Usefulness Of Serum Klotho In Early Detection Of Acute Kidney Injury After Cardiac Valve Replacement Surgery

[Background]:Acute kidney injury (AKI) is a common and severe complication after cardiac surgery and is an independent risk factor for a series of adverse outcomes, including prolonged intensive care and hospital stays, and increased long-term mortality rate. The incidence of cardiopulmonary bypass associated acute kidney injury(CPB-AKI) is reported about5%-47%. The possible mechanisms of CPB-AKI are followed as below:The low flow and pulseless perfusion during the cardiopulmonary bypass, activation of proinflammatory mediators during the contact between blood and surface of CPB tube, the release of free hemoglobin and myohemoglobin during CPB caused by the hemolysis and injury of muscle can also lead to the damage of renal tubular, besides the hemodilution,generation of microemboli,kidney toxicant may also play a subtle role in CPB-AKI.The serum creatinine and urinary volume are used most commonly in the detection of CPB-AKI recently,however,the level of serum creatinine can be susceptible to gender,age,weight,muscle mass and so on,besides,it is believed associated only with the GFR which can not reflect the injury of renal tubular,finally, under the unstable state during the CPB, it is reported that serum creatinine cannot be an excellent reflect of GFR.Urinary output is easily influenced by volume load and the use of diureticum.Therefore, it is influential to porbe the sensitive and specific biomarkers which could be used in early detection of CPB-AKI. Cystatin C is a kind of non-glycosylated protein which can be synthetised by karyocytes and released into the blood at a constant speed. Cystatin C can be filtered from renal glomerulus and reabsorbted by the proximal tubules completely.Particularly,the amount of Cystatin C can hardly be affected by the age,weight,muscle mass and so on,which theoretically become an ideal biomarker for the filtration function. Whereas,til now, it is still a debatable issue when it comes to a preferential choice between SCr and Cystatin C for detection of CPB-AKI. With the development of genomic and proteomics,to probe some new biomarkers which are used to detect AKI has become the hot spot in this field.Four biomarkers has exited interests of scientists.1.Neutrophil gelatinase-associated lipocalin (NGAL). Using genomic, transcriptomic, and proteomic screening techniques for novel renal biomarkers and innovative research on embryonic tissues, NGAL has been recently described as an early, highly sensitive and specific renal biomarker and to be implicated in the differentiation of kidney epithelia. NGAL was nephroprotective when administered simultaneously with renal ischemia reperfusion. Kidney epithelia express and excrete massive quantities of NGAL when damaged by ischemia-reperfusion injury, nephrotoxins, and sepsis,as demonstrated initially in rats, mice, and pigs and then in human neonates, children, and adults.In a prospective landmark study of71children undergoing CPB, AKI (defined as a50%increase in serum creatinine) occurred in28%of the subjects, but the diagnosis using serum creatinine was possible only1to3days after surgery. In marked contrast, NGAL measurements revealed a10-fold or greater increase in the urine and plasma within2to6h of surgery in patients who subsequently developed AKI. Both urine and plasma NGAL were independent predictors of AKI, with areas under the receiver-operating characteristic curves (AUCs) of0.998for the2-h urine NGAL measurement and0.91for the2-h plasma NGAL measurement. The results of this study were confirmed in several further studies in pediatric cardiac surgery.In adults, several trials showed NGAL to be of varying value for subsequent AKI, with AUC values ranging from0.56to0.96. In a recent metaanalysisof diagnostic test studies on the performance of NGAL for AKI after cardiac surgery including10studies with1,204patients, the mean AUC was0.78(range0.67to0.87).2.Fatty acid-binding proteins. Fatty acid-binding proteins are intracellular carrier proteins of14kDa with different expression in the kidney. So far,2types of fatty acidbinding proteins have been isolated from the human kidney. Liver-type fatty acid-binding protein (L-FABP) is another member of the lipocalin superfamily. It is reabsorbed by the proximal tubule via megalin-dependent endocytosis and is localized in the cytoplasm of proximal renal tubular cells and in the liver and the small intestine. By contrast, heart-type fatty acid-binding protein is localized in the renal distal tubules, heart, small intestine, and skeletal muscles. Both proteins facilitate the transport of intracellular long-chain fatty acids. Fatty acid-binding proteins are endogenous antioxidants by promoting free fatty acid metabolism and by binding long chain fatty acid oxidation products.Portilla et al demonstrated that L-FABP predicts the development of AKI in children undergoing cardiac surgery. They found that increases of this biomarker within4h after cardiac surgery anticipated the