Titanium Particle-Challenged Osteoblasts Promote Osteoclastogenesis and Osteolysis in a Murine Model of Periprosthestic Osteolysis

Abstract

The current study investigates the interactive behavior of titanium alloy particle-challenged osteoblastic bone marrow stromal cells (BMSCs) and macrophage lineage cells in a murine knee-prosthesis failure model. BMSCs were isolated from male BALB/c mice femurs and induced in osteogenic medium. At 24 hours after isolation, BMSCs in complete induction medium were challenged with 1, 3, or 5mg/ml titanium particles for 7 days. Culture media were collected at 2, 4 and 6 days and cells were harvested at 7 days for alkaline phosphatase (ALP) assay/stains. Cell proliferation in the presence of Ti particles was periodically evaluated by MTT assay. Mice implanted with titanium-pin tibial implants were given an intra-articular injection of 50μl medium containing 5×105 Ti particles-challenged bone marrow derived osteoblastic cells, followed by a repeat injection at 2 weeks post-op. Control mice with titanium-pin implants received a naïve osteoblastic cell transfusion. After sacrifice at 4 week, the implanted knee joint of each group was collected for biomechanical pin-pullout testing, histological evaluation and RT-PCR analysis of mRNA extracted from the joint tissues. Ti-particles significantly stimulated the proliferation of BMSC-derived osteoblastic cells at both high and low particle concentrations (p<0.05), with no marked differences between the particle doses. ALP expression was diminished following Ti-particle interactions, especially in the high dose particle group (p<0.05). In addition, the culture media collected from short-term challenged (48 hours) osteoblasts significantly increased the numbers of TRAP+ cells when added to mouse peripheral blood monocytes cultures, in comparison with the monocytes cells receiving naïve osteoblasts media (p<0.05). Intra-articular introduction of the osteoblastic cells to the mouse pin-implant failure model resulted in reduced implant interfacial shear strength and thicker peri-implant soft-tissue formation, suggesting that titanium particles-challenged osteoblasts contributed to periprosthetic osteolysis. Comparison of the gene expression profiles among the peri-implant tissue samples following osteoblast injection did not find significant difference in RunX2 or Osterix/Sp7 between the groups. However, MMP-2, IL-1, TNF-α, RANKL, and TRAP gene expressions were elevated in the challenged-osteoblast group (p<0.05). In conclusion, titanium alloy particles were shown to interfere with the growth, maturation, and functions of the bone marrow osteoblast progenitor cells. Particle-challenged osteoblasts appear to express mediators that regulate osteoclastogenesis and peri-prosthetic osteolysis.