Osteocalcin is related to enhanced insulin secretion in gestational diabetes mellitus

There is growing evidence that osteocalcin, an osteoblast-derived protein locally acting on bone formation, can increase insulin secretion as well as insulin sensitivity and thus prevent the development of obesity and diabetes in experimental animals. In humans, osteocalcin has been reported to be decreased in patients with type 2 diabetes. Because gestational diabetes mellitus (GDM) can serve as a model of pre-type 2 diabetes, the aim of this study was to investigate osteocalcin in GDM.

Osteocalcin measurement and an oral glucose tolerance test were performed in 78 pregnant women (26 women had GDM and 52 women had normal glucose tolerance [NGT] during pregnancy; women were matched for age and BMI) and in 34 women postpartum.

During pregnancy osteocalcin was significantly higher in the women with GDM than in the women with NGT (15.6 +/- 6.4 vs. 12.6 +/- 4.0 ng/ml; P < 0.015), whereas no difference was observed between the two groups at 12 weeks postpartum (36.2 +/- 10.2 vs. 36.2 +/- 13.0 ng/ml), when osteocalcin was found to be increased compared with the level in the pregnant state in all women (+145 +/- 102% in GDM vs. +187 +/- 119% in NGT; P < 0.0001). Moreover, osteocalcin showed a significant correlation with basal and total insulin secretion in the whole study group (R = 0.3, P < 0.01).

In GDM osteocalcin was higher and thus less restrained than in women with NGT during pregnancy and furthermore correlated with insulin secretion parameters. Therefore, it could be hypothesized that osteocalcin can enhance insulin secretion in insulin-resistant states; alternatively an effect of hyperinsulinemia on osteocalcin secretion cannot be excluded.