Critical role of reactive nitrogen species in lung ischemia-reperfusion injury

The effects of apigenin administration on the inhibition of inflammatory responses and oxidative stress in the lung injury models: a systematic review and meta-analysis of preclinical evidence

BACKGROUND/OBJECTIVE

Apigenin is a member of the flavonoid family that can regulate various biological processes, which is characterized as a treatment of different inflammatory disorders and pathological problems associated with oxidative stress (OS). Recent research has focused on apigenin immunomodulatory properties as a potential treatment for different types of lung injuries. This meta-analysis was designed to determine the impact of apigenin treatment on inflammatory markers and OS parameters in animal models of lung injuries.

METHODS

The comprehensive literature search was conducted using electronic databases such as Google Scholar, PubMed, Web of Science, Scopus, and Embase up to August 2021. To assess apigenin's effect on inflammatory mediators and OS biomarkers in lung injury animal models, we used the I² statistic to determine the heterogeneity. We then pooled data as standardized mean difference (SMD) with a 95% confidence interval (CI).

RESULTS

Our meta-analysis of the pooled data for inflammatory biomarkers demonstrated that the apigenin administration significantly decreased the NF-κB expression (SMD - 1.60, 95% CI [- 2.93 to - 0.26]; I² = 89.0%, p < 0.001), IL-1β (SMD - 4.30, 95% CI [- 6.24 to - 2.37]; I² = 67.3%, p = 0.047), IL-6 (SMD - 4.10, 95% CI [- 5.04 to - 3.16]; I² = 72.6%, p < 0.001), TNF-α (SMD - 3.74, 95% CI [- 4.67 to - 2.82]; I² = 84.1%, p < 0.001), and TNF-α gene expression (SMD - 3.44, 95% CI [- 4.44 to - 2.43]; I² = 0.0%, p = 0.622). This study also indicated the efficacy of apigenin in increasing the level of CAT (SMD 4.56, 95% CI [3.57 to 5.55]; I² = 15.3%, p = 3.15), GSH (SMD 5.12, 95% CI [3.53 to 6.70]; I² = 77.6%, p < 0.001), and SOD (SMD 3.45, 95% CI [2.50 to 4.40]; I² = 79.2%, p < 0.001), and decreasing the level of MDA (SMD - 3.87, 95% CI [- 5.25 to - 2.49]; I² = 80.3%, p < 0.001) and MPO (SMD - 4.02, 95% CI [- 5.64 to - 2.40]; I² = 88.9%, p < 0.001), TGF- β (SMD - 3.81, 95% CI [- 4.91 to - 2.70]; I² = 73.4%, p = 0.001) and W/D level (SMD - 3.22, 95% CI [- 4.47 to - 1.97]; I² = 82.1%, p < 0.001) than control groups.

CONCLUSION

Overall, our findings showed the immunomodulatory potential of apigenin as an alternative treatment for the suppression of inflammatory responses and OS in different types of lung injury diseases. Nevertheless, due to the paucity of clinical studies, reliable preclinical models, and clinical settings, evaluating the influence of apigenin on lung injury is required in the future. Before conducting large-scale clinical trials, detailed human pharmacokinetic studies are also needed to establish dosage ranges and determine the initial safety and tolerability of apigenin.

Nitroxidized-Albumin Advanced Glycation End Product and Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease whose major clinical consequence is inflammation of small joints and contiguous structures. Oxidative and nitrosative stress along with increased formation of advanced glycation end products (AGEs) play an important role in the disease process. Generation of reactive species during glycation of proteins further adds to the oxidative and nitrosative stress. Albumin, being the most abundant plasma protein, is frequently targeted by different oxidizing and nitrating agents, including peroxynitrite (OONO-) anion. Albumin is also targeted and modified by dicarbonyl metabolites (glyoxal and methylglyoxal) which are formed in oxidative and non-oxidative processes during the synthesis of AGEs. The endogenously formed OONO- and dicarbonyls may modify plasma albumin including those albumin that have travelled or migrated to synovial cells and caused nitration, oxidation, and glycation. These modifications may produce crosslinks, aggregate in albumin and confer immunogenicity. Simultaneous modification of albumin by OONO- and dicarbonyls may generate nitroxidized-AGE-albumin which may persist in circulation for a longer duration compared to native albumin. Nitroxidized-AGE-albumin level (or serum autoantibodies against nitroxidized- AGE-albumin) along with other pre-clinical features may help predict the likely onset of RA.

Lung Ischaemia-Reperfusion Injury: The Role of Reactive Oxygen Species

Lung ischaemia-reperfusion injury (LIRI) occurs in many lung diseases and during surgical procedures such as lung transplantation. The re-establishment of blood flow and oxygen delivery into the previously ischaemic lung exacerbates the ischaemic injury and leads to increased microvascular permeability and pulmonary vascular resistance as well as to vigorous activation of the immune response. These events initiate the irreversible damage of the lung with subsequent oedema formation that can result in systemic hypoxaemia and multi-organ failure. Alterations in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) have been suggested as crucial mediators of such responses during ischaemia-reperfusion in the lung. Among numerous potential sources of ROS/RNS within cells, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidases, nitric oxide synthases and mitochondria have been investigated during LIRI. Against this background, we aim to review here the extensive literature about the ROS-mediated cellular signalling during LIRI, as well as the effectiveness of antioxidants as treatment option for LIRI.

Apigenin Reduces NF-κB and Subsequent Cytokine Production as Protective Effect in a Rodent Animal Model of Lung Ischemia-Reperfusion Injury

PURPOSE

Lung ischemia-reperfusion injury (LIRI) can complicate lung transplantation or cardiac surgery with cardiopulmonary bypass, increasing morbidity and mortality. In LIRI, pro-inflammatory cytokines are activated, reactive oxygen species are generated and nuclear factor-κB (NF-κB) is up-regulated, altering lung mechanics. We tested the effect of the flavonoid apigenin on a rodent model of LIRI.

METHODS

Thirty-seven Wistar rats were subjected to LIRI with or without a single or double dose of apigenin. Induction of LIRI involved sternotomy and clamping of either the left lung hilum or the pulmonary artery alone for 30 min, followed by 60 min of reperfusion. Control groups consisted of LIRI plus NaCl, a sham group and a baseline group. At the end of the experiments, both lungs were analyzed by RT-PCR, Western blot, and light microscopy.

RESULTS

In placebos, the expression levels of pro-inflammatory markers were increased in both lungs significantly, whereas NF-κB was markedly up-regulated. Administration of apigenin reduced the activation of NF-κB and the expression of TNFα, iNOS, and IL-6. These effects were observed in total lung ischemia. Histology showed greater hemorrhage and exudation in the pulmonary periphery of all groups, whereby damage was practically absent in the central lung regions of the apigenin animals. A second dose of apigenin did not outclass a single one.

CONCLUSIONS

We conclude that apigenin given intraperitoneally can reduce activation of NF-κB and also attenuate the expression of TNFα, IL-6, and iNOS in a surgical model of LIRI. The surgical procedure itself can induce significant damage to the lungs.

Therapeutic potential of peroxynitrite decomposition catalysts: a patent review

INTRODUCTION

Peroxynitrite is a cytotoxic oxidant species implicated in a host of pathologies, including inflammatory and neurodegenerative diseases, cancer, radiation injury and chronic pain. With the recognition of the role of peroxynitrite in disease, numerous experimental and therapeutic tools have arisen to probe peroxyntirite's pathophysiological contribution and attenuate its oxidative damage. Peroxynitrite decomposition catalysts (PNDCs) are redox-active compounds that detoxify peroxynitrite by catalyzing its isomerization or reduction to nitrate or nitrite.

AREAS COVERED

This review discusses recent research articles and patents published 1995 - 2014 on the development and therapeutic use of PNDCs. Iron and manganese metalloporphyrin PNDCs attenuate the toxic effects of peroxynitrite and are currently being developed for clinical applications. Additionally, some Mn porphyrin-based PNDCs have optimized pharmaceutical properties such that they exhibit greater peroxynitrite selectivity. Other classes of PNDC agents, including bis(hydroxyphenyl)dipyrromethenes and metallocorroles, have demonstrated preclinical efficacy, oral availability and reduced toxicity risk.

