Acid and particulate-induced aspiration lung injury in mice: importance of MCP-1

A model of aspiration lung injury was developed in WT C57BL/6 mice to exploit genetically modified animals on this background, i.e., MCP-1(-/-) mice. Mice were given intratracheal hydrochloric acid (ACID, pH 1.25), small nonacidified gastric particles (SNAP), or combined acid plus small gastric particles (CASP). As reported previously in rats, lung injury in WT mice was most severe for "two-hit" aspiration from CASP (40 mg/ml particulates) based on the levels of albumin, leukocytes, TNF-alpha, IL-1beta, IL-6, MCP-1, KC, and MIP-2 in bronchoalveolar lavage (BAL) at 5, 24, and 48 h. MCP-1(-/-) mice given 40 mg/ml CASP had significantly decreased survival compared with WT mice (32% vs. 80% survival at 24 h and 0% vs. 72% survival at 48 h). MCP-1(-/-) mice also had decreased survival compared with WT mice for CASP aspirates containing reduced particulate doses of 10-20 mg/ml. MCP-1(-/-) mice given 5 mg/ml CASP had survival similar to WT mice given 40 mg/ml CASP. MCP-1(-/-) mice also had differing responses from WT mice for several inflammatory mediators in BAL (KC or IL-6 depending on the particle dose of CASP and time of injury). Histopathology of WT mice with CASP (40 mg particles/ml) showed microscopic areas of compartmentalization with prominent granuloma formation by 24 h, whereas lung tissue from MCP-1(-/-) mice had severe diffuse pneumonia without granulomas. These results indicate that MCP-1 is important for survival in murine aspiration pneumonitis and appears to act partly to protect uninjured lung regions by promoting isolation and compartmentalization of tissue with active inflammation.     

Surfactant dysfunction and lung injury due to the E. coli virulence factor hemolysin in a rat pneumonia model

This study tests the hypothesis that the virulence factor hemolysin (Hly) expressed by extraintestinal pathogenic Escherichia coli contributes to surfactant dysfunction and lung injury in a rat model of gram-negative pneumonia. Rats were instilled intratracheally with CP9 (wild type, Hly-positive), CP9hlyA (Hly-minus), CP9/pEK50 (supraphysiological Hly), or purified LPS. At 6 h postinfection, rats given CP9 had a decreased percentage content of large surfactant aggregates in cell-free bronchoalveolar lavage (BAL), decreased large aggregate surface activity, decreased Pa(O2)/FiO2) ratio, increased BAL albumin/protein levels, and increased histological evidence of lung injury compared with rats given CP9hlyA or LPS. In addition, rats given CP9/pEK50 or CP9 had decreased large aggregate surface activity, decreased Pa(O2)/FiO2) ratios, and increased BAL albumin/protein levels at 2 h postinfection compared with rats given CP9hlyA. The severity of permeability lung injury based on albumin/protein levels in BAL at 2 h was ordered as CP9/pEK50 > CP9 > CP9hlyA > normal saline controls. Total lung titers of bacteria were increased at 6 h in rats given CP9 vs. CP9hlyA, but bacterial titers were not significantly different at 2 h, indicating that increased surfactant dysfunction and lung injury were associated with Hly as opposed to bacterial numbers per se. Further studies in vitro showed that CP9 could directly lyse transformed pulmonary epithelial cells (H441 cells) but that indirect lysis of H441 cells secondary to Hly-induced neutrophil lysis did not occur. Together, these data demonstrate that Hly is an important direct mediator of surfactant dysfunction and lung injury in gram-negative pneumonia.     

Effects of ventilation on the surfactant system in sepsis-induced lung injury.

