Alkaline phosphatase: a marker of alveolar type II cell differentiation

TBHQ alleviates pyroptosis and necroptosis in chicken alveolar epithelial cells induced by fine particulate matter from broiler houses

Fine particulate matter (PM2.5) from poultry houses has adverse effects on the health of animals and workers. Tert-butylhydroquinone (TBHQ), an antioxidant, is widely used in feed additives. The present study investigated the effects of TBHQ on broiler house PM2.5-induced damage in chicken primary alveolar epithelial cells (AECII) extracted from 16-day-old chicken embryos using the method of differential adhesion. AECII were exposed to PM2.5 and TBHQ alone or in combination, and then, cell membrane integrity, pyroptosis, and necroptosis were detected. Our results showed that PM2.5 from broiler houses caused cell rupture and loss of cell membrane integrity. This result was confirmed by the obvious increases in lactate dehydrogenase (LDH) release and propidium iodide (PI)-positive cells compared to the control group. In addition, the intracellular reactive oxygen species (ROS) levels and the expression levels of pyroptosis-related genes (NLRP3, IL-18, IL-1β) and necroptosis-related genes (RIPK3) were also significantly enhanced. However, TBHQ significantly inhibited intracellular ROS, improved cell viability, and reduced the release of LDH and the number of PI-positive cells compared to those in the PM2.5 group. The expression levels of pyroptosis-related genes (Caspase-1, NLRP3, IL-18, IL-1β) and necroptosis-related genes (RIPK3) were also significantly decreased in the co-treatment group. In summary, these results indicated that TBHQ can alleviate PM2.5-mediated cell pyroptosis and necroptosis in chicken AECII and provide a basis for overcoming the danger that air pollutants from broiler houses pose to the health of chickens.

Immortalisation of primary human alveolar epithelial lung cells using a non-viral vector to study respiratory bioreactivity in vitro

To overcome the scarcity of primary human alveolar epithelial cells for lung research, and the limitations of current cell lines to recapitulate the phenotype, functional and molecular characteristics of the healthy human alveolar epithelium, we have developed a new method to immortalise primary human alveolar epithelial lung cells using a non-viral vector to transfect the telomerase catalytic subunit (hTERT) and the simian virus 40 large-tumour antigen (SV40). Twelve strains of immortalised cells (ICs) were generated and characterised using molecular, immunochemical and morphological techniques. Cell proliferation and sensitivity to polystyrene nanoparticles (PS) were evaluated. ICs expressed caveolin-1, podoplanin and receptor for advanced glycation end-products (RAGE), and most cells were negative for alkaline phosphatase staining, indicating characteristics of AT1-like cells. However, most strains also contained some cells that expressed pro-surfactant protein C, classically described to be expressed only by AT2 cells. Thus, the ICs mimic the cellular heterogeneity in the human alveolar epithelium. These ICs can be passaged, replicate rapidly and remain confluent beyond 15 days. ICs showed differential sensitivity to positive and negatively charged PS nanoparticles, illustrating their potential value as an in vitro model to study respiratory bioreactivity. These novel ICs offer a unique resource to study human alveolar epithelial biology.

Trafficking of newly synthesized surfactant protein B to the lamellar body in alveolar type II cells

Lung surfactant accumulates in the lamellar body (LB) via not only the secretory (anterograde) pathway but also the endocytic (retrograde) pathway. Our previous studies suggested that the major surfactant components, phosphatidylcholine and surfactant protein A take independent trafficking routes in alveolar type II cells. Thus, trafficking of surfactant protein B (SP-B), a major hydrophobic surfactant apoprotein, should be re-evaluated by a straightforward method. Radiolabeling of cells and subsequent cell fractionation were employed to pursue the sequential trafficking of newly synthesized SP-B in rabbit alveolar type II cells. The LB fraction was prepared by gradient ultracentrifugation. Immunoprecipitation from the culture medium, total cells, and LB fraction was carried out with anti-SP-B antibody. Newly synthesized [³⁵S]-pro-SP-B (~ 42 kDa) was detected in the cells after 1 h. An ~ 8-kDa mature form of [³⁵S]-SP-B was detected in the cells after 3 h and in the LB after 6 h. Mature [³⁵S]-SP-B was predominant in the cells after 24 h, and the dominant portion was present in the LB. In contrast, only a small amount of mature [³⁵S]-SP-B was present in the culture medium. Molecular processing of ~ 42 kDa [³⁵S]-pro-SP-B and transport to the LB was inhibited by brefeldin A, which disassembles the Golgi apparatus. These results suggest that newly synthesized SP-B is sorted to the LB via the Golgi and stored until exocytosis. This pathway is distinct from the pathways reported for phosphatidylcholine and surfactant protein A.

Type 2 secretory cells are primary source of ATP release in mechanically stretched lung alveolar cells

Extracellular ATP and its metabolites are potent paracrine modulators of lung alveolar cell function, including surfactant secretion and fluid transport, but the sources and mechanism of intra-alveolar ATP release remain unclear. To determine the contribution of gas-exchanging alveolar type 1 (AT1) and surfactant-secreting type 2 (AT2) cells to stretch-induced ATP release, we used quantitative real-time luminescence ATP imaging and rat primary alveolar cells cultured on silicon substrate for 2-7 days. When cultured on solid support, primary AT2 cells progressively transdifferentiated into AT1-like cells with ~20% of cells showing AT1 phenotype by day 2-3 (AT2:AT1 ≈ 4:1), while on day 7, the AT2:AT1 cell ratio was reversed with up to 80% of the cells displaying characteristics of AT1 cells. Stretch (1 s, 5-35%) induced ATP release from AT2/AT1 cell cultures, and it was highest on days 2 and 3 but declined in older cultures. ATP release tightly correlated with the number of remaining AT2 cells in culture, consistent with ~10-fold lower ATP release by AT1 than AT2 cells. ATP release was unaffected by inhibitors of putative ATP channels carbenoxolone and probenecid but was significantly diminished in cells loaded with calcium chelator BAPTA. These pharmacological modulators had similar effects on stretch-induced intracellular Ca²⁺ responses measured by Fura2 fluorescence. The study revealed that AT2 cells are the primary source of stretch-induced ATP release in heterocellular AT2/AT1 cell cultures, suggesting similar contribution in intact alveoli. Our results support a role for calcium-regulated mechanism but not ATP-conducting channels in ATP release by alveolar epithelial cells.

Scanning electrochemical microscopy in the development of enzymatic sensors and immunosensors

Scanning electrochemical microscopy (SECM) is very useful, non-invasive tool for the analysis of surfaces pre-modified with biomolecules or by whole cells. This review focuses on the application of SECM technique for the analysis of surfaces pre-modified with enzymes (horseradish peroxidase, alkaline phosphatase and glucose oxidase) or labelled with antibody-enzyme conjugates. The working principles and operating modes of SECM are outlined. The applicability of feedback, generation-collection and redox competition modes of SECM on surfaces modified by enzymes or labelled with antibody-enzyme conjugates is discussed. SECM is important in the development of miniaturized bioanalytical systems with enzymes, since it can provide information about the local enzyme activity. Technical challenges and advantages of SECM, experimental parameters, used enzymes and redox mediators, immunoassay formats and analytical parameters of enzymatic SECM sensors and immunosensors are reviewed.

