Original Full Length Article Temporal changes in systemic and local expression of bone turnover markers during six months of sclerostin antibody administration to ovariectomized rats ☆ , ☆☆ Marina Stolina 1 , Denise Dwyer 1 , Qing-Tian Niu 1 , Kelly S. Villasenor 1 , Pam Kurimoto 1 , Mario Grisanti 1 , Chun-Ya Han 1 , Min Liu 1 , Xiaodong Li 1 , Michael S. Ominsky 1 , Hua Z. Ke 1 , Paul J. Kostenuik ⁎ Department of Metabolic Disorders, Amgen Inc., Thousand Oaks, CA, USA abstract article info Article history: Received 29 January 2014 Revised 19 June 2014 Accepted 25 July 2014 Available online 2 August 2014 Edited by: Nuria Guanabens Keywords: Sclerostin Bone formation DKK-1 Osteoporosis Bone turnover markers Bone resorption Sclerostin (Scl) is an osteocyte protein that decreases bone formation, and its inhibition by neutralizing antibodies (Scl-Ab) increases bone formation, mass and strength. We investigated the effects of Scl-Ab in mature ovariecto- mized (OVX) rats with a mechanistic focus on longer-term responses of osteoclasts, osteoblasts and osteocytes. Four-month-old Sprague–Dawley rats had OVX or sham surgery. Two months later, sham controls received sc vehicle while OVX rats received vehicle (OVX-Veh) or Scl-Ab (25 mg/kg) once weekly for 6 or 26 weeks followed by necropsy (n = 12/group). Terminal blood was collected for biochemistry, non-adherent marrow cells were har- vested from femurs for ex vivo osteoclast formation assays, and vertebrae and tibiae were collected for dynamic histomorphometry and mRNA analyses. Scl-Ab treatment led to progressively thicker but fewer trabeculae in the vertebra, leading to increased trabecular bone volume and reduced trabecular surfaces. Scl-Ab also increased corti- cal bone volume in the tibia, via early periosteal expansion and progressive endocortical contraction. Scl-Ab signif- icantly reduced parameters of bone resorption at week 6 relative to OVX-Veh controls, including reduced serum TRACP-5b, reduced capacity of marrow cells to form osteoclasts ex vivo, and N 80% reductions in vertebral trabecular and tibial endocortical eroded surfaces. At week 26, serum TRACP-5b and ex vivo osteoclast formation were no longer reduced in the Scl-Ab group, but eroded surfaces remained N 80% lower than in OVX-Veh controls without evidence for altered skeletal mRNA expression of opg or rankl. Scl-Ab significantly increased parameters of bone for- mation at week 6 relative to OVX-Veh controls, including increases in serum P1NP and osteocalcin, and increased trabecular, endocortical and periosteal bone formation rates (BFRs). At week 26, surface-referent trabecular BFR remained significantly increased in the Scl-Ab group versus OVX-Veh controls, but after adjusting for a reduced extent of trabecular surfaces, overall (referent-independent) trabecular BFR was no longer significantly elevated. Similarly, serum P1NP and osteocalcin were no longer significantly increased in the Scl-Ab group at week 26. Tibial endocortical and periosteal BFR were increased at week 6 in the Scl-Ab group versus OVX-Veh controls, while at week 26 only endocortical BFR remained increased. The Scl-Ab group exhibited significant increments in skeletal mRNA expression of several osteocyte genes, with sost showing the greatest induction in both the tibia and vertebra. We propose that Scl-Ab administration, and/or the gains in bone volume that result, may have increased osteocytic expression of Scl as a possible means of regulating gains in bone mass. © 2014 Elsevier Inc. All rights reserved. Introduction Sclerostin (Scl) is an endogenous inhibitor of osteoblasts that reduces bone formation and accrual of bone mass [1–3]. Therapeutic an- tibodies that inhibit Scl (Scl-Ab) can thus increase bone formation, and a variety of preclinical studies show that this effect leads to increased bone volume and bone strength (reviewed in [4]). Scl-Ab administration can also reduce bone resorption parameters, which may also contribute to improved bone mass and strength in animals [5,6]. Clinical studies in postmenopausal women showed that a single injection of Scl-Ab led to dose-dependent increases in bone formation markers, an acute reduction in the resorption marker serum CTx, Bone 67 (2014) 305–313 ☆ Funding source: This study was funded by Amgen Inc. and UCB Pharma. ☆☆ Parts of the manuscript were presented at the 34th Annual Meeting of the American Society for Bone and Mineral Research in Minneapolis, Minnesota, October 12–15, 2012. ⁎ Corresponding author at: One Amgen Center Drive, M/S 15-2-A, Thousand Oaks, CA 91320, USA. E-mail addresses: mstolina@amgen.com (M. Stolina), ddwyer@amgen.com (D. Dwyer), qniu@amgen.com (Q.-T. Niu), kwarming@amgen.com (K.S. Villasenor), kurimoto@amgen.com (P. Kurimoto), grisanti@amgen.com (M. Grisanti), ehan@amgen.com (C.-Y. Han), minl@amgen.com (M. Liu), xli@amgen.com (X. Li), mominsky@amgen.com (M.S. Ominsky), hke@amgen.com (H.Z. Ke), paulk@amgen.com (P.J. Kostenuik). 1 One Amgen Center Drive, M/S 15-2-A, Thousand Oaks, CA 91320, USA. http://dx.doi.org/10.1016/j.bone.2014.07.031 8756-3282/© 2014 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Bone journal homepage: www.elsevier.com/locate/bone