Effects of Dietary Phosphate on Adynamic Bone Disease in Rats with Chronic Kidney Disease – Role of Sclerostin?

High phosphate intake is known to aggravate renal osteodystrophy along various pathogenetic pathways. Recent studies have raised the possibility that dysregulation of the osteocyte Wnt/β-catenin signaling pathway is also involved in chronic kidney disease (CKD)-related bone disease. We investigated the role of dietary phosphate and its possible interaction with this pathway in an experimental model of adynamic bone disease (ABD) in association with CKD and hypoparathyroidism. Partial nephrectomy (Nx) and total parathyroidectomy (PTx) were performed in male Wistar rats. Control rats with normal kidney and parathyroid function underwent sham operations. Rats were divided into three groups and underwent pair-feeding for 8 weeks with diets containing either 0.6 % or 1.2 % phosphate: sham 0.6%, Nx+PTx 0.6%, and Nx+PTx 1.2%. In the two Nx+PTx groups, serum creatinine increased and blood ionized calcium decreased compared with sham control group. They also presented hyperphosphatemia and reduced serum parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) levels. Fractional urinary excretion of phosphate increased in Nx+PTx 1.2 % rats despite lower PTH and FGF23 levels than in sham group. These biochemical changes were accompanied by a decrease in bone formation rates. The Nx+PTx 1.2 % group had lower bone volume (BV/TV), higher osteoblast and osteocyte apoptosis, and higher SOST and Dickkopf-1 gene expression than the Nx +PTx 0.6 % group. Nx+PTx 0.6 % rat had very low serum sclerostin levels, and Nx+PTx 1.2 % had intermediat