The Therapeutic Effects Of The P38MAPK Inhibition Combination Of G-CSF On The Mice Received γ-ray Total Body Irradiation

The patients received radiotherapy for various diseases in clinic and the victims of nuclear events might develop different irradiation injuries. It is well known that hematopoietic system is hypersensitive to irradiation, so hematopoietic injury is the key of the radiation protection and therapy. The prevention and therapy of hematopoietic radiation injury is very essential for the clinic and society.P38mitogen-activated protein kinases (p38MAPK, p38) play important role in the development, senescence and apoptosis of the hematopoietic cells, and are over activated after irradiation. Inhibition of p38either with pharmacological inhibitors or by genetic approaches has been shown to reduce the severity of acquired aplastic anemia and myelodysplastic syndromes by inhibiting apoptosis of hematopoietic stem and progenitor cells. So in the present study, we discussed whether inhibition of p38with SB203580(SB) alone could prevent TBI-induced BM injury.The feasibility of SB as radiation prevention drug was evaluated by the30-day survival rates of the mice exposed to radiation. Mice were given SB at15mg/kg via intraperitoneal injection (ip)30min before irradiation, and then thereafter every other day for a total of6injections. Our results showed that p38inhibition with SB had significant effect on the30-day survival rates of the mice exposed to7.2Gy TBI. In addition, SB could elevate the white blood cells (WBC) and bone marrow mononucleated cells (BMNCs) count, enhance the hematopoietic progenitor cells colony ability by decreasing the reactive oxygen species (ROS) levels in bone marrow cells of the mice exposed to6Gy TBI. We proved firstly that p38might be used as the targets of radioprotection.Granulocytes colony-stimulating factor (G-CSF) has been approved to be used on the low WBCs patients caused by radio and chemo-therapy in clinic. But in clinic, the G-CSF used in acute radiation syndrome was low dosage and continued long time, had no obvious effects on patients received high irradiation doses. The clinical trials demonstrated G-CSF during radiotherapy could exhaust the bone marrow capacity, probably via promoting HSPC proliferation and differentiation to negatively affect the self-renewal of HSCs. So in the present study, we examined whether inhibition of p38with SB in combination with G-CSF can mitigate TBI-induced BM injury.For SB treatment, mice were given SB at15mg/kg via ip24h after irradiation, and then thereafter every other day for a total of5injections. For G-CSF treatment, mice were administered with G-CSF at a dose of1μg/each by ip at2h and6h after irradiation on the first day, and then twice every day for5days. For combination therapy, mice were given both SB and G-CSF as described above. As a control, mice were irradiated and then treated with vehicle in a similar manner as described for SB and/or G-CSF.To test the effects of SB and/or G-CSF on TBI-induced lethality in mice, we first observed the survival rates of mice after exposure of them to7.2Gy TBI. Our results showed that p38inhibition with SB had no significant effect on the30-day survival rates of the mice exposed to7.2Gy TBI when it was used alone but increased the survival of the mice when it was combined with G-CSF. To determine whether SB and/or G-CSF increase hematopoiesis after TBI by stimulating hematopoietic progenitor cells, we examined the effects of SB and/or G-CSF on CFU-GM. The effect of SB plus G-CSF on CFU-GM frequencies was greater than either agent alone. The effects of SB and/or G-CSF on the hematopoietic function of mouse BM HSCs received4Gy TBI were analyzed by a CAFC assay. The effects of SB plus G-CSF on CAFC frequencies were higher than IR, SB or G-CSF alone.The mechanism of SB radioprotection was explored. The bone marrow cells ROS levels were detected; our results suggested that SB and/or G-CSF might decrease the ROS level of bone marrow cells. SB could mitigate the CAFC ability of bone marrow cells in vitro experiments. The16genes regulated by IR and p38were screened out by Mouse MAP Kinases Signaling Pathway PCR Array. In addition to the MAPK related genes, the CDK4/6, CyclinD2cell cycle genes and other translation factors genes were also regulated by IR and SB.In summary, SB alone showed preventive effects on the hematopoietic irradiation injury. After combined with G-CSF, the shortcomings of G-CSF were attenuated, the combination showed better therapeutic effects than each alone especially after4Gy TBI, which provides new experiments results for the development of new radiation prevention and treatment methods in clinic. SB might enhance the hematopoietic system function by decreasing bone marrow cells ROS levels to elevate the30-day survival rates of the mice exposed to7.2Gy TBI, the detailed mechanism still needed to be further explored.