| 摘要: | 第二型糖尿病是一種慢性代謝性疾病，起源於胰臟分泌不足或是周邊組織（脂肪、肝臟和肌肉) 無法正常代謝胰島素所造成，而後者通常稱為胰島素阻抗，通常是第二型糖尿病的典型特點。在現今的社會，我們可以看到糖尿病的發展呈現快速增加並且達到流行的趨勢，研究指出大多數第二型糖尿病患者會有肥胖或超重現象，並且改變他們的膳食習慣成為 「西方飲食模式」。市面上有很多開發的藥物治療糖尿病，但少部分藥物由於有嚴重的副作用，已經從市場撤回。因此，如何從自然界尋找天然產品和補充品備受糖尿病患者關注。從數幾千年至今，藥用植物一直是世界各地傳統醫療的一部分。世界衛生組織在2002年推廣全面的傳統醫學策略，以促進更經濟實惠、有效率、安全，和互補性的替代醫學。
甘藷於民間宣稱具有抗糖尿病、降血壓、抗發炎、抗菌、以及抗氧化活性的特性。最近研究顯示甘藷含有大量的維生素、纖維素、礦物質、花青素和其他植化物。儘管甘藷的英文名字有”sweet” (甜) 這個名稱，它還是有助於糖尿病患者的食物。從動物研究的初步顯示甘藷有助於血糖穩定，改善胰島素阻抗功效，藉由體外實驗技術可用來快速闡明具有降血糖物質其體內降糖作用機制。研究指出肌肉組織負責80％ 餐後葡萄糖的吸收，因此本論文利用小鼠C2C12骨骼肌細胞進行體外實驗，以驗證甘藷降血糖功效。
本研究首先利用TNFα誘發C2C12細胞產生胰島素阻抗，然後以常用糖尿病藥-噻唑烷二酮（TZD）作為陽性對照組，利用葡萄糖吸收實驗比較細胞介入西蒙1號和台農66甘藷萃取物的成效。根據共聚焦顯微鏡和免疫印記法 (Western blot) 實驗結果，食用兩組甘薯萃取物都能增加阻抗細胞對於葡萄糖的吸收量，其反應機轉是透過PI3K的路徑中：胰島素受體、胰島素受體基質-1、和Akt的磷酸化作用以增加膜轉運蛋白質GLUT4的表現及葡萄糖的運送。兩組甘薯萃取物分別以福林酚試劑（Folin-Ciocalteu reagent）測量總多酚含量，顯示西蒙1號和台農66總多酚含量與樣品中自由基的清除率有很強的相關性，推測甘藷可以抗胰島素阻抗是源自於於抗氧化特性。此外，兩組水萃物自由基清除率相對較低，然而亦能夠增加胰島素阻抗細胞C2C12葡萄糖的吸收。
整體而言，本論文研究成果顯示無論是西蒙1號或台農66甘薯塊根萃取物，顯示出具有開發成為降血糖藥物、健康食品或是膳食補充品的潛力，然而仍需進一步使用動物或人類糖尿病研究模式，以確認細胞學研究成果。
Type 2 diabetes is a chronic metabolic disorder, which is caused either because the pancreas does not produce enough amount of insulin, or the peripheral tissues (fat, liver and muscle) cannot utilize insulin properly. The last one is called insulin resistance, which is the hallmark of type 2 diabetes.
Most people with type 2 diabetes are obese or overweight; and with an unfavorable trend of changing their diet to the ‘western style’, we can see a rapidly increasing trend of developing diabetes; reaching epidemic status in our society. There are a lot of medications developed, but many of them have already withdrawn from the market due to severe side effects. Therefore finding natural products and developing food supplements got more attention recently. Medicinal plants have been part of the great healing traditions around the world going back thousands of years. In 2002 WHO launched its first comprehensive traditional medicine strategy to promote affordable, effective and safe use of traditional medicine and complementary alternative medicine.
Sweet potato is known to have antidiabetic, antihypertensive, anti-inflammatory, antimicrobial, and antioxidant activity since a long time. It has lots of vitamins, fibers and minerals, anthocyanins and other phytochemicals, which has been recently investigated. Despite the name "sweet", it may be a beneficial food for diabetic patients. Preliminary studies on animals have revealed it helps to stabilize blood sugar levels and to ameliorate insulin resistance.
Many in vitro models have been developed to elucidate the action mechanism of hypoglycemic agents discovered by in vivo bioassays. As muscle is responsible for around 80% of the postprandial glucose uptake, C2C12 skeletal mouse muscle cell line is a good choice for these studies.
The study aim was to develop insulin resistance in C2C12 cells by TNFα, and then to treat these cells by Simon No.1 and Tainong 66 sweet potato extracts and compare with the effects by Thiazolidinedione (TZD) as a positive control using glucose uptake test.
According to our results, extracts from both sweet potatoes have the ability to increase glucose uptake by the cells. This was also confirmed by confocal microscopy and western blot analysis. Western blot also revealed that the increased glucose uptake involved GLUT4 translocation to the membrane and the upregulation of the proteins along the PI3K pathway, namely insulin receptor, insulin receptor substrate-1 and Akt.
Both Simon No.1 and Tainong 66 are abundant in polyphenols measured by Folin-Ciocalteu assay. The total phenol content showed strong correlation with the free radical scavenging activity of the samples. We proposed that the anti-insulin resistant effects of sweet potatoes are due to their anti-oxidative properties. However, water extracts, which had relatively low scavenging activities, were also able to increase glucose uptake sufficiently in C2C12 myotubes.
Overall we conclude that not only Simon No.1, but also Tainong 66 sweet potato root extracts demonstrated promising potentials to be developed into antidiabetic drugs, healthy food, or dietary supplement. However, future animal and human diabetic studies are necessary to confirm the results. |
