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

ABSTRACT Objective: 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. Subjects and methods: 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. Results: 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). Conclusion: 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.

摘要
研究目的：骨钙素已被证实与能量及葡萄糖代谢的多种效应相关，但羧化不全骨钙素（undercarboxylated osteocalcin, U-osc）——骨钙素的激素活性异构体——的生理作用仍存在争议。本研究旨在探讨绝经后女性血清U-osc水平与骨密度（bone mineral density, BMD）及代谢参数的相关性。

研究对象与方法：本研究为横断面研究，纳入105名绝经后女性（年龄56.5±6.1岁，体质量指数[BMI]28.2±4.9 kg/m²），根据国际糖尿病联盟（International Diabetes Federation, IDF）制定的代谢综合征诊断标准，按满足3项及以下、4项、5项代谢综合征标准进行分组。所有受试者接受双能X线吸收测定法（dual-energy X-ray absorptiometry, DXA）检测体成分与骨密度，并采集血液样本以测定U-osc及骨特异性碱性磷酸酶（bone-specific alkaline phosphatase, BSAP）水平。

研究结果：受试者的U-osc平均水平为3.1±3.4 ng/mL（中位数2.3 ng/mL，范围0.0~18.4 ng/mL），BSAP平均水平为12.9±4.0 ng/mL（中位数12.1 ng/mL，范围73~24.4 ng/mL）。未观察到U-osc与BSAP水平与血清代谢参数存在相关性。在U-osc/股骨骨密度比值升高的受试者中，空腹血糖水平更低（3.61±4 ng/mL 对比 10.2±1.6 ng/mL，p=0.036）。当按U-osc/股骨骨密度及U-osc/腰椎骨密度比值将受试者分为三分位组时，比值升高与空腹血糖水平降低相关（分别为p=0.029和p=0.042）。

研究结论：基于U-osc与BMD的比值，本研究证实U-osc与葡萄糖代谢存在相关性，但未观察到U-osc与整体代谢参数存在关联。U-osc/BMD比值是一种校正骨量相关U-osc水平的创新方法。