Experimental chemotherapy against Trypanosoma cruzi infection: essential role of endogenous interferon-gamma in mediating parasitologic cure

Disruption of the inositol phosphorylceramide synthase gene affects Trypanosoma cruzi differentiation and infection capacity

Sphingolipids (SLs) are essential components of all eukaryotic cellular membranes. In fungi, plants and many protozoa, the primary SL is inositol-phosphorylceramide (IPC). Trypanosoma cruzi is a protozoan parasite that causes Chagas disease (CD), a chronic illness for which no vaccines or effective treatments are available. IPC synthase (IPCS) has been considered an ideal target enzyme for drug development because phosphoinositol-containing SL is absent in mammalian cells and the enzyme activity has been described in all parasite forms of T. cruzi. Furthermore, IPCS is an integral membrane protein conserved amongst other kinetoplastids, including Leishmania major, for which specific inhibitors have been identified. Using a CRISPR-Cas9 protocol, we generated T. cruzi knockout (KO) mutants in which both alleles of the IPCS gene were disrupted. We demonstrated that the lack of IPCS activity does not affect epimastigote proliferation or its susceptibility to compounds that have been identified as inhibitors of the L. major IPCS. However, disruption of the T. cruzi IPCS gene negatively affected epimastigote differentiation into metacyclic trypomastigotes as well as proliferation of intracellular amastigotes and differentiation of amastigotes into tissue culture-derived trypomastigotes. In accordance with previous studies suggesting that IPC is a membrane component essential for parasite survival in the mammalian host, we showed that T. cruzi IPCS null mutants are unable to establish an infection in vivo, even in immune deficient mice.

Novel diamides inspired by protein kinase inhibitors as anti-Trypanosoma cruzi agents: in vitro and in vivo evaluations

Background: Chagas disease is a life-threatening illness caused by Trypanosoma cruzi. The involvement of serine-/arginine-rich protein kinase in the T. cruzi life cycle is significant. Aims: To synthesize, characterize and evaluate the trypanocidal activity of diamides inspired by kinase inhibitor, SRPIN340. Material & Methods: Synthesis using a three-step process and characterization by infrared, nuclear magnetic resonance and high-resolution mass spectrometry were conducted. The selectivity index was obtained by the ratio of CC50/IC50 in two in vitro models. The most active compound, 3j, was evaluated using in vitro cytokine assays and assessing in vivo trypanocidal activity. Results: 3j activity in the macrophage J774 lineage showed an anti-inflammatory profile, and mice showed significantly reduced parasitemia and morbidity at low compound dosages. Conclusion: Novel diamide is active against T. cruzi in vitro and in vivo.

Preclinical advances and the immunophysiology of a new therapeutic chagas disease vaccine

INTRODUCTION

Chronic infection with the protozoal parasite Trypanosoma cruzi leads to a progressive cardiac disease, known as chronic Chagasic cardiomyopathy (CCC). A new therapeutic Chagas disease vaccine is in development to augment existing antiparasitic chemotherapy drugs.

AREAS COVERED

We report on our current understanding of the underlying immunologic and physiologic mechanisms that lead to CCC, including parasite immune escape mechanisms that allow persistence and the subsequent inflammatory and fibrotic processes that lead to clinical disease. We report on vaccine design and the observed immunotherapeutic effects including induction of a balanced T_H1/T_H2/T_H17 immune response that leads to reduced parasite burdens and tissue pathology. Further, we report vaccine-linked chemotherapy, a dose sparing strategy to further reduce parasite burdens and tissue pathology.

EXPERT OPINION

Our vaccine-linked chemotherapeutic approach is a multimodal treatment strategy, addressing both the parasite persistence and the underlying deleterious host inflammatory and fibrotic responses that lead to cardiac dysfunction. In targeting treatment towards patients with chronic indeterminate or early determinate Chagas disease, this vaccine-linked chemotherapeutic approach will be highly economical and will reduce the global disease burden and deaths due to CCC.

Assessment of a combined treatment with a therapeutic vaccine and benznidazole for the Trypanosoma cruzi chronic infection

The difficulties encountered in achieving treatments for chronic Chagas disease have promoted the investigation of new therapeutic strategies. In this study, we used two murine models of Trypanosoma cruzi chronic infection to determine the usefulness of applying a therapeutic vaccine alone or followed by benznidazole (Bz) chemotherapy. A vaccine formulation based on an N-terminal fragment of Trans-sialidase (TS) and Immunostimulant Particle Adjuvant (ISPA) - TSNt-ISPA was obtained. Firstly, the immunogenicity and protective capacity of TSNt-ISPA was demonstrated as a prophylactic formulation in an acute model of infection. Later, the formulation was assessed as a therapeutic vaccine alone or combined with (Bz) using two models of chronic infection. BALB/c mice chronically infected with Sylvio X10/4 or Tulahuen cl2 T. cruzi strains were not treated as control or treated only with the therapeutic vaccine TSNt-ISPA, with a combined treatment TSNt-ISPA+Bz (Bz applied after the vaccine), or only with Bz. The vaccination schedule consisted of TSNt-ISPA administration at days110, 120, and 130 post-infection (pi) and Bz administration was performed daily from day 140 to 170 pi. At day 273 pi, electrocardiographic (ECG) parameters, heart parasite load, myocarditis, and heart fibrosis were assessed. In both models, therapeutic administration of TSNt-ISPA reduced ECG alterations and the cardiac tissue damage observed in the chronic phase. Moreover, vaccine treatment significantly decreased heart parasite load in both Sylvio X10/4 and Tulahuen cl2 infected mice. The combined treatment, but not Bz or vaccine administration alone, allowed to restore ECG parameters in Tulahuen cl2 infected mice. The results indicate the usefulness of the therapeutic TSNt-ISPA formulation in BALB/c mice chronically infected with Sylvio X10/4 or Tulahuen cl2 strain. For the mice infected with T. cruzi Tulahuen cl2 strain, the combined treatment with the vaccine and Bz had a more positive effect on the course of heart disease than the individual treatments with the vaccine or Bz alone.

Oral Trypanosoma cruzi Acute Infection in Mice Targets Primary Lymphoid Organs and Triggers Extramedullary Hematopoiesis

During the acute phase of Chagas disease, Trypanosoma cruzi circulation through the bloodstream leads to high tissue parasitism in the host. In primary lymphoid organs, progenitor cell reduction paralleled transient immunosuppression. Herein we showed that acute oral infection in mice promotes diffuse parasitism in bone marrow cells at 14 and 21 days post-infection (dpi), with perivascular regions, intravascular regions, and regions near the bone being target sites of parasite replication. Phenotypic analysis of hematopoietic differentiation in the bone marrow of infected mice showed that the cell number in the tissue is decreased (lineage-negative and lineage-positive cells). Interestingly, analysis of hematopoietic branching points showed that hematopoietic stem and progenitor cells (HSPCs) were significantly increased at 14 dpi. In addition, the pool of progenitors with stem plasticity (HSC-MPP3), as well as multipotent progenitors (MPPs) such as MPP4, also showed this pattern of increase. In contrast, subsequent progenitors that arise from MPPs, such as common lymphoid progenitors (CLPs), lymphoid-primed MPPs (LMPPs), and myeloid progenitors, were not enhanced; conversely, all presented numeric decline. Annexin V staining revealed that cell death increase in the initial hematopoietic branching point probably is not linked to CLPs and that myeloid progenitors decreased at 14 and 21 dpi. In parallel, our investigation provided clues that myeloid progenitor decrease could be associated with an atypical expression of Sca-1 in this population leading to a remarkable increase on LSK-like cells at 14 dpi within the HSPC compartment. Finally, these results led us to investigate HSPC presence in the spleen as a phenomenon triggered during emergency hematopoiesis due to mobilization or expansion of these cells in extramedullary sites. Splenocyte analysis showed a progressive increase in HSPCs between 14 and 21 dpi. Altogether, our study shows that the bone marrow is a target tissue in T. cruzi orally infected mice, leading to a hematopoietic disturbance with LSK-like cell bias accounting on HSPCs possibly affecting myeloid progenitor numbers. The LMPP and CLP reduction converges with defective thymocyte development. Lastly, it is tempting to speculate that the extramedullary hematopoiesis seen in the spleen is a mechanism involved in the hematological maintenance reported during the acute phase of oral T. cruzi infection.

