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

Characterization of the binding of cytosolic phospholipase A2 alpha and NOX2 NADPH oxidase in mouse macrophages

BACKGROUND

Previous studies have demonstrated that cytosolic phospholipase A₂α (cPLA₂α) is required for NOX2 NADPH oxidase activation in human and mouse phagocytes. Moreover, upon stimulation, cPLA₂α translocates to the plasma membranes by binding to the assembled oxidase, forming a complex between its C2 domain and the PX domain of the cytosolic oxidase factor, p47^phox in human phagocytes. Intravenous administration of antisense against cPLA₂α that significantly inhibited its expression in mouse peritoneal neutrophils and macrophages also inhibited superoxide production, in contrast to cPLA₂α knockout mice that showed normal superoxide production. The present study aimed to determine whether there is a binding between cPLA₂α-C2 domain and p47^phox-PX in mouse macrophages, to further support the role of cPLA₂α in oxidase regulation also in mouse phagocytes.

METHODS AND RESULTS

A significant binding of mouse GST-p47^phox-PX domain fusion protein and cPLA₂α in stimulated mouse phagocyte membranes was demonstrated by pull-down experiments, although lower than that detected by the human p47^phox-PX domain. Substituting the amino acids Phe98, Asn99, and Gly100 to Cys98, Ser99, and Thr100 in the mouse p47^phox-PX domain (present in the human p47^phox-PX domain) caused strong binding that was similar to that detected by the human p47^phox-PX domain CONCLUSIONS: The binding between cPLA₂α-C2 and p47^phox-PX domains exists in mouse macrophages and is not unique to human phagocytes. The binding between the two proteins is lower in the mice, probably due to the absence of amino acids Cys98, Ser 99, and Thr100in the p47^phox-PX domain that facilitate the binding to cPLA₂α.

The anti-inflammatory effect of ε-viniferin by specifically targeting formyl peptide receptor 1 on human neutrophils

The uncontrol respiratory burst in neutrophils can lead to inflammation and tissue damage. This study investigates the effect and the underlying mechanism of ε-viniferin, a lignan from the root of Vitis thunbergii var. thunbergii, inhibits N-formyl-L-methionyl-L-leucyl-l-phenylalanine (fMLP) induced respiratory burst by antagonizing formyl peptide receptor 1 in human neutrophils. Briefly, ε-viniferin specifically inhibited fMLP (0.1 μM: formyl peptide receptor 1 agonist or 1 μM: formyl peptide receptor 1, 2 agonist)-induced superoxide anion production in a concentration-dependent manner (IC₅₀ = 2.30 ± 0.96 or 9.80 ± 0.21 μM, respectively) without affecting this induced by formyl peptide receptor 2 agonist (WKYMVM). ε-viniferin inhibited fMLP (0.1 μM)-induced phosphorylation of ERK, Akt, Src or intracellular calcium mobilization without affecting these caused by WKYMVM. The synergistic suppression of fMLP (1 μM)-induced superoxide anion production was observed only in the combination of ε-viniferin and formyl peptide receptor 2 antagonist (WRW4) but not in combination of ε-viniferin and formyl peptide receptor 1 antagonist (cyclosporine H). ε-viniferin inhibited FITC-fMLP binding to formyl peptide receptors. Moreover, the synergistic suppression of FITC-fMLP binding was observation only in the combination of ε-viniferin and WRW4 but not in other combinations. ATPγS induced superoxide anion production through formyl peptide receptor 1 in fMLP desensitized neutrophils and this effect was inhibited by ε-viniferin. The concentration-response curve of fMLP-induced superoxide anion was not parallel shifted by ε-viniferin. Furthermore, the inhibiting effect of ε-viniferin on fMLP-induced superoxide anion production was reversible. These results suggest that ε-viniferin is an antagonist of formyl peptide receptor 1 in a reversible and non-competitive manner.

The protein kinase A negatively regulates reactive oxygen species production by phosphorylating gp91phox/NOX2 in human neutrophils

Superoxide anion production by neutrophils is essential for host defense against microbes. Superoxide anion generates other reactive oxygen species (ROS) that are very toxic for microbes and host cells, therefore their excessive production could induce inflammatory reactions and tissue injury. Cyclic adenosine monophosphate (cAMP) elevating agents are considered to be physiological inhibitors of superoxide production by neutrophils but the mechanisms involved in this inhibitory effect are poorly understood. Superoxide is produced by the phagocyte NADPH oxidase, a complex enzyme composed of two membrane subunits, gp91^phox or NOX2 and p22^phox, and four cytosolic components p47^phox, p67^phox, p40^phox, and Rac2. Except Rac2, these proteins are known to be phosphorylated upon neutrophil stimulation. Here we show that forskolin, an activator of the adenylate cyclase-cAMP-PKA pathway, induced phosphorylation of gp91phox/NOX2 and inhibited fMLF-induced NADPH oxidase activation in human neutrophils. H89, a PKA inhibitor prevented the forskolin-induced phosphorylation of gp91phox and restored NADPH oxidase activation. Furthermore, PKA phosphorylated the recombinant gp91phox/NOX2-cytosolic C-terminal region in vitro only on a few specific peptides containing serine residues, as compared to PKC. Interestingly, phosphorylation of NOX2-Cter by PKA alone did not induce interaction with the cytosolic components p47^phox, p67^phox and Rac2, however it induced inhibition of PKC-induced interaction. Furthermore, PKA alone did not induce NOX2 electron transfer activity, however it inhibited PKC-induced activation. These results suggest that PKA phosphorylates NOX2 in human neutrophils, a process essential to limit ROS production and inflammation under physiological conditions. Our data identify the cAMP-PKA-NOX2-axis as a critical gatekeeper of neutrophil ROS production.

Pharmacological intervention with oxidative burst in human neutrophils

In this study we investigated the effect of five therapeutically used drugs and four natural polyphenolic compounds on the mechanism of oxidative burst of human neutrophils concerning their participation in the generation of reactive oxygen species (ROS). The compounds investigated decreased the oxidative burst of whole blood in the rank order of potency: N-feruloylserotonin > quercetin > curcumin > arbutin > dithiaden > carvedilol. The generation of intracellular reactive oxygen species in isolated neutrophils decreased in the same rank order, while carvedilol was ineffective. Scavenging of extracellular oxygen radicals followed the rank order of potency: N-feruloylserotonin > curcumin > quercetin > dithiaden. Arbutin and carvedilol had no effect. All compounds tested increased the activity of caspase-3 in cell-free system indicating a positive effect on apoptosis of neutrophils. Activation of protein kinase C was significantly decreased by dithiaden, curcumin, quercetin and N-feruloylserotonin. Carvedilol, dithiaden, quercetin and arbutin reduced activated neutrophil myeloperoxidase release more significantly compared with their less pronounced effect on superoxide generation The presented results are indicative of pharmacological intervention with neutrophils in pathological processes. Of particular interest was the effect of natural compounds. Intracellular inhibition of oxidative burst in isolated neutrophils by the drugs tested and natural antioxidants has to be further analysed since ROS play an important role in immunological responses of neutrophils.

