Carcinogenesis and related cell and tissue responses to asbestos: a review

A review of the literature reveals that chrysotile asbestos has a mulitiplicity of effects on cells and tissues which can provide a framework for assessment of its role(s) in initiation, promotion, or as a co-carcinogen which acts in concert with chemical carcinogens found in cigarette smoke in the development of lung cancer. Several caveats important in the interpretation of these data include the general lack of dose-response protocols both for in vivo and for in vitro studies as well as the absence, in many studies, of minerals which are appropriate positive or negative controls based on epidemiological data in man. Other factors which may account for disparities in results between studies include the use of different preparations of chrysotile fibres with distinct chemical and physical compositions and different cell types and species. Whether chrysotile is an initiator of lung cancer or mesothelioma in human cells is unclear, as evidence of chromosomal aberrations in human bronchial epithelial cells are for the most part negative (Kodoma et al., 1993; see Mossman, B., this Workshop): only one study employing pleural mesothelial cells from four individuals, two of whom exhibited chromosomal abnormalities before exposure to asbestos, has documented chromosomal changes with chrysotile, crocidolite and amosite asbestos, and this study did not use a non-pathogenic dust as a negative control. Studies using human lymphocytes show chromosomal changes after exposure to latex beads or chrysotile at equal weight concentrations (Korkina et al., 1992; see Mossman, B., this Workshop). Lastly, although both chrysotile and crocidolite asbestos demonstrated dose-dependent increase in aberrant anaphases in an SV40 T antigen-transformed human mesothelial cell line (Pelin et al., 1992, see Mossman, B., this Workshop), erionite, a potent mesotheliomagenic fibre in rodents and humans, caused no aberrations in this bioassay. Several studies have been performed to determine the interactions of chrysotile with rodent cells or isolated bacterial DNA. Results in a number of bioassays have been positive, but chrysotile is less potent on a fibre number comparative basis than crocidolite and no-observed-effect-levels (NOELs) have been observed in several systems. Cell proliferation by asbestos may be a more relevant phenomenon to tumour development and promotion, and the ability of chrysotile to stimulate cell proliferation, using a number of biomarkers, has been demonstrated both in vitro and after inhalation by rats.(ABSTRACT TRUNCATED AT 400 WORDS)