Disruption of Active Trans-Sialidase Genes Impairs Egress from Mammalian Host Cells and Generates Highly Attenuated Trypanosoma cruzi Parasites

Trans-sialidases (TS) are unusual enzymes present on the surface of Trypanosoma cruzi, the causative agent of Chagas disease. Encoded by the largest gene family in the T. cruzi genome, only few members of the TS family have catalytic activity. Active trans-sialidases (aTS) are responsible for transferring sialic acid from host glycoconjugates to mucins, also present on the parasite surface. The existence of several copies of TS genes has impaired the use of reverse genetics to study this highly polymorphic gene family. Using CRISPR-Cas9, we generated aTS knockout cell lines displaying undetectable levels of TS activity, as shown by sialylation assays and labeling with antibodies that recognize sialic acid-containing mucins. In vitro infection assays showed that disruption of aTS genes does not affect the parasite's capacity to invade cells or to escape from the parasitophorous vacuole but resulted in impaired differentiation of amastigotes into trypomastigotes and parasite egress from the cell. When inoculated into mice, aTS mutants were unable to establish infection even in the highly susceptible gamma interferon (IFN-γ) knockout mice. Mice immunized with aTS mutants were fully protected against a challenge infection with the virulent T. cruzi Y strain. Altogether, our results confirmed the role of aTS as a T. cruzi virulence factor and indicated that aTS play a major role during the late stages of intracellular development and parasite egress. Notably, mutants lacking TS activity are completely avirulent in animal models of infection and may be used as a live attenuated vaccine against Chagas disease. IMPORTANCE Trypanosoma cruzi is the causative agent of Chagas disease, a neglected tropical disease that affects approximately 6 to 8 million people and for which there is no effective treatment or vaccine. The parasite expresses a family of surface proteins, named trans-sialidases, responsible for transferring sialic acid from host glycoconjugates to parasite mucins. Although recognized as a main virulence factor, the multiple roles of these proteins during infection have not yet been fully characterized, mainly because the presence of several copies of aTS genes has impaired their study using reverse genetics. By applying CRISPR-Cas9, we generated aTS knockout parasites and showed that, although aTS parasite mutants were able to infect cells in vitro, they have an impaired capacity to egress from the infected cell. Importantly, aTS mutants lost the ability to cause infection in vivo but provided full protection against a challenge infection with a virulent strain.

Chagas disease: Immunology of the disease at a glance

Chagas disease is an important neglected disease that affects 6-7 million people worldwide. The disease has two phases: acute and chronic, in which there are different clinical symptoms. Controlling the infection depends on innate and acquired immune responses, which are activated during the initial infection and are critical for host survival. Furthermore, the immune system plays an important role in the therapeutic success. Here we summarize the importance of the immune system cytokines in the pathology outcome, as well as in the treatment.

Why do few drug delivery systems to combat neglected tropical diseases reach the market? An analysis from the technology's stages

INTRODUCTION

Many drugs used to combat schistosomiasis, Chagas disease, and leishmaniasis (SCL) have clinical limitations such as: high toxicity to the liver, kidneys and spleen; reproductive, gastrointestinal, and heart disorders; teratogenicity. In this sense, drug delivery systems (DDSs) have been described in the literature as a viable option for overcoming the limitations of these drugs. An analysis of the level of development (TRL) of patents can help in determine the steps that must be taken for promising technologies to reach the market.

AREAS COVERED

This study aimed to analyze the stage of development of DDSs for the treatment of SCL described in patents. In addition, we try to understand the main reasons why many DDSs do not reach the market. In this study, we examined DDSs for drugs indicated by WHO and treatment of SCL, by performing a search for patents.

EXPERT OPINION

In this present work we provide arguments that support the hypothesis that there is a lack of integration between academia and industry to finance and continue research, especially the development of clinical studies. We cite the translational research consortia as the potential alternative for developing DDSs to combat NTDs.

4-Chlorophenylthioacetone-derived thiosemicarbazones as potent antitrypanosomal drug candidates: Investigations on the mode of action

Chagas disease (ChD), caused by Trypanosoma cruzi, remains a challenge for the medical and scientific fields due to the inefficiency of the therapeutic approaches available for its treatment. Thiosemicarbazones and hydrazones present a wide spectrum of bioactivities and are considered a platform for the design of new anti-T. cruzi drug candidates. Herein, the potential antichagasic activities of [(E)-2-(1-(4-chlorophenylthio)propan-2-ylidene)-hydrazinecarbothioamides] (C1, C3), [(E)-N'-(1-((4-chlorophenyl)thio)propan-2-ylidene)benzohydrazide] (C2), [(E)-2-(1-(4-, and [(E)-2-(1-((4-chlorophenyl)thio)propan-2-ylidene)hydrazinecarboxamide] (C4) were investigated. Macrophages (MOs) from C57BL/6 mice stimulated with C1 and C3, but not with C2 and C4, reduced amastigote replication and trypomastigote release, independent of nitric oxide (NO) and reactive oxygen species production and indoleamine 2,3-dioxygenase activity. C3, but not C1, reduced parasite uptake by MOs and potentiated TNF production. In cardiomyocytes, C3 reduced trypomastigote release independently of NO, TNF, and IL-6 production. C1 and C3 were non-toxic to the host cells. A reduction of parasite release was found during infection of MOs with trypomastigotes pre-incubated with C1 or C3 and MOs pre-stimulated with compounds before infection. Moreover, C1 and C3 acted directly on trypomastigotes, killing them faster than Benznidazole, and inhibited T. cruzi proliferation at various stages of its intracellular cycle. Mechanistically, C1 and C3 inhibit parasite duplication, and this process cannot be reversed by inhibiting the DNA damage response. In vivo, C1 and C3 attenuated parasitemia in T. cruzi-infected mice. Moreover, C3 loaded in a lipid nanocarrier system (nanoemulsion) maintained anti-T. cruzi activity in vivo. Collectively, these data suggest that C1 and C3 are candidates for the treatment of ChD and present activity in both the host and parasite cells.

Pharmacokinetics of Benznidazole in Experimental Chronic Chagas Disease Using the Swiss Mouse-Berenice-78 Trypanosoma cruzi Strain Model

Chronic Chagas disease might have an impact on benznidazole pharmacokinetics with potential alterations in the therapeutic dosing regimen. This study aims to investigate the influence of chronic Trypanosoma cruzi infection on the pharmacokinetics and biodistribution of benznidazole in mice. Healthy (n = 40) and chronically T. cruzi (Berenice-78 strain)-infected (n = 40) Swiss female 10-month-old mice received a single oral dose of 100 mg/kg of body weight of benznidazole. Serial blood, heart, colon, and brain samples were collected up to 12 h after benznidazole administration. The serum and tissue samples were analyzed using a high-performance liquid chromatography instrument coupled to a diode array detector. Chronic infection by T. cruzi increased the values of the pharmacokinetic parameters absorption rate constant (K_a ) (3.92 versus 1.82 h^-1), apparent volume of distribution (V/F) (0.089 versus 0.036 liters), and apparent clearance (CL/F) (0.030 versus 0.011 liters/h) and reduced the values of the time to the maximum concentration of drug in serum (T _max) (0.67 versus 1.17 h) and absorption half-life (t _{1/2 a} ) (0.18 versus 0.38 h). Tissue exposure (area under the concentration-versus-time curve from 0 h to time t for tissue [AUC_{0- t ,tissue}]) was longer and higher in the colon (8.15 versus 21.21 μg · h/g) and heart (5.72 versus 13.58 μg · h/g) of chronically infected mice. Chronic infection also increased the benznidazole tissue penetration ratios (AUC_{0- t ,tissue}/AUC_{0- t ,serum} ratios) of brain, colon, and heart by 1.6-, 3.25-, and 3-fold, respectively. The experimental chronic Chagas disease inflammation-mediated changes in the regulation of membrane transporters probably influence the benznidazole pharmacokinetics and the extent of benznidazole exposure in tissues. These results advise for potential alterations in benznidazole pharmacokinetics in chronic Chagas disease patients with possibilities of changes in the standard dosing regimen.

