1,720,963 research outputs found
A comparative analysis of the cytotoxicity of cyanotoxins using in vitro (cell culture) and in vivo (mouse) assays
Get PDFDissertation (MSc (Paraclinical Studies))--University of Pretoria, 2007.The main objective of this study was the application and comparison of different assays in assessing toxicity of cyanobacterial samples, and also characterizing toxicity of the field samples. Therefore, toxicity of purified microcystin-LR (MC-LR) and cyanobacterial samples collected from the Hartbeespoort (HBP) Dam (winter and summer seasons of 2005/2006) and Kruger National Park (KNP) were investigated and compared using the ELISA, mouse bioassay, catfish primary hepatocytes (in vitro assay) and protein phosphatase inhibition (PPi) assays. During sampling in the summer season at the HBP Dam, the dam surface was covered with a thick-green layer of cyanobacterial scum and a foul smell coming from the water surface was always present. Only blue-green streaks of cyanobacteria covered the dam surface during the winter season. All HBP Dam samples (winter and summer samples) and KNP samples (Nhlanhanzwani Dam, Mpanama Dam and Sunset Dam) were dominated by Microcystis aeruginosa with the exception of Makhohlola Dam samples which were found to have no cyanobacteria. The World Health Organization (WHO) has proposed a guideline value for human use of 1.0 µg/L (0.001 mg/L) for MC-LR, the most common microcystin (MC) variant, in drinking water (WHO 1998), whereas 2 000 Microcystis cells/mL have been recommended as the limit of cyanobacteria in drinking water for animals (DWAF 1996). Cyanotoxin concentrations exceeding the prescribed guideline value were detected in all HBP Dam samples (ELISA results ranging between 3.67 to 86.08 mg/L; PPi results ranging between 2.99 to 54.90 mg/L) and KNP samples (ELISA results ranging between 0.1 to 49.41 mg/L; PPi results ranging between 0.006 to 10.95 mg/L) using both the ELISA and PPi assays. In the current study, a dose of about 175 µg/kg of purified MC-LR was demonstrated to be lethal in male CD-1 SPF mice. The HBP Dam summer samples and Nhlanganzwani Dam samples were the only cyanobacterial samples that resulted in death (acute toxicity) of mice. In order to be able to investigate further the in vivo effects of cyanotoxins, transmission electron microscopy (TEM) was used to complement results obtained from the in vivo assay. Ultrastructural changes of varying degree were observed in livers of mice exposed to both the HBP Dam winter and summer samples. Early stages of hepatocyte to hepatocyte disassociation, slight vesiculation of endoplasmic reticulum (ER) and swollen mitochondria were the most significant ultrastructural changes produced in mouse hepatocyte tissues by the HBP Dam winter samples. The most significant ultrastructural changes produced in mouse hepatocyte tissues by the HBP Dam summer samples were massive hepatic haemorrhage indicated by the appearance of erythrocytes between hepatocytes and the extensive vesiculation of ER. This is the first time that the African sharptooth catfish primary hepatocyte model has been used to assess the hepatotoxicity of purified MC-LR and cyanotoxin-containing water samples. In this study, the toxicity of cyanobacterial samples and purified MC-LR to cause hepatotoxicity in mice was confirmed in vitro using the catfish primary cell line. A comparison among the cyanobacterial samples using EC50 showed the following hepatotoxicity trend in the catfish primary cell line: HBP Dam summer samples > Nhlanganzwani Dam samples > HBP Dam winter samples > Mpanama Dam samples > Sunset Dam samples > Makhohlola Dam samples. The HBP Dam samples were the most hepatotoxic and Makhohlola Dam samples were the least hepatotoxic. The EC50 for purified MC-LR using the catfish primary hepatocytes was about 91 nM. A statistical comparison of the assays used in this study (i.e. ELISA, PPi, mouse test and cytotoxicity [catfish primary hepatocyte] assays) was performed based on the Kappa coefficient (K). An almost perfect agreement (K > 0.80) was observed between the mouse test and cytotoxicity assay; mouse test and ELISA; cytotoxicity assay and ELISA; and ELISA and PPi assay. In conclusion, field samples collected