Procollagen Type I Amino-Terminal Propeptide: Pediatric Reference Data and Relationship with Procollagen Type I Carboxyl-Terminal Propeptide

Abstract

Type I collagen is the predominant collagen in bone and soft tissue. The rate of synthesis of type I collagen can be assessed by measuring plasma concentrations of the C-terminal (PICP) and N-terminal (PINP) propeptides released during extracellular processing of its procollagen precursor (1). However, the propeptides have different clearance routes, PICP being cleared by mannose receptors (2) and PINP by scavenger receptors (3) in liver endothelial cells. Clearance of PICP may be modulated by the hormonal milieu, whereas scavenger receptors apparently are not influenced by hormones (4)(5). Within-individual biological variability is similar for PICP and PINP (6), but PINP displays greater dynamic changes than PICP in response to disease and interventions (7)(8). PINP has been shown to be a useful marker of bone formation in adults (7)(8)(9)(10)(11)(12). During childhood growth, markers of bone turnover circulate at higher concentrations than in adults and correlate with height velocity (13)(14). These markers have been used to investigate bone dynamics in childhood disorders of bone and growth (13)(14)(15), but a lack of appropriate reference data has hampered use of PINP in pediatrics. Here, we report age- and sex-related reference data for plasma PINP in children from birth to 19 years of age. We also investigated the relationship between PINP and PICP to determine whether their relative clearance rates differ through childhood and adolescence. Surplus plasma remaining after routine biochemical tests had been completed was retrieved for 43 neonates, infants, and children (23 males) younger than 5 years, who presented with various minor conditions that were considered not to have either a short- or long-term effect on growth; children with systemic disease or concurrent infections were excluded. Samples were deidentified and stored at …