Copper, zinc-superoxide dismutase and hydrogen peroxide: a hydroxyl radical generating system.
Because superoxide (O2-.) is a mediator of inflammation, Cu,Zn-superoxide dismutase (Cu,Zn-SOD) has been employed as an anti-inflammatory compound. However, Cu,Zn-SOD can increase intra- and extracellular H2O2. This may react with the Cu atom of SOD in a Fenton-type reaction producing the hydroxyl radical (.OH). With a non-physiological concentration of H2O2 (0.8 mmol/l) to stimulate chemiluminescence (CL) at a level < 2 mV, it was observed that the addition of Cu,Zn-SOD (100 micrograms/ml) yielded an increase of 204.7 +/- 78.2 mV (P < 0.05). This increase in CL depended on the concentrations of H2O2 and Cu,Zn-SOD and was only seen with luminol (reacts with O2-. and .OH) but not with lucigenin (reacts with O2-.). No CL was observed when Cu,Zn-SOD was heat inactivated, or when Mn-SOD was used. Dissipators of H2O2, copper chelators and .OH scavengers attenuated this CL. In electron paramagnetic resonance, with the use of the spin-trap dimethylpyrroline-N-oxide (DMPO), it was demonstrated that, in the reaction between H2O2 and Cu,Zn-SOD, .OH was generated. The oxidation of keto-methylthiobutyric acid (KMB) to ethylene, assessed by gas chromatography, demonstrated that H2O2/Cu,Zn-SOD-generated .OH can react with KMB and not only with the SOD molecule itself. We conclude that H2O2 reduces SOD-bound Cu2+ to Cu1+ which, in reaction with H2O2 catalyses its reduction to OH. Whether this 'pro-inflammatory' reaction occurs in vivo remains to be established.
Department of Gastroenterology, University Hospital, Utrecht, The Netherlands.
J C
JC
Koningsberger
B S
BS
van Asbeck
E
E
van Faassen
L J
LJ
Wiegman
J
J
van Hattum
G P
GP
van Berge Henegouwen
J J
JJ
Marx
D000166:Acridines / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry; D002849:Chromatography, Gas; D004578:Electron Spin Resonance Spectroscopy; D016166:Free Radical Scavengers; D006861:Hydrogen Peroxide / Q000737:chemistry*; D017665:Hydroxyl Radical; D008163:Luminescent Measurements; D008165:Luminol / Q000737:chemistry; D013482:Superoxide Dismutase / Q000737:chemistry*
D000166:Acridines; D002614:Chelating Agents; D016166:Free Radical Scavengers; C033472:10,10'-dimethyl-9,9'-biacridinium; D017665:Hydroxyl Radical; D008165:Luminol; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase