Cell and Tissue Response to Polyethylene Terephthalate Mesh Containing Bone Allograft in Vitro and in Vivo

AUTHORS

D. Joshua Cohen, Lisa Ferrara, Marcus B. Stone, Zvi Schwartz and Barbara D. Boyan

ABSTRACT

Background Extended polyethylene terephthalate mesh (PET, Dacron) can provide containment of compressed particulate allograft and autograft. This study assessed if PET mesh would interfere with osteoprogenitor cell migration from vertebral plates through particulate graft, and its effect on osteoblast differentiation or the quality of bone forming within fusing vertebra during vertebral interbody fusion.

Methods The impact of PET mesh on the biological response of normal human osteoblasts (NHOst cells) and bone marrow stromal cells (MSCs) to particulate bone graft was examined in vitro. Cells were cultured on rat bone particles +/− mesh; proliferation and osteoblast differentiation were assessed. The interface between the vertebral endplate, PET mesh, and newly formed bone within consolidated allograft contained by mesh was examined in a sheep model via microradiographs, histology, and mechanical testing.

Results Growth on bone particles stimulated proliferation and early differentiation of NHOst cells and MSCs, but delayed terminal differentiation. This was not negatively impacted by mesh. New bone formation in vivo was not prevented by use of a PET mesh graft containment device. Fusion was improved in sites containing allograft/demineralized bone matrix (DBM) versus autograft and was further enhanced when stabilized using pedicle screws. Only sites treated with allograft/DBM+screws exhibited greater percent bone ingrowth versus discectomy or autograft. These results were mirrored biomechanically.

Conclusions PET mesh does not negatively impact cell attachment to particulate bone graft, proliferation, or initial osteoblast differentiation. The results demonstrated that bone growth occurs from vertebral endplates into graft material within the PET mesh. This was enhanced by stabilization with pedicle screws leading to greater bone ingrowth and biomechanical stability across the fusion site.

Improved bone regeneration using bone anabolic drug conjugates (C3 and C6) with deproteinized bovine bone mineral as a carrier in rat mandibular defects

AUTHORS

Zeeshan Sheikh, Mohamed-Nur Abdallah, Faik Al-Jaf, Gang Chen, Nader Hamdan, Robert N. Young, Marc D. Grynpas, Michael Glogauer

ABSTRACT

Background

Deproteinized bovine bone mineral (DBBM) has been extensively studied and used for bone regeneration in oral and maxillofacial surgery. However, it lacks an osteoinductive ability. We developed two novel bone anabolic conjugated drugs, known as C3 and C6, of an inactive bisphosphonate and a bone activating synthetic prostaglandin agonist. The aim was to investigate whether these drugs prebound to DBBM granules have the potential to achieve rapid and enhanced bone regeneration.

Methods

Bilateral defects (4.3 mm diameter circular through and through) were created in mandibular angles of 24 Sprague-Dawley rats were filled with DBBM Control, DBBM with C3 or DBBM with C6 (n = 8 defects per group/ each timepoint). After 2 and 4 weeks, postmortem samples were analyzed by microcomputed tomography followed by backscattering electron microscopy and histology.

Results

DBBM grafts containing the C3 and C6 conjugated drugs showed significantly more bone formation than DBBM control at 2 and 4 weeks. The C6 containing DBBM demonstrated the highest percentage of new bone formation at 4 weeks. There was no significant difference in the percentage of the remaining graft between the different groups at 2 or 4 weeks.

Conclusions

DBBM granules containing conjugated drugs C3 and C6 induced greater new bone volume generated and increased the bone formation rate more than the DBBM controls. This is expected to allow the development of clinical treatments that provide more predictable and improved bone regeneration for bone defect repair in oral and maxillofacial surgery.

