[Evaluating thrombolytic efficacy and thrombus targetability of RGDS-liposomes encapsulating subtilisin FS33 in vivo]

A novel fibrinolytic enzyme subtilisin FS33, which exhibits much higher activity for decomposing fibrin than urokinase, was purified from Douchi, a traditional soybean-fermented food in China. In order to increase bio-utilization and thrombus targetability of subtilisin FS33 labeled by fluorescein isothiocyanate (FITC), the surface modified liposomes encapsulating subtilisin FS33 and FITC with a synthetic peptide Arg-Gly-Asp-Ser (RGDS), being putatively a specific antagonist of fibrinogen receptor on platelet membrane, were prepared and used to evaluate the therapeutic efficacy in a rat model thrombotic carotid artery. The arterial thrombosis was induced by applying two pieces of filter paper (1 x 2 cm) saturated with 10% of ferric chloride (FeCl3). The rats were infused via the jugular vein with either liposomes carrying BSA (control group) or RGDS-liposomes carrying subtilisin FS33 at doses of 2000 and 4000 U/kg. The plasma of the group infused with RGDS-liposomes showed higher antithrombotic and fibrinolytic activity than did the control group within 15-120 min after infusing. The higher the dose was gived, the higher the activity was shown. APTT(activiated partial thromboplastin time), PT (prothrombin time) and TT (thrombin time) were extended remarkably (P < 0.05, P < 0.01), and FDP (fibrinogen degradation products) also increased greatly (P < 0.01), while ELT (euglobulinlysis time) decreased obviously (P < 0.05). FITC content in heart and brain evidently increased (P < 0.05), and results of D-dimer test were all positive. In addition, the venous thrombi in brain and kidney were dissolved totally or partly as observed by patholgical section. All these indicated that subtilisin FS33 enhanced the antithrombotic and fibrinolytic activities in rat, and RGDS-liposomes improved, in a certain degree, the thrombolytic specificity for targeting to thrombus.