Biomedical subjects

H Sprecher

Publications and source records attributed to H Sprecher.

At least 109 records · Page 6Linked to original sources

PubMed1986

Selective incorporation of various C-22 polyunsaturated fatty acids in Ehrlich ascites tumor cells.

Three 14C-labeled 22-carbon polyunsaturated fatty acids, 7,10,13,16-[14C]docosatetraenoic acid (22:4(n-6)), 7,10,13,16,19-[14C]docosapentaenoic acid (22:5(n-3)), and 4,7,10,13,16,19-[14C]docosahexaenoic acid (22:6(n-3)), were compared with [3H]arachidonic acid (20:4(n-6] and [14C]linoleic acid (18:2(n-6)) to characterize their incorporation into the lipids of Ehrlich ascites cells. The relatively rapid incorporation of the labeled 22-carbon acids into phosphatidic acid indicated that substantial amounts of these acids may be incorporated through the de novo pathway of phospholipid synthesis. In marked contrast to 20:4(n-6), the 22-carbon acids were incorporated much less into choline glycerophospholipids (CGP) and inositol glycerophospholipids (IGP). No selective preference was apparent for the (n-3) or (n-6) type of fatty acids. The amounts of the acids incorporated into diacylglycerophosphoethanolamine were in the order of: 22:6(n-3) greater than 20:4(n-6) much greater than 22:5(n-3) greater than or equal to 22:4(n-6) greater than 18:2(n-6), whereas for alkylacylglycerophosphoethanolamine they were in the order of: 22:4(n-6) greater than 22:6(n-3) greater than 22:5(n-3) much greater than 20:4(n-6) greater than 18:2(n-6). Of the mechanisms possibly responsible for the selective entry of 22-carbon acids into ethanolamine glycerophospholipids, the most reasonable explanation was that the cytidine-mediated ethanolamine phosphotransferase may have a unique double selectivity: for hexaenoic species of diacylglycerol and for 22-carbon polyunsaturated fatty acid-containing species of alkylacylglycerol. The relative distribution of fatty acids between newly incorporated and already maintained lipid classes suggested that IGP may function in Ehrlich cells as an intermediate pool for the retention of polyunsaturated fatty acids in glycerolipids.

Animals↗

PubMed1985

Paradoxical conservation of cardiac and renal arachidonate content in essential fatty acid deficiency.

The effects of essential fatty acid (EFA) deprivation on the arachidonate content and phospholipid composition of different tissues are quite diverse. When C57B1 mice were placed on a fat-free diet, hepatic liquids were readily depleted of arachidonate. In contrast, the renal cortex tenaciously retained arachidonate, whereas surprisingly the heart showed a doubling of its content of arachidonate. This increase in cardiac arachidonate was due to a four-fold increase in arachidonylphosphatidylethanolamine (PE). The renal cortex showed preservation of its arachidonate content in PE, phosphatidylserine, and phosphatidylcholine. Only phosphatidylinositol was depleted of arachidonate in heart or renal cortex. Using an in vivo labeling technique, it was shown that the liver incorporated most of the [1-14C]arachidonate initially following intraperitoneal injection. Over 11 days, as levels of labeled arachidonate fell in liver, the EFA-deficient heart accumulated arachidonate selectively in PE (8-fold greater than control), and the EFA-deficient renal cortex accumulated arachidonate in PE, phosphatidylserine, and phosphatidylcholine (2-3-fold greater than control). This uptake was shown to be specific for arachidonate over 20:3(n-9). Despite the conservation of cardiac and renal arachidonate seen with EFA deficiency, prostaglandin production by the isolated perfused EFA-deficient heart and kidney was markedly decreased relative to control in response to specific agonist stimulation with angiotensin II, although it was equivalent to control in response to nonspecific stimulation by ischemia. These data suggest that the liver serves to supply other tissues with arachidonate in EFA deficiency, and that the heart and renal cortex both contain mechanisms to accumulate arachidonate selectively in certain phospholipids. However, phosphatidylinositol, which is uniquely depleted of arachidonate in heart and renal cortex with EFA deficiency, appears to be the principal source of arachidonate in response to receptor-mediated agonists.

