Analysis of serum undercarboxylated osteocalcin level in rats with type 2 diabetes mellitus and the correlation with cognitive impairment

The aim of the study was to investigate the correlation between the serum undercarboxylated osteocalcin (ucOC) level and the blood biochemistry and cognitive impairment in rats with type 2 diabetes mellitus (T2DM). Sprague-Dawley (SD) rats were randomly divided into the normal control group (NC) and type 2 DM group. DM group received the high-fat and high-sugar diet combined with the intraperitoneal injection of low-dose STZ to establish the type 2 DM rat model. After 12 weeks of feeding, a Morris water maze was used to observe the rats' cognitive ability, and the levels of blood lipid, ucOC, insulin and adiponectin in the two groups were measured. The results showed that blood glucose of rats in DM group was increased significantly at 2–12 weeks (p<0.01) and the body weight was significantly increased at 4–12 weeks (p<0.01). The levels of serum triglyceride (TG), total cholesterol, low-density lipoprotein and insulin in rats in DM group were significantly increased compared with those in NC group (p<0.01) and the levels of high-density lipoprotein, adiponectin and ucOC were significantly decreased compared with those in the NC group (p<0.01). The place navigation and spatial exploration capacities of rats in DM group were significantly decreased compared with those in NC group (p<0.01). In the DM group, the place navigation and spatial exploration capacities of rats in the low ucOC group were significantly decreased compared with those in the high ucOC group (p<0.01). Additionally, single-factor correlation analysis revealed that ucOC was negatively correlated with blood glucose, TG and escape latency (p<0.01), but was positively correlated with adiponectin, residence time in target quadrant and traversing times (p<0.05 or p<0.01). In conclusion, the decreased serum ucOC level in rats with type 2 diabetes mellitus has a certain correlation with cognitive impairment.