Contemporary issues in fiber toxicology

Our plain-English summary of Contemporary issues in fiber toxicology, by D.B. Warheit, K.E. Driscoll, G. Oberdoerster, et al (Fundamental and Applied Toxicology, 1995).

The study

• Authors: D.B. Warheit, K.E. Driscoll, G. Oberdoerster, C. Walker, M. Kuschner, T.W. Hesterberg
• Journal: Fundamental and Applied Toxicology
• Published: 1995;25(2):171-83
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This article was a written overview of a symposium, not a new study. It summarized six presentations on how fibers, including man-made fibers promoted as asbestos substitutes, are studied for toxicity. It drew mainly on earlier rodent and cell experiments. Topics included fiber dimensions and durability in the lung, inflammatory signaling proteins, lung "overload" from high dust burdens, molecular changes in rat mesothelioma cells, and differences between rat and human lung disease. The overview reported rat inhalation results. At 10 mg/m³, crocidolite or chrysotile asbestos induced pulmonary fibrosis, lung tumors and mesothelioma. At 30 mg/m³, refractory ceramic fibers also produced fibrosis, lung tumors and mesothelioma. Fiberglass and slag wool at that level produced no fibrosis or mesotheliomas. In hamsters, refractory ceramic fibers induced a 38% incidence of mesotheliomas. Rat mesothelial cell lines transformed by asbestos expressed the growth factor TGF-α. One presenter stated that human lung cancer associated with inhaled fibers appears to require the added contribution of cigarette smoking. The authors concluded that a fiber's ability to cause disease depends on more than simply its dose, dimensions and durability in the lung.

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: Symposium overview (review) summarizing six presentations on fiber toxicology, drawing largely on previously published animal and cell studies
• Who was studied: No single study population. The presentations reviewed mainly rat and hamster inhalation and instillation studies, cultured rat mesothelial cell lines, and comparisons with human lung disease. In the man-made fiber inhalation studies, hamsters were exposed for 18 months and rats for 24 months.
• Exposure: Asbestos fibers (chrysotile, crocidolite, amosite), erionite, and man-made vitreous fibers: refractory ceramic fibers, insulation fiberglass, and rock and slag wool. Doses included 10 mg/m³ asbestos and 30 mg/m³ man-made fibers in the inhalation studies.
• Main results:
  • In the rat inhalation studies described by one presenter, 10 mg/m³ of crocidolite or chrysotile asbestos induced pulmonary fibrosis, lung tumors, and mesothelioma in rats.
  • In rats, 30 mg/m³ of refractory ceramic fibers resulted in pulmonary fibrosis and significant increases in lung tumors and mesothelioma.
  • In hamsters, 30 mg/m³ of refractory ceramic fibers induced a 38% incidence of mesotheliomas.
  • In rats exposed to 30 mg/m³ of fiberglass or slag wool, an inflammatory response was seen but no lung fibrosis, no mesotheliomas, and no significant increase in lung tumors.
  • In rats held without further exposure after 13 weeks of exposure, much of the alkali and alkaline earth content had leached from fiberglass recovered from the lungs, while refractory ceramic fiber chemistry changed only slightly.
  • In an earlier study cited in the overview (Davis et al., 1986), rats exposed for 1 year to short amosite fibers showed no histopathological effects. One-third of rats exposed to long amosite fibers developed lung tumors.
  • In earlier rat studies cited in the overview (Roggli et al.), long fibers were selectively retained in the lungs after both chrysotile and crocidolite exposure. Longitudinal splitting of fibers occurred only with chrysotile.
  • In an earlier study cited in the overview (Davis et al., 1991), rats were exposed to amosite or chrysotile asbestos together with titanium dioxide. Lung tumors and mesotheliomas were significantly increased compared with the fibers alone.
  • In the presenter's laboratory work, rat mesothelial cell lines transformed by asbestos expressed transforming growth factor α (TGF-α). Spontaneously transformed lines expressed insulin-like growth factor II (IGF-II).
  • One presenter stated that human lung carcinoma associated with inhaled fibers appears to require the added contribution of cigarette smoking. Rat lesions progress to cancer without an additional outside factor.
• The authors' conclusion: The authors concluded that fiber dimension, durability and surface chemistry play roles in fiber-related disease. They added that the man-made fiber inhalation studies indicated a fiber's ability to cause disease depends on more than simply its dose, dimension and durability in the lung.
• Limitations the authors state:
  • How the altered TGF-α and IGF-II production in rat mesotheliomas relates to human disease was not known.
  • Rats develop a type of lung tumor not seen in humans, which causes uneasiness in equating rat and human tumors.
  • There was no generally agreed definition of the maximum tolerated dose for particle inhalation studies.
  • More studies were needed to determine whether a fiber's leachability is a critical determinant of its toxicity to the lung.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

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