Inhibition of lung fluid clearance and epithelial Na+ channels by chlorine, hypochlorous acid, and chloramines

Epithelial Na + Channels Function as Extracellular Sensors

The epithelial Na + channel (ENaC) resides on the apical surfaces of specific epithelia in vertebrates and plays a critical role in extracellular fluid homeostasis. Evidence that ENaC senses the external environment emerged well before the molecular identity of the channel was reported three decades ago. This article discusses progress toward elucidating the mechanisms through which specific external factors regulate ENaC function, highlighting insights gained from structural studies of ENaC and related family members. It also reviews our understanding of the role of ENaC regulation by the extracellular environment in physiology and disease. After familiarizing the reader with the channel's physiological roles and structure, we describe the central role protein allostery plays in ENaC's sensitivity to the external environment. We then discuss each of the extracellular factors that directly regulate the channel: proteases, cations and anions, shear stress, and other regulators specific to particular extracellular compartments. For each regulator, we discuss the initial observations that led to discovery, studies investigating molecular mechanism, and the physiological and pathophysiological implications of regulation. © 2024 American Physiological Society. Compr Physiol 14:5407-5447, 2024.

[The role of the pulmonologist in an armed conflict]

INTRODUCTION

Recent news points to the eventuality of an armed conflict on the national territory.

STATE OF THE ART

In this situation, pulmonologists will in all likelihood have a major role to assume in caring for the injured, especially insofar as chest damage is a major cause of patient death.

PERSPECTIVES

The main injuries that pulmonologists may be called upon to treat stem not only from explosions, but also from chemical, biological and nuclear hazards. In this article, relevant organizational and pedagogical aspects are addressed. Since exhaustiveness on this subject is unattainable, we are proposing training on specific subjects for interested practitioners.

CONCLUSION

The resilience of the French health system in a situation of armed conflict depends on the active participation of all concerned parties. With this in mind, it is of prime importance that the pneumological community be sensitized to the potential predictable severity of war-related injuries.

Halogen-Induced Chemical Injury to the Mammalian Cardiopulmonary Systems

The halogens chlorine (Cl₂) and bromine (Br₂) are highly reactive oxidizing elements with widespread industrial applications and a history of development and use as chemical weapons. When inhaled, depending on the dose and duration of exposure, they cause acute and chronic injury to both the lungs and systemic organs that may result in the development of chronic changes (such as fibrosis) and death from cardiopulmonary failure. A number of conditions, such as viral infections, coexposure to other toxic gases, and pregnancy increase susceptibility to halogens significantly. Herein we review their danger to public health, their mechanisms of action, and the development of pharmacological agents that when administered post-exposure decrease morbidity and mortality.

Formulation and clinical perspectives of inhalation-based nanocarrier delivery: a new archetype in lung cancer treatment

Despite tremendous research in targeted delivery and specific molecular inhibitors (gene delivery), cytotoxic drug delivery through inhalation has been seen as a core part in the treatment of the lung cancer. Inhalation delivery provides a high dose of the drug directly to the lungs without affecting other body organs, increasing the therapeutic ratio. This article reviews the research performed over the last several decades regarding inhalation delivery of various cancer therapeutics for the treatment of lung cancer. Nevertheless, pulmonary administration of nanocarrier-based cancer therapeutics for lung cancer therapy is still in its infancy and faces greater than expected challenges. This article focuses on the current inhalable nanocarrier-based drugs for lung cancer treatment.

Hyaluronan and halogen-induced airway hyperresponsiveness and lung injury

Chlorine (Cl2 ) and bromine (Br2 ) are produced in large quantities throughout the world and used in the industry and the sanitation of water. These halogens can pose a significant threat to public health when released into the atmosphere during transportation and industrial accidents, or as acts of terrorism. In this review, we discuss the evidence showing that the activity of Cl2 and Br2 , and of products formed by their interaction with biomolecules, fragment high-molecular-weight hyaluronan (HMW-HA), a key component of the interstitial space and present in epithelial cells, to form proinflammatory, low-molecular-weight hyaluronan fragments that increase intracellular calcium (Ca2+ ) and activate RAS homolog family member A (RhoA) in airway smooth muscle and epithelial and microvascular cells. These changes result in airway hyperresponsiveness (AHR) to methacholine and increase epithelial and microvascular permeability. The increase in intracellular Ca2+ is the result of the activation of the calcium-sensing receptor by Cl2 , Br2 , and their by-products. Posthalogen administration of a commercially available form of HMW-HA to mice and to airway cells in vitro reverses the increase of Ca2+ and the activation of RhoA, and restores AHR to near-normal levels of airway function. These data have established the potential of HMW-HA to be a countermeasure against Cl2 and Br2 toxicity.

Reactive species generated by heme impair alveolar epithelial sodium channel function in acute respiratory distress syndrome

We previously reported that the highly reactive cell-free heme (CFH) is increased in the plasma of patients with chronic lung injury and causes pulmonary edema in animal model of acute respiratory distress syndrome (ARDS) post inhalation of halogen gas. However, the mechanisms by which CFH causes pulmonary edema are unclear. Herein we report for the first time that CFH and chlorinated lipids (formed by the interaction of halogen gas, Cl₂, with plasmalogens) are increased in the plasma of patients exposed to Cl₂ gas. Ex vivo incubation of red blood cells (RBC) with halogenated lipids caused oxidative damage to RBC cytoskeletal protein spectrin, resulting in hemolysis and release of CFH. Patch clamp and short circuit current measurements revealed that CFH inhibited the activity of amiloride-sensitive epithelial Na⁺ channel (ENaC) and cation sodium (Na⁺) channels in mouse alveolar cells and trans-epithelial Na⁺ transport across human airway cells with EC₅₀ of 125 nM and 500 nM, respectively. Molecular modeling identified 22 putative heme-docking sites on ENaC (energy of binding range: 86-1563 kJ/mol) with at least 2 sites within its narrow transmembrane pore, potentially capable of blocking Na⁺ transport across the channel. A single intramuscular injection of the heme-scavenging protein, hemopexin (4 μg/kg body weight), one hour post halogen gas exposure, decreased plasma CFH and improved lung ENaC activity in mice. In conclusion, results suggested that CFH mediated inhibition of ENaC activity may be responsible for pulmonary edema post inhalation injury.

