Glutamate Uptake is Inhibited by Tamoxifen and Toremifene in Cultured Retinal Pigment Epithelial Cells

Abstract

Abstract:The systemic drugs chloroquine and tamoxifen have caused retinal defects in human eye. The aim of our study was to investigate the effects of the amphiphilic drug tamoxifen, of its homologue toremifene, and of chloroquine on the glutamate uptake in retinal pigment epithelial (RPE) cells. Cultured human RPE cell line D407 and pig RPE cells were used in the study. Glutamate uptake was characterised and the glutamate transporters of pig RPE cells and the human RPE cell line D407 were compared to each other. The uptake of glutamate was studied using L-[ 3 H]glutamate as a tracer. The radioactivity in the solubilised RPE was measured with a liquid scintillation counter. In the uptake experiments, the cells were exposed to the test drugs, to the selected glutamate receptor antagonists, and to the glutamate transporter inhibitors. Both RPE cell types exhibited a high-affinity transport system for glutamate. The glutamate transporter in RPE exhibited features characteristic of the uptake systems of neurotransmitters. The transport was Na π -dependent, and L-and D-aspartate were transported into the cell by the same transporter. Chloroquine had no effect on glutamate uptake, but tamoxifen and toremifene decreased the glutamate uptake of RPE cells dose-dependently both in pig RPE cells and in human RPE cell line. The IC 50 values of tamoxifen and toremifene were lower for pig RPE cells, compared to the human RPE cell line D407. The glutamate uptake was a sensitive target for the effects of tamoxifen and toremifene, and disturbances in this function could be considered as one of the possible mechanisms of retinal defects.

Both B1R and B2R act as intermediate signaling molecules in high glucose‐induced stimulation of glutamate uptake in ARPE cells

“…Five glutamate transporter subtypes have been identified: GLAST, GLT-1, EAAC1, EAAT4, and EAAT5 (Kanai and Hediger, 2004). Among these glutamate transporters, EAAC1 and EAAT4 are expressed in ARPE cells (Maenpaa et al, 2002), and our results …”

“…Several lines of evidence have suggested that the levels of glutamate within the vitreous of patients with diabetes and in diabetic rat retina are elevated (Ward et al, 2005;Santiago et al, 2006). High-affinity glutamate transporters, which keep the resting extracellular glutamate concentration low, have been found in ARPE cells, and RPE cells likely help regulate the glutamate concentration in the subretinal space (Maenpaa et al, 2002;Miyamoto and Del Monte, 2004). However, the regulation of glutamate uptake in ARPE cells under diabetic conditions is unknown.…”

Bradykinin stimulates glutamate uptake via both B1R and B2R activation in a human retinal pigment epithelial cells

“…Retinal pigment epithelial (RPE) cells constitute an important organ facilitating vision in association with amino acid transporters such as glutamate transporters (Maenpaa et al, 2004). High-affinity glutamate transporters such as excitatory amino acid transporter 4 (EAAT4) and excitatory amino acid carrier 1 (EAAC1) have been found in a human RPE (ARPE) cells, and RPE cells are believed to take part in regulating the glutamate concentration in the subretinal space (Miyamoto et al, 1994;Maenpaa et al, 2002). A recent report also demonstrated that glutamate transporters are necessary to prevent excitotoxic retinal damage (Harada et al, 2007).…”

Potential Effects of Hormone Therapy in Type 2 Idiopathic Macular Telangiectasia

“…The pathogenesis of tamoxifen-induced retinal toxicity is unclear, it may act in vivo as an antagonist of glutamate transporters in retinal pigment epithelial cells, as already demonstrated in vitro [29]. A presumed increase in glutamate could explain the axonal degeneration observed in histopathology specimens and the formation of crystalline deposits.…”