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Macrophages stimulate bone resorption when they phagocytose particles
1University of Cambridge Orthopaedic Research Unit, Addenbrooke's Hospital, England.
Abstract:
We investigated in vitro a mechanism by which particulate debris may induce bone resorption and cause implant loosening. We first studied two standard particles: latex, which is considered to be inert, and zymosan, which is inflammatory. Macrophages that phagocytosed either particle became activated, and stimulated 15 times as much bone resorption as did control macrophages. For activation to occur, 100 times more latex than zymosan had to be phagocytosed. We also found that bone cement and polyethylene particles activated macrophages in a similar manner, and that the necessary amounts of these were intermediate between those of latex and zymosan. None of the particles were toxic. It was concluded that implant loosening may result from bone resorption stimulated by mediators released by macrophages that have phagocytosed particles of bone cement or polyethylene.
Insights
Particulate debris from implants can activate macrophages, leading to significant bone resorption and potential implant loosening. Even inert particles like latex, when phagocytosed in sufficient quantities, stimulate this process.
Area of Science:
- Biomaterials Science
- Immunology
- Orthopedic Research
Background:
- Implant loosening is a major complication in orthopedic surgery.
- Particulate debris generated from implants is a suspected cause of implant failure.
- The precise mechanism by which particles induce bone loss remains incompletely understood.
Purpose of the Study:
- To investigate the in vitro mechanism of particle-induced bone resorption.
- To compare the effects of different types of particles on macrophage activation and bone resorption.
Main Methods:
- In vitro study using macrophages and various particles (latex, zymosan, bone cement, polyethylene).
- Assessed macrophage activation and bone resorption stimulation.
- Quantified the amount of phagocytosed particles required for activation.
Main Results:
- Macrophages phagocytosing latex or zymosan particles showed significantly increased bone resorption (15-fold).
- Activation required 100 times more inert latex particles than inflammatory zymosan particles.
- Bone cement and polyethylene particles demonstrated intermediate activation potential.
- None of the tested particles exhibited cytotoxicity.
Conclusions:
- Macrophages activated by phagocytosing implant debris (bone cement, polyethylene) can stimulate bone resorption.
- This process, mediated by released factors, is a likely mechanism for implant loosening.
- Particle quantity and type influence the degree of macrophage activation and subsequent bone resorption.