Physiologic Targets and Modes of Action for CBL0137, a Lead for Human African Trypanosomiasis Drug Development

CBL0137 is a lead drug for human African trypanosomiasis, caused by Trypanosoma brucei Herein, we use a four-step strategy to 1) identify physiologic targets and 2) determine modes of molecular action of CBL0137 in the trypanosome. First, we identified fourteen CBL0137-binding proteins using affinity chromatography. Second, we developed hypotheses of molecular modes of action, using predicted functions of CBL0137-binding proteins as guides. Third, we documented effects of CBL0137 on molecular pathways in the trypanosome. Fourth, we identified physiologic targets of the drug by knocking down genes encoding CBL0137-binding proteins and comparing their molecular effects to those obtained when trypanosomes were treated with CBL0137. CBL0137-binding proteins included glycolysis enzymes (aldolase, glyceraldehyde-3-phosphate dehydrogenase, phosphofructokinase, phosphoglycerate kinase) and DNA-binding proteins [universal minicircle sequence binding protein 2, replication protein A1 (RPA1), replication protein A2 (RPA2)]. In chemical biology studies, CBL0137 did not reduce ATP level in the trypanosome, ruling out glycolysis enzymes as crucial targets for the drug. Thus, many CBL0137-binding proteins are not physiologic targets of the drug. CBL0137 inhibited 1) nucleus mitosis, 2) nuclear DNA replication, and 3) polypeptide synthesis as the first carbazole inhibitor of eukaryote translation. RNA interference (RNAi) against RPA1 inhibited both DNA synthesis and mitosis, whereas RPA2 knockdown inhibited mitosis, consistent with both proteins being physiologic targets of CBL0137. Principles used here to distinguish drug-binding proteins from physiologic targets of CBL0137 can be deployed with different drugs in other biologic systems. SIGNIFICANCE STATEMENT: To distinguish drug-binding proteins from physiologic targets in the African trypanosome, we devised and executed a multidisciplinary approach involving biochemical, genetic, cell, and chemical biology experiments. The strategy we employed can be used for drugs in other biological systems.

Iboga Inspired N-Indolylethyl-Substituted Isoquinuclidines as a Bioactive Scaffold: Chemoenzymatic Synthesis and Characterization as GDNF Releasers and Antitrypanosoma Agents

The first stage of the drug discovery process involves the identification of small compounds with biological activity. Iboga alkaloids are monoterpene indole alkaloids (MIAs) containing a fused isoquinuclidine-tetrahydroazepine ring. Both the natural products and the iboga-inspired synthetic analogs have shown a wide variety of biological activities. Herein, we describe the chemoenzymatic preparation of a small library of novel N-indolylethyl-substituted isoquinuclidines as iboga-inspired compounds, using toluene as a starting material and an imine Diels-Alder reaction as the key step in the synthesis. The new iboga series was investigated for its potential to promote the release of glial cell line-derived neurotrophic factor (GDNF) by C6 glioma cells, and to inhibit the growth of infective trypanosomes. GDNF is a neurotrophic factor widely recognized by its crucial role in development, survival, maintenance, and protection of dopaminergic neuronal circuitries affected in several neurological and psychiatric pathologies. Four compounds of the series showed promising activity as GDNF releasers, and a leading structure (compound 11) was identified for further studies. The same four compounds impaired the growth of bloodstream Trypanosoma brucei brucei (EC₅₀ 1-8 μM) and two of them (compounds 6 and 14) showed a good selectivity index.

Chemical Derivatization and Characterization of Novel Antitrypanosomals for African Trypanosomiasis

The search for novel antitrypanosomals and the investigation into their mode of action remain crucial due to the toxicity and resistance of commercially available antitrypanosomal drugs. In this study, two novel antitrypanosomals, tortodofuordioxamide (compound 2) and tortodofuorpyramide (compound 3), were chemically derived from the natural N-alkylamide tortozanthoxylamide (compound 1) through structural modification. The chemical structures of these compounds were confirmed through spectrometric and spectroscopic analysis, and their in vitro efficacy and possible mechanisms of action were, subsequently, investigated in Trypanosoma brucei (T. brucei), one of the causative species of African trypanosomiasis (AT). The novel compounds 2 and 3 displayed significant antitrypanosomal potencies in terms of half-maximal effective concentrations (EC₅₀) and selectivity indices (SI) (compound 1, EC₅₀ = 7.3 μM, SI = 29.5; compound 2, EC₅₀ = 3.2 μM, SI = 91.3; compound 3, EC₅₀ = 4.5 μM, SI = 69.9). Microscopic analysis indicated that at the EC₅₀ values, the compounds resulted in the coiling and clumping of parasite subpopulations without significantly affecting the normal ratio of nuclei to kinetoplasts. In contrast to the animal antitrypanosomal drug diminazene, compounds 1, 2 and 3 exhibited antioxidant absorbance properties comparable to the standard antioxidant Trolox (Trolox, 0.11 A; diminazene, 0.50 A; compound 1, 0.10 A; compound 2, 0.09 A; compound 3, 0.11 A). The analysis of growth kinetics suggested that the compounds exhibited a relatively gradual but consistent growth inhibition of T. brucei at different concentrations. The results suggest that further pharmacological optimization of compounds 2 and 3 may facilitate their development into novel AT chemotherapy.

Novel aspects of iron homeostasis in pathogenic bloodstream form Trypanosoma brucei

Iron is an essential regulatory signal for virulence factors in many pathogens. Mammals and bloodstream form (BSF) Trypanosoma brucei obtain iron by receptor-mediated endocytosis of transferrin bound to receptors (TfR) but the mechanisms by which T. brucei subsequently handles iron remains enigmatic. Here, we analyse the transcriptome of T. brucei cultured in iron-rich and iron-poor conditions. We show that adaptation to iron-deprivation induces upregulation of TfR, a cohort of parasite-specific genes (ESAG3, PAGS), genes involved in glucose uptake and glycolysis (THT1 and hexokinase), endocytosis (Phosphatidic Acid Phosphatase, PAP2), and most notably a divergent RNA binding protein RBP5, indicative of a non-canonical mechanism for regulating intracellular iron levels. We show that cells depleted of TfR by RNA silencing import free iron as a compensatory survival strategy. The TfR and RBP5 iron response are reversible by genetic complementation, the response kinetics are similar, but the regulatory mechanisms are distinct. Increased TfR protein is due to increased mRNA. Increased RBP5 expression, however, occurs by a post-transcriptional feedback mechanism whereby RBP5 interacts with its own, and with PAP2 mRNAs. Further observations suggest that increased RBP5 expression in iron-deprived cells has a maximum threshold as ectopic overexpression above this threshold disrupts normal cell cycle progression resulting in an accumulation of anucleate cells and cells in G2/M phase. This phenotype is not observed with overexpression of RPB5 containing a point mutation (F61A) in its single RNA Recognition Motif. Our experiments shed new light on how T. brucei BSFs reorganise their transcriptome to deal with iron stress revealing the first iron responsive RNA binding protein that is co-regulated with TfR, is important for cell viability and iron homeostasis; two essential processes for successful proliferation.

Drug reformulation for a neglected disease. The NANOHAT project to develop a safer more effective sleeping sickness drug

Background

Human African trypanosomiasis (HAT or sleeping sickness) is caused by the parasite Trypanosoma brucei sspp. The disease has two stages, a haemolymphatic stage after the bite of an infected tsetse fly, followed by a central nervous system stage where the parasite penetrates the brain, causing death if untreated. Treatment is stage-specific, due to the blood-brain barrier, with less toxic drugs such as pentamidine used to treat stage 1. The objective of our research programme was to develop an intravenous formulation of pentamidine which increases CNS exposure by some 10–100 fold, leading to efficacy against a model of stage 2 HAT. This target candidate profile is in line with drugs for neglected diseases inititative recommendations.

Methodology

To do this, we evaluated the physicochemical and structural characteristics of formulations of pentamidine with Pluronic micelles (triblock-copolymers of polyethylene-oxide and polypropylene oxide), selected candidates for efficacy and toxicity evaluation in vitro, quantified pentamidine CNS delivery of a sub-set of formulations in vitro and in vivo, and progressed one pentamidine-Pluronic formulation for further evaluation using an in vivo single dose brain penetration study.

Principal Findings

Screening pentamidine against 40 CNS targets did not reveal any major neurotoxicity concerns, however, pentamidine had a high affinity for the imidazoline₂ receptor. The reduction in insulin secretion in MIN6 β-cells by pentamidine may be secondary to pentamidine-mediated activation of β-cell imidazoline receptors and impairment of cell viability. Pluronic F68 (0.01%w/v)-pentamidine formulation had a similar inhibitory effect on insulin secretion as pentamidine alone and an additive trypanocidal effect in vitro. However, all Pluronics tested (P85, P105 and F68) did not significantly enhance brain exposure of pentamidine.

Significance

These results are relevant to further developing block-copolymers as nanocarriers, improving BBB drug penetration and understanding the side effects of pentamidine.

Sleeping sickness or human African Trypanosomiasis (HAT) is a disease caused by a parasite, which is transferred to humans by the bite of an infected tsetse fly. There are two disease stages: the first stage is the blood-based stage of the disease and the second stage affects the brain. It is fatal if left untreated. The blood-brain barrier (BBB) makes the brain stage difficult to treat because it prevents 99% of all drugs from entering the brain from the blood. Those anti-HAT drugs that do enter the brain are toxic and have serious side effects. Pentamidine is a less toxic blood stage drug, which our research has shown has a limited ability to cross the BBB due to its removal by proteins called transporters. The objective of this study was to use Pluronic to improve pentamidine delivery to target sites, whilst reducing its side effects. Pluronic is a polymer, which can assemble into micelles and encapsulate the drug. Thus, prolonging its circulation time and protecting it. Our study indicated that the selected Pluronics did not increase the brain delivery of pentamidine. However. Pluronic-pentamidine formulations were identified that harboured trypanocidal activity and did not increase safety concerns compared to unformulated pentamidine.

