The Role Of Complement-neutrophil Feedback In Overtraining-induced Acute Kidney Injury

Overtraining refers to excessive training load,long-term imbalance between sports and recovery time,which is common in sports competition and high-intensity military training.Kidney is one of the most common target organs of sports injury.When over exercise,the blood flow perfusion of muscle,heart and lung increased,and the blood flow perfusion of kidney decreased significantly,which is very easy to cause renal ischemia and hypoxia injury.The incidence rate,mortality and disability rate of acute kidney injury caused by overtraining-induced acute kidney injury(OTIAKI)are high.Research shows that the incidence of acute renal injury caused by extreme sports such as marathon is as high as 30%-80%,and the serious ones are life-threatening.However,up to now,the mechanism of OTIAKI is not clear,and there is a lack of effective prevention and treatment measures in acute renal injury.The main function of complement system is to participate in host defense,eliminate invasive pathogens and regulate inflammatory responses.Complement act as a bridge between innate immunity and adaptive immunity in many kidney diseases.It has been shown that the complement-inflammation cascade is one of the important pathogenesis of renal ischemia-reperfusion injury.This suggests that complement-neutrophil feedback may be involved in the pathogenesis of OTIAKI.Therefore,it is of great clinical significance to explore the role of complement-neutrophil feedback played in OTIAKI,so as to provide theoretical basis and therapeutic target for clinical treatment.Objective:To deepen the understanding of the pathogenesis of overtraining-induced acute kidney injury,and provide new targets and measures for its prevention and treatment.We established the model ofovertraining-induced acute kidney injury in rats,and observed the changes of complement,inflammation and renal injury in the rat models.Methods:The thirty five clean male Wistar rats were randomly divided into normal control group(NC,n =5),model group(OT,n =15),overtraining and cobra venom factor injection group(CVF+OT,n =15).Except NC group,the rats in the other two groups were killed at 0h,6h and 24h(each time point have 5 rats)after overtraining.The OTIAKI model was established by swimming exhaustion.Except NC group,CVF+OT group injected 50μg/kg cobra venom factor into abdominal cavity 12 hours earlier before swimming,OT group injected saline of equal volume into abdominal cavity 12 hours earlier before swimming.Serum creatinine(CR)and urea nitrogen(BUN)were measured by automatic biochemical analyzer,HE staining was used to observe renal injury,determination of IL-1 β in renal tissue were measured by ELISA,the activity of myeloperoxidase(MPO)were measured by colorimetry,the expression of C3,C5 a and C5b-9 were measured by immunohistochemistry and Western-blot.Results:1.Changes of renal function in each groupCompared with NC group,Cr and BUN in OT group were significantly higher than those in control group,with the highest level in 6h(P<0.05),and decreased to the level of NC 24h(P>0.05);the two indexes in CVF+OT group were lower,but still higher than those in NC group at the same time point(P<0.05).2.Changes of renal tissue structure in each groupHE staining shows renal tubule damage and inflammatory cell infiltration,and the damage gradually increased with time.The damage was mainly seen in the renal tubules at the junction of cortex and medulla.With the time going on,exfoliated and necrotic epithelial cells of renal tubules can be seen in the lumen of renal tubules.Compared with OT group,the renal injury of CVF+OTgroup was improved.Compared with NC group,the renaltubular injury score of OT group was significantly higher(P<0.05);compared with OT group at the same time point,the renal tubular injury score of CVF+OT group was lower(P<0.05).3.Changes of IL-1 β and MPO in each groupCompared with NC group,the level of IL-1 β and MPO in OT group was significantly higher than that in NC group,the highest level of IL-1 βwas found in 6h,MPO was increased progressively(P<0.05),and the two indexes in CVF+OT group were lower than that in OT group at the same time point(P<0.05).4.Changes of C3,C5 a,C5b-9 expression in renal tissue of rats in each groupThe expression of C3,C5 a and C5b-9 was very low or not expressed in NC group.Compared with NC group,the expression of C3,C5 a and C5b-9 in OT group was higher,and mainly deposited in renal tubules.These complement showed a progressive increasing trend(P<0.05).The expression of C3,C5 a and C5b-9 in CVF+OT group was lower than that in OT group at the same time point,but not decreased to NC group level(P<0.05).Conclusion:1 In the kidney of OTIAKI rats,the complement C3,C5 a and C5b-9were over-activated.The rats were given CVF intraperitoneally in advance,then the complement was depleted and kidney damage is reduced.2 In OTIAKI rats,complement C3,C5 a,C5b-9 are activated.They chemotactic neutrophils infiltrate into the kidney,and promote the release of IL-1β by neutrophils,which relates to inflammatory response.More importantly,the inflammatory mediators released by neutrophil promote complement activation in turn.This is the complement-neutrophil feedback,which is participated in the pathogenesis of OTIAKI.