Nitric oxide-forming reactions of the water-soluble nitric oxide spin-trapping agent, MGD

The objective of this study was to elucidate the nitric oxide-forming react ions of the iron-N-methyl-D-glucamine dithiocarbamate (Fe-MGD) complex from the nitrogen-containing compound hydroxyurea. The Fe2+(MGD)(2) complex is commonly used in electron paramagnetic resonance (EPR) spectroscopic detect ion of NO both in vivo and in vitro. The reaction of Fe2+(MGD)(2) with NO y ields the resultant NO-Fe2+(DETC)(2) complex, which has a characteristic tr iplet EPR signal. It is widely believed that only NO reacts with Fe2+(MGD)( 2) to form the NO-Fe2+(MGD)(2) complex. In this report, the mechanism leadi ng to the formation of NO-Fe2+(MGD)(2) was investigated using oxygen-uptake studies in conjunction with the EPR spin-trapping technique. We found that the air oxidation of Fe2+(MGD)(2) complex results in the formation of the Fe3+(MGD)(3) complex, presumably concomitantly with superoxide (O-2(.-)). D ismutation of superoxide forms hydrogen peroxide, which can subsequently re duce Fe3+(MGD)(3) back to Fe2+(MGD)(2). The addition of NO to the Fe3+(MGD) (3), complex resulted in the formation of the NO-Fe2+(MGD)(2) complex. Hydr oxyurea is not considered to be;a spontaneous NO donor, but has to be oxidi zed in order to form NO. We present data showing that in the presence of ox ygen, Fe2+(MCD)(2) can oxidize hydroxyurea to yield the stable NO-Fe2+(MGD) (2) complex. These results imply that hydroxyurea can be oxidized by reacti ve oxygen species that are formed from the air oxidation of the Fe2+(MGD)(2 ) complex. Formation of the NO-Fe2+(MGD)(2) complex in this case could erro neously be interpreted as spontaneous formation of NO from hydroxyurea. The chemistry of the Fe2+(MGD)(2) complexes in aerobic conditions must be take n into account in order to avoid erroneous conclusions. In addition, the us e of these complexes may contribute to the overall oxidative stress of the system under investigation. (C) 1999 Elsevier Science Inc.