The neutrophil respiratory burst. Responses to fatty acids, N-formylmethionylleucylphenylalanine and phorbol ester suggest divergent signalling mechanisms

Protectin DX, a double lipoxygenase product of DHA, inhibits both ROS production in human neutrophils and cyclooxygenase activities

Neutrophils play a major role in inflammation by releasing large amounts of reactive oxygen species (ROS) produced by NADPH oxidase (NOX) and myeloperoxidase (MPO). This ROS overproduction is mediated by phosphorylation of the NOX subunits in an uncontrolled manner. Therefore, targeting neutrophil subunits would represent a promising strategy to moderate NOX activity, lower ROS, and other inflammatory agents, such as cytokines and leukotrienes, produced by neutrophils. For this purpose, we investigated the effects of protectin DX (PDX)-a docosahexaenoic acid di-hydroxylated product which inhibits blood platelet aggregation-on neutrophil activation in vitro. We found that PDX decreases ROS production, inhibits NOX activation and MPO release from neutrophils. We also confirm, that PDX is an anti-aggregatory and anti-inflammatory agent by inhibiting both cyclooxygenase-1 and -2 (COX-1 and COX-2, E.C. 1.14.99.1) as well as COX-2 in lipopolysaccharides-treated human neutrophils. However, PDX has no effect on the 5-lipoxygenase pathway that produces the chemotactic agent leukotriene B4 (LTB4). Taken together, our results suggest that PDX could be a protective agent against neutrophil invasion in chronic inflammatory diseases.

Roles of phospholipase D in phorbol myristate acetate-stimulated neutrophil respiratory burst

The phorbol myristate acetate (PMA) stimulated nutrophil respiratory burst has been considered to simply involve the activation of protein kinase C (PKC). However, the PLD activity was also increased by 10-fold in human neutrophils stimulated with 100 nM PMA. Unexpectedly, U73122, an inhibitor of phospholipase C, was found to significantly inhibit PMA-stimulated respiratory burst in human neutrophils. U73122 at the concentrations, which were sufficient to inhibit the respiratory burst completely, caused partial inhibition of the PLD activity but no inhibition on PKC translocation and activation, suggesting that PLD activity is also required in PMA-stimulated respiratory burst. Using 1-butanol, a PLD substrate, to block phosphatidic acid (PA) generation, the PMA-stimulated neutrophil respiratory burst was also partially inhibited, further indicating that PLD activation, possibly its hydrolytic product PA and diacylglycerol (DAG), is involved in PMA-stimulated respiratory burst. Since GF109203X, an inhibitor of PKC that could completely inhibit the respiratory burst in PMA-stimulated neutrophils, also caused certain suppression of PLD activation, it may suggest that PLD activation in PMA-stimulated neutrophils might be, to some extent, PKC dependent. To further study whether PLD contributes to the PMA stimulated respiratory burst through itself or its hydrolytic product, 1,2-dioctanoyl-sn-glycerol, an analogue of DAG , was used to prime cells at low concentration, and it reversed the inhibition of PMA-stimulated respiratory burst by U73122. The results indicate that U73122 may act as an inhibitor of PLD, and PLD activation is required in PMA-stimulated respiratory burst.

Electrochemical monitoring of hydrogen peroxide released from leucocytes on horseradish peroxidase redox polymer coated electrode chip

We developed an electrochemical-sensing device for continuous monitoring extracellular hydrogen peroxide (H(2)O(2)). The device consists of an indium-tin-oxide electrode coated with osmium-polyvinylpyridine gel polymer containing horseradish peroxidase (Os-HRP) and a poly-dimethyl siloxane well to house the cells on the chip. Granulocyte-like differentiated HL-60 cells were accommodated in the well and stimulated with phorbol 12-myristate 13-acetate (PMA), which triggered the generation of H(2)O(2). The extracellular H(2)O(2) released from the cells was enzymatically reduced at the Os-HRP-modified electrode chip using Os(II) as an electron donor, resulting in reduction current responses by the device. The reduction current increased immediately upon PMA stimulation and this current transient was similar to that obtained by conventional chemiluminescence assays using sodium luminol. Apocynin, an inhibitor of NADPH oxidase activation, eliminated both the electrochemical and chemiluminescence signals. On the other hand, superoxide dismutase (SOD) increased the amperometric signals and catalase (CAT) decreased, whereas SOD decreased luminescence emission and CAT did not. These results were in accordance with the expected reaction mechanism, and strongly indicate that this new electrochemical-sensing device successfully detects extracellular H(2)O(2) production.

Inhibition of neutrophil leukotriene B4 production by a novel synthetic N-3 polyunsaturated fatty acid analogue, beta-oxa 21:3n-3

