Cobalt nanoparticles (CoNPs) released from hip joint implants are known to have a toxic effect on several organs. The aim of this study was to examine the effects of CoNP toxicity on vascular endothelium and to elucidate the underlying mechanisms. Moreover, the role of three ferrous ion (Fe2+)containing agents in conferring resistance to the effects of CoNPs was investigated. Vascular endothelial HUVEC and HMEC-1 cells were cultured in a medium supplemented with CoNPs. Ferrous lactate [Fe(CH3CHOHCOO)2], ferrous succinate [Fe(CH2COO)2], and ferrous chloride (FeCl2) were added to the cells in varying concentrations. CoNP toxicity was evaluated by measuring cell viability, rate of apoptosis and LDH release, and intracellular ROS levels. Treatment with CoNPs decreased cell viability, LDH release, and ROS production and increased apoptosis. CoNPs increased hypoxia-inducible factor-1α (HIF-1α) protein level and mRNA levels of VEGF and GLUT1 downstream of HIF-1α signalling. Silencing HIF-1α attenuated CoNP toxicity, as seen by recovery of cell viability, LDH release, and ROS levels and reduced apoptosis. CoNPs caused a pronounced reduction of Fe2+ in cells, but supplementation with Fe(CH3CHOHCOO)2, Fe(CH2COO)2, and FeCl2 restored Fe2+ levels and inhibited HIF-1α activation. Moreover, all three Fe2+-containing agents conferred protection from CoNPs; Fe(CH3CHOHCOO)2 and Fe(CH2COO)2 more effectively than FeCl2. In summary, this study revealed that CoNPs exert their toxicity on human vascular endothelial cells by depleting intracellular Fe2+ level, which causes activation of HIF-1α signalling. Supplements of Fe2+, especially in the form of Fe(CH3CHOHCOO)2 and Fe(CH2COO)2, mitigated CoNP toxicity.
Keywords: CoNPs; Fe2+-containing agents; hypoxia-inducible factor; vascular endothelial cells.
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