Differential inhibition and potentiation of chemoattractant-induced superoxide formation in human neutrophils by the cell-permeant analogue of cyclic GMP, N2,2'-O-dibutyryl guanosine 3':5'-cyclic monophosphate

Holistic Methods for the Analysis of cNMP Effects

Cyclic nucleotide monophosphates (cNMPs) typify the archetype second messenger in living cells and serve as molecular switches with broad functionality. cAMP and cGMP are the best-described cNMPs; however, there is a growing body of evidence indicating that also cCMP and cUMP play a substantial role in signal transduction. Despite research efforts, to date, relatively little is known about the biology of these noncanonical cNMPs, which is due, at least in part, to methodological issues in the past entailing setbacks of the entire field. Only recently, with the use of state-of-the-art techniques, it was possible to revive noncanonical cNMP research. While high-sensitive detection methods disclosed relevant levels of cCMP and cUMP in mammalian cells, knowledge about the biological effectors and their physiological interplay is still incomplete. Holistic biophysical readouts capture cell responses label-free and in an unbiased fashion with the advantage to detect concealed aspects of cell signaling that are arduous to access via traditional biochemical assay approaches. In this chapter, we introduce the dynamic mass redistribution (DMR) technology to explore cell signaling beyond established receptor-controlled mechanisms. Both common and distinctive features in the signaling structure of cCMP and cUMP were identified. Moreover, the integrated response of whole live cells revealed a hitherto undisclosed additional effector of the noncanonical cNMPs. Future studies will show how holistic methods will become integrated into the methodological arsenal of contemporary cNMP research.

B-Type natriuretic peptide suppression of neutrophil superoxide generation: mechanistic studies in normal subjects

Many acute cardiovascular disease states are associated with neutrophil infiltration of myocardium and subsequent release of superoxide (O2 (-) ) and myeloperoxidase (MPO), which contribute to inflammatory reactions. B-Type natriuretic peptide (BNP) is known to exert anti-inflammatory and antifibrotic effects, but it is not known whether these may include interactions with neutrophils. In neutrophils isolated from 20 healthy subjects, we assessed the effect of BNP on the 'neutrophil burst' (O2 (-) production and MPO release) stimulated by phorbol myristate acetate (PMA) and N-formyl-methionyl-leucyl-phenylalanine (fMLP), respectively. Effects of BNP on cGMP accumulation, and the effects of the cell-permeable cGMP analogue 8-(4-chlorophenylthio) guanosine-cGMP (8-p-CPT-cGMP) and protein kinase G (PKG) inhibition with KT5823 on the neutrophil-BNP interaction were also evaluated. B-Type natriuretic peptide suppressed O2 (-) release from neutrophils by 23 ± 6% (P < 0.001) and 24 ± 8% (P < 0.05) following PMA and fMLP stimulation, respectively. Although BNP did not significantly increase cGMP formation, 8-p-CPT-cGMP suppressed both PMA- and fMLP-induced neutrophil O2 (-) release by 16% and 28%, respectively (P < 0.05). The PKG inhibitor KT5823 attenuated the effects of BNP on both fMLP- and PMA-associated O2 (-) production. Neither BNP nor 8-p-CPT-cGMP significantly affected MPO release from neutrophils. Suppression of O2 (-) release from neutrophils by BNP may contribute to its anti-inflammatory and antifibrotic actions.

From canonical to non-canonical cyclic nucleotides as second messengers: pharmacological implications

This review summarizes our knowledge on the non-canonical cyclic nucleotides cCMP, cUMP, cIMP, cXMP and cTMP. We place the field into a historic context and discuss unresolved questions and future directions of research. We discuss the implications of non-canonical cyclic nucleotides for experimental and clinical pharmacology, focusing on bacterial infections, cardiovascular and neuropsychiatric disorders and reproduction medicine. The canonical cyclic purine nucleotides cAMP and cGMP fulfill the criteria of second messengers. (i) cAMP and cGMP are synthesized by specific generators, i.e. adenylyl and guanylyl cyclases, respectively. (ii) cAMP and cGMP activate specific effector proteins, e.g. protein kinases. (iii) cAMP and cGMP exert specific biological effects. (iv) The biological effects of cAMP and cGMP are terminated by phosphodiesterases and export. The effects of cAMP and cGMP are mimicked by (v) membrane-permeable cyclic nucleotide analogs and (vi) bacterial toxins. For decades, the existence and relevance of cCMP and cUMP have been controversial. Modern mass-spectrometric methods have unequivocally demonstrated the existence of cCMP and cUMP in mammalian cells. For both, cCMP and cUMP, the criteria for second messenger molecules are now fulfilled as well. There are specific patterns by which nucleotidyl cyclases generate cNMPs and how they are degraded and exported, resulting in unique cNMP signatures in biological systems. cNMP signaling systems, specifically at the level of soluble guanylyl cyclase, soluble adenylyl cyclase and ExoY from Pseudomonas aeruginosa are more promiscuous than previously appreciated. cUMP and cCMP are evolutionary new molecules, probably reflecting an adaption to signaling requirements in higher organisms.