The present study examined the effects of mechanical ventilation, with or without positive end-expiratory pressure (PEEP), on the alveolar surfactant system in an animal model of sepsis-induced lung injury. Septic animals ventilated without PEEP had a significant deterioration in oxygenation compared with preventilated values (arterial PO(2)/inspired O(2) fraction 316 +/- 16 vs. 151 +/- 14 Torr; P < 0.05). This was associated with a significantly lower percentage of the functional large aggregates (59 +/- 3 vs. 72 +/- 4%) along with a significantly reduced function (minimum surface tension 17.7 +/- 1.8 vs. 11.8 +/- 3.8 mN/m) compared with nonventilated septic animals (P < 0.05). Sham animals similarly ventilated without PEEP maintained oxygenation, percent large aggregates and surfactant function. With the addition of PEEP, the deterioration in oxygenation was not observed in the septic animals and was associated with no alterations in the surfactant system. We conclude that animals with sepsis-induced lung injury are more susceptible to the harmful effects of mechanical ventilation, specifically lung collapse and reopening, and that alterations in alveolar surfactant may contribute to the development of lung dysfunction.     

Total extracellular surfactant is increased but abnormal in a rat model of gram-negative bacterial pneumonia

An in vivo rat model was used to evaluate the effects of Escherichia coli pneumonia on lung function and surfactant in bronchoalveolar lavage (BAL). Total extracellular surfactant was increased in infected rats compared with controls. BAL phospholipid content in infected rats correlated with the severity of alveolar-capillary leak as reflected in lavage protein levels (R(2) = 0.908, P < 0.0001). Western blotting showed that levels of surfactant protein (SP)-A and SP-D in BAL were significantly increased in both large and small aggregate fractions at 2 and 6 h postinstillation of E. coli. SP-B was also increased at these times in the large aggregate fraction of BAL, whereas SP-C levels were increased at 2 h and decreased at 6 h relative to controls. The small-to-large (S/L) aggregate ratio (a marker inversely proportional to surfactant function) was increased in infected rats with >50 mg total BAL protein. There was a significant correlation (R(2) = 0.885, P < 0.0001) between increasing S/L ratio in BAL and pulmonary damage assessed by total protein. Pulmonary volumes, compliance, and oxygen exchange were significantly decreased in infected rats with >50 mg of total BAL protein, consistent with surfactant dysfunction. In vitro surface cycling studies with calf lung surfactant extract suggested that bacterially derived factors may have contributed in part to the surfactant alterations seen in vivo.     

Bone‐marrow‐derived mesenchymal stem cells inhibit gastric aspiration lung injury and inflammation in rats

Gastric aspiration lung injury is one of the most common clinical events. This study investigated the effects of bone‐marrow‐derived mesenchymal stem cells (BMSCs) on combined acid plus small non‐acidified particle (CASP)‐induced aspiration lung injury. Enhanced green fluorescent protein (EGFP⁺) or EGFP^? BMSCs or 15d‐PGJ₂ were injected via the tail vein into rats immediately after CASP‐induced aspiration lung injury. Pathological changes in lung tissues, blood gas analysis, the wet/dry weight ratio (W/D) of the lung, levels of total proteins and number of total cells and neutrophils in bronchoalveolar lavage fluid (BALF) were determined. The cytokine levels were measured using ELISA. Protein expression was determined by Western blot. Bone‐marrow‐derived mesenchymal stem cells treatment significantly reduced alveolar oedema, exudation and lung inflammation; increased the arterial partial pressure of oxygen; and decreased the W/D of the lung, the levels of total proteins and the number of total cells and neutrophils in BALF in the rats with CASP‐induced lung injury. Bone‐marrow‐derived mesenchymal stem cells treatment decreased the levels of tumour necrosis factor‐α and Cytokine‐induced neutrophil chemoattractant (CINC)‐1 and the expression of p‐p65 and increased the levels of interleukin‐10 and 15d‐PGJ₂ and the expression of peroxisome proliferator‐activated receptor (PPAR)‐γ in the lung tissue in CASP‐induced rats. Tumour necrosis factor‐α stimulated BMSCs to secrete 15d‐PGJ₂. A tracking experiment showed that EGFP⁺ BMSCs were able to migrate to local lung tissues. Treatment with 15d‐PGJ₂ also significantly inhibited CASP‐induced lung inflammation and the production of pro‐inflammatory cytokines. Our results show that BMSCs can protect lung tissues from gastric aspiration injury and inhibit lung inflammation in rats. A beneficial effect might be achieved through BMSC‐derived 15d‐PGJ₂ activation of the PPAR‐γ receptor, reducing the production of proinflammatory cytokines.     

