The Neuroprotective Effect Of Octreotide And The Underlying Mechanism In Experimental Ischemic Stroke

Objectives: Stroke is one of the leading causes of mortality and morbidity.Ischemic stroke accounts for approximately80-85%of all cases. Brain injuryfollowing stroke, associated with aggravation of the illness and the recoveryof patients, results from the complex interplay of multiple pathways includinginflammation, oxidative stress, mitochondrial inhibition, Ca2+overload,apoptosis and so on. It’s well known that oxidative stress plays a critical rolein cerebral ischemic pathogenesis. Overexpression of reactive oxygen species(ROS)/reactive nitrogen species (RNS) results from brain ischemia, far morethan the ability of endogenous antioxidant system to removal them, led toreduction of many endogenous antioxidant enzyme activity in the brain tissueand exacerbate the brain injury. Recent studies reviewed that nuclear factorerythroid2-related factor2(Nrf2)/antioxidant response element (ARE) signalpathway was one of the major mechanisms in the cellular defense againstoxidative and electrophilic stress. Nrf2is normally localized to the cytoplasmwith inactive form, tethered to the regulatory protein Keap1. Oxidative stress,or electrophilic agents can modify key conformation in the Keap1-Nrf2complex, allowing dissociation and nuclear translocation of Nrf2. ActivatedNrf2specifically targets corresponding sites with ARE, led to target geneexpression of ARE. Activation of the Nrf2/ARE signaling pathway can inducea variety expression of gene of detoxification enzymes and elimination ofROS and electrophilic agents, increase activity of antioxidant enzymes andenhance cellular antioxidant capacity. Recent clinical researches found thatoctreotide therapy led to significant improvements in patients with ischemicand idiopathic dilated cardiomyopathy. Experimental studies showed thatoctreotide could ameliorate liver, retinal, pancreatic ischemia or ischemia-reperfusion injury through antioxidant mechanisms. Besides, octreotide exert antidepressant-like activity in chronic mild stress via antioxidant effect.However, little is known regarding the neuroprotective effect of octreotide inischemic stroke and the underlying mechanism. The purpose of this study is toinvestigate the neuroprotetion of octreotide in experimental ischemic strokeinduced by permanent middle cerebral artery occlusion (pMCAO) and theeffect on the expression of Nrf2and HO-1and the activites of MDA.Methods: Healthy, adult, male Sprague-Dawley rats were subjected tomodified right permanent middle cerebral artery occlusion (pMCAO), asdescribed by Longa previously. Rats were randomly assigned to four groups:Sham operated group (Sham), MCAO group, OCT-L group (MCAO+octreotide50μg/kg) and OCT-H group (MCAO+octreotide100μg/kg).Octreotide was injected intraperitoneally immediately after MCAO, Sham andMCAO groups accepted equal volumn normal saline. At24h after MCAO,neurological deficit was evaluated using a modified six point scale,2to4scores were brought into this study. Brain water content was measured by wet-dry method, infarct size were analyzed with2,3,5-triphenyltetrazoliumchloride (TTC) staining. Immunohistochemistry and western blotting wereused to analyze the expression of Nrf2and HO-1; activites of malondiadehyde(MDA) content were measured by spectrophotometer.Results:1Rats in Sham group performed well, while rats in MCAO group, OCT-Lgroup and OCT-H group showed a right palsy. Neurological deficit score inOCT-H group was decreased compared with MCAO group（P <0.05）.There was no significant difference in the neurological deficit score betweenOCT-L group and MCAO group（P>0.05）.2The brain water content of ipsilateral hemispheres of Sham group is79.49%±0.40%, while it’s significant higher in MCAO group:85.31±0.93%. Compared with MCAO group, OCT-L and OCT-H group showed asignificant decline in the brain water content in the ischemic hemisphere(MCAO group vs. OCT-L group:85.31±0.93%vs.84.00±0.74%, P <0.05;MCAO group vs. OCT-H group:85.31±0.93%vs.82.93±1.00%, P <0.05). 3No lesion was observed in Sham group. High dose of octreotidesignificantly reduced the infarct volume after MCAO（OCT-H vs. MCAO:30.56%±4.01%vs.43.16%±2.32%，P <0.05）. However, the infarctvolume was not significantly decreased in OCT-L group.4The number of Nrf2and HO-1positive cells was significantly increasedby high dose of octreotide (P <0.05). The expression of Nrf2and HO-1inprotein level was increased significantly in OCT-H group (P <0.05). Lowdose of octreotide also upregulated the positive cells and protein levels of Nrf2and HO-1, but the trend is unstable.5Octreotide decreased the activities of MDA compared with MCAO group(P <0.05).Conclusions： This work shows that octreotide could protect the brainagainst focal ischemic injury, ameliorate the neurological deficit, attenuate thebrain edema and decrease the infarct size, this may be through up-regulationexpression of Nrf2、HO-1, down-regulation MDA activities.