蜂膠及茶類中類黃酮化合物之癌症化學預防機制探討

Studies on the Mechanisms of Cancer Chemoprevention by Flavonoids from Propolis and Tea

翁孟仕(Meng-Shih Weng)

指導教授 ： 林仁混

國立臺灣大學/醫學院/生物化學暨分子生物學研究所/博士(2006年)

https://doi.org/10.6342/NTU.2006.10445

摘要

癌症化學預防的目的是預防、停滯，或反轉致癌劑的起始作用，或使癌細胞變成癌症的過程。在細胞以及動物模式的實驗中，有大量天然以及合成性的分子具有預防癌症的特性。植物中幾種特殊的酚類化合物，特別是類黃酮，已被報導指出具有抑制突變以及致癌的作用。類黃酮具有許多生物活性包括了，意志細胞週期、細胞增生以、抑制細胞內氧化壓力，以及誘發細胞凋亡，因為這些作用使得它具有癌症化學預防的作用。在本論文中，我們研究蜂膠及茶中的一些類黃酮的癌症化學預防機制。希望我們的研究可以提供開發新癌症化學預防分子的一個方向。
蜂膠已被發表指出具有廣泛的生物活性，包括抗癌、以及抗氧化活性。然而對於蜂膠中有效成分的抗癌分子機制並不全然了解。在我們的實驗中，我們研究Chrysin (5, 7-dihydroxyflavone)及蜂膠內的新成分propolin H對於細胞週期的調控。我們的數據指出，chrysin 以及propolin H能分別抑制C6神經膠瘤細胞以及人類肺癌細胞H460生長週期的進行，並使細胞停留在G1期。CDK2以及CDK4兩者的活性都被chrysin以及propolin H所抑制，此外處裡chrysin的C6神經膠瘤細胞及處裡propolin H的人類肺癌細胞H460細胞中都可以觀察到p21Waf1/Cip1很明顯的增加。而在處裡propolin H的人類肺癌細胞H460細胞中p21Waf1/Cip1的增加是跟p53有關，但是處裡chrysin的C6神經膠瘤細胞中p21Waf1/Cip1的增加是和p53無關。接著我們也觀察到chrysin活化了p38-MAPK，而抑制p38-MAPK會降低chrysin所誘發的p21Waf1/Cip1表現。在處理propolin H的細胞中，propolin H也會在失去p53功能的肺癌細胞中活化p21Waf1/Cip1的表現，進而引起癌細胞的細胞週期停滯或細胞凋亡。這樣的結果顯示，chrysin以及propolin H抑制細胞生長的能力主要是經由活化p21Waf1/Cip1蛋白以及抑制CDK們的活性，接著使細胞週期停滯。
在世界各國中，肥胖是個逐漸生長的問題，並伴隨著許多危害健康的風險，譬如癌症的發生。茶多酚已經被報導指出具有許多生物性以及藥物性的影響，例如它具有抗氧化、抗致癌機轉以及抗致粥瘤性的功能。然而茶多酚對於脂質代謝以及體內脂肪的累積方面的影響，這方面的研究是非常的少。在我們的研究中，我們給予大白鼠餵食茶葉，並去研究烏龍茶、紅茶、普洱茶以及綠茶對於活體動物降血脂效應。研究結果指出，在降低體重以及血清內三酸甘油脂的能力方面，烏龍和普洱茶明顯高於綠茶。但是在抑制總膽固醇方面，普洱茶以及綠茶比烏龍茶以及紅茶更有效。在低密度脂蛋白方面，四種茶都能夠很明顯的降低低密度脂蛋白。由以上的結果顯示，完全發酵的普洱茶以及紅茶和部份發酵的烏龍茶對於抑制生長以及降血脂效應是比未發酵的綠茶來的有效。
為了更進ㄧ步研究茶多酚對於脂質代謝的分子機制。我們研究紅茶中的茶多酚，theanaphthoquinone (TNQ)對於乳癌細胞內脂肪合成酶的影響。脂肪合成酶(FAS)是扮演著脂質代謝的一個重要的酵素，同時此酵素也和許多的人類疾病有關，包括了肥胖、心血管疾病以及癌症。我們發現在乳癌細胞MDA-MB-231中，TNQ能抑制生長因子EGF所誘發的FAS蛋白、mRNA以及抑制轉錄因子SREBP-1進入到細胞核內的表現。而TNQ的這些抑制效用是藉由調控PI 3-kinase/Akt所造成的。更進一步研究發現，抑制EGFR和ErbB-2的活性會降低EGF誘發的FAS蛋白表現。此外， TNQ也能抑制大量表現FAS的乳癌細胞，而這種的抑制現象最後會誘發細胞死亡。最後我們的研究指出蜂膠及茶中之類黃酮可成為一有效的化學預防試劑。

