Selenoprotein P inhibits radiation-induced late reactive oxygen species accumulation and normal cell injury.
OBJECTIVE
Radiation is a common mode of cancer therapy whose outcome is often limited because of normal tissue toxicity. We have shown previously that the accumulation of radiation-induced late reactive oxygen species (ROS) precedes cell death, suggesting that metabolic oxidative stress could regulate cellular radiation response. The purpose of this study was to investigate whether selenoprotein P (SEPP1), a major supplier of selenium to tissues and an antioxidant, regulates late ROS accumulation and toxicity in irradiated normal human fibroblasts (NHFs).


METHODS
Flow cytometry analysis of cell viability, cell cycle phase distribution, and dihydroethidium oxidation, along with clonogenic assays, were used to measure oxidative stress and toxicity. Human antioxidant mechanisms array and quantitative real-time polymerase chain reaction assays were used to measure gene expression during late ROS accumulation in irradiated NHFs. Sodium selenite addition and SEPP1 overexpression were used to determine the causality of SEPP1 regulating late ROS accumulation and toxicity in irradiated NHFs.


RESULTS
Irradiated NHFs showed late ROS accumulation (4.5-fold increase from control; P<.05) that occurs after activation of the cell cycle checkpoint pathways and precedes cell death. The mRNA levels of CuZn- and Mn-superoxide dismutase, catalase, peroxiredoxin 3, and thioredoxin reductase 1 increased approximately 2- to 3-fold, whereas mRNA levels of cold shock domain containing E1 and SEPP1 increased more than 6-fold (P<.05). The addition of sodium selenite before the radiation treatment suppressed toxicity (45%; P<.05). SEPP1 overexpression suppressed radiation-induced late ROS accumulation (35%; P<.05) and protected NHFs from radiation-induced toxicity (58%; P<.05).


CONCLUSIONS
SEPP1 mitigates radiation-induced late ROS accumulation and normal cell injury.
Free Radical and Radiation Biology Division, Department of Radiation Oncology, University of Iowa, Iowa City, Iowa.
Jaimee C
JC
Eckers
Amanda L
AL
Kalen
Wusheng
W
Xiao
Ehab H
EH
Sarsour
Prabhat C
PC
Goswami
D059447:Cell Cycle Checkpoints / Q000502:physiology / Q000528:radiation effects; D016923:Cell Death; D002470:Cell Survival; D004307:Dose-Response Relationship, Radiation; D004996:Ethidium / Q000031:analogs & derivatives / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism / Q000528:radiation effects; D016341:Genes, vif; D006801:Humans; D018384:Oxidative Stress / Q000235:genetics; D011832:Radiation Injuries / Q000517:prevention & control*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D051149:Selenoprotein P / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018038:Sodium Selenite / Q000494:pharmacology
D017382:Reactive Oxygen Species; D051149:Selenoprotein P; C067883:dihydroethidium; D004996:Ethidium; D018038:Sodium Selenite