EXPERT OPINION

Interest in the drug-like properties of peroxynitrite-neutralizing agents has grown with the realization that PNDCs will be powerful tools in the treatment of disease. The design of compounds with enhanced oral availability and peroxynitrite selectivity is a critical step toward the availability of safe, effective and selective redox modulators for the treatment of peroxynitrite-associated pathologies.

Ischemia-reperfusion lung injury is attenuated in MyD88-deficient mice

Ischemia-reperfusion lung injury is a common cause of acute morbidity and mortality in lung transplant recipients and has been associated with subsequent development of bronchiolitis obliterans syndrome. Recognition of endogenous ligands released during cellular injury (damage-associated molecular patterns; DAMPs) by Toll-like receptors (TLRs), especially TLR4, has increasingly been recognized as a mechanism for inflammation resulting from tissue damage. TLR4 is implicated in the pathogenesis of ischemia-reperfusion injury of multiple organs including heart, liver, kidney and lung. Additionally, activation of TLRs other than TLR4 by DAMPs has been identified in tissues other than the lung. Because all known TLRs, with the exception of TLR3, signal via the MyD88 adapter protein, we hypothesized that lung ischemia-reperfusion injury was mediated by MyD88-dependent signaling. To test this hypothesis, we subjected C57BL/6 wildtype, Myd88^-/-, and Tlr4^-/- mice to 1 hr of left lung warm ischemia followed by 4 hr of reperfusion. We found that Myd88^-/- mice had significantly less MCP-1/CCL2 in the left lung following ischemia-reperfusion as compared with wildtype mice. This difference was associated with dramatically reduced lung permeability. Interestingly, Tlr4^-/- mice had only partial protection from ischemia-reperfusion as compared to Myd88^-/- mice, implicating other MyD88-dependent pathways in lung injury following ischemia-reperfusion. We also found that left lung ischemia-reperfusion caused remote inflammation in the right lung. Finally, using chimeric mice with MyD88 expression restricted to either myeloid or non-myeloid cells, we found that MyD88-dependent signaling in myeloid cells was necessary for ischemia-reperfusion induced lung permeability. We conclude that MyD88-dependent signaling through multiple receptors is important in the pathogenesis of acute lung inflammation and injury following ischemia and reperfusion.

A novel two-hit rodent model of postoperative acute lung injury: priming the immune system leads to an exaggerated injury after pneumonectomy

OBJECTIVES

Postoperative acute lung injury (PALI) is a rare, poorly understood, usually fatal condition, accounting for the majority of deaths following lung resection. Its low frequency and unpredictable development make the identification of the mechanisms of injury from clinical studies alone almost impossible. Multiple validated 'two-hit models' exist for ALI secondary to other causes. We describe a novel rodent 'two-hit' model of PALI: a low-grade immune stimulus, such as sepsis, greatly aggravates the injury in the remaining lung observed following pneumonectomy.

METHODS

Under general anaesthesia, rats received either low-dose intratracheal lipopolysaccharide (IT-LPS) challenge (10 μg for 1 h) followed by left posterolateral thoracotomy, one-lung ventilation (OLV), pneumonectomy and 3 h of ventilation; 500 μl IT 0.9% saline followed by the same surgery or IT-LPS followed by sham surgery and ventilation. All other conditions were constant. Lung injury is heralded by neutrophil accumulation, which was determined by right lung bronchoalveolar lavage cell count. Data are presented as mean ± standard error of the mean. The T-test was used to compare normally distributed groups with correction for multiple comparisons.

RESULTS

A dose-response curve identified the clinically relevant 'low dose' of LPS to be used in further studies. Ventilatory parameters were standardized to reflect clinical practice (volume-control, tidal volume of 6 ml/kg, positive end-expiratory pressure of 2 cmH2O, maximum airway pressure of <15 cmH2O). There was a degree of adaptation to obtain a consistent and robust model with retest validity. OLV and pneumonectomy alone produced a small lung injury (65.1 ± 5), as did 10 µg intratracheal LPS alone (50.7 ± 6.9). However, when OLV, pneumonectomy and 10 µg LPS were combined, an exaggerated injury occurred (161.4 ± 10.3), P = 0.007.

CONCLUSIONS

Early results show that a two-hit model of PALI is viable and that sepsis aggravates the response to pneumonectomy. The model is now being further characterized. Once established, this model will offer the chance to better understand PALI and to develop and test novel therapies and risk reduction strategies for the condition.

Effects of FP15, a peroxynitrite decomposition catalyst on cardiac and pulmonary function after cardiopulmonary bypass

OBJECTIVE

Peroxynitrite, a toxic nitrogen species, has been implicated in the development of ischemia/reperfusion injury. The aim of the present study was to investigate the effects of the potent peroxynitrite decomposition catalyst, FP15, on myocardial, endothelial, and pulmonary function in an experimental model of cardioplegic arrest and extracorporal circulation.

METHODS

Twelve anesthetized dogs underwent hypothermic cardiopulmonary bypass. After 60 min of hypothermic cardiac arrest, reperfusion was started and either saline vehicle (control, n = 6) or FP15 (n = 6) was administered. Left-ventricular preload-recruitable stroke work (PRSW) was measured by a combined pressure-volume conductance catheter at baseline and after 60 min of reperfusion. Left anterior descending (LAD) coronary (CBF) and pulmonary blood flow (PBF), endothelium-dependent vasodilatation to acetylcholine (ACh), and alveolo-arterial O2 gradient were determined.

RESULTS

The administration of FP15 led to a significantly better recovery of PRSW (given as percent of baseline: 93 ± 9 vs 62 ± 6%, p < 0.05). CBF was also significantly higher in the FP15 group (44 ± 6 vs 25 ± 4 ml min(-1), p < 0.05). Injection of ACh resulted in a significantly higher increase in CBF (70 ± 6 vs 35 ± 5%, p < 0.05) in the FP15-treated animals. The alveolo-arterial O2 gradient was significantly lower after FP15 administration (83 ± 7 vs 49 ± 6 mmHg, p < 0.05). Catalytic peroxynitrite decomposition did not affect baseline cardiovascular and pulmonary functions.

CONCLUSIONS

Application of FP15 improves myocardial, endothelial, and pulmonary function after cardiopulmonary bypass with hypothermic cardiac arrest. The observed protective effects imply that catalytic peroxynitrite decomposition could be a novel therapeutic option in the treatment of ischemia/reperfusion injury.

Effects of a potent peroxynitrite decomposition catalyst in murine models of endotoxemia and sepsis

Excessive free-radical production due to various bacterial components released during bacterial infection has been linked to cell death and tissue injury. Peroxynitrite is a highly reactive oxidant produced by the combination of nitric oxide (NO) and superoxide anion, which has been implicated in cell death and tissue injury in various forms of critical illness. Pharmacological decomposition of peroxynitrite may represent a potential therapeutic approach in diseases associated with the overproduction of NO and superoxide. In the present study, we tested the effect of a potent peroxynitrite decomposition catalyst in murine models of endotoxemia and sepsis. Mice were injected i.p. with LPS 40 mg/kg with or without FP15 [Fe(III) tetrakis-2-(N-triethylene glycol monomethyl ether)pyridyl porphyrin] (0.1, 0.3, 1, 3, or 10 mg/kg per hour). Mice were killed 12 h later, followed by the harvesting of samples from the lung, liver, and gut for malondialdehyde and myeloperoxidase measurements. In other subsets of animals, blood samples were obtained by cardiac puncture at 1.5, 4, and 8 h after LPS administration for cytokine (TNF-α, IL-1β, and IL-10), nitrite/nitrate, alanine aminotransferase, and blood urea nitrogen measurements. Endotoxemic animals showed an increase in survival from 25% to 80% at the FP15 doses of 0.3 and 1 mg/kg per hour. The same dose of FP15 had no effect on plasma levels of nitrite/nitrate. There was a reduction in liver and lung malondialdehyde in the endotoxemic animals pretreated with FP15, as well as in hepatic myeloperoxidase and biochemical markers of liver and kidney damage (alanine aminotransferase and blood urea nitrogen). In a bacterial model of sepsis induced by cecal ligation and puncture, FP15 treatment (0.3 mg/kg per day) significantly protected against mortality. The current data support the view that peroxynitrite is a critical factor mediating liver, gut, and lung injury in endotoxemia and septic shock: its pharmacological neutralization may be of therapeutic benefit.

