Browsing by Author "de Kock, Maryna"

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    The effects of PGA2 on cell cycle progression in oesophageal carcinoma cells
    (University of the Western Cape, 2003) Samodien, Sedicka; de Kock, Maryna
    The molecular mechanisms causing anti-mitotic and cytotoxic effects of prostaglandin .A2 [PGA2 (CzoHroOa)] treatment of human oesophageal carcinoma (WHCO3) cells were investigated. WHCO3 cells, incubated with cytotoxic doses of PGAz (20 and 50pg/ml) for 3, 24 and 48 hrs showed characteristic morphological features of apoptosis such as chromatin condensation, nuclear fragmentation, as well the formation of apoptotic bodies. Chromatin condensation was more prevalent in cells exposed to 201tglml PGAz for 24 hrs. Apoptosis induction was found at both concentrations and cells exposed to 50pg/ml showed apoptosis at 3 hrs already. An increase in abnormal metaphases was observed in cells exposed to 2\pg/ml PGAz for 24 hrs. This outspoken increase in metaphases could be due to the activation of the spindle assembly checkpoint. Activation of this checkpoint blocks the onset of anaphase and arrests cells in metaphase. The flow cytometry studies also showed an increase of cells in metaphase. Metaphase arrest occurs when any of the following situations have effect: unattachment of a single kinetochore to the microtubules, unbalanced tension on chromosomes or if there is abnormal dynamic behaviour of the microtubules attached to the kinetochore (Bunz et al., 1998; Gorbsky, 1997; Gorbsky, 2001; Murray, 1994). WHCO3 cells exposed to 20pglml PGAz for 24 hrs showed an accumulation of cells with condensed chromosomes and according to Cahill et aL.,1998, this accumulation is characteristic of a mitotic block. After 48 hrs, cells exposed to 2}pglml PGAz showed a decrease in the number of apoptotic cells and it appeared that the cells were able to overcome the arrest. Indirect immunofluorescent studies of otubulin showed that PGAz had varied effects on the cytoskeleton. Fewer but intact microtubules were observed when cells were exposed to 201tglml PGA2 for 24 hrs, whereas the results obtained from cells exposed to z}p/ml PGA2 for 48 hrs showed some normal spindles, a few abnormal arranged spindles and others disrupted microtubules. Cotter et al., 1992 showed that disrupted microtubules prevent the formation of apoptosis. The results of the 2lpglml PGAz studies for 24 and 48 hrs can possibly be explained by this phenomenon. The cells exposed to 20pglml PGAz for 24 hrs showed increased chromatin condensation and apoptosis formation, whilst the cells exposed to the same concentration for 48 hrs showed a decrease in apoptosis formation. This result can possibly be ascribed to either the ability of the cell to overcome the spindle assembly checkpoint or an increase in the disruption of the microtubule arrangement, thus preventing the induction of apoptosis. In cells exposed to 50pg/ml PGAz total rearrangement of o-tubulin was very much evident and this rearrangement could be a cause of apoptosis induction as indicated by the large amount of apoptotic cells (28.93%o and 5l.63oh during 24 and 48 hrs respectively) with flow cytometry. Silver staining of PGAz treated WHCO3 cells showed segregation of granular and fibrillar components. This segregation is usually associated with non-functional nucleoli and indicative of an inhibition in protein synthesis (Hadjiolov, 1985). DNA fragmentation was also observed with the two higher concentrations of PGAz. On agarose gel electrophoresis, DNA laddering was evident in the cells exposed to 50pg/ml for 3 hrs and 20pglml for 24 hrs. It was furthermore found that caspase 3 could possibly play a role in the induction of apoptosis, internucleosomal DNA degradation, chromatin condensation, membrane blebbing and disassembly into membrane bound vesicles at the higher concentrations.
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    Gene expression of xenobiotic metabolising enzymes in rat liver and kidney: differential effects of rooibos and honeybush herbal teas
    (2011) Abrahams, S.; Gelderblom, W.C.A; Joubert, E.; de Kock, Maryna
    Laboratory studies, epidemiological investigations and human clinical trials indicate that flavonoids have important effects on cancer chemoprevention and therapy. Flavonoids may interfere in several steps that lead to cancer development but may also lead to toxicity as the inhibition of carcinogen-activating enzymes may also cause potential toxic flavonoid-drug interactions. However, the potential toxicity of these dietary components has not been well studied. The use of polyphenol enriched supplements prepared from South African herbal teas, rooibos(Aspalathus linearis)and honeybush (Cyclopia spp.) are being marketed to alleviate symptoms that are known to be “cured” by the herbal teas. However, there is a lack of information regarding the possible health promoting effects of these polyphenol-enriched extracts on xenobiotic metabolism. In the present study, the modulating effects of aspalathinenriched rooibos and mangiferin-enriched C. genistoides and C. subternata extracts on the gene expression of xenobiotic metabolising enzymes (XMEs) were investigated in vivo in the rat liver and kidneys. An in vitro study, utilising a primary rat hepatocyte cell model, was included to further evaluate changes in the expression of selected XMEs by the herbal tea extracts, including their major polyphenolic constituents, aspalathin and mangiferin. The use of the in vitro primary hepatocytes assay as a predictive cell model for the modulation of the expression of XMEs genes by the herbal tea extracts in vivo was critically evaluated.In the liver and kidneys, the C. subternata polyphenol-enriched herbal tea extract effected the majority of changes regarding the expression of XMEs genes when compared to the rooibos and C. genistoides. Variations in the modulation of gene expression of the XMEs by the herbal tea extracts were related to differences in their polyphenol constituents, although non-polyphenolic constituent could also be involved.Overall the herbal teas regulated alcohol,energy, drug and steroid metabolism in the liver, whereas in the kidneys the gene expression of phase I, phase II, steroid metabolising enzymes, as well as drug transporters were modulated. It would appear that the herbal teas are likely to exhibit both beneficial and adverse effects in vivo,depending on the specific organ, the xenobiotic and/or drug that are involved. The primary rat hepatocytes model display varying effects with respect to modulating gene expression of specific XMEs by the polyphenol-enriched herbal tea extracts. Apart from the reduction in 17 -hydroxysteroid dehydrogenase gene expression care should be taken to directly extrapolate the in vitro findings to changes that prevail in vivo.However, interesting results regarding the masking effect of complex mixture on the modulation of XME gene expression of individual polyphenols were encountered. In addition differences in the dose and duration of exposure between the in vitro and in vivo studies were not comparable and should be further explored to validate the in vitro primary hepatocytes model to predict changes in vivo. Future studies should investigate the effects of the herbal tea extracts, its polyphenols and metabolites on XME induction at a protein level as well as varying herb-drug-enzyme interactions.