subsequent development of AKI with an accuracy of81%. In human L-FABP transgenic mice, urinary L-FABP levels allowed the accurate and earlier detection of both histological and functional insults in ischemia-induced AKI. In adult patients, the presence of tubular damage and the deterioration of tubular structure were risk factors for the onset of AKI, and urinary L-FABP was a useful biomarker for early detection of AKI and was a good early predictor for the onset of AKI.3.Human KIM-1is a type1transmembrane glycoproteinwith an immunoglobulin and mucin domain that is not detectable in normal kidney tissue or urine, but is expressed at very high levels in dedifferentiated proximal tubule epithelial cells in human and rodent kidneys after ischemic or toxic injury. The KIM-1(designated as Kim-1in rodents, KIM-1in humans) was found to be markedly up-regulated after24-48h in the proximal tubule of the post-ischemic rat kidney (Ichimura et al.,1998). The A soluble form of human KIM-1can be detected in the urine of patients with ATN and may serve as a useful biomarker for renal proximal tubule injury facilitating the early diagnosis of the disease and serving as a diagnostic discriminator (Han et al.,2002). Furthermore, high urinary KIM-1expression was evaluated prospectively in a cohort of201hospitalized patients with AKI and was also associated with adverse clinical outcome (death and need for dialysis) in patients with AKI (Liangos et al,2007).4.IL-18is a proinflammatory cytokine that is constitutively expressed in the intercalated cell of the late distal convoluted tubule, the connecting tubule, and the collecting duct of the healthy human kidney. In a first cross-sectional study in humans with various renal diseases, urine levels of IL-18were significantly greater and had a high sensitivity and specificity for the diagnosis of ATN in comparison with PA, UTI, chronic kidney disease, and normal renal function in healthy control subjects. IL-18may serve as a marker for proximal tubular injury in ATN (Parikh et al.,2004). Furthermore, urinary IL-18was significantly up-regulated prior to the increase in serum creatinine in patients with acute respiratory distress syndrome who developed AKI, predicting mortality at the time of mechanical ventilation (Parikh et al.,2005). Early urine IL-18measurements correlated with the severity of AKI as well as mortality, however, in prospective analysis IL-18demonstrated no ability to predict the subsequent development of AKI.K1gene is closely related to senility and mainly expressed in kidney and brain choroid, especially in the renal tubular epithelial cells,the fuction of which includes regulating the metabolism of calcium and phosphorus, antioxidation,depressing apoptosis. Recently,it is reported that expression of Kl gene decreases in CKD patients and returns to normal with the improvement of renal function. Whats more, Hu et al found that ischemia-reperfusion injury (IRI) in rodents reduced Klotho in the kidneys, urine, and blood, all of which were restored upon recovery.In the clinical context,cardiac surgery is one of the most typical IRI models, whether or not the Kl expression in patients with CPB-AKI will show the similar change which was present in CKD patients and IRI rats? What the characteristic of change in Klotho expression according to the time course after CPB-AKI? Whether or not the Klotho will possess a usefulness in early detection of CPB-AKI? The questions above have no clear conclusions.[Objective]:Observing and evaluating the significance in the change of serum Klotho according to the time course after CPB-AKI.Estimating the usefulness of serum Klotho in early detection of CPB-AKI using area under the receiver operating characteristic curve(AUC-ROC).Comparing the potency of serum Klotho, serum creatinine and Cystatin C in early detection of CPB-AKI[Methods]:1.A total of90patients undergoing cardiac valve replacement surgery were enrolled in a retrospective study.From each patient, blood samples were collected preoperatively and on postoperative2h, days1to4respectively to detect serum cystatin C and creatinine levels. Comparing the potency of serum creatinine and Cystatin C in early detection of CPB-AKI.2.According to the exclusion criterion,a total of35patients undergoing cardiac valve replacement surgery were enrolled in a prospective study. From each patient, blood samples were collected preoperatively and on postoperative0h,4h,days1to3respectively to detect serum Klotho, serum creatinin,SCr/Kl and serumcystatin C levels. All patients enrolled who all came from department of thoracic cardiovascular surgery, nanfang hospital were divided into AKI team or non-AKI team according to AKIN criteria (acute kidney injury network), which is an absolute increase in SCr of≥26.5μmol/L(0.3mg/dl) from baseline or a relative increase in SCr of>1.5-fold from baseline within the first48h after cardiac surgery.