Influence of the sialic acid content of the membrane on its susceptibility to chrysotile

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.

Pulmonary toxicology of silica, coal and asbestos

Mineral particles are customarily inhaled as mixtures, though one component may predominate and determine the response. Although the lesions often possess a characteristic structure, according to the main type of particle deposited, morphology affords little indication of pathogenesis. Being a major element in the evolution of dust lesions, macrophage behavior has been examined extensively in vitro after treatment with mineral particles, attention being directed to membrane and biochemical changes; however, no clear lead to the origin of the lesions has emerged. Pulmonary fibrosis, as one of the ultimate consequences of dust accumulation, required a direct in vitro approach in which the products of the macrophage-particle interaction were utilized to provoke collagen formation by fibroblasts in a two-phase system. By this means, silica and asbestos stimulated connective tissue formation and application of the technique to coal dusts appears promising. Coal workers may develop a peculiar type of emphysema in relation to lesions whose fibrous content is comparatively small. Type II alveolar epithelium is also stimulated by inhaled particles and lipid accumulation follows. Alveolar lipidosis interferes with the fibrotic response by preventing contact between macrophage and particles. This phenomenon may account in part for anomalies, apparent in coal workers, between epidemiological findings and dust composition. Carcinogenesis is a well-recognized feature of asbestos exposure, but, as with fibrosis, risk prediction on the basis of in vitro tests of cytotoxicity is premature and may not be valid.

Hemolysis by chrysotile asbestos fibers. I. Influence of the sialic acid content in human, rat, and sheep red blood cell membranes

Complete removal of accessible sialic acids from human, rat, and sheep red cell membranes does not inhibit the hemolytic properties of chrysotile asbestos fibers. After 60 min of contact, the percentages of hemolysis are comparable between the treated and the nontreated groups. Nevertheless, with low concentrations of fibers the initial velocity of hemolysis of rat and sheep red blood cells is lower in the neuraminidase-treated group. Although sialic acids are not essential for the expression of the hemolytic activity of asbestos, we suggest that these acids could play a role during the first seconds or minutes of the hemolytic process by increasing the electrostatic attraction between the red blood cell membranes and the fibers. However, it is clear that asbestos fibers provoke hemolysis by acting on some other cell membrane component(s).

Mechanism of haemolysis by chrysotile fibres

Haemolysis by chrysotile fibres may be related to an adsorption of the red blood cell (RBC) membranes on the fibres and not to an interaction between magnesium (Mg) from the fibres and sialic acid from RBC. This was demonstrated using neuraminidase (NANASE)-treated RBC and Mg-depleted chrysotile fibres. The mechanism may be extended to other minerals since a relationship can be obtained between the ability of various minerals to adsorb liposomes of dipalmitoyl phosphatidylcholine (DPPC) and their haemolytic activity.