Role of P-selectin, β2-integrins, and Src tyrosine kinases in mouse neutrophil–platelet adhesion

Summary. Background: The initial interaction of human polymorphonuclear leukocytes (PMN) with activated human platelets is mediated by P‐selectin and its leukocyte ligand PSGL‐1; subsequently the interaction is strengthened by activation of αMβ2 via protein tyrosine phosphorylation mediated by Src kinases and binding of activated αMβ2 to its platelet counterreceptor(s). Objectives: Because mouse models are being used to define the role of PMN–platelet interactions in thrombosis and the response to vascular injury, we investigated the molecular determinants responsible for the interaction of murine PMNs with activated murine platelets. Methods: Mouse platelets were labeled with the green fluorescent dye BCECF and then activated with thrombin and fixed with 1% paraformaldehyde. Mouse PMNs were labeled with the red fluorescent dye hydroethidine and then stirred with the fixed platelets. After stopping the reaction with paraformaldehyde, formation of mixed cell conjugates was analyzed by flow cytometry. Results: In time course experiments, 90 ± 1.9% of PMNs formed mixed conjugates with platelets after 2 min and the mean (± SEM) number of platelets per positive PMN was 8.4 ± 1.5. A monoclonal antibody to P‐selectin reduced the percentage of PMNs with attached platelets to 16 ± 2.4% (P = 0.001), and only 8 ± 5% of PMNs interacted with platelets from P‐selectin?/? mice. In contrast, monoclonal antibodies to PSGL‐1, β₂‐integrin, and αIIbβ3 had much less or no effect on the production of mixed cell aggregates. To better identify a secondary contribution of β₂‐integrins, P‐selectin interactions were disrupted by briefly adding 5 mm EGTA to already‐formed mixed cell aggregates. Brief EGTA treatment alone reduced the percentage of PMNs with attached platelets to 70 ± 3.5% (P = 0.004 vs. no treatment), but did not modify the number of platelets per positive PMN (9.5 ± 1.7). The combination of brief EGTA treatment and a monoclonal antibody to β₂‐integrin lowered the percentage of PMN with attached platelets to 50 ± 7% and reduced the number of platelets attached per positive PMN to 3.6 ± 0.7 (P = 0.03 vs. brief EGTA treatment only). Brief EGTA treatment did not modify the effect of the other antibodies. When the incubation was stopped with EGTA the Src inhibitors PP1 and PP2 reduced PMN–platelet adhesion, while the inactive analog PP3 was ineffective. Conclusions: These results confirm that P‐selectin plays a prominent role in mediating the initial interactions between mouse PMN and platelets, and provide support for additional contributions from β₂‐integrins and Src family kinases.     

Lipid complexing decreases amphotericin B inflammatory activation of human neutrophils compared with that of a desoxycholate-suspended preparation of amphotericin B (Fungizone).

Amphotericin B (AmB) has toxic effects and alters neutrophil (polymorphonuclear leukocyte [PMN]) function. A lipid-complexed formulation of AmB (AmB-LC) has been reported (A. S. Janoff, L. T. Boni, M. C. Popescu, S. R. Minchey, P. R. Cullis, T. D. Madden, T. Taraschi, S. M. Gruner, E. Shyamsunder, M. W. Tate, R. Mendelsohn, and D. Bonner, Proc. Natl. Acad. Sci. USA 85:6122-6126, 1988) to be less toxic than a desoxycholate-suspended preparation of AmB (AmB-des; Fungizone). In this study we compared the effects of AmB-des and AmB-LC on in vitro PMN function. Neither form of AmB stimulated PMN chemiluminescence, but AmB-des (2 micrograms/ml) nearly tripled PMN chemiluminescence in response to f-Met-Leu-Phe (fMLP), a phenomenon known as priming. Because AmB stimulates monocytes to release cytokines which can affect PMN function, we studied the effects of AmB on PMNs in mixed leukocyte cultures. AmB-des (1 to 2 micrograms/ml) increased the chemiluminescence of PMNs plus mixed mononuclear leukocytes (MNLs) to fMLP. The activity was about three times that of PMNs plus MNLs and seven times the activity of PMNs stimulated with fMLP in the absence of MNLs. Cell-free AmB-des (2 micrograms/ml)-stimulated, MNL-conditioned medium primed pure PMNs to a level equal to that of whole MNLs treated with AmB-des. AmB-LC was much less potent. AmB-LC (20 micrograms/ml) increased fMLP-stimulated chemiluminescence to two times that of PMNs plus MNLs without AmB-LC. AmB-des (2 micrograms/ml) (but not AmB-LC [2 micrograms/ml]) increased nitroblue tetrazolium reduction by PMNs in whole blood from 31 to 52% of positive cells. Neither form of AmB increased Mac-1 (the CD11b/CD18 integrin) expression of pure PMNs. AmB-des (0.5 to 2 micrograms/ml) (but not AmB-LC [< or = 40 micrograms/ml]) nearly doubled PMN Mac-1 expression in the presence of MNLs, and cell-free AmB-des (2 micrograms/ml)-stimulated, MNL-conditioned medium stimulated PMN Mac-1 to 125% of the control level. AmB-des (0.2 to 2 micrograms/ml) (but not AmB-LC [< or = 40 micrograms/ml]) decreased chemotaxis of pure PMNs to fMLP by as much as 35% and that of PMNs in the presence of MNLs by as much as 50%. Desoxycholate by itself had no effect on PMN function. These differences in activity between AmB-des and AmB-LC may explain the lessened toxicity observed with AmB-LC.     

