Brain Selective Hypothermia With Intra-arterial Cold Infusions Plus Early Normobaric Hyperoxygenation for Neuroprotection in Experimental Acute Ischemic Stroke

Introduction: Characterized by strong and brain-selective cooling performance paired with only minor (systemic) adverse effects, intra-arterial cold infusions (IACI) into brain-supplying arteries have been reported as neuroprotective in experimental acute ischemic stroke (AIS). Combining normobaric hyperoxygenation (NBHO) with IACI might potentiate neuroprotection by increasing oxygen supply and, at the same time, reducing metabolism during ischemia and mitigating oxidative stress during reperfusion. Methods: To investigate potentially synergistic effects, we tested NBHO+IACI vs. NBHO vs. IACI vs. controls in a transient (60 minutes) filament middle cerebral artery occlusion (MCAO) rat model (n = 16 per group). NBHO (100 % oxygen) was initiated 10 minutes after MCAO, continuous IACI (0 °C, 12 mL) into the internal carotid artery were started two minutes prior to reperfusion, both treatments were stopped (simultaneously) after 65 and 15 minutes. Infarct and edema growth were estimated by MRI incl. perfusion, diffusion and T2 during ischemia, at 24 hours and two weeks. Neurological tests were performed for functional outcome. NeuN, IB4 and GFAP staining was used to illustrate selective neuron loss (SNL), microglia activation and gliosis at two weeks. Effect of arterial on penumbral oxygenation was evaluated with pre/post-treatment blood gas analyses and MBA1 staining at 24 hours. Results: In accordance with previous studies, NBHO reduced infarct growth (primary endpoint; T2 infarct at two weeks minus perfusion ischemic core during MCAO) by 50 % vs. controls. Cerebral edema, penumbral oxygenation and functional outcome as well as SNL, microglia activation and gliosis were also improved or reduced. In contrast, IACI were not beneficial and no synergistic neuroprotection was found for NBHO+IACI. Conclusions: Our findings confirm strong NBHO-mediated neuroprotection in AIS, while IACI were not neuroprotective. Longer duration of brain-selective hypothermia might be the key, but IACI volume is the limiting factor. MRI, functional and histological results will be discussed in the context of current literature.