cCMP and cUMP: emerging second messengers

The cyclic purine nucleotides cAMP and cGMP are established second messengers. By contrast, the existence of the cyclic pyrimidine nucleotides cytidine 3',5'-cyclic monophosphate (cCMP) and uridine 3',5'-cyclic monophosphate (cUMP) has been controversial for decades. The recent development of highly sensitive mass spectrometry (MS) methods allowed precise quantitation and unequivocal identification of cCMP and cUMP in cells. Importantly, cCMP and cUMP generators, effectors, cleaving enzymes, and transporters have now been identified. Here, I discuss evidence in support of cCMP and cUMP as bona fide second messengers, the emerging therapeutic implications of cCMP and cUMP signaling, and important unresolved questions for this field.

N4-monobutyryl-cCMP activates PKA RIα and PKA RIIα more potently and with higher efficacy than PKG Iα in vitro but not in vivo

There is increasing evidence for a role of cytidine 3',5'-cyclic monophosphate (cCMP) as second messenger. In a recent study, we showed that cCMP activates both purified guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinase Iα (PKG Iα) and adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase (PKA) isoenzymes with the regulatory subunits RIα and RIIα. Moreover, the membrane-permeant cCMP analog dibutyryl (DB)-cCMP induces effective vasodilation and inhibition of platelet aggregation via PKG Iα, but not via PKA. These data prompted us to conduct a systematic analysis of the effects of cyclic nucleotide (cNMP) analogs on purified PKG Iα and PKA RIα and RIIα We also studied the effect of DB-cCMP on PKA-dependent phosphorylation of the transcription factor cAMP response-binding protein (CREB) in S49 wild-type lymphoma cells and S49 kin(-) cells, devoid of the catalytic subunit of PKA. The major cellular metabolite of the prodrug DB-cCMP, N(4)-monobutyryl (4-MB)-cCMP, was a partial and low-potency activator of purified PKG Iα and a full and moderate-potency activator of PKA RIα and RIIα. Sp-cCMPS and Sp-cAMPS activated PKA RIα and RIIα with much higher potency and efficacy than PKG Iα. Molecular modeling suggested that the cytidine ring interacts with PKG Iα mainly via hydrophobic interactions, while the butyryl group projects away from the kinase. In contrast to DB-cAMP, DB-cCMP did not induce PKA-dependent phosphorylation in intact cells. Taken together, our data show that N(4)-monobutyryl-cCMP (4-MB-cCMP) activates PKA RIα and PKA RIIα more potently and with higher efficacy than PKG Iα in vitro but not in vivo. cNMP phosphorothioates constitute a starting point for the development of PKA activators with high selectivity relative to PKG.

Evidence for ligand-specific conformations of the histamine H(2)-receptor in human eosinophils and neutrophils

