The biochemistry of the mode of action of drugs and the detoxication mechanisms in Trypanosoma cruzi

Elucidating the impact of low doses of nano-formulated benznidazole in acute experimental Chagas disease

Background

Chagas disease is a neglected parasitic infection caused by the protozoan Trypanosoma cruzi (T. cruzi) that affects more than 6 million people, mainly in Latin America. Benznidazole is still the drug of choice in many countries to treat it in spite of its dosage regimen and adverse side effects such as such as allergic dermatitis, peripheral neuropathy and anorexia. Thus, novel, safer, and more efficacious treatments for such neglected infection are urgently required.

Methodology

In this study, the efficacy of orally administered low doses of benznidazole (BNZ) nanoparticles was evaluated during the acute phase in mice infected with T. cruzi Nicaragua (TcN) that were immunosuppressed during the chronic stage of the disease. Moreover, the production of T. cruzi-specific antibodies, cardiac tissue inflammation and reactive oxygen species generation by Vero cells treated with both BNZ nanoparticles (BNZ-nps) and raw BNZ (R-BNZ) were also evaluated.

Principal findings

T. cruzi infected mice treated with 10, 25 or 50 mg/kg/day of BNZ-nps survived until euthanasia (92 days post infection (dpi)), while only 15% of infected untreated mice survived until the end of the experiment. PCR analysis of blood samples taken after induction of immunosuppression showed that a dosage of 25 mg/kg/day rendered 40% of the mice PCR-negative. The histological analysis of heart tissue showed a significant decrease in inflammation after treatments with 25 and 50 mg/kg/day, while a similar inflammatory damage was observed in both infected mice treated with R-BNZ (50 mg/kg/day) and untreated mice. In addition, only BNZ-nps treated mice led to lower levels of T. cruzi-specific antibodies to 50–100%. Finally, mammalian Vero cells treated with BNZ-nps or R-BNZ lead to a significant increase in ROS production.

Conclusions

Based on these findings, this research highlights the in-vitro/in-vivo efficacy of nanoformulated BNZ against T. cruzi acute infections in immunosuppressed and non-immunosuppressed mice and provides further evidence for the optimization of dosage regimens to treat Chagas disease.

Chagas disease is a neglected parasitic infection caused by the protozoan Trypanosoma cruzi (T. cruzi) that affects more than 6 million people, mainly in Latin America. Benznidazole is still the drug of choice in many countries to treat it in spite of its dosage regimen and adverse side effects such as such as allergic dermatitis, peripheral neuropathy and anorexia. In this study, the efficacy of low doses of benznidazole, formulated as nanoparticles, against T. cruzi acute infections in immunosuppressed and non-immunosuppressed mice was investigated in order to establish future treatment strategies. In-vivo experiments showed that all infected mice treated with low doses of nanoformulated benznidazole survived until the end of the assay (92 dpi), while only 15% of infected untreated mice survived to the end of the same period of time. Moreover, such novel formulation was able to decrease the parasite burden and, consequently, heart inflammation and lesions were significantly reduced. Clearly, low doses of benznidazole exhibited, at least, the same efficacy in infected mice as the usual dose, confirming the usefulness of nanoformulated benznidazole for an improved treatment of Chagas disease.

Trypanothione reductase inhibitors: Overview of the action of thioridazine in different stages of Chagas disease

Thioridazine (TDZ) is a phenothiazine that has been shown to be one of the most potent phenothiazines to inhibit trypanothione reductase irreversibly. Trypanothione reductase is an essential enzyme for the survival of Trypanosoma cruzi in the host. Here, we reviewed the use of this drug for the treatment of T. cruzi experimental infection. In our laboratory, we have studied the effect of TDZ for the treatment of mice infected with different strains of T. cruzi and treated in the acute or in the chronic phases of the experimental infection, using two different schedules: TDZ at a dose of 80 mg/kg/day, for 3 days starting 1h after infection (acute phase), or TDZ 80 mg/kg/day for 12 days starting 180 days post infection (d.p.i.) (chronic phase). In our experience, the treatment of infected mice, in the acute or in the chronic phases of the infection, with TDZ led to a large reduction in the mortality rates and in the cardiac histological and electrocardiographical abnormalities, and modified the natural evolution of the experimental infection. These analyses reinforce the importance of treatment in the chronic phase to decrease, retard or stop the evolution to chagasic myocardiopathy. Other evidence leading to the use of this drug as a potential chemotherapeutic agent for Chagas disease treatment is also revised.

Indazoles: a new top seed structure in the search of efficient drugs against Trypanosoma cruzi

For years, Chagas disease treatment has been limited to only two drugs of highly questionable and controversial use (Nifurtimox® and Benznidazole®). In the search of effective drugs, many efforts have been made, but only a few structures have emerged as actual candidates. Heading into this, the multitarget-directed approach appears as the best choice. In this framework, indazoles were shown to be potent Trypanosoma cruzi growth inhibitors, being able to lead both the formation of reactive oxygen species and the inhibition of trypanothione reductase. Herein, we discuss the main structural factors that rule the anti-T. cruzi properties of indazoles, and how they would be involved in the biological properties as well as in the action mechanisms, attempting to make parallels between the old paradigms and current evidences in order to outline what could be the next steps to follow in regard to the future drug design for Chagas disease treatment.

