The relationships between endotoxins, nitric oxide and inflammatory cytokines in blood and intestinal tissues in experimental Trypanosoma brucei brucei infections

Trypanosoma brucei metabolite indolepyruvate decreases HIF-1α and glycolysis in macrophages as a mechanism of innate immune evasion

The parasite Trypanasoma brucei causes African trypanosomiasis, known as sleeping sickness in humans and nagana in domestic animals. These diseases are a major burden in the 36 sub-Saharan African countries where the tsetse fly vector is endemic. Untreated trypanosomiasis is fatal and the current treatments are stage-dependent and can be problematic during the meningoencephalitic stage, where no new therapies have been developed in recent years and the current drugs have a low therapeutic index. There is a need for more effective treatments and a better understanding of how these parasites evade the host immune response will help in this regard. The bloodstream form of T. brucei excretes significant amounts of aromatic ketoacids, including indolepyruvate, a transamination product of tryptophan. This study demonstrates that this process is essential in bloodstream forms, is mediated by a specialized isoform of cytoplasmic aminotransferase and, importantly, reveals an immunomodulatory role for indolepyruvate. Indolepyruvate prevents the LPS-induced glycolytic shift in macrophages. This effect is the result of an increase in the hydroxylation and degradation of the transcription factor hypoxia-inducible factor-1α (HIF-1α). The reduction in HIF-1α levels by indolepyruvate, following LPS or trypanosome activation, results in a decrease in production of the proinflammatory cytokine IL-1β. These data demonstrate an important role for indolepyruvate in immune evasion by T. brucei.

Haemato-biochemical and oxidative status of buffaloes naturally infected with Trypanosoma evansi

Blood samples were collected from 05 clinically healthy and 10 adult female water buffaloes naturally infected with Trypanosoma evansi. Confirmation of disease free and infected status of buffaloes was made on clinical signs, observation of T. evansi parasites in the blood smear and duplex PCR based assay. Blood samples were evaluated for levels of haemoglobin (Hb), packed cell volume (PCV), differential leucocytes count (DLC), lipid peroxidation (LPO), calcium, phosphorous, magnesium sodium and potassium and activities of superoxide dismutase (SOD), catalase (CAT), aspartate transaminase (AST), lactate dehydogenase (LDH) and alkaline phosphatase (ALP). The results of the study revealed substantial decrease in levels of Hb, PCV and increase in LPO, SOD, CAT and AST in infected animals compared to healthy animals. However other haematological and biochemical indices did not show significant variations in infected and healthy buffaloes. The enhanced erythrocytic oxidation and reduction of hematological indices, suggests that the enhanced oxidation of the erythrocytes may be a contributory factor in erythrocytic destruction and progression of the anaemia in T. evansi infection in water buffaloes.

Pathogenic mechanisms of Trypanosoma evansi infections

Insect-borne diseases exact a high public health burden and have a devastating impact on livestock and agriculture. To date, control has proved to be exceedingly difficult. One such disease that has plagued sub-Saharan Africa is caused by the protozoan African trypanosomes (Trypanosoma species) and transmitted by tsetse flies (Diptera: Glossinidae). This presentation describes Trypanosoma evansi (T. evansi) which causes the disease known as trypanosomosis (Surra) or trypanosomiasis in which several attempts have being made to unravel the clinical pathogenic mechanisms in T. evansi infections, yielding various reports which have implicated hemolysis associated to decrease in life span of erythrocytes and extensive erythrophagocytosis being among those that enjoy prominence. T. evansi generates Adenosine Triphosphate (ATP) from glucose catabolism which is required for the parasite motility and survival. Oxidation of the erythrocytes induces oxidative stress due to free radical generation. Lipid peroxidation of the erythrocytes causes membrane injury, osmotic fragility and destruction of the red blood cell (RBC) making anemia a hallmark of the pathology of T. evansi infections.

