Surface and tissue forces, surfactant protein A, and the phospholipid components of pulmonary surfactant in bleomycin-induced pulmonary fibrosis in the rat

Notch1 Induces Defective Epithelial Surfactant Processing and Pulmonary Fibrosis

Rationale: Although type II alveolar epithelial cells (AEC2s) are chronically injured in idiopathic pulmonary fibrosis (IPF), they contribute to epithelial regeneration in IPF. Objectives: We hypothesized that Notch signaling may contribute to AEC2 proliferation, dedifferentiation characterized by loss of surfactant processing machinery, and lung fibrosis in IPF. Methods: We applied microarray analysis, kinome profiling, flow cytometry, immunofluorescence analysis, western blotting, quantitative PCR, and proliferation and surface activity analysis to study epithelial differentiation, proliferation, and matrix deposition in vitro (AEC2 lines, primary murine/human AEC2s), ex vivo (human IPF-derived precision-cut lung slices), and in vivo (bleomycin and pepstatin application, Notch1 [Notch receptor 1] intracellular domain overexpression). Measurements and Main Results: We document here extensive SP-B and -C (surfactant protein-B and -C) processing defects in IPF AEC2s, due to loss of Napsin A, resulting in increased intra-alveolar surface tension and alveolar collapse and induction of endoplasmic reticulum stress in AEC2s. In vivo pharmacological inhibition of Napsin A results in the development of AEC2 injury and overt lung fibrosis. We also demonstrate that Notch1 signaling is already activated early in IPF and determines AEC2 fate by inhibiting differentiation (reduced lamellar body compartment, reduced capacity to process hydrophobic SP) and by causing increased epithelial proliferation and development of lung fibrosis, putatively via altered JAK (Janus kinase)/Stat (signal transducer and activator of transcription) signaling in AEC2s. Conversely, inhibition of Notch signaling in IPF-derived precision-cut lung slices improved the surfactant processing capacity of AEC2s and reversed fibrosis. Conclusions: Notch1 is a central regulator of AEC2 fate in IPF. It induces alveolar epithelial proliferation and loss of Napsin A and of surfactant proprotein processing, and it contributes to fibroproliferation.

Revisiting the role of pulmonary surfactant in chronic inflammatory lung diseases and environmental exposure

Pulmonary surfactant is a crucial and dynamic lung structure whose primary functions are to reduce alveolar surface tension and facilitate breathing. Though disruptions in surfactant homeostasis are typically thought of in the context of respiratory distress and premature infants, many lung diseases have been noted to have significant surfactant abnormalities. Nevertheless, preclinical and clinical studies of pulmonary disease too often overlook the potential contribution of surfactant alterations - whether in quantity, quality or composition - to disease pathogenesis and symptoms. In inflammatory lung diseases, whether these changes are cause or consequence remains a subject of debate. This review will outline 1) the importance of pulmonary surfactant in the maintenance of respiratory health, 2) the diseases associated with primary surfactant dysregulation, 3) the surfactant abnormalities observed in inflammatory pulmonary diseases and, finally, 4) the available research on the interplay between surfactant homeostasis and smoking-associated lung disease. From these published studies, we posit that changes in surfactant integrity and composition contribute more considerably to chronic inflammatory pulmonary diseases and that more work is required to determine the mechanisms underlying these alterations and their potential treatability.

TGF beta inhibits expression of SP-A, SP-B, SP-C, but not SP-D in human alveolar type II cells

TGF beta is a multifunctional cytokine that regulates alveolar epithelial cells as well as immune cells and fibroblasts. TGF beta inhibits surfactant protein A, B and C expression in fetal human lung and can inhibit type II cell proliferation induced by FGF7 (KGF). However, little is known about direct effects of TGF beta on adult human type II cells. We cultured alveolar type II cells under air/liquid interface conditions to maintain their state of differentiation with or without TGF beta. TGF beta markedly decreased expression of SP-A, SP-B, SP-C, fatty acid synthase, and the phospholipid transporter ABCA3. However, TGF beta increased protein levels of SP-D with little change in mRNA levels, indicating that it is regulated independently from other components of surfactant. TGF beta is a negative regulator of both the protein and the phospholipid components of surfactant. TGF beta did not induce EMT changes in highly differentiated human type II cells. SP-D is an important host defense molecule and regulated independently from the other surfactant proteins. Taken together these data are the first report of the effect of TGF beta on highly differentiated adult human type II cells. The effects on the surfactant system are likely important in the development of fibrotic lung diseases.

