Neutral lipids associated with haemozoin mediate efficient and rapid beta-haematin formation at physiological pH, temperature and ionic composition

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dc.contributor.authorAmbele, Melvinen_ZA
dc.contributor.authorEgan, Timothyen_ZA
dc.date.accessioned2015-11-18T04:04:34Z
dc.date.available2015-11-18T04:04:34Z
dc.date.issued2012en_ZA
dc.description.abstractBACKGROUND: The malaria parasite disposes of host-derived ferrihaem (iron(III)protoporphyrin IX, Fe(III)PPIX) by conversion to crystalline haemozoin in close association with neutral lipids. Lipids mediate synthetic haemozoin (beta-haematin) formation very efficiently. However, the effect on reaction rates of concentrations of lipid, Fe(III)PPIX and physiologically relevant ions and biomolecules are unknown. METHODS: Lipid emulsions containing Fe(III)PPIX were prepared in aqueous medium (pH 4.8, 37degreesC) to mediate beta-haematin formation. The reaction was quenched at various times and free Fe(III)PPIX measured colorimetrically as a pyridine complex and the kinetics and yields analysed. Products were also characterized by FTIR, TEM and electron diffraction. Autofluorescence was also used to monitor beta-haematin formation by confocal microscopy. RESULTS: At fixed Fe(III)PPIX concentration, beta-haematin yields remained constant with decreasing lipid concentration until a cut-off ratio was reached whereupon efficiency decreased dramatically. For the haemozoin-associated neutral lipid blend (NLB) and monopalmitoylglycerol (MPG), this occurred below a lipid/Fe(III)PPIX (L/H) ratio of 0.54. Rate constants were found to increase with L/H ratio above the cut-off. At 16 muM MPG, Fe(III)PPIX concentration could be raised until the L/H ratio reached the same ratio before a sudden decline in yield was observed. MPG-mediated beta-haematin formation was relatively insensitive to biologically relevant cations (Na+, K+, Mg2+, Ca2+), or anions (H2PO4, HCO3, ATP, 2,3-diphosphoglycerate, glutathione). Confocal microscopy demonstrated beta-haematin formation occurs in association with the lipid particles. CONCLUSIONS: Kinetics of beta-haematin formation have shown that haemozoin-associated neutral lipids alone are capable of mediating beta-haematin formation at adequate rates under physiologically realistic conditions of ion concentrations to account for haemozoin formation.en_ZA
dc.identifier.apacitationAmbele, M., & Egan, T. (2012). Neutral lipids associated with haemozoin mediate efficient and rapid beta-haematin formation at physiological pH, temperature and ionic composition. <i>Malaria Journal</i>, http://hdl.handle.net/11427/15111en_ZA
dc.identifier.chicagocitationAmbele, Melvin, and Timothy Egan "Neutral lipids associated with haemozoin mediate efficient and rapid beta-haematin formation at physiological pH, temperature and ionic composition." <i>Malaria Journal</i> (2012) http://hdl.handle.net/11427/15111en_ZA
dc.identifier.citationAmbele, M. A., & Egan, T. J. (2012). Neutral lipids associated with haemozoin mediate efficient and rapid β-haematin formation at physiological pH, temperature and ionic composition. Malar J, 11, 337.en_ZA
dc.identifier.ris TY - Journal Article AU - Ambele, Melvin AU - Egan, Timothy AB - BACKGROUND: The malaria parasite disposes of host-derived ferrihaem (iron(III)protoporphyrin IX, Fe(III)PPIX) by conversion to crystalline haemozoin in close association with neutral lipids. Lipids mediate synthetic haemozoin (beta-haematin) formation very efficiently. However, the effect on reaction rates of concentrations of lipid, Fe(III)PPIX and physiologically relevant ions and biomolecules are unknown. METHODS: Lipid emulsions containing Fe(III)PPIX were prepared in aqueous medium (pH 4.8, 37degreesC) to mediate beta-haematin formation. The reaction was quenched at various times and free Fe(III)PPIX measured colorimetrically as a pyridine complex and the kinetics and yields analysed. Products were also characterized by FTIR, TEM and electron diffraction. Autofluorescence was also used to monitor beta-haematin formation by confocal microscopy. RESULTS: At fixed Fe(III)PPIX concentration, beta-haematin yields remained constant with decreasing lipid concentration until a cut-off ratio was reached whereupon efficiency decreased dramatically. For the haemozoin-associated neutral lipid blend (NLB) and monopalmitoylglycerol (MPG), this occurred below a lipid/Fe(III)PPIX (L/H) ratio of 0.54. Rate constants were found to increase with L/H ratio above the cut-off. At 16 muM MPG, Fe(III)PPIX concentration could be raised until the L/H ratio reached the same ratio before a sudden decline in yield was observed. MPG-mediated beta-haematin formation was relatively insensitive to biologically relevant cations (Na+, K+, Mg2+, Ca2+), or anions (H2PO4, HCO3, ATP, 2,3-diphosphoglycerate, glutathione). Confocal microscopy demonstrated beta-haematin formation occurs in association with the lipid particles. CONCLUSIONS: Kinetics of beta-haematin formation have shown that haemozoin-associated neutral lipids alone are capable of mediating beta-haematin formation at adequate rates under physiologically realistic conditions of ion concentrations to account for haemozoin formation. DA - 2012 DB - OpenUCT DO - 10.1186/1475-2875-11-337 DP - University of Cape Town J1 - Malaria Journal LK - https://open.uct.ac.za PB - University of Cape Town PY - 2012 T1 - Neutral lipids associated with haemozoin mediate efficient and rapid beta-haematin formation at physiological pH, temperature and ionic composition TI - Neutral lipids associated with haemozoin mediate efficient and rapid beta-haematin formation at physiological pH, temperature and ionic composition UR - http://hdl.handle.net/11427/15111 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/15111
dc.identifier.urihttp://dx.doi.org/10.1186/1475-2875-11-337
dc.identifier.vancouvercitationAmbele M, Egan T. Neutral lipids associated with haemozoin mediate efficient and rapid beta-haematin formation at physiological pH, temperature and ionic composition. Malaria Journal. 2012; http://hdl.handle.net/11427/15111.en_ZA
dc.language.isoengen_ZA
dc.publisherBioMed Central Ltden_ZA
dc.publisher.departmentDepartment of Chemistryen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.rightsThis is an Open Access article distributed under the terms of the Creative Commons Attribution Licenseen_ZA
dc.rights.holder2012 Ambele and Egan; licensee BioMed Central Ltd.en_ZA
dc.rights.urihttp://creativecommons.org/licenses/by/2.0en_ZA
dc.sourceMalaria Journalen_ZA
dc.source.urihttp://www.malariajournal.com/en_ZA
dc.subject.othermalaria parasiteen_ZA
dc.subject.otherblood-feeding organismsen_ZA
dc.subject.otherhelminthSchistosoma mansonien_ZA
dc.subject.otherinsectsen_ZA
dc.subject.otherkissing bug Rhodnius prolixusen_ZA
dc.subject.otherhaemoglobinen_ZA
dc.titleNeutral lipids associated with haemozoin mediate efficient and rapid beta-haematin formation at physiological pH, temperature and ionic compositionen_ZA
dc.typeJournal Articleen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceArticleen_ZA
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