Monocyte-derived alveolar macrophage apolipoprotein E participates in pulmonary fibrosis resolution

Recent studies have presented compelling evidence that it is not tissue-resident, but rather monocyte-derived alveolar macrophages (TR-AMs and Mo-AMs, respectively) that are essential to development of experimental lung fibrosis. However, whether apolipoprotein E (ApoE), which is produced abundantly by Mo-AMs in the lung, plays a role in the pathogenesis is unclear. In this study, we found that pulmonary ApoE was almost exclusively produced by Mo-AMs in mice with bleomycin-induced lung fibrosis. We showed that, although ApoE was not necessary for developing maximal fibrosis in bleomycin-injured lung, it was required for the resolution of this pathology. We found that ApoE directly bound to Collagen I and mediated Collagen I phagocytosis in vitro and in vivo, and this process was dependent on low-density lipoprotein receptor-related protein 1 (LPR1). Furthermore, interference of ApoE/LRP1 interaction impaired the resolution of lung fibrosis in bleomycin-treated WT mice. In contrast, supplementation of ApoE promoted this process in ApoE-/- animals. In conclusion, Mo-AM-derived ApoE is beneficial to the resolution of lung fibrosis, supporting the notion that Mo-AMs may have distinct functions in different phases of lung fibrogenesis. The findings also suggest a potentially novel therapeutic target for treating lung fibrosis, to which effective remedies remain scarce.

Heme scavenging reduces pulmonary endoplasmic reticulum stress, fibrosis, and emphysema

Pulmonary fibrosis and emphysema are irreversible chronic events after inhalation injury. However, the mechanism(s) involved in their development remain poorly understood. Higher levels of plasma and lung heme have been recorded in acute lung injury associated with several insults. Here, we provide the molecular basis for heme-induced chronic lung injury. We found elevated plasma heme in chronic obstructive pulmonary disease (COPD) (GOLD stage 4) patients and also in a ferret model of COPD secondary to chronic cigarette smoke inhalation. Next, we developed a rodent model of chronic lung injury, where we exposed C57BL/6 mice to the halogen gas, bromine (Br2) (400 ppm, 30 minutes), and returned them to room air resulting in combined airway fibrosis and emphysematous phenotype, as indicated by high collagen deposition in the peribronchial spaces, increased lung hydroxyproline concentrations, and alveolar septal damage. These mice also had elevated pulmonary endoplasmic reticulum (ER) stress as seen in COPD patients; the pharmacological or genetic diminution of ER stress in mice attenuated Br2-induced lung changes. Finally, treating mice with the heme-scavenging protein, hemopexin, reduced plasma heme, ER stress, airway fibrosis, and emphysema. This is the first study to our knowledge to report elevated heme in COPD patients and establishes heme scavenging as a potential therapy after inhalation injury.

Halogen Inhalation-Induced Lung Injury and Acute Respiratory Distress Syndrome

OBJECTIVE

Exposure to halogens, such as chlorine or bromine, results in environmental and occupational hazard to the lung and other organs. Chlorine is highly toxic by inhalation, leading to dyspnea, hypoxemia, airway obstruction, pneumonitis, pulmonary edema, and acute respiratory distress syndrome (ARDS). Although bromine is less reactive and oxidative than chlorine, inhalation also results in bronchospasm, airway hyperresponsiveness, ARDS, and even death. Both halogens have been shown to damage the systemic circulation and result in cardiac injury as well. There is no specific antidote for these injuries since the mechanisms are largely unknown.

DATA SOURCES

This review was based on articles published in PubMed databases up to January, 2018, with the following keywords: "chlorine," "bromine," "lung injury," and "ARDS."

STUDY SELECTION

The original articles and reviews including the topics were the primary references.

RESULTS

Based on animal studies, it is found that inhaled chlorine will form chlorine-derived oxidative products that mediate postexposure toxicity; thus, potential treatments will target the oxidative stress and inflammation induced by chlorine. Antioxidants, cAMP-elevating agents, anti-inflammatory agents, nitric oxide-modulating agents, and high-molecular-weight hyaluronan have shown promising effects in treating acute chlorine injury. Elevated free heme level is involved in acute lung injury caused by bromine inhalation. Hemopexin, a heme-scavenging protein, when administered postexposure, decreases lung injury and improves survival.

CONCLUSIONS

At present, there is an urgent need for additional research to develop specific therapies that target the basic mechanisms by which halogens damage the lungs and systemic organs.

Influenza virus infection alters ion channel function of airway and alveolar cells: mechanisms and physiological sequelae

The cystic fibrosis transmembrane conductance regulator (CFTR) and the amiloride-sensitive epithelial sodium channels (ENaC) are located in the apical membranes of airway and alveolar epithelial cells. These transporters play an important role in the regulation of lung fluid balance across airway and alveolar epithelia by being the conduits for chloride (Cl^-) and bicarbonate ([Formula: see text]) secretion and sodium (Na⁺) ion absorption, respectively. The functional role of these channels in the respiratory tract is to maintain the optimum volume and ionic composition of the bronchial periciliary fluid (PCL) and alveolar lining fluid (ALF) layers. The PCL is required for proper mucociliary clearance of pathogens and debris, and the ALF is necessary for surfactant homeostasis and optimum gas exchange. Dysregulation of ion transport may lead to mucus accumulation, bacterial infections, inflammation, pulmonary edema, and compromised respiratory function. Influenza (or flu) in mammals is caused by influenza A and B viruses. Symptoms include dry cough, sore throat, and is often followed by secondary bacterial infections, accumulation of fluid in the alveolar spaces and acute lung injury. The underlying mechanisms of flu symptoms are not fully understood. This review summarizes our present knowledge of how influenza virus infections alter airway and alveolar epithelial cell CFTR and ENaC function in vivo and in vitro and the role of these changes in influenza pathogenesis.

Morphometric characteristics of neutrophils stimulated by adhesion and hypochlorite

The aim of this work was to compare cell form, size and volume as well as the locomotor activity of polymorphonuclear leukocytes (PMNLs) stimulated by adhesion to glass and exposed to hypochlorous acid at non-toxic dose. After 20min of adhesion to a glass surface, volume, cell surface area and projection area of PMNLs were equaled to 143.1±21.4μm³, 288.8±28.8μm² and 248.3±32.3μm², respectively. Projection area of PMNLs exposed to NaOCl was noticeably enlarged as compared with control samples. The cell volume of 20min adherent cells exposed to NaOCl was enlarged in comparison with both control cells and 5min adhered exposed to NaOCl cells. NaOCl exposure induced a degranulation of PMNLs as measured by lysozyme release. Granules could be found both above the cell surface and on the substratum near the cell. The S/V ratio for PMNLs increased (from 1.52 to 2.02μm^-1) with the increasing of cell activation time. But at NaOCl addition the reverse tendency was observed (from 2.10 to 1.87μm^-1). In cells exposed to NaOCl the redistribution and decrease of concentration of F-actin took place. This observation supports the hypothesis that the priming of PMNLs with hypochlorous acid modifies cell motility and morphology and reflects also on other functions.

