Endogenous phospholipid metabolism in stimulated neutrophils differential activation by FMLP and PMA

Role of the phospholipid binding sites, PX of p47phox and PB region of Rac1, in the formation of the phagocyte NADPH oxidase complex NOX2

In phagocytes, superoxide anion (O2-), the precursor of reactive oxygen species, is produced by the NADPH oxidase complex to kill pathogens. Phagocyte NADPH oxidase consists of the transmembrane cytochrome b558 (cyt b558) and four cytosolic components: p40phox, p47phox, p67phox, and Rac1/2. The phagocyte activation by stimuli leads to activation of signal transduction pathways. This is followed by the translocation of cytosolic components to the membrane and their association with cyt b558 to form the active enzyme. To investigate the roles of membrane-interacting domains of the cytosolic proteins in the NADPH oxidase complex assembly and activity, we used giant unilamellar phospholipid vesicles (GUV). We also used the neutrophil-like cell line PLB-985 to investigate these roles under physiological conditions. We confirmed that the isolated proteins must be activated to bind to the membrane. We showed that their membrane binding was strengthened by the presence of the other cytosolic partners, with a key role for p47phox. We also used a fused chimera consisting of p47phox(aa 1-286), p67phox(aa 1-212) and Rac1Q61L, as well as mutated versions in the p47phox PX domain and the Rac polybasic region (PB). We showed that these two domains have a crucial role in the trimera membrane-binding and in the trimera assembly to cyt b558. They also have an impact on O2.- production in vitro and in cellulo: the PX domain strongly binding to GUV made of a mix of polar lipids; and the PB region strongly binding to the plasma membrane of neutrophils and resting PLB-985 cells.

The Influence of Winter Swimming on Oxidative Stress Indicators in the Blood of Healthy Males

Baths in cold water are a popular physical activity performed to improve health. This study aimed to determine whether repeated cold-water exposure leads to the up-regulation of antioxidant defenses and whether or not this leads to a reduction in basal and/or acute pulses of oxidative distress in humans. The study group consisted of 28 healthy male members of the WS club (average age 39.3 ± 6.1 years). The study sessions occurred at the beginning and the end of the WS season. During the WS season, the participants took 3-min cold-water baths in a cold lake once a week. Blood samples were collected three times during each session: before the bath, 30 min after the bath, and 24 h after the bath. The activity of selected antioxidant enzymes, including superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx), as well as the concentration of lipid peroxidation (LPO) products, including thiobarbituric acid-reactive substances (TBARS) and conjugated dienes (CD), were determined in erythrocytes. The concentration of TBARS, CD, retinol, and α-tocopherol were determined in the blood plasma, whereas the level of other LPO products, including 4-hydroxynonenal and 8-iso-prostaglandin F2α, were determined in the blood serum. The repeated cold exposure up-regulated most antioxidant defenses, and this led to an attenuation of most indicators of oxidative stress at the baseline and acute pulses in response to cold exposure. In conclusion, due to regular cold exposure, the antioxidant barrier of winter swimmers was stimulated. Thus, short cold-bath sessions seem to be an effective intervention, inducing promoting positive adaptive changes such as the increased antioxidant capacity of the organism.

Role of Human 15-Lipoxygenase-2 in the Biosynthesis of the Lipoxin Intermediate, 5S,15S-diHpETE, Implicated with the Altered Positional Specificity of Human 15-Lipoxygenase-1

The oxylipins, 5S,12S-dihydroxy-6E,8Z,10E,14Z-eicosatetraenoic acid (5S,12S-diHETE) and 5S,15S-dihydroxy-6E,8Z,11Z,13E-eicosatetraenoic acid (5S,15S-diHETE), have been identified in cell exudates and have chemotactic activity toward eosinophils and neutrophils. Their biosynthesis has been proposed to occur by sequential oxidations of arachidonic acid (AA) by lipoxygenase enzymes, specifically through oxidation of AA by h5-LOX followed by h12-LOX, h15-LOX-1, or h15-LOX-2. In this work, h15-LOX-1 demonstrates altered positional specificity when reacting with 5S-HETE, producing 90% 5S,12S-diHETE, instead of 5S,15S-diHETE, with kinetics 5-fold greater than that of h12-LOX. This is consistent with previous work in which h15-LOX-1 reacts with 7S-HDHA, producing the noncanonical, DHA-derived, specialized pro-resolving mediator, 7S,14S-diHDHA. It is also determined that oxygenation of 5S-HETE by h15-LOX-2 produces 5S,15S-diHETE and its biosynthetic k_cat/K_M flux is 2-fold greater than that of h15-LOX-1, suggesting that h15-LOX-2 may have a greater role in lipoxin biosynthesis than previously thought. In addition, it is shown that oxygenation of 12S-HETE and 15S-HETE by h5-LOX is kinetically slow, suggesting that the first step in the in vitro biosynthesis of both 5S,12S-diHETE and 5S,15S-diHETE is the production of 5S-HETE.

Uteroglobin, a possible ligand of the lipoxin receptor inhibits serum amyloid A-driven inflammation

Serum amyloid A (SAA) production is increased by inflamed arthritic synovial tissue, where it acts as a cytokine/chemoattractant for inflammatory and immune cells and as an inducer of matrix degrading enzymes. SAA has been shown to bind lipoxin A4 receptor, a member of the formyl-peptide related 2 G-protein coupled receptor family (ALX) and elicit proinflammatory activities in human primary fibroblast-like synoviocytes (FLS). We report on the identification of uteroglobin, a small globular protein with potent anti-inflammatory activities, as a possible ligand of ALX. Uteroglobin-specific association with ALX was demonstrated by an enzyme immunoassay experiment employing a cell line engineered to express the human ALX receptor. Uteroglobin's interaction with ALX resulted in the inhibition of SAA responses, such as attenuation of phospholipase A2 activation and cellular chemotaxis. In FLS, uteroglobin showed an antagonism against SAA-induced interleukin-8 release and decreased cell migration. These novel roles described for uteroglobin via ALX may help elucidate genetic and clinical observations indicating that a polymorphism in the uteroglobin promoter is linked to disease outcome, specifically prediction of bone erosion in patients with rheumatoid arthritis or severity of IgA glomerulonephritis and sarcoidosis.

