Tiludronate inhibits prostaglandin F2α-induced vascular endothelial growth factor synthesis in osteoblasts

We have previously reported that prostaglandin F2α (PGF2α) activates p44/p42 mitogen-activated protein (MAP) kinase through protein kinase C (PKC), resulting in the synthesis of vascular endothelial growth factor (VEGF) in osteoblast-like MC3T3-E1 cells, and that incadronate, a bisphosphonate, amplifies the VEGF synthesis. In the present study, we investigated the effects of tiludronate and etidronate, other bisphosphonates, on the PGF2α-stimulated VEGF synthesis in these cells. Tiludronate reduced the synthesis of VEGF induced by PGF2α. The PGF2α-stimulated phosphorylation of p44/p42 MAP kinase was suppressed by tiludronate. On the other hand, etidronate affected neither the VEGF synthesis nor the phosphorylation of p44/p42 MAP kinase elicited by PGF2α. Tiludronate attenuated the phosphorylation of both Raf-1 and MEK1/2 induced by PGF2α. The VEGF synthesis stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA), a direct activator of PKC, was suppressed by tiludronate. The TPA-induced phosphorylations of Raf-1, MEK1/2 and p44/p42 MAP kinase were inhibited by tiludronate. These results strongly suggest that tiludronate but not etidronate suppresses the PGF2α-stimulated VEGF synthesis in osteoblasts, and that the effect of tiludronate is exerted at the point between PKC and Raf-1.