Bile acid aspiration in suspected ventilator-associated pneumonia

Aspiration Pneumonia

Aspiration pneumonia is a lower respiratory tract infection that results from inhalation of foreign material, often gastric and oropharyngeal contents. It is important to distinguish this from a similar entity, aspiration with chemical pneumonitis, as treatment approaches may differ. An evolving understanding of the human microbiome has shed light on the pathogenesis of aspiration pneumonia, suggesting that dysbiosis, repetitive injury, and inflammatory responses play a role in its development. Risk factors for aspiration events involve a complex interplay of anatomical and physiological dysfunctions in the nervous, gastrointestinal, and pulmonary systems. Current treatment strategies have shifted away from anaerobic organisms as leading pathogens. Prevention of aspiration pneumonia primarily involves addressing oropharyngeal dysphagia, a significant risk factor for aspiration pneumonia, particularly among elderly individuals and those with cognitive and neurodegenerative disorders.

Prevalence of Micro-Aspiration of Bile Acids in Patients with Primary Lung Cancer: A Cross-Sectional Study

Background

Lung cancer remains a serious public health problem and is the first cause of cancer-related death worldwide. There is some evidence suggests that bile acid micro-aspiration may contribute to the development of lung diseases. This study aimed to assess the prevalence of micro-aspiration of bile acids in patients with primary lung cancer.

Methods

In a cross-sectional study, 52 patients with primary lung cancer referred to a teaching hospital affiliated with Kerman University of Medical Sciences, Kerman, Iran were enrolled. Patients with pathology-confirmed lung cancer who did not receive specific treatment were included in the present study. All patients underwent bronchoscopy and the levels of bile acid was assessed in their Broncho-Alveolar Lavage (BAL) samples.

Results

According to the results, 53.85% of patients were in the age group of 40 to 59 years. Of the participants, 88.46% were male, 82.69% were smokers, and 69.23% were opium addicted. The most common presenting clinical symptoms of patients were heartburn (61.55%), hoarseness (17.31%), and epigastric pain (9.61%), respectively. Ninety-two point thirty-two percent of patients had endobronchial lesions in bronchoscopy. Squamous cell carcinoma, small-cell lung carcinoma and adenocarcinoma accounts for 48.08%, 34.61% and 17.31% of all cases of lung cancer, respectively. Bile acids were found in the BAL sample of all patients with primary lung cancer. The mean Bile acids levels in patients were 63.42 (SD=7.03) µmol/Lit.

Conclusion

According to the results of present study, there was a micro-aspiration of bile acids in all patients with primary lung cancer that may participate in shaping early events in the etiology of primary lung cancer. It seems that developing clinical strategies preventing the micro-aspiration of bile acids into the lungs could remove a key potential trigger in this process.

Bile acids-induced lung injury: update of reverse translational biology

The presence of bile acids in lung tissue is associated with some clinical features observed in various medical specialties, but it took time to understand that these are due to a "bile acid-induced lung injury" since specific translational studies and cross-disciplinary awareness were lacking. We used a reverse translational approach to update and summarize the current knowledge about the mechanisms of bile acid-induced lung injury. This has been done in a cross-disciplinary fashion since these conditions may occur in patients of various age and in different medical fields. We here define these clinical conditions, then we review the physiopathology of these conditions and the animal models used to mimic them and, finally, their pathobiology. Mechanisms of bile acid-induced lung injury have been partially clarified overtime and are represented by: 1) the interaction with secretory phospholipase A2 pathway, 2) the effect on surfactant function and structure, 3) the biological effects on inflammation and local immunity, 4) the direct cellular toxicity. These mechanisms are schematically illustrated and histological comparisons between ARDS induced by bile acids and other triggers are also provided. Based on these mechanisms we propose possible direct therapeutic applications and, finally, we discuss further research steps to improve the understanding of processes that generate pathological clinical conditions.

Salivary Alpha Amylase Bronchial Measure for Early Aspiration Pneumonia Diagnosis in Patients Treated With Therapeutic Hypothermia After Out-of-hospital Cardiac Arrest

Background

Aspiration pneumonia is the most common respiratory complication following out-of-hospital cardiac arrests (OHCA). Alpha-amylase (α-amylase) in pulmonary secretions is a biomarker of interest in detecting inhalation. The main goal of this study is to evaluate the performance of bronchoalveolar levels of α-amylase in early diagnosis of aspiration pneumonia, in patients admitted to intensive care unit (ICU) after OHCA.

Methods

This is a prospective single-center trial, led during 5 years (July 2015 to September 2020). We included patients admitted to ICU after OHCA. A protected specimen bronchial brushing and a mini-bronchoalveolar lavage (mini-BAL) were collected during the first 6 h after admission. Dosage of bronchial α-amylase and standard bacterial analysis were performed. Investigators confirmed pneumonia diagnosis using clinical, radiological, and microbiological criteria. Every patient underwent targeted temperature management.

Results

88 patients were included. The 34% (30 patients) developed aspiration pneumonia within 5 days following admission. The 55% (17) of pneumonias occurred during the first 48 h. The 57% of the patients received a prophylactic antibiotic treatment on their admission day. ICU mortality was 50%. Median value of bronchial α-amylase did not differ whether patients had aspiration pneumonia (15 [0–94]) or not (3 [0–61], p = 0,157). Values were significantly different concerning early-onset pneumonia (within 48 h) [19 (7–297) vs. 3 (0–82), p = 0,047]. If one or more microorganisms were detected in the initial mini-BAL, median value of α-amylase was significantly higher [25 (2–230)] than in sterile cultures (2 [0–43], p = 0,007). With an 8.5 IU/L cut-point, sensitivity and specificity of α-amylase value for predicting aspiration pneumonia during the first 2 days were respectively 74 and 62%. True positive and negative rates were respectively 44 and 86%. The area under the ROC curve was 0,654 (CI 95%; 0,524–0,785). Mechanical ventilation duration, length of ICU stay, and mortality were similar in both groups.

