Antiglycation effects of theaflavins in black tea

• Main Authors: Yen-Jung Wang, 王延融
• Other Authors: 羅至佑
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/s6nypm

碩士 === 國立嘉義大學 === 食品科學系研究所 === 106 === Glycation is a nonenzymatic reaction starting with the reaction of protein and reducing sugar. Schiff base is generated from an amino group in protein and carbonyl group in sugar. The Schiff base then undergoes amadori rearrangement to form amadori products. The amadori products can further undergo a series of reactions to form advanced glycation endproducts (AGEs). AGEs accumulation in tissues and cells will cause diabetic complications. In this study three kinds of theaflavins were purified through liquid phase extraction and LH-20 column chromatography of black tea extract, including theaflavin (TF1), theaflavin monogallate (TF2), and theaflavin digallate (TF3). Furthermore, we have purified these compounds by flash column and the purity of TF1-3 was 98.4%, 99.9% and 99.9%, respectively. The first step was to examine inhibitory effects of TF1, TF2, and TF3 on AGEs formation. TF1, TF2, and TF3 were individually added in the reaction mixture which included bovine serum albumin (BSA) and fructose. The mixtures were incubated at 50℃ for 24 h and aminoguanidine (AG) was treated as a control. The fluorescent AGEs inhibitory effect was concentration-dependently through the addition of TF1, TF2, and TF3. The half maximal inhibitory concentration (IC50) on fluorescent AGEs of TF1, TF2, TF3, and AG was 513.57 ± 5.38, 239.75 ± 1.83, 162.24 ± 6.09, and 5751.25 ± 142.75 M, respectively. Furthermore, we have illustrated the possible mechanisms. We discovered that theaflavin prepared from black tea extract decreased the formation of dicarbonyl compounds, fructosamine (an amadori product), and carbonyl content on protein associated with the reduction of protein aggregation. TF3 showed the best antiglycation performance among the three theaflavins. Therefore TF3 was further investigated in the following cellular model. In cellular experiments, we chose Madin-Darby canine kidney (MDCK) epithelial cells to evaluate the protective effect of TF3 on high level glucose (30 mM) incubation. AG was used as a control group. The results showed that TF3 could not only significantly increase the cell viability but also decrease the intracellular reactive oxygen species (ROS) content. With the decrease of ROS, significantly down-regulated expression of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a key factor in the intracellular antioxidant mechanism occurred, also the superoxide dismutase 1 (SOD-1), a downstream protein of Nrf2 antioxidant mechanism, decreased significantly. In addition, the protein expression of heme oxygenase-1 (HO-1) showed a tendency of decline, but there was no significant change in catalase (Cat) and receptor for advanced glycation endproducts (RAGE).