On the pharmacology of oxidative burst of human neutrophils

The effect of three therapeutically used drugs and five polyphenolic compounds on the mechanism of oxidative burst was compared in whole blood and isolated neutrophils at cellular and molecular level. In 10 microM concentration, the compounds investigated decreased the oxidative burst of whole blood in the rank order of potency: N-feruloylserotonin (N-f-5HT) > curcumin (CUR) > quercetin (QUER) > arbutin (ARB) > resveratrol (RES) > dithiaden (DIT) > carvedilol (CARV) > brompheniramine (BPA). The ratio between the percentage inhibition of extracellular versus intracellular chemiluminescence (CL) followed the rank order QUER > N-f-5HT > RES > CUR > DIT and is indicative of the positive effect of the compounds tested against oxidative burst of neutrophils, demonstrating suppression of reactive oxygen species extracellularly with minimal alteration of intracellular reactive oxygen species (ROS). Activation of protein kinase C was significantly decreased by DIT, CUR, QUER and N-f-5HT. CARV, DIT, QUER and ARB reduced activated neutrophil myeloperoxidase release more significantly compared with the effect on superoxide anion generation. All compounds tested increased the activity of caspase-3 in cell-free system. It is suggested that other regulatory mechanisms than protein kinase C might participate in the inhibition of neutrophil activation with the compounds tested. Different mechanisms are concerned in controlling the assembly of NADPH oxidase and the regulatory role of calcium ions is suggested. Compounds decreasing the amount of extracellular ROS generation, yet affecting but minimally intracellular ROS generation, are promising for further investigation in vivo.

The anti-inflammatory effect of 2-(4-hydroxy-3-prop-2-enyl-phenyl)-4-prop-2-enyl-phenol by targeting Lyn kinase in human neutrophils

The undesirable respiratory burst in neutrophils can lead to inflammation and tissue damage. This study investigates the effect and the underlying mechanism of 2-(4-hydroxy-3-prop-2-enyl-phenyl)-4-prop-2-enyl-phenol (honokiol), a lignan extracted from the stem bark of Magnolia officinalis Rehd. et Wils (Magnoliaceae), on N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-induced respiratory burst in human neutrophils. Signaling pathways regulated by honokiol which modulate fMLP-induced respiratory burst and cathepsin G release were evaluated by phosphorylation of Src family kinase induced by fMLP, Src family kinases activities and by immunoblotting analysis of the downstream targets of Src kinase. Briefly, honokiol inhibited fMLP-induced superoxide anion production (IC50 = 9.80 ± 0.21 μM, n = 4), cathepsin G release (IC50 = 14.23 ± 1.43 μM, n = 4) and migration (IC50 = 5.69 ± 1.51 μM, n = 4) in a concentration dependent manner. Further, honokiol specifically suppresses fMLP-induced Lyn (a member of the Src kinase family) phosphorylation, by inhibiting Lyn kinase activity. Consequently, honokiol attenuated the downstream targets of Lyn kinase, such as Tec translocation from the cytosol to the inner leaflet of the plasma membrane, phosphorylation of AKT, P38, PLCγ2, protein kinase C and membrane localization of p47(phox). On the other hand, fMLP-induced phosphorylation of Hck, Fgr kinase activity (other members of Src kinase), downstream phosphorylation of Vav1 and extracellular signal-regulated kinase remained unaffected. In addition, honokiol neither inhibited NADPH oxidase activity nor increased cyclic AMP levels. Honokiol is not a competitive or allosteric antagonist of fMLP. In conclusion, honokiol specifically modulates fMLP-mediated neutrophil activation by inhibiting Lyn activation which subsequently interferes with the activation of PLCγ2, AKT, p38, protein kinase C, and p47(phox).

Cyclic AMP-mediated suppression of neutrophil extracellular trap formation and apoptosis by the Bordetella pertussis adenylate cyclase toxin

The adenylate cyclase toxin (ACT) of Bordetella pertussis intoxicates target cells by generating supraphysiologic levels of intracellular cyclic AMP (cAMP). Since ACT kills macrophages rapidly and potently, we asked whether ACT would also kill neutrophils. In fact, ACT prolongs the neutrophil life span by inhibiting constitutive apoptosis and preventing apoptosis induced by exposure to live B. pertussis. Imaging of B. pertussis-exposed neutrophils revealed that B. pertussis lacking ACT induces formation of neutrophil extracellular traps (NETs), whereas wild-type B. pertussis does not, suggesting that ACT suppresses NET formation. Indeed, ACT inhibits formation of NETs by generating cAMP and consequently inhibiting the oxidative burst. Convalescent-phase serum from humans following clinical pertussis blocks the ACT-mediated suppression of NET formation. These studies provide novel insight into the phagocyte impotence caused by ACT, which not only impairs neutrophil function but also inhibits death of neutrophils by apoptosis and NETosis.

5-Hydroxy-7-methoxyflavone inhibits N-formyl-L-methionyl-L-leucyl-L-phenylalanine-induced superoxide anion production by specific modulate membrane localization of Tec with a PI3K independent mechanism in human neutrophils

Respiratory burst mediates crucial bactericidal mechanism in neutrophils. However, undesirable respiratory burst leads to pathological inflammation and tissue damage. This study investigates the effect and the underlying mechanism of 5-hydroxy-7-methoxyflavone (MCL-1), a lignan extracted from the leaves of Muntingia calabura L. (Tiliaceae), on N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-induced respiratory burst and cathepsin G release in human neutrophils. Signaling pathways regulated by MCL-1 to oppose fMLP-induced respiratory burst were evaluated by membrane localization of Tec induced by fMLP and by immunoblotting analysis of downstream phosphorylation targets of Tec. Briefly, MCL-1 specific inhibited fMLP-induced superoxide anion production in a concentration-dependent (IC(50)=0.16±0.01 μM) and Tec kinase-dependent manner, however, MCL-1 did not affect fMLP-induced cathepsin G release. Further, MCL-1 suppressed fMLP-induced Tec translocation from the cytosol to the inner leaflet of the plasma membrane, and subsequently activation of phospholipase Cγ2 (PLCγ2). Moreover, MCL-1 attenuated PLCγ2 activity and intracellular calcium concentration notably through extracellular calcium influx. Consequently, fMLP-induced phosphorylation of protein kinase C (PKC) and membrane localization of p47(phox) were decreased by MCL-1 in a Tec-dependent manner, while the phosphorylation of extracellular signal-regulated kinase (ERK), p38, AKT and Src tyrosine kinase family remained unaffected. In addition, MCL-1 neither inhibited NADPH oxidase activity nor increased cyclicAMP levels. MCL-1 specific opposes fMLP-mediated respiratory burst by inhibition of membrane localization of Tec and subsequently interfered with the activation of PLCγ2, protein kinase C, and p47(phox).

