Age-related effects of X-ray irradiation on mouse hippocampus

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Abstract

Therapeutic irradiation of pediatric and adult patients can profoundly affect adult neurogenesis, and cognitive impairment manifests as a deficit in hippocampal-dependent functions. Age plays a major role in susceptibility to radiation, and younger children are at higher risk of cognitive decay when compared to adults. Cranial irradiation affects hippocampal neurogenesis by induction of DNA damage in neural progenitors, through the disruption of the neurogenic microenvironment, and defective integration of newborn neurons into the neuronal network. Our goal here was to assess cellular and molecular alterations induced by cranial X-ray exposure to low/moderate doses (0.1 and 2 Gy) in the hippocampus of mice irradiated at the postnatal ages of day 10 or week 10, as well as the dependency of these phenomena on age at irradiation. To this aim, changes in the cellular composition of the dentate gyrus, mitochondrial functionality, proteomic profile in the hippocampus, as well as cognitive performance were evaluated by a multidisciplinary approach. Our results suggest the induction of specific alterations in hippocampal neurogenesis, microvascular density and mitochondrial functions, depending on age at irradiation. A better understanding of how irradiation impairs hippocampal neurogenesis at low and moderate doses is crucial to minimize adverse effects of therapeutic irradiation, contributing also to radiation safety regulations.

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Most cited references 67

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Mechanisms and functional implications of adult neurogenesis.

Chunmei Zhao, Wei Deng, Fred Gage (2008)

The generation of new neurons is sustained throughout adulthood in the mammalian brain due to the proliferation and differentiation of adult neural stem cells. In this review, we discuss the factors that regulate proliferation and fate determination of adult neural stem cells and describe recent studies concerning the integration of newborn neurons into the existing neural circuitry. We further address the potential significance of adult neurogenesis in memory, depression, and neurodegenerative disorders such as Alzheimer's and Parkinson's disease.

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Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study

Mark S. Pearce, Jane Salotti, Mark Little … (2012)

Summary Background Although CT scans are very useful clinically, potential cancer risks exist from associated ionising radiation, in particular for children who are more radiosensitive than adults. We aimed to assess the excess risk of leukaemia and brain tumours after CT scans in a cohort of children and young adults. Methods In our retrospective cohort study, we included patients without previous cancer diagnoses who were first examined with CT in National Health Service (NHS) centres in England, Wales, or Scotland (Great Britain) between 1985 and 2002, when they were younger than 22 years of age. We obtained data for cancer incidence, mortality, and loss to follow-up from the NHS Central Registry from Jan 1, 1985, to Dec 31, 2008. We estimated absorbed brain and red bone marrow doses per CT scan in mGy and assessed excess incidence of leukaemia and brain tumours cancer with Poisson relative risk models. To avoid inclusion of CT scans related to cancer diagnosis, follow-up for leukaemia began 2 years after the first CT and for brain tumours 5 years after the first CT. Findings During follow-up, 74 of 178 604 patients were diagnosed with leukaemia and 135 of 176 587 patients were diagnosed with brain tumours. We noted a positive association between radiation dose from CT scans and leukaemia (excess relative risk [ERR] per mGy 0·036, 95% CI 0·005–0·120; p=0·0097) and brain tumours (0·023, 0·010–0·049; p<0·0001). Compared with patients who received a dose of less than 5 mGy, the relative risk of leukaemia for patients who received a cumulative dose of at least 30 mGy (mean dose 51·13 mGy) was 3·18 (95% CI 1·46–6·94) and the relative risk of brain cancer for patients who received a cumulative dose of 50–74 mGy (mean dose 60·42 mGy) was 2·82 (1·33–6·03). Interpretation Use of CT scans in children to deliver cumulative doses of about 50 mGy might almost triple the risk of leukaemia and doses of about 60 mGy might triple the risk of brain cancer. Because these cancers are relatively rare, the cumulative absolute risks are small: in the 10 years after the first scan for patients younger than 10 years, one excess case of leukaemia and one excess case of brain tumour per 10 000 head CT scans is estimated to occur. Nevertheless, although clinical benefits should outweigh the small absolute risks, radiation doses from CT scans ought to be kept as low as possible and alternative procedures, which do not involve ionising radiation, should be considered if appropriate. Funding US National Cancer Institute and UK Department of Health.

