Immunohistochemical localization of nitric oxide synthase and the oxidant peroxynitrite in lung transplant recipients with obliterative bronchiolitis

Primary graft dysfunction grade 3 following pediatric lung transplantation is associated with chronic lung allograft dysfunction

BACKGROUND

Severe primary graft dysfunction (PGD) is associated with the development of bronchiolitis obliterans syndrome (BOS), the most common form of chronic lung allograft dysfunction (CLAD), in adults. However, PGD associations with long-term outcomes following pediatric lung transplantation are unknown. We hypothesized that PGD grade 3 (PGD 3) at 48- or 72-hours would be associated with shorter CLAD-free survival following pediatric lung transplantation.

METHODS

This was a single center retrospective cohort study of patients ≤ 21 years of age who underwent bilateral lung transplantation between 2005 and 2019 with ≥ 1 year of follow-up. PGD and CLAD were defined by published criteria. We evaluated the association of PGD 3 at 48- or 72-hours with CLAD-free survival by using time-to-event analyses.

RESULTS

Fifty-one patients were included (median age 12.7 years; 51% female). The most common transplant indications were cystic fibrosis (29%) and pulmonary hypertension (20%). Seventeen patients (33%) had PGD 3 at either 48- or 72-hours. In unadjusted analysis, PGD 3 was associated with an increased risk of CLAD or mortality (HR 2.10, 95% CI 1.01-4.37, p=0.047). This association remained when adjusting individually for multiple potential confounders. There was evidence of effect modification by sex (interaction p = 0.055) with the association of PGD 3 and shorter CLAD-free survival driven predominantly by males (HR 4.73, 95% CI 1.44-15.6) rather than females (HR 1.23, 95% CI 0.47-3.20).

CONCLUSIONS

PGD 3 at 48- or 72-hours following pediatric lung transplantation was associated with shorter CLAD-free survival. Sex may be a modifier of this association.

Beneficial effects of cerium oxide nanoparticles in development of chondrocyte-seeded hydrogel constructs and cellular response to interleukin insults

The harsh inflammatory environment associated with injured and arthritic joints represents a major challenge to articular cartilage repair. In this study, we report the effect of cerium oxide nanoparticles, or nanoceria, in modulating development of engineered cartilage and in combating the deleterious effects of interleukin-1α. Nanoceria was found to be biocompatible with bovine chondrocytes up to a concentration of 1000 μg/mL (60,000 cells/μg of nanoceria), and its presence significantly improved compressive mechanical properties and biochemical composition (i.e., glycosaminoglycans) of engineered cartilage. Raman microspectroscopy revealed that individual chondrocytes with internalized nanoceria have increased concentrations of proline, procollagen, and glycogen as compared with cells without the nanoparticles in their vicinity. The inflammatory response due to physiologically relevant quantities of interluekin-1α (0.5 ng/mL) is partially inhibited by nanoceria. To the best of the authors' knowledge, these results are the first to demonstrate a high potential for nanoceria to improve articular cartilage tissue properties and for their long-term treatment against an inflammatory reaction.

Intracellular regulation of matrix metalloproteinase-2 activity: new strategies in treatment and protection of heart subjected to oxidative stress

Much is known regarding cardiac energy metabolism in ischemia/reperfusion (I/R) injury. Under aerobic conditions, the heart prefers to metabolize fatty acids, which contribute to 60-80% of the required ATP. During ischemia, anaerobic glycolysis increases and becomes an important source of ATP for preservation of ion gradients. With reperfusion, fatty acid oxidation quickly recovers and again predominates as the major source of mitochondrial oxidative metabolism. Although a number of molecular mechanisms have been implicated in the development of I/R injury, their relative contributions remain to be determined. One such mechanism involves the proteolytic degradation of contractile proteins, such as troponin I (TnI), myosin heavy chain, titin, and the myosin light chains (MLC1 and MLC2) by matrix metalloproteinase-2 (MMP-2). However, very little is known about intracellular regulation of MMP-2 activity under physiological and pathological conditions. Greater understanding of the mechanisms that govern MMP-2 activity may lead to the development of new therapeutic strategies aimed at preservation of the contractile function of the heart subjected to myocardial infarction (MI) or I/R. This review discusses the intracellular mechanisms controlling MMP-2 activity and highlights a new intracellular therapeutic direction for the prevention and treatment of heart injury.

Early detection of chronic pulmonary allograft dysfunction by exhaled biomarkers

RATIONALE

Early detection of bronchiolitis obliterans syndrome (BOS) is important because therapies are more likely to be effective if employed early in the disease process.

OBJECTIVES

To compare the performance of exhaled NO and CO (which reflect airway inflammation) and the slope of the alveolar plateau for helium (which reflects heterogeneity of ventilation distribution) for detection of BOS stages 0-p and 1.

METHODS

Recipients of bilateral (n=64) and single (n=1) lung grafts were prospectively monitored for 1,249 days; the helium slope was derived from single-breath washouts and exhaled NO and CO were measured by chemiluminescence on 933 occasions.