Naturally appearing N-feruloylserotonin isomers suppress oxidative burst of human neutrophils at the protein kinase C level

N-feruloylserotonin (N-f-5HT) isomers, isolated from seeds of Leuzea carthamoides (Wild) DC, inhibited dose-dependent oxidative burst in human whole blood and isolated neutrophils in vitro, which were measured by luminol- and/or isoluminol-enhanced chemiluminescence in the following rank order of stimuli: PMA > OpZ > calcium ionophore A23187. In isolated neutrophils that were stimulated with PMA, N-f-5HT isomers were effective against extracellular and intracellular reactive oxygen species. Liberation of ATP, analysis of apoptosis, and recombinant caspase-3 activity revealed that N-f-5HT isomers, used in concentrations up to 100 μM, did not alter the viability and integrity of isolated neutrophils. Western blot analysis documented that in concentrations of 10 and 100 μM, N-f-5HT isomers significantly decreased PMA-induced phosphorylation of PKC α/β II. The results suggest that N-f-5HT isomers are an effective, naturally occurring substance with a potent pharmacological effect on the oxidative burst of human neutrophils. It should be further investigated for its pharmacological activity against oxidative stress in ischemia-reperfusion, inflammation and other pathological conditions.

5-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-3,7-dimethoxy-4H-chromen-4-one (MSF-2) suppresses fMLP-mediated respiratory burst in human neutrophils by inhibiting phosphatidylinositol 3-kinase activity

Respiratory burst mediates crucial bactericidal mechanism in neutrophils. However, undesirable respiratory burst leads to pathological inflammation and tissue damage. This study investigates the effect and the underlying mechanism of 5-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-3,7-dimethoxy-4H-chromen-4-one (MSF-2), a lignan extracted from the fruit of Melicope Semecarprifolia, on fMLP-induced respiratory burst in human neutrophils and suggests a possible therapeutic approach to ameliorate disease associated with neutrophil hyperactivation. MSF-2 inhibited fMLP-induced neutrophil superoxide anion production, cathepsin G release and migration in human neutrophils isolated from healthy volunteers, reflecting inhibition of phosphatidylinositol 3-kinase (PI3K) activation. Specifically, PI3K/AKT activation results in migration, degranulation and superoxide anion production in neutrophils. MSF-2 suppresses PI3K activation and phosphatidylinositol (3,4,5)-trisphosphate (PIP3) production, and consequently inhibits downstream activation of PDK1 and AKT. Further, PI3K also stimulates respiratory burst via PLC-dependent elevation of intracellular calcium. MSF-2 reduces fMLP-mediated PLCγ2 activation and intracellular calcium accumulation notably through extracellular calcium influx in a PI3K and PLC-dependent manner. However, MSF-2 is not a competitive or allosteric antagonist of fMLP. Additionally, in an in vivo study, MSF-2 prevents fMLP-induced neutrophil infiltration and inflammation in mice. In conclusion, MSF-2 opposes fMLP-mediated neutrophil activation and inflammation by inhibiting PI3K activation and subsequent activation of AKT and PLCγ2.

Mitigation of chlorine lung injury by increasing cyclic AMP levels

Chlorine is considered a chemical threat agent to which humans may be exposed as a result of accidental or intentional release. Chlorine is highly reactive, and inhalation of the gas causes cellular damage to the respiratory tract, inflammation, pulmonary edema, and airway hyperreactivity. Drugs that increase intracellular levels of the signaling molecule cyclic AMP (cAMP) may be useful for treatment of acute lung injury through effects on alveolar fluid clearance, inflammation, and airway reactivity. This article describes mechanisms by which cAMP regulates cellular processes affecting lung injury and discusses the basis for investigating drugs that increase cAMP levels as potential treatments for chlorine-induced lung injury. The effects of beta(2)-adrenergic agonists, which stimulate cAMP synthesis, and phosphodiesterase inhibitors, which inhibit cAMP degradation, on acute lung injury are reviewed, and the relative advantages of these approaches are compared.

Diabetes-induced oxidative stress is mediated by Ca2+-independent phospholipase A2 in neutrophils

Neutrophils from people with poorly controlled diabetes present a primed phenotype and secrete excessive superoxide. Phospholipase A(2) (PLA(2))-derived arachidonic acid (AA) activates the assembly of NADPH oxidase to generate superoxide anion. There is a gap in the current literature regarding which PLA(2) isoform regulates NADPH oxidase activation. The aim of this study was to identify the PLA(2) isoform involved in the regulation of superoxide generation in neutrophils and investigate if PLA(2) mediates priming in response to pathologic hyperglycemia. Neutrophils were isolated from people with diabetes mellitus and healthy controls, and HL60 neutrophil-like cells were grown in hyperglycemic conditions. Incubating neutrophils with the Ca(2+)-independent PLA(2) (iPLA(2)) inhibitor bromoenol lactone (BEL) completely suppressed fMLP-induced generation of superoxide. The nonspecific actions of BEL on phosphatidic acid phosphohydrolase-1, p47(phox) phosphorylation, and apoptosis were ruled out by specific assays. Small interfering RNA knockdown of iPLA(2) inhibited superoxide generation by neutrophils. Neutrophils from people with poorly controlled diabetes and in vitro incubation of neutrophils with high glucose and the receptor for advanced glycation end products ligand S100B greatly enhanced superoxide generation compared with controls, and this was significantly inhibited by BEL. A modified iPLA(2) assay, Western blotting, and PCR confirmed that there was increased iPLA(2) activity and expression in neutrophils from people with diabetes. AA (10 microM) partly rescued the inhibition of superoxide generation mediated by BEL, confirming that NADPH oxidase activity is, in part, regulated by AA. This study provides evidence for the role of iPLA(2) in enhanced superoxide generation in neutrophils from people with diabetes mellitus and presents an alternate pathway independent of protein kinase C and phosphatidic acid phosphohydrolase-1 hydrolase signaling.

Regulatory role of cytosolic phospholipase A2alpha in NADPH oxidase activity and in inducible nitric oxide synthase induction by aggregated Abeta1-42 in microglia

In Alzheimer's disease, extracellular deposits of amyloid beta(1-42) (Abeta(1-42)) may induce activation of microglial cells by releasing proinflammatory factors that contribute to the neurodegeneration process. Since the activation of cytosolic phospholipase A(2)alpha (cPLA(2)alpha) has been reported in inflammatory conditions, its role in primary rat microglial cell activated by aggregated Abeta(1-42) was elucidated. The results of the present study show that activation of microglia by 5 microM aggregated Abeta(1-42) (as evident by the amoeboid morphology and increased CD68 immunofluorescence reactivity) caused an immediate activation of cPLA(2)alpha, measured by its phosphorylated form and its specific activity, followed by a gradual elevation of its expression and activity during 24 h. Inhibition of cPLA(2)alpha expression and activity by the presence of 1 microM specific antisense resulted in a significant decrease in NADPH oxidase activity that releases superoxides, PGE(2) formation, iNOS expression, and NO production, indicating a major role for cPLA(2)alpha in the regulation of these inflammatory processes. NADPH oxidase activity, which is under cPLA(2)alpha regulation, was found to upregulate cPLA(2)alpha and COX-2 protein expression through the redox-sensitive NFkappaB activation as evident by its phosphorylation on Ser-536, resulting in increased PGE(2) formation. The secreted PGE(2) induced the synthesis of iNOS and the production of NO through the PKA-CREB pathway. Taken together, our results suggest that the response of cPLA(2)alpha to aggregated Abeta(1-42) is probably a key player in the oxidative stress present in AD, regulating potent oxidative agents: the production of superoxides by NADPH oxidase and NO formation by iNOS.

