Polyphenols from Acorn Leaves ( Quercus liaotungensis ) Protect Pancreatic Beta Cells and Their Inhibitory Activity against α-Glucosidase and Protein Tyrosine Phosphatase 1B

Acorn leaves, which possess potential pharmacologic effects, are traditionally consumed as food in China. Phytochemical investigations of acorn leaves yielded one new and 25 known polyphenols, and their structures were identified by extensive spectroscopic analysis. Three antidiabetes assays were conducted. Compound considerably increased the survival of pancreatic beta cells by reducing the production of reactive oxygen species and enhancing the activities of superoxide dismutase, catalase, and glutathione in MIN6 cells damaged by H₂O₂. The preliminary mechanism by which compound protects pancreatic beta cells was through the nuclear factor erythroid-2-related factor 2 (Nrf2)/heme oxygenase-1 HO-1 pathway. Most of the tested isolates showed strong inhibitory activity against α-glucosidase and protein tyrosine phosphatase 1B. The IC values of most compounds were much lower than those of the positive control. The results suggest that polyphenols from acorn leaves are potential functional food ingredients that can be used as antidiabetic agents.