Exogenous nitric oxide elicits chemotaxis of neutrophils in vitro

Nitric oxide functions in stromal cell-derived factor-1-induced cytoskeleton changes and the migration of Jurkat cells

Stromal cell-derived factor-1 (SDF-1) regulates multiple cell signal pathways in a variety of cellular functions, including cell migration, proliferation, survival and angiogenesis. SDF-1-induced chemotaxis is an important step of lymphocyte migration. However, the molecular mechanisms that modulate SDF-1-mediated lymphocyte migration are not well identified. Nitric oxide (NO) has been found to function as a signaling molecule in a number of signaling pathways, including migration. In the present study, the potential role of NO in SDF-1-induced migration and the association between NO and the cytoskeletal changes of Jurkat cells was investigated. The present study demonstrated that Jurkat cells induced the production of NO by SDF-1 stimulation, using Griess reaction method and western blot analysis, and that NO was involved in SDF-1-induced rearrangement and polymerization of the cytoskeleton, using NOS inhibitor L-NMMA. Furthermore, NO was required for the migration of Jurkat cells. The research suggested that NO signaling pathways exerted a critical role in SDF-1-induced cytoskeleton changes and the migration of Jurkat cells. This work provides insight into the migration mechanism of acute lymphoblastic leukemia and provides an effective theoretical basis for therapy strategies for acute lymphoblastic leukemia.

Effect of Nitric Oxide on the Expression of Matrix Metalloproteinase and Its Association with Migration of Cultured Trabecular Meshwork Cells

Purpose

To determine the effect of exogenous nitric oxide (NO) on the migration of trabecular meshwork (TM) cells and its association with expression of matrix metalloproteinases (MMPs).

Methods

Primary human TM cells treated with 1 or 10 µM S-nitroso-N-acetyl-penicillamine (SNAP) and examined for changes in adherence. TM cells were seeded onto transwell culture inserts, and changes in their migratory activity were quantified. Reverse transcription polymerase chain reaction was performed to determine the relative changes in mRNA expression of MMPs and tissue inhibitor of metalloproteinases (TIMPs).

Results

Treatment with SNAP did not significantly suppress TM cell adhesion or migration (p > 0.05). Treatment of TM cells with 10 µM SNAP decreased expression of MMP-2 and increased expression of membrane type MMP-1 and TIMP-2. Treatment with interleukin-1α triggered MMP-3 expression but did not exert significant effects on MMP-3 activation in response to SNAP.

Conclusions

These data suggest that NO revealed no significant effect on the migration of TM cells because NO decreased MMP-2 and increased TIMP-2 expression. Although expression of certain MMPs and TIMPs change in response to NO donors, NO may modulate trabecular outflow by changing the cellular production of extracellular matrix without having a significant effect on the migration of TM cells.

Production of nitric oxide by carp (Cyprinus carpio L.) kidney leukocytes is regulated by cyclic 3',5'-adenosine monophosphate

The inducible nitric oxide synthase (iNOS) plays a central role in the inflammatory reactions that follow infection or tissue damage. Induction of nitric oxide (NO) synthesis by bacterial lipopolysaccharide (LPS) depends on activation of G protein-coupled receptors in mammals. Thus, it was our intention to evaluate whether similar mechanisms are involved in iNOS activation in fish leukocytes. Therefore, the participation of membrane-bound receptors which activate effectors via G proteins has been confirmed using the G protein inhibitor suramin. Furthermore, the NO produced by iNOS performs both beneficial and detrimental actions. It is thus conceivable that regulatory mechanisms exist which control the timing and intensity of NO production by iNOS in order to outweigh protective effects against detrimental ones. The second messenger cAMP produced by adenylyl cyclases (ACs) plays a key role in the regulation of many cellular functions. Since cAMP signaling inhibits numerous immunological reactions, studies have been carried out to determine whether cAMP-dependent pathways could inhibit NO production by carp leukocytes as well. To measure cellular responses such as NO production by carp leukocytes derived from head and trunk kidneys treatments were performed with the cAMP elevating agents forskolin and dibutyryl-cAMP (db-cAMP) prior to stimulation with Aeromonas hydrophila. Pharmacological studies in stimulated kidney leukocytes showed that increased intracellular cAMP levels lead to reduced NO formation. This reduction of NO production was not due to decreased cell numbers, since a tetrazolium dye-based assay revealed no reduction of cell viability by cyclic nucleotide elevating agents. Thus, our data provide evidence that the AC/cAMP signaling pathway is well established in carp leukocytes. Cyclic AMP leads to type II immune response. We provide evidence that the predominant AC in fish leukocytes is a particulate enzyme due to its sensitivity to forskolin. Treatment of leukocytes with agents increasing intracellular cAMP gave clear evidence for participation of this cyclic nucleotide in immune signaling.

