Alterations of serum lipid, lipoprotein and inflammatory cytokine profiles of rabbits infected with Trypanosoma brucei brucei

Pathogenicity and virulence of African trypanosomes: From laboratory models to clinically relevant hosts

African trypanosomes are vector-borne protozoa, which cause significant human and animal disease across sub-Saharan Africa, and animal disease across Asia and South America. In humans, infection is caused by variants of Trypanosoma brucei, and is characterized by varying rate of progression to neurological disease, caused by parasites exiting the vasculature and entering the brain. Animal disease is caused by multiple species of trypanosome, primarily T. congolense, T. vivax, and T. brucei. These trypanosomes also infect multiple species of mammalian host, and this complexity of trypanosome and host diversity is reflected in the spectrum of severity of disease in animal trypanosomiasis, ranging from hyperacute infections associated with mortality to long-term chronic infections, and is also a main reason why designing interventions for animal trypanosomiasis is so challenging. In this review, we will provide an overview of the current understanding of trypanosome determinants of infection progression and severity, covering laboratory models of disease, as well as human and livestock disease. We will also highlight gaps in knowledge and capabilities, which represent opportunities to both further our fundamental understanding of how trypanosomes cause disease, as well as facilitating the development of the novel interventions that are so badly needed to reduce the burden of disease caused by these important pathogens.

Evaluation of clinical signs, parasitemia, hematologic and biochemical changes in cattle experimentally infected with Trypanosoma vivax

Abstract Infections by Trypanosoma vivax cause great losses to livestock in Africa and Central and South Americas. Outbreaks due this parasite have been occurred with increasing frequency in Brazil. Knowledge of changes caused byT. vivax during the course of this disease can be of great diagnostic value. Thus, clinical signs, parasitemia, hematologic and biochemical changes of cattle experimentally infected by this hemoparasite were evaluated. Two distinct phases were verified during the infection – an acute phase where circulating parasites were seen and then a chronic phase where fluctuations in parasitemia were detected including aparasitemic periods. A constant reduction in erythrocytes, hemoglobin and packed cell volume (PVC) were observed. White blood cells (WBC) showed pronounced changes such as severe neutropenia and lymphopenia during the acute phase of the illness. Decreases in cholesterol, albumin, aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and increases in glucose, globulin, protein, and alkaline phosphatase (ALP) were observed. The “Lins” isolate of T. vivax showed pathogenicity for cattle, and intense parasitemia was detected in the early stages of infection. Circulating parasites were detected for about two months. The most evident laboratory abnormalities were found in WBC parameters, including thrombocytopenia.

Discovery of Infection Associated Metabolic Markers in Human African Trypanosomiasis

Human African trypanosomiasis (HAT) remains a major neglected tropical disease in Sub-Saharan Africa. As clinical symptoms are usually non-specific, new diagnostic and prognostic markers are urgently needed to enhance the number of identified cases and optimise treatment. This is particularly important for disease caused by Trypanosoma brucei rhodesiense, where indirect immunodiagnostic approaches have to date been unsuccessful. We have conducted global metabolic profiling of plasma from T.b.rhodesiense HAT patients and endemic controls, using 1H nuclear magnetic resonance (NMR) spectroscopy and ultra-performance liquid chromatography, coupled with mass spectrometry (UPLC-MS) and identified differences in the lipid, amino acid and metabolite profiles. Altogether 16 significantly disease discriminatory metabolite markers were found using NMR, and a further 37 lipid markers via UPLC-MS. These included significantly higher levels of phenylalanine, formate, creatinine, N-acetylated glycoprotein and triglycerides in patients relative to controls. HAT patients also displayed lower concentrations of histidine, sphingomyelins, lysophosphatidylcholines, and several polyunsaturated phosphatidylcholines. While the disease metabolite profile was partially consistent with previous data published in experimental rodent infection, we also found unique lipid and amino acid profile markers highlighting subtle but important differences between the host response to trypanosome infections between animal models and natural human infections. Our results demonstrate the potential of metabolic profiling in the identification of novel diagnostic biomarkers and the elucidation of pathogenetic mechanisms in this disease.