Sensitive detection and estimation of cell-derived peroxynitrite fluxes using fluorescein-boronate

The specific and sensitive detection of peroxynitrite (ONOO^-/ONOOH) in biological systems is a great challenge due to its high reactivity towards several biomolecules. Herein, we validated the advantages of using fluorescein-boronate (Fl-B) as a highly sensitive fluorescent probe for the direct detection of peroxynitrite under biologically-relevant conditions in two different cell models. The synthesis of Fl-B was achieved by a very simply two-step conversion synthetic route with high purity (>99%) and overall yield (∼42%). Reactivity analysis of Fl-B with relevant biological oxidants including hydrogen peroxide (H₂O₂), hypochlorous acid (HOCl) and peroxynitrite were performed. The rate constant for the reaction of peroxynitrite with Fl-B was 1.7×10⁶M^-1s^-1, a million times faster than the rate constant measured for H₂O₂ (k=1.7M^-1s^-1) and 2,700 faster than HOCl (6.2×10²M^-1s^-1) at 37°C and pH 7.4. The reaction of Fl-B with peroxynitrite was significant even in the presence of physiological concentrations of CO₂, a well-known peroxynitrite reactant. Experimental and simulated kinetic analyses confirm that the main oxidation process of Fl-B takes place with peroxynitrite itself via a direct bimolecular reaction and not with peroxynitrite-derived radicals. Fl-B was successfully applied for the detection of endogenously-generated peroxynitrite by endothelial cells and in macrophage-phagocyted parasites. Moreover, the generated data allowed estimating the actual intracellular flux of peroxynitrite. For instance, ionomycin-stimulated endothelial cells generated peroxynitrite at a rate of ∼ 0.1μMs^-1, while immunostimulated macrophages do so in the order of ∼1μMs^-1 inside T. cruzi-infected phagosomes. Fl-B revealed not to be toxic in concentrations up to 1mM for 24h. Cellular peroxynitrite detection was achieved by conventional laboratory fluorescence-based methods including flow cytometry and epi-fluorescence microscopy. Fl-B was shown to be more sensitive than the coumarin boronate due to a higher molar absorption coefficient and quantum yield. Overall, our results show that Fl-B is a kinetically selective and highly sensitive probe for the direct detection of cell-derived peroxynitrite.

Formation of chlorinated lipids post-chlorine gas exposure

Exposure to chlorine (Cl2) gas can occur during accidents and intentional release scenarios. However, biomarkers that specifically indicate Cl2 exposure and Cl2-derived products that mediate postexposure toxicity remain unclear. We hypothesized that chlorinated lipids (Cl-lipids) formed by direct reactions between Cl2 gas and plasmalogens serve as both biomarkers and mediators of post-Cl2 gas exposure toxicities. The 2-chloropalmitaldehyde (2-Cl-Pald), 2-chlorostearaldehyde (2-Cl-Sald), and their oxidized products, free- and esterified 2-chloropalmitic acid (2-Cl-PA) and 2-chlorostearic acid were detected in the lungs and plasma of mouse and rat models of Cl2 gas exposure. Levels of Cl-lipids were highest immediately post-Cl2 gas exposure, and then declined over 72 h with levels remaining 20- to 30-fold higher at 24 h compared with baseline. Glutathione adducts of 2-Cl-Pald and 2-Cl-Sald also increased with levels peaking at 4 h in plasma. Notably, 3-chlorotyrosine also increased after Cl2 gas exposure, but returned to baseline within 24 h. Intranasal administration of 2-Cl-PA or 2-Cl-Pald at doses similar to those formed in the lung after Cl2 gas exposure led to increased distal lung permeability and inflammation and systemic endothelial dysfunction characterized by loss of eNOS-dependent vasodilation. These data suggest that Cl-lipids could serve as biomarkers and mediators for Cl2 gas exposure and toxicity.

Chlorine-induced cardiopulmonary injury

Chlorine (Cl2 ) is utilized worldwide for a diverse range of industrial applications, including pulp bleaching, sanitation, and pharmaceutical development. Though Cl2 has widespread use, little is known regarding the mechanisms of toxicity associated with Cl2 exposure, which occurs during industrial accidents or acts of terrorism. Previous instances of Cl2 exposure have led to reported episodes of respiratory distress that result in high morbidity and mortality. Furthermore, studies suggest that acute Cl2 exposure also results in systemic vascular injury and subsequent myocardial contractile dysfunction. Here, we review both lung and cardiac pathology associated with acute Cl2 inhalation and discuss recently published data that suggest that mitochondrial dysfunction underlies the pathogenesis of Cl2 -induced toxicity. Last, we discuss our findings that suggest that upregulation of autophagy protects against Cl2 -induced lung inflammation and can be a potential therapeutic target for ameliorating the toxic effects of Cl2 exposure.

Heme Attenuation Ameliorates Irritant Gas Inhalation-Induced Acute Lung Injury

AIMS

Exposure to irritant gases, such as bromine (Br2), poses an environmental and occupational hazard that results in severe lung and systemic injury. However, the mechanism(s) of Br2 toxicity and the therapeutic responses required to mitigate lung damage are not known. Previously, it was demonstrated that Br2 upregulates the heme degrading enzyme, heme oxygenase-1 (HO-1). Since heme is a major inducer of HO-1, we determined whether an increase in heme and heme-dependent oxidative injury underlies the pathogenesis of Br2 toxicity.

RESULTS

C57BL/6 mice were exposed to Br2 gas (600 ppm, 30 min) and returned to room air. Thirty minutes postexposure, mice were injected intraperitoneally with a single dose of the heme scavenging protein, hemopexin (Hx) (3 μg/gm body weight), or saline. Twenty-four hours postexposure, saline-treated mice had elevated total heme in bronchoalveolar lavage fluid (BALF) and plasma and acute lung injury (ALI) culminating in 80% mortality after 10 days. Hx treatment significantly lowered heme, decreased evidence of ALI (lower protein and inflammatory cells in BALF, lower lung wet-to-dry weight ratios, and decreased airway hyperreactivity to methacholine), and reduced mortality. In addition, Br2 caused more severe ALI and mortality in mice with HO-1 gene deletion (HO-1-/-) compared to wild-type controls, while transgenic mice overexpressing the human HO-1 gene (hHO-1) showed significant protection.

INNOVATION

This is the first study delineating the role of heme in ALI caused by Br2.