Alveolar Proteinosis and Phospholipidoses of the Lungs

Three pulmonary disease conditions result from the accumulation of phospholipids in the lung. These conditions are the human lung disease known as pulmonary alveolar proteinosis, the lipoproteinosis that arises in the lungs of rats during acute silicosis, and the phospholipidoses induced by numerous cationic amphiphilic therapeutic agents. In this paper, the status of phospholipid metabolism in the lungs during the process of each of these lung conditions has been reviewed and possible mechanisms for their establishment are discussed. Pulmonary alveolar proteinosis is characterized by the accumulation of tubular myelin-like multilamellated structures in the alveoli and distal airways of patients. These structures appear to be formed by a process of spontaneous assembly involving surfactant protein A and surfactant phospholipids. Structures similar to tubular myelin-like multilamellated structures can be seen in the alveoli of rats during acute silicosis and, as with the human condition, both surfactant protein A and surfactant phospholipids accumulate in the alveoli. Excessive accumulation of surfactant protein A and surfactant phospholipids in the alveoli could arise from their overproduction and hypersecretion by a subpopulation of Type II cells that are activated by silica, and possibly other agents. Phospholipidoses caused by cationic amphiphilic therapeutic agents arise as a result of their inhibition of phospholipid catabolism. Inhibition of phospholipases results in the accumulation of phospholipids in the cytoplasm of alveolar macrophages and other cells. While inhibition of phospholipases by these agents undoubtedly occurs, there are many anomalous features, such as the accumulation of extracellular phospholipids and surfactant protein A, that cannot be accounted for by this simplistic hypothesis.

Pneumoproteins as markers of paraquat lung injury: a clinical case

OBJECTIVE

To describe the changes in lung-specific secretory proteins in biological fluids in a fatal case of paraquat ingestion and to present immunostaining data obtained on postmortem lung tissue specimens.

METHODS

A 20-year-old man committed suicide by ingesting 100ml of a 20% paraquat solution. Surfactant associated proteins A (SP-A), B (SP-B) and Clara cell 16kDa protein (CC16) were determined in the serum and on broncho-alveloar lavage performed 18h after admission. Renal failure progressed rapidly and the patient died from refractory hypoxia. Immunostaining studies using antibodies directed against CC16, SP-A and SP-B were performed on postmortem lung tissue specimens.

RESULTS

Serum CC16 seemed to increase gradually with the progression of renal impairment. Serum SP-A and SP-B levels increased before any significant changes in pulmonary gas exchanges. The immunostaining study showed that the labeling for SP-A and SP-B was reduced or absent following paraquat toxicity, while Clara cells were relatively preserved.

CONCLUSIONS

The elevation of serum CC16 with paraquat toxicity is probably mainly related to a reduced renal clearance. The increase of serum SP-A and SP-B could reflect an increased lung to blood leakage, independently of the alteration of the renal function.

Phospholipid concentration in lung lavage fluid as biomarker for pulmonary fibrosis

Pulmonary surfactant comprised primarily of phospholipids is a phospholipid-protein complex synthesized by type II alveolar epithelial cells or Clara cells and secreted to the pulmonary alveoli. As changes have been found in phospholipid concentrations in the bronchoalveolar lavage fluid (BALF) of patients with pulmonary fibrosis, phospholipid is considered to be involved in the process of fibrois/fibrotic process. Therefore, we made a crystalline silica rat model and measured phospholipid concentrations in lung lavage fluid in order to study the relationship of phospholipid to particle-induced pulmonary fibrosis. Eight-week-old Wistar male rats (n = 35) were injected with 2 mg crystalline silica particles suspended in 0.4 ml physiological saline. Rats in the control group (n = 35) were injected with physiological saline only. There were 7 rats in each of the ten subgroups. Rats were sacrificed and dissected at 3 days, 1 wk, 1 mo, 3 mo, and 6 mo after injection. Bronchoalveolar lavage was conducted on bronchoalveoli recovered from the right lung of each rat, the lavage fluid was centrifuged, and the supernatant was used to measure phospholipid concentration. The results were compared with previously reported inflammation scores. Phospholipid concentrations in lung lavage fluid for the exposed group showed a statistically significant increase compared to the control group throughout the observation period. Moreover, when compared to histopathologically examined inflammation scores, a positive correlation was found between the two. Judging from the facts that phospholipid concentrations in lung lavage fluid increased and that this increase correlated with the severity of inflammation, this experiment indicated that phospholipids are involved in particle-induced lung disorders.

