DETANONOate, a nitric oxide donor, decreases amiloride-sensitive alveolar fluid clearance in rabbits

Molecularly self-fueled nano-penetrator for nonpharmaceutical treatment of thrombosis and ischemic stroke

Thrombotic cerebro-cardiovascular diseases are the leading causes of disability and death worldwide. However, current drug therapeutics are compromised by narrow therapeutic windows, unsatisfactory thrombolysis effects, severe bleeding events, and high recurrence rates. In this study, we exploit a self-propelling nano-penetrator with high fuel loading and controllable motion features, which is molecularly co-assembled using a photothermal photosensitizer (DiR) and a photothermal-activable NO donor (BNN6). The precisely engineered nano-penetrator of the BNN6-DiR fuel pair shows distinct advantages in terms of NO productivity and autonomous motion under laser irradiation. In animal models of artery/vein thrombosis and acute ischemic stroke, the self-fueled nano-penetrator enables self-navigated thrombus-homing accumulation, self-propelled clot deep penetration, fluorescence image-guided photothermal/mechanical thrombolysis, and NO-mediated prevention of thrombosis recurrence and acute ischemic stroke salvage. As expected, the molecularly self-fueled nano-penetrator displayed favorable therapeutic outcomes without bleeding risk compared to the clinically available thrombolytic drug. This study offers a facile, safe, and effective nonpharmaceutical modality towards the clinical treatment of thrombosis and ischemic stroke.

Hypoxia Aggravates Inhibition of Alveolar Epithelial Na-Transport by Lipopolysaccharide-Stimulation of Alveolar Macrophages

Inflammation and hypoxia impair alveolar barrier tightness, inhibit Na- and fluid reabsorption, and cause edema. We tested whether stimulated alveolar macrophages affect alveolar Na-transport and whether hypoxia aggravates the effects of inflammation, and tested for involved signaling pathways. Primary rat alveolar type II cells (rA2) were co-cultured with rat alveolar macrophages (NR8383) or treated with NR8383-conditioned media after stimulation with lipopolysaccharide (LPS; 1 µg/mL) and exposed to normoxia and hypoxia (1.5% O2). LPS caused a fast, transient increase in TNFα and IL-6 mRNA in macrophages and a sustained increase in inducible nitric oxide synthase (NOS2) mRNA in macrophages and in rA2 cells resulting in elevated nitrite levels and secretion of TNF-α and IL-6 into culture media. In normoxia, 24 h of LPS treated NR8383 decreased the transepithelial electrical resistance (TEER) of co-cultures, of amiloride-sensitive short circuit current (ISCΔamil); whereas Na/K-ATPase activity was not affected. Inhibition was also seen with conditioned media from LPS-stimulated NR8383 on rA2, but was less pronounced after dialysis to remove small molecules and nitrite. The effect of LPS-stimulated macrophages on TEER and Na-transport was fully prevented by the iNOS-inhibitor L-NMMA applied to co-cultures and to rA2 mono-cultures. Hypoxia in combination with LPS-stimulated NR8383 totally abolished TEER and ISCΔamil. These results indicate that the LPS-stimulation of alveolar macrophages impairs alveolar epithelial Na-transport by NO-dependent mechanisms, where part of the NO is produced by rA2 induced by signals from LPS stimulated alveolar macrophages.

Inflammatory Responses Regulating Alveolar Ion Transport during Pulmonary Infections

