Rate Of Alveolar Fluid Clearance Research Articles

Gene transfer of MRCK\u03b1 rescues lipopolysaccharide-induced acute lung injury by restoring alveolar capillary barrier function

Acute Lung Injury/Acute Respiratory Distress Syndrome (ALI/ARDS) is characterized by alveolar edema accumulation with reduced alveolar fluid clearance (AFC), alveolar-capillary barrier disruption, and substantial inflammation, all leading to acute respiratory failure. Enhancing AFC has long been considered one of the primary therapeutic goals in gene therapy treatments for ARDS. We previously showed that electroporation-mediated gene delivery of the Na+, K+-ATPase β1 subunit not only increased AFC, but also restored alveolar barrier function through upregulation of tight junction proteins, leading to treatment of LPS-induced ALI in mice. We identified MRCKα as an interaction partner of β1 which mediates this upregulation in cultured alveolar epithelial cells. In this study, we investigate whether electroporation-mediated gene transfer of MRCKα to the lungs can attenuate LPS-induced acute lung injury in vivo. Compared to mice that received a non-expressing plasmid, those receiving the MRCKα plasmid showed attenuated LPS-increased pulmonary edema and lung leakage, restored tight junction protein expression, and improved overall outcomes. Interestingly, gene transfer of MRCKα did not alter AFC rates. Studies using both cultured microvascular endothelial cells and mice suggest that β1 and MRCKα upregulate junctional complexes in both alveolar epithelial and capillary endothelial cells, and that one or both barriers may be positively affected by our approach. Our data support a model of treatment for ALI/ARDS in which improvement of alveolar-capillary barrier function alone may be of more benefit than improvement of alveolar fluid clearance.

Resolvin Conjugates in Tissue Regeneration 1 Promote Alveolar Fluid Clearance by Activating Alveolar Epithelial Sodium Channels and Na, K-ATPase in Lipopolysaccharide-Induced Acute Lung Injury.

Acute respiratory distress syndrome (ARDS), a common and fatal clinical condition, is characterized by the destruction of epithelium and augmented permeability of the alveolar-capillary barrier. Resolvin conjugates in tissue regeneration 1 (RCTR1) is an endogenous lipid mediator derived from docosahexaenoic acid , exerting proresolution effects in the process of inflammation. In our research, we evaluated the role of RCTR1 in alveolar fluid clearance (AFC) in lipopolysaccharide-induced ARDS/acute lung injury (ALI) rat model. Rats were injected with RCTR1 (5 μg/kg) via caudal veins 8 hours after lipopolysaccharide (LPS) (14 mg/kg) treatment, and then AFC was estimated after 1 hour of ventilation. Primary type II alveolar epithelial cells were incubated with LPS (1 ug/ml) with or without RCTR1 (10 nM) for 8 hours. Our results showed that RCTR1 significantly enhanced the survival rate, promoted the AFC, and alleviated LPS-induced ARDS/ALI in vivo. Furthermore, RCTR1 remarkably elevated the protein expression of sodium channels and Na, K-ATPase and the activity of Na, K-ATPase in vivo and in vitro. Additionally, RCTR1 also decreased neural precursor cell expressed developmentally downregulated 4-2 (Nedd4-2) level via upregulating Ser473-phosphorylated-Akt expression. Besides this, inhibitors of receptor for lipoxin A4 (ALX), cAMP, and phosphatidylinositol 3-kinase (PI3K) (BOC-2, KH-7, and LY294002) notably inhibited the effects of RCTR1 on AFC. In summary, RCTR1 enhances the protein levels of sodium channels and Na, K-ATPase and the Na, K-ATPase activity to improve AFC in ALI through ALX/cAMP/PI3K/Nedd4-2 pathway, suggesting that RCTR1 may become a therapeutic drug for ARDS/ALI. SIGNIFICANCE STATEMENT: RCTR1, an endogenous lipid mediator, enhanced the rate of AFC to accelerate the resolution of inflammation in the LPS-induced murine lung injury model. RCTR1 upregulates the expression of epithelial sodium channels (ENaCs) and Na, K-ATPase in vivo and in vitro to accelerate the AFC. The efficacy of RCTR1 on the ENaC and Na, K-ATPase level was in an ALX/cAMP/PI3K/Nedd4-2-dependent manner.

Alcohol inhibits alveolar fluid clearance through the epithelial sodium channel via the A2 adenosine receptor in acute lung injury.

