Closure of the Blood-Brain Barrier by Matrix Metalloproteinase Inhibition Reduces rtPA-Mediated Mortality in Cerebral Ischemia With Delayed Reperfusion

Abstract

Intravenous recombinant tissue plasminogen activator (rtPA) can be beneficial in ischemic stroke despite an increased risk of hemorrhage and potential neurotoxic effects. We hypothesized that rtPA-mediated adverse effects depend on the timing of reperfusion and injury to the blood-brain barrier (BBB). Male Wistar rats had middle cerebral artery occlusion (MCAO) by intraluminal thread placement. Intervals of ischemia/reperfusion, respectively, in hours were 0/18, 1.5/16.5, 3/15, 6/12, 18/0, and 6/1. Animals received either rtPA or saline for 1 hour at the time of reperfusion or, for the 18/0 trial, starting 1 hour after MCAO. Outcome parameters were mortality, matrix metalloproteinase-2 and -9 (MMP-2 and -9) concentrations, tissue hemoglobin, and brain water content. We analyzed the permeability of the BBB by using the brain 14C[sucrose] uptake method. Effects of the MMP inhibitor BB-94 on the BBB without rtPA treatment and on mortality with rtPA were tested in animals with 6/1 and 6/12, respectively. In delayed reperfusion (6/12), rtPA increased mortality from 17% to 83% (P<0.01) without significantly affecting other outcome parameters. In 6/1, sucrose uptake in the ischemic hemisphere was markedly increased (8.80+/-1.14% vs 2.15+/-0.26%; P<0.01). This uptake was reduced by treatment with BB-94 (3.95+/-1.48%, P<0.01). Furthermore, BB-94 reduced rtPA-mediated mortality in 6/12 to 33% (P<0.05). rtPA-mediated mortality in delayed reperfusion is associated with early opening of the BBB. Closure of the BBB with BB-94 given before rtPA treatment reduced mortality, suggesting that treatment with MMP inhibitors might reduce the risk associated with thrombolysis.