Nitric oxide inhibits numerous features of mast cell-induced inflammation

Nitric-Oxide-Releasing Dexamethasone Derivative NCX-1005 Improves Lung Function and Attenuates Inflammation in Experimental Lavage-Induced ARDS

Acute respiratory distress syndrome (ARDS) is a common complication of critical illness and remains a major source of morbidity and mortality in the intensive care unit (ICU). ARDS is characterised by diffuse lung inflammation, epithelial and endothelial deterioration, alveolar–capillary leak and oedema formation, and worsening respiratory failure. The present study aimed to investigate the anti-inflammatory activity of nitric-oxide-releasing dexamethasone derivative NCX-1005 as a potential novel drug for ARDS. Adult rabbits with lavage-induced ARDS were treated with dexamethasone i.v. (0.5 mg/kg; DEX) and nitro-dexamethasone i.v. (0.5 mg/kg, NCX-1005) or were untreated (ARDS). Controls represented healthy ventilated animals. The animals were subsequently oxygen-ventilated for an additional 4 h and respiratory parameters were recorded. Lung oedema, inflammatory cell profile in blood and bronchoalveolar lavage, levels of the cytokines (IL-1β, IL-6, IL-8, TNF-α), and oxidative damage (TBARS, 3NT) in the plasma and lung were evaluated. Nitric oxide-releasing dexamethasone derivative NCX-1005 improved lung function, reduced levels of cytokines, oxidative modifications, and lung oedema formation to similar degrees as dexamethasone. Only NCX-1005 prevented the migration of neutrophils into the lungs compared to dexamethasone. In conclusion, the nitric oxide-releasing dexamethasone derivative NCX-1005 has the potential to be effective drug with anti-inflammatory effect in experimental ARDS.

Serum L-arginine and endogenous methylarginine concentrations predict irritable bowel syndrome in adults: A nested case-control study

BACKGROUND & AIMS: Nitric oxide, a major inhibitory nonadrenergic, noncholinergic neurotransmitter that relaxes smooth muscle, may be implicated in the pathophysiology of visceral hypersensitivity in irritable bowel syndrome (IBS). Impaired bioavailability of the nitric oxide precursor molecule L-arginine and higher concentrations of methylarginines (endogenous inhibitors of nitric oxide synthesis) are known to impair nitric oxide synthesis in numerous gastrointestinal cell types. We therefore examined serum concentrations of L-arginine and the methylarginines in a nested case-control study, to assess whether these factors are associated with adult IBS.

METHODS

Data on clinical characteristics, methylarginines, and L-arginine (measured using LC-MS/MS) were collected from a random population-based cohort of Australian adults (median age = 64 years; IQR = 60-70). Cases of IBS, defined according to Rome III criteria (N = 156), and controls (N = 332) were identified from within the cohort at the 5-year follow-up.

RESULTS

In adjusted logistic regression analyses, L-arginine, asymmetric dimethylarginine, symmetric dimethylarginine, L-arginine/asymmetric dimethylarginine ratio, and Kessler-10 psychological distress scores were significantly associated with IBS (p < 0.05). [Correction added on 18 September 2021, after first online publication: In the preceding sentence, the value (p > 0.05) has been changed to (p < 0.05)]. Similar results were found for IBS subtypes. Higher serum L-arginine concentration had the strongest association with IBS diagnosis, with an odds ratio of 9.03 for those with serum L-arginine at the 75th (84 μmol/L) versus 25th (46 μmol/L) percentile (95% CI: 5.99-13.62). L-arginine had the best discriminative ability with a bias-adjusted area under the receiver operator characteristic curve of 0.859.

CONCLUSIONS

Higher serum concentrations of L-arginine and endogenous methylarginines are strongly associated with IBS in adults.

Endothelial Nitric Oxide Pathways in the Pathophysiology of Dengue: A Prospective Observational Study

BACKGROUND

Dengue can cause increased vascular permeability that may lead to hypovolemic shock. Endothelial dysfunction may underlie this; however, the association of endothelial nitric oxide (NO) pathways with disease severity is unknown.

METHODS

We performed a prospective observational study in 2 Vietnamese hospitals, assessing patients presenting early (<72 hours of fever) and patients hospitalized with warning signs or severe dengue. The reactive hyperemic index (RHI), which measures endothelium-dependent vasodilation and is a surrogate marker of endothelial function and NO bioavailability, was evaluated using peripheral artery tonometry (EndoPAT), and plasma levels of l-arginine, arginase-1, and asymmetric dimethylarginine were measured at serial time-points. The main outcome of interest was plasma leakage severity.

RESULTS

Three hundred fourteen patients were enrolled; median age of the participants was 21(interquartile range, 13-30) years. No difference was found in the endothelial parameters between dengue and other febrile illness. Considering dengue patients, the RHI was significantly lower for patients with severe plasma leakage compared to those with no leakage (1.46 vs 2.00; P < .001), over acute time-points, apparent already in the early febrile phase (1.29 vs 1.75; P = .012). RHI correlated negatively with arginase-1 and positively with l-arginine (P = .001).

CONCLUSIONS

Endothelial dysfunction/NO bioavailability is associated with worse plasma leakage, occurs early in dengue illness and correlates with hypoargininemia and high arginase-1 levels.

The nitric oxide pathway and possible therapeutic options in pre-eclampsia

Pre-eclampsia is a serious multisystem disorder with diverse clinical manifestations. Although not causal, endothelial dysfunction and reduced nitric oxide bioavailability are likely to play an important role in the maternal and fetal pathophysiology of this condition. Lack of treatment modalities that can target the underlying pathophysiological changes and reverse the endothelial dysfunction frequently leads to iatrogenic preterm delivery of the fetus, causing neonatal morbidity and mortality, and the condition itself is associated with short- and longer term maternal morbidity and mortality. Drugs that target various components of the nitric oxide-soluble guanylyl cyclase pathway can help to increase NO bioavailability. The purpose of this review is to outline the current status of clinical research involving these therapeutic modalities in the context of pre-eclampsia, with the focus being on the following: nitric oxide donors, including organic nitrates and S-nitrosothiols; l-arginine, the endogenous precursor of NO; inhibitors of cyclic guanosine 3',5'-monophosphate breakdown, including sildenafil; and other novel inhibitors of NO donor metabolism. The advantages and limitations of each modality are outlined, and scope for development into established therapeutic options for pre-eclampsia is explored.

Decrease of cerebral mast cell degranulation after systemic administration of lipopolysaccharide

INTRODUCTION

The mast cell is an immunocyte, but its functions in the brain remain unclear.

MATERIALS AND METHODS

In a rat model of weak inflammation, we analyzed the effect of a gram-negative bacterial lipopolysaccharide injection (100 μg/kg) on thalamic mast cell (MC) population.

CONCLUSION

We demonstrate a significant decrease of their degranulation, which suggests the implication of MC in preventing sepsis on the brain.

