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- Abramenkovs, Andris, 1989-
(författare)
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Induction and repair of clustered DNA damage sites after exposure to ionizing radiation
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The mechanisms that maintain genomic stability safeguard cells from constant DNA damage produced by endogenous and external stressors. Therefore, this thesis aimed to specifically address questions regarding the requirement and involvement of DNA repair proteins in the repair of various types of radiation-induced DNA damage.The first aim was to determine whether the phosphorylation of DNA-PKcs, a major kinase involved in non-homologous end joining pathway, can be utilized to score the DNA double-strand break (DSB) content in cells. DNA-PKcs phosphorylated (pDNA-PKcs) at T2609 was more sensitive to the cellular DSB content than ɣH2AX, as analyzed by flow cytometry. Further, pDNA-PKcs at T2609 could discriminate between DSB repair-compromised and normal cells, confirming that the pDNA-PKcs can be used as a DSB repair marker. In paper II, the DSB repair was assessed in cells with reduced levels of DNA-PKcs. The reduction in DNA-PKcs resulted in decreased cell survival and unaffected DSB repair. These results clearly indicate that DNA-PKcs plays an additional role in promoting cell survival in addition to its function in DSB repair.The second part of the thesis focused on the characterization of complex DNA damage. DNA damage was investigated after exposure to α-particles originating from Ra-223. The Ra-223 treatment induced a nonrandom DSB distribution consistent with damage induced by high-linear energy transfer radiation. The exposure to Ra-223 significantly reduced cell survival in monolayers and 3D cell structures. The last paper unraveled the fate of heat-sensitive clustered DNA damage site (HSCS) repair in cells. HSCS repair was independent of DSB repair, and these lesions did not contribute to the generation of additional DSBs during repair. Prolonged heating of DNA at relatively low temperatures induced structural changes in the DNA that contributed to the production of DNA artifacts.In conclusion, these results demonstrate that DNA-PKcs can be used to monitor DSB repair in cells after exposure to ionizing radiation. However, the functions of DNA-PKcs are not limited to DSB repair, as it can promote cell survival through other mechanisms. The complexity of the DNA damage produced by high-LET radiation is a major contributor to cell death. However, not all clusters produced in irradiated cells are converted into DSBs during repair.
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| 2. |
- Abramenkovs, Andris, et al.
(författare)
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Measurement of DNA-Dependent Protein Kinase Phosphorylation Using Flow Cytometry Provides a Reliable Estimate of DNA Repair Capacity
- 2017
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Ingår i: Radiation Research. - : RADIATION RESEARCH SOC. - 0033-7587 .- 1938-5404. ; 188:6, s. 597-604
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Tidskriftsartikel (refereegranskat)abstract
- Uncontrolled generation of DNA double-strand breaks (DSBs) in cells is regarded as a highly toxic event that threatens cell survival. Radiation-induced DNA DSBs are commonly measured by pulsed-field gel electrophoresis, microscopic evaluation of accumulating DNA damage response proteins (e.g., 53BP1 or gamma-H2AX) or flow cytometric analysis of gamma-H2AX. The advantage of flow cytometric analysis is that DSB formation and repair can be studied in relationship to cell cycle phase or expression of other proteins. However, gamma-H2AX is not able to monitor repair kinetics within the first 60 min postirradiation, a period when most DSBs undergo repair. A key protein in non-homologous end joining repair is the catalytic subunit of DNA-dependent protein kinase. Among several phosphorylation sites of DNA-dependent protein kinase, the threonine at position 2609 (T2609), which is phosphorylated by ataxia telangiectasia mutated (ATM) or DNA-dependent protein kinase catalytic subunit itself, activates the end processing of DSB. Using flow cytometry, we show here that phosphorylation at T2609 is faster in response to DSBs than gamma-H2AX. Furthermore, flow cytometric analysis of T2609 resulted in a better representation of fast repair kinetics than analysis of gamma-H2AX. In cells with reduced ligase IV activity, and wild-type cells where DNA-dependent protein kinase activity was inhibited, the reduced DSB repair capacity was observed by T2609 evaluation using flow cytometry. In conclusion, flow cytometric evaluation of DNA-dependent protein kinase T2609 can be used as a marker for early DSB repair and gives a better representation of early repair events than analysis of gamma-H2AX.
