Metabolic activation of A549 human airway epithelial cells by organic dust: a study based on microphysiometry

IDH3 mediates apoptosis of alveolar epithelial cells type 2 due to mitochondrial Ca2+ uptake during hypocapnia

In adult respiratory distress syndrome (ARDS) pulmonary perfusion failure increases physiologic dead-space (V_D/V_T) correlating with mortality. High V_D/V_T results in alveolar hypocapnia, which has been demonstrated to cause edema formation, atelectasis, and surfactant depletion, evoked, at least in part, by apoptosis of alveolar epithelial cells (AEC). However, the mechanism underlying the hypocapnia-induced AEC apoptosis is unknown. Here, using fluorescent live-cell imaging of cultured AEC type 2 we could show that in terms of CO₂ sensing the tricarboxylic acid cycle enzyme isocitrate dehydrogenase (IDH) 3 seems to be an important player because hypocapnia resulted independently from pH in an elevation of IDH3 activity and subsequently in an increase of NADH, the substrate of the respiratory chain. As a consequence, the mitochondrial transmembrane potential (ΔΨ) rose causing a Ca²⁺ shift from cytosol into mitochondria, whereas the IDH3 knockdown inhibited these responses. Furthermore, the hypocapnia-induced mitochondrial Ca²⁺ uptake resulted in reactive oxygen species (ROS) production, and both the mitochondrial Ca²⁺ uptake and ROS production induced apoptosis. Accordingly, we provide evidence that in AEC type 2 hypocapnia induces elevation of IDH3 activity leading to apoptosis. This finding might give new insight into the pathogenesis of ARDS and may help to develop novel strategies to reduce tissue injury in ARDS.

Biomarkers for differentiation of causes of respiratory distress in dogs and cats: Part 2--Lower airway, thromboembolic, and inflammatory diseases

OBJECTIVES

To review the current veterinary and relevant human literature regarding biomarkers of respiratory diseases leading to dyspnea and to summarize the availability, feasibility, and practicality of using respiratory biomarkers in the veterinary setting.

DATA SOURCES

Veterinary and human medical literature: original research articles, scientific reviews, consensus statements, and recent textbooks.

HUMAN DATA SYNTHESIS

Numerous biomarkers have been evaluated in people for discriminating respiratory disease processes with varying degrees of success.

VETERINARY DATA SYNTHESIS

Although biomarkers should not dictate clinical decisions in lieu of gold standard diagnostics, their use may be useful in directing care in the stabilization process. Serum immunoglobulins have shown promise as an indicator of asthma in cats. A group of biomarkers has also been evaluated in exhaled breath. Of these, hydrogen peroxide has shown the most potential as a marker of inflammation in asthma and potentially aspiration pneumonia, but methods for measurement are not standardized. D-dimers may be useful in screening for thromboembolic disease in dogs. There are a variety of markers of inflammation and oxidative stress, which are being evaluated for their ability to assess the severity and type of underlying disease process. Of these, amino terminal pro-C-type natriuretic peptide may be the most useful in determining if antibiotic therapy is warranted. Although critically evaluated for their use in respiratory disorders, many of the biomarkers which have been evaluated have been found to be affected by more than one type of respiratory or systemic disease.

CONCLUSION

At this time, there are point-of-care biomarkers that have been shown to reliably differentiate between causes of dyspnea in dogs and cats. Future clinical research is warranted to understand of how various diseases affect the biomarkers and more bedside tests for their utilization.

