Altered calcium regulation and function of human neutrophils during multiple trauma

Altered intracellular Ca2+ concentration is a pivotal regulatory mechanism of leukocyte function. Since polymorphonuclear neutrophils (PMN) are involved in traumatic organ dysfunction, we prospectively investigated Ca2+ regulation and function of circulating PMN multiple trauma patients (Group A: ISS < 27; Group B: ISS > or = 27). Circulating PMN were isolated during 12 days, followed by determination of formyl-methionyl-leucyl-phenylalanine (fMLP)-induced PMN-superoxide production (PMN-SOP) by SOD-inhibitable ferricytochrome C reduction, and PMN cytosolic Ca2+ concentration ([Ca2+]i) by fluorescent fura2/AM (340/380 ratio). PMN-SOP was significantly higher in Group B (mean ISS: 39.9 +/- 2; n = 21) at day of admission than in controls and Group A (mean ISS: 18.2 +/- 1; n = 22) (P< 0.05). In Group B, the significant rise of basal [Ca2+]i between Day 2 and Day 4 was associated with significant lower PMN-SOP during that period (P < 0.05). The fMLP-induced [Ca2+]i response was supranormal in both groups. PMN-elastase concentrations were substantially higher in Group B compared with Group A until Day 4. Circulating IL-6, IL-8, and soluble TNF-receptor (55 kD) were significantly increased in Group B compared with Group A at the day of trauma (P < 0.05). Severe trauma is characterized by a biphasic pattern of neutrophil priming characterized by early increase and secondary suppression. The association of depressed neutrophil superoxide production (deactivation) and elevated basal [Ca2+]i suggests Ca2+-mediated disturbance of neutrophil NADPH-oxidase metabolism.     

Generation of superoxide radicals by human peripheral neutrophils activated by chemotactic factor. Evidence for the role of calcium.

In response to activation by the synthetic chemotactic factor FMLP, human peripheral neutrophils generated superoxide radicals as assessed by ferricytochrome C reduction. A dose-dependent increase in the amount of superoxide induced by FMLP over the concentration range of 1 X 10(-8) M to 1.6 X 10(-7) M was observed. Examination of the kinetics of the response revealed large amounts of superoxide generated by 1 min of incubation at 37 degrees C at an optimal dose of FMLP and a plateau effect after 5 min of incubation. Divalent cations did not influence the binding of 3H-FMLP to the cell, but superoxide generation by FMLP-activated neutrophils was observed to be dependent on the presence of divalent cations in the medium. In the absence of Mg2+, increasing Ca2+ ion concentration in the medium led to progressive increases in superoxide generation up to 4 mM, after which the response declined slightly. Mg2+, 0.25 to 4 mM, increased FMLP-induced superoxide generation to a much lower extent than did Ca2+. Lanthanum ion, 0.1 to 1 mM, in the presence of 1 mM Ca2+ inhibited the production of superoxide by FMLP 4 X 10(-8 ) M. Over the concentration range 3.3 X 10(-5 M to 3 X 10(-4 M, verapamil, a drug which selectively blocks the calcium channel, caused a dose-dependent inhibition of superoxide production and calcium-45 uptake in response to FMLP. This effect of verapamil could be overcome by increasing the concentration of Ca2+ in the medium. These observations suggest that a calcium influx plays an important role in the superoxide-generating capacity of the neutrophil.     

Interactions between alkylglycerols and human neutrophil granulocytes

We evaluated whether various alkylglycerols would initiate a functional response of human neutrophils or modify responses induced by a formyl peptide (fMLP) in vitro. We found that platelet activating factor (PAF) was the most potent with regard to the ability to produce an oxidative response (assessed by cytochrome c reduction and/or chemiluminescence), followed by ET-16-OCH3. Lyso-PAF, ET-18-OCH3, batyl- and chimyl alcohols exhibited only a weak activity. PAF was also the most efficient lipid conferring a rise of intracellular calcium concentrations ([Ca2+]i). ET-16-OCH3, ET-18-OCH3 and lysoPAF were less potent, although maximal [Ca2+]i levels were similar to that of 0.1 mumol/l fMLP. The kinetics of the calcium responses were highly specific for each ether lipid. When neutrophils had been treated with PAF or ET-18-OCH3 and were subsequently stimulated by fMLP, enhancement of the oxidative response was noted. Thus, this study shows that there was an association between the ability of an alkylglycerol to initiate oxidative and calcium responses, indicating strict structure-activity relationships for these lipids.     