We recently reported the synthesis and anti-inflammatory properties of a novel long chain polyunsaturated fatty acid (PUFA) with an oxygen atom in the beta-position, beta-oxa-21:3 n-3 (Z,Z,Z)-(octadeca-9,12,15-trienyloxy) acetic acid). Our data, from studies aimed at elucidating the mechanism of its action, show that pretreatment of human neutrophils with the beta-oxa-PUFA substantially depresses the production of leukotriene B(4) (LTB(4)) in response to calcium ionophore, A23187, comparable to standard leukotriene inhibitors such as zileuton and nordihydroguaiaretic acid. Interestingly, the n-6 equivalent, beta-oxa 21:3 n-6, is also a strong inhibitor of LTB(4) production. In contrast, naturally occurring PUFA only slightly reduce, for eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acids, or increase, for arachidonic acid (20:4n-6), the formation of LTB(4). The parent beta-oxa-21:3n-3 molecule, rather than its derivatives (methyl ester, saturated, monohydroperoxy, or monohydroxy forms), is exclusively responsible for attenuation of LTB(4) formation. beta-Oxa-21:3n-3 inhibits the conversion of [(3)H]20:4n-6 to [(3)H]5-hydroxyeicosatetraenoic acid and [(3)H]LTB(4) by neutrophils in the presence of calcium ionophore and also suppresses the activity of purified 5-lipoxygenase, but not cyclooxygenase 1 and 2. Beta-oxa-21:3n-3 is taken up by neutrophils and incorporated into phospholipids and neutral lipids. In the presence of calcium ionophore, the leukocytes convert a marginal amount of beta-oxa-21:3n-3 to a 16-monohydroxy-beta-oxa-21:3n-3 derivative. After administration to rodents by gavage or i.p. injection, beta-oxa-21:3n-3 is found to be incorporated into the lipids of various tissues. Thus, beta-oxa-21:3n-3 has the potential to be used in the treatment of inflammatory diseases, which are mediated by products of the lipoxygenase pathway.

Unique effect of arachidonic acid on human neutrophil TNF receptor expression: up-regulation involving protein kinase C, extracellular signal-regulated kinase, and phospholipase A2

Arachidonic acid (AA) regulates the function of many cell types, including neutrophils. Although much emphasis has been placed on agonist-induced down-regulation of TNFR, our data show that AA caused a rapid (10-20 min) and dose-dependent (0.5-30 micro M) increase in the surface expression of both classes of TNFR (TNFR1 and TNFR2) on human neutrophils. This increased TNFR expression correlated with an increase in TNF-induced superoxide production. In contrast, the omega3 fatty acids eicosapentaenoic acid, docosahexaenoic acid, and linolenic acid failed to stimulate TNFR expression. Although fMLP and LPS reduced the neutrophil expression of TNFR, when pretreated with AA, fMLP caused an increase in TNFR expression. Consistent with this result was the finding that AA prevented the fMLP-induced receptor release in neutrophil cultures. AA also caused an increase in TNFR expression in matured HL-60 cells (neutrophil-like cells), but a decrease in nonmatured cells and HUVEC. The AA effects were independent of the lipoxygenase and cyclooxygenase pathways, but dependent on protein kinase C, the extracellular signal-regulated kinases 1 and 2, and cytosolic phospholipase A(2). The data demonstrate a unique effect of AA in the inflammatory reaction, through its action on neutrophil TNFR expression, and suggest that AA may regulate the response of neutrophils to TNF by altering its receptor number.

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.

Polyunsaturated fatty acids, inflammation, and immunity

The fatty acid composition of inflammatory and immune cells is sensitive to change according to the fatty acid composition of the diet. In particular, the proportion of different types of polyunsaturated fatty acids (PUFA) in these cells is readily changed, and this provides a link between dietary PUFA intake, inflammation, and immunity. The n-6 PUFA arachidonic acid (AA) is the precursor of prostaglandins, leukotrienes, and related compounds, which have important roles in inflammation and in the regulation of immunity. Fish oil contains the n-3 PUFA eicosapentaenoic acid (EPA). Feeding fish oil results in partial replacement of AA in cell membranes by EPA. This leads to decreased production of AA-derived mediators. In addition, EPA is a substrate for cyclooxygenase and lipoxygenase and gives rise to mediators that often have different biological actions or potencies than those formed from AA. Animal studies have shown that dietary fish oil results in altered lymphocyte function and in suppressed production of proinflammatory cytokines by macrophages. Supplementation of the diet of healthy human volunteers with fish oil-derived n-3 PUFA results in decreased monocyte and neutrophil chemotaxis and decreased production of proinflammatory cytokines. Fish oil feeding has been shown to ameliorate the symptoms of some animal models of autoimmune disease. Clinical studies have reported that fish oil supplementation has beneficial effects in rheumatoid arthritis, inflammatory bowel disease, and among some asthmatics, supporting the idea that the n-3 PUFA in fish oil are anti-inflammatory and immunomodulatory.

Extracellular release of free fatty acids by rat T lymphocytes is stimulus-dependent and is affected by dietary lipid manipulation

[(3)H]-Arachidonic acid-labelled rat T lymphocytes released radioactivity extracellularly when stimulated by the calcium ionophore A23187 or by monoclonal antibodies to some cell surface structures (CD2, CD5, CD11a, CD18, CD54, T-cell receptor) but not to others (CD49d, CD62L); release was greater with the calcium ionophore. Almost all of the radioactivity released from anti-CD2-stimulated lymphocytes was recovered in the free fatty acid fraction, whereas only about 50 per cent of that released after A23187 stimulation was recovered in this fraction. A23187 stimulation resulted in release of arachidonic acid from a variety of phospholipids (phosphatidylinositol, phosphatidylcholine and perhaps phosphatidylethanolamine), while the monoclonal antibody stimulation released arachidonic acid from phosphatidylinositol and perhaps phosphatidylcholine. Unstimulated lymphocytes released a range of fatty acids extracellularly, with palmitic acid accounting for 35-40 per cent and arachidonic acid for 5 per cent of released fatty acid. Stimulation of lymphocytes with either anti-CD2 or A23187 increased total fatty acid release 1.5- to 1.8-fold. In both cases palmitic acid remained the most predominant fatty acid released but the contribution of arachidonic acid increased. The type of lipid fed to the rats significantly influenced the amount and type of fatty acid released. Fish oil feeding significantly reduced extracellular fatty acid release by stimulated lymphocytes.

