Effects of tamoxifen, toremifene and chloroquine on the lysosomal enzymes in cultured retinal pigment epithelial cells

Retinal pigment epithelial cells carry out phagocytosis and digestion of ma terial shed from the photoreceptor outer segments. In this process, the int egrity of lysosomal enzymes is of major importance. In the present study th e effects of tamoxifen, toremifene and chloroquine on the activity of two l ysosomal enzymes (cathepsin D and N-acetyl-beta-D-glucosamindase) in the re tinal pigment epithelial cells were studied. Retinal pigment epithelial cel ls from pig eyes were cultured for two weeks in Dulbecco's Modified Eagle M edium, after which the cells were exposed to 1-40 mu M concentrations of ta moxifen citrate, toremifene citrate and chloroquine diphosphate. To elimina te possible medium-borne oestrogenic mechanisms, the test was repeated usin g phenol red-free medium with charcoal-stripped fetal calf serum. The expos ure time was one week, after which the lysosomal enzymes cathepsin D and N- acetyl-beta-glucosaminidase were determined. Cellular injuries were assesse d by quantifying the leakage of lactate dehydrogenase into the culture medi um. Cathepsin D and N-acetyl-beta-D-glucosaminidase showed different sensit ivities to tamoxifen, toremifene and chloroquine. The main lysosomal protea se cathepsin D was more sensitive than N-acetyl-beta-D-glucosaminidase to t he effects of tamoxifen and toremifene, possibly due to their antioestrogen ic properties. The phenol red-free medium with charcoal-stripped serum seem ed to make the drugs more effective than the reference medium. Chloroquine had only a minor effect on the lysosomal protease cathepsin D, but a cleare r effect could be seen on N-acetyl-beta-glucosaminidase.