Humulus scandens extract stimulates endogenous glucagon-like peptide-1 secretion by increasing colonic pitheduloside D and isorhamnetin levels, delaying type 2 diabetes progression in prediabetic db/db mice

Herbal medicine has shown potential to delay the progression from prediabetes to type 2 diabetes (T2D), but the pharmacological effects of many herbs remain unclear. This study investigated the effects of Humulus scandens (HS) extract on delaying T2D progression, based on prior bioinformatic evidence suggesting its antidiabetic potential. Sixteen 6-week-old male db/db mice at the prediabetic stage (fasting blood glucose between 200-249 mg/dL) were used in a 42-day study and were divided into control (normal water) or treatment (water containing 750 mg/kg HS extract) groups. HS extract administration significantly delayed T2D progression, as shown by improved body condition, higher circulating glucagon-like peptide-1 (GLP-1) and insulin levels, and lower appetite, fasting blood glucose, and hemoglobin A1C levels. Immunofluorescence analysis showed increased fluorescence intensity of GLP-1- and insulin-secreting cells in the colon and pancreas. Metabolomics analysis of colonic metabolites indicated that HS extract administration upregulated 11 metabolites and downregulated 36; nine of the upregulated metabolites correlated positively with circulating GLP-1 levels. Molecular docking of these nine metabolites to apical surface receptors on enteroendocrine L cells indicated that pitheduloside D and isorhamnetin were key metabolites. Retrosynthetic analysis revealed that 2’,3,4,4’,6’-pentahydroxychalcone, quercetin, luteolin, and kaempferol are HS extract-sourced components that contribute to the increase in isorhamnetin, whereas the precursor of pitheduloside D remains unidentified. Therefore, administration of 750 mg/kg HS extract increases colonic levels of pitheduloside D and isorhamnetin, activates multiple apical surface receptors of enteroendocrine L cells to enhance endogenous GLP-1 and insulin secretion, and thereby delays the progression from prediabetes to T2D. • HS extract administration delayed T2D progression in prediabetic mice by enhancing endogenous GLP-1 levels. • Administration of HS extract increased colonic isorhamnetin and pitheduloside D levels; these metabolites are key regulators of endogenous GLP-1 secretion via activation of apical surface receptors on enteroendocrine L cells. • Retrosynthetic analysis indicated that flavonoid compounds in HS extract are precursors of isorhamnetin biosynthesis, while the precursors of pitheduloside D may be novel or unknown bidesmosidic oleanane saponins requiring further investigation.