Hypertonic saline inhibits neutrophil (PMN) priming via attenuation of p38 MAPK signaling

Priming of the neutrophil cytotoxic response is central to the pathogenesis of early postinjury multiple organ failure (MOF). Platelet-activating factor (PAF) has been implicated as a key inflammatory mediator in postinjury neutrophil priming and requires p38 MAPK signaling to produce its biologic effects. Hypertonic saline (HTS) resuscitation decreases the postinjury inflammatory response following shock in animals and decreases receptor-mediated neutrophil (PMN) cytotoxic functions in vitro. We hypothesized that HTS attenuates PAF priming of the PMN cytotoxic response by interfering with PAF-mediated p38 MAPK signal transduction. Isolated PMNs were preincubated in isotonic buffer or HTS (Na+ = 180 mM), then primed with PAF. Neutrophil CD11b/CD18 expression was measured by flow cytometry. Receptor-dependent (fMLP), N-formyl-methionyl-leucyl-phenylalanine, fMLP) and receptor-independent (PMA) O2- production was measured by reduction of cytochrome c in resting and PAF primed PMNs. Total p38 MAPK protein PAF-mediated p38 MAPK activation was assessed by western blot of PMN lysates. Clinically relevant levels of HTS attenuated PAF-mediated beta2-integrin expression. While HTS attenuated receptor-dependent (fMLP and PAF/fMLP) O2- production, receptor-independent (PMA) O2- production was unaffected. Conversely, HTS attenuated PAF priming of PMA-mediated O2- production. PAF and HTS did not alter total cellular p38 MAPK content. Clinically relevant levels of HTS alone did not activate p38 MAPK but inhibited PAF mediated p38 MAPK activation. HTS attenuates PAF priming of the PMN cytotoxic response by altering intracellular signal transduction. Therefore, HTS resuscitation may attenuate postinjury PMN priming and ultimately the risk of developing MOF.     

Polymorphonuclear leukocyte dysfunction syndrome in patients with increasing sepsis severity

Production of oxygen radicals is required for both microbicidal and tissue-toxic effector functions of granulocytes. Inasmuch as an ambivalent role of polymorphonuclear leukocytes (PMNs) may become apparent during sepsis, we studied levels of hydrogen peroxide (H2O2) production by PMNs depending upon the nature of different particulate and soluble stimuli in patients with increasing sepsis severity. Patients with sepsis (n = 15), severe sepsis (n = 12), or septic shock (n = 33) were prospectively enrolled in the study. Healthy volunteers of comparable age and sex served as controls (n = 50). Unopsonized and opsonized zymosan particles were used to assess adhesion, phagocytosis, and the associated H2O2 production. Zymosan particles are rich in beta-glucans and lectin structures that are known to trigger H2O2 production via two major non-toll-like receptor pathogen recognition receptors, comprising the lectin-binding site in the alpha-chain (CD11b) of the complement receptor type 3 and the more recently identified nonclassical C-type lectin, dectin-1. To determine H2O2 production upon cell activation by soluble stimuli, PMNs were activated by the chemotactic tripeptide (N-formyl-methionyl-leucyl-phenylalanine [fMLP]) alone or after priming of cells by preincubation with tumor necrosis factor alpha. To get insight into the changes of fMLP receptor classical intracellular signaling pathways, PMNs were also incubated with the calcium ionophore A23187 and the phorbol ester phorbol myristate acetate, bypassing receptor-dependent signal transduction to directly activate calcium/calmodulin kinase- and protein kinase C-dependent pathways, respectively. As compared with healthy volunteers, levels of H2O2 production by PMNs from septic patients varied depending upon the nature of the activating signal: reduced (zymosan), unchanged (phorbol myristate acetate, opsonized zymosan), and enhanced (spontaneous, fMLP, fMLP + tumor necrosis factor alpha, A23187), with the changes most pronounced in patients with septic shock. Specifically, phagocytosis of zymosan and the associated H2O2 production were significantly decreased whereas spontaneous and stimulated H2O2 production elicited by soluble stimuli strongly increased. Thus, these findings suggest the development of a PMN dysfunction syndrome in patients with increasing sepsis severity. Moreover, as binding of zymosan particles to the PMNs' surface remained unchanged despite increasingly suppressed phagocytosis and associated H2O2 production, observed effects are likely to reflect defects in signaling by the lectin-binding site of CD11b and/or the beta-glucan receptor dectin-1, respectively.     

Selective inhibition of polymorphonuclear neutrophils by resuscitative concentration of hypertonic saline

Objectives

This study investigated the effect of hypertonic saline on the role of polymorphonuclear neutrophils (PMNs) in the inflammatory response and the effect of hypertonic saline infused at different phases in relation to an inflammatory stimulus.

