In vivo evidence of hydroxyl radical formation after acute copper and ascorbic acid intake: electron spin resonance spin-trapping investigation.

Copper has been suggested to facilitate oxidative tissue injury through a free radical-mediated pathway analogous to the Fenton reaction. By applying the ESR spin-trapping technique, evidence for hydroxyl radical formation in vivo was obtained in rats treated simultaneously with copper and ascorbic acid. A secondary radical spin-trapping technique was used in which the hydroxyl radical formed the methyl radical upon reaction with dimethylsulfoxide. The methyl radical was then detected by ESR spectroscopy as its adduct with the spin trap phenyl-N-t-butylnitrone (PBN). Because copper excreted into the bile from treated animals is expected to be maintained in the Cu(I) state (by ascorbic acid or glutathione), a chelating agent that would redox-stabilize it in the Cu(I) state was used to prevent ex vivo redox chemistry. Bile samples were collected directly into solutions of bathocuproinedisulfonic acid, a Cu(I)-stabilizing agent, and 2,2'-dipyridyl, a Fe(II)-stabilizing agent. If these precautions were not taken, radical adducts were generated ex vivo and could be mistaken for radical adducts generated in vivo and excreted into the bile. Besides the PBN/.CH3 adduct, three other radical adducts were produced in vivo and excreted in bile.