Changes in pulmonary surfactant function and composition in bleomycin-induced pneumonitis and fibrosis

Bleomycin is a widely accepted cancer drug but may induce life-threatening interstitial lung disease in a subset of patients. We evaluated the effect of bleomycin administration on pulmonary surfactant function and composition in rabbit lungs. In order to obtain a uniform response to bleomycin, aerosol technology was employed for bronchoalveolar delivery of 1.8 U/kg b.w. bleomycin. On days 4, 8, 16, 24, 32, and 64 after challenge, bronchoalveolar lavages were performed. Sham-aerosolized rabbits served as controls. In the early acute respiratory distress syndrome (ARDS)-like post-bleomycin period (4-16 days), marked loss of surface activity of the large surfactant aggregate (LA) fraction of surfactant was noted. In parallel, reduced percentages of LA, but only minor changes in surfactant apoproteins (SP)-A, SP-B, and SP-C, were encountered. Analysis of the surfactant lipid profile showed impressively enhanced cholesterol and significantly decreased phosphatidylglycerol (PG) levels. The relative content of dipalmitoyl-PC (DPPC) was slightly increased, and a several-fold increase within the 1-O-alkyl-2-acyl subclass of PC was observed. During the prolonged fibroproliferative period, a highly significant downregulation of SP-B and SP-C levels was observed. This was paralleled by an upregulation of the total extracellular phospholipid pool, with a far-reaching normalization of the (phospho)-lipid profile. The biophysical surfactant function never fully normalized within the 64-day observation period. In conclusion, bleomycin caused marked abnormalities of pulmonary surfactant, with the profile of changes being different between the early ARDS and the late fibrotic phase.

Prevention of Bleomycin-induced Lung Fibrosis by Aerosolization of Heparin or Urokinase in Rabbits

Bleomycin is a well known fibrogenic agent, provoking an initial adult respiratory distress syndrome-like injury with subsequent strong fibroproliferative response. Severe abnormalities of the alveolar surfactant system, which may be linked to the appearance of alveolar fibrin deposition, have been implicated in the pathogenetic sequence of events. Using a model of standardized aerosol delivery of 1.8 U bleomycin/kg body weight in rabbits, we investigated the influence of repetitive nebulization of heparin or urokinase-type plasminogen activator (u-PA) on the development of lung fibrosis. In an "early" (Days 2-12 postbleomycin) or "late" (Days 14-24 post-bleomycin) treatment protocol, approximately 3,500 U heparin or approximately 6,500 U u-PA was delivered to the bronchoalveolar space. Within four weeks, the bleomycin challenge provoked severe pulmonary fibrosis with reduction of lung compliance, marked increase in soluble collagen (bronchoalveolar lavage fluid) and hydroxyproline content (lung tissue), a typical reticular fibrosis pattern on high-resolution computed tomography, and typical histologic findings. Therapeutic intervention resulted in a far-reaching normalization of compliance, suppression of soluble collagen and hydroxyproline accumulation, and virtual abrogation of the computed tomography scan and histologic features of lung fibrosis, with most prominent effects seen in the early heparin and late u-PA administration. No bleeding complications occurred. These findings strongly support the concept that alveolar fibrin generation is an important event in the development of postbleomycin lung fibrosis. "Compartmentalized" anticoagulation and/or fibrinolysis via inhalational deposition of interventional agents in the alveolar compartment may thus offer a new therapeutic strategy for prevention of fibrosis.