Chronic alcohol abuse increases the risk of mortality and poor outcomes in patients with acute respiratory distress syndrome. However, the underlying mechanisms remain to be elucidated. The present study aimed to investigate the effects of chronic alcohol consumption on lung injury and clarify the signaling pathways involved in the inhibition of alveolar fluid clearance (AFC). In order to produce rodent models with chronic alcohol consumption, wild-type C57BL/6 mice were treated with alcohol. A2a adenosine receptor (AR) small interfering (si)RNA or A2bAR siRNA were transfected into the lung tissue of mice and primary rat alveolar type II (ATII) cells. The rate of AFC in lung tissue was measured during exposure to lipopolysaccharide (LPS). Epithelial sodium channel (ENaC) expression was determined to investigate the mechanisms underlying alcohol-induced regulation of AFC. In the present study, exposure to alcohol reduced AFC, exacerbated pulmonary edema and worsened LPS-induced lung injury. Alcohol caused a decrease in cyclic adenosine monophosphate (cAMP) levels and inhibited α-ENaC, β-ENaC and γ-ENaC expression levels in the lung tissue of mice and ATII cells. Furthermore, alcohol decreased α-ENaC, β-ENaC and γ-ENaC expression levels via the A2aAR or A2bAR-cAMP signaling pathways in vitro. In conclusion, the results of the present study demonstrated that chronic alcohol consumption worsened lung injury by aggravating pulmonary edema and impairing AFC. An alcohol-induced decrease of α-ENaC, β-ENaC and γ-ENaC expression levels by the A2AR-mediated cAMP pathway may be responsible for the exacerbated effects of chronic alcohol consumption in lung injury.

Salbutamol for transient tachypnea of the newborn.

Transient tachypnea of the newborn is characterized by tachypnea and signs of respiratory distress. Transient tachypnea typically appears within the first two hours of life in term and late preterm newborns. Although transient tachypnea of the newborn is usually a self-limited condition, it is associated with wheezing syndromes in late childhood. The rationale for the use of salbutamol (albuterol) for transient tachypnea of the newborn is based on studies showing that β-agonists can accelerate the rate of alveolar fluid clearance. This review was originally published in 2016 and updated in 2020. To assess whether salbutamol compared to placebo, no treatment or any other drugs administered to treat transient tachypnea of the newborn, is effective and safe for infants born at 34 weeks' gestational age with this diagnosis. We searched the Cochrane Central Register of Controlled Trials (CENTRAL, 2020, Issue 4) in the Cochrane Library; PubMed(1996 to April2020), Embase (1980 to April 2020); and CINAHL (1982 to April 2020). We applied no language restrictions. We searched the abstracts of the major congresses in the field (Perinatal Society of Australia New Zealand and Pediatric Academic Societies) from 2000 to 2020 and clinical trial registries. Randomized controlled trials, quasi-randomized controlled trials and cluster trials comparing salbutamol versus placebo or no treatment or any other drugs administered to infants born at 34 weeks' gestational age or more and less than three days of age with transient tachypnea of the newborn. We used standard Cochrane methodology for data collection and analysis. The primary outcomes considered in this review were duration of oxygen therapy, need for continuous positive airway pressure and need for mechanical ventilation.We used the GRADE approach to assess the certainty of evidence. Seven trials, which included 498 infants, met the inclusion criteria. Alltrials compared a nebulized dose of salbutamol with normal saline.Four studies used one single dose of salbutamol; in two studies,three to four doses were provided; in one study, additional doses were administered if needed.The certainty of the evidence was low forduration of hospital stay and very low for the other outcomes.Among the primary outcomes of this review, four trials (338infants) reported the duration of oxygen therapy, (mean difference (MD) -19.24 hours, 95% confidence interval (CI) -23.76 to -14.72); one trial (46 infants) reported theneed for continuous positive airway pressure (risk ratio (RR) 0.73, 95% CI 0.38 to 1.39; risk difference (RD) -0.15, 95% CI -0.45 to 0.16),and three trials (254 infants) reported the need for mechanical ventilation (RR 0.60, 95% CI 0.13 to 2.86; RD -0.01, 95% CI -0.05 to 0.03). Both duration of hospital stay (4 trials; 338 infants) and duration of respiratory support (2 trials, 228 infants)were shorter in the salbutamol group(MD -1.48, 95% CI -1.8 to -1.16; MD -9.24, 95% CI -14.24 to -4.23, respectively). One trial (80 infants) reported duration of mechanical ventilationand pneumothorax butdata could not be extracted due to the reporting of these outcomes (type of unitsof effect measure and unclearnumber of events, respectively). Five trials are ongoing. There was limited evidence to establish the benefits and harmsof salbutamol in the management of transient tachypnea of the newborn.We are uncertain whethersalbutamol administration reduces theduration of oxygen therapy, duration of tachypnea,need for continuous positive airway pressure and for mechanical ventilation. Salbutamolmay slightly reduce hospital stay.Five trials are ongoing. Given the limited and low certainty of the evidence available, we could notdetermine whether salbutamol was safe or effective for the treatment of transient tachypnea of the newborn.

