Phosphodiesterases (PDEs) hydrolyze cyclic nucleotides and thereby regulate diverse cellular functions. The reports on the skeletal effects of PDE inhibitors are conflicting. Here, we screened 17 clinically used non-xanthine PDE inhibitors (selective and non-selective) using mouse calvarial osteoblasts (MCO) where the readout was osteoblast differentiation. From this screen, we identified sildenafil and vardenafil (both PDE5 inhibitors) having the least osteogenic EC50. Both drugs significantly increased vascular endothelial growth factor (VEGF) and VEGF receptor 2 (VEGFR2) expressions in MCO and the nitric oxide synthase inhibitor L-NAME completely blocked VEGF expression induced by these drugs. Sunitinib, a tyrosine receptor kinase inhibitor that also blocks VEGFR2 blocked sildenafil-/vardenafil-induced osteoblast differentiation. At half of their human equivalent doses, i.e. 6.0 mg/kg sildenafil and 2.5 mg/kg vardenafil, the maximum bone marrow level of sildenafil was 32% and vardenafil was 21% of their blood levels. At these doses, both drugs enhanced bone regeneration at the femur osteotomy site and completely restored bone mass, microarchitecture, and strength in OVX mice. Furthermore, both drugs increased surface referent bone formation and serum bone formation marker (P1NP) without affecting the resorption marker (CTX-1). Both drugs increased the expression of VEGF and VEGFR2 in bones and osteoblasts and increased skeletal vascularity. Sunitinib completely blocked the bone restorative and vascular effects of sildenafil and vardenafil in OVX mice. Taken together, our study suggested that sildenafil and vardenafil at half of their adult human doses completely reversed osteopenia in OVX mice by an osteogenic mechanism that was associated with enhanced skeletal vascularity.

中文翻译：

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磷酸二酯酶 5 抑制剂在骨质减少小鼠中的骨骼修复：药物的骨合成代谢和骨血管生成作用的证据

磷酸二酯酶 (PDE) 水解环状核苷酸，从而调节多种细胞功能。关于 PDE 抑制剂的骨骼效应的报道是相互矛盾的。在这里，我们使用小鼠颅骨成骨细胞 (MCO) 筛选了 17 种临床使用的非黄嘌呤 PDE 抑制剂（选择性和非选择性），其中读数为成骨细胞分化。从这个筛选中，我们确定了具有最少成骨 EC50 的西地那非和伐地那非（两种 PDE5 抑制剂）。这两种药物都显着增加了 MCO 中血管内皮生长因子 (VEGF) 和 VEGF 受体 2 (VEGFR2) 的表达，一氧化氮合酶抑制剂 L-NAME 完全阻断了这些药物诱导的 VEGF 表达。舒尼替尼是一种酪氨酸受体激酶抑制剂，也可阻断 VEGFR2 阻断西地那非/伐地那非诱导的成骨细胞分化。在其人体等效剂量的一半，即 6.0 mg/kg 西地那非和 2.5 mg/kg 伐地那非时，西地那非的最大骨髓水平为 32%，伐地那非为血液水平的 21%。在这些剂量下，两种药物都增强了股骨截骨部位的骨再生，并完全恢复了 OVX 小鼠的骨量、微结构和强度。此外，这两种药物都增加了表面参照骨形成和血清骨形成标志物 (P1NP)，而不影响再吸收标志物 (CTX-1)。这两种药物都增加了骨骼和成骨细胞中 VEGF 和 VEGFR2 的表达，并增加了骨骼血管。舒尼替尼完全阻断了西地那非和伐地那非对 OVX 小鼠的骨恢复和血管作用。综合起来，