Basic Research On The Application Of Novel High-Efficiency Radioprotective Agents For Small Intestine

Background:To deal with the radiation damage caused by either accidental or deliberate radiation exposure,it is of great significance to carry out radiation protection research.With the widespread application of radiation therapy in the field of oncotherapy,ionizing radiation could kill the rapidly proliferating tumor cells,it is also inevitable to damage normal cells that are undergoing rapid self-renewal,such as stem cells located in the crypt of the small intestine.Human beings exposed to above 10 Gy irradiation will suffer from considerable gastrointestinal syndrome,which is characterized with severe small intestinal injury,and even die within a few weeks.Therefore,in the field of radiation medicine,it is of great strategic significance to explore the prevention and treatment strategies for radiation-induced small intestinal injury.Although some progress has been developed in the mechanism of radiation-induced gastrointestinal injury and the research on radioprotectants at present,there are still some problems and challenges,such as drug stability,the precise radiation protection of small intestinal tissues,the biosafety of radioprotective agents and unclear mechanism.In addition,some cell populations and cytokines have been found to be effective in maintaining the homeostasis of the small intestine and promoting intestinal regeneration for the past few years.However,the mechanism of radiation-induced cell death and the cellular targets of gastrointestinal syndrome remain controversial Therefore,it is imperative to develop novel radioprotective countermeasures based on the damage mechanism of small intestinal stem cells and the special physiological structure of small intestine to attenuate the radiation-induced gastrointestinal syndrome.Objective:This paper focuses on improving the stability of radioprotective agents,targeting of small intestine and biological safety.It systematically studied the small intestine radiation protection effects and mechanisms of three radioprotective agents.The aim is to develop radioprotective agents with clinical application value,improve the prognosis of patients with radiation-induced small intestine damage,and provide a research basis for the clinical transformation of novel radioprotectors.The main research contents are as follows:(1)Smart Oral Administration of Polydopamine-Coated Nanodrugs for Efficient Attenuation of Radiation-Induced Gastrointestinal SyndromeHigh-dose ionizing radiation can lead to death from the unrecoverable damage of gastrointestinal tract,especially the small intestine.Until now,the lack of predilection for small intestine and rapid clearance by digestive fluid limit the effects of conventional radioprotective formulations.Objective:Herein,an innovative radioprotective strategy is developed for attenuating gastrointestinal syndrome by smart oral administration nanodrugs.Methods:The nanodrug is first engineered by encapsulating thalidomide into chitosan-based nanoparticles,and then coated with polydopamine.The safety and radioprotective effect of the nanodrug ex vivo are demonstrated using a three-dimensional tissue culture model of intestinal crypts.The behaviors of gastric acid-resistance,and pH-switchable controlled release in the small intestine were performed under simulated gastrointestinal conditions.Fluorescent image analysis was taken to track the time prediction and site specificity of the Cy5.5-conjugated PDA@Arg-CS(THA).Lethal dose of whole abdominal irradiation was performed on the mice to investigate the radioprotective effect of nanodrugs.Results:Nanodrugs have good biocompatibility and radioprotective effect in vitro.We also found that PDA@Arg-CS(THA)nanodrugs showed smart pH-responsive drug release under simulated gastrointestinal conditions.In a mouse model,nanodrugs demonstrate prolonged small intestinal residence time for up to 48 h and accessibility to the crypt region deep in the mucus.Furthermore,the nanodrugs ameliorate survival rates of C57BL/6J mice irradiated by 14 Gy of subtotal body irradiation and also maintain their epithelial integrity.Conslusion:This work may provide a promising new approach for efficiently attenuating lethal radiation-induced gastrointestinal syndrome and add insights into developing nanodrug-based therapies with improved efficacy and minimum side effects.