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.

The efficacy of ascofuranone in a consecutive treatment on Trypanosoma brucei brucei in mice

Consecutive administration of ascofuranone without glycerol was found to have therapeutic efficacy against Trypanosoma brucei brucei infection in mice. A suspension of ascofuranone (25-100 mg/kg) was administrated intraperitoneally every 24 h for 1-4 consecutive days to trypanosome-infected mice and efficacy was compared with oral treatment. With intraperitoneal administration, all mice treated with 100 mg/kg ascofuranone for 4 consecutive days were cured. On contrary, with oral treatment a higher dose of ascofuranone (400 mg/kg) was needed for 8 consecutive days to cure the mice. With intraperitoneal treatment, parasitemia was strongly suppressed, with almost all long slender bloodstream forms of the parasite changed to short stumpy forms by day 3 and the parasites have been eliminated 4 days after the start of treatment. These ascofuranone-induced short stumpy forms were morphologically analogous to the stumpy forms 2 days after peak parasitemia of pleomorphic clone of T. b. brucei GUTat 3.1. However, the properties of ubiquinol oxidase activity, which is the target of ascofuranone, in mitochondria isolated from before and after treatment, were almost same. The enzymatic activities of ubiquinol oxidase were only decreased to approximately 30% within a day after treatment, and then kept at nearly the same level. In the present study, we have improved regimen for administration of ascofuranone without glycerol, and demonstrated that consecutively administrated ascofuranone showed trypanocidal effects in T. b. brucei infected mice. Our present results strongly suggest that consecutive administration of ascofuranone may be an effective chemotherapy for African trypanosomiasis.

[Human African trypanosomiasis in Ivory Coast: biological characteristics after treatment. 812 cases treated in the Daloa focus (Ivory Coast)]

The treatment and post therapeutic follow up of patients diagnosed with HAT are important for HAT control. A longitudinal survey was implemented in the focus of Daloa (Côte d'Ivoire). A total of 812 patients infected with Trypanosoma brucei gambiense in meningoencephalitic stage and treated with melarsoprol were included, this study pointed out the biological characteristics of patients after treatment. The relapse occurs between 1 and 24 months after treatment. It is essentially neurological, and characterised by the presence in the CSF of antibodies, by the increase of cell count compared with value immediately after treatment, or by the presence of trypanosomes. The cure can be confirmed from 18 months after treatment, and is characterised by the absence of antibodies and trypanosomes in the CSF, by a normal cell count and a normal proteinorachy. Biological scares were recorded on some of the patients after 18 months of follow up, but no relapse occurred among them.

Lipid-drug-conjugate (LDC) nanoparticles as novel carrier system for the hydrophilic antitrypanosomal drug diminazenediaceturate

The objective of the present study was to incorporate the hydrophilic drug diminazenediaceturate at a high loading into lipid nanoparticles by creating nanoparticles from lipid-drug conjugates (LDC). IR and DSC data showed that the antitrypanosomal drug diminazene is able to react with fatty acids to form water-insoluble salts like diminazenedistearate and -dioleate. The salts could be transformed into nanoparticles using high-pressure homogenization technique, established for solid lipid nanoparticles (SLN). By using polysorbate 80 as surfactant, physically stable LDC nanoparticle dispersions of both salts could be obtained. The mean PCS diameters and polydispersity indices were 364 nm and 0.233 for diminazenedistearate and 442 nm and 0.268 for diminazenedioleate, respectively. Due to the composition of the LDC bulk materials, nanoparticles with a high drug load of 33% (w/w) were obtained even for this highly water-soluble drug diminazenediaceturate. The new carrier system of LDC nanoparticles overcomes one limitation of SLN, i.e. the limited loading capacity for hydrophilic drugs. Transforming water-soluble hydrophilic drugs into LDC and formation of nanoparticles allows prolonged drug release and targeting to specific sites by i.v. injection. These results provide a first basis of using LDC-polysorbate 80 nanoparticles for brain delivery of diminazene to treat second stage human African trypanosomiasis (HAT).