WEB2170, a specific platelet-activating factor antagonist, attenuates neutrophil priming by human serum after clinical burn injury: the 1991 Moyer Award.

Primed neutrophils may contribute to endothelial and end-organ damage after burn injury because of increased endothelial adherence and enhanced toxic oxygen metabolite generation in response to a "second insult" such as bacterial sepsis. The purposes of this study were to determine: (1) whether serum from patients with thermal injury causes priming of the neutrophil NADPH:O2 oxidoreductase, (2) whether time after burn (early vs late) influences neutrophil priming, and (3) whether priming could be attenuated by a specific platelet-activating factor antagonist, WEB2170. Normal human neutrophils were incubated with 10% sera that was obtained from healthy adult controls (normal human sera) and with 10% sera from patients with greater than 30% total body surface area burns, which was collected early (early postburn sera) (i.e., between 12 and 48 hours after burn) or late (late postburn sera) (5 to 15 days, after burn). Priming of the neutrophil oxidase was tested for by measurement of the generation of superoxide anion after a stimulus of 10(-6) mol/L formyl-methionine-leucine-phenylalanine (fMLP). In separate experiments, neutrophils were pretreated with WEB2170 before serum incubation and fMLP stimulation to block any priming that may be mediated by platelet-activating factor. All sera caused an increased rate of superoxide anion production in response to fMLP and thus "primed" the neutrophil NADPH:O2 oxidoreductase. Greater priming occurred after incubation with late postburn sera than with other sera. WEB2170 completely inhibited priming by normal human sera and early postburn sera and partially inhibited priming by late postburn sera.(ABSTRACT TRUNCATED AT 250 WORDS)     

N-乙酰半胱氨酸对人离体中性白细胞释放超氧阴离子的影响

目的用人离体中性白细胞研究N-乙酰半胱氨酸(N-acetylcysteine,NAC)对中性白细胞释放超氧阴离子的影响。方法细胞色素C还原法测定NAC对三种刺激剂介导的中性白细胞释放超氧阴离子量。用抗原抗体法检测丝或苏氨酸磷酸化。结果NAC可呈浓度依赖性抑制N-甲酰甲硫氨酰-亮氨酰-苯丙氨酸(fMLP)和佛波豆蔻醚乙酸盐(PMA)介导的中性白细胞释放超氧阴离子;而对花生四烯酸(AA)介导的中性白细胞释放超氧阴离子无影响。Western blot结果显示NAC可呈浓度依赖性抑制fMLP和PMA介导的丝氨酸或苏氨酸的磷酸化。结论NAC可能通过膜受体通道抑制细胞内的蛋白激酶C及其上游的蛋白质激酶,抑制中性白细胞释放超氧阴离子的产生。     

Verapamil impairs human neutrophil chemotaxis by a non-calcium-mediated mechanism

The in vitro effect of pharmacologic concentrations (10(-8) to 10(-6) mol/L) of verapamil on human neutrophil migration and response to chemotactic signals was examined. Human neutrophils were preincubated (15 minutes) in verapamil and then assayed for chemotactic response to formyl-methionyl-leucyl-phenylalanine (f-Met-Leu-Phe) (10(-8) mol/L). Cell viability was not affected by verapamil treatment. Verapamil-treated cells displayed 40% to 50% reductions in directed migration at all concentrations (P less than 0.02). Activated random migration (chemokinesis) was also impaired by verapamil treatment, but random locomotion was not affected except at a high concentration (10(-6) mol/L). This pharmacologic action of verapamil was not rapidly reversible by washing cells free of drug, but it was necessary that cells be exposed to drug before the chemotactic signal. In addition to f-Met-Leu-Phe, chemotactic response to activated human serum was also reduced for neutrophils. Several experiments were conducted to determine whether verapamil affected neutrophils as a calcium antagonist. Calcium antagonist binding-site assays using radiolabeled dihydropyridines provided no evidence for the presence of calcium channels in neutrophil membranes. Also, 45Ca2+ uptake assays demonstrated increased uptake of 45Ca2+ by f-Met-Leu-Phe-stimulated neutrophils, but no effect on uptake by verapamil exposures (10(-6) mol/L). Finally, the cytosolic calcium-chelating dye, quin 2 acetomethoxy ester (quin 2), was used as a fluorescent indicator to measure cytosolic Ca2+ concentrations, [Ca2+]i, in neutrophils. Verapamil exposures over a wide concentration range (10(-6) to 10(-4) mol/L) did not affect resting [Ca2+]i or [Ca2+]i transients after f-Met-Leu-Phe (10(-8) mol/L) stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differential regulation of Ca2+ influx by fMLP and PAF in human neutrophils: possible involvement of store-operated Ca2+ channel

