José Clóvis do Prado

Influence of male gonadal hormones on the parasitemia and humoral response of male Calomys callosus infected with the Y strain of Trypanosoma cruzi

Abstract Effects of orchiectomy on male Calomys callosus infected with the Y strain of Trypanosoma cruzi were studied. Male C. callosus of the same age and weight were divided into three groups: intact, sham operated, and castrated. After 1 month they were inoculated (i.p.) with 4000 blood trypomastigotes. Parasitemia was lower in orchiectomized animals than in the intact and sham groups. Hormone replacement with decanoate testosterone raised the parasitemia of castrated animals to levels similar to those of their intact and sham counterparts. Antibody levels were monitored by complement-mediated lysis. The trypomastigote lysis percentage varied through the course of infection, according to hormonal status and number of parasites during the acute phase. The most significant differences were found on the 30th day after infection, when lytic antibodies of intact males were high compared to the orchiectomized and sham groups. Higher resistance with lower lysis indexes were observed after orchiectomy, compared to intact and sham males.

Melatonin treatment reduces the severity of experimental Trypanosoma cruzi infection

Abstract:  Prior studies show that melatonin enhances the immune response. This study investigated the possible therapeutic effects of melatonin during the course of Trypanosoma cruzi infection. T. cruzi‐infected male Wistar rats were orally treated with 5 mg/kg body weight/day of melatonin. Animals treated with melatonin showed a significant reduction in the number of blood trypomastigotes during the acute phase of infection compared with untreated animals (P < 0.05). A significant increase in leucocytes numbers during the peak of parasitaemia was also observed (P < 0.05). Moreover, both prior and concomitant treatment with melatonin increased interleukin‐2 levels, especially 9 days postinfection (P < 0.05). Histopathological observations of heart tissue revealed that melatonin administration also resulted in fewer and smaller amastigote burdens, and less inflammatory infiltrate and tissue disorganization, indicating a reduced parasitism of this tissue. These results show that melatonin is effective in controlling parasite replication and suggest that melatonin might serve as an effective therapeutic agent in the treatment of American trypanosomiasis.

Melatonin enhances pro-inflammatory cytokine levels and protects against Chagas disease

Abstract:  Pro‐inflammatory and modulatory cytokines have an essential role in host defense against human and murine Trypanosoma cruzi infection. Control of T. cruzi parasitism during the acute phase of infection is considered to be critically dependent on direct macrophage activation by cytokines. Melatonin has been proposed to regulate the immune system by affecting cytokine production in immunocompetent cells, enhancing the production of several T helper (Th)1 cytokines. The aims of this work were to evaluate in rats, the influences of exogenous melatonin treatment on T. cruzi‐infected host’s immune responses. With this in mind, several immunological parameters were analyzed, including tumor necrosis factor‐α, γ‐interferon, interleukin‐12, nitric oxide (NO) and macrophage count. The melatonin therapy was provided in one of two different treatment regimens, that is, either beginning 7 days prior to infection or concomitant with the infection. Both treatments triggered an up‐regulation of the immune response, with the concomitant treatment being more effective; in this case all cytokines studied, with exception of NO, displayed enhanced concentrations and there was a higher number of peritoneal macrophages, which displayed reduced concentrations under melatonin therapy. We conclude that melatonin plays a pivotal role in up‐regulating the Th1 immune response thus controlling parasite replication.

Suppressive action of melatonin on the TH-2 immune response in rats infected with Trypanosoma cruzi

Abstract:  Control of the acute phase of Trypanosoma cruzi infection is critically dependent on cytokine‐mediated macrophage activation to intracellular killing, natural killer (NK) cells, CD4+ T cells, CD8+ T cells and B cells. Cell‐mediated immunity in T. cruzi infection is also modulated by cytokines, but in addition to parasite‐specific responses, autoimmunity can be also triggered. Importantly, cytokines may also play a role in the cell‐mediated immunity of infected subjects. Here we studied the role of cytokines in the regulation of innate and adaptive immunity during the acute phase of T. cruzi infection in Wistar rats. Melatonin is an effective regulator of the immune system. Macrophages and T lymphocytes, which have melatonin receptors, are target cells for the immunomodulatory function of melatonin. In this paper melatonin was orally given via two protocols: prior to and concomitant with infection. Both treatments were highly effective against T. cruzi with enhanced action for the concomitant treatment. The data suggest an up‐regulation of the TH‐1 immune response as all analyzed parameters, interleukin (IL)‐4, IL‐10, transforming growth factor‐β1 and splenocyte proliferation, displayed reduced levels as compared with the untreated counterparts. However, the direct effects of melatonin on immune cells have not been fully investigated during T. cruzi infection. We conclude that in light of the current results, melatonin exerted important therapeutic benefits through its immune regulatory effects.

Protective actions of melatonin against heart damage during chronic Chagas disease.

Chronic cardiomyopathy is the most important clinical form of Chagas disease, and it is characterised by myocarditis that is associated with fibrosis and organ dysfunction. Alternative treatment options are important tools to modulate host immune responses. The main goal of this work was to evaluate the anti-inflammatory actions of melatonin during the chronic phase of Chagas disease. TNF-α, IL-10 and nitrite concentrations were evaluated as predictive factors of immune modulation. Creatine phosphokinase-MB (CK-MB), cardiac inflammatory foci and heart weight were assessed to evaluate the efficacy of the melatonin treatment. Male Wistar rats were infected with 1×10(5) blood trypomastigotes of the Y strain of Trypanosoma cruzi and kept untreated for 60 days to mimic chronic infection. After this period, the rats were orally treated with melatonin 50mg/kg/day, and the experiments were performed 90, 120, and 180 days post-infection. Melatonin treatment significantly increased the concentration of IL-10 and reduced the concentrations of NO and TNF-α produced by cardiomyocytes. Furthermore, it led to decreased heart weight, serum CK-MB levels and inflammatory foci when compared to the untreated and infected control groups. We conclude that melatonin therapy is effective at protecting animals against the harmful cardiac inflammatory response that is characteristic of chronic T. cruzi infection.

