Protective effects of inhibitors of nitric oxide synthase in immune complex-induced vasculitis

NOS3 Inhibition Confers Post-Ischemic Protection to Young and Aging White Matter Integrity by Conserving Mitochondrial Dynamics and Miro-2 Levels

White matter (WM) damage following a stroke underlies a majority of the neurological disability that is subsequently observed. Although ischemic injury mechanisms are age-dependent, conserving axonal mitochondria provides consistent post-ischemic protection to young and aging WM. Nitric oxide synthase (NOS) activation is a major cause of oxidative and mitochondrial injury in gray matter during ischemia; therefore, we used a pure WM tract, isolated male mouse optic nerve, to investigate whether NOS inhibition provides post-ischemic functional recovery by preserving mitochondria. We show that pan-NOS inhibition applied before oxygen-glucose deprivation (OGD) promotes functional recovery of young and aging axons and preserves WM cellular architecture. This protection correlates with reduced nitric oxide (NO) generation, restored glutathione production, preserved axonal mitochondria and oligodendrocytes, and preserved ATP levels. Pan-NOS inhibition provided post-ischemic protection to only young axons, whereas selective inhibition of NOS3 conferred post-ischemic protection to both young and aging axons. Concurrently, genetic deletion of NOS3 conferred long-lasting protection to young axons against ischemia. OGD upregulated NOS3 levels in astrocytes, and we show for the first time that inhibition of NOS3 generation in glial cells prevents axonal mitochondrial fission and restores mitochondrial motility to confer protection to axons by preserving Miro-2 levels. Interestingly, NOS1 inhibition exerted post-ischemic protection selectively to aging axons, which feature age-dependent mechanisms of oxidative injury in WM. Our study provides the first evidence that inhibition of glial NOS activity confers long-lasting benefits to WM function and structure and suggests caution in defining the role of NO in cerebral ischemia at vascular and cellular levels.SIGNIFICANCE STATEMENT White matter (WM) injury during stroke is manifested as the subsequent neurological disability in surviving patients. Aging primarily impacts CNS WM and mechanisms of ischemic WM injury change with age. Nitric oxide is involved in various mitochondrial functions and we propose that inhibition of glia-specific nitric oxide synthase (NOS) isoforms promotes axon function recovery by preserving mitochondrial structure, function, integrity, and motility. Using electrophysiology and three-dimensional electron microscopy, we show that NOS3 inhibition provides a common target to improve young and aging axon function, whereas NOS1 inhibition selectively protects aging axons when applied after injury. This study provides the first evidence that inhibition of glial cell NOS activity confers long-lasting benefits to WM structure and function.

Effect of Nitric Oxide Synthase Inhibition in Experimental Pseudomonas keratitis in Rabbits

Purpose

The aim of this study was to assess the efficacy of the nitric oxide synthase inhibitor L-NG-nitro-arginine-methyleser (L-NAME) in the treatment of experimental Pseudomonas keratitis.

Methods

Twelve young New Zealand white rabbits were given intrastromal injections of Pseudomonas aeruginosa strains. Twenty-four hours later, the rabbits were randomly divided into four groups: group 1 was treated with topical 0.3% ciprofloxacin drops and a single subconjunctival injection of L-NAME (150 mg/kg); group 2 received topical 0.3% ciprofloxacin drops alone; group 3 received a single subconjunctival injection of L-NAME alone; group 4, the control group, was treated with topical balanced salt solution (BSS) drops. One drop of either ciprofloxacin of BSS was applied at each treatment interval. Twenty-six hours after the start of treatment, the eyes were examined by slit lamp to assess inflammation. Aqueous humor specimens were collected from each eye to measure the nitric oxide concentration. Corneas were removed to count bacteria results.

Results

Slit lamp examination cell scores were significantly lower for groups 1 and 3 than groups 2 and 4 eyes (p = 0.002 to p = 0.004). No viable bacteria were detected in the corneas of groups 1 and 2. Group 3 corneas had significantly fewer bacteria (6.33 ± 0.42 × 103) than group 4 (5.94 ± 0.16 × 104) (p < 0.05). Nitric oxide levels in the aqueous humor were significantly lower for group 1 eyes than for groups 2, 3, or 4 (p = 0.02, p = 0.01, and p = 0.003, respectively).

Conclusions

We conclude that nitric oxide synthase inhibitors may be a useful adjunct but are not a replacement for traditional antibiotic drop therapy.

Role of Antioxidants in Horse Serum-mediated Vasculitis in Swine: Potential Relevance to Early Treatment in Mitigation of Coronary Arteritis in Kawasaki Disease

BACKGROUND

Horse serum-induced immune complex coronary vasculitis in swine is the first experimental model to mimic most of the pictures of Kawasaki disease. Immune complex mechanism has been implicated as one of the possible mechanisms in the pathogenesis of vasculitis in Kawasaki disease. Antioxidants have a significant role in the reduction of cardiovascular diseases in both human and animal studies. We tried giving vitamins A, E, and C to treat immune complex vasculitis, in the hope of mitigating coronary vasculitis in Kawasaki disease.

METHODS

Our study group consisted of 30 pure bred male piglets of 2-3 months of age, and they were divided into test and control groups. The test (AEC) group (n = 20) received two doses of horse serum, 10 mL (0.65 g protein)/kg body weight at 5-day intervals, and oral vitamins A, E, and C once daily for 14 days. The control group (n = 10) was further divided into the saline group (n = 3) receiving two doses of normal saline and the horse serum group (n = 7) receiving two doses of horse serum at 5-day intervals. Piglets were observed for the rashes and coronary artery dimensions.

RESULTS

Both the AEC and the control horse serum group developed rashes after horse serum infusions, but the AEC group developed significantly fewer rashes, and no rashes were seen in the saline group. The control horse serum group (mean ± standard deviation = 2.13 ± 0.72) showed significant coronary artery dilatation, whereas there was no significant dilatation in the AEC group (mean ± standard deviation = 0.81 ± 0.58) or the control saline group (p = 0.002).

CONCLUSION

Serum sickness is a prototype of immune complex vasculitis, and the severity can be ameliorated with antioxidants. A trial of therapeutic dosages of vitamins A, E, and C in acute phase of Kawasaki disease, may be effective in mitigation of coronary artery lesion in addition to intravenous immunoglobulin and aspirin.

Stellera chamaejasme and its constituents induce cutaneous wound healing and anti-inflammatory activities

Stellera chamaejasme L. (Thymelaeaceae) is a perennial herb that is widely used in traditional Chinese medicine to treat tumours, tuberculosis and psoriasis. S. chamaejasme extract (SCE) possesses anti-inflammatory, analgesic and wound healing activities; however, the effect of S. chamaejasme and its active compounds on cutaneous wound healing has not been investigated. We assessed full-thickness wounds of Sprague-Dawley (SD) rats and topically applied SCE for 2 weeks. In vitro studies were performed using HaCaT keratinocytes, Hs68 dermal fibroblasts and RAW 264.7 macrophages to determine cell viability (MTT assay), cell migration, collagen expression, nitric oxide (NO) production, prostaglandin E₂ (PGE₂) production, inflammatory cytokine expression and β-catenin activation. In vivo, wound size was reduced and epithelisation was improved in SCE-treated SD rats. In vitro, SCE and its active compounds induced keratinocyte migration by regulating the β-catenin, extracellular signal-regulated kinase and Akt signalling pathways. Furthermore, SCE and its active compounds increased mRNA expression of type I and III collagen in Hs68 fibroblasts. SCE and chamechromone inhibited NO and PGE₂ release and mRNA expression of inflammatory mediators in RAW 264.7 macrophages. SCE enhances the motility of HaCaT keratinocytes and improves cutaneous wound healing in SD rats.

Immune Complex-Induced, Nitric Oxide-Mediated Vascular Endothelial Cell Death by Phagocytes Is Prevented with Decoy FcγReceptors

Autoimmune vasculitis is an endothelial inflammatory disease that results from the deposition of immune-complexes (ICs) in blood vessels. The interaction between Fcgamma receptors (FcγRs) expressed on inflammatory cells with ICs is known to cause blood vessel damage. Hence, blocking the interaction of ICs and inflammatory cells is essential to prevent the IC-mediated blood vessel damage. Thus we tested if uncoupling the interaction of FcγRs and ICs prevents endothelium damage. Herein, we demonstrate that dimeric FcγR-Igs prevented nitric oxide (NO) mediated apoptosis of human umbilical vein endothelial cells (HUVECs) in an in vitro vasculitis model. Dimeric FcγR-Igs significantly inhibited the IC-induced upregulation of inducible nitric oxide synthase (iNOS) and nitric oxide (NO) release by murine monocytic cell line. However, FcγR-Igs did not affect the exogenously added NO-induced upregulation of pro-apoptotic genes such as Bax (15 fold), Bak (35 fold), cytochrome-C (11 fold) and caspase-3 (30 fold) in HUVECs. In conclusion, these data suggest that IC-induced NO could be one of the major inflammatory mediator promoting blood vessel inflammation and endothelial cell death during IC-mediated vasculitis which can be effectively blocked by dimeric decoy FcγRs.

