Intervertebral disc degeneration, one of the major causes of
low-back pain, is known to result from alteration in biosynthesis of
proteoglycan in the disc. Therefore, upregulating the synthesis of
proteoglycan in intervertebral disc cells may be one approach in treating
disc degeneration. Based on the finding that low-intensity pulsed ultrasound stimulates
proteoglycan synthesis in rat chondrocytes, we investigated whether low-intensity pulsed ultrasound stimulates biological properties of rabbit intervertebral disc cells in vitro. Nucleus pulposus cells and annulus fibrosus cells isolated from rabbits were cultured in
alginate beads. Cells were stimulated for 20 min each day for 5-12 days, starting on the third day after seeding. An ultrasound signal consisting of a 200 micros burst sine wave of 0.5 MHz repeating at 1 kHz, with an intensity of 0, 7.5, 15, 30, 60, 120 mW/cm2 spatial and temporal average, was applied.
DNA and
proteoglycan synthesis were evaluated by measuring [3H]-
thymidine and [35S]-
sulfate incorporation.
DNA and
proteoglycan content in beads were measured by
Hoechst 33258 dye method and
dimethylmethylene blue assay. Results demonstrated positive effects on
DNA synthesis and content, following low-intensity pulsed ultrasound stimulation with intensities of 7.5 and 15 mW/cm2. Furthermore, ultrasound stimulation significantly upregulated [35S]-
sulfate incorporation and
proteoglycan content compared to the control group, following 5 days of stimulation in both nucleus pulposus and annulus fibrosus cells. These findings suggest the possible application of low-intensity pulsed ultrasound in biological repair of
intervertebral disc degeneration.