Välimäki Ville-Valtteri, Yrjans Jessica J, Vuorio Eero I, Aro Hannu T
Orthopedic Research Unit, Department of Orthopedic Surgery and Traumatology, University of Turku, Finland.
Tissue Eng. 2005 Mar-Apr;11(3-4):387-94. doi: 10.1089/ten.2005.11.387.
Bioactive glass is a promising osteoconductive silica-based biomaterial for guidance of new bone growth. On the basis of several in vitro studies, the material appears able to promote osteoblast functions. In our in vivo study, the osteopromotive effect of bioactive glass microspheres seemed to surpass the osteoinductive action of direct adenovirus-mediated human bone morphogenetic protein 2 (BMP-2) gene transfer in a noncritical size bone defect model. The current study was initiated to elucidate the molecular mechanism behind bioactive glass action with or without adjunct BMP-2 gene transfer. A standardized bone defect of the rat tibia was filled with bioactive glass microspheres and injected with adenovirus carrying the human BMP-2 gene (RAdBMP-2). Control defects were left empty or filled with bioactive glass microspheres with injection of adenovirus carrying the lacZ reporter gene or saline. Quantitative polymerase chain reaction confirmed the expression of the transferred human BMP-2 gene at the defect area at 4 days, but not in intact reference tissues. Bone matrix components (collagens I, II, and III, osteocalcin, osteonectin, and osteopontin) and resorption markers (cathepsin K and MMP-9), determined by Northern analysis, showed a completely different pattern of gene expression in defects filled with bioactive glass compared with control defects left to heal without filling. Bioactive glass induced a long-lasting production of bone matrix with concurrent upregulation of osteoclastic markers, a sign of high bone turnover. Combining RAdBMP-2 gene transfer with bioactive glass decelerated the high turnover, but did not influence the balance of synthesis and resorption. This molecular analysis confirmed not only the highly osteopromotive effect of bioactive glass microspheres, but also the accelerated rate of new bone resorption on its surface. At least in noncritical size defects this impact of bioactive glass seems to saturate new bone formation on its surface and thereby overshadow the effect of BMP-2 gene transfer.
生物活性玻璃是一种很有前景的基于二氧化硅的具有骨传导性的生物材料，可引导新骨生长。基于多项体外研究，该材料似乎能够促进成骨细胞功能。在我们的体内研究中，在非临界尺寸骨缺损模型中，生物活性玻璃微球的促骨作用似乎超过了直接腺病毒介导的人骨形态发生蛋白2（BMP-2）基因转移的骨诱导作用。开展本研究是为了阐明生物活性玻璃作用背后的分子机制，无论有无辅助BMP-2基因转移。将大鼠胫骨的标准化骨缺损用生物活性玻璃微球填充，并注射携带人BMP-2基因的腺病毒（RAdBMP-2）。对照缺损保持空置，或用生物活性玻璃微球填充，并注射携带lacZ报告基因的腺病毒或生理盐水。定量聚合酶链反应证实，在4天时转移的人BMP-2基因在缺损区域表达，但在完整的对照组织中未表达。通过Northern分析确定的骨基质成分（I型、II型和III型胶原蛋白、骨钙素、骨连接蛋白和骨桥蛋白）和吸收标志物（组织蛋白酶K和基质金属蛋白酶-9）显示，与未填充而自行愈合的对照缺损相比，填充生物活性玻璃的缺损中基因表达模式完全不同。生物活性玻璃诱导骨基质的长期产生，同时破骨细胞标志物上调，这是高骨转换的迹象。将RAdBMP-2基因转移与生物活性玻璃相结合可减缓高转换率，但不影响合成与吸收的平衡。这种分子分析不仅证实了生物活性玻璃微球具有高度的促骨作用，还证实了其表面新骨吸收速率加快。至少在非临界尺寸缺损中，生物活性玻璃的这种影响似乎使其表面的新骨形成饱和，从而掩盖了BMP-2基因转移的效果。
