GENERATION OF OXYGEN RADICALS FROM IRON COMPLEX OF ORELLANINE, A MUSHROOM NEPHROTOXIN - PRELIMINARY ESR AND SPIN-TRAPPING STUDIES

Orellanine, [2,2'-bipyridine]-3,3',4,4'-tetrol-1,1'-dioxide, is the to xin responsible for the lethal nephrotoxicity of some Cortinarius mush rooms. Our present ESR and spin-trapping studies of the redox properti es of the system of non-illuminated orellanine, ferrous iron and dioxy gen contribute to understanding the molecular mechanism of its toxicit y. UV-visible spectrophotometry, cyclic voltammetry and ESR in frozen medium showed the formation of a wine-red tris complex, Fe(III)Or(3). This ferric complex is easily reducible (E-p = -565 mV vs Ag/AgCl/3M K Cl at pH 7), involving a one-electron reversible process. Spin-trappin g using DMPO is employed to detect the generation of superoxide anion and hydroxyl radicals. The instantaneous one-electron oxidation of fer rous ions in the presence of the toxin under air is concomitant with d ioxygen consumption as supported by dioxygen consumption. GSH involves the toxin and ferrous ions under air in a redox cycling process resul ting in the production of glutathionyl and oxygen free radicals, obser ved for the first time with an iron complex of a mushroom toxin. In mo st cases, EDTA is not able to prevent the Fe(III)Or(3) and radical for mation. The ortho-dihydroxylated groups borne by the di-N-oxidized bip yridine structure and not the bipyridine structure itself, are respons ible for the formation of a stable ferric complex at pH 7, as they are for the generation of an apparently stable ortho-semiquinone anion ra dical. These one-electron mechanisms may play a major role in some of the known toxic effects of orellanine.