The effects of polyvinyl pyridine-N-oxide (P204) on the cytopathogenic action of chrysotile asbestos in vivo and in vitro

A series of experiments was undertaken to test the action of polyvinyl pyridine-N-oxide (P204) on the cytopathic effects of chrysotile asbestos dust in experimental animals. Organ culture studies were undertaken using pieces of guinea-pig lung, and in addition to this the lesions produced by the intrapleural injection of chrysotile were studied after treatment with varying doses of P204. The results from both series of experiments were unfortunately negative and P204 appeared unable to modify asbestos lesions in any way. These findings contrast sharply with the marked ability of P204 to protect tissues from the effects of silica dust. It is suggested that these differences are due to the fact that while silica is rapidly toxic to macrophages, asbestos is not and many healthy macrophages and giant cells can be found in asbestos lesions packed with dust several weeks after injection. The fibrous tissue that is eventually produced in response to asbestos dust is probably produced by a slower and more insidious process than that stimulated by silica, and this process is not modified by the presence of P204.