Pulmonary Edema Formation Research Articles

Calcium-activated Potassium Channels as Amplifiers of TRPV4-mediated Pulmonary Edema Formation in Male Mice.

As a mechanosensitive cation channel and key regulator of vascular barrier function, endothelial transient receptor potential vanilloid type 4 (TRPV4) contributes critically to ventilator-induced lung injury and edema formation. Ca2+ influx via TRPV4 can activate Ca2+-activated potassium (KCa) channels, categorized into small (SK1-3), intermediate (IK1), and big (BK) KCa, which may in turn amplify Ca2+ influx by increasing the electrochemical Ca2+ gradient and thus promote lung injury. The authors therefore hypothesized that endothelial KCa channels may contribute to the progression of TRPV4-mediated ventilator-induced lung injury. Male C57Bl/6J mice were ventilated for 2 h with low or high tidal volumes in the presence or absence of the nonselective KCa antagonists apamin and charybdotoxin or the selective IK1 antagonist TRAM34. Lung injury was similarly assessed in overventilated, endothelial-specific TRPV4-deficient mice or TRAM34-treated C57Bl/6J mice challenged with intratracheal acid installation. Changes in intracellular calcium Ca2+ concentration ([Ca2+]i) were monitored by real-time imaging in isolated-perfused lungs in response to airway pressure elevation or in human pulmonary microvascular endothelial cells in response to TRPV4 activation with or without inhibition of KCa channels. Analogously, changes in intracellular potassium concentration ([K+]i) and membrane potential were imaged in vitro. Endothelial TRPV4 deficiency or inhibition of KCa channels, and most prominently inhibition of IK1 by TRAM34, attenuated ventilator-induced lung injury as demonstrated by reduced lung edema, protein leak, and quantitative lung histology. All KCa antagonists reduced the [Ca2+]i response to mechanical stimulation or direct TRPV4 activation in isolated lungs. TRAM34 and charybdotoxin yet not apamin prevented TRPV4-induced potassium efflux and membrane hyperpolarization in human pulmonary microvascular endothelial cells. TRAM34 also attenuated the TRPV4 agonist-induced Ca2+ influx in vitro and reduced acid-induced lung injury in vivo. KCa channels, specifically IK1, act as amplifiers of TRPV4-mediated Ca2+ influx and establish a detrimental feedback that promotes barrier failure and drives the progression of ventilator-induced lung injury.

Electrical cell‐substrate impedance sensing (ECIS) in lung biology and disease

AbstractThe lungs are exposed to a hostile environment from both sites: the airways and the vasculature. However, an efficient gas exchange of oxygen (O2) and CO2 is only possible through a very thin alveolo‐capillary membrane. Therefore, maintaining cell barrier integrity is essential for respiratory health and function. On the vascular site, endothelial cells form a natural barrier, while in the airways epithelial cells are most important for protection of the lung tissues. Moreover, fibroblasts, by transforming to myofibroblasts, are essential for wound closure after mechanical and chemical microinjuries in the respiratory tract. Along this line, loss of cell resistance in vascular endothelial and lung epithelial cells enhances invasion of pathogens (e.g., SARS‐CoV‐2) and results in pulmonary edema formation, while increasing barrier function of pulmonary (myo)fibroblasts blocks gas exchange in patients with pulmonary fibrosis. Therefore, electrical cell‐substrate impedance sensing‐based quantification of changes in cell barrier function in lung endothelial and epithelial cells as well as fibroblasts after application of harmful triggers (e.g., hypoxia, receptor agonists, and toxicants) is a convenient and state‐of‐the‐art technique. After isolation of primary cells from mouse models and human tissues, changes in cell resistance can be detected in real time. By using lung cells from gene‐deficient mouse models, microRNAs or the small‐interfering RNA technology essential proteins for cell adhesion, for example, ion channels of the transient receptor potential family are identified in comparison to wild‐type control cells. In the future, these proteins may be useful as drug targets for novel therapeutic options in patients with lung edema or pulmonary fibrosis.