Optimization of a Clinically Relevant Model of White Matter Stroke in Mice: Histological and Functional Evidences

BACKGROUND AND PURPOSE

White matter (WM) injury during stroke increases the risk of disability and gloomy prognosis of post-stroke rehabilitation. However, modeling of WM loss in rodents has proven to be challenging.

METHODS

We report improved WM injury models in male C57BL/6 mice. Mice were given either endothelin-1 (ET-1) or L-N5-(1-iminoethyl)ornitine (L-NIO) into the periventricular white matter (PVWM), in the corpus callosum (CC), or in the posterior limb of internal capsule (PLIC). Anatomical and functional outcomes were quantified on day 7 post injection.

RESULTS

Injection of ET-1 or L-NIO caused a small focal lesion in the injection site in the PVWM. No significant motor function deficits were observed in the PVWM lesion model. We next targeted the PLIC by using single or double injections of L-NIO and found that this strategy induced small focal infarction. Interestingly, injection of L-NIO in the PLIC also resulted in gliosis, and significant motor function deficits.

CONCLUSIONS

By employing different agents, doses, and locations, this study shows the feasibility of inducing brain WM injury accompanied with functional deficits in mice. Selective targeting of the injury location, behavioral testing, and the agents chosen to induce WM injury are all keys to successfully develop a mouse model and subsequent testing of therapeutic interventions against WM injury.

Considerations for the Optimization of Induced White Matter Injury Preclinical Models

White matter (WM) injury in relation to acute neurologic conditions, especially stroke, has remained obscure until recently. Current advances in imaging technologies in the field of stroke have confirmed that WM injury plays an important role in the prognosis of stroke and suggest that WM protection is essential for functional recovery and post-stroke rehabilitation. However, due to the lack of a reproducible animal model of WM injury, the pathophysiology and mechanisms of this injury are not well studied. Moreover, producing selective WM injury in animals, especially in rodents, has proven to be challenging. Problems associated with inducing selective WM ischemic injury in the rodent derive from differences in the architecture of the brain, most particularly, the ratio of WM to gray matter in rodents compared to humans, the agents used to induce the injury, and the location of the injury. Aging, gender differences, and comorbidities further add to this complexity. This review provides a brief account of the techniques commonly used to induce general WM injury in animal models (stroke and non-stroke related) and highlights relevance, optimization issues, and translational potentials associated with this particular form of injury.

Modulation of nitric oxide synthase activity in macrophages

L-Arginine is converted to the highly reactive and unstable nitric oxide (NO) and L-citrulline by an enzyme named nitric oxide synthase (NOS). NO decomposes into other nitrogen oxides such as nitrite (NO₂^-) and nitrate (NO₂^-), and in the presence of superoxide anion to the potent oxidizing agent peroxynitrite (ONOO⁻). Activated rodent macrophages are capable of expressing an inducible form of this enzyme (iNOS) in response to appropriate stimuli, i.e., lipopolysaccharide (LPS) and interferon-γ (IFNγ). Other cytokines can modulate the induction of NO biosynthesis in macrophages. NO is a major effector molecule of the anti-microbial and cytotoxic activity of rodent macrophages against certain micro-organisms and tumour cells, respectively. The NO synthesizing pathway has been demonstrated in human monocytes and other cells, but its role in host defence seems to be accessory. A delicate functional balance between microbial stimuli, host-derived cytokines and hormones in the microenvironment regulates iNOS expression. This review will focus mainly on the known and proposed mechanisms of the regulation of iNOS induction, and on agents that can modulate NO release once the active enzyme has been expressed in the macrophage.

Nitric oxide decreases intestinal haemorrhagic lesions in rat anaphylaxis independently of mast cell activation

The purpose of this study is to assess the role of nitric oxide (NO) in the intestinal lesions of passive anaphylaxis, since this experimental model resembles necrotizing enterocolitis. Sprague-Dawley rats were sensitized with IgE anti-dinitrophenol monoclonal antibody. Extravasation of protein-rich plasma and haemorrhagia were measured in the small intestine. Plasma histamine was measured to assess mast cell activation. The effect of exogenous NO on the lesions was assessed by using two structurally unrelated NO-donors: sodium nitroprusside and S-nitroso-Nacetyl-penicillamine (SNAP). An increased basal production of NO was observed in cells taken after anaphylaxis, associated with a reduced response to platelet-activating factor, interleukin 1beta, and IgE/DNP-bovine serum albumin complexes. The response to bacterial lipopolysaccharide and dibutyryl cyclic adenosine monophosphate (AMP) was enhanced 24 h after challenge, but at earlier times was not significantly different from that observed in controls. Treatment with either sodium nitroprusside or SNAP produced a significant reduction of the haemorrhagic lesions, which are a hallmark of rat anaphylaxis. The extravasation of protein-rich plasma was not influenced by NO-donors. The increase of plasma histamine elicited by the anaphylactic challenge was not influenced by SNAP treatment. NO-donors protect intestinal haemorrhagic lesions of rat anaphylaxis by a mechanism apparently independent of mast cell histamine release.

Early and sharp nitric oxide production and anoxic depolarization in the rat hippocampus during transient forebrain ischemia

This study was designed to characterize nitric oxide (NO) production and anoxic depolarization in the rat hippocampus during transient forebrain ischemia using two NO synthase (NOS) inhibitors, L-N(5)-(1-iminoethyl)ornithine (L-NIO), a relatively selective endothelial NOS (eNOS) inhibitor, and 7-nitroindazole, a relatively selective neuronal NOS (nNOS) inhibitor, and an NO scavenger, [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] (carboxy-PTIO). We measured the mean arterial blood pressure, hippocampal blood flow, NO concentration and direct current potential before, during and after transient forebrain ischemia, which was induced by 4-vessel occlusion for 10 min. Saline, L-NIO (20 mg/kg), 7-nitroindazole (25 mg/kg), L-NIO (20 mg/kg)+7-nitroindazole (25 mg/kg) or carboxy-PTIO (1 mg/kg) was administered intraperitoneally 20 min before the onset of ischemia. We observed early and sharp NO production in the hippocampus during ischemia in the saline group. This NO increase during ischemia was significantly reduced by L-NIO (20 mg/kg)+7-nitroindazole (25 mg/kg) or carboxy-PTIO (1 mg/kg), but not L-NIO (20 mg/kg) or 7-nitroindazole (25 mg/kg). On the other hand, NO production after ischemia was significantly reduced by 7-nitroindazole (25 mg/kg), L-NIO (20 mg/kg)+7-nitroindazole (25 mg/kg) or carboxy-PTIO (1 mg/kg), but not L-NIO (20 mg/kg). The peak latency of NO production during ischemia always preceded the onset latency of anoxic depolarization in both the saline group and the carboxy-PTIO group. In the carboxy-PTIO group, the onset latency of anoxic depolarization was significantly longer than that in the saline group. Moreover, carboxy-PTIO significantly reduced the anoxic depolarization amplitude, compared with that of the saline group. These results suggest that both NOS-dependent and-independent NO formation contributes to early and sharp NO production during ischemia, and that this NO increase is, at least in part, related to the triggering of anoxic depolarization.

Association of Endothelin with Lung Hemorrhage Induced by Immune Complexes in Rats

The participation of endothelins (ETs) in a model of neutrophil-dependent lung injury induced by intrabronchial instillation of rabbit antibodies to ovalbumin followed by i.v. injection of the antigens (Arthus reaction) was investigated. Hemorrhagic lesions were evaluated by measuring the extravasations of hemoglobin in lung parenchyma. From 5 min to 24 h after the Arthus reaction (AR), endothelin (ir-ET) levels in bronchoalveolar lavage fluid (BALF) and in plasma were measured by radioimmunoassay. BALF levels of ir-ET were not different between control and AR animals for the first 90 min after the antigen challenge but increased from 2 to 24 h after induction of AR. ET levels in the plasma did not change from the respective controls over the same 24 h period. Increased ir-ET in BALF was not affected by pretreatment with L-NAME (30 mg/kg, i.v.). A PAF antagonist (BN52021; 5 and 10 mg/kg, i.v.) increased ET content in BALF and decreased the intensity of the AR. Thiorphan (2 mg/kg, i.v.) inhibited the AR-induced hemorrhagic lesions in lungs. An ET(A) receptor antagonist, BQ-123 (1 mg/kg, i.v.) potentiated, whereas the ET(B) antagonist, BQ-788 (1 mg/kg, i.v.) inhibited the lung hemorrhage. It is concluded that ETs are released during and play a role in the lung AR.

