Six known compounds, namely two halisulfates 1 and 2 and four epidioxy sterols 3–6, were isolated from the marine sponge Coscinoderma sp. The structures of these compounds were confirmed by nuclear magnetic resonance (1H and 13C NMR) spectroscopy, and their antiplasmodial activities were determined against the chloroquine-resistant Dd2 strain of Plasmodium falciparum. The epidioxy steroids 3–6 all showed moderate to weak antiplasmodial activity, with IC50 values of 2.7 μM for (24S)-5α,8α-epidioxy-24-methylcholesta-6-en-3β-ol (3), 11.6 μM for 5α,8α-epidioxycholesta-6,24(28)-dien-3β-o1 (4), 2.33 μM for 5α,8α-epidioxy-24-methylcholesta-6,9(11)-24(28)-trien-3β-ol (5), and between 12 and 24 μM for 5α,8α-epidioxycholesta-6-en-3β-ol (6). In contrast, halisulfate 2 (1) was inactive, and halisulfate 1 (2) had an of IC50 value of about 24 μM.
By binding to the adaptor protein SKP1 and serving as substrate receptors for the Skp1, Cullin, F-box E3 ubiquitin ligase complex, F-box proteins regulate critical cellular processes including cell cycle progression and membrane trafficking. While F-box proteins are conserved throughout eukaryotes and are well studied in yeast, plants, and animals, studies in parasitic protozoa are lagging. We have identified eighteen putative F-box proteins in the Toxoplasmagenome of which four have predicted homologs in Plasmodium. Two of the conserved F-box proteins were demonstrated to be important for Toxoplasma fitness and here we focus on an F-box protein, named TgFBXO1, because it is the most highly expressed by replicative tachyzoites and was also identified in an interactome screen as a Toxoplasma SKP1 binding protein. TgFBXO1 interacts with Toxoplasma SKP1 confirming it as a bona fide F-box protein. In interphase parasites, TgFBXO1 is a component of the Inner Membrane Complex (IMC), which is an organelle that underlies the plasma membrane. Early during replication, TgFBXO1 localizes to the developing daughter cell scaffold, which is the site where the daughter cell IMC and microtubules form and extend from. TgFBXO1 localization to the daughter cell scaffold required centrosome duplication but before kinetochore separation was completed. Daughter cell scaffold localization required TgFBXO1 N-myristoylation and was dependent on the small molecular weight GTPase, TgRab11b. Finally, we demonstrate that TgFBXO1 is required for parasite growth due to its function as a daughter cell scaffold effector. TgFBXO1 is the first F-box protein to be studied in apicomplexan parasites and represents the first protein demonstrated to be important for daughter cell scaffold function.
Carlos Gustavo Baptista, Agnieszka Lis, Bowen Deng, Elisabet Gas-Pascual, Ashley Dittmar, Wade Sigurdson, Christopher M. West, Ira J. Blader. PLoS Pathog. 2019 Jul 26;15(7):e1007946. doi: 10.1371/journal.ppat.1007946.
In response to the recent publication “Is onchocerciasis elimination in Africa feasible by 2025: a perspective based on lessons learnt from the African control programmes” by Dadzie et al., it is important to clarify and highlight the positive and unequivocal research and operational contributions from the American experience towards the worldwide elimination of human onchocerciasis (river blindness).
The strategies of twice or more rounds of mass drug administration (MDA) of ivermectin per year, as well as the use of OV-16 serology have allowed four American countries to be verified by World Health Organization to have eliminated transmission of Onchocerca volvulus, the etiological agent. These advances were also implemented in Sudan and Uganda; currently, both are the only African countries where ivermectin MDA was safely stopped in several transmission zones.
Programmatic treatment and evaluation approaches, pioneered in the Americas, are the most efficient among the existing tools for elimination, and their broader use could catalyze the successful elimination of this disease in Africa.
Entomopathogenic nematodes and parasitoid wasps are used as biological control agents for management of insect pests such as the Indian meal moth, Plodia interpunctella. The parasitoid wasp Habrobracon hebetor injects a paralytic venom into P. interpunctella larvae before laying eggs. A previous study reported that the entomopathogenic nematode Heterorhabditis indica preferentially infects P. interpunctella that have been envenomed by H. hebetor while results in this study showed a similar preference by the entomopathogenic nematode, Steinernema glaseri. We therefore tested four hypotheses for why nematode infection rates are higher in envenomed hosts: 1) elevated CO2 emission from envenomed hosts attracts nematodes, 2) paralysis prevents hosts from escaping nematodes, 3) volatile chemicals emitted from envenomed hosts attract nematodes and increase infection, and 4) reduced immune defenses in envenomed hosts increase nematode survival. Results showed that envenomed P. interpunctella larvae emitted lower amounts of CO2 than non-envenomed larvae. Physical immobilization of P. interpunctella larvae did not increase infection rates by S. glaseri but did increase infection rates by H. indica. Emissions from envenomed hosts were collected and analyzed by thermal desorption gas chromatography/mass spectrometry. The most abundant compound, 3-methyl-3-buten-1-ol, was found to be an effective cue for S. glaseri attraction and infection but was not an effective stimulus for H. indica. Envenomed P. interpunctellaexhibited a stronger immune response toward nematodes than non-envenomed hosts. Altogether, we conclude that different mechanisms underlie preferential infection in the two nematode species: host immobilization for H. indica and chemical cues for S. glaseri.
