Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark, 7100, Vejle, Denmark.
Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of British Columbia, Vancouver, Canada.
Calcif Tissue Int. 2019 Jan;104(1):92-101. doi: 10.1007/s00223-018-0472-7. Epub 2018 Sep 7.
Cathepsin K (CatK) inhibition allows reducing bone resorption with specific advantages compared to the existing anti-osteoporosis drugs. Its clinical use appears even more promising with the recent development of ectosteric inhibitors. A confusing observation, however, is that a low dose of the active site CatK inhibitor odanacatib (ODN) was reported to decrease bone mineral density and increase serum levels of the bone resorption marker carboxy-terminal collagen crosslinks (CTX). The present study provides a possible explanation for this paradox. The resorptive activity of human osteoclasts seeded on bone slices was inhibited when subjected to ODN at doses of 20 nM, but about 100-fold lower doses induced a significant increase in CTX levels and in eroded surface (12 repeats). This low-dose-induced stimulation was prevented by inhibition of non-CatK cysteine proteinases, thereby indicating that the stimulation results from an interplay between CatK and other cysteine proteinases. Effective interplay between these proteinases was also shown in enzymatic assays where the CatK-mediated degradation of collagen was enhanced upon addition of cathepsins B or L. Furthermore, extracts of osteoclasts subjected to a low dose of ODN showed higher levels of cathepsin B compared with extracts of control osteoclasts. In conclusion, the low-dose-induced stimulation of resorption observed in the clinical study can be reproduced in osteoclasts cultured in the absence of any other cell. Our data support an osteoclast-intrinsic mechanism where a mild inhibition of CatK results in increased levels of other proteinases contributing to the collagen degradation process.
组织蛋白酶 K（CatK）抑制作用可减少骨吸收，与现有抗骨质疏松药物相比具有特定优势。最近外源性抑制剂的发展使 CatK 的临床应用更具前景。然而，一个令人困惑的观察结果是，活性位点 CatK 抑制剂odanacatib（ODN）的低剂量被报道会降低骨密度并增加骨吸收标志物羧基末端胶原交联（CTX）的血清水平。本研究为这一矛盾现象提供了可能的解释。当将 ODN 施用于骨切片上的人类破骨细胞时，其吸收活性在 20 nM 的剂量下被抑制，但约 100 倍低剂量会导致 CTX 水平和侵蚀表面显著增加（12 次重复）。这种低剂量诱导的刺激可通过抑制非 CatK 半胱氨酸蛋白酶来预防，从而表明刺激是由 CatK 和其他半胱氨酸蛋白酶之间的相互作用引起的。在酶促测定中也显示了这些蛋白酶之间的有效相互作用，其中 CatK 介导的胶原降解在添加组织蛋白酶 B 或 L 时得到增强。此外，与对照破骨细胞的提取物相比，经低剂量 ODN 处理的破骨细胞提取物显示出更高水平的组织蛋白酶 B。总之，在临床研究中观察到的低剂量诱导的吸收刺激可以在没有任何其他细胞的情况下培养的破骨细胞中重现。我们的数据支持破骨细胞内在机制，其中 CatK 的轻度抑制导致参与胶原降解过程的其他蛋白酶水平增加。
