Osteocalcin: the relationship between bone metabolism and glucose homeostasis in diabetes mellitus

Abstract

Recent studies have demonstrated the importance of bone as an endocrine organ that produces biologically active substances, which regulate both local bone metabolism and metabolic functions throughout the body. In the process of bone remodeling (formation/destruction), the active cells secrete specific biomarkers that help detect osteometabolic dysfunction. Among bone hormones, osteocalcin plays an important role as a coordinator of bone modeling processes, energy homeostasis, metabolism of glucose, lipids and minerals. Osteocalcin is a structural protein of the bone matrix, which is synthesized by osteoblasts and enters the bloodstream in the process of bone resorption. The level of osteocalcin in the serum is used as a specific marker of bone formation. Osteocalcin promotes pancreatic β-cell proliferation and insulin secretion, and also affects the insulin sensitivity of peripheral tissues. The inverse association of glycemia with the level of osteocalcin was revealed. Patients with type 2 diabetes mellitus usually have normal or even slightly elevated bone mineral density compared to age-appropriate controls. Decreased bone quality and increased risk of fractures are associated with changes in bone microarchitecture and local humoral environment. An imbalance in osteoblast/osteoclast activity may be due to oxidative stress and the accumulation of glycosylation end products, which contributes to chronic inflammation and bone resorbtion in patients with diabetes. It is shown that the level of osteocalcin in the blood serum is significantly reduced compared to healthy controls, both in patients with type 1 diabetes mellitus and, especially, in type 2 diabetes mellitus. Given the importance of developing new approaches to the diagnosis and correction of metabolic disorders in diabetic patients, the study of the influence of bone hormones on hormonal and metabolic parameters and bone status, including the risk of fractures, remains relevant in modern diabetology.