| 1. |
- Jönsson, K. Ingemar, 1959-, et al.
(författare)
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Radiation tolerance in the eutardigrade Richtersius coronifer
- 2005
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Ingår i: International Journal of Radiation Biology. - : Taylor & Francis. - 0955-3002 .- 1362-3095. ; 81:9, s. 649-656
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Tardigrades have a reputation of being extremely tolerant to extreme environmental conditions including tolerance to ionizing radiation while in a desiccated, anhydrobiotic state. However, the evidence for radio-tolerance in tardigrades is based on only one previous report, and there is an obvious need for complementary studies. In this paper we report an investigation on radio-tolerance in desiccated and hydrated specimens of the eutardigrade Richtersius coronifer.MATERIALS AND METHODS: Groups of 30 - 50 tardigrades were exposed to gamma-radiation at doses between 1.0 - 9.0 (anhydrobiotic animals) or 0.5 - 5.0 (hydrated animals) kGy and the animals were followed until all were dead. Radiation tolerance of both desiccated and hydrated tardigrades was studied.RESULTS: Both desiccated and hydrated animals irradiated with 0.5 and 1 kGy did not deviate in survival from the control groups. Animals from all exposed groups underwent their moulting and egg production cycle, but at decreasing frequency for doses above 1 kGy. No eggs laid by irradiated animals hatched, while eggs laid by controls did so.CONCLUSION: Our study suggests that radiation tolerance in tardigrades is not due to biochemical protectants connected with the desiccated state. Rather, cryptobiotic tardigrades may rely on efficient mechanisms of DNA repair, the nature of which is currently unknown.
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| 2. |
- Torudd, Jesper, 1964-
(författare)
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Induction of apoptosis in relation to chromatin structure and inhibition of replication by DNA damage from ionizing radiation
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The theme of this thesis has been chromatin organization ranging from methodological studies to involvement in apoptotic response. The aims have been: (i) to compare the information obtained by the AVTD method and comet assay concerning DNA-loop organization, (ii) to test the hypothesis that DNA-loop relaxation could be the triggering signal for induction of apoptosis in G0-lymphocytes, and (iii) to study the dose response for inhibition of the replication fork movement and pathways for the DNA repair process at the replication fork. AVTD was evaluated and compared with the established comet assay by studying changes in DNA-loop structure, induced by ethidium bromide. DNA-loops either relaxed or condensed in a dose dependent manner and changes in viscosity correlated with the length of comet tails. The dose response relations for induction of apoptosis in G0-lymphocytes were determined and compared with the dose response relations for relaxation of DNA-loops. Relaxation was shown to saturate at doses of 2-3 Gy after γ-irradiation, a dose in which approximately one SSB per chromatin loop of DNA was induced. Apoptotic markers such as chromatin condensation, p53 stabilization and DNA fragmentation also saturated at 2-3 Gy, suggesting that SSB dependent loop relaxation may trigger apoptosis. Radiation induced inhibition of replication fork movement was studied in proliferating Chinese hamster ovary cells. Doses over 100 Gy were needed to inhibit the fork elongation, as verified by both the ADU and by the DNA combing assay. Checkpoint signalling was shown not to be involved in this retarded elongation. On the other hand, the initiation of replication was sensitive to low doses of ionizing radiation. A dose of 12.5 Gy was enough to stop firing of new replicons and caffeine attenuated this inhibition. By measuring the speed of replication fork progression in repair deficient cell lines we concluded that replication forks are retarded by un-repaired DSBs, SSBs and/or base lesions.
