Uptake of dihomo-gamma-linolenic acid by murine macrophages increases series-1 prostaglandin release following lipopolysaccharide treatment

Administration of dihomo-gamma-linolenic acid is useful for atopic dermatitis and atherosclerosis in mice; however, the metabolites of dihomo-gamma-linolenic acid have been little studied. We employed a method which enabled simultaneous analysis of nine prostaglandins using liquid chromatography-tandem mass spectrometry, and determined the concentrations of prostaglandins in the supernatants of cultures of mouse peritoneal macrophages stimulated with lipopolysaccharide after pre-incubation with dihomo-gamma-linolenic acid, arachidonic acid, or eicosapentaenoic acid. Accumulated prostaglandin concentrations from mouse macrophages with dihomo-gamma-linolenic acid uptake increased in a dihomo-gamma-linolenic acid concentration-dependent fashion. These increases were mainly due to prostaglandin D(1) and prostaglandin E(1). The order of accumulated prostaglandin concentrations was dihomo-gamma-linolenic acid>arachidonic acid>eicosapentaenoic acid in supernatants with the same concentration of polyunsaturated fatty acid. Since mouse macrophages can clearly produce series-1 prostaglandins, they must be formed in vivo. These findings suggest that the effects of dihomo-gamma-linolenic acid on diseases may be due to series-1 prostaglandins.

Inhibitory action of polyunsaturated fatty acids on IMP dehydrogenase

We screened the inhibitor of mouse inosine 5'-monophosphate dehydrogenase (IMPDH) type II from natural compounds, and found that a fatty acid, linoleic acid (C18:2), inhibited IMPDH activity. In the C18:2 fatty acid derivatives, all trans-configuration (i.e., linoelaidic acid), ester form, alcohol form, and addition of the hydroxyl group of linoleic acid had no effect on inhibitory activity. Therefore, both parts of a carboxylic acid and an alkyl chain containing cis-type double bonds of fatty acid might be essential for inhibition. Among the various carbon atom lengths and double bonds of fatty acids examined, the strongest inhibitor was C20:2-fatty acid, eicosadienoic acid, and 50% inhibition was observed at a concentration of 16.1 microM. Eicosadienoic acid induced the inhibition of IMPDH activity and was competitive with respect to IMP (K(i)=3.1 microM). For inhibitory effect, the C20-fatty acids ranked as follows: C20:2>C20:3>C20:1>> C20:4>C20:5, and C20:0 showed no inhibition. The energy-minimized three-dimensional structures of linear-chain C20-fatty acids were calculated, and it was found that a length of 20.7-22.5A and width of 4.7-7.2A in the fatty acid molecular structure was suggested to be important for IMPDH inhibition. Docking simulation of C20-fatty acids and mouse IMPDH type II, which was homology modeled from human IMPDH type II (PDB code: 1NF7), was performed, and the fatty acid could bind to Cys331, which is a amino acid residue of the active site, competitively with IMP. Based on these results, the IMPDH-inhibitory mechanism of fatty acids is discussed.

Docosahexaenoic acid stabilizes soluble amyloid-β protofibrils and sustains amyloid-β-induced neurotoxicity in vitro

Enrichment of diet and culture media with the polyunsaturated fatty acid docosahexaenoic acid has been found to reduce the amyloid burden in mice and lower amyloid-beta (Abeta) levels in both mice and cultured cells. However, the direct interaction of polyunsaturated fatty acids, such as docosahexaenoic acid, with Abeta, and their effect on Abeta aggregation has not been explored in detail. Therefore, we have investigated the effect of docosahexaenoic acid, arachidonic acid and the saturated fatty acid arachidic acid on monomer oligomerization into protofibrils and protofibril fibrillization into fibrils in vitro, using size exclusion chromatography. The polyunsaturated fatty acids docosahexaenoic acid and arachidonic acid at micellar concentrations stabilized soluble Abeta42 wild-type protofibrils, thereby hindering their conversion to insoluble fibrils. As a consequence, docosahexaenoic acid sustained amyloid-beta-induced toxicity in PC12 cells over time, whereas Abeta without docosahexaenoic acid stabilization resulted in reduced toxicity, as Abeta formed fibrils. Arachidic acid had no effect on Abeta aggregation, and neither of the fatty acids had any protofibril-stabilizing effect on Abeta42 harboring the Arctic mutation (AbetaE22G). Consequently, AbetaArctic-induced toxicity could not be sustained using docosahexaenoic acid. These results provide new insights into the toxicity of different Abeta aggregates and how endogenous lipids can affect Abeta aggregation.

Cyclooxygenase inhibitors not inhibit resting lung cancer A549 cell proliferation

Cyclooxygenase (COX) inhibitors were regarded as anticarcinogenic agents for lung cancer at least partly via PGE2; but these were based on cytokin stimulation experiment on A549 cell. In order to clarify whether COX inhibitors directly inhibit A549 cell, three COX inhibitors, NS398 (selective COX-2 inhibitor), SC560 (selective COX-1 inhibitor), and acetyl salicylic acid (ASA, non-selective COX inhibitor), were studied. NS398, and ASA, can inhibit PGE2 generation via COX-2 inhibition. The viability of A549 cell was assayed by MTT. However, without cytokin stimulation, all the three inhibitors (NS398 0.2-20 microM; SC560 1.0-100 nM; ASA 0.01-1.0 mM) were not able to inhibit A549 cell proliferation, in the other way round, NS398 promoted cell growth. And arachidonic acid (AA) and lipopolysaccharide (LPS) did not disturb the property of its growth. These data suggested that without cytokin stimulation, COX and PGE2 may not be the kernel molecules involved in A549 cell proliferation, and COX inhibitors could not inhibit A549 cell growth directly.

Suppression of cyclooxygenase-2 overexpression by 15S-hydroxyeicosatrienoic acid in androgen-dependent prostatic adenocarcinoma cells

Emerging reports now implicate alterations of arachidonic acid (AA) metabolism with prostate carcinogenesis. To test this hypothesis, androgen-primed benign hyperplastic (BHC) and malignant tumorigenic (MTC) cells derived from the Lobund-Wistar rat model of autochthonous prostate adenocarcinoma were incubated with (14)C-AA. Our data using MTCs revealed enhanced dual metabolism of (14)C-AA via COX to generate increased PGE(2) and via 5-lipoxygenase (LOX) to generate increased 5S-HETE in tumorigenic cells. Western blot of MTCs revealed upregulation of COX-2 expression. This paralleled the increased biosynthesis of PGE(2). Since some polyunsaturated fatty acids have been reported to modulate AA metabolism and tumorigenesis, we primed the cells with either gamma-linolenic acid (GLA) or its in vivo metabolite, 15S-HETrE, prior to incubation with AA. Our data revealed suppression of COX-2 expression/PGE(2) biosynthesis. In parallel, priming cells with 15S-HETrE resulted in greater suppression of COX-2 expression/PGE(2) biosynthesis. These findings suggest that 15S-HETrE could function in vivo after dietary intake of GLA to suppress DHT-enhanced prostatic COX-2 expression/PGE(2) biosynthesis and, thus, alleviate tumor growth and progression.

Functional conversion between A-type and delayed rectifier K+ channels by membrane lipids

Voltage-gated potassium (Kv) channels control action potential repolarization, interspike membrane potential, and action potential frequency in excitable cells. It is thought that the combinatorial association between distinct alpha and beta subunits determines whether Kv channels function as non-inactivating delayed rectifiers or as rapidly inactivating A-type channels. We show that membrane lipids can convert A-type channels into delayed rectifiers and vice versa. Phosphoinositides remove N-type inactivation from A-type channels by immobilizing the inactivation domains. Conversely, arachidonic acid and its amide anandamide endow delayed rectifiers with rapid voltage-dependent inactivation. The bidirectional control of Kv channel gating by lipids may provide a mechanism for the dynamic regulation of electrical signaling in the nervous system.