Materials and methods

PMNs were isolated from peripheral blood of healthy volunteers (Boyum''s method) and cultured in three different media ([Na⁺] = 140 mmol/l, 180 mmol/l, and 200 mmol/l). PMNs were then stimulated with fMLP (N‐formyl‐methionyl‐leucyl‐phenylalanine) and H₂O₂ synthesis was quantified by flow cytometry at 5, 30, 60, 120, and 180 minutes. PMNs were treated with hypertonic saline before, simultaneously with, and after fMLP stimulation, and H₂O₂ synthesis quantified again.

Results

H₂O₂ synthesis was two or three times higher in fMLP stimulated than in non‐stimulated PMNs, and it reached maximum level at 120 minutes. In the absence of fMLP stimulation, there was no significant difference between control and hypertonic saline with regard to activity of H₂O₂ synthesis. In the presence of fMLP stimulation, H₂O₂ synthesis significantly decreased in PMNs treated with hypertonic saline. There was no significant difference between the two hypertonic saline solutions ([Na⁺] = 180 mmol/l and 200 mmol/l) with regard to H₂O₂ synthesis. However, H₂O₂ synthesis decreased in PMNs treated with hypertonic saline before and simultaneously with fMLP stimulation, but was not significantly decreased in the cells treated with hypertonic saline after fMLP stimulation.

Conclusions

Hypertonic saline appears to decrease H₂O₂ in stimulated neutrophils. This may be a further beneficial role of hypertonic saline when used clinically as an early resuscitation fluid.     

Magnesium Attenuates the Neutrophil Respiratory Burst in Adult Asthmatic Patients

Introduction: IV magnesium (Mg²⁺) has been proposed as an emergent treatment for acute asthma exacerbations. Recent studies have focused on the effects of Mg²⁺ on bronchial smooth muscle, yet asthma is primarily an inflammatory disease. Objective: To assess the effects of Mg²⁺ on the neutrophil respiratory burst of adult patients with asthma. Methods: A prospective, blind study of volunteer adult asthmatic patients was performed. The patients' polymorphonuclear neutrophils (PMNs) were isolated, purified, and placed into phosphate-buffered saline with the following test conditions: concentrations of magnesium chloride (MgCl₂) added: 0 mmol MgCl₂, 1 mmol MgCl₂ (low), and 10 mmol MgCl₂ (high) both with and without the calcium (Ca) ionophore A23187 (0.1 mmol). PMNs were activated using N-formyl-methionyl-leucyl-phenylalanine (fMLP) (10 pmol), and the production of superoxide (O^-₂) was measured by the spectrophotometric reduction of cytochrome c. Results: Mg²⁺ reduced activated PMN O^-₂ production compared with that for no Mg²⁺ (1.0 ± 0.1 nmol O^-₂/5 ± 10⁵ PMN/min) in both low (-0.52* ± 0.3 nmol O^-₂/5 ± 10⁵ PMN/min) and high (-0.76* ± 0.3 nmol O^-₂/5 ± 10⁵ PMN/min; *p < 0.05) concentrations. The addition of A23187 increased O^-₂ production in both the high (0.53* ± 0.02 nmol O^-₂/5 ± 10⁵ PMN/min) and the low (1.5* ± 0.6 nmol O^-₂/5 ± 10⁵ PMN/ min) Mg²⁺ groups, with no change in the control group (1.2 ± 0.2 nmol O^-₂/10⁵ PMN/min). Conclusions: In clinically relevant concentrations, Mg²⁺ attenuates the neutrophil respiratory burst in adult asthmatic patients. Mg²⁺ appears to affect PMNs by interfering with extracellular Ca²⁺ influx. Mg²⁺ may have a beneficial anti-inflammatory effect in asthmatic individuals.     

Acute hypoxemia in humans enhances the neutrophil inflammatory response

The neutrophil (PMN) is regarded as a key component in the hyperinflammatory response known as the systemic inflammatory response syndrome. Acute respiratory distress syndrome (ARDS) and subsequent multiple organ failure (MOF) are related to the severity of this hyperinflammation. ICU patients who are at highest risk of developing MOF may have acute hypoxic events that complicate their hospital course. This study was undertaken to evaluate the effects of acute hypoxia and subsequent hypoxemia on circulating PMNs in human volunteers. Healthy subjects were exposed to a changing O2/N2 mixture until their O2 saturation (SaO2) reached a level of 68% saturation. These subjects were then exposed to room air and then returned to their baseline SaO2. PMNs were isolated from pre- and post-hypoxemic arterial blood samples and were then either stimulated with N-formyl-methionyl-leucyl-phenylalanine (fMLP) or PMA alone, or they were primed with L-alpha-phosphatidylcholine, beta-acetyl-gamma-O-alkyl (PAF) followed by fMLP activation. Reactive oxygen species generation as measured by superoxide anion production was enhanced in primed PMNs after hypoxemia. Protease degranulation as measured by elastase release was enhanced in both quiescent PMNs and primed PMNs after fMLP activation following the hypoxemic event. Adhesion molecule upregulation as measured by CD11b/CD18, however, was not significantly changed after hypoxemia. Apoptosis of quiescent PMNs was delayed after the hypoxemic event. TNFalpha, IL-1, IL-6, and IL-8 cytokine levels were unchanged following hypoxemia. These results indicate that relevant acute hypoxemic events observed in the clinical setting enhance several PMN cytotoxic functions and suggest that a transient hypoxemic insult may promote hyperinflammation.     

