The mechanisms by which the exposure of mice to Cl2 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 Cl2, and identified the mechanisms involved. We measured amiloride-sensitive short-circuit currents (Iamil) 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 Cl2, 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 Cl2 increased concentrations of reactive intermediates, leading to ERK1/2 phosphorylation and decreased Iamil and α-ENaC concentrations at 1 hour and 24 hours after exposure. The administration of antioxidants to ATII cells before and after exposure to Cl2 decreased concentrations of reactive intermediates and ERK1/2 activation, which mitigated the decrease in Iamil and ENaC concentrations. The reactive intermediates formed during and after exposure to Cl2 activated ERK1/2 in ATII cells in vitro and in vivo, leading to decreased ENaC concentrations and activity.
lung slices; patch clamp; radicals
Chlorine (Cl2) 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 Cl2 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 Cl2 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.
acute lung injury; oxidative stress; survival; aerosols; antioxidants
Chlorine gas (Cl2) exposure during accidents or in the military setting results primarily in injury to the lungs. However, the potential for Cl2 exposure to promote injury to the systemic vasculature leading to compromised vascular function has not been studied. We hypothesized that Cl2 promotes extrapulmonary endothelial dysfunction characterized by a loss of endothelial nitric oxide synthase (eNOS)-derived signaling. Male Sprague Dawley rats were exposed to Cl2 for 30 minutes, and eNOS-dependent vasodilation of aorta as a function of Cl2 dose (0–400 ppm) and time after exposure (0–48 h) were determined. Exposure to Cl2 (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 Cl2–exposed versus air-exposed rats. Moreover, inducible nitric oxide synthase (iNOS) mRNA was up-regulated in circulating leukocytes and aorta isolated 24 hours after Cl2 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 Cl2–exposed animals, suggesting that iNOS-derived NO compensates for decreased eNOS-derived NO. These results highlight the potential for Cl2 exposure to promote postexposure systemic endothelial dysfunction via disruption of vascular NO homeostasis mechanisms.
endothelium; nitric oxide; inflammation; inhaled reactive oxidants
Exposure to chlorine (Cl2) damages airway and alveolar epithelia, resulting in acute lung injury and reactive airway dysfunction syndrome. We evaluated the efficacy and mechanisms by which arformoterol, a long-term β2-agonist, administered after exposure, mitigated the extent of this injury. Exposure of C57BL/6 mice to 400 ppm Cl2 for 30 minutes increased respiratory system resistance and airway responsiveness to aerosolized methacholine (assessed by FlexiVent) up to 6 days after exposure, and decreased Na+-dependent alveolar fluid clearance (AFC). Inducible Nitric Oxide Synthase (iNOS) knockout mice developed similar degrees of airway hyperreactivity as wild-type controls after Cl2 exposure, indicating that reactive intermediates from iNOS do not contribute to Cl2-induced airway dysfunction in our model. Intranasal administration of arformoterol mitigated the Cl2 effects on airway reactivity and AFC, presumably by increasing lung cyclic AMP level. Arformoterol did not modify the inflammatory responses, as evidenced by the number of inflammatory cells and concentrations of IL-6 and TNF-α in the bronchoalveolar lavage. NF-κB activity (assessed by p65 Western blots and electrophoretic mobility shift assay) remained at control levels up to 24 hours after Cl2 exposure. Our results provide mechanistic insight into the effectiveness of long-term β2-agonists in reversing Cl2-induced reactive airway dysfunction syndrome and injury to distal lung epithelial cells.
alveolar fluid clearance; cAMP; iNOS; NF-κB; lung injury
Despite respiratory syncytial virus (RSV) bronchiolitis remaining the most common cause of lower respiratory tract disease in infants worldwide, treatment has progressed little in the past 30 years. The aim of our study was to determine whether post-infection administration of de novo pyrimidine synthesis inhibitors could prevent the reduction in alveolar fluid clearance (AFC) and hypoxemia that occurs at Day 2 after intranasal infection of BALB/c mice with RSV. BALB/c mice were infected intranasally with RSV strain A2. AFC was measured in anesthetized, ventilated mice after instillation of 5% bovine serum albumin into the dependent lung. Post-infection systemic treatment with leflunomide has no effect on AFC. However, when added to the AFC instillate, leflunomide's active metabolite, A77-1726, blocks RSV-mediated inhibition of AFC at Day 2. This block is reversed by uridine (which allows pyrimidine synthesis via the scavenger pathway) and not recapitulated by genistein (which mimics the tyrosine kinase inhibitor effects of A77-1726), indicating that the effect is specific for the de novo pyrimidine synthesis pathway. More importantly, when administered intranasally at Day 1, A77-1726, but not its vehicle dimethyl sulfoxide, maintains its beneficial effect on AFC and lung water content until Day 2. Intranasal instillation of A77-1726 at Day 1 also reduces bronchoalveolar lavage nucleotide levels, lung inflammation, and hypoxemia at Day 2 without impairing viral replication at Day 2 or viral clearance at Day 8. Post-infection intranasal or aerosolized treatment with pyrimidine synthesis inhibitors may provide symptomatic relief from the pathophysiologic sequelae of impaired AFC in children with RSV bronchiolitis.
