Friday, May 30, 2008

Toxoplasma gondii infection in humans and animals in the United States

Int J Parasitol. 2008 Apr 11. [Epub ahead of print]

Toxoplasma gondii infection in humans and animals in the United States

Dubey JP, Jones JL.

United States Department of Agriculture, Agricultural Research Service, Animal and Natural Resources Institute, Animal Parasitic Diseases Laboratory, Building 1001, Beltsville, MD 20705-2350, USA.

This paper reviews clinical and asymptomatic Toxoplasma gondii infection in humans and other animals in the USA. Seroprevalence of T. gondii in humans and pigs is declining. Modes of transmission, epidemiology and environmental contamination with oocysts on land and sea are discussed.

PMID: 18508057 [PubMed - as supplied by publisher]

Thursday, May 29, 2008

Temporal and spatial distribution of Toxoplasma gondii differentiation into bradyzoites and tissue cyst formation in vivo

Infect Immun. 2008 May 27. [Epub ahead of print]

Temporal and spatial distribution of Toxoplasma gondii differentiation into bradyzoites and tissue cyst formation in vivo

Di Cristina M, Marocco D, Galizi R, Proietti C, Spaccapelo R, Crisanti A.

Department of Experimental Medicine and Biochemical Sciences, University of Perugia, Via Del Giochetto, 06122 Perugia Italy; Division of Molecular and Cell Biology, Imperial College, Imperial College Road, London SW7 2AZ United Kingdom.

During Toxoplasma gondii infection a fraction of the multiplying parasites, the tachyzoites, converts into bradyzoites, a dormant stage, that form tissue cysts mainly localized in brain, heart and skeletal muscles that persist for several years after infection. At this stage the parasite is protected from the immune system and it is believed to be inaccessible to drugs. While the long persistence of tissue cysts does not represent a medical problem for healthy individuals, this condition represents a major risk for patients with a compromised immune system, who can develop recrudescent life threatening T. gondi infections. We have investigated for the first time the dynamics and the kinetics of tachyzoite-to-bradyzoite interconversion and cyst formation in vivo by using stage specific bioluminescent parasites in a mouse model. Our findings provide a new framework for understanding the process of bradyzoite differentiation in vivo. We have also demonstrated that complex molecules such as D-luciferin have access to tissue cysts and are metabolically processed, thus providing a rationale for developing drugs that attack the parasite at this developmental stage.

PMID: 18505811 [PubMed - as supplied by publisher]

Thursday, May 15, 2008

The plastid-like organelle of apicomplexan parasites as drug target

Curr Pharm Des. 2008;14(9):855-71.

The plastid-like organelle of apicomplexan parasites as drug target

Wiesner J, Reichenberg A, Heinrich S, Schlitzer M, Jomaa H.

Institut für Klinische Chemie und Pathobiochemie, Justus-Liebig-Universität Giessen, Giessen, Germany.

Apicomplexan parasites infectious to humans include Plasmodium spp., Babesia spp., Toxoplasma gondii, Cryptosporidium spp., Isospora belli and Cyclospora cayetanensis. With exception of Cryptosporidium spp., these parasites possess a non-photosynthetic plastid-like organelle called apicoplast. The apicoplast possesses a small circular genome and harbours prokaryotic-type biochemical pathways. As the most important metabolic functions, the mevalonate independent 1-deoxy-D-xylulose 5-phosphate pathway of isoprenoid synthesis and the type II fatty acid synthesis system are operative inside the apicoplast. Classical antibacterial drugs such as ciprofloxacin, tetracycline, doxycycline, clindamycin and spiramycin inhibit the apicoplast-located gyrase and translation machinery, respectively, and are currently used in the clinic for the treatment of infections with apicomplexan parasites. As an inhibitor of isoprenoid synthesis, fosmidomycin was proven to be effective against acute P. falciparum malaria in clinical phase II studies. Triclosan, an inhibitor of fatty acid synthesis, was active in a malaria mouse model. In vitro antimalarial activity was shown for inhibitors of peptide deformylase and the import of apicoplast-targeted proteins. Work on various other inhibitors of apicoplast-located biochemical processes is ongoing.