Serum SP-D is a marker of lung injury in rats

Pulmonary surfactant protein D (SP-D) is expressed in alveolar type II and bronchiolar epithelial cells and is secreted into alveoli and conducting airways. However, SP-D has also been measured in serum and is increased in patients with acute respiratory distress syndrome, pulmonary fibrosis, and alveolar proteinosis. To demonstrate that SP-D can be measured in rat serum, we instilled rats with keratinocyte growth factor, which produces type II cell hyperplasia and an increase in SP-D in bronchoalveolar lavage fluid (BALF). To evaluate serum SP-D as a biomarker of lung injury, we examined several injury models. In rats treated with 1 unit of bleomycin, serum SP-D was elevated on days 3, 7, 14, and 28 after instillation, and SP-D mRNA was increased in focal areas as detected by in situ hybridization. However, there was no increase in whole lung SP-D mRNA when the expression was normalized to whole lung 18S rRNA. After instillation of 2 units of bleomycin, the serum levels of SP-D were higher, and SP-D was also increased in BALF and lung homogenates. In another model of subacute injury, serum SP-D was increased in rats treated with paraquat plus oxygen. Finally to evaluate acute lung injury, we instilled rats with HCl; SP-D was increased at 4 h after instillation. Our data indicate that serum SP-D may be a useful indicator of lung injury and type II cell hyperplasia in rats.

Maintenance of surfactant protein A and D secretion by rat alveolar type II cells in vitro

Secretion of surfactant proteins A and D (SP-A and SP-D) has been difficult to study in vitro because a culture system for maintaining surfactant secretion has been difficult to establish. We evaluated several growth factors, corticosteroids, rat serum, and a fibroblast feeder layer for the ability to produce and maintain a polarized epithelium of type II cells that secretes SP-A and SP-D into the apical medium. Type II cells were plated on a filter insert coated with an extracellular matrix and were cultured at an air-liquid interface. Keratinocyte growth factor (KGF) stimulated type II cell proliferation and secretion of SP-A and SP-D more than fibroblast growth factor-10 (FGF-10), hepatocyte growth factor (HGF), or heparin-binding epidermal-like growth factor (HB-EGF). Cells cultured in the presence of KGF and rat serum with or without fibroblasts had high surfactant protein mRNA levels and exhibited a high level of SP-A and SP-D secretion. Dexamethasone inhibited type II cell proliferation but increased expression of SP-B. In the presence of KGF, rat serum, and dexamethasone, the mRNAs for the surfactant proteins were maintained at high levels. Secretion of SP-A and SP-D was found to be independent of phospholipid secretion.

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.

Alterations in surfactant neutral lipid composition during the development of bleomycin-induced pulmonary fibrosis

The purpose of this investigation was to correlate changes in the neutral lipids of pulmonary surfactant with previously observed changes in surfactant phospholipids and lung compliance in the rat model of bleomycin-induced pulmonary fibrosis. Bronchoalveolar lavage fluid (BAL) obtained at 0, 1, 3, 7, 14, 30 and 120 days after transtracheal instillation of bleomycin was used as a source of surfactant lipids. The mean concentration of neutral lipids in normal BAL was 439 nmol/lung and was composed of 55% cholesterol (CHO), 27% cholesterol ester (CE) and 19% free fatty acids (FFA). CHO was elevated at 1 day, reaching a maximum 4-fold increase in concentration at 14 days before subsiding to normal at 120 days. In contrast to CHO, CE and FFA were significantly reduced at 1 day after bleomycin with FFA below detectable levels. However, both these species were twice normal levels at 3-30 days before returning to normal at 120 days. The fatty acid composition of CE did not change; however, unsaturated fatty acids were significantly increased in FFA between 3 and 120 days. The data indicate that there are significant alterations in the neutral lipid composition of pulmonary surfactant at various stages of bleomycin induced lung injury. The significance of these changes are not fully understood; however, the possibility exists that an abnormal surfactant results which in turn affects lung function.

