The native form of thePlasmodium falciparum Pf68 neutral proteinase is a 105,000-Da polypeptide

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Glutathione reductase-catalyzed cascade of redox reactions to bioactivate potent antimalarial 1,4-naphthoquinones--a new strategy to combat malarial parasites.

Our work on targeting redox equilibria of malarial parasites propagating in red blood cells has led to the selection of six 1,4-naphthoquinones, which are active at nanomolar concentrations against the human pathogen Plasmodium falciparum in culture and against Plasmodium berghei in infected mice. With respect to safety, the compounds do not trigger hemolysis or other signs of toxicity in mice. Concerning the antimalarial mode of action, we propose that the lead benzyl naphthoquinones are initially oxidized at the benzylic chain to benzoyl naphthoquinones in a heme-catalyzed reaction within the digestive acidic vesicles of the parasite. The major putative benzoyl metabolites were then found to function as redox cyclers: (i) in their oxidized form, the benzoyl metabolites are reduced by NADPH in glutathione reductase-catalyzed reactions within the cytosols of infected red blood cells; (ii) in their reduced forms, these benzoyl metabolites can convert methemoglobin, the major nutrient of the parasite, to indigestible hemoglobin. Studies on a fluorinated suicide-substrate indicate as well that the glutathione reductase-catalyzed bioactivation of naphthoquinones is essential for the observed antimalarial activity. In conclusion, the antimalarial naphthoquinones are suggested to perturb the major redox equilibria of the targeted infected red blood cells, which might be removed by macrophages. This results in development arrest and death of the malaria parasite at the trophozoite stage

Synthesis of New 4-Aminoquinolines and Evaluation of Their In Vitro Activity against Chloroquine-Sensitive and Chloroquine-Resistant Plasmodium falciparum

International audienceThe efficacy of chloroquine, once the drug of choice in the fight against Plasmodium falcipa-rum, is now severely limited due to widespread resistance. Amodiaquine is one of the most potent antimalarial 4-aminoquinolines known and remains effective against chloroquine-resistant parasites, but toxicity issues linked to a quinone-imine metabolite limit its clinical use. In search of new compounds able to retain the antimalarial activity of amodiaquine while circumventing quinone-imine metabolite toxicity, we have synthesized five 4-amino-quinolines that feature rings lacking hydroxyl groups in the side chain of the molecules and are thus incapable of generating toxic quinone-imines. The new compounds displayed high in vitro potency (low nanomolar IC 50), markedly superior to chloroquine and comparable to amodiaquine, against chloroquine-sensitive and chloroquine-resistant strains of P. falcipa-rum, accompanied by low toxicity to L6 rat fibroblasts and MRC5 human lung cells, and metabolic stability comparable or higher than that of amodiaquine. Computational studies indicate a unique mode of binding of compound 4 to heme through the HOMO located on a biphenyl moeity, which may partly explain the high antiplasmodial activity observed for this compound

Spectrin-based skeleton in red blood cells and malaria.

PURPOSE OF REVIEW: Malaria represents one of the most important selective factors affecting human populations. Several inherited diseases of red blood cells lead to resistance at the erythrocytic stage. Among patients who experience hereditary elliptocytosis related to mutations of erythrocyte membrane proteins, molecular studies have shown the prevalence of particular spectrin mutations in patients from black ethnic extraction, leading one to question the selection of new malaria-resistant genes. RECENT FINDINGS: Prospective epidemiological and molecular studies in West Africa have confirmed the prevalence (between 0.6 and 1.6%) of particular spectrin mutations related to hereditary elliptocytosis. These studies have also revealed the frequency of alpha-spectrin chain polymorphisms, associated in cis with elliptocytogenic spectrin mutations and defining particular spectrin allele haplotypes. Culture studies of Plasmodium falciparum in elliptocytes bearing such elliptocytogenic alleles of spectrin showed that these alleles are supplementary genetic factors of malaria resistance in vitro. SUMMARY: Certain instances of spectrin mutations or polymorphisms have not yet been shown to constitute new factors of innate resistance to malaria in vivo. Epidemiological surveys of hereditary elliptocytosis and parasite culture studies, however, have argued that the relationships between parasite and spectrin-based skeleton should be examined more closely and the molecular interactions between parasite ligands and particular spectrin chain domains should be characterized

