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Objective To investigate the role of PF-06650833, a highly potent and selective small-molecule inhibitor of interleukin-1-associated kinase 4 (IRAK4), in autoimmune pathophysiology in vitro, in vivo, and in the clinical setting. Methods Rheumatoid arthritis (RA) inflammatory pathophysiology was modeled in vitro through 1) stimulation of primary human macrophages with anti-citrullinated protein antibody immune complexes (ICs), 2) RA fibroblast-like synoviocyte (FLS) cultures stimulated with Toll-like receptor (TLR) ligands, as well as 3) additional human primary cell cocultures exposed to inflammatory stimuli. Systemic lupus erythematosus (SLE) pathophysiology was simulated in human neutrophils, dendritic cells, B cells, and peripheral blood mononuclear cells stimulated with TLR ligands and SLE patient ICs. PF-06650833 was evaluated in vivo in the rat collagen-induced arthritis (CIA) model and the mouse pristane-induced and MRL/lpr models of lupus. Finally, RNA sequencing data generated with whole blood samples from a phase I multiple-ascending-dose clinical trial of PF-06650833 were used to test in vivo human pharmacology. Results In vitro, PF-06650833 inhibited human primary cell inflammatory responses to physiologically relevant stimuli generated with RA and SLE patient plasma. In vivo, PF-06650833 reduced circulating autoantibody levels in the pristane-induced and MRL/lpr murine models of lupus and protected against CIA in rats. In a phase I clinical trial (NCT02485769), PF-06650833 demonstrated in vivo pharmacologic action pertinent to SLE by reducing whole blood interferon gene signature expression in healthy volunteers. Conclusion These data demonstrate that inhibition of IRAK4 kinase activity can reduce levels of inflammation markers in humans and provide confidence in the rationale for clinical development of IRAK4 inhibitors for rheumatologic indications.

Background PF-06650833 is a potent, selective inhibitor of interleukin-1 receptor-associated kinase 4 (IRAK4). Two randomized, double-blind, sponsor-open phase 1 studies evaluated the safety, pharmacokinetics, and pharmacodynamics of single (SAD) and multiple ascending doses (MAD) of PF-06650833 immediate-release (IR) and modified-release (MR) oral formulations in healthy adult subjects. Methods Study 1 (NCT02224651) was a 96-day, placebo-substitution, SAD study of once-daily (QD) oral PF-06650833 IR 1 to 6000 mg and MR 30 to 300 mg in fasted and fed states. Study 2 (NCT02485769) was a 14-day, placebo-controlled, MAD study of PF-06650833 IR 25 to 750 mg twice daily, IR 1000 mg four times per day, IR 330 mg three times per day, and MR 300 mg QD. Results PF-06650833 was generally well tolerated, with no dose-limiting treatment-emergent adverse events (TEAEs) identified in either study. TEAEs were generally mild in severity, with headache, gastrointestinal disorders, and acne most commonly reported. No serious AEs or deaths were reported. A maximum tolerated dose was not established in either study. In the SAD study, food intake delayed absorption of IR 30 mg and increased total exposure by 33%. Delayed absorption was achieved with the MR formulation (Tmax of 1 h versus 8 h for IR 100 mg and MR 100 mg formulations, respectively). Food had no effect on total exposure for MR 30 mg, but reduced half-life 1.8-fold and increased Cmax by 62%. In the MAD study, accumulation ranged from 0.9-fold to 1.4-fold for AUCtau and 0.9-fold to 1.3-fold for Cmax. Less than 1% of the dose was recovered unchanged in urine for all dose groups, with renal clearance ranging from 14 to 23 mL/min for IR Conclusions PF-06650833, the first IRAK4 inhibitor to enter clinical development, has a favorable safety and pharmacokinetic profile and has shown evidence of pharmacological effect. The data support continued evaluation in human clinical trials for the treatment of rheumatic and autoimmune diseases. Trial registration Clinicaltrials.gov, NCT02224651, registered 25 August 2014; NCT02485769, registered 30 June 2015

