Amino acid consumption by the parasitic, amoeboid protists Entamoeba histolytica and E. invadens

Abstract

Amino acid consumption by Entamoeba histolytica and E. invadens has been measured in order to assess the possible roles of amino acids as energy substrates. Mixtures of amino acids enhanced the growth of the parasites in complex medium and their survival in simple medium. The consumption of several amino acids by the parasites suspended in simple media was greater when glucose was absent, suggesting that they may act as alternative energy sources. Under these conditions, asparagine was consumed extremely rapidly by E. histolytica in particular, and arginine, leucine and threonine were used greatly by both species. There was also a marked consumption of aspartate, but this occurred even when glucose was present. These five amino acids and phenylalanine were the ones consumed in greatest amounts during growth of E. histolytica in complex medium. Under the same growth conditions, E. invadens also used asparagine, arginine, leucine and threonine and in addition there was a large consumption of serine and especially glutamate. In contrast, the aspartate concentration in the complex medium increased and there was also a net increase in the concentration of some other amino acids. Alanine was produced by both species when the parasites were incubated in simple medium with glucose, and in greater amounts during growth in complex media, suggesting that it is an end product of energy metabolism. The findings provide support for the suggestion that energy generation through amino acid catabolism may be a characteristic feature of anaerobic parasitic protists.

Nitric Oxide Production by Human Intestinal Epithelial Cells and Competition for Arginine as Potential Determinants of Host Defense Against the Lumen-Dwelling Pathogen Giardia lamblia

“…These interactions differ from those previously reported for invasive and intracellular pathogens, which induce iNOS expression and NO production after invasion of host cells (18,22,26). Furthermore, the findings with the extracellular pathogen, G. lamblia, suggest a concept that may also apply to other extracellular pathogens, such as Entamoeba histolytica, that consume amino acids in the host microenvironment and where NO constitutes a potent host defense (43,44).…”

Metabolic Profiling of the Protozoan Parasite Entamoeba invadens Revealed Activation of Unpredicted Pathway during Encystation

“…It was previously reported that amino acids such as aspartate, asparagines, and arginine also serve as an energy source in anaerobic parasitic protists [39].…”

Cytotoxic effect of amide derivatives of trifluoromethionine against the enteric protozoan parasite Entamoeba histolytica

“…It is conceivable to assume that TFM is incorporated into the amoebae by amino acid transporter(s). It has also been reported that the parasite incorporates amino acids directly from the culture medium [12]. However, it remains to be clarified whether the TFM derivatives are incorporated via the presumed amino acid transporter(s) or by passive diffusion due to their hydrophobic nature.…”