Inhibition of formyl-methionyl-leucyl-phenylalanine-stimulated respiratory burst in human neutrophils by adrenaline: inhibition of Phospholipase A2 activity but not p47phox phosphorylation and translocation

The polymorphonuclear neutrophil (PMN)-respiratory burst plays a key role in host defense and inflammatory reactions. Modulation of this key neutrophil function by endogenous agents and the mechanisms involved are poorly understood. This study was designed to analyze the mechanisms involved in the effect of adrenaline on neutrophil superoxide anions production. Using the superoxide dismutase (SOD)-inhibitable cytochrome c reduction assay, we report here that the beta-adrenergic agonist, adrenaline at physiologic concentrations (5-100 nM) inhibited formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated but not phorbol-myristate-acetate (PMA)-stimulated PMN superoxide anion production. The inhibitory effect of adrenaline runs in parallel with an increase in intracellular levels of cAMP which was reversed by the protein kinase A (PKA) inhibitor H-89, suggesting a role for PKA in mediating the inhibitory effect of adrenaline on fMLP-induced superoxide production. Adrenaline at physiological concentrations did not inhibit the fMLP-stimulated membrane translocation of the NADPH oxidase components p47phox and p67phox, nor the fMLP-stimulated phosphorylation of p47phox. However, adrenaline strongly depressed the activity of the cytosolic isoform of Phospholipase A(2) (cPLA(2)). We suggest that adrenaline inhibits fMLP induced superoxide production upstream of the NADPH oxidase via a mechanism involving PKA and cPLA(2).

Mechanisms of free-radical induction in relation to fenretinide-induced apoptosis of neuroblastoma

The mechanisms of fenretinide-induced cell death of neuroblastoma cells are complex, involving signaling pathways mediated by free radicals or reactive oxygen species (ROS). The aim of this study was to identify mechanisms generating ROS and apoptosis of neuroblastoma cells in response to fenretinide. Fenretinide-induced ROS or apoptosis of SH-SY5Y or HTLA 230 neuroblastoma cells were not blocked by Nitro l-argenine methyl ester (l-NAME), an inhibitor of nitric oxide synthase. Flavoprotein-dependent superoxide-producing enzymes such as NADPH oxidase were also not involved in fenretinide-induced apoptosis or ROS generation. Similarly, ketoconazole, a cytochrome P450 inhibitor, and inhibitors of cyclooxygenase (COX) were also ineffective. In contrast, inhibition of phospholipase A(2) or lipoxygenases (LOX) blocked the induction of ROS and apoptosis in response to fenretinide. Using specific inhibitors of LOX, blocking 12-LOX but not 5- or 15-LOX inhibited both fenretinide-induced ROS and apoptosis. The effects of eicosatriynoic acid, a specific 12-LOX inhibitor, were reversed by the addition of the 12-LOX products, 12 (S)-hydroperoxyeicosatetraenoic acid and 12 (S)-hydroxyeicosatetraenoic acid. The targeting of 12-LOX in neuroblastoma cells may thus be a novel pathway for the development of drugs inducing apoptosis of neuroblastoma with improved tumor specificity.

Differential modulation of NMDA-induced calcium transients by arachidonic acid and nitric oxide in cultured hippocampal neurons

We have examined the effect of arachidonic acid on the transient increases in intracellular Ca2+ evoked by NMDA and AMPA in cultured hippocampal pyramidal cells loaded with Fura-2 AM. Repeated brief pulses of NMDA elicited Ca2+ transients that showed a modest run down. This run down was enhanced if the preparation was shielded from UV light and was reduced by conducting the experiments in the presence of the nitric oxide synthase inhibitor l-nitroarginine (100 micro m). Arachidonic acid (2 micro m) enhanced the Ca2+ transients evoked by NMDA but not those evoked by AMPA. Other C20 unsaturated fatty acids did not alter the time course of the response to NMDA. These experiments suggest that elevated intracellular Ca2+ activates nitric oxide synthase and the resulting synthesis of nitric oxide depresses the Ca2+ response to NMDA while arachidonic acid augments these responses. Therefore two substances implicated in synaptic plasticity (arachidonic acid and nitric oxide) differentially modulate NMDA-mediated Ca2+ entry into hippocampal neurons.

Contribution of 5-hydroxytryptamine1B receptors and 20-hydroxyeiscosatetraenoic acid to fall in cerebral blood flow after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

This study examined the interaction between 5-hydroxytryptamine1B (5-HT1B) receptors and 20-hydroxyeiscosatetraenoic acid (20-HETE) in contributing to the acute fall in regional cerebral blood flow (rCBF) after subarachnoid hemorrhage (SAH) in rats.

METHODS

The effects of intracisternal injection of 0.3 mL of arterial blood, artificial cerebrospinal fluid, and 5-HT on rCBF and the levels of 20-HETE and 5-HT in cerebrospinal fluid were measured in rats pretreated with vehicle, a 5-HT1B receptor antagonist (isamoltane hemifumarate), or an inhibitor of the synthesis of 20-HETE (HET0016). The effects of HET0016 and isamoltane on the vasoconstrictor response and changes in [Ca2+]i to 5-HT were also studied in middle cerebral arteries and vascular smooth muscle cells isolated from these vessels.

RESULTS

20-HETE and 5-HT levels in cerebrospinal fluid rose from 172+/-10 to 629+/-44 ng/mL and from 6+/-4 to 1163+/-200 nmol/mL, respectively, after SAH. rCBF fell by 30% 10 minutes after SAH, and it remained at this level for the next 2 hours. Blockade of 5-HT1B receptors prevented the sustained fall in rCBF seen after SAH. Intracisternal injection of 5-HT mimicked SAH by increasing 20-HETE levels in cerebrospinal fluid to 475+/-94 ng/mL and reducing rCBF by 30%. Blockade of the synthesis of 20-HETE with HET0016 prevented the fall in rCBF produced by 5-HT. Isamoltane and HET0016 reduced the vasoconstrictor response of isolated MCA to 5-HT by >60% and diminished the rise in [Ca2+]i produced by 5-HT in vascular smooth muscle cells isolated from these arteries.

CONCLUSIONS

These results suggest that the release of 5-HT after SAH activates 5-HT1B receptors and the synthesis of 20-HETE and that 20-HETE contributes to the acute fall in rCBF by potentiating the vasoconstrictor response of cerebral vessels to 5-HT.

Inhibitors of glycosphingolipid biosynthesis reduce transepithelial electrical resistance in MDCK I and FRT cells

Madin-Darby canine kidney (MDCK) I and Fisher rat thyroid (FRT) cells exhibit transepithelial electrical resistance (TER) values in excess of 5,000 Omega. cm(2). When these cells were incubated in the presence of various inhibitors of sphingolipid biosynthesis, a >5-fold reduction of TER was observed without changes in the gate function for uncharged solutes or the fence function for apically applied fluorescent lipids. The localization of ZO-1 and occludin was not altered between control and inhibitor-treated cells, indicating that the tight junction was still intact. Furthermore, the complexity of tight junction strands, analyzed by freeze-fracture microscopy, was not reduced. Once the inhibitor was removed and the cells were allowed to synthesize sphingolipids, a gradual recovery of the TER was observed. Interestingly, these inhibitors did not attenuate the TER of MDCK II cells, a cell line that typically exhibits values below 800 omega x cm(2.) These results suggest that glycosphingolipids play a role in regulating the electrical properties of epithelial cells.

Activation of peroxisome proliferator-activated receptor (PPAR)-gamma by 15S-hydroxyeicosatrienoic acid parallels growth suppression of androgen-dependent prostatic adenocarcinoma cells

Although dietary gamma-linolenic acid (GLA) and its 15-lipoxygenase metabolite, 15S-hydroxyeicosatrienoic acid (15S-HETrE), have been reported to exert antiproliferative activities in other systems, their role in prostatic carcinogenesis is unknown. To evolve a possible mechanism for the suppressive effect on growth of prostatic cells, we incubated GLA and 15S-HETrE with androgen-dependent prostatic adenocarcinoma cells. 15S-HETrE but not GLA markedly inhibited [(3)H]thymidine uptake in parallel with the upregulation of peroxisome proliferator-activated receptor-gamma expression (a growth modulating nuclear receptor). The data, taken together, suggest that dietary GLA via its in vivo metabolite 15S-HETrE could serve as an endogenous adjunct to attenuate prostatic tumorigenesis.