COPD is characterized by inflammation and lung function decline. p38 MAPK inhibition may be an anti-inflammatory therapeutic approach to COPD. The efficacy and safety of PH-797804 (PH), a potent, selective oral p38 inhibitor, was tested in three studies including patients with GOLD stage II/III COPD. Studies were randomized, double-blind, placebo-controlled, parallel-group, and of 6–12 weeks duration; with differing concomitant COPD treatment (PRN short-acting bronchodilators (SABD); tiotropium (TIO, 18 mg QD); or salmeterol/fluticasone combination (SFC, BID)). PH doses ranged from 0.25–10 mg QD, with 6 mg being common to all studies. The common primary endpoint was placebo-adjusted change from baseline in trough FEV 1 at end of treatment. TDI, symptoms, and blood inflammatory biomarkers were measured. FEV 1 was improved in all studies, which varied with background treatment (Table). Symptoms and TDI were inconsistently improved across studies. Plasma hs-CRP decreased by 40 to 43% (p 1 ; decreased systemic anti-inflammatory biomarkers; and produced adverse events both known (i.e., rash) and not known (i.e., AF and QTc prolongation) to be associated with p38 inhibition. Supported by Pfizer, Inc.

Background. Reperfusion injury with pulmonary edema continues to be a major complication after lung transplantation. Alveolar fluid homeostasis is regulated by Na + /K + -ATPase activity on the basolateral surface of alveolar epithelial cells. Intact Na + /K + -AT-Pase is essential to the resolution of pulmonary edema. We characterized the effects of cold ischemia and reperfusion on expression of Na + /K + -ATPase mRNA and protein. Methods. Baseline values for Na + /K + -ATPase mRNA and protein were determined from freshly harvested lungs with no cold storage time or reperfusion (group I). Group II lungs were analyzed after cold storage times of 12 or 24 hr without subsequent reperfusion. Group III lungs were analyzed after cold storage times of 12 or 24 hr with subsequent reperfusion. Lungs were flushed with either Euro-Collins (EC) or University of Wisconsin (UW) solution in each group. All samples were quantified for Na + /K + -ATPase mRNA and Na + /K + -ATPase protein. Physiological parameters including oxygenation and compliance were also measured. Results. There were no significant differences in the level of mRNA and protein for samples that were cold stored without reperfusion (group II). With reperfusion (group III) there was a significant increase in the level of the Na + /K + -ATPase mRNA after 12 hr of storage for both EC and UW. After 24 hr of storage and subsequent reperfusion, lungs flushed with EC had significantly decreased Na + /K + -ATPase protein and mRNA, although lungs preserved with UW maintained their increased levels of Na + /K + -ATPase protein and mRNA. Conclusions. Our data suggest that ischemia-reperfusion injury results in an initial up-regulation of Na + / K + -ATPase mRNA. With prolonged injury in lungs preserved with EC, the level of the mRNA decreased with a corresponding decrease in the Na + /K + -ATPase protein. The different response seen in EC versus UW may be explained by better preservation of pump function with UW than EC and correlates with improved physiological function in lungs preserved with UW solution.

Using the patch-clamp technique, we studied the effects of epidermal growth factor (EGF) on whole cell and single channel currents in adult rat alveolar epithelial type II cells in primary culture in the presence or absence of EGF for 48 h. In symmetrical sodium isethionate solutions, EGF exposure caused a significant increase in the type II cell whole cell conductance. Amiloride (10 μM) produced ∼20–30% inhibition of the whole cell conductance in both the presence and absence of EGF, such that EGF caused the magnitude of the amiloride-sensitive component to more than double. Northern analysis showed that α-, β- and γ-subunits of rat epithelial Na+ channel (rENaC) steady-state mRNA levels were all significantly decreased by EGF. At the single channel level, all active inside-out patches demonstrated only 25-pS channels that were amiloride sensitive and relatively nonselective for cations ([Formula: see text]/[Formula: see text]≈ 1.0:0.48). Although the biophysical characteristics (conductance, open-state probability, and selectivity) of the channels from EGF-treated and untreated cells were essentially identical, channel density was increased by EGF; the modal channel per patch was increased from 1 to 2. These findings indicate that EGF increases expression of nonselective, amiloride-sensitive cation channels in adult alveolar epithelial type II cells. The contribution of rENaC to the total EGF-dependent cation current under these conditions is quantitatively less important than that of the nonselective cation channels in these cells.