The respiratory epithelium is lined by a tightly balanced fluid layer that allows normal O₂ and CO₂ exchange and maintains surface tension and host defense. To maintain alveolar fluid homeostasis, both the integrity of the alveolar–capillary barrier and the expression of epithelial ion channels and pumps are necessary to establish a vectorial ion gradient. However, during pulmonary infection, auto- and/or paracrine-acting mediators induce pathophysiological changes of the alveolar–capillary barrier, altered expression of epithelial Na,K-ATPase and of epithelial ion channels including epithelial sodium channel and cystic fibrosis membrane conductance regulator, leading to the accumulation of edema and impaired alveolar fluid clearance. These mediators include classical pro-inflammatory cytokines such as TGF-β, TNF-α, interferons, or IL-1β that are released upon bacterial challenge with Streptococcus pneumoniae, Klebsiella pneumoniae, or Mycoplasma pneumoniae as well as in viral infection with influenza A virus, pathogenic coronaviruses, or respiratory syncytial virus. Moreover, the pro-apoptotic mediator TNF-related apoptosis-inducing ligand, extracellular nucleotides, or reactive oxygen species impair epithelial ion channel expression and function. Interestingly, during bacterial infection, alterations of ion transport function may serve as an additional feedback loop on the respiratory inflammatory profile, further aggravating disease progression. These changes lead to edema formation and impair edema clearance which results in suboptimal gas exchange causing hypoxemia and hypercapnia. Recent preclinical studies suggest that modulation of the alveolar–capillary fluid homeostasis could represent novel therapeutic approaches to improve outcomes in infection-induced lung injury.

Gasotransmitters: novel regulators of epithelial na(+) transport?

The vectorial transport of Na(+) across epithelia is crucial for the maintenance of Na(+) and water homeostasis in organs such as the kidneys, lung, or intestine. Dysregulated Na(+) transport processes are associated with various human diseases such as hypertension, the salt-wasting syndrome pseudohypoaldosteronism type 1, pulmonary edema, cystic fibrosis, or intestinal disorders, which indicate that a precise regulation of epithelial Na(+) transport is essential. Novel regulatory signaling molecules are gasotransmitters. There are currently three known gasotransmitters: nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H(2)S). These molecules are endogenously produced in mammalian cells by specific enzymes and have been shown to regulate various physiological processes. There is a growing body of evidence which indicates that gasotransmitters may also regulate Na(+) transport across epithelia. This review will summarize the available data concerning NO, CO, and H(2)S dependent regulation of epithelial Na(+) transport processes and will discuss whether or not these mediators can be considered as true physiological regulators of epithelial Na(+) transport biology.

ENaCs and ASICs as therapeutic targets

The epithelial Na(+) channel (ENaC) and acid-sensitive ion channel (ASIC) branches of the ENaC/degenerin superfamily of cation channels have drawn increasing attention as potential therapeutic targets in a variety of diseases and conditions. Originally thought to be solely expressed in fluid absorptive epithelia and in neurons, it has become apparent that members of this family exhibit nearly ubiquitous expression. Therapeutic opportunities range from hypertension, due to the role of ENaC in maintaining whole body salt and water homeostasis, to anxiety disorders and pain associated with ASIC activity. As a physiologist intrigued by the fundamental mechanics of salt and water transport, it was natural that Dale Benos, to whom this series of reviews is dedicated, should have been at the forefront of research into the amiloride-sensitive sodium channel. The cloning of ENaC and subsequently the ASIC channels has revealed a far wider role for this channel family than was previously imagined. In this review, we will discuss the known and potential roles of ENaC and ASIC subunits in the wide variety of pathologies in which these channels have been implicated. Some of these, such as the role of ENaC in Liddle's syndrome are well established, others less so; however, all are related in that the fundamental defect is due to inappropriate channel activity.

Nitric oxide inhibits highly selective sodium channels and the Na+/K+-ATPase in H441 cells

Nitric oxide (NO) is an important regulator of Na(+) reabsorption by pulmonary epithelial cells and therefore of alveolar fluid clearance. The mechanisms by which NO affects epithelial ion transport are poorly understood and vary from model to model. In this study, the effects of NO on sodium reabsorption by H441 cell monolayers were studied in an Ussing chamber. Two NO donors, (Z)-1-[N-(3-aminopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2-diolate and diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate, rapidly, reversibly, and dose-dependently reduced amiloride-sensitive, short-circuit currents across H441 cell monolayers. This effect was neutralized by the NO scavenger hemoglobin and was not observed with inactive NO donors. The effects of NO were not blocked by 8-bromoguanosine-3',5'-cyclic monophosphate or by soluble guanylate cyclase inhibitors (methylene blue and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) and were therefore independent of soluble guanylate cyclase signaling. NO targeted apical, highly selective, amiloride-sensitive Na(+) channels in basolaterally permeabilized H441 cell monolayers. NO had no effect on the activity of the human epithelial sodium channel heterologously expressed in Xenopus oocytes. NO decreased Na(+)/K(+)-ATPase activity in apically permeabilized H441 cell monolayers. The inhibition of Na(+)/K(+)-ATPase activity by NO was reversed by mercury and was mimicked by N-ethylmaleimide, which are agents that reverse and mimic, respectively, the reaction of NO with thiol groups. Consistent with these data, S-NO groups were detected on the Na(+)/K(+)-ATPase α subunit in response to NO-donor application, using a biotin-switch approach coupled to a Western blot. These data demonstrate that, in the H441 cell model, NO impairs Na(+) reabsorption by interfering with the activity of highly selective Na(+) channels and the Na(+)/K(+)-ATPase.

