Reactive oxygen species (ROS) are key signaling molecules that play an important role in the progression of inflammatory disorders. An enhanced ROS generation by polymorphonuclear neutrophils (PMNs) at the site of inflammation causes endothelial dysfunction and tissue injury. The vascular endothelium plays an important role in passage of macromolecules and inflammatory cells from the blood to tissue. Under the inflammatory conditions, oxidative stress produced by PMNs leads to the opening of inter-endothelial junctions and promotes the migration of inflammatory cells across the endothelial barrier. The migrated inflammatory cells not only help in the clearance of pathogens and foreign particles but also lead to tissue injury. The current review compiles the past and current research in the area of inflammation with particular emphasis on oxidative stress-mediated signaling mechanisms that are involved in inflammation and tissue injury.

Reactive Oxygen Species in Inflammation and Tissue Injury

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite "sensor" that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

https://www.physiology.org/doi/pdf/10.1152/physrev.00012.2005

Signaling Mechanisms Regulating Endothelial Permeability

Pulmonary arterial hypertension (PAH) is a chronic and progressive disease leading to right heart failure and ultimately death if untreated. The first classification of PH was proposed in 1973. In 2008, the fourth World Symposium on PH held in Dana Point (California, USA) revised previous classifications. Currently, PH is devided into five subgroups. Group 1 includes patients suffering from idiopathic or familial PAH with or without germline mutations. Patients with a diagnosis of PAH should systematically been screened regarding to underlying mutations of BMPR2 gene (bone morphogenetic protein receptor type 2) or more rarely of ACVRL1 (activine receptor-like kinase type 1), ENG (endogline) or Smad8 genes. Pulmonary veno occusive disease and pulmonary capillary hemagiomatosis are individualized and designated as clinical group 1'. Group 2 'Pulmonary hypertension due to left heart diseases' is divided into three sub-groups: systolic dysfonction, diastolic dysfonction and valvular dysfonction. Group 3 'Pulmonary hypertension due to respiratory diseases' includes a heterogenous subgroup of respiratory diseases like PH due to pulmonary fibrosis, COPD, lung emphysema or interstitial lung disease for exemple. Group 4 includes chronic thromboembolic pulmonary hypertension without any distinction of proximal or distal forms. Group 5 regroup PH patients with unclear multifactorial mechanisms. Invasive hemodynamic assessment with right heart catheterization is requested to confirm the definite diagnosis of PH showing a resting mean pulmonary artery pressure (mPAP) of ≥ 25 mmHg and a normal pulmonary capillary wedge pressure (PCWP) of ≤ 15 mmHg. The assessment of PCWP may allow the distinction between pre-capillary and post-capillary PH (PCWP > 15 mmHg). Echocardiography is an important tool in the management of patients with underlying suspicion of PH. The European Society of Cardiology and the European Respiratory Society (ESC-ERS) guidelines specify its role, essentially in the screening proposing criteria for estimating the presence of PH mainly based on tricuspid regurgitation peak velocity and systolic artery pressure (sPAP). The therapy of PAH consists of non-specific drugs including oral anticoagulation and diuretics as well as PAH specific therapy. Diuretics are one of the most important treatment in the setting of PH because right heart failure leads to fluid retention, hepatic congestion, ascites and peripheral edema. Current recommendations propose oral anticoagulation aiming for targeting an International Normalized Ratio (INR) between 1.5-2.5. Target INR for patients displaying chronic thromboembolic PH is between 2–3. Better understanding in pathophysiological mechanisms of PH over the past quarter of a century has led to the development of medical therapeutics, even though no cure for PAH exists. Several specific therapeutic agents were developed for the medical management of PAH including prostanoids (epoprostenol, trepoprostenil, iloprost), endothelin receptor antagonists (bosentan, ambrisentan) and phosphodiesterase type 5 inhibitors (sildenafil, tadalafil). This review discusses the current state of art regarding to epidemiologic aspects of PH, diagnostic approaches and the current classification of PH. In addition, currently available specific PAH therapy is discussed as well as future treatments.