Effect of arachidonic and eicosapentaenoic acids on acute lung injury induced by hypochlorous acid

BACKGROUND

Hypochlorous acid (HOCl) is the main oxidant of activated polymorphonuclear neutrophil granulocytes (PMN) and generated by myeloperoxidase during respiratory burst. This study investigates the effects of HOCl on pulmonary artery pressure (PAP) and vascular permeability and characterises the influence of arachidonic acid (AA) and eicosapentaenoic acid (EPA) on the observed effects.

METHODS

HOCl (500, 1,000, 2,000 nmol/min) was continuously infused into the perfusate (Krebs-Henseleit buffer solution, KHB). AA or EPA in subthreshold doses (both 2 nmol/min) or buffer were simultaneously infused using a separate port. PAP, pulmonary venous pressure (PVP), ventilation pressure, and lung weight gain were continuously recorded. The capillary filtration coefficient (Kf,c) was calculated before and 30, 60, and 90 minutes after starting the HOCl infusion.

RESULTS

HOCl application resulted in a dose dependent increase in PAP and Kf,c. The onset of these changes was inversely related to the HOCl dose used. The combined infusion of AA with HOCl resulted in a significant additional rise in pressure and oedema formation which forced premature termination of all experiments. The combination of EPA with HOCl did not result in an enhancement of the HOCl induced rise in pressure and oedema formation.

CONCLUSIONS

Changes in the pulmonary microvasculature caused by HOCl are differently influenced by omega-6 and omega-3 polyunsaturated free fatty acids, suggesting a link between neutrophil derived oxidative stress and pulmonary eicosanoid metabolism.

Saturated triglycerides and fatty acids activate neutrophils depending on carbon chain-length

BACKGROUND

Unsaturated fatty acids are known as neutrophil activators. In the present study we investigated whether saturated triglycerides and fatty acids may also contribute to the previously observed activation of neutrophils by nutritional lipid emulsions. Furthermore we tested the hypothesis that carbon-chain length is of importance in this respect.

MATERIALS AND METHODS

Neutrophils (1 x 10(6) mL(-1)) were isolated from the blood of nine volunteers. Chemiluminescence was used to evaluate neutrophil activation, characterized by the production of oxygen radicals by neutrophils during incubation with 1 mmol L(-1) saturated fatty acid (6-20 carbon) or triglycerides (6-12 carbon fatty acid), dissolved in aqueous medium by preparing micelles with dipalmitoyl phosphatidylcholine (DPPC). Results were expressed as means +/- SEMs of the overall luminescence signal relative to the signal of cells incubated in medium.

RESULTS

Similar to a positive control, the polyunsaturated fatty acid arachidonic acid (C20 : 4), the triglycerides tricaproin (TC6 : 0), tricaprylin (TC8 : 0) and trilaurin (TC12 : 0) as well as the fatty acids lauric acid (C12 : 0), palmitic acid (C16 : 0), stearic acid (C18 : 0) and arachidic acid (C20 : 0) all induced oxygen radical production in neutrophils, while the medium-chain triglyceride tricaprin (TC10 : 0) and fatty acids caproic acid (C6 : 0), caprylic acid (C8 : 0) and capric acid (C10 : 0) exerted no clear effects, similar to negative controls (DPPC and glycerol).

CONCLUSIONS

Besides their (poly)-unsaturated counterparts, saturated triglycerides and fatty acids also activate neutrophils. Carbon chain-length is pivotal in the interaction of fatty acids and triglycerides and cells of the immune system.

Influence of dietary supplementation with long-chain n-3 or n-6 polyunsaturated fatty acids on blood inflammatory cell populations and functions and on plasma soluble adhesion molecules in healthy adults

Greatly increasing the amounts of flaxseed oil [rich in alpha-linolenic acid (ALNA)] or fish oil (FO); [rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] in the diet can decrease inflammatory cell functions and so might impair host defense. The objective of this study was to determine the effect of dietary supplementation with moderate levels of ALNA, gamma-linolenic acid (GLA), arachidonic acid (ARA), DHA, or FO on inflammatory cell numbers and functions and on circulating levels of soluble adhesion molecules. Healthy subjects aged 55 to 75 yr consumed nine capsules per day for 12 wk. The capsules contained placebo oil (an 80:20 mix of palm and sunflowerseed oils) or blends of placebo oil with oils rich in ALNA, GLA, ARA, or DHA or FO. Subjects in these groups consumed 2 g ALNA; approximately 700 mg GLA, ARA, or DHA; or 1 g EPA plus DHA (720 mg EPA + 280 mg DHA) daily from the capsules. Total fat intake from the capsules was 4 g per day. None of the treatments affected inflammatory cell numbers in the bloodstream; neutrophil and monocyte phagocytosis or respiratory burst in response to E. coli; production of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 in response to bacterial lipopolysaccharide; or plasma concentrations of soluble intercellular adhesion molecule-1. In contrast, the ALNA and FO treatments decreased the plasma concentrations of soluble vascular cell adhesion molecule-1 (16 and 28% decrease, respectively) and soluble E-selectin (23 and 17% decrease, respectively). It is concluded that, in contrast to previous reports using higher amounts of these fatty acids, a moderate increase in consumption of long-chain n-6 or n-3 polyunsaturated fatty acids does not significantly affect inflammatory cell numbers or neutrophil and monocyte responses in humans and so would not be expected to cause immune impairment. Furthermore, we conclude that moderate levels of ALNA and FO, which could be incorporated into the diet, can decrease some markers of endothelial activation and that this mechanism of action may contribute to the reported health benefits of n-3 fatty acids.

Effect of oral eicosapentaenoic acid on weight loss in patients with pancreatic cancer

Eicosapentaenoic acid (EPA) has been shown to modulate aspects of the inflammatory response that may contribute to weight loss in cancer. This study aimed to evaluate the acceptability and effects of oral supplementation with high-purity EPA in weight-losing patients with advanced pancreatic cancer. Twenty-six patients were entered into the study. EPA (95% pure) was administered as free acid starting at 1 g/day; the dose was increased to 6 g/day over four weeks, and then a maintenance dose of 6 g/day was administered. Patients were assessed before EPA and at 4, 8, and 12 weeks while receiving EPA, for weight, body composition, hematologic and clinical chemistry variables, acute-phase protein response, and performance status. Overall survival was noted. Supplementation was well tolerated, with only five patients experiencing side effects possibly attributable to the EPA. Before starting EPA, all patients had been losing weight at a median rate of 2 kg/mo. In general, after EPA supplementation, weight was stable. After four weeks of EPA supplementation, patients had a median weight gain of 0.5 kg (p = 0.0009 vs. rate of weight loss at baseline), and this stabilization of weight persisted over the 12-week study period. Total body water as a percentage of body weight remained stable, as did the proportion of patients with an acute-phase protein response, patients' nutritional intake, and performance status. Overall median survival from diagnosis in this study was 203 days. This study suggests that EPA is well tolerated, may stabilize weight in cachectic pancreatic cancer patients, and should be tested as an anticachectic agent in controlled trials.

Facilitation by arachidonic acid of acetylcholine release from the rat hippocampus

We investigated the effect of arachidonic acid (AA) on the release of [3H]acetylcholine ([3H]ACh) from the rat hippocampus. AA (3-30 microM) increased the basal tritium outflow and the field-electrically evoked release of [3H]ACh from hippocampal slices in a concentration-dependent manner. AA (30 microM) produced a 69+/-7% facilitation of the evoked and a 36+/-3% facilitation of basal tritium outflow. The effect of AA (30 microM) on the evoked tritium release was prevented by bovine serum albumin (BSA, 1%), which quenches AA, and was unaffected by the cyclooxygenase inhibitor, indomethacin (100 microM), and the lipooxygenase inhibitor, nordihydroguaiaretic acid (50 microM). Phospholipase A2 (PLA2, 2 U/ml), an enzyme that releases AA from the sn-2 position of phospholipids, mimicked the facilitatory effect of AA on the evoked tritium release (86+/-14% facilitation), an effect prevented by BSA (1%). The PLA2 activator, melittin (1 microM), enhanced the evoked tritium release by 98+/-11%, an effect prevented by the PLA2 inhibitor, arachidonyl trifluromethylketone (AACOCF3, 20 microM), and by BSA (1%). AA (30 microM), but not arachidic acid (30 microM), also facilitated (72+/-9%) the veratridine (10 microM)-evoked [3H]ACh release from superfused hippocampal synaptosomes, whereas PLA2 (2 U/ml) and melittin (1 microM) caused a lower facilitation (46+/-1% and 38+/-5%, respectively). The present results show that both exogenously added and endogenously produced AA increase the evoked release of [3H]ACh from rat hippocampal nerve terminals. Since muscarinic activation triggers AA production and we now observed that AA enhances ACh release, it is proposed that AA may act as a facilitatory retrograde messenger in hippocampal cholinergic muscarinic transmission as it has been proposed to act in glutamatergic transmission.