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| 3. |
- Haghdoost, Siamak, 1968-
(författare)
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Biomarkers of oxidative stress and their application for assessment of individual radiosensitivity
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Radiotherapy is one of the most common therapeutic methods for treatment of many types of cancer. Despite many decades of development and experience there is much to improve, both in efficacy of treatment and to decrease the incidences of adverse healthy tissue reactions. Around 20 % of the radiotherapy patients show a broad range in the severity of normal tissue reactions to radiotherapy, and dose limits are governed by severe reactions in the most radiosensitive patients (< 5 %). Identification of patients with low, moderate or high clinical radiosensitivity before commencing of radiotherapy would allow individual adaptation of the maximum dose with an overall increase in the cure rate. Characterization of factors that may modify the biological effects of ionizing radiation has been a subject of intense research efforts. Still, there is no assay currently available that can reliably predict the clinical radiosensitivity. The aim of this work has been to investigate the role of oxidative stress in individual radiosensitivity and evaluate novel markers of radiation response, which could be adapted for clinical use.8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), a general marker of oxidative stress, is one of the major products of interaction of ionizing radiation with DNA and the nucleotide pool of the cell. As 8-oxo-dG is highly mutagenic due to incorrect base pairing with deoxyadenosine, various repair mechanisms recognize and remove 8-oxo-dG. The repaired lesions are released from cells to the extracellular milieu (serum, urine and cell culture medium) where they can be detected as markers for free radical reactions with the nucleic acids.Significant variations in background levels as well as in radiation induced levels of 8-oxo-dG in urine have been demonstrated in breast cancer patients (paper 1). Two major patterns were observed: high background and no therapy-related increase vs. low background and significant increase during radiotherapy for the radiosensitive and non radiosensitive patients respectively.Studies in paper 2 indicated major contribution of the nucleotide pool to the extracellular 8-oxo-dG levels. The results also implicated induction of prolonged endogenous oxidative stress in the irradiated cells. RNA “knock-down” experiments on the nucleotide pool sanitization enzyme hMTH1 in paper 3 lend further experimental evidence to this assumption.The applicability of 8-oxo-dG as a diagnostic marker of oxidative stress was demonstrated in paper 4. Studies on dialysis patients revealed a good correlation between inflammatory responses (known to be associated with persistent oxidative stress) and extracellular 8-oxo-dG.In summary, our results confirm that extracellular 8-oxo-dG is a sensitive in vivo biomarker of oxidative stress, primarily formed by oxidative damage of dGTP in the nucleotide pool with a potential to become a clinical tool for prediction of individual responses to radiotherapy.
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| 4. |
- Haghdoost, Siamak, et al.
(författare)
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The nucleotide pool is a significant target for oxidative stress
- 2006
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Ingår i: Free Radical Biology & Medicine. - : Elsevier Inc.. - 0891-5849 .- 1873-4596. ; 41:4, s. 620-626
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Tidskriftsartikel (refereegranskat)abstract
- Oxidative stress is considered to be one of the most important phenomena involved in the process of aging and age-related diseases. 8-Oxo-7,8-dihydro-2′-deoxyguanosine (8-oxo-dG) has been frequently used as a marker for oxidative stress. However, the origin of extracellular 8-oxo-dG is not well understood. The aim of this work was to investigate the nucleotide pool and the role of the human mutT homologue protein (hMTH1) in the appearance of extracellular 8-oxo-dG in a cellular model system. For this purpose we used primary human fibroblast cells, which were transfected by siRNAs homologous to hMTH1. Extracellular 8-oxo-dG in cell culture media after exposure of the cells to ionizing radiation was measured as enzyme-linked immunosorbent assay reactivity. Our results demonstrate the profound effect of both hMTH1 expression and nucleotide pool size on the cellular excretion of 8-oxo-dG, suggesting that the nucleotide pool is a significant target for the formation of extracellular 8-oxo-dG.
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| 5. |
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| 6. |
- Jönsson, K. Ingemar, 1959-, et al.
(författare)
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Tardigrades survive exposure to space in low earth orbit
- 2008
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Ingår i: Current Biology. - 0960-9822 .- 1879-0445. ; 18:17, s. R729-R731
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Tidskriftsartikel (refereegranskat)abstract
- Vacuum (imposing extreme dehydration) and solar/galactic cosmic radiation prevent survival of most organisms in space . Only anhydrobiotic organisms, which have evolved adaptations to survive more or less complete desiccation, have a potential to survive space vacuum, and few organisms can stand the unfiltered solar radiation in space. Tardigrades, commonly known as water-bears, are among the most desiccation and radiation-tolerant animals and have been shown to survive extreme levels of ionizing radiation. Here, we show that tardigrades are also able to survive space vacuum without loss in survival, and that some specimens even recovered after combined exposure to space vacuum and solar radiation. These results add the first animal to the exclusive and short list of organisms that have survived such exposure.
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| 7. |
- Jönsson, K. Ingemar, et al.
