S-nitroso-N-acetylpenicillamine reduces leukocyte adhesion to type I collagen

Role of p38 MAPK pathway in induction of iNOS expression in neutrophils and peripheral blood mononuclear cells in patients with squamous cell carcinoma of the oral cavity

PURPOSE

The aim of the present study was to assess the role of the p38 mitogen-activated protein kinase (MAPK) pathway in the induction of inducible nitric oxide synthase (iNOS) expression and the production of NO by neutrophils (polymorphonuclear neutrophils [PMNs]) and peripheral blood mononuclear cells (PBMCs) in patients with squamous cell carcinoma (SCC) of the oral cavity.

PATIENTS AND METHODS

PMNs and PBMCs were isolated from 24 patients with SCC. The expression of iNOS and phospho-p38 MAPK was estimated by Western blotting. Total NO was measured in the cell supernatants and serum using the Griess method. The generation of superoxide anion radicals by the cells was estimated using the cytochrome-c reduction test. The cyclic guanosine monophosphate level in the cell supernatants and plasma was assessed using an enzyme-linked immunosorbent assay kit, and the concentrations of malonyldialdehyde in serum were assessed using a thiobarbituric acid method.

RESULTS

The results of the present study of patients with stage II and III disease showed lowered expression of iNOS and phospho-p38 MAPK in PMNs and PBMCs. Moreover, in these patients, a lower production of NO by PMNs and PBMCs was observed. However, the opposite relationship was observed between the expression of phospho-p38 MAPK and iNOS in the leukocytes of patients with stage IV disease. The concentration of total NO in the PMN and PBMC supernatants of patients with advanced disease stages did not differ from that of the control group. In all the patients with SCC, a lowered ability of neutrophils to generate superoxide anion radicals and an increased production of cyclic guanosine monophosphate by PMNs and PBMCs was confirmed. Furthermore, a greater concentration of cyclic guanosine monophosphate was found in the plasma and total NO in the serum of patients with stage IV disease compared with the levels in the control group. A greater concentration of malonyldialdehyde in the serum of all patients compared with that in the control group was also observed.

CONCLUSIONS

Our results indicate that in the leukocytes of patients with stage II and III SCC, the p38 MAPK pathway performs an essential role in the induction of iNOS expression, and the process of lipid peroxidation is not dependent on NO. In contrast, in patients with advanced-stage SCC, iNOS expression did not seem to be linked with the p38 MAPK pathway, and NO directly influenced the process of lipid peroxidation.

Leishmania donovani: Inhibition of phagosomal maturation is rescued by nitric oxide in macrophages

Leishmania donovani promastigotes, the causative agent of visceral leishmaniasis, survive inside macrophages by inhibiting phagosomal maturation. The main surface glycoconjugate on promastigotes, lipophosphoglycan (LPG), is crucial for parasite survival. LPG has several detrimental effects on macrophage function, including inhibition of periphagosomal filamentous actin (F-actin) breakdown during phagosomal maturation. However, in RAW 264.7 macrophages pre-stimulated with lipopolysaccharide (LPS) and interferon gamma (IFNgamma), known to up-regulate inducible nitric oxide synthase (iNOS) and nitric oxide (NO) production, L. donovani promastigotes are unable to inhibit periphagosomal F-actin breakdown and phagosomal maturation proceeds normally. Moreover, the iNOS inhibitor aminoguanidine, blocked the positive effects of LPS/IFNgamma suggesting that NO is a key player in F-actin remodeling. In conclusion, production of NO by stimulated macrophages seems to allow phagosomal maturation following uptake of L. donovani promastigotes, suggesting a novel mechanism whereby NO facilitates killing of an intracellular pathogen.

