Heeremans J L, Los P, Prevost R, Crommelin D J, Kluft C
Department of Pharmaceutics, Utrecht University, Netherlands.
Thromb Haemost. 1996 Jan;75(1):134-9.
In this study, the fibrin binding properties of liposomes containing a number of plasminogen (Plg) molecules on the outside were compared to those of free (non-liposomal) Plg in an in vitro model system. Fibrin monolayer coated 96-wells plates were used, containing fibrin monomer at a density of around 3.4 to 3.9 x 10(-4) nmol/cm2. These densities are similar to liposomal Plg-densities, thus allowing multivalent interactions to occur. In the panel of experimental conditions that was chosen, binding of free Plg and liposomes with Plg showed three main differences in characteristics. Firstly, in the fibrin binding of Plg-liposomes not all Plg may be involved, but on the average 40% of the total amount of liposomal Plg. This was shown by lysing the liposomes after binding to the fibrin and estimation of truly bound Plg. With Plg-densities on the liposomes below the fibrin binding sites density, the maximal number of bound Plg molecules remains below the amount of available fibrin binding sites. Secondly, a higher binding rate by at least one order of magnitude was observed for liposomes with Plg compared to free Plg. Thirdly, liposomes with Plg exhibit a fibrin binding affinity which increases with Plg-density, because of the multivalent character of interaction. Liposomal Plg can successfully compete for fibrin binding sites with a 100 fold higher concentration of free Plg. These in vitro findings indicate that in view of avid and rapid fibrin binding, liposomes with attached plasminogen may be suitable for in vivo targeting to fibrin based thrombi.
在本研究中，在体外模型系统中，将外部含有若干纤溶酶原（Plg）分子的脂质体的纤维蛋白结合特性与游离（非脂质体）Plg的纤维蛋白结合特性进行了比较。使用了包被有纤维蛋白单层的96孔板，其中纤维蛋白单体的密度约为3.4至3.9×10⁻⁴ nmol/cm²。这些密度与脂质体Plg密度相似，因此允许发生多价相互作用。在所选择的一组实验条件下，游离Plg和含Plg脂质体的结合在特性上显示出三个主要差异。首先，在Plg-脂质体与纤维蛋白的结合中，并非所有Plg都可能参与，但平均而言，脂质体Plg总量的40%参与其中。这是通过在与纤维蛋白结合后裂解脂质体并估计真正结合的Plg来证明的。当脂质体上的Plg密度低于纤维蛋白结合位点密度时，结合的Plg分子的最大数量仍低于可用纤维蛋白结合位点的数量。其次，观察到与游离Plg相比，含Plg脂质体的结合速率至少高一个数量级。第三，含Plg脂质体表现出纤维蛋白结合亲和力，该亲和力随Plg密度增加，这是由于相互作用的多价性质。脂质体Plg可以成功地与浓度高100倍的游离Plg竞争纤维蛋白结合位点。这些体外研究结果表明，鉴于对纤维蛋白的强烈且快速的结合，附着有纤溶酶原的脂质体可能适用于体内靶向基于纤维蛋白的血栓。
