14C]Stearic acid incorporation was also reduced in phosphatidylcholine and phosphatidylethanolamine fractions of persistently infected cells.

Animals↗

Relative degradation of different molecular species of phosphatidylcholine in thrombin-stimulated human platelets.

The relative degradation of the various molecular species of [3H]phosphatidylcholine in response to thrombin was studied in human platelets following prelabeling with [3H]glycerol and compared to results obtained following labeling with [14C]oleic, [14C]linoleic, or [14C]arachidonic acids. This was of interest since previous work using radioactive fatty acids had led to the conclusion that the 1-acyl-2-arachidonoyl species of phosphatidylcholine is exclusively hydrolyzed in thrombin-stimulated platelets. Within 90 s, the thrombin-dependent release of [14C]arachidonic acid from phosphatidylcholine amounted to 25% but only 3 and 6% for oleic and linoleic acids, respectively, in general agreement with previous work. However, for [3H]glycerol-labeled phosphatidylcholine, all molecular species (saturates, monoenes, dienes, trienes, tetraenes, and greater than tetraenes) were subject to significant hydrolysis in the presence of thrombin within 90 s, ranging from 12-24% across the various classes. Furthermore, the degradation of the tetraenoic species (1-acyl-2-arachidonoyl) of [3H]phosphatidylcholine was found to be only 1.5 and 1.4 times that for the monoenoic (predominantly 1-acyl-2-oleoyl) and dienoic (predominantly 1-acyl-2-linoleoyl) species, respectively. A much heavier proportional labeling of plasma membrane relative to whole platelet phosphatidylcholine was observed with [3H]glycerol as compared to [14C] oleate or [14C]arachidonate. These results indicate that the 1-acyl-2-arachidonoyl species of phosphatidylcholine are not exclusively degraded by phospholipase A2 activity in thrombin-stimulated platelets and suggest that the differential compartmentation of molecular species of phosphatidylcholine according to their metabolic origins can influence their apparent susceptibility to hydrolysis.

Blood Platelets↗

Importance of lipolysis in oral cavity for orosensory detection of fat.

Lingual lipase is usually secreted from von Ebner's glands, although there is great variation between species. Lingual lipase is thought to be an auxiliary enzyme for fat digestion and absorption in mammals; however, the reason for lipolysis in the oral cavity is not known. We focused on the gustatory sense and investigated the significance of lingual lipase in the perception of a fat taste by using orlistat, a potent lipase inhibitor. Five-minute two-bottle preference tests demonstrated that the addition of orlistat diminished the preference for triacylglycerides but not for free fatty acids. Radioactive triolein applied on rats' circumvallate papilla revealed that lingual lipase was released continuously to generate significant amounts of fatty acids and other lipolytic products within 1-5 s, which was enough time to taste fat. These findings suggest that lingual lipase is released to perceive the taste of triacylglycerides and to find nutritive lipids in food.

Animals↗

Translation and characterization of the fatty acid synthetase messenger RNA.

Fatty acid synthetase messenger RNA was obtained from rat liver polysomal RNA and then injected into Xenopus laevis oocytes. The radioactive fatty acid synthetase protein synthesized in the oocytes was identified by immunoprecipitation with anti-fatty acid synthetase antibody and the immunoprecipitate was then characterized by electrophoresis on sodium dodecyl sulfate-polyacrylamide gel. Co-migration of authentic fatty acid synthetase and the labeled product synthesized in oocytes was observed. Based on sucrose density gradient analysis, the rat liver fatty acid synthetase mRNA has a sedimentation coefficient of approximately 33 S, which agrees with the predicted minimum size necessary to code for the fatty acid synthetase protein. In addition, this mRNA was partially purified with oligo(dT)-cellulose, which indicates that it has a polyadenylate region. The relative in vivo rate of synthesis of fatty acid synthetase and the level of fatty acid synthetase mRNA in liver were also determined during the course of dietary induction of this enzyme. The results indicate that the dietary-induced increase in the level of fatty acid synthetase is probably due to an increased level of the fatty acid synthetase mRNA.