Nitric oxide inhibits neutrophil migration by a mechanism dependent on ICAM-1: Role of soluble guanylate cyclase

In the present study, we addressed the role of intercellular adhesion molecule type 1 (ICAM-1/CD54) in neutrophil migration to inflammatory site and whether the inhibitory effect of nitric oxide (NO) upon the neutrophil rolling, adhesion and migration involves down-modulation of ICAM-1 expression through a cyclic GMP (cGMP) dependent mechanism. It was observed that neutrophil migration induced by intraperitoneal administration of endotoxin (LPS), carrageenan (Cg) or N-formyl peptide (fMLP) in ICAM-1 deficient (ICAM-1-/-) is similar to that observed in wild type (WT) mice. The treatment of mice with NO synthase (NOS) inhibitors, NG-nitro-l-arginine, aminoguanidine or with a soluble guanylate cyclase (sGC) inhibitor, ODQ enhanced LPS- or Cg-induced neutrophil migration, rolling and adhesion on venular endothelium. These parameters induced by LPS were also enhanced by 1400 W, a specific iNOS inhibitor, treatment. On the other hand, the treatment of the mice with S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, reduced these parameters induced by LPS or Cg by a mechanism sensitive to ODQ pretreatment. The NOS inhibitors did not enhance LPS-, Cg- or fMLP-induced migration and adhesion in ICAM-1-/- mice. Moreover, genetic (iNOS-/- mice) or pharmacological inhibition of NOS or of sGC enhanced LPS-induced ICAM-1 expression on mesenteric microcirculation vessels of WT mice. By contrast, SNAP reduced the ICAM-1 expression by a mechanism dependent on cGMP. In conclusion, the results suggest that although during inflammation, ICAM-1 does not contribute to neutrophil migration, it is necessary for the down-modulatory effect of inflammation-released NO on the adhesion and transmigration of neutrophils. Moreover, these NO effects are mediated via cGMP.

Neutrophil migration in inflammation: nitric oxide inhibits rolling, adhesion and induces apoptosis

There is controversy in the literature over whether nitric oxide (NO) released during the inflammatory process has a pro- or inhibitory effect on neutrophil migration. The aim of the present investigation was to clarify this situation. Treatment of rats with non-selective, NG-nitro-L-arginine (nitro), or selective inducible NO synthase (iNOS), aminoguanidine (amino) inhibitors enhanced neutrophil migration 6h after the administration of low, but not high, doses of carrageenan (Cg) or Escherichia coli endotoxin (LPS). The neutrophil migration induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP) was also enhanced by nitro or amino treatments. The enhancement of Cg-induced neutrophil migration by NOS inhibitor treatments was reversed by co-treatment with L-arginine, suggesting an involvement of the L-arginine/NOS pathway in the process. The administration of Cg in iNOS deficient (iNOS(-/-)) mice also enhanced the neutrophil migration compared with wild type mice. This enhancement was markedly potentiated by treatment of iNOS(-/-) mice with nitro. Investigating the mechanisms by which NOS inhibitors enhanced the neutrophil migration, it was observed that they promoted an increase in Cg-induced rolling and adhesion of leukocytes to endothelium and blocked the apoptosis of emigrated neutrophils. Similar results were observed in iNOS(-/-) mice, in which these mechanisms were potentiated and reverted by nitro and L-arginine treatments, respectively. In conclusion, these results suggest that during inflammation, NO released by either constitutive NOS (cNOS) or iNOS down-modulates the neutrophil migration. This NO effect seems to be a consequence of decreased rolling and adhesion of the neutrophils on endothelium and also the induction of apoptosis in migrated neutrophils.

Nitric oxide production by carpet shell clam (Ruditapes decussatus) hemocytes

We have demonstrated that carpet shell clam (Ruditapes decussatus) hemocytes produce nitric oxide (NO) in response to zymosan or bacterial lipopolysaccharide (LPS). This NO production was partially inhibited by the NO synthase inhibitor, N-omega-nitro-L-arginine (L-NAME). The capability of clam hemocytes to produce NO in response to the bacterial pathogen Vibrio tapetis was also studied. Incubation with bacteria induced a significant NO production by clam hemocytes, even though exogenous NO only slightly decreased the growth of V. tapetis. The effect of exogenous NO on the capability of clam hemocytes to phagocytose labeled Escherichia coli was studied using two different NO donors S-nitroso-N-acetyl-penicillamine (SNAP), and diethylenetriamine NO adduct (DETA/NO). Exogenous NO did not increase hemocyte phagocytosis, indicating that NO does not mediate phagocytosis in this species. These results are in accordance to those observed in other mollusk species, in which NO was independent of phagocytosis and constitutes an alternative method of killing invading pathogens.

