Biological actions of nitrogen-containing bisphosphonates on bone remodeling using an ex-vivo live calvarial bone organ model system
Liu, Jess Li-Je
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Bisphosphonates (BP) are a class of drugs that are stable analogues of inorganic pyrophosphate which are capable of inhibiting bone resorption and decreasing bone remodeling through the reduction of osteoclastic cell number and activity. Clinical used Alendronate (ALN) and Pamidronate (PAM) are two nitrogen-containing bisphosphonate (NBP) analogues that are widely used in the treatment of osteoporosis, Paget's disease, and other metabolic bone diseases. Studies have proposed the mechanism by which NBP inhibits osteoclastic activity through inhibition of post-translational prenylation of GTP-binding protein in the mevalonate pathway. Such inhibition has shown to cause alteration of osteoclast (OC) cell morphology, replication, and intracellular signal transduction that ultimately triggers cell apoptosis. Due to its therapeutic effect in inhibiting bone resorption, the effect of BP on OC have been studied extensively and well understood, nevertheless little attention has been placed on the effect of NBP on osteoblast (OB). Up till now, several in vitro studies have shown NBP at concentrations of 10 [superscript] -5 M and greater inhibits both OC and OB differentiation, proliferation, and promotes apoptosis. In addition to this, other in vitro studies have suggested BP exhibits a biphasic effect on OB, whereby concentration of 10 [superscript] -5 M and greater inhibits OB, While lower concentration ranging from 10 [superscipt] -9 - 10 [superscipt] -6 M demonstrates an anti-apoptotic effect on OB. Most of the woks carried out using BPs were either in vivo or in isolated cell cultures of OCs or OBs. While in vivo studies can reveal some of the biological actions of BPs, such as inhibiting bone resorption, it does not easily evaluate the effects on OBs and new bone formation or the effects on OC differentiation. In addition isolated cell cultures of OCs or OBs also have certain limitations. For these reasons, as well as to clarify some of the conflicting results and uncertainties, we have utilized an ex vivo live calvaria bone organ culture system, which has multicellular responses to added factors and closely mimic in vivo bone microenviroment. This system permits studies to be performed with the dissociation of bone resorption and bone formation process that are involved in overall bone remodeling. Hence, separate effects of NBP on OC and OB can be monitored carefully. In the parathyroid hormone-induced bone resorption model, 30 [mega]M ALN and 30 [mega]M PAM demonstrated inhibition of both OC formation and bone resorption. In the ascorbate-induced bone formation model, 50 nM ALN and 50 nM PAM exhibited OB cell proliferation while no significant bone formation was observed as compared to the control. Both concentration at 3 [mega]M and 100[mega] M of ALN and PAM did not have any significant effect on calcium uptake. However, 100 [mega]M ALN and 100[mega]M PAM showed a decrease in Tartrate-resistant acid phosphatase enzyme activity, a marker for osteoclast activity, demonstrating an inhibitory effect of OC. Our results are in agreement with various studies indicating ALN and PAM exert an inhibitory effect on OC and OB formation at concentration higher than 10 [superscript] -6 M. In addition our results support the purposed "biphasic effect" of NBP on OB.
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact firstname.lastname@example.org.Thesis (MSD) --Boston University, Goldman School of Dental Medicine, 2013 (Department of Periodontology and Oral Biology).Includes bibliography: leaves 102-109.
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