Glycolysis in the human parasite Entamoeba histolytica is characterized by the absence of cooperative modulation and the prevalence of pyrophosphatedependent (over ATP-dependent) enzymes. To determine the flux-control distribution of glycolysis and understand its underlying control mechanisms, a kinetic model of the pathway was constructed by using the software gepasi. The model was based on the kinetic parameters determined in the purified recombinant enzymes, and the enzyme activities, and steady-state fluxes and metabolite concentrations determined in amoebal trophozoites. The model predicted, with a high degree of accuracy, the flux and metabolite concentrations found in trophozoites, but only when the pyrophosphate concentration was held constant; at variable pyrophosphate, the model was not able to completely account for the ATP production ⁄ consumption balance, indicating the importance of the pyrophosphate homeostasis for amoebal glycolysis. Control analysis by the model revealed that hexokinase exerted the highest flux control (73%), as a result of its low cellular activity and strong AMP inhibition. 3-Phosphoglycerate mutase also exhibited significant flux control (65%) whereas the other pathway enzymes showed little or no control. The control of the ATP concentration was also mainly exerted by ATP consuming processes and 3-phosphoglycerate mutase and hexokinase (in the producing block). The model also indicated that, in order to diminish the amoebal glycolytic flux by 50%, it was required to decrease hexokinase or 3-phosphoglycerate mutase by 24% and 55%, respectively, or by 18% for both enzymes. By contrast, to attain the same reduction in flux by inhibiting the pyrophosphate-dependent enzymes pyrophosphate-phosphofructokinase and pyruvate phosphate dikinase, they should be decreased > 70%. On the basis of metabolic control analysis, steps whose inhibition would have stronger negative effects on the energy metabolism of this parasite were identified, thus becoming alternative targets for drug design.Abbreviations ADH, alcohol dehydrogenase; AK, adenylate kinase; ALDO, fructose 1,6-bisphosphate aldolase; AldDH, aldehyde dehydrogenase; ATP-PFK, ATP-dependent phosphofructokinase; DHAP, dihydroxyacetone phosphate; ENO, enolase; EtOH, ethanol; F6P, fructose 6-phosphate; F(1,6)P 2 , fructose 1,6-bisphosphate; G6P, glucose 6-phosphate; G6PDH, glucose 6-phosphate dehydrogenase; G3P, glyceraldehyde 3-phosphate; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; Gly3PDH, glycerol 3-phosphate dehydrogenase; HK, hexokinase; HPI, hexose 6-phosphate isomerase; HXT, hexose transporter; LDH, lactate dehydrogenase; MCA, metabolic control analysis; PGAM, 3-phosphoglycerate mutase; PGK, phosphoglycerate kinase; PGM, phosphoglucomutase; 3PGDH, 3-phosphoglycerate dehydrogenase; PEP, phosphoenolpyruvate; 2PG, 2-phosphoglycerate; 3PG, 3-phosphoglycerate; PPi, pyrophosphate; PPi-PFK, pyrophosphate-dependent phosphofructokinase; PPP, pentose phosphate pathway; PFOR, pyruvate:ferredoxin oxidoreductase; PFOR-AldDH, lumped reacti...
More than one quarter of human world's population is exposed to intestinal helminth parasites. The Taenia solium tapeworm carrier is the main risk factor in the transmission of both human neurocysticercosis and porcine cysticercosis. Sex steroids play an important role during T. solium infection, particularly progesterone has been proposed as a key immunomodulatory hormone involved in susceptibility to human taeniosis in woman and cysticercosis in pregnant pigs. Thus, we evaluated the effect of progesterone administration upon the experimental taeniosis in golden hamsters (Mesocricetus auratus). Intact female adult hamsters were randomly divided into 3 groups: progesterone-subcutaneously treated; olive oil-treated as the vehicle group; and untreated controls. Animals were treated every other day during 4 weeks. After 2 weeks of treatment, all hamsters were orally infected with 4 viable T. solium cysticerci. After 2 weeks post infection, progesterone-treated hamsters showed reduction in adult worm recovery by 80%, compared to both vehicle-treated and non-manipulated infected animals. In contrast to control and vehicle groups, progesterone treatment diminished tapeworm length by 75% and increased proliferation rate of leukocytes from spleen and mesenteric lymph nodes of infected hamsters by 5-fold. The latter exhibited high expression levels of IL-4, IL-6 and TNF-α at the duodenal mucosa, accompanied with polymorphonuclear leukocytes infiltration. These results support that progesterone protects hamsters from the T. solium adult tapeworm establishment by improving the intestinal mucosal immunity, suggesting a potential use of analogues of this hormone as novel inductors of the gut immune response against intestinal helminth infections and probably other bowel-related disorders.
