Background:
Tissue-type plasminogen activator (t-PA) is approved for treatment of ischemic stroke patients, but it may increase the risk of intracranial bleeding (ICB). Matrix metalloproteinases (MMPs), which can be activated through the plasminogen/plasmin system, may contribute to ICB after ischemic stroke.
Objectives:
To explore the contribution of plasminogen, MMP-3 and MMP-9 to ICB associated with t-PA treatment after ischemic stroke.
Methods:
Using a thrombotic middle cerebral artery occlusion (MCA-O) model, ICB was studied in mice with genetic deficiencies of plasminogen (Plg
−/ −
), stromelysin-1 (MMP-3
−/ −
) or gelatinase B (MMP-9
−/ −
) and their corresponding wild-type (WT) littermates. t-PA (10 mg/kg) or its equivalent volume of solvent was administered intravenously 4 hours after MCA-O. The induction of MMP-3 and MMP-9 was also studied in C57BL/6 WT mice.
Results:
In MMP-3
+/+
WT mice given solvent, ICB was 4.3 ± 2.9 mm
3
(mean ± SD), which was significantly increased with tPA treatment to 9.7 ± 4.7 mm
3
(P<0.05), whereas ICB in MMP-3
−/ −
mice was not altered by t-PA treatment (5.7 ± 2.7 mm
3
, as compared to 5.1 ± 1.8 mm
3
without tPA; n = 7–9 in each group). ICB induced by t-PA was significantly less in Plg
−/ −
(5.7 ± 3.9 mm
3
) than in WT mice (8.8 ± 3.2 mm
3
, p<0.05) but ICB by t-PA in MMP-9
−/ −
(8.3 ± 2.3 mm
3
) was comparable with that in WT (8.3 ± 3.1 mm
3
; n=8 –12 in each group). Administration of the broad-spectrum MMP inhibitor GM6001 after t-PA treatment reduced ICB significantly in MMP-3
+/+
(from 6.4 ± 1.9 mm
3
to 4.1 ± 1.9 mm
3
, p<0.05) but not in MMP-3
−/ −
mice (2.2 ± 0.6 mm
3
without versus 2.9 ± 1.5 mm
3
with GM6001; n=6 – 8 in each group). MMP-3 expression was significantly enhanced at the ischemic hemisphere; with placebo treatment, it was expressed only in neurons, whereas it was upregulated in endothelial cells with t-PA treatment. Although MMP-9 expression was also significantly enhanced at the ischemic brain, the amount and the distribution were comparable in mice with and without t-PA treatment.
Conclusions:
Our data with gene deficient mice suggest that plasminogen and MMP-3 are relatively more important than MMP-9 for the increased ICB induced by t-PA treatment of ischemic stroke.
Role of Tissue-Type Plasminogen Activator in Ischemic Stroke