We investigated the effects of epidermal growth factor (EGF) on active Na+absorption by alveolar epithelium. Rat alveolar epithelial cells (AEC) were isolated and cultivated in serum-free medium on tissue culture-treated polycarbonate filters. mRNA for rat epithelial Na+channel (rENaC) α-, β-, and γ-subunits and Na+pump α1- and β1-subunits were detected in day 4 monolayers by Northern analysis and were unchanged in abundance in day 5 monolayers in the absence of EGF. Monolayers cultivated in the presence of EGF (20 ng/ml) for 24 h from day 4 to day 5 showed an increase in both α1and β1Na+pump subunit mRNA but no increase in rENaC subunit mRNA. EGF-treated monolayers showed parallel increases in Na+pump α1- and β1-subunit protein by immunoblot relative to untreated monolayers. Fixed AEC monolayers demonstrated predominantly membrane-associated immunofluorescent labeling with anti-Na+pump α1- and β1-subunit antibodies, with increased intensity of cell labeling for both subunits seen at 24 h following exposure to EGF. These changes in Na+pump mRNA and protein preceded a delayed (>12 h) increase in short-current circuit (measure of active transepithelial Na+transport) across monolayers treated with EGF compared with untreated monolayers. We conclude that EGF increases active Na+resorption across AEC monolayers primarily via direct effects on Na+pump subunit mRNA expression and protein synthesis, leading to increased numbers of functional Na+pumps in the basolateral membranes.

We investigated the role of keratinocyte growth factor (KGF) in regulation of alveolar epithelial cell (AEC) phenotype in vitro. Effects of KGF on cell morphology, expression of surfactant apoproteins A, B, and C (SP-A, -B, and -C), and expression of aquaporin 5 (AQP5), a water channel present in situ on the apical surface of alveolar type I (AT1) cells but not expressed in alveolar type II (AT2) cells, were evaluated in AECs grown in primary culture. Observations were made on AEC monolayers grown in serum-free medium without KGF (control) or grown continuously in the presence of KGF (10 ng/ml) from either Day 0 (i.e., the time of plating) or Day 4 or 6 through Day 8 in culture. AECs monolayers express AQP5 only on their apical surfaces as determined by cell surface biotinylation studies. Control AECs grown in the absence of KGF through Day 8 express increasing levels of AQP5, consistent with transition toward the AT1 cell phenotype. Exposure of AECs to KGF from Day 0 results in decreased AQP5 expression, retention of a cuboidal morphology, and greater numbers of lamellar bodies relative to control on Day 8 in culture. AECs treated with KGF from Day 4 or 6 exhibit a decrease in AQP5 expression through subsequent days in culture, as well as an increase in expression of surfactant apoproteins. These data, showing that KGF both prevents and reverses the increase in AQP5 (and decrease in surfactant apoprotein) expression that accompanies progression of the AT2 toward the AT1 cell phenotype, support the concepts that transdifferentiation between AT2 and AT1 cell phenotypes is at least partially reversible and that KGF may play a major role in modulating AEC phenotype.

