Sato Masahiro, Nakamichi Yuko, Nakamura Midori, Sato Nobuaki, Ninomiya Tadashi, Muto Akinori, Nakamura Hiroaki, Ozawa Hidehiro, Iwasaki Yukiko, Kobayashi Emi, Shimizu Masato, DeLuca Hector F, Takahashi Naoyuki, Udagawa Nobuyuki
Graduate School of Oral Medicine, Matsumoto Dental University, Nagano 399-0781, Japan.
Bone. 2007 Feb;40(2):293-304. doi: 10.1016/j.bone.2006.09.007. Epub 2006 Oct 25.
2-Methylene-19-nor-(20S)-1alpha,25-dihydroxyvitamin D3 (2MD), an analog of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3], has been shown to strongly induce bone formation both in vitro and in vivo. We have synthesized four substituents at carbon 2 of 2MD (2MD analogs), four stereoisomers at carbon 20 of the respective 2MD analogs (2MD analog-C20 isomers) and four 2MD analogs with an oxygen atom at carbon 22 (2MD-22-oxa analogs) and examined their ability to stimulate osteoclastogenesis and induce hypercalcemia. 2MD analogs were 100 times as potent as 1alpha,25(OH)2D3 in stimulating the formation of osteoclasts in vitro and in inducing the expression of receptor activator of NF-kappaB ligand (RANKL) and 25-hydroxyvitamin D3-24 hydroxylase mRNAs in osteoblasts. The osteoclast-inducing activities of 2MD analog-C20 isomers and 2MD 22-oxa analogs were much weaker than those of 2MD analogs. In addition, the activity of a 2MD analog in inducing dentine resorption was much stronger than that of 1alpha,25(OH)2D3 in the pit formation assay. Affinities to the vitamin D receptor and transcriptional activities of these compounds did not always correlate with their osteoclastogenic activities. Osteoprotegerin-deficient (OPG-/-) mice provide a suitable model for investigating in vivo effects of 2MD analogs because they exhibit extremely high concentrations of serum RANKL. The same amounts of 2MD analogs and 1alpha,25(OH)2D3 were administered daily to OPG-/- mice for 2 days. The elevation in serum concentrations of RANKL and calcium was much greater in 2MD analog-treated OPG-/- mice than in 1alpha,25(OH)2D3-treated ones. A 2MD analog was much more potent than 1alpha,25(OH)2D3 in causing hypercalcemia and in increasing soluble RANKL with enhanced osteoclastogenesis even in wild-type mice. In contrast, the administration of the 2MD analog to c-fos-deficient mice failed to induce osteoclastogenesis and hypercalcemia. These results suggest that new substituents at carbon 2 of 2MD strongly stimulate osteoclast formation in vitro and in vivo, and that osteoclastic bone resorption is indispensable for their hypercalcemic action of 2MD analogs in vivo.
2-亚甲基-19-去甲-（20S）-1α，25-二羟基维生素D3（2MD）是1α，25-二羟基维生素D3[1α，25（OH）2D3]的类似物，已显示在体外和体内均能强烈诱导骨形成。我们在2MD的C2位合成了四个取代基（2MD类似物），在各自2MD类似物的C20位合成了四个立体异构体（2MD类似物-C20异构体），以及在C22位带有氧原子的四个2MD类似物（2MD-22-氧杂类似物），并检测了它们刺激破骨细胞生成和诱导高钙血症的能力。2MD类似物在体外刺激破骨细胞形成以及诱导成骨细胞中核因子κB受体活化因子配体（RANKL）和25-羟基维生素D3-24羟化酶mRNA表达方面的效力是1α，25（OH）2D3的100倍。2MD类似物-C20异构体和2MD 22-氧杂类似物的破骨细胞诱导活性远低于2MD类似物。此外，在凹坑形成试验中，一种2MD类似物诱导牙本质吸收的活性比1α，25（OH）2D3强得多。这些化合物对维生素D受体的亲和力和转录活性并不总是与其破骨细胞生成活性相关。骨保护素缺陷（OPG-/-）小鼠为研究2MD类似物的体内作用提供了一个合适的模型，因为它们的血清RANKL浓度极高。将相同剂量的2MD类似物和1α，25（OH）2D3每日给予OPG-/-小鼠，持续2天。2MD类似物处理的OPG-/-小鼠血清中RANKL和钙浓度的升高比1α，25（OH）2D3处理的小鼠大得多。即使在野生型小鼠中，一种2MD类似物在引起高钙血症和增加可溶性RANKL以及增强破骨细胞生成方面也比1α，25（OH）2D3有效得多。相比之下，将2MD类似物给予c-fos缺陷小鼠未能诱导破骨细胞生成和高钙血症。这些结果表明，2MD的C2位新取代基在体外和体内均能强烈刺激破骨细胞形成，并且破骨细胞性骨吸收对于2MD类似物在体内的高钙血症作用是必不可少的。
