L-012, a luminol-based chemiluminescent (CL) probe, is widely used in vitro and in vivo to detect NADPH oxidase (Nox)-derived superoxide (O2(*-)) and identify Nox inhibitors. Yet understanding of the free radical chemistry of the L-012 probe is still lacking. We report that peroxidase and H2O2 induce superoxide dismutase (SOD)-sensitive, L-012-derived CL in the presence of oxygen. O2(*-) alone does not react with L-012 to emit luminescence. Self-generated O2(*-) during oxidation of L-012 and luminol analogs artifactually induce CL inhibitable by SOD. These aspects make assays based on luminol analogs less than ideal for specific detection and identification of O2(*-) and NOX inhibitors.
Keywords: 8-amino-5-chloro-7-phenylpyrido[3,4–d]pyridazine-1,4(2H,3H)dione; CAT; CL; Free radicals; HE; HRP; HX; L-012; Luminescence; Luminol; NADPH oxidase; NADPH oxidases; Nox; O(2)(−); ROS; Redox cycling; Redox probe; SOD; Superoxide radical anion; XO; catalase; chemiluminescence; diethylenetriaminepentaacetate; dtpa; horseradish peroxidase; hydroethidine; hypoxanthine; reactive oxygen species; superoxide dismutase; superoxide radical anion; xanthine oxidase.
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