Calcium (Ca2+) influx into human polymorphonuclear cells (PMNs) in response to N-formyl-Met-Leu-Phe (fMLP) and platelet-activating factor (PAF) stimulation was studied. Whole blood was taken by venous puncture from healthy human volunteers. PMNs were isolated, diluted, and incubated with 2 microM fura-2 AM. The cytosolic free calcium concentration, [Ca2+]i, in human neutrophils was determined by microfluorometry. We found that the net area under the fMLP- or PAF-induced [Ca2+]i rise curve in Ca2+-free medium decreased to 75% or 30% of the area under the curve in Ca2+ medium. Treatment of PMNs with phorbol myristate acetate (PMA), a protein kinase C activator, completely abolished the intracellular Ca2+ level stimulated by PAF, but not the intracellular Ca2+ level stimulated by fMLP. Treatment of PMNs with PAF did not abolish the intracellular Ca2+ level elevation stimulated by fMLP. In addition, treatment of PMNs with fMLP did not abolish intracellular Ca2+ level elevation stimulated by PAF. Loperamide, a positive modulator for store-operated calcium (SOC) channels, elicited an increase in intracellular calcium after the activation of SOC channels stimulated by fMLP or PAF. After the addition of guanosine 3',5'-cyclic monophosphate, N2,2'-O-Dibutyryl-, sodium salt (db-cGMP), the initial increase of PAF- or fMLP-induced PMNs intracellular Ca2+ fluorescences was well preserved, but the slope and the peak height of fluorescence curves declined compared with the curves without db-cGMP. In conclusion, we found that PAF and fMLP regulate the Ca2+ influx of PMNs in different ways. Most of the PAF-induced [Ca2+]i rise resulted from Ca2+ influx, and most of the fMLP-induced [Ca2+]i elevation resulted from intracellular stores release. The initial mobilization of intracellular Ca2+ stores in PAF-stimulated signals is mediated by protein kinase C (PKC) phosphorylation, but not in fMLP-stimulated route. SOC channels are present and important in the fMLP- or PAF-induced PMNs Ca2+ influx. There was no apparent cross-regulation between PAF- and fMLP-stimulated intracellular Ca2+ influx.     

Chemotactic peptide activation of human neutrophils and HL-60 cells. Pertussis toxin reveals correlation between inositol trisphosphate generation, calcium ion transients, and cellular activation.

The mechanism of neutrophil activation by the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (FMLP) has been studied by pretreatment of human neutrophils with pertussis toxin. Upon stimulation with FMLP, the cytosolic-free calcium concentration, [Ca2+]i, is increased both by stimulation of calcium influx and mobilization of cellular calcium. We have measured [Ca2+]i as well as the generation of the phospholipid breakdown product inositol trisphosphate (IP3), which is thought to mediate Ca2+ mobilization. As the phosphoinositide pool in human neutrophils is difficult to prelabel with [3H]myoinositol, experiments were also carried out in the cultured human promyelocytic leukemia cell line HL-60 after differentiation with dimethylsulfoxide. Pertussis toxin pretreatment of both cell types inhibited FMLP stimulated membrane depolarization, exocytosis, and superoxide production in a dose-dependent manner. This toxin effect was selective for the receptor agonist, since stimulation of these parameters by two substances bypassing the transduction mechanism, the calcium ionophore ionomycin and the phorbolester phorbol myristate acetate, were unaffected. Rises in [Ca2+]i, as well as generation of IP3 in response to FMLP, were inhibited in parallel; for the inhibition of functional responses, slightly lower toxin concentrations were required. The attentuation of the [Ca2+]i rise was more marked in the absence of extracellular calcium, i.e., when the rise is due only to calcium mobilization. The results provide evidence that phospholipase C stimulation by FMLP resulting in IP3 generation is involved in the signal transduction mechanism. Coupling of FMLP receptor occupancy to phospholipase C activation is sensitive to pertussis toxin, suggesting the involvement of a GTP binding protein (N protein), which has been shown to be a pertussis toxin substrate. The parallel changes in [Ca2+]i and IP3 further support the hypothesis that IP3 is the calcium-mobilizing mediator in FMLP-activated cells.     

