Thesis (Ph. D.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains viii, 84 p. : ill. Includes abstract. Includes bibliographical references (p. 58-84).

Thesis (Ph.D.)--Flinders University, School of Medicine, Dept. of Haematology and Genetic Pathology. / Typescript bound. Includes bibliographical references: (leaves 248-282) Also available in an electronic version.

Thesis (PH.D.)--Michigan State University. Biochemistry and Molecular Biology, 2008. / Title from PDF t.p. (viewed on Aug. 11, 2009) Includes bibliographical references. Also issued in print.

Phenolic antioxidants reduce the effect of oxidative stress within cells. They are found in a various fruits, vegetables and as food additives to reduce spoilage. Consumption of antioxidants by humans has been linked with increased lifespan and reduced incidence of cancer and cardiovascular disorders (Cabrera et al. 2006; Kuriyama 2008). In cultured mammalian cells however, some of these phenolic antioxidants have been reported to generate reactive oxygen species (ROS), leading to chromosomal breakage (Long et al. 2007; Long & Halliwell 2001). It is clear then, that amongst this group of compounds, in vitro toxicological study is not a reliable prediction of human hazard. It is for this reason that the work described in this thesis was undertaken: the principal aim was to gain a better understanding of the reasons underlying this contradiction. It has been suggested that excessive ROS generated in vitro might be a result of the higher levels of oxygen (~20%) compared to (1-7%) in vivo: (Yusa et al. 1984; Turrens et al. 1982). With clearer understanding, new experimental approaches might be taken to highlight or reduce positive in vitro genotoxicity test results that might be considered misleading. A diverse set of test compounds was first chosen. It included polyphenolic (PPA), monophenolic (MPA) and non-phenolic antioxidants (NPA), in addition to mechanistically characterised oxidants, genotoxins and cytotoxic, non-genotoxins as controls. Genotoxicity was assessed in vitro using the GADD45a, GFP reporter assay and in silico using Derek Nexus™. Amongst the 19 antioxidants assessed, the 11 of 12 of PPAs, 0 of 4 MPAs and 1 of 3 NPAs (ethoxyquin) produced positive results in vitro and 8 of 12 PPAs generated alerts of at least plausible genotoxicity in silico. To discover whether these results were the result of cellular hyperoxia-promoted generation of physiologically irrelevant ROS in cells, genotoxicity was reassessed in the presence of 1 and 5% oxygen. This reduced oxygen exposure had no effect upon the qualitative result for any of the assessed compounds and a negligible effect upon the dose at which any positive result was produced. An assessment of the ability of antioxidants to generate potentially genotoxic ROS within cells was carried out using the intracellular fluorescent dye, dichlorofluorescin diacetate (DCFH-DA). 10 of 12 PPAs, 0 of 4 MPAs and 1 of 3 NPAs (ethoxyquin) were shown to increase the level of ROS within TK6 human lymphoblastoid cells within 4 hours of compound exposure. Within this same timeframe, the mitochondrial membranes in cells treated with 10 of 12 PPAs, 2 of 4 MPAs and 1 of 3 NPAs (ethoxyquin) were shown to become depolarised using JC-1 dye. It was unclear however, whether mitochondrial membrane depolarisation was a cause or a consequence of ROS generation within the cells. In order to assess whether the increase in intracellular ROS led to an increase in oxidised DNA within treated cells, 8-oxoguanine (8-OG) was quantified using a FITC conjugated anti8-OG antibody. This assessment revealed that levels of the oxidised base were only increased in cells exposed to two of the 12 PPAs (quercetin and resorcinol). The level of 8OG detected was lower than the vehicle control for cells treated with 10 of the 15 antioxidants. One interpretation of this is that these agents induce the repair pathway for oxidative damage, which leads to a lower level of oxidised DNA bases in the genome. The results showed that while a large proportion of PPAs produce genotoxic results in vitro and lead to increased levels of ROS, the amount of oxidised DNA is not higher in treated cells. This would suggest the presence of a different mechanism for the observed genotoxicity.

M.Sc. (Biochemistry) / Tuberculosis (TB) is an infectious disease that worldwide, is more prevalent in Africans compared to Caucasians. TB also affects males to a greater extent than females. Genetic associations between VDR sequence variants and TB is often inconsistent across different populations. Epigenetic and environmental factors, as well as ethnicity may confound associations found between VDR and TB...

Methylmercury (MeHg) is the most toxic form of Hg to wildlife, partly because of its ability to biomagnify through the food chain. Previous studies have shown that river otter (Lutra canadensis) is particularly susceptible to increased exposure and body burdens of MeHg due to the piscivorous nature of its diet. The objectives of this study were to attempt to establish a relationship between MeHg concentrations in otter tissues and DNA fragmentation using single cell electrophoresis (comet assay) as well as evaluate the effectiveness of the comet assay as a tool in genotoxicity assessment in field samples. Results of preliminary experiments indicate that both time and storage temperature markedly influence the rate of spontaneous DNA degradation. Increased numbers of freeze/thaw cycling also appear to have a negative effect on DNA integrity. In addition, a cell culture experiment was set up to measure the effects of differing levels of MeHg on a neuroblastoma cell line.