Cryosurgery: A review

Cryosurgery dates back to the 19th century, with the description of the benefits of local application of cooling for conditions such as pain control. Once commercial liquefied gases became available, more progress was made in the use of cryotherapy for localized lesions. As understanding of disease response to freezing increased, safer techniques for performing freezing procedures helped prepare its clinical application in different clinical situations, such as prostate disease and bronchial cancers. Cryosurgical techniques are less invasive and have lower morbidity compared with surgical resection. However, the use of cryosurgery has been limited by a lack of good understanding of the underlying mechanisms of tissue destruction. To apply cryosurgery clinically, and to extend its use, it is important to understand the mechanisms of freeze injury on cells, and to control the thermal parameters.

Regulation of phosphatidylinositol 3-kinase by polyisoprenyl phosphates in neutrophil-mediated tissue injury

Neutrophils play a central role in host defense, inflammation, and tissue injury. Recent findings indicate a novel role for polyisoprenyl phosphates (PIPPs) as natural down-regulatory signals in neutrophils. The relationship between PIPPs and neutrophil early activating signals, such as phosphoinositides, has not been previously determined. Here, we establish presqualene diphosphate (PSDP) as an endogenous PIPP regulator of phosphatidylinositol 3-kinase (PI3K). In human neutrophils, leukotriene B4 (LTB4) triggered rapid decreases in PSDP and reciprocal increases in PI3K activity. In addition, PSDP was identified by gas chromatography/mass spectrometry in p110gamma-PI3K immunoprecipitates obtained 30 s after LTB4, indicating a physical interaction between PSDP and PI3K in activated neutrophils. Moreover, PSDP (0.4-800 pmol) directly inhibited recombinant human p110gamma-PI3K activity. During an experimental model of lung injury and inflammation, a reciprocal relationship was also present in vivo for lung PSDP and PI3K activity. To investigate its therapeutic potential, we developed a new PSDP structural mimetic that blocked human neutrophil activation and mouse lung PI3K activity and inflammation. Together, our findings indicate that PSDP is an endogenous PI3K inhibitor, and suggest that in inflammatory diseases characterized by excessive neutrophil activation, PIPPs can serve as structural templates in a novel antineutrophil therapeutic strategy to limit tissue injury.

Effect of arachidonic acid reacylation on leukotriene biosynthesis in human neutrophils stimulated with granulocyte-macrophage colony-stimulating factor and formyl-methionyl-leucyl-phenylalanine

Priming of human neutrophils with granulocyte-macrophage colony-stimulating factor (GM-CSF) followed by treatment with formyl-methionyl-leucyl-phenylalanine (fMLP) stimulates cells in a physiologically relevant manner with modest 5-lipoxygenase activation and formation of leukotrienes. However, pretreatment of neutrophils with thimerosal, an organomercury thiosalicylic acid derivative, led to a dramatic increase (>50-fold) in the production of leukotriene B(4) and 5-hydroxyeicosatetraenoic acid, significantly higher than that observed after stimulation with calcium ionophore A23187. Little or no effect was observed with thimerosal alone or in combination with either GM-CSF or fMLP. Elevation of [Ca(2+)](i) induced by thimerosal in neutrophils stimulated with GM-CSF/fMLP was similar but more sustained compared with samples where thimerosal was absent. However, [Ca(2+)](i) was significantly lower compared with calcium ionophore-treated cells, suggesting that a sustained calcium rise was necessary but not sufficient to explain the effects of this compound on the GM-CSF/fMLP-stimulated neutrophil. Thimerosal was found to directly inhibit neutrophil lysophospholipid:acyl-CoA acyltransferase activity at the doses that stimulate leukotriene production, and analysis of lysates from neutrophil preparations stimulated in the presence of thimerosal showed a marked increase in free arachidonic acid, supporting the inhibition of the reincorporation of this fatty acid into the membrane phospholipids as a mechanism of action for this compound. The dramatic increase in production of leukotrienes by neutrophils when a physiological stimulus such as GM-CSF/fMLP is employed in the presence of thimerosal suggests a critical regulatory role of arachidonate reacylation that limits leukotriene biosynthesis in concert with 5-lipoxygenase and cytosolic phospholipase A(2)alpha activation.

Platelets abrogate leukotriene B(4) generation by human blood neutrophils stimulated with monosodium urate monohydrate or f-Met-Leu-Phe in vitro

Neutrophils are physiologically associated with platelets in whole blood. Inflammatory reactions can be modulated by the presence of platelets. To investigate the influence of platelets on neutrophil activity, we studied the 5-lipoxygenase (5-LOX) metabolic pathway in normal human blood neutrophils stimulated with f-Met-Leu-Phe (fMLP) or monosodium urate monohydrate (MSUM) in the presence of autologous platelets. Platelets inhibited by more than 90% the synthesis of leukotriene B(4) and 5-HETE in neutrophils activated with fMLP or MSUM. The addition of exogenous arachidonic acid did not reverse the inhibitory effect of platelets on 5-LOX-generated metabolites in fMLP- or MSUM-activated neutrophils. Preincubation of neutrophils with adenosine deaminase reversed the inhibitory effect of platelets in fMLP-treated neutrophils, indicating that adenosine was responsible for the platelet inhibition of leukotriene B(4) and 5-HETE formation. In contrast, adenosine deaminase had no influence on the inhibitory effects of platelets in MSUM-stimulated cells. These results suggest that platelets can inhibit the synthesis of 5-LOX products (a). by acting mainly downstream to phospholipase A(2) in cells stimulated by fMLP or MSUM, (b). through adenosine when neutrophils are activated with fMLP, and (c). by an adenosine-independent mechanism in MSUM-activated neutrophils by an as-yet-unidentified mediator.

