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(Stroke. 2005;36:1059.)
© 2005 American Heart Association, Inc.
Original Contributions |
From INSERM-Avenir (K.B., D.V., C.A.), Centre Cyceron, Université de Caen, France; CNRS UMR 6185 (K.B., M.F.-M., S.V., O.T.), Université de Caen, Centre Cyceron, France; Laboratoire de Physiopathologie de la Barrière Hémato-Encéphalique (V.B., J.B., M.-P.D., R.C.), EA 2465, Université dArtois, Faculté des sciences Jean Perrin, France; and the Department of Pharmacology (M.F.-M. current affiliation), State University of New York, Stony Brook, NY.
Correspondence to Prof Denis Vivien, INSERM-Avenir, Centre Cyceron, Université de Caen, Boulevard Becquerel, 14074 Caen Cedex, France. E-mail d.vivien{at}neuro.unicaen.fr
Background and Purpose Despite uncontroversial benefit from its thrombolytic activity, the documented neurotoxic effect of tissue plasminogen activator (tPA) raises an important issue: the current emergency stroke treatment might not be optimum if exogenous tPA can enter the brain and thus add to the deleterious effects of endogenous tPA within the cerebral parenchyma. Here, we aimed at determining whether vascular tPA crosses the bloodbrain barrier (BBB) during cerebral ischemia, and if so, by which mechanism.
Methods First, BBB permeability was assessed in vivo by measuring Evans Blue extravasation following intravenous injection at 0 or 3 hours after middle cerebral artery electrocoagulation in mice. Second, the passage of vascular tPA was investigated in an in vitro model of BBB, subjected or not to oxygen and glucose deprivation (OGD).
Results We first demonstrated that after focal permanent ischemia in mice, the BBB remains impermeable to Evans Blue in the early phase (relative to the therapeutic window of tPA), whereas at later time points massive Evans Blue extravasation occurs. Then, the passage of tPA during these 2 phases, was investigated in vitro and we show that in control conditions, tPA crosses the intact BBB by a low-density lipoprotein (LDL) receptor-related protein (LRP)-dependent transcytosis, whereas OGD leads to an exacerbation of tPA passage, which switches to a LRP-independent process.
Conclusion We evidence 2 different mechanisms through which vascular tPA can reach the brain parenchyma, depending on the state of the BBB. As discussed, these data show the importance of taking the side effects of blood-derived tPA into account and offer a basis to improve the current thrombolytic strategy.
Key Words: bloodbrain barrier stroke thrombolytic therapy tissue plasminogen activator
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