Ethyl pyruvate protects rats from phosgene-induced pulmonary edema by inhibiting cyclooxygenase2 and inducible nitric oxide synthase expression

Phosgene is a poorly water-soluble gas penetrating the lower respiratory tract which can induce acute lung injury characterized by a latent phase of fatal pulmonary edema. Pulmonary edema caused by phosgene is believed to be a consequence of oxidative stress and inflammatory responses. Ethyl pyruvate (EP) has been demonstrated to have anti-inflammatory and anti-oxidative properties in vivo and in vitro. The potential therapeutic role of EP in phosgene-induced pulmonary edema has not been addressed so far. In the present study, we aim to investigate the protective effects of EP on phosgene-induced pulmonary edema and the underlying mechanisms. Rats were administered with EP (40 mg kg(-1)) and RAW264.7 cells were also incubated with it (0, 2, 5 or 10 µm) immediately after phosgene (400 ppm, 1 min) or air exposure. Wet-to-dry lung weight ratio (W:D ratio), nitric oxide (NO) and prostaglandin E(2) (PGE(2)) production, cyclooxygenase2 (COX-2) and inducible nitric oxide synthase (iNOS) expression, and mitogen-activated protein kinases activities (MAPKs) were measured. Our results showed that EP treatment attenuated phosgene-induced pulmonary edema and decreased the level of NO and PGE(2) dose-dependently. Furthermore, EP significantly reduced COX-2 expression, iNOS expression and MAPK activation induced by phosgene. Moreover, specific inhibitors of MAPKs reduced COX-2 and iNOS expression induced by phosgene. These findings suggested that EP has a protective role against phosgene-induced pulmonary edema, which is mediated in part by inhibiting MAPK activation and subsequently down-regulating COX-2 and iNOS expression as well as decreasing the production of NO and PGE(2).

The peroxynitrite catalyst WW-85 improves pulmonary function in ovine septic shock

Systemic inflammatory response syndrome is associated with excessive production of nitric oxide (NO·) and superoxide (O2), forming peroxynitrite, which in turn, acts as a terminal mediator of cellular injury by producing cell necrosis and apoptosis. We examined the effect of the peroxynitrite decomposition catalyst, WW-85, in a sheep model of acute lung injury and septic shock. Eighteen sheep were operatively prepared and randomly allocated to the sham, control, or WW-85 group (n = 6 each). After a tracheotomy, acute lung injury was produced in the control and WW-85 groups by insufflation of four sets of 12 breaths of cotton smoke. Then, a 30-mL suspension of live Pseudomonas aeruginosa bacteria (containing 2 - 5 × 10¹¹ colony-forming units) was instilled into the lungs according to an established protocol. The sham group received only the vehicle (30 mL saline). The sheep were studied in awake state for 24 h and ventilated with 100% oxygen. WW-85 was administered 1 h after injury as bolus infusion (0.1 mg/kg), followed by a continuous infusion of 0.02 mg·kg⁻¹·h⁻¹ until the end of the 24-h experimental period. Compared with injured but untreated controls, WW-85-treated animals had significantly improved gas exchange, reductions in airway obstruction, shunt formation, lung myeloperoxidase concentrations, lung malondialdehyde concentrations, lung 3-nitrotyrosine concentrations, and plasma nitrate-to-nitrite levels. Animals treated with WW-85 exhibited less microvascular leakage and improvements in pulmonary function. These results provide evidence that blockade of the nitric oxide-peroxynitrite pathway improves disturbances from septic shock, as demonstrated in a clinically relevant ovine experimental model.

The peroxynitrite catalyst WW-85 improves microcirculation in ovine smoke inhalation injury and septic shock

This prospective, randomized, controlled experimental study examined the effects of the peroxynitrite decomposition catalyst WW-85 on global hemodynamics and regional microvascular blood flow (RMBF) in an established ovine model of septic shock following severe smoke inhalation injury. Twenty-one sheep were randomized into a sham group (no injury), a control group (smoke/sepsis), and a treatment group (smoke/sepsis/WW-85; n=7 each). WW-85 was administered 1h after injury as a bolus (0.1 mg/kg), followed by a continuous infusion of 0.02 mg/kg/h RMBF was analyzed using colored microspheres. All control animals developed a hypotensive, hyperdynamic circulation and increased plasma levels of nitrate/-nitrite (NOx). All hemodynamic variables and NOx levels were significantly improved in the treatment group. In visceral organs of controls, blood flow to trachea, ileum, and spleen significantly increased (p<0.05). Blood flow to kidneys and pancreas significantly decreased (p<0.05). Treatment with WW-85 stabilized blood flow to ileum, spleen, and kidneys on baseline levels and was significantly improved compared to controls (p<0.05). Cerebral blood flow deteriorated in controls, but was significantly improved in cerebral cortex, cerebellum, pons, medulla oblongata, and thalamus (p<0.05) by WW-85. These results provide evidence that WW-85 blocks NO production, thereby improving cardiovascular function and microcirculation.

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.

Peroxynitrite induces HMGB1 release by cardiac cells in vitro and HMGB1 upregulation in the infarcted myocardium in vivo

AIMS

High-mobility group box 1 (HMGB1) is a nuclear protein actively secreted by immune cells and passively released by necrotic cells that initiates pro-inflammatory signalling through binding to the receptor for advance glycation end-products. HMGB1 has been established as a key inflammatory mediator during myocardial infarction, but the proximal mechanisms responsible for myocardial HMGB1 expression and release in this setting remain unclear. Here, we investigated the possible involvement of peroxynitrite, a potent cytotoxic oxidant formed during myocardial infarction, on these processes.

METHODS AND RESULTS

The ability of peroxynitrite to induce necrosis and HMGB1 release in vitro was evaluated in H9c2 cardiomyoblasts and in primary murine cardiac cells (myocytes and non-myocytes). In vivo, myocardial HMGB1 expression and nitrotyrosine content (a marker of peroxynitrite generation) were determined following myocardial ischaemia and reperfusion in rats, whereas peroxynitrite formation was inhibited by two different peroxynitrite decomposition catalysts: 5,10,15,20-tetrakis(4-sulphonatophenyl) porphyrinato iron (III) (FeTPPS) or Mn(III)-tetrakis(4-benzoic acid) porphyrin chloride (MnTBAP). In all types of cells studied, peroxynitrite (100 μM) elicited significant necrosis, the loss of intracellular HMGB1, and its passive release into the medium. In vivo, myocardial ischaemia-reperfusion induced significant myocardial necrosis, cardiac nitrotyrosine formation, and marked overexpression of myocardial HMGB1. FeTPPS reduced nitrotyrosine, decreased infarct size, and suppressed HMGB1 overexpression, an effect that was similarly obtained with MnTBAP.

CONCLUSION

These findings indicate that peroxynitrite represents a key mediator of HMGB1 overexpression and release by cardiac cells and provide a novel mechanism linking myocardial oxidative/nitrosative stress with post-infarction myocardial inflammation.

Peroxynitrite decomposition catalyst prevents matrix metalloproteinase activation and neurovascular injury after prolonged cerebral ischemia in rats

Matrix metalloproteinases (MMPs) play an important role in reperfusion-induced brain injury following ischemia. To define the effects of peroxynitrite decomposition catalyst on MMP activation and neurovascular reperfusion injury, 5,10,15,20-tetrakis (2,4,6-trimethyl-3,5-disulfonatophenyl)-porphyrin iron (III) (FeTMPyP) was administered intravenously 30 min prior to reperfusion following a middle cerebral artery occlusion. Activation of MMP was assessed by in situ and gel zymography. Neurovascular injury was assessed using endothelial barrier antigen, collagen IV immunohistochemistry and Cresyl violet staining. Results were compared with sham and ischemia alone groups. We found that administration of FeTMPyP just before reperfusion after ischemia inhibited MMP-9 activation and total MMP-2 increases in the cortex and decreased active MMP-9 along with the total amounts of active MMP-9 and active MMP-2 in the striatum. Reperfusion-induced injury to the basal lamina of collagen IV-immunopositive microvasculature and neural cells in cortex and striatum was ameliorated by FeTMPyP. Losses of blood vessel endothelium produced by ischemia or reperfusion were also decreased in the cortex. These results suggest that administration of FeTMPy prior to reperfusion decreases MMP activation and neurovascular injury after prolonged cerebral ischemia. This strategy may be useful for future therapies targeted at preventing breakdown of the blood-brain barrier and hemorrhagic transformation.

