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Leo A Kim, Dhanesh Amarnani, Wen A Tseng, Demetrios G Vavvas, Patricia A D'Amore; Tamoxifen Toxicity of the Retinal Pigment Epithelium is Mediated by RIP Kinase and the NLRP3 Inflammasome. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1741.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the mechanism of tamoxifen-induced cell death in human cultured retinal pigment epithelial cells (RPE), and to investigate the relative contribution of cell death mechanisms including apoptosis, necroptosis, and pyroptosis to tamoxifen toxicity of the RPE.
Human RPE cells (ARPE-19 cells) were cultured until confluence and treated with 20 μM tamoxifen; subsequent cell death was measured by detecting lactate dehydrogenase (LDH) release. Lysosomal membrane permeabilization was assessed using acridine orange staining. The roles of lysosomal enzymes cathepsin B and L were examined by blocking their activity with Z-FF-FMK, CA-074-Me, and Z-FY(t-Bu)-DMK. Caspase activity was evaluated by caspase-1, 3-, 8-, and 9-specific inhibition using Z-YVAD-FMK, Z-DEVD-FMK, Z-LETD-FMK, and Z-LEHD-FMK respectively. Cells were primed with IL-1α and treated with tamoxifen and IL-1β production was quantified via ELISA. Caspase activity was verified with the fluorochrome-labeled inhibitor of caspases (FLICA) probe specific for each caspase. Necroptosis was evaluated using necrostatin-1 (Nec-1) to inhibit RIP1 kinase.
Cell death occurred within two hours of tamoxifen treatment of confluent ARPE-19 cells, and was accompanied by lysosomal membrane permeabilization. Tamoxifen toxicity was shown to occur through both caspase-dependent and non-caspase-dependent cell death pathways. Blockage of cathepsin activity resulted in a significant decrease in cell death, indicating that lysosomal destabilization and cathepsin release are upstream of these cell death pathways. Simultaneous treatment of ARPE-19 cells with caspase inhibitors and Nec-1 resulted in a near complete rescue from cell death.
Tamoxifen-induced cell death occurs through multiple cell death mechanisms. Simultaneous inhibition of caspase-dependent and caspase-independent cell death pathways is required to protect cells from tamoxifen. Inhibition of upstream activators such as cathepsin B/L may be a feasible approach to block multiple cell death pathways.
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