Altered regulation of surfactant phospholipid and protein A during acute pulmonary inflammation

Biochemical changes in the pulmonary surfactant system caused by exposure to toxicants are often accompanied by an influx of inflammatory cells into the lungs. We have investigated the possibility that the inflammatory and surfactant biochemical effects might be connected. Co-treatment with dexamethasone, a synthetic anti-inflammatory glucocorticoid, mitigated the increases in free cells and total intracellular surfactant phospholipid normally seen in animals given silica alone, suggesting a relationship between the free cell population of the alveoli and the surfactant system during alveolitis. Furthermore, we have investigated whether induction of the surfactant system is a universal response to alveolar inflammation. Inflammation was induced in the lungs by intratracheal injections of titanium dioxide, silica, bleomycin or lipopolysaccharide (LPS) suspended in isotonic saline. Inflammatory cell and surfactant responses were measured at 3 days and 14 days following injection. There was a distinct alveolar inflammatory cell profile following administration of each agent, at each time point, indicating a dynamic inflammatory cell population during the course of the study. Furthermore, surfactant phospholipid and protein A (SP-A) pools exhibited unique responses to the inflammatory agents. Only silica-treated lungs maintained elevated levels of surfactant phospholipids and SP-A throughout the course of the experiment. We conclude that both the surfactant components and the inflammatory cell population of the alveoli undergo dynamic changes following treatment with these inflammatory agents and that activation of the surfactant system is not a universal response to alveolar inflammation, since surfactant components were not always elevated during times of increased alveolar cellularity. The unique inflammatory cell infiltrate elicited by silica is of particular interest in that surfactant components were elevated throughout the course of the experiment in this group. Indeed, we have shown that the size of the intracellular pool of surfactant is directly proportional to the number of polymorphonuclear leukocytes but not alveolar macrophages or lymphocytes in the alveoli following silica treatment. Finally, our data suggest that the phospholipid and SP-A components of surfactant respond differentially to the pulmonary toxicants in this study.

Monoclonal antibodies to surfactant protein D: evaluation of immunoreactivity in normal rat lung and in a radiation-induced fibrosis model

This report describes the development of a new panel of monoclonal antibodies established after immunization of mice with purified surfactant protein D of the rat. To enhance the detection of SP-D in formalin- or Schaffer-fixed samples, immunohistochemistry was performed by using microwave pretreatment of paraffin sections. Using these new antibodies that bind to type II epithelial cells, Clara cells, and alveolar macrophages, the responses of lung parenchymal cells were examined in a radiation-induced fibrosis model. Increased accumulation of extracellular SP-D in the alveolar space was found. Double staining with anti-surfactant protein A antibodies revealed different Clara cell populations containing one or both types of surfactant proteins.

Toxicological investigations on silicon carbide. 2. In vitro cell tests and long term injection tests

Silicon carbide (SiC) dust and other dusts for comparison were injected intratracheally at a high dose (50 mg) into rats and the response of the lungs and the lymph nodes was studied after an appropriate experimental period. The indices studied were: histological changes in the lung and lymph nodes, organ weights, the formation of collagenous fibres, and the appearance of quartz typical areas. According to several epidemiological investigations and previous experimental animal studies, SiC produces silicogenic (fibrogenic) effects. No changes in the tissues studied in terms of damaging fibrogenic effects could be found after eight months (first series) and three and 12 months (second series). In particular, the histological findings and the absence of quartz typical areas as well as the quantitative determination of collagen fibres show that SiC had no harmful effects on tissues. Based on these results, the extent to which other exposures during the production of SiC can be responsible for the established radiological alterations is discussed. Without doubt the following may be confounders: SiC fibres, crystalline SiO2 (quartz, cristobalite, tridymite), and possibly gaslike emissions (SO2). From the hygienic medical point of view the workplaces during SiC manufacture should be examined carefully. The substance SiC dust as such can be considered as inert from the experimental results based on qualitative and extremely sensitive procedures. A revision of the present threshold value for SiC in ther German MAK list is called for.

