Local suppression of pro-inflammatory cytokines and the effects in BMP-2-induced bone regeneration

The objective of this study is to investigate the effect of local inflammation suppression on the bone regeneration. Gelatin hydrogels incorporating mixed immunosuppressive triptolide-micelles and bone morphogenic protein-2 (BMP-2) were prepared. The controlled release of both the triptolide and BMP-2 from the hydrogels was observed under in vitro and in vivo conditions. When either J774.1 macrophage-like or MC3T3-E1 osteoblastic cells were cultured in the hydrogels incorporating mixed 2.5, 5 or 10 mg of triptolide-micelles and BMP-2, the expression level of pro- and anti-inflammatory cytokines including interleukin (IL)-6 and IL-10 was down-regulated, but the alkaline phosphatase (ALP) activity was promoted compared with those of hydrogels incorporating BMP-2 without triptolide-micelles. When implanted into a critical-sized bone defect of rats, the hydrogels incorporating mixed 2.5 or 5 mg of triptolide-micelles and BMP-2 showed significantly lower number of neutrophils, lymphocytes, macrophages or dendritic and mast cells infiltrated into the defect, and lower expression level of IL-6, TNF-α, and IL-10 than those incorporating BMP-2 without triptolide-micelles. The reduced local inflammation responses at the defects implanted with the hydrogels incorporating mixed 2.5 or 5 mg of triptolide-micelles and BMP-2 subsequently enhanced the bone regeneration thereat. It is concluded that the proper local modulation of inflammation responses is a promising way to achieve the enhanced bone regeneration.