Primaquine-induced hemolytic anemia: Hemotoxicity of 5-hydroxyprimaquine (5-HPQ).

摘要

Primaquine is an important antimalarial agent because of its activity against exoerythrocytic forms of Plasmodium sp. Methemoglobinemia and hemolytic anemia, however, are dose-limiting side effects of primaquine therapy. These hemotoxic effects are believed to be mediated by metabolites, though the identity of the toxic specie(s) and the mechanism underlying hemotoxicity have remained unclear. Previous studies showed that an N-hydroxylated metabolite of primaquine, 6-methoxy-8-hydroxylaminoquinoline, was capable of mediating primaquine-induced hemotoxicity. The present studies were undertaken to investigate the hemolytic mechanism of 5-hydroxyprimaquine (5-HPQ), a phenolic metabolite that has been detected in experimental animals.; 5-HPQ was synthesized, isolated by flash chromatography and characterized by NMR spectroscopy and mass spectrometry. In vitro exposure of 51Cr-labeled erythrocytes to 5-HPQ induced a concentration-dependent decrease in erythrocyte survival (TC50 ∼40 muM) when the exposed cells were returned to the circulation of isologous rats. 5-HPQ also induced methemoglobin formation and depletion of glutathione (GSH) when incubated with suspensions of rat erythrocytes. Furthermore, when red cell GSH was depleted (>95%) by titration with diethyl maleate to mimic GSH instability in human glucose-6-phosphate dehydrogenase deficiency, a 5-fold enhancement of hemolytic activity was observed. These data indicate that 5-HPQ also has the requisite properties to contribute to the hemotoxicity of primaquine.; To investigate the fate of erythrocytes in vivo after in vitro exposure to 5-HPQ, rat 51Cr-labeled erythrocytes were incubated with hemolytic concentrations of 5-HPQ and then re-administered intravenously to rats. The time-course of loss of radioactivity from blood and uptake into the spleen and liver was measured. In rats given 5-HPQ-treated erythrocytes, an increased rate of removal of radioactivity from the circulation was observed as compared to the vehicle control. The loss of blood radioactivity was accompanied by a corresponding increase in radioactivity appearing in the spleen but not in the liver. When rats were pretreated with clodronate-loaded liposomes to deplete splenic macrophages, there was a decreased rate of removal of radioactivity from the circulation and a markedly diminished uptake into the spleen.