Superoxide dismutase mimics: chemistry, pharmacology, and therapeutic potential

Oxidative stress has become widely viewed as an underlying condition in a number of diseases, such as ischemia-reperfusion disorders, central nervous system disorders, cardiovascular conditions, cancer, and diabetes. Thus, natural and synthetic antioxidants have been actively sought. Superoxide dismutase is a first line of defense against oxidative stress under physiological and pathological conditions. Therefore, the development of therapeutics aimed at mimicking superoxide dismutase was a natural maneuver. Metalloporphyrins, as well as Mn cyclic polyamines, Mn salen derivatives and nitroxides were all originally developed as SOD mimics. The same thermodynamic and electrostatic properties that make them potent SOD mimics may allow them to reduce other reactive species such as peroxynitrite, peroxynitrite-derived CO(3)(*-), peroxyl radical, and less efficiently H(2)O(2). By doing so SOD mimics can decrease both primary and secondary oxidative events, the latter arising from the inhibition of cellular transcriptional activity. To better judge the therapeutic potential and the advantage of one over the other type of compound, comparative studies of different classes of drugs in the same cellular and/or animal models are needed. We here provide a comprehensive overview of the chemical properties and some in vivo effects observed with various classes of compounds with a special emphasis on porphyrin-based compounds.

Lung ischemia-reperfusion injury: a molecular and clinical view on a complex pathophysiological process

Lung ischemia-reperfusion injury remains one of the major complications after cardiac bypass surgery and lung transplantation. Due to its dual blood supply system and the availability of oxygen from alveolar ventilation, the pathogenetic mechanisms of ischemia-reperfusion injury in the lungs are more complicated than in other organs, where loss of blood flow automatically leads to hypoxia. In this review, an extensive overview is given of the molecular and cellular mechanisms that are involved in the pathogenesis of lung ischemia-reperfusion injury and the possible therapeutic strategies to reduce or prevent it. In addition, the roles of neutrophils, alveolar macrophages, cytokines, and chemokines, as well as the alterations in the cell-death related pathways, are described in detail.

Effects of a metalloporphyrinic peroxynitrite decomposition catalyst, ww-85, in a mouse model of spinal cord injury

The aim of the present study was to assess the effect of a metalloporphyrinic peroxynitrite decomposition catalyst, ww-85, in the pathophysiology of spinal cord injury (SCI) in mice. Spinal cord trauma was induced by the application of vascular clips to the dura via a four-level T5-T8 laminectomy. SCI in mice resulted in severe trauma characterized by oedema, neutrophil infiltration, production of inflammatory mediators, tissue damage and apoptosis. ww-85 treatment (30-300 microg/kg, i.p. 1 h after the SCI) significantly reduced in a dose-dependent manner: (1) the degree of spinal cord inflammation and tissue injury, (2) neutrophil infiltration (myeloperoxidase activity), (3) nitrotyrosine formation and PARP activation, (4) pro-inflammatory cytokines expression, (5) NF-kappaB activation and (6) apoptosis. Moreover, ww-85 significantly ameliorated the recovery of limb function (evaluated by motor recovery score) in a dose-dependent manner. The results demonstrate that ww-85 treatment reduces the development of inflammation and tissue injury associated with spinal cord trauma.

Erythropoietin attenuates lung injury in lipopolysaccharide treated rats

BACKGROUND

Erythropoietin (EPO) elicits protective effects in lung ischemia-reperfusion, hyperoxia, acute necrotizing pancreatitis, and some other tissues. In the present study, we investigated the possible protective roles of EPO in the lipopolysaccharide (LPS) induced lung injury.

MATERIALS AND METHODS

Male Sprague-Dawley rats were treated with EPO (3000 U/kg, i.p.) or vehicle (saline), 30 min prior to LPS administration (6 mg/kg, i.v.). Four h following LPS injection, samples of pulmonary tissue were collected. Optical microscopy was performed to examine pathological changes in lungs. Validated methods were used to measure wet/dry ratios (W/D), myeloperoxidase (MPO) activity, malondialdehyde (MDA) concentrations, and nitrite/nitrate (NO(2)(-)/NO(3)(-)) levels in lungs. Western blotting was performed to study the pulmonary expression of inducible nitric oxide synthase (iNOS) and nitrotyrosine protein.

RESULTS

Pretreatment with EPO led to (1) significant attenuation of endotoxemia induced evident lung histologic injury and edema; (2) inhibition of LPS mediated induction in MPO activity and MDA concentration; (3) inhibition of LPS mediated overproduction of pulmonary NO(2)(-)/NO(3)(-) levels; and (4) marked suppression in endotoxin induced expression of iNOS and nitrotyrosine.

CONCLUSIONS

This study provides considerable evidence that EPO has an ability to significantly attenuate endotoxin-induced acute lung injury in rats.

Lung-protective effects of the metalloporphyrinic peroxynitrite decomposition catalyst WW-85 in interleukin-2 induced toxicity

Recombinant interleukin-2 (IL-2) therapy for malignancy is associated with a pulmonary vascular leakage syndrome (VLS) similar to that seen in sepsis. We investigated the possibility that the IL-2-induced VLS may be associated with the release of peroxynitrite (ONOO(-)), and used a model of IL-2-induced VLS in sheep to test the effects of the ONOO(-) decomposition catalyst WW-85. Eighteen sheep were chronically instrumented and randomly divided into three groups (n=6 per group): sham: lactated Ringer's solution, control: IL-2, and treatment: IL-2 and WW-85. Treatment with WW-85 significantly improved lung transvascular fluid flux, decreased lipid peroxidation, limited iNOS as well as PAR intensity, prevented tachycardia, and attenuated the increase in core body temperature resulting from IL-2 treatment. These findings suggest that ONOO(-) plays a pivotal role in the pathology of IL-2-induced pulmonary VLS, and that WW-85 may become a useful treatment option.

Preconditioning by inhaled nitric oxide prevents hyperoxic and ischemia/reperfusion injury in rat lungs

Since the generation of nitric oxide (NO) is an essential step in the trigger phase of ischemic preconditioning, short-term inhalation of NO before ischemia should ameliorate ischemia/reperfusion (I/R) injury of the lung. We tested this hypothesis in high oxygen (>99%) ventilated rats in order to additionally evaluate compatibility of NO and exposure to hyperoxia. Male adult Sprague-Dawley rats inhaled NO (15 ppm, 10 min) before the left lung hilum was clamped for 1 h, and the reperfusion phase was observed for 4 h (NO group). Animals in the I/R group underwent the same treatment, but without NO inhalation. A third group without I/R served as time-matched controls. Animals in the I/R group showed severe I/R injury in terms of arterial pO2 (apO2), which was reduced to 22% of surgical controls (SCs) at time point 30 min reperfusion, and increased endothelial permeability (Evans blue procedure). The pretreatment with NO attenuated these effects. The pO2 after 4 h reperfusion was still 3.0-fold higher in the NO group compared to I/R. In contrast, the I/R- and hyperoxia-induced invasion of leukocytes, as determined by measuring myeloperoxidase (MPO) activity, was not affected by NO. These data were correlated with the activity of major cellular signaling pathways by measuring the phosphorylation at activating and inhibitory sites of extracellular-signal regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38, protein kinase B (AKT), and glycogen synthase kinase 3beta (GSK-3beta), and by determination of cGMP in plasma and lung tissue. Inhalation of NO partly prevented the loss of activation by I/R and hyperoxic ventilation of ERK, JNK, and AKT, and it reduced the I/R-induced activation of GSK-3beta. The level of cGMP in plasma and lung tissue was increased in the NO group after 4 h reperfusion. In conclusion, application of inhaled NO in the preconditioning mode prevented I/R injury in the rat lung without interfering effects of hyperoxic ventilation. The effects of NO on cellular signaling pathways resemble mechanisms of ischemic preconditioning, but further studies have to evaluate the physiological relevance of these results.