Conclusion

In our study, dosage of bronchial α-amylase was not useful in predicting aspiration pneumonia within the first 5 days after ICU admission for OHCA. Performance in predicting early-onset pneumonia was moderate.

Systems Biology and Bile Acid Signalling in Microbiome-Host Interactions in the Cystic Fibrosis Lung

The study of the respiratory microbiota has revealed that the lungs of healthy and diseased individuals harbour distinct microbial communities. Imbalances in these communities can contribute to the pathogenesis of lung disease. How these imbalances occur and establish is largely unknown. This review is focused on the genetically inherited condition of Cystic Fibrosis (CF). Understanding the microbial and host-related factors that govern the establishment of chronic CF lung inflammation and pathogen colonisation is essential. Specifically, dissecting the interplay in the inflammation–pathogen–host axis. Bile acids are important host derived and microbially modified signal molecules that have been detected in CF lungs. These bile acids are associated with inflammation and restructuring of the lung microbiota linked to chronicity. This community remodelling involves a switch in the lung microbiota from a high biodiversity/low pathogen state to a low biodiversity/pathogen-dominated state. Bile acids are particularly associated with the dominance of Proteobacterial pathogens. The ability of bile acids to impact directly on both the lung microbiota and the host response offers a unifying principle underpinning the pathogenesis of CF. The modulating role of bile acids in lung microbiota dysbiosis and inflammation could offer new potential targets for designing innovative therapeutic approaches for respiratory disease.

Aspiration of conjugated bile acids predicts adverse lung transplant outcomes and correlates with airway lipid and cytokine dysregulation

INTRODUCTION

Duodeno-gastroesophageal reflux aspiration is associated with chronic lung allograft dysfunction (CLAD). Reflux aspirate can contain bile acids (BA), functional molecules in the gastro-intestinal tract with emulsifying properties. We sought to determine and quantify the various BA species in airways of the lung transplant recipients to better understand the various effects of aspirated BA that contribute to post-transplantation outcomes.

METHODS

Bronchial washings (BW) were prospectively collected from lung transplant recipients and subsequently assayed by liquid chromatography-mass spectrometry for 13 BA and 25 lipid families. Patients were monitored for CLAD, rejection, inflammation and airway infections.

RESULTS

Detectable BA were present in 45/50 patients (90%) at 3 months after transplant. Elevated BA and predominance of conjugated species were independent predictors of CLAD (hazard ratio 7.9; 95% confidence interval 2.7-23.6; p < 0.001 and 7.3; 2.4-22; p < 0.001, respectively) and mortality (hazard ratio 4.4; 1.5-12.7; p = 0.007 and 4.8; 1.4-15.8; p = 0.01, respectively). High BA associated with increased positive bacterial cultures (60% vs 25%, p = 0.02). Primary conjugated species independently correlated with the rate of bacterial cultures during the first-year post-transplant (Beta coefficient: 0.77; 0.28-1.26; p = 0.003) and changes in airway lipidome and cytokines.

CONCLUSIONS

Higher BA levels and predominance of conjugated BA are independent predictors of chronic lung allograft dysfunction, mortality and bacterial infections. Primary conjugated BA are related to distinct changes in airway lipidome and inflammatory cytokines. This elucidates novel evidence into the mechanism following BA aspiration and proposes novel markers for prediction of adverse post-transplant outcomes.

High-fiber diets attenuate emphysema development via modulation of gut microbiota and metabolism

Dietary fiber functions as a prebiotic to determine the gut microbe composition. The gut microbiota influences the metabolic functions and immune responses in human health. The gut microbiota and metabolites produced by various dietary components not only modulate immunity but also impact various organs. Although recent findings have suggested that microbial dysbiosis is associated with several respiratory diseases, including asthma, cystic fibrosis, and allergy, the role of microbiota and metabolites produced by dietary nutrients with respect to pulmonary disease remains unclear. Therefore, we explored whether the gut microbiota and metabolites produced by dietary fiber components could influence a cigarette smoking (CS)-exposed emphysema model. In this study, it was demonstrated that a high-fiber diet including non-fermentable cellulose and fermentable pectin attenuated the pathological changes associated with emphysema progression and the inflammatory response in CS-exposed emphysema mice. Moreover, we observed that different types of dietary fiber could modulate the diversity of gut microbiota and differentially impacted anabolism including the generation of short-chain fatty acids, bile acids, and sphingolipids. Overall, the results of this study indicate that high-fiber diets play a beneficial role in the gut microbiota-metabolite modulation and substantially affect CS-exposed emphysema mice. Furthermore, this study suggests the therapeutic potential of gut microbiota and metabolites from a high-fiber diet in emphysema via local and systemic inflammation inhibition, which may be useful in the development of a new COPD treatment plan.

Reflux-Aspiration in Chronic Lung Disease

Microaspiration, or silent aspiration, is commonly suspected in patients with refractory respiratory symptoms, including unexplained chronic cough, asthma, chronic obstructive pulmonary disease, bronchiolitis, bronchiectasis, and idiopathic pulmonary fibrosis. This suspicion is driven by the high prevalence of gastroesophageal reflux in these otherwise disparate disorders. Frequently, patients receive aggressive treatment for gastroesophageal reflux disease as a means of treating their underlying respiratory conditions, even in the absence of overt symptoms of reflux. However, clinical trials have not demonstrated a clear impact on outcomes with this strategy, and in some instances there may be potential for harm. Mechanistic studies have increasingly used gastric biomarkers obtained directly from the airways to confirm the association between reflux and respiratory disease, but results are limited by methodologic flaws and correlation. The best evidence of aspiration directly causing respiratory disorders is the histopathologic detection of foreign bodies. For most of the other chronic respiratory disorders, microaspiration may be uncommon or a secondary aggravating factor, as in patients with acute exacerbations of chronic obstructive pulmonary disease or idiopathic pulmonary fibrosis. In some cases, microaspiration is probably not a significant factor at all, such as in unexplained chronic cough. It is important to distinguish between conditions in which aspiration is primarily or directly causal and conditions in which aspiration may be indirectly aggravating, to help identify whether interventions targeting reflux and aspiration precautions should be recommended to patients. Our clinical review examines some of the evidence supporting reflux-aspiration as a mechanism for several chronic respiratory disorders and offers some management considerations when reflux-aspiration is suspected.

