Evaluation of osteogenesis and angiogenesis of icariin loaded on micro/nano hybrid structured hydroxyapatite granules as a local drug delivery system for femoral defect repair

Icariin has been identified to promote osteogenic differentiation of bone mesenchymal stem cells (BMSCs). However, whether icariin could enhance angiogenic factor expression of BMSCs, which may be vital for bone repair, needs to be explored. Moreover, how to construct a delivery system of icariin and its repair capability in bone defects are still unknown. In the present study, the effects of icariin on the osteogenic differentiation and angiogenic factor expression of BMSCs were firstly evaluated. Moreover, new micro/nano hybrid structured HAp (micro/nano HAp) granules were fabricated to construct the delivery system of icariin, and the osteogenesis and angiogenesis of icariin loaded on micro/nano HAp granules in a rat femoral plug defect model were evaluated by micro-CT measurements, sequential fluorescent labeling and the histological assay. The in vitro results showed that icariin significantly improved osteogenic differentiation of rat BMSCs demonstrated by the enhanced alkaline phosphatase (ALP) activity and gene expression of runt-related transcription factor-2 (Runx2), ALP, collagen type I (Col I), osteocalcin (OCN) and OCN protein secretion. Moreover, icariin induced the angiogenic genes expression of BMSCs, such as vascular endothelial growth factor (VEGF) and angiotensin 1 (ANG1). Furthermore, the activation of the AKT signaling pathway was observed in BMSCs upon treatment with icariin, and these enhancement effects could be blocked by LY294002, which suggested that the AKT signaling pathway was involved in the osteogenic differentiation and angiogenic factor expression of BMSCs induced by icariin. More importantly, micro/nano HAp granules with rod-like shapes were successfully fabricated and acted as delivery carriers for icariin. Consequently, icariin loaded on micro/nano HAp granules could promote new bone formation and blood vessel formation. These results demonstrated that icariin could enhance osteogenic differentiation and angiogenic factor expression of BMSCs via the AKT signaling pathway, moreover, the novel micro/nano HAp granules could act as carriers for icariin to repair bone defects via enhancing osteogenesis and angiogenesis.