P2X3 receptor antagonism attenuates the progression of heart failure.

Despite advances in the treatment of heart failure, prognosis is poor, mortality high and there remains no cure. Heart failure is associated with reduced cardiac pump function, autonomic dysregulation, systemic inflammation and sleep-disordered breathing; these morbidities are exacerbated by peripheral chemoreceptor dysfunction. We reveal that in heart failure the carotid body generates spontaneous, episodic burst discharges coincident with the onset of disordered breathing in male rats. Purinergic (P2X3) receptors were upregulated two-fold in peripheral chemosensory afferents in heart failure, and when antagonized abolished these episodic discharges, normalized both peripheral chemoreceptor sensitivity and the breathing pattern, reinstated autonomic balance, improved cardiac function, and reduced both inflammation and biomarkers of cardiac failure. Aberrant ATP transmission in the carotid body triggers episodic discharges that via P2X3 receptors play a crucial role in the progression of heart failure and as such offer a distinct therapeutic angle to reverse multiple components of its pathogenesis.

Melatonin regulates antioxidant defense and inflammatory response by activating Nrf2-dependent mechanisms and inhibiting NFkappaB expression in middle-aged T. cruzi infected rats.

Oxidative stress with higher levels of leptin and inflammatory response are key processes related to pathogenesis of both T. cruzi infection and aging. Nuclear factor erythroid 2-related factor 2 (Nrf2) controls the expression of several genes implicated in the oxidative stress response in many pathological conditions. Melatonin is a pleiotropic hormone with, antioxidant, anti-inflammatory and anti-aging actions. Then, we hypothesized that Nrf2 response is impaired during the acute T. cruzi (9 days) infection and that melatonin rescues Nrf2 responses. Young (5 weeks-old) and middle-aged (18 months-old) male Wistar rats were infected with T. cruzi. Nrf2 translocation and markers of inflammation and oxidative stress were analyzed in blood and spleen. Increased apoptosis levels and oxidative stress indicators were observed in the rat spleen during T. cruzi infection. These responses were accompanied by decreased Nrf2 expression and increased expression of nuclear factor kappa B (NFκB). Melatonin (5 mg/kg/day; p.o. gavage) attenuated the superoxide anion (O2-) and hydrogen peroxide (H2O2) production induced by T. cruzi infection. Increased expressions of catalase and superoxide dismutase (SOD) were detected in the spleen of melatonin-treated rats infected with T. cruzi. Melatonin treatment inhibited the spleen NF-κB activation and downregulates the levels of circulating interleukin (IL)-4, IL-10 and tumor necrosis factor (TNF)-α in T. cruzi middle-aged infected rats. Increased levels of the chemokine CXCL1 in middle-aged control rats was observed, confirming that aging alters the production of this chemokine. In T. cruzi infected young animals, CXCL1 was up-regulated when compared to non-infected young ones. For young or middle-aged animals, melatonin treatment had no significant effect on CXCL1 levels. Our findings demonstrate an important role for Nrf2/NF-kB regulation as a possible mechanism by which melatonin attenuates oxidative stress, and provide new insights for further studies of this indoleamine as a therapeutic co-adjuvant agent against T. cruzi infection.

Melatonin down-regulates steroidal hormones, thymocyte apoptosis and inflammatory cytokines in middle-aged T. cruzi infected rats.

Chagas disease, triggered by the flagellate protozoan Trypanosoma cruzi (T. cruzi) plays a potentially threat to historically non-endemic areas. Considerable evidence established that the immuno-endocrine balance could deeply influence the experimental T. cruzi progression inside the host's body. A high-resolution multiple reaction monitoring approach (MRMHR) was used to study the influence of melatonin on adrenal and plasma steroidal hormones profile of T. cruzi infected Wistar rats. Young (5 weeks) and middle-aged (18 months) male Wistar rats received melatonin (5 mg/Kg, orally) during the acute Chagas disease. Corticosterone, 11-dehydrocorticosterone (11-DHC), cortisol, cortisone, aldosterone, progesterone and melatonin concentration were evaluated. Interleukin-1 alpha and ß (IL-1α and ß), IL-6 and transforming growth factor beta (TGF-ß) were also analyzed. Our results revealed an increased production of corticosterone, cortisone, cortisol and aldosterone in middle-aged control animals, thus confirming the aging effects on the steroidal hormone profile. Serum melatonin levels were reduced with age and predominantly higher in young and middle-aged infected rats. Melatonin treatment reduced the corticosterone, 11-DHC, cortisol, cortisone, aldosterone and progesterone in response to T. cruzi infection. Decreased IL-1 α and ß concentrations were also found in melatonin treated middle-aged infected animals. Melatonin treated middle-aged control rats displayed reduced concentrations of TGF-ß. Melatonin levels were significantly higher in all middle-aged rats treated animals. Reduced percentages of early and late thymocyte apoptosis was found for young and middle-aged melatonin supplemented rats. Finally, our results show a link between the therapeutic and biological effects of melatonin controlling steroidal hormones pathways as well as inflammatory mediators.