MEASUREMENTS AND MAIN RESULTS

At the end of follow-up, 9 patients were in stage 0-p and 16 patients were in BOS stage 1 or higher; 21 patients had at least one measurement made in BOS stage 0-p. All markers increased in BOS stage 0-p, but only the helium slope increased in BOS stage 1. The helium slope had better sensitivity for detection of stages 0-p and 1 than either exhaled NO or CO, but considering exhaled NO and CO together improved their sensitivity; the best sensitivity was found with the three markers in combination. The biomarkers had high negative predictive values, but low specificity and positive predictive values.

CONCLUSIONS

After lung transplantation, (1) the helium slope and exhaled NO, but also exhaled CO, increase in BOS stage 0-p, (2) the helium slope has better sensitivity than exhaled NO and CO for the detection of BOS stages 0-p and 1, and (3) exhaled biomarkers have high negative predictive values, but low specificity and positive predictive values.

Prolongation of alloskin graft survival by catalytic scavengers of reactive oxygen species

We tested the effects of salen manganese (Salen-Mn) complexes, which are scavengers of reactive oxygen species exhibiting superoxide dismutase and catalase activities on the rejection of and alloresponse to fully allogeneic skin grafts in mice. We showed that pre-transplant treatment of C57Bl/6 donor skin or of BALB/c recipients with Salen-Mn complexes significantly delayed allograft rejection. ELISPOT analysis of alloimmune response of treated mice revealed a significant reduction of the frequency of type 1 cytokine (pro-inflammatory) producing T-cells, while the number of activated T-cells producing type 2 cytokines was elevated. In addition, anti-oxidative treatment of graft recipients resulted in a profound inhibition of their donor-specific cytotoxic T-cell response. Our results indicate that salen manganese complexes mediate their effect on graft rejection both by reducing the susceptibility of graft tissue to ROS-mediated injury and by exerting an anti-inflammatory effect in recipients.

Pulmonary infections increase exhaled nitric oxide in lung transplant recipients: a longitudinal study

The aim of this longitudinal study was to test whether pulmonary infections influence fractional exhaled nitric oxide levels (FENO) in otherwise clinically-stable lung transplant recipients. Levels of FENO were measured at least on 11 occasions in nine lung transplant recipients who attended for routine or urgent clinical review over 27.0 +/- 3.2 months period. Diagnosis of infection was based on clinical symptoms, functional measurements and radiological findings. Concentrations of FENO were also determined in 12 healthy volunteers. During follow-up, six patients had one, two had three, and one had four episodes of pulmonary infections. Overall, six upper and 10 lower respiratory tract infections were noted. Recipients with active infections developed increased FENO levels as compared with their own baseline levels measured in the clinically well period (10.8 +/- 1.3 vs. 7.6 +/- 1.1 ppb, p < 0.05). After antibiotic treatment, elevated FENO concentrations returned to baseline in association with full clinical recovery. Baseline FENO levels in lung transplant recipients and in healthy volunteers (6.0 +/- 0.5 ppb) were similar. The sensitivity and specificity of FENO measurement in detecting pulmonary infections were 57 and 96%, respectively. Our data suggest that pulmonary infections are associated with increased FENO levels in patients with lung allografts. Nevertheless, the measurement of FENO by itself as a screening tool for infections seems to be limited by its low sensitivity.

Enhanced peroxynitrite decomposition protects against experimental obliterative bronchiolitis

Obliterative bronchiolitis (OB) affects over half of all survivors following lung or heart-lung transplantation. Respiratory epithelial cell injury, peribronchial inflammation, and proliferation of fibrovascular tissue causing airway occlusion characterize the lesion. While peroxynitrite is known to participate in other models of acute lung injury, its role in the evolution of OB is unclear. Using a rat model of experimental OB, tracheas from Brown-Norway or Lewis rats were transplanted into Lewis recipients. Treated animals received FP-15, a peroxynitrite decomposition catalyst, at 1 mg/kg/day intraperitoneal for 14 days. Luminal obstruction, epithelial loss, and inflammatory infiltrate were examined, as was nitrotyrosine staining by immunohistochemistry in explanted tracheas. By postoperative day 14, control allografts demonstrated marked peribronchial inflammation, near complete loss of respiratory epithelium and extensive intraluminal proliferation of fibrovascular connective tissue, with a mean 83% reduction in airway cross-sectional area. Allograft recipients treated with FP-15 showed reduced nitrotyrosine formation, preservation of respiratory epithelium, limited peribronchial inflammation, and only 14% (P <.001) reduction in airway cross-sectional area. Peroxynitrite therefore appears to play a role in the development of obliterative bronchiolitis in rats. The peroxynitrite decomposition catalyst, FP-15, is protective when administered daily and warrants investigation into its potential clinical utility.

