Gamma-tocotrienol在肝癌細胞模式中抑制膽固醇合成路徑探討

Mechanistic studies on the cholesterol synthesis inhibition by gamma-tocotrienol in HepG2 cell model

林怡慧(Yi-Huei Lin)

指導教授 ： 黃卓治

國立屏東科技大學/農學院/生物科技研究所/碩士(2013年)

https://doi.org/10.6346/NPUST.2013.00030

摘要

二羥甲戊酸途徑(mevalonate pathway)速率控制酵素為HMG-CoA reductase (3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, HMGR)，經由此代謝途徑可產生膽固醇。Gamma-生育三烯醇(γ-tocotrienol) 化學構造與金合歡醇類似，故推測γ-tocotrienol可促進 HMG-CoA reductase之降解，本研究是以人類肝癌細胞株(HepG2)為研究模式，探討測試γ-tocotrienol對膽固醇生合成關鍵酵素HMG-CoA reductase抑制機制探討。紅麴含有一些化合物統稱為monacolins，為抑制膽固醇合成的物質。其中之一為monacolin K，是HMG-CoA還reductase的抑製劑，也稱為mevinolin或洛伐他汀(lovastatin)。根據西方墨點法得知γ-tocotrienol抑制HMG-CoA reductase蛋白表現，γ-tocotrienol 及 monacolin K隨著劑量的增加可減少總膽固醇生成，再以共軛焦顯微鏡觀察，發現經由γ-tocotrienol處理後Ras不活化，綜合上述之結果，γ-tocotrienol使信號蛋白無法異戊二烯化(Isoprenylation)，導致Ras不活化，抑制HMG-CoA reductase蛋白表現，進而降低膽固醇生合成之能力。

關鍵字

HMG CoA reductase ； 膽固醇 ； Gamma-生育三烯醇 ； monacolin K ； 異戊二烯化 ； Ras

並列摘要

HMG-CoA reductase is the rate-controlling enzyme of the mevalonate pathway, the metabolic pathway produces cholesterol. γ-Tocotrienol and farnesol has the similar chemical structure and both of them promote the degradation of HMG-CoA reductase. In this study, human hepatoma HepG2 cell line was used to investigate how γ-tocotrienol inactivate HMG-CoA reductase and reduce the biosynthesis of cholesterol. Red yeast rice contains several compounds collectively known as monacolins, substances known to inhibit cholesterol synthesis as well. One of these, monacolin K is a potent inhibitor of HMG-CoA reductase, and is also known as mevinolin or lovastatin. Western blot assay showed that γ-tocotrienol inhibited HMG-CoA reductase protein expression. γ-Tocotrienol and monacolin K were found to decrease total cholesterol in HepG2 cell in a dose dependent manner. γ-Tocotrienol treatment was found to inhibit the translocation of Ras inactivate in HepG2 cell by using confocal microscopy. Taken together, these data suggest that γ-tocotrienol inhibit isoprenylation, and leading to Ras inactivation, subsequently inhibiting HMG-CoA reductase protein expression, and reducing the biosynthesis of cholesterol.

並列關鍵字

HMG-CoA reductase ； cholesterol ； γ-tocotrienol ； monacolin K ； isoprenylation ； Ras

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