In Chronic Kidney Disease, Serum α-Klotho is Related to Serum Bicarbonate and Proteinuria

Objectives Klotho is an "aging-suppressor" gene and encodes a single-pass transmembrane protein predominantly expressed in renal tubules. Whether chronic kidney disease (CKD) affects serum Klotho is poorly documented. We aimed to measure the relationship of serum α-Klotho with renal function, acid–base status, bone biomarkers, and proteinuria in CKD patients. Design Setting, Participants, and Measurements We measured serum α-Klotho, serum FGF23, and glomerular filtration rate by inulin clearance in 60 CKD patients between January and July 2011. We also measured serum creatinine, bicarbonate, calcium, phosphorus, parathyroid hormone, C-reactive protein, and 25-OH vitamin D. Proteinuria was obtained from a 24-h urine collection. Results The median serum α-Klotho was 478 (348-658) pg/mL. We found an inverse relationship between serum α-Klotho and serum creatinine ( r  = −0.36, P  = .007), proteinuria ( r  = −0.36, P  = .013), and a positive relationship with serum bicarbonate ( r  = 0.33, P  = .011). There was no further significant relation between serum α-Klotho and inulin clearance or serum FGF23. Multiple regression analysis including serum bicarbonate, serum creatinine, and proteinuria indicated that only serum bicarbonate was associated with serum α-Klotho ( P  = .003). Conclusions This study shows that in CKD, serum α-Klotho is related to serum bicarbonate and proteinuria and not to renal function. Further research is required to determine whether correcting these 2 amenable conditions would improve serum α-Klotho.