Lipid peroxides, nitric oxide and essential fatty acids in patients with Plasmodium falciparum malaria

Long chain polyunsaturated fatty acids derived from essential fatty acids have been shown to be toxic to Plasmodium falciparum both in vitro and in vivo. Here, we present evidence to suggest that in patients with Plasmodium falciparum malaria the levels of lipid peroxides (a marker of free radical generation) nitric oxide (a potent free radical with immunomodulatory actions), and concentrations of linoleic acid (LA) and alpha-linolenic acid (ALA) are low, whereas those of eicosapentaenoic acid (EPA) are high. The ability of the fatty acids to kill P. falciparum is dependent on their capacity to stimulate free radical generation in neutrophils and macrophages. EPA is more potent than LA in killing the parasite. In view of this, the results of the present study suggest that in patients with P. falciparum malaria the decreased levels of lipid peroxides and nitric oxide may contribute to the persistence of the infection, whereas elevated levels of EPA may be a feeble attempt to overcome this defect.

Activation of phospholipase A2 in human neutrophils by polyunsaturated fatty acids and its role in stimulation of superoxide production

Although polyunsaturated fatty acids (PUFA) have been shown to stimulate neutrophil responses such as the oxygen-dependent respiratory burst (superoxide production), the mechanisms involved still remain undefined. Here we investigate the effect of PUFA on the phospholipase A2 (PLA2)-signal transduction process in human neutrophils. Exogenous eicosatetraenoic acid [arachidonic acid; C20:4(n-6)] or docosahexaenoic acid [C22:6(n-3)] promoted the release of [3H]C20:4(n-6) from prelabelled neutrophils in a time- and dose-dependent manner, which is indicative of PLA2 activation. The release of [3H]C20:4(n-6) from the cells by C20:4(n-6) and C22:6(n-3) was suppressed by PLA2 inhibitors. Other PUFA ¿eicosapentaenoic [C20:5(n-3)], octadecatrienoic [gamma-linolenic; C18:3(n-6)] and octadecadienoic [linoleic; C18:2(n-6)] acids¿ also had the ability to release [3H]C20:4(n-6); however, certain C20:4(n-6) derivatives [15-hydroperoxyeicosatetraenoic acid, 15-hydroxyeicosatetraenoic acid and C20:4(n-6) methyl ester] and saturated fatty acids [octadecanoic (stearic; C18:0) and eicosanoic (arachidic; C20:0) acids] had no significant effect. Treatment of the neutrophils with exogenous C22:6(n-3) caused the mass of endogenous unesterified C20:4(n-6) to increase. Incubation of the leucocytes with C20:4(n-6) or C22:6(n-3) evoked activation of the 85 kDa cytosolic PLA2 (cPLA2) and the 14 kDa secretory PLA2 (sPLA2), but not the cytosolic Ca2+-independent PLA2. In contrast, C20:0 did not activate any of the PLA2 isoforms. Activation of cPLA2 by PUFA was found to precede that of sPLA2. C22:6(n-3), C20:4(n-6) and other PUFA induced punctate localization of cPLA2 in the cells, which was not observed with saturated fatty acids. Pretreatment of the leucocytes with PLA2 inhibitors markedly decreased superoxide production induced by C20:4(n-6). These results show that PUFA activate PLA2 in neutrophils, which might have a mandatory role in biological responses.

Leukotriene B4 Activates the NADPH Oxidase in Eosinophils by a Pertussis Toxin-Sensitive Mechanism That Is Largely Independent of Arachidonic Acid Mobilization

Experiments were designed to investigate whether leukotriene (LTB4) receptors can couple directly to phospholipase A2 (PLA2) in guinea pig eosinophils and the role of endogenous arachidonic acid (AA) in LTB4-induced activation of the NADPH oxidase. LTB4 (EC50 ∼ 16 nM) and AA (EC50 ∼ 6 μM) generated hydrogen peroxide (H2O2) in a concentration-dependent manner and at an equivalent maximum rate (5–6 nmol/min/106 cells). LTB4 stimulated PLA2 over a similar concentration range that activated the NADPH oxidase, although kinetic studies revealed that the release of [3H]AA (t1/2 ∼ 2 s) preceded H2O2 generation (t1/2 > 30 s). Pretreatment of eosinophils with pertussis toxin abolished the increase in inositol(1,4,5)trisphosphate mass, [Ca2+]c, [3H]AA release, and H2O2 generation evoked by LTB4. Qualitatively identical results were obtained in eosinophils in which phospholipase C (PLC) was desensitized by 4β-phorbol 12,13-dibutyrate with the exception that [3H]AA release was largely unaffected. Additional studies performed with the protein kinase C inhibitor, Ro 31-8220, and under conditions in which Ca2+ mobilization was abolished, provided further evidence that LTB4 released [3H]AA independently of signal molecules derived from the hydrolysis of phosphatidylinositol(4,5)bisphosphate by PLC. Pretreatment of eosinophils with the PLA2 inhibitor, mepacrine, abolished LTB4-induced [3H]AA release at a concentration that inhibited H2O2 by only 36%. Collectively, the results of this study indicate that agonism of LTB4 receptors on guinea pig eosinophils mobilizes AA by a mechanism that does not involve the activation of PLC. In addition, although LTB4 effectively stimulated PLA2, a central role for AA in the activation of the NADPH oxidase was excluded.

