Glutathione and trypanothione in several strains of Trypanosoma cruzi: effect of drugs.

Glutathione (GSH), trypanothione (T(SH)2) and glutathionyl spermidine (GSH-SP) concentrations were determined in the Tulahuén and LQ strains and the DM 28c clone of Trypanosoma cruzi. The concentrations of GSH, T(SH)2 and GSH-SP, expressed as nmol of GSH per g of parasite fresh weight, were 60.1, 397.8 and 103.9, respectively, for the Tulahuén strain. For the DM 28c clone, the values were 113.9, 677.9 and 164.1, respectively, and for the LQ strain they were 199.1, 1100.5 and 55.3, respectively. When the parasites were treated with 10 microM nifurtimox or 50 microM benznidazole for 2 h, the concentrations of all three reduced thiols decreased strongly. The total amount of T(SH)2 decreased by more than 50%. Treatment of the parasites with 5 mM buthionine sulfoximine, an inhibitor of GSH synthesis, for 6 h diminished the concentrations of the reduced thiols by between 27% and 53% with respect to the controls. Cyclohexylamine, an inhibitor of spermidine synthesis, decreased the concentrations of T(SH)2 and GSH-SP but not that of GSH. It is possible to conclude from this study that trypanothione is the most important thiol involved in the detoxication of nifurtimox and benznidazole in T. cruzi and that electrophilic reduced metabolites of both drugs are most probably conjugated with GSH, T(SH)2 and GSH-SP, thus decreasing their concentrations. GSH biosynthesis is an important drug target.

A cytosolic flavin-containing enzyme catalyzing reduction of cytochrome c in Trypanosoma cruzi: kinetic studies with cytochrome c as substrate.

The kinetic mechanism of cytochrome c reduction by a Trypanosoma cruzi cytosolic flavoenzyme was investigated by initial velocity determinations, by product inhibition patterns, and by the characteristics of inhibition by analogs. The data suggest a two-site ping-pong mechanism in which NADPH reduces the flavin, which is then reoxidized in two one-electron steps by reaction with two molecules of cytochrome c. The two-site nature of the mechanism is probably related to the dimeric nature of the enzyme, and the binding sites of cytochrome c and NADPH are probably on opposite sites of the FAD.

Ultrastructural modifications during the metabolism of metronidazole by Trypanosoma cruzi.

Trypanosoma cruzi epimastigotes incubated in the presence of [14C] metronidazole are capable of a rapid uptake of the drug as shown by timecourse experiments and by autoradiography of the cells. The drug is metabolized to a more polar compound which has the chromatographic behavior of 2-methyl-5-nitroimidazole-1-yl-acetic acid. Mass spectral analysis of the metabolite shows diagnostic mass values (185, 184, 126) which are compatible with the 2-methyl-5-nitroimidazole-1-yl-acetic acid derivative. Flavone dramatically increases the production of the metabolite both in control and cells pretreated with phenobarbital. The cells show the presence of vesicles whose number is not significantly increased by phenobarbital. Metronidazole, on the other hand, significantly increases the number of vesicles in both control and cells grown in phenobarbital. The vesicles do not contain acid phosphatase and/or polyphosphates. It is concluded that the vesicles may correspond to a marked proliferation of the endoplasmic reticulum. A secondary effect of flavone is the proliferation of the mitochondrial membranes.

Echinococcus antigens.

Much of the work on immunology of hydatidosis has so far been devoted to the development of suitable methods for serological diagnosis. The precise nature of hydatid antigens and their chemical characterization has still not been worked out, largely because of the complex life-history of the parasite and the difficulties of in vitro cultivation. The most widely used antigen for routine serological testing in hydatidosis caused by Echinococcus granulosus is fluid taken from the cyst. This fluid is, however, a complex mixture of substances and contains several protein and carbohydrate fractions as well as end-products of carbohydrate and protein metabolism. The cyst fluid from different sources is variable in its antigenic properties, and the fluid from sterile cysts is especially lacking in antigenic activity. Antigens from tissue extracts of hydatid cysts appear to have greater specificity. Cyst extracts of E. multilocularis, the cysts of which contain relatively little fluid, have also been used but are poor antigens, and contain measurable amounts of host protein. Antigens prepared from other cestodes and metabolic antigens are also reviewed.Biochemical analysis of Echinococcus antigens covering polysaccharides, proteins, lipids, and blood-group substances is considered, together with the characterization of antigens by electrophoresis, column chromatography and gel-diffusion methods. The problems associated with the standardization of antigens are discussed. Recent data on the character and reactivity of antigens employed in Echinococcus studies are summarized.