Korean J Radiol.  2016 Oct;17(5):715-724. 10.3348/kjr.2016.17.5.715.

Assessment of Blood-Brain Barrier Permeability by Dynamic Contrast-Enhanced MRI in Transient Middle Cerebral Artery Occlusion Model after Localized Brain Cooling in Rats

• Kim ES
• Lee SK
• Kwon MJ
• Lee PH
• Ju YS
• Yoon DY
• Kim HJ
• Lee KS

• KMID: 2458063
• DOI: http://doi.org/10.3348/kjr.2016.17.5.715

Abstract

OBJECTIVE
The purpose of this study was to evaluate the effects of localized brain cooling on blood-brain barrier (BBB) permeability following transient middle cerebral artery occlusion (tMCAO) in rats, by using dynamic contrast-enhanced (DCE)-MRI.
MATERIALS AND METHODS
Thirty rats were divided into 3 groups of 10 rats each: control group, localized cold-saline (20℃) infusion group, and localized warm-saline (37℃) infusion group. The left middle cerebral artery (MCA) was occluded for 1 hour in anesthetized rats, followed by 3 hours of reperfusion. In the localized saline infusion group, 6 mL of cold or warm saline was infused through the hollow filament for 10 minutes after MCA occlusion. DCE-MRI investigations were performed after 3 hours and 24 hours of reperfusion. Pharmacokinetic parameters of the extended Tofts-Kety model were calculated for each DCE-MRI. In addition, rotarod testing was performed before tMCAO, and on days 1-9 after tMCAO. Myeloperoxidase (MPO) immunohisto-chemistry was performed to identify infiltrating neutrophils associated with the inflammatory response in the rat brain.
RESULTS
Permeability parameters showed no statistical significance between cold and warm saline infusion groups after 3-hour reperfusion 0.09 ± 0.01 min-1 vs. 0.07 ± 0.02 min-1, p = 0.661 for K(trans); 0.30 ± 0.05 min-1 vs. 0.37 ± 0.11 min-1, p = 0.394 for kep, respectively. Behavioral testing revealed no significant difference among the three groups. However, the percentage of MPO-positive cells in the cold-saline group was significantly lower than those in the control and warm-saline groups (p < 0.05).
CONCLUSION
Localized brain cooling (20℃) does not confer a benefit to inhibit the increase in BBB permeability that follows transient cerebral ischemia and reperfusion in an animal model, as compared with localized warm-saline (37℃) infusion group.

Keyword

Brain; Ischemia; Middle cerebral artery; Blood-brain barrier; Permeability; Dynamic contrast-enhanced-MRI; DCE-MRI

MeSH Terms

Animals
Blood-Brain Barrier/*physiology
Brain/diagnostic imaging
Disease Models, Animal
Hypothermia, Induced/*methods
Infarction, Middle Cerebral Artery/diagnostic imaging/pathology/*physiopathology
Ischemic Attack, Transient/diagnostic imaging/physiopathology
Magnetic Resonance Imaging/methods
Male
Permeability
Rats, Sprague-Dawley
Reperfusion Injury/diagnostic imaging/physiopathology/prevention & control
Sodium Chloride
Sodium Chloride

Figure

• 

  Fig. 1 Brain MRI of mouse. Contrast enhancement can be seen at infarcted area of left brain (A, D, G). Color coded permeability maps of Ktrans obtained 3 hours (B, E, H) and 24 hours (C, F, I) after reperfusion show increased permeability in infracted area. Mean Ktrans values were 0.15 ± 0.03 min-1, 0.12 ± 0.02 min-1 in control groups, 0.07 ± 0.02 min-1, 0.09 ± 0.02 min-1 in warm saline group and 0.09 ± 0.01 min-1, 0.05 ± 0.02 min-1 in cold saline group.

• 

  Fig. 2 Permeability changes at 2 different time points after reperfusion (mixed model). A. Ktrans (min-1) shows significant decrease in control group, as compared with warn and cold saline group (control vs. cold saline infusion [p = 0.0095], control vs. warm saline infusion [p = 0.017]). Permeability parameters show no statistical significance between cold and warm saline infusion groups (p = 0.661). B. Kep (min-1) is significantly lower in cold saline infusion group, as compared with control group (p = 0.046). Permeability parameters show no statistical significance between cold and warm saline infusion groups (p = 0.394), and between control and warm saline groups (p = 0.163).

• 

  Fig. 3 Immunohistochemical staining of mouse brain. A. High-power views (400 ×) of hematoxylin and eosin (H&E)-stained sections. In cool-saline group, foamy macrophages and inflammatory cells in perimicrovascular area are decreased, as compared with control and warm saline group. B. High-power views (400 ×) of myeloperoxidase (MPO)-immunostained sections of rat brain. In control group, MPO-positive neutrophils (arrow) infiltrate perimicrovascular area. There are decreases in number of MPO-positive cells (arrows) in warm-saline and cold-saline groups, as compared with control group.

• 

  Fig. 4 Comparison of percentage of MPO-positive cells in total mixed population of inflammatory cells. Each box plot represents mean and standard deviation and line through box plot indicates range. Percentage of MPO-positive cells is significantly higher in control group than in cold-saline and warm-saline groups (p < 0.05). In addition, percentage of MPO-positive cells in cold-saline group is significantly lower than that of warm-saline group (p < 0.05). MPO = myeloperoxidase

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