Secondary bacterial infection in plasma endotoxin levels and the acute-phase response of mice infected with Trypanosoma brucei brucei

Murine Trypanosoma brucei brucei infection leads to elevated plasma endotoxin-like activity levels not related to parasitaemia levels accompanied by the development of acute-phase response and increased plasma levels of serum amyloid P (SAP) and haptoglobin (Hp). To determine the source of the endotoxin-like activity and role of secondary bacterial infection in the pathogenesis of trypanosomosis, infected mice were treated with the antibiotic ciprofloxacin. Plasma endotoxin-like activity levels, irrespective of treatment, were elevated three- to fourfold, beginning 7 days after infection. Plasma protein concentrations increased markedly following infection from 7 days after infection (DAI). Peak Hp and SAP concentrations in ciprofloxacin-treated and -untreated infected mice were attained 7 and 14 DAI, respectively. Thereafter, both protein levels gradually declined until the end of the experiment, but Hp levels for non-treated mice declined up to 21 DAI and thereafter significantly increased on 28 and 35 DAI. Whole-trypanosome lysate and the membrane-enriched fraction demonstrated endotoxin-like activity, with the former having higher levels. The results suggest that the endotoxin-like activity in trypanosome fractions and plasma of infected mice is due to the trypanosome. Further elevation of haptoglobin during the late stages of infection in non-treated mice suggests the involvement of secondary bacterial infection.

Acute phase response in mice experimentally infected with Trypanosoma congolense: a molecular gauge of parasite-host interaction

Mice infected with Trypanosoma congolense developed a severe anaemia 1 week after infection, which persisted till treatment with diminazine aceturate when the packed cell volume (PCV) recovered to pre-infection levels. This was accompanied by a marked increase in the plasma levels of the acute phase proteins (APP), serum amyloid P-component (SAP) and haptoglobin (Hp). The initial peak levels of Hp and SAP were attained 7 and 12 days post-infection (DPI), respectively. Thereafter SAP levels decreased significantly to near pre-infection levels, but later increased even after treatment to give a second peak 34 DPI after which there was a decline till the study was terminated. The Hp levels on the other hand decreased to an intermediate level after the initial peak increasing to a second peak 22 DPI. Thereafter Hp decreased significantly following diminazine aceturate treatment to reach pre-infection levels within 5 days post-treatment. This indicates that T. congolense-infected mice develop severe anaemia accompanied by an acute phase response leading to an increase in SAP and Hp but that following treatment divergent responses occurred indicating differences in the pathways for stimulation of the APP. Haptoglobin was shown to be an earlier indicator of infection and a better marker in monitoring the response to treatment.

Endothelial cell activation in the presence of African trypanosomes

During human African trypanosomiasis, trypanosomes (Trypanosoma brucei gambiense or T. b. rhodesiense) invade the central nervous system (CNS). Mechanisms of blood-brain barrier and blood-cerebrospinal fluid barrier leakage remain unknown. To better understand the relationships between trypanosomes and endothelial cells, the principal cell population of those barriers, we cultured a human bone marrow endothelial cell (HBMEC) line in the presence or absence of T. b. gambiense, to study cell activation. As indicated by NF-kappaB translocation to the nucleus, cells were activated in the presence of trypanosomes. The expression of the adhesion molecules ICAM-1, E-selectin and VCAM-1 increased in co-culture. The parasites induced the synthesis of the pro-inflammatory cytokines TNF-alpha, IL-6 and IL-8, and of nitric oxide (NO) by HBMEC. Cells were also cultured in the presence of parasite variant surface glycoproteins (VSGs), and an increase in TNF-alpha, IL-6, IL-8, and NO synthesis was also observed. Soluble VSGs induced NF-kappaB translocation, and the expression of adhesion molecules, indicating that they could possibly be the molecular soluble factor responsible for endothelial cell activation. The permeability coefficient of HBMEC layer increased when cells were cultured in the presence of trypanosomes, parasite culture supernatant, or VSGs. Thus, T. b. gambiense can activate endothelial cells in vitro, through the release of soluble activating factors. Consequences of endothelial cell activation by parasite products may include a potentiation of the inflammatory reaction, leukocyte recruitment, passage of trypanosomes into the CNS, and barrier dysfunction observed during CNS involvement of HAT.

