Granulocyte/macrophage colony-stimulating factor treatment improves alveolar epithelial barrier function in alcoholic rat lung

Chronic alcohol abuse increases the risk of developing acute lung injury approximately threefold in septic patients, and ethanol ingestion for 6 wk in rats impairs alveolar epithelial barrier function both in vitro and in vivo. Granulocyte/macrophage colony-stimulating factor (GM-CSF) is a trophic factor for the alveolar epithelium, and a recent phase II clinical study suggests that GM-CSF therapy decreases sepsis-mediated lung injury. Therefore, we hypothesized that GM-CSF treatment could improve ethanol-mediated defects in the alveolar epithelium during acute stresses such as endotoxemia. In this study, we determined that recombinant rat GM-CSF improved lung liquid clearance (as reflected by lung tissue wet:dry ratios) in ethanol-fed rats anesthetized and then challenged with 2 ml of saline via a tracheostomy tube. Furthermore, GM-CSF treatment improved lung liquid clearance and decreased epithelial protein leak in both control-fed and ethanol-fed rats after 6 h of endotoxemia induced by Salmonella typhimurium lipopolysaccharide given intraperitoneally, but with the greater net effect seen in the ethanol-fed rats. Our previous studies indicate that chronic ethanol ingestion decreases lung liquid clearance by increasing intercellular permeability. Consistent with this, GM-CSF treatment in vitro decreased permeability of alveolar epithelial monolayers derived from both control-fed and ethanol-fed rats. As in the endotoxemia model in vivo, the effect of GM-CSF was most dramatic in the ethanol group. Together, these results indicate that GM-CSF treatment has previously unrecognized effects in promoting alveolar epithelial barrier integrity and that these salutary effects may be particularly relevant in the setting of chronic alcohol abuse.     

Alveolar epithelial fluid transport can be simultaneously upregulated by both KGF and beta-agonist therapy.

Although keratinocyte growth factor (KGF) protects against experimental acute lung injury, the mechanisms for the protective effect are incompletely understood. Therefore, the time-dependent effects of KGF on alveolar epithelial fluid transport were studied in rats 48-240 h after intratracheal administration of KGF (5 mg/kg). There was a marked proliferative response to KGF, measured both by in vivo bromodeoxyuridine staining and by staining with an antibody to a type II cell antigen. In controls, alveolar liquid clearance (ALC) was 23 +/- 3%/h. After KGF pretreatment, ALC was significantly increased to 30 +/- 2%/h at 48 h, to 39 +/- 2%/h at 72 h, and to 36 +/- 3%/h at 120 h compared with controls (P < 0.05). By 240 h, ALC had returned to near-control levels (26 +/- 2%/h). The increase in ALC was explained primarily by the proliferation of alveolar type II cells, since there was a good correlation between the number of alveolar type II cells and the increase in ALC (r = 0.92, P = 0.02). The fraction of ALC inhibited by amiloride was similar in control rats (33%) as in 72-h KGF-pretreated rats (38%), indicating that there was probably no major change in the apical pathways for Na uptake in the KGF-pretreated rats at this time point. However, more rapid ALC at 120 h, compared with 48 h after KGF treatment, may be explained by greater maturation of alpha-epithelial Na channel, since its expression was greater at 120 than at 48 h, whereas the number of type II cells was the same at these two time points. beta-Adrenergic stimulation with terbutaline 72 h after KGF pretreatment further increased ALC to 50 +/- 7%/h (P < 0.5). In summary, KGF induced a sustained increase over 120 h in the fluid transport capacity of the alveolar epithelium. This impressive upregulation in fluid transport was further enhanced with beta-adrenergic agonist therapy, thus providing evidence that two different treatments can simultaneously increase the fluid transport capacity of the alveolar epithelium.     

Extracellular glutathione inhibits oxygen-induced permeability changes in alveolar epithelial monolayers.