Adrenomedullin and total nitrite levels in children with Henoch-Schönlein purpura

Nitric oxide (NO) is synthesized from endothelium and has an important role in the control of vascular tonus. Adrenomedullin (AM) is a potent vasodilator, and cytoprotective peptide is produced not only in adrenal medulla, but also in the vascular smooth muscle and endothelial cells. To investigate the endothelial synthesis of AM and NO, and endothelial injury in Henoch-Schönlein purpura (HSP), we measured their levels in 16 children with HSP, who were evaluated during the acute and remission phases, and compared with 12 healthy controls. Plasma AM levels (pmol/ml) were significantly higher in acute phase children (46.87+/-11.49) than in those in remission (35.59+/-12.39, p<0.01) and controls (30.70+/-9.12, p<0.001). Similarly, plasma total nitrite levels (mumol/l) were higher in acute phase patients (47.50+/-12.30) than in those in remission (35.94+/-10.08, p<0.005) and controls (34.56+/-11.51, p<0.05). Urinary excretion of AM (pmol/mg creatinine) was higher in acute phase patients (53.85+/-23.22) than in remission patients (29.97+/-9.33, p<0.01) and controls (37.43+/-15.78, p<0.05). Patients had increased urinary nitrite excretion (mumol/mg creatinine) in acute phase (2.39+/-1.18) compared to those in remission (1.53+/-0.90, p<0.05) and controls (1.05+/-0.61, p<0.005). There was no significant difference between remission phase and controls in AM and nitrite levels ( p>0.05). This study concluded that AM and NO may have a role in the immunoinflammatory process of HSP, especially in the active stage, although whether this perpetuates, or protects against, further vascular injury is not clear. Further studies are needed to clearly establish the roles of AM and NO in the pathogenesis of HSP.

Simvastatin ameliorates injury in an experimental model of lung ischemia-reperfusion

OBJECTIVES

Statins are lipid-lowering drugs with anti-inflammatory and antioxidant properties. This study explores the potential of these commonly prescribed agents to ameliorate lung ischemia-reperfusion injury.

METHODS

Left lungs of Long-Evans rats were rendered ischemic for 90 minutes and reperfused for up to 4 hours. Treated animals received simvastatin orally (0.5 mg/kg) for 5 days before the experiment. Injury was quantitated in terms of tissue myeloperoxidase content, vascular permeability ((125)I bovine serum albumin extravasation), and bronchoalveolar lavage leukocyte and cytokine content. Changes in nuclear translocation of transcription factors were evaluated by electromobility shift assay. Additional animals received N(G)-nitro-L-arginine methyl ester before ischemia-reperfusion to assess whether inhibition of nitric oxide synthase could reverse simvastatin's protective effects. The presence of nicotinamide adenine dinucleotide phosphate oxidase was also evaluated using enzyme staining both histologically and in native electrophoresis.

RESULTS

Lung vascular permeability was reduced in treated animals by 71% compared with positive controls (P <.001). Administration of N(G)-nitro-L-arginine methyl ester reversed this protection. The protective effects of statin pretreatment correlated with a 68% reduction in tissue myeloperoxidase content (P <.01), marked reductions in bronchoalveolar lavage leukocyte accumulation, and decreased expression of proinflammatory cytokines. Nicotinamide adenine dinucleotide phosphate oxidase expression also decreased with statin treatment.

CONCLUSION

In addition to its antioxidant properties, the protective effects of simvastatin are likely mediated by modulation of endothelial nitric oxide synthase. The potential to pretreat recipients of lung transplantation with statins to ameliorate reperfusion injury is promising.

Role of nitric oxide in acute lung inflammation: lessons learned from the inducible nitric oxide synthase knockout mouse

OBJECTIVE

Acute lung inflammation is characterized by complex interactions among cytokines, chemokines, adhesion molecules, leukocytes, and other mediators. Proinflammatory cytokines have been implicated in the up-regulation of the inducible form of nitric oxide synthase (iNOS), which produces large amounts of nitric oxide (NO). Conversely, in some systems, NO regulates the expression of cytokines to affect leukocyte recruitment. Thus, the role of NO both exogenously administered and endogenously produced by iNOS in acute lung inflammation has not been fully elucidated. The current studies suggest a proinflammatory role for inhaled NO in a compartmentalized model of lung injury, whereas blocking of iNOS afforded protection. These results and other previous investigations have been complicated by the use of nonselective blockers of the iNOS isoform.

MEASUREMENTS AND MAIN RESULTS

In an attempt to circumvent this, we examined the response of the lung to direct endotoxin challenge in mice in which iNOS had been genetically deleted (iNOS-/-). We observed a significant decrease in the inflammatory response in the iNOS-/- mice compared with wild-type mice as characterized by decreases in neutrophil accumulation and cytokine expression. Additionally, the lung cytokine response in the iNOS-/- mice was characterized by a significant increase in interleukin-12 and an inability to up-regulate interleukin-10.

CONCLUSIONS

Induction of NO may be a key mediator in driving the cytokine response to endotoxin toward an increased type-2 (interleukin-10) response and a diminished type-1 (interleukin-12) response.

Different effects of eNOS and nNOS inhibition on transient forebrain ischemia

To clarify the functions of nitric oxide (NO) induced by either neuronal NO synthase (nNOS) or endothelial NO synthase (eNOS) after transient cerebral ischemia, we investigated the effects of L-N(5)-(1-iminoethyl)ornithine (L-NIO), a relatively selective eNOS inhibitor, and 7-nitroindazole (7-NI), a relatively selective nNOS inhibitor, on hippocampal dysfunction caused by cerebral ischemia. We measured mean arterial blood pressure (MABP), hippocampal blood flow, direct current (DC) potential, CA1 population spike (PS) and extracellular concentrations of glutamate from rat hippocampus after transient forebrain ischemia, which was induced by four-vessel occlusion for 10 min. L-NIO (20 mg/kg) and 7-NI (25 mg/kg) were administered intraperitoneally 20 min before ischemia. L-NIO, but not 7-NI, increased MABP before, during and after ischemia, compared with the vehicle group. 7-NI, but not L-NIO, reduced the amplitude of anoxic depolarization induced by ischemia. 7-NI recovered the PS amplitude in part 60 min after ischemia. 7-NI, but not L-NIO, reduced the ischemia-induced levels of glutamate. These results indicate that nNOS inhibition with 7-NI improves, at least in part, hippocampal dysfunction after ischemia, while eNOS inhibition with L-NIO worsens it.

Nitric oxide-peroxynitrite-poly(ADP-ribose) polymerase pathway in the skin

In the last decade it has become well established that in the skin, nitric oxide (NO), a diffusable gas, mediates various physiologic functions ranging from the regulation of cutaneous blood flow to melanogenesis. If produced in excess, NO combines with superoxide anion to form peroxynitrite (ONOO-), a cytotoxic oxidant that has been made responsible for tissue injury during shock, inflammation and ischemia-reperfusion. The opposite effects of NO and ONOO- on various cellular processes may explain the 'double-edged sword' nature of NO depending on whether or not cellular conditions favour peroxynitrite formation. Peroxynitrite has been shown to activate the nuclear nick sensor enzyme, poly(ADP-ribose) polymerase (PARP). Overactivation of PARP depletes the cellular stores of NAD+, the substrate of PARP, and the ensuing 'cellular energetic catastrophy' results in necrotic cell death. Whereas the role of NO in numerous skin diseases including wound healing, burn injury, psoriasis, irritant and allergic contact dermatitis, ultraviolet (UV) light-induced sunburn erythema and the control of skin infections has been extensively documented, the intracutaneous role of peroxynitrite and PARP has not been fully explored. We have recently demonstrated peroxynitrite production, DNA breakage and PARP activation in a murine model of contact hypersensitivity, and propose that the peroxynitrite-PARP route represents a common pathway in the pathomechanism of inflammatory skin diseases. Here we briefly review the role of NO in skin pathology and focus on the possible roles played by peroxynitrite and PARP in various skin diseases.

