MITOGENIC ACTION OF HYDROCHLOROTHIAZIDE ON HUMAN OSTEOBLASTS IN-VITRO- REQUIREMENT FOR PLATELET-DERIVED GROWTH-FACTOR

Long-term use of hydrochlorothiazide (HCTZ), a common diuretic agent f or hypertension, has been associated with increased bone density and r educed hip fracture rates in patients. In this study, we sought to exa mine whether HCTZ has an anabolic effect on the proliferation of human osteoblasts (derived from either vertebrate or rib bone samples) in v itro. Cell proliferation was determined by [H-3]thymidine incorporatio n and cell number counting. In medium supplemented with 1% bovine calf serum, HCTZ significantly and reproducibly increased [H-3]thymidine i ncorporation and cell number. The stimulatory effect was dose dependen t in a biphasic manner, with the maximal stimulation (approximately 60 % above control, P < 0.001) seen at 1 mu M HCTZ. In fresh serum-free m edium, HCTZ was ineffective as a bone cell mitogen, indicating that th e bone cell mitogenic activity of HCTZ required a serum growth factor (GF). HCTZ at doses greater than 10 mu M was inhibitory in the presenc e or the absence of serum, presumably because of the cytotoxic effects . The serum requirement for the bone cell mitogenic activity of HCTZ c ould be replaced with a conditioned medium (conditioned with normal hu man osteoblasts for 24 hours), or with a mitogenic dose (1 ng/ml) of P DGF. The GF requirement was specific for PDGF, because other bone cell -derived growth factors (i.e., TGF beta, IGF-I, IGF-II, and bFGF) were unable to replace serum for the bone cell mitogenic activity of HCTZ. In summary, this study shows that (1) HCTZ stimulated the proliferati on of normal, untransformed, human osteoblasts in vitro; (2) the bone cell mitogenic effect of HCTZ required the presence of a serum GF; (3) the serum requirement could be replaced with a bone cell GF in condit ioned medium; (4) the GF requirement was specific for PDGF. In conclus ion, we have demonstrated for the first time that HCTZ has a direct an abolic effect on human osteoblasts in vitro, and that the mitogenic ac tivity is dependent on the presence of PDGF. Because increased bone ce ll proliferation is a key determinant of bone formation, these observa tions raise the interesting possibility that HCTZ could act directly o n bone cells to stimulate bone formation in patients.