Exposure to high fractional inspired oxygen for 24 h increases permeability of the alveolar epithelium, contributing to the clinical manifestations of oxygen toxicity. Utilizing a model of the alveolar epithelium in which isolated rat type II cells form polarized monolayers on polycarbonate filters [transepithelial resistance (R(t)) > 1 k Omega x cm(2) by day 4], we evaluated the ability of reduced glutathione (GSH) to ameliorate these changes. On day 4, apical fluid was replaced with culture medium containing 1) no additives, 2) GSH (500 microM), or 3) GSH (500 microM) + glutathione reductase (0.5 U/ml) + nicotinamide adenine dinucleotide phosphate (250 microM). Monolayers were exposed (for 24 h) to room air (control) or 95% O(2), each containing 5% CO(2). After 24 h of hyperoxia, R(t) for condition 1 decreased by 45% compared with control (P < 0.001). In conditions 2 and 3, R(t) did not decrease significantly (P = not significant). Hyperoxia-induced decreases in active ion transport were observed for conditions 1 and 2 (P < 0.05), but not for condition 3 (P = not significant). These findings indicate that extracellular GSH may protect the alveolar epithelium against hyperoxia-induced injury. Addition of glutathione reductase and nicotinamide adenine dinucleotide phosphate may further augment these protective effects of GSH.     

Transforming growth factor-beta1 decreases expression of the epithelial sodium channel alphaENaC and alveolar epithelial vectorial sodium and fluid transport via an ERK1/2-dependent mechanism

Acute lung injury (ALI) is characterized by the flooding of the alveolar airspaces with protein-rich edema fluid and diffuse alveolar damage. We have previously reported that transforming growth factor-beta1 (TGF-beta1) is a critical mediator of ALI after intratracheal administration of bleomycin or Escherichia coli endotoxin, at least in part due to effects on lung endothelial and alveolar epithelial permeability. In the present study, we hypothesized that TGF-beta1 would also decrease vectorial ion and water transport across the distal lung epithelium. Therefore, we studied the effect of active TGF-beta1 on 22Na+ uptake across monolayers of primary rat and human alveolar type II (ATII) cells. TGF-beta1 significantly reduced the amiloride-sensitive fraction of 22Na+ uptake and fluid transport across monolayers of both rat and human ATII cells. TGF-beta1 also significantly decreased alphaENaC mRNA and protein expression and inhibited expression of a luciferase reporter downstream of the alphaENaC promoter in lung epithelial cells. The inhibitory effect of TGF-beta1 on sodium uptake and alphaENaC expression in ATII cells was mediated by activation of the MAPK, ERK1/2. Consistent with the in vitro results, TGF-beta1 inhibited the amiloride-sensitive fraction of the distal airway epithelial fluid transport in an in vivo rat model at a dose that was not associated with any change in epithelial protein permeability. These data indicate that increased TGF-beta1 activity in the distal airspaces during ALI promotes alveolar edema by reducing distal airway epithelial sodium and fluid clearance. This reduction in sodium and fluid transport is attributable in large part to a reduction in apical membrane alphaENaC expression mediated through an ERK1/2-dependent inhibition of the alphaENaC promoter activity.     

Influenza virus inhibits ENaC and lung fluid clearance

Fluid-free alveolar space is critical for normal gas exchange. Influenza virus alters fluid transport across respiratory epithelia producing rhinorrhea, middle ear effusions, and alveolar flooding. However, the mechanism of fluid retention remains unclear. We investigated influenza virus strain A/PR/8/34, which can attach and enter mammalian cells but is incapable of viral replication and productive infection in mammalian epithelia, on epithelial sodium channels (ENaC) in rat alveolar type II (ATII) cells. In parallel, we determined the effects of virus on amiloride-sensitive (i.e., ENaC-mediated) fluid clearance in rat lungs in vivo. Although influenza virus did not change the inulin permeability of ATII monolayers, it rapidly reduced the net volume transport across monolayers. Virus reduced the open probability of single ENaC channels in apical cell-attached patches. U-73122, a phospholipase C (PLC) inhibitor, and PP2, a Src inhibitor, blocked the effect of virus on ENaC. GF-109203X, a protein kinase C (PKC) inhibitor, also blocked the effect, suggesting a PKC-mediated mechanism. In parallel, intratracheal administration of influenza virus produced a rapid inhibition of amiloride-sensitive (i.e., ENaC-dependent) lung fluid transport. Together, these results show that influenza virus rapidly inhibits ENaC in ATII cells via a PLC- and Src-mediated activation of PKC but does not increase epithelial permeability in this same rapid time course. We speculate that this rapid inhibition of ENaC and formation of edema when the virus first attaches to the alveolar epithelium might facilitate subsequent influenza infection and may exacerbate influenza-mediated alveolar flooding that can lead to acute respiratory failure and death.     