T. cruzi infection among aged rats: Melatonin as a promising therapeutic molecule.

Although T. cruzi was identified as the cause of Chagas disease more than 100 years ago, satisfactory treatments still do not exist, especially for chronic disease. Here we review work suggesting that melatonin could have promise as a Chagas therapeutic. Melatonin has remarkably diverse actions. It is an immunomodulator, an anti-inflammatory, an antioxidant, a free radical scavenger, and has antiapoptotic and anti-aging effects. The elderly (aged 60 years or more) as a group are growing faster than any other age group. Here we discuss the major effects and the mechanisms of action of melatonin on aged T. cruzi-infected rats. Melatonin's protective effects may be consequences of its cooperative antioxidant and immunomodulatory actions. Melatonin modulates oxidative damage, inducing an antioxidant response and reversing age-related thymus regression. Its protective actions could be the result of its anti-apoptotic activity, and by its counteracting the excessive production of corticosterone. This review describes our work showing that host age plays an important and variable influence on the progression of systemic T. cruzi infection and supporting the hypothesis that melatonin should be considered as a powerful therapeutic compound with multiple activities that can improve host homeostasis during experimental T. cruzi infection.

Cytokine modulation, oxidative stress and thymic dysfunctions: Role of age-related changes in the experimental Trypanosoma cruzi infection: Age-related thymic dysfunctions and Trypanosoma cruzi infection.

Aging is linked with a thymic oxidative damage and some infectious diseases such as Chagas' disease may aggravate this process. The aim of this study was to evaluate the production of distinct cytokines as well as the antioxidant/oxidant status of the thymus and thymocytes populations during Trypanosoma cruzi (T. cruzi) infection. Young (5 weeks old) and aged (18 weeks old) male Wistar rats were inoculated with blood trypomastigotes forms of the Y strain of T. cruzi. On the 16th day after T. cruzi infection, increased concentrations of transforming growth factor ß (TGF-ß), interleukin (IL)-12, IL-17 were detected in aged infected subjects as compared to young infected ones. Interestingly, a reduction in the production of tumor necrose factor (TNF)-α was observed in aged infected rats when compared to young infected subjects. Aged-infected rats presented increased O2- levels, compared to young counterparts. Significant raise in the generation of O2- in aged infected animals, as compared to uninfected counterparts was observed. Up-regulated expression of Nox2 in the thymus of young and aged infected animals was observed. An increased SOD2 expression was detected in the thymus of young animals infected with T. cruzi, when compared to uninfected young rats. Aged animals showed reduced thymus weight and the number of thymocytes. Decreased percentages of SPCD4+ and SPCD8+T cells were detected in aged and control groups when compared to young counterparts. In summary, this is the first data to directly examine the influence of aging on age-related dysfunctions during the acute phase of experimental Chagas disease. Concerning to oxidative stress, it is clear from our analysis that aged infected rats suffer a more intense oxidative damage when compared to young and infected ones. Age and infection triggered a dynamic interplay of cytokines, oxidative stress and thymic dysfunctions which led to impaired response from aged and infected rats. Such findings may have significant functional relevance in therapeutic strategies in order to reestablish the thymic immunological function which occurs in aged and T. cruzi infected subjects.

The treatment with selenium increases placental parasitismin pregnant Wistar rats infected with the Y strain of Trypanosoma cruzi.