Impaired neutrophil store-mediated calcium entry in Type 2 diabetes

BACKGROUND: In Type 2 diabetes impaired neutrophil function leads to increased bacterial infection and cardiovascular disease. Many neutrophil functions depend on calcium signalling, which involves release of calcium from intracellular stores and subsequently translocation of stores via the cytoskeleton to the plasma membrane, causing store-mediated calcium entry (SMCE) into the cell. We hypothesized that in Type 2 diabetes there would be a defect in SMCE. MATERIALS AND METHODS: Neutrophils were prepared from patients with Type 2 diabetes (DM, n=15) and controls (NC, n=15). Free cytosolic calcium [Ca2+]i was measured with Fura-2 in resting cells and after stimulation of calcium release with fMLP and thapsigargin. RESULTS: Baseline [Ca2+]i was higher in neutrophils from the patients than the controls (NC 65 +/- 5 nm, DM 80 +/- 4 nm, P<0.05). However, after fMLP-treatment [Ca2+]i was significantly lower in the patients (NC 301 +/- 28 nm, DM 210 +/- 20 nm, P<0.01). The greater increase in controls was not observed when cells were treated with fMLP in the absence of extracellular calcium (-fold increase NC 2.9 +/- 0.5, DM 2.7 +/- 0.3). Treatment of cells with thapsigargin caused a similar greater increase in [Ca2+]i in the controls than in the patients that was not seen in the absence of extracellular calcium (-fold increase with Ca2+ NC 5.2 +/- 1.0, DM 3.0 +/- 0.4, P<0.05; fold increase without Ca2+ NC 2.5 +/- 0.4, DM 2.2 +/- 0.2). CONCLUSIONS: In Type 2 diabetes there is a defect in neutrophil calcium signalling which results in a lesser increase in free cytosolic calcium owing to impaired influx across the plasma membrane. Abnormal calcium signalling is likely to be important in the pathogenesis of diabetic complications.     

Lipopolysaccharide priming of human neutrophils for an enhanced respiratory burst. Role of intracellular free calcium.

Lipopolysaccharide (LPS) pretreatment "primes" neutrophils to release increased amounts of superoxide anion (O2-) when stimulated. We investigated the molecular basis of this enhanced activity. Comparison of kinetic parameters of the respiratory burst NADPH oxidase in unstimulated LPS-primed and control neutrophils disclosed a similar Km for NADPH and no difference was seen in the content of cytochrome b. Pertussis toxin, which inhibits some G proteins, did not prevent priming. Change in membrane potential (delta psi) was five-fold greater in LPS-primed cells and paralleled the increased O2- release. Cytofluorographic analysis indicated that the increased change in delta psi was due to the creation of a new population of active cells. Changes in the concentration of intracellular free Ca2+ ([Ca2+]i) are believed to antecede changes in delta psi. There was a consistent increment (67 +/- 8%, n = 12) in resting [Ca2+]i in cells preincubated with LPS compared with control. When stimulated, the peak [Ca2+]i was significantly higher in LPS-primed cells. Ca2+-dependent protein kinase C activity was unaltered in resting and FMLP-stimulated neutrophils preexposed to LPS. Addition to cells of the intracellular Ca2+ chelator MAPTAM before preincubation with LPS blocked the changes in [Ca2+]i and the enhanced respiratory burst that characterize LPS priming. The increased resting [Ca2+]i in LPS-primed cells may enhance stimulus-induced cellular activity by modifying a Ca2+-dependent step in signal transduction.     

Nitric oxide, an endothelial cell relaxation factor, inhibits neutrophil superoxide anion production via a direct action on the NADPH oxidase.

