Primaquine-Induced Hemolytic Anemia: Formation and Hemotoxicity of the Arylhydroxylamine Metabolite 6-Methoxy-8-hydroxylaminoquinoline

摘要

Primaquine is an important antimalarial agent because of its activity against exoerythrocytic forms of Plasmodium spp. However, methemoglobinemia and hemolytic anemia are dose- limiting side effects of primaquine therapy that limit its efficacy. These hemotoxicities are thought to be mediated by metabo- lites; however, the identity of the toxic species has remained unclear. Since N-hydroxy metabolites are known to mediate the hemotoxicity of several arylamines, the present studies were undertaken to determine whether 6-methoxy-8-aminoquinoline (6-MAQ), a known human metabolite of primaquine, could un- dergo N-hydroxylation to form a hemotoxic metabolite. When 6-MAQ was incubated with rat and human liver microsomes, a single metabolite was detected by high performance liquid chromatography (HPLC) with electrochemical detection. This metabolite was identified as 6-methoxy-8-hydroxylamin-oquinoline (MAQ-NOH) by HPLC and mass spectral analyses. As measured by decreased survival of 5'Cr-Iabeled erythro- cytes in rats, MAQ-NOH was hemolytic in vivo. Furthermore, in vitro exposure of 5' Cr-Iabeled erythrocytes to MAQ-NOH caused a concentration-dependent decrease in erythrocyte survival (EC50 of 350 ILM) when the exposed cells were returned to the circulation of isologous rats. MAQ-NOH also induced the formation of methemoglobin when incubated with suspensions of rat erythrocytes. These data indicate that 6-MAQ can be metabolized to MAQ-NOH by both rat and human liver micro- somes and that MAQ-NOH has the requisite properties to be a hemotoxic metabolite of primaquine. The contribution of MAQ- NOH to the hemotoxicity of primaquine in vivo remains to be assessed.