Erythrocyte Coupled tPA Improves Outcomes of Percussion Brain Trauma in Rats.

Coupling tissue plasminogen activator (tPA) to carrier red blood cells (RBC): i) restricts tPA’s permeation into tissues and pre-existing hemostatic clots, minimizing hemorrhage; ii) protects it from plasma inhibitors; and iii) prolongs its circulation, permitting incorporation into nascent clots and their lysis from within. These features support the thromboprophylactic utility of RBC coupled tPA (RBC/tPA). In this study we explored the utility of RBC/tPA in traumatic brain injury (TBI), a disorder in which both cerebral thrombosis leading to cerebral ischemia and intracerebral hemorrhage (ICH) have been implicated. Eleven male, Sprague-Dawley rats (340–400g) were subjected to a moderate (avg. peak pressure 2.6atm) lateral fluid percussion injury to the left hemisphere. Rats were given a single intravenous dose of RBC/tPA (0.05mg/Kg, n=5) or vehicle (n=4), 15 min post-injury. Animals were sacrificed 48h later for histopathology and staining for fibrin. The lesions in control animals occupied 8.3 ± 2.8% (mean±SD) of the hemispheric volume. Animals treated with RBC/tPA had a significant decrease in mean lesion volume (1.4±0.7%; p<0.001). Thrombotic burden was reduced from a mean of 10 clots in vehicle-treated to 1 per RBC/tPA-treated rats p<0.001). These data indicate that RBC/tPA attenuates post-traumatic thrombosis without aggravating hemorrhage induced by TBI. These observations support the safety of RBC/tPA in thromboprophylaxis even in the context of brain trauma, due to intravascular containment of RBC/tPA, among other factors. Durable lysis of post-traumatic thrombi by long-circulating RBC/tPA may alleviate secondary brain ischemia and resultant ICH. Correlation between reduction of thrombotic burden and lesion size implicate thrombosis in the pathophysiology of parenchymal brain damage after head trauma. Supported by PENN Research Foundation, HL66442, HL60169 and in part by NS38104.