Effects of a dual endothelin-1 receptor antagonist on airway obstruction and acute lung injury in sheep following smoke inhalation and burn injury

HIF-1α Enhances Vascular Endothelial Cell Permeability Through Degradation and Translocation of Vascular Endothelial Cadherin and Claudin-5 in Rats With Burn Injury

The mechanism underlying burn injury-induced enhanced vascular endothelial permeability and consequent body fluid extravasation is unclear. Here, the rat aortic endothelial cells (RAECs) were treated with the serum derived from rats with burn injury to elucidate the mechanism. Sprague-Dawley (SD) rats were grouped as follows (10 rats/group): control, 2, 4, 8, 12, and 24 hours postburn groups. The heart, liver, kidney, lung, jejunum, and ileum of rats injected with 2% Evans blue (EB) through the tail vein were excised to detect the EB level in each organ. The serum levels of hypoxia-inducible factor-1α (HIF-1α) and endothelin-1 (ET-1) were examined using enzyme-linked immunosorbent assay (ELISA). The effect of serum from 12-hour postburn group on the membrane permeability of RAEC monolayer, as well as on the mRNA and protein levels of ET-1, endothelin receptor A (ETA), ETB, and zonula occludens (ZO-1), was analyzed using quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting. The membrane permeability of GV230/HIF-1α-transfected or shRNA-HIF-1α-transfected RAECs, as well as the expression levels of HIF-1α, ET-1, ETA, ETB, vascular endothelial (VE)-cadherin, and claudin-5, was analyzed using qRT-PCR and western blotting, whereas the localization of VE-cadherin and claudin-5 was examined using immunofluorescence. The serum HIF-1α and ET-1 levels in the burn groups, which peaked at 12 hours postburn, were significantly upregulated (P < .01) when compared with those in the control group. Additionally, the serum HIF-1α levels were positively correlated with vascular permeability. Compared with the shRNA-negative control-transfected RAECs, the shRNA-II/HIF-1α-transfected RAECs exhibited downregulated expression of HIF-1α, ET-1, ETA, and ETB (P < .01), and upregulated expression of ZO-1, claudin-5, and VE-cadherin (P < .05). Compared with the GV230-transfected RAECs, the GV230/HIF-1α-transfected RAECs exhibited upregulated expression of HIF-1α, ET-1, ETA, and ETB (P < .01), and downregulated expression of ZO-1, claudin-5, and VE-cadherin (P < .05). The GV230/HIF-1α-transfected RAECs exhibited degradation and translocation of VE-cadherin and claudin-5. In addition to degradation of VE-cadherin and claudin-5, HIF-1α mediated enhanced endothelial cell permeability through upregulation of ET-1, ETA, and ETB, and downregulation of ZO-1 and VE-cadherin in rats with burn injury.

Endothelin receptor antagonist improves donor lung function in an ex vivo perfusion system

BACKGROUND

A lung transplant is the last resort treatment for many patients with advanced lung disease. The majority of donated lungs come from donors following brain death (BD). The endothelin axis is upregulated in the blood and lung of the donor after BD resulting in systemic inflammation, lung damage and poor lung graft outcomes in the recipient. Tezosentan (endothelin receptor blocker) improves the pulmonary haemodynamic profile; however, it induces adverse effects on other organs at high doses. Application of ex vivo lung perfusion (EVLP) allows the development of organ-specific hormone resuscitation, to maximise and optimise the donor pool. Therefore, we investigate whether the combination of EVLP and tezosentan administration could improve the quality of donor lungs in a clinically relevant 6-h ovine model of brain stem death (BSD).

METHODS

After 6 h of BSD, lungs obtained from 12 sheep were divided into two groups, control and tezosentan-treated group, and cannulated for EVLP. The lungs were monitored for 6 h and lung perfusate and tissue samples were processed and analysed. Blood gas variables were measured in perfusate samples as well as total proteins and pro-inflammatory biomarkers, IL-6 and IL-8. Lung tissues were collected at the end of EVLP experiments for histology analysis and wet-dry weight ratio (a measure of oedema).

