Mixed beams of ionizing radiation in our environment originate from space, the bedrock and our own houses. Radiotherapy patients treated with boron neutron capture therapy or with high energy photons are also exposed to mixed beams of gamma radiation and neutrons. Earlier investigations have reported additivity as well as synergism (a greater than additive response) when combining radiations of different linear energy transfer. However, the outcome seemed to be dependent on the experimental setup, especially the order of irradiation and the temperature at exposure. A unique facility allowing simultaneously exposure of cells to X-rays and 241Am alpha particles at 37 ºC was constructed and characterized at the Stockholm University (Paper I). To investigate the cytogenetic response to mixed beam irradiation (graded doses of alpha particles, X-rays or a mixture of both) several different cell types were utilized. AA8 Chinese Hamster Ovary cells were analyzed for clonogenic survival (Paper I), human peripheral blood lymphocytes were analyzed for micronuclei and chromosomal aberrations (Paper II and Paper III respectively) and VH10 normal human fibroblasts were scored for gamma-H2AX foci (Paper IV). For clonogenic survival, mixed beam results were additive, while a significant synergistic effect was observed for micronuclei and chromosomal aberrations. The micronuclei dose responses were linear, and a significant synergistic effect was present at all investigated doses. From the analysis of micronuclei distributions we speculated that the synergistic effect was due to an impaired repair of X-ray induced DNA damage, a conclusion that was supported by chromosomal aberration results. Gamma-H2AX foci dose responses were additive 1 h after exposure, but the kinetics indicated that the presence of low LET-induced damage engages the DNA repair machinery, leading to a delayed repair of the more complex DNA damage induced by alpha particles. These conclusions are not necessary contradictory since fast repair does not necessarily equal correct repair. Taken together, the observed synergistic effects indicate that the risks of stochastic effects from mixed beam exposure may be higher than expected from adding the individual dose components. / <p>At the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper nr 3: Manuscript; Paper nr 4: Manuscript.</p> / DNA damage and repair in cells exposed to mixed beams of radiation

The main aim of this thesis was to study the role of the indirect actions of γ-rays and α-particles on the complexity of primary DNA damages and the repair fidelity of major DNA repair pathways: non-homologous end joining (NHEJ), homologous recombination repair (HRR) and base excision repair (BER). The complexity of radiation-induced damages increases and the proximity between damages decreases with increasing LET due to formation of ionization clusters along the particle track. The complexity of damages formed can be modified by the free radical scavenger dimethyl sulfoxide (DMSO). In addition, the effects of low doses of low dose rate γ-radiation on cellular response in terms of differentiation were investigated. Paper I investigates the role of the indirect effect of radiation on repair fidelity of HRR, NHEJ and BER when damages of different complexity were induced by radiation or by potassium bromate. We found that potassium bromate induces complex DNA damages through processing of base modifications and that the indirect effect of radiation has a high impact on the NHEJ pathway. Results in paper II confirmed our conclusions in paper I that the indirect effect from both γ-rays and α-particles has an impact on all three repair pathways studied and NHEJ benefits the most when the indirect effect of radiation is removed. In paper III we investigated the effects of low dose/dose rate γ-radiation on the developmental process of neural cells by using cell models for neurons and astrocytes. Our results suggest that low dose/dose rate γ-radiation attenuates differentiation and down-regulates proteins involved in the differentiation process of neural cells by an epigenetic rather than cytotoxic mechanism. / <p>At the time of doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.</p>