Nitrotyrosine formation and its role in various pathological conditions

The formation of peroxynitrite and nitrotyrosine was examined in a variety of in vitro and in vivo animal models and its relation to cell or tissue damage was examined. polymorphonuclear leukocyte (PMN)-induced injury to cardiac myocytes endothelial cells, activated PMN produced peroxynitrite. Peroxynitrite appears to be responsible for the injury but it was not a major mediator of endothelial cell injury. In the experiment of ischemia-reperfusion injury of the rat brain nitrotyrosine was formed in the peri-infarct and core-of infarct regions. The degradation curve of nitrotyrosine revealed that its t(1/2) was about 2.2 hours. In the radiation-induced lung injury of rats, nitrotyrosine was also formed but it was not the sole mechanism for the injury. Levels of nitrotyrosine correlated with the severity of myocardial dysfunction in the canine model of cytokine-induced cardiac injury. Inhibition of NO generation abolished the formation of peroxynitrite and nitrotyrosine in all experiments. In conclusion; although nitrotyrosine is formed in a variety of pathological conditions where the generation of NO is increased, its presence does not always correlate with the severity of injury.

Chitinous materials inhibit nitric oxide production by activated RAW 264.7 macrophages

Chitinous materials have been studied in wound healing and artificial skin substitutes for many years. Nitric oxide (NO) has been shown to contribute to cytotoxicity in cell proliferation during inflammation of wound healing. In this study, we examined the effect of chitin and its derivatives on NO production by activated RAW 264.7 macrophages. Chitin and chitosan showed a significantly inhibitory effect on NO production by the activated macrophages. Hexa-N-acetylchitohexaose and penta-N-acetylchitopentaose also inhibited NO production but with less potency. However, N-acetylchitotetraose, -triose, -biose, and monomer of chitin, N-acetylglucosamine and glucosamine had little effect on NO production by the activated cells. These results suggest that the promotive effect of chitinous material on wound healing be related, at least partly, to inhibit NO production by the activated macrophages.

Nitric oxide and its role in lipid peroxidation

Nitric oxide (NO) is a free radical with an unpaired electron in the highest orbital. This is why it behaves as a potential antioxidant agent by virtue of its ability to reduce other molecules. In vitro experiments support this concept inasmuch as NO is able to inhibit lipid peroxidation. However, NO is rapidly inactivated by the superoxide anion (O(*2) to form peroxynitrite (ONOO-), which is a potent oxidant. Therefore, in the presence of O(*2), NO behaves as a potent pro-oxidant. This is the mechanism that accounts for the low density lipoprotein (LDL) oxidation that occurs when NO and O(*2) are simultaneously present in the medium. As NO and O(*2) are simultaneously released by cells such as endothelial cells, the balance between these two radicals is crucial in understanding the net effect of NO on lipid peroxidation. Thus an excess of NO will favour lipid peroxidation inhibition, while an excess of O(*2) or equimolar concentration of NO and O(*2) will induce lipid peroxidation. Modulation of this balance may have important clinical implications, particularly in the atherosclerotic process in which oxidant stress seems to play a pivotal role in the onset and progression of vascular lesions.

Effects of NG-nitro L-arginine and corticosteroids on aqueous humor levels of nitric oxide and cytokines after cataract surgery

PURPOSE

To assess the efficacy of nitric oxide synthesis (NOS) inhibitor, topical steroids, and nonsteroidal anti-inflammatory drugs on aqueous levels of nitric oxide (NO) and cytokines after cataract surgery.

SETTING

Research Laboratory, Inonu University Turgut Ozal Medical Center, Malatya, Turkey.

METHODS

Fifteen rabbits had intercapsular phacoemulsification and were randomly divided into 3 treatment groups: Group 1 was treated with topical prednisolone acetate 1% drops 5 times a day for 1 week; Group 2, flurbiprofen 0.03% drops 5 times a day for 1 week; Group 3, a 0.1 cc subconjunctival injection of NG-nitro L-arginine (L-NAME) (150 mg/kg) 1 day and 3 days after surgery. Three rabbits serving as controls received a subconjunctival injection of an equal volume of balanced salt solution (BSS) at the same times as the L-NAME injections. Aqueous humor specimens were collected from each eye to determine NO and cytokine levels including interleukin-1-beta (IL-1 beta), interleukin-2R (IL-2R), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha).

RESULTS

The levels of IL-1 beta and IL-6 were higher in Group 2 and the control group than in Groups 1 and 3 at all times. The differences were not statistically significant (P < .05). Nitric oxide and TNF-alpha levels in Groups 1 and 3 were significantly lower than in Groups 2 and the controls 1, 3, and 7 days postoperatively (P < .05).

CONCLUSION

These findings suggest a strong inhibitory effect of NOS inhibitors and corticosteroids on aqueous levels of TNF-alpha and NO and no inhibitory effect on IL-1 beta and IL-6 levels after cataract surgery.

L-Arginine supplementation increases mesangial cell injury and subsequent tissue fibrosis in experimental glomerulonephritis

BACKGROUND

Mesangial cell lysis in the antithymocyte serum (ATS)-induced model of glomerulonephritis is dependent on the generation of cytotoxic nitric oxide (NO) through transient induction of NO synthase (iNOS). We hypothesized that increased availability of L-arginine (L-Arg) during mesangial cell lysis might provide iNOS with increased substrate leading to increased lysis, and that this increased lysis would be reflected in more severe fibrotic disease at day 6.

METHODS

To ensure whole body equilibration with high L-Arg at the time of injury, rats were pretreated with 1% L-Arg in drinking water for one week prior to the administration of ATS. Animals were sacrificed six hours after ATS injection when previous experiments had indicated iNOS induction had occurred and at six days. At six hours, plasma was obtained for L-Arg levels and nitrite/nitrate (NOx) content. Renal tissues were taken for histological evaluation of glomerular cell counts, macrophage infiltration (ED-1), and iNOS expression. Glomeruli were isolated for detection of iNOS mRNA and placed in culture to study the dependence of NO production on L-Arg concentration. In rats sacrificed at six days, L-Arg supplementation was stopped 16 hours after ATS injection. Fibrotic disease was evaluated by urinary protein excretion, histological assessment of glomerular cell number, matrix accumulation, and production of transforming growth factor-beta1 and matrix components fibronectin and plasminogen activator inhibitor type-1 (PAI-1) by isolated glomeruli in culture.

RESULTS

At six hours, the glomerular cell number was significantly reduced by ATS injection (P < 0.01) and further significantly (P < 0. 05) reduced by L-Arg feeding [normal control (NC) = 64.2 +/- 1, ATS = 53.4 +/- 0.7, ATS + L-Arg = 50.8 +/- 0.7]. Disease increased macrophage infiltration and iNOS protein and iNOS mRNA levels markedly (P < 0.01), whereas L-Arg feeding did not further increase these variables. Plasma L-Arg levels (nmol/ml) were reduced by disease (NC = 121 +/- 9, ATS = 84 +/- 13, P < 0.01) and elevated by L-Arg feeding (ATS + L-Arg = 166 +/- 12, P < 0.01). Plasma NOx was significantly increased by ATS and further increased by ATS + L-Arg (P < 0.05). Production of NOx by cultured glomeruli showed striking L-Arg concentration dependence in six hours but not in normal glomeruli. In the group sacrificed at day 6, day 2 proteinuria was higher in the ATS + L-Arg group compared with the ATS alone group (P < 0.05). Measures of fibrotic disease at day 6 all showed large increases over control with ATS alone (P < 0.01), and further small, but significant increases when L-Arg was combined with ATS (P < 0.05).

CONCLUSIONS

The results indicate that if given during disease induction, L-Arg supplementation can enhance iNOS-dependent tissue injury by providing increased substrate. Although the increase in injury with L-Arg supplementation was small, it led to increased fibrosis at day 6. These data predict that in diseases with repeated iNOS-dependent tissue injury, L-Arg supplementation may produce cumulative increases in tissue fibrosis.

