Date of Award
Ph.D. in Pharmaceutical Sciences
Babu L. Tekwani
Larry A. Walker
John M. Rimoldi
The 8-aminoquinoline (8AQ) antimalarial drug primaquine (PQ) is the only drug for prevention of malaria relapse. Moreover, PQ also has gametocytocidal activity against Plasmodium falciparum. However, clinical use of PQ has been limited due to its hemolytic toxicity, especially in glucose-6-phosphate dehydrogenase deficient (G6PDd) individuals. Phenolic and quinone metabolites generated via cytochrome P450-dependent pathways appear to be responsible for hemolytic effects of PQ. However, the mechanism for the hemolytic toxicity of PQ is still poorly understood. To explore the mechanism, targets, and pathways for toxicity of PQ, normal and G6PDd human erythrocytes were treated with the potential hemotoxic metabolites of PQ namely, 5-hydroxy-primaquine (5-HPQ), 5,6-orthoquinone primaquine (5,6-OQPQ) and 6-methoxy-8-hydroxylaminoquinoline (MHQ). The early and late biomarkers of hemotoxicity were investigated to explore the mechanism of PQ toxicity. 5HPQ, 5,6-OQPQ, and MHQ caused marked increase in methemoglobin formation and generated robust oxidative stress in both normal and G6PDd human erythrocytes. However, these metabolites depleted reduce glutathione (GSH) levels selectively in G6PDd human erythrocytes. Treatment with 5,6-OQPQ also induced eryptosis in G6PDd erythrocytes, as determined by phosphatidylserine exposure (Annexin V binding). This study was further extended to investigate the role of NRH-quinone oxidoreductase 2 (NQO2) in PQ-induced hemolytic toxicity. NQO2, has a potential function in metabolic detoxification or activation of quinones and quinone-based drugs. Co-treatment of erythrocytes with NQO2 inhibitors potentiated the hemotoxic response of PQ metabolites. The computational docking studies suggested stronger interactions of PQ metabolites with NQO2 compared to melatonin (the NQO2 inhibitor) and menadione (the NQO2 substrate). Together these results suggest that NQO2 might have a protective role against PQ-induced hemolytic toxicity. The PQ metabolite, 5,6-OQPQ was further evaluated for the effects on the non-targeted global metabolomic profile of normal and G6PDd human erythrocytes. The GSH-methionine-glutamate pathway metabolites were greatly affected by G6PD deficiency. Treatment with 5,6-OQPQ also significantly modified GSH-methionine-glutamic acid pathway in erythrocytes. Treatment also increased the levels of antioxidant and hemolysis related markers in erythrocytes. These studies provide a better insight into the pathophysiology of hemolytic toxicity caused by PQ in the G6PDd population.The new knowledge generated would provide rational bases for controlling toxicity of PQ and designing 8AQ analogs with better safety and therapeutic profiles.
Jain, Jagrati, "Biochemical and Molecular Assessment of Toxicity of Primaquine Metabolites on Erythrocytes" (2017). Electronic Theses and Dissertations. 1480.