Animals↗

PubMed1985

A unique cardiac cytosolic acyltransferase with preferential selectivity for fatty acids that form cyclooxygenase/lipoxygenase metabolites and reverse essential fatty acid deficiency.

The rabbit heart contains a cytosolic enzyme which selectively incorporates polyunsaturated fatty acids into phosphatidylcholine. This unique acyltransferase is selective for fatty acids, thus far tested, that are substrates for cyclooxygenase or lipoxygenase (i.e., arachidonic, eicosapentaenoic, linoleic and dihomo-gamma-linoleic acids) or which reverse the symptoms of essential fatty acid deficiency (columbinic acid). On the other hand, palmitic, oleic, 5,8,11-eicosatrienoic (n-9, Mead acid), and docosatetraenoic acid (n-6, adrenic acid) were not incorporated in phospholipids by the cytosolic acyltransferase. No such fatty acid selectivity was exhibited by the cytosolic acyl-CoA synthetase or by the acyltransferase activities present in cardiac microsomes and mitochondria.

Acyltransferases↗

PubMed1985

Metabolism of 4,7,10,13,16-docosapentaenoic acid by human platelet cyclooxygenase and lipoxygenase.

Washed human platelets are shown to metabolize 4,7,10,13,16-docosapentaenoic acid into three major metabolites which were purified by reverse-phase HPLC. The mass spectra of the methyl ester-trimethylsilyl ether and ethyl ester-trimethylsilyl ether of compound A established it as delta 4-dihomo-thromboxane B2. Compound B was shown to be 14-hydroxy-4,7,10,12-nonadecatetraenoic acid, which is analogous to 12-hydroxy-5,8,10-heptadecatrienoic acid from arachidonic acid. Compound C was produced via an indomethacin-insensitive pathway and was identified as 14-hydroxy-4,7,10,12,16-docosapentaenoic acid. Time- and substrate-dependent studies showed that compounds A,B and C were produced approximately 10,15 and 65% of the extent to which thromboxane B2, 12-hydroxy-5,8,10-heptadecatrienoic acid and 12-hydroxy-5,8,10,14-eicosatetraenoic acid were produced, respectively, from arachidonic acid.

Arachidonic Acid↗

PubMed1985

Physiologic effects of columbinic acid and its metabolites on rat skin.

Columbinic acid and its cyclooxygenase and lipoxygenase metabolites were applied topically to the skin of essential fatty acid-deficient rats and their transepidermal water loss was measured. Despite the ability of the major lipoxygenase metabolite to reverse the scaly dermatitis, neither metabolite of columbinate was able to normalize the epidermal water loss, but the parent acid lowered the measurements in a dose-dependent fashion. These results indicate that some essential fatty acids have important functions as such, and not merely as precursors for other, biologically active, oxygenated metabolites.

Animals↗

PubMed1985

22-Carbon polyenoic acids. Incorporation into platelet phospholipids and the synthesis of these acids from 20-carbon polyenoic acid precursors by intact platelets.

The types of unsaturated fatty acids found in platelet phospholipids must be regulated by a series of controls which include specificity for activation and acylation as well as modification of circulating fatty acids by platelets prior to incubation into phospholipids. In this study we show that washed human platelets not only incorporate [1-14C]6,9,12-18:3, [1-14C]6,9,12,15-18:4, [1-14C]5,8,11-20:3, [1-14C]5,8,11,14-20:4, and [1-14C]5,8,11,14,17-20:5 into their phospholipids but also chain elongate each of these acids with subsequent acylation of the chain elongated products into phospholipids. Platelets incubated alone with 1-14C-labeled 5,8,11-20:3, 5,8,11,14-20:4, 5,8,11,14,17-20:5, 7,10,13,16,19-22:5, or 4,7,10,13,16,19-22:6 incorporated each of these acids into individual phosphoglycerides with phosphatidylinositol having the highest specific activity followed by phosphatidylcholine with phosphatidylserine approximately equal to phosphatidylethanolamine. The incorporation specificity of 4,7,10,13,16,19-22:6 was atypical since it was a relatively poor substrate for acylation into all phospholipids except phosphatidylethanolamine. The 20-carbon acids were better substrates for incorporation into phospholipids than were the 22-carbon compounds. Simultaneous incubation of 10 microM [1-14C]5,8,11,14-20:4 with increasing levels (5 to 15 microM) of each of the above five other 1-14C-labeled acids showed a concentration-dependent increase in the amount of the second fatty acid incorporated into platelet phospholipids. Dietary fat modification thus has the potential of increasing the plasma pool of 22-carbon acids for incorporation into platelets. In addition the activation of 20-carbon eicosanoid precursors by the high affinity platelet activating enzyme (Wilson, D. B., Prescott, S. M. and Majerus, P. W. (1982) J. Biol. Chem. 257, 3510-3515) will yield an acyl-CoA for both acylation and chain elongation followed by subsequent incorporation of 22-carbon acids into phosphoglycerides.

