Spermidine Attenuates Oxidative Stress-Induced Apoptosis via Blocking Ca(2+) Overload in Retinal Pigment Epithelial Cells Independently of ROS

Retinal pigment epithelial (RPE) cells occupy the outer layer of the retina and perform various biological functions. Oxidative damage to RPE cells is a major risk factor for retinal degeneration that ultimately leads to vision loss. In this study, we investigated the role of spermidine in a hydrogen peroxide (H(2)O(2))-induced oxidative stress model using human RPE cells. Our findings showed that 300 μM H(2)O(2) increased cytotoxicity, apoptosis, and cell cycle arrest in the G2/M phase, whereas these effects were markedly suppressed by 10 μM spermidine. Furthermore, spermidine significantly reduced H(2)O(2)-induced mitochondrial dysfunction including mitochondrial membrane potential and mitochondrial activity. Although spermidine displays antioxidant properties, the generation of intracellular reactive oxygen species (ROS) upon H(2)O(2) insult was not regulated by spermidine. Spermidine did suppress the increase in cytosolic Ca(2+) levels resulting from endoplasmic reticulum stress in H(2)O(2)-stimulated human RPE cells. Treatment with a cytosolic Ca(2+) chelator markedly reversed H(2)O(2)-induced cellular dysfunction. Overall, spermidine protected against H(2)O(2)-induced cellular damage by blocking the increase of intracellular Ca(2+) independently of ROS. These results suggest that spermidine protects RPE cells from oxidative stress, which could be a useful treatment for retinal diseases.