Effect of high glucose and low intensity pulsed ultrasound on osteoblasts

Diabetes mellitus is a general metabolic disease commonly leading patients to skeletal disorders such as osteoporosis and bone fracture. Previous studies had shown that appropriate stimulation with low intensity pulsed ultrasound (LIPUS) may accelerate the proliferation and differentiation of osteoblasts for promoting fracture healing. In vitro experiments were carried out on the mouse osteoblastic cells which were cultured in the medium with either a normal glucose concentration of 5mM or high glucose concentration of 33mM. A 1 MHz LIPUS of a 100 mW/cm2 SATA intensity arranged from 20% duty cycle of a 1 kHz pulse repetition frequency was applied to daily stimulate osteoblasts for ten minutes. The responses of obsteoblasts with insonification were assessed by cell proliferation and gene expression from measurements of reverse transcriptase-ploymerase chain reaction (RT-PCR), osteoprotegerin (OPG), alkaline phosphatase (ALP), and osteocalcin (OCN) mRNA expression. Experiments were grouped into A: cells cultured in normal medium; B: cells cultured in normal medium and insonified with LIPUS; C: cells cultured in high glucose medium; D: cells cultured in high glucose medium and insonified with LIPUS. Results obtained from groups B, C, and D all showed that the corresponding growth of osteoblasts tended to increase compared to that of cells from the control group A. Specifically, the highest proliferation was found associated with osteoblasts of group D. The RT-PCR results revealed that mRNA levels of OPG corresponding to experimental groups of B, C, and D were respectively to be 1.29, 1.38, 1.62-fold more than that of control group; mRNA levels of ALP were respectively to be 1.18, 1.17, 1.38-fold more than that of control group and mRNA levels of OCN were respectively to be 1.41, 0.73, 1.22-fold more than that of control group. OCN mRNA expression was increased for those osteoblasts insonified with LIPUS from groups B and D, and that tended to be decreased for cells cul- - tured in high glucose from group C. In conclusion, LIPUS exposure was found to be able to increase cell viability and mRNA expression of osteoblasts. Even culture under a high glucose medium, the proliferation and gene expression of osteoblasts could still be promoted by the insonification of LIPUS. These results indicated that the LIPUS may have the ability to decrease the inhibitory effect of osteoblasts associated with high glucose level and to facilitate other cell functions.