Inducible nitric oxide synthase and nitrotyrosine in mice with radiation-induced lung damage

The purpose of this study was to determine if radiation-induced lung damage is associated with induction of nitric oxide synthase (NOS) II and nitrotyrosine in an irradiated lung mouse model. The thorax of BALBc mice were exposed to 14 Gy radiation (experimental) or no radiation (control) and killed after at 1, 3, 6, 12, and 24 hours; 3, 15, and 30 days; and 3 and 6 months after treatment. Lung sections were processed for immunohistochemistry using NOS II and nitrotyrosine polyclonal antisera and in situ hybridization using 35S labeled probes for mouse NOS II. Quantitative analysis of experimental and control sections showed significant induction of NOS II and nitrotyrosine in alveolar macrophages from 6 hours to 30 days postirradiation, which was diminished by 3 months. The airway and alveolar epithelium and vascular endothelium showed strong NOS II expression at 15 to 30 days postirradiation. Nitrotyrosine immunostaining was also strongly evident in the alveolar epithelium and vascular endothelium during this period. There was little or no NOS II or nitrotyrosine in the sham control lungs throughout the study. These findings demonstrate increased formation of both NO and nitrotyrosine after radiation treatment and suggest a role for these molecules in the pathogenesis of radiation-induced lung damage.

Pulmonary NO synthase expression is attenuated in a fetal baboon model of chronic lung disease

Nitric oxide (NO), produced by NO synthase (NOS), serves multiple functions in the perinatal lung. In fetal baboons, neuronal (nNOS), endothelial (eNOS), and inducible NOS (iNOS) are all primarily expressed in proximal respiratory epithelium. In the present study, NOS expression and activity in proximal lung and minute ventilation of NO standard temperature and pressure (VeNO(STP)) were evaluated in a model of chronic lung disease (CLD) in baboons delivered at 125 days (d) of gestation (term = 185 d) and ventilated for 14 d, obtaining control lung samples from fetuses at 125 or 140 d of gestation. In contrast to the normal 73% increase in total NOS activity from 125 to 140 d of gestation, there was an 83% decline with CLD. This was related to marked diminutions in both nNOS and eNOS expression and enzymatic activity. nNOS accounted for the vast majority of enzymatic activity in all groups. The normal 3.3-fold maturational rise in iNOS protein expression was blunted in CLD, yet iNOS activity was elevated in CLD compared with at birth. The contribution of iNOS to total NOS activity was minimal in all groups. VeNO(STP) remained stable in the range of 0.5-1.0 nl x kg(-1) x min(-1) from birth to day 7 of life, and it then rose by 2.5-fold. Thus the baboon model of CLD is characterized by deficiency of the principal pulmonary isoforms, nNOS and eNOS, and enhanced iNOS activity over the first 2 wk of postnatal life. It is postulated that these alterations in NOS expression and activity may contribute to the pathogenesis of CLD.

Recipient iNOS but not eNOS deficiency reduces luminal narrowing in tracheal allografts

Chronic airway rejection is characterized by prolonged inflammation, epithelial damage, and eventual luminal obliterative bronchiolitis (OB). In cardiac allografts, the inducible nitric oxide synthase (iNOS) promotes acute rejection but paradoxically reduces neointimal formation, the hallmark of chronic rejection. The specific roles of NOS isoforms in modulating lymphocyte traffic and airway rejection are not known. Using a double lumen mouse tracheal transplant model, tracheal grafts from B10.A (allo) or C57BL/6J (iso) mice were transplanted into cyclosporine-treated wild-type (WT) iNOS(-/-) or endothelial NOS (eNOS)(-/-) recipients. OB was observed in WT tracheal allografts at 3 weeks (53 +/- 2% luminal occlusion vs. 17 +/- 1% for isografts, P < 0.05) with sites of obstructive lesion formation coinciding with areas of CD3(+) CD8(+) T cell-rich lymphocytic bronchitis. In contrast, allografts in iNOS(-/-) recipients exhibited reductions in local expression of proinflammatory chemokines and cytokines, graft T cell recruitment and apoptosis, and luminal obliteration (29 +/- 2%, P < 0.05 vs. WT allografts). Recipient eNOS deficiency, however, suppressed neither chemokine expression, lymphocyte infiltration, nor airway occlusion (54 +/- 2%). These data demonstrate that iNOS exacerbates luminal obliteration of airway allografts in contrast with the known suppression by iNOS of cardiac allograft vasculopathy. Because iNOS(-/-) airways transplanted into WT allograft hosts are not protected from rejection, these data suggest that iNOS expressed by graft-infiltrating leukocytes exerts the dominant influence on airway rejection.

Nitric oxide in the development of obliterative bronchiolitis in a heterotopic pig model

BACKGROUND

Inflammation, epithelial cell injury, and development of fibrosis and airway obliteration are the major histological features of posttransplant obliterative bronchiolitis (OB). The expression of inducible nitric oxide synthase (iNOS) in the damaged epithelium, accompanied by peroxynitrite, suggests that endogenous nitric oxide (NO) mediates the epithelial destruction preceding obliteration. To elucidate the role of NO in this cascade, heterotopic bronchial allografts were studied in pigs.

