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      Local application of an ibandronate/collagen sponge improves femoral fracture healing in ovariectomized rats

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          Abstract

          Non-union is a major clinical problem in the healing of fractures, especially in patients with osteoporosis. The systemic administration of drugs is time consuming and large doses are demanding and act slowly, whereas local release acts rapidly, increases the quality and quantity of the bone tissue. We hypothesize that local delivery demonstrates better therapeutic effects on an osteoporotic fracture. The aim of this paper is to investigate the effect of the local application of ibandronate loaded with a collagen sponge on regulating bone formation and remodeling in an osteoporotic rat model of fracture healing. We found that the local delivery of ibandronate exhibited excellent effects on improving the bone microarchitecture and suppressed effects on bone remodeling. At 4 weeks, more callus formation and improvement of mechanical character and microstructure were observed in a local delivery via μCT, mechanical test, histological research and serum analysis. The suppression of bone remodeling was compared with a systemic treatment at 12 weeks, and the structural mechanical properties and microarchitecture were also improved with local delivery. This research identifies an earlier, safer and integrated approach for local delivery of ibandronate with collagen and provides a better strategy for the treatment of osteoporotic fracture in rats.

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          Cellular mechanisms of bone remodeling

          Bone remodeling is a tightly regulated process securing repair of microdamage (targeted remodeling) and replacement of old bone with new bone through sequential osteoclastic resorption and osteoblastic bone formation. The rate of remodeling is regulated by a wide variety of calcitropic hormones (PTH, thyroid hormone, sex steroids etc.). In recent years we have come to appreciate that bone remodeling proceeds in a specialized vascular structure,—the Bone Remodeling Compartment (BRC). The outer lining of this compartment is made up of flattened cells, displaying all the characteristics of lining cells in bone including expression of OPG and RANKL. Reduced bone turnover leads to a decrease in the number of BRCs, while increased turnover causes an increase in the number of BRCs. The secretion of regulatory factors inside a confined space separated from the bone marrow would facilitate local regulation of the remodeling process without interference from growth factors secreted by blood cells in the marrow space. The BRC also creates an environment where cells inside the structure are exposed to denuded bone, which may enable direct cellular interactions with integrins and other matrix factors known to regulate osteoclast/osteoblast activity. However, the denuded bone surface inside the BRC also constitutes an ideal environment for the seeding of bone metastases, known to have high affinity for bone matrix. Circulating osteoclast- and osteoblast precursor cells have been demonstrated in peripheral blood. The dominant pathway regulating osteoclast recruitment is the RANKL/OPG system, while many different factors (RUNX, Osterix) are involved in osteoblast differentiation. Both pathways are modulated by calcitropic hormones.
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            Cellular and molecular mechanisms of action of bisphosphonates.

            Bisphosphonates currently are the most important class of antiresorptive agents used in the treatment of metabolic bone diseases, including tumor-associated osteolysis and hypercalcemia, Paget's disease, and osteoporosis. These compounds have high affinity for calcium and therefore target to bone mineral, where they appear to be internalized selectively by bone-resorbing osteoclasts and inhibit osteoclast function. This article reviews the pharmacology of bisphosphonates and the relation between the chemical structure of bisphosphonates and antiresorptive potency, and describes recent new discoveries of their molecular mechanisms of action in osteoclasts. Bisphosphonates can be grouped into two pharmacologic classes with distinct molecular mechanisms of action. Nitrogen-containing bisphosphonates (the most potent class) act by inhibiting the mevalonate pathway in osteoclasts, thereby preventing prenylation of small GTPase signaling proteins required for osteoclast function. Bisphosphonates that lack a nitrogen in the chemical structure do not inhibit protein prenylation and have a different mode of action that may involve the formation of cytotoxic metabolites in osteoclasts or inhibition of protein tyrosine phosphatases. Bisphosphonates are highly effective inhibitors of bone resorption that selectively affect osteoclasts. After more than 30 years of clinical use, their molecular mechanisms of action are only just becoming clear.
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              The molecular mechanism of nitrogen-containing bisphosphonates as antiosteoporosis drugs.

              Osteoporosis and low bone mass are currently estimated to be a major public health risk affecting >50% of the female population over the age of 50. Because of their bone-selective pharmacokinetics, nitrogen-containing bisphosphonates (N-BPs), currently used as clinical inhibitors of bone-resorption diseases, target osteoclast farnesyl pyrophosphate synthase (FPPS) and inhibit protein prenylation. FPPS, a key branchpoint of the mevalonate pathway, catalyzes the successive condensation of isopentenyl pyrophosphate with dimethylallyl pyrophosphate and geranyl pyrophosphate. To understand the molecular events involved in inhibition of FPPS by N-BPs, we used protein crystallography, enzyme kinetics, and isothermal titration calorimetry. We report here high-resolution x-ray structures of the human enzyme in complexes with risedronate and zoledronate, two of the leading N-BPs in clinical use. These agents bind to the dimethylallyl/geranyl pyrophosphate ligand pocket and induce a conformational change. The interactions of the N-BP cyclic nitrogen with Thr-201 and Lys-200 suggest that these inhibitors achieve potency by positioning their nitrogen in the proposed carbocation-binding site. Kinetic analyses reveal that inhibition is competitive with geranyl pyrophosphate and is of a slow, tight binding character, indicating that isomerization of an initial enzyme-inhibitor complex occurs with inhibitor binding. Isothermal titration calorimetry indicates that binding of N-BPs to the apoenzyme is entropy-driven, presumably through desolvation entropy effects. These experiments reveal the molecular binding characteristics of an important pharmacological target and provide a route for further optimization of these important drugs.
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                Author and article information

