Effects of chrysotile on a lysosomal enzyme preparation and on the hydrolytic enzyme activity of cultured alveolar macrophages

Cancer risk from inorganics

Inorganic metals and minerals for which there is evidence of carcinogenicity are identified. The risk of cancer from contact with them in the work place, the general environment, and under conditions of clinical (medical) exposure is discussed. The evidence indicates that minerals and metals most often influence cancer development through their action as cocarcinogens. The relationship between the physical form of mineral fibers, smoking and carcinogenic risk is emphasized. Metals are categorized as established (As, Be, Cr, Ni), suspected (Cd, Pb) and possible carcinogens (Table 6), based on the existing in vitro, animal experimental and human epidemiological data. Cancer risk and possible modes of action of elements in each class are discussed. Views on mechanisms that may be responsible for the carcinogenicity of metals are updated and analysed. Some specific examples of cancer risks associated with the clinical use of potentially carcinogenic metals and from radioactive pharmaceuticals used in therapy and diagnosis are presented. Questions are raised as to the effectiveness of conventional dosimetry in accurately measuring risk from radiopharmaceuticals.

Biochemical and cellular mechanisms of dust-induced lung fibrosis

The sequence of cellular and biochemical events in response to the deposition of dust particles in lung tissue is described. Primary reactions at the lung surface include changes in the free cell population, the alveolar surface protein and in the quantity of pulmonary surfactant, a lipoprotein-rich material secreted by Type II cells. The relationship between these changes and lung fibrogenesis is discussed. It is suggested that such primary changes are protective mechanisms which may assist in the prevention of fibrogenesis rather than lead to an increase in collagen formation and deposition. If these primary defenses are overcome, then the interstitial fibroblastlike cell may have a prominent role in fibrogenesis. Therefore detailed observations of the interaction between lung fibroblasts and mineral dusts in vitro are described. As fibrogenesis may be arrested in vivo, or possibly reversed, and does not always progress to fibrosis, final consideration is given to the step from fibrogenesis to fibrosis. It is suggested that this step may involve other tissue proteins apart from collagen and that the irreversible nature of fibrosis can be explained by the formation of strong intermolecular crosslinks between different proteins. The types of crosslinks that may be involved are discussed. Emphasis is placed on the role of calcium-dependent transglutaminases in fibrosis, as these enzymes have hitherto received little attention.