Biological effects of corticosteroids on pneumococcal pneumonia in Mice—translational significance

BackgroundStreptococcus pneumoniae is the most common bacterial cause of community acquired pneumonia and the acute respiratory distress syndrome (ARDS). Some clinical trials have demonstrated a beneficial effect of corticosteroid therapy in community acquired pneumonia, COVID-19, and ARDS, but the mechanisms of this benefit remain unclear. The primary objective of this study was to investigate the effects of corticosteroids on the pulmonary biology of pneumococcal pneumonia in a mouse model. A secondary objective was to identify shared transcriptomic features of pneumococcal pneumonia and steroid treatment in the mouse model and clinical samples.MethodsWe carried out comprehensive physiologic, biochemical, and histological analyses in mice to identify the mechanisms of lung injury in Streptococcus pneumoniae with and without adjunctive steroid therapy. We also studied lower respiratory tract gene expression from a cohort of 15 mechanically ventilated patients (10 with Streptococcus pneumoniae and 5 controls) to compare with the transcriptional studies in the mice.ResultsIn mice with pneumonia, dexamethasone in combination with ceftriaxone reduced (1) pulmonary edema formation, (2) alveolar protein permeability, (3) proinflammatory cytokine release, (4) histopathologic lung injury score, and (5) hypoxemia but did not increase bacterial burden. Transcriptomic analyses identified effects of steroid therapy in mice that were also observed in the clinical samples.ConclusionsIn combination with appropriate antibiotic therapy in mice, treatment of pneumococcal pneumonia with steroid therapy reduced hypoxemia, pulmonary edema, lung permeability, and histologic criteria of lung injury, and also altered inflammatory responses at the protein and gene expression level. The transcriptional studies in patients suggest that the mouse model replicates some of the features of pneumonia in patients with Streptococcus pneumoniae and steroid treatment. Overall, these studies provide evidence for the mechanisms that may explain the beneficial effects of glucocorticoid therapy in patients with community acquired pneumonia from Streptococcus Pneumoniae.

Activation of KCa channels downstream of TRPV4 amplify pulmonary edema formation

Study objective: In patients with acute respiratory failure (ARDS), mechanical ventilation is the only life-saving treatment. However, mechanical ventilation also can cause ventilator-induced lung injury (VILI) due to the excessive biomechanical forces acting on the distal lung and especially the microvascular endothelium, which in turn further exacerbate endothelial barrier failure thus initiating a vicious cycle leading to irreversible lung damage. The endothelial mechanosensitive transient receptor potential vanilloid 4 (TRPV4) is directly activated by mechanical force and leads to Ca2+ influx, which can activate Ca2+-activated K+ (KCa) channels, categorized into small (SK1-3), intermediate (IK1), and big (BK) KCa. We hypothesized that KCa channels acting downstream of TRPV4 may in turn amplify Ca2+ influx by increasing the electrochemical Ca2+ gradient and thus, promote stretch-induced barrier failure and aggravate lung injury in a positive feedback loop. Methods: Male C57Bl/6J wild-type mice were ventilated for 2 h with low or high tidal volumes in the presence or absence of the non-selective KCa antagonists apamin, charybdotoxin, or the selective IK1 antagonist TRAM34. In a second model, male wild-type mice were challenged with intratracheal HCl instillation (pH 1.5) and ventilated with a low tidal volume for 2h with or without TRAM34. Changes in endothelial Ca2+ concentration ([Ca2+]i) were monitored by real-time imaging of Fura-2 AM in isolated-perfused lungs in response to airway pressure elevation or in human pulmonary microvascular endothelial cells (HPMECs) in response to TRPV4 activation with or without inhibition of KCa channels. Analogously, changes in intracellular potassium concentration ([K+]i) and membrane potential ( Vm) were imaged in vitro. Results: In our established experimental lung injury models, pharmacological inhibition of KCa channels, in particular IK1 attenuated characteristic hallmarks of lung injury in response to high tidal volume ventilation or HCl instillation. Consistent with these findings, inhibition of IK1 channels in the ex vivo perfused lung reduced the sustained [Ca2+]i response to airway pressure elevation over time. In HPMECs, TRPV4-mediated Ca2+ influx induced a pronounced K+ efflux, which in turn caused membrane hyperpolarization. These effects could be prevented by different KCa inhibitors, with IK1 inhibition by TRAM34 showing the most pronounced protective effect. Antagonizing KCa channels as downstream mediators of TRPV4 also reduced endothelial [Ca2+]i transients in response to TRPV4 activation in vitro, indicating that KCa channels, and specifically IK1 serve as amplifiers by increasing the electrochemical gradient for TRPV4-mediated Ca2+ influx. Conclusion: KCa channels, specifically IK1 amplify TRPV4-mediated Ca2+ influx in lung endothelial cells and as such, establish a detrimental feedback that promotes barrier failure and drives the progression of VILI in overventilated lungs. WMK is supported by the German Research Foundation (DFG) (SFB-TR84: subprojects A02 & C09, SFB-1449 subproject B01, SFB 1470 subproject A04, KU1218/9-1, KU1218/11-1, and KU1218/12-1), the Berlin Institute of Health (BIH), the German Federal Ministry of Education and Research (BMBF) in the framework of the projects PROVID (01KI20160A) and SYMPATH (01ZX1906A), and the German Centre for Cardiovascular Research (DZHK). LM is supported by the German Centre for Cardiovascular Research (DZHK) (81X3100216). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Giant Left Atrial Myxoma Revealed by Neurological Manifestation in a Young Female Patient

