Intratracheal dopamine attenuates pulmonary edema and improves survival after ventilator-induced lung injury in rats

Dopamine D1 receptor agonist alleviates acute lung injury via modulating inflammatory responses in macrophages and barrier function in airway epithelial cells

Acute lung injury (ALI) or its severe form, acute respiratory distress syndrome (ARDS) is a life-threatening illness without effective therapeutic interventions currently. Multiple lines of evidence indicated that overwhelming inflammatory responses and impaired epithelial barrier contributed to the pathogenesis of ALI/ARDS. Recently, dopamine (DA) system was identified to participate in various pulmonary diseases. Here, we discovered that dopamine D1-like receptors mainly expressed in macrophages and airway epithelial cells (AECs), which were downregulated by lipopolysaccharide (LPS) challenge in ALI mouse lung. SKF38393 (SKF) is a selective agonist for D1-like receptors and was demonstrated to inhibit excessive inflammatory responses and oxidative stress in THP-1 cell-derived macrophages and Beas-2B cells, as well as improve airway epithelial barrier dysfunction induced by LPS stimulation. Moreover, SKF administration could effectively decrease pulmonary inflammation, ameliorate tissue damage in the LPS-triggered ALI mice. The broad protective actions of SKF might be attributed to the activation of Nrf2 antioxidative system by use of the specific inhibitor, ML385. This study offers evidence of potent immunoregulatory activity of SKF in macrophages, AECs as well as ALI mouse model, which opens novel therapeutic avenues for the intervention of ALI/ARDS.

Mechanistic Understanding of Lung Inflammation: Recent Advances and Emerging Techniques

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury characterized by an acute inflammatory response in the lung parenchyma. Hence, it is considered as the most appropriate clinical syndrome to study pathogenic mechanisms of lung inflammation. ARDS is associated with increased morbidity and mortality in the intensive care unit (ICU), while no effective pharmacological treatment exists. It is very important therefore to fully characterize the underlying pathobiology and the related mechanisms, in order to develop novel therapeutic approaches. In vivo and in vitro models are important pre-clinical tools in biological and medical research in the mechanistic and pathological understanding of the majority of diseases. In this review, we will present data from selected experimental models of lung injury/acute lung inflammation, which have been based on clinical disorders that can lead to the development of ARDS and related inflammatory lung processes in humans, including ventilation-induced lung injury (VILI), sepsis, ischemia/reperfusion, smoke, acid aspiration, radiation, transfusion-related acute lung injury (TRALI), influenza, Streptococcus (S.) pneumoniae and coronaviruses infection. Data from the corresponding clinical conditions will also be presented. The mechanisms related to lung inflammation that will be covered are oxidative stress, neutrophil extracellular traps, mitogen-activated protein kinase (MAPK) pathways, surfactant, and water and ion channels. Finally, we will present a brief overview of emerging techniques in the field of omics research that have been applied to ARDS research, encompassing genomics, transcriptomics, proteomics, and metabolomics, which may recognize factors to help stratify ICU patients at risk, predict their prognosis, and possibly, serve as more specific therapeutic targets.

Attenuation of ventilator-induced lung injury through suppressing the pro-inflammatory signaling pathways: A review on preclinical studies

Mechanical ventilation (MV) is a relatively common medical intervention in ICU patients. The main side effect of MV is the so-called "ventilator-induced lung injury" (VILI). The pathogenesis of VILI is not completely understood; however, it has been reported that MV might be associated with up-regulation of various inflammatory mediators within the lung tissue and that these mediators might act as pathogenic factors in lung tissue injury. One potential mechanism for the generation of inflammatory mediators is through the release of endogenous molecules known as damage associated molecular patterns (DAMPs). These molecules are released from injured tissues and can bind to pattern recognition receptors (PRRs). PRR activation generally leads to the production and release of inflammation-related molecules including innate immune cytokines and chemokines. It has been suggested that blocking DAMP/PRR signaling pathways might diminish the progression of VILI. Herein, we review the latest findings with regard to the effects of DAMP/PRRs and their blockade, as well as the potential therapeutic targets and future research directions in VILI. Results of studies performed on human samples, animal models of disease, as well as relevant in vitro systems will be discussed.

DRD1 downregulation contributes to mechanical stretch-induced lung endothelial barrier dysfunction

Rationale: The lung-protective effects of dopamine and its role in the pathology of ventilator-induced lung injury (VILI) are emerging. However, the underlying mechanisms are still largely unknown.

Objective: To investigate the contribution of dopamine receptor dysregulation in the pathogenesis of VILI and therapeutic potential of dopamine D1 receptor (DRD1) agonist in VILI.