Role of reactive oxygen and nitrogen species in the vascular responses to inflammation

Inflammation is a complex and potentially life-threatening condition that involves the participation of a variety of chemical mediators, signaling pathways, and cell types. The microcirculation, which is critical for the initiation and perpetuation of an inflammatory response, exhibits several characteristic functional and structural changes in response to inflammation. These include vasomotor dysfunction (impaired vessel dilation and constriction), the adhesion and transendothelial migration of leukocytes, endothelial barrier dysfunction (increased vascular permeability), blood vessel proliferation (angiogenesis), and enhanced thrombus formation. These diverse responses of the microvasculature largely reflect the endothelial cell dysfunction that accompanies inflammation and the central role of these cells in modulating processes as varied as blood flow regulation, angiogenesis, and thrombogenesis. The importance of endothelial cells in inflammation-induced vascular dysfunction is also predicated on the ability of these cells to produce and respond to reactive oxygen and nitrogen species. Inflammation seems to upset the balance between nitric oxide and superoxide within (and surrounding) endothelial cells, which is necessary for normal vessel function. This review is focused on defining the molecular targets in the vessel wall that interact with reactive oxygen species and nitric oxide to produce the characteristic functional and structural changes that occur in response to inflammation. This analysis of the literature is consistent with the view that reactive oxygen and nitrogen species contribute significantly to the diverse vascular responses in inflammation and supports efforts that are directed at targeting these highly reactive species to maintain normal vascular health in pathological conditions that are associated with acute or chronic inflammation.

Oxidative modifications of DAMPs suppress inflammation: the case for S100A8 and S100A9

Several S100 Ca(2+)-binding proteins are considered damage-associated molecular pattern molecules (DAMPs). They are actively secreted or released from necrotic cells in response to tissue injury or stress and have various functions important in innate immunity. Here, we review several DAMPs, with particular focus on S100A8 and S100A9, which are susceptible to oxidative modifications by various forms of reactive oxygen species. We discuss the unique posttranslational modifications generated in S100A8 by hypochlorite and the likely structural consequences that alter function. We propose that some reversible modifications act as regulatory switches, representing a mechanism to arrest their novel antiinflammatory activities. These may be important in dampening mast cell activation and altering properties of the activated microcirculation to limit leukocyte adhesion, transmigration, and accumulation. S-nitrosylation of S100A8 in the vasculature could regulate nitric oxide transport and contribute to vessel reflow during resolution of inflammation.

Toxoplasma gondii: the role of IFN-gamma, TNFRp55 and iNOS in inflammatory changes during infection

In order to examine the role of IFN-gamma, TNFRp55 and iNOS in inflammatory reaction during toxoplasmosis, IFN-gamma(-/-), TNFRp55(-/-) and iNOS(-/-) mice were experimentally infected with Toxoplasma gondii ME-49 strain. The organs of the mice were evaluated for histology and immunohistochemistry in detection of tissue parasitism and iNOS positive cells. IFN-gamma(-/-) mice presented mild inflammation in peripheral organs associated with a high parasitism and mortality in the acute phase of infection. In contrast, the peripheral organs of WT, TNFRp55(-/-) and iNOS(-/-) mice, presented a significant inflammatory reaction and low tissue parasitism in the same period of infection. The inflammatory lesions and tissue parasitism were increased and more severe in the Central Nervous System (CNS) of TNFRp55(-/-) and iNOS(-/-) with a progression of infection, when compared to WT mice. In these knockout animals, the inflammatory changes were associated with low levels or no expression of iNOS in TNFRp55(-/-) and iNOS(-/-) mice, respectively.

Edematogenic activity of scorpion venoms from the Buthidae family and the role of platelet-activating factor and nitric oxide in paw edema induced by Tityus venoms

We compared the edematogenic activity of venoms of scorpions from the Buthidae family, Tityus bahiensis (Tbv), Tityus serrulatus (Tsv) and Rhopalurus rochai (Rrv). Three doses (20, 40 and 80 microg/kg sc) of each venom were administrated in hind paw of mice and edema was measured from 5 min to 24 h. Tbv and Tsv both induced edema of rapid onset (135% of increase at 15 min); Rrv induced only a mild edema (40% of increase). We then investigated the involvement of platelet-activating factor (PAF) and endogenous nitric oxide (NO) in Tbv and Tsv-induced paw edema. Pretreatment of mice with a PAF antagonist (WEB-2170) inhibited Tsv but not Tbv-induced edema. Pretreatment with a non selective inhibitor of NO-synthases (L: -NAME) inhibited or increased the edema depending on the dose and the time the edema was measured. In conclusion, the venoms from Tityus are stronger inducers of edema than the venom from the Rhopalurus scorpion. The venoms of Tityus species are similar in potency and time-course edema development. PAF is involved in the edema induced only by Tsv.

S-nitrosylated S100A8: novel anti-inflammatory properties

S100A8 and S100A9, highly expressed by neutrophils, activated macrophages, and microvascular endothelial cells, are secreted during inflammatory processes. Our earlier studies showed S100A8 to be an avid scavenger of oxidants, and, together with its dependence on IL-10 for expression in macrophages, we postulated that this protein has a protective role. S-nitrosylation is an important posttranslational modification that regulates NO transport, cell signaling, and homeostasis. Relatively few proteins are targets of S-nitrosylation. To date, no inflammation-associated proteins with NO-shuttling capacity have been identified. We used HPLC and mass spectrometry to show that S100A8 and S100A9 were readily S-nitrosylated by NO donors. S-nitrosylated S100A8 (S100A8-SNO) was the preferred nitrosylated product. No S-nitrosylation occurred when the single Cys residue in S100A8 was mutated to Ala. S100A8-SNO in human neutrophils treated with NO donors was confirmed by the biotin switch assay. The stable adduct transnitrosylated hemoglobin, indicating a role in NO transport. S100A8-SNO suppressed mast cell activation by compound 48/80; intravital microscopy was used to demonstrate suppression of leukocyte adhesion and extravasation triggered by compound 48/80 in the rat mesenteric microcirculation. Although S100A8 is induced in macrophages by LPS or IFN-gamma, the combination, which activates inducible NO synthase, did not induce S100A8. Thus, the antimicrobial functions of NO generated under these circumstances would not be compromised by S100A8. Our results suggest that S100A8-SNO may regulate leukocyte-endothelial cell interactions in the microcirculation, and suppression of mast cell-mediated inflammation represents an additional anti-inflammatory property for S100A8.

The role of reactive oxygen species and nitric oxide in mast cell-dependent inflammatory processes

Reactive oxygen species (ROS) and reactive nitrogen oxide species (RNOS), including nitric oxide, are produced in cells by a variety of enzymatic and non-enzymatic mechanisms. At high levels, both types of oxidants are used to kill ingested organisms within phagocytes. At low levels, RNOS may diffuse outside cells where they impact the vasculature and nervous system. Recent evidence suggests that low levels of ROS produced within cells are involved in cell signaling. Along with these physiological roles, many pathological conditions exist where detrimental high-level ROS and RNOS are produced. Many situations in which ROS/RNOS are associated also involve mast cell activation. In innate immunity, such mast cells are involved in the immune response toward pathogens. In acquired immunity, activation of mast cells by cross-linking of receptor-bound immunoglobulin E causes the release of mediators involved in the allergic inflammatory response. In this review, we describe the principle pathways for ROS and RNOS generation by cells and discuss the existence of such pathways in mast cells. In addition, we examine the evidence for a functional role for ROS and RNOS in mast cell secretory responses and discuss evidence for a direct relationship between ROS, RNOS, and mast cells in mast cell-dependent inflammatory conditions.

S-nitrosoglutathione-containing hydrogel accelerates rat cutaneous wound repair

BACKGROUND

Nitric oxide (NO) plays a key role in wound repair and S-nitrosothiols like S-nitrosoglutathione (GSNO) are well known NO donors.

