Improved purification of human bone sialoprotein and development of a homologous radioimmunoassay.

Bone sialoprotein (BSP) is a phosphorylated skeletal glycoprotein. Here we describe a new procedure for the purification of BSP involving wide-pore reversed-phase HPLC, and the development of a homologous RIA for human BSP. The immunoassay showed linearity between 3 and 120 micrograms/L, a lower detection limit of 0.7 micrograms/L, and a mean recovery rate of 99.4%. Intraassay variation was 7.0% (mean = 10.9 micrograms/L) and 6.1% (mean = 38.8 micrograms/L), and interassay variation was 9.2% (mean = 11.1 micrograms/L) and 9.4% (mean = 39.0 micrograms/L). No cross-reactivity was detected with osteocalcin, osteonectin, or bone alkaline phosphatase. Preliminary clinical evaluation in healthy controls (n = 90) showed a mean serum BSP concentration on 12.1 +/- 5.0 micrograms/L (+/- SD). BSP was significantly increased in patients with Paget disease of bone, primary and secondary hyperparathyroidism, and also in subjects with renal failure without skeletal involvement. Impairment of hepatic function did not affect serum BSP concentrations.