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PubMed1978

Hydrolysis of biliary phospholipids in the upper small intestine of the chick.

Chick endogenous phospholipids were doubly labeled by an intravenous injection of [32P] phosphate and [1-14C] oleic acid, and the free fatty acid and phospholipid fraction of gall bladder bile and in contents of upper small intestine were analyzed 4 days later. There was evidence of hydrolysis of biliary phosphatidylcholine to lysophosphatidylcholine in the duodenum and jejunum, but this did not account for the pronounced increase in the 14C radioactivity of the free fatty acids relative to the 32P phospholipid radioactivity between bile and upper intestinal segments. It is suggested that phosphatidylcholine is largely absorbed in the duodenum of the chick while the remainder is progressively hydrolyzed and absorbed.

Animals↗
PubMed1995

Hexachlorocyclohexanes affect the arachidonic acid release from phosphatidylinositol but not from other phospholipid classes in tubular cell cultures.

Gamma- and delta-isomers of hexachlorocyclohexane caused marked decreases in the levels of radioactive phospholipids, and increases in the levels of [3H]arachidonate incorporated into free fatty acids in rat renal tubular cells. The increased radioactivity of free fatty acids arises from the decrease of [3H]arachidonate incorporated into phosphatidylinositol, but not into phosphatidylcholine, phosphatidylserine or phosphatidylethanolamine. This fact suggests that phosphatidylinositol can be broken down to the fatty acid from the sn-2 position and lysophospholipid by a phospholipase activity increased by hexachlorocyclohexanes. The observed specific toxicant action could be achieved in two ways: (a) operating upon a specific phospholipase A2 that acts on phosphatidylinositol, but not on other phospholipids as substrates and/or (b) involving substrate-phospholipase A2 interactions. Interestingly, the observed effect of the delta-isomer was more pronounced than that of the gamma-one.

Animals↗
PubMed1988

The nonpolar lipids of pig epidermis.

Epidermis was removed from several sites on the intact bodies of each of seven pigs and the lipids were extracted and analyzed by thin-layer chromatography. The principal nonpolar components were cholesterol, free fatty acids and cholesteryl esters. Small and variable amounts of paraffin hydrocarbons, triglycerides, and an unidentified lipid were noted. In a series of time-course experiments, epidermal lipids were labeled by intradermal injection of [1-14C] acetate at varying times up to 21 days before removal of the epidermis. The hydrocarbons never acquired radioactivity, while the triglycerides retained label only for about 1 day after injection. Squalene and lanosterol retained considerable radioactivity for up to 12 h after labeling. Radioactivity appeared in free fatty acids and cholesteryl esters 2-3 days after labeling and began to decline after 21 days. Epidermis from uninjected sites did not acquire significant radioactivity. From these results it was concluded that cholesterol, cholesteryl esters and free fatty acids are synthesized locally in the epidermis and remain until lost by desquamation. Triglycerides are also synthesized but do not persist into the stratum corneum, so the small amounts found there may be environmental contaminants. Alkanes are not synthesized, and are most probably derived from petroleum waxes.

Animals↗
PubMed1976

Contribution of intermuscular fat to lipogenesis from dietary glucose carbon in mice.

We assessed the contribution of various tissues to the synthesis of fat from glucose carbon in mice during rapid lipogenic activation induced by a glucose test meal. Nibbling and gorging mice were maintained on a 58% glucose, fat-free diet. The mice were fasted 22 h and refed 5-10 muCi [U-14C]glucose (120 mg/20 g body weight) either by gastric intubation or as a test meal (58% glucose diet). The muscular carcass in both nibblers an gorgers contained more than 75% of the total radioactivity in the fatty acids derived from glucose; liver and epididymal fat pad accounted for only a small percentage. Mort than half the carcass activity was in the "muscular" tissue as neutral lipid acids. We could isolate a discrete fat body in the popliteal region of the leg muscle ("muscle fat", "intermuscular fat"). The popliteal fat converted glucose carbon to fatty acids an order of magnitude faster, per unit weight, than the epididymal fat pad or skeletal muscle. The fatty acid moiety of the triacylglycerols had the major portion of the label in the popliteal fat 2 and 6 h after ingestion of the glucose test meals. The diacylglycerol pool was active at 2 h and its activity faded at 6 h implicating its intermediary role in lipid metabolism similar to published findings in epididymal fat pad. These results indicate that fat cells associated with the muscular carcass may play a major role in the de novo synthesis of fat from dietary carbohydrate in mice.

Adipose Tissue↗
PubMed1982

Nonpolar lipid methylation-identification of nonpolar methylated products synthesized by rat basophilic leukemia cells, retina and parotid.

