Biphasic electric current stimulates proliferation and induces VEGF production in osteoblasts

Abstract

This study investigated biphasic electric current (BEC) functions as a new type of electrical stimulation to induce rat calvarial osteoblasts to proliferate, differentiate and synthesize cytokines. The culture system was designed so that biphasic current flowed between upper and lower gold plates. BEC helps to minimize the net charge accumulation during cell exposure to the electrical stimulation. Osteoblasts were exposed to electrical stimulation of 1.5 μA/cm 2 at 3000 Hz, and the effect of BEC was assessed in the interrupted mode (6 h daily) and in the continuous mode (24 h daily), depending on the interval of stimulation. Whereas proliferation increased by 31% after stimulation in the continuous mode for 2 days, it was unaffected in the interrupted mode. The transcriptional expression of osteogenesis-related genes such as alkaline phosphatase (ALP), osteopontin, and type I collagen was unchanged 4 days after stimulation in both modes, while cbfa1 was decreased under the same conditions. There was no detectable change in mRNA expression of growth factors (BMP-2, -4, IGF-2 and TGF-β1) that promote osteoblast differentiation. However, real-time RT-PCR and ELISA demonstrated that vascular endothelial growth factor (VEGF) was markedly up-regulated by BEC. Induction of VEGF by BEC was not hypoxia driven. In conclusion, the present in vitro study demonstrates that BEC increases cell proliferation and induces the production of VEGF. The BEC was more effective with continuous stimulation than with interrupted stimulation. To confirm whether BEC can enhance osteogenesis, further in vivo studies are needed.