Ehrbar Martin, Zeisberger Steffen M, Raeber George P, Hubbell Jeffrey A, Schnell Christian, Zisch Andreas H
Department of Cranio-Maxillofacial Surgery, University Hospital Zurich, Switzerland.
Biomaterials. 2008 Apr;29(11):1720-9. doi: 10.1016/j.biomaterials.2007.12.002. Epub 2007 Dec 26.
A major challenge for therapeutic delivery of angiogenic agents such as vascular endothelial growth factor (VEGF) is to achieve sustained, low dose signaling leading to durable neovessel formation. To this end, we recently created a variant of VEGF(121), TG-VEGF(121) that directly binds to fibrin and gets released locally in proteolysis-triggered manner. Here we combined noninvasive biophotonic monitoring of VEGF receptor 2 gene activation in transgenic VEGFR2-luc mice and histomorphometry to compare endothelial activation and long-term neovascularization by actively released TG-VEGF(121)versus passively released, diffusible wild-type VEGF(121) in subcutaneous fibrin implants. Monitoring in real-time over 3 weeks of luciferase signal driven by the VEGFR2 promoter revealed endothelial activation in skin exposed to wild-type VEGF(121), but no detectable elevation over fibrin alone by TG-VEGF(121). Histology at 3 weeks, however, demonstrated that TG-VEGF(121) promoted vessel growth significantly more effectively and reliably than wild-type VEGF(121). The majority of vessels surviving to 3 weeks contained stabilizing smooth muscle cells. Yet, by 6 weeks, no extra vessels induced by exogenous VEGF were left. In conclusion, release of fibrin-conjugated variant TG-VEGF(121) elicited lower VEGFR2-luc activation than wild-type VEGF(121) yet significantly more vascularization. In the absence of true physiological demand, even stabilized vessels are ultimately regressed.
对于血管生成因子（如血管内皮生长因子，VEGF）的治疗性递送而言，一个主要挑战是实现持续的低剂量信号传导，从而促成持久的新血管形成。为此，我们最近创建了一种VEGF(121)变体，即TG-VEGF(121)，它能直接与纤维蛋白结合，并以蛋白水解触发的方式在局部释放。在此，我们结合对转基因VEGFR2-荧光素酶小鼠中VEGF受体2基因激活的非侵入性生物光子监测和组织形态计量学，以比较主动释放的TG-VEGF(121)与被动释放的、可扩散的野生型VEGF(121)在皮下纤维蛋白植入物中引发的内皮细胞激活和长期血管生成情况。对由VEGFR2启动子驱动的荧光素酶信号进行为期3周的实时监测发现，暴露于野生型VEGF(121)的皮肤中有内皮细胞激活，但TG-VEGF(121)并未使信号在仅含纤维蛋白的基础上出现可检测到的升高。然而，3周时的组织学检查表明，TG-VEGF(121)促进血管生长的效果比野生型VEGF(121)显著更有效且更可靠。存活至3周的大多数血管都含有起稳定作用的平滑肌细胞。然而，到6周时，外源性VEGF诱导生成的额外血管已不复存在。总之，纤维蛋白结合变体TG-VEGF(121)的释放引发的VEGFR2-荧光素酶激活低于野生型VEGF(121)，但血管生成显著更多。在缺乏真正生理需求的情况下，即使是已稳定的血管最终也会消退。