A Preclinical Safety Study of Thyroid Hormone Instilled into the Lungs of Healthy Rats-an Investigational Therapy for ARDS.

Acute respiratory distress syndrome (ARDS) is a severe, life-threatening form of respiratory failure characterized by pulmonary edema, inflammation, and hypoxemia due to reduced alveolar fluid clearance (AFC). Alveolar fluid clearance is required for recovery and effective gas exchange, and higher rates of AFC are associated with reduced mortality. Thyroid hormones play multiple roles in lung function, and L-3,5,3'-triiodothyronine (T3) has multiple effects on lung alveolar type II cells. T3 enhances AFC in normal adult rat lungs when administered intramuscularly and in normal or hypoxia-injured lungs when given intratracheally. The safety of a commercially available formulation of liothyronine sodium (synthetic T3) administered intratracheally was assessed in an Investigational New Drug Application-enabling toxicology study in healthy rats. Instillation of the commercial formulation of T3 without modification rapidly caused tracheal injury and often mortality. Intratracheal instillation of T3 that was reformulated and brought to a neutral pH at the maximum feasible dose of 2.73 µg T3 in 300 µl for 5 consecutive days had no clinically relevant T3-related adverse clinical, histopathologic, or clinical pathology findings. There were no unscheduled deaths that could be attributed to the reformulated T3 or control articles, no differences in the lung weights, and no macroscopic or microscopic findings considered to be related to treatment with T3. This preclinical safety study has paved the way for a phase I/II study to determine the safety and tolerability of a T3 formulation delivered into the lungs of patients with ARDS, including coronavirus disease 2019-associated ARDS, and to measure the effect on extravascular lung water in these patients. SIGNIFICANCE STATEMENT: There is growing interest in treating lung disease with thyroid hormone [triiodothyronine (T3)] in pulmonary edema and acute respiratory distress syndrome (ARDS). However, there is not any published experience on the impact of direct administration of T3 into the lung. An essential step is to determine the safety of multiple doses of T3 administered in a relevant animal species. This study enabled Food and Drug Administration approval of a phase I/II clinical trial of T3 instillation in patients with ARDS, including coronavirus disease 2019-associated ARDS (T3-ARDS ClinicalTrials.gov Identifier NCT04115514).

Adenosine A2B receptor activation stimulates alveolar fluid clearance through alveolar epithelial sodium channel via cAMP pathway in endotoxin-induced lung injury.

Clinical studies have established that the capacity of removing excess fluid from alveoli is impaired in most patients with acute respiratory distress syndrome. Impaired alveolar fluid clearance (AFC) correlates with poor outcomes. Adenosine A2B receptor (A2BAR) has the lowest affinity with adenosine among four adenosine receptors. It is documented that A2BAR can activate adenylyl cyclase (AC) resulting in elevated cAMP. Based on the understanding that cAMP is a key regulator of epithelial sodium channel (ENaC), which is the limited step in sodium transport, we hypothesized that A2BAR signaling may affect AFC in acute lung injury (ALI) through regulating ENaC via cAMP, thus attenuating pulmonary edema. To address this, we utilized pharmacological approaches to determine the role of A2BAR in AFC in rats with endotoxin-induced lung injury and further focused on the mechanisms in vitro. We observed elevated pulmonary A2BAR level in rats with ALI and the similar upregulation in alveolar epithelial cells exposed to LPS. A2BAR stimulation significantly attenuated pulmonary edema during ALI, an effect that was associated with enhanced AFC and increased ENaC expression. The regulatory effects of A2BAR on ENaC-α expression were further verified in cultured alveolar epithelial type II (ATII) cells. More importantly, activation of A2BAR dramatically increased amiloride-sensitive Na+ currents in ATII cells. Moreover, we observed that A2BAR activation stimulated cAMP accumulation, whereas the cAMP inhibitor abolished the regulatory effect of A2BAR on ENaC-α expression, suggesting that A2BAR activation regulates ENaC-α expression via cAMP-dependent mechanism. Together, these findings suggest that signaling through alveolar epithelial A2BAR promotes alveolar fluid balance during endotoxin-induced ALI by regulating ENaC via cAMP pathway, raising the hopes for treatment of pulmonary edema due to ALI.

