Endothelin-1 has a priming effect on production of superoxide anion by alveolar macrophages: its possible correlation with bronchopulmonary dysplasia

The effects of bosentan on hyperoxia-induced lung injury in neonatal rats

BACKGROUND

Bronchopulmonary dysplasia (BPD) remains an important cause of morbidity and mortality in premature infants. There is currently no proven effective treatment modality for BPD, and inflammation and oxidative injury play an important role in the pathogenesis of this disease. This study investigated the histopathological and biochemical effects of bosentan, which is a non-specific endothelin receptor antagonist with known antioxidant and anti-inflammatory properties, on hyperoxia-induced lung injury (HILI) in neonatal rats.

METHODS

The experiment was performed on newborn rats from the 3rd to the 13th postnatal day. The rats were randomly divided into six groups: Group 1 (air-exposed + saline, n = 6); Group 2 (HILI, n = 8); Group 3 (air-exposed + bosentan, n = 7); Group 4 (HILI + saline, n = 7); Group 5 (HILI + early bosentan-treated group, n = 6), and Group 6 (HILI + late bosentan-treated group, n = 7). Bosentan was administered (30 mg/kg/day) intraperitoneally. The histopathological effects of bosentan on lung tissue were assessed by their alveolar surface area, fibrosis, and smooth muscle actin (SMA) scores, and the biochemical effects on lung tissue were assessed by interleukin-1 beta (IL-1β), IL-6, IL-10, and tumor necrosis factor-alpha (TNF-α).

RESULTS

The alveolar surface area and fibrosis scores were found to be significantly higher in HILI groups compared with Group 1 (P < 0.01). The SMA scores in HILI groups were also significantly higher than Group 1 (P < 0.01). Bosentan treatment, especially late therapy, reduced all of these histopathological scores and the levels of IL-6 and TNF-α in the hyperoxia groups (P < 0.01).

CONCLUSION

This experimental study showed that bosentan had a protective effect on hyperoxic lung injury through its anti-inflammatory properties.

Inflammatory mediators in the immunobiology of bronchopulmonary dysplasia

Inflammation is important in the development of bronchopulmonary dysplasia (BPD). Polymorphonuclear cells and macrophages and proinflammatory cytokines/chemokines denote early inflammation in clinical scenarios such as in utero inflammation with chorioamnionitis or initial lung injury associated with respiratory distress syndrome or ventilator-induced lung injury. The persistence and non-resolution of lung inflammation contributes greatly to BPD, including altering the lung's ability to repair, contributing to fibrosis, and inhibiting secondary septation, alveolarization, and normal vascular development. Further understanding of the role of inflammation in the pathogenesis of BPD, in particular, during the chronic inflammatory period, offers us the opportunity to develop inflammation-related prevention and treatment strategies of this disease that has long-standing consequences for very premature infants.

Vascular endothelial function in health and diseases

The vascular endothelium constitutes approximately 1% of body mass (1kg) and has a surface area of approximately 5000m(2). The endothelium is a multifunctional endocrine organ strategically placed between the vessel wall and the circulating blood, and has a key role in vascular homeostasis. The endothelium is both a target for and mediator of cardiovascular disease. The endothelium releases several relaxing and constricting factors, which can affect vascular homeostasis. Endothelial dysfunction, whether caused by physical injury or cellular damage, leads to compensatory responses that alter the normal homeostatic properties of the endothelium. In this review, we summarized some physiological aspects of endothelial function and then we discussed endothelial dysfunction during some pathological conditions.

Oxidative and nitrosative stress in pediatric pulmonary hypertension: roles of endothelin-1 and nitric oxide