Arachidonic Acid↗

PubMed1985

Prostaglandin E2-like activity of 20:3n-9 platelet lipoxygenase end-product.

5,8,11-Icosatrienoic acid (20:3n-9), a fatty acid associated with platelet hyperactivity, was oxygenated by platelet lipoxygenase. The end-product of this pathway was purified by high-performance liquid chromatography (HPLC) and characterized as 12-hydroxy-5,8,10-icosatrienoic acid [12-OH-20:3(5,8,10)] by capillary gas-liquid mass spectrometry. When tested upon platelet aggregation, 12-OH-20:3(5,8,10) exhibited a biphasic effect. At low concentrations (below 5 X 10(-7) M) it potentiated aggregation but inhibited it at higher levels, a pattern similar to that obtained with prostaglandin E2. However, since the amounts of 12-OH-20:3(5,8,10) generated under thrombin stimulation are in the range of concentrations with potentiating effects, it seems that the 12-OH derivative is responsible for the hyperaggrebility of 20:3n-9-rich platelets.

8,11,14-Eicosatrienoic Acid↗

PubMed1985

Characterization of an arachidonic acid-selective acyl-CoA synthetase from murine T lymphocytes.

Evidence is presented that the murine thymoma EL4 and cytotoxic T lymphocyte clones possess two distinct long-chain fatty acyl-CoA synthetase activities. One enzyme shows activity toward a broad spectrum of fatty acid substrates, similar to the long-chain fatty acyl-CoA synthetase from rat liver. The other enzyme is selective for arachidonic acid and related fatty acids. Fatty acid competition studies using EL4 microsomes demonstrate that [14C]palmitoyl-CoA synthesis (Km = 13 +/- 1 microM, Vmax = 7 +/- 1 nmol/mg per min) is inhibited by unlabeled palmitate, oleate, linoleate or linolenate (Ki = 15-25 microM) and weakly by arachidonate (Ki greater than 100 microM). Similar inhibition is observed for the activation of [14C]oleate (Km = 31 +/- 3 microM, Vmax = 6 +/- 2 nmol/mg per min). On the other hand, [14C]arachidonyl-CoA synthetase (Km = 15 +/- 3 microM, Vmax = 13 +/- 2 nmol/mg per min) is inhibited by unlabeled arachidonic acid (Ki = 20 microM) but not by unlabeled palmitate, oleate, linoleate and linolenate. The description of arachidonoyl-CoA synthetase in cytotoxic T lymphocyte clones represents the first example of a cell with little or no capacity to synthesize arachidonic acid metabolites, yet which possesses a selective esterification mechanism for the fatty acid. Studies on the specificity of the arachidonic acid-selective acyl-CoA synthetase utilized arachidonic acid metabolites and structurally related fatty acids and yielded two points of interest: (1) metabolism of arachidonic acid to monohydroxy fatty acids (HETEs) resulted in compounds with significantly decreased ability to be activated by the arachidonate-selective acyl-CoA synthetase; (2) arachidonate was a much better substrate than was 5,8,11-eicosatrienoic acid (Km = 41 microM), the fatty acid which accumulates during essential fatty acid deficiency. The possible role of an arachidonic acid-selective acyl-CoA synthetase in lymphocyte activation and as a homeostatic mechanism during essential fatty acid deficiency is discussed.

Adenosine Triphosphate↗

PubMed1985

Metabolism of 7,10,13,16-docosatetraenoic acid to dihomo-thromboxane, 14-hydroxy-7,10,12-nonadecatrienoic acid and hydroxy fatty acids by human platelets.