CONCLUSION

The data suggest that attenuating heme may prove to be a useful adjuvant therapy to treat patients with ALI.

Upregulation of autophagy decreases chlorine-induced mitochondrial injury and lung inflammation

The mechanisms of toxicity during exposure of the airways to chlorinated biomolecules generated during the course of inflammation and to chlorine (Cl2) gas are poorly understood. We hypothesized that lung epithelial cell mitochondria are damaged by Cl2 exposure and activation of autophagy mitigates this injury. To address this, NCI-H441 (human lung adenocarcinoma epithelial) cells were exposed to Cl2 (100 ppm/15 min) and bioenergetics were assessed. One hour after Cl2, cellular bioenergetic function and mitochondrial membrane potential were decreased. These changes were associated with increased MitoSOX signal, and treatment with the mitochondrial redox modulator MitoQ attenuated these bioenergetic defects. At 6h postexposure, there was significant increase in autophagy, which was associated with an improvement of mitochondrial function. Pretreatment of H441 cells with trehalose (an autophagy activator) improved bioenergetic function, whereas 3-methyladenine (an autophagy inhibitor) resulted in increased bioenergetic dysfunction 1h after Cl2 exposure. These data indicate that Cl2 induces bioenergetic dysfunction, and autophagy plays a protective role in vitro. Addition of trehalose (2 vol%) to the drinking water of C57BL/6 mice for 6 weeks, but not 1 week, before Cl2 (400 ppm/30 min) decreased white blood cells in the bronchoalveolar lavage fluid at 6h after Cl2 by 70%. Acute administration of trehalose delivered through inhalation 24 and 1h before the exposure decreased alveolar permeability but not cell infiltration. These data indicate that Cl2 induces bioenergetic dysfunction associated with lung inflammation and suggests that autophagy plays a protective role.

Respiratory syncytial virus infection increases chlorine-induced airway hyperresponsiveness

Exposure to chlorine (Cl2) damages airway and alveolar epithelia resulting in acute lung injury and reactive airway hyperresponsiveness (AHR) to methacholine. However, little is known about the effect of preexisting respiratory disease on Cl2-induced lung injury. By using a murine respiratory syncytial virus (RSV) infection model, we found that preexisting RSV infection increases Cl2 (187 ppm for 30 min)-induced lung inflammation and airway AHR at 24 h after exposure (5 days after infection). RSV infection and Cl2 exposure synergistically induced oxygen desaturation and neutrophil infiltration and increased MCP-1, MIP-1β, IL-10, IFN-γ, and RANTES concentrations in the bronchoalveolar lavage fluid (BALF). In contrast, levels of type 2 cytokines (i.e., IL-4, IL-5, IL-9, and IL-13) were not significantly affected by either RSV infection or Cl2 exposure. Cl2 exposure, but not RSV infection, induced AHR to methacholine challenge as measured by flexiVent. Moreover, preexisting RSV infection amplified BALF levels of hyaluronan (HA) and AHR. The Cl2-induced AHR was mitigated by treatment with inter-α-trypsin inhibitor antibody, which inhibits HA signaling, suggesting a mechanism of HA-mediated AHR from exacerbated oxidative injury. Our results show for the first time that preexisting RSV infection predisposes the lung to Cl2-induced injury. These data emphasize the necessity for further research on the effects of Cl2 in vulnerable populations and the development of appropriate treatments.

Hyaluronan mediates airway hyperresponsiveness in oxidative lung injury

Chlorine (Cl2) inhalation induces severe oxidative lung injury and airway hyperresponsiveness (AHR) that lead to asthmalike symptoms. When inhaled, Cl2 reacts with epithelial lining fluid, forming by-products that damage hyaluronan, a constituent of the extracellular matrix, causing the release of low-molecular-weight fragments (L-HA, <300 kDa), which initiate a series of proinflammatory events. Cl2 (400 ppm, 30 min) exposure to mice caused an increase of L-HA and its binding partner, inter-α-trypsin-inhibitor (IαI), in the bronchoalveolar lavage fluid. Airway resistance following methacholine challenge was increased 24 h post-Cl2 exposure. Intratracheal administration of high-molecular-weight hyaluronan (H-HA) or an antibody against IαI post-Cl2 exposure decreased AHR. Exposure of human airway smooth muscle (HASM) cells to Cl2 (100 ppm, 10 min) or incubation with Cl2-exposed H-HA (which fragments it to L-HA) increased membrane potential depolarization, intracellular Ca(2+), and RhoA activation. Inhibition of RhoA, chelation of intracellular Ca(2+), blockade of cation channels, as well as postexposure addition of H-HA, reversed membrane depolarization in HASM cells. We propose a paradigm in which oxidative lung injury generates reactive species and L-HA that activates RhoA and Ca(2+) channels of airway smooth muscle cells, increasing their contractility and thus causing AHR.

Postexposure aerosolized heparin reduces lung injury in chlorine-exposed mice

Chlorine (Cl2) is a highly reactive oxidant gas that, when inhaled, may cause acute lung injury culminating in death from respiratory failure. In this study, we tested the hypothesis that exposure of mice to Cl2 causes intra-alveolar and systemic activation of the coagulation cascade that plays an important role in development of lung injury. C57Bl/6 mice were exposed to Cl2 (400 for 30 min or 600 ppm for 45 min) in environmental chambers and then returned to room air for 1 or 6 h. Native coagulation (NATEM) parameters such as blood clotting time and clot formation time were measured in whole blood by the viscoelastic technique. D-dimers and thrombin-anti-thrombin complexes were measured in both plasma and bronchoalveolar lavage fluid (BALF) by ELISA. Our results indicate that mice exposed to Cl2 gas had significantly increased clotting time, clot formation time, and D-dimers compared with controls. The thrombin-anti-thrombin complexes were also increased in the BALF of Cl2 exposed animals. To test whether increased coagulation contributed to the development of acute lung injury, mice exposed to Cl2 and returned to room air were treated with aerosolized heparin or vehicle for 20 min. Aerosolized heparin significantly reduced protein levels and the number of inflammatory cells in the BALF at 6 h postexposure. These findings highlight the importance of coagulation abnormities in the development of Cl2-induced lung injury.

