Inhibition by L-arginine of the endothelin-mediated increase in cytosolic calcium in human neutrophils

Endothelin-1 acutely increases nitric oxide production via the calcineurin mediated dephosphorylation of Caveolin-1

Endothelin (ET)-1 is an endothelial-derived peptide that exerts biphasic effects on nitric oxide (NO) levels in endothelial cells such that acute exposure stimulates-while sustained exposure attenuates-NO production. Although the mechanism involved in the decrease in NO generation has been identified but the signaling involved in the acute increase in NO is still unresolved. This was the focus of this study. Our data indicate that exposing pulmonary arterial endothelial cells (PAEC) to ET-1 led to an increase in NO for up to 30min after which levels declined. These effects were attenuated by ET receptor antagonists. The increase in NO correlated with significant increases in pp60Src activity and increases in eNOS phosphorylation at Tyr83 and Ser1177. The ET-1 mediated increase in phosphorylation and NO generation were attenuated by the over-expression of a pp60Src dominant negative mutant. The increase in pp60Src activity correlated with a reduction in the interaction of Caveolin-1 with pp60Src and the calcineurin-mediated dephosphorylation of caveolin-1 at three previously unidentified sites: Thr91, Thr93, and Thr95. The calcineurin inhibitor, Tacrolimus, attenuated the acute increase in pp60Src activity induced by ET-1 and a calcineurin siRNA attenuated the ET-1 mediated increase in eNOS phosphorylation at Tyr83 and Ser1177 as well as the increase in NO. By using a Caveolin-1 celluSpot peptide array, we identified a peptide targeting a sequence located between aa 41-56 as the pp60Src binding region. This peptide fused to the TAT sequence was found to decrease caveolin-pp60Src interaction, increased pp60Src activity, increased eNOS pSer1177 and NO levels in PAEC and induce vasodilation in isolated aortic rings in wildtype but not eNOS knockout mice. Together, our data identify a novel mechanism by which ET-1 acutely increases NO via a calcineurin-mediated dephosphorylation of caveolin-1 and the subsequent stimulation of pp60Src activity, leading to increases in phosphorylation of eNOS at Tyr83 and Ser1177.

The endothelin B receptor plays a crucial role in the adhesion of neutrophils to the endothelium in sickle cell disease

Although the primary origin of sickle cell disease is a hemoglobin disorder, many types of cells contribute considerably to the pathophysiology of the disease. The adhesion of neutrophils to activated endothelium is critical in the pathophysiology of sickle cell disease and targeting neutrophils and their interactions with endothelium represents an important opportunity for the development of new therapeutics. We focused on endothelin-1, a mediator involved in neutrophil activation and recruitment in tissues, and investigated the involvement of the endothelin receptors in the interaction of neutrophils with endothelial cells. We used fluorescence intravital microscopy analyses of the microcirculation in sickle mice and quantitative microfluidic fluorescence microscopy of human blood. Both experiments on the mouse model and patients indicate that blocking endothelin receptors, particularly ET_B receptor, strongly influences neutrophil recruitment under inflammatory conditions in sickle cell disease. We show that human neutrophils have functional ET_B receptors with calcium signaling capability, leading to increased adhesion to the endothelium through effects on both endothelial cells and neutrophils. Intact ET_B function was found to be required for tumor necrosis factor α-dependent upregulation of CD11b on neutrophils. Furthermore, we confirmed that human neutrophils synthesize endothelin-1, which may be involved in autocrine and paracrine pathophysiological actions. Thus, the endothelin-ET_B axis should be considered as a cytokine-like potent pro-inflammatory pathway in sickle cell disease. Blockade of endothelin receptors, including ET_B, may provide major benefits for preventing or treating vaso-occlusive crises in sickle cell patients.

Endothelin-1 downregulates sperm phagocytosis by neutrophils in vitro: A physiological implication in bovine oviduct immunity

The oviduct is an active contractile tube that provides the proper environment for sperm transport, capacitation and survival. Oviductal contractions are regulated by autocrine/paracrine secretion of several factors, such as prostaglandins (PGs) and endothelin-1 (EDN-1). We have previously shown that during the preovulatory stage, sperm are exposed to polymorphonuclear neutrophils (PMNs) in the bovine oviduct, and the bovine oviduct epithelial cells (BOECs) secrete molecules including PGE2 that suppress sperm phagocytosis by PMNs in vitro. In this study, we investigated the possible effects of EDN-1 on the phagocytic activity of PMNs toward sperm. The local concentrations of EDN-1 in oviduct fluid and BOEC culture medium ranged from 10^–10 to 10^–11 M as determined by EIA. Phagocytosis and superoxide production were assayed by co-incubation of sperm pretreated to induce capacitation with PMNs exposed to EDN-1 (0, 10^–11, 10^–10, 10^–9, and 10^–8 M) for 2 h. EDN-1 suppressed dose dependently (10^–11 to 10^–8 M) the phagocytic activity for sperm and superoxide production of PMNs in response to capacitated sperm. Moreover, this suppression was eliminated by an ET_B receptor antagonist (BQ-788). EDN-1 suppressed mRNA expression of EDN-1 and ET_B but not ET_A receptors in PMNs, suggesting the ET_B receptor-mediated pathway. Scanning electron microscopic observation revealed that incubation of PMNs with EDN-1 (10^–9 M) completely suppressed the formation of DNA-based neutrophil extracellular traps for sperm entanglement. The results provide evidence indicating that EDN-1 may be involved in the protection of sperm from phagocytosis by PMNs in the bovine oviduct, supporting sperm survival until fertilization.