METHODS

Animals were separated in two groups and submitted to excisional wounds on the dorsal surface at the first day. GSNO (100 microm)-containing hydrogels were topically applied on the wound bed in the GSNO group, daily, during the first 4 days. Control group was topically treated with hydrogel without GSNO for the same period. Wound contraction and re-epithelialization were measured. Animals were sacrificed 21 days after wounding. Samples of lesion and normal tissue were formalin-fixed, paraffin embedded for histological analysis.

RESULTS

Wound contraction, measured 14 and 21 days after wounding, was greater in the GSNO group than in the control group (P<0.05 for both). The re-epithelialized wound area, measured 14 days after wounding, was higher in the GSNO group than in the control group (P<0.05). A higher amount of inflammatory cells was observed in superficial and deep areas of the granulation tissue of the control group compared to the GSNO group. Twenty-one days after wounding, thin red-yellow collagen fibers arranged perpendicularly to the surface were found in the granulation tissue of the control group, whereas in the GSNO-treated group collagen fibers were thicker and arranged parallel to the surface. Increased number of mast cells was observed in the GSNO group compared with that in the control group. Vascularization and myofibroblast distribution were similar in both groups.

CONCLUSION

Topical application of GSNO-containing hydrogel during the early phases of rat cutaneous wound repair accelerates wound closure and re-epithelialization and affects granulation tissue organization.

S100A12 provokes mast cell activation: a potential amplification pathway in asthma and innate immunity

BACKGROUND

The calcium-binding protein S100A12 might provoke inflammation and monocyte recruitment through the receptor for advanced glycation end products.

OBJECTIVE

Because inflammation elicited by S100A12 in vivo had characteristics of mast cell (MC) activation, we aimed to define the mechanism.

METHODS

Various MC populations were used to test S100A12 activation assessed on the basis of morphology, histamine release, leukotriene production, and cytokine induction. MC dependence of S100A12-provoked inflammation was tested in mice and on the rat microcirculation by means of intravital microscopy. Immunohistochemistry localized S100A12 in the asthmatic lung, and levels in sputum from asthmatic patients were quantitated by means of ELISA. Expression of the receptor for advanced glycation end products was evaluated by means of RT-PCR and Western blotting.

RESULTS

S100A12 provoked degranulation of mucosal and tissue MCs in vitro and in vivo and amplified IgE-mediated responses. It induced a cytokine profile indicating a role in innate/T(H)1-mediated responses. S100A12-induced edema and leukocyte rolling, adhesion, and transmigration in the microcirculation were MC dependent. Eosinophils in airway tissue from asthmatic patients were S100A12 positive, and levels were increased in sputum. S100A12 responses were partially blocked by an antagonist to the receptor for advanced glycation end products, but MCs did not express mRNA or protein, suggesting an alternate receptor.

CONCLUSION

This novel pathway highlights the potential importance of S100A12 in allergic responses and in infectious and chronic inflammatory diseases.

CLINICAL IMPLICATIONS

MC activation by S100A12 might exacerbate allergic inflammation and asthma. S100A12 might provide a novel marker for eosinophilic asthma.

Whole-body periodic acceleration modifies experimental asthma in sheep

RATIONALE

Nitric oxide is released from vascular endothelium in response to increased pulsatile shear stress. Nitric oxide inhibits mast cell activation and is antiinflammatory and therefore might be protective in asthma.

OBJECTIVES

We determined if a noninvasive motion platform that imparts periodic sinusoidal inertial forces to the whole body along the spinal axis (pGz) causing release of endothelial nitric oxide modulates experimental asthma in sheep.

METHODS

Allergic sheep were untreated (control) or were treated with pGz alone or after receiving intravenously the nitric oxide synthase inhibitor N(w)-nitro-L-arginine methyl ester (L-NAME) before aerosol challenge with Ascaris suum, and the effect on antigen-induced airway responses was determined. Bronchoalveolar lavage cells obtained 6 h after antigen challenge were analyzed for nuclear factor-kappaB (NF-kappaB) activity in the respective groups.

RESULTS

pGz treatment for 1 h before antigen challenge reduced the early airway response and blocked the late airway response but did not prevent the antigen-induced airway hyperresponsiveness 24 h after challenge. Administration of L-NAME before pGz completely reversed this protection, whereas L-NAME alone did not affect the antigen-induced responses. NF-kappaB activity was 1.9- and 1.8-fold higher in the control and L-NAME + pGz groups, respectively, compared with pGz-treated animals. Extending the pGz treatment to twice daily for 3 d and then 1 h before antigen challenge blocked the early and late airway responses, the 24-h airway hyperresponsiveness, and the airway inflammatory cell response.

CONCLUSION

Whole-body pGz modulates allergen-induced airway responses in allergic sheep.

Nitric oxide synthesis inhibition alters rat cutaneous wound healing

BACKGROUND

Nitric oxide (NO) is an important molecule that participates in wound repair, but its effects on cutaneous wound healing are not well understood. The aim of this study was to investigate the effects of NO synthesis blockade on rat cutaneous wound healing by the administration of N(G)-nitro-L-arginine methyl ester (L-NAME), a non-selective inhibitor of NO synthases.

METHODS

NO synthesis was inhibited by administration of L-NAME (20 mg/kg/day) in drinking water. An excisional wound was done, and the animals were killed 7, 14, and 21 days later. Wound contraction and blood pressure were evaluated. The lesion and adjacent skin were formalin fixed and paraffin embedded. Mast cells were quantified, and vessels were evaluated using stereological methods.

RESULTS

L-NAME-treated animals presented delayed wound contraction, alterations in collagen organization, and neoepidermis thickness. The inhibition of NO synthesis increased mast cell migration 7 days after wounding, but decreased 21 days after wounding. Volume density of vessels was decreased in L-NAME-treated animals, 21 days after lesion. Surface density of vessels was frequently smaller in L-NAME-treated animals than in controls. CONCLUSIONS; The blockade of NO synthesis impaired cutaneous wound healing, acting in early and late phases of wound repair.

Developments in Glucocorticoid Therapy

Recent evidence for a disease-modifying potential of low-dose glucocorticoids (GCs) in the treatment of rheumatoid arthritis has renewed the debate on the risk benefit ratio with this therapy. Two recent developments are described that might have a positive influence on these risk benefit ratios. One is the improvement in new GC compounds--designer GCs, alterations in bioactivity, and alterations in formulations. The other is a better understanding and management of the toxicity of GCs.

Bronchoconstriction and endogenous nitric oxide in isolated lungs of spontaneously hypertensive rats

Bronchoconstrictor responses were measured in lungs isolated from spontaneously hypertensive (SHR) and normotensive rats, perfused via the airways. Lungs from SHRs were more responsive than lungs from normotensive rats to methacholine, 5-hydroxytryptamine (5-HT), arachidonic acid or prostaglandin H(2). The responses of SHR airways to methacholine or 5-HT were unaffected by pretreatment in vivo with an inhibitor of nitric oxide (NO) synthase, N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME, 30 mg kg(-1)), although responses in normotensive airways to methacholine, but not to 5-HT, were enhanced. Antigen challenge of isolated lungs from actively sensitized rats elicited bronchoconstriction, not different between strains. Pretreatment with L-NAME increased the response to antigen challenge only in normotensive lungs. Compound 48/80 induced bronchoconstriction in lungs from either strain, equally. These responses to compound 48/80 were unaffected by L-NAME pretreatment. Thus, SHR airways lack relaxing factors and degranulation of mast cells in SHR lungs was not affected by endogenous NO.