Induction of epithelial-mesenchymal transition by flagellin in cultured lung epithelial cells

Toll-like receptor 5 (TLR5) recognizes bacterial flagellin and activates host inflammatory responses, mainly through activation of the NF-κB pathway. Although pulmonary fibrosis occurs in some cases of lung infection by flagellated bacteria, the pathological roles of TLR5 stimulation in pulmonary fibrosis have yet to be elucidated. In the present study, we first confirmed that flagellin activated the NF-κB pathway in cultured A549 alveolar epithelial cells. Next, we examined the types of genes whose expression was modulated by flagellin in the cells. Microarray analysis of gene expression indicated that flagellin induced a change in gene expression that had a similar trend to transforming growth factor-β1 (TGF-β1), a key factor in the induction of epithelial-mesenchymal transition (EMT). Biochemical analysis revealed that TGF-β1 and flagellin increased the level of fibronectin protein, while they reduced the level of E-cadherin protein after 30 h of treatment. Interestingly, simultaneous treatment with TGF-β1 and flagellin significantly augmented these EMT-related changes. Flagellin strongly activated p38 MAP kinase, and the activation was sustained for longer than 30 h. SB203580, an inhibitor of p38 MAP kinase, inhibited the upregulation of fibronectin by both flagellin and TGF-β1. Simultaneous treatment with TGF-β1 and flagellin augmented the activation of p38 MAP kinase by TGF-β1 or flagellin alone. These results strongly suggest that flagellin cooperates with TGF-β1 in the induction of EMT in alveolar epithelial cells.

The application of exhaled breath gas and exhaled breath condensate analysis in the investigation of the lower respiratory tract in veterinary medicine: A review

The analysis of biomarkers in exhaled breath (EB) and exhaled breath condensate (EBC) may allow non-invasive and repeatable assessment of respiratory health and disease in mammals. Compared to human medicine, however, research data from EB and EBC analysis in veterinary medicine are limited and more patient variables influencing concentrations of EB/EBC analytes may be present. In addition, variations in methodologies between studies may influence results. A comparison of the approaches used in veterinary research by different groups may aid in the identification of potentially reliable and repeatable biomarkers suitable for further investigation. To date, changes in acid-base status and increased concentrations of inflammatory mediators have been the main findings in studies of pulmonary disease states in animals. Whilst these biomarkers are unlikely to represent specific and sensitive diagnostic parameters, they do have potential application in monitoring disease progression and treatment response.

Biomarkers of airway acidity and oxidative stress in exhaled breath condensate from grain workers

RATIONALE

Grain workers report adverse respiratory symptoms due to exposures to grain dust and endotoxin. Studies have shown that biomarkers in exhaled breath condensate (EBC) vary with the severity of airway inflammation.

OBJECTIVES

The purpose of the study was to evaluate biomarkers of airway acidity (pH and ammonium [NH(4)(+)]) and oxidative stress (8-isoprostane) in the EBC of grain workers.

METHODS

A total of 75 workers from 5 terminal elevators participated. In addition to EBC sampling, exposure monitoring for inhalable grain dust and endotoxin was performed; spirometry, allergy testing, and a respiratory questionnaire derived from that of the American Thoracic Society were administered.

MEASUREMENTS AND MAIN RESULTS

Dust and endotoxin levels ranged from 0.010 to 13 mg/m(3) (median, 1.0) and 8.1 to 11,000 endotoxin units/m(3) (median, 610) respectively. EBC pH values varied from 4.3 to 8.2 (median, 7.9); NH(4)(+) values from 22 to 2,400 microM (median, 420); and 8-isoprostane values from 1.3 to 45 pg/ml (median, 11). Univariate and multivariable analyses revealed a consistent effect of cumulative smoking and obesity with decreased pH and NH(4)(+), and intensity of grain dust and endotoxin with increased 8-isoprostane. Duration of work on the test day was associated with decreased pH and NH(4)(+), whereas duration of employment in the industry was associated with decreased 8-isoprostane.

CONCLUSIONS

Chronic exposures are associated with airway acidity, whereas acute exposures are more closely associated with oxidative stress. These results suggest that the collection of EBC may contribute to predicting the pathological state of the airways of workers exposed to acute and chronic factors.

Airway acidification and gastroesophageal reflux

Although challenging to study, researchers recently recognized the relevance of airway pH to the pathophysiology of several respiratory diseases, ranging from asthma and cystic fibrosis to pneumonia. The airway epithelium is extraordinarily sensitive to acid. Gastroesophageal reflux can and does cause respiratory symptoms, through both neurally mediated pathways and direct aspiration. Direct aspiration has a variety of immunologic, biochemical, and physiologic effects that aggravate asthma and other respiratory diseases, yet strategies to diagnose and treat gastroesophageal reflux-related respiratory symptoms remain imprecise.

