Matsumoto Takumi, Nagase Yuichi, Iwasawa Mitsuyasu, Yasui Tetsuro, Masuda Hironari, Kadono Yuho, Nakamura Kozo, Tanaka Sakae
University of Tokyo, Bunkyo-ku, Tokyo, Japan.
Arthritis Rheum. 2011 Dec;63(12):3908-17. doi: 10.1002/art.30646.
Nitrogen-containing bisphosphonates are one of the most successful therapeutics for osteoporosis. The aim of this study was to elucidate the functional mechanism of one of the typical nitrogen-containing bisphosphonates, risedronate.
Osteoclasts generated from murine bone marrow macrophages were treated with risedronate in vitro, and its effects on apoptosis and bone-resorbing activity were examined. The mechanism of action of risedronate was examined by gene induction of constitutively active Akt-1 and constitutively active MEK-1, and by gene deletion of Bim. Bim(-/-) mice, in which osteoclasts were resistant to apoptosis, were treated with risedronate and analyzed radiographically, biochemically, and histologically.
Risedronate induced osteoclast apoptosis through the mitochondria-dependent pathway with an increased expression of Bim, and the proapoptotic effect of risedronate was suppressed by Bim deletion and constitutively active MEK-1 introduction. In contrast, the risedronate-induced suppression of bone resorption was completely reversed by inducing constitutively active Akt-1, but not by Bim deletion or constitutively active MEK-1 introduction. These results suggested that apoptosis and bone-resorbing activity of osteoclasts were regulated through the ERK/Bim axis and the Akt pathway, respectively, both of which were suppressed by risedronate. Although osteoclast apoptosis in response to risedronate administration was suppressed in the Bim(-/-) mice, risedronate treatment increased bone mineral density in Bim(-/-) mice at a level equivalent to that in wild-type mice.
Our findings indicate that the antiresorptive effect of risedronate in vivo is mainly mediated by the suppression of the bone-resorbing activity of osteoclasts and not by the induction of osteoclast apoptosis.
含氮双膦酸盐是治疗骨质疏松症最成功的药物之一。本研究的目的是阐明一种典型的含氮双膦酸盐利塞膦酸盐的作用机制。
用利塞膦酸盐体外处理从小鼠骨髓巨噬细胞生成的破骨细胞，并检测其对细胞凋亡和骨吸收活性的影响。通过组成型活性Akt-1和组成型活性MEK-1的基因诱导以及Bim的基因缺失来研究利塞膦酸盐的作用机制。对破骨细胞抗凋亡的Bim(-/-)小鼠给予利塞膦酸盐治疗，并进行影像学、生化和组织学分析。
利塞膦酸盐通过线粒体依赖性途径诱导破骨细胞凋亡，同时Bim表达增加，Bim缺失和组成型活性MEK-1的导入可抑制利塞膦酸盐的促凋亡作用。相反，组成型活性Akt-1的诱导可完全逆转利塞膦酸盐诱导的骨吸收抑制作用，而Bim缺失或组成型活性MEK-1的导入则不能。这些结果表明，破骨细胞的凋亡和骨吸收活性分别通过ERK/Bim轴和Akt途径调节，而这两条途径均被利塞膦酸盐抑制。虽然在Bim(-/-)小鼠中，利塞膦酸盐给药引起的破骨细胞凋亡受到抑制，但利塞膦酸盐治疗使Bim(-/-)小鼠的骨密度增加，其水平与野生型小鼠相当。
我们的研究结果表明，利塞膦酸盐在体内的抗吸收作用主要是通过抑制破骨细胞的骨吸收活性介导的，而不是通过诱导破骨细胞凋亡。