Chemical characterization of Saudi propolis and its antiparasitic and anticancer properties

Propolis, is a gummy material produced by honey bees from different parts of plants and is enriched with varied biological active compounds like flavonoids, phenolics and phenolic acids with wide applicability in the food, pharmaceutical and cosmetics industries. The current report is focused on the characterisation of propolis collected from Asir region, South-west of Saudi Arabia and its effect on Trypanosoma brucei (the causative organism of African sleeping sickness) and cytotoxic effect against U937 human leukemia cells. The Chemical composition and spectral characteristics of Saudi propolis was studied by Liquid Chromatography Mass Spectrometry (LC-MS) and High-performance liquid chromatography-evaporative light scattering detector (HPLC-ELSD).The two main active compounds isolated from Saudi propolis via column chromatography and size exclusion chromatography were fisetinidol and ferulic acid. High resolution electrospray ionization-mass spectrophotometer (HRESI-MS) and nuclear magnetic resonance (NMR) were used to elucidate the structures of the isolated compounds. All crudes extracts, fractions as well as isolated compounds were subjected for biological testing against Trypanosoma brucei (S427 WT), and their cytotoxicity against U937 human leukemia cells. Amongst the various samples investigated, S-6 fraction demonstrated highest anti-trypanosomal activity at 2.4 µg/ml MIC followed by fisetinidol at 4.7 µg/ml reflecting that the anti-trypanosomal activity is attributable to the presence of fisetinidol in the fraction. Similarly, all the tested samples exhibited cytotoxicity with an IC50 > 60 µg/ml. S-6 fractions exhibited highest cytotoxic activity against U937 cells with an IC50 of 58.7 µg/ml followed by ferulic acid with an IC50 87.7 µg/ml indicating that the cytotoxic effect of propolis might be due to the presence of ferulic acid. In conclusion, the biological activity of propolis could be attributed to the synergistic action of the two active compounds-ferulic acid and fisetinidol. The data obtained in the study is thus indicative of the role of propolis as potential anti-trypanosomal and anticancer agent for effective cancer therapy.

Fast acting allosteric phosphofructokinase inhibitors block trypanosome glycolysis and cure acute African trypanosomiasis in mice

The parasitic protist Trypanosoma brucei is the causative agent of Human African Trypanosomiasis, also known as sleeping sickness. The parasite enters the blood via the bite of the tsetse fly where it is wholly reliant on glycolysis for the production of ATP. Glycolytic enzymes have been regarded as challenging drug targets because of their highly conserved active sites and phosphorylated substrates. We describe the development of novel small molecule allosteric inhibitors of trypanosome phosphofructokinase (PFK) that block the glycolytic pathway resulting in very fast parasite kill times with no inhibition of human PFKs. The compounds cross the blood brain barrier and single day oral dosing cures parasitaemia in a stage 1 animal model of human African trypanosomiasis. This study demonstrates that it is possible to target glycolysis and additionally shows how differences in allosteric mechanisms may allow the development of species-specific inhibitors to tackle a range of proliferative or infectious diseases.

VSG mRNA levels are regulated by the production of functional VSG protein

The bloodstream form of Trypanosoma brucei persists in mammalian hosts through a population survival strategy depending on antigenic variation of a cell surface coat composed of the variant surface glycoprotein (VSG). The integrity of the VSG coat is essential and blocking its synthesis results in a cell division cycle arrest just prior to cytokinesis. This observation indicates that VSG levels are monitored and that the cell has mechanisms to respond to a disruption of synthesis. Here, the regulation of VSG mRNA levels has been investigated by first measuring VSG mRNA copy number, and second using ectopic expression of VSG transgenes containing premature termination codons. The findings are that (i) VSG mRNA copy number varies with the identity of the VSG and (ii) a pathway detects synthesis of non-functional VSG protein and results in an increase in VSG mRNA levels.

The function of apolipoproteins L (APOLs): relevance for kidney disease, neurotransmission disorders, cancer and viral infection

The discovery that apolipoprotein L1 (APOL1) is the trypanolytic factor of human serum raised interest about the function of APOLs, especially following the unexpected finding that in addition to their protective action against sleeping sickness, APOL1 C-terminal variants also cause kidney disease. Based on the analysis of the structure and trypanolytic activity of APOL1, it was proposed that APOLs could function as ion channels of intracellular membranes and be involved in mechanisms triggering programmed cell death. In this review, the recent finding that APOL1 and APOL3 inversely control the synthesis of phosphatidylinositol-4-phosphate (PI(4)P) by the Golgi PI(4)-kinase IIIB (PI4KB) is commented. APOL3 promotes Ca2+ -dependent activation of PI4KB, but due to their increased interaction with APOL3, APOL1 C-terminal variants can inactivate APOL3, leading to reduction of Golgi PI(4)P synthesis. The impact of APOLs on several pathological processes that depend on Golgi PI(4)P levels is discussed. I propose that through their effect on PI4KB activity, APOLs control not only actomyosin activities related to vesicular trafficking, but also the generation and elongation of autophagosomes induced by inflammation.

NUDIX hydrolases with inorganic polyphosphate exo- and endopolyphosphatase activities in the glycosome, cytosol and nucleus of Trypanosoma brucei

Trypanosoma brucei, a protist parasite that causes African trypanosomiasis or sleeping sickness, relies mainly on glycolysis for ATP production when in its mammalian host. Glycolysis occurs within a peroxisome-like organelle named the glycosome. Previous work from our laboratory reported the presence of significant amounts of inorganic polyphosphate (polyP), a polymer of three to hundreds of orthophosphate units, in the glycosomes and nucleoli of T. brucei In this work, we identified and characterized the activity of two Nudix hydrolases (NHs), T. brucei Nudix hydrolase (TbNH) 2 and TbNH4, one located in the glycosomes and the other in the cytosol and nucleus, respectively, which can degrade polyP. We found that TbNH2 is an exopolyphosphatase with higher activity on short chain polyP, while TbNH4 is an endo- and exopolyphosphatase that has similar activity on polyP of various chain sizes. Both enzymes have higher activity at around pH 8.0. We also found that only TbNH2 can dephosphorylate ATP and ADP but with lower affinity than for polyP. Our results suggest that NHs can participate in polyP homeostasis and therefore may help control polyP levels in glycosomes, cytosol and nuclei of T. brucei.

Colonization of the tsetse fly midgut with commensal Kosakonia cowanii Zambiae inhibits trypanosome infection establishment

Tsetse flies (Glossina spp.) vector pathogenic trypanosomes (Trypanosoma spp.) in sub-Saharan Africa. These parasites cause human and animal African trypanosomiases, which are debilitating diseases that inflict an enormous socio-economic burden on inhabitants of endemic regions. Current disease control strategies rely primarily on treating infected animals and reducing tsetse population densities. However, relevant programs are costly, labor intensive and difficult to sustain. As such, novel strategies aimed at reducing tsetse vector competence require development. Herein we investigated whether Kosakonia cowanii Zambiae (Kco_Z), which confers Anopheles gambiae with resistance to Plasmodium, is able to colonize tsetse and induce a trypanosome refractory phenotype in the fly. Kco_Z established stable infections in tsetse’s gut and exhibited no adverse effect on the fly’s survival. Flies with established Kco_Z infections in their gut were significantly more refractory to infection with two distinct trypanosome species (T. congolense, 6% infection; T. brucei, 32% infection) than were age-matched flies that did not house the exogenous bacterium (T. congolense, 36% infected; T. brucei, 70% infected). Additionally, 52% of Kco_Z colonized tsetse survived infection with entomopathogenic Serratia marcescens, compared with only 9% of their wild-type counterparts. These parasite and pathogen refractory phenotypes result from the fact that Kco_Z acidifies tsetse’s midgut environment, which inhibits trypanosome and Serratia growth and thus infection establishment. Finally, we determined that Kco_Z infection does not impact the fecundity of male or female tsetse, nor the ability of male flies to compete with their wild-type counterparts for mates. We propose that Kco_Z could be used as one component of an integrated strategy aimed at reducing the ability of tsetse to transmit pathogenic trypanosomes.

Tsetse flies transmit pathogenic African trypanosomes, which are the causative agents of socio-economically devastating human and animal African trypanosomiases. These diseases are currently controlled in large part by reducing the population size of tsetse vectors through the use of insecticides, traps and sterile insect technique. However, logistic and monetary hurdles often preclude the prolonged application of procedures necessary to maintain these control programs. Thus, novel strategies, including those aimed at sustainably reducing the ability of tsetse to transmit trypanosomes, are presently under development. Herein we stably colonize tsetse flies with a bacterium (Kosakonia cowanii Zambiae, Kco_Z) that acidifies their midgut, thus rendering the environment inhospitable to infection with two distinct, epidemiologically important trypanosome strains as well as an entomopathogenic bacteria. In addition to inducing a trypanosome refractory phenotype, colonization of tsetse with Kco_Z exerts only a modest fitness cost on the fly. Taken together, these findings suggest that Kco_Z could be applied to enhance the effectiveness of currently employed tsetse control programs.

Morphological changes, nitric oxide production, and phagocytosis are triggered in vitro in microglia by bloodstream forms of Trypanosoma brucei

The flagellated parasite Trypanosoma brucei is the causative agent of Human African Trypanosomiasis (HAT). By a mechanism not well understood yet, trypanosomes enter the central nervous system (CNS), invade the brain parenchyma, and cause a fatal encephalopathy if is not treated. Trypanosomes are fast dividing organisms that, without any immune response, would kill the host in a short time. However, infected individuals survive either 6-12 months or more than 3 years for the acute and chronic forms, respectively. Thus, only when the brain defense collapses a lethal encephalopathy will occur. Here, we evaluated interactions between trypanosomes and microglial cells, which are the primary immune effector cells within the CNS. Using co-cultures of primary microglia and parasites, we found clear evidences of trypanosome phagocytosis by microglial cells. Microglia activation was also evident; analysis of its ultrastructure showed changes that have been reported in activated microglia undergoing oxidative stress caused by infections or degenerative diseases. Accordingly, an increase of the nitric oxide production was detected in supernatants of microglia/parasite co-cultures. Altogether, our results demonstrate that microglial cells respond to the presence of the parasite, leading to parasite's engulfment and elimination.

