Stem Cell Recruitment in Osteoporosis Therapy

Osteoporosis is an important health problem in the rapidly-aging demographic. Fragility fractures are devastating consequences of osteoporosis. The most common treatment approach in osteoporosis is inhibition of bone resorption with drugs like alendronate (ALN). Parathyroid hormone (PTH) stimulates bone formation and is the only anabolic drug available. Dual therapy with ALN and PTH is not as effective as single-drug therapy in preventing fracture. Bone progenitor cells (MSCs) are recruited to sites of bone remodeling when a growth factor called Transforming Growth Factor Beta (TGF-β1) is released from bone. Different osteoporosis medicines may have differing effects on this process. The effects of ALN versus PTH on bone progenitor recruitment in humans are unknown. This is a randomized, clinical trial of ALN, PTH, and calcium and vitamin D in post-menopausal women with low bone mass. Women will be treated for 3 months with ALN or PTH or calcium and vitamin D. Data collected will include bone biopsies for histomorphometry and micro computed tomography (µCT), bone marrow aspirates for molecular studies, peripheral blood to detect circulating bone progenitor cells and dual X-ray absorptiometry. The investigators hypothesize that in humans, PTH will 1) increase bone progenitor number, 2) enhance recruitment of bone progenitor cells to bone resorption sites, and 3) increase bone progenitor number in peripheral circulation. Furthermore, the investigators hypothesize that ALN treatment will have the opposite effect. Understanding the differences in bone progenitor cell activity and recruitment during osteoporosis therapy will provide a mechanistic rationale for effective use of PTH and anti-resorptive drugs in osteoporosis treatment.