Oxidative and nitrosative stress in pediatric pulmonary hypertension: roles of endothelin-1 and nitric oxide

An increasing number of studies implicate oxidative stress in the development of endothelial dysfunction and the pathogenesis of cardiovascular disease. Further, this oxidative stress has been shown to be associated with alterations in both the endothelin-1 (ET-1) and nitric oxide (NO) signaling pathways such that bioavailable NO is decreased and ET-1 signaling is potentiated. However, recent data, from our groups and others, have shown that oxidative stress, ET-1, and NO are co-regulated in a complex fashion that appears to be dependent on the cellular levels of each species. Thus, when ROS levels are transiently elevated, NO signaling is potentiated through transcriptional, post-transcriptional, and post-translational mechanisms. However, in pediatric pulmonary hypertensive disorders, when reactive oxygen species (ROS) increases are sustained by ET-1 mediated activation of smooth muscle cell ET(A) subtype receptors, NOS gene expression and NO signaling are reduced. Further, increases in oxidative stress can stimulate both the expression of the ET-1 gene and the secretion of the ET-1 peptide. Finally, the addition of exogenous NO, and increasingly utilized therapy for pulmonary hypertension, can also lead to increases ROS generation via the activation of ROS generating enzymes and through the induction of mitochondrial dysfunction. Thus, this manuscript will review the available data regarding the interaction of oxidative and nitrosative stress, endothelial dysfunction, and its role in the pathophysiology of pediatric pulmonary hypertension. In addition, we will suggest avenues of both basic and clinical research that will be important to develop novel pulmonary hypertension treatment and prevention strategies, and resolve some of the remaining clinical issues regarding the use of NO augmentation.

ET-1- and NO-mediated signal transduction pathway in human brain capillary endothelial cells

Previous studies have demonstrated that functional interaction between endothelin (ET)-1 and nitric oxide (NO) involves changes in Ca(2+) mobilization and cytoskeleton in human brain microvascular endothelial cells. The focus of this investigation was to examine the possible existence of analogous interplay between these vasoactive substances and elucidate their signal transduction pathways in human brain capillary endothelial cells. The results indicate that ET-1-stimulated Ca(2+) mobilization in these cells is dose-dependently inhibited by NOR-1 (an NO donor). This inhibition was prevented by ODQ (an inhibitor of guanylyl cyclase) or Rp-8-CPT-cGMPS (an inhibitor of protein kinase G). Treatment of endothelial cells with 8-bromo-cGMP reduced ET-1-induced Ca(2+) mobilization in a manner similar to that observed with NOR-1 treatment. In addition, NOR-1 or cGMP reduced Ca(2+) mobilization induced by mastoparan (an activator of G protein), inositol 1,4,5-trisphosphate, or thapsigargin (an inhibitor of Ca(2+)-ATPase). Interestingly, alterations in endothelial cytoskeleton (actin and vimentin) were associated with these effects. The data indicate for the first time that the cGMP-dependent protein kinase colocalizes with actin. These changes were accompanied by altered levels of phosphorylated vasodilator-stimulated phosphoprotein, which were elevated in endothelial cells incubated with NOR-1 and significantly reduced by ODQ or Rp-8-CPT-cGMPS. The findings indicate a potential mechanism by which the functional interrelationship between ET-1 and NO plays a role in regulating capillary tone, microcirculation, and blood-brain barrier function.

Endothelin-1 changes polymorphonuclear leukocytes' deformability and CD11b expression and promotes their retention in the lung

Endothelin (ET)1 influences polymorphonuclear leukocyte (PMN)- endothelial cell interactions. The aim of this study was to examine the effect of ET-1 on factors that influence PMN-endothelial interaction and retention in the lung both in vitro and in vivo. In vitro, high concentration of ET-1 (> or = 10(-8) M) rapidly increased PMN F-actin content (10(-7) M: 58 +/- 6% increase, P<0.01), whereas lower concentration of ET-1 (< or = 10(-9) M) caused a small but consistent decrease in F-actin content (10(-10) M: 6.9+/-1.5% decrease, P< 0.01). Preincubation of PMNs with the nitric oxide donor sodium nitroprusside (SNP) inhibited the F-actin content increase by 10(-7) M of ET-1 (P<0.01), and enhanced the F-actin content decrease by 10(-10) M of ET-1 (P<0.01). Preincubation of PMNs with Nomega-nitro-L-arginine methylester prevented the F-actin content decrease by 10(-10) M of ET-1. ET-1 (10(-7) M) reduced the deformability of PMNs (P<0.01), which was inhibited by preincubation of PMNs with SNP (P<0.05). ET-1 (10(-9) to 10(-7) M) increased CD11b expression of PMNs (P<0.01), which was inhibited by preincubation of PMNs with SNP. In vivo studies showed that the retention of PMNs treated with ET-1 increased from 45+/-8 to 70+/-5% compared with naive PMNs during their first pass through the lung (P<0.05). We conclude that ET-1 changes the F-actin content, the deformability, and the CD11b expression of PMNs in a dose-dependent fashion and that this leads to increased PMN sequestration in pulmonary microvessels.

