Concurrent generation of nitric oxide and superoxide damages surfactant protein A

Reversal of high-glucose-induced transcriptional and epigenetic memories through NRF2 pathway activation

Diabetes complications such as nephropathy, retinopathy, or cardiovascular disease arise from vascular dysfunction. In this context, it has been observed that past hyperglycemic events can induce long-lasting alterations, a phenomenon termed "metabolic memory." In this study, we evaluated the genome-wide gene expression and chromatin accessibility alterations caused by transient high-glucose exposure in human endothelial cells (ECs) in vitro. We found that cells exposed to high glucose exhibited substantial gene expression changes in pathways known to be impaired in diabetes, many of which persist after glucose normalization. Chromatin accessibility analysis also revealed that transient hyperglycemia induces persistent alterations, mainly in non-promoter regions identified as enhancers with neighboring genes showing lasting alterations. Notably, activation of the NRF2 pathway through NRF2 overexpression or supplementation with the plant-derived compound sulforaphane, effectively reverses the glucose-induced transcriptional and chromatin accessibility memories in ECs. These findings underscore the enduring impact of transient hyperglycemia on ECs' transcriptomic and chromatin accessibility profiles, emphasizing the potential utility of pharmacological NRF2 pathway activation in mitigating and reversing the high-glucose-induced transcriptional and epigenetic alterations.

Halogen-Induced Chemical Injury to the Mammalian Cardiopulmonary Systems

The halogens chlorine (Cl₂) and bromine (Br₂) are highly reactive oxidizing elements with widespread industrial applications and a history of development and use as chemical weapons. When inhaled, depending on the dose and duration of exposure, they cause acute and chronic injury to both the lungs and systemic organs that may result in the development of chronic changes (such as fibrosis) and death from cardiopulmonary failure. A number of conditions, such as viral infections, coexposure to other toxic gases, and pregnancy increase susceptibility to halogens significantly. Herein we review their danger to public health, their mechanisms of action, and the development of pharmacological agents that when administered post-exposure decrease morbidity and mortality.

NOS-2 Inhibition in Phosgene-Induced Acute Lung Injury

Phosgene exposure via an industrial or warfare release produces severe acute lung injury (ALI) with high mortality, characterized by massive pulmonary edema, disruption of epithelial tight junctions, surfactant dysfunction, and oxidative stress. There are no targeted treatments for phosgene-induced ALI. Previous studies demonstrated that nitric oxide synthase 2 (NOS-2) is upregulated in the lungs after phosgene exposure; however, the role of NOS-2 in the pathogenesis of phosgene-induced ALI remains unknown. We previously demonstrated that NOS-2 expression in lung epithelium exacerbates inhaled endotoxin-induced ALI in mice, mediated partially through downregulation of surfactant protein B (SP-B) expression. Therefore, we hypothesized that a selective NOS-2 inhibitor delivered to the lung epithelium by inhalation would mitigate phosgene-induced ALI. Inhaled phosgene produced increases in bronchoalveolar lavage fluid protein, histologic lung injury, and lung NOS-2 expression at 24 h. Administration of the selective NOS-2 inhibitor 1400 W via inhalation, but not via systemic delivery, significantly attenuated phosgene-induced ALI and preserved epithelial barrier integrity. Furthermore, aerosolized 1400 W augmented expression of SP-B and prevented downregulation of tight junction protein zonula occludens 1 (ZO-1), both critical for maintenance of normal lung physiology and barrier integrity. We also demonstrate for the first time that NOS-2-derived nitric oxide downregulates the ZO-1 expression at the transcriptional level in human lung epithelial cells, providing a novel target for ameliorating vascular leak in ALI. Our data demonstrate that lung NOS-2 plays a critical role in the development of phosgene-induced ALI and suggest that aerosolized NOS-2 inhibitors offer a novel therapeutic strategy for its treatment.

Resolution of experimental lung injury by monocyte-derived inducible nitric oxide synthase

Although early events in the pathogenesis of acute lung injury (ALI) have been defined, little is known about the mechanisms mediating resolution. To search for determinants of resolution, we exposed wild type (WT) mice to intratracheal LPS and assessed the response at intervals to day 10, when injury had resolved. Inducible NO synthase (iNOS) was significantly upregulated in the lung at day 4 after LPS. When iNOS-/- mice were exposed to intratracheal LPS, early lung injury was attenuated; however, recovery was markedly impaired compared with WT mice. iNOS-/- mice had increased mortality and sustained increases in markers of lung injury. Adoptive transfer of WT (iNOS+/+) bone marrow-derived monocytes or direct adenoviral gene delivery of iNOS into injured iNOS-/- mice restored resolution of ALI. Irradiated bone marrow chimeras confirmed the protective effects of myeloid-derived iNOS but not of epithelial iNOS. Alveolar macrophages exhibited sustained expression of cosignaling molecule CD86 in iNOS-/- mice compared with WT mice. Ab-mediated blockade of CD86 in iNOS-/- mice improved survival and enhanced resolution of lung inflammation. Our findings show that monocyte-derived iNOS plays a pivotal role in mediating resolution of ALI by modulating lung immune responses, thus facilitating clearance of alveolar inflammation and promoting lung repair.

Pathophysiological roles of peroxynitrite in circulatory shock

Peroxynitrite is a reactive oxidant produced from nitric oxide and superoxide, which reacts with proteins, lipids, and DNA, and promotes cytotoxic and proinflammatory responses. Here, we overview the role of peroxynitrite in various forms of circulatory shock. Immunohistochemical and biochemical evidences demonstrate the production of peroxynitrite in various experimental models of endotoxic and hemorrhagic shock both in rodents and in large animals. In addition, biological markers of peroxynitrite have been identified in human tissues after circulatory shock. Peroxynitrite can initiate toxic oxidative reactions in vitro and in vivo. Initiation of lipid peroxidation, direct inhibition of mitochondrial respiratory chain enzymes, inactivation of glyceraldehyde-3-phosphate dehydrogenase, inhibition of membrane Na+/K+ ATPase activity, inactivation of membrane sodium channels, and other oxidative protein modifications contribute to the cytotoxic effect of peroxynitrite. In addition, peroxynitrite is a potent trigger of DNA strand breakage, with subsequent activation of the nuclear enzyme poly(ADP-ribose) polymerase, which promotes cellular energetic collapse and cellular necrosis. Additional actions of peroxynitrite that contribute to the pathogenesis of shock include inactivation of catecholamines and catecholamine receptors (leading to vascular failure) and endothelial and epithelial injury (leading to endothelial and epithelial hyperpermeability and barrier dysfunction), as well as myocyte injury (contributing to loss of cardiac contractile function). Neutralization of peroxynitrite with potent peroxynitrite decomposition catalysts provides cytoprotective and beneficial effects in rodent and large-animal models of circulatory shock.

