In vitro method for the screening and monitoring of estrogen-deficiency osteoporosis by targeting peripheral circulating monocytes.

Bone loss occurs insidiously and initially asymptomatically; therefore, osteoporosis is frequently diagnosed only after the first clinical fracture. The aim of this study was to test the hypothesis is that by simply observing the behavior of cultured peripheral monocytes, it might be possible to diagnose altered bone remodeling and, therefore, limit the complications associated with osteoporosis, especially fractures. Monocytes isolated as mononuclear precursors from healthy and ovariectomized rats were cultured both in basal and differentiation medium for up to 3 weeks. Viability and differentiation capability towards the osteoclastic phenotype was checked by light microscopy at early times, whereas differentiation state and synthetic activity (tartrate-resistant acid phosphatase (TRAP) staining; phalloidin, fluorescin isothiocynate (FITC) staining, cathepsin K, metalloproteinase 7 and 9, MMP-7 and MMP-9) were measured at 1, 2, and 3 weeks. Compared to their controls, monocytes isolated from ovariectomized rats proliferate and lean toward the osteoclastic phenotype in the absence of differentiating factors. In both culture conditions, osteoclasts from ovariectomized rats showed significantly higher productions of cathepsin K, MMP-7, and MMP-9 than those of cells isolated from healthy rats, steadily over time. These results obtained in an animal osteoporotic model, if confirmed by clinical studies, open up the possibility to assess the presence of an alteration in bone remodeling with a simple in vitro diagnostic test requiring a small blood sample and less than 48 h. This might allow to early select patients with a spontaneous viability and differentiation of monocytes to osteoclasts for further diagnostic techniques.