Restoration of neutrophil immunocompetence after cardiopulmonary bypass by beta-adrenergic blockers

BACKGROUND

To evaluate the possible protective effect of sympatholytic medications with respect to neutrophil function, we evaluated the influence of a nonselective beta-blocker medication on the interaction of neutrophils and epinephrine after cardiopulmonary bypass. Therefore, we studied the importance of adrenoceptors for the immunomodulation of neutrophils by catecholamines in vitro.

METHODS

First, we investigated the modulation of neutrophils from healthy volunteers, after stimulation with n-formyl-l-methionyl-l-leucyl-l-phenylalanin (FMLP) in the presence of epinephrine with or without the addition of one of the following adrenergic receptor antagonists: atenolol, butoxamine, pindolol, prazosin, or RS79984. The second part included an investigation of the modulation of neutrophils from patients after operative coronary revascularization with or without extracorporeal circulation after stimulation with FMLP and addition of epinephrine. After loading with anti-CD62l or anti-CD11b antibodies or dihydrorhodamine, the expression of CD62l and CD11b and generation of oxidative free radicals were assessed by flow cytometry.

RESULTS

The suppression of oxidative free radical generation, inhibition of CD62l downregulation after stimulation with FMLP, and suppression of CD11b upregulation after FMLP stimulation from epinephrine were all mediated by beta(2)-adrenoceptors. After cardiac surgery with cardiopulmonary bypass, epinephrine inhibited the CD62l downregulation, the suppression of CD11b upregulation, and the generation of oxidative free radicals after FMLP stimulation. The pre-operative administration of beta-blockers abolished the immunomodulatory effects of epinephrine on CD62l and CD11b expression and the generation of oxidative free radicals.

CONCLUSION

The immunomodulatory effects of epinephrine on neutrophils remained unchanged irrespective of cardiopulmonary bypass and could contribute to the detrimental effects of epinephrine after heart surgery. The preoperative administration of nonselective beta-blockers abolished the immunomodulatory effects of epinephrine in vitro and in patients, and it enhanced the immunocompetence of neutrophils in a context of increased catecholamine levels.

Functional and phenotypic changes in polymorphonuclear neutrophils induced by catecholamines

PURPOSE

To elucidate differential functional and phenotypic changes in response to relevant catecholamines, the generation of oxidative free radicals by PMN, and changes in the expression of L-selectin and Mac-1 on the surface of PMN were examined in the presence of epinephrine, norepinephrine and dopamine in physiological and pharmacological concentrations.

MATERIALS AND METHODS

Human polymorphonuclear neutrophils were obtained from healthy donors and pretreated with 0.5 nM or 500 nM epinephrine; 1.18 nM or 1 180 nM norepinephrine; or 0.26 nM or 261 nM dopamine, followed by stimulation with FMLP. Stimulated neutrophils were incubated with antibodies against CD 11 b or CD 62 l and assessed by flow cytometry. Additional probes were assessed by flow cytometry for the generation of oxidative free radicals.

RESULTS

All catecholamines in high concentration inhibited the suppression of CD 62 l expression and CD 11 b upregulation following stimulation with FMLP. A high concentration of epinephrine suppresses generation of oxidative free radicals.

CONCLUSIONS

The effect of catecholamines on the expression of CD 62 l explains the increased expression of L-selection on PMN observed after trauma. The suppression of CD 11 b reduces leukocyte adherence and consecutive abnormalities in microvascular flow. Epinephrine inhibits the generation of oxidative free radicals by PMN with potentially detrimental effects with respect to bacterial clearance.

Effects of short chain fatty acids on effector mechanisms of neutrophils

Short chain fatty acids (SCFAs) are metabolic by products of anaerobic bacteria fermentation. These fatty acids, despite being an important fuel for colonocytes, are also modulators of leukocyte function. The aim of this study was to evaluate the effects of SCFAs (acetate, propionate, and butyrate) on function of neutrophils, and the possible mechanisms involved. Neutrophils obtained from rats by intraperitoneal lavage 4 h after injection of oyster glycogen solution (1%) were treated with non toxic concentrations of the fatty acids. After that, the following measurements were performed: phagocytosis and destruction of Candida albicans, production of ROS (O(2)(*-), H(2)O(2), and HOCl) and degranulation. Gene expression (p47(phox) and p22(phox)) and protein phosphorylation (p47(phox)) were analyzed by real time reverse transcriptase chain reaction (RT-PCR) and Western blotting, respectively. Butyrate inhibited phagocytosis and killing of C. albicans. This SCFA also had an inhibitory effect on production of O(2)(*-), H(2)O(2), and HOCl by neutrophils stimulated with PMA or fMLP. This effect of butyrate was not caused by modulation of expression of NADPH oxidase subunits (p47(phox) and p22(phox)) but it was in part due to reduced levels of p47(phox) phosphorylation and an increase in the concentration of cyclic AMP. Acetate increased the production of O(2)(*-) and H(2)O(2) in the absence of stimuli but had no effect on phagocytosis and killing of C. albicans. Propionate had no effect on the parameters studied. These results suggest that butyrate can modulate neutrophil function and thus could be important in inflammatory neutrophil-associated diseases.

No evidence of enhanced oxidant production in blood obtained from patients with obstructive sleep apnea

Background

Obstructive sleep apnea syndrome (OSAS) is a recognized risk factor for cardiovascular morbidity and mortality, perhaps due to causative exacerbations of systemic oxidative stress. Putative oxidative stress related to numerous episodes of intermittent hypoxia, may be an oxidants chief driving force in OSAS patients.

Methods

We assessed the resting and n-formyl-methionyl-leucyl-phenylalanine (fMLP)- induced whole blood chemiluminescence (as a measure of oxidant production by polymorphonuclear leukocytes and monocytes), ferric reducing ability of plasma (FRAP) and H₂O₂ generation in the whole blood of 27 untreated OSAS patients, 22 subjects after a night of CPAP therapy and 11 controls without OSAS. All of them were matched to age, BMI (body mass index) and smoking habits. All parameters were measured before and after polysomnography-controlled sleep, individual results were obtained as a mean from duplicated experiments.

Results

No significant differences were distinguished between evening and morning blood chemiluminescence, H₂O₂ activity and FRAP within and between all three study groups.

