Targeted Release Of SDF-1? By ROS-sensitive Nanoparticles Results In BMSCs Homing And Repair Of Vascular Injury Caused By Electrical Burns

BackgroundElectrical burns are unique accidents in the modern industrial society.Although its incidence is not high,its damage is three dimensional and has sandwich-like necrosis and progressive necrosis characteristics,resulting in serious damage in local tissues.The amputation rate in hospitalized patients exceeds 30%,and limbs are often associated with varying degrees of dysfunction.Blood is a good conductor of electricity.After electric current enters the body,it passes through blood causing blood vessel damage.Tissue ischemic and hypoxic necrosis resulted from vascular damage is an important reason for the progressive necrosis of electric burn.At present,there is no clinical treatment specific for vascular injury reduction or vascular repair promotion.Therefore,how to promote the rapid repair of local blood vessels caused by electrical burns is of important significance in reducing tissue necrosis and improving prognosis.Bone marrow stromal cells(BMSCs)have the potential to develop into multiple cell types.Under the pathological conditions of burns,BMSCs can quickly mobilize from the bone marrow into the peripheral circulation,home to the injury site and differentiate into endothelial progenitor cells(EPCs),which further differentiate into vascular endothelial cells to repair the injury.The mobilization,chemotaxis,and aggregation of BMSCs mainly depend on chemotaxis induced by stromal cell-derived factor 1?(SDF-1?),which relies on the local high concentration of SDF-1?,as well as the SDF-1? gradient in the circulation.Therefore,the establishment of local high SDF-1? concentration and SDF-1? gradient in the circulation is essential for chemotaxis and the capture of stem cells for vascular repair.How to form local high concentrations of SDF-1? at the injury site and the SDF-1? gradient in the circulation,however,remains a challenge.Direct intravascular injection of SDF-1? can be rapidly diluted in the blood,and therefore effective local concentrations at the injury site cannot be established continuously;direct injection of SDF-1? in the tissue may result in uneven distribution and easy degradation,and therefore its efficiency in entering the circulation is uncertain.With the development of drug carrier materials,SDF-1? can be delivered in a biodegradable nanoparticle system,which not only can effectively prevent its rapid degradation in the body,but also targets SDF-1? to the effective sites in the body,achieving the goal of directional and long time release.In order to achieve the targeted release of nanoparticle-carried drugs,it is essential to determine the specific physical,chemical,or biological characteristics at the lesion site.Reactive oxygen species(ROS)is a pathogenic factor for the pathogenicity in an organism,which provides a target for the targeted release of nanoparticle-carried drugs.In our previous study,the ROS-sensitive thiol ketal polymer PPADT was used as a nanoparticle carrier to encapsulate SDF-1?,forming SDF-1?-PPADT nanoparticles.This nanoparticle degrades and releases drugs in response to the high ROS concentrations in lesion tissues,achieving the goal of targeted therapy.This study used the rat vascular injury model of electrical burns,and injected SDF-1?-PPADT nanoparticles through the tail vein,to evaluate the effects of targeted release of SDF-1? and the chemotaxis of BMSCs on the repair of vascular injury caused by electrical burns.Methods1.Establishing the vascular injury model of electrical burnsThe electrical equipment for generating electrical burns was designed,rats were continuously exposed to 220 V for 6 s.2.Identification of vascular injury resulted from electrical burnsMuscle tissue along the medial extremity,including the main arteries at the site of electrical shock,was collected.Tissues at the same location were collected from the sham rats.HE staining and CD31 antibody immunohistochemical staining was used to observe the vascular injury.3.Measurement of local ROS levels at the injury siteROS fluorescence staining and antioxidant enzyme mRNA levels by RealTime PCR were used to observe the changes of ROS level after injury.4.Measurement of the local SDF-1? levels in injured tissueThe shock time was adjusted to produce different degrees of injury,and SDF-1? level in local tissues were measured using the ELISA method.5.SDF-1?-PPADT nanoparticle preparationNanoparticle preparation followed the procedures described in our previous study.ROS-sensitive PPADT molecules encapsulating SDF-1? protein were generated using the multiple emulsion solvent evaporation method.6.Observation of ROS-sensitive targeted release of SDF-1?The distribution and concentrations of SDF-1? protein were used to observe nanoparticles targeted SDF-1? release in the injured tissue after nanoparticles injection.7.Directional chemotaxis and homing of BMSCsSDF-1?-PPADT nanoparticles were injected together with exogenous GFP-BMSCs,the chemotaxis homing effect of nanoparticles on BMSCs was observed by immunofluorescence staining.8.Effects of SDF-1?-PPADT nanoparticles on vascular repairHE staining and CD31 antibody immunohistochemical staining was used to observe the vascular repair after nanoparticles injection.Results1.General observation after the electrical burnsAll rats survived after receiving electrical burns.A third-degree burn wound formed in the area where the electrode plate was applied,and rats were limping on both hind limbs after electrical burns.2.Electrical burns caused vascular damageThe vascular endothelial cells in the rats with electrical burns formed protrusions into the lumen and were discontinuous,some of which were even stripped from the lumen,and the lumen is narrow.3.ROS level significantly increased at the injury siteThe distribution of ROS green fluorescence in vascular injury rats was significantly and the levels of SOD,CAT and GSH-Px mRNA were increased.4.Within a certain range of injury,the degree of local electrical burns was inverselyrelated to the SDF-1? levelThe mild electrical burns caused increased local SDF-1? production,and with the increasing degree of electrical burns,SDF-1? synthesis reduced.The local SDF-1? concentration at the injury site remained at a low level when received 6 s electrical burns.5.SDF-1?-PPADT nanoparticles had targeted drug release propertiesAfter nanoparticles injection,Cy5 fluorescence distribution suggested that SDF-1? was targetedly distributed at the injury site,and the local SDF-1? levels at the injury site significantly increased.6.SDF-1?-PPADT nanoparticle directed BMSCs chemotaxis and homingOn the 7 d after nanoparticles injection,pathological analysis showed that GFP+ cells clearly accumulated at the injury site.7.SDF-1?-PPADT nanoparticle promoted vascular repairOn the 10 d after nanoparticles injection,the morphology of blood vessels in electrical burn rats is relative intact,and the endothelial cell arrangement was better organized and continuous.There were also more blood vessels and the lumens were round or oval in electrical burn rats.Conclusions1.Continuous exposure to 220 V for 6 s resulted in significant vascular damage in rats.2.SDF-1? encapsulated in ROS-sensitive nanoparticles could be released targetedly at the injury site,to direct BMSCs chemotaxis and homing,thereby promote vascular repair caused by electrical burns.