Immunopathology of a two-hit murine model of acid aspiration lung injury

In a two-hit model of acid aspiration lung injury, mice were subjected to nonlethal cecal ligation and puncture (CLP). After 48 h, intratracheal (IT) acid was administered, and mice were killed at several time points. Recruitment of neutrophils in response to acid was documented by myeloperoxidase assay and neutrophil counts in bronchoalveolar lavage (BAL) fluid and peaked at 8 h post-IT injection. Albumin in BAL fluid, an indicator of lung injury, also peaked at 8 h. When the contributions of the two hits were compared, neutrophil recruitment and lung injury occurred in response to acid but were not greatly influenced by addition of another hit. Neutrophil sequestration was preceded by elevations in KC and macrophage inflammatory protein-2alpha in plasma and BAL fluid. KC levels in BAL fluid were higher and peaked earlier than macrophage inflammatory protein-2alpha levels. When KC was blocked with specific antiserum, neutrophil recruitment was significantly reduced, whereas albumin in BAL fluid was not affected. In conclusion, murine KC mediated neutrophil recruitment but not lung injury in a two-hit model of aspiration lung injury.     

Respiratory distress after intratracheal bleomycin: selective deficiency of surfactant proteins B and C

Intratracheal bleomycin in rats is associated with respiratory distress of uncertain etiology. We investigated the expression of surfactant components in this model of lung injury. Maximum respiratory distress, determined by respiratory rate, occurred at 7 days, and surfactant dysfunction was confirmed by increased surface tension of the large-aggregate fraction of bronchoalveolar lavage (BAL). In injured animals, phospholipid content and composition were similar to those of controls, mature surfactant protein (SP) B was decreased 90%, and SP-A and SP-D contents were increased. In lung tissue, SP-B and SP-C mRNAs were decreased by 2 days and maximally at 4--7 days and recovered between 14 and 21 days after injury. Immunostaining of SP-B and proSP-C was decreased in type II epithelial cells but strong in macrophages. By electron microscopy, injured lungs had type II cells lacking lamellar bodies and macrophages with phagocytosed lamellar bodies. Surface activity of BAL phospholipids of injured animals was restored by addition of exogenous SP-B. We conclude that respiratory distress after bleomycin in rats results from surfactant dysfunction in part secondary to selective downregulation of SP-B and SP-C.     

Surfactant phospholipid changes after antigen challenge: a role for phosphatidylglycerol in dysfunction

In asthma, inflammation-mediated surfactant dysfunction contributes to increased airway resistance, but the mechanisms for dysfunction are not understood. To test mechanisms that alter surfactant function, atopic asthmatics underwent endobronchial antigen challenge and bronchoalveolar lavage (BAL). BAL fluids were sequentially separated into cells, surfactant, and supernatant, and multiple end points were analyzed. Each end point's unique relationship to surfactant dysfunction was determined. Our results demonstrate that minimum surface tension (gamma(min)) of surfactant after antigen challenge was significantly increased with a spectrum of responses that included dysfunction in 6 of 13 asthmatics. Antigen challenge significantly altered the partitioning of surfactant phospholipid measured as a decreased ratio of large surfactant aggregates (LA) to small surfactant aggregates (SA), LA/SA ratio. Phosphatidylglycerol (PG) was significantly reduced in the LA of the dysfunctional asthmatic BALs. There was a corresponding significant increase in the ratio of phosphatidylcholine to PG, which strongly correlated with both increased gamma(min) and decreased LA/SA. Altered surfactant phospholipid properties correlated with surfactant dysfunction as well or better than either increased eosinophils or protein. Secretory phospholipase activity, measured in vitro, increased after antigen challenge and may explain the decrease in surfactant PG. In summary, alteration of phospholipids, particularly depletion of PG, in the LA of surfactant may be an important mechanism in asthma-associated surfactant dysfunction.     

