Assessment of circulatory and pulmonary endothelin-1 levels in a lavage-induced surfactant-depleted lung injury rabbit model with repeated open endotracheal suctioning and hyperinflation

Roles of alpha-7 nicotinic acetylcholine receptors and spleen in the lung injury induced by a repeated saline lavage in rat

BACKGROUND

The study aimed to determine whether or notα7 nicotinic acetylcholine receptors (α7nAChR) induce anti-inflammatory effects directly in the lung or through the spleen pathway in a sterile model of lung injury by saline lavage.

METHODS

Male Sprague Dawley rats were divided into seven groups; Sham, splenectomy (SPX), saline lavage (LAV), LAV treated with α7nAChR agonist nicotine (LAV + NIC), and LAV treated with NIC and a selective α7nAChR antagonist MLA (LAV+MLA+NIC), LAV and splenectomy (LAV+SPX), and LAV+SPX treated with nicotine (LAV+SPX+NIC). Tracheostomy and catheterization of the femoral artery were performed under deep anesthesia. Animals were subjected to volume-controlled ventilation and lung injury by 10 repeated saline lavages. Splenectomy was achieved one week before the induction of lung injury. The recovery phase lasted for 3 h, and drugs were injected 1 h after the last lavage.

RESULTS

Mean arterial blood pressure (MBP), heart rate (HR), PaO₂, PaO₂/FiO₂ ratio, and pH decreased, whereas, maximal inspiratory (MIP) and expiratory (MEP) pressures, and PaCO₂ increased 1 h after the saline lavage. Nicotine corrected entirely all the above parameters in the LAV + NIC group. MLA or SPX prevented the effects of nicotine on the above parameters, except that MLA had no extra effect on MIP or MEP. In addition, nicotine improved lung compliance in the LAV + NIC and LAV + SPX + NIC groups, though it was inhibited by MLA in the LAV + MLA + NIC group. The increases of plasma and lung tissue malondialdehyde (MDA) in the LAV group were diminished by nicotine, whereas, MLA and SPX prevented these reductions. Besides, nicotine could reduce plasma MDA in the LAV + SPX + NIC group. Total BAL cell count, protein BAL/protein plasma ratio, and lung histological scores were attenuated by nicotine in the LAV + NIC group, whereas, MLA reversed the mentioned alterations in the LAV + MLA + NIC group. However, splenectomy could not stop the decreasing effect of nicotine on the total BAL cell in the LAV + SPX + NIC group.

CONCLUSIONS

In this study, we indicated that α7nAChR and spleen play roles in cholinergic anti-inflammatory pathways in saline lavage-induced lung injury. However, our results are in favor of at least some direct effects of α 7nAChR in the lung.

Biomarkers in premature calves with and without respiratory distress syndrome

BACKGROUND

Approaches to the evaluation of pulmonary arterial hypertension (PAH) in premature calves by using lung-specific epithelial and endothelial biomarkers are needed.

OBJECTIVE

To investigate the evaluation of PAH in premature calves with and without respiratory distress syndrome (RDS) by using lung-specific epithelial and endothelial biomarkers and determine the prognostic value of these markers in premature calves.

ANIMALS

Fifty premature calves with RDS, 20 non-RDS premature calves, and 10 healthy term calves.

METHODS

Hypoxia, hypercapnia, and tachypnea were considered criteria for RDS. Arterial blood gases (PaO2 , PaCO2 , oxygen saturation [SO2 ], base excess [BE], and serum lactate concentration) were measured to assess hypoxia. Serum concentrations of lung-specific growth differentiation factor-15 (GDF-15), asymmetric dimethylarginine (ADMA), endothelin-1 (ET-1), vascular endothelial growth factor (VEGF), and surfactant protein D (SP-D) were measured to assess PAH.

RESULTS

Arterial blood pH, PaO2 , SO2 , and BE of premature calves with RDS were significantly lower and PaCO2 and lactate concentrations higher compared to non-RDS premature and healthy calves. The ADMA and SP-D concentrations of premature calves with RDS were lower and serum ET-1 concentrations higher than those of non-RDS premature and healthy calves. No statistical differences for GDF-15 and VEGF were found among groups.

CONCLUSIONS AND CLINICAL IMPORTANCE

Significant increases in serum ET-1 concentrations and decreases in ADMA and SP-D concentrations highlight the utility of these markers in the diagnosis of PAH in premature calves with RDS. Also, we found that ET-1 was a reliable diagnostic and prognostic biomarker for PAH and predicting mortality in premature calves.