RESULTS

Our results showed a significant improvement in gas exchange [elevated partial pressure of oxygen (P = 0.02) and reduced partial pressure of carbon dioxide (P = 0.03)] in tezosentan-treated lungs compared to controls. However, the lungs hematoxylin-eosin staining histology results showed minimum lung injuries and there was no difference between both control and tezosentan-treated lungs. Similarly, IL-6 and IL-8 levels in lung perfusate showed no difference between control and tezosentan-treated lungs throughout the EVLP. Histological and tissue analysis showed a non-significant reduction in wet/dry weight ratio in tezosentan-treated lung tissues (P = 0.09) when compared to control.

CONCLUSIONS

These data indicate that administration of tezosentan could improve pulmonary gas exchange during EVLP.

Emerging drugs for acute lung injury

INTRODUCTION

Acute respiratory distress syndromes (ARDS) are devastating disorders of overwhelming pulmonary inflammation and hypoxemia, resulting in high morbidity and mortality.

AREAS COVERED

The main pharmacological treatment strategies have focused on the attempted inhibition of excessive inflammation or the manipulation of the resulting physiological derangement causing respiratory failure. Additionally, such interventions may allow reduced occurence mechanical ventilation injury. Despite promising preclinical and small clinical studies, almost all therapies have been shown to be unsuccessful in large-scale randomized controlled trials. The evidence for pharmacological treatment for ARDS is reviewed. Potential future treatments are also presented.

EXPERT OPINION

We suggest for future clinical trials addressing prevention and early intervention to attenuate lung injury and progression to respiratory failure.

Effect of the endothelin receptor antagonist tezosentan on alpha-naphthylthiourea-induced lung injury in rats

Acute lung injury is an inflammatory syndrome that increases the permeability of the blood-gas barrier, resulting in high morbidity and mortality. Despite intensive research, treatment options remain limited. We investigated the protective efficacy of tezosentan, a novel, dual endothelin receptor antagonist, in an experimental model of alpha-naphthylthiourea (ANTU)-induced acute lung injury in rats. ANTU was intraperitoneally (i.p.) injected into rats at a dose of 10 mg/kg. Tezosentan was injected 30 minutes before ANTU was subcutaneously (s.c.) injected at doses of 2, 10, or 30 mg/kg, 60 minutes before ANTU was injected at doses of 2, 10, or 30 mg/kg (i.p.), and 90 minutes before ANTU at a dose of 10 mg/kg (i.p.). Four hours later, the lung weight/body weight (LW/BW) ratio and pleural effusion (PE) were measured. When injected 30 minutes before ANTU at doses of 2, 10, or 30 mg/kg (s.c.), tezosentan had no effect on lung pathology. When injected 60 minutes before ANTU at doses of 2, 10, or 30 mg/kg (i.p.) or 90 minutes before ANTU (10 mg/kg, i.p.), tezosentan significantly decreased the PE/BW ratio and had a prophylactic effect on PE formation at all doses. Therefore, tezosentan may attenuate lung injury. Furthermore, its acute and inhibitory effects on fluid accumulation were more effective in the pleural cavity than in the interstitial compartment in this experimental model.

A novel in vivo ovine model of transfusion-related acute lung injury (TRALI)

BACKGROUND AND OBJECTIVES

Even with the introduction of specific risk-reduction strategies, transfusion-related acute lung injury (TRALI) continues to be a leading cause of transfusion-related morbidity and mortality. Existing small animal models have not yet investigated TRALI resulting from the infusion of heat-treated supernatant from whole blood platelet concentrates. In this study, our objective was the development of a novel in vivo two-event model of TRALI in sheep.

MATERIALS AND METHODS

Lipopolysaccharide (LPS; 15 μg/kg) as a first event, modelled clinical infection. Transfusion (estimated at 10% of total blood volume) of heat-treated pooled supernatant from date-of-expire human whole blood platelet concentrates (d5-PLT-S/N) was used as a second event. TRALI was defined by both hypoxaemia that developed either during the transfusion or within two hours of its completion and post-mortem histological evidence of pulmonary oedema.