The profibrotic effects of chronic microaspiration of bile acids on lungs of rats at different stages

This study aimed to explore the profibrotic effects of chronic microaspiration of two major bile acids, including chenodeoxycholic acid (CDCA) and deoxycholic acid (DCA), on lungs of rats at different stages, as well as the underlying mechanisms in vivo. A rat model was induced by weekly intratracheal instillation of DCA and CDCA. Our results showed that chronic microaspiration of bile acids resulted in alveolar structure disorder, and inflammatory cells infiltration in the pulmonary interstitium at the early stage. Subsequently, numerous fibroblasts were proliferated, and collagen deposition was profoundly increased over the interstitium of the airways and vessels. Compared with control group, the expression of α-smooth muscle actin, type I collagen, hydroxyproline, transforming growth factor-β1 (TGF-β1), and matrix metalloproteinase-9 in the lung tissues were remarkably elevated at the 2nd week, reached the highest level at the 6th week, and maintained high at the 8th week in both DCA- and CDCA-treated groups (P < 0.05). Furthermore, chronic microaspiration of bile acids led to higher levels of glutathione and malondialdehyde, while lower level of superoxide dismutase in lung tissues compared with controls (P < 0.05), thereby resulting in the oxidant/antioxidant enzyme imbalance in the formation of fibrosis. In addition, we also found a consistent growth in the expression of farnesoid X receptor (FXR) in both DCA- and CDCA-treated groups. Our findings suggested that chronic microaspiration of bile acids could initiate the process of pulmonary fibrosis from the early phase and promote its progression in a time-dependent manner, which likely involved the TGF-β1, oxidative stress, and FXR-related pathways.

Immediate Prone Positioning After Massive Gastric Aspiration Reduces Lung Injury Possibly by Attenuating Interleukin-6-Mediated Lung-Tissue Inflammation in Pigs

Gastric aspiration, which can cause acute, diffuse, inflammatory lung injury, is of particular concern in critically ill patients. This study aimed to determine the effects of immediate prone positioning on the degree of lung injury and inflammatory response induced by gastric aspiration. Following induction of gastric aspiration by injection of gastric fluid, 16 healthy pigs were randomized to one of two groups: supine position (SP) or prone position (PP). After ventilation and monitoring for 6 hr, all pigs were euthanized. The ratio of the partial pressure of arterial oxygen/fraction of inspired oxygen (P_aO2/F_IO2) and the partial pressure of arterial carbon dioxide (P_aCO2) were recorded during the 6-hr study period. Serum levels of interleukin (IL)-6 were measured every 2 hr, and the mean optical density (MOD) of IL-6 in lung tissues and lung-injury scores were measured at the end of the experiment. The PP group showed a significantly higher P_aO2/F_IO2 ratio, lower serum IL-6 concentration (p = .015), lower lung-injury scores (p = .012), and lower IL-6 concentration and MOD of IL-6 in lung tissue, especially in dorsal (p = .001, p = .021, respectively) and nondependent regions (p = .005, p = .035, respectively) than the SP group. There were no statistically significant differences in P_aCO2 between the groups. Lung-injury severity was positively correlated with the IL-6 concentration and MOD of IL-6 in lung tissues (p < .05). These results suggest that immediate prone positioning alleviated the degree of aspiration-induced lung injury, possibly through mitigating IL-6-mediated lung inflammation.

Guts and Gall: Bile Acids in Regulation of Intestinal Epithelial Function in Health and Disease

Epithelial cells line the entire surface of the gastrointestinal tract and its accessory organs where they primarily function in transporting digestive enzymes, nutrients, electrolytes, and fluid to and from the luminal contents. At the same time, epithelial cells are responsible for forming a physical and biochemical barrier that prevents the entry into the body of harmful agents, such as bacteria and their toxins. Dysregulation of epithelial transport and barrier function is associated with the pathogenesis of a number of conditions throughout the intestine, such as inflammatory bowel disease, chronic diarrhea, pancreatitis, reflux esophagitis, and cancer. Driven by discovery of specific receptors on intestinal epithelial cells, new insights into mechanisms that control their synthesis and enterohepatic circulation, and a growing appreciation of their roles as bioactive bacterial metabolites, bile acids are currently receiving a great deal of interest as critical regulators of epithelial function in health and disease. This review aims to summarize recent advances in this field and to highlight how bile acids are now emerging as exciting new targets for disease intervention.

Significance of Mini Bronchoalveolar Lavage Fluid Amylase Level in Ventilator-Associated Pneumonia: A Prospective Observational Study

OBJECTIVES

Aspiration of oropharyngeal or gastric contents in intubated patients can lead to ventilator-associated pneumonia. Amylase in respiratory secretion has been reported as a possible marker of aspiration. We studied whether elevated α-amylase in mini bronchoalveolar lavage specimens can be suggestive of ventilator-associated pneumonia in intubated patients with high clinical suspicion.

DESIGN

Prospective single-center observational study.

SETTING

Department of Critical Care Medicine, tertiary care academic institute.