Mast cells, histamine and the pathogenesis of intestinal damage in experimental Trypanosoma brucei brucei infections

Intestinal damage with increased permeability is a prominent feature of experimental African trypanosomiasis. The possible involvement of mast cells and histamine in the altered gut integrity was investigated, at the level of the jejunum, in BALB/c mice infected with Trypanosoma brucei brucei. Mast cells were studied by selective staining of granule content with Alcian Blue/Safranin and quantitative histology, and histamine concentrations were determined by a fluorimetric method. Mast-cell activation, shown by a marked reduction in the numbers of positive-staining cells seen per villous section, was prominent on days 7 and 14 post-infection (there was, for example, a reduction to 36% of the control value by day 14; P=0.0001). By day 21, however, there were 131% more staining cells per villous section in the infected mice than in the uninfected controls (P=0.003). Histamine levels in homogenates of the jejunal mucosae of the infected mice were found to be significantly elevated at each time-point. The maximum increase was observed on day 14, when the numbers of granulated mast cells were at their lowest, with mean (S.E.) concentrations of 6.744 (0.890) ng/mg tissue for the infected mice and 2.813 (0.321) ng/mg for the uninfected controls (P=0.0008). The jejunal mucosa suffered progressive morphological damage during the infection, with oedema of the lamina propria and villi and disruption of the endothelium. These results indicate that mast cells are involved with the intestinal pathology that develops during experimental African trypanosomiasis.

Trypanosome apoptotic factor mediates apoptosis in human brain vascular endothelial cells

Human African trypanosomiasis (HAT, sleeping sickness) is a devastating disease caused by infection with Trypanosoma brucei ssp. These hemoflagellates invade the central nervous system (CNS) and induce meningo-encephalitis, neuronal demyelination, blood-brain-barrier (BBB) dysfunction, peri-vascular infiltration, astrocytosis and apoptosis. The molecular basis of these manifestations is unclear. We previously reported T. brucei-induced apoptosis in cerebella and brain-stem nuclei in mice at peak parasitemia. Here, we identify and characterize a trypanosome apoptotic factor (TAF) expressed by T. brucei that mediates apoptosis in mouse-brain and human-brain vascular endothelial cells (HBVEC). Molecular, biochemical and apoptotic assays, coupled with surface enhanced laser desorption ionization (SELDI), and protein database analyses were utilized to show that TAF is a soluble, non-serum, parasite-derived, heat-labile protein that causes DNA laddering and apoptosis in HBVEC. Protein-chip assay analysis of the SELDI spectrum of infected mouse serum and procyclic culture supernatants revealed a single major peak at 8652.7 Da. Further database analysis indicated that the TAF may be a procyclin or procyclin derivative. A synthetic 27 mer peptide (ProEP2-1), corresponding to a region common to EP procyclins (EP2-1), induced apoptosis in HBVEC and in cerebella of mice similar to that induced in T. brucei-infected mice. Western blot analysis utilizing an anti-procyclin monoclonal antibody (mAb) revealed that TAF is present in infected but not uninfected brain tissue lysates. Furthermore, this mAb blocked T. brucei- and ProEP2-1-induced apoptosis in HBVEC in vitro. We conclude that T. brucei TAF or its derivative(s) play a major role in the apoptosis associated with HAT pathology.

Enhanced endothelial nitric oxide-synthase activity in mice infected with Trypanosoma brucei

Infection of humans with Trypanosoma brucei causes sleeping sickness, which is invariably fatal if left untreated. The course of infection is characterised, among others, by multiple organ damage including cardiovascular dysfunctions such as hypotension and breakdown of the blood-brain barrier. The latter eventually leads to the parasite invasion into central nervous system and ultimately to the death of the patient. Nitric oxide (NO) synthesised from L-arginine via endothelial NO-synthase (eNOS) is involved in the control of vascular tone and permeability. The present study explores the effect of T. brucei infection on the endothelium-dependent in vitro vasomotor response of isolated mouse aortas. Aorta rings were suspended in organ chambers for isometric tension recording. The endothelium-dependent NO-mediated relaxation in response to acetylcholine (10(-9) to 10(-5) M) was markedly enhanced in the infected mice compared to controls (P<0.05), whereas the endothelium-independent vasodilation to an exogenous NO-donor, sodium nitroprusside, was comparable in both groups. Norepinephrine-stimulated contraction was also comparable in the absence or presence of the NO-synthase inhibitor N(omega)-Nitro-L-arginine methyl ester (L-NAME; 10(-4)M) in both groups. The enhanced endothelium-dependent relaxation in the infected mice correlated well with a 3.5-fold increase in eNOS protein level in these aortas as compared to those of control mice (P=0.05). Thus, T. brucei infection enhances eNOS protein expression in the endothelium, causing a pronounced vasodilation. Overproduction of NO in trypanosomiasis may be involved in the observed generalised hypotension and in an increased vascular permeability that facilitates T. brucei invasion into surrounding tissues and its penetration into the central nervous system in later phases of infection.