Modification of surfactant protein D by reactive oxygen-nitrogen intermediates is accompanied by loss of aggregating activity, in vitro and in vivo

Surfactant protein D (SP-D) is an important effector of innate immunity. We have previously shown that SP-D accumulates at sites of acute bacterial infection and neutrophil infiltration, a setting associated with the release of reactive species such as peroxynitrite. Incubation of native SP-D or trimeric SP-D lectin domains (NCRDs) with peroxynitrite resulted in nitration and nondisulfide cross-linking. Modifications were blocked by peroxynitrite scavengers or pH inactivation of peroxynitrite, and mass spectroscopy confirmed nitration of conserved tyrosine residues within the C-terminal neck and lectin domains. Mutant NCRDs lacking one or more of the tyrosines allowed us to demonstrate preferential nitration of Tyr314 and the formation of Tyr228-dependent cross-links. Although there was no effect of peroxynitrite or tyrosine mutations on lectin activity, incubation of SP-D dodecamers or murine lavage with peroxynitrite decreased the SP-D-dependent aggregation of lipopolysaccharide-coated beads, supporting our hypothesis that defective aggregation results from abnormal cross-linking. We also observed nitration, cross-linking of SP-D, and a significant decrease in SP-D-dependent aggregating activity in the lavage of mice acutely exposed to nitrogen dioxide. Thus, modification of SP-D by reactive oxygen-nitrogen species could contribute to alterations in the structure and function of SP-D at sites of inflammation in vivo.

Physiopathological effects of the NO donor 3-morpholinosydnonimine on rat cortical synaptosomes

The NO donor 3-Morpholinosydnonimine (SIN-1) releases NO in the presence of molecular oxygen. In this study, we evaluated the effect of SIN-1 on mitochondria of rat cortical synaptosomes. We demonstrated in vitro that the amount of ONOO(-) generated and H(2)O(2) formation directly correlated with SIN-1 concentration. The mean oxygen consumption by synaptosomal mitochondria was approximately 3.8 nmol of O(2) min(-1) mg(-1) protein, which decreased significantly in the presence of SIN-1 1 mM to 2.5 nmol O(2) min(-1) mg(-1). This decrease was not modified by catalase or Trolox, demonstrating that ONOO(-) was responsible for the effect. The same concentration of SIN-1 caused a significant decrease of ATP production by synaptosomal mitochondria and depolarized the mitochondrial membrane. Moreover, ROS production increased progressively and was completely inhibited by pre-incubation of synaptosomes with Trolox. Finally, phosphatidylserine was externalized and, at the same time, intrasynaptosomal lactate dehydrogenase decreased confirming both, the external membrane breakdown after the addition of SIN-1 and the damage to the synaptosomes.

Mitigation of chlorine-induced lung injury by low-molecular-weight antioxidants

Chlorine (Cl(2)) is a highly reactive oxidant gas used extensively in a number of industrial processes. Exposure to high concentrations of Cl(2) results in acute lung injury that may either resolve spontaneously or progress to acute respiratory failure. Presently, the pathophysiological sequelae associated with Cl(2)-induced acute lung injury in conscious animals, as well as the cellular and biochemical mechanisms involved, have not been elucidated. We exposed conscious Sprague-Dawley rats to Cl(2) gas (184 or 400 ppm) for 30 min in environmental chambers and then returned them to room air. At 1 h after exposure, rats showed evidence of arterial hypoxemia, respiratory acidosis, increased levels of albumin, IgG, and IgM in bronchoalveolar lavage fluid (BALF), increased BALF surfactant surface tension, and significant histological injury to airway and alveolar epithelia. These changes were more pronounced in the 400-ppm-exposed rats. Concomitant decreases of ascorbate (AA) and reduced glutathione (GSH) were also detected in both BALF and lung tissues. In contrast, heart tissue AA and GSH content remained unchanged. These abnormalities persisted 24 h after exposure in rats exposed to 400 ppm Cl(2). Rats injected systemically with a mixture of AA, deferoxamine, and N-acetyl-L-cysteine before exposure to 184 ppm Cl(2) had normal levels of AA, lower levels of BALF albumin and normal arterial Po(2) and Pco(2) values. These findings suggest that Cl(2) inhalation damages both airway and alveolar epithelial tissues and that resulting effects were ameliorated by prophylactic administration of low-molecular-weight antioxidants.

Animal models of acute lung injury

Acute lung injury in humans is characterized histopathologically by neutrophilic alveolitis, injury of the alveolar epithelium and endothelium, hyaline membrane formation, and microvascular thrombi. Different animal models of experimental lung injury have been used to investigate mechanisms of lung injury. Most are based on reproducing in animals known risk factors for ARDS, such as sepsis, lipid embolism secondary to bone fracture, acid aspiration, ischemia-reperfusion of pulmonary or distal vascular beds, and other clinical risks. However, none of these models fully reproduces the features of human lung injury. The goal of this review is to summarize the strengths and weaknesses of existing models of lung injury. We review the specific features of human ARDS that should be modeled in experimental lung injury and then discuss specific characteristics of animal species that may affect the pulmonary host response to noxious stimuli. We emphasize those models of lung injury that are based on reproducing risk factors for human ARDS in animals and discuss the advantages and disadvantages of each model and the extent to which each model reproduces human ARDS. The present review will help guide investigators in the design and interpretation of animal studies of acute lung injury.

Potential Benefits of Peroxynitrite

Peroxynitrite (PN) is generated by the reaction of nitric oxide (NO) and superoxide in one of the most rapid reactions in biology. Studies have reported that PN is a cytotoxic molecule that contributes to vascular injury in a number of disease states. However, it has become apparent that PN has beneficial effects including vasodilation, inhibition of platelet aggregation, inhibition of inflammatory cell adhesion, and protection against ischemia/reperfusion injury in the heart. It is our hypothesis that PN may serve to inactivate superoxide and prolong the actions of NO in the circulation. This manuscript reviews the beneficial effects of PN in the cardiovascular system.