Activation of human neutrophil NADPH oxidase by phosphatidic acid or diacylglycerol in a cell-free system. Activity of diacylglycerol is dependent on its conversion to phosphatidic acid

The superoxide-generating neutrophil NADPH oxidase can be activated in cell-free reconstitution systems by several agonists, most notably arachidonic acid and the detergent sodium dodecyl sulfate. In this study, we show that both phosphatidic acids and diacylglycerols can serve separately as potent, physiologic activators of NADPH oxidase in a cell-free system. Stimulation of superoxide generation by these lipids was dependent upon both Mg(2+) and agonist concentration. Activation of NADPH oxidase by phosphatidic acids did not appear to require their conversion to corresponding diacylglycerols by phosphatidate phosphohydrolase, since diacylglycerols were much slower than phosphatidic acids to activate the system and required the presence of ATP. Stimulation of the oxidase by dioctanoylglycerol proved to be by a means other than the activation of protein kinase C. Instead, dioctanoylglycerol was converted to dioctanoylphosphatidic acid by an endogenous diacylglycerol kinase present in the cell-free reaction system. This conversion was sensitive to the diacylglycerol kinase inhibitor R59949 and explains the markedly slower kinetics of activation and the novel ATP requirement seen with dioctanoylglycerol. The level of dioctanoylphosphatidic acid formed was suboptimal for NADPH oxidase activation but could synergize with the unmetabolized dioctanoylglycerol to activate superoxide generation.

The role of free radicals in cold injuries

Cold injury is a tissue trauma produced by exposure to freezing temperatures and even brief exposure to a severely cold and windy environment. Rewarming of frozen tissue is associated with blood reperfusion and the simultaneous generation of free oxygen radicals. In this review is discussed the current understanding of the mechanism of action of free oxygen radicals as related to cold injury during rewarming. Decreased energy stores during ischaemia lead to the accumulation of adenine nucleotides and liberation of free fatty acids due to the breakdown of lipid membranes. On rewarming, free fatty acids are metabolized via cyclo-oxygenase and adenine nucleotides are metabolized via the xanthine oxidase pathway. These may be the source of free oxygen radicals. Leukocytes may also play a major role in the pathogenesis of cold injury. Oxygen radical scavengers, such as superoxide dismutase and catalase, may help to reduce the cold induced injury but their action is limited due to the inability readily to cross the plasma membrane. Lipid soluble antioxidants are likely to be more effective scavengers because of their presence in membranes where peroxidative reactions can be arrested.

Effects of protein I of Neisseria gonorrhoeae on neutrophil activation: generation of diacylglycerol from phosphatidylcholine via a specific phospholipase C is associated with exocytosis

Upon engagement of chemoattractant receptors, neutrophils generate inositol trisphosphate and diacylglycerol (DG) by means of a phosphatidylinositol-specific phospholipase C (PI-PLC) which is regulated by a GTP-binding protein(s). We have previously reported (Reibman, J., H. M. Korchak, L. B. Vosshall, K. A. Haines, A. M. Rich, and G. Weissmann. 1988. J. Biol. Chem. 263:6322-6328) a biphasic rise in DG after exposure of neutrophils to the chemoattractant FMLP: a rapid (less than or equal to 15 s) phase ("triggering") and a slow (greater than or equal to 30 s) phase ("activation"). These derive from distinct intracellular lipid pools. To study the source of rapid and slow DG, we have used a unique probe, protein I, a porin that is the major outer membrane protein of Neisseria gonorrhoeae. Treatment of neutrophils with protein I inhibits exocytosis and homotypic cell adhesion provoked by FMLP without inhibiting assembly of the NADPH oxidase responsible for O2-. generation. DG turnover in PMN labeled with [3H]arachidonate and [14C]glycerol was profoundly altered by protein I. Whereas the rapid peak of DG was only modestly diminished (FMLP vs. FMLP plus protein I = DG labeled with [3H]arachidonic acid (3H-a.a.-DG): 142 +/- 14% SEM vs. 125 +/- 22%; DG labeled with the glycerol backbone with [14C]glycerol (D-14C-G): 125 +/- 10% SEM vs. 107 +/- 8.5% SEM), the slow rise in both 3H-a.a.-DG and D-14C-G was essentially abolished. Moreover, treatment of neutrophils with 4-4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), which, like protein I, inhibits exocytosis without affecting O2-. generation also inhibited slow DG. However, protein phosphorylation and dephosphorylation (47phox, 66phox) were unaffected in the absence of slow DG. To determine the source of the slow DG, we have analyzed radiolabeled phospholipid (PL) turnover after FMLP +/- protein I (P.I.). Treatment of PMN with FMLP (0.1 microM) resulted in breakdown of phosphatidylcholine (PC), beginning at 30 s, and reaching a nadir at 60 s (3H-PC = 59 +/- 10.2% SEM of resting, 14C-PC = 57 +/- 6.4%). Protein I (0.25 microM) significantly inhibited PC turnover after FMLP ([3H]PC = 95 +/- 5.6% and [14C]PC = 86 +/- 8.4% of resting at 60 s), but failed to alter the metabolism of 3H- or 14C-phosphatidylinositol after FMLP (91 +/- 19.6 and 88 +/- 16.5% vs. 92 +/- 9.2 and 91 +/- 16% at 60 s).(ABSTRACT TRUNCATED AT 400 WORDS)

Cytoplasmic lipid bodies of neutrophils: formation induced by cis-unsaturated fatty acids and mediated by protein kinase C

Lipid bodies, nonmembrane-bound cytoplasmic inclusions, serve as repositories of esterified arachidonate and are increased in cells associated with inflammatory reactions. We have evaluated stimuli and mechanisms responsible for lipid body formation within human polymorphonuclear leukocytes (PMNs). Arachidonic acid and oleic acid stimulated dose-dependent formation of lipid bodies over 0.5-1 h. Other C20 and C18 fatty acids were less active and demonstrated rank orders as follows: cis-unsaturated fatty acids were much more active than trans-fatty acids, and activity diminished with decreasing numbers of double bonds. Lipid bodies elicited in vitro with cis-fatty acids were ultrastructurally identical to lipid bodies present in PMNs in vivo. Lipid body induction was not because of fatty acid-elicited oxidants or fatty acid-induced ATP depletion. Cis-fatty acid-induced activation of protein kinase C (PKC) was involved in lipid body formation as evidenced by the capacity of other PKC activators, 1-oleoyl-2-acetyl-glycerol and two active phorbol esters, phorbol myristate acetate, and phorbol 12,13 dibutyrate, but not an inactive phorbol, to induce lipid body formation. The PKC inhibitor, 1-O-hexadecyl-2-O-methyl-glycerol, inhibited PMN lipid body formation induced by oleic and arachidonic acids and by 1-oleoyl-2-acetyl-glycerol and phorbol myristate acetate. Other PKC inhibitors (staurosporine, H-7) also inhibited lipid body formation. Formation of lipid bodies in PMNs is a specific cellular response, stimulated by cis-fatty acids and diglycerides and apparently mediated by PKC, which results in the mobilization and deposition of lipids within discrete, ultrastructurally defined cytoplasmic domains.

