The American Journal of Physiology

Our medical research library holds 18 studies published in The American Journal of Physiology (1977–1999). Each entry links to the study's record on PubMed and, where there is one, to the publisher's page and a free full text. 18 have an abstract, the authors' own summary as PubMed records it: open "Abstract" to read it.

About the journal

• Publisher: American Physiological Society
• Published: 1898 to the present, United States
• Language: English
• ISSN: 0002-9513 (print), 2163-5773 (electronic)
• Its record in the NLM Catalog

1990s

• Asbestos exposure upregulates the adhesion of pleural leukocytes to pleural mesothelial cells via VCAM-1. N. Choe, J. Zhang, A. Iwagaki, et al. 1999;277(2):L292-300. PubMed · Publisher

  Abstract

  This study was designed to assess the effects of in vitro and in vivo asbestos exposure on the adhesion of rat pleural leukocytes (RPLs) labeled with the fluorochrome calcein AM to rat pleural mesothelial cells (RPMCs). Exposure of RPMCs for 24 h to either crocidolite or chrysotile fibers (1.25-10 microgram/cm(2)) increased the adhesion of RPLs to RPMCs in a dose-dependent fashion, an effect that was potentiated by interleukin-1beta. These findings were not observed with nonfibrogenic carbonyl iron particles. Crocidolite and chrysotile plus interleukin-1beta also upregulated vascular cell adhesion molecule-1 mRNA and protein expression in RPMCs, and the binding of RPL to asbestos-treated RPMCs was abrogated by anti-vascular cell adhesion molecule-1 antibody. PRLs exposed by intermittent inhalation to crocidolite for 2 wk manifested significantly greater binding to RPMCs than did RPLs from sham-exposed animals. The ability of asbestos fibers to upregulate RPL adhesion to RPMCs may play a role in the induction and/or potentiation of asbestos-induced pleural injury.

• Asbestos-induced phosphorylation of epidermal growth factor receptor is linked to c-fos and apoptosis. C.L. Zanella, C.R. Timblin, A. Cummins, et al. 1999;277(4):L684-93. PubMed · Publisher

  Abstract

  We examined the mechanisms of interaction of crocidolite asbestos fibers with the epidermal growth factor (EGF) receptor (EGFR) and the role of the EGFR-extracellular signal-regulated kinase (ERK) signaling pathway in early-response protooncogene (c-fos/c-jun) expression and apoptosis induced by asbestos in rat pleural mesothelial (RPM) cells. Asbestos fibers, but not the nonfibrous analog riebeckite, abolished binding of EGF to the EGFR. This was not due to a direct interaction of fibers with ligand, inasmuch as binding studies using fibers and EGF in the absence of membranes showed that EGF did not adsorb to the surface of asbestos fibers. Exposure of RPM cells to asbestos caused a greater than twofold increase in steady-state message and protein levels of EGFR (P < 0.05). The tyrphostin AG-1478, which inhibits the tyrosine kinase activity of the EGFR, but not the tyrphostin A-10, which does not affect EGFR activity, significantly ameliorated asbestos-induced increases in mRNA levels of c-fos but not of c-jun. Pretreatment of RPM cells with AG-1478 significantly reduced apoptosis in cells exposed to asbestos. Our findings suggest that asbestos-induced binding to EGFR initiates signaling pathways responsible for increased expression of the protooncogene c-fos and the development of apoptosis. The ability to block asbestos-induced elevations in c-fos mRNA levels and apoptosis by small-molecule inhibitors of EGFR phosphorylation may have therapeutic implications in asbestos-related diseases.

