Sensitization of Erythrocytes to Suicidal Erythrocyte Death Following Water Deprivation

Background/Aims : Klotho deficiency results in excessive formation of 1,25(OH)₂D₃, accelerated ageing and early death. Moreover, klotho deficiency enhances eryptosis, the suicidal erythrocyte death characterized by phosphatidylserine exposure at the erythrocyte surface. Triggers of eryptosis include increase of cytosolic Ca²⁺-activity ([Ca²⁺]_i), glucose depletion, hyperosmotic shock and oxidative stress. Klotho expression is decreased and 1,25(OH)₂D₃-formation enhanced by dehydration. The present study thus explored whether dehydration influences eryptosis. Methods : Blood was drawn from hydrated or 36h dehydrated mice. Plasma osmolarity was determined by vapour pressure method, plasma 1,25(OH)₂D₃ and aldosterone concentrations using ELISA, and plasma Ca²⁺-concentration utilizing photometry. Erythrocytes were exposed to Ca²⁺-ionophore ionomycin (1 µM, 30 min), energy depletion (12 h glucose removal), hyperosmotic shock (500 mM sucrose added, 2 h) and oxidative stress (100 µM tert-butyl-hydroperoxide, 30 min) and phosphatidylserine exposure at the erythrocyte surface estimated from annexin V binding. Results : Dehydration increased plasma osmolarity and plasma 1,25(OH)₂D₃ and aldosterone concentrations. Dehydration did not significantly modify phosphatidylserine-exposure of freshly drawn erythrocytes but significantly enhanced the increase of phosphatidylserine-exposure under control conditions and following treatment with ionomycin, glucose-deprivation, hyperosmolarity or tert-butyl-hydroperoxide. Conclusions : Dehydration sensitizes the erythrocytes to spontaneous eryptosis and to the triggering of eryptosis by excessive Ca²⁺-entry, energy depletion, hyperosmotic shock and oxidative stress.