Calcium entry in Trypanosoma brucei is regulated by phospholipase A2 and arachidonic acid

In contrast with mammalian cells, little is known about the control of Ca2+ entry into primitive protozoans. Here we report that Ca2+ influx in pathogenic Trypanosoma brucei can be regulated by phospholipase A2 (PLA2) and the subsequent release of arachidonic acid (AA). Several PLA2 inhibitors blocked Ca2+ entry; 3-(4-octadecyl)-benzoylacrylic acid (OBAA; IC50 0.4+/-0.1 microM) was the most potent. We identified in live trypanosomes PLA2 activity that was sensitive to OBAA and could be stimulated by Ca2+, suggesting the presence of positive feedback control. The cell-associated PLA2 activity was able to release [14C]AA from labelled phospholipid substrates. Exogenous AA (5-50 microM) also initiated Ca2+ entry in a manner that was inhibited by the Ca2+ antagonist La3+ (100 microM). Ca2+ entry did not depend on AA metabolism or protein kinase activation. The cell response was specific for AA, and fatty acids with greater saturation than tetraeicosanoic acid (AA) or with chain lengths less than C20 exhibited greatly diminished ability to initiate Ca2+ influx. Myristate and palmitate inhibited PLA2 activity and also inhibited Ca2+ influx. Overall, these results demonstrate that Ca2+ entry into T. brucei can result from phospholipid hydrolysis and the release of eicosanoic acids.

Epoxygenase metabolites of arachidonic acid affect electrophysiologic properties of rat tracheal epithelial cells1

Epoxyeicosatrienoic acids (EETs) and dihydroxyeicosatrienoic acids, products of the cytochrome P450 arachidonic acid epoxygenase pathway, have been shown to affect electrolyte transport in the kidney; however, the effects of these compounds on airway epithelial ion transport have not been investigated. Intact rat tracheas and primary cultures of rat tracheal epithelial cells were mounted in Ussing chambers to monitor changes in transepithelial voltage (Vt), short circuit current (Isc) and electrical resistance (Rt), with or without the addition of increasing concentrations (10(-9)-10(-6) M) of arachidonic acid, each of the four regioisomeric EETs and each of the corresponding dihydroxyeicosatrienoic acids. In intact tracheas, 11,12-EET caused dose-dependent decreases in Vt and Isc (DeltaVt = 0. 4 +/- 0.1 mV, DeltaIsc = -16.9 +/- 5.4 microA/cm2 at 10(-6) M, P < . 05 vs. vehicle), whereas changes in Rt were not significantly different than vehicle alone. 11,12-dihydroxyeicosatrienoic acid caused less impressive decreases in Vt and Isc, although arachidonic acid and the other compounds tested were without significant effects. 11,12-EET induced similar changes in cultured tracheal epithelial cell electrical parameters at concentrations as low as 10(-9) M. The effects of 11,12-EET were highly stereoselective, with activity limited to 11(R),12(S)-EET, the least abundant rat lung enantiomer. Pretreatment with amiloride or mucosal exposure to sodium free media did not significantly alter the 11,12-EET-induced changes in Vt. In contrast, pretreatment with bumetanide abolished the 11,12-EET electrophysiologic effects, suggesting that these effects may be mediated through inhibition of a chloride conductive pathway. We conclude that arachidonic acid epoxygenase metabolites cause significant changes in rat airway electrical parameters and may be involved in the control of lung fluid and electrolyte transport.

[Effect of docanol on the status of hemostasis and fibrinolysis systems, as well as lipid spectrum in patients with ischemic heart disease depending on the initial level of fibrinolytic activity]

Forty patients with coronary heart disease (CHD) concurrent with hyperlipidemia were divided into 2 groups according to the baseline fibrinolytic activity. The group with the depressed fibrinolytic system displayed the highest atherogenicity index and levels of cholesterol, low and very low density lipoprotein cholesterol and half levels of high density lipoproteins. After 45-day ingestion of docanol, a new Russian food additive containing docosahexanoic and eicosapentaenoic acids there were positive changes in the lipid spectrum in the both groups. The fibrinolytic changes were heterodirectional: activator and plasma activities increased in the group of fibrinolytic depression while in the group of baseline normal fibrinolysis the activity of plasminogen activator fell.

5-Oxo-eicosanoids are potent eosinophil chemotactic factors. Functional characterization and structural requirements

Human eosinophils produce upon treatment with 5-oxo-eicosatetraenoic acid or (5S,15S)-dihydroxyeicosatetraenoic acid a potent eosinophil-chemotactic eicosanoid, 5-oxo-15-hydroxy-(6E,8Z,11Z,13E)-eicosatetraenoi c acid (5-oxo-15-HETE). 5-Oxo-15-HETE induces human eosinophil (Eo) chemotaxis at nanomolar concentrations with an efficacy in vitro comparable to that seen for platelet activating factor. Comparison of Eo chemotactic activities of several structurally related eicosanoids with different substituents and/or double bound geometry led to the conclusion that maximal potency and efficacy of eosinophil-chemotactic and chemokinetic activity is present in 5-oxo-(6E,8Z,11Z,14Z)-eicosatetraenoic acid (5-oxo-ETE). The presence of a hydroxyl group at position C-15 is not necessary for potent chemotactic activity, whereas a geometric isomer having trans instead of cis double bond at C-atom 8, as well as esterified 5-oxo-ETE usually show a 5-10-fold lower potency. 5-Oxo-eicosanoids elicit a dose-dependent transient rise of intracellular Ca2+ levels in human Eos, however, in contrast to some other Eo chemotaxins do not induce degranulation. Cross-desensitization of Ca2+ mobilization and Eo chemotaxis revealed that the geometric isomers of 5-oxo-eicosanoids, 5(S)-HETE, and (5S,15S)-di-HETE cross-deactivate Eo responses to each other, whereas other, unrelated stimuli did not interfere with these lipids indicating that 5-oxo-eicosanoids activate Eos via a separate receptor.

Effects of fatty acids on proliferation and activation of human synovial compartment lymphocytes

The object of this study was to determine the effects of eicosanoid precursor fatty acids on activation and proliferation of T lymphocytes from synovial fluid and synovial tissue of rheumatoid arthritis patients. Proliferation was determined by direct cell counts; phenotypic characterization of surfaces molecules was by cytofluorometric analysis. Dihomogammalinolenic acid, arachidonic acid, and eicosapentaenoic acid suppressed proliferation of interleukin-2-dependent lymphocytes by as much as 80%; cell viability was not altered by fatty acids. Administration of particular fatty acids may prove to be a useful therapeutic intervention in rheumatoid arthritis patients because of their ability to suppress activation and proliferation of synovial compartment T lymphocytes.

Fungal metabolites. Part 14. Novel potent immunosuppressants, mycestericins, produced by Mycelia sterilia

Mycestericins A, B, C, D and E were isolated from the culture broth of Mycelia sterilia ATCC 20349 along with thermozymocidin (= myriocin). Their structures were elucidated on the basis of spectroscopic studies and chemical evidence. The acetate of mycestericin C was identical with the acetate of 6,7-dihydromyriocin. Mycestericins suppressed the proliferation of lymphocytes in the mouse allogeneic mixed lymphocyte reaction, with a potency similar to that of myriocin.