Nitric oxide provokes vasodilation and inhibits platelet aggregation. We examined the effect of nitric oxide on superoxide anion production by three sources: activated intact neutrophils, xanthine oxidase/hypoxanthine, and the NADPH oxidase. Nitric oxide significantly inhibited the generation of superoxide anion by neutrophils exposed to either FMLP (10(-7)M) or PMA (150 ng/ml) (IC50 = 30 microM). To determine whether the effect of nitric oxide on the respiratory burst was due to simple scavenging of O2+, kinetic studies that compared effects on neutrophils and the cell-free xanthine oxidase system were performed. Nitric oxide inhibited O2+ produced by xanthine oxidase only when added simultaneously with substrate, consistent with the short half-life of NO in oxygenated solution. In contrast, the addition of nitric oxide to neutrophils 20 min before FMLP resulted in the inhibition of O2+ production, which suggests formation of a stable intermediate. The effect of nitric oxide on the cell-free NADPH oxidase superoxide-generating system was also examined: The addition of NO before arachidonate activation (t = -6 min) significantly inhibited superoxide anion production. Nitric oxide did not inhibit O2+ when added at NADPH initiation (t = 0). Treatment of the membrane but not cytosolic component of the oxidase was sufficient to inhibit O2+ generation. The data suggest that nitric oxide inhibits neutrophil O2+ production via direct effects on membrane components of the NADPH oxidase. This action must occur before the assembly of the activated complex.     

Selective differentiation and proliferation of human eosinophils from umbilical cord blood: calcium fluxes and superoxide ion secretion

Investigation of the physiologic mechanisms involved in the activation of eosinophils is crucial to comprehend their role in the pathogenesis of allergic reactions. To overcome the difficulty of obtaining large numbers of eosinophils, we differentiated in vitro eosinophils from human umbilical cord blood mononuclear cells. These cells responded to fMLP or PAF with an increase in [Ca2+]i, associated with O2 production. Deprivation or chelation of extracellular calcium induced a reduction of fMLP or PAF-induced [Ca2+]i rise and O2- production. Similar results were obtained with extracellular Ni2+ addition. Chelation of intracellular calcium induced an inhibition of fMLP- or PAF-induced [Ca2+]i rise and a decrease in O2- production. Our results indicate that fMLP- and PAF-dependent O2- production in eosinophils requires intra- and extracellular Ca2+ and that Ca2+ influx is necessary for optimal activation.     

Monophosphoryl lipid A inhibits neutrophil priming by lipopolysaccharide

It is known that lipopolysaccharides (endotoxin) prime neutrophils for oxygen radical production. Monophosphoryl lipid A is a nontoxic derivative of lipid A that protects against lethal endotoxemia. We examined the effects of Salmonella minnesota monophosphoryl lipid A on S. minnesota lipopolysaccharide-induced priming of neutrophil superoxide anion generation. Human neutrophils were preincubated with and without either lipopolysaccharide or monophosphoryl lipid A before stimulation with 10(-5) formyl-norleucyl-leucyl-phenylalanine. Neutrophil priming reached a plateau at a concentration of 100 ng/ml of lipopolysaccharide, where superoxide anion generation increased from 10.1 +/- 0.8 to 25.2 +/- 1.7 nmol superoxide anions/10(6) neutrophils/10 min (p less than 0.01). In contrast, monophosphoryl lipid A did not exhibit any priming activity. Monophosphoryl lipid A also exhibited a time-dependent inhibitory effect on lipopolysaccharide-induced priming of neutrophils, which was maximal when monophosphoryl lipid A was added 15 minutes before lipopolysaccharide. Preincubation with monophosphoryl lipid A induced a dose-dependent inhibition of neutrophil priming by 1000 ng/ml lipopolysaccharide. Neutrophil superoxide anion generation decreased by 47% from 19.0 +/- 0.6 to 10.0 +/- 0.7 nmol superoxide anions/10(6) neutrophils/10 min by 2000 ng/ml monophosphoryl lipid A (p less than 0.01). These data indicate that monophosphoryl lipid A does not enhance neutrophil superoxide generation in response to formyl-norleucyl-leucyl-phenylalanine. Monophosphoryl lipid A also inhibits lipopolysaccharide-induced priming in a dose-dependent manner that may reflect blocking of lipopolysaccharide by monophosphoryl lipid A at cellular binding sites.     