Endothelin-1-induced PMN infiltration and mucosal dysfunction in the rat small intestine

The objectives of this study were to characterize the effects of endothelin (ET)-1 on intestinal mucosal parameters and to assess the contribution of polymorphonuclear leukocytes (PMNs), intercellular adhesion molecule-1 (ICAM-1), and a platelet-activating factor (PAF) to the mucosal dysfunction induced by ET-1. Different concentrations of ET-1 (100, 200, and 400 pmol/kg) were infused into the superior mesenteric artery for 10 min, and tissue samples were obtained 30 min after terminating the infusion. ET-1 administration significantly elevated tissue myeloperoxidase activity, plasma carbonyl content, and tissue chemiluminescence intensity, indicating that ET-1 produces PMN infiltration and oxidant stress. Blood-to-lumen clearance of (51)Cr-EDTA significantly increased after ET-1 infusion (400 pmol/kg). Monoclonal antibodies against ICAM-1 (1A29, 2 mg/kg), antineutrophil serum, and PAF antagonist (WEB-2086, 10 mg/kg) attenuated the mucosal barrier dysfunction induced by ET-1. Overall, our data indicate that ET-1 causes PMN accumulation, oxidant stress, and mucosal dysfunction in the rat small intestine and that ET-1-induced mucosal dysfunction involves a mechanism that includes a role for PMNs, ICAM-1, and PAF.

Interaction of the protein C/protein S anticoagulant system, the endothelium and pregnancy

Normal pregnancy is associated with significant changes in haemostasis, lipid metabolism and endothelial function. This suggests that maternal adaptation in these systems is required for successful pregnancy outcome. A number of acquired and heritable prothrombotic abnormalities are associated with complications in pregnancy. A common feature of these abnormalities is their ability to alter endothelial function or the protein C/protein S system and increase thrombin generation. In this review the normal function of the endothelium and the protein C/protein S system is detailed. The changes which characterize normal and complicated pregnancies are outlined and the evidence for the impact of heritable and acquired disorders of the protein C/protein S system on pre-eclampsia and fetal loss are discussed.

Nitric oxide modulates endothelin 1-induced Ca2+ mobilization and cytoskeletal F-actin filaments in human cerebromicrovascular endothelial cells

A functional interrelation between nitric oxide (NO), the endothelial-derived vasodilating factor, and endothelin 1 (ET-1), the potent vasoconstrictive peptide, was investigated in microvascular endothelium of human brain. Nor-1 dose-dependently decreased the ET-1-stimulated mobilization of Ca2+. This response was mimicked with cGMP and abrogated by inhibitors of guanylyl cyclase or cGMP-dependent protein kinase G. These findings indicate that NO and ET-1 interactions involved in modulation of intracellular Ca2+ are mediated by cGMP/protein kinase G. In addition, Nor-1-mediated effects were associated with rearrangements of cytoskeleton F-actin filaments. The results suggest mechanisms by which NO-ET-1 interactions may contribute to regulation of microvascular function.

The involvement of protein kinase G in stimulation of neutrophil migration by endothelins

Activation of human neutrophil migration by endothelin-1 and endothelin-3 is inhibited by guanylate cyclase inhibitors, by antagonists of protein kinase G (G-kinase), and by KT-5823, an inhibitor of G-kinase. Although no direct effect of endothelins on cGMP level could be established, these results suggest that the effect of these endothelins on migration is mediated by cGMP, and that the effect of cGMP proceeds via a G-kinase. There was little or no effect of guanylate cyclase inhibitors and G-kinase antagonists on endothelin-2-activated migration, indicating that the role of cGMP and G-kinase in endothelin-2-induced activation was either absent or at least different from that of the other endothelins. As compared with other activators, the role of G-kinase in formyl-methionyl-leucyl-phenylalanyl(fMLP-)activated migration resembled that of endothelin-activated migration, while the role of G-kinase in interleukin-8- or leukotriene B4-activated migration was less pronounced.

