Abstract
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) 5 mg/kg body weight (1 mg 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 45−60 min 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.
Highlights
Glucagon-like peptide-1 (GLP-1) is a type of incretin, secreted from enteroendocrine L-cells, that stimulates glucose-dependent insulin secretion and the proliferation of pancreatic β-cells (Buteau, Foisy, Joly, & Prentki, 2003; Kreymann, Williams, Ghatei, & Bloom, 1987; Mojsov, Weir, & Habener, 1987)
We investigated that the plasma concentrations of GLP-1 and insulin were significantly increased after oral administration of delphinidin 3-r utinoside (D3R)-rich blackcurrant extract (BCE), which resulted in the amelioration of hyperglycemia after intraperitoneal (IP) glucose injections in rats
Serum insulin concentrations were significantly higher at 15 and 30 min after IP glucose in the BCE group (Figure 1B). To confirm that this glucose-lowering effect that accompanied insulin secretion was due to the stimulation of GLP-1, BCE was administered prior to IP glucose injections, and blood samples were collected from the portal vein
Summary
Glucagon-like peptide-1 (GLP-1) is a type of incretin, secreted from enteroendocrine L-cells, that stimulates glucose-dependent insulin secretion and the proliferation of pancreatic β-cells (Buteau, Foisy, Joly, & Prentki, 2003; Kreymann, Williams, Ghatei, & Bloom, 1987; Mojsov, Weir, & Habener, 1987). We screened anthocyanins to find molecules that stimulate GLP-1 secretion and found that delphinidin 3-rutinoside (D3R) significantly increased secretion in GLUTag cells (enteroendocrine L cell line) (Kato, Tani, Terahara, & Tsuda, 2015). It is not clear whether D3R, or D3R-rich berries directly enhances the secretion of GLP-1 in vivo, which results in reduced blood glucose levels via the stimulation of insulin secretion.
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