Trypanosoma cruzi: interaction with vertebrate cells in vitro. IV. Environmental temperature effects

New metabolic signature for Chagas disease reveals sex steroid perturbation in humans and mice

The causative agent of Chagas disease (CD), Trypanosoma cruzi, claims thousands of lives each year. Current diagnostic tools are insufficient to ensure parasitological detection in chronically infected patients has been achieved. A host-derived metabolic signature able to distinguish CD patients from uninfected individuals and assess antiparasitic treatment efficiency is introduced. Serum samples were collected from chronic CD patients, prior to and three years after treatment, and subjected to untargeted metabolomics analysis against demographically matched CD-negative controls. Five metabolites were confirmed by high-resolution tandem mass spectrometry. Several database matches for sex steroids were significantly altered in CD patients. A murine experiment corroborated sex steroid perturbation in T. cruzi-infected mice, particularly in male animals. Proteomics analysis also found increased steroidogenesis in the testes of infected mice. Metabolic alterations identified in this study shed light on the pathogenesis and provide the basis for developing novel assays for the diagnosis and screening of CD patients.

Clathrin coated pit dependent pathway for Trypanosoma cruzi internalization into host cells

A number of intracellular pathogens are internalized by host cells via multiple endocytic pathways, including Trypanosoma cruzi, the etiological agent of Chagas disease. Clathrin-mediated endocytosis is the most characterized endocytic pathway in mammalian cells. Its machinery was described as being required in mammalian cells for the internalization of large particles, including pathogenic bacteria, fungi, and large virus. To investigate whether T. cruzi entry into host cells can also take advantage of the clathrin-coated vesicle-dependent process, we utilized well-known inhibitors of clathrin-coated vesicle formation (sucrose hypertonic medium, chlorpromazine hydrochloride and pitstop 2) and small interference RNA (siRNA). All treatments drastically reduced the internalization of infective trypomastigotes and amastigotes of T. cruzi by phagocytic (macrophages) and epithelial cells. Clathrin labeling, as observed by fluorescence and electron microscopy, was also observed around the parasites from the initial stages of infection until the complete formation of the parasitophorous vacuole. These unexpected observations suggest the participation of the clathrin pathway in the T. cruzi entry process.

Mammalian cellular culture models of Trypanosoma cruzi infection: a review of the published literature

Cellular culture infection with Trypanosoma cruzi is a tool used to dissect the biological mechanisms behind Chagas disease as well as to screen potential trypanocidal compounds. Data on these models are highly heterogeneous, which represents a challenge when attempting to compare different studies. The purpose of this review is to provide an overview of the cell culture infectivity assays performed to date. Scientific journal databases were searched for articles in which cultured cells were infected with any Trypanosoma cruzi strain or isolate regardless of the study’s goal. From these articles the cell type, parasite genotype, culture conditions and infectivity results were extracted. This review represents an initial step toward the unification of infectivity model data. Important differences were detected when comparing the pathophysiology of Chagas disease with the experimental conditions used in the analyzed studies. While Trypanosoma cruzi preferentially infects stromal cells in vivo, most of the assays employ epithelial cell lines. Furthermore, the most commonly used parasite strain (Tulahuen-TcVI) is associated with chagasic cardiomyopathy only in the Southern Cone of South America. Suggestions to overcome these discrepancies include the use of stromal cell lines and parasite genotypes associated with the known characteristics of the natural history of Chagas disease.

Experimental chemotherapy and approaches to drug discovery for Trypanosoma cruzi infection

In the 100 years since the discovery of Chagas disease, only two drugs have been developed and introduced into clinical practice, and these drugs were introduced over 40 years ago. The tools of drug discovery have improved dramatically in the interim; however, this has not translated into new drugs for Chagas disease. This has been largely because the main practitioners of drug discovery are pharmaceutical companies who are not financially motivated to invest in Chagas disease and other "orphan" diseases. As a result, it has largely been up to academic groups to bring drug candidates through the discovery pipeline and to clinical trials. The difficulty with drug discovery in academia has been the challenge of bringing together the diverse expertise in biology, chemistry, and pharmacology in concerted efforts towards a common goal of developing therapeutics. Funding is often inadequate, but lack of coordination amongst academic investigators with different expertise has also contributed to the slow progress. The purpose of this chapter is to provide an overview of approaches that can be accomplished in academic settings for preclinical drug discovery for Chagas disease. The chapter addresses methods of drug screening against Trypanosoma cruzi cultures and in animal models and includes general topics on compound selection, testing for drug-like properties (including oral bioavailability), investigating the pharmacokinetics and toxicity of compounds, and finally providing parameters to help with triaging compounds.

