中國橄欖甲醇萃取-乙酸乙酯區分層對3T3-L1葡萄糖攝取之功效與機制探討

Abstract

根據衛福部最新數據統計台灣糖尿病在十大死因中高居第五名，且罹病人口有逐漸攀升的趨勢，其主要的病因為肥胖所造成的胰島素阻抗。胰島素阻抗是由於周邊組織對於胰島素的反應不敏感，導致葡萄糖無法被周邊組織有效攝取利用。而其中脂肪組織扮演重要角色，過多的脂肪堆積容易造成胰島素阻抗。中國橄欖含有豐富的多酚類、黃酮類之衍生物，具有抗發炎、抗菌、抗氧化及抗癌細胞增生等功效。本實驗室在動物實驗中發現中國橄欖甲醇萃取-乙酸乙酯區分層 (COE) 具有緩減糖尿病的功能，因此本研究將以3T3-L1小鼠脂肪細胞模式探討其機轉。葡萄糖攝取試驗結果顯示COE可以刺激成熟脂肪細胞對2-NBDG的攝取，並在胰島素阻抗的情況下亦可增加2-NBDG的攝取量，而COE的給予可增加3T3-L1之Glucose transpoter 1 (GLUT1) 基因表現量且具有劑量效應，此外利用PI3K、GLUT及AMPK抑制劑均無法完全阻斷COE所促進的葡萄糖攝取。而COE對於3T3-L1 AMPK活性調節並不明確，僅可確定COE可促進AKT活性表現，且可稍微增加GLUT4轉位細胞膜上的量。 由此可推論COE對於刺激脂肪細胞葡萄糖攝取可能不同於PI3K及AMPK路徑。而COE是透過何種訊息傳導路徑來增加GLUT1基因表現及其對於葡萄糖攝取的影響則仍需更一步的研究與探討

Diabetes ranks the fourth leading cause of death in Taiwan, according to the latest report by Ministry of Health and Welfare, and the prevalence is going up. The major cause of diabetes is obesity-induced insulin resistance, which is reduced glucose uptake by peripheral tissues due to compromised sensitivity to insulin as a result of excess lipid accumulation in adipose tissues. Chinese olive is rich in bioactive compounds such as phenolics and flavonoids, and shows anti-inflammatory, antibacterial, anti-oxidative, and anti-proliferative effects. Previous in vivo studies indicate that the ethyl acetate fraction of methanol extract of Chinese olive (COE) ameliorates diabetes. The present study then aims to investigate the underlying mechanism for COE’s anti-diabetic effects using 3T3-L1 mouse adipocytes. Results of glucose uptake test show COE stimulates the uptake of 2-NBDG by mature adipocytes, and such effect is not ablated in the presence of insulin resistance, nor completely abolished by the use of inhibitors for PI3K, GLUT, or AMPK. In addition, treatment of COE can dose-dependently increase transcription of the glucose transporter 1 gene in 3T3-L1. Its regulatory role in AMPK activity in 3T3-L1 is not certain, but it is clear that COE can stimulate the expression of AKT and increase GLUT4 translocation to plasma membrane. Therefore it is postulated that the mechanism behind COE’s stimulatory effect on glucose uptake of adipocytes is different from PI3K and AMPK signaling pathways. Further study is needed to understand the underlying mechanism of how COE increases GLUT1 gene expression and glucose uptake.