| The small intestine is radiation sensitive tissue. Gastrointestinal mucosa is the mainlimiting factor in abdominal tumor radiotherapy and sudden radiation exposure protection.So there is an urgent need to find the drugs to prevent or treat intestinal radiation injury.Toll-like receptor5agonist flagellin in protection and medical treatment of intestinalradiation injury has brought exciting results among numerous studies of radiationprotection agent of the gut. Studies showed that TLR2agonists help maintain completefunctional barrier of the intestinal epithelial cells and TLR2gene deletion would acceleratethe mucosal injury and the susceptibility of colitis. In2011, polysaccharide krestin (PSK),a mushroom extract from Trametes versicolor, had been identified as a selective and potentTLR2agonist and revealed the potential to enhance the function of NK cell and CD8+Tcells to suppress tumor. In view of this, we emphatically examined which target cells of thesmall intestine were protected by PSK and its mechanism in it. Then we applied PSKbefore mouse colorectal carcinoma in situ models radiotherapy to study its effect andmechanism to inhibit tumor growth and explored the possibility of PSK treatment inclinical abdominal tumor radiotherapy.Part1: Protection against Radiation-induced Intestinal Damage after10Gy total bodyirradiation by TLR2agonist polysaccharide KrestinPurpose: The objective of the present paper was to study the mechanism ofprotection against radiation-induced intestinal damage after10Gy total body irradiation viaTLR2agonist polysaccharide Krestin. Methods and Materials: C57BL/6J mice were randomly divided into PSKadministration group0.5hours before irradiation, PSK administration group24hours afterirradiation and10Gy irradiation group. The concentration of PSK was200mg/kg.C57BL/6mice were sacrificed for apoptosis studies at4,6,14,24,48,72, and96hoursafter total body irradiation (TBI) with10Gy of X-ray. Intestines were collected,endothelial, epithelial and crypt cells’ apoptosis was detected by immunofluorescence (IF)double staining and TUNEL method. Intestinal proliferation was examined byimmunohistochemical staining of Ki-67and PCNA. The expression of Bax, Bcl-2, Akt1,Akt2, Akt3, p-Akt were shown by IF staining and immunohistochemical staining. Thesurviving curve was studied on C57BL/6, TLR2-/-, AKT1+/-mice to show the role of TLR2and AKT1gene in the effect of PSK.Results: Intestine endothelial cells apoptosis peaked at4and6hours post10Gy TBI;epithelial cells apoptosis was significantly increased at6and96hours; crypt cellsapoptosis was obvious at each time point after irradiation. PSK given0.5hour beforeirradiation significantly reduced apoptosis of endothelial cells by reducing the apoptosisprotein Bax expression and increasing anti-apoptotic protein Akt2, p-Akt, Bcl-2expression,but PSK could not reduce epithelial cell and crypt cell apoptosis. When PSK was given24hours after irradiation, it significantly promoted the proliferation of crypt by increasingAkt1, Akt3and p-Akt. PSK significantly prolonged C57BL/6mice survival given0.5hourbefore or24hours after10Gy irradiation, but this effect was aborted on the TLR2-/-miceand AKT1mutant mice.Conclusion: PSK given0.5hours before irradiation significantly reduced apoptosisof intestinal endothelial cells and when given24hours after irradiation, PSK promoted theproliferation of crypt. PSK has great potential for practice to prevent and treat radiation-induced gastrointestinal syndrome through TLR2/Akt pathway. Part2: Study of effects of TLR2agonist polysaccharide Krestin on reduction ofangiogenesis and proliferation in colorectal cancer when combined with radiotherapyPurpose: The mouse models of colorectal carcinoma in situ were established to studythe effect of PSK treatment during colorectal cancer radiotherapy.Methods and Materials: The azoxymethane (AOM)/dextran sodium sulfate (DSS)induced colorectal carcinoma models in situ were established in C57BL/6mice. The modelmice were divided into4groups, namely non-treated group (untreated), singleadministration group (PSK),10Gy irradiation group (10Gy),10Gy irradiation plus PSKadministration group (10Gy+PSK). Every group had22mice.10Gy electron beam (6MeV,200cGy/min) irradiation was given to mice abdomen once a week for a total of4times. PSK was given half an hour before radiotherapy at the concentration of200mg/kg.11mice of each group were used to observe body weight changes and survival; another11of each group were sacrificed at the forth week to observe the tumor volume anddistribution, microvessel density, expression of VEGF, the pathological changes ofintestinal tissue and the expression of Angiopoietin-1.Results:10Gy+PSK group, compared with non-treated group, PSK group and10Gyradiation group, significantly reduced tumor volume.10Gy+PSK group, compared withthe irradiation group, significantly reduced tumor microvessel density.10Gy+PSK group,compared with irradiation group, keep intestinal structure integrity, but had no effect onthe expression of Angiopoietin-1.10Gy+PSK group significantly reduced weight lossand prolonged the survival time of the model mice.Conclusion: PSK used combined with radiotherapy can significantly reduce tumorvolume of colorectal cancer and the microvascular density in tumor tissue and keepintestinal structure integrity, reduce weight loss and prolong the survival time of micecompared with radiotherapy.In summary, the study found that PSK had great potential for practice to prevent andtreat radiation-induced gastrointestinal syndrome through TLR2/Akt pathway. Furthermore,PSK can assist radiotherapy to reduce tumor volume and microvessel density, to protectintestinal structure integrity, to reduce weight loss and prolong the survival time of mice model. This provided the experimental support for PSK being used as drugs to treatintestinal radiation sickness and abdominal radiotherapy. |
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