Clodronate stimulates osteoblast differentiation in ST2 and MC3T3-E1 cells and rat organ cultures.

We investigated the direct effects of various bisphosphonates on osteoblasts. At 10(-5) M, clodronate increased alkaline phosphatase activity in cultured MC3T3-E1 (osteoblast-like line) and ST2 (pluripotent mesenchymal line) cells. Etidronate significantly increased alkaline phosphatase activity at 10(-5) M only in MC3T3-E1 cells. These effects were due to an increase in alkaline phosphatase-positive cell numbers, and the differentiation-enhanced cells were capable of mineralization (von Kossa stain). Other bisphosphonates (pamidronate, alendronate, and incadronate) did not increase alkaline phosphatase activity in either cell line. In cultured rat calvariae, clodronate stimulated the expression of genes for alkaline phosphatase and osteocalcin (osteoblast-differentiation markers), but decreased the expression of the gene for tartrate-resistant acid phosphatase (osteoclast marker). Clodronate, etidronate, and incadronate inhibited protein Tyr phosphatase and Ser/Thr phosphatase activities in MC3T3-E1 cells. These data suggest that clodronate acts directly on mesenchymal cells to enhance osteoblast differentiation, and this effect may be partly expressed through inhibition of protein Tyr phosphatase and/or Ser/Thr phosphatase activity.

Reductions in bone mass, structure, and strength in axial and appendicular skeletons associated with increased turnover after ovariectomy in mature cynomolgus monkeys and preventive effects of clodronate.

Over 16 months, we evaluated the effects of ovariectomy (OVX) and bisphosphonate clodronate (CLO) on bone in 48 cynomolgus monkeys (9-15 years old) fed a normal calcium diet. We established three OVX groups (oral CLO at 0 [OVX control], 12, or 60 mg/kg per day) and one sham-operated (SHAM) group. At 16 months, the bone mineral density (BMD) values (percentage of group baseline; OVX control vs. SHAM) for lumbar bone (L3-L5), proximal femur, midfemur, radius, and tibia were -2.6% versus 11.2%, -3.5% versus 8.9%, -3.0% versus 9.0%, -5.5% versus 15.7%, and -6.7% versus 13.9%, respectively. In OVX control (i) tibia showed significant loss of bone mineral content (BMC; vs. baseline), (ii) urinary deoxypyridinoline (DPD) and serum osteocalcin (OC) levels increased (peak = 182% and 168%, respectively, of SHAM), (iii) in lumbar bone and midfemur, ultimate load (UL) was reduced (vs. SHAM), (iv) in lumbar bone, trabecular bone-formation rates (BFRs) were not changed significantly, but tibial endocortical and intracortical bone formation rates were significantly raised (vs. SHAM), (v) the volumetric BMD (vBMD) and geometry of the tibial cortex (measured by peripheral quantitative computed tomography [pQCT]) were significantly reduced (vs. SHAM). CLO, 60 mg/kg per day but not 12 mg/kg per day, significantly inhibited OVX-induced changes, age-dependent increases in bone mass, and ability to maintain structure. Thus, in OVX mature cynomolgus monkeys (possibly, a unique model of the cortical bone loss secondary to estrogen deficiency), the post-OVX increases in systemic bone markers were slight, but stimulation of local turnover in the cortical envelope was enough to cause bone loss (more so in tibia than in lumbar trabecular bone). High-dose CLO prevented these changes.