大蒜中有機硫化合物成份在肝腫瘤細胞對麩胺基硫轉移酵素 的調節

大蒜中有機硫化合物成份在肝腫瘤細胞對麩胺基硫轉移酵素 的調節

 很多研究報告發現，大蒜及其中所富含的有機硫化合物成份 (organosulfur compounds)

具有預防癌症發生的作用。大蒜抑制癌症的其中一個可能機轉是藉由改變生物體內解毒酵素 (drug metabolizing enzymes) 的活性，麩胺基硫轉移酵素 (GST, glutathione S-

transferase) 即為其中一種解毒酵素。在動物實驗 (in vivo) 中已得知，以大蒜萃取物

餵食老鼠，會增加其體內 GST 酵素活性 , 但有關的詳細機轉尚未被確認出來。所以，本研究 乃以體外實驗 (in vitro) 來探討，大蒜的有機硫化合物成份 dially sulfide (DAS) 在細胞

培養 (cell culture) 的實驗模型中，是否會誘導 GST 的酵素活性 , 並進一步去探討其對此

酵素的調節機轉。實驗結果顯示，小老鼠肝腫瘤細胞株 (Hepa-1c1c7) 的 GST 酵素在 5 mM DAS 處理之後，於 16 、 24 和 48 小時活性有顯著性增加的現象。而細胞以不同濃度 DAS 培養 24 小時 後 ， 0.5 、 1 和 5 mM DAS 組的 GST 酵素活性和對照組比較有顯著增加情形；若將培養時間改為 48 小 時則只有 5 mM DAS 組的 GST 酵素活性有顯著增加。利用 SDS-PAGE 和 Western blot 分析 GST 的 三種酵素異構物 (isoenzymes) , GST-alpha 、 GST-mu 和 GST-pi 的蛋白質含量，得知三種

酵素異構物的蛋白質含量有隨 DAS 濃度增加而增加的趨勢，但並無統計上差異。由此可知，

DAS 這種大蒜有機硫化合物成份，在 Hepa-1c1c7 細胞中可能會增加 GST 三種酵素異構物的 蛋白質含量並增加 GST 酵素活性，推論可能進一步增強生物體的解毒功能，達到抑制癌症的 發生。

Regulation of glutathione S-transferase by organos ulfur compounds derived from garlic in hepatoma c

ells

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Many studies have demonstrated that garlic and its organosulfur compounds can protect against various kinds of cancer and chemically induced toxicity.

Modification of the expression of drug metabolizing enzymes such as

glutathione S-transferase (GST) is thought to be one of the mechanisms of the anticarcinogenic effect of garlic. It has been revealed the GST enzyme

activities could be enhanced in the animals fed with garlic extracts. To obtain further insight on the induction of the GST enzyme activities and on the anticarcinogenic action of garlic, we have used a cultured cell system to study the effect of DAS, an organosulfur compound derived from garlic, on the induction of GST. When murine hepatoma cell line, Hepa-1c1c7 (Hepa-1), was treated with 5 mM DAS, the GST enzyme activity increased significantly after 16, 24 and 48 h treatment. When the cells were treated with 0.5, 1 and 5 mM DAS for 24 h, the GST activity increased with increased DAS concentrations.

Furthermore, Western blotting analysis showed that three GST proteins, GST-alpha, GST-mu and GST-pi, tend to increase with increasing DAS

concentration. In summary, the results suggest that GST enzyme activity can be enhanced by DAS in Hepa-1 cells, and the increased expression of the corresponding GST proteins contributes to the augementation. The increased GST activity may explain, at least in part, the auticarcinogenic effect of

garlic.