Incorporation of radioactivity from [3H- or 14C-methyl] methionine into nonpolar lipids had been investigated in rat basophilic leukemia (RBL) cells, retina, and rat parotid gland. These nonpolar methylated lipids were extracted into heptane and characterized by thin-layer chromatography, high performance liquid chromatography, gas chromatography, and mass spectrometry. The major methylated nonpolar lipid product in the RBL cells themselves was ubiquinone-9, which accounted for about 90% of the nonpolar lipid and 20-30% of the total radioactive lipid formed. There was a modest increase in the methylation of nonpolar lipids upon stimulation of the RBL cells with IgE and anti-IgE, but the significance of this change is uncertain. In contrast to whole cells, RBL membrane fractions (incubated with [3H-methyl]-S-adenosylmethionine) incorporated radioactivity primarily into fatty acid methyl esters and not ubiquinone. A third product, 2-(methylthio)-benzothiazole, was formed by RBL cells, retina and minced parotid upon incubation in enriched media. This product was formed enzymatically, apparently by the known enzyme S-thiolmethyltransferase, using the thiol substrate which contaminates these media. Evidence suggest that the enzyme may reside, at least in part, on the surface of the cells.

Animals↗
PubMed1971

The subcellular distribution of platelet lipids labeled by acetate-1-14C.

The lipids of intact human platelets were labeled in vitro with acetate-1-(14)C, and the distribution of radioactivity in individual fatty acids and in lipid classes was examined in platelet subcellular fractions separated by sucrose density gradient ultracentrifugation. The distribution of newly formed fatty acids among individual lipid classes was similar in all subcellular components, and no highly unusual or characteristic lipid metabolic pool was present in either the soluble, membrane, or granule fractions.

Acetates↗
PubMed1979

Lipogenesis in the developing brain: utilization of radioactive leucine, isoleucine, octanoic acid and beta-hydroxybutyric acid.

Incorporation of radioactivity from intracranially injected radioactive leucine, isoleucine (ketogenic amino acids), octanoic acid and beta-hydroxybutyric acid into the brain lipids of 15 to 16 day-old rats was examined. The results showed that radioactivity from all the above precursors was incorporated into brain lipids. Radioactivity from injected isoleucine was incorporated into odd numbered fatty acids indicating an alternate pathway to alpha-oxidation for the biosynthesis of these fatty acids in the brain. For some as yet unclear reasons, a substantial portion of the radioactivity from injected octanoic acid was incorporated into free fatty acids. Utilization of these compounds for providing carbon for lipogenesis during development under unstressed normal conditions is discussed.

Animals↗
PubMed1968

Investigations on vitamin D esters synthesized rats. Detection and identification.

1. Vitamin D-deficient rachitic rats were given [1-(3)H]cholecalciferol by gastric intubation. After 24hr., diethyl ether extracts of liver and kidney contained 5-11% and 4.5-20% respectively of total vitamin D apparently esterified with long-chain fatty acids. 2. A two-dimensional thin-layer chromatographic technique was devised that completely separated seven synthetic vitamin D esters according to the chain length and number of double bonds in the fatty acid component. When the ;vitamin D ester' fraction from liver or kidney was co-chromatographed with the standard esters, radioactivity appeared mainly in vitamin D palmitate, stearate, oleate and linoleate regions. The proportion of radioactivity in the saturated fatty acid esters was higher in kidney than in liver. 3. The same percentage of tissue vitamin D in the esterified form was found at each of two dosages of vitamin D. 4. The possible specificity of a vitamin D esterification mechanism is discussed.

Animals↗
PubMed1980

Studies on the biosynthesis of ceramide. Does the reversed ceramidase reaction yield ceramides?

During studies on the biosynthetic pathways of sphingomyelin, the condensation reaction between free fatty acids and sphingenine to ceramide catalysed in the reversed ceramidase reaction as proposed by Gatt (J. Biol. Chem. 238, PC 3131-3133 (1963) was reinvestigated. Radioactive long-chain fatty acids (palmitate and oleate) condense with ethanolamine, one of the buffer components of the original studies and yield N-acylethanolamine. N-Palmitoylethanolamine was isolated on a preparative scale from incubation mixtures and identified directly and also after derivatization by mass spectroscopy and comparison with the authentic synthetic compound. It is concluded that only the acyl-CoA-dependent ceramide synthesis is of biological significance.

Amidohydrolases↗
PubMed1989

Fate of fatty acids taken up as cholesteryl ester by rat hepatocytes in primary culture from high-density lipoprotein.

