Coloured Rice Phenolic Extracts Increase Expression of Genes Associated with Insulin Secretion in Rat Pancreatic Insulinoma β-cells

Glucose-induced oxidative stress is associated with the overproduction of reactive oxygen species (ROS), which may dysregulate the expression of genes controlling insulin secretion leading to β-cell dysfunction, a hallmark of type 2 diabetes mellitus (T2DM). This study investigated the impact of coloured rice phenolic extracts (CRPEs) on the expression of key genes associated with β-cell function in pancreatic β-cells (INS-1E). These genes included glucose transporter 2 (Glut2), silent mating type information regulation 2 homolog 1 (Sirt1), mitochondrial transcription factor A (Tfam), pancreatic/duodenal homeobox protein 1 (Pdx-1) and insulin 1 (Ins1). INS-1E cells were cultured in high glucose (25 mM) to induce glucotoxic stress conditions (HGSC) and in normal glucose conditions (NGC-11.1 mM) to represent normal β-cell function. Cells were treated with CRPEs derived from two coloured rice cultivars, Purple and Yunlu29-red varieties at concentrations ranged from 50 to 250 µg/mL. CRPEs upregulated the expression of Glut2, Sirt1 and Pdx-1 significantly at 250 µg/mL under HGSC. CRPEs from both cultivars also upregulated Glut2, Sirt1, Tfam, Pdx-1 and Ins1 markedly at 250 µg/mL under NGC with Yunlu29 having the greatest effect. These data suggest that CRPEs may reduce β-cell dysfunction in T2DM by upregulating the expression of genes involved in insulin secretion pathways.