Asbestos exposure increases human bronchial epithelial cell fibrinolytic activity

Our plain-English summary of Asbestos exposure increases human bronchial epithelial cell fibrinolytic activity, by T.J. Gross, S.M. Cobb, D.C. Gruenert, et al (The American Journal of Physiology, 1993).

The study

• Authors: T.J. Gross, S.M. Cobb, D.C. Gruenert, M.W. Peterson
• Journal: The American Journal of Physiology
• Published: 1993;264(3 Pt 1):L276-83
• Cited by: 13 articles, as counted by NIH iCite
• Read it: 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.

In plain English

This laboratory study used a cultured line of human bronchial epithelial (airway lining) cells. No people or animals were exposed to asbestos; plasma from normal human volunteers was used only to form the clots tested. The authors exposed the cells to cryogenically ground chrysotile asbestos, mostly at 100 micrograms per milliliter for 24 hours, and measured how well the cells broke down plasma clots (fibrinolysis). The asbestos did not measurably kill the cells. Exposed cells broke down more clot than unexposed cells, and the effect rose with dose. At 24 hours, clot breakdown was 138%, 277% and 448% of control levels at 1, 10 and 100 micrograms per milliliter; the lowest dose was not statistically significant. The effect needed direct fiber-cell contact. Latex beads, a fiber-free extract, and fibers held behind a filter did not produce it. It depended on the enzyme urokinase (uPA). This activity in the cells doubled after 24 hours, and the extra activity was located at the cell surface. The increase needed new RNA and protein synthesis. The authors concluded this may help explain how chronic asbestos exposure leads to fibrotic lung disease, while noting the link remains speculative.

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: Laboratory (in vitro) cell culture experiment
• Who was studied: A cultured human bronchial epithelial (HBE) cell line derived from human segmental bronchial cells transformed with SV40 large T antigen, used between passages 3 and 20. Plasma for the clots came from normal human volunteers. The volunteers were not exposed to asbestos.
• Exposure: Cryogenically ground chrysotile asbestos with an average fiber length of 1 micrometer and a length-to-width ratio of 14 to 1. Doses were 1, 10 and 100 micrograms per milliliter, mostly for 24 hours. Comparison exposures were latex beads, an asbestos aqueous extract, bacterial lipopolysaccharide, and asbestos separated from the cells by a filter insert.
• Main results:
  • A 24-hour exposure to 100 micrograms per milliliter of asbestos did not significantly change cell number: 3.8 plus or minus 0.7 versus 3.5 plus or minus 0.5 times 10 to the 5th cells per well for control and asbestos-treated monolayers (n = 12).
  • Release of the enzyme LDH (a marker of cell damage) did not increase: 8.8 plus or minus 3.5% versus 8.7 plus or minus 0.9% of total LDH for control and asbestos-treated monolayers.
  • In asbestos-exposed cells, the increased clot breakdown was first detected 16 hours after the plasma clot formed.
  • The increase was dose dependent. At 24 hours, clot lysis was 138 plus or minus 33% of control at 1 microgram per milliliter (P greater than 0.2, not significant). It was 277 plus or minus 40% at 10 micrograms per milliliter (P less than 0.015) and 448 plus or minus 51% at 100 micrograms per milliliter (P less than 0.001), with n = 9.
  • Latex beads of similar size did not increase clot breakdown.
  • The authors reported that the increase was specific to the asbestos particles. It required direct contact between fibers and cells; an asbestos extract and fibers separated from the cells by a filter insert did not produce it.
  • Under both control and asbestos-exposed conditions, the cells made a single plasminogen activator, urokinase (uPA). The plasmin inhibitor EACA and the uPA inhibitor amiloride completely blocked clot breakdown.
  • Medium conditioned by the cells did not break down clots. The authors concluded that clot breakdown was not due to an enzyme secreted into the medium.
  • Cells exposed to asbestos for 24 hours contained twice as much plasminogen activator activity as unexposed cells.
  • This activity was significantly higher than in controls by 8 hours after exposure began.
  • The increase was blocked by actinomycin D or cycloheximide, drugs that stop RNA and protein synthesis.
  • Measured per microgram of protein, plasminogen activator activity was 10.6 plus or minus 1.6 in control cells versus 22.2 plus or minus 2.7 milli-International Units in asbestos-exposed cells.
  • An acid wash, which strips enzyme bound to the cell surface, reduced control cells' activity by about 25%. It removed all of the extra activity seen after asbestos exposure.
• The authors' conclusion: The authors concluded that chrysotile asbestos increased the airway cells' clot-dissolving activity by increasing urokinase-dependent activation at the cell surface. They suggested this may offer a novel explanation for how chronic asbestos exposure leads, through ongoing inflammation, to fibrotic lung disease.
• Limitations the authors state:
  • The authors stated that how this increase in clot-dissolving activity relates to the development of interstitial inflammation and fibrosis remains speculative.
  • The authors stated that whether the effect depends on cells taking up the fibers, or only on fibers touching the cell surface, needs further investigation.

Topics

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

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