paramyxovirus; leflunomide; dihydroorotate dehydrogenase; pulmonary edema
Despite respiratory syncytial virus (RSV) bronchiolitis remaining the most common cause of lower respiratory tract disease in infants worldwide, treatment has progressed little in the past 30 years.
To determine whether postinfection administration of de novo pyrimidine synthesis inhibitors could prevent the reduction in alveolar fluid clearance (AFC) and hypoxemia that occurs at day 2 following intranasal infection of BALB/c mice with RSV.
BALB/c mice were infected intranasally with RSV strain A2. AFC was measured in anesthetized, ventilated mice following instillation of 5% BSA into the dependent lung.
Post-infection systemic treatment with leflunomide has no effect on AFC. However, when added to the AFC instillate, leflunomide’s active metabolite, A77-1726, blocks RSV-mediated inhibition of AFC at day 2. This block is reversed by uridine (which allows pyrimidine synthesis via the scavenger pathway) and not recapitulated by genistein (which mimics the tyrosine kinase inhibitor effects of A77-1726), indicating that the effect is specific for the de novo pyrimidine synthesis pathway. More importantly, when administered intranasally at day 1, A77-1726, but not its vehicle DMSO, maintains its beneficial effect on AFC and lung water content until day 2. Intranasal instillation of A77-1726 at day 1 also reduces BAL nucleotide levels, lung inflammation, and hypoxemia at day 2 without impairing viral replication at day 2 or viral clearance at day 8.
Post-infection intranasal or aerosolized treatment with pyrimidine synthesis inhibitors may provide symptomatic relief from the pathophysiologic sequelae of impaired AFC in children with RSV bronchiolitis.
Paramyxovirus; leflunomide; dihydroorotate dehydrogenase; pulmonary edema
The most common mutation in the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene, ΔF508, results in the production of a misfolded protein that is rapidly degraded. The mutant protein is temperature sensitive, and prior studies indicate that the low-temperature–rescued channel is poorly responsive to physiological stimuli, and is rapidly degraded from the cell surface at 37°C. In the present studies, we tested the effect of a recently characterized pharmacological corrector, 2-(5-chloro-2-methoxy-phenylamino)-4′-methyl-[4,5′bithiazolyl-2′-yl]-phenyl-methanone (corr-4a), on cell surface stability and function of the low-temperature–rescued ΔF508 CFTR. We demonstrate that corr-4a significantly enhanced the protein stability of rescued ΔF508 CFTR for up to 12 hours at 37°C (P < 0.05). Using firefly luciferase–based reporters to investigate the mechanisms by which low temperature and corr-4a enhance rescue, we found that low-temperature treatment inhibited proteasomal function, whereas corr-4a treatment inhibited the E1-E3 ubiquitination pathway. Ussing chamber studies indicated that corr-4a increased the cAMP-mediated ΔF508 CFTR response by 61% at 6 hours (P < 0.05), but not at later time points. However, addition of the CFTR channel activator, 4-methyl-2-(5-phenyl-1H-pyrazol-3-yl)-phenol, significantly augmented cAMP-stimulated currents, revealing that the biochemically detectable cell surface ΔF508 CFTR could be stimulated under the right conditions. Our studies demonstrate that stabilizing rescued ΔF508 CFTR was not sufficient to obtain maximal ΔF508 CFTR function in airway epithelial cells. These results strongly support the idea that maximal correction of ΔF508 CFTR requires a chemical corrector that: (1) promotes folding and exit from the endoplasmic reticulum; (2) enhances surface stability; and (3) improves channel activity.
