Astragaloside ? Protects Against Cerebral Ischemia/reperfusion Injury Via AKT-mTOR-dependent Autophagy

Stroke is one of the most common diseases that cause death and disability all over the world.The guideline for stroke therapy is restoring the cerebral blood flow(reperfusion)as soon as possible by thrombolysis,protecting the survival brain tissue in the ischemic penumbra and preventing cerebral secondary injury.Tissue-type plasminogen activator(tPA)is the only FDA-approved treatment for stroke.However,clinical use of tPA was constrained to roughly 3% of eligible patients because of a narrow 3-4.5 h time window for safe administration.If the time of thrombolysis exceeds three hours,the risk rate of hemorrhagic transformation and fatal cerebral edema caused by cerebral ischemia/reperfusion(I/R)injury will be increased.Astragalus membranaceus was routinely used in traditional Chinese medicine for patients who suffered stroke or chronic debilitating disease.Sometimes,it was even used for normal people who want to further improve their vital function.It is demonstrated that astragalus membranaceus has the potential of inhibiting the oxidative stress,antiedema and anti-apoptosis.Astragaloside IV is a purified small molecular saponin from astragalus membranaceus.It is one of the major components of astragalus membranaceus.Pharmacological studies have demonstrated that astragaloside IV can exert the effect of decreasing oxidative stress and infarction volume.Therefore,this study mainly discusses the role of Astragaloside IV in ischemic cerebrovascular disease.72 healthy SD rats were randomly divided into sham operation,model,antophagy inducer(rapamycin,1 mg/kg)and Astragaloside IV(20 mg/kg,50 mg/kg and 100 mg/kg)groups.The rat model was established by middle cerebral artery occlusion(MCAO).Astragaloside IV or rapamycin was intragastrical administration 60 min before cerebral ischemia,respectively.24 h after reperfusion,brains were collected and the tissue structure of cerebral and the apoptosis of neural cells was detected by HE staining and TUNEL method respectively.Cerebral infarction size in rats after treatment of I/R is determined with TTC method.Transmission electron microscopy observed the autophagosomes.In addition,the expressions of Bcl-2,caspase-3,LC3I/II,Beclin1,ATG5,p62,LAMP2,AKT/p-AKT and mTOR/p-mTOR were determined by Western blot.Edema and the nucleus disappeared were observed in hippocampus in model group,and Astragaloside IV significantly reduced these injuries compared with model group,as well as rapamycin treatment.Cerebral infarction size of rapamycin and Astragaloside IV-treated rats was obviously smaller than that of I/R rats.The number of apoptotic neural cells and the expression of Caspase-3,p62,p-AKT and p-mTOR proteins were significantly increased,but the number of autophagic neural cells and the expression of Bcl-2,LC3 II,Beclin1,ATG5 and LAMP2 proteins were decreased,in model than in sham group.Compared with the model group,the number of apoptotic neural cells and the expression of Caspase-3,p62,p-AKT and p-mTOR proteins were significantly lower in Astragaloside IV group,but the number of autophagic neural cells and the expression of Bcl-2,LC3 II,Beclin1,ATG5 and LAMP2 proteins were significantly increased.In summary,the present study demonstrates that Astragaloside IV could protect against neural cell injury in cerebral ischemia/reperfusion rats,which may be related to AKT/mTOR-dependent autophagy.