Alveolar macrophage secretory products augment the response of rat pulmonary artery endothelial cells to hypoxia and reoxygenation

BACKGROUND

Endothelial cell activation is an important response to ischemia and reperfusion in a variety of vascular beds. Endothelial cells secrete a multitude of proinflammatory mediators and express adhesion molecules that promote leukocyte recruitment into injured tissues. Pulmonary artery endothelial cell response to lung ischemia-reperfusion injury does not appear robust enough to drive the development of lung injury independently. Rather, the alveolar macrophage is the key cell in the development of ischemia-reperfusion injury of the lung. Macrophages are known to be a rich source of inflammatory mediators, but the precise mechanism whereby they amplify injury is unknown. The aim of this study was to determine whether alveolar macrophage secretory products amplify the response of the endothelial cell using an in vitro model of lung reperfusion injury.

METHODS

Macrophages were exposed to hypoxia and reoxygenation and the media collected. Cultured endothelial cells were then exposed to macrophage media and maintained at normoxia or subjected to hypoxia and reoxygenation. To assess any reciprocal effects of endothelial cell products on macrophage activation, macrophages were likewise exposed to activated endothelial cell media.

RESULTS

Exposure of endothelial cells to activated alveolar macrophage media enhanced chemokine secretion in response to hypoxia and reoxygenation. In the reciprocal experiment, activated endothelial cell media increased the production of macrophage inflammatory protein 1alpha from macrophages.

CONCLUSIONS

Alveolar macrophages drive the development of lung reperfusion injury, by enhancing the production of proinflammatory chemokines from endothelial cells, which impart a degree of positive feedback on alveolar macrophages.

Proteasome inhibitor attenuates skeletal muscle reperfusion injury by blocking the pathway of nuclear factor-kappaB activation

BACKGROUND

Nuclear factor-kappaB is a key transcriptional factor in the regulation of inflammatory factors that are involved in tissue reperfusion injury, but conflicting data have been presented in the literature. The proteasome regulates proteins that control cell-cycle progression and apoptosis, and inhibition of the proteasome has been shown to reduce nuclear factor-kappaB activation and reperfusion injury. Although bortezomib is a potent proteasome inhibitor, its role in skeletal muscle reperfusion injury has not been documented, and its effects on the regulation of inflammatory factors in reperfused tissue are unclear. In this study, the authors investigated the role of nuclear factor-kappaB in skeletal muscle reperfusion injury and the effect of bortezomib (a proteasome inhibitor) on reperfusion injury.

METHODS

Pedicled cremaster muscle flaps from bortezomib-treated and phosphate-buffered saline-treated control mice were subjected to 4.5 hours of ischemia and 90 minutes of reperfusion.

RESULTS

During reperfusion, arterial diameters and blood flow recovered earlier and more completely in bortezomib-treated muscle than in controls. Compared with controls, Western blot analysis demonstrated a significant reduction in degradation of nuclear factor-kappaB inhibitory protein and expression of inducible nitric oxide synthase protein in bortezomib-treated muscle at the end of reperfusion. Immunohistochemistry showed decreased nuclear factor-kappaB p65-binding activity and down-regulated protein expression of intercellular adhesion molecule-1 and nitrotyrosine, accompanied by less muscle edema and inflammation as proven by histologic examination.

CONCLUSIONS

Bortezomib effectively blocks nuclear factor-kappaB activation in attenuating muscle reperfusion injury through inhibiting nuclear factor-kappaB inhibitory protein degradation. Therefore, inhibition of proteasome activity may provide a novel therapeutic strategy for the treatment of skeletal muscle reperfusion injury.

Peroxynitrite: biochemistry, pathophysiology and development of therapeutics

Peroxynitrite--the product of the diffusion-controlled reaction of nitric oxide with superoxide radical--is a short-lived oxidant species that is a potent inducer of cell death. Conditions in which the reaction products of peroxynitrite have been detected and in which pharmacological inhibition of its formation or its decomposition have been shown to be of benefit include vascular diseases, ischaemia-reperfusion injury, circulatory shock, inflammation, pain and neurodegeneration. In this Review, we first discuss the biochemistry and pathophysiology of peroxynitrite and then focus on pharmacological strategies to attenuate the toxic effects of peroxynitrite. These include its catalytic reduction to nitrite and its isomerization to nitrate by metalloporphyrins, which have led to potential candidates for drug development for cardiovascular, inflammatory and neurodegenerative diseases.

Lung ischemia-reperfusion injury: implications of oxidative stress and platelet-arteriolar wall interactions

Pulmonary ischemia-reperfusion (IR) injury may result from trauma, atherosclerosis, pulmonary embolism, pulmonary thrombosis and surgical procedures such as cardiopulmonary bypass and lung transplantation. IR injury induces oxidative stress characterized by formation of reactive oxygen (ROS) and reactive nitrogen species (RNS). Nitric oxide (NO) overproduction via inducible nitric oxide synthase (iNOS) is an important component in the pathogenesis of IR. Reaction of NO with ROS forms RNS as secondary reactive products, which cause platelet activation and upregulation of adhesion molecules. This mechanism of injury is particularly important during pulmonary IR with increased iNOS activity in the presence of oxidative stress. Platelet-endothelial interactions may play an important role in causing pulmonary arteriolar vasoconstriction and post-ischemic alveolar hypoperfusion. This review discusses the relationship between ROS, RNS, P-selectin, and platelet-arteriolar wall interactions and proposes a hypothesis for their role in microvascular responses during pulmonary IR.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Preconditioning effects of peroxynitrite in the rat lung

Ischaemic preconditioning of the lung leads to a protective effect against ischaemia-reperfusion injury, but the underlying mechanisms of this protection are not well documented in the lung. The aim of this study was to investigate the role of endogenous and exogenous peroxynitrite (ONOO(-)) in preconditioning of isolated rat lungs. Lungs, obtained from male rats, were mounted on a perfusion apparatus, perfused by Krebs-Henseleit solution at the rate of 0.03mlg(-1)min(-1) and inflated with room air. Pulmonary perfusion pressure was measured by a pressure transducer and recorded continuously on a computer by using data acquisition system. Lungs were preconditioned for 5min by either ischaemia or ONOO(-) administration at 10microM, which were followed by 5min reperfusion and 2h of ischaemia and 10min reperfusion. Two hours of ischaemia without preconditioning depressed potassium chloride (KCl)-and phenylephrine hydrochloride (PE)-induced responses. Pretreatment of the lungs with ONOO(-) scavenger, uric acid (1mM), or poly ADP-ribose synthase inhibitors, 3-aminobenzamid (3-AB, 1mM) or nicotinamide (1mM), reversed the effects ischaemia and ONOO(-)-induced preconditioning and decreased KCl- and PE-induced increases in perfusion pressures. Wet/dry weight ratio was markedly reduced in ischaemia and ONOO(-)-induced preconditioning groups indicating that preconditioning prevents lung oedema. Lung malondialdehyde (MDA) levels were significantly depressed in ischaemic and ONOO(-) preconditioning groups. These results suggest that ONOO(-) is able to precondition the isolated rat lung and plays a significant role in the protective effects of preconditioning.

Interleukin-6 Regulation of Direct Lung Ischemia Reperfusion Injury

BACKGROUND

Lung ischemia reperfusion injury continues to adversely affect patient and graft survival after transplantation. While the role of interleukin-6 has been studied in ischemia-reperfusion models of intestine, liver, and heart, its participation in lung reperfusion injury has not been characterized.

METHODS

We administered recombinant interleukin-6 to rat lungs through the intratracheal route before inducing left lung ischemia and reperfusion. Multiple in-vivo indicators of left lung injury were studied, as were transactivation patterns for nuclear factor kappa B and signal transduction and activators of transcription-3. Downstream effects on the elaboration of proinflammatory chemokines and cytokines were also studied.

RESULTS

Recombinant interleukin-6 reduced endothelial disruption and neutrophil sequestration in left lung and alveolar spaces, resulting in improved oxygenation after ischemia and 4 hours of reperfusion. This protection was associated with decreased nuclear factor kappa B and signal transduction and activators of transcription-3 nuclear translocation early in reperfusion, and diminished proinflammatory mediator secretion late in reperfusion.

