Cytotoxicity of respirable dusts from industrial minerals: comparison of two naturally occurring and two man-made silicates

Our plain-English summary of Cytotoxicity of respirable dusts from industrial minerals: comparison of two naturally occurring and two man-made silicates, by D. Nadeau, L. Fouquette-Couture, D. Paradis, et al (Drug and Chemical Toxicology, 1987).

The study

• Authors: D. Nadeau, L. Fouquette-Couture, D. Paradis, J. Khorami, D. Lane, J. Dunnigan
• Journal: Drug and Chemical Toxicology
• Published: 1987;10(1-2):49-86
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The membranolytic and cytotoxic properties of two naturally occurring (chrysotile asbestos; attapulgite clay) and two man-made (Fiberfrax, an aluminium-silicate, and xonotlite, a calcium silicate) industrial minerals were compared. "Short" fiber fractions of chrysotile and Fiberfrax were obtained by sedimentation in demineralized water, while the attapulgite and xonotlite samples were used as obtained. The aluminium silicate fibers were found to be non- hemolytic, while for the other three silicates, chrysotile had the strongest hemolysis potential, followed very closely by xonotlite; attapulgite was less hemolytic than the former two silicates, but was nevertheless highly hemolytic to the rat erythrocytes. Using rat pulmonary alveolar macrophages, the in vitro cytotoxicity assays showed that with fresh cell monolayers, all four silicates were equivalent in causing cell damages at a dose of 250 micrograms; at a lower dose (50 micrograms), the intensity of the cytotoxic effect was in the decreasing order: Fiberfrax greater than attapulgite greater than chrysotile greater than xonotlite. With one day-old cultured cell monolayers, a dose of 250 micrograms of the silicates fibers was less cytotoxic, with the exception of the attapulgite fibers which remained essentially as cytotoxic as with the fresh cell monolayers. The reduced cytotoxic response was especially noticeable with the chrysotile fibers. At 50 micrograms, the cytotoxicity scale of the mineral dusts with one day-old cell monolayers was essentially the same as the one obtained with the fresh cell monolayers, that is: Fiberfrax approximately equal to attapulgite greater than chrysotile greater than or equal to xonotlite. Overall, these in vitro tests imply: 1) that all four industrial silicates tested can be considered to be "biologically active"; 2) that on the basis of their different reactivities with the two types of cell culture conditions used, their biological reactivity in vivo might be quite distinct. This might be especially true for at least the chrysotile, attapulgite and xonotlite short fibers, considering that these three types of silicate dusts have very similar dimensions. Moreover, for the chrysotile and attapulgite samples, fiber numbers is probably not an important factor, since the density of the two silicates is roughly the same. The unaltered cytotoxic responses of the American attapulgite fibers in the two macrophage assays correlate well with the fact that short attapulgite fibers seems to have a stronger in vivo reactivity than short chrysotile fibers. In fact, it might be the strongest of the four industrial silicates tested.(ABSTRACT TRUNCATED AT 400 WORDS)

In plain English

This was a test-tube study. It compared two natural silicates, chrysotile asbestos and attapulgite clay, with two man-made ones, Fiberfrax (an aluminium silicate) and xonotlite (a calcium silicate). Short-fiber fractions of chrysotile and Fiberfrax were separated out by letting the material settle in demineralized water; attapulgite and xonotlite were used as supplied. The authors tested the dusts on rat red blood cells and on rat lung macrophages, both fresh and after one day in culture. Fiberfrax caused no significant red-cell damage, even at the highest dose; chrysotile caused the most, followed closely by xonotlite, then attapulgite. With fresh macrophages, all four dusts were highly toxic at 250 micrograms, cutting the cells' ATP, a measure of cell energy, by 80%. At 50 micrograms, chrysotile, attapulgite and the aluminium silicate had significant toxic effects, and xonotlite lowered ATP by about 20%. In one-day-old cells, chrysotile's toxicity was greatly reduced, while attapulgite and the aluminium silicate stayed highly toxic at 50 micrograms. The authors concluded that testing dusts on both fresh and cultured macrophages may help predict their harmfulness in living animals. They noted that test-tube results cannot easily be extrapolated to living animals.

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 laboratory experiment comparing four silicate dusts in a red-blood-cell damage (hemolysis) assay and a cytotoxicity assay on rat pulmonary alveolar macrophages
• Who was studied: Red blood cells and pulmonary alveolar macrophages taken from rats
• Exposure: Short-fiber fractions of chrysotile asbestos and Fiberfrax (aluminium silicate), obtained by sedimentation in demineralized water; attapulgite clay and xonotlite (calcium silicate) as supplied
• Main results:
  • Red blood cells: the authors described the aluminium silicate (Fiberfrax) as non-hemolytic, reporting no significant hemolytic activity even at the highest dose tested. Of the other three silicates, chrysotile had the strongest hemolysis potential, followed very closely by xonotlite.
  • Red blood cells: attapulgite was less hemolytic than chrysotile and xonotlite, but was still highly hemolytic to the rat red blood cells.
  • Fresh macrophages, 250 micrograms: all four dusts were highly cytotoxic.
  • Fresh macrophages, 250 micrograms: the low viability of the cells was confirmed by an 80% decrease in cell ATP content.
  • Fresh macrophages, 50 micrograms: only chrysotile, attapulgite and the aluminium silicate had a significant cytotoxic effect.
  • Fresh macrophages, 50 micrograms: xonotlite significantly reduced cell ATP content by about 20%.
  • One-day-old cultured macrophages, 250 micrograms: all four dusts were cytotoxic, but chrysotile's cytotoxicity was greatly reduced in these older cells.
  • One-day-old cultured macrophages, 50 micrograms: attapulgite and the aluminium silicate were still highly cytotoxic, while the calcium silicate (xonotlite) was not very toxic.
  • Fiber size: the authors described the chrysotile, xonotlite and attapulgite samples as 100% respirable.
• The authors' conclusion: The authors concluded that combining fresh and cultured rat lung macrophages to test mineral dusts in vitro may be useful for extrapolating how harmful the dusts are in living animals.
• Limitations the authors state:
  • The authors stated that test-tube cytotoxicity data on mineral dusts cannot easily be extrapolated to the dusts' potential to cause disease in living animals.
  • The authors stated it was not known whether the non-fibrous particles in the Fiberfrax sample accounted for its cytotoxic effect.
  • The authors noted that lactic acid production was a less sensitive measure of cell viability than ATP, especially with older cells.

Topics

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

Medical terms in this study, explained in our Lexicon: Silicate, Chrysotile, Palygorskite (Attapulgite), Alveolar Macrophage, Damages, Macrophage.

Related studies

• Rat lung reactivity to natural and man-made fibrous silicates following short-term exposure — I. Lemaire, P.G. Dionne, et al. (1989)
• The biological reactivity of calcium silicate composites: in vivo studies — R.J. Richards, T.D. Tetley, et al. (1981)
• Biological reactivity of calcium silicate composites--in vitro studies — J. Hunt, F.D. Pooley, et al. (1981)
• Measurement of reactive oxygen metabolites produced by human monocyte-derived macrophages exposed to mineral dusts — P. Nyberg, M. Klockars (1990)
• Mortality among a cohort of US man-made mineral fiber workers: 1985 follow-up — G.M. Marsh, P.E. Enterline, et al. (1990)
• A retrospective cohort mortality study of males mining and milling attapulgite clay — R.J. Waxweiler, R.D. Zumwalde, et al. (1988)

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