Classical ligands bind tubulin of trypanosomes and inhibit their growth in vitro

Tubulin ligands known to be toxic to certain organisms or cells were tested for their ability to inhibit proliferation of trypanosomes in culture. Tubulin was purified from Trypanosoma brucei brucei or rat brain by poly-L-lysine affinity chromatography and used in binding studies in order to compare the binding of [3H]mebendazole to trypanosome and mammalian tubulin. All the compounds tested in culture inhibited trypanosome proliferation in a concentration-dependent manner. The concentration required to inhibit trypanosome proliferation by 50 or 90% (IC50 or IC90) in 24 hr was determined for each compound. There were no significant differences (P > 0.05) among the benzimidazoles (BZs), but colchicine and vinblastine caused significantly greater inhibitions than the BZs (P < 0.02 and P < 0.005, respectively). Increasing the incubation time to 72 hr caused a 2- to 4-fold lowering of the IC50 and IC90 values for all the drugs. In the binding assays, there was higher total binding of [3H]mebendazole to trypanosome than rat brain tubulin. The results suggest that the inhibition of trypanosome growth was caused by the specific interaction of these ligands with trypanosome tubulin. Trypanosome tubulin is, therefore, a reasonable target against which novel drugs can be developed to control trypanosomiasis.

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

Increased levels of circulating endotoxins are a feature of both human and experimental African trypanosomiasis. Studies with rats and mice have shown that these may originate from intestinal damage with altered permeability of the gut epithelium. Endotoxins are potent immunomodulatory substances which can initiate the production of a range of cytokines and mediators from different cell types. In rats infected with T.b. brucei we have examined possible associations of the endotoxin increases with increases in levels of TNF-alpha, IL-1beta, IL-6, IFN-gamma and nitric oxide (NO). Significant increases in each substance occurred at days 21 and 33 post-infection (p.i.). The increases in cytokines were highly correlated with the endotoxin levels (e.g. at day 21 p.i. the correlation-regression values were as follows: TNF-alpha, r = 0.9, P < 0.01; IL-1beta, r = 0.83, P < 0.01; IL-6, r = 0.9, P < 0.01; IFN-gamma, r = 0.7, P < 0.01). There were also strong correlations between the increased levels of several individual cytokines. Biopsies of chopped sections of small intestine tissues of rats showed a parallel production of cytokines, again with significant correlations with the circulating endotoxins. The production of NO and cytokines by the intestine may be associated with the increased transepithelial permeability which occurs during the infection.

Chemotherapy of human African trypanosomiasis

Human African trypanosomiasis or sleeping sickness is resurgent [1,2]. The disease is caused by subspecies of the parasitic haemoflagellate, Trypanosoma brucei. Infection starts with the bite of an infected tsetse fly (Glossina spp.). Parasites move from the site of infection to the draining lymphatic vessels and blood stream. The parasites proliferate within the bloodstream and later invade other tissues including the central nervous system. Once they have established themselves within the CNS, a progressive breakdown of neurological function accompanies the disease. Coma precedes death during this late phase. Two forms of the disease are recognised, one caused by Trypanosoma brucei rhodesiense, endemic in Eastern and Southern Africa, in which parasites rapidly invade the CNS causing death within weeks if untreated. T. b. gambiense, originally described in West Africa, but also widespread in Central Africa, proliferates more slowly and can take several years before establishing a CNS-involved infection. Many countries are in the midst of epidemics caused by gambiense-type parasites. Four drugs have been licensed to treat the disease [3]; two of them, pentamidine and suramin, are used prior to CNS involvement. The arsenic-based drug, melarsoprol is used once parasites are established in the CNS. The fourth, eflornithine, is effective against late stage disease caused by T. b. gambiense, but is ineffective against T. b. rhodesiense. Another drug, nifurtimox is licensed for South American trypanosomiasis but also been used in trials against melarsoprol-refractory late sage disease. This review focuses on what is known about modes of action of current drugs and discusses targets for future drug development.

The effects of drug-sensitive and drug-resistant Trypanosoma congolense infections on the pharmacokinetics of homidium in Boran cattle

