No-Observed-Effect Level of Silver Phosphate in Carbonate Apatite Artificial Bone on Initial Bone Regeneration.

Fracture-related infections require both treatments for bacteria removal and bone reconstruction. The use of combined broad-spectrum antibacterial silver compounds and artificial bone with high osteogenic activity is considered to be an effective strategy for achieving these treatments in one surgery. However, silver compounds are toxic for living tissues even at low concentrations. Herein, we investigated the no-observed-effect level (NOEL) of silver phosphate (AgPO) in a bone substitute composed of carbonate apatite (COAp), a bone mineral, using in vitro and in vivo experiments. In vitro experiments demonstrated that the COAp artificial bone containing ≥0.1 wt % AgPO exerted antibacterial effects against , while those containing ≤0.3 wt % AgPO did not affect cellular adhesion, proliferation, differentiation, and calcification of osteoblast-like MC3T3-E1 cells. In vivo experiments demonstrated that the COAp artificial bone containing ≤0.3 wt % AgPO replaced a new bone to the same levels as those without AgPO 4 weeks after implantation into the bone defect of the rabbit femur condyle. However, the COAp artificial bone containing 0.3 wt % AgPO caused an inflammatory reaction, whereas those containing ≤0.1 wt % AgPO did not. Thus, both bone regeneration and infection control without any adverse effects were achieved using the COAp artificial bone containing 0.1 wt % AgPO, indicating that the NOEL of AgPO was 0.1 wt %. Our results provide an effective strategy for the treatments of fracture-related infections.