For instance patients with untreated OSAS had similar morning and evening resting whole blood chemiluminescence (2.3 +/- 2.2 vs. 2.4 +/- 2.2 [aU·10^-4 phagocytes]), total light emission after stimulation with fMLP (1790 +/- 1371 vs. 1939 +/- 1532 [aU·s·10^-4 phagocytes]), as well as FRAP after 3 min. plasma incubation (602 +/- 202 vs. 671 +/- 221 [uM]). Although, in the subgroup of 11 patients with severe OSAS (apnea/hypopnea index 58 +/- 18/h and oxygen desaturation index 55 +/- 19/h), the morning vs. evening resting chemiluminescence and total light emission after stimulation with fMLP observed a propensity to elevate 2.5 +/- 2.7 vs. 1.9 +/- 1.8 [aU·10^-4 phagocytes] and 1778 +/- 1442 vs. 1503 +/- 1391 [aU·s·10^-4 phagocytes], respectively, these did not attain statistical significance (p > 0.05).

Conclusion

Our investigation exposed no evidence in the overproduction of oxidants via circulating phagocytes, once considered a culprit in the oxidative stress of OSAS patients.

A benzodiazepines derived compound, 4-(3-chlorophenyl)-1,3-dihydronaphtho [2,3-b][1,4]diazepin-2-one (ND700C), inhibits fMLP-induced superoxide anion release by activating protein phosphatase 2A in human neutrophils

We studied the mechanism underlying the inhibitory effect of a benzodiazepines derivative, 4-(3-chlorophenyl)-1,3-dihydronaphtho [2,3-b][1,4]diazepin-2-one (ND700C), on superoxide anion production induced by formly-methionyl-leucyl-phenylalanine (fMLP) in human neutrophils. ND700C inhibited the fMLP-induced superoxide anion production and cathepsin G release in a concentration-dependent manner with respective IC50 values of 5.0+/-0.5 and 8.7+/-0.8muM. In addition, ND700C was found to suppress fMLP-induced intracellular calcium mobilization and the phosphorylation of ERK and Akt. In another study, ND700C was observed to cause a rapid increase in intracellular cAMP level by up to threefold. Furthermore, when H89 was used to inhibit cAMP-dependent protein kinase A (PKA), we discovered that ND700C's suppressive effects on calcium mobilization, phosphorylation, and superoxide anion production were abrogated. ND700C demonstrated additive effect on the PGE1-induced increase in cAMP. However, this additive effect was not demonstrated with the IBMX-induced rise in cAMP. Our results indicated that ND700C did not directly inhibit the activity of phosphodiesterase 4. In another set of experiments, calyculin A and okadaic acid (both protein phosphatase 2A inhibitors) were found to reverse ND700C's positive effect on cAMP level. This observation suggested the involvement of protein phosphatase 2A in ND700C's cAMP-elevating mechanism. We found that the activity of protein phosphatase 2A was activated by ND700C. Furthermore, protein phosphatase 2A was co-immunoprecipitated with phosphodiesterase 4 after ND700C treatment in human neutrophils.

CONCLUSION

ND700C inhibited fMLP-induced superoxide anion production through a PKA-dependent pathway. ND700C increased cAMP by activating protein phosphatase 2A, which subsequently inhibited phosphodiesterase 4.

Cyclic AMP: master regulator of innate immune cell function

Cyclic adenosine monophosphate (cAMP) was the original "second messenger" to be discovered. Its formation is promoted by adenylyl cyclase activation after ligation of G protein-coupled receptors by ligands including hormones, autocoids, prostaglandins, and pharmacologic agents. Increases in intracellular cAMP generally suppress innate immune functions, including inflammatory mediator generation and the phagocytosis and killing of microbes. The importance of the host cAMP axis in regulating antimicrobial defense is underscored by the fact that microbes have evolved virulence-enhancing strategies that exploit it. Many clinical situations that predispose to infection are associated with increases in cAMP, and therapeutic strategies to interrupt cAMP generation or actions have immunostimulatory potential. This article reviews the anatomy of the cAMP axis, the mechanisms by which it controls phagocyte immune function, microbial strategies to dysregulate it, and its clinical relevance.

Immunoendocrine response to cycling following ingestion of caffeine and carbohydrate

PURPOSE

This study investigated the effect of caffeine consumed with and without carbohydrate (CHO) on immunoendocrine responses after exercise.

METHODS

On four occasions, 12 recreational male cyclists cycled for 2 h at 65% V O2max. Sixty minutes before exercise, participants ingested 6 mg.kg(-1) body mass of caffeine (CAF) or placebo (PLA), then during exercise they consumed a 6% CHO or placebo (PLA) drink, providing CAF/CHO, PLA/CHO, CAF/PLA, and PLA/PLA conditions.

RESULTS

f-MLP-stimulated neutrophil oxidative burst responses were significantly higher after exercise on CAF/CHO and PLA/CHO (both P<0.05) than PLA/PLA when expressed as a percentage of baseline value. The response on CAF/PLA tended to be higher than PLA/PLA at this point (P=0.056). No significant differences between CAF/CHO, PLA/CHO, and CAF/PLA were observed after exercise; however, only PLA/CHO showed no significant postexercise decline. Coingestion of CAF/CHO significantly attenuated epinephrine (P<0.05) and IL-6 (P<0.05) responses that occurred after ingestion of CAF alone (CAF/PLA) and significantly attenuated the transient alterations in circulating leukocyte (P<0.05) and neutrophil (P<0.01) counts. Plasma cortisol concentration was significantly lower on PLA/CHO than CAF/PLA and PLA/PLA after exercise (P<0.05). Perceived exertion during exercise was significantly lower on CAF/CHO than the other three trials (P<0.05).

CONCLUSION

Taken together, this suggests that coingestion of caffeine and CHO has greater influence on immunoendocrine responses than neutrophil functional responses to prolonged exercise.

Inhibition of superoxide anion and elastase release in human neutrophils by 3'-isopropoxychalcone via a cAMP-dependent pathway

1 Chalcone is abundantly present in the plant kingdom and has various biological activities such as anti-inflammatory and antioxidant. In this study, the semisynthetic chalcone derivative, 3'-isopropoxychalcone (H2O7D), was demonstrated to inhibit the generation of superoxide and the release of elastase, as well as to accelerate resequestration of cytosolic calcium in formyl-L-methionyl-L-leucyl-L-phenylalanine-activated human neutrophils. 2 H2O7D displayed no antioxidant or superoxide-scavenging ability, and it failed to alter the subcellular NADPH oxidase activity. 3 H2O7D induced a substantial increase in cAMP but not cGMP levels. The elevation of cAMP formation by H2O7D was inhibited by adenosine deaminase (ADA). Furthermore, The inhibitory effects of H2O7D were reversed by protein kinase (PK)A inhibitors, as well as ADA and a selective A2a-receptor antagonist. 4 H2O7D inhibited phosphodiesterase (PDE) activities, but it did not alter adenylyl cyclase and soluble guanylyl cyclase activities. These results show that the cAMP-elevating effect of H2O7D results from the inhibition of PDE activity and not from the stimulation of cyclase function. Consistent with this, H2O7D potentiated the PGE(1)-caused inhibitory effects and cAMP formation. 5 In summary, these results indicate that the inhibitory effect of H2O7D is cAMP/PKA dependent, and that it occurs through inhibition of cAMP PDE, which potentiates the autocrine functions of endogenous adenosine. Inhibition of respiratory burst and degranulation in human neutrophils may give this drug the potential to protect against the progression of inflammation.