Human platelets metabolize 7,10,13,16-docosatetraenoic acid (22:4(n - 6)) into dihomo-thromboxane B2 and 14-hydroxy-7,10,12-nonadecatrienoic acid at about twenty percent of the rate they convert arachidonic acid to thromboxane B2 and 12-hydroxy-5,8,10-heptadecatrienoic acid. 14-Hydroxy-7,10,12,16-docosatetraenoic was the major metabolite produce via the lipoxygenase pathway. Several other hydroxy acids were also produced in small amounts via an indomethacin-insensitive pathway. Incubation of 20 microM arachidonic acid with various levels of 22:4(n - 6) resulted in a dose-dependent inhibition of both thromboxane B2 and 12-hydroxy-5,8,10-heptadecatrienoic acid production. Conversely, 12-hydroxy-5,8,10,14-eicosatetraenoic acid synthesis was stimulated because of substrate shunting to the lipoxygenase pathway. These results show that 22:4(n - 6) may modify platelet function both by serving as a precursor for a 22-carbon thromboxane and by suppressing the synthesis of thromboxane A2 from arachidonic acid. In addition, our results suggest that simultaneous release of 22:4(n - 6) and arachidonic acid from platelet phospholipids will result in an elevation of both 12-hydroxy-5,8,10,14-eicosatetraenoic acid levels as well as simultaneous synthesis of 14-hydroxy-7,10,12,16-docosatetraenoic acid.

Blood Platelets↗

PubMed1985

Metabolism of icosa-5,11,14-trienoic acid in human platelets and the inhibition of arachidonic acid metabolism in human platelets by icosa-5,8,14-triynoic and icosa-5,11,14-triynoic acids.

Two fatty acids differing from arachidonic acid in lacking one of the internal double bonds (20:35,8,14 and 20:35,11,14) and their 1-C14 and acetylenic analogues were synthesized. 20:35,8,14 was not metabolized by human platelets but 20:35,11,14 yielded a small amount (1.5% conversion) of two hydroxy fatty acids in a three (11-hydroxy-5,12,14-icosatrienoic acid) to one (15-hydroxy-5,11,13-icosatrienoic acid) proportion. Indomethacin inhibited formation of both hydroxy fatty acids indicating that they are produced via cyclooxygenase. Both ethylenic acids were weak inhibitors of cyclooxygenase (substrate 20 microM arachidonic acid) (ID50: 8.8 microM 20:35,8,14; 11.2 microM 20:35,11,14) but were inactive against lipoxygenase (ID50 greater than 100 microM). Similarly, both acetylenic analogues were poor inhibitors of lipoxygenase (ID50: 23.4 microM 20:35,8,14; 47.8 microM 20:35,11,14) but although 20:35,8,14 was inactive against cyclooxygenase (ID50 greater than 100 microM) the 20:35,11,14 was a potent inhibitor (ID50: 0.35 microM). The results are interpreted on the basis that hydrogen removal by the lipoxygenase is from C10 and by the cyclooxygenase from C13 but only in 20:35,11,14 are these hydrogens (C13) located at the center of a 1,4 cis cis pentadiene system (ethylenic) or a 1,4 pentadiyne system (acetylenic).

Arachidonate Lipoxygenases↗

PubMed1985

Inhibition of cytotoxic T lymphocyte-mediated lysis by ETYA: effect independent of arachidonic acid metabolism.

Cytotoxic T lymphocyte (CTL)-mediated lysis of target cells was inhibited by 5,8,11,14-eicosatetraynoic acid (ETYA) and other inhibitors of the lipoxygenase pathway at concentrations that inhibited arachidonic acid metabolism in mixed lymphocyte cultures. Inhibition was reversible and selective for the "lethal hit" stage in the CTL-target interaction. Studies to define CTL-specific arachidonic acid metabolites demonstrated that cloned CTL populations have little or no capacity to metabolize arachidonic acid. Therefore, inhibitor actions appear to be independent of the effects on CTL arachidonic acid metabolism. Alternative explanations for inhibitory effects are discussed.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

PubMed1984

Synthesis of two hydroxy fatty acids from 7,10,13,16,19-docosapentaenoic acid by human platelets.