Toxicological investigations on silicon carbide. 1. Inhalation studies

The question of lung damage as a result of exposure to silicon carbide (SiC) was investigated by inhalation experiments to obtain information on the qualitative response of lung tissue to the test substance (SiC). For comparison, quartz, kaolinite, and tempered clay dusts were used. The indices for the effects of the dusts studied were organ weights, numbers of bronchoalveolar cells, lung surfactant phospholipid concentrations including subfractions, and lung clearance. Exposure to the test samples was carried out according to the Essen inhalation model in two independent series. The results of the two series were similar: Compared with sham controls, exposure to SiC did not affect the indices studied. Even at a low dose (a quarter of the SiC dose) quartz gave pronounced deviations in all indices. In particular, an increase in granulocytes indicated toxic properties of the dust. The long term elimination of quartz from the lung was worse than that of SiC. The kaolinite and tempered clay dusts were intermediate between SiC and quartz based on several of the indices studied. It is concluded that SiC is deposited practically inert in the lung.

Surfactant-associated proteins (SP-A, SP-B) are increased proportionally to alveolar phospholipids in sheep silicosis

In silicosis, a profile of surfactant overproduction associated with type II epithelial cell hypertrophy and hyperplasia has been documented. In addition, enhanced accumulation of surfactant-associated protein A (SP-A) has been seen in the rat model of acute silicosis by 2 independent groups, but the exact role of these surfactant changes in silicosis are incompletely understood. In this study we measured in lung lavage surfactant total phospholipids and surfactant-associated proteins A and B (SP-A, SP-B). In addition, the surface tension reducing activities of lipid extracts of bronchoalveolar lavage fluids (BALFs) in the sheep silicosis model were examined using a pulsating bubble surfactometer. Two groups of animals (n = 18) were investigated: a saline-exposed (PBS-PBS) group and a silica-exposed (Si-PBS) group. Total surfactant phospholipids in the silicotic sheep increased 2-fold over the control sheep values (p < 0.05), as previously reported. In addition, we found a substantial rise in total surfactant-associated proteins, with significant increase in SP-A (1.16 +/- 0.22 micrograms/ml Si-PBS group vs. 0.70 +/- 0.07 micrograms/ml PBS-PBS group, p < 0.05) and a parallel but not significant increase in SP-B (2.68 +/- 0.90 micrograms/ml Si-PBS group vs. 1.10 +/- 0.30 micrograms/ml PBS-PBS group). The surface-tension-reducing activities of alveolar fluid lipid extracts did not differ significantly between the groups (Si-PBS group at maximal bubble radius [Rmax]: 27.0 +/- 1.6 and at minimal bubble radius [Rmin]: 1.0 +/- 0.7 milli Newton/m, vs. PBS-PBS group Rmax: 27.0 +/- 2.2 and Rmin: 0.7 +/- 0.3 milli Newton/m at 4 min pulsation). The ratios of SP-A and SP-B to lipid phosphorus levels document a proportional enhancement of surfactant-associated proteins and phospholipids, thus suggesting a co-ordinated upregulation of both surfactant-associated proteins and phospholipids in this model of silicosis. However, on an individual basis, these changes were not related, suggesting a more complex model of regulation. This study documents significant increases of the surfactant apoproteins proportional to changes in phospholipids in the lung of silicotic sheep. In spite of these alterations of surfactant components, organic solvent lipid extracts of BAPLFs surfactant remained equally effective in reducing surface tension.

Surfactant protein A (SP-A) is decreased in acute parenchymal lung injury associated with polytrauma

To further investigate if the pulmonary surfactant system is altered in acute parenchymal lung injury of adults following polytrauma we measured SP-A level and phospholipid composition in 150 sequentially obtained lung lavage samples from poly-traumatized patients (n = 19) beginning at the day of trauma and ending 18 days later or when the patient was extubated. Out of the 19 patients studied 10 had severe parenchymal lung injury (ARDS), nine had moderate lung injury. SP-A was measured using a two-monoclonal sandwich ELISA-assay. Phospholipids were separated using high-performance liquid chromatography and their composition was calculated by comparison with standard phospholipid mixtures. We found immunoreactive SP-A concentrations ranging from 0.1 micrograms ml-1 to 8.5 micrograms ml-1 lung lavage fluid obtained from all patients. The mean SP-A concentration in patients who had severe parenchymal lung injury (ARDS) was 1.06 +/- 0.16 micrograms ml-1 lavage fluid, the mean concentration in patients who had only moderate parenchymal lung injury was 1.92 +/- 0.18 micrograms ml-1 lavage fluid. Both concentrations were lower than in healthy controls (2.74 +/- 0.3 micrograms ml-1 lavage fluid; n = 12). In patients who had moderate lung injury the SP-A level normalized, but in patients who had severe lung injury the SP-A level remained low during the timespan examined. SP-A alterations did not correlate to changes in phospholipid composition as determined in lung lavage samples of individual patients. We conclude that alveolar SP-A concentrations decrease in polytraumatized patients who have acute parenchymal lung injury soon after the trauma occurs.(ABSTRACT TRUNCATED AT 250 WORDS)