Animals↗

Removal by bovine serum albumin of fatty acids from membrane vesicles and its effect on proline transport activity in Escherichia coli.

Bovine serum albumin appreciably stimulated the initial rate and the steady-state level of proline uptake in membrane vesicles, while it had no effect on the oxidase activity for ascorbate-phenazine methosulfate, on which the transport activity depends. Bovine serum albumin showed the strongest stimulatory effect on the transport system among the proteins tested. Three other proteins did not show any effect, while beta-lactoglobulin showed a weaker but appreciable effect on the transport activity. The incubation of membrane vesicles with bovine serum albumin resulted in extensive removal of fatty acids, while none of the other membrane components, including proteins and phospholipids, was removed by this treatment. Fatty acids inhibited the proline transport activity, while the inhibited activity was appreciably restored by incubation with the albumin. An experiment with radioactive fatty acids showed that exogenously-added fatty acids bound firmly to the membrane vesicles and were removed by subsequent incubation with the albumin. The incubation of membrane vesicles for several hours resulted in an increase of fatty acids with a concomitant loss of the transport activity. Subsequent incubation with the albumin resulted in the removal of fatty acids and the partial restoration of the transport activity. Based on these results, it is concluded that bovine serum albumin specifically removed fatty acids from membrane vesicles, resulting in activation of the proline transport system.

Biological Transport↗

Cloricromene inhibits leukotriene formation by human polymorphonuclear leucocytes by suppressing arachidonate release from membrane phospholipids.

Cloricromene, an antithrombotic agent known to inhibit the release of arachidonic acid (AA) in stimulated human platelets, was tested for its effects on arachidonate release and metabolism in human polymorphonuclear leucocytes (PMNs). Cloricromene dose-dependently suppressed the release of leukotriene B4 (LTB4), as assessed by radioimmunoassay, from both isolated PMNs and human whole blood stimulated with the calcium ionophore A23187 or with serum-treated zymosan (STZ). The inhibitory effect was higher when the concentration of the stimulating agent was weaker. Cloricromene also inhibited dose-dependently the liberation of LTB4, LTC4, LTD4 and 5-hydroxy-6,8,11,14-eicosatraenoic acid as assessed by HPLC in the supernantant of A23187-stimulated PMNs. Finally, the drug was able to suppress the release of [3H]AA from purified human PMNs prelabeled with the radioactive fatty acid and stimulated with either A23187 or with STZ. The A23187-induced decrease in the radioactivity of phosphatidylinositol, the phospholipid class mainly involved in AA release in stimulated PMNs, was also inhibited by cloricromene. Cloricromene suppresses leukotriene formation in human PMNs by reducing AA release from membrane phospholipids, possibly through interference with phospholipase A2 activation; this activity may contribute to the leucocyte-inhibitory effects reported previously for cloricromene.

Arachidonic Acid↗

Effect of propionyl-L-carnitine treatment on membrane phospholipid fatty acid turnover in diabetic rat erythrocytes.

In this work we have examined the effect of the oral administration of propionyl-L-carnitine (PLC) on the membrane phospholipid fatty acid turnover of erythrocytes from streptozotocin-induced diabetic rats. A statistically significant reduction in radioactive palmitate, oleate, and linoleate, but not arachidonate, incorporation into membrane phosphatidylcholine (PC) of diabetic rat erythrocytes with respect to control animals was found. Changes in radioactive fatty acid incorporation were also found in diabetic red cell phosphatidylethanolamine (PE), though they were not statistically significant. Oral propionyl-L-carnitine (PLC) treatment of diabetic rats partially restored the ability of intact red cells to reacylate membrane PC with palmitate and oleate, and reacylation with linoleate was fully restored. The analysis of the membrane phospholipid fatty acid composition revealed a consistent increase of linoleate levels in diabetic rat red cells, a modest decrease of palmitate, oleate and arachidonate. The phospholipid fatty acid composition of diabetic red blood cells was not affected by the PLC treatment. Lysophosphatidylcholine acyl-CoA transferase (LAT) specific activity measured with either palmitoyl-CoA or oleyl-CoA was significantly reduced in diabetic erythrocyte membranes in comparison to controls. In addition, LAT kinetic parameters of diabetic erythrocytes were altered. The reduced LAT activity could be partially corrected by PLC treatment of diabetic rats. Our data suggest that the impaired erythrocyte membrane physiological expression induced by the diabetic disease may be attenuated by the beneficial activity of PLC on the red cell membrane phospholipid fatty acid turnover.

