Osteoporosis-Improving Effects of Extracellular Vesicles from Human Amniotic Membrane Stem Cells in Ovariectomized Rats

Osteoporosis is a common skeletal disease characterized by decreased bone density, leading to bone fragility and fractures, especially in menopausal women. The purpose of this study is to confirm the anti-osteoporosis activity of stem cell extracellular vesicles (EVs) as a material of regenerative medicine. Mesenchymal stem cells have a potential to differentiate into osteocytes, so directly reconstruct bone tissue or facilitate bone regeneration via paracrine effects. Paracrine effects are mediated by functional molecules delivered in EVs released from stem cells. EVs containing high concentrations of growth factors (GFs) and neurotrophic factors (NFs) were attained via hypoxia culture of human amniotic membrane stem cells (AMSCs). From the EVs with a mean diameter of 77 nm, 751 proteins and 15 species of lipids were identified. Sprague-Dawley rats were ovariectomized, and eight weeks later, intravenously injected with EVs at doses of 1 × 108, 3 × 108 or 1 × 109 particles/100 μL/body, weekly for eight weeks. One week after the final administration, the serum and bone parameters related to bone density were analyzed. Serum 17β-estradiol, alkaline phosphatase, and calcium levels that decreased in ovariectomized rats were restored by EVs in a dose-dependent manner. Bone parameters such as bone mineral density, bone mineral content, bone volume/tissue volume ratio, trabecular number, trabecular space, and bending strength were also improved by treatment with EVs. Such effects were confirmed by morphological findings of micro-computed tomography. Taken together, it is suggested that AMSC-EVs containing high concentrations of GFs and NFs preserve bone soundness by promoting bone regeneration and inhibiting bone resorption.