Lipoxin A4 and lipoxin B4 stimulate the release but not the oxygenation of arachidonic acid in human neutrophils: dissociation between lipid remodeling and adhesion

The profiles of actions of lipoxin A4 (LXA4) and lipoxin B4 (LXB4), two lipoxygenase-derived eicosanoids, were examined with human neutrophils. At nanomolar concentrations, LXA4 and LXB4 each stimulated the release of [1-14C]arachidonic acid from esterified sources in neutrophils. Lipoxin-induced release of [1-14C]arachidonic acid was both dose- and time-dependent and was comparable to that induced by the chemotactic peptide f-met-leu-phe. Time-course studies revealed that lipoxin A4 and lipoxin B4 each induced a biphasic release of [1-14C]arachidonic acid, which was evident within seconds (5-15 sec) in its initial phase and minutes (greater than 30 sec) in the second phase. In contrast, the all-trans isomers of LXA4 and LXB4 did not provoke [1-14C]AA release. Lipoxin-induced release of arachidonic acid was inhibited by prior treatment of the cells with pertussis toxin but not by its beta-oligomers, suggesting the involvement of guaninine nucleotide-binding regulatory proteins in this event. Dual radiolabeling of neutrophil phospholipid classes with [1-14C]arachidonic acid and [3H]palmitic acid showed that phosphatidylcholine was a major source of lipoxin-induced release of [1-14C]arachidonic acid. They also demonstrated that lipoxins rapidly stimulate both formation of phosphatidic acid as well as phospholipid remodeling. Although both LXA4 and LXB4 (10(-8)-10(-6) M) stimulated the release of [1-14C]arachidonic acid, neither compound evoked its oxygenation by either the 5- or 15-lipoxygenase pathways (including the formation of LTB4, 20-COOH-LTB4, 5-HETE, or 15-HETE). LXA4 and LXB4 (10(-7) M) each stimulated the elevation of cytosolic Ca2+ as monitored with Fura 2-loaded cells, albeit to a lesser extent than equimolar concentrations of FMLP. Neither lipoxin altered the binding of [3H]LTB4 to its receptor on neutrophils. In addition, they did not stimulate aggregation or induce adhesion of neutrophils to human endothelial cells. Results indicate that both LXA4 and LXB4 stimulate the rapid remodeling of neutrophil phospholipids to release arachidonic acid without provoking either aggregation or the formation of lipoxygenase-derived products within a similar temporal and dose range. Together they indicate that LXA4 and LXB4 display selective actions with human neutrophils and suggest that these eicosanoids possess unique profiles of action which may regulate neutrophil function during inflammation.

Quantitative analysis of phospholipids and demonstration of plasmalogen in human neutrophil subcellular fractions by high-performance liquid chromatography

The subcellular distribution of phospholipids in unstimulated neutrophils was investigated by high-performance liquid chromatography of lipid extracts of granule and plasma membranes obtained from Percoll density gradients. The mobile phase contained acetonitrile:methanol:85% phosphoric acid (131:3:0.8 v/v/v). Post-nuclear supernatants contained 2.3 micrograms lipid phosphorus/mg protein. Phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine and phosphatidylcholine were demonstrated in azurophil granules, specific granules and in a combined fraction of secretory granules and plasma membranes. Separate estimates of each phospholipid class by peak areas obtained by high-performance liquid chromatography showed that secretory granules and plasma membranes contained most of the phosphatidylinositol and phosphatidylcholine (p less than 0.005 vs peaks areas obtained in azurophil and specific granules), whereas a major part of the phosphatidylethanolamine was located in the specific granules (p less than 0.005 vs peak areas obtained in azurophil granules, and plasma membrane and secretory granules). High-performance liquid chromatography proved to be a useful principle for the demonstration of plasmalogen because the acidic solvent caused hydrolysis of phosphatidalethanolamine, which was recovered as lysophosphatidylethanolamine. Additionally, sphingomyelin was demonstrated in all subfractions by thin-layer chromatography.

Phospholipase C-mediated hydrolysis of phosphatidylcholine is activated by muscarinic agonists

The phospholipase C-catalysed breakdown of inositol-containing phospholipids is an important source of diacylglycerol in cells stimulated by several agonists. However, recent experimental evidence suggests that major phospholipids such as phosphatidylcholine may also be substrates of the phosphodiesteratic hydrolysis activated by hormones, growth factors and oncogene products. We show here that stimulation of muscarinic agonists activates the release of phosphocholine, which, along with diacylglycerol, is a metabolic product of phospholipase C-mediated hydrolysis of phosphatidylcholine. Fluoroaluminates mimic this muscarinic effect, strongly suggesting that carbachol-activated release of phosphocholine may be mediated by a guanine-nucleotide-binding protein. Evidence for this was obtained from experiments using permeabilized cells in which non-hydrolysable analogues of GTP activated phosphocholine release synergistically with carbachol.

The metabolism of arachidonic and eicosapentaenoic acids in human neutrophils stimulated by A23187 and FMLP

A23187 stimulates the metabolism of endogenous as well as exogenous arachidonic acid (AA) and eicosapentaenolc acid (EPA) to their corresponding leukotrienes in human neutrophils. In contrast, conflicting results have been obtained concerning the effect of FMLP on the metabolism of these fatty acids. In the present study we compared the effect of A23187 and FMLP on the release and metabolism of these fatty acids in neutrophils. Stimulation of neutrophils with A23187, but not with FMLP, resulted in detectable levels of AA in the presence or absence of BW755C (a dual inhibitor of cyclooxygenase and lipoxygenase). The absolute amount of nonesterified AA in the extracts of neutrophils exposed to the agonist A23187 in the presence of BW755C was 20% higher than that obtained in the absence of BW755C, indicating that only a small fraction of the released AA was converted to lipoxygenase products. Furthermore, significant quantities of AA and EPA metabolites were detected only after treatment of neutrophils with A23187, but not with FMLP. Both A23187 and FMLP stimulated the conversion of exogenous EPA to 5-lipoxygenase products, with A23187 being somewhat more effective. In addition, significant differences were noted on the effect of EPA and DHA on the conversion of AA to its metabolites in A23187-stimulated neutrophils. Our results provide strong evidence that the amounts of eicosanoid precursors mobilized in response to FMLP are extremely small, if any, and this appears to be the likely explanation for the lack of eicosanoid detection by HPLC in FMLP-stimulated neutrophils.