Chimeric SOD2/3 inhibits at the endothelial-neutrophil interface to limit vascular dysfunction in ischemia-reperfusion

After an ischemic episode, reperfusion causes profound oxidative stress in the vasculature of the afflicted tissue/organ. The dysregulated accumulation of reactive oxygen species (ROS), such as superoxide, has been closely linked to the production and release of proinflammatory mediators, a profound increase in adhesion molecule expression by the vascular endothelium, and infiltration of neutrophils during ischemia-reperfusion (I/R). Superoxide dismutase (SOD) has been shown to protect tissues and organs against I/R-induced injury; however, the drug had to be continuously perfused or kidneys had to be occluded to prevent clearance. We used intravital microscopy, a system that allowed us to visualize neutrophil-endothelial interactions within the mesenteric postcapillary venules of cats subjected to I/R and tested the hypothesis that I/R-induced neutrophil recruitment was inhibited by treatment with SOD2/3. SOD2/3 is a chimeric fusion gene product that contains the mature SOD2 as well as the COOH-terminal "tail" of SOD3 and, unlike the three naturally occurring SODs (SOD1, SOD2, and SOD3), which bear a net negative charge at pH 7.4, SOD2/3 is positively charged and physiologically stable. Our results suggest that not only does SOD2/3 have a much greater efficacy in vivo than the native human SOD2, but its administration prevents I/R-induced neutrophil-endothelial cell interactions and microvascular dysfunction. Moreover, our data support the hypothesis that reactive oxidants mediate I/R-induced injury and that the chimeric recombinant SOD2/3 has the potential to be a therapeutic agent against this debilitating illness.

Anti-inflammatory effects of nitric oxide-releasing hydrocortisone NCX 1022, in a murine model of contact dermatitis

1 The concept that nitric oxide (NO) release can be beneficial in inflammatory conditions has raised more attention in the recent years, particularly with the development of nitric oxide-releasing anti-inflammatory drugs. There is considerable evidence that NO is capable of enhancing the anti-inflammatory benefits of conventional anti-inflammatory drugs. 2 Since hydrocortisone is the most widely used anti-inflammatory drug for the treatment of skin inflammation, we compared the anti-inflammatory effects of hydrocortisone to an NO-releasing derivative of hydrocortisone, NCX 1022, in a murine model of irritant contact dermatitis, induced by epidermal application of benzalkonium chloride. 3 Topical pre- and post-treatment with NCX 1022 (3 nmol) in C57BL6 mice not only reduced ear oedema formation in a dose-dependent manner, but also was significantly more effective than the parent compound during the initial stages of inflammation (from 1 to 5 h). NCX 1022, but not hydrocortisone, significantly inhibited granulocyte recruitment (tissue myeloperoxidase activity). Histological samples of mouse ears treated with NCX 1022 showed significant reduction in both the number of infiltrated cells and disruption of the tissue architecture compared to hydrocortisone-treated tissues. 4 With intravital microscopy, we observed that both pre- and post-treatments with NCX 1022 were more effective than hydrocortisone in terms of inhibiting benzalkonium chloride-induced leukocyte adhesion to the endothelium, without affecting the flux of rolling leukocytes or venule diameter. 5 These results suggest that by releasing NO, NCX 1022 modulates one of the early events of skin inflammation: the recruitment of leukocytes to the site of inflammation. Overall, we have shown that NO-hydrocortisone provided faster and greater protective effects, reducing major inflammatory parameters (leukocyte adhesion and recruitment, oedema formation, tissue disruption) compared to its parental compound.

Microcirculatory dysfunction during intestinal ischemia-reperfusion

Oxido-reductive stress is a crucial factor of the tissue response during ischemia-reoxygenation injuries. Reperfusion affects primarily the microvasculature in a manner consistent with an acute inflammatory reaction. In this respect, the salient data suggest an important connection between endothelial cell-derived humoral mediators and the perivascular mast cell system. Increased endothelin-1 and decreased nitric oxide formation, mast cell degranulation and leukocyte accumulation coexist in gastrointestinal ischemia-reperfusion syndromes too. Constitutively produced nitric oxide inhibits, while increasingly formed endothelin-1 significantly enhances the degranulation of the intestinal mast cells. The endothelin-A receptor-dependent mast cell degranulation per se plays a secondary role in reperfusion-induced structural injury, but contributes significantly to leukocyte recruitment into the reperfused intestinal mucosa. It is conceivable therefore, that the nitric oxide--endothelin-1--mast cell cycle is involved in the mechanism of ischemia-reperfusion-induced endothelial cell-leukocyte interactions, where mast cells act to amplify the process of leukocyte sequestration. The alteration in the balance between endothelial cell-derived proadhesive vasoconstrictor and antiadhesive vasodilator factors exerts a significant influence on the mucosal integrity, and the antagonism of endothelin-A receptor activation in this setting tips the equilibrium toward tissue salvage.

Mast Cell-Independent Mechanisms of Immediate Hypersensitivity: A Role for Platelets

Mast cells have been implicated as the central effectors in allergic responses, yet a fatal anaphylactic response can be induced in mast cell-deficient mice. In this study, we examined the immediate hypersensitivity response in wild-type (WT) and mast cell-deficient mice (W/W(v)) in two different tissues (skin and skeletal muscle). Vascular permeability and leukocyte recruitment were studied after immediate challenge or 4 h postchallenge in OVA-sensitized mice. In skin, immediate challenge induced a significant increase in vascular permeability (75%) within 30 min and was accompanied by increased leukocyte adhesion 4 h postchallenge. In the absence of mast cells, no changes in vascular permeability or leukocyte recruitment were observed in skin. In WT skeletal muscle, immediate challenge induced a rapid increase (80%) in vascular permeability within 5 min and significant leukocyte recruitment after 4 h. Surprisingly, in W/W(v), a gradual increase in vascular permeability was observed, reaching a maximum (50%) within 30 min. Despite the absence of mast cells, subsequent leukocyte emigration was similar to that observed in WT mice. Pretreatment with anti-platelet serum in W/W(v) returned Ag-induced vascular permeability and leukocyte recruitment to baseline. Platelets were shown to interact with endothelium in skeletal muscle, but not dermal microvasculature. These data illustrate that mast cells play a prominent role in vascular permeability and leukocyte recruitment in skin in response to Ag, however, in skeletal muscle; these changes can occur in the absence of mast cells, and are mediated, in part, by the presence of platelets.

Effect of transdermal nitroglycerin on inflammatory mediators in patients with peripheral atherosclerotic vascular disease

OBJECTIVE

To demonstrate that nitroglycerin improves biological markers of arterial inflammation in patients with peripheral vascular disease.

BACKGROUND

Atherosclerosis is an inflammatory disease in which there is an increase in active inflammation markers such as C-reactive protein and other factors released by endothelial cells. Nitroglycerin acts by a chemical liberation of nitric oxide. We have previously published the results from several controlled clinical trials confirming an anti-inflammatory action of nitroglycerin.

METHODS

Forty patients with peripheral vascular disease entered a randomized, double-blind, placebo-controlled pilot study for 6 weeks. Twenty-one patients were treated with continuous application of a transdermal nitroglycerin patch (15 mg/24 hours) on the anterior face of the thigh. Venous blood samples were obtained before treatment and 2 and 6 weeks after. We measured plasma levels of C-reactive protein, cGMP (also intraplatelet cGMP), E-selectin, ICAM, VCAM-1, IL-6, and nitrites/nitrates.

