Consumption of Galactose by Trypanosoma cruzi Epimastigotes Generates Resistance against Oxidative Stress.

In this study, we demonstrate that Trypanosoma cruzi epimastigotes previously grown in LIT medium supplemented with 20 mM galactose and exposed to sub-lethal concentrations of hydrogen peroxide (100 µM) showed two-fold and five-fold viability when compared to epimastigotes grown in LIT medium supplemented with two different glucose concentrations (20 mM and 1.5 mM), respectively. Similar results were obtained when exposing epimastigotes from all treatments to methylene blue 30 µM. Additionally, through differential centrifugation and the selective permeabilization of cellular membranes with digitonin, we found that phosphoglucomutase activity (a key enzyme in galactose metabolism) occurs predominantly within the cytosolic compartment. Furthermore, after partially permeabilizing epimastigotes with digitonin (0.025 mg × mg-1 of protein), intact glycosomes treated with 20 mM galactose released a higher hexose phosphate concentration to the cytosol in the form of glucose-1-phosphate, when compared to intact glycosomes treated with 20 mM glucose, which predominantly released glucose-6-phosphate. These results shine a light on T. cruzi's galactose metabolism and its interplay with mechanisms that enable resistance to oxidative stress.

Subcellular localization of glycolytic enzymes and characterization of intermediary metabolism of Trypanosoma rangeli.

Trypanosoma rangeli is a hemoflagellate protist that infects wild and domestic mammals as well as humans in Central and South America. Although this parasite is not pathogenic for human, it is being studied because it shares with Trypanosoma cruzi, the etiological agent of Chagas' disease, biological characteristics, geographic distribution, vectors and vertebrate hosts. Several metabolic studies have been performed with T. cruzi epimastigotes, however little is known about the metabolism of T. rangeli. In this work we present the subcellular distribution of the T. rangeli enzymes responsible for the conversion of glucose to pyruvate, as determined by epifluorescense immunomicroscopy and subcellular fractionation involving either selective membrane permeabilization with digitonin or differential and isopycnic centrifugation. We found that in T. rangeli epimastigotes the first six enzymes of the glycolytic pathway, involved in the conversion of glucose to 1,3-bisphosphoglycerate are located within glycosomes, while the last four steps occur in the cytosol. In contrast with T. cruzi, where three isoenzymes (one cytosolic and two glycosomal) of phosphoglycerate kinase are expressed simultaneously, only one enzyme with this activity is detected in T. rangeli epimastigotes, in the cytosol. Consistent with this latter result, we found enzymes involved in auxiliary pathways to glycolysis needed to maintain adenine nucleotide and redox balances within glycosomes such as phosphoenolpyruvate carboxykinase, malate dehydrogenase, fumarate reductase, pyruvate phosphate dikinase and glycerol-3-phosphate dehydrogenase. Glucokinase, galactokinase and the first enzyme of the pentose-phosphate pathway, glucose-6-phosphate dehydrogenase, were also located inside glycosomes. Furthermore, we demonstrate that T. rangeli epimastigotes growing in LIT medium only consume glucose and do not excrete ammonium; moreover, they are unable to survive in partially-depleted glucose medium. The velocity of glucose consumption is about 40% higher than that of procyclic Trypanosoma brucei, and four times faster than by T. cruzi epimastigotes under the same culture conditions.

Interaction of Trypanosoma evansi with the plasminogen-plasmin system.

Trypanosoma evansi is a widely-distributed haemoflagellated parasite of veterinary importance that infects a variety of mammals including horses, mules, camels, buffalos, cattle and deer. It is the causal agent of a trypanosomiasis known as Surra which produces epidemics of great economic importance in Africa, Asia and South America. The main pathology includes an enlarged spleen with hypertrophy of lymphoid follicles, congested lungs, neuronal degeneration and meningoencephalitis, where migration of the parasites from the blood to the tissues is essential. Most cells, including pathogenic cells, use diverse strategies for tissue invasion, such as the expression of surface receptors to bind plasminogen or plasmin. In this work, we show that T. evansi is able to bind plasminogen and plasmin on its surface. The analysis of this binding revealed a high affinity dissociation constant (Kd of 0.080±0.009µM) and 1×10(5) plasminogen binding sites per cell. Also a second population of receptors with a Kd of 0.255±0.070µM and 3.2×10(4) plasminogen binding sites per cell was determined. Several proteins with molecular masses between ∼18 and ∼70kDa are responsible for this binding. This parasite-plasminogen interaction may be important in the establishment of the infection in the vertebrate host, where the physiological concentration of available plasminogen is around 2µM.

[Adenosine deaminase in experimental trypanosomiasis: future implications]. / Adenosin deaminasa en la tripanosomiasis experimental: futuras implicaciones.