Methods: The role of dopamine receptors in mechanical stretch-induced endothelial barrier dysfunction and lung injury was studied in DRD1 knockout mice, in isolated mouse lung vascular endothelial cells (MLVECs), and in lung samples from patients who underwent pulmonary lobectomy with mechanical ventilation for different time periods.

Measurements and Main Results: DRD1 was downregulated in both surgical patients and mice exposed to mechanical ventilation. Prophylactic administration of dopamine or DRD1 agonist attenuated mechanical stretch-induced lung endothelial barrier dysfunction and lung injury. By contrast, pulmonary knockdown or global knockout of DRD1 exacerbated these effects. Prophylactic administration of dopamine attenuated mechanical stretch-induced α-tubulin deacetylation and subsequent endothelial hyperpermeability through DRD1 signaling. We identified that cyclic stretch-induced glycogen-synthase-kinase-3β activation led to phosphorylation and activation of histone deacetylase 6 (HDAC6), which resulted in deacetylation of α-tubulin. Upon activation, DRD1 signaling attenuated mechanical stretch-induced α-tubulin deacetylation and subsequent lung endothelial barrier dysfunction through cAMP/exchange protein activated by cAMP (EPAC)-mediated inactivation of HDAC6.

Conclusions: This work identifies a novel protective role for DRD1 against mechanical stretch-induced lung endothelial barrier dysfunction and lung injury. Further study of the mechanisms involving DRD1 in the regulation of microtubule stability and interference with DRD1/cAMP/EPAC/HDAC6 signaling may provide insight into therapeutic approaches for VILI.

Where Is Dopamine and how do Immune Cells See it?: Dopamine-Mediated Immune Cell Function in Health and Disease

Dopamine is well recognized as a neurotransmitter in the brain, and regulates critical functions in a variety of peripheral systems. Growing research has also shown that dopamine acts as an important regulator of immune function. Many immune cells express dopamine receptors and other dopamine related proteins, enabling them to actively respond to dopamine and suggesting that dopaminergic immunoregulation is an important part of proper immune function. A detailed understanding of the physiological concentrations of dopamine in specific regions of the human body, particularly in peripheral systems, is critical to the development of hypotheses and experiments examining the effects of physiologically relevant dopamine concentrations on immune cells. Unfortunately, the dopamine concentrations to which these immune cells would be exposed in different anatomical regions are not clear. To address this issue, this comprehensive review details the current information regarding concentrations of dopamine found in both the central nervous system and in many regions of the periphery. In addition, we discuss the immune cells present in each region, and how these could interact with dopamine in each compartment described. Finally, the review briefly addresses how changes in these dopamine concentrations could influence immune cell dysfunction in several disease states including Parkinson's disease, multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, as well as the collection of pathologies, cognitive and motor symptoms associated with HIV infection in the central nervous system, known as NeuroHIV. These data will improve our understanding of the interactions between the dopaminergic and immune systems during both homeostatic function and in disease, clarify the effects of existing dopaminergic drugs and promote the creation of new therapeutic strategies based on manipulating immune function through dopaminergic signaling. Graphical Abstract.

Patients Admitted to Three Spanish Intensive Care Units for Poisoning: Type of Poisoning, Mortality, and Functioning of Prognostic Scores Commonly Used

Objectives. To evaluate the gravity and mortality of those patients admitted to the intensive care unit for poisoning. Also, the applicability and predicted capacity of prognostic scales most frequently used in ICU must be evaluated. Methods. Multicentre study between 2008 and 2013 on all patients admitted for poisoning. Results. The results are from 119 patients. The causes of poisoning were medication, 92 patients (77.3%), caustics, 11 (9.2%), and alcohol, 20 (16,8%). 78.3% attempted suicides. Mean age was 44.42 ± 13.85 years. 72.5% had a Glasgow Coma Scale (GCS) ≤8 points. The ICU mortality was 5.9% and the hospital mortality was 6.7%. The mortality from caustic poisoning was 54.5%, and it was 1.9% for noncaustic poisoning (p < 0.001). After adjusting for SAPS-3 (OR: 1.19 (1.02–1.39)) the mortality of patients who had ingested caustics was far higher than the rest (OR: 560.34 (11.64–26973.83)). There was considerable discrepancy between mortality predicted by SAPS-3 (26.8%) and observed (6.7%) (Hosmer-Lemeshow test: H = 35.10; p < 0.001). The APACHE-II (7,57%) and APACHE-III (8,15%) were no discrepancies. Conclusions. Admission to ICU for poisoning is rare in our country. Medication is the most frequent cause, but mortality of caustic poisoning is higher. APACHE-II and APACHE-III provide adequate predictions about mortality, while SAPS-3 tends to overestimate.