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    The modulating effect of fatty acids on the lipid profile in colon epithelial mucosa in Vivo
    (University of the Western Cape, 2009) Abrahams, Celeste H.; Abel, Stefan; Gelderblom, Wentzel; de Kock, Maryna; Dept. of Medical BioSciences; Faculty of Science
    Several abnormal conditions, including some cancers, have been associated with changes in the membrane lipid and FA composition. Dietary fat serves as a major source of lipids and FA, particularly the polyunsaturated fatty acids (PUFA), n-6 and n-3. High intakes of n-6 PUFA have been linked to the development of colon cancer in association with low n-3 PUFA intake. Therefore understanding the differences in the lipid and FA profiles between cancer and normal cells in the colon, and the role diet plays in these factors may be invaluable in understanding their role in carcinogenesis. This study compares the lipid profile of azoxymethane (AOM) induced colon polyps to that of the surrounding mucosa tissue in rats fed a diet high in n-6 PUFA. Male Fischer rats were fed the AIN-76A diet containing sunflower oil that has high n-6 PUFA content for a period of nine months. Results indicate that the lipid and FA content of the colon polyps differs significantly from the surrounding mucosa. Colon polyps had an increase in membrane phopholipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Changes in membrane fluidity were indicated by the decrease (0.05) in the PC/PE and cholesterol/phospholipids (chol/PL) ratios, and increase (0.05) in the polyunsaturated FA/saturated FA (P/S) ratio. Metabolism of FA was significantly altered in the polyps favouring n-6 FA metabolism and the production of prostaglandin E2. No clear indication of impaired & Delta;6-desauturase enzyme activity was noticed. Increases in the n-6 PUFA content could be a reflection of the dietary FA intake that increases FA incorporation in the polyps. Changes in the FA parameters of the polyps, particularly an increase in C20:4n-6 and the n6/n3 ratio have been shown to contribute to the rapid growth of cancer tissue. These lipid changes associated with the development of colon polyps could provide unique targets for developing strategies in chemoprevention by dietary manipulation.
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    Radiosensitization effects of gold nanoparticles in proton therapy
    (University of the Western Cape, 2017) Cunningham, Charnay; de Kock, Maryna
    Despite recent advances in radiotherapy, some tumours have shown to be resistant to treatment and patients still experience long term side effects. Gold nanoparticles (AuNPs) have been identified as effective radiosensitizers when employed concurrently with kilovoltage X-rays, which could selectively increase the dose delivered to a patient's tumour. The clinical application of proton radiation has gained renewed attention due to the lower integral body dose of protons compared to traditional X-ray based therapy. While extensive research has been formed on the behaviour of AuNPs in photon beams, limited information is available on the combination of AuNPs and proton radiation. Several questions remain regarding the interaction of protons with the AuNPs and possible dose enhancement effects at different depths along the Spread Out Bragg Peak (SOBP).
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    Tumour suppression and subdual of cancer (tussc) in elephants: An in vitro study to shed light on Peto’s paradox
    (University of the Western Cape, 2022) Jansen van Vuuren, Amѐlia; de Kock, Maryna
    Logic would suggest that cancer incidence is related to body mass and longevity. Gigantic animals such as elephants with a longer lifespan (more lifetime of cell divisions) and a larger body size (more cells) will have more time during their lifetime to accumulate a cancer-causing mutation in comparison to small-bodied, short-lived animals, such as mice. However, several studies and the mere existence of large-bodied, long-lived mammals such as elephants and whales, suggest that there is no correlation between body mass, lifespan and cancer incidence across different mammalian species. This is a phenomenon known as Peto’s paradox. As there is a selection for large body size in evolution, there is likely also a selection for cancer suppression mechanisms that allow an organism to grow large and reproduce successfully. One of the rationales in the African savanna elephant (Loxondonta africana) is the duplication of a crucial tumour suppressor gene (TP53) encoding the tumour protein 53 (p53).