Investigation of the role of nitric oxide and cyclic GMP in both the activation and inhibition of human neutrophils

1. The aim of this study was to establish the role of nitric oxide (NO) and cyclic GMP in chemotaxis and superoxide anion generation (SAG) by human neutrophils, by use of selective inhibitors of NO and cyclic GMP pathways. In addition, inhibition of neutrophil chemotaxis by NO releasing compounds and increases in neutrophil nitrate/nitrite and cyclic GMP levels were examined. The ultimate aim of this work was to resolve the paradox that NO both activates and inhibits human neutrophils. 2. A role for NO as a mediator of N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced chemotaxis was supported by the finding that the NO synthase (NOS) inhibitor L-NMMA (500 microM) inhibited chemotaxis; EC50 for fMLP 28.76 +/- 5.62 and 41.13 +/- 4.77 pmol/10(6) cells with and without L-NMMA, respectively. Similarly the NO scavenger carboxy-PTIO (100 microM) inhibited chemotaxis; EC50 for fMLP 19.71 +/- 4.23 and 31.68 +/- 8.50 pmol/10(6) cells with and without carboxy-PTIO, respectively. 3. A role for cyclic GMP as a mediator of chemotaxis was supported by the finding that the guanylyl cyclase inhibitor LY 83583 (100 microM) completely inhibited chemotaxis and suppressed the maximal response; EC50 for fMLP 32.53 +/- 11.18 and 85.21 +/- 15.14 pmol/10(6) cells with and without LY 83583, respectively. The same pattern of inhibition was observed with the G-kinase inhibitor KT 5823 (10 microM); EC50 for fMLP 32.16 +/- 11.35 and > 135 pmol/10(6) cells with and without KT 5823, respectively. 4. The phosphatase inhibitor, 2,3-diphosphoglyceric acid (DPG) (100 microM) which inhibits phospholipase D, attenuated fMLP-induced chemotaxis; EC50 for fMLP 19.15 +/- 4.36 and 61.52 +/- 16.2 pmol/10(6) cells with and without DPG, respectively. 5. Although the NOS inhibitors L-NMMA and L-canavanine (500 microM) failed to inhibit fMLP-induced SAG, carboxy-PTIO caused significant inhibition (EC50 for fMLP 36.15 +/- 7.43 and 86.31 +/- 14.06 nM and reduced the maximal response from 22.14 +/- 1.5 to 9.8 +/- 1.6 nmol O2-/10(6) cells/10 min with and without carboxy-PTIO, respectively). This suggests NO is a mediator of fMLP-induced SAG. 6. A role for cyclic GMP as a mediator of SAG was supported by the effects of G-kinase inhibitors KT 5823 (10 microM) and Rp-8-pCPT-cGMPS (100 microM) which inhibited SAG giving EC50 for fMLP of 36.26 +/- 8.77 and 200.01 +/- 43.26 nM with and without KT 5823, and 28.35 +/- 10.8 and 49.25 +/- 16.79 nM with and without Rp-8-pCTP-cGMPS. 7. The phosphatase inhibitor DPG (500 microM) inhibited SAG; EC50 for fMLP 33.93 +/- 4.23 and 61.12 +/- 14.43 nM with and without DPG, respectively. 8. The NO releasing compounds inhibited fMLP-induced chemotaxis with a rank order of potency of GEA 3162 (IC50 = 14.72 +/- 1.6 microM) > GEA 5024 (IC50 = 18.44 +/- 0.43 microM) > SIN-1 (IC50 > 1000 microM). This order of potency correlated with their ability to increase cyclic GMP levels rather than the release of NO, where SIN-1 was most effective (SIN-1 (EC50 = 37.62 +/- 0.9 microM) > GEA 3162 (EC50 = 39.7 +/- 0.53 microM) > GEA 5024 (EC50 = 89.86 +/- 1.62 microM)). 9. In conclusion, chemotaxis and SAG induced by fMLP can be attenuated by inhibitors of phospholipase D, NO and cyclic GMP, suggesting a role for these agents in neutrophil activation. However, the increases in cyclic GMP and NO induced by fMLP, which are associated with neutrophil activation, are very small. In contrast much larger increases in NO and cyclic GMP, as observed with NO releasing compounds, inhibit chemotaxis.

Role of endothelin in the pathophysiology of renal ischemia-reperfusion in normal rabbits

The present study addressed the acute effects of endothelin-1 on renal function and neutrophils accumulation in the setting of in vivo severe (60 min) acute ischemia/reperfusion. Ischemia/reperfusion decreased renal functional parameters and increased renal neutrophil accumulation and medullary congestion. All these parameters markedly improved with the intrarenal administration of anti-endothelin-1 antiserum. Comparatively, the intrarenal infusion of endothelin-1 decreased renal function and increased neutrophil accumulation. Abnormalities in renal histology were, however, less pronounced than with ischemia/ reperfusion. In experiments using rabbit isolated perfused kidneys, endothelin-1 induced the accumulation of labeled neutrophils. This accumulation was similar to that observed in kidneys obtained after 60 minutes of ischemia plus 60 minutes of reperfusion. Both endothelin and ischemia/ reperfusion effects were counteracted by an anti-endothelin antibody. In further in vitro studies, we found that endothelin-1-induced the expression of the CD18 antigens on the neutrophil surface. In subsequent experiments based on this effect of ET-1 on CD18 antigens, a blockade of both ischemia/reperfusion-induced and endothelin-1-induced neutrophil accumulation was obtained by infusion an anti-CD18 antibody. In conclusion, our experiments disclosed the critical role of endothelin-1 as a major promoter of early neutrophil accumulation after ischemia/reperfusion, which occurred through an integrin-mediated mechanism.

