TY - JOUR T1 - Primaquine-Induced Hemolytic Anemia: Role of Splenic Macrophages in the Fate of 5-Hydroxyprimaquine-Treated Rat Erythrocytes JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 980 LP - 986 DO - 10.1124/jpet.105.090407 VL - 315 IS - 3 AU - Zachary S. Bowman AU - David J. Jollow AU - David C. McMillan Y1 - 2005/12/01 UR - http://jpet.aspetjournals.org/content/315/3/980.abstract N2 - Primaquine-induced hemolytic anemia is known to result from premature sequestration of damaged (but intact) erythrocytes by the spleen. We have shown previously that a phenolic metabolite, 5-hydroxyprimaquine (5-HPQ), is a direct-acting hemolytic agent in rats, suggesting that 5-HPQ is a mediator of the hemolytic response to 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 readministered 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 with 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. A role for phagocytic removal of 5-HPQ-treated red cells was confirmed in vitro using the J774A.1 macrophage cell line. Furthermore, depletion of red cell GSH with diethyl maleate significantly enhanced in vitro phagocytosis of 5-HPQ-treated red cells. The data indicate that splenic macrophages are responsible for removing 5-HPQ-treated red cells and support the postulate that this metabolite is a contributor to the hemolytic anemia induced after administration of the parent compound. The American Society for Pharmacology and Experimental Therapeutics ER -