title: Deconvoluting heme biosynthesis to target blood-stage malaria parasites.
abstract: Heme metabolism is central to blood-stage infection by the malaria parasite Plasmodium falciparum. Parasites retain a heme biosynthesis pathway but do not require its activity during infection of heme-rich erythrocytes, where they can scavenge host heme to meet metabolic needs. Nevertheless, heme biosynthesis in parasite-infected erythrocytes can be potently stimulated by exogenous 5-aminolevulinic acid (ALA), resulting in accumulation of the phototoxic intermediate protoporphyrin IX (PPIX). Here we use photodynamic imaging, mass spectrometry, parasite gene disruption, and chemical probes to reveal that vestigial host enzymes in the cytoplasm of Plasmodium-infected erythrocytes contribute to ALA-stimulated heme biosynthesis and that ALA uptake depends on parasite-established permeability pathways. We show that PPIX accumulation in infected erythrocytes can be harnessed for antimalarial chemotherapy using luminol-based chemiluminescence and combinatorial stimulation by low-dose artemisinin to photoactivate PPIX to produce cytotoxic reactive oxygen. This photodynamic strategy has the advantage of exploiting host enzymes refractory to resistance-conferring mutations.
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St Louis, United States.
authors.forename: Paul A
authors.identifier: http://orcid.org/0000-0002-3464-3042
authors.initials: PA
authors.lastname: Sigala
authors.affiliation: Center for Women's Infectious Disease Research, Washington University School of Medicine, St. Louis, United States.
authors.forename: Jan R
authors.initials: JR
authors.lastname: Crowley
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St Louis, United States.
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Henderson
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St Louis, United States.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Goldberg
mesh_terms: D000622:Aminolevulinic Acid / Q000378:metabolism; D037621:Artemisinins / Q000378:metabolism; D053898:Biosynthetic Pathways; D004912:Erythrocytes / Q000469:parasitology*; D006418:Heme / Q000096:biosynthesis*; D006801:Humans; D007783:Lactones / Q000378:metabolism; D017319:Photosensitizing Agents / Q000378:metabolism; D010963:Plasmodium falciparum / Q000378:metabolism*; D011524:Protoporphyrins / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D037621:Artemisinins; D007783:Lactones; D017319:Photosensitizing Agents; D011524:Protoporphyrins; D017382:Reactive Oxygen Species; D006418:Heme; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX; C075875:artemisin
keywords: E. coli; P. falciparum; biochemistry; heme biosynthesis; human; infectious disease; malaria; metabolism; microbiology; photodynamic therapy