Protective role of Bacillus anthracis exosporium in macrophage-mediated killing by nitric oxide

The ability of the endospore-forming, gram-positive bacterium Bacillus anthracis to survive in activated macrophages is key to its germination and survival. In a previous publication, we discovered that exposure of primary murine macrophages to B. anthracis endospores upregulated NOS 2 concomitant with an .NO-dependent bactericidal response. Since NOS 2 also generates O(2).(-), experiments were designed to determine whether NOS 2 formed peroxynitrite (ONOO(-)) from the reaction of .NO with O(2).(-) and if so, was ONOO(-) microbicidal toward B. anthracis. Our findings suggest that ONOO(-) was formed upon macrophage infection by B. anthracis endospores; however, ONOO(-) does not appear to exhibit microbicidal activity toward this bacterium. In contrast, the exosporium of B. anthracis, which exhibits arginase activity, protected B. anthracis from macrophage-mediated killing by decreasing .NO levels in the macrophage. Thus, the ability of B. anthracis to subvert .NO production has important implications in the control of B. anthracis-induced infection.

Effects of macrophage inducible nitric oxide synthase in murine septic lung injury

Inducible nitric oxide synthase (iNOS) contributes importantly to septic pulmonary protein leak in mice with septic acute lung injury (ALI). However, the role of alveolar macrophage (AM) iNOS in septic ALI is not known. Thus we assessed the specific effects of AM iNOS in murine septic ALI through selective AM depletion (via intratracheal instillation of clodronate liposomes) and subsequent AM reconstitution (via intratracheal instillation of donor iNOS+/+ or iNOS−/− AM). Sepsis was induced by cecal ligation and perforation, and ALI was assessed at 4 h: protein leak by the Evans blue (EB) dye method, neutrophil infiltration via myeloperoxidase (MPO) activity, and pulmonary iNOS mRNA expression via RT-PCR. In iNOS+/+ mice, AM depletion attenuated the sepsis-induced increases in pulmonary microvascular protein leak (0.3 ± 0.1 vs. 1.4 ± 0.1 μg EB·g lung−1·min−1; P < 0.05) and MPO activity (37 ± 4 vs. 67 ± 8 U/g lung; P < 0.05) compared with that shown in non-AM-depleted mice. In AM-depleted iNOS+/+ mice, septic pulmonary protein leak was restored by AM reconstitution with iNOS+/+ AM (0.9 ± 0.3 μg EB·g lung−1·min−1) but not with iNOS−/− donor AM. In iNOS−/− mice, sepsis did not induce pulmonary protein leak or iNOS mRNA expression, despite increased pulmonary MPO activity. However, AM depletion in iNOS−/− mice and subsequent reconstitution with iNOS+/+ donor AM resulted in significant sepsis-induced pulmonary protein leak and iNOS expression. Septic pulmonary MPO levels were similar in all AM-reconstituted groups. Thus septic pulmonary protein leak is absolutely dependent on the presence of functional AM and specifically on iNOS in AM. AM iNOS-dependent pulmonary protein leak was not mediated through changes in pulmonary neutrophil influx.

Peroxynitrite mediates TNF-alpha-induced endothelial barrier dysfunction and nitration of actin

We tested the hypothesis that tumor necrosis factor (TNF)-alpha induces a peroxynitrite (ONOO(-))-dependent increase in permeability of pulmonary microvessel endothelial monolayers (PMEM) that is associated with generation of nitrated beta-actin (NO(2)-beta-actin). The permeability of PMEM was assessed by the clearance rate of Evans blue-labeled albumin. beta-Actin was extracted from PMEM lysate with a DNase-Sepharose column. The extracted beta-actin was quantified in terms of its nitrotyrosine/beta-actin ratio with anti-nitrotyrosine and anti-beta-actin antibodies, sequentially, by dot-blot assays. The cellular compartmentalization of NO(2)-beta-actin was displayed by showing confocal localization of nitrotyrosine-immunofluorescence with beta-actin-immunofluorescence but not with F-actin fluorescence. Incubation of PMEM with TNF (100 ng/ml) for 0.5 and 4.0 h resulted in increases in permeability to albumin. There was an increase in the nitrotyrosine/beta-actin ratio at 0.5 h with minimal association of the NO(2)-beta-actin with F-actin polymers. The TNF-induced increase in the nitrotyrosine/beta-actin ratio and permeability were prevented by the anti-ONOO(-) agent Urate. The data indicate that TNF induces an ONOO(-)-dependent barrier dysfunction, which is associated with the generation of NO(2)-beta-actin.

Nitric oxide decreases surfactant protein gene expression in primary cultures of type II pneumocytes

Inhaled nitric oxide (NO) is a selective pulmonary vasodilator effective in treating persistent pulmonary hypertension in newborns and in infants following congenital heart disease surgery. Recently, multiple in vivo and in vitro studies have shown a negative effect of NO on surfactant activity as well as surfactant protein gene expression. Although the relationship between NO and surfactant has been studied previously, the data has been hard to interpret due to the model systems used. The objective of the current study was to characterize the effect of NO on surfactant protein gene expression in primary rat type II pneumocytes cultured on a substratum that promoted the maintenance of type II cell phenotype. Exposure to a NO donor, S-nitroso-N-acetylpenicillamine (SNAP), decreased surfactant protein (SP)-A, (SP)-B, and (SP)-C mRNA levels in type II pneumocytes in a time- and dose-dependent manner. The effect was mediated in part by an increase in endothelin-1 secretion and a decrease in the intracellular messenger, phosphorylated ERK1/2 mitogen-activated protein kinases (MAPK). Exposing type II pneumocytes to endothelin-1 receptor antagonists PD-156707 or bosentan before exposure to SNAP partially prevented the decrease in surfactant protein gene expression. The results showed that NO mediated the decrease in surfactant protein gene expression at least in part through an increase in endothelin-1 secretion and a decrease in phosphorylated ERK1/2 MAPKs.