Low-dose carbon monoxide treatment attenuates early pulmonary neutrophil recruitment after acid aspiration

Exogenous carbon monoxide (CO) has anti-inflammatory and cytoprotective properties that show promise in the treatment of numerous pulmonary diseases. However, the effectiveness of CO in acute pulmonary injury associated with direct lung insult has not been shown conclusively. The purpose of this study was to determine if exogenous CO would modulate the pulmonary inflammation and lung injury that develops after acid aspiration. Groups of mice were given intratracheal (IT) injections of either saline or an acidic solution. After the IT injection, some of the mice in each group were allowed to spontaneously inhale CO (500 ppm). Mice exposed to CO for 6 h after IT acid had a significant decrease in bronchoalveolar lavage (BAL) fluid neutrophil counts and in histological evidence of lung injury. These results could not be explained by changes in BAL fluid chemokine levels or altered CXCR2 expression. The reduced neutrophil recruitment was associated with a decrease in the percentage of peripheral blood neutrophils expressing CD11b protein. However, within 24 h, the BAL neutrophil counts increased and were not different from animals without CO exposure. In addition, indices of vascular integrity were not different between animals with acid aspiration regardless of CO exposure at the later time point. These results showed that CO can modulate the early development of acute lung inflammation in this model of acid aspiration. Although these effects were eventually overwhelmed, the results suggest that CO may have efficacy during the initial treatment of aspiration lung injury.     

Platelet-activating factor (PAF)-acetylhydrolase and PAF-like compounds in the lung: effects of hyperoxia.

Platelet-activating factor (PAF)-acetylhydrolase is the enzyme modulating in tissues and biological fluids the concentration of the proinflammatory factors PAF and PAF-like oxidation products of phospholipids (PAF-like compounds). We investigated whether there is a relation between PAF-acetylhydrolase activity and the concentration of PAF-like compounds in bronchoalveolar lavage (BAL). We found that alveolar type II cells are an additional source of PAF-acetylhydrolase in BAL beside macrophages. Secretion of PAF-acetylhydrolase was stimulated by phorbol ester in alveolar type II cells but not in macrophages. Studies in BAL suggested that secreted PAF-acetylhydrolase was bound to alveolar surfactant. Exposure of rats to high oxygen concentration reduced the activity of PAF-acetylhydrolase in BAL and macrophages, but not in plasma or alveolar type II cells. In contrast, hyperoxia increased the concentration of PAF-like-compounds, lipid hydroperoxides and malonedialdehyde in plasma but not in BAL. Therefore, we conclude that neither the oxidant-induced decrease of the PAF-acetylhydrolase activity nor the direct peroxidation of surfactant lipids in the alveoli provide a likely mechanism for hyperoxia-induced lung injury. Instead, lung injury is apparently caused by lipid peroxidation in plasma rather than by high oxygen pressure in the alveoli.     

Effect of exogenous surfactant instillation on experimental acute lung injury

Pulmonary surfactant replacement has previously been shown to be effective in the human neonatal respiratory distress syndrome. The value of surfactant replacement in models of acute lung injury other than quantitative surfactant deficiency states is, however, uncertain. In this study an acute lung injury model using rats with chronic indwelling arterial catheters, injured with N-nitroso-N-methylurethane (NNNMU), has been developed. The NNNMU injury was found to produce hypoxia, increased mortality, an alveolitis, and alterations in the pulmonary surfactant system. Alterations of surfactant obtained by bronchoalveolar lavage included a reduction in the phospholipid-to-protein ratio, reduced surface activity, and alterations in the relative percentages of the individual phospholipids compared with controls. Treatment of the NNNMU-injured rats with instilled exogenous surfactant (Survanta) improved oxygenation; reduced mortality to control values; and returned the surfactant phospholipid-to-protein ratio, surface activity, and, with the exception of phosphatidylglycerol, the relative percentages of individual surfactant phospholipids to control values.     