Nitric oxide regulates neutrophil migration through microparticle formation

The role of nitric oxide (NO) in regulating neutrophil migration has been investigated. Human neutrophil migration to interleukin (IL)-8 (1 nmol/L) was measured after a 1-hour incubation using a 96-well chemotaxis plate assay. The NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME) significantly (P < 0.001) enhanced IL-8-induced migration by up to 45%. Anti-CD18 significantly (P < 0.001) inhibited both IL-8-induced and L-NAME enhanced migration. Antibodies to L-selectin or PSGL-1 had no effect on IL-8-induced migration but prevented the increased migration to IL-8 induced by L-NAME. L-NAME induced generation of neutrophil-derived microparticles that was significantly (P < 0.01) greater than untreated neutrophils or D-NAME. This microparticle formation was dependent on calpain activity and superoxide production. Only microparticles from L-NAME and not untreated or D-NAME-treated neutrophils induced a significant (P < 0.01) increase in IL-8-induced migration and transendothelial migration. Pretreatment of microparticles with antibodies to L-selectin (DREG-200) or PSGL-1 (PL-1) significantly (P < 0.001) inhibited this effect. The ability of L-NAME-induced microparticles to enhance migration was found to be dependent on the number of microparticles produced and not an increase in microparticle surface L-selectin or PSGL-1 expression. These data show that NO can modulate neutrophil migration by regulating microparticle formation.

Nitric oxide released by accessory cells mediates the gastrin-releasing peptide effect on murine lymphocyte chemotaxis

Several neuropeptides, including gastrin-releasing peptide (GRP), modulate the immune response, specifically lymphocyte chemotaxis. In the present work the effect of GRP on the chemotaxis of murine lymphocytes from different immune locations in both, total leukocyte populations and populations depleted of adherent cells have been studied. Specificity of the GRP effect on chemotaxis using an antagonist of the GRP receptor, as well as the implication of nitric oxide (NO), using inhibitors of NO synthase and donors of NO, were investigated. The effects of GRP stimulating the chemotaxis of lymphocytes from peritoneum, axillary nodes and spleen and decreasing the chemotaxis from thymus were receptor-specific and disappeared in lymphocytes from populations depleted of adherent cells. NO synthase inhibitors blocked the GRP effect on lymphocyte chemotaxis, and this action was reversed in the presence of l-arginine. Thus, the effect of GRP on murine lymphocyte chemotaxis appears to be mediated by NO secreted by adherent cells.

Expression of a muscle-specific, nitric oxide synthase transgene prevents muscle membrane injury and reduces muscle inflammation during modified muscle use in mice

Nitric oxide (NO) can function as either a pro-inflammatory or anti-inflammatory molecule, depending upon its concentration and the microenvironment in which it is produced. We tested whether muscle-derived NO affects muscle inflammation and membrane lysis that occur in modified muscle use. Transgenic mice with muscle-specific over-expression of neuronal NO synthase (nNOS) were generated in which transgene expression was driven by the human skeletal muscle actin promoter. Transgenic mice and non-transgenic littermates were subjected to hindlimb muscle unloading followed by reloading, which causes muscle inflammation and membrane lysis. NOS expression decreased in transgenic and non-transgenic mice during muscle unloading. Muscle inflammation was assessed by immunohistochemistry after 24 h of muscle reloading following 10 days of unloading. Soleus muscles of non-transgenic mice showed significant increases in the concentrations of neutrophils (4.8-fold) and macrophages (11.3-fold) during reloading, compared to mice that experienced unloading only. Muscles of transgenic mice showed 51 % fewer neutrophils in reloaded muscles than those of non-transgenic mice, but macrophage concentrations did not differ from non-transgenic mice. Muscle membrane damage was determined by measuring influx of an extracellular marker dye. Significantly more membrane damage occurred in muscles of non-transgenic mice experiencing reloading than in ambulatory controls. However, membrane damage in the reloaded muscles of transgenic mice did not differ from that in ambulatory mice. In vitro cytotoxicity assays confirmed that mouse neutrophils lyse muscle cell membranes, and showed that inhibition of NOS in muscle and neutrophil co-cultures significantly increased neutrophil-mediated lysis of muscle cells. Together, these data show that muscle-derived NO can function as an anti-inflammatory molecule in muscle that experiences modified loading, and that NO can prevent neutrophil-mediated damage of muscle cell membranes in vivo and in vitro.

Mice lacking inducible nitric oxide synthase show strong resistance to anti-Fas antibody-induced fulminant hepatitis

Although nitric oxide (NO) plays important roles in pathogenesis of various liver diseases, the role of NO in the in vivo mechanism of Fas-mediated fulminant hepatitis is not known well. The effect of anti-Fas antibody (Jo2) on the survival, liver function, and histology was analyzed in wild-type (WT) and inducible NO synthase (iNOS)-deficient (iNOS(-/-)) mice. Upon intravenous injection of a lethal dose of Jo2, WT mice died on fulminant hepatitis within 12h. Under identical conditions, however, iNOS(-/-) mice showed strong resistance to Jo2 and survived without revealing liver injury. In conclusion, these observations suggest that regulation of NO metabolism may have therapeutic potential in the treatment of patients with fulminant hepatitis.

Hemin, a heme oxygenase substrate analog, both inhibits and enhances neutrophil random migration and chemotaxis

BACKGROUND

Carbon monoxide (CO), is an endogenously produced gas, generated by the rate-limiting enzyme heme oxygenase (HO), present in man throughout the respiratory tract. CO can elicit important physiological responses like bronchial relaxation and vasodilation. Both HO expression and CO levels in the airways increase in response to hypoxic challenge and to a wide variety of inflammatory stimuli, such as intermittent allergic rhinitis, asthma and upper respiratory tract infections. A role for CO in airway regulation and inflammation has therefore been suggested. However, information about CO-induced effects on cells involved in airway inflammation is scarce. The present study was designed to investigate if the HO substrate analog hemin could affect neutrophil random migration, and N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) induced chemotaxis.

