title: Importance of the HIF pathway in cobalt nanoparticle-induced cytotoxicity and inflammation in human macrophages.
abstract: Recent, unexpected high failure rates of metal-on-metal hip implants have reintroduced the issue of cobalt toxicity. An adverse reaction to cobalt ions and cobalt-induced lung injury occurs during environmental exposure and is now strictly controlled. Currently adverse reaction occurs to cobalt nanoparticles during wear and tear of metal-on-metal hip implants of which the underlying mechanism is not fully understood. The putative role of the hypoxia-inducible factor (HIF) pathway in the mechanism of cobalt nanoparticle (Co-NPs) toxicity was examined using the U937 cell line, human alveolar macrophages and monocyte-derived macrophages. Co-NPs (5-20 μg/ml)-induced cytotoxicity (viability ranged from 75% to <20% of control, respectively) and reactive oxygen species (ROS), whereas a comparable concentration of cobalt ions (Co(II); up to 350 μM) did not. Co-NPs induced HIF-1α stabilization. Addition of ascorbic acid (100 µM) and glutathione (1 mM) both prevented the increased ROS. However, only treatment with ascorbic acid reduced HIF-1α levels and prevented cell death, indicating that a ROS-independent pathway is involved in Co-NPs-induced cytotoxicity. Replenishing intracellular ascorbate, which is crucial in preventing HIF pathway activation, modified Co-induced HIF target gene expression and the inflammatory response, by decreasing interleukin-1 beta (IL-1β) mRNA and protein expression. Addition of glutathione had no effect on Co-NPs-induced HIF target gene expression or inflammatory response. Thus, Co-NPs induce the HIF pathway by depleting intracellular ascorbate, leading to HIF stabilization and pathway activation. This suggests a strong, ROS-independent role for HIF activation in Co-NPs-induced cytotoxicity and a possible role for HIF in metal-on-metal hip implant pathology.
authors: a National Heart & Lung Institute, Imperial College London , London , UK and.
authors: Agata
authors: A
authors: Nyga
authors: b Institute of Orthopaedics & Musculoskeletal Science, Royal National Orthopaedic Hospital, University College London , London , UK.
authors: Alister
authors: A
authors: Hart
authors: a National Heart & Lung Institute, Imperial College London , London , UK and.
authors: Teresa D
authors: TD
authors: Tetley
mesh_terms: D001205:Ascorbic Acid / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects*; D002478:Cells, Cultured; D003035:Cobalt / Q000737:chemistry / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D005978:Glutathione / Q000494:pharmacology; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007249:Inflammation / Q000139:chemically induced / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism; D053758:Nanoparticles / Q000737:chemistry / Q000633:toxicity*; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D017382:Reactive Oxygen Species; D003035:Cobalt; D005978:Glutathione; D001205:Ascorbic Acid
keywords: Ascorbic acid; cobalt nanoparticles; cytotoxicity; hypoxia-inducible factor; macrophages