Studies On Anti-obesity Effects Of Tea Extracts On High Fat Diet Induced Obese Rats And Their Potential Mechanisms

Obesity is closely related to metabolic syndrome. A mass of research data indicates that obesity can cause cardiovascular disease, diabetes, cancer, endocrine disorders. Obesity can increase mortality. When the BMI (body mass index)>30kg/m2, the rate of mortality is almost in a linear increase with the BMI increase. When BMI is35kg/m2, the rate of mortality is about30%-40%. A lot of research has shown that almost all kinds of teas have effects on preventing obesity, insulin resistance, high blood pressure, and hyperlipidemia disease. As knowledge about obesity deepens, development of natural anti-obesity products without any side effects, based on tea extracts, will have wide application prospects. The aim of this study was to investigate the anti-obesity effects of green tea, black tea, oolong tea (Tieguanyin tea) and dark tea (Fuzhuan tea) on high fat diet induced rats. In order to reveal the potential anti-obesity mechanisms, gene expression related to energy metabolism and lipid homeostasis and differentially expressed proteins in rat liver were also studied. The main results are as follows:1. Study on anti-obesity effects of four kinds of teasThe selected teas used for evaluating anti-obesity effects were green tea, black tea, oolong tea (Tieguanyin tea), and dark tea (Fuzhuan tea). Experimental obese rats induced by high fat diet were orally administered with tea aqueous extracts at different concentrations, which were of75,150,300mg/kg·BW, respectively, and the same amount of distilled water was orally administered to normal control and model control groups. After treatment with tea extracts for40days, the results showed that the body weight gains and the weights of perinephric fat pads and epididymal adipose tissues were reduced in rats for all of the tea extract treatment groups, compared with the model control group. Histological analysis also showed that all of the tea aqueous extracts had suppressive effects on number and size of the adipose tissue fat cells. Comparing the different treatment dosages, high dosages of green tea, oolong tea and Fuzhuan tea extracts could more significantly reduce rat weight (P<0.01). Among these3treatments, the high dosage of green tea aqueous extract had the most significant effect so that the fat coefficient of rats in this treatment was close to normal control, and the high dosage of Tieguanyin tea aqueous extract was the second most effective treatment. Moreover, all of the tea aqueous extracts showed effects on adjusting and improving hyperlipidemia caused by feeding on high fat diet, including reducing the contents of blood TG, TC, LDL-C, increasing the content of HDL-C and improving liver steatosis. Compared to the other3kinds of teas, Fuzhuan tea had the best effect on adjusting and improving hyperlipidemia.2. Analyzing the expression of genes related to energy metabolism and lipid homeostasis in the obese rats treated with Fuzhuan tea, by qPCR technologyRat livers from the model control, low-and high-dose Fuzhuan tea treatment groups were chosen as experimental samples. Six genes expressed in rat liver and related to lipid metabolism were detected. To investigate the changes of gene expression at the mRNA level, qPCR analysis was performed. The results indicated, compared with the model control group, that Fuzhuan tea administration led to down-regulation of gene expression, including C/EBP-a, FAS and SREBP-lc, and up-regulation of gene expression as well, including LDLR, PPAR-a and CPT-1a.3. Detection of differentially expressed proteins in liver of obese rats treated with Fuzhuan tea, by2-D electrophoresisIn this study,2-D electrophoresis proteomic analysis system of rat liver was successfully established, which showed good repeatability and high resolution. The established method was used to detect the differential expression of liver proteins in obese rats treated with a high dosage of Fuzhuan tea aqueous extract. Each treatment was repeated four times. Based on the2-D electrophoresis protein spot maps, there were in total about700protein spots that were detected from all of the test samples. Quantitative analysis revealed that36protein spots showed a significant change (p<0.05) in intensity by more than1.5times after a high dosage of Fuzhuan tea aqueous extract was administered to the obese rats. Compared with the model control group, among these36proteins,24proteins showed up-regulation expression, and12proteins showed down-regulation expression.