Selenium (Se) is an essential micronutrient in the diet of mammals and has an important role in the immune function. Selenium is a key element in selenoproteins involved in the in the maintenance of the antioxidant defense. Diet with selenium is beneficial for the treatment of diseases correlated with high levels of oxidative stress, also observed in the Chagas disease. Chagas disease is a neglected disease caused by the protozoan Trypanosoma cruzi and several research groups are focused on the illness treatment. Immunomodulation of the infection using microelements is an important tool to avoid deleterious effects of the Chagas disease. Therefore, our objective was to evaluate the effects of selenium supplementation on pregnant Wistar rats infected with T. cruzi. Selenium treatment stimulated the weight and length of fetuses and placentas allied to the decrease of blood parasitemia. However, selenium demonstrated a low influence on T cells, diminishing the B cell population (CD45RA+). Moreover, the production of pro-inflammatory cytokines was downregulated under selenium administration. Low pro-inflammatory cytokines levels probably are related to the increase in the number of amastigote nests in infected and treated animals. Thus, selenium supplementation during pregnancy could impair the local placental immune response. Further studies are necessary to assess the interaction between selenium and the acute Chagas' disease during pregnancy, which will base future supplementation strategies.

Ageing is not associated with an altered immune response during Trypanosoma cruzi infection: Ageing and Trypanosoma cruzi infection.

The aims of this work were to evaluate the influence of ageing on the magnitude of the immune response in male Wistar rats infected with the Y strain of Trypanosoma cruzi (T. cruzi). Infected young animals displayed enhanced CD4+ T cells as compared to uninfected counterparts. Ageing also triggered a significant reduction in CD8+ T cells compared to young and uninfected groups. The percentage of spleen NKT cells was reduced for all groups, regardless of the infection status. Significant decreased B-cells was noted in aged controls and infected animals as compared to young counterparts. A significant decrease in MHC class II (RT1B) expression in all aged animals was observed, whether infected or not. The highest and significant levels of Thiobarbituric Acid Reactive Substances (TBARS) were noted in the aged and infected animals as compared to young-infected ones (16day). Consequently superoxide dismutase (SOD) activity was reduced for both control and infected aged animals. Significant elevation of 8-isoprostane levels was found in aged control and infected animals. Plasma glutathione (GSH) concentration was reduced in aged control animals, as well as, in the young infected animals. NO production was increased in both infected and uninfected aged animals compared to young infected and uninfected animals. Corticosterone levels were elevated in aged animals, whether infected or not. Thus, our results are inedited since the immune response is not worsened by the simple fact of animals being older. Ageing by itself triggered a damaged immune response as well as enhanced reactive oxygen species, when compared to young counterparts, but it did not contribute to impair the immune response of T. cruzi infected and aged rats.

Immunoregulatory actions of melatonin and zinc during chronic Trypanosoma cruzi infection.

After one century of the discovery of Chagas' disease and the development of an efficient drug with amplitude of actions both in the acute and chronic phase is still a challenge. Alternative immune modulators have been exhaustively used. For that purpose, melatonin and zinc were administered during chronic Trypanosoma cruzi-infected Wistar rats and several endpoints were assessed. Melatonin has a remarkable functional versatility, being associated with important antioxidant, anti-inflammatory, and anti-apoptotic effects. The cross-talk between zinc and the immune system includes its ability to influence the production and signaling of numerous inflammatory cytokines in a variety of cell types. Our study showed that zinc triggered a decrease in the generation of IFN-γ for TCD4(+) cells. Reduced percentage of CD4(+) T cells producing TNF-α was observed in control melatonin or zinc-and-melatonin-treated animals as compared with untreated rats. On the other hand, a significant increase in the percentage of IL-4 from CD4(+) and CD8(+) T lymphocytes producers was observed 60 days after infection, for all zinc-treated animals, whether infected or not. Melatonin and zinc therapies increased the percentages of CD4(+) and CD8(+) T lymphocytes IL-10 producers. CD4(+) CD25(high) Foxp3(+) T cells were also elevated in zinc- and melatonin-treated animals. The modulation of the immune system influenced by these molecules affected cytokine production and the inflammatory process during chronic T. cruzi infection. Elucidation of the interplay between cytokine balance and the pathogenesis of Chagas' disease is extremely relevant not only for the comprehension of the immune mechanisms and clinical forms but, most importantly, also for the implementation of efficient and adequate therapies.