PATIENTS

Adult patients on mechanical ventilation for more than 48 hours with with clinically suspected ventilator-associated pneumonia as per defined criteria, admitted between December 2014 and May 2016.

METHODS

Mini bronchoalveolar lavage samples were collected within 72 hours of endotracheal intubation. Samples were sent for α-amylase level assay and quantitative culture. Ventilator-associated pneumonia was confirmed from mini bronchoalveolar lavage microbial culture of greater than or equal to 10 cfu/mL, and patients were divided into ventilator-associated pneumonia and no ventilator-associated pneumonia groups. Pre- and postintubation risk factors for aspiration were also noted.

RESULTS

The prevalence of ventilator-associated pneumonia was 64.9% among 151 patients in whom it was clinically suspected. Median (interquartile range) mini bronchoalveolar lavage α-amylase levels in ventilator-associated pneumonia and no ventilator-associated pneumonia groups on the day of study inclusion were 287 U/L (164-860 U/L) and 94 U/L (59-236 U/L), respectively (p < 0.001). Median (interquartile range) α-amylase levels in patients with 0, 1, 2, and 3 preintubation risk factors were 65 U/L (35-106 U/L), 200 U/L (113-349 U/L), 867 U/L (353-1,425 U/L), and 3,453 U/L (1,865-4,304 U/L), respectively (p < 0.001) and 472 U/L (164-1,452 U/L) and 731 U/L (203-1,403 U/L) in patients with 1 and 2 postintubation risk factors, respectively (p < 0.001). A mini bronchoalveolar lavage α-amylase of 163 U/L or more yielded sensitivity and specificity of 73% and 68.6%, respectively, with area under the receiver operating characteristic curve of 0.746 (95% CI, 0.66-0.83).

CONCLUSIONS

Patients with ventilator-associated pneumonia within 72 hours from intubation have significantly elevated α-amylase concentrations in mini bronchoalveolar lavage fluid. Mini bronchoalveolar lavage α-amylase concentrations increase with increasing number of aspiration risk factors.

The Relationship between Airway Inflammation and Exacerbation in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is associated with abnormal inflammatory response and airflow limitation. Acute exacerbation involves increased inflammatory burden leading to worsening respiratory symptoms, including dyspnea and sputum production. Some COPD patients have frequent exacerbations (two or more exacerbations per year). A substantial proportion of COPD patients may remain stable without exacerbation. Bacterial and viral infections are the most common causative factors that breach airway stability and lead to exacerbation. The increasing prevalence of exacerbation is associated with deteriorating lung function, hospitalization, and risk of death. In this review, we summarize the mechanisms of airway inflammation in COPD and discuss how bacterial or viral infection, temperature, air pollution, eosinophilic inflammation, and concomitant chronic diseases increase airway inflammation and the risk of exacerbation.

Chronic microaspiration of bile acids induces lung fibrosis through multiple mechanisms in rats

Gastroesophageal reflux (GER) and microaspiration of duodenogastric refluxate have been recognized as a risk factor for pulmonary fibrosis. Recent evidence suggests that bile acid microaspiration may contribute to the development of lung fibrosis. However, the molecular evidence is scarce and the underlying mechanisms remain to be elucidated. We have recently demonstrated that bile acids induce activation of alveolar epithelial cells (AECs) and lung fibroblasts in vitro In the present study, a rat model of bile acid microaspiration was established by weekly intratracheal instillation of three major bile acids including chenodeoxycholic acid (CDCA), deoxycholic acid (DCA), and lithocholic acid (LCA). Repeated microaspiration of CDCA, DCA, and LCA caused fibrotic changes, including alveolar wall thickening and extensive collagen deposition, in rat lungs. Bile acid microaspiration also induced alveolar epithelial-mesenchymal transition (EMT), as indicated by up-regulation of mesenchymal markers α-smooth muscle actin (α-SMA) and vimentin, as well as down-regulaton of epithelial markers E-cadherin and cytokeratin in alveolar epithelium of rat lungs. The expression of fibrogenic mediators, including transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and periostin, was significantly elevated in rat lungs exposed to microaspiration of bile acids. Furthermore, microaspiration of bile acids also induced p-Smad3 and farnesoid X receptor (FXR) expression in rat lungs. Our findings suggest that microaspiration of bile acids could promote the development of pulmonary fibrosis in vivo, possibly via stimulating fibrogenic mediator expression and activating TGF-β1/Smad3 signaling and FXR.

Effects of bile acids on human airway epithelial cells: implications for aerodigestive diseases

Gastro-oesophageal reflux and aspiration have been associated with chronic and end-stage lung disease and with allograft injury following lung transplantation. This raises the possibility that bile acids may cause lung injury by damaging airway epithelium. The aim of this study was to investigate the effect of bile acid challenge using the immortalised human bronchial epithelial cell line (BEAS-2B). The immortalised human bronchial epithelial cell line (BEAS-2B) was cultured. A 48-h challenge evaluated the effect of individual primary and secondary bile acids. Post-challenge concentrations of interleukin (IL)-8, IL-6 and granulocyte-macrophage colony-stimulating factor were measured using commercial ELISA kits. The viability of the BEAS-2B cells was measured using CellTiter-Blue and MTT assays. Lithocholic acid, deoxycholic acid, chenodeoxycholic acid and cholic acid were successfully used to stimulate cultured BEAS-2B cells at different concentrations. A concentration of lithocholic acid above 10 μmol·L-1 causes cell death, whereas deoxycholic acid, chenodeoxycholic acid and cholic acid above 30 μmol·L-1 was required for cell death. Challenge with bile acids at physiological levels also led to a significant increase in the release of IL-8 and IL6 from BEAS-2B. Aspiration of bile acids could potentially cause cell damage, cell death and inflammation in vivo. This is relevant to an integrated gastrointestinal and lung physiological paradigm of chronic lung disease, where reflux and aspiration are described in both chronic lung diseases and allograft injury.

