Effects of Cadmium on Differentiation and Cell Cycle Progression in Cultured XenopusKidney Distal Epithelial (A6) Cells

Cadmium (Cd) is an important industrial and environmental pollutant, and the kidney is the primary organ to be affected. To elucidate the effects of Cd on cell proliferation, an epithelial cell line (A6) originally derived from the distal part of the Xenopus laeviskidney was cultured in media containing 10% fetal bovine serum. The effects of Cd (added as CdCl2) on cellular growth and differentiation from single cells to confluent epithelia were investigated by visual inspection and by measurement of the degree to which living cells covered a unit area. Over a concentration range from 5 to 50µM, Cd did not affect the settling and adherence of single cells to the bottom of the culture well. The addition of 5µM Cd for 4 days did not affect the ability of the A6 cells to develop confluent epithelia, measured as the area covered by adherent living epithelial cells (99 ± 4% of the control value). However, 10µM Cd did effectively inhibit development of confluent epithelia to 13 ± 5% compared to control. Visual inspection of adherent cells exposed to 50µM Cd for 7 days revealed no increase in cell number or in cell death, which indicated the induction of cell cycle arrest. Flow cytometric analysis showed that treatment of cells with Cd (0.4mM) for 24 hours induced a significant increase in the proportion of G1 phase cells from 58.6 ± 3.9 to 80.6 ± 3.7%, and a corresponding reduction in the proportion of cells in both the S and G2 phases from 24.0 ± 3.6 to 13.4 ± 3.3% and 17.2 ± 1.7 to 5.8 ± 2.1%, respectively. This study showed that Cd stopped cell proliferation in a very narrow concentration range, between 5 and 10µM, and cell cycle analysis indicated that Cd arrested the cells in the G1 phase of the cell cycle.