Zopolrestat Induced Suicidal Death of Human Erythrocytes

Abstract

Background/Aims: The aldose reductase inhibitor zopolrestat has been shown to either decrease or increase apoptosis, the suicidal death of nucleated cells. Erythrocytes may similarly enter suicidal death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include oxidative stress, Ca²⁺ entry with increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), and ceramide formation. The present study explored, whether and how zopolrestat induces eryptosis. Methods: Phosphatidylserine exposure at the cell surface was estimated from annexin V binding, cell volume from forward scatter, oxidative stress from DCFDA dependent fluorescence, [Ca²⁺]_i from Fluo3-fluorescence, and ceramide abundance utilizing specific antibodies. Results: A 48 hours exposure of human erythrocytes to zopolrestat (≥ 150 µg/ml) significantly increased the percentage of annexin-V-binding cells, significantly decreased forward scatter (≥ 125 µg/ml), significantly increased Fluo3-fluorescence (200 µg/ml), significantly increased ceramide abundance (150 µg/ml), but did not significantly modify DCFDA fluorescence. The effect of zopolrestat on annexin-V-binding was significantly blunted, but not abolished by removal of extracellular Ca²⁺. Conclusions: Exposure of human erythrocytes to zopolrestat triggers cell shrinkage and cell membrane scrambling, an effect in part due to Ca²⁺ entry and ceramide.