• Asbestos-induced lung epithelial permeability: potential role of nonoxidant pathways. M.W. Peterson, J. Kirschbaum. 1998;275(2):L262-8. PubMed · Publisher

  Abstract

  Asbestos fibers are an important cause of lung fibrosis; however, the biological mechanisms are incompletely understood. The lung epithelium serves an important barrier function in the lung, and disrupting the epithelial barrier can contribute to lung fibrosis. Lung epithelial permeability is increased in patients with asbestosis, and asbestos fibers increase permeability across cultured human lung epithelium. However, the mechanism of this increased permeability is not known. Many of the biological effects of asbestos are postulated to be due to its ability to generate oxidants, and oxidants are known to increase epithelial permeability. However, we previously reported that altering the iron content of asbestos (important in oxidant generation) had no effect on its ability to increase permeability. For that reason, we undertook these studies to determine whether asbestos increases epithelial permeability through nonoxidant pathways. Both extracellular (H2O2) and intracellular (menadione) oxidants increase paracellular permeability across human lung epithelial monolayers. Extracellular catalase but not superoxide dismutase prevented increased permeability after both oxidant exposures. However, catalase offered no protection from asbestos-induced permeability. We next depleted the cells of glutathione or catalase to determine whether depleting normal cellular antioxidants would increase the sensitivity to asbestos. Permeability was the same in control cells and in cells depleted of these antioxidants. In addition to generating oxidants, asbestos also activates signal transduction pathways. Blocking protein kinase C activation did not prevent asbestos-induced permeability; however, blocking tyrosine kinase with tyrophostin A25 did prevent asbestos-induced permeability, and blocking tyrosine phosphatase with sodium vanadate enhanced the effect of asbestos. These data demonstrate that asbestos may increase epithelial permeability through nonoxidant pathways that involve tyrosine kinase activation. This model offers an important system for studying pathways involved in regulating lung epithelial permeability.

• Cigarette smoke increases amosite asbestos fiber binding to the surface of tracheal epithelial cells. A. Churg, J. Sun, K. Zay. 1998;275(3):L502-8. PubMed · Publisher

  Abstract

  Binding of asbestos fibers to the cell surface appears to be important in the initiation of intracellular signaling events as well as in initiation of particle uptake by the cell. We have previously shown that cigarette smoke increases the uptake of asbestos fibers by tracheal epithelial cells in explant culture. Whether smoke acts by increasing surface binding of fibers is not known. In this study, we exposed rat tracheal explants to air or cigarette smoke and then to a suspension of amosite asbestos. Explants were harvested after 1 or 24 h of dust exposure and washed by repeated dips in culture medium to remove loosely bound fibers, and the number of fibers adhering to the apical cell surfaces was determined by scanning electron microscopy. Smoke-exposed explants retained significantly more surface fibers than air-exposed explants. After four washes, binding levels were similar at 1 and 24 h. The smoke effect was still present when incubations were carried out at 4 degrees C, but binding was decreased approximately 25%. Preincubation of the asbestos fibers with iron chloride to increase surface iron increased fiber binding in both air- and smoke-exposed explants, whereas preincubation of the fibers with the iron chelator deferoxamine decreased binding after air exposure and completely eliminated the smoke effect. Inclusion of mannitol or catalase in the medium or preincubation of the explants with GSH produced decreases in binding of 10-25% in air-exposed explants and generally greater decreases in smoke-exposed explants. We conclude that 1) amosite binding is a very rapid process that does not require active cellular metabolism, 2) cigarette smoke increases adhesion of fibers to the epithelial surfaces, and 3) iron on the asbestos fiber appears to play an important role in binding, probably through an active oxygen species-mediated process.

• Resistance of pleural mesothelioma cell lines to apoptosis: relation to expression of Bcl-2 and Bax. S.R. Narasimhan, L. Yang, B.I. Gerwin, et al. 1998;275(1):L165-71. PubMed · Publisher

