Hansen-Algenstaedt Nils, Joscheck Claudia, Wolfram Lars, Schaefer Christian, Müller Ingo, Böttcher Antje, Deuretzbacher Georg, Wiesner Lothar, Leunig Michael, Algenstaedt Petra, Rüther Wolfgang
Department of Zentrum Biomechanik, University Medical Center Hamburg-Eppendorf. Hamburg, Germany.
Acta Orthop. 2006 Jun;77(3):429-39. doi: 10.1080/17453670610046361.
Angiogenesis, the process of new vessel formation from a pre-existing vascular network, is essential for bone development and repair. New vessel formation and microvascular functions are crucial during bone repair, not only for sufficient nutrient supply, transport of macromolecules and invading cells, but also because they govern the metabolic microenvironment. Despite its central role, very little is known about the initial processes of vessel formation and microvascular function during bone repair.
To visualize and quantify the process of vessel formation and microvascular function during bone repair, we transplanted neonatal femora with a substantial defect into dorsal skin-fold chambers in severe combined immunodeficient (SCID) mice for continuous noninvasive in-vivo evaluation. We employed intravital microscopic techniques to monitor effective microvascular permeability, functional vascular density, blood flow rate and leukocyte flux repeatedly over 16 days. Oxytetracyclin and v. Kossa/v. Giesson staining was performed to quantify the calcification process in vivo and in vitro.
Development of a hematoma surrounding the defect area was the initial event, which was accompanied by a significant increase in microvascular permeability and blood flow rate. With absorption of the hematoma and vessel maturation, permeability decreased continuously, while vascular density and tissue perfusion increased. Histological evaluation revealed that the remodeling of the substantial defect prolonged the in-vivo monitored calcification process.
The size of the initial substantial defect correlated positively with increased permeability, suggesting improved release of permeability-inducing cytokines. The unchanged permeability in the control group with boiled bones and a substantial defect corroborated these findings. The adaptation to increasing metabolic demands was initially mediated by increased blood flow rate, later with increasing vascular density through increased tissue perfusion rate. These insights into the sequence of microvascular alterations may assist in the development of targeted drug delivery therapies and caution against the use of permeability-altering drugs during bone healing.
血管生成是指从预先存在的血管网络形成新血管的过程，对骨骼发育和修复至关重要。新血管形成和微血管功能在骨修复过程中至关重要，不仅因为它们能提供充足的营养供应、运输大分子和侵入细胞，还因为它们控制着代谢微环境。尽管血管生成起着核心作用，但对于骨修复过程中血管形成和微血管功能的初始过程却知之甚少。
为了可视化和量化骨修复过程中血管形成和微血管功能的过程，我们将有严重缺损的新生股骨移植到严重联合免疫缺陷（SCID）小鼠的背部皮褶腔中，以便进行连续的非侵入性体内评估。我们采用活体显微镜技术，在16天内反复监测有效微血管通透性、功能性血管密度、血流速度和白细胞通量。进行土霉素和v.科萨/v.吉森染色，以量化体内和体外的钙化过程。
缺损区域周围血肿的形成是初始事件，同时伴有微血管通透性和血流速度的显著增加。随着血肿的吸收和血管成熟，通透性持续下降，而血管密度和组织灌注增加。组织学评估显示，严重缺损的重塑延长了体内监测的钙化过程。
初始严重缺损的大小与通透性增加呈正相关，提示通透性诱导细胞因子的释放增加。用煮沸的骨头和严重缺损的对照组中通透性不变，证实了这些发现。对不断增加的代谢需求的适应最初是通过增加血流速度介导的，后来随着组织灌注率的增加，血管密度增加。这些对微血管变化序列的见解可能有助于开发靶向药物递送疗法，并提醒在骨愈合过程中慎用改变通透性的药物。