Modulation by fatty acids of Ca2+ fluxes in sarcoplasmic-reticulum vesicles

The fatty acids palmitic (C16:0), stearic (C18:0), arachidic (C20:0) and arachidonic (C20:4) acids inhibit Ca2+ uptake and enhance Ca2+ efflux measured in vesicles derived from the sarcoplasmic reticulum of skeletal muscle. These effects of the fatty acids are impaired by the Ca(2+)-ATPase ligands Mg2+, Ca2+ and K+, and by drugs that block the leakage of Ca2+ through the Ca(2+)-ATPase such as Ruthenium Red, spermine [de Meis (1991) J. Biol. Chem. 266, 5736-5742] and thapsigargin [de Meis and Inesi (1992) FEBS Lett. 299, 33-35].

Eicosapolyynoic acids, inhibitors of lipoxygenases, weaken the short-term plasticity of cholinoreceptors of neurons of the edible snail

The influence of three polyacetylenic analogs of natural polyenoic acids which are inhibitors of their lipoxygenase oxidation on the dynamics of the extinction of the inward current induced by repeated iontophoretic applications of acetylcholine to the soma was investigated in identified RPa3 and LPa3 of the edible snail using the method of bielectrode recording of the potential on the membrane. It was found that eicosa-5,8,11,14-tetraynoic acid (30-60 mumole/liter) and eicosa-5,8,11,14,17-pentaynoic acid (4-50 mumole/liter) decrease the amplitude of the inward current induced by application of acetylcholine, and attenuate its extinction during repeated applications. The third analog, eicosa-8,11,14-triaynoic acid, does not exert a modulating influence on the magnitude of the current and its extinction. It was hypothesized that the lipoxygenase metabolites of the polyenoic acids regulate the plasticity of the cholinoreceptors of the neurons of the edible snail. Taking the nonidentical inhibition by the compounds used of the various lipoxygenases into account, the participation in the plasticity of the cholinoreceptors of those eicosanoids which are formed from arachidonic acid under the influence of 5-lipoxygenases is most probable. At the same time, a regulatory role of the eicosanoids formed under the influence of other lipoxygenases is not excluded.

The biosynthesis of polyunsaturated fatty acids by rat sertoli cells

1. The biosynthesis of polyunsaturated fatty acids (PUFA) of the n-6 and n-3 series was investigated in cultured Sertoli cells. 18:2n-6, 18:3n-6, 20:2n-6, 18:3n-3 and 20:3n-3 were added individually at a concentration of 20 mumol to culture media. 2. Maximum incorporation of 20- and 22-carbon PUFA into membrane lipids was observed after 72 hr of incubation with all the exogenous substrates used. 3. As reported in other cell systems, the delta 6 desaturation was the first rate-limiting step; the major factor regulating this activity was the concentration of linoleic acid or alpha-linolenic acid in the medium. 4. Our data show that the delta 5-desaturation represents a second regulatory step in PUFA biosynthesis. 5. The sum of n-6 and n-3 PUFA of the 22 carbon chain length constantly represented between 11 and 12% of total fatty acids, regardless of the exogenous substrate used. 6. Our kinetic studies of the incorporation of PUFA of the n-6 and n-3 series did not permit detection of a delta 8 desaturase activity.

Inhibition of protein synthesis in intact mammalian cells by arachidonic acid

Optimal translation initiation in intact mammalian cells requires sequestered intracellular Ca2+. Arachidonic acid, which releases sequestered Ca2+ from cells and isolated organelles, was studied to assess its potential role in the regulation of protein synthesis via Ca2+ mobilization. Unsaturated fatty acids at microM concentrations inhibited protein synthesis in intact GH2 pituitary, C6 glial tumour and HeLa cells in a manner dependent on degree of unsaturation and cell number. Arachidonate was generally the most, and the fully saturated arachidic acid the least, potent of the fatty acids tested. At 2 x 10(6) GH3 cells/ml, amino incorporation into a broad spectrum of polypeptides was inhibited by 80-90% by 10-20 microM fatty acid. Inhibition was maximal at 4-8 min and was attenuated by 1-2 h and more pronounced at lower pH. Protein synthesis was maximally inhibited when arachidonate mobilized approx. 40% of cell-associated Ca2+. At lower concentrations (10 microM) arachidonate suppressed translational initiation, with the inhibition being reversed as extracellular Ca2+ concentrations were increased to supraphysiological values. At higher concentrations (20 microM) arachidonate inhibited peptide-chain elongation in a Ca(2+)-independent manner. Arachidonate also blocked elongation in reticulocyte lysates. The effects of arachidonate in intact cells were reversible with time via its metabolism or by washes containing BSA. Sufficient arachidonate appears to be synthesized during ischaemic stress to inhibit translation by either mechanism.

Substitution by fatty acids for phosphatidylserine in a reconstitution of phorbol ester binding to protein kinase C

1. Fatty acids can be substituted or phosphatidylserine in a reconstitution of phorbol ester binding to protein kinase C. 2. Phorbol ester, however, does not seem to be effectively utilized for the activation of the enzyme. 3. It is suggested that fatty acids play a role on the activation of protein kinase C in the abnormal conditions such as ischemia, while the phospholipid-dependent activation has a physiological significance in normal conditions.

Pharmacological characterization of mediators and vagal influence in the acute allergic bronchoconstriction in guinea pigs

The allergic bronchoconstriction in guinea pigs has been attributed mainly to the release of mast cell mediators. Histamine has been involved in the first minutes of the anaphylactic reaction and new-formed compounds in the subsequent response. In this asthma model the vagal influence has been sparsely investigated. In the present work we evaluated the pharmacological modification of the acute allergic bronchoconstrictor response in guinea pigs sensitized to ovalbumin through aerosol exposure. Pyrilamine (20 micrograms/kg), diethylcarbamazine (a lipoxygenase inhibitor, 10 mg/kg) and dexamethasone (4 mg/kg) each reduced the antigen-induced bronchoconstriction throughout the 30 min studied. Indomethacin (3.1 mg/kg) did not modify the response to the antigen. Atropine (2 mg/kg) plus bilateral vagotomy also diminished this response from 5 min onward. On the other hand, from 5 min ahead pyrilamine-resistant bronchoconstriction was partially inhibited by dexamethasone, and it was almost completely blocked during all of the response when atropine plus bilateral vagotomy were added to dexamethasone. Dipyridamole (an inhibitor of the adenosine uptake, 0.4 mg/kg) enhanced the bronchoconstriction, though this was significant only in the 2-5 min time-interval of the response. These results suggest that histamine and vagal influence play an important role in the whole response to antigen, that other mediators, probably leukotrienes, participate in this response from 5 min onward, and that adenosine could exert a potentiation effect on this response.

Clinical studies on the effects of n-3 fatty acids on cells and eicosanoids in the cardiovascular system

Epidemiological, clinical and experimental studies suggest that dietary fatty acids belonging to two different families, the n-6 and n-3 fatty acids, might be important nutritional factors contributing to the natural history of atherothrombotic and inflammatory disorders. The relationship of these dietary fatty acids to plasma and cell membrane phospholipid composition, the eicosanoid system and related lipid mediators, and the mechanisms involved in cell stimulus-response coupling (such as phospholipase C and phospholipase A2 activation and Ca2+ release) might reveal and modify processes underlying those disorders. It may thus open the development of new approaches to prevention and therapy.