Primary cultures of rat hepatocytes were incubated in the presence of high-density lipoproteins (HDL) labelled with [1-14C]oleyl or [1-14C]linoleyl cholesteryl ester. Labelled HDL were prepared by selective delipidation with heptane, relipidation and sequential ultracentrifugations. Hepatocytes took up cholesteryl esters and cholesteryl ether their non-hydrolizable analog, at the same rate. The uptake increased with time, the cholesteryl ester/protein ratio and the amount of added HDL. It was not dependent on the nature of acyl chain or on the nature of the bond. The uptake did not depend on a specific interaction between HDL and cell membranes, since cholesteryl ester was taken up from HDL to the same extent as from albumin complexes. Linoleic and oleic acids released from cholesteryl esters taken up by hepatocytes were mainly reesterified into phosphatidylcholine and triacylglycerols. Linoleic acid was preferentially channelled into PC. A portion of these lipids were secreted by hepatocytes during a 24-h reincubation in a medium devoid of lipoprotein. Nearly the same amount of radioactivity was recovered in secreted phospholipids as in secreted triacylglycerols, in contrast with hepatocytes labelled with free fatty acids which secreted very little radioactivity as phospholipids. From these results and the high content in polyunsaturated fatty acids of cholesteryl esters, one can hypothesize that hepatic cholesteryl ester uptake may contribute to biliary phosphatidylcholine production, and therefore to polyunsaturated fatty acid sparing.

Animals↗
PubMed1976

Metabolism of erucic acid in the isolated perfused rat heart.

In the present work the uptake and utilization of [14C]erucic acid by the perfused rat heart has been investigated and compared with those of [14C]-palmitic acid. Both fatty acids were found to be taken up by the heart at the same rate. On the other hand, the incorporation of erucic acid into tissue lipid during 30 min perfusion were significantly high and CO2 production low as compared with palmitic acid. Incorporation of erucic acid into diacylglycerol, triacylglycerol and cholesterol ester was considerably higher than that of palmitic acid. During a 30-min period, a large amount of [14C]erucic acid was accumulated in tissue fatty acid fraction. Similarly, relatively high labelling was found in the fatty acid and diacylglycerol fraction during the initial 300 s of perfusion with erucic acid. When [14C]erucic acid and unlabelled palmitic acid was used, the radioactivity was very high in the fatty acid fraction of the heart lipid in comparison with the experiment when [14C]palmitate and unlabelled erucic acid was used. Therefore, erucic acid is poorly oxidized by the heart and is preferentially incorporated into heart lipids. There was relatively high incorporation of [14C]erucic acid into diacylglycerol and addition of unlabelled palmitic acid tended to decrease it, probably converting more diacylglycerol to triacylglycerol. When [14C]palmitic acid and erucic acid were used together, incorporation to triacylglycerol was high and diacylglycerol low. These results, therefore suggest that palmitic acid is a more suitable acyl donor than erucic acid for the C-3 position of triacylglycerol, especially when the diacylglycerol contains erucoyl moieties.

Animals↗
PubMed1978

Glyceroneogenesis in rat and guinea pig adipose tissue during the fed and fasted states.

While both pyruvate and lactate are good substrates for glyceride-glycerol synthesis in isolated adipocytes from fed rats and guinea pigs, neither alanine nor serine appear to support glyceroneogenesis. Fasting increases the proportion of radioactive pyruvate or lactate incorporated into glyceride-glycerol and reciprocally decreases the proportion incorporated into fatty acids. However, the total incorporation of radioactivity into triacylglycerol is considerably lower in isolated adipocytes from fasted than from fed animals. Addition of glucose to the incubation medium promotes the incorporation of radioactive lactate into both fatty acids and glyceride-glycerol by adipocytes from fasted as well as fed animals. The concentration of alpha-glycerolphosphate is considerably higher in adipose tissue of fed than fasted animals. In general, these results support the presence of a glyceroneogenic pathway in rat and guinea pig adipose tissue. However, it would appear that the physiologic significance of this pathway is less important in the fasted than the fed state, where it may play some role in the esterification of intracellular fatty acids.

Adipose Tissue↗
PubMed1979

[Influence of Silybin-dihemisuccinate on fatty acid synthesis in rat liver (author's transl)].

1. The influence of silybin-dihemisuccinate, a derivative of the flavonolignane silybin from silybum marianum L. Gaertn., on fatty acid biosynthesis of rat liver was studied measuring the radioactivity incorporation of [1-14C]-acetate and 3H2O in fatty acids of the postmitochondrial supernatant of liver homogenates and in fatty acids of liver slices as well as the activities of enzymes involved in do novo synthesis of fatty acids. 2. In the postmitochondrial supernatant of liver homogenates or in liver slices, prepared 30 or 60 min after i.v. injection of 150.6 mg/kg silybin-dihemisuccinate, radioactivity incorporation of 14C-acetate or 3H2O in fatty acids was lowered by about 25%. Adding silybin-dihemisuccinate to incubation mixture in vitro in the concentration of 0.45--0.6 mmol/l silybin the radioactivity incorporation was linearly diminished with increased concentration of silybin. 3. After in vitro addition of varying concentrations of silybin to incubation mixtures in the presence of 0.1 mmol/l silybin activities of acetyl-CoA-carboxylase, fatty-acid-synthetase and ATP-citrate-lyase were diminished by about 50%, while activity of NADP-malate-dehydrogenase was lowered by 20% in the presence of 1 mmol/l silybin. 4. Our results suggest that silybin caused an unspecific and, under in vivo conditions, transitory inhibition of fatty acid synthesis in rat liver.