Chlorine gas exposure disrupts nitric oxide homeostasis in the pulmonary vasculature

Exposure to chlorine (Cl2) gas during industrial accidents or chemical warfare leads to significant airway and distal lung epithelial injury that continues post exposure. While lung epithelial injury is prevalent, relatively little is known about whether Cl2 gas also promotes injury to the pulmonary vasculature. To determine this, rats were subjected to a sub-lethal Cl2 gas exposure (400 ppm, 30 min) and then brought back to room air. Pulmonary arteries (PA) were isolated from rats at various times post-exposure and contractile (phenylephrine) and nitric oxide (NO)-dependent vasodilation (acetylcholine and mahmanonoate) responses measured ex vivo. PA contractility did not change, however significant inhibition of NO-dependent vasodilation was observed that was maximal at 24-48 h post exposure. Superoxide dismutase restored NO-dependent vasodilation suggesting a role for increased superoxide formation. This was supported by ∼2-fold increase in superoxide formation (measured using 2-hydroethidine oxidation to 2-OH-E+) from PA isolated from Cl2 exposed rats. We next measured PA pressures in anesthetized rats. Surprisingly, PA pressures were significantly (∼4 mmHg) lower in rats that had been exposed to Cl2 gas 24 h earlier suggesting that deficit in NO-signaling observed in isolated PA experiments did not manifest as increased PA pressures in vivo. Administration of the iNOS selective inhibitor 1400W, restored PA pressures to normal in Cl2 exposed, but not control rats suggesting that any deficit in NO-signaling due to increased superoxide formation in the PA, is offset by increased NO-formation from iNOS. These data indicate that disruption of endogenous NO-signaling mechanisms that maintain PA tone is an important aspect of post-Cl2 gas exposure toxicity.

Chlorine induces the unfolded protein response in murine lungs and skin

Chlorine (Cl2) is an important industrial chemical. Accidental full body exposure to Cl2 poses an environmental, occupational, and public health hazard characterized mainly by injury to the lung, skin, and ocular epithelia. The cellular mechanisms underlying its acute toxicity are incompletely understood. This study examined whether whole body exposure of BALB/c mice to Cl2 in environmental chambers leads to the up-regulation of the unfolded protein response (UPR) in their lungs and skin. Shaved BALB/c mice were exposed to a sublethal concentration of Cl2 (400 ppm for 30 min) and returned to room air for 1 or 6 hours and killed. IL-6 and TNF-α were increased significantly at 1 and 6 hours after Cl2 exposure in the lungs and at 6 hours in the skin. These changes were accompanied by increased UPR signaling (i.e., activation of protein kinase RNA-like endoplasmic reticulum kinase, inositol-requiring enzyme 1 α, and activating transcription factor 6α) at these time points. The expression of hepcidin, which regulates tissue accumulation and mobilization of iron, was increased in the skin and lungs of Cl2-exposed mice. The data shown herein indicate for the first time the up-regulation of UPR signaling and hepcidin in the skin and lungs of Cl2-exposed mice, which persisted when the mice were returned to room air for 6 hours.

Ethanol alters alveolar fluid balance via Nadph oxidase (NOX) signaling to epithelial sodium channels (ENaC) in the lung

Chronic alcohol consumption is associated with increased incidence of ICU-related morbidity and mortality, primarily from acute respiratory distress syndrome (ARDS). However, the mechanisms involved are unknown. One explanation is that alcohol regulates epithelial sodium channels (ENaC) via oxidant signaling to promote a pro- injury environment. We used small rodent models to mimic acute and chronic alcohol consumption and tested the hypothesis that ethanol (EtOH) would affect lung fluid clearance by up-regulating ENaC activity in the lung. Fluorescence labeling of rat lung slices and in vivo mouse lung revealed an increase in ROS production in response to acute EtOH exposure. Using western blots and fluorescein-5-maleimide labeling, we conclude that EtOH exposure modifies cysteines of α-ENaC while data from single channel patch clamp analysis confirm that 0.16% EtOH increased ENaC activity in rat alveolar cells. In vivo lung fluid clearance demonstrated a latent increase in fluid clearance in mice receiving EtOH diet. Ethanol mice given a tracheal instillation of LPS demonstrated early lung fluid clearance compared to caloric control mice and C57Bl/6 mice. Standard biochemical techniques reveal that chronic EtOH consumption resulted in greater protein expression of the catalytic gp91^phox subunit and the obligate Rac1 protein. Collectively these data suggest that chronic EtOH consumption may lead to altered regulation of ENaC, contributing to a ‘pro-injury’ environment in the alcohol lung.

Integrative assessment of chlorine-induced acute lung injury in mice

The genetic basis for the underlying individual susceptibility to chlorine-induced acute lung injury is unknown. To uncover the genetic basis and pathophysiological processes that could provide additional homeostatic capacities during lung injury, 40 inbred murine strains were exposed to chlorine, and haplotype association mapping was performed. The identified single-nucleotide polymorphism (SNP) associations were evaluated through transcriptomic and metabolomic profiling. Using ≥ 10% allelic frequency and ≥ 10% phenotype explained as threshold criteria, promoter SNPs that could eliminate putative transcriptional factor recognition sites in candidate genes were assessed by determining transcript levels through microarray and reverse real-time PCR during chlorine exposure. The mean survival time varied by approximately 5-fold among strains, and SNP associations were identified for 13 candidate genes on chromosomes 1, 4, 5, 9, and 15. Microarrays revealed several differentially enriched pathways, including protein transport (decreased more in the sensitive C57BLKS/J lung) and protein catabolic process (increased more in the resistant C57BL/10J lung). Lung metabolomic profiling revealed 95 of the 280 metabolites measured were altered by chlorine exposure, and included alanine, which decreased more in the C57BLKS/J than in the C57BL/10J strain, and glutamine, which increased more in the C57BL/10J than in the C57BLKS/J strain. Genetic associations from haplotype mapping were strengthened by an integrated assessment using transcriptomic and metabolomic profiling. The leading candidate genes associated with increased susceptibility to acute lung injury in mice included Klf4, Sema7a, Tns1, Aacs, and a gene that encodes an amino acid carrier, Slc38a4.

Targeted aerosolized delivery of ascorbate in the lungs of chlorine-exposed rats

BACKGROUND

Chlorine (Cl(2))-induced lung injury is a serious public health threat that may result from industrial and household accidents. Post-Cl(2) administration of aerosolized ascorbate in rodents decreased lung injury and mortality. However, the extent to which aerosolized ascorbate augments depleted ascorbate stores in distal lung compartments has not been assessed.

METHODS

We exposed rats to Cl(2) (300 ppm for 30 min) and returned them to room air. Within 15-30 min postexposure, rats breathed aerosolized ascorbate and desferal or vehicle (mean particle size 3.3 μm) through a nose-only exposure system for 60 min and were euthanized. We measured the concentrations of reduced ascorbate in the bronchoalveolar lavage (BAL), plasma, and lung tissues with high-pressure liquid chromatography, protein plasma concentration in the BAL, and the volume of the epithelia lining fluid (ELF).