RESULTS

No biological parameter was modified in the placebo group. On the contrary, nitroglycerin significantly reduced plasma levels of C-reactive protein and sE-selectin and increased the levels of intraplatelet cGMP.

CONCLUSIONS

The results of this preliminary study show that nitroglycerin has an anti-inflammatory action in patients with peripheral vascular disease. This may provide a new therapeutic approach to understanding the efficacy of nitrovasodilators in the improvement of atherosclerotic syndromes.

Role of nitric oxide in leukocyte-independent endothelial damage during experimental endotoxemia

Endothelial damage during early endotoxemia has been shown to be leukocyte independent. Platelet-activating factor and serotonin receptor antagonism has been shown to reduce leukocyte-independent macromolecular leakage significantly. Nevertheless, the exact mechanisms involved in leukocyte-independent endothelial dysfunction are unknown. Therefore, it was the aim of the study to investigate the effects of nitric oxide (NO) on leukocyte-independent endothelial damage during endotoxemia. In male Wistar rats, venular wall shear rate, macromolecular efflux, and leukocyte-endothelial interaction were determined in mesenteric postcapillary venules using intravital microscopy at baseline and at 60 and 120 min after start of the experiment. The animals received fucoidin to prevent leukocyte-endothelial interaction. The experiments were divided into three parts. In part 1, we investigated the effects of the NO-inhibitor L-NAME on leukocyte-independent endothelial damage during endotoxemic and nonendotoxemic conditions. The efficiency of the NO-donor (SIN-1) used, part 2, was investigated by the inhibitory properties of SIN-1 on NO-inhibition-induced macromolecular efflux. Finally, part 3, we analyzed the effects of the NO-donor SIN-1 on endothelial damage during endotoxemia. Both the combined challenge of the animals with L-NAME and endotoxin and the challenge with L-NAME alone resulted in a strong increase in macromolecular efflux, showing significant differences to control groups at an earlier time point than endotoxin challenge alone. Interestingly, combined L-NAME and endotoxin challenge, L-NAME challenge alone, and endotoxin challenge alone showed a similar macromolecular efflux at the end of the experiment. SIN-1 prevented both the increase in macromolecular efflux seen after L-NAME challenge (part 2) and was highly effective in preventing significantly the increase in macromolecular leakage that is seen during leukocyte-independent endotoxemia (part 3). In conclusion, our data indicate that during early states of endotoxemia endogenous NO preserves endothelial integrity in a leukocyte-independent setting. Exogenous NO prevents endothelial damage during early leukocyte-independent endotoxemia. Summarizing these data, endothelial integrity during leukocyte-independent endotoxemia is a NO-mediated event.

Endogenous nitric oxide does not modulate mesenteric mast cell degranulation in rats

The inhibitory effects of endogenous nitric oxide could explain the decreased mesenteric mast cell degranulation after anaphylaxis in genetically hypertensive rats (SHR). SHR and normotensive rats (NT) were sensitized to ovalbumin and challenged 14 days later. Degranulation of mast cells was assessed in duodenum, mesentery and skin by increased microvascular permeability using extravasation of Evans blue dye (20mg/kg, i.v.), and in the mesentery also by light microscopy after staining with toluidine blue. Pretreatment with an inhibitor of nitric oxide synthesis, L-NAME (30 mg/kg, i.v.) did not change dye extravasation after immunological challenge or after compound 48/80 in mesentery of either SHR or NT. PCA was also defective in SHR. Pretreatment with L-NAME did not affect either the defective PCA in SHR or the normal PCA reaction in NT. Our results show that inhibition by endogenous nitric oxide is not the cause of the defective mast cell degranulation in the SHR nor did it modulate degranulation of mesenteric or skin mast cells in NT.

Protective effect of dietary nitrate on experimental gastritis in rats

Nitrates have long been considered as harmful dietary components and judged responsible for deleterious effects on human health, leading to stringent regulations concerning their levels in food and water. However, recent studies demonstrate that dietary nitrate may have a major role in human health as a non-immune mechanism for host defence, through its metabolism to NO in the stomach. NO is a versatile molecule and although evidence exists showing that administration of low doses of exogenous NO protects against gastrointestinal inflammation, higher NO doses have been shown to exacerbate injury. So, the effect of an ingestion of nitrates in doses corresponding to a normal diet in human consumers on an experimental gastritis induced by iodoacetamide in rats was investigated. During gastritis one of the following compounds was given orally: water; KNO3; the NO donor sodium nitroprusside; the NO scavenger haemoglobin given with either water or KNO3. N(G)-nitro-l-arginine methyl ester (l-NAME), a non-specific NO synthase inhibitor, was administered with either water, iodoacetamide alone, or combined with KNO3. After killing, the stomach was resected and microscopic damage scores, myeloperoxidase and NO synthase activities were determined. Iodoacetamide-induced gastritis was significantly reduced by KNO3 administration, an effect which was reproduced by sodium nitroprusside and reversed by haemoglobin. l-NAME induced gastric mucosal damage in itself, and KNO3 did not prevent the gastritis induced by iodoacetamide associated with l-NAME. In conclusion, dietary nitrate exerts a protective effect against an experimental gastritis in rats by releasing NO in the stomach but such an effect requires the production of endogenous NO.

Generation of innovative anti-inflammatory and anti-arthritic glucocorticoid derivatives that release NO: the nitro-steroids

Addition to the prednisolone structure of a chemical moiety (linker+nitric ester) that releases NO species yielded a novel glucocorticoid (nitro-prednisolone or NCX-1015) with enhanced anti-inflammatory activities. Nitro-prednisolone was much more potent than prednisolone and the derivative devoid of the nitric ester in an acute peritonitis model (higher impact on neutrophil migration and soluble mediator generation) as well as in models of chronic inflammation (air-pouch granuloma and collagen II-induced arthritis). In the collagen II-induced arthritis model, NCX-1015 abrogated the plasma levels of a catabolite of cartilage and bone metabolism, indication of a disease modifying action. In an in vitro assay of bone resorption, NCX-1015 did not activate osteoclast activity, whereas prednisolone did. This lack of effect of NCX-1015 was chiefly due to NO. We propose that NCX-1015 is the prototype of a new class of glucocorticoids, the nitro-steroids, endowed with enhanced anti-inflammatory properties and reduced side effects. These and other experimental observations here reviewed may prompt the assessment of the clinical impact of the nitro-steroids on rheumatoid arthritis and inflammatory bowel disease.

Nitric oxide in respiratory diseases

The formation and modulation of nitric oxide (NO) in the lungs is reviewed. Its beneficial and deleterious roles in airways diseases, including asthma, chronic obstructive pulmonary disease, and cystic fibrosis, and in animal models is discussed. The pharmacological effects of agents that modulate NO production or act as NO donors are described. The clinical pharmacology of these agents is described and the therapeutic potential for their use in airways disease is considered.

