荖葉水萃取物抗脂質氧化及抗肝癌功效評估

在過去的研究中指出荖葉水萃取物具有抗發炎、解毒以及抗氧化等功效。在本篇研究中我們利用銅離子氧化人類低密度脂蛋白的模式，評估荖葉水萃取物的抗氧化活性，以及在細胞實驗中觀察氧化型低密度脂蛋白(oxidised low density lipoprotein, oxLDL)累積於巨噬細胞中形成泡沫細胞的機制是否受到影響。我們實驗證實荖葉水萃取物在體外實驗能有效抑制LDL氧化，並降低脂質累積於巨噬細胞當中，減緩泡沫細胞之生成。進一步分析其機轉為荖葉水萃取物能活化巨噬細胞表面清除者接受器(scanvenger receptor) SR-A以及CD36蛋白表現增加，而大量吞噬oxLDL，並透過膽固醇逆轉轉運體(reverse cholesterol transport, RCT)的機制，活化轉錄因子Liver X receptor (LXR)以及ATP-binding cassette transport A1 (ABCA1)表現，使巨噬細胞達到降低脂質累積並，減少泡沫細胞(foam cell)生成，具有降低心血管動脈粥狀硬化之可能性。而另一方面，對於p53缺失功能之人類肝細胞癌Hep3B經由細胞以及異種移植動物實驗發現，荖葉水萃取物在0.1到1.0 mg/ml的濃度下，對於細胞具有劑量以及時間依賴性的毒殺作用。經由流式細胞儀以及西方墨點法證實，荖葉水萃取物可開啟ATM-cAbl-p73蛋白系統，以及活化JNK、p38 MAP kinase以及AMPK等調控機制，促使細胞生長停滯並走向非依賴立現體細胞凋亡機制(mitochondria-independent apoptosis)，以及細胞自噬性死亡(autophagy)。在帶有Hep3B腫瘤之老鼠動物模式中，亦發現荖葉水萃取物可經由活化MAPK-p73此途徑而有效抑制腫瘤之生長。綜合以上實驗得知，荖葉水萃取物可活化膽固醇逆轉轉運體機制，增加巨噬細胞對於oxLDL之代謝，並減緩泡沫細胞生成以及心血管之損傷；此外經由in vitro以及in vivo實驗證實荖葉水萃取物可經由活化p73途徑，達到對於人類肝細胞癌的治療功效，對於外來是可期待之化學預防試劑。

關鍵字

細胞凋亡；動脈粥狀硬化；細胞自噬死亡；肝癌；氧化低密度脂蛋白；荖葉； p73 ；膽固醇逆轉轉運體

並列摘要

Extracts of Piper betle leaf (PBLs) have been reported with the biological capabilities of detoxification, anti-inflammation agent and anti-oxidantion. In this study, we evaluated the anti-oxidative activity of the extract of Piper betle leaves (PBLs) on the basis of Cu2+-mediated oxidation, and its ability to prevent foam cell formation in a model for oxidised low density lipoprotein (oxLDL)-induced lipid accumulation in macrophages. Our data demonstrated that PBLs were able to inhibit LDL oxidation in vitro and reduce the lipid accumulation in macrophages. We showed the underlying mechanisms to be the followings, PBLs up-regulated the protein levels of the class A and class B scavenger receptors, the membrane lipid transporter ABCA1, and its upstream regulator Liver X receptor (LXR) in the macrophages exposed to oxLDL. In the other hand, Hep3B cells which are p53 null were used to investigate the anti-tumor effect of PBLs in cell and in xenograft model. The results revealed that PBLs (0.1 to 1 mg/ml) induced a does- or time-dependent increase of cell toxicity. The underlying mechanisms as evidenced by flow cytometry and Western blot analysis showed that PBLs triggered ATM, cAbl, and p73 expressions and activated JNK, p38 and AMPK pathways that subsequently led to cell cycle arrest, mitochondria-dependent apoptosis and autophagy cell death. PBLs also inhibited tumor growth in Hep3B-bearing mice via inducing the MAPK-p73 pathway. Above all data suggested that PBLs activated the reverse cholesterol transport mechanism to enhance the metabolism of the oxLDL that could prevent both lipid accumulation and foam cell formation and further minimise the possible damage of vessels caused by the oxLDL. Beside, our results also demonstrated the in vitro and in vivo anti-tumor potential of PBLs supporting their application as a novel chemopreventive agent for the treatment of human hepatocellular carcinoma (HCC) in the future via targeting the p73 pathway.

並列關鍵字

Apoptosis ； Atherosclerosis ； Autophagy ； Hepatocellular carcinoma ； Oxidised low density lipoprotein ； Piper betle leaf ； p73 ； Reverse cholesterol transport

參考文獻

財團法人肝病防治學術基金會

Guan Y-S, He Q, La Z (2006) Roles of p53 in carcinogenesis, diagnosis and treatment of hepatocellular carcinoma. J Cancer Mol 2:191-197

Sridharan S, Jain K, Basu A (2011) Regulation of autophagy by kinases. Cancers 3(2):2630-2654

Abbas T, Dutta A (2009) p21 in cancer: intricate networks and multiple activities. Nature Reviews Cancer 9(6):400-414

Alsafadi S, Tourpin S, Andre F, Vassal G, Ahomadegbe J (2009) P53 family: at the crossroads in cancer therapy. Current medicinal chemistry 16(32):4328-4344

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荖葉水萃取物抗脂質氧化及抗肝癌功效評估

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