RESULTS

Cl(2)-exposed rats that breathed aerosolized vehicle had lower values of ascorbate in their BAL, ELF, and lung tissues compared to air-breathing rats. Delivery of aerosolized ascorbate increased reduced ascorbate in BAL, ELF, lung tissues, and plasma of both Cl(2) and air-exposed rats without causing lung injury. Based on mean diameter of aerosolized particles and airway sizes we calculated that approximately 5% and 1% of inhaled ascorbate was deposited in distal lung regions of air and Cl(2)-exposed rats, respectively. Significantly higher ascorbate levels were present in the BAL of Cl(2)-exposed rats when aerosol delivery was initiated 1 h post-Cl(2).

CONCLUSIONS

Aerosol administration is an effective, safe, and noninvasive method for the delivery of low molecular weight antioxidants to the lungs of Cl(2)-exposed individuals for the purpose of decreasing morbidity and mortality. Delivery is most effective when initiated 1 h postexposure when the effects of Cl(2) on minute ventilation subside.

Assessment of locomotion in chlorine exposed mice by computer vision and neural networks

Assessment of locomotion following exposure of animals to noxious or painful stimuli can offer significant insights into underlying mechanisms of injury and the effectiveness of various treatments. We developed a novel method to track the movement of mice in two dimensions using computer vision and neural network algorithms. By using this system we demonstrated that mice exposed to chlorine (Cl(2)) gas developed impaired locomotion and increased immobility for up to 9 h postexposure. Postexposure administration of buprenorphine, a common analgesic agent, increased locomotion and decreased immobility times in Cl(2)- but not air-exposed mice, most likely by decreasing Cl(2)-induced pain. This method can be adapted to assess the effectiveness of various therapies following exposure to a variety of chemical and behavioral noxious stimuli.

Nadph oxidase regulates alveolar epithelial sodium channel activity and lung fluid balance in vivo via O⁻₂ signaling

To define roles for reactive oxygen species (ROS) and epithelial sodium channel (ENaC) in maintaining lung fluid balance in vivo, we used two novel whole animal imaging approaches. Live X-ray fluoroscopy enabled quantification of air space fluid content of C57BL/6J mouse lungs challenged by intratracheal (IT) instillation of saline; results were confirmed by using conventional lung wet-to-dry weight ratios and Evans blue as measures of pulmonary edema. Visualization and quantification of ROS produced in lungs was performed in mice that had been administered a redox-sensitive dye, hydro-Cy7, by IT instillation. We found that inhibition of NADPH oxidase with a Rac-1 inhibitor, NSC23766, resulted in alveolar flooding, which correlated with a decrease in lung ROS production in vivo. Consistent with a role for Nox2 in alveolar fluid balance, Nox2(-/-) mice showed increased retention of air space fluid compared with wild-type controls. Interestingly, fluoroscopic analysis of C57BL/6J lungs IT instilled with LPS showed an acute stimulation of lung fluid clearance and ROS production in vivo that was abrogated by the ROS scavenger tetramethylpiperidine-N-oxyl (TEMPO). Acute application of LPS increased the activity of 20 pS nonselective ENaC channels in rat type 1 cells; the average number of channel and single-channel open probability (NPo) increased from 0.14 ± 0.04 to 0.62 ± 0.23. Application of TEMPO to the same cell-attached recording caused an immediate significant decrease in ENaC NPo to 0.04 ± 0.03. These data demonstrate that, in vivo, ROS has the capacity to stimulate lung fluid clearance by increasing ENaC activity.

Post-exposure antioxidant treatment in rats decreases airway hyperplasia and hyperreactivity due to chlorine inhalation

We assessed the safety and efficacy of combined intravenous and aerosolized antioxidant administration to attenuate chlorine gas-induced airway alterations when administered after exposure. Adult male Sprague-Dawley rats were exposed to air or 400 parts per million (ppm) chlorine (a concentration likely to be encountered in the vicinity of industrial accidents) in environmental chambers for 30 minutes, and returned to room air, and they then received a single intravenous injection of ascorbic acid and deferoxamine or saline. At 1 hour and 15 hours after chlorine exposure, the rats were treated with aerosolized ascorbate and deferoxamine or vehicle. Lung antioxidant profiles, plasma ascorbate concentrations, airway morphology, and airway reactivity were evaluated at 24 hours and 7 days after chlorine exposure. At 24 hours after exposure, chlorine-exposed rats had significantly lower pulmonary ascorbate and reduced glutathione concentrations. Treatment with antioxidants restored depleted ascorbate in lungs and plasma. At 7 days after exposure, in chlorine-exposed, vehicle-treated rats, the thickness of the proximal airways was 60% greater than in control rats, with twice the amount of mucosubstances. Airway resistance in response to methacholine challenge was also significantly elevated. Combined treatment with intravenous and aerosolized antioxidants restored airway morphology, the amount of airway mucosubstances, and airway reactivity to control levels by 7 days after chlorine exposure. Our results demonstrate for the first time, to the best of our knowledge, that severe injury to major airways in rats exposed to chlorine, as characterized by epithelial hyperplasia, mucus accumulation, and airway hyperreactivity, can be reversed in a safe and efficacious manner by the post-exposure administration of ascorbate and deferoxamine.

Extended diagnostic criteria used for indirect challenge testing in elite asthmatic swimmers

The aim of the study was to investigate the prevalence of asthma with or without exercise induced symptoms among elite and elite aspiring swimmers and to compare sport specific exercise provocation with mannitol provocation.

METHODS

101 adolescent swimmers were investigated with mannitol provocation and sport specific exercise challenge test. Mannitol positivity was defined as either direct FEV(1) PD15 (ordinary criteria) or as β(2)-reversibility ≥15% after challenge (extended criteria). A direct positive exercise test was defined as a drop in FEV(1) of 10% (ordinary criteria) or a difference in FEV of ≥15% either spontaneous, variability, or with β2-agonist, reversibility (extended criteria).

RESULTS

We found a high prevalence of mannitol and/or exercise positivity. Twenty-six swimmers were mannitol direct positive and 14 were direct exercise positive using ordinary criteria. Using extended criteria 43 were mannitol positive and 24 were exercise positive. When including reversibility and variability to define a positive test the sensitivity for current asthma with or without exercise induced symptoms increased while the specificity remained roughly unchanged. Direct positivity for mannitol and exercise poorly overlapped using ordinary criteria but improved using extended criteria.

CONCLUSION

We found a high prevalence of asthma among elite swimmers. The use of variability and reversibility (liability) as additional criteria to define a positive test provided to our mind relevant information and should be considered.