Molecular mechanism of the interaction between activated factor XIII and its glutamine donor peptide substrate

Summary. Background: Activated factor XIII (FXIII), a dimer of truncated A‐subunits (FXIII‐A₂*), is a transglutaminase that crosslinks primary amines to peptide‐bound glutamine residues. Because in the few natural substrates of FXIII‐A₂* no consensus sequence could be identified around the reactive glutamine, studying the interaction between individual substrates and FXIII‐A₂* is of primary importance. Most of the α₂‐plasmin inhibitor (α₂PI) molecules become truncated by a plasma protease, and the truncated isoform (N1‐α₂PI) is an important substrate of FXIII‐A₂*. The crosslinking of N1‐α₂PI to fibrin plays a major role in protecting fibrin from fibrinolysis. Methods: We studied the interaction of FXIII‐A₂* with its dodecapeptide glutamine donor substrate, N1‐α₂PI(1–12), the sequence of which corresponds to the N‐terminal sequence of N1‐α₂PI. Kinetic parameters for N1‐α₂PI(1–12) and for its truncated or synthetic mutants were determined by a spectrophotometric assay. The interaction of N1‐α₂PI(1–12) with FXIII‐A₂* was investigated by proton nuclear magnetic resonance (NMR) and saturating transfer difference (STD) NMR. Results and Conclusions: Kinetic experiments with peptides in which the Asn1 residue was either truncated or replaced by alanine and proton NMR analysis of the FXIII‐A₂*–N1‐α₂PI(1–12) complex demonstrated that Asn1 is essential for effective enzyme–substrate interaction. Experiments with C‐terminally truncated peptides proved that amino acids 7–12 are essential for the interaction of N1‐α₂PI(1–12) with the enzyme, and suggested the existence of a secondary binding site on FXIII‐A₂*. Hydrophobic residues, particularly Leu10 and the C‐terminal Lys12, seemed to be especially important in this respect, and direct interaction between hydrophobic C‐terminal residues and FXIII‐A₂* was demonstrated by STD NMR.     

Enhancement of fibrinolysis by inhibiting enzymatic cleavage of precursor α2‐antiplasmin

Summary. Background and objective: Resistance of thrombi to plasmin digestion depends primarily on the amount of α₂‐antiplasmin (α₂AP) incorporated within fibrin. Circulating prolyl‐specific serine proteinase, antiplasmin‐cleaving enzyme (APCE), a homologue of fibroblast activation protein (FAP), cleaves precursor Met‐α₂AP between ‐Pro12‐Asn13‐ to yield Asn‐α₂AP, which is crosslinked to fibrin approximately 13× more rapidly than Met‐α₂AP and confers resistance to plasmin. We reasoned that an APCE inhibitor might decrease conversion of Met‐α₂AP to Asn‐α₂AP and thereby enhance endogenous fibrinolysis. Methods and results: We designed and synthesized several APCE inhibitors and assessed each vs. plasma dipeptidyl peptidase IV (DPPIV) and prolyl oligopeptidase (POP), which have amino acid sequence similarity with APCE. Acetyl‐Arg‐(8‐amino‐3,6‐dioxaoctanoic acid)‐d ‐Ala‐l ‐boroPro selectively inhibited APCE vs. DPPIV, with an apparent K_i of 5.7 nm vs. 6.1 μm , indicating that an approximately 1000‐fold greater inhibitor concentration is required for DPPIV than for APCE. An apparent K_i of 7.4 nm was found for POP inhibition, which is similar to 5.7 nm for APCE; however, the potential problem of overlapping FAP/APCE and POP inhibition was negated by our finding that normal human plasma lacks POP activity. The inhibitor construct caused a dose‐dependent decrease of APCE‐mediated Met‐α₂AP cleavage, which ultimately shortened plasminogen activator‐induced plasma clot lysis times. Incubation of the inhibitor with human plasma for 22 h did not lessen its APCE inhibitory activity, with its IC₅₀ value in plasma remaining comparable to that in phosphate buffer. Conclusion: These data establish that inhibition of APCE might represent a therapeutic approach for enhancing thrombolytic activity.     

Increased neutrophil motility by beta-glucan in the absence of chemoattractant.