during the summer season were found to have very high levels of toxins and a higher degree of toxicity when compared to the winter samples. The cytotoxicity assay using African sharptooth catfish (Clarias gariepinus) primary hepatocytes has been shown for the first time to produce results similar to those observed when using the mouse bioassay in assessing cyanobacterial toxicity. Therefore, this primary cell line may be used as a potential alternative to the mouse assay in toxicity testing of cyanotoxins. Three KNP dams (Nhlanganzwani Dam, Mpanama Dam and Sunset Dam) investigated in this study were found to contain Microcystis aeruginosa. All four KNP dams (Nhlanganzwani Dam, Mpanama Dam, Makhohlola Dam and Sunset Dam) had cyanotoxin levels above the prescribed guideline value, which is of concern and warrants further investigations to the effects on wildlife in the park. Future studies will include use of High Performance Liquid Chromatography (HPLC) to investigate the toxin profile of the field samples in order to fully describe the different classes/or types of toxins present in the samples. More validation studies that could give a more comprehensive understanding about the sensitivity of the catfish primary cell line for microcystins will also be undertaken.Paraclinical Sciencesunrestricte
Diplodiosis : cytotoxicity and ultrastructural changes induced by diplodiatoxin, dipmatol and diplonine, toxic metabolites isolated from Stenocarpella maydis
Get PDFThesis (PhD)--University of Pretoria, 2014.Stenocarpella maydis (previously known as Diplodia maydis) is one of the most
prevalent ear and stalk rot pathogens of maize globally, causing reductions of grain
quality and yield. Ingestion of S. maydis infected maize causes diplodiosis, a
neuromycotoxicosis of cattle and sheep. To date, diplodiatoxin, dipmatol, diplonine and
chaetoglobosins (K, L, M and O) have been isolated from S. maydis infected cultures. The mechanism of action of these metabolites is poorly understood and consequently, it
is not known whether these metabolites play a role in the aetiology of diplodiosis.
The toxicity and mechanism of action of the three S. maydis metabolites (i.e.
diplodiatoxin, dipmatol and diplonine) were evaluated for the first time in this study
using in vitro cell cultures, namely the mouse neuroblastoma (Neuro-2a), Chinese
hamster ovary (CHO-K1) and Mardin-Darby bovine kidney (MDBK) cells.
The cytotoxicity was firstly evaluated after exposure of the three cell lines to various
concentrations of diplodiatoxin, dipmatol and diplonine for 24, 48 and 72 h. The
xCELLigence, tetrazolium 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide
(MTT) and protein measurement assays were used. To better understand the
mechanism(s) involved in the observed cytotoxicity, necrotic and apoptotic cell death
pathways were investigated. The lactate dehydrogenase (LDH) and propidium iodide (PI)
flow cytometry assays were used to assess necrotic changes, and the caspase-3/7 and
Annexin V-FITC flow cytometry assays were used for apoptosis. Finally, transmission
electron microscopy (TEM) was used to evaluate the subcellular changes induced by the
S. maydis toxins in vitro.
Results obtained in this study indicate that both diplodiatoxin and dipmatol induced a
concentration-dependent cytotoxicity in Neuro-2a, CHO-K1 and MDBK cells and also
affected the activity of the mitochondrial succinate dehydrogenase enzyme. Conversely,
diplonine was not cytotoxic at comparable concentrations. Diplodiatoxin and dipmatol, at high concentrations, exerted their toxicity via the necrotic and the caspase-dependent
apoptotic cell death pathways. Mitochondrial damage, cytoplasmic vacuolation and
nuclear fragmentation were the major subcellular changes induced by diplodiatoxin and
dipmatol. Except for the elongation of mitochondria, no major subcellular changes were
observed following exposure of MDBK cells to diplonine. Collectively, these results
indicate that mitochondrial damage could be central in the toxicity of the two S. maydis
metabolites and possibly in the development of diplodiosis.tm2015Paraclinical SciencesPhDUnrestricte
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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