CONCLUSIONS

Further studies focusing on the effects of recombinant interleukin-6 in large animal models are warranted, as this may be a novel strategy to improve outcomes after lung transplantation. Intratracheal administration may focus its efficacy on the lung while reducing effects on other organ systems during organ procurement.

Histophysiological effects of fluid resuscitation on heart, lung and brain tissues in rats with hypovolemia

The efficacy of using colloids and crystalloids in the treatment of hypovolemia still remains controversial. An important aspect in treating hypovolemia is to re-establish normal tissue hemodynamics after fluid resuscitation. Production of nitric oxide (NO) or growth factors such as transforming growth factor beta (TGF-beta) has been identified as a key mechanism in physiological and pathological processes in the different systems. This study was designed to investigate the histophysiological effects of resuscitation with different plasma substitutes on the heart, lung and brain tissues following acute blood loss in male Sprague-Dawley rats weighing 250-280g (n=30). After anesthesia with sodium pentobarbital, the left femoral vein and artery were cannulated for the administration of volume expanders and for direct measurement of arterial pressure and heart rate. Twenty rats were bled (5ml/10min) and infused (5ml/10min) with one of four randomly selected solutions, (a) human albumin, (b) gelatin (Gelofusine), (c) dextran-70 (Macrodex); or (d) physiological saline (0.9% isotonic saline). Five control rats were bled without infusion. Tissue samples were taken and fixed in 10% formalin solution, then processed for embedding in paraffin wax. Sections were cut and stained with hematoxylin and eosin. Indirect immunohistochemical labelling was performed to reveal binding of primary antibodies against endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and TGF-beta. Mild immunoreactivity of eNOS was observed in endothelial cells of vessels in brain, heart and lung tissues. Increased immunoreactivities of eNOS, iNOS and TGF-beta were observed in the non-fluid resuscitated group in these organs; mild, moderate, moderate and strong immunoreactivities were seen in the albumin, gelatin, physiological saline and dextran-70 treated groups, respectively. Immunoreactivities of iNOS and TGF-beta in the non-fluid resuscitated group were increased significantly, in comparison to the other groups, apart from the dextran-70 treated group. The results of this study show that gelatin solution and physiological saline may be of use after acute blood loss, and dextran-70 is not the preferred resuscitation fluid in the early stages of acute blood loss. It was concluded that albumin solution is the preferred fluid for resuscitation.

The regulation and pharmacology of endothelial nitric oxide synthase

Nitric oxide (NO) is a small, diffusible, lipophilic free radical gas that mediates significant and diverse signaling functions in nearly every organ system in the body. The endothelial isoform of nitric oxide synthase (eNOS) is a key source of NO found in the cardiovascular system. This review summarizes the pharmacology of NO and the cellular regulation of endothelial NOS (eNOS). The molecular intricacies of the chemistry of NO and the enzymology of NOSs are discussed, followed by a review of the biological activities of NO. This information is then used to develop a more global picture of the pharmacological control of NO synthesis by NOSs in both physiologic conditions and pathophysiologic states.

Crosstalk Between Thrombosis and Inflammation in Lung Reperfusion Injury

BACKGROUND

Activation of extravascular coagulation has been reported in acute lung injury models of sepsis and acute respiratory distress syndrome. Thrombin, the main effector protease of extravascular coagulation, activates proinflammatory cell types, including macrophages, endothelial cells, and neutrophils, each of which participates in lung ischemia-reperfusion injury. We used hirudin, a potent, specific direct thrombin inhibitor, to define the role of thrombin in lung ischemia-reperfusion injury.

METHODS

Rats were pretreated with hirudin 30 minutes before warm, in situ left lung ischemia and reperfusion. Multiple in vivo assessments of lung injury were determined, and mechanistic studies assessed transcriptional regulation early in reperfusion and proinflammatory protein secretion late in reperfusion. Immunohistochemistry localized thrombin activation.

RESULTS

Thrombin localized to macrophages and endothelial and epithelial cells early in reperfusion. Hirudin significantly limited lung ischemia-reperfusion injury-induced derangements in vascular permeability and intraalveolar inflammatory cell sequestration, resulting in improved arterial oxygenation after ischemia and 4 hours of reperfusion. The protection was transcriptionally mediated by attenuated activator protein-1 and early growth response-1 transactivation, but not nuclear factor kappa B transactivation. This was associated with reduced chemokine, but not tumor necrosis factor alpha, secretion late in reperfusion.

CONCLUSIONS

Thrombin promotes lung ischemia-reperfusion injury, as hirudin protected against experimental acute lung injury. Hirudin conferred protection through a mechanism independent of nuclear factor kappa B and tumor necrosis factor alpha, suggesting that its effects may be mediated by a parallel, synergistic inflammatory pathway through activator protein-1 and early growth response-1.

HIF-1α has an anti-apoptotic effect in human airway epithelium that is mediated via Mcl-1 gene expression

Hypoxia-inducible factor-1alpha (HIF-1alpha) and myeloid cell leukemia-1 (Mcl-1) proteins have been shown to regulate apoptosis in some cell systems but have not been studied in this context in airway epithelium. Using a model of anoxia/reoxygenation (A/R), the present study employed RNA interference (RNAi) targeting HIF-1alpha and Mcl-1 to evaluate their possible anti-apoptotic effects on HBE1 cells, an immortalized human bronchial epithelial cell line. The cells were either cultured under normoxic conditions or were transfected with small interfering RNA (siRNA) duplexes targeting HIF-1alpha or Mcl-1 mRNA and then immediately exposed to A/R. As controls, non-transfected HBE1 cells and cells transfected with scrambled RNA duplexes were subjected to A/R. Apoptosis was evaluated by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay and RNAi was assessed by knockdown of HIF-1alpha and Mcl-1 mRNA and protein expression using real-time quantitative RT-PCR (Q-PCR), immunohistochemistry, and Western blots. HBE1 cells transfected with siRNA duplexes targeting either HIF-1alpha or Mcl-1 and subjected to A/R manifested considerable apoptosis, a finding not observed in either non-transfected cells or cells transfected with scrambled RNA duplexes. Specific knockdown of mRNA and protein expression by RNAi in HBE1 cells after A/R was shown for siRNA duplexes targeting either HIF-1alpha or Mcl-1. Unexpectedly, knockdown of HIF-1alpha induced parallel knockdown of Mcl-1 mRNA and protein expression, whereas Mcl-1 knockdown had no noticeable effect on HIF-1alpha expression. Thus, although both of these proteins were shown to be anti-apoptotic, the action of HIF-1alpha appeared to be mediated in part via Mcl-1.

Rosiglitazone, a peroxisome proliferator-activated receptor-gamma agonist, reduces acute lung injury in endotoxemic rats

OBJECTIVE

Rosiglitazone, a potent agonist of peroxisome proliferator-activated receptor (PPAR)-gamma, exerts anti-inflammatory effects in vitro and in vivo. This study was designated to determine the effects of rosiglitazone on endotoxin-induced acute lung injury in rats.

DESIGN

Prospective, experimental study.

SETTING

University research laboratory.

SUBJECTS

Thirty-six male Wistar rats.

INTERVENTIONS

All the animals were randomly assigned to one of six groups (n = 6 per group) and were given either lipopolysaccharide (6 mg/kg intravenously) or saline, pretreated with rosiglitazone (0.3 mg/kg intravenously) or vehicle (10% dimethyl sulphoxide) 30 mins before lipopolysaccharide. The selective PPAR-gamma antagonist GW9662 (0.3 mg/kg intravenously) or its vehicle (10% dimethyl sulphoxide) was given 20 mins before rosiglitazone.

MEASUREMENTS AND MAIN RESULTS

Endotoxemia for 4 hrs induced evident lung histologic injury and edema, both of which were significantly attenuated by rosiglitazone pretreatment. The protective effects of rosiglitazone were correlated with the reduction by 71% of the increase of myeloperoxidase activity and the reduction by 84% of the increase of malondialdehyde in the lung tissue. The pulmonary hyperproduction of nitric oxide was reduced by 82% of the increase related to lipopolysaccharide challenge. Pretreatment with rosiglitazone also markedly suppressed lipopolysaccharide-induced expression of inducible nitric oxide synthase messenger RNA and protein in the lung, as demonstrated by reverse transcription-polymerase chain reaction or Western blot analysis. Immunohistochemical analysis revealed that rosiglitazone inhibited the formation of nitrotyrosine, a marker for peroxynitrite reactivity, in the lung tissue. In addition, the specific PPAR-gamma antagonist GW9662 antagonized the effects of rosiglitazone.