Involvement of NO in the failure of neutrophil migration in sepsis induced by Staphylococcus aureus

1. Sepsis induced by S. aureus was used to investigate whether neutrophil migration failure to infectious focus correlates with lethality in Gram-positive bacteria-induced sepsis in mice. 2. By contrast with the sub-lethal (SL-group), the lethal (L-group) intraperitoneal inoculum of S. aureus caused failure of neutrophil migration (92% reduction), high CFU in the exudate, bacteremia and impairment of in vitro neutrophil chemotactic activity. 3. Pre-treatments of L-group with adequate doses of aminoguanidine prevented the neutrophil migration failure and improved the survival of the animals (pre-treated: 43%; untreated: 0% survival). Thus, the impairment of neutrophil migration in the L-group appears to be mediated by nitric oxide (NO). 4. The injection of S. aureus SL-inoculum in iNOS deficient (-/-) or aminoguanidine-treated wild-type mice (pre- and post-treatment), which did not present neutrophil migration failure, paradoxically caused severe peritonitis and high mortality. This fact is explainable by the lack of NO dependent microbicidal activity in migrated neutrophils. 5. In conclusion, although the NO microbicidal mechanism is active in neutrophils, the failure of their migration to the infectious focus may be responsible for the severity and outcome of sepsis.

Endothelial dysfunction in ischemic acute renal failure: rescue by transplanted endothelial cells

There is accumulating circumstantial evidence suggesting that endothelial cell dysfunction contributes to the "no-reflow" phenomenon in postischemic kidneys. Here, we demonstrated the vulnerability of in vitro, ex vivo, and in vivo endothelial cells exposed to pathophysiologically relevant insults, such as oxidative and nitrosative stress or ischemia. All of these stimuli compromised the integrity of the endothelial lining. Next, we performed minimally invasive intravital microscopy of blood flow in peritubular capillaries, which provided direct evidence of the existence of the no-reflow phenomenon, attributable, at least in part, to endothelial injury. In an attempt to ameliorate the hemodynamic consequences of lost endothelial integrity, we transplanted endothelial cells or surrogate cells expressing endothelial nitric oxide synthase into rats subjected to renal artery clamping. Implantation of endothelial cells or their surrogates expressing functional endothelial nitric oxide synthase in the renal microvasculature resulted in a dramatic functional protection of ischemic kidneys. These observations strongly suggest that endothelial cell dysfunction is the primary cause of the no-reflow phenomenon, which, when ameliorated, results in prevention of renal injury seen in acute renal failure.

Endothelin-1 and nitric oxide affect human cerebromicrovascular endothelial responses and signal transduction

Endothelium plays a central role in regulating the vascular tone, blood flow and blood brain barrier (BBB) permeability. The experiments presented here examine the mechanisms by which nitric oxide (NO) and endothelin-1 (ET-1) may be involved in these processes. The findings indicate that ET-1-stimulated [Ca2+]i accumulation occurs through activation of ETA receptor. The capacity of NO to affect this response was indicated by results showing: 1) a two-fold increase in ET-1-stimulated [Ca2+]i by L-NAME, the inhibitor of nitric oxide synthase, and 2) a dose-dependent decrease in [Ca2+]i accumulation by pretreatment with Nor-1 (NO donor). Abrogation of this Nor-1 effect by ODQ (an inhibitor of guanylyl cyclase) or Rp-8-pCPT-cGMPS (an inhibitor of protein kinase G) and inhibition of ET-1 stimulated intracellular Ca2+ accumulation by 8-bromo-cGMP (a permeable, analog of cGMP) substantiate the involvement of interplay between ET-1 and NO in [Ca2+]i accumulation in HBMEC. ET-1 treatment also increased thickness of F-actin cytoskeletal filaments in HBMEC. This effect was attenuated by pretreatment with NO; NO also rarefied F-actin filaments in control cultures. The findings support a linkage between NO and ET-1 in regulating microvascular tone, microcirculation and BBB permeability and indicate a role for cGMP/cGMP protein kinase system and cytoskeletal changes in responses of HBMEC.