An increasing number of studies implicate oxidative stress in the development of endothelial dysfunction and the pathogenesis of cardiovascular disease. Further, this oxidative stress has been shown to be associated with alterations in both the endothelin-1 (ET-1) and nitric oxide (NO) signaling pathways such that bioavailable NO is decreased and ET-1 signaling is potentiated. However, recent data, from our groups and others, have shown that oxidative stress, ET-1, and NO are co-regulated in a complex fashion that appears to be dependent on the cellular levels of each species. Thus, when ROS levels are transiently elevated, NO signaling is potentiated through transcriptional, post-transcriptional, and post-translational mechanisms. However, in pediatric pulmonary hypertensive disorders, when reactive oxygen species (ROS) increases are sustained by ET-1 mediated activation of smooth muscle cell ET(A) subtype receptors, NOS gene expression and NO signaling are reduced. Further, increases in oxidative stress can stimulate both the expression of the ET-1 gene and the secretion of the ET-1 peptide. Finally, the addition of exogenous NO, and increasingly utilized therapy for pulmonary hypertension, can also lead to increases ROS generation via the activation of ROS generating enzymes and through the induction of mitochondrial dysfunction. Thus, this manuscript will review the available data regarding the interaction of oxidative and nitrosative stress, endothelial dysfunction, and its role in the pathophysiology of pediatric pulmonary hypertension. In addition, we will suggest avenues of both basic and clinical research that will be important to develop novel pulmonary hypertension treatment and prevention strategies, and resolve some of the remaining clinical issues regarding the use of NO augmentation.

Peptide growth factors in tracheal aspirates of mechanically ventilated preterm neonates

Basic fibroblast growth factor (bFGF or FGF-2), vascular endothelial growth factor (VEGF), and endothelin-1 (ET-1) are peptide growth factors (PGF) mediating normal lung development, maturation, injury, and repair. These PGF may therefore be involved in the pathogenesis of bronchopulmonary dysplasia (BPD). We hypothesized that elevated levels of these PGF in tracheal aspirates would be associated with a) BPD and/or death; b) markers of cell injury and apoptosis; and c) chorioamnionitis, a risk factor for BPD. Tracheal aspirates collected in 29 preterm (<34 wk gestation, 500-2000 g birth weight), mechanically ventilated infants on d 1 of life were assayed for PGF and histone-associated DNA fragments by ELISA and for LDH by enzyme assay. Clinical and pathologic examination was performed for chorioamnionitis. BPD was defined as oxygen requirement/mechanical ventilation at 28 d postnatal age. The birth weight (mean +/- SE) was 1009 +/- 85 g and median gestational age was 26 wk (range, 22-33). Eighteen infants died or developed BPD. bFGF levels were elevated in infants who died or developed BPD [median (25%,75%) level of 36 (23, 44) pg/mL versus 14 (6, 30) in the survivors without BPD, p = 0.01]. bFGF levels correlated with apoptosis (r = 0.73, p < 0.001) and LDH levels (r = 0.59, p < 0.001). VEGF and ET-1 levels were not associated with apoptosis or with BPD/death. PGF levels were not associated with chorioamnionitis. We conclude that elevated bFGF levels in the preterm trachea correlate with BPD/death and markers of cell injury and apoptosis but not with chorioamnionitis. We speculate that bFGF may play a role in the development of BPD.

Inflammation and bronchopulmonary dysplasia

Pulmonary inflammation is a key feature in the pathogenesis of bronchopulmonary dysplasia (BPD). This inflammatory process, induced by multiple risk factors, is characterized by the presence of inflammatory cells, cytokines and an arsenal of additional humoral mediators in the airways and pulmonary tissue of preterm infants with the condition. Several mediators have a direct detrimental effect on pulmonary structures by affecting cell integrity and inducing apoptosis. An imbalance between pro-inflammatory and anti-inflammatory factors can generally be considered to be a hallmark of lung injury. Intrauterine exposure to pro-inflammatory cytokines or antenatal infection may prime the fetal lung such that minimally injurious postnatal events provoke an excessive pulmonary inflammatory response that most certainly affects normal alveolization and pulmonary vascular development in preterm infants with BPD.

