Normobaric Hyperoxia Extends Neuro-And Vasoprotection Of N-Acetylcystein In Transient Focal Ischemia

Ischemic stroke is caused by severe arterial occlusion, resulting in local inadequate blood perfusion. Cerebral ischemia and reperfusion induced a variety of pathological changes, such as hypoxia, excitatory toxicity, oxidative stress, inflammation, acid excess, MMP activation, BBB damage, which led to the death of nerve cells and neurological dysfunction. It has been reported that NAC is a kind of antioxidant, as a precursor of glutathione, which can reduce oxidative stress and inflammatory reaction, and can decrease the brain injury induced by reperfusion when it was administered pre-ischemia. But antioxidants did not show a positive effect in stroke’s clinical trials. This motivated the scientists to seek combinational therapeutic approaches targeting injury at different stages to treat acute ischemic stroke. Little is known about the effect of post-ischemia N-Acetylcystein(NAC) administration in focal ischemia. In this study, we investigated the neuro- and vaso-protection of post-ischemia NAC administration as well as combining NAC(targeting reperfusion) with normobaric hyperoxia(NBO, targeting ischemia). Furthermore, underlying molecular mechanisms of the protection were investigated.Objective:Using a middle cerebral artery occlusion(MCAO) model to study the neuro- and vaso-protection of NAC when it was administered post-ischemia as well as combining NAC(targeting reperfusion) with normobaric hyperoxia(NBO, targeting ischemia);To explore the effective strategies of NAC in the treatment of ischemic reperfusion injury.Methods: Animals were randomly assigned into four different treatment groups: 1) air plus vehicle group, Air + Veh; 2) air plus NAC group, Air + NAC; 3) NBO plus NAC group, NBO + NAC; 4) NBO plus vehicle group, NBO +Veh. Sprague-Dawley rats weighing 270 to 290 g were anesthetized with isoflurane and subjected to middle cerebral artery occlusion(MCAO) surgery. Five min after the onset of MCAO, anesthesia was discontinued, and the rats were put into an air-tight box which was ventilated with air(21% O2, air) or a gas mixture of 95% O2+5% CO2(NBO) until the end of 2-hr MCAO. Five min before reperfusion onset, NAC at 60 mg/kg body weight or vehicle was administered to rats via intraperitoneal injection. 48 hours after reperfusion, the cerebral infarction, edema, BBB damage, oxygen free radicals, HIF-1, VEGF, PAR, PARP-1 were tested. 7 days after reperfusion, the brain shrinkage, lesion volume, neurological function score, and forelimb foot-fault-placing test were measured.Results:(1) Neuro-protection in acute phase: NAC or NBO treatments has no obvious effect on the reduction of infarction volume and hemispheric swelling volume,but combination therapy showed greater reduction by inhibit the production of oxygen free radicals as well as the PARP-1 activation.(2) Vaso-protection in acute phase: Ischemia and reperfusion resulted in the increase of blood-brain barrier permeability and degradation of tight junction protein, NAC or NBO treatment had limited effect, but combination therapy aiming at the different stages significantly reduced the damage of the blood brain barrier by inhibition of HIF-1 and VEGF.(3) The recovery of neurological function in chronic phase. Combination therapy but not NAC showed improved neurological assessment and motor function which were sustained for 7 days after reperfusion.Conclusion: Our results showed that although post-ischemia NAC administration had limited protection, combination treatment of NAC plus NBO effectively prevented BBB damage and significantly improved the outcome of brain injury, providing new evidence to support the concept that "cocktails" treatment targeting different stage provide better neuro- and vaso-protection than current individual treatment that has all failed in their clinical trials.