Wijewickreme A N, Kitts D D
University of British Columbia, Department of Food Science, Vancouver, Canada.
Food Chem Toxicol. 1998 Jul;36(7):543-53. doi: 10.1016/s0278-6915(98)00007-6.
PM2 bacteriophage DNA was exposed to non-dialysable Maillard reaction products (MRPs) isolated from brewed (Br), boiled (Bo) and instant (I) coffee brew extracts in a Fe2+ catalysed Fenton reaction at four pH conditions (i.e. 7.5, 4.0, 3.2, 2.6). MRPs were incubated with DNA either directly with Fe2+, or following a short preincubation period conducted with Fe2+ in an atmosphere of oxygen or argon. Damage to supercoiled DNA resulting in strand scissions as characterized by both nicked circular and linear forms were found to occur either with coffee MRPs or Fe2+ alone, in a dose-dependent manner at all pH conditions tested. At low MRP concentrations, damage to DNA with respect to Fe2+ was lowered only when MRPs were preincubated with Fe2+ in argon or oxygen before incubating with DNA. The addition of MRPs and Fe2+ to DNA without preincubation, had no effects in protecting DNA damage. This finding showed that a preincubation step is necessary for MRPs to chelate Fe2+ in order to mitigate the Fenton reaction. In contrast, the protective effects against Fe2+-induced DNA breakage by MRPs were lost at high coffee MRP concentrations, irrespective of the incubation method used. Increasingly higher concentrations of MRPs in combination with Fe2+ actually enhanced the breakage of DNA with respect to the control. These results indicate that MRPs at high concentrations do not improve Fe2+ ion chelation, but rather accelerate the DNA breakage by possibly changing the redox state of the transition element.
在四种pH条件下（即7.5、4.0、3.2、2.6），将PM2噬菌体DNA暴露于从冲泡（Br）、煮沸（Bo）和速溶（I）咖啡冲泡提取物中分离出的非透析美拉德反应产物（MRPs），使其在Fe2+催化的芬顿反应中发生反应。MRPs与DNA一起，要么直接与Fe2+孵育，要么在Fe2+存在下于氧气或氩气气氛中进行短暂预孵育后再与DNA孵育。发现无论是咖啡MRPs单独存在还是Fe2+单独存在，在所有测试的pH条件下，都会以剂量依赖的方式导致超螺旋DNA损伤，产生以带切口的环状和线性形式为特征的链断裂。在低MRP浓度下，只有当MRPs在氩气或氧气中与Fe2+预孵育后再与DNA孵育时，相对于Fe2+对DNA的损伤才会降低。未进行预孵育就将MRPs和Fe2+添加到DNA中，对保护DNA损伤没有作用。这一发现表明，MRPs螯合Fe2+以减轻芬顿反应需要一个预孵育步骤。相比之下，无论采用何种孵育方法，在高咖啡MRP浓度下，MRPs对Fe2+诱导的DNA断裂的保护作用都会丧失。与对照组相比，越来越高浓度的MRPs与Fe2+结合实际上增强了DNA的断裂。这些结果表明，高浓度的MRPs不会改善Fe2+离子螯合，而是可能通过改变过渡元素的氧化还原状态加速DNA断裂。