A glutaredoxin in the mitochondrial intermembrane space has stage-specific functions in the thermo-tolerance and proliferation of African trypanosomes

Trypanosoma brucei glutaredoxin 2 (Grx2) is a dithiol glutaredoxin that is specifically located in the mitochondrial intermembrane space. Bloodstream form parasites lacking Grx2 or both, Grx2 and the cytosolic Grx1, are viable in vitro and infectious to mice suggesting that neither oxidoreductase is needed for survival or infectivity to mammals. A 37 °C to 39 °C shift changes the cellular redox milieu of bloodstream cells to more oxidizing conditions and induces a significantly stronger growth arrest in wildtype parasites compared to the mutant cells. Grx2-deficient cells ectopically expressing the wildtype form of Grx2 with its C31QFC34 active site, but not the C34S mutant, regain the sensitivity of the parental strain, indicating that the physiological role of Grx2 requires both active site cysteines. In the procyclic insect stage of the parasite, Grx2 is essential. Both alleles can be replaced if procyclic cells ectopically express authentic or C34S, but not C31S/C34S Grx2, pointing to a redox role that relies on a monothiol mechanism. RNA-interference against Grx2 causes a virtually irreversible proliferation defect. The cells adopt an elongated morphology but do not show any significant alteration in the cell cycle. The growth retardation is attenuated by high glucose concentrations. Under these conditions, procyclic cells obtain ATP by substrate level phosphorylation suggesting that Grx2 might regulate a respiratory chain component.

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Bloodstream T. brucei lacking glutaredoxin 2 are fully viable in vitro and in vivo.

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A temperature rise shifts the cellular redox state to more oxidizing conditions.

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Glutaredoxin 2-deficiency confers bloodstream cells with thermo-tolerance.

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The insect stage requires redox-active glutaredoxin 2 for viability and morphology.

Decoding the network of Trypanosoma brucei proteins that determines sensitivity to apolipoprotein-L1

In contrast to Trypanosoma brucei gambiense and T. b. rhodesiense (the causative agents of human African trypanosomiasis), T. b. brucei is lysed by apolipoprotein-L1 (apoL1)-containing human serum trypanolytic factors (TLF), rendering it non-infectious to humans. While the mechanisms of TLF1 uptake, apoL1 membrane integration, and T. b. gambiense and T. b. rhodesiense apoL1-resistance have been extensively characterised, our understanding of the range of factors that drive apoL1 action in T. b. brucei is limited. Selecting our bloodstream-form T. b. brucei RNAi library with recombinant apoL1 identified an array of factors that supports the trypanocidal action of apoL1, including six putative ubiquitin modifiers and several proteins putatively involved in membrane trafficking; we also identified the known apoL1 sensitivity determinants, TbKIFC1 and the V-ATPase. Most prominent amongst the novel apoL1 sensitivity determinants was a putative ubiquitin ligase. Intriguingly, while loss of this ubiquitin ligase reduces parasite sensitivity to apoL1, its loss enhances parasite sensitivity to TLF1-dominated normal human serum, indicating that free and TLF1-bound apoL1 have contrasting modes-of-action. Indeed, loss of the known human serum sensitivity determinants, p67 (lysosomal associated membrane protein) and the cathepsin-L regulator, 'inhibitor of cysteine peptidase', had no effect on sensitivity to free apoL1. Our findings highlight a complex network of proteins that influences apoL1 action, with implications for our understanding of the anti-trypanosomal action of human serum.

Aquaglyceroporin-null trypanosomes display glycerol transport defects and respiratory-inhibitor sensitivity

Aquaglyceroporins (AQPs) transport water and glycerol and play important roles in drug-uptake in pathogenic trypanosomatids. For example, AQP2 in the human-infectious African trypanosome, Trypanosoma brucei gambiense, is responsible for melarsoprol and pentamidine-uptake, and melarsoprol treatment-failure has been found to be due to AQP2-defects in these parasites. To further probe the roles of these transporters, we assembled a T. b. brucei strain lacking all three AQP-genes. Triple-null aqp1-2-3 T. b. brucei displayed only a very moderate growth defect in vitro, established infections in mice and recovered effectively from hypotonic-shock. The aqp1-2-3 trypanosomes did, however, display glycerol uptake and efflux defects. They failed to accumulate glycerol or to utilise glycerol as a carbon-source and displayed increased sensitivity to salicylhydroxamic acid (SHAM), octyl gallate or propyl gallate; these inhibitors of trypanosome alternative oxidase (TAO) can increase intracellular glycerol to toxic levels. Notably, disruption of AQP2 alone generated cells with glycerol transport defects. Consistent with these findings, AQP2-defective, melarsoprol-resistant clinical isolates were sensitive to the TAO inhibitors, SHAM, propyl gallate and ascofuranone, relative to melarsoprol-sensitive reference strains. We conclude that African trypanosome AQPs are dispensable for viability and osmoregulation but they make important contributions to drug-uptake, glycerol-transport and respiratory-inhibitor sensitivity. We also discuss how the AQP-dependent inverse sensitivity to melarsoprol and respiratory inhibitors described here might be exploited.

Nitrotriazole-based acetamides and propanamides with broad spectrum antitrypanosomal activity

3-Nitro-1H-1,2,4-triazole-based acetamides bearing a biphenyl- or a phenoxyphenyl moiety have shown remarkable antichagasic activity both in vitro and in an acute murine model, as well as substantial in vitro antileishmanial activity but lacked activity against human African trypanosomiasis. We have shown now that by inserting a methylene group in the linkage to obtain the corresponding propanamides, both antichagasic and in particular anti-human African trypanosomiasis potency was increased. Therefore, IC50 values at low nM concentrations against both T. cruzi and T. b. rhodesiense, along with huge selectivity indices were obtained. Although several propanamides were active against Leishmania donovani, they were slightly less potent than their corresponding acetamides. There was a good correlation between lipophilicity (clogP value) and trypanocidal activity, for all new compounds. Type I nitroreductase, an enzyme absent from the human host, played a role in the activation of the new compounds, which may function as prodrugs. Antichagasic activity in vivo was also demonstrated with representative propanamides.

Interleukin (IL)-6 and IL-10 Are Up Regulated in Late Stage Trypanosoma brucei rhodesiense Sleeping Sickness

BACKGROUND

Sleeping sickness due to Trypanosoma brucei rhodesiense has a wide spectrum of clinical presentations coupled with differences in disease progression and severity across East and Southern Africa. The disease progresses from an early (hemo-lymphatic) stage to the late (meningoencephalitic) stage characterized by presence of parasites in the central nervous system. We hypothesized that disease progression and severity of the neurological response is modulated by cytokines.

METHODS

A total of 55 sleeping sickness cases and 41 healthy controls were recruited passively at Lwala hospital, in Northern Uganda. A panel of six cytokines (IFN-γ, IL1-β, TNF-α, IL-6, TGF-β and IL-10) were assayed from paired plasma and cerebrospinal fluid (CSF) samples. Cytokine concentrations were analyzed in relation to disease progression, clinical presentation and severity of neurological responses.

RESULTS

Median plasma levels (pg/ml) of IFN-γ (46.3), IL-6 (61.7), TGF-β (8755) and IL-10 (256.6) were significantly higher in cases compared to controls (p< 0.0001). When early stage and late stage CSF cytokines were compared, IL-10 and IL-6 were up regulated in late stage patients and were associated with a reduction in tremors and cranioneuropathy. IL-10 had a higher staging accuracy with a sensitivity of 85.7% (95% CI, 63.7%-97%) and a specificity of 100% (95% CI, 39.8%-100%) while for IL-6, a specificity of 100% (95% CI, 47.8%-100%) gave a sensitivity of 83.3% (95% CI, 62.2%-95.3%).

CONCLUSION

Our study demonstrates the role of host inflammatory cytokines in modulating the progression and severity of neurological responses in sleeping sickness. We demonstrate here an up-regulation of IL-6 and IL-10 during the late stage with a potential as adjunct stage biomarkers. Given that both cytokines could potentially be elevated by other CNS infections, our findings should be further validated in a large cohort of patients including those with other inflammatory diseases such as cerebral malaria.

MIF contributes to Trypanosoma brucei associated immunopathogenicity development

African trypanosomiasis is a chronic debilitating disease affecting the health and economic well-being of many people in developing countries. The pathogenicity associated with this disease involves a persistent inflammatory response, whereby M1-type myeloid cells, including Ly6C^high inflammatory monocytes, are centrally implicated. A comparative gene analysis between trypanosusceptible and trypanotolerant animals identified MIF (macrophage migrating inhibitory factor) as an important pathogenic candidate molecule. Using MIF-deficient mice and anti-MIF antibody treated mice, we show that MIF mediates the pathogenic inflammatory immune response and increases the recruitment of inflammatory monocytes and neutrophils to contribute to liver injury in Trypanosoma brucei infected mice. Moreover, neutrophil-derived MIF contributed more significantly than monocyte-derived MIF to increased pathogenic liver TNF production and liver injury during trypanosome infection. MIF deficient animals also featured limited anemia, coinciding with increased iron bio-availability, improved erythropoiesis and reduced RBC clearance during the chronic phase of infection. Our data suggest that MIF promotes the most prominent pathological features of experimental trypanosome infections (i.e. anemia and liver injury), and prompt considering MIF as a novel target for treatment of trypanosomiasis-associated immunopathogenicity.

