Dose-dependent effects of eltrombopag iron chelation on platelet formation.

Iron deficiency is associated with thrombocytosis in patients, although thrombocytopenia can occur in cases of severe iron deficiency anemia. Eltrombopag (EP), a thrombopoietic agent approved for immune thrombocytopenia, also acts as an iron chelator. Our study demonstrates that megakaryocytes (MKs) exhibit an increased requirement for iron as they mature and acquire the ability to form proplatelets and release platelets. Although low EP concentrations maintain MK functions, high EP concentrations disrupt iron homeostasis, reducing proplatelet formation. Mechanistically, EP-dependent iron chelation impairs MK cytoskeletal dynamics, induces higher extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, and reduces posttranslational glutathionylation of tubulin protein. Addition of exogenous iron or oxidized glutathione to high-dose EP-treated MKs counteracts the negative effect on iron status and ERK1/2 signaling, thereby rescuing proplatelet formation. Overall, these data reveal the complex role of iron status on MK cytoskeletal dynamics and platelet biogenesis and may explain the varied clinical manifestations of iron deficiency on platelet counts.