PMID: 18473835 [PubMed - in process]

Ultrastructural alterations in organelles of parasitic protozoa induced by different classes of metabolic inhibitors

Curr Pharm Des. 2008;14(9):925-38.

Ultrastructural alterations in organelles of parasitic protozoa induced by different classes of metabolic inhibitors

Rodrigues JC, de Souza W.

Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, CCS, Bloco G, subsolo, Ilha do Fundão, Rio de Janeiro, RJ, 21.941-902, Brazil.

Parasitic protozoa such as Leishmania, Trypanosoma, Plasmodium, Toxoplasma gondii, Giardia and Trichomonas are able to cause several diseases affecting millions of people around the world with dramatic consequences to the socio-economic life of the affected countries. Diseases like malaria, leishmaniasis and trypanosomiasis have been classified by the World Health Organization as neglected diseases, because they have been almost completely forgotten by the governments as well as the pharmaceutical companies. The specific chemotherapy currently employed for the treatment of these diseases has serious limitations due to lack of efficacy, toxic side effects, growth of drug-resistance and high costs. Thus, it is urgent to develop new chemotherapeutic agents that are more effective, safe and accessible. In this context, several works have been focused on understanding the effect of different drug-treatments on these parasitic protozoa. Organelles and structures such as mitochondrion, kinetoplast, apicoplast, glycosome, acidocalcisome, hydrogenosome, plasma membrane and the cytoskeleton have been studied using different approaches to identify new targets for the development of new chemotherapeutic agents that are required. Some studies on alterations in the fine structure, as assayed using electron microscopy, have indicated the nature of lesions induced by several drugs, allowing deductions on possible modes of action. Here, we briefly review the available data of the effects of several drugs on the ultrastructure of parasitic protozoa and show how electron microscopy can contribute to elucidate the different mechanisms of these anti-parasitic drugs.

Publication Types:
Research Support, Non-U.S. Gov't

PMID: 18473841 [PubMed - in process]

Wednesday, May 14, 2008

Comparative genomics of the Rab protein family in Apicomplexan parasites

Microbes Infect. 2008 Feb 8 [Epub ahead of print]

Comparative genomics of the Rab protein family in Apicomplexan parasites

Langsley G, van Noort V, Carret C, Meissner M, de Villiers EP, Bishop R, Pain A.

Laboratoire de Biologie Cellulaire Comparative des Apicomplexes, Département de Maladies Infectieuses, Institut Cochin, Inserm, U567, CNRS, UMR 8104, Faculté de Médecine Paris V – Hôpital Cochin, 27, rue du Faubourg Saint-Jacques, 75014 Paris, France.

Rab genes encode a subgroup of small GTP-binding proteins within the ras super-family that regulate targeting and fusion of transport vesicles within the secretory and endocytic pathways. These genes are of particular interest in the protozoan phylum Apicomplexa, since a family of Rab GTPases has been described for Plasmodium and most putative secretory pathway proteins in Apicomplexa have conventional predicted signal peptides. Moreover, peptide motifs have now been identified within a large number of secreted Plasmodium proteins that direct their targeting to the red blood cell cytosol, the apicoplast, the food vacuole and Maurer's clefs; in contrast, motifs that direct proteins to secretory organelles (rhoptries, micronemes and microspheres) have yet to be defined. The nature of the vesicle in which these proteins are transported to their destinations remains unknown and morphological structures equivalent to the endoplasmic reticulum and trans-Golgi stacks typical of other eukaryotes cannot be visualised in Apicomplexa. Since Rab GTPases regulate vesicular traffic in all eukaryotes, and this traffic in intracellular parasites could regulate import of nutrient and drugs and export of antigens, host cell modulatory proteins and lactate we compare and contrast here the Rab families of Apicomplexa.

PMID: 18468471 [PubMed - as supplied by publisher]

Phylogenetic and structural information on glyceraldehyde-3-phosphate dehydrogenase (G3PDH)

Infect Genet Evol. 2008 Mar;8(2):205-12.

Phylogenetic and structural information on glyceraldehyde-3-phosphate dehydrogenase (G3PDH) in Plasmodium provides functional insights
Akinyi S, Gaona J, Meyer EV, Barnwell JW, Galinski MR, Corredor V.

