Characterization of Plasmodium berghei glutathione synthetase

Plasmodium berghei contained 0.454 ± 0.031 U/mg of glutathione synthetyase (GS). GS was purified using solid ammonium sulfate and Sephadex G-200 from P. berghei infected mouse erythrocytes. SDS-PAGE showed purified GS as a single band protein of 70 kDa and its Km for γ-glutamylcysteine, glycine and ATP being 0.33 mM, 8.3 mM and 0.43 mM respectively with noncompetitive inhibition by GSH. The malaria parasite enzyme was optimally active at 37 °C and pH 8.0–8.5. Heavy metals significantly inhibited parasite GS activity.     

Malic Dehydrogenase Heterogeneity in Malaria (Plasmodium lophurae and P. berghei)*

SYNOPSIS. Molecular heterogeneity of malic dehydrogenase (MDH) in malaria was shown by zone electrophoresis in potato starch, starch gel, and by enzymatic activity with analogs of the coenzyme diphosphopyridine nucletide. A single anodal peak of MDH characterized the normal duck red blood cell whereas P. lophurae free of the host cell had a cathodal form of the enzyme. Infected duck erythrocytes had a combination of these electrophoretic forms. The isolated enzymes had different pH optima with oxaloacetate as substrate: pH 7.4 for the duck red cell and 6.4 for the plasmodial enzyme. The Km of each enzyme for oxaloacetate varied with the pH. The Km at pH 7.4 was 4.1 and 4.4 × 10⁵ M for parasite and host, respectively, whereas at 6.4 it was 2.0 × 10⁵ M for P. lophurae and 6.3 × 10⁵M for the duck erythrocyte. At pH 7.4 both enzymes were inhibited by oxaloacetate concentrations greater than 10^?4 M. P. berghei MDH also had a different electrophoretic character from that of the mouse red blood cell. Quantitatively, MDH activity increased with parasitization, and erythrocyte-free P. lophurae contained approximately twice the activity found in the uninfected duck erythrocyte. The quantity of MDH activity of the infected cell was ca. 50% less than the sum of the activities of the parasite and the uninfected cell. It is suggested that these properties of the parasite MDH may give it a physiologic advantage over the red cell under the conditions which prevail intraerythrocytically.     

γ-glutamylcysteine synthetase from Plasmodium berghei

γ-glutamylcysteine synthetase (l-glutamate-l-cysteine ligase, γ-GCS, EC 6.3.2.2.), the rate limiting enzyme in glutathione biosynthetic pathway has been analysed in the asexual erythrocytic stages of rodent malaria parasite, Plasmodium berghei and its host erythrocytes. Cell-free parasite isolated by saponin lysis contained about 2 and 8 times higher activity of γ-GCS compared to P. berghei-infected and normal mice erythrocytes respectively. Subcellular fractionation revealed that the enzyme was mainly confined to the cytosolic part of the parasite. γ-GCS from P. berghei was purified employing ammonium sulphate precipitation, Sephadex G-200 gel filtration and anionic exchange chromatography on DEAE-cellulose. There was 51.6 fold purification of enzyme and its specific activity was 39.5 U/mg. SDS-PAGE showed P. berghei γ-GCS as a heterodimer dissociating into two non-identical sub-units of 66 kDa and 57 kDa. The enzyme was observed as white band of activity on native polyacrylamide gel stained for specific γ-GCS activity. Km values for l-Cys, ATP and l-Glu were 0.53 mM, 0.92 mM and 0.75 mM, respectively. The inhibition of γ-GCS activity by glutathione was found to be competitive with respect to glutamate (Ki = 1.53 mM) and non competitive to ATP and cysteine. Antimalarial drugs did not show any significant effect on parasite γ-GCS. Parasite enzyme induced humoral response in mice demonstrated by ELISA, IFA and immunoblotting and exhibited partial protection against P. berghei infection suggesting a significant role of P. berghei γ-GCS in malaria control.     

Plasmodium knowlesi: glycolytic intermediate levels of enzyme activities of infected rhesus monkey erythrocytes

In vitro glycolytic enzyme activities and in vivo glycolytic intermediate concentrations were assayed in Plasmodium knowlesi-infected rhesus monkey erythrocytes and control erythrocytes. The enzyme activities of infected erythrocytes were greater than controls indicating that P. knowlesi had its own glycolytic system and that parasite glycolysis was the source of the increased rate of glucose consumption by infected erythrocytes. The P. knowlesi glycolytic enzymes phosphofructokinase and hexokinase were less sensitive to acid inhibition than uninfected red cells.P. knowlesi-infected monkey erythrocytes and Plasmodium berghei-infected mouse erythrocytes had similar in vivo glycolytic profiles and in vitro enzyme activity increases.     