Supplemental L-arginine HCl augments bacterial phagocytosis in human polymorphonuclear leukocytes

That L-arginine (L-Arg) augments the host response to acute bacterial sepsis suggests that this amino acid intervenes early in the immune response, perhaps via the nitric oxide synthetase (NOS) pathway. The effect of L-Arg supplementation on in vitro phagocytosis of fluorescein-labeled, heat-killed Staphylococcus aureus by peripheral blood neutrophils (PMNs) from 12 normal human volunteers was studied. Separated PMNs were incubated for 2 h with labeled bacteria, with and without supplemental L-Arg, D-arginine, glycine, and/or the NOS inhibitors L-canavanine, aminoguanidine, or L-NG-nitroarginine methyl ester. PMNs were fixed and extracellular fluorescence quenched with crystal violet. By flow cytometry and confocal microscopy, L-Arg supplementation was shown to result in a highly significant increase in PMN bacterial phagocytosis, the maximal effect being seen with L-Arg 380 microM and falling off with higher concentrations. This augmentation was completely abrogated by NOS inhibitors in molar excess, but inhibitors alone did not suppress phagocytosis below that of unsupplemented controls. Neither D-arginine nor glycine affected phagocytosis; the L-Arg effect was stereospecific and not related to utilization of L-Arg as an energy source. L-Arg supplementation significantly enhances bacterial phagocytosis in human neutrophils, perhaps by effects on cytoskeletal phenomena, and this appears to be mediated through NOS activity. Phagocytosis by nonspecific immune cells which intervene early in the response to sepsis is critically important, and beneficial effects of L-Arg on the clinical course of sepsis may be due at least in part to augmentation of phagocyte function.

The role of cyclic nucleotides in neutrophil migration

1. The literature concerning the effects of cAMP and especially cGMP on neutrophil migration is reviewed. 2. Experiments with agents that enhance cGMP level, and with electroporated neutrophils in which cGMP was introduced, show that the nucleotide has different effects. There is a maximal stimulation at a specific concentration while higher concentrations are less effective or even inhibitory. 3. Some physiologically active peptides such as granulocyte-macrophage colony-stimulating factor (GM-CSF), atrial natriuretic factor, and endothelin appear to modify neutrophil migration via a cGMP-dependent mechanism. 4. Dependent on concentration and conditions (random migration vs. fMLP-activated migration, using nitric oxide (NO), NO donors, and inhibitors of NO synthase), NO has stimulatory or inhibitory effects on neutrophil migration. 5. The differential effects of cGMP and cAMP on neutrophil migration are discussed with regard to intracellular actions, metabolism, interaction with calcium, and relation to structural changes required for cell movement.

Regulation of endothelin receptors by nitric oxide in cultured rat vascular smooth muscle cells

Two important mediators of endothelium-dependent regulation of vascular smooth muscle tone and proliferation are nitric oxide (NO) and endothelin (ET-1). An imbalance between NO and ET-1 may contribute to the alterations in vascular tone characteristic of cardiovascular disease. The objective of this study was to determine whether NO regulates ET receptors in cultured rat superior mesenteric artery vascular smooth muscle cells (RVSMC). Chronic treatment of quiescent RVSMC with any one of three chemically dissimilar NO-generating drugs, S-nitroso-N-acetyl penicillamine (SNAP), sodium nitroprusside (SNP), and isosorbide dinitrate (ISDN) produced a significant dose- and time-dependent increase in the number of ET-A receptors, while concomitantly increasing the affinity of ET-1 for this receptor. This effect was mimicked by both 8-bromo-cGMP and 8-bromo-cAMP. The requirement of both protein and RNA synthesis and activation of a cAMP-dependent protein kinase (A-kinase) was demonstrated following inhibition of this regulation by cycloheximide, actinomycin D and KT5720 (a specific A-kinase inhibitor), respectively. In addition, the cytokine interleukin 1 beta (IL-1 beta) which induced NOS activity with subsequent NO synthesis in vascular smooth muscle, also caused a similar upregulation of ET receptors. This effect was attenuated in the presence of the specific NOS inhibitor, L-NAME. To assess the possible functional consequences of this NO-mediated upregulation, the effect of SNAP pretreatment on isolated vessel reactivity was determined. In both superior mesenteric artery and thoracic aorta rings, SNAP pretreatment caused a significant increase in the maximal force of contraction to ET-1. Collectively, these data suggest that NO regulates ET-A receptors in vitro through a cGMP-dependent mechanism via activation of the cAMP-dependent protein kinase. We conclude that a similar interaction between NO and ET-1 may be operational in vivo.

Endothelin-1 does not prime polymorphonuclear leukocytes for enhanced production of reactive oxygen metabolites

The in vitro effect of endothelin-1 (ET-1) on the capacity of polymorphonuclear leukocytes (PMNLs) to generate reactive oxygen species (ROS) was investigated. Human PMNLs were separated from healthy volunteers and preincubated for 10 min. at 37 degrees C with varying concentrations (10(-7)-10(-12) M) of ET-1. After subsequent stimulation with FMLP (10(-7) M) or opsonized zymosan (0.5 mg/ml) the intra- and extracellular generation of ROS was assessed by luminol-amplified chemiluminescence, superoxide radical (.O2-) and hydrogen peroxide (H2O2) production.

