MODULATION OF METAL-INDUCED CYTOTOXICITY BY MAILLARD REACTION-PRODUCTS ISOLATED FROM COFFEE BREW

Nondialyzable Maillard reaction products (MRPs) were recovered from th ree different coffee brew extracts (i.e., brewed, boiled, instant) to evaluate the efficacy of MRPs in modulating in vitro metal-induced cyt otoxicity in C3H/10T1/2 mouse embryo fibroblast cells, cultured in the presence of Fe2+, Fe3+, or Cu2+ ions. Preliminary experiments were pe rformed in an vitro linoleic acid emulsion model system to characteriz e the anti- or pro-oxidant activity of coffee MRPs. Cytotoxicity exper imental protocols involved both the direct application of metal ions a nd coffee MRPs to fibroblast cells, and the premixing of metal ions wi th coffee MRPs at room temperature prior to incubating with fibroblast cells. Fe2+ and Cu2+ significantly lowered the colonization efficienc y (CE) of cells at all three concentrations (i.e., 0.1, 10, 50 mu M) u sed. Similar Fe3+ activity was observed only at 50 mu M concentration. None of the coffee MRPs alone or together with 0.1 and 10 mu M of Fe2 + or Fe3+ produced cytotoxic effects during direct application. The pr emixing step, however, significantly enhanced the CE of cells compared to the control, denoting cytoprotection, only in the presence of Fe2. In addition, the application of MRPs with 0.1 or 10 mu M of Cu2+ sig nificantly lowered the CE of cells than the control, but enhanced the CE of cells than the Cu2+ added control. These results corresponded di rectly with the results of model linoleic acid emulsion test, thereby demonstrating that lipid hydroperoxide generation is the source for fi broblast cell toxicity when MRPs are added to cells together with meta l ions. These results further indicate that coffee MRPs can suppress i n vitro metal-induced cytotoxicity to a certain extent when Fe2+, Cu2, or Fe3+ ions are present below a concentration of 50 mu M, possibly by chelating the metal ions. Ionic reducing capacity of coffee MRPs, a lbeit small, may explain the potential for increased cytotoxicity at h igher coffee MRP concentrations.