Uncontrolled inflammation is a major contributor to pathogenicity development during many chronic parasitic infections, including African trypanosome infections. Hence, therapies should aim at re-establishing the balance between pro- and anti-inflammatory responses to reduce tissue damage. Our experiments uncovered that macrophage migration inhibitory factor (MIF) plays a pivotal role in trypanosomiasis-associated pathogenicity development. Hereby, MIF-deficient and neutralizing anti-MIF antibody-treated wild type (WT) T. brucei-infected mice exhibited decreased inflammatory responses, reduced liver damage and anemia (i.e. the most prominent pathogenicity features) compared to WT control mice. The reduced tissue damage coincided with reduced infiltration of pathogenic monocytic cells and neutrophils, whereby neutrophil-derived MIF contributed more significantly than monocyte-derived MIF to tissue damage. MIF also promoted anemia development by suppressing red blood cell production and enhancing their clearance. The clinical significance of these findings follows from human genetic data indicating that low-expression (protective) MIF alleles are enriched in Africans. The current findings therefore offer promise for human translation and open the possibility of assessing MIF levels or MIF genotype as an indication of an individual's risk for severe trypanosomiasis. Furthermore, given the unmet medical need of African trypanosomiasis affecting millions of people, these findings highlight MIF as a potential new therapeutic target for treatment of trypanosomiasis-associated pathogenicity.

Cyclical appearance of African trypanosomes in the cerebrospinal fluid: new insights in how trypanosomes enter the CNS

It is textbook knowledge that human infective forms of Trypanosoma brucei, the causative agent of sleeping sickness, enter the brain across the blood-brain barrier after an initial phase of weeks (rhodesiense) or months (gambiense) in blood. Based on our results using an animal model, both statements seem questionable. As we and others have shown, the first infection relevant crossing of the blood brain border occurs via the choroid plexus, i.e. via the blood-CSF barrier. In addition, counting trypanosomes in blood-free CSF obtained by an atlanto-occipital access revealed a cyclical infection in CSF that was directly correlated to the trypanosome density in blood infection. We also obtained conclusive evidence of organ infiltration, since parasites were detected in tissues outside the blood vessels in heart, spleen, liver, eye, testis, epididymis, and especially between the cell layers of the pia mater including the Virchow-Robin space. Interestingly, in all organs except pia mater, heart and testis, trypanosomes showed either a more or less degraded appearance of cell integrity by loss of the surface coat (VSG), loss of the microtubular cytoskeleton and loss of the intracellular content, or where taken up by phagocytes and degraded intracellularly within lysosomes. This is also true for trypanosomes placed intrathecally into the brain parenchyma using a stereotactic device. We propose a different model of brain infection that is in accordance with our observations and with well-established facts about the development of sleeping sickness.

Independent pathways can transduce the life-cycle differentiation signal in Trypanosoma brucei

African trypanosomes cause disease in humans and livestock, generating significant health and welfare problems throughout sub-Saharan Africa. When ingested in a tsetse fly bloodmeal, trypanosomes must detect their new environment and initiate the developmental responses that ensure transmission. The best-established environmental signal is citrate/cis aconitate (CCA), this being transmitted through a protein phosphorylation cascade involving two phosphatases: one that inhibits differentiation (TbPTP1) and one that activates differentiation (TbPIP39). Other cues have been also proposed (mild acid, trypsin exposure, glucose depletion) but their physiological relevance and relationship to TbPTP1/TbPIP39 signalling is unknown. Here we demonstrate that mild acid and CCA operate through TbPIP39 phosphorylation, whereas trypsin attack of the parasite surface uses an alternative pathway that is dispensable in tsetse flies. Surprisingly, glucose depletion is not an important signal. Mechanistic analysis through biophysical methods suggests that citrate promotes differentiation by causing TbPTP1 and TbPIP39 to interact.

African trypanosomes are important pathogens transmitted by tsetse flies in sub-Saharan Africa. Upon transmission, trypanosomes detect citrate and cis-aconitate in the bloodmeal, this inactivating a negative regulator of differentiation, the tyrosine phosphatase TbPTP1. One TbPTP1 substrate is another phosphatase, TbPIP39, which is more active when phosphorylated (after TbPTP1 inhibition) and promotes differentiation. These differentiation regulators have provided tools to monitor whether one or more environmental signals are used to initiate trypanosome development and their relevance in vivo. This is important because different studies over the last 30 years have disputed the physiological importance of different signals. Here we have, firstly, compared the efficacy of the different reported differentiation signals, establishing their relative importance. We then monitored TbPIP39 phosphorylation to show that two signalling pathways operate: one signalled by citrate or mild acid, the other stimulated by external protease activity. Thereafter, we showed that, of these different signals, protease activity is dispensable for differentiation in tsetse flies. Finally, we used biophysical methods to investigate how citrate causes TbPIP39 and TbPTP1 to interact, enabling their regulatory cross-talk. These studies have established the importance of different developmental signals in trypanosomes, providing molecular insight into how the development signal is transduced within the pathogen.

The TgsGP gene is essential for resistance to human serum in Trypanosoma brucei gambiense

Trypanosoma brucei gambiense causes 97% of all cases of African sleeping sickness, a fatal disease of sub-Saharan Africa. Most species of trypanosome, such as T. b. brucei, are unable to infect humans due to the trypanolytic serum protein apolipoprotein-L1 (APOL1) delivered via two trypanosome lytic factors (TLF-1 and TLF-2). Understanding how T. b. gambiense overcomes these factors and infects humans is of major importance in the fight against this disease. Previous work indicated that a failure to take up TLF-1 in T. b. gambiense contributes to resistance to TLF-1, although another mechanism is required to overcome TLF-2. Here, we have examined a T. b. gambiense specific gene, TgsGP, which had previously been suggested, but not shown, to be involved in serum resistance. We show that TgsGP is essential for resistance to lysis as deletion of TgsGP in T. b. gambiense renders the parasites sensitive to human serum and recombinant APOL1. Deletion of TgsGP in T. b. gambiense modified to uptake TLF-1 showed sensitivity to TLF-1, APOL1 and human serum. Reintroducing TgsGP into knockout parasite lines restored resistance. We conclude that TgsGP is essential for human serum resistance in T. b. gambiense.

Trypanosoma brucei gambiense causes 97% of all cases of African sleeping sickness, a fatal disease of sub-Saharan Africa. Most species of trypanosome, such as T. b. brucei, are unable to infect humans due to trypanolytic factors in human serum. Understanding how T. b. gambiense overcomes these factors and infects humans is of major importance in the fight against this disease. Previous work indicated that a failure to take up some trypanolytic factors by T. b. gambiense contributes to resistance, although other mechanisms are involved. Here, we have examined a T. b. gambiense specific gene, TgsGP, for involvement in resistance to human serum. We show that TgsGP is essential for resistance to lysis as deletion of TgsGP in T. b. gambiense renders the parasites sensitive to most trypanolytic factors. TgsGP deletion in T. b. gambiense modified to overcome the sub-species trait to reduce uptake of some trypanolytic factors resulted in sensitivity to all trypanolytic factors. Reintroducing TgsGP into these knockout parasite lines restored resistance. We conclude that TgsGP is essential for human serum resistance in T. b. gambiense.

Cynaropicrin targets the trypanothione redox system in Trypanosoma brucei

In mice cynaropicrin (CYN) potently inhibits the proliferation of Trypanosoma brucei-the causative agent of Human African Trypanosomiasis-by a so far unknown mechanism. We hypothesized that CYNs α,β-unsaturated methylene moieties act as Michael acceptors for glutathione (GSH) and trypanothione (T(SH)2), the main low molecular mass thiols essential for unique redox metabolism of these parasites. The analysis of this putative mechanism and the effects of CYN on enzymes of the T(SH)2 redox metabolism including trypanothione reductase, trypanothione synthetase, glutathione-S-transferase, and ornithine decarboxylase are shown. A two step extraction protocol with subsequent UPLC-MS/MS analysis was established to quantify intra-cellular CYN, T(SH)2, GSH, as well as GS-CYN and T(S-CYN)2 adducts in intact T. b. rhodesiense cells. Within minutes of exposure to CYN, the cellular GSH and T(SH)2 pools were entirely depleted, and the parasites entered an apoptotic stage and died. CYN also showed inhibition of the ornithine decarboxylase similar to the positive control eflornithine. Significant interactions with the other enzymes involved in the T(SH)2 redox metabolism were not observed. Alongside many other biological activities sesquiterpene lactones including CYN have shown antitrypanosomal effects, which have been postulated to be linked to formation of Michael adducts with cellular nucleophiles. Here the interaction of CYN with biological thiols in a cellular system in general, and with trypanosomal T(SH)2 redox metabolism in particular, thus offering a molecular explanation for the antitrypanosomal activity is demonstrated. At the same time, the study provides a novel extraction and analysis protocol for components of the trypanosomal thiol metabolism.

Identification and Functional Characterisation of CRK12:CYC9, a Novel Cyclin-Dependent Kinase (CDK)-Cyclin Complex in Trypanosoma brucei

The protozoan parasite, Trypanosoma brucei, is spread by the tsetse fly and causes trypanosomiasis in humans and animals. Both the life cycle and cell cycle of the parasite are complex. Trypanosomes have eleven cdc2-related kinases (CRKs) and ten cyclins, an unusually large number for a single celled organism. To date, relatively little is known about the function of many of the CRKs and cyclins, and only CRK3 has previously been shown to be cyclin-dependent in vivo. Here we report the identification of a previously uncharacterised CRK:cyclin complex between CRK12 and the putative transcriptional cyclin, CYC9. CRK12:CYC9 interact to form an active protein kinase complex in procyclic and bloodstream T. brucei. Both CRK12 and CYC9 are essential for the proliferation of bloodstream trypanosomes in vitro, and we show that CRK12 is also essential for survival of T. brucei in a mouse model, providing genetic validation of CRK12:CYC9 as a novel drug target for trypanosomiasis. Further, functional characterisation of CRK12 and CYC9 using RNA interference reveals roles for these proteins in endocytosis and cytokinesis, respectively.