METHODS

Allografts or autografts were harvested serially 3-90 days after transplantation and processed for histology and immunocytochemistry for iNOS, nitrotyrosine, a marker of peroxynitrite formation, and superoxide dismutase (SOD).

RESULTS

During initial ischemic damage to the epithelium, iNOS, nitrotyrosine, and SOD were found to be strongly expressed in the epithelium of all implants as well as later, after partial recovery, parallel to onset of epithelial destruction and subsequent airway obliteration in allografts. The levels of expression of iNOS in fibroblasts during the early phase of obliteration paralleled the onset of fibrosis. Constant expression of iNOS and SOD, but not nitrotyrosine, occurred in autografts and allografts with blocked alloimmune response.

CONCLUSIONS

These findings suggest that an excessive amount of NO promotes posttransplant obliterative bronchiolitis by destroying airway epithelium and stimulating fibroblast activity. SOD may provide protection by binding reactive molecules and preventing peroxynitrite formation.

Deficiency in inducible nitric oxide synthase protects mice from ozone-induced lung inflammation and tissue injury

Inhalation of ozone causes Type I epithelial cell necrosis and Type II cell hyperplasia and proliferation. This is associated with an accumulation of activated macrophages in the lower lung, which we have demonstrated contribute to tissue injury. Nitric oxide (NO) is a highly reactive cytotoxic macrophage-derived mediator that has been implicated in lung damage. In the present studies we used knockout mice with a targeted disruption of the gene for inducible nitric oxide synthase (NOSII) to analyze the role of NO in ozone-induced lung inflammation and tissue injury. Treatment of wild-type control mice with ozone (0.8 ppm) for 3 h resulted in a time-dependent increase in protein and cells in bronchoalveolar lavage fluid, which reached a maximum 24-48 h after exposure. Alveolar macrophages isolated from animals treated with ozone were found to produce increased amounts of NO, as well as peroxynitrite. This was correlated with induction of NOSII protein and nitrotyrosine staining of lung macrophages in tissue sections and in culture. Production of superoxide anion and prostaglandin (PG)E2 by alveolar macrophages was also increased after ozone inhalation. In contrast, alveolar macrophages from NOSII knockout mice did not produce reactive nitrogen intermediates even after ozone inhalation. Moreover, production of PGE2 was at control levels. NOSII knockout mice were also protected from ozone-induced inflammation and tissue injury, as measured by bronchoalveolar lavage protein and cell number. There was also no evidence of peroxynitrite-mediated lung damage in these animals. Taken together, these data demonstrate that NO, produced via NOSII, and potentially, its reactive oxidative product peroxynitrite, play a critical role in ozone-induced release of inflammatory mediators and in tissue injury.

Tyrosine nitration: localisation, quantification, consequences for protein function and signal transduction

The nitration of free tyrosine or protein tyrosine residues generates 3-nitrotyrosine the detection of which has been utilised as a footprint for the in vivo formation of peroxynitrite and other reactive nitrogen species. The detection of 3-nitrotyrosine by analytical and immunological techniques has established that tyrosine nitration occurs under physiological conditions and levels increase in most disease states. This review provides an updated, comprehensive and detailed summary of the tissue, cellular and specific protein localisation of 3-nitrotyrosine and its quantification. The potential consequences of nitration to protein function and the pathogenesis of disease are also examined together with the possible effects of protein nitration on signal transduction pathways and on the metabolism of proteins.

Association of reactive nitrogen species metabolites, myeloperoxidase, and airway inflammation in lung transplants

BACKGROUND

We have previously reported that patients who had single or double lung transplants had higher concentrations than controls of nitrite and nitrate, which are metabolites of reactive nitrogen species (RNS), in bronchoalveolar lavage fluid (BALF) and serum.

METHODS

This study investigates implications of RNS metabolites as markers of airway inflammation in a distinct group of lung transplant patients (n = 40). All patients underwent spirometry, routine surveillance transbronchial lung biopsies, and bronchoalveolar lavage as required by clinical protocol. Four normal controls also had bronchoscopy for measurement of BALF nitrite (NO2-) and nitrate (NO3-). BALF NO2- and NO3-, myeloperoxidase (MPO), protein, and urea were assayed. Total nitrite (NO2- plus enzymatically reduced NO3-) and urea were measured in serum.

RESULTS

BALF RNS metabolites were mainly NO3-. Forced expiratory volume in 1 s (FEV1) obtained near bronchoscopy was compared with best postoperative FEV1. Total nitrite in transplant patients' BALF and serum were 3.8 +/- 0.2 and 49 +/- 5 microM, respectively. Total nitrite in controls' BALF and serum were 2.2 +/- 0.7 and 19 +/- 2 microM, respectively (P < 0.05 compared with transplant values). Serum total nitrite correlated (Pearson product moment) with percentage of neutrophils in BALF (R = 0.650, P < 0.0001), MPO (R = 0.431, P = 0.0055), change in FEV1 from baseline (deltaFEV1) (R = -0348, P = 0.0298), and days after transplantation (R = 0.345, P = 0.0294). None of the associated variables, airway inflanmmation (quantified as a score, "B"), deltaFEV1, serum, or BALF total nitrite, were explained by infection. Univariate analysis of airway inflammation in patients showed that it was associated with BALF neutrophils, deltaFEV1, and serum total nitrite.

