PubMed Health⌕ Search

Biomedical subjects

E Hempelmann

Publications and source records attributed to E Hempelmann.

18 recordsLinked to original sources
PubMed1999

The role of superoxide dismutation in malaria parasites.

Oxidant stress is associated with the generation of reactive oxygen species that are responsible for the damage of a variety of cellular components. The prevention of such biological damage can be achieved by dismutation of superoxide to H2O2 which in turn is removed by catalase and GSH peroxidase. However, redox-active iron released during the development of plasmodia in the erythrocyte can mediate the conversion of H2O2 to hydroxyl radical which is more reactive. The roles of SOD and the nitroxide SOD mimic 4-OH,2,2,6,6,tetramethyl piperidine-N-oxyl (Tempol) were examined in P. falciparum grown in vitro. Both compounds did not prevent the interference with growth inflicted by various inducers of oxidant stress. Moreover, Tempol inhibited parasite growth, in agreement with previous experiments depicting accelerated mortality in SOD overexpressing mouse model of malaria. Probably, effective defense against ROS requires balanced increments in antioxidant enzymes and is not necessarily improved by an increase in the activity of one enzyme.

Adaptation, Physiological↗
PubMed1994

Glycophorin variants and Plasmodium falciparum: protective effect of the Dantu phenotype in vitro.

Experimental work was carried out to establish the growth characteristics of Plasmodium falciparum in an in vitro culture system using cells with the Dantu, Henshaw and S-s-U- blood-group variants. A flow cytometric technique, using the dye thiazole orange, was adapted for use on the Epics Profile II flow cytometer to count the parasites. This was performed at 24, 48 and 72 h. The ability of the parasites to grow in red cells of the Dantu and Henshaw phenotypes was also assayed by 3[H] hypoxanthine incorporation. Relative to control red cells, S-s-U- cells and Dantu cells were less suitable as host cells for P. falciparum in vitro. In contrast, cells expressing the Henshaw antigen were equally sensitive to P. falciparum infection as were normal controls. These data support the notion that glycophorins play an important role in P. falciparum infection. Further studies are required to evaluate the epidemiological significance of these results.

Animals↗
PubMed1994

Analysis of malaria pigment from Plasmodium falciparum.

The biochemical pathway for the production of malaria pigment (haemozoin) forms a fundamental difference between host and parasite and is likely to be an important drug target. A simple method for the isolation of malaria pigment is described. The resultant product retained the in vivo crystalline appearance of pigment as judged by polarizing microscopy. Conditions were found for the disaggregation and separation of pigment. As malaria pigment can adsorb drugs, haem, and iron, such separation techniques are useful tools for studies on the impairment of haemoglobin digestion and pigment formation by antimalarials.

Animals↗
PubMed1993

Malaria pigment and extracellular iron. Possible target for iron chelating agents.

Extracellular iron is necessary for many biochemical reactions involved in Plasmodium falciparum growth and multiplication. The incorporation of radioactive iron taken up by the parasite was found, electrophoretically and via gamma counting, to be mainly associated with the haemozoin only in the presence of the active metabolism of the parasite. The potent antimalarial activity of desferrioxamine, a ferric iron chelating agent, has shown that iron deprivation is inhibitory to the parasite. We propose that the mechanism of action of desferrioxamine in addition to the chelation of iron from the parasitic compartment, chelates iron from the haemozoin crystal resulting in free radical generation and parasite death. The ability of desferrioxamine and not the ferrous iron chelating agent, 2,2'-bipyridyl, to chelate the non-haem iron from the haemozoin structure indicates that the oxidative state of iron associated with the haemozoin structure is ferric in nature.

2,2'-Dipyridyl↗
PubMed1988

Glutathione reductase inhibitors as potential antimalarial drugs. Effects of nitrosoureas on Plasmodium falciparum in vitro.

Malarial parasites are believed to be more susceptible to oxidative stress than their hosts. BCNU(1,3-bis(2-chloroethyl)-1-nitrosourea) and HeCNU(1-(2-chloroethyl)-3-(2-hydroxythyl)-1-nitrosourea), inhibitors of the antioxidant enzyme glutathione reductase, were found to prevent the growth of Plasmodium falciparum in all intraerythrocytic stages. When exposing infected red blood cells to 38 microM BCNU or 62 microM HeCNU for one life cycle of synchronously growing parasites, the parasitemia decreased by 90%. During the formation of new ring forms, the parasites are even more susceptible to these drugs. The treatment with BCNU or HeCNU produced a rapid depletion of GSH in the parasites and their host cells; in addition, protection against lipid peroxidation was impaired in these cells. Possible mechanisms for the antimalarial action of the inhibitors are discussed. Our results suggest that erythrocyte glutathione reductase, an enzyme of known structure, might be considered as a target for the design of antimalarial drugs.

