Microarchitecture and Nanomechanical Properties of

Authors: Zhaoyang Li Songlin Peng Haobo Pan Bin Tang Raymond W M Lam William W Lu

Publish Date: 2011/08/04

Volume: 145, Issue: 1, Pages: 39-46

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Abstract

Strontium Sr ralenate is a new agent used for the prevention and treatment of osteoporosis As a boneseeking element 98 of Sr is deposited in the bone and teeth after oral ingestion However the effect of Sr treatment on bone microarchitecture and bone nanomechanical properties remains unclear In this study 18 osteoporotic goats were divided into four groups according to the treatment regimen control calcium alone Ca calcium and Sr at 24 mg/kg Ca + 24Sr and calcium and Sr at 40 mg/kg Ca + 40Sr The effects of Sr administration on bone microarchitecture and nanomechanical properties of trabecular bones were analyzed with microCT and nanoindentation test respectively Serum Sr levels increased six and tenfold in the Ca + 24Sr and Ca + 40Sr groups respectively Similarly Sr in the bone increased four and sixfold in these two groups Sr administration significantly increased trabecular bone volume fraction trabecular thickness and doublelabeled new bone area Sr administration however did not significantly change the nanomechanical properties of trabecular bone elastic modulus and hardness The data suggested that Sr administration increased trabecular bone volume and improved the microarchitecture while maintaining the intrinsic tissue properties in the osteoporotic goat modelOsteoporosis is characterized by impaired bone quality which leads to decreased bone strength and increased susceptibility to fractures Strontium Srcontaining compounds have been reported to exert anabolic effects on the skeleton when orally administered to animals 1 2 and postmenopausal women 3 4 5 Treatment with these agents increases bone mineral content and density particularly at skeletal sites that are rich in trabecular bone such as the lumbar spine 2 3 6 7 In humans studies on the mechanical properties of bone responsible for the anabolic action of Sr is mainly achieved by evaluation of fracture risks 3 4 5 Human studies are limited by the difficulty in obtaining consistent specimens suitable for rigorous examination So far information on the microarchitecture and nanomechanical properties in response to Sr treatment in large osteoporosis animal models is lackingNanoindentation has been proven to be a powerful tool for the measurement of local mechanical properties and is a fairly mature technique for measurements in biological tissues of the intrinsic material mechanical properties This method circumvents common limitations that arise when applying largescale mechanical testing techniques to biological tissues 8 9 10 With the help of nanoindentation measurement of localized changes due to enhanced or inhibited bone mineralization and remodeling becomes feasible In recent years microcomputerized tomography μCT has been used to measure 3D bone structure of animals due to its relative ease in sample preparation its noninvasive nature and the high spatial resolution as compared with conventional histology 11 Studies have demonstrated that μCT analysis of change patterns in 3D bone parameters may serve as a valuable tool for the evaluation of both antiresorptive and anabolic agents in ovariectomized OVX animals 12Low dosage of Sr was employed in this study as Sr at high dosage may have deleterious effects on the bone 13 14 15 16 For instance Sr at high dosage may induce rickets a disease characterized by the softening of bone due simply to high levels of this element in soil together with the possible contributions from the lack of sunshine and Ca dietary deficiency 17 18 Since the main target populations for Sr treatment are postmenopausal osteoporotic women who are also susceptible to reduced renal function the risk for osteomalacia should be considered Ca and P supplements are added into the treatment regimen of Sr as the efficient absorption of these two elements plays an essential role in any increase in bone mass by forming osteoid and hydroxyapatite which compose the bulk of bones 19 20In a previous study we reported that Sr–Ca coadministration stimulated new bone formation as assessed by histomorphometry and molecular analysis of gene expressions 21 In this work we aimed to evaluate bone microarchitecture and nanomechanics at the lumbar spine of skeletally mature OVX goats after Sr–Ca coadministration for 16 weeks The trabecular microarchitectural parameters were quantified from μCT while the nanomechanical properties of single trabecula were determined by nanoindentation tests

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