Priming by grepafloxacin on respiratory burst of human neutrophils: its possible mechanism

Grepafloxacin is a broad-spectrum fluoroquinolone derivative that has good tissue penetration. We demonstrated that grepafloxacin showed a priming effect on neutrophil respiratory burst, triggered by either a chemotactic factor N-formyl-methionyl-leucyl-phenylalanine (fMLP) or leukotriene B4 (LTB4), but not by the phorbol ester phorbol 12-myristate 13-acetate (PMA). The priming effect of grepafloxacin on fMLP-stimulated superoxide generation by human neutrophils correlated with the penetration of grepafloxacin into cells. Removal of extracellular grepafloxacin did not inhibit the priming effect on fMLP-stimulated superoxide generation. Furthermore, grepafloxacin induced the translocation of p47-phox and p67-phox to the membrane fraction of neutrophils, whereas tyrosine phosphorylation was hardly observed in neutrophils exposed to grepafloxacin. The priming effect of grepafloxacin on superoxide generation from neutrophils was not inhibited by treatment with pertussis toxin, a protein-tyrosine kinase inhibitor (ST-638) or a protein kinase C inhibitor (calphostin C), or chelation of extracellular calcium. Grepafloxacin did not change the fMLP receptor-binding properties. Taken together, these findings suggest that grepafloxacin evokes a priming effect on neutrophil superoxide generation intracellularly through the translocation of p47-phox and even p67-phox protein to the membrane fractions. GTP binding protein, protein-tyrosine phosphorylation and protein kinase C activation are not involved in the priming effect.     

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.     

Inhibition of neutrophil and natural killer cell function by human seminal fluid acid phosphatase

The major acid phosphatase of human seminal fluid was purified to homogeneity by chromatography on Sephadex G-150, and DEAE-Sephadex, and by isoelectric focusing (pI, 4.3). This purified preparation of seminal fluid acid phosphatase blocked superoxide anion production by neutrophils stimulated with fMet-Leu-Phe (fMLP) by 50%. The phosphatase also hydrolysed myo-inositol 1,4,5-trisphosphate (IP3) in vitro, an intracellular second messenger which releases Ca2+ from intracellular pools, at nearly one-third the rate at which the nonphysiologic substrate 4-methylumbelliferylphosphate (MUP) was cleaved. In contrast, two phosphoinositide lipids, namely phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-monophosphate, were poor phosphatase substrates. Following fMLP stimulation of [3H]inositol-labeled neutrophils, the quantity of IP3 produced by phosphatase-treated cells was reduced by 69%. These results indicate that the human seminal fluid acid phosphatase may compromise the neutrophil's microbicidal response to the organism by hydrolyzing a second messenger (IP3) which is directly involved in the regulation of intracellular Ca2+ concentrations. The seminal fluid phosphatase also inhibited by 85% the ability of murine natural killer (NK) cells to inactivate target cells.     

Faropenem,a new oral penem: antibacterial activity against selected anaerobic and fastidious periodontal isolates

The in vitro activity of faropenem, an oral penem, was compared with those of penicillin, co-amoxiclav, cefoxitin, clindamycin, erythromycin and metronidazole against 106 isolates of anaerobic pathogens involved in systemic infections. The organisms tested comprised Porphyromonas gingivalis (29), Prevotella spp. (eight), Prevotella melaninogenica (seven), Prevotella intermedia (five), Actinomyces spp. (25), Fusobacterium nucleatum (14), Peptostreptococcus spp. (11), Bacteroides ureolyticus (five) and Bacteroides forsythus (two). The antimicrobial properties of faropenem were investigated by studying MICs, MBCs, time-kill kinetics and post-antibiotic effect (PAE). Faropenem was highly active against all the anaerobes tested (MIC(90) < or = 0.5 mg/L) and was bactericidal against both beta-lactamase-positive and -negative anaerobes, with a maximum bactericidal effect at 10 x MIC at between 12 and 24 h. In addition, faropenem had an in vitro PAE on all the tested isolates and this was not influenced by beta-lactamase production. Faropenem may be useful for treating infections caused by periodontal bacteria or oral flora.     