Efficacy of Quercetin as a potent sensitizer of β2-AR in combating the impairment of fluid clearance in lungs of rats under hypoxia

BackgroundHypoxia reportedly increases free radical generation in the body, causing oxidative stress and inhibiting β2-AR signaling. The present study correlates the prophylactic potential of quercetin and salbutamol in ameliorating fluid clearing capacity of lungs by re-sensitizing β2-AR signaling under hypoxia. MethodsMale SD rats supplemented orally with quercetin (50 mg/Kg BW), and salbutamol (2 mg/Kg BW) were exposed to hypobaric hypoxia at 7620 m for 6 h. Western blotting and ELISA quantitated NFĸB and related genes and GPCR pathway proteins. The binding affinities of drugs with receptor were determined by SPR spectroscopy and further confirmed insilico. ResultsQuercetin and salbutamol pre-treatment significantly up-regulated the expressions of β2-AR, GPR-1, GPR-10, GCSα, cAMP content, and down-regulated GRK-2, β-arrestin, ROS, NFκB (p < 0.001), thus, enhancing alveolar fluid clearance (AFC). SPR and insilico findings revealed a higher binding affinity of β2-AR with quercetin over salbutamol. ConclusionResults indicated quercetin to be a better prophylactic that augmented AFC in rats exposed to hypoxia by attenuating inflammation and stimulating β2-AR.

Novel insights into the role of LRRC8A in ameliorating alveolar fluid clearance in LPS induced acute lung injury

Leucine-rich repeat-containing 8A (LRRC8A) protein was recently identified as an essential component of volume-regulated anion channel which plays a central role in maintaining cell volume. The aim of this study was to elucidate the role of LRRC8A in alveolar fluid clearance (AFC) and the effect of inflammatory cytokines on LRRC8A and the underlying mechanism. Lipopolysaccharide (LPS) was used to generate a rat acute lung injury model. The results showed that the concentrations of IL-1β, TNF-α and IL-6 in bronchoalveolar lavage fluid increased significantly, but the expression of LRRC8A in the lung tissue decreased dramatically in the acute lung injury group followed by a decline in the AFC rate. Additionally, LRRC8A knockdown reduced AFC in normal rats. However, specific overexpression of LRRC8A in the lung could increase AFC. Furthermore, we observed the effects of LPS, IL-1β, TNF-α and IL-6 on the LRRC8A current in alveolar type II (ATII) cells, and IL-1β showed the greatest inhibition among them, which was involved in phospho-p38 activation. Overall, LRRC8A plays an essential role in the progression of AFC in LPS-induced acute lung injury, and chronic treatment with IL-1β or TNF-α could inhibit the function of LRRC8A in ATII cells by targeting phospho-p38. All of the findings suggested that LRRC8A could be a new partner in AFC and a potential target for the treatment of acute lung injury.

Effects of dexmedetomidine on alveolar fluid clearance in rats with acute lung injury induced by lipopolysaccharide

Objective To investigate effects of dexmedetomidine(Dex) on alveolar fluid clearance (AFC) in rats with acute lung injury induced by lipopolysaccharide (LPS). Methods Forty-eight male Wistar rats were randomly divided into normal saline control (NS) group, LPS group, and Dex treatment (LPS+Dex) group. The rats in NS group were intravenously injected with 0.9% normal saline (5 ml/kg) followed by influsion of 0.9% normal saline (5 μg·kg-1·h-1). The rats in LPS group were intravenously injected with LPS (10 mg/kg) followed by influsion of 0.9% normal saline (5 μg·kg-1·h-1). The rats in LPS+Dex group were intravenously injected with LPS (10 mg/kg) followed by influsion of Dex (5 μg·kg-1·h-1). The rats were sacrificed 6 h after intravenous injection of LPS or NS, PaO2 was measured, AFC was determined by Evans blue-tagged albumin concentration changes. Histology of the lungs were assayed with H-E staining. The wet/dry weight ratio (W/D) of the lung was determined. The levels of TNF-α and IL-1β in the lung tissues were assessed by ELISA. The protein levels of potassium sodium adenosine triphosphate enzyme (Na-K-ATPase), alveolar epithelial sodium channel (ENaC) were detected by Western blot and immunohistochemistry. Results Compared with NS group, PaO2 was lower in LPS group, and this drop was reversed by Dex (in LPS+Dex group)(P<0.01). The W/D and the concentrations of TNF-α and IL-1β in the pulmonary tissues were increased in the LPS group, relative to the NS group, but the increases were compromised in the LPS+Dex group(P<0.01). AFC was reduced in LPS group, relative to NS group, but the reduction was compensat in LPS+Dex group(P<0.01). The expression of Na-K-ATPase and ENaC was lower in the LPS group than the NS group, but they were normalized in the LPS+Dex group(P<0.01). Conclusions Our findings suggest that dexmedetomidine may alleviate pulmonary edema by increasing AFC and the expression of Na-K-ATPase and ENaC in rats with acute lung injury induced by lipopolysaccharide. Key words: Dexmedetomidine; Acute lung injury; Alveolar fluid clearance; Potassium sodium adenosine triphosphate enzyme; Alveolar epithelial sodium channel

