W.W. Lu

The cross-talk between osteoclasts and osteoblasts in response to strontium treatment: involvement of osteoprotegerin.

BACKGROUNDnThe mechanism for the uncoupling effects of Sr on bone remains to be evaluated. Osteoblasts play important roles in osteoclastogenesis through regulating receptor activated nuclear factor kappa B (RANK) ligand (RANKL) and osteoprotegerin (OPG) expression. We hypothesize that OPG plays an important role in the cross-talk between osteoclasts and osteoblasts in response to Sr treatment.nnnMATERIALS AND METHODSnMC3T3E1 cells were treated with Sr chloride (0-3 mM) and conditioned media were collected at 24h after the treatment. The effect of conditioned media on osteoclastogenesis was evaluated by tartrate-resistant acid phosphatase (TRAP) staining and bone resorption pits analysis. OPG and RANKL mRNA expressions in osteoblastic cells and protein secretion in the conditioned media were analyzed with real-time PCR and ELISA assay, respectively. The role of OPG in Sr-mediated inhibition of osteoclastogenesis was further evaluated with anti-OPG antibody in pre-osteoclastic cells. The role of OPG in Sr-mediated uncoupling effects on osteoporotic bone was evaluated by an animal study. Ovariectomized rats were oral administrated with vehicle or Sr chloride for two months supplemented with anti-IgG antibody (control) or anti-OPG antibody. The effects of OPG neutralization after Sr treatment on bone metabolism were analyzed by microCT, bone histomorphometry and biochemical analysis.nnnRESULTSnThe conditioned media derived from Sr-treated osteoblastic cells exerted a dose-dependent inhibitory effect on osteoclastic differentiation and resorptive activity in pre-osteoclastic cells. OPG mRNA expression and protein secretion in osteoblastic cells were significantly increased after Sr treatment. Neutralization with anti-OPG antibody abolished the inhibitory effect of conditioned media on RANKL-induced osteoclastogenesis. The uncoupling effects of Sr treatment on trabecular bone were evidenced by greater bone volume and trabecular number, greater osteoid surface and bone formation rate, while less osteoclast surface. These effects were attenuated by the OPG neutralization by anti-OPG antibody injection.nnnCONCLUSIONnThe evidences from the in vitro and in vivo studies suggested that OPG played an important role in the uncoupling effect of Sr on bone metabolism, possibly by acting as a cross-talk molecule between osteoclasts and osteoblasts in response to Sr treatment.

Osteoprotegerin deficiency attenuates strontium‐mediated inhibition of osteoclastogenesis and bone resorption

Strontium (Sr) exerts an anabolic and antiresorptive effect on bone, but the mechanism remains unknown. Osteoprotegerin (OPG) expressed by osteoblasts plays an important role in regulating bone homeostasis by inhibiting osteoclastogenesis and bone resorption. This study aims at evaluating the role of OPG in Sr‐mediated inhibition of osteoclastogenesis and bone resorption. Six‐week‐old Opg knockout (KO) male mice and their wild‐type (WT) littermates were treated orally with vehicle (Veh) or Sr compound (4u2009mmol/kg) daily for 8 weeks. Bone mass and microstructure in the lumbar spine (L4) and proximal tibia were analyzed with micro–computed tomography (µCT). Bone remodeling was evaluated with serum biochemical analysis and static and dynamic bone histomorphometry. Osteoclast differentiation potential and gene expression were analyzed in bone marrow cells. The findings demonstrate that Sr compound treatment results in greater bone volume and trabecular number than Veh treatment in WT mice. The anabolic response of trabecular bone to Sr treatment is attenuated in KO mice. Although Sr treatment significantly decreases in vitro osteoclastogenesis and bone resorption in WT mice, these effects are attenuated in KO mice. Furthermore, Sr treatment profoundly increases Opg gene expression in the tibias and OPG protein levels in the sera of WT mice. This study concludes that the inhibition of osteoclastogenesis and bone resorption is possibly associated with OPG upregulation by Sr treatment.

Extracellular matrix stability of primary mammalian chondrocytes and intervertebral disc cells cultured in alginate-based microbead hydrogels.

