Early blood-brain barrier (BBB) disruption resulting from excessive neurovascular proteolysis by
matrix metalloproteinases (
MMPs) is closely associated with hemorrhagic transformation events in
ischemic stroke. We have shown that normobaric
hyperoxia (NBO) treatment reduces MMP-9 increase in the ischemic brain. The aim of this study was to determine whether NBO could attenuate MMP-9-mediated early BBB disruption following
ischemic stroke. Rats were exposed to NBO (95% O(2)) or normoxia (30% O(2)) during 90-min
middle cerebral artery occlusion, followed by 3-hour reperfusion. NBO-treated rats showed a significant reduction in
Evan's blue extravasation in the ischemic hemisphere compared with normoxic rats. Topographically,
Evan's blue leakage was mainly seen in the subcortical regions including the striatum, which was accompanied by increased gelatinolytic activity and reduced immunostaining for
tight-junction protein,
occludin. Increased gelatinolytic activities and
occludin protein loss were also observed in isolated ischemic microvessels. Gel
gelatin zymography identified that MMP-9 was the main enzymatic source in the cerebral microvessels. Incubation of brain slices or isolated microvessels with purified MMP-9 revealed specific degradation of
occludin. Inhibition of MMP-9 by NBO or
MMP-inhibitor, BB1101, significantly reduced
occludin protein loss in ischemic microvessels. These results suggest that NBO attenuates early BBB disruption, and inhibition of MMP-9-mediated
occludin degradation is an important mechanism for this protection.