Entamoeba histolytica and Entamoeba dispar: Morphological and Behavioral Differences Induced by Fibronectin through GTPases Activation and Actin-Binding Proteins

Effect of Stevioside (Stevia rebaudiana) on Entamoeba histolytica Trophozoites

Human amoebiasis still represents a major health problem worldwide. Metronidazole has been used as the most common drug to treat the disease; however, it is also known that the drug causes undesirable side effects. This has led to the search for new pharmacological alternatives which include phytochemical compounds with antiamoebic effects. We analyzed the amoebicidal activity of stevioside (STV), a diterpene glycoside present in Stevia rebaudiana, on trophozoites of E. histolytica. Different concentrations of STV were tested, and an inhibitory concentration of 50% of cell viability (IC50) was determined with an exposition of 9.53 mM for 24 h. Trophozoites exposed to STV showed morphological changes evidenced by the decrease in the basic structures related to the movement and adherence to the substrate, as well as ultrastructural features characterized by a loss of regularity on the cell membrane, an increase in cytoplasmic granularity, and an increase in apparent autophagic vacuoles. Also, the decrease in cysteine protease expression and the proteolytic activity of trophozoites to degrade the cell monolayer were analyzed. A histological analysis of hamster livers inoculated with trophozoites and treated with STV showed changes related to the granulomatous reaction of the liver parenchymal tissue. Our results constitute the first report related to the possible use of STV as a therapeutic alternative in amoebiasis.

Alpha-terthienyl increases filamentous actin of Entamoeba histolytica

This study aimed to know if alpha terthienyl (α-T) affects E. histolytica viability and to analyze its effect on the actin cytoskeleton. Trophozoites of E. histolytica HM1-IMSS were treated with α-T, then, cell viability and morphology were evaluated using tetrazolium salts and scanning electron microscopy, respectively; while actin filaments (F-actin) were stained with rhodamine-phalloidin, observed by confocal microscopy and quantified by fluorometry. Data showed that α-T inhibited cell viability of trophozoites (IC₅₀, 19.43 µg / mL), affected the cell morphology, and increased the F-actin in a dose-dependent manner. Production of reactive oxygen species and RhoA-GTP levels remained normal in α-T-treated amebas. Two inhibitors that affect the organization of the trophozoites cytoskeleton, one that interacts directly with actin, Cytochalasin D (CD), and one that affects the Rho signaling pathway by inhibiting the downstream effector Rock, Y27632, were tested. Y27632 did not affect the increase of polymerized actin observed with α-T, this compound partially ameliorates the potent disrupting effects of CD on actin filaments. Docking results suggest that α-T could be an antagonist of CD for the same interaction zone in actin, however, more studies are needed to define the action mechanism of this compound.