Administration, Oral↗

Phorbol ester plus calcium ionophore induces release of arachidonic acid from membrane phospholipids of a human B cell line.

Binding of LA350, a lymphoblastoid human B cell line, by phorbol myristate acetate (PMA) plus a calcium ionophore, either ionomycin or A23187, produced unique alterations in the release of arachidonic acid (AA) from cellular phospholipids. After equilibrium labeling of cells with radioactive fatty acids, [14C]AA demonstrated a selective enhanced release from the cells in response to the binding of PMA plus calcium ionophore as compared to the release of [14C]stearic acid (STE), [3H]oleic acid (OLE) and [3H]palmitic acid (PAL). The major phospholipid sources of the released [14C]AA were shown to be phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol. The participation of protein kinase C (PKC) in the enhanced synergistic release of [14C]AA was demonstrated by the inhibition of the release by the PKC inhibitor, staurosporine. Approximately 2-6% of the labeled AA liberated was converted to 5-hydroxyeicosatetraenoic acid by an endogenous 5-lipoxygenase. Therefore during cell activation the B cell is capable of liberating AA via a PKC-dependent mechanism, implicating AA and/or its metabolites in signal transduction.

Arachidonic Acid↗

Thrombin induces a biphasic 1,2-diacylglycerol production in human platelets.

The 1,2-diacylglycerol (DAG) mass content was measured in thrombin-stimulated human platelets. Thrombin stimulates a biphasic accumulation of DAG, with an early phase reaching a peak at 10 s and a later phase reaching a peak at 2-3 min. The time course of first-phase DAG production corresponded well to that of Ins(1,4,5)P3 formation, which was rapid and transient. The second phase of DAG accumulation occurred after the level of Ins(1,4,5)P3 returned to nearly basal. Thrombin stimulated the decrease in PtdIns and phosphatidylcholine contents. The source of second-phase DAG was examined in platelets prelabelled with three radioactive fatty acids, i.e. arachidonic, palmitic and myristic. Thrombin stimulated the increase in radioactivity of DAG with decline of PtdIns in platelets labelled with [3H]arachidonic acid or [3H]palmitic acid, in which PtdIns was considerably labelled. In contrast, significant accumulation of [3H]DAG was not observed in [3H]myristic acid-labelled platelets, in which PtdIns was poorly labelled. In platelets prelabelled with [3H]inositol, an increase in InsP in response to thrombin was seen for more than 5 min. In contrast, upon stimulation, significant increases in [3H]phosphocholine and [3H]choline were not observed in [methyl-3H]choline-labelled platelets. Thrombin induced a small production of phosphatidylethanol, when ethanol was present during stimulation. However, the formation of DAG and phosphatidic acid was not significantly affected by ethanol. These results suggest that thrombin stimulates a biphasic accumulation of DAG, initially from PtdInsP2 and later from PtdIns in human platelets.

Arachidonic Acid↗

Unsaturated fatty acids stimulate the formation of lipoxygenase and cyclooxygenase products in rat spleen lymphocytes.

Rat spleen lymphocytes prelabelled with [14C] arachidonate were suspended in fresh medium in the presence or absence of exogenous non-radioactive fatty acids added in ethanol. It was found that fatty acids stimulate thromboxane B2, PGE2, HHT and HETE formation. The effect is specific for unsaturated fatty acids. It occurs at 50 micron concentrations and is apparent after 20 minutes incubation. Unsaturated fatty acids may serve an important role in the regulation of prostaglandin and hydroxy fatty acid metabolism in vivo. This may indicate a mechanism for the action of fatty acids on the immune response.

