Delphinidin 3-rutinoside-rich blackcurrant extract ameliorates glucose tolerance by increasing the release of glucagon-like peptide-1 secretion

Glucagon-like peptide-1 (GLP-1) is an incretin that is secreted from enteroendocrine L-cells. Dietary factor-stimulation of endogenous GLP-1 is a promising strategy for increasing the action of GLP-1. Recent studies have shown that berries rich in anthocyanins improve insulin sensitivity and reduce the risk of type 2 diabetes. Our previous study found that the anthocyanin delphinidin 3-rutinoside (D3R) significantly increases GLP-1 secretion in GLUTag cells (enteroendocrine L cell line). Blackcurrants are berries that contain high levels of anthocyanins, particularly D3R. Pre-administered blackcurrant extract (BCE) 5mg/kg body weight (1mg D3R/kg) significantly ameliorated glucose tolerance after intraperitoneal glucose injection in rats by stimulating the secretion of GLP-1 and subsequently inducing insulin secretion. D3R did not break down significantly in the gastrointestinal tract for at least 45-60min after BCE was administered, suggesting that BCE-induced GLP-1 secretion is mainly mediated by D3R and not its degradation products. These findings demonstrate the novel biological function of D3R-rich BCE as a GLP-1 secretagogue. An increase in endogenous GLP-1 secretion induced by BCE may help to reduce the dosages of diabetic medicines and prevent diabetes.