Malaria circumsporozoite protein inhibits the respiratory burst in Kupffer cells

After transmission by infected mosquitoes, malaria sporozoites rapidly travel to the liver. To infect hepatocytes, sporozoites traverse Kupffer cells, but surprisingly, the parasites are not killed by these resident macrophages of the liver. Here we show that Plasmodium sporozoites and recombinant circumsporozoite protein (CSP) suppress the respiratory burst in Kupffer cells. Sporozoites and CSP increased the intracellular concentration of cyclic adenosyl mono-phosphate (cAMP) and inositol 1,4,5-triphosphate in Kupffer cells, but not in hepatocytes or liver endothelia. Preincubation with cAMP analogues or inhibition of phosphodiesterase also inhibited the respiratory burst. By contrast, adenylyl cyclase inhibition abrogated the suppressive effect of sporozoites. Selective protein kinase A (PKA) inhibitors failed to reverse the CSP-mediated blockage and stimulation of the exchange protein directly activated by cAMP (EPAC), but not PKA inhibited the respiratory burst. Both blockage of the low-density lipoprotein receptor-related protein (LRP-1) with receptor-associated protein and elimination of cell surface proteoglycans inhibited the cAMP increase in Kupffer cells. We propose that by binding of CSP to LRP-1 and cell surface proteoglycans, malaria sporozoites induce a cAMP/EPAC-dependent, but PKA-independent signal transduction pathway that suppresses defence mechanisms in Kupffer cells. This allows the sporozoites to safely pass through these professional phagocytes and to develop inside neighbouring hepatocytes.

Manipulation of host signalling pathways by anthrax toxins

Infectious microbes face an unwelcoming environment in their mammalian hosts, which have evolved elaborate multicelluar systems for recognition and elimination of invading pathogens. A common strategy used by pathogenic bacteria to establish infection is to secrete protein factors that block intracellular signalling pathways essential for host defence. Some of these proteins also act as toxins, directly causing pathology associated with disease. Bacillus anthracis, the bacterium that causes anthrax, secretes two plasmid-encoded enzymes, LF (lethal factor) and EF (oedema factor), that are delivered into host cells by a third bacterial protein, PA (protective antigen). The two toxins act on a variety of cell types, disabling the immune system and inevitably killing the host. LF is an extraordinarily selective metalloproteinase that site-specifically cleaves MKKs (mitogen-activated protein kinase kinases). Cleavage of MKKs by LF prevents them from activating their downstream MAPK (mitogen-activated protein kinase) substrates by disrupting a critical docking interaction. Blockade of MAPK signalling functionally impairs cells of both the innate and adaptive immune systems and induces cell death in macrophages. EF is an adenylate cyclase that is activated by calmodulin through a non-canonical mechanism. EF causes sustained and potent activation of host cAMP-dependent signalling pathways, which disables phagocytes. Here I review recent progress in elucidating the mechanisms by which LF and EF influence host signalling and thereby contribute to disease.

Prostaglandin E2 receptor subtype 2 (EP2) regulates microglial activation and associated neurotoxicity induced by aggregated alpha-synuclein

BACKGROUND

The pathogenesis of idiopathic Parkinson's disease (PD) remains elusive, although evidence has suggested that neuroinflammation characterized by activation of resident microglia in the brain may contribute significantly to neurodegeneration in PD. It has been demonstrated that aggregated alpha-synuclein potently activates microglia and causes neurotoxicity. However, the mechanisms by which aggregated alpha-synuclein activates microglia are not understood fully.

METHODS

We investigated the role of prostaglandin E2 receptor subtype 2 (EP2) in alpha-synuclein aggregation-induced microglial activation using ex vivo, in vivo and in vitro experimental systems.

RESULTS

Results demonstrated that ablation of EP2(EP2-/-) significantly enhanced microglia-mediated ex vivo clearance of alpha-synuclein aggregates (from mesocortex of Lewy body disease patients) while significantly attenuating neurotoxicity and extent of alpha-synuclein aggregation in mice treated with a parkinsonian toxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Furthermore, we report that reduced neurotoxicity by EP2-/- microglia could be attributed to suppressed translocation of a critical cytoplasmic subunit (p47-phox) of NADPH oxidase (PHOX) to the membranous compartment after exposure to aggregated alpha-synuclein.

CONCLUSION

Thus, it appears that microglial EP2 plays a critical role in alpha-synuclein-mediated neurotoxicity.

Sustained activation of proton channels and NADPH oxidase in human eosinophils and murine granulocytes requires PKC but not cPLA2 alpha activity

The prevailing hypothesis that a signalling pathway involving cPLA(2)alpha is required to enhance the gating of the voltage-gated proton channel associated with NADPH oxidase was tested in human eosinophils and murine granulocytes. This hypothesis invokes arachidonic acid (AA) liberated by cPLA(2)alpha as a final activator of proton channels. In human eosinophils studied in the perforated-patch configuration, phorbol myristate acetate (PMA) stimulation elicited NADPH oxidase-generated electron current (I(e)) and enhanced proton channel gating identically in the presence or absence of three specific cPLA(2)alpha inhibitors, Wyeth-1, pyrrolidine-2 and AACOCF(3) (arachidonyl trifluoromethyl ketone). In contrast, PKC inhibitors GFX (GF109203X) or staurosporine prevented the activation of either proton channels or NADPH oxidase. PKC inhibition during the respiratory burst reversed the activation of both molecules, suggesting that ongoing phosphorylation is required. This effect of GFX was inhibited by okadaic acid, implicating phosphatases in proton channel deactivation. Proton channel activation by AA was partially reversed by GFX or staurosporine, indicating that AA effects are due in part to activation of PKC. In granulocytes from mice with the cPLA(2)alpha gene disrupted (knockout mice), PMA or fMetLeuPhe activated NADPH oxidase and proton channels in a manner indistinguishable from the responses of control cells. Thus, cPLA(2)alpha is not essential to activate the proton conductance or for a normal respiratory burst. Instead, phosphorylation of the proton channel or an activating molecule converts the channel to its activated gating mode. The existing paradigm for regulation of the concerted activity of proton channels and NADPH oxidase must be revised.