Mechanisms of complement lectin pathway activation and resistance by trypanosomatid parasites

Studies in the past decade have demonstrated a crucial role for the complement lectin pathway in host defence against protozoan microbes. Recognition of pathogen surface molecules by mannan-binding lectin and ficolins revealed new mechanisms of innate immune defence and a diversity of parasite strategies of immune evasion. In the present review, we will discuss the current knowledge of: (1) the molecular mechanism of lectin pathway activation by trypanosomes; (2) the mechanisms of complement evasion by trypanosomes; and (3) host genetic deficiencies of complement lectin pathway factors that contribute to infection susceptibility and disease progression. This review will focus on trypanosomatids, the parasites that cause Chagas disease, leishmaniasis and sleeping sickness (African trypanosomiasis).

Molecular regulation of Trypanosoma congolense-induced nitric oxide production in macrophages

BALB/c mice are highly susceptible while C57BL/6 mice are relatively resistant to experimental Trypanosoma congolense infection. Several reports show that an early interferon-gamma (IFN-γ) response in infected mice is critically important for resistance via the activation of macrophages and production of nitric oxide (NO). NO is a pivotal effector molecule and possesses both cytostatic and cytolytic properties for the parasite. However, the molecular mechanisms leading to T. congolense (TC)-induced NO release from macrophages are not known. In this study, we investigated the signaling pathways induced by trypanosomes in immortalized macrophage cell lines from the highly susceptible BALB/c (BALB.BM) and relatively resistant C57Bl/6 (ANA-1) mice. We found that T. congolense whole cell extract (TC-WCE) induces significantly higher levels of NO production in IFN-γ-primed ANA-1 than BALB.BM cells, which was further confirmed in primary bone marrow-derived macrophage (BMDM) cultures. NO production was dependent on mitogen-activated protein kinase (MAPK, including p38, Erk1/2, and JNK) phosphorylation and was significantly inhibited by specific MAPK inhibitors in BALB.BM, but not in ANA-1 cells. In addition, T. congolense- and IFN-γ-induced NO production in ANA-1 and BALB.BM cells was dependent on STAT1 phosphorylation and was totally suppressed by the use of fludarabine (a specific STAT1 inhibitor). We further show that T. congolense induces differential iNOS transcriptional promoter activation in IFN-γ-primed cells, which is dependent on the activation of both GAS1 and GAS2 transcription factors in BALB.BM but only on GAS1 in ANA-1 cells. Taken together, our findings show the existence of differential signalling events that lead to NO production in macrophages from the highly susceptible and relatively resistant mice following treatment with IFN-γ and T. congolense. Understanding these pathways may help identify immunomodulatory mechanisms that regulate the outcome of infection during Trypanosome infections.

A MAP6-related protein is present in protozoa and is involved in flagellum motility

In vertebrates the microtubule-associated proteins MAP6 and MAP6d1 stabilize cold-resistant microtubules. Cilia and flagella have cold-stable microtubules but MAP6 proteins have not been identified in these organelles. Here, we describe TbSAXO as the first MAP6-related protein to be identified in a protozoan, Trypanosoma brucei. Using a heterologous expression system, we show that TbSAXO is a microtubule stabilizing protein. Furthermore we identify the domains of the protein responsible for microtubule binding and stabilizing and show that they share homologies with the microtubule-stabilizing Mn domains of the MAP6 proteins. We demonstrate, in the flagellated parasite, that TbSAXO is an axonemal protein that plays a role in flagellum motility. Lastly we provide evidence that TbSAXO belongs to a group of MAP6-related proteins (SAXO proteins) present only in ciliated or flagellated organisms ranging from protozoa to mammals. We discuss the potential roles of the SAXO proteins in cilia and flagella function.

Biochemical and morphological changes in Trypanosoma brucei brucei-infected rats treated with homidium chloride and diminazene aceturate

BACKGROUND

Chemotherapy which is one of the major methods for controlling trypanosomal infections is beset with several challenges including unwanted toxicity and limited efficacy. These factors and others underscore research efforts aimed at finding safer and more effective therapeutic agents for trypanosomiasis. Homidium chloride and diminazene aceturate are registered drugs for the treatment of animal trypanosomiasis.

METHODS

Study investigated and compared, in an experimental Trypanosoma infection, the effects of two trypanocides on the pathology of tissues and some biochemical indices in rats.

RESULTS

Data revealed that the levels of alkaline phosphatase, alanine transaminase and aspartate transaminase in infected positive animals were significantly (p<0.05) elevated relative to uninfected negative controls but showed no significant difference when compared with the trypanocide-treatment groups. The histopathological presentations in the infected and treatment groups are a demonstration of the inimical cellular alterations associated with Trypanosoma brucei brucei infection.

CONCLUSIONS

The inimical alterations to biochemical and morphological parameters observed in the infected as well as the treatment groups is an implication suggesting shortcomings of the investigated trypanocides to alleviate pathology associated with Trypanosoma brucei brucei infection. We present evidence that further supports the urgent need for the development of safer and more effective trypanocides.

IL-10 limits production of pathogenic TNF by M1 myeloid cells through induction of nuclear NF-κB p50 member in Trypanosoma congolense infection-resistant C57BL/6 mice

A balance between parasite elimination and control of infection-associated pathogenicity is crucial for resistance to African trypanosomiasis. By producing TNF and NO, CD11b(+) myeloid cells with a classical activation status (M1) contribute to parasitemia control in experimental Trypanosoma congolense infection in resistant C57BL/6 mice. However, in these mice, IL-10 is required to regulate M1-associated inflammation, avoiding tissue/liver damage and ensuring prolonged survival. In an effort to dissect the mechanisms behind the anti-inflammatory activity of IL-10 in T. congolense-infected C57BL/6 mice, we show, using an antibody blocking the IL-10 receptor, that IL-10 impairs the accumulation and M1 activation of TNF/iNOS-producing CD11b(+) Ly6C(+) cells in the liver. Using infected IL-10(flox/flox) LysM-Cre(+/+) mice, we show that myeloid cell-derived IL-10 limits M1 activation of CD11b(+) Ly6C(+) cells specifically at the level of TNF production. Moreover, higher production of TNF in infected IL-10(flox/flox) LysM-Cre(+/+) mice is associated with reduced nuclear accumulation of the NF-κB p50 subunit in CD11b(+) M1 cells. Furthermore, in infected p50(-/-) mice, TNF production by CD11b(+) Ly6C(+) cells and liver injury increases. These data suggest that preferential nuclear accumulation of p50 represents an IL-10-dependent anti-inflammatory mechanism in M1-type CD11b(+) myeloid cells that regulates the production of pathogenic TNF during T. congolense infection in resistant C57BL/6 mice.

A tryparedoxin-dependent peroxidase protects African trypanosomes from membrane damage

Hydroperoxide detoxification in African trypanosomes is achieved by 2-Cys-peroxiredoxin (TXNPx)- and non-selenium glutathione peroxidase (Px)-type enzymes which both obtain their reducing equivalents from the unique trypanothione/tryparedoxin system. Previous RNA interference approaches revealed that the cytosolic TXNPx and the Px-type enzymes are essential for Trypanosoma brucei. Because of partially overlapping in vitro substrate specificities and subcellular localisation the physiological function of the individual enzymes was not yet clear. As shown here, TXNPx and Px are expressed at comparable levels and in their active reduced state. Px-overexpressing parasites were less sensitive toward linoleic acid hydroperoxide but not hydrogen peroxide. Kinetic studies confirmed that Px-but not TXNPx-reduces lipophilic hydroperoxides including phospholipids with high efficiency. Most interestingly, the severe proliferation defect of Px-depleted bloodstream cells could be rescued by Trolox, but not by hydrophilic antioxidants, in the medium. This allowed us to knock-out the three Px genes individually and thus to distinguish their in vivo role. Deletion of the cytosolic Px I and II resulted in extremely fast membrane peroxidation followed by cell lysis. Cells lacking specifically the mitochondrial Px III showed a transient growth retardation and cardiolipin peroxidation but adapted within 24h to normal proliferation.

High affinity nanobodies against the Trypanosome brucei VSG are potent trypanolytic agents that block endocytosis

The African trypanosome Trypanosoma brucei, which persists within the bloodstream of the mammalian host, has evolved potent mechanisms for immune evasion. Specifically, antigenic variation of the variant-specific surface glycoprotein (VSG) and a highly active endocytosis and recycling of the surface coat efficiently delay killing mediated by anti-VSG antibodies. Consequently, conventional VSG-specific intact immunoglobulins are non-trypanocidal in the absence of complement. In sharp contrast, monovalent antigen-binding fragments, including 15 kDa nanobodies (Nb) derived from camelid heavy-chain antibodies (HCAbs) recognizing variant-specific VSG epitopes, efficiently lyse trypanosomes both in vitro and in vivo. This Nb-mediated lysis is preceded by very rapid immobilisation of the parasites, massive enlargement of the flagellar pocket and major blockade of endocytosis. This is accompanied by severe metabolic perturbations reflected by reduced intracellular ATP-levels and loss of mitochondrial membrane potential, culminating in cell death. Modification of anti-VSG Nbs through site-directed mutagenesis and by reconstitution into HCAbs, combined with unveiling of trypanolytic activity from intact immunoglobulins by papain proteolysis, demonstrates that the trypanolytic activity of Nbs and Fabs requires low molecular weight, monovalency and high affinity. We propose that the generation of low molecular weight VSG-specific trypanolytic nanobodies that impede endocytosis offers a new opportunity for developing novel trypanosomiasis therapeutics. In addition, these data suggest that the antigen-binding domain of an anti-microbial antibody harbours biological functionality that is latent in the intact immunoglobulin and is revealed only upon release of the antigen-binding fragment.