CD8low T cells expanded following acute Trypanosoma cruzi infection and benznidazole treatment are a relevant subset of IFN-γ producers

CD8 T cells are regarded as pivotal players in both immunoprotection and immunopathology following Trypanosoma cruzi infection. Previously, we demonstrated the expansion of CD8⁺ T lymphocytes in the spleen of T. cruzi-infected mice under treatment with benznidazole (N-benzyl-2-nitroimidazole acetamide; Bz), a drug available for clinical therapy. This finding underlies the concept that the beneficial effects of Bz on controlling acute T. cruzi infection are related to a synergistic process between intrinsic trypanocidal effect and indirect triggering of the active immune response. In the present study, we particularly investigated the effect of Bz treatment on the CD8⁺ T cell subset following T. cruzi infection. Herein we demonstrated that, during acute T. cruzi infection, Bz treatment reduces and abbreviates the parasitemia, but maintains elevated expansion of CD8⁺ T cells. Within this subset, a remarkable group of CD8^low cells was found in both Bz-treated and non-treated infected mice. In Bz-treated mice, early pathogen control paralleled the lower frequency of recently activated CD8^low cells, as ascertained by CD69 expression. However, the CD8^low subset sustains significant levels of CD44^highCD62L^low and CD62L^lowT-bet^high effector memory T cells, in both Bz-treated and non-treated infected mice. These CD8^low cells also comprise the main group of spontaneous interferon (IFN)-γ-producing CD8⁺ T cells. Interestingly, following in vitro anti-CD3/CD28 stimulation, CD8⁺ T cells from Bz-treated T. cruzi-infected mice exhibited higher frequency of IFN-γ⁺ cells, which bear mostly a CD8^low phenotype. Altogether, our results point to the marked presence of CD8^low T cells that arise during acute T. cruzi infection, with Bz treatment promoting their significant expansion along with a potential effector program for high IFN-γ production.

Chagas disease is a neglected illness caused by the protozoan Trypanosoma cruzi, which affects 6 to 7 million people worldwide. The current treatment for acutely-infected patients is mostly limited to the benznidazole (Bz) drug, reaching up to 80% of cure. It has been proposed that Bz therapy efficacy involves both trypanocidal and immunonodulatory effects. In this sense, we previously suggested that CD8⁺ T cells, highly expanded after Bz treatment of acute T. cruzi-infected mice, might play a particular role in parasite control. Here, by further investigating those expanded CD8⁺ T cells, we observed that they bear a clear-cut effector phenotype and that a significant part of them stand out as a subpopulation bearing low levels of CD8 on their surface. Interestingly, besides the evident parasite control, Bz-treated mice sustain a group of effector CD8^low cells with spontaneous IFN-γ production. Moreover, in vitro-stimulated CD8⁺ T cells, sorted from infected and Bz-treated mice, present a relevant group of IFN-γ⁺ cells with a CD8^low phenotype. Altogether, our data indicate the particular subset of CD8^low cells as potentially contributing for a sustained protective immunity in T. cruzi-infected animals under Bz therapy.

Thioridazine aggravates skeletal myositis, systemic and liver inflammation in Trypanosoma cruzi-infected and benznidazole-treated mice

While thioridazine (Tio) inhibits the antioxidant defenses of Trypanosoma cruzi, the gold standard antitrypanosomal drug benznidazole (Bz) has potent anti-inflammatory and pro-oxidant properties. The combination of these drugs has never been tested to determine the effect on T. cruzi infection. Thus, we compared the impact of Tio and Bz, administered alone and in combination, on the development of skeletal myositis and liver inflammation in T. cruzi-infected mice. Swiss mice were randomized into six groups: uninfected untreated, infected untreated, treated with Tio (80 mg/kg) alone, Bz (50 or 100 mg/kg) alone, or a combination of Tio and Bz. Infected animals were inoculated with a virulent T. cruzi strain (Y) and treated by gavage for 20 days. Mice untreated or treated with Tio alone developed the most intense parasitemia, highest parasitic load, elevated IL-10, IL-17, IFN-γ, and TNF-α plasma levels, increased N-acetylglucosaminidase and myeloperoxidase activity in the liver and skeletal muscle, as well as severe myositis and liver inflammation (P < 0.05). All parameters were markedly attenuated in animals receiving Bz alone (P < 0.05). However, the co-administration of Tio impaired the response to Bz chemotherapy, causing a decrease in parasitological control (parasitemia and parasite load), skeletal muscle and liver inflammation, and increased microstructural damage, when compared to the group receiving Bz alone (P < 0.05). Altogether, our findings indicated that Tio aggravates systemic inflammation, skeletal myositis and hepatic inflammatory damage in T. cruzi-infected mice. By antagonizing the antiparasitic potential of Bz, Tio limits the anti-inflammatory, myoprotectant and hepatoprotective effects of the reference chemotherapy, aggravating the pathological remodeling of both organs. As the interaction of T. cruzi infection, Bz and Tio is potentially toxic to the liver, inducing inflammation and microvesicular steatosis; this drug combination represents a worrying pharmacological risk factor in Chagas disease.

Resolvin D1 Administration Is Beneficial in Trypanosoma cruzi Infection

Chagas disease is a major public health issue, affecting ∼10 million people worldwide. Transmitted by a protozoan named Trypanosoma cruzi, this infection triggers a chronic inflammatory process that can lead to cardiomyopathy (Chagas disease). Resolvin D1 (RvD1) is a novel proresolution lipid mediator whose effects on inflammatory diseases dampens pathological inflammatory responses and can restore tissue homeostasis. Current therapies are not effective in altering the outcome of T. cruzi infection, and as RvD1 has been evaluated as a therapeutic agent in various inflammatory diseases, we examined if exogenous RvD1 could modulate the pathogenesis of Chagas disease in a murine model. CD-1 mice infected with the T. cruzi Brazil strain were treated with RvD1. Mice were administered 3 μg/kg of body weight RvD1 intraperitoneally on days 5, 10, and 15 to examine the effect of RvD1 on acute disease or administered the same dose on days 60, 65, and 70 to examine its effects on chronic infection. RvD1 therapy increased the survival rate and controlled parasite replication in mice with acute infection and reduced the levels of interferon gamma and transforming growth factor β (TGF-β) in mice with chronic infection. In addition, there was an increase in interleukin-10 levels with RvD1 therapy in both mice with acute infection and mice with chronic infection and a decrease in TGF-β levels and collagen content in cardiac tissue. Together, these data indicate that RvD1 therapy can dampen the inflammatory response, promote the resolution of T. cruzi infection, and prevent cardiac fibrosis.

Could phenothiazine-benznidazole combined chemotherapy be effective in controlling heart parasitism and acute infectious myocarditis?

Phenothiazines inhibit major antioxidant defense mechanisms in trypanosomatids and exhibit potent cytotoxic effects in vitro. However, the relevance of these drugs in the treatment of Trypanosoma cruzi-induced acute myocarditis is poorly explored, especially in combination with reference trypanocidal drugs. Thus, we compared the antiparasitic and cardioprotective potential of thioridazine (TDZ) and benznidazole (Bz) administered in monotherapy and combined in a murine model of T. cruzi-induced acute myocarditis. Female mice were randomized into six groups: (i) uninfected untreated, (ii) infected untreated, or infected treated with (iii) Bz (100 mg/kg), (iv) TDZ (80 mg/kg), (v) Bz (100 mg/kg) + TDZ (80 mg/kg), or (vi) Bz (50 mg/kg) + TDZ (80 mg/kg). Infected animals were inoculated with 2000 T. cruzi trypomastigotes and treated by gavage for 20 days. Animals that received TDZ alone presented the highest levels of parasitemia, parasitic load and anti-T. cruzi immunoglobulin G titers; cardiac upregulation of N-acetyl-β-D-glucosaminidase activity, nitric oxide, malondialdehyde and cytokines (IFN-γ, TNF-α, IL-10 and IL-17); as well as microstructural damage compared to the other groups (p < 0.05). These parameters were reduced in groups receiving Bz monotherapy compared to the other groups (p < 0.05). The combination of TDZ and Bz attenuated the response to treatment, worsening parasitological control, oxidative heart damage and myocarditis compared to the group treated with Bz alone (p < 0.05). Our results indicate that when administered alone, TDZ potentiated the pathological outcomes in animals infected with T. cruzi. Moreover, TDZ attenuated the antiparasitic effect of Bz when administered together, impairing parasitological control, potentiating inflammation, molecular oxidation and pathological microstructural remodeling of the heart. Thus, our findings indicate that TDZ acts as a pharmacological risk factor and Bz-based monotherapy remains a better cardioprotective drug against Trypanosoma cruzi-induced acute myocarditis.