CONCLUSIONS

Serum nitrite appears to reflect the degree of airway inflammation in this lung-transplant study group.

IL-4 plays a crucial role in regulating oxidative damage in the liver during schistosomiasis

Liver enlargement and hepatocyte proliferation, normal responses in wild-type (WT) mice infected with the parasitic helminth Schistosoma mansoni, were found to be severely impaired in infected IL-4(-/-) mice. Compared with WT mice, increased levels of O(2)(-), NO, and the more highly reactive ONOO(-) were detected in the liver and produced by lesional cells isolated from liver granulomas of infected IL-4(-/-) mice. Concurrently, antioxidant defenses in the liver, specifically catalase levels, diminished dramatically during the course of infection in these animals. This contrasted to the situation in infected WT mice, where catalase levels remained as high as those in normal mice. Actual levels of reactive oxygen and nitrogen intermediates in the livers of infected IL-4(-/-) animals are thus likely to be considerably higher than those in the livers of infected WT mice. To determine whether these changes contributed to the development of the more severe disease that characterizes infection in the IL-4(-/-) animals, we treated infected IL-4(-/-) mice with uric acid, a potent scavenger of ONOO(-). This resulted in significantly increased hepatocyte proliferation, decreased morbidity, and prolonged survival. Taken together, these data indicate that IL-4 is playing a protective role during schistosomiasis by controlling the tight regulation of the generation of reactive oxygen and nitrogen intermediates in the liver.

Post-lung transplant bronchiolitis obliterans syndrome (BOS) is characterized by increased exhaled nitric oxide levels and epithelial inducible nitric oxide synthase

In conditions characterized by airway inflammation, exhaled nitric oxide (eNO) levels are increased. Post-lung transplant bronchiolitis obliterans syndrome (BOS) is characterized by airway inflammation and development of progressive airway narrowing and fibrosis. We have previously shown that in stable lung transplant recipients (LTR), mean eNO levels were not elevated but were still related to the degree of airway neutrophilia within the group. The hypothesis now tested is that in BOS, eNO levels are increased in association with even greater airway neutrophilia and enhanced expression of inducible (iNOS) nitric oxide synthase in the bronchial epithelium. We determined eNO levels in 40 LTR in four groups: well and "stable": LTR (n = 20), BOS (n = 8), bacterial airway infection (BI, n = 6), and acute rejection (AR, n = 6). Following bronchoscopic sampling, we performed a quantitative assessment of iNOS and constitutive nitric oxide synthase (cNOS) expression in endobronchial biopsies by immunohistochemistry. Mean +/- SEM eNO levels in BOS and BI were significantly higher than in stable LTR (20 +/- 1.2 parts per billion [ppb] and 24.7 +/- 1.7 ppb versus 12.5 +/- 0.9 ppb; p < 0.01 for both). In AR, eNO levels (13.4 ppb +/- 0.5) were not different in stable LTR (p = 0.34). When compared with stable LTR, there was increased expression of iNOS in the bronchial epithelium and generally in the lamina propria (LP) in patients with BOS and BI. In AR, iNOS expression was increased but only in the LP in a perivascular distribution. Expression of cNOS was reduced in BOS but not in BI and AR compared with the stable group. Using regression analysis, only iNOS expression in the bronchial epithelium (r(2) = 0.77; p < 0.0001) and %BAL neutrophils (r(2) = 0. 79; p < 0.0001) were positively related to eNO in stable LTR and BOS. We conclude that epithelial iNOS appears to be the major source of eNO. Exhaled NO levels also appear to reflect the degree of airway neutrophilia in both stable LTR and BOS groups. This suggests that serial eNO measurements may be able to predict the early development of BOS.

Inducible nitric oxide synthase transcription in human lung transplantation

BACKGROUND

Recent animal data suggest that inducible nitric oxide synthase (iNOS) mRNA expression in the bronchoalveolar lavage (BAL) may be useful for the diagnosis of lung rejection. The aim of this study was to evaluate iNOS mRNA transcription in the BAL fluid of human lung allografts.

METHODS

iNOS mRNA transcription was quantified by competitive reverse transcription-polymerase chain reaction in 51 BAL cell pellets of lung transplant patients. According to bacteriological and histological results, BAL samples were divided into three groups: normal (n=21), acute rejection (AR, n=15), and infection (INF, n=15).

RESULTS

Compared with the control group, iNOS transcription increased significantly with INF (P=0.0005) but only slightly with AR (P>0.05). INF values were significantly higher than AR values (P=0.0029).