cell surface trafficking; cystic fibrosis transmembrane conductance regulator; ΔF508 rescue; short-circuit current
A variety of studies have shown that Na+ reabsorption across epithelial cells depends on the protease–antiprotease balance. Herein, we investigate the mechanisms by which α1-antitrypsin (A1AT), a major anti-serine protease in human plasma and lung epithelial fluid and lacking a Kunitz domain, regulates amiloride-sensitive epithelial Na+ channel (ENaC) function in vitro and in vivo. A1AT (0.05 mg/ml = 1 μM) decreased ENaC currents across Xenopus laevis oocytes injected with human α,β,γ-ENaC (hENaC) cRNAs, and human lung Clara-like (H441) cells expressing native ENaC, in a partially irreversible fashion. A1AT also decreased ENaC single-channel activity when added in the pipette but not in the bath solutions of ENaC-expressing oocytes patched in the cell-attached mode. Incubation of A1AT with peroxynitrite (ONOO−), an oxidizing and nitrating agent, abolished its antiprotease activity and significantly decreased its ability to inhibit ENaC. Intratracheal instillation of normal but not ONOO−-treated A1AT (1 μM) in C57BL/6 mice also decreased Na+-dependent alveolar fluid clearance to the same level as amiloride. Incubation of either H441 cells or ENaC-expressing oocytes with normal but not ONOO−-treated A1AT decreased their ability to cleave a substrate of serine proteases. A1AT had no effect on amiloride-sensitive currents of oocytes injected with hENaC bearing Liddle mutations, presumably because these channels remain at the surface longer than the wild-type channels. These data indicate that A1AT may be an important modulator of ENaC activity and of Na+-dependent fluid clearance across the distal lung epithelium in vivo by decreasing endogenous protease activity needed to activate silent ENaC.
alveolar fluid clearance; serine proteases; H441 cells; Xenopus oocytes; ENaC
We investigated the mechanisms by which respiratory syncytial virus (RSV) infection decreases vectorial Na+ transport across respiratory epithelial cells. Mouse tracheal epithelial (MTE) cells from either BALB/c or C57BL/6 mice and human airway H441 cells were grown on semipermeable supports under an air–liquid interface. Cells were infected with RSV-A2 and mounted in Ussing chambers for measurements of short-circuit currents (Isc). Infection with RSV for 24 hours (multiplicity of infection = 1) resulted in positive immunofluorescence for RSV antigen in less than 10% of MTE or H441 cells. In spite of the limited number of cells infected, RSV reduced both basal and amiloride-sensitive Isc in both MTE and H441 cells by approximately 50%, without causing a concomitant reduction in transepithelial resistance. Agents that increased intracellular cAMP (forskolin, cpt-CAMP, and IBMX) increased mainly Cl− secretion in MTE cells and Na+ absorption in H441 cells. RSV infection for 24 hours blunted both variables. In contrast, ouabain sensitive Isc, measured across apically permeabilized H441 monolayers, remained unchanged. Western blot analysis of H441 cell lysates demonstrated reductions in α- but not γ-ENaC subunit protein levels at 24 hours after RSV infection. The reduction in amiloride-sensitive Isc in H441 cells was prevented by pretreatment with inhibitors of de novo pyrimidine or purine synthesis (A77-1726 and 6-MP, respectively, 50 μM). Our results suggest that infection of both murine and human respiratory epithelial cells with RSV inhibits vectorial Na+ transport via nucleotide release. These findings are consistent with our previous studies showing reduced alveolar fluid clearance after RSV infection of BALB/c mice.
short circuit current; epithelial Na+ channels; H441 cells; uridine triphosphate; A77-1726
Matriptase is a type II transmembrane protease that is characterized by an N-terminal transmembrane and multiple extracellular domains, in addition to the conserved extracellular serine protease catalytic domain. The expression pattern of matriptase suggests that this protease may play broad roles in the biology of surface lining epithelial cells. In this study we report that α1-antitrypsin (AAT), an endogenous inhibitor of serine proteases, inhibits the catalytic domain of human recombinant matriptase in vitro. Co-incubation of AAT with matriptase (at a molar ratio 1:2) resulted in the formation of heat stable complexes, clearly seen in sodium dodecyl sulfate electrophoresis and Western blots. AAT was found to be a slow, tight-binding inhibitor of the catalytic domain of matriptase with a second order reaction rate constant of 0.31 × 103 M−1s−1. Notably, the oxidized form of AAT, which lacks serine protease inhibitor activity, failed to generate matriptase complexes and to inhibit matriptase activity. Since matriptase is involved in a number of physiologic processes, including activation of epithelial sodium channels, our findings offer considerable new insights into new regulatory function of AAT in vivo.