關鍵字

化學預防 ； 蜂膠 ； 細胞週期 ； 茶 ； 降血脂效應 ； 脂肪合成酶

並列摘要

Chemoprevention of cancer aims to prevent, arrest, or reverse either the initiation phase of carcinogenesis or the progression of neoplastic cells to cancer. A large number of natural and synthetic compounds have cancer preventive properties in cell culture or animal model studies. Several specific plant phenolic compounds, especially flavonoids, were reported to inhibit mutagenesis and carcinogenesis. Flavonoids have shown many biological properties, including inhibit the cell cycle, cell proliferation, and oxidative stress, and to induce apoptosis that may account for cancer chemoprevention. In this dissertation, we investigate the cancer chemoprevention of some flavonoids from propolis and tea. We hope our studies could provide a new direction to investigate new chemopreventive compounds for cancer control.
Propolis has been reported to exert a widely spectrum of biological functions, including anticancer and antioxidant activities. However, the molecular mechanisms of the anti-cancer properities of propolis components have not been completely understood. In our study, we investigate the molecular mechanism of chrysin (5, 7-dihydroxyflavone) and a novel component namely propolin H on cell cycle regulation. Our data indicated that chrysin and propolin H blocked rat C6 glioma and H460 lung carcinoma cell line cell cycle progression at the G1 phase, respectively. Both cyclin-dependent kinase 2 (CDK2) and 4 (CDK4) kinase activities were down-regulated by chrysin and propolin H, and the expression of cyclin-dependent kinase inhibitor, p21Waf1/Cip1, to be significantly increased in chrysin-and propolin H-treated C6 glioma and H460 lung carcinoma cells, respectively. The content of the p21Waf1/Cip1 protein was increased in correlated with the elevation in p53 levels in propolin H-treated H460 cells but not in chrysin-treated C6 glioma cells. We also showed that chrysin induced p38-MAPK activation, and inhibition of p38-MAPK attenuated chrysin-induced p21Waf1/Cip1 expression. In propolin H-treated cells, propolin H also enhanced the expression of p21Waf1/Cip1 in p53-mutant and p53-null lung carcinoma cell lines following the induction of G1 arrest and apoptosis. These results suggest that chrysin and propolin H exerts its growth-inhibitory effects through activation of p21Waf1/Cip1 protein and then inhibition of CDKs kinase activities followed by blockade cell cycle progression.
Obesity is a growing problem in many countries worldwide and is associated with many health risks such as cancer. Tea catechins have been reported to possess various biological and pharmacological effects, such as anti-oxidation, anti-carcinogenic and anti-atherogenic activities, but little information is available about the effects of tea catechins on lipid metabolism and body fat accumulation. In our study, we investigate the hypolipidemic effect of oolong, black, pu-erh, and green tea leaves in male Sprague-Dawley rats. In lowering body weight and serum triglyceride levels, oolong and pu-erh tea leaves seem to have stronger effect than green tea leaves. However, in lowering the level of total cholesterol, pu-erh and green tea were more efficient than oolong and black tea. Furthermore, the level of LDL-C was significant decrease in feeding all of teas. These results indicated that the fully-fermented pu-erh and black tea leaves and partially-fermented oolong tea leaves were more effective on their hypolipidemic effects as compared to the non-fermented green tea leaves.
To further investigate the mechanism of tea polyphenols on lipid metabolism. We investigated the effects of black tea polyphenol, theanaphthoquinone (TNQ) on the expression of Fatty acid synthase in human breast cancer cells. Fatty acid synthase (FAS) is an important enzyme participating in lipid metabolism and is related to various human diseases including obesity, cardiovascular disease and cancer. In this study, TNQ was found to suppress EGF-induced FAS mRNA and protein expressions and nuclear translocation of SREBP-1 in MDA-MB-231 cells. This suppression was through down-regulation of PI 3-kinase/Akt sinaling. Furthermore, suppression of EGFR or ErbB-2 activation resulted in down-regulation of EGF-induced FAS expression. Our data also indicated that TNQ inhibited constitutive FAS expression and induced cell death in ErbB-2-overexpressed cells. Finally, our study indicated that flavonoids from propolis and tea could serve as a candidate to become chemopreventive agent

並列關鍵字

Chemoprevention ； Propolis ； Cell cycle ； Tea ； Hypolipidemic ； Fatty acid synthase

參考文獻

1. Ahmad N, Cheng P, Mukhtar H. 2000. Cell cycle dysregulation by green tea polyphenol epigallocatechin-3-gallate. Biochem Biophys Res Commun 275: 328-334.

2. Alblas J, Slager-Davidov R, Steengergh PH, Sussenbach JS, van der Berg B. 1998. The role of MAP kinase in TPA-mediated cell cycle arrest of human breast cancer cells. Oncogene 16: 131-139.

3. Anderson, N.G., Ahmad, T., Chan, K., Dobson, R., Bundred, N.J., 2001. ZD1839 (Iressa), a novel epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, potently inhibits the growth of EGFR-positive cancer cell lines with or without erbB2 overexpression. Int. J. Cancer. 94, 774-782

4. Aziz MH, Kumar R, Ahmad N. 2003. Cancer chemoprevention by resveratrol: in vitro and in vivo studies and the underlying mechanisms. Int J Oncol 23: 17-28.

5. Balmanno K, Cook SJ. 1999. Sustained MAP kinase activation is required for the expression of cyclin D1, p21Cip1 and a subset of AP-1 proteins in CCL39 cells. Oncogene 18: 3085-3097.