Two groups of five Boran (Bos indicus) cattle were infected with one of two populations of Trypanosoma congolense; one drug-sensitive (IL1180), and one drug-resistant (IL3330). The animals were then treated intramuscularly with homidium bromide at a dose rate of 1.0 mg kg(-1) bodyweight 7 days after trypanosomes were detected in the peripheral blood of all the five animals in each group. Following treatment of cattle infected with drug-sensitive trypanosomes, parasites could no longer be detected in the bloodstream of four out of five cattle after 24 h, and after 48 h for the fifth animal. The animals remained aparasitaemic up to the end of the observation period of 90 days and serum drug concentrations determined by enzyme-linked immunosorbent assay (ELISA) remained above the detection limit of 0.1 ng ml(-1) for the entire period. Following treatment of cattle infected with drug-resistant trypanosomes, parasites did not disappear from the bloodstream in any of the five animals. The rate of drug elimination was greater in cattle infected with drug-resistant trypanosomes and the drug was no longer detectable approximately 3 weeks after treatment. Non-compartmental pharmacokinetic analysis showed that the values for t(12)beta of 75.5 +/- 16.9 h, the area under the curve (AUC(0-infinity)) of 1.33 +/- 0.156 microg h ml(-1) and the MRT(0-infinity) of 32.8 +/- 4.45 h obtained in cattle infected with the drug-resistant trypanosome population were significantly lower than the values of 424 +/- 146 h for t(12)beta, 1.67 +/- 0.233 microg h ml(-1) for AUC(0-infinity) and 297 +/- 159 h for MRT(0-infinity) obtained in cattle infected with the drug-sensitive population. The persistence of drug-resistant infections in cattle following homidium treatment was associated with more rapid drug elimination than in those in which infections with drug-sensitive parasites were cleared by the drug.

The physiological significance of transferrin receptor variations in Trypanosoma brucei

Trypanosoma brucei escapes destruction by the host immune system by regularly replacing its Variant Surface Glycoprotein (VSG) coat. The VSG is expressed in a VSG expression site, together with expression site associated gene (ESAG) 6 and 7, encoding the heterodimeric transferrin receptor (Tf-R). There are around 20 VSG expression sites, and trypanosomes can change the site that is active. Since ESAG6 and 7 in different expression sites differ somewhat in sequence, expression site switching results in the production of a slightly different Tf-R. We have studied the physiological relevance of Tf-R variation for the survival of T. brucei in mammalian sera. Trypanosomes with an active 221 expression site, encoding a Tf-R with a very low affinity for canine Tf (Kd>1 microM), were cultured in canine serum based medium. This resulted in selection of trypanosomes that had switched to the VO2, the 223 or the bR-2 expression site, each encoding a Tf-R with higher affinity for canine Tf than the 221 site Tf-R. Adding bovine Tf to the medium could prevent the switch, indicating that the low uptake of Tf provided the selection against 221 trypanosomes. Horse serum based medium also induced switching to the VO2 expression site, but this was not prevented by bovine Tf. In the presence of physiological concentrations of anti-Tf-R antibody, only a high-affinity Tf allowed the growth of 221 Tf-R expressing trypanosomes. Our results suggest that a high-affinity Tf-R not only ensures efficient Tf uptake, but is also required to allow sufficient iron uptake by the trypanosome in the presence of anti-Tf-R antibodies.

Pharmacokinetic investigations in patients from northern Angola refractory to melarsoprol treatment

Melarsoprol, an organo-arsenical drug, has been the drug of choice for late-stage trypanosomiasis for 50 years. Because of the lack of alternatives any abatement of this medication will have a dramatic negative impact on the perspectives for patients. As a large number of patients refractory to melarsoprol treatment was recently reported from northern Uganda and northern Angola, we investigated in northern Angola whether interpatient pharmacokinetic differences influence the outcome of melarsoprol treatment. Drug levels were determined by a biological assay in serum and cerebrospinal fluid (CSF) of 22 patients. Nine patients could be successfully treated, eight were refractory and the outcome was unclear or no adequate follow-up information was available for five patients. No differences in the pharmacokinetic parameters (maximum serum concentration Cmax, half-life t1/2 beta, total clearance CL and the volume of distribution Vss) could be detected between the groups. Serum and CSF concentrations for all patients were in the expected range. This result indicates that other underlying factors are responsible for treatment failures.

Trypanosoma brucei brucei crosses the blood-brain barrier while tight junction proteins are preserved in a rat chronic disease model