Rationale/Objective: Excess lung cancer risks associated with exposure to inhaled radon decay products among uranium miners has well been established. Although ingestion is also a potentially important route of exposure, the relationship between ingested radon decay products and gastrointestinal cancer risks are not well examined. The objective of this study is to determine the relationship between exposure to radon decay products and the incidence and mortality of gastrointestinal (esophagus, stomach, and colorectal) cancer among men employed as uranium miners in Ontario. Secondly, to determine whether the duration of exposure (dose rate), years since last exposure and age at first exposure modify these associations. Methods: A cohort of miners who had ever worked in an Ontario uranium mine between 1954 and 1996 was created using the Mining Master File and the National Dose Registry. Cumulative radon exposures measured in Working Level Months (WLM) were previously estimated for each miner. Cancer diagnoses (1964-2004) and cancer deaths (1954-2004) occurring in Ontario were determined by probabilistic record linkage with the Ontario Cancer Registry. To calculate person-years at risk, non-cancer deaths were also ascertained from the Ontario mortality file for the period between 1954 and 2004. Poisson regression methods for grouped data were used to estimate the relative risks (RR) and 95% Confidence Intervals (CI) by exposure level. Results/Conclusions: The final cohort consisted of 28,273 Ontario uranium miners. By the end of 2004, 34 miners had been diagnosed with esophageal cancer, 86 with stomach cancer, and 359 with colorectal cancer. There were 40 deaths due to esophageal cancer, 69 from stomach cancer, and 176 from colorectal cancer. When comparing the highest cumulative exposure category (>40 WLM) to the referent group (0 WLM), significant increases in both stomach (RRIncidence= 2.30, 95% CI;1.02-5.17 and RRMortality=2.90, 95% CI;1.11-7.63) and colorectal cancers (RRIncidence =1.56, 95% CI;1.07-2.27 and RRMortality =1.74, 95% CI;1.01-2.99) after adjusting for age at risk and period effects. However, no relationships were observed for esophageal cancer. Suggestive evidence of modifying effects of these associations by duration of employment (dose rate) and years since last exposure for colorectal cancer was also observed.

Rationale/Objective: Excess lung cancer risks associated with exposure to inhaled radon decay products among uranium miners has well been established. Although ingestion is also a potentially important route of exposure, the relationship between ingested radon decay products and gastrointestinal cancer risks are not well examined. The objective of this study is to determine the relationship between exposure to radon decay products and the incidence and mortality of gastrointestinal (esophagus, stomach, and colorectal) cancer among men employed as uranium miners in Ontario. Secondly, to determine whether the duration of exposure (dose rate), years since last exposure and age at first exposure modify these associations. Methods: A cohort of miners who had ever worked in an Ontario uranium mine between 1954 and 1996 was created using the Mining Master File and the National Dose Registry. Cumulative radon exposures measured in Working Level Months (WLM) were previously estimated for each miner. Cancer diagnoses (1964-2004) and cancer deaths (1954-2004) occurring in Ontario were determined by probabilistic record linkage with the Ontario Cancer Registry. To calculate person-years at risk, non-cancer deaths were also ascertained from the Ontario mortality file for the period between 1954 and 2004. Poisson regression methods for grouped data were used to estimate the relative risks (RR) and 95% Confidence Intervals (CI) by exposure level. Results/Conclusions: The final cohort consisted of 28,273 Ontario uranium miners. By the end of 2004, 34 miners had been diagnosed with esophageal cancer, 86 with stomach cancer, and 359 with colorectal cancer. There were 40 deaths due to esophageal cancer, 69 from stomach cancer, and 176 from colorectal cancer. When comparing the highest cumulative exposure category (>40 WLM) to the referent group (0 WLM), significant increases in both stomach (RRIncidence= 2.30, 95% CI;1.02-5.17 and RRMortality=2.90, 95% CI;1.11-7.63) and colorectal cancers (RRIncidence =1.56, 95% CI;1.07-2.27 and RRMortality =1.74, 95% CI;1.01-2.99) after adjusting for age at risk and period effects. However, no relationships were observed for esophageal cancer. Suggestive evidence of modifying effects of these associations by duration of employment (dose rate) and years since last exposure for colorectal cancer was also observed.

