Putative Role of the Aldo-Keto Reductase from Trypanosoma cruzi in Benznidazole Metabolism
ABSTRACTBenznidazole (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(TcAKR), a NADPH-dependent oxido-reductase previously described by our group, uses Bz as the substrate. We demonstrated that both recombinant and nativeTcAKR enzymes reduce Bz by using NADPH, but not NADH, as a cofactor.TcAKR-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 thatTcAKR is involved in Bz detoxification instead of activation. To understand the role ofTcAKR in Bz metabolism, we studiedTcAKR expression and NADPH/NADH-dependent Bz reductase activities in twoT. cruzistrains with differential susceptibility to Bz: CL Brener and Nicaragua. Taking into account the results obtained withTcAKR-overexpressing epimastigotes, we expected the more resistant strain, Nicaragua, to have higherTcAKR levels than CL Brener. However, the results were the opposite. CL Brener showed 2-fold higherTcAKR 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 althoughTcAKR uses Bz as the substrate,TcAKR 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.