Effects of electrostatic charge on the pathogenicity of chrysotile asbestos

In vitro assessment of biopersistence using mammalian cell systems

Biopersistence of fibers in the respiratory airways is a concept including both the physical durability of the fibers and their chemical stability. Physical durability results from several events of diverse origins: fiber epuration by the lung clearance mechanisms, internalization by scavenger cells and fiber splitting. Fibers residing in the lung milieu will be attacked and modified chemically, structurally, and physically (size and shape). Fiber toxicity, which is very likely to be dependent on physical fiber characteristics, will also be dependent on the duration of the fiber's stay in the tissue. Biopersistence, therefore, will be a key issue in determining fiber toxicity. So far, few in vitro systems have been used to study parameters involved in biopersistence. However, examples exist of investigations of fiber phagocytosis by mammalian cells in culture, either by macrophages, or epithelial or mesothelial cells, and studies have also been reported of the fate of internalized fibers in relation to fiber dimensions and chemical stability, especially within macrophages and mesothelial cells. The methods will be presented and discussed to determine to what extent the development of in vitro biophysical models could help in determining those parameters, known or thought to be relevant to fiber persistence.

Experimental studies in rats on the effects of asbestos inhalation coupled with the inhalation of titanium dioxide or quartz

Rats were exposed for 1 year, with a 2-year follow-up, to dust clouds consisting of a mixture of amosite or chrysotile asbestos with either titanium dioxide or quartz. The addition of titanium dioxide to asbestos did not increase levels of pulmonary fibrosis above the amounts produced by chrysotile or amosite alone. Quartz, however, greatly increased fibrosis above that produced by the asbestos types alone. Both particulate dusts caused an increase in the numbers of pulmonary tumours and mesotheliomas compared to asbestos alone but while tumours in animals treated with asbestos and quartz tended to occur earlier than tumours with asbestos alone, in animals treated with dusts containing titanium dioxide, tumour production occurred later than with asbestos alone. In animals treated with mixtures of asbestos and quartz, there was evidence of increased transport of fibres across the visceral pleural surface and this may be associated with the finding of a higher proportion of pleural mesotheliomas than previously reported in experimental inhalation studies from any laboratory using the main asbestos varieties. The presence of particulate dusts made little difference to the amounts of amosite fibre retained in the lung tissue but, with chrysotile, titanium dioxide appeared to increase retention while quartz reduced it.

Minerals, fibrosis, and the lung

Determinants of pulmonary fibrosis induced by inhaled mineral dusts include quantity retained, particle size, and surface area, together with their physical form and the reactive surface groups presented to alveolar cells. The outstanding problem is to ascertain how these factors exert their deleterious effects. Both compact and fibrous minerals inflict membrane damage, for which chemical mechanisms still leave uncertainty. A major weakness of cytotoxicity studies, even when lipid peroxidation and reactive oxygen species are considered, lies in tacitly assuming that membrane damage suffices to account for fibrogenesis, whereas the parallel occurrence of such manifestations does not necessarily imply causation. The two-phase procedure established that particles, both compact and fibrous, induce release of a macrophage factor that provokes fibroblasts into collagen synthesis. The amino acid composition of the macrophage fibrogenic factor was characterized and its intracellular action explained. Fibrous particles introduce complexities respecting type, durability, and dimensions. Asbestotic fibrosis is believed to depend on long fibers, but scrutiny of the evidence from experimental and human sources reveals that a role for short fibers needs to be entertained. Using the two-phase system, short fibers proved fibrogenic. Other mechanisms, agonistic and antagonistic, may participate. Growth factors may affect the fibroblast population and collagen production, with cytokines such as interleukin-1 and tumor necrosis factor exerting control. Immune involvement is best regarded as an epiphenomenon. Downregulation of fibrogenesis may follow collagenase release from macrophages and fibroblasts, while augmented type II cell secretion of lipid can interfere with the macrophage-particle reaction.

IgG and IgA enhance the chrysotile-induced production of reactive oxygen metabolites by human polymorphonuclear leucocytes

Chrysotile asbestos fibres induce a rapid generation of reactive oxygen metabolites by human polymorphonuclear leucocytes (PMNL) in vitro. This effect was markedly enhanced by the presence of 10-200 micrograms/ml of human gammaglobulin, purified polyclonal IgG, and monoclonal IgG and IgA myeloma proteins. Purified monoclonal IgD, IgM, kappa light chain proteins, and secretory IgA inhibited this chrysotile-induced response. No enhancing effect of IgG was observed when quartz dust or opsonized zymosan were used as stimulators of PMNL metabolism. The enhancing effect of IgG was shown to depend on opsonization of the asbestos fibre. We suggest that the IgG and IgA potentiating effect on the asbestos fibre-induced production of tissue-damaging reactive oxygen metabolites by inflammatory cells is dependent on a particle-specific binding of immunoglobulin to the fibre surface, with subsequent Fc receptor-mediated effects on cells. Such an interaction between certain immunoglobulins and asbestos may explain a number of in vivo phenomena in which immunological responses (hypergammaglobulinemia, circulating immune complexes, etc.) have been shown to relate to the progression of pulmonary asbestosis. The differences between various immunoglobulin classes and monoclonal immunoglobulins could represent an individual inflammation-modulating mechanism in the development of acute or chronic pulmonary asbestosis.