AnIn VitroStudy of the Toxic Effects ofStachybotrys chartarumMetabolites on Lung Cells

During a study of indoor fungal colonisation, several isolates of Stachybotrys chartarum were recovered, and the effects of metabolites from four isolates on lung epithelial Type II cells and alveolar macrophages were studied in vitro. All the isolates showed toxic effects on both cell types, and they differed only in the extent of the changes induced. In Type II cells, the number of alkaline phosphatase positive cells was reduced, the pattern of Maclura pomifera agglutinin (MPA) binding was changed, and acid phosphatase activity in alveolar macrophages was diminished. In both cell types, the production of monocyte chemotactic protein-1 (MCP-1) and tumour necrosis factor-alpha (TNF-alpha) was changed, and parameters related to antioxidant status (superoxide dismutase, glutathione peroxidase, glutathione) were decreased.

Immunotoxicological impact and biodistribution assessment of bismuth selenide (Bi2Se3) nanoparticles following intratracheal instillation in mice

Variously synthesized and fabricated Bi2Se3 nanoparticles (NPs) have recently been explored for their theranostic properties. Herein, we investigated the long term in-vivo biodistribution of Bi2Se3 NPs and systematically screened its immune-toxic potential over lungs and other secondary organs post intratracheal instillation. X-Ray CT scan and ICP MS results revealed significant particle localization and retention in lungs monitored for 1 h and 6 months time period respectively. Subsequent particle trafficking was observed in liver, the major reticuloendothelial organ followed by gradual but incomplete renal clearance. Pulmonary cytotoxicity was also found to be associated with persistent neutrophilic and ROS generation at all time points following NP exposure. The inflammatory markers along with ROS generation further promoted oxidative stress and exaggerated additional inflammatory pathways leading to cell death. The present study, therefore, raises serious concern about the hazardous effects of Bi2Se3 NPs and calls for further toxicity assessments through different administration routes and doses as well.

Immune Defense Protein Expression in Highly Purified Mouse Lung Epithelial Cells

Lung epithelial cells play critical roles in initiating and modulating immune responses during pulmonary infection or injury. To better understand the spectrum of immune response-related proteins present in lung epithelial cells, we developed an improved method of isolating highly pure primary murine alveolar type (AT) II cells and murine tracheal epithelial cells (mTECs) using negative selection for a variety of lineage markers and positive selection for epithelial cell adhesion molecule (EpCAM), a pan-epithelial cell marker. This method yielded 2-3 × 10(6) ATII cells/mouse lung and 1-2 × 10(4) mTECs/trachea that were highly pure (>98%) and viable (>98%). Using these preparations, we found that both ATII cells and mTECs expressed the Lyn tyrosine kinase, which is best studied as an inhibitory kinase in hematopoietic cells. However, we found little or no expression of Syk in either ATII cells or mTECs, which is in contrast to earlier published reports. Both cell types expressed C-type lectin receptors, anaphylatoxin receptors, and various Toll-like receptors (TLRs). In addition, stimulation of ATII cells with TLR ligands led to secretion of various cytokines and chemokines. Interestingly, lyn(-/-) ATII cells were hyperresponsive to TLR3 stimulation, suggesting that, as in hematopoietic cells, Lyn might be playing an inhibitory role in ATII cells. In conclusion, the improved isolation method reported here, along with expression profiles of various immune defense proteins, will help refocus investigations of immune-related signaling events in pulmonary epithelium.

Toxicogenomics analysis of mouse lung responses following exposure to titanium dioxide nanomaterials reveal their disease potential at high doses

Titanium dioxide nanoparticles (TiO₂NPs) induce lung inflammation in experimental animals. In this study, we conducted a comprehensive toxicogenomic analysis of lung responses in mice exposed to six individual TiO₂NPs exhibiting different sizes (8, 20 and 300nm), crystalline structure (anatase, rutile or anatase/rutile) and surface modifications (hydrophobic or hydrophilic) to investigate whether the mechanisms leading to TiO₂NP-induced lung inflammation are property specific. A detailed histopathological analysis was conducted to investigate the long-term disease implications of acute exposure to TiO₂NPs. C57BL/6 mice were exposed to 18, 54, 162 or 486 µg of TiO₂NPs/mouse via single intratracheal instillation. Controls were exposed to dispersion medium only. Bronchoalveolar lavage fluid (BALF) and lung tissue were sampled on 1, 28 and 90 days post-exposure. Although all TiO₂NPs induced lung inflammation as measured by the neutrophil influx in BALF, rutile-type TiO₂NPs induced higher inflammation with the hydrophilic rutile TiO₂NP showing the maximum increase. Accordingly, the rutile TiO₂NPs induced higher number of differentially expressed genes. Histopathological analysis of lung sections on Day 90 post-exposure showed increased collagen staining and fibrosis-like changes following exposure to the rutile TiO₂NPs at the highest dose tested. Among the anatase, the smallest TiO₂NP of 8nm showed the maximum response. The anatase TiO₂NP of 300nm was the least responsive of all. The results suggest that the severity of lung inflammation is property specific; however, the underlying mechanisms (genes and pathways perturbed) leading to inflammation were the same for all particle types. While the particle size clearly influenced the overall acute lung responses, a combination of small size, crystalline structure and hydrophilic surface contributed to the long-term pathological effects observed at the highest dose (486 µg/mouse). Although the dose at which the pathological changes were observed is considered physiologically high, the study highlights the disease potential of certain TiO₂NPs of specific properties.

Effects of Granulocyte Colony-Stimulating Factor (G-CSF) on Bleomycin-Induced Lung Injury of Varying Severity

We evaluated the effects of granulocyte colony-stimulating factor (G-CSF) on bleomycin (BLM)-induced lung injury that developed diffuse alveolar damage and subsequent pulmonary fibrosis (PF) of varying severity. G-CSF (100 μg/kg/day) was administered subcutaneously to BLM (0.2, 20, 2,000 μg)-treated or -untreated rats for 3 or 14 days. In the BLM 0.2 μg group, slight alveolar mononuclear cell infiltration was observed, although PF was not noted. In the BLM 20- μg and 2,000- μg groups, diffuse alveolar damage along with neutrophil infiltration and subsequent PF were observed. In the saline + G-CSF group and BLM 0.2 μg + G-CSF group, a marked increase in the number of alkaline phosphatase (ALP)-positive neutrophils was noted in the alveolar capillaries, although there was neither neutrophil infiltration in alveoli nor exacerbation of lung injury. In the BLM 20 μg + G-CSF and BLM 2,000 μg + G-CSF groups, an exacerbation of lung injury along with an increase in the number of ALP-positive neutrophils in the alveoli was observed. These results indicate that the administration of G-CSF to rats with slight lung injury bearing no PF does not exacerbate the lung injury. The exacerbating effects of G-CSF seem to be associated not only with the marked infiltration of activated neutrophils but also with the severity of underlying lung injury.