The contribution of epithelial sodium channels to alveolar function in health and disease

Amiloride-sensitive epithelial sodium channels (ENaC) play an important role in lung sodium transport. Sodium transport is closely regulated to maintain an appropriate fluid layer on the alveolar surface. Both alveolar type I and II cells have several different sodium-permeable channels in their apical membranes that play a role in normal lung physiology and pathophysiology. In many epithelial tissues, ENaC is formed from three subunit proteins: alpha, beta, and gamma ENaC. Part of the diversity of sodium-permeable channels in lung arises from assembling different combinations of these subunits to form channels with different biophysical properties and different mechanisms for regulation. Thus, lung epithelium has enormous flexibility to alter the magnitude of salt and water transport. In lung, ENaC is regulated by many transmitter and hormonal agents. Regulation depends upon the type of sodium channel but involves controlling the number of apical channels and/or the activity of individual channels.

Role of endothelin-1 in acute lung injury

The alveolar-capillary membrane serves as a barrier that prevents the accumulation of fluid in the alveolar space and restricts the diffusion of large solutes while facilitating an efficient gas exchange. When this barrier becomes dysfunctional, patients develop acute lung injury (ALI), which is characterized by pulmonary edema and increased lung inflammation that leads to a life-threatening impairment of gas exchange. In addition to the increase of inflammatory cytokines, plasma levels of endothelin-1 (ET-1), which is a primarily endothelium-derived vasoconstrictor, are increased in patients with ALI. As patients recover, ET-1 levels decrease, which suggests that ET-1 may not only be a marker of endothelial dysfunction but may have a role in the pathogenesis of ALI. While pulmonary edema accumulates, alveolar fluid clearance (AFC) is of critical importance, as failure to return to normal clearance is associated with poor prognosis in patients with pulmonary edema. AFC involves active transport mechanisms where sodium (Na(+)) is actively transported from the alveolar airspaces, across the alveolar epithelium, and into the pulmonary circulation, which creates an osmotic gradient that is responsible for the clearance of lung edema. In this article, we review the relevance of ET-1 in the development of ALI, not only as a vasoconstrictor molecule but also by inhibiting AFC via the activation of endothelial ET-B receptors and generation. Furthermore, this review highlights the therapeutic role of drugs such as beta-adrenergic agonists and, in particular, of endothelin receptor antagonists in patients with ALI.

Endothelin-1 impairs alveolar epithelial function via endothelial ETB receptor

RATIONALE

Endothelin-1 (ET-1) is increased in patients with high-altitude pulmonary edema and acute respiratory distress syndrome, and these patients have decreased alveolar fluid reabsorption (AFR).

OBJECTIVES

To determine whether ET-1 impairs AFR via activation of endothelial cells and nitric oxide (NO) generation.

METHODS

Isolated perfused rat lung, transgenic rats deficient in ETB receptors, coincubation of lung human microvascular endothelial cells (HMVEC-L) with rat alveolar epithelial type II cells or A549 cells, ouabain-sensitive 86Rb+ uptake.