Immunomodulatory properties and anti-apoptotic effects of zinc and melatonin in an experimental model of chronic Chagas disease.

The immunomodulatory effects of melatonin and zinc during chronic experimental Chagas' disease were studied. Early and late apoptosis by Annexin V-propidium iodide staining were evaluated. The expression of CD28, CD80, CD86, CD45RA and CD4(+)T and CD8(+)T cells were also evaluated by flow cytometry analysis. The combination of zinc and melatonin notably reduced the apoptotic ratios of splenic cells in the infected and treated animals when compared to untreated rats, during early and late stages of apoptosis. The percentages of CD8(+)T cells in Zn, Mel or Zn and Mel treated rats were reduced when compared to infected and untreated animals. Higher percentages of CD28 expression in CD4(+) and CD8(+) T cell populations were observed in control and infected Zn-treated group as compared to untreated ones. Zn, Mel or the combination of both did not induce any statistically significant differences for B cells when comparing to treated control and infected groups. Zinc or Mel-treated animals presented a lower expression of CD86 when compared to untreated counterparts. According to our data, this work strongly suggest that the modulation of the immune system operated by zinc and melatonin administration affected the balance among T cell immune response, apoptosis and expression of co-stimulatory molecules during chronic Trypanosoma cruzi infection, inducing important changes in the host's immune response against the parasite. Future experiments in this field should be focused in improving our understanding of the key mechanisms underlying the involvement of melatonin and zinc in the immune response during chronic Chagas' disease.

Does orchiectomy enhance the immune-stimulatory effects of melatonin during experimental Chagas' disease?

Melatonin has been reported to play a fundamental role in T-cell immunoregulation. Control of Trypanosoma cruzi parasitism during the acute phase of infection is considered to be critically dependent on direct macrophage activation by cytokines. The aim of this work was to evaluate the influence of exogenous melatonin treatment and the influences exerted by sexual hormones during the acute phase of the experimental Chagas' disease in rats. With melatonin treatment, orchiectomized animals (CMOR and IMOR) displayed the highest concentrations of IFN-γ and TNF-α. On the 7th day post-infection, untreated and treated orchiectomized animals (IOR and IMOR) showed an enhanced number of peritoneal macrophages. Nitric oxide levels were also increased in untreated and treated orchiectomized (IOR and IMOR) when compared to the other groups, with or without LPS. Our data suggest that melatonin therapy associated with orchiectomy induced a stimulating effect on the immune response to the parasite.

Melatonin and zinc treatment: distinctive modulation of cytokine production in chronic experimental Trypanosoma cruzi infection.

Melatonin by exhibiting antioxidant, anti-aging, and immunomodulatory properties favorably modulate the immune function, protecting the hosts from several infectious diseases. Zinc is an essential trace element important for the efficiency of the immune system in reason of its widespread role in the activity of enzymes, transcription factors and cytokines. The etiology of Chagas' disease, caused by a protozoan parasite Trypanosoma cruzi, has been the focus of considerable discussion, although chronic phase still remains not fully understood. This study showed that zinc and melatonin treatment did not affect the percentage of both CD4+ and CD8+ T lymphocytes subsets in chronically infected animals. Increased levels of IL-2 and IL-10, as well as, enhanced thymocyte proliferation in T. cruzi infected groups under zinc and melatonin therapy was observed as compared to untreated group. Conversely, during the chronic phase of infection, macrophages counts were reduced in melatonin and zinc-melatonin treated animals. The combined actions of zinc and melatonin have beneficial effects in counteracting parasite-induced immune dysregulation, protecting animals against the harmful actions of chronic T. cruzi infection. Furthermore, our results provide an experimental basis for further studies on the role of immunomodulatory therapies.

Prolactin: does it exert an up-modulation of the immune response in Trypanosoma cruzi-infected rats?