Systemic candidasis is a life-threatening complication of antibiotic and immunosuppressive therapies and can alter host defense mechanisms through pathways that are poorly understood. Promotion of polymorphonuclear leukocyte (PMN) chemotaxis by beta-glucan towards fMLP or IL-8 gradients demonstrates a fundamental effect on host defenses by pathogenic fungi. The aim of the present study was to determine whether recognition of beta-glucan is sufficient to alter PMN motility in the absence of agonists of G-coupled protein chemotactic receptors. Present findings demonstrate a profound increase in PMN motility by beta-glucan supplementation of a fibronectin substratum in an underagarose migration assay. Motility on beta-glucan included a 3-fold increase in distance of migration, as well as a 5-fold increase in the number of PMNs recruited into the motile phase as compared to motility on fibronectin alone. This promotion of motility is determined by the beta2 integrin complement receptor 3 (CR3) (CD11b/CD18) rather than the beta1 integrin very late antigen 3 (VLA-3), which mediates chemotaxis on beta-glucan-supplemented matrix towards fMLP. PMN motility on beta-glucan-supplemented fibronectin was selectively decreased by inhibitors of pp60 src and ras, whereas motility was promoted by inhibition of p38-MAPK. No effect of these inhibitors was seen on PMNs migrating on fibronectin alone. Migration on beta-glucan-supplemented fibronectin, but not on fibronectin alone, was negatively regulated by protein kinase C (PKC) or cAMP activation. These findings indicate that beta-glucan is sufficient to alter the migratory capacity of PMN in the absence of costimulation by fMLP. Enhanced PMN migration on beta-glucan is mediated through specific integrins and second messenger pathways that are distinct from those utilized by PMNs migrating in the absence of beta-glucan.     

Retention of thrombin inhibitory activity by recombinant serpins expressed as integral membrane proteins tethered to the surface of mammalian cells

Summary. Background: Serpins form a widely distributed protein superfamily, but no integral membrane serpins have been described. Objectives: To anchor three serpins –α₁‐proteinase inhibitor (α₁PI) (M358R), antithrombin (AT), and heparin cofactor II (HCII) – in the plasma membranes of transfected mammalian cells and assess their ability to inhibit thrombin. Methods: Serpin cDNAs were altered to include N‐terminal, non‐cleavable plasma membrane‐targeting sequences from the human transferrin receptor (TR) (TR‐serpin) or the human asialoglycoprotein receptor (AR) (AR‐serpin), and used to transfect COS‐1 or HEK 293 cells. Cells were analyzed for serpin expression by immunoblotting of subcellular fractions, by immunofluorescence microscopy, or by flow cytometry, with or without exposure to exogenous thrombin; AR‐serpins and TR‐serpins were also compared with their soluble recombinant counterparts. Results: Both TR‐α₁PI (M358R) and AR‐α₁PI (M358R) were enriched in the integral membrane fraction of transfected COS‐1 or HEK 293 cells, and formed inhibitory complexes with thrombin, although less rapidly than soluble α₁PI (M358R). Thrombin inhibition was abrogated by an additional T345R mutation in AR‐α₁PI (M358R). Surface‐displayed AR‐AT also formed serpin–enzyme complexes with thrombin, but to a lesser extent than AR‐α₁PI (M358R); AR‐HCII inhibitory function was not detected. Immunofluorescence detection and flow cytometric quantification of bound thrombin also supported the status of AR‐α₁PI (M358R) and AR‐AT as thrombin inhibitors. Conclusions: Two of three thrombin‐inhibitory serpins retained functionality when expressed as integral membrane proteins. Our findings could be applied to create and screen hypervariable serpin libraries expressed in mammalian cells, or to confer protease resistance on engineered cells in vivo.     

Neutrophil heterogeneity in patients with blunt trauma

To determine whether neutrophil (PMN) dysfunction observed in patients with blunt trauma could be explained by alterations in PMN functional subpopulations and to further study the origins of PMN heterogeneity, we studied PMN subpopulations in 18 patients with severe blunt trauma by using a micropore filter chemotactic assay and a mouse monoclonal antibody (31D8 Mab). A major PMN subpopulation binds 31D8 Mab avidly (31D8 "bright") and depolarizes and responds chemotactically to formyl peptide (fMLP) and C5a; a minor PMN subpopulation binds 31D8 Mab weakly (31D8 "dull") and fails to depolarize and responds poorly to fMLP and C5a. Fourteen patients with trauma had marked alteration of PMN 31D8 expression compared with healthy controls 52% +/- 20% versus 92% +/- 4% bright PMNs, respectively (p less than 0.01). These patients also had significantly decreased PMN chemotaxis and increased band counts compared with controls 30 +/- 10 micron versus 53 +/- 19 micron (p less than 0.01) and 34% +/- 14% versus 6% +/- 1% (p less than 0.01), respectively. Four patients with less-severe injuries had unaltered 31D8 PMN expression and normal PMN chemotaxis. In patients whose band counts exceeded 20%, there was a strong correlation between the number of bands and the percentage of 31D8 dull PMNs. PMNs that weakly express the 31D8 antigen appear to be less mature than PMNs that strongly express the antigen regardless of cell morphology (i.e., bands, multilobed cells). The data suggest that the decreased PMN chemotaxis and increased infection rate in patients with blunt trauma is caused partly by an increase in the number of poorly functioning 31D8 dull PMNs.     

Purine catabolism in polymorphonuclear neutrophils. Phorbol myristate acetate-induced accumulation of adenosine owing to inactivation of extracellularly released adenosine deaminase.