Suppression of acute and chronic inflammation by dietary gamma linolenic acid

We examined the effect of diets enriched in gamma linolenic acid (GLA) on acute inflammation induced by monosodium urate crystals, and on subacute and chronic inflammation induced by complete Freund's adjuvant in the rat subcutaneous air pouch and in rats with adjuvant induced arthritis. Diets were enriched (15% fat) with borage seed oil (23% GLA) or safflower oil (less than 1% GLA). Diets enriched with GLA suppressed inflammation markedly in all models, whereas the safflower oil diet did not influence the inflammatory response. The degree of inflammation was quantified by measuring pouch exudate cell concentration, lysosomal enzyme activity, volume, protein concentration and prostaglandin E2 and leukotriene B4 concentrations. In the chronic air pouch model, the pouch lining was thickened, invaded by mononuclear cells and exhibited proliferation of lining cells 14 days after adjuvant injection. The lesion was far less severe and usual pouch lining architecture was maintained in animals given dietary GLA. Livers of rats fed borage seed oil were enriched in GLA and dihomo gamma linolenic acid (DGLA), and the DGLA/arachidonate ratio was increased 5-fold compared with animals fed safflower oil. Enrichment of diet with plant seed oils rich in GLA may provide a way to alter generation of prostaglandins and leukotrienes and to influence acute and chronic inflammatory responses.

Macrophages rapidly internalize their tumor necrosis factor receptors in response to bacterial lipopolysaccharide

The effect of bacterial lipopolysaccharide (LPS) on macrophage receptors for tumor necrosis factor/cachectin (TNF-R) was studied. At equilibrium, iodinated recombinant human TNF alpha (rTNF alpha) bound to 1100 +/- 200 sites/cell on macrophage-like RAW 264.7 cells with a Kd of 1.3 +/- 0.1 x 10(-9) M. Preexposure of RAW 264.7 cells to 10 ng/ml LPS for 1 h at 37 degrees C resulted in complete loss of cell surface TNF alpha binding sites. 50% loss ensued after 1 h with 0.6 ng/ml LPS, or after 15 min with 10 ng/ml LPS. Complete loss of TNF alpha binding sites occurred without change in numbers of complement receptor type 3. No decrease in TNF-R followed preexposure to LPS at 4 degrees C, nor could LPS displace 125I-rTNF alpha from its binding sites. Although TNF-R disappeared from the surface of intact macrophages following exposure to LPS, specific TNF alpha binding sites were unchanged in permeabilized macrophages, indicating that TNF-R were rapidly internalized. Conditioned media from LPS-treated RAW 264.7 cells induced 30% down-regulation of TNF-R on macrophages from LPS-hyporesponsive mice (C3H/HeJ), suggesting that a soluble macrophage product may be responsible for a minor portion of the LPS effect. Additional evidence against endogenous TNF alpha being the major cause of TNF-R internalization was the rapid onset of the effect of LPS on TNF-R compared to the reported onset of TNF alpha production, the relatively high concentrations of exogenous rTNF alpha required to mimic the effect of LPS, and the inability of TNF alpha-neutralizing antibody to block the effect of LPS. LPS-induced down-regulation of TNF-R was complete or nearly complete not only in RAW 264.7 cells, but also in primary macrophages of both human and murine origin, was less marked in human endothelial cells, and was absent in human granulocytes and melanoma cells and mouse L929 cells. Thus, in situ, macrophages and some other host cells may be resistant to the actions of TNF alpha produced during endotoxinemia, because such cells may internalize their TNF-R in response to LPS before TNF alpha is produced.

Eicosanoids are regulatory molecules in gamma-interferon-induced endothelial antigenicity and adherence for leucocytes

When the endothelial cells (ECs) were stimulated with gamma-interferon (gIFN) in the presence of methylprednisolone (MP) or prostaglandin E2 (PGE2), MP enhanced gIFN-induced Ia antigen expression, whereas PGE2 inhibited it. On the other hand, while PGE2 had no effect on leucocyte binding to ECs, MP entirely inhibited it. By using selective inhibitors of the cyclo-oxygenase pathway (indomethacin, IM) and the 5-lipoxygenase pathway (L651.392), we found that addition of IM to gIFN-stimulated ECs enhanced Ia expression but had no effect on leucocyte adherence to ECs. Instead, addition of L651.392 to gIFN-stimulated ECs partially reduced leucocyte adherence to ECs but had no effect on Ia expression. Pretreatment of the ECs or leucocytes or both with monoclonal anti-class II antibody, had no effect on gIFN-induced leucocyte binding to ECs. These findings suggest that gIFN-induced endothelial cell antigenicity and leucocyte adherence are regulated independently of each other by different molecular pathways. Moreover, arachidonic acid metabolites appear to be the regulatory molecules in gIFN effects on the ECs.

Inhibition of eicosanoid-mediated coronary constriction during myocardial ischemia

Thromboxane A2 and cysteinyl leukotrienes are highly effective microvessel constrictors in normally perfused myocardium. Their release during acute coronary thrombosis might augment myocardial underperfusion. The constrictor action of these substances could be modified substantially, however, by concomitant myocardial ischemia. We compared the effects of the two eicosanoid constrictors in normally perfused and ischemic myocardium of 24 open-chest, pentobarbital-anesthetized pigs. Left anterior descending coronary flow was measured after intracoronary bolus injections of the stable thromboxane A2 analog U46619 (1-10 micrograms) or leukotriene D4 (LTD4, 1-10 micrograms). Each dose was given before and during myocardial ischemia induced by a snare adjusted to produce 63 +/- 2% decrease in coronary flow for 10 min. Marked dose-independent inhibition of eicosanoid-induced coronary flow decrease occurred during ischemia. With 10 micrograms U46619, coronary flow decrease in the unoccluded state (25 +/- 2 from 55 +/- 4 ml/min pretreatment baseline) was virtually eliminated during snare occlusion (1 +/- 1 from 21 +/- 3 ml/min pretreatment baseline, P less than 0.001). Similar results occurred with LTD4. Distal coronary pressure during ischemia indicated a lack of microvessel responsiveness to the eicosanoids rather than a buffering of resistance change by the snare. U46619 and LTD4 did induce transient, small reductions in regional shortening fraction during ischemia. Our data suggest that eicosanoid-induced constriction of myocardial resistance vessels is not a likely complication of acute coronary thrombosis. However, eicosanoids could depress residual contractility in moderately ischemic regions.

Regulation of the proliferation of primary rat hepatocytes by eicosanoids

DNA synthesis in primary adult rat hepatocyte cultures was promoted by epidermal growth factor (EGF), arachidonic acid, and prostaglandins E2 and F2 alpha (PGE2 and PGF2 alpha). Growth promotion by EGF was blocked by 0.1 mM indomethacin and 1 mM aspirin, without affecting cell viability. If verapamil was present in the medium when EGF was added, the growth response was inhibited. Hepatocytes stimulated by EGF or arachidonic acid released PGE2 and PGF2 alpha into the culture medium. This was diminished if 0.1 mM indomethacin was also in the medium. The importance of autocrine regulation of hepatocyte growth by prostaglandins is discussed.

The role of eicosanoids in paediatrics

Prostanoids are unsaturated cyclic fatty acids, are synthesized primarily from arachidonic acid, and, like the leukotrienes, belong to the growing family of eicosanoids. As tissue hormones, prostanoids act on specific receptors near their site of synthesis and degradation. Prostanoids operate as modulators and mediators in a large spectrum of physiological processes. They are involved in the regulation of maternal and fetal circulation, patency of the ductus arteriosus, platelet-vessel wall interaction and kidney function. Besides their physiological function in protecting organ perfusion under stress conditions, they are also involved in diseases as described in the hyperprostaglandin E2-syndrome or--together with leukotrienes--in inflammatory processes. More specific pharmacological tools than the nonsteroidal antiinflammatory drugs, such as receptor antagonists, selective synthesis inhibitors, and eicosanoid analogues offer the prospect of enriching our arsenal of pharmacotherapeutic interventions in a variety of diseases. Before active intervention, however, more and specific biochemical analyses are required to identify the pathophysiological role of eicosanoid.

