Entamoeba histolytica lacks trypanothione metabolism

Entamoeba histolytica lacks glutathione reductase activity and the ability to synthesise glutathione de novo. However, a recent report suggested that exogenous glutathione can be taken up and conjugated to spermidine to form trypanothione. a metabolite found so far only in trypanosomatids. Given the therapeutic implications of this observation, we have carefully analysed E . histolytica for evidence of trypanothione metabolism. Using a sensitive f luorescence-based HPLC detection system we could confirm previous reports t hat cysteine and hydrogen sulphide are the principal low molecular mass thi ols. However, we were unable to detect trypanothione or its precursor N-1-g lutathionylspermidine [ < 0.01 nmol (10(6) cells)(-1) or < 1.7 mu M]. In co ntrast, Trypanosoma cruzi epimastigotes (grown in a polyamine-supplemented medium) and Leishmania donovani promastigotes contained intracellular conce ntrations of trypanothione two to three orders of magnitude greater than th e limits of detection. Likewise, trypanothione reductase activity was not d etectable in E, histolytica [ < 0.003 U (mg protein)(-1)] and therefore at least 100-fold less than trypanosomatids. Moreover, although E. histolytica were found to contain trace amounts of glutathione (approximately 20 mu M) , glutathione reductase activity was below the limits of detection [ < 0.00 5 U (mg protein)(-1)]. These findings argue against the existence of trypan othione metabolism in E. histolytica. (C) 1999 Elsevier Science B.V. All ri ghts reserved.