The histamine H(2)-receptor (H(2)R) couples to G(S)-proteins and induces adenylyl cyclase-mediated cAMP accumulation. In human neutrophils and eosinophils, the H(2)R reduces chemotactic peptide-stimulated superoxide anion (O(2)(-)) formation. However, pharmacological characterization of the H(2)R in these cells is far from being complete. The aim of this study was to provide a comprehensive profiling of the H(2)R in neutrophils and eosinophils. Histamine inhibited O(2)(-) formation in human neutrophils more effectively than in eosinophils. H(2)R agonists mimicked the effects of histamine and H(2)R antagonists blocked the effects of histamine. We noticed multiple discrepancies in the potencies and efficacies of H(2)R agonists with respect to cAMP accumulation and inhibition of O(2)(-) formation in both cell types. There were also differences in the antagonist profiles between cAMP accumulation and inhibition of O(2)(-) formation in neutrophils. Moreover, the pharmacological profile of the recombinant H(2)R did not match the H(2)R profile in native cells. The H(2)R sequence identified in human neutrophils corresponds to the published H(2)R sequence, excluding the exclusive expression of a new H(2)R isoform as explanation for the differences. Very likely, the differences between ligands are explained by the existence of ligand-specific receptor conformations with unique affinities, potencies and efficacies. Thus, our data provide evidence for the notion that the concept of ligand-specific receptor conformations can be extended from recombinant systems to native cells.

Soluble guanylyl cyclase activator YC-1 inhibits human neutrophil functions through a cGMP-independent but cAMP-dependent pathway

3-(5'-Hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1), a novel type of soluble guanylyl cyclase (sGC) activator, is useful in investigating the signaling of cGMP and may provide a new approach for treating cardiovascular diseases. Herein, YC-1 was demonstrated to inhibit the generation of superoxide anion (O2-) and the release of beta-glucuronidase release, to diminish the membrane-associated p47phox and to accelerate resequestration of cytosolic calcium in formyl-l-methionyl-l-leucyl-l-phenylalanine-activated human neutrophils. YC-1 not only directly promoted sGC activity and cGMP formation but also dramatically potentiated sodium nitroprusside-induced sGC activity and cGMP formation in human neutrophils. However, the synergistic increase in the amount of cGMP was inconsistent with its cellular response. Moreover, neither an sGC inhibitor nor protein kinase G inhibitors reversed the inhibitory effect of YC-1. Interestingly, YC-1 also increased the cAMP concentration and protein kinase (PK)A activity. The inhibitory effect of YC-1 was significantly enhanced by prostaglandin (PG)E1 and isoproterenol, and almost abolished by PKA inhibitors. These results show that cAMP, but not cGMP, mediates the YC-1-induced inhibition of human neutrophils. YC-1 increased the PGE1- and forskolin-induced but not 3-isobutyl-1-methylxanthine-produced cAMP formation, suggesting inhibition of phosphodiesterase. These findings thus reveal novel mechanism-mediated anti-inflammatory properties of YC-1 in human neutrophils, which can influence the progression of cardiovascular disease. cAMP, but not cGMP, plays an important role in the regulation of respiratory burst and degranulation in human neutrophils.

Inhibition of superoxide anion generation by YC-1 in rat neutrophils through cyclic GMP-dependent and -independent mechanisms

3-(5'-Hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1), a soluble guanylyl cyclase (sGC) activator, inhibited formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide anion (O(2)*(-)) generation and O(2) consumption in rat neutrophils (IC(50) values of 12.7+/-3.1 and 17.7+/-6.9 microM, respectively). Inhibition of O(2)*(-) generation by YC-1 was partially reversed by the cyclic GMP-lowering agent 6-anilinoquinoline-5,8-quinone (LY83583) and by the Rp isomer of 8-(4-chlorophenylthio)guanosine-3',5'-monophosphorothioate (Rp-8-pCPT-cGMPS), a cyclic GMP-dependent protein kinase inhibitor. In cell-free systems, YC-1 failed to alter O(2)*(-) generation during dihydroxyfumaric acid autoxidation, phorbol 12-myristate 13-acetate (PMA)-activated neutrophil particulate NADPH oxidase preparation, and arachidonic acid-induced NADPH oxidase activation. YC-1 increased cellular cyclic GMP levels through the activation of sGC and the inhibition of cyclic GMP-hydrolyzing phosphodiesterase activity. The plateau phase, but not the initial spike, of fMLP-induced [Ca(2+)](i) changes was inhibited by YC-1 (IC(50) about 15 microM). fMLP- but not PMA-induced phospholipase D activation was inhibited by YC-1 (IC(50) about 28 microM). Membrane-associated ADP-ribosylation factor and Rho A in cell activation was also reduced by YC-1 at a similar concentration range. Neither cytosolic protein kinase C (PKC) activity nor PKC membrane translocation was altered by YC-1. YC-1 did not affect either fMLP-induced phosphatidylinositol 3-kinase activation or p38 mitogen-activated protein kinase phosphorylation, but slightly attenuated the phosphorylation of extracellular signal-regulated kinase. Collectively, these results indicate that the inhibition of the fMLP-induced respiratory burst by YC-1 is mediated by cyclic GMP-dependent and -independent signaling mechanisms.