The vasodilator-stimulated phosphoprotein is regulated by cyclic GMP-dependent protein kinase during neutrophil spreading

The expression and phosphorylation state of the vasodilator-stimulated phosphoprotein (VASP), a membrane-associated focal adhesion protein, was investigated in human neutrophils. Adhesion and spreading of neutrophils induced the rapid phosphorylation of VASP. The phosphorylation of VASP was dependent on cell spreading, as VASP was expressed as a dephosphorylated protein in round adherent cells and was phosphorylated at the onset of changes in cell shape from round to spread cells. Immunofluorescence microscopy demonstrated that VASP was localized at the cell cortex in round cells and redistributed to focal adhesions at the ventral surface of the cell body during cell spreading. Dual labeling of spread cells indicated that VASP was colocalized with F-actin in filopodia and in focal adhesions, suggesting that the phosphorylation of VASP during cell spreading may be involved in focal adhesion complex organization and actin dynamics. VASP is a prominent substrate for both cGMP-dependent protein kinase (cGK) and cAMP-dependent protein kinase. Evidence suggested that cGK regulated neutrophil spreading, as both VASP phosphorylation and neutrophil spreading were inhibited by Rp-8-pCPT-cGMPS (cGK inhibitor), but not KT5720 (cAMP-dependent protein kinase inhibitor). In contrast, neutrophil spreading was accelerated when cGMP levels were elevated with 8-Br-cGMP, a direct activator of cGK. Furthermore, the same conditions that lead to VASP phosphorylation during neutrophil adherence and spreading induced significant elevations of cGMP in neutrophils. These results indicate that cGMP/cGK signal transduction is required for neutrophil spreading, and that VASP is a target for cGK regulation.

Glucose scavenging of nitric oxide

Endothelial dysfunction accompanies suboptimal glucose control in patients with diabetes mellitus. A hallmark of endothelial dysfunction is a deficiency in production or bioavailability of vascular nitric oxide (NO). Here we demonstrate that acute exposure of human endothelial cells to glucose, at levels found in plasma of diabetic patients, results in a significant blunting of NO responses to the endothelial nitric oxide synthase (eNOS) agonists bradykinin and A-23187. Monitoring of NO generation by purified recombinant bovine eNOS in vitro, using amperometric electrochemical detection and an NO-selective porphyrinic microelectrode, showed that glucose causes a progressive and concentration-dependent attenuation of detectable NO. Addition of glucose to pure NO solutions similarly elicited a sharp decrease in NO concentration, indicating that glucose promotes NO loss. Electrospray ionization-tandem mass spectrometry, using negative ion monitoring, directly demonstrated the occurrence of a covalent reaction involving unitary addition of NO (or a derived species) to glucose. Collectively, our findings reveal that hyperglycemia promotes the chemical inactivation of NO; this glucose-mediated NO loss may directly contribute to hypertension and endothelial dysfunction in diabetic patients.

Workshop: endothelial cell dysfunction leading to diabetic nephropathy : focus on nitric oxide

Clinical manifestations of diabetic nephropathy are an expression of diabetic microangiopathy. This review revisits the previously proposed Steno hypothesis and advances our hypothesis that development of endothelial cell dysfunction represents a common pathophysiological pathway of diabetic complications. Specifically, the ability of glucose to scavenge nitric oxide is proposed as the initiation phase of endothelial dysfunction. Gradual accumulation of advanced glycated end products and induction of plasminogen activator inhibitor-1, resulting in the decreased expression of endothelial nitric oxide synthase and reduced generation of nitric oxide, are proposed to be pathophysiologically critical for the maintenance phase of endothelial dysfunction. The proposed conceptual shift toward the role of endothelial dysfunction in diabetic complications may provide new strategies for their prevention.

Nitric oxide modulates intracellular translocation of pigment organelles in Xenopus laevis melanophores

Pigment organelles in Xenopus laevis melanophores are used by the animal to change skin color, and they provide a good model for studying intracellular organelle transport. Movement of organelles and vesicles along the cytoskeleton is essential for many processes, such as axonal transport, endocytosis, and intercompartmental trafficking. Nitric oxide (NO) is a signaling molecule that plays a role in, among other things, relaxation of blood vessels, sperm motility, and polymerization of actin. Our study focused on the effect NO exerts on cytoskeleton-mediated transport, which has previously received little attention. We found that an inhibitor of NO synthesis, N-nitro-L-arginine methyl ester (L-NAME), reduced the melatonin-induced aggregation of the pigment organelles, melanosomes. Preaggregated melanosomes dispersed after treatment with L-NAME but not after exposure to the inactive stereoisomer (D-NAME) or the substrate for NO synthesis (L-arginine). Signal transduction by NO can be mediated through the activation of soluble guanylate cyclase (sGC), which leads to increased production of cGMP and activation of cGMP-dependent kinases (PKG). We found that both the sGC inhibitor 1H-(1,2,4) oxadiazolo(4,3-a)quinoxalin-1-one (ODQ) and the cGMP analogue 8-bromoguanosine 3':5'-cyclic monophosphate (8-Br-cGMP) reduced melanosome aggregation, whereas the PKG inhibitor KT582 did not. Our results demonstrate that melanosome aggregation depends on synthesis of NO, and NO deprivation causes dispersion. It seems, thus, as if NO and cGMP are essential and can regulate melanosome translocation.