Stimulation of phosphorylcholine turnover and diacylglycerol production in human polymorphonuclear leukocytes. Novel assay for phosphorylcholine

Receptor-bypassing stimulants of human polymorphonuclear leukocytes (PMNLs), such as ionomycin or phorbol 12-myristate 13-acetate (PMA), generate an increase in diacylglycerol (DAG) which is independent of a phospholipase C specific for phosphatidylinositol 4,5,-bisphosphate (PIP2). Activation of a phospholipase C specific for phosphatidylcholine (PC) has been implicated as a source of DAG in other cells by measuring the release of radiolabelled phosphorylcholine. However, since PMNLs could not be labelled sufficiently with [3H]choline, we developed an h.p.l.c. assay to quantify mass levels of phosphorylcholine after enzymic conversion to [32P]CDP-choline with CTP-phosphorylcholine (choline phosphate) cytidylyltransferase (EC 2.7.7.15). This assay was linear to at least 20 nmol, and was sensitive to 10 pmol of phosphorylcholine. Baseline phosphorylcholine levels in unstimulated PMNLs were 2300 +/- 510 pmol/10(7) cells and were decreased by pretreatment with PMA (166 nM) or ionomycin (1 microM) for 10 min by 360 +/- 130 and 600 +/- 290 pmol/10(7) cells respectively (P less than 0.05). In contrast, baseline DAG levels were 147.6 +/- 11.7 pmol/10(7) cells in unstimulated PMNLs, and were increased by PMA or ionomycin by 1320 +/- 222 and 1891 +/- 264 pmol/10(7) cells respectively (P less than 0.05). Similarly, the chemoattractant fMet-Leu-Phe raised DAG levels by 731 +/- 111 pmol/10(7) cells and decreased phosphorylcholine levels by 180 +/- 60 pmol/10(7) cells. Activation of PMNLs by PMA, ionophore or fMet-Leu-Phe thus leads to the sustained production of DAG accompanied by the disappearance of phosphorylcholine. This suggests that these stimulants enhance PC turnover via a hydrolytic mechanism which is independent of phospholipase C, with activation of a PC-specific phospholipase D being a plausible mechanism.

Mass determination of receptor-mediated accumulation of phosphatidate and diglycerides in human neutrophils measured by Coomassie blue staining and densitometry

Quantitation of 1,2-diacylglycerol (AAG), 1-0-alkyl-2-acylglycerol (EAG) and phosphatidic acid (PA) was conducted in polymorphonuclear leukocytes (PMN) labeled with 1-0-[3H]alkyl-2-acyl-GPC following stimulation with 1 microM fMLP using Coomassie blue staining and densitometry. At 5s AAG and PA increased by 80% and 107%, respectively, over controls. The accumulation of PA, which reached a maximum by 30s, was higher than AAG by 302% at 5s, and 550% at 30s. EAG accumulation was delayed by 15s following stimulation of PMN. These results show that AAG accumulates before EAG and support the role of AAG in cellular activation, perhaps, via the stimulation of protein kinase C (PKC). EAG may serve to counter the effects of AAG or may itself elicit responses. The high concentrations of PA which accumulate early suggest that PA may be generated by the activation of phospholipase D in PMN stimulated with fMLP.

Leukotriene B4 triggers highly characteristic and specific functional responses in neutrophils: studies of stimulus specific mechanisms

By using human neutrophils we studied the on-off phenomenon for leukotriene B4 (LTB4) -induced functional responses compared with fMetLeuPhe (fMLP). LTB4 induced rapidly appearing and disappearing neutrophil chemiluminescent (CL), superoxide anion formation, aggregatory and membrane depolarizing responses, whereas fMLP responses were slower both in onset and termination. Increases of intracellular calcium concentrations (as reflected by quin2 and fura-2 fluorescence) were of similar magnitude for both stimuli; however, LTB4 responses were more rapidly terminated and fMLP responses were biphasic. When intracellular calcium fluxes, calmodulin or protein kinase C activities were inhibited by quin2, trifluoperazine, verapamil or 3,4,5-trimethoxybenzoic acid 8-diethylamino)octyl ester (TMB-8), profound changes were noted for chemiluminescent and aggregation kinetics induced by fMLP, whereas kinetics of LTB4 responses were less affected. When drugs were used to modulate cAMP levels, or to inhibit cyclo- and lipoxygenase metabolites of arachidonic acid, no effects on response kinetics were observed. Cytochalasin B both amplified and delayed responses although chemiluminescent responses to fMLP were amplified more than those to LTB4. Despite those effects cytochalasin B did not enhance peak fura-2 or quin2 responses to either fMLP or LTB4. Thus, LTB4 rapidly initiates functional responses in neutrophils, and stimulus-specific response patterns are already discernable during the mobilization of calcium, and can be modulated by interference with calcium-dependent reactions.

Increased membrane heterogeneity in stimulated human granulocytes

TMA-DPH fluorescence decay in human PMN before and after stimulation with FMLP was studied using frequency domain fluorometry. Membrane heterogeneity was assessed by the width of the continuous distributions of lifetime values of Lorentzian shape used to describe the fluorescence decay. In non-stimulated granulocytes TMA-DPH fluorescence decay is characterized by two distributions of lifetime values centered at 6.5 and 1.0 ns and full width at half maximum of 0.3 and 1.2 ns, respectively. Within 15 min after stimulation, the center values of the two distribution components were 5.1 and 0.8 ns and the distribution width was 0.8 and 0.6 ns, respectively. These results indicate changes of membrane domain organization which can be ascribed to compositional changes and redistribution of membrane components.