African trypanosomiasis, sleeping sickness in humans, is caused by the systemic infection of the host by the extracellular parasite, the African trypanosome. The pathogenetic mechanisms of the severe symptoms of central nervous system involvement are still not well understood. The present study examined the routes of haematogenous spread of Trypanosoma brucei brucei (Tbb) to the brain, in particular on the question whether parasites can cross the blood-brain barrier, as well as their effect on tight junction proteins. Rats were infected with Tbb and at various times post-infection, the location of the parasite in the central nervous system was examined in relation to the brain vascular endothelium, visualized with an anti-glucose transporter-1 antibody. The tight junction-specific proteins occludin and zonula occludens 1, and the possible activation of the endothelial cell adhesion molecules ICAM-1 and VCAM-1 were also studied. At 12 and 22 days post-infection, the large majority of parasites were confined within blood vessels. At this stage, however, some parasites were also clearly observed in the brain parenchyma. This was accompanied by an upregulation of ICAM-1/VCAM-1. At later stages, 42, 45 and 55 days post-infection, parasites could still be detected within or in association with blood vessels. In addition, the parasite was now frequently found in the brain parenchyma and the extravasation of parasites was more prominent in the white matter than the cerebral cortex. A marked penetration of parasites was seen in the septal nuclei. In spite of this, occludin and zonula occludens 1 staining of the vessels was preserved. The results indicate that the Tbb parasite is able to cross the blood-brain barrier in vivo, without a generalized loss of tight junction proteins.

Uptake and mode of action of drugs used against sleeping sickness

Sleeping sickness is resurgent in Africa. Adverse side-effects and drug-resistance are undermining the few drugs currently licensed for use against this disease, which is caused by parasitic protozoa of the Trypanosoma brucei group. Pentamidine and suramin are used before parasites become manifest in the central nervous system, after which the organic arsenical melarsoprol is used. Eflornithine is also useful in late-stage disease. A mode of action has been elucidated only for the ornithine decarboxylase inhibitor eflornithine. Both uptake and potential intracellular targets need to be considered when contemplating modes of action. The melaminophenyl arsenicals are accumulated via an unusual amino-purine transporter termed P2, which also seems to have a role in the uptake of the diamidine class of drugs to which pentamidine belongs. Since loss of this transporter leads to drug-resistance, other uptake mechanisms also need to be considered in generating novel trypanocides. Some nitroheterocyclic drugs have prolific activity against trypanosomes, although the fact that they are mutagenic in Ames' tests is acting as a barrier to further development. New drugs are urgently needed and the advent of genome sequencing and target validation using genetic modification will hopefully accelerate this process.

Importance of L-tryptophan metabolism in trypanosomiasis

African trypanosomiasis or sleeping sickness is caused by extracellular trypanosomes. The presence of seric antibodies directed to a tryptophan-like epitope in trypanosome infected patients and animals led us to investigate the roles of tryptophan in trypanosomiasis. These antibodies are directed against a tryptophan-rich conserved sequence inside the major parasite surface glycoprotein. In vitro, a rapid uptake of tryptophan by trypanosomes is measured. Seric tryptophan levels are decreased during trypanosomiasis. This decrease may be linked with an increase in indoleamine 2,3-dioxygenase (IDO) induced by Interferon-gamma. In vivo inhibition of IDO by norharman provokes a dramatic increase in circulating parasite number. All these data show the essential role of tryptophan in parasite growth. Moreover, antibodies against tryptophan, the decreased concentration of the neurotransmitter serotonin in the brain following infection and the tryptophan metabolites (tryptophol) produced by trypanosomes may participate to the pathophysiological mechanisms provoking sleeping sickness.

Inducible nitric oxide synthase and nitrotyrosine in the central nervous system of mice chronically infected with Trypanosoma brucei brucei

Human African trypanosomiasis, or sleeping sickness, evolves toward a meningoencephalitic stage, with a breakage in the blood-brain barrier, perivascular infiltrates, and astrocytosis. The involvement of nitric oxide (NO) has been evoked in the pathogenic development of the illness, since NO was found to be increased in the brain of animals infected with Trypanosoma brucei (T. b.) brucei. An excessive NO production can lead to alterations of neuronal signaling and to cell damage through the cytotoxicity of NO and its derivatives, especially peroxynitrites. In African trypanosomiasis, the sites of NO production and its role in the pathogenicity of lesions in the central nervous system (CNS) are unknown. In a chronic model of African trypanosomiasis (mice infected with T. b. brucei surviving with episodic suramin administration), NADPH-diaphorase staining of brain slides revealed that NO synthase (NOS) activity is located not only in endothelial cells, choroid plexus ependymal cells, and neurons as in control mice but also in mononuclear inflammatory cells located in perivascular and parenchyma infiltrates. An immunohistochemical study showed that the mononuclear inflammatory cells expressed an inducible NOS activity. Furthermore, the presence of nitrotyrosine in inflammatory lesions demonstrated an increased NO production and the intermediate formation of peroxynitrites. The detection of extensive formation of nitrotyrosine in the CNS parenchyma was observed in mice having shown neurological disorders, suggesting the role of peroxynitrites in the appearance of neurological troubles. In conclusion, this study confirmed the increased NO synthesis in the CNS of mice infected with T. b. brucei and suggests a deleterious role for NO, through the formation of peroxynitrites, in the pathogenesis of African CNS trypanosomiasis.