Absence of host tumor necrosis factor receptor 1 attenuates manifestations of idiopathic pneumonia syndrome

The interaction of TNF-alpha with TNF receptor 1 (TNFR1) activates several signal transduction pathways that lead to apoptosis or NF-kappa B-dependent inflammation and immunity. We hypothesized that host TNFR1 expression contributes to noninfectious lung injury and inflammation commonly observed after bone marrow transplantation (BMT), termed idiopathic pneumonia syndrome (IPS). C57BL/6 TNFR1-sufficient (TNFR1(+/+)) and -deficient (TNFR1(-/-)) mice were total body irradiated with or without cyclophosphamide conditioning and were given bone marrow plus IPS-inducing donor spleen T cells from B10.BR wild-type mice. TNFR1(-/-) recipient mice exhibited improved early post-BMT survival associated with decreased permeability edema. In addition, the low lung compliance measured in anesthetized, ventilated TNFR1(+/+) mice on day 7 after BMT was restored to baseline during TNFR1 deficiency. Importantly, bronchoalveolar lavage fluid (BALF) inflammatory cells from TNFR1(-/-) vs. TNFR1(+/+) mice generated less nitric oxide (.NO) and nitrating species and exhibited suppressed programmed cell death as assessed using flow cytometry. However, cellular infiltration and levels of proinflammatory cytokines and chemokines were generally higher in BALF collected on day 7 after BMT from TNFR1(-/-) compared with TNFR1(+/+) recipient mice. Our results support a major role of host TNFR1 in regulation of .NO production and lung dysfunction after allogeneic BMT.

Mutations in the extracellular loop of alpha-rENaC alter sensitivity to amiloride and reactive species

We studied the effects of two mutations of the extracellular loop of the alpha-subunit of the (ENaC) on amiloride-sensitive current in Xenopus laevis oocytes and the inhibition of this current by 3-morpholinosydnonimine (SIN-1). Injection of oocytes with wild-type (wt) alpha-,beta-,gamma-rENaC cRNA (8.3 ng/subunit) resulted 48-72 h later in inward Na(+) currents (-5.5 +/- 0.8 microA; means +/- SE at -100 mV; n = 21), which were completely inhibited by amiloride. Oocytes injected with either alpha(Y279A)- or alpha(Y283A)- and beta-,gamma-rENaC cRNAs had significantly lower Na(+) currents. Furthermore, alpha(Y279A)-,beta-,gamma-rENaC-injected oocytes had a higher K(i) for amiloride (0.54 +/- 0.97 vs. 0.10 +/- 0.04 microM; P < 0.01). Exposure of oocytes to SIN-1 (1 mM) for 5 min decreased both total Na(+) and amiloride-sensitive currents across wt and alpha(Y279A)- but not alpha(Y283A)-,beta-,gamma-rENaC. Furthermore, exposure to SIN-1 increased the K(i) for amiloride across wt but not alpha(Y279A)-,beta-,gamma-rENaC-injected oocytes. These data indicate that both tyrosines are important for proper ENaC function and their oxidative modifications contribute to altered ENaC function.

Increased pulmonary blood flow does not alter surfactant protein gene expression in lambs within the first week of life

Neonates and infants with congenital heart disease with increased pulmonary blood flow suffer morbidity from poor oxygenation and decreased lung compliance. In a previous experiment involving 4-wk-old lambs with pulmonary hypertension secondary to increased pulmonary blood flow following an in utero placement of an aortopulmonary vascular graft, we found a decrease in surfactant protein (SP)-A gene expression as well as a decrease in SP-A and SP-B protein contents. To determine the timing of these changes, the objective of the present study was to characterize the effect of increased pulmonary blood flow and pulmonary hypertension on SP-A, -B, and -C gene expressions and protein contents within the first week of life. Of eight fetal lambs that underwent the in utero placement of the shunt, there was no difference in the expression of SP-A, -B, and -C mRNA levels or SP-A and -B protein contents compared with age-matched controls. The results showed that, in this model of congenital heart disease with pulmonary hypertension and increased pulmonary blood flow, the effect of the shunt on SP gene expression and protein content was not apparent within the first week of life.

Human SP-A genetic variants and bleomycin-induced cytokine production by THP-1 cells: effect of ozone-induced SP-A oxidation

Surfactant protein A (SP-A) plays a role in innate host defense. Human SP-A is encoded by two functional genes (SP-A1 and SP-A2), and several alleles have been characterized for each gene. We assessed the effect of in vitro expressed human SP-A genetic variants, on TNF-alpha and IL-8 production by THP-1 cells in the presence of bleomycin, either before or after ozone-induced oxidation of the variants. The oligomerization of SP-A variants was also examined. We found 1) cytokine levels induced by SP-A2 (1A, 1A(0)) were significantly higher than those by SP-A1 (6A(2), 6A(4)) in the presence of bleomycin. 2) In the presence of bleomycin, ozone-induced oxidation significantly decreased the ability of 1A and 1A/6A(4), but not of 6A(4), to stimulate TNF-alpha production. 3) The synergistic effect of bleomycin/SP-A, either before or after oxidation, can be inhibited to the level of bleomycin alone by surfactant lipids. 4) Differences in oligomerization were also observed between SP-A1 and SP-A2. The results indicate that differences among SP-A variants may partly explain the individual variability of pulmonary complications observed during bleomycin chemotherapy and/or in an environment that may promote protein oxidation.

Inhaled nitric oxide increases surfactant protein gene expression in the intact lamb

Inhaled nitric oxide (iNO) is used to treat a number of disease processes. Although in vitro data suggest that nitric oxide (NO) alters surfactant protein gene expression, the effects in vivo have not been studied. The objective of this study was to evaluate the effects of iNO on surfactant protein (SP)-A, -B, and -C gene expression in the intact lamb. Thirteen 4-wk-old lambs were mechanically ventilated with 21% oxygen and received iNO at 40 ppm (n = 7) or vehicle gas (n = 6) for 24 h. Peripheral lung biopsies were obtained at 0, 12, and 24 h and analyzed for surfactant mRNA, protein, and total DNA content. Inhaled NO increased SP-A and SP-B mRNA content by 80% from 0 to 12 h and by 78 and 71%, respectively, from 0 to 24 h. There was an increase in SP-A and SP-B protein content by 45% from 0 to 12 h, and a decrease by 70 and 65%, respectively, from 0 to 24 h. DNA content was unchanged. The mechanisms and physiological effects of these findings warrant further investigation.