The goal of this thesis was to examine the sources and ecological behaviour of genotoxic organics in the St. Lawrence river system. A rapid and effective version of the SOS Chromotest was developed to accomplish the task of genotoxicity assessment. The method, validated with standard reference materials, is particularly well suited to complex environmental extracts. The endpoint investigated throughout the thesis, SOS genotoxicity, is empirically related to more familiar endpoints such as mutagenicity and carcinogenicity. Analyses of literature data confirmed correlations between SOS genotoxicity and both Ames/Salmonella mutagenicity and animal carcinogenicity. Analyses of industrial and municipal wastewaters revealed that organic and inorganic chemical production facilities, metal refining and founding facilities and petroleum refineries release high potency wastes. Loading values indicate that low potency sources (e.g. municipal wastewater and pulp & paper facilities) often have exceptionally high loadings. A substantial portion (2.3-99.8%) of industrial genotoxins are associated with suspended particulates. Sorption partition efficients (K$ sb{ rm d-genotox}$) indicate that municipal wastewater and pulp & paper facilities release particularly soluble genotoxins. Extracts of suspended particulate matter collected near industrial discharges are direct-acting. Bottom sediment extracts are less potent and usually require S9 metabolic activation. Genotoxicity of both bottom sediment and suspended particulates are empirically related to the genotoxicity of regional industrial emissions. Direct-acting substances in the water column appear to be less stable and may be converted to more stable pro-genotoxic substances present in the bottom sediments. A mass balance of genotoxicity for St. Lawrence surface waters revealed that domestic, rather than industrial sources make the largest contribution to observed genotoxicity. The importance of domestic wastes was confirmed

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Orientador: Classius de Oliveira / Coorientador: Javier Goldberg / Banca: Daniela de Melo e Silva / Banca: Lia Raquel de Souza Santos / Banca: Carlos Eurico dos Santos Fernandes / Banca: Patrícia Simone Leite Vilamaior / Resumo: Os anfíbios são bons indicadores de qualidade ambiental devido a várias características que os tornam suscetíveis a alterações do ambiente. A contaminação aquática, principalmente por desreguladores endócrinos, tem sido apontada como uma causa para o declínio dos anfíbios. O 4-nonilfenol (NP) é um detergente com efeito estrogênico, que já demonstrou efeitos deletérios em alguns grupos de vertebrados. Já o Acetato de Ciproterona (CPA) é um medicamento com propriedade antiandrogênica e, apesar da maioria dos estudos serem com roedores, tem-se observado alto potencial tóxico deste composto. Neste estudo o objetivo foi avaliar os efeitos genotóxicos do NP e do CPA, e sua ação na pigmentação hepática, um biomarcador morfológico de efeito, importante para confirmar a ação dos compostos, além da morfologia gonadal e da contagem leucocitária de girinos e jovens de Rana catesbeiana, em três diferentes concentrações ambientalmente relevantes, após exposição por 28 dias. Nossos resultados mostraram que o NP e o CPA são genotóxicos para os girinos, sendo o CPA de toxicidade muito maior em todas as concentrações, enquanto nos jovens apenas o CPA gerou resposta, nas duas maiores dosagens. Na pigmentação hepática houve aumento apenas nos jovens expostos à concentração média de NP e mínima de CPA. A gônada dos girinos ainda estava indiferenciada, portanto não pode ser avaliada, enquanto na dos jovens não houve alteração na razão sexual nem condições intersexuais. Já o perfil leucocitário... / Abstract: Amphibians are good indicators of environmental quality due to several characteristics that make them susceptible to environmental changes. Aquatic contamination, especially by endocrine disrupters, has been indicated as a cause for amphibian decline. 4-nonylphenol (NP) is a detergent with estrogenic effect, which has already demonstrated deleterious effects in some groups of vertebrates. Cyproterone Acetate (CPA), in turn, has antiandrogenic properties, it is used in medicines, and although most of the studies are with rodents, it has been observed a high toxic potential of this compound. In this study, our aim was to evaluate the genotoxic effects of NP and CPA, and its action on hepatic pigmentation, a morphological biomarker, important to confirm the effects of the compounds, as well as gonadal morphology and leukocyte count of tadpoles and juveniles of Rana catesbeiana, in three different environmentally relevant concentrations, after 28 days exposure. Our results showed that NP and CPA are both genotoxic for tadpoles, but CPA showed much higher toxicity at all concentrations, while in juveniles only CPA increased nuclear abnormalities at the two highest dosages. In hepatic pigmentation there was an increase only in the juveniles exposed to the medium concentration of NP and minimum dosage of CPA. The tadpole gonad was still undifferentiated, so it can not be evaluated, while in the juvenile there was no change in the sex ratio and any intersexual conditions. The ... / Doutor