Nitroxide stable radical prevents primaquine-induced lysis of red blood cells

Primaquine (PQ), an antimalarial drug, is known to produce multiple oxidative effects in red blood cells (RBC). Because H₂O₂, OH and intracellular superoxide are implicated in this oxidation, the effect of cell-permeable nitroxide, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) capable of scavenging O₂^._ has been studied. PQ caused RBC lysis and facilitated the oxidation of oxyhemoglobin (oxyHb) to methemoglobin (MetHb). The lysis was partially inhibited by catalase and by the metal chelating agent, 2,2-dipyridyl. TEMPO blocked PQ-induced RBC lysis in dose-dependent manner (2 mM IC₅₀)_bu enhanced the oxidation of oxyHb to MetHb. PQ facilitated the lysis also in the presence of CO without affecting Hb oxidation. This hemolysis, was inhibited by TEMPO. The results indicated that: (a) no causative relationship exists between PQ-induced Hb oxidation and RBC lysis; (b) TEMPO can directly oxidize heme-iron without causing membrane injury; (c) the aerobic toxicity of PQ in this system is mediated by O₂^._ and H₂O₂ and possibly by redox-active labile metals (d) TEMPO can protect by detoxifying O₂^._ and oxidizing reduced labile metal ions and thus blocking their participation in Fenton reaction.