CONCLUSIONS

This study provides evidence, for the first time, that the PPAR-gamma agonist rosiglitazone significantly reduces endotoxin-induced acute lung injury in rats.

Inhibition of inducible nitric oxide synthase attenuates platelet adhesion in subpleural arterioles caused by lung ischemia-reperfusion in rabbits

Oxidative stress, induced by lung ischemia-reperfusion, leads to platelet and leukocyte activation and may contribute to decreased alveolar perfusion by platelet adhesion to the arteriolar wall. We investigated the hypothesis that ischemia-reperfusion injury increases inducible nitric oxide synthase (iNOS) activity and subsequent generation of reactive nitrogen species with P-selectin-dependent platelet-endothelial interactions and vasoconstriction during lung reperfusion. Subpleural arterioles, labeled platelets, and leukocytes were examined in anesthetized, open-chest rabbits by intravital fluorescence microscopy. Ischemia was caused by reversible occlusion of the right pulmonary artery for 1 or 2 h (1IR and 2IR groups). During 2 h of reperfusion, postischemic platelet rolling and adhesion were independent from leukocyte-arteriolar wall interactions and correlated with pulmonary arteriolar constriction in proportion to the length of ischemia. In rabbits treated with an iNOS inhibitor (1400W) before occlusion (2IR + 1400W group), platelet-arteriolar wall interactions and vasoconstriction were prevented. iNOS expression and activity in ischemic lung tissue were markedly greater than control and also were proportional to ischemia duration. NOS activity, immunochemically detected P-selectin, and nitrotyrosine expression in ischemic lung tissue from animals subjected to ischemia-reperfusion, as well as the plasma level of soluble P-selectin, were significantly higher than in nonischemic lungs and were inhibited by pretreatment with 1400W. These results show that platelet adhesion and arteriolar constriction during early reperfusion in the ventilated lung can result from increased iNOS activity and is highly correlated with reactive nitrogen species and P-selectin expression.

The effect of anti-inflammatory properties of mycophenolate mofetil on the development of lung reperfusion injury

BACKGROUND

Lung ischemia-reperfusion injury (LIRI) is associated with an increased incidence of both primary graft failure and obliterative bronchiolitis. The immunosuppressant mycophenolate mofetil (MMF) has recently been shown to attenuate inflammatory injury in acute ischemia-reperfusion models via a mechanism that is presently unclear. These experiments studied the effects of MMF in a warm, in situ LIRI model, focusing on transcriptional regulation of pro-inflammatory mediators.

METHODS

Left lungs of rats were rendered ischemic for 90 minutes and reperfused for up to 4 hours. Treated animals received 10 mg/kg of intravenous MMF at 2 hours before ischemia. Left lung injury was quantitated by myeloperoxidase (MPO) content, permeability indices and bronchoalveolar lavage (BAL) inflammatory cell counts. Lungs were analyzed by electrophoretic mobility shift assay (EMSA) for transcription factor transactivation and by enzyme-linked immunoassay for BAL chemokine protein content.

RESULTS

MMF significantly reduced lung vascular permeability indices, MPO content and alveolar leukocyte counts at 4 hours of reperfusion. There was significant attenuation of activator protein 1 (AP-1) and early growth response 1 (EGR-1) transactivation, whereas nuclear factor-kappaB (NF-kappaB) was unaffected. Reductions in bronchoalveolar lavage monocyte chemoattractant protein 1 (MCP-1) and cytokine-induced neutrophil chemoattractant (CINC) protein content were found at 4 hours of reperfusion.

CONCLUSIONS

MMF limits lung ischemia-reperfusion-induced increases in vascular permeability and inflammatory cell sequestration in lung parenchyma and alveolar spaces. The protection is mediated at the transcriptional level via an attenuation of early EGR-1 and AP-1 transactivation, which was found to be associated with reduced late MCP-1 and CINC protein secretion. The use of MMF in concert with an agent that affects NF-kappaB activation may provide even further protection against lung reperfusion injury as multiple inflammatory pathways are inhibited.

Protective mechanisms of a metalloporphyrinic peroxynitrite decomposition catalyst, WW85, in rat cardiac transplants

Nitric oxide (NO) derived from inducible NO synthase has been implicated in cardiac rejection. However, little is known about the role of the reactive nitrogen species peroxynitrite. We examined the protective actions of a peroxynitrite decomposition catalyst, WW85, in an experimental model of acute cardiac rejection. Heterotopic, abdominal transplantation of rat donor hearts was performed. Groups included isografts, allografts, or allografts treated with WW85, cyclosporine, or cyclosporine + WW85. We determined graft survival, histological rejection, and graft function (by in situ sonomicrometry). Intragraft biochemical analysis of cytokines and proapoptotic and antiapoptotic gene expression using reverse transcriptase-polymerase chain reaction were determined. Treatment with WW85 or cyclosporine alone prolonged graft survival, improved graft function, and decreased histological rejection. Graft survival was further significantly (P < 0.001) enhanced by combination treatment. A decrease was also shown in nitrotyrosine, poly(ADP-ribose) polymerase (PARP) activation, and lipid peroxide formation by WW85 that was potentiated when given in combination with cyclosporine. Benefits could not be ascribed to changes in intragraft myeloperoxidase activity. Only combination therapy produced significant decreases in inflammatory cytokine gene expression, suggesting that WW85 acted primarily downstream of these stimuli. In general, WW85 had no direct action on expression of the proapoptotic gene, Fas ligand; however, WW85 given alone or with cyclosporine enhanced expression of antiapoptotic genes Bcl-2 and Bcl-xL. Collectively, these findings suggest a protective action of the peroxynitrite decomposition catalyst WW85 on graft rejection that is independent of any action on leukocyte sequestration and cytokine gene expression. Rather, effects seem to be downstream on decreased protein nitration, decreased lipid peroxidation, and decreased PARP activation.

Inhibition of iNOS attenuates skeletal muscle reperfusion injury in extracellular superoxide dismutase knockout mice

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are closely involved in the mechanism of skeletal muscle ischemia/reperfusion (I/R) injury. This study was designed to determine the effects of inducible nitric oxide synthase (iNOS) inhibitor 1400 W on the reperfused cremaster muscle in extracellular super-oxide dismutase knockout (EC-SOD(-/-)) mice. The muscle was exposed to 4.5 h of ischemia, followed by 90 min of reperfusion. Mice received either 3 mg/kg of 1400 W or the same amount of phosphate-buffered saline (PBS, as a control) subcutaneously at 10 min before the start of reperfusion. 1400 W treatment markedly improved the recovery speed of vessel diameter and blood flow in the reperfused cremaster muscle of EC-SOD(-/-) mice compared to controls. Histological examination showed reduced edema in the interstitial space and muscle fiber, and reduced density of nitrotyrosine (a marker of total peroxi-nitrate (ONOO(-)) level) in 1400 W-treated muscles compared to controls. Our results suggest that iNOS and ONOO(-) products are involved in skeletal muscle I/R injury. Reduced I/R injury by using selective inhibition of iNOS perhaps works by limiting cytotoxic ONOO(-) generation, a reaction product of nitric oxide (NO) and super-oxide anion (O(2) (-)). Thus, inhibition of iNOS appears to be a treatment strategy for reducing clinical I/R injury.