Since physiological concentrations (0.1-1 microM) of adenosine influence the functions of human polymorphonuclear neutrophils (PMNs), we investigated the metabolism of adenosine in suspensions of stimulated and unstimulated PMNs. Stimulation with phorbol myristate acetate (PMA, 1 microM), but not by zymosan (0.5 mg/ml) or N-formyl-methionyl-leucyl-phenylalanine (fMLP, 1 microM), provoked an accumulation of endogenous adenosine at a rate of 2.3 +/- 1.0 amol/cell per minute. A similar accumulation was observed with both unstimulated and stimulated PMNs after the addition of deoxycoformycin (dCF, 1-100 microM), an inhibitor of adenosine deaminase. Exogenous adenosine (10 microM) was deaminated at a rate of 9.8 +/- 3.7 amol/cell per minute in control or zymosan or fMLP-stimulated PMN suspensions. This deamination was nearly completely suppressed when the PMNs had been stimulated with PMA. In contrast, the activity of adenosine deaminase in PMN lysates (231 +/- 72 amol/cell per minute) was not modified by PMA stimulation. alpha, beta-Methyleneadenosine 5'-diphosphate (AMPCP, 2.5 mM), an inhibitor of membranous ecto-5'-nucleotidase, profoundly inhibited endogenous adenosine accumulation under all conditions. PMA stimulation also provoked an inactivation of extracellular adenosine deaminase, purine nucleoside phosphorylase, and lactate dehydrogenase in PMN suspensions. We concluded that PMNs, even when not stimulated, continuously produce adenosine by dephosphorylation of extracellularly released adenylates; and that stimulation of PMNs by PMA causes adenosine accumulation owing to the inactivation of adenosine deaminase released by broken cells.     

Lenograstim with or without dexamethasone for neutrophil mobilization in healthy donors: short-term kinetics of white blood cells and effects of granulocyte apheresis

Objectives : To determine the optimal time schedule for neutrophil collection after single mobilization with glycosylated recombinant granulocyte colony‐stimulating factor (G‐CSF, lenograstim) with or without dexamethasone (DXM). Donors and Methods : In this prospective randomized trial, 26 healthy volunteers were randomly assigned to a single subcutaneous dose of lenograstim 6 μg/kg plus 8‐mg DXM (G‐CSF/DXM, n = 13) or placebo (G‐CSF/placebo, n = 13). Hematological and biochemical parameters were analyzed before and 12, 15, 18, 21, 24, 27, 29, 36, 48, 60, 72, and 84 h and 7 and 30 days after mobilization. Six G‐CSF/DXM subjects underwent standard neutrophil apheresis (NA) 12 and 36 h after mobilization. Results : Polymorphonuclear neutrophil (PMN) counts 12 and 21 h after mobilization were 22.7 (16.6?32.8) × 10⁹/L and 22.4 (18.6?30.6) × 10⁹/L for G‐CSF/placebo versus 33.1 (24.2–44.9) × 10⁹/L and 32.5 (17.4–39.6) × 10⁹/L for G‐CSF/DXM. This mobilization plateau was followed by slow normalization at 72–84 h. The six NA subjects had median PMN yields of 62 (47–101) × 10⁹ and 39 (23–42) × 10⁹ per therapeutic unit. After the first apheresis, PMN counts sharply decreased to 21.1 (14.8–26.3) × 10⁹/L and then temporarily recovered to 25.9 (18.9–36.5) × 10⁹/L (P ≤ 0.001) over the next 8 h. Conclusions : Single doses of lenograstim with or without DXM induced a PMN plateau that lasted 9 h (12–21 h after mobilization), with PMN counts suitable for neutrophil collection. Lenograstim plus DXM made it possible to perform NA twice, 12 and 36 h after mobilization. © 2011 Wiley Periodicals, Inc.     

Effects of adenosine on functions of polymorphonuclear leukocytes from patients with septic shock

Inasmuch as polymorphonuclear leukocytes (PMNs) play a major role in antibacterial defense but can also cause substantial tissue injury, drugs are needed which are able to attenuate tissue-toxic PMN reactions without inhibiting bactericidal mechanisms. Adenosine as a retaliatory metabolite is produced in response to metabolically unfavorable conditions like inflammation. However, it is not known whether adenosine can selectively downregulate adverse PMN reactions in sepsis. In this prospective clinical study, we characterized the effects of adenosine ex vivo on PMN functions in patients with septic shock ([SS] n = 33) and healthy volunteers ([HV] n = 33). The PMNs were primed by tumor necrosis factor-alpha (TNF-alpha) and subsequently stimulated with N-formyl methionyl-leucyl-phenylalanine (fMLP) to test for the formation of hydrogen peroxide (H2O2) in response to soluble inflammatory stimuli. The PMNs were also challenged by opsonized zymosan particles to assess adhesion, phagocytosis, and the associated H2O2 production.As compared with HV, PMNs from SS patients showed strongly enhanced tissue-toxic H2O2 production elicited by TNF-alpha/fMLP. Increasing concentrations of adenosine dose-dependently reduced this tissue-toxic H2O2 production in both groups with a half-maximal inhibitory concentration of 25 nmol/L and 114 nmol/L in HV and SS patients, respectively. This 4.6-fold decrease in the adenosine-mediated inhibition of PMNs from patients with septic shock was compensated by a 3-fold increase in the plasma concentrations of the nucleoside (HV, 42.5 +/- 2.9 nmol/L vs. SS, 125.6 +/- 18.2 nmol/L; mean +/- SEM). When the effects of adenosine were tested at a very high A2A receptor saturating concentration of 10 mol/L, neither adhesion, phagocytosis, nor the associated H2O2 production induced by opsonized zymosan was affected in both groups. These results were confirmed by the highly selective A2A agonist, CGS21680.Thus, adenosine or A2A agonists may be useful to selectively inhibit the potentially tissue-toxic H2O2 production elicited by soluble inflammatory mediators in patients with septic shock.     

