| Molecular Characteristics of Kidney Cancer | |
Abstract/OtherAbstract
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Background: The vast majority of all human cancers, including kidney cancer, are caused by xenobiotica. Two-year rodent bioassays play the central role in evaluating the carcinogenicity of chemicals and are mainly based on a post-mortem evaluation of tumor incidences and other pathological changes after two years of exposure. However, such lifetime bioassays are time-consuming and costly, require large numbers of animals and a high amount of compound for continuous dosing over the entire period of the assay. In addition, widespread age-related pathologies, unspecific high-dose effects, or rodent-specific carcinogenic effects with little or no relevance to humans can confound the outcome of these studies. Furthermore, they do not account for possible additive effects of other cancer risk factors, such as diet-induced obesity. Therefore, interest in developing short, sensitive but robust, and mechanistically based in vivo studies has grown, allowing a more reliable human risk assessment. The overall aim of this thesis was to elucidate whether short-term in vivo assays in combination with microarray technology can be used to identify renal carcinogens. In addition, a more detailed understanding of potential additive effects of high fat diet exposure, and molecular mechanisms underlying chemically induced renal carcinogenesis, should be obtained. Experimental Setup: I) TSC2-mutant Eker and wild type rats were gavaged daily with the genotoxic renal carcinogens aristolochic acid (AA) and methylazoxymethanol acetate (MAMAc), or with the non-genotoxic ochratoxin A (OTA), respectively. Subsequent 1, 3, 7 and 14 days of exposure, gene-expression profiles from kidney cortex homogenates, histopathology, and cell proliferation were assessed. II) Eker rats were gavaged with AA, MAMAc and OTA for 3 or 6 months. Subsequently, renal histopathology and cell proliferation were evaluated. In addition, a novel protocol for reproducible and reliable gene expression analysis from laser-microdissected pre-neoplastic renal lesions was established, and gene expression profiles of different stages of preneoplastic lesions and healthy tubules were examined from 6 months AA-, OTA- and vehicle-treated male Eker rats. Key findings from transcriptome analyses were verified by immunohistochemistry. III) The respective impacts of dietary lipids and high body adiposity on renal pathology and pathways involved in renal cancer were delineated in diet-induced obesity-sensitive and diet-induced obesity-resistant subpopulations of male Wistar rats vs. chow-fed controls, subsequent to 11 months of high fat diet or standard chow exposure, respectively. Results/Discussion: Renal histopathology and gene expression profiling of kidney homogenates of short-term AA-, MAMAc-, and OTA-treated rats revealed that microarray technology is a sensitive tool to study earliest events of renal carcinogenesis. In addition, gene expression profiles allowed dissecting genotoxic from non-genotoxic modes of action. Most importantly, early gene expression changes after short-term exposure were predictive for the incidence and number of preneoplastic lesions after 3 or 6 months of exposure. Gene expression profiles from microdissected preneoplastic lesions of 6-month AA-, OTA- or control rats revealed marked gene deregulations, when compared to healthy tissue of control animals. Notably, gene expression changes were similar in different lesion progression stages and after treatment with genotoxic or non-genotoxic carcinogens. Furthermore, gene expression profiles of microdissected healthy tubules of AA- and OTA-treated rats were only marginally changed, suggesting a low compound-sensitivity. These findings suggested that the number of preneoplastic lesions initially formed during a critical period of exposure may primarily drive the incidence and number of solid tumors. In contrast, clonal expansion of these lesions may be compound-independent and instead be driven by a disturbed feedback inhibition of the mTOR pathway. Last, high fat diet exposure of male Wistar rats revealed a clear adverse effect of dietary lipids, and a minor role of the degree of body adiposity, on renal morphology. In addition, immunohistochemical analyses suggested a major role of the mTOR pathway in dietary lipid-induced pre-neoplastic pathology. Conclusion: Microarray-based short-term in vivo assays not only help to delineate molecular events important for renal cancer, but also fulfill the most important prerequisites for reliable carcinogenicity testing, i.e. high sensitivity, high specificity, and high predictivity. Thus, the duration of the standard two-year rodent bioassay can be reduced to a shorter period of time by using novel and sensitive methodology such as microarrays. Ultimately, this thesis provides encouraging first results that may help to reduce, refine and one day even replace animal experiments. |
Authors
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Stemmer, Kerstin |
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Publication Detail
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Publisher : Universität Konstanz, Fachbereich Biologie. Fachbereich Biologie Type : Thesis.Doctoral Format : application/pdf |
Date Detail
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2008 |
Subject
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Niere, Tumor, Microarray, Kidney, tumor, microarray, Life sciences |
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Source
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Copyright Information
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Other Details
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Languages : eng |
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