Asbestos Inhalation and Cell Proliferation in Lung and Pleural Cells

The risk of developing mesothelioma can vary depending on certain factors such as duration and degree of exposure and the fiber type of asbestos.  One interesting study is called, "Comparative Proliferative and Histopathologic Changes in Rat Lungs after Inhalation of Chrysotile or Crocidolite Asbestos" by Kelly A. BéruBéa, Timothy R. Quinlana, Gerald Moultona, David Hemenwayb, Patrick O'Shaughnessyb, Pamela Vacekc and Brooke T. Mossmana - Toxicology and Applied Pharmacology - Volume 137, Issue 1, March 1996, Pages 67-74.  Here is an excerpt: "Abstract - Patterns of cell proliferation in lung and pleura and development of histopathologic lesions were studied in lungs from Fischer 344 rats after inhalation exposure to chrysotile or crocidolite asbestos at average airborne concentrations of approximately 8 mg/m3air for 5 and 20 days and after 20 days of exposure followed by an additional 20 days in room air (20 + 20 days). To assess cell proliferation rats were injected with 5-bromo-2′-deoxyuridine (BrdU) at various time points after initiation of exposure to asbestos.

Image analysis was used to quantitate the effects of chrysotile and crocidolite on BrdU labeling indices in the following lung compartments: (1) interstitium, (2) alveolar duct region, (3) bronchial epithelium, and (4) visceral mesothelium. With the exception of mesothelium, which exhibited significant increases in BrdU incorporation in rats exposed to crocidolite at 20 + 20 days, asbestos-induced elevations in BrdU uptake in other compartments were transient with labeling comparable to sham controls at later time points. Histopathology of rat lungs revealed fibrotic lesions of a greater extent and severity at 20 days in rats exposed to crocidolite, but fibrosis occurred in both asbestos-exposed groups after an additional 20 days in clean air (20 + 20). Quantification of fiber burden in rat lung after inhalation of comparable airborne concentrations of either fiber type demonstrated that inhalation of crocidolite asbestos led to a higher fiber retention when compared to chrysotile asbestos. Our results indicate that chrysotile and crocidolite asbestos induce different patterns of cell proliferation in lung and pleural cells. The protracted increases in BrdU labeling of mesothelial cells by crocidolite may reflect increased retention of fibers and/or inherent differences between types of asbestos."

Another interesting study is called, "Influence of dose and fiber type on respiratory malignancy risk in asbestos cement manufacturing." By Weill H, Hughes J, Waggenspack C.  Am Rev Respir Dis. 1979 Aug;120(2):345-54.  Here is an excerpt: "Abstract - This investigation provides information concerning the risk or respiratory malignancy in relation to duration, degree, and fiber type of exposure to asbestos in a manufacturing cohort of 5,645 with long-term follow-up. Excess mortality for this cause was found in groups with moderate and high cumulative exposure (standard mortality ratios of 290 and 226). Analysis of the influence of components of total exposure dose (duration, average concentration) revealed no detectable excess risk in persons employed for less than 2 years or with low-degree average exposure. Exposure to corcidolite (blue) fiber in addition to the predominantly used chrysotile in pipe making appeared to be associated with higher risk than was exposure to chrysotile alone."

A third study worth examining is called, "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, V. Timbrell - Radiation Oncology Investigations
Volume 22 Issue 6, Pages 721 – 727.  Here is an excerpt: "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 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 m. This is compared with the sizes of fibre previously reported to induce mesotheliomata when implanted into the pleural cavities of rats."

If you found any of these excerpts interesting, please read the studies in their entirety.  We all owe a great debt to these researchers for their important work.