Mechanism of cobalt nanoparticle-induced cytotoxicity and inflammation in human macrophages.

Abstract

The underlying mechanism of metal-on-metal (MoM) implants failure is still unclear. Cobalt could be the active agent due to its high toxicity and Co exposure can also occur in the environment and industry. Co(II) mimics hypoxia by stabilizing hypoxia-inducible factor (HIF)-1α, responsible for cellular and systematic responses to low oxygen levels. The hypothesis is that the HIF pathway plays an essential role in cobalt nanoparticle (Co-NP)-induced cytotoxicity and inflammation in the U937 cell line, monocyte-derived macrophages and alveolar macrophages. Ascorbic acid (AA) is essential in maintaining the activity of prolyl hydroxylases responsible for HIF-1α degradation and Co depletes intracellular AA. AA addition reduced the Co-NPs-induced HIF response and prevented Co-NPs-induced cytotoxicity. AA and glutathione (GSH) prevented reactive oxygen species (ROS) formation, but GSH had no effect on cell viability. This suggests that the AA-induced mechanism of cell protection is ROS-independent. Co-NPs, but not ions, increased release of IL-1β, which was prevented by co-exposure to AA. Caspase-1 is essential in cleaving the pro-IL-1β into its active form and AA can affect caspases activity. Preliminary results showed that AA did not affect caspase-1 suggesting a caspase-independent pathway, but further tests are required. Lathe and hip simulator CoCr-NPs stabilized HIF-1α, caused cytotoxicity and an increase in inflammatory cytokines. The lathe CoCr-NPs were more cytotoxic after 6 hours of exposure, while the hip simulator CoCr-NPs were most toxic after 24 hours. GSH was more protective than AA. MoM periprosthetic tissue showed inflammation surrounding wear debris and increased gene expression of HIF target genes, which was not observed in blood samples from patients with well-functioning MoM. This study shows for the first time the potential involvement of the HIF-1α pathway in toxicity of Co-NPs via depleting intracellular AA in a ROS- and caspase-independent manner. This new knowledge could help to explain the adverse reaction observed in patients with MoM.