(2)Prussian Blue-Based Nanomedicine Injection for Small Intestinal RadioprotectionRadiation therapy is extensively used for management of abdominal malignancies,which causes damage to surrounding normal tissues,especially the small intestine.However,most of the medical countermeasure approaches aimed at reducing the severity of radiation injury are still experimental so far.Various side effects and lack of predilection for small intestine limit the effects of conventional radioprotective formulations for use as potential therapeutics to alleviate intestinal injury induced by radiotherapy.Objective:We herein develop a Prussian blue-based nanomedicine injection(Res@PVP-HMPB)with predilection for small intestine.Methods:The biocompatibility and the radiative effect on the small intestinal epithelial cells were detected through CCK8 assay.The nanodrug was labeled with fluorescent dye to detect the organ distribution.A mouse model was established to test the protective effect of nanodrug.The mechanism of radioprotective effect was further studied by analyzing the DNA strand breaks and the expression level of apoptosis-related proteins.Results:The good biocompatibility and enhanced radioprotective ability for small intestinal epithelial provide the favorable prerequisites for it to be used as the gastrointestinal radioprotector.Res@PVP-HMPB concentrates in the small intestine after injection which effectively enhances the bioavailability of the nanomedicine.In a mouse model,Res@PVP-HMPB maintain the epithelial integrity of C57BL/6J mice irradiated by 14 Gy of subtotal body irradiation.Furthermore,we also deeply study the radioprotective mechanism of RES@PVP-HMPB for small intestine,which indicate that the nanomedicine effectively alleviates the DNA damage of stem cells located in crypts,and thus reduce the apoptosis of stem cells.Conclusion:Our finding suggests a new application of Prussian blue-based nanoparticles,which not only promotes the development of new radioprotector for small intestine,but also has a great potential for clinical transformation.(3)Critical Role of Neutral Sphingomyelinase Inhibitor GW4869 on Attenuation of Radiation-Induced Small Intestine DamageRadiation causes DNA damage and selectively targets rapidly proliferating cells such as normal small intestinal stem cells,which results in grievous cell death and radiation-induced gastrointestinal syndrome.In response to double-strand DNA damage,the inflammatory caspase determines pyroptosis by releasing N-terminal cleavage product of Gasdermin D,which leads to irreversible cell death of intestinal stem cells by forming membrane pores and breaking the integrity of cell membrane.Objective:In the present study,we discover that GW4869 preserves the integrity of small intestine,which prevents lethal radiation-induced gastrointestinal syndrome in mice.Methods:A mouse model and a three-dimensional tissue culture model of intestinal crypts are established and performed with lethal radiation exposure.The activity of neutral sphingomyelinase and the expression levels of pyrolysis-related proteins after ionizing radiation were measured.Results:GW4869 can protect the small intestinal stem cells and progenitor cells to preserve the integrity of small intestine,which improve the survival rate of mice.Furthermore,GW4869 can significantly abrogate the radiation-induced GSDMD pore formation on the plasma membrane of intestinal stem cells.Mechanically,by inhibiting the activity of neutral sphingomyelinase,GW4869 promotes the endocytosis process which results in the degradation of the N-terminal fragments of GSDMD and rescues cells from GSDMD-mediated pyroptosis.Conclusion:Our findings provide mechanistic insights into how GW4869 attenuates radiation-induced gastrointestinal syndrome,and reveal new regimens that maintain the homeostasis of small intestine exposed to lethal ionizing radiation.Summary:In this study,we focus on the basic research on the application of novel high-efficiency radioprotective agents for small intestine.An innovative radioprotective strategy is developed for attenuating gastrointestinal syndrome by smart oral administration nanodrugs,which significantly improves the survival rate of mice irradiated by 14 Gy of subtotal body irradiation.Prussian blue-based nanomedicine injection(Res@PVP-HMPB)with predilection for small intestine is developed to alleviate the DNA damage of stem cells.We also discover that administration of neutral sphingomyelinase inhibitor GW4869 protects mice from whole abdominal irradiation by maintaining the integrity of the plasma membrane.These researches provide new strategies to protect the small intestine during abdominal radiation therapy,which have a great potential for clinical application.