Abstract
Malaria is one of the most devastating diseases with lethal outcome in more than 1 million humans per year. The course of the disease is not only a function of the pathogen but is heavily influenced by properties of the host. Mechanisms possibly conferring protection against a severe course of malaria include suicidal death of the infected cell. A particular form of suicidal erythrocyte death is eryptosis, which is characterized by Ca2+-entry with subsequent activation of Ca2+-sensitive K+ channels, KCl exit and erythrocyte shrinkage, Ca2+-sensitive scrambling of phospholipids resulting in the breakdown of cell membrane phosphatidylserine asymmetry and phosphatidylserine exposure at the cell surface, as well as Ca2+ dependent activation of calpain, proteolytic degradation of cytoskeletal proteins and cell membrane blebbing. Eryptosis is triggered by different well-known pro apoptotic stressors, namely hyperosmotic shock, oxidative stress and energy depletion, which all activate Ca2+ -permeable nonselective cation channels allowing Ca2+ entry into the erythrocyte. Eryptosis is enhanced in several inherited erythrocyte disorders such as, phosphate depletion, hemolytic uremic syndrome, sepsis, and Wilson disease. As macrophages are equipped with receptors specific for phosphatidylserine, cells exposing phosphatidylserine at their surface will be rapidly recognized, engulfed, degraded and thus cleared from circulating blood Infection of erythrocytes with Plasmodium falciparum has been shown to trigger eryptosis, at least in part due to activation of host cell channels via oxidation of the cell membrane. Accelerated death of infected erythrocytes has been suggested to delay the development of parasitemia and protect against a severe course of the disease. Erythrocyte death could be triggered by induction of eryptosis. Triggers of eryptosis include hemolysin, PGE2, platelet activating factor, heavy metals like mercury, iron deficiency, L-NAME, Pb(NO3)2 or chlorpromazine. The present studies has been performed to explore whether the addition of L-NAME or Pb(NO3)2 or chlorpromazine to the drinking water may modify the course of malaria and survival of Plasmodium berghei -infected mice and also to explore whether iron deficiency influences the course of malaria. As a result, iron deficiency increased the phosphatidylserine exposure in P. falciparum infected human erythrocytes, an effect significantly more marked in iron deficiency erythrocytes than compared to control erythrocytes. Moreover, iron deficiency impairs in vitro intraerythrocytic growth and infection of erythrocytes. In mice, iron deficient erythrocytes are more rapidly cleared from circulating blood, an effect increased by infection with P. berghei. Parasitemia in P. berghei infected mice was significantly decreased (from 54% to 33% of circulating erythrocytes, 20 days after infection) and mouse survival significantly enhanced (from 0% to 20%, 30 days after infection) in iron deficient mice. L-NAME (≥10 µM) increased phosphatidylserine exposure of P. falciparum infected human erythrocytes, an effect significantly more marked than in noninfected human erythrocytes. In parallel, parasitemia in P. berghei infected mice was significantly decreased (from 50% to 18% of circulating erythrocytes 20 days after infection) by addition of L-NAME (1mg/ml) to the drinking water. According to CFSE labelling, L-NAME treated infected erythrocytes disappeared more rapidly from circulating blood than nontreated erythrocytes Pb(NO3)2 (≥10 µM) increased phosphatidylserine exposure of P. falciparum infected erythrocytes, an effect significantly more marked than in noninfected cells. We further show that Pb(NO3)2 treated erythrocytes are more rapidly cleared from circulating blood than nontreated erythrocytes. Parasitemia in P. berghei infected mice was significantly decreased (from 50% to 18% of circulating erythrocytes 20 days after infection) and mouse survival significantly enhanced (from 0% to 38% 30 days after infection) by addition of 100 µM Pb(NO3)2 (20 ppm) to the drinking water. The treatment did not significantly decrease erythrocyte number and hematocrit in noninfected mice and in infected animals mainly triggered the disappearance of P. berghei harbouring erythrocytes. Chlorpromazine (≥10 µM) during in vitro infection of human erythrocytes increased phosphatidylserine exposure and decreased forward scatter. Chlorpromazine did not significantly alter intraerythrocytic DNA/RNA amplification but significantly (≥5 µM) decreased in vitro parasitemia. Erythrocytes from chlorpromazine treated mice were more rapidly cleared from circulating blood than nontreated erythrocytes. Parasitemia in P. berghei infected mice was significantly decreased (from 50% to 28% of circulating erythrocytes 22 days after infection) and mouse survival significantly enhanced (from 0% to 80% 30 days after infection) upon addition of 1mM chlorpromazine to the drinking water from the first day of infection. In conclusion, iron deficiency, L-NAME, Pb(NO3)2 or chlorpromazine enhances the susceptibility of eythrocytes to eryptosis. As a result, erythrocytes undergo accelerated eryptosis following infection with Plasmodium. The accelerated eryptosis precedes the full intraerythrocytic maturation of the pathogen and thus blunts the increase of parasitemia. The observations support the view that accelerated suicidal death of infected erythrocytes is a host mechanism to counteract infection with the intracellular pathogen. The observations may not only serve to understand the mechanisms of host defence against the malaria pathogen but open new perspectives for pharmacological treatment of this devastating disease.
Author and committee
dc:creator, dc:contributor.*- Author
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- Koka, Sai Sudha
Identifiers
dc:identifier.*- Identifier
- hdl:10900/49142