| Yellow tea is one of the six major tea categories in China, and is also famous for its special stew process, which results in its unique quality characteristics. In recent years, with the development of the yellow tea industry, yellow tea has become a delicacy loved by more people. Hunan is major producing area of yellow tea. Junshan silver needle tea as the famous yellow tea of Hunan province has been named as one often famous teas in China. Currently, most researches of yellow tea were focus on its processing technologies and the analyses of chemical compositions, and few studies were reported on its protective functions for human health. In response to meet tea industry needs, reveal the unique health benefits of yellow tea and increase the understanding of people on tea functions, we chose Junshan silver needle as the representation of yellow tea to systematically investigate its effect and mechanism on regulating glucose and lipid metabolic disorder in this paper. We hope that this study will provide some scientific bases for the high-value utility of tea resources, the increase consumption of yellow tea, and the development of efficient and safe drugs in metabolic syndrome treatment. The main results are as follows:1. Chemical ingredient’s analyses of Junshan silver needle tea.Biological activity of tea is determined by its chemical constituents. Based on this, we analyzed the chemical compositions of the Junshan silver needle using several detection methods. The result showed that, the content of tea polyphenol was the highest (17.04%) in tea water extracts, then followed by the soluble sugar (6.33%), free amino acid (5.62%) and alkaloid. Caffeine is the main component of alkaloid, accounted for more than70%of total alkaloid. In order to investigate the difference between yellow tea and other tea categories, we chose Junshan silver needle tea and other three representative teas for the comparison. The research results showed that there was obvious differences at the contents of main chemical components in different teas, especially tea polyphenol with the most evident difference in the range from5.36%to19.03%. Typically, compared with this in Xin yanghong and Fuzhuan brick tea, the content of tea polyphenol in Junshan silver needle was obviously higher, and almost equal to this in Biluochun tea, which might be related with the slight fermentation of manufacturing process of yellow tea, and also indicated tea polyphenol and other relative components of Junshan silver needle might be the main chemical constituents for the bio-active function of human health.2. Effect of Junshan silver needle tea on regulating lipid metabolism based on fat emulsion-induced L-O2cell steatosis model.Liver L-O2cell was induced with medical fat emulsion to establish the model of liver cell steatosis. The model cell could reflect the basic characteristics of fatty liver cells:TG accumulation in liver cell and the increases of AST and ALT levels in cultural medium. When the model cell was treated with Junshan sliver needle water extracts, the TG content in cell and activity levels of AST and ALT in culture medium were reduced in a dose-depended manner. Especially, the high dose group of Junshan sliver needle had a significant difference compared to the model group, and the remedial effect was close to the positive drug. Thus, these results indicated that Junshan silver needle water extracts could improve lipid metabolism and fat accumulation, and restore cell injury induced by oxidative stress.3. Effect of Junshan silver needle tea on regulating lipid metabolism in rat model of hyperlipidemia.The study results indicated that, compared with model group, the groups of Junshan silver needle tea effectively inhibited the formation of hyperlipidemia in rats induced by high fat diet, and contents of TG, TC and LDL-C in serum and/or liver homogenate were also significantly reduced, while serum HDL-C level were increased. Meanwhile, serum AST and ALT levels were decreased and A/G ratio was increased in Junshan silver needle group. Besides, MDA content of liver homogenate was reduced, activity levels of AST and ALT in liver homogenate were enhanced, and liver index and TG accumulation was reduced to normal extent. Altogether, these results demonstrated that, lipid metabolism disorder and liver injury induced by the high fat diet was obviously ameliorated, which might be associated with more active components retained in yellow tea such as tea polyphenols. Then, gene expression analysis showed DGAT2, ACC1, ACAT1and HMGR were down-regulated, while CPT-1a were up-regulated, which demonstrated Junshan silver needle tea could perform hypolipidemic effect by inhibiting lipogenesis, stimulating lipid catabolism and increasing energy consumption.4. Intervention effect of Junshan silver needle tea on insulin resistance and glucose and lipid metabolism on HepG2cell. HepG2cell was induced with palmitic acid to establish the model of insulin resistance. The model cell showed the typical characteristics of insulin resistance and the disorder of glucose and lipid metabolism: the decreases of cell glucose intake and glycogenesis and the increases of cell TG and TC levels. When the model cell was treated with Junshan sliver needle water extracts, the glucose intake and glycogenesis of HepG2model cell were increased. Especially, the middle and high dose groups of Junshan sliver needle had a significant difference compared to model group. Besides, Junshan sliver needle could ameliorate TG accumulation in a dose-depended manner especially the high dose group with statistical significance, but total TC level was slightly changed. Altogether, these results declared that Junshan sliver needle water extracts could efficiently improve insulin resistance and glucose and lipid metabolic disorder on HepG2model cell.5. Effect of Junshan silver needle tea on ameliorating insulin resistance in diabete rats.The diabete rat model induced by high fat and sucrose diet combined with peritoneal injection of streptozocin. After intragastric adminstration of Junshan silver needle water extracts, some symptoms of model rat were improved to a certain extent, but the whole effect is not very obvious, and only the high dose group had a significant difference compared with model group, which might be the reason that the combined method for the development of rat model led to more serious symptoms of diabetes, and Junshan silver needle water extract even positive drug could not restore the serious injury. However, Junshan silver needle water extract, especially with a high dose, could significantly restore serum TG, TC, LDL-C, HDL-C, AST and ALT levels, which also demonstrated that Junshan silver needle water extract would ameliorate organ injury and regulate glucose and lipid metabolism to some extent. These ameliorative effects might be related with the high contents of tea polyphenols, sugars and alkaloids in Junshan silver needle. Then, gene expression analysis showed that, GLUT2was up-regulated, PEPCK was down-regulated and AMPKa2, FAS and ACC2were reversed to a normal range by tea treatment, which demonstrated that Junshan silver needle tea could ameliorate insulin resistance and glucose lipid disorder by enhancing glucose intake, inhibiting glycogenesis and lipogenesis, stimulating lipid catabolism and increasing energy consumption, etc. In conclusion, this research preliminarily investigated the main chemical composition characteristics of yellow tea. Also, based on cell and animal models, effects and mechanisms of Junshan silver needle tea on regulating glucose and lipid metabolism were systematically explored. |
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