RESULTS

ET-1 alone failed to stimulate ROS generation. Neither the capacity for extracellular generation of oxygen metabolites nor the production of ROS with an intracellular origin was changed after preincubation of PMNLs with ET-1. ET-1 did not cause a shift of the .O2-/H2O2 production ratio after stimulation of PMNLs with FMLP. These findings suggest that ET-1 in vitro does not prime human PMNLs for enhanced production of ROS.

Enhancing and inhibitory effects of nitric oxide on superoxide anion generation in human polymorphonuclear leukocytes

1. The effects of sodium nitroprusside (SNP, a nitric oxide donor) and authentic nitric oxide (NO) on superoxide anion (O2-) generation were investigated in human polymorphonuclear leukocytes (PMNs). 2. Neither SNP (10 nM to 10 microM) nor NO (40 nM to 40 microM) alone induced O2- generation or change of intracellular Ca2+ concentration ([Ca2+]i) in human PMNs. 3. Pretreatment with SNP or NO at the concentrations used (SNP, 10 nM to 10 microM: NO, 40 nM to 40 microM) showed a biphasic concentration-dependent effect on O2- generation induced by f-methionyl-leucyl-phenylalanine (FMLP). Low concentrations of SNP (10 nM to 100 nM) and NO (400 nM) did not affect either basal cyclic GMP levels or cyclic GMP levels stimulated by FMLP, but enhanced FMLP-induced O2- generation and [Ca2+]i elevation. On the other hand, high concentrations of SNP (10 microM) and NO (40 microM) alone elevated cyclic GMP levels and inhibited FMLP-induced O2- generation and [Ca2+]i elevation. 4. 8-Bromo-cyclic GMP (8-Br-cyclic GMP) at concentrations ranging from 1 microM to 1 mM did not induce O2- generation on its own and had little effect on FMLP-induced O2- generation and [Ca2+]i elevation. 5. Addition of a high concentration of NO (40 microM) decreased authentic O2- formation by pyrogallol in a cell-free system, but a low concentration of NO (400 nM) had no effect on this. On the other hand, addition of SNP in the concentration-ranges used had no effect on authentic O2- formation by pyrogallol. 6. In this study, we have shown that SNP and NO have dual effects (enhancement and inhibition) on 02- generation induced by FMLP in human peripheral PMNs. The results suggest that the enhancement observed with SNP and NO at low concentrations is not mediated by activation of the guanylate cyclase-cyclic GMP pathway. The suppressive effect of SNP and NO at higher concentrations is mediated by the NO-induced O2--scavenging effect and activation of the guanylate cyclase-cyclic GMP pathway.

Effects of aspirin on platelet-neutrophil interactions. Role of nitric oxide and endothelin-1

BACKGROUND

In recent studies, the hypothesis has been raised that the mechanisms by which aspirin acts as a protective anti-ischemic agent exceed the inhibition of platelet thromboxane A2 synthesis. Recently, new data have been obtained disclosing a platelet-antiaggregating effect by neutrophils, which occurs through a nitric oxide (NO)/cGMP-dependent pathway.

METHODS AND RESULTS

The present study, using platelets and neutrophils from normal subjects, was undertaken to assess the putative effect of aspirin on the neutrophil-mediated, platelet-inactivating effect. Aspirin facilitated the inhibitory effect of neutrophils on platelet activation by thrombin, ADP, or epinephrine. This effect was equally evident in vitro and in blood samples of normal individuals taking aspirin. A significant stimulation of NO-mediated mechanisms in the presence of aspirin was disclosed by different methods, as follows: (1) the increased metabolism of arginine to citrulline, (2) the increase of cGMP in the platelet/neutrophil system, and (3) the inhibitory action of the L-arginine (L-Arg)-competitive analogue L-NMMA, which was reversed by L-Arg. The effect of aspirin appeared to be related to cyclooxygenase inhibition, since it was reproduced by using indomethacin. The vasoconstricting peptide endothelin-1 (ET-1) reversed the effect of aspirin through the endogenous production of platelet-activating factor (PAF) by neutrophils, as judged by the marked inhibitory effect of the PAF antagonist BN-52021.

CONCLUSIONS

Our results show that a significant part of the effect of aspirin on platelet activation involves a neutrophil-mediated, NO/cGMP-dependent mechanism. The presence of ET-1 counterbalances these effects of neutrophils on platelet activation, therefore acting as an indirect proactivating agent. These results add new elements for interpreting the effects of aspirin on the interactions between blood cells, with special reference to high endothelin states (for example, ischemia/reperfusion processes).

