title: Phagocytic uptake of oxidized heme polymer is highly cytotoxic to macrophages.
abstract: Apoptosis in macrophages is responsible for immune-depression and pathological effects during malaria. Phagocytosis of PRBC causes induction of apoptosis in macrophages through release of cytosolic factors from infected cells. Heme polymer or β-hematin causes dose-dependent death of macrophages with LC50 of 132 µg/ml and 182 µg/ml respectively. The toxicity of hemin or heme polymer was amplified several folds in the presence of non-toxic concentration of methemoglobin. β-hematin uptake in macrophage through phagocytosis is crucial for enhanced toxicological effects in the presence of methemoglobin. Higher accumulation of β-hematin is observed in macrophages treated with β-hematin along with methemoglobin. Light and scanning electron microscopic observations further confirm accumulation of β-hematin with cellular toxicity. Toxicological potentiation of pro-oxidant molecules toward macrophages depends on generation of H2O2 and independent to release of free iron from pro-oxidant molecules. Methemoglobin oxidizes β-hematin to form oxidized β-hematin (βH*) through single electron transfer mechanism. Pre-treatment of reaction mixture with spin-trap Phenyl-N-t-butyl-nitrone dose-dependently reverses the β-hematin toxicity, indicates crucial role of βH* generation with the toxicological potentiation. Acridine orange/ethidium bromide staining and DNA fragmentation analysis indicate that macrophage follows an oxidative stress dependent apoptotic pathway to cause death. In summary, current work highlights mutual co-operation between methemoglobin and different pro-oxidant molecules to enhance toxicity towards macrophages. Hence, methemoglobin peroxidase activity can be probed for subduing cellular toxicity of pro-oxidant molecules and it may in-turn make up for host immune response against the malaria parasite.
authors: Malaria Research Group, Department of Biotechnology, Indian Institute of Technology-Guwahati, Assam, India.
authors: Rohitas
authors: R
authors: Deshmukh
authors: Malaria Research Group, Department of Biotechnology, Indian Institute of Technology-Guwahati, Assam, India.
authors: Vishal
authors: V
authors: Trivedi
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000009:adverse effects / Q000627:therapeutic use; D017209:Apoptosis; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism; D006418:Heme / Q000502:physiology* / Q000633:toxicity; D006420:Hemeproteins / Q000502:physiology* / Q000633:toxicity; D006861:Hydrogen Peroxide / Q000378:metabolism; D007928:Lethal Dose 50; D015227:Lipid Peroxidation; D008264:Macrophages / Q000187:drug effects / Q000502:physiology*; D016778:Malaria, Falciparum / Q000188:drug therapy / Q000276:immunology; D008706:Methemoglobin / Q000502:physiology* / Q000633:toxicity; D051379:Mice; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010587:Phagocytosis; D010963:Plasmodium falciparum / Q000502:physiology; D011108:Polymers / Q000633:toxicity; D050050:Protein Carbonylation; D017382:Reactive Oxygen Species / Q000633:toxicity
chemical_list: D000962:Antimalarials; D006420:Hemeproteins; D011108:Polymers; D017382:Reactive Oxygen Species; C020753:hemozoin; D006418:Heme; D008706:Methemoglobin; D006861:Hydrogen Peroxide; D005978:Glutathione