Effect of formoterol and salmeterol on IL-6 and IL-8 release in airway epithelial cells

Beta(2)-adrenoceptors are widely distributed and occur on airway epithelial cells. The aim of this study was to find out whether the two long-acting beta(2)-agonists formoterol and salmeterol influence interleukin-6 (IL-6) and -8 (IL-8) release from airway epithelial cells in vitro. A549 cells and primary bronchial epithelial cells (PBEC) were stimulated with organic dust from pig barns. Non-stimulated and dust-stimulated cells were incubated for 24h with formoterol or salmeterol (10(-13)-10(-6)M) and the release of IL-6 and IL-8 into the medium was assessed by ELISA technique. Propranolol (10(-5)M) or sotalol (10(-3)M) were used to block the beta(2)-agonist mediated effects. Formoterol and salmeterol both induced enhancement of IL-6 and IL-8 release and added to the effect of organic dust. This enhanced release was blocked by a beta-blocker in PBEC but not in A549 cells. To our knowledge, this is the first time beta(2)-agonists have been shown to stimulate IL-6 release from airway epithelial cells. The results indicate different mechanisms of beta(2)-agonist action in bronchial and alveolar epithelial cells. Furthermore, our results indicate that A549 cells do not possess functional beta(2)-adrenoceptors.

Airway acidification: interactions with nitrogen oxides and airway inflammation

Airway acidification is increasingly appreciated to occur in inflammatory obstructive airway diseases, resulting from acid reflux and aspiration and from direct acid formation in the airways. Acidity activates oxidants and nitrogen oxides to create a potent antimicrobial environment. Neurogenic inflammation is triggered by airway or esophageal acidification, innate immune cells are affected by acidity, and there are pathways by which the acquired immune system also can be activated by the chemistry of an acidic airway. Measuring airway acidity is now readily achievable with noninvasive breath assays, a procedure that has opened a window on the need to understand airway pH homeostasis in health and pH dysregulation in disease.

Effects of hypoxia and hypercapnia on surfactant protein expression proliferation and apoptosis in A549 alveolar epithelial cells

During lung injury alveolar epithelial cells are directly exposed to changes in PO(2) and PCO(2). Integrity of alveolar epithelial type II cells (AECII) is critical in lung injury but the effect of hypoxia and hypercapnia on AECII function, viability and proliferation has not been clearly investigated. Aim of the present work was to determine the direct effect of hypoxia and hypercapnia on surfactant protein expression, proliferation and apoptosis of lung epithelial cells in vitro. A549 alveolar epithelia cells were subjected to hypoxia (1%O(2)-5% CO(2)) or hypercapnia (21% O(2-) 15% CO(2)) and expression of surfactant protein C was measured and compared to normal conditions (21% O(2)- 5% CO(2)). Cell cycle progression and apoptosis were measured by flow cytometric analysis.

RESULTS

A549 alveolar epithelial cells produce surfactant proteins, including surfactant protein C, when cultured under normal conditions, which is reduced under hypoxic conditions. Specifically, pro-SpC expression is moderately decreased after 8 h of culture in hypoxia, and is completely attenuated after 48 h. Hypercapnia decreases pro-SpC expression only after 48 h of exposure. Stimulation with TNF-alpha partly reverses pSPC decrease observed under hypoxic and hypercapnic conditions. Hypoxic culture of A549 cells results in progressive arrest of cells in the G1 phase of the cell cycle and increased apoptosis first observed 4 h following exposure and peaking at 24 h. In contrast hypercapnia has no significant effect on alveolar epithelial cell proliferation or apoptosis.

CONCLUSIONS

Taken together we can conclude that hypoxia rapidly and severely affects AECII function and viability while hypercapnia has an inhibitory effect on pro-SpC production only after prolonged exposure.