Cardiac myxoma is a prevalent benign neoplasm that arises inside the cardiac tissue and exhibits a gradual growth pattern. The annual incidence rate of cardiac myxoma is approximately 0.5–1 cases per 1,000,000 persons. The fragmentation of a cardiac tumor may be influenced by cerebrovascular events. Ischemic stroke is a relatively infrequent occurrence in pediatric populations and can occasionally be attributed to cardiac myxoma. In instances of ischemic stroke, neurological impairments are observed as a result of emboli or thrombi originating from the myxoma. Echocardiography is a valuable tool for promptly diagnosing myxoma and facilitating immediate surgical removal of the myxoma. We report a 17 years old female with neurological deficit weakness in the upper and lower right extremities since 2 months ago as the chief complaint with intermittent shortness of breath. Haemodynamic parameters was stable. The patient underwent brain imaging with result a lesion of the left lentiform nucleus, transthoracic echocardiography and trans esophageal echocardiography with oscillating septated mass on left atrial, attached to the anterior mitral leaflet (AML). Primary cardiac tumors are a very uncommon cause of cardiac embolic events. An atrial myxoma, a benign growth, can form on either the left or right side of the upper part of the heart. Untreated atrial myxoma can lead to adverse effects such as arrhythmia, pulmonary edema, and emboli formation that obstruct blood flow in the heart's veins. Ischemic stroke causes a specific functional impairment. Neurological symptoms in stroke can be an extra cardiac manifestation of atrial myxoma. The use of transthoracic and tran seso phageal is important in diagnosing atrial myxoma.

Combination of Phycocyanin, Zinc, and Selenium Improves Survival Rate and Inflammation inthe Lipopolysaccharide-Galactosamine Mouse Model.

Sepsis is related to systemic inflammation and oxidative stress, the primary causes of death in intensive care units. Severe functional abnormalities in numerous organs can arise due to sepsis, with acute lung damage being the most common and significant morbidity. Spirulina, blue-green algae with high protein, vitamins, phycocyanin, and antioxidant content, shows anti-inflammatory properties by decreasing the release of cytokines. In addition, zinc (Zn) and selenium (Se) act as an antioxidant by inhibiting the oxidation of macromolecules, as well as the inhibition of the inflammatory response. The current study aimed to examine the combined properties of Zn, Se, and phycocyanin oligopeptides (ZnSePO) against lipopolysaccharide-D-galactosamine (LPS-GalN)-induced septic lung injury through survival rate, inflammatory, and histopathological changes in Balb/c mice. A total of 30 mice were allocated into three groups: normal control, LPS-GalN (100ng of LPS plus 8mg of D-galactosamine), LPS-GalN + ZnSePO (ZnPic, 52.5µg/mL; SeMet, 0.02µg/mL; and phycocyanin oligopeptide (PO), 2.00mg/mL; at 1h before the injection of LPS-GalN). Lung tissue from mice revealed noticeable inflammatory reactions and typical interstitial fibrosis after the LPS-GalN challenge. LPS-GalN-induced increased mortality rate and levels of IL-1, IL-6, IL-10, TGF-β, TNF-α, and NF-κB in lung tissue. Moreover, treatment of septic mice LPS-GalN + ZnSePO reduced mortality rates and inflammatory responses. ZnSePO considerably influenced tissue cytokine levels, contributing to its capacity to minimize acute lung injury (ALI) and pulmonary inflammation and prevent pulmonary edema formation in LPS-GalN-injected mice. In conclusion, ZnSePO treatment enhanced the survival rate of endotoxemia mice via improving inflammation and oxidative stress, indicating a possible therapeutic effect for patients with septic infections.

Circulating Myeloid Cell-derived Extracellular Vesicles as Mediators of Indirect Acute Lung Injury.