Effect of total alkaloids from Alstonia scholaris on airway inflammation in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Alstonia scholaris (Apocynaceae) have been traditionally used for treatment of respiratory diseases in "dai" ethnopharmacy for hundreds years, especially for cough, asthma, phlegm, chronic obstructive pulmonary disease and so on. The formulas including the leaf extract have also been prescribed in hospitals and sold over the retail pharmacies.

AIM OF THE STUDY

A. scholaris is used as a traditional herbal medicine for the treatment of respiratory tract inflammation. However, there is no scientific evidence to validate the use of total alkaloids of A. scholaris in the literature. Here, we investigated the protective activity of total alkaloids (TA), extracted from the leaves of Alstonia scholaris, against lipopolysaccharide (LPS)-induced airway inflammation (AI) in rats.

MATERIALS AND METHODS

200 μg/μL LPS was instilled intratracheally in each rat, and then the modeling animals were divided into six groups (n=10, each) randomly: sham group, LPS group, Dexamethasone [1.5mg/kg, intra-gastricly (i.g.)] group, and three different doses (7.5, 15, and 30 mg/kg, i.g.) of total alkaloids-treated groups. Corresponding drugs or vehicles were orally administered once per day for 7 days consecutively. The concentration of albumin (ALB), alkaline phosphatase (AKP), lactate dehydrogenase (LDH), and the number of inflammatory cells in bronchoalveolar lavage fluid (BALF) were determined by fully automatic biochemical analyzer and blood counting instrument. Nitric oxide (NO) level, malondialdehyde (MDA) content, and superoxide dismutase (SOD) activities were examined by multiskan spectrum, and histological change in the lungs was analyzed by H.E. staining. The levels of inflammatory cytokine tumor necrosis factor-α (TNF-α) and interleukin-8 (IL-8) were measured using ELISA.

RESULTS

Total alkaloids decreased the percentage of neutrophil, number of WBC, levels of ALB, AKP and LDH in the BALF, while increased the content of ALB in serum. It also improved SOD activity and increased NO level in the lungs, serum and BALF, and reduced the concentration of MDA in the lungs. Total alkaloids also inhibited the production of inflammatory cytokines TNF-α and IL-8 in the BALF and lung. Finally, histopathological examination indicated that total alkaloids attenuated tissue injury of the lungs in LPS-induced AI.

CONCLUSIONS

Total alkaloids have an inhibitory effect against LPS-induced airway inflammation in rats.

Molecular composition of the alveolar lining fluid in the aging lung

As we age, there is an increased risk for the development of pulmonary diseases, including infections, but few studies have considered changes in lung surfactant and components of the innate immune system as contributing factors to the increased susceptibility of the elderly to succumb to infections. We and others have demonstrated that human alveolar lining fluid (ALF) components, such as surfactant protein (SP)-A, SP-D, complement protein C3, and alveolar hydrolases, play a significant innate immune role in controlling microbial infections. However, there is a lack of information regarding the effect of increasing age on the level and function of ALF components in the lung. Here we addressed this gap in knowledge by determining the levels of ALF components in the aging lung that are important in controlling infection. Our findings demonstrate that pro-inflammatory cytokines, surfactant proteins and lipids, and complement components are significantly altered in the aged lung in both mice and humans. Further, we show that the aging lung is a relatively oxidized environment. Our study provides new information on how the pulmonary environment in old age can potentially modify mucosal immune responses, thereby impacting pulmonary infections and other pulmonary diseases in the elderly population.

Mechanisms regulating airway nucleotides

In the respiratory system, extracellular nucleotides and nucleosides serve as signaling molecules for a wide spectrum of biological functions regulating airway defenses against infection and toxic material. Their concentrations are controlled by a complex network of cell surface enzymes named ectonucleotidases. This highly integrated metabolic network combines the activities of three dephosphorylating ectonucleotidases, namely nucleoside triphosphate diphosphohydrolases (NTPDases), nucleotide pyrophosphatase/phosphodiesterases (NPPs) and alkaline phosphatases (APs). Extracellular nucleotides are also inter-converted by the transphosphorylating activities of ecto adenylate kinase (ectoAK) and nucleoside diphosphokinase (NDPK). Different cell types use specific combinations of ectonucleotidases to regulate local concentrations of P2 receptor agonists (ATP, UTP, ADP and UDP). In addition, they provide AMP for the activity of ecto 5'-nucleotidase (ecto 5'-NT; CD73), which produces the P1 receptor agonist: adenosine (ADO). Finally, mechanisms are in place to prevent the accumulation of airway ADO, namely adenosine deaminases and nucleoside transporters. This chapter reviews the properties of each enzyme and transporter, and the current knowledge on their distribution and regulation in the airways.

Regulation of airway nucleotides in chronic lung diseases

The physiological relevance of the purinergic signaling network for airway defenses is emerging through cumulating reports of abnormal ATP and adenosine (ADO) levels in the airway secretions of patients with asthma, chronic pulmonary obstructive diseases, cystic fibrosis and idiopathic pulmonary fibrosis. The consequences for airway defenses range from abnormal clearance responses to the destruction of lung tissue by excessive inflammation. This chapter reviews the challenges of assessing airway purines in human subjects, and identifies the general trend in aberrant airway composition. Most diseases are associated with an accumulation of ATP and/or ADO in bronchoalveolar lavage, sputum or exhaled breadth condensate. Intriguing is the case of cystic fibrosis patients, which do not accumulate airway ADO, but its precursor, AMP. This observation launched the investigation of ectonucleotidases as target proteins for the correction of airway purine levels in chronic respiratory diseases. This chapter exposes the extensive rearrangement of the enzymatic network taking place in diseased airways, and identifies signaling pathways likely involved in the aberrant regulation of the airway purines.

Hypercapnic acidosis confers antioxidant and anti-apoptosis effects against ventilator-induced lung injury

Hypercapnic acidosis may attenuate ventilator-induced lung oxidative stress injury and alveolar cell apoptosis, but the underlying mechanisms are poorly understood. We examined the effects of hypercapnic acidosis on the role of apoptosis signal-regulating kinase 1 (ASK1), which activates the c-Jun N-terminal kinase (JNK) and p38 cascade in both apoptosis and oxidative reactions, in high-pressure ventilation stimulated rat lungs. Rats were ventilated with a peak inspiratory pressure (PIP) of 30 cmH2O for 4 h and randomly given FiCO2 to achieve normocapnia (PaCO2 at 35-45 mm Hg) or hypercapnia (PaCO2 at 80-100 mm Hg); normally ventilated rats with PIP of 15 cmH2O were used as controls. Lung injury was quantified by gas exchange, microvascular leaks, histology, levels of inflammatory cytokines, and pulmonary oxidative reactions. Apoptosis through the ASK1-JNK/p38 mitogen-activated protein kinase (MAPK) cascade in type II alveolar epithelial cells (AECIIs) were evaluated by examination of caspase-3 activation. The results showed that injurious ventilation caused significant lung injury, including deteriorative oxygenation, changes of histology, and the release of inflammatory cytokines. In addition, the high-pressure mechanical stretch also induced apoptosis and caspase-3 activation in the AECIIs. Hypercapnia attenuated these responses, suppressing the ASK1 signal pathways with its downstream kinase phosphorylation of p38 MAPK and JNK, and caspase-3 activation. Thus, hypercapnia can attenuate cell apoptosis and oxidative stress damage in rat lungs during injurious ventilation, at least in part, due to the suppression of the ASK1-JNK/p38 MAPK pathways.