Inhibition of calpain is a component of nitric oxide-induced down-regulation of human mast cell adhesion

Nitric oxide is an important messenger that regulates mast cell activity by modifications to gene expression and intracellular pathways associated with exocytosis and adhesion. Integrin interactions with extracellular matrix components modulate an array of cell activities, including mediator production and secretion. To investigate the molecular mechanisms underlying NO regulation of mast cell function, we studied its effects on adhesion of a human mast cell line (HMC-1) to fibronectin (FN). The NO donors S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine strongly down-regulated the adhesion of HMC-1 to FN. Inhibitors of soluble guanylate cyclase and protein kinase G did not alter the response of cells to NO. A peroxynitrite scavenger did not affect modulation of adhesion by NO, nor could the effect of NO be mimicked by the peroxynitrite-producing compound 3-morpholinosydnonimine. NO donors inhibited the cysteine protease, calpain, while calpain inhibitors mimicked the effect of NO and led to a decrease in the ability of HMC-1 cells to adhere to FN. Thus, NO is an effective down-regulator of human mast cell adhesion. The mechanism for this action does not involve peroxynitrite or activation of soluble guanylate cyclase. Instead, a portion of NO-induced down-regulation of adhesion may be attributed to inhibition of the cysteine protease, calpain, an enzyme that has been associated with control of integrin activation in other cell types. The inhibition of calpain is most likely mediated via nitrosylation of its active site thiol group. Calpain may represent a novel therapeutic target for the regulation of mast cell activity in inflammatory disorders.

Mast cells mediate the microvascular inflammatory response to systemic hypoxia

Systemic hypoxia produces an inflammatory response characterized by increases in reactive O(2) species (ROS), venular leukocyte-endothelial adherence and emigration, and vascular permeability. Inflammation is typically initiated by mediators released from activated perivascular cells that generate the chemotactic gradient responsible for extravascular leukocyte accumulation. These experiments were directed to study the possible participation of mast cells in hypoxia-induced microvascular inflammation. Mast cell degranulation, ROS levels, leukocyte adherence and emigration, and vascular permeability were studied in the mesenteric microcirculation by using intravital microscopy of anesthetized rats. The main findings were 1) activation of mast cells with compound 48/80 in normoxia produced microvascular effects similar, but not identical, to those of hypoxia; 2) systemic hypoxia resulted in rapid mast cell degranulation; 3) blockade of mast cell degranulation with cromolyn prevented or attenuated the hypoxia-induced increases in ROS, leukocyte adherence/emigration, and vascular permeability; and 4) mast cell degranulation during hypoxia was prevented by administration of the antioxidant lipoic acid and of nitric oxide. These results show that mast cells play a key role in hypoxia-induced inflammation and suggest that alterations in the ROS-nitric oxide balance may be involved in mast cell activation during hypoxia.

Nitric oxide: a regulator of mast cell activation and mast cell-mediated inflammation

Nitric oxide (NO) plays diverse roles in physiological and pathological processes. During immune and inflammatory responses, for example in asthma, NO is generated at relatively high and sustained levels by the inducible form of nitric oxide synthase (NOS-2). NOS-2 derived NO regulates the function, growth, death and survival of many immune and inflammatory cell types. In the case of mast cells, NO suppresses antigen-induced degranulation, mediator release, and cytokine expression. The action of NO on mast cells is time dependent, requiring several hours, and noncGMP mediated, most probably involving chemical modification of proteins. NO inhibits a number of mast cell-dependent inflammatory processes in vivo, including histamine mediated vasodilatation, vasopermeation and leucocyte-endothelial cell attachment. In human asthma and animal models of lung inflammation the role of NO is harder to define. However, although there are conflicting data, the balance of evidence favours a predominantly protective role for NO. Mimicking or targeting NO dependent pathways may prove to be a valuable therapeutic approach to mast cell mediated diseases.

Effects of sepsis on mast cells in rat dura mater: influence of L-NAME and VIP

1. The influence of lipopolysaccharide (LPS)-induced sepsis on the various mast cell phenotypes of rat dura mater were examined both by immunohistochemical and biochemical methods. 2. Three different populations of mast cells were identified in control rats: connective tissue type mast cells (CTMC) which contain rat mast cell protease1 (RMCP1), histamine, serotonin and heparin, mucosal type mast cells (MMC) which contain RMCP2, histamine and serotonin, and intermediate type which contains both RMCP1 and RMCP2 and probably various proportions of amines and heparin. 3. LPS (25 mg kg(-1) i.p.) caused changes in the proportions of the various types of mast cells. The number of MMC and intermediate type mast cells significantly increased and the number of mast cells immunopositive for both heparin and serotonin significantly decreased. Biochemical analysis showed that the histamine concentration of dura increased while its serotonin concentration decreased. 4. While vasoactive intestinal peptide (VIP) (25 ng kg(-1) i.p.) appears to potentiate LPS effects on dura mater mast cells, non-selective inhibition of nitric oxide (NO) synthase by N(g)-nitro-L-arginine methyl ester (L-NAME) (30 mg kg(-1) i.p.) did not influence sepsis-induced mast cell changes. 5. These findings suggest that mast cells of dura mater may play a role in brain protection during sepsis.

Mast cells and nitric oxide: control of production, mechanisms of response

Mast cells are involved in numerous activities ranging from control of the vasculature, to tissue injury and repair, allergic inflammation and host defences. They synthesize and secrete a variety of mediators, activating and modulating the functions of nearby cells and initiating complex physiological changes. Interestingly, NO produced by mast cells and/or other cells in the microenvironment appears to regulate these diverse roles. This review outlines some of the pathways central to the production of NO by mast cells and identifies many of the tightly controlled regulatory mechanisms involved. Several cofactors and regulatory elements are involved in NO production, and these act at transcriptional and post-translational sites. Their involvement in NO production will be outlined and the possibility that these pathways are critically important in mast cell functions will be discussed. The effects of NO on mast cell functions such as adhesion, activation and mediator secretion will be examined with a focus on molecular mechanisms by which NO modifies intracellular signalling pathways dependent or independent of cGMP and soluble guanylate cyclase. The possibility that NO regulates mast cell function through effects on selected ion channels will be discussed. Metabolic products of NO including peroxynitrite and other reactive species may be the critical elements that affect the actions of NO on mast cell functions. Further understanding of the actions of NO on mast cell activities may uncover novel strategies to modulate inflammatory conditions.

Nitric oxide in immunity and inflammation

Nitric oxide (NO) is synthesised by many cell types involved in immunity and inflammation. The principal enzyme involved is the inducible type-2 isoform of nitric oxide synthase (NOS-2), which produces high-level sustained NO synthesis. NO is important as a toxic defense molecule against infectious organisms. It also regulates the functional activity, growth and death of many immune and inflammatory cell types including macrophages, T lymphocytes, antigen-presenting cells, mast cells, neutrophils and natural killer cells. However, the role of NO in nonspecific and specific immunity in vivo and in immunologically mediated diseases and inflammation is poorly understood. NO does not act through a receptor-its target cell specificity depends on its concentration, its chemical reactivity, the vicinity of target cells and the way that target cells are programmed to respond. At high concentrations as generated by NOS-2, NO is rapidly oxidised to reactive nitrogen oxide species (RNOS) that mediate most of the immunological effects of NOS-2-derived NO. RNOS can S-nitrosate thiols to modify key signalling molecules such as kinases and transcription factors. Several key enzymes in mitochondrial respiration are also inhibited by RNOS and this leads to a depletion of ATP and cellular energy. A combination of these interactions may explain the multiple actions of NO in the regulation of immune and inflammatory cells.