Blood-borne myeloid cells, neutrophils and monocytes, play a central role in the development of indirect acute lung injury (ALI) during sepsis and noninfectious systemic inflammatory response syndrome. By contrast, the contribution of circulating myeloid cell-derived extracellular vesicles (EVs) to ALI is unknown, despite acute increases in their numbers during sepsis and systemic inflammatory response syndrome. Here, we investigated the direct role of circulating myeloid-EVs in ALI using a mouse isolated perfused lung system and a human cell coculture model of pulmonary vascular inflammation consisting of lung microvascular endothelial cells and peripheral blood mononuclear cells. Total and immunoaffinity-isolated myeloid (CD11b+) and platelet (CD41+) EVs were prepared from the plasma of intravenous LPS-injected endotoxemic donor mice and transferred directly into recipient lungs. Two-hour perfusion of lungs with unfractionated EVs from a single donor induced pulmonary edema formation and increased perfusate concentrations of RAGE (receptor for advanced glycation end products), consistent with lung injury. These responses were abolished in the lungs of monocyte-depleted mice. The isolated myeloid- but not platelet-EVs produced a similar injury response and the acute intravascular release of proinflammatory cytokines and endothelial injury markers. In the invitro human coculture model, human myeloid- (CD11b+) but not platelet- (CD61+) EVs isolated from LPS-stimulated whole blood induced acute proinflammatory cytokine production and endothelial activation. These findings implicate circulating myeloid-EVs as acute mediators of pulmonary vascular inflammation and edema, suggesting an alternative therapeutic target for attenuation of indirect ALI.

Relaxin does not prevent development of hypoxia-induced pulmonary edema in rats

Acute hypoxia impairs left ventricular (LV) inotropic function and induces development of pulmonary edema (PE). Enhanced and uneven hypoxic pulmonary vasoconstriction is an important pathogenic factor of hypoxic PE. We hypothesized that the potent vasodilator relaxin might reduce hypoxic pulmonary vasoconstriction and prevent PE formation. Furthermore, as relaxin has shown beneficial effects in acute heart failure, we expected that relaxin might also improve LV inotropic function in hypoxia. Forty-two rats were exposed over 24 h to normoxia or hypoxia (10% N2 in O2). They were infused with either 0.9% NaCl solution (normoxic/hypoxic controls) or relaxin at two doses (15 and 75 μg kg−1 day−1). After 24 h, hemodynamic measurements and bronchoalveolar lavage were performed. Lung tissue was obtained for histological and immunohistochemical analyses. Hypoxic control rats presented significant depression of LV systolic pressure by 19% and of left and right ventricular contractility by about 40%. Relaxin did not prevent the hypoxic decrease in LV inotropic function, but re-increased right ventricular contractility. Moreover, hypoxia induced moderate interstitial PE and inflammation in the lung. Contrasting to our hypothesis, relaxin did not prevent hypoxia-induced pulmonary edema and inflammation. In hypoxic control rats, PE was similarly distributed in the apical and basal lung lobes. In relaxin-treated rats, PE index was 35–40% higher in the apical than in the basal lobe, which is probably due to gravity effects. We suggest that relaxin induced exaggerated vasodilation, and hence pulmonary overperfusion. In conclusion, the results show that relaxin does not prevent but rather may aggravate PE formation.

The SRPK inhibitor N-(2-(piperidin-1-yl)-5-(trifluoromethyl)phenyl) isonicotinamide (SRPIN340) increases the immune response against metastatic melanoma in mice

Cancers have a strong relationship with immune cells in their microenvironment, which significantly influences tumor proliferation and progression. Thus, pharmacological strategies that stimulate the immune system to combat tumor cells are promising for better therapeutic efficacy. Deregulated expression of the splicing regulatory serine arginine protein kinases (mostly SRPK1 and SRPK2) has been found in different cancer types, leading to the expression of isoforms related to tumor growth and metastasis. The microenvironment of melanoma exhibits a strong presence of immune cells, which significantly influences tumor progression, and around 50% of cutaneous melanoma patients benefit from targeted immunotherapy. Here, we analyzed human malignant melanoma single-cell gene expression data and observed that SRPK1/2 overexpression correlates with immune system pathway alterations. In further analysis, we observed an increased presence of immune cells in biopsies from mice bearing metastatic melanoma treated with SRPIN340, a well-known SRPK1/2 pharmacological inhibitor. Local treatments increased the expression of proinflammatory cytokines at the tumor lesions and the activity of the spleen, accompanied by reduced pulmonary metastasis foci, edema formation, and alveolar congestion. In in vitro assays, SRPIN340 also potentiated immunological susceptibility, by increasing the expression of the antigen presenting MHCI and MHCII molecules and by increasing the ability of B16F10 cells to attract splenic cells in transwell assays. Taken together, these results reveal that the antimetastatic effect of SRPIN340 can also involve an increased immune response, which suggests additional functional clues for SRPKs in tumor biology.

