Abstract
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.
Footnotes
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This study was supported by National Institutes of Health Grants AI46424 (to D.C.M.) and C06 RR015455 to the MUSC BSB/CRI Animal Facility. The studies reported in this article were presented in part at the Experimental Biology Meeting, 2004 April 17–21; Washington, DC (Z.S.B.) and the 44th Annual Meeting of the Society of Toxicology, 2005 March 6–10; New Orleans, LA (Z.S.B.).
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doi:10.1124/jpet.105.090407.
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ABBREVIATIONS: G6PD, glucose-6-phosphate dehydrogenase; 5-HPQ, 5-hydroxyprimaquine; GSH, reduced glutathione; ROS, reactive oxygen species; DEM, diethyl maleate; HBSS, Hanks' buffered saline solution.
- Received June 2, 2005.
- Accepted August 10, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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