serine proteases; α1-antitrypsin; matriptase; complex formation; kinetics
We investigated the cellular mechanisms by which nitric oxide (NO) increases chloride (Cl−) secretion across lung epithelial cells in vitro and in vivo. Addition of (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl) amino] diazen-1-ium-1, 2-diolate (DETANONOate [DETANO];1–1,000 μM) into apical compartments of Ussing chambers containing Calu-3 cells increased short-circuit currents (Isc) from 5.2 ± 0.8 to 15.0 ± 2.1 μA/cm2 (X ± 1 SE; n = 7; P < 0.001). NO generated from two nitrated lipids (nitrolinoleic and nitrooleic acids; 1–10 μM) also increased Isc by about 100%. Similar effects were noted across basolaterally, but not apically, permeabilized Calu-3 cells. None of these NO donors increased Isc in Calu-3 cells pretreated with 10 μM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (an inhibitor of soluble guanylyl cyclase). Scavenging of NO either prevented or reversed the increase of Isc. These data indicate that NO stimulation of soluble guanylyl cyclase was sufficient and necessary for the increase of Isc via stimulation of the apical cystic fibrosis transmembrane regulator (CFTR). Both Calu-3 and alveolar type II (ATII) cells contained CFTR, as demonstrated by in vitro phosphorylation of immunoprecipitated CFTR by protein kinase (PK) A. PKGII (but not PKGI) phosphorylated CFTR immuniprecipitated from Calu-3 cells. Corresponding values in ATII cells were below the threshold of detection. Furthermore, DETANO, 8-Br-cGMP, or 8-(4-chlorophenylthio)-cGMP (up to 2 mM each) did not increase Cl− secretion across amiloride-treated ATII cells in vitro. Measurements of nasal potential differences in anesthetized mice showed that perfusion of the nares with DETANO activated glybenclamide-sensitive Cl− secretion. These findings suggest that small concentrations of NO donors may prove beneficial in stimulating Cl− secretion across airway cells without promoting alveolar edema.
Calu-3 cells; cystic fibrosis transmembrane conductance regulator; nasal potential difference; protein kinase G type II; alveolar type II cells
Surfactant dysfunction was studied in C57BL/6 (B6), B6.SP-A−/−, and B6.iNOS−/− mice with pulmonary mycoplasma infection (107 colony-forming units). Cell-free bronchoalveolar lavage (BAL) from uninfected B6.SP-A−/− versus B6 mice had a reduced content of very large aggregates (VLA) and an increase in intermediate large aggregates (ILA), with no difference in total large aggregates (LA = VLA + ILA). However, LA from uninfected B6.SP-A−/− versus B6 mice contained less protein and were more sensitive to inhibition by serum albumin and lysophosphatidylcholine in pulsating bubble studies in vitro. Infection with Mycoplasma pulmonis caused significant lung injury and surfactant abnormalities in B6.SP-A−/−, B6.iNOS−/−, and B6 mice at 24, 48, 72 h after infection compared with uninfected mice of the same strain. Analyses of time-pooled data indicated that mycoplasma-infected B6.SP-A−/− and B6.iNOS−/− mice had significantly lower levels of LA and higher protein/phospholipid ratios in BAL compared with infected B6 mice. Infected B6.iNOS−/− versus B6 mice also had increased minimum surface tensions on the pulsating bubble and decreased levels of surfactant protein (SP)-B in BAL. These results indicate that pulmonary mycoplasma infection in vivo causes lung injury and surfactant abnormalities that are dependent in part on iNOS and SP-A. In addition, SP-A deficiency modifies surfactant aggregate content and lowers the inhibition resistance of LA surfactant in vitro compared with congenic normal mice.
lung injury; minimum surface tension; SP-B; lipid aggregate fractions; M. pulmonis
Protective ventilation strategies have been universally embraced because of reduced mortality. We tested the hypothesis that tidal volume (VT) in an in vivo model of mechanical ventilation would modulate bactericidal function of alveolar macrophages (AMs). Adult New Zealand White rabbits were mechanically ventilated for 4 h with a VT of 6 ml/kg (low) or a VT of 12 ml/kg (traditional), with each group receiving 3 cm H2O positive end-expiratory pressure with and without intratracheal lipopolysaccharide (LPS) instillation (20 mg/kg). AMs were isolated from bronchoalveolar lavage fluid taken from the whole left lung and used for bacterial killing assays. There were no significant differences in steady-state levels of nitrite or AM phagocytosis and killing of Klebsiella pneumoniae, although these values trended to be slightly higher in the traditional VT group. However, bronchoalveolar lavage fluid protein concentrations were significantly increased in traditional VT groups receiving LPS compared with animals ventilated with a low VT (1,407.8 ± 121.4 versus 934.7 ± 118.2; P < 0.001). Lung wet:dry weight ratio in the traditional VT group was increased when compared with the low VT group without LPS (7.3 ± 0.4 versus 6.1 ± 0.3, respectively; P < 0.05). Additionally, IL-8 expression was significantly greater under conditions of LPS treatment and mechanical ventilation at VT of 12 ml/kg. These results suggest that the traditional ventilator approach (12 ml/kg VT) in a model of in vivo mechanical ventilation results in lung pathology without affecting AM antibacterial function.
acute lung injury; acute respiratory distress syndrome; alveolar macrophages; lipopolysaccharide; protective ventilation