COVID-19 and Liquid Homeostasis in the Lung-A Perspective through the Epithelial Sodium Channel (ENaC) Lens.

Infections with a new corona virus in 2019 lead to the definition of a new disease known as Corona Virus Disease 2019 (COVID-19). The sever cases of COVID-19 and the main cause of death due to virus infection are attributed to respiratory distress. This is associated with the formation of pulmonary oedema that impairs blood oxygenation and hypoxemia as main symptoms of respiratory distress. An important player for the maintenance of a defined liquid environment in lungs needed for normal lung function is the epithelial sodium channel (ENaC). The present article reviews the implications of SARS-CoV-2 infections from the perspective of impaired function of ENaC. The rationale for this perspective is derived from the recognition that viral spike protein and ENaC share a common proteolytic cleavage site. This cleavage site is utilized by the protease furin, that is essential for ENaC activity. Furin cleavage of spike ‘activates’ the virus protein to enable binding to host cell membrane receptors and initiate cell infection. Based on the importance of proteolytic cleavage for ENaC function and activation of spike, it seems feasible to assume that virus infections are associated with impaired ENaC activity. This is further supported by symptoms of COVID-19 that are reminiscent of impaired ENaC function in the respiratory tract.

Agonists for Bitter Taste Receptors T2R10 and T2R38 Attenuate LPS-Induced Permeability of the Pulmonary Endothelium in vitro.

One of the hallmarks of acute respiratory distress syndrome (ARDS) is an excessive increase in pulmonary vascular permeability. In settings of ARDS, the loss of barrier integrity is mediated by cell–cell contact disassembly and actin remodelling. Studies into molecular mechanisms responsible for improving microvascular barrier function are therefore vital in the development of therapeutic targets for reducing vascular permeability seen in ARDS. Bitter taste receptors (T2Rs) belong to the superfamily of G-protein-coupled receptors found in several extraoral systems, including lung epithelial and smooth muscle cells. In the present study, we show for the first time that several T2Rs are expressed in human pulmonary arterial endothelial cells (HPAECs). Our results focus on those which are highly expressed as: T2R10, T2R14 and T2R38. Agonists for T2R10 (denatonium) and T2R38 (phenylthiourea), but not T2R14 (noscapine), significantly attenuated lipopolysaccharide (LPS)-induced permeability and VE-cadherin internalisation in HPAECs. In T2R10- or T2R38-siRNA knockdown cells, these endothelial-protective effects were abolished, indicating a direct effect of agonists in regulating barrier integrity. Our further findings indicate that T2R10 and T2R38 exert their barrier-protective function through cAMP but via Rac1-dependent and independent pathways, respectively. However, using an in vivo model of ARDS, the T2R38 agonist, phenylthiourea, was not able to protect against pulmonary edema formation. Taken together, these studies identify bitter taste sensing in the pulmonary endothelium to regulate barrier integrity in vitro through cAMP-Rac1 signalling.

Normothermic Negative Pressure Ventilation <em>Ex Situ</em> Lung Perfusion: Evaluation of Lung Function and Metabolism

