Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, 60 Musk Ave, Kelvin Grove, Brisbane, Queensland 4059, Australia; Australia-China Centre for Tissue Engineering and Regenerative Medicine, Queensland University of Technology, Brisbane, 60 Musk Ave, Kelvin Grove, Brisbane, Queensland 4059, Australia.
Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, 60 Musk Ave, Kelvin Grove, Brisbane, Queensland 4059, Australia.
Biomaterials. 2015 Aug;61:126-38. doi: 10.1016/j.biomaterials.2015.04.044. Epub 2015 May 14.
Osteoblast lineage cells are direct effectors of osteogenesis and are, therefore, commonly used to evaluate the in vitro osteogenic capacity of bone substitute materials. This method has served its purposes when testing novel bone biomaterials; however, inconsistent results between in vitro and in vivo studies suggest the mechanisms that govern a material's capacity to mediate osteogenesis are not well understood. The emerging field of osteoimmunology and immunomodulation has informed a paradigm shift in our view of bone biomaterials-from one of an inert to an osteoimmunomodulatory material-highlighting the importance of immune cells in materials-mediated osteogenesis. Neglecting the importance of the immune response during this process is a major shortcoming of the current evaluation protocol. In this study we evaluated a potential angiogenic bone substitute material cobalt incorporated with β-tricalcium phosphate (CCP), comparing the traditional "one cell type" approach with a "multiple cell types" approach to assess osteogenesis, the latter including the use of immune cells. We found that CCP extract by itself was sufficient to enhance osteogenic differentiation of bone marrow stem cells (BMSCs), whereas this effect was cancelled out when macrophages were involved. In response to CCP, the macrophage phenotype switched to the M1 extreme, releasing pro-inflammatory cytokines and bone catabolic factors. When the CCP materials were implanted into a rat femur condyle defect model, there was a significant increase of inflammatory markers and bone destruction, coupled with fibrous encapsulation rather than new bone formation. These findings demonstrated that the inclusion of immune cells (macrophages) in the in vitro assessment matched the in vivo tissue response, and that this method provides a more accurate indication of the essential role of immune cells when assessing materials-stimulated osteogenesis in vitro.
成骨细胞系细胞是成骨作用的直接效应物，因此通常用于评估骨替代材料的体外成骨能力。在测试新型骨生物材料时，这种方法已经达到了目的；然而，体外和体内研究之间的不一致结果表明，控制材料介导成骨能力的机制尚未得到很好的理解。骨免疫学和免疫调节的新兴领域使我们对骨生物材料的看法发生了转变——从惰性材料转变为具有骨免疫调节作用的材料——强调了免疫细胞在材料介导的成骨作用中的重要性。在这个过程中忽视免疫反应的重要性是当前评估方案的一个主要缺点。在这项研究中，我们评估了一种潜在的血管生成骨替代材料——钴结合β-磷酸三钙（CCP），将传统的“单一细胞类型”方法与“多种细胞类型”方法进行比较，以评估成骨作用，后者包括使用免疫细胞。我们发现，CCP 提取物本身足以增强骨髓干细胞（BMSCs）的成骨分化，而当涉及巨噬细胞时，这种作用就会被抵消。对 CCP 的反应使巨噬细胞表型向 M1 极端转变，释放促炎细胞因子和骨分解因子。当 CCP 材料被植入大鼠股骨髁缺损模型中时，炎症标志物和骨破坏显著增加，伴随着纤维包裹而不是新骨形成。这些发现表明，将免疫细胞（巨噬细胞）纳入体外评估与体内组织反应相匹配，并且该方法提供了更准确的指示，表明在评估材料刺激的体外成骨作用时免疫细胞的重要作用。