published_or_final_version / Radioisotope / Master / Master of Philosophy

Τα αποτελέσματα ποικίλων δόσεων ακτινών Χ στην κυτταρική απόπτωση, τον πολλαπλασιασμό, την έκφραση του υποδοχέα του επιδερμικού αυξητικού παράγοντα (EGFR) και των μεταλλοπρωτεϊνασών-2 (MMP-2), μελετήθηκαν σε δύο κυτταρικές σειρές ανθρώπινου γλοιοβλαστώματος. Μέθοδος: Οι κυτταρικές σειρές LN18 και M059K ακτινοβολήθηκαν σε θερμοκρασία δωματίου με δόσεις κυμαινόμενες από 0,5 έως 15 Gy με τη χρήση πηγής 6 MV. Η απόπτωση μελετήθηκε με τη μέθοδο annexin V, ο πολλαπλασιασμός με τη μέθοδο MTT (methyl tetrazolium) και η έκκριση των MMP-2 με ζυμογράφημα. H καταγραφή των επιπέδων του φωσφοριωμένου EGFR έγινε με ELISA. Αποτελέσματα: Ο κυτταρικός πολλαπλασιασμός ανεστάλη με δόσο-εξαρτώμενο τρόπο ενώ η απόπτωση αυξήθηκε σημαντικά μετά την ακτινοβολία. Σε δόσεις μικρότερες των 2 Gy δεν καταγράφηκε καμία μεταβολή στην απόπτωση και τον κυτταρικό πολλαπλασιασμό. Τα επίπεδα των MMP-2 αυξήθηκαν 48 ώρες μετά την ακτινοβόληση με δόσο-εξαρτώμενο τρόπο. Αντιθέτως, η έκφραση του EGFR αυξήθηκε σημαντικά 15 λεπτά μετά την ακτινοβόληση και κατά δόσο-εξαρτώμενο τρόπο. Συμπέρασμα: Η ιοντίζουσα ακτινοβολία επάγει την έκφραση του EGFR και αυξάνει την έκκριση των MMP-2 γεγονός που αιτιολογεί την διηθητική και κακοήθη συμπεριφορά των γλοιωμάτων καθώς και την ανταπόκριση τους στην ιοντίζουσα ακτινοβολία. / The effect of different doses of X(-)rays on apoptosis, proliferation, epidermal growth factor receptor (EGFR) and matrix metalloproteinase (MMP-2) expression was investigated in a human glioblastoma cell line. Materials and Methods: The cell line LN18 was irradiated at room temperature with doses ranging from 0.5 to 15 Gy using 6 MV X(-)rays. Apoptosis was assessed using the annexin V binding assay, proliferation by the methyl tetrazolium (MTT) assay and MMP-2 secretion with zymography. The levels of phosphorylated (pEGFR) were estimated using a commercially available ELISA kit. Results: Cell proliferation decreased in a dose-dependent manner, while apoptosis was increased after radiation. Doses below 2 Gy did not affect proliferation or apoptosis. MMP-2 levels were increased 48 h after radiation in a dose-dependent manner. In contrast, EGFR signaling was significantly activated 15 min after radiation in a dose-dependent manner. Conclusion: Ionizing radiation activates EGFR signalling and enhances MMP-2 secretion, suggesting that the molecular pathways involved may contribute to the invasiveness and malignant behaviour of glioma cells and help to explain the response of gliomas to ionizing radiation.

Worldwide, people are being exposed to natural and man-made sources of radiation. Epidemiological studies have shown an increased risk of vascular diseases in populations that have been exposed to ionizing radiation. Vascular endothelium is implicated as one of the targets for radiation leading to the development of cardiovascular diseases. However, the molecular mechanisms behind the development of radiation-induced cardiovascular disease in acute or chronic exposed people are not fully elucidated. The hypothesis that chronic low dose rate ionizing radiation accelerates the onset of senescence of primary human umbilical vein endothelial cells has been tested in papers I and II presented in this thesis. In vitro studies show that, when exposed to continuous low dose rate gamma radiation these cells enter premature senescence much earlier than non-irradiated control cells. Quantitative proteomic analysis using isotope coded protein labeling coupled to LC-ESI-mass spectrometry and followed by protein network analysis identified changes in senescence-related biological pathways including cytoskeletal organisation, cell-cell communication and adhesion, and inflammation influenced by radiation. Moreover, the role of PI3K/Akt/mTOR pathway was implicated during the senescence process. Thus, chronic low dose rated endothelial senescence may contribute to increased risk of radiation-induced cardiovascular disease. Paper III analyse the long-term effects of local high doses of radiation to the heart using a mouse model. The results from proteomic and bioinformatics analysis indicated that an impaired activity of the peroxisome proliferator-activated receptor-alpha (PPARA) is involved in mediating the radiation response. Ionizing radiation markedly changed the phosphorylation and ubiquitination status of PPARA. This was reflected by the decreased expression of PPARA target genes involved in energy metabolism and mitochondrial respiratory chain. This in vivo study suggests that alteration of cardiac metabolism contributes to the impairment of heart structure and function after radiation. Taken together, these in vitro and in vivo studies provide novel information on the pathways in heart and endothelial cells that are affected over longer periods of time by ionizing radiation.

No description available.

Lic.-avh. (sammanfattning) Stockholm : Tekn. högsk., 2006. / Härtill 3 uppsatser.

Thesis (Ph.D.)--Rochester Institute of Technology, 2008. / Typescript. Includes bibliographical references (leaves 151-155).