Improving Microcirculatory Reperfusion Reduces Parenchymal Oxygen Radical Formation and Provides Neuroprotection.
BACKGROUND AND PURPOSE
Reperfusion is the most significant determinant of good outcome after ischemic stroke. However, complete reperfusion often cannot be achieved, despite satisfactory recanalization. We hypothesized that microvascular protection was essential for achieving effective reperfusion and, hence, neuroprotection. To test this hypothesis, we have developed an in vivo model to differentially monitor parenchymal and vascular reactive oxygen species (ROS) formation. By comparing the ROS-suppressing effect of N-tert-butyl-α-phenylnitrone (PBN) with its blood-brain barrier impermeable analog 2-sulfo-phenyl-N-tert-butylnitrone (S-PBN), we assessed the impact of vascular ROS suppression alone on reperfusion and stroke outcome after recanalization.


METHODS
The distal middle cerebral artery was occluded for 1 hour by compressing with a micropipette and then recanalized (n=60 Swiss mice). ROS formation was monitored for 1 hour after recanalization by intravital fluorescence microscopy in pial vasculature and cortical parenchyma with topically applied hydroethidine through a cranial window. PBN (100 mg/kg) or S-PBN (156 mg/kg) was administered shortly before recanalization, and suppression of the vascular and parenchymal hydroethidine fluorescence was examined (n=22). Microcirculatory patency, reperfusion, ischemic tissue size, and neurological outcome were also assessed in a separate group of mice 1 to 72 hours after recanalization (n=30).


RESULTS
PBN and S-PBN completely suppressed the reperfusion-induced increase in ROS signal within vasculature. PBN readily suppressed ROS produced in parenchyma by 88%. S-PBN also suppressed the parenchymal ROS by 64% but starting 40 minutes later. Intriguingly, PBN and S-PBN comparably reduced the size of ischemic area by 65% and 48% (P>0.05), respectively. S-PBN restored the microvascular patency and perfusion after recanalization, suggesting that its delayed parenchymal antioxidant effect could be secondary to improved microcirculatory reperfusion.


CONCLUSIONS
Promoting microvascular reperfusion by protecting vasculature can secondarily reduce parenchymal ROS formation and provide neuroprotection. The model presented can be used to directly assess pharmacological end points postulated in brain parenchyma and vasculature in vivo.
['Taskiran-Sag|Aslihan|A|', 'Yemisci|Muge|M|', 'Gursoy-Ozdemir|Yasemin|Y|', 'Erdener|Sefik Evren|SE|', 'Karatas|Hulya|H|', 'Yuce|Deniz|D|', 'Dalkara|Turgay|T|']
D000818:Animals D001557:Benzenesulfonates D001812:Blood-Brain Barrier D002540:Cerebral Cortex D002560:Cerebrovascular Circulation D003497:Cyclic N-Oxides D005456:Fluorescent Dyes D020244:Infarction, Middle Cerebral Artery D000069416:Intravital Microscopy D008297:Male D051379:Mice D008833:Microcirculation D008856:Microscopy, Fluorescence D018696:Neuroprotective Agents D010617:Phenanthridines D010841:Pia Mater D017382:Reactive Oxygen Species D015424:Reperfusion
neuroprotection reactive oxygen species animals ischemia nitrones no-reflow phenomenon reperfusion injury