Association between undercarboxylated osteocalcin, bone mineral density, and metabolic parameters in postmenopausal women.

Leila C B Zanatta,Victoria Z C Borba,Cesar L Boguszewski,Carolina A Moreira

doi:10.20945/2359-3997000000061

Abstract

Osteocalcin has been associated with several effects on energy and glucose metabolism. However, the physiological role of undercarboxylated osteocalcin (U-osc; the hormonally active isoform of osteocalcin) is still controversial. To correlate the serum levels of U-osc with bone mineral density (BMD) values and metabolic parameters in postmenopausal women. Cross-sectional study including 105 postmenopausal women (age 56.5 ± 6.1 years, body mass index [BMI] 28.2 ± 4.9 kg/m2) grouped based on the presence of three or less, four, or five criteria of metabolic syndrome according to the International Diabetes Federation (IDF). The subjects underwent dualenergy x-ray absorptiometry (DXA) for the assessment of body composition and BMD and blood tests for the measurement of U-osc and bone-specific alkaline phosphatase (BSAP) levels. The mean U-osc level was 3.1 ± 3.4 ng/mL (median 2.3 ng/mL, range 0.0-18.4 ng/mL) and the mean BSAP level was 12.9 ± 4.0 ng/mL (median 12.1 ng/mL, range 73-24.4 ng/mL). There were no associations between U-osc and BSAP levels with serum metabolic parameters. Lower fasting glucose levels were observed in participants with increased values of U-osc/femoral BMD ratio (3.61 ± 4 ng/mL versus 10.2 ± 1.6 ng/mL, p = 0.036). When the participants were stratified into tertiles according to the U-osc/ femoral BMD and U-osc/lumbar BMD ratios, lower fasting glucose levels correlated with increased ratios (p = 0.029 and p = 0.042, respectively). Based on the ratio of U-osc to BMD, our study demonstrated an association between U-osc and glucose metabolism. However, no association was observed between U-osc and metabolic parameters.The U-osc/BMD ratio is an innovative way to correct the U-osc value for bone mass.

Highlights

Some studies over the past decade have shown that bone is associated with important physiologic mechanisms involving the control of energy metabolism and glucose homeostasis, attracting great interest in the understanding of the role of bone as an endocrine organ [1,2,3,4,5,6,7,8,9].Osteocalcin is a protein produced by osteoblasts and present in two forms, carboxylated and undercarboxylated (U-osc)
Serum undercarboxylated osteocalcin (U-osc) and bone-specific alkaline phosphatase (BSAP) levels, as well as the ratios U-osc/ femoral bone mineral density (BMD) and U-osc/lumbar BMD were compared with the following metabolic parameters: body mass index (BMI), waist circumference, systolic and diastolic blood pressure, and total fat percentage assessed by dual-energy x-ray absorptiometry (DXA; total fat), TG, high-density lipoprotein (HDL)-cholesterol, fasting glucose, insulin, homeostasis model assessment of insulin resistance (HOMA-IR), and C-reactive protein (CRP)
The results of this cross-sectional study show an inverse association between the ratio U-osc/femoral BMD with blood glucose levels, which was demonstrated by greater ratio values in the subgroup of patients with normal glucose levels

Summary

Introduction

Some studies over the past decade have shown that bone is associated with important physiologic mechanisms involving the control of energy metabolism and glucose homeostasis, attracting great interest in the understanding of the role of bone as an endocrine organ [1,2,3,4,5,6,7,8,9].Osteocalcin is a protein produced by osteoblasts and present in two forms, carboxylated and undercarboxylated (U-osc). According to the IDF 2005 recommendations, the participants were deemed as having a normal waist circumference when this measurement was below 80 cm, and normal blood pressure when the values were below 130/85 mmHg. The finding of serum glucose levels below 100 mg/dL, TG below 150 mg/dL, and HDL-cholesterol above 50 mg/dL was considered normal.

Results

Conclusion