Hormone studies in Myxine glutinosa: effects of the eicosanoids arachidonic acid, prostaglandin E1, E2, A2, F2 alpha, thromboxane B2 and of indomethacin on plasma cortisol, blood pressure, urine flow and electrolyte balance

Hagfish, Myxine glutinosa, were used in an investigation of the possible effects of various eicosanoids and the prostaglandin synthetase inhibitor indomethacin, on cortisol production, blood pressure control, urine flow and electrolyte balance. Cortisol levels in plasma of untreated control animals and plasma from animals 1 h following injection of 50 micrograms kg-1 prostaglandin E1, E2, A2, F2 alpha TXB2 and indomethacin were not detectable. However, plasma cortisol levels rose to between 10 and 26 pg ml-1 1 h following injection of either 50 micrograms kg-1 arachidonic acid or prostaglandin E2. This rise was similar in magnitude to that produced 1 h following administration of 50 micrograms kg-1 porcine ACTH. The resting dorsal aortic blood pressure of between 3.50 and 3.75 mmHg was reduced on average by 50% for 12-15 min when animals received 10 micrograms kg-1 arachidonic acid, prostaglandin E1, E2, A2, and TXB2 and was effectively reduced to zero for 20 min or more following 50 micrograms kg-1 of these eicosanoids. Similar doses of prostaglandin F2 alpha, however, evoked an increase in blood pressure (19-33%) whilst indomethacin was without effect. Control measurements of urine flow in Myxine were estimated to be between 540 and 660 microliters h-1 kg-1. There was a marked reduction in urine output following the arterial vasodepression induced by arachidonic acid, prostaglandin E1, E2, A2 and TXB2 in doses of 10 micrograms kg-1, an effect which became even more pronounced following injection of 50 micrograms kg-1 quantities, leading in some cases to complete anuria.(ABSTRACT TRUNCATED AT 250 WORDS)

Protamine reversal of anticoagulation achieved with a low molecular weight heparin. The effects on eicosanoids, clotting and complement factors

Hemodynamic and hematologic effects of protamine reversal of low molecular weight heparin (LMWH) anticoagulation with and without protamine pretreatment, as well as reversal of anticoagulation with unfractionated standard heparin (SH), were studied in canine subjects. Protamine reversal caused less severe thrombocytopenia in the two LMWH groups compared to SH animals, while neutropenia occurred equally in all groups. Cl-esterase inhibitor levels were minimally increased, whereas C3 levels and leucotriene levels were unaltered. TxB2 and 6-keto-PGF1 alpha increased during protamine reversal of LMWH anticoagulation. TCT and APTT were affected less with LMWH than SH anticoagulation. Anti-Xa levels increased with anticoagulation in all animals, but protamine did not reverse the elevated anti-Xa levels in LMWH anticoagulated dogs to the same degree as occurred with SH anticoagulation. TCT, APTT and bleeding times were normalized by protamine in all animals. Protamine reversal of LMWH anticoagulation with or without protamine pretreatment did not reveal any clear differences in eicosanoids or complement factors compared to SH anticoagulation, although differences in anti-Xa activity clearly separated these two heparins.

Site of the action of a synthetic atrial natriuretic peptide evaluated in humans

The renal site of the natriuretic effect of human, atrial natriuretic peptide (hANP) was studied using clearance techniques in eight salt-loaded normal volunteers undergoing maximal water diuresis. Lithium was used as a marker of proximal sodium reabsorption. According to a two-way, single blind, crossover design, hANP (Met12-(3-28)-eicosahexapeptide, (2 micrograms/min) or its vehicle (Ve) were infused for two hours, followed by a two-hour recovery period. Blood pressure, heart rate and insulin clearance remained unchanged. During hANP infusion, the filtration fraction increased slightly from 19.6 to 24.3% (P less than 0.001), fractional water excretion rose transiently at the beginning of the infusion. Fractional excretion of sodium increased markedly from 2.2% to 7.4% (P less than 0.001) but remained unchanged with Ve. ANP increased fractional excretion of lithium slightly from 46 to 58% (P less than 0.01), while it remained stable at 47% during Ve. The distal tubular rejection fraction of sodium calculated from sodium and lithium clearances rose markedly from 4.7 to 13% (P less than 0.001) and returned to 6.2% at the end of the recovery period. Thus, under salt loading and water diuresis conditions, hANP infusion did not alter GFR, but reduced proximal reabsorption of sodium, and markedly enhanced the fraction of sodium escaping distal tubular reabsorption, suggesting that hANP-induced natriuresis is due, for an important part, to inhibition of sodium reabsorption in the distal nephron.

Injury to rat hearts produced by an exogenous free radical generating system. Study into the role of arachidonic acid and eicosanoids

This study was designed to evaluate the effect of an exogenous free radical generating system consisting of purine plus xanthine oxidase on the isolated rat heart and in particular to assess the possible contribution of arachidonic acid or its metabolites to toxicity produced by this drug combination. Purine plus xanthine oxidase produced a time-dependent depression in cardiac contractility which was associated with stimulated release of lactate dehydrogenase (LDH). Electron microscopic analysis revealed a distinct separation of the glycocalyx from the sarcolemmal membrane with no apparent intracellular defects. Purine plus xanthine oxidase was a potent stimulus for 6-keto-prostaglandin F1 alpha (6K-PGF1 alpha) synthesis but leukotriene production was undetectable under any condition. Eicosatetraynoic acid, which totally prevents the metabolism of arachidonic acid, accelerated the loss in force and increased LDH release invoked by purine plus xanthine oxidase, but produced no noticeable change in sarcolemmal ultrastructure. Cyclooxygenase inhibitors produced little influence although pretreatment with either acetylsalicylic acid or ibuprofen decreased contractility toward the end of purine plus xanthine oxidase perfusion. Nordihydroguarietic acid, a purported inhibitor of 5'-lipoxygenase accelerated the loss in force produced by purine plus xanthine oxidase. The nordihydroguarietic acid effects were associated with reduced 6K-PGF1 alpha efflux but LDH release was unaffected. We also examined whether modification of arachidonic acid release through changes in calcium concentration was associated with altered response to purine plus xanthine oxidase. Lowering the calcium concentration to 0.41 mM (from 1.25 mM control) reduced markedly 6K-PGF1 alpha, efflux as well as LDH release. Although the latter is suggestive of protection, hypocalcemic perfusion resulted in a greater loss in force due to free radical generation. Furthermore, cells from these hearts exhibited a greater degree of glycocalyx separation. Increasing the calcium concentration to 2.50 mM produced no further toxic manifestations in the response to purine plus xanthine oxidase, although the release of 6K-PGF1 alpha was increased. Our results suggest complex toxicity induced by an exogenously generated free radical system. The injury produced by this method is restricted to sarcolemmal changes, the latter being dependent on the external calcium concentration. The study further suggests that accumulation of intracellular unesterified arachidonic acid, which may result from peroxidation of membrane lipids, increases tissue injury caused by exogenous free radicals.

Altered fatty acid membrane composition modifies lymphocyte localization in vivo

In the present paper, we report the results of a study on the in vivo localization of 51Cr-labeled lymphocytes with an altered lipid bilayer. In vitro treatment of lymphocytes with fatty acids (arachidic and linolenic acids) modifies the relative composition of plasma membrane fatty acids. Phospholipids of the plasma membrane of lymphocytes incubated with arachidic acid show a preferential increase of fatty acids with chain length between C:12 and C:16. Cells incubated with linolenic acid show an increase percentage of fatty acids C:16 to C:20 and the relative amount of the fatty acids with chain length superior to C:20 is higher in cells treated with linolenic than with arachidic acid. We have found that these alterations in plasma membrane fatty acid composition can modify the normal pattern of lymphocyte localization in vivo after iv transfer into syngeneic hosts. The possible role of factors such as cell to cell adhesion and/or fluidity of plasma membranes in the control of lymphocyte migration are discussed.