Haemoparasites, such as African trypanosomes, have developed potent immune evasion mechanisms to avoid antibody-mediated elimination. Consequently, trypanosome surface antigen-specific immunoglobulins in the absence of complement are non-trypanocidal. In contrast, certain monovalent nanobodies (Nb), monomeric antigen-binding domains derived from camelid Heavy-Chain Antibodies (HCAb) and which have a much lower molecular weight (15 kDa) than classical antibodies (150 kDa), efficiently lyse trypanosomes both in vitro and in vivo. This is surprising as classically immunoglobulin effector functions are mediated via the Fc-domain, which is absent from the Nb. We demonstrate that the Nb-mediated trypanolysis depends on the low molecular weight, monovalency and high affinity and is associated with loss of motility, a major block to endocytosis, energy depletion and cell death. Overall, targeting the parasite surface with low molecular weight, high affinity Nbs is sufficient to exert a direct therapeutic action. Therefore, the exploitation of Nbs against African trypanosomiasis represents a novel therapeutic strategy. Furthermore, demonstration that a high affinity antigen-binding Nb or Fab fragment lacking an effector domain (i.e., Fc-domain or an attached toxin) can exert a direct biological function, suggests that intact antibodies likely harbour latent functionality which only become revealed upon removal of the Fc-domain.

A comprehensive genetic analysis of candidate genes regulating response to Trypanosoma congolense infection in mice

Background

African trypanosomes are protozoan parasites that cause “sleeping sickness” in humans and a similar disease in livestock. Trypanosomes also infect laboratory mice and three major quantitative trait loci (QTL) that regulate survival time after infection with T. congolense have been identified in two independent crosses between susceptible A/J and BALB/c mice, and the resistant C57BL/6. These were designated Tir1, Tir2 and Tir3 for Trypanosoma infection response, and range in size from 0.9–12 cM.

Principal Findings

Mapping loci regulating survival time after T. congolense infection in an additional cross revealed that susceptible C3H/HeJ mice have alleles that reduce survival time after infection at Tir1 and Tir3 QTL, but not at Tir2. Next-generation resequencing of a 6.2 Mbp region of mouse chromosome 17, which includes Tir1, identified 1,632 common single nucleotide polymorphisms (SNP) including a probably damaging non-synonymous SNP in Pram1 (PML-RAR alpha-regulated adaptor molecule 1), which was the most plausible candidate QTL gene in Tir1. Genome-wide comparative genomic hybridisation identified 12 loci with copy number variants (CNV) that correlate with differential gene expression, including Cd244 (natural killer cell receptor 2B4), which lies close to the peak of Tir3c and has gene expression that correlates with CNV and phenotype, making it a strong candidate QTL gene at this locus.

Conclusions

By systematically combining next-generation DNA capture and sequencing, array-based comparative genomic hybridisation (aCGH), gene expression data and SNP annotation we have developed a strategy that can generate a short list of polymorphisms in candidate QTL genes that can be functionally tested.

About one-third of cattle in sub-Saharan Africa are at risk of contracting “Nagana”—a disease caused by Trypanosoma parasites similar to those that cause human “Sleeping Sickness.” Laboratory mice can also be infected by trypanosomes, and different mouse breeds show varying levels of susceptibility to infection, similar to what is seen between different breeds of cattle. Survival time after infection is controlled by the underlying genetics of the mouse breed, and previous studies have localised three genomic regions that regulate this trait. These three “Quantitative Trait Loci” (QTL), which have been called Tir1, Tir2 and Tir3 (for Trypanosoma Infection Response 1–3) are well defined, but nevertheless still contain over one thousand genes, any number of which may be influencing survival. This study has aimed to identify the specific differences associated with genes that are controlling mouse survival after T. congolense infection. We have applied a series of analyses to existing datasets, and combined them with novel sequencing, and other genetic data to create short lists of genes that share polymorphisms across susceptible mouse breeds, including two promising “candidate genes”: Pram1 at Tir1 and Cd244 at Tir3. These genes can now be tested to confirm their effect on response to trypanosome infection.

Cerebral and peripheral changes occurring in nitric oxide (NO) synthesis in a rat model of sleeping sickness: identification of brain iNOS expressing cells

BACKGROUND

The implication of nitric oxide (NO) in the development of human African trypanosomiasis (HAT) using an animal model, was examined. The manner by which the trypanocidal activity of NO is impaired in the periphery and in the brain of rats infected with Trypanosoma brucei brucei (T. b. brucei) was analyzed through: (i) the changes occurring in NO concentration in both peripheral (blood) and cerebral compartments; (ii) the activity of nNOS and iNOS enzymes; (iii) identification of the brain cell types in which the NO-pathways are particularly active during the time-course of the infection.

METHODOLOGY/PRINCIPAL FINDINGS

NO concentration (direct measures by voltammetry) was determined in central (brain) and peripheral (blood) compartments in healthy and infected animals at various days post-infection: D5, D10, D16 and D22. Opposite changes were observed in the two compartments. NO production increased in the brain (hypothalamus) from D10 (+32%) to D16 (+71%), but decreased in the blood from D10 (-22%) to D16 (-46%) and D22 (-60%). In parallel with NO measures, cerebral iNOS activity increased and peaked significantly at D16 (up to +700%). However, nNOS activity did not vary. Immunohistochemical staining confirmed iNOS activation in several brain regions, particularly in the hypothalamus. In peritoneal macrophages, iNOS activity decreased from D10 (-83%) to D16 (-65%) and D22 (-74%) similarly to circulating NO.

CONCLUSION/SIGNIFICANCE

The NO changes observed in our rat model were dependent on iNOS activity in both peripheral and central compartments. In the periphery, the NO production decrease may reflect an arginase-mediated synthesis of polyamines necessary to trypanosome growth. In the brain, the increased NO concentration may result from an enhanced activity of iNOS present in neurons and glial cells. It may be regarded as a marker of deleterious inflammatory reactions.

Kynurenine pathway inhibition reduces central nervous system inflammation in a model of human African trypanosomiasis

Human African trypanosomiasis, or sleeping sickness, is caused by the protozoan parasites Trypanosoma brucei rhodesiense or Trypanosoma brucei gambiense, and is a major cause of systemic and neurological disability throughout sub-Saharan Africa. Following early-stage disease, the trypanosomes cross the blood-brain barrier to invade the central nervous system leading to the encephalitic, or late stage, infection. Treatment of human African trypanosomiasis currently relies on a limited number of highly toxic drugs, but untreated, is invariably fatal. Melarsoprol, a trivalent arsenical, is the only drug that can be used to cure both forms of the infection once the central nervous system has become involved, but unfortunately, this drug induces an extremely severe post-treatment reactive encephalopathy (PTRE) in up to 10% of treated patients, half of whom die from this complication. Since it is unlikely that any new and less toxic drug will be developed for treatment of human African trypanosomiasis in the near future, increasing attention is now being focussed on the potential use of existing compounds, either alone or in combination chemotherapy, for improved efficacy and safety. The kynurenine pathway is the major pathway in the metabolism of tryptophan. A number of the catabolites produced along this pathway show neurotoxic or neuroprotective activities, and their role in the generation of central nervous system inflammation is well documented. In the current study, Ro-61-8048, a high affinity kynurenine-3-monooxygenase inhibitor, was used to determine the effect of manipulating the kynurenine pathway in a highly reproducible mouse model of human African trypanosomiasis. It was found that Ro-61-8048 treatment had no significant effect (P = 0.4445) on the severity of the neuroinflammatory pathology in mice during the early central nervous system stage of the disease when only a low level of inflammation was present. However, a significant (P = 0.0284) reduction in the severity of the neuroinflammatory response was detected when the inhibitor was administered in animals exhibiting the more severe, late central nervous system stage, of the infection. In vitro assays showed that Ro-61-8048 had no direct effect on trypanosome proliferation suggesting that the anti-inflammatory action is due to a direct effect of the inhibitor on the host cells and not a secondary response to parasite destruction. These findings demonstrate that kynurenine pathway catabolites are involved in the generation of the more severe inflammatory reaction associated with the late central nervous system stages of the disease and suggest that Ro-61-8048 or a similar drug may prove to be beneficial in preventing or ameliorating the PTRE when administered as an adjunct to conventional trypanocidal chemotherapy.

Role of iron homeostasis in trypanosomiasis-associated anemia

Anemia is a well-established infection-associated immunopathological feature of trypanosomiasis and the degree of the anemia is a reliable indicator of the severity of infection. Since infections with trypanosomes triggers a strong cytokine production and a type I immune response, the trypanosome-elicited anemia may be type I cytokine driven. This type of anemia termed anemia of chronic disease is characterized by an imbalance between erythrophagocytosis and erythropoiesis that is linked to a perturbed iron homeostasis including altered iron recycling by macrophages and iron sequestration. To further unravel the mechanisms underlying trypanosome-elicited anemia the expression profile of genes involved in erythrophagocytosis, uptake of iron-containing complexes and iron homeostasis was performed during the acute and chronic phase of experimental Trypanosoma brucei infections in a murine model. The results suggest that liver-associated erythrophagocytosis mediated by cytokine-activated macrophages (M1 cells) is the most likely main initiating event of aggressive anemia during the acute phase of infection. Persistence of strong type I cytokine production during the chronic phase of infection leads to hyper-activated M1 cells and a more progressive anemia. RT-PCR analysis of liver tissue demonstrates a strong increase of cell surface receptors involved in uptake of RBC and iron-containing compounds. For genes involved in iron processing we found an increase of ferroportin-1 (FPN-1), transferrin (Tf) and ceruloplasmin (CP) only in the acute phase, suggesting that export of iron is hampered in the chronic phase of infection. Our results suggest that in the chronic phase of trypanosomiasis, the iron-processing pathway is skewed towards iron sequestration, as evidenced by increased ferritin expression, while enhanced uptake of RBC/iron-containing compounds is maintained.