Aggressive pulmonary calcification developed after living donor kidney transplantation in a patient with primary hyperparathyroidism

Metastatic pulmonary calcification, defined as calcium deposition in the intact lung, is commonly seen in patients with chronic renal failure, and it is known to be a benign clinical condition when detected by chance in an asymptomatic patient. Here we report the case of a 33-year-old woman who developed rapid and aggressive metastatic pulmonary calcification shortly after a living donor kidney transplantation, which induced acute antibody-mediated rejection. The patient's metastatic pulmonary calcification was successfully improved by extensive treatment for graft rejection, the correction of her accompanying primary hyperparathyroidism, and medical treatment with a bisphosphonate and sodium thiosulfate. Aggressive pulmonary calcification is reported as a rare complication seen in patients who have undergone a failed renal transplantation. A failed renal graft and accompanying secondary hyperparathyroidism seem to accelerate metastatic calcification. Most of the patients who develop aggressive pulmonary calcification suffer from the rapid progression of dyspnea and occasionally fever, and they die of respiratory failure. Pulmonary calcification should be considered in a patient developing dyspnea and unexplained pulmonary infiltrate, especially in the context of renal graft rejection; otherwise the prognosis of the patient will be very poor.

Francisella DnaK inhibits tissue-nonspecific alkaline phosphatase

Following pulmonary infection with Francisella tularensis, we observed an unexpected but significant reduction of alkaline phosphatase, an enzyme normally up-regulated following inflammation. However, no reduction was observed in mice infected with a closely related gram-negative pneumonic organism (Klebsiella pneumoniae) suggesting the inhibition may be Francisella-specific. In similar fashion to in vivo observations, addition of Francisella lysate to exogenous alkaline phosphatase (tissue-nonspecific isozyme) was inhibitory. Partial purification and subsequent proteomic analysis indicated the inhibitory factor to be the heat shock protein DnaK. Incubation with increasing amounts of anti-DnaK antibody reduced the inhibitory effect in a dose-dependent manner. Furthermore, DnaK contains an adenosine triphosphate binding domain at its N terminus, and addition of adenosine triphosphate enhances dissociation of DnaK with its target protein, e.g. alkaline phosphatase. Addition of adenosine triphosphate resulted in decreased DnaK co-immunoprecipitated with alkaline phosphatase as well as reduction of Francisella-mediated alkaline phosphatase inhibition further supporting the binding of Francisella DnaK to alkaline phosphatase. Release of DnaK via secretion and/or bacterial cell lysis into the extracellular milieu and inhibition of plasma alkaline phosphatase could promote an orchestrated, inflammatory response advantageous to Francisella.

Inhibitory effect of receptor for advanced glycation end products (RAGE) on the TGF-β-induced alveolar epithelial to mesenchymal transition

Idiopathic pulmonary fibrosis (IPF) is a lethal parenchymal lung disease characterized by myofibroblast proliferation. Alveolar epithelial cells (AECs) are thought to produce myofibroblasts through the epithelial to mesenchymal transition (EMT). Receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily of cell surface receptors whose activation is associated with renal fibrosis during diabetes and liver fibrosis. RAGE is expressed at low basal levels in most adult tissues except the lung. In this study, we evaluated the interaction of ligand advanced glycation end products (AGE) with RAGE during the epithelial to myofibroblast transition in rat AECs. Our results indicate that AGE inhibited the TGF-β-dependent alveolar EMT by increasing Smad7 expression, and that the effect was abolished by RAGE siRNA treatment. Thus, the induction of Smad7 by the AGE-RAGE interaction limits the development of pulmonary fibrosis by inhibiting TGF-β-dependent signaling in AECs.

Hyalinization of the pyloric stomach in CD-1 mice following oral (dietary) administration of the corticosteroid agonists mometasone furoate, budesonide, and flunisolide

The purpose of this study was to compare the toxicity of three marketed corticosteroid receptor agonists (mometasone furoate, budesonide, or flunisolide) to the stomach of female CD-1 mice following oral administration via the diet for up to 52 weeks, with a 16-week recovery period (budesonide and flunisolide). A range of tissues was examined by light microscopy, accompanied by clinical pathology measurements to assess anticipated corticosteroid effects as a surrogate marker of systemic drug exposure. Microscopic changes seen in the stomach with each corticosteroid included pyloric hyalinization. This previously unreported finding was investigated using histochemical and immunohistochemical techniques and was found to consist of hyalinized collagen, in association with increased immunohistochemical signal for transglutaminase-2 and osteopontin. The significance of the osteopontin finding is unclear; however, the ability of transglutaminase-2 to facilitate the formation of degradation resistant protein bonds implies this protein may be involved in the pathogenesis of this change. Furthermore, published evidence that transglutaminase-2 may be induced by a corticosteroid agonist raises the possibility that pyloric stomach hyalinization may be a class effect of corticosteroids via the action of this enzyme.

Human lung hydrolases delineate Mycobacterium tuberculosis-macrophage interactions and the capacity to control infection

Pulmonary surfactant contains homeostatic and antimicrobial hydrolases. When Mycobacterium tuberculosis is initially deposited in the terminal bronchioles and alveoli, as well as following release from lysed macrophages, bacilli are in intimate contact with these lung surfactant hydrolases. We identified and measured several hydrolases in human alveolar lining fluid and lung tissue that, at their physiological concentrations, dramatically modified the M. tuberculosis cell envelope. Independent of their action time (15 min to 12 h), the effects of the hydrolases on the M. tuberculosis cell envelope resulted in a significant decrease (60-80%) in M. tuberculosis association with, and intracellular growth of the bacteria within, human macrophages. The cell envelope-modifying effects of the hydrolases also led to altered M. tuberculosis intracellular trafficking and induced a protective proinflammatory response to infection. These findings add a new concept to our understanding of M. tuberculosis-macrophage interactions (i.e., the impact of lung surfactant hydrolases on M. tuberculosis infection).

Extensive Analysis of Elastase-Induced Pulmonary Emphysema in Rats: ALP in the Lung, a New Biomarker for Disease Progression?

It is accepted that pulmonary exposure of rodents to porcine pancreatic elastase (ELT) induces lesions that morphologically resemble human emphysema. Nonetheless, extensive analysis of this model has rarely been conducted. The present study was designed to extensively examine the effects of ELT on lung inflammation, cell damage, emphysematous change, and cholinergic reactivity in rats. Intratracheal administration of two doses of ELT induced 1) a proinflammatory response in the lung that was characterized by significant infiltration of macrophages and an increased level of interleukin-1beta in lung homogenates, 2) lung cell damage as indicated by higher levels of total protein, lactate dehydrogenase, and alkaline phosphatase (ALP) in lung homogenates, 3) emphysema-related morphological changes including airspace enlargement and progressive destruction of alveolar wall structures, and 4) airway responsiveness to methacholine including an augmented Rn value. In addition, ELT at a high dose was more effective than that at a low dose. This is the novel study to extensively analyze ELT-induced lung emphysema, and the analysis might be applied to future investigations that evaluate new therapeutic agents or risk factors for pulmonary emphysema. In particular, ALP in lung homogenates might be a new biomarker for the disease progression/exacerbation.