Endothelium removal induces iNOS in rat aorta in organ culture, leading to tissue damage

After endothelial damage in vivo, there is an induction of nitric oxide synthase (NOS) in the underlying smooth muscle cells. We hypothesized that intrinsic factors could induce NOS independently of blood elements. This was tested using an in vitro organ culture technique. Rat aortas with endothelium removed before 24-h organ culture (ERB) failed to constrict to phenylephrine after culture, whereas with endothelium removal after culture there was a normal constrictor response. Constrictor activity in ERB aortas was restored by the concomitant treatment with either the protein synthesis inhibitor cycloheximide (1 microM) or the NOS inhibitor L-N5-(1-iminoethyl)ornithine hydrochloride (L-NIO, 100 microM). The ERB aortas also had an elevated NOS activity and induced NOS (iNOS) immunoreactivity. The constrictor response to phenylephrine in ERB aortas was only partially restored by acute application of L-NIO subsequent to the 24-h organ culture, which suggests that other effects during culture contributed to the diminished tissue response. When ERB aortas were treated with reduced glutathione (GSH, 3 mM for 24 h), acute application of L-NIO then fully restored the constrictor effect. This suggests that peroxynitrite produced during culture may in part be responsible for loss of constrictor effects, and this was substantiated by the presence of nitrated tyrosine residues in aortic proteins and also widespread DNA damage, which was prevented by both L-NIO and GSH. Thus some of the immediate (24-h) effects of endothelium removal involve intrinsic mechanisms resulting in iNOS synthesis, which leads to both nitric oxide and peroxynitrite generation, with resultant tissue damage and loss of contractile function.

Effect of inhibition of nitric oxide synthase on Pseudomonas aeruginosa infection of respiratory mucosa in vitro

We studied the effect of the nitric oxide synthase (NOS) inhibitor asymmetric dimethyl arginine (ADMA) and the inactive enantiomer N G-methyl-D-arginine (D-NMMA) on Pseudomonas aeruginosa infection of the respiratory mucosa in nasal turbinate organ cultures. We also investigated the effect of P. aeruginosa culture filtrate on the expression of inducible NOS (iNOS) messenger RNA (mRNA) by an epithelial cell line (A549). Organ cultures were preincubated with ADMA (0.1 to 4 x 10(-4) M) or D-NMMA (2 x 10(-4) M) for 30 min prior to bacterial infection. Infected organ cultures (8 h) had significantly (P <= 0.05) greater epithelial damage and fewer ciliated and unciliated cells than did control cultures. There was an increased level of nitrite in the medium feeding infected organ cultures as compared with control cultures. ADMA significantly (P <= 0.05) reduced both bacterially induced epithelial damage and loss of ciliated cells in a concentration-dependent manner. D-NMMA did not influence the effect of P. aeruginosa infection of the mucosa. ADMA, but not D-NMMA, significantly (P <= 0.04) reduced total bacterial numbers adherent to the respiratory mucosa. P. aeruginosa culture filtrates (24 h and 36 h) significantly (P = 0.02) increased iNOS with respect to glyceraldehyde-3-phosphate dehydrogenase mRNA expression. These results show that P. aeruginosa stimulates iNOS expression by a cell line and NO production by an organ culture. ADMA reduces mucosal damage and loss of ciliated cells, which suggests that NO may be a mediator of epithelial damage caused by P. aeruginosa.

Lipid mediators, tumor necrosis factor and nitric oxide and their interactions in immune-complex-induced lung injury

We investigated the contribution of eicosanoids, platelet-activating factor, tumor necrosis factor and nitric oxide to the neutrophil influx and development of pulmonary haemorrhagic lesions following immune-complex-induced pneumonitis in rats and possible interactions between these mediators. Increased levels of leukotriene B4 and tumor necrosis factor, measured by enzyme immunoassay and L-929 cytotoxicity assay, were found in the bronchoalveolar lavage 1 and 4 h after induction of the reaction, respectively, and their release was dependent on the previous generation of platelet activating factor. Antagonism of leukotriene B4 receptors by RO-0254094 (2-[(5-carboxypentyl])oxy]-6-[6-[3,4-dihydro-4-oxo-8-propyl-2H-1-benzopy ran-7-yl)oxy]hexyl] benzenepropanoic acid), inhibition of nitric oxide synthesis by L-NAME (Nw-nitro-L-arginine methyl ester) and antagonism of PAF-receptors by WEB-2170 (5-(2-chlorphenyl)-3-4-dihydro-10-methyl-3-((4-morpholinyl)carbony l)-2 H,7H-cyclopenta (4,5)thieno(3,2-f)(1,2,4)-triazolo-4,3,a)91,4)diazepine), significantly inhibited the intensity of haemorrhage, evaluated by the increased levels of extravascular hemoglobin in homogenates of lung tissues. Little evidence support the role of tumor necrosis factor in these lesions. The infiltration of neutrophils, evaluated by measuring myeloperoxidase in homogenates of lungs, was reduced by compounds L-663,536 (3-[1-(4 chlorobenzyl)-3-t-butyl thio-5-isopropylindol-2-yl]-2-2-dimethylpropanoic acid), WEB-2170 and L-NAME. These results indicate that neutrophil infiltration and haemorrhagic lesions in immune-complex-induced lung inflammation are mediated by platelet activating factor, leukotriene B4 and nitric oxide and point out to interesting interactions between these mediators.

Modulation of leukocyte-endothelial interactions by reactive metabolites of oxygen and nitrogen: relevance to ischemic heart disease

Ischemia and reperfusion (I/R) are thought to play an important role in the pathophysiology of ischemic diseases of the heart. It is now well appreciated that leukocyte-endothelial cell interactions are important determinants for I/R-induced microvascular injury and dysfunction. There is a growing body of experimental data to suggest that reactive metabolites of oxygen and nitrogen are important physiological modulators of leukocyte-endothelial cell interactions. A number of investigators have demonstrated that I/R enhances oxidant production within the microcirculation resulting in increases in leukocyte adhesion and transendothelial cell migration. Several other studies have shown that exogenous nitric oxide (NO) donors may attenuate leukocyte and platelet adhesion and/or aggregation in a number of different inflammatory conditions including I/R. The objective of this review is to discuss the physiological chemistry of reactive metabolites of oxygen and nitrogen with special attention given to those interactions that may modulate leukocyte-endothelial cell interactions, provide an overview of the evidence implicating reactive metabolites of oxygen and nitrogen as modulators of leukocyte-endothelial cell interactions in vivo, and discuss how these mechanisms may be involved in the pathophysiology of ischemic heart disease.

Aminoguanidine reduces glomerular inducible nitric oxide synthase (iNOS) and transforming growth factor-beta 1 (TGF-beta1) mRNA expression and diminishes glomerulosclerosis in NZB/W F1 mice

Over-expression of iNOS is implicated in the pathogenesis of glomerulonephritis in animal models of systemic lupus erythematosus. The aim of this study was to evaluate the effect of aminoguanidine, a selective inhibitor of iNOS, for the protection from glomerulosclerosis in NZB/W F1 mice. Female NZB/W F1 mice (n = 8) were treated with aminoguanidine (1 g/l) in drinking water for 4 months starting at age 2 months before the onset of glomerulonephritis. Controls were age- and sex-matched mice (n = 10) without aminoguanidine treatment. By glomerular microdissection and reverse-transcription competitive polymerase chain reaction, we found that glomerular iNOS/beta-actin and TGF-beta1/beta-actin mRNA ratios were reduced 15.1% (P<0.05) and 61.3% (P<0.01), respectively, in aminoguanidine-treated mice. Aminoguanidine significantly reduced the glomerular iNOS staining, urinary nitrite production and degree of glomerulosclerosis. In addition, the glomerular volume and mean glomerular cell number were reduced 33.2% (P<0.01) and 32.8% (P<0.01), respectively. Likewise, the urinary proteinuria was also significantly reduced by aminoguanidine. These results indicate that administration of aminoguanidine may reduce the progression of glomerulosclerosis in NZB/W F1 mice, possibly through inhibition of glomerular nitric oxide production.

The therapeutic potential of nitric oxide in lung transplantation

Endogenously produced oxides of nitrogen appear to play important roles in tissue and organ homeostasis. Endogenous production of nitric oxide, which can be altered in response to various stimuli, can modulate vascular tone, oxyradical cascades, cell adhesion, and other aspects of inflammation. Because exogenously administered (inhaled) nitric oxide can mediate pulmonary vasodilatation and improve pulmonary function in some patients with lung injury, treatment of lung allograft recipients with inhaled nitric oxide may ameliorate ischemia-reperfusion injury, thereby improving perioperative pulmonary function and diminishing ventilatory support requirements. This review examines the biology of nitric oxide and present data that support its potential therapeutic effects for lung transplant recipients.

