Clinical implication of urinary midkine as a sensitive biomarker of acute kidney injury

急性肾损伤（acute kidney injury，AKI）是重症监护病房（ICU）中最重要的预后指标，但在血肌酐升高之前，尚无敏感的生物标志物诊断AKI。最近，几种尿生物标志物如NGAL、IL-18、KIM-1、NHE3、KC和L-FABP被报道为AKI的新的敏感生物标志物的候选者。我们报道了中期因子（MK），一种肝素结合生长因子，在患病肾脏中被诱导，并在缺血性肾再灌注损伤的动物模型中促进白细胞的趋化性（Sato W.，et.例如，J Immunol 2001; 167：3463 - 3469）。缺血损伤后MK表达增强主要在近端肾小管。在此，我们评估了人MK是否从肾小管上皮细胞脱落到尿液中，并可能作为人类急性肾损伤的有效尿液生物标志物。Western印迹分析显示，在培养的肾小管上皮细胞的培养基中检测到MK的表达增加。 关于我们 艾德对缺氧处理的人肾小管上皮细胞（HK 2）进行了诱导，但对20 μ M BSA处理的HK 2细胞未进行诱导。尿MK测定包括正常对照组（n = 33）、急性肾小管坏死（ATN）组（n = 33）和其他慢性肾脏疾病组（n = 517）共583例患者。采用酶联免疫法测定尿MK水平，ATN患者尿MK水平显著高于其他慢性肾脏疾病患者和对照组。尿MK浓度诊断ATN的受试者工作特征（ROC）曲线分析显示，以70.0 pg/ml为界值，敏感性为97.0%，特异性为91.1%，提示尿MK水平可作为ATN的敏感生物标志物，有助于ATN的早期诊断。我们获得了专利（2008 - 048954，参考号：K20070222）“用于AKI早期诊断的临床检查：尿MK测量”。少

Although acute kidney injury (AKI) is the most important predictor of the prognosis of the patients treated in the field of ICU, there have been no sensitive biomarkers to diagnose AKI before the rising of serum creatinine. Recently, several urinary biomarkers such as NGAL, IL-18, KIM-1, NHE3, KC, and L-FABP are reported as a candidate of new sensitive biomarker of AKI.We reported that midkine(MK), a heparin-binding growth factor, was induced in the diseased kidneys and promoted chemotaxis of leukocytes in the animal models of an ischemic renal reperfusion injury(Sato W., et. al., J Immunol 2001 ; 167 : 3463-3469). The enhanced expression of MK was detected mainly in the proximal tubules after ischemic injuries. Here, we evaluated whether human MK is shed into urine from the tubular epithelial cells, and may serve as a potent urinary biomarker of acute kidney injuries in human.Western blot analysis showed that the increased expression of MK was detected in the culture media from cultur … More ed human tubular epithelial(HK2)cells treated with hypoxia, but not from HK2 cells treated with 20 μM BSA. There were no differences in the MK expression in the cell lysates.For the measurement of urinary MK, 583 patients, including controls (n=33), patients with different forms of acute tubular necrosis (ATN) (n=33), and patients with other chronic renal diseases(n= 517), were studied. Urinary MK level was determined by enzyme-linked immunoassay.The urinary MK levels were significantly higher in patients with ATN compared to levels in patients with other chronic renal diseases or controls. For concentration in urine of MK, the receiver-operating characteristic(ROC)curve analysis for diagnosis of ATN showed that sensitivity was 97.0 %, and specificity was 91.1 % for a cut-off value of 70.0 pg/ml.We have confirmed that urinary MK level serves as a sensitive biomarker of ATN facilitating the early diagnosis of the disease. We obtained the patent(2008-048954, Ref : K20070222)for "Clinical examination for the early diagnosis of AKI : Urinary MK measurement". Less