Protectin DX increases alveolar fluid clearance in rats with lipopolysaccharide-induced acute lung injury

Acute respiratory distress syndrome is a life-threatening critical syndrome resulting largely from the accumulation of and the inability to clear pulmonary edema. Protectin DX, an endogenously produced lipid mediator, is believed to exert anti-inflammatory and pro-resolution effects. Protectin DX (5 µg/kg) was injected i.v. 8 h after LPS (14 mg/kg) administration, and alveolar fluid clearance was measured in live rats (n = 8). In primary rat ATII epithelial cells, protectin DX (3.605 × 10−3 mg/l) was added to the culture medium with LPS for 6 h. Protectin DX improved alveolar fluid clearance (9.65 ± 1.60 vs. 15.85 ± 1.49, p < 0.0001) and decreased pulmonary edema and lung injury in LPS-induced lung injury in rats. Protectin DX markedly regulated alveolar fluid clearance by upregulating sodium channel and Na, K-ATPase protein expression levels in vivo and in vitro. Protectin DX also increased the activity of Na, K-ATPase and upregulated P-Akt via inhibiting Nedd4–2 in vivo. In addition, protectin DX enhanced the subcellular distribution of sodium channels and Na, K-ATPase, which were specifically localized to the apical and basal membranes of primary rat ATII cells. Furthermore, BOC-2, Rp-cAMP, and LY294002 blocked the increased alveolar fluid clearance in response to protectin DX. Protectin DX stimulates alveolar fluid clearance through a mechanism partly dependent on alveolar epithelial sodium channel and Na, K-ATPase activation via the ALX/PI3K/Nedd4–2 signaling pathway.

Inhibition of the Receptor for Advanced Glycation End-Products in Acute Respiratory Distress Syndrome: A Randomised Laboratory Trial in Piglets

Background: The receptor for advanced glycation end products (RAGE) modulates the pathogenesis of acute respiratory distress syndrome (ARDS). RAGE inhibition was recently associated with attenuated lung injury and restored alveolar fluid clearance (AFC) in a mouse model of ARDS. However, clinical translation will first require assessment of this strategy in larger animals. Methods: Forty-eight anaesthetised Landrace piglets were randomised into a control group and three treatment groups. Animals allocated to treatment groups underwent orotracheal instillation of hydrochloric acid i) alone; ii) in combination with intravenous administration of a RAGE antagonist peptide (RAP), a S100P-derived peptide that prevents activation of RAGE by its ligands, or iii) in combination with intravenous administration of recombinant soluble (s)RAGE that acted as a decoy receptor. The primary outcome measure was net AFC at 4 h. Arterial oxygenation was assessed hourly for 4 h and alveolar-capillary permeability, alveolar inflammation, lung histology and lung mRNA expression of the epithelial sodium channel (α1-ENaC), α1-Na,K-ATPase and aquaporin (AQP)-5 were assessed at 4 h. Findings: Treatment with either RAP or sRAGE improved net AFC rates (median [interquartile range], 21.2 [18.8-21.7] and 19.5 [17.1-21.5] %/h, respectively, versus 12.6 [3.2-18.8] %/h in injured, untreated controls), improved oxygenation and decreased alveolar inflammation and histological evidence of tissue injury after acid-induced ARDS. RAGE inhibition also restored lung mRNA expression of α1-Na, K-ATPase and AQP-5. Interpretation: RAGE inhibition restored AFC and attenuated lung injury in a piglet model of acid-induced ARDS. Funding: Auvergne Regional Council, Agence Nationale de la Recherche, Direction Generale de l'Offre de Soins. Declaration of Interest: No conflict of interest, other source of financial support, corporate involvement, patent holdings, etc. is to be declared for all authors. Ethical Approval: Animals were maintained and all procedures were performed with the approval of the ethics committee of the French Ministere de l’Education Nationale, de l’Enseignement Superieur et de la Recherche in the Centre International de Chirurgie Endoscopique, School of Medicine - University of Clermont-Ferrand (approval number 01505.03). All experiments were performed in accordance with the “Animal Research: Reporting In Vivo Experiments” (ARRIVE) guidelines.

Salbutamol for transient tachypnea of the newborn.

