Comparison of proton and electron radiation effects on biological responses in liver, spleen and blood.
OBJECTIVE
To determine whether differences exist between proton and electron radiations on biological responses after total-body exposure.


METHODS
ICR mice (n=45) were irradiated to 2 Gray (Gy) using fully modulated 70 MeV protons (0.5 Gy/min) and 21 MeV electrons (3 Gy/min). At 36 h post-irradiation liver gene expression, white blood cell (WBC), natural killer (NK) cell and other analyses were performed.


RESULTS
Oxidative stress-related gene expression patterns were strikingly different for irradiated groups compared to 0 Gy (P<0.05). Proton radiation up-regulated 15 genes (Ctsb, Dnm2, Gpx5, Il19, Il22, Kif9, Lpo, Nox4, Park7, Prdx4, Prdx6, Rag2, Sod3, Srxn1, Xpa) and down-regulated 2 genes (Apoe, Prdx1). After electron irradiation, 20 genes were up-regulated (Aass, Ctsb, Dnm2, Gpx1, Gpx4, Gpx5, Gpx6, Gstk1, Il22, Kif9, Lpo, Nox4, Park7, Prdx3, Prdx4, Prdx5, Rag2, Sod1, Txnrd3, Xpa) and 1 was down-regulated (Mpp4). Of the modified genes, only 11 were common to both forms of radiation. Comparison between the two irradiated groups showed that electrons significantly up-regulated three genes (Gstk1, Prdx3, Scd1). Numbers of WBC and major leukocyte types were low in the irradiated groups (P<0.001 vs. 0 Gy). Hemoglobin and platelet counts were low in the electron-irradiated group (P<0.05 vs. 0 Gy). However, spleens from electron-irradiated mice had higher WBC and lymphocyte counts, as well as enhanced NK cell cytotoxicity, compared to animals exposed to protons (P<0.05). There were no differences between the two irradiated groups in body mass, organ masses, and other assessed parameters, although some differences were noted compared to 0 Gy.


CONCLUSIONS
Collectively, the data demonstrate that at least some biological effects induced by electrons may not be directly extrapolated to protons.
Department of Radiation Medicine, Radiation Research Laboratories, Loma Linda University and Medical Center, Loma Linda, CA 92354, USA. dgridley@dominion.llumc.edu
Daila S
DS
Gridley
Tanya L
TL
Freeman
Adeola Y
AY
Makinde
Andrew J
AJ
Wroe
Xian
X
Luo-Owen
Jian
J
Tian
Xiao Wen
XW
Mao
Steven
S
Rightnar
Ann R
AR
Kennedy
James M
JM
Slater
Michael J
MJ
Pecaut
D000818:Animals; D001772:Blood Cell Count / Q000379:methods; D001773:Blood Cells / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004583:Electrons; D015870:Gene Expression / Q000528:radiation effects; D007694:Killer Cells, Natural / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D007962:Leukocytes / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D008099:Liver / Q000378:metabolism / Q000528:radiation effects*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D018384:Oxidative Stress / Q000528:radiation effects; D011522:Protons; D011839:Radiation, Ionizing; D013154:Spleen / Q000378:metabolism / Q000528:radiation effects*; D013997:Time Factors; D014916:Whole-Body Irradiation / Q000379:methods
D011522:Protons