Animals↗

Biosynthetic incorporation of fatty acids with photosensitive groups into membrane lipids of cells in tissue culture.

The physical methods (13C-NMR-spectroscopy and fluorescence spectroscopy) hitherto used for the elucidation of lipid-lipid and lipid-protein interactions in artificial and simple natural membranes were extended to the application of fatty acids, phospholipids and sphingolipids with photochemical labels (azide group) in defined positions, which on photolysis generate nitrenes. These highly reactive groups react with neighbouring molecules, either lipids or polypeptide chains, with insertion or addition. Highly radioactive 12-azido[9,10-3H2]stearic acid, 12-azido[12-3H]oleic acid and 18-azido-[9,10,12,13-3H4]linoleic acid were added to the growth medium of eukaryotic cell lines in tissue culture (BHK 21 cells and Chang liver cells). They were incorporated into neutral, phosphoand sphingolipids in amounts comparable with the unsubstituted parent fatty acids. The distribution of the azido fatty acids in the phospholipids has been determined by enzymatic hydrolysis (phospholipase A2) on the basis of the distribution of their radioactivity. Radio gas chromatography and combined gas chromatography and mass spectroscopy revealed that the azide group of the radioactive fatty acids remained unaltered.

Animals↗

Lipoprotn lipase content and triglyceride fatty acid uptake in adipose tissue of rats of differing body weights.

Increasing body weight appears to alter lipid metabolism in adipose tissue. We have measured the content of lipoprotein lipase and the uptake of chylomicron triglyceride fatty acids in epididymal fat pads of rats of different weights. In order that the results might be expressed in terms of cell numbers, the relationship between the weights of fat pads and the numbers and volumes of fat cells isolated from them was determined. Highly significant correlations were found between fat pad weight and both the number and the volume of the individual adipocytes. In rats weighing from 140 to 350 g, the increase in the size of fat pads was attributable almost equally to increases in cell size and in cell number. Lipoprotein lipase activity was measured in acetone powders of whole fat pads and of isolated fat cell preparations. With both, lipoprotein lipase activity per cell diminished significantly as the weight of fat tissue increased, i.e., larger fat cells contained less enzyme per cell than smaller cells. The uptake of triglyceride fatty acid radioactivity was measured after incubation of fat pads with radiolabeled rat lymph chylomicrons in flasks containing either buffer alone or with added glucose or glucose plus insulin. The addition of glucose and insulin led to a mean increase of 70% in the uptake of radioactivity, but larger adipocytes were stimulated less than smaller cells. This resulted in a significant negative correlation between the weights of fat pads and the uptake of radioactivity. Enlargement of fat cells also led to a diminution in their capacity to esterify fatty acids.

Adipose Tissue↗

The regiospecific hydroxylation of lauric acid by rainbow trout (Oncorhynchus mykiss) cytochrome P450s.

