重组葡激酶和水蛭素融合蛋白的血栓靶向性机制

为解释以凝血因子Xa(FXa)的识别序列为连接肽的葡激酶和水蛭素的融合蛋白(命名为SFH)在体内的强溶栓和低出血的特征,研究分析了SFH的两个血栓靶向性作用机理.首先采用ELISA和免疫组化的方法在体外分析了由水蛭素游离的C末端赋予的SFH对血栓的靶向性,结果显示SFH对凝血酶和富含凝血酶的血栓具有更高的亲和力.为阐明SFH抗凝活性在血栓部位的靶向性释放,构建表达了仅在水蛭素N末端连接FXa识别序列的水蛭素衍生物(命名为FH).体外试验结果表明完整的FH无抗凝活性,在体内FH可以发挥抗栓作用,且出血副作用较低,这些结果说明FXa的识别序列可以封闭水蛭素的抗凝活性,在体内FH可以由于FXa的成功裂解而释放其抗凝活性,且其抗凝活性可能仅局限于血栓局部.这就间接说明了SFH的抗凝活性可以在血栓局部进行靶向性释放.以上两个血栓靶向性作用机理是SFH在体内发挥更高溶栓效率和降低出血副作用的重要机制.

Two Characteristics of a Recombinant Fusion Protein Composed of Staphylokinase and Hirudin: High Thrombus Affinity and Thrombus-targeting Release of Anticoagulant Activity

To improve thrombolytic effect, a fusion protein SFH composed of staphylokinase (SAK) and hirudin (HV) with blood coagulation factor Xa (FXa) recognition peptide as a linker, was designed. SFH showed improved thrombolytic effect and low bleeding in vivo. Two thrombus-targeting mechanisms might account for the above features of SFH. This study was designed to study the two thrombus-targeting mechanisms of SFH. ELISA and immunohistochemistry assay were used to study the improved thrombus selectivity of SFH and the results showed that SFH, compared with SAK, displayed higher affinity for thrombin and thrombin-rich thrombus. To verify the thrombus-targeting release of anticoagulant activity of SFH, FH-a derivative of HV with only FXa recognition sequence at N terminus of HV was designed and used in animal tests. In inferior vena cava thrombosis model, FH showed equal antithrombotic effect as HV, indicating that HV could be successfully released from FH by FXa cleavage in vivo. More importantly, no prolongation of plasma TT, APTT and PT were found in FH group, but significant prolongations were discovered in HV group. This revealed that the anticoagulant activity of FH was released in thrombus-targeting way and limited in the vicinity of the thrombus, and this could be extrapolated to SFH. In conclusion, the high thrombus affinity and thrombus-targeting release of anticoagulant activity of SFH assigned low bleeding risk to SFH.