METHODS

Hemin was added to and incubated with whole blood and the effects of the anticipated CO production were then evaluated on isolated neutrophils using a chemotaxis chamber.

RESULTS

A biphasic dose-response curve emerged for both the neutrophil spontaneous random migration and the fMLP-induced chemotaxis. Low concentrations of hemin (10(-11) m to 10(-9) m) enhanced the migratory response, whereas higher concentrations (10(-7) m and 10(-5) m) inhibited migration. The inhibition induced by hemin on fMLP-induced migration was abolished after pre-treatment with Rp-8Br-cyclicGMPS, an inhibitor of cyclicGMP.

CONCLUSIONS

The present data indicate that endogenously produced CO can affect both spontaneous and stimulated neutrophil migration, partly via a cyclicGMP-related process, hence strengthening the idea of a role for CO in airway inflammation.

Interactions between muscle and the immune system during modified musculoskeletal loading

Interactions between the immune system and skeletal muscle may play a significant role in modulating the course of muscle injury and repair after modified musculoskeletal loading. Current evidence indicates that activation of the complement system is an early event during modified loading, which then leads to inflammatory cell invasion. However, the functions of those inflammatory cells are complex and they seem to be capable of promoting additional injury and repair. Recent findings implicate an early invading neutrophil population in increasing muscle damage that is detected by the presence of muscle membrane lesions. Macrophages that invade subsequently serve to remove cellular debris, and seem to promote repair. However, macrophages also have the ability to increase damage in muscle in which there is an impaired capacity to generate nitric oxide. In vivo and in vitro evidence indicates that muscle-derived nitric oxide can serve an important role in protecting muscle from membrane damage by invading inflammatory cells. Collectively, these findings indicate that the dynamic balance between inflammatory cells, the complement system, and muscle-derived free radicals can play important roles in the secondary damage of muscle during modified musculoskeletal loading.

Role of nitric oxide in allergic inflammation and bronchial hyperresponsiveness

The role of nitric oxide (NO) in allergic inflammation and bronchial hyperresponsiveness is unclear. We studied a selective prodrug nitric oxide synthase (NOS)-2 inhibitor, L-N(6)-(1-iminoethyl)lysine 5-tetrazole amide (SC-51). In ovalbumin-sensitized and challenged rats, exhaled NO levels increased by 3 h following challenge (3.73 +/- 0.74 ppb; P < 0.05), peaking at 9 h (11.0 +/- 2.75; P < 0.01) compared to saline controls (1.87 +/- 0.26; P < 0.05 and 2.81 +/- 0.18; P < 0.01). Immunoreactive lung NOS2 expression was increased in ovalbumin-challenged rats compared with ovalbumin-sensitized, saline-challenged rats at 8 h post-challenge. SC-51 (10 mg/kg; p.o.) inhibited allergen-induced increase in exhaled NO levels to 1.3 +/- 0.17 ppb. SC-51 inhibited bronchial hyperresponsiveness in ovalbumin-sensitized and challenged rats (P < 0.05). In sensitized non-exposed rats, SC-51 increased bronchial responsiveness (P < 0.05). SC-51 reduced the allergen-induced increase in bronchoalveolar lavage neutrophils, but caused a nonsignificant reduction in bronchial mucosal eosinophil numbers. NO generated through NOS2 contributes to allergen-induced bronchial hyperresponsiveness but not to bronchial eosinophilia, indicating that these are independently expressed.

Hemin, a heme oxygenase substrate analog, inhibits the cell surface expression of CD11b and CD66b on human neutrophils

BACKGROUND

Neutrophils are signaled to sites of infection and inflammation by different chemotactic stimuli. In order to reach the airways they have to adhere to, and then migrate through, the endothelium of pulmonary vessels. Carbon monoxide (CO) is a gaseous mediator, endogenously produced in the human airways. Increased CO production has been demonstrated during airway inflammation and CO as well as hemin, a substrate for CO producing enzymes, has been shown to affect neutrophil migration. Our objective was to investigate if the neutrophil cell surface expression of CD11b, CD66b and CD63 was changed during intermittent allergic rhinitis and to establish whether CO could affect the expression of these markers of cellular activation.

METHODS

Blood from 10 healthy volunteers was drawn and incubated with different concentrations of hemin. Blood from 12 other healthy volunteers and from 12 patients with intermittent allergic rhinitis was also drawn during grass pollen season. Neutrophils were then isolated from all these three sets, and their expression of CD antigens measured using flow cytometry.

RESULTS

Patients with symptomatic intermittent allergic rhinitis exhibited lower levels of CD11b and CD66b on the neutrophil cell surface. Incubation with hemin decreased the expression of CD11b and CD66b. CD63 was generally weakly expressed and not significantly affected by hemin incubation.

CONCLUSION

Our results demonstrate that expressions of neutrophil cell surface glycoproteins are changed during the season in patents with intermittent allergic rhinitis and that hemin, a substrate for CO production, may act as an inhibitor of neutrophil activation. This indicates a possible role for CO in the immune defense system.

Reactive nitrogen species modulate the effects of rhein, an active component of senna laxatives, on human epithelium in vitro

BACKGROUND

Senna laxatives are used worldwide. However, their misuse can lead to chronic mucosal inflammation with the accumulation of pigment-laden leukocytes and may cause colon cells to undergo apoptosis. This study explores the mechanisms by which rhein, an active component of senna, acts on a human intestinal cell line to induce ion secretion, apoptosis, and indirect chemotaxis of polymorphonuclear leukocytes.