MEASUREMENTS AND MAIN RESULTS

The ET-1-induced decrease in AFR was prevented by blocking the endothelin receptor ETB, but not ETA. Endothelial-epithelial cell interaction is required, as direct exposure of alveolar epithelial cells (AECs) to ET-1 did not affect Na,K-ATPase function or protein abundance at the plasma membrane, whereas coincubation of HMVEC-L and AECs with ET-1 decreased Na,K-ATPase activity and protein abundance at the plasma membrane. Exposing transgenic rats deficient in ETB receptors in the pulmonary vasculature (ET-B(-/-)) to ET-1 did not decrease AFR or Na,K-ATPase protein abundance at the plasma membrane of AECs. Exposing HMVEC-L to ET-1 led to increased NO, and the ET-1-induced down-regulation of Na,K-ATPase was prevented by the NO synthase inhibitor l-NAME, but not by a guanylate cyclase inhibitor.

CONCLUSIONS

We provide the first evidence that ET-1, via an endothelial-epithelial interaction, leads to decreased AFR by a mechanism involving activation of endothelial ETB receptors and NO generation leading to alveolar epithelial Na,K-ATPase down-regulation in a cGMP-independent manner.

DETANO and nitrated lipids increase chloride secretion across lung airway cells

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 microM) into apical compartments of Ussing chambers containing Calu-3 cells increased short-circuit currents (I(sc)) from 5.2 +/- 0.8 to 15.0 +/- 2.1 microA/cm(2) (X +/- 1 SE; n = 7; P < 0.001). NO generated from two nitrated lipids (nitrolinoleic and nitrooleic acids; 1-10 microM) also increased I(sc) by about 100%. Similar effects were noted across basolaterally, but not apically, permeabilized Calu-3 cells. None of these NO donors increased I(sc) in Calu-3 cells pretreated with 10 microM 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 I(sc). These data indicate that NO stimulation of soluble guanylyl cyclase was sufficient and necessary for the increase of I(sc) 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.

Nitric oxide-dependent inhibition of alveolar fluid clearance in hydrostatic lung edema

Formation of cardiogenic pulmonary edema in acute left heart failure is traditionally attributed to increased fluid filtration from pulmonary capillaries and subsequent alveolar flooding. Here, we demonstrate that hydrostatic edema formation at moderately elevated vascular pressures is predominantly caused by an inhibition of alveolar fluid reabsorption, which is mediated by endothelial-derived nitric oxide (NO). In isolated rat lungs, we quantified fluid fluxes into and out of the alveolar space and endothelial NO production by a two-compartmental double-indicator dilution technique and in situ fluorescence imaging, respectively. Elevation of hydrostatic pressure induced Ca(2+)-dependent endothelial NO production and caused a net fluid shift into the alveolar space, which was predominantly attributable to impaired fluid reabsorption. Inhibition of NO production or soluble guanylate cyclase reconstituted alveolar fluid reabsorption, whereas fluid clearance was blocked by exogenous NO donors or cGMP analogs. In isolated mouse lungs, hydrostatic edema formation was attenuated by NO synthase inhibition. Similarly, edema formation was decreased in isolated mouse lungs of endothelial NO synthase-deficient mice. Chronic heart failure results in endothelial dysfunction and preservation of alveolar fluid reabsorption. These findings identify impaired alveolar fluid clearance as an important mechanism in the pathogenesis of hydrostatic lung edema. This effect is mediated by endothelial-derived NO acting as an intercompartmental signaling molecule at the alveolo-capillary barrier.

Prenatal estrogen and progesterone deprivation impairs alveolar formation and fluid clearance in newborn piglets

Exposure to high levels of estradiol (E2) and progesterone (P) derived from the fetoplacentomaternal unit during the last trimester of pregnancy may play a crucial role in prenatal lung development and immediate postnatal alveolar fluid clearance (AFC). To measure prenatal alveolar formation and postnatal amiloride-sensitive AFC after pharmacological deprivation of E2 and P in utero, fetuses from five sows received an intramuscular depot injection of the E2 receptor blocker ICI 182.780 (ICI) and the P receptor blocker RTI 3021-022 (RTI) and fetuses of five other sows received a placebo injection (control group) during a laparotomy at 90 d of gestation (term gestation, 115 d). Piglets were delivered by cesarean section on d 114 of gestation. Of 95 live-born piglets, 35 were mechanically ventilated. The airways of the right lower lobe were isolated by a balloon catheter wedged in the bronchus and 5% albumin in 0.9% NaCl with or without 1 mmol/L amiloride was instilled. Amiloride-sensitive AFC was calculated from the protein concentration changes in fluid recovered after 120 min as the percentage of absorbed fluid. Lungs were removed under standardized conditions to perform alveolar counts. Prenatal treatment with ICI and RTI resulted in a significantly lower amiloride-sensitive AFC (median, 31%; min-max, -4-58) than placebo (74%, 18-231). Median alveolar counts per visual field were significantly lower in piglets that were exposed to ICI and RTI (38, 21-78) compared with placebo (56, 32-113). We conclude that prenatal E2 and P deprivation significantly impaired alveolar formation and amiloride-sensitive AFC.