Adiponectin Reduces Bone Stiffness: Verified in a Three-Dimensional Artificial Human Bone Model In Vitro

AUTHORS

Sigrid Haugen, iJianying He, Alamelu Sundaresan, Astrid Kamilla Stunes, Kristin Matre Aasarød, Hanna Tiainen, Unni Syversen, Bjørn Skallerud and Janne Elin Reseland

ABSTRACT

Primary human osteoblasts and osteoclasts incubated in a rotating coculture system without any scaffolding material, form bone-like tissue that may be used to evaluate effects of various compounds on mechanical strength. Circulating adiponectin has been found to be negatively associated with BMD and strength and was therefore assessed in this system. Osteospheres of human osteoblasts and osteoclasts were generated with and without adiponectin. The osteospheres were scanned using micro-computed tomography, the mechanical properties were tested by flat punch compression using nanoindentation equipment, and the cellular morphology characterized by microscopy. The association between autologously produced adiponectin and biomechanical properties was further evaluated by quantitation of adiponectin levels using quantitative polymerase chain reaction (qPCR) and immunoassays, and identification of stiffness by bending test of rat femurs. The molecular mechanisms were examined in vitro using human bone cells. Mechanical testing revealed that adiponectin induced a more compliant osteosphere compared with control. The osteospheres had a round, lobulated appearance with morphologically different areas; inner regions containing few cells embedded in a bone-like material surrounded by an external area with a higher cell quantity. The expression of adiponectin was found to correlate positively to ultimate bending moment and ultimate energy absorption and deflection, on the other hand, it correlated negatively to bending stiffness, indicating autocrine and/or paracrine effects of adiponectin in bone. Adiponectin enhanced proliferation and expression of collagen, leptin, and tumor necrosis factor-alpha in osteoblasts and stimulated proliferation, but not the functional activity of osteoclasts. Our results indicate that both administration of adiponectin during osteosphere production and in situ elevated levels of adiponectin in rat femurs, reduced stiffness of the bone tissues. An increase in undifferentiated cells and extracellular matrix proteins, such as collagen, may explain the reduced bone stiffness seen in the osteospheres treated with adiponectin.

Age-related epigenetic changes in hippocampal subregions of four animal models of Alzheimer's disease

AUTHORS

Roy Lardenoije, Daniël L.A. van den Hove, Monique Havermans, Annevan Casteren, Kevin X. Le, Roberta Palmour, Cynthia A. Lemere, Bart P.F. Rutten

ABSTRACT

Both aging and Alzheimer's disease (AD) are associated with widespread epigenetic changes, with most evidence suggesting global hypomethylation in AD. It is, however, unclear how these age-related epigenetic changes are linked to molecular aberrations as expressed in animal models of AD. Here, we investigated age-related changes of epigenetic markers of DNA methylation and hydroxymethylation in a range of animal models of AD, and their correlations with amyloid plaque load. Three transgenic mouse models, including the J20, APP/PS1dE9 and 3xTg-AD models, as well as Caribbean vervets (a non-transgenic non-human primate model of AD) were investigated. In the J20 mouse model, an age-related decrease in DNA methylation was found in the dentate gyrus (DG) and a decrease in the ratio between DNA methylation and hydroxymethylation was found in the DG and cornu ammonis (CA) 3. In the 3xTg-AD mice, an age-related increase in DNA methylation was found in the DG and CA1-2. No significant age-related alterations were found in the APP/PS1dE9 mice and non-human primate model. In the J20 model, hippocampal plaque load showed a significant negative correlation with DNA methylation in the DG, and with the ratio a negative correlation in the DG and CA3. For the APP/PS1dE9 model a negative correlation between the ratio and plaque load was observed in the CA3, as well as a negative correlation between DNA methyltransferase 3A (DNMT3A) levels and plaque load in the DG and CA3. Thus, only the J20 model showed an age-related reduction in global DNA methylation, while DNA hypermethylation was observed in the 3xTg-AD model. Given these differences between animal models, future studies are needed to further elucidate the contribution of different AD-related genetic variation to age-related epigenetic changes.