Purines and neutrophil leukocytes

1. Adenosine is a normal constituent of all body fluids and its levels are raised, for example, by hypoxia and ischemia. In addition, both adenosine and ATP can be released by endothelial cells and neutrophils in response to physiologic stimulation. 2. Human neutrophil leukocytes possess multiple adenosine receptors and P2 purinoceptors. 3. ATP can increase intracellular Ca2+ levels in neutrophils, cause degranulation and enzyme release, potentiate the oxidative burst and enhance their adhesion to the endothelium. ATP is broken down to adenosine by ecto-enzymes. Via A1 receptors, adenosine can increase neutrophil chemotaxis and, via A2A receptors, it can decrease the oxidative burst, degranulation and adhesion to endothelium. 4. Adenosine and adenine nucleotides are important endogenous modulators of neutrophil functions, and drugs may exert important actions via purinoceptors on neutrophil leukocytes.

Migration of neutrophils from blood to tissue: alteration of modulatory effects of prostanoid on superoxide generation in rabbits and humans

Alteration of neutrophil function is associated with their migration from blood into tissue. We evaluated this alteration in both human and rabbit neutrophils, by comparing the inhibitory effects of prostanoids on formylmethionyl-leucyl-phenylalanine (fMLP)-stimulated superoxide generation in human circulating blood neutrophils with those in saliva, and also comparing rabbit circulating blood neutrophils with those exudated into peritoneal cavity. We showed that EP-receptor agonists (PGE1) EP2/EP3 agonist (misoprostol), EP2-receptor agonist (butaprost) and DP-receptor agonist (PGD2) inhibited fMLP-stimulated superoxide production from human blood neutrophils in a concentration-dependent manner. In contrast, these prostanoids produced a significantly smaller maximum inhibition of fMLP-stimulated superoxide production in salivary neutrophils compared to those in blood neutrophils. Similar differences were observed for rabbit blood and peritoneal neutrophils. The inhibitory effect of EP2 agonist (butaprost) on the fMLP-stimulated superoxide generation in human blood neutrophils was significantly higher than that of EP3 agonist (ONO-AP-324). The EP1 antagonist (SC-51322) and EP4 antagonist (AH23848B) employed in this study could not antagonize the inhibitory effect of PGE2. TP agonist (U-46619) failed to show any inhibitory effect in either blood or salivary neutrophils. These results indicated that EP2 and DP receptors are the primary receptors mediating the prostanoids inhibition of fMLP-stimulated superoxide generation from neutrophils. Furthermore, it can be concluded that neutrophils become less responsive to prostanoids in terms of fMLP-stimulated superoxide production in association with their migration from blood to tissue.

Effects of SCA40 on human isolated bronchus and human polymorphonuclear leukocytes: comparison with rolipram, SKF94120 and levcromakalim

