Characteristics of tumors and tumor cells cultured from experimental asbestos-induced mesotheliomas in rats

Our plain-English summary of Characteristics of tumors and tumor cells cultured from experimental asbestos-induced mesotheliomas in rats, by J.E. Craighead, N.J. Akley, L.B. Gould, et al (The American Journal of Pathology, 1987).

The study

• Authors: J.E. Craighead, N.J. Akley, L.B. Gould, B.L. Libbus
• Journal: The American Journal of Pathology
• Published: 1987;129(3):448-62
• Cited by: 65 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

Mesotheliomas developed in rats in the abdominal cavity 6-23 months after peritoneal introduction of chrysotile and crocidolite asbestos. The tumors were strikingly similar to those occurring in man both with regard to histologic features and growth patterns. The authors have cultured cells from these tumors and established epithelial lines with a variety of karyologic features and doubling times shorter than those of normal mesothelial cells. Lines of diploid or near-diploid tumor cells required serum in the medium to replicate, whereas most aneuploid cell lines were maintained in a serum-free medium. In serum-free medium, the aneuploid line monolayers produced anchorage-independent excrescent masses of cells which "bud" and float free. These spheroids, which strikingly resemble the papillary structures in human mesotheliomas, are composed of mesothelial-like cells that produce hyaluronic acid and have a rich complement of intermediate filaments, predominantly cytokeratins. Aneuploid cells also replicated in soft agar with high efficiency, whereas the diploid and near-diploid cells did not. All but one cultured cell line, regardless of karyotype, produced tumors after subcutaneous or intraperitoneal inoculation (or both). Aneuploid cells caused lung tumors sporadically when introduced intravenously. Comparative analysis of the nuclear DNA of primary tumors and cultured cells demonstrated a high degree of chromosomal instability and selection among cells during early passage in vitro.

In plain English

This was an animal experiment, which the authors called a preliminary characterization. About 200 weanling female Fischer 344 rats per fiber received 25 mg of crocidolite or chrysotile into the abdomen. Tumors appeared in the abdomen 8-23 months later with both fibers. The crocidolite experiment ended at 75 weeks, when 68% had tumors. In chrysotile-treated rats, observed 98 weeks, over 80% developed mesotheliomas. Exact tumor incidence could not be calculated. Deeply invasive tumors and metastasis were not seen. The authors established 29 cell lines from crocidolite-treated and 14 from chrysotile-treated rats. The Results said tumor cells multiplied faster than normal mesothelial cells; the Discussion said aneuploid cells doubled more slowly. Six lines grew without serum and shed floating cell clusters (spheroids). Growth in soft agar strongly correlated with abnormal chromosome numbers. All but one cultured line formed tumors when injected into the abdomen, under the skin, or both, regardless of karyotype. Intravenous injection caused lung tumors only sporadically, if at all, and only with aneuploid cells. The authors presumed, but had not proven, that the tumors arise from the asbestos-induced granuloma response.

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 (asbestos injection in rats) with tissue culture and inoculation of cultured tumor cells into rats; described by the authors as a preliminary characterization
• Who was studied: Weanling female Fischer 344 rats, about 200 inoculated with each asbestos type (Department of Pathology, University of Vermont); cultured cells were later inoculated into syngeneic weanling rats
• Exposure: A single intraperitoneal injection of 25 mg of UICC standard crocidolite or Canadian chrysotile suspended in Hanks' balanced salt solution
• Main results:
  • Tumors developed in the abdominal cavity 8-23 months after inoculation, in both the chrysotile and the crocidolite groups
  • Crocidolite group: the experiment ended at 75 weeks, when 68% of animals had developed tumors
  • Chrysotile group: observed for 98 weeks, during which mesotheliomas developed in more than 80%
  • Most asbestos-inoculated rats had widespread tumor implants on peritoneal surfaces, but deeply invasive tumors and metastasis were not observed
  • 29 tumor cell lines were established from crocidolite-inoculated rats and 14 from chrysotile-inoculated rats; the authors did not believe the difference reflected biologic differences between fiber types
  • Results section: tumor cells multiplied faster than nonneoplastic mesothelial cells
  • Discussion section: aneuploid cells overall had a longer doubling time than normal fibroblasts, mesothelial cells and HeLa cells, which conflicts with the Results statement
  • Six lines were established in serum-free medium. Each produced free-floating cell masses (spheroids). Cytokeratins and hyaluronic acid were found in the spheroid cells.
  • Ability to grow in soft agar (anchorage-independent growth) strongly correlated with aneuploidy and polyploidy
  • All but one cultured cell line, regardless of karyotype, produced tumors after subcutaneous or intraperitoneal inoculation, or both
  • After intravenous inoculation of cultured cells, the cells either failed to cause lung tumors or did so sporadically, and only aneuploid cells yielded pulmonary metastasis
  • A single passage in culture dramatically changed the cell populations, and heterogeneity increased by the fifth or sixth passage
• The authors' conclusion: The authors presumed, but had not proven, that a cell from the foreign-body granuloma response to asbestos gives rise to the tumor
• Limitations the authors state:
  • Exact tumor incidence could not be determined, because some animals died without tumors or of bowel obstruction; latency periods could not be assessed
  • Cultured cells came mostly from tumors with predominantly epithelial elements and may not represent all the tumors
  • Selection and chromosome instability in culture produced cells that differed from those in the original tumors
  • Whether a cell line could be established depended partly on technical factors
  • The DNA analyses could not exclude minor chromosome changes, and host stromal cells probably accounted for some of the diploid cells in primary tumors

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Chrysotile, Crocidolite, Mesothelial Cells, Hyaluronic Acid.

Related studies

• Experimentally induced mesothelioma in white rats in response to intraperitoneal administration of amorphous crocidolite asbestos: preliminary report — K. Kolev (1982)
• Cell-substrate adhesion and metastatic potential of cultured mesothelioma cells induced by asbestos — M.M. Lee, F.H. Green, et al. (1994)
• Experimental lung tumors following specific intrabronchial application of chrysotile asbestos. Longitudinal light and electron microscopic investigations in rats — E. Fasske (1988)
• Differential diagnosis of malignant tumours in the abdominal cavity of rats after intraperitoneal injection of crocidolite or benzo[a]pyrene — J. Friemann, M. Varnai, et al. (1996)
• Pathogenesis of experimentally induced asbestos mesothelioma in rats — L.A. Vasilieva, L.N. Pylev, et al. (1998)
• Tumorigenic effect of fibrous dusts in experimental animals — F. Pott, F. Huth, et al. (1974)

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