Extracellular heat shock protein 72 is a marker of the stress protein response in acute lung injury

Previous studies have shown that heat shock protein 72 (Hsp72) is found in the extracellular space (eHsp72) and that eHsp72 has potent immunomodulatory effects. However, whether eHsp72 is present in the distal air spaces and whether eHsp72 could modulate removal of alveolar edema is unknown. The first objective was to determine whether Hsp72 is released within air spaces and whether Hsp72 levels in pulmonary edema fluid would correlate with the capacity of the alveolar epithelium to remove alveolar edema fluid in patients with ALI/ARDS. Patients with hydrostatic edema served as controls. The second objective was to determine whether activation of the stress protein response (SPR) caused the release of Hsp72 into the extracellular space in vivo and in vitro and to determine whether SPR activation and/or eHsp72 itself would prevent the IL-1beta-mediated inhibition of the vectorial fluid transport across alveolar type II cells. We found that eHsp72 was present in plasma and pulmonary edema fluid of ALI patients and that eHsp72 was significantly higher in pulmonary edema fluid from patients with preserved alveolar epithelial fluid clearance. Furthermore, SPR activation in vivo in mice and in vitro in lung endothelial, epithelial, and macrophage cells caused intracellular expression and extracellular release of Hsp72. Finally, SPR activation, but not eHsp72 itself, prevented the decrease in alveolar epithelial ion transport induced by exposure to IL-1beta. Thus SPR may protect the alveolar epithelium against oxidative stress associated with experimental ALI, and eHsp72 may serve as a marker of SPR activation in the distal air spaces of patients with ALI.     

Acute lung injury edema fluid decreases net fluid transport across human alveolar epithelial type II cells

Most patients with acute lung injury (ALI) have reduced alveolar fluid clearance that has been associated with higher mortality. Several mechanisms may contribute to the decrease in alveolar fluid clearance. In this study, we tested the hypothesis that pulmonary edema fluid from patients with ALI might reduce the expression of ion transport genes responsible for vectorial fluid transport in primary cultures of human alveolar epithelial type II cells. Following exposure to ALI pulmonary edema fluid, the gene copy number for the major sodium and chloride transport genes decreased. By Western blot analyses, protein levels of alphaENaC, alpha1Na,K-ATPase, and cystic fibrosis transmembrane conductance regulator decreased as well. In contrast, the gene copy number for several inflammatory cytokines increased markedly. Functional studies demonstrated that net vectorial fluid transport was reduced for human alveolar type II cells exposed to ALI pulmonary edema fluid compared with plasma (0.02 +/- 0.05 versus 1.31 +/- 0.56 microl/cm2/h, p < 0.02). An inhibitor of p38 MAPK phosphorylation (SB202190) partially reversed the effects of the edema fluid on net fluid transport as well as gene and protein expression of the main ion transporters. In summary, alveolar edema fluid from patients with ALI induced a significant reduction in sodium and chloride transport genes and proteins in human alveolar epithelial type II cells, effects that were associated with a decrease in net vectorial fluid transport across human alveolar type II cell monolayers.     

