Improvement of insulin sensitivity by osteocalcin inhibits inflammation in the adipose tissue of obese mice

AIM: To explore the improving effect of osteocalcin on obesity-related insulin resistance and inflammation in the adipose tissue of obese mice.METHODS: The C57BL/6 mice were fed with high-fat diet for 12 weeks to obtain obese mice. Osteocalcin (30 ng/kg or 3 ng/kg) and saline solution (control) were intraperitoneally injected for other 4 weeks. The fat mass, body weight, serum triglycerides and serum free fatty acid were analyzed. Intraperitoneal glucose tolerance test and insulin tolerance test were carried out. Macrophage infiltration degree in the adipose tissue was observed by immunohistochemical staining. The mRNA expression of monocyte chemotactic protein-1 (MCP-1) and CD68 was detected by real-time fluorescence quantitative PCR.RESULTS: Osteocalcin (30 ng/kg or 3 ng/kg) treatment for 4 weeks significantly reduced the body weight, fat mass and insulin level, and improved abnormal glucose tolerance and insulin resistance in the obese mice. Moreover, the macrophage infiltration decreased, and the mRNA expression of MCP-1 and CD68 was down-regulated in the adipose tissue of obese mice treated with osteocalcin at 30 ng/kg.CONCLUSION: Osteocalcin at 30 ng/kg significantly reduces body weight and fat mass, and attenuates the severity of insulin resistance through down-regulating the mRNA expression of MCP-1 and CD68 and inbihiting macrophage infiltration in the adipose tissue of obese mice induced by high-fat diet.