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Quantitative small-animal surrogate to evaluate drug efficacy in preventing wear debris-induced osteolysis
E M Schwarz1, E B Benz, A P Lu
1Department of Medicine, University of Rochester Medical Center, New York 14642, USA.
Abstract:
Individuals who suffer from severe joint destruction caused by the various arthritidies often undergo total joint arthroplasty. A major limitation of this treatment is the development of aseptic loosening of the prosthesis in as many as 20% of patients. The current paradigm to explain aseptic loosening proposes that wear debris generated from the prosthesis initiates a macrophage-mediated inflammatory response by resident macrophages, leading to osteoclast activation and bone resorption at the implant interface. No therapeutic interventions have been proved to prevent or inhibit aseptic loosening. The development of therapeutic strategies is limited due to the absence of a quantitative surrogate in which drugs can be screened rapidly in large numbers of animals. We have previously described a model in which titanium particles implanted on mouse calvaria induce an inflammatory response with osteolysis similar to that observed in clinical aseptic loosening. Here, we present new methods by which the osteolysis in this model can be quantified. We determined that 6-8-week-old mice in normal health have a sagittal suture area of 50 (+/-6) microm2, which contains approximately five osteoclasts. As a result of the titanium-induced inflammation and osteolysis, the sagittal suture area increases to 197 (+/-27) microm2, with approximately 30 osteoclasts, after 10 days of treatment. The sagittal suture area and the number of osteoclasts in the calvaria of sham-treated mice remained unchanged during the 10 days. We also determined the effects of pentoxifylline, a drug that blocks the responses of tumor necrosis factor-alpha to wear debris, and the osteoclast inhibitor alendronate. We found that both drugs effectively block wear debris-induced osteolysis but not osteoclastogenesis. In conclusion, we found the measurements made with this model to be reproducible and to permit quantitative analysis of agents that are to be screened for their potential to prevent aseptic loosening.
Insights
A new quantitative method effectively measures aseptic loosening in a mouse model, enabling rapid screening of potential therapies for this common joint replacement complication.
Area of Science:
- Biomaterials Science
- Orthopedic Surgery
- Immunology
Background:
- Aseptic loosening affects up to 20% of patients following total joint arthroplasty.
- Current understanding implicates macrophage-mediated inflammation and osteoclast activation due to wear debris.
- Lack of quantitative models hinders the development of preventative therapies.
Purpose of the Study:
- To present and validate a quantitative method for assessing osteolysis in a mouse model of aseptic loosening.
- To establish a reproducible surrogate for screening potential therapeutic agents.
Main Methods:
- Implantation of titanium particles onto mouse calvaria to induce inflammation and osteolysis.
- Quantification of sagittal suture area and osteoclast number as measures of osteolysis.
- Assessment of pentoxifylline and alendronate efficacy in blocking wear debris-induced osteolysis.
Main Results:
- Titanium particle implantation significantly increased sagittal suture area and osteoclast numbers within 10 days.
- Sham-treated mice showed no changes in these parameters.
- Both pentoxifylline and alendronate demonstrated efficacy in blocking wear debris-induced osteolysis.
Conclusions:
- The developed quantitative method is reproducible and suitable for large-scale drug screening.
- This model provides a valuable tool for identifying novel interventions to prevent aseptic loosening.
- Therapeutic strategies targeting osteolysis, not just osteoclastogenesis, may be crucial.