Platelets metabolize 7,10,13,16,19-docosapentaenoic acid (22:5(n-3] into 11-hydroxy-7,9,13,16,19- and 14-hydroxy-7,10,12,16,19-docosapentaenoic acid via an indomethacin-insensitive pathway. Time-dependent studies with 20 microM substrate show a lag in the synthesis of both the 11- and 14-isomers which was not observed for the synthesis of thromboxane B2 (TXB2), 5,8,10-heptadecatrienoic acid, and 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) from arachidonic acid. When platelets were incubated with increasing concentrations of 22:5(n-3), the 11- and 14-isomers were not produced until the substrate concentration exceeded 5 microM unless arachidonic acid was also added to the incubations. The stimulatory effect of arachidonic acid was not blocked by indomethacin thus suggesting that 12-hydroperoxyeicosatetraenoic acid or 12-HETE derived from arachidonic acid may activate the platelet lipoxygenase(s) which metabolize 22:5(n-3). Incubations containing 20 microM 22:5(n-3) and increasing levels of [1-14C]arachidonic acid show that the (n-3) acid inhibits the synthesis of both 5,8,10-heptadecatrienoic acid and TXB2 from arachidonic acid. At the same time, 12-HETE synthesis increased due to substrate shunting to the lipoxygenase pathway.

Arachidonic Acid↗

PubMed1984

Long-chain acyl-coenzyme A synthetase from rat brain microsomes. Kinetic studies using [1-14C]docosahexaenoic acid substrate.

The activation of docosahexaenoic acid by rat brain microsomes was studied using an assay method based on the extraction of unreacted [1-14C]docosahexaenoic acid and the insolubility of [1-14C]docosahexaenoyl-CoA in heptane. This reaction showed a requirement for ATP, CoA, and MgCl2 and exhibited optimal activity at pH 8.0 in the presence of dithiothreitol and when incubated at 45 degrees C. The apparent Km values for ATP (185 microM), CoA (4.88 microM), MgCl2 (555 microM) and [1-14C]docosahexaenoic acid (26 microM) were determined. The presence of bovine serum albumin or Triton X-100 in the incubation medium caused a significant decrease in the Km and Vm values for [1-14C]docosahexaenoic acid. The enzyme was labile at 45 degrees C (t1/2:3.3 min) and 37 degrees C (t1/2:26.5 min) and lost 36% of its activity after freezing and thawing. The transition temperature (Tc) obtained from Arrhenius plot was 27 degrees C with the activation energies of 74 kJ/mol between 0 degrees C and 27 degrees C and 30 kJ/mol between 27 degrees C and 45 degrees C. [1-14C]Palmitic acid activation in rat brain and liver microsomes showed apparent Km values of 25 microM and 29 microM respectively, with V values of 13 and 46 nmol X min-1 X mg protein-1. The presence of Triton X-100 (0.05%) in the incubation medium enhanced the V value of the liver enzyme fourfold without affecting the Km value. Brain palmitoyl-CoA synthetase, on the other hand, showed a decreased Km value in the presence of Triton X-100 with unchanged V. The Tc obtained were 25 degrees C and 28 degrees C for brain and liver enzyme with an apparent activation energy of 109 and 24 kJ/mol below and above Tc for brain enzyme and 86 and 3.3 kJ/mol for liver enzyme. The similar results obtained for the activation of docosahexaenoate and palmitate in brain microsomes suggest the possible existence of a single long-chain acyl-CoA synthetase. The differences observed in the activation of palmitate between brain and liver microsomes may be due to organ differences. Fatty acid competition studies showed a greater inhibition of labeled docosahexaenoic and palmitic acid activation in the presence of unlabeled unsaturated fatty acids. The Ki values for unlabeled docosahexaenoate and arachidonate were 38 microM and 19 microM respectively for the activation of [1-14C]docosahexaenoate. In contrast, the competition of unlabeled saturated fatty acids for activation of labeled docosahexaenoate is much less than that for activation of labeled palmitate.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1984

De novo biosynthesis of docosahexaenoyl-phosphatidic acid in bovine retinal microsomes.

