Correction to: Pigment Epithelium-Derived Factor Improves Paracellular Blood-Brain Barrier Integrity in the Normal and Ischemic Mouse Brain.

The original version of the article unfortunately contained an error in the unit of the protein concentrations under 'Stereotactic Intraparenchymal Injections' subsection in 'Methods' section.

Pigment Epithelium-Derived Factor Improves Paracellular Blood-Brain Barrier Integrity in the Normal and Ischemic Mouse Brain.

Pigment epithelium-derived factor (PEDF) is a neurotrophic factor with neuroprotective, antiangiogenic, and antipermeability effects. In the brain, blood-brain barrier (BBB) function is essential for homeostasis. Its impairment plays a crucial role in the pathophysiology of many neurological diseases, including ischemic stroke. We investigated (a) whether PEDF counteracted vascular endothelial growth factor (VEGF)-induced BBB disruption in the mouse brain, (b) the time course and route of BBB permeability and the dynamics of PEDF expression after cerebral ischemia, and (c) whether intraventricular infusion of PEDF ameliorated brain ischemia by reducing BBB impairment. C57Bl6/N mice received intraparenchymal injections of CSF, VEGF, or a combination of VEGF and PEDF. PEDF increased paracellular but not transcellular BBB integrity as indicated by an increase in the tight junction protein claudin-5. In another group of mice undergoing 60-min middle cerebral artery occlusion (MCAO), transcellular BBB permeability (fibrinogen staining in the absence of a loss of claudin-5) increased as early as 6 h after reperfusion. PEDF immunofluorescence increased at 24 h, which paralleled with a decreased paracellular BBB permeability (claudin-5). PEDF after MCAO originated from the blood stream and endogenous pericytes. In the third experiment, the intraventricular infusion of PEDF decreased edema and cell death after MCAO, potentially mediated by the improvement of the paracellular route of BBB permeability (claudin-5) in the absence of an amelioration of Evans Blue extravasation. Together, our data suggest that PEDF improves BBB function after cerebral ischemia by affecting the paracellular but not the transcellular route. However, further quantitative data of the different routes of BBB permeability will be required to validate our findings.

Visualization of cell death in mice with focal cerebral ischemia using fluorescent annexin A5, propidium iodide, and TUNEL staining.

To monitor stroke-induced brain damage and assess neuroprotective therapies, specific imaging of cell death after cerebral ischemia in a noninvasive manner is highly desirable. Annexin A5 has been suggested as a marker for imaging cell death under various disease conditions including stroke. In this study, C57BL6/N mice received middle cerebral artery occlusion (MCAO) and were injected intravenously with either active or inactive Cy5.5-annexin A5 48 hours after reperfusion. Some mice also received propidium iodide (PI), a cell integrity marker. Only in mice receiving active Cy5.5-annexin A5 were fluorescence intensities significantly higher over the hemisphere ipsilateral to MCAO than on the contralateral side. This was detected noninvasively and ex vivo 4 and 8 hours after injection. The majority of cells positive for fluorescent annexin A5 were also positive for PI and fragmented DNA as detected by terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL) staining. This study demonstrates the high specificity of annexin A5 for visualization of cell death in a mouse model of stroke. To our knowledge, this is the first study to compare the distribution of injected active and inactive annexin A5, PI, and TUNEL staining. It provides important information on the experimental and potential clinical applications of annexin A5-based imaging agents in stroke.

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 4-8h and a second impairment at 12-16h after reperfusion. No EB extravasation was detected at 8-12h. 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.