Cultivation of Trypanosoma cruzi in irradiated muscle cells: improved synchronization and enhanced trypomastigote production

Since the in vitro production of trypomastigote stages of Trypanosoma cruzi in cell culture is frequently limited by (1) host cell overgrowth and (2) by the unequal redistribution of parasites after cell division resulting in asynchronous release of trypomastigotes, a culture system was devised in which host cell mitosis was inhibited by irradiation prior to parasite infection. L-6 rat myoblast cells when exposed to 3000 rad. of gamma radiation lost their ability to divide but remained susceptible to infection with, and capable of supporting the intracellular growth of, T. cruzi. Using this approach it proved possible to have virtually 100% of cells infected and achieve much better synchronization of trypomastigote release than with conventional culture systems. Additionally, the total number of parasites provided approached 1 x 10(9) trypomastigotes/150 cm2 flask, a significant increase over other culture systems. Preliminary studies with Plasmodium fallax an Eimeria tenella indicate that irradiated host cells may be utilized to advantage for the cultivation of other intracellular protozoa.

Adhesion and interiorization of Trypanosoma cruzi in mammalian cells

A quantitative method for experimentally separating the adhesion and interiorization phases of the interaction of Trypanosoma cruzi with mammalian cells was developed. Incubation of confluent monolayers of mammalian cells with epimastigotes or trypomastigotes at 4 degrees C allowed the evaluation of the number of adhered parasites that do not become interiorized at this temperature. Quantification of interiorized parasites at 34 degrees C was achieved by employing hypotonic lysis to eliminate the extracellularly adhered trypomastigotes. Both adhesion and interiorization were found to be proportional to the time of exposure of cells to parasites and to the multiplicity of infection. These phenomena occur normally for trypomastigotes in the absence of serum with LLC-MK2 cells, HeLa cells, and 3T3 fibroblasts. Moreover, it was possible to obtain trypomastigotes that presented the same infectivity to LLC-MK2 cells as did parasites obtained in the presence of 2% fetal calf serum after 10 serial passages in a medium devoid of serum. Inhibition of adhesion (of epimastigotes and trypomastigotes) and of interiorization (of trypomastigotes) was obtained with inactivated normal serum from several sources, a saturation effect being observed at a final concentration of 20%. Bovine serum albumin, at the concentrations present in the sera, had no inhibitory effect. Trypomastigotes that have been pre-incubated with 40% FCS (45 min at 4 degrees C) showed decreased adhesion and interiorization indices, effects that can be reversed by trypsinization of the parasites prior to exposure of the cells. A progressive internalization of previously attached trypomastigotes was observed on raising the temperature from 4 degrees C to 34 degrees C; no spontaneous detachment of parasites was detected up to 120 min. Approximately 75% of the adhered parasites were found inside the cells after 45 min at 34 degrees C. The presence of normal inactivated calf serum during incubation at 34 degrees C resulted in a certain degree of detachment and in a lower interiorization index.

Trypanosoma cruzi: pattern of RNA synthesis following infection of vertebrate cells

The pattern of RNA synthesis of intracellular Trypanosoma cruzi amastigotes, immediately following infection of Lesch-Nyhan human fibroblasts, was studied by autoradiography. Amastigote RNA synthesis, determined by [3H]guanine incorporation, was not detected until 2 h after infection. At 8 h postinfection more than 90% of intracellular amastigotes were labeled. It was verified that extracellular trypomastigotes also synthesized RNA. Therefore it was concluded that, if RNA is required for trypomastigote-to-amastigote transformation, this nucleic acid is already present in the trypomastigotes before infection of the vertebrate cell. It is probable that the RNA synthesized by amastigotes during the prereplicative lag period (the period between initial infection and the onset of DNA synthesis) is required for intracellular growth and reproduction.

Trypanosoma cruzi: interaction with vertebrate cells. DNA synthesis and growth of intracellular amastigotes and their relationship to host cell DNA synthesis and growth

DNA synthesis of intracellular Trypanosoma cruzi amastigotes, following the infection of bovine embryo skeletal muscle (BESM) cells, was studied by autoradiography. After penetration, there was a prereplicative lag period (similar to or approximately 12 h) followed by a synchronous round of DNA synthesis which was found to be independent of parasite number/BESM cell cand the host cell DNA synthesis cycle. Parasite reproduction occurred, for the first time, at approximately 21 h postinfection. It was concluded that T. cruzi trypomastigotes are in the G1/G0 phase of their cell division cycle and that after penetration parasite reproduction occurs independent of events controlling host cell DNA synthesis and growth. The early synchronous growth of intracellular amastigotes should facilitate further studies on the biochemical events controlling trypomastigote-to-amastigote transformation and amastigote reproduction. A further application is envisaged for studies on the mode of action of drugs with trypanocidal activity.