Acid aspiration increases sensitivity to increased ambient oxygen concentrations

Previously we have demonstrated that prolonged exposure to 100% ambient oxygen leads to a marked loss in functional lung volume and lung compliance, hypoxemia, and surfactant system abnormalities similar to acute respiratory distress syndrome (ARDS). However, 50% oxygen administration is believed to be safe in most clinical settings. In the present study, we have evaluated the effects of a 24-h exposure to 50% oxygen in rabbits immediately following experimental gastric acid aspiration. Mild hypoxemia, but no changes in mortality, lung volume, lung compliance, surfactant metabolism, or edema formation occurred after 24 h of normoxia postacid aspiration. Conversely, a relatively short (24-h) exposure to 50% oxygen after acid aspiration results in increased pulmonary edema, physical signs of respiratory distress, and mortality, as well as decreased arterial oxygenation, lung volume, lung compliance, and type II alveolar cell surfactant synthesis. These results suggest that acid aspiration alters the "set point" for oxygen toxicity, possibly by "priming" cells through activation of inflammatory pathways. This pathogenic mechanism may contribute to the progression of aspiration pneumonia to ARDS.     

Alterations to surfactant precede physiological deterioration during high tidal volume ventilation

Lung injury due to mechanical ventilation is associated with an impairment of endogenous surfactant. It is unknown whether this impairment is a consequence of or an active contributor to the development and progression of lung injury. To investigate this issue, the present study addressed three questions: Do alterations to surfactant precede physiological lung dysfunction during mechanical ventilation? Which components are responsible for surfactant's biophysical dysfunction? Does exogenous surfactant supplementation offer a physiological benefit in ventilation-induced lung injury? Adult rats were exposed to either a low-stretch [tidal volume (Vt) = 8 ml/kg, positive end-expiratory pressure (PEEP) = 5 cmH2O, respiratory rate (RR) = 54-56 breaths/min (bpm), fractional inspired oxygen (Fi(O2)) = 1.0] or high-stretch (Vt = 30 ml/kg, PEEP = 0 cmH2O, RR = 14-16 bpm, Fi(O2) = 1.0) ventilation strategy and monitored for either 1 or 2 h. Subsequently, animals were lavaged and the composition and function of surfactant was analyzed. Separate groups of animals received exogenous surfactant after 1 h of high-stretch ventilation and were monitored for an additional 2 h. High stretch induced a significant decrease in blood oxygenation after 2 h of ventilation. Alterations in surfactant pool sizes and activity were observed at 1 h of high-stretch ventilation and progressed over time. The functional impairment of surfactant appeared to be caused by alterations to the hydrophobic components of surfactant. Exogenous surfactant treatment after a period of high-stretch ventilation mitigated subsequent physiological lung dysfunction. Together, these results suggest that alterations of surfactant are a consequence of the ventilation strategy that impair the biophysical activity of this material and thereby contribute directly to lung dysfunction over time.     

The role of iNOS inhibitors on lung injury induced by gastrointestinal decontamination agents aspiration

Aspiration is a devastating complication during decontamination procedure in poisoning patients. We have investigated whether S-methylisothiourea protects different pulmonary aspiration gastrointestinal decontamination agent-induced lung injury in rats. Forty-two male Sprague-Dawley rats were assigned to one of six groups (n = 7): normal saline, activated charcoal, polyethylene glycol, normal saline + S-methylisothiourea treated activated charcoal + S-methylisothiourea treated and polyethylene glycol + S-methylisothiourea treated. Normal saline, activated aharcoal and polyethylene glycol were instilled into the lungs. The rats received S-methylisothiourea i.p twice daily for 7 days. Serum surfactant protein D, oxidative stress products and inducible nitric oxide synthase expression in the lung were investigated. The aspiration of activated charcoal significantly increased all histopathological scores (P < 0.01). Only peribronchial inflammatory cell infiltration, alveolar edema, and alveolar histiocytes were increased in the polyethylene glycol groups as compared to the normal saline group (P < 0.05). Pulmonary aspiration increased serum malondialdehyde (P < 0.001), and surfactant protein D (P < 0.05) levels and decreased serum superoxide dismutase levels (P < 0.05). S-methylisothiourea treatment decreased all histopathological scores in the activated charcoal treated S-methylisothiourea group (P < 0.01) and only decreased alveolar edema and alveolar histiocytes in the polyethylene glycol-treated S-methylisothiourea group (P < 0.05). S-methylisothiourea treatment reduced elevated oxidative factors, inducible nitric oxide synthase activity and serum surfactant protein D levels. Our findings showed that S-methylisothiourea may be a protective drug against Activated Charcoal and Polyethylene Glycol-induced lung injury.     