Nitric oxide inhibition of lipid peroxidation: kinetics of reaction with lipid peroxyl radicals and comparison with alpha-tocopherol

The reaction between nitric oxide (*NO) and lipid peroxyl radicals (LOO*) has been proposed to account for the potent inhibitory properties of *NO toward lipid peroxidation processes; however, the mechanisms of this reaction, including kinetic parameters and nature of termination products, have not been defined. Here, the reaction between linoleate peroxyl radicals and *NO was examined using 2, 2'-azobis(2-amidinopropane) hydrochloride-dependent oxidation of linoleate. Addition of *NO (0.5-20 microM) to peroxidizing lipid led to cessation of oxygen uptake, which resumed at original rates when all *NO had been consumed. At high *NO concentrations (>3 microM), the time of inhibition (Tinh) of chain propagation became increasingly dependent on oxygen concentration, due to the competing reaction of oxygen with *NO. Kinetic analysis revealed that a simple radical-radical termination reaction (*NO:ROO* = 1:1) does not account for the inhibition of lipid oxidation by *NO, and at least two molecules of *NO are consumed per termination reaction. A mechanism is proposed whereby *NO first reacts with LOO* (k = 2 x 10(9) M-1 s-1) to form LOONO. Following decomposition of LOONO to LO* and *NO2, a second *NO is consumed via reaction with LO*, with the composite rate constant for this reaction being k = 7 x 10(4) M-1 s-1. At equal concentrations, greater inhibition of oxidation was observed with *NO than with alpha-tocopherol. Since *NO reacts with LOO* at an almost diffusion-limited rate, steady state concentrations of 30 nM *NO would effectively compete with endogenous alpha-tocopherol concentrations (about 20 microM) as a scavenger of LOO* in the lipid phase. This indicates that biological *NO concentrations (up to 2 microM) will significantly influence peroxidation reactions in vivo.

Interferon (IFN)-alpha activation of human blood mononuclear cells in vitro and in vivo for nitric oxide synthase (NOS) type 2 mRNA and protein expression: possible relationship of induced NOS2 to the anti-hepatitis C effects of IFN-alpha in vivo

Although researchers have noted high level activation of rodent mononuclear phagocytes for nitric oxide (NO) synthase type 2 (S2) expression and NO production with a variety of agents such as interferon (IFN) gamma and endotoxin, it has been difficult to demonstrate activation of human mononuclear phagocytes. The purpose of this study was to determine if IFN-alpha serves as an activator in vitro and in vivo in humans. Treatment of normal monocytes or mononuclear cells in vitro with IFN-alpha caused a dose-dependent increase in monocyte NOS2 activity and NO production, and increased expression of NOS2 protein and mRNA expression. To determine if in vivo administration of IFN-alpha also modulated NOS2, we studied blood cells from patients with hepatitis C before and after IFN-alpha therapy. Untreated patients with chronic hepatitis C virus infection had levels of NOS activity and NOS2 antigen in freshly isolated mononuclear cells similar to those of healthy subjects, and they expressed minimal or no NOS2 mRNA. However, IFN-alpha treatment of patients with hepatitis C infection was associated with a significant elevation in mononuclear cell NOS activity, NOS2 antigen content, and NOS2 mRNA content. IFN-alpha-treated patients had significant decreases in levels of serum alanine aminotransferase and plasma hepatitis C mRNA. The degree of IFN-alpha-enhanced mononuclear cell NOS2 antigen content correlated significantly with the degree of reduction in serum alanine aminotransferase levels. Thus, IFN-alpha treatment of cells in vitro or administration of IFN-alpha to hepatitis C patients in vivo increases expression of mononuclear cell NOS2 mRNA expression, NOS activity, NOS2 antigen expression, and NO production. Since NO has been reported to have antiviral activity for a variety of viruses, we speculate that induced NO production may be related to the antiviral action(s) of IFN-alpha in hepatitis C infection.

Clinical and serologic manifestations of autoimmune disease in MRL-lpr/lpr mice lacking nitric oxide synthase type 2

Nitric oxide (NO) is an important mediator of the inflammatory response. MRL-lpr/lpr mice overexpress inducible nitric oxide synthase (NOS2) and overproduce NO in parallel with the development of an autoimmune syndrome with a variety of inflammatory manifestations. In previous studies, we showed that inhibiting NO production with the nonselective nitric oxide synthase (NOS) inhibitor NG-monomethyl-arginine reduced glomerulonephritis, arthritis, and vasculitis in MRL-lpr/lpr mice. To define further the role of NO and NOS2 in disease in MRL-lpr/lpr mice, mice with targeted disruption of NOS2 were produced by homologous recombination and bred to MRL-lpr/lpr mice to the N4 generation. MRL-lpr/lpr littermates homozygous for disrupted NOS2 (-/-), heterozygous for disrupted NOS2 (+/-), or wildtype (+/+) were derived for this study. Measures of NO production were markedly decreased in the MRL-lpr/lpr (-/-) mice compared with MRL-lpr/lpr (+/+) mice, with intermediate production by the MRL-lpr/lpr (+/-) mice. There was no detectable NOS2 protein by immunoblot analysis of the spleen, liver, kidney, and peritoneal macrophages of the (-/-) animals, whereas that of (+/+) was high and (+/-) intermediate. The (-/-) mice developed glomerular and synovial pathology similar to that of the (+/-) and (+/+) mice. However, (-/-) mice and (+/-) mice had significantly less vasculitis of medium-sized renal vessels than (+/+) mice. IgG rheumatoid factor levels were significantly lower in the (-/-) mice as compared with (+/+) mice, but levels of anti-DNA antibodies were comparable in all groups. Our findings show that NO derived from NOS2 has a variable impact on disease manifestations in MRL-lpr/lpr mice, suggesting heterogeneity in disease mechanisms.

Persistence of effects of nitric oxide synthase inhibitors: comparisons on blood flow and plasma exudation in guinea pig skin

Plasma protein extravasation has been measured in guinea pig skin using 125I-albumin and blood flow using 133Xenon (133Xe) clearance. The nitric oxide (NO) synthase inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME), N(G)-monomethyl-L-arginine (l-NMMA) and N(G)-nitro-L-arginine (L-NOArg) and the alpha-adrenoceptor agonist, phenylephrine, inhibited bradykinin induced plasma protein extravasation when co-injected with the peptide. The inhibitory effects of L-NAME and L-NOArg lasted for up to 8 and 4 h, respectively, whereas phenylephrine and L-NMMA had no persistent inhibitory effects. When co-injected with 133Xe, L-NAME, L-NMMA, L-NOArg and phenylephrine, but not D-NAME, produced significant reductions in skin blood flow. When injected prior to 133Xe, L-NAME and L-NOArg, but not phenylephrine or L-NMMA, significantly reduced flow. The effect of L-NAME on flow was not significant at 8 h. Thus, although the inhibitory effects of the NO synthase inhibitors on mediator induced plasma protein extravasation show correlations with their effects on blood flow, the persistent effect of L-NAME on exudation appears to extend beyond its effect on flow.

Suppression of adjuvant arthritis and synovial macrophage inducible nitric oxide by N-iminoethyl-L-ornithine, a nitric oxide synthase inhibitor

Nitric oxide (NO.) is a pro-inflammatory effector molecule in certain inflammatory diseases, including arthritis. We investigated the production of NO. by adjuvant arthritis (AA) synovial macrophages, and studied the effects of a NO. synthase inhibitor. N-iminoethyl-L-ornithine (L-NIO). Compared to control rats, rats treated with L-NIO in vivo exhibited significantly lower articular index (p < 0.05), paw volume (p < 0.05), and synovial fluid cell count (p < 0.05). No effect on cutaneous delayed-type hypersensitivity to the disease-initiating antigen was observed. Inducible NO. synthase (iNOS) was detected in AA synovial macrophages, and cultured AA synovial macrophage iNOS levels were increased by a factor of 138 +/- 17% (p < 0.01) by 1 microgram/ml LPS in vitro. Constitutive NO. production by AA synovial macrophages (43 +/- 1 nmol/10(5) cells/24 h) was significantly inhibited by 10 nM L-NIO in vitro (32 +/- 0.5, p < 0.01). NO. production induced by 1 microgram/ml LPS (48 +/- 2) was also decreased by L-NIO (39 +/- 2, p < 0.05). In vivo L-NIO treatment also inhibited alveolar macrophage NO. production (p < 0.05). The ability of L-NIO to decrease iNOS-mediated synovial macrophage NO. production and inhibit the clinical parameters of AA implicate macrophage-derived NO. in the pathogenesis of this disease.