                Contributors
                Role: ConceptualizationRole: ResourcesRole: VisualizationRole: Writing – original draftRole: Writing – review & editing
                Role: Funding acquisition
                Role: Investigation
                Role: Methodology
                Role: MethodologyRole: Supervision
                Role: Formal analysisRole: Methodology
                Role: Visualization
                Role: Software
                Role: Data curation
                Role: InvestigationRole: Methodology
                Role: Resources
                Role: Data curation
                Role: ConceptualizationRole: Funding acquisitionRole: MethodologyRole: Project administrationRole: Validation
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                6 November 2017
                2017
                : 12
                : 11
                : e0187683
                Affiliations
                [1 ] Department of Orthopaedic Surgery, the Third Hospital of Hebei Medical University, Shijiazhuang, P. R., China
                [2 ] Key Laboratory of Orthopaedic Biomechanics of Hebei Province, Shijiazhuang, P. R., China
                [3 ] Orthopaedic Research Institution of Hebei Province, Hebei, P. R., China
                [4 ] VSD Medical Science & Technology Co., Ltd, Hubei, P. R., China
                Mayo Clinic Minnesota, UNITED STATES
                Author notes

                Competing Interests: We have the following interests: Author YL was employed by VSD Medical Science & Technology Co., Ltd, during the course of the study. There are no patents, products in development or marketed products to declare. This does not alter our adherence to all the PLOS ONE policies on sharing data and materials.

                Author information
                http://orcid.org/0000-0001-7400-5216
                Article
                PONE-D-17-19103
                10.1371/journal.pone.0187683
                5673204
                29108027
                2a98e07c-9965-4054-a232-4cb08e309e6f
                © 2017 Guo et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 19 May 2017
                : 24 October 2017
                Page count
                Figures: 7, Tables: 1, Pages: 22
                Funding
                Funded by: Hebei Provincial 333 Talent Projection Foundation of China
                Award ID: A2016015062
                Award Recipient :
                The authors acknowledge the support from Hebei Provincial 333 Talent Projection Foundation of China (No. A2016015062) (QZ). The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Author YL was employed by VSD Medical Science & Technology Co., Ltd, during the course of the study. The commercial company VSD Medical Science & Technology Co., Ltd had no direct relation with this experiment. The author from VSD is a senior fellow apprentice of the first author who focused on basal experiment in his doctor research, and he guided the procedure of ovariectomy before conducting this experiment. He has left the company now, and has a job in another company. The author did not play a role in the process of the experiment. VSD Medical Science & Technology Co., Ltd, provided support in the form of salary for author YL, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific role of this author is articulated in the ‘author contributions’ section.
                Categories
                Research Article
                Medicine and Health Sciences
                Critical Care and Emergency Medicine
                Trauma Medicine
                Traumatic Injury
                Bone Fracture
                Biology and Life Sciences
                Biochemistry
                Proteins
                Collagens
                Biology and Life Sciences
                Physiology
                Physiological Processes
                Bone Remodeling
                Medicine and Health Sciences
                Physiology
                Physiological Processes
                Bone Remodeling
                Medicine and Health Sciences
                Surgical and Invasive Medical Procedures
                Reproductive System Procedures
                Ovariectomy
                Medicine and Health Sciences
                Surgical and Invasive Medical Procedures
                Surgical Excision
                Ovariectomy
                Biology and Life Sciences
                Physiology
                Physiological Processes
                Tissue Repair
                Medicine and Health Sciences
                Physiology
                Physiological Processes
                Tissue Repair
                Medicine and Health Sciences
                Pharmaceutics
                Drug Delivery
                Biology and Life Sciences
                Anatomy
                Bone
                Bone Density
                Medicine and Health Sciences
                Anatomy
                Bone
                Bone Density
                Biology and Life Sciences
                Anatomy
                Biological Tissue
                Connective Tissue
                Bone
                Bone Density
                Medicine and Health Sciences
                Anatomy
                Biological Tissue
                Connective Tissue
                Bone
                Bone Density
                Biology and Life Sciences
                Developmental Biology
                Organism Development
                Organogenesis
                Bone Development
                Custom metadata
                All relevant data are within the paper and its Supporting Information files.

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