Animals↗
PubMed1987

Lysis of malarial parasites and erythrocytes by ferriprotoporphyrin IX-chloroquine and the inhibition of this effect by proteins.

Ferriprotoporphyrin IX(FP) lysed both erythrocytes and isolated Plasmodium falciparum as judged by decrease in turbidity of erythrocyte and parasite suspensions. The lytic effect of FP on erythrocytes was enhanced by chloroquine (CQ). In the presence of 2.5-20 microM CQ, 5 microM FP led to complete hemolysis within 45 min. However, the lytic effect of FP or FP-CQ on both erythrocytes and parasites was inhibited completely by proteins. The protein inhibition was non-specific. This finding, the failure of FP and FP--CQ to cause hemolysis and lysis of malarial parasites in a protein-containing medium, does not support the "FP--CQ complex hypothesis" for the antimalarial action of chloroquine.

Chloroquine↗
PubMed1987

Glutathione and peroxide metabolism in malaria-parasitized erythrocytes.

The glutathione metabolism of Plasmodium falciparum, P. vinckei and P. berghei has been investigated. Human erythrocytes with low glutathione reductase and synthetase activity are still capable of harbouring P. falciparum. Both enzymes have been demonstrated in Plasmodium spp. Moreover, evidence is given for a selenium-independent glutathione peroxidase in malaria parasites.

Animals↗
PubMed1987

Studies on glutathione reductase and methemoglobin from human erythrocytes parasitized with Plasmodium falciparum.

An improved protein-blotting procedure and a thin layer isoelectric focusing technique are introduced to study glutathione reductase and methemoglobin (Met-Hb). According to our results, there is only one form of glutathione reductase in normal red blood cells. A similar protein was shown to be present at higher concentration in isolated merozoites. Both proteins have a subunit Mr of ca. 50,000 and react with anti-human glutathione reductase serum. Red cells with schizonts do not possess a higher proportion of Met-Hb than non-parasitized erythrocytes. This finding suggests that Met-Hb is not an indicator of metabolic alterations in malaria-infected erythrocytes.

Animals↗
PubMed1986

Immunoprecipitation of malarial acid endopeptidase.

Electrophoresis of extracts of schizonts of Plasmodium knowlesi in non-dissociating polyacrylamide gels, separates several bands of acid endopeptidase activity. A polyclonal antiserum, produced by immunization with purified merozoites, failed to distinguish between different bands of the parasite enzyme, indicating that they are serologically related. Apart from the loss of one minor peak, extraction in Triton X-100 did not reduce the enzyme's electrophoretic heterogeneity. The antiserum did not react with red cell acid proteases.

Animals↗
PubMed1986

Antibodies to the glutamate dehydrogenase of Plasmodium falciparum.

Polyclonal antisera raised against Plasmodium knowlesi reacted with NADP-specific glutamate dehydrogenase (GLDH) of P. knowlesi, GLDH of P. falciparum and GLDH of Proteus spp. The antisera did not react with NAD(P) GLDH from bovine liver. Polyclonal antisera raised against the GLDH of Proteus spp. cross-reacted with GLDH from P. falciparum. Monoclonal antibodies (McAbs) obtained from mice immunized with Proteus GLDH were either specific for the bacterial enzyme or cross-reacted with P. falciparum GLDH. The selected McAbs did not react with GLDH from P. knowlesi, P. chabaudi or P. berghei. The GLDH of P. falciparum was shown to be a cytosolic protein (by FAT) with a subunit molecular weight of approximately 49 000 Da (by immunoprecipitation) having a predominantly hexameric form (by sucrose density gradient). Implications of the conserved sequences of GLDHs and other enzymes are discussed.

Animals↗
PubMed1985

Unusual protein pattern of Opisthorchis viverrini.

The proteins of homogenized adult Opisthorchis viverrini were separated by polyacrylamide gel electrophoresis and isoelectric focusing in the presence of detergents. By far the most abundant component(s) had a Mr of 18,000 to 19,000, represented about 47% of the total parasite protein, and did not separate in isotypes.

Actins↗
PubMed1981

S-antigens and isozymes in strains of Plasmodium falciparum.