Lysophosphatidic acid stimulated several-fold the formation of docosahexaenoyl-phosphatidic acid from 14C-labeled docosahexaenoic acid (22:6 (n-3] in the bovine retina. 1-Palmitoyl- and 1-oleoyl-sn-glycerol 3-phosphate were the preferred acceptors. Most of the activity was localized in the 105 000 X g microsomal fraction. Despite the very high content of 22:6 in the phospholipids of photoreceptor membranes, only about 1% of the microsomal activity was found in discs isolated from rod outer segments. The newly synthesized docosahexaenoyl-phosphatidic acid was further metabolized to diacylglycerols, triacylglycerols, phosphatidylcholine and phosphatidylserine. The de novo synthesis of docosahexaenoyl-phosphatidylcholine was stimulated by 1 mM CDPcholine. Lysophosphatidic acid and lysophosphatidylcholine up to 50 microM do not compete with each other for 22:6 in the formation of their respective diacylated lipids. This suggests that this fatty acid is introduced into phosphatidic acid and phosphatidylcholine via different acylation systems. We conclude that, in addition to the deacylation-acylation cycle, there is also an active pathway for the acylation of 22:6 into glycerolipids during the de novo biosynthesis of phosphatidic acid.

Animals↗

PubMed1984

Leukotriene B formation by neutrophils from essential fatty acid-deficient rats.

Analysis of neutrophil phospholipids from rats fed an essential fatty acid-deficient diet revealed a 33% reduction in arachidonate and a 90% reduction in linoleate compared to neutrophil phospholipids of rats fed a normal diet. The neutrophil phospholipids from rats fed the essential fatty acid-deficient diet also contained significant amounts of 5,8,11-eicosatrienoate, a fatty acid not found in the neutrophils of rats fed a normal diet. Analysis of the production of leukotrienes of the B series by ionophore-stimulated neutrophils from rats fed an essential fatty acid-deficient diet revealed a 87% reduction in leukotriene B4 compared to neutrophils from rats fed a normal diet even though the arachidonate content was reduced by only 34%. Essential fatty acid-deficient neutrophils converted endogenous 5,8,11-eicosatrienoic acid to leukotriene A3 and its nonenzymatic degradation products, but little or no leukotriene B3 was formed. Neutrophils from rats fed a normal diet incubated with ionophore and exogenous 5,8,11-eicosatrienoate also produced leukotriene A3 and its nonenzymatic degradation products but little or no leukotriene B3. Exogenous 5,8,11-eicosatrienoate incubated with ionophore-stimulated normal neutrophils caused a dose-dependent inhibition of leukotriene A hydrolase resulting in diminished production of leukotriene B4 from endogenous arachidonate. Assays of leukotriene A hydrolase in the 10,000 X g supernatant fraction of a homogenate of RBL-1 cells revealed that a lipoxygenase metabolite of 5,8,11-eicosatrienoate rather than 5,8,11-eicosatrienoate itself is the inhibitor of leukotriene A hydrolase. Thus the finding that leukotriene B4 production by neutrophils from essential fatty acid-deficient rats is diminished out of proportion to the decrease in arachidonate content appears to be due to inhibition of leukotriene A hydrolase by a lipoxygenase metabolite.

8,11,14-Eicosatrienoic Acid↗

PubMed1984

Arachidonic acid, 5,8,11-eicosatrienoic acid and 5,8,11,14, 17-eicosapentaenoic acid. Dietary manipulation of the levels of these acids in rat liver and platelet phospholipids and their incorporation into human platelet lipids.