  Abstract

  A failure of normal apoptosis, often due to mutant p53, may contribute to the formation of a cancer and to its resistance to therapy. Mesothelioma, an asbestos-induced tumor, is highly resistant to therapy but generally expresses wild-type p53. We asked whether mesothelioma was resistant to apoptosis and whether resistance was associated with altered expression of the antiapoptotic protein Bcl-2 or proapoptotic protein Bax. We found that three mesothelioma cell lines (1 with wild-type p53) were highly resistant to apoptosis induced by oxidant stimuli (asbestos, H2O2) or nonoxidant stimuli (calcium ionophore) compared with primary cultured mesothelial cells. By immunostaining, one of these three lines expressed Bcl-2 but only during mitosis. By immunoblotting, 3 of 14 additional mesothelioma lines (9 of 14 with wild type p53) expressed Bcl-2 but all 14 of 14 expressed the proapoptotic Bax, giving a low ratio of Bcl-2 to Bax. We conclude that mesothelioma cell lines are resistant to apoptosis and that the failure in apoptosis is not explained by Bcl-2 but by other mechanisms that counteract the proapoptotic effect of Bax.

• Involvement of the ICE family of proteases in silica-induced apoptosis in human alveolar macrophages. R. Iyer, A. Holian. 1997;273(4):L760-7. PubMed · Publisher

  Abstract

  Exposure to silica dust can result in lung inflammation that may progress to fibrosis for which there is no effective clinical treatment. The mechanisms involved in the development of pulmonary silicosis have not been well defined; however, most current evidence implicates a central role for alveolar macrophages in this process. We have previously demonstrated that fibrotic agents, such as asbestos and silica, induce apoptosis in human alveolar macrophages. The goal of this study was to identify molecular events in the silica-induced apoptotic process to better understand the mechanism by which fibrotic agents may be inducing apoptosis in human alveolar macrophages. To elucidate the possible mechanism by which silica causes apoptosis, we investigated the involvement of the interleukin-converting enzyme (ICE) family of proteases. Human alveolar macrophages were treated with silica in vitro and were examined for the involvement of ICE, Ich-1L, and cpp32beta in silica-induced apoptosis. Pretreatment of cells with 10 microM of the ICE inhibitor z-Val-Ala-Asp-fluoromethyl ketone and the cpp32beta inhibitor Asp-Glu-Val-Asp-fluoromethyl ketone completely blocked silica-induced apoptosis. Additionally, an increased formation of the active p20 fragments of ICE and Ich-1L as well as degradation of the inactive zymogen form of cpp32beta protein were observed in silica-treated human alveolar macrophages, indicating activation of these proteases. Furthermore, degradation of the nuclear protein poly(ADP-ribose) polymerase was observed within 2 h of silica treatment. These results suggest that silica-induced apoptosis involves activation of the ICE family of proteases and is the first step in elucidating the intracellular mechanism of particulate-induced apoptosis in human alveolar macrophages.

• Role of extracellular signal-regulated protein kinases in apoptosis by asbestos and H2O2. L.A. Jiménez, C. Zanella, H. Fung, et al. 1997;273(5):L1029-35. PubMed · Publisher

  Abstract

  Stimulation of cell signaling cascades by oxidants may be important in the pathogenesis of pulmonary and pleural diseases. Here, we demonstrate in rat pleural mesothelial cells that apoptotic concentrations of crocidolite asbestos and H2O2 induce phosphorylation and activation of extracellular signal-regulated protein kinases (ERK). Activation of c-jun-NH2-terminal protein kinases (JNK)/stress-activated protein kinases was also observed in response to H2O2. In contrast, asbestos caused more protracted activation of ERK without JNK activation. Both H2O2- and asbestos-induced activation of ERK was abolished by catalase. Moreover, chelation of surface iron from crocidolite fibers or addition of N-acetyl-L-cysteine prevented ERK activation and apoptosis by crocidolite, indicating an oxidative mechanism of cell signaling. The MEK1 inhibitor PD-98059 abrogated asbestos-induced apoptosis, confirming a causal relationship between ERK activation and apoptosis. These results suggest that distinct cell-signaling cascades may be important in phenotypic responses elicited by oxidant stresses.