We have reexamined the hydroxylation of [1-14C]-lauric acid by trout liver microsomes and reconstituted trout P450s using a new HPLC system that gave an improved separation of hydroxylauric acids. Under these conditions, hepatic microsomes from yearling juvenile trout were shown to form omega-, (omega-1)-, (omega-2)-, (omega-3)-, (omega-4)-, (omega-5)-, and (omega-6)-OH lauric acid oxidation products (12-OH, 11-OH, 10-OH, 9-OH, 8-OH, 7-OH, and 6-OH lauric acid, respectively) as verified by GC/MS analysis. Microsomes from male and female juvenile trout liver formed (omega-1)-OH lauric acid as the major metabolite (23-29% of total radioactivity) and no major differences were observed between males and females. By contrast, liver microsomes from 3-year-old sexually mature trout had substantially lower lauric acid hydroxylase activity than juvenile microsomes and produced small quantities of only the (omega-1)-, (omega-2)-, and (omega-6)-hydroxylation products. Moreover, microsomes from sexually mature female trout had markedly lower lauric acid hydroxylase activity than those from the sexually mature male trout. Rat liver microsomes were quite catalytically active but formed mostly the omega- and omega-1 lauric acid oxidation products. Lauric acid metabolism also was analyzed in reconstituted systems containing purified juvenile trout LMC1 (CYP2M1) and LMC2 (CYP2K1) and with hepatic microsomes from juvenile trout in the presence of rabbit polyclonal antibodies raised against the two purified trout P450s. CYP2M1 catalyzed the (omega-6)-hydroxylation of lauric acid while the trout CYP2K1 form produces mainly (omega-1)-OH lauric acid together with a smaller quantity of the (omega-2)-hydroxylation product. All of the trout and rat radiometric lauric acid metabolism results were confirmed by direct mass spectrometric analysis of derivatized lauric acid metabolism mixtures. Use of direct mass spectrometric analysis for the hydroxylated lauric acids offers considerable advantages since the method did not require use of a radioactive fatty acid, completely separated all of the lauric acid hydroxylation products, confirmed identification of each metabolite, and was more sensitive than the radiometric analysis method.

Animals↗

The incorporation of arachidonic acid into triacylglycerol in P388D1 macrophage-like cells.

When 388D1 cells are incubated in media containing 10 microM [3H]arachidonic acid (delta4Ach), the label is rapidly incorporated into phospholipids and triacylglycerol. However, incorporation of [3H]delta4Ach into phospholipids clearly precedes incorporation into triacylglycerol, indicating that the phospholipid pool constitutes the primary metabolic fate of the delta4Ach via a remodelling pathway. In contrast, [3H]delta4Ach is incorporated into triacylglycerol almost exclusively via de novo synthesis, as evidenced by studies using propranolol, a phosphatidate phosphohydrolase inhibitor. This compound induced a time-dependent and concentration-dependent increase in the levels of [3H]delta4Ach-containing phosphatidate that is directly correlated with a decrease in the levels of [3H]delta4Ach-containing triacylglycerol. In addition, no change in the levels of [3H]delta4Ach-containing diacylglycerol and monoacylglycerol were apparent along the time course of fatty acid incorporation into triacylglycerol. However, a sharp and transient accumulation of cell-associated free [3H]delta4Ach was detected shortly after exposure of the cells to the radioactive fatty acid. Collectively, the results reported herein suggest that free delta4Ach availability determines the patterns of incorporation and distribution of this fatty acid among the various lipid classes of P338D1 cells.

Animals↗

Arachidonate incorporation and prostaglandin production in cultured endothelial and smooth muscle cells from pig aorta.

In order to investigate the utilization of arachidonic acid by vascular cells, we have compared cultured endothelial and smooth muscle cells from piglet aorta, after a 24 hour incubation with [ 3H ]-arachidonic acid [( 3H ] -AA). We studied both the release of labeled cyclo-oxygenase products, and the distribution of the radioactive fatty acid among lipids as determined by thin layer chromatography. As already described by others the main prostaglandins (PG) released by endothelial cells were PGF2 alpha and 6 keto-PGF1 alpha whereas smooth muscle cells mainly produced PGE2. These differences were associated with marked modification of the radioactivity distribution among the various lipid classes. In particular, the proportion of [ 3H ] -AA incorporated into neutral lipids was much more important in smooth muscle than in endothelial cells (approximately 40% of the total incorporated radioactivity versus 8%). On the other hand, the distribution of [ 3H ] -oleic acid into cell lipids after a 24 hour incorporation was very similar in both types of cells. These results suggest the existence of precise mechanisms controlling the incorporation and the availability of the PG precursor in the various types of cells. This might in part explain the differences observed for different cell types in the PG secretion pattern.

6-Ketoprostaglandin F1 alpha↗

Absorption and metabolism of [3H]arachidonic and [14C]linoleic acid in essential fatty acid-deficient rats.

