R-tPA Resistance Is Specific for Platelet-Rich Stroke Thrombi and Can Be Overcome by Targeting Nonfibrin Components

BACKGROUND: Resistance to r-tPA (recombinant tissue-type plasminogen activator) is a well-known but poorly understood phenomenon that hampers successful recanalization in patients with acute ischemic stroke. Using clinically relevant thrombi from patients with acute ischemic stroke, we investigated if and how thrombus composition impacts r-tPA-mediated lysis. In addition, we explored strategies to overcome r-tPA resistance. METHODS: Thrombi were split into 2 parts, 1 of which was used for thrombolysis and the other for detailed histological analysis. Thrombolysis was performed in normal human plasma using r-tPA alone, using r-tPA in combination with DNase-1 or using r-tPA in combination with N,N′-diacetyl- l -cystine. Thrombus lysis was calculated as the percentage of residual thrombus weight compared with its initial weight and the degree of lysis was linked to thrombus composition determined via histology. RESULTS: Interestingly, we found that the efficacy of r-tPA-mediated thrombolysis was strongly correlated with the composition of the thrombi. Thrombi containing high amounts of red blood cells and low amounts of DNA and von Willebrand Factor were efficiently degraded by r-tPA, whereas thrombi containing low amounts of red blood cells and higher amounts of DNA and von Willebrand Factor were resistant to r-tPA. Importantly, combination of r-tPA with DNase-1 or N,N′-diacetyl- l -cystine significantly and specifically improved the lysis of these r-tPA-resistant thrombi. CONCLUSIONS: Using patient thrombus material, our results for the first time show that the composition of stroke thrombi largely determines their susceptibility to r-tPA-mediated thrombolysis. Red blood cell-poor thrombi have a specific resistance to r-tPA, which can be overcome by targeting nonfibrin components using DNase-1 or N,N′-diacetyl- l -cystine.