Quantification of Bax and Bcl2 in polymorphonuclear leukocytes from haemodialysis patients: relation to hydrogen peroxide

Background Bax and Bcl2 are two apoptosis‐related molecules that play an important role in determining cell fate following oxidative injury. In the present study, we explored the relation of hydrogen peroxide (H₂O₂) generation by polymorphonuclear cells (PMNs) to the cytosolic expression of Bax and Bcl2 proteins and apoptosis in haemodialysis (HD) patients. Methods Cytosolic generation of H₂O₂ by PMNs from control subjects and HD patients was measured by flow cytometry using the dichlorofluorescin diacetate assay. Bax and Bcl2 expression was detected by flow cytometry using FITC‐conjugated antibodies. Apoptosis was quantified by flow cytometry using propidium iodide nuclear staining. To examine the effect of H₂O₂ on Bcl2 and Bax expression, PMNs from control subjects were briefly exposed to H₂O₂ (0·1–100 µM) for 10 min and then washed and cultured for 6 h, with or without catalase, a H₂O₂ detoxifying molecule. Bcl2 and Bax expression was determined by Western blot analysis. Results Basal H₂O₂ generation by resting PMNs was significantly higher in HD patients compared with control subjects (211 ± 115 vs. 23 ± 5 MFI; P = 0·002). However, PMNs from HD patients did not undergo accelerated programmed cell death compared with control subjects (58 ± 7% vs. 46 ± 5; P = 0·14). Polymorphonuclear cells cytosolic Bcl2 was undetected in control subjects but detected in 25% of HD patients, and Bax was more frequently detected in PMNs from HD patients (75% vs. 67%; P = 0·04). In the HD patients with detectable cytosolic Bax and Bcl2 proteins, the Bax to Bcl2 ratio inversely correlated with H₂O₂ levels (P < 0·0001). Finally, brief exposure of PMNs to 0·1–100 µM of H₂O₂ resulted in a marked increase in Bcl2 expression (P = 0·001), which was prevented by catalase (P = 0·05). There was no apparent effect on Bax expression. Conclusions This study demonstrates that in HD patients, high‐resting cytosolic H₂O₂ production by PMNs is not associated with accelerated in vitro apoptosis, and that the Bax/Bcl2 system may counter‐balance the deleterious effects of reactive oxygen species in human PMNs.     

Hyperosmolarity abrogates neutrophil cytotoxicity provoked by post-shock mesenteric lymph

Hypertonic saline (HTS) resuscitation inhibits acute lung injury in animal models of shock, but some argue this may simply represent more efficient fluid resuscitation. Inflammatory mediators within mesenteric lymph have been identified as a link between splanchnic hypoperfusion and acute respiratory distress syndrome (ARDS). We hypothesize that HTS resuscitation abrogates post-shock lymph-mediated neutrophil (PMN) priming and PMN-mediated human endothelial cell cytotoxicity. Mesenteric lymph was collected from rats (n = 5) before (control), during non-lethal hemorrhagic shock, defined as a mean arterial pressure (MAP) of 40 mmHg for 30 min, and after resuscitation (shed blood + 2 x lactated Ringers (LR) versus 7.5% NaCl, 4 cc/kg, over 5 min). Isolated human PMNs were primed with physiologic concentrations (5% v:v) of lymph either from animals resuscitated with LR or HTS and activated with either PMA or fMLP. In a separate set of experiments, human PMNs were primed with LR lymph after incubation with HTS (180 mM NaCl). The maximal rate of superoxide production was measured by reduction of cytochrome C. In addition, the effect of HTS pretreatment on PMN adherence to human pulmonary microvascular endothelial cells (HMVEC) and PMN-mediated cytotoxicity was determined after lymph-mediated PMN priming. PHSML primed isolated PMNs above buffer controls and pre-shock lymph in a normotonic environment; HTS resuscitation abrogated this effect. HTS preincubation of isolated PMNs inhibited PHSML-induced PMN priming, adherence to HMVECs, and PMN-mediated HMVEC cytotoxicity. Hypertonic resuscitation (HTS) abrogates PHSML pniming of the PMN and PMN-mediated HMVEC cytotoxicity. Furthermore, incubation of PMNs in clinically relevant HTS (180 mM NaCl) prevents PHSML PMN priming and PMN:HMVEC interactions. These studies suggest inhibition of PMN signal transduction is a mechanism whereby HTS resuscitation abrogates acute lung injury.     