• Asbestos induces apoptosis in human alveolar macrophages. R.F. Hamilton, L.L. Iyer, A. Holian. 1996;271(5 Pt 1):L813-9. PubMed · Publisher

  Abstract

  Asbestos refers to a group of fibrous minerals implicated in the development of several lung diseases, including fibrosis (asbestosis), cancer, and malignant mesothelioma. Although major health risks exist in occupationally exposed individuals, low-level exposures of asbestos may still contribute to health problems. The mechanism by which asbestos causes lung disease is not clearly understood but has been proposed to involve the alveolar macrophage (AM). We propose that asbestos induces apoptosis of AM, resulting in the development of an inflammatory state. In this study, we examined two forms of asbestos, chrysotile (CHR) and crocidolite (CRO), along with a control fiber, wollastonite (WOL), to characterize their relative cytotoxicity and ability to stimulate apoptosis in vitro. AM were cultured for 24 h with these particulates and examined for cell viability (trypan blue exclusion) and apoptosis (morphology, levels of cytosolic oligonucleosomal DNA fragments, and DNA ladder). In the absence of a decrease in cell viability, both CHR and CRO produced changes in cell morphology consistent with apoptosis. In addition, levels of cytoplasmic oligonucleosomal DNA (Cell Death Detection enzyme-linked immunosorbent assay) were significantly enhanced for CHR (3-25 micrograms/ml) and CRO (25-75 micrograms/ml) in a dose-dependent manner (a process that was inhibitable by 10 microM Z-Val-Ala-Asp fluoromethyl ketone, an interleukin-converting enzyme inhibitor). In contrast, WOL (up to 400 micrograms/ml) produced no significant DNA fragmentation in a 24-h culture. Neither CHR nor CRO caused DNA ladder formation in 24-h cell cultures. However, in 48-h cell cultures, both CHR- and CRO-exposed cells, but not WOL, resulted in the formation of DNA ladders characteristic of apoptosis. In summary, these results suggest that, unlike nonfibrogenic particulates, low doses of asbestos fibers cause apoptosis in cultured human AM that may be an early step in the development of lung fibrosis.

• Fibronectin expression and organization in mesothelial and mesothelioma cells. P.C. Ferriola, W. Stewart. 1996;271(5 Pt 1):L804-12. PubMed · Publisher

  Abstract

  Mesothelial cells are believed to be the progenitor cells for malignant mesothelioma, a tumor associated with exposure to asbestos and other mineral fibers. Little is known regarding fibronectin (Fn) function in mesothelial and mesothelioma cells. Fn RNA, protein levels, and localization were assessed in secondary cultures and later passages of spontaneously immortalized rat pleural mesothelial (NRM) cells and in neoplastic cell lines derived from asbestos-induced mesotheliomas. NRM cells expressed similar levels of Fn RNA regardless of passage number or cell density, as determined by Northern blotting and ribonuclease protection assays. Western blotting showed that Fn protein was both secreted by NRM cells and associated with cell lysates. Immunofluorescent confocal laser scanning microscopy demonstrated that secondary cultures of NRM cells assembled Fn into abundant homogeneous fibrillar arrays organized primarily between cells, whereas later passages of NRM cells displayed abundant but less homogeneous Fn organization. Fn RNA and protein levels in neoplastic mesothelial cells were slightly less or similar to levels in NRM cells. Organization of Fn in neoplastic cells was heterogeneous compared with secondary cultures of NRM cells, but Fn fibril formation was still apparent. F-actin microfilaments were organized in both NRM and neoplastic cells; however, actin stress fibers were maintained in neoplastic cells, whereas NRM cells displayed dense actin peripheral bands at high density. The maintenance of organized Fn and actin in mesothelioma cells is surprising and may contribute to the localized growth and invasive properties of these tumors.

