l -Arginine-dependent suppression of apoptosis in Trypanosoma cruzi : Contribution of the nitric oxide and polyamine pathways

Abstract

Until recently, a capacity for apoptosis and synthesis of nitric oxide ( ⅐ NO) were viewed as exclusive to multicellular organisms. The existence of these processes in unicellular parasites was recently described, with their biological significance remaining to be elucidated. We have evaluated L-arginine metabolism in Trypanosoma cruzi in the context of human serum-induced apoptotic death. Apoptosis was evidenced by the induction of DNA fragmentation and the inhibition of [ 3 H]thymidine incorporation, which were inhibited by the caspase inhibitor Ac-Asp-Glu-Val-aspartic acid aldehyde (DEVD-CHO). In T. cruzi exposed to death stimuli, supplementation with L-arginine inhibited DNA fragmentation, restored [ 3 H]thymidine incorporation, and augmented parasite ⅐ NO production. These effects were inhibited by the ⅐ NO synthase inhibitor N -nitroarginine methyl ester (L-NAME). Exogenous ⅐ NO limited DNA fragmentation but did not restore proliferation rates. Because L-arginine is also a substrate for arginine decarboxylase (ADC), and its product agmatine is a precursor for polyamine synthesis, we evaluated the contribution of polyamines to limiting apoptosis. Addition of agmatine, putrescine, and the polyamines spermine and spermidine to T. cruzi sustained parasite proliferation and inhibited DNA fragmentation. Also, the ADC inhibitor difluoromethylarginine inhibited L-arginine-dependent restoration of parasite replication rates, while the protection from DNA fragmentation persisted. In aggregate, these results indicate that T. cruzi epimastigotes can undergo programmed cell death that can be inhibited by L-arginine by means of (i) a ⅐ NO synthase-dependent ⅐ NO production that suppresses apoptosis and (ii) an ADC-dependent production of polyamines that support parasite proliferation.

Leishmaniadisease development depends on the presence of apoptotic promastigotes in the virulent inoculum

“…This argument also fits an apoptotic program for single-celled organisms when such organisms are regarded as a population. Apoptosis-like death has been described for several single-celled eukaryote organisms; these include Trypanosomas and both promastigote as well as amastigote forms of Leishmania (17,30). The apoptosis-like phenotype of parasite death may reduce the onset of inflammation and favor parasite evasion from the immune system (29).…”

Prostaglandin-induced programmed cell death in Trypanosoma brucei involves oxidative stress

“…[55][56][57][58][59] To date, the physiological role of PCD in single-cell organisms has not clearly been defined. However, PCD functions similar to those known for metazoa have been suggested for unicellular organisms too, 59,60 because protozoa behave as a population, that is, as a complex community with many cell-cell interactions, which in many ways resemble metazoa.…”

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

“…T. cruzi epimastigotes (CL-Brener, wt) were cultured at 28°C in brain heart infusion (BHI) containing heat-inactivated bovine fetal serum (10% vol/vol) as described previously (65). T. cruzi epimastigotes overexpressing TcAPx-CcP were obtained as described previously (5,15).…”