The effect of benznidazole dose among the efficacy outcome in the murine animal model. A quantitative integration of the literature

Despite more than 100 years since it was firstly described Chagas disease, only two drugs are available to treat Chagas disease: Nifurtimox launched by Bayer in 1965 and benznidazole launched by Roche in 1971. Drug discovery initiatives have been looking for new compounds as an alternative to these old drugs. Although new platforms have been used with the latest technologies, a critical step on that process still relies on the in vivo model. Unfortunately, to date, available animal models have limited predictive value and there is no standardization. With the aim to better understand the role of benznidazole, the current standard of care of Chagas disease, we performed this review. We intend to analyze the influence of the experimental design of the most used animal model, the murine model, in the assessment of the efficacy endpoint.

Distinct Treatment Outcomes of Antiparasitic Therapy in Trypanosoma cruzi-Infected Children Is Associated With Early Changes in Cytokines, Chemokines, and T-Cell Phenotypes

Background: In contrast to adults, Trypanosoma cruzi-infected children have more broadly functional Trypanosoma cruzi-specific T cells, and the total T-cell compartment exhibits fewer signs of immune exhaustion. However, not much is known about the link between immunocompetence and the treatment efficacy for human Chagas disease.

Methods: Using cytokine enzyme-linked immunosorbent spot (ELISPOT) polychromatic flow cytometry, cytometric bead assay, multiplex serological assays and quantitative PCR, we evaluated T. cruzi-specific T-cell and antibody immune responses, T-cell phenotypes and parasitemia in children in the early chronic phase of Chagas disease undergoing anti-Trypanosoma cruzi treatment.

Results: Treatment with benznidazole or nifurtimox induced a decline in T. cruzi-specific IFN-γ- and IL-2-producing cells and proinflammatory cytokines and chemokines. T-cell responses became detectable after therapy in children bearing T-cell responses under background levels prior to treatment. The total frequencies of effector, activated and antigen-experienced T cells also decreased following anti-T. cruzi therapy, along with an increase in T cells expressing the receptor of the homeostatic cytokine IL-7. Posttreatment changes in several of these markers distinguished children with a declining serologic response suggestive of successful treatment from those with sustained serological responses in a 5-year follow-up study. A multivariate analysis demonstrated that lower frequency of CD4⁺CD45RA⁻CCR7⁻CD62L⁻ T cells prior to drug therapy was an independent indicator of successful treatment.

Conclusions: These findings further validate the usefulness of alternative metrics to monitor treatment outcomes. Distinct qualitative and quantitative characteristics of T cells prior to drug therapy may be linked to treatment efficacy.

Vaccine-Linked Chemotherapy Improves Benznidazole Efficacy for Acute Chagas Disease

Chagas disease affects 6 to 7 million people worldwide, resulting in significant disease burdens and health care costs in countries of endemicity. Chemotherapeutic treatment is restricted to two parasiticidal drugs, benznidazole and nifurtimox. Both drugs are highly effective during acute disease but are only minimally effective during chronic disease and fraught with significant adverse clinical effects. In experimental models, vaccines can be used to induce parasite-specific balanced T_H1/T_H2 immune responses that effectively reduce parasite burdens and associated inflammation while minimizing adverse effects. The objective of this study was to determine the feasibility of vaccine-linked chemotherapy for reducing the amount of benznidazole required to significantly reduce blood and tissue parasite burdens. In this study, we were able to achieve a 4-fold reduction in the amount of benznidazole required to significantly reduce blood and tissue parasite burdens by combining the low-dose benznidazole with a recombinant vaccine candidate, Tc24 C4, formulated with a synthetic Toll-like 4 receptor agonist, E6020, in a squalene oil-in-water emulsion. Additionally, vaccination induced a robust parasite-specific balanced T_H1/T_H2 immune response. We concluded that vaccine-linked chemotherapy is a feasible option for advancement to clinical use for improving the tolerability and efficacy of benznidazole.

Changes of RAPD profile of Trypanosoma cruzi II with Canova and Benznidazole

Chagas disease, caused by the protozoan Trypanosoma cruzi, involves immunomediated processes. Canova (CA) is a homeopathic treatment indicated in the diseases in which the immune system is depressed. This study evaluated the Random Amplification of Polymorphic DNA (RAPD) profile of T. cruzi under the influence of CA and Benznidazole (BZ). Mice infected with the genetic lineage of T. cruzi II (Y strain) were divided into 4 groups:

Infected animals treated with saline solution (control group); treated with CA; treated with BZ; treated with CA and BZ combined.

Treatment was given at the 5th–25th days of infection (D5–25). The parasites were isolated by haemoculture in Liver Infusion Tryptose (LIT) medium: at D5 (before treatment), D13, 15 and 25 (during treatment) and D55 and 295 (after treatment). DNA was extracted from the mass of parasites. RAPD was done with the primers λgt11-F, M13F-40 and L15996, the amplified products were eletrophoresed through a 4% polyacrylamide gel. Data were analyzed by the coefficient of similarity using the DNA-POP program.

163 markers were identified, 5 of them monomorphic. CA did not act against the parasites when used alone. The RAPD profiles of parasites treated with BZ and CA + BZ were different from those in the control group and in the group treated with CA. The actions of the CA and BZ were different and the action of BZ was different from the action of CA + BZ. These data suggest that CA may interact with BZ. The differences in the RAPD profile of the Y strain of T. cruzi produced by BZ, CA + BZ and the natural course of the infection suggest selection/suppression of populations.

Benznidazole affects expression of Th1, Th17 and Treg cytokines during acute experimental Trypanosoma cruzi infection

Background

The present study evaluated the effect of treatment with benznidazole on mRNA expression of IFN-γ, IL-17, IL-10, TGF-β and FoxP3 in spleen and heart tissue of BALB/c mice in the acute phase of an experimental infection with Trypanosoma cruzi, strains JLP or Y.

Methods

The mRNA expression of cytokines and parasite load were assessed by q-PCR. Dependent groups were compared using Student's paired t-test and independent groups were compared using Student's unpaired t-test.

Results

Infection with the JLP or Y strains increased expression of IFN-γ in the heart and of IL-10 and IL-17 in the spleen and heart compared to uninfected animals. Treatment increased the expression of IFN-γ and decreased the expression of IL-17, IL-10, TGF- β and Foxp3 in spleen and heart tissue compared to untreated infected animals.

Conclusion

Benznidazole can induce Th1 profile in the initial of the acute phase. The treatment decreased the parasite load in both organs, although the number of parasites in Y-strain-infected mice remained high. The data suggest that benznidazole may modulate cytokine expression in infection and can be dependent of the strain. However, treatment was not fully effective in the infection provoked by Y strain, probably due to the characteristics of the strain itself.

Canova medication changes TNF-α and IL-10 serum levels in mice infected with Trypanosoma cruzi Y strain

OBJECTIVE

To identify whether Canova medication changes TNF-α and IL-10 serum levels in mice infected with Trypanosoma cruzi Y strain.

