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

流行病学证据表明，经常食用葱属植物可降低人类患胃癌和肠癌的风险。一些来自葱属蔬菜的多硫化物，如大蒜和洋葱，已被证明对啮齿动物具有化学保护作用。有人认为这种效应是由于它们对II期酶的诱导活性。相比之下，据报道家畜和农场动物食用大蒜和洋葱后出现毒性作用，包括红细胞氧化损伤和由此引起的溶血性贫血。在本研究中，我们比较了单、二和三硫化物在RL34细胞中产生ROS和诱导GST活性的能力。我们通过DCF荧光在RL34细胞中成功地证明了含硫醇的三硫化物能有效地产生ROS。所有不含硫醇的硫化物和含硫醇的单硫化物均不产生ROS。在质粒DNA与三硫化物和硫醇孵育后，在体外检测超卷曲DNA向开放环状形式的转化。在相同条件下，添加自由基清除剂、金属螯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-多硫途径产生的。我们还发现三硫化物在RL34细胞中表现出最有效的GST诱导活性。因此，三硫化物可以有效地承受细胞内硫醇的氧化还原应激，三硫化物可能真正有助于诱导allin蔬菜的细胞毒性和抗癌作用。

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.