1. SCA40 (0.1 nM-0.1 mM) produced concentration-dependent suppression of the spontaneous tone of human isolated bronchus (-log EC50 = 6.85 +/- 0.09; n = 10) and reached a maximal relaxation similar to that of theophylline (3 mM). The potency (-log EC50 values) of SCA40 compared to other relaxants was rolipram (7.44 +/- 0.12; n = 9) > SCA40 > or = levcromakalim (6.49 +/- 0.04; n = 6) > SKF94120 (5.87 +/- 0.10; n = 9). 2. When tested against the activity of the isoenzymes of cyclic nucleotide phosphodiesterase (PDE) isolated from human bronchus, SCA40 proved highly potent against PDE III (-log IC50 = 6.47 +/- 0.16; n = 4). It was markedly less potent against PDE IV (4.82 +/- 0.18; n = 4) and PDE V (4.32 +/- 0.11; n = 4). 3. Human polymorphonuclear leukocytes (PMNs) stimulated with N-formylmethionyl-leucyl-phenylalanine (FMLP) produced a concentration-dependent superoxide anion generation and elastase release. SCA40 (1 nM-10 microM) produced a concentration-related inhibition of FMLP (30 nM approximately EC50)-induced superoxide production (-log IC50 = 5.48 +/- 0.10; n = 6) and elastase release (-log IC50 = 5.50 +/- 0.26; n = 6). Rolipram was an effective inhibitor of superoxide generation and elastase release (-log IC50 values approximately 8) while SKF94120 and levcromakalim were scarcely effective. 4. FMLP (30 nM) and thimerosal (20 microM) induced leukotriene B4 production and elevation of intracellular calcium concentration in human PMNs. The production of leukotriene B4 was inhibited by SCA40 in a concentration-related manner (-log IC50 = 5.94 +/- 0.22; n = 6) but SCA40 was less effective against the elevation of intracellular calcium. Rolipram was an effective inhibitor of leukotriene B4 synthesis (-log IC50 approximately 7) and intracellular calcium elevation (-log IC50 approximately 6) while SKF94120 and levcromakalim were scarcely effective. 5. It is concluded that SCA40 is an effective inhibitor of the inherent tone of human isolated bronchus. The bronchodilatation produced by SCA40 appears mainly related to PDE inhibition since the potency of SCA40 as a relaxant of human isolated bronchus was found to be close to its potency as inhibitor of PDE III activity isolated from human bronchus. In addition, SCA40 exhibited inhibitory effects on human PMN function stimulated by FMLP. These effects may be related to the ability of SCA40 to inhibit PDE IV from human PMNs while the contribution of PDE V inhibition is uncertain. We found no evidence of a role for levcromakalim-sensitive plasmalemmal K+-channels in human PMNs.

Involvement of platelet cyclic GMP but not cyclic AMP suppression in leukocyte-dependent platelet adhesion to endothelial cells induced by platelet-activating factor in vitro

1. Incubation of endothelial cells with platelets in the absence or the presence of PAF (10 nM) markedly increased platelet cyclic AMP levels, which were significantly decreased by indomethacin (3 microM). Co-incubation of endothelial cells and platelets with polymorphonuclear leukocytes (PMNs) did not change the platelet cyclic AMP levels. 2. Incubation of endothelial cells with platelets in the absence of PAF increased platelet cyclic GMP levels, which were increased 3.5 fold by PAF. These cyclic GMP levels were significantly decreased by NG-nitro-L-arginine (100 microM), and completely by methylene blue (10 microM). When endothelial cells and platelets were co-incubated with PMNs, the cyclic GMP level in the cell mixture was 42.5 and 65.3% lower than that in endothelial cells and platelets without and with PAF stimulation, respectively. 3. PAF induced platelet adhesion to endothelial cells only when PMNs were present. Methylene blue dose-dependently potentiated the PMN-dependent platelet adhesion induced by PAF, although it had no effect in the absence of PMNs. 4. Sodium nitroprusside and 8-bromo cyclic GMP but not dibutyryl cyclic AMP significantly, although partially, inhibited the platelet adhesion. Inhibition of cyclic GMP-specific phosphodiesterase by zaprinast slightly inhibited the PMN-induced platelet adhesion and potentiated the inhibitory effect of 8-bromo cyclic GMP, while these drugs markedly inhibited the adhesion of platelet aggregates induced by PMN sonicates. 5. These results suggest that the impairment by activated PMNs of EDRF-induced platelet cyclic GMP formation is involved in part in the mechanism of PMN-dependent platelet adhesion to endothelial cells induced by PAF in vitro. The precise mechanism still remains to be clarified.

