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Biomedical subjects

C A Hunter

Publications and source records attributed to C A Hunter.

At least 91 records · Page 5Linked to original sources
PubMed1992

Subcurative chemotherapy and fatal post-treatment reactive encephalopathies in African trypanosomiasis.

The treatment of late-stage African sleeping sickness in man is often complicated by a post-treatment reactive encephalopathy. The bases of this pathological reaction was investigated in a mouse model of African trypanosomiasis. Subcurative treatment with diminazene aceturate, which did not clear parasites from the central nervous system, resulted in a post-treatment meningoencephalitis similar to that seen in man. By contrast, a curative regimen of melaminylthioarsenite and 5-nitroimidazole, which cleared parasites from the central nervous system, did not cause any pathological reaction in the mice. This result indicates that subcurative treatment leads to the development of the post-treatment encephalopathy. Evidence that this may also be the case in man was provided by the detection of trypanosome DNA with the polymerase chain reaction in the brains of 9 patients who had died as the result of a post-treatment reaction. Our findings suggest that more aggressive treatment regimens, which ensure the elimination of trypanosomes from the central nervous system, may prevent post-treatment reactions in patients.

Adolescent↗
PubMed1992

Kinetics of cytokine mRNA production in the brains of mice with progressive toxoplasmic encephalitis.

C57BL/10 ScSn (B10) mice infected orally with Toxoplasma gondii were killed on days 5, 10, 15, 20 and 30 post infection and their brains excised. These were either used to count total tissue cyst numbers or divided for RNA purification and histopathological studies. The first signs of inflammation were on day 10 post infection, before the appearance of cysts in the brain, and correlating with the appearance of activated astrocytes. These mice had a mild meningitis with areas of encephalitis. Small numbers of cyst stages were first observed in the brain on day 15 and by day 20 the cyst numbers had increased dramatically but were not always associated with inflammation. After this time point, total cyst numbers did not increase significantly though there developed a marked variation in tissue cyst size with larger cysts becoming more numerous. The use of the polymerase chain reaction to assist in the amplification of brain RNA allowed the characterization of the kinetics of cytokine production within the brains of these animals. Only IL-1 alpha was found to be expressed constitutively in control mice. Transcripts for other cytokines associated with activated monocytes, microglial cells and astrocytes [tumor necrosis factor (TNF)-alpha and interleukin (IL)-6] were present on day 10, (IL-6) and day 15 (TNF-alpha) post infection. Thereafter, these cytokines were present in all infected animals. Of the T cell-associated cytokines, IL-4, a characteristic product of the T helper (Th)2 cell subset, was detected on days 10 and 15, while granulocyte macrophage colony stimulating factor (GM-CSF) which can be produced not only by this cell type but also by Th1 cells and CD8+ T cells, was also present on day 15 but not thereafter. Transcripts for interferon (IFN)-gamma, present from day 15 post infection, were probably produced by CD8+ T cells, as IL-2 which would indicate Th1 cell involvement was only detected 30 days after infection. The continual presence of IFN-gamma and TNF-alpha, cytokines with reported anti-toxoplasmic activity, in the CNS of B10 mice throughout the latter half of the experimental period did not diminish the severity of infection. These results indicate that the CD4+ Th2 subset may allow a rapid rise in cyst numbers and so be important in determining susceptibility to toxoplasmic encephalitis.

Animals↗
PubMed1992

Hydrolysis of L-leucine methyl ester by Leishmania mexicana mexicana amastigote cysteine proteinases.

The main cysteine proteinases of the amastigote form of Leishmania mexicana mexicana were partially purified by gel filtration and ion exchange chromatography. The latter procedure resulted in the separation of some individual cysteine proteinases, as demonstrated by gelatin-sodium dodecyl sulphatepolyacrylamide gel electrophoresis. Fractions containing the partially purified proteinases rapidly hydrolysed L-leucine methyl ester to leucine. The activity towards this compound co-eluted with and resembled the parasite's cysteine proteinase activity. The results suggest that amastigotes of L.m.mexicana are susceptible to L-leucine methyl ester because this compound is rapidly hydrolysed by cysteine proteinases that occur in abundance in the megasomes of this stage.

Animals↗
PubMed1992

Correlation of autoantibody titres with central nervous system pathology in experimental African trypanosomiasis.