Chronic sodium salicylate treatment exacerbates brain neurodegeneration in rats infected with Trypanosoma brucei

We have reported previously that axonal degeneration in specific brain regions occurs in rats infected with the parasite Trypanosoma brucei. These degenerative changes occur in spatiotemporal association with over-expression of pro-inflammatory cytokine messenger RNAs in the brain. To test how aspirin-like anti-inflammatory drugs might alter the disease process, we fed trypanosome-infected rats with 200mg/kg of sodium salicylate (the first metabolite of aspirin) daily in their drinking water. Sodium salicylate treatment in uninfected rats did not cause any neural damage. However, sodium salicylate treatment greatly exacerbated neurodegeneration in trypanosome-infected rats, resulting in extensive terminal and neuronal cell body degeneration in the cortex, hippocampus, striatum, thalamus, and anterior olfactory nucleus. The exaggerated neurodegeneration, which occurred in late stages of infection, was temporally and somewhat spatially associated with a late-appearing enhancement of messenger RNA expression of interleukin-1beta, interleukin-1beta converting enzyme, tumor necrosis factor-alpha, and inhibitory factor kappaBalpha in the brain parenchyma. Restricted areas showed elevations in messenger RNA expression of interleukin-1 receptor antagonist, interleukin-6, inducible nitric oxide synthase, interferon-gamma, and inducible cyclooxygenase. The association suggests that increased production of pro-inflammatory cytokines in the brain may be an underlying mechanism for neural damage induced by the chronic sodium salicylate treatment. Furthermore, the results reveal a serious complication in using aspirin-like drugs for the treatment of trypanosome infection.

Uptake of the nitroimidazole drug megazol by African trypanosomes

Megazol, CL 64,855 (2-amino-5-[1-methyl-5-nitro-2-imidazolyl]-1,3, 4-thiazole) has been shown to be extremely effective in clearing experimental infections of African trypanosomes. An unusual amino-purine transporter termed P2, implicated in the transport of both the diamidine and melaminophenyl arsenical classes of drug in Trypanosoma brucei, recognised chemical groups on compounds which are also present on megazol. Megazol interacted with this carrier protein, as judged by its ability to inhibit P2 adenosine transport and to abrogate in vitro arsenical-induced lysis in a dose-dependent manner. However, parasites resistant to melaminophenyl arsenical and diamidine drugs due to lack of the P2 transporter showed no resistance to megazol. This is because passive diffusion represented the major route of entry. Initial rates of uptake were not saturable within the limit of megazol's solubility and did not conform to thermodynamic precepts compatible with carrier-mediated uptake. Adenosine and other P2 transporter substrates, even at high concentration, had little impact on megazol uptake. Uptake was biphasic, with a very rapid equilibration across the membrane followed by a slower accumulation over time. The equilibration phase represented a simple passive diffusion, with the subsequent uptake probably being due to metabolism of the drug.

Chemokines are produced in the brain early during the course of experimental African trypanosomiasis

African trypanosomiasis is characterized by progressive central nervous system (CNS) involvement. Using single and double immunohistochemistry, we evaluated the induction of alpha- and beta-chemokines in brains of Sprague-Dawley rats infected with Trypanosoma brucei brucei (T. b. brucei) and identified their cellular source. The results showed high production of MIP-2, RANTES and MIP-1alpha and to a lower extend MCP-1 in infected animals compared to controls. MIP-2, RANTES and MIP-1alpha were produced early by astrocytes and microglia and later by macrophages and T-cells. These findings suggest that chemokines may contribute to the immunopathogenesis that occurs in the CNS early during infections.