Fas inhibition attenuates lipopolysaccharide-induced apoptosis and cytokine release of rat type II alveolar epithelial cells

The aim of this study is to investigate whether silencing of Fas could have an influence on type II alveolar epithelial cell (AEC) apoptosis and inflammatory cytokine production, which prevents alveolar healing after acute lung injury (ALI). Rat primary type II AECs were isolated by elastase cell dispersion and IgG panning. The cells were transfected with Fas-specific small interfering RNA (siRNA) followed by treatment with lipopolysaccharide (LPS), Fas ligand (FasL) or both. The effects of siRNA-mediated silencing of Fas on LPS-induced apoptosis and cytokine release were then assessed. Notably, LPS, either alone or together with FasL, significantly stimulated type II AEC apoptosis and the release of tumor necrosis factor-alpha (TNF-α) and monocyte chemoattractant protein 1 (MCP-1) (P < 0.05 versus the control without treatment). Moreover, the effects exerted by both LPS and FasL were considerably counteracted by pretreatment with Fas-siRNA (P < 0.05 versus treatment with LPS and FasL). In conclusion, inhibition of Fas can diminish LPS-induced apoptosis and inflammatory cytokine production in type II AECs, and Fas specific siRNAs may have therapeutic potentials for intervention of ALI/ARDS.

Isolation and characterization of metabolically competent pulmonary epithelial cells from pig lung tissue

Administration of drugs by inhalation opens new possibilities for entry into the systemic circulation and cultures of porcine pulmonary epithelial cells (PECs) may prove to be valuable in the prediction of pulmonary metabolism of drugs in humans. This paper, therefore, reports a method for the routine isolation and cultivation of PECs from slaughterhouse animals. On average 1.5x10(6) cells g-1 tissue were isolated by discontinuous density-gradient centrifugation. Cells were subsequently cultivated on collagen-coated plates and characterized by staining for alkaline phosphatase, by tannic acid staining of lamellar bodies and by surfactant protein (SP) expression at days 0, 3 and 6 in culture. Over 70% of purified cells were positive for SP-C and tannic acid staining and thus defined as epithelial cells of alveolar origin (AECs). The AEC phenotype was also confirmed by specific binding of marker lectins (Maclura pomifera and Helix pomatia) and by studying gene expression and activity of cytochrome P450 monooxygenases. Testosterone, ethoxyresorufin, benzyloxyresorufin and verapamil were used as substrates for cytochrome P450-catalysed oxidations and cultured cells were found to be differentiated as well as metabolically competent during cultivation. Therefore, this culture system enables in depth pulmonary biotransformation and toxicity studies.

Immortalization of human alveolar epithelial cells to investigate nanoparticle uptake

Primary human alveolar type 2 (AT2) cells were immortalized by transduction with the catalytic subunit of telomerase and simian virus 40 large-tumor antigen. Characterization by immunochemical and morphologic methods demonstrated an AT1-like cell phenotype. Unlike primary AT2 cells, immortalized cells no longer expressed alkaline phosphatase, pro-surfactant protein C, and thyroid transcription factor-1, but expressed increased caveolin-1 and receptor for advanced glycation end products (RAGE). Live cell imaging using scanning ion conductance microscopy showed that the cuboidal primary AT2 cells were approximately 15 microm and enriched with surface microvilli, while the immortal AT1 cells were attenuated more than 40 microm, resembling these cells in situ. Transmission electron microscopy highlighted the attenuated morphology and showed endosomal vesicles in some immortal AT1 cells (but not primary AT2 cells) as found in situ. Particulate air pollution exacerbates cardiopulmonary disease. Interaction of ultrafine, nano-sized particles with the alveolar epithelium and/or translocation into the cardiovasculature may be a contributory factor. We hypothesized differential uptake of nanoparticles by AT1 and AT2 cells, depending on particle size and surface charge. Uptake of 50-nm and 1-microm fluorescent latex particles was investigated using confocal microscopy and scanning surface confocal microscopy of live cells. Fewer than 10% of primary AT2 cells internalized particles. In contrast, 75% immortal AT1 cells internalized negatively charged particles, while less than 55% of these cells internalized positively charged particles; charge, rather than size, mattered. The process was rapid: one-third of the total cell-associated negatively charged 50-nm particle fluorescence measured at 24 hours was internalized during the first hour. AT1 cells could be important in translocation of particles from the lung into the circulation.

Comparative characterization of pulmonary surfactant aggregates and alkaline phosphatase isozymes in human lung carcinoma tissue

Alkaline phosphatase (AP) isozymes are surfactant-associated proteins (SPs). Since several different AP isozymes have been detected in the pneumocytes of lung cancer patients, we attempted to identify the relationship between pulmonary surfactant aggregate subtypes and AP isozymes. Pulmonary surfactant aggregates were isolated from carcinoma and non-carcinoma tissues of patients with non-small cell carcinoma of the lung. Upon analysis, ultraheavy, heavy, and light surfactant aggregates were detected in the non-carcinoma tissues, but no ultraheavy surfactant aggregates were found in the carcinoma tissues. Surfactant-associated protein A (SP-A) was detected as two bands (a 27-kDa band and a 54-kDa band) in the ultraheavy, heavy, and light surfactant aggregates found in the non-carcinoma tissues. Although both SP-A bands were detected in the heavy and light surfactant aggregates from adenocarcinoma tissues, the 54-kDa band was not detected in squamous cell carcinoma tissues. Liver AP (LAP) was detected in the heavy and light surfactant aggregates from both non-carcinoma and squamous carcinoma tissues, but not in heavy surfactant aggregates from adenocarcinoma tissues. A larger amount of bone type AP (BAP) was found in light surfactant aggregate fractions from squamous cell carcinomas than those from adenocarcinoma tissues or non-carcinoma tissues from patients with either type of cancer. LAP, BAP, and SP-A were identified immunohistochemically in type II pneumocytes from non-carcinoma tissues and adenocarcinoma cells, but no distinct SP-A staining was observed in squamous cell carcinoma tissues. The present study has thus revealed several differences in pulmonary surfactant aggregates and AP isozymes between adenocarcinoma tissue and squamous cell carcinoma tissue.

Effect of SP-B peptides on the uptake of liposomes by alveolar cells

BACKGROUND

Exogenous surfactant has been accepted worldwide as a therapy of RDS in premature and term infants. Exogenous surfactant is usually derived from lung extracts containing phospholipids and the surfactant proteins SP-B and SP-C. Synthetic peptides of SP-B and SP-C are being tested with the aim to develop a completely synthetic surfactant preparation. Nevertheless, the effects of these peptides on the endogenous surfactant metabolism remain unknown.