CD-1 mice infected with the protozoan parasite Trypanosoma brucei brucei developed few signs of central nervous system pathology associated with the invasion of the central nervous system by these parasites and did not survive beyond 5-6 weeks with deaths common before this time point. However, use of the trypanocidal drug diminazene aceturate (40 mg/kg), which fails to cross the blood-brain barrier, on day 21 post-infection led to the development of central nervous system pathology similar to that seen in the fatal post-treatment reactive encephalopathies that can occur in human African trypanosomiasis. Enzyme-linked immunosorbent assays were used to measure autoantibody titres to double-stranded DNA, myelin basic protein and to the myelin-specific galactocerebrosides and gangliosides in groups of infected mice, with or without the post-treatment reaction, on day 30 post-infection and compared with uninfected controls. Infection with T. brucei brucei raised the titres of all of these autoantibodies. Treatment of infected mice with diminazene aceturate resulted in elevated levels of all of these autoantibodies compared to the untreated animals. There was a strong positive correlation between the central nervous system pathology and the levels of autoantibodies to myelin basic protein, galactocerebrosides and gangliosides, but not to double-stranded DNA. The elevated titres observed may be a consequence of the polyclonal B cell activation that is believed to occur in African trypanosomiasis, parasite epitopes that are cross-reactive with these central nervous system (CNS)-specific antigens or result from the CNS damage associated with sub-curative chemotherapy.

Animals↗
PubMed1992

The use of azathioprine to ameliorate post-treatment encephalopathy associated with African trypanosomiasis.

The treatment of human African sleeping sickness is complicated by a post-treatment meningoencephalitis that may be fatal. Using a mouse model this study assesses the use of the non-steroidal anti-inflammatory drug, azathioprine, in the management of this post-treatment reaction. Female NIH mice treated with the trypanocidal compound diminazene aceturate (40 mg/kg), 28 days after infection, developed a similar post-treatment reaction to that seen in humans. Administration of azathioprine (100 mg/kg) for 5 days before and 5 days after trypanocidal chemotherapy abrogated the pathology in the central nervous system although this returned approximately 15 days after cessation of azathioprine. Activated astrocytes associated with the later stages of the infection did not appear to be affected by the use of azathioprine.

Animals↗
PubMed1992

Detection of cytokine mRNA in the brains of mice with toxoplasmic encephalitis.

C57Bl/10 ScSn mice infected with Toxoplasma gondii developed a meningoencephalitis, characterized by areas of tissue destruction and cellular infiltration including foci of neutrophils. Large numbers of cyst stages were found throughout the brain but were not always associated with inflammation. The use of immunocytochemistry to detect glial fibrillary acidic protein, an astrocyte specific marker, showed a widespread astrocyte activation. This was particularly prominent in areas of intense inflammation but cysts were negative for glial fibrillary acidic protein, indicating that astrocytes were not host cells for the bradyzoites. The use of the polymerase chain reaction to assist in the amplification of total brain RNA allowed the characterization of the cytokines being produced locally within the brains of infected animals. beta-actin transcripts were detected in all of the uninfected and infected mice. In only one of the seven uninfected control mice were other transcripts found. Transcripts for tumour necrosis factor-alpha, interleukin-1 alpha and beta, interleukin-6, macrophage inflammatory protein-1 and interferon-gamma as well as the CD4 marker were detected in all of the infected mice. However, transcripts for IL-2 and IL-4 were not present. Several of the cytokines present are capable of initiating meningeal inflammation and may play a role in the immunopathogenesis of toxoplasmic encephalitis.

Animals↗
PubMed1992

Astrocyte activation correlates with cytokine production in central nervous system of Trypanosoma brucei brucei-infected mice.

