The circulating calcification inhibitors, fetuin-A and osteoprotegerin, but not Matrix Gla protein, are associated with vascular stiffness and calcification in children on dialysis

Background. Vascular calcification occurs in the majority of patients with chronic kidney disease, but a subset of patients does not develop calcification despite exposure to a similar uraemic environment. Physiological inhibitors of calcification, fetuin-A, osteoprotegerin (OPG) and undercarboxylated-matrix Gla protein (uc-MGP) may play a role in preventing the development and progression of ectopic calcification, but there are scarce and conflicting data from clinical studies. Methods. We measured fetuin-A, OPG and uc-MGP in 61 children on dialysis and studied their associations with clinical, biochemical and vascular measures. Results. Fetuin-A and OPG were higher and uc-MGP lower in dialysis patients than controls. In controls, fetuin-A and OPG increased with age. Fetuin-A showed an inverse correlation with dialysis vintage (P = 0.0013), time-averaged serum phosphate (P = 0.03) and hs-CRP (P = 0.001). Aortic pulse wave velocity (PWV) and augmentation index showed a negative correlation with fetuin-A while a positive correlation was seen with PWV and OPG. Patients with calcification had lower fetuin-A and higher OPG than those without calcification. On multiple linear regression analysis Fetuin-A independently predicted aortic PWV (P = 0.004, ss = -0.45, model R-2 = 48%) and fetuin-A and OPG predicted cardiac calcification (P = 0.02, ss = -0.29 and P = 0.014, ss = 0.33, respectively, model R-2 = 32%). Conclusions. This is the first study to define normal levels of the calcification inhibitors in children and show that fetuin-A and OPG are associated with increased vascular stiffness and calcification in children on dialysis. Higher levels of fetuin-A in children suggest a possible protective upregulation of fetuin-A in the early stages of exposure to the pro-calcific and pro-inflammatory uraemic environment.