Serum concentrations of eicosanoids and lipids in dogs naturally infected with Babesia canis

Canine babesiosis is a tick-borne disease with world-wide significance caused by intraerythrocytic protozoa of the genus Babesia. The eicosanoids, as inflammatory mediators, are involved in the regulation of the immune response and inflammatory reaction. Metabolism of lipids is of great importance in babesiosis. In this study it was aimed to investigate the dynamics of serum concentration of prostaglandin E2 (PGE2), thromboxane B2 (TxB2), leukotriene B4 (LTB4), triglycerides, total cholesterol (Chol), HDL- and LDL-cholesterol in dogs naturally infected with Babesia canis and healthy dogs. Both groups were measured for all parameters on the admission day and on the first, second and seventh day of the disease. Dogs that were included in this study had systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS). It was demonstrated that the level of LTB4, PGE2, TxB2 in dogs naturally infected with B. canis significantly changed during the disease. The level of LTB4 was significantly higher during the study, while the concentration of PGE2 was significantly higher second, third and seventh day of disease in relation with healthy dogs. The level of TxB2 was significantly lower at the beginning of the disease, but after seven days concentration was significantly higher. Both group of patients with SIRS and MODS had significantly higher level of LTB4. Substained high concentrations of PGE2 were observed in dogs with MODS after therapy but not in dogs with SIRS, and LTB4 followed a similar tendency. On the other hand, increases in TxB2 were only significant in dogs with SIRS. The lipid profile in naturally infected dogs with B. canis infection was significantly changed. Further studies are needed to assess the prognostic values of lipid mediators in dogs with B. canis infection, and the ability of these markers to predict the progress of SIRS and MODS.

Hyperlipidaemia in trypanosomiasis of naturally infected horses: possible cachexia-anorexia syndrome?

Trypanosomiasis caused by Trypanosoma evansi commonly produces wasting disease with signs of emaciation and cachexia mainly at the end stage. The present study was conducted to explore the possible hyperlipaemia or hyperlipidaemia and its association with cachexia-anorexia in equine trypanosomiasis. Out of the fifteen confirmed animals, none of the plasma sample was opaque. There was a significant increase in plasma triglyceride, total cholesterol and blood urea nitrogen and a highly significant increase in low-density lipoprotein (LDL) levels. A mild increase in high-density lipoprotein (HDL) and very low-density lipoprotein levels were observed, while the relative percentage of HDL and LDL was altered with high significance. A moderate increase in triglyceride and highly significant increase in LDL might be the reasons for retention of appetite and lipolysis. Possible protein breakdown and presence of lipolysis might be the reasons for cachexia in equine trypanosomiasis.

Alternatively activated myeloid cells limit pathogenicity associated with African trypanosomiasis through the IL-10 inducible gene selenoprotein P

Uncontrolled inflammation is a major cause of tissue injury/pathogenicity often resulting in death of a host infected with African trypanosomes. Thus, comparing the immune response in hosts that develop different degrees of disease severity represents a promising approach to discover processes contributing to trypanosomiasis control. It is known that limitation of pathogenicity requires a transition in the course of infection, from an IFN-gamma-dependent response resulting in the development of classically activated myeloid cells (M1), to a counterbalancing IL-10-dependent response associated with alternatively activated myeloid cells (M2). Herein, mechanisms and downstream effectors by which M2 contribute to lower the pathogenicity and the associated susceptibility to African trypanosomiasis have been explored. Gene expression analysis in IL-10 knockout and wild-type mice, that are susceptible and relatively resistant to Trypanosoma congolense infection, respectively, revealed a number of IL-10-inducible genes expressed by M2, including Sepp1 coding for selenoprotein P. Functional analyses confirm that selenoprotein P contributes to limit disease severity through anti-oxidant activity. Indeed, Sepp1 knockout mice, but not Sepp1(Delta)(240-361) mice retaining the anti-oxidant motif but lacking the selenium transporter domain of selenoprotein P, exhibited increased tissue injury that associated with increased production of reactive oxygen species and increased apoptosis in the liver immune cells, reduced parasite clearance capacity of myeloid cells, and decreased survival. These data validate M2-associated molecules as functioning in reducing the impact of parasite infection on the host.