Viscolin, a new chalcone from Viscum coloratum, inhibits human neutrophil superoxide anion and elastase release via a cAMP-dependent pathway

The mistletoe Viscum coloratum is used in traditional Chinese medicine to treat inflammatory diseases. In this study, a cellular model in isolated human neutrophils, which are important in the pathogenesis of rheumatoid arthritis, chronic obstructive pulmonary disease, and other inflammatory diseases, was established to elucidate the anti-inflammatory functions of V. coloratum. The partially purified extract of V. coloratum (PPE-SVC) potently inhibited formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP)-induced superoxide anion generation and elastase release in a concentration-dependent manner with IC(50) values of 0.58+/-0.03 and 4.93+/-0.54 microg/ml, respectively. Furthermore, a new chalcone derivative, viscolin (4',4''-dihydroxy-2',3',6',3''-tetramethoxy-1,3-diphenylpropane), was isolated from PPE-SVC. Viscolin was demonstrated to inhibit superoxide anion generation and elastase release, as well as to accelerate resequestration of cytosolic calcium in FMLP-activated human neutrophils. Furthermore, the inhibitory effects of viscolin were reversed by protein kinase A (PKA) inhibitor, suggesting that PKA mediates the viscolin-caused inhibitions. Viscolin induced a substantial increase in cAMP levels, and that occurred through the inhibition of phosphodiesterase (PDE) activity but not an increase in adenylate cyclase function. Consistent with this, viscolin potentiated the PGE(1)-caused inhibition of superoxide anion release and calcium mobilization, as well as elevation of cAMP formation. These results demonstrate that inhibition of inflammatory responses in human neutrophils by viscolin is associated with an elevation of cellular cAMP through inhibition of PDE. Comparable results were also observed by PPE-SVC, indicating that the effect of PPE-SVC is at least partly mediated by viscolin. In summary, viscolin is a novel inhibitor of PDE and might be useful for treatment of neutrophilic inflammation.

Inhibition of the neutrophil oxidative response by propofol

BACKGROUND AND OBJECTIVE

Propofol has been shown to inhibit a variety of functions of neutrophils in vitro, but there is a lack of in vivo data. To analyse the effects of propofol on neutrophil function in vivo we chose to investigate cataract surgery since it represents a small surgical procedure with minimal immunomodulatory effects induced by surgery. We sought to analyse any immunosuppressive effects of propofol after short-term administration in vivo in comparison to local anaesthesia as well as to in vitro effects of propofol.

METHODS

The study was designed as an open randomized trial enrolling 20 patients undergoing general or local anaesthesia. The neutrophil oxidative response and propofol plasma concentration were assessed prior, during and after anaesthesia. Neutrophil function was determined flow cytometrically based on dihydrorhodamine 123 oxidation.

RESULTS

Propofol concentrations which yielded a marked suppression in vitro did not alter the neutrophil oxidative response during cataract surgery in vivo. However, after local anaesthesia the neutrophil oxidative response declined to 37%, compared to the control response prior to anaesthesia.

CONCLUSIONS

Although we could detect the well established suppression of neutrophil function by propofol in vitro it was not evident in vivo. This may be due to compensating effects on neutrophil function during surgery in vivo. The decline in the neutrophil oxidative response in the local anaesthesia group might be due to increased stress and catecholamine concentrations or a direct interaction of local anaesthetics with neutrophil intracellular signalling.

The role of cytosolic phospholipase A2-alfa in regulation of phagocytic functions

Phospholipase A2(s) (PLA2(s)) are a family of enzymes that is present in a variety of mammalian and nonmammalian sources. Phagocytic cells contain cytosolic PLA2 (cPLA2) as well as several types of secreted PLA2, all of which have the potential to produce proinflammatory lipid mediators. The role of the predominant form of cPLA2 present in neutrophils is cPLA2alpha was studied by many groups. By modulating its expression in a variety of phagocytes it was found that it plays a major role in formation of eicosanoids. In addition, it was reported that cPLA2alpha also regulates the NADPH oxidase activation. The specificity of its effect on the NADPH oxidase is evident by results demonstrating that the differentiation process as well as other phagocytic functions are normal in cPLA2alpha-deficient PLB cell model. The novel dual subcellular localization of cPLA2alpha in different compartments, in the plasma membranes and in the nucleus, provides a molecular mechanism for the participation of cPLA2alpha in different processes (stimulation of NADPH oxidase and formation of eicosanoids) in the same cells.

Activation state-dependent interaction between Galphai and p67phox

The phagocyte NADPH oxidase consists of multiple protein subunits that interact with each other to form a functional superoxide-generating complex. Although the essential components for superoxide production have been well characterized, other proteins potentially involved in the regulation of NADPH oxidase activation remain to be identified. We report here that the Galphai subunit of heterotrimeric G proteins is a novel binding partner for p67phox in transfected HEK293T cells and peripheral blood polymorphonuclear leukocytes. p67phox preferably interacted with inactive Galphai. Expression of p67phox caused a dose-dependent decrease in intracellular cyclic AMP concentration, suggesting altered function of Galphai. We identified a fragment of p67phox, consisting of the PB1 domain and the C-terminal SH3 domain, to be critical for the interaction with Galphai. Because these domains are involved in the interaction with p47phox and p40phox, the relationship between the respective binding events was investigated. Wild-type Galphai, but not its QL mutant, could promote the interaction between p67phox and p47phox. However, the interaction between p67phox and p40phox was not affected by either Galphai form. These results provide the first evidence for an interaction between p67phox and an alpha subunit of heterotrimeric G proteins, suggesting a potential role for Galphai in the regulation or activation of NADPH oxidase.

Differential effects of short-acting beta2-agonists on human granulocyte functions

BACKGROUND

beta2-Adrenergic agonists play a pivotal role in the management of bronchial asthma. Although the major effect of short-acting beta2-agonists on the airway is relaxation of smooth muscles, they may also have several effects on surrounding immunomodulatory cells.

METHODS

We examined whether widely used short-acting beta2-agonists differ in their ability to modulate granulocyte functions, such as superoxide anion (O2-) production and degranulation.

RESULTS

Procaterol (PC), a full agonist, significantly inhibited both O2- production by granulocytes (neutrophils and eosinophils) and their degranulation at the clinically relevant concentrations, whereas salbutamol and tulobuterol (partial agonists) showed smaller effects. PC inhibited N-formyl methionyl-leucyl-phenylalanine-induced O2- production and peroxidase release, but failed to inhibit responses induced by phorbol 12-myristate 13-acetate and/or opsonized zymosan. Exposure to 5 x 10(-8)M PC for 120 min resulted in approximately 50% inhibition of O2- production and degranulation of neutrophils. The effects of beta2-agonists were more obvious in neutrophils than in eosinophils. A selective beta2-receptor antagonist, ICI-118551, reversed the inhibitory effect of beta2-agonists (PC, salbutamol, tulobuterol B) on N-formyl methionyl-leucyl-phenylalanine-induced O2- production.

CONCLUSIONS

These results suggest that beta2-agonists had an inhibitory effect on granulocyte functions, mainly mediated viareceptors and their efficacy. Our observations support that beta2-agonists with a rapid onset of action and high intrinsic efficacy (short-acting and full agonists) may be optimal for the rescue therapy against acute asthma attack and sedation of its airway inflammation in an early phase.

Inhibition of in vitro neutrophil migration through a bilayer of endothelial and epithelial cells using beta2-agonists: concomitant effects on IL-8 and elastase secretion and impact of glucocorticosteroids

BACKGROUND

Beta2-agonists and glucocorticosteroids are two common treatments for COPD and they are often used in combination. Glucocorticosteroids mediate the anti-inflammatory response through the glucocorticosteroid receptors (GRs). Beta2-agonists are potent bronchodilators but they can have some anti-inflammatory properties by elevating the level of intracellular cAMP. In this study we aimed to investigate the anti-inflammatory effect of combination therapy in vitro.