The surfactant system of the adult lung: physiology and clinical perspectives

Pulmonary surfactant is synthesized and secreted by alveolar type II cells and constitutes an important component of the alveolar lining fluid. It comprises a unique mixture of phospholipids and surfactant-specific proteins. More than 30 years after its first biochemical characterization, knowledge of the composition and functions of the surfactant complex has grown considerably. Its classically known role is to decrease surface tension in alveolar air spaces to a degree that facilitates adequate ventilation of the peripheral lung. More recently, other important surfactant functions have come into view. Probably most notable among these, surfactant has been demonstrated to enhance local pulmonary defense mechanisms and to modulate immune responses in the alveolar milieu. These findings have prompted interest in the role and the possible alterations of the surfactant system in a variety of lung diseases and in environmental impacts on the lung. However, only a limited number of studies investigating surfactant changes in human lung disease have hitherto been published. Preliminary results suggest that surfactant analyses, e.g., from bronchoalveolar lavage fluids, may reveal quantitative and qualitative abnormalities of the surfactant system in human lung disorders. It is hypothesized that in the future, surfactant studies may become one of our clinical tools to evaluate the activity and severity of peripheral lung diseases. In certain disorders they may also gain diagnostic significance. Further clinical studies will be necessary to investigate the potential therapeutic benefits of surfactant substitution and the usefulness of pharmacologic manipulation of the secretory activity of alveolar type II cells in pulmonary medicine.

N-nitrosoheptamethyleneimine-induced pulmonary and esophageal carcinogenesis and effects of concomitant treatment with bleomycin in rats

The combination effects of bleomycin with N-nitrosoheptamethyleneimine (NHMI) or dihydroxy-di-N-propylnitrosamine (DHPN) on pulmonary carcinogenesis were investigated. Male F344 rats were given NHMI (20 or 40 ppm) or DHPN (200 ppm) in the drinking water and intraperitoneally injected with bleomycin (1 mg/kg) once a week for 18 weeks and then killed at week 24. Many rats treated with NHMI died before the termination of the experiment due to toxicity or development of advanced esophageal carcinomas, considered to be the main cause of death. Detailed histological examination performed on rats killed at week 24 revealed no statistically significant effects of bleomycin on NHMI or DHPN induction of neoplastic lesions in the lung or esophagus, although pulmonary carcinomas were only found in two rats treated with NHMI plus bleomycin. Under the present experimental conditions, NHMI exerted stronger carcinogenic activity in the esophagus than in the lung, and no obvious modifying effects of simultaneously administered bleomycin were evident on NHMI- or DHPN-induced pulmonary carcinogenesis.

Increased expression of pulmonary surfactant proteins in oxygen-exposed rats

Exposure of adult rats to 85% ambient oxygen increased the content of surfactant proteins SP-A, SP-B, and SP-C recovered from alveolar lavage. The surfactant proteins increased during 1 to 7 d of oxygen exposure. The increased surfactant protein was associated with increased relative abundance of mRNA encoding each of the proteins in lung tissue. Exposure to hyperoxia progressively increased the amounts of the surfactant proteins in alveolar lavage fluid as estimated by immunoblot analysis after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The mRNAs encoding SP-A (1.7 and 1.0 kb), SP-B (1.6 kb), and SP-C (0.9 kb) increased significantly after oxygen exposure for 5 d. The present findings support the concept that oxygen exposure mediates surfactant protein expression at a pretranslational level.