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Automated chromosome damage analysis to investigate thresholds for genotoxic agents. / Katja Brusehafer

Swansea University Author: Katja Brusehafer

Abstract

Genotoxicology involves the assessment of a substance’s ability to induce DNA damage after exposure to humans. DNA damage is an underlying cause of mutations that are likely to initiate carcinogenesis. Furthermore, the investigation of low dose responses in genotoxicology testing helps to improve he...

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Published: 2013
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
URI: https://cronfa.swan.ac.uk/Record/cronfa43178
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first_indexed 2018-08-02T18:56:28Z
last_indexed 2020-08-28T03:05:56Z
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spelling 2020-08-27T16:07:54.2790326 v2 43178 2018-08-02 Automated chromosome damage analysis to investigate thresholds for genotoxic agents. 0d275c61ef0b6cd0083ef318631ec219 NULL Katja Brusehafer Katja Brusehafer true true 2018-08-02 Genotoxicology involves the assessment of a substance’s ability to induce DNA damage after exposure to humans. DNA damage is an underlying cause of mutations that are likely to initiate carcinogenesis. Furthermore, the investigation of low dose responses in genotoxicology testing helps to improve health risk assessment by establishing whether DNA reactive compounds follow linear or non-linear (thresholded) dose response relationships.The current assumption for direct acting genotoxins is that the relationship between exposure to genotoxic chemicals, DNA damage formation and the induction of mutagenic changes is linear. However, it is known that mutations are not produced directly by DNA adducts as DNA repair activity limits the proportion of adducts processed into mutations. It is therefore possible, that no observed effect levels (NOEL) may exist for some genotoxins.The main aim of this thesis was to improve in vitro genotoxicity testing by assessing the low dose response relationships for the genotoxic agents mitomycin-C (MMC), 4-nitroquinoline 1-oxide (4NQO) and cytosine arabinoside (araC). Furthermore, the automated micronucleus slide scoring system Metafer was validated and used for these studies.In addition, the mechanism of action of each test component was further investigated by follow up experiments to gain a better understanding of the processes involved in this type of damage.The in vitro micronucleus assay for the detection of chromosomal damage revealed non­linear dose response relationships following low dose exposure of MMC and araC, while 4NQO revealed a weak clastogenic potential. The semi-automated scoring protocol for the Metafer-System proved to be a rapid and accurate system for scoring micronuclei.DNA repair plays most likely a major role in these non-linear responses by removing genetic damage induced at low levels. Furthermore, p53 was shown to be involved in the DNA damage response in human lymphoblastoid cells, through cell cycle delay and the induction of apoptosis.In addition, this work confirmed that a proper dosing regime, accurate toxicity measurements and the appropriate choice of cell type are cmcial criteria for defining the dose response relationships and the induction of genotoxicity and cytotoxicity. E-Thesis Genotoxicity 31 12 2013 2013-12-31 COLLEGE NANME Swansea University Medical School COLLEGE CODE Swansea University Doctoral Ph.D 2020-08-27T16:07:54.2790326 2018-08-02T16:24:31.5062208 Faculty of Medicine, Health and Life Sciences Swansea University Medical School - Medicine Katja Brusehafer NULL 1 0043178-02082018162552.pdf 10821570.pdf 2018-08-02T16:25:52.6130000 Output 31738560 application/pdf E-Thesis true 2018-08-02T00:00:00.0000000 false
title Automated chromosome damage analysis to investigate thresholds for genotoxic agents.
spellingShingle Automated chromosome damage analysis to investigate thresholds for genotoxic agents.
Katja Brusehafer
title_short Automated chromosome damage analysis to investigate thresholds for genotoxic agents.
title_full Automated chromosome damage analysis to investigate thresholds for genotoxic agents.
title_fullStr Automated chromosome damage analysis to investigate thresholds for genotoxic agents.
title_full_unstemmed Automated chromosome damage analysis to investigate thresholds for genotoxic agents.
title_sort Automated chromosome damage analysis to investigate thresholds for genotoxic agents.
author_id_str_mv 0d275c61ef0b6cd0083ef318631ec219
author_id_fullname_str_mv 0d275c61ef0b6cd0083ef318631ec219_***_Katja Brusehafer
author Katja Brusehafer
author2 Katja Brusehafer
format E-Thesis
publishDate 2013
institution Swansea University
college_str Faculty of Medicine, Health and Life Sciences
hierarchytype
hierarchy_top_id facultyofmedicinehealthandlifesciences
hierarchy_top_title Faculty of Medicine, Health and Life Sciences
hierarchy_parent_id facultyofmedicinehealthandlifesciences
hierarchy_parent_title Faculty of Medicine, Health and Life Sciences
department_str Swansea University Medical School - Medicine{{{_:::_}}}Faculty of Medicine, Health and Life Sciences{{{_:::_}}}Swansea University Medical School - Medicine
document_store_str 1
active_str 0
description Genotoxicology involves the assessment of a substance’s ability to induce DNA damage after exposure to humans. DNA damage is an underlying cause of mutations that are likely to initiate carcinogenesis. Furthermore, the investigation of low dose responses in genotoxicology testing helps to improve health risk assessment by establishing whether DNA reactive compounds follow linear or non-linear (thresholded) dose response relationships.The current assumption for direct acting genotoxins is that the relationship between exposure to genotoxic chemicals, DNA damage formation and the induction of mutagenic changes is linear. However, it is known that mutations are not produced directly by DNA adducts as DNA repair activity limits the proportion of adducts processed into mutations. It is therefore possible, that no observed effect levels (NOEL) may exist for some genotoxins.The main aim of this thesis was to improve in vitro genotoxicity testing by assessing the low dose response relationships for the genotoxic agents mitomycin-C (MMC), 4-nitroquinoline 1-oxide (4NQO) and cytosine arabinoside (araC). Furthermore, the automated micronucleus slide scoring system Metafer was validated and used for these studies.In addition, the mechanism of action of each test component was further investigated by follow up experiments to gain a better understanding of the processes involved in this type of damage.The in vitro micronucleus assay for the detection of chromosomal damage revealed non­linear dose response relationships following low dose exposure of MMC and araC, while 4NQO revealed a weak clastogenic potential. The semi-automated scoring protocol for the Metafer-System proved to be a rapid and accurate system for scoring micronuclei.DNA repair plays most likely a major role in these non-linear responses by removing genetic damage induced at low levels. Furthermore, p53 was shown to be involved in the DNA damage response in human lymphoblastoid cells, through cell cycle delay and the induction of apoptosis.In addition, this work confirmed that a proper dosing regime, accurate toxicity measurements and the appropriate choice of cell type are cmcial criteria for defining the dose response relationships and the induction of genotoxicity and cytotoxicity.
published_date 2013-12-31T03:54:24Z
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score 11.014067

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