METHODS

Neutrophils or the bilayer of endothelial and epithelial cells were preincubated with salbutamol, budesonide or budesonide followed by salbutamol. FMLP-induced IL-8, elastase release and neutrophil migration through the bilayer was measured.

RESULTS

Salbutamol at concentrations of 10(-4), 10(-5) and 10(-9) M inhibited IL-8, elastase release and migration of neutrophils in an inverse bell-shaped concentration-response manner. When given after budesonide (10(-9) and 10(-8)M), the inhibitory effect on migration was additive. This additive effect was not observed for elastase and IL-8 release.

CONCLUSIONS

Salbutamol inhibits neutrophil migration and IL-8 and elastase release in a concentration-dependent manner. Preincubation with low concentration of budesonide enhanced the inhibition of migration achieved by low concentrations of salbutamol.

Sympathoadrenal-dependent sexually dimorphic effect of nonhabituating stress on in vivo neutrophil recruitment in the rat

Since stress both activates the sympathoadrenal axis and profoundly affects inflammation and inflammatory diseases, many of which are sexually dimorphic, we tested whether the effect of stress on neutrophil recruitment, a primary component of the acute inflammatory response, is sexually dimorphic. The effect of intermittent sound (over 4 days), a nonhabituating stress, on lipopolysaccharide (LPS)-induced recruitment of neutrophils was evaluated in vivo in the rat air pouch model. At 24 h following the last stress exposure, LPS-induced neutrophil recruitment was enhanced in male rats, but not in females. When gonadectomized prepubertally and tested as adults, stress significantly inhibited the magnitude of LPS-induced neutrophil recruitment in males, while it still had no effect in gonadectomized females. In males, following adrenal denervation, the increase in LPS-induced neutrophil recruitment produced by stress was prevented. Since these data suggest that the effect of stress is dependent on the sympathoadrenal axis, we tested the hypothesis that catecholamines mediate the stress effects. In male rats, the effect of stress on LPS-induced neutrophil recruitment was significantly attenuated by continuous administration of the beta-adrenergic receptor antagonist, propranolol (4 mg kg(-1) day(-1)), during sound stress exposure, and administration of isoproterenol (10 nmoles, i.v.) significantly increased neutrophil recruitment in males, an effect that was qualitatively and quantitatively similar to the effect of stress. Propranolol significantly increased neutrophil recruitment in nonstressed female rats, but did not significantly affect neutrophil recruitment in stressed females. These findings indicate a marked male sex hormone-dependent sexual dimorphism in the sympathoadrenal-dependent effect of stress on neutrophil migration, a primary component of the inflammatory response, and suggest that the sympathoadrenal axis contributes to this effect via release of epinephrine.

Suppression of respiratory burst in human neutrophils by new synthetic pyrrolo-benzylisoquinolines

Reactive oxygen species produced by neutrophils contribute to the pathogenesis of inflammatory diseases. In this study, the inhibition of superoxide anion (O2*-) generation in human neutrophils by new synthetic pyrrolo-benzylisoquinoline derivatives was determined. We found that KW-2, KW-5, and KW-7 (8,9-dimethoxyl-1-(R-phenyl)-5,6-dihydro-pyrrolo[2,1-a]isoquinoline-2,3-dione; where R is 3-chloro, 3-bromo, and 4-methoxy, respectively) were the most effective inhibitors of formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP)-induced O2*- release in human neutrophils. KW-2, KW-5, and KW-7 displayed no antioxidant or O2*--scavenging ability. The inhibition of O2*- generation was reversed by the protein kinase (PK)A inhibitor, N-(2-((p-bromocinnamyl)amino)ethyl)-5-isoquinolinesulfonamide (H89), but not by the PKG inhibitor (8R,9S,11S)-(-)-2-methyl-9-methoxy-9-methoxycarbonyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1H,8H,11H-2,7b,11a-triazadibenzo(a,g)cyclocta(cde)trinen-1-one (KT5823), or the soluble guanylate cyclase (sGC) inhibitor, 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ). KW derivatives increased cellular cyclic AMP concentrations through the inhibition of phosphodiesterase (PDE) activity but not the elevation of adenylate cyclase (AC) activity. These results indicate that inhibition of FMLP-induced respiratory burst in human neutrophils by KW derivatives are cyclic AMP/PKA-dependent and are due to inhibition of PDE. The new chemical skeleton of PDE inhibitors may protect against the progression of inflammation.

LPS-Stimulated PMN Activation and Proinflammatory Mediator Synthesis is Downregulated by Phosphodiesterase Inhibition: Role of Pentoxifylline

BACKGROUND

Excessive production of reactive oxygen species by PMN is associated with tissue damage during inflammation. LPS interacts with the cell surface receptor CD14, which generates transmembrane signals through Toll-like protein 4 leading to mitogen activated protein kinase (MAPK) p38 activation, cytokine synthesis, PMN beta2-integrin expression and oxidative burst. Phosphodiesterase inhibition decreases proinflammatory cytokine production and tissue injury after LPS challenge. Its effects on PMN function after LPS stimulation, however, have not been fully investigated. We hypothesized that LPS-induced TNF-alpha synthesis and subsequent PMN beta2-integrin expression and oxidative burst are downregulated by concomitant treatment with the non-specific phosphodiesterase inhibitor pentoxifylline (PTX).

METHODS

Whole blood was incubated with HBSS (control), LPS (100 microg/mL), fMLP (1 micromol/L), LPS+PTX (2 mmol/L) and fMLP+PTX for different time intervals at 37C. Oxidative burst, CD14, and CD-11b expression were measured by flow cytometry. Serum TNF-alpha levels were measured by ELISA. In an attempt to localize the site of action of PTX (proximal or distal to PKC) cell surface receptors were bypassed by PMA stimulation (1 microg/mL) and oxidative burst was measured with and without PTX.

RESULTS

Up-regulation of CD14 expression was similar in LPS and LPS+PTX groups. LPS stimulation caused a significant increase in PMN oxidative burst, CD11b expression, and TNF-alpha serum levels. In addition, PMA and fMLP stimulation also caused significant increase in oxidative burst compared with controls. Concomitant addition of PTX to LPS led to a significant decrease in PMN oxidative burst (65%; p < 0.0001), PMN CD11b expression (20%; p = 0.012), and TNF-alpha levels (93%; p < 0.0001). Also, PMA- and fMLP-induced PMN oxidative burst were significantly decreased by PTX [77.5% (p < 0.0001) and 50% (p < 0.01), respectively].

CONCLUSIONS

These results suggest that PTX-inhibition of oxidative burst occurs distal to PKC and may be either due to direct inhibition of NADPH oxidase or inhibition of MAPK phosphorylation, leading to decreased adhesion molecule expression and TNF-alpha synthesis. Its use in clinical scenarios in which PMN are primed may be of clinical relevance.