Regulation of alveolar epithelial Na+ channels by ERK1/2 in chlorine-breathing mice

The mechanisms by which the exposure of mice to Cl(2) decreases vectorial Na(+) transport and fluid clearance across their distal lung spaces have not been elucidated. We examined the biophysical, biochemical, and physiological changes of rodent lung epithelial Na(+) channels (ENaCs) after exposure to Cl(2), and identified the mechanisms involved. We measured amiloride-sensitive short-circuit currents (I(amil)) across isolated alveolar Type II (ATII) cell monolayers and ENaC single-channel properties by patching ATII and ATI cells in situ. α-ENaC, γ-ENaC, total and phosphorylated extracellular signal-related kinase (ERK)1/2, and advanced products of lipid peroxidation in ATII cells were measured by Western blot analysis. Concentrations of reactive intermediates were assessed by electron spin resonance (ESR). Amiloride-sensitive Na(+) channels with conductances of 4.5 and 18 pS were evident in ATI and ATII cells in situ of air-breathing mice. At 1 hour and 24 hours after exposure to Cl(2), the open probabilities of these two channels decreased. This effect was prevented by incubating lung slices with inhibitors of ERK1/2 or of proteasomes and lysosomes. The exposure of ATII cell monolayers to Cl(2) increased concentrations of reactive intermediates, leading to ERK1/2 phosphorylation and decreased I(amil) and α-ENaC concentrations at 1 hour and 24 hours after exposure. The administration of antioxidants to ATII cells before and after exposure to Cl(2) decreased concentrations of reactive intermediates and ERK1/2 activation, which mitigated the decrease in I(amil) and ENaC concentrations. The reactive intermediates formed during and after exposure to Cl(2) activated ERK1/2 in ATII cells in vitro and in vivo, leading to decreased ENaC concentrations and activity.

Enhancement of alveolar epithelial sodium channel activity with decreased cystic fibrosis transmembrane conductance regulator expression in mouse lung

We sought to establish whether the cystic fibrosis transmembrane conductance regulator (CFTR) regulates the activity of amiloride-sensitive sodium channels (ENaC) in alveolar epithelial cells of wild-type, heterozygous (Cftr(+/-)), knockout (Cftr(-/-)), and ΔF508-expressing mice in situ. RT-PCR studies confirmed the presence of CFTR message in freshly isolated alveolar type II (ATII) cells from wild-type mice. We patched alveolar type I (ATI) and ATII cells in freshly prepared lung slices from these mice and demonstrated the presence of 4-pS ENaC channels with the following basal open probabilities (P(o)): wild-type=0.21 ± 0.015: Cftr(+/-)=0.4 ± 0.03; ΔF508=0.55 ± 0.01; and Cftr(-/-)=and 0.81 ± 0.016 (means ± SE; n ≥ 9). Forskolin (5 μM) or trypsin (2 μM), applied in the pipette solution, increased the P(o) and number of channels in ATII cells of wild-type, Cftr(+/-), and ΔF508, but not in Cftr(-/-) mice, suggesting that the latter were maximally activated. Western blot analysis showed that lungs of all groups of mice had similar levels of α-ENaC; however, lungs of Cftr(+/-) and Cftr(-/-) mice had significantly higher levels of an α-ENaC proteolytic fragment (65 kDa) that is associated with active ENaC channels. Our results indicate that ENaC activity is inversely correlated to predicted CFTR levels and that CFTR heterozygous and homozygous mice have higher levels of proteolytically processed ENaC fragments in their lungs. This is the first demonstration of functional ENaC-CFTR interactions in alveolar epithelial cells in situ.

Mitigation of chlorine gas lung injury in rats by postexposure administration of sodium nitrite

Nitrite (NO(2)(-)) has been shown to limit injury to the heart, liver, and kidneys in various models of ischemia-reperfusion injury. Potential protective effects of systemic NO(2)(-) in limiting lung injury or enhancing repair have not been documented. We assessed the efficacy and mechanisms by which postexposure intraperitoneal injections of NO(2)(-) mitigate chlorine (Cl(2))-induced lung injury in rats. Rats were exposed to Cl(2) (400 ppm) for 30 min and returned to room air. NO(2)(-) (1 mg/kg) or saline was administered intraperitoneally at 10 min and 2, 4, and 6 h after exposure. Rats were killed at 6 or 24 h. Injury to airway and alveolar epithelia was assessed by quantitative morphology, protein concentrations, number of cells in bronchoalveolar lavage (BAL), and wet-to-dry lung weight ratio. Lipid peroxidation was assessed by measurement of lung F(2)-isoprostanes. Rats developed severe, but transient, hypoxemia. A significant increase of protein concentration, neutrophil numbers, airway epithelia in the BAL, and lung wet-to-dry weight ratio was evident at 6 h after Cl(2) exposure. Quantitative morphology revealed extensive lung injury in the upper airways. Airway epithelial cells stained positive for terminal deoxynucleotidyl-mediated dUTP nick end labeling (TUNEL), but not caspase-3. Administration of NO(2)(-) resulted in lower BAL protein levels, significant reduction in the intensity of the TUNEL-positive cells, and normal lung wet-to-dry weight ratios. F(2)-isoprostane levels increased at 6 and 24 h after Cl(2) exposure in NO(2)(-)- and saline-injected rats. This is the first demonstration that systemic NO(2)(-) administration mitigates airway and epithelial injury.

Ascorbate and deferoxamine administration after chlorine exposure decrease mortality and lung injury in mice

Chlorine (Cl(2)) gas exposure poses an environmental and occupational hazard that frequently results in acute lung injury. There is no effective treatment. We assessed the efficacy of antioxidants, administered after exposure, in decreasing mortality and lung injury in C57BL/6 mice exposed to 600 ppm of Cl(2) for 45 minutes and returned to room air. Ascorbate and deferoxamine were administered intramuscularly every 12 hours and by nose-only inhalation every 24 hours for 3 days starting after 1 hour after exposure. Control mice were exposed to Cl(2) and treated with vehicle (saline or water). Mortality was reduced fourfold in the treatment group compared with the control group (22 versus 78%; P = 0.007). Surviving animals in the treatment group had significantly lower protein concentrations, cell counts, and epithelial cells in their bronchoalveolar lavage (BAL). Lung tissue ascorbate correlated inversely with BAL protein as well as with the number of neutrophils and epithelial cells. In addition, lipid peroxidation was reduced threefold in the BAL of mice treated with ascorbate and deferoxamine when compared with the control group. Administration of ascorbate and deferoxamine reduces mortality and decreases lung injury through reduction of alveolar-capillary permeability, inflammation, and epithelial sloughing and lipid peroxidation.

