The effect of fibre size on the in vitro biological activity of three types of amphibole asbestos

Our plain-English summary of The effect of fibre size on the in vitro biological activity of three types of amphibole asbestos, by R.C. Brown, M. Chamberlain, D.M. Griffiths, et al (International Journal of Cancer, 1978).

The study

• Authors: R.C. Brown, M. Chamberlain, D.M. Griffiths, V. Timbrell
• Journal: International Journal of Cancer
• Published: 1978;22(6):721-7
• Cited by: 74 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Three standard (UICC) samples of amphibole asbestos were subjected to ball-milling; the main effect of this procedure was to reduce the length of the fibres present in each sample. The numbers of fibres in unit masses, and the distribution of fibre sizes in all the samples, both parent and milled, were estimated from electron micrographs. The ability of all the samples to reduce the plating efficiency of V79-4 cells is compared, on the basis of mass, fibre number and fibre number number above various length thresholds. This biological activity of all the samples correlated best with the number of fibres above a threshold length of 6.5 micron. This is compared with the sizes of fibre previously reported to induce mesotheliomata when implanted into the pleural cavities of rats.

In plain English

This laboratory study, from the Medical Research Council Pneumoconiosis Unit, tested whether asbestos fibre length affects toxicity to cells grown in dishes. It used cells, not animals or people. The authors ball-milled standard UICC samples of three amphibole asbestos types (crocidolite, amosite and anthophyllite) for 1 to 8 hours, which mainly shortened the fibres. They measured fibre sizes and counts by electron microscopy and tested each sample on Chinese hamster lung V79-4 cells. Toxicity of the milled amosite and anthophyllite fell as milling time increased. For crocidolite, toxicity followed fibre length rather than milling time. When 4-hour milled crocidolite was added to unmilled crocidolite, the mixture was exactly as toxic as unmilled crocidolite alone at the highest milled-sample concentration tested, 30 micrograms per millilitre. Toxicity matched best the number of fibres longer than about 6.5 micrometres (range 4.5 to 9.5). The authors noted that this estimate is uncertain, that pooling fibre types may not be valid, and that other factors also mattered. They suggested this cell test may help study how fibres interact with cells when tumours form.

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 (cell culture toxicity tests of unmilled and ball-milled asbestos samples)
• Who was studied: Standard UICC reference samples of crocidolite, amosite and anthophyllite, unmilled and ball-milled, tested on Chinese hamster lung V79-4 cells in culture at the Medical Research Council Pneumoconiosis Unit, Penarth, UK. Four replicate plates were used at each dust concentration, and about 1,000 fibres were measured for each size distribution.
• Exposure: UICC crocidolite, amosite and anthophyllite asbestos, unmilled or ball-milled in a ceramic mill for periods from 1 to 8 hours to shorten the fibres. Cells were exposed to different masses of each sample.
• Main results:
  • The toxicity of the milled anthophyllite and amosite samples to V79-4 cells declined as milling time increased.
  • For the crocidolite samples, toxicity did not follow milling time directly but did relate to the fibre length distributions.
  • The number of fibres in equally toxic masses rose with milling, so the authors concluded that total fibre number did not determine toxicity.
  • When the 4-hour milled crocidolite sample was added to a toxicity test of unmilled UICC crocidolite, at the highest milled-sample concentration used (30 micrograms per millilitre) the mixture was exactly as toxic as UICC crocidolite alone.
  • From that test, the authors concluded that milling had not produced material that blocks toxicity.
  • Measurements of surface charge on the milled crocidolite samples found no significant or systematic differences.
  • Toxicity across all samples correlated best with the number of fibres longer than a threshold length. The best estimate of that threshold was 6.5 micrometres, within a range of 4.5 to 9.5 micrometres.
  • When survival data were replotted against the number of fibres longer than 6.5 micrometres, the curves for the different dusts were not identical. The authors concluded that other factors also influence activity.
  • If the 6.5-micrometre threshold is valid, about 5% of fibres in UICC crocidolite and 30% in amosite and anthophyllite would be active in this test system.
• The authors' conclusion: The authors suggested that the toxicity of mineral fibres to V79-4 cells may prove a useful model for investigating the fibre-cell interactions involved when these fibres induce tumours.
• Limitations the authors state:
  • The 6.5-micrometre threshold is subject to error. This comes partly from difficulty estimating equally toxic mass concentrations and partly from random errors in measuring and counting only about 1,000 fibres.
  • Pooling data from different dusts may not be valid. Similar-sized fibres of different composition may not be equally active, and data points from different dusts showed some separation.
  • Contamination of the fibre surface by material from the ceramic mill could not be ruled out.
  • The surface charge measurements covered only fibres visible in the light microscope.

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Asbestos, UICC.

Related studies

• In vitro determinants of asbestos fiber toxicity: effect on the relative toxicity of Libby amphibole in primary human airway epithelial cells — K.E. Duncan, P.M. Cook, et al. (2014)
• Biological effects of naturally occurring and man-made fibres: in vitro cytotoxicity and mutagenesis in mammalian cells — R. Okayasu, L. Wu, et al. (1999)
• Pulmonary effects in rats inhaling size-separated chrysotile asbestos fibres or p-aramid fibrils: differences in cellular proliferative responses — D.B. Warheit, M.A. Hartsky, et al. (1996)
• Biological in vitro and in vivo responses of chrysotile versus amphiboles — J. Bignon, M.C. Jaurand (1983)
• Comparison of fibre types and size distributions in lung tissues of paraoccupational and occupational cases of malignant mesothelioma — A.R. Gibbs, D.M. Griffiths, et al. (1990)
• Cytotoxic action of mineral dusts on CHV 79 cells in vitro: factors affecting toxicity — S.O. Lock, M. Chamberlain (1983)

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