Angiotensin II mediates glutathione depletion, transforming growth factor-beta1 expression, and epithelial barrier dysfunction in the alcoholic rat lung

Alcohol abuse markedly increases the risk of sepsis-mediated acute lung injury. In a rat model, ethanol ingestion alone (in the absence of any other stress) causes pulmonary glutathione depletion, increased expression of transforming growth factor-beta1 (TGF-beta1), and alveolar epithelial barrier dysfunction, even though the lung appears grossly normal. However, during endotoxemia, ethanol-fed rats release more activated TGF-beta1 into the alveolar space where it can exacerbate epithelial barrier dysfunction and lung edema. Ethanol ingestion activates the renin-angiotensin system, and angiotensin II is capable of inducing oxidative stress and TGF-beta1 expression. We determined that lisinopril, an angiotensin-converting enzyme inhibitor that decreases angiotensin II formation, limited lung glutathione depletion, and treatment with either lisinopril or losartan, a selective angiotensin II type 1 receptor blocker, normalized TGF-beta1 expression. The glutathione precursor procysteine also prevented TGF-beta1 expression, suggesting that TGF-beta1 may be induced indirectly by angiotensin II-mediated oxidative stress and glutathione depletion. Importantly, lisinopril treatment normalized barrier function in alveolar epithelial cell monolayers from ethanol-fed rats, and treatment with either lisinopril or losartan normalized alveolar epithelial barrier function in ethanol-fed rats in vivo, as reflected by lung liquid clearance of an intratracheal saline challenge, even during endotoxemia. In parallel, lisinopril treatment limited TGF-beta1 protein release into the alveolar space during endotoxemia. Together, these results suggest that angiotensin II mediates oxidative stress and the consequent TGF-beta1 expression and alveolar epithelial barrier dysfunction that characterize the alcoholic lung.     

Fluid transport across cultured rat alveolar epithelial cells: a novel in vitro system

Previous studies have used fluid-instilled lungs to measure net alveolar fluid transport in intact animal and human lungs. However, intact lung studies have two limitations: the contribution of different distal lung epithelial cells cannot be studied separately, and the surface area for fluid absorption can only be approximated. Therefore, we developed a method to measure net vectorial fluid transport in cultured rat alveolar type II cells using an air-liquid interface. The cells were seeded on 0.4-microm microporous inserts in a Transwell system. At 96 h, the transmembrane electrical resistance reached a peak level (1,530 +/- 115 Omega.cm(2)) with morphological evidence of tight junctions. We measured net fluid transport by placing 150 microl of culture medium containing 0.5 microCi of (131)I-albumin on the apical side of the polarized cells. Protein permeability across the cell monolayer, as measured by labeled albumin, was 1.17 +/- 0.34% over 24 h. The change in concentration of (131)I-albumin in the apical fluid was used to determine the net fluid transported across the monolayer over 12 and 24 h. The net basal fluid transport was 0.84 microl.cm(-2).h(-1). cAMP stimulation with forskolin and IBMX increased fluid transport by 96%. Amiloride inhibited both the basal and stimulated fluid transport. Ouabain inhibited basal fluid transport by 93%. The cultured cells retained alveolar type II-like features based on morphologic studies, including ultrastructural imaging. In conclusion, this novel in vitro system can be used to measure net vectorial fluid transport across cultured, polarized alveolar epithelial cells.     

Reactive nitrogen species inhibit alveolar epithelial fluid transport after hemorrhagic shock in rats

Our recent experimental work demonstrated that a neutrophil-dependent inflammatory response in the lung prevented the normal up-regulation of alveolar fluid clearance by catecholamines following hemorrhagic shock. In this study, we tested the hypothesis that the release of NO within the airspaces of the lung was responsible for the shock-mediated failure of the alveolar epithelium to respond to catecholamines in rats. Hemorrhagic shock was associated with an inducible NO synthase (iNOS)-dependent increase in the lung production of NO and a failure of the alveolar epithelium to up-regulate vectorial fluid transport in response to beta-adrenergic agonists. Inhibition of iNOS restored the normal catecholamine-mediated up-regulation of alveolar liquid clearance. Airspace instillation of dibutyryl cAMP, a stable analog of cAMP, restored the normal fluid transport capacity of the alveolar epithelium after prolonged hemorrhagic shock, whereas direct stimulation of adenyl cyclase by forskolin had no effect. Pretreatment with pyrrolidine dithiocarbamate or sulfasalazine attenuated the iNOS-dependent production of NO in the lung and restored the normal up-regulation of alveolar fluid clearance by catecholamines after prolonged hemorrhagic shock. Based on in vitro studies with an alveolar epithelial cell line, A549 cells, the effect of sulfasalazine appeared to be mediated in part by inhibition of NF-kappaB activation, and the protective effect was mediated by the inhibition of IkappaBalpha protein degradation. In summary, these results provide the first in vivo evidence that NO, released within the airspaces of the lung probably secondary to the NF-kappaB-dependent activation of iNOS, is a major proximal inflammatory mediator that limits the rate of alveolar epithelial transport after prolonged hemorrhagic shock by directly impairing the function of membrane proteins involved in the beta-adrenergic receptor-cAMP signaling pathway in alveolar epithelium.     