• Asbestos causes DNA strand breaks in cultured pulmonary epithelial cells: role of iron-catalyzed free radicals. D.W. Kamp, V.A. Israbian, S.E. Preusen, et al. 1995;268(3 Pt 1):L471-80. PubMed · Publisher

  Abstract

  Asbestos causes pulmonary fibrosis and various malignancies by mechanisms that remain uncertain. Reactive oxygen species in part cause asbestos toxicity. However, it is not known whether asbestos-induced free radical production causes alveolar epithelial cell (AEC) cytotoxicity by inducing DNA strand breaks (DNA-SB). We tested the hypothesis that asbestos-induced AEC injury in vitro is due to iron-catalyzed free radical generation, which in turn causes DNA-SB. We found that amosite asbestos damages cultured human pulmonary epithelial-like cells (WI-26 cells) as assessed by 51Cr release and that an iron chelator, phytic acid (500 microM), attenuates these effects. A role for iron causing these effects was supported by the observation that ferric chloride-treated phytic acid did not diminish WI-26 cell injury. Production of hydroxyl radical-like species (.OH) was assessed based upon the .OH-dependent formation of formaldehyde (HCHO) in the presence of dimethyl sulfoxide. A variety of mineral dusts induced significant levels of .OH formation (nmol HCHO at 30 min: carbonyl iron, 85 +/- 21; amosite asbestos, 14 +/- 2; chrysotile asbestos, 7 +/- 1; titanium dioxide, 2.5 +/- 0.5). Phytic acid significantly diminished the asbestos-induced .OH production. DNA damage to AEC was assessed by the alkaline unwinding, ethidium bromide fluorometric technique. Hydrogen peroxide caused dose-dependent DNA-SB in WI-26 cells after a 30-min exposure period [50% effective dose (ED50): 5 microM] that was similar to other cell lines. Amosite asbestos induced dose-dependent DNA-SB in WI-26, A549, and primary isolated rat alveolar type II cells maintained in culture for 7-10 days (alveolar type I-like). Lower doses of amosite (0.5-5 micrograms/ml or 0.25-2.5 micrograms/cm2) caused significant WI-26 cell DNA-SB after prolonged exposure periods (> or = 2 days). Phytic acid ameliorated DNA damage in all three cultured AEC. There was a direct correlation between mineral dust-induced .OH production at 30 min and DNA-SB in WI-26 cells at 4 h (P < 0.0005). These data suggest that mineral dusts can be directly genotoxic to relevant target cells of asbestos, AEC. Furthermore, these results provide additional support for the premise that iron-catalyzed free radicals mediate asbestos-induced pulmonary toxicity.

• Urokinase receptor in human malignant mesothelioma cells: role in tumor cell mitogenesis and proteolysis. S. Shetty, A. Kumar, A. Johnson, et al. 1995;268(6 Pt 1):L972-82. PubMed · Publisher

  Abstract

  Urokinase (uPA) interacts with its receptor (uPAR) to promote proteolysis and tumor migration, functions of potential importance in the pathogenesis of malignant mesothelioma. Immunohistochemistry of human malignant mesothelioma tissue and mesothelioma cells (MS-1) showed that mesothelioma cells express uPAR. We isolated uPAR from MS-1 cells by metabolic labeling and showed that it could be induced by phorbol myristate acetate (PMA), lipopolysaccharide (LPS), a transforming growth factor-beta (TGF-beta) or tumor necrosis factor-alpha (TNF-alpha). Experiments with MS-1 cells showed that uPA binding was saturable, specific, and reversible with a mean dissociation constant (Kd) of 5.4 +/- 1.1 nM. Binding was inhibited by a blocking antibody to uPAR and by the uPA amino-terminal fragment (ATF), but not by low molecular weight uPA. uPAR expression was regulated transcriptionally and translationally; antisense oligonucleotides blocked expression of uPAR protein. Plasminogen activator inhibitor-1 (PAI-1) inhibited PA activity of preformed uPA/uPAR complexes and increased cycling of the receptor from the cell surface. Stimulation of subconfluent MS-1 cells by high molecular weight or recombinant uPA, but not ATF or low molecular weight fragment, caused concentration-dependent incorporation of [3H]thymidine. These data indicate a novel mechanism by which malignant mesothelioma cells localize pericellular proteolysis and concurrently regulate tumor cell proliferation.

