Effects And Mechanisms Of Bexarotene(Bex)on Skin Tissues Exposed To Radiation

AIM:The occurrences of radioactive unclear accidents,the pretreatments of bone marrow transplantation and the radiotherapy of tumors,there are always followed by different degrees of radiation skin injury.Evidences at home and abroad show amifostine,oral enzymes,oxpentifylline and traditional Chinese medicine,to some extent,worked up to prevent radio dermatitis.However,in clinical therapy,drug therapy for radiation-induced skin injury is not clear yet.RXR agonist Bexarotene works up by Signal transduction pathway,which effecting its binding receptor.It was curative effects for Cutaneous T-cell lymphoma(CTCL),hand dermatitis,Psoriasis and so on.The research arm at discuss the effect of early application of Retinoic acid X receptor agonist(RXRA)bexarotene(Bex)on radiation skin injury.METHODS:Local skin of SD Rats irradiated by electron radiation to establish the animal model of radiation-induced skin injury.Divided models into two group:(1)Bex,(2)Pbs.After two weeks,observe the degree and prognosis of radiation-induced skin injury in rats.Samples were obtained by kill the model rates after 60 days later.Human epidermal fibroblasts(WS1 Cell)were be used.CCK test has been used to assess the relationship between different concentrations of,Bex and proliferation of radiated WS1 cell;Flow cytometry be used for test the influences between different concentrations of Bex and apoptosis of radiated WS1 cell;The expression of RXRA in radiated WS1 cells and nuclei by Bex depends on Western-blot and immune fluorescent test.Reactive oxygen species(ROS)test and immunofluorescence microscopy aimed at observing and detecting the changes of reactive oxygen species in radiated WS1 Cell by Bex.RESULTS:Compared with the Bex mice and the Pbs mice.The degree of skin injury of Bex group was remarkably changed in 3 weeks after exposed to radiation.The damaged area of Pbs group was remarkably less than mice of Bex,and goes on everywhere before death.Time Curve Chart showed:Diversity of damaged area slowly increased in third week and peaked around the fifth week.HE staining tissue section showed:Compared with two groups.The injury area and healing area were no significantly changed And the proportion of damage area was different,CCK8 test showed:When Bex concentration at 0.01 umol/1 to 1 umol/l,can obviously promote the proliferation of WS1 cells exposed on radiation.But,in 1 umol/1 to 3 umol/1,Bex had a certain cytotoxic effect.Pretreatment with appropriate concentration of Bex before irradiation did not significantly affect the inhibition of radiation on the proliferation of WS1 cells.While similar concentration of Bex was given after WS1 Cells exposed on radiation,the inhibition of radiation on proliferation of cells were significantly alleviated.Four hours after pretreatment with 0.1 umol/1 Bex in irradiated WS1 cells,the late phase rate of apoptos were increased.But,compared with 24 hours'pretreatment,it has ever increased.The Apoptosis rate of WS1 Cells can significantly increase after pretreated with 0.5umol/1 Bex.The Apoptosis rate of WS1 Cells were increased after 10Gy irradiation.Pretreated with concentration of 0.1 umol/1 and 0.5umol/l Bex did not significantly improve apoptotic rate,Four hours after treated WS1 Cells exposed to 10Gy radiation with 0.1umol/1 Bex,thapoptosis rate decreased to a certain extent.And,24 hours later,it declined from 16.33%to 9.75%.Immunofluorescence showed:Before radiation stimulation.The concentration of 0.1 umol/1 Bex did not remarkably influence the expression of RXRA protein in the nucleus.After radiation stimulation,the expression of RXRA protein in the nucleus of WS1 cells increased and the expression of RXRA protein in the nucleus of WS1 cells decreased after Bex treatment.Western-blot test showed:After 10Gy irradiation,the total RXRA protein level of WS1 cells decreased,and after 0.1 umol/1 Bex treatment,the protein level less than the former.Reactive oxygen species(ROS)test showed:After 15 minutes,30 minutes and 60 minutes of irradiation,the level of ROS remarkably increased in WS1 Cells.And with 0.1 umol/1 Bex pretreatment compared with the former,he level of ROS decreased significantly.After 2 hours 4 hours,6 hours 8 hours and 10 hours of irradiation.The fluctuation of ROS level has no obvious regularity whether or not Bex was used.CONCLUSION:Bex can effectively shorten the course of skin injury and promote skin repair in SD rats after 45 Gy irradiation-pretreatment of Bex before radiation stimulation did not significantly effect.The proliferation and apoptosis of cells.Inhibitory effect of radiation on cell proliferation and apoptotic rate after irradiation can be effectively reduced after treated with Bex under radiation stimulation.RXRA in the nucleus of WS1 cells is at low level concentration and the radiation protection of Bex is extremely limited,before exposed on radiation.RXRA in the nucleus increased effectively after radiation stimulation.The biological function of Bex is to bind RXRA and corresponding receptors.The results of Western-blot and immunofluorescence were different.RXRA outside the nucleus was more important than inside.Based on this conclusion,both test not eventually show the changes of protein on the nucleus.And further verification of plasmid-nuclear separation is still necessary.The mechanism of Bex mitigating radiation damage may be as follows:Early after radiation stimulation,Bex may active RXRA and bind receptor,act as extranclear agent,and reduce the number of intracellular ROX effectively.By reducing the production of cytokines and chemokines,antioxidant and anti-inflammatory effects can be exerted.This study revealed the effective radiation protection effect of Bex at appropriate concentration on SD rats and WS1 cells.And it puts forward a conjecture with basis for the relevant mechanism.To provide new ideas for the prevention and treatment of skin injury exposed on radiation.