Differential expression of fat body genes in Glossina morsitans morsitans following infection with Trypanosoma brucei brucei

To determine which fat body genes were differentially expressed following infection of Glossina morsitans morsitans with Trypanosoma brucei brucei we generated four suppression subtractive hybridisation (SSH) libraries. We obtained 52 unique gene fragments (SSH clones) of which 30 had a known orthologue at E-05 or less. Overall the characteristics of the orthologues suggest: (i) that trypanosome infection has a considerable effect on metabolism in the tsetse fly; (ii) that self-cured flies are mounting an oxidative stress response; and (iii) that self-cured flies are displaying increased energy usage. The three most consistently differentially expressed genes were further analysed by gene knockdown (RNAi). Knockdown of Glossina transferrin transcripts, which are upregulated in self-cured flies compared with flies infected with trypanosomes, results in a significant increase in the number of trypanosome infections establishing in the fly midgut, suggesting transferrin plays a role in the protection of tsetse flies from trypanosome infection.

Hemoglobin is a co-factor of human trypanosome lytic factor

Trypanosome lytic factor (TLF) is a high-density lipoprotein (HDL) subclass providing innate protection to humans against infection by the protozoan parasite Trypanosoma brucei brucei. Two primate-specific plasma proteins, haptoglobin-related protein (Hpr) and apolipoprotein L-1 (ApoL-1), have been proposed to kill T. b. brucei both singularly or when co-assembled into the same HDL. To better understand the mechanism of T. b. brucei killing by TLF, the protein composition of TLF was investigated using a gentle immunoaffinity purification technique that avoids the loss of weakly associated proteins. HDL particles recovered by immunoaffinity absorption, with either anti-Hpr or anti-ApoL-1, were identical in protein composition and specific activity for T. b. brucei killing. Here, we show that TLF-bound Hpr strongly binds Hb and that addition of Hb stimulates TLF killing of T. b. brucei by increasing the affinity of TLF for its receptor, and by inducing Fenton chemistry within the trypanosome lysosome. These findings suggest that TLF in uninfected humans may be inactive against T. b. brucei prior to initiation of infection. We propose that infection of humans by T. b. brucei causes hemolysis that triggers the activation of TLF by the formation of Hpr-Hb complexes, leading to enhanced binding, trypanolytic activity, and clearance of parasites.

Sleeping glands? - The role of endocrine disorders in sleeping sickness (T.b. gambiense Human African Trypanosomiasis)

Symptoms consistent with hypothyroidism or adrenal insufficiency, such as lethargy, anorexia, cold intolerance, weakness, hypotension or paraesthesia, are frequently reported in the literature in patients with Human African Trypanosomiasis (HAT), but an endocrine origin for these symptoms has not yet been demonstrated. Thyroid and adrenocortical function were assessed in 60 patients with late-stage HAT and compared to those in 60 age- and gender-matched healthy controls. Clinical assessment and endocrine laboratory examinations were performed on admission, within 2 days after the end of treatment and at follow-up 3 months later. Signs and symptoms of hypothyroidism, such as fatigue, cold sensation, constipation, paraesthesia, peripheral oedema and dry skin, were significantly more frequent in HAT patients than in the controls. However, these signs and symptoms could not be attributed to hypothyroidism due to the lack of supporting laboratory data, and thus empirical replacement therapy for the clinically suspected hypothyroidism was not warranted. Signs and symptoms consistent with adrenal insufficiency, such as weakness, anorexia, weight loss or hypotension, were significantly more frequent in HAT patients than in controls, but they could not be associated with an insufficiency of the adrenocortical axis. Higher basal levels of cortisol were found in HAT patients than in controls, which can be viewed as a stress response to the infection. However, a transitory adrenal insufficiency was suspected in 8% of HAT patients at admission and in 9% at discharge. All values were normal at follow-up 3 months later.

A systematic strategy for large-scale analysis of genotype phenotype correlations: identification of candidate genes involved in African trypanosomiasis

It is increasingly common to combine Microarray and Quantitative Trait Loci data to aid the search for candidate genes responsible for phenotypic variation. Workflows provide a means of systematically processing these large datasets and also represent a framework for the re-use and the explicit declaration of experimental methods. In this article, we highlight the issues facing the manual analysis of microarray and QTL data for the discovery of candidate genes underlying complex phenotypes. We show how automated approaches provide a systematic means to investigate genotype-phenotype correlations. This methodology was applied to a use case of resistance to African trypanosomiasis in the mouse. Pathways represented in the results identified Daxx as one of the candidate genes within the Tir1 QTL region. Subsequent re-sequencing in Daxx identified a deletion of an amino acid, identified in susceptible mouse strains, in the Daxx-p53 protein-binding region. This supports recent experimental evidence that apoptosis could be playing a role in the trypanosomiasis resistance phenotype. Workflows developed in this investigation, including a guide to loading and executing them with example data, are available at http://workflows.mygrid.org.uk/repository/myGrid/PaulFisher/.

Tumor necrosis factor (TNF) receptor-1 (TNFp55) signal transduction and macrophage-derived soluble TNF are crucial for nitric oxide-mediated Trypanosoma congolense parasite killing

Control of Trypanosoma congolense infections requires an early cell-mediated immune response. To unravel the role of tumor necrosis factor (TNF) in this process, 6 different T. congolense strains were used in 6 different gene-deficient mouse models that included TNF(-/-), TNF receptor-1 (TNFp55)(-/-), and TNF receptor-2 (TNFp75)(-/-) mice, 2 cell type-specific TNF(-/-) mice, as well as TNF-knock-in mice that expressed only membrane-bound TNF. Our results indicate that soluble TNF produced by macrophages/neutrophils and TNFp55 signaling are essential and sufficient to control parasitemia. The downstream mechanism in the control of T. congolense infection depends on inducible nitric oxide synthase activation in the liver. Such a role for nitric oxide is corroborated ex vivo, because the inhibitor N(G)-monomethyl-l-arginine blocks the trypanolytic activity of the adherent liver cell population, whereas exogenous interferon- gamma that stimulates nitric oxide production enhances parasite killing. In conclusion, the control of T. congolense infection depends on macrophage/neutrophil-derived soluble TNF and intact TNFp55 signaling, which induces trypanolytic nitric oxide.

Targeting of toxic compounds to the trypanosome's interior

Drugs can be targeted into African trypanosomes by exploiting carrier proteins at the surface of these parasites. This has been clearly demonstrated in the case of the melamine-based arsenical and the diamidine classes of drug that are already in use in the treatment of human African trypanosomiasis. These drugs can enter via an aminopurine transporter, termed P2, encoded by the TbAT1 gene. Other toxic compounds have also been designed to enter via this transporter. Some of these compounds enter almost exclusively through the P2 transporter, and hence loss of the P2 transporter leads to significant resistance to these particular compounds. It now appears, however, that some diamidines and melaminophenylarsenicals may also be taken up by other routes (of yet unknown function). These too may be exploited to target new drugs into trypanosomes. Additional purine nucleoside and nucleobase transporters have also been subverted to deliver toxic agents to trypanosomes. Glucose and amino acid transporters too have been investigated with a view to manipulating them to carry toxins into Trypanosoma brucei, and recent work has demonstrated that aquaglyceroporins may also have considerable potential for drug-targeting. Transporters, including those that carry lipids and vitamins such as folate and other pterins also deserve more attention in this regard. Some drugs, for example suramin, appear to enter via routes other than plasma-membrane-mediated transport. Receptor-mediated endocytosis has been proposed as a possible way in for suramin. Endocytosis also appears to be crucial in targeting natural trypanocides, such as trypanosome lytic factor (TLF) (apolipoprotein L1), into trypanosomes and this offers an alternative means of selectively targeting toxins to the trypanosome's interior. Other compounds may be induced to enter by increasing their capacity to diffuse over cell membranes; in this case depending exclusively on selective activity within the cell rather than selective uptake to impart selective toxicity. This review outlines studies that have aimed to exploit trypanosome nutrient uptake routes to selectively carry toxins into these parasites.

Gene expression profiling in a mouse model for African trypanosomiasis

This study aimed to provide the foundation for an integrative approach to the identification of the mechanisms underlying the response to infection with Trypanosoma congolense, and to identify pathways that have previously been overlooked. We undertook a large-scale gene expression analysis study comparing susceptible A/J and more tolerant C57BL/6 mice. In an initial time course experiment, we monitored the development of parasitaemia and anaemia in every individual. Based on the kinetics of disease progression, we extracted total RNA from liver at days 0, 4, 7, 10 and 17 post infection and performed a microarray analysis. We identified 64 genes that were differentially expressed in the two strains in non-infected animals, of which nine genes remained largely unaffected by the disease. Gene expression profiling at stages of low, peak, clearance and recurrence of parasitaemia suggest that susceptibility is associated with high expression of genes coding for chemokines (e.g. Ccl24, Ccl27 and Cxcl13), complement components (C1q and C3) and interferon receptor alpha (Ifnar1). Additionally, susceptible A/J mice expressed higher levels of some potassium channel genes. In contrast, messenger RNA levels of a few immune response, metabolism and protease genes (e.g. Prss7 and Mmp13) were higher in the tolerant C57BL/6 strain as compared to A/J.

Novel antitrypanosomal agents

Trypanosomes are the causative agents of Chagas' disease in Central and South America and sleeping sickness in sub-Saharan Africa. The current chemotherapy of the human trypanosomiases relies on only six drugs, five of which were developed > 30 years ago. In addition, these drugs display undesirable toxic side effects and the emergence of drug-resistant trypanosomes has been reported. Therefore, the development of new drugs in the treatment of Chagas' disease and sleeping sickness is urgently required. This article summarises the recent progress in identifying novel lead compounds for antitrypanosomal chemotherapy. Particular emphasis is placed on those agents showing promising, selective antitrypanosomal activity.