[3H]arachidonic acid (20:4) and [14C]linoleic acid (18:2) were fed in a triolein emulsion to essential fatty acid-deficient (EFAD) rats and to age-matched controls. Tissues were analyzed for radioactivity of different lipid classes after 1, 2, and 4 h. As in earlier studies [Nilsson and Melin. Am. J. Physiol. 255 (Gastrointest. Liver Physiol. 19): G612-G618, 1988], control rats retained more [3H]20:4 than [14C]18:2 in all organs except adipose tissue. In EFAD rats, recovery of [14C]18:2 was increased in small intestine, liver, heart, and kidneys. In comparison to controls, EFAD rats retained much more [14C]18:2 in phospholipids of these organs. The increase in the incorporation of both 3H and 14C into phosphatidylethanolamine was particularly pronounced. Another striking feature was the drastic increase in the retention after 4 h of 14C in cardiolipin, which is specifically located in the inner mitochondrial membrane. In contrast, incorporation of both 3H and 14C into phosphatidylinositol was decreased or unchanged in EFAD rats. Although fecal fat excretion was increased there was no evidence for a malabsorption or an increased retention in intestinal triacyglycerol of the radioactive fatty acids in EFAD rats. The proportion of [14C]18:2 that had been converted to [14C]20:4 was generally low but increased significantly with time in the liver and intestine of EFAD rats.

Aging↗

In vitro synthesis and transbilayer movement of phosphatidylethanolamine molecules labelled with different fatty acids in chick brain microsomes.

The transbilayer fatty acid distribution of diacylglycerophosphoethanolamine and the translocation of newly synthesized phosphatidylethanolamine molecules labelled with different fatty acids has been investigated in chick brain microsomes using trinitrobenzensulfonic acid. The determination of the fatty acid composition of diacylglycerophosphoethanolamine in both the outer and the inner leaflet of the microsomal vesicles revealed a similar distribution indicating that both leaflets share the same molecular species. The in vitro incorporation of radioactive fatty acids (16:0, 18:1 and 20:4(n-6] into ethanolamine phospholipids, known to be catalyzed by the lyosphosphatidylethanolamine acyl transferase, showed that the radioactive diacylglycerophosphoethanolamine molecules appeared first in the outer leaflet and were thereafter transferred to the inner leaflet. The apparent rate of translocation of the newly synthesized ethanolamine phospholipid molecules was the highest for those labelled with 16:0 and the lowest for those labelled with 20:4(n-6). The results indicate that the active site of the acyl-CoA:lysophosphatidylethanolamine acyltransferases is located on the outer leaflet of the microsomal vesicles and that the different newly synthesized molecular species of diacylglycerophosphoethanolamine may be translocated from the outer to the inner leaflet at different rates.

Animals↗

Acylation of cellular proteins with endogenously synthesized fatty acids.

A number of cellular proteins contain covalently bound fatty acids. Previous studies have identified myristic acid and palmitic acid covalently linked to protein, the former usually attached to proteins by an amide linkage and the latter by ester or thio ester linkages. While in a few instances specific proteins have been isolated from cells and their fatty acid composition has been determined, the most frequent approach to the identification of protein-linked fatty acids is to biosynthetically label proteins with fatty acids added to intact cells. This procedure introduces possible bias in that only a selected fraction of proteins may be labeled, and it is not known whether the radioactive fatty acid linked to the protein is identical with that which is attached to the protein when the fatty acid is derived from endogenous sources. We have examined the distribution of protein-bound fatty acid following labeling with [3H]acetate, a general precursor of all fatty acids, using BC3H1 cells (a mouse muscle cell line) and A431 cells (a human epidermoid carcinoma). Myristate, palmitate, and stearate account for essentially all of the fatty acids linked to protein following labeling with [3H]acetate, but at least 30% of the protein-bound palmitate in these cells was present in amide linkage. In BC3H1 cells, exogenous palmitate becomes covalently bound to protein such that less than 10% of the fatty acid is present in amide linkage. These data are compatible with multiple protein acylating activities specific for acceptor protein fatty acid chain length and linkage.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