Cellular antiendotoxin activities of lung surfactant protein C in lipid vesicles

The respiratory system is continuously exposed to airborne particles containing lipopolysaccharide. Our laboratory established previously that the hydrophobic surfactant protein C (SP-C) binds to lipopolysaccharide and to one of its cellular receptors, CD14. Here we examined the influence of SP-C, and of a synthetic analog, on some cellular in vitro effects of lipopolysaccharide. When associated with vesicles of dipalmitoylphosphatidylcholine, SP-C inhibits the binding of a tritium-labeled lipopolysaccharide to the macrophage cell line RAW 264.7. Under similar conditions of presentation, SP-C inhibits the mitogenic effect of lipopolysaccharide on mouse splenocytes, and inhibits the lipopolysaccharide-induced production of tumor necrosis factor-alpha by peritoneal and alveolar macrophages, and of nitric oxide by RAW 264.7 cells. In contrast, tumor necrosis factor-alpha production induced by a lipopeptide, and nitric oxide production induced by picolinic acid, were not affected by SP-C. The lipopolysaccharide-binding capacity of SP-C is resistant to peroxynitrite, a known mediator of acute lung injury formed by reaction of nitric oxide with superoxide anions. These results indicate that SP-C may play a role in lung defense; SP-C resists degradation under inflammatory conditions and traps lipopolysaccharide, preventing it from inducing production of noxious mediators in alveolar cells.

Pseudomonas aeruginosa elastase degrades surfactant proteins A and D

Both in vitro and in vivo studies provide evidence that surfactant protein (SP)-A and SP-D have an important role in the innate immune response to Pseudomonas aeruginosa. In preliminary experiments characterizing the binding of SP-A to this bacteria, we observed the appearance of apparent degradation products of SP-A, and therefore we hypothesized that P. aeruginosa produces an enzyme that degrades SP-A. Incubation of SP-A with P. aeruginosa organisms from several clinical isolates resulted in concentration- and temperature-dependent degradation of SP-A that was inhibited by a metalloproteinase inhibitor, phosphoramidon. The degradative enzyme was purified by anion exchange chromatography and identified by ion trap mass spectroscopy as Pseudomonas elastase, which was shown to directly degrade SP-A and SP-D. Incubation of P. aeruginosa or purified elastase with cell-free bronchoalveolar lavage (BAL) resulted in degradation of SP-A. Furthermore, SP-A degradation fragments were detectable in BAL from lung transplant patients with cystic fibrosis. We speculate that degradation of SP-A and SP-D is a virulence mechanism in the pathogenesis of chronic P. aeruginosa infection.

Peroxynitrite causes endothelial cell monolayer barrier dysfunction

Nitric oxide (.NO) attenuates hydrogen peroxide (H(2)O(2))-mediated barrier dysfunction in cultured porcine pulmonary artery endothelial cells (PAEC) (Gupta MP, Ober MD, Patterson C, Al-Hassani M, Natarajan V, and Hart, CM. Am J Physiol Lung Cell Mol Physiol 280: L116-L126, 2001). However,.NO rapidly combines with superoxide (O) to form the powerful oxidant peroxynitrite (ONOO(-)), which we hypothesized would cause PAEC monolayer barrier dysfunction. To test this hypothesis, we treated PAEC with ONOO(-) (500 microM) or 3-morpholinosydnonimine hydrochloride (SIN-1; 1-500 microM). SIN-1-mediated ONOO(-) formation was confirmed by monitoring the oxidation of dihydrorhodamine 123 to rhodamine. Both ONOO(-) and SIN-1 increased albumin clearance (P < 0.05) in the absence of cytotoxicity and altered the architecture of the cytoskeletal proteins actin and beta-catenin as detected by immunofluorescent confocal imaging. ONOO(-)-induced barrier dysfunction was partially reversible and was attenuated by cysteine. Both ONOO(-) and SIN-1 nitrated tyrosine residues, including those on beta-catenin and actin, and oxidized proteins in PAEC. The introduction of actin treated with ONOO(-) into PAEC monolayers via liposomes also resulted in barrier dysfunction. These results indicate that ONOO(-) directly alters endothelial cytoskeletal proteins, leading to barrier dysfunction.

Roles for platelet-activating factor and *NO-derived oxidants causing neutrophil adherence after CO poisoning

Studies were conducted with rats to investigate whether platelet activating factor (PAF) and nitric oxide (*NO)-derived oxidants played roles in the initial adherence of neutrophils to vasculature in the brain after carbon monoxide (CO) poisoning. Before CO poisoning, rats were treated with the competitive PAF receptor antagonist WEB-2170 or with the peroxynitrite scavenger selenomethionine. Both agents caused significantly lower concentrations of myeloperoxidase in the brain after poisoning, indicating fewer sequestered neutrophils. Similarly, both agents reduced the concentration of nitrotyrosine, indicating less oxidative stress due to *NO-derived oxidants. There were no alterations in whole brain homogenate PAF concentration measured by immunoassay and bioassay, nor were there changes in phosphatidylcholine concentration. Immunohistochemical imaging showed PAF to be more heavily localized within perivascular zones after CO poisoning. Neutrophils colocalized with both PAF and nitrotyrosine in brains of rats killed immediately after CO poisoning. We conclude that qualitative changes in brain PAF are responsible for neutrophil adherence immediately after CO poisoning and that activated neutrophils trigger the initial rise in brain nitrotyrosine. Persistent PAF-mediated neutrophil adherence required production of *NO-derived oxidants because when oxidants were scavenged, neutrophil adherence was not maintained.

iNOS upregulation mediates oxidant-induced disruption of F-actin and barrier of intestinal monolayers

Using oxidant-induced hyperpermeability of monolayers of intestinal (Caco-2) cells as a model for the pathophysiology of inflammatory bowel disease (IBD), we previously showed that oxidative injury to the F-actin cytoskeleton is necessary for the disruption of monolayer barrier integrity. We hypothesized that this cytoskeletal damage is caused by upregulation of an inducible nitric oxide (NO) synthase (iNOS)-driven pathway that overproduces reactive nitrogen metabolites (RNMs) such as NO and peroxynitrite (OONO(-)), which cause actin nitration and disassembly. Monolayers were exposed to H(2)O(2) or to RNMs with and without pretreatment with antioxidants or iNOS inhibitors. H(2)O(2) concentrations that disassembled and/or disrupted the F-actin cytoskeleton and barrier integrity also caused rapid iNOS activation, NO overproduction, and actin nitration. Added OONO(-) mimicked H(2)O(2); iNOS inhibitors and RNM scavengers were protective. Our results show that oxidant-induced F-actin and intestinal barrier disruption are caused by rapid iNOS upregulation that further increases oxidant levels; a similar positive feedback mechanism may underlie the episodic recurrence of the acute IBD attack. Confirming these mechanisms in vivo would provide a rationale for developing novel anti-RNM therapies for IBD.