Overexpression of farnesoid X receptor in small airways contributes to epithelial to mesenchymal transition and COX-2 expression in chronic obstructive pulmonary disease

BACKGROUND

Epithelial-mesenchymal transition (EMT) and cyclooxygenase-2 (COX-2) contribute to airway remodelling and inflammation in chronic obstructive pulmonary disease (COPD). Recent data suggest that the farnesoid X receptor (FXR), a nuclear receptor traditionally considered as bile acid-activated receptor, is also expressed in non-classical bile acids target tissues with novel functions beyond regulating bile acid homeostasis. This study aimed to investigate the potential role of FXR in the development of COPD, as well as factors that affect FXR expression.

METHODS

Expression of FXR, EMT biomarkers and COX-2 was examined by immunohistochemistry in lung tissues from non-smokers, smokers, and smokers with COPD. The role of FXR in TGF-β1-induced EMT and COX-2 expression in human bronchial epithelial (HBE) cells was evaluated in vitro. Factors regulating FXR expression were assessed in cultured HBE cells and a cigarette smoke-induced rat model of COPD.

RESULTS

Expression of FXR, EMT markers and COX-2 was significantly elevated in small airway epithelium of COPD patients compared with controls. The staining scores of FXR in small airway epithelium were negatively related with FEV₁% of predicted of smokers without and with COPD. FXR agonist GW4064 remarkably enhanced and FXR antagonist Z-Guggulsterone significantly inhibited EMT changes in TGF-β1-treated HBE cells. Both chenodeoxycholic acid (CDCA) and GW4064 increased COX-2 expression in HBE cells, whereas Z-Guggulsterone dramatically restrained CDCA-induced COX-2 expression. Finally, FXR expression is induced by IL-4 and IL-13 in HBE cells, as well as by cigarette smoke exposure in a rat model of COPD.

CONCLUSIONS

Overexpression of FXR in small airway may contribute to airway remodelling and inflammation in COPD by regulating EMT and COX-2 expression.

Bile acids induce activation of alveolar epithelial cells and lung fibroblasts through farnesoid X receptor-dependent and independent pathways

BACKGROUND AND OBJECTIVE

The roles of bile acid microaspiration and bile acid-activated farnesoid X receptor (FXR) in the pathogenesis of idiopathic pulmonary fibrosis (IPF) remain unclear. We hypothesized that bile acids activate alveolar epithelial cells (AECs) and lung fibroblasts, which may be regulated by FXR activation.

METHODS

Human AECs and normal or IPF-derived lung fibroblast cells were incubated with the three major bile acids: lithocholic acid (LCA), deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA). The AECs injury indices, epithelial-mesenchymal transition (EMT) and lung fibroblast activation were evaluated. FXR expression in IPF lungs and the roles of FXR and FXR-independent pathways in bile acid-induced profibrotic effects were also investigated.

RESULTS

LCA, DCA and CDCA reduced cell viability and increased intracellular reactive oxygen species (ROS) production in A549 cells. They all induced EMT, as shown by enhanced α-SMA and vimentin and decreased E-cadherin levels. LCA directly induced differentiation of lung fibroblasts to myofibroblasts. All three bile acids promoted cellular migration but not proliferation of lung fibroblasts. FXR expression was upregulated in IPF lungs, and inhibition of FXR restrained the bile acid-induced EMT and lung fibroblast activation. Differentiation and proliferation were enhanced in lung fibroblasts exposed to conditioned medium from bile acid-stimulated A549 cells, which contained increased levels of profibrotic factors. TGF-β/Smad3 signaling was also involved in the bile acid-induced EMT and lung fibroblast differentiation.

CONCLUSION

Bile acid microaspiration may promote the development of pulmonary fibrosis by inducing activation of AECs and lung fibroblasts via FXR-dependent and independent pathways.

Bile acid aspiration in people with cystic fibrosis before and after lung transplantation

Cystic fibrosis (CF) is a genetic condition that is caused by abnormalities in the CF transmembrane conductance regulator (CFTR) gene. People with CF experience life-long morbidity and premature mortality, the vast majority of which is associated with lung disease.

Bile acids are detectable in the lower airway in advanced CF lung disease and persist after lung transplantationhttp://ow.ly/RTvNW

Bile acids repress hypoxia-inducible factor 1 signaling and modulate the airway immune response

Gastroesophageal reflux (GER) frequently occurs in patients with respiratory disease and is particularly prevalent in patients with cystic fibrosis. GER is a condition in which the duodenogastric contents of the stomach leak into the esophagus, in many cases resulting in aspiration into the respiratory tract. As such, the presence of GER-derived bile acids (BAs) has been confirmed in the bronchoalveolar lavage fluid and sputum of affected patients. We have recently shown that bile causes cystic fibrosis-associated bacterial pathogens to adopt a chronic lifestyle and may constitute a major host trigger underlying respiratory infection. The current study shows that BAs elicit a specific response in humans in which they repress hypoxia-inducible factor 1α (HIF-1α) protein, an emerging master regulator in response to infection and inflammation. HIF-1α repression was shown to occur through the 26S proteasome machinery via the prolyl hydroxylase domain (PHD) pathway. Further analysis of the downstream inflammatory response showed that HIF-1α repression by BAs can significantly modulate the immune response of airway epithelial cells, correlating with a decrease in interleukin-8 (IL-8) production, while IL-6 production was strongly increased. Importantly, the effects of BAs on cytokine production can also be more dominant than the bacterium-mediated effects. However, the effect of BAs on cytokine levels cannot be fully explained by their ability to repress HIF-1α, which is not surprising, given the complexity of the immune regulatory network. The suppression of HIF-1 signaling by bile acids may have a significant influence on the progression and outcome of respiratory disease, and the molecular mechanism underpinning this response warrants further investigation.

