Therapeutic ultrasound on bone cellular and in vivo adaptation

Objective: It is well documented that ultrasound, as a mechanical signal, can produce a wide variety of biological effects in vitro and in vivo. The purpose of the current study was to (1) develop a methodology to allow for in-vitro manipulating osteoblastic cells using acoustic radiation force generated by ultrasound, (2) use this methodology to determine the morphological and biological responses of bone cells to ultrasound, and (3) mitigate bone loss under estrogen deficient osteopenia. Methods: In Vitro Cellular Manipulation: We used a therapy focused transducer, which has spherical cap with 64 mm diameter and 62.64 mm focal length. A laser guide MC3T3-E1 osteoblastic cells were cultured in α-MEM containing 1% penicillin-streptomycin and 10% decomplemented newborn calf serum. In Vivo OVX Model: 72, 16 w.o. Sprague-Dawley rats were divided into six groups; baseline control, age-matched control, OVX control, OVX + 5 mW/cm2 ultrasound (US), OVX + 30 mW/cm2 US and OVX + 100 mW/cm2 US. Low intensity pulsed ultrasound (LIPUS) was delivered transdermally at the L4/L5 vertebrae, using gel-coupled plane wave US transducers. The signal was applied 20 min/day, 5 days/week for 4 weeks. Results: In Vitro Cellular Response: The developed methodology allowed manipulation of MC3T3-E1 cells by acoustic radiation force. The deformation of cell membranes was observed by the US manipulation, which appeared after 15s treatment of pulsed ultrasound in 6W. We also imaged the movement of primary cilia, which showed corresponding movement when subjected to pulsed ultrasound. In Vivo Response: LIPUS treatment significantly increased BVF compared to OVX controls for the 100mW/cm2 treated group. Interestingly, the 100mW/cm2 treated groups showed a significant improvement over the 5mW/cm2 treated group. Discussion and Conclusions: Pulsatile focused ultrasound can create local fluid flow nearby cells. The observed primary cilia can be triggered to dynamic movement by the acoustic force as a mechanobiologic effect. In vivo results suggest that low-intensity pulse ultrasound can induced mechanical wave in tissue and initiate bone adaptation. These findings support the hypothesis that LIPUS can inhibit bone loss and preserve bone strength under conditions of estrogen deficient osteopenia. Keywords: quantitative ultrasound, therapeutic ultrasound, bone mechanotransduction, osteoporosis, bone remodeling