During the course of infection by Trypanosoma cruzi, the host immune system is involved in distinct, complex interactions with the endocrine system, and prolactin (PRL) is one of several hormones involved in immunoregulation. Although intensive studies attempting to understand the mechanisms that underlie Chagas' disease have been undertaken, there are still some pieces missing from this complex puzzle. Because data are scarce concerning the role of PRL involvement in Chagas' disease and taking into account the existence of crosstalk between neuroendocrine hormones and the immune system, the current study evaluates a possible up-regulation of the cellular immune response triggered by PRL in T. cruzi-infected rats and the role of PRL in reversing immunosuppression caused by the parasitic infection. The data shown herein demonstrate that PRL induces the proliferation of T lymphocytes, coupled with an activation of macrophages and the production of nitric oxide (NO), leading to a reduction in the number of blood trypomastigotes during the peak of parasitemia. During the acute phase of T. cruzi infection, an enhancement of both CD3+CD4+ and CD3+CD8+ T cell populations were observed in infected groups, with the highest numbers of these T cell subsets found in the infected group treated with PRL. Because NO is a signaling molecule involved in a number of cellular interactions with components of the immune system and the neuroendocrine system, PRL can be considered an alternative hormone able to up-regulate the host's immune system, consequently lowering the pathological effects of a T. cruzi infection.

Prior and concomitant dehydroepiandrosterone treatment affects immunologic response of cultured macrophages infected with Trypanosoma cruzi in vitro?

DHEA, a steroid hormone synthesized from cholesterol by cells of the adrenal cortex, plays an essential role in enhancing the host's resistance to different experimental infections. Receptors for this hormone can be found in distinct immune cells (especially macrophages) that are known to be the first line defense against Trypanosoma cruzi infection. These cells operate through an indirect pathway releasing nitric oxide (NO) and cytokines such TNF-α and IL-12 which in turn trigger an enhancement of natural killer cells and lymphocytes which finally secrete pro and anti-inflammatory cytokines. The effects of pre- and post-infection DHEA treatment on production of IL-12, TNFα and NO were evaluated. T. cruzi infected macrophages post treated with DHEA displayed enhanced concentrations of TNF-α, IL-12 and NO. Probably, the mechanisms that induced the production of cytokines by infected cells are more efficient when the immune system has been stimulated first by parasite invasion, suggesting that the protective role of DHEA is greater when administered post infection.

Corticosterone evaluation in Wistar rats infected with the Y strain of Trypanosoma cruzi during the chronic phase.

Understanding the mechanisms responsible for mediating the effects of stress on Trypanosoma cruzi infection is crucial for determining the full impact of stress on Chagas' disease and for devising effective interventions. Dehydroepiandrosterone (DHEA), a steroid hormone synthesized from pregnenolone, is secreted by the adrenal cortex in response to stress. Although its physiologic role has not been fully defined, DHEA has been shown to modulate immune function. In the present study, we evaluated the levels of corticosterone and the ability of T. cruzi infection to modulate the expression of Th2 cytokines in Wistar rats with chronic Chagas' disease submitted to repetitive stress. The animals submitted to stress displayed enhanced levels of corticosterone as compared to control counterparts. Stress and infection triggered the most elevated concentrations of corticosterone. DHEA significantly reduced corticosterone levels for infected and stressed animals with DHEA. The infected animals displayed enhanced levels of IL-10 and IL-4 as compared to control ones. Stress combined with infection triggered the higher levels of IL-10 and IL-4. DHEA alone and combined with infection and stress significantly increased IL-10 and IL-4 levels. Then, this study might provide additional clues about factors that regulate some of the immunoregulatory aspects of T. cruzi infection and might offer new opportunities for therapeutic interventions.

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 host's immune response, reducing blood parasites and the immunosuppressive effects of male androgens besides increasing IL-12 concentrations and decreasing TNF-alpha levels.

Effects of dehydroepiandrosterone-sulfate (DHEA-S) and benznidazole treatments during acute infection of two different Trypanosoma cruzi strains.