Emory Vaccine Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA 30329, USA

Plasmodium is dependent on glycolysis for ATP production. The glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (G3PDH) plays an important role in glycolysis and is, therefore, a potential target for antimalarial drug development. The g3pdh gene of nine Plasmodium species was sequenced from genomic DNA and the type and origin determined by phylogenetic analysis. Substitutions were analyzed over a wide phylogenetic spectrum in relation to the known three-dimensional structures of the P. falciparum and human proteins. Substitutions were found within the functional domains (Rossman NAD+-binding and catalytic domains). A number of replacements within the adenosyl-binding surfaces were found to be conserved within the Chromoalveolates, others in the Apicomplexa, and still others within the genus Plasmodium, all of which were different from the human sequence. These sites may prove to be of functional importance and provide insights for drug-targeting studies, as have other regions examined in Leishmania and Toxoplasma G3PDH research.

PMID: 18472435 [PubMed - in process]

Wednesday, May 07, 2008

Insect-cell expression, crystallization and X-ray data collection of the bradyzoite-specific antigen BSR4 from Toxo

Acta Crystallogr Sect F Struct Biol Cryst Commun. 2008 May 1;64(Pt 5):425-7. Epub 2008 Apr 30.

Insect-cell expression, crystallization and X-ray data collection of the bradyzoite-specific antigen BSR4 from Toxoplasma gondii

Grujic O, Grigg ME, Boulanger MJ.

Biochemistry and Microbiology, University of Victoria, PO Box 3055 STN CSC, Victoria, BC, V8W 3P6, Canada.

Toxoplasma gondii is an important global pathogen that infects nearly one third of the world's adult population. A family of developmentally expressed structurally related surface-glycoprotein adhesins (SRSs) mediate attachment to and are utilized for entry into host cells. The latent bradyzoite form of T. gondii persists for the life of the host and expresses a distinct family of SRS proteins, of which the bradyzoite-specific antigen BSR4 is a prototypical member. Structural studies of BSR4 were initiated by first recombinantly expressing BSR4 in insect cells, which was followed by crystallization and preliminary X-ray data collection to 1.95 A resolution. Data processing showed that BSR4 crystallized with one molecule in the asymmetric unit of the P4(1)2(1)2 or P4(3)2(1)2 space group, with a solvent content of 60% and a corresponding Matthews coefficient of 2.98 A(3) Da(-1).

Publication Types:
Research Support, Non-U.S. Gov't

PMID: 18453717 [PubMed - in process]

Gene expression signatures and small-molecule compounds link a protein kinase to Plasmodium falciparum motility

Nat Chem Biol. 2008 May 4 [Epub ahead of print]

Gene expression signatures and small-molecule compounds link a protein kinase to Plasmodium falciparum motility

Kato N, Sakata T, Breton G, Le Roch KG, Nagle A, Andersen C, Bursulaya B, Henson K, Johnson J, Kumar KA, Marr F, Mason D, McNamara C, Plouffe D, Ramachandran V, Spooner M, Tuntland T, Zhou Y, Peters EC, Chatterjee A, Schultz PG, Ward GE, Gray N, Harper J, Winzeler EA.

[1] Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, ICND202 La Jolla, California 92037, USA. [2] Genomics Institute of the Novartis Research Foundation, 10675 John Jay Hopkins Drive, San Diego, California 92121, USA.

Calcium-dependent protein kinases play a crucial role in intracellular calcium signaling in plants, some algae and protozoa. In Plasmodium falciparum, calcium-dependent protein kinase 1 (PfCDPK1) is expressed during schizogony in the erythrocytic stage as well as in the sporozoite stage. It is coexpressed with genes that encode the parasite motor complex, a cellular component required for parasite invasion of host cells, parasite motility and potentially cytokinesis. A targeted gene-disruption approach demonstrated that pfcdpk1 seems to be essential for parasite viability. An in vitro biochemical screen using recombinant PfCDPK1 against a library of 20,000 compounds resulted in the identification of a series of structurally related 2,6,9-trisubstituted purines. Compound treatment caused sudden developmental arrest at the late schizont stage in P. falciparum and a large reduction in intracellular parasites in Toxoplasma gondii, which suggests a possible role for PfCDPK1 in regulation of parasite motility during egress and invasion.

