Synthetic peptide-based immunoassay for amino-terminal propeptide of type I procollagen: application for evaluation of bone formation.

Serum biochemical markers are powerful tools for the evaluation of bone turnover. In this study, we developed a radioimmunoassay, using a synthetic peptide for the N-terminal fragment of human type I [alpha 1(I)] procollagen (N-PCP). A 14-amino acid peptide was synthesized from the amino terminus and used to generate antibodies in rabbits. The synthetic peptide was used as standard and tracer in the assay. Both native type I amino procollagen (PINP), which was purified from skin fibroblasts, and human serum displaced tracer binding in parallel with the synthetic peptide. The range for measurement of N-PCP in serum was 0.7 to 30 micrograms/L (0.21-9.18 nmol/L). In a sample of 17 normal adults and 13 children (ages 9-16 years) there was a strong correlation between serum N-PCP determined by this assay and both skeletal alkaline phosphatase isoenzyme and osteocalcin, markers of bone formation. Serum concentrations of N-PCP in a group of normal children were eightfold higher than concentrations in normal adults, with no overlap between the two groups. N-PCP also correlated with C-terminal type I procollagen determined with a commercially available kit (r = 0.92).