肥胖為世界上常見的健康問題，與糖尿病、高血壓和心血管疾病等慢性疾病有密不可分的關係。而肥胖症起因是由於體內的脂肪細胞數目的堆積或者是脂肪細胞內油滴的堆積所導致。在之前的報告指出，第一型類胰島素可以刺激3T3-L1前脂肪細胞的生長。然而含有唲茶素的綠茶萃取物可減輕老鼠的體重與增加人類能量的消耗和脂肪酸的氧化，以及抑制3T3-L1前脂肪細胞的生長，但是其中真正的機制仍然不清楚。因此，本論文的目的是，使用鼠類3T3-L1前脂肪細胞作為研究素材，透過細胞學以及生化學的角度，來證實綠茶唲茶素是否調節第一型類胰島素對前脂肪細胞生長之刺激，並進一步探討其調控的真正機制為何。結果發現綠茶唲茶素中的EGCG比較其他化學結構相似的唲茶素如EC、EGC、ECG等，可以有效降低由第一型類胰島素所調節的3T3-L1前脂肪細胞的細胞數目。而EGCG同時也降低的CDK-2的活性以及MEK的活性，並影響IRS-1與Shc的磷酸化以及與IGF-IR之間交互作用，而IGF-I接受體本身的磷酸化情形亦受到EGCG的影響。因此，我們的結論是EGCG會抑制由第一型類胰島素所引發的細胞增生訊息傳遞，最後使3T3-L1前脂肪細胞之生長受到抑制。 Obesity is considered as a common disease in the world as well as is associated with the risk of diabetes, hypertension, and cardiovascular disease. Obesity results from increases in the fat cell number and/or accumulation of lipid droplets inside of fat cells. Early studies have indicated that IGF-I stimulates the growth of 3T3-L1 preadipocytes; and that catechin-containing green tea reduces body weight of rats, increases energy expenditure and fat acid oxidation of human, and inhibits growth of 3T3-L1 preadipocytes. The exact mechanism of green tea catechin action is still not clear. The present study was to use murine 3T3-L1 preadipocytes to demonstrate at cellular and biochemical levels whether green tea catechins modulate IGF-I stimulation of preadipocyte growth and, if so, to investigate the mechanism of modulation. We found that green tea EGCG was more effective than structurally-related EC, EGC or ECG in reducing the IGF-I-stimulated growth of 3T3-L1 preadipocytes. Further study showed that EGCG reduced activities of CDK-2 and MEK, as indicated by the decreases in the phosphorylation of histone H1 and Erk-1 and Erk-2, respectively. Also, EGCG, but not EC, EGC, or ECG, reduced phosphorylation of IGF-IR, the binding between IGF-IR and IRS-1, and the phosphorylation of IRS-1 and Shc. We conclude that EGCG reduces IGF-I-stimulated growth of 3T3-L1 preadipocytes through inhibiting the pathway of IGF-I signaling transduction.