Optical microscopy of antibody-dependent phagocytosis and lysis of erythrocytes by living normal and chronic granulomatous disease neutrophils: a role of superoxide anions in extra- and intra-cellular lysis

Novel optical microscopic techniques have been developed to observe neutrophil-mediated effector functions at the level of individual cells. Conventional absorption spectrophotometry has shown that exposure of hemoglobin to superoxide anions decreases the intensity of the Soret band and shifts it to lower wavelengths. This oxidative event can be visualized within intact erythrocytes using bright-field microscopy in conjunction with violet illumination at 430 nm. The sequential oxidation of IgG-opsonized sheep erythrocytes bound to normal human neutrophils can be observed. Chronic granulomatous disease (CGD) neutrophils which do not generate superoxide anions were not capable of influencing target absorption at 430 nm. Cytolytic events were visualized by fluorescence microscopy. Cytosolic or membrane compartments of sheep erythrocytes were labeled with eosin Y or fluorescein isothiocyanate, respectively. Time-dependent studies of erythrolysis show that targets are lysed extra- and intra-cellularly. The fluorescent diffusion gradient generated at the site of membrane rupture suggests that a pore of approximately 30 nm in diameter is formed in the target membrane. The site of pore formation is not found at the target-effector cell interface. CGD neutrophils did not display these cytolytic phenomena. Furthermore, the cytosolic label eosin Y could be followed into an associated granule compartment; we suggest that the phenomenon of piranhalysis may participate in antibody-dependent effector mechanisms. Phagocytosis can also be observed using fluorescently-labeled erythrocytes. Determinations of phagocytic index are more reliable with this approach. These microscopical methods are both simple and efficient. To our knowledge, these are the first direct microscopic studies of effector cell-mediated target cell oxidation and cytolysis. These experiments provide a fresh approach to the study of phagocyte effector functions at the cellular level and illuminate the importance of superoxide anions in antibody-dependent erythrolysis.

Phorbol ester binding to a human lymphoblastoid B-cell line, LA350, stimulates 32P incorporation into selected phospholipids and immunoglobulin secretion

Anti-mu antibody binds to surface IgM on LA350, a transformed human B-cell line, and causes the immediate (5 min) hydrolysis of phosphatidylinositol (PI) into inositol 1,4,5-triphosphate (IP3) and diacylglycerol followed by a subsequent (48-72 hr) increase in immunoglobulin M (IgM) production. Phorbol myristate acetate (PMA) in a dose-dependent fashion inhibited completely the anti-mu-stimulated hydrolysis of PI and its resynthesis (PI cycle) from phosphatidic acid (PA) (P less than 0.001). Phorbol dibutyrate (PD), but not the inactive methyl ester derivative of PMA (PMA-ME), inhibited the anti-mu stimulation of the PI cycle (P less than 0.001). Conversely, PMA and PD, but not PMA-ME, stimulated in a dose-dependent fashion the metabolic events consistent with an activation of a putative phosphatidylcholine (PC) cycle. For example, at 10(-8) M PMA there was a 300% increase in the acute (1 hr) incorporation of [3H]choline into PC (P less than 0.001), a 680% increase in the acute (1 hr) incorporation of 32P into PC (P less than 0.001), but no net synthesis of PC as measured by the lack of PMA-stimulated incorporation of 32P into PC in LA350 prelabeled for 24 hr. Also in cells labeled to equilibrium with [3H]choline and in pulse-chase experiments we established that PMA produces a rapid incorporation of choline phosphate into PC and a rapid breakdown of PC, yielding choline metabolites released as choline itself into external medium surrounding the cell. Binding studies with [3H]PD demonstrated a dissociation constant of 20 mM and 5.3 x 10(5) total binding sites per cell. PMA was as effective as cold PD in inhibiting [3H]PD binding (P less than 0.001), but PMA-ME was ineffective. PMA and PD, but not PMA-ME, produced a similar dose-dependent (maximal at 10(-8) M) increase (300%) in immunoglobulin production as measured by either an ELISA assay or a reverse hemolytic plaque assay (P less than 0.001). Thus, activation of either the PI or the PC cycle results in significant enhancement in immunoglobulin production in LA350. Although PMA turns off the PI cycle, it turns on the PC cycle. A common mechanism to explain these findings might be the activation of protein kinase C, indirect via diacylglycerol release in the PI cycle stimulation by anti-mu and direct in the PC cycle stimulation by PMA by virtue of direct binding to protein kinase C.

Human neutrophils incorporate arachidonic acid and saturated fatty acids into separate molecular species of phospholipids

The incorporation of radiolabeled arachidonic acid and saturated fatty acids into choline-linked phosphoglycerides (PC) of rabbit and human neutrophils was investigated by resolving the individual molecular species by reversed-phase high performance liquid chromatography. PC from neutrophils incubated with a mixture of [3H]arachidonic acid and [14C]stearic or [14C]palmitic acid contains both radiolabels; however, double labeling of individual molecular species is minimal. After labeling for 2 h, the [3H]arachidonate is distributed almost equally between diacyl and 1-O-alkyl-2-acyl species, but it is incorporated into diacyl species containing unlabeled stearate or palmitate at the sn-1 position. In contrast, labeled saturated fatty acids are incorporated only into diacyl species and contain predominantly oleate and linoleate at the sn-2 position. Labeled linoleate is not incorporated into ether-linked species, but is found in the same species as labeled stearate. The findings suggest that mechanisms exist in neutrophils for specific shunting of exogenous arachidonic acid into certain phospholipid molecular species and support the concept that the 1-O-alkyl-2-arachidonoyl species may be a functionally segregated pool of arachidonic acid within the PC of neutrophils.

Calcium ionophore, phorbol ester, and chemotactic peptide-induced cytoskeleton reorganization in human neutrophils

Formyl-methionylleucylphenylalanine (fMLP) activation of neutrophils causes an increase in intracellular Ca2+, activation of protein kinase C and an increase in F-actin content. To examine the role of Ca2+ and protein kinase C activation as determinants of change in F-actin content of neutrophils, we used the NBD-phallacidin extraction assay to compare the kinetics and extent of change in F-actin content of cells activated with fMLP, the calcium ionophore A23187 or phorbol myristate acetate (PMA). All stimuli increase the F-actin content in a dose-dependent manner; however, the rate of increase is slower and the maximum F-actin content is less for calcium ionophore and PMA than for fMLP-activated cells. The A23187-induced increase in F-actin content, but not that of fMLP, depends upon external free [Ca2+]. In A23187-activated cells, F-actin content increases at [Ca2+]free greater than or equal to 5 microM, is maximal at [Ca2+]free greater than or equal to 10 microM and is negligible at physiologic free [Ca2+] (10(-7)-10(-6) M). Combinations of PMA with A23187 or fMLP inhibit the A23187, but not the fMLP, activated actin polymerization. Comparison and combination of these activators shows that neither Ca2+-dependent activation with A23187 nor activation with PMA alone or in combination mimic the fMLP-induced changes in cytoskeleton organization of neutrophils.

