Ischemic stroke is a cerebrovascular disease characterized by the interruption of blood flow to the brain followed by an ischemic cascade that disrupts the blood-brain barrier (BBB). Under ischemia, BBB permeability increases, allowing the entry of proinflammatory compounds and damaging the brain. Despite this, little is known on the pathological mechanisms of BBB dysfunction during subacute and chronic ischemic stroke. The aim of this study is to evaluate BBB integrity, neuroinfammatory response and matrix metalloproteinases (MMPs) activity in the following month after ischemia.

Adult male Sprague Dawley rats (N=62) were subjected to a transient intraluminal occlusion of the middle cerebral artery (tMCAO) for 75 min, followed by reperfusion. In vivo BBB integrity was assessed using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with gadolinium as a contrast agent, before (day 0) and at days 1, 3, 7, 14, 21 and 28 after a preclinical model of ischemic stroke (N=21). On the other hand, Ex vivo BBB permeability and neuroinflammatory response after stroke was measured by Evans Blue extravasation and vascular cell adhesion molecule (VCAM) expression with immunohistochemistry, respectively (N=34). Finally, MMPs activity was quantified through the uptake of the radiotracer [18F]BR351 using positron emission tomography (PET) and zymography studies (N=7).

BBB permeability showed an increase during the first week (subacute phase), with a peak at day 7 after reperfusion. This increase was subsequently followed by a recovery of BBB integrity from days 14 to 28 (chronic phase). Immunohistochemical analysis showed significant positive correlation between a higher percentage of inflamed vessels and BBB leakage, where VCAM expression increased on the subacute phase along with Evans Blue extravasation. Conversely, PET imaging studies revealed a [18F]BR351-PET uptake signal increase during the first 24 hours, followed by a signal decrease during the following weeks after stroke.

In summary, the characterization of BBB integrity and neuroinflammation was carried out after experimental ischemia in rats. Our results showed an increase in BBB permeability and VCAM expression during the first week after stroke and displayed a positive correlation between BBB disruption and vascular inflammation. Despite this, BBB dysfunction during the subacute phase of ischemic stroke did not correlate with MMP activity measured by PET.

More information:

• https://www.achucarro.org/laboratory/neuroimaging-and-biomarkers-of-inflammation/