BACKGROUND: During the late-stage disease associated with human African trypanosomiasis, caused by infection with either Trypanosoma gambiense or T. rhodesiense, parasites invade the central nervous system (CNS), eventually leading to development of CNS pathology. This can be exacerbated by subcurative chemotherapy. The mechanisms through which the inflammatory processes within the CNS are controlled remain unclear. EXPERIMENTAL DESIGN: Mice infected with T. b. brucei were treated with a trypanocidal drug regimen on day 28 postinfection that cleared parasites from all sites except the brain. Brains of mice killed at different times during infection and after chemotherapy were analyzed, using immunocytochemistry for astrocyte activation and polymerase chain reaction assisted amplification of RNA to detect cytokine transcripts. RESULTS: Drug-treated animals developed a posttreatment meningoencephalitis similar to that which can occur in humans with late-stage African trypanosomiasis. Between days 14 and 21 postinfection, before chemotherapy and the subsequent development of inflammatory lesions in the brain, astrocytes became activated. The production of several cytokines correlated with this astrocyte activation. Low levels of interleukin-1 alpha transcripts were detected in uninfected controls, but levels increased with astrocyte activation in the infected animals. Transcripts for the macrophage inflammatory protein-1 and tumor necrosis factor-alpha were first detected on day 21 postinfection, with higher levels in mice after development of the posttreatment meningoencephalitis, whereas granulocyte macrophage-colony stimulating factor was detected only in animals that developed posttreatment reaction. Interleukin-6 and interferon-gamma were also first detected on day 21 postinfection, correlating with astrocyte activation but subsequently declined with time in both treated and untreated mice. CONCLUSIONS: These results indicate that cytokines are being produced within the CNS before any inflammation and that astrocytes may be the source of some of these cytokines. Thus astrocyte activation may be key in the control and development of the CNS inflammatory processes that occur in African sleeping sickness.

Animals↗
PubMed1991

Pi-pi interactions: the geometry and energetics of phenylalanine-phenylalanine interactions in proteins.

The geometries of aromatic-aromatic interactions between phenylalanine residues in proteins are analysed in detail and correlated with energy calculations. A new definition of the interplanar angle is important for distinguishing favourable edge-to-face and unfavourable face-to-face orientations. The experimental observations are scattered over a wide range of conformational space, with no strongly preferred single orientation. However, Phe-Phe interactions occur almost exclusively in electrostatically attractive geometries: electrostatically unfavourable regions are only sparsely populated. Electrostatics dominate the geometry of interaction, while van der Waals' interactions are less significant, probably due to the hydrophobic environment of the protein core. The observations on proteins support the Hunter-Sanders rules for pi-pi interactions. In particular, offset stacked geometries, which theory predicts to be favourable, are observed experimentally. For monocyclic aromatics, use of a C-H dipole, the approach used in molecular mechanics calculations, accounts well for these aromatic-aromatic interactions. Comparison with the results obtained from the small molecules database indicates that the protein and small molecule crystal environments are very different.

Databases, Factual↗
PubMed1991

Immunopathology of experimental African sleeping sickness: detection of cytokine mRNA in the brains of Trypanosoma brucei brucei-infected mice.

The immunopathology of Trypanosoma brucei brucei in the central nervous system was studied by using an experimental model of chronic meningoencephalitis in outbred CD-1 mice. Mice infected with T. b. brucei were treated with a subcurative dose of the trypanocidal compound diaminazine aceturate. These mice relapsed and were again drug treated. The brains were examined histologically and by immunocytochemistry to identify activated astrocytes. The polymerase chain reaction was used to detect cytokine RNA transcripts. The infected and treated animals developed severe chronic meningoencephalitis characterized by large numbers of inflammatory cells and widespread astrocyte proliferation. In uninfected controls, only interleukin 1 and beta-actin RNA transcripts were detected while transcripts for beta-actin, tumor necrosis factor alpha, macrophage inflammatory protein 1 and interleukins 1 and 4 were demonstrated in the brains of infected animals. Gamma interferon and interleukin 6 were also detected in a few of the infected animals, but interleukin 2 was not found in any of these animals.

Animals↗
PubMed1991

Aluminum phthalocyanine-streptavidin: new, sensitive fluorescent tracer for immunoassay.

A new fluorescent reagent based on aluminum phthalocyanine has been developed for general application to immunoassay. This highly sensitive fluorophore, Ultralite 680, may be covalently attached to a variety of biological entities for use as a tracer. We report the use of an Ultralite 680-streptavidin-digoxin conjugate as a tracer in a direct, competitive, heterogeneous, fluorescent immunoassay of digoxin. The assay is performed manually with 50 microL of serum and no sample pre-treatment. Primary anti-digoxin antibody is incubated with a serum sample containing digoxin and Ultralite 680-streptavidin-digoxin. Bound and free tracer are separated, and the bound fluorescence is released and quantified with a commercially available spectrofluorometer. Assay precision was good (CV = 7.05% at a digoxin concentration of 2.00 micrograms/L) and results by our method correlated well with those by a conventional RIA (r = 0.9650, n = 24).

