Protective effects of (-)-epigallocatechin-3-gallate on D-galactose-induced neuronal apoptosis in mice

BACKGROUND: The neuroprotective effects of (-)-epigallocatechin-3-gallate (EGCG), the mainpolyphenolic constituent of green tea, have been widely reported. However, the action mechanisms,in particular in D-galactose-induced aging mice, remain poorly understood.OBJECTIVE: The present study investigated the protective effects of EGCG onD-galactose-induced hippocampus neuronal apoptosis in aging mice, as well as the relationship withexpression of p75ICD, JNK2, and p53 proteins.DESIGN, TIME AND SETTING: A randomized, controlled, molecular biological, animal experimentwas performed at the Laboratory of Pharmacology, Pharmaceutical College of China MedicalUniversity, China, from September 2006 to July 2008.MATERIALS: D-galactose and EGCG (Sigma, USA), as well as terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick-end labeling (TUNEL) In Situ Cell Apoptosis Detection Kit(Promega, USA), were used in this study.METHODS: A total of 64 mice were equally and randomly divided into D-galactose model, low-doseEGCG, high-dose EGCG, and control groups. Mice in the D-galactose model, low-dose EGCG,and high-dose EGCG groups were subcutaneously injected with 3% D-galactose (150 mg/kg),daily for 6 weeks, to establish a mouse model of aging. Mice in the control group were treated withsaline (5 mL/kg). At 3 weeks following injection, mice in the low-dose EGCG and high-dose EGCGgroups were orally administered EGCG at a dose of 2 mg/kg and 6 mg/kg, respectively, once a day,for 4 consecutive days. Mice in the control and D-galactose model groups received distilled water(5 mL/kg).MAIN OUTCOME MEASURES: Memory function was evaluated using a step-through passiveavoidance test. Neuronal apoptosis in the mouse hippocampus was detected using TUNEL staining.Expression levels of the intracellular domain of the p75 neurotrophin receptor (p75NTR)-p75ICD,JNK2, and p53 proteins in the hippocampus were determined using Western blot analysis.RESULTS: The aging mouse model was induced by subcutaneous injection of D-galactose, whichresulted in obvious memory impairment, increased apoptotic index, and increased proteinexpression levels of p75ICD, JNK2, and p53 in the hippocampus, compared with control mice (P <0.01). Oral EGCG administration (2 or 6 mg/kg) for 4 weeks significantly improved levels of memorydeficit in the aging mice and reduced apoptotic indices and protein expression levels of p75ICD,JNK2, and p53 in the mouse hippocampus (P < 0.01).CONCLUSION: Results from this study demonstrated increased protein expression levels ofp75ICD, JNK2, and p53, as well as increased hippocampal neuronal apoptosis in aD-galactose-induced mouse model of aging. EGCG provided protective effects againstD-galactose-induced neuronal apoptosis in the hippocampus by reducing protein expression levelsof p75ICD, JNK2, and p53 proteins in the hippocampus of aging mice.