Electrochemical detection of nitric oxide production in human polymorphonuclear neutrophil leukocytes.

The detection of nitric oxide (NO) release by human polymorphonuclear neutrophil leukocytes (PMNs) presents several difficulties, mainly due to concomitant production of O2- and H2O2, which could interfere with the measurements. A Nafion and nickel porphyrin-coated microelectrode was used to measure NO production in PMNs in vitro. It allowed detection of 6.3 +/- 1.9 nM NO in a PMN-containing system and was unaffected by added chemicals. Addition of the chemotactic oligopeptide f-met-leu-phe (fMLP; 100 nM) induced a NO release which reached a value of 71 +/- 30 pmol NO/10(6) PMN x ml(-1) 5 min after stimulation in the presence of SOD (150 U/ml). If SOD was omitted, the corresponding value was 36 +/- 20 pmol NO/10(6) PMN x ml(-1). Presence or absence of catalase did not alter the amount of NO measured. Addition of the NO-synthase inhibitor N(G)-monomethyl-L-arginine (LNMMA; 1 mM) reduced the current by 82 +/- 20%. These results agree with the rate of NO production in human PMNs when measured spectrophotometrically using the NO-dependent oxidation of oxyhaemoglobin to methaemoglobin. The NO production in human PMN was dependent on fMLP concentrations, but independent of cell-concentrations of 0.5-3.5 x 10(6)/ml. This paper shows that a electrochemical method, e.g. Nafion and porphyrin-coated microelectrode, is suitable for studies of NO release from stimulated human PMNs.     

Entry of gut lymph into the circulation primes rat neutrophil respiratory burst in hemorrhagic shock.

OBJECTIVE: Endothelial cell injury by polymorphonuclear neutrophil (neutrophil [PMN]) respiratory burst after trauma and hemorrhagic shock (T/HS) predisposes subjects to acute respiratory distress syndrome and multiple organ failure. T/HS mesenteric lymph injures endothelial cell and lymph duct ligation (LDL) before T/HS prevents pulmonary injury. We investigated the role of mesenteric lymph in PMN priming by T/HS. DESIGN: Prospective experiment in rats. SETTING: University hospital laboratory. SUBJECTS: Adult male rats. INTERVENTIONS: Mesenteric lymph was obtained from rats undergoing T/HS (30 mm Hg, 90 mins) or sham shock (T/SS). Plasma was harvested from uninstrumented control (UC), T/HS, T/SS, and T/HS+LDL rats. PMNs were isolated from UC, T/HS, and T/HS+LDL rats. MEASUREMENTS AND MAIN RESULTS: PMNs from UC rats were incubated in buffer, 1% T/HS lymph, and 1% T/SS lymph. PMNs from UC rats were incubated in UC, T/HS, T/SS, and T/HS+LDL plasma. PMN respiratory burst was initiated by using macrophage inflammatory protein (MIP)-2/platelet-aggregating factor (PAF) or phorbol myristate acetate. Cytosolic calcium ([Ca2+]i) responses to MIP-2/PAF were assayed in PMN from UC, T/HS, and T/HS+LDL rats. PMN preincubated in T/HS lymph showed significant elevations in MIP/PAF-elicited respiratory burst compared with T/HS lymph or buffer only (p <.05; analysis of variance/Tukey's test). T/HS lymph incubation also increased (p <.05) phorbol myristate acetate elicited respiratory burst compared with buffer or T/SS. Preincubation in T/HS plasma increased MIP-2/PAF-elicited respiratory burst (p <.05) compared with UC or T/SS plasma. LDL blocked T/HS priming of respiratory burst. Control PMN [Ca2+]i responses to MIP-2 and PAF were low. T/SS PMN were significantly more responsive, but the T/HS PMN showed still higher responses (p <.01). LDL reversed the priming of [Ca2+]i responses by T/HS (p <.01). CONCLUSIONS: PMNs are primed by T/HS lymph but not T/SS lymph and by T/HS plasma but not T/SS plasma. LDL before shock prevents T/HS plasma from priming PMN. The magnitude of respiratory burst found here paralleled the [Ca2+]i responses seen to receptor dependent initiating agonists. Mesenteric lymph is both necessary and sufficient to prime PMN after T/HS in the rat, and it primes PMN in part by enhancing [Ca2+]i responses to G-protein coupled chemoattractants. Mesenteric lymph mediates postshock PMN dysfunction.     

Ciprofloxacin transport by chemoattractant-activated polymorphonuclear leukocytes: regulation by priming and protein kinase C

At infection sites, polymorphonuclear leukocyte (PMN) function is enhanced ("primed") by granulocyte-macrophage colony-stimulating factor (GM-CSF) or lipopolysaccharide (LPS) and activated by formyl peptides. In this study, GM-CSF or LPS alone had no significant effects on PMN ciprofloxacin transport. Through a mechanism involving protein kinase C, activation by formyl-Met-Leu-Phe (fMLP) significantly decreased the K(m) of ciprofloxacin transport and enhanced ciprofloxacin accumulation. This effect was dramatically enhanced when PMNs were primed with GM-CSF or LPS prior to activation by fMLP.