G-protein-coupled receptors in HL-60 human leukemia cells

1. HL-60 human leukemia cells are a widely employed model system for the analysis of signal transduction processes mediated via regulatory heterotrimeric guanine nucleotide-binding proteins (G-proteins). HL-60 promyelocytes are pluripotent and can be differentiated into neutrophilic or monocytic cells. 2. HL-60 cells express formyl peptide-, complement C5a-, leukotriene B4 (LTB4)- and platelet-activating factor receptors, receptors for purine and pyrimidine nucleotides, histamine H1- and H2-receptors, beta 2-adrenoceptors and prostaglandin receptors. 3. The major G-proteins in HL-60 cells are pertussis toxin (PTX)-sensitive Gi-proteins (Gi2 > Gi3). Gs-proteins and G-proteins of the Gq-family (e.g., G16) are expressed, too. 4. G-protein-regulated effector systems in HL-60 cells are adenylyl cyclase and phospholipase C-beta 2 (PLC-beta 2) and, possibly, phospholipase D (PLD), nonselective cation (NSC) channels and NADPH oxidase. 5. The expression of signal transduction pathways in HL-60 cells strongly depends on the differentiation state of cells. 6. Formyl peptides, via Gi-proteins, mediate activation of PLC, PLD, NSC channels, NADPH oxidase and azurophilic granule release and are referred to as full secretagogues. In dibutyryl cAMP (Bt2cAMP)-differentiated HL-60 cells, C5a and LTB4 are partial and incomplete secretagogues, respectively. There are substantial differences in the Gi-protein activations induced by formyl peptides, C5a and LTB4. 7. In HL-60 promyelocytes, purine and pyrimidine nucleotides mediate activation of PLC and NSC channels largely via PTX-insensitive G-proteins and induce functional differentiation. In Bt2cAMP-differentiated HL-60 cells, they additionally activate PLD, NADPH oxidase and granule release via PTX-sensitive and -insensitive pathways. ATP and UTP are partial secretagogues. Multiple types of receptors (i.e., P2Y- and P2U-receptors and pyrimidinocyeptors) may mediate the effects of nucleotides in HL-60 cells. 8. Bt2cAMP- and 1 alpha,25-dihydroxycholecalciferol-differentiated HL-60 cells express H1-receptors coupled to Gi-proteins and PTX-insensitive G-proteins. In the former cells, histamine mediates activation of PLC and NSC channels, and in the latter, activation of NSC channels. Histamine is an incomplete secretagogue in these cells. 9. HL-60 promyelocytes express H2-receptors coupled to adenylyl cyclase, PLC, and NSC channels. There are substantial differences in the agonist/antagonist profiles of H2-receptor-mediated cAMP formation and rises in cytosolic Ca2+ concentration, indicative of the involvement of different H2-receptor subtypes. H2-receptors mediate functional differentiation of HL-60 cells. 10. Certain cationic-amphiphilic histamine receptor ligands (i.e., 2-substituted histamines, lipophilic guanidines, and a histamine trifluoromethyl-toluidide derivative) show stimulatory effects in HL-60 cells that are attributable to receptor-independent activation of Gi-proteins.

Differential activation of dibutyryl cAMP-differentiated HL-60 human leukemia cells by chemoattractants

Dibutyryl cAMP-differentiated HL-60 human leukemia cells possess receptors for the chemoattractants N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), C5a and leukotriene B4 (LTB4). We compared the effects of these chemoattractants in HL-60 membranes and in intact HL-60 cells. fMLP, C5a and LTB4 stimulated GTP hydrolysis and guanosine 5'-O-[3-thio]triphosphate (GTP[gamma S]) binding in HL-60 membranes with similar effectiveness and in a pertussis toxin (PTX)-sensitive manner. They also stimulated photolabeling of the alpha-subunits of the guanine nucleotide-binding proteins (G-proteins), Gi2 and Gi3 with similar effectiveness. Chloride salts of monovalent cations differentially enhanced and inhibited chemoattractant-induced GTP hydrolyses. C5a was less effective than fMLP in enhancing cholera toxin-catalysed ADP-ribosylation of Gi alpha 2 and Gi alpha 3, and LTB4 was ineffective. fMLP was more effective than C5a and LTB4 in stimulating Ca2+ influx in HL-60 cells. C5a- and LTB4-induced rises in cytosolic Ca2+ concentration ([Ca2+]i) were PTX-sensitive, whereas the effect of fMLP was partially PTX-insensitive. LTB4-induced rises in [Ca2+]i were more sensitive towards homologous desensitization than those induced by C5a, and the effect of fMLP was resistant in this regard. C5a was considerably less effective than fMLP in activating superoxide anion formation and azurophilic granule release, and LTB4 was ineffective. Our data suggest that fMLP, C5a and LTB4 effectively activate the G-proteins, Gi2 and Gi3, in HL-60 cells and that fMLP may additionally activate PTX-insensitive G-proteins. fMLP, C5a and LTB4 are full, partial and incomplete secretagogues, respectively, and these differences may be due to differences in homologous receptor desensitization and qualitative Gi-protein activation.