METHODS

Animals were divided into five groups: non-treated infected animals (I); benznidazole-treated infected animals (Bz; 100 mg/kg body weight, single daily dose by gavage); Canova medication (CM) treated infected animals (CM; 0.2 mL/animal, single daily dose by gavage); benznidazole- and Canova medication-treated infected animals with the above-mentioned dose (Bz+CM); and non-infected animals (C). TNF-α and IL-10 levels were determined in serum aliquots after 4, 7, 10, 13, and 29 days of infection. An ELISA technique was employed with R&D System Inc. antibody pairs.

RESULTS

A high increase in TNF-α and IL-10 levels occurred in the infected and CM-treated groups within the treatment employed on the 10th day after infection, coupled with a IL-10 decrease on the 13th day after infection when compared with the other experimental groups.

CONCLUSIONS

CM may change the balance between plasma cytokine levels (TNF-α and IL-10) in mice infected with Y strain T. cruzi, with important consequences leading towards a more severe infection.

Regulatory role of Toll-like receptor 2 during infection with Trypanosoma cruzi

Previous studies have emphasized the role of Toll-like receptors (TLRs) and myeloid differentiation factor 88 (MyD88) during infection with protozoan parasites. TLR2 was shown to be important for induction of cytokine synthesis by macrophages exposed to the purified glycosylphosphatidylinositol (GPI)-anchored mucin-like glycoproteins of Trypanosoma cruzi trypomastigotes (tGPIm). On the other hand, MyD88 —/— mice, but not TLR2 —/— mice, showed impaired cytokine production and resistance to infection with T. cruzi parasites. Here we evaluate the importance of MyD88 and TLR2 in MAPK activation and cytokine synthesis by macrophages exposed to live T. cruzi parasites and compared to tGPIm. The absence of MAPK phosphorylation in TLR2- and MyD88-deficient macrophages exposed to tGPIm correlated with the incapacity to induce cytokine release in these cells. In contrast, activation of MAPK and synthesis of pro-inflammatory cytokines were not abrogated in TLR2-deficient macrophages exposed to live T. cruzi parasites. We also showed that pretreatment with tGPIm significantly reduces cytokine release by macrophages in response to T. cruzi in a TLR2-dependent manner. Consistently, TLR2-/- mice were shown to produce enhanced levels of cytokines upon in vivo challenge with T. cruzi parasites. Together, these results suggest the involvement of additional TLR(s) in the pro-inflammatory response of macrophages to whole parasites, and that, in vivo, TLR2 may have a predominant immunoregulatory role during acute infection with T. cruzi parasites .

Nitrotriazole-based acetamides and propanamides with broad spectrum antitrypanosomal activity

3-Nitro-1H-1,2,4-triazole-based acetamides bearing a biphenyl- or a phenoxyphenyl moiety have shown remarkable antichagasic activity both in vitro and in an acute murine model, as well as substantial in vitro antileishmanial activity but lacked activity against human African trypanosomiasis. We have shown now that by inserting a methylene group in the linkage to obtain the corresponding propanamides, both antichagasic and in particular anti-human African trypanosomiasis potency was increased. Therefore, IC50 values at low nM concentrations against both T. cruzi and T. b. rhodesiense, along with huge selectivity indices were obtained. Although several propanamides were active against Leishmania donovani, they were slightly less potent than their corresponding acetamides. There was a good correlation between lipophilicity (clogP value) and trypanocidal activity, for all new compounds. Type I nitroreductase, an enzyme absent from the human host, played a role in the activation of the new compounds, which may function as prodrugs. Antichagasic activity in vivo was also demonstrated with representative propanamides.

Combination Chemotherapy with Suboptimal Doses of Benznidazole and Pentoxifylline Sustains Partial Reversion of Experimental Chagas' Heart Disease

Chronic chagasic cardiomyopathy (CCC) progresses with parasite persistence, fibrosis, and electrical alterations associated with an unbalanced immune response such as high plasma levels of tumor necrosis factor (TNF) and nitric oxide (NO). Presently, the available treatments only mitigate the symptoms of CCC. To improve CCC prognosis, we interfered with the parasite load and unbalanced immune response using the trypanocidal drug benznidazole (Bz) and the immunoregulator pentoxifylline (PTX). C57BL/6 mice chronically infected with the Colombian strain of Trypanosoma cruzi and with signs of CCC were treated for 30 days with a suboptimal dose of Bz (25 mg/kg of body weight), PTX (20 mg/kg), or their combination (Bz plus PTX) and analyzed for electrocardiographic, histopathological, and immunological changes. Bz (76%) and Bz-plus-PTX (79%) therapies decreased parasite loads. Although the three therapies reduced myocarditis and fibrosis and ameliorated electrical alterations, only Bz plus PTX restored normal heart rate-corrected QT (QTc) intervals. Bz-plus-PTX-treated mice presented complementary effects of Bz and PTX, which reduced TNF expression (37%) in heart tissue and restored normal TNF receptor 1 expression on CD8⁺ T cells, respectively. Bz (85%) and PTX (70%) therapies reduced the expression of inducible nitric oxide synthase (iNOS/NOS2) in heart tissue, but only Bz (58%) reduced NO levels in serum. These effects were more pronounced after Bz-plus-PTX therapy. Moreover, 30 to 50 days after treatment cessation, reductions of the prolonged QTc and QRS intervals were sustained in Bz-plus-PTX-treated mice. Our findings support the importance of interfering with the etiological agent and immunological abnormalities to improve CCC prognosis, opening an opportunity for a better quality of life for Chagas' disease (CD) patients.

Treatment Success in Trypanosoma cruzi Infection Is Predicted by Early Changes in Serially Monitored Parasite-Specific T and B Cell Responses

BACKGROUND

Chagas disease is the highest impact parasitic disease in Latin America. We have proposed that changes in Trypanosoma cruzi-specific immune responses might serve as surrogate indicators of treatment success. Herein, we addressed in a long-term follow-up study whether cure achieved after treatment can be predicted by changes in non-conventional indexes of anti-parasite serological and T cell activities.

METHODOLOGY/PRINCIPAL FINDINGS

T. cruzi-specific T cell responses, as measured by interferon-γ ELISPOT and T. cruzi-specific antibodies assessed by ELISA, hemagglutination and immunofluorescence tests as well as by a multiplex assay incorporating 14 recombinant T. cruzi proteins were measured in 33 patients at 48-150 months post-benznidazole treatment. Cure - as assessed by conventional serological tests - was associated with an early decline in T. cruzi-specific IFN-γ-producing T cells and in antibody titers measured by the multiplex serological assay. Changes in the functional status and potential of T. cruzi-specific T cells, indicative of reduced antigen stimulation, provided further evidence of parasitological cure following benznidazole treatment. Patients showing a significant reduction in T. cruzi-specific antibodies had higher pre-therapy levels of T. cruzi-specific IFN-γ- producing T cells compared to those with unaltered humoral responses post-treatment.

CONCLUSIONS/SIGNIFICANCE

Monitoring of appropriate immunological responses can provide earlier and robust measures of treatment success in T. cruzi infection.

1,2,3-Triazole-based analogue of benznidazole displays remarkable activity against Trypanosoma cruzi

The current treatment of Chagas disease is based on the use of two drugs, nifurtimox and benznidazole, which present limited efficacy in the chronic stage of the disease and toxic side effects. Although some progress has been made in the development of new drugs to treat this disease, the discovery of novel compounds is urgently required. In this work we report the synthesis and biological evaluation of 1,2,3-triazole-based analogues of benznidazole. A small series of 27 compounds was successfully synthesized via microwave-assisted copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) and ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC) from N-benzyl-2-azidoacetamide (1) and a set of commercial terminal alkynes. Analogues 24 (IC50 40 μM) and 28 (IC50 50 μM) showed comparable activities to benznidazole (IC50 34 μM) against trypomastigote form and analogue 15 (IC50 7 μM) was found to be the most active. Regarding the cytotoxicity assessment of the series, most compounds were not cytotoxic. This work shows that the designed strategy is efficiently capable of generating novel benzindazole analogues and reveals one analogue is more active than benznidazole.

