Generation of (OH)-O-. initiated by interaction of Fe2+ and Cu+ with dioxygen; comparison with the Fenton chemistry

Iron and copper toxicity has been presumed to involve the formation of hydr oxyl radical ((OH)-O-.) from H2O2 in the Fenton reaction. The aim of this s tudy was to verify that Fe2+-O-2 and Cu+-O-2 chemistry is capable of genera ting (OH)-O-. in the quasi physiological environment of Krebs-Henseleit buf fer (KH), and to compare the ability of the Fe2+-O-2 system and of the Fent on system (Fe2+ + H2O2) to produce (OH)-O-.. The addition of Fe2+ and Cu+ ( 0-20 muM) to KH resulted in a concentration-dependent increase in (OH)-O-. formation, as measured by the salicylate method. While Fe3+ and Cu2+ (0-20 muM) did not result in (OH)-O-. formation, these ions mediated significant (OH)-O-. production in the presence of a number of reducing agents. The (OH )-O-. yield from the reaction mediated by Fe2+ was increased by exogenous F e3+ and Cu2+ and was prevented by the deoxygenation of the buffer and reduc ed by superoxide dismutase, catalase, and desferrioxamine. Addition of 1 mu M, 5 muM or 10 muM Fe2+ to a range of H2O2 Concentrations (the Fenton syste m) resulted in a H2O2-concentration-dependent rise in (OH)-O-. formation. F or each Fe2+ concentration tested, the (OH)-O-. yield doubled when the rati o [H2O2]:[Fe2+] was raised from zero to one. In conclusion: (i) Fe2+-O-2 an d Cu+-O-2 chemistry is capable of promoting (OH)-O-. generation in the envi ronment of oxygenated KH, in the absence of pre-existing superoxide and/or H2O2, and possibly through a mechanism initiated by the metal autoxidation; (ii) The process is enhanced by contaminating Fe3+ and Cu2+; (iii) In the presence of reducing agents also Fe3+ and Cu2+ promote the (OH)-O-. formati on; (iv) Depending on the actual [H2O2]:[Fe2+] ratio, the efficiency of the Fe2+-O-2 chemistry to generate (OH)-O-. is greater than or, at best, equal to that of the Fe2+-driven Fenton reaction.