• Asbestos exposure increases paracellular transport of fibrin degradation products across human airway epithelium. T.J. Gross, S.M. Cobb, M.W. Peterson. 1994;266(3 Pt 1):L287-95. PubMed · Publisher

  Abstract

  The inflammatory response to asbestos fiber inhalation suggests that the distal respiratory epithelium is an important early target of asbestos-induced injury. We have previously found that asbestos exposure increases the fibrinolytic activity and mannitol permeability of human airway epithelial cell monolayers. Because fibrin degradation products (FDP) are potent inflammatory mediators, we asked whether asbestos fiber exposure would increase the transepithelial flux of FDP into the interstitial space. To stimulate the pericellular environment following fiber deposition, asbestos-exposed epithelial monolayers grown on permeable filters were covered with human plasma containing fluorescein isothiocyanate (FITC)-labeled human fibrinogen. After 24 h, nearly twice as much FITC-FDP appeared in the abluminal chamber of asbestos-exposed monolayers compared with unexposed controls. This did not result solely from increased degradation product production because asbestos-exposed epithelium was more permeable at all apical FDP concentrations. The proteins that crossed asbestos-exposed monolayers included biologically relevant high-molecular-weight FDP, as demonstrated by streptavidin blotting of biotin-labeled FDP. We also found that FDP flux was not vectorial, was not saturable, did not involve proteolytic processing of FDP, and did not require active transport. Thus asbestos exposure increases the paracellular flux of intact FDP across human airway epithelium. This represents a novel mechanism whereby fiber-induced epithelial dysfunction may initiate and sustain inflammation in the distal airspace.

• Contrasting effects of alveolar macrophages and neutrophils on asbestos-induced pulmonary epithelial cell injury. D.W. Kamp, M.M. Dunn, J.S. Sbalchiero, et al. 1994;266(1 Pt 1):L84-91. PubMed · Publisher

  Abstract

  Pulmonary toxicity from asbestos may be due in part to oxidant-mediated mechanisms. The purpose of this study was to determine whether alveolar macrophages (AM) contribute to asbestos-induced alveolar epithelial cell injury by oxidant-dependent mechanisms similar to that previously described for polymorphonuclear leukocytes (PMN). We assessed 51Cr release from cultured rat alveolar epithelial cells (RAEC) and transformed human pulmonary epithelial-like cell lines (rat L2 and human WI-26: HPEC). Amosite asbestos caused dose-dependent injury to both RAEC and L2 cells after an 18-h incubation period. Rat PMN increased asbestos-induced injury to RAEC (11 vs. 20% 51Cr release). In contrast, rat AM diminished asbestos-induced injury to RAEC and L2 cells by 60-80%. Human monocytes cultured for 72 h also attenuated asbestos-induced HPEC damage. Asbestos stimulated more H2O2 release from PMN than from AM isolated from the same rats (5.3 +/- 0.6 vs. 0.3 +/- 0.1 nmol x 10(6) cells-1 x 2h-1). The protective effect of rat AM, as opposed to PMN, was not due to differences in asbestos-induced toxicity to each cell type, since > 90% of AM and PMN were nonviable after 18 h. Transmission electron microscopy demonstrated comparable uptake of asbestos by AM and PMN after a 2-h incubation period. However, after an 18-h exposure period, the PMN were completely lysed, whereas over 90% of the AM contained fibers, despite morphologic evidence of cytotoxicity. These results demonstrate that AM, unlike PMN, can reduce alveolar epithelial cell injury in this model.(ABSTRACT TRUNCATED AT 250 WORDS)

• Dibutyryl cAMP attenuates asbestos-induced pulmonary epithelial cell cytotoxicity and decline in ATP levels. V.A. Israbian, S.A. Weitzman, D.W. Kamp. 1994;267(5 Pt 1):L518-25. PubMed · Publisher

