The Study Of Whether Local Irradiation Promotes The Homing Of Mesenchymal Stem Cells To Rat Large Vessels With Radiation Injury

Background:Radiation vasculitis is one of the most common detrimental effects of radiotherapy for malignant tumors.This is developed at the vasculature of adjacent organs.Transplantation of mesenchymal stem cells(MSCs)was demonstrated to have therapeutic effect on radiation injury.But the population of MSCs being engrafted into irradiated vessels is very low in the conventional models.This is presumably because circulating MSCs are dispersed in adjacent tissues being irradiated simultaneously.Thus,the population of homed MSCs per body volume is significantly reduced,rendering the investigation of MSC homing difficult.To verify this assumption,we employed the approach of RT(radiation)-plus-TX(transplantation)by which the targeted vessels was irradiated without injury to the adjacent normal tissues.It was determined whether the homing of MSCs was improved by the method.Objective:The purpose of our study was to explore whether local irradiation promoted the homing of MSC to rat large vessels with radiation injury.Methods: In the RT-only group,rat abdominal aorta was irradiated by 160 k V X-ray at a single dose of 35 Gy.The irradiation was localized to a square-shaped field of 3 cm ×3 cm encompassing the central abdominal region by using a lead shield.The viscera especially small bowel and colon were left off the irradiation field to avoid the devastating gastrointestinal adverse effect.In the RT-plus-TX model,a 1.5cm segment of rat abdominal aorta was procured and grafted to the healthy counterpart.The F344 inbred rats was served as both donors and recipients to exclude the possibility of immune rejection.On the 90 th day after irradiation,the aorta was procured for biomedical analysis.Hematoxylin-eosin and Masson’s trichrome were used to evaluate vasculopathy.The expression of myeloperoxidase(MPO)in tissue section was analyzed by using standard avidin-biotin complex technique.QPCR was used to evaluate the expression level of inflammatory factors including TNF-α,TGF-β,IL-1βand IL-2.Finally,the frequency of MSC engraftment was investigated by counting the GFP-labeled MSC under a fluorescent microscope and assessing the level of sex determine gene Sry.Results: In the Hematoxylin-eosin and Masson’s trichrome stain,RT-only group and RT-plus-TX group showed hyperplastic intima and diffuse vascular fibrosis after irradiation.The expression level of the inflammatory factors including TNF-α,TGF-β,IL-1β and IL-2 was also increased in the two groups.After MSC infusion,the fluorescent microscopy showed that the GFP-labelled cells were preferably engrafted into intima layer at the average density of 3.30 cells/HPF in the RT-plus-TX+MSC group.In contrast,GFP-labelled cells were nearly invisible in the RT-only+MSC group.Moreover,the Sry gene level in the RT-plus-TX+MSC group was significantly higher when compared to the RT-only+MSC group.The intimal thickness was significantly lower in RT-plus-TX+MSC group,and expression of TGF-β of irradiated aortas in RTplus-TX+MSC group was also declined.Conclusions: Local irradiation promoted the homing of MSC to rat large vessels with radiation injury.