Colon water transport in transgenic mice lacking aquaporin-4 water channels

Transgenic null mice were used to test the hypothesis that water channel aquaporin-4 (AQP4) is involved in colon water transport and fecal dehydration. AQP4 was immunolocalized to the basolateral membrane of colonic surface epithelium of wild-type (+/+) mice and was absent in AQP4 null (-/-) mice. The transepithelial osmotic water permeability coefficient (P(f)) of in vivo perfused colon of +/+ mice, measured using the volume marker (14)C-labeled polyethylene glycol, was 0.016 +/- 0.002 cm/s. P(f) of proximal colon was greater than that of distal colon (0.020 +/- 0.004 vs. 0. 009 +/- 0.003 cm/s, P < 0.01). P(f) was significantly lower in -/- mice when measured in full-length colon (0.009 +/- 0.002 cm/s, P < 0. 05) and proximal colon (0.013 +/- 0.002 cm/s, P < 0.05) but not in distal colon. There was no difference in water content of cecal stool from +/+ vs. -/- mice (0.80 +/- 0.01 vs. 0.81 +/- 0.01), but there was a slightly higher water content in defecated stool from -/- mice (0.68 +/- 0.01 vs. 0.65 +/- 0.01, P < 0.05). Despite the differences in water permeability with AQP4 deletion, theophylline-induced secretion was not impaired (50 +/- 9 vs. 51 +/- 8 microl. min(-1). g(-1)). These results provide evidence that transcellular water transport through AQP4 water channels in colonic epithelium facilitates transepithelial osmotic water permeability but has little or no effect on colonic fluid secretion or fecal dehydration.     

Dopamine increases lung liquid clearance during mechanical ventilation

Short-term mechanical ventilation with high tidal volume (HVT) causes mild to moderate lung injury and impairs active Na+ transport and lung liquid clearance in rats. Dopamine (DA) enhances active Na+ transport in normal rat lungs by increasing Na+-K+-ATPase activity in the alveolar epithelium. We examined whether DA would increase alveolar fluid reabsorption in rats ventilated with HVT for 40 min compared with those ventilated with low tidal volume (LVT) and with nonventilated rats. Similar to previous reports, HVT ventilation decreased alveolar fluid reabsorption by ~50% (P < 0.001). DA increased alveolar fluid reabsorption in nonventilated control rats (by ~60%), LVT ventilated rats (by approximately 55%), and HVT ventilated rats (by ~200%). In parallel studies, DA increased Na+-K+-ATPase activity in cultured rat alveolar epithelial type II cells (ATII). Depolymerization of cellular microtubules by colchicine inhibited the effect of DA on HVT ventilated rats as well as on Na+-K+-ATPase activity in ATII cells. Neither DA nor colchicine affected the short-term Na+-K+-ATPase alpha1- and beta1-subunit mRNA steady-state levels or total alpha1- and beta1-subunit protein abundance in ATII cells. Thus we reason that DA improved alveolar fluid reabsorption in rats ventilated with HVT by upregulating the Na+-K+-ATPase function in alveolar epithelial cells.     