Activated neutrophil by endothelin-1 caused tissue damage in human umbilical cord

Immunostaining of human neutrophils incubated with endothelin-1 (ET-1) showed intense and spreading pattern of anti human granulocyte elastase within the cytosol. That reflected neutrophil activation followed by the release of granule contents by ET-1. In contrast, PBS (phosphate buffered saline) treated neutrophils showed localized and faintly stained granules. Intracellular calcium in fura-2 loaded neutrophils was measured at 340/380 nm. A dose and time dependent increase in intracellular calcium by ET-1 occurred in human single neutrophil. Elastase activity assay was done with chromogenic substrate S2484. ET-1 induces dose and time dependent increase in elastase activity in neutrophil suspensions like ionophore A23187. A similar time dependent increase in elastase activity was retained even after repeated wash and ET-1 treatment. That confirmed the viability of most of the neutrophils after each treatment. In umbilical cord preparations, ET-1 treated neutrophils could migrate from the venous lumen into the tissue matrix of the umbilical cords. Hematoxylin and eosin staining revealed a massive tissue destruction in ET-1 activated neutrophil treated cords when compared to sham control and untreated neutrophil injected cords. Immunostaining with monoclonal anti human elastase revealed an intense staining in former sections when compared to the others. We suggest that ET-1 activated neutrophil might play a major role in endothelial injury and tissue damage in conditions with high blood level of endothelin.

Endothelin-induced activation of neutrophil migration

Migration of rabbit peritoneal neutrophils was stimulated by endothelin-1 (ET-1) up to 2.10(-8) M. Higher concentrations inhibited random migration. The stimulating effect of ET-1 was inhibited by BQ-123, a specific antagonist of the ETA receptor. A checkerboard assay showed that the stimulating effect of ET-1 on neutrophil migration was chemokinetic rather than chemotactic. Extracellular Ca2+ was required for the activating effect of ET-1. Non-selective calcium channel blockers such as econazole and La3+ strongly inhibited ET-1-activated migration but had little effect on fMLP-activated migration, underlining the importance of Ca2+ influx for ET-1-activated migration. Studies with electroporated neutrophils showed that the increase in migration was most pronounced at calcium concentrations between 100 nM and 1 microM. ET-1-activated migration of electroporated cells was completely blocked by low concentrations of calcium-channel blockers such as verapamil and nitrendipine. Migration by intact cells was inhibited by the same concentration of verapamil, but to a lesser degree; nitrendipine had little effect on migration of intact cells. This suggests that calcium derived from intracellular stores is required for migration activated by ET-1. Protein kinase C, protein tyrosine kinase, and phosphatase activity were involved in the activating effect of ET-1 on neutrophil migration. ET-1 did not induce exocytotic enzyme release, in neither the presence nor the absence of cytochalasin B.

Decreased production of nitric oxide by human neutrophils during septic multiple organ dysfunction syndrome. Comparison with endotoxin and cytokine effects on normal cells

The objective of this study was to determine nitric oxide (NO) and superoxide anion release (O-2) by neutrophils (PMNs) in the septic multiple organ dysfunction syndrome (MODS) and to compare them with the response of normal cells to lipopolysaccharide (LPS) and cytokines. NO production was measured by the release of nitrites in the medium, its maximal production rate by a modified oxyhemoglobin assay and O-2 by standard methods. Normal cells were incubated with LPS, gamma interferon (IFN-gamma), or tumor necrosis factor (TNF-alpha) alone or in combination. Results showed that PMN release of both NO and O-2 was reduced in septic samples; in contrast, an association of LPS, IFN-gamma, and TNF-alpha promoted maximal NO release by normal cells (40-50%). We conclude that while interaction of normal PMNs with cytokines increases NO and O-2 release, progression of sepsis to a multiple organ dysfunction impairs these responses in both functions.

Termination of endothelin signaling: role of nitric oxide

Cellular mechanisms responsible for the termination of ET-1 signal are poorly understood. In order to examine the hypothesis that nitric oxide serves as a physiological brake of ET-1 signaling, Chinese hamster ovary (CHO) cells stably transfected with the ETA receptor cDNA (CHO-ET) were studied. CHO-ET responded to ET-1 with robust [Ca2+]i transients and developed a long-lasting homologous desensitization. Donors of nitric oxide (NO), 3-morpholino-sydnonimine HCl (SIN-1), or sodium nitroprusside (SNP) reduced the amplitude of these responses, accelerated the rate of [Ca2+]i recovery, and counteracted the development of homologous desensitization by a cyclic GMP-independent mechanism, suggesting an alternative mode for NO modulation of ET-1 responses. Stimulation of CHO-ET cells with mastoparan, a wasp venom acting directly on G proteins (bypassing receptor activation), was inhibited by NO, revealing a postreceptoral target for NO-induced modulation of [Ca2+]i mobilization. Using a lys9-biotinylated ET-1 (ET-1 [BtK9]), binding sites were "mapped" in CHO-ET cells. Receptor-ligand complexes did not exhibit spontaneous dissociation during 60-min observations. Quantitative fluorescence microscopy revealed that SNP or SIN-1 caused a rapid, concentration-dependent, and reversible dissociation of biotinylated ET-1 from ETA receptor (EC50 = 75 microM and 6 microM, respectively), an effect that was not mimicked by 8-bromo-cyclic GMP. "Sandwich" co-culture of endothelial cells with CHO-ET showed that activation of NO production by endothelial cells similarly resulted in dissociation of ET-1 [BtK9] from ETA receptors. We hypothesize that NO plays a role in physiological termination of ET-1 signalling by dual mechanisms: (1) displacement of bound ET-1 from its receptor, thus preventing homologous desensitization, and (2) interference with the postreceptoral pathway for [Ca2+]i mobilization, hence inhibiting end-responses to ET-1.

