Effect of high glucose and low intensity pulsed ultrasound on osteoblasts

Diabetes mellitus is a general metabolic disease commonly leading patientsto skeletal disorders such as osteoporosis and bone fracture. Previous studieshad shown that appropriate stimulation with low intensity pulsed ultrasound(LIPUS) may accelerate the proliferation and differentiation of osteoblasts forpromoting fracture healing. In vitro experiments were carried out on the mouseosteoblastic cells which were cultured in the medium with either a normalglucose concentration of 5mM or high glucose concentration of 33mM. A 1 MHzLIPUS of a 100 mW/cm² SATA intensity arranged from 20% duty cycle ofa 1 kHz pulse repetition frequency was applied to daily stimulate osteoblastsfor ten minutes. The responses of obsteoblasts with insonification were assessedby cell proliferation and gene expression from measurements of reversetranscriptase-ploymerase chain reaction (RT-PCR), osteoprotegerin (OPG),alkaline phosphatase (ALP), and osteocalcin (OCN) mRNA expression. Experimentswere grouped into A: cells cultured in normal medium; B: cells cultured innormal medium and insonified with LIPUS; C: cells cultured in high glucosemedium; D: cells cultured in high glucose medium and insonified with LIPUS.Results obtained from groups B, C, and D all showed that the correspondinggrowth of osteoblasts tended to increase compared to that of cells from thecontrol group A. Specifically, the highest proliferation was found associatedwith osteoblasts of group D. The RT-PCR results revealed that mRNA levels of OPGcorresponding to experimental groups of B, C, and D were respectively to be1.29, 1.38, 1.62-fold more than that of control group; mRNA levels of ALP wererespectively to be 1.18, 1.17, 1.38-fold more than that of control group andmRNA levels of OCN were respectively to be 1.41, 0.73, 1.22-fold more than thatof control group. OCN mRNA expression was increased for those osteoblastsinsonified with LIPUS from groups B and D, and that tended to be decreased forcells cultured in high glucose from group C. In conclusion, LIPUS exposure wasfound to be able to increase cell viability and mRNA expression of osteoblasts.Even culture under a high glucose medium, the proliferation and gene expressionof osteoblasts could still be promoted by the insonification of LIPUS. Theseresults indicated that the LIPUS may have the ability to decrease the inhibitoryeffect of osteoblasts associated with high glucose level and to facilitateother cell functions.