Three-dimensional alginate constructs are widely used as carrier systems for transplantable cells. In the present study, we evaluated the chondrogenic matrix stability of primary rat chondrocytes and intervertebral disc (IVD) cells cultured in three different alginate-based microbead matrices to determine the influence of microenvironment on the cellular and metabolic behaviors of chondrogenic cells confined in alginate microbeads. Cells entrapped in calcium, strontium, or barium ion gelled microbeads were monitored with the live/dead dual fluorescent cell viability assay kit and the 1,9-dimethylmethylene blue (DMB) assay designed to evaluate sulfated glycosaminoglycan (s-GAG) production. Expression of chondrogenic extracellular matrix (ECM) synthesis was further evaluated by semiquantitative RT-PCR of sox9, type II collagen, and aggrecan mRNAs. Results indicate that Ca and Sr alginate maintained significantly higher population of living cells compared to Ba alginate (p < 0.05). Production of s-GAG was similarly higher in Ca and Sr alginate microbead cultures compared to Ba alginate microbeads. Although there was no significant difference between strontium and calcium up to day 14 of culture, Sr alginate showed remarkably improved cellular and metabolic activities on long-term cultures, with chondrocytes expressing as much as 31% and 44% greater s-GAG compared to calcium and barium constructs, respectively, while IVD cells expressed 63% and 74% greater s-GAG compared to calcium and barium constructs, respectively, on day 28. These findings indicate that Sr alginate represent a significant improvement over Ca- and Ba alginate microbeads for the maintenance of chondrogenic phenotype of primary chondrocytes and IVD cells.

Intervention timing of strontium treatment on estrogen depletion‐induced osteoporosis in rats: Bone microstructure and mechanics

To evaluate the effect of intervention timing of Sr treatment on trabecular bone microstructure and mechanics.

Effect of Cryopreservation on the Biomechanical Properties of the Intervertebral Discs

Intervertebral Disc (IVD) allograft transplantation is presented to be a practical treatment of severe Degenerative Disc Disease (DDD). Limited availability of fresh allograft tissues necessitate the establishment of tissue banking for long-term storage. However, the effects of the cryopreservants on the mechanical properties of the IVD remains unknown. We hypothesize that the appropriate use of cryopreservants can preserve the mechanical properties of the IVD. In this study porcine discs were cryopreserved in different cryopreservative agent (CPA) concentration following a stepwise freezing protocol. After four weeks of storage in liquid nitrogen, dynamic viscoelastic properties of the IVDs were tested using uniaxial compression at different frequencies. Compared to fresh IVDs, no significant differences were found in the elastic modulus (E’), viscous modulus (E”) and loss tangent (E”/E’) in the discs cryopreserved with 0-20% CPA. However, cryopreservation at 20% CPA mixture resulted in lower E’ and E”. Our data suggest properly cryopreserved IVD is able to maintain both elastic and viscous characteristics and distribute loads as of a normal IVD.

Bioactivity and Corrosion Resistance of NiTi After Calcium Plasma Immersion Ion Implantation

Summary form only given. Plasma immersion ion implantation (PHI) is an effective approach to enhance the surface properties of various types of biomaterials. In order to enhance the surface bioactivity and corrosion resistance of NiTi shape memory alloy, calcium ions were implanted into NiTi alloys that have been pre-plasma-implanted with oxygen and nitrogen. The results are compared to samples without pre-treatment. The bioactivity of calcium-implanted NiTi was evaluated by immersion tests in simulated body fluid (SBF). The surface of NiTi before and after immersion tests was characterized by X-ray photoelectron spectroscopy (XPS). The XPS results reveal that the structure of the calcium-implanted layer in all the samples is composed of calcium oxide and gradually becomes a Ca-P layer after a period incubation in SBF. This Ca-P film also can be detected by scanning electron microscopy (SEM). To evaluate the anti-corrosion performance of NiTi, electrochemical potentiodynamic polarization tests were conducted on the NiTi samples in SBF. NiTi samples with pre-oxygen and nitrogen plasma implantation exhibit better corrosion resistance than single calcium-implanted samples. Our results indicate that calcium implantation can enhance the bioactivity of NiTi alloy due to the formation of calcium phosphate on the surface of the alloy. Plasma ion implantation can also improve the corrosion resistance of NiTi.