The adenosine deaminase represents a control point in the regulation of extracellular adenosine levels, thus playing a critical role in the modulation of purinergic responses to certain pathophysiological events. Several studies have shown that serum and plasma enzyme levels are elevated in some diseases caused by microorganisms, which may represent a compensatory mechanism due to the elevated levels of adenosine and the release of inflammatory mediators. Recent research indicates that adenosine deaminase activity decreases and affects hematological parameters of infected animals with Trypanosoma evansi, so that such alterations could have implications in the pathogenesis of the disease. In addition, the enzyme has been detected in this parasite; allowing the inference that it could be associated with the vital functions of the same, similar to what occurs in mammals. This knowledge may be useful in the association of chemotherapy with specific inhibitors of the enzyme in future studies.

Adenosin deaminasa en la tripanosomiasis experimental: futuras implicaciones / Adenosine deaminase in experimental trypanosomiasis: future implications

La adenosin deaminasa representa un punto de control en la regulación de los niveles extracelulares de adenosina, desempeñando así un papel fundamental en la modulación de las respuestas purinérgicas a ciertos eventos patofisiológicos. Diversos estudios señalan que los niveles séricos y plasmáticos de la enzima se elevan en algunas enfermedades causadas por microorganismos, lo cual podría representar un mecanismo compensatorio como consecuencia de la elevación de las concentraciones de adenosina y la liberación de mediadores inflamatorios. Recientes investigaciones indican que la actividad de la adenosin deaminasa disminuye e influye en los parámetros hematológicos de animales infectados con Trypanosoma evansi, de manera que tales alteraciones podrían tener implicaciones en la patogénesis de la enfermedad. Adicionalmente, la enzima ha sido detectada en este parásito; lo que permite inferir que podría estar asociada a las funciones vitales del mismo, de manera similar a lo que ocurre en los mamíferos. Este conocimiento puede ser útil al asociar la quimioterapia con inhibidores específicos de la enzima en futuros estudios.

The adenosine deaminase represents a control point in the regulation of extracellular adenosine levels, thus playing a critical role in the modulation of purinergic responses to certain pathophysiological events. Several studies have shown that serum and plasma enzyme levels are elevated in some diseases caused by microorganisms, which may represent a compensatory mechanism due to the elevated levels of adenosine and the release of inflammatory mediators. Recent research indicates that adenosine deaminase activity decreases and affects hematological parameters of infected animals with Trypanosoma evansi, so that such alterations could have implications in the pathogenesis of the disease. In addition, the enzyme has been detected in this parasite; allowing the inference that it could be associated with the vital functions of the same, similar to what occurs in mammals. This knowledge may be useful in the association of chemotherapy with specific inhibitors of the enzyme in future studies.

Antígenos parasitarios de O-Glicosilación incompleta: Un enfoque inmunoterapeutico contra el cáncer / Incomplete O-Glycosylation parasite antigens: An immunotherapeutic approach against cancer

Es cada vez mayor la evidencia experimental y clínica de que el sistema inmune interviene activamente en la patogénesis y el control de la progresión tumoral. Una respuesta antitumoral efectiva depende de la correcta interacción de diversos componentes del sistema inmune, como las células presentadoras de antígeno y diferentes sub-poblaciones de células T. Sin embargo, los tumores malignos desarrollan numerosos mecanismos para evadir su reconocimiento y eliminación. Diversos estudios reportan que estructuras asociadas a tumor tales como los antígenos Tn y sialil-Tn se expresan en algunos parásitos protozoarios y helmintos, planteando numerosas interrogantes a nivel de la interacción parásito-hospedador. Considerando que existe una correlación negativa entre ciertas infecciones parasitarias y el desarrollo de cáncer, los antígenos de O-glicosilación incompleta obtenidos de parásitos podrían ser potenciales estructuras miméticas para la inducción de respuestas cruzadas contra antígenos tumorales. Actualmente, el área de la glicobiología del cáncer tiene muchas expectativas para encontrar solución a uno de los grandes problemas de salud que afecta a la población tanto desde el punto de vista económico como social.

There is increasing experimental and clinical evidence that the immune system plays an active role in the pathogenesis and control of tumor progression. An effective antitumor response depends on the correct interaction of the various components of the immune system, such as antigen presenting cells and sub-populations of T cells. However, malignant tumors develop numerous mechanisms to evade recognition and elimination. Several studies report that structures associated with tumors such as Tn and sialyl-Tn antigens are expressed in some protozoan parasites and helminths, thus raising many questions regarding parasite-host interactions. The negative correlation between certain parasite infections and cancer development suggests that antigens from incomplete O-glycosylation obtained from parasites could represent potential mimetic structures for inducing cross responses against tumor antigens. Currently, cancer glycobiology is a promising area in the search for a solution to one of the major health problems affecting the population both from an economic and a social perspective.