Oxygen-dependent free radicals in spermine oxidation cytostasis and chemiluminescence and the role of superoxide dismutase

Abstract

Spermine interacted with serum polyamine oxidase (PAO) to arrest proliferation of cultured Bri8 lymphocytes. Arrest was independent of catalase activity and was not directly due to an H₂O₂ byproduct. Arrest was averted by 3-hydroxybenzyloxyamine, which inactivates the pyridoxal co-factor of PAO. The oxidation of spermine in the presence of different concentrations of PAO was non-linear, which implied complex intermediate events for conversion of spermine to labile di-oxidized spermine (N,N′-bis(3-propionaldehyde)-1,4-butanediamine) with, perhaps, overall generation of free radicals (O₂^-· and ·OH) which are damaging to cells. Exogenous free radicals were apparently neither direct participants in cytostasis, nor in the chemiluminescence demonstrable for spermine oxidation. Thiourea, an ·OH scavenger, protected against both proliferation arrest and luminescence. Many other powerful ·OH scavengers, however, were ineffective. Though reaction mixtures reduced ferricytochrome c initially, reduction was not inhibited by superoxide dismutase (SOD) which indicated that the anion O₂^-· had not been generated. The powerful reducing capability of di-oxidized spermine itself could have competed against any O₂^-· for ferricytochrome c reduction. Nevertheless, O₂^-· was generated during further PAO conversion and/or auto-oxidation of di-oxidized spermine. Curiously, addition of SOD to destroy presumptive O₂^-· variably potentiated cytotoxicity. Blockage of any anion channels in the cell plasma membrane by stilbene derivatives did not influence cytotoxicity. Thus, findings support our previous evidence that cationic di-oxidized spermine is a potent G₁ inhibitor of cell proliferation. The possibility of intracellular free-radical and thiol involvement is discussed.