Deficient metabolic utilization of hydrogen peroxide in Trypanosoma cruzi

Abstract

The glutathione peroxidase-glutathione reductase system, an alternative pathway for metabolic utilization of H2O2 [Chance, Sies & Boveris (1979) Physiol. Rev. 59, 527-605], was investigated in Trypanosoma cruzi, an organism lacking catalase and deficient in peroxidase [Boveris & Stoppani (1977) Experientia 33, 1306-1308]. The presence of glutathione (4.9 +/- 0.7 nmol of reduced glutathione/10(8) cells) and NADPH-dependent glutathione reductase (5.3 +/- 0.4 munit/10(8) cells) was demonstrated in the cytosolic fraction of the parasite, but with H2O2 as substrate glutathione peroxidase activity could not be demonstrated in the same extracts. With t-butyl hydroperoxide or cumene hydroperoxide as substrate, a very low NADPH-dependent glutathione peroxidase activity was detected (equivalent to 0.3-0.5 munit of peroxidase/10(8) cells, or about 10% of glutathione reductase activity). Blank reactions of the glutathione peroxidase assay (non-enzymic oxidation of glutathione by hydroperoxides and enzymic oxidation of NADPH) hampered accurate measurement of peroxidase activity. The presence of superoxide dismutase and ascorbate peroxidase activity in, as well as the absence of catalase from, epimastigote extracts was confirmed. Ascorbate peroxidase activity was cyanide-sensitive and heat-labile, but no activity could be demonstrated with diaminobenzidine, pyrogallol or guaiacol as electron donor. The summarized results support the view that T. cruzi epimastigotes lack an adequate enzyme defence against H2O2 and H2O2-related free radicals.

Trypanosoma cruzi expresses a plant-like ascorbate-dependent hemoperoxidase localized to the endoplasmic reticulum

“…These enzymes have been located in all oxy-radical-generating compartments in plants, with multiple isoforms identified (14). In T. cruzi, significant levels of ascorbate and its oxidized form, dehydroascorbate (DHA), have been detected and previous studies have identified a microsomal-associated ascorbate-dependent peroxidase activity (2,15,16). Here we show that T. cruzi expresses an unusual plant-like ascorbate-dependent hemoperoxidase whose activity is linked to the trypanothione system.…”

“…In contrast to most eukaryotes, T. cruzi lacks catalase and selenium-dependent glutathione peroxidases, enzymes capable of rapidly metabolizing high levels of H 2 O 2 (2,4,5). Instead it has an array of enzyme-mediated mechanisms in which the trypanosomatid-specific thiol trypanothione (N 1 ,N 8 -bisglutathionylspermidine) plays a pivotal role.…”

“…With no prospect of a vaccine, the search for parasite-specific traits exploitable in terms of chemotherapy is a priority (1). It has been reported that trypanosomatids have a limited ability to deal with reactive oxygen species (2,3). In the parasite these are generated by endogenous processes and as a result of external influences such as host immune responses and drug metabolism.…”

Cloning, Sequencing and Functional Expression of Dihydrolipoamide Dehydrogenase from the Human Pathogen Trypanosoma Cruzi

“…Trypanosomes and leishmania are much more sensitive towards oxidative stress than their respective hosts which may be due to the lack of glutathione peroxidase and catalase (Boveris et al, 1980;Carnieri et al, 1993). In trypanosomatids glutathione reductase is replaced by trypanothione reductase (Fairlamb and Cerami, 1992;Schirmer et al, 1995).…”

Kinetics, subcellular localization, and contribution to parasite virulence of a Trypanosoma cruzi hybrid type A heme peroxidase ( Tc APx-CcP)

“…It has been shown that the parasite antioxidant systems are essential for parasite survival and establishment of the infection in the vertebrate host (4)(5)(6)(7). In contrast to most eukaryotes, T. cruzi lacks catalase and selenium-dependent glutathione peroxidases, which are enzymes capable of rapidly metabolizing high levels of H 2 O 2 (8,9). Instead, it expresses an array of complex enzyme-mediated mechanisms in which the trypanosomatid-specific thiol trypanothione ([T(SH) 2 ], N 1 ,N 8 -bisglutathionylspermidine) plays a central role in the funneling of reducing equivalents to the different peroxidase antioxidant systems (10).…”