ATP Citrate (pro-S)-Lyase↗
PubMed1975

A new approach to the study of phospholipid-protein interactions in biological membranes. Synthesis of fatty acids and phospholipids containing photosensitive groups.

In a general approach to the study, in vivo and in vitro, of the interactions between phospholipids and proteins in biological membranes, a variety of fatty acids containing photosensitive groups in different positions in the alkyl chains has been synthesized. The fatty acids synthesized include: 16-azidopalmitelaidic acid, 12-azidooleic acid, 6-, 9-, 11-, and 12-azidostearic acid, 12-omicron-(ethyl-2-diazomalonyl)stearic and -oleic acids, 12-omicron-(4-azido-2-nitrophenyl)stearic and -oleic acids, and 12-oxo-10-octadecenoic acid. Some of the above synthetic fatty acids were also prepared in the radioactively labeled form. For in vitro studies, many of the above fatty acids were used to acylate the 2 position in the preparation of a number of mixed acylphosphatidylcholines and mixed acylphosphatidylethanolamines. On sonication, the synthetic phospholipids formed sealed vesicles. Intermolecular cross-linking of the fatty acyl chains in phospholipids was demonstrated on photolysis of the vesicles.

Fatty Acids↗
PubMed1978

Polyenoic acid metabolism in cultured human skin fibroblasts.

The incorporation of [1-14C]linoleic acid, and [1-14C]linolenic acid into cellular lipids of cultured human skin fibroblasts was studied. Cultured cells took up both labeled fatty acids at nearly the same rate and incorporated them into a variety of lipid classes. At the end of 1 hr incubation with [1-14C]linoleic acid, radioactivity was found in the triacylglycerol (TG) and choline phosphoglyceride (CPG) pools preferentially. Incorporation into the TG fraction decreased rapidly, while the uptake into CPG, serine phosphoglyceride (SPG), and ethanolamine phosphoglyceride (EPG) fractions increased progressively with longer incubation times. Similar results were obtained with [1-14C]linolenic acid as precursor. At the end of 24 hr, desaturation and chain elongation of 18:3 n-3 was more extensive than conversion of 18:2 n-6 to higher polyenoic acids. During pulse-chase experiments with either fatty acid precursor, the incorporated radioactivity was progressively lost from cellular lipids, particularly from the TG and CPG fractions, but continued to increase in the SPG and EPG pools. The similar labeling pattern of cellular phospholipids with linoleic or linolenic acids, and data from pulse-chase studies suggest that a direct transfer of fatty acids from CPG to EPG is a likely pathway in fibroblast cultures. Incorporation into the EPG pool during the pulse-chase experiments paralleled extensive desaturation and elongation of linoleic acid to 20:4 n-6, and 22:4 n-6; and of linolenic acid into 22.5 n-3 and 22:6 n-3.

Cells, Cultured↗
PubMed1968

Lipogenesis from glucose and pyruvate in fat cells from genetically obese rats.

Subcutaneous fat cells were isolated from genetically obese rats and from rats with obesity produced by hypothalamic lesions. Insulin did not augment the oxidation of fatty acids or their synthesis from glucose-1-(14)C or glucose-1-(3)H by fat cells from either group. Radioactivity from pyruvate-3-(14)C was incorporated into fatty acids to the same degree by fat cells from these two groups. The presence of 5 mm glucose in the incubation medium containing fat cells and pyruvate-3-(14)C or aspartate-3-(14)C stimulated the synthesis of fatty acids to a greater extent in cells of genetically obese rats. Fasting, in contrast, reduced the incorporation of radioactivity from pyruvate and glucose into fatty acids by fat cells from the genetically obese animals. In all experiments the fat cells from genetically obese rats converted more radioactivity into glyceride-glycerol relative to CO(2) than did fat cells from hypothalamic obese rats. Parabiosis between one thin and one genetically obese litter mate was performed in three pairs of rats without influencing growth of either rat. Thus in the present studies fat cells from genetically obese rats showed two differences from normal fat cells: they channeled more radioactivity from pyruvate into fatty acids in the presence of glucose, and they uniformly converted more radioactivity into glyceride-glycerol.

Adipose Tissue↗