Direct electrical stimulation enhances osteogenesis by inducing Bmp2 and Spp1 expressions from macrophages and preosteoblasts

The capability of electrical stimulation (ES) in promoting bone regeneration has already been addressed in clinical studies. However, its mechanism is still being investigated and discussed. This study aims to investigate the responses of macrophages (J774A.1) and pre-osteoblasts (MC3T3-E1) to ES and the faradic by-products from ES. It is found that pH of the culture media was not significantly changed, whereas H2O2 concentration was increased by 3.6 and 5.4 µM after 1 and 2 hours of ES, respectively. The upregulation of Bmp2 and Spp1 mRNAs was observed after 3 days of stimulation, which is consistent among two cell types. It is also found that Spp1 expression of macrophages was also enhanced by faradic by-products. Osteogenic differentiation of pre-osteoblasts was not observed during the early stage of ES as the level of Runx2 expression remains unchanged. However, cell proliferation was impaired by the excessive current density from the electrodes, and also faradic by-products in the case of macrophages. This study shows that macrophages could respond to ES and potentially contribute to the bone formation alongside pre-osteoblasts. The upregulation of Bmp2 and Spp1 expressions induced by ES and faradic by-products could be one of the mechanisms behind the electrically stimulated osteogenesis