CONCLUSION

BAL iNOS mRNA transcript determination by competitive reverse transcription-polymerase chain reaction may be useful in differentiating infected from normal and/or acutely rejecting allografts.

Protein nitration, metabolites of reactive nitrogen species, and inflammation in lung allografts

This study investigated nitration and chlorination of epithelial lining fluid (ELF) proteins in patients (n = 29) who had undergone lung allotransplantation. We assayed lung lavage nitrotyrosine (NT) and chlorotyrosine (CT) by HPLC. We measured NT, nitrate (NO(3)(-)), and nitrate (NO(2)(-)) in bronchoalveolar lavage fluid (BALF) and total nitrite (NO(2)(-) + NO(3)(-)) in serum of another group of lung transplant patients (n = 82). In the first group (n = 29), percent nitration of tyrosines (Tyr) (NT/total Tyr x 100) in BALF proteins was: patients, 0.01 (0.00-0.12)%; median (25th-75th% confidence interval), and control subjects 0.01 (0.00-0.02)%. CT (CT/ total Tyr x 100) occurred only in the patients' BALF: 0.01 (0. 00- 0.02)%. In the second group (n = 82), nitrotyrosine (NT) was detected by ELISA in the BALF of patients: 9 (0-41) pmol/mg pro and control subjects: 28 (26-33). Total nitrite (NO(2)(-) + NO(3)(-)) in BALF of the patients: 3.3 (1.9-5.1) microM significantly exceeded that in control subjects: 1.3 (0.8-1.3) microM; p = 0.0133. Serum nitrite also was significantly higher in patients: 37 (26-55) microM than control subjects: 19 (17-20) microM; p = 0.0037. Airway inflammation in transbronchial biopsies (B score) correlated with NT in BALF (p = 0.0369). Lung transplants have increased airway concentrations of reactive nitrogen species (RNS) metabolites. NT, a marker of peroxynitrite (ONOO(-)), is related to the degree of airway inflammation in lung transplants.

Up-regulation of inducible nitric oxide synthase in fibroblasts parallels the onset and progression of fibrosis in an experimental model of post-transplant obliterative airway disease

The main cause of mortality following lung transplantation is chronic rejection, manifesting morphologically as obliterative bronchiolitis (OB). It has been suggested that damage to the respiratory epithelium initiates proliferation of mesenchymal cells, leading to dense collagenous scarring in small airways. Inducible nitric oxide synthase (iNOS) is strongly expressed in the damaged epithelium in human OB, along with high levels of peroxynitrite, suggesting that endogenous NO mediates the epithelial destruction. To examine further the role of iNOS in this process, heterotopic airway implants were studied in rats, an acknowledged disease model. Specimens of iso- or allografted trachea, collected 3-60 days after implantation, were processed for histology and immunocytochemistry for iNOS and, as a marker of peroxynitrite formation, nitrotyrosine. In both iso- and allografts at the earliest stage (day 3), ischaemia was associated with severe epithelial damage or loss. These changes progressed until day 7 and were accompanied by strong expression of iNOS and nitrotyrosine in epithelial cells. In isografts, epithelial recovery was seen, with abundant iNOS immunoreactivity but little nitrotyrosine. In contrast, the epithelium in allografts did not regenerate and progressive inflammation and fibroproliferation occurred until complete obliteration of the tracheal lumen at day 60. The fibroproliferation was associated with changes in morphology of fibroblasts that were accompanied by alterations in their iNOS expression. iNOS immunoreactivity was dense in the plump fibroblasts of early lesions, in some cases as early as post-operative day 5, but very weak in elongated fibroblasts in totally occluded grafts. The intensity of immunoreactivity for nitrotyrosine corresponded to that of iNOS. These results indicate a dual role for NO in the airway obliteration that follows transplantation, through destruction of epithelium and stimulation of fibroblast activity.

Alterations of nitric oxide synthase expression and activity during rat lung transplantation

Decreased nitric oxide (NO) production has been reported during lung transplantation in patients. To study the effects of ischemia and reperfusion on endogenous NO synthase (NOS) expression, both an ex vivo and an in vivo lung injury model for transplantation were used. Donor rat lungs were flushed with cold low-potassium dextran solution and subjected to either cold (4 degrees C for 12 h) or warm (21 degrees C for 4 h) ischemic preservation followed by reperfusion with an ex vivo model. A significant increase in inducible NOS and a decrease in endothelial NOS mRNA was found after reperfusion. These results were confirmed in a rat single-lung transplant model after warm preservation. Interestingly, protein contents of both inducible NOS and endothelial NOS increased in the transplanted lung after 2 h of reperfusion. However, the total activity of NOS in the transplanted lungs remained at very low levels. We conclude that ischemic lung preservation and reperfusion result in altered NOS gene and protein expression with inhibited NOS activity, which may contribute to the injury of lung transplants.