Cyclic AMP- and Ca2(+)-dependent protein kinases in Plasmodium falciparum

The cyclic AMP- and Ca2(+)-dependent protein kinase activities of Plasmodium falciparum were partially characterized after purification of parasites from host erythrocytes by N2 cavitation and Percoll gradient centrifugation. Proteins of molecular weights 80, 54, 51, and 31.5 kDa were phosphorylated in a cAMP-dependent manner in cytosolic extracts of isolated P. falciparum. Cytosolic extracts also contained cAMP-dependent histone II-A kinase activity with an average Vmax of 131.1 pmol/32P/min/mg protein and a Km for cAMP of 85nM. Upon photoaffinity labeling with [32P]-8-N3-cAMP, a 53-kDa protein was specifically labeled in parasite cytosol. A metabolically labeled protein of the same molecular weight was identified by cAMP-agarose affinity chromatography. The 53-kDa protein cochromatographed with cAMP-dependent histone II-A kinase activity on DEAE-cellulose, suggesting that it is the regulatory subunit of the kinase. Ca2(+)-dependent phosphorylation of proteins of molecular weights 195, 158, 51, 47.5, and 15 kDa was demonstrated in a membrane fraction from parasites free of the erythrocyte membrane. This activity was not stimulated by either calmodulin or phospholipid plus diacylglycerol and was absent from the membranes of uninfected erythrocytes. Of several exogenous substrates tested, none were found to be a substrate for this Ca2(+)-dependent kinase. Both cAMP- and Ca2(+)-dependent kinases phosphorylated serine and threonine residues.     

Ameliorative role of Ziziphus spina-christi leaf extracts against hepatic injury induced by Plasmodium chabaudi infected erythrocytes

One of the most common deadliest parasitic diseases is Malaria. The biology and the pathogenesis of this fascinating parasite are not yet fully understood which make discovering effective alternative drugs a challenging task. Moreover, the emergence of resistant strains added an additional burden in the journey of malaria elimination. Traditional medicine used to be an alternative therapy choice owing to the presence of potent natural products. Ziziphus spina-christi (L.) considered being one of the common potent natural plant in gulf region and other nations. Therefore, this study designed to evaluate the ameliorative role of Z. spina-christi leaf extracts (ZSCLE) against Plasmodium chabaudi-induced hepatic injury. The study involved three groups were as follows; a vehicle control group, infected with 10⁶P. chabaudi-parasitized erythrocytes group and ZSCLE treated-infected mice with 10⁶P. chabaudi-parasitized erythrocytes group. The results showed a remarkable reduction of parasitemia level and notable reverse of the anemic picture among ZSCLE treated-infected mice. The effects of ZSCLE on the liver functions enzymes and on the histopathological pictures of liver were significant. It could be concluded that Z. spina-christi leaf extracts have a protective role against Plasmodium infection that also marked through significant restoration of hepatic oxidative markers.     

Rodent and nonrodent malaria parasites differ in their phospholipid metabolic pathways

Malaria, a disease affecting humans and other animals, is caused by a protist of the genus Plasmodium. At the intraerythrocytic stage, the parasite synthesizes a high amount of phospholipids through a bewildering number of pathways. In the human Plasmodium falciparum species, a plant-like pathway that relies on serine decarboxylase and phosphoethanolamine N-methyltransferase activities diverts host serine to provide additional phosphatidylcholine and phosphatidylethanolamine to the parasite. This feature of parasitic dependence toward its host was investigated in other Plasmodium species. In silico analyses led to the identification of phosphoethanolamine N-methyltransferase gene orthologs in primate and bird parasite genomes. However, the gene was not detected in the rodent P. berghei, P. yoelii, and P. chabaudi species. Biochemical experiments with labeled choline, ethanolamine, and serine showed marked differences in biosynthetic pathways when comparing rodent P. berghei and P. vinckei, and human P. falciparum species. Notably, in both rodent parasites, ethanolamine and serine were not significantly incorporated into phosphatidylcholine, indicating the absence of phosphoethanolamine N-methyltransferase activity. To our knowledge, this is the first study to highlight a crucial difference in phospholipid metabolism between Plasmodium species. The findings should facilitate efforts to develop more rational approaches to identify and evaluate new targets for antimalarial therapy.     