Conservative fluid management prevents age-associated ventilator induced mortality

BACKGROUND

Approximately 800 thousand patients require mechanical ventilation in the United States annually with an in-hospital mortality rate of over 30%. The majority of patients requiring mechanical ventilation are over the age of 65 and advanced age is known to increase the severity of ventilator-induced lung injury (VILI) and in-hospital mortality rates. However, the mechanisms which predispose aging ventilator patients to increased mortality rates are not fully understood. Ventilation with conservative fluid management decreases mortality rates in acute respiratory distress patients, but to date there has been no investigation of the effect of conservative fluid management on VILI and ventilator associated mortality rates. We hypothesized that age-associated increases in susceptibility and incidence of pulmonary edema strongly promote age-related increases in ventilator associated mortality.

METHODS

2month old and 20month old male C57BL6 mice were mechanically ventilated with either high tidal volume (HVT) or low tidal volume (LVT) for up to 4h with either liberal or conservative fluid support. During ventilation, lung compliance, total lung capacity, and hysteresis curves were quantified. Following ventilation, bronchoalveolar lavage fluid was analyzed for total protein content and inflammatory cell infiltration. Wet to dry ratios were used to directly measure edema in excised lungs. Lung histology was performed to quantify alveolar barrier damage/destruction. Age matched non-ventilated mice were used as controls.

RESULTS

At 4h, both advanced age and HVT ventilation significantly increased markers of inflammation and injury, degraded pulmonary mechanics, and decreased survival rates. Conservative fluid support significantly diminished pulmonary edema and improved pulmonary mechanics by 1h in advanced age HVT subjects. In 4h ventilations, conservative fluid support significantly diminished pulmonary edema, improved lung mechanics, and resulted in significantly lower mortality rates in older subjects.

CONCLUSION

Our study demonstrates that conservative fluid alone can attenuate the age associated increase in ventilator associated mortality.

Tidal volume in animal models of hemorrhagic and endotoxic shock

The aim of this study was to examine the characteristics of lung, kidney and small intestine injury caused by early resuscitation from hemorrhagic shock (HS) and endotoxic shock (ES) when ventilating with different tidal volumes (Vts). The study also considered the determination of the appropriate Vt for use in mechanical ventilation (MV) during treatment for shock. Resuscitated rabbits were ventilated with varying Vts for 120 min following 60 min of HS or ES. The histopathology, ultrastructure and apoptotic index (AI) of the lung, kidney and small intestine were then measured. Organs from the high-Vt groups (VT=12-15 ml/kg) showed the highest pathological scores (PSs; P<0.05). For HS, the renal PS and AI of the HS-M group (Vt=8-10 ml/kg)were lower than those of the HS-L group (Vt=4-6 ml/kg) and the lung PS and AI of the HS-C (control) group were lower compared with those of the HS-M group. For ES, the lung PS of the ES-L group was lower compared with that of the ES-M group (Vt=8-10 ml/kg) and the lung AI of the ES-C (control) group was lower compared with that of the ES-L group (Vt=4-6 ml/kg). When ventilated with the same Vt, ES resulted in higher PSs in the lung and intestine and a lower renal PS (P<0.05) than HS. MV was not recommended for either shock type. When it was necessary for MV to be applied, low Vt (4-6 ml/kg) protected the lung in ES. Moderate Vt (8-10 ml/kg) may be relatively safe to use for HS.

GABA receptor ameliorates ventilator-induced lung injury in rats by improving alveolar fluid clearance

Introduction

Mechanical ventilators are increasingly used in critical care units. However, they can cause lung injury, including pulmonary edema. Our previous studies indicated that γ-aminobutyric acid (GABA) receptors are involved in alveolar-fluid homeostasis. The present study investigated the role of GABA receptors in ventilator-induced lung injury.

Methods

Adult female Sprague-Dawley rats were subjected to high-tidal-volume ventilation of 40 ml/kg body weight for 1 hour, and lung injuries were assessed.

Results

High-tidal-volume ventilation resulted in lung injury, as indicated by an increase in total protein in bronchoalveolar fluid, wet-to-dry ratio (indication of pulmonary edema), and Evans Blue dye extravasation (indication of vascular damage). Intratracheal administration of GABA before ventilation significantly reduced the wet-to-dry ratio. Further, histopathologic analysis indicated that GABA reduced ventilator-induced lung injury and apoptosis. GABA-mediated reduction was effectively blocked by the GABA_A-receptor antagonist, bicuculline. The GABA-mediated effect was not due to the vascular damage, because no differences in Evans Blue dye extravasation were noted. However, the decrease in alveolar fluid clearance by high-tidal-volume ventilation was partly prevented by GABA, which was blocked by bicuculline.

