Protective Effects Of Gypenoside Against Glutamate-Induced Hippocampus Injury In Rats

ObjectiveAt present,glutamate is known to be a kind of important excitatory neurotransmitters,participates in many nervous functions,such as nourishing the nervous system,promoting the growth and development of neurons and the axons,on the other hand,it is also one kind of neurotoxins.Too much glutamate present in nervous system will induce brain damage.The mechanism of some neurodegerative diseases,such as Alzheimer's Disease(AD),Parkinson's disease(PD) are related with the neurotoxin.First,glutamate has excitatory that can lead to the neurocytes damage with many factors,such as oxygen-derived free radicals.The second,inhibition of glutamate/cystine transporter was believed to be a contributive mechanism.Gynostemma pentaphyllum(Thunb)Makino is a widespread herb in South China. The molecular components responsible for its function are Gypenosides(GP).It was reported that Gypenosides(GP) have many pharmacological activities including inhibiting carcinoma,anti-aging,anti-oxidative stress in experimental animal models. But gypenosides protective activities have not been researched on the nervous system either in vivo or in vitro,the research field involved in the protective effects of gypenosides on glutamate-induced toxicity remains to be untouched.This experiment was carried on using the hippocampus damage rat animal which were injected with glutamate through the lateral ventricle,through detection of the MDA content in the homogenate of hippocampus,the activity of SOD and GSH-Px and the hydroxyl radical generation capacity,theα-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor(AMPA) receptor subunit 2(GluR2) protein expression level,further discusses the function and mechanism of GP anti- glutamate resulting in nerve injury,provide the experiment data for using GP to prevent nerve injury and central nervous system recession vigorous sickness created by massive releases of glutamate.MethodsOne hundred male Wistar rats were used in the experiment.After fed for a week, animals were randomly divided into five groups:sham-operation group,glutamateinduced injury group,GP low(200 mg/kg),medium(400mg/kg) and high(800mg /kg) dose group.GP was administered by intra-gastric administration for10d.2h after injected with glutamate through the lateral ventricle,the homogenate of hippocampus were collected and the MDA,SOD,GSH-Px activity and the hydroxy radical generation capacity were determined;the pathologic changes in hippocampus of rats were observed by HE stain.Using Immuohistochemistry assay and RT-PCR methods, the changes of AMPA receptor GluR2 subunit mRNA and protein expressions were observed in hippocampal neurons of rats induced by glutamate.ResultsAnimals treated with GP had a significant decrease in MDA concentration and hydroxy radical generation capacity compared with the glutamate-induced injury group(P＜0.01).The activity of SOD and GSH-Px were obviously increased (P＜0.01) by GP treatment;the neuron death and denaturation in hippocampus were significantly decreased in GP group rats.The results suggested that the expression of AMPA receptor GluR2 subunit mRNA and protein were decreased in hippocampus compared with the sham-operation group.And the expression of AMPA receptor GluR2 subunit mRNA and protein in GP group rats significantly increased in comparision with the glutamate-induced injury group(P＜0.01).The results of the image analysis and the statistics indicated that the average optical density of GluR2-IR cells in the glutamate-induced injury groups,was significantly decreased when compared with the sham-operation group(P＜0.01).The protective effects of GP 400mg/kg is of the most obvious.ConclusionGP can enhance the expression of mRNA and protein of GluR2 in AMPA receptor, then decrease the neuron system damage induced by glutamate,meanwhile decrease the oxidative nervous system damage induced by glutamate and exert it protective function.