Enhancement of neutrophil-mediated killing of Plasmodium falciparum asexual blood forms by fatty acids: importance of fatty acid structure

Effects of fatty acids on human neutrophil-mediated killing of Plasmodium falciparum asexual blood forms were investigated by using a quantitative radiometric assay. The results showed that the antiparasitic activity of neutrophils can be greatly increased (>threefold) by short-term treatment with fatty acids with 20 to 24 carbon atoms and at least three double bonds. In particular, the n-3 polyenoic fatty acids, eicosapentaenoic and docosahexaenoic acids, and the n-6 fatty acid, arachidonic acid, significantly enhanced neutrophil antiparasitic activity. This effect was >1.5-fold higher than that induced by an optical concentration of the known agonist cytokine tumor necrosis factor alpha (TNF-alpha). At suboptimal concentrations, the combination of arachidonic acid and TNF-alpha caused a synergistic increase in neutrophil-mediated parasite killing. The fatty acid-induced effect was independent of the availability of serum opsonins but dependent on the structure of the fatty acids. The length of the carbon chain, degree of unsaturation, and availability of a free carboxyl group were important determinants of fatty acid activity. The fatty acids which increased neutrophil-mediated killing primed the enhanced superoxide radical generation of neutrophils in response to P. falciparum as detected by chemiluminescence. Scavengers of oxygen radicals significantly reduced the fatty acid-enhanced parasite killing, but cyclooxygenase and lipoxygenase inhibitors had no effect. These findings have identified a new class of immunoenhancers that could be exploited to increase resistance against Plasmodium species.

N-6 and n-3 polyunsaturated fatty acids stimulate translocation of protein kinase Calpha, -betaI, -betaII and -epsilon and enhance agonist-induced NADPH oxidase in macrophages

The polyunsaturated fatty acids (PUFA), arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were poor inducers of oxygen-dependent respiratory activity (chemiluminescence) in human monocytes and macrophages, but markedly enhanced the response to the tripeptide, N-formylmethionyl-leucyl-phenylalanine. The effects of these fatty acids were seen at concentrations of 1 microg/ml. A similar enhancement was seen with PMA, a stimulus that acts on protein kinase C (PKC), or calcium ionophore (A23187), which increases intracellular calcium, suggesting that the effect of the fatty acids was post-surface receptor binding. HL-60 cells, differentiated to macrophage-like cells by culture in the presence of vitamin D3, were similarly affected by the fatty acids. In experiments in which the time of pre-exposure of the monocytes to PUFA was varied, it was found that the priming effect induced by AA, EPA and DHA was maximal at 5 min. The ability of these fatty acids to synergize with other agonists was completely lost if the fatty acids were either methylated or oxidized to the hydro and hydroperoxy derivatives. Saturated fatty acids were inactive. Western blot analysis demonstrated that the PUFA induced the translocation of PKCalpha, -betaI, -betaII and -epsilon isoenzymes to a particulate fraction. The synergistic response between fatty acids and A23187 was completely inhibited by pretreating the cells with a PKC inhibitor, GF-109203X, or by pretreatment of monocytes with PMA for 18 h, to deplete PKC levels. From these investigations it is evident that PUFA prime macrophages, causing increased/synergistic oxidative respiratory burst activity to other stimuli and that this priming is dependent on PKC translocation and activation.

Activation of neutral sphingomyelinase in human neutrophils by polyunsaturated fatty acids

Although unesterified polyunsaturated fatty acids (PUFA) have been shown to elicit marked changes in neutrophil function, the associated signal transduction processes require clarification. In this study we examined the effect of PUFA on the sphingomyelin (SM)-signalling cycle in human neutrophils. Treatment of neutrophils with eicosatetraenoic acid [arachidonic acid, 20:4(n-6)] caused a decrease in the mass of cellular SM and an increase in the level of ceramide. 20:4(n-6)-stimulated neutral sphingomyelinase (SMase) activity of the leucocytes in a time- and concentration-dependent manner. Other unsaturated fatty acids, docosahexaenoic [22:6(n-3)], eicosapentaenoic [20:5(n-3)], octadecenoic [oleic, 18:1(n-9)] and octadecadienoic [linoleic, 18:2(n-6)] acids also had the capacity to activate neutral SMase; however, certain 20:4(n-6) derivatives ¿20:4(n-6) methyl ester [20:4(n-6)ME], 15-hydroperoxyeicosatetraenoic (15-HPETE) and 15-hydroxyeicosatetraenoic (15-HETE) acids¿, very-long-chain PUFA ¿tetracosatetraenoic [24:4(n-6)] and octacosatetraenoic [28:4(n-6)] acids¿ and saturated fatty acids [octadecanoic (stearic, 18:0) and eicosanoic (arachidic, 20:0) acids] had no significant effect. Activation of neutral SMase by 20:4(n-6) appeared to involve metabolism via 20:4(n-6)CoA (arachidonoyl CoA) and was not dependent on prostaglandin and leukotriene synthesis. All of the fatty acids and derivatives tested failed to activate acidic SMase of neutrophils. Ceramide was found to inhibit 20:4(n-6)-induced superoxide generation by the cells. It is envisaged that the PUFA-induced ceramide production in neutrophils plays a role in the regulation of biological responses.