/pdf/pulmonary-arterial-hypertension-2on5ybg6k5.pdf

Pulmonary arterial hypertension

Introduction Nitric Oxide Source of NO in exhaled air Measurement Asthma COPD Cystic fibrosis Bronchiectasis Primary ciliary dyskinesia Rhinitis Interstitial lung diseases Pulmonary hypertension Occupational diseases Infections Chronic cough Lung cancer Lung transplant rejection Adult respiratory distress syndrome Diffuse Panbronchiolitis Carbon Monoxide Source of exhaled CO Measurement Asthma COPD Bronchiectasis Cystic fibrosis Interstitial lung disease Allergic rhinitis Infections Other conditions Exhaled Hydrocarbons Origin Measurement Asthma COPD Cystic Fibrosis Other lung diseases Exhaled Breath Condensate Origin Hydrogen peroxide Eicosanoids Products of lipid peroxidation Vasoactive amines NO-related products Ammonia Electrolytes Hydrogen ions Proteins and cytokines Other Methods Exhaled temperature Combined gas chromatography/spectroscopy The selected ion flow tube (SIFT) technique Polymer-coated surface-acoustic-wave resonators Future Directions Standardization of measurements Clinical application Profiles of mediators Measuring devices New markers

https://www.atsjournals.org/doi/pdf/10.1164/ajrccm.163.7.2009041

Exhaled markers of pulmonary disease.

Endothelial cells that make up brain capillaries and constitute the blood-brain barrier become different from peripheral endothelial cells in response to inductive factors found in the nervous system. We have established a cell culture model of the blood-brain barrier by treating brain endothelial cells with a combination of astrocyte-conditioned medium and agents that elevate intracellular cAMP. These cells form high resistance tight junctions and exhibit low rates of paracellular leakage and fluid-phase endocytosis. They also undergo a dramatic structural reorganization as they form tight junctions. Results from these studies suggest modes of manipulating the permeability of the blood-brain barrier, potentially providing the basis for increasing the penetration of drugs into the central nervous system.

/pdf/a-cell-culture-model-of-the-blood-brain-barrier-o49u0mvc9n.pdf

A cell culture model of the blood-brain barrier.

Cyclic adenosine monophosphate (AMP) has numerous important effects on cell structure and function, but its role in endothelial cells is unclear. Since cyclic AMP has been shown to affect transmembrane transport, cell growth and morphology, cellular adhesion, and cytoskeletal organization, it may be an important determinant of endotelial barrier properties. To test this we exposed bovine pulmonary artery endothelial cell monolayers to substances known to increase cyclic AMP and measured their effect on endothelial permeability to albumin and endothelial cell cyclic AMP concentrations. Cholera toxin (CT), a stimulant of the guanine nucleotide binding subunit of adenylate cyclase, led to a concentration-dependent 2-6-told increase in cyclic AMP which was associated with a 3–10-fold reduction in albumin transfer across endothelial monolayers. The effect was not specific to albumin as similar barrier-enhancing effects were also noted with an unrelated macromolecule, fluorescein isothiocyanate (FITC)-dextran (MW 70,000). Barrier enhancement with cyclic AMP elevation was also observed with forskolin, a stimulant of the catalytic subunit of adenylate cyclase. The temporal pattern of barrier enhancement seen with these agents paralleled their effects on increasing cyclic AMP, and the barrier enhancement could be reproduced by incubation with either dibutyryl cyclic AMP or Sp-cAMPS, cyclic AMP-dependent protein kinase agonists. Furthermore, the forsko-lin effect on barrier enhancement was partially reversed with Rp-cAMPS, an antagonist of cyclic AMP-dependent protein kinase. Since endothelial actin polymerization may be an important determinant of endothelial barrier function, we sought to determine whether the cyclic AMP-induced effects were associated with increases in the polymerized actin pool (F-actin). Both cholera toxin and forskolin led to apparent endothelial cell spreading and quantitative increases in endothelial cell F-actin fluorescence. In conclusion, increased endothelial cell cyclic adenine nucleotide activity was an important determinant of endothelial barrier function in vitro. The barrier enhancement was associated with increased endothelial apposition and increases in F-actin, suggesting that influences on cytoskeletal assembly may be involved in this process.

Role of cyclic adenosine monophosphate in the induction of endothelial barrier properties.