A catalytic antioxidant attenuates alveolar structural remodeling in bronchopulmonary dysplasia

Superoxide anion and other oxygen-free radicals have been implicated in the pathogenesis of bronchopulmonary dysplasia. We tested the hypothesis that a catalytic antioxidant metalloporphyrin AEOL 10113 can protect against hyperoxia-induced lung injury using a fetal baboon model of bronchopulmonary dysplasia. Fetal baboons were delivered by hysterotomy at 140 days of gestation (term = 185 days) and given 100% oxygen for 10 days. Morphometric analysis of alveolar structure showed that fetal baboons on 100% oxygen alone had increased parenchymal mast cells and eosinophils, increased alveolar tissue volume and septal thickness, and decreased alveolar surface area compared with animals given oxygen as needed. Treatment with AEOL 10113 (continuous intravenous infusion) during 100% oxygen exposure partially reversed these oxygen-induced changes. Hyperoxia increased the number of neuroendocrine cells in the peripheral lung, which was preceded by increased levels of urine bombesin-like peptide at 48 hours of age. AEOL 10113 inhibited the hyperoxia-induced increases in urine bombesin-like peptide and numbers of neuroendocrine cells. An increasing trend in oxygenation index over time was observed in the 100% oxygen group but not the mimetic-treated group. These results suggest that AEOL 10113 might reduce the risk of pulmonary oxygen toxicity in prematurely born infants.

Endothelin receptor antagonists in cardiology clinical trials

Endothelin-1 (ET-1) is enhanced and has been demonstrated to be a prognostic marker in patients with advanced stages of heart failure, acute ischaemic syndromes, myocardial infarction and pulmonary hypertension. Activation of the endothelin (ET) system is associated with adverse haemodynamic consequences in patients with congestive heart failure and results in coronary vasoconstriction in patients with coronary artery disease (CAD). Moreover, ET-1 raises blood pressure, induces vascular and myocardial hypertrophy and acts as the natural counterpart of nitric oxide (NO), which exerts vasodilating, antithrombotic and antiproliferative effects. This article reviews recently completed and ongoing clinical trials examining the effects of ET receptor antagonists in patients with heart failure, CAD, arterial hypertension and pulmonary hypertension.

Gadolinium chloride inhibits pulmonary macrophage influx and prevents O(2)-induced pulmonary hypertension in the neonatal rat

Newborn rats exposed to 60% O(2) for 14 d demonstrated a bronchopulmonary dysplasia-like lung morphology and pulmonary hypertension. A 21-aminosteroid antioxidant, U74389G, attenuated both pulmonary hypertension and macrophage accumulation in the O(2)-exposed lungs. To determine whether macrophage accumulation played an essential role in the development of pulmonary hypertension in this model, pups were treated with gadolinium chloride (GdCl(3)) to reduce lung macrophage content. Treatment of 60% O(2)-exposed animals with GdCl(3) prevented right ventricular hypertrophy (p < 0.05) and smooth muscle hyperplasia around pulmonary vessels, but had no effect on morphologic changes in the lung parenchyma. In addition, GdCl(3) inhibited 60% O(2)-mediated increases in endothelin-1, 8-isoprostane, and nitrotyrosine residues. Organotypic cultures of fetal rat distal lung cells were subjected to cyclical mechanical strain to assess the potential role of GdCl(3)-induced blockade of stretch-mediated cation channels in these effects. Mechanical strain caused a moderate increase of endothelin-1 (p < 0.05), which was unaffected by GdCl(3), but had no effect on 8-isoprostane or nitric oxide synthesis. A critical role for endothelin-1 in O(2)-mediated pulmonary hypertension was confirmed using the combined endothelin receptor antagonist SB217242. We concluded that pulmonary macrophage accumulation, in response to 60% O(2), mediated pulmonary hypertension through up-regulation of endothelin-1.

Endothelin in cardiovascular disease: from atherosclerosis to heart failure

Since the discovery of endothelin (ET) as a potent vasoconstrictor, increasing evidence supports the role of ET in the pathogenesis of cardiovascular diseases including coronary artery disease and congestive heart failure. This peptide not only alters vascular tone and cardiac hemodynamics, but also has a substantial role in the regulation of cellular proliferation and apoptosis, activation of monocytes and cellular matrix production. Thus, ET may play a role in the pathogenesis of cardiovascular diseases through multiple mechanisms. The development of ET receptor antagonists has lead to a greater understanding of the role of the endogenous ET system in both physiologic and pathophysiologic states. Endothelin receptor antagonists are becoming new therapeutic tools for the treatment of cardiovascular disease and their study will lead to a greater understanding of the role of ET in disease progression.

