Injection of mscs mitigates particle associated chronic inflammation of bone

Abstract

Background & Aim Chronic inflammation is a common feature in many diseases of different organ systems, including bone. Unfortunately, there are few interventions to mitigate chronic inflammation and preserve host tissue. We have used diverse strategies to regulate chronic inflammation including polarization of local macrophages to an M2 anti-inflammatory phenotype and modulation of the transcription factor NF-kB. In the current study, we investigate local injection of unmodified and pre-conditioned MSCs (pMSCs) in a model of chronic inflammation of bone: the murine continuous femoral intramedullary polyethylene particle infusion model. Methods, Results & Conclusion Methods: Osmotic pumps were connected to vinyl catheter tubing and a hollow titanium rod was press-fit into the distal femur through the intercondylar region of 11-12 week BALB/c mice. At primary surgery, the pumps were filled with 10% BSA/PBS +/- 1.25% polyethylene (PE) particles and 10 ng/ml of LPS (contaminated polyethylene particles, cPE). For preparation of pMSCs, murine MSCs were seeded at 5,000 cells/cm2 and treated with 20 ng/ml TNF-a and 20 mg/ml LPS for 3 days. Three weeks after primary surgery, pumps were changed to new ones for 3 more weeks. In specific treatment groups, 5 × 105 murine primary MSCs or pMSCs were injected intramedullary at the second surgery. There were six groups +/- PE/cPE and +/- treatment with MSCs or pMSCs (7-9 mice/group). MicroCT analysis was carried out 6 weeks after primary surgery. A three-dimensional region of interest (ROI: 4 × 4 × 3 mm) was created in the distal femur. Bone mineral density (BMD, mg/mm3) was quantified. Histomorphological analysis was performed of the area of osteoclasts (TRAP staining) and alkaline phosphatase (ALP) staining; immunohistochemistry was used to calculate the total number of macrophages (F4/80+), and the number of M1 (iNOS+) and M2 (arginase+) phenotypes. A one-way ANOVA with Tukey's post-hoc test was performed to quantify the results. Results Contaminated polyethylene particles increased total macrophages, M1 macrophage phenotype, and the percentage of TRAP positive area in the ROI, and decreased M2 macrophage phenotype (Figures 1 and 2). Injection of un-modified MSCs or pMSCs reversed these findings. There were no significant effects on BMD for the treatments in the polyethylene particle groups. Conclusion Local injection of MSCs may be a potential intervention to mitigate the adverse effects of chronic inflammation of bone due to contaminated polyethylene particles.