A significant role for hormones in regulating the balance of Th1- and Th2-associated cytokines with a role in modulating diseases has been accumulating. Previously, we reported that dehydroepiandrosterone (DHEA), the most abundant steroid hormone synthesized by the adrenal cortex, markedly reduced the blood and tissue parasites in experimentally Trypanosoma cruzi-infected rats. Based on these findings, the main purpose of this study was to investigate the effect of dehydroepiandrosterone-sulfate ester (DHEA-S) therapy alone or in combination with benznidazole (BNZ) (recommended in Brazil for the treatment of T. cruzi infection) will be effective during the acute phase of two different lineages of T. cruzi strains: type I (Y strain) and type II (Bolivia strain) of T. cruzi. Administration of either DHEA-S or BNZ alone or in combination significantly reduced the Y strain parasite load as compared with untreated. Furthermore treatment with DHEA-S resulted in Bolivia strain clearance. This protective effect of DHEA-S was associated with the host's immune response, as evidence by enhanced levels of interferon-gamma and interleukin-2. DHEA-S treatment also increased peritoneal macrophages levels and nitrite production. DHEA-S treatment was effective in reducing the mortality rate as compared to BNZ alone or to combiner DHEA-S+BNZ treatment of T. cruzi Bolivia strain infected animals. These findings suggest that hormonal therapy may have a protective effect in the treatment of T. cruzi infection.

Experimental Chagas' disease in orchiectomized Calomys callosus infected with the CM strain of Trypanosoma cruzi.

The incidence and progression of disorders associated with an unbalanced immune response has among many factors the gender as a contributory factor. The aims of this work were to evaluate the effects of orchiectomy and the immune response during the experimental Trypanosoma cruzi infection. Young adult, male Calomys callous were i.p. inoculated with 1 x 10(5) blood trypomastigotes of the CM strain of T. cruzi and divided in groups: Control, Sham and Castrated. Castrated group displayed significantly lower values for prostate and seminal vesicle weights indicating a drastic drop of testosterone plasmatic levels. Orchiectomized animals also displayed lesser number of blood parasites, enhanced lytic antibody percentage, splenocyte proliferation and NO concentration when compared to its sham and control counterparts, indicating that steroid gonadal ablation actually influences immune response triggering a more efficient cellular and humoral response which led animals to become more resistant against T. cruzi infection.

Trypanosoma cruzi: do different sylvatic strains trigger distinct immune responses?

Strains of Trypanosoma cruzi are multiclonal populations that can be classified in groups or genotypes, differing in pathogenicity, virulence, and histotropism. In this experiment the distinct behavior of two strains of T. cruzi, MORC-1 and MORC-2, was documented. Blood parasitemia, spleen proliferation, nitric oxide, histopathology of the spleen and heart were used as tools to evaluate parasite persistence. Groups of male mice were separated and divided in three groups: Control (C), Infected (IM-1) and Infected (IM-2). The peak of parasitemia occurred on 10days post infection for both strains. LPS stimulated animals, infected MORC-2 group displayed significant higher concentrations of NO when compared to infected MORC-1 group (P<0.05). For ConA stimulated lymphoproliferation, infected MORC-1 group displayed higher proliferation index as compared to infected MORC-2 group. An opposite behavior for IL-4 and TNF-alpha was observed according to the strain. For MORC-1 enhanced concentrations of IL-4 were present with concomitant reduced levels of TNF-alpha, while for MORC-2 enhanced concentrations of TNF-alpha and reduced levels of IL-4 were found. The histopathology of heart and spleen showed important differences in which MORC-1 displayed statistically enhanced number of amastigote in the heart and spleen as compared to MORC-2. Concluding, each strain triggered a distinct immune response with enhanced cytokine TH-1 profile for MORC-2 and TH-2 for MORC-1.

Immunomodulatory effects of zinc and DHEA on the Th-1 immune response in rats infected with Trypanosoma cruzi.

Chagas' disease is considered the sixth most important neglected tropical disease worldwide. Considerable knowledge has been accumulated concerning the role of zinc on cellular immunity. The steroid hormone dehydroepiandrosterone (DHEA) is also known to modulate the immune system. The aims of this paper were to investigate a possible synchronization of their effects on cytokines and NO production and the resistance to Trypanosoma cruzi during the acute phase of infection. It was found that zinc, DHEA or zinc and DHEA supplementation enhanced the immune response, as evidenced by a significant reduction in parasitemia levels. Zinc and DHEA supplementation exerted additive effects on the immune response by elevation of macrophage counts, and by increasing concentrations of IFN-gamma and NO.

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

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 microm). 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.