OBJECTIVES

The effect of synthetic SP-B peptides on uptake of surfactant-like liposomes was investigated in alveolar cells. Native SP-B and seven SP-B peptides were included: monomeric and dimeric SP-B(1-25) (Cys-11 --> Ala-11), SP-B(63-78)and Ala-SP-B(63-78) (Cys-71 --> Ala-71;Cys-77 --> Ala-77)and their serine mutants.

METHODS

In vitro, alveolar macrophages (AM) and alveolar type II cells (ATII) were incubated with liposomes containing SP-B or one of its peptides. In vivo, rats received intratracheally various SP-B peptides (SP-B/lipid ratio 1:33 w/w) incorporated in fluorescent surfactant-like liposomes. One hour after instillation, AM and ATII were isolated and cell-associated fluorescence was determined using flow cytometry. Confocal laser microscopy was performed to ensure internalization of the liposomes.

RESULTS

In vitro uptake by AM or ATII was not influenced by the SP-B peptides. In vivo, SP-B(1-25) and Ser-SP-B(1-25) increased the uptake by AM whereas dSP-B(1-25) decreased the uptake. Neither SP-B(1-25) nor dSP-B(1-25 )affected total uptake by ATII. The overall uptake by SP-B(63-78) variants was not changed.

CONCLUSIONS

Surface-active synthetic SP-B peptides do not interfere with the normal uptake of surfactant by ATII.

The influence of refractory ceramic fibres on pulmonary morphology, redox and immune system in rats

Refractory ceramic fibres (RCF) were studied in male SPRD rats by both in vivo long term sequential and in vitro methods. RCF was administered by single intratracheal instillation and the lungs were examined at the end of months 1, 3 and 6 after exposure. In addition, the direct toxicity of the fibres was examined in a primary culture of alveolar macrophages (AM) and in pneumocytes type II (T2). Pulmonary morphological changes, a number of parameters of the redox system, such as activity of extracellular Cu,Zn/superoxide dismutase (EC-SOD), total glutathione content of the lungs (GSH) and immunoglobulins in bronchoalveolar lavage (IgA, IgG, IgM) and in the blood were measured. The composition of the original RCF and the elemental content of the lung tissue were compared by energy dispersive x-ray analysis (EDXA) before and after exposure. Macrophage alveolitis became confluent and moderate fibrosis developed by the end of month 3, and after 6 months of exposure the intensity decreased to the level of the first month. The RCF did not significantly influence the activity of EC-SOD or the total glutathione content of the lungs. Although aluminium and silicon could be demonstrated by EDXA in the lung tissue at the end of month 3, these elements were no longer detectable by the end of month 6. The RCF decreased IgA significantly in bronchoalveolar lavage (BAL). The main components of RCF induced pulmonary alterations, whereas no significant change could be detected in EC-SOD and GSH. Injuries caused by direct toxicity could be observed in the cell membranes only at the highest concentration. On the basis of these results RCF can be determined as moderately toxic fibres.

Porcine alveolar epithelial cells in primary culture: morphological, bioelectrical and immunocytochemical characterization

PURPOSE

The purpose of this study was to establish a primary culture of porcine lung epithelial cells as an alternative to the currently existing cell cultures from other species, such as e.g., rat or human. Primary porcine lung epithelial cells were isolated, cultivated and analyzed at distinct time points after isolation.

MATERIALS AND METHODS

The main part of the work focused on the morphology of the cells and the detection of alveolar epithelial cell markers by using electron microscopy, immunofluorescence microscopy and immunoblotting. Regarding a later use for in vitro pulmonary drug absorption studies the barrier properties of the cell monolayer were evaluated by monitoring bioelectrical parameters and by marker transport.

RESULTS

Epithelial cells isolated from porcine lung grew to confluent monolayers with typical intercellular junctions within a few days. Maximum transepithelial resistance of about 2,000 Omega cm2 was achieved and demonstrated the formation of a tight epithelial barrier. Permeability data of sodium fluorescein recommended a minimal transepithelial resistance of 600 Omega cm2 for transport studies. The cell population changed from a heterogeneous morphology and marker distribution (caveolin-1, pro-SP-C, surface sugars) towards a monolayer consisting of two cell types resembling type I and type II pneumocytes.

CONCLUSIONS

The porcine alveolar epithelial primary cell culture holds promise for drug transport studies, because it shares major hallmarks of the mammalian alveolar epithelium and it is easily available and scaled up for drug screening.

Clathrin-mediated endocytosis of FITC-albumin in alveolar type II epithelial cell line RLE-6TN

We examined mechanisms of FITC-albumin uptake by alveolar type II epithelial cells using cultured RLE-6TN cells. Alkaline phosphatase activity and the expression of cytokeratin 19 mRNA, which are characteristic features of alveolar type II epithelial cells, were detected in RLE-6TN cells. The uptake of FITC-albumin by the cells was time and temperature dependent and showed the saturation kinetics of high- and low-affinity transport systems. FITC-albumin uptake was inhibited by native albumin, by chemically modified albumin, and by metabolic inhibitors and bafilomycin A1, an inhibitor of vacuolar H+-ATPase. Confocal laser scanning microscopic analysis after FITC-albumin uptake showed punctate localization of fluorescence in the cells, which was partly localized in lysosomes. FITC-albumin taken up by the cells gradually degraded over time, as shown by fluoroimage analyzer after SDS-PAGE. The uptake of FITC-albumin by RLE-6TN cells was not inhibited by nystatin, indomethacin, or methyl-β-cyclodextrin (inhibitors of caveolae-mediated endocytosis) but was inhibited by phenylarsine oxide and chlorpromazine (inhibitors of clathrin-mediated endocytosis) in a concentration-dependent manner. Uptake was also inhibited by potassium depletion and hypertonicity, conditions known to inhibit clathrin-mediated endocytosis. These results indicate that the uptake of FITC-albumin in cultured alveolar type II epithelial cells, RLE-6TN, is mediated by clathrin-mediated but not by caveolae-mediated endocytosis, and intracellular FITC-albumin is gradually degraded in lysosomes. Possible receptors involved in this endocytic system are discussed.

Primary rat alveolar epithelial cells for use in biotransformation and toxicity studies

The alveolar epithelium may function as a barrier for airborne xenobiotics, and in vitro models mimicking this barrier are useful for metabolism and toxicity studies. To gain insight into the metabolic competence of alveolar epithelial cells (AECs), we investigated transcript expression of 10 different cytochrome P450 monooxygenases as well as expression of surfactant proteins A to D. We also investigated gene expression of the transcription factors PCNA, TTF-1, HNF3beta , GATA-6, C/EBPalpha and C/EBPdelta which drive, at least in part, development and differentiation of alveolar epithelium. We further studied the metabolism of testosterone, a substrate for cytochrome P450 (CYP) monooxygenases, in cultures of AECs. Essentially, medium supplementation with 5% rat serum, as opposed to 10% FCS, promoted a high level of differentiation, as judged by the mRNA expression of CYP monooxygenases, e.g. 1A1, 1A2, 2B1 and 2J3, the expression of the surfactant proteins A, B, and C, the immunohistochemical staining for surfactant protein C, and staining for alkaline phosphatase activity. Further, AECs, when cultured in the presence of 5% rat serum, promoted metabolic competence, as evidenced by the fingerprinting of individual testosterone metabolites. We thus characterized AECs in culture and found these respiratory epithelial cells to express an array of differentiation markers and showed these cultures to be metabolically competent under optimized culture conditions.