Discovery of new targets for antimalarial chemotherapy

International audienceThe understanding of the biology and the biochemistry of malaria parasites has considerably increased over the past two decades with the discovery of many potential targets for new antimalarial drugs. The decrypted genomes of several Plasmodium species and the new post-genomic tools further enriched our "reservoir" of targets and increased our ability to validate potential drug targets or to study the entire parasite metabolism. This review discusses targets involved in calcium metabolism, protein prenylation and apicoplast functions that have emerged by different approaches

RESEARCH NOTE - Biochemical Characterization of Cathepsin D from Adult Schistosoma mansoni Worms

Schistosomes ingest and lyse host blood cells, releasing the haemoglobin (Hb) into their gut. AR Timms and E Bueding found an acid protease activity in Schistosoma mansoni which was capable of hydrolysing Hb; they suggested that host Hb degradation provided the major amino acid source for the synthesis of parasite proteins. From 1979 on, Hb degradation by schistosomes was considered mostly due to cysteine proteinase (CP) activity. Several S. mansoni and S. japonicum CPs have been reported to be possibly involved in the degradation of this substrate which includes cathepsin B (Sm31, Sj31 antigens), cathepsin L and an asparaginyl endopeptidase (Sm32, Sj32 antigens). However, a proteinase-processing, rather than a direct Hb-digesting role for the Sm32 have been suggested by JP Dalton and PJ Brindley. On the other hand, cathepsin L has been mainly located in the reproductive system of the worms and it is present in smaller amount than cathepsin B in the adult worm vomitus of several Schistosoma species, suggesting a minor role of this enzyme in the digestion of Hb. An important proportion of the Hb degradation exerted by S. mansoni extracts occurs in the absence of thiols between pH 3.5 and 4.5 and this activity is inhibited by pepstatin A (a classic aspartyl proteinase inhibitor) but not by thiol-, serine- and metalloproteinase inhibitors. Using mercury-labeled pepstatin, BJ Bogitsh and KF Kirschner localized an aspartyl proteinase in the cecal lumen and to the gastrodermis of S. japonicum. Immunocytochemical studies using heterologous antiserum to bovine cathepsin D indicated that the S. japonicum cathepsin D-like enzyme is also localized to the dorsal and lateral surfaces of the tegument and tubercles of male worms. A cDNA encoding this proteinase was isolated and the native enzyme biochemically characterized at pH 3.5

Discovery of new targets for antimalarial chemotherapy

International audienceThe understanding of the biology and the biochemistry of malaria parasites has considerably increased over the past two decades with the discovery of many potential targets for new antimalarial drugs. The decrypted genomes of several Plasmodium species and the new post-genomic tools further enriched our "reservoir" of targets and increased our ability to validate potential drug targets or to study the entire parasite metabolism. This review discusses targets involved in calcium metabolism, protein prenylation and apicoplast functions that have emerged by different approaches

Ultrastructure of Selenidium pendula, the Type Species of Archigregarines, and Phylogenetic Relations to Other Marine Apicomplexa

International audienceArchigregarines, an early branching lineage within Apicomplexa, are a poorly-known group of invertebrate parasites. By their phylogenetic position, archigregarines are an important lineage to understand the functional transition that occurred between free-living flagellated predators to obligatory parasites in Apicomplexa. In this study, we provide new ultrastructural data and phylogenies based on SSU rDNA sequences using the type species of archigregarines, the Selenidiidae Selenidium pendula Giard, 1884. We describe for the first time the syzygy and early gamogony at the ultrastructural level, revealing a characteristic nuclear multiplication with centrocones, cryptomitosis, filamentous network of chromatin, a cyst wall secretion and a 9 + 0 flagellar axoneme of the male gamete. S. pendula belongs to a monophyletic lineage that includes several other related species, all infecting Sedentaria Polychaeta (Spionidae, Sabellaridae, Sabellidae and Cirratulidae). All of these Selenidium species exhibit similar biological characters: a cell cortex with the plasma membrane - inner membrane complex - subpellicular microtubule sets, an apical complex with the conoid, numerous rhoptries and micronemes, a myzocytosis with large food vacuoles, a nuclear multiplication during syzygy and young gamonts. Two other distantly related Selenidium-like lineages infect Terebellidae and Sipunculida, underlying the ability of archigregarines to parasite a wide range of marine hosts