METHODS

Human colonic adenocarcinoma (CaCo-2) monolayer cells, in the presence or in the absence of rhein, were used to monitor the production of reactive nitrogen species using the Griess reaction. Modified Ussing chambers were used to study electrolyte secretion. The capacity to recruit human polymorphonuclear leukocytes was evaluated using masked well chemotaxis chambers. Rhein-induced apoptosis was investigated by counting apoptotic nuclei stained with Hoechst 33258 dye.

RESULTS

Rhein caused a dose-dependent increase in short-circuit current that was abolished in chloride-free bathing buffer or by preincubating with 100 micromol/L NG-nitro-L-arginine (L-NAME) methyl ester. The concentration that maximally stimulated intestinal secretion, 50 micromol/L rhein, induced nitrate production. Supernatants obtained from CaCo-2 cultures after incubation with 50 micromol/L rhein stimulated a time-dependent polymorphonuclear leukocytes chemotaxis that was significantly decreased with 100 micromol/L L-NAME, whereas rhein per se was not active. Neutralizing antibodies anti-interleukin-8 (IL-8) and anti-ENA78 also inhibited chemotaxis. Overnight rhein incubation produced an increased number of apoptotic cells in the culture supernatant that was significantly decreased by preincubation with 100 micromol/L L-NAME. Light-degraded rhein had no effects on CaCo-2 monolayers.

CONCLUSIONS

The integrity of rhein is crucial to generating nitric oxide, which mediates, with different time courses, ion secretion, chemotaxis, and apoptosis of human-derived cells.

Role of nitric oxide in acidosis-induced intestinal injury in anesthetized rats

We investigated the pathogenic mechanism(s) of small intestinal injury during acidosis in relation to circulating nitric oxide (NO) in an experimental rat model. Rats were anesthetized, paralyzed, and mechanically ventilated with room air. Hydrochloric acid (0.16 mmol bolus followed by 0.132 mmol/kg/h) was infused through the jugular vein for 5 hours. Control rats received a saline infusion. Arterial blood gases, blood pressure, and blood pH were measured every 30 minutes. The involvement of NO in this acidosis model was assessed by measuring plasma concentration of nitrite/nitrate (NOx) and by evaluating inducible NO synthase (iNOS) expression in small intestinal mucosa. Intestinal injury was assessed by measuring myeloperoxidase (MPO) activity, thiobarbituric acid reactants (TBARS), and histologic scores. HCl infusion was associated with hypotension, decreased blood pH, increased plasma concentration of NOx, augmented intestinal mucosal iNOS expression, MPO activity, TBARS, and histopathologic injury scores. Pretreatment with an iNOS inhibitor, aminoguanidine (AG, 50 mg/kg), reversed HCl-induced hypotension without a change in blood pH. HCl-induced lesions, MPO activity, TBARS, and plasma NOx production were decreased by AG. Our data show that the pathogenic mechanisms of acidosis-induced small intestinal lesions involve up-regulation of NO production by increased expression of iNOS and augmentation of superoxide radicals and MPO activity.

Nitric oxide synthase activity in neutrophils from patients with localized aggressive periodontitis

BACKGROUND

Localized aggressive periodontitis (LAgP) is associated with neutrophil dysfunction including defective chemotaxis and reduced calcium influx factor activity. Nitric oxide (NO) and its enzyme, nitric oxide synthase (NOS), have been suggested to be involved in chemotaxis. Some reports, however, were unable to detect either NO or NOS in human neutrophils. In this study, we focused on NOS activity in LAgP neutrophils and examined the involvement of NOS in chemotaxis of normal neutrophils and NOS activity in neutrophils from normal subjects and patients with LAgP.

METHODS

Neutrophils from 10 normal subjects and 10 LAgP patients were isolated from peripheral venous blood. Membrane associated-NOS (MA-NOS) and soluble NOS (S-NOS) were extracted from cells with or without FMLP stimulation. NOS activity was measured using the radiolabeled L-arginine to L-citrulline conversion assay.

RESULTS

N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NOS, significantly inhibited FMLP-induced chemotaxis (P<0.01) and dibutyryl cGMP, an activator of cGMP-dependent protein kinase, significantly attenuated the inhibition by L-NAME (P<0.01). Unstimulated and FMLP-stimulated MA-NOS activity in LAgP neutrophils was statistically significantly higher than that in normal neutrophils (P<0.05). S-NOS activity in LAgP neutrophils was higher than that in normal neutrophils.

CONCLUSIONS

This study suggests that NOS is present in human neutrophils and may be involved in FMLP-induced chemotaxis in normal neutrophils. NOS activity is increased in LAgP and is negatively correlated to chemotaxis response.