Modulation of Trypanosoma cruzi-specific T-cell responses after chemotherapy for chronic Chagas disease

The aim of this review is to describe the contributions of the knowledge of T-cell responses to the understanding of the physiopathology and the responsiveness to etiological treatment during the chronic phase of Chagas disease. T-helper (Th)1 and interleukin (IL)-10 Trypanosoma cruzi-specific T-cells have been linked to the asymptomatic phase or to severe clinical forms of the disease, respectively or vice versa, depending on the T. cruzi antigen source, the patient's location and the performed immunological assays. Parasite-specific T-cell responses are modulated after benznidazole (BZ) treatment in chronically T. cruzi-infected subjects in association with a significant decrease in T. cruzi-specific antibodies. Accumulating evidence has indicated that treatment efficacy during experimental infection with T. cruzi results from the combined action of BZ and the activation of appropriate immune responses in the host. However, strong support of this interaction in T. cruzi-infected humans remains lacking. Overall, the quality of T-cell responses might be a key factor in not only disease evolution, but also chemotherapy responsiveness. Immunological parameters are potential indicators of treatment response regardless of achievement of cure. Providing tools to monitor and provide early predictions of treatment success will allow the development of new therapeutic options.

Biomarkers of therapeutic responses in chronic Chagas disease: state of the art and future perspectives

The definition of a biomarker provided by the World Health Organization is any substance, structure, or process that can be measured in the body, or its products and influence, or predict the incidence or outcome of disease. Currently, the lack of prognosis and progression markers for chronic Chagas disease has posed limitations for testing new drugs to treat this neglected disease. Several molecules and techniques to detect biomarkers in Trypanosoma cruzi-infected patients have been proposed to assess whether specific treatment with benznidazole or nifurtimox is effective. Isolated proteins or protein groups from different T. cruzi stages and parasite-derived glycoproteins and synthetic neoglycoconjugates have been demonstrated to be useful for this purpose, as have nucleic acid amplification techniques. The amplification of T. cruzi DNA using the real-time polymerase chain reaction method is the leading test for assessing responses to treatment in a short period of time. Biochemical biomarkers have been tested early after specific treatment. Cytokines and surface markers represent promising molecules for the characterisation of host cellular responses, but need to be further assessed.

Toxic and therapeutic effects of Nifurtimox and Benznidazol on Trypanosoma cruzi ex vivo infection of human placental chorionic villi explants

Nifurtimox (Nfx) and Benznidazole (Bnz) are the only available drugs in use for the treatment of Chagas disease. These drugs are recommended but not fully validated in evidence-based medicine and reports about the differential toxicity of both drugs are controversial. Here, we evaluated the toxic and therapeutic effects of Nfx and Bnz on human placental chorionic villi explants (HPCVE) during ex vivo infection of Trypanosoma cruzi, performing histopathological, histochemical, immunohistochemical as well as immunofluorescence analysis of the tissue. Additionally, we determined the effect of both drugs on parasite load by real time PCR. Bnz prevents the parasite induced tissue damage in ex vivo infected HPCVE compared to Nfx, which is toxic per se. The presence of T. cruzi antigens and DNA in infected explants suggests that these drugs do not impair parasite invasion into the HPCVE. Additionally, our results confirm reports suggesting that Bnz is less toxic than Nfx and support the need for the development of more effective and better-tolerated drugs.

Deficient regulatory T cell activity and low frequency of IL-17-producing T cells correlate with the extent of cardiomyopathy in human Chagas' disease

Background

Myocardium damage during Chagas' disease results from the immunological imbalance between pro- and production of anti-inflammatory cytokines and has been explained based on the Th1–Th2 dichotomy and regulatory T cell activity. Recently, we demonstrated that IL-17 produced during experimental T. cruzi infection regulates Th1 cells differentiation and parasite induced myocarditis. Here, we investigated the role of IL-17 and regulatory T cell during human Chagas' disease.

Methodology/Principal Findings

First, we observed CD4⁺IL-17⁺ T cells in culture of peripheral blood mononuclear cells (PBMC) from Chagas' disease patients and we evaluated Th1, Th2, Th17 cytokine profile production in the PBMC cells from Chagas' disease patients (cardiomyopathy-free, and with mild, moderate or severe cardiomyopathy) cultured with T. cruzi antigen. Cultures of PBMC from patients with moderate and severe cardiomyopathy produced high levels of TNF-α, IFN-γ and low levels of IL-10, when compared to mild cardiomyopathy or cardiomyopathy-free patients. Flow cytometry analysis showed higher CD4⁺IL-17⁺ cells in PBMC cultured from patients without or with mild cardiomyopathy, in comparison to patients with moderate or severe cardiomyopathy. We then analyzed the presence and function of regulatory T cells in all patients. All groups of Chagas' disease patients presented the same frequency of CD4⁺CD25⁺ regulatory T cells. However, CD4⁺CD25⁺ T cells from patients with mild cardiomyopathy or cardiomyopathy-free showed higher suppressive activity than those with moderate and severe cardiomyopathy. IFN-γ levels during chronic Chagas' disease are inversely correlated to the LVEF (P = 0.007, r = −0.614), while regulatory T cell activity is directly correlated with LVEF (P = 0.022, r = 0.500).

Conclusion/Significance

These results indicate that reduced production of the cytokines IL-10 and IL-17 in association with high levels of IFN-γ and TNF-α is correlated with the severity of the Chagas' disease cardiomyopathy, and the immunological imbalance observed may be causally related with deficient suppressor activity of regulatory T cells that controls myocardial inflammation.

Dilated cardiomyopathy is one of the clinical forms of Chagas' disease (CD) after the infection caused by the parasite Trypanosoma cruzi. Even though strategies adopted in most Latin-American countries in the last decades towards vector control have been effective in reducing the incidence of CD, active transmission is maintained in some regions, and secondary prevention approaches are still required for the infected patients, mostly because the specific anti-parasitic medications are toxic and perhaps of limited efficacy in chronically infected individuals. Moreover, there are no markers to predict the risk of developing dilated cardiomyopathy in asymptomatic, chronically infected patients, although the failure in the mechanisms that control the immune response can be involved in the development of Chagas' heart disease. In this study we show that preserved activity of regulatory T cells and the production of the cytokine IL-17 are connected with a more benign evolution of the disease, which brings a new understanding on the mechanisms associated with progression of CD.

Methodological advances in drug discovery for Chagas disease

INTRODUCTION: Chagas disease is the highest impact human infectious disease in Latin America, and the leading worldwide cause of myocarditis. Despite the availability of several compounds that have demonstrated efficacy in limiting the effects of T. cruzi, these compounds are rarely used due to their variable efficacy, substantial side effects and the lack of methodologies for confirming their effectiveness. Furthermore, the development of more efficacious compounds is challenged by limitations of systems for assessing drug efficacy in vitro and in vivo. AREAS COVERED: Herein, the authors review the development of Chagas disease drug discovery methodology, focusing on recent developments in high throughput screening, in vivo testing methods and assessments of efficacy in humans. Particularly, this review documents the significant progress that has taken place over the last 5 years that have paved the way for both target-focused and high-throughput screens of compound libraries. EXPERT OPINION: The tools for in vitro and in vivo screening of anti-T. cruzi compounds have improved dramatically in the last few years and there are now a number of excellent in vivo testing models available; this somewhat alleviates the bottleneck issue of quickly and definitively demonstrating in vivo efficacy in a relevant host animal system. These advances emphasize the potential for additional progress resulting in new treatments for Chagas disease in the coming years. That being said, national and international agencies must improve the coordination of research and development efforts in addition to cultivating the funding sources for the development of these new treatments.

Splenectomy increases mortality in murine Trypanosoma cruzi infection

The spleen is a secondary lymphoid organ that harbours a variety of cells such as T and B lymphocytes and antigen-presenting cells important to immune response development. In this study, we evaluated the impact of spleen removal in the immune response to experimental Trypanosoma cruzi infection. C57BL/6 mice were infected with Y strain of the parasite and infection was followed daily. Mice that underwent splenectomy had fewer parasites in peripheral blood at the peak of infection; however, mortality was increased. Histological analysis of heart and liver tissues revealed an increased number of parasites and inflammatory infiltrates at these sites. Spleen removal was associated with reduction in IFN-γ and TNF-α production during infection as well as with a decrease in specific antibody secretion. Haematological disorders were also detected. Splenectomized mice exhibited severe anaemia and decreased bone marrow cell numbers. Our results indicate that spleen integrity is critical in T. cruzi infection for the immune response against the parasite, as well as for the control of bone marrow haematological function.

