Ionizing radiation induces severe oxidative stress, resulting in individual death by acute radiation syndrome. The nuclear factor-erythroid-2-related factor 2 (Nrf2) plays an important role in the antioxidant response pathway. Recently, romiplostim (RP), an idiopathic thrombocytopenic purpura therapeutic drug, was reported to completely rescue mice exposed to lethal total-body irradiation (TBI). However, the details underlying the mechanism for reducing radiation damage remain largely unknown. To elucidate the involvement of the master redox regulator Nrf2 in the radio-mitigative efficacy of RP on TBI-induced oxidative stress, expression of Nrf2 target genes in hematopoietic tissues such as bone marrow, spleen, and lung from mice treated with RP for three consecutive days after 7 Gy of X-ray TBI was analyzed. RP promoted the recovery of bone marrow cells from day 10 and the significant up-regulation of reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H) dehydrogenase quinone 1 (Nqo1), glutamate-cysteine ligase catalytic subunit (Gclc) and glutamate-cysteine ligase modifier subunit (Gclm) was observed compared to the TBI mice. RP also promoted the recovery of splenic cells on day 18, and the significant up-regulation of Nqo1, Gclc and Gclm in spleen both on day 10 and 18 and Nqo1 and Gclm in lung on day 10 was observed compared to the TBI mice. The present study suggests that the radio-mitigative effects of RP indicates on the activation of Nrf2 target genes involved in redox regulation and the antioxidative function, especially Nqo1, Gclc and Gclm. It is indicating the importance of these genes in the maintenance of biological homeostasis in response to radiation-induced oxidative stress. Key words accute radiation syndrome; romiplostim; radio-mitigative effect; nuclear factor-erythroid-2-related factor 2 (Nrf2) target gene; reduced nicotinamide adenine dinucleotide phosphate dehydrogenase quinone 1 (Nqo1); glutamate-cysteine ligase modifier subunit (Gclm)

Background:It has been reported that the high-dosage administration of domestically approved pharmaceutical drugs, especially granulocyte colony-stimulating factor (G-CSF) and romiplostim (RP), is a rapid and appropriate medical treatment for preventing severe acute radiation syndrome (ARS) of victims exposed to lethal total-body irradiation (TBI). However, it remains unclear whether or not the clinical dosage administration of these drugs can ameliorate TBI-induced ARS and related high mortality in order to find various drug treatment options and less toxic optimum protocol depending on the situation surrounding the radiological accidents.Methods:We assessed the clinical dosageadministration in combination with G-CSF and RP as intraperitoneal injection in C57BL/6J mice exposed to more than 7-Gy lethal dose of X-ray TBI for the survival studyevaluated by the log-rank test. Bone marrow and splenic cellswere collected on the 21st day, when1 week have passed from last administration, to detect the level of cell apoptosis, intracellular reactive oxygen species (ROS), and nuclear factor erythroid 2-related factor 2 (Nrf2)-related anti-oxidative gene expressions, and enzyme-linked immune sorbent assayusing serawas performed for cell senescence and inflammationstatusanalyzed with one-way ANOVA and Tukey-Kramer or Bonferroni/Dunn multiple comparison tests.Results: The combined once-daily administration of 10 μg/kg G-CSF for 4 times and 10 μg/kgRP once a week for 3 times improve the 30-day survival rate of lethal TBI mice compared with untreated TBI mice, accompanied by a gradual increase in the body weight and hematopoietic cell numbers. The radio-mitigative effect is probably attributed to the scavenging of ROS and the reduction in cell apoptosis. These changes were associated with the upregulation of Nrf2 and its downstream anti-oxidative targets in TBI mice. Furthermore, this combination modulated TBI-induced cell senescence and inflammation markers. Conclusions:This study suggested that the clinical dosage administration in combination with G-CSF and RP may also have radio-mitigative effects on mice exposed to lethal TBI and may be a potent therapeutic agent for mitigating radiation-induced severe ARS.

