Chemical studies on the effect of cooking and processing for functional sulfur-containing compounds in vegetables

流行病学证据表明，经常食用葱属植物与降低人类患胃癌和肠癌的风险有关。从大蒜和洋葱中提取的一些多硫化物已被证明对啮齿动物具有化学保护作用。有人认为，这种作用是由于它们对II相酶的诱导活性。相比之下，家畜和农场动物在食用大蒜和洋葱后有毒性反应的报道，包括对红细胞的氧化损伤和随后的溶血性贫血。在本研究中，我们比较了单硫化物、二硫化物和三硫化物在RL34细胞中产生ROS和诱导GST活性的能力。我们成功地证明了含有硫醇的三硫化物通过DCF荧光在RL34细胞中有效地产生了ROS。所有不含硫醇的硫化物和含有硫醇的单硫化物均不产生ROS。用三硫化物和硫醇与质粒DNA孵育，在体外检测到超螺旋DNA转化为开放环状DNA。在相同条件下，加入自由基清除剂、金属络合剂或过氧化氢酶可部分抑制硫醇激活的DNA切割。这些数据表明，超氧化物是通过硫醇-多硫化物途径产生的。我们还发现，三硫化合物在RL34细胞中显示出最强的GST诱导活性。因此，细胞内含有硫醇的三硫化物可以有效地承受氧化还原胁迫，并且三硫化物可能确实有助于诱导Allimn蔬菜的细胞毒性和防癌作用。

Epidemiological evidence indicates that regular consumption of the Allium genus is associated with a decrease of risk for stomach and intestine cancers in human. Some polysulfides from the Allium vegetables, such as garlic and onions, have been shown the chemoprotective effect in rodents. It has been suggested that this effect is due to their induction activity for phase II enzymes. In contrast, toxic effects have been reported in domestic and farm animals after consumption of garlic and onions, involving oxidative damage to erythrocytes and consequent hemolytic anemia. In the present study, we compared the ability of mono-, di-and trisulfides to generate ROS and induce GST activity in RL34 cells. We successfully demonstrated that trisulfides with thiols potently generated ROS by means of DCF fluorescence in RL34 cells. All sulfides without thiols and monosulfide with thiols did not generate any ROS. Upon incubation of plasmid DNA with trisulfides and thiols, the conversion of supercoiled DNA to its open circular form was detected in vitro. Under the same conditions, thiol-activated DNA cleavage was partially inhibited by the addition of radical scavengers, metal chelator or catalase. These data suggested that superoxide was generated through the thiol-polysulfide pathway. We also found that trisulfides showed the most potent induction activity of GST in RL34 cells. Therefore, redox stress could be effectively underwent by trisulfides with thiols inside the cells, and trisulfides may truly contribute to induce both cytotoxic and cancer-protective effects of Allimn vegetables.