Antioxidants suitable for use with chemiluminescence to identify oxyradical species

Abstract

From a panel of 24 alleged antioxidants the most suitable antioxidants (AO) for use with chemiluminescence (CL) experiments were determined. Superoxide dismutase (SOD), using luminol as the chemiluminescence probe (Lum-CL), was inhibitory only towards O₂^•- and not HO^• or ¹O₂. SOD was thus a suitable antioxidant for O₂^•-, as was tiron. Tiron had advantages, however, since SOD acted as a pro-oxidant in the presence of H₂O₂ or H₂O₂/HO^• generators. The two most suitable antioxidants for ¹O₂ were diphenylisobenzofuran (DBF) and tryptophan, for both Lum and Lucigenin-CL (Luc-CL). Desferrioxamine, with both Lum and Luc-CL, was a very effective scavenger for HO^•, but appeared to be an even more effective scavenger for ¹O₂. Cysteamine showed the best discrimination between IC₅₀s when the two ¹O₂ generators NaOCl/H₂O₂ and NDPO₂ were compared. Cysteamine was, therefore, the only scavenger that was appropriate for studies with hypochlorite. Melatonin, with Lum-CL, was found to be the most suitable scavenger for HO^•. Mannitol, the classical AO for HO^•, was not suitable when used with CL since it acted as a pro-oxidant. Some of the AOs revealed either calyx- or bell-shaped CL inhibition profiles and presumably, therefore, may act as both pro- or antioxidants at different concentrations. Antioxidants showing these kinds of dual activities should be used with caution in CL studies.