Blood-Brain Barrier Leakage and Microvascular Lesions in Cerebral Amyloid Angiopathy

Abstract

Background and Purpose— Cerebral amyloid angiopathy (CAA) is a common small vessel disease that independently effects cognition in older individuals. The pathophysiology of CAA and CAA-related bleeding remains poorly understood. In this postmortem study, we explored whether blood-brain barrier leakage is associated with CAA and microvascular lesions. Methods— Eleven CAA cases (median [IQR] age=69 years [65–79 years], 8 males) and 7 cases without neurological disease or brain lesions (median [IQR] age=77 years [68–92 years], 4 males) were analyzed. Cortical sections were sampled from each lobe, and IgG and fibrin extravasation (markers of blood-brain barrier leakage) were assessed with immunohistochemistry. We hypothesized that IgG and fibrin extravasation would be increased in CAA cases compared with controls, that this would be more pronounced in parietooccipital brain regions compared with frontotemporal brain regions in parallel with the posterior predilection of CAA, and would be associated with CAA severity and number of cerebral microbleeds and cerebral microinfarcts counted on ex vivo magnetic resonance imaging of the intact brain hemisphere. Results— Our results demonstrated increased IgG positivity in the frontotemporal ( P =0.044) and parietooccipital ( P =0.001) cortex in CAA cases compared with controls. Within CAA cases, both fibrin and IgG positivity were increased in parietooccipital brain regions compared with frontotemporal brain regions ( P =0.005 and P =0.006, respectively). The percentage of positive vessels for fibrin and IgG was associated with the percentage of amyloid-β–positive vessels (Spearman ρ=0.71, P =0.015 and Spearman ρ=0.73, P =0.011, respectively). Moreover, the percentage of fibrin and IgG-positive vessels, but not amyloid-β–positive vessels, was associated with the number of cerebral microbleeds on magnetic resonance imaging (Spearman ρ=0.77, P =0.005 and Spearman ρ=0.70, P =0.017, respectively). Finally, we observed fibrin deposition in walls of vessels involved in cerebral microbleeds. Conclusions— Our results raise the possibility that blood-brain barrier leakage may be a contributory mechanism for CAA-related brain injury.

Different microvascular alterations underlie microbleeds and microinfarcts

“…21 However, the correlation between microbleed numbers and Aβ levels within CAA cases has not been assessed to date, likely due to the relatively small number of patients who have undergone PET imaging. 9 The absence of a correlation between cortical microinfarcts and CAA severity at the whole-brain or regional level may be related to the poor detection of microinfarcts on MRI. However, we did not find a strong relationship between the number of microbleeds and CAA severity at the whole-hemisphere or regional level.…”

“…8,9 All cases had received a clinical diagnosis of possible or probable CAA during life. 8,9 All cases had received a clinical diagnosis of possible or probable CAA during life.…”

“…8,9 To assess SMCs, sections underwent fluorescent immunohistochemistry to visualize Aβ (rabbit; IBL, Hamburg, Germany; 1:500 and antirabbit Alexa Fluor 350, 1:250, as the secondary), SMCs (mouse, Dako, 1:250 and antimouse Alexa Fluor 488, 1:500, as the secondary), and endothelial cells (DyLight 594-labeled Lycopersicon esculentum [Tomato] Lectin; Vector Laboratories, Burlingame, CA; 1:500) within the same vessel. H&E and Luxol fast blue H&E staining was performed using standard histology protocols.…”

“…Thirteen intact brains were received through an ongoing brain donation program initiated within the hemorrhagic stroke research group at the Massachusetts General Hospital (MGH) aimed at the evaluation of MRI markers and their underlying histopathology in the context of CAA. 8,9 All cases had received a clinical diagnosis of possible or probable CAA during life. 1 At autopsy, brains were extracted and fixed in 10% formalin for several weeks, after which the hemispheres were separated by a single midsagittal cut.…”

“…Bright field immunohistochemistry against Aβ (mouse, clone 6F/3D; Agilent Technologies, Santa Clara, CA; 1:200), GFAP (rabbit, G9269; Sigma, St Louis, MO; 1:1,000), and fibrin(ogen) (rabbit; Dako, Carpinteria, CA; 1:500) was performed as described previously. 8,9 To assess SMCs, sections underwent fluorescent immunohistochemistry to visualize Aβ (rabbit; IBL, Hamburg, Germany; 1:500 and antirabbit Alexa Fluor 350, 1:250, as the secondary), SMCs (mouse, Dako, 1:250 and antimouse Alexa Fluor 488, 1:500, as the secondary), and endothelial cells (DyLight 594-labeled Lycopersicon esculentum [Tomato] Lectin; Vector Laboratories, Burlingame, CA; 1:500) within the same vessel. Negative controls were included by omitting the primary antibodies and showed no immunopositivity.…”