Evidence was found for the independent reassortment of parasite genes for S-antigens and isozymes. The Lagos and Palo Alto strains of Plasmodium falciparum had the same isozyme forms of PGD and LDH but different S-antigens. In contrast, the BW (Gambia) and Palo Alto strains had different isozyme forms of GDH but shared some S-antigens. From artificial mixtures of parasites with different isozymes of GDH and different S-antigens, clones were derived in vitro which had a single isozyme type of GDH and a single type of S-antigen.

Animals↗
PubMed1981

Detection of glucose-6-phosphate dehydrogenase in malarial parasites.

The ability to carry out the initial reaction of the pentose phosphate pathway was investigated with extracts of mouse erythrocytes infected with Plasmodium chabaudi, purified merozoites of P. knowlesi, and schizonts of P. falciparum grown in vitro in human erythrocytes. Glucose-6-phosphate dehydrogenase activity (G-6pd) was detected in extracts of all the cells after electrophoresis on polyacrylamide gels. Separate host cell and parasite glucose-6-phosphate dehydrogenase activities were demonstrated with extracts of P. knowlesi and P. falciparum but not with P. chabaudi.

Animals↗
PubMed1981

Effect of physostigmine on Plasmodium falciparum in culture.

Human erythrocytes contain 7 electrophoretically different alpha-naphthyl acetate esterases. Their solubility properties indicate that 5 are present in the erythrocyte cytoplasm and 2 are tightly bound to the stroma; the stroma-bound esterases can be inhibited by 10(-5) M physostigmine. No additional physostigmine-sensitive enzymes were detectable in Plasmodium falciparum-infected cells. Addition of physostigmine to malaria parasites in culture killed the parasites rapidly.

Acetylcholinesterase↗
PubMed1980

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.

Animals↗
PubMed1975

[Glutathionestatus of Plasmodium vinckei parasitized erythrocytes in correlation to the intraerythrocytic development of the parasite (author's transl)].

The glutathione status of Plasmodium vinckei parasitized erythrocytes of mice was determined in correlation to the intraerythrocytic stage of maturation of the parasite. The different stages of blood schizogony were separated by discontinuous Dextran-density-centrifugation. The changes of protein content, glutathione concentration (reduced/oxidized and bound/free glutathione) and in the specific activities of the following enzymes: gamma-glutamyl-cysteine-synthetase (GC-synthetase), glutathione-reductase (GR), glucose-6-phosphate dehydrogenase (Gl-DH), glutathione-peroxydase (G-POD) and catalase were investigated in dependence of the intraerythrocytic stage of development. The following changes of the investigated metabolic parameters were observed during the schizogony: - the protein content decreased to about one half, - the glutathione concentration increased about 10-fold, while the relations reduced/oxidized and free/bound glutathione remained constant, - Gl-DH activity appeared and increased steeply, - the specific activities of GC-synthetase and of GR increased more than 2-fold, while G-POD remained almost constant, - and the activities of G-6-PDH and catalase showed a significant, strong decrease to about 25% of the original values. It is tried to relate the observed changes to the growing parasite or to the host cell. The significance of the results for the metabolism of malaria parasites and for a possible adaptation to the mosquito by a GSH mediated protection of the malaria parasite against an enzymatic defence-reaction of the mosquito, is discussed.

Animals↗
PubMedDate not supplied

Characterisation of synthetic beta-haematin and effects of the antimalarial drugs quinidine, halofantrine, desbutylhalofantrine and mefloquine on its formation.

Infrared spectroscopy, elemental analysis and X-ray powder diffraction show that the product of 30 min of reaction of haematin in 4.5 M acetate, pH 4.5 at 60 degrees C is identical to beta-haematin prepared in 4.5 M acetic acid at 70 degrees C overnight (pH 2.6). There is no evidence for formation of haem-acetate complex, which could not be isolated, even from 11.4 M acetate solution. The antimalarial drugs quinidine, halofantrine, desbutylhalofantrine and mefloquine were found to inhibit formation of beta-haematin, while 5-, 6- and 8-aminoquinoline and quinoline were found to have no effect. Quinidine was shown to form a complex with ferriprotoporphyrin IX in 40% DMSO with log K = 5.02 +/- 0.03. Log K values for halofantrine and desbutylhalofantrine are 5.29 +/- 0.02 and 5.15 +/- 0.02 respectively (solutions containing 30% acetonitrile in addition to DMSO to solubilise these drugs), which are both stronger than chloroquine under the same conditions (log K = 4.56 +/- 0.02).

Antimalarials↗