Lung transplantation (LTx) remains the standard of care for end-stage lung disease. A shortage of suitable donor organs and concerns over donor organ quality exacerbated by excessive geographic transportation distance and stringent donor organ acceptance criteria pose limitations to current LTx efforts. Ex situ lung perfusion (ESLP) is an innovative technology that has shown promise in attenuating these limitations. The physiologic ventilation and perfusion of the lungs outside of the inflammatory milieu of the donor body affords ESLP several advantages over traditional cold static preservation (CSP). There is evidence that negative pressure ventilation (NPV) ESLP is superior to positive pressure ventilation (PPV) ESLP, with PPV inducing more significant ventilator-induced lung injury, pro-inflammatory cytokine production, pulmonary edema, and bullae formation. The NPV advantage is perhaps due to the homogenous distribution of intrathoracic pressure across the entire lung surface. The clinical safety and feasibility of a custom NPV-ESLP device have been demonstrated in a recent clinical trial involving extender criteria donor (ECD) human lungs. Herein, the use of this custom device is described in a juvenile porcine model of normothermic NPV-ESLP over a 12 h duration, paying particular attention to management techniques. Pre-surgical preparation, including ESLP software initialization, priming, and de-airing of the ESLP circuit, and the addition of anti-thrombotic, anti-microbial, and anti-inflammatory agents, is specified. The intraoperative techniques of central line insertion, lung biopsy, exsanguination, blood collection, cardiectomy, and pneumonectomy are described. Furthermore, particular focus is paid to anesthetic considerations, with anesthesia induction, maintenance, and dynamic modifications outlined. The protocol also specifies the custom device's initialization, maintenance, and termination of perfusion and ventilation. Dynamic organ management techniques, including alterations in ventilation and metabolic parameters to optimize organ function, are thoroughly described. Finally, the physiological and metabolic assessment of lung function is characterized and depicted in the representative results.

Normothermic Negative Pressure Ventilation Ex Situ Lung Perfusion: Evaluation of Lung Function and Metabolism.

Lung transplantation (LTx) remains the standard of care for end-stage lung disease. A shortage of suitable donor organs and concerns over donor organ quality exacerbated by excessive geographic transportation distance and stringent donor organ acceptance criteria pose limitations to current LTx efforts. Ex situ lung perfusion (ESLP) is an innovative technology that has shown promise in attenuating these limitations. The physiologic ventilation and perfusion of the lungs outside of the inflammatory milieu of the donor body affords ESLP several advantages over traditional cold static preservation (CSP). There is evidence that negative pressure ventilation (NPV) ESLP is superior to positive pressure ventilation (PPV) ESLP, with PPV inducing more significant ventilator-induced lung injury, pro-inflammatory cytokine production, pulmonary edema, and bullae formation. The NPV advantage is perhaps due to the homogenous distribution of intrathoracic pressure across the entire lung surface. The clinical safety and feasibility of a custom NPV-ESLP device have been demonstrated in a recent clinical trial involving extender criteria donor (ECD) human lungs. Herein, the use of this custom device is described in a juvenile porcine model of normothermic NPV-ESLP over a 12 h duration, paying particular attention to management techniques. Pre-surgical preparation, including ESLP software initialization, priming, and de-airing of the ESLP circuit, and the addition of anti-thrombotic, anti-microbial, and anti-inflammatory agents, is specified. The intraoperative techniques of central line insertion, lung biopsy, exsanguination, blood collection, cardiectomy, and pneumonectomy are described. Furthermore, particular focus is paid to anesthetic considerations, with anesthesia induction, maintenance, and dynamic modifications outlined. The protocol also specifies the custom device's initialization, maintenance, and termination of perfusion and ventilation. Dynamic organ management techniques, including alterations in ventilation and metabolic parameters to optimize organ function, are thoroughly described. Finally, the physiological and metabolic assessment of lung function is characterized and depicted in the representative results.

New insights in ARDS pathogenesis

Acute respiratory distress syndrome (ARDS) is a life-threatening condition in critically ill patients characterized by hypoxemia and non-compliant lung. In this review, we discuss the pathophysiology of ARDS, including the mechanisms involved in the formation of pulmonary edema, the dysregulated inflammatory and immune responses, the activation of procoagulant events, the cellular communication by extracellular vesicles (EVs) between different types of cells and the interaction of the lung with other organs. Activation of inflammation, coagulation, and cell death processes result in the disruption of the alveolar-capillary membrane and the consequent protein-rich edema formation in the alveoli, in which structural and functional alterations of the alveolar epithelium play an essential role. Inflammation and activated endothelial cells trigger coagulation cascades and platelets that generate a procoagulant state in both the airspace and the intravascular compartment with the formation of fibrin in airspaces and thrombi in the microvasculature that aggravate alveolar injury and gas exchange. The crosstalk between epithelial/endothelial cells, platelets, and immune cells is mediated by EVs, whose role in the pathogenesis of ARDS is not known. Finally, the interaction of the lung with other organs has become an important determinant in the development and resolution of ARDS. Understanding the pathophysiological mechanisms involved in ARDS is crucial to developing new therapeutic strategies.

L-PGDS Attenuates Acute Lung Injury by Prostaglandin D2 in Both Dependent and Independent Ways.

