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Background: Recent studies have shown that ovariectomy-induced osteoporosis in rats can be reversed by infusion of osteoblasts cultured from mesenchymal stem cells (MSCs). This study compares the influence of MSCs, osteoblasts, and exosomes derived from osteoblasts for the treatment of osteoporosis. Methods: Osteoporosis was induced in 40 female Sprague Dawley rats by performing ovariectomy. After 12 weeks, bone marrow was harvested and MSCs separated from bone-marrow aspirate as described by Piao et al. After 15 days, autologous osteogenically differentiated cells from the MSCs were available. Exosomes were isolated from osteoblasts by modification of the technique described by Ge et al. MSCs and osteoblasts (10 6 cells in 0.5 mL normal saline) and exosomes (100 µg protein) were injected into the tail veins of the animals. Animals were euthanized after 12 weeks and femurs and lumbar spines dissected and analyzed using high-resolution peripheral quantitative computed tomography. Results: When compared to the control group, osteoblast-treated animals showed significant differences in all parameters compared, with P -values ranging between <0.002 and <0.0001. Comparison among osteoblasts, MSCs, and exosomes, showed that osteoblasts had positive and statistically significant new-bone formation. The comparison for the spine was similar to the distal femur for osteoblasts. Conclusion: This study showed robust positive bone-forming changes after osteoblast injection in the distal femur and the spine when compared to controls, MSCs, and exosomes.

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