The role of NO in contact hypersensitivity

Contact dermatitis or contact hypersensitivity (CHS) is a common T lymphocyte-mediated allergic disease characterized by local inflammatory skin reactions following contact with small reactive compounds called haptens. In common with other allergic processes, the development of contact dermatitis proceeds in two phases: a sensitization phase which occurs on first exposure to allergen, and an elicitation phase which occurs on subsequent exposure when the clinical manifestations of the disease are observed. This process is hapten-specific. While the pathophysiology of the sensitization phase is well characterized, our understanding of the elicitation phase is still incomplete, including the relative contribution of the different effector cells and mediators involved. Here we summarize current knowledge of the contribution of nitric oxide (NO) to skin inflammation with special focus on CHS. A number of inflammatory stimuli trigger expression of NO in human and animal skin, and topical application of an NO-releasing cream results in inflammation. Moreover, expression of the inducible isoform of nitric oxide synthase (iNOS) is induced in CHS and iNOS inhibitors injected intradermally suppress CHS responses. However, iNOS-deficient mice develop an aggravated CHS response late in the elicitation phase, suggesting that NO is involved in downregulation of CHS. Based on these data, we propose a comprehensive model of the role of NO in CHS.

Susceptibility to cerulein-induced pancreatitis in inducible nitric oxide synthase-deficient mice

Production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) has been proposed as a pathogenic factor in acute pancreatitis, but its role has still not been fully examined. The present study explored the role of iNOS in cerulein-induced acute pancreatitis using iNOS-deficient mice. Twelve- to 14-week-old male mice (C57B1/6 and iNOS-deficient) were administered cerulein by intraperitoneal (i.p.) injection at hourly intervals for 7 hours and killed 24 hours later after the first dose. Pancreatic wet weight, pancreatic myeloperoxidase (MPO) activity, and levels of plasma nitrite and serum amylase were measured. In another experiment isosorbide dinitrate (an NO donor) was given by oral gavage every 6 hours for 24 hours beginning simultaneously with cerulein injections in iNOS-deficient mice. Cerulein administration dose-dependently increased pancreatic wet weight, myeloperoxidase activity, and levels of nitrite and amylase in C57B1/6 mice. These parameters (except nitrite levels) were significantly intensified in iNOS-deficient mice. At the dose employed, cerulein failed to increase nitrite levels in iNOS-deficient mice. The susceptibility to cerulein toxicity in iNOS-deficient mice was abolished by NO donor treatment. NO release from an iNOS source appears to play a protective role in cerulein-induced pancreatitis. At least in part, NO may prevent neutrophil accumulation after cerulein administration.

New agents for the medical treatment of interstitial cystitis

Interstitial cystitis (IC) is a painful, sterile, disorder of the urinary bladder characterised by urgency, frequency, nocturia and pain. IC occurs primarily in women but also in men with recent findings indicating that chronic, abacterial prostatitis may be a variant of this condition. The prevalence of IC has ranged from about 8 - 60 cases/100,000 female patients depending on the population evaluated. About 10% of patients have severe symptoms that are associated with Hunner's ulcers on bladder biopsy; the rest could be grouped in those with or without bladder inflammation. Symptoms of IC are exacerbated by stress, certain foods and ovulatory hormones. Many patients also experience allergies, irritable bowel syndrome (IBS) and migraines. There have been various reports indicating dysfunction of the bladder glycosaminoglycan (GAG) protective layer and many publications showing a high number of activated bladder mast cells. Increasing evidence suggests that neurogenic inflammation and/or neuropathic pain is a major component of IC pathophysiology. Approved treatments so far include intravesical administration of dimethylsulphoxide (DMSO) or oral pentosanpolysulphate (PPS). New treatments focus on the combined use of drugs that modulate bladder sensory nerve stimulation (neurolytic agents), inhibit neurogenic activation of mast cells, or provide urothelial cytoprotection, together with new drugs with anti-inflammatory activity.

Nitric oxide synthase inhibitors have opposite effects on acute inflammation depending on their route of administration

The bulk of published data has shown that NO is proinflammatory. However, there also exists the conflicting notion that NO may be protective during an inflammatory insult. In an attempt to resolve this issue, we have compared the effects on inflammation of a range of NO synthase (NOS) inhibitors given either directly to the site of the inflammatory lesion or systemically. It was found that in the carrageenin-induced pleurisy, a single intrapleural injection of the selective inducible NO inhibitors S-(2-aminoethyl) isothiourea (AE-ITU; 3 and 10 mg/kg) and N-(3-(aminomethyl)-benzyl) acetamidine (1400W; 10 mg/kg) or the selective endothelial cell NOS inhibitor L-N(5)(1-iminoethyl)-ornithine (10 mg/kg) not only exacerbated inflammation at the very early stages of the lesion (1-6 h), but also prevented inflammatory resolution. By contrast, administering NOS inhibitors systemically ameliorated the severity of inflammation throughout the reaction. To elucidate the mechanisms by which inhibition of NO synthesis locally worsened inflammation, we found an increase in histamine, cytokine-induced neutrophil chemoattractant, superoxide, and leukotriene B(4) levels at the inflammatory site. In conclusion, this work shows that the local production of NO is protective by virtue of its ability to regulate the release of typical proinflammatory mediators and, importantly, that NOS inhibitors have differential anti-inflammatory effects depending on their route of administration.

Constitutive nitric oxide release modulates neurally-evoked chloride secretion in guinea pig colon

The role of constitutive nitric oxide (NO) release in enteric neural pathways regulating ion transport was examined in guinea pig distal colon, in vitro and ex vivo. In in vitro studies, 43% of colonic preparations exhibited oscillations in baseline short-circuit current (Isc), which were reduced by tetrodotoxin (TTX). The NO chelator, hemoglobin (Hb), and neuronal NO synthase inhibitor, 7-nitroindazole (7-NI), significantly increased the baseline Isc in these tissues, which was reduced by TTX. In tissues without oscillations in baseline Isc, Hb reduced the Isc, while 7-NI had little effect. In all tissues, electrical field stimulation (EFS; 15 V/10 Hz) caused a biphasic increase in the Isc which was enhanced by both Hb and 7-NI. In the ex vivo studies, basal release of nitric oxide was significantly lower in colonic segments isolated from guinea pigs administered N omega-nitro-L-arginine methyl ester (L-NAME) i.p. compared to control tissues. Moreover, carbachol, caused a 10-fold increase in NO release in control tissues, but had no effect in tissues isolated from the L-NAME group. L-NAME increased tissue conductance and EFS-induced changes in Isc, which were reversed by L-arginine. However, carbachol-induced ion secretion was unaltered in the L-NAME group compared to control animals. The results suggest that, in guinea pig colon, constitutive enteric NO release tonically suppresses submucous neural activity and it is involved in the maintenance of basal epithelial chloride secretion and mucosal permeability. Hence, constitutive NO promotes a delicate balance between pro-absorptive and pro-secretory processes in guinea pig colon.

