Trimer procyanidin oligomers contribute to the protective effects of cinnamon extracts on pancreatic 13-cells in vitro

Aim： Cinnamon extracts rich in procyanidin oligomers have shown to improve pancreatic β-cell function in diabetic db/db mice. The aim of this study was to identify the active compounds in extracts from two species of cinnamon responsible for the pancreatic β-cell protection in vitro. Methods： Cinnamon extracts were prepared from Cinnamomum tamala （CT-E） and Cinnamomum cassia （CC-E）. Six compounds procyanidin B2 （cpdl）, （-）-epicatechin （cpd2）, cinnamtannin B1 （cpd3）, procyanidin C1 （cpd4）, parameritannin A1 （cpd5） and cinnamtannin D1 （cpd6） were isolated from the extracts. INS-1 pancreatic β-cells were exposed to palmitic acid （PA） or H2O2to induce lipotoxicity and oxidative stress. Cell viability and apoptosis as well as ROS levels were assessed. Glucose-stimulated insulin secretion was examined in PA-treated β-cells and murine islets. Results： CT-E, CC-E as well as the compounds, except cpd5, did not cause cytotoxicity in the β-cells up to the maximum dosage using in this experiment. CT-E and CC-E （12.5-50 μg/mL） dose-dependently increased cell viability in both PA- and H2O2-treated β-cells, and decreased ROS accumulation in H202-treated β-cells. CT-E caused more prominent β-cell protection than CC-E. Furthermore, CT-E （25 and 50 μg/mL） dose-dependently increased glucose-stimulated insulin secretion in PA-treated β-cells and murine islets, but CC-E had little effect. Among the 6 compounds, trimer procyanidins cpd3, cpd4 and cpd4 （12.5-50 pmol/L） dose-dependently increased the cell viability and decreased ROS accumulation in H2O2-treated β-cells. The trimer procyanidins also increased glucose-stimulated insulin secretion in PA-treated β-cells. Conclusion： Trimer procyanidins in the cinnamon extracts contribute to the pancreatic β-cell protection, thus to the anti-diabetic activity.