Stromal cell-derived factor 1 alpha-induced chemotaxis in T cells is mediated by nitric oxide signaling pathways

Stromal cell-derived factor 1 alpha (SDF1 alpha) and its cognate chemokine receptor CXCR4 act as potent chemoattractants and regulate trafficking and homing of hematopoietic progenitor cells and lymphocytes. However, the molecular mechanisms regulating SDF1 alpha-driven cell migration are not well defined. In this study, we have explored the roles of the second messenger NO and the transcription factor NF-kappa B in SDF1 alpha-induced T cell migration. SDF1 alpha treatment of Jurkat T cells increased the activity of NO synthase, which catalyzes the generation of NO. We observed that pretreatment of Jurkat cells or activated PBLs with several NO donors significantly enhanced the SDF1 alpha-induced migration, whereas various inhibitors of NO synthase markedly abrogated the chemotactic response in a concentration-dependent manner. Furthermore, we observed that inhibitors of the transcription factor NF-kappa B, which is linked to NO signaling pathways, also significantly blocked the SDF1 alpha-induced chemotactic response. However, these compounds did not have a significant effect on SDF1 alpha-induced mitogen-activated protein kinase activity. In addition, the MAP/Erk kinase kinase inhibitor PD98059 did not abrogate SDF1 alpha-induced chemotaxis. AKT, which has been shown to mediate NO production, was also phosphorylated upon SDF1 alpha stimulation. These studies suggest that NO-related signaling pathways may mediate SDF1 alpha-induced chemotaxis, but not mitogen-activated protein kinase activation.

iNOS expression by activated neutrophils from patients with sepsis

BACKGROUND

Enhanced production of nitric oxide (NO) is associated with various inflammatory diseases such as sepsis. Although activated neutrophils are presumably involved in septic organ injury, the expression of inducible nitric oxide synthase (iNOS) by these cells has not been elucidated. The authors investigated whether activated neutrophils in sepsis could induce mRNA for iNOS and produce NO.

METHODS

Peripheral blood neutrophils were obtained from healthy volunteers, and septic patients underwent a surgical operation. The neutrophils of the healthy volunteers were stimulated with lipopolysaccharide (LPS) and/or tumour necrosis factor-alpha (TNF-alpha). The iNOS expression and NO production were examined by the reverse transcription-polymerase chain reaction and Griess method, respectively.

RESULTS

Circulating neutrophils obtained from patients with sepsis expressed higher levels of iNOS mRNA than those from patients with systemic inflammatory response syndrome (SIRS). Resting neutrophils from normal controls did not express iNOS mRNA and thus did not produce NO. After in vitro stimulation with LPS and TNF-alpha, the neutrophils did express iNOS mRNA and thus produce NO.

CONCLUSION

Activated neutrophils may be one source of NO production in sepsis.

Nitric oxide-dependent neutrophil recruitment: role in nasal secretion

Leukotriene B4 (LTB4), an inflammatory mediator, is a potent chemoattractant for neutrophils that plays an important role in nasal secretion via release of elastase. Nitric oxide (NO) is an important modulator of leucocyte-endothelial cell interactions, endogenously produced in large quantities in the paranasal sinuses. To examine the role of NO in LTB4-stimulated nasal secretion. A newly-developed method for isolating and superfusing a nasal segment in dogs was used. Instillation of LTB4 into the nasal segment caused a time-dependent increase in the volume of airway fluid and in the recruitment of neutrophils. N(G)-nitro-L-arginine-methylester (L-NAME), an inhibitor of NO synthase, prevented LTB4-induced neutrophil recruitment and nasal secretion. These studies show that NO modulates LTB4-induced neutrophil recruitment and subsequent fluid secretion in the nose, and they suggest a therapeutic role for NO inhibitors in modulating neutrophil-dependent nasal secretion.

Nitric oxide induces chemotaxis of neutrophil-like HL-60 cells and translocation of cofilin to plasma membranes

Nitric oxide (NO) plays various important roles in the physiological system. With regard to chemotaxis of neutrophils, there are reports that endogenous NO is a mediator of chemotaxis, and others that exogenous NO inhibits chemotaxis. It is also reported that NO itself expressed chemotactic activity. On the other hand, we have recently proposed the importance of cofilin, an actin-binding phosphoprotein, in phagocyte functions through dephosphorylation and translocation to the plasma membrane regions. Because chemotaxis is a phenomenon of dynamic cell movement, cofilin, a regulator of the cytoskeletal system, may be involved in its mechanisms. To clarify further the effect of NO on functions of leukocytes and to examine the effect of NO on cofilin, we investigated the chemotaxis of neutrophil-like HL-60 cells induced by NO, as well as the influence of NO on the phosphorylation and intracellular distribution of cofilin. Two NO donors, 3-[2-hydroxy-1-(1-methylethyl)-2-nitrosohydrazino]-1-propanamin e (NOC5) and S-nitroso-N-acetylpenicillamine (SNAP), were shown to cause chemotaxis, and, 2-(4-carboxyphenyl)-4,4,5, 5-tetramethylimidazole-1-oxyl 3-oxide (carboxy-PTIO), a NO-specific scavenger, inhibited the chemotaxis induced by NO-donors, suggesting that NO itself released from the NO donors has chemotactic activity. LY-83583 and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ), inhibitors of soluble guanylate cyclase, inhibited the chemotaxis to NO donors, which implies that soluble guanylate cyclase is involved in the signaling pathway of this NO action. We also found that NO caused translocation of cofilin to the cell periphery, though dephosphorylation of cofilin was not detected. These results demonstrate that NO has chemotactic activity for neutrophils and caused the translocation of cofilin to the plasma membrane regions without its dephosphorylation.