Rats were fed diets in which the sole source of fat was either ethyl oleate, linoleate, linolenate or an equal mixture of ethyl linoleate and linolenate. The fatty acid composition of individual phospholipids from platelets and liver was compared to define how total body metabolism regulates which unsaturated fatty acids are produced and incorporated into platelet lipids for potential release and conversion to eicosanoids. The level of 20:4(n-6) in all phospholipids was not markedly altered by feeding linoleate versus that found in chow-fed controls. In oleate fed rats, the 20:3(n-9)/20:4(n-6) ratio varied from 0.5 in liver PE to 4.1 for liver PI, while ratios of 1.0, 1.1, 0.7 and 1.3 were found respectively for platelet PE, PC, PS and PI. Platelet PE contained a component tentatively identified as 22:3(n-9), which is consistent with the finding that this lipid contains significant amounts of 22:4(n-6) and 22:5(n-3) when rats received respectively linoleate or linolenate. Rats fed linolenate have a tight coupling between the regulation of unsaturated fatty acid biosynthesis and the selective acylation of 20:5(n-3) into all lipids. The 20:5(n-3)/20:4(n-6) ratio, however, varied between lipids. In liver PE, PC, PS and PI it was respectively 4.3, 4.9, 3.8 and 0.4, while in the analogous platelet lipids it was 3.0, 4.0, 0.9 and 0.6. Feeding linolenate did not markedly elevate the levels of 22:5(n-3) or 22:6(n-3) in platelet PI, but the combined amounts of 22:5(n-3) and 22:6(n-3) in liver PI were 21.2%, versus 2.9% in chow-fed controls. When the diet contained linoleate and linolenate, there was selective conversion of 18:2(n-6) to 20:4(n-6) and its acylation into lipids versus analogous metabolism of 18:3(n-3) to 20:5(n-3) and its subsequent incorporation. Again, the 20:5(n-3)/20:4(n-6) ratio was lowest for platelet PI and PS and liver PI. Washed human platelets readily incorporated 20:3(n-9), 20:4(n-6) and 20:5(n-3) into phospholipids. With each substrate, PI had the highest specific activity; this effect was most pronounced with 20:3(n-9). These incorporation studies are consistent with the feeding studies which show that oleate is converted to 20:3(n-9) and incorporated into PI more readily than the analogous metabolism of 18:3(n-3) to 20:5(n-3) and its acylation into PI, which is an important source of unsaturated fatty acids for prostaglandin biosynthesis.

8,11,14-Eicosatrienoic Acid↗

PubMed1984

Fatty acid structural requirements for activity of arachidonoyl-CoA synthetase.

We have examined the fatty acid substrate specificity of arachidonoyl-CoA synthetase from human platelet membranes. A variety of positional isomers and chain-length analogs of arachidonic acid [20:4(5, 8, 11, 14)] were synthesized, and assayed for their ability to inhibit arachidonoyl-CoA formation or to serve as substrates for the synthetase. The chain-length specificity of the synthetase for delta 8,11,14 trienoic fatty acids was C19 greater than C18 = C20 much greater than C21 greater C22. Inhibition activity by positional isomers of arachidonate was 20:4(5, 8, 11, 14) approximately equal to 20:4(6, 9, 12, 15) = 20:4(7, 10, 13, 16) much greater than 20:4(4, 7, 10, 13), however, Vmax for arachidonate was greater than that for 20:4(6, 9, 12, 15). The enzyme apparently "counts" double bonds from the carboxyl terminus. As counted from the methyl terminus we found that several n-6,-9,-12 fatty acids were ineffective as inhibitors [18:3(6, 9, 12); 19:4)4, 7, 10, 13); 21:3(9, 12, 15)], whereas all methylene-interrupted tri- and tetraenoic fatty acids which contained delta 8 and delta 11 double bonds were potent inhibitors. The delta 11 double bond was best associated with optimal inhibition: 20:3(5, 11, 14) had a lower Ki than 20:3(5, 8, 14). 13-Methyl-20:3(8, 11, 14) did not inhibit the enzyme. Partially purified enzyme from calf brain, depleted of nonspecific long-chain acyl-CoA synthetase, exhibited the same fatty acid specificity as crude platelet enzyme.

Animals↗

PubMed1983

Products derived from 5,8,11-eicosatrienoic acid by the 5-lipoxygenase-leukotriene pathway.

Analysis of products derived from 5,8,11-eicosatrienoic acid via the 5-lipoxygenase-leukotriene pathway showed that this fatty acid is readily converted to leukotriene (LT)A3. When 10,000 X g supernatant from rat basophilic leukemia cell homogenates was incubated with 30 microM fatty acid, 5,8,11-eicosatrienoic acid produced 6.2 +/- 1.1 nmol of LTA3 and arachidonic acid 15.5 +/- 1.9 nmol of LTA4 (n = 4). However, only insignificant amounts of LTB3 were formed (0.15 +/- 0.04 nmol of LTB3 and 4.2 +/- 0.4 nmol of LTB4, n = 4). These data indicate that the LTA-hydrolase requires not only the three double bonds of the triene but also the double bond at C-14 to efficiently convert LTA to LTB. These findings have significant implications for essential fatty acid deficiency.

8,11,14-Eicosatrienoic Acid↗