H2-antagonist inhibition of human neutrophil superoxide anion synthesis

In the mmol/L concentration range, cimetidine and ranitidine suppress superoxide anion generation by isolated intact human neutrophils. However, at normal pharmacologic concentrations in the mumol/L range, even prolonged exposure of neutrophils to these agents has no demonstrable effect on toxic oxygen species synthesis. In vitro inhibition does not involve neutrophil activation-densensitization or neutrophil cytotoxicity and is reversible to a great extent by drug washout. In the examination of possible free-radical scavenging action of these drugs, it was demonstrated that both drugs inhibit superoxide anion production by xanthine oxidase but not by chelated iron. This raises the possibility that these agents may bear structural similarities to oxypyrazolopyrimidines such as allopurinol.     

Adenosine: a physiological modulator of superoxide anion generation by human neutrophils

The effects of adenosine were studied on human neutrophils with respect to their generation of superoxide anion, degranulation, and aggregation in response to soluble stimuli. Adenosine markedly inhibited superoxide anion generation by neutrophils stimulated with N-formyl methionyl leucyl phenylalanine (FMLP), concanavalin A (Con A), calcium ionophore A23187, and zymosan-treated serum; it inhibited this response to PMA to a far lesser extent. The effects of adenosine were evident at concentrations ranging from 1 to 1,000 microM with maximal inhibition at 100 microM. Cellular uptake of adenosine was not required for adenosine-induced inhibition since inhibition was maintained despite the addition of dipyridamole, which blocks nucleoside uptake. Nor was metabolism of adenosine required, since both deoxycoformycin (DCF) and erythro-9-(2-hydroxy-3-nonyl) adenine did not interfere with adenosine inhibition of superoxide anion generation. The finding that 2-chloroadenosine, which is not metabolized, resembled adenosine in its ability to inhibit superoxide anion generation added further evidence that adenosine metabolism was not required for inhibition of superoxide anion generation by neutrophils. Unexpectedly, endogenously generated adenosine was present in supernatants of neutrophil suspensions at 0.14-0.28 microM. Removal of endogenous adenosine by incubation of neutrophils with exogenous adenosine deaminase (ADA) led to marked enhancement of superoxide anion generation in response to FMLP. Inactivation of ADA with DCF abrogated the enhancement of superoxide anion generation. Thus, the enhancement was not due to a nonspecific effect of added protein. Nor was the enhancement due to the generation of hypoxanthine or inosine by deamination of adenosine, since addition of these compounds did not affect neutrophil function. Adenosine did not significantly affect either aggregation or lysozyme release and only modestly affected beta-glucuronidase release by neutrophils stimulated with FMLP. These data indicate that adenosine (at concentrations that are present in plasma) acting via cell surface receptors is a specific modulator of superoxide anion generation by neutrophils.     

Rebamipide suppresses formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide production by inhibiting fMLP-receptor binding in human neutrophils

The purpose of the present work was to investigate the mechanism underlying the inhibitory action of rebamipide on superoxide anion (O2) production induced by the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (fMLP) in human neutrophils. Phosphatidylinositol 3,4,5-trisphosphate (PIP(3)), a product of phosphoinositide 3-OH-kinase (PI 3-kinase) accumulated in response to fMLP and this accumulation was well correlated with O2 production in human neutrophils. Rebamipide inhibited PIP(3) production in parallel with the inhibition of fMLP-induced O2 production. PI 3-kinase activity in anti-PI 3-kinase p85 immunoprecipitates was not affected by the presence of rebamipide, therefore rebamipide did not have a direct inhibitory action on PI 3-kinase activity. Since rebamipide had no inhibitory effect on O2 production induced by NaF, a direct activator of G protein, the target of the inhibitory action of rebamipide appears to be a component of the signal transduction pathway upstream of G protein. Scatchard analysis of [3H]fMLP binding to human neutrophil membrane revealed that rebamipide increased the K(D) value of [3H]fMLP without altering the number of [3H]fMLP binding sites, suggesting that rebamipide has a competitive antagonistic action against the fMLP-receptor. The competitive antagonistic action was further confirmed by the finding that rebamipide caused a parallel shift to the right in the dose-response curve of O2 production induced by fMLP. These results provide evidence that the competitive inhibitory action of rebamipide on the fMLP-receptor plays a main role in its inhibitory action on fMLP-induced O2 production.