Differential expression of a V-type ATPase C subunit gene, Atp6v1c2, during culture of rat lung type II pneumocytes

The lung alveolar epithelium consists of type I and type II pneumocytes. In vivo, the type II cell is the progenitor cell from which the type I cell originates. When freshly-isolated type II cells are cultured under conventional conditions they rapidly lose their phenotypic properties and attain characteristics of type I cells. Taking advantage of this transdifferentiation, we sought to identify genes that are differentially expressed during culture of rat type II cells. Using suppression subtractive hybridization (SSH), a vacuolar-type H+-ATPase (V-ATPase) C2 subunit gene (Atp6v1c2) was found to be enriched in freshly isolated rat type II cells compared to those cultured for 4 days. Northern blotting and reverse-transcription polymerase chain reaction (RT-PCR) confirmed the differential expression of Atp6v1c2 during in vitro culture of isolated type II cells. Expression ofAtp6v1c2 was significantly reduced early during in vitro culture: almost 90% reduction was observed after 24 h of incubation as determined by real-time PCR. In situ hybridization showed that Atp6v1c2 is expressed in both bronchiolar and alveolar lung epithelial cells, an expression pattern similar to that of surfactant protein B (SP-B). Multi-tissue Northern blotting revealed a unique tissue distribution with Atp6v1c2 expression limited to lung, kidney and testis. The presence and expression of Atp6v1c2 gene transcript isoforms, resulting from alternative splicing, were also investigated. Elucidation of differential expression of Atp6v1c2 in type II cells and further studies of its regulation may provide information useful in understanding the molecular mechanism underlying phenotypic and functional changes during transdifferentiation of alveolar epithelial cells.

Cell culture models of the respiratory tract relevant to pulmonary drug delivery

The respiratory tract holds promise as an alternative site of drug delivery due to fast absorption and rapid onset of drug action, with avoidance of hepatic and intestinal first-pass metabolism as an additional benefit compared to oral drug delivery. At present, the pharmaceutical industry increasingly relies on appropriate in vitro models for the faster evaluation of drug absorption and metabolism as an alternative to animal testing. This article reviews the various existing cell culture systems that may be applied as in vitro models of the human air-blood barrier, for instance, in order to enable the screening of large numbers of new drug candidates at low cost with high reliability and within a short time span. Apart from such screening, cell culture-based in vitro systems may also contribute to improve our understanding of the mechanisms of drug transport across such epithelial tissues, and the mechanisms of action how advanced drug carriers, such as nanoparticles or liposomes, can help to overcome these barriers. After all, the increasing use and acceptance of such in vitro models may lead to a significant acceleration of the drug development process by facilitating the progress into clinical studies and product registration.

Metabolism of verapamil in cultures of rat alveolar epithelial cells and pharmacokinetics after administration by intravenous and inhalation routes

Administration of therapeutic entities by inhalation opens new possibilities for drug entry into systemic circulation, but this requires passage through the alveolar epithelium. Little is known about the pulmonary metabolism of verapamil. Specifically, this cardiovascular drug suffers from extensive first pass metabolism. We therefore evaluated the metabolism of verapamil in cultured alveolar epithelium and compared findings with results after administration by inhalation and intravenous routes. Specifically, cell culture of alveolar epithelium was characterized by gene expression of surfactant proteins A, B, C, and D, by immunohistochemistry of surfactant protein C, by staining for laminar bodies, and by gene expression of cytochrome P450 monooxygenases. During 6 days of culture expression, all cellular differentiation markers were obvious, albeit at different levels. With testosterone as substrate, we found alveolar epithelial cells to produce several stereo- and site-specific hydroxylation products. This provided evidence for metabolic competence of cultured alveolar epithelial cells. With verapamil as substrate, only limited production of metabolites was observed in cell culture assays, and similar results were recorded after administration by inhalation and intravenous routes. Likewise, elimination of verapamil from lung tissue and plasma was similar by both routes of administration. In conclusion, administration of verapamil by inhalation-abrogated extensive first pass metabolism frequently seen after oral application, and this may well be extended to the development of drugs with similar pharmacokinetic defects.

Influence of phosphatidylglycerol on the uptake of liposomes by alveolar cells and on lung function

The effect of phosphatidylglycerol on the uptake of surfactant-like liposomes by alveolar type II cells and alveolar macrophages as well as the effect on endogenous surfactant function was studied in vivo. Healthy ventilated rats were intratracheally instilled with fluorescent labeled liposomes with different concentrations of phosphatidylglycerol. Lung function was determined by monitoring arterial oxygenation and, at the end of the experiment, by recording static pressure-volume curves. In addition, alveolar cells were isolated, and cell-associated fluorescence was determined using flow cytometry. The results show that, in the presence of cofactors (Ca(2+), Mg(2+)), phosphatidylglycerol stimulates the uptake by alveolar macrophages but hardly affects the uptake by alveolar type II cells. High concentrations of phosphatidylglycerol reduce the number of alveolar macrophages in the alveolar space and deteriorate lung function. On the other hand, the presence of cofactors protects the lung against the negative effects of phosphatidylglycerol on endogenous surfactant and alveolar macrophages. This study indicates that the phosphatidylglycerol concentration may play a fundamental role in the surfactant function and metabolism depending on the presence of so-called cofactors like calcium and magnesium; further study is needed to clarify the mechanisms involved.

The effect of stone-wool on rat lungs and on the primary culture of rat alveolar macrophages and type II pneumocytes

The effect of stone-wool has been studied in both in vivo long term sequential and in vitro methods in male Sprague-Dawley rats. Stone-wool was administered by single intratracheal instillation and the lungs were examined after 1, 3 and 6 months of exposure by morphological methods. UICC crocidolite was applied as a positive control. In addition, the effects of both fibres were examined in primary cultures of alveolar macrophages (AM) and type II pneumocytes (T2) by morphological, biochemical and immunological methods. By the end of 6 months stone-wool induced moderate pulmonary interstitial inflammation and fibrosis without progression, whereas crocidolite induced progressive interstitial inflammation and fibrosis as a function of time. Although stone-wool inhibited phagocytosis, it did not induce serious membrane damage to the cells examined and did not destroy their ultrastructure. It significantly reduced the activity of Cu,Zn/superoxide dismutase (SOD) and alkaline phosphatase (AP) in alveolar macrophages and significantly decreased the activity of AP and gamma-glutamyl transpeptidase (GGT) in type II pneumocytes. Crocidolite, on the other hand, decreased the activity of all enzymes (glutathione peroxidase, GSH-Px; glutathione reductase, GSH-Rd) of glutathione metabolism as well as alkaline phosphatase in alveolar macrophages. It decreased the activity of all enzymes in type II pneumocytes, except for Cu,Zn/SOD. On exposure to stone-wool, the production of inflammatory proteins, macrophage chemoattractant protein-1 (MCP-1) and macrophage inhibitory protein-1alpha (MIP-1alpha) increased in both cultured cells but did not reach the level induced by crocidolite. Our results suggested that stone-wool is less toxic than crocidolite. Whether it is carcinogenic or not, is still an open question.