Effects of nitric oxide donor on the lung functions in a saline lavage-induced model of ARDS

Acute respiratory distress syndrome (ARDS) is characterized by acute hypoxemia, neutrophil-mediated inflammation, and lung edema formation. Whereas lung damage might be alleviated by nitric oxide (NO), goal of this study was to evaluate if intratracheal NO donor S-nitroso-N-acetylpenicillamine (SNAP) can positively influence the lung functions in experimental model of ARDS. New Zealand rabbits with respiratory failure induced by saline lavage (30 ml/kg, 9+/-3 times) were divided into: ARDS group without therapy, ARDS group treated with SNAP (7 mg/kg i.t.), and healthy Control group. During 5 h of ventilation, respiratory parameters (blood gases, ventilatory pressures) were estimated. After anesthetics overdosing, left lung was saline-lavaged and cell count, cell viability and protein content in bronchoalveolar lavage fluid (BALF) were measured. Right lung tissue was used for estimation of wet/dry weight ratio, concentration of NO metabolites, and histomorphological investigation. Repetitive lung lavage induced lung injury, worsened gas exchange, and damaged alveolar-capillary membrane. Administration of SNAP reduced cell count in BALF, lung edema formation, NO metabolites, and histopathological signs of injury, and improved respiratory parameters. Treatment with intratracheal SNAP alleviated lung injury and edema and improved lung functions in a saline-lavaged model of ARDS suggesting a potential of NO donors also for patients with ARDS.

Effects of PDE3 Inhibitor Olprinone on the Respiratory Parameters, Inflammation, and Apoptosis in an Experimental Model of Acute Respiratory Distress Syndrome

This study aimed to investigate whether a selective phosphodiesterase-3 (PDE3) inhibitor olprinone can positively influence the inflammation, apoptosis, and respiratory parameters in animals with acute respiratory distress syndrome (ARDS) model induced by repetitive saline lung lavage. Adult rabbits were divided into 3 groups: ARDS without therapy (ARDS), ARDS treated with olprinone i.v. (1 mg/kg; ARDS/PDE3), and healthy ventilated controls (Control), and were oxygen-ventilated for the following 4 h. Dynamic lung-thorax compliance (Cdyn), mean airway pressure (MAP), arterial oxygen saturation (SaO2), alveolar-arterial gradient (AAG), ratio between partial pressure of oxygen in arterial blood to a fraction of inspired oxygen (PaO2/FiO2), oxygenation index (OI), and ventilation efficiency index (VEI) were evaluated every hour. Post mortem, inflammatory and oxidative markers (interleukin (IL)-6, IL-1β, a receptor for advanced glycation end products (RAGE), IL-10, total antioxidant capacity (TAC), 3-nitrotyrosine (3NT), and malondialdehyde (MDA) and apoptosis (apoptotic index and caspase-3) were assessed in the lung tissue. Treatment with olprinone reduced the release of inflammatory mediators and markers of oxidative damage decreased apoptosis of epithelial cells and improved respiratory parameters. The results indicate a future potential of PDE3 inhibitors also in the therapy of ARDS.

Acupoint Catgut Embedding Improves the Lipopolysaccharide-Induced Acute Respiratory Distress Syndrome in Rats

Background

This study investigated the potential therapeutic effects of acupoint catgut embedding (ACE) at ST36 and BL13 on lipopolysaccharide- (LPS-) induced acute respiratory distress syndrome (ARDS) in rats.

Materials and Methods

Male Sprague-Dawley rats were randomized into the normal saline (NS group with a sham procedure), lipopolysaccharide (LPS group with a sham procedure), and LPS plus ACE (LPS+ACE with ACE at bilateral BL13 and ST36 acupoints one day before LPS injection) groups. After intratracheal instillation of normal saline or LPS (0.5 mg/kg), all rats were subjected to mechanical ventilation for 4 h. Their blood gas was analyzed before and after lung injury, and their lung pressure-volumes were measured longitudinally. The levels of TNF-α, IL-6, IL-10, and phosphatidylcholine (PC) and total proteins (TP) in bronchial alveolar lavage fluid (BALF) were assessed. Their wet to dry lung weight ratios, histology, myeloperoxidase (MPO), superoxide dismutase (SOD) activity, and malondialdehyde (MDA) levels were measured. Their lung aquaporin 1 (AQP1) and Occludin protein levels were analyzed.

Results

LPS administration significantly decreased the ratios of PaO₂/FiO₂ and pressure-volumes and induced lung inflammation and injury by increased concentrations of TNF-α, IL-6, IL-10, and TP in BALF and MPO and MDA in the lung but decreased PC in BALF and SOD activity in the lungs. LPS also reduced AQP1 and Occludin protein levels in the lung of rats. In contrast, ACE significantly mitigated the LPS-induced lung injury, inflammation, and oxidative stress and preserved the AQP1 and Occludin contents in the lung of rats.