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| 3. |
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| 4. |
- Abramenkovs, Andris, et al.
(författare)
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Removal of heat-sensitive clustered damaged DNA sites is independent of double-strand break repair
- 2018
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 13:12
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Tidskriftsartikel (refereegranskat)abstract
- DNA double-strand breaks (DSBs) are the most deleterious lesions that can arise in cells after ionizing radiation or radiometric drug treatment. In addition to prompt DSBs, DSBs may also be produced during repair, evolving from a clustered DNA damaged site, which is composed of two or more distinct lesions that are located within two helical turns. A specific type of cluster damage is the heat-sensitive clustered site (HSCS), which transforms into DSBs upon treatment at elevated temperatures. The actual lesions or mechanisms that mediate the HSCS transformation into DSBs are unknown. However, there are two possibilities; either these lesions are transformed into DSBs due to DNA lesion instability, e.g., transfer of HSCS into single-strand breaks (SSBs), or they are formed due to local DNA structure instability, e.g., DNA melting, where two SSBs on opposite strands meet and transform into a DSB. The importance of these processes in living cells is not understood, but they significantly affect estimates of DSB repair capacity. In this study, we show that HSCS removal in human cells is not affected by defects in DSB repair or inhibition of DSB repair. Under conditions where rejoining of prompt DSBs was almost completely inhibited, heat-sensitive DSBs were successfully rejoined, without resulting in increased DSB levels, indicating that HSCS do not transfer into DSB in cells under physiological conditions. Furthermore, analysis by atomic force microscopy suggests that prolonged heating of chromosomal DNA can induce structural changes that facilitate transformation of HSCS into DSB. In conclusion, the HSCS do not generate additional DSBs at physiological temperatures in human cells, and the repair of HSCS is independent of DSB repair.
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| 5. |
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| 6. |
- Buratovic, Sonja, et al.
(författare)
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Developmental effects of fractionated low-dose exposure to gamma radiation on behaviour and susceptibility of the cholinergic system in mice
- 2016
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Ingår i: International Journal of Radiation Biology. - : Informa UK Limited. - 0955-3002 .- 1362-3095. ; 92:7, s. 371-379
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To investigate whether neonatal exposure to fractionated external gamma radiation and co-exposure to radiation and nicotine can affect/exacerbate developmental neurotoxic effects, including altered behavior/cognitive function and the susceptibility of the cholinergic system in adult male mice. Materials and methods: Neonatal male Naval Medical Research Institute (NMRI) mice were irradiated with one 200 mGy fraction/day and/or exposed to nicotine (66 μg/kg b.w.) twice daily on postnatal day (PND) 10, 10–11, 10–12 or 10–13 (nicotine only). At 2 months of age the animals were tested for spontaneous behavior in a novel home environment, habituation capacity and nicotine-induced behavior. Results: Fractionated irradiation and co-exposure to radiation and nicotine on three consecutive days disrupted behavior and habituation and altered susceptibility of the cholinergic system. All observed effects were significantly more pronounced in mice co-exposed to both radiation and nicotine. Conclusions: The fractionated irradiation regime affects behavior/cognitive function in a similar manner as has previously been observed for single-dose exposures. Neonatal co-exposure to radiation and nicotine, during a critical period of brain development in general and cholinergic system development in particular, enhance these behavioral defects suggesting that the cholinergic system can be a target system for this type of developmental neurotoxic effects.
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| 7. |
- Buratovic, Sonja, 1986-, et al.
