3-Hydroxykynurenine, a Tryptophan Metabolite Generated during the Infection, Is Active Against Trypanosoma cruzi

The antiparasitic activity of 3-hydroxykynurenine (3-HK), one of the major tryptophan catabolites of the kynurenine pathway, against both Trypanosoma cruzi evolutive forms that are important for human infection, trypomastigotes (Tps) and amastigotes (Am), possible targets in the parasite and the drug toxicity to mammalian cells have been investigated. 3-HK showed a potent activity against Am with IC₅₀ values in the micromolar concentration range, while the IC₅₀ values to cause Tps death was ∼6000-times higher, indicating that the replicative form present in the vertebrate hosts is much more susceptible to 3-HK than bloodstream Tps. In addition, 3-HK showed activity against Tps and Am, at concentrations that did not exhibit toxicity to mammalian cells. Ultrastructural analysis and flow cytometry studies indicated that Am and Tps mitochondrion and nuclei contain 3-HK targets. The potency and selectivity of 3-HK, which is generated during T. cruzi infection in human and mice, suggest that 3-HK may be a suitable candidate for drug research and development for Chagas disease.

3-Hydroxy kynurenine treatment controls T. cruzi replication and the inflammatory pathology preventing the clinical symptoms of chronic Chagas disease

Background

3-Hydroxy Kynurenine (3-HK) administration during the acute phase of Trypanosoma. cruzi infection decreases the parasitemia of lethally infected mice and improves their survival. However, due to the fact that the treatment with 3-HK is unable to eradicate the parasite, together with the known proapoptotic and immunoregulatory properties of 3-HK and their downstream catabolites, it is possible that the 3-HK treatment is effective during the acute phase of the infection by controlling the parasite replication, but at the same time suppressed the protective T cell response before pathogen clearance worsening the chronic phase of the infection. Therefore, in the present study, we investigated the effect of 3-HK treatment on the development of chronic Chagas’ disease.

Principal Findings

In the present study, we treated mice infected with T. cruzi with 3-HK at day five post infection during 5 consecutive days and investigated the effect of this treatment on the development of chronic Chagas disease. Cardiac functional (electrocardiogram) and histopathological studies were done at 60 dpi. 3-HK treatment markedly reduced the incidence and the severity of the electrocardiogram alterations and the inflammatory infiltrates and fibrosis in heart and skeletal muscle. 3-HK treatment modulated the immune response at the acute phase of the infection impairing the Th1- and Th2-type specific response and inducing TGF-β-secreting cells promoting the emergence of regulatory T cells and long-term specific IFN-γ secreting cells. 3-HK in vitro induced regulatory phenotype in T cells from T. cruzi acutely infected mice.

Conclusions

Our results show that the early 3-HK treatment was effective in reducing the cardiac lesions as well as altering the pattern of the immune response in experimental Chagas’ disease. Thus, we propose 3-HK as a novel therapeutic treatment able to control both the parasite replication and the inflammatory response.

Excretory-secretory products (ESP) from Fasciola hepatica induce tolerogenic properties in myeloid dendritic cells

Fasciola hepatica is a helminth trematode that migrates through the host tissues until reaching bile ducts where it becomes an adult. During its migration the parasite releases different excretory-secretory products (ESP), which are in contact with the immune system. In this study, we focused on the effect of ESP on the maturation and function of murine bone marrow derived-dendritic cells (DC). We found that the treatment of DC with ESP failed to induce a classical maturation of these cells, since ESP alone did not activate DC to produce any cytokines, although they impaired the ability of DC to be activated by TLR ligands and also their capacity to stimulate an allospecific response. In addition, using an in vitro ovalbumin peptide-restricted priming assay, ESP-treated DC exhibited a capacity to drive Th2 and regulatory T cell (Treg) polarization of CD4(+) cells from DO11.10 transgenic mice. This was characterized by increased IL-4, IL-5, IL-10 and TGF-beta production and the expansion of CD4(+)CD25(+)Foxp3(+) cells. Our results support the hypothesis that ESP from F. hepatica modulate the maturation and function of DC as part of a generalized immunosuppressive mechanism that involves a bias towards a Th2 response and Treg development.