綠茶萃出物對維持酵母菌基因穩定性之影響

Abstract

綠茶已知含豐富多酚化合物，並被視為具抗癌與抗致突變性之物質。本篇研究探討綠茶萃出物對紫外線照射所誘發的酵母菌基因不穩定性之影響。將綠茶萃出物添加於培養液中進行酵母菌培養，之後再對酵母菌施予紫外光照射，以觀察其細胞存活率、細胞突變率、細胞週期、活性氧自由基群與修復相關基因之表現。結果顯示，綠茶組在紫外線照射後，其活性氧自由基群含量隨時間而下降;但控制組或EGCG及咖啡因處理組別則呈現上升之趨勢。然而，綠茶添加與否並無影響因紫外線照射所引起之細胞週期停滯現象。在抗氧化相關酵素基因表現的研究上則發現，綠茶可調節硫氧還原蛋白過氧化脢、超氧岐化脢與過氧化氫催化脢之基因表現。且DNA修復蛋白，RAD14和RAD51也在綠茶添加組有較強之基因表現。因此，綠茶添加組別顯現較控制組與其他對照組更高的細胞存活率，且其紫外線誘導基因突變比率，也是所有組別中最低的。綜合上述結論得知，綠茶萃出物可藉由降低活性氧自由基群，與活化氧化還原和DNA修復系統來達到穩定酵母菌基因體之正面效應。而本研究結果也證明，酵母菌可應用於探討生物活性成分之功能。

Green tea is renowned for containing rich polyphenols that are considered the anti-carcinogenic and anti-mutagenic agents. In this study, we investigated how green tea extract (GTE) affects yeast genome instability induced by UVB irradiation. Yeast was cultured in mediums with or without GTE. After UVB irradiation, the cells were collected for assays of survival, gene mutation, reactive oxygen species (ROS), cell cycle, and expressions of redox and repair genes. The reactive oxygen species (ROS) levels in cells were declined gradually after UVB exposure in GTE-treated group; nevertheless, an increasing trend was observed in control or EGCG or caffeine-treated group. However, the G1/S phase cell cycle arrest induced by UVB damage was unaffected by the addition of GTE. Furthermore, the gene expressions of antioxidative enzymes, TSA1, SOD1 and CTT1 were modulated by GTE. DNA-repair genes, RAD14 and RAD51, responsible for nucleotide excision repair and homologous recombination repair pathways respectively, were activated with GTE treatment. As a result, the cell survival rates were elevated while the gene mutation rates were decreased with the administration of GTE. In conclusion, we found that GTE had positive effects on the maintenance of genome stability in yeast through effectively lowering ROS levels, and activating redox and DNA repair systems. These results also demonstrate that yeast can be a powerful tool for distinguishing the biological functions of bioactive compounds.