Altered responses of human macrophages to lipopolysaccharide by hydroperoxy eicosatetraenoic acid, hydroxy eicosatetraenoic acid, and arachidonic acid. Inhibition of tumor necrosis factor production

The regulation of allergic and autoimmune inflammatory reactions by polyunsaturated fatty acids and their metabolic products (eicosanoids) continues to be of major interest. Our data demonstrate that arachidonic acid 5,8,11,14-eicosatetraenoic acid (20:4n-6) and its hydroxylated derivatives 15(s)-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE) and 15(s)-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) regulate agonist-induced tumor necrosis factor alpha (TNF) production, a cytokine that plays a role in inflammatory diseases. Although 20:4n-6 and 15-HETE caused a reduction in production of TNF in mononuclear leukocytes stimulated with phytohaemagglutinin, pokeweed mitogen, concanavalin A, and Staphylococcus aureus, 15-HPETE was far more active. 15-HPETE was also found to dramatically depress the ability of bacterial lipopolysaccharide to induce TNF production in monocytes and the monocytic cell line Mono Mac 6. These fatty acids depressed the expression of TNF mRNA in Mono Mac 6 cells stimulated with LPS; 15-HPETE was fivefold more active than 20:4n-6 and 15-HETE. While 15-HPETE treatment neither affected LPS binding to Mono Mac 6 cells nor caused a decrease in CD14 expression, the fatty acid significantly reduced the LPS-induced translocation of PKC (translocation of alpha, betaI, betaII, and epsilon isozymes), suggesting that 15-HPETE acts by abrogating the early signal transduction events. The findings identify another molecule that could form the basis for development of antiinflammatory pharmaceuticals.

The effect in vitro of high-density lipoprotein from healthy and infected humans on the oxidative metabolism of polymorphonuclear leukocytes

We studied the effects in vitro of high-density lipoprotein from healthy (N-HDL) and from infected humans (AP-HDL) on the oxidative metabolism of human polymorphonuclear leukocytes (PMN). Products of the H2O2-MPO-halide system were monitored by luminol-enhanced chemiluminescence and superoxide anion formation was monitored by lucigenin-enhanced chemiluminescence during stimulation of human PMN with phorbol myristate acetate (PMA) or an opsonized stimulus (OS). The results showed that N-HDL and AP-HDL affect the oxidative metabolism of PMN in different ways. The possible role of this effect is discussed.

Effect of amphotericin B associated with a lipid emulsion on the oxidative burst of human polymorphonuclear leukocytes

1. Despite its toxicity, amphotericin B (AB) continues to be the drug of choice for the treatment of systemic fungal infection. The drug acts on several cell types, including polymorphonuclear leukocytes (PMN), where it inhibits the oxidative burst of cells submitted to several stimuli. 2. It was previously shown that the association of AB with a triglyceride-rich emulsion that physiologically mimics chylomicrons reduces toxicity. 3. We found that the association of AB with a triglyceride-rich emulsion reduces the loss of PMN viability produced by the drug. 4. The inhibition of the PMN oxidative burst triggered by phorbol 12-myristate 13-acetate (PMA) and opsonized zymosan (OZ) also was decreased by the association of the drug with this lipid emulsion. 5. Delivery of AB in a lipid emulsion may be of advantage in the treatment of immunosuppressed patients.

Activation of signaling pathways in HL60 cells and human neutrophils by farnesylthiosalicylate

Effects of the farnesylcysteine mimetic, farnesylthiosalicylate on the activation of myeloid cells were studied. In dimethyl-sulfoxide-differentiated HL60 cells and in human neutrophils farnesylthiosalicylate (< or = 20 microM) dose-dependently elevated cytosolic Ca2+ concentrations, suggesting phospholipase-C-mediated release of the ion from intracellular stores. In human neutrophils, in addition to the production of inositol trisphosphate, farnesylthiosalicylate induced activation of the NADPH oxidase and translocation of the cytosolic oxidase components p47-phox and p67-phox to the membrane. The calcium signal, inositol-trisphosphate production and superoxide generation elicited by farnesylthiosalicylate were partially blocked by treatment of the cells with pertussis toxin, consistent with participation of pertussis-toxin-sensitive and pertussis-toxin-resistant elements. In HL60 cells, farnesylthiosalicylate (< or = 20 microM) did not activate NADPH oxidase but dose-dependently augmented PMA-elicited activity of the enzyme. This effect was resistant to pertussis-toxin treatment. In vitro augmentation of PKC-mediated phosphorylation of histone and cytosolic p47-phox by farnesylthiosalicylate and the finding that downregulation of PKC abrogated potentiation of NADPH oxidase activity by farnesylthiosalicylate were compatible with the involvement of PKC in the response of HL60 cells to farnesylthiosalicylate. It is suggested that the effects of farnesylthiosalicylate on myeloid cells reflect interaction of the analog with prenylcysteine-docking sites on cellular signaling elements.

Essential fatty acids: the effects of dietary supplementation among children with recurrent respiratory infections

The impact of dietary supplementation with essential fatty acids (EFA) on recurrent respiratory infections (RRI) in children was evaluated by means of a randomized cross-over double-blind study. Linoleic acid (596 mg/day) and alpha-linolenic acid [855 mg/day] as a commercial preparation or placebo (olive oil) were administered for two consecutive winter seasons (November to February, T0-T120) to 20 children affected by RRI, aged between 36 and 49 months. Plasma levels of n-3 and n-6 metabolites increased after the administration of EFA. The number of infective episodes, days' fever and days' absence from school were reduced significantly during the observation period (extended from T120 to T180) in children receiving EFA supplementation. Our results suggest that n-3 and n-6 polyunsaturated fatty acids may play a favourable role in the defence mechanism of these subjects.

