Normobaric Oxygen (NBO) Therapy Reduces Cerebral Ischemia/Reperfusion Injury through Inhibition of Early Autophagy.

Meng Wang,Yuchuan Ding,Chaitu Dandu,Xiaokun Geng,Radhika Patel,Elisha R Injeti

doi:10.1155/2021/7041290

Abstract

Objectives Normobaric oxygen (NBO) therapy has great clinical potential in the treatment of ischemic stroke, but its underlying mechanism is unknown. Our study aimed to investigate the role of autophagy during the application of NBO on cerebral ischemia/reperfusion injury. Methods Male Sprague Dawley rats received 2 hours of middle cerebral artery occlusion (MCAO), followed by 2, 6, or 24 hours of reperfusion. At the beginning of reperfusion, rats were randomly given NBO (95% O2) or room air (21% O2) for 2 hours. In some animals, 3-methyladenine (3-MA, autophagy inhibitor) was administered 10 minutes before reperfusion. The severity of the ischemic injury was determined by infarct volume, neurological deficit, and apoptotic cell death. Western blotting was used to determine the protein expression of autophagy and apoptosis, while mRNA expression of apoptotic molecules was detected by real-time PCR. Results NBO treatment after ischemia/reperfusion significantly decreased infarct volume and neurobehavioral defects. The increased expression of the autophagy markers, including microtubule-associated protein 1A light chain 3 (LC3) and Beclin 1, after ischemia/reperfusion was reversed by NBO, while promoting Sequestosome 1 (p62/SQSTM1) expression. In addition, NBO reduced cerebral apoptosis in association with alleviated BAX expression and increased BCL-2 expression. 3-MA reduced autophagy and apoptotic death but did not further improve NBO-attenuated ischemic damage. Conclusion NBO induced remarkable neuroprotection from ischemic injury, which was correlated with blocked autophagy activity.

Highlights

Physiological Parameters. ere were no significant differences in blood pH, blood glucose, PaCO2, and mean arterial pressure (MAP) between the sham, Normobaric oxygen (NBO), and room air groups
In all ischemia/reperfusion groups, infarct volumes were increased. e NBO group had significantly decreased brain infarction at different reperfusion points than the room air group (p < 0.05; Figures 1(a) and 1(b)). e neurological deficit score was significantly reduced in the NBO group after 2, 6, and 24 hours of reperfusion compared to the room air group (p < 0.05; Figure 1(c)). ese data demonstrate that after ischemia, NBO can provide quick neuroprotection with only two hours of reperfusion
After 24 hours of ischemia/reperfusion, NBO did not significantly alter the expression of autophagic markers compared with the room air. ese results suggest that NBO mainly mitigates autophagy in the early stages of reperfusion

Summary

Introduction

Ischemic stroke mortality has decreased over the past decade due to intravenous thrombolysis and mechanical thrombectomy restoring blood supply to ischemic neurons [1,2,3]. Oxygen inhalation has emerged as an effective neuroprotective strategy for restoring blood flow to an infarcted brain by increasing oxygen supply and improving microcirculation to the ischemic penumbra—a viable yet nonfunctioning area surrounding an ischemic core [8]. Previous studies with rodents have shown that short durations of NBO in the early stages of ischemia onset could extend the reperfusion time window and protect the blood-brain barrier [9,10,11]. Us far, the anti-ischemia effect of NBO has proven to improve tissue oxygenation, increase cerebral blood flow, protect the bloodbrain barrier (BBB), and decrease cell apoptosis [10, 13,14,15]. Even though NBO is believed to have neuroprotective effects, its clinical application has remained stagnant, and research on its potential mechanisms continues

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