Background: It has been reported that the high-dosage administration of domestically approved pharmaceutical drugs, especially granulocyte colony-stimulating factor (G-CSF) and romiplostim (RP), is a rapid and appropriate medical treatment for preventing severe acute radiation syndrome (ARS) of victims exposed to lethal total-body irradiation (TBI). However, it remains unclear whether or not the clinical dosage administration of these drugs can ameliorate TBI-induced ARS and related high mortality in order to find various drug treatment options and less toxic optimum protocol depending on the situation surrounding the radiological accidents. Methods: We assessed the clinical dosage administration in combination with G-CSF and RP as intraperitoneal injection in C57BL/6 J mice exposed to more than 7-Gy lethal dose of X-ray TBI for the survival study evaluated by the log-rank test. Bone marrow and splenic cells were collected on the 21st day, when 1 week has passed from last administration, to detect the level of cell apoptosis, intracellular reactive oxygen species (ROS), and nuclear factor erythroid 2-related factor 2 (Nrf2)-related anti-oxidative gene expressions, and enzyme-linked immune sorbent assay using sera was performed for cell senescence and inflammation status analyzed with one-way ANOVA and Tukey-Kramer or Bonferroni/Dunn multiple comparison tests. Results: The combined once-daily administration of 10 μg/kg G-CSF for 4 times and 10 μg/kg RP once a week for 3 times improve the 30-day survival rate of lethal TBI mice compared with untreated TBI mice, accompanied by a gradual increase in the body weight and hematopoietic cell numbers. The radio-mitigative effect is probably attributed to the scavenging of ROS and the reduction in cell apoptosis. These changes were associated with the upregulation of Nrf2 and its downstream anti-oxidative targets in TBI mice. Furthermore, this combination modulated TBI-induced cell senescence an d inflammation markers. Conclusions: This study suggested that the clinical dosage administration in combination with G-CSF and RP may also have radio-mitigative effects on mice exposed to lethal TBI and may be a potent therapeutic agent for mitigating radiation-induced severe ARS.

Background: It has been reported that the high-dosage administration of domestically approved pharmaceutical drugs, especially granulocyte colony-stimulating factor (G-CSF) and romiplostim (RP), is a rapid and appropriate medical treatment for preventing severe acute radiation syndrome (ARS) of victims exposed to lethal total-body irradiation (TBI). However, it remains unclear whether or not the clinical dosage administration of these drugs can ameliorate TBI-induced ARS and related high mortality in order to find various drug treatment options and less toxic optimum protocol depending on the situation surrounding the radiological accidents.Methods: We assessed the clinical dosage administration in combination with G-CSF and RP as intraperitoneal injection in C57BL/6J mice exposed to more than 7-Gy lethal dose of X-ray TBI for the survival study evaluated by the log-rank test. Bone marrow and splenic cells were collected on the 21st day, when 1 week have passed from last administration, to detect the level of cell apoptosis, intracellular reactive oxygen species (ROS), and nuclear factor erythroid 2-related factor 2 (Nrf2)-related anti-oxidative gene expressions, and enzyme-linked immune sorbent assay using sera was performed for cell senescence and inflammation status analyzed with one-way ANOVA and Tukey-Kramer or Bonferroni/Dunn multiple comparison tests.Results: The combined once-daily administration of 10 μg/kg G-CSF for 4 times and 10 μg/kg RP once a week for 3 times improve the 30-day survival rate of lethal TBI mice compared with untreated TBI mice, accompanied by a gradual increase in the body weight and hematopoietic cell numbers. The radio-mitigative effect is probably attributed to the scavenging of ROS and the reduction in cell apoptosis. These changes were associated with the upregulation of Nrf2 and its downstream anti-oxidative targets in TBI mice. Furthermore, this combination modulated TBI-induced cell senescence and inflammation markers. Conclusions: This study suggested that the clinical dosage administration in combination with G-CSF and RP may also have radio-mitigative effects on mice exposed to lethal TBI and may be a potent therapeutic agent for mitigating radiation-induced severe ARS.