Reactive species mediate inhibition of alveolar type II sodium transport during mycoplasma infection

RATIONALE

Mycoplasma pneumoniae is a significant cause of pneumonia in humans.

OBJECTIVES

To determine the impact of mycoplasma infection and the host inflammatory response on alveolar type II (ATII) cell ion transport in vivo and in vitro.

METHODS

Mice were infected with M. pulmonis for measurements of alveolar fluid clearance (AFC) in vivo and isolation of ATII cells. ATII cells were infected in vivo for determination of epithelial Na+ channel (ENaC) total and cell surface protein levels by biotinylation and Western blot and in vitro for whole cell patch clamp recording and measurement of nitric oxide (NO) production by chemiluminescence.

RESULTS

Mycoplasma infection significantly inhibited AFC at 24 h and total and amiloride-sensitive AFC by 48 h postinfection (pi). In contrast, infected myeloperoxidase-deficient mice had similar basal and amiloride-sensitive AFC values to uninfected control mice at 48 h pi. Addition of forskolin restored total and amiloride-sensitive AFC to control values at 48 h pi. ATII cells isolated from infected mice demonstrated normal alpha, beta, and gamma ENaC total protein levels; however, infected whole-lung cell-surface levels of gamma ENaC were significantly decreased. Patch-clamp recordings demonstrated a significant decrease in total and amiloride-sensitive Na+ currents at 24 h pi. ATII cells demonstrated a significant increase in the production of NO at 24 h pi and inhibition of NO by ATII cells before infection reversed the decrease in total Na+ currents.

CONCLUSIONS

These data indicate that mycoplasma infection results in decreased AFC and functional ENaC via the production of reactive oxygen nitrogen intermediates.

Regulation of amiloride-sensitive Na(+) transport by basal nitric oxide

We investigated the mechanisms of endogenous nitric oxide (NO) modulation of lung sodium (Na(+)) transport. C57BL/6 mice injected intraperitoneally with the specific inducible NO synthase (iNOS) inhibitor 1400W (10 mg/kg every 8 h for 72 h) exhibited decreased alveolar nitrite levels and Na(+)-dependent amiloride-sensitive alveolar fluid clearance as compared with mice injected with vehicle. Similarly, pretreatment of mouse tracheal epithelial cells with 1400W abolished the inhibitory effects of amiloride on their Na(+) short circuit currents. On the other hand, mouse tracheal epithelial cells pretreated with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, a specific inhibitor of guanylate cyclase, had lower levels of cGMP, but normal values of amiloride-sensitive Na(+) currents. Amiloride also inhibited whole-cell Na(+) currents across A549 cells treated with vehicle (K(i) = 249 nM), but had no effect in A549 cells treated with 1400W. Western blotting studies showed significantly lower levels of alpha and gammaENaC in lung tissues and alveolar type II (ATII) cells from iNOS(-/-) as well as iNOS(+/+) mice treated with 1400W, as compared with the corresponding values from vehicle-treated iNOS(+/+) mice. Similar values for ratios of alpha, beta, and gammaenac to gapdh were obtained by real-time polymerase chain reaction for iNOS(+/+) mice and iNOS(-/-) mice. We concluded that NO derived from iNOS under basal conditions is necessary for amiloride-sensitive Na(+) transport across lung epithelial cells and modulates the amount of alpha and gammaENaC via post-transcriptional, cGMP-independent mechanisms.