Protein transport across the lung epithelial barrier

Alveolar lining fluid normally contains proteins of important physiological, antioxidant, and mucosal defense functions [such as albumin, immunoglobulin G (IgG), secretory IgA, transferrin, and ceruloplasmin]. Because concentrations of plasma proteins in alveolar fluid can increase in injured lungs (such as with permeability edema and inflammation), understanding how alveolar epithelium handles protein transport is needed to develop therapeutic measures to restore alveolar homeostasis. This review provides an update on recent findings on protein transport across the alveolar epithelial barrier. The use of primary cultured rat alveolar epithelial cell monolayers (that exhibit phenotypic and morphological traits of in vivo alveolar epithelial type I cells) has shown that albumin and IgG are absorbed via saturable processes at rates greater than those predicted by passive diffusional mechanisms. In contrast, secretory component, the extracellular portion of the polymeric immunoglobulin receptor, is secreted into alveolar fluid. Transcytosis involving caveolae and clathrin-coated pits is likely the main route of alveolar epithelial protein transport, although relative contributions of these internalization steps to overall protein handling of alveolar epithelium remain to be determined. The specific pathways and regulatory mechanisms responsible for translocation of proteins across lung alveolar epithelium and regulation of the cognate receptors (e.g., 60-kDa albumin binding protein and IgG binding FcRn) expressed in alveolar epithelium need to be elucidated.     

Transforming Growth Factor ��1 Inhibits Cystic Fibrosis Transmembrane Conductance Regulator-dependent cAMP-stimulated Alveolar Epithelial Fluid Transport via a Phosphatidylinositol 3-Kinase-dependent Mechanism

Exogenous or endogenous β₂-adrenergic receptor agonists enhance alveolar epithelial fluid transport via a cAMP-dependent mechanism that protects the lungs from alveolar flooding in acute lung injury. However, impaired alveolar fluid clearance is present in most of the patients with acute lung injury and is associated with increased mortality, although the mechanisms responsible for this inhibition of the alveolar epithelial fluid transport are not completely understood. Here, we found that transforming growth factor β1 (TGF-β1), a critical mediator of acute lung injury, inhibits β₂-adrenergic receptor agonist-stimulated vectorial fluid and Cl⁻ transport across primary rat and human alveolar epithelial type II cell monolayers. This inhibition is due to a reduction in the cystic fibrosis transmembrane conductance regulator activity and biosynthesis mediated by a phosphatidylinositol 3-kinase (PI3K)-dependent heterologous desensitization and down-regulation of the β₂-adrenergic receptors. Consistent with these in vitro results, inhibition of the PI3K pathway or pretreatment with soluble chimeric TGF-β type II receptor restored β₂-adrenergic receptor agonist-stimulated alveolar epithelial fluid transport in an in vivo model of acute lung injury induced by hemorrhagic shock in rats. The results demonstrate a novel role for TGF-β1 in impairing the β- adrenergic agonist-stimulated alveolar fluid clearance in acute lung injury, an effect that could be corrected by using PI3K inhibitors that are safe to use in humans.     

Impairment of transalveolar fluid transport and lung Na(+)-K(+)-ATPase function by hypoxia in rats.

We examined whether hypoxic exposure in vivo would influence transalveolar fluid transport in rats. We found a significant decrease in alveolar fluid clearance of the rats exposed to 10% oxygen for 48 h. Terbutaline did not stimulate alveolar fluid clearance, and alveolar fluid cAMP levels were lower than those determined in normoxia experiment. Hypoxia did not influence the alveolar fluid lactate dehydrogenase levels, Evans blue dye fluid-to-serum concentration ratio, or lung wet-to-dry weight ratio, indicating no significant change in the permeability of alveolar-capillary barrier. Histological examination showed no significant fluid accumulation into the interstitium and the alveolar space. Hypoxia did not reduce lung ATP content; however, we found significant decrease in Na(+)-K(+)-ATPase hydrolytic activity in lung tissue preparations and isolated alveolar type II cells. Our data indicate that hypoxic exposure in vivo impairs transalveolar fluid transport, and this impairment is related to the decrease in alveolar epithelial Na(+)-K(+)-ATPase hydrolytic activity but is not secondary to the alteration of cellular energy source.     