RESULTS

LPS infusion did not cause lung injury itself, but did result in decreased circulating levels of lymphocytes and neutrophils with evidence of the latter becoming sequestered in the lungs. Sheep that received LPS (first event) followed by d5-PLT-S/N (second event) displayed decreased pulmonary compliance, decreased end tidal CO(2) and increased arterial partial pressure of CO(2) relative to control sheep, and 80% of these sheep developed TRALI.

CONCLUSIONS

This novel ovine two-event TRALI model presents a new tool for the investigation of TRALI pathogenesis. It represents the first description of an in vivo large animal model of TRALI and the first description of TRALI caused by transfusion with heat-treated pooled supernatant from human whole blood platelet concentrates.

Muscarinic receptor antagonist therapy improves acute pulmonary dysfunction after smoke inhalation injury in sheep

OBJECTIVES

Inhalation injury contributes to the morbidity and mortality of burn victims. In humans and in an ovine model of combined smoke inhalation and burn injury, bronchospasm and acute airway obstruction contribute to progressive pulmonary insufficiency. This study tests the hypothesis that muscarinic receptor antagonist therapy with tiotropium bromide, an M1 and M3 muscarinic receptor antagonist, will decrease the airway constrictive response and acute bronchial obstruction to improve pulmonary function compared to injured animals without treatment.

DESIGN

Randomized, prospective study involving 32 sheep.

SETTING

Large-animal intensive care research laboratory.

INTERVENTIONS

The study consisted of six groups: a sham group (n=4, instrumented noninjured), a control group (n=6, injured and not treated), and tiotropium bromide-treated groups, including both preinjury and postinjury nebulization protocols. Treatments for these groups included nebulization with 36 μg of tiotropium bromide 1 hr before injury (n=6) and postinjury nebulization protocols of 18 μg (n=6), 36 μg (n=6), and 72 μg (n=4) administered 1 hr after injury. All treated groups received an additional 14.4 μg every 4 hrs for the 24-hr study period.

MAIN RESULTS

Pretreatment with tiotropium bromide significantly attenuated the increases in ventilatory pressures, pulmonary dysfunction, and upper airway obstruction that occur after combined smoke inhalation and burn injury. Postinjury treatments with tiotropium bromide were as effective as pretreatment in preventing pulmonary insufficiency, although a trend toward decreased obstruction was present only in all post-treatment conditions. There was no improvement noted in pulmonary function in animals that received a higher dose of tiotropium bromide.

CONCLUSIONS

This study describes a contribution of acetylcholine to the airway constrictive and lumenal obstructive response after inhalation injury and identifies low-dose nebulization of tiotropium bromide as a potentially efficacious therapy for burn patients with severe inhalation injury.

ACUTE BRONCHIAL OBSTRUCTION IN SHEEP: HISTOPATHOLOGY AND GLAND CYTOKINE EXPRESSION

An ovine model of smoke inhalation and burn (S+B) injury models the pathophysiology of these injuries in humans. This study examines the degree of airway obstruction, associated histopathology, and bronchial gland cell expression of cytokines during the first 24 hours after S+B injury in sheep. Changes in the mean degree of obstruction were limited to the bronchial airways, showing significant increases in obstruction with time, P<.05. At 4 hours after injury, the obstructive material was predominantly mucus, with neutrophils clustered around and within gland acini. At 8 to 24 hours, bronchial obstruction was characterized by increased inflammatory cell accumulation. Immunohistochemical results showed that gland cells constitutively express and secrete interleukin (IL)-1beta, and that after injury there is an increase in the percentage of gland cells staining for IL-1alpha, IL-8, and tumor necrosis factor (TNF)-alpha, P<.05.

Respiratory burst function of ovine neutrophils

BACKGROUND

Respiratory burst function resulting in the release of reactive oxygen species such as superoxide anion (O2-) from neutrophils is one of the key mechanisms of the innate immune system, and maladaptive control of this mechanism is thought to play a pivotal role in the development of pathologies such as acute lung injury and sepsis. Ovine models of these pathologies are limited by the poor understanding of ovine neutrophil respiratory burst function.