Meningoencephalitic African trypanosomiasis: Brain IL-10 and IL-6 are associated with protection from neuro-inflammatory pathology

The relationship of neuropathology to CNS inflammatory and counter-inflammatory cytokine production in African trypanosome-infected mice was studied using an infection model with a defined disease progression. The initial phase of CNS infection by trypanosomes, where only mild neuropathology is evident, was characterised by high levels of IL-10 and IL-6. In the later phase of CNS infection and in a post-drug treatment model, moderate to severe neuropathology was associated with high levels of IFN-gamma and TNF-alpha. The relationship of these cytokines to neuropathological grade suggests that IL-10 and IL-6 protect the CNS from inflammatory pathology when parasites first enter the brain and the data reconcile previously contradictory clinical measurements of CSF cytokines in meningoencephalitic patients with post-mortem histopathology observations.

Influence of an experimental Trypanosoma congolense infection and plane of nutrition on milk production and some biochemical parameters in West African Dwarf goats

The interactions of trypanosomosis and plane of nutrition on health and productivity of multiparous and primiparous West African Dwarf (WAD) does were studied in a multi-factorial experiment including diet (supplementation or basal diet) and infection (infected or control). Experimental does were infected with Trypanosoma congolense at the beginning of the second week post-kidding and monitored for 16 weeks after infection. Trypanosome infection significantly reduced packed cell volume (PCV) (control: 30.1+/-0.3% versus infected: 22.2+/-0.3%; P<0.0001). Regardless of infection, the drop in PCV from the pre-infection period to the end of the experiment was more severe in animals under restricted diet (interaction dietxperiod, P<0.001). Trypanosome parasitaemia tended to be higher in the supplemented group than in the basal diet group (P>0.05) and multiparous animals had a higher parasitaemia (score: 2.6+/-0.1) than primiparous animals (score: 2.2+/-0.1) (P<0.05). Trypanosome infection as well as dietary supplement had a significant effect on lactation length. Milk off-take from trypanosome-infected does was significantly lower than that from the uninfected control group (17.5+/-3.2l versus 35.5+/-3.2l, P<0.001) and there was a positive effect of plane of nutrition (supplemented: 32.8+/-3.2l and basal diet: 20.2+/-3.5l, P=0.01). The drop in milk off-take due to trypanosome infection was more severe in the supplemented group (control: 46.7+/-4.7l versus infected: 18.9+/-4.2l) than in the group receiving a basal diet (control: 24.2+/-5.0l versus infected: 16.1+/-4.7l) (interaction infectionxdiet, P=0.04) due to the number of does from the supplemented group that were withdrawn from the experiment. The effect of trypanosome infection on doe's live-weight was only noticeable during the first 8 weeks of lactation and there was no significant effect on offspring growth rate unless the mother died. Plasma total protein (TP), albumin and cholesterol concentrations were significantly reduced by the infection but were significantly increased by supplementation. Supplemented does had a higher level of cholesterol and a tendency for a higher parasitaemia. Does of high parity also had a higher cholesterol level than primiparous does and, based on the number of animals that were withdrawn from the experiment, they showed a lower resistance to the infection.

The trypanosome lytic factor of human serum and the molecular basis of sleeping sickness

Trypanosoma brucei brucei infects a wide range of mammals but is unable to infect humans because this subspecies is lysed by normal human serum (NHS). The trypanosome lytic factor is associated with High Density Lipoproteins (HDLs). Several HDL-associated components have been proposed as candidate lytic factors, and contradictory hypotheses concerning the mechanism of lysis have been suggested. Elucidation of the process by which Trypanosoma brucei rhodesiense resists lysis and causes human sleeping sickness has indicated that the HDL-bound apolipoprotein L-I (apoL-I) could be the long-sought after lytic component of NHS. This research also allowed the identification of a specific diagnostic DNA probe for T. b. rhodesiense, and may lead to the development of novel anti-trypanosome strategies for use in the field.

Cerebral vessel laminins and IFN-gamma define Trypanosoma brucei brucei penetration of the blood-brain barrier

Subspecies of Trypanosoma brucei cause severe brain diseases after penetration of the blood-brain barrier. We investigated whether cytokines that modulate inflammatory cell infiltration into the brain also influence T. brucei neuroinvasion. Migration of a rodent pathogenic T. brucei strain from the cerebral blood vessels into the brain parenchyma was impeded in IFN-gamma(-/-), IFN-gamma receptor(-/-) (IFN-gammaR(-/-)), IL-12p40(-/-), and recombinant activating gene-1(-/-) (RAG-1(-/-)) mice as compared with their WT littermates despite higher levels of parasitemia in the mutant strains. Parasites accumulated in the perivascular compartment, confined between the endothelial and the parenchymal basement membranes, in certain areas of the brains of IFN-gamma(-/-), IFN-gammaR(-/-), and RAG-1(-/-) mice. This accumulation occurred around endothelial basement membranes containing the laminin alpha4 chain, while blood vessels showing robust laminin alpha5 chain immunostaining were not associated with parasite infiltration. The number of CD4+ and CD8+ T cells infiltrating the brain parenchyma was also reduced in the IFN-gamma(-/-) and IFN-gammaR(-/-) mice. Our findings suggest that lymphocyte-derived IFN-gamma facilitates trypanosome penetration across cerebral blood vessels and that the site of penetration is determined by the composition of the basement membranes of these vessels.

Drug transport and drug resistance in African trypanosomes

Drug resistance in African trypanosomes has been studied for almost a hundred years. Beginning with Paul Ehrlich's work that led to the chemoreceptor hypothesis, reduction of net drug uptake has emerged as the most frequent cause of resistance. This review, therefore, focuses on trypanosomal drug transporter genes. TbAT1 encodes purine permease P2, which mediates influx of melarsoprol and diamidines. Disruption of TbAT1 in Trypanosoma brucei reduced sensitivity to these trypanocides. TbMRPA encodes a putative trypanothione-conjugate efflux pump, and overexpression of TbMRPA in T. brucei causes melarsoprol resistance. It will be important to determine the role of TbAT1 and TbMRPA in sleeping sickness treatment failures.

The pharmacokinetics of eflornithine (?-difluoromethylornithine) in patients with late-stage T.b. gambiense sleeping sickness

OBJECTIVE

To investigate the plasma, cerebrospinal fluid (CSF) levels and pharmacokinetics of eflornithine (DFMO) in patients with late-stage T.b. gambiense sleeping sickness who were treated with an oral DFMO at 100 mg/kg or 125 mg/kg body weight every 6 h for 14 days.

METHODS

Plasma and CSF concentrations of DFMO were measured during day 10 and day 15 in patients following oral DFMO at 100 mg/kg (group I: n=12) and 125 mg/kg (group II: n=13) body weight every 6 h for 14 days. Clinical and parasitological assessments were performed at 24 h after the last dose of DFMO and at 12 months.

RESULTS

Patients in each group had a good initial response, but relapse was observed in six patients (three patients for each group) during 12 months follow-up. Plasma DFMO concentrations did not increase proportionally to doses when the dose increased from 100 mg/kg to 125 mg/kg body weight given every 6 h (60-70% of the expected increase). In most cases, concentration-time profiles of DFMO in each group were best fit using a two-compartment open model with first-order input, with absorption lag-time and first-order elimination. Average trough (C(ss-min)) and average (C(ss-ave)) plasma DFMO concentrations during steady state varied between 189-448 nmol/ml and 234-528 nmol/ml, following 100 mg/kg and 125 mg/kg dose group, respectively. C(max), t(max) and AUC(0- infinity ) values following the last dose were 296-691 nmol/l, 2-3 h, and 2911-6286 nmol h/ml, respectively. V(z)/F, CL/F and t(1/2z) values were 0.47-2.66 l/kg, 0.064-0.156 l/h/kg, and 3.0-16.3 h, respectively. CSF concentrations at steady state varied between 22.3 nmol/ml and 64.7 nmol/ml. Patients who had treatment failure tended to have lower plasma and CSF DFMO concentrations than those who had successful treatment.

CONCLUSION

Oral DFMO at the dose of 125 mg/kg body weight given every 6 h for 14 days may not produce adequate therapeutic plasma and CSF levels for patients with late-stage T.b. gambiense sleeping sickness.

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.

Glycosylinositolphosphate soluble variant surface glycoprotein inhibits IFN-gamma-induced nitric oxide production via reduction in STAT1 phosphorylation in African trypanosomiasis

Macrophages are centrally involved in the host immune response to infection with Trypanosoma brucei rhodesiense, a protozoan parasite responsible for human sleeping sickness in Africa. During trypanosome infections, the host is exposed to parasite-derived molecules that mediate macrophage activation, specifically GPI anchor substituents associated with the shed variant surface glycoprotein (VSG), plus the host-activating agent IFN-gamma, which is derived from activated T cells and is essential for resistance to trypanosomes. In this study, we demonstrate that the level and timing of exposure of macrophages to IFN-gamma vs GPI ultimately determine the macrophage response at the level of induced gene expression. Treatment of macrophages with IFN-gamma followed by GIP-sVSG (the soluble form of VSG containing the glycosylinositolphosphate substituent that is released by parasites) stimulated the induction of gene expression, including transcription of TNF-alpha, IL-6, GM-CSF, and IL-12p40. In contrast, treatment of macrophages with GIP-sVSG before IFN-gamma stimulation resulted in a marked reduction of IFN-gamma-induced responses, including transcription of inducible NO synthase and secretion of NO. Additional experiments revealed that the inhibitory activity of GIP-sVSG was associated with reduction in the level of STAT1 phosphorylation, an event required for IFN-gamma-induced macrophage activation. These results suggest that modulation of specific aspects of the IFN-gamma response may be one mechanism by which trypanosomes overcome host resistance during African trypanosomiasis.