Indapamide, a thiazide-like diuretic, decreases bone resorption in vitro

We recently showed that indapamide (IDP), a thiazide-related diuretic, incr eases bone mass and decreases bone resorption in spontaneously hypertensive rats supplemented with sodium. In the present study, we evaluated the in v itro effects of this diuretic on bone cells, as well as those of hydrochlor othiazide (HCTZ), the reference thiazide, and acetazolamide (AZ), a carboni c anhydrase (CA) inhibitor. We showed that 10(-4) M IDP and 10(-4) M AZ, as well as 10(-5) M pamidronate (APD), decreased bone resorption in organ cul tures and in cocultures of osteoblast-like cells and bone marrow cells in t he presence of 10(-8) M 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3]. We inve stigated the mechanism of this antiresorptive effect of IDP; IDP decreased osteoclast differentiation as the number of osteoclasts developing in cocul ture of marrow and osteoblast-like cells was decreased markedly. We then in vestigated whether IDP affected osteoblast-like cells because these cells a re involved in the osteoclast differentiation. Indeed, IDP increased osteob last-like cell proliferation and alkaline phosphatase (ALP) expression. Nev ertheless, it did not modify the colony-stimulating factor 1 (CSF-1) produc tion by these cells. In addition, osteoblast-like cells expressed the Na+/C l- cotransporter that is necessary for the renal action of thiazide diureti cs, but IDP inhibited bone resorption in mice lacking this cotransporter, s o the inhibition of bone resorption and osteoclast differentiation did not involve this pathway. Thus, we hypothesized that IDP may act directly on ce lls of the osteoclast lineage. We observed that resorption pits produced by spleen cells cultured in the presence of soluble osteoclast differentiatio n factor (sODF) and CSF-1 were decreased by 10(-4) M IDP as well as 10(-5) M APD. In conclusion, in vitro IDP increased osteoblast proliferation and d ecreased bone resorption at least in part by decreasing osteoclast differen tiation via a direct effect on hematopoietic precursors.