(författare)
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Tardigrades survive exposure to space in low earth orbit
- 2008
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Ingår i: Current Biology. - : Cell Press. - 0960-9822 .- 1879-0445. ; 18:17, s. R729-R731
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Tidskriftsartikel (refereegranskat)abstract
- Vacuum (imposing extreme dehydration) and solar/galactic cosmic radiation prevent survival of most organisms in space . Only anhydrobiotic organisms, which have evolved adaptations to survive more or less complete desiccation, have a potential to survive space vacuum, and few organisms can stand the unfiltered solar radiation in space. Tardigrades, commonly known as water-bears, are among the most desiccation and radiation-tolerant animals and have been shown to survive extreme levels of ionizing radiation. Here, we show that tardigrades are also able to survive space vacuum without loss in survival, and that some specimens even recovered after combined exposure to space vacuum and solar radiation. These results add the first animal to the exclusive and short list of organisms that have survived such exposure.
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| 8. |
- Olsson, Gunilla
(författare)
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Involvement of Homologous Recombination in Response to Different Qualities of DNA Damage
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present studies aimed at elucidate the role of homologous recombination (HR) for the repair of different qualities of DNA damages and/or changes in chromatin structure induced by a variety of radiation qualities.Radiation qualities used to expose cells in culture ranged from non-ionizing radiation with extremely low frequency (ELF), of energies too low to disrupt chemical or molecular bonds, to radiation qualities with energies able to induce ionizations and break chemical bonds. The ionizing radiation (IR) used was both of low- or high-linear energy transfer (LET) producing a range of ionization densities. The higher the ionization density, the worse the cellular outcome in terms of survival, this can also be described as higher relative biological effectiveness (RBE).Homologous recombination that is involved in the repair of double-strand breaks operates mainly in the S and G2/M-phases of the cell cycle when a sister chromatid with the required homology sequence is available as template. HR is also involved in reinitiating stalled or collapsed replication forks, which may be the main task for this pathway.The data obtained with non-ionizing radiation suggest that ELF exposure may either stimulate or inhibit cell growth depending on the state of the cells in terms of chromatin conformation. Although ELF magnetic fields are not directly capable of inducing DNA breaks, a weak but significant increase in DNA fragmentation was observed. However, no induction of HR was indicated. Neither did ELF increase chromatin loop relaxation.A novel finding presented here is that HR seems to process DSBs produced by high-LET relatively more frequently compared to DSBs produced by low-LET. These results in combination with data suggesting that HR (as well as the fast NHEJ and BER) predominantly operates in open chromatin would indicate that a substantial fraction of DSBs induced by high-LET may also originate from the indirect effect.
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| 9. |
- Qvarnström, Fredrik, 1976-
(författare)
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DNA Damage Response of Normal Epidermis in the Clinical Setting of Fractionated Radiotherapy : Evidence of a preserved low-dose hypersensitivity response
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Investigations of DNA damage response (DDR) mechanisms in normal tissues have implications for both cancer prevention and treatments. The accumulating knowledge about protein function and molecular markers makes it possible to directly trace and interpret cellular DDR in a tissue context. Using immunohistochemical techniques and digital image analysis, we have examined several principal DDR events in epidermis from patients undergoing fractionated radiotherapy. Acquiring biopsies from different regions of the skin provides the possibility to determine in vivo dose response at clinically relevant dose levels throughout the treatment. A crucial event in cellular DDR is the repair of DNA double strand breaks (DSBs). These serious lesions can be directly visualised in cells by detecting foci forming markers such as γH2AX and 53BP1. Our results reveal that DSB-signalling foci can be detected and quantified in paraffin-embedded tissues. More importantly, epidermal DSB foci dose response reveals hypersensitivity, detected as elevated foci levels per dose unit, for doses below ~0.3Gy. The low-dose hypersensitive dose response is observed throughout the treatment course and also in between fractions: at 30 minutes, 3 hours and 24 hours following delivered fractions. The dose response at 24 hours further reveals that foci levels do not return to background levels between fractions. Furthermore, a low-dose hypersensitive dose response is also observed for these persistent foci. Investigations of end points further downstream in the DDR pathways confirmed that the low-dose hypersensitivity was preserved for: the checkpoint regulating p21 kinase inhibitor; mitosis suppression; apoptosis induction and basal keratinocyte reduction. Our results reveal preserved low-dose hypersensitivity both early and late in the DDR pathways. A possible link between the dose-response relationships is therefore suggested. The preserved low-dose hypersensitivity is a cause for re-evaluation of the risks associated with low-dose exposure and has implications for cancer treatments, diagnostics and radiation protection.
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