Proton/hydroxide conductance through phospholipid bilayer membranes: effects of phytanic acid

Mechanisms of proton/hydroxide conductance (GH/OH) were investigated in planar (Mueller-Rudin) bilayer membranes made from decane solutions of phospholipids or phospholipids plus phytanic acid (a 20-carbon, branched chain fatty acid). At neutral pH, membranes made from diphytanoylphosphatidylcholine or bacterial phosphatidylethanolamine had GH/OH values in the range of (2-5) X 10(-9) S X cm-2, corresponding to H+/OH- 'net' permeabilities of about (0.4-1.0) X 10(-5) cm X s-1. GH/OH was inhibited by serum albumin, phloretin, glycerol and low pH, but was increased by chlorodecane and voltage greater than 80 mV. Water permeability and GH/OH were not correlated, suggesting that water and H+/OH- cross the membrane by separate pathways. Addition of phytanic acid to the phospholipids caused an increase in GH/OH which was proportional to the first power of the phytanic acid concentration. In membranes containing phytanic acid, GH/OH was inhibited by albumin, phloretin, glycerol and low pH, but was increased by chlorodecane and voltages greater than 80 mV. The results suggest that phytanic acid acts as a simple (A- type) proton carrier. The qualitative similarities between the behavior of GH/OH in unmodified and phytanic-acid containing membranes suggest that phospholipids may contain weakly acidic contaminants which cause most of GH/OH at pH greater than 4. However, there is also a significant background (pH independent) GH/OH which may be due to hydrogen-bonded water chains. The ability of phytanic acid to act as a proton carrier may help to explain the toxicity of phytanic acid in Refsum's disease, a metabolic disorder in which phytanic acid accumulates to high levels in plasma, cells and tissues.

Cholinergic and non-cholinergic components of the inotropism evoked by electric field stimulation in the isolated rat urinary bladder. Influence of some eicosanoids

The present study explores whether some arachidonic acid (AA) metabolites formed via cyclo-oxygenase or lipoxygenase pathways influence the inotropism of isolated rat urinary bladders evoked by electric field stimulation (EFS), both in presence of or in absence of atropine. The EFS consisted in square wave pulses of 5 Hz, 5 msec duration and supramaximal voltage, applied every 3 min for a period of 10 sec. Acetylsalicylic acid (ASA) at 10(-4) M, decreased around 30% the magnitude of inotropic responses to EFS and prostaglandin E2 (PGE2, partially at 10(-9) M and fully at 10(-8) M), restored control inotropic levels. PGI2 was also active but only at 10(-7) M; whereas PGF2 alpha, at all concentrations tested (10(-9)-10(-7) M), failed to counteract the diminishing effect of ASA. Moreover, dose-response curves for added acetylcholine (ACh) were not modified by ASA. On the other hand, in presence of atropine (10(-5) M), a diminution of around 40% in the magnitude of control responses to EFS, was detected and when ASA (10(-4) M) was added to atropine-exposed preparations, the atropine resistant component of the EFS-evoked inotropism, was reduced around 30%. Although recovering effects of added PGs were again observed, they were not identical to those observed in absence of atropine. Indeed, PGE2 fully restored the magnitude of contractile responses but it did so only at concentrations 10 times higher than without the cholinergic receptor blocker. On the other hand, PGI2 as well as PGF2 alpha, even at 10(-7) M, were devoid of significant influence. In determining whether lipoxygenase products of AA were also able to modulate the EFS-evoked inotropism, tissue preparations were incubated with nordihydroguaiaretic acid (NDGA), an inhibitor of lipoxygenases, and tested for contractile responses to electric stimulation. NDGA (10(-7) M), failed to alter rat urinary bladder inotropic response to EFS, both in presence of or in absence of atropine. Results suggest that the cholinergic, as well as the non-cholinergic components of the EFS-evoked contractions in isolated rat urinary bladders, are modulated by some cyclo-oxygenase formed AA metabolites, particularly certain PGs, like PGE2.

Myoblast fusion is regulated by a prostanoid of the one series independently of a rise in cyclic AMP

The role of prostanoids in the regulation of chick myoblast differentiation has been investigated. At 3 X 10(-6) M, indomethacin and chloroquine specifically inhibit cell fusion. They do not affect cell proliferation, alignment, or the expression of two muscle-specific proteins, namely, the acetylcholine receptor and the muscle-specific form of creatine phosphokinase. The results demonstrate that it is indomethacin's activity as an inhibitor of prostaglandin synthesis at the cyclooxygenase step that causes the block of cell fusion, whereas chloroquine probably acts at the earlier step of phospholipase A. Prostaglandin E1 (PGE1), but not prostaglandin E2 (PGE2), rapidly reverses the inhibition of fusion imposed by indomethacin or chloroquine. The dose response of the myoblasts to PGE1 is a bell-shaped curve with a 100% reversal of fusion at approximately 10(-9) M. Eicosatrienoate and linoleate reverse the inhibition of fusion with similar kinetics, whereas arachidonate is completely ineffective. The ability of PGE1 and eicosatrienoate but not PGE2 and arachidonate to restore fusion to control levels implies that fusion is specifically regulated by a prostanoid of the one series. The reversal of the fusion-block by linoleate further suggests that this fatty acid provides the necessary source of eicosatrienoate in the myoblast plasma membrane. At 10(-8) M and above, PGE1 and PGE2 stimulate adenylate cyclase and depress control fusion as does 10(-5) M isoproterenol. The beta-adrenergic blocker propranolol abolishes both isoproterenol's inhibition of myoblast fusion and its activation of adenylate cyclase. The similar depressions imposed on cell fusion by 10(-8)-10(-6) M prostanoid and 10(-5) M isoproterenol suggest that in both cases the depressive effects are mediated by cyclic AMP. It is concluded that a prostanoid of the one series regulates fusion by a cyclic AMP-independent mechanisms.

Leukotriene modulation of chloride transport in frog cornea

The present study has identified the metabolites of arachidonic acid (AA) formed by the isolated frog cornea and has shown that this tissue is capable of the biosynthesis of both lipoxygenase and cyclo-oxygenase pathway metabolites. The cyclo-oxygenase (CO) metabolites found in greatest abundance were the prostaglandins E2 and F2a (PGE2 and PGF2a). The major lipoxygenase (LO) pathway metabolite found by thin-layer chromatography (TLC) was leukotriene B4 (LTB4), whereas leukotriene C4 (LTC4) biosynthesis was detected by radioimmunoassay. These leukotrienes (LTs) are highly potent modulators of active chloride transport, since incubation with LTC4 (10(-7)-10(-9) M) resulted in a dose-dependent stimulation of both the Cl- originated short-circuit current (SCC) and potential difference (PD). In contrast, LTB4 (10(-7)-10(-9) M) inhibited both of these parameters. Both LTC4 and LTB4 exerted these effects only when applied to the endothelial side. Preincubation with the leukotriene receptor antagonist, FPL 55712 completely blocked the response to LTC4, indicating that the action of LTC4 in the cornea is receptor-mediated. In this report the authors show that LTB4 and LTC4 are formed by the cornea and that they are potent modulators of the SCC and PD in chamber experiments. The possibility exists that LTB4 and LTC4 may function as endogenous regulators of net Cl- transport in the cornea, since the addition of these metabolites resulted in a dose-dependent stimulation (with LTC4), and inhibition (with LTB4), of both the short-circuit current (SCC) and potential difference (PD).

Angiotensin II and eicosanoids in the control of glomerular size in the rat and human

We examined the possibility that glomerular prostaglandin E2 (PGE2) regulates the action of angiotensin II (ANG II) on mesangial contraction and filtration surface area. Using isolated rat glomeruli we indirectly assessed mesangial contraction and filtration surface area through measurements of glomerular planar surface area (GPSA) by image-analysis microscopy. ANG II reduced GPSA by approximately 20% in human and rat glomeruli, with threshold concentrations of 1 X 10(-13) M and maximum effect at 5 X 10(-11) M ANG II. Inhibition of glomerular PG synthesis with indomethacin or meclofenamate potentiated the threshold response of ANG II to reduce GPSA. Arachidonic acid (5 micrograms/ml) blunted both the threshold and the maximum responses of GPSA to ANG II. PGE2, 10(-8) and 10(-9) M, also decreased glomerular contraction to ANG II. Endoperoxide (EP) analogues decreased GPSA and EP 045, a thromboxane A2 (TXA2) receptor blocker, eliminated the contractile responses of glomeruli to the EP analogues. Authentic TXA2, synthesized from sheep platelet microsomes, also reduced GPSA. We conclude that glomerular products of arachidonate cyclooxygenation may either relax or contract the mesangium, thereby preserving or reducing filtration surface area. PGE2 exerts protective actions to reduce the mesangial contraction of ANG II, primarily through postreceptor effects. TXA2 may decrease glomerular filtration rate in certain diseases through direct actions on the mesangium.