Browsing by Subject "Heme"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Restricted
    The crystal structure of halofantrine–ferriprotoporphyrin IX and the mechanism of action of arylmethanol antimalarials.
    (Elsevier, 2008) de Villiers, Katherine A; Marques, Helder; Egan, Timothy J
    The crystal structure of the complex formed between the antimalarial drug halofantrine and ferriprotoporphyrin IX (Fe(III)PPIX) has been determined by single crystal X-ray diffraction. The structure shows that halofantrine coordinates to the Fe(III) center through its alcohol functionality in addition to p-stacking of the phenanthrene ring over the porphyrin. The length of the Fe(III)–O bond is consistent with an alkoxide and not an alcohol coordinating group. The iron porphyrin is five coordinate and monomeric. Changes in the electronic spectrum of Fe(III)PPIX upon addition of halofantrine base in acetonitrile solution are almost identical to those observed upon addition of quinidine free base in the same solvent. This suggests homologous binding. Molecular mechanics modeling of Fe(III)PPIX complexes of quinidine, quinine, 9-epiquinine and 9-epiquinidine based on this homology suggests that the antimalarially active quinidine and quinine can readily adopt conformations that permit formation of an intramolecular salt bridge between the protonated quinuclidine tertiary amino group and unprotonated heme propionate group, while the inactive epimers 9-epiquinidine and 9-epiquinine have to adopt high energy conformations in order to accommodate such salt bridge formation. We propose that salt bridge formation may interrupt formation of the hemozoin precursor dimer formed during the heme detoxification pathway and so account for the strong activity of the two active isomers.
  • Thumbnail Image
    Item
    Open Access
    Increase on the initial soluble heme levels in acidic conditions is an important mechanism for spontaneous heme crystallization in vitro
    (Public Library of Science, 2010) Stiebler, Renata; Hoang, Anh N; Egan, Timothy J; Wright, David W; Oliveira, Marcus F
    BACKGROUND: Hemozoin (Hz) is a heme crystal that represents a vital pathway for heme disposal in several blood-feeding organisms. Recent evidence demonstrated that β-hematin (βH) (the synthetic counterpart of Hz) formation occurs under physiological conditions near synthetic or biological hydrophilic-hydrophobic interfaces. This seems to require a heme dimer acting as a precursor of Hz crystals that would be formed spontaneously in the absence of the competing water molecules bound to the heme iron. Here, we aimed to investigate the role of medium polarity on spontaneous βH formation in vitro . METHODOLOGY/PRINCIPAL FINDINGS: We assessed the effect of water content on spontaneous βH formation by using the aprotic solvent dimethylsulfoxide (DMSO) and a series of polyethyleneglycols (PEGs). We observed that both DMSO and PEGs (3.350, 6.000, 8.000, and 22.000) increased the levels of soluble heme under acidic conditions. These compounds were able to stimulate the production of βH crystals in the absence of any biological sample. Interestingly, the effects of DMSO and PEGs on βH formation were positively correlated with their capacity to promote previous heme solubilization in acidic conditions. Curiously, a short chain polyethyleneglycol (PEG 300) caused a significant reduction in both soluble heme levels and βH formation. Finally, both heme solubilization and βH formation strongly correlated with reduced medium water activity provided by increased DMSO concentrations. CONCLUSIONS: The data presented here support the notion that reduction of the water activity is an important mechanism to support spontaneous heme crystallization, which depends on the previous increase of soluble heme levels.
  • Thumbnail Image
    Item
    Open Access
    Interference with hemozoin formation represents an important mechanism of schistosomicidal action of antimalarial quinoline methanols
    (Public Library of Science, 2009) Soares, Juliana B R Corrêa; Menezes, Diego; Vannier-Santos, Marcos A; Ferreira-Pereira, Antonio; Almeida, Giulliana T; Venancio, Thiago M; Verjovski-Almeida, Sergio; Zishiri, Vincent K; Kuter, David; Hunter, Roger
    Author Summary Heme is an essential molecule to most living organisms, but once in a free state it exerts toxic effects. Blood-feeding organisms evolved efficient ways to detoxify free heme derived from hemoglobin digestion. A key mechanism present in some hematophagous organisms consists of the crystallization of heme into a pigment named hemozoin. Schistosoma mansoni is one of the etiologic agents of human schistosomiasis, a parasitic disease that affects over 200 million people in tropical and subtropical areas. Hemozoin formation represents the main heme detoxification pathway in S. mansoni . Here, we report that the antimalarial quinoline methanols quinine and quinidine exert schistosomicidal effects notably due to their capacity to interfere with hemozoin formation. When quinine or quinidine were administered intraperitoneally during seven days to S. mansoni -infected mice (75 mg/kg/day), both worm and eggs burden were significantly reduced. Interestingly, hemozoin content in female worms was drastically affected after treatment with either compound. We also found that quinine caused important changes in the cellular organization of worm gastrodermis and increased expression of genes related to musculature, protein synthesis and repair mechanisms. Together, our results indicate that interference with hemozoin formation is a valid chemotherapeutic target for development of new schistosomicidal agents.
  • Thumbnail Image
    Item
    Open Access
    Unsaturated glycerophospholipids mediate heme crystallization: biological implications for hemozoin formation in the kissing bug Rhodnius prolixus
    (Public Library of Science, 2014) Stiebler, Renata; Majerowicz, David; Knudsen, Jens; Gondim, Katia C; Wright, David W; Egan, Timothy J; Oliveira, Marcus F
    Hemozoin (Hz) is a heme crystal produced by some blood-feeding organisms, as an efficient way to detoxify heme derived from hemoglobin digestion. In the triatomine insect Rhodnius prolixus , Hz is essentially produced by midgut extracellular phospholipid membranes known as perimicrovillar membranes (PMVM). Here, we investigated the role of commercial glycerophospholipids containing serine, choline and ethanolamine as headgroups and R. prolixus midgut lipids (RML) in heme crystallization. All commercial unsaturated forms of phospholipids, as well as RML, mediated fast and efficient β-hematin formation by means of two kinetically distinct mechanisms: an early and fast component, followed by a late and slow one. The fastest reactions observed were induced by unsaturated forms of phosphatidylethanolamine (uPE) and phosphatidylcholine (uPC), with half-lives of 0.04 and 0.7 minutes, respectively. β-hematin crystal morphologies were strikingly distinct among groups, with uPE producing homogeneous regular brick-shaped crystals. Interestingly, uPC-mediated reactions resulted in two morphologically distinct crystal populations: one less representative group of regular crystals, resembling those induced by uPE, and the other largely represented by crystals with numerous sharp edges and tapered ends. Heme crystallization reactions induced by RML were efficient, with a heme to β-hematin conversion rate higher than 70%, but clearly slower (t1/2 of 9.9-17.7 minutes) than those induced by uPC and uPE. Interestingly, crystals produced by RML were homogeneous in shape and quite similar to those mediated by uPE. Thus, β-hematin formation can be rapidly and efficiently induced by unsaturated glycerophospholipids, particularly uPE and uPC, and may play a role on biological heme crystallization in R. prolixus midgut.