Carbon dioxide enhances nitration of surfactant protein A by activated alveolar macrophages

We assessed whether reactive oxygen-nitrogen intermediates generated by alveolar macrophages (AMs) oxidized and nitrated human surfactant protein (SP) A. SP-A was exposed to lipopolysaccharide (100 ng/ml)-activated AMs in 15 mM HEPES (pH 7.4) for 30 min in the presence and absence of 1.2 mM CO(2). In the presence of CO(2), lipopolysaccharide-stimulated AMs had significantly higher nitric oxide synthase (NOS) activity (as quantified by the conversion of L-[U-(14)C]arginine to L-[U-(14)C]citrulline) and secreted threefold higher levels of nitrate plus nitrite in the medium [28 +/- 3 vs. 6 +/- 1 (SE) nmol. 6.5 h(-1). 10(6) AMs(-1)]. Western blotting studies of immunoprecipitated SP-A indicated that CO(2) enhanced SP-A nitration by AMs and decreased carbonyl formation. CO(2) (0-1.2 mM) also augmented peroxynitrite (0.5 mM)-induced SP-A nitration in a dose-dependent fashion. Peroxynitrite decreased the ability of SP-A to aggregate lipids, and this inhibition was augmented by 1.2 mM CO(2). Mass spectrometry analysis of chymotryptic fragments of peroxynitrite-exposed SP-A showed nitration of two tyrosines (Tyr(164) and Tyr(166)) in the absence of CO(2) and three tyrosines (Tyr(164), Tyr(166), and Tyr(161)) in the presence of 1.2 mM CO(2). These findings indicate that physiological levels of peroxynitrite, produced by activated AMs, nitrate SP-A and that CO(2) increased nitration, at least partially, by enhancing enzymatic nitric oxide production.

High-dose nitric oxide inhalation increases lung injury after gastric aspiration

BACKGROUND

Inhaled nitric oxide is often used in patients with adult respiratory distress syndrome. However, nitric oxide also may be significantly toxic, especially if administered concurrently with hyperoxia. The authors evaluated the isolated effect of nitric oxide and the combined effects of nitric oxide and hyperoxia on lung injury in rats after acid aspiration.

METHODS

Animals were injured by instillation of 1.2 ml/kg hydrogen chloride in low-pH saline (the acid group) or acidified gastric particles (the casp group) into the lungs under halothane anesthesia via a tracheal catheter. Controls received no injury vehicle but rather underwent the surgical process. After recovery from anesthesia, the animals were exposed to 20% or 90% oxygen with or without 20, 40, or 80 ppm nitric oxide for 5 h. The permeability index, alveolar-arterial oxygen difference, the ratio of oxygen pressure to the inspired fraction of oxygen, and the ratio of wet to dry weight were assessed 5 h after injury as indices of lung injury. Data were assessed using analysis of variance.

RESULTS

Each group included 6-10 rats. Exposure to nitric oxide (80 ppm) in air increased protein permeability in the lungs to a permeability index of 1.42+/-0.12 after acid aspiration. The combination of nitric oxide (80 ppm) and hyperoxia further increased protein leakage to a permeability index of 2.1+/-0.25. Exposure to lower concentrations of nitric oxide (e.g., 20 and 40 ppm) increased the permeability index of the lungs (1.44+/-0.21, 1.75+/-0.29, respectively) in the presence of hyperoxia, although it did not affect the permeability index of the lungs during exposure to air. Pretreatment of animals with deferoxamine and methylene blue partially inhibited the adverse effect of hyperoxia and nitric oxide, which suggested a complex underlying mechanism involving both reactive-species generation and pulmonary vasomotor changes.

CONCLUSIONS

These results show that inhaled nitric oxide at 80 ppm for a short duration (5 h) increases the severity of the inflammatory microvascular lung injury after acid aspiration. The pulmonary damage is exacerbated further in the presence of high oxygen concentrations. Although lower concentrations of nitric oxide did not increase the extent of lung injury, longer exposure times need to be assessed.

Effects of reactive oxygen and nitrogen metabolites on RANTES- and IL-5-induced eosinophil chemotactic activity in vitro

Eosinophils and increased production of nitric oxide (NO) and superoxide, components of peroxynitrite, have been implicated in the pathogenesis of a number of allergic disorders including asthma. Peroxynitrite induced protein nitration may compromise enzyme and protein function. We hypothesized that peroxynitrite may modulate eosinophil migration by modulating chemotactic cytokines. To test this hypothesis, the eosinophil chemotactic responses of regulated on activation, normal T cell expressed and secreted (RANTES) and interleukin (IL)-5 incubated with and without peroxynitrite were evaluated. Peroxynitrite-attenuated RANTES and IL-5 induced eosinophil chemotactic activity (ECA) in a dose-dependent manner (P < 0.05) but did not attenuate leukotriene B4 or complement-activated serum ECA. The reducing agents deferoxamine and dithiothreitol reversed the ECA inhibition by peroxynitrite, and exogenous L-tyrosine abrogated the inhibition by peroxynitrite. PAPA-NONOate, a NO donor, or superoxide generated by lumazine or xanthine and xanthine oxidase, did not show an inhibitory effect on ECA. The peroxynitrite generator, 3-morpholinosydnonimine, caused a concentration-dependent inhibition of ECA. Peroxynitrite reduced RANTES and IL-5 binding to eosinophils and resulted in nitrotyrosine formation. These findings are consistent with nitration of tyrosine by peroxynitrite with subsequent inhibition of RANTES and IL-5 binding to eosinophils and suggest that peroxynitrite may play a role in regulation of eosinophil chemotaxis.