Protective effects of elevated endogenous surfactant pools to injurious mechanical ventilation

Depletion of alveolar macrophages (AM) leads to an increase in endogenous surfactant that lasts several days beyond the repletion of AM. Furthermore, impairment to the endogenous pulmonary surfactant system contributes to ventilation-induced lung injury. The objective of the current study was to determine whether increased endogenous surfactant pools induced via AM depletion was protective against ventilation-induced lung injury. Adult rats were intratracheally instilled with either control or dichloromethylene diphosphonic acid (DMDP) containing liposomes to deplete AMs and thereby increase endogenous surfactant pools. Either 3 or 7 days following instillation, rats were exposed to 2 h of injurious ventilation using either an ex vivo or in vivo ventilation protocol and were compared with nonventilated controls. The measured outcomes were oxygenation, lung compliance, lavage protein, and inflammatory cytokine concentrations. Compared with controls, the DMDP-treated animals had significantly reduced AM numbers and increased surfactant pools 3 days after instillation. Seven days after instillation, AM numbers had returned to normal, but surfactant pools were still elevated. DMDP-treated animals at both time points exhibited protection against ventilation-induced lung injury, which included superior physiological parameters, lower protein leakage, and lower inflammatory mediator release into the air space, compared with animals not receiving DMDP. It is concluded that DMDP-liposome administration protects against ventilation-induced lung injury. This effect appears to be due to the presence of elevated endogenous surfactant pools.     

Inhibition of surfactant activity by Pneumocystis carinii organisms and components in vitro

This study examines the direct inhibitory effects of Pneumocystis carinii (Pc) organisms and chemical components on the surface activity and composition of whole calf lung surfactant (WLS) and calf lung surfactant extract (CLSE) in vitro. Incubation of WLS suspensions with intact Pc organisms (10(7) per milligram of surfactant phospholipid) did not significantly alter total phospholipid levels or surfactant protein A content. Incubation with intact Pc organisms also did not impair dynamic surface tension lowering in suspensions of WLS or centrifuged large surfactant aggregates on a bubble surfactometer (37 degrees C, 20 cycles/min, 0.5 and 2.5 mg phospholipid/ml). However, exposure of WLS or CLSE to disrupted (sonicated) Pc organisms led to severe detriments in activity, with minimum surface tensions of 17-19 mN/m vs. <1 mN/m for surfactants alone. Extracted hydrophobic chemical components from Pc (98.8% lipids, 0.1 mM) reduced the surface activity of WLS and CLSE similarly to sonicated Pc organisms, whereas extracted hydrophilic chemical components from Pc (primarily proteins) had only minor effects on surface tension lowering. These results indicate that in addition to surfactant dysfunction induced by inflammatory lung injury and edema-derived inhibitors in Pc pneumonia, disrupted Pc organisms in the alveolar lumen also have the potential to directly inhibit endogenous and exogenous lung surfactants in affected patients.     

The effect of diet-induced serum hypercholesterolemia on the surfactant system and the development of lung injury

Acute respiratory distress syndrome (ARDS) is a pulmonary disorder associated with alterations to the pulmonary surfactant system. Recent studies showed that supra-physiological levels of cholesterol in surfactant contribute to impaired function. Since cholesterol is incorporated into surfactant within the alveolar type II cells which derives its cholesterol from serum, it was hypothesized that serum hypercholesterolemia would predispose the host to the development of lung injury due to alterations of cholesterol content in the surfactant system.Wistar rats were randomized to a standard lab diet or a high cholesterol diet for 17–20 days. Animals were then exposed to one of three models of lung injury: i) acid aspiration ii) ventilation induced lung injury, and iii) surfactant depletion. Following physiological monitoring, lungs were lavaged to obtain and analyze the surfactant system.The physiological results showed there was no effect of the high cholesterol diet on the severity of lung injury in any of the three models of injury. There was also no effect of the diet on surfactant cholesterol composition. Rats fed a high cholesterol diet had a significant impairment in surface tension reducing capabilities of isolated surfactant compared to those fed a standard diet exposed to the surfactant depletion injury. In addition, only rats that were exposed to ventilation induced lung injury had elevated levels of surfactant associated cholesterol compared to non-injured rats.It is concluded that serum hypercholesterolemia does not predispose rats to altered surfactant cholesterol composition or to lung injury. Elevated cholesterol within surfactant may be a marker for ventilation induced lung damage.     