Aspirated bile: a major host trigger modulating respiratory pathogen colonisation in cystic fibrosis patients

Chronic respiratory infections are a leading global cause of morbidity and mortality. However, the molecular triggers that cause respiratory pathogens to adopt persistent and often untreatable lifestyles during infection remain largely uncharacterised. Recently, bile aspiration caused by gastro-oesophageal reflux (GOR) has emerged as a significant complication associated with respiratory disease, and cystic fibrosis (CF) in particular. Based on our previous finding that the physiological concentrations of bile influence respiratory pathogens towards a chronic lifestyle in vitro, we investigated the impact of bile aspiration on the lung microbiome of respiratory patients. Sputum samples (n = 25) obtained from a cohort of paediatric CF patients were profiled for the presence of bile acids using high-resolution liquid chromatography-mass spectrometry (LC-MS). Pyrosequencing was performed on a set of ten DNA samples that were isolated from bile aspirating (n = 5) and non-bile aspirating (n = 5) patients. Both denaturing gradient gel electrophoresis (DGGE) and pyrosequencing revealed significantly reduced biodiversity and richness in the sputum samples from bile aspirating patients when compared with non-aspirating patients. Families and genera associated with the pervasive CF microbiome dominated aspirating patients, while bacteria associated with the healthy lung were most abundant in non-aspirating patients. Bile aspiration linked to GOR is emerging as a major host trigger of chronic bacterial infections. The markedly reduced biodiversity and increased colonisation by dominant proteobacterial CF-associated pathogens observed in the sputum of bile aspirating patients suggest that bile may play a major role in disease progression in CF and other respiratory diseases.

Bile acids increase alveolar epithelial permeability via mitogen-activated protein kinase, cytosolic phospholipase A2 , cyclooxygenase-2, prostaglandin E2 and junctional proteins

BACKGROUND AND OBJECTIVE

Bile acid (BA) aspiration is associated with various lung diseases. It was hypothesized that BA may induce changes in alveolar epithelium permeability and contribute to the pathogenesis of lung injury.

METHODS

Human alveolar epithelial cells were grown in monolayer and stimulated with a major component of BA, chenodeoxycholic acid (CDCA). Transepithelial electrical resistance (TER) and paracellular fluxes were measured to assess permeability alteration. Prostaglandin E2 ( PGE2 ) production was measured, and its effect on TER and junctional proteins (JP) was also examined. Reverse transcription polymerase chain reaction and Western blots were used to investigate the expression of messenger RNA and JP.

RESULTS

CDCA induced significant p38 and c-Jun N-terminal kinase (JNK) phosphorylation, cytosolic phospholipase A2 (cPLA2 ) and cyclooxygenase-2 (COX-2) messenger RNA expression, PGE2 production, TER reduction and decay of JP (including occludin, zonula occludens-1 (ZO-1) and E-cadherin, in which ZO-1 had maximal change). CDCA also increased paracellular fluxes, which was abolished by dexamethasone. Both CDCA and PGE2 contributed to TER reduction in an identical trend and a dose-response manner. PGE2 also reduced ZO-1 expression, which was similar to that observed by CDCA stimulation. Pretreatment with inhibitors of p38 (SB203580), JNK (SP600125), cPLA2 (mepacrine) and COX-2 (NS398) as well as dexamethasone reversed the CDCA-induced PGE2 production, TER reduction and decay of ZO-1.

CONCLUSIONS

The increase in alveolar permeability was associated with decay of JP. BA may induce permeability alteration through the upregulation of mitogen-activated protein kinase, cPLA2 , COX-2, PGE2 and JP, which may contribute to the pathogenesis of BA-associated lung injury.

Accuracy of alpha amylase in diagnosing microaspiration in intubated critically-ill patients

OBJECTIVES

Amylase concentration in respiratory secretions was reported to be a potentially useful marker for aspiration and pneumonia. The aim of this study was to determine accuracy of α-amylase in diagnosing microaspiration in critically ill patients.

METHODS

Retrospective analysis of prospectively collected data collected in a medical ICU. All patients requiring mechanical ventilation for at least 48 h, and included in a previous randomized controlled trial were eligible for this study, provided that at least one tracheal aspirate was available for α-amylase measurement. As part of the initial trial, pepsin was quantitatively measured in all tracheal aspirates during a 48-h period. All tracheal aspirates were frozen, allowing subsequent measurement of α-amylase for the purpose of the current study. Microaspiration was defined as the presence of at least one positive tracheal aspirate for pepsin (>200 ng.mL-1). Abundant microaspiration was defined as the presence of pepsin at significant level in >74% of tracheal aspirates.

RESULTS

Amylase was measured in 1055 tracheal aspirates, collected from 109 patients. Using mean α-amylase level per patient, accuracy of α-amylase in diagnosing microaspiration was moderate (area under the receiver operator curve 0.72±0.05 [95%CI 0.61-0.83], for an α-amylase value of 1685 UI.L-1). However, when α-amylase levels, coming from all samples, were taken into account, area under the receiver operator curve was 0.56±0.05 [0.53-0.60]. Mean α-amylase level, and percentage of tracheal aspirates positive for α-amylase were significantly higher in patients with microaspiration, and in patients with abundant microaspiration compared with those with no microaspiration; and similar in patients with microaspiration compared with those with abundant microaspiration. α-amylase and pepsin were significantly correlated (r2 = 0.305, p = 0.001).

CONCLUSION

Accuracy of mean α-amylase in diagnosing microaspiration is moderate. Further, when all α-amylase levels were taken into account, α-amylase was inaccurate in diagnosing microaspiration, compared with pepsin.