Mode of action of natural and synthetic drugs against Trypanosoma cruzi and their interaction with the mammalian host

Current knowledge of the biochemistry of Trypanosoma cruzi has led to the development of new drugs and the understanding of their mode of action. Some trypanocidal drugs such as nifurtimox and benznidazole act through free radical generation during their metabolism. T. cruzi is very susceptible to the cell damage induced by these metabolites because enzymes scavenging free radicals are absent or have very low activities in the parasite. Another potential target is the biosynthetic pathway of glutathione and trypanothione, the low molecular weight thiol found exclusively in trypanosomatids. These thiols scavenge free radicals and participate in the conjugation and detoxication of numerous drugs. Inhibition of this key pathway could render the parasite much more susceptible to the toxic action of drugs such as nifurtimox and benznidazole without affecting the host significantly. Other drugs such as allopurinol and purine analogs inhibit purine transport in T. cruzi, which cannot synthesize purines de novo. Nitroimidazole derivatives such as itraconazole inhibit sterol metabolism. The parasite's respiratory chain is another potential therapeutic target because of its many differences with the host enzyme complexes. The pharmacological modulation of the host's immune response against T. cruzi infection as a possible chemotherapeutic target is discussed. A large set of chemicals of plant origin and a few animal metabolites active against T. cruzi are enumerated and their likely modes of action are briefly discussed.

Increased expression of iron-containing superoxide dismutase-A (TcFeSOD-A) enzyme in Trypanosoma cruzi population with in vitro-induced resistance to benznidazole

Superoxide dismutase (SOD) removes excess superoxide radicals via dismutation to oxygen and hydrogen peroxide. In this work, we have characterized TcFeSOD-A gene from 25 Trypanosoma cruzi populations and clones susceptible, naturally resistant or with in vitro-induced (17 LER) or in vivo-selected resistance to benznidazole (BZR). In the 17 LER T. cruzi population, the levels of TcFeSOD-A mRNA were at least 3-fold higher than its drug-susceptible counterpart 17 WTS. The levels of TcFeSOD-A mRNA were similar among the other T. cruzi populations and clones regardless of the drug-resistance phenotype. We determined whether the increase in mRNA levels was due to gene amplification using Southern blot analysis of the T. cruzi populations and clones. We found that the number of TcFeSOD-A gene copies was similar for all samples tested, except for 17 LER that presented twice as many copies. The chromosomal location of the TcFeSOD-A gene and polymorphisms detected in nucleotide and amino acid sequences of TcFeSOD-A were associated with the zymodeme of the T. cruzi strain but not with drug-resistance phenotype. We observed a 23 kDa TcFeSOD-A polypeptide in all analysed T. cruzi strains. The level of this polypeptide was increased only in the 17 LER population. Specific enzyme activity analysis of TcFeSOD in the T. cruzi samples revealed a correlation between expression and activity. Our findings show an increased expression of the TcFeSOD-A enzyme in the T. cruzi population with in vitro-induced resistance to benznidazole.

The trypanothione-thiol system in Trypanosoma cruzi as a key antioxidant mechanism against peroxynitrite-mediated cytotoxicity

Peroxynitrite, the reaction product between superoxide (O(*2)) and nitric oxide (*NO), is a powerful oxidizing species that contributes to macrophage competence against pathogens. In this context, peroxynitrite appears to play an important role in controlling infection by Trypanosoma cruzi, the unicellular parasite responsible for Chagas disease. T. cruzi contains various enzyme systems for the decomposition of hydroperoxides, all of which involve the participation of the low-molecular-weight dithiol trypanothione (N(1),N(8)-bis(glutathionyl)spermidine) as a critical redox partner. A large fraction of the trypanothione-dependent antioxidant capacity of T. cruzi is linked to the tryparedoxin-tryparedoxin peroxidase system which has critical protein thiol groups. In this report we demonstrate that dihydrotrypanothione is readily consumed during peroxynitrite challenge to cells to yield the corresponding trypanothione disulfide. On the other hand, glutathione, which is present in T. cruzi at lower concentrations than trypanothione, is consumed to a much lesser extent and mainly evolves to glutathione-protein mixed disulfides. The inhibition of glutathione biosynthesis by buthionine sulfoximine, which decreases glutathione concentration to 10% of control after 20 h, neither affects the concentration of dihydrotrypanothione nor sensitizes T. cruzi to peroxynitrite-mediated cytotoxicity. On the other hand, pretreatment of T. cruzi with diamide, which leads to a significant depletion (>70%) of dihydrotrypanothione, largely increases the extent of cellular nitration and inhibition of cell growth caused by peroxynitrite. Altogether, our findings support a key protective role for dihydrotrypanothione and the trypanothione-dependent antioxidant system in T. cruzi against peroxynitrite, which may facilitate the survival of trypanosomes within the oxidative environment of activated macrophages.