Effects of homocysteine on endothelial nitric oxide production

Hyperhomocysteinemia (HHCy) is an independent and graded cardiovascular risk factor. HHCy is prevalent in patients with chronic renal failure, contributing to the increased mortality rate. Controversy exists as to the effects of HHCy on nitric oxide (NO) production: it has been shown that HHCy both increases and suppresses it. We addressed this problem by using amperometric electrochemical NO detection with a porphyrinic microelectrode to study responses of endothelial cells incubated with homocysteine (Hcy) to the stimulation with bradykinin, calcium ionophore, or L-arginine. Twenty-four-hour preincubation with Hcy (10, 20, and 50 microM) resulted in a gradual decline in responsiveness of endothelial cells to the above stimuli. Hcy did not affect the expression of endothelial nitric oxide synthase (eNOS), but it stimulated formation of superoxide anions, as judged by fluorescence of dichlorofluorescein, and peroxynitrite, as detected by using immunoprecipitation and immunoblotting of proteins modified by tyrosine nitration. Hcy did not directly affect the ability of recombinant eNOS to generate NO, but oxidation of sulfhydryl groups in eNOS reduced its NO-generating activity. Addition of 5-methyltetrahydrofolate restored NO responses to all agonists tested but affected neither the expression of the enzyme nor formation of nitrotyrosine-modified proteins. In addition, a scavenger of peroxynitrite or a cell-permeant superoxide dismutase mimetic reversed the Hcy-induced suppression of NO production by endothelial cells. In conclusion, electrochemical detection of NO release from cultured endothelial cells demonstrated that concentrations of Hcy >20 microM produce a significant indirect suppression of eNOS activity without any discernible effects on its expression. Folates, superoxide ions, and peroxynitrite scavengers restore the NO-generating activity to eNOS, collectively suggesting that cellular redox state plays an important role in HCy-suppressed NO-generating function of this enzyme.

Rebound from nitric oxide inhibition triggers enhanced monocyte activation and chemotaxis

Exposure of human peripheral blood monocytes to the NO donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) resulted in a rapid shift in cellular conformation of spontaneously activated cells from ameboid to round. The population of activated cells, approximately 7. 1 +/- 1.2%, was reduced 7-fold to 1.1 +/- 0.4% following 0.5 h exposure to SNAP. Observation of monocytes for 6 h demonstrated a gradual release from NO inhibition initiating at 2.5 h following SNAP treatment and a period of hyperactivity that was maximal at approximately 5 h following SNAP exposure. During the rebound from the NO inhibition phase, there was a significant increase in the population of activated monocytes and an increased responsiveness to chemotactic agents such as IL-1, IL-8, and fMLP relative to that of cells treated with the chemotactic agents alone. Conformational changes induced by SNAP were associated with a reduction in F-actin and loss of filopodial extension. The loss and recovery of F-actin staining paralleled changes in cell activity, suggesting that NO may alter cellular activity by modulation of cytoskeletal actin. These data taken together suggest that inhibition of monocyte activity by NO results in an excitatory phase observed subsequent to release from NO inhibition and increased sensitivity to chemotactic agents. We propose that this rebound from NO inhibition may provide increased immunosurveillance to rectify immunological problems that have been encountered during the period of inhibition.