Human neurocysticercosis by Taenia solium is considered an emergent severe brain disorder in developing and developed countries. Discovery of new antiparasitic drugs has been recently aimed to restrain differentiation and establishment of the T. solium adult tapeworm, for being considered a central node in the disease propagation to both pigs and humans. Tamoxifen is an antiestrogenic drug with cysticidal action on Taenia crassiceps, a close relative of T. solium. Thus, we evaluated the effect of tamoxifen on the in vitro evagination and the in vivo establishment of T. solium. In vitro, tamoxifen inhibited evagination of T. solium cysticerci in a dose-time dependent manner. In vivo, administration of tamoxifen to hamsters decreased the intestinal establishment of the parasite by 70%, while recovered tapeworms showed an 80% reduction in length, appearing as scolices without strobilar development. Since tamoxifen did not show any significant effect on the proliferation of antigen-specific immune cells, intestinal inflammation, and expression of Th1/Th2 cytokines in spleen and duodenum, this drug could exert its antiparasite actions by having direct detrimental effects upon the adult tapeworm. These results demonstrate that tamoxifen exhibits a strong cysticidal and antitaeniasic effect on T. solium that should be further explored in humans and livestock.
Human amoebiasis is a disease produced by infection with the protozoan Entamoeba histolytica currently affecting many millions of people worldwide. Amoebic colitis is the most common clinical manifestation. Host protective immunity involves participation of both humoral and cellular responses. However, the mechanisms involved in immune evasion are not clear and remain under investigation. One of these mechanisms could be associated with the ability of parasite proteases to modulate or interfere with the inflammation process, which is initiated by expression of pro-inflammatory cytokines such as chemokines. To further clarify the potential role of cysteine proteases in modulating chemokine-mediated functions, we have analysed the ability of Entamoeba histolytica cysteine protease 2 (EhCP2) to have an effect on the chemotaxis of leucocytes by chemokine cleavage. We find that EhCP2 is capable of cleaving chemokines CCL2, CCL13 and CXCL8, and the resulting proteolysis products modulate the chemotaxis of leucocytes when compared to that induced by intact chemokine. Thus, the extracellular activity of the cysteine proteases affects chemokine-mediated responses and could be considered as part of the mechanisms used by Entamoeba histolytica to circumvent the host immune responses.
Tritiated dityrosine and isotrityrosine were detected by high performance liquid chromatography (HPLC) of acid hydrolysates of cuticular proteins from larval Ascaris suum following their 96-hr in vitro incubation in [3H]tyrosine. Sixty percent of the HPLC-recovered radiolabel was present as tyrosine, 20% as dityrosine, and 6% as isotrityrosine. Approximately 13% of radioactivity was associated with several unidentified peaks. A similar distribution of radioactivity was observed in acid hydrolysates of cuticular proteins from young adults of A. suum following 48 hr in vitro incubation with [3H]tyrosine. The 2-mercaptoethanol (2ME)-insoluble cuticular protein from the larval stages had a higher rate of synthesis of [3H]dityrosine than did the 2ME-soluble cuticular proteins, whereas the 2ME-soluble cuticular proteins had higher rates of synthesis of [3H]isotrityrosine. Pulse-chase studies of A. suum larvae demonstrated a relatively low rate of synthesis of both dityrosine and isotrityrosine. The addition to the culture media of the peroxidase inhibitors, phenylhydrazine (PHEN), 3-amino-1,2,4-triazole (AT), and N-acetyltyrosine (NAT) reduced the amount of [3H]tyrosine synthesized into both dityrosine and isotrityrosine. In a cell-free system, soluble extracts of A. suum larvae also converted radiolabeled tyrosine to dityrosine; isotrityrosine was produced by some extracts. The rate of conversion correlated with time of incubation and the volume of added extract and was inhibited by AT, NAT, and PHEN, with PHEN being the most potent inhibitor. The results of the present study suggest that the tyrosine residues of the cuticular proteins are posttranslationally modified by the formation of dityrosine and isotrityrosine cross-links. This modification is most likely mediated by a peroxidase.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.