Biosynthesized nanosilver as anti-oxidant,anti-apoptotic and anti-inflammatory agent against Plasmodium chabaudi infection in the mouse liver

In recent years, the use of plant-mediated nanoparticle synthesis to combat infectious diseases has become increasingly significant. Malaria is one of the world's most infectious diseases caused by Plasmodium species. The antioxidant, anti-apoptotic, and anti-inflammatory properties of nanosilver biosynthesized from Indigofera oblongifolia leaf extracts (NS) against Plasmodium chabaudi infection of the mouse liver were investigated in this research. Male mice were infected with P. chabaudi infected erythrocytes then treated with NS for 7 days. The parasitemia was suppressed by approximately 24, 28, 47 and 75% on days 4, 5, 6 and 7 postinfection, respectively after treatment of mice with NS. Also, NS was able to regulate the leucocytes count and the IL1β and TNF-α-mRNA expression in mice. Ns could increase the antioxidant activity in liver of mice and was able to regulate the apoptotic genes, Bcl2 and Casp3. We showed that NS has antioxidant, anti-apoptotic, and anti-inflammatory properties when it was used to treat the livers of mice infected with P. chabaudi.     

Influence of Reticulocytosis on the Course of Infection of Plasmodium chabaudi and P. berghei*

SYNOPSIS. Reticulocytosis, stimulated by the destruction of red blood cells by phenylhydrazine, altered the course of infection of both Plasmodium chabaudi and P. berghei in the mouse. P. chabaudi, lacking a preference for reticulocytes, was adversely affected when young cells were present in abundance. Parasitemias diminished and most of the animals survived the otherwise fatal infection. P. berghei preferentially invaded reticulocytes to the extent that the parasitemia became contained largely in the reticulocyte population. This was accompanied by a delay in time to death.     

Endopeptidases from Plasmodium knowlesi

Extracts of rhesus monkey erythrocytes infected with Plasmodium knowlesi were fractionated by polyacrylamide gel electrophoresis (PAGE) and several zones of endopeptidase activity were demonstrated by an imprint-digest method. The enzymes were active only under acid conditions; activity was detected at pH 3.2 but not between pH 6.4 and 8.9 using haemoglobin, albumin or erythrocyte lysate as the substrate. Optimized PAGE conditions separated highly active parasite enzymes with Rf values of 73, 63 and 53 (+/- 7%), as well as a red cell endopeptidase, Rf44. Of two other minor bands of activity, one was associated with platelets.     

Long-term in vitro cultures of Plasmodium berghei and preliminary observations on gametocytogenesis

Several long-term in vitro cultures of the rodent malaria parasite Plasmodium berghei were established. In these cultures, ranging over 17–90 days, peak parasitaemias of over 20% and multiplication rates of up to 7·7 were observed. A previously described culture method was used. The method for medium refreshment was changed and rat erythrocytes were used as host cells. The long-term cultivation of Plasmodium berghei enables us to study the process of gametocytogenesis since male and female gametocytes were produced in all cultures and reached full maturity, demonstrated by exflagellation and fertilization in vitro.     

Long-term live imaging reveals cytosolic immune responses of host hepatocytes against Plasmodium infection and parasite escape mechanisms

Plasmodium parasites are transmitted by Anopheles mosquitoes to the mammalian host and actively infect hepatocytes after passive transport in the bloodstream to the liver. In their target host hepatocyte, parasites reside within a parasitophorous vacuole (PV). In the present study it was shown that the parasitophorous vacuole membrane (PVM) can be targeted by autophagy marker proteins LC3, ubiquitin, and SQSTM1/p62 as well as by lysosomes in a process resembling selective autophagy. The dynamics of autophagy marker proteins in individual Plasmodium berghei-infected hepatocytes were followed by live imaging throughout the entire development of the parasite in the liver. Although the host cell very efficiently recognized the invading parasite in its vacuole, the majority of parasites survived this initial attack. Successful parasite development correlated with the gradual loss of all analyzed autophagy marker proteins and associated lysosomes from the PVM. However, other autophagic events like nonselective canonical autophagy in the host cell continued. This was indicated as LC3, although not labeling the PVM anymore, still localized to autophagosomes in the infected host cell. It appears that growing parasites even benefit from this form of nonselective host cell autophagy as an additional source of nutrients, as in host cells deficient for autophagy, parasite growth was retarded and could partly be rescued by the supply of additional amino acid in the medium. Importantly, mouse infections with P. berghei sporozoites confirmed LC3 dynamics, the positive effect of autophagy activation on parasite growth, and negative effects upon autophagy inhibition.     

Plasmodium berghei: biological variation in immune serum-treated mice.

Antiserum was obtained from mice which had been immunized with irradiated Plasmodium berghei parasitized erythrocytes and which survived subsequent challenge. This antiserum suppressed P. berghei infections in mice; parasitemia and mortality were delayed 7–8 days as compared to those of control animals. Parasites surviving in antiserum-treated animals were isolated by inoculation of blood into normal recipients. When antiserum was tested against this derived parasite population, there was no observable effect on parasitemia or mortality. The derived parasites also exhibited a decreased virulence for mice. This work confirms the previous observation that antiserum treatment can result in a biologically variant population of P. berghei.     