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Estimated risks of radiation-induced fatal cancer from pediatric CT.

D. Brenner, C Elliston, E. Hall … (2001)

In light of the rapidly increasing frequency of pediatric CT examinations, the purpose of our study was to assess the lifetime cancer mortality risks attributable to radiation from pediatric CT. Organ doses as a function of age-at-diagnosis were estimated for common CT examinations, and estimated attributable lifetime cancer mortality risks (per unit dose) for different organ sites were applied. Standard models that assume a linear extrapolation of risks from intermediate to low doses were applied. On the basis of current standard practice, the same exposures (milliampere-seconds) were assumed, independent of age. The larger doses and increased lifetime radiation risks in children produce a sharp increase, relative to adults, in estimated risk from CT. Estimated lifetime cancer mortality risks attributable to the radiation exposure from a CT in a 1-year-old are 0.18% (abdominal) and 0.07% (head)-an order of magnitude higher than for adults-although those figures still represent a small increase in cancer mortality over the natrual background rate. In the United States, of approximately 600,000 abdominal and head CT examinations annually performed in children under the age of 15 years, a rough estimate is that 500 of these individuals might ultimately die from cancer attributable to the CT radiation. The best available risk estimates suggest that pediatric CT will result in significantly increased lifetime radiation risk over adult CT, both because of the increased dose per milliampere-second, and the increased lifetime risk per unit dose. Lower milliampere-second settings can be used for children without significant loss of information. Although the risk-benefit balance is still strongly tilted toward benefit, because the frequency of pediatric CT examinations is rapidly increasing, estimates that quantitative lifetime radiation risks for children undergoing CT are not negligible may stimulate more active reduction of CT exposure settings in pediatric patients.

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Author and article information

Journal

Journal ID (nlm-ta): Oncotarget

Journal ID (iso-abbrev): Oncotarget

Journal ID (publisher-id): Oncotarget

Journal ID (publisher-id): ImpactJ

Title: Oncotarget

Publisher: Impact Journals LLC

ISSN (Electronic): 1949-2553

Publication date Collection: 10 May 2016

Publication date (Electronic): 4 April 2016

Volume: 7

Issue: 19

Pages: 28040-28058

Affiliations

¹ Laboratory of Biomedical Technologies, Agenzia Nazionale per le Nuove Tecnologie, l'Energia e lo Sviluppo Economico Sostenibile (ENEA), Rome, Italy

² National Public Health Center - National Research Directorate for Radiobiology and Radiohygiene, Budapest, Hungary

³ Physiology Unit, School of Medicine, IISPV, Rovira I Virgili University (URV), Reus, Spain

⁴ Institute of Radiation Biology, Helmholtz Zentrum Munchen, German Research Center for Environmental Health GmbH, Neuherberg, Germany

⁵ Institute of Radiation Biology, Technical University Munich, Munich, Germany

⁶ Research Unit Protein Science, Helmholtz Zentrum München, German Research Center for Environmental Health GmbH, Neuherberg, Germany

⁷ Radiobiology Unit, Belgian Nuclear Research Centre, SCK•CEN, Belgium

⁸ Present address: Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark

Author notes

Correspondence to: Simonetta Pazzaglia, simonetta.pazzaglia@ 123456enea.it

Article

Publisher ID: 8575

DOI: 10.18632/oncotarget.8575

PMC ID: 5053708

PubMed ID: 27057631

SO-VID: b039572a-2ab8-4956-8c17-ef58d06ee632

License:

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

History

Date received : 11 February 2016

Date accepted : 27 March 2016

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Age-related effects of X-ray irradiation on mouse hippocampus

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Most cited references 67

Mechanisms and functional implications of adult neurogenesis.

Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study

Estimated risks of radiation-induced fatal cancer from pediatric CT.

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