Asbestos Mesothelioma and Environmental Controls in the Workplace

Asbestos has proven to be one of the most deadly industrial materials ever put to use.  This revelation has been an impetus to the creation of great environmental controls in the workplace.  One interesting study that explores this issue is called, "The relationship between respiratory impairment and asbestos-related pleural abnormality in an active work force." By Bourbeau J, Ernst P, Chrome J, Armstrong B, Becklake MR. - Am Rev Respir Dis. 1990 Oct;142(4):837-42.  Here is an excerpt: "Abstract - With the general improvement in environmental controls in workplaces where asbestos is used, an increasing number of workers are seen who exhibit isolated pleural plaques. The question as to whether these are associated with respiratory impairment independently of parenchymal disease remains unresolved. The question was reinvestigated using quantitative gallium-67 lung scanning to take into account early parenchymal change not evident on the chest radiograph. We carried out a cross-sectional study of 110 construction insulators all currently at work. Overall, 58.2% had pleural abnormality, 52.5% pleural plaques only, and 5.5% diffuse pleural thickening as assessed from the PA chest radiograph. Compared with those without, those with any pleural abnormality had a decrease in FEV1 and FVC on average of 222 and 402 ml (p less than 0.05), and those with isolated pleural plaques, a decrease on average of 200 and 350 ml (p less than 0.05), after taking into account age, height, smoking status, and the presence of parenchymal abnormality as assessed by chest radiography and gallium uptake. The complaint of dyspnea with strenuous activities was also significantly related to the width and extent of chest wall pleural thickening (p less than 0.05), independently of parenchymal disease. This study suggests that the most common radiographic findings in asbestos-exposed, isolated pleural plaques are associated with a significant reduction in FEV1 and FVC, which cannot be attributed to the presence of radiographic and subradiographic pulmonary fibrosis."

One interesting article is called, "Increased epidermal growth factor-receptor protein in a human mesothelial cell line in response to long asbestos fibers." By J. C. Pache, Y. M. Janssen, E. S. Walsh, T. R. Quinlan, C. L. Zanella, R. B. Low, D. J. Taatjes, and B. T. Mossman - Am J Pathol. 1998 February; 152(2): 333–340.   Here is an excerpt: "Epidermal growth factor (EGF) is a potent mitogen for human mesothelial cells, and autophosphorylation of the EGF receptor (EGF-R) occurs in these cell types after exposure to asbestos, a carcinogen associated with the development of mesothelioma. Here, the intensity and distribution of EGF-R protein was documented by immunocytochemistry in a human mesothelial cell line (MET5A) exposed to various concentrations of crocidolite asbestos and man-made vitreous fibers (MMVF-10). Whereas cells in contact with or phagocytizing shorter asbestos fibers (<60 microm length) or MMVF-10 at a range of concentrations showed no increase in EGF-R protein as determined by immunofluorescence, elongated cells phagocytizing and surrounding longer fibers (> or =60 microm) showed intense staining for EGF-R.

In contrast, human A549 lung carcinoma cells showed neither elongation nor increased accumulation of EGF-R protein in response to long fibers. Patterns of aggregation and increases in EGF-R protein in mesothelial cells phagocytizing long asbestos fibers were distinct from diffuse staining of phosphotyrosine residues observed in asbestos-exposed cultures. These studies indicate that aggregation of EGF-R by long fibers may initiate cell signaling cascades important in asbestos-induced mitogenesis and carcinogenesis."

A third interesting study is called, "Asbestos Bodies in Human Lungs at Autopsy" by Dzidra Cauna, MD; Robert S. Totten, MD; Paul Gross, MD - JAMA. 1965;192(5):371-373.  Here is an excerpt: "Abstract - The incidence of asbestos bodies in the lungs was investigated in 100 autopsies of adults. Lung smears were taken from the sectioned surfaces of the upper and lower lobes of both lungs. The slides were dried and mounted without staining, and approximately 400 low-power fields were examined in each slide. Routine histological sections of unexpanded lungs were also examined in all cases. Asbestos bodies were found in 41% of the subjects. They were not encountered in persons up to 24 years of age. Among males the incidence was 47%, and in females 34%. Although significant microscopic pulmonary fibrosis was encountered in two positive cases, no instance of classical asbestosis was found. Mesothelioma of the pleura was not encountered. Primary lung carcinoma occurred in one patient with asbestos bodies and in one without."

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.