Transient tachypnea of the newborn is characterized by tachypnea and signs of respiratory distress. Transient tachypnea typically appears within the first two hours of life in term and late preterm newborns. Although transient tachypnea of the newborn is usually a self limited condition, it is associated with wheezing syndromes in late childhood. The rationale for the use of salbutamol (albuterol) for transient tachypnea of the newborn is based on studies showing that β-agonists can accelerate the rate of alveolar fluid clearance. To assess whether salbutamol compared to placebo, no treatment or any other drugs administered to treat transient tachypnea of the newborn, is effective and safe in the treatment of transient tachypnea of the newborn in infants born at 34 weeks' gestational age or more. We searched the Cochrane Central Register of Controlled Trials (CENTRAL, 2016, Issue 3), MEDLINE (1996 to March 2016), EMBASE (1980 to March 2016) and CINAHL (1982 to March 2016). We applied no language restrictions. We searched the abstracts of the major congresses in the field (Perinatal Society of Australia New Zealand and Pediatric Academic Societies) from 2000 to 2015 and clinical trial registries. Randomized controlled trials, quasi-randomized controlled trials and cluster trials comparing salbutamol versus placebo or no treatment or any other drugs administered to infants born at 34 weeks' gestational age or more and less than three days of age with transient tachypnea of the newborn. For each of the included trials, two review authors independently extracted data (e.g. number of participants, birth weight, gestational age, duration of oxygen therapy, need for continuous positive airway pressure and need for mechanical ventilation, duration of mechanical ventilation, etc.) and assessed the risk of bias (e.g. adequacy of randomization, blinding, completeness of follow-up). The primary outcomes considered in this review were duration of oxygen therapy, need for continuous positive airway pressure and need for mechanical ventilation. Three trials, which included 140 infants, met the inclusion criteria. All three trials compared a nebulized dose of salbutamol with placebo; in one of the three trials newborns were assigned to two different doses of the intervention. We found differences in the duration of oxygen therapy (mean difference (MD) -43.10 hours, 95% confidence interval (CI) -81.60 to -4.60). There were no differences in the need for continuous positive airway pressure (risk ratio (RR) 0.73, 95% CI 0.38 to 1.39; risk difference (RD) -0.15, 95% CI -0.45 to 0.16; 1 study, 46 infants) or the need for mechanical ventilation (RR 1.50, 95% CI 0.06 to 34.79; RD 0.03, 95% CI -0.08 to 0.14; 1 study, 46 infants). Tests for heterogeneity were not applicable for any of the analyses as only one study was included. Among secondary outcomes, we found no differences in terms of duration of hospital stay and tachypnea. The quality of the evidence was very low due to the imprecision of the estimates. One trial is ongoing. At present there is insufficient evidence to determine the efficacy and safety of salbutamol in the management of transient tachypnea of the newborn. The quality of evidence was low due to paucity of included trials, small sample sizes and overall poor methodologic quality.

Net alveolar fluid clearance is associated with lung morphology phenotypes in acute respiratory distress syndrome

BackgroundThe acute respiratory distress syndrome (ARDS) is a heterogeneous syndrome that encompasses multiple phenotypes, e.g. with regards to lung morphology as assessed by computed tomography (CT). Focal or non-focal lung morphology may influence the response to positive end-expiratory pressure (PEEP), recruitment manoeuvres and prone position. Lung morphology has been hypothesized to be associated with alveolar fluid clearance (AFC), thus explaining various responses to such therapeutic interventions; however, this hypothesis has not been specifically studied in humans. MethodsWe measured net AFC rates in 30 patients with ARDS as a secondary data analysis of a prospective single-centre study. Net AFC rates were compared between patients with focal ARDS and those with non-focal ARDS, as assessed by lung CT-scans. ResultsNet AFC rates were significantly lower in patients with non-focal ARDS (n=23; median [interquartile range], 1.5 [0–5.5] %/h) as compared to those with focal ARDS (n=7; 10.3 [4.5–15] %/h) (P=0.01). The area under the receiver-operating characteristic curve when net AFC rates were used to differentiate the presence from absence of non-focal ARDS was 0.93 (95% confidence interval, 0.81–1). Tidal volumes and PEEP levels differed between focal and non-focal ARDS patients, but there was no difference in arterial oxygenation or in alveolar-capillary permeability. ConclusionsNon-focal lung morphology may be characterized by a functional endotype consistent with marked AFC impairment. Despite study limitations and the need for validating studies in larger cohorts, such novel findings may reinforce our understanding of the association between ARDS phenotypes and therapeutic responses.

The Role of Angiotensin II and Cyclic AMP in Alveolar Active Sodium Transport.

