Platelet rich clots are resistant to lysis by thrombolytic therapy in a rat model of embolic stroke

Abstract

BackgroundEarly recanalization of occluded vessels in stroke is closely associated with improved clinical outcome. Microbubble-enhanced sonothrombolysis is a promising therapy to improve recanalization rates and reduce the time to recanalization. Testing any thrombolytic therapy requires a model of thromboembolic stroke, but to date these models have been highly variable with regards to clot stability. Here, we developed a model of thromboembolic stroke in rats with site-specific delivery of platelet-rich clots (PRC) to the main stem of the middle cerebral artery (MCA). This model was used in a subsequent study to test microbubble-enhanced sonothrombolysis.MethodsIn Study 1 we investigated spontaneous recanalization rates of PRC in vivo over 4 hours and measured infarct volumes at 24 hours. In Study 2 we investigated tPA-mediated thrombolysis and microbubble-enhanced sonothrombolysis in this model.ResultsStudy 1 demonstrated stable occlusion out to 4 hours in 5 of 7 rats. Two rats spontaneously recanalized at 40 and 70 minutes post-embolism. Infarct volumes were not significantly different in recanalized rats, 43.93 ± 15.44% of the ischemic hemisphere, compared to 48.93 ± 3.9% in non-recanalized animals (p = 0.7). In Study 2, recanalization was not observed in any of the groups post-treatment.ConclusionsSite specific delivery of platelet rich clots to the MCA origin resulted in high rates of MCA occlusion, low rates of spontaneous clot lysis and large infarction. These platelet rich clots were highly resistant to tPA with or without microbubble-enhanced sonothrombolysis. This resistance of platelet rich clots to enhanced thrombolysis may explain recanalization failures clinically and should be an impetus to better clot-type identification and alternative recanalization methods.Electronic supplementary materialThe online version of this article (doi:10.1186/s13231-014-0014-y) contains supplementary material, which is available to authorized users.

Structural analysis of ischemic stroke thrombi: histological indications for therapy resistance

“…However, it is only effective in less than half of the patients that receive rt-PA. 2,3 The mechanisms underlying this so called "rt-PA-resistance" are not completely understood but previous reports indicated that RBC-dominant thrombi respond better to rt-PA than platelet-dominant thrombi. [18][19][20][21][22][23][24][25][26] Our histological findings provide new molecular insights on the composition of RBC-rich and platelet-rich thrombus material. It seems plausible that rt-PA, which promotes the degradation of fibrin, can have a direct and efficient thrombolytic effect on the RBC-rich areas in which thin fibrin is the main extracellular scaffold.…”

Successful recanalization in acute basilar artery occlusion treated with endovascular therapy is independent of thrombus length

“…It is well known that erythrocyte-rich thrombi have a higher density than platelet-rich thrombi on NECCT 21 22. It has been claimed that erythrocyte-rich thrombi with little fibrin content are more susceptible to pharmacological23 and mechanical therapy 24. In a recent systematic review and meta-analysis, the authors concluded that patients with a mean thrombus density of 55.1±3.1 HU had a good angiographic outcome whereas those with a mean thrombus density of 48.9±1.9 HU had a poor angiographic outcome 25.…”

ADAMTS13-mediated thrombolysis of t-PA–resistant occlusions in ischemic stroke in mice

“…1 The exact nature of this so-called t-PA resistance is not yet fully understood, but location, size, and composition of the occluding thrombus have been reported to be important factors influencing t-PA outcome. [4][5][6][7][8] Interestingly, various studies have shown that in particular arterial platelet-rich clots are more resistant to thrombolysis with t-PA. 7,[9][10][11] Surprisingly little is known about the precise composition of human stroke clots. Nevertheless, such information is crucial for the design of novel thrombolytic strategies.…”