Early changes in alveolar fluid clearance by nitric oxide after endotoxin instillation in rats

Alveolar fluid clearance may be inhibited and/or stimulated under pathologic conditions. We examined the early change of alveolar fluid clearance after endotoxin instillation in adult rats. We employed electron paramagnetic resonance nitric oxide (NO) trapping technique with iron complex with N,N-diethyldithiocarbamate as an NO trapping agent. We found that lung NO signals reached the highest magnitude by 6 hours after endotoxin instillation. NO production was accompanied by increases in lung cyclic guanosine monophosphate levels. Alveolar fluid clearance decreased significantly 6 hours after the administration of the endotoxin and increased further at 24 hours. These changes were shown to be related to the function of amiloride-sensitive sodium ion channels. Treatment with gadolinium chloride and aminoguanidine significantly decreased lung NO and cyclic guanosine monophosphate levels and completely ameliorated the decrease in alveolar fluid clearance. In addition, the increase in alveolar fluid clearance at 24 hours returned to normal levels after treatment with gadolinium chloride and aminoguanidine. We found immunoreactive inducible nitric oxide synthase to be abundantly expressed in the cytoplasm of alveolar macrophages. Our results suggest that alveolar endotoxin inhibits alveolar fluid clearance at 6 hours by NO. NO is produced via inducible NO synthase in endotoxin-stimulated alveolar macrophages and was also shown to increase alveolar fluid clearance at 24 hours.

Oxidant-antioxidant balance in acute lung injury

ARDS is a disease process that is characterized by diffuse inflammation in the lung parenchyma. The involvement of inflammatory mediators in ARDS has been the subject of intense investigation, and oxidant-mediated tissue injury is likely to be important in the pathogenesis of ARDS. In response to various inflammatory stimuli, lung endothelial cells, alveolar cells, and airway epithelial cells, as well as activated alveolar macrophages, produce both nitric oxide and superoxide, which may react to form peroxynitrite, which can nitrate and oxidize key amino acids in various lung proteins, such as surfactant protein A, and inhibit their functions. The nitration and oxidation of a variety of crucial proteins present in the alveolar space have been shown to be associated with diminished function in vitro and also have been identified ex vivo in proteins sampled from patients with acute lung injury (ALI)/ARDS. Various enzymes and low-molecular-weight scavengers that are present in the lung tissue and alveolar lining fluid decreased the concentration of these toxic species. The purpose of this brief chapter is to review the results from various studies demonstrating increased levels of reactive oxygen-nitrogen intermediates in the alveolar spaces of patients with ALI/ARDS.

Reactive oxygen nitrogen species decrease cystic fibrosis transmembrane conductance regulator expression and cAMP-mediated Cl- secretion in airway epithelia

We investigated putative mechanisms by which nitric oxide modulates cystic fibrosis transmembrane conductance regulator (CFTR) expression and function in epithelial cells. Immunoprecipitation followed by Western blotting, as well as immunocytochemical and cell surface biotinylation measurements, showed that incubation of both stably transduced (HeLa) and endogenous CFTR expressing (16HBE14o-, Calu-3, and mouse tracheal epithelial) cells with 100 microm diethylenetriamine NONOate (DETA NONOate) for 24-96 h decreased both intracellular and apical CFTR levels. Calu-3 and mouse tracheal epithelial cells, incubated with DETA NONOate but not with 100 microm 8-bromo-cGMP for 96 h, exhibited reduced cAMP-activated short circuit currents when mounted in Ussing chambers. Exposure of Calu-3 cells to nitric oxide donors resulted in the nitration of a number of proteins including CFTR. Nitration was augmented by proteasome inhibition, suggesting a role for the proteasome in the degradation of nitrated proteins. Our studies demonstrate that levels of nitric oxide that are likely to be encountered in the vicinity of airway cells during inflammation may nitrate CFTR resulting in enhanced degradation and decreased function. Decreased levels and function of normal CFTR may account for some of the cystic fibrosis-like symptoms that occur in chronic inflammatory lung diseases associated with increased NO production.

Lack of amiloride-sensitive transport across alveolar and respiratory epithelium of iNOS(-/-) mice in vivo

The extent to which endogenously generated nitric oxide alters Na(+) transport across the mammalian alveolar epithelium in vivo has not been documented. Herein we measured alveolar fluid clearance and nasal potential differences in mice lacking the inducible form of nitric oxide synthase [iNOS; iNOS(-/-)] and their corresponding wild-type controls [iNOS(+/+)]. Alveolar fluid clearance values in iNOS(+/+) and iNOS(-/-) anesthetized mice with normal oxygenation and acid-base balance were ~30% of instilled fluid/30 min. In both groups of mice, fluid absorption was dependent on vectorial Na(+) movement. Amiloride (1.5 mM) decreased alveolar fluid clearance in iNOS(+/+) mice by 61%, whereas forskolin (50 microM) increased alveolar fluid clearance by 55% by stimulating amiloride-insensitive pathways. Neither agent altered alveolar fluid clearance in iNOS(-/-) mice. Hyperoxia upregulated iNOS expression in iNOS(+/+) mice and decreased their amiloride-sensitive component of alveolar fluid clearance but had no effect on the corresponding values in iNOS(-/-) mice. Nasal potential difference measurements were consistent with alveolar fluid clearance in that both groups of mice had similar baseline values, which were amiloride sensitive in the iNOS(+/+) but not in the iNOS(-/-) mice. These data suggest that nitric oxide produced by iNOS under basal conditions plays an important role in regulating amiloride-sensitive Na(+) channels in alveolar and airway epithelia.

Nitric oxide contributes to control of effusion in experimental otitis media

OBJECTIVES/HYPOTHESIS

Nitric oxide (NO) is a small, short-lived free radical involved in cellular signaling and known to play a role in inflammation. It is generated on demand by the enzyme nitric oxide synthase (NOS) on arginine. We have previously found that mRNA encoding NOS is produced in the middle ear during otitis media. The role of NO was therefore explored in an experimental model of immune-mediated otitis media.

STUDY DESIGN AND METHODS

Guinea pigs were systemically immunized and later challenged in the middle ear with the same antigen. One ear of each animal was challenged with antigen alone. In the opposite ear, antigen was combined with a potent inhibitor of NOS, N(G)-amino-L-arginine (L-NAA). After survival for 24, 48, or 72 hours, the middle ears were evaluated for otitis media.

RESULTS

Inhibition of NOS resulted in significantly increased middle ear effusion at all three time periods. This increase was blocked by the addition of excess 1-arginine, which bypasses the inhibitory effects of L-NAA. The infiltration of cells into the middle ear lumen and the hyperplasia of the middle ear mucosa were unaffected by L-NAA administration.

CONCLUSIONS

The results suggest that NO is involved in regulating the permeability of the middle ear vascular, the transudation of serum into the middle ear mucosa, and/or the movement of extracellular fluid across the middle ear mucosal epithelium.

Increased levels of nitrate and surfactant protein a nitration in the pulmonary edema fluid of patients with acute lung injury

Levels of nitrite (NO2-) and nitrate (NO3-) were measured in pulmonary edema fluid and plasma from 34 patients with early acute lung injury (ALI) and 20 patients with hydrostatic pulmonary edema. Pulmonary edema fluid from patients with ALI had significantly higher levels of NO2- + NO3- compared with pulmonary edema fluid from patients with hydrostatic pulmonary edema (108 +/- 13 microM versus 66 +/- 9 microM; means +/- SEM; p < 0.05). In addition, patients with shock had higher plasma NO2- + NO3- levels than those without shock (79 +/- 11 microM versus 53 +/- 12 microM, p < 0.05). Acidemia and increased anion gap, markers of systemic hypoperfusion, were also associated with twofold higher plasma NO2- + NO3- levels (p < 0.01). Increased levels of NO2- + NO3- in edema fluid samples were associated with slower rates of alveolar fluid clearance. Nitrated pulmonary surfactant protein A (SP-A) was also detected in the edema fluid of patients with ALI after immunoprecipitation with a specific antibody against this protein. Previously, we have shown that nitration of SP-A impairs its host- defense properties. In aggregate, the results of this study indicate that reactive oxygen-nitrogen species may play a role in the pathogenesis of human ALI.