High bone mass in mice can be linked to lower osteoclast formation, resorptive capacity, and restricted in vitro sensitivity to inhibition by stable sulforaphane.

Mouse strains can have divergent basal bone mass, yet this phenotype is seldom reflected in the design of studies seeking to identify new modulators of bone resorption by osteoclasts. Sulforaphane exerts inhibitory effects on in vitro osteoclastogenesis in cells from C57BL/6 mice. Here, we explore whether a divergent basal bone mass in different mouse strains is linked both to in vitro osteoclastogenic potential and to SFX-01 sensitivity. Accordingly, osteoclasts isolated from the bone marrow (BM) of C57BL/6, STR/Ort and CBA mice with low, high, and intermediate bone mass, respectively, were cultured under conditions to promote osteoclast differentiation and resorption; they were also treated with chemically stabilised sulforaphane (SFX-01) and respective sensitivity to inhibition evaluated by counting osteoclast number/resorption activity on dentine discs. We observed that osteoclastogenesis exhibited different macrophage colony-stimulating factor/receptor activator of nuclear factor kappa-Β ligand sensitivity in these mouse strains, with cells from C57BL/6 and CBA generating higher osteoclast numbers than STR/Ort; the latter formed only half as many mature osteoclasts. We found that 100 nM SFX-01 exerted a potent and significant reduction in osteoclast number and resorptive activity in cells derived from C57BL/6 mice. In contrast, 10-fold higher SFX-01 concentrations were required for similar inhibition in CBA-derived cells and, strikingly, a further 2.5-fold greater concentration was required for significant restriction of osteoclast formation/function in STR/Ort. These data are consistent with the notion that the BM osteoclast precursor population contributes to the relative differences in mouse bone mass and that mice with higher bone mass exhibit lower in vitro osteoclastogenic potential as well as reduced sensitivity to inhibition by SFX-01.