(författare)
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Effects on adult cognitive function after neonatal exposure to clinically relevant doses of ionising radiation and ketamine in mice
- 2018
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Ingår i: British Journal of Anaesthesia. - : ELSEVIER SCI LTD. - 0007-0912 .- 1471-6771. ; 120:3, s. 546-554
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Tidskriftsartikel (refereegranskat)abstract
- Background: Radiological methods for screening, diagnostics and therapy are frequently used in healthcare. In infants and children, anaesthesia/sedation is often used in these situations to relieve the patients' perception of stress or pain. Both ionising radiation (IR) and ketamine have been shown to induce developmental neurotoxic effects and this study aimed to identify the combined effects of these in a murine model. Methods: Male mice were exposed to a single dose of ketamine (7.5 mg kg(-1) body weight) s.c. on postnatal day 10. One hour after ketamine exposure, mice were whole body irradiated with 50-200 mGy gamma radiation (Cs-137). Behavioural observations were performed at 2, 4 and 5 months of age. At 6 months of age, cerebral cortex and hippocampus tissue were analysed for neuroprotein levels. Results: Animals co-exposed to IR and ketamine displayed significant (P <= 0.01) lack of habituation in the spontaneous behaviour test, when compared with controls and single agent exposed mice. In the Morris Water Maze test, co-exposed animals showed significant (P <= 0.05) impaired learning and memory capacity in both the spatial acquisition task and the relearning test compared with controls and single agent exposed mice. Furthermore, in co-exposed mice a significantly (P <= 0.05) elevated level of tau protein in cerebral cortex was observed. Single agent exposure did not cause any significant effects on the investigated endpoints. Conclusion: Co-exposure to IR and ketamine can aggravate developmental neurotoxic effects at doses where the single agent exposure does not impact on the measured variables. These findings show that estimation of risk after paediatric low-dose IR exposure, based upon radiation dose alone, may underestimate the consequences for this vulnerable population.
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| 8. |
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| 9. |
- Buratovic, Sonja, 1986-
(författare)
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Low-Dose Ionizing Radiation Induces Neurotoxicity in the Neonate : Acute or fractionated doses and interaction with xenobiotics in mice
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examines the developmental neurotoxic effects of exposure to low-dose ionizing radiation (IR), alone or together with xenobiotics, during a critical period of neonatal brain development in mice.During mammalian brain development there is a period called the brain growth spurt (BGS), which involves extensive growth and maturation of the brain. It is known that neonatal exposure during the BGS to xenobiotics can have a negative impact on neonatal brain development, resulting in impaired cognitive function in the adult mouse. In humans, the BGS starts during the third trimester of pregnancy and continues for approximately 2 years in the child. The present thesis has identified a defined critical period, during the BGS, when IR can induce developmental neurotoxicity in mice. The observed neurotoxicity was not dependent on sex or strain and manifested as altered neurobehaviour in the adult mouse. Furthermore, fractionated dose exposures appear to be as potent as a higher acute dose. The cholinergic system can be a target system for developmental neurotoxicity of IR, since alterations in adult mouse cholinergic system susceptibility were observed. Co-exposure to IR and nicotine exacerbated the behavioural disturbances and cholinergic system dysfunction. Furthermore, co-exposure with the environmental agent paraquat has indicated that the dopaminergic system can be a potential target. In this thesis, clinically relevant doses of IR and a sedative/anesthetic agent (ketamine) were shown to interact and exacerbate defects in adult mouse neurobehaviour, learning and memory, following neonatal exposure, at doses where the single agents did not have any impact on the measured variables. This indicates a shift in the dose-response curve for IR, towards lower doses, if exposure occurs during the neonatal brain development. In addition, co-exposed mice, showing cognitive defects, expressed elevated levels of tau protein in the cerebral cortex. Furthermore, exacerbation of neurochemical deviations were observed following co-exposure compared to irradiation alone.Further investigations of neurotoxic effects following fractionated or acute low-dose IR, modelling the clinical situation during repeated CT scans or levels of radiation deposited in non-target tissue during radiotherapy, and possible interaction effects with xenobiotics, is of great importance in the field of radioprotection.
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