Putative Role of the Aldo-Keto Reductase from Trypanosoma cruzi in Benznidazole Metabolism

Benznidazole (Bz), the drug used for treatment of Chagas' disease (caused by the protozoanTrypanosoma cruzi ), is activated by a parasitic NADH-dependent type I nitroreductase (NTR I). However, several studies have shown that other enzymes are involved. The aim of this study was to evaluate whether the aldo-keto reductase fromT. cruzi (Tc AKR), a NADPH-dependent oxido-reductase previously described by our group, uses Bz as the substrate. We demonstrated that both recombinant and nativeTc AKR enzymes reduce Bz by using NADPH, but not NADH, as a cofactor.Tc AKR-overexpressing epimastigotes showed higher NADPH-dependent Bz reductase activity and a 50% inhibitory concentration (IC50 ) value for Bz 1.8-fold higher than that of the controls, suggesting thatTc AKR is involved in Bz detoxification instead of activation. To understand the role ofTc AKR in Bz metabolism, we studiedTc AKR expression and NADPH/NADH-dependent Bz reductase activities in twoT. cruzi strains with differential susceptibility to Bz: CL Brener and Nicaragua. Taking into account the results obtained withTc AKR-overexpressing epimastigotes, we expected the more resistant strain, Nicaragua, to have higherTc AKR levels than CL Brener. However, the results were the opposite. CL Brener showed 2-fold higherTc AKR expression and 5.7-fold higher NADPH-Bz reduction than the Nicaragua strain. In addition, NADH-dependent Bz reductase activity, characteristic of NTR I, was also higher in CL Brener than in Nicaragua. We conclude that althoughTc AKR uses Bz as the substrate,Tc AKR activity is not a determinant of Bz resistance in wild-type strains and may be overcome by other enzymes involved in Bz activation, such as NADPH- and NADH-dependent reductases.