Early Ischemic Blood Brain Barrier Damage: A Potential Indicator for Hemorrhagic Transformation Following Tissue Plasminogen Activator (tPA) Thrombolysis?

Expression of tissue plasminogen activator (tPA) substantially determines endothelial-dependent fibrinolysis. We used a blood-brain barrier (BBB) model to analyze regulation of brain capillary endothelial tPA and its inhibitor, plasminogen activator inhibitor-1 (PAI-1). This model consists of coculture of murine astrocytes with bovine brain capillary endothelial cells grown as capillary-like structures (CS); after 1 week, astrocytes become extensively associated with CS, and the BBB-associated enzyme γ-glutamyl transpeptidase is present. We measured tPA and PAI-1 mRNA and tPA activity in this model. Reverse transcription-polymerase chain reaction (RT-PCR) studies showed similar tPA and PAI-1 mRNA levels after 1 day mono-culture (endothelial cells only) versus astrocyte-endothelial coculture preparations. After 7 days (i.e., when elements of the BBB are present), astrocyte-endothelial cocultures (compared with endothelial mono-cultures) showed a 50.7% ± 27.1% (mean ± SD) reduction in tPA mRNA ( P < 0.03) and a 183.3% ± 86.9% increase in PAI-1 mRNA expression ( P < 0.02). Moreover, 7-day cocultures demonstrated reduced tPA activity compared with mono-cultures (14.6 ± 2.9 IU/mL versus 30.2 ± 7.7 IU/mL, P < 0.01); 1-day cocultures and mono-cultures had similar tPA activity. These findings demonstrate that astrocytes regulate brain capillary endothelial expression of tPA when elements of the BBB phenotype are present in this model. These data suggest an important role for astrocytes in the regulation of brain capillary endothelial fibrinolysis.

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Quantitative MRI Reveals the Elderly Ischemic Brain is Susceptible to Increased Early Blood—Brain Barrier Permeability Following Tissue Plasminogen Activator Related to Claudin 5 and Occludin Disassembly

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.2011.79 ◽

2011 ◽

Vol 31 (9) ◽

pp. 1874-1885 ◽

Cited By ~ 26

Author(s):

Jaspreet Kaur ◽

Ursula I Tuor ◽

Zonghang Zhao ◽

Philip A Barber

Keyword(s):

Plasminogen Activator ◽

Tissue Plasminogen Activator ◽

Blood Brain Barrier ◽

The Elderly ◽

Quantitative Mri ◽

Brain Barrier ◽

Ischemic Brain ◽

Blood Brain ◽

Brain Barrier Permeability ◽

Tissue Plasminogen

Great uncertainty exists as to whether aging enhances the detrimental effects of tissue plasminogen activator (tPA) on vascular integrity of the ischemic brain. We hypothesized that tPA treatment would augment ischemic injury by causing increased blood-brain barrier (BBB) breakdown as determined by quantitative serial T1 and T2 magnetic resonance imaging (MRI), and the transfer constant for gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA) from blood to brain in aged (18 to 20 months) compared with young (3 to 4 months) Wistar rats after middle cerebral artery occlusion, mediated through the acute disassembly of claudin 5 and occludin. Increased T2 values over the first hour of postreperfusion were independently augmented following treatment with tPA ( P < 0.001) and aging ( P < 0.01), supporting a synergistic effect of tPA on the aged ischemic brain. Blood-brain barrier permeability for Gd-DTPA ( KGd) was substantial following reperfusion in all animal groups and was exacerbated by tPA treatment in the elderly rat ( P < 0.001). The frequency of hematoma formation was proportionately increased in the elderly ischemic brain ( P < 0.05). Both tPA and age independently increased claudin 5 and occludin phosphorylation during ischemia. Early BBB permeability detected by quantitative MRI following ischemic stroke is enhanced by increased age and tPA and is related to claudin 5 and occludin phosphorylation.

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