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Role of phagocytosis in Syrian hamster cell transformation and cytogenetic effects induced by asbestos and short and long glass fibers.

We have shown previously that asbestos and other mineral dusts, including glass fibers, induce cell transformation and chromosomal mutations in Syrian hamster embryo cells in culture. In the present study, we observed that both asbestos and glass fibers were phagocytized by these cells and accumulated in the perinuclear region of the cytoplasm. In order to understand the mechanism of fiber length-dependent cellular effects, we examined the phagocytosis and intracellular distribution of glass fibers of differing lengths in cells at various times after treatment. Glass fiber length was decreased by milling with a mortar and pestle. Cells treated with an equal dose of milled glass fibers (on a weight per surface area basis) were exposed to 7-fold more fibers since milling of glass fibers resulted in a 7-fold decrease in length with little change in diameter. However, cells exposed to milled glass fibers phagocytized a similar number of fibers as cells exposed to an equal mass of unmilled glass fibers, indicating that milled fibers were less readily phagocytized. In cells treated with either unmilled or milled glass fibers, the length of the intracellular fibers was more than 2-fold greater than the length of the fibers on the surface, suggesting that cells selectively internalized longer fibers. Fiber length, however, did not appear to affect the migration of intracellular fibers to the perinuclear region of the cytoplasm. Even though cells treated with milled glass fibers contained a similar number of fibers as those treated with unmilled glass fibers, the resulting cytotoxicity, transformation frequency, and frequency of micronuclei were greatly reduced in the cultures treated with milled glass fibers. Thus, fiber length appears to affect the phagocytosis of fibers as well as the ability of intracellular fibers to induce cytogenetic damage and the resultant transformation.