Stimulus-specific induction of phospholipid and arachidonic acid metabolism in human neutrophils

Phospholipid remodeling resulting in arachidonic acid (AA) release and metabolism in human neutrophils stimulated by calcium ionophore A23187 has been extensively studied, while data obtained using physiologically relevant stimuli is limited. Opsonized zymosan and immune complexes induced stimulus-specific alterations in lipid metabolism that were different from those induced by A23187. [3H]AA release correlated with activation of phospholipase A2 (PLA2) but not with cellular activation as indicated by superoxide generation. The latter correlated more with calcium-dependent phospholipase C (PLC) activation and elevation of cellular diacylglycerol (DAG) levels. When cells that had been allowed to incorporate [3H]AA were stimulated with A23187, large amounts of labeled AA was released, most of which was metabolized to 5-HETE and leukotriene B4. Stimulation with immune complexes also resulted in the release of [3H]AA but this released radiolabeled AA was not metabolized. In contrast, stimulation with opsonized zymosan induced no detectable release of [3H]AA. Analysis of [3H]AA-labeled lipids in resting cells indicated that the greatest amount of label was incorporated into the phosphatidylinositol (PI) pool, followed closely by phosphatidylcholine and phosphatidylserine, while little [3H]AA was detected in the phosphatidylethanolamine pool. During stimulation with A23187, a significant decrease in labeled PI occurred and labeled free fatty acid in the pellet increased. With immune complexes, only a small decrease was seen in labeled PI while the free fatty acid in the pellets was unchanged. In contrast, opsonized zymosan decreased labeled PI, and increased labeled DAG. Phospholipase activity in homogenates from human neutrophils was also assayed. A23187 and immune complexes, but not zymosan, significantly enhanced PLA2 activity in the cell homogenates. On the other hand, PLC activity was enhanced by zymosan and immune complexes. Stimulated increases in PLC activity correlated with enhanced superoxide generation induced by the stimulus.

Influence of lysophospholipids and PAF on the oxidative burst of PMNL

Lysophosphatidylcholine (LC), platelet activating factor (PAF) and its precursor lysophosphatidalcholine (LP) enhance O-2-release by polymorphonuclear leucocytes (PMNL) triggered by PMA whereas lysophospholipids with other polar headgroups fail to do so. The generation of these lysophosphatidylcholine-like molecules appears to represent an essential step in the activation of the oxidative burst of the PMNL triggered by PMA since inhibition of phospholipase A2 (PLA2) by p-bromophenacylbromide (BB) or mepacrine results in an inhibition of the O-2 release. This inhibition seems to be due to the reduced generation of the phospholipids studied as it could be reversed by LP. In addition, stimulation of the oxidative burst of the PMNL by the chemotactic stimuli, N-formyl-methionyl-leucylphenylalanine (FMLP), and the complement fragment C5a could also be significantly enhanced by LP as shown by chemiluminescence. However, the response to the phagocytic stimulus, opsonized zymosan (Zx), is not affected by LP. These data provide evidence for the participation of phospholipid metabolism in the initiation of the oxidative burst of PMNL induced by the soluble monomeric stimuli PMA, FMLP and C5a.

Phospholipid metabolism in human neutrophils activated by N-formyl-methionyl-leucyl-phenylalanine. Degranulation is not required for release of arachidonic acid: studies with neutrophils and neutrophil-derived cytoplasts

Neutrophils respond to chemoattractants by aggregating, degranulating, remodelling of phospholipids and releasing arachidonic acid. To determine whether ligand-induced remodelling of phospholipids depends on redistribution of intracellular organelles (degranulation), we compared phospholipid remodelling of human neutrophils with that of neutrophil-derived cytoplasts. Cytoplasts, organelle-depleted vesicles of cytosol surrounded by plasmalemma, cannot degranulate. Without a stimulus, [3H]arachidonate was incorporated preferentially into phosphatidylinositol (PI) and phosphatidylcholine (PC). Exposure of cytoplasts and neutrophils prelabelled with [3H]arachidonate or [14C]glycerol to fMet-Leu-Phe (10(-7) M) induced rapid changes in distribution of label and mass of individual phospholipids: [3H]arachidonate in phosphatidic acid (PA) increased 500% (120 s), [14C]glycerol incorporation and mass of PA approached 200% of unstimulated values, and [3H]arachidonate in PI decreased continuously; these data are compatible with activity of a PI/PA cycle. However, the mass of PI in both preparations and [14C]glycerol label in intact neutrophils increased initially (5 s), suggesting net synthesis and mobilization of more than one pool of PI. Heterogeneity of PC pools was also observed: [3H]arachidonate was lost from PC immediately upon addition of stimulus, whereas mass and [14C]glycerol values increased. Thus, net phospholipid synthesis, redistribution of arachidonate and activation of the PI/PA cycle are immediate responses of the neutrophil to receptor occupancy by chemoattractants. Furthermore, the similarity in response to fMet-Leu-Phe of neutrophils and granule-free cytoplasts indicates that these processes are independent of degranulation.

Stimulus-dependent mobilization of protein kinase C

Protein kinase C and its associated phorbol myristate acetate receptor moved from cytosol to membranes in human neutrophils stimulated with direct activators of the kinase, calcium ionophores, or chemotactic peptides. However, the peptides acted only in the presence of cytochalasin B and neither platelet-activating factor nor leukotriene B4 (+/- cyclochalasin B) induced this movement. Thus, protein kinase C appears variably involved in neutrophil responses: physiological agents may bypass or depend minimally upon the phosphorylating enzyme to elicit function.

Diacylglycerols and mezerein activate neutrophils by a phorbol myristate acetate-like mechanism

rac-1-O-Myristoyl-2-O-acetylglycerol, rac-1-O-palmitoyl-2-O-acetylglycerol, and rac-1-O-oleoyl-2-O-acetylglycerol acted like phorbol myristate acetate and mezerein in stimulating human neutrophil aggregation. Responses to these agents were equally influenced by cytochalasin B, extracellular calcium and magnesium, arachidonate antimetabolites, and procedures that rendered the cells desensitized to other agonists. The compounds also inhibited the binding of [3H]-phorbol myristate acetate to its receptor on neutrophils. Thus, these agents are biologically homologous. They act by binding to a common receptor. This receptor may function physiologically as a transducer for endogenous glycerides that form in cells challenged by other stimuli.