Aluminum↗
PubMed1988

Vesicular systems (niosomes and liposomes) for delivery of sodium stibogluconate in experimental murine visceral leishmaniasis.

Suppression of Leishmania donovani liver amastigotes by sodium stibogluconate has been determined in a murine model of experimental visceral leishmaniasis. Niosomal and liposomal drug formulations were equiactive and both increased drug efficacy by an order of magnitude compared with that of free drug. Niosomes containing 30 mol % cholesterol were prepared from three different non-ionic surfactants and no significant difference in activity was detected among the different drug-loaded niosomes. Both negatively charged and neutral vesicles were found to be equally effective. However, vesicle cholesterol content had a slight influence on the antiparasitic activity of the drug-loaded niosomes. Empty vesicles produced a dose-dependent parasite suppression for all vesicles studied. Studies of antimony distribution in the mouse using neutron activation analysis showed high liver levels after i.v. administration of the carrier forms of the drug.

Animals↗
PubMed1987

Biodegradable microspheres: polyacryl starch microparticles as a delivery system for the antileishmanial drug, sodium stibogluconate.

Liver parasite burdens of Leishmania donovani in the mouse have been determined after treatment with intravenous administration of sodium stibogluconate in the free or carrier form. The carrier form, in which the drug was covalently bound to polyacryl starch microparticles, was up to 100x more effective than the free form in this murine model of visceral leishmaniasis. Empty microparticles had no effect on liver parasite burdens and the enhanced in-vivo antileishmanial activity of the carrier form of the drug was apparently due to passive drug delivery to the infected liver.

Animals↗
PubMed1986

Similarity in variable antigen type composition of Trypanosoma brucei rhodesiense populations in different sites within the mouse host.

Trypanosoma brucei rhodesiense subpopulations in different sites within the body of infected mice were isolated and enumerated on day 6 of cyclically transmitted infections. Most trypanosomes were in the blood vasculature and spleen but approximately 6% occurred in lymph nodes and about 9% were extravascular. Most of the extravascular trypanosomes were in the peritoneal and pleural cavities; significant numbers also occurred in the brain and kidneys. Six major variable antigen types (VATs) were detected by immunofluorescence using specific antisera and monoclonal antibodies. The prevalence of each VAT was essentially the same in subpopulations in the blood, mesenteric and inguinal lymph nodes, brain, kidneys and peritoneal and pleural cavities. This similarity of VAT composition in different subpopulations is probably caused by high rates of dynamic interchange of trypanosomes between sites. Extravascular trypanosomes, therefore, form a significant proportion of the total population in acute infections of mice but they do not appear to play any special role in the population biology of antigenic variation at this stage of infection.

Animals↗
PubMed1984

Presence of delta-sleep-inducing peptide-like material in human milk.

Delta-sleep-inducing peptide (DSIP)-like material was detected in human breast milk of two women by RIA with a recovery of about 90%. The high concentration of DSIP-like immunoreactivity (DSIP-LI) in colostrum (30 ng/ml) decreased to about 10 ng/ml in milk. The concentration continued to decrease over the next 2 months in one women. In the same woman, a significant circadian rhythm of the amount of breast milk DSIP was found with the peak in the afternoon and the trough in the morning. A significant effect of the sampling procedure was detected in the other woman examined; lower amounts of DSIP-LI were found when the milk was collected before and higher concentrations after nursing. Gel chromatography revealed that most of the immunoreactive DSIP-LI in milk and colostrum occurred in a form larger than the nonapeptide. The presence of DSIP itself, however, was demonstrated by high pressure liquid chromatography, which also showed additional peptides reacting with the antibody. Digestion of the large immunoreactive DSIP-LI by trypsin produced a peak on Sephadex G-10 that coeluted with DSIP. This peak contained three immunoreactive fractions with retention times on high pressure liquid chromatography similar to DSIP, phosphorylated DSIP, and N-tyrosine-DSIP. Plasma samples taken during pregnancy were assayed for DSIP but no difference from normal values was found. Slightly higher amounts were found in placenta than in blood, which might be due to interfering substances. No Tyr-MIF-1 or corticotropin-releasing hormone was detected by RIA in human breast milk. Peptides and proteins of milk can be absorbed from the gastrointestinal tract of babies, but it is not known if the DSIP-LI in human milk is involved in the induction of a sleep-wake cycle in neonates.

Chromatography, Gel↗