Influence of 8-bromo-cyclicAMP on interleukin -6 and -8 mRNA levels in A549 human lung epithelial cells exposed to organic dust: a time-kinetic study

Exposure in a swine confinement building of previously unexposed subjects leads to an intense inflammatory reaction with increased number of inflammatory cells and mediators in the upper and lower respiratory tract. In vitro the organic dust induces cytokine release from respiratory epithelial cells. Whether the dust-induced release of IL-6 and IL-8 protein from A549 lung epithelial cells is a result of sustained mRNA expression during the 24 h exposure generally applied is unknown. Furthermore, it is not known if the previously demonstrated effects on basal and dust-induced IL-6 and IL-8 protein production by 8-bromo-cyclicAMP are time-dependent, since only cumulative effects are observed by measurement of cytokine release. In the present study reverse transcription- (RT-) PCR was applied to investigate expression of IL-6 and IL-8 mRNA in A549 cells exposed to organic dust in a time-kinetic manner. The dust increased IL-6 and IL-8 mRNA expression at all times tested (1 h-48 h). The IL-6 mRNA expression peaked at 1-1.5 h and was reduced with time, whereas the dust-induced IL-8 mRNA expression remained elevated. At 1-1.5 h, 8-bromo-cAMP stimulated basal and dust-induced IL-6 mRNA expression and attenuated dust-induced IL-8 mRNA expression by activation of protein kinase A- (PKA), as assessed with the PKA inhibitor H-89. On prolonged exposure (>3 h), the dust-induced IL-6 mRNA was PKA-dependently decreased, whereas at 17 h and longer the IL-8 mRNA expression induced by a dust-suspension with 8-bromo-cAMP was similar to, or enhanced, relative to the dust-induced IL-8 mRNA. Thus, 8-bromo-cAMP exerted opposite action on dust-induced IL-6 and IL-8 mRNA expression with time.

A microphysiometer for simultaneous measurement of changes in extracellular glucose, lactate, oxygen, and acidification rate

A microphysiometer capable of measuring changes in extracellular glucose, lactate, oxygen, and acidification rate has been developed by incorporating modified electrodes into a standard Cytosensor Microphysiometer plunger. Glucose and lactate are measured indirectly at platinum electrodes by amperometric oxidation of hydrogen peroxide, which is produced from catalysis of glucose and lactate at films containing their respective entrapped oxidase. Oxygen is measured amperometrically at a platinum electrode coated with a Nafion film, while the acidification rate is measured potentiometrically by a Cytosensor Microphysiometer. Analytical information is obtained during the Cytosensor stop-flow cycles, where the electrodes measure changes in the extracellular medium corresponding to the consumption or production of the analyte by the cells. Modification of the Cytosensor plunger for multianalyte determination is described, and the operation of the technique is illustrated by the simultaneous measurement of all four analytes during the addition of fluoride and DNP to Chinese hamster ovary cells and fluoride and antimycin A to mouse fibroblast cells. Cell metabolic recovery and dynamics after exposure to agents can also be observed in specific cases.

Acid stress in the pathology of asthma

Although alteration of airway pH may serve an innate host defense capacity, it also is implicated in the pathophysiology of obstructive airway diseases. Acid-induced asthma appears in association with gastroesophageal reflux after accidental inhalation of acid (fog, pollution, and workplace exposure) and in the presence of altered airway pH homeostasis. Endogenous and exogenous exposures to acids evoke cough, bronchoconstriction, airway hyperreactivity, microvascular leakage, and heightened production of mucous, fluid, and nitric oxide. Abnormal acidity of the airways is reflected in exhaled breath assays. The intimate mechanisms of acid-induced airway obstruction are dependent on activation of capsaicin-sensitive sensory nerves. Protons activate these nerves with the subsequent release of tachykinins (major mediators of this pathway) that, in conjunction with kinins, nitric oxide, oxygen radicals, and proteases, modulate diverse aspects of airway dysfunction and inflammation. The recognition that acid stress might initiate or exacerbate airway obstructive symptomatology has prompted the consideration of new therapies targeting pH homeostasis.