The role of endogenous circulating or locally produced endothelin-1 (ET-1) in pulmonary hypertensive states is unknown. To investigate this we measured ET-1 levels and preproendothelin-1 (prepro-ET-1) mRNA expression at various ages in control Sprague-Dawley (SDR) rats and in fawn-hooded rats (FHR), a strain which develops idiopathic pulmonary hypertension. Although serum ET-1 levels were similar in SDR and FHR, we found twofold increases in FHR whole lung homogenate ET-1 levels by radioimmunoassay. Coexisting threefold increases in preproET-1 mRNA expression were found in FHR lungs by densitometric analysis of Northern blots and by filter hybridization, suggesting the increase in lung ET-1 was due to enhanced intrapulmonary production of the peptide. To test whether the increase in lung preproET-1 mRNA was primary or secondary to established pulmonary hypertension, we compared preproET-1 mRNA expression prior to development of pulmonary hypertension in fetal (19 day gestation) and neonatal (5 day old) FHR and SDR. Despite similar right ventricular size in SDR and FHR, preproET-1 mRNA was already elevated in neonatal FHR lungs. Furthermore, we found no increase in lung preproET-1 mRNA or ET-1 levels in adult SDR with an equivalent degree of pulmonary hypertension due to chronic hypoxia, implying that the increases in ET-1 production in FHR were not a common consequence of all pulmonary hypertensive states. The functional significance of these observations remains unclear but raises the possibility of a role for ET-1 in the pathophysiology of pulmonary hypertension in the FHR.

Increased lung endothelin-1 production in rats with idiopathic pulmonary hypertension.

Fawn hooded rats (FHR), a strain of rat with a hereditary bleeding tendency due to a genetic defect in platelet aggregation, have recently been found to develop pulmonary hypertension. However, whether the pulmonary hypertension in FHR has a genetic basis or simply reflects the influence of extrinsic factors known to increase pulmonary artery pressure in other rat strains has not been fully evaluated. To further examine the structural and hemodynamic changes of pulmonary hypertension in FHR, and to investigate the extent to which alveolar hypoxia may have promoted these abnormalities, hemodynamic and morphometric measurements were made in FHR (4 to 24 wk) and compared with age-matched Sprague-Dawley (SDR) control rats. Increases in mean pulmonary artery pressure, total pulmonary resistance, and right ventricular enlargement were present in both male and female FHR and were evident at an early age (4 wk). Morphometric analysis of barium gelatin—infused lungs revealed marked pulmonary vascular remodelling i...

Factors influencing the idiopathic development of pulmonary hypertension in the fawn hooded rat.

Endothelin (ET-1) has been shown to be co-mitogenic for vascular smooth muscle cells (SMC) from human systemic arteries. A more modest growth-promoting effect has also been described in SMC from the bovine and porcine pulmonary circulation. Whether ET-1 has mitogenic properties in the human pulmonary circulation, and which ET receptor subtype mediates this response, is unknown. We first examined the effects of ET-1, ET-3, and the selective ETB agonist, Sarafotoxin 6c, on human pulmonary artery SMC growth. Cells were harvested from normal lung transplant donors. Growth was assessed by change in cell number 3 days after stimulation of quiescent cells. ET-1 in the presence of 0.3% serum produced a dose-dependent increase (82 +/- 1.5%) in cell number (threshold, 10(-11) M; maximal, 10(-7) M). ET-3 also stimulated growth (36 +/- 3.8%) but was less potent than ET-1 (threshold, 10(-9) M; maximal, 10(-7) M). The ETB selective agonist Sarafotoxin 6c had no proliferative effect. The effects of BQ123, a selective ETA receptor antagonist, on ET-1-induced growth were then assessed. BQ123 inhibited (threshold, 1.5 x 10(-7) M; maximal, 1.5 x 10(-5) M) ET-1-induced growth but had no effect on proliferation stimulated by the non-ET receptor-mediated growth factors, platelet-derived growth factor BB and 5-hydroxytryptamine. These results suggest that ET-1 is a potent co-mitogen for human proximal pulmonary artery SMC and that this effect is transduced by selective activation of the ETA receptor.

BQ123, an ETA Receptor Antagonist, Inhibits Endothelin-1-mediated Proliferation of Human Pulmonary Artery Smooth Muscle Cells

To investigate the role of endothelin-1 (ET-1) in the pathogenesis of hypoxic pulmonary hypertension, we studied the effects of a recently described endothelin-receptor antagonist (ETA), BQ123, on ...

Thomas J. Stelzner

Papers

Role of cyclic adenosine monophosphate in the induction of endothelial barrier properties.

Increased lung endothelin-1 production in rats with idiopathic pulmonary hypertension.

Factors influencing the idiopathic development of pulmonary hypertension in the fawn hooded rat.

BQ123, an ETA Receptor Antagonist, Inhibits Endothelin-1-mediated Proliferation of Human Pulmonary Artery Smooth Muscle Cells

BQ123, an ETA-receptor antagonist, attenuates hypoxic pulmonary hypertension in rats.