Near-infrared fluorescence imaging with fluorescently labeled albumin: A novel method for non-invasive optical imaging of blood–brain barrier impairment after focal cerebral ischemia in mice

Impairment of the blood–brain barrier (BBB) after cerebral ischemia leads to extravasation of plasma constituents into the brain parenchyma. We describe a novel method using non-invasive near-infrared fluorescence (NIRF) imaging and bovine serum albumin labeled with a NIRF dye (NIRF–BSA) to detect BBB impairment after middle cerebral artery occlusion (MCAO) in mice. We first explored the time course of BBB impairment after transient MCAO using Evans blue (EB), which binds to plasma albumin in vivo. An initial BBB impairment was observed at 4–8 h and a second impairment at 12–16 h after reperfusion. No EB extravasation was detected at 8–12 h. Non-invasive NIRF imaging with NIRF–BSA confirmed biphasic BBB impairment. Upon co-injection of NIRF–BSA with EB we found a strong correlation between the detected NIRF signal and the amount of extravasated EB (r = 0.857, P = 0.00178). When MCAO mice received NIRF–BSA together with gadolinium–diethylene triamine penta-acetic acid (Gd–DTPA), T1-weighted images showed Gd–DTPA enhancement at all times while NIRF imaging showed biphasic BBB impairment. In conclusion, NIRF–BSA is a suitable marker of plasma albumin extravasation in the mouse brain. Non-invasive NIRF imaging with NIRF–BSA is a useful tool to study BBB integrity in preclinical models of central nervous system pathology.