Optimal care and design of the tracheal cuff in the critically ill patient

Despite the increasing use of non-invasive ventilation and high-flow nasal-oxygen therapy, intubation is still performed in a large proportion of critically ill patients. The aim of this narrative review is to discuss recent data on long-term intubation-related complications, such as microaspiration, and tracheal ischemic lesions. These complications are common in critically ill patients, and are associated with substantial morbidity and mortality. Recent data suggest beneficial effects of tapered cuffed tracheal tubes in reducing aspiration. However, clinical data are needed in critically ill patients to confirm this hypothesis. Polyurethane-cuffed tracheal tubes and continuous control of cuff pressure could be beneficial in preventing microaspiration and ventilator-associated pneumonia (VAP). However, large multicenter studies are needed before recommending their routine use. Cuff pressure should be maintained between 20 and 30 cmH₂O to prevent intubation-related complications. Tracheal ischemia could be prevented by manual or continuous control of cuff pressure.

The effect of gastric juice on interleukin-8 production by cystic fibrosis primary bronchial epithelial cells

CF patients are often treated with proton pump inhibitors (PPIs) to reduce acidic gastro-esophageal reflux (GER) and bronchial aspiration of duodeno-gastric contents is common in CF. We have previously demonstrated that gastric juice (GJ) from patients "on" PPI can induce interleukin-8 (IL-8) production by bronchial epithelial cells in culture. We hypothesized that such effect would be more pronounced in CF patients known to have high inflammatory susceptibility. We aimed to evaluate the effect of GJ on IL-8 production by primary bronchial epithelial cells (PBEC), derived from a CF patient and a healthy subject.

METHODS

PBEC obtained from one donor (normal PBEC) and one receptor (CF-PBEC) for lung transplantation were stimulated with GJ from patients "off" and "on" PPI. IL-8 levels were measured in the supernatant.

RESULTS

GJ from patients "on" PPI provoked a significant higher IL-8 production compared to GJ from patients "off" PPI, both in normal PBEC [462 (200-1468) vs. 11 (4-28) pg/ml, p=0.0001] as in CF-PBEC [1468 (841-2449) vs. 85 (26-131) pg/ml, p<0.0001]. Exposure of the cells to GJ "off" PPI and "on" PPI provoked significantly higher IL-8 production in the CF-PBEC compared to the normal PBEC ["off" PPI 85 (26-131) vs. 11 (4-28) pg/ml, p=0.01; "on" PPI 1468 (841-2449) vs. 462 (200-1468) pg/ml, p=0.01]. Filtration (0.20 μm) of the GJ "on" PPI, to eliminate large particles and bacterial sub-products, resulted in a significant decrease of IL-8 production.

CONCLUSION

Patients with CF, treated with PPIs, have GJ with high pH and high endotoxin levels. These patients often have GER and bronchial aspiration. The aspirated material (GJ "on" PPI) has a significantly enhanced inflammatory effect on CF bronchial epithelial cells in culture. As chronic PPI treatment in CF may result in a paradoxically increased inflammatory effect in the airways, alternative anti-reflux therapies should be considered in CF.

Respiratory pathogens adopt a chronic lifestyle in response to bile

Chronic respiratory infections are a major cause of morbidity and mortality, most particularly in Cystic Fibrosis (CF) patients. The recent finding that gastro-esophageal reflux (GER) frequently occurs in CF patients led us to investigate the impact of bile on the behaviour of Pseudomonas aeruginosa and other CF-associated respiratory pathogens. Bile increased biofilm formation, Type Six Secretion, and quorum sensing in P. aeruginosa, all of which are associated with the switch from acute to persistent infection. Furthermore, bile negatively influenced Type Three Secretion and swarming motility in P. aeruginosa, phenotypes associated with acute infection. Bile also modulated biofilm formation in a range of other CF-associated respiratory pathogens, including Burkholderia cepacia and Staphylococcus aureus. Therefore, our results suggest that GER-derived bile may be a host determinant contributing to chronic respiratory infection.

The role of total bile acid in oral secretions in ventilator-associated pneumonia

PURPOSE

The aim of this study was to investigate the role of inflammatory biomarkers and total bile acid (TBA) in oral secretions in the development of ventilator-associated pneumonia (VAP).

MATERIALS

This prospective study was conducted in an intensive care unit. Oral secretions were collected from mechanically ventilated patients who met the selection criteria for VAP prevention protocol. The levels of interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor α, soluble intercellular adhesion molecule-1, monocyte chemoattractant protein-1, C-reactive protein, surfactant protein D, and TBA in oral secretions were measured and compared between the patients with and those without VAP.

RESULTS

Thirty-nine patients with and 39 patients without VAP were studied. The levels of inflammatory biomarkers in oral secretions showed no significant difference between the 2 groups. However, the patients with VAP had significantly higher values of TBA in oral secretions than did those without VAP (median and 25th-75th interquartile range, 9.59 and 1.37-24.66 μmol/L vs 2.74 and 0.00-8.22 μmol/L; P < .003). No significant correlations were found between TBA and inflammatory biomarkers in oral secretions.

CONCLUSIONS

Duodenogastroesophageal reflux as evidenced by the presence of TBA in oral secretions is common in mechanically ventilated patients and may play a role in the development of VAP.

Reflux aspiration in children with neurodisability--a significant problem, but can we measure it?