Inhibition by nitric oxide-donors of human polymorphonuclear leucocyte functions

1. The study was designed to test the hypothesis that nitric oxide (NO)-releasing compounds increase guanosine 3':5'-cyclic monophosphate (cyclic GMP) production in human polymorphonuclear leucocytes (PMNs) and concomitantly inhibit PMN functions, i.e. leukotriene B4 (LTB4) synthesis, degranulation, chemotaxis and superoxide anion (O2-) release. The effects of two new NO-releasing compounds, GEA 3162 and GEA 5024 were compared to 3-morpholino-sydnonimine (SIN-1) and S-nitroso-N-acetyl-penicillamine (SNAP). 2. GEA 3162 and GEA 5024 (1-100 microM) inhibited Ca ionophore A23187-induced LTB4 and beta-glucuronidase release, chemotactic peptide FMLP-induced chemotaxis and opsonized zymosan-triggered chemiluminescence dose-dependently in human PMNs. SIN-1 and SNAP were weaker inhibitors. 3. Cellular cyclic GMP production was increased after exposure to NO-donors concomitantly with the inhibition of PMN functions. No alterations in the levels of adenosine 3':5'-cyclic monophosphate (cyclic AMP) were detected. 4. The results suggest that NO, possibly through increased cyclic GMP, inhibits the activation of human PMNs and may thus act as a local modulator in inflammatory processes.

Preparations of Rp-cyclic adenosine 3',5'-phosphorothioate (Rp-cAMPS) can contain biologically active amounts of adenosine

Superoxide anion (O2-.) production from human neutrophils stimulated by N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP, 1 microM) was inhibited by preparations of the inhibitor of cAMP-dependent protein kinase, Rp-cyclic adenosine 3',5'-phosphorothioate (Rp-cAMPS, 100 microM). This effect of Rp-cAMPS was reversed by xanthine amine congener (0.1 microM), an adenosine receptor antagonist, and by low concentrations of adenosine desaminase (0.02 mg/ml). HPLC analysis shows that these preparations of Rp-cAMPS contained concentrations of adenosine which could produce significant inhibition of fMLP-induced O2-. production. These results suggest that Rp-cAMPS should be used with caution in cells or tissues containing adenosine receptors, and that preparations of Rp-cAMPS should be treated with adenosine desaminase before use to avoid activation of adenosine receptors.

Molsidomine inhibits the chemoattractant-induced respiratory burst in human neutrophils via a no-independent mechanism

3-Morpholino-sydnonimine (SIN-1) is a NO-releasing compound which mimics the effects of cGMP through activation of soluble guanylyl cyclase. Its prodrug, molsidomine (SIN-10), does not release NO but does modulate various cell functions. These findings prompted us to study the effects of SIN-10 and SIN-1 on the respiratory burst in human neutrophils. SIN-10 was more effective than SIN-1 in inhibiting superoxide anion (O2-) formation induced by N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe) and by C5a. The effects of SIN-1 and SIN-10 on O2- formation were additive or less than additive, indicating the sydnonimines acted through a common mechanism. The sydnonimines showed no effect on O2- formations induced by gamma-hexachlorocyclohexane, arachidonic acid and a phorbol ester. They did not inhibit O2- formation induced by xanthine oxidase, by autoxidation of pyrogallol and in a cell-free system from HL-60 leukemic cells. Neutrophils did not convert SIN-10 to SIN-1 as assessed by O2 consumption which accompanies NO release from SIN-1. The cell-permeant analogue of cGMP, N2,2'-O-dibutyryl guanosine 3':5'-monophosphate (Bt2cGMP), and SIN-10 but not SIN-1 inhibited fMet-Leu-Phe-induced O2 consumption. SIN-1 and SIN-10 slightly enhanced agonist binding to formyl peptide receptors, whereas Bt2cGMP was inhibitory. The sydnonimines did not affect GTP hydrolysis of heterotrimeric regulatory guanine nucleotide-binding proteins in HL-60 membranes. SIN-1 but not SIN-10 stimulated ADP-ribosylation of a 39-kDa protein in the cytosol of HL-60 cells. SIN-10 reduced fMet-Leu-Phe-induced rises in cytosolic Ca2+ concentration in neutrophils. These data suggest that SIN-10 inhibits the respiratory burst via a NO-independent mechanism which may involve inhibition of rises in cytosolic Ca2+ concentration.