Abstract
Background
Mechanisms underlying implant failure remain incompletely described, though the presence of macrophage-mediated inflammatory reactions is well documented. Hypoxia has a critical role in many diseases and is known to be interdependent with inflammation. Metals used for joint replacements have also been reported to provoke hypoxia-like conditions. In view of this, we aim to investigate hypoxia-associated factors in aseptic loosening and osteoarthritis with a focus on macrophages.
Methods
Western blotting, calorimetric assay, haematoxylin-eosin staining, immunohistochemistry, double-immunofluorescence and transmission electron microscopy were performed on capsular tissue obtained from patients undergoing primary implantation of a total hip replacement for osteoarthritis and from patients undergoing revision surgery for aseptic loosening to investigate the presence of hypoxia-associated factors.
Results
Tissues from patients with osteoarthritis and aseptic loosening showed the presence of inflammatory cells, many of which were macrophages as confirmed with CD68 immunostaining. In aseptic loosening, macrophages containing metal particles were present in clusters. This was observed both at the light and electron microscopic levels. Under the electron microscope, endothelial cells appeared to be hypertrophied and some showed signs of degeneration. The presence of hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and nitric oxide was demonstrated by western blotting and colorimetric assay. Macrophages were the predominant cell type to release HIF-1α, VEGF, inducible nitric oxide synthase (iNOS). This was confirmed by double-immunofluorescence showing co-localization of HIF-1α, VEGF, iNOS with the macrophage marker CD68. Endothelial cells were stained for endothelial nitric oxide synthase as assessed by immunohistochemistry.
Conclusion
This study demonstrates the release of hypoxia-associated factors by macrophages. The presence of hypoxia-associated factors in both, osteoarthritis and aseptic loosening suggest that hypoxia may be a factor underlying both pathologic conditions.
This study was supported by research grant (NMRC/CNIG/1147/2016) from National Medical Research Council (NMRC), Singapore.