Lipocalin-type PG D synthase (L-PGDS) has two roles: it can be a PGD synthase, or it can be a carrier protein of hydrophobic small molecules. In this study, we investigated the dual roles of L-PGDS in acute lung injury by using L-PGDS-deficient and point-mutated mice, which lack PGD2 producibility but maintain lipocalin ability. Hydrochloride (HCl) administration (0.1 M intratracheally for 6 h) caused hemorrhage and dysfunction in the wild-type (WT) mouse lung. These symptoms were accompanied by an increase in PGD2 production. Both deficiency and point mutation of L-PGDS aggravated the HCl-induced hemorrhage and dysfunction. Although both the gene modifications decreased PGD2 production, only L-PGDS-deficient mice, but not point mutation mice, lacked protein expressions of L-PGDS in the lungs. In the WT mice, HCl administration caused pulmonary edema, indexed as an increase in lung water content and protein leakage in bronchoalveolar lavage fluid. L-PGDS deficiency and point mutation similarly aggravated edema formation. HCl administration also stimulated mucin production and bronchoalveolar lavage fluid leukocyte infiltration in the WT mouse lungs. Of interest, L-PGDS deficiency, but not point mutation, exacerbated these manifestations. Consistently, only L-PGDS deficiency increased the mRNA expression of IL-33, which stimulates mucin production in the inflamed lung. These results show that L-PGDS attenuated HCl-induced acute lung injury progresses in two different ways: L-PGDS produced PGD2, which inhibited pulmonary edema formation, whereas its lipocalin ability decreased mucin formation and inflammatory cell infiltration in the inflamed lung.

Linear Association Between Hypoalbuminemia and Increased Risk of Acute Respiratory Distress Syndrome in Critically Ill Adults.

Retrospective analysis of prospective cohort. Medical, surgical, and cardiovascular ICUs at Vanderbilt University Medical Center. Patients (n = 993) with serum albumin measured for clinical reasons within 24 hours of study enrollment on ICU day 2 were included. The primary outcome was presence of acute respiratory distress syndrome at any time during the first 4 days in the ICU, as defined by the Berlin definition. Secondary outcomes included ventilator-free days and ICU length of stay. In an unadjusted analysis, lower serum albumin levels were associated with a higher occurrence rate of acute respiratory distress syndrome (p < 0.001). In a multivariable analysis controlling for prespecified confounders, lower serum albumin was independently associated with an increased risk of acute respiratory distress syndrome (odds ratio, 1.48 per 1-g/dL decrease in albumin; 95% CI, 1.14-1.94; p = 0.004). Additionally, lower serum albumin was associated with increased mortality (odds ratio, 1.56 per 1-g/dL decrease in albumin; 95% CI, 1.19-2.04; p = 0.001), increased ICU length of stay (incidence rate ratio, 1.19; 95% CI, 1.15-1.23; p < 0.001), higher Sequential Organ Failure Assessment score (p < 0.001), and fewer ventilator-free days (incidence rate ratio, 1.21; 95% CI, 1.19-1.24; p < 0.001). Among adult ICU patients, lower serum albumin was independently associated with increased risk of acute respiratory distress syndrome after controlling for severity of illness and potential confounders. These findings support the hypothesis that low plasma oncotic pressure contributes to pulmonary edema formation in patients at risk for acute respiratory distress syndrome, independent of severity of illness.

Subnormothermic ex vivo lung perfusion attenuates ischemia reperfusion injury from donation after circulatory death donors.

Use of normothermic ex vivo lung perfusion (EVLP) was adopted in clinical practice to assess the quality of marginal donor lungs. Subnormothermic perfusion temperatures are in use among other solid organs to improve biochemical, clinical and immunological parameters. In a rat EVLP model of donation after circulatory death (DCD) lung donors, we tested the effect of four subnormothermic EVLP temperatures that could further improve organ preservation. Warm ischemic time was of 2 hours. EVLP time was of 4 hours. Lung physiological data were recorded and metabolic parameters were assessed. Lung oxygenation at 21°C and 24°C were significantly improved whereas pulmonary vascular resistance and edema formation at 21°C EVLP were significantly worsened when compared to 37°C EVLP. The perfusate concentrations of potassium ions and lactate exiting the lungs with 28°C EVLP were significantly lower whereas sodium and chlorine ions with 32°C EVLP were significantly higher when compared to 37°C EVLP. Also compared to 37°C EVLP, the pro-inflammatory chemokines MIP2, MIP-1α, GRO-α, the cytokine IL-6 were significantly lower with 21°C, 24°C and 28°C EVLP, the IL-18 was significantly lower but only with 21°C EVLP and IL-1β was significantly lower at 21°C and 24°C EVLP. Compared to the 37°C EVLP, the lung tissue ATP content after 21°C, 24°C and 28°C EVLP were significantly higher, the carbonylated protein content after 28°C EVLP was significantly lower and we measured significantly higher myeloperoxidase activities in lung tissues with 21°C, 24°C and 32°C. The 28°C EVLP demonstrated acceptable physiological variables, significantly higher lung tissue ATP content and decreased tissue carbonylated proteins with reduced release of pro-inflammatory cytokines. In conclusion, the 28°C EVLP is a non inferior setting in comparison to the clinically approved 37°C EVLP and significantly improve biochemical, clinical and immunological parameters and may reduce I/R injuries of DCD lung donors.