Active alveolar fluid clearance is important in keeping airspaces free of edema. Angiotensin II plays a role in the pathogenesis of hypertension, heart failure and others. However, little is known about its contribution to alveolar fluid clearance. Angiotensin II effects are mediated by two specific receptors; AT1 and AT2. The localization of these two receptors in the lung, specifically in alveolar epithelial cells type II, was recently reported. We hypothesize that Angiotensin II may have a role in the regulation of alveolar fluid clearance. We investigated the effect of Angiotensin II on alveolar fluid clearance in rats using the isolated perfused lung model and isolated rat alveolar epithelial cells. The rate of alveolar fluid clearance in control rats was 8.6% ± 0.1 clearance of the initial volume and decreased by 22.5%, 28.6%, 41.6%, 48.7% and 39% in rats treated with 10-10 M, 10-9 M, 10-8 M, 10-7 M or 10-6 M of Ang II respectively (P < 0.003). The inhibitory effect of Angiotensin II was restored in losartan, an AT1 specific antagonist, pretreated rats, indicating an AT1 mediated effect of Ang II on alveolar fluid clearance. The expression of Na,K-ATPase proteins and cAMP levels in alveolar epithelial cells were down-regulated following the administration of Angiotensin II; suggesting that cAMP may be involved in AngII-induced reduced Na,K-ATPase expression, though the contribution of additional factors could not be excluded. We herein suggest a novel mechanism of clinical relevance by which angiotensin adversely impairs the ability of the lungs to clear edema.

Soluble Receptor for Advanced Glycation End-Products Predicts Impaired Alveolar Fluid Clearance in Acute Respiratory Distress Syndrome.

Levels of the soluble form of the receptor for advanced glycation end-products (sRAGE) are elevated during acute respiratory distress syndrome (ARDS) and correlate with severity and prognosis. Alveolar fluid clearance (AFC) is necessary for the resolution of lung edema but is impaired in most patients with ARDS. No reliable marker of this process has been investigated to date. To verify whether sRAGE could predict AFC during ARDS. Anesthetized CD-1 mice underwent orotracheal instillation of hydrochloric acid. At specified time points, lung injury was assessed by analysis of blood gases, alveolar permeability, lung histology, AFC, and plasma/bronchoalveolar fluid measurements of proinflammatory cytokines and sRAGE. Plasma sRAGE and AFC rates were also prospectively assessed in 30 patients with ARDS. The rate of AFC was inversely correlated with sRAGE levels in the plasma and the bronchoalveolar fluid of acid-injured mice (Spearman's ρ = -0.73 and -0.69, respectively; P < 10(-3)), and plasma sRAGE correlated with AFC in patients with ARDS (Spearman's ρ = -0.59; P < 10(-3)). Similarly, sRAGE levels were significantly associated with lung injury severity, and decreased over time in mice, whereas AFC was restored and lung injury resolved. Our results indicate that sRAGE levels could be a reliable predictor of impaired AFC during ARDS, and should stimulate further studies on the pathophysiologic implications of RAGE axis in the mechanisms leading to edema resolution. Clinical trial registered with www.clinicaltrials.gov (NCT 00811629).

Synergistic Inhibition of β2-adrenergic Receptor-mediated Alveolar Epithelial Fluid Transport by Interleukin-8 and Transforming Growth Factor-β.

Patients with acute respiratory distress syndrome who retain maximal alveolar fluid clearance (AFC) have better clinical outcomes. The release of endogenous catecholamines associated with shock or the administration of β2-adrenergic receptor (β2AR) agonists enhances AFC via a 3'-5'-cyclic adenosine monophosphate-dependent mechanism. The authors have previously reported that transforming growth factor-β1 (TGF-β1) and interleukin-8 (IL-8), two major mediators of alveolar inflammation associated with the early phase of acute respiratory distress syndrome, inhibit AFC upregulation by β2AR agonists via a phosphoinositol-3-kinase (PI3K)-dependent mechanism. However, whether TGF-β1 and IL-8 cause an additive or synergistic inhibition of AFC is unclear. Thus, the central hypothesis of the study was to determine whether they synergistically inhibit the β2AR-stimulated AFC by activating two different isoforms of PI3K. The effects of TGF-β1 or IL-8 on β2AR agonist-stimulated net alveolar fluid transport were studied using short-circuit current studies. Molecular pathways of inhibition were confirmed by pharmacologic inhibitors and Western blotting of p-Akt, G-protein-coupled receptor kinase 2, protein kinase C-ζ, and phospho-β2AR. Finally, our observations were confirmed by an in vivo model of AFC. Combined exposure to TGF-β1 and IL-8/cytokine-induced neutrophil chemoattractant-1 caused synergistic inhibition of β2AR agonist-stimulated vectorial Cl across alveolar epithelial type II cells (n = 12 in each group). This effect was explained by activation of different isoforms of PI3K by TGF-β1 and IL-8/cytokine-induced neutrophil chemoattractant-1 (n = 12 in each group). Furthermore, the inhibitory effect of TGF-β1 on 3'-5'-cyclic adenosine monophosphate-stimulated alveolar epithelial fluid transport required the presence of IL-8/cytokine-induced neutrophil chemoattractant-1 (n = 12 in each group). Inhibition of cytokine-induced neutrophil chemoattractant-1 prevented TGF-β1-mediated heterologous β2AR downregulation and restored physiologic β2AR agonist-stimulated AFC in rats (n = 6 in each group). TGF-β1 and IL-8 have a synergistic inhibitory effect on β2AR-mediated stimulation of pulmonary edema removal by the alveolar epithelium. This result may, in part, explain why a large proportion of the patients with acute respiratory distress syndrome have impaired AFC.