Neutrophil oxygen radical generation. Synergistic responses to tumor necrosis factor and mono/polyunsaturated fatty acids

In inflammatory reactions there are complex interactions of protein mediators (cytokines) and mediators derived from lipids. An important event in inflammation is superoxide production, in relation to microbicidal activity as well as tissue damage. We have studied interactions of lipid mediators with a cytokine mediator tumor necrosis factor alpha (TNF) in stimulating superoxide production by human neutrophils for this reason and because it throws light on intracellular signals activating this response. Pretreatment of neutrophils with TNF markedly augmented the amount of superoxide produced in response to AA but not to either a 20 carbon saturated fatty acid, or the hydroxy- or hydroperoxy-derivatives of AA. Not only were other polyunsaturated fatty acids (eicosapentanoic, docosahexaenoic, linolenic, linoleic acid) as effective as AA but so was the monounsaturated fatty acid, oleic acid. Indeed TNF primed the neutrophils for an increased response to a major mediator of inflammation, leukotriene B4, which is a product of AA metabolism via the lipoxygenase pathway. The data demonstrate that two major types of mediators generated during an inflammatory response have synergistic action on neutrophils in the generation of reactive oxygen species. In contrast, neutrophils primed with TNF and challenged with PGE2, a product of AA metabolism via the cyclooxygenase pathway, showed a reduced chemiluminescence response. This identifies an important interaction between unsaturated lipids and cytokines which is likely to play a critical role in disease processes and nutrient modulation of the immune responses.

Human neutrophil functions are inhibited in vitro by clinically relevant ethanol concentrations

Neutrophils [polymorphonuclear neutrophils (PMNs)] play a pivotal role in host defense in man. These defenses may be compromised, however, in alcohol users and abusers. We therefore evaluated the effect of ethanol levels (12.5 to 500 mg/dl), on key functions of human PMNs-chemotaxis and production of reactive oxygen species-and on changes in cytosolic-free calcium ([Ca2+]i), a pivotal intracellular mechanism of PMN activation. Ethanol significantly inhibited chemotaxis as evaluated by formyl-methionyl-leucyl-phenylalanine (fMLP)-induced upregulation of surface adhesion molecules (CD11b). fMLP-induced PMN elongation was only inhibited by a very high ethanol concentration of 500 mg/dl. Production of reactive oxygen species by normal PMNs was assessed by either chemiluminescence (CL) for hypochlorous acid or ferricytochrome c reduction (FCR) for superoxide anions. For PMN stimulated by fMLP, ethanol inhibited CL but not FCR. For PMNs activated by phorbol myristate acetate, ethanol inhibited both CL and FCR. Ethanol did not alter baseline [Ca2+]i, as assessed by videomicroscopy using the Ca(2+)-sensing fluorescent dye Fura-2-AM, but did significantly potentiate the increase in peak [Ca2+]i levels that occurs in response to stimulation by fMLP. Calcium channel blockers attenuated ethanol's inhibition of CL. Thus, acute in vitro ethanol, at clinically relevant concentrations, can inhibit several critical aspects of PMN functions. But, in PMNs, unlike neural cells, these inhibitory effects do not seem to be mediated by decreases in Ca2+ influx or in [Ca2+]i.

Polyenoic very-long-chain fatty acids mobilize intracellular calcium from a thapsigargin-insensitive pool in human neutrophils. The relationship between Ca2+ mobilization and superoxide production induced by long- and very-long-chain fatty acids

Fatty acids with more than 22 carbon atoms (very-long-chain fatty acids; VLCFAs) are normal cellular components that have been implicated in the pathophysiology of a number of peroxisomal disorders. To date, however, essentially nothing is known regarding their biological activities. Ca2+ mobilization is an important intracellular signalling system for a variety of agonists and cell types. Given that several polyunsaturated long-chain fatty acids mobilize intracellular Ca2+ and that we have postulated that the VLCFAs may be involved in signal transduction, we examined whether the tetraenoic VLCFA induced Ca2+ mobilization in human neutrophils. We report that fatty acid-induced intracellular Ca2+ mobilization declined for fatty acid species of more than 20 carbon atoms, but increased again as the carbon chain length approached 30. This Ca2+ mobilization occurred independently of inositol 1,4,5-triphosphate production and protein kinase C translocation and involved both the release of Ca2+ from the intracellular stores and changes to the influx or efflux of the ion. We further observed that triacontatetraenoic acid [30:4(n-6)] mobilized Ca2+ from a thapsigargin-insensitive intracellular pool distinct from the thapsigargin-sensitive pools affected by arachidonic acid [20:4(n - 6)] or N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP). 20:4 (n - 6) induced strong superoxide production (chemiluminescence) which was inhibited by thapsigargin pretreatment. In contrast, fatty acid-induced superoxide production progressively declined as the carbon chain length increased beyond 20-22 carbon atoms. Further studies suggested that the thapsigargin-insensitive Ca2+ mobilization elicited by 30:4 (n - 6) was not related to oxyradical formation, while the thapsigargin-sensitive Ca2+ mobilization induced by 20:4 (n - 6) may be involved in the initiation but not necessarily the maintenance of superoxide production. In conclusion, this is the first report to demonstrate a biological activity for the VLCFA and indicates that 30:4 (n - 6) influences second messenger systems in intact cells that differ from those affected by long-chain fatty acids such as 20:4 (n - 6).

Bradykinin stimulates phospholipase D in PC12 cells by a mechanism which is independent of increases in intracellular Ca2+

These experiments were designed to learn the role of bradykinin induced changes in intracellular Ca2+ in the activation of phospholipase D activity in PC12 cells. Ionomycin at a concentration of 0.1 microM caused an increase in intracellular Ca2+ comparable to bradykinin, but had no effect on phospholipase D activity. Carbachol, ATP, and thapsigargin also increased intracellular Ca2+ but had no effect on phospholipase D activity. Increases in intracellular Ca2+ may be a necessary but not a sufficient factor in the activation of phospholipase D. To investigate this issue, the bradykinin induced increase in intracellular Ca2+ was blocked by preincubating the cells in Ca(2+)-free media plus EGTA or in media containing the intracellular Ca2+ chelator BAPTA/AM. These preincubations completely blocked the bradykinin induced increase in intracellular Ca2+ but only attenuated the bradykinin mediated activation of phospholipase D. Physiological increases in intracellular Ca2+ apparently do not mediate the effect of bradykinin on phospholipase D.