Heteromeric TRP Channels in Lung Inflammation.

Activation of Transient Receptor Potential (TRP) channels can disrupt endothelial barrier function, as their mediated Ca2+ influx activates the CaM (calmodulin)/MLCK (myosin light chain kinase)-signaling pathway, and thereby rearranges the cytoskeleton, increases endothelial permeability and thus can facilitate activation of inflammatory cells and formation of pulmonary edema. Interestingly, TRP channel subunits can build heterotetramers, whereas heteromeric TRPC1/4, TRPC3/6 and TRPV1/4 are expressed in the lung endothelium and could be targeted as a protective strategy to reduce endothelial permeability in pulmonary inflammation. An update on TRP heteromers and their role in lung inflammation will be provided with this review.

Never Change a Flowing System? The Effects of Retrograde Flow on Isolated Perfused Lungs and Vessels.

Retrograde perfusion may occur during disease, surgery or extracorporeal circulation. While it is clear that endothelial cells sense and respond to changes in blood flow, the consequences of retrograde perfusion are only poorly defined. Similar to shear stress or disturbed flow, retrograde perfusion might result in vasomotor responses, edema formation or inflammation in and around vessels. In this study we investigated in rats the effects of retrograde perfusion in isolated systemic vessels (IPV) and in pulmonary vessels of isolated perfused lungs (IPL). Anterograde and retrograde perfusion was performed for 480 min in IPV and for 180 min in the IPL. Perfusion pressure, cytokine levels in perfusate and bronchoalveolar lavage fluid (BALF), edema formation and mRNA expression were studied. In IPV, an increased perfusion pressure and initially also increased cytokine levels were observed during retrograde perfusion. In the IPL, increased edema formation occurred, while cytokine levels were not increased, though dilution of cytokines in BALF due to pulmonary edema cannot be excluded. In conclusion, effects of flow reversal were visible immediately after initiation of retrograde perfusion. Pulmonary edema formation was the only effect of the 3 h retrograde perfusion. Therefore, further research should focus on identification of possible long-term complications of flow reversal.

Role of Endothelial Cell Specific Adhesion Molecule in the Development of Pulmonary Microvascular Dysfunction in HFpEF

Pulmonary complications are common in patients with heart failure with preserved ejection fraction (HFpEF), but the nature of pathomechanisms is poorly understood. The uninephrectomized and aldosterone infused (UNX-aldo) mice was employed to test the hypothesis that pulmonary microvascular dysfunction develops in HFpEF. Using echocardiography, we found that 4 weeks after UNX-aldo procedure mice exhibit increased left ventricle (LV) mass and reduced E/A ratio (E=early, A=late mitral inflow peak velocities) and increased DT (E wave deceleration time,) with no change in ejection fraction, similar to that of seen in human HFpEF. The UNX-Aldo mice had increased lung weight and wet to dry ratios, and displayed an increased pulmonary vascular resistance, when assessed in isolated perfused lungs. UNX-Aldo mice also had a reduced luminal diameter and increased wall thickness, when measured in isolated and pressurized small pulmonary arteries. Along with these pulmonary vascular changes we found that the serum level and protein expression of endothelial cell specific adhesion molecule (ESAM) in pulmonary arteries were significantly elevated in UNX-Aldo mice. Mice with genetic deletion of ESAM were protected against the development of LV diastolic dysfunction and displayed reduced pulmonary edema formation and pulmonary vascular resistance. Collectively, these results indicate a novel pathological role for ESAM in the development of pulmonary microvascular dysfunction in HFpEF.