| 摘要: | 研究已指出胰島素、抗胰島素激素、第一型內皮素和表沒食子酸酯型兒茶素酸酯分別會調節肥胖症和脂肪堆積。本研究探討3T3－L1 和C3H10T1/2脂肪細胞中表沒食子酸酯型兒茶素酸酯調節胰島素和調節第一型內皮素刺激葡萄糖攝入所涉及的途徑。結果發現表沒食子酸酯型兒茶素酸酯抑制胰島素和抑制第一型內皮素刺激脂肪細胞的葡萄糖攝入，且會隨表沒食子酸酯型兒茶素酸酯劑量升高和處理時間增長而逐漸增強其抑制效果；以5-10μM濃度的表沒食子酸酯型兒茶素酸酯處理兩個小時後會減少50%-80%胰島素或是第一型內皮素所刺激的葡萄糖攝入量。表沒食子酸酯型兒茶素酸酯劑量相關抑制胰島素和第一型內皮素刺激葡萄糖攝入的效應，也在3T3 L1和C3H10T1/2前脂肪細胞，C2C12肌肉纖維母細胞和H4IIEC3肝癌細胞上觀察到。此外，表沒食子酸酯型兒茶素酸酯的抑制效果比表兒茶素、表沒食子兒茶素和表兒茶素沒食子酸酯更有效的多，這表示是一種兒茶素類型相關的效應。在脂肪細胞裡鑑定到一個已經在肺癌細胞裡推測為表沒食子酸酯型兒茶素酸酯接受子 [已知為67－kilodalton laminin接受子(67LR)]。將脂肪細胞前處理67LR 抗體，可以防止表沒食子酸酯型兒茶素酸酯對胰島素或者第一型內皮素增加葡萄糖攝入的影響。而且，前處理脂肪細胞AMPK抑制劑，例如compound C，會中止表沒食子酸酯型兒茶素酸酯抗胰島素和抗第一型內皮素葡萄糖攝入的影響，但前處理GSH 活化劑，例如N-acetyl-L –cysteine，則沒有影響其效果。這些數據顯示在脂肪細胞中表沒食子酸酯型兒茶素酸酯抗胰島素和抗第一型內皮素葡萄糖攝入的影響是透過67LR和AMPK的途徑，而不是透過GSH途徑。有趣的是，表沒食子酸酯型兒茶素酸酯會提升抗胰島素抑制胰島素激素對脂肪細胞葡萄糖攝入的效果，並且會降低胰島素和第一型內皮素對於葡萄糖攝入上的協合效應。由於葡萄糖在脂肪細胞內會代謝而產生三酸甘油酯的前驅物，所以本研究的結果也許可以支持表沒食子酸酯型兒茶素酸酯會調節激素調解脂質的含量。 Insulin, resistin, endothelin-1 (ET-1), and (-)-epigallocatechin gallate (EGCG) have been reported to regulate obesity and fat accumulation, respectively. This study investigated the pathways involved in EGCG modulation of insulin- and/or ET-1-stimulated glucose uptake in 3T3-L1 and C3H10T1/2 adipocytes. EGCG inhibited insulin and/or ET-1 stimulation of adipocyte glucose uptake in a dose- and time-dependent manner. The concentration of EGCG that decreased the insulin- or ET-1-stimulated glucose uptake by 50%-80% was approximately 5-10 μM for a range of 2 h. The dose-dependent effect of EGCG in suppressing the insulin and ET-1 stimulation of glucose uptake was also observed in 3T3-L1 and C3H10T1/2 preadipocytes, C2C12 myoblast, and H4IIEC3 hepatoma cells. At 10 μM EGCG was more effective than (-)-epicatechin, (-)-epigallocatechin, and (-)-epicatechin-3-gallate. This suggests a catechin type-dependent effect. A putative EGCG receptor [also known as the 67-kilodalton laminin receptor (67LR)] was discovered in lung cancer cells and then identified in fat cells. Pretreatment of adipocytes with 67LR antibody, but not normal rabbit immunoglobulin, prevented the effects of EGCG on insulin- or ET-1-increased glucose uptake in adipocytes. Moreover, pretreatment with the AMP-activated protein kinase (AMPK) inhibitor, such as compound C, but not with the GSH activator, such as N-acetyl-L-cysteine, blocked the anti-insulin and anti-ET-1 effects of EGCG on adipocyte glucose uptake. These data suggest that EGCG exerts its anti-insulin and anti-ET-1 actions on adipocyte glucose uptake via the 67LR and AMPK, but not GSH, pathways. Interestingly, EGCG was found to enhance the anti-insulin effect of resistin on adipocyte glucose uptake, and it reduced the synergistic effects of insulin and ET-1 on adipocyte glucose uptake. As glucose serves as the metabolite to produce one of the precursors of triglycerides, results of this study may possibly support that EGCG modulates hormone-mediated fat content. |