  Abstract

  Adenosine 3',5'-cyclic monophosphate (cAMP) analogues prevent lung injury in various models by mechanisms that remain unknown. We speculated that cAMP attenuates asbestos-induced pulmonary epithelial cell injury by limiting the effects of an oxidant stress. Agents that increase intracellular cAMP [dibutyryl cAMP (DBcAMP), terbutaline, or aminophylline] but not guanosine 3',5'-cyclic monophosphate (cGMP) attenuated WI-26 cell-specific 51Cr release caused by asbestos. The protective effects of DBcAMP were associated with negligible alterations in asbestos-induced .OH formation or decline in WI-26 cell glutathione levels. Cycloheximide, an inhibitor of protein synthesis, failed to diminish the effects of DBcAMP. ATP levels were measured to determine whether the effects of DBcAMP are due to preservation of cellular ATP. Asbestos caused dose-dependent reductions in cellular ATP and DB-cAMP attenuated these effects. To determine whether the protective effects of DBcAMP related to alterations in WI-26 cell growth, we assessed the effects of DBcAMP on WI-26 cell number over time. DBcAMP diminished WI-26 cell replication and increased the doubling time. These results demonstrate that DBcAMP diminishes asbestos-induced cytotoxicity to cultured WI-26 cells in part by maintaining intracellular ATP levels and inhibiting cellular replication. The reduction in asbestos-induced WI-26 cell injury occurs despite a persistent oxidant stress. The data suggest a novel strategy to limit pulmonary toxicity from asbestos that warrants further investigation.

• Asbestos directly increases lung epithelial permeability. M.W. Peterson, M.E. Walter, T.J. Gross. 1993;265(3 Pt 1):L308-17. PubMed · Publisher

  Abstract

  Asbestos causes the fibrotic lung disease asbestosis, but the biologic basis for this is unknown. Lung epithelial dysfunction including increased permeability is hypothesized to contribute to lung scarring in other forms of pulmonary fibrosis. Lung epithelial permeability is increased in both animals and humans exposed to asbestos. It is not known whether the increased epithelial permeability results from direct effects of asbestos or occurs as a result of the inflammatory reaction to asbestos fibers. To address this question we used a cultured human lung epithelial model, and we measured the direct effect of asbestos on lung epithelial barrier integrity as measured by mannitol permeability. We exposed the monolayer to chryogenically ground, respirable-sized chrysotile asbestos particles. This chrysotile asbestos caused a dose- and time-dependent increase in mannitol permeability across the epithelial monolayer. Increased mannitol permeability occurred both in the presence and in the absence of serum, was not due to cytotoxicity as measured by lactate dehydrogenase release, and was not associated with altered actin cytoskeleton at the light microscopic level. Permeability to 70 kDa neutral dextran also increased after asbestos exposure; however, the absolute permeability to dextran was less than mannitol permeability. Neither latex beads nor tantalum caused any change in permeability, suggesting that our findings are not explained by nonspecific effects of particles. Increased permeability did not reverse in the continued presence of asbestos and persisted even after removing the asbestos. Finally, surface-bound iron did not appear to be necessary for this effect because neither chelating iron with deferoxamine nor iron-loading the asbestos altered the effect on mannitol permeability. These results show that asbestos has direct effects on lung epithelial permeability. Together with the recent observation that asbestos directly increases epithelial fibrinolytic activity, our results suggest a novel mechanism for asbestos-induced lung injury.

• Asbestos exposure increases human bronchial epithelial cell fibrinolytic activity. T.J. Gross, S.M. Cobb, D.C. Gruenert, et al. 1993;264(3 Pt 1):L276-83. PubMed · Publisher

