New Means Of Prevention And Management Of Osteolysis Via Dual Regulation Of Bone Resorption And Osteogenesis

OBJECTIVEAseptic loosening is a main cause of loss of long-term efficacy of artificial joint replacement. The culprit for aseptic loosening is wear particle-induced periprosthetic osteolysis. The occurrence of this process is closely related to three events: infiltration of inflammatory cytokines, elevated bone resorption and osteogenesis disfunction. The three occur in concert to produce aseptic loosening and underestimating the effect of any one of them would costly in the prevention and management of aseptic loosening. Meanwhile, prosthetic infection is one of the most common complications in joint replacement, which could bring about disastrous consequence. Once infection happens, the implant has always to be retracted and revision surgery is inevitable. Bacterial adhesion and biofilm formation on implant surfaces represent a crucial initial step in prosthetic infection. Paradoxically, good biological compatibility is the prerequisite for bone implants, which in turn could be benefit for bacterial adhesion and survival. Therefore, one promising bone implant calls for both anti-infection and osteointegration-induction activity. In conjunction with the pathogenesis of wear particle-induced osteolysis, and in terms of anti-inflammatory cytokine release, inhibition of bone resorption and promotion of bone formation, this study investigates the potential applicable effect of local micro-environment produced by magnesium degradation in the prevention and management of wear particle-induced osteolysis. We also investigate the role of magnesium in bacterial infection. Concurrently, based on the regulation of systemic bone metabolism, this study investigates the bone protective effect of plant extract andrographolide, a Chinese medicinal agent. It is expected that the result of this study could provide new means of preventing and managing aseptic loosening by combating the pathogenesis of wear particle-induced osteolysis based on local and systemic factors.CONTENT AND METHODSBone marrow stromal cells(BMSC) bone marrow-derived macrophages(BMMS) were obtained to establish osteoblast and osteoclast culture systems.1. Magnesium(99.9%) was soaked according to ISO10993 to simulate magnesium degradation. The effects of magnesium degradation on BMMs proliferation, osteoclastogengesis and bone resorption were examined, to investigate osteoclastic responses induced by magnesium degradation. A wear particle-induced osteolysis model was established, to examine the inhibitory effect of magnesium degradation on osteolysis by means of micro-CT and histomorphology analysis. The effects of magnesium degradation on BMSC proliferation, adhesion, spreadability and osteoblast differentiation were observed, to investigate osteoblastic responses induced by magnesium degradation.2. Examined anti-MRSA property of magnesium in vitro, and evaluated its anti-infection ability in acute proximal tibia infection model of SD rats using X-ray imaging, micro-CT scanning and microbiological analysis.3. Examined the effects of andrographolide on the differentiation and functions of osteoblasts and osteoclasts, and investigate its mechanisms. Wear particle-induced osteolysis model and LPS-induced inflammatory osteolysis model were established, inject andrographolide intraperitoneally, to examine its bone protection activity.RESULTS1. In vitro, magnesium degradation severely inhibit osteoclasts formation and bone resorption under combined action of magnesium ions and elevated PH values, molecularly inhibited the transcription activity of a key osteoclast transcription factor, NFATc1, and down-regulated the expression of osteoclast–specific genes. In vivo, in comparison to wear particle-induced osteolysis, magnesium degradation retained higher bone mass and had reduced local inflammatory cytokine level. Meanwhile, magnesium degradation rescued osteoblast functions that were damaged in pathological environment, promoted the expression of osteoblast alkaline phosphatase and integrin α3/α5/β1, and up-regulated the expression of SMAD4 protein and osteoblast-specific genes. However, the elevated p H level demonstrated cytotoxicity and high magnesium ion concentration inhibited calcium deposition of osteoblasts.2. In vitro, magnesium significantly inhibited adhesion and biofilm formation caused by MRSA on its surface. Further studies suggested that magnesium could down-regulate the bacterial virulence-associated gene expression. In vivo anti-infective research showed that magnesium could obviously inhibit rats tibial infection caused by MRSA compared with Ti.3. In vitro, andrographolide concentration-dependently inhibited osteoclast differentiation and bone resorption, through blocking the classic RANKL/NF- B pathway and the downstream expression of osteoclast-specific genes. Meanwhile, andrographolide promoted osteoblast calcium deposition, osteoblast-specific genes expression and OPG/RANKL levels, prompted bone formation metabolism. In vivo, andrographolide showed significantly bone protection activity in osteolysis models both locally and systemicly.CONCLUSIONS1. The microenvironment produced by local magnesium degradation could inhibit inflammatory response, positively regulate bone metabolism, and inhibit wear particles-induced bone loss.2. Magnesium represents a new antibacterial biomaterial in the prevention and treatment of orthopedic implant-related infections.3. Andrographolide could inhibit osteoclastic bone resorption, promote osteoblast differentiation, and provide significant bone protection through systemic dual-regulation of bone metabolism.