Effects And Mechanisms Of Remote Ischemic Preconditioning On Spinal Cord Ischemia Reperfusion Injury In Rabbits

BackgroundClinically,thoracoabdominal aortic aneurysm repair surgery can lead to spinal cord ischemia-reperfusion?I/R?injury.However,a main,devastating and unpredictable complication after spinal cord injury is paraplegia^[1-2].To date,various intervening measures have been used to protect the spinal cord from ischemic injury^[3];nonetheless,complications still cannot be prevented completely.Therefore,a more effective strategy should be developed to protect the spinal cord against I/R injury.Some studies have indicated that ischemic preconditioning or dexmedetomidine or sevoflurane preconditioning can reduce permeability of blood-spinal cord barrier?BSCB?,thus maintaining the integrity of BSCB and improving the neurological outcome^[4-5].BSCB is the physiological and metabolic substance diffusion barrier between blood circulation and spinal cord tissues.This barrier strictly regulates the stability of the spinal cord microenvironment.It has been found that BSCB disruption is one of the major pathologic changes during spinal cord I/R,and plays an important role in the spinal cord edema,evolution of spinal cord I/R injury and neuronal damage.Consequently,taking some interventions to stabilize BSCB structure will contribute to improve outcomes of spinal cord I/R injury.A large number of studies have shown the protection of remote ischemic preconditioning?RIPC?for spinal cord I/R injury^[6-7].However,the underlying mechanisms of this treatment strategy is not entirely clear,and little is known about the effects of RIPC on BSCB breakdown after spinal cord I/R injury.Brain derived neurotrophic factor?BDNF?is a member of the neurotrophic family of proteins,which plays a key role in regulating neurons differentiation and development and myelination.One study reported that ischemic preconditioning can increase BDNF protein expression via PKC?activation in both in vivo and in vitro rats brain ischemia model^[8].PKC?is ubiquitously expressed and plays a certain role in remote conditioning induced cardioprotection^[9-10].It was also found that RIPC could reduce I/R injury by PKC?activation^[11].Nevertheless,whether RIPC can up-regulate BDNF expression via PKC?activation has not been reported yet.ObjectiveTo investigate the effects and possible mechanisms of RIPC on BSCB and BDNF after spinal cord I/R injury,then further reveals the potential mechanisms of RIPC prevents spinal cord from I/R injury.Methods72 male Japanese white rabbits,weighing 1.5-2.0 kg,were purchased from Wuhan Institute of Biological Products Co.,Ltd.Animals were randomly divided into 3 groups?n=24?,namely sham-operation group?group S?,ischemia-reperfusion group?group I/R?and remote ischemic preconditioning group?group R?.In group I/R and group R,abdominal aorta of the rabbits was blocked for 30min.RIPC was achieved by bilateral femoral artery occlusion?10min ischemia/10min reperfusion,2cycles?1 h before abdominal aortic cross clamping in group R.All rabbits were sacrificed at 24 and 48h following reperfusion for detection of the following indexes:1.neurological function was assessed using modified Tarlov criteria 2.spinal cord tissue pathological changes were detected by hematoxylin and eosin?HE?staining 3.BSCB integrity was measured by extravasation of evans blue?EB?4.occludin,MMP-9,BDNF and PKC?protein expression in the injured spinal cord tissue was detected by Western blot 5.MMP-9,BDNF and PKC?mRNA expression in the injured spinal cord tissue was detected by reverse real-time fluorescence quantitative polymerase chain reaction?RT-qPCR?analysis.ResultsAt 24 and 48h after surgery,compared to group I/R,the scores of neurological function improved significantly?P<0.01?,the remaining motor neurons in anterior horn increased,the extravasation of EB reduced?P<0.01?markedly and spinal cord expression of occludin increased?P<0.01?and MMP-9 reduced?P<0.01?in group R.In addition,spinal cord expression of BDNF and PKC?in group R were higher than those in group I/R?P<0.01?.ConclusionRIPC preserves the BSCB integrity through inhibiting the down-regulation of occludin and up-regulation of MMP-9 induced by spinal cord I/R injury.Meanwhile,on the basis of maintaining BSCB structural integrity,RIPC may up-regulate BDNF expression through activating PKC?,and thus protect spinal cord against I/R injury.