Control of schistosomiasis presently relies largely on preventive chemotherapy with praziquantel through mass drug administration (MDA) programs. The Schistosomiasis Consortium for Operational Research and Evaluation has concluded five studies in four countries (Côte d’Ivoire, Kenya, Mozambique, and Tanzania) to evaluate alternative approaches to MDA. Studies involved four intervention years, with final evaluation in the fifth year. Mass drug administration given annually or twice over 4 years reduced average prevalence and intensity of schistosome infections, but not all villages that were treated in the same way responded similarly. There are multiple ways by which responsiveness to MDA, or the lack thereof, could be measured. In the analyses presented here, we defined persistent hot spots (PHSs) as villages that achieved less than 35% reduction in prevalence and/or less than 50% reduction in infection intensity after 4 years of either school-based or community-wide MDA, either annually or twice in 4 years. By this definition, at least 30% of villages in each of the five studies were PHSs. We found no consistent relationship between PHSs and the type or frequency of intervention, adequacy of reported MDA coverage, and prevalence or intensity of infection at baseline. New research is warranted to identify PHSs after just one or a few rounds of MDA, and new adaptive strategies need to be advanced and validated for turning PHSs into responder villages.
Nupur Kittur, Charles H. King, Carl H. Campbell Jr., Safari Kinung’hi, Pauline N. M. Mwinzi, Diana M. S. Karanja, Eliezer K. N’Goran, Anna E. Phillips, Pedro H. Gazzinelli-Guimaraes, Annette Olsen, Pascal Magnussen, W. Evan Secor, Susan P. Montgomery, Juerg Utzinger, Joseph W. Walker, Sue Binder and Daniel G. Colley. Am J Trop Med Hyg. 2019 Jul 8. doi: 10.4269/ajtmh.19-0193
Skp1 is hydroxylated by an O2-dependent prolyl hydroxylase (PhyA) that contributes to O2-sensing in the social amoeba Dictyostelium and the mammalian pathogen Toxoplasma gondii. HO-Skp1 is subject to glycosylation and the resulting pentasaccharide affects Skp1 conformation in a way that influences association of Skp1 with F-box proteins, and potentially the assembly of E3(SCF) ubiquitin ligase complexes that mediate the poly-ubiquitination of target proteins that are degraded in the 26S-proteasome. To investigate the conservation and specificity of these modifications, we analyzed proteins from the oomycete Pythium ultimum, an important crop plant pathogen. Putative coding sequences for Pythium’s predicted PhyA and first glycosyltransferase in the predicted five-enzyme pathway, a GlcNAc-transferase (Gnt1), predict a bifunctional enzyme (Phgt) that, when expressed in Dictyostelium, rescued knockouts of phyA but not gnt1. Though recombinant Phgt was also unable to glycosylate Dictyostelium HO-Skp1, it could hydrolyze UDP-GlcNAc and modify a synthetic hydroxypeptide from Dictyostelium Skp1. Pythium encodes two highly similar Skp1 isoforms, but only Skp1A was efficiently modified in vitro. While kinetic analysis revealed no evidence for processive processing of Skp1, the physical linkage of the two activities implies dedication to Skp1 in vivo. These findings indicate a widespread occurrence of the Skp1 modification pathway across protist phylogeny, suggest that both Gnt1 and PhyA are specific for Skp1, and indicate that the second Skp1 provides a bypass mechanism for O2-regulation in Pythium and other protists that conserve this gene.