Effect of fatty acid structure on neutrophil adhesion, degranulation and damage to endothelial cells

Neutrophils have been implicated in ischaemic heart disease, unstable angina pectoris and acute myocardial infarction. Alterations in dietary levels of specific 18- and 20-carbon polyunsaturated fatty acids have significant clinical benefits in cardiovascular disease. However, to date there has been no concerted effort to identify the structural basis for polyunsaturated fatty acid-induced alterations in key neutrophil functions. We have investigated the influence of fatty acid structure and involvement of lipoxygenase/cyclooxygenase pathways on fatty acid-induced neutrophil functions. When neutrophils were incubated with 18-carbon fatty acids containing one to four double bonds (10-33 mumol/l), a significant increase in adherence and release of specific granule constituents occurred compared with control cells. In general, as the number of double bonds in the 18-carbon fatty acid increased, so did its ability to stimulate these functions. There was less stimulation of adherence and specific granule release by 18:3(n-3) than its isomer 18:3(n-6). Smaller effects were seen on azurophilic granule release. A further increase in adherence and degranulation was observed with increasing carbon chain length (20:3(n-6) and 20:4(n-6)). Differences were found in the ability of isomers of 20:3 to stimulate neutrophil function. Of the fatty acids tested only 20:4(n-6) was able to induce significant neutrophil-mediated endothelial detachment. Introduction of either internal hydroperoxy or hydroxyl groups into 20:4(n-6) abolished its adherence stimulating activity and considerably reduced its ability to stimulate release of both specific and azurophilic granules. Preincubation of neutrophils with either lipoxygenase (caffeic acid) or cyclooxygenase (indomethacin) inhibitors had no effect on 20:4(n-6) stimulated function. These studies show that the number and position of double bonds, carbon chain length and oxidation state can be critical to the neutrophil stimulatory properties of these fatty acids.

Eicosanoids, fatty acids and neutrophils: their relevance to the pathophysiology of disease

PUFA and their eicosanoid metabolites are potent biological modifiers. They have beneficial effects in a number of diseases, which may result in part from their direct actions on neutrophils as well as from their ability to modulate eicosanoid biosynthesis. A consideration of their interactions with other cell types, e.g. lymphocytes and macrophages, is beyond the scope of this review. Small alterations in structure can result in large changes in the neutrophil response. This will have important implications for the further development and use of fatty acids for therapeutic purposes.

Very long chain fatty acids in higher animals--a review

Fatty acids with greater than 22 carbon atoms (very long chain fatty acids, VLCFA) are present in small amounts in most animal tissues. Saturated and monoenoic VLCFA are major components of brain, while the polyenoic VLCFA occur in significant amounts in certain specialized animal tissues such as retina and spermatozoa. Biosynthesis of VLCFA occurs by carbon chain elongation of shorter chain fatty acid precursors while beta-oxidation takes place almost exclusively in peroxisomes. Mitochondria are unable to oxidize VLCFA because they lack a specific VLCFA coenzyme A synthetase, the first enzyme in the beta-oxidation pathway. VLCFA accumulate in the tissues of patients with inherited abnormalities in peroxisomal assembly, and also in individuals with defects in enzymes catalyzing individual reactions along the beta-oxidation pathway. It is believed that the accumulation of VLCFA in patient tissues contributes to the severe pathological changes which are a feature of these conditions. However, little is known of the role of VLCFA in normal cellular processes, and of the molecular basis for their contribution to the disease process. The present review provides an outline of the current knowledge of VLCFA including their biosynthesis, degradation, possible function and involvement in human disease.

Neutrophil-independence of the initiation of colonic injury. Comparison of results from three models of experimental colitis in the rat

Although the role of neutrophils in the pathogenesis of several forms of gastrointestinal injury has been well demonstrated, their role in the development of experimental colonic injury is less clear. To examine whether neutrophils play a role in the development of experimental colitides, the effects of a sustained neutropenia on multiple indices of colonic injury in rats was examined 24 hr following the initiation of colitis with the intrarectal application of acetic acid, trinitrobenzene sulfonic acid (TNBS)-ethanol, or the potent proinflammatory agent, phorbol-12-myristate-13-acetate (PMA). In comparison to animals with normal neutrophil counts and colitis induced by any of the three agents, no attenuation in macroscopic damage or histopathologic injury was observed in neutropenic animals exhibiting a greater than 95% reduction in circulating neutrophils and 85% reduction in tissue-associated myeloperoxidase activity. Although the tissue edema associated with acetic acid or PMA-induced colitis was not reduced by neutropenia, the colonic edema associated with TNBS colitis was attenuated by prior neutrophil depletion with anti-neutrophil antiserum. Despite our initial hypothesis that neutrophils played a key role in the genesis of experimental colitis (especially that induced by PMA), the results demonstrated that these cells are not essential for the development of the major pathological features of colitis induced by this agent, acetic acid, or TNBS. Although these results support the proposal that in these models of colitis, inflammation develops secondary to injury (rather than the converse), further studies will be necessary to elucidate the role of inflammatory cells other than neutrophils in the genesis of experimental colitides.

