The spin-trapping of enzymatically and chemically catalyzed free radicals from indolic compounds.

A nitrogen-centered free radical was spin-trapped from superoxide-catalyzed oxidation of indolic compounds, using the spin-trap phenyl-t-butyl-nitrone. The hyperfine splitting constants observed were aN = 13.9 G, a beta N = 3.6 G and a beta H = 2.3 G. Incubation of various indolic compounds with goat lung microsomes showed that only 3-methylindole was able to generate a free radical in the NADPH-dependent microsomal system, as tested by spin-trapping. The splitting constants were the same as those seen with superoxide incubations with 3-methylindole. The study demonstrates the generality of formation of a nitrogen-centered free radical from various indolic compounds. Enzymatic radical formation from 3-methylindole suggests a microsomal-activated free radical mechanism for the specificity of 3-methylindole-induced pulmonary toxicity.