Effect of antioxidants on induction time of luminol luminescence elicited by 3-morpholinosydnonimine (SIN-1)

The reaction between luminol as a chemiluminescence probe and 3-morpholinos ydnonimine (SIN-1) as a peroxynitrite donor was evaluated in order to deter mine the action of several antioxidants. Several well-known antioxidants fo und in biological fluids or cells modify the light profile of the reaction between SIN-1 and luminol. One main modification was characterized by a tra nsient suppression of the light signal, thus permitting evaluation of an in duction time (sigma) which is linearly related to the concentration of the additive. From induction time measurements and using Trolox as a reference antioxidant, the trapping ability of a compound against oxidants and radica ls produced in the luminol SIN-1 reaction at pH 7.4 was determined. Uric ac id showed higher antioxidant capacity than Trolox, while bilirubin and asco rbic acid, in decreasing order, were slightly less efficient. On the other hand the main modification of the light signal produced by superoxide dismu tase, desferrioxamine and myoglobin was characterized by a decrease of the luminescence during the course of the reaction. The reaction luminol-SIN-1 was compared with the known luminol-ABAP (2,2'-azo-bis-2-amidinopropane) me thod for evaluation of antioxidant capacity in human plasma, since this bio logical fluid modifies the luminol-SIN-1 reaction with well-defined inducti on times. Samples were obtained from patients with sepsis, a condition wher e it has been postulated that excess oxygen radicals including peroxynitrit e are produced. Using Trolox as reference, the results (mean +/- standard e rror of mean) of both assays showed that the patients (SIN-1, 263 +/- 16; A BAP, 218 +/- 13; n = 19) have significantly (SIN-1, p < 0.02; ABAP, p < 0.0 01) lower values in comparison to non-septic controls (SIN-1, 330 +/- 16; A BAP, 398 +/- 16; n = 20). SIN-1 could be useful as a source of oxidant for the characterization of antioxidant behaviour in a system where superoxide and nitric oxide are simultaneously generated. Copyright (C) 1999 John Wile y & Sons, Ltd.