The Reparation And Mechanism Of EGCG On The Lead-induced Impairments Of Oxidative Stress And Synaptic Plasticity In Rat Hippocampus

Recent studies have shown that lead causes oxidative stress by inducing the generation of reactive oxygen species(ROS) and reducing the antioxidant defense system of cells,which suggests that antioxidants may play an important role in the treatment of lead poisoning.As a kind of excellent scavenger of free radicals, modulator of immune systems and chelator of heavy metal,whether Epigallocatechin-3-gallate(EGCG) have the protective effects on altered oxidative stress parameter after lead treatment in vivo and in vitro systems remains unclear.The present study was designed to elucidate whether EGCG have any protective effects on the accumulation of ROS and a decrease of mitochondrial membrane potential(⊿Ψ_m) in lead-exposed cultures of hippocampal neurons and whether EGCG could reverse the changes on redox states in rat hippocampus caused by lead exposure.Our results showed that glutathione(GSH) and superoxide dismutase(SOD) activity decreased accompanied with LTP amplitude decrease in CAl area of hippocampus in the lead-exposed group.EGCG supplementation following lead intoxication resulted in increases in the GSH and SOD levels and increases in the LTP amplitude. Malondialdehyde(MDA) levels,a major lipid peroxidation byproduct,increased following lead exposure and decreased following EGCG treatment.In hippocampal neuron culture model,lead exposure(20μM) significantly inhibited the viability of neurons which was followed by an accumulation of ROS and a decrease of⊿Ψ_m. Treatment by EGCG(10-50μM) effectively increased cell viability,decreased ROS formation and improved⊿Ψ_m in hippocampal neurons exposed to lead.These observations suggest that EGCG is a potential complementary agent in the treatment of chronic lead intoxication through its antioxidative character.Our previous study showed that EGCG has pro-oxidant effects at high concentration.Thus,in this study,we tried to examine the possible pathway of EGCG-induced cell death in cultures of rat hippocampal neurons.Our results showed that EGCG caused a rapid elevation of intracellular free calcium levels([Ca²⁺]_i) in a dose-dependent way.Exposure to EGCG dose- and time-dependently increased the production of ROS and reducedΔΨ_m as well as the Bcl-2/Bax expression ratio. Importantly,BAPTA-AM,EGTA and vitamin E could attenuate EGCG-induced apoptotic responses,including ROS generation,mitochondrial dysfunction,and finally partially prevented EGCG-induced cell death.Furthermore,treatment of hippocampal neurons with EGCG resulted in an elevation of caspase-3 and caspase-9 activities with no significant accompaniment of lactate dehydrogenase(LDH) release, which provided further evidence that apoptosis was the dominant mode of EGCG-induced cell death in cultures of hippocampal neurons.Taken together,these findings indicated that EGCG induced hippocampal neuron death through the mitochondrion-dependent pathway.The present study was designed to elucidate whether EGCG protected altered oxidative stress parameters in Wistar rats and cultures of hippocampal neurons exposed to lead.The hypothesis was evidenced both in EGCG-treated Wistar rats and cell models exposed to lead.Therefore it can be deduced that the increased cell viability andΔψ_m,the decreased ROS accumulation,the increases in the GSH and SOD levels and increases in the LTP amplitude in lead-exposed cultures of hippocampal neurons and lead-exposed Wistar rats,respectively could reflect the antioxidant action of EGCG in lead-treated Wistar rats and neurons.The investigation also placed EGCG at high doses into radical-generating toxicological agents. Therefore,much consideration to safety should be required when EGCG are used as therapeutical reagents or nutrition supplement compounds and the optimum dosage and duration of treatment to obtain better clinical recoveries should also be explored.