In vitro assays to predict the pathogenicity of mineral fibers

Our plain-English summary of In vitro assays to predict the pathogenicity of mineral fibers, by B.T. Mossman, A.M. Sesko (Toxicology, 1990).

The study

• Authors: B.T. Mossman, A.M. Sesko
• Journal: Toxicology
• Published: 1990;60(1-2):53-61
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A number of mineral dusts are associated with the development of inflammation in lung and pulmonary interstitial fibrosis. In an effort to find alternative approaches to animal testing, cells (rat alveolar macrophages, hamster tracheal epithelial cells, rat lung fibroblasts) of the respiratory tract have been evaluated for cytotoxic and metabolic changes after exposure to fibers (defined as a greater than 3:1 length to diameter ratio) and particles. In all bioassays, fibrous materials provoked greater biological responses in cells in comparison to non-fibrous, chemically similar particulates at identical concentrations. For example, release of superoxide (O2-.) from alveolar macrophages (AMs) was increased (in comparison to that observed in untreated cells) after exposure to the fibers, crocidolite asbestos, erionite, Code 100 fiberglass and sepiolite. Riebeckite, mordenite and glass particles elicited minimal generation of O2-. at similar concentrations of dusts. In hamster tracheal epithelial (HTE) cells, fibers such as chrysotile asbestos, crocidolite asbestos, and Code 100 fiberglass caused increased release of 51Chromium in comparison to the particles antigorite, riebeckite and glass. Another area of exploration is the measurement of collagen and non-collagen protein in a cell line (RL-82) of rat lung fibroblasts as an indication of the fibrogenic potential of minerals. Crocidolite asbestos caused an increase in the ratio of cell-associated collagen to non-collagen protein in these cell types whereas glass beads did not affect biosynthesis of collagen. Results suggest that a battery of in vitro assays can be used to screen the capability of minerals to elicit cell damage and inflammatory changes in the respiratory tract.

In plain English

This was a laboratory study in cultured cells. The authors tested whether fibers, defined as more than three times longer than wide, caused more cell changes than chemically similar non-fibrous particles. The fibers were crocidolite and chrysotile asbestos, erionite, Code 100 fiberglass and sepiolite. The comparison particles were riebeckite, antigorite, mordenite and glass beads. In rat alveolar macrophages, crocidolite, Code 100 fiberglass and erionite caused significant dose-related increases in superoxide release compared with untreated cells. Five- to ten-fold higher concentrations of riebeckite, glass beads and mordenite were needed for comparable responses. In hamster tracheal epithelial cells, crocidolite, chrysotile and Code 100 fiberglass increased release of radioactive chromium, a sign of membrane damage, while riebeckite, antigorite and glass beads did not. In rat lung fibroblasts, crocidolite raised the ratio of collagen to non-collagen protein at 48 and 72 hours; glass beads did not. The authors concluded that fibrous dusts produced greater cell changes than their non-fibrous analogs. They noted that short-term cell tests cannot assess how durable fibers are or how they are cleared from the lung.

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 study comparing fibers with chemically similar non-fibrous particles
• Who was studied: Alveolar macrophages washed from the lungs of 200 male Fischer 344 rats; a tracheal epithelial cell line from a female golden Syrian hamster; and a rat lung fibroblast cell line (RL-82). The study was done at the University of Vermont. No study dates are given.
• Exposure: Fibers: crocidolite and chrysotile asbestos (UICC reference samples), erionite, Code 100 fiberglass and sepiolite. Non-fibrous particles: riebeckite, antigorite, mordenite and glass beads. Concentrations were 2.5 to 25 micrograms per square centimetre of dish (macrophages) and 0.01 to 20 (tracheal cells). Fibroblasts received crocidolite at 1.0, 2.5 and 5.0, or glass beads at 5.0.
• Main results:
  • In rat alveolar macrophages, crocidolite asbestos, Code 100 fiberglass and erionite caused significant dose-related increases in superoxide production compared with untreated cultures.
  • Five- to ten-fold greater concentrations of the particles riebeckite, glass beads and mordenite were required to produce comparable superoxide responses in macrophages.
  • Sepiolite, described as a mixture of short fibers and particles, also caused superoxide release from macrophages, but only at a high concentration (25 micrograms per square centimetre of dish).
  • In hamster tracheal epithelial cells, crocidolite asbestos, chrysotile asbestos and Code 100 fiberglass caused significant dosage-dependent increases in chromium release, starting at about 1 microgram per square centimetre of dish (the comparison symbol is garbled in the scan).
  • The non-fibrous analogs riebeckite, antigorite and glass beads did not increase chromium release from tracheal epithelial cells compared with untreated cultures.
  • In rat lung fibroblasts exposed to crocidolite, there was no change in the collagen to non-collagen protein ratio after 24 hours.
  • At 48 hours, the fibroblasts showed a significant increase (P less than 0.05) in the ratio at the lower crocidolite concentrations (1.0 and 2.5). At 72 hours, crocidolite at 5.0 increased the ratio. Figure 3 shows a typical experiment with 4 per group.
  • Glass beads did not change the collagen to non-collagen protein ratio in fibroblasts at any time point. These data were not shown.
• The authors' conclusion: The authors concluded that fibrous dusts produced greater cytotoxic and metabolic changes in respiratory tract cells than their non-fibrous, chemically similar analogs. They judged the chromium release assay more promising than superoxide release for telling fibers from non-fibrous particles. They suggested in vitro screening may help choose which materials to study in long-term tests.
• Limitations the authors state:
  • Short-term cell tests cannot assess other fiber properties, such as durability and clearance from the lung, that may matter in causing disease.
  • Code 100 fiberglass produced responses similar to asbestos in these tests. The authors state that glass fibers do not cause respiratory disease in humans, presumably because they dissolve in the lung.
  • In the macrophage superoxide assay, non-fibrous dusts also caused superoxide release, though only at extremely high concentrations.
  • Only crocidolite was tested in the fibroblast collagen assay. Further studies are needed to see whether other asbestiform fibers test positive.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Mineral Fiber, Inflammation, Interstitial Fibrosis, Alveolar Macrophage, Fibroblast, Superoxide, Crocidolite, erionite.

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