Role of complement, chemokines, and regulatory cytokines in acute lung injury

The roles of complement, proinflammatory cytokines and regulatory cytokines in lung inflammatory injury are becoming defined. Like the proinflammatory cytokines (TNF alpha and IL-1), complement activation products (C5a and/or the membrane attack complex, C5b-9) can directly activate endothelial cells to cause upregulation of adhesion molecules (P-selectin) or can function in a synergistic manner with TNF alpha to cause enhanced upregulation of ICAM-1 and E-selectin. The beta chemokine, MIP-1 alpha, appears to function in vivo as an autocrine activator, enhancing TNF alpha production by pulmonary macrophages, which, in turn, enhances the inflammatory response. Finally, IL-4 and IL-10 have strong regulatory effects by suppressing in vivo production of TNF alpha. There is now compelling evidence to suggest that, in IgG immune-complex-induced lung inflammation in rats, endogenous IL-10 is produced and regulates the intensity of the inflammatory response. Blocking of endogenous IL-10 substantially increases lung TNF alpha production, the recruitment of neutrophils, and the intensity of lung inflammatory injury. Accordingly, the network of cytokines carefully regulates lung inflammatory responses.

Increased nitric oxide formation in recurrent thrombotic microangiopathies: a possible mediator of microvascular injury

The term thrombotic microangiopathy (TMA) has been used extensively to encompass hemolytic uremic syndrome and thrombotic thrombocytopenic purpura, two syndromes of hemolytic anemia, and thrombocytopenia associated with renal or brain involvement or both. There is evidence that endothelial damage is a crucial feature in the sequence of events that precedes the development of microvascular lesions. More recent studies would suggest that endothelial dysfunction could be a consequence of neutrophil activation. Activated neutrophils generate superoxide anions (O2-) that, combining with endothelial-derived nitric oxide (NO), form the highly cytotoxic hydroxyl radical. Seven patients with recurrent forms of TMA and seven healthy volunteers were studied. Plasma concentrations of the NO metabolites, nitrites/nitrates, were elevated in the acute phase of TMA, indicating an increased NO synthesis in vivo. In addition, elevated serum concentrations of tumor necrosis factor, a potent inducer of endothelial NO synthase, were found in acute TMA. Serum from patients with acute TMA induced NO synthesis in cultured endothelial cells more than normal serum. Enhanced stimulatory activity was no longer found in the recovery phase. Release of O2- by neutrophils ex vivo was higher than normal in patients with acute TMA, but decreased in the recovery phase. Exactly the same trend was observed for plasma malondialdehyde and conjugated dienes, indicating that excessive oxygen radical formation in acute TMA is associated with increased lipid peroxidation. Thus, in recurrent forms of TMA, NO formation was increased as compared with controls. This was associated with signs of lipid peroxidation, likely the consequence of the interaction of NO with neutrophil-derived oxygen products.

Aggravation of experimental allergic encephalomyelitis (EAE) by administration of nitric oxide (NO) synthase inhibitors

Macrophages constitute a large proportion of the inflammatory cells that infiltrate the central nervous system (CNS) of animals with EAE. Through the production of inflammatory mediators these infiltrating macrophages can contribute to the regulation of the immune reaction within the CNS, that eventually results in neurological deficits associated with EAE. NO, a free radical produced by macrophages and other cell types, has been put forward as such an immune mediator. In the present study we show that macrophages isolated from the CNS of Lewis rats with clinical signs of EAE produce elevated amounts of NO. We treated rats, in which EAE was induced, with N(omega) -nitro-L-arginine-methylester or N(g)-monomethyl-L-arginine, inhibitors of NO synthase, either systemically via intraperitoneal injection, or intracerebrally via a cannula placed in the lateral ventricle. Both treatments resulted in a marked aggravation of clinical signs of EAE. These data point to an important role of NO, produced by infiltrating macrophages, as an immune-suppressor in the disease process during EAE.

Modulation of superoxide-dependent oxidation and hydroxylation reactions by nitric oxide

The rapid and spontaneous interaction between superoxide (O2-.) and nitric oxide (NO) to yield the potent oxidants peroxynitrite (ONOO-) and peroxynitrous acid (ONOOH), has been suggested to represent an important pathway by which tissue may be injured during inflammation. Although several groups of investigators have demonstrated substantial oxidizing and cytotoxic activities of chemically synthesized ONOO-, there has been little information available quantifying the interaction between O2-. and NO in the absence or the presence of redox-active iron. Using the hypoxanthine (HX)/xanthine oxidase system to generate various fluxes of O2-. and H2O2 and the spontaneous decomposition of the spermine/NO adduct to produce various fluxes of NO, we found that in the absence of redox-active iron, the simultaneous production of equimolar fluxes of O2-. and NO increased the oxidation of dihydrorhodamine (DHR) from normally undetectable levels to approximately 15 microM, suggesting the formation of a potent oxidant. Superoxide dismutase, but not catalase, inhibited this oxidative reaction, suggesting that O2-. and not hydrogen peroxide (H2O2) interacts with NO to generate a potent oxidizing agent. Excess production of either radical virtually eliminated the oxidation of DHR. In the presence of 5 microM Fe+3-EDTA to insure optimum O2-.-driven Fenton chemistry, NO enhanced modestly HX/xanthine oxidase-induced oxidation of DHR. As expected, both superoxide dismutase and catalase inhibited this Fe-catalyzed oxidation reaction. Excess NO production with respect to O2-. flux produced only modest inhibition (33%) of DHR oxidation. In a separate series of studies, we found that equimolar fluxes of O2-. and NO in the absence of iron only modestly enhanced hydroxylation of benzoic acid from undetectable levels to 0.6 microM 2-hydroxybenzoate. In the presence of 5 microM Fe+3-EDTA, HX/xanthine oxidase-mediated hydroxylation of benzoic acid increased dramatically from undetectable levels to 4.5 microM of the hydroxylated product. Superoxide dismutase and catalase were both effective at inhibiting this classic O2-.-driven Fenton reaction. Interestingly, NO inhibited this iron-catalyzed hydroxylation reaction in a concentration-dependent manner such that fluxes of NO approximating those of O2-. and H2O2 virtually abolished the hydroxylation of benzoic acid. We conclude that in the absence of iron, equimolar fluxes of NO and O2-. interact to yield potent oxidants such as ONOO-/ONOOH, which oxidize organic compounds. Excess production of either radical remarkably inhibits these oxidative reactions. In the presence of low molecular weight redox-active iron complexes, NO may enhance or inhibit O2-.-dependent oxidation and hydroxylation reactions depending upon their relative fluxes.

Nitric oxide and interleukin-8 as inflammatory components of cystic fibrosis

We examined the production of reactive nitrogen intermediates in the tracheo-bronchial tree of patients with cystic fibrosis (CF). Examination of the soluble phase of sputa from 17 CF patients revealed the presence of high levels of NO2-/NO3- assayed by the Greiss reaction. We also examined the presence of the chemotactic cytokine interleukin-8 (IL-8) in these samples so as to assess another important inflammatory marker; high levels of IL-8 were present in the sputa of cystic fibrosis subjects. The elevated nitrite was not produced by the presence of Pseudomonas bacteria in the sputa, inasmuch as bacteria in culture released undetectable amounts of nitrite in culture media. Neutrophils from the sputa of CF patients with disease exacerbation released higher amounts of nitrite and IL-8. Neutrophils from the sputa were also shown to spontaneously release substantial amounts of nitrite in the supernatants, and this release was partly blocked by the antagonist NG-mono-methyl-L-arginine (L-NMMA). Blood neutrophils were shown to release nitrite only in response to challenge with CF-associated strains of Pseudomonas, and not exposure to cytokines. There was no significant differences in nitrite release between normal and CF blood polymorphonuclear leucocytes (PMNs). A study of upper airway epithelial cell lines showed that these cells released low amounts of nitrite after infection with CF-associated strains of Pseudomonas but not after cytokine exposure. Epithelial cell lines with CF or normal phenotypes were shown to release similar quantities of nitrite, upon stimulation with Pseudomonas. These data demonstrate that elevated levels of reactive nitrogen intermediates and IL-8 are produced in the tracheo-bronchial tree of subjects with CF. Levels of IL-8 and nitrite were higher in the secretions of CF subjects with disease exacerbation. The involvement of nitric oxide and other reactive nitrogen intermediates produced by neutrophils and other cells in the tissue damaging processes in CF deserves further investigation.

