The lung biological activity of American attapulgite

Our plain-English summary of The lung biological activity of American attapulgite, by R. Bégin, S. Massé, M. Rola-Pleszczynski, et al (Environmental Research, 1987).

The study

• Authors: R. Bégin, S. Massé, M. Rola-Pleszczynski, M. Geoffroy, M. Martel, Y. Desmarais, P. Sébastien
• Journal: Environmental Research
• Published: 1987;42(2):328-39
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Attapulgite is a fibrous mineral industrially consumed at the rate of over a million tons per year but the biological activity of the material is not fully known. To evaluate the in vivo toxicity of the fibrous material, we exposed the tracheal lobe of 16 sheep to a single exposure of either 100 ml saline, 100 mg UICC asbestos fibers in 100 ml saline, 100 mg short asbestos fibers in 100 ml saline, or 100 mg attapulgite in 100 ml saline. The animals were studied by bronchoalveolar lavage (BAL) at Days 2, 12, 24, 40, and 60 and by autopsy at Day 60. In the saline-exposed sheep, BAL and lung histology did not change. In the UICC asbestos-exposed animals, we reproduced the BAL changes previously reported (R. Bégin, M. Rola-Pleszczynski, S. Massé, Y. Berthiaume, and G. Drapeau, 1985, Environ. Res. 36, 389-404). In the short asbestos-exposed sheep, there were no significant BAL changes. In the attapulgite sheep, we found significant and sustained increases in total BAL cells (X2, P less than 0.05), macrophages (X2, P less than 0.05), neutrophils (X5, P less than 0.01), fibronectin (X2-3, P less than 0.05), lactate dehydrogenase (X2, P less than 0.05), beta-glucuronidase (X2, P less than 0.05), but BAL cellularity returned to control levels by Day 60 whereas in the UICC asbestos-exposed sheep, it remained significantly above control. Lung histology demonstrated the characteristic peribronchiolar fibrosing alveolitis in the UICC asbestos-exposed sheep, whereas macrophagic alveolitis with minimal airway distortion was seen in the short asbestos-exposed sheep and in all of the attapulgite-exposed sheep but three which had typical peribronchiolar alveolitis quite similar to that observed in UICC-exposed sheep, but of lower intensity. In conclusion, the study documents that attapulgite is not an inert material for lung tissue; it does produce a macrophagic and neutrophilic alveolitis in the early inflammatory phase of lung reaction with peribronchiolar involvement in some sheep. Whether or not this initial attapulgite induced alveolitis leads to lung fibrosis remains to be evaluated in a longer follow-up study of attapulgite-exposed animals.

In plain English

This was an animal experiment in sheep. The authors compared American attapulgite, a fibrous clay mineral from northern Florida, with UICC Canadian chrysotile, short chrysotile fibers and saline alone. Four groups of 16 sheep each received one infusion of 100 mg of fiber (or saline only) into one lung lobe. The authors then sampled lung fluid by lavage over 60 days and examined the lung tissue at Day 60. In attapulgite-exposed sheep, cell counts in lung fluid rose above controls at Days 12, 24 and 40 but were back to control levels by Day 60. Two enzymes, lactate dehydrogenase and beta-glucuronidase, and the protein fibronectin were significantly above control after exposure. Lung tissue showed inflammation mostly in the air sacs. In three of the 16 attapulgite-exposed sheep, the lesions around small airways resembled those caused by UICC chrysotile but were less intense. The authors concluded that attapulgite is biologically active in the lung. They believed the lesions should progress to fibrosis, but said this needed longer follow-up. They also wrote that attapulgite dust at work should be controlled as strictly as asbestos dust.

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: Animal experiment (sheep), with each group receiving a single infusion of material into the tracheal lobe of the lung
• Who was studied: 64 sheep weighing 25-40 kg, in four groups of 16 (saline, UICC asbestos, short asbestos, attapulgite), studied at the Université de Sherbrooke, Quebec, Canada. Lung fluid was sampled before exposure and at Days 12, 24, 40 and 60, and all sheep were killed for lung examination at Day 60.
• Exposure: A single dose of 100 mg in 100 ml saline of one of three materials, or saline alone. The materials were UICC Canadian chrysotile; University of Sherbrooke short chrysotile (mean length 0.92 µm); and American attapulgite from northern Florida (mean length 0.8 µm, range 0.25-4 µm, diameter 0.02 µm).
• Main results:
  • Attapulgite-exposed sheep: total lung-fluid cells and cell subgroups rose significantly above controls at Days 12, 24 and 40, but were back to control levels by Day 60.
  • Attapulgite-exposed sheep: macrophages increased about twofold (P less than 0.05) and neutrophils about fivefold (P less than 0.01).
  • Attapulgite-exposed sheep: albumin and procollagen III did not differ from control. Fibronectin and two enzymes, lactate dehydrogenase (LDH) and beta-glucuronidase, were significantly above control after exposure.
  • UICC asbestos-exposed sheep: lung-fluid cell counts stayed significantly raised, with total cells averaging 50 plus or minus 10 × 10^4 per ml. Saline-exposed sheep averaged 22 plus or minus 3 × 10^4 per ml.
  • Short asbestos-exposed sheep: all lung-fluid chemistry measures were comparable to those of saline-exposed sheep.
  • Lung tissue at Day 60: UICC asbestos-exposed sheep showed early fibrosis around small airways, with distortion of those airways.
  • Lung tissue at Day 60, attapulgite-exposed sheep (16 in the group, per the methods): inflammation was mostly in the air sacs. In three sheep, lesions around small airways were quite similar to those of UICC asbestos-exposed sheep, though less intense.
  • Overall, the lung lesions in attapulgite-exposed sheep were 75-85% less intense than those in UICC asbestos-exposed sheep.
• The authors' conclusion: The authors concluded that attapulgite is biologically active in the lung and can cause lesions comparable to those of short chrysotile fibers. They believed the attapulgite-induced lesions should progress to fibrosis, to be assessed by longer follow-up. They also wrote that, together with available human data, their findings suggested attapulgite dust in the workplace should be controlled as stringently as asbestos dust.
• Limitations the authors state:
  • The study followed the animals for only 60 days. Whether the attapulgite-induced lesions progress to fibrosis was not tested and is left to longer follow-up.

Topics

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

Medical terms in this study, explained in our Lexicon: Palygorskite (Attapulgite), UICC, Bronchoalveolar Lavage (BAL), Autopsy, Histology, Macrophage, Lactate Dehydrogenase (LDH), Fibrosis.

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• A retrospective cohort mortality study of males mining and milling attapulgite clay — R.J. Waxweiler, R.D. Zumwalde, et al. (1988)
• Characterisation of palygorskite specimens from different geological locales for health hazard evaluation — R.P. Nolan, A.M. Langer, et al. (1991)
• Rat lung reactivity to natural and man-made fibrous silicates following short-term exposure — I. Lemaire, P.G. Dionne, et al. (1989)
• Cytotoxicity of respirable dusts from industrial minerals: comparison of two naturally occurring and two man-made silicates — D. Nadeau, L. Fouquette-Couture, et al. (1987)
• Carborundum pneumoconiosis. Fibers in the mineral activate macrophages to produce fibroblast growth factors and sustain the chronic inflammatory disease — R. Bégin, A. Dufresne, et al. (1989)

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