Alterations triggered by steroid gonadal hormones in triglycerides and the cellular immune response of Calomys callosus infected with the Y strain of Trypanosoma cruzi

Calomys callosus is a wild rodent found naturally infected with different Trypanosoma cruzi strains. In the work described here, groups of male and female C. callosus were subjected to orchiectomy, ovariectomy and sham operation. One month after surgery, animals were inoculated intraperitoneally (i.p.) with 4x10(4) blood trypomastigotes of the "Y" strain of T. cruzi. Parasitemia, triglycerides, nitric oxide (NO) and concanavalin A (ConA)-induced proliferation were evaluated. Parasitemia during the course of infection was significantly higher in infected and sham operated animals as compared to infected orchiectomized animals. The opposite was observed in the ovariectomized and infected group. Orchiectomized and infected animals displayed elevated triglyceride levels, as well as a more vigorous immune response, with higher splenocyte proliferation and elevated concentrations of NO. Ovariectomy resulted in an impaired immune response, as observed by a reduction of splenocyte proliferation and NO concentration. The results suggest a pivotal role for gonadal hormones in the modulation of triglyceride levels and the magnitude of the immune response during the acute phase of T. cruzi infection.

Intraventricular infusion of antagonists of IL-1 and TNF alpha attenuates neurodegeneration induced by the infection of Trypanosoma brucei

Infection of Trypanosoma brucei causes specific patterns of neurodegeneration in association with chronic expression of proinflammatory cytokines in the brain. To investigate whether the induction of proinflammatory cytokines contributed to the observe pathology in this disease, we infected rats with T. brucei and treated them with intracerebral infusion of the cytokine antagonists interleukin-1 receptor antagonist (IL-1ra) and/or soluble type-I receptor of the tumor necrosis factor (sTNFr1). Infusion of IL-1ra, not sTNFr1, restored the reduction of body weight gain induced by the infection. Infusion of IL-1ra+sTNFr1 reduced the expression of IL-1beta and the cytokine response gene IkappaBalpha, but not TNFalpha. Infusion of sTNFr1 reduced trypanosome-induced neurodegeneration. Further reduction of neurodegeneration was seen after IL-1ra+sTNFr1 infusion. Infusion of IL-1ra alone, however, did not significantly affect the patterns of neurodegeneration. These results suggest that TNFalpha is a major mediator for trypanosome-induced neurodegeneration although its neurotoxic effects can be augmented by IL-1.

Hypolipemia associated with the wasting condition of rabbits infected with Strongyloides papillosus

Rabbits develop a wasting condition in the intestinal stage of Strongyloides papillosus infection. Serum inflammatory cytokine and lipid profiles were investigated in five rabbits infected with S. papillosus and five uninfected pair-fed controls to ascertain whether the disease is inflammatory cytokine-mediated cachexia. Tumor necrosis factor alpha (TNF alpha) was detected in one infected animal at Day 7 after infection. Interleukin (IL)-1 was detected in three infected, and one control, animals at Day 28. IL-6 remained unchanged in both the groups. Infected animals developed hypolipemia, including hypotriglyceridemia in the intestinal stage of infection. Control animals lost body weight in the same manner as the infected animals, but had elevated cholesterols and phospholipids with normal triglyceride concentrations. The results suggested that the wasting condition has no association with cachexia induced by TNF alpha. IL-1 or IL-6, and that hepatic function for lipid synthesis is affected during the intestinal stage of S. papillosus infection.

Induction of tumor necrosis factor alpha and nitric oxide in rabbits inoculated with a cyst extract of Sarcocystis cruzi

Rabbits develop a toxic reaction similar to endotoxemia following inoculation with a Sarcocystis cruzi cyst extract. To analyze the pathophysiology of the reaction, serum tumor necrosis factor alpha (TNFalpha), nitric oxide (NO) and lipid-lipoprotein profiles were investigated in rabbits given the cyst extract and lipopolysaccharide (LPS) by subcutaneous inoculation. In animals given the cyst extract, overproduction of TNFalpha was detected, together with an increase in NO. The animals developed derangement of lipid metabolism, which was considered to have resulted from TNFalpha induction, consisting of elevated triglyceride and very low density lipoprotein levels and decreased high density lipoprotein (HDL) levels. Serum interleukin-6-like activity also increased transiently in the animals. Capability of the cyst extract to induce TNFalpha, NO and the lipid profile derangement were completely lost by boiling. In animals given LPS, TNFalpha was induced and HDL decreased moderately, without inactivation of those activities of LPS by boiling. These results indicated that S. cruzi cyst extract is a potent, but thermolabile inducer of TNFalpha and NO for rabbits. It is likely that TNFalpha and NO play important roles as mediators in the reaction associated with toxicity of the cyst extract in rabbits.