Phenolic-enriched blueberry-leaf extract attenuates glucose homeostasis, pancreatic β-cell function, and insulin sensitivity in high-fat diet–induced diabetic mice

Blueberry fruit exhibits strong antioxidant activity owing to the presence of anthocyanin. As blueberry-leaf extract (BLE) contains chlorogenic acid and flavonol glycosides, we hypothesized that phenolic-enriched BLE would improve glucose homeostasis and insulin sensitivity. In this study, we examined whether BLE administration decreases the glucose levels and enhances the pancreatic function in mice with high-fat diet (HFD)-induced obesity and diabetes. C57BL/6J mice were divided into the following four groups: control diet (CD), HFD (60 kcal% fat diet), BLE (HFD with 1% BLE wt/wt diet), and yerba mate extract (YME; HFD with 0.5% YME wt/wt diet). Dietary BLE and YME reduced glucose tolerance, body weight, and plasma glucose, glycated hemoglobin, insulin, homeostasis model assessment of insulin resistance, triglyceride (TG), and non-esterified fatty acid levels. Compared with those of the HFD group, BLE was found to significantly reduce the pancreatic islet size and insulin content. Moreover, it increased the mRNA levels of pancreatic β-cell proliferation-related genes, Ngn3, MafA, Pax4, Ins1, and Ins2, and pancreatic insulin signaling-related genes, IRS-1, IRS-2, PIK3ca, PDK1, PKCε, and GLUT-2, and decreased the transcriptional expression of the β-cell apoptosis-related gene, FoxO1. Both BLE and YME improved insulin sensitivity by inhibiting TG synthesis and enhancing lipid utilization in the liver and white adipose tissue (WAT). In pancreatic MIN6 β-cells, BLE and its main component (chlorogenic acid) increased β-cell proliferation and promoted insulin signaling. Overall, BLE enriched with phenolic compounds has the capacity to prevent HFD-induced glucose tolerance and hyperglycemia by improving the pancreatic β-cell function.