This study was conducted to evaluate the in vitro and in vivo hypoglycemic potential of the water extract of pepper (Capcicum annuum L. cultivar Dangjo) leaves (WEPL) and the active constituent luteolin 7-O-glucoside (LG) isolated from WEPL. WEPL showed in vitro a-glucosidase and a-amylase inhibitory activity.LG also showed a similar a-glucosidase and a-amylase inhibitory activity, suggesting that the ability of WEPL to inhibit both enzymes may be due to the presence of LG and other polyphenols in WEPL. Supporting this observation, both WEPL and LG significantly reduced blood glucose levels in streptozocin-induced diabetic mice when challenged with oral administration of sucrose, but not after oral glucose challenge. Hence, inhibition of a-glucosidase and a-amylase may possibly be one of the mechanisms for WEPL and LG to exert hypoglycemic activity, indicating that pepper leaves may be considered as a potential candidate for the management of type 2 diabetes mellitus.
PRACTICAL APPLICATIONSLeaves of pepper cultivars, including Dangjo pepper, are commonly consumed as food in Korea. The findings of this study demonstrate that the water extract of pepper leaves exhibits the capacity to inhibit carbohydrate hydrolyzing enzymes (a-glucosidase and a-amylase) in vitro and in vivo and these beneficial effects appear to be due to some specific bioactive compounds in pepper leaves, in particular luteolin 7-O-glucoside. Our preliminary observation provides a rationale for a possible use of pepper leaves for the management of postprandial hyperglycemia.
To investigate whether the local production of glucagon-like peptide-1 (GLP-1) in the intestine can differentiate intestinal stem/progenitor cells into insulin-producing cells, we intra-intestinally injected a recombinant adenovirus expressing GLP-1 (rAd-GLP-1) into diabetic mice. There were no significant differences in body weight or food intake between rAd-GLP-1- and rAd-betaGAL-treated control mice. rAd-GLP-1-treated mice showed intestinal insulin mRNA expression, insulin- and glucagon-positive cells in the intestine, and significantly increased serum insulin, but not glucagon. rAd-GLP-1 injection significantly reduced blood glucose levels and improved glucose tolerance compared with controls. Expression of transcription factors related to beta cell differentiation, neurogenin 3 (ngn3) and neurogenin differentiation factor (NeuroD), was detected in the intestine at 2 weeks after rAd-GLP-1 injection. We suggest that expression of GLP-1 in the intestine by intra-intestinal delivery of rAd-GLP-1 may induce differentiation of intestinal stem/progenitor cells into insulin-producing cells, mediated by ngn3 and NeuroD expression, contributing to lowered blood glucose levels in diabetic mice.
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