Identification of Adipsin as a Biomarker of Beta Cell Function in Patients with Type 2 Diabetes

Background/Objectives: Adipsin, an adipokine, is known to play an important role in maintaining the function of pancreatic beta cells in mice. This study aimed to investigate whether adipsin could be a circulating biomarker for evaluating the function of beta cells in patients with type 2 diabetes (T2D). Methods: Plasma adipsin concentrations were measured using immunoassay in three distinct subject groups: normoglycemia, T2D without insulin treatment (T2D-w/o-insulin), and T2D treated with insulin (T2D-with-insulin). Adipsin expressions were evaluated in three distinct mouse groups: normal diet (ND), high-fat diet (HFD), and HFD with streptozotocin (STZ) and nicotinamide (NA). Results: The T2D-with-insulin group exhibited a significant decrease in plasma adipsin concentration (3.91 ± 1.51 μg/mL) compared to the T2D-w/o-insulin group (5.11 ± 1.53 μg/mL; p < 0.001), whereas the T2D-w/o-insulin group showed a significantly increased plasma adipsin concentration compared to the normoglycemia group (4.53 ± 1.15 μg/mL). Plasma adipsin concentration was positively correlated with fasting C-peptide level (p < 0.001), 2-h C-peptide level (p < 0.001), and 2-h C-peptidogenic index (p < 0.001) in the diabetic groups. HFD mice showed a significant increase in pancreatic islet size, plasma insulin and adipsin levels, as well as adipsin expression in white adipose tissue (WAT) compared to ND mice. In contrast, the insulin-deficient T2D model (HFD-STZ-NA) demonstrated a marked reduction in pancreatic islet size, plasma insulin and adipsin concentrations, and adipsin expression in WAT compared to the HFD mice. Conclusions: plasma adipsin may be useful for evaluating pancreatic beta cell function in patients with T2D.