Conclusions

ACE significantly improved respiratory function by mitigating inflammation and oxidative stress and preserving AQP1 and Occludin expression in the lung in a rat model of LPS-induced ARDS.

Effects of roflumilast, a phosphodiesterase-4 inhibitor, on the lung functions in a saline lavage-induced model of acute lung injury

Acute lung injury (ALI) is associated with deterioration of alveolar-capillary lining and transmigration and activation of inflammatory cells. Whereas a selective phosphodiesterase-4 (PDE4) inhibitor roflumilast has exerted potent anti-inflammatory properties, this study evaluated if its intravenous delivery can influence inflammation, edema formation, and respiratory parameters in rabbits with a lavage-induced model of ALI. ALI was induced by repetitive saline lung lavage (30 ml/kg). Animals were divided into 3 groups: ALI without therapy (ALI), ALI treated with roflumilast i.v. (1 mg/kg; ALI+Rofl), and healthy ventilated controls (Control), and were ventilated for following 4 h. Respiratory parameters (blood gases, ventilatory pressures, lung compliance, oxygenation indexes etc.) were measured and calculated regularly. At the end of experiment, animals were overdosed by anesthetics. Total and differential counts of cells in bronchoalveolar lavage fluid (BAL) were estimated microscopically. Lung edema was expressed as wet/dry lung weight ratio. Treatment with roflumilast reduced leak of cells (P<0.01), particularly of neutrophils (P<0.001), into the lung, decreased lung edema formation (P<0.01), and improved respiratory parameters. Concluding, the results indicate a future potential of PDE4 inhibitors also in the therapy of ALI.

Experimental Models of Acute Lung Injury in the Newborns

Acute lung injury in the preterm newborns can originate from prematurity of the lung and insufficient synthesis of pulmonary surfactant. This situation is known as respiratory distress syndrome (RDS). In the term neonates, the respiratory insufficiency is related to a secondary inactivation of the pulmonary surfactant, for instance, by action of endotoxins in bacterial pneumonia or by effects of aspirated meconium. The use of experimental models of the mentioned situations provides new information on the pathophysiology of these disorders and offers unique possibility to test novel therapeutic approaches in the conditions which are very similar to the clinical syndromes. Herewith we review the advantages and limitations of the use of experimental models of RDS and meconium aspiration syndrome (MAS) and their value for clinics.

Hyperinflation deteriorates arterial oxygenation and lung injury in a rabbit model of ARDS with repeated open endotracheal suctioning

Background

Hyperinflation (HI) is performed following open endotracheal suctioning (OES), whose goals include: to stimulate a cough, recover oxygenation and improve compliance. However, it may also induce unintended consequences, including: lung stress and strain, failure to maintain high distending pressure, and subsequently cycling recruitment and derecruitment. Here, our aim was to investigate the effects of hyperinflation after repeated OES on sequential alteration of arterial oxygenation and lung injury profile using a saline lavage-induced surfactant depleted ARDS rabbit model.

Methods

Briefly, 30 Japanese White Rabbits were anesthetized and ventilated in pressure-controlled setting with a tidal volume of 6-8 ml/kg. Animals were divided into four groups, i.e.; Control, ARDS, OES, and HI. Saline-lavage-induced lung injury was induced except for Control group. Thereafter, rabbits were ventilated with positive-end expiratory pressure (PEEP) at 10 cm H₂O. The ARDS group received ventilation with the same PEEP without derecruitment. As intervention, OES and HI were performed in ARDS animals. OES was performed for 15 seconds at 150 mm Hg, whereas HI was performed with PEEP at 0 cm H₂O and peak inspiratory pressure at +5 cm H₂O for a minute. Total duration of the experiment was for 3 hours. OES and HI were performed every 15 minutes from beginning of the protocol.

Results

PaO₂ was maintained at about 400 mm Hg in both control and ARDS groups for the duration of this study, while in both OES and HI groups, PaO₂ decreased continuously up to 3 hours, dropped to a mean (±SD) of 226 ± 28.9 and 97.0 ± 30.7 mmHg at 3 h, respectively. HI group had the lowest PaO₂ in the present investigation. Histological lung injury score was the highest in HI group than other three groups. Pulmonary TNF-α and IL-8 levels were the highest in HI group compared to other groups, but without significant alterations at circulatory level in all the experimental groups.

Conclusions

We show in the present study that hyperinflation following repeated OES deteriorate arterial oxygenation and the severity of lung injury in a rabbit model of ARDS undergoing mechanical ventilation.