Pharmacokinetics, metabolism and excretion of megazol in a Trypanosoma brucei gambiense primate model of human African trypanosomiasis. Preliminary study

The pharmacokinetics of megazol (2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazol, CAS 19622-55-0) was investigated after a 100 mg/kg oral administration to six primates infected with Trypanosoma brucei gambiense. The plasma levels of megazol were between 0.2 microgram/ml and 46 micrograms/ml 24 h after dosing in all animals. In animals with prolonged infection, megazol absorption was accelerated (Tmax was 4 h compared with 8 h, for day 53 and day 39 post inoculation) but the amount absorbed was not modified. The megazol concentrations in the cerebrospinal fluid represented between 5.5% and 10.6% of the plasma levels at the same times. Unchanged megazol was eliminated predominantly via the kidneys: 46-96% of the ingested dose was recovered in the urine, compared with 0-5% in the faeces. Furthermore, this urinary elimination of megazol was altered in animals with prolonged infections. In the urine, 4 unknown metabolites were observed, unchanged megazol was characterized by LC-MS/MS. This study indicates that megazol crosses the blood-brain barrier after oral administration. Prolonged infections affect the absorption of megazol and its urinary elimination.

Chronic overexpression of proinflammatory cytokines and histopathology in the brains of rats infected with Trypanosoma brucei

Overproduction of proinflammatory cytokines in the brains of transgenic animals causes brain pathology. To investigate the relationship between brain cytokines and pathology in the brains of animals with adult-onset, pathophysiologically induced brain cytokine expression, we studied rats infected with the parasite Trypanosoma brucei. Several weeks after infection, in situ hybridization histochemistry showed a pattern of chronic overexpression of the mRNAs for proinflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha in the brains of the animals. Similar spatiotemporal inductions of mRNAs for inhibitory factor kappaBalpha and interleukin-1beta converting enzyme were found and quantified. The mRNAs for inducible nitric oxide synthase and interleukin-1 receptor antagonist were highly localized to the choroid plexus, which showed evidence of structural abnormalities associated with the parasites' presence there. The mRNAs for interleukin-6, interferon-gamma, and inducible cyclooxygenase showed restricted induction patterns. Another set of animals was processed for degeneration-induced silver staining, TdT-mediated dUTP-digoxigenin nick end-labeling (TUNEL) staining, glial fibrillary acidic protein (GFAP) immunohistochemistry, and several other histological markers. Apoptosis of scattered small cells and degeneration of certain nerve fibers was found in patterns spatially related to the cytokine mRNA patterns and to cerebrospinal fluid diffusion pathways. Furthermore, striking cytoarchitectonically defined clusters of degenerating non-neuronal cells, probably astrocytes, were found. The results reveal chronic overexpression of potentially cytotoxic cytokines in the brain and selective histopathology patterns in this natural disease model. J. Comp. Neurol. 414:114-130, 1999. Published 1999 Wiley-Liss, Inc.

Interferon-gamma and interleukin-12 genes are preferentially expressed during early experimental African trypanosomiasis and suppressed by denervation of the spleen

The cross talk between the central nervous system (CNS) and the immune system includes among others, the modulation of immune responses by the autonomic nervous system. Here, we investigated the effects of a splenic denervation on cytokine induction in early experimental African trypanosomiasis. Profiles of the cytokine mRNA expression for interleukin (IL)-4, interleukin (IL)-6, interleukin (IL)-10, interleukin (IL)-12, tumour necrosis factor (TNF)-alpha, tumour necrosis factor (TNF)-beta, transforming growth factor (TGF)-beta and interferon (IFN)-gamma were examined at 4 h, 8 h and 12 h postinfection (p.i.), and in noninfected controls. Only IFN-gamma and IL-12 were significantly expressed over noninfected controls. Already at 4 h p.i. both cytokines were expressed and showed more increased levels at 12 h. Sympathetic denervation of the spleen markedly reduced the mRNA expression for both IFN-gamma and IL-12. Con A was used as a positive control and showed an enhanced mRNA expression, which was also suppressed by a splenic denervation. To demonstrate that the mRNA expression had resulted in a cytokine production, we looked for the protein level of IFN-gamma at 4 h p.i. by immunohistochemistry and found increased levels of IFN-gamma, which was also inhibited by the denervation. Sham-operated animals exhibited similar responses as the nondenervated controls. Our data present for the first time very early kinetics for a cytokine gene expression during an experimental African trypanosomiasis. Furthermore, the data suggest a regulatory role for the autonomic nervous system on cytokine responses at both the mRNA and the protein levels.