21-NO-prednisolone is a novel nitric oxide-releasing derivative of prednisolone with enhanced anti-inflammatory properties

1. Anti-inflammatory effects of a novel derivative of the glucocorticoid prednisolone were investigated. NCX-1015 (prednisolone 21-[(4'-nitrooxymethyl)benzoate]) incubation in human platelet-rich plasma produced a time (0 - 60 min) and concentration (3 - 300 microM) dependent release of nitrite, that was mirrored by accumulation of cyclic guanosine monophosphate in the human platelets. Intraperitoneal injection of NCX-1015 to mice (up to 27.7 micromol kg(-1)) produced nitrite accumulation in the peritoneal cavity maximal at 60 min. 2. NCX-1015 dose-dependently induced the steroid sensitive cell surface marker CD163 in human peripheral blood mononuclear cells (PBMCs). NCX-1015 was more potent than prednisolone in inducing CD163. Similarly, lipopolysaccharide induced interleukin-1 beta release from these cells was inhibited by NCX-1015 with higher potency than prednisolone. 3. In the zymosan peritonitis model, NCX-1015 was more active than prednisolone in suppressing neutrophil extravasation (ED(50) of 5.5 and 25.8 micromol kg(-1), respectively), nitrite accumulation (ED(50) of 1.38 and 22.2 micromol kg(-1), respectively) and release of the chemokine KC (ED(50) of 5.5 and 27.7 micromol kg(-1), respectively) as determined at the 4 h time-point. No differences were measured for the levels of interleukin-1 beta or prostaglandin E(2). NCX-1015 administered orally was also found to be equally active. Co-administration of the nitric oxide donors NOC-18 ((z)-1-[(2-aminoethyl)-N-(2-aminoethyl)amino] diazen-1-ium-1, 2-diolate; 7.9 micromol kg(-1)) or sodium nitroprusside (13.8 micromol kg(-1)) with prednisolone resulted in an additive anti-migratory action. 4. In a chronic model of granulomatous tissue inflammation, administration of NCX-1015 (13.9 micromol kg(-1)) from day 1 (i.e. after induction of inflammation) was more effective than prednisolone in reducing the granuloma dry weight, and this was associated to a lower anti-angiogenic effect. 5. In conclusion we show that NCX-1015 is more potent than prednisolone in controlling several, though not all, parameters of acute and chronic inflammation, and propose that this effect may be due to a co-operation between the steroid moiety and nitric oxide or related species released in biological fluids. Whereas this aspect needs to be further clarified, we propose NCX-1015 as the first member of a novel class of anti-inflammatory compounds, the nitro-steroids.

Differential effects of L-NAME on rat venular hydraulic conductivity

The role of nitric oxide (NO) in microvascular permeability remains unclear because both increases and decreases in permeability by NO synthase (NOS) inhibitors have been reported. We sought to determine whether blood-borne constituents modify venular permeability responses to the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). We assessed hydraulic conductivity (L(p)) of pipette-perfused rat mesenteric venules before and after exposure to 10(-4) M L-NAME. In the absence of blood-borne constituents, L-NAME reduced L(p) by nearly 50% (from a median of 2.4 x 10(-7) cm x s(-1) x cmH(2)O(-1), n = 17, P < 0.001). The reduction in L(p) by L-NAME was inhibited by a 10-fold molar excess of L-arginine but not D-arginine (n = 6). In a separate group of venules, blood flow was allowed to resume during exposure to L-NAME. In vessels perfused by blood during L-NAME exposure, L(p) increased by 78% (from 1.4 x 10(-7) cm x s(-1) x cmH(2)O(-1), n = 10, P < 0.01). N(G)-nitro-D-arginine methyl ester did not affect L(p) in either of the two groups. These data imply that NO has direct vascular effects on permeability that are opposed by secondary changes in permeability mediated by blood-borne constituents.

Obligatory role of nitric oxide in platelet-activating factor-induced microvascular leakage

We examined the independent and interdependent effects of platelet-activating factor (PAF) and nitric oxide (NO) on microvascular leakage of fluorescein isothiocyanate (FITC)-dextran in the cheek pouch microcirculation of anesthetized hamsters. Superfusing the cheek pouch microcirculation with 100-nM PAF elicited rapid leakage of FITC-dextran that was markedly inhibited by prior treatment with a nitric oxide synthase (NOS) inhibitor, N(omega)-nitro-L-arginine (L-NA; 1 microM). This inhibition by L-NA was completely reversed by application of a NO donor (S-nitroso-N-acetylpenicillamine, SNAP; 10 microM) at the same time PAF was applied. SNAP alone, however, did not cause leakage of FITC-dextran; neither did it enhance PAF-induced leakage. PAF-induced leakage was completely inhibited by prior treatment with the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ, 10 microM). 8-bromoguanosine 3',5'-cyclic monophosphate (8-br-cGMP) did not reverse this inhibition by ODQ although this cell permeable cGMP analog was able to completely reverse arteriolar vasoconstriction produced by ODQ. These results indicate that PAF-induced leakage of FITC-dextran in the hamster cheek pouch microcirculation requires an intact NO/cGMP pathway, although NO production does not cause PAF-induced leakage. This supports the hypothesis that NO plays an obligatory role in PAF-induced leakage.

Aminoethyl-isothiourea, a nitric oxide synthase inhibitor and oxygen radical scavenger, improves survival and counteracts hemodynamic deterioration in a porcine model of streptococcal shock

OBJECTIVE

To test the effect of a continuous infusion of the nitric oxide (NO) synthase (S) inhibitor aminoethyl-isothiourea (AE-ITU) on survival time, hemodynamics, and oxygen transport in a porcine model of live group A streptococcal (GAS) sepsis. Furthermore, to examine the role of endothelin-1, histamine, and reactive oxygen species (ROS) in streptococcal shock.

DESIGN

Prospective, randomized trial.

SETTING

Laboratory at a university hospital.

SUBJECTS

Twenty-eight pigs with an average weight of 25 kg.

INTERVENTIONS

Sixteen animals received a continuous infusion of live Streptococcus pyogenes 1.3 x 10(10) colony forming units/hr: eight received fluids only, and the other eight received an intravenous infusion of AE-ITU 10 mg/kg/hr starting 30 mins before the GAS challenge. Six control pigs received AE-ITU 10 mg/kg/hr iv for 5 hrs. Another six animals received half the dose of GAS over 5 hrs.

MEASUREMENTS AND MAIN RESULTS

GAS infusion caused a rapid increase in pulmonary, hepatic, and systemic vascular resistance, followed by hypotension with a 90% lethality at 4 hrs. Treatment with AE-ITU increased 4-hr survival in septic animals from 1/8 to 8/8 and 5-hr survival from 0/8 to 5/8, prevented hypotension, and increased urine output. AE-ITU attenuated the decrease in cardiac output, liver blood flow, and oxygen delivery, and hepatic arterial blood flow as a fraction of cardiac output increased (all p < .05). Plasma nitrate/nitrite levels decreased in all animals. Inducible NOS and endothelial constitutive NOS activities in liver, gut, and lung were not increased during sepsis, nor were they decreased after AE-ITU. Plasma levels of endothelin-1 and methylhistamine increased in all septic animals and were not modified by AE-ITU. AE-ITU prevented the increase in monocyte ROS production caused by GAS. In control animals, AE-ITU caused an increase in mean arterial pressure, liver blood flow, and oxygen delivery.

CONCLUSIONS

In this model of porcine GAS-induced septic shock, which was not associated with enhanced NO production, infusion of the NOS inhibitor AE-ITU prolonged survival, prevented hypotension, and improved cardiac contractility, organ perfusion, and tissue oxygenation. These beneficial effects of AE-ITU might be a result of the combined effect of ROS scavenging and modulation of local NO production, thus improving the balance of vasodilator and vasoconstrictor forces and reducing oxidative stress.