A murine photothrombotic stroke model with an increased fibrin content and improved responses to tPA-lytic treatment

Abstract

The Rose Bengal (RB) dye-based photothrombotic stroke (PTS) model has many methodological advantages including consistent location and size of infarct, low mortality, and relatively simple surgical procedures. However, the standard PTS has the caveat of poor responses to tissue-type plasminogen activator (tPA)-mediated lytic treatment, likely as a result of the platelet-rich, fibrin-poor content of the blood clots. Here we tested whether the admixture of thrombin (80 U/kg) and RB dye (50 mg/kg) in the proximal middle cerebral artery (MCA)-targeted PTS will modify the clot composition and elevate the responsiveness to tPA-lytic treatment (Alteplase, 10 mg/kg). Indeed, intravital imaging, immunostaining, and immunoblot analyses showed less-compacted platelet aggregates with a higher fibrin content in the modified thrombin (T) plus RB photothrombotic stroke (T1RB-PTS) model compared with the standard RB-PTS-induced clots. Both RB-PTS and T1RB-PTS showed steady recovery of cerebral blood flow (CBF) in the ischemic border from 1 day after infarction, but without recanalization of the proximal MCA branch. Intravital imaging showed high potency of restoring the blood flow by tPA after single vessel-targeted T1RB-PTS. Further, although intravenous tPA failed to restore CBF or attenuate infarction in RB-PTS, it conferred 25% recovery of CBF and 55% reduction of the infarct size in T1RB-PTS (P , .05) if tPA was administered within 2 hours postphotoactivation. These results suggest that T1RB-PTS produces mixed platelet:fibrin clots closer to the clinical thrombus composition and enhanced the sensitivity to tPA-lytic treatment. As such, the modified photothrombosis may be a useful tool to develop more effective thrombolytic therapies of cerebral ischemia.