RESULTS

Aspects of ovine neutrophil respiratory burst function to be characterised were: i) the maximum rate of O2- generated (Vmax); ii) the time taken to reach Vmax; iii) the total amount of O2- generated during the reaction; and iv) the duration of the reaction. As well as for unstimulated neutrophils, these aspects were also characterised after incubation with a priming agonist (platelet activating factor [PAF], tumour necrosis factor alpha [TNF-alpha] and lipopolysaccharides [LPS]) activating agonists (N-formylmethionyl-leucyl-phenylalanine [fMLP] and phorbol 12-myristate 13-acetate [PMA]) or a combination of a priming and an activating agonist. In the absence of priming or activating agonists, ovine neutrophils displayed a low level of respiratory burst function which was not enhanced by either PAF, TNF-alpha, LPS or fMLP, but was significantly enhanced by PMA. The PMA-induced respiratory burst function was further enhanced by pre-incubation with PAF, but not with TNF-alpha or LPS. By varying the length of pre-incubation with PAF it was demonstrated that this effect decreased as the duration of pre-incubation with PAF increased, and that PAF was enhancing PMA's effects rather than PMA enhancing PAF's effects.

CONCLUSION

This study successfully adapted a commonly used method of measuring human neutrophil respiratory burst function to characterise different aspects of ovine neutrophil respiratory burst function. This improved understanding of ovine neutrophils will facilitate the validitation of ovine biomedical models of human pathologies in which neutrophils have been implicated.

Endothelin-1 impairs alveolar epithelial function via endothelial ETB receptor

RATIONALE

Endothelin-1 (ET-1) is increased in patients with high-altitude pulmonary edema and acute respiratory distress syndrome, and these patients have decreased alveolar fluid reabsorption (AFR).

OBJECTIVES

To determine whether ET-1 impairs AFR via activation of endothelial cells and nitric oxide (NO) generation.

METHODS

Isolated perfused rat lung, transgenic rats deficient in ETB receptors, coincubation of lung human microvascular endothelial cells (HMVEC-L) with rat alveolar epithelial type II cells or A549 cells, ouabain-sensitive 86Rb+ uptake.

MEASUREMENTS AND MAIN RESULTS

The ET-1-induced decrease in AFR was prevented by blocking the endothelin receptor ETB, but not ETA. Endothelial-epithelial cell interaction is required, as direct exposure of alveolar epithelial cells (AECs) to ET-1 did not affect Na,K-ATPase function or protein abundance at the plasma membrane, whereas coincubation of HMVEC-L and AECs with ET-1 decreased Na,K-ATPase activity and protein abundance at the plasma membrane. Exposing transgenic rats deficient in ETB receptors in the pulmonary vasculature (ET-B(-/-)) to ET-1 did not decrease AFR or Na,K-ATPase protein abundance at the plasma membrane of AECs. Exposing HMVEC-L to ET-1 led to increased NO, and the ET-1-induced down-regulation of Na,K-ATPase was prevented by the NO synthase inhibitor l-NAME, but not by a guanylate cyclase inhibitor.

CONCLUSIONS

We provide the first evidence that ET-1, via an endothelial-epithelial interaction, leads to decreased AFR by a mechanism involving activation of endothelial ETB receptors and NO generation leading to alveolar epithelial Na,K-ATPase down-regulation in a cGMP-independent manner.

Effects of endothelin receptor antagonism on acute lung injury induced by chlorine gas

OBJECTIVE

To test the hypothesis that the endothelin system is involved in chlorine gas-induced lung injury.

DESIGN

Experimental study.

SETTING

Academic research laboratory.

SUBJECTS

Twenty-four domestic juvenile pigs.

INTERVENTIONS

Anesthetized, ventilated pigs were exposed to chlorine gas (400 parts per million in air) for 20 mins and then randomly allocated to four groups (n=6 in each group). The tezosentan pretreatment group received the dual endothelin receptor antagonist tezosentan 20 mins before and hyperoxic gas (Fio2 0.6) after chlorine gas exposure. The tezosentan postinjury treatment group received hyperoxic gas after chlorine gas exposure and tezosentan 60 mins later. Animals in the oxygen group received hyperoxic gas after chlorine gas exposure. Pigs in the fourth group (air) were ventilated with room air (Fio2 0.21) throughout the experiment.