Obliterative bronchiolitis after lung transplantation

Despite marked improvements in early survival, long-term outcome after lung transplantation is still threatened by obliterative bronchiolitis (OB). Thought to be a manifestation of chronic allograft rejection, OB affects up to 65% of patients at 5 years after surgery and produces a relentless airflow obstruction. Early and late acute rejection are the primary risk factors for OB, but cytomegalovirus infection and airway ischemia may also play a role. In most patients, OB responds poorly to augmented immunosuppression and eventually leads to infectious complications and terminal respiratory failure. Because early diagnosis is associated with better prognosis, every effort should be made to detect OB in a preclinical stage. This may be best achieved by combining several techniques, such as surveillance transbronchial biopsy and bronchoalveolar lavage, measurements of ventilation distribution and exhaled nitric oxide, and expiratory computed tomography.

Implications of inducible nitric oxide synthase expression and enzyme activity

We summarize here our current knowledge about inducible nitric oxide synthase (NOS) activity in human diseases and disorders. As basic research discovers more and more effects of low or high concentrations of NO toward molecular and cellular targets, successful therapies involving inhibition of NO synthesis or application of NO to treat human diseases are still lacking. This is in part due to the fact that the impact of NO on cell function or death are complex and often even appear to be contradictory. NO may be cytotoxic but may also protect cells from a toxic insult; it is apoptosis-inducing but also exhibits prominent anti-apoptotic activity. NO is an antioxidant but may also compromise the cellular redox state via oxidation of thiols like glutathione. NO may activate specific signal transduction pathways but is also reported to inhibit exactly these, and NO may activate or inhibit gene transcription. The situation may even be more complicated, because NO, depending on its concentration, may react with oxygen or the superoxide anion radical to yield reactive species with a much broader chemical reaction spectrum than NO itself. Thus, the action of NO during inflammatory reactions has to be considered in the context of timing and duration of its synthesis as well as stages and specific events in inflammation.

In stable lung transplant recipients, exhaled nitric oxide levels positively correlate with airway neutrophilia and bronchial epithelial iNOS

In conditions characterized by airway inflammation, exhaled nitric oxide (eNO) levels are increased. Variable degrees of airway inflammation are present in stable lung transplant recipients (LTR), and may lead to airway remodeling and chronic graft dysfunction. The hypothesis tested is that in stable LTR, eNO concentrations would reflect the expression of inducible (iNOS) (but not constitutive [cNOS] nitric oxide synthase) in the bronchial epithelium as well as the degree of airway inflammation. We determined eNO concentrations in 20 stable LTR, free of infection, rejection, or obliterative bronchiolitis (OB). At routine bronchoscopy, we measured the differential cell count on bronchoalveolar lavage (BAL) and a quantitative assessment of iNOS and cNOS expression in endobronchial biopsies by immunohistochemistry. Mean +/- SEM eNO concentrations in stable LTR were not significantly different from control subjects (13 +/- 0.7 ppb versus 14.2 +/- 0.49; p = 0.42). Percent BAL neutrophils was 11.5 +/- 3.2 which was significantly higher than in a group of local control subjects (1.7 +/- 0.6; p < 0.001). The bronchial epithelium and lamina propria contained abundant iNOS but cNOS was present only in the lamina propria. Using regression analysis, percent BAL neutrophils (r(2) = 0.82; p < 0.0001) and iNOS expression in the bronchial epithelium (r(2) = 0.75; p < 0.0001), but not in the lamina propria (r(2) = 0.16; p = 0.08), were positively predictive of eNO. There was an inverse relationship between cNOS and eNO. We conclude that eNO concentrations although normal for the group, still reflect the degree of airway inflammation in stable LTR. Epithelial iNOS appears to be the major source of eNO and expression of cNOS may be downregulated with increasing iNOS expression.

High levels of peroxynitrite are generated in the lungs of irradiated mice given cyclophosphamide and allogeneic T cells. A potential mechanism of injury after marrow transplantation

In a murine bone-marrow transplant (BMT) model designed to determine risk factors for lung dysfunction in irradiated mice, we reported that cyclophosphamide (Cy)-induced injury and lethality depended on the infusion of donor spleen T cells. In the study reported here, we hypothesized that alveolar macrophage (AM)-derived reactive oxygen/nitrogen species are associated with lung dysfunction caused by allogeneic T cells, which stimulate nitric oxide (.NO) production, and by Cy, which stimulates superoxide production.NO reacts with superoxide to form peroxynitrite, a tissue-damaging oxidant. On Day 7 after allogeneic BMT, bronchoalveolar lavage fluid (BALF) obtained from mice injected with T cells contained increased levels of nitrite, which was associated with increased lactate dehydrogenase and protein levels, both of which are indices of lung injury. The injury was most severe in mice receiving both T cells and Cy. Messenger RNA (mRNA) for inducible nitric oxide synthase was detected only in murine lungs injected with T cells +/- Cy. AMs obtained on Day 7 after BMT from mice receiving T cells +/- Cy spontaneously generated between 20 and 40 microM nitrite in culture, versus < 2 microM generated by macrophages obtained from mice undergoing BMT but not receiving T cells. The level of 3-nitrotyrosine, the stable byproduct of the reaction of peroxynitrite with tyrosine residues, was increased in the BALF proteins of mice injected with both T cells and Cy. We conclude that allogeneic T cells stimulate macrophage-derived.NO, and that the addition of Cy favors peroxynitrite formation. Peroxynitrite generation clarifies the dependence of Cy-induced lung injury and lethality on the presence of allogeneic T cells.

