CARCINOGENICITY TESTING OF ASBESTOS FIBRES - A PRELIMINARY STUDY

Transcription

1 CARCINOGENICITY TESTING OF ASBESTOS FIBRES - A PRELIMINARY STUDY Extensive data is available on lung cancer and pleural mesothelioma caused by asbestos in man and animals. The object of the present work was to test the carcinogenicity of some types of asbestos mined in India. Asbestos samples obtained from Andhra Pradesh and Rajasthan were examined for their physical and chemical characteristics. The carcinogenicity of asbestos sample was studied in rats by intratracheal administration. Special attention was given to the morphological changes seen at variable periods in lung and pleura. MATERIALS AND METHODS * Andhra Pradesh (AP-I) sample (Ann. Rep., 1976e) was utilized for testing in experimental animals because it was observed that it differed in chemical constitution from samples obtained from Canada and U. S. S. R. Trace metals like chromium, nickel, etc. were present in large concentration in this sample (Ann. Rep., 1976e). These metals are known carcinogens. They may also act synergistically and may enhance the cancer induction by asbestos fibres. The detailed plan of the experiment was described earlier (Ann. Rep., 1976e). The animals are grouped as follows and given the treatment as indicated. Each group contained 20 male and 20 female rats. Group I The asbestos dust was extracted with hot benzene to remove traces of benzopyrene. After extraction the asbestos fibres were dried at 80 C. 2mg of asbestos dust {which is the 63

2 tolerable dose} was thoroughly mixed with 0.2 ml of sterile salin and instilled 3 times at monthly intervals. Group II: 200 mg of dust was mixed in 40 ml. of benzen solution of benzopyrene (B.P.). The concentration of adsorbe B.P. on asbestos fibre was mg. Such treated asbestos wa administered 3 times at monthly intervals. This technique wa adopted, because asbestos fibres are known to have a. low concentra tion of B.P. Group In: 2. mg of dust plus 5 mg of B. P. instilled once. Group IV: 5 mg of B.P. given only once. Group IV is control for Group III RESULTS The results are summarised in Table 27. In addition tt inflammatory changes, precancerous lesions in the lungs an< pleura were very distinctly seen. Only in three cases in the second and third groups, clear~cut cases of tumours were observed The development of less number of tumours is possibly due t( short period of the experiment (the animals were killed after t year). When asbestos was given alone, precancerous lesions were observed in nearly 15% of the rats. The addition of B. P. increas ed the frequency of these lesions to 50%. The difference between group I and group II was significant No significant difference was observed between group II anc group III. Figs. 9 to 13 indicate the sequential changes till the development of lung tumour. Grossly the lung appeared very much enlarged in size grey,ish brownish in appearance and in a few cases greyish whitish nodular structures were apparent in pleural surfaces. In a case of lung carcinoma and adenocarcinoma extensive metastasis was seen in all the organs including peritoneum, though the primary tumours were in the lung and in the bronchi respectively. 64

3 Sequential change in the development of lung tumour Fig. 9 Diffuse irregular hyperlasia of mesothelial eel of peritoneum x 300 Fig. 10 Hyperplastic areas obs erved in the lining of bronchial epithelium. x 300

4 Fig. 11 Section showing Pal iiiomatous out growt x 300 Fig. 12 Section of lung showing oat cell carcinoma x 200 Fig. 13 Section of lung show Adenocarcinoma x 200

5 III IV 21 TABLE of Alveolar bronchial pleural of Diffuse mesothelial mucous irregular epithelium glands cells hyperplasia and of GROUP Lesions Induced in Experinlental I Rats after on~ year - The histological findings have been summarized in Table 27. 'The usual morphological lesions seen. were diffuse irregular hyperplasia of alveolar epithelium. At places focal growth of alveolar epithelium was also seen. There was also a diffuse irregular hyperplasia of bronchial epithelium. Focal growth of bronchial epithelium with or without metaplasia was also seen. In cases where asbestos was given intratracheally with B. P., Iocal papillomatous growth of bronchial epithelium and bronchial glands were quite apparent. In one case, a focal adenomatous growth also appeared in pleural mesothelium. The turnouts observed were mainly medium sized oat cell carcinoma and adenocarcinoma, and metastasing in other organs. It is, therefore, evident from this preliminary data that in animals treated with pure asbestos only, an!::1signific::mtnumber of the animals dev-ioped precancerous lung lesions. No tumour was found in any of the 14 killed 67

6 animals in this group. Analogus injection of asbestos and B.P. resulted in more number of precancerous lung lesions. Three cas<!sin group II and III of oat cell carcinoma and adenocarcinoma were also recorded. The experiment is being continued for 24 months and the results will be analysed later. It is also evident that reactive proliferation may be a primary step in neoplastic development. It has been presumed earlier by Pylev (1969) that asbestos retards the removal of B. P. from the lungs and in this way contributes to the development of neoplastic growth. The preliminary results obtained so far are in agre<!ment with this hypothesis. 68