Arsenic exposure exacerbates atherosclerotic plaque formation and increases nitrotyrosine and leukotriene biosynthesis

A correlation between arsenic and cardiovascular disease (CVD) has been established through epidemiological studies, although the mechanisms are unknown. Using a mouse model that develops atherosclerotic lesions on a normal chow diet, we have confirmed a connection between long-term arsenic intake and CVD. Our results reveal a significant increase in the degree of atherosclerotic plaque stenosis within the innominate artery of ApoE-/-/LDLr-/- mice treated with 10 ppm sodium arsenite (133 microM) in drinking water for 18 weeks compared to controls. Immunohistochemistry shows nitrotyrosine formation, a marker of reactive nitrogen species generation, is significantly higher within the atherosclerotic plaque of arsenic-treated mice. In addition, there is a significant increase in the 5-lipoxygenase (5-LO) product, leukotriene E4 (LTE4), in the serum of arsenic-treated mice. This is supported by induction of the 5-LO protein and subsequent increases in LTE4 synthesis in bovine aortic endothelial cells. This increase in LTE4 is partially inhibited by inhibitors of nitric oxide synthase, suggesting a link between reactive nitrogen species and arsenic-induced inflammation. Furthermore, there is a significant increase in prostacyclin (PGI2) in the serum of arsenic-treated mice. We conclude that changes in specific inflammatory mediators such as LTE4 and PGI2 are related to arsenic-induced atherosclerosis. In addition, amplified synthesis of reactive species such as peroxynitrite results in increased protein nitration in response to arsenic exposure. This finding is consistent with the pathology seen in human atherosclerotic plaques.

Neuroprotective efficacy and therapeutic time window of peroxynitrite decomposition catalysts in focal cerebral ischemia in rats

Free radicals have been implicated in cerebral ischemia reperfusion (IR) injury. Massive production of nitric oxide and superoxide results in continuous formation of peroxynitrite even several hours after IR insult. This can produce DNA strand nicks, hydroxylation and/or nitration of cytosolic components of neuron, leading to neuronal death. Peroxynitrite decomposition catalysts 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron (III) (FeTMPyP) and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) (FeTPPS) have been demonstrated to protect neurons in in vitro cultures; however, their neuroprotective efficacy in cerebral IR injury has not been explored. In the present study, we investigated the efficacy and the therapeutic time window of FeTMPyP and FeTPPS in focal cerebral ischemia (FCI). FCI was induced according to the middle cerebral artery occlusion (MCAO) method. After 2 h of MCAO and 70 h of reperfusion, the extent of neurological deficits, infarct and edema volume were measured in Sprague-Dawley rats. FeTMPyP and FeTPPS were administered at different time points 2, 6, 9 and 12 h post MCAO. FeTMPyP and FeTPPS (3 mg kg(-1), i.v.) treatment at 2 and 6 h post MCAO produced significant reduction in infarct volume, edema volume and neurological deficits. However, treatment at latter time points did not produce significant neuroprotection. Significant reduction of peroxynitrite in blood and nitrotyrosine in brain sections was observed on FeTMPyP and FeTPPS treatment. As delayed treatment of FeTMPyP and FeTPPS produced neuroprotection, we tested whether treatment had any influence over the apoptotic neuronal death. DNA fragmentation and in situ nick end-labeling assays showed that FeTMPyP and FeTPPS treatment reduced IR injury-induced DNA fragmentation. In conclusion, peroxynitrite decomposition catalysts (FeTMPyP and FeTPPS) produced prominent neuroprotection even if administered 6 h post MCAO and the neuroprotective effect is at least in part due to the reduction of peroxynitrite and apoptosis.

Peroxynitrite decomposition catalysts prevent myocardial dysfunction and inflammation in endotoxemic rats

OBJECTIVES

The aim of this study was to test whether peroxynitrite neutralizers would reduce peroxynitrite accumulation and improve myocardial contractile dysfunction and inflammation in endotoxin-treated rats.

BACKGROUND

Release of endogenous proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha in response to endotoxin is responsible for the production of large amounts of nitric oxide (NO), which may exert detrimental effects on the myocardium in animal models, isolated hearts, and isolated cardiac myocytes. Recent studies have indicated that many of the deleterious effects of NO are mediated by peroxynitrite, a powerful oxidant generated from a fast diffusion-limited reaction of NO and superoxide anion.

METHODS

We studied the effects of peroxynitrite neutralizers, such as mercaptoethylguanidine (MEG) sodium succinate (10 mg/kg) and 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrinato iron (III) (FeTPPS) (30 mg/kg) on peroxynitrite accumulation, in vivo endothelial cell-leukocyte activation on the mesenteric venule, and myocardial contractile dysfunction and inflammation in a model of sepsis induced by injection of endotoxin (10 mg/kg) in rats.

RESULTS

Mercaptoethylguanidine sodium succinate and FeTPPS largely prevented the accumulation of peroxynitrite as measured by plasma rhodamine fluorescence and heart nitrotyrosine staining. Interestingly, MEG sodium succinate and FeTPPS improved endotoxin-induced myocardial contractile dysfunction, which was associated with reduced degradation of nuclear factor kappa B inhibitory protein I-kappa-B, plasma TNF-alpha levels, and microvascular endothelial cell-leukocyte activation.

CONCLUSIONS

These observations suggest that the beneficial effects of MEG and FeTPPS on endotoxin-induced myocardial contractile dysfunction could be related to the unique effects of these compounds on cardiovascular inflammation processes.

Intratracheal poly (ADP) ribose synthetase inhibition ameliorates lung ischemia reperfusion injury

BACKGROUND

We previously demonstrated that intravenous poly (ADP) ribose synthetase (PARS) inhibition protects against experimental lung ischemia reperfusion injury (LIRI) in an in situ, hilar occlusion model. This study determined its efficacy when administered intratracheally (IT).

METHODS

Left lungs of rats were rendered ischemic for 90 minutes, and reperfused for up to 4 hours. Treated animals received INO-1001, a PARS inhibitor, intratracheally 30 minutes before ischemia, while controls were given IT vehicle at equivalent volumes. All groups contained at least 4 animals. Lung injury was quantitated utilizing vascular permeability to radiolabeled albumin, tissue myeloperoxidase (MPO) content, alveolar leukocyte cell counts, and arterial pO(2) at 4 hours of reperfusion. Electrophoretic mobility shift assays (EMSA) assessed the nuclear translocation of NFkappaB and AP-1 in injured left lungs, while ELISAs quantitated secreted cytokine induced neutrophil chemoattractant (CINC) and MCP-1 protein in bronchoalveolar lavage fluid.

RESULTS

Intratracheal PARS inhibition was 73% (p < 0.0001) and 87% (p < 0.0001) protective against increases in vascular permeability and alveolar leukocyte accumulation, respectively, and improved arterial pO(2) (p < 0.0004) at 4 hours of reperfusion. Myeloperoxidase (MPO) activity in treated lungs was reduced by 70% (p < 0.02). The nuclear translocation of NFkappaB and AP-1 was attenuated at 15 minutes of reperfusion, and the secretion of CINC and MCP-1 (p < 0.05) protein into the alveolus was diminished at 4 hours of reperfusion.

CONCLUSIONS

Intratracheal INO-1001 protects against experimental LIRI. The reduction in secreted chemokine protein at 4 hours of reperfusion appears to be mediated at the pretranscriptional level through attenuated NFkappaB and AP-1 activation. This route may optimize future donor organ management and improve lung recipient outcomes.

Proinflammatory response of alveolar type II pneumocytes to in vitro hypoxia and reoxygenation

Type II pneumocytes (T2P) are integral in preserving the integrity of the alveolar space by modulating the fluid composition surrounding the alveolar epithelium. There is also mounting evidence supporting their contribution to the development of acute inflammatory lung injury subsequent to oxidative stress. This study characterized the response of T2P to in vitro hypoxia and reoxygenation (H&R). Rat T2P from a cultured cell line (RLE-6TN) were rendered hypoxic for 2 h, and reoxygenated for up to 6 h. Activation of signaling kinases, the nuclear translocation of proinflammatory transcription factors, and quantification of secreted cytokine and chemokine protein content were assessed. Type II pneumocytes expressed activated extracellular signal regulated kinase (ERK) 1/2 maximally at 15 min of reoxygenation. C-jun n-terminal kinase (JNK) and p38 activation was minimal at all time points studied. The nuclear translocation of nuclear factor kappa B (NFkappaB) and activator protein (AP)-1 were dramatic after 15 min of reoxygenation. There was a significant increase in the protein secretion of CINC (p = 0.03), IL-1beta (p = 0.02), and monocyte chemoattractant protein-1 (p < 0.001) at 6 h of reoxygenation. Type II pneumocytes respond directly to H&R. ERK 1/2 activity peaks at 15 min of reoxygenation, and correlates temporally with the nuclear translocation of NFkappaB and AP-1. These signaling cascades likely promote the elaboration of proinflammatory mediators.