Comparison of proton and electron radiation effects on biological responses in liver, spleen and blood

Purpose: To determine whether differences exist between proton and electron radiations on biological responses after total-body exposure. Materials and 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. Conclusion: Collectively, the data demonstrate that at least some biological effects induced by electrons may not be directly extrapolated to protons.