Mechanisms for regulation of fluid shear stress response in circulating leukocytes

We have shown that leukocytes retract their pseudopods and detach from substrates after exposure to physiological fluid shear stresses ( approximately 1.5 dyn/cm(2)). In inflammation, however, pseudopod projection during spreading and firm adhesion on endothelium is observed even in microvessels with normal blood flow and fluid shear stresses. Thus, we examined mechanisms that may serve to regulate the shear stress response of circulating leukocytes. In the presence of inflammatory mediators (platelet-activating factor [PAF] f-met-leu-phe), a subgroup of cells ceases to respond to shear stress. cGMP analogs and nitric oxide (NO) donors enhance the shear stress response and reverse the inhibitory effect of inflammatory mediators on the shear stress response, whereas depletion of cGMP leads to cessation of the shear stress response even in unstimulated leukocytes. The ability of cGMP to enhance the shear stress response is not associated with CD18 expression, because cGMP has no effect on CD18 expression in response to shear stress. The shear stress response of leukocytes in endothelial nitric oxide synthase (-/-) mice, in which NO level in blood is decreased, is attenuated compared with that in wild-type mice. In rat mesentery venules stimulated by PAF under normal blood flow, a cGMP analog diminishes pseudopod projection of leukocytes, whereas inhibition of NO leads to enhanced pseudopod projection and spreading. The evidence suggests that inflammatory mediators suppress the shear stress response of leukocytes leading to spreading even under normal physiological shear stress, whereas cGMP may serve to maintain shear stress response even in inflammation.

A pivotal role of nitric oxide in endothelial cell dysfunction

The functional role of the vascular endothelium is a subject of growing interest and appreciation. Some of the key functions of the endothelium are modulated by the activity and expression of endothelial nitric oxide synthase (eNOS), suggesting a role for this enzyme in endothelial dysfunction. Several well-known angiogenic stimulators exert their effect only in the presence of the functional eNOS. In this setting NO production is responsible for the scalar podokinetic cell motility, which is a prerequisite for the acquisition of vectorial movement when guidance cues are applied. The mode of this NO action appears to lie in the accelerated turnover of focal adhesions through the process of activation/inactivation of protein tyrosine phosphatases. Localization of eNOS to the caveolar domains, in the proximity of clustered beta1 integrins, provides an additional level of regulatory complexity through the modulation of caveolar dynamics and the state of caveolin oligomerization. Therefore, eNOS serves various important functions in the endothelium and is a putative target for therapeutic interventions.

Podokinesis in endothelial cell migration: role of nitric oxide

Previously, we demonstrated the role of nitric oxide (NO) in transforming epithelial cells from a stationary to locomoting phenotype [E. Noiri, T. Peresleni, N. Srivastava, P. Weber, W.F. Bahou, N. Peunova, and M. S. Goligorsky. Am. J. Physiol. 270 (Cell Physiol. 39): C794-C802, 1996] and its permissive function in endothelin-1-stimulated endothelial cell migration (E. Noiri, Y. Hu, W. F. Bahou; C. Keese, I. Giaever, and M. S. Goligorsky, J. Biol: Chem. 272: 1747-1753, 1997). In the present study, the role of functional NO synthase in executing the vascular endothelial growth factor (VEGF)-guided program of endothelial cell migration and angiogenesis was studied in two independent experimental settings. First, VEGF, shown to stimulate NO release from simian virus 40-immortalized microvascular endothelial cells, induced endothelial cell transwell migration, whereas NG-nitro-L-arginine methyl ester (L-NAME) or antisense oligonucleotides to endothelial NO synthase suppressed this effect of VEGF. Second, in a series of experiments on endothelial cell wound healing, the rate of VEGF-stimulated cell migration was significantly blunted by the inhibition of NO synthesis. To gain insight into the possible mode of NO action, we next addressed the possibility that NO modulates cell matrix adhesion by performing impedance analysis of endothelial cell monolayers subjected to NO. The data showed the presence of spontaneous fluctuations of the resistance in ostensibly stationary endothelial cells. Spontaneous oscillations were induced by NO, which also inhibited cell matrix adhesion. This process we propose to term "podokinesis" to emphasize a scalar from of micromotion that, in the presence of guidance cues, e.g., VEGF, is transformed to a vectorial movement. In conclusion, execution of the program for directional endothelial cell migration requires two coexisting messages: NO-induced podokinesis (scalar motion) and guidance cues, e.g., VEGF, which imparts a vectorial component to the movement. Such a requirement for the dual signaling may explain a mismatch in the demand and supply with newly formed vessels in different pathological states accompanied by the inhibition of NO synthase.

