Serum under-carboxylated osteocalcin levels in women with polycystic ovary syndrome: weight-dependent relationships with endocrine and metabolic traits

Background: Under-carboxylated osteocalcin (ucOC), the precursor substrate of bone biomarker OC is a potent regulator of energy metabolism by promoting insulin production and adiponectin synthesis and decreasing fat stores. The aim of the present study was to point out the potential role of ucOC in the physiopathology of polycystic ovary syndrome (PCOS), a common disorder defined by the constellation of anovulation, insulinresistance, hyperinsulinemia, obesity and androgen excess. Methods: In this prospective case-control investigation, 78 young premenopausal women, i.e. 52 PCOS patients and 26 age- and body mass index (BMI)-matched healthy controls, were successively enrolled. Recruitment of PCOS patients was performed according to Androgen Excess-Polycystic Ovary Syndrome (AE-PCOS) Society 2006 criteria. All study participants were subjected to clinical examination, whole-body composition assessment and measurements of serum ucOC, OC (1-49), glucose and lipids, insulin, total testosterone (TT), estradiol, sex-hormone binding globulin (SHBG), high-sensitivity C-reactive protein (Hs-CRP) and beta-CrossLaps. Results: BMI-stratified multivariate analysis revealed significantly higher ucOC levels in PCOS vs. controls in lean (p = 0.001) but not overweight and obese study participants (p = 0.456). Notably, a positive correlation between ucOC and TT (p = 0.018), calculated free testosterone (cFT, p = 0.028) and serum insulin (p = 0.036), respectively, was found to be confined to the lean analysis subgroup. Furthermore, in stepwise multiple regression models, beta-CrossLaps and cFT were able to predict 46.71% of serum ucOC variability. (1-43/49) OC failed to be significantly associated to any PCOS trait. Conclusions: Circulating ucOC concentration is related to key endocrine PCOS characteristics in a weight-dependent manner. Within the bone-pancreas loop, high ucOC may favor insulin release in lean hyperandrogenic women to compensate for impaired insulin sensitivity.