MEASUREMENTS AND MAIN RESULTS

Hemodynamics, gas exchange, lung mechanics, and plasma endothelin-1 were evaluated for 6 hrs. Chlorine gas exposure induced an increase in circulating endothelin-1 by 90% (p<.05). The acute chlorine gas-induced rise in pulmonary vascular resistance was partly blocked by tezosentan pretreatment (p<.001). Tezosentan postinjury treatment also decreased pulmonary vascular resistance to levels significantly lower than in the air and oxygen groups (p<.001). Recovery of peak airway pressure was better in the tezosentan-treated groups than in the air group. There were significant linear relationships between circulating endothelin-1 and pulmonary vascular resistance (r=.47, p<.001) and endothelin-1 and peak airway pressure (r=.41, p<.001). These relationships were modified by tezosentan.

CONCLUSIONS

Tezosentan modified chlorine gas-induced pulmonary dysfunction, indicating that the endothelin system is involved in this mode of acute lung injury.

Treatment of pulmonary hypertension with selective pulmonary vasodilators

PURPOSE OF REVIEW

Pulmonary vasodilators are important in the management of pulmonary hypertension. Although systemic vasodilators may be effective in lowering pulmonary artery pressure, systemic vasodilation is the main limitation to dose titration. This review summarizes the latest research and developments in pulmonary vasodilators in the management of acute and chronic pulmonary hypertension.

RECENT FINDINGS

Nitric oxide, the prototype of selective pulmonary vasodilators, remains an effective option in the management of pulmonary hypertension; however, cost and complexity of administration have led to consideration of other pulmonary vasodilators. Animal research suggests that nitric oxide may have an important role in the prevention of pulmonary hypertension after cardiopulmonary bypass. Experience with phosphodiesterase inhibitors, as monotherapy or as part of combination therapy, suggests that these agents improve cardiopulmonary hemodynamics and can be considered as alternatives and/or adjuncts to nitric oxide. Prostacyclins are a versatile class of pulmonary vasodilator as they have been shown to improve pulmonary hemodynamics administered intravenously or via inhalation. Endothelin receptor antagonists have been shown to be effective for long-term management of pulmonary hypertension. Several gene therapy strategies are currently undergoing evaluation.

SUMMARY

Selective pulmonary vasodilation can be achieved through delivery of vasodilators directly to the lungs or targeting pulmonary specific processes. Several therapeutic options are available that demonstrate selectivity for the pulmonary vasculature. These agents can facilitate optimization of cardiopulmonary hemodynamics.

Pharmacological therapy for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is an Inflammatory process caused by a variety of direct and indirect injuries to the lungs. Despite improvements in supportive care and advances in ventilator management, mortality in patients with ARDS remains high. Multiple pharmacological interventions have been investigated but have not shown improved survival. Clinical trials using corticosterolds, prostaglandins, nitric oxide, prostacyclin, surfactant, lisofylline, ketoconazole, N-acetylcystelne, and fish oil have been unable to show a statistically significant Improvement in patient mortality. As more is understood about the pathophyslology of ARDS, treatment strategies such as increasing alveolar fluid clearance through activation of sodium channels, enhancing repair of alveolar epithelium with growth factors, inhibiting fibrin deposition, blocking proinflammatory transcription factors, preventing the effect of potent vasocontrictors such as endothelin, and using antibodies against key inflammatory cytokines are being explored. This review focuses on the pharmacological treatments studied clinically, proposed reasons for their lack of success, and new concepts emerging in ARDS therapy.

Endothelin antagonists: new bullets against lung injury?

Acute lung injury is a syndrome of inflammation and of increased permeability of the blood–gas barrier. Endothelins are thought to exert proinflammatory effects. Kuklin and colleagues show that the endothelin receptor antagonist tezosentan reduces pulmonary edema in endotoxemic sheep, in parallel with a prevention of protein kinase C-α activation. In turn, the level of some cytokines increased after tezosentan treatment. Whether these contrasting effects of endothelin blockade on inflammatory mechanisms have clinical relevance and whether these agents might benefit patients with acute lung injury is unknown.