Association between circulating osteoprogenitor cell numbers and bone mineral density in postmenopausal osteoporosis.

Summary. The role of circulating osteoprogenitor cells in postmenopausal osteoporosis is unknown. We found that alkaline-phosphatase-positive (AP+) cells are the lacking cells in osteoporosis, whose reduction is related to bone loss. Conversely, the increased number of alkaline phosphatase/CD34-positive cells may reflect the reactive bone marrow contribution to bone formation. Introduction. Circulating osteoprogenitor cells mineralize in vitro and in vivo. Loss of osteogenic cells may account for bone loss in osteoporosis. We studied whether there is an association between the number of circulating osteoprogenitor cells and bone mineral density (BMD) in postmenopausal women with and without osteoporosis. Methods. The number of circulating AP+, osteocalcinpositive (OCN+), AP+/CD34+, and OCN+/CD34+ cells was quantified in 54 postmenopausal osteoporotic women and 36 age-matched nonosteoporotic controls. Results. The number of AP+ cells was lower in osteoporotic women than in controls (127±16 vs 234±23 per microliter; p<0.001); higher levels of AP+/CD34+, OCN+, and OCN+/ CD34+ cells were found in osteoporotic than controls (p<0.01 for all). The number of AP+ cells was correlated with lumbar BMD (rho=0.29; p=0.008) and proximal femur BMD (rho=0.31; p=0.005) whereas inverse correlations were found between AP+/CD34+ cells, OCN+, OCN+/ CD34+, and BMD. Reduced AP+ cells and increased AP+/CD34+, OCN+, and OCN+/CD34+ cells were predictors of low BMD, independent of traditional risk factors for osteoporosis. Conclusion. In postmenopausal osteoporotic women, a reduced number of circulating AP+ cells and increased levels of AP+/CD34+, OCN+, and OCN+/CD34+ cells are associated with reduced bone mineral density, the interpretation of such a cellular imbalance needing exploration.