  Abstract

  Chronic exposure to asbestos fibers results in fibrotic lung disease. The distal pulmonary epithelium is an early target of asbestos-mediated injury. Local plasmin activity may be important in modulating endoluminal inflammatory responses in the lung. We studied the effects of asbestos exposure on cell-mediated plasma clot lysis as a marker of pericellular plasminogen activation. Exposing human bronchial epithelial (HBE) cells to 100 micrograms/ml of asbestos fibers for 24 h resulted in increased plasma clot lysis. Fibrinolytic activity was augmented in a dose-dependent fashion, was not due to secreted protease, and occurred only when there was direct contact between the plasma clot and the epithelial monolayer. Further analysis showed that asbestos exposure increased HBE cell-associated urokinase-type plasminogen activator (uPA) activity in a time-dependent manner. The increased cell-associated PA activity could be removed by acid washing. The increase in PA activity following asbestos exposure required new protein synthesis because it was abrogated by treatment with either cycloheximide or actinomycin D. Therefore, asbestos exposure increases epithelial-mediated fibrinolysis by augmenting expression of uPA activity at the cell surface by mechanisms that require new RNA and protein synthesis. These observations suggest a novel mechanism whereby exposure of the distal epithelium to inhaled particulates may result in a chronic inflammatory response that culminates in the development of fibrotic lung disease.

• A novel system for the culture of human lung: lung development and the response to injury. M.T. Hsu, M. Dimaio, O.K. Reiss, et al. 1992;263(3 Pt 1):L308-16. PubMed · Publisher

  Abstract

  Existing methods of fetal lung organ culture are complicated and require special skills. With the use of a polyester-based plastic sheet, we have developed a simpler human fetal lung organ culture that is viable for 6 wk. This novel method permits the study of growth and differentiation, pulmonary surfactant secretion, and the response of human lung tissue to injury in vitro. Lung tissues, obtained from human fetuses ranging in gestational age from 14 to 18 wk, were cultured on the polyester sheet in Dulbecco's modified Eagle medium supplemented with 15% fetal calf serum and gentamicin. Microscopic study of the fetal lung before culturing revealed round epithelial tubules, lined by glycogen-rich columnar cells and a thick cellular interstitium. After 1 wk in culture, morphological examination showed the development and expansion of alveolar saccules and thinning of the interstitium; type I and II pneumocytes as well as fibroblasts and myofibroblasts were present. Lipid analysis of the tissues, 2 wk after the initiation of the culture, demonstrated a high percentage of dipalmitoyl phosphatidylcholine characteristic of pulmonary surfactant. Treatment of the organ culture with asbestos fibers induced type II cell hyperplasia, increased numbers of collagen fiber bundles within the interstitium, and the accumulation of multi-lamellated surfactant material within the alveolar lumens. We conclude that this organ culture system is suitable for studying lung growth, development, and injury in human tissue.

1970s

• Mucopolysaccharide osmotic pressure in the measurement of interstitial pressure. P.D. Snashall. 1977;232(6):H608-16. PubMed · Publisher

  Abstract

  Subatmospheric pressures were recorded from cotton wicks inserted into Wharton's jelly of human umbilical cords (mean=-7.6+/-5.0 (SD) cmH2O; n=10). Hyaluronate concentrations (mean=0.69+/-0.30 g/100 g) and wick pressures correlated negatively (r=-0.825; P less than 0.01) but calculated hyaluronate osmotic pressures (mean=4.0+/-2.7 cmH2O) were insufficient to explain the full wick pressure. In model systems composed of asbestos fibers (mean radius=0.5 micron) and 0.9% saline, subatmospheric pressures were recorded which varied with the volume of saline added. When hyaluronate (1 g/100 g) was substituted for saline, lower wick pressures were recorded at each volume. The pressure lowering effect of hyaluronate was not seen in a matrix of glass fibers (mean radius=1.0 micron). It is suggested that the effect of hyaluronate in asbestos fibers is due to its immobilization by the matrix and the consequent development of osmotic pressure recorded via the wick. In the coarser glass-fiber matrix, hyaluronate was not immobilized and therefore had no osmotic effect. These experiments support the hypothesis that subatmospheric interstitial pressures result from osmotic pressure of immobilized mucopolysaccharide macromolecules.

Browse every journal in the library or the library by type of article, or return to medical research.