Chlorine gas exposure causes systemic endothelial dysfunction by inhibiting endothelial nitric oxide synthase-dependent signaling

Chlorine gas (Cl(2)) exposure during accidents or in the military setting results primarily in injury to the lungs. However, the potential for Cl(2) exposure to promote injury to the systemic vasculature leading to compromised vascular function has not been studied. We hypothesized that Cl(2) promotes extrapulmonary endothelial dysfunction characterized by a loss of endothelial nitric oxide synthase (eNOS)-derived signaling. Male Sprague Dawley rats were exposed to Cl(2) for 30 minutes, and eNOS-dependent vasodilation of aorta as a function of Cl(2) dose (0-400 ppm) and time after exposure (0-48 h) were determined. Exposure to Cl(2) (250-400 ppm) significantly inhibited eNOS-dependent vasodilation (stimulated by acetycholine) at 24 to 48 hours after exposure without affecting constriction responses to phenylephrine or vasodilation responses to an NO donor, suggesting decreased NO formation. Consistent with this hypothesis, eNOS protein expression was significantly decreased (∼ 60%) in aorta isolated from Cl(2)-exposed versus air-exposed rats. Moreover, inducible nitric oxide synthase (iNOS) mRNA was up-regulated in circulating leukocytes and aorta isolated 24 hours after Cl(2) exposure, suggesting stimulation of inflammation in the systemic vasculature. Despite decreased eNOS expression and activity, no changes in mean arterial blood pressure were observed. However, injection of 1400W, a selective inhibitor of iNOS, increased mean arterial blood pressure only in Cl(2)-exposed animals, suggesting that iNOS-derived NO compensates for decreased eNOS-derived NO. These results highlight the potential for Cl(2) exposure to promote postexposure systemic endothelial dysfunction via disruption of vascular NO homeostasis mechanisms.

Mechanisms and modification of chlorine-induced lung injury in animals

Chlorine (Cl(2)) is a reactive oxidant gas used extensively in industrial processes. Exposure of both humans and animals to high concentrations of Cl(2) results in acute lung injury, which may resolve spontaneously or progress to acute respiratory failure. Injury to airway and alveolar epithelium may result from chemical reactions of Cl(2), from HOCl (the hydrolysis product of Cl(2)), and/or from the various reaction products, such as chloramines, that are formed from the reactions of these chlorinating species with biological molecules. Subsequent reactions may initiate self-propagating reactions and induce the production of inflammatory mediators compounding injury to pulmonary surfactant, ion channels, and components of lung epithelial and airway cells. Low-molecular-weight antioxidants, such as ascorbate, glutathione, and urate, present in the lung epithelial lining fluid and tissue, remove Cl(2) and HOCl and thus decrease injury to critical target biological targets. However, levels of lung antioxidants of animals exposed to Cl(2) in concentrations likely to be encountered in the vicinity of industrial accidents decrease rapidly and irreversibly. Our measurements show that prophylactic administration of a mixture containing ascorbate and desferal N-acetyl-cysteine, a precursor of reduced glutathione, prevents Cl(2)-induced injury to the alveolar epithelium of rats exposed to Cl(2). The clinical challenge is to deliver sufficient quantities of antioxidants noninvasively, after Cl(2) exposure, to decrease morbidity and mortality.

Elucidating mechanisms of chlorine toxicity: reaction kinetics, thermodynamics, and physiological implications

Industrial and transport accidents, accidental releases during recreational swimming pool water treatment, household accidents due to mixing bleach with acidic cleaners, and, in recent years, usage of chlorine during war and in acts of terror, all contribute to the general and elevated state of alert with regard to chlorine gas. We here describe chemical and physical properties of Cl(2) that are relevant to its chemical reactivity with biological molecules, including water-soluble small-molecular-weight antioxidants, amino acid residues in proteins, and amino-phospholipids such as phosphatidylethanolamine and phosphatidylserine that are present in the lining fluid layers covering the airways and alveolar spaces. We further conduct a Cl(2) penetration analysis to assess how far Cl(2) can penetrate the surface of the lung before it reacts with water or biological substrate molecules. Our results strongly suggest that Cl(2) will predominantly react directly with biological molecules in the lung epithelial lining fluid, such as low-molecular-weight antioxidants, and that the hydrolysis of Cl(2) to HOCl (and HCl) can be important only when these biological molecules have been depleted by direct chemical reaction with Cl(2). The results from this theoretical analysis are then used for the assessment of the potential benefits of adjuvant antioxidant therapy in the mitigation of lung injury due to inhalation of Cl(2) and are compared with recent experimental results.

Lipopolysaccharide hyperpolarizes guinea pig airway epithelium by increasing the activities of the epithelial Na(+) channel and the Na(+)-K(+) pump

Earlier, we found that systemic administration of lipopolysaccharide (LPS; 4 mg/kg) hyperpolarized the transepithelial potential difference (V(t)) of tracheal epithelium in the isolated, perfused trachea (IPT) of the guinea pig 18 h after injection. As well, LPS increased the hyperpolarization component of the response to basolateral methacholine, and potentiated the epithelium-derived relaxing factor-mediated relaxation responses to hyperosmolar solutions applied to the apical membrane. We hypothesized that LPS stimulates the transepithelial movement of Na(+) via the epithelial sodium channel (ENaC)/Na(+)-K(+) pump axis, leading to hyperpolarization of V(t). LPS increased the V(t)-depolarizing response to amiloride (10 μM), i.e., offset the effect of LPS, indicating that Na(+) transport activity was increased. The functional activity of ENaC was measured in the IPT after short-circuiting the Na(+)-K(+) pump with basolateral amphotericin B (7.5 μM). LPS had no effect on the hyperpolarization response to apical trypsin (100 U/ml) in the Ussing chamber, indicating that channel-activating proteases are not involved in the LPS-induced activation of ENaC. To assess Na(+)-K(+) pump activity in the IPT, ENaC was short-circuited with apical amphotericin B. The greater V(t) in the presence of amphotericin B in tracheas from LPS-treated animals compared with controls revealed that LPS increased Na(+)-K(+) pump activity. This finding was confirmed in the Ussing chamber by inhibiting the Na(+)-K(+) pump via extracellular K(+) removal, loading the epithelium with Na(+), and observing a greater hyperpolarization response to K(+) restoration. Together, the findings of this study reveal that LPS hyperpolarizes the airway epithelium by increasing the activities of ENaC and the Na(+)-K(+) pump.