Nitric oxide dysfunction in the pathophysiology of preeclampsia

Researchers disagree as to the importance of nitric oxide (NO) in preeclampsia. Many researchers have alluded to NO's possible primary or secondary role in the development of preeclampsia, but few have correlated the dysfunction of nitric oxide production with the other metabolic derangements seen in this condition. This paper will review the evidence that the primary dysfunction in preeclampsia is a relative deficiency of available NO (secondary to oxidative degradation) and an excess of peroxynitrite (ONOO(-)). The combination of a deficiency of NO and an increase in ONOO(-) can directly or indirectly initiate the vast majority of physiological and serological changes associated with preeclampsia, such as blood pressure, increased glomerular filtration rate, proteinuria, platelet dysfunction, increased thromboxane and endothelin, and a decrease in prostacyclin. Understanding the complex role of nitric oxide in this condition may explain why previous interventions have been unsuccessful and suggest possible strategies for prevention and treatment in the future.

CyA and OxLDL cause endothelial dysfunction in isolated arteries through endothelin-mediated stimulation of O(2)(-) formation

BACKGROUND

Cyclosporin A (CyA) and oxidized low-density lipoprotein (OxLDL) cause endothelial dysfunction, partly through stimulation of O(2)(-) formation (which can inactivate nitric oxide). We investigated whether CyA and OxLDL potentiate their influence on oxidative stress, whether endothelin (ET) is a mediator of CyA- and OxLDL-induced O(2)(-) formation, and whether enhanced oxidative stress results in further attenuation of endothelium-dependent vasodilation.

METHODS AND RESULTS

Human LDL was oxidized by Cu(++). O(2)(-) formation of isolated rat aortic rings was measured using a chemiluminescence assay. Incubation (60 min) of aortic rings with CyA (10 ng-10 microg/ml) or with OxLDL (300 microg/ml) caused a significant, dosedependent increase of the basal O(2)(-) formation. Pretreatment of the aortic rings with CyA (10 ng/ml) further enhanced the OxLDL-induced O(2)(-) formation by factor 1.9. The enhancement of the OxLDL-induced stimulation of O(2)(-) formation by CyA could be completely blocked by BQ123, a selective endothelin-1 (ET-1) receptor antagonist. Likewise, exogenously applied ET-1 (1 nM) potentiated the OxLDL-induced O(2)(-) formation by factor 1.8. Endothelium-dependent dilation was measured in isolated rings of rabbit aorta superfused with physiological salt solution in an organ bath. Incubation of the aortic rings with CyA (10 microg/ml, 60 min) or with OxLDL (300 microg/ml, 60 min) alone did not attenuate endothelium-dependent dilations. However, coincubation of the aortic rings with CyA+OxLDL in the presence of diethyl-dithio-carbamate, an inhibitor of the endogenous superoxide dismutase, caused a 60% inhibition of acetylcholine-induced dilator responses.

CONCLUSIONS

Coincubation of isolated aortic rings with CyA and OxLDL causes a potent enhancement of vascular O(2)(-) formation. ET-1 seems to be mediator of the CyA-induced O(2)(-) formation. Enhanced oxidative stress results in further attenuation of endothelium dependent vasodilation.

Early increase in endothelin-1 in tracheal aspirates of preterm infants: correlation with bronchopulmonary dysplasia

OBJECTIVES

To determine whether endothelin-1 (ET-1) in tracheal aspirates (TA) is a specific marker for acute lung injury in preterm infants with respiratory distress syndrome (RDS) who progress to bronchopulmonary dysplasia (BPD); and to investigate the relationship between TA ET-1 and the proinflammatory cytokines, interleukin-6 (IL-6) and IL-8, as early mediators of BPD.

STUDY DESIGN

We measured TA ET-1, IL-6, and IL-8 levels in preterm infants whose lungs were mechanically ventilated for RDS, categorized into two groups, BPD or non-BPD, on the basis of oxygen requirement at 36 weeks' postconceptional age.

