Modulation of Metal-induced Genotoxicity by Maillard Reaction Products Isolated from Coffee

Abstract

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 Fe 2+ 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 Fe 2+, or following a short preincubation period conducted with Fe 2+ 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 Fe 2+ alone, in a dose-dependent manner at all pH conditions tested. At low MRP concentrations, damage to DNA with respect to Fe 2+ was lowered only when MRPs were preincubated with Fe 2+ in argon or oxygen before incubating with DNA. The addition of MRPs and Fe 2+ to DNA without preincubation, had no effects in protecting DNA damage. This finding showed that a preincubation step is necessary for MRPs to chelate Fe 2+ in order to mitigate the Fenton reaction. In contrast, the protective effects against Fe 2+-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 Fe 2+ actually enhanced the breakage of DNA with respect to the control. These results indicate that MRPs at high concentrations do not improve Fe 2+ ion chelation, but rather accelarate the DNA breakage by possibly changing the redox state of the transition element.