Normobaric hyperoxia combined with minocycline provides greater neuroprotection than either alone in transient focal cerebral ischemia

Normobaric hyperoxia (NBO), which maintains penumbral oxygenation, reduces brain injury during cerebral ischemia, and minocycline, a tetracycline derivative, reduces reperfusion injury, including inflammation, apoptosis and matrix metalloproteinases (MMPs) activation. Since they have different mechanisms of action, we hypothesized that combining them would provide greater neuroprotection. To test the hypothesis, we evaluated the neuroprotective effects of the combination of NBO with minocycline. Male Sprague-Dawley rats were exposed to NBO (95% O₂) or normoxia (21% O₂) during 90-min filament occlusion of the middle cerebral artery, followed by 48h of reperfusion. Minocycline (3mg/kg) or vehicle was intravenously administered to rats 15min after reperfusion onset. Treatment with NBO and minocycline alone resulted in 36% and 30% reductions in infarction volume, respectively. When the two treatments were combined, there was a 68% reduction in infarction volume. The combination therapy also significantly reduced hemispheric swelling, which was absent with monotherapy. In agreement with its greater neuro- and vasoprotection, the combination therapy showed greater inhibitory effects on MMP-2/9 induction, occludin degradation, caspase-3 and -9 activation and apoptosis inducing factor (AIF) induction in ischemic brain tissue. Our results show that NBO plus minocycline effectively reduces brain injury in transient focal cerebral ischemia with protection due to inhibition on MMP-2/9-mediated occludin degradation and attenuation of caspase-dependent and independent apoptotic pathways.