Altered function of pulmonary surfactant in fatty acid lung injury

To determine whether acute fatty acid lung injury impairs pulmonary surfactant function, we studied anesthetized ventilated rabbits given oleic acid (55 mg/kg iv, n = 11) or an equivalent volume of saline (n = 8). Measurements of pulmonary mechanics indicated a decrease in dynamic compliance within 5 min of injury and a decrease in lung volume that was disproportionately large at low pressures, consistent with diminished surfactant activity in vivo. Bronchoalveolar lavage fluid obtained 1 h after injury had significantly increased erythrocytes and total leukocytes, largely polymorphonuclear cells. The phospholipid content and composition of the cell-free fraction had only minor changes from those of controls, but the protein content was increased 35-fold. Measurements of lavage surface activity in vitro showed an increase in average minimum surface tension from 1.3 +/- 0.4 (SE) dyn/cm in controls to 20.2 +/- 3.9 dyn/cm in injured animals. The alterations in static pressure-volume curves and decrease in lavage surface activity suggest a severe alteration of surfactant function in this form of lung injury that occurs despite the presence of normal amounts of surfactant phospholipids.     

Determinants of surfactant function in acute lung injury and early recovery

Relationships between lung function and surfactant function and composition were examined during the evolution of acute lung injury in guinea pigs. Lung mechanics and gas exchange were assessed 12, 24, or 48 h after exposure to nebulized lipopolysaccharide (LPS). Bronchoalveolar lavage (BAL) fluid was processed for phospholipid and protein contents and surfactant protein (SP) A and SP-B levels; surfactant function was measured by pulsating bubble surfactometry. Lung elastance, tissue resistance, and arterial-alveolar gradient were moderately elevated by 12 h after LPS exposure and continued to increase over the first 24 h but began to recover between 24 and 48 h. Similarly, the absolute amount of 30,000 g pelleted SP-A and SP-B, the phospholipid content of BAL fluid, and surfactant function declined over the first 24 h after exposure, with recovery between 24 and 48 h. BAL fluid total protein content increased steadily over the first 48 h after LPS nebulization. In this model of acute lung injury, the intra-alveolar repletion of surfactant components in early recovery led to improved surfactant function despite the presence of potentially inhibitory plasma proteins.     

Influence of DMT1 and iron status on inflammatory responses in the lung

Divalent metal transporter 1 (DMT1) is the major iron transporter responsible for duodenal dietary iron absorption and is required for erythropoiesis. Recent studies suggest that loss of DMT1 activity could be involved in metal-related lung injury, but little is known about the effects of iron status and DMT1 function on pulmonary inflammation. To better define the role of DMT1 and iron status in pulmonary inflammatory responses, we performed bronchoalveolar lavage (BAL) following intratracheal instillation of lipopolysaccharide (LPS) to the Belgrade rat, an animal model deficient in DMT1 function. In the basal state, the BAL fluid of Belgrade rats had more macrophages and higher lactate dehydrogenase, myeloperoxidase, albumin, and hemoglobin levels compared with heterozygote control rats. Following LPS instillation, the macrophage fraction relative to total BAL cell content and levels of albumin and IgM were increased in Belgrade rats compared with controls. In contrast, heterozygote Belgrade rats made anemic by diet-induced iron deficiency exhibited attenuated inflammatory responses to LPS. These combined results show that pulmonary inflammation can be modified by both DMT1 and iron status. Loss of DMT1 alters pulmonary responses necessary for lung homeostasis in the basal state and enhances LPS-induced inflammation and therefore would contribute to progression of lung injury.