Serum Soluble Klotho Level Is Associated with Abdominal Aortic Calcification in Patients on Maintenance Hemodialysis

Background: Klotho is a single transmembrane protein originally identified as an 'aging suppressor'. Emerging evidence reveals that soluble Klotho (sKl) in the circulation plays important roles in anti-aging, anti-oxidation, anti-apoptosis and Wnt signaling. However, the role of serum sKl in the vascular calcification in hemodialysis patients is not clear. The aim of this study was to determine the associations of sKl with abdominal aortic calcification in patients on maintenance hemodialysis (MHD). Methods: 129 MHD patients were enrolled prospectively. Serum sKl level was detected by ELISA. Abdominal aortic calcification was measured by abdomen lateral plain radiograph, and the abdominal aorta calcification (AAC) score was calculated. The sKl levels were observed in patients with different degrees of calcification. Logistic regression analysis was used to determine the risk factor of abdominal aortic calcification in MHD patients. The diagnostic value of sKl for abdominal aortic calcification was assessed using receiver operator characteristic (ROC). Results: Abdominal aortic calcification was seen in 87 of 129 patients. The median AAC score was 4.0 (0.00, 11.00) and the median sKl level was 616.29 (378.19, 821.61) pg/ml. Serum sKl levels were inversely associated with AAC. When evaluated as AAC categories (<5, 5-15, >15) with ordinal logistic regression, each SD higher sKl was associated with 37.1% lower odds of AAC severity (proportional odds ratio: 0.629; 95% confidence interval: 0.413-0.959, p = 0.031) in models adjusted for demographic data, lifestyle factors, traditional CVD risk factors and uremic risk factors. Multivariate logistic regression analysis showed that serum sKl levels and smoking were independent risk factors for severe AAC. The area under the receiver-operating characteristic curve (AUC) of serum sKl for severe abdominal aortic calcification was 0.746 (0.612-0.880, p = 0.001), sensitivity was 0.885, and specificity was 0.562 for a cutoff value of 265.39 pg/ml. Conclusions: Lower serum sKl levels are independently associated with severe AAC. Serum sKl might have a diagnostic value for the severe AAC in MHD patients.