Conclusions

These results suggest that GABA reduces pulmonary edema induced by high-tidal-volume ventilation via its effects on alveolar fluid clearance and apoptosis.

Amiloride-sensitive sodium channels and pulmonary edema

The development of pulmonary edema can be considered as a combination of alveolar flooding via increased fluid filtration, impaired alveolar-capillary barrier integrity, and disturbed resolution due to decreased alveolar fluid clearance. An important mechanism regulating alveolar fluid clearance is sodium transport across the alveolar epithelium. Transepithelial sodium transport is largely dependent on the activity of sodium channels in alveolar epithelial cells. This paper describes how sodium channels contribute to alveolar fluid clearance under physiological conditions and how deregulation of sodium channel activity might contribute to the pathogenesis of lung diseases associated with pulmonary edema. Furthermore, sodium channels as putative molecular targets for the treatment of pulmonary edema are discussed.

Effects of pentoxifylline on inflammation and lung dysfunction in ventilated septic animals

Acute respiratory distress syndrome secondary to sepsis is associated with high morbidity and mortality. The purpose of this study was to characterize the effects of ventilatory strategy and the modulating activity of pentoxifylline in a sepsis-induced lung dysfunction model. Male Wistar rats were randomly divided into six groups, undergoing two different ventilatory strategies. Rats received live Escherichia coli or saline intraperitoneally. After 6 hours, the septic animals were treated with either pentoxifylline (25 mg/kg for 20 minutes) or normal saline infusion and ventilated with low tidal volume (6 mL/kg; septic animals with E. coli intraperitoneal [IP] infusion, PTX-treated and ventilated with low tidal volume and septic animals with E. coli IP infusion and ventilated with low tidal volume, respectively) or high tidal volume (12 mL/kg; septic animals with E. coli IP infusion, PTX-treated and ventilated with high tidal volume and septic animals with E. coli IP infusion and ventilated with high tidal volume, respectively) for 3 hours. The control animals received normal saline infusion and, after 6 hours, were ventilated with low or high tidal volume (control animals with saline infusion and ventilated with low tidal volume and control animals with saline infusion and ventilated with high tidal volume, respectively). Lung dysfunctions were assessed by wet-to-dry lung ratios, total cell count, total protein, malondialdehyde, and tumor necrosis factor-alpha concentrations in bronchoalveolar lavage (BAL). Septic animals with E. coli IP infusion and ventilated with high tidal volume presented increased wet-to-dry lung ratios, total cell count, total protein, and malondialdehyde in BAL compared with the septic animals ventilated with low tidal volume. Septic animals treated with pentoxifylline presented higher arterial oxygenation and lower cellular influx, protein leakage, malondialdehyde concentration, and tumor necrosis factor-alpha levels in BAL compared with septic animals undergoing the same ventilatory support strategies (septic animals with E. coli IP infusion and ventilated with low tidal volume and septic animals with E. coli IP infusion and ventilated with high tidal volume). Ventilatory strategy modulated the inflammatory response and pulmonary alterations in a sepsis-induced acute lung injury model, and these effects are improved by pentoxifylline.

Year in review 2008: Critical Care--respirology

Original research contributions published in Critical Care in 2008 in the fields of respirology and critical care medicine are summarized. Eighteen articles were grouped into the following categories: acute lung injury and acute respiratory distress syndrome, mechanical ventilation, mechanisms of ventilator-induced lung injury, and tracheotomy decannulation and non-invasive ventilation.

Improving survival by increasing lung edema clearance: is airspace delivery of dopamine a solution?

In this issue of Critical Care Chamorro-Marin and coworkers provide new evidence that dopamine instilled into airspaces is beneficial in a rat model of ventilator-induced lung injury. This study is important because it is the first to explore the effects of dopamine on survival, albeit short term. The delivery of dopamine into the airspaces in vivo is also novel and builds upon previous studies describing the mechanisms by which dopamine exerts its effect by upregulating active Na⁺ transport in the lungs. Dopamine appears to increase active Na⁺ transport via activation of amiloride-sensitive sodium channels and the basolateral Na⁺/K⁺-ATPase within minutes, and it has been shown to be effective in normal lungs and several models of lung injury. This information is relevant to current clinical trials exploring the effects of alveolar fluid clearance stimulation in patients with acute lung injury.