As an extension of our project aimed at the search for new chemotherapeutic agents against Chagas disease and toxoplasmosis, several 1,1-bisphosphonates were designed, synthesized and biologically evaluated against Trypanosoma cruzi and Toxoplasma gondii, the etiologic agents of these diseases, respectively. In particular, and based on the antiparasitic activity exhibited by 2-alkylaminoethyl-1,1-bisphosphonates targeting farnesyl diphosphate synthase, a series of linear 2-alkylaminomethyl-1,1-bisphosphonic acids (compounds 21–33), that is, the position of the amino group was one carbon closer to the gem-phosphonate moiety, were evaluated as growth inhibitors against the clinically more relevant dividing form (amastigotes) of T. cruzi. Although all of these compounds resulted to be devoid of antiparasitic activity, these results were valuable for a rigorous SAR study. In addition, unexpectedly, the synthetic designed 2-cycloalkylaminoethyl-1,1-bisphosphonic acids 47–49 were free of antiparasitic activity. Moreover, long chain sulfur-containing 1,1-bisphosphonic acids, such as compounds 54–56, 59, turned out to be nanomolar growth inhibitors of tachyzoites of T. gondii. As many bisphosphonate-containing molecules are FDA-approved drugs for the treatment of bone resorption disorders, their potential nontoxicity makes them good candidates to control American trypanosomiasis and toxoplasmosis.
Tamila Galaka, Bruno N. Falcone, Catherine Li, Sergio H. Szajnman, Silvia N.J. Moreno, Roberto Docampo, Juan B.Rodriguez. Bioorg Med Chem. 2019 Jul 4. pii: S0968-0896(19)30740-0. doi: 10.1016/j.bmc.2019.07.004.
Cryptosporidium is a leading cause of diarrheal disease and an important contributor to early childhood mortality, malnutrition, and growth faltering. Older children in high endemicity regions appear resistant to infection, while previously unexposed adults remain susceptible. Experimental studies in humans and animals support the development of disease resistance, but we do not understand the mechanisms that underlie protective immunity to Cryptosporidium. Here, we derive an in vivo model of Cryptosporidium infection in immunocompetent C57BL/6 mice by isolating parasites from naturally infected wild mice. Similar to human cryptosporidiosis, this infection causes intestinal pathology, and interferon-γ controls early infection while T cells are critical for clearance. Importantly, mice that controlled a live infection were resistant to secondary challenge and vaccination with attenuated parasites provided protection equal to live infection. Both parasite and host are genetically tractable and this in vivo model will facilitate mechanistic investigation and rational vaccine design.
Adam Sateriale, Jan Šlapeta, Rodrigo Baptista, Julie B. Engiles, Jodi A. Gullicksrud, Gillian T. Herbert, Carrie F. Brooks, Emily M. Kugler, Jessica C. Kissinger, Christopher A. Hunter, Boris Striepen. Cell Host Microbe. 2019 Jun 18. pii: S1931-3128 (19) 30251-3. doi: 10.1016/j.chom.2019.05.006.
The Asian tiger mosquito, Aedes albopictus, transmits several arboviruses of public health importance, including chikungunya and dengue. Since its introduction to the United States in 1985, the species has invaded more than 40 states, including temperate areas not previously at risk of Aedes-transmitted arboviruses. Mathematical models incorporate climatic variables in predictions of site-specific Ae. albopictus abundances to identify human populations at risk of disease. However, these models rely on coarse resolutions of environmental data that may not accurately represent the climatic profile experienced by mosquitoes in the field, particularly in climatically heterogeneous urban areas. In this study, we pair field surveys of larval and adult Ae. albopictus mosquitoes with site-specific microclimate data across a range of land use types to investigate the relationships between microclimate, density of larval habitat, and adult mosquito abundance and determine whether these relationships change across an urban gradient. We find no evidence for a difference in larval habitat density or adult abundance between rural, suburban, and urban land classes. Adult abundance increases with increasing larval habitat density, which itself is dependent on microclimate. Adult abundance is strongly explained by microclimate variables, demonstrating that theoretically derived, laboratory-parameterized relationships in ectotherm physiology apply to the field. Our results support the continued use of temperature-dependent models to predict Ae. albopictus abundance in urban areas.
Polydnaviruses (PDVs) were originally viewed as large DNA viruses that are beneficial symbionts of parasitoid wasps. Two groups of PDVs were also recognized: bracoviruses (BVs), which are associated with wasps in the family Braconidae, and ichnoviruses (IVs), which are associated with wasps in the family Ichneumonidae. Results to date indicate that BVs are endogenous virus elements (EVEs) that evolved from an ancient betanudivirus. IVs are also likely EVEs but are unrelated to BVs. BVs and IVs are very unusual relative to most known EVEs because they retain many viral functions that benefit wasps in parasitizing hosts. However, BVs and IVs cannot be considered beneficial symbionts because all components of their genomes are fixed in wasps. Recent studies indicate that other nudiviruses have endogenized in insects. Each exhibits a different functional fate from BVs but shares certain architectural features. We discuss options for classifying BVs and other endogenized nudiviruses. We also discuss future directions.