Nitric oxide and cGMP regulate endothelial permeability and F-actin distribution in hydrogen peroxide-treated endothelial cells

We have previously reported that hydrogen peroxide (H2O2) has a concentration-dependent effect on endothelial permeability and F-actin distribution. In the present study, we considered the involvement of endogenous production of nitric oxide (NO) in the indicated effect of H2O2. This was done by measuring endothelial permeability to sodium fluorescein (MW 376 Da, Na-F) and to different-sized fluorescein-isothiocynate-labeled dextrans (FITC-dextrans) and by staining F-actin with rhodamine-labeled phalloidin in cultured bovine aortic endothelial cells growing on filters. A low concentration of H2O2 (10(-5) M) had no effect on either dense peripheral bands of F-actin (DPBs) or permeability. When N-nitro-l-arginine methylester (l-NAME), an inhibitor of NO production, was coadministrated with 10(-5) M H2O2, DPBs were disrupted and the permeability to FITC-dextran 40 and FITC-dextran 70, but not to Na-F and FITC-dextran 20, was increased. Combining of 10(-5) M H2O2 with l-arginine, a substrate for nitric oxide synthase, caused an increase in DPBs and a decrease in permeability to FITC-dextran 40 and FITC-dextran 70. l-arginine or l-NAME alone had no effect on either F-actin structure or endothelial permeability. A 10-fold higher concentration of H2O2 caused a disruption of DPBs and an increase in permeability; this could be prevented by adding l-arginine. An analogue of cGMP, i.e., 8-Br-cGMP, maintained DPBs and abolished the increase in permeability induced by the treatment with either 10(-4) M H2O2 or a combination of H2O2 and l-NAME. These results suggest that the endogenous production of NO is involved in maintaining endothelial junctions in H2O2-treated cells and that this involvement occurs via a cGMP-dependent mechanism.

Nitric oxide-releasing particles inhibit phagocytosis in human neutrophils

We have constructed a yeast (Saccharomyces cerevisiae) particle capable of releasing NO, by loading heat-killed yeast particles with a hydrophobic NO-generating substance, GEA-5171. This particle decreased phagocytosis in solution, as measured with flow cytometry, to about 80% of control values. Phagocytosis on a surface, as counted under the microscope, was also decreased by about 20%. The nitric oxide furthermore counteracted the production of oxygen metabolites by neutrophils to about 20% of control values. The inhibitory effect was most pronounced for the intracellular production, as could be seen when neutrophils preincubated with NO-releasing particles were stimulated with chemotactic agent (FMLP) or phorbol ester (PMA). In conclusion, NO has inhibitory effects on both phagocytosis and the respiratory burst of neutrophils. Since nitric oxide is a hydrophobic gas and an air pollutant, there is a possibility that it accumulates in particles which then become more resistant to elimination.

Neutrophil activation by adhesion: mechanisms and pathophysiological implications

Neutrophil adhesion plays an essential role in the formation of an inflammatory exudate. Moreover, adhesion activates selective neutrophil functions and regulates the cell response to additional stimuli. In this review we summarize the information available on adhesion molecules involved in neutrophil adhesion to endothelial cells and extracellular matrix proteins and the experimental approaches which have been developed to block neutrophil adhesion and neutrophil mediated tissue damage. We also address the mechanisms of activation of selective neutrophil functions by adhesion molecules and, in particular the mechanisms of signal transduction by neutrophil integrins. On the basis of recent results obtained in our and other laboratories we propose a model hypothesizing mechanisms of signaling by neutrophil integrins involved in regulation of selective functions.

Nitric oxide regulates the chemiluminescence from stimulated human neutrophils

Nitric oxide produced from L-arginine by a variety of cells, is a biologically active compound that can react with iron and thiols. The objective of this study was to investigate the effects of nitric oxide on the respiratory burst from human neutrophils. Treatment with nitroprusside increased the chemiluminescence from neutrophils stimulated with PMA or collagen, but not from cells stimulated with FMLP. Addition of L-arginine increased the chemiluminescence after stimulation with any of the three stimuli, while N omega-nitro-L-arginine methyl ester decreased it. Low doses of nitric oxide, either endogenously or exogenously produced, probably inhibited catalase or glutathione, leading to an increase in hydrogen peroxide available for chemiluminescence detection. This indicates that nitric oxide may reduce the protection against hydrogen peroxide in tissue and in invading catalase-positive bacteria.