Shift of serum osteocalcin components between cord blood and blood at day 5 of life

Vitamin K deficiency is a relatively common condition in neonates. However, the role of vitamin K in neonatal bone metabolism remains to be determined. Osteocalcin (OC) is the most abundant noncollagenous protein in bone, and is regulated to be gamma-carboxylated by vitamin K. In this study, we measured gamma-carboxylated osteocalcin (Gla-OC) and non- or undercarboxylated osteocalcin (Glu-OC) separately, and examined the effects of vitamin K on osteocalcin metabolism. Eighteen full-term healthy neonates were enrolled in this study. In the cord and d-5 blood samples, the OC levels were determined by three different methods to examine the intact OC by immunoradiometric assay (IRMA), Gla-OC, and Glu-OC. Serum vitamin K fractions, hepaplastin test, and type 1 procollagen carboxyl extension peptide were also determined. Urine samples were also collected from the first voiding and on d 5 to determine urinary pyridinoline, deoxypyridinoline, and gamma-carboxylated glutamic acid. Serum levels of phylloquinone (PK) and menaquinone (MK)-4 increased on d 5 following vitamin K administration and increased intake in breast milk and/or formula. The OC levels determined by IRMA did not change between cord and d-5 blood samples, but the Gla-OC level increased remarkably and Glu-OC reduced to a negligible level. OC in cord blood is mainly Glu-OC, and Glu-OC is replaced with Gla-OC within 5 d of life after vitamin K supplement. The IRMA assay fails to distinguish Gla-OC from Glu-OC and caution is needed to estimate bone turnover with this method in the perinatal period.