Effects of clomipramine on Trypanosoma cruzi infection in mice

Trypanosoma cruzi, widely distributed in Latin American countries, provokes Chagas disease, characterized by cardiomyopathy and mega-viscera. The drugs used currently for treatment of acute Chagas disease are highly toxic; the side-effects are undesirable and patients may abandon treatment. We have previously demonstrated that clomipramine (CLO) exerts trypanocidal effects upon epimastigotes and trypomastigotes in vitro with anticalmodulin activity. The present study analyses the effectiveness of CLO treatment in mice infected with a low number of T. cruzi, an animal model that reproduces acute, indeterminate and chronic phases of this trypanosomiasis. In this work, our results demonstrated that CLO 5 mg/kg daily for 30 days, or 2 doses of CLO 40 mg/kg given intraperitoneally at 1 h and 7 days after infection, was not toxic for the host, but was effective against the parasite in that parasitaemias became negative and only mild heart structural and electrocardiographic alterations were detected in the chronic phase in the group treated with CLO 5 mg/kg. In mice treated with CLO 40 mg/kg, none of these alterations was detected. Cardiac beta receptor density and affinity returned to normal in the chronic stage in both experimental groups. T. cruzi enzymes such as calmodulin and trypanothione reductase represent potential drug targets. It has been reported that both can be inhibited by CLO, a tricyclic drug used in clinical therapeutics. We have shown that CLO strongly decreased the mortality rate and electrocardiographic alterations; in addition cardiac beta receptor density and heart histology returned to, or close to, normality 135 days post infection. These results clearly demonstrated that CLO treatment modified significantly the natural evolution of T. cruzi infection.

The sesquiterpene lactone dehydroleucodine (DhL) affects the growth of cultured epimastigotes of Trypanosoma cruzi

Here, we report an inhibitory effect of a sesquiterpene lactone dehydroleucodine (DhL) on the growth of Trypanosoma cruzi in culture. At concentrations of the drug between 5 and 10 microg/ml in the medium,the parasites remained alive for at least 4 days. Higher concentrations of DhL were lethal for the parasites within a few hours. The effect of DhL is irreversible. Morphological changes induced by DhL were also observed in the parasites. The effect of DhL was blocked by the presence of reducing substrates such as glutathione or dithiothreitol, but these agents were not able to reverse the effect of DhL if added 2 days after the start of drug exposure.

Phenotype of recombinant Trypanosoma cruzi which overexpress elongation factor 1-gamma: possible involvement of EF-1gamma GST-like domain in the resistance to clomipramine

In previous studies, molecular and immunological approaches have been used to characterize the Trypansosoma cruzi elongation factor 1gamma (TcEF-1gamma). A primary sequence homology search revealed that the TcEF-1gamma N-terminal domain showed significant homology to glutathione S-transferases (GSTs). Although studies have suggested the involvement of EF-1gamma in the protein synthesis machinery, the exact function of this protein, particularly the role of its GST-like domain, is not fully understood. Therefore, we have used the protozoan parasite T. cruzi, as a recipient for a shuttle vector which allows overexpression of TcEF-1gamma in order to gain insight into its biological function. The growth of parasites which overexpress TcEF-1gamma and control cells was equally sensitive to inhibition by nifurtimox and benznidazole, which exert a trypanocidal activity through the production of free radicals. In contrast, a strong resistance of transformed organisms to the tricyclic antidepressant drug, clomipramine, a lipophilic compound, was observed, whereas control cells were highly sensitive. Our findings suggest that TcEF-1gamma participates in the detoxification of lipophilic compounds probably by conjugation with glutathione through its GST-like domain. To our knowledge, this is the first report showing that the eukaryotic EF-1gamma GST conserved enzymatic model could play a role in drug resistance. Furthermore, these results reinforce the notion that the aggressiveness of certain tumours could in part be linked to overexpression of EF-1gamma. They also raise a central question regarding the GST as target for chemotherapeutic drugs in cancer research.

Trypanosoma cruzi: a possible control of transfusion-induced Chagas' disease by phenolic antioxidants

The following phenolic antioxidant food additives were evaluated against Trypanosoma cruzi epimastigotes: BHT, BHA, gallic acid and its methyl, propyl, octyl, and lauryl esters, 2,4-di-tert-butyl-6-(4-methoxybenzyl)-phenol, 4,4'-isopropilidenediphenol, and protocatechuic acid and its ethyl ester. The inhibition of the respiration; the changes in motility, shape, and lysis of the parasites; and the human blood hemolysis caused by these chemicals were studied. Human blood samples experimentally contaminated with 2000 or 150,000 trypomastigotes per milliliter were freed of parasites after treatment for 24 hr at 4 degrees C with 5 or 10 mM BHT (2,6-di-tert-butyl-4-hydroxytoluene), respectively. Consequently, BHT and other phenolic compounds deserve further study to determine their role in preventing the transmission of Chagas' disease by blood transfusion.