Freshly isolated rat alveolar type I cells, type II cells, and cultured type II cells have distinct molecular phenotypes

We used microarray analysis with Affymetrix rat chips to determine gene expression profiles of freshly isolated rat type I (TI) and TII cells and cultured TII cells. Our goals were 1) to describe molecular phenotypic "fingerprints" of TI and TII cells, 2) to gain insight into possible functional differences between the two cell types through differentially expressed genes, 3) to identify genes that might indicate potential functions of TI cells, since so little is known about this cell type, and 4) to ascertain the similarities and differences in gene expression between cultured TII cells and freshly isolated TI cells. For these experiments, we used preparations of isolated TI and TII cells that contained <2% cross-contamination. With a false discovery rate of 1%, 601 genes demonstrated over twofold different expression between TI and TII cells. Those genes with very high levels of differential expression may be useful as markers of cell phenotype and in generating novel hypotheses about functions of TI and TII cells. We found similar numbers of differentially expressed genes between freshly isolated TI or TII cells and cultured TII cells (698, 637 genes) and freshly isolated TI and TII cells (601 genes). Tests of sameness/difference including cluster dendrograms and log/log identity plots indicated major differences between the phenotypes of freshly isolated TI cell and cultured type II cell populations. The latter results suggest that experiments with TII cells cultured under these conditions should be interpreted with caution with respect to biological relevance to TI or TII cells.

Ambroxol reduces LPS toxicity mediated by induction of alkaline phosphatases in rat lung

Alkaline phosphatases (APs) have been suggested to detoxify lipopolysaccharide (LPS) by dephosphorylation. Ambroxol, a bronchial expectorant, is known to accelerate the secretion of pulmonary surfactant particles including AP molecules as a pharmacological action. In the present study, some beneficial effects of ambroxol on LPS toxicity in the rat lung were investigated. In an experiment using the rat lung organ culture, AP activities were enhanced in a time-dependent manner by incubation with 25 microM of ambroxol in both the tissue and the medium. Western blot analysis indicated that AP activity was elevated by the treatment with ambroxol, due to the induction of surfactant proteins (SPs) and AP molecules. In the in vivo experiment, the serum LPS content was markedly increased after LPS administration to rats by intratracheal instillation of 20 mg/kg. However, when the rats were pretreated with oral ambroxol (1.0 mg/kg) at 1 h before LPS challenge, the area under the concentration--time curve (AUC) of serum LPS was significantly decreased. These results suggest that ambroxol inhibits the translocation of LPS from the lung into the circulation as well as its detoxification effect via the elevation of AP activity. Bromhexine, another expectorant, is less effective than ambroxol as an LPS detoxificant. Maintenance of high AP activity level in the lung suggests APs to have physiological significant effects against the inflammatory events induced by LPS.

Distinct effects of SP-B and SP-C on the uptake of surfactant-like liposomes by alveolar cells in vivo and in vitro

The effects of surfactant protein B (SP-B) and SP-C on the uptake of surfactant-like liposomes by alveolar type II cells and alveolar macrophages were studied both in vivo and in vitro. In vivo, mechanically ventilated rats were intratracheally instilled with fluorescently labeled liposomes that had SP-B and/or SP-C incorporated in different concentrations. Consequently, the alveolar cells were isolated, and cell-associated fluorescence was determined using flow cytometry. The results show that the incorporation of SP-B does not influence the uptake, and it also does not in the presence of essential cofactors. The inclusion of SP-C in the liposomes enhanced the alveolar type II cells at a SP-C to lipid ratio of 2:100. If divalent cations (calcium and magnesium) were present at physiological concentrations in the liposome suspension, uptake of liposomes by alveolar macrophages was also enhanced. In vitro, the incorporation of SP-B affected uptake only at a protein-to-lipid ratio of 8:100, whereas the inclusion of SP-C in the liposomes leads to an increased uptake at a protein-to-lipid ratio of 1:100. From these results, it can be concluded that SP-B is unlikely to affect uptake of surfactant, whereas SP-C in combination with divalent cations and other solutes are capable of increasing the uptake.

A Common Pathway for the Uptake of Surfactant Lipids by Alveolar Cells

The uptake of different surfactant lipids-dipalmitoylphosphatidylcholine (DPPC), phosphatidylglycerol (PG), or phosphatidylinositol (PI)-and liposomes with a surfactant-like composition by alveolar type II cells (alveolar type II cells) and macrophages (alveolar macrophages) was studied in vitro. Fluorescent-labeled liposomes containing either 86% of the studied lipid, i.e., DPPC, PG, PI, and 6% labeled phosphatidylethanolamine (PE) and 8% cholesterol or a lipid mixture similar to surfactant (DPPC, PG, PI, phosphatidylcholine, PE, and cholesterol in a weight ratio of 55:8:2:21:8:6) were incubated with alveolar macrophages and alveolar type II cells. The cell-associated fluorescence assessed by flow cytometry demonstrated a higher uptake of PG and PI by both alveolar macrophages and alveolar type II cells, and a lower uptake of DPPC by alveolar macrophages. In addition, fewer alveolar type II cells take up DPPC, whereas there are no differences for the alveolar macrophages in the number of cells involved in the uptake. Competition experiments with Texas Red-labeled liposomes and either DPPC liposomes or PI liposomes labeled with Bodipy indicated that all these liposomes are internalized via the same pathway by alveolar cells. Thus, lipid composition directly influences the (re)uptake of surfactant.

Evidence of a functional CFTR Cl(-) channel in adult alveolar epithelial cells

The cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in the fetal lung, but during lung development it gradually disappears in cells of future alveolar spaces. Recent studies have implicated the CFTR in fluid transport by the adult alveolar epithelium, but its presence has not been demonstrated directly. This study re-evaluated CFTR expression and activity in the adult pulmonary epithelium by using freshly isolated rat alveolar type II (ATII) cells. CFTR mRNA was detected by semiquantitative polymerase chain reaction on the day of cell isolation but was rapidly reduced by 60% after 24 h of cell culture. This was paralleled by a similar decrease of surfactant protein A expression and alkaline phosphatase staining, markers of the ATII cell phenotype. CFTR expression increased significantly on day 4 in cells grown on filters at the air-liquid interface compared with cells submerged or grown on plastic. Significantly higher CFTR expression was detected in distal lung tissue compared with the trachea. The CFTR was also found at the protein level in Western blot experiments employing lysates of freshly isolated alveolar cells. Whole cell patch-clamp experiments revealed cAMP-stimulated, 5-nitro-2-(3-phenylpropylamino)-benzoate-sensitive Cl(-) conductance with a linear current-voltage relationship. In cell-attached membrane patches with 100 microM amiloride in pipette solution, forskolin stimulated channels of approximately 4 pS conductance. Our results indicate that 50-250 of functional CFTR Cl(-) channels occur in adult alveolar cells and could contribute to alveolar liquid homeostasis.