[Results]:1.At2h after surgery,serum creatinine increased significantly in patients with AK1(P<0.01). The AUC-ROC for AKI prediction was0.75. On postoperative day1, ROC analysis confiemed excellent accuracy of SCr in AKI diagnosis (AUC=0.90,95%confidence interval:0.84to0.96), and the diagnostic sensitivity and specificity were0.81and0.83respectively when the cutoff value was101.5μmol/L. The level of SCr peaked and reached the AKIN criteria on postoperative day1, which was sustained till the endpoint of study, whereas the diagnosis accuracy of SCr for AKI was decreased gradually within the last3days. On postoperative day1, cystatin C increased significantly in patients with AK1(P<0.01). The area under the curve (AUC) was0.70. The level of cystatin C and its accuracy for CPB-AKI diagnosis were increased parallel. On postoperative day3, the accuracy for AKI diagnosis was superior to SCr(AUC=0.83,95%confidence interval:0.75to0.92).2. At Oh after surgery,serum Klotho decreased significantly in patients with AK1(121.64±19.87vs101.97±16.93,P<0.01).The AUC-ROC for AKI prediction was0.801,95%confidence interval:0.652to0.953,P=0.03, and the diagnostic sensitivity and specificity were0.895and0.562respectively when the cutoff value was119.15U/L.On postoperative4h, AUC-ROC for AKI diagnosis was0.743,95%confidence interval:0.587to0.916,P=0.014, and the diagnostic sensitivity and specificity were0.896and0.500respectively when the cutoff value was121.36U/L. On postoperative1d, serum Klotho has recovered markedly toward the preoperative level. The AUC-ROC for AKI diagnosis was0.646,95%confidence interval:0.447to0.845,P=0.15, and the diagnostic specificity was noly0.437while the sensitivity was outstanding when the cutoff value was128.96U/L.The changes of serum Klotho levels at every time point among patients without CPB-AKI did not reveal any statistical significance. At Oh after surgery,serum creatinine increased significantly in patients with AKI. The AUC-ROC for AKI diagnosis was0.872,95%confidence interval:0.764to0.992, P<0.01), and the diagnostic sensitivity and specificity were0.84and0.81respectively when the cutoff value was86.5μmol/L. At4h after surgery,the AUC-ROC for AKI diagnosis was0.915,95%confidence interval:0.813to1.019, P<0.01), and the diagnostic sensitivity and specificity were0.895and0.875respectively when the cutoff value was106μmol/L. On postoperative4h to3d, serum creatinine levels revealed a platform gradually with good diagnosis of AUC-ROC (0.892,0.857,0.828) for postoperative1to3d respectively, At4h after surgery, cystatin C increased significantly in patients with AK1which was posterior to that of serum Klotho and serum creatinine.The AUC-ROC for AKI diagnosis on postoperative Oh was poor. On postoperative4h, ROC analysis confiemed good accuracy of cystatin C in AKI diagnosis (AUC=0.862,95%confidence interval:0.742to0.982), and the diagnostic sensitivity and specificity were0.79and0.75respectively when the cutoff value was1.15mg/L. On postoperative1to3d, cystatin C levels increased gradually with excellent diagnosis of AUC-ROC (0.969,0.972,0.944) for postoperative1to3d respectively. Taking advantage of the changes in opposite directions between serum creatinine and Klotho,the ratio of SCr and Klotho revealed an outstanding diagnosis performance. On postoperative Oh, ROC analysis confiemed excellent accuracy of SCr/Kl in AKI diagnosis (AUC=0.924,95%confidence interval:0.831to1.018),and the diagnostic sensitivity and specificity were0.947and0.875respectively when the cutoff value was0.695which was superior to that of serum creatinine and Klotho. On postoperative4h to3d, SCr/Kl also showed ideal performances in diagnosis of CPB-AKI. [Conclusions]:Immediatelly after cardiac valve replacement surgery,CPB-AKI patients experienced a markedly decrease in Klotho which reached statistical significance.In spite of the poor diagnostic specificity,its sensitivity was excellent. On postoperative Id, with the rapid recovery toward the preoperative level, the usefulness of serum Klotho was declined. On postoperative4h,the SCr had been reached the level of diagnosing CPB-AKI according to the AKIN criteria. When the cutoff value was106μmol/L,the diagnostic sensitivity and specificity were all excellent. On postoperative4h to3d, serum creatinine levels revealed a platform gradually with good diagnostic specificity but a poor sensitivity.The serum Klotho possessed excellent sensitivity but poor specificity in early detecting CPB-AKI which indicated that serum Klotho may play an potential role in early diagnosis of exclusion for CPB-AKI. Immediatelly after cardiac valve replacement surgery, SCr/Kl showed exceptional significance in early detection of CPB-AKI and such a usefulness sustained till the endpoint.It was noticeable that the SCr/Kl and AKIN criteria were highly correlated which may indicate that SCr/Kl was a useful biomarker for early detection of CPB-AKI and was a good early predictor for the onset of CPB-AKI. Cystatin C increased significantly on postoperative Oh which was the same as that of serum Klotho and SCr,but its diagnostic efficacy was fair. On postoperative4h to3d,the diagnostic efficacy of cystatin C reached an ideal level and sustained till the endpoint.