Comparative permeability of the blood-brain barrier to albumin, DTPA, and sucrose: effects of inflammation-induced disruption

Blood-brain barrier (BBB) disruptions are increasingly recognized in a wide range of diseases and conditions, resulting in a need to detect and quantitate such disruptions. In humans, gadolinium (Gd)-labeled compounds including diethylenetriaminepentaacetic acid (Gd-DTPA) as detected by magnetic resonance imaging (MRI) and technetium (99mTc) labeled-DTPA as detected by single photon emission computed tomography (SPECT) are commonly used, whereas 14C-sucrose, 99mTc-DTPA, and radioactively labeled albumin are commonly used in animals. How these agents compare to one another and in different species has seldom been investigated, making comparisons between human and animal studies difficult. Here, we compared the three agents of radioactively labeled albumin, 99mTc-DTPA, and 14C-sucrose in monolayers of human induced pluripotent stem cell (iPSC)-derived brain endothelial-like cells (iBECs), in control mice, and in mice whose BBB was disrupted by one or three doses of the inflammatory agent lipopolysaccharide (LPS). In iBECs, all three agents crossed with permeation dramatically decreasing as transendothelial electrical resistance (TEER) increased. Permeation of sucrose and DTPA were nearly identical with albumin being 10–20 times less permeable at all levels of TEER. In mice with an intact BBB, penetration of sucrose across the BBB was 2–15 times greater than DTPA, which was about 5.5 times greater than penetration of albumin (sucrose > DTPA > albumin). Uptake was about twice baseline levels for each of these agents in the 3 dose LPS (more inflamed) mice. However, in the one dose LPS (less inflamed) mice, sucrose more readily showed BBB disruption than did DTPA and DTPA more readily showed disruption than albumin (sucrose > DTPA > albumin). Linear regression analysis showed good correlations between BBB disruption as measured between albumin and DTPA (r = 0.783) and between DTPA and sucrose (r = 0.623). However, Bland-Altman analysis showed discordance between albumin and DTPA in the mice with the greatest disruption. Bland-Altman analysis also showed that disruption to sucrose was greater at any given level of inflammation than to DTPA. These subtle differences support the view that the BBB can become disrupted in different ways and that agents, which differ in size and/or structure, may vary subtly in the type or mechanism of disruption that they measure.