Study Of Renal Injury And The Protective Effects Of Erythropoietin In A Rat Cardiopulmonary Bypass Model

An increasing number of patients are undergoing cardiac surgery and a cardiopulmonary bypass (CPB) is required in most condition. This technique is aggressive, and patients are subjected to a high degree of organ injury. Today lots of studies have being focused on organ protection after CPB. However, these studies usually study organs such as heart, lung and liver, in clinical situation, about7-40%of cardiac surgical patients with CPB, suffer from renal injury.Therefore, studies concentrating on mechanisms of CPB-induced renal injury is essential.Erythropoietin (EPO), a hematopoietic cytokine produced by the fetal liver and adult kidney in response to hypoxia, has been extended from the classical role of erythroid maturation to one that offers protection against ischemia-reperfusion injury in a wide variety of tissues. Several studies have explored the underlying mechanism of EPO protection. The effect of EPO involves an ability to modulate local responses to injury by attenuating both inflammatory and apoptotic causes of cell death.Thus, the study was designed to examine whether EPO would attenuate the CPB-induced renal injury, even to explorer the protective mechanism in a rat CPB model. Part one:Renal injury in a rat cardiopulmonary bypass modelObjectiveThis study was designed to test the hypothesis that CPB would induce and aggravate the renal injury in a rat model.Materials and methodsMale Sprague-Dawley rats were randomly divided into two groups (n=15):sham group, CPB group. Blood samples were collected at the beginning, at the end of CPB, and at0.5,1,2and24h post operation. Kidney samples were harvested at24h after operation. Levels of serum creatinine(Cr) and blood ureanitrogen(BUN) were assayed, tumor necrosis factor-α(TNF-α)、interleukin-1β(IL-1β) and interleukin-6(IL-6) levels in the renal tissue were determined,expression levels of nuclear factor kappa B p65(NF-κB p65)、intercellular adhesion molecule1(ICAM-1) protein and gene were determined. Each tissue was prepared for histological analysi. Statistical analyses were performed by using SPSS13.0. A value of p<0.05was considered statistically significant.ResultsComparing with the Sham group, Cr and BUN levels in serum as well as TNF-α、 IL-1β and IL-6levels in tissues increased significantly in CPB group. Furthermore, NF-κB p65、ICAM-1transcription and expression were significantly upregulated in CPB group. In addition,histological findings further supported the results:no abnormal histologic changes were noticed in the kidney of sham rats.Histologic changes, including tubular dilatation, tubular necrosis, and vacuole formation, were observed in the kidneys of CPB group. Degenerative glomeruli and cellular infiltration in interstitial tissue were also detected. Cortical tubular dilatation and vacuole formation were observed to some extent in all groups except the Sham group.Conclusions1、The rat model of CPB could be performed simply and could reduce the spending of animals and of equipments obviously. With this technology, we can study the CPB-related renal injury2、Our experiment suggest that CPB induced severe renal injury in a rat model, which is evidenced by both biochemical indices and morphology examinations. And renal injury after CPB is mainly caused by inflammatory response. Part two:Erythropoietin ameliorates renal injury in a rat cardiopulmonary bypass modelObjectiveThis study tested the hypothesis that erythropoietin could attenuate the renal injury in a rat CPB modelMaterials and methodsMale Sprague-Dawley rats were randomly divided into three groups (n=12): sham group, control (CPB) group,and EPO (3000U/kg) group. Blood samples were collected at the beginning, at the end of CPB, and at0.5,1,2and24h post operation. Kidney samples were harvested at24h after operation. Levels of serum Cr and BUN were assayed, TNF-α、IL-1β andIL-6levels in the renal tissue were determined,expression levels of NF-kB p65、ICAM-1protein and gene were determined. Each tissue was prepared for histological analysi. Statistical analyses were performed by using SPSS13.0. A value of p<0.05was considered statistically significant.ResultsCr and BUN levels in serum as well as TNF-α IL-1β and IL-6levels in tissues increased significantly in CPB group. However, changes were markedly reversed in EPO group. Furthermore, NF-kB p65、ICAM-1transcription and expression were significantly downregulated in EPO group compared with CPB group. In addition, histological findings further supported the results. Histologic damage were worsened from normal (sham group) to mild (EPO group) and severe (CPB group).ConclusionsAll results indicated that EPO potently protected against CPB-induced renal injury by inhibiting expression of NF-kB p65and inflammatory response.