Identification of type-2 phosphatidic acid phosphohydrolase (PAPH-2) in neutrophil plasma membranes

Plasma membrane phosphatidic acid phosphohydrolase (PAPH) plays an important role in signal transduction by converting phosphatidic acid to diacylglycerol. PAPH-2, a Mg(2+)-independent, detergent-dependent enzyme involved in cellular signal transduction, is reportedly absent from the plasma membranes of neutrophilic leukocytes, a cell that responds to metabolic stimulation with abundant phospholipase D-dependent diacylglycerol generation. The present study was designed to resolve this discrepancy, focusing on the influence of cellular disruption techniques, detergent availability and cation sensitivity on the apparent distribution of PAPH in neutrophil subcellular fractions. The results clearly indicate the presence of two distinct types of PAPH within the particulate and cytosolic fractions of disrupted cells. Unlike the cytosolic enzyme, the particulate enzymes was not potentiated by magnesium and was strongly detergent-dependent. The soluble and particulate enzymes displayed dissimilar pH profiles. Separation of neutrophil particulate material into fractions rich in plasma membranes, specific granules and azurophilic granules by high speed discontinuous density gradient centrifugation revealed that the majority of the particulate activity was confined to plasma membranes. This activity was not inhibited by pretreatment with n-ethyl-maleimide in concentrations as high as 25 mM. PAPH activity recovered in the cytosolic fraction of disrupted neutrophils was almost completely inhibited by 5.0 mM n-ethylmaleimide. We conclude that resting neutrophils possess n-ethylmaleimide-resistant PAPH (type 2) within their plasma membranes. This enzyme may markedly influence the kinetics of cell activation by metabolizing second messengers generated as a result of activation of plasma membrane phospholipase D.

Neutrophil migration inhibitory properties of polyunsaturated fatty acids. The role of fatty acid structure, metabolism, and possible second messenger systems

The n-3 polyunsaturated fatty acids (PUFA) appear to have antiinflammatory properties that can be partly explained by their biological activity on leukocytes. Since leukocyte emigration is an essential component of the inflammatory response, we have examined the effects of the n-3 PUFA (eicosapentaenoic and docosahexaenoic acids) on neutrophil random and chemotactic movement. Preexposure of neutrophils for 15-30 min to 1-10 micrograms/ml PUFA reduced the random and chemotactic migration to both FMLP- and fungi-activated complement. The inhibitory effect diminished with increasing saturation and carbon chain length, and methylation abolished this activity. Arachidonic and docosahexaenoic acids were the most active fatty acids. The PUFA concentration required to inhibit migration was dependent on cell number, suggesting that the fatty acid effects on leukocyte migration in vivo may be governed by the stage of the inflammatory response. It was concluded that the PUFA rather than their metabolites were responsible for the inhibition since: (a) antioxidants did not prevent the PUFA-induced migration inhibition and the hydroxylated intermediates were less active, and (b) inhibitors of the cyclooxygenase and lipoxygenase pathways were without effect. Inhibitors of protein kinases and calmodulin-dependent enzyme system did not prevent the PUFA-induced migration inhibition, which was also independent of phospholipase D-catalyzed hydrolysis of phospholipids. It is also shown that PUFA decrease the FMLP-induced Ca2+ mobilization.

Pentoxifylline and CD14 antibody additively inhibit priming of polymorphonuclear leukocytes for enhanced release of superoxide by lipopolysaccharide: possible mechanism of these actions

Lipopolysaccharide (LPS) primes human polymorphonuclear leukocytes (PMN) for enhanced O2- production in response to stimulation by N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe). Serum factor is essential for priming at lower concentrations of LPS. Complexes of LPS and LPS-binding protein are recognized by CD14 on PMN. We investigated the effects of a monoclonal antibody against CD14 (MY4) and of pentoxifylline (POF), a membrane fluidizer, alone and in combination, on LPS-LPS-binding protein activation of phospholipase D evidenced by increased phosphatidic acid formation. Phosphatidic acid formation and O2- production were inhibited by MY4 and POF. Our results suggest that the actions of these agents occur at an early step in the excitation-response sequence. In the absence of a second stimulus, LPS plus serum caused an increase in the amount of Gi alpha 2 associated with the membrane via CD14. POF, however, had no effect on Gi alpha 2 in the membrane. POF alone significantly changed the affinity (KD) of the fMet-Leu-Phe receptor of PMN (from 25.2 +/- 4.5 nM to 15.2 +/- 2.4 nM [P < 0.01; n = 4]) at 37 degrees C. The differences between the sites of action of MY4 and POF may lead to cooperation by these agents for inhibition of priming by LPS plus serum for enhanced O2- production. Clinical use of the antibody and POF may diminish tissue damage caused by PMN in clinical endotoxic shock.

Diacylglycerol: formation and function in phospholipid-mediated signal transduction

1. Properties, distribution and multiplicity of phosphoinositidases (phospholipase C, PLC) are investigated. 2. Generation of diacylglycerol (DAG) by a variety of enzymes such as phosphoinositide and phosphatidylcholine specific PLC, by a combination of phospholipase D and phosphatidic hydrolase, and by triglyceride lipase is examined. 3. Ca2+ and phospholipid-dependent protein kinase C act as the target of DAG messenger action. 4. There are differences in the formation of DAG in normal and transformal cell.

Phospholipase D: regulation and functional significance

PLD is a major route for hydrolysis of PC in most tissues, consistent with it playing an important role in signal transduction. The enzyme appears to be activated by a variety of different mechanisms in different tissues, suggesting there might be several different isoforms. Little, however, is known at present about its enzymology and molecular biology. There is little direct evidence to indicate the functional significance of PLD activation but an accumulation of indirect evidence links PLD with prolonged changes in cell function. In particular, two areas where there is strong evidence for a role for PLD are mitogenesis and leukocyte hyperresponsiveness. An important area for future work will be the investigation of how products from the PLD pathway exert these effects. Current evidence suggests an important role for Ca(2+)-independent PKC isoforms and probably also for novel cellular targets for the putative second messenger PA.