PMID: 18454143 [PubMed - as supplied by publisher]

A quantitative competitive PCR method to determine the parasite load in the brain of Toxo-infected mice

Parasitol Int. 2008 Mar 20 [Epub ahead of print]

A quantitative competitive PCR method to determine the parasite load in the brain of Toxoplasma gondii-infected mice

Piña-Vázquez C, Saavedra R, Hérion P.

Departamento de Inmunología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México. México, DF, México.

Efficacy of vaccine candidates against toxoplasmosis may be expressed in terms of reduction in cyst number in brains of animals vaccinated and then challenged with a cyst-forming strain of Toxoplasma gondii, compared to non-vaccinated animals. Cyst number generally has been determined by microscopic examination of brain homogenate samples, a technique which has a low sensitivity and is time-consuming. Here we describe a quantitative competitive PCR method, which allows quantifying T. gondii DNA in brain samples. The method uses a primer pair, which allows the amplification of a 301 bp fragment of the 35-fold repeated T. gondii B1 gene and an internal standard (non-homologous competitor) derived from phage lambda, which can be amplified using the same primers and whose size and G/C content are similar to that of the B1 target sequence. The method is sensitive (as few as 10 parasites can be quantified), reproducible, and is not affected by the presence of DNA extracted from mouse brain by means of a simple and rapid technique. It is suitable to quantify the parasite load in the brain of infected mice and to evaluate efficacy of toxoplasmosis vaccine candidates.

PMID: 18456545 [PubMed - as supplied by publisher]

Sunday, May 04, 2008

Type X Toxoplasma gondii in a wild mussel and terrestrial carnivores from coastal California

Int J Parasitol. 2008 Feb 26 [Epub ahead of print]

Type X Toxoplasma gondii in a wild mussel and terrestrial carnivores from coastal California: New linkages between terrestrial mammals, runoff and toxoplasmosis of sea otters

Miller MA, Miller WA, Conrad PA, James ER, Melli AC, Leutenegger CM, Dabritz HA, Packham AE, Paradies D, Harris M, Ames J, Jessup DA, Worcester K, Grigg ME.

California Department of Fish and Game, Marine Wildlife Veterinary Care and Research Center, 1451 Shaffer Road, Santa Cruz, CA 95060, United States.

Sea otters in California are commonly infected with Toxoplasma gondii. A unique Type X strain is responsible for 72% of otter infections, but its prevalence in terrestrial animals and marine invertebrates inhabiting the same area was unknown. Between 2000 and 2005, 45 terrestrial carnivores (lions, bobcats, domestic cats and foxes) and 1396 invertebrates (mussels, clams and worms) were screened for T. gondii using PCR and DNA sequencing to determine the phylogeographic distribution of T. gondii archetypal I, II, III and Type X genotypes. Marine bivalves have been shown to concentrate T. gondii oocysts in the laboratory, but a comprehensive survey of wild invertebrates has not been reported. A California mussel from an estuary draining into Monterey Bay was confirmed positive for Type X T. gondii by multilocus PCR and DNA sequencing at the B1 and SAG1 loci. This mussel was collected from nearshore marine waters just after the first significant rainfall event in the fall of 2002. Of 45 carnivores tested at the B1, SAG1, and GRA6 typing loci, 15 had PCR-confirmed T. gondii infection; 11 possessed alleles consistent with infection by archetypal Type I, II or III strains and 4 possessed alleles consistent with Type X T. gondii infection. No non-canonical alleles were identified. The four T. gondii strains with Type X alleles were identified from two mountain lions, a bobcat and a fox residing in coastal watersheds adjacent to sea otter habitat near Monterey Bay and Estero Bay. Confirmation of Type X T. gondii in coastal-dwelling felids, canids, a marine bivalve and nearshore-dwelling sea otters supports the hypotheses that feline faecal contamination is flowing from land to sea through surface runoff, and that otters can be infected with T. gondii via consumption of filter-feeding marine invertebrates.

PMID: 18452923 [PubMed - as supplied by publisher]

Pre-transplant Toxo seropositivity among heart transplant recipients and mortality

J Am Coll Cardiol. 2008 May 6;51(18):1827; author reply 1827-8.