Recurrent respiratory problems are common in children with severe neurodisability, and respiratory deterioration is a leading cause of premature death in this group. Although the etiology is multifactorial, recurrent pulmonary aspiration is thought to play a significant role. Gastroesophageal reflux is known to be common, as is oral-motor discoordination. Differentiating direct aspiration of food and saliva and gastric reflux aspiration is difficult and presents a challenge in managing patients and assessing their suitability for surgical antireflux procedures. This is particularly the case when children present with predominantly respiratory symptoms, where there may be direct aspiration, reflux aspiration, neither, or both. A clinical biomarker to identify and quantify reflux aspiration would therefore be useful in surgical assessment and may also be applicable as an outcome measure for clinical trials of antireflux surgery. In this review, we discuss the evidence base behind existing and potentially novel biomarkers of aspiration in bronchoalveolar lavage fluid. We highlight the limitations of the lipid-laden macrophage index, particularly with regard to its specificity and interrater/intrarater reliability. We discuss the laboratory methods available to measure promising new biomarkers (pepsin and bile acids) and highlight their potential advantages and disadvantages. Finally, to understand how aspiration causes clinical signs and symptoms in our patients, we need to study the effect of aspirated substances on the lung, and here we review the available in vivo and in vitro literature.

Bile acids in sputum and increased airway inflammation in patients with cystic fibrosis

BACKGROUND

Up to 80% of patients with cystic fibrosis (CF) may have increased gastroesophageal reflux and aspiration of duodenogastric contents into the lungs. We aimed to assess aspiration in patients with CF by measuring duodenogastric components in induced sputum and to investigate whether the presence of bile acids (BAs) in sputum was correlated with disease severity and markers of inflammation.

METHODS

In 41 patients with CF, 15 healthy volunteers, 29 patients with asthma, and 28 patients with chronic cough, sputum was obtained after inhalation of hypertonic saline. Sputum supernatant was tested for BA and neutrophil elastase. Spirometry and BMI were assessed on the day of sputum collection.

RESULTS

Two of 15 healthy patients (13%), eight of 29 patients (28%) with asthma, four of 28 patients (14%) with chronic cough, and 23 of 41 patients (56%) with CF had BA in sputum. BA concentrations were similar in patients who are positive for BA with genotype F508del homozygote, F508del heterozygote, and other CF mutations and were not related with BMI and age. Patients with CF with BA in sputum had a higher concentration of neutrophil elastase compared with patients without BA in sputum (31.25 [20.33-54.78] μg/mL vs 14.45 [7.11-27.88] μg/mL, P < .05). There was a significant correlation between BA concentrations and dynamic lung volumes (FEV(1) % predicted [r = -0.53, P < .01], FVC% [r = -0.59, P < .01]) as well as with number of days of antibiotic IV treatment (r = 0.58, P < .01).

CONCLUSIONS

BAs are present in the sputum of more than one-half of patients with CF, suggesting aspiration of duodenogastric contents. Aspiration of BA was associated with increased airway inflammation. In patients with BA aspiration, the levels of BA were clearly associated with the degree of lung function impairment as well as the need for IV antibiotic treatment.

Gastric emptying and different types of reflux in adult patients with cystic fibrosis

BACKGROUND

Increased gastro-oesophageal reflux (GER) is common in patients with cystic fibrosis (CF). Previous studies showed delayed gastric emptying (GE) and a high prevalence of bile acids in saliva suggesting duodenogastro-oesophageal reflux (DGER).

AIM

To assess different types of reflux (acid, weakly acidic and bile) and their relationship with rate of GE in adult CF patients.

METHODS

Gastric emptying was assessed in 33 CF patients using breath tests, reflux was monitored in 42 patients using impedance-pH-metry and 14 CF patients underwent combined impedance-pH-Bilitec monitoring.

RESULTS

Delayed GE was found in 33%, increased GER (predominantly acid) in 67% and pathological DGER in 35% of the CF patients. There was a significant correlation between oesophageal bile and acid exposure (P < 0.0001, r = 0.85). Patients with increased DGER had a higher proximal extent of reflux compared to those without DGER [17 (9-35) vs. 5 (1-12), P = 0.04]. There was no correlation between GE and reflux parameters, however, in a subgroup of 10 patients studied by impedance-pH-Bilitec and GE, there was a strong correlation between GE rate and bile exposure (P = 0.005, r = 0.83).

CONCLUSIONS

Delayed gastric emptying is present in 1/3 of patients with cystic fibrosis. There is a subgroup of these patients with both delayed gastric emptying and increased acidic duodenogastro-oesophageal reflux with high proximal extent and risk of aspiration. Controlled studies should be performed to evaluate the effect of prokinetics or antireflux surgery on the clinical cystic fibrosis evolution in these patients.

Integrative metabolome and transcriptome profiling reveals discordant energetic stress between mouse strains with differential sensitivity to acrolein-induced acute lung injury

SCOPE

This investigation sought to better understand the metabolic role of the lung and to generate insights into the pathogenesis of acrolein-induced acute lung injury. A respiratory irritant, acrolein is generated by overheating cooking oils or by domestic cooking using biomass fuels, and is in environmental tobacco smoke, a health hazard in the restaurant workplace.

METHODS AND RESULTS

Using SM/J (sensitive) and 129X1/SvJ (resistant) inbred mouse strains, the lung metabolome was integrated with the transcriptome profile before and after acrolein exposure. A total of 280 small molecules were identified and mean values (log 2 >0.58 or <-0.58, p<0.05) were considered different for between-strain comparisons or within-strain responses to acrolein treatment. At baseline, 24 small molecules increased and 33 small molecules decreased in the SM/J mouse lung as compared to 129X1/SvJ mouse lung. Notable among the increased compounds was malonylcarnitine. Following acrolein exposure, several molecules indicative of glycolysis and branched chain amino acid metabolism increased similarly in both strains, whereas SM/J mice were less effective in generating metabolites related to fatty acid β-oxidation.

CONCLUSION

These findings suggest management of energetic stress varies between these strains, and that the ability to evoke auxiliary energy generating pathways rapidly and effectively may be critical in enhancing survival during acute lung injury in mice.