We investigated the polarized distribution and isoform specificity of anion exchange (Cl(-)-HCO3- exchange) in alveolar epithelial cell monolayers. Rat alveolar type II epithelial cell monolayers were grown in primary culture on detachable tissue culture-treated nuclepore filters. Each filter was mounted in a cuvette containing two fluid compartments (apical and basolateral) separated by the monolayer, the cells loaded with pH-sensitive dye, and intracellular pH (pHi) measured spectrofluorometrically. To assay for Cl(-)-HCO3- exchange, monolayers were incubated in medium containing 24 mM HCO3-/5% CO2 and 140 mM NaCl at pH 7.4 and acutely alkalinized by replacement of the fluid by HCO3(-)-free buffer containing Hepes (6 mM) at pH 7.4. Monolayers exhibited basolateral (but not apical) Cl(-)-dependent, Na(+)-independent recovery from an alkaline load that was abolished when Cl- was substituted by equimolar gluconate in the basolateral fluid, or if DIDS (500 microM) was present basolaterally. Substitution of gluconate for Cl- in the basolateral fluid, but not the apical fluid, resulted in a rise in steady-state pHi that was reversible on replacement of the basolateral fluid with Cl(-)-containing buffer, which occurred in HCO3(-)- but not Hepes-buffered medium. These data indicate that alveolar epithelial cells express basolateral membrane domain of these cells. Northern analysis of alveolar epithelial cell mRNA using anion exchanger (AE) isoform-specific cDNA probes indicates that alveolar epithelial cells express the AE2 isoform predominantly, if not exclusively, and do not express detectable AE1 (i.e., band-3 protein) or AE3.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum contains a number of polypeptide growth factors, hormones, and soluble matrix components and may influence the state of differentiation of epithelial cells in general and of alveolar epithelial cells (AEC) in particular. To evaluate the influence of sera on the transition from the type II toward the type I cell phenotype, we compared the effects of newborn bovine serum (NBS) and rat serum (RS) on morphologic changes and expression of a type I cell-specific epitope in AEC monolayers with time in primary culture. Rat type II AEC were harvested and cultured in defined serum-free medium (MDSF), MDSF + RS (5%), or MDSF + NBS (10%). Monolayer integrity was monitored by measuring transepithelial resistance (approximately 2,000 omega.cm2) and short-circuit current (approximately 4 microA/cm2). Binding of the type I cell-specific monoclonal antibody VIIIB2 was assessed between day 1 and day 11 by cell-based enzyme-linked immunosorbent assay (ELISA) and by immunoelectron microscopy (IEM). By ELISA, in MDSF and MDSF + NBS, VIIIB2 binding increased markedly after day 2, rising approximately 4-fold by day 8 (compared with day 1). In dramatic contrast, there was essentially no increase in VIIIB2 binding through day 11 in MDSF + RS. Results from IEM for apical surface binding of VIIIB2 were similar to those obtained by ELISA. Some morphologic differences were also noted, with cells in MDSF + RS being somewhat less spread at later times than those in MDSF or MDSF + NBS. These data indicate that the rate of rat type II AEC differentiation toward the type I cell phenotype is significantly modulated by soluble factor(s) present in rat serum.

Rationale The effectiveness of varenicline for smoking cessation has been established, but little is known about the psychological processes that mediate this clinical outcome. Objectives This study evaluated the effect of a single dose of varenicline on tonic and cue-provoked changes in craving, withdrawal, and affect using a randomized, double-blind, placebo-controlled, cross-over design. Methods Following overnight abstinence, 38 non-treatment-motivated smokers received either varenicline 2 mg or matched placebo, then tonic measures of craving, withdrawal, and positive and negative affect were obtained at 30-min intervals. At 4-h post-administration, a cue exposure session obtained the same subjective measures at three time-points following the physical handling of a lit cigarette versus the sharpening and handling of a pencil. Results At 4-h post-administration, varenicline reduced tonic craving as well as craving across the smoking and neutral cue conditions, relative to placebo. By contrast, the capacity of the smoking cue to enhance craving relative to the neutral cue was unaffected by varenicline. Measures of withdrawal and positive and negative affect produced mixed results. Conclusions Acute varenicline selectively attenuates tonic but not cue-provoked craving. This dissociation provides insight into the specific psychological processes that might mediate the effectiveness of varenicline, and highlights cue-provoked craving as a discrete target for advancing smoking cessation pharmacotherapy.

To investigate the cell physiologic and biological properties of the alveolar epithelium, we studied rat alveolar epithelial cell monolayers grown on permeable supports in primary culture. Type II alveolar epithelial cells were disaggregated using elastase, and partially purified on a discontinuous metrizamide gradient. These isolated cells were plated onto tissue culture-treated Nuclepore membrane filters at 1.5×106 cells/cm2 and maintained in a humidified incubator (5% CO2 in air, 37° C). After 2 days in culture, the bathing media on both sides of the cell monolayers were changed to fresh culture medium, thus removing nonadherent cells (mostly leukocytes). These monolayers exhibit a high transmonolayer resistance (>2000 Ω-cm2) and actively transport ions. Radionuclide flux studies indicate that Na+ is the predominant ionic species absorbed actively under baseline conditions, accounting for about 80% of the total active ion transport. Cl− seems to be passively transported across the epithelium. However, when the epithelium is exposed to a beta-agonist (terbutaline), active absorption of Na+ is increased and active absorption of Cl− occurs. Although it is clear that both active Na+ and Cl− transport are dependent on Na+/K+-ATPase activity, and that Na+ enters cells predominantly through channels, the specific mechanisms by which Cl− enters and exits the alveolar epithelial cells remain unclear. The stimulated reabsorption of Na+ and Cl− may be important in helping to remove excess fluid from alveolar air spaces in the lung.