Comparative effects of several nitric oxide donors on intracellular cyclic GMP levels in bovine chromaffin cells: correlation with nitric oxide production

1. Sodium nitroprusside, S-nitroso-N-acetyl-D,L-penicillamine, Spermine NONOate and DEA NONOate raised cyclic GMP levels in bovine chromaffin cells in a time and concentration dependent manner with different potencies, the most potent being DEA/NO with an EC50 value of 0.38 +/- 0.02 microM. 2. Measurements of NO released from these donors revealed that DEA/NO decomposed with a half-life (t1/2) of 3.9 +/- 0.2 min. The t1/2 for SPER/NO was 37 +/- 3 min. SNAP decomposed more slowly (t1/2 = 37 +/- 4 h) and after 60 min the amount of NO produced corresponded to less than 2% of the total SNAP present. The rate of NO production from SNAP was increased by the presence of glutathione. 3. For DEA/NO and SPER/NO there was a clear correlation between nitric oxide production and cyclic GMP increases. Their threshold concentrations were 0.05 microM and maximal effective concentration between 2.5 and 5 microM. 4. For SNAP, threshold activation was seen at 1 microM, whereas full activation required a higher concentration (500-750 microM). The dose-response for SNAP increases in cyclic GMP was shifted nearly two orders of magnitude lower in the presence of glutathione. At higher concentrations an inhibition of cyclic GMP accumulation was found. This effect was not observed with either the nitric oxide-deficient SNAP analogue or other NO donors. 5. Although NO-donors are likely to be valuable for studying NO functions, their effective concentrations and the amount of NO released by them are very different and should be assessed in each system to ensure that physiological concentrations of NO are used.

Peroxynitrite Mediates IL-8 Gene Expression and Production in Lipopolysaccharide-Stimulated Human Whole Blood

Recent evidence indicates that free oxygen radicals, in particular hydroxyl radicals, may act as intracellular second messengers for the induction of IL-8, a potent chemoattractant and activator of neutrophil granulocytes. Here we report that peroxynitrite (ONOO−), formed by a reaction of nitric oxide (NO) with superoxide, mediates IL-8 gene expression and IL-8 production in LPS-stimulated human whole blood. The NO synthase inhibitors aminoguanidine and NG-nitro-l-arginine methyl ester (L-NAME) blocked IL-8 release by ∼90% in response to LPS (1 μg/ml), but did not affect the production of IL-1β or TNF-α. Both aminoguanidine and L-NAME blocked the induction of IL-8 mRNA by LPS. Authentic ONOO− (2.5–80 μM) augmented IL-8 mRNA expression and stimulated IL-8 release in a concentration-dependent manner, whereas the NO-releasing compounds, S-nitroso-N-acetyl-dl-penicillamine and sodium nitroprusside failed to induce cytokine production. Combination of the NO-generating chemicals with a superoxide-generating system (xanthine/xanthine oxidase) markedly increased IL-8 release. Enhanced ONOO− formation was detected in granulocytes, monocytes, lymphocytes, and plasma after challenge with LPS. Furthermore, pyrrolidine dithiocarbamate, an inhibitor of activation of nuclear factor-κB, markedly attenuated the induction of IL-8 mRNA expression and IL-8 release by either LPS or ONOO−. Our study identifies ONOO− as a novel signaling mechanism for IL-8 gene expression and suggests that inhibition of ONOO− formation or scavenging ONOO− may represent a novel therapeutic approach to inhibit IL-8 production that could lead to reduction of neutrophil accumulation and activation.

Asbestos inhalation induces reactive nitrogen species and nitrotyrosine formation in the lungs and pleura of the rat

To determine whether asbestos inhalation induces the formation of reactive nitrogen species, three groups of rats were exposed intermittently over 2 wk to either filtered room air (sham-exposed) or to chrysotile or crocidolite asbestos fibers. The rats were killed at 1 or 6 wk after exposure. At 1 wk, significantly greater numbers of alveolar and pleural macrophages from asbestos-exposed rats than from sham-exposed rats demonstrated inducible nitric oxide synthase protein immunoreactivity. Alveolar macrophages from asbestos-exposed rats also generated significantly greater nitrite formation than did macrophages from sham-exposed rats. Strong immunoreactivity for nitrotyrosine, a marker of peroxynitrite formation, was evident in lungs from chrysotile- and crocidolite-exposed rats at 1 and 6 wk. Staining was most evident at alveolar duct bifurcations and within bronchiolar epithelium, alveolar macrophages, and the visceral and parietal pleural mesothelium. Lungs from sham-exposed rats demonstrated minimal immunoreactivity for nitrotyrosine. Significantly greater quantities of nitrotyrosine were detected by ELISA in lung extracts from asbestos-exposed rats than from sham-exposed rats. These findings suggest that asbestos inhalation can induce inducible nitric oxide synthase activation and peroxynitrite formation in vivo, and provide evidence of a possible alternative mechanism of asbestos-induced injury to that thought to be induced by Fenton reactions.

3-Nitrotyrosine in the proteins of human plasma determined by an ELISA method

The modification of tyrosine residues in proteins to 3-nitrotyrosine by peroxynitrite or other potential nitrating agents has been detected in biological systems that are subject to oxidative stress. A convenient semi-quantitative method has been developed to assay nitrated proteins in biological fluids and homogenates using a competitive ELISA developed in our laboratory. This assay selectivity detected 3-nitro-l-tyrosine residues in a variety of peroxynitrite-treated proteins (BSA, human serum albumin (HSA), alpha1-antiprotease inhibitor, pepsinogen and fibrinogen) and also in a nitrated peptide, but had a low affinity for free 3-nitro-L-tyrosine and 3-chloro-L-tyrosine. The IC50 values for the inhibition of antibody binding by different nitrated proteins were in the range 5-100 nM, suggesting that the antibody discriminated between nitrotyrosine residues in different environments. The presence of nitrotyrosine in plasma proteins was detected by Western blot analysis and quantified by the ELISA. A concentration of 0. 12+/-0.01 microM nitro-BSA equivalents was measured in the proteins of normal plasma which was increased in peroxynitrite-treated plasma and was elevated in inflammatory conditions. HSA and low-density lipoprotein (LDL) isolated from plasma contained 0.085+/-0.04 and 0. 03+/-0.006 nmol nitro-BSA equivalents/mg protein, respectively. Comparison of the level of nitration in peroxynitrite-treated HSA and LDL in the presence and absence of plasma indicates that nitration and presumably oxidation is inhibited by plasma antioxidants. The presence of nitrotyrosine in LDL is consistent with previous reports implicating peroxynitrite in the oxidative modification of lipoproteins and the presence of a low concentration of oxidized LDL in the blood.

