Significance of mass and number of fibers in the correlation of V79 cytotoxicity with tumorigenic potential of mineral fibers

Our plain-English summary of Significance of mass and number of fibers in the correlation of V79 cytotoxicity with tumorigenic potential of mineral fibers, by L.D. Palekar, B.M. Most, D.L. Coffin (Environmental Research, 1988).

The study

• Authors: L.D. Palekar, B.M. Most, D.L. Coffin
• Journal: Environmental Research
• Published: 1988;46(2):142-52
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The cytotoxicity of four tumorigenic minerals: erionite(w), erionite(c), UICC crocidolite, UICC chrysotile and nontumorigenic mordenite was compared in Chinese hamster lung V79 cells. The results indicate that the tumorigenic minerals were toxic by showing more than 50% toxicity for at least one dose between 10 and 100 micrograms/ml. Mordenite was nontoxic. Higher potency of erionite, however, was not evident in this system when the dose considered was expressed in mass units. On the other hand, when the degree of cytotoxicity was considered per number of mineral fibers, it was clear that fewer erionite fibers of all three dimensions (A greater than or equal to 3; L greater than or equal to 8.0 micrometers, W less than or equal to 0.25 micrometer; and L less than 5.0 micrometers, W less than or equal to 0.1 micrometer) than those of UICC crocidolite and UICC chrysotile were needed to produce similar toxicity. This suggests that the dose in number of fibers may be a better parameter than the total mass dose as a correlate of tumorigenic potential.

In plain English

This was a laboratory study of cells grown in dishes, not a study of people or animals. The authors exposed V79 Chinese hamster lung cells for 6 days to two erionite samples from Rome, Oregon, prepared in different ways (erionite(w) and erionite(c)), to UICC crocidolite, to UICC chrysotile, and to mordenite, a nonfibrous mineral used as a negative control. Doses ranged from 10 to 100 micrograms per ml, and the authors counted surviving cell colonies. They compared toxicity by weight of mineral and by number of fibers in three size categories. By weight, the four fibrous minerals reduced colony survival by at least 50% at one or more doses, while mordenite showed no appreciable toxicity. Chrysotile and erionite(w) ranked most toxic by weight. By fiber number, fewer erionite fibers than crocidolite or chrysotile fibers were needed for similar toxicity in each size category, and chrysotile needed the most. The authors wrote that this fiber-number ranking matched the expected ranking by tumor-causing potential. They concluded that weight alone is not an appropriate measure for judging the minerals' activity in such tests.

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 (cell culture) laboratory experiment comparing cytotoxicity by mass dose and by number of fibers
• Who was studied: V79 cell line from Chinese hamster lungs. About 200 cells were plated per dish, with five replicate dishes per concentration, and the experiment was repeated twice. Untreated dishes served as controls.
• Exposure: Erionite(w) and erionite(c), two preparations of fibrous erionite from Rome, Oregon; UICC crocidolite; UICC chrysotile; and mordenite (nonfibrous, negative control). Doses were 10, 20, 40, 60, 80 and 100 micrograms per ml for 6 days. Fiber-number doses were calculated for three size categories: aspect ratio at least 3; length at least 8 micrometers and width no more than 0.25 micrometer; and length no more than 5 micrometers and width no more than 0.1 micrometer.
• Main results:
  • By mass dose, erionite(c), erionite(w), UICC crocidolite and UICC chrysotile each showed more than 50% toxicity at one or more doses between 10 and 100 micrograms per ml.
  • Mordenite did not show appreciable toxicity at any dose.
  • At the lower doses of 10 to 20 micrograms per ml, cytotoxicity did not differ significantly among the minerals.
  • By mass, toxicity ranked UICC chrysotile = erionite(w), then erionite(c), then UICC crocidolite, then mordenite.
  • Estimated LD50 (dose giving 50% colony survival) by mass was 35 for erionite(w), 52 for erionite(c), 73 for UICC crocidolite and 32 for UICC chrysotile, in micrograms per ml. In fibers at least 8 micrometers long and no more than 0.25 micrometer wide, the LD50 was 1.16, 1.09, 6.28 and 348.80 (times 10 to the 5th fibers per ml as printed) for the same four samples.
  • Counted by fiber number, fewer erionite(c) and erionite(w) fibers than UICC crocidolite or UICC chrysotile fibers were needed for similar toxicity in each fiber-size category.
  • For fibers at least 8 micrometers long and no more than 0.25 micrometer wide, UICC chrysotile needed a significantly higher number of fibers than both erionites and UICC crocidolite for similar toxicity.
  • For fibers no more than 5 micrometers long and no more than 0.1 micrometer wide, UICC chrysotile was significantly less toxic than the two erionites at all three toxicity levels compared (25, 50 and 75% survival).
  • For fibers with aspect ratio at least 3, the erionites were significantly more toxic than UICC crocidolite and UICC chrysotile.
  • The authors reported that the ranking by fiber number matched the expected ranking by tumorigenicity, while the ranking by mass conflicted with it.
• The authors' conclusion: The authors concluded that mass dose as the only parameter for judging the in vitro reactivity of mineral fibers is not appropriate, and that dose in number of fibers may better correlate with tumorigenic potential.
• Limitations the authors state:
  • The authors noted that comparisons by fiber number are most precise near the middle of the dose range. This may detect significant differences that are not seen outside the linear part of the dose-response curves.
  • For the fiber-dose analysis, observations were combined so that only 2 independent observations per dose were used.

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: Mineral Fiber, erionite, UICC, Crocidolite, Chrysotile.

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