An understanding of the process of alveolar epithelial cell growth and differentiation requires the ability to trace and analyze the phenotypic transitions that the cells undergo. This analysis demands specific phenotypic probes to type II and, especially, type I pneumocytes. To this end, monoclonal antibodies have been generated to type I alveolar epithelial cells using an approach designed to enhance production of lung-specific clones from a crude lung membrane preparation. The monoclonal antibodies were screened by a combination of enzyme-linked immunosorbent assay and immunohistochemical techniques, with the determination of type I cell specificity resting primarily on immunoelectron microscopic localization. Two of these new markers of the type I pneumocyte phenotype (II F1 and VIII B2) were used to analyze primary cultures of type II cells growing on standard tissue culture plastic and on a variety of substrata reported to affect the morphology of these cells in culture. On tissue culture plastic, the antibodies fail to react with early (days 1 to 3) type II cell cultures. The cells become progressively more reactive with time in culture to a plateau of approximately 6 times background by day 8, with a maximum rate of increase between days 3 and 5. This finding is consistent with the hypothesis that type II cells in primary culture undergo at least partial differentiation into type I cells. Type II cells grown on laminin, which reportedly delays the loss of type II cell appearance, and on fibronectin, which has been reported to facilitate cell spreading and loss of type II cell features, develop the type I cell markers during cultivation in vitro with kinetics similar to those on uncoated tissue culture plastic. Cells on type I collagen and on tissue culture-treated Nuclepore filters, which have been reported to support monolayers with type I cell-like morphology, also increase their expression of the II F1 and VIII B2 epitopes around days 3 to 5. Taken together with available morphologic information, these data suggest that expression of different alveolar epithelial cell phenotypic markers by type II cells in primary culture may be independently regulated. The monoclonal antibody probes described in this report should prove useful in the continued investigation of the mechanisms and regulation of alveolar epithelial cell differentiation.

We evaluated the effects of epidermal growth factor (EGF) on transepithelial resistance (Rt) and active ion transport by alveolar epithelial cell (AEC) monolayers on tissue culture-treated polycarbonate filters. Rat type II cells were cultured in completely defined serum-free medium (MDSF) or MDSF supplemented with EGF. The addition of EGF from either day 0 (chronic) or day 4 (subacute) resulted in significant increases in Rt and short-circuit current (ISC) on day 5. After subacute exposure, these effects were delayed in onset by 6-12 h and sustained for > 24 h. Basolateral (but not apical) EGF was responsible for these effects, which were prevented by preincubation with tyrphostin RG-50864, a reversible specific inhibitor of the EGF receptor tyrosine kinase. ISC decreased, with a sensitivity to apical inhibitors of sodium transport in the order benzamil > amiloride > 5-(N-ethyl-N-isopropyl) amiloride in MDSF +/- EGF, and was completely inhibited by the addition of basolateral ouabain. Net sodium flux and Na+, K+ -ATPase activity both increased approximately 50% in the presence of EGF. These results indicate that 1) EGF decreases tight junctional permeability and increases active sodium transport by AEC monolayers via basolaterally located EGF receptors, and 2) the pathways for AEC sodium entry and exit (+/- EGF) are apical high amiloride affinity sodium channels and basolateral sodium pumps.

Alveolar epithelial type II (AT2) cells have been thought to be the progenitors of terminally differentiated type I (AT1) cells in the adult animal in vivo. In this study, we used an AT1 cell-specific monoclonal antibody (mAb VIII B2) to investigate expression of the AT1 cell phenotype accompanying reversible changes in expression of the AT2 cell phenotype. AT2 cells were isolated and cultured either on attached collagen gels or on gels detached 1 or 4 days after plating and maintained thereafter as floating gels. Monolayers on both attached and floating gels were harvested on days 4 and 8 and analyzed by electron microscopy for changes in morphology and binding of mAb VIII B2. Results indicate that: (1) alveolar epithelial cells (AEC) on attached gels develop characteristics of the AT1 cell phenotype, (2) AEC on gels detached on day 1 maintain features of the AT2 cell phenotype (and do not react with mAb VIII B2), and (3) the expression of AT1 cell phenotypic traits seen by day 4 on attached gels is reversed after detachment. We conclude that commitment to the AT1 and AT2 cell lineages requires continuous regulatory input to maintain the differentiated states, and that transdifferentiation between AT2 and AT1 cells may be reversible.