Inducible nitric oxide synthase inhibitors suppress airway inflammation in mice through down-regulation of chemokine expression

Growing evidence demonstrates that inducible NO synthase (iNOS) is induced in the airways of asthmatic patients. However, the precise role of NO in the lung inflammation is unknown. This study investigated the effect of both selective and nonselective iNOS inhibitors in an allergen-driven murine lung inflammation model. OVA challenge resulted in an accumulation of eosinophils and neutrophils in the airways. Expression of iNOS immunostaining in lung sections together with an increase in calcium-independent NOS activity in lung homogenates was also observed after OVA challenge. Treatment with iNOS inhibitors from the day of challenge to the day of sacrifice resulted in an inhibition of the inflammatory cell influx together with a down-regulation of macrophage inflammatory protein-2 and monocyte chemoattractant protein-1 production. In contrast, eosinophilic and neutrophilic inhibition was not observed with treatment during the sensitization. Both treatments induced an increased production of Th2-type cytokines (IL-4 and IL-5) with a concomitant decrease in production of Th1-type cytokine (IFN-gamma). In vitro exposure of primary cultures of murine lung fibroblasts to a NO donor, hydroxylamine, induced a dose-dependent release of macrophage inflammatory protein-2 and monocyte chemoattractant protein-1. Our results suggest that lung inflammation after allergen challenge in mice is partially dependent on NO produced mainly by iNOS. NO appears to increase lung chemokine expression and, thereby, to facilitate influx of inflammatory cells into the airways.

Nitric oxide synthase inhibitors attenuate ozone-induced airway inflammation in guinea pigs. Possible role of interleukin-8

Nitric oxide (NO) is increased in exhaled air of asthmatics. We hypothesized that endogenous NO contributes to airway inflammation and hyperresponsiveness, and that interleukin-8 (IL-8) might be involved in this mechanism. In human transformed bronchial epithelial cells in vitro, NO donors increased IL-8 production dose-dependently. In addition, tumor necrosis factor-alpha (TNF-alpha) plus IL-1beta plus interferon-gamma (IFN-gamma) increased IL-8 in culture supernatant of epithelial cells; the combination of NO synthase (NOS) inhibitors, aminoguanidine (AG) plus N(G)-nitro-L-arginine methyl ester (L-NAME) attenuated the cytokine-induced IL-8 production in epithelial cells. In guinea pigs in vivo, ozone exposure induced airway hyperresponsiveness to acetylcholine and increased neutrophils in bronchoalveolar lavage fluid (BALF), and these changes persisted for at least 5 h. Pretreatment with NOS inhibitors had no effect on airway hyperresponsiveness or neutrophil accumulation immediately after ozone, but significantly inhibited the changes 5 h after ozone. NOS inhibitors also attenuated the increases of nitrite/nitrate levels in BALF and the IL-8 mRNA expression in epithelial cells and in neutrophils in guinea pig airways 5 h after ozone. These results suggest that endogenous NO may play an important role in the persistent airway inflammation and hyperresponsiveness after ozone exposure, presumably partly through the upregulation of IL-8.

The function of nitric oxide in wound repair: inhibition of inducible nitric oxide-synthase severely impairs wound reepithelialization

Recently, we demonstrated a large induction of inducible nitric oxide synthase (iNOS) during cutaneous wound repair. In this study, we established an in vivo model in mice to investigate the role of NO during the wound healing process. During excisional repair, mice were treated with L-N6-(1-iminoethyl)lysine (L-NIL), a selective inhibitor of iNOS enzymatic activity. Compared with control mice, L-NIL-treated animals were characterized by a severely impaired reepithelialization process, as the hyperproliferative epithelia at the wound edges appeared to be delayed and characterized by an atrophied morphology. Immunohistochemical labeling for detection of proliferating cells (BrdU-, Ki67-staining) revealed a strong reduction in proliferating keratinocyte cell numbers during the process of re-epithelialization after inhibition of iNOS activity during repair. Western blot analysis of total wound lysates from PBS- and L-NIL-treated mice clearly demonstrated a reduction in proliferating cell nuclear antigen, representing a marker for cell proliferation, in lysates isolated from L-NIL-treated mice. The dependency between keratinocyte proliferation and NO availability observed during wound repair in vivo is further supported by the observation that proliferation of the keratinocyte cell line (HaCaT) is stimulated by low concentrations of NO-donors also in vitro. In summary, our data demonstrate that the presence of a functionally active iNOS is a crucial prerequisite for normal wound reepithelialization.

Nitric oxide and the gut

Nitric oxide (NO) has been implicated as a modulator of blood flow, motility, electrolyte and water transport, and the function of endothelial cells, platelets, mast cells, and macrophages within the digestive system. In addition, a number of reports have demonstrated that NO possesses potent anti-inflammatory properties, whereas results from an equally impressive number of studies suggest that NO may promote inflammation-induced cell and tissue dysfunction. Consideration of the physiologic chemistry of NO and its interaction with molecular oxygen and/or superoxide may allow us to identify which of the NO-dependent reactions are important in modulating physiologic and pathophysiologic responses in the gut.