RESULTS

A total of 106 TA samples were obtained from 34 infants with gestational ages ranging from 24 to 28 weeks on days 1, 3, 5, and 7 of life. There was a wide range of ET-1 concentration. TA ET-1 levels were significantly elevated on days 1, 3, and 7 in infants in whom BPD developed, in comparison with the non-BPD group (Mann-Whitney U test: p < 0.01). TA IL-8 levels were elevated on days 1, 3, 5, and 7 in the BPD group (p < 0.01); TA IL-6 levels were elevated (p < 0.05) only on day 5. There was a similarity in pattern of increase of TA ET-1 and TA IL-8 levels in the BPD group, with both being elevated in the first 24 hours of life and through the first week. There was no correlation between ET-1 and IL-8 values.

CONCLUSION

Early significant increase in the TA ET-1 and IL-8 concentrations in preterm infants with acute lung injury correlates with subsequent progression to BPD.

Rat peritoneal macrophages express endothelin ET(B) but not endothelin ET(A) receptors

The properties of endothelin receptors on rat peritoneal macrophages were examined in in vitro receptor autoradiographic binding experiments and in a reverse transcription-polymerase chain reaction (RT-PCR) study. Dense and specific [(125)I]endothelin-1 binding sites were detected on the macrophages. [(125)I]Tyr13-Suc-[Glu9,Ala(11,15)]-endothelin-1(8-21) , IRL1620, a selective endothelin ET(B) receptor ligand, but not [(125)I](N-[(hexahydro-1-azepinyl)carbonyl])L-Leu(1-Me)D-Trp-D-Tyr , PD151242, a selective endothelin ET(A) receptor ligand, specifically bound to rat macrophages (Kd = 0.75 +/- 0.19 nM, Bmax = 7.77 +/- 2.50 fmol/mg). RT-PCR experiments also showed the expression of endothelin ET(B) receptor mRNA, but not endothelin ET(A) receptor mRNA, in these macrophages. These results indicate that rat peritoneal macrophages apparently express the endothelin ET(B) receptor but not the endothelin ET(A) receptor.

Expression of endothelin receptors and nitric oxide synthase in the brain of stroke-prone spontaneously hypertensive rats with cerebral apoplexy

Endothelin (ET) receptors, ET-1-like immunoreactivity and nitric oxide synthase (NOS) were examined in the brain of stroke-prone spontaneously hypertensive rats (SHRSPs) with cerebral apoplexy. Our receptor autoradiographic method with 125I-ET-1 and unlabeled selective ligands for ET receptors revealed de novo expressions of ET(A) and ET(B) receptors in areas of neural lesions with cerebrovascular damage in SHRSPs. Immunohistochemical staining for ET-1 showed clear ET-1-like immunoreactivity in areas with highly expressed ET receptors. Histochemical studies on astrocytes and microglia suggested that these glial cells, aggregating in lesions, may carry ET receptors, ET-1-like immunoreactivity. Furthermore, NOS detected histochemically using an NADPH-diaphorase staining method was rich on glial cells in damaged areas of the brain in SHRSPs with cerebral apoplexy. Our data suggest the pathophysiological significance of glial ET(A) and ET(B) receptors, ET-1 and NOS in neural lesions of SHRSPs.

High endothelin-1 in the airways of preterm infants is associated with less severe respiratory distress during the early postnatal period

OBJECTIVE

To study the relationship between endothelin-1 (ET-1) in the airways and respiratory distress in preterm infants.

METHODS

ET-1 was determined in 60 tracheal aspirates from 11 preterm intubated infants (gestational age 28.0 +/- 2.5 weeks) during the first week of life.

RESULTS

The concentration of ET-1 of the aspirates was 6 to 2760 pg/mL (median 293 pg/mL). Negative correlations existed between mean log ET-1 and mean airway pressure (R2 = .812) and fraction of inspired oxygen (R2 = .591), whereas a positive correlation was found between the arteriolar/alveolar oxygenation ratio within 3 hours of birth and mean log ET-1 on the first day (R2 = .555).

CONCLUSION

The association of high ET-1 in the airways with less severe respiratory distress in the early postnatal period may be attributable to effects of ET-1 on surfactant secretion or development of airway epithelium.