In vitro cytotoxicity of asbestos and man-made vitreous fibers: roles of fiber length, diameter and composition

Our plain-English summary of In vitro cytotoxicity of asbestos and man-made vitreous fibers: roles of fiber length, diameter and composition, by G.A. Hart, L.M. Kathman, T.W. Hesterberg (Carcinogenesis, 1994).

The study

• Authors: G.A. Hart, L.M. Kathman, T.W. Hesterberg
• Journal: Carcinogenesis
• Published: 1994;15(5):971-7
• Cited by: 59 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The present study investigated (i) the impact of various fiber parameters on in vitro toxicity to cells and (ii) the validity of an in vitro test system as a toxic screen for fibrous materials. Chinese hamster ovary cells were exposed in vitro to a series of size-selected inorganic test fibers that represented a range of different diameters, lengths and compositions (glass, refractory ceramic, mineral wool, asbestos). Toxic end-points included inhibition of proliferation, induction of micronuclei and polynuclei and viability. For all compositions tested, toxic effects were similar: a concentration-dependent decrease in proliferation and increase in incidence of morphologically abnormal nuclei with minor decreases in viability. Diameter-dependent differences in toxicity were slight or absent for fiber diameters ranging from 0.3-7 microns when concentration was expressed as number of fibers/cm2. Length-dependent differences in toxicity were, however, striking. EC50 values (concentration in fibers/cm2 that reduced cell proliferation to 50% of unexposed control cultures) plotted against fiber length produced a hyperbolic curve, demonstrating that toxicity increases with fiber length up to 20 microns. All fibers tested fell on this hyperbola. These data suggest that: (a) the primary toxic effect of fibers on CHO cells is the induction of nuclear morphologic alterations resulting in cytostasis; (b) fiber diameter has little or no impact on in vitro toxicity when concentration is calculated as fibers/cm2; (c) fiber length is directly proportional to in vitro toxicity; and (d) toxicity of asbestos and vitreous fibers to CHO cells is not affected by composition. The lack of compositional effect in CHO cells does not correlate with findings from recent rodent inhalation studies using the same test fibers. Thus CHO cells may not be an appropriate in vitro model of fiber pathogenesis and would not constitute a valid toxicologic screening system for fibers.

In plain English

This laboratory study exposed cultured Chinese hamster ovary (CHO) cells to size-selected fibers of 13 compositions. These included crocidolite and chrysotile asbestos, glass, refractory ceramic fibers, rock wool and slag wool. The authors measured cell growth and abnormal nuclei, and tested cell survival at high doses of four fibers. All fibers slowed cell growth and increased abnormal nuclei, but few cells died: viability was about 90% at high doses. With dose counted as fibers per square centimeter, fiber thickness from 0.3 to 7 micrometers made little or no difference. Glass fiber toxicity fell 2-fold when diameter rose 23-fold. Length mattered more. For asbestos, toxicity rose 75-fold as average length rose 8-fold, from UICC chrysotile (1.4 micrometers) to long NIEHS crocidolite (11.4 micrometers). Toxicity did not rise further between average lengths of 22 and 31 micrometers. Fibers of similar length had similar effects whatever their composition. This did not match rodent inhalation studies of the same fibers. The authors concluded that CHO cells may not be an appropriate model of fiber disease and would not be a valid screening system for fibers.

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: CHO-K1 Chinese hamster ovary cells grown in culture, obtained from the American Type Culture Collection. No people or animals were studied.
• Exposure: Size-selected fibers of 13 compositions were tested. Asbestos was represented by UICC crocidolite, UICC chrysotile, and NIEHS crocidolite sorted into three lengths. The others were three glasses, two mineral wools (rock wool MMVF21 and slag wool MMVF22), four refractory ceramic fibers (RCF1 to RCF4) and one experimental fiber (X607). Glass fibers were also sorted by diameter (0.3 to 7 micrometers) and by length (average 3.5 to 31 micrometers). Dose was expressed as number of fibers per square centimeter of culture dish.
• Main results:
  • Four test fibers (FG15, MvL 475 Code 108, RCF2 and UICC crocidolite asbestos) were tested for 3 days at high concentrations, 2 to 3 times the EC50. In these cultures, cell viability was about 90% while cell proliferation was almost entirely inhibited. Unexposed control cultures had 99% viability.
  • For MvL 475 glass fibers, when dose was counted per fiber, toxicity decreased only 2-fold when diameter increased 23-fold. The EC50 was 6 x 10^4 fibers per square centimeter for 0.3 micrometer fibers and 12 x 10^4 for 7 micrometer fibers.
  • For MvL 901 glass fibers, toxicity per fiber increased 25-fold when average length increased 6-fold. The EC50 was 310 (x 10^4 fibers per square centimeter) for short 3.5 micrometer fibers and 11 for long 22 micrometer fibers. The values for the shortest fibers were estimated by extrapolation from a graph.
  • For asbestos, toxicity increased 75-fold with an 8-fold increase in average length. The EC50 went from 678 (x 10^4 fibers per square centimeter) for UICC chrysotile (average length 1.4 micrometers) to 9 for long NIEHS crocidolite (average length 11.4 micrometers).
  • Across asbestos and man-made vitreous fibers, toxicity increased with average length from 1.4 to 22 micrometers. It did not increase from 22 to 31 micrometers.
  • All 13 compositions had quantitatively and qualitatively similar toxic effects when average fiber lengths were similar.
  • At the EC50 concentration of the various fibers, 20% to 36% of cells had abnormal nuclei.
  • Refractory ceramic fiber, fibrous glass and rock/slag wool had similar toxicity in CHO cells. This did not match the rodent (TIMA) inhalation studies, in which only refractory ceramic fiber induced mesotheliomas and a significant increase in lung neoplasms.
• The authors' conclusion: Composition had no effect in CHO cells, but it did in rodent inhalation studies of the same fibers. The authors therefore concluded that CHO cells may not be an appropriate in vitro model of fiber disease and would not be a valid toxicologic screening system for fibers.
• Limitations the authors state:
  • CHO cells are not related to any of the tissues where fiber disease develops.
  • In vitro studies are short and cannot measure the effect of long-term fiber dissolution and compositional changes.
  • The results are based on average fiber lengths, but each fiber sample contained a wide range of lengths.
  • The thickest (7 micrometer) glass sample contained large non-fibrous particles that could not be separated out and were included in the fiber counts.

Topics

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

Medical terms in this study, explained in our Lexicon: Vitreous, Fiber Length, Micronuclei.

Related studies

• Effects of asbestos and man-made vitreous fibers on cell division in cultured human mesothelial cells in comparison to rodent cells — K. Pelin, P. Kivipensas, et al. (1995)
• Biological effects of naturally occurring and man-made fibres: in vitro cytotoxicity and mutagenesis in mammalian cells — R. Okayasu, L. Wu, et al. (1999)
• Comparison of cytotoxicity of man-made vitreous fibres — K. Luoto, M. Holopainen, et al. (1997)
• Long-term health effects in hamsters and rats exposed chronically to man-made vitreous fibres — D.M. Smith, L.W. Ortiz, et al. (1987)
• Relationship between lung biopersistence and biological effects of man-made vitreous fibers after chronic inhalation in rats — T.W. Hesterberg, W.C. Miiller, et al. (1994)
• Synthetic silica fibers of different length, diameter and shape: synthesis and interaction with rat (NR8383) and human (THP-1) macrophages in vitro, including chemotaxis and gene expression profile — N. Białas, N. Rosenkranz, et al. (2024)

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