In vivo blockage of nitric oxide with aminoguanidine inhibits immunosuppression induced by an attenuated strain of Salmonella typhimurium, potentiates Salmonella infection, and inhibits macrophage and polymorphonuclear leukocyte influx into the spleen

Our laboratory has previously shown that after immunization with a strain of Salmonella typhimurium, SL3235, made avirulent by a blockage in the pathway of aromatic synthesis, murine splenocytes were profoundly suppressed in their capacity to mount an in vitro antibody plaque-forming cell (PFC) response to sheep erythrocytes. Evidence indicated that suppression was mediated by nitric oxide (NO), since the in vitro addition of NG-monomethyl-L-arginine blocked suppression. The present studies examined the effect of blocking NO production on Salmonella-induced immunosuppression by in vivo administration of aminoguanidine hemisulfate (AG). AG was administered to C3HeB/FeJ mice in their drinking water (2.5% solution) for 7 days prior to intraperitoneal inoculation with SL3235. AG treatment inhibited the increase in nitrate and nitrite levels in plasma and nitrite levels in the spleen seen in immunized mice. Importantly, AG treatment completely blocked suppression of the splenic PFC response and markedly attenuated the suppression of the response to concanavalin A in immunized mice, providing further evidence that Salmonella-induced immunosuppression is mediated by NO. AG treatment also alleviated the majority of the splenomegaly associated with SL3235 inoculation, which correlated with a blockage of influx of neutrophils and macrophages into spleens, as assessed by flow cytometry. AG treatment unexpectedly resulted in 90% mortality in mice injected with the highly attenuated vaccine strain of Salmonella, SL3235. Increased mortality in AG-treated mice correlated with inability to clear organisms from the spleen by day 15 postinoculation and with persistent bacteremia, compared with control mice. Collectively, these in vivo results underscore the dual biological consequences of NO production following Salmonella infection, with NO being necessary for host defense, but also having the potentially adverse effect of immunosuppression. A unifying hypothesis to explain how these seemingly paradoxical effects could both result from NO production is presented.

Acidosis stimulates nitric oxide production and lung damage in rats

Systemic hypotension during sepsis is thought to be due to nitric oxide (NO) overproduction, but it may also be due to acidosis. We evaluated in healthy rats the consequences of acid infusion on NO and blood pressure. Sprague-Dawley rats were anesthetized, and ventilated with room air. The animals were randomized into four groups. Group 1 (C, n = 10) received only normal saline at rates comparable to the other groups. Group 2 (A1, n = 10) received hydrochloric acid at 0.162 mmol in the first 15 to 30 min, followed by a continuous infusion of 0.058 mmol/h for 5 h. Group 3 (AG+A1, n = 6) was pretreated with aminoguanidine (AG, 50 mg/kg), and HCl was infused as above. Group 4 (A2, n = 7) received HCl at twice the rate used in A1. Nitric oxide concentration in the exhaled gas (ENO), blood gases, and mean arterial pressure were measured every 30 min. Acid infusion in A1 caused the pH to fall gradually from 7.43 +/- 0. 01 to 7.13 +/- 0.05. This moderate decrease in pH was associated with a marked increase in ENO (1.6 +/- 0.3 to 114.2 +/- 22.3 ppb), an increase in plasma nitrite/nitrate (17.3 +/- 3.7 to 35.2 +/- 4.3 microM), and a significant decrease in blood pressure (110.5 +/- 6.3 to 63.3 +/- 15.0 mm Hg). Furthermore, acidosis caused lung inflammation, as suggested by the increase in lung myeloperoxidase activity (282.2 +/- 24.7 to 679.3 +/- 57.3 U/min/g) and lung injury score (1.7 +/- 0.2 to 3.5 +/- 0.6). Acidosis after AG pretreatment was associated with a similar change in pH, but the increase in ENO, nitrite/nitrate, and systemic hypotension were prevented. Furthermore, lung injury was attenuated by AG, as suggested by a lower myeloperoxidase activity, though lung injury score was not altered. In this model, moderate acidosis causes increases in NO, hypotension, and lung inflammation. Lung inflammation and injury are due in part to acidosis and NO production. This is the first report to show a direct effect of chronic acidosis on NO production and lung injury. These results have profound implications on the role of acidosis on NO production and lung injury during sepsis.

Dual action of iNOS-derived nitric oxide in allergen-induced airway hyperreactivity in conscious, unrestrained guinea pigs

Using a guinea pig model of acute allergic asthma, we recently established that a deficiency of nitric oxide (NO) contributes to airway hyperreactivity (AHR) after the early asthmatic reaction (EAR) and that restoration of NO activity may contribute to the (partial) reversal of AHR after the late asthmatic reaction (LAR). In the present study, we investigated the role of iNOS-derived NO in the regulation of AHR to histamine after the LAR. Inhalation of a selective dose of the specific iNOS inhibitor aminoguanidine (0.1 mM, 3 min) had no effect on basal airway reactivity to histamine in unchallenged, ovalbumin-sensitized animals and did not affect the allergen-induced AHR after the EAR. By contrast, this dose of aminoguanidine significantly potentiated the partially reduced AHR after the LAR to the level of AHR observed after the EAR, indicating that induction of iNOS during the LAR contributes to the reversal of AHR. Inhalation of a higher aminoguanidine concentration (2.5 mM) shortly before the onset of the LAR diminished the AHR after the LAR and reduced the number of neutrophils, lymphocytes, and ciliated epithelial cells in the bronchoalveolar lavage at this time point. The results indicate that iNOS-derived NO may have both beneficial and detrimental effects on allergen-induced AHR to histamine after the LAR by functional antagonism of histamine-induced bronchoconstriction, and by promoting airway inflammation and epithelial damage on the other hand, respectively.

Neutrophil sequestration in the lung following acute aortic occlusion starts during ischaemia and can be attenuated by tumour necrosis factor and nitric oxide blockade

OBJECTIVES

To investigate the role of lower extremity ischaemia in acute lung injury with special emphasis on the role of tumour necrosis factor (TNF) and nitric oxide (NO) as mediators of neutrophil (PMN) chemotaxis in the lung.

DESIGN

Prospective randomised study.