Mechanism of production of toxic oxygen radicals by granulocytes and macrophages and their function in the inflammatory process

The paper deals with 1) the features of the respiratory burst (increase of the respiration with production of O2 metabolites, O2-, H2O2, OH) of the inflammatory cells; 2) the factors responsible for its activation; 3) the methods for its measurement; 4) the molecular events which take place at the level of the plasma membrane following the interaction between the stimuli and the cell surface (the Ca++ changes, the modification of membrane potential, the activation of phospholipid turnover) and the hypothesis of the activation of the protein kinase C; 5) the nature of the NADPH oxidase whose activation is responsible for the respiratory burst and the production of O2 metabolites; 6) the defensive, toxic, proinflammatory and modulatory effects due to the reactivity of the oxygen metabolites.

In vitro cisplatin effects on phagocyte functions

The effects of cis-diamminedichloroplatinum (II) (cisplatin), a drug used in cancer chemotherapy, on the oxidative metabolism, endocytosis, chemotaxis and exocytosis of guinea-pig polymorphonuclear leukocytes were studied. All these functions were negatively influenced, but the same effect (50% inhibition) was observed at different drug concentrations (3 X 10(-5) M for chemotaxis, 10(-4) M for O2 consumption by FMLP and beta-glucuronidase release, 10(-3) M for O2 consumption by PMA and for zymosan engulfment). The effects of the drug can be explained by its ability to bind to membrane proteins, essentially to -SH groups.

Inhibition by verapamil of neutrophil responses to formylmethionylleucylphenylalanine and phorbol myristate acetate. Mechanisms involving Ca2+ changes, cyclic AMP and protein kinase C

Verapamil inhibits in human neutrophils the respiratory burst, the secretion and the change of transmembrane potential induced by formylmethionylleucylphenylalanine, a Ca2+-dependent stimulus, and by phorbol myristate acetate, a Ca2+-independent stimulus. Besides the blocking of Ca2+ channels, many mechanisms are responsible for the inhibition of neutrophil responses. In fact, verapamil (i) increases the intracellular cAMP concentration, potentiates the cAMP response induced by the chemotactic peptide and induces the appearance of a cAMP response also when the stimulant is phorbol myristate acetate; (ii) causes a decrease of Ca2+ association to cell membranes, so depleting the pools of exchangeable Ca2+ and depressing the 'Ca2+ response' in terms of rise in [Ca2+]i monitored with Quin 2 and of rapid mobilization from cell membranes monitored by chlorotetracycline fluorescence change; (iii) inhibits the Ca2+-activated phospholipid-dependent protein kinase C. The data, discussed in relation to the biochemical mechanisms of the stimulus-response coupling, are compatible with the hypothesis of an involvement of the activation of protein kinase C as key step in the sequence of transduction events for the induction of many neutrophil functions.

Pertussis toxin inhibits chemotactic peptide-stimulated generation of inositol phosphates and lysosomal enzyme secretion in human leukemic (HL-60) cells

The binding of the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine to its cell surface receptor rapidly elicits the hydrolysis of phosphatidylinositol 4,5-bisphosphate by phospholipase C to form the putative second messengers inositol 1,4,5-trisphosphate and sn-1,2-diacylglycerol. To investigate the possible role of a guanine nucleotide binding protein in transduction of this membrane signal, we examined the effects of pertussis toxin on chemotactic peptide-stimulated inositol phospholipid metabolism in differentiated HL-60 cells labeled with [3H]inositol. Pertussis toxin inhibited the chemotactic tripeptide-stimulated production of inositol mono-, bis-, and trisphosphates and secretion of N-acetyl-beta-D-glucosaminidase in a time- and concentration-dependent manner. Treatment with pertussis toxin did not alter the total incorporation or the distribution of [3H]inositol in inositol phospholipid. Chemotactic peptide receptor number was unchanged, although a slight decrease in binding affinity was observed. These findings suggest a role for a guanine nucleotide binding protein in coupling the chemotactic peptide receptor to phospholipase C.

Phorbol 12-myristate, 13-acetate potentiates the action of the calcium ionophore in stimulating arachidonic acid release and production of phosphatidic acid in rabbit neutrophils

The addition of the tumor-promoting phorbol 12-myristate, 13-acetate to rabbit neutrophils greatly potentiates the effect of the calcium ionophore A23187 on [3H]-arachidonic acid release and [32P]-phosphatidic acid generation. At 5 X 10(-8) M A23187, the addition of 20 ng/ml PMA potentiates the action of the ionophore on [3H]-arachidonic acid release by 5-fold. At 5 X 10(-7) M A23187, PMA enhances [32P]-phosphatidic acid production by 1.5-fold. Incubation of the neutrophils with 5 X 10(-7) M ionophore for two minutes causes a significant increase in the [32P] phosphatidic acid production but does not affect the levels of [32P]-phosphatidylinositol or [32P]-phosphatidylinositol 4,5 bis-phosphate. In addition, increasing the sodium chloride concentrations in the suspending medium causes an increase in the level of phosphatidylinositol 4,5 bis-phosphate. These results suggest that the phorbol ester either acting directly or through the activation of protein kinase C modulates significantly the activities of the various forms of phospholipases, particularly A2, and/or increases the availability or amounts of their substrates.

Interactions of arachidonate metabolism and protein kinase C in mediating neutrophil function

Diglyceride activators of protein kinase C (i.e., 1-0-myristoyl-, 1-0-palmitoyl-, and 1-0-oleoyl-2-acetylglycerol) interacted synergistically with an arachidonate metabolite, 5-hydroxyicosatetraenoate, to stimulate neutrophil degranulation and superoxide anion generation. Contrastingly, combinations of 15-hydroxyicosatetraenoate with the glycerides or 5-hydroxyicosatetraenoate with a dialkylglyceride (1-0-hexadecyl-2-ethylglycerol) produced no such synergy. The data support a view of stimulus-response coupling wherein protein kinase C is activated in parallel with the mobilization of arachidonate. Respective products of these events, e.g., phosphorylated proteins and hydroxyicosatetraenates, then interact to mediate function.