Bone Abstracts

Introduction: Osteocalcin (OC) is the noncollagenous protein of bone matrix produced by osteoblasts which play an important role in bone metabolism. In its carboxylated form (c-OC) osteocalcin binds to hydroxyapatite in bone and plays a regulatory role in bone formation and mineralization. In contrast, undercarboxylated OC (uc-OC) binds less effectively to hydroxyapatite and a significant association has been found between fracture incidence and uc-OC in elderly subjects. Undercarboxylated OC is recognized as a functional marker of vitamin K status. Deficiency of vitamin K, observed in subjects with cystic fibrosis, may play an important role in bone health in these groups of patients. The aim of this study was to assess the serum levels of c-OC and uc-OC in prepubertal children with cystic fibrosis.

Materials/Methods: The study group consisted of 25 children aged 5–9 years (median 7.0 years) with confirmed cystic fibrosis attending the CF Clinic at the Institute of Mother and Child (Warsaw, Poland). The control group included 25 healthy children matched for age and gender without infections and diseases that might influence bone status. Serum concentrations of total OC, carboxylated OC, and undercarboxylated OC were determined by immunoenzymatic ELISA assay. Statistical analyses were performed using the Statistica software program, version 10.0 PL.

Results: Total OC levels were comparable in cystic fibrosis patients and in healthy children. However, in children with cystic fibrosis we observed lower c-OC (median values: 25.4 vs 29.8 ng/ml, P=0.058) and significantly higher uc-OC concentrations (median values: 40.7 vs 31.2 ng/ml, P=0.031). The ratio of c-OC to uc-OC was significantly lower in children with CF compared to healthy ones (P<0.05).

Conclusion: Children with cystic fibrosis have significantly lower u-OC and higher uc-OC concentrations than healthy subjects. Reduced c-OC may lead to abnormal bone formation in these patients.