title: Low-dose photons modify liver response to simulated solar particle event protons.
abstract: The health consequences of exposure to low-dose radiation combined with a solar particle event during space travel remain unresolved. The goal of this study was to determine whether protracted radiation exposure alters gene expression and oxidative burst capacity in the liver, an organ vital in many biological processes. C57BL/6 mice were whole-body irradiated with 2 Gy simulated solar particle event (SPE) protons over 36 h, both with and without pre-exposure to low-dose/low-dose-rate photons ((57)Co, 0.049 Gy total at 0.024 cGy/h). Livers were excised immediately after irradiation (day 0) or on day 21 thereafter for analysis of 84 oxidative stress-related genes using RT-PCR; genes up or down-regulated by more than twofold were noted. On day 0, genes with increased expression were: photons, none; simulated SPE, Id1; photons + simulated SPE, Bax, Id1, Snrp70. Down-regulated genes at this same time were: photons, Igfbp1; simulated SPE, Arnt2, Igfbp1, Il6, Lct, Mybl2, Ptx3. By day 21, a much greater effect was noted than on day 0. Exposure to photons + simulated SPE up-regulated completely different genes than those up-regulated after either photons or the simulated SPE alone (photons, Cstb; simulated SPE, Dctn2, Khsrp, Man2b1, Snrp70; photons + simulated SPE, Casp1, Col1a1, Hspcb, Il6st, Rpl28, Spnb2). There were many down-regulated genes in all irradiated groups on day 21 (photons, 13; simulated SPE, 16; photons + simulated SPE, 16), with very little overlap among groups. Oxygen radical production by liver phagocytes was significantly enhanced by photons on day 21. The results demonstrate that whole-body irradiation with low-dose-rate photons, as well as time after exposure, had a great impact on liver response to a simulated solar particle event.
authors.affiliation: Department of Radiation Medicine, Molecular Radiation Biology Laboratories, Loma Linda University and Medical Center, Loma Linda, California 92354, USA. dgridley@dominion.llumc.edu
authors.forename: Daila S
authors.initials: DS
authors.lastname: Gridley
authors.forename: George B
authors.initials: GB
authors.lastname: Coutrakon
authors.forename: Asma
authors.initials: A
authors.lastname: Rizvi
authors.forename: Erben J M
authors.initials: EJ
authors.lastname: Bayeta
authors.forename: Xian
authors.initials: X
authors.lastname: Luo-Owen
authors.forename: Adeola Y
authors.initials: AY
authors.lastname: Makinde
authors.forename: Farnaz
authors.initials: F
authors.lastname: Baqai
authors.forename: Peter
authors.initials: P
authors.lastname: Koss
authors.forename: James M
authors.initials: JM
authors.lastname: Slater
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Pecaut
mesh_terms: D000818:Animals; D003359:Cosmic Radiation; D004307:Dose-Response Relationship, Radiation; D005260:Female; D008099:Liver / Q000378:metabolism* / Q000528:radiation effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D018384:Oxidative Stress / Q000502:physiology / Q000528:radiation effects; D017785:Photons; D011829:Radiation Dosage; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012993:Solar Energy; D013026:Space Flight; D018561:Space Simulation / Q000379:methods*; D014916:Whole-Body Irradiation / Q000379:methods*
chemical_list: D017382:Reactive Oxygen Species