Tamoxifen induces changes in the lipid composition of the retinal pigment epithelium cell line D407

Tamoxifen, the antioestrogenic drug prescribed for long-term, low-dose therapy of breast cancer, induces retinopathy. This study evaluates the effects of tamoxifen on the human retinal pigment epithelial cell line D407, attempting to identify the underlying mechanisms on tamoxifen-induced retinopathy and the involvement of cellular membranes in the cytotoxic action mechanism. We demonstrate that the tamoxifen-induced decrease in the cell growth of the D407 cell line results from pyknosis and cell cycle arrest rather than from necrosis. Furthermore, D407 cells influence the lipid composition of both plasma membrane and intracellular membranes in response to tamoxifen. Tamoxifen increases the physical order of the lipid bilayer. We observed a compensatory decrease in the cholesterol content of the plasma membrane which results in an increase of the plasma membrane fluidity. In intracellular membranes the phosphatidylcholine content is reduced to 50% of the controls. This reduction may be related to the formation of a second messenger via phospholipase pathway and sustained activation of protein kinase C. Since increased plasma membrane fluidity as well as sustained activation of protein kinase C influence the rod outer segments binding and/or ingestion by retinal pigment epithelial cells, our results suggest that membrane-mediated pathways contribute to the tamoxifen-induced retinopathy.