Department of Agricultural Biotechnology, WCU, Seoul National University, Seoul, Republic of Korea.
Int J Obes (Lond). 2013 Apr;37(4):584-92. doi: 10.1038/ijo.2012.85. Epub 2012 May 29.
To investigate the inhibitory effect of cocoa polyphenol extract (CPE) on adipogenesis and obesity along with its mechanism of action.
3T3-L1 preadipocytes were cultured with isobutylmethylxanthine, dexamethasone and insulin (MDI), and male C57BL/6N mice (N=44) were fed a high-fat diet (HFD) for 5 weeks with or without CPE. CPE at 100 or 200 μg ml(-1) inhibited MDI-induced lipid accumulation without diminishing cell viability. In particular, CPE reduced the protein expression levels of PPARγ and CEBPα, and blocked mitotic clonal expansion (MCE) of preadipocytes by reducing proliferating signaling pathways. This in turn attenuates lipid accumulation during the differentiation of 3T3-L1 preadipocytes. CPE effectively suppressed MDI-induced phosphorylation of extracellular signal-regulated kinase (ERK) and Akt, and their downstream signals. We then examined whether CPE regulates insulin receptor (IR), a common upstream regulator of ERK and Akt. We found that although CPE does not affect the protein expression level of IR, it significantly inhibits the activity of IR kinase via direct binding. Collectively, the results suggested that CPE, a direct inhibitor of IR kinase activity, inhibits cellular differentiation and lipid accumulation in 3T3-L1 preadipocytes. Consistently, CPE attenuated HFD-induced body weight gain and fat accumulation in obese mice fed with a HFD. We also found that HFD-induced increased fasting glucose levels remained unaffected by CPE.
This study demonstrates that CPE inhibits IR kinase activity and its proliferative downstream signaling markers, such as ERK and Akt, in 3T3-L1 preadipocytes, and also prevents the development of obesity in mice fed with a HFD.
研究可可多酚提取物（CPE）对脂肪生成和肥胖的抑制作用及其作用机制。
用异丁基甲基黄嘌呤、地塞米松和胰岛素（MDI）培养 3T3-L1 前脂肪细胞，并用高脂饮食（HFD）喂养雄性 C57BL/6N 小鼠（N=44）5 周，同时给予或不给予 CPE。CPE 在 100 或 200μg/ml 时抑制 MDI 诱导的脂质积累，而不降低细胞活力。特别是，CPE 通过减少有丝分裂克隆扩增（MCE）来降低 PPARγ 和 CEBPα 的蛋白表达水平，从而阻止前脂肪细胞的增殖信号通路。这反过来又减弱了 3T3-L1 前脂肪细胞分化过程中的脂质积累。CPE 有效抑制 MDI 诱导的细胞外信号调节激酶（ERK）和 Akt 及其下游信号的磷酸化。然后，我们研究了 CPE 是否调节胰岛素受体（IR），ERK 和 Akt 的共同上游调节剂。我们发现，尽管 CPE 不影响 IR 的蛋白表达水平，但它通过直接结合显著抑制 IR 激酶的活性。总的来说，这些结果表明，CPE 作为 IR 激酶活性的直接抑制剂，可抑制 3T3-L1 前脂肪细胞的细胞分化和脂质积累。一致地，CPE 减轻了 HFD 喂养的肥胖小鼠的体重增加和脂肪堆积。我们还发现，CPE 对 HFD 诱导的空腹血糖水平升高没有影响。
本研究表明，CPE 抑制 3T3-L1 前脂肪细胞中 IR 激酶活性及其增殖下游信号标志物，如 ERK 和 Akt，并防止 HFD 喂养的肥胖小鼠肥胖的发展。