MATERIALS AND METHODS

Sprague-Dawley rats were randomized into four groups: group 1 (x-clmap): aorta clamped just above the bifurcation for 3 h; group 2 (AG): 50 mg/kg aminoguanidine, a specific inducible NO synthase (iNOS) inhibitor, was administered prior to aortic occlusion; group 3 (Steroids): 1 mg/kg dexamethasone was administered prior to aortic occlusion; and group 4 (TNFbp): 2 mg/kg TNFbp, a PEGylated dimeric form of the high affinity TNF receptor I (R1) was administered prior to aortic occlusion to block TNF action. Groups 2, 3 and 4 were subjected to the same ischaemia time as group 1. NO concentration in the exhaled gas (ENO) was measured in 30 min intervals. At the end of the 3 h ischaemia, one lung was excised and fixed for routine histological evaluation, and the other underwent bronchoalveolar lavage (BAL). PMN chemotaxis towards the BAL fluid was then measured using the blindwell technique.

RESULTS

ENO in group 1 increased from 0.9 +/- 0.3 ppb at baseline, to 41.3 +/- 9.2 ppb at the end of ischaemia. Animals in this group exhibited significant lung inflammation. Aminoguanidine, dexamethasone and TNFbp blocked NO production (peak ENO values of 7.2 +/- 1.9, 12.6 +/- 1.3 and 8.9 +/- 1.7 ppb for groups 2, 3 and 4 respectively), decreased PMN chemotaxis and sequestration in the lung, and attenuated lung inflammation.

CONCLUSIONS

Acute lung injury resulting from distal aortic occlusion starts during ischaemia. TNF and NO blockade decrease PMN chemotaxis and sequestration and attenuate the lung injury process.

Inhibition of Inducible Nitric Oxide Synthase Prevents LPS-Induced Acute Lung Injury in Dogs

Nitric oxide (NO) is produced by inducible NO synthase (iNOS) after LPS stimulation, and reacts with superoxide to form peroxynitrite. We hypothesize that in LPS-induced lung injury, NO generated by iNOS plays a key role through the formation of peroxynitrite. We developed an acute lung injury dog model by injecting LPS, and examined the effects of selective iNOS inhibitors, aminoguanidine (AG) and S-methylisothiourea sulfate (SMT), on the LPS-induced lung injury. At 24 h after LPS injection, arterial oxygen tension and mean arterial pressure decreased, and shunt ratio and lung wet-to-dry weight ratio increased. On histology, the LPS group had marked neutrophil infiltration and widening of the alveolar septa. On immunohistochemistry, iNOS and nitrotyrosine, a major product of nitration of protein by peroxynitrite, were observed in the interstitium, capillary wall, and neutrophils in the airspaces of the LPS group. Treatments with AG and SMT prevented worsening of gas exchange, hemodynamics, and wet-to-dry weight ratio. On histology, AG and SMT treatments markedly suppressed lung injury, iNOS protein, and nitrotyrosine production. We conclude that NO released by iNOS may play a critical role in the pathogenesis of LPS-induced acute lung injury. This study suggests that iNOS inhibitors may have potential in the treatment of LPS-induced acute respiratory distress syndrome.

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.

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.

Signaling in unicellular eukaryotes

Aspects of intercellular and intracellular signaling systems in cell survival, proliferation, differentiation, chemosensory behavior, and programmed cell death in free-living unicellular eukaryotes have been reviewed. Comparisons have been made with both bacteria and metazoa. The central organisms were flagellates (Trypanosoma, Leishmania, and Crithidia), slime molds (Dictyostelium), yeast cells (Saccharomyces cerevisiae), and ciliates (Paramecium, Euplotes, and Tetrahymena). There are two novel aspects in this review. First, cellular responses are viewed in an evolutionary perspective, rather than from the more prevailing one, in which the unicellular eukaryotes are seen by the mammalian organisms. Second, results obtained with cell cultures in minimal, chemically defined nutrient media at low cell densities where intercellular signaling is strongly reduced are discussed. These results shed light on control mechanisms and their cooperation inside the living cell. Intracellular systems have many common features in unicellular and multicellular organisms.

Potentiation and inhibition of fMLP-activated exocytosis in neutrophils by exogenous nitric oxide

Exogenous nitric oxide (NO), not derived from NO-donors, but applied directly, could enhance exocytosis of rabbit peritoneal neutrophils induced by suboptimal concentrations of the chemotactic peptide fMLP. The enhancement was maximal at 30 microM NO. Higher concentrations of NO strongly inhibited fMLP-induced exocytosis. The potentiation of fMLP-induced exocytosis by NO could not be reversed by the inhibitors of guanosine-3',5'-cyclic monophosphate (cGMP) accumulation, LY-83583 and methylene blue, or the antagonists of cGMP-dependent protein kinase, Rp-8-pCPT-cGMPS and Rp-8-Br-cGMPS. The concentration of NO needed to enhance fMLP-induced exocytosis was much higher than the concentration leading to an increase in intracellular cGMP levels. These observations suggest that the enhancement of exocytosis by NO is not likely to be mediated by cGMP. At the concentration which inhibited fMLP-induced exocytosis, NO reduced the intracellular level of glutathione. Since it is known that inactivation of intracellular sulfhydryl groups causes complete inhibition of the exocytotic response, it seems evident that the very strong inhibition of exocytosis by high NO concentrations is due to the reaction of NO with glutathione or with other sulfhydryl group-containing targets.