AUTHOR=Chi Oak Z. , Liu Xia , Cofano Sean , Patel Nikhil , Jacinto Estela , Weiss Harvey R. 

TITLE=Rapalink-1 Increased Infarct Size in Early Cerebral Ischemia–Reperfusion With Increased Blood–Brain Barrier Disruption

JOURNAL=Frontiers in Physiology

VOLUME=Volume 12 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2021.706528

DOI=10.3389/fphys.2021.706528

ISSN=1664-042X

ABSTRACT=It has been reported that the mTOR pathway is involved in cerebral ischemia-reperfusion injury.  One of the important pathological changes during reperfusion after cerebral ischemia is disruption of blood-brain barrier (BBB).  Rapamycin, a first generation mTOR inhibitor, produces divergent effects on neuronal survival and alteration in BBB disruption.  Here, we investigated how Rapalink-1, a third generation mTOR inhibitor, would affect neuronal survival and BBB disruption in the very early stage of cerebral ischemia-reperfusion that is within the thrombolysis therapy time window.  Middle cerebral artery occlusion (MCAO) was performed in rats under isoflurane anesthesia with controlled ventilation.  Two mg/kg of Rapalink-1 or vehicle was administered intraperitoneally 10 min after MCAO.  After one hour of MCAO and two hours of reperfusion, the transfer coefficient (Ki) of 14C-α-aminoisobutyric acid (104 Da) and the volume of 3H-dextran (70,000 Da) distribution were determined to assess the degree of BBB disruption.  At the same time points, phosphorylated S6 (Ser240/244) and Akt (Ser473) as well as MMP2 protein level were determined by Western blot along with the infarct size using tetrazolium stain.  Rapalink-1 increased the Ki in the ischemic-reperfused cortex (+23 %), p < 0.05) without a significant change in the volume of dextran distribution.  Rapalink-1 increased the percentage of cortical infarct out of the total cortical area (+41 %, p < 0.005).  Rapalink-1 significantly decreased phosphorylated S6 as well as Akt to half the level of the control rats in the ischemic-reperfused cortex, which suggests both mTORC1 and mTORC2 were inhibited.  The MMP2 level was increased suggesting that BBB disruption could be aggravated by Rapalink-1.  Taken together, our data suggest that inhibiting both mTORC1 and mTORC2 by Rapalink-1 could worsen the neuronal damage in the early stage of cerebral ischemia-reperfusion and that aggravation of BBB disruption could be one of the contributing factors.