Asbestos exposure increases paracellular transport of fibrin degradation products across human airway epithelium

Our plain-English summary of Asbestos exposure increases paracellular transport of fibrin degradation products across human airway epithelium, by T.J. Gross, S.M. Cobb, M.W. Peterson (The American Journal of Physiology, 1994).

The study

• Authors: T.J. Gross, S.M. Cobb, M.W. Peterson
• Journal: The American Journal of Physiology
• Published: 1994;266(3 Pt 1):L287-95
• Cited by: 7 articles, as counted by NIH iCite
• Read it: 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.

In plain English

This was a laboratory (in vitro) study using monolayers of a human bronchial epithelial cell line (HBE, SV40-transformed) grown on collagen-coated permeable filters to model the distal airway, with an apical (luminal) and a basolateral (interstitial) chamber. Monolayers were exposed for 24 hours to cryogenically ground chrysotile asbestos at 100 micrograms per millilitre, or to medium alone. Asbestos exposure lowered transepithelial resistance to 280 ± 10 ohms, compared with 1,560 ± 195 ohms in unexposed monolayers (n = 100), without changes in cell number, trypan-blue-assessed viability or lactate dehydrogenase release, and without ultrastructural signs of injury. When monolayers were covered with human plasma clots containing FITC-labelled fibrinogen, asbestos-exposed monolayers showed greater clot lysis and nearly twice as much fluorescence crossing to the basolateral chamber (P less than 0.001; n = 14); the plasmin inhibitor E-aminocaproic acid blocked this. More labelled fibrin degradation products crossed asbestos-treated monolayers at all apical concentrations, and streptavidin blotting showed intact high-molecular-mass products, including D-dimer, appearing basolaterally only after asbestos exposure. Flux was bidirectional, not saturable, and persisted after glutaraldehyde fixation.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: In vitro cell-culture experiment using human bronchial epithelial cell monolayers on permeable filters, with electron microscopy, fluorescent and radiolabelled tracer flux assays and gel electrophoresis
• Who was studied: A human bronchial epithelial cell line (HBE), derived from human segmental bronchial epithelial cells transformed with SV40 large T antigen, used between passages 3 and 20 and grown to confluence on collagen-coated permeable filters (University of Iowa; article received July 1993)
• Exposure: Cryogenically ground chrysotile asbestos, average fiber length 1 micrometre, aspect ratio 14:1, applied apically at 100 micrograms per millilitre for 24 hours; controls received unsupplemented growth media
• Main results:
  • After 24 h of asbestos exposure, transepithelial resistance fell to 280 ± 10 ohms, versus 1,560 ± 195 ohms in unexposed monolayers (n = 100); cell-free inserts read 150 ± 5 ohms (n = 30)
  • The asbestos exposure protocol did not alter cell number, trypan-blue-assessed viability or lactate dehydrogenase release
  • On electron microscopy, asbestos-treated cells remained intact with visible tight junctions, and no signs of cellular injury were seen, even in cells that had ingested fibers
  • With FITC-labelled plasma clots on the monolayers, asbestos-exposed epithelium showed significantly increased 24-h specific clot lysis, about three times the apical soluble fluorescence, and about twice as much fluorescence crossing into the basolateral chamber (P less than 0.001; n = 14)
  • The plasmin inhibitor E-aminocaproic acid (1 mM) in the clots blocked the asbestos-induced increase in basolateral fluorescence
  • Monolayers retained substantial barrier function: about 80% of solubilized fluorescence crossed cell-free filters, versus less than 15% across control or asbestos-treated cells
  • Using FDP generated by in vitro plasmic digestion, more labelled FDP crossed asbestos-treated than control monolayers at every apical concentration tested (P less than 0.002; n = 12)
  • FDP applied apically at up to 500 micrograms per millilitre for 24 h did not reduce transepithelial resistance of control monolayers (790 ± 29 ohms before versus 769 ± 13 ohms after; n = 12)
  • Streptavidin blotting of biotin-labelled FDP: no labelled protein was detected basolaterally in control monolayers, while the FDP species added apically (including the roughly 180 kDa D-dimer) appeared intact in the basolateral chamber of asbestos-treated monolayers
  • FDP flux was equal in both directions across control and asbestos-treated monolayers, and was unchanged by a 10-fold excess (1 mg/ml) of unlabelled FDP
  • After glutaraldehyde fixation, asbestos-exposed cells still showed a fourfold increase in FITC-FDP flux over unexposed control monolayers over 4 hours, with only a small decrement from fixation
  • Permeability to mannitol, 70 kDa dextran and 500 kDa dextran all increased significantly after asbestos exposure and remained stable 24 h later, while size selectivity was maintained; cell-free filters exceeded 1,600 x 10 to the minus 4 cm/h for all tracers
• The authors' conclusion: The authors concluded that asbestos exposure increases the paracellular flux of intact fibrin degradation products across human airway epithelium, which they propose as a mechanism by which fiber-induced epithelial dysfunction may initiate and sustain inflammation in the distal airspace

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Epithelium, Interstitial, Deposition, Inflammation.

Related studies

• Asbestos exposure increases human bronchial epithelial cell fibrinolytic activity — T.J. Gross, S.M. Cobb, et al. (1993)
• Asbestos directly increases lung epithelial permeability — M.W. Peterson, M.E. Walter, et al. (1993)
• Cultured airway epithelium responses to mineral particles: role of the oxidative stress — C. Guilianelli, A. Baeza-Squiban, et al. (1996)
• Enhanced retention of asbestos fibers in the airways of human smokers — A. Churg, B. Stevens (1995)
• A dynamical model of the transport of asbestos fibres in the human body — A. DeStefano, C.F. Martin, et al. (2017)
• Cigarette smoke increases the penetration of asbestos fibers into airway walls — D. McFadden, J. Wright, et al. (1986)

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