| Food sciences |
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| Overview of tea constituents against type 2 diabetes |
| LU Peng, WANG Xiaochang, WANG Yingqi |
| Institute of Tea Science, Zhejiang University, Hangzhou 310058, China |
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Abstract Type 2 diabetes mellitus (T2D) was a metabolic disorder， which was characterized by hyperglycemia in the context of insulin resistance and relative lack of insulin. The prevalence of T2D resulted in 90% of diabetic individuals suffering from it. In China, the percentage increased by 95%. The usage of anti-diabetic drug, however, could be associated with serious undesirable side effects, the most commonly observed are being hypoglycemia, mass gain, and gastrointestinal disturbances. Thus, it was necessary to find anti-diabetic therapies that are not only safe and effective in controlling blood glucose levels, but also without serious side effects. Tea was a kind of natural anti-diabetic material and had been studied for a long time because it was abundant in polyphenol. Previous studies mainly focused on type 1 diabetes mellitus (T1D), but recently, research about anti-T2D increased. At present, three main approaches of remedies could be concluded from the global researches. Glucose concentration in the body was directly influenced by insulin, so that insulin approach was one of the main therapies to treat T2D. Numerous reports showed that tea extracts could enhance insulin properties which could be subdivided into the amelioration of insulin resistance, improvement of insulin sensitivity and stimulation of incretin in cell or animal models. In detail, studies showed that tea extracts, especially epigallocatechin gallate (EGCG) could inhibit protein tyrosine phosphates 1b (PTP1B) to enhance insulin sensitivity and relieve insulin resistance via inhibiting 11beta-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Similar results were also found that unknown extracts from tea could alleviate insulin resistance or enhance insulin secretion by inhibiting dipeptidyl peptidase Ⅳ (DPP-Ⅳ). This kind of approach includes two remedies, enhancing glycolysis and inhibiting gluconeogenesis. In skeletal muscle and adipose cells, tea extracts, particularly EGCG, could analog the function of insulin to stimulate glucose transporter protein-4 (GLUT 4) and enhance AMP-activated protein kinase (AMPK) pathway or PI3K/Akt pathway to strengthen the usage of glucose. In hepatic cells, EGCG from tea, down-regulated the mRNA of phosphoenolpyruvate carboxylase (PEPCK) and up-regulated the mRNA of glucose-6-phosphatase (G6Pase) through enhancing calmodulin dependent protein kinase kinases-β (CaMKK-β） and AMPK pathway. Anti-oxidants have been proved to play a significant role in T2D and complications. Tea, as a natural anti-oxidant, could definitely scavenge free radicals. Studies have reported that it could prevent T2D and its complications through enhancing polyol pathway flux, increasing formation of advanced glycation end products (AGEs), increasing expression of the receptor for AGEs and its activating ligands, activation of protein kinase C isoforms, and overactivity of the hexosamine pathway. Additionally, tea polyphenols including EGCG could also keep the balance between nitric oxide (NO) and endothelin (ET-1) and inhibit 11β-HSD1 to prevent T2D from happening indirectly. As a kind of natural functional beverage, tea and its extracts would be totally tested on resistance to T2D and could be recommended for combined use with present antidiabetic drugs in the treatment of T2D in the future.
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Published: 20 May 2016
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茶叶在抵抗Ⅱ型糖尿病中的作用
糖尿病(diabetes mellitus,DM)已经是世界上最常见的非传染性疾病之一。其中全球已被诊断的糖尿病成人患者中,90%是Ⅱ型糖尿病(type 2 diabetes mellitus,T2D)。 在中国T2D同样占了总病人数量的95%。由于治疗T2D常见药物具有一定的不良反应, 如低血糖,体质量增加和胃肠道功能紊乱等,因此,寻找没有不良反应,但相对低疗效的膳食疗法成为治疗糖尿病的替代疗法之一。富含茶多酚的茶叶(Camellia sinensis)一直是我国的传统健康功能性饮料,它作为一种天然降血糖材料已经被广泛研究。过去的研究多集中在抵抗T1D的研究,近年来对T2D的研究在快速增多。根据现有结果,可将茶叶抵抗糖尿病T2D的作用机制概括为胰岛素途径、糖代谢途径和其他3大途径。胰岛素途径主要表现在茶能促进胰岛素分泌,增强胰岛素活性和敏感性,增强肠促胰岛素活性这3个方面。糖代谢途径则主要表现在茶能促进糖酵解过程和抑制糖异生。第3大途径则主要是以茶多酚的抗氧化功能为主。茶作为一种健康饮料,在Ⅱ型糖尿病的膳食治疗中将发挥越来越多的作用。
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