Effect of endothelin-1 on neutrophil adhesion to endothelial cells and perfused heart

BACKGROUND

Based on recent evidence showing that endothelin-1 stimulates several activation mechanisms on neutrophils, the aim of the present study was to analyze the effects of endothelin-1 on neutrophil adhesion to endothelial cells and neutrophil accumulation in the heart.

METHODS AND RESULTS

The experiments included (1) adhesion of 51Cr-labeled human neutrophils to bovine endothelial cells in culture both in the presence and absence of monoclonal antibodies against the alpha- and beta-subunits of integrins; (2) surface expression of the alpha- and beta-integrin antigens; (3) accumulation of 51Cr-labeled neutrophils on the isolated perfused rabbit heart; (4) in vivo accumulation of autologous neutrophils in the heart, as assessed by myeloperoxidase activity. Endothelin-1 stimulated neutrophil adhesion to endothelial cells (increase of 1 x 10(5) +/- 1 x 10(4) neutrophils per well). The endothelin-1-induced adhesion was blocked (83 +/- 6%) by the anti-CD18 antibody TS1/18 and by several anti-alpha-subunit antibodies. The expression of CD18 and CD11b on the neutrophil surface was also increased by endothelin-1. Endothelin-1 enhanced neutrophil accumulation in the isolated rabbit heart by 4.2 times throughout a TS1/18-inhibitable mechanism. Myeloperoxidase activity increased by 4.2 times in hearts infused in vivo with endothelin-1.

CONCLUSIONS

Endothelin-1 stimulates neutrophil adhesion to endothelial cells by an effect on the expression of adhesive molecules on the neutrophil surface. Endothelin-1 stimulates neutrophil accumulation in vivo and in vitro in the heart. Antibodies against the integrin complex block the endothelin-1-dependent neutrophil adhesion. These findings have potential importance in the pathophysiology of endothelin-1-increased states.

Nitric oxide-generating system as an autocrine mechanism in human polymorphonuclear leucocytes

Recent data [Lopéz-Farré, Riesco, Moliz, Egido, Casado, Hernando and Caramelo (1991) Biochem. Biophys. Res. Commun. 178, 884-891] revealed that endothelin 1 (ET-1) increases intracellular free [Ca2+] in polymorphonuclear leucocytes (PMN) by a mechanism that can be inhibited by L-arginine. The aim of the present study was to clarify the mechanisms of the interaction between the effects of ET-1 and L-arginine in human PMN. The experimental findings showed that in human PMN: (a) ET-1 and the chemoattractant peptide N-formylmethionyl- leucyl-phenylalanine (fMLP) induce both the metabolism of L-arginine to L-citrulline and cyclic GMP (cGMP) formation; (b) the ET-1-induced cGMP production is inhibitable by the L-arginine antagonist NG-monomethyl-L-arginine, therefore suggesting the involvement of NO; (c) the ET-1- or fMLP-induced NO/cGMP stimulation is critically dependent on the availability of L-arginine; (d) human PMN possess a L-arginine transport system with both Na(+)-dependent and -independent components; (e) the L-arginine transport system in PMN appears to be feedback-regulated by NO/cGMP in ET-1-stimulated conditions, but not under baseline conditions; (f) the L-arginine transport system in PMN is independent of the gamma-glutamyl cycle and is not modified by either ET-1 or fMLP. The L-arginine/NO/cGMP-dependent mechanisms characterized in the present study may be relevant in the regulation of PMN activation in pathophysiological conditions in vivo.

Aggregation of human polymorphonuclear leukocytes by endothelin: role of platelet-activating factor

The mechanisms by which endothelin-1 (ET-1) acts on polymorphonuclear leukocytes (PMN) are insufficiently known. In this study, we assessed the hypotheses that ET-1 is a PMN-aggregating agent, and that platelet-activating factor (PAF) is the principal mediator of ET-1-induced PMN aggregation. ET-1 induced dose-related PMN aggregation, which started 1 min after ET-1 exposure. Two different specific PAF receptor antagonists blocked the effect of ET-1 on PMN aggregation. In addition, ET-1 induced a significant increase in the production of PAF by PMN after 2 to 5 min of ET-1 incubation. ET-1 induced PAF release from PMN rather than accumulation. This PAF production was dependent on intra- and extracellular Ca2+. In this regard, the PAF receptor antagonists significantly blunted the ET-1-induced peak in cytosolic free Ca2+ ([Ca2+]i). Our results, therefore, indicate that ET-1 is effective in causing aggregation of human PMN and that its action appears to be mediated by PAF production via a Ca(2+)-dependent mechanism.