The involvement of nitric oxide in a mouse model of adult respiratory distress syndrome

The release of free radicals and pro-inflammatory cytokines such as nitric oxide (NO) and tumor necrosis factor alpha (TNF alpha) is commonly observed in adult respiratory distress syndrome (ARDS) following infection or exposure to microbial products. The aim of this study was to scrutinize the involvement of NO in ARDS in a mouse model determined by the sequential exposure to lipopolysaccharide (LPS) and formyl-norleucyl-phenylalanine (FNLP). Nitrite measurements in bronchoalveolar lavage fluids (BALF) and sera demonstrated that exposure to microbial products elicits large amounts of NO in LPS/FNLP-challenged mice. This release was significantly inhibited by infusion with the inducible NO synthase antagonist, aminoguanidine (AG). Our results show that LPS/FNLP exposure induces lung damage as demonstrated by protein and lactate dehydrogenase (LDH) increases in BALF. Liver damage was also detected in LPS/FNLP-challenged mice with increases in serum ornithine-carbamoyltransferase (OCT) levels. LPS/FNLP infusion led to elevated levels of the cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF alpha) in the sera. LPS/FNLP also led to neutrophil adhesion in the lung vasculature, as seen by increased levels of myeloperoxydase. Interestingly, inhibition of NO release in challenged mice led to an important increase in markers of tissue damage in the lungs and livers, but a decrease in neutrophil recruitment. Infusion of AG in LPS/FNLP-challenged mice led to a much increased level of sera TNF alpha. These data suggest that after exposure to microbial products, NO generated as a result of activation of the inducible NO synthase blocks the full expression of tissue damage in the lungs.

The role of nitric oxide in lipoxin A4-induced polymorphonuclear neutrophil-dependent cytotoxicity to human vascular endothelium in vitro

OBJECTIVE

To assess the mechanism for the cytotoxicity of human polymorphonuclear neutrophils (PMN) to human umbilical vein endothelial cells (HUVEC) induced by the 5- and 15-lipoxygenase product of arachidonate, lipoxin A4 (LXA4), and the phorbol ester, phorbol myristate acetate (PMA).

METHODS

HUVEC were grown to confluence and labeled with 51Cr. PMN and stimuli were added, and the release of 51Cr into supernatants was assessed after 4 hours.

RESULTS

Both LXA4 and PMA conferred highly significant PMN-dependent cytolysis. The cytotoxicity activated by LXA4 was inhibited by NG-monomethyl-L-arginine (L-NMA) and by nitro-L-arginine methyl ester, specific inhibitors of the nitric oxide (NO)-producing enzyme NO synthase. Also, the scavenger of extracellular NO, oxyhemoglobin (HbO2), prevented LXA4-induced cytolysis in a dose-dependent manner. In sharp contrast, L-NMA did not significantly affect the cytolysis induced by PMA, whereas HbO2 showed a modest inhibitory action. In experiments without PMN, addition of the NO donor S-nitroso-N-acetyl-penicillamine to HUVEC induced marked cytolysis, which was inhibited by HbO2, but not by L-NMA. Addition of L-arginine or arginine analogs did not affect superoxide anion production in a cell-free hypoxanthine/xanthine oxidase system. Both LXA4 and PMA induced the production of superoxide anion from PMN and of NO from HUVEC:

CONCLUSION

NO produced by HUVEC, interacting with PMN which produce superoxide anions, is of marked significance for the endothelial cell damage in this in vitro model of vasculitis. This is probably due to the subsequent formation, via a radical-radical interaction between NO and .O2-, of cytotoxic products, such as peroxynitrite and its metabolites. Furthermore, although LXA4 and PMA induced comparable cytolysis at optimal concentrations, the relative importance of NO compared with other mechanisms mediating cytotoxicity was stimulus dependent, and NO was relatively more important for LXA4-induced PMN-dependent endothelial injury.

Nitric oxide-based possibilities for pharmacotherapy

The goal of nitric oxide (NO) based pharmacotherapy is to reach proper homeostasis of NO metabolism in the target tissue where endogenous production of NO is either too weak or excessively increased. In addition to the classic NO-based therapy of cardiovascular conditions with nitrates, a variety of new therapeutic possibilities have emerged including sexual disorders, gastrointestinal system, immunology, tumour growth regulation and respiratory disorders. NO levels of target tissues can be affected directly by NO donors, or indirectly by increasing the level of L-arginine, a substrate of nitric oxide synthase (NOS). While increased production of NO by induceable NO (iNOS) by, for example, cytokines does not at present seem therapeutically meaningful, increased NO production by constitutive NOS (cNOS) may be involved in the beneficial effects of ACE inhibitors or oestrogens. NO production may be pharmacologically decreased by inhibition of expression of iNOS by glucocorticoids while both cNOS and iNOS derived NO production is inhibited by administration of false substrates, for example L-NAME. Additionally, the respiratory system and related vessels can be reached directly and more selectively by inhalation of pure NO gas. Possible problems in administering NO and perhaps some NO-donors include the toxic nature of the compound itself whereby vital enzyme systems may be inhibited and tissue damaging radicals formed. Future prospects of NO-based pharmacotherapy may feature selective ligands to different NOS isoforms and tissue selective donors that release NO in a controlled fashion.

Potential role of nitric oxide in a model of chronic colitis in rhesus macaques

BACKGROUND/AIMS

Excess nitric oxide formation, via the inducible NO synthase isoform, has been implicated in the pathogenesis of experimental and clinical inflammatory bowel disease. The aim of this study was to assess the site, enzyme source, and magnitude of NO production in juvenile rhesus macaques with idiopathic colitis.

METHODS

NO production was assessed systemically from plasma and urine levels of reactive nitrogen intermediates and locally by the formation of [3H]citrulline from [3H]arginine and reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry. Inducible NO synthase gene expression was assessed by reverse-transcription polymerase chain reaction.

RESULTS

Plasma and urine levels of reactive nitrogen intermediates were greater in colitic animals than in control monkeys by 13- and 5-fold, respectively. NADPH diaphorase activity in normal animals was confined to the myenteric plexus. In colitis, staining was also apparent in crypt abscesses and superficial epithelial and mucosal bands. Gene expression for inducible NO synthase was only found in colitic specimens. Colonic [3H]citrulline formation was markedly elevated in colitic specimens, and the inducible isoform accounted for 58% of total activity.

CONCLUSIONS

It is proposed that excess NO, formed via the inducible form of NO synthase, contributes to the mucosal inflammation and symptoms of this idiopathic colitis model.

Platelet-activating factor: the effector of protein-rich plasma extravasation and nitric oxide synthase induction in rat immune complex peritonitis

1. The involvement of platelet-activating factor (PAF) in immune complex-induced/polymorphonuclear-mediated tissue injury was studied by use of a reverse passive Arthus (RPA) model in the peritoneal cavity of rats. 2. Extravasation of protein-rich plasma, accumulation of polymorphonuclear leukocytes (PMN), and the production of nitric oxide (NO) by resident peritoneal mononuclear phagocytes were assayed. 3. Treatment of rats with either UR-12460 or BB-823, two compounds which possess different chemical structures, but elicit the same antagonistic effect on the PAF receptor, abrogated protein-rich plasma extravasation. In contrast, they did not show any effect on the accumulation of PMN. 4. Inhibition of NO production with both NG-mono methyl-L-arginine and NG-nitro-L-arginine failed to prevent protein-rich plasma extravasation. 5. The production of NO by peritoneal adherent cells following RPA was measured in cells maintained for 2 to 28 h in culture, and it was significantly increased in cells removed as early as 15 min after RPA induction, as compared to controls. 6. Addition of 10 nM PAF to the culture medium reduced the generation of NO by peritoneal cells from RPA rats, whereas this mediator enhanced NO production in cells from naive control animals. 7. Treatment with either UR-12460 or BB-823 prior to the induction of RPA produced an almost complete inhibition of NO production. 8. Assay of nitric oxide synthase activity in cell homogenates from peritoneal cells showed that the activity was due to the inducible form of the enzyme. 9. Study by Northen blotting of mRNA coding for the inducible NO synthase (iNOS) showed transcription at 6 and 18 h after the induction of RPA, which was inhibited in UR-12460-treated rats.10. These data indicate that PAF is the main mediator of the early plasma leakage observed in RPA,and also that PAF is implicated in the triggering of long-term changes via induction of specific genes, as judged from its ability to promote the expression of iNOS.

Interactions between cytokines and nitric oxide

There is now an impressive range of evidence supporting the important role of cytokines in sleep regulation (see Krueger et al., 1995; De Simoni et al., 1995). It has also been reported that inhibition of nitric oxide (NO) synthesis suppresses sleep in rabbits (Kapás et al., 1994). This is not surprising, since NO is closely involved in neurotransmission (Garthwaite, 1991; Schuman and Madison, 1994) and cytokines are the major inducers of NO synthesis (Hibbs et al., 1990). Further, it is now clear that NO plays an important role in modulating immune responses, possibly through the differential regulation of cytokine synthesis (Taylor-Robinson et al., 1994). In this article, I will provide evidence for the interactions between cytokines and nitric oxide, and discuss their implications in the regulation of immune responses. I shall illustrate these mainly with results from my coworkers and I, from our laboratory rather than attempting an exhaustive review of the subject.