The endless race between Trypanosoma cruzi and host immunity: lessons for and beyond Chagas disease

Infection with the protozoan parasite Trypanosoma cruzi, the agent of Chagas disease, is characterised by a variable clinical course - from symptomless cases to severe chronic disease with cardiac and/or gastrointestinal involvement. The variability in disease outcome has been attributed to host responses as well as parasite heterogeneity. In this article, we review studies indicating the importance of immune responses as key determinants of host resistance to T. cruzi infection and the pathogenesis of Chagas disease. Particular attention is given to recent studies defining the role of cognate innate immune receptors and immunodominant CD8+ T cells that recognise parasite components - both crucial for host-parasite interaction and disease outcome. In light of these studies we speculate about parasite strategies that induce a strong and long-lasting T-cell-mediated immunity but at the same time allow persistence of the parasite in the vertebrate host. We also discuss what we have learned from these studies for increasing our understanding of Chagas pathogenesis and for the design of new strategies to prevent the development of Chagas disease. Finally, we highlight recent studies employing a genetically engineered attenuated T. cruzi strain as a vaccine shuttle that elicits potent T cell responses specific to a tumour antigen and protective immunity against a syngeneic melanoma cell line.

In vitro and in vivo high-throughput assays for the testing of anti-Trypanosoma cruzi compounds

BACKGROUND

The two available drugs for treatment of T. cruzi infection, nifurtimox and benznidazole (BZ), have potential toxic side effects and variable efficacy, contributing to their low rate of use. With scant economic resources available for antiparasitic drug discovery and development, inexpensive, high-throughput and in vivo assays to screen potential new drugs and existing compound libraries are essential.

METHODS

In this work, we describe the development and validation of improved methods to test anti-T. cruzi compounds in vitro and in vivo using parasite lines expressing the firefly luciferase (luc) or the tandem tomato fluorescent protein (tdTomato). For in vitro assays, the change in fluorescence intensity of tdTomato-expressing lines was measured as an indicator of parasite replication daily for 4 days and this method was used to identify compounds with IC(50) lower than that of BZ.

FINDINGS

This method was highly reproducible and had the added advantage of requiring relatively low numbers of parasites and no additional indicator reagents, enzymatic post-processes or laborious visual counting. In vivo, mice were infected in the footpads with fluorescent or bioluminescent parasites and the signal intensity was measured as a surrogate of parasite load at the site of infection before and after initiation of drug treatment. Importantly, the efficacy of various drugs as determined in this short-term (<2 weeks) assay mirrored that of a 40 day treatment course.

CONCLUSION

These methods should make feasible broader and higher-throughput screening programs needed to identify potential new drugs for the treatment of T. cruzi infection and for their rapid validation in vivo.

Specific chemotherapy of Chagas disease: relevance, current limitations and new approaches

A critical review of the development of specific chemotherapeutic approaches for the management of American Trypanosomiasis or Chagas disease is presented, including controversies on the pathogenesis of the disease, the initial efforts that led to the development of currently available drugs (nifurtimox and benznidazole), limitations of these therapies and novel approaches for the development of anti-Trypanosoma cruzi drugs, based on our growing understanding of the biology of this parasite. Among the later, the most promising approaches are ergosterol biosynthesis inhibitors such as posaconazole and ravuconazole, poised to enter clinical trials for chronic Chagas disease in the short term; inhibitors of cruzipain, the main cysteine protease of T. cruzi, essential for its survival and proliferation in vitro and in vivo; bisphosphonates, metabolic stable pyrophosphate analogs that have trypanocidal activity through the inhibition of the parasite's farnesyl-pyrophosphate synthase or hexokinase; inhibitors of trypanothione synthesis and redox metabolism and inhibitors of hypoxanthine-guanine phosphoribosyl-transferase, an essential enzyme for purine salvage in T. cruzi and related organisms. Finally, the economic and political challenges faced by development of drugs for the treatment of neglected tropical diseases, which afflict almost exclusively poor populations in developing countries, are analyzed and recent potential solutions for this conundrum are discussed.

Chagas' disease: an update on immune mechanisms and therapeutic strategies

The final decade of the 20th century was marked by an alarming resurgence in infectious diseases caused by tropical parasites belonging to the kinetoplastid protozoan order. Among the pathogenic trypanosomatids, some species are of particular interest due to their medical importance. These species include the agent responsible for Chagas’ disease, Trypanosoma cruzi. Approximately 8 to 10 million people are infected in the Americas, and approximately 40 million are at risk. In the present review, we discuss in detail the immune mechanisms elicited during infection by T. cruzi and the effects of chemotherapy in controlling parasite proliferation and on the host immune system.

Trypanosoma cruzi: Immunological predictors of benznidazole efficacy during experimental infection

C3H/HeN male mice were infected with a lethal population of Trypanosoma cruzi and treated with benznidazole (Bz). Parasitemia, body weight and survival rate were registered during the therapy with significant improvement for T. cruzi-infected Bz-treated animals. Besides, flow cytometry resulted a useful method to discriminate between cured animals from those not cured by monitoring IgG(1) bound to live trypomastigotes levels. At the end of Bz therapy, the LT splenocyte compartment was studied for activation/memory cell surface markers (CD(69)(+) and CD(44)(+)). Cytofluorometric analysis showed that T. cruzi-infected untreated mice increased their activated LT numbers and this effect was completely abolished only in cured mice at the end of Bz administration. The same behavior was observed for the memory LT subpopulation correlating to an effector memory (CD(62L)(-)) displayed by T. cruzi infection. Bz treatment was able to modulate the immunological response by reducing the deleterious effect of the acute phase in all T. cruzi-infected mice.

Innate and Acquired Immunity in the Pathogenesis of Chagas Disease

The apparent discrepancy between the intensity of inflammatory reaction and scarce number of parasites in chronic chagasic myocarditis prompt several investigators to hypothesize that an autoimmune process was involved in the pathogenesis of Chagas disease. Here, we recapitulate diverse molecular and cellular mechanisms of innate and acquired immunity involved in the control of parasite replication and in the build up of myocarditis observed during infection with Trypanosoma cruzi. In addition, we review the immunoregulatory mechanisms responsible for preventing excessive immune response elicited by this protozoan parasite. Ongoing studies in this research area may provide novel therapeutic strategies that could enhance the immunoprotective response while preventing the deleterious parasite-elicited responses observed during Chagas disease.

Reduction of parasite levels in blood improves pregnancy outcome during experimental Trypanosoma cruzi infection

Infection with a myotropic Trypanosoma cruzi clone induces maternal fertility failure. In the current work, we evaluated whether reduction of maternal parasitaemia before mating has beneficial effects on pregnancy outcome. Female mice were subjected to benznidazole (Bz) treatment after infection. On day 30 of therapy, mating was assessed and pregnancy outcome was determined on day 14 of gestation. Fetal resorptions diminished in T. cruzi-infected Bz-treated mice compared with T. cruzi-infected untreated mice. This was in agreement with the reduction in the blood/solid tissue parasite load and with the percentage of necrotic foci in placental samples from T. cruzi-infected Bz-treated females. To study eventual changes in the immune homeostasis of T. cruzi-infected Bz-treated mice, activation of the immune system was evaluated at the end of Bz therapy and before mating. We found specific IgG1 reduction resulting in a predominance of specific IgG2a, reduced numbers of CD69+ CD4+ cells and diminished frequency and numbers of CD44+ T cells. Concanavalin A-stimulated splenocytes from T. cruzi-infected Bz-treated mice produced higher amounts of IFN-gamma than T. cruzi-infected untreated mice. These results indicate that reduction of maternal parasite load improves pregnancy outcome. These findings correlate with a favourable modulation of the immune response.

