Near-infrared fluorescent imaging of cerebral thrombi and blood-brain barrier disruption in a mouse model of cerebral venous sinus thrombosis

An intravital microscopy imaging method was developed to visualize active cerebral thrombus and blood-brain barrier (BBB) disruption using Near Infrared Fluorescent (NIRF) probes. A circular craniotomy was made in CD-1 mice. Thrombi were formed by applying 10%-FeCl₃ to the entire exposed superior sagittal sinus (SSS, 5 mm), or to the posterior 2.5 mm of the SSS for 5 mins. Control animals were pretreated with heparin (50 U/kg) before thrombus induction. Three hours after thrombus formation, a FXIIIa-targeted NIRF imaging probe (A15) was intravenously injected, and the SSS was imaged by intravital microscopy. This was followed by injection of indocyanine green (ICG) to assess BBB permeability. The A15 optical probe bound to thrombus, and the fluorescent signal emitted by the bound agent corresponded well with histologically confirmed thrombus. A15 initially remained intravascular, followed by excretion and subsequent decrease in all tissues except for thrombus, where it was retained. The subsequent ICG was also intravascular immediately after injection, but then began to leak into the cerebral parenchyma at 3 to 5 mins. The sites of leakage were adjacent to thrombosed areas. Heparin pretreatment prevented thrombus formation and reduced ICG leakage significantly. This demonstrates the feasibility of simultaneous in vivo monitoring of thrombus and BBB permeability in an animal model of cerebral venous thrombosis.