Pre-transplant Toxoplasma gondii seropositivity among heart transplant recipients and mortality

Flores-Ríos X, Paniagua-Martín MJ, Muñiz-García J, Crespo-Leiro MG.

Publication Types:

PMID: 18452795 [PubMed - in process]

A prospective study of diagnosis of Toxoplasma gondii infection after bone marrow transplantation

APMIS. 2008 May;116(5):345-51.

A prospective study of diagnosis of Toxoplasma gondii infection after bone marrow transplantation

Edvinsson B, Lundquist J, Ljungman P, Ringdén O, Evengård B.

Swedish Institute for Infectious Disease Control, Karolinska University Hospital Huddinge, Stockholm, Sweden.

Active infection with Toxoplasma gondii in immunocompromised transplant recipients can lead to toxoplasmosis, which may have a rapid disease course and in some cases be fatal. It is of paramount importance to diagnose toxoplasmosis at an early stage, and to initiate specific treatment to improve the outcome. Polymerase chain reaction (PCR) is today the primary diagnostic tool to diagnose toxoplasmosis in immunocompromised patients. Timely diagnosis may, however, be difficult if toxoplasmosis is at first asymptomatic. To investigate the magnitude of toxoplasmosis after bone marrow transplantation (BMT), we conducted a screening study by PCR where 21 autologous and 12 allogeneic BMT recipients were included. Peripheral blood samples were taken one week prior to BMT; thereafter, blood samples were drawn weekly for the first 6 months, and monthly up to one year after BMT. The samples were analyzed by conventional PCR and real-time PCR. T. gondii DNA was detected in peripheral blood from one patient 5 days post allogeneic BMT. There were no clinical signs of toxoplasmosis. Medical records were reviewed and showed a previously undiagnosed eye infection in another allogeneic BMT recipient. These two patients were seropositive for T. gondii. We concluded that monitoring for T. gondii DNA in peripheral blood samples using PCR might be a valuable method for identifying toxoplasma-seropositive stem cell transplant recipients.

PMID: 18452424 [PubMed - in process]

Friday, May 02, 2008

Back from the dormant stage: second messenger cyclic ADP-ribose essential for Toxo pathogenicity

Sci Signal. 2008 Apr 29;1(17):pe18.

Back from the dormant stage: second messenger cyclic ADP-ribose essential for Toxoplasma gondii pathogenicity

Guse AH.

The Calcium Signalling Group, Institute of Biochemistry and Molecular Biology I: Cellular Signal Transduction, Centre of Experimental Medicine, University Medical Centre Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany.

Cyclic adenosine diphosphoribose (cADPR) is an endogenous Ca2+-mobilizing second messenger found in cells of animals, plants, and protozoans. It is formed by a specific class of enzymes, the ADP-ribosyl cyclases. cADPR stimulates Ca2+ release by means of ryanodine receptors located in the sarcoplasmic and endoplasmic reticulum. Recently, a role for cADPR has been demonstrated in the obligate intracellular protozoan pathogen Toxoplasma gondii. In T. gondii, stress conditions evoked synthesis of the plant hormone abscisic acid by the apicoplast, a remnant organelle of an algal endosymbiont of T. gondii. Abscisic acid in turn activated formation of cADPR within T. gondii, resulting in Ca2+ release and secretion of proteins involved in egress of T. gondii from its host cell. Evidence for a synthetic pathway of plant origin was obtained with the ABA synthesis inhibitor fluridone, which antagonized cellular egress and induced differentiation of long-lived semidormant cystic forms of T. gondii. Moreover, fluridone protected mice from toxoplasmosis.

PMID: 18445834 [PubMed - in process]

Diagnosis of cerebral toxoplasmosis by detection of tachyzoites in cerebrospinal fluid

J Neurol. 2008 Apr 30 [Epub ahead of print]

Diagnosis of cerebral toxoplasmosis by detection of Toxoplasma gondii tachyzoites in cerebrospinal fluid

Palm C, Tumani H, Pietzcker T, Bengel D.

Dept. of Neurology, University Hospital Ulm, Ulm, Germany.

PMID: 18446314 [PubMed - as supplied by publisher]