EFFECT OF SULFITE ON THE OXIDATIVE-METABOLISM OF HUMAN NEUTROPHILS - STUDIES WITH LUCIGENIN-DEPENDENT AND LUMINOL-DEPENDENT CHEMILUMINESCENCE

To assess the effect of sulphite on the oxidative metabolism of human neutrophils, chemiluminescence (CL) measurements were performed using lucigenin and luminol as chemiluminigenic probes. Lucigenin-dependent CL was used for measuring superoxide anion (O-2(-)) production. and lu minol-dependent CL was used for determination of myeloperoxidase (MPO) -connected processes. With sulphite concentrations of 0.01 to 1 mmol/L , resting neutrophils showed an up to sixfold increase of lucigenin-de pendent CL, but only a 1.9-fold increase of luminol-dependent CL. Subs equent stimulation of sulphite-treated neutrophils with phorbol myrist ate acetate (PMA) (soluble stimulant) or zymosan (particulate stimulan t) resulted in an additional significant increase of lucigenin-depende nt CL compared to stimulated control cells, whereas luminol-dependent CL increased slightly by 0.01 mmol/L sulphite and decreased then conti nuously. Sulphite concentrations above 1 mmol/L decreased both lucigen in- and luminol-dependent CL of resting and PMA- or zymosan-stimulated neutrophils. Lucigenin-dependent CL of sulphite-treated and subsequen tly stimulated neutrophils was strongly inhibited by extracellularly a dded superoxide dismutase, whereas luminol-dependent CL was markedly r educed by the MPO inhibitor azide. The intracellular activity of MPO i n neutrophils stimulated with PMA in the presence of sulphite (2 mmol/ L) was reduced by 55%. Sulphite (0.1 mmol/L) also inhibited strongly t he activity of MPO in a cell-free system. These results indicate that micromolar concentrations of sulphite exert a stimulating effect on th e O-2(-) production of neutrophils extracellularly, but have an inhibi tory effect on MPO-catalysed reactions intracellularly.