Protective effects of tea polyphenols on cerebral nerve cell apoptosis induced by d-galactose and beta-amyloid peptide 25-35

BACKGROUND: Some researches demonstrate that tea polyphenols (TP) has protective effects on neurotoxicity of hippocampal nerve cells induced by β-amyloid peptide (Aβ), 6-hydroxydopamine (6-OHDA) and oxidative substances. In addition, clinical preliminary examination indicates that TP plays a certain preventive and therapeutic effects on the reduction of recognition function in high-risk population with Alzheimer disease (AD); however, its target and mechanism are still hot topics. OBJECTIVE: To observe the interfering effects of TP on cerebral nerve cell apoptosis induced by D-galactose and Aβ25-35 in mice. DESIGN: Randomized controlled animal study. SETTING: Department of Pharmacology, Pharmacological College of Jinan University. MATERIALS: The experiment was carried out in the Experimental Center of Jinan University from September 2004 to January 2005. A total of 90 healthy Kumning mice, aged 2 months, each gender in half, weighing 26-28 g, were provided by Guangdong Provincial Medical Laboratory Animal Center. Tea polyphenols was provided by Zhejiang Oriental Tea Science and Technology Corporation (batch number: 20040203); D-galactose by Shanghai Number 2 Reagent Plant (batch number: 20030708); Aβ25-35 by Sigma (batch number: 13/01/2004); vitamin E (Vit-E) by Shanghai Xinyi Pharmaceutical Factory (batch number: 20030708). METHODS: Experimental interference: Mice based on body mass were randomly divided into 6 groups: sham operation group (n =17), model group (n =16), vitamin E group (n =16), low-dose (n =13), moderate-dose (n =14) and high-dose (n =14) tea polyphenols groups. In above-mentioned animals, except those in the sham operation group, all were given 120 mg/(kg·d) D-galactose for 12 consecutive weeks, and Aβ25-35 (4 nmol) was slowly injected into the lateral cerebral ventricle. In sham operation group, the same volume of artificial cerebral spinal fluid (CSF) was internally injected into lateral ventricle. Drug treatment began at the first week. Mice in the sham operation group and model group were given distilled water, and the animals in other groups were given the above-mentioned drugs (100 mg/kg Vit-E, 100, 250 and 625 mg/kg TP), respectively. The volume of perfusion was 10 mL/kg, and the treatment lasted for 12 consecutive weeks. Experimental evaluation: After administration, LW-II water maze was used to measure learning and memory condition; brain, liver tissues and serum were obtained to measure activity of superoxide dismutase (SOD) and content of malondialdehyde (MDA); Fura-2/AM loading method was used to measure Ca2+ concentration in erythrocytes and neurons; flow cytometer was used to detect cerebral nerve cell apoptosis. MAIN OUTCOME MEASURES: ① Learning and memory ability; ② SOD activity and MDA content in serum, liver and brain tissues; ③ Ca2+ concentration in erythrocytes and neurons; ④ cerebral nerve cell apoptosis. RESULTS: All 90 mice were involved in the final analysis. ① At 12 weeks after administration, time to swim out of the water maze in the moderate-dose and high-dose TP groups and Vit-E group was shorter than that in the model group, and numbers of errors in passing the blind alleys in the water maze was reduced as compared with those in the model group, and there was significant difference (P < 0.05-0.01). ② SOD activities in the moderate-dose and high-dose TP groups were increased as compared with that in the model group, but MDA content in the high-dose TP group was decreased as compared with that in the model group. There was significant difference (P < 0.05-0.01). ③ Ca2+ concentration in erythrocytes and neurons in the moderate-dose and high-dose TP groups and Vit-E group was lower than that in the model group, and there was significant difference (P < 0.05-0.01). ④ The rates of brain neurons apoptosis in treatment groups with different doses of TP were 12.6%, 18.6%, and 24.1% respectively, exhibiting significant difference as compared with the mice in sham operation group (P < 0.05-0.01) CONCLUSION: TP can inhibit cerebral nerve cell apoptosis induced by D-galactose and Aβ25-35 and improve learning and memory ability in model mice. The effects may be related to its action of raising general anti-oxidative ability and improvement of intracellular Ca overload induced by oxidative stress injury.