Variation in mitogenic response of cardiac and pulmonary fibroblasts to cerium

Fibroproliferative response of rat heart and lung fibroblasts to the lanthanide cerium was examined, as the element has been implicated in the causation of cardiac and pulmonary fibrosis. Fibroblasts from both of the organs were morphologically identical, and the response to fetal bovine serum, a nonspecific mitogen, was also comparable. The oxygen radical generator (hypoxanthine + xanthine oxidase [Hyp. + XO]) induced a proliferative response that was neutralized in both cardiac and lung fibroblasts by free-radical scavengers. Superoxide dismutase was more effective than catalase in reducing the mitogenic effect of Hyp. + XO. The free-radical scavenger N-acetyl-L-cysteine neutralized the free-radical-mediated changes in pulmonary fibroblasts but had a negative effect in cardiac fibroblasts, indicating a tissue-dependent variation. Reactive oxygen species are known to act as biological mediators of tissue fibrosis induced by metallic compounds. Exposure to low levels of cerium (0.5 microM) stimulated a mitogenic response in cardiac fibroblasts, but the pulmonary fibroblasts were not sensitized by the element. Tissue-dependent variation in proliferative response to cerium shows a positive association with intracellular generation of reactive oxygen species. Fibrotic changes in cerium pneumoconiosis may either be replacement fibrosis following tissue damage or mediated by nonfibroblastic cells. The study confirms that cardiac and pulmonary fibroblasts are dissimilar cellular subtypes.