The GPI biosynthetic pathway as a therapeutic target for African sleeping sickness

African sleeping sickness is a debilitating and often fatal disease caused by tsetse fly transmitted African trypanosomes. These extracellular protozoan parasites survive in the human bloodstream by virtue of a dense cell surface coat made of variant surface glycoprotein. The parasites have a repertoire of several hundred immunologically distinct variant surface glycoproteins and they evade the host immune response by antigenic variation. All variant surface glycoproteins are anchored to the plasma membrane via glycosylphosphatidylinositol membrane anchors and compounds that inhibit the assembly or transfer of these anchors could have trypanocidal potential. This article compares glycosylphosphatidylinositol biosynthesis in African trypanosomes and mammalian cells and identifies several steps that could be targets for the development of parasite-specific therapeutic agents.

Neuronal activity and transcription of proinflammatory cytokines, IkappaBalpha, and iNOS in the mouse brain during acute endotoxemia and chronic infection with Trypanosoma brucei brucei

Trypanosoma brucei brucei (Tbb) infection is a model of chronic immune response associated with severe neurological disorders believed to lead to coma and death. We hypothesized that exaggerated production of proinflammatory molecules within the cental nervous system (CNS) may be involved in the etiology of the disease, i.e., African Tripanosomiasis. The purpose of the present study was therefore to verify the effects of the parasite Tbb on the genetic expression of the immediate-early gene c-fos (index of cellular activity), tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), inhibitory factor kappa B alpha (IkappaBalpha, index of the nuclear factor kappaB activity, the transcription factor of numerous proinflammatory molecules), and inducible nitric oxide synthase (iNOS) in the mouse brain. Adult male BALB/c mice received a single intraperitoneal injection of lipopolysaccharide (LPS, used as positive control for these markers that are induced in a transient manner by the endotoxin), Tbb, or vehicle solution and were sacrificed at multiple times (1 hr to 7 days) following the injection. Acute and chronic models induced a robust expression of c-fos in numerous regions of the brain, including the circumventricular organs (CVOs) and different nuclei involved in autonomic control. Although the effect of LPS was rapid and transient, Tbb pathogen stimulated c-fos only within 5 to 7 days. The genes encoding TNF-alpha and IL-6 cytokines were expressed in the CVOs and choroid plexus 1 and 3 hr after LPS injection, whereas no convincing hybridization signal was detected in the brains of Tbb-infected mice at any time. IL-6 and iNOS-expressing cells were also found along large blood vessels of LPS-treated mice, while scattered small TNF-alpha-expressing cells were observed across the brain 12 and 24 hr after the endotoxin treatment. Tbb caused a low to moderate expression of iNOS and IkappaBalpha genes in perivascular cells, but this effect was apparent only several days following the parasite infection. Taken together, these data indicate that LPS and Tbb stimulate c-fos expression in similar nuclei involved in autonomic control, an event occurring within the first 3 hr after the LPS insult and only 5 days post-Tbb injection. The mRNAs encoding proinflammatory cytokines were, however, not detected in Tbb-infected brains, which may be explained by the Tbb variant (MiTat 1.5) that caused high parasitaemias and mortality within 5 to 7 days.

Microglia activation in a model of sleep disorder: an immunohistochemical study in the rat brain during Trypanosoma brucei infection

Microglial cells play a key role in the events triggered by infection, injury or degeneration in the central nervous system not only as scavenger cells but also as immune effector elements. We analyzed the features and distribution of cells of the microglia/macrophage lineage with OX-42 and ED-1 immunohistochemistry in the brain of experimental rats infected with the extracellular parasite Trypanosoma brucei. Such experimental infection provides a rat model of sleeping sickness or African trypanosomiasis, and is hallmarked in its advanced stages by severe alterations of the animals' sleep structure. In infected rats a remarkable activation of microglia, revealed by OX-42 immunoreactivity, became evident in the 3rd week post-infection in periventricular and subpial brain regions, with a prevalence in the hypothalamus. These features were concomitant with the onset of sleep anomalies, monitored with electroencephalographic recordings. Microglia activation increased in the following weeks, paralleling the progressive alterations of sleep parameters, and was most marked in the terminal stages of the infection, corresponding to the 6th-7th weeks. In addition, ED-1-immunoreactive macrophages and ramified microglia, confined to hypothalamic periventricular and basal regions, were evident after 4 weeks of disease. Degeneration of neuronal perikarya was not detected histologically in the infected brains at any time point. These data provide evidence for a reaction of microglia and macrophages in the brain of trypanosome-infected rats, and point out a selective distribution of these activated cells. The findings are discussed in relation to the animals' sleep disorder during trypanosome infection.