vitamin-k-semiquinone-radical and Malaria

Not all clinicians give vitamin K to severe malaria patients with systemic bleeding. Vitamin K injections may not be useful to stop bleeding in severe malaria patients with predominant hepatocellular jaundice. However, vitamin K may be justified in bleeding patients who have prolonged fasting of more than 3-7 days, underlying malnutrition, or predominant cholestatic jaundice. The decision to give vitamin K to severe malaria patients with systemic bleeding should be based on underlying diseases, type of jaundice, risk for vitamin K deficiency, and allergy to the drug.

Topics: Blood Coagulation Disorders; Drug-Related Side Effects and Adverse Reactions; Hemorrhagic Disorders; Humans; Injections; Malaria; Patient Selection; Vitamin K

We have developed inhibitors of glutathione reductase that improve on the inhibition of literature lead compounds by up to three orders of magnitude. Thus, analogues of Safranine O and menadione were found to be strong, reversible inhibitors of yeast glutathione reductase. Safranine O exhibited partial, uncompetitive inhibition with Ki and alpha values of 0.5 mM and 0.15, respectively. Thionine O was a partial (hyperbolic) uncompetitive inhibitor with Ki and alpha values of 0.4 microM and 0.15, respectively. LY83583 and 2-anilino-1,4-naphthoquinone also showed (hyperbolic) partial, uncompetitive inhibition with micromolar Ki values. For Nile Blue A a model for two-site binding with (parabolic) uncompetitive inhibition fitted the data with a Ki value of 11 microM and a kinetic cooperativity between the sites of 0.12, increased to 0.46 by preincubation of the enzyme and Nile Blue A in the presence of glutathione disulphide. Analysis of the effects of preincubation on the kinetics and cooperativity indicated the possibility of a slow conformational change in the homodimeric enzyme, the first such indication of kinetic cooperativity in the native enzyme to our knowledge. Further evidence of conformational changes for this enzyme came from studies of the effects of dimethyl sulphoxide which indicated that this co-solvent, which at low concentrations has no apparent effect on initial velocities under normal assay conditions, induced a slow conformational change in the enzyme. Thionine O, Nile Blue A and LY83583 were redox-cycling substrates producing superoxide ion, detectable by means of cytochrome c reduction, but leading to no loss of glutathione reductase activity, under aerobic or anaerobic conditions. The water-soluble Safranine analogues Methylene Blue, Methylene Green, Nile Blue A and Thionine O (5 mg/kg i.p. x 5) were effective antimalarial agents in vivo against P. berghei, but their effect was small and a higher dose (50 mg/kg i.p. x 1) was toxic in mice. Comparison was made with human glutathione reductase and its literature-reported interactions with several tricyclic inhibitors as studied by X-ray diffraction. It is possible that the conformational changes detected in the present study from alterations in detailed kinetic inhibition mechanisms may shed light on information transfer through the glutathione reductase molecule from the dimer interface ligand pocket to the active-site.

Topics: Animals; Antimalarials; Dimethyl Sulfoxide; Glutathione Reductase; Malaria; Mice; Oxazines; Phenazines; Phenothiazines; Saccharomyces cerevisiae; Vitamin K

Hemoglobin in glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes is abnormally vulnerable to oxidative denaturation, which may release ferriheme, a known cytolytic agent. We found 13.3 nmol of ferriheme in G6PD-deficient erythrocyte membranes (per gram of total erythrocyte hemoglobin) using a spectrophotometric assay, as compared to 9.8 in normal membranes (P less than .05). After incubation of erythrocytes with 250 mumol/L menadione, an oxidant drug, the values increased by 37.4 nmol in G6PD-deficient membranes and by 26 in normal membranes (P less than .005), indicating increased hemoglobin denaturation. To verify that hemoglobin denaturation in G6PD-deficient erythrocytes releases ferriheme in a form available to interact with other ligands, [14C]-chloroquine binding to intact erythrocytes was measured. With an initial concentration of 5 mumol/L chloroquine in a medium containing no menadione, an excess of 14.8 nmol of chloroquine was bound in G6PD-deficient erythrocytes (per gram of hemoglobin) as compared to normal erythrocytes (P less than .005). In the presence of 250 mumol/L menadione, chloroquine binding increased by 17.9 nmol in G6PD-deficient and by 7.2 in normal erythrocytes (P less than .005). These results indicate that ferriheme becomes available to interact with endogenous ligands and, thus, to mediate menadione-induced hemolysis in patients with G6PD deficiency. Furthermore, the increase in ferriheme may mediate the selective toxicity of menadione for Plasmodium falciparum parasites growing in G6PD-deficient erythrocytes. Ferriheme release in response to the intraerythrocytic oxidant stress introduced by malaria parasites also may account for the resistance to malaria afforded by G6PD deficiency. This is a US government work. There are no restrictions on its use.

Topics: Chloroquine; Erythrocyte Membrane; Ferric Compounds; Glucosephosphate Dehydrogenase Deficiency; Heme; Hemolysis; Humans; Malaria; Male; Vitamin K

Ferriprotoporphyrin IX (FP) is released from hemoglobin by oxidative denaturation or by proteolytic degradation. FP added exogenously to cells or released intracellularly is a lytic toxin. Chloroquine enhances the accumulation of exogenous FP in cellular membranes and potentiates its lytic effect. Menadione is an example of an oxidant drug that denatures hemoglobin, releases FP intracellularly, and thereby lyses cells. Chloroquine increases the accumulation of FP in the membranes of menadione-treated erythrocytes and enhances the hemolysis induced by menadione. Intraerythrocytic malaria parasites release FP from hemoglobin by proteolytic degradation, but they ordinarily survive the exposure either because FP interacts with a soluble intracellular substance, which renders it nontoxic, or because FP is sequestered in an innocuous, insoluble form in malaria pigment. Chloroquine binds tightly to FP, diverts it away from the soluble detoxifying substance in malaria parasites, and delays its sequestration into malarial pigment. Malaria parasites exposed to chloroquine while degrading hemoglobin accumulate a chloroquine-FP complex, which is sufficiently toxic to kill them. FP has a detergent-like effect on biological membranes which may account for its lytic toxicity.

Topics: Aminoquinolines; Animals; Antimalarials; Cell Membrane; Chloroquine; Erythrocytes; Heme; Hemin; Hemolysis; Malaria; Oxidation-Reduction; Plasmodium berghei; Rabbits; Vitamin K

Topics: Adult; Cells, Cultured; Erythrocytes; Fetal Hemoglobin; Glucosephosphate Dehydrogenase Deficiency; Glutathione; Humans; Malaria; Oxidation-Reduction; Oxygen; Plasmodium falciparum; Riboflavin; Thalassemia; Vitamin K

Topics: Animals; Chromatography, Paper; Chromatography, Thin Layer; Ducks; Malaria; Plasmodium; Spectrum Analysis; Ubiquinone; Vitamin K