Absence of CD4+ T lymphocytes, CD8+ T lymphocytes, or B lymphocytes has different effects on the efficacy of posaconazole and benznidazole in treatment of experimental acute Trypanosoma cruzi infection

We investigated the influence of CD4(+) T lymphocytes, CD8(+) T lymphocytes, and B lymphocytes on the efficacy of posaconazole (POS) and the reference drug benznidazole (BZ) during treatment of acute Trypanosoma cruzi infection in a murine model. Wild-type mice infected with T. cruzi and treated with POS or BZ presented no parasitemia, 100% survival, and 86 to 89% cure rates, defined as the percentages of animals with negative hemocultures at the end of the observation period. CD4(+)-T-lymphocyte-knockout (KO) mice infected with T. cruzi and treated with BZ or POS controlled parasitemia during treatment, although circulating parasites reappeared after drug pressure cessation, leading to only a 6% survival rate and no cure. CD8(+)-T-lymphocyte-KO mice infected with T. cruzi and treated with POS or BZ had intermediate results, displaying discrete parasitemia after the treatment was ended, 81 and 86% survival, and cure rates of 31 and 66%, respectively. B-lymphocyte-KO mice infected with T. cruzi and treated with BZ relapsed with parasitemia 1 week after the end of treatment and had a 67% survival rate and only a 22% cure rate. In contrast, the activity of POS was much less affected in these animals, with permanent suppression of parasitemia, 100% survival, and a 71% cure rate. Our results demonstrate that abrogation of different lymphocytes' activities has distinct effects on the efficacy of POS and BZ in this experimental model, probably reflecting different parasite stages preferentially targeted by the two drugs and distinct cooperation patterns with the host immune system.

Chemotherapy of chronic indeterminate Chagas disease: a novel approach to treatment

Treatment of Chagas disease is a controversial issue because the available drugs are highly toxic. Clomipramine is a tricyclic antidepressant drug that inhibits Trypanosoma cruzi's trypanothione reductase, provoking the death of the parasite and preventing the cardiac damage when used for the treatment of acutely infected mice. Here, we studied the effectiveness of clomipramine (5 mg/kg/day for one month) as chemotherapy for T. cruzi-infected mice in the chronic indeterminate stage of the infection. The animals were analyzed in the cardiac chronic phase. Survival of treated animals was 84% while for the untreated ones was 40%; most of the animals presented electrocardiographic abnormalities. Affinity and density of cardiac beta receptors from infected and treated mice were similar to those in the indeterminate phase, showing that clomipramine treatment stopped the increment of functional alterations provoked by the infection, while untreated mice presented affinity and density significantly diminished. Hearts from infected and untreated mice in the chronic stage presented mononuclear cells, necrosis and fiber dissolution while hearts from treated animals showed only isolated inflammatory infiltrates. Present results demonstrate that clomipramine used in the chronic indeterminate phase of the T. cruzi infection modified the natural evolution of the chagasic cardiopathy.

Drug-induced cure drives conversion to a stable and protective CD8+ T central memory response in chronic Chagas disease

In this study, we document the development of stable, antigen-independent CD8+ T cell memory after drug-induced cure of a chronic infection. By establishing a system for drug cure of chronic Trypanosoma cruzi infection, we present the first extensively documented case of total parasite clearance after drug treatment of this infection. Cure resulted in the emergence of a stable, parasite-specific CD8+ T cell population with the characteristics of central memory cells, based upon expression of CD62L, CCR7, CD127, CD122, Bcl-2 and a reduced immediate in vivo CTL function. CD8+ T cells from treated and cured mice also expanded more rapidly and provided greater protection following challenge than those from chronically infected mice. These results show that complete pathogen clearance results in stable, antigen-independent and protective T cell memory, despite the potentially exhausting effects of prior long-term exposure to antigen in this chronic infection.

Modulation of autoimmunity by treatment of an infectious disease

Chagas' heart disease (CHD), caused by the parasite Trypanosoma cruzi, is the most common form of myocarditis in Central America and South America. Some humans and experimental animals develop both humoral and cell-mediated cardiac-specific autoimmunity during infection. Benznidazole, a trypanocidal drug, is effective at reducing parasite load and decreasing the severity of myocarditis in acutely infected patients. We hypothesized that the magnitude of autoimmunity that develops following T. cruzi infection is directly proportional to the amount of damage caused by the parasite. To test this hypothesis, we used benznidazole to reduce the number of parasites in an experimental model of CHD and determined whether this treatment altered the autoimmune response. Infection of A/J mice with the Brazil strain of T. cruzi leads to the development of severe inflammation, fibrosis, necrosis, and parasitosis in the heart accompanied by vigorous cardiac myosin-specific delayed-type hypersensitivity (DTH) and antibody production at 21 days postinfection. Mice succumbed to infection within a month if left untreated. Treatment of infected mice with benznidazole eliminated mortality and decreased disease severity. Treatment also reduced cardiac myosin-specific DTH and antibody production. Reinfection of treated mice with a heart-derived, virulent strain of T. cruzi or immunization with myosin led to the redevelopment of myosin-specific autoimmune responses and inflammation. These results provide a direct link between the levels of T. cruzi and the presence of autoimmunity and suggest that elimination of the parasite may result in the reduction or elimination of autoimmunity in the chronic phase of infection.

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.

The Anti-Trypanosoma cruzi activity of posaconazole in a murine model of acute Chagas' disease is less dependent on gamma interferon than that of benznidazole

We have investigated the influences of gamma interferon (IFN-gamma) and interleukin-12 (IL-12) on the efficacy of posaconazole (POS) treatment of acute experimental infections with Trypanosoma cruzi; the standard drug, benznidazole (BZ), was used as a positive control. Wild-type (WT) mice infected with T. cruzi and treated with POS or BZ had no parasitemia, 100% survival, and cure rates of 86 to 89%. IFN-gamma-knockout (KO) mice infected with T. cruzi and treated with BZ controlled the infection during treatment but relapsed after the drug pressure ceased and had 0% survival, while those receiving POS better controlled the infection after the end of treatment and had 70% survival (P<0.0001 compared to the results for both untreated and BZ-treated animals). IL-12-KO mice infected and treated with POS or BZ had intermediate results, displaying enhanced parasitemia, decreased survival (77 to 83%), and reduced cure rates (35 to 39%) compared with those of the WT animals. Our results demonstrate that either IFN-gamma or IL-12 deficiency reduces the efficacy of POS or BZ in this experimental model but also indicate that the anti-T. cruzi activity of POS is much less dependent on the activity of IFN-gamma than that of BZ is.

Mice Deficient in LRG-47 Display Enhanced Susceptibility toTrypanosoma cruziInfection Associated with Defective Hemopoiesis and Intracellular Control of Parasite Growth

IFN-gamma is known to be required for host control of intracellular Trypanosoma cruzi infection in mice, although the basis of its protective function is poorly understood. LRG-47 is an IFN-inducible p47GTPase that has been shown to regulate host resistance to intracellular pathogens. To investigate the possible role of LRG-47 in IFN-gamma-dependent control of T. cruzi infection, LRG-47 knockout (KO) and wild-type (WT) mice were infected with the Y strain of this parasite, and host responses were analyzed. When assayed on day 12 after parasite inoculation, LRG-47 KO mice, in contrast to IFN-gamma KO mice, controlled early parasitemia almost as effectively as WT animals. However, the infected LRG-47 KO mice displayed a rebound in parasite growth on day 15, and all succumbed to the infection by day 19. Additional analysis indicated that LRG-47-deficient mice exhibit unimpaired proinflammatory responses throughout the infection. Instead, reactivated disease in the KO animals was associated with severe splenic and thymic atrophy, anemia, and thrombocytopenia not observed in their WT counterparts. In addition, in vitro studies revealed that IFN-gamma-stimulated LRG-47 KO macrophages display defective intracellular killing of amastigotes despite normal expression of TNF and NO synthetase type 2 and that both NO synthetase type 2 and LRG-47 are required for optimum IFN-gamma-dependent restriction of parasite growth. Together, these data establish that LRG-47 can influence pathogen control by simultaneously regulating macrophage-microbicidal activity and hemopoietic function.