Cytokine-treated human neutrophils contain inducible nitric oxide synthase that produces nitration of ingested bacteria

Although the production of NO within rodent phagocytes is well-characterized, its production and function within human phagocytes are less clear. We show here that neutrophils within human buffy coat preparations stimulated with a mixture of interleukin 1, tumor necrosis factor alpha, and interferon gamma contain inducible NO synthase mRNA and protein, one of the enzymes responsible for NO production. The protein colocalizes with myeloperoxidase within neutrophil primary granules. Using an inhibitor of NO synthase, L-N-monomethyl arginine, we show that activity of this enzyme is required for the formation of nitrotyrosine around phagocytosed bacteria, most likely through the intermediate production of peroxynitrite, a reaction product of NO and superoxide anions.

DNA strand breakage, activation of poly (ADP-ribose) synthetase, and cellular energy depletion are involved in the cytotoxicity of macrophages and smooth muscle cells exposed to peroxynitrite

The free radicals nitric oxide and superoxide anion react to form peroxynitrite (ONOO-), a highly toxic oxidant species. In vivo formation of ONOO- has been demonstrated in shock and inflammation. Herein we provide evidence that cytotoxicity in cells exposed to ONOO- is mediated by DNA strand breakage and the subsequent activation of the DNA repair enzyme poly(ADP ribose) synthetase (PARS). Exposure to ONOO- (100 microM to 1 mM) inhibited mitochondrial respiration in cultured J774 macrophages and in rat aortic smooth muscle cells. The loss of cellular respiration was rapid, peaking 1-3 h after ONOO- exposure, and reversible, with recovery after a period of 6-24 h. The inhibition of mitochondrial respiration was paralleled by a dose-dependent increase in DNA strand breakage, reaching its maximum at 20-30 min after exposure to ONOO-. We observed a dose-dependent increase in the activity of PARS in cells exposed to ONOO-. Inhibitors of PARS such as 3-aminobenzamide (1 mM) prevented the inhibition of cellular respiration in cells exposed to ONOO-. Activation of PARS by ONOO--mediated DNA strand breakage resulted in a significant decrease in intracellular energy stores, as reflected by a decline of intracellular NAD+ and ATP content. 3-Aminobenzamide prevented the loss of NAD+ and ATP in cells exposed to ONOO-. In contrast, impairment of cellular respiration by the addition of the nitric oxide donors S-nitroso-N-acetyl-DL-penicillamine or diethyltriamine nitric oxide complex, was not associated with the development of DNA strand breaks, in concentrations up to 1 mM, and was largely refractory to PARS inhibition. Our results suggest that DNA damage and activation of PARS, an energy-consuming futile repair cycle, play a central role in ONOO--mediated cellular injury.

Increased expression and activity of sodium channels in alveolar type II cells of hyperoxic rats

We investigated the cellular and molecular events associated with the increase in sodium transport across the alveolar epithelium of rats exposed to hyperoxia (85% O2 for 7 days followed by 100% O2 for 4 days). Alveolar type II (ATII) cell RNA was isolated and probed with a cDNA for one of the rat colonic epithelial sodium channel subunits (alpha rENaC). The alpha rENaC mRNA (3.7-kb transcript) increased 3-fold in ATII cell RNA isolated from rats exposed to 85% O2 for 7 days and 6-fold after 4 days of subsequent exposure to 100% O2. In situ hybridization revealed increased expression of alpha rENaC mRNA transcripts in both airway and alveolar epithelial cells of hyperoxic rats. When immunostained with a polyclonal antibody to kidney sodium channel protein, ATII cells from hyperoxic rats exhibited a significant increase in the amount of immunogenic protein present in both the plasma membrane and the cytoplasm. When patched in the whole-cell mode, ATII cells from hyperoxic rats exhibited amiloride and 5-(N-ethyl-N-isopropyl)-2',4'-amiloride (EIPA)-sensitive currents that were 100% higher compared with those obtained from air-breathing rats. Single-channel sodium currents (mean conductance of 25 pS) were seen in ATII cells patched in both the inside-out and cell-attached modes. The number and open probability of these channels increased significantly during exposure to hyperoxia. Exposure to sublethal hyperoxia up-regulated both alpha rENaC mRNA and the functional expression of sodium channels in ATII cells.

Quantitation of nitrotyrosine levels in lung sections of patients and animals with acute lung injury

Activated alveolar macrophages and epithelial type II cells release both nitric oxide and superoxide which react at near diffusion-limited rate (6.7 x 10(9) M-1s-1) to form peroxynitrite, a potent oxidant capable of damaging the alveolar epithelium and pulmonary surfactant. Peroxynitrite, but not nitric oxide or superoxide, readily nitrates phenolic rings including tyrosine. We quantified the presence of nitrotyrosine in the lungs of patients with the adult respiratory distress syndrome (ARDS) and in the lungs of rats exposed to hyperoxia (100% O2 for 60 h) using quantitative immunofluorescence. Fresh frozen or paraffin-embedded lung sections were incubated with a polyclonal antibody to nitrotyrosine, followed by goat anti-rabbit IgG coupled to rhodamine. Sections from patients with ARDS (n = 5), or from rats exposed to hyperoxia (n = 4), exhibited a twofold increase of specific binding over controls. This binding was blocked by the addition of an excess amount of nitrotyrosine and was absent when the nitrotyrosine antibody was replaced with nonimmune IgG. In additional experiments we demonstrated nitrotyrosine formation in rat lung sections incubated in vitro with peroxynitrite, but not nitric oxide or reactive oxygen species. These data suggest that toxic levels of peroxynitrite may be formed in the lungs of patients with acute lung injury.