Glutathione Reductase and Thioredoxin Reductase: Novel Antioxidant Enzymes from Plasmodium berghei

Malaria parasites adapt to the oxidative stress during their erythrocytic stages with the help of vital thioredoxin redox system and glutathione redox system. Glutathione reductase and thioredoxin reductase are important enzymes of these redox systems that help parasites to maintain an adequate intracellular redox environment. In the present study, activities of glutathione reductase and thioredoxin reductase were investigated in normal and Plasmodium berghei-infected mice red blood cells and their fractions. Activities of glutathione reductase and thioredoxin reductase in P. berghei-infected host erythrocytes were found to be higher than those in normal host cells. These enzymes were mainly confined to the cytosolic part of cell-free P. berghei. Full characterization and understanding of these enzymes may promise advances in chemotherapy of malaria.     

Plasmodium chabaudi: Expression of active recombinant chabaupain-1 and localization studies in Anopheles sp.

Plasmodium cysteine proteases have been shown to be immunogenic and are being used as malaria potential serodiagnostic markers and vaccine targets. Genes encoding two Plasmodium chabaudi cysteine proteases chabaupain-1 (CP-1) and chabaupain-2 (CP-2) were identified and further expressed in Escherichia coli. Solubilisation of recombinant CP-1 and CP-2 was achieved by decreasing the temperature of induction.Anopheles gambiae tissues infected with Plasmodium were analyzed by Western blotting using the anti-CP-1 antibody showing that CP-1 is only present in the A. gambiae midguts being absent from other infected mosquito biological material. Anti-CP-1 anti-serum recognized a 30 kDa band in P. chabaudi, Plasmodium berghei and Plasmodium yoelii lysates but does not recognize the recombinant CP-2 extracts suggesting high antibody specificity.     

Exoerythrocytic Plasmodium Parasites Secrete a Cysteine Protease Inhibitor Involved in Sporozoite Invasion and Capable of Blocking Cell Death of Host Hepatocytes

Plasmodium parasites must control cysteine protease activity that is critical for hepatocyte invasion by sporozoites, liver stage development, host cell survival and merozoite liberation. Here we show that exoerythrocytic P. berghei parasites express a potent cysteine protease inhibitor (PbICP, P. berghei inhibitor of cysteine proteases). We provide evidence that it has an important function in sporozoite invasion and is capable of blocking hepatocyte cell death. Pre-incubation with specific anti-PbICP antiserum significantly decreased the ability of sporozoites to infect hepatocytes and expression of PbICP in mammalian cells protects them against peroxide- and camptothecin-induced cell death. PbICP is secreted by sporozoites prior to and after hepatocyte invasion, localizes to the parasitophorous vacuole as well as to the parasite cytoplasm in the schizont stage and is released into the host cell cytoplasm at the end of the liver stage. Like its homolog falstatin/PfICP in P. falciparum, PbICP consists of a classical N-terminal signal peptide, a long N-terminal extension region and a chagasin-like C-terminal domain. In exoerythrocytic parasites, PbICP is posttranslationally processed, leading to liberation of the C-terminal chagasin-like domain. Biochemical analysis has revealed that both full-length PbICP and the truncated C-terminal domain are very potent inhibitors of cathepsin L-like host and parasite cysteine proteases. The results presented in this study suggest that the inhibitor plays an important role in sporozoite invasion of host cells and in parasite survival during liver stage development by inhibiting host cell proteases involved in programmed cell death.     

Indigofera oblongifolia leaf extract regulates spleen macrophage response during Plasmodium chabaudi infection

Malaria is a major health problem that still affects numerous countries. The current study aimed to identify the role of Indigofera oblongifolia leaf extract in regulating mouse spleen macrophages during the progression of Plasmodium chabaudi infection. Three doses of the leaf extract (100, 200, and 300 mg/kg) were administered to mice inoculated with P. chabaudi infected erythrocytes. The weight of the infected mice improved after the treatment with I. oblongifolia. The infection causes disorganization of macrophage distribution in the spleen. After the mice had been treated with the leaf extract, the macrophages appeared to be reorganized in the white and red pulp areas. In addition, the I. oblongifolia leaf extract (IOLE) significantly increased the total antioxidant capacity of the mice spleens infected with P. chabaudi. The phagocytic activity of spleen macrophages was increased in the infected group as indicated by the significant decrease in the number of fluorescent particles in the spleen sections. This number increased in the mice spleens after treatment with IOLE. Based on these results, it is suggested that IOLE regulate macrophage response of the spleen during the blood stage of malaria in mice.