How to measure alterations in alveolar barrier function as a marker of lung injury.

The alveolar capillary membrane maintains the proper water and solute content of the epithelial lining fluid at the alveolar air-liquid interface, which is critical for adequate gas exchange in the lung. This is possible due to the alveolar fluid clearance (AFC) capacity of this membrane that assists in the removal of salt and water from the alveolar air spaces. The alveolar capillary membrane also provides a barrier that restricts the passage of proteins and water from the interstitial and vascular compartments into the alveolar air spaces. This restricted passage is due to the presence of tight junctions between adjacent alveolar epithelial cells. Severe injury to the alveolar epithelial/endothelial membrane results in increased protein permeability and impairment of AFC, which leads to the formation of protein-rich edema with the consequent deterioration of gas exchange. Many animal models of lung injury, focused on damage of the alveolar-capillary membrane, assess the AFC capacity and the barrier function. We describe a simple method to assess the AFC rate in normal and pathological conditions in mice. We also describe two complementary methods to assess the alveolar-capillary barrier function, which require measuring the concentration of endogenous plasma proteins in bronchoalveolar lavage fluid and detection of tight-junction proteins in lung tissue by immunofluorescence.

Elevated levels of soluble RAGE predict impaired alveolar fluid clearance in a translational mouse model of acute respiratory distress syndrome

Receptor for advanced glycation endproducts (RAGE) is a transmembrane receptor expressed in the lung and primarily located on alveolar type I cells. RAGE is implicated in acute respiratory distress syndrome to alveolar inflammation and, when its soluble form sRAGE is assayed in plasma or pulmonary edema fluid, as a marker of AT I cell injury. Functional activity of AT 1 cells can be assessed by the measurement of the alveolar fluid clearance (AFC) rate [1], but the relationship between sRAGE plasma levels of sRAGE and AFC rates has never been investigated. Our objectives were to report plasma levels of sRAGE in a mouse model of direct acid-induced epithelial injury, and to test their correlation with AFC rates.

Donor Smoking Is Associated With Pulmonary Edema, Inflammation and Epithelial Dysfunction in Ex Vivo Human Donor Lungs

Although recipients of donor lungs from smokers have worse clinical outcomes, the underlying mechanisms are unknown. We tested the association between donor smoking and the degree of pulmonary edema (as estimated by lung weight), the rate of alveolar fluid clearance (AFC; measured by airspace instillation of 5% albumin) and biomarkers of lung epithelial injury and inflammation (bronchoalveolar lavage [BAL] surfactant protein-D (SP-D) and IL-8) in ex vivo lungs recovered from 298 organ donors. The extent of pulmonary edema was higher in current smokers (n = 127) compared to nonsmokers (median 408 g, interquartile range [IQR] 364-500 vs. 385 g, IQR 340-460, p = 0.009). Oxygenation at study enrollment was worse in current smokers versus nonsmokers (median PaO2 /FiO2 214 mm Hg, IQR 126-323 vs. 266 mm Hg, IQR 154-370, p = 0.02). Current smokers with the highest exposure (≥20 pack years) had significantly lower rates of AFC, suggesting that the effects of cigarette smoke on alveolar epithelial fluid transport function may be dose related. BAL IL-8 was significantly higher in smokers while SP-D was lower. These findings indicate that chronic exposure to cigarette smoke has important effects on inflammation, gas exchange, lung epithelial function and lung fluid balance in the organ donor that could influence lung function in the lung transplant recipient.

0853. Elevated levels of soluble rage predict impaired alveolar fluid clearance in a translational mouse model of acute respiratory distress syndrome (ARDS)

Receptor for advanced glycation endproducts (RAGE) is a transmembrane pattern-recognition receptor of the immunoglobulin superfamily that is abundantly expressed in the lung and primarily located on the basal surface of alveolar type I cells. RAGE is implicated in ARDS as an important pathway to alveolar inflammation and, when its soluble form sRAGE is assayed in plasma or pulmonary edema fluid, as a marker of AT I cell injury [1]. Functional activity of AT 1 cells can be assessed by the measurement of alveolar fluid clearance (AFC) rate [2], but the relationship between sRAGE plasma levels of sRAGE and AFC rates has never been investigated.