Alveolar macrophages contribute to alveolar barrier dysfunction in ventilator-induced lung injury

In patients requiring mechanical ventilation for acute lung injury or acute respiratory distress syndrome (ARDS), tidal volume reduction decreases mortality, but the mechanisms of the protective effect have not been fully explored. To test the hypothesis that alveolar macrophage activation is an early and critical event in the initiation of ventilator-induced lung injury (VILI), rats were ventilated with high tidal volume (HV(T)) for 10 min to 4 h. Alveolar macrophage counts in bronchoalveolar lavage (BAL) fluid decreased 45% by 20 min of HV(T) (P < 0.05) consistent with activation-associated adhesion. Depletion of alveolar macrophages in vivo with liposomal clodronate significantly decreased permeability and pulmonary edema following 4 h of HV(T) (P < 0.05). BAL fluid from rats exposed to 20 min of HV(T) increased nitric oxide synthase activity nearly threefold in na?ve primary alveolar macrophages (P < 0.05) indicating that soluble factors present in the air spaces contribute to macrophage activation in VILI. Media from cocultures of alveolar epithelial cell monolayers and alveolar macrophages exposed to 30 min of stretch in vitro also significantly increased nitrite production in na?ve macrophages (P < 0.05), but media from stretched alveolar epithelial cells or primary alveolar macrophages alone did not, suggesting alveolar epithelial cell-macrophage interaction was required for the subsequent macrophage activation observed. These data demonstrate that injurious mechanical ventilation rapidly activates alveolar macrophages and that alveolar macrophages play an important role in the initial pathogenesis of VILI.     

Glutathione availability modulates alveolar macrophage function in the chronic ethanol-fed rat

We have previously demonstrated that chronic alcohol exposure decreases glutathione in the alveolar space. Although alcohol use is associated with decreased alveolar macrophage function, the mechanism by which alcohol impairs macrophage phagocytosis is unknown. In the current study, we examined the possibility that ethanol-induced alveolar macrophage dysfunction was secondary to decreased glutathione and subsequent chronic oxidative stress in the alveolar space. After 6 wk of ethanol ingestion, oxidant stress in the alveolar macrophages was evidenced by a 30-mV oxidation of the GSH/GSSG redox potential (P 相似文献   

Sepsis impairs alveolar epithelial function by downregulating Na-K-ATPase pump

Widespread vascular endothelial injury is the major mechanism for multiorgan dysfunction in sepsis. Following this process, the permeability of the alveolar capillaries is augmented with subsequent increase in water content and acute respiratory distress syndrome (ARDS). Nevertheless, the role of alveolar epithelium is less known. Therefore, we examined alveolar fluid clearance (AFC) using isolated perfused rat lung model in septic rats without ARDS. Sepsis was induced by ligating and puncturing the cecum with a 21-gauge needle. AFC was examined 24 and 48 h later. The expression of Na-K-ATPase proteins was examined in type II alveolar epithelial cells (ATII) and basolateral membrane (BLM). The rate of AFC in control rats was 0.51 ± 0.02 ml/h (means ± SE) and decreased to 0.3 ± 0.02 and 0.33 ± 0.03 ml/h in 24 and 48 h after sepsis induction, respectively (P < 0.0001). Amiloride, significantly decreased AFC in sepsis; conversely, isoproterenol reversed the inhibitory effect of sepsis. The alveolar-capillary barrier in septic rats was intact; therefore the finding of increased extravascular lung water in early sepsis could be attributed to accumulation of protein-poor fluid. The expression of epithelial sodium channel and Na-K-ATPase proteins in whole ATII cells was not different in both cecal ligation and puncture and control groups; however, the abundance of Na-K-ATPase proteins was significantly decreased in BLMs of ATII cells in sepsis. Early decrease in AFC in remote sepsis is probably related to endocytosis of the Na-K-ATPase proteins from the cell plasma membrane into intracellular pools, with resultant inhibition of active sodium transport in ATII cells.