Recent studies in fetal lung using immunological and molecular probes have revealed type I and type II cell phenotypic markers in primordial lung epithelial cells prior to the morphogenesis of these cell types. We have recently developed monoclonal antibodies specific for adult type I cells. To evaluate further the temporal appearance of the type I cell phenotype during alveolar epithelial cell ontogeny, we analyzed fetal lung development using one of our monoclonal antibodies (mAb VIII B2). The epitope recognized by mAb VIII B2 first appears in the canalicular stage of fetal lung development, at approx. embryonic day 19 (E19), in occasional, faintly stained tubules. Staining with this type I cell probe becomes more intense and more widespread with increasing gestational age, during which time the pattern of staining changes. Initially, all cells of the distal epithelial tubules are uniformly labelled along their apical and basolateral surfaces. As morphological differentiation of the alveolar epithelium proceeds, type I cell immunoreactivity appears to become restricted to the apical surface of the primitive type I cells in a pattern approaching that seen in the mature lung. We concurrently analyzed developing fetal lung with an antiserum to surfactant apoprotein-A (alpha-SP-A). Consistent with the findings of others, labeling of SP-A was first detectable in scattered cuboidal cells at E18. Careful examination of the double-labeled specimens suggested that some cells were reactive with both the VIII B2 and SP-A antibodies, particularly at E20. Confocal microscopic analysis of such sections from E20 lung confirmed this impression. Three populations of cells were detected: cells labeled only with alpha-SP-A, cells labeled only with mAb VIII B2, and a smaller subset of cells labeled by both.(ABSTRACT TRUNCATED AT 250 WORDS)

We investigated expression of the α3-integrin subunit by rat alveolar epithelial cells (AECs) grown in primary culture as well as the effects of monoclonal antibodies with blocking activity against the α3-integrin subunit on AEC monolayer formation. α3-Integrin subunit mRNA and protein were detectable in AECs on day 1 and increased with time in culture. α3- and β1-integrin subunits coprecipitated in immunoprecipitation experiments with α3- and β1-subunit-specific antibodies, consistent with their association as the α3β1-integrin receptor at the cell membrane. Treatment with blocking anti-α3monoclonal antibody from day 0 delayed development of transepithelial resistance, reduced transepithelial resistance through day 5 compared with that in untreated AECs, and resulted in large subconfluent patches in monolayers viewed by scanning electron microscopy on day 3. These data indicate that α3- and β1-integrin subunits are expressed in AEC monolayers where they form the heterodimeric α3β1-integrin receptor at the cell membrane. Blockade of the α3-integrin subunit inhibits formation of confluent AEC monolayers. We conclude that the α3-integrin subunit modulates formation of AEC monolayers by virtue of the key role of the α3β1-integrin receptor in AEC adhesion.

We evaluated the effects of keratinocyte growth factor (KGF) on alveolar epithelial cell (AEC) active ion transport and on rat epithelial Na channel (rENaC) subunit and Na+-K+-adenosinetriphosphatase (ATPase) subunit isoform expression using monolayers of AEC grown in primary culture. Rat alveolar type II cells were plated on polycarbonate filters in serum-free medium, and KGF (10 ng/ml) was added to confluent AEC monolayers on day 4 in culture. Exposure of AEC monolayers to KGF on day 4 resulted in dose-dependent increases in short-circuit current ( Isc) compared with controls by day 5, with further increases occurring through day 8. Relative Na+-K+-ATPase α1-subunit mRNA abundance was increased by 41% on days 6 and 8 after exposure to KGF, whereas α2-subunit mRNA remained only marginally detectable in both the absence and presence of KGF. Levels of mRNA for the β1-subunit of Na+-K+-ATPase did not increase, whereas cellular α1- and β1-subunit protein increased 70 and 31%, respectively, on day 6. mRNA for α-, β-, and γ-rENaC all decreased in abundance after treatment with KGF. These results indicate that KGF upregulates active ion transport across AEC monolayers via a KGF-induced increase in Na pumps, primarily due to increased Na+-K+-ATPase α1-subunit mRNA expression. We conclude that KGF may enhance alveolar fluid clearance after acute lung injury by upregulating Na pump expression and transepithelial Na transport across the alveolar epithelium.