Validation of lucigenin (bis-N-methylacridinium) as a chemilumigenic probe for detecting superoxide anion radical production by enzymatic and cellular systems

Abstract

Lucigenin is most noted for its wide use as a chemiluminescent detector of superoxide anion radical (O2-.) production by biological systems. However, its validity as a O2-.-detecting probe has recently been questioned in view of its ability to undergo redox cycling in several in vitro enzymatic systems, which produce little or no O2-.. Whether and to what extent lucigenin redox cycling occurs in systems that produce significant amounts of O2-. has not been carefully investigated. We examined and correlated three end points, including sensitive measurement of lucigenin-derived chemiluminescence (LDCL), O2 consumption by oxygen polarography, and O2-. production by 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide spin trapping to characterize the potential of lucigenin to undergo redox cycling and as such to act as an additional source of O2-. in various enzymatic and cellular systems. Marked LDCL was elicited at lucigenin concentrations ranging from 1 to 5 microM in all of the O2-.-generating systems examined, including xanthine oxidase (XO)/xanthine, lipoamide dehydrogenase/ NADH, isolated mitochondria, mitochondria in intact cells, and phagocytic NADPH oxidase. These concentrations of lucigenin were far below those that stimulated additional O2 consumption or O2-. production in the above systems. Moreover, a significant linear correlation between LDCL and superoxide dismutase-inhibitable cytochrome c reduction was observed in the XO/ xanthine and phagocytic NADPH oxidase systems. In contrast to the above O2-.-generating systems, no LDCL was observed at non-redox cycling concentrations of lucigenin in the glucose oxidase/glucose and XO/NADH systems, which do not produce a significant amount of O2-.. Thus, LDCL still appears to be a valid probe for detecting O2-. production by enzymatic and cellular sources.