Melatonin and dehydroepiandrosterone combination: does this treatment exert a synergistic effect during experimental Trypanosoma cruzi infection?

Abstract:  Previous studies showed that melatonin or dehydroepiandrosterone (DHEA) enhances the immune response against parasitic pathogens. The present study investigated the in vitro activity of melatonin combined with DHEA in a period of 24 hr during the course of in vivo T. cruzi infection. The in vitro activity of melatonin or DHEA alone, as well as together, were tested for the trypomastigote forms (doses ranging from 0.5 to 128 μm). In vitro, neither melatonin nor DHEA alone had any activity against trypomastigote forms, although when the highest concentration of combined melatonin and DHEA was used, it was active against the trypomastigote forms of the parasite. However, for this concentration, a quite toxicity on peritoneal macrophages was observed. For in vivo evaluation, male Wistar rats were infected with the Y strain of T. cruzi. They were orally treated with 10 mg/kg body weight/day of melatonin and subcutaneously with 40 mg/kg body weight/day of DHEA. Treatment with melatonin, DHEA and the association showed a significant reduction in the number of blood trypomastigotes during the acute phase of infection as compared to untreated animals (P < 0.05). A significant increase in the number of macrophages and nitric oxide (NO) concentrations were observed during the peak of parasitaemia with melatonin alone or combined with DHEA. However, with DHEA alone the highest concentration of NO was observed (P < 0.05). Moreover, DHEA treatment increased TNF‐alpha levels during the infection (P < 0.05). These results show that melatonin, DHEA or the combination of both reduces parasitemia during the acute phase of infection. The combined action of both molecules did not exert a synergic action on the host’s ability to fight infection, and it seems that among all treatments DHEA induces a more efficient immune response.

DHEA and testosterone therapies in Trypanosoma cruzi-infected rats are associated with thymic changes.

The ability of the gonadal hormones to influence diverse immunological functions during the course of several infections has been extensively studied in the latest decades. Testosterone has a suppressive effect on immune response of vertebrates and increases susceptibility toward numerous parasitic diseases. Dehydroepiandrosterone is an abundant steroid hormone secreted by the human adrenal cortex and it is considered potent immune-activator. In this paper, it was examined the effects of DHEA and testosterone supplementation in the thymic atrophy in rats infected with Trypanosoma cruzi, by comparing blood parasitism, thymocyte proliferation, TNF-alpha and IL-12 levels. Our data point in the direction that DHEA treatment triggered enhanced thymocyte proliferation as compared to its infected counterparts and reduced production of TNF-alpha during the acute phase of infection. Oppositely, the lowest values for cells proliferation and IL-12 concentrations were reached in testosterone-supplied animals. The combined treatment testosterone and DHEA improves the effectiveness of the hosts immune response, reducing blood parasites and the immunosuppressive effects of male androgens besides increasing IL-12 concentrations and decreasing TNF-alpha levels.

Trypanosoma cruzi: the effects of zinc supplementation during experimental infection.

It is well recognized that zinc is an essential trace element, influencing growth and affecting the development and integrity of the immune system. The use of oligoelements as zinc can be considered a tool in modulating the effectiveness of the immune response. In this work zinc was daily and orally supplied in male Wistar rats infected with the Y strain of Trypanosoma cruzi. Parasitemia was evaluated and a significant reduction on blood parasites was observed. In order to check some immunological parameters peritoneal macrophages were counted revealing higher percentages for zinc supplied group. Consequently enhanced concentrations of IFN-gamma was found and for the first time NO was evaluated in T. cruzi infected animals under the influence of zinc therapy, revealing enhanced concentrations when compared to unsupplied counterparts. We conclude that zinc is able to up-regulate the hosts immune response against parasite replication.

Trypanosoma cruzi: dehydroepiandrosterone (DHEA) and immune response during the chronic phase of the experimental Chagas' disease.

Dehydroepiandrosterone (DHEA) has long been considered as a precursor for many steroid hormones. It also enhances the immune responses against a wide range of viral, bacterial, and parasitic pathogens. The aims of this work were to evaluate the influences of exogenous DHEA treatment on Wistar rats infected with the Y strain of Trypanosoma cruzi during the acute and its influence on the chronic phase of infection. Animals were subcutaneous treated with 40 mg/kg body weight/day of DHEA. DHEA treatment promoted increased lymphoproliferative responses as well as enhanced concentrations of NO and IL-12. So, we point in the direction that our results validate the utility of the use of DHEA as an alternative therapy candidate against T. cruzi.

Trypanosoma cruzi : Orchiectomy and dehydroepiandrosterone therapy in infected rats

The ability of gonadal hormones to influence and induce diverse immunological functions during the course of a number of parasitic infections has been extensively studied in the latest decades. Dehydroepiandrosterone and its sulfate are the most abundant steroid hormones secreted by the human adrenal cortex and are considered potent immune-activators. The effects of orchiectomy on the course of Trypanosoma cruzi infection in rats, treated and untreated with DHEA were examined, by comparing blood and cardiac parasitism, macrophage numbers, nitric oxide and IFN-gamma levels. Orchiectomy enhanced resistance against infection with elevated numbers of macrophages, enhanced concentrations of NO and IFN-gamma and reduced amastigote burdens in heart when compared to control animals. DHEA replacement exerted a synergistic effect, up-modulating the immune response. Male sex steroids appear to play fundamental role in determining the outcome of disease, through the regulation and modulation of the activity of the immune response.