Krishnan Laxminarayanan, Priddy Lauren B, Esancy Camden, Klosterhoff Brett S, Stevens Hazel Y, Tran Lisa, Guldberg Robert E
Parker H. Petit Institute for Bioengineering & Bioscience, Georgia Institute of Technology, 315 Ferst Drive NW, Atlanta, GA 30332, USA.
Parker H. Petit Institute for Bioengineering & Bioscience, Georgia Institute of Technology, 315 Ferst Drive NW, Atlanta, GA 30332, USA; Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, 313 Ferst Drive NW, Atlanta, GA 30332, USA.
Acta Biomater. 2017 Feb;49:101-112. doi: 10.1016/j.actbio.2016.12.012. Epub 2016 Dec 8.
Bone morphogenetic protein-2 (BMP-2), delivered on absorbable collagen sponge, is frequently used to treat bone defects. However, supraphysiological BMP-2 doses are common and often associated with complications such as heterotopic ossification and inflammation, causing pain and impaired mobility. This has prompted investigations into strategies to spatially control bone regeneration, for example growth factor delivery in appropriate scaffolds. Our objective was to investigate the spatiotemporal effects of high dose BMP-2 on bone regeneration as a function of the delivery vehicle. We hypothesized that an alginate delivery system would spatially restrict bone formation compared to a collagen sponge delivery system. In vitro, BMP-2 release was accelerated from collagen sponge compared to alginate constructs. In vivo, bone regeneration was evaluated over 12weeks in critically sized rat femoral segmental defects treated with 30μg rhBMP-2 in alginate hydrogel or collagen sponge, surrounded by perforated nanofiber meshes. Total bone volume, calculated from micro-CT reconstructions, was higher in the alginate group at 12weeks. Though bone volume within the central defect region was greater in the alginate group at 8 and 12weeks, heterotopic bone volume was similar between groups. Likewise, mechanical properties from ex vivo torsional testing were comparable between groups. Histology corroborated these findings and revealed heterotopic mineralization at 2weeks post-surgery in both groups. Overall, this study recapitulated the heterotopic ossification associated with high dose BMP-2 delivery, and demonstrated that the amount and spatial pattern of bone formation was dependent on the delivery matrix.
Alginate hydrogel-based BMP-2 delivery has induced better spatiotemporal bone regeneration in animals, compared to clinically used collagen sponge, at lower BMP-2 doses. Lack of clear dose-response relationships for BMP-2 vis-à-vis bone regeneration has contributed to the use of higher doses clinically. We investigated the potential of the alginate system, with comparatively favorable BMP-2 release-kinetics, to reduce heterotopic ossification and promote bone regeneration, when used with a high BMP-2 dose. While defect mineralization improved with alginate hydrogel, the initial high-release phase and likely early tissue exposure to BMP-2 appeared sufficient to induce heterotopic ossification. The characterization presented here should provide the framework for future evaluations of strategies to optimize bone formation and minimize adverse effects of high dose BMP-2 therapy.
负载于可吸收胶原海绵上的骨形态发生蛋白-2（BMP-2）常用于治疗骨缺损。然而，超生理剂量的BMP-2很常见，且常伴有诸如异位骨化和炎症等并发症，导致疼痛和活动能力受损。这促使人们研究在空间上控制骨再生的策略，例如在合适的支架中递送生长因子。我们的目的是研究高剂量BMP-2作为递送载体的函数对骨再生的时空效应。我们假设与胶原海绵递送系统相比，藻酸盐递送系统将在空间上限制骨形成。在体外，与藻酸盐构建体相比，BMP-2从胶原海绵中的释放加速。在体内，用30μg重组人BMP-2在藻酸盐水凝胶或胶原海绵中治疗的临界尺寸大鼠股骨节段性缺损，在12周内评估骨再生情况，缺损周围用穿孔纳米纤维网包裹。根据微型计算机断层扫描重建计算，藻酸盐组在12周时的总骨体积更高。虽然在8周和12周时藻酸盐组中央缺损区域内的骨体积更大，但两组之间的异位骨体积相似。同样，体外扭转试验的力学性能在两组之间具有可比性。组织学证实了这些发现，并显示两组在术后2周均有异位矿化。总体而言，本研究概括了与高剂量BMP-2递送相关的异位骨化，并表明骨形成的数量和空间模式取决于递送基质。
与临床使用的胶原海绵相比，基于藻酸盐水凝胶的BMP-2递送在较低BMP-2剂量下在动物中诱导了更好的时空骨再生。BMP-2与骨再生之间缺乏明确的剂量反应关系导致临床上使用更高剂量。我们研究了藻酸盐系统在与高剂量BMP-2一起使用时，凭借相对有利的BMP-2释放动力学来减少异位骨化和促进骨再生的潜力。虽然藻酸盐水凝胶改善了缺损矿化，但最初的高释放阶段以及组织可能早期暴露于BMP-2似乎足以诱导异位骨化。此处呈现的特征应为未来评估优化骨形成和最小化高剂量BMP-2治疗不良反应的策略提供框架。