Nitric oxide production and nitric oxide synthase type 2 expression by human mononuclear phagocytes: a review

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Poly (ADP-ribose) synthetase activation mediates pulmonary microvascular and intestinal mucosal dysfunction in endotoxin shock

Endotoxin shock is known to impair critical cellular functions and is associated with the development of multiple organ dysfunction. Recent in vitro and in vivo studies demonstrated that oxidants produced during shock and inflammation trigger the activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS), resulting in intracellular energetic failure and tissue dysfunction. Here we examined the role of PARS activation in the development of barrier dysfunction of the intestine and lung during endotoxemia in rats. Ileal mucosal permeability was assessed by the measurement of the lumen to plasma directional passage of the hydrophil solute sodium fluorescein. Microvascular permeability in the lung was examined by the measurement of the extravasation of Evans blue. Inhibition of PARS was achieved by treating the animals with 3-aminobenzamide 30 min prior and 3 hr after lipopolysaccharide injection (10 mg/kg). Endotoxemia (E. coli bacterial lipopolysaccharide, 5-10 mg/kg) resulted in an increased epithelial permeability in the ileum and a microvascular hyperpermeability and neutrophil accumulation in the lung in 6 hr. The PARS inhibitor 3-aminobenzamide significantly reduced the lipopolysaccharide-induced hyperpermeability in both organs, without affecting neutrophil deposition. Thus, PARS activation plays a role in mediating endothelial and epithelial dysfunction and hyperpermeability during endotoxin shock.

Pathophysiology of nitric oxide and related species: free radical reactions and modification of biomolecules

Since its initial discovery as an endogenously produced bioactive mediator, nitric oxide (.NO) has been found to play a critical role in the cellular function of nearly all organ systems. Furthermore, aberrant production of .NO or reactive nitrogen species (RNS) derived from .NO, has been implicated in a number of pathological conditions, such as acute lung disease, atherosclerosis and septic shock. While .NO itself is fairly non-toxic, secondary RNS are oxidants and nitrating agents that can modify both the structure and function of numerous biomolecules both in vitro, and in vivo. The mechanisms by which RNS mediate toxicity are largely dictated by its unique reactivity. The study of how reactive nitrogen species (RNS) derived from .NO interact with biomolecules such as proteins, carbohydrates and lipids, to modify both their structure and function is an area of active research, which is lending major new insights into the mechanisms underlying their pathophysiological role in human disease. In the context of .NO-dependent pathophysiology, these biochemical reactions will play a major role since they: (i) lead to removal of .NO and decreased efficiency of .NO as an endothelial-derived relaxation factor (e.g. in hypertension, atherosclerosis) and (ii) lead to production of other intermediate species and covalently modified biomolecules that cause injury and cellular dysfunction during inflammation. Although the physical and chemical properties of .NO and .NO-derived RNS are well characterised, extrapolating this fundamental knowledge to a complicated biological environment is a current challenge for researchers in the field of .NO and free radical research. In this review, we describe the impact of .NO and .NO-derived RNS on biological processes primarily from a biochemical standpoint. In this way, it is our intention to outline the most pertinent and relevant reactions of RNS, as they apply to a diverse array of pathophysiological states. Since reactions of RNS in vivo are likely to be vast and complex, our aim in this review is threefold: (i) address the major sources and reactions of .NO-derived RNS in biological systems, (ii) describe current knowledge regarding the functional consequences underlying .NO-dependent covalent modification of specific biomolecules, and (iii) to summarise and critically evaluate the available evidence implicating these reactions in human pathology. To this end, three areas of special interest have been chosen for detailed description, namely, formation and role of S-nitrosothiols, modulation of lipid oxidation/nitration by RNS, and tyrosine nitration mechanisms and consequences.

Biological tyrosine nitration: a pathophysiological function of nitric oxide and reactive oxygen species

Analytical and immunological methodologies and occasionally both methodologies have been applied to detect and quantify 3-nitrotyrosine in almost every major organ system. In certain diseases increased levels of 3-nitrotyrosine have been correlated with elevated levels of other indices of oxidative stress. Numerous reports have established that nitration is a biological process derived from the biochemical interaction of nitric oxide or nitric oxide-derived secondary products with reactive oxygen species. This article addresses critical issues regarding this biological process, namely the biochemical pathways for nitration of tyrosine residues in vivo, potential protein targets, and pathophysiological consequences of protein tyrosine nitration.