Previous studies have indicated that low intensity ultrasounds could accelerate the repair of fibula fracture and facilitate the proliferation of osteoblasts. To further investigate the effect of low intensity ultrasounds, two different frequency of ultrasound, 1 MHz and 3 MHz, were applied to osteoblasts. The cells were stimulated for a typical 20% duty cycle of ultrasound with various intensities ranged from 50 to 150 mW/cm2 (ISATA) for 3 minutes once daily for 6 days. The cellular responses, in terms of cell number and morphological change, associated with ultrasound stimulations were estimated using a hemocytometer and microscopic morphology in which cells were stained with trypan blue. Results showed that the proliferation rates of osteoblasts for particular stimulated group are larger than those of control groups. The largest proliferation rate corresponds to those cells culture at 24 hours after seeding. Ultrasound increased approximately the cell proliferation proportional to ultrasonic intensity at which the exposure of 100 mW/cm2 intensity of 1 MHz ultrasound 1.1 fold, and 50 mW/cm2 intensity of 3 MHz ultrasound 1.2 fold than that of the control group. These finding suggest that the growth of cell may be controlled by appropriate ultrasonic mechanical stress.
Previous studies have shown that Amyloid-beta (A beta) may induce the apoptosis of neuronal cells leading to the syndrome of Alzheimer's disease (AD). The stimulation by optical energy was found able to greatly inhibit A beta induced apoptosis. This study aims to further explore the effect of different doses of ultrasonic insonification on neuronal cells. Experiments were carried out using PC12 cells added with A beta 25-35 of a 20 microM during pre-cultured preparation. These cells were respectively stimulated by a single and multiple insonification for three minutes with a 20% duty cycle ultrasound of the intensity of 150 mW/cm2 (SATA). The cellular response was assessed, using the microscopic morphology, cell death measured by the typical MTT assay, and annexin V/PI double stain assay, for 8 times within 72 hours after that cells were stimulated. Results showed that both stimulations by single and multiple does ultrasound may diminish A beta induced neuronal cells apoptosis. The diminish effects tend to be time dependent corresponding to 72 and 12